Tensile properties of dissimilar martensitic steel/austenitic stainless steel joints at 450°C fabricated via flux-assisted TIG welding with EHEA interlayer

Dissimilar as-welded martensitic steel/austenitic stainless steel joints were fabricated using flux-assisted tungsten inert gas (TIG) welding with an AlCoCrFeNi2.1 eutectic high entropy alloy interlayer. Hot tensile properties and fractography at 450°C were compared with room-temperature (25°C) performance and base metals. The weld metal displayed a dual-phase structure of freshly formed martensite and austenite (Creq/Nieq = 1.62). At 25°C, the joint achieved 670 MPa tensile strength, 38% elongation, 417 HV weld metal hardness, and 98.5% joint efficiency and failed in the softer austenitic stainless steel base metal region. At 450°C, thermal softening reduced strength to 420 MPa (37.3% drop) and elongation to 13.7% (63.9% drop). Notably, joint elongation matched that of martensitic steel (13.3%) and was far below austenitic stainless steel (43%). The ductility loss stems from high dislocation density in the freshly formed martensite, restricting plastic deformation, and dynamic strain aging (DSA) that pins dislocations. DSA noticed at 450°C caused inhomogeneous flow, reduced work-hardening, severe strain localisation, and early necking in the austenitic stainless steel base metal region, where failure occurred via a ductile mechanism with equiaxed dimples and microvoids, coarser than at room temperature. These findings provide insights for elevated-temperature application of as-welded dissimilar martensitic/austenitic stainless steel joints.