Fatigue-performance of PWHT welded joints: As-welded vs. high-frequency mechanical impact treatment

Abstract

In the study, fatigue tests were conducted to discuss the detrimental effect of local softening induced by post-weld heat treatment (PWHT) on the fatigue behavior of welded joints and subsequent high frequency mechanical impact treatment (HFMI) improvement. According to the distribution of stress and strain by numerical simulation, the difference between fatigue behavior of welded joints with and without PWHT becomes significant with the increase of stress range since the dominant mechanism of fatigue behavior changes from ‘stress-controlled’ to ‘strain-controlled’. The fatigue life of as-welded joints treated by HFMI is longer than that with PWHT+HFMI treatment. In particular, the difference is more obvious with the decrease of stress range due to the difference among the release amounts of compressive residual stress induced by HFMI. The fatigue crack initiation sites are dependent on stress range, local softening effect by PWHT and HFMI treatment.