Steel annealing quenching and tempering process
1 steel annealing
Annealing is used in the production of preliminary heat treatment process. Most machines parts and labor, mold blank after annealing to eliminate casting, forging and welding pieces of internal stress and composition inhomogeneity; able to improve and adjust the mechanical properties of steel, prepare the organization for the next process to prepare . On performance requirements, the less important parts and some ordinary castings, weldments, annealing can be used as the final heat treatment.
Annealing the steel strip is heated to a suitable temperature, holding a certain time, and then slowly cooled to obtain a tissue close to the equilibrium heat treatment process. The purpose of annealing is to uniform chemical composition, mechanical properties and process performance improvement, elimination or reduction of the stress and the final heat treatment of the part is possible tissue preparation.
Many types of steel annealing process, according to the heating temperature can be divided into two categories: one is the critical temperature (Ac3 or Ac1) above annealing, also known as phase-change recrystallization annealing. Including fully annealed, incomplete annealing, isothermal annealing, the ball and the diffusion annealing annealing; another is in critical temperature (Ac1) following annealing, also known as low-temperature annealing. Including recrystallization annealing, stress and dehydrogenation annealing. Cooling can be divided by continuous cooling and isothermal annealing annealing.
Steel quenching and tempering heat treatment process is a very important, very extensive application process. Quenching can significantly improve the strength and hardness of steel. If matched with different temperature tempering, you can eliminate (or reduce) quenching stress, but also get strength, hardness and toughness of the match, to meet different requirements. Therefore, quenching and tempering are inseparable two heat treatment process.
2.1 steel quenching
Heating the steel is quenched to above the critical point, heat greater than the critical cooling rate after (Vc) cooled to obtain a martensite or bainite in the heat treatment process.
2.2 tempered steel
Tempering the quenched steel is heated to a temperature of A1 less heat after a certain time, cooled to room temperature in an appropriate manner of the heat treatment process. It was immediately before the next road hardening heat treatment process, and decided to use the state of the steel in the organization and performance, the relationship between the life of the workpiece, it is the key process.
The main purpose of tempering is to reduce or eliminate the quenching stress; ensure appropriate organizational changes, so that the workpiece size and performance stability; improve the thermal properties of steel and plastic, choose a different tempering temperature to obtain hardness, strength, ductility or toughness appropriate cooperation in order to meet the performance requirements of different workpieces
