Microstructure and hardness characterisation of laser coatings produced with a mixture of AlSI 420 stainless steel and Fe-C-Cr-Nb-B-Mo steel alloy powders

Fe-C-Cr-Nb-B-Mo alloy powder and AlSI 420 SS powder are deposited using laser cladding to increase the hardness for wear resistant applications. Mixtures from 0 to 100 wt.% were evaluated to understand the effect on the elemental composition, microstructure, phases, and microhardness. The mixture of carbon, boron and niobium in the Fe-C-Cr-Nb-B-Mo alloy powder introduces complex carbides into a Fe-based matrix of AlSI 420 SS which increases its hardness. Hardness increased linearly with increasing Fe-C-Cr-Nb-B-Mo alloy, but substantial micro cracking was observed in the clad layer at additions of 60 wt.% and above; related to a transition from a hypoeutectic alloy containing alpha-Fe/alpha' dendrites with an (Fe,Cr)(2)B and gamma-Fe eutectic to primary and continuous carbo-borides M2B (where M represents Fe and Cr) and M-23(B,C)(6) carbides (where M represents Fe, Cr, Mo) with MC particles (where M represents Nb and Mo). The highest average hardness, for an alloy without micro cracking, of 952 HV was observed in a 40 wt.% alloy. High stress abrasive scratch testing was conducted on all alloys at various loads (500, 1500, 2500 N). Alloy content was found to have a strong effect on the wear mode and the abrasive wear rate, and the presence of micro-cracks was detrimental to abrasive wear resistance. (C) 2016 Elsevier B.V. All rights reserved.