Experimental investigation on microstructure and mechanical properties of joining stainless steel 316LN to Low Activation Ferritic Martensitic steel (LAFM) using activated flux TIG welding

One of the most significant requirements for joining dissimilar materials is to produce a minimum number of deeper-penetration welds and thereby avoid flaws. The Activated Flux TIG welding process improves penetration depth in a single pass, reducing the number of weldments. The dissimilar weld between LAFM – Stainless Steel 316LN also possesses the same requirement for a particular application. The present study aims to investigate the structure-property relationship and mechanical properties of dissimilar weldments of LAFM – SS 316LN using conventional TIG and Activated TIG welding using TiO2 and Co3O4 oxide fluxes. The microstructure study of conventional TIG weld reveals the fine lath martensitic structure as compared to weld prepared with A-TIG using TiO2 flux due to difference in the cooling rate. Also, the carbide formation in conventional TIG and A-TIG using TiO2 confirms the presence of delta ferrite But, the same observation was not confirmed with A-TIG weldments prepared using Co3O4. Similarly, the hardness results also support the microstructure study. The higher transverse tensile strength of weld indicates that it is stronger than base metal. The lower impact energy in case of Activated Flux TIG welding process was reported due to presence of oxide flux.