Laser hardfacing of 1050 mild steel using NiCoCrB for enhancing cavitation erosion-corrosion resistance

Laser surface modification of mild steel AISI 1050 was achieved using a hardfacing powder NiCoCrB. NiCoCrB was flame-sprayed on the substrate and then consolidated by a 2-kW NdYAG laser. The microstructures of the laser-modified specimens were studied by SEM, optical microscopy and XRD. The modified layers contained austenite as the main phase, with carbides and borides as the minor phases. The maximum hardness of the specimens was increased to 545 Hv. The cavitation erosion resistance in deionized water and 3.5% NaCl was improved by a factor of 4.4 and 8.3, respectively. The increase in erosion resistance was attributed to the presence of Co, which decreased the stacking-fault energy and enhanced the strain-induced martensitic transformability, and to the presence of carbides and borides, which resulted in an increase in hardness. On the other hand, the presence of Cr and Ni, together with a refined microstructure, led to an improvement in the corrosion resistance.