Surface Residual Stress Distribution of 6.8 Grade Cold Heading Bolts

The axial and tangential surface residual stress and its distribution of 6.8 grade bolts before and after heat treatment were measured by X-ray residual stress tester, and the effects of cold heading and necking down on the residual stress of screw and bolt head transition fillet were analyzed. The results show that the distribution of surface residual stress of the bolts before heat treatment was nonuniform, the maximum residual tensile stress was 155.8 MPa, and the amplitude of decline was up to 50% after heat treatment. In the radius direction, with the increase of the depth, the residual stress changed from compress stress to tensile stress.