Effect of molybdenum on the microstructure and wear resistance of cobalt-base Stellite hardfacing alloys

The Stellite 6 hardfacing alloys with different Mo contents have been deposited on AISI 1045-carbon steel using a Plasma Transferred Arc (PTA) welding machine. The effect of Mo on the microstructures and wear resistance properties of the Stellite 6 hardfacing alloys were investigated using optical microscopy, scanning electron microscopy, electron probe microanalysis and X-ray diffraction. With an increase in Mo contents, the M23C6 and M6C type carbides were formed instead of Cr-rich M7C3 and M23C6 type carbides observed in the interdenritic region of the Mo-free Stellite 6 hardfacing alloy. The size of Cr-rich carbides in interdendritic region decreased, but that of M6C type carbide increased as well as the refinement of Co-rich dendrites. The volume fraction of Cr-rich carbides slightly increased, but that of M6C type carbide abruptly increased. This microstructural change was responsible for the improvement of the mechanical properties such as hardness and wear resistance of the Mo-modified Stellite 6 hardfacing alloy.