Method of X-ray residual stress measurement for phase transformed welds

In this study, we attempted to evaluate the residual stress distribution in welds accompanied by phase transformation using X-ray stress measurement. First, relationship between the phase transformation behavior and the residual stress of welded specimens with different phase transformation was discussed. In the specimen with martensite in the weld, reduction in tensile stress due to martensite transformation shown in residual stress distribution followed conventional behavior. However, in the specimen with bainitic ferrite in the weld, the residual stress in the transverse direction was almost the same as the residual stress in the longitudinal direction, and the residual stress did not follow conventional behavior. Next, X-ray elastic constant in the weld was measured, and then the residual stress was reevaluated. In the specimen with bainitic ferrite in the weld, X-ray elastic constant had anisotropy, and the reevaluated residual stress followed conventional behavior. In conclusion, it was shown that depending on the phase transformation behavior, it is difficult to use X-ray elastic constant estimated by Kröner model; however, if we use the measured value, we are able to evaluate the residual stress more accurately.