Resistance Spot Weldability of Ferritic and Martensitic Dissimilar Stainless Steel

Abstract

Ferritic stainless steel and martensitic stainless steel are joined by resistance spot welding technology. The macrostructure, microstructure, hardness distribution, and mechanical properties of joints are investigated. The results show that nugget size is a key to the tensile shear load of joint. The tensile shear load reaches its maximum of 5.6 kN when the nugget size reaches its peak of 5.6 mm at 8 kA welding current. The nugget consists of lath martensite and delta ferritic which lead to a higher hardness than base materials. The ferrite grains on the heat-affected zone coarsen on the AISI 409L side. The constitution of heat-affected zone on the AISI 410 side changes from martensite and a mixture of ferrite and martensite to a mixture of tempered martensite and carbide at a distance far away from nugget. The hardness peak of the whole spot-welded joint is located in the upper critical heat-affected zone of the AISI 410 side. Hardness distribution has a notable influence on load-bearing capacity of joints under high electrode force. All joints fail at pull-out mode and the failure propagates along the heat-affected zone on AISI 409L side with severe plastic deformation in the failure process.