What is the purpose of annealing

What is annealing: annealing is a heat treatment method that heats stamping parts to a specific temperature range, holds them for a certain time, and then cools them slowly.

What is the purpose of annealing: reduce material hardness, improve plasticity, eliminate work hardening and residual stress, refine grain and improve structure, etc.

In the process of multi pass deep drawing or multi process cold extrusion, the semi-finished products undergo severe plastic deformation, almost all of which produce varying degrees of work hardening and residual stress. Work hardening makes the strength and hardness of materials increase, while the plasticity decreases. It brings difficulties to the continuous processing of materials. The existence of residual stress reduces the toughness and other technological properties of the material, and even cracks the material itself in severe cases. When work hardening and residual stress hinder further drawing and cold extrusion, intermediate annealing process can be inserted in multiple processes to eliminate work hardening and residual stress.

There are two main types of intermediate annealing:

1) Low temperature (recrystallization) annealing is performed by heating to a temperature slightly lower than the eutectic point, and then cooling in air. As a result of low temperature annealing, the material will be recrystallized, and its work hardening will be eliminated and its plasticity will be restored.

2) For some materials, if the result of low temperature annealing is not satisfactory, high temperature annealing can be used.

Intermediate annealing shall be carried out as soon as possible to avoid deformation and cracking of metal stampings under internal residual stress due to long-term storage.

In addition, in order to prevent regular local cracking of stamping parts, flame or electric heating method can be used for local annealing to eliminate internal stress and improve the plasticity of metal stamping parts.

In the annealing of some stamping parts, in order to minimize the oxide layer, the blank can be annealed in a neutral or reducing atmosphere furnace. This method is called bright annealing.