Effects of melting-mixing ratio on the interfacial microstructure and tensile properties of austenitic–ferritic stainless steel joints

Abstract

In this study, the microstructure and mechanical properties of dissimilar austenitic–ferritic stainless steel joints welded by gas tungsten arc welding were investigated. Different offsets of the tungsten electrode's tip from the centerline of the assembled workpieces were used to obtain different elemental melting-mixing ratios. In tensile tests, two failure modes were found: the weld/workpiece interface failure mode (low strength and ductility) and the AISI 430 base metal failure mode (high strength and ductility). With a large offset (≥0.5mm) toward the AISI 304 side, additional elemental Ni was melted into the welding pool, which changed the solidification mode from ferritic to ferritic–austenitic. This leads to a dramatic microstructure and local property change at the weld/workpiece interface. The local stress–strain curves of various heat-affected zones from different joints were obtained by the digital image correlation technique. This technique showed that the steep local microstructural and mechanical property transition of the dissimilar austenitic–ferritic joints will lead to failure at the weld/workpiece interface.