Effect of Material Property Factors on the Interfacial Residual Stress Gradient in High-Manganese Steel/STS304 Dissimilar Butt Welds

Cryogenic high-manganese austenitic steel is used in liquefied natural gas (LNG) storage tanks and has a lower thermal expansion coefficient than other cryogenic steels. Because it is joined to stainless steel in the loading system, dissimilar welding is required. Three-dimensional thermal elastic–plastic finite element analysis and sectioning measurements were performed on 15-mm-thick high-manganese steel/STS304 dissimilar butt welds, and the residual stress was analysed separately in the longitudinal and transverse components. The analysis predicted a steep gradient at the weld metal–STS304 interface 8.5 mm from the weld centre, where the transverse stress falls to about −230 MPa. The longitudinal peak differed from the homogeneous joint by only 77 MPa (−11.7%), within the analysis–measurement deviation (RMSE 103–127 MPa). Of the four properties substituted individually, the expansion coefficient gave the highest reproduction ratio (57.9% on average) and alone reproduced the interfacial compression; substituting all four reproduced the effect almost completely (102.4%). The transverse stress range increased linearly with the expansion mismatch (R2 = 0.978), whereas the longitudinal range did not (R2 = 0.002). Assessment by peak residual stress alone therefore misses the interfacial gradient and the compressive zone specific to dissimilar joints.