Investigations on different hardfacing processes for High temperature applications of Ni-Cr-B-Si alloy hardfaced on austenitic stainless steel components

Ni-Cr-B-Si alloy is used for hardfacing of 316 L N Stainless Steel components in Sodium-cooled Fast Reactors (SFRs) to enhance wear resistance and also to prevent self-welding. Since the shear force is acting between the substrate and the deposit due to dissimilar thermal expansion during high temperature operating conditions, it is necessary to focus on the hardfacing process which provides good bonding shear strength between them. Though low substrate dilution is advisable to attain high microhardness of the deposit, the deposit should not get de-bonded due to shear. To seek solution to this problem, three major hardfacing processes, viz., Plasma Transferred Arc, Gas Tungsten Arc and Laser processes were considered. Hardfaed shear specimens were prepared using each process and tested as per the ASTM A264. Faster cooling rate leads to finer grains and higher microhardness. The influence of dilution on the microhardness was studied. Scanning Electron Mircographs and Energy Dispersive Spectroscopic studies at the fractured surfaces were done to ascertain the reason for strength. Finally, the laser hardfacing process which provides a combination of good shear strength, high microhardness as well as low dilution is recommended for hardfacing of the components of the SFRs for their reliable operations.