Effect of amount and distribution of primary TiC on the wear behavior of a 12%Cr–3%C white iron under dry sliding conditions’

Abstract

From this study, titanium additions of 1, 3