What is Stainless Steel
What is Stainless Steel?
Table of Contents
- Elements in Stainless Steel
- Main characteristics of stainless steel
- Types of stainless steel
- What is ferritic stainless steel
- What is austenitic stainless steel
- What is duplex stainless steel
- What is precipitation hardening stainless steel
- What is martensitic stainless steel
- What are the pros and cons of stainless steel?
- Chemical Composition of Stainless Steel
- Comparison Conversion of Stainless Steel
- Density of Stainless Steel
- Mechanical Properties of Stainless Steel
- Physical Properties of Stainless Steel
- Corrosion Resistance of Stainless Steel
- Heat Treating of Stainless Steel
- Electrolytic polishing of stainless steel
- Surface Roughness of Stainless Steel
- High Temperature Properties Stainless Steel
- Drawn and spun stainless steels
- Bending stainless steel
- Welding stainless steel
- Brazing stainless steel
- General Principles of Machining Stainless Steel
- Cutting tools for stainless steel
- Theoretical weight calculation of stainless steel products
- Stainless Steel “L” and “H” Grades
- Difference between 304 304L and 321
- Grade 316 vs. Grade 316L vs. 316Ti Stainless Steel
- 347 stainless Steel VS 321 stainless Steel
- Chemical composition
- Uniform corrosion
- High temperature oxidation resistance
- Physical properties
- Mechanical properties
- How to choose stainless steel
- Life Cycle Costing of Stainless Steel
- Stainless steel in energy saving and emission reduction
- Applications of stainless steel
- Can stainless steel rust?
Stainless steel is stainless, corrosion resistance as the main characteristic, and chromium content of at least 10.5%, the maximum carbon content of not more than 1.2% of the steel.
Stainless steel is short for stainless acid-resistant steel, resistant to weak corrosive media such as air, steam, water is called stainless steel; and will be resistant to chemically corrosive media (acid, alkali, salt and other chemical leaching) corrosion of steel is called acid-resistant steel.
Due to the differences in the chemical composition of the two and their corrosion resistance is different, ordinary stainless steel is generally not resistant to chemical media corrosion, while acid-resistant steel is generally stainless. The term “stainless steel” does not simply refer to a stainless steel, but indicates that more than one hundred industrial stainless steel, each stainless steel developed in its specific application has good performance. The key to success is first to identify the application and then to determine the correct steel grade. There are usually only six steel grades related to the application area of building construction. They all contain 17 to 22 percent chromium, and the better grades also contain nickel. The addition of molybdenum can further improve atmospheric corrosion, especially the resistance to corrosion of atmospheres containing chlorides.
In general, the hardness of stainless steel is higher than that of aluminum alloys, and the cost of stainless steel is higher than that of aluminum alloys.
The historical origin of stainless steel
The invention and use of stainless steel goes back to the First World War period. At that time, the British guns in the battlefield, always due to the chamber wear can not be used and shipped back to the rear. Military production department ordered Brearley to develop high-strength wear-resistant alloy steel, specifically to study the solution to the problem of wear of the chamber. Brearley and his assistant collected various types of steel produced at home and abroad, a variety of different properties of alloy steel, performance experiments on a variety of different properties of machinery, and then select the more applicable steel made of guns. One day, they experimented with an alloy steel containing a large amount of chromium, and after the wear-resisting experiment, it was found that this alloy was not wear-resistant, indicating that this could not be made into a gun, so they recorded the experiment results and threw it to the corner. One day, a few months later, an assistant came rushing in with a shiny piece of steel and said to Brearley, “Sir, this is the alloy steel I found when cleaning the warehouse from Mr. Maura, do you experiment to see what special effect it actually has!” “Good!” Brierly looked at the shiny and dazzling steel and said happily.
Experimental results proved: it is a piece of stainless steel that is not afraid of acids, alkalis and salts. This stainless steel was invented by the German Maura in 1912, however, Maura does not know what use this stainless steel.
Brearley heart calculations: “This is not wear-resistant but corrosion-resistant steel, can not make guns, whether it can do tableware?” He said dry, hands-on production of stainless steel fruit knives, forks, spoons, fruit plates and folding knives and so on.
Brearley invented stainless steel in 1916 to obtain the British patent and began mass production, so far, from the trash heap of stainless steel found by chance will become popular around the world, Henry Brearley is also known as the “father of stainless steel.
Elements in Stainless Steel
Chemical elements are known to have more than 100 kinds of industrial materials used in steel can be encountered in about more than 20 kinds of chemical elements. For people in the fight against corrosion for long term practice of this particular form of stainless steel series, the most commonly used in a dozen elements, in addition to the basic elements of the composition of steel other than iron, the performance of stainless steel and organizations most affected.
The elements are: Carbon, Chromium, Nickel, Manganese, Silicon, Molybdenum, Niobium, Titanium and Miobium, Nitrogen, Copper, Cobalt, Aluminum, Sulfur and Selenium.
These elements, in addition to carbon, silicon, other than nitrogen, are located in the periodic table of chemical elements of transition. In fact the application of the stainless steel tube industry at the same time there are several elements as well as a dozen, when the number of elements co-exist in a continuum of stainless steel tubing, they separate the impact of the presence of more much more complex, because in this cases not only have to consider the role of the various elements of their own, and they should pay attention to the impact of each other, so the organization decided to stainless steel pipe of various elements in the sum of the impact.
1. Various elements on the performance of stainless steel and the impact and role of organizations
1-1. Chromium in the stainless steel a decisive role in stainless steel is a decision of only one element, that is, chromium, stainless steel each contain a certain amount of chromium. To date, no non-chromium stainless steel. Chromium stainless steel performance decision has become the main element, the fundamental reason is to add chromium as an alloying element, the internal contradiction of campaign in favor of resistance to the development of corrosion damage.
Such a change can be obtained from the following description:
- 1. Chromium Fe-based solid solution so that the electrode potential to improve;
- 2. Chromium electronic absorption of iron so that iron-passivated.
Anodic passivation is due to be prevented from arising from reaction of metal and alloy corrosion resistance phenomenon can be improved. Passivation of metals and alloys constitute the theory of many major film theory, deals with the electronic order of adsorption.
The influence of chromium on the properties of stainless steel
Chromium plays a decisive role in the corrosion resistance of stainless steel, in the definition of stainless steel, ω (Cr) ≥ 10.5%, which is the main element of stainless steel, the higher the corrosion resistance, the higher the chromium content, the higher the corrosion resistance. This is because the steel can form Cr2O3 in oxidizing media as a stable surface protection film of the matrix (about 10 μm), resulting in passivation, in which the chromium layer is enriched into a film.
At the same time, chromium effectively increases the electrode potential of the solid solution (ferrite, martensite or austenite), so that the electrode potential of the original iron (mild steel) from negative to positive, so that the steel from corrosion. With the addition of chromium stainless steel, the electrode potential changes by volume with n/8. When the chromium content per atom is 1/8, 2/8, 3/8.. . 8, or 12.5%, 25%, 37.5%…. The larger the molar fraction, the higher the electrode potential and the weaker the corrosion. The atomic concentration of chromium compared to 1/8 (or 12.5%, molar fraction), if 11.7% by mass, the chromium content of chromium stainless steel is generally above 12% (by mass). When the chromium atomic content reaches 25%, a secondary mutation occurs, when the corrosion resistance of chromium steel is further improved.
In addition, chromium has a good effect on the mechanical properties and process properties of stainless steel. Chromium can improve the hardenability of stainless steel, in the low-alloy organization has been widely used. Such as reducing the rate of transformation of chromium austenite to ferrite and carbide, so that the isothermal transformation diagram of austenite is shifted to the right, thus reducing the critical cooling rate of stainless steel quenching, thus improving the hardenability of steel some martensitic stainless steel air quenched martensite available.
Chromium can improve the oxidation resistance of stainless steel, with the increase of chromium content in steel, oxidation resistance significantly increased. In martensitic chromium stainless steel, oxidation resistance is 4 to 9 times higher than ordinary stainless steel, martensitic chromium stainless steel can not withstand the surface temperature of about 700 to 850 ℃.
Chromium is the only valuable element in passivated steel and stainless steel that gives good corrosion resistance for industrial use. As the chromium content increases, it can improve the resistance to atmospheric corrosion. In oxidizing media (such as dilute nitric acid), with the increase in chromium content, the corrosion resistance of stainless steel increases; but in reducing media, with the increase in chromium content, the corrosion resistance of stainless steel decreases.
Chromium can affect the physical properties of steel as follows: chromium can increase the lattice constant of steel, than the chromium content increases linearly with volume, and significantly reduces the thermal conductivity of iron-chromium alloy, but also increases the resistance of steel. The resistance of martensitic chromium stainless steel is 4 to 6 times that of ordinary stainless steel. Under quenched conditions, the hardness and tensile strength of the steel are reduced due to the increased stability of chromium ferrite. Under annealed conditions, the chromium content of low-carbon iron-chromium alloys increases, increasing strength and hardness and slightly decreasing elongation.
The maximum solubility of chromium in pure γ-iron is about 12.0%; at ω(C) ≈ 0.5%, the maximum solubility in austenite is about 20%. The solubility in pure α-iron is infinity. In Cr-Mn-N steels the solubility of N can be increased. The chromium carbides formed in the steel tend to be less than manganese and less than tungsten. In Cr steels, this temperature increases the strength and wear resistance of high-carbon steels.
1-2. Carbon in the stainless steel tubing in the dual nature of carbon steel is the industry one of the key elements, steel and organizational performance to a large extent determined by the carbon content in steel and its distribution in the form of the impact of carbon stainless steel is particularly significant. Carbon in the stainless steel on the impact of organizations mainly in two ways, on the one hand is stable austenite carbon element, and the extent of the role of a large (approximately 30 times for nickel), on the other hand, as a result of the affinity of carbon and chromium is large, with the formation of chromium – series of complex carbides. Therefore, the candle from the intensity and decay properties, both in terms of carbon in the role of stainless steel are mutually contradictory.
Recognizing the impact of the law, we can use from different requirements of different carbon content stainless steel. For example, most widely used in industry, but also the stainless steel at least – 0Crl3 – 4Cr13 five standard steel grades chromium amount is 12 – 14%, that is, the carbon to form chromium carbide and chromium factors taken into account after determined that the purpose is to make the combination of carbon and chromium as chromium carbide, the solid solution of chromium in the amount of not less than 11.7% of the minimum amount of chromium.
No.5 on the steel is due to the different carbon content, strength and corrosion resistance is also differentiated, 0Cr13 – 2Crl3 better corrosion resistance of steel but lower than the 3Crl3 and 4Cr13 strength steel, used in the manufacture of the structure of many parts, after As the No. 2 steel with higher carbon intensity will be high and more used in the manufacture of springs, cutting tools, such as high strength and wear-resistant parts. Another example is in order to overcome the 18-8 Cr-Ni stainless steel intergranular corrosion, can be carbon steel to 0.03% below, or by adding chromium and carbon affinity than the larger elements (titanium or niobium), so that does not form a carbide chromium, Another example is when the high hardness and wear resistance as a major requirement, we can increase the carbon content of steel at the same time to suitably increase the amount of chromium so that not only satisfy the requirements of the hardness and wear resistance, but also take into account – will be corrosion-resistant function, used for industrial bearings, has a stainless steel blade measuring and 9Cr18 and 9Cr17MoVCo steel, although the carbon content as high as 0.85 – 0.95%, due to their chromium also increased accordingly, it is still guaranteed the corrosion resistance of requirements.
Generally speaking, the current industry access to the application of the carbon content of stainless steel pipe are relatively low, most of the carbon content of stainless steel in the 0.1 – 0.4%, and acid-resistant carbon steel with 0.1 to 0.2% of the majority. Greater than 0.4% carbon content of stainless steel grade is only a small fraction of the total, which is used because in most conditions, to corrosion-resistant stainless steel is always the primary purpose. In addition, the lower carbon content is also a process for some requirements, such as the ease of welding and cold deformation.
1-3. Nickel in the role of stainless steel and chromium in the play after the Nickel is an excellent corrosion-resistant materials, is also an important steel alloying elements. Nickel in the austenitic stanless steel pipe is the formation of the elements,such as 304,316,321.but the low-carbon steel to obtain pure nickel austenite, the volume of nickel to achieve 24%; and only when 27 percent nickel steel, in some medium resistance significant changes in corrosion. Thus alone can not constitute a nickel stainless steel. But at the same time the existence of nickel and chromium in the stainless steel, the nickel-containing stainless steel but has many valuable properties. Based on the above circumstances, we can see that nickel as alloying elements in the role of stainless steel is that it allows high-chromium steel changes, so that corrosion resistance of stainless steel and certain to improve process performance.
The role of nickel in stainless steel
Nickel is an alloying element that forms austenite, but the role of nickel and chromium has only been fully proved. If only nickel is used, the pure nickel structure in the low-carbon austenite phase needs to have a nickel content of more than 24% (mass fraction). In fact, it needs to have a nickel content of 27% (mass fraction) in order to significantly improve the corrosion resistance of stainless steel. Therefore, nickel is not used alone as an alloy element in stainless steel.
