1. Complete annealing
The ingot and cast steel after casting and mold cooling, or the hot forging rolled parts with high final rolling temperature, have coarse grain, easy to get Weischell structure, and there are internal stresses. It can be completely annealed to fine grain, uniform structure, eliminate internal stress, reduce hardness, facilitate cutting, and prepare the structure for quenching of processed parts.
Full annealing is only suitable for hypoeutectoid steel and should not be used for hypereutectoid steel. If the hypereutectoid steel is heated to the single phase austenite region above Acm, the network secondary cementation will be precipitated after slow cooling, which greatly reduces the strength, characteristic and toughness of the steel.
2. Incomplete annealing
Hypoeutectoid steel is heated in the two-phase zone between Ac1-Ac3 or hypereutectoid steel is heated in the two-phase zone between Ac1-Accm, and the heat treatment process of slow cooling is called incomplete annealing.
If the final rolling termination temperature of hypoeutectoid steel is appropriate, it does not cause grain coarsening, and the distribution of ferrite and pearlite is not abnormal, partial recrystallization can be carried out by incomplete annealing to refine the grain, improve the structure, reduce hardness and eliminate internal stress. The incomplete annealing temperature of hypoeutectoid steel is generally 740-780 ° C, which has the advantages of low heating temperature, good operating conditions, saving fuel and time.
The annealing of hypereutectoid steel is to refine and even the structure, reduce the hardness and eliminate the internal stress.
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