TWI Industrial Member Report Summary 283/1985
By R V Sharples
The characteristics of the plasma transferred arc (PTA) process were investigated for depositing two common cobalt-based hardfacing materials onto a C-Mn steel. Ranges of welding variables, deposition rate, bead thickness and powder utilisation efficiency were established. Dilution was shown to be dependent on current level, preheat temperature and plasma and shielding gas flow rates, approximately linear relationships being found for the range investigated. For both hardfacing alloys, deposit hardness decreased with increasing dilution. Cracking in Stellite 6 was found to be associated with lack of inter-run fusion and was eliminated by the introduction of one-sided dwell into the weaving motion. Sound deposits of Stellite 6 were produced, without preheat, at dilutions of less than 5%, at 2-4mm thickness. Cracking in Stellite 1 occurred with preheats of up to ~300°C. The relationship of microstructure to the crack susceptibility of the deposits was considered.