Performance and application of industrial pure zirconium
The chemical composition, processing, heat treatment, performance, safety and application of industrial pure zirconium in my country are briefly introduced.
The symbol of zirconium is Zr, which is located in the IV-B group of the periodic table. It is a silver-white metal. It has a high melting point, a moderate density, good strength and plasticity matching, and a small thermal neutron absorption cross-section. It is an important structural material for the nuclear industry. Zirconium, like titanium, has excellent corrosion resistance in many acid and alkali media. Therefore, zirconium is an excellent chemical corrosion-resistant structural material.
The main products of industrial pure zirconium include plates, pipes, forgings, bars, welding wires, etc., which are used to make pressure vessels, heat exchangers, towers, stirrers and other structural parts. The working temperature can reach 300℃～375℃. Zirconium ore usually contains hafnium, and it is difficult and costly to separate hafnium from zirconium ore. Zirconium in the nuclear industry needs to remove hafnium. Industrial pure zirconium is composed of 95.5%-99.2% zirconium and hafnium, among which hafnium, the maximum content allowed in the standard is 4.5%. As we all know, under most corrosion-resistant application conditions, the element hafnium will not significantly change the mechanical properties and corrosion resistance of zirconium. Therefore, the standard allows the content of hafnium to be maintained at a natural level, which can greatly reduce costs. Industrial pure zirconium processed products mainly have two chemical composition levels, one is low-oxygen grade, the Chinese brand is Zr-1, and the American brand is UNS R60700. Its high plasticity is mainly used for explosive composite materials and also used for plasticity requirements. High field; the other is high-oxygen grade, our brand is Zr-3, and the American brand is UNS R60702; each has excellent corrosion resistance,
The two are only slightly different in mechanical properties.
In recent years, in view of the technical transformation and technological progress of domestic zirconium sponge enterprises, it is possible to mass produce zirconium sponge that meets industrial requirements.
Therefore, the two grades of industrial pure zirconium have been produced on an industrial scale and have been widely used in petroleum, chemical, pesticide, and metallurgical industries.
This article briefly introduces the chemical composition, processing, heat treatment process, performance, main application and safety of industrial pure zirconium in our country, and provides a reference for a more reasonable selection of the metal processing and heat treatment process and the selection of this metal material.
Technical indicators stipulated by the standard
In 2009, my country’s newly formulated national standard “Zirconium and Zirconium Alloy Grades and Chemical Composition” and the American advanced ASTM/ASME material standards stipulated the chemical composition of industrial pure zirconium, respectively, as shown in Table 1.
Table.1 Chemical composition of industrial pure zirconium (wt%)
|Standard||Grade||Element content, not more than|
|Chinese National Standard (GB/T)||Zr-1||≥99.2||4.5||0.2||0.05||0.025||0.005||0.1|
|United States (ASTM/ASME)||R 60700||≥99.2||4.5||0.2||0.05||0.025||0.005||0.1|
|Chinese National Standard (GB/T)||Zr-3||≥99.2||4.5||0.2||0.05||0.025||0.005||0.16|
|United States (ASTM/ASME)||R 60702||≥99.2||4.5||0.2||0.05||0.025||0.005||0.16|
In 2009, my country’s newly formulated national standards, non-ferrous industry standards, Baotai corporate standards and the American advanced ASTM/ASME material standards stipulate the mechanical properties of industrial pure zirconium as shown in Table 2.
Table.2 Mechanical properties of annealed industrial pure zirconium materials
ASTM/ASME B551: Zirconium and zirconium alloy strip, thin plate and thick plate
Thin and thick plates
|China Nonferrous Industry Standard YS/T: Industrial zirconium and zirconium alloy sheets for pressure vessels||Zr-1||≤380||≤305||≥20|
|ASTM/ASME B523/B658 seamless and welded zirconium and zirconium alloy pipes||R 60702||≥380||≥205||≥16|
|Chinese National Standard GB/T: Zirconium and Zirconium Alloy Pipe||Zr-3||≥380||≥205||≥16|
|ASTM/ASME B550: Zirconium and zirconium alloy rods and wires||R 60702||≥380||≥205||≥16|
|Chinese National Standard GB/T: Zirconium and zirconium alloy rods and wires||Zr-3||≥380||≥205||≥16|
|ASTM/ASME B493: Zirconium and zirconium alloy forgings||R 60702||≥380||≥205||≥16|
|Baotai Enterprise Standard Q/BS6333: Zirconium and zirconium alloy forgings||Zr-3||≥380||≥205||≥16|
Processing and heat treatment
The mechanical properties of the two grades of industrial pure zirconium depend to a large extent on the purity of the sponge zirconium used for smelting. As the content of impurity elements (especially oxygen, nitrogen and iron) rises, the tensile strength and hardness increase rapidly.
