Microstructural analysis and mechanical characterization of dissimilar welds between nickel-based and steel-based superalloys post-cryogenic treatment using hotwire GTAW

This study explores the dissimilar welding of nickel superalloy 59 with Fe-Ni superalloy 904 L using the Gas Tungsten Arc Welding with Hot Wire technique (HW-GTAW). The HW-GTAW process produced defect-free weldments with complete penetration, as confirmed by macroscopic analysis. Microstructural analysis using FESEM and EDS revealed fine equiaxed and columnar dendrites in the fusion zone and identified a secondary phase enriched with chromium. XRD analysis supported the presence of predominant austenitic phases and indicated the formation of Cr23C6-type carbide. The grain size of the weld joint, determined using the Gaussian method and Scherer formula, was 44.53 nm, slightly smaller than base metals. Microhardness tests revealed values ranging from 226 ± 5 HV 10 to 243 ± 5 HV 10, with the highest values observed in the deep cryogenic treatment (DCT). The Mo in the ERNiCrMo-13 filler and the effects of DCT, which promote grain refinement, are responsible for this increase in hardness. Residual stress measurements revealed a maximum tensile stress of 315 MPa along the longitudinal axis and a maximum compressive stress of 355 MPa along the transverse axis. DCT enhanced the weldment's tensile strength by up to 12% compared to as-welded samples, with a 6% increase compared to shallow cryogenic-treated (SCT) samples. Charpy impact testing indicated a value of 88 J in the fusion zone, which is 1.2% less than alloy 59 and 9% higher than 904 L. Tensile fracture analysis revealed ductile dimples, while impact fractography showed a mix of ductile dimples and brittle, glassy cleavage facets.