What is an alloy
What is an alloy?
Table of Contents
- What is an alloy?
- Fabrication and synthesis of alloy
- Classification of alloys
- General properties of alloys
- Special alloy
- New alloy
- Alloy processing
Alloy is a material with metallic properties synthesized by two or more metals and metals or nonmetals through certain methods. It is generally obtained by melting into uniform liquid and solidification. According to the number of constituent elements, it can be divided into binary alloy, ternary alloy and multicomponent alloy.
Human beings began to produce alloys from bronzes. The earliest producers of alloys in the world were the Babylonians of Cuba. The Babylonians of Cuba began to refine bronze (the alloy of red copper and tin) 6000 years ago. China is also one of the earliest countries in the world to study and produce alloys. The bronze (copper tin alloy) process was very developed in the Shang Dynasty (more than 3000 years ago); Sharp swords were forged (and overheated) around the 6th century BC (late spring and Autumn period).
Alloy is a macroscopically homogeneous multicomponent chemical substance containing metal elements, which generally has metal properties Any element can be used as an alloy element, but a large amount of metal is still added The most basic and independent substances that make up an alloy are called components, or elements for short The alloy composed of two components is called binary alloy, the alloy composed of three components is called ternary alloy, and the alloy composed of more than three components is called multicomponent alloy In solid state, the alloy may be single-phase or multiphase mixture; It may be crystalline, quasicrystal or amorphous Depending on the atomic radius, electronegativity and electron concentration of its constituent elements, the possible phases in crystalline alloys are solid solutions with the same structure as the base pure elements and interphase phases with the same structure as any constituent elements The mesophase includes normal valence compound, electronic compound, Laves phase σ Phase, interstitial phase and interstitial compounds with complex structure, etc The possible phases of the alloy in equilibrium can be seen from the phase equilibrium diagram
The structure and properties of the constituent phases in the alloy play a decisive role in the properties of the alloy At the same time, the change of alloy structure, that is, the change of relative number, grain size, shape and distribution of each phase in the alloy, also has a great influence on the properties of the alloy Therefore, the combination of various elements can be used to form different alloy phases, which may meet different performance requirements after appropriate treatment
The term alloy is also used in polymer chemistry, which refers to the composite material formed by mixing polymer or copolymer with another polymer or elastomer under certain conditions, such as styrene acrylonitrile copolymer resin and butadiene acrylonitrile rubber
Fabrication and synthesis of alloy
Metal materials with metallic properties formed by alloying processes (melting, mechanical alloying, sintering, vapor deposition, etc.) with two or more metal elements or metal based addition of other non-metallic elements are often called alloys. But alloys may contain only one metal element, such as steel. (steel is a general term for ferroalloys with carbon content ranging from 0.02% to 2.00% by mass)
Here, we need to note that the alloy is not a general conceptual mixture, or even a pure substance, such as a single-phase metal intermetallic alloy. The added alloy elements can form solid solutions and compounds, and produce endothermic or exothermic reactions, so as to change the properties of the metal matrix.
The formation of alloys often improves the properties of elemental elements. For example, the strength of steel is greater than that of its main component element iron. The physical properties of the alloy, such as density, reactivity, Young’s modulus, conductivity and thermal conductivity, may be similar to the constituent elements of the alloy, but the tensile strength and shear strength of the alloy are usually very different from the properties of the constituent elements. This is due to the great difference in the arrangement of atoms between the alloy and the simple substance.
A small amount of an element may have a great impact on the properties of the alloy. For example, impurities in ferromagnetic alloys can change the properties of the alloy.
Unlike pure metals, most alloys have no fixed melting point. When the temperature is in the melting temperature range, the mixture is in the state of solid-liquid coexistence. Therefore, it can be said that the melting point of the alloy is lower than that of the component metal. See eutectic mixture. In common alloys, brass is an alloy of copper and zinc; Bronze is an alloy of tin and copper used in carvings, decorations, and church clocks. Alloys (such as nickel alloys) are used in the currencies of some countries.
Classification of alloys
According to the name of the main metal with large content in the alloy, it is classified as XX alloy. For example, the one with high copper content is copper alloy, and its performance mainly maintains the performance of copper.
Type of alloy
- (1) Mixed alloy (eutectic mixture): when the liquid alloy solidifies, the components constituting the alloy crystallize respectively, such as solder, bismuth cadmium alloy, etc;
- (2) Solid melt alloy, an alloy that forms a solid solution when the liquid alloy solidifies, such as gold and silver alloy;
- (3) An alloy in which components form compounds with each other, such as brass composed of copper and zinc（ β- Brass γ- Brass and ε- Brass), etc.
