Influence of laser surface melting on the characteristics of Stellite 12 plasma transferred arc hardfacing deposit

Stellite 12 hardfacing alloy deposited by plasma transferred arc (PTA) process on the 4140 steel substrate was subjected to laser surface melting (LSM) process. The effect of LSM on the PTA deposit was studied in terms of changes in microstructure and resultant variations in sliding wear properties. In the PTA state the microstructure, which consisted of Cr-rich (Cr7C3 and/or Cr23C6) and complex ((CoCrW)6C) carbides in Co matrix, was altered upon the application of LSM process. In short, LSM process led to the formation of a duplex layer, on the surface, consisting of carbide deficient and rich zones whose thickness tended to decrease with increase in the laser scan speed. As the result of formation of carbide rich zone at the outermost surface, LSM process provided an enhancement in surface hardness. On the other hand, the positive effect of LSM process on wear resistance became more apparent at high wear testing load causing carbide cracking and removal on the contact surface of Stellite 12 PTA hardfacing deposit.