Heat treatment of forgings

Many forgings are also subject to heat treatment. In the heat treatment of forgings, the heat treatment stress is an important consideration in the process of formulating the process. Some stresses are generated in the process of heating and cooling, and disappear with the end of these processes, which is instantaneous stress; Some stresses are equilibrium stresses that still exist in the forging after heat treatment, which is residual stress. In the process of heat treatment, if the instantaneous stress reaches the yield point of the material at this temperature, the forging will produce plastic deformation and relax the stress. If the instantaneous stress is greater than the breaking strength of the material, it is possible to crack the forging until it breaks. Even if the instantaneous stress is less than the strength limit of the material, there are always some metallurgical defects in the large forging, resulting in great stress concentration at these defects, so as to further expand the original defects and even cause the fracture of the forging. Therefore, controlling the magnitude of instantaneous stress is an important issue in the formulation of heat treatment process of large forgings. The influence of heat treatment residual stress on the workpiece is twofold, both good and bad. If the residual stress is the same as the working stress symbol of the part, the strength of the part can be reduced. If it is opposite, the strength of the part will be improved. For some important large forgings, the allowable participating stress should be less than 10% of the material yield point. In order to ensure the quality of forgings and improve the service performance and service life of products, in addition to checking the quality of forgings at any time during the production process, forgings must also be inspected by full-time personnel before warehousing. The contents of forging inspection include: forging geometry and size, surface quality, internal quality, mechanical properties and chemical composition, and each aspect includes several contents.