There are various types of thick walled steel pipes, and different grades of steel are used. The chemical composition of the same type of steel pipe may also be different, but the steel pipe can meet the relevant technical requirements after heat treatment.
There are mainly five types of heat treatment processes for thick walled steel pipes:
1. Quenching+high-temperature tempering (also known as quenching and tempering treatment)
Heat the steel pipe to the quenching temperature, convert the internal structure of the steel pipe into austenite, and then rapidly cool it at a rate greater than the critical quenching rate to transform the internal structure of the steel pipe into martensite. Combined with high-temperature tempering, the steel pipe structure is finally transformed into a uniform tempered martensite structure.
This process can not only improve the strength and hardness of steel pipes, but also organically combine the strength, plasticity, and toughness of steel pipes.
2. Normalization (also known as normalization)
Heat the thick walled steel pipe to the normalizing temperature, so that the internal structure of the steel pipe is completely transformed into austenitic structure, and then cool it with air as the medium. Different metal structures, such as pearlite, bainite, martensite, or their mixed structures, can be obtained after normalizing.
This method can not only refine the grain size, make the composition uniform, eliminate stress, but also improve the hardness and cutting performance of the steel pipe.
3. Normalization+tempering.
Heat the thick walled steel pipe to the normalizing temperature to completely transform the internal structure of the pipe into austenitic structure, then cool it in air and cooperate with the tempering process. Steel structures mainly consist of ferrite+pearlite, ferrite+bainite, tempered bainite, tempered martensite, and tempered sorbite.
The results indicate that this method can stabilize the microstructure of steel pipes, improve plasticity and toughness.
4. Annealing
Heat the thick walled steel pipe to annealing temperature and maintain it for a certain period of time, then slowly cool it to a certain temperature with the furnace, and then let the green billet cool down.
This process function:
① Reduce the hardness of thick walled steel pipes, improve plasticity, and facilitate subsequent cutting or cold deformation processing; The second is to refine the grain size, eliminate structural defects, make the internal structure and composition uniform, and improve the performance or subsequent processes of the steel pipe; ③ Eliminate the internal stress of thick walled steel pipes to prevent deformation or cracking.
5. Solid solution treatment.
Heat the steel pipe to the solid solution temperature, allowing carbides and various alloy elements to fully and uniformly dissolve into austenite, and then rapidly cool to allow carbon and alloy elements to precipitate without time, resulting in a heat treatment process with a single austenite structure.
This process function:
① The internal structure of the steel pipe is uniform, and the composition of the thick walled steel pipe is uniform;
② The processing does not produce hardening, making it easier for subsequent cold deformation processing; ③ Restore the corrosion resistance of stainless steel.