Comparison of microstructure, dilution and wear behavior of Stellite 21 hardfacing on H13 steel using cold metal transfer and plasma transferred arc welding processes

A comparative study of the Stellite 21 hardfacing on H13 steel produced by cold metal transfer (CMT) process and conventional plasma transferred arc welding (PTAW) process was carried out. The lower heat input of the CMT process resulted in finer microstructure and lesser dilution in the Stellite 21 coating than the PTAW process. The volumetric dilution values showed much scatter across the thickness of the PTAW coating than CMT. The effect of lower dilution and finer structure of the CMT coating resulted in a marginal increase in the microhardness. The room temperature (RT) and high temperature (600 degrees C) wear performance of the coatings were studied using a ball-on-disc tribometer using alumina ball. The wear tracks were analyzed using an optical profilometer and the volume loss was calculated. The CMT deposited coating showed better wear performance than PTAW coating. X-ray diffraction (studies of the room temperature wear tracks showed the transformation of gamma-fcc phase in the as-deposited coating to epsilon-hcp phase after the wear. The volume percentage of the epsilon-hcp was observed higher for CMT deposited coating than the PTAW coatings, which can be attributed to lower dilution and finer microstructure of the former.