Evaluation of Microstructure at Interfaces of Welded Joint Between Low Alloy Steel and Stainless Steel

In the present investigation, welded joints between low alloy steel and 304LN stainless steel were considered. The joints were fabricated using Inconel 152 and 182 as buttering materials. A thin layer of martensite, Type-I boundary, and Type-II boundary were revealed near the fusion boundary between low alloy steel and the buttering material. The polygonal grain structure and unmixed zone were found near the fusion boundary between the weld metal and austenitic stainless steel. During a uniaxial in situ deformation test in an SEM, it was revealed that crack initiation and propagation were through the buttering material. In this respect, the weld fabricated with the Inconel 152 buttering material exhibited better joint efficiency and a higher strain-hardening exponent than the joint produced with the Inconel 182 buttering material. The improved strength of the former joint was attributed to a fine grain structure, fine-scale distribution of complex carbide phases, and qualitatively high dislocation density within the Inconel 152 buttering material.