Industrial pure zirconium has good processing properties under hot conditions, similar to industrial pure titanium, and can be subjected to pressure processing such as forging, extrusion, and rolling. Industrial pure zirconium also has good cold workability. Plates, pipes and wires can be cold rolled or drawn, and its cold workability is equivalent to industrial pure titanium.
The processing technology of zirconium depends on the basic properties of zirconium and the special requirements of zirconium components. The most widely used plate and seamless pipe processing main processes are: preparation of consumable electrodes, melting and casting, forging, hot rolling or hot extrusion (tube blank), cold working, and finishing. The vacuum consumable electric arc furnace smelting method is the most common method of zirconium industrial production. Only by adopting the correct method of adding additional elements, a suitable industrial sponge zirconium and a reasonable casting system can we obtain high-quality ingots.
The structural properties of industrial pure zirconium processed materials can be achieved by controlling the amount of processing deformation and annealing process system. Therefore, the use of reasonable deformation and annealing process systems is an important process measure to ensure the performance of processed materials.
Ingot opening is generally carried out in the β phase zone, the secondary forging temperature is lower than the opening temperature, and the final forging temperature is generally not less than 700°C. The hot rolling temperature is similar to the secondary forging temperature, and the extrusion temperature is lower. In order to obtain good comprehensive performance
The total deformation rate of cold rolling before finished products should reach 50% or more.
The annealing of cold-worked materials must be carried out in a vacuum furnace, and the vacuum degree should be higher than 4×10-2Pa. The intermediate annealing temperature is 500°C to 700°C. The vacuum annealing temperature of the plate is 600℃～750℃, and the holding time is 60min. The annealing temperature of the pipe is 550℃～650℃. After explosive compounding, zirconium clad steel plates should be delivered in a stress-relieving state, the annealing temperature is 540℃～600℃, and the holding time is 3h～5h.
Physical properties of industrial pure zirconium
- Density: 6.59g/cm3; melting point: 1852°C; boiling point: 3580°C;
- Phase transition temperature: 860℃～870℃; when it is above the phase transition temperature, it is a body-centered cubic lattice (β phase), when it is below the phase transition temperature, it is a dense hexagonal lattice (α phase);
Elastic modulus, thermal diffusivity, thermal conductivity:
|Temperature, ℃||Elastic modulus E(GPa)||Thermal diffusivity (10-6m2/s)||Thermal conductivity (W•m-1•K-1)|
- Shear modulus: 36.5Gpa;
- Poisson’s ratio μ: 0.33;
Thermal expansion performance:
|Temperature difference T, ℃||Average linear expansion coefficient а, X10-6/℃|
Typical mechanical properties of industrial pure zirconium
Table.3 Room temperature mechanical properties of typical materials
|Product type||Grade||Tensile strength Rm||Specified non-proportional extension strength, Rp0.2||Elongation A50,%|
|Cold rolled tube||Zr-3||462||287||32|
|Cold rolled bar||Zr-3||450||318||21|
Zirconium has much better weldability than alloy steel and aluminum. It can be welded by fusion welding, brazing, solid welding and other methods. One of its common welding methods is TIG welding. The solubility of iron in zirconium is very low, zirconium and steel are not suitable for direct fusion welding. Iron should not be mixed in the welding of zirconium-lined vessels and zirconium composite plate vessels, so the welding structure should adopt a special structure like titanium. Zirconium can be welded with titanium, tantalum, etc., but there are not many applications in engineering. The weldability of zirconium is similar to that of chromium-nickel stainless steel. The thermal expansion coefficient of zirconium is small, only about 2/3 of titanium, 1/2 of nickel and ferritic steel, 1/3 of copper and austenitic steel, and 1/4 of aluminum. It is among various engineering metal materials The lowest, so the welding deformation is small; the elastic modulus of zirconium is small, about 1/2 of that of steel and nickel, so the welding residual stress is small; the welding crack sensitivity of zirconium is low. The high melting point of zirconium makes the welding site clean. The mechanical properties of zirconium are very sensitive to intermittently dissolved elements such as nitrogen, oxygen, carbon, and hydrogen. In addition to controlling the content of these elements in zirconium materials and welding wires, special attention should be paid to the cleaning of the welding parts and welding wires before welding. To prevent the entry of these elements, the purity of argon should not be less than 99.998%. Zirconium is highly active and has a strong affinity for hydrogen, oxygen, and nitrogen in the ambient gas. When the heat-affected zone and backside of the weld pool and the weld during cooling are at a temperature above 350-400℃, they should be placed Under inert gas protection. Zirconium oxide has a high solubility in zirconium, and slag inclusion is usually not easy to produce in the weld. Zirconium welds have the possibility of producing pores, so pollution during welding should be avoided to prevent hydrogen from entering the zirconium molten pool.