When nickel and chromium are combined, the role of nickel in improving the corrosion resistance of steel can be clearly shown. For example, adding a small amount of nickel to ferritic stainless steel can change the single-phase microstructure of ferrite into austenite ferrite phase, so that its strength can be improved through heat treatment. If the content of nickel is further increased, it can become single-phase austenite, such as ω (CR) =18% steel containing 8% nickel by mass can obtain complete austenite. This is the widely used chromium nickel austenitic 18-8 stainless steel, which has high corrosion resistance, good deformation and weldability, and is not magnetic.
The role of nickel in stainless steel and the role of chromium in stainless steel nickel is an excellent corrosion-resistant material and an important alloy element in steel. Nickel is a forming element in austenitic stainless steel, such as 304, 316 and 321. However, in order to obtain pure nickel austenite in low carbon steel, the nickel content should reach 24%; Only when the nickel content reaches 27%, the corrosion resistance of steel in some media will change significantly. Therefore, nickel stainless steel cannot be formed by this alone. However, due to the existence of nickel and chromium in stainless steel, stainless steel containing nickel has many valuable properties. Based on the above situation, we can see that the role of nickel as an alloy element in stainless steel is that it can change the high chromium steel, so as to improve the corrosion resistance and process performance of stainless steel.
Nickel in pure α- The maximum solubility of Fe is 25% – 30%. At this time, it stays in ferrite which still contains carbon. Its function is to make the solid solubility of steel not harden. The passivation of nickel expands the range of improving corrosion resistance, especially in non oxidizing media (such as sulfuric acid).
The formation tendency of Ni Fe carbides is weaker than that which can promote graphitization, and weakens the hardenability of the steel, which is insensitive to the cold impact of the steel. In carbon steel and high carbon steel with effective concentration, austenite is preferentially retained during quenching.
1-4. Manganese and Nitrogen can substitute for Ni-Cr-Ni stainless steel, Cr-Ni austenitic steels. Although many of the advantages, but in recent decades as a result of nickel-based heat-resistant nickel alloy and the heat below 20% of the large number of strong steel development and applications, as well as the growing chemical industry of the increasing demand of stainless steel The greater the amount of the nickel deposits less concentrated in a few areas, it appeared in the world and the need for nickel in the conflict area. Therefore, in stainless steel alloys and many other fields (such as a large forging steel, tool steel, heat strong steel, etc.), especially the lack of nickel resources of the country, carried out extensive section of nickel and nickel on behalf of other elements in the scientific research and production practice, in this regard the research and application is based on a relatively large number of manganese and nitrogen to replace the stainless steel and heat-resistant nickel steel.
For the role of manganese and nickel austenitic similar. But to be more exact, the role of manganese does not lie in the formation of austenite, but it reduced the critical quenching rate of steel in cooling to increase the stability of austenite and suppress the decomposition of austenite, so that the formation of high temperature austenite to room temperature is maintained. In improving the corrosion resistance of steel, the manganese plays a minor role, such as manganese steel increased from 0 to 10.4% change, do not make steel in the air with the acid corrosion resistance of significant change. This is because the manganese to iron-based solid solution to increase the electrode potential does not help the formation of the protective role of the oxide film is very low, so the industry although some of the austenitic manganese steel alloys (such as 40Mn18Cr4, 50Mn18Cr4WN, ZGMn13 steel, etc.), but they can not be used as the use of stainless steel. Manganese in steel is about the role of a stable austenitic nickel half, that is 2% of nitrogen in steel is the role of austenite
stability and the role of larger than nickel. For example, to save with 18% chromium steel austenitic at room temperature under the body to manganese and nitrogen on behalf of low-nickel stainless steel and nickel chromium nickel element nitrogen does not induce manganese steel has been applied in industry, and some has successfully replaced the classic chrome-nickel stainless steel 18-8.
1-5. Titanium or Niobium is to prevent intergranular corrosion.
1-6. Molybdenum and Copper can increase some of the corrosion resistance of stainless steel.
1-7. Other elements on the performance of stainless steel and organizational impact
More than nine major elements of stainless steel performance and the impact of organizations, in addition to these elements and organizational performance of stainless steel elements of a greater impact, the stainless steel contains a number of other elements. Some, like steel and general for the regular deposit of impurity elements, such as silicon, sulfur and phosphorus. Also some specific purpose in order to join, such as cobalt, boron, selenium, and other rare earth elements. From the stainless steel corrosion resistance of the nature of the main, these elements have been discussed in relation to the nine elements are non-key aspects, although the case, but can not be completely ignored because their performance of stainless steel and organizations have also taken place in the same impact.
Silicon is a ferrite forming element, in general, always keep the stainless steel for the impurity elements. Cobalt as alloying elements in steel by the application of small, this is because the high price of cobalt and in other ways (such as high-speed steel, carbide, cobalt-based heat-resistant alloys, magnetic or hard magnetic alloy, etc.) has a more important purposes. Stainless steel in the general increase in the cobalt alloy elements for not more commonly used stainless steel, such as 9Crl7MoVCo (including 1.2-1.8% cobalt) plus cobalt, the purpose is not to improve corrosion resistance and to improve hardness, which are mainly used for stainless steel slicing machinery manufacturing cutting tools, such as scissors and blades.
Boron high-chromium ferritic stainless steel Crl7Mo2Ti plus 0.005% of boron, can in boiling 65% acetic acid can enhance the corrosion resistance. Add small amount of boron (0.0006 – 0.0007%) austenitic stainless steel will enable the plastic to improve the thermal state. A small amount of boron due to the formation of low melting point eutectic, so that when austenitic steel welding hot cracking tendency to increase, but contains more boron (0.5 – 0.6%) when it prevents the emergence of hot cracking . When containing 0.5 – 0.6% of boron, the formation of austenite – two-phase boride organizations to lower the melting point of weld. Coagulation bath temperature is below half the melting zone, the base metal in the cooling of the tensile stress generated by the liquid is. Solid- state under the weld metal, is at this time without causing cracks even in the near seam zone formed a crack, it can be in liquid – solid metal by filling the pool. B-containing austenitic stainless steel of the Cr-Ni in the atomic energy industry has a special purpose.
Phosphorus in the general impurity elements are stainless steel, but its in danger of austenitic stainless steel in general is not as significant in steel, it allows a higher concentration, if the information up to 0.06%, to control in favor of smelting. Individual austenite manganese steel output of about 0.06% phosphorus (such as 201 stainless steel). The use of phosphorus on the strengthening of the role of steel as well as age-hardening increases phosphorus alloying elements of stainless steel, PH17-10P steel (containing 0.25% phosphorus) is a PH-HNM steel (containing 0.30 P) and so on.
Sulfur and selenium in the general stainless steel is also often of impurity elements. However, China and Canada to the stainless steel 0.2 – 0.4% of sulfur, can improve the cutting performance of stainless steel, selenium also has the same effect. Sulfur and selenium to improve the cutting performance of stainless steel because they reduce the toughness of stainless steel, such as the 18-8 Cr-Ni stainless steel in general the impact of the value of up to 30 kg / cm 2. Containing 0.31% sulfur 18-8 steel (0.084% C, 18.15% Cr, 9.25% Ni) the impact of the value of 1.8 kg / cm2; containing 0.22% selenium 18 -8 steel (0.094% C, 18.4% Cr, 9% Ni) the impact of a value of 3.24 kilograms / square centimeters. Both sulfur and selenium to reduce the corrosion resistance of stainless steel, so the practical application of them as a stainless steel alloy of the rare element.
Rare-earth element rare-earth element used in stainless steel pipe, the key is to improve the process performance. Crl7Ti such as the steel and steel plus Cr17Mo2Ti a small number of rare earth elements, can be eliminated in ingot caused by hydrogen bubbles and the reduction of cracks in the slab. Austenitic and austenitic – ferritic stainless steel in 0.02 – 0.5% increase in the rare earth elements (Ce-La alloy), can significantly improve the performance of forging. Had a 19.5 percent containing chromium, nickel 23% copper and molybdenum austenitic manganese steel, due to thermal processing performance in the past only the production of castings, after the increase of rare earth elements can be rolled into various sections.
Main characteristics of stainless steel
The requirements of welding performance vary depending on the use of the product. A class of tableware on the welding performance is generally not required, even including some of the pot enterprises. But the vast majority of products need raw materials welding performance is good, like the second class tableware, insulation cups, steel pipes, water heaters, water dispensers, etc.
The vast majority of stainless steel products require good corrosion resistance, like one or two types of tableware, kitchenware, water heaters, drinking fountains, etc. Some foreign businessmen on the product also do corrosion resistance test: NACL aqueous solution heated to boiling, pour off the solution after a period of time, wash and dry, weigh the loss, to determine the degree of corrosion (Note: product polishing, because of the composition of the sand cloth or sandpaper containing Fe, will lead to test (when the surface rust spots)
Today’s society, stainless steel products in the production of general polishing process, only a few products such as water heaters, drinking fountains, etc. do not need polishing. Therefore, this requires the polishing performance of raw materials is very good. The main factors affecting the polishing performance are the following.
- ① Raw material surface defects. Such as scratches, pockmarks, over acid washing, etc..
- ② Raw material material problems. Hardness is too low, polishing is not easy to polish bright (BQ sex is not good), and hardness is too low, in deep drawing surface prone to orange peel phenomenon, thus affecting the BQ sex. High hardness of BQ sex is relatively good.
- ③ After deep drawing of the product, the surface of the area with great deformation will also be small black spots and RIDGING, which affects the BQ property.
Heat resistance performance
Heat resistance performance refers to the high temperature stainless steel can still maintain its excellent physical and mechanical properties.
The effect of carbon: carbon in austenitic stainless steel is a strong formation and stabilization of austenite and expand the austenite zone of the element. The ability of carbon to form austenite is about 30 times that of nickel, and carbon is an interstitial element that can significantly improve the strength of austenitic stainless steel by solid solution strengthening. Carbon can also improve the stress and corrosion resistance of austenitic stainless steel in highly concentrated chlorides (such as 42% MgCl2 boiling solution).
However, in austenitic stainless steel, carbon is often regarded as a harmful element, mainly due to the corrosion resistance of stainless steel in some conditions (such as welding or heating by 450 – 850 ℃), carbon can be formed with the chromium in the steel of high chromium Cr23C6 type carbon compounds thus leading to local chromium depletion, so that the corrosion resistance of steel, especially intergranular corrosion resistance decreased. Therefore. 60s since the new development of chromium-nickel austenitic stainless steel is mostly less than 0.03% carbon content or 0.02% ultra-low carbon type, you can know that with the carbon content is reduced, the steel intergranular corrosion susceptibility is reduced, when the carbon content is less than 0.02% to have the most obvious effect, some experiments also pointed out that carbon will also increase the chromium austenitic stainless steel pitting corrosion points tendency. Due to the harmful effects of carbon, not only in the austenitic stainless steel smelting process should be required to control the carbon content as low as possible, but also in the subsequent process of hot and cold processing and heat treatment to prevent the stainless steel surface carbonization, to avoid chromium carbide precipitation.
When the amount of chromium in steel atomic number of not less than 12.5%, can make a sudden change in the electrode potential of steel, from negative to positive electrode potential. Stop electrochemical corrosion.
Types of stainless steel
Stainless steel is often divided into: martensitic steel, ferritic steel, austenitic steel, austenitic-ferritic (duplex) stainless steel and precipitation-hardening stainless steel, etc. according to the tissue state. In addition, it can be divided into: chromium stainless steel, chromium-nickel stainless steel and chromium-manganese-nitrogen stainless steel, etc. according to the composition. There are also special stainless steels used for pressure vessels “GB24511_2009_stainless steel plates and strips for pressure-bearing equipment”.
What is ferritic stainless steel
Ferritic steel is a low-carbon chromium stainless steel containing more than 14% chromium, and chromium stainless steel containing more than 27% chromium of any carbon content. Those belonging to this category are Crl7, Cr17Mo2Ti, Cr25, Cr25Mo3Ti, Cr28, etc.
Conventional ferritic/martensitic steels can only reach a maximum working temperature of 550 to 600 °C. OxideDispersion St rengthened (ODS) ferritic steels can increase the working temperature to 700 °C. ODS ferritic steels have a BCC crystal structure and have very low irradiation swelling at 200 dpa neutron irradiation. In addition, ODS ferritic steels have excellent oxidation and corrosion resistance. The development of ODS ferritic steels is of great significance to improve the thermal efficiency of reactors, reduce environmental pollution, and ensure the safety and long-life operation of reactors.
The alloying elements (Fe, Cr, Ti, W, Ta, C) are required to meet the requirements of low activation, and the determination of Cr content should take into account ductility, fracture toughness and corrosion resistance. The most commonly used process for the preparation of ODS ferritic steels is hot extrusion: first, Y2O3 particles are uniformly dispersed in the matrix using mechanical alloying (MA) in a high-purity Ar atmosphere, and then the alloy powder is confined in a mild steel tube and hot extruded at 1150°C. The hot extruded master tube is cold rolled in multiple passes, and intermediate heat treatment is carried out between each pass, resulting in a thin-walled clad tube after the final heat treatment.
