Residual stress comparison of cast iron cylinder head of engine before and after heat treatment

The indentation strain-gage method, the sectioning relaxation strain-gage method and the deep-hole drill (DHD) method were used to detect the residual stress of four types of the cast iron cylinder head in two materials of engine before and after heat treatment. The effect of heat treament to eliminate the residual stress of cylinder head. The results showed that the residual stress on the surface of cylinder head measured by indentation strain-gage method and sectioning relaxation strain-gage method was basically compressive stress. The residual stress levels measured by the two methods were similar, except for no. 3 cylinder head, the peak value of surface compressive stress of other cylinder heads had not decreased. The tensile stress in the depth direction of cylinder head was measured by DHD method, and heat treatment process did not reduce the peak value of tensile stress in the depth direction of cylinder head. The heat treatment process could be used for no. 3 cylinder head to eliminate surface residual stress, and the residual stress level of remaining cylinder heads before heat treatment were relatively low, no need for heat treatment.