Effect of tempering-induced alloy carbide precipitation on residual stress and flatness of 700L plate

Tempering is an important method for controlling residual stress in metallic materials. Previous studies have found that carbide precipitation is the main mechanism of residual stress relaxation during the tempering process. However, quantitative investigations on the effect of carbide precipitation on residual stress relaxation capability are rarely reported. In this study, a combined approach integrating tempering behavior investigation, finite element simulation, and crack compliance residual stress measurement were adopted to reveal the effects of alloy carbide precipitation on stress relaxation and flatness of 700L steel plates, and to predict the evolution of residual stress during the tempering process. The results show that the tempering-induced precipitation of alloy carbides reduces the residual stress on the plate surface from 287 MPa to 95 MPa, and the core residual stress from -189 MPa to -65 MPa (the negative sign indicates compressive stress), with the degree of residual stress relaxation reaching 66.8% and 65.6%, respectively. Simultaneously, the precipitation of alloy carbides significantly contributes to controlling the non-uniform distribution of residual stress:the residual stress difference between the mid-width and edge regions of the plate surface is reduced from 145 MPa to 19 MPa, which lowers the risk of flatness shape defects. Furthermore, following tempering-induced alloy carbide precipitation, the warpage of the 700L plate is reduced from (5±0.7)mm to (2±0.3)mm, demonstrating a marked improvement in flatness.