Effects of niobium macro-additions to high chromium white cast iron on microstructure, hardness and abrasive wear behaviour

• High chromium white cast irons containing niobium macro-additions show great promise in abrasive wear applications. • Increasing niobium content of the alloy linearly increased the hardness of heat-treated dual-reinforced hypo-eutectic high-Cr white irons. • Clear beneficial effect of Nb macro-addition on abrasive wear behaviour was observed under both less-competent and competent abrasive rocks. • In optimum addition ranges, life improvements of 37% and 7% per 1 wt%Nb were achieved under less-competent and competent abrasives, respectively. • Resultant NbC particles mostly protruded above matrix and Cr-rich carbides in the wear scars under controlling wear mechanism of micro-fracture. Abrasive wear is a principal cost in mining and mineral processing operations. High chromium white cast iron (WCI) further reinforced with niobium carbide (NbC) shows promise to increase component wear lives. This work investigates the effect of niobium macro-additions on microstructure, hardness and high-stress abrasive wear behaviour of Nb-containing high-Cr WCIs. Eight alloys with Nb between 0 and 10.7 wt% were produced by sand casting. Increasing niobium carbide volume fraction (Nb-CVF) increased hardness from 724 to 812 HV (7.3 HV per 1% Nb-CVF). Abrasive wear resistance, assessed using the ball mill abrasion test in basalt (less competent) and quartzite (competent rock), showed clear beneficial effect of NbC macro-addition up to 11.4 and 7 vol% in basalt and quartzite, respectively. These correspond to life improvements of 37% and 7% per 1% Nb-CVF in the optimum range of Nb macro-addition, in basalt and quartzite respectively. Micro-mechanistic observations of worn surfaces showed that NbC particles not only protrude from the matrix but do so more than Cr-rich M 7 C 3 carbides. In deep wear grooves created by quartzite, M 7 C 3 particles were cut flush with the matrix, whereas NbC protruded, visibly impeding the progress of the abrasion event.