A-TIG welding of dissimilar P92 steel and 304H austenitic stainless steel: Mechanisms, microstructure and mechanical properties

The present study focuses on the dissimilar joining of P92 steel and 304H austenitic stainless steel plates of thickness 8 mm using A-TIG welding with aim to select a proper flux for through thickness penetration. The effect of four different oxide fluxes named: Cr2O3, MoO3, SiO2 and TiO2 on weld bead geometry was studied. A detailed investigation on possible mechanism for increase in depth of penetration has been carried out. Out of four oxide fluxes, TiO2 provided through thickness penetration. Further, the integrity of weld joint developed using TiO2 flux was assessed in light of microscopy, hardness test, tensile test and impact toughness test. Microstructure study of the weld joint showed the formation of untempered martensite, polygonal austenite grains and ferrite stringers in different zones of weld joint. In tensile testing, the specimens were failed from 304H austenitic stainless steel base metal. The tensile properties were found as tensile strength 688.6 MPa, yield strength 562.2 MPa and elongation 37.4%. The V-notch Charpy impact toughness of the weld joint (30 J) was quite lower than the base metals due to the formation of untempered martensitic structure.