Near-threshold fatigue crack growth behavior of the weld metal and heat-affected zone in an ex-service CrMoV steel joint

Threshold value (??Kth) and fatigue crack growth behavior at different temperatures and stress ratios were investigated in weld metal (WM) and heat-affected zone (HAZ) of an ex-service CrMoV steel joint. Compared with the ??Kth at 25 ??C, the ??Kth at 500 ??C and 540 ??C were still high, because significant oxide-induced crack closure (OICC) occurred in WM and HAZ during high-temperature tests. The high-temperature ??Kth of HAZ were higher than those of WM, due to their more severe oxidation and more significant OICC. This was owing to the lower Si and Cr content and smaller grain size in HAZ.