The effect of postweld heat treatment on hydrogen-assisted cracking of 8630/Alloy 625 overlay

The weld interface of Alloy 625 clad onto AISI 8630 steel requires postweld heat treatment (PWHT) to reduce the heat-affected zone (HAZ) hardness of the steel to meet industry standards. This PWHT results in carbon diffusion and pile up in the transition zone at the fusion boundary which potentially embrittles the 8630/625 interface. For the 8630/625 overlay, the PWHT needs to be carefully selected to reduce the potential for hydrogen-assisted cracking (HAC) and/or sulfide stress cracking (SSC). In this work, a wide range of PWHT conditions defined by the Hollomon-Jaffe parameter (HJP) was studied using the delayed hydrogen cracking test (DHCT). The effect of PWHT on HAC behavior was quantified using this test and the optimal HJP range for resistance to HAC was determined to be in the range from 18,500 to 19,500. Fracture surface analysis was conducted on failed samples to further evaluate the effect of PWHT and confirm the optimal HJP range. The HAC behavior of the 8630/625 overlay was compared with that of the F22/625 overlay reported previously.