Many properties of alloys are better than pure metals, so alloys are mostly used in application materials (see ferroalloy and stainless steel).
General properties of alloys
Each type of alloy has the following general properties:
- (1) The melting point of most alloys is lower than that of any of their constituent metals;
- (2) The hardness is generally greater than that of any metal in its components; (special case: sodium potassium alloy is liquid and is used as heat conducting agent in atomic reactor)
- (3) The conductivity and thermal conductivity of the alloy are lower than that of any component metal. Using this characteristic of alloy, high resistance and high thermal resistance materials can be manufactured. It can also produce materials with special properties.
- (4) Some have strong corrosion resistance (such as stainless steel), such as adding 15% chromium and 9% nickel into iron to obtain a corrosion-resistant stainless steel, which is suitable for the chemical industry.
Ductile iron, manganese steel, stainless steel, brass, bronze, white copper, solder, hard aluminum, 18K gold, 18K platinum, etc.
Steel is an alloy composed of iron, C, Si, Mn, P, s and a small amount of other elements. In addition to Fe, the content of C plays a major role in the mechanical properties of iron and steel, so it is collectively referred to as iron carbon alloy. It is the most important and most used metal material in engineering technology.
Classification and properties of iron and steel
According to different carbon content, iron carbon alloy is divided into steel and pig iron. Steel is iron carbon alloy with carbon content of 0.03% ~ 2%. Carbon steel is the most commonly used ordinary steel, which has the advantages of convenient smelting, easy processing and low price, and can meet the use requirements in most cases, so it is widely used. According to different carbon content, carbon steel is divided into low carbon steel, medium carbon steel and high carbon steel.
With the increase of carbon content, the hardness of carbon steel increases and the toughness decreases. Alloy steel, also known as special steel, adds one or more alloy elements on the basis of carbon steel, so it has some special properties, such as high hardness, high wear resistance, high toughness, corrosion resistance, etc. Alloying elements often added to steel include Si, W, Mn, Cr, Ni, Mo, V, Ti, etc. China is rich in alloy steel resources. In addition to the shortage of Cr and CO and the low grade of Mn, the reserves of W, Mo, V, Ti and rare earth metals are very high.
Pig iron is hard and brittle, but it is pressure resistant and wear-resistant. Gray iron and ductile iron. The carbon in white iron is silvery white with Fe3C fracture, which is hard and brittle and cannot be machined. It is the raw material for steelmaking, so it is also called steelmaking pig iron.
Carbon in the form of flake graphite is called gray iron. The fracture is silver gray, easy to cut, easy to cast and wear-resistant. If carbon is distributed in spheroidal graphite, it is called nodular cast iron, and its properties and processability are close to that of steel. Special cast iron can be obtained by adding special alloy elements into cast iron. If Cr is added, the wear resistance can be greatly improved, which has a very important application under special conditions.
Ferrosilicon is made from coke, steel chips and quartz (or silica) by electric furnace smelting. Silicon and oxygen are easily converted into silica. Therefore, ferrosilicon is often used as deoxidizer in steelmaking. At the same time, due to the large amount of heat released during the formation of SiO2, it is also beneficial to improve the temperature of molten steel while deoxidizing. Ferrosilicon is used as alloying element additive.
It is widely used in low alloy structural steel, bonded steel, spring steel, bearing steel, heat-resistant steel and electrical silicon steel. Ferrosilicon is commonly used as reducing agent in ferroalloy production and chemical industry. The silicon content is 95% – 99%. Pure silicon is often used to manufacture monocrystalline silicon or prepare nonferrous metal alloys.
Ferromanganese is made from manganese ore. It is melted in a blast furnace or electric furnace. Ferromanganese is also a commonly used deoxidizer in steel. Manganese also plays a role in desulfurization and reducing the harmful effects of sulfur. Therefore, almost all kinds of steel and cast iron contain a certain amount of manganese. Ferromanganese is also used as an important alloying agent. Widely used in structural steel. Tool steel, stainless heat-resistant steel. Wear resistant steel and other alloy steel.
