Factors that can cause stress concentration in different parts of the quenched parts (including metallurgical defects) have a promoting effect on the generation of quenching cracks, but they will only appear in the tensile stress field, especially under the maximum tensile stress. If they are in the compressive stress field, there will be no crack promoting effect.
Quenching cooling rate is an important factor that can affect the quenching quality and determine the residual stress. It is also a factor that can have an important or even decisive influence on quenching cracks. In order to achieve the purpose of quenching, it is usually necessary to accelerate the cooling rate of the parts in the high temperature section and make it exceed the critical quenching cooling rate of the steel to obtain the martensitic structure. As far as residual stress is concerned, this can increase the thermal stress value that offsets the effect of structural stress, so it can reduce the tensile stress on the surface of the workpiece and achieve the purpose of inhibiting longitudinal cracking. Its effect will increase with the acceleration of high temperature cooling rate. Moreover, under the condition of being able to be hardened, the larger the cross-sectional size of the workpiece, the greater the risk of cracking, although the actual cooling rate is slower.
Carbon steel tubes
