Annealing Process of Seamless Steel Pipe

Annealing process of seamless steel pipe:
1. Fully annealed. After casting, forging and welding, the coarse and overheated structures with poor mechanical properties of medium and low carbon steel are refined. Heat the workpiece to a temperature 30 to 50 ° C higher than the temperature at which the ferrite completely transforms into austenite, and keep it for a period of time, then cool it slowly with the furnace. During the cooling process, austenite transforms again, which can refine the steel structure.


2. Spheroidizing annealing. It is used to reduce the high hardness of tool steel and bearing steel after forging. Heat the workpiece to a temperature 20 to 40 ° C higher than the temperature at which the steel begins to form austenite, and cool it slowly after holding. During the cooling process, the lamellar cementite in pearlite becomes spherical, which reduces the hardness.


3. Isothermal annealing. It is used to reduce the high hardness of some alloy structural steels with high nickel and chromium content for cutting. Generally, it is first cooled to the most unstable temperature of austenite at a relatively fast speed, and after holding for a proper time, austenite transforms into austenite or sorbite, and hardness can be reduced.


4. Recrystallization annealing. It is used to eliminate the hardening phenomenon (hardness increase and plasticity decrease) of metal wire rod and plate during cold drawing and cold rolling. The heating temperature is usually 50 to 150 ℃ lower than the temperature at which the steel begins to form austenite. Only in this way can the work hardening effect be weakened.


5. Graphitization annealing. It is used to make malleable cast iron with good plasticity from cast iron with large amount of cementite. The technical operation is to heat the casting to about 950 ° C, and then cool it properly after holding for a certain period of time to decompose the cementite and form flocculent graphite.


6. Diffusion annealing. It is used for homogenizing the chemical composition of alloy castings and improving their properties. The method is to heat the casting to the highest possible temperature without melting, keep it warm for a long time, and then cool it slowly after all elements in the alloy tend to be evenly distributed.


7. Stress relief annealing. It is used to eliminate internal stress of steel castings and weldments.


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