Aluminum is a widely distributed element. Its content in the earth’s crust is second only to oxygen and silicon, and is the highest in metals. Pure aluminum has a low density of 2.7g/cm3, good thermal conductivity and conductivity (second only to Au, Ag and Cu), good ductility and high plasticity, and can be used for various machining. The chemical property of aluminum is active. It oxidizes rapidly in the air to form a dense and firm oxide film, so it has good corrosion resistance. However, the strength of pure aluminum is low, and various aluminum alloys that can be used as structural materials can be obtained only through alloying.
Characteristics of aluminum alloy
Aluminum alloy is characterized by low density and high strength. Al Mn and Al Mg alloys formed by adding Mn and Mg into aluminum have good corrosion resistance, good plasticity and high strength. They are called antirust aluminum alloys and are used to manufacture oil tanks, containers, pipes, rivets, etc. The strength of duralumin alloy is higher than that of antirust aluminum alloy, but the corrosion resistance decreases. This kind of alloy includes Al Cu mg system and Al Cu mg Zn system. The newly developed high-strength duralumin has further improved its strength, reduced its density by 15% compared with ordinary duralumin, and can be extruded. It can be used as motorcycle frame, rim and other components. Al Li alloy can be used to make aircraft parts and advanced sports equipment bearing load.
Application of aluminum alloy
High strength aluminum alloys are widely used in the manufacture of aircraft, ships and trucks, which can increase their load capacity and speed, and have the characteristics of anti seawater erosion and anti magnetism.
Pure copper is purplish red, so it is also called red copper. It has excellent thermal conductivity and conductivity. Its conductivity is second only to silver and ranks second to metal. Copper has excellent chemical stability and corrosion resistance. It is an excellent metal material for electrical engineering.
Classification of copper alloys
Copper alloys widely used in industry include brass, bronze and white copper.
The alloy of Cu and Zn is called brass, in which Cu accounts for 60% ~ 90% and Zn accounts for 40% ~ 10%. It has excellent thermal conductivity and corrosion resistance and can be used as various instrument parts. Another example is adding a small amount of Sn into brass, which is called Navy brass, which has good resistance to seawater corrosion. A small amount of Pb with lubricating effect is added to brass, which can be used as sliding bearing material.
Bronze is the metal material with the longest history of human use. It is Cu and Sn alloy. The addition of tin significantly improves the strength of copper, improves its plasticity and enhances its corrosion resistance. Therefore, tin bronze is often used to manufacture wear-resistant parts and corrosion-resistant accessories such as gears. SN is expensive. A series of bronze alloys have been obtained by replacing Sn with Al, Si and Mn. The corrosion resistance of aluminum bronze is better than that of tin bronze. Beryllium bronze is the highest strength copper alloy. It is non-magnetic and has excellent corrosion resistance. It is a spring material that can compete with steel.
White copper is a Cu Ni alloy with excellent corrosion resistance and high resistance, so it can be used as the material of parts and resistors working under harsh corrosion conditions.
Brass contains zinc and a small amount of tin, lead, aluminum, etc.
An alloy composed of zinc based and other elements. Commonly added alloy elements include aluminum, copper, magnesium, cadmium, lead, titanium, etc. Zinc alloy has low melting point, good fluidity, easy fusion welding, brazing and plastic processing, corrosion resistance in the atmosphere, and the residual waste is easy to recycle and remelt; However, the creep strength is low, and it is easy to change the size due to natural aging. Prepared by melting method, die-casting or pressure processing. According to the manufacturing process, it can be divided into cast zinc alloy and deformed zinc alloy.
Application of zinc alloy and others
The main added elements of zinc alloy are aluminum, copper and magnesium Zinc alloys can be divided into deformation and casting zinc alloys according to processing technology Cast zinc alloy has good fluidity and corrosion resistance. It is suitable for die-casting instruments, automobile parts, housings, etc.
1. Characteristics of zinc alloy
- The ratio is significant.
- Good casting performance, can die cast precision parts with complex shape and thin wall, and the casting surface is smooth.
- Surface treatment: electroplating, spraying and painting.
- When melting and die casting, it does not absorb iron, corrode the pressure mold and stick the mold.
- Good mechanical properties and wear resistance at room temperature.
- Low melting point, melting at 385 ℃, easy to die cast.
Classification of lead tin alloys
According to the use of lead tin alloy:
- ① Lead base or tin base bearing alloy. And lead base bearing alloys are collectively referred to as Babbitt alloys. It contains 3% ~ 15% antimony and 3% ~ 10% copper. Some alloy varieties also contain 10% lead. Antimony and copper are used to improve the strength and hardness of the alloy. It has small friction coefficient and good toughness, thermal conductivity and corrosion resistance. It is mainly used to manufacture sliding bearings.
