Heat treatment method for reducing residual stress of forgings

Abstract

The invention provides a heat treatment method for reducing the residual stress of forgings, which comprises heating the forgings to the medium holding temperature and holding them for a period of time; Cool down to AC3+(10~60)℃, keep it warm for a while; finally quench and cool. The invention adds "cooling the forging to AC3+(10-60)°C, and keeping it warm for a period of time", and the improved parts are few, which ensures the versatility of the heat treatment equipment. When it is reduced to AC3+ (10-60°C), the alloying elements are still in the stage of remelting and homogenization, which has no effect on the homogenization of the alloy composition in the later stage. On the premise that the cooling method does not change, the temperature at the center and edge of the workpiece can be reduced Difference, to reduce the impact of thermal stress on the workpiece. The reduction of the quenching temperature reduces the cross-sectional temperature difference of the workpiece during the quenching process and reduces the thermal stress, thereby reducing the overall residual stress of the forging after quenching.

Description

technical field [0001] The invention relates to the technical field of forging, in particular to a heat treatment method for reducing the residual stress of a forging. Background technique [0002] Large-scale forgings have a large thickness. During the performance heat treatment, that is, the quenching process, when cooling down, the temperature drop rates of the surface and the core are inconsistent, and there is a time difference, thus forming an uneven temperature field; There is a difference in the cooling rate of the center and the core, resulting in asynchronous tissue transformation, uneven temperature field and asynchronous tissue transformation, forming residual stress inside the forging. Generally speaking, residual stress is harmful and will cause parts. Deformation or even cracking, etc. [0003] Gas turbine, steam turbine or motor forgings have higher requirements on the residual stress level of the workpiece due to the requirements of the working conditions. ...

AI Technical Summary

Problems solved by technology

However, since the AC3 temperature of the SA-508Gr.3 material is 820°C, when the temperature of the forging is reduced to 788°C-820°C, since the temperature is lower than the AC3 temperature (820°C), it is difficult to maintain the remelting and homogenization of the alloying elements. After that, the composition of the forging may not be uniform enough, which will affect the performance

In addition, air cooling is used to cool the forging from 880°C-920°C to 788°C-820°C. First, the operation is troublesome. The forging needs to be taken out of the furnace to cool, and then it needs to be put back into the furnace when it is kept warm. The number of pick-and-place forgings, thick and large forgings are heavy, it takes a long time to pick and place, affects efficiency, and it is difficult to accurately control the temperature; second, the cooling speed of air cooling is faster, for thick and large forgings, the surface temperature drops rapidly, and the center The temperature drops slowly and is prone to thermal stress

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