Sliding wear of spray-formed high-chromium white cast iron alloys

Abstract

The sliding wear resistance of high-chromium white cast iron obtained by spray-forming was studied to determine how the refined microstructures produced by this process, the structure of the matrix, and the amount and distribution of carbides affect the material. Three alloys containing different concentrations of carbon and chromium, namely 2.4 wt.%C–15 wt.%Cr, 3.5 wt.%C–15 wt.%Cr, and 3 wt.%C–19 wt.%Cr, were spray-formed and conventionally cast. Pin-on-disk wear tests were conducted according to the ASTM G99-95 standard. White cast iron pins having an 8-mm diameter and 15-mm length were tested against a counterpart VC 131 tool steel disk hardened to 63HRC. The wear resistance was evaluated as a function of the samples’ weight loss and the wear mechanisms were observed by scanning electron microscopy (SEM). These wear mechanisms, which were active in all the materials, were fracture and detachment of carbides and oxidation, which suggests three-body abrasion, in addition to the presence of cracks in the matrix, particularly in the materials containing large amounts of austenite. Disk wear rates were found to be higher than high-chromium white cast iron pin wear rates. These wear rates were more pronounced when the disks were tested against the conventionally cast pins, which showed coarser carbides. The spray-formed alloy, 3.0 wt.%C–19.0 wt.%Cr, showed better wear resistance in this study than the other alloys because of its more refined microstructure, greater balance among the austenite, martensite and M 7C 3 carbide phases, and greater resistance to oxidation.