- ② Lead tin solder. It is mainly tin lead alloy, and some tin solders also contain a small amount of antimony. Tin alloy containing 38.1% lead, commonly known as solder, with a melting point of about 183 ℃, is used for the welding of components in the electrical instrument industry and the sealing of automobile radiators, heat exchangers, food and beverage containers.
- ③ Lead tin alloy coating. Using the corrosion resistance of tin alloy, it is coated on the surface of various electrical components, which is both protective and decorative. Commonly used are tin lead system, tin nickel system coating, etc.
- ④ Lead tin alloy (including lead tin alloy and lead-free tin alloy) can be used to produce all kinds of exquisite alloy jewelry and alloy handicrafts, such as rings, necklaces, bracelets, earrings, brooches, buttons, tie clips, hat decorations, craft decorations, alloy photo frames, religious emblems, miniature statues, souvenirs, etc.
Characteristics of lead tin alloy
Characteristics of lead tin alloy (used as alloy jewelry and alloy handicraft materials)
- 1. Lead tin alloy has stable performance, low melting point, good fluidity and small shrinkage.
- 2. The lead tin alloy has fine grains, good toughness, suitable hardness and softness, smooth surface, no sand holes, defects and cracks, and good polishing and electroplating effects.
- 3. Lead tin alloy centrifugal casting has good performance and strong toughness. It can cast precision parts with complex shape and thin wall, and the casting surface is smooth.
- 4. Lead tin alloy products can be subject to surface treatment: electroplating, spraying and painting.
- 5. The crystal structure of lead tin alloy is dense. In terms of raw materials, it ensures that the dimensional tolerance of castings is small, the surface is exquisite, and there are few post-treatment defects.
There are thousands of alloys used in industry. Now only a few of them are briefly introduced.
Corrosion resistant alloy
The ability of metal materials to resist medium corrosion in corrosive media is called the corrosion resistance of metals. High corrosion resistance in pure metal usually meets one of the following three conditions:
- ① Metals with high thermodynamic stability. Generally, it can be judged by its standard electrode potential, and the stability of its value is higher than that of the positive one; The negative ones have lower stability. Precious metals with good corrosion resistance, such as Pt, Au, Ag and Cu, belong to this category.
- ② Easily passivated metal. Many metals can form a dense oxide film with protective effect in oxidizing medium, which is called passivation. The most easily passivated metals are Ti, Zr, Ta, Nb, Cr and al.
- ③ A metal whose surface can form a corrosion product film with insoluble and good protective properties. This occurs only when the metal is in a specific corrosive medium. For example, Pb and Al are in H2SO4 solution, Fe is in H3PO4 solution, Mo is in hydrochloric acid and Zn is in the atmosphere.
Therefore, in industry, according to the above principle, a series of corrosion-resistant alloys are obtained by alloying. Generally, there are three corresponding methods:
① Improve the thermodynamic stability of metal or alloy, that is, add alloy elements with high thermodynamic stability to the original non corrosion resistant metal or alloy to form solid solution, improve the electrode potential of the alloy and enhance its corrosion resistance. For example, adding AU to Cu and adding Cu, Cr, etc. to Ni belong to this category. However, the application of this method of adding a large amount of precious metals in industrial structural materials is limited.
② Adding easily passivated alloy elements, such as Cr, Ni, Mo, etc., can improve the corrosion resistance of the base metal. Chromium stainless steel can be prepared by adding an appropriate amount of Cr into the steel.
Experiments show that in stainless steel, the corrosion resistance can only be played when the Cr content is generally greater than 13%. The higher the Cr content, the better the corrosion resistance. This kind of stainless steel has good corrosion resistance in oxidizing medium, but poor corrosion resistance in non oxidizing medium such as dilute sulfuric acid and hydrochloric acid. This is because the non oxidizing acid is not easy to make the alloy form an oxide film, and it also dissolves the oxide film.
③ Another way to produce corrosion-resistant alloy surface is to add elements. For example, the atmospheric corrosion resistance of steel is due to the formation of a dense compound hydroxyiron oxide [FeOx · (OH) 23-2x] on its surface, which can play a protective role. The addition of Cu and P or P and Cr to steel can promote the formation of this protective film. Therefore, Cu, P or P and Cr can be used to make atmospheric corrosion-resistant low alloy steel.
