A comparative study between the mechanical and microstructural properties of resistance spot welding joints among ferritic AISI 430 and austenitic AISI 304 stainless steel

In this study, 1.5-mm-thickness ferritic AISI 430 and austenitic AISI 304 stainless steel are resistance spot-welded by combining 304/304, 304/430 and 430/430. The dissimilar 304/430 nugget displays a strong texture and consists of α-ferrite columnar grains, with some γ-austenite and α′-martensite dispersed over the grains’ boundary zone. Lap-shear tests are performed for each welding combination under different parameters. The results show that the interfacial failure to pull-out failure mode transition tendency is in the following order: 304/430 > 304/304 > 430/430. This is because: (1) the nugget of 304/430 samples are harder than that of the 304/304 samples, which makes the former less likely to fracture under nugget plastic failure; (2) the 304/430 nugget samples possess higher local toughness than the 430/430 samples, a property that makes 304/430 joints resistant to fracture under nugget brittle rupture. Besides, the 304/304 joints possess high energy absorption in the lap-shear test, even for interfacial failure mode samples. This is confirmed in the digital image correlation tests which show the presence of a massive plastic deformation in the 304/304 joint fracture in interfacial failure mode.