Effects of matrix chromium-to-carbon ratio on high-stress abrasive wear behavior of high chromium white cast irons dual-reinforced by niobium carbides

Abstract

Wear behavior of white cast irons (WCIs) is largely attributable to the particulate-reinforced composite phenomenon, in which both reinforcing particles and matrix play important roles. In high-Cr WCIs, matrix properties are influenced by chromium-to-carbon (Cr:C) ratio. Without a strong matrix, the carbides would not have sufficient support during the abrasion interactions. The effects of Cr:C ratio on the wear properties of plain-Cr WCIs have been only partially studied; but its effect on Nb-containing WCIs has never been explored. This work studies the influence of Cr:C ratio on high-stress abrasion performance of WCIs further reinforced by niobium carbides (NbC). The alloys covered wide range of Cr:C ratios, resulting in considerable variation in hardness — low hardness for both very-low and very-high Cr:C. Abrasion resistance was assessed by the ball mill abrasion test in quartzite and basalt, showing an optimum matrix Cr:C around 14.6 and 18, respectively. The very-high Cr:C alloy exhibited poorest resistance in both abrasives, and the very-low Cr:C alloy was second-poorest. SEM of worn surfaces revealed the effects of Cr:C ratio on the type and level of damages to microstructure, manifested by various morphologies and depths of indentations and grooves on the matrix, and various types and severities of damages to Cr-rich carbides, including micro-cutting and micro-fracture. NbC particles appeared to be protective across the full range of Cr:C ratios.