The heat treatment process of seamless steel pipe mainly includes the following 5 categories:
1. Quenching + high temperature tempering
The steel pipe is heated to the quenching temperature to transform the internal structure of the steel pipe into austenite, and then rapidly cooled at a speed greater than the critical quenching speed to transform the internal structure of the steel pipe into martensite, and then with high temperature tempering, the steel pipe structure is finally transformed into a uniform Tempered sorbite structure. This process can not only improve the strength and hardness of the steel pipe, but also organically combine the strength, plasticity and toughness of the steel pipe.
After heating the steel pipe to normalizing temperature, the internal structure of the steel pipe is completely transformed into austenite structure, and then it is a heat treatment process that uses air as a medium for cooling. Different metal structures can be obtained after normalizing, such as pearlite, bainite, martensite or their mixed structure. This process can not only refine the grains, uniform the composition, and eliminate the stress, but also increase the hardness of the steel pipe and improve its cutting performance.
3. Normalizing + tempering
After the steel pipe is heated to the normalizing temperature, the internal structure of the steel pipe is completely transformed into austenite structure, and then it is cooled in the air and then matched with the tempering process. The steel pipe structure is tempered ferrite + pearlite, or ferrite + bainite, or tempered bainite, or tempered martensite, or tempered sorbite. This process can stabilize the internal structure of the steel pipe and improve the plasticity and toughness of the steel pipe.
After the steel pipe is heated to the annealing temperature and kept for a certain period of time, it is slowly cooled to a certain temperature with the furnace and then discharged from the furnace for cooling. Reduce the hardness of the steel pipe and increase its plasticity to facilitate subsequent cutting or cold deformation processing; Refine grains, eliminate structural defects, uniform internal structure and composition, improve the performance of the steel pipe or prepare for subsequent processes; Eliminate the inner part of the steel pipe Stress to prevent deformation or cracking.
5. Solution treatment
The steel pipe is heated to the solid solution temperature, so that the carbides and various alloying elements are fully and uniformly dissolved in the austenite, and then quickly cooled, so that the carbon and alloying elements are too late to precipitate and obtain a heat treatment process for a single austenite structure. The function of the process: To uniform the internal structure of the steel pipe and the composition of the steel pipe; Eliminate the hardening during processing to facilitate subsequent cold deformation processing; Restore the corrosion resistance of stainless steel pipe