There are two keys to the preparation of ODS ferritic steel: first, to obtain uniformly distributed nano-oxide particles and appropriate amount of residual α2Fe, thus improving creep properties; second, to prepare thin-walled clad tubes by hot extrusion process and to change the elongated grain morphology to eliminate material anisotropy. Focus on the analysis of Y2O3 particle dissolution / analysis, the formation of residual α2Fe, thin-walled cladding tube preparation process of intermediate heat treatment and change the elongated grain shape.
What is austenitic stainless steel
Austenitic stainless steel is a stainless steel with austenitic organization at room temperature. When the steel contains about 18% Cr, 8%-25% Ni and about 0.1% C, it has a stable austenitic organization. Austenitic chromium-nickel stainless steel including the famous 18Cr-8Ni steel and on the basis of this increase in Cr, Ni content and the addition of Mo, Cu, Si, Nb, Ti and other elements developed by the high Cr-Ni series of steel. Austenitic stainless steel is non-magnetic and has high toughness and plasticity, but the strength is low, it is not possible to strengthen it through phase transformation, and can only be strengthened through cold working, such as the addition of S, Ca, Se, Te and other elements, it has good machinability.
Austenitic stainless steel production process performance is good, especially chromium-nickel austenitic stainless steel, the use of conventional means of producing special steel can be smoothly produced a variety of commonly used specifications of the plate, pipe, strip, wire, bar and forgings and castings. Due to the high content of alloying elements (especially chromium) and low carbon content, the use of electric arc furnace plus argon oxygen decarburization (AOD) or vacuum deoxidation decarburization (VOD) method of mass production of such stainless steel, for advanced grades of small batch products can be used in vacuum or non-vacuum non-induction furnace smelting, if necessary, plus electroslag remelting.
Chromium-nickel austenitic stainless steel excellent thermoplastic makes it easy to apply forging, rolling, hot perforation and extrusion and other thermal processing, ingot heating temperature of 1150 – 1260 ℃, deformation temperature range is generally 900 – 1150 ℃, containing copper, nitrogen and titanium, niobium stabilization of steel grades rely on low temperature, while high chromium, molybdenum steel grades rely on high temperature. Due to poor thermal conductivity, holding time should be longer. The workpiece can be air-cooled after thermal processing. Chromium manganese austenitic stainless steel thermal cracking sensitivity is strong, ingot open billet to small deformation, multiple passes, forgings should be stacked cold. Can be cold-rolled, cold-drawn and spinning and other cold processing processes and stamping, bending, rolled edges and folding and other forming operations. Chromium-nickel austenitic stainless steel processing hardening tendency is weaker than chromium-manganese steel, a cold deformation after annealing can reach 70% to 90%, but chromium-manganese austenitic stainless steel due to deformation resistance, processing hardening tendency is strong, should increase the number of intermediate softening annealing. General intermediate softening annealing treatment for 1050 – 1100 ℃ water cooling.
Austenitic stainless steel can also be produced castings. In order to improve the fluidity of the steel, improve casting performance, casting steel alloy composition should be adjusted: improve the silicon content, relax the chromium, nickel content of the interval, and improve the impurity element sulfur content limit.
Austenitic stainless steel should be solid solution treatment before use, in order to maximize the steel carbide and other precipitation phase solid solution to the austenite matrix, but also to homogenize the organization and stress relief, so as to ensure excellent corrosion resistance and mechanical properties. The correct solid solution treatment system for 1050 – 1150 ℃ after heating water cooling (thin parts can also be air-cooled). Solution treatment temperature depends on the degree of steel alloying: no molybdenum or low molybdenum steel grades should be lower (≤ 1100 ℃), and more highly alloyed grades such as 00Cr20Ni18Mo-6CuN, 00Cr25Ni22Mo2N, etc. should be higher (1080 – 1150 ℃).
Production widely used in advanced technology, such as furnace refining rate of 95% or more, continuous casting ratio of more than 80%, high-speed rolling mill and fine, fast forging machine and other commonly promoted. Especially in the smelting and processing process to achieve electronic computer control, to ensure the reliability and stability of product quality and performance.
What is duplex stainless steel
Duplex Stainless Steel (DSS), refers to the ferrite and austenite each about 50%, generally less phase content needs to reach a minimum of 30% of the stainless steel. In the case of lower C content, Cr content in 18% to 28%, Ni content in 3% to 10%. Some steels also contain Mo, Cu, Nb, Ti, N and other alloying elements.
This type of steel has both austenitic and ferritic stainless steel characteristics, compared with ferritic, plasticity, higher toughness, no room temperature embrittlement, intergranular corrosion resistance and welding performance are significantly improved, while also maintaining a ferritic stainless steel 475 ℃ brittleness and high thermal conductivity, with super plasticity and other characteristics. Compared with austenitic stainless steel, high strength and resistance to intergranular corrosion and chloride stress corrosion has been significantly improved. Duplex stainless steel has excellent resistance to pore corrosion and is also a nickel saving stainless steel.
Since its birth in the United States in the 1940s, duplex stainless steel has been developed into the third generation. Its main feature is that the yield strength can reach 400-550MPa, which is two times that of ordinary stainless steel, so it can save material and reduce the cost of equipment manufacturing. In terms of corrosion resistance, especially the media environment is relatively harsh (such as seawater, high chloride ion content) conditions, duplex stainless steel resistance to pitting, crevice corrosion, stress corrosion and corrosion fatigue performance is significantly better than ordinary austenitic stainless steel, can be comparable to high-alloy austenitic stainless steel.
Performance characteristics of duplex stainless steel
Due to the characteristics of two-phase organization, through the correct control of chemical composition and heat treatment process, duplex stainless steel has the advantages of both ferritic stainless steel and austenitic stainless steel, it will have the excellent toughness and weldability of austenitic stainless steel and ferritic stainless steel has a higher strength and resistance
Chloride stress corrosion resistance combined together, it is these superior properties make duplex stainless steel as a weldable structural materials developed rapidly, since the 80s has become and martensitic, austenitic and ferritic stainless steel alongside a steel class. Duplex stainless steel has the following performance characteristics.
- (1) Molybdenum-containing duplex stainless steel has good resistance to chloride stress corrosion under low stress. General 18-8 austenitic stainless steel in more than 60 ° C neutral chloride solution is prone to stress corrosion fracture, in trace amounts of chloride and hydrogen sulfide industrial media with this type of stainless steel manufactured heat exchangers, evaporators and other equipment have a tendency to produce stress corrosion fracture, while duplex stainless steel has good resistance.
- (2) Molybdenum-containing duplex stainless steel has good resistance to pore corrosion. In the same pore corrosion resistance equivalent value (PRE = Cr% + 3.3Mo% + 16N%), duplex stainless steel and austenitic stainless steel critical pore corrosion potential is similar. Duplex stainless steel and austenitic stainless steel pore corrosion resistance is comparable to AISI 316L. Containing 25% Cr, especially the high chromium duplex stainless steel containing nitrogen resistance to pore corrosion and crevice corrosion performance exceeds that of AISI 316L.
- (3) Has good resistance to corrosion fatigue and wear corrosion performance. In some corrosive media conditions, suitable for making pumps, valves and other power equipment.
- (4) Good overall mechanical properties. Have high strength and fatigue strength, yield strength is 18-8 austenitic stainless steel 2 times. The elongation of the solid solution state reaches 25%, and the toughness value AK (V-notch) is above 100J.
- (5) Good weldability, low thermal cracking tendency, generally no preheating before welding, no heat treatment after welding, can be welded with 18-8 austenitic stainless steel or carbon steel and other dissimilar species.
- (6) Containing low chromium (18% Cr) duplex stainless steel heat processing temperature range than 18-8 type austenitic stainless steel, resistance is small, without forging, direct rolling open billet production steel plate. Containing high chromium (25% Cr) duplex stainless steel hot processing than austenitic stainless steel is slightly more difficult, can produce plates, tubes and wires and other products.
- (7) Cold processing than 18-8 austenitic stainless steel process hardening effect is large, in the tube, plate bear deformation at the beginning, need to apply greater stress to deformation.
- (8) Compared with austenitic stainless steel, the thermal conductivity is large, the coefficient of linear expansion is small, suitable for use as the lining of equipment and the production of composite plates. Also suitable for making the core of the heat exchanger, heat transfer efficiency is higher than austenitic stainless steel.
- (9) There are still various brittle tendencies of high chromium ferritic stainless steel, should not be used in working conditions higher than 300°C. The lower the chromium content in duplex stainless steel, the less hazardous the brittle phase such as σ.
The use of duplex stainless steel
Used for refining, fertilizer, paper, petroleum, chemical and other seawater resistant high temperature resistant concentrated nitric acid and other heat exchangers and cold showers and devices.
The structure and type of duplex stainless steel
Duplex stainless steel has the characteristics of both austenitic stainless steel and ferritic stainless steel because of the austenitic + ferrite duplex organization, and the content of the two phase organizations are basically equivalent. Yield strength up to 400Mpa – 550MPa, is two times the ordinary austenitic stainless steel. Compared with ferritic stainless steel, duplex stainless steel has high toughness, low brittle transition temperature, intergranular corrosion resistance and welding performance are significantly improved; while retaining some characteristics of ferritic stainless steel, such as 475 ℃ brittleness, high thermal conductivity, small coefficient of linear expansion, superplasticity and magnetic properties. Compared with austenitic stainless steel, duplex stainless steel has high strength, especially the yield strength is significantly improved, and pore corrosion resistance, stress corrosion resistance, corrosion fatigue resistance and other properties have also been significantly improved.
Duplex stainless steel according to its chemical composition classification, can be divided into Cr18 type, Cr23 (without Mo) type, Cr22 type and Cr25 type four categories. For the Cr25 type duplex stainless steel can be divided into ordinary and super duplex stainless steel, which is used more Cr22 type and Cr25 type. Duplex stainless steel used in China is mainly produced in Sweden, the specific grades are: 3RE60 (Cr18), SAF2304 (Cr23), SAF2205 (Cr22), SAF2507 (Cr25).
Classification of duplex stainless steel
The first category is a low-alloy type, the representative grade UNS S32304 (23Cr-4Ni-0.1N), the steel does not contain molybdenum, PREN value of 24-25, in the stress corrosion resistance can be used instead of AISI304 or 316.
The second category is a medium-alloy type, the representative grade is UNS S31803 (22Cr-5Ni-3Mo-0.15N), PREN value of 32-33, its corrosion resistance between AISI 316L and 6% Mo + N austenitic stainless steel.
The third category is a high-alloy type, generally containing 25% Cr, also contains molybdenum and nitrogen, some also contain copper and tungsten, the standard grade UNSS32550 (25Cr-6Ni-3Mo-2Cu-0.2N), PREN value of 38-39, the corrosion resistance of this type of steel is higher than 22% Cr duplex stainless steel.
The fourth category is a super duplex stainless steel type, containing high molybdenum and nitrogen, the standard grade UNS S32750 (25Cr-7Ni-3.7Mo-0.3N), some also contain tungsten and copper, PREN value greater than 40, can be applied to harsh media conditions, with good corrosion resistance and mechanical properties, comparable with super austenitic stainless steel.
What is precipitation hardening stainless steel
Precipitation-hardening stainless steel is a type of high-strength stainless steel, referred to as PH steel, in which different types and quantities of strengthening elements are added to the chemical composition of stainless steel, and different types and quantities of carbides, nitrides, carbon-nitrides and intermetallic compounds are precipitated through the precipitation-hardening process to both improve the strength of the steel and maintain sufficient toughness.
Classification of precipitation hardening stainless steel
According to the content of the main alloying elements in the steel and the hardening elements added and divided into four categories, namely.
- (1) Martensitic precipitation-hardening stainless steel, containing generally low 0.1% carbon. Strengthened by the addition of hardening elements (copper, aluminum, titanium and aluminum, etc.) to compensate for the lack of strength. Chromium content is generally higher than 17%, and the addition of a moderate amount of nickel to improve corrosion resistance.
- (2) Martensitic aging stainless steel, containing no more than 0.03% carbon to ensure the toughness, corrosion resistance, weldability and workability of the martensitic matrix, containing not less than 12% chromium to ensure corrosion resistance. In addition to the addition of the alloying element cobalt to further improve the heat treatment of steel.
- (3) Semi-austenitic, i.e., transition precipitation hardening stainless steel, containing not less than 12% chromium. Low carbon content, and aluminum as its main precipitation hardening element this type of steel than martensitic precipitation hardening stainless steel has a better overall performance.
- (4) Austenitic precipitation hardening stainless steel, is in the quenched state and aging state are stable austenitic organization of stainless steel, containing nickel (higher than 25%) and manganese are high, containing chromium higher than 13% to ensure good corrosion resistance and oxidation resistance usually add titanium, aluminum, vanadium or phosphorus as precipitation hardening elements, while adding trace amounts of boron, vanadium, nitrogen and other elements, in order to obtain excellent overall performance.