The annealed industrial pure zirconium sheet can be easily bent in ordinary press brakes or forming processing equipment, reaching a bending radius of 5T at room temperature and 3T at 200°C to 300°C. When cold forming zirconium tubes, it is recommended to use
The bending radius is 3 times the diameter. For smaller bending radii, it is necessary to perform thermoforming at a temperature of 200°C to 425°C, or use special bending techniques. When the zirconium tube is bent, springback may be encountered due to its work hardening. In addition, during bending, both the internal and external surfaces should maintain a certain tension to prevent the pipe from twisting and the pipe wall from becoming thinner.
The work hardening tendency of zirconium is obvious, and the machining should adopt slow speed, large feed rate, and use sufficient coolant and lubricant. Hard alloy is commonly used for cutting tools, high-speed steel can also be used, and the grinding wheel is silicon carbide wheel.
Zirconium is a passivation metal. The standard electrode potential of zirconium is -1.539V. Zirconium has a strong affinity for oxygen, and it can react with oxygen in the air at room temperature to form a dense oxide film with strong adhesion. The oxide film protects the base metal from
Chemical or mechanical damage, resistant to certain highly corrosive environments including various inorganic acids (such as hydrochloric acid, sulfuric acid, nitric acid, etc.), alkalis, most organic acids (such as acetic acid, formic acid, etc.), various salt solutions and molten alkali corrosion . Zirconium has excellent corrosion resistance in all concentrations and temperatures up to the boiling point of hydrochloric acid, and is not prone to crevice corrosion, pitting corrosion and stress corrosion. Zirconium can withstand the boiling point in sulfuric acid and is higher than the boiling point, with a concentration of 70%. When the concentration is lower than 65%, a small amount of oxidizing ions in sulfuric acid will not affect the corrosion resistance of zirconium. When the concentration of sulfuric acid is lower than 40%, zirconium allows a large amount of oxidizing ions to exist. Zirconium has good corrosion resistance at 150°C and 90% nitric acid containing oxidizing ions, and at 200°C and 30-70% nitric acid containing oxidizing ions and chloride ions. Zirconium is resistant to corrosion in organic acids, but is not resistant to corrosion in hydrofluoric acid, concentrated sulfuric acid, concentrated phosphoric acid, aqua regia, bromine water, hydrobromic acid, fluorosilicic acid, calcium hypochlorite, and fluoroboric acid. It is not resistant to corrosion in oxidizing chlorides, such as copper chloride and ferric chloride solutions, but it is resistant to corrosion in reducing chloride solutions.
There is a major preventive measure that must be considered when processing zirconium. It is non-toxic, but due to its exothermic reaction with oxidizing elements such as oxygen, zirconium is easy to catch fire. Large pieces of thin plates, thick plates, rods, tubes and ingots can be heated to a very high temperature without catching fire, but small chips are easily ignited and burned at high temperatures. Therefore, it is necessary to prevent a large amount of hoarding of scraps or other small pieces of zirconium, and care should be taken to store this material in non-flammable containers and enclosed areas. Zirconium scraps should be removed from the machine frequently and placed in a suitable storage container. An effective way to store zirconium scraps is to put them in a container with water, with a layer of oil on top of the water to prevent evaporation. It is important to keep all storage containers well covered to prevent stray sparks from igniting the zirconium. If zirconium catches fire, do not use ordinary fire extinguishers or water. Dry sand, powdered graphite or special metal powder should be used.
Application of industrial pure zirconium:
- In hydrogen peroxide production, acrylic acid and acrylic fiber production: all zirconium heat exchanger tubes replace graphite heat exchangers;
- In the production of methacrylate from sulfuric acid: high-pressure vessels, towers, heat exchangers, pipeline system pumps and valves are all made of zirconium;
- Sulfuric acid reboiler made of zirconium is used in butanol production;
- In the production of azo dye coupling reaction, zirconium heat exchanger, pump and stirrer are used;
- In the production of food and medicine, the use of zirconium equipment not only solves the corrosion problem of hydrochloric acid, but also ensures the purity of food and medicine;
- In the production of nitric acid, zirconium tower and zirconium regenerator replace the original 316L, titanium and FRP;
- In the production of low-pressure carbonylation acetic acid, many containers, heat exchangers, pump valves, etc. use zirconium materials.
In summary, industrial pure zirconium has excellent comprehensive properties such as corrosion resistance, welding, and processing. It can be used to produce plates, pipes, bars, wires, forgings, castings and other products. It is used in petroleum, chemical, pharmaceutical, fertilizer, Promotion and application in metallurgy, ships and other industrial fields.
Source: China Flanges 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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