Narrow gap welding of low alloy and austenitic stainless steels using different Inconel alloys: comparison of microstructure and properties

In the present investigation, SA508 low alloy steel and 304LN austenitic stainless steel were joined by hot wire narrow gap gas tungsten arc welding. Inconel 82 and 52 were used as filler alloys. Evaluation of microstructure, micro-hardness, and tensile strength through in situ test in scanning electron microscope were attempted for the welded assemblies. Low alloy steel consisted of a heat affected zone adjacent to interface. A thin layer of martensite and Type-I boundary were revealed near the fusion boundary between low alloy steel and weld metal. Micro-hardness distribution showed a peak near the fusion boundary between low alloy steel and filler alloy owing to the presence of lath martensite, Type-I boundary, and complex alloy carbides. The micro-hardness was further dropped within the filler alloy. During the in situ tensile test, deformation was confined within the filler alloy, as it was the weakest link across the fusion boundary. It was revealed that the joint produced with Inconel 82 filler alloy has a better mechanical strength than the assembly fabricated with Inconel 52 filler alloy. Inferior quality of the latter was attributed to the relatively coarser grain structure and the presence of larger alloy carbides within filler alloy when compared with the former. Improved strength of the weld with Inconel 82 filler alloy was further endorsed by the lower slip distance for dislocation movement and higher strain hardening rate in comparison to the weld fabricated with Inconel 52 filler alloy.