Influence of Filler Choice on Residual Stress of 347H Stainless Steel Weld Repairs

Austenitic stainless-steel (SS) welds, particularly 347H SS, may experience stress relaxation cracking (SRC) within months to years in service due to susceptible microstructure development and weld induced tensile residual stresses. Repair welding procedures are typically implemented to repair weld cracks; however, these procedures may worsen or further enable SRC susceptibility. Understanding residual stress changes before and after repair welding and with different weld fillers will help elucidate their influence on SRC susceptibility. In this study, residual stress, including longitudinal (LD), transverse (TD), and normal directions (ND), was measured with neutron diffraction (using HIDRA instrument at ORNL) in an ex-serviced 347H SS 40-mm thick plate double V groove weld and repair welds with matching E347 and E16.8.2 weld fillers. Longitudinal residual stresses were determined to be the highest in the E347 repair weld FZ, while the transverse stresses in the HAZ were similar for both repair welds. Overall, repair welding raises the peak von Mises residual stresses by 90% from 220 to 420 MPa and causes the peak stress location to change from mid-thickness weld root of ex-serviced weld to the weld center of repair weld. The steady state and weld stop locations of both repair welds were compared to the ex-serviced weld, which showed similar stress trends in both repair welds although higher peak stress in the stop location was observed with matching E347 repair weld. Post weld heat treatment (PWHT) may be needed to still reduce residual stress in repair welds but reheat cracking may occur during this process. Stress relaxation weldability testing using a Gleeble was conducted at PWHT relevant temperatures (800-850^°C) using measured peak residual stresses. The E16.8.2 repair weld did not fracture completely, while E347 repair weld fractured completely within a few hours, demonstrating higher reheat cracking susceptibility during PWHT in repair welds with E347 filler.