What is martensitic stainless steel
Martensitic steel (MS-MartensiticSteel) microstructure is almost entirely martensitic. Mainly through high temperature austenitic tissue rapid quenching transformation into slatted martensitic tissue, can be achieved by hot rolling, cold rolling, martensitic steel has a high tensile strength, its maximum strength of up to 1600MPa, the need for tempering treatment to improve its plasticity, so that it still has sufficient forming properties at such a high strength, is the highest strength level of commercial high-strength steel plate steel. Usually can only be produced by roll forming or stamping simple-shaped parts, mainly used for forming parts such as door bumpers with low requirements to replace tubular parts and reduce manufacturing costs. Martensitic steel is mainly 600MPa or more some high strength steel, such as 800MPa or more levels of construction machinery steel, 600MPa or more levels of pressure vessels and storage tanks steel. Generally, there are two production processes: online quenching and tempering and post-rolling quenching and tempering (tempering treatment). The high strength of martensite is due to the high density of dislocations, fine twins, carbon bias, and the martensite squareness of the interstitial solid solution. The morphology of low-carbon martensite is basically lath-like, lath-like between the small angle grain boundaries, lath within a high density of dislocations, and sometimes can be seen between the distribution of twin crystal martensite lath. However, the quenched martensite plastic toughness is poor, generally martensitic steel after quenching are to be tempered through the tempering process to adjust the steel strength and toughness match.
Martensitic stainless steel chromium content is generally in the range of 12%-18%, when the chromium exceeds 15%, it is often necessary to add a certain amount of nickel or appropriate to increase the carbon content to balance the organization.
This type of steel is heated to high temperatures when the organization for austenite, cooled to room temperature, transformed into martensite, so you can heat treatment to strengthen. Generally used in the quenched-tempered (tempered) state.
Martensitic stainless steel has the following types.
- (1) Ordinary Cr13 steel such as 1Cr13, 2Cr13, 3Cr13 and 4Cr13 and so on for the most commonly used steel. These steels can be hardened by high-temperature heating after air-cooling, quenching the strength, hardness with the increase in carbon content, but corrosion resistance and plasticity, toughness is subsequently reduced. The first two types of steel are mainly used in the medium temperature corrosive medium and require medium strength structural parts, the latter two types of steel are mainly used for high strength, high wear resistance and corrosion resistance requirements of certain parts.
- (2) Hot martensitic steel is based on Cr12 after complex alloying of martensitic steel, such as 2Cr12WMoV, 2Cr12MoV, 2Cr12Ni3MoV, etc.. Likewise, they can be hardened by air cooling after high temperature heating. These steels not only have high instantaneous strength at medium temperature, but also have excellent medium-temperature durability and creep properties, good stress corrosion resistance and hot and cold fatigue properties. Very suitable for the production of 500-600 ℃ and below the wet and hot conditions of the work of the load-bearing parts, complex forgings and welded parts. This type of steel in the addition of Mo, W, V at the same time, often then raise the carbon some, so its hardening tendency is greater, generally by the tempering treatment. This is a new type of martensitic high-strength steel. Its characteristics
- (3) Ultra-low carbon complex martensitic steel. This is the carbon content down to 0.05% or less, and add nickel (w (Ni) = 4%-7%), in addition to a small amount of Mo, Ti or Si, etc.. High strength and high toughness can be obtained by quenching and tempering treatment with ultra-fine complex phase organization. Can also be used in the quenched state, because the low-carbon martensite organization and no hard brittleness. This type of steel is suitable for barrels, pressure vessels and low-temperature parts.
- (4) Martensitic heat-resistant steel can be broadly divided into two categories of a simple Cr13 type of horse 2Cr13, etc.; the other is based on Cr12 type of multiples, such as 1Cr13, gold-reinforced martensitic steel, such as Cr12Ni2W2MoV, Cr12WMoNiB, etc.. The former is generally used for corrosion resistance and require a certain strength of the parts, such as turbine blades; the latter is mainly used as a hot steel, such as the main steam pipe of thermal power plants. The common feature of both is the high-temperature heating after air-cooling has a great tendency to harden, generally after tempering treatment to give full play to the performance characteristics of such steel. Although martensitic heat-resistant steel alone for a class, but can be found ordinary Cr13 martensitic stainless steel and hot strong martensitic stainless steel is also heat-resistant steel.
Martensitic stainless steel containing 13%-18% chromium, quenched and tempered state, used for turbine blades (lower carbon content), medical surgical tools, measuring tools, springs, etc. (higher carbon content); martensitic precipitation hardening stainless steel, chromium-nickel content than the former is high, by high temperature solution, quenching, and then in 400-500 ℃ aging treatment, in the martensitic matrix precipitation of a large number of matrix manipulation with the co-grid The second phase of the relationship, used in chemical pressure vessels, aircraft structures, etc. Martensitic heat-resistant steel containing chromium 7.5%-20.5%, containing 0.15%-0.85% carbon and a variety of alloying elements, tempered at 650-700 ℃, the formation of fine carbide dispersion in the matrix, mainly used for automotive and other engine valves, turbine blades, nozzles, bolts, etc. Maraging steel, containing higher nickel 18%-25%, molybdenum 5%, cobalt 8% and a small amount of titanium and aluminum, after solid solution air cooling and then aging treatment at 480 ℃.
Strengthened by the precipitation of intermetallic compounds in martensite, it is generally used for important structural parts in aviation, aerospace and marine technology, such as rocket engine cases, aircraft landing gear, important molds, etc. due to its high cost.
What are the pros and cons of stainless steel?
Stainless steel is a very strong and durable material that can be used for a wide variety of projects. It is easy to clean and maintain, which means your finished product will look great for years to come. Here are some of the pros and cons of stainless steel:
Stainless steel is rust free, stain free, and corrosion free, so it should last forever!
Stainless Steel is very easy to clean and maintain. You can just wipe it down with soap water then rinse it off. This makes Stainless Steel a good choice if you have pets or young children who might dirty other materials like wood or plastic. Stainless Steel can also be painted in any color you choose which makes it perfect for matching any decor style from modern sleek designs all the way back through history’s most popular styles like Victorian or contemporary design styles as well!
Stainless Steel has been around since 1820 when Sir Henry Bessemer invented this new form of metal; today there are over 1 million tons produced annually worldwide making up 75% all manufactured metals globally! However because this material can still scratch easily in certain situations (e.g., touching another metal), you’ll probably want something else if that’s an issue: colored aluminum might work better depending on what type of project you’re doing (and whether or not they’ll be touching each other). Also note that while there are many different grades available based on their composition – stainless steels are not all created equal either so remember to ask about these differences first before buying one made out specifically for what purpose!”) }
stainless steel is rust free, stain free, and corrosion free.
Stainless steel is a metal alloy that’s resistant to rust and corrosion. It’s extremely strong, making it a suitable choice for outdoor projects like railings, gates, and fences. Stainless steel is also a good option if your project will get wet frequently (such as your deck railing).
Stainless steel comes in two basic types: austenitic and ferritic. Austenitic stainless steels are magnetic and have lower nickel content than ferritic varieties; they don’t corrode as easily as ferritic alloys do—but they’re much more expensive than their counterparts. Ferritic alloys are less expensive but can still be used effectively for many applications; however, these types of stainless steels tend to be more susceptible to corrosion from chloride exposure than other kinds of alloys.
stainless steel is very easy to clean and maintain.
Stainless steel is a very durable material that can be used for many household items. The material is easy to clean and maintain, making it extremely practical for use in kitchens, bathrooms, and other common areas of the house.
Stainless steel is also resistant to rust and corrosion. It can be cleaned with soap and water or disinfectant wipes or sprays without having to worry about it becoming damaged through overuse of harsh chemicals or improper cleaning techniques!
This means you don’t have to worry about maintaining your stainless steel products; they will last longer because they aren’t as susceptible as other materials would be under similar circumstances (especially when exposed regularly).
Stainless steel is affordable in most cases.
Stainless steel is an affordable option in most cases. The price of stainless steel varies depending on the type and grade of the steel, but it typically falls between $0.50 and $1 per pound. This is lower than the cost of copper (which can be as high as $2 per pound), but higher than aluminum ($0.10-$0.30 per pound). In general, however, stainless steel tends to be more expensive than other materials—such as aluminum or copper—when considering both initial costs and long-term maintenance costs over time.
In many cases you’re looking at a material that’s just under half the price of copper or aluminum, but with better corrosion resistance thanks to those chromium or nickel components we mentioned earlier!
You can buy stainless steel in a variety of colors and finishes and it can be custom made.
Stainless steel is a beautiful color and it can be made in almost any shape, which makes it the perfect option for custom designs.
Stainless steel is also available in many different finishes including brushed, polished, satin and hammered as well as other options. This means you can choose the look that will best suit your needs.
Stainless steel is highly durable, however it can still scratch.
Stainless steel is a durable material, but it can still be scratched. The best way to avoid this is to buy stainless steel with a protective coating or finish. If you’re not sure what type of protective coating you want, ask your local commercial kitchen equipment dealer for their recommendations.
You can also use stainless steel for many projects in your home and office, such as building shelves or tables and making chairs out of pipe fittings!
Stainless steel might be your best choice for a material in your next project
Stainless steel is durable, affordable and easy to clean. Many people choose stainless steel for their kitchen appliances because of its long-lasting quality. Stainless steel can also be found in bathroom fixtures, such as showerheads and faucets.
Stainless steel is easy to maintain because it requires minimal care: You just need to wipe the surface clean with soap and water or a special cleaning solution once in a while. You can also use conical brushes made specifically for cleaning sinks that have hard-to-reach spots (like behind the spout).
It’s also possible to customize your stainless steel product by picking out exactly which color finish you want—from bright silver alloys with mirror reflectivity all the way down through matte black finishes—or what kind of pattern you want on top (think brushed aluminum). This versatility makes it an attractive choice for many DIYers looking for something sleekly modern yet affordable enough not break their budget completely!
Stainless steel is one of the best materials for any project. It is durable, low maintenance and easy to clean. If you are looking for a material that will not rust, stain or corrode then stainless steel might be the answer for you!
What is the disadvantage of stainless steel?
Stainless steel contains nickel.
Nickel is a known carcinogen, and its inclusion in stainless steel cookware can cause skin irritation and respiratory problems. A study in 2008 revealed that nickel sulfate is released when cooking acidic foods with stainless steel pots and pans, which can lead to neurological problems. The U.S. Food and Drug Administration (FDA) notes that long-term exposure to nickel may cause cardiovascular problems as well.
Stainless steel is not as thermo-conductive as carbon steel.
This means that it’s slower at transferring heat from the pan to your food, which can make a difference in how quickly you’re able to bring something to a boil or even just browning meat. The same principle applies when using it for cooking: if you want your pan handle to be cool enough for safe handling after cooking with high heat, you may not want stainless steel because of its poorer conductivity.
Stainless steel is expensive.
Stainless steel is more expensive than carbon steel. The cost of stainless steel varies depending on the grade of stainless steel and the size of your order. In general, however, you should expect that it will be more expensive than carbon steel.
In addition to being higher in price, there are other disadvantages as well:
The disadvantages of stainless steel is that it contains Nickel and isn’t as thermo-conductive as carbon steel.
Stainless steel is not as thermally conductive as carbon steel. Stainless steel contains nickel, which is a heavy metal that can cause cancer, skin rashes, and allergic reactions in some people.
What is the advantage of stainless steel?
Stainless steel is a product of advanced metallurgy that is often used within the manufacturing industry. It is a versatile material and has many advantages over other metals. Let’s explore some of the benefits and uses of stainless steel!
Stainless steel is often used in a variety of applications, such as building and construction, medical equipment, aerospace, food processing and many other fields. It’s also a popular choice for cookware because it resists rusting and corrosion.
While stainless steel can be used as a structural material in building construction, it’s usually only used for small parts such as handrails or door frames. This is because stainless steel is much more expensive than other metals like aluminum or copper. In addition to being strong enough to be used in a variety of applications (see below), stainless steel resists corrosion from moisture better than most other alloys used by humans today
Oxidation and oxidation resistance
What is oxidation?
Oxidation is the process by which a substance loses electrons. Metals are naturally prone to oxidation, but stainless steel has a higher resistance than other metals and can be used in many environments where other metals would rust or corrode.
Stainless steel is more expensive than other metals. A stainless steel carafe can cost $30 while a copper version will cost $15. However, this doesn’t mean that all stainless steel objects are more expensive than other materials. For example, a quality chef’s knife made of high carbon steel will be more expensive than one made of stainless steel but not as good in quality or performance; it won’t hold an edge as well and will require frequent sharpening.
Stainless steel is a great conductor of both heat and electricity. That’s because stainless steel is a good conductor, which means it can easily pass on electrical charges. If you’re looking for something that conducts these two elements well, look no further than stainless steel!
Stainless steel is a durable, sturdy material that resists corrosion and rust.
Stainless steel is a strong, durable material that resists corrosion and rust. It can be used for many applications because it is resistant to wear and tear, heat and cold. For example, if you have a stainless steel sink in your kitchen then you won’t have to worry about using chemicals like bleach or ammonia on it because these chemicals will not damage the sink.
