What is steel annealing? What are the types of annealing and its applications?

What is steel annealing? What are the types of annealing and its applications?

Annealing of steel: Annealing is a heat treatment process in which steel is heated to a temperature above or below the critical point AC1, and then slowly cooled with the furnace after a certain period of heat preservation to obtain a near-equilibrium state structure.

Annealing types: According to the heating temperature, it can be divided into annealing above or below the critical temperature AC1. The former includes complete annealing, incomplete annealing, spheroidizing annealing, and homogenization annealing. The latter includes recrystallization annealing and stress relief annealing. According to the cooling method, it can be divided into isothermal annealing and continuous cooling annealing.

Annealing purposes: 1. Complete annealing: Heat the steel to 20-30℃ above AC3, and slowly cool it with the furnace after heat preservation. It is mainly used for hypoeutectoid steel, which can refine grains, eliminate internal stress, etc., improve cutting performance, and eliminate defects in medium carbon structural steel. 2. For hypoeutectoid steel, heat to between AC1-AC3; for hypereutectoid steel, heat to between AC1-ACcm, and slowly cool it with the furnace after heat preservation. It can eliminate internal stress and reduce hardness. For hypereutectoid steel, a spheroidal pearlite structure can be obtained to improve cutting performance. 3. Spheroidizing annealing: spheroid carbides in steel, are mainly used for eutectoid steel, hypereutectoid steel, and alloy tool steel. The purpose is to reduce hardness, improve cutting performance, and prepare the organization for quenching. 4. Homogenizing annealing: heat the steel ingot to a temperature slightly lower than the solidus line for a long time, and then cool it slowly. The purpose is to eliminate segregation and make the composition and organization uniform. 5. Recrystallization annealing: heat the cold-deformed metal to above the recrystallization temperature, keep it warm, and then cool it slowly. Transform the deformed grains into equiaxed grains, eliminate work hardening and residual internal stress. 6. Stress relief annealing: heat the cold-deformed metal to a temperature below the recrystallization temperature, keep it warm and then cool it slowly. Eliminate residual internal stress in castings and other workpieces, improve dimensional stability, and reduce deformation and cracking tendencies.