Stainless steel head in the process of heating and cooling, due to the stainless steel head the surface and core of the cooling speed and time is not consistent, forming the different temperature, will lead to volume expansion and contraction of uneven stress, that is, thermal stress. Under the thermal stress, the surface temperature is lower than the core, and the contraction is larger than the core, so that the core is under tension. That is, under the thermal stress, the surface of the workpiece will be compressed and the core will be pulled. This phenomenon is affected by factors such as cooling rate, material composition and heat treatment process. The faster the cooling rate, the higher the carbon content and alloy composition, the greater the uneven plastic deformation caused by thermal stress during cooling, and the greater the residual stress formed.

On the other hand, in the process of heat treatment, when steel turns into austenite to martensite, the increase of specific volume is accompanied by the expansion of the volume of the workpiece, and the parts of the workpiece are successively transformed, resulting in inconsistent volume growth and tissue formation. stress. The final result of the structural stress change of the stainless steel head is that the surface layer is subjected to tensile stress and the core is subjected to compressive stress, which is exactly opposite to the thermal stress. The magnitude of the tissue stress is related to the cooling rate, shape, and chemical composition of the workpiece in the martensitic transformation zone. However, the thermal stress has already produced a stainless steel head before the tissue transformation, and the tissue stress is generated during the tissue transformation. During the whole cooling process, the combined effect of thermal stress and tissue stress is the actual existence in the workpiece. Stress. However, the thermal stress has already produced a stainless steel head before the tissue transformation, and the tissue stress is generated during the tissue transformation. During the whole cooling process, the combined effect of thermal stress and tissue stress is the actual existence in the workpiece. Stress. The result of the combined effects of these two stresses is very complex and is influenced by many factors such as composition, shape, and heat treatment process. There are only two types in the development process, namely thermal stress and tissue stress. When the action direction is opposite, the two cancel each other. When the action direction is the same, the two are superimposed. Whether it is offsetting or superimposing each other, the two stresses should have a dominant factor. When the thermal stress is dominant, the result is that the core of the workpiece is pulled and the surface is pressed. The result of the action of the tissue stress is that the surface of the workpiece is stressed.