Effect of heat treatment on the microstructure of additive manufactured Ni-based hardfacing alloy deposits on stainless steel

Ni based (NiCrFeSiBC) hardfacing alloy was deposited on 304 L SS build plate by laser rapid manufacturing (LRM) process. As-deposited specimen showed nearly a precipitate free zone at the interface, grain boundary (GB) precipitation in stainless steel up to 10 mu m, thin dilution layer (similar to 60 mu m) followed by formation of zones with distinct microstructure, microhardness and microchemistry in the deposit. To investigate the effect of thermal exposure on the interface microstructure, deposits were heat treated in the temperature range of 823-1123 K for 5-100 h. Up to 923 K, structure of the LRM deposits resembled that of as-deposited specimen. A planar interface region devoid of precipitates was present even after thermal exposure up to 923 K. With further increase in the temperature, formation of CrB precipitates with globular morphology was observed along the deposit/build plate interface with simultaneous increase in hardness. Thermal exposures beyond 923 K promoted coarsening of M7C3 and Cr2B precipitates. Diffusion of carbon and boron from the deposit to the build plate promoted the grain boundary precipitation of chromium carbides up to a maximum distance of similar to 1000 mu m for the highest temperature of 1123 K.