Metal corrosion is the most harmful spontaneous process in industry. Therefore, the development and application of corrosion-resistant alloys has great social significance and economic value.
Heat resistant alloy, also known as superalloy, is of great significance for industrial departments and application technology fields under high temperature conditions.
Generally speaking, the higher the melting point of metal materials, the higher the temperature limit they can use. This is because with the increase of temperature, the mechanical properties of metal materials decrease significantly, and the trend of oxidation and corrosion increases accordingly. Therefore, general metal materials can only work at 500 ℃ ~ 600 ℃ for a long time. Metals that can work at high temperatures above 700 ℃ are commonly known as heat-resistant alloys. “Heat resistance” means that it can maintain sufficient strength and good oxidation resistance at high temperature.
There are two ways to improve the oxidation resistance of steel: one is to add Cr, Si, Al and other alloy elements to the steel, or alloying Cr, Si and Al on the surface of the steel. They can quickly form a dense oxide film in an oxidizing atmosphere and firmly adhere to the surface of steel, so as to effectively prevent the continuation of oxidation. Second, high temperature resistant coatings such as oxides, carbides and nitrides with high melting point are formed on the surface of steel by various methods.
There are many methods to improve the high-temperature strength of steel. From the chemical point of view of structure and properties, there are roughly two main methods:
- One is to increase the bonding force between atoms in steel at high temperature. It is pointed out that the binding force in metals, that is, the strength of metal bonds, is mainly related to the number of unpaired electrons in atoms. From the periodic table, the metal bond of element ⅵ B is the strongest in the same period. Therefore, the effect of adding CR, Mo, W and other atoms to steel is the best.
- The second is to add elements that can form various carbides or intermetallic compounds to strengthen the steel matrix. Carbides formed by some transition metals and carbon atoms belong to interstitial compounds. They add covalent bonds on the basis of metal bonds, so they have great hardness and high melting point. For example, the addition of W, Mo, V and Nb can generate carbides such as WC, W2C, MOC, Mo2C, VC and NBC, thus increasing the high-temperature strength of steel.
In addition to iron-based heat-resistant alloys, nickel based, molybdenum based, niobium based and tungsten based heat-resistant alloys can also be prepared by alloy method. They have good mechanical properties and chemical stability at high temperature. Among them, nickel base alloy is the best super heat resistant metal material, and the matrix in the structure is Ni? Cr? After treatment, the service temperature of CO solid solution and Ni3Al metal compound can reach 1000 ℃ ~ 1100 ℃.
Titanium is the IVB element in the periodic table. It looks like steel and has a melting point of 1672 ℃. It is a refractory metal. Titanium is abundant in the earth’s crust, much higher than common metals such as Cu, Zn, Sn and Pb. China is extremely rich in titanium resources. Only in the super large vanadium titanomagnetite found in Panzhihua area, Sichuan Province, the associated titanium metal reserves are about 420 million tons, which is close to the total proven titanium reserves abroad.
Pure titanium has strong mechanical properties, good plasticity and easy processing. If there are impurities, especially o, N and C, it will improve the strength and hardness of titanium, but reduce its plasticity and increase its brittleness.
Titanium is a metal that is easy to passivate, and its passivation film can heal itself after being damaged in oxygen-containing environment. Therefore, the dry corrosive medium is stable. Titanium and titanium alloys have excellent corrosion resistance and can only be eroded by the concentration of hydrofluoric acid. Especially stable. After titanium or titanium alloy is taken out, it is still bright as before, which is much better than stainless steel.
Liquid titanium can dissolve almost all metals and form various alloys such as solid solutions or metal compounds. The addition of alloying elements such as Al, V, Zr, Sn, Si, Mo and Mn can improve the properties of titanium to meet the needs of different departments. For example, Ti Al Sn alloy has high thermal stability and can work for a long time at quite high temperature; The superplastic alloy represented by Ti-Al-V alloy can be elongated by 50% ~ 150%, and its maximum elongation can reach 2000%. The maximum elongation of plastic processing of general alloys shall not exceed 30%. In addition, titanium alloys usually have low density, high strength and wide application value.
Due to the above excellent properties, titanium enjoys the reputation of “future metal”. Titanium alloy has been widely used in all sectors of the national economy. It is an indispensable material for rockets, missiles and space shuttles. Titanium alloys are widely used in ships, chemical industry, electronic devices and communication equipment, as well as some light industrial departments. However, the price of titanium is relatively expensive, which limits its wide use.
