The hot-rolled ferritic ferrite crystals are subjected to about 80 to 95% cold working in the cold rolling process, and the crystal grains are elongated into fibrous structures. Due to the high dislocation density, the cold working hardens and the strength increases, and the processing performance is basically the same. Completely lost. In order to restore the processing performance of the tin-plated original plate, the work-hardened original plate is heated to a high temperature, and after a certain period of time, it is slowly cooled. -- This process is annealing.
Annealing cycle principle: rapid heating to about 680 °C, heat for 20 to 25 seconds, then cooling to 480 °C at controlled speed, rapid cooling to near room temperature
Hood Annealing: BA, Continuous Annealing: CA
Three stages of annealing
(1) Reply stage
The internal stress of the steel plate decreases, the dislocations in the wall are newly arranged, and the dislocation density in the structure continuously decreases;
(2) Recrystallization stage
From the cold-rolled fibrous tissue, tiny new grains appear and the period of rapid full expansion. After the recrystallization is completed, the new dislocation within the grain returns to the state before the cold rolling.
(3) Grain growth stage
Grain size and strength can be based on the Cottler-Page formula
Σy = σ0+kd-1/2
The finer the grains, the higher the strength. Therefore, after the soaking for a certain period of time, after the recrystallization reaches a certain stage, it must be rapidly cooled to room temperature to prevent the crystal grains from growing up and make the material too soft.
Several important parameters of annealing and their effects
(1) Heating speed: The faster the heating, the finer the grains, the higher the hardness
(2) Soaking speed: The lower the temperature, the finer the grains, the higher the hardness
(3) Soaking time: the shorter the time, the finer the grains, the higher the hardness
(4) Cold rolling: The greater the reduction, the finer the grains, the higher the hardness