Examination on joining of 2 mm thick dissimilar stainless steel plates using resistance spot welding

Abstract

In the present study, dissimilar metals such as austenitic stainless steel (ASS) and duplex stainless steel (DSS) with a thickness of 2 mm are joined by resistance spot welding process to investigate the welding metallurgy and failure behavior under different heat inputs. Non-uniform electrode impressions are observed on ASS and DSS sides due to their different thermal conductivity and electrical resistivity. The microstructure of the Fusion Zone (FZ) shows that higher heat input accelerates the growth of Intra Granular Austenite (IGA) due to faster cooling. Scanning electron microscopy (SEM) - Energy Dispersive x-ray (EDX) investigation at FZ showed that Chromium & Molybdenum decrease with increasing heat input due to a decrease in ferrite content. X-ray diffraction analysis confirmed that ferrite formation is limited at higher heat input. Microhardness study revealed that the higher hardness is in the middle of the weld nugget, which is due to the presence of equiaxed grains and IGA. The lowest hardness on the ASS side of Heat Affected Zone (HAZ) is due to the phenomenon of grain growth, and the HAZ DSS side has a higher hardness than DSS Base Metal (BM) due to the mechanism of solid solution strengthening. The tensile shear test showed that the tensile shear strength increases with the addition of heat. SEM Examination of the fracture surface revealed the presence of an equiaxed dimple structure on the ASS side, confirming ductile fracture, and torn bonds on the DSS side, confirming quasi-gap fracture due to the work-hardening ability of both plates. This study is carried out to understand the relationship between mechanical, metallurgical, and failure behaviours, because, researches on joining of dissimilar (AISI 316 L and DSS 2205) stainless steel sheets using Resistance Spot Welding process is very limited and need to be studied in detail.