In the external magnetic field, the material can show three situations:
- ① what is not attracted by the magnetic field is called diamagnetic material;
- ② What is weakly attracted by the magnetic field is called paramagnetic material;
- ③ Ferromagnetic materials are strongly attracted by the magnetic field. Their magnetism increases sharply with the strengthening of the external magnetic field, and can still retain magnetism after the external magnetic field is removed. In metal materials, most transition metals have Paramagnetism; Only a few metals such as Fe, CO and Ni are ferromagnetic.
The main elements of permanent magnet materials in metals are Fe, Co, Ni and some rare earth elements. Are the permanent magnet alloys used rare earth? Cobalt, iron? Chromium? Cobalt and manganese? aluminium Carbon alloys.
Magnetic alloys are widely used in emerging technology fields such as power, electronics, computer, automatic control and Electro Optics.
Potassium sodium alloy
Silvery soft solid or liquid In case of acid, carbon dioxide, moisture and water, it will react violently and release hydrogen, which will ignite immediately, and sometimes even explode Density: 0.847 g / ml (100 ℃) (k78%, Na22%); 0.886 g / ml (100 ℃) (K56%, na44%) melting point: – 11 ℃ (k78%, Na22%); 19℃(K56%，Na44%);
Boiling point: 784 ℃ (k78%, Na22%); 825℃(K56%，Na44%);
Application of potassium sodium alloy
The coolant used in liquid metal nuclear reactor is sodium potassium alloy, which is liquid at room temperature.
With the development of science and technology, the types of new alloys are increasing day by day. Here are some main ones.
Aluminum lithium alloy has the characteristics of high specific strength (breaking strength / density), high specific stiffness and low relative density. If it is used as skin material of modern aircraft, a large passenger aircraft can reduce the weight by 50kg. Take Boeing 747 as an example. For every 1kg reduction, it can make a profit of $2000 a year. Titanium alloy is lighter than steel, corrosion-resistant, non-magnetic and high strength. It is an ideal material for aviation and ships.
Hydrogen storage alloy
Due to the limited reserves of oil and coal, and the problems of environmental pollution in the process of use, especially the global oil crisis in the 1970s, hydrogen energy as a new clean fuel has become a research hotspot. In the process of hydrogen energy utilization, hydrogen storage and transportation is an important link. In 1969, Philips company of the Netherlands developed LaNi5 hydrogen storage alloy, which has the properties of large amount of reversible absorption and release of hydrogen. The density of hydrogen in lani5h6 alloy hydride is equivalent to that of liquid hydrogen, about 1000 times that of hydrogen.
Hydrogen storage alloy is an alloy composed of two specific metals, one of which can absorb a large amount of hydrogen to form stable hydride, while the other metal has little affinity with hydrogen, but hydrogen is easy to move in it. Mg, CA, Ti, Zr, y and La belong to the first metal, and Fe, Co, Ni, Cr, Cu and Zn belong to the second metal. The former controls the hydrogen storage and the latter controls the reversibility of hydrogen release. An ideal hydrogen storage material capable of reversible hydrogen absorption and desorption at room temperature was prepared by adjusting the hydrogen absorption and desorption properties of the alloy.
Super heat resistant alloy
Nickel cobalt alloy can withstand high temperature of 1200 ℃, and can be used in components of jet aircraft and gas turbine. Nickel cobalt iron non-magnetic heat-resistant alloy still has the characteristics of high strength and good toughness at 1200 ℃. It can be used in parts of space shuttle and control rods of atomic reactor. Looking for alloy materials that meet the requirements of high temperature resistance, long-time operation (more than 10000 hours), corrosion resistance and high strength is still the direction of future research.
Shape memory alloy
They have the characteristics of high elasticity, metal rubber performance and high strength. After plastic deformation under stress at low temperature, they return to their shape before heating after heating. Such as Ni Ti, Ag CD, Cu CD, Cu al Ni, Cu Al Zn and other alloys, which can be used for elastic elements of regulating devices (such as clutch, throttle valve, temperature control element, etc.), thermal engine materials, medical materials (orthodontic materials), etc.
