Seamless Steel Pipe: Annealing and Non-Annealing

The main difference between seamless steel pipe annealing and non-annealing lies in their organizational structure, hardness, machinability, and corrosion resistance.

Structural organization and performance transformation: After the seamless steel pipe undergoes annealing treatment, its organizational structure will change. For example, annealing can reduce the hardness of the steel pipe, increase plasticity, enhance machinability, and corrosion resistance. While the steel pipe that has not been annealed may have higher hardness and strength, but it is difficult to process and handle.

Annealing types: The annealing of seamless steel pipe includes full annealing, spheroidizing annealing, stress-relief annealing, etc. Full annealing aims to reduce the hardness of seamless steel pipe and eliminate the non-uniform organization and internal stress in the steel. For spheroidizing annealing, the seamless steel pipe needs to be heated to 750 degrees, held for a period of time and then slowly cooled down to below 500 degrees, and finally cooled in the air. It is mainly applied to high-carbon steel with the purpose of reducing hardness and improving cutting performance. Stress-relief annealing, also known as low-temperature annealing, is to heat the seamless steel pipe to 500-600 degrees, hold it for a period of time, and then cool it slowly along with the furnace to below 300 degrees, and then cool at room temperature. The main purpose is to eliminate the internal stress of the seamless steel pipe.

Application: It is determined whether to implement annealing treatment according to specific needs. For example, high-carbon steel and low-alloy steel pipes usually need to use annealing to reduce hardness and strength, improve plasticity, and eliminate internal stress and uneven organization, so as to facilitate the machining of the steel pipe and lay an organizational foundation for the final heat treatment of the steel pipe.

In conclusion, the choice of whether the seamless steel pipe is annealed depends on its expected purpose and performance requirements. Annealing treatment can improve the processing performance and corrosion resistance of the steel pipe, while the non-annealed steel pipe may have higher hardness and strength, which is suitable for specific high-strength application occasions.