Stainless steel can also be used as a heat exchanger or as the outer layer of a refrigerator or freezer unit because they are resistant to extreme temperatures. This means that they will not rust when exposed to moisture at high temperatures.
The next time you need a strong, resilient material, consider stainless steel. It is affordable and versatile, making it useful for a wide variety of applications. We hope this guide has given you the information to determine if stainless steel is right for your needs!
Chemical Composition of Stainless Steel
Stainless steel is composed of various elements to enhance the corrosion resistance of the steel. The main alloying component in all stainless steel metals is chromium (minimum 10.5%).
The elemental chemical composition of stainless steel is mainly composed of iron (Fe) and chromium (Cr), and other alloying elements in the chemical composition include carbon (C), silicon (Si), manganese (Mn), phosphorus (P), sulfur (S), nickel (Ni), molybdenum (Mo), titanium (Ti), nitrogen (N) and copper (Cu). Only when the Cr percentage composition reaches a certain value, this steel has corrosion resistance. Therefore, the chromium content of stainless steel metal is usually at least 10.5%.
The following table lists the chemical composition of stainless steel alloys, including austenitic SS 304, 304L 316, 316L, 321, 303, 302, 301, 904L, 201, etc., martensitic SS 440A, 440B, 440C, 420, etc., ferritic SS 430, duplex stainless steels 2205, 2507, 329, etc.
Note: UOS (unless otherwise specified)
|Stainless Steel Chemical Composition Chart, Percentage (%)|
|Stainless Steel||C, ≤||Mn, ≤||P, ≤||S, ≤||Si, ≤||Cr||Ni||Mo||N, ≤||Other Elements, ≤, UOS|
|321||0.08||2.00||0.045||0.03||1.00||17.0-19.0||9.0-12.0||–||0.10||≥ Ti 5×(C+N), ≤ 0.70|
|309Cb||0.08||2.00||0.045||0.03||1.00||22.0-24.0||12.0-16.0||–||–||≥ Cb 10 x C, ≤1.10|
|309HCb||0.04-0.10||2.00||0.045||0.03||0.75||22.0-24.0||12.0-16.0||–||–||≥ Cb 10 x C, ≤1.10|
|310Cb||0.08||2.00||0.045||0.03||1.5||24.0-26.0||19.0-22.0||–||–||≥ Cb 10 x C, ≤ 1.10|
|316Ti||0.08||2.00||0.045||0.03||1.00||16.0-18.0||10.0-14.0||2.00-3.00||0.1||≥ Ti 5 × (C + N), ≤0.70|
|316Cb||0.08||2.00||0.045||0.03||1.00||16.0-18.0||10.0-14.0||2.00-3.00||0.1||≥ Cb 10 × C, ≤ 1.10|
|321||0.08||2.00||0.045||0.03||1.00||17.0-19.0||9.0-12.0||–||0.1||≥ Ti 5 × (C + N), ≤ 0.70|
|321H||0.04-0.10||2.00||0.045||0.03||0.75||17.0-19.0||9.0-12.0||–||–||≥ Ti 4 × (C + N), ≤ 0.70|
|334||0.08||1.00||0.03||0.015||1.00||18.0-20.0||19.0-21.0||–||–||Al 0.15-0.60, Ti 0.15-0.60|
|347||0.08||2.00||0.045||0.03||1.00||17.0-19.0||9.0-12.0||–||–||≥ Cb 10 × C, ≤ 1.00|
|347H||0.04-0.10||2.00||0.045||0.03||0.75||17.0-19.0||9.0-13.0||–||–||≥ Cb 8 × C, ≤ 1.00|
|347LN||0.005-0.020||2.00||0.045||0.03||1.00||17.0-19.0||9.0-13.0||–||0.06-0.10||Cb 0.20-0.50, 15 × C ≥|
|348||0.08||2.00||0.045||0.03||1.00||17.0-19.0||9.0-12.0||–||–||Cb 10×C-1.10, Ta 0.10, Co 0.20|
|348H||0.04-0.10||2.00||0.045||0.03||0.75||17.0-19.0||9.0-13.0||–||–||(Cb + Ta) 8×C ≥ , 1.00 ≤, Ta 0.10, Co 0.20|
|420FSe||0.20-0.40||1.25||0.06||0.15||1.00||12.0-14.0||0.5||–||–||Se 0.15; Cu 0.60|
|422||0.20-0.25||0.50-1.00||0.025||0.025||0.5||11.0-12.5||0.50-1.00||0.90-1.25||–||V (0.20-0.30), W (0.90-1.25)|
|439||0.03||1.00||0.04||0.03||1.00||17.0-19.0||0.5||–||0.03||≥ Ti [0.20+4(C+N)], ≤ 1.10; Al 0.15|
|436||0.12||1.00||0.04||0.03||1.00||16.0-18.0||–||0.75-1.25||–||≥ Cb 5×C, ≤ 0.80|
|440FSe||0.95-1.20||1.25||0.06||0.06||1.00||16.0-18.0||0.5||–||–||Se ≤0.15; Cu ≤0.60|
|444||0.025||1.00||0.04||0.03||1.00||17.5-19.5||1.00||1.75-2.50||0.035||Ti+Cb 0.20+4 × (C+N)-0.80|
|800||0.1||1.5||0.045||0.015||1.00||19.0-23.0||30.0-35.0||–||–||Cu 0.75; ≥ FeH 39.5; Al 0.15-0.60|
|800H||0.05-0.10||1.5||0.045||0.015||1.00||19.0-23.0||30.0-35.0||–||–||Cu 0.75; ≥ FeH 39.5; Al 0.15-0.60|
|Alloy 20||0.07||2.00||0.045||0.035||1.00||19.0-21.0||32.0-38.0||2.00-3.00||–||Cu 3.0-4.0; ≥ Nb 8 × C; ≤1.00|
|XM-19||0.06||4.0-6.0||0.045||0.03||1.00||20.5-23.5||11.5-13.5||1.50-3.00||0.20-0.40||Cb 0.10-0.30, V 0.10-0.30|
|XM-27||0.01||0.4||0.02||0.02||0.4||25.0-27.5||0.5||0.75-1.50||0.015||Cu 0.20; Cb 0.05-0.20; (Ni + Cu) 0.50|
|XM-33||0.06||0.75||0.04||0.02||0.75||25.0-27.0||0.5||0.75-1.50||0.04||Cu 0.20; Ti 0.20-1.00; ≥ Ti 7(C+N)|
|15-5 PH||0.07||1||0.04||0.03||1||14.0-15.5||3.5-5.5||–||–||2.5-4.5 Cu; 0.15-0.45 Nb|
|17-4 PH||0.07||1||0.04||0.03||1||15.5-17.5||3.0-5.0||–||–||3.0-5.0 Cu; 0.15-0.45 Nb|
|17-7 PH||0.09||1||0.04||0.04||1||16.0-18.0||6.5-7.75||–||–||0.75-1.5 Al|
|Stainless Steel||C, ≤||Mn, ≤||P, ≤||S, ≤||Si, ≤||Cr||Ni||Mo||N, ≤||Other Elements, ≤, UOS|
Comparison Conversion of Stainless Steel
|301||X 12 CrNi 17 7||1.431||Z 12 CN 17-07||SUS 301||X 12 CrNi 1707||X 12 CrNi 17 7||X 12 CrNi 17-07|
|302||X 5 CrNi 18 7||1.4319||Z 10 CN 18-09||SUS 302||X 10 CrNi 1809||X 10 CrNi 18 9||X 10 CrNi 18-09||12KH18N9|
|303||X 10 CrNiS 18 9||1.4305||Z 10 CNF 18-09||SUS 303||X 10 CrNiS 1809||X 10 CrNiS 18 9||X 10 CrNiS 18-09|
|303||Z 10 CNF 18-09||SUS 303 Se||X 10 CrNiS 1809||X 10 CrNiS 18-09||12KH18N10E|
|304||X 5 CrNi 18 10 X 5 CrNi 18 12||1.4301 1.4303||Z 6 CN 18-09||SUS 304||X 5 CrNi 1810||X 6 CrNi 18 10||X 6 CrNi 19-10||08KH18N10 06KH18N11|
|304 N||SUS 304N1||X 5 CrNiN 1810|
|304H||SUS F 304H||X 8 CrNi 1910||X 6 CrNi 19-10|
|304L||X 2 CrNi 18 11||1.4306||Z 2 CN 18-10||SUS 304L||X 2 CrNi 1911||X 3 CrNi 18 10||X 2 CrNi 19-10||03KH18N11|
|X 2 CrNiN 18 10||1.4311||Z 2 CN 18-10-Az||SUS 304LN||X 2 CrNiN 1811|
|305||Z 8 CN 18-12||SUS 305||X 8 CrNi 1812||X 8 CrNi 18 12||X 8 CrNi 18-12|
|Z 6 CNU 18-10||SUS XM7||X 6 CrNiCu 18 10 4 Kd|
|309||X 15 CrNiSi 20 12||1.4828||Z 15 CN 24-13||SUH 309||X 16 CrNi 2314||X 15 CrNi 23 13|
|309S||SUS 309S||X 6 CrNi 2314||X 6 CrNi 22 13|
|310||X 12 CrNi 25 21||1.4845||SUH 310||X 22 CrNi 2520||20KH23N18|
|310S||X 12 CrNi 25 20||1.4842||Z 12 CN 25-20||SUS 310S||X 5 CrNi 2520||X 6 CrNi 25 20||10KH23N18|
|314||X 15 CrNiSi 25 20||1.4841||Z 12 CNS 25-20||X 16 CrNiSi 2520||X 15 CrNiSi 25 20||20KH25N20S2|
|316||X 5 CrNiMo 17 12 2||1.4401||Z 6 CND 17-11||SUS 316||X 5 CrNiMo 1712||X 6 CrNiMo 17 12 2||X 6 CrNiMo 17-12-03|
|316||X 5 CrNiMo 17 13 3||1.4436||Z 6 CND 17-12||SUS 316||X 5 CrNiMo 1713||X 6 CrNiMo 17 13 3||X 6 CrNiMo 17-12-03|
|316 F||X 12 CrNiMoS 18 11||1.4427|
|316 N||SUS 316N|
|316 H||SUS F 316H||X 8 CrNiMo 1712||X 5 CrNiMo 17-12|
|316 H||X 8 CrNiMo 1713||X 6 CrNiMo 17-12-03|
|316 L||X 2 CrNiMo 17 13 2||1.4404||Z 2 CND 17-12||SUS 316L||X 2 CrNiMo 1712||X 3 CrNiMo 17 12 2||X 2 CrNiMo 17-12-03||03KH17N14M2|
|X 2 CrNiMoN 17 12 2||1.4406||Z 2 CND 17-12-Az||SUS 316LN||X 2 CrNiMoN 1712|
|316 L||X 2 CrNiMo 18 14 3||1.4435||Z 2 CND 17-13||X 2 CrNiMo 1713||X 3 CrNiMo 17 13 3||X 2 CrNiMo 17-12-03||03KH16N15M3|
|X 2 CrNiMoN 17 13 3||1.4429||Z 2 CND 17-13-Az||X 2 CrNiMoN 1713|
|X 6 CrNiMoTi 17 12 2||1.4571||Z6 CNDT 17-12||X 6 CrNiMoTi 1712||X 6 CrNiMoTi 17 12 2||X 6 CrNiMoTi 17-12-03||08KH17N13M2T 10KH17N13M2T|
|X 10 CrNiMoTi 18 12||1.4573||X 6 CrNiMoTi 1713||X 6 CrNiMoTI 17 13 3||X 6 CrNiMoTi 17-12-03||08KH17N13M2T 10KH17N13M2T|
|X 6 CrNiMoNb 17 12 2||1.458||Z 6 CNDNb 17-12||X 6 CrNiMoNb 1712||X 6 CrNiMoNb 17 12 2||08KH16N13M2B|
|X 10 CrNiMoNb 18 12||1.4583||X 6 CrNiMoNb 1713||X 6 CrNiMoNb 17 13 3||09KH16N15M3B|
|317||SUS 317||X 5 CrNiMo 1815|
|317L||X 2 CrNiMo 18 16 4||1.4438||Z 2 CND 19-15||SUS 317L||X 2 CrNiMo 1815||X 3 CrNiMo 18 16 4|
|317 L||X 2 CrNiMo 18 16 4||1.4438||Z 2 CND 19-15||SUS 317L||X 2 CrNiMo 1816||X 3 CrNiMo 18 16 4|
|330||X 12 NiCrSi 36 16||1.4864||Z 12NCS 35-16||SUH 330|
|321||X 6 CrNiTi 18 10 X 12 CrNiTi 18 9||1.4541 1.4878||Z 6 CNT 18-10||SUS 321||X 6 CrNiTi 1811||X 6 CrNiTi 18 10||X 6 CrNiTi 18-11||08KH18N10T|
|321H||SUS 321H||X 8 CrNiTi 1811||X 7 CrNiTi 18-11||12KH18N10T|
|329||X 8 CrNiMo 27 5||1.446||SUS 329J1|
|347||X 6 CrNiNb 18 10||1.455||Z 6 CNNb 18-10||SUS 347||X 6 CrNiNb 1811||X 6 CrNiNb 18 10||X 6 CrNiNb 18-11||08KH18N12B|
|347H||SUS F 347H||X 8 CrNiNb 1811||X 7 CrNiNb 18-11|
|904L||1.4539||Z 12 CNDV 12-02|
|X 20 CrNiSi 25 4||1.4821|
|S31803||X 2 CrNiMoN 22 5||1.4462|
|S32760||X 3 CrNiMoN 25 7||1.4501||Z 3 CND 25-06Az|
|403||X 6 Cr 13 X 10 Cr 13 X 15 Cr 13||1.4000 1.4006 1.4024||Z 12 C 13||SUS 403||X 12 Cr 13||X 10 Cr 13 X 12 Cr 13||X 6 Cr 13||12Kh13|
|405||X 6 CrAl 13||1.4002||Z 6 CA 13||SUS 405||X 6 CrAl 13||X 6 CrAl 13||X 6 CrAl 13|
|X 10 CrAl 7||1.4713||Z 8 CA 7||X 10 CrAl 7|
|X 10 CrAl 13||1.4724||X 10 CrAl 12||10Kh13SYu|
|X 10 CrAl 18||1.4742||X 10 CrSiAl 18||15Kh18SYu|
|409||X 6 CrTi 12||1.4512||Z 6 CT 12||SUH 409||X 6 CrTi 12||X 5 CrTi 12|
|X 2 CrTi 12|
|410||X 6 Cr 13 X 10 Cr 13 X 15 Cr 13||1.4000 1.4006 1.4024||Z 10 C 13 Z 12 C 13||SUS 410||X 12 Cr 13||X 12 Cr 13||X 12 Cr 13||12Kh13|
|410S||X 6 Cr 13||1.4||Z 6 C 13||SUS 410S||X 6 Cr 13||X 6 Cr 13||08Kh13|
Density of Stainless Steel
The following table lists the density of stainless steel 304, 316, 303, 304L, 316L and other AISI type stainless.