The shape memory effect comes from a thermoelastic martensitic transformation. The general method of martensitic transformation as the quenching strengthening of steel is to heat the steel above a certain critical temperature for a period of time, and then cool it rapidly, such as directly inserting it into cold water (called quenching). At this time, the steel changes into a martensitic structure and hardens the steel. Later, another so-called thermoelastic martensite transformation different from the above was found in some alloys. Once thermoelastic martensite is produced, it can continue to grow with the decrease of temperature. On the contrary, when the temperature rises, the growing martensite can shrink again until it returns to the original state, that is, the martensite can grow or shrink reversibly with the change of temperature. Thermoelastic martensitic transformation is accompanied by shape change.
In addition to the above categories of new metal functional materials, there are also damping alloys that can reduce noise; Biomedical materials that can replace, enhance and repair human organs and tissues; Intelligent materials with sensors, signal processors, communication and controllers and actuators embedded in materials or structures, so that materials or structures have intelligent functions and life characteristics such as self diagnosis, self adaptation, and even damage self-healing.
-  Medium carbon steel: there are 30, 35, 40 and 45 representative steels, as well as ML30, ML35, ml40 and ml45. They have relatively stable room temperature performance and are used for small and medium-sized structural parts, fasteners, transmission shafts, gears, etc.
-  Manganese steel: representative steel types: 40Mn2 and 50mn2. It has overheating sensitivity, high temperature tempering brittleness, water quenching is easy to crack, and the hardenability is higher than that of carbon steel.
-  Silicon manganese steel: representative steel types 35SiMn and 42SiMn. High fatigue strength, decarburization and overheating sensitivity and temper brittleness. It is used to manufacture gears, shafts, rotating shafts, connecting rods, worms, etc. with medium speed, medium and high load but little impact. It can also manufacture fasteners below 400 ℃.
-  Boron steel: representative steel types 40B, 45B, 50BA and ml35b. It has high hardenability and higher comprehensive mechanical properties than carbon steel, which is equivalent to 40Cr. It is used to manufacture parts and fasteners with small section size.
-  Manganese boron steel: the representative steel is 40MnB. The hardenability is slightly higher than 40Cr, with high strength, toughness and low-temperature impact toughness, and tempering brittleness. 40MnB is often used to replace 40Cr to manufacture large section parts and 40crni to manufacture small parts; 45mnb replaces 40Cr and 45Cr; 45mn2b replaces 45Cr and partially replaces 40crni and 45CrNi as important shafts. Ml35mnb is also used in fastener production.
-  Manganese vanadium boron steel: representative steel types: 20mnvb, 40mnvb. Quenching and tempering properties and hardenability are better than 40Cr, with small overheating tendency and tempering brittleness. It is often used to replace 40Cr, 45Cr, 38crsi, 42CrMo and 40crni to manufacture important quenched and tempered parts. It is also used for bolts with small and medium specifications below grade 10.9 and ml20mnvb.
-  Manganese tungsten boron steel: representative steel 40mnwb. Good low temperature impact performance, no tempering brittleness. Equivalent to 35CrMo and 40crni, it is used to manufacture parts below 70mm.
-  Silicon manganese molybdenum tungsten steel: representative steel 35simn2mow. It has high hardenability. Calculated by 50% martensite, the diameter of water quenching is 180 and the diameter of oil quenching is 100; The tendency of quenching cracking and tempering brittleness is small; It has high strength and toughness. Instead of 35crnimoa and 40CrNiMo, it can be used to manufacture shafts, connecting rods and bolts with large section and heavy load.
-  Silicon manganese molybdenum tungsten vanadium steel: representative steel 37simn2mowva. Water quenching diameter 100, oil quenching diameter 70; Good tempering stability, low-temperature impact toughness, high-temperature strength and low tempering brittleness. It is used to manufacture shaft parts with large section.
-  Chromium steel: represented by 40Cr alloy steel pipe and ml40cr. The hardenability is good, with water quenching of 28-60mm and oil quenching of 15-40mm. High comprehensive mechanical properties, good low-temperature impact toughness, low notch sensitivity and temper brittleness. Used for manufacturing shafts, connecting rods, gears and bolts.
-  Chromium silicon steel: representative steel 38crsi. The hardenability is better than 40Cr, the strength and low-temperature impact are higher, the tempering stability is better, and the tempering brittleness tendency is larger. It is commonly used to manufacture 30-40mm shafts, bolts and gears with small modulus.
-  Chromium molybdenum steel: representative steel types: 30crmoa, 42CrMo.
Source: Network Arrangement – China Alloy Flange 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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