Study of mechanism, microstructure and mechanical properties of activated flux TIG welded P91 Steel-P22 steel dissimilar metal joint

The current work investigates activated flux TIG welding of dissimilar steel combination of 8 mm thick plates of Modified 9Cr-1Mo (P91) steel and 2.25Cr-1Mo (P22) steel. The effect of different fluxes namely- SiO2, TiO2, Cr2O3, MoO3 and CuO on the weld bead geometry was investigated. The possible mechanism for the increase in depth of penetration has been discussed. The integrity of the weld joint made with MoO3 flux was investigated by evaluating metallurgical and mechanical characteristics in as-welded and post weld heat treated (750 °C/2 h) conditions. The occurrence of carbon migration was confirmed by optical microscopy and elemental redistribution through EPMA analysis. The precipitation of carbides of M23C6 type in the carbon enriched zone was confirmed through TEM analysis. The beneficial effect of A-TIG welding in reducing the widths of carbon enriched/depleted regions at the P22 steel-weld interface after post weld heat treatment has been discussed with the help of DICTRA simulations. The weld joints failed from P22 steel base metal in both as-welded and post weld heat treated conditions during a tensile test. The impact toughness was found to be improved after post weld heat treatment.