Investigation on microstructure, Mn segregation behavior and mechanical properties of high-Mn steel joints

Shielded metal arc welding (SMAW) and submerged arc welding (SAW) were used to join 20 mm-thick 25Mn austenitic steel plates for cryogenic applications.The weld microstructure, Mn segregation, local stacking fault energy (SFE), and mechanical properties were compared.Both weld metals were predominantly γ-austenitic.SMAW produced finer columnar dendrites and higher geometrically necessary dislocation densities, whereas SAW produced coarser, more directionally aligned dendrites.Electron backscatter diffraction revealed more pronounced differences between the second and third SMAW layers than between the corresponding SAW layers.Interdendritic Mn enrichment occurred in both weld metals, with local segregation indices of approximately 12.5 % for SMAW and 33.8 % for SAW.Calculated SFE values were 24.0-30.5 mJ m -2 and 21.6-33.7 mJ m -2 , respectively, suggesting a tendency for twinninginduced plasticity.SMAW exhibited higher tensile strength and microhardness, whereas SAW showed greater elongation after fracture and higher absorbed impact energy at -196 • C. The mean weld-metal impact energies were 68 J and 91 J, respectively.These results link the differences in strength and ductility to microstructural refinement, dislocation substructures, and heterogeneity between and within weld layers.