- 1 g/cm3 = 1 kg/dm3
- The specific weight value in the following table is equal to the density value (g/cm3, metric).
|Density of Stainless Steel|
|Stainless Steel||Density (g/cm3), or specific weight||Density (kg/m3)||Density (lb/in3)||Density (lb/ft3)|
|304, 304L, 304N||7.93||7930||0.286||495|
|316, 316L, 316N||8.0||8000||0.29||499|
|302, 302B, 302Cu||7.93||7930||0.286||495|
|440 (440A, 440B, 440C)||7.7||7700||0.28||481|
Mechanical Properties of Stainless Steel
Required mechanical properties are normally given in purchase specifications for stainless steel. Minimum mechanical properties are also given by the various standards relevant to the material and product form. Meeting these standard mechanical properties indicates that the material has been properly manufactured to an appropriate quality system. Engineers can then confidently utilise the material in structures that meet safe working loads and pressures.
Mechanical properties specified for flat rolled products are normally tensile strength, yield stress (or proof stress), elongation and Brinell or Rockwell hardness. Property requirements for bar, tube, pipe and fittings typically state tensile strength and yield stress.
Yield Strength of Stainless Steel
Unlike mild steels, the yield strength of annealed austenitic stainless steel is a very low proportion of the tensile strength. Mild steel yield strength is typically 65-70% of the tensile strength. This figure tends to only be 40-45% in the austenitic stainless family.
Cold working rapidly and greatly increases the yield strength. Some forms of stainless steel, like spring tempered wire, can be cold worked to lift the yield strength to 80-95% of the tensile strength.
Hardness of Stainless Steel
Hardness is the resistance to penetration of the material surface. Hardness testers measure the depth that a very hard indenter can be pushed into the surface of a material. Brinell, Rockwell and Vickers machines are used. Each of these has a different shaped indenter and method of applying the known force. Conversions between the different scales are therefore only approximate.
Martensitic and precipitation hardening grades can be hardened by heat treatment. Other grades can be hardened through cold working.
Tensile Strength of Stainless Steel
Tensile strength is generally the only mechanical property required to define bar and wire products. Identical material grades may be used at various tensile strengths for completely different applications. The supplied tensile strength of bar and wire products directly relates to the final use after fabrication.
Spring wire tends to have the highest tensile strength after fabrication. The high strength is imparted by cold working into coiled springs. Without this high strength the wire would not function properly as a spring.
Such high tensile strengths are not required for wire to be used in forming or weaving processes. Wire or bar used as raw material for fasteners, like bolts and screws, needs to be soft enough for a head and thread to be formed but still strong enough to perform adequately in service.
in 2in or 50mm length %
Hardness (Max) ASTM E18
Hardness (Max) ASTM E18
|201||95 ||38 ||35||219 HBW||95 HRB|
|304||75 ||30 ||35||192 HBW||90 HRB|
|304L||70 ||25 ||35||192 HBW||90 HRB|
|304H||75 ||30 ||35||192 HBW||90 HRB|
|304N||80 ||35 ||35||192 HBW||90 HRB|
|309S||75 ||30 ||35||192 HBW||90 HRB|
|309H||75 ||30 ||35||192 HBW||90 HRB|
|310S||75 ||30 ||35||192 HBW||90 HRB|
|310H||75 ||30 ||35||192 HBW||90 HRB|
|316||75 ||30 ||35||192 HBW||90 HRB|
|316L||70 ||25 ||35||192 HBW||90 HRB|
|316H||75 ||30 ||35||192 HBW||90 HRB|
|316Ti||75 ||30 ||35||192 HBW||90 HRB|
|317||75 ||30 ||34||192 HBW||90 HRB|
|317L||75 ||30 ||35||192 HBW||90 HRB|
|321||75 ||30 ||35||192 HBW||90 HRB|
|321H||75 ||30 ||35||192 HBW||90 HRB|
|347||75 ||30 ||35||192 HBW||90 HRB|
|TP347H||75 ||30 ||35||192 HBW||90 HRB|
|N08904||71 ||31 ||35||192 HBW||90 HRB|
|N08020||80 ||35 ||30||217 HBW||95 HRB|
|75 ||30 ||30||192 HBW||90 HRB|
|65 ||25 ||30||192 HBW||90 HRB|
|65 ||25 ||30||192 HBW||90 HRB|
|N10276||100 ||41 ||40|
|N06022||100 ||45 ||45|
|S31803||90 ||65 ||25||290 HBW||30 HRC|
|S31803||90 ||65 ||25||290 HBW||30 HRC|
Wall≤0.187 in. [5.00 mm]
Wall≤0.187 in. [5.00 mm]
|30||290 HBW||30 HRC|
|S32205||95 ||70 ||25||290 HBW||30 HRC|
|S32550||110 ||80 ||15||297 HBW||31 HRC|
OD 1 in. [25 mm] and Under
OD over 1 in. [25 mm]
OD 1 in. [25 mm] and Under
OD over 1 in. [25 mm]
|S32750||116 ||80 ||15||300 HBW||32 HRC|
|S32760||109 ||80 ||25||300 HBW||…|
Physical Properties of Stainless Steel
The reason for choosing stainless steel is normally due to advantages given by physical properties such as corrosion resistance.
In addition to corrosion resistance, the advantageous physical properties of stainless steel include:
- High and low temperature resistance
- Ease of fabrication
- High Strength
- Aesthetic appeal
- Hygiene and ease of cleaning
- Long life cycle
- Low magnetic permeability
Corrosion Resistance of Stainless Steel
Corrosion is the gradual degradation of a metal through a chemical reaction (usually electrochemical) with its surroundings. It affects material properties such as mechanical strength, appearance, and resistance to liquids and gases.
Although stainless steels are often chosen for their corrosion resistance, they are not immune to corrosion. The resistance of stainless steel to corrosion in a given environment depends on the combination of its chemical composition and environmental aggressiveness.
How Corrosion Occurs
If the minimum chromium content of stainless steel is approximately 10.5%, the corrosion resistance of stainless steel is attributed to the thin passivation film that forms spontaneously on its surface in an oxidizing environment.
The electrochemical reaction leading to corrosion is effectively stopped as the film adheres firmly to the metal substrate and protects it from contact with the surrounding environment. If localized damage, such as a scratch, the film can be “healed” by spontaneous repassivation in an oxidizing environment.
All types of corrosion affecting stainless steel are associated with permanent damage to the passivation film, through complete or partial breakdown. Factors such as chemical environment, pH, temperature, surface finish, product design, manufacturing methods, contamination and maintenance procedures all affect the corrosion behavior of steel and the type of corrosion that can occur.
Corrosion can be divided into two categories: wet corrosion and high temperature corrosion.
The assessment of corrosion resistance in any particular environment, therefore, usually involves a consideration of specific corrosion mechanisms.
These mechanisms are principally:
- Crevice corrosion
- Pitting corrosion
- Intergranular corrosion (or intercrystalline)(IC)
- Stress corrosion cracking (SCC)
- Bimetallic (galvanic) corrosion
Stainless steel tube are generally very corrosion resistant and will perform satisfactorily in most environments. The limit of corrosion resistance of a given stainless steel depends on its constituent elements which means that each grade has a slightly different response when exposed to a corrosive environment. Care is therefore needed to select the most appropriate grade of stainless steel for a given application. As well as careful material grade selection, good detailing and workmanship can significantly reduce the likelihood of staining and corrosion.
Pitting corrosion: Pitting is a localised form of corrosion which can occur as a result of exposure to specific environments, most notably those containing chlorides. In most structural applications, the extent of pitting is likely to be superficial and the reduction in section of a component is negligible. However, corrosion products can stain architectural features. A less tolerant view of pitting should be adopted for services such as ducts, Stainless Steel and containment structures. If there is a known pitting hazard, then a molybdenum bearing stainless steel will be required.
Crevice corrosion: Crevice corrosion is a localised form of attack which is initiated by the extremely low availability of oxygen in a crevice. It is only likely to be a problem in stagnant solutions where a build-up of chlorides can occur. The severity of crevice corrosion is very dependent on the geometry of the crevice; the narrower (around 25 micro-metres) and deeper the crevice, the more severe the corrosion. Crevices typically occur between nuts and washers or around the thread of a screw or the shank of a bolt. Crevices can also occur in welds which fail to penetrate and under deposits on the steel surface.
Bimetallic galvanic corrosion: Bimetallic (galvanic) corrosion may occur when dissimilar metals are in contact in a common electrolyte (e.g. rain, condensation etc.). If current flows between the two, the less noble metal (the anode) corrodes at a faster rate than would have occurred if the metals were not in contact.
The rate of corrosion also depends on the relative areas of the metals in contact, the temperature and the composition of the electrolyte. In particular, the larger the area of the cathode in relation to that of the anode, the greater the rate of attack. Adverse area ratios are likely to occur with fasteners and at joints. Carbon steel bolts in stainless steel members should be avoided because the ratio of the area of the stainless steel to the carbon steel is large and the bolts will be subject to aggressive attack. Conversely, the rate of attack of a carbon steel member by a stainless steel bolt is much slower. It is usually helpful to draw on previous experience in similar sites because dissimilar metals can often be safely coupled under conditions of occasional condensation or dampness with no adverse effects, especially when the conductivity of the electrolyte is low.
The prediction of these effects is difficult because the corrosion rate is determined by a number of complex issues. The use of potential tables ignores the presence of surface oxide films and the effects of area ratios and different solution (electrolyte) chemistry. Therefore, uninformed use of these tables may produce erroneous results. They should be used with care and only for initial assessment.
Austenitic stainless steels usually form the cathode in a bimetallic couple and therefore do not suffer corrosion. Contact between austenitic stainless steels and zinc or aluminium may result in some additional corrosion of the latter two metals. This is unlikely to be significant structurally, but the resulting white/grey powder may be deemed unsightly. Bimetallic corrosion may be prevented by excluding water from the detail (e.g. by painting or taping over the assembled joint) or isolating the metals from each other (e.g. by painting the contact surfaces of the dissimilar metals). Isolation around bolted connections can be achieved by non-conductive plastic or rubber gaskets and nylon or teflon washers and bushes. This system is a time consuming detail to make on site and it is not possible to provide the necessary level of site inspection to check that all the washers and sleeves have been installed properly.
The general behaviour of metals in bimetallic contact in rural, urban, industrial and coastal environments is fully documented in PD 6484 ‘Commentary on corrosion at bimetallic contacts and its alleviation’.
Stress corrosion cracking (SCC)
The development of stress corrosion cracking (SCC) requires the simultaneous presence of tensile stresses and specific environmental factors. It is uncommon in normal building atmospheres. The stresses do not need to be very high in relation to the proof stress of the material and may be due to loading and/or residual effects from manufacturing processes such as welding or bending. Caution should be exercised when stainless steel members containing high residual stresses (e.g. due to cold working) are used in chloride rich environments (e.sg. swimming pools enclosures, marine, offshore).
General (uniform) corrosion
General corrosion is much less severe in stainless steel than in other steels. It only occurs when the stainless steel tubing is at a pH value < 1.0. Reference should be made to tables in manufacturers’ literature, or the advice of a corrosion engineer should be sought, if the stainless steel is to come into contact with chemicals.
