Annealing process of stainless steel pipe
Annealing is a heat treatment process of stainless steel pipe, its purpose is to eliminate residual stress, stabilize size, reduce deformation and crack tendency. It is difficult to distinguish whether stainless steel pipe is annealed by naked eye, so some methods can be adopted to help you distinguish.
Why does stainless steel pipe need annealing?
Table of Contents
- In order to reduce the hardness and improve the plasticity of the steel, it is beneficial to cutting and cold deformation.
- Refining grain, unifying the structure and composition of the steel, improving the properties of the steel or preparing for future heat treatment.
- The residual internal stress in the steel is eliminated to prevent deformation and cracking.
What is stainless steel annealing?
With the production of cold processed pipes, carbide precipitation, lattice defects, microstructure and composition are not consistent, which makes the corrosion resistance of stainless steel decline. At this time, annealing treatment (or solution treatment) is needed.
What are the annealing processes in stainless steel pipe?
Annealing process of 304 stainless steel strip
In production, annealing process is widely used. According to different annealing purposes, there are many kinds of annealing process specifications, such as stress relief annealing, complete annealing and spheroidizing annealing.
Stress relief annealing. The common equipment for stainless steel pipe stress relief annealing is stainless steel pipe continuous bright annealing furnace, which is a muffle type bright annealing furnace. The protective gas source is ammonia decomposition furnace with gas purification device. The transmission mode can select “stainless steel mesh belt” or “stainless steel strip” according to the requirements of users. The equipment has the characteristics of advanced control, remarkable energy saving and convenient maintenance. PID automatic multi zone temperature control is adopted in the heating area of the whole line.
The stainless steel belt is evenly arranged on the feeding frame and sent to the annealing furnace through the conveyor belt. Under the protection of controllable atmosphere, it is heated to 1050 ~ 1080 ℃ and then kept for a short time. All carbides can be dissolved in the austenite structure, and then quickly cooled to below 350 ℃. The supersaturated solid solution, that is, uniform unidirectional austenite structure, can be obtained.
Complete annealing. It is used to refine the coarse overheated structure of medium and low carbon steel with poor mechanical properties after casting, forging and welding. When the workpiece is heated to 30-50 ℃ above the temperature at which all ferrite transforms into austenite, it is kept for a period of time, and then slowly cooled with the furnace. During the cooling process, austenite transforms again, which can make the microstructure of the steel finer.
Spheroidizing annealing. To reduce the high hardness of tool steel and bearing steel after forging. When the workpiece is heated to 20-40 ℃ above the temperature at which austenite begins to form in the steel, it is cooled slowly after holding. During the cooling process, the lamellar cementite in pearlite becomes spherical, thus reducing the hardness.
Source: China Titanium Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.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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