Friction Stir Welding of 2.25Cr–1Mo Steel to AISI 316LN Stainless Steel

This study explored the role of tool rpm in the microstructure evolution and its significant effect on hardness measurement of friction stir welded 2.25Cr–1Mo (P22) steel to AISI 316LN stainless steel. Irrespective of rotational tool speeds, the martensitic phase transformation was found in the P22 steel side of the dissimilar weldments due to the higher peak temperature, and a higher degree of plastic deformation evolved during friction stir welding. Hardness measurements revealed that the average hardness of the martensitic structure that existed in the friction stir weldment of the P22 steel side is 405 ± 5HV0.2. Evolution of martensitic structure with higher hardness emphasizes that the post-weld heat treatment is mandatory for the dissimilar weldment.