Microstructure and mechanical properties of dissimilar ferritic (S355)–austenitic (AISI 304) steel joints welded by robotic GMAW

Abstract In applications requiring high corrosion resistance, it is crucial to utilize dissimilar welding techniques that incorporate structural steels in critical areas to reduce costs, rather than constructing the entire structure from high-cost stainless steels. Ferritic steels are often preferred due to their higher strength compared to stainless steels. In this study, Gas Metal Arc Welding (GMAW) was performed on 12 mm thick S355 structural steel and AISI 304 austenitic stainless steel using SG307 austenitic filler metal. Following welding operations with three different heat inputs, macrostructural assessments were carried out according to the EN ISO5817:2023(E) standard on the welds deemed successful based on nondestructive tests. Microstructural characterization, microhardness tests, tensile test, and impact tests (performed by notching different regions of the weld joint) were also conducted. The results demonstrated that undesirable changes in mechanical properties due to microstructural transformations in the welding of carbon steels with austenitic stainless steels can be mitigated with the correct parameters and proper filler metal selection. Thus, the mechanical properties required to ensure the expected performance of the welded structure were successfully achieved. Results revealed that the dissimilar joint efficiency with respect to yield strength of ferritic steel was calculated as 103.77 % and 175.42 % for austenitic AISI 304 steel. The impact toughness test results for the heat-affected zone (HAZ) of S355 steel showed satisfactory levels. Although the dissimilar weld metal region exhibited lower toughness values, they remained above 100 J.