Superior Stress Relaxation Cracking Resistance of UNS S34752

Abstract It has been known that Stress Relaxation Cracking (SRC) in welded joints or cold deformed area is a severe problem for continuous operation in the temperature range between 550 and 750°C in a complex refinery, petrochemical plants etc. In API Technical Report 942-B, SRC susceptibility ranking of heat resistant austenitic stainless steels containing high C content over 0.04% was reported as S31609 < S30409 < S32109 < N08810 < S34709 < N08811. Osuki et al [9] investigated the SRC mechanism with thermodynamic calculations. They studied precipitation hardening by carbide formation at dislocations and softening by Cr depletion through M23C6 precipitation on grain boundaries during stress relaxation at 650 C. Based on this research, S34751 indicated a higher SRC resistance than S34709. In this study, SRC susceptibility of S34752, containing both high Cu and B content was examined because of both the similar alloy design to S34751 and higher creep strength than S34751 and S34709. It was clarified that S34752 indicated higher SRC resistance than S31609, which was reported as having the lowest SRC susceptibility among conventional heat resistant austenitic stainless steels, by the stress relaxation test at 650°C according to ASTM E328.