When the core of stainless steel manhole is not hardened, that is to say, the surface changes to austenite, and the core changes to ferrite type mechanism, because the specific volume of the surface has to expand obviously, and the core restricts it not to expand at will, so the hardening layer is subject to stress in situ, and the core is tensile stress, and its internal stress distribution is similar to the internal stress caused by hot and cold in situ stress.
The ground stress caused by the whole process of quenching and tempering is not separated from the welding stress. In fact, the in-situ stress produced in the steel parts is the result of the comprehensive effect of welding stress and mechanism in-situ stress. The elements that endanger the welding stress of stainless steel manhole and the in-situ stress of mechanism are various, such as the composition, heat transfer, thermal expansion, hardenability, phase change temperature, symmetry of mechanism, appearance and specification of steel parts, heating rate, heating temperature, water cooling rate and water cooling mode, etc.
Therefore, the internal stress of heat-treated steel parts is more complicated than that of simple welding stress or mechanism in-situ stress, and the transformation of instantaneous velocity in-situ stress in the whole process of chilling is more complicated. The internal stress condition of 47mm diameter Fe Ni alloy (11.7% Ni) cylinder after heat treatment in cold water at 800 ° C.