Intergranular attack and weld decay
When austenitic stainless steel are subject to prolonged heating between 450-8500 C, the carbon in the steel diffuses to the grain boundaries and precipitates chromium carbide. This removes chromium from the solid solution and leaves a lower chromium content adjacent to the grain boundaries. Steels in this condition are termed ‘sensitised’. The grain boundaries become prone to preferential attack on subsequent exposure to a corrosive environment. This phenomenon is known as weld decay when it occurs in the heat affected zone of a weldment.
Grades of stainless steel which have a low carbon content (-0.03%) will not become sensitised, even for plate thicknesses up to 20 mm when welded by arc processes (giving rapid heating and cooling). Furthermore, modern steelmaking processes mean that a carbon content of 0.05% or less is generally achieved in the standard carbon grades 304 and 316, so these grades will not be prone to weld decay when welded by arc processes.
Other related mechanism can also occur, which include:
- Erosion – corrosion
- Corrosion fatigue
Localised corrosion is often associated with chloride ions in aqueous environments. Acidic conditions (low PH) and increases in temperature all contribute to localised mechanisms of crevice corrosion and pitting corrosion. The addition of tensile strength, whether applied by loading or from residual stress, provides the conditions for stress corrosion cracking (SCC). These mechanisms are all associated with a localised breakdown of the passive layer. A good supply of oxygen to all surface of the steel is essential to maintaining the passive layer but higher levels of chromium, nickel, molybdenum & nitrogen all help in their individual ways to prevent these forms of attack.Resistance to localised forms of corrosion
As a general rule increased corrosion resistance can be expected by moving through the grades:
|1.4512 to 1.4016||409 to 430||increasing chromium from 11 to 17%|
|1.4301||304||adding nickel which aids the reformation of the passive layer if it is disturbed|
|1.4401||316||adding molybdenum reduces the effectiveness of chloride ions in locally breaking down the passive layer|
|1.4539 and 1.4547||904L and 6% molybdenum grades||further increases in chromium, nickel and molybdenum result in overall improved localised corrosion resistance|
Duplex grades such as S32205 (1.4462/S31803) are specifically designed to combat SCC by ‘balancing’ the structure to increase its strength, but additionally molybdenum and nitrogen enhance the pitting resistance, which in turn has the additional benefit in improving their SCC resistance.
Stainless steels are generally considered to be resistant to uniform corrosion in a given environment if the corrosion rate does not exceed 0.1 mm/year. Resistance to uniform corrosion usually increases with increasing chromium, nickel and molybdenum content.
All stainless steels have good corrosion resistance. Low alloy grades resist corrosion under normal conditions. Higher alloys resist corrosion in most acidic and alkaline solutions and chloride environments.
The corrosion resistance of stainless steel depends on its chromium content. Typically, the chromium content of stainless steel is at least about 10.5%. The chromium in the alloy forms a self-healing protective transparent oxide layer that forms spontaneously in air. The self-healing nature of the oxide layer means that its corrosion resistance remains unchanged, regardless of the manufacturing method used. Even if the material surface is cut or damaged, it will heal itself and remain corrosion resistant.
Heat Treating of Stainless Steel
Forged stainless steels are solution annealed after machining and hot working to dissolve carbides and sigma. carbides may form during heating in the 425 to 900°C (800 to 1650°F) range or during slow cooling in this range. Sigma tends to form at temperatures below 925°C (1700°F). Specifications typically call for solution annealing at 1035C (1900°F) with rapid quenching. Grades containing molybdenum are typically solution annealed at higher temperatures of 1095 to 1120°C (2000 to 2050°F) to better homogenize the molybdenum.
Stainless steel can be stress relieved. Several stress relieving treatments are available. Follow the guidelines.
Stress redistribution at 290 to 425°C (550 to 800°F), below the sensitization range.
When stainless steel sheet and bar are cold deformed greater than 30% and subsequently heated to 290-425°C (550-800°F), peak stresses are significantly redistributed and both tensile and yield strengths increase. stress redistribution heat treatment at 290-425°C (550-800°F) will reduce movement in later machining operations and is occasionally used to increase strength. Since stress redistribution treatments are performed at temperatures below 425°C (800°F), carbide precipitation and intergranular corrosion sensitization (IGA) are not a problem for higher carbon grades.
Stress relief at 425 to 595°C (800 to 1100°F) is usually sufficient to minimize distortion that would otherwise exceed dimensional tolerances after machining. Only low carbon “L” grades or stable 321 and 347 grades should be used in weldments stress relieved above 425°C (800°F) because the higher carbon grades are sensitive to IGA when heated above 425°C (800°F).
Stress relief at 815 to 870°C (1500 to 1600°F) is occasionally required when fully stress relieved components are required. Only low carbon “L” grades 321 and 347 should be used in assemblies that are heat treated in this range. Even when using low carbon and stable grades, it is best to test for IGA sensitivity according to ASTM A262 to ensure that there is no sensitization during the stress relief treatment in this temperature range.
For assemblies that will be used in the temperature range of 400 to 900°C (750 to 1650°F), heat stabilization is occasionally performed at 900°C (1650°F) for a minimum of 1 to 10 hours. Heat stabilization is designed to agglomerate carbides, thereby preventing further precipitation and intergranular corrosion (IGA). For stress relief at 815 to 870°C (1500 to 1600°F), it is best to test for IGA sensitivity in accordance with ASTM A262.
Electrolytic polishing of stainless steel
Most stainless steels can be successfully electropolished. However, electrolytic polishing of sulfide free processing grades does not provide a high standard of surface finish. The anodic dissolution of thin surface layers is in principle similar to electrolytic polishing that can be performed on other metals. The removal of approximately 20 to 40 microns leaves a smooth surface that optimizes the corrosion resistance of the steel in any given environment.
Stainless steel electrolytic polishing process
This process uses a relatively low voltage between 12 and 18 volts, but a high current between 750 and 3000 amps. This results in an anode current density of approximately 20 to 40 amps/m2. The stainless steel part being electrolytically polished is the anode in this DC electrolyzer. The electrolyte used is usually a mixture of phosphoric acid and sulfuric acid.
The process takes about 10-20 minutes.
The process results in a “peak” or high point of preferential dissolution on the surface of the part. This results in a net smoothing of the surface, which also facilitates the removal of surface stresses left by the mechanical polishing pretreatment. Contaminants and debris left behind by mechanical surface preparation can also be removed by electrolytic polishing. However, scratches and visible surface irregularities are less likely to be removed by electrolytic polishing. Non-metallic inclusions on the steel surface may be more visible after electropolishing than after mechanical polishing methods. Electrolytic polishing can be used to check the integrity of the casting surface.
The design of the clamping fixture is critical, especially on complex shapes, as it affects the consistency of the polished surface and reduces the risk of gas streaking. Both hydrogen and oxygen are dual products of the process, with the oxygen coming from the stainless steel “anode”. This means that there is no risk of hydrogen embrittlement in stainless steel during the electrolytic polishing process.
Advantages of electropolishing stainless steel surfaces
Optimizes the corrosion resistance of finished stainless steel parts. Eliminates micro cracks on the surface. The electropolished surface should be completely passivated, eliminating the need for further passivation treatments.
Can be used for complex shapes such as wire radiator grilles where mechanical polishing is difficult or impossible.
Improve surface reflectivity.
Removes machined burrs from small parts, thereby reducing the risk of surface contamination from previous mechanical polishing. This provides the added benefit of easier and more efficient cleaning in the use of electropolished items.
In paper and textile processing applications, there is less tendency for contact material to adhere (filter cake) to the component surface and for fibers to “snag”.
Improved surface cleanliness compared to machined surfaces.
Lower bacterial growth rates in food industry applications.
Reduced surface stress on machined components. Improved fatigue life of electropolished stainless steel springs, especially when compared to normal shot peening.
Elimination of clogging surface gases in items operating under high vacuum conditions.
Surface Roughness of Stainless Steel
|Less Frequent Range|
Top Number – Micrometers
Bottom Number – (Microinches)
|50 (2000)||25 (1000)||12.5 (500)||6.3 (250)||3.2 (125)||1.6 (63)||0.80 (32)||0.40 (16)||0.20 (8)||0.10 (4)||0.05 (2)||0.025 (1)||0.012 (.5)|
|EDM Elect Discharge Machining|
|50 (2000)||25 (1000)||12.5 (500)||6.3 (250)||3.2 (125)||1.6 (63)||0.80 (32)||0.40 (16)||0.20 (8)||0.10 (4)||0.05 (2)||0.025 (1)||0.012 (.5)|
|Permanent Mold Casting|
|Cold Rolling, Drawing|
|50 (2000)||25 (1000)||12.5 (500)||6.3 (250)||3.2 (125)||1.6 (63)||0.80 (32)||0.40 (16)||0.20 (8)||0.10 (4)||0.05 (2)||0.025 (1)||0.012 (.5)|
Ra = Roughness, average in micro-meters & micro-inches
|China’s old standard (finish)||China New standard (roughness) Ra||American Standard(microns), Ra||American Standard (Micro-inch), Ra|
|China Old Grade||
Machining surface finish chart: Ra vs RMS
|USA Ra(µm)||USA Ra (Micro inch)||USA RMS (Micro inch)||Machining Finish Method|
|50.0||2000||2200||The most coarse machining or good rough casting surfaces|
|25.0||1000||1100||Machining marks very obvious. Rough turning, boring, planning, drilling|
|12.5||500||550||Machining marks obvious. Normal turning, boring, planning, drilling, grinding|
|8.00||320||352||Machining marks visible. Normal turning, boring, planning, drilling , grinding|
|6.30||250||275||Machining marks visible. Normal turning, boring, planning, drilling , grinding|
|5.00||200||220||Machining marks not obvious. But still visible. Normal turning, boring, planning, drilling, grinding.|
|4.00||160||176||Machining marks not obvious. But still visible. Normal turning, boring, planning, drilling, grinding.|
|3.20||125||137.5||Machining marks not obvious. But still visible. Normal turning, boring, planning, drilling, grinding.|
|2.50||100||110||Machining marks blur, but direction obvious. Number controlled turning, boring, planning, drilling, grinding.|
|2.00||80||88||Machining marks blur, but direction obvious. Number controlled turning, boring, planning, drilling, grinding.|
|1.60||63||69.3||Machining marks blur, but direction obvious. Number controlled turning, boring, planning, drilling, grinding.|
|1.25||50||55||Machining marks direction blur, but still visible. Number controlled turning, boring, planing, drilling, grinding.|
|1.00||40||44||Machining marks direction blur, but still visible. Number controlled turning, boring, planing, drilling, grinding.|
|0.80||32||35.2||Machining marks direction blur, but still visible. Number controlled turning, boring, planing, drilling, grinding.|
|0.63||25||27.5||Machining marks direction blur. Reaming, grinding, boring, rolling.|
|0.50||20||22||Machining marks direction blur. Reaming, grinding, boring, rolling.|
|0.40||16||17.6||Machining marks direction blur. Reaming, grinding, boring, rolling.|
|0.20||12.5||13.75||Machining marks direction invisible. Grinding, super machining|
|0.20||10||11||Machining marks direction invisible. Grinding, super machining|
|0.20||8||8.8||Machining marks direction invisible. Grinding, super machining|
|0.10||4||4.4||Surface dark gloss. Surper machining|
High Temperature Properties Stainless Steel
Stainless steel have good strength and good resistance to corrosion and oxidation at elevated temperatures. Stainless steel are used at temperatures up to 1700° F for 304 and 316 and up to 2000 F for the high temperature stainless grade 309(S) and up to 2100° F for 310(S). Stainless steel is used extensively in heat exchanger, super-heaters, boiler, feed water heaters, valves and main steam lines as well as aircraft and aerospace applications.
Figure.1 gives a broad concept of the hot strength advantages of stainless steel in comparison to low carbon unalloyed steel. Table 1 shows the short term tensile strength and yield strength vs temperature. Table 2 shows the generally accepted temperatures for both intermittent and continuous service.
With time and temperature, changes in metallurgical structure can be expected with any metal. In stainless steel, the changes can be softening, carbide precipitation, or embrittlement. Softening or loss of strength occurs in the 300 series (304, 316, etc.) stainless steel at about 1000° F and at about 900° F for the hardenable 400 (410<, 420, 440) series and 800° F for the non-hardenable 400 (409, 430) series (refer to Table 1).
Carbide precipitation can occur in the 300 series in the temperature range 800 – 1600° F. It can be deterred by choosing a grade designed to prevent carbide precipitation i.e., 347 (Cb added) or 321 (Titanium added). If carbide precipitation does occur, it can be removed by heating above 1900° and cooling quickly.
Hardenable 400 series with greater than 12% chromium as well as the non-hardenable 400 series and the duplex stainless steel are subject to embrittlement when exposed to temperature of 700 – 950° F over an extended period of time. This is sometimes call 885F embrittlement because this is the temperature at which the embrittlement is the most rapid. 885F embrittlement results in low ductility and increased hardness and tensile strength at room temperature, but retains its desirable mechanical properties at operating temperatures.
