Microstructural characterization and mechanical properties of K-TIG welded SAF2205/AISI316L dissimilar joint

Motivated by increasing productivity and cost-effectiveness, the feasibility of Keyhole Tungsten Inert Gas (K-TIG) welding for joining SAF2205/AISI316L dissimilar materials was presented. Single pass autogenous welding was achieved on 5.6 mm thick plates at a speed of 35 cm/min without using any filler materials and edge preparation. In-depth investigation into the weld was conducted by optical microscope, scanning electron microscope, Thermo-Calc simulation, microhardness, tensile test and impact toughness test. The results show that in order to produce defect free dissimilar joint, the torch deviation should be kept at zero to one mm towards AISI316L side. The austenite fraction increased with torch deviation shifted from SAF2205 side to AISI316L side, along with the variation in ferrite morphology from massive type to lath shape. Defect free joints possess better tensile properties than AISI316L base metal, indicating sufficient strength level for such dissimilar joint. Poorer toughness of the samples with 1 mm torch deviation towards SAF2205 side and 2 mm deviation towards 316L side is a result of imbalanced phase structure, ferritic-asutenitic solidification mode as well as harmful precipitates in the weld. It has been demonstrated that the K-TIG welding process offers an efficient way to produce sound and high quality dissimilar joint between SAF2205 and AISI316L, with 0-1 mm torch deviation towards 316L side being the desired options in terms of overall material properties.