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Cast iron heat treatment steps

Update time:2015-02-03 17:22:34Hit:4215
Heat treatment can be mainly divided into the following several kinds:
(1) to stress annealing treatment; (2) the graphitization heat treatment; (3) changing the matrix microstructure heat treatment. This chapter briefly introduces the heat treatment process of the theoretical foundation and technological characteristics.
The first section stress annealing
Stress relief annealing is cast in a certain temperature, and then slowly cooling, in order to eliminate the casting residual stress in. For gray iron, stress relief annealing can stabilize the casting geometry size, machining deformation decreases after. For white cast iron, stress relief annealing can avoid casting in the storage, transport and use process by vibration or environment changes deformation and cracking on its own.
First, casting residual stress generation
The volume shrinkage or expansion to the cooling process of casting during solidification and the future, this volume change often gets between the parts and castings outside constraints and not free, so they produced a casting stress. If the cause of stress is removed, then eliminate casting stress, the stress is called temporary casting stress. If the cause of stress after elimination of the casting stress still exists, the stress is called the casting residual stress.
Casting during solidification and subsequent cooling process, because of different thickness, different cooling conditions, the various parts of the temperature and the degree of transformation will be different, resulting in various parts of the volume change of different amount of castings. If this casting alloy has been in the elastic state, between the various parts of the casting will produce mutual restriction. The casting residual stress is often the due to temperature difference and the degree of transformation caused by different stress.
Two, to be the theoretical basis of stress annealing
Research shows that the casting residual elastic modulus temperature and casting alloy of each part of force and casting cooling process is directly proportional to the. For a long time in the past, people thought the casting alloy exists the elastic-plastic transition temperature in the cooling process, and that the iron elastic-plastic transition temperature of 400 DEG C. Based on this understanding, to be heating temperature stress annealing should be 400 degrees. However, practice has proved that the heating temperature is not ideal. Recent studies show that, the alloy material does not exist the elastic-plastic transition temperature, even in the alloy solid-liquid coexistence remains flexible.
(Author:dong)
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