Table 1 Short Term Tensile Strength vs Temperature (in the annealed condition except for 410)
* heat treated by oil quenching from 1800° F and tempering at 1200° F
Table 2 Generally Accepted Service Temperatures
|304||1600°F (870°C)||1700°F (925°C)|
|316||1600°F (870°C)||1700°F (925°C)|
|309||1800°F (980°C)||2000°F (1095°C)|
|310||1900°F (1035°C)||2100°F (1150°C)|
|410||1500°F (815°C)||1300°F (705°C)|
|420||1350°F (735°C)||1150°F (620°C)|
|430||1600°F (870°C)||1500°F (815°C)|
It may seem to be illogical that the “continuous” service temperature would be higher than the “intermittent” service temperature for the 300 series grades. The answer is that intermittent service involves “thermal cycling”, which can cause the high temperature scale formed to crack and spall. This occurs because of the difference in the coefficient of expansion between the stainless steel and the scale. As a result of this scaling and cracking, there is a greater deterioration of the surface than will occur if the temperature is continuous. Therefore the suggested intermittent service temperatures are lower. This is not the case for the 400 series (both ferritic and martensitic grades). The reason for this is not known.
Drawn and spun stainless steels
Drawing stainless steel
Spinning stainless steel
Bending stainless steel
Bending flat steel materials and bars
The centerline bend radius for stainless steel material is generally considered to be a minimum of 2 x pipe diameter.
Welding stainless steel
Brazing stainless steel
- Brazing in air using flux
- Brazing under reducing atmosphere
- Vacuum brazing
- Brazing in air with flux
- The amount of solder applied to the joint needs to be sufficient
- Brazing time should be as short as possible
- Brazing temperature should be as low as possible
General Principles of Machining Stainless Steel
- tool breakages
- power requirements
Cutting tools for stainless steel
Theoretical weight calculation of stainless steel products
Stainless Steel “L” and “H” Grades
- “L” grade is more expensive.
- Carbon has high physical strength at high temperatures.
- The higher the carbon content, the greater the yield strength.
|Type 304||The most common of austenitic grades, containing approximately 18% chromium and 8% nickel. It is used for chemical processing equipment, for food, dairy, and beverage industries, for heat exchangers, and for the milder chemicals.|
|Type 316||Contains 16% to 18% chromium and 11% to 14% nickel. It also has molybdenum added to the nickel and chrome of the 304. The molybdenum is used to control pit type attack. Type 316 is used in chemical processing, the pulp and paper industry, for food and beverage processing and dispensing and in the more corrosive environments. The molybdenum must be a minimum of 2%.|
|Type 317||Contains a higher percentage of molybdenum than 316 for highly corrosive environments. It must have a minimum of 3% “moly”. It is often used in stacks which contain scrubbers.|
|Type 317L||Restricts maximum carbon content to 0.030% max. and silicon to 0.75% max. for extra corrosion resistance.|
|Type 317LM||Requires molybdenum content of 4.00% min.|
|Type 317LMN||Requires molybdenum content of 4.00% min. and nitrogen of .15% min.|
|These types have been developed for corrosive resistance for repeated intermittent exposure to temperature above 800 degrees F. Type 321 is made by the addition of titanium and Type 347 is made by the addition of tantalum/columbium. These grades are primarily used in the aircraft industry.|
Difference between 304 304L and 321
- 321 = (17-19Cr, 9-12Ni + titanium)
- 304 L grade low carbon, usually 0.035% max
- 304 grade medium carbon, usually 0.08% max
Grade 316 vs. Grade 316L vs. 316Ti Stainless Steel
Are 316Ti and 316L interchangeable?
Alloy 321 (UNS S32100) is a very stable stainless steel. When the temperature reaches 800-1500 ° F (427-816 ° C) and chromium carbide precipitates, it still has good intergranular corrosion resistance. Because of the addition of titanium in the composition, 321 stainless steel can still maintain stability in the case of chromium carbide formation. However, the addition of coltan and tantalum to maintain the stability of alloy 347.
Because of its excellent mechanical properties, 347 stainless steel has advantages in high temperature environment. Compared with 304 alloy, 347 alloy stainless steel has better ductility and stress fracture resistance. In addition, 304L can also be used to resist sensitization and intergranular corrosion.
ASTM A240 and ASME SA-240:
|Component||Unless otherwise specified, the weight percentage is the maximum value listed in the table|
|Coltan + Tantalum**||—||10xc min 1.00 Max|
|Titanium**||5x (c + n) min 0.70 Max||—|
|Nitrogen||zero point one zero||—|
* The carbon content of grade H is 0.04/0.10%.
** Grade H minimum stabilizers are different formulations.
Stress corrosion cracking
Pitting corrosion / crevice corrosion
High temperature oxidation resistance
The physical properties of alloys 321 and 347 are quite similar, but in fact, they can be regarded as the same. The values listed in the table are applicable to both alloys.If properly annealed, alloy 321 and 347 stainless steels mainly contain austenite and titanium carbide or niobium carbide. A small amount of ferrite may or may not appear in the microstructure. A small amount of sigma phase may be formed if exposed to temperatures between 1000 ° F and 1500 ° F (593 ° c-816 ° C) for a long time.Heat treatment does not harden the stable alloy 321 and 347 stainless steels.The total heat transfer coefficient of metal depends not only on the thermal conductivity of metal, but also on other factors. In most cases, the heat dissipation coefficient of the film, rust scale and surface condition of the metal. Stainless steel keeps the surface clean, so it has better heat transfer than other metals with higher thermal conductivity.
Stable alloys 321 and 347 are generally not magnetic. In the annealed state, its magnetic conductivity is less than 1.02. The permeability changes with composition and increases with cold working. The permeability of weld with ferrite will be higher.
Ductility at high temperature
Typical mechanical properties of alloys 321 and 347 at high temperatures are shown in the table below. At 1000 ° F (538 ° C) and above, the strength of these stabilized alloys is significantly higher than that of the unstable 304 alloy.
Alloys 321h and 347h (uns32109 and s34700) with high carbon content have higher strength at temperatures above 1000 ° F (537 ° C). The ASME maximum allowable design stress data of alloy 347h show that the strength of this grade is higher than that of alloy 347 with low carbon content. Alloy 321h is not permitted for Section VIII applications and is limited to temperatures of 800 ° F (427 ° C) or less for section III applications.
Creep and stress rupture properties
Typical creep and stress rupture data for alloy 321 and 347 stainless steels are shown in the table below. The creep and stress rupture strength of the stabilized alloy is higher than that of the unstable alloy 304 and 304L at high temperature. These superior properties of alloy 321 and 347 make it suitable for high temperature service pressure parts, such as our common boilers and pressure vessels.
The impact toughness of 321 and 347 is very good both indoors and in the environment below zero.
In fact, the fatigue strength of each metal is affected by corrosion environment, surface finish, product morphology and average stress. For this reason, it is not possible to use an exact number to represent the fatigue strength values under all operating conditions. The fatigue limit of alloy 321 and 347 is about 35% of its tensile strength.
Austenitic stainless steel is considered to be the most easily welded alloy steel and can be welded with all fusion materials, as well as resistance welding.
Two factors should be considered in the production of austenitic stainless steel welding joints: 1) to maintain its corrosion resistance, 2) to avoid cracking.
Attention must be paid to maintaining the stabilizing elements in alloys 321 and 347 during welding. Alloy 321 is more likely to lose titanium, while alloy 347 is more likely to lose coltan. Carbon in oil and other sources of pollution and nitrogen in the air need to be avoided. Therefore, it is necessary to keep clean and protect inert gas when welding stable alloy or unstable alloy.
When welding the metal with austenite structure, it is easy to split during operation. Due to this reason, a small amount of ferrite is needed to reduce the crack sensitivity of alloy 321 and 347 to the minimum. The stainless steel containing coltan is more prone to hot cracking than the stainless steel containing titanium.
The matching filler metal can be used for welding of alloy 321 and 347. The matching filler metal of alloy 347 can also be used for welding of alloy 321.
These stable alloys can be added to other stainless steels or carbon steels. Alloy 309 (23% cr-13.5% Ni) or nickel based filler metals can be used for this purpose.
How to choose stainless steel
Slope properties to consider for selection include
Life Cycle Costing of Stainless Steel
Sometimes stainless steel is considered to be an expensive material. However, experience has shown that using a corrosion resistant material in order to avoid future maintenance, downtime and replacement costs can produce economic benefits which far outweigh higher initial material costs.
Life cycle costing (LCC) quantifies all the costs – initial and ongoing – associated with a project or installation. It uses the standard accountancy principle of discounted cash flow to reduce all those costs to present day values. This allows a realistic comparison to be made of the options available and the potential long term benefits of using stainless steel to be assessed against other material selection.
The present day value represent the amount of money which would have to be invested today in order to meet all the future operating costs – including running costs, maintenance, replacement and production lost through downtime. These are added to the initial costs to give the total LCC:
In the formula:
Once the cost data have been gathered, the calculation of the life cycle cost is straightforward. Software packages are available which prompt the user to collect the relevant data, carry out the calculation and allow different options to be compared easily.
Not only was the stainless steel option only slightly more expensive initially (because of the lower installation cost) but it showed a distinct life cycle cost advantage following the anticipated replacement of the galvanised steel plant after 15 years (refer to graph). The stainless steel option was chosen.
Stainless steel in energy saving and emission reduction
Applications of stainless steel
Can stainless steel rust?
Rust is a reddish-brown coating that forms on the surface of iron or steel when the metal oxidizes and dissolves in water. Stainless steel is an alloy that contains at least 10.5 percent chromium, which makes it resistant to rust. Stainless steel can still rust in certain conditions. If your stainless steel item is damaged in a way that exposes the metal underneath, you can use an abrasive to remove the rust. You can also buff out surface scratches with water and baking soda. If your stainless steel item has been soaked in saltwater, you should clean off the salt with dish soap, rinse it with water and use a soft cloth to buff away any remaining rust spots. To keep stainless steel from rusting, always dry your stainless steel items after washing them and keep them away from saltwater.”
Rust is a reddish-brown coating that forms on the surface of iron or steel when the metal oxidizes and dissolves in water. Rusting occurs when iron combines with oxygen in the presence of water, forming iron oxide (Fe2O3). The rate at which rust forms depends on several factors, including moisture content, temperature and humidity. In other words:
Rust is a reaction between iron and oxygen (or water) that causes oxidation of your metal piece.
While rust technically refers to any type of corrosion on metal surfaces, we’re most familiar with its reddish hue. Rust may appear as small spots or large swaths across a surface depending on how much contact there was with water or air during exposure to it—and what kind of alloy was used for your stainless steel product!
Stainless steel is an alloy that contains at least 10.5 percent chromium, which makes it resistant to rust.
Chromium is a metal that contains many different compounds and is resistant to rust. When exposed to oxygen, iron can corrode and form rust if there are other elements present in the air or water surrounding it. This process can be slowed by adding chromium to your stainless steel kitchenware, but it will never be completely immune from oxidation because even stainless steel has trace amounts of copper in its composition (which means you’ll always want to avoid using copper pots on your stove top).
Stainless steel can still rust in certain conditions.
While stainless steel is not susceptible to rusting, it can still corrode and degrade over time if the surface is scratched or exposed to harsh conditions. This includes exposure to saltwater, acidic substances, high temperatures and moisture.
If your stainless steel item is damaged in a way that exposes the metal underneath, you can use an abrasive to remove the rust. You can also buff out surface scratches with water and baking soda.
Use a fine grit sandpaper to remove any rust from the metal.
Use a toothbrush to scrub off any remaining rust particles or residue left by the sandpaper (this will prevent further buildup of rust).
Use a soft cloth to buff out any scratches or corrosion caused by removing corrosion with an abrasive like sandpaper (buffing will make your item shine).
Apply stainless steel cleaner as directed on its packaging (use cleaning products specifically for stainless steel) and then wipe clean with a soft cloth or paper towel.
For added shine, apply polish as directed on its packaging then wipe clean immediately after applying.
If your stainless steel item has been soaked in saltwater, you should clean off the salt with dish soap, rinse it with water and use a soft cloth to buff away any remaining rust spots. Dry your stainless steel item after washing it. Keep your stainless steel item away from saltwater as much as possible to prevent future corrosion.
To keep stainless steel from rusting, always dry your stainless steel items after washing them and keep them away from saltwater.
The best way to prevent rust from forming on your stainless steel is by not leaving it in water. If you have a sink full of dishes, take them out immediately and hand-dry them. If you are washing something in the dishwasher, remove it as soon as possible and place it somewhere dry.
If you have a shower with lots of steam, try using a squeegee to wipe away any excess moisture before drying off your items with a towel or cloth. This will help prevent condensation from forming on your item and causing rusting later on down the road when temperatures drop again.
When doing yard work such as gardening or working on vehicles outside during cold weather months, make sure that all tools used outdoors are dried thoroughly before storing so they don’t rust over time!
However, if you are not careful and let your stainless steel item get damaged, it may rust. The best way to avoid this problem is by drying off your items and storing them somewhere where they won’t get wet.
Source: China Stainless Steel Pipes Manufacturer – Yaang Pipe Industry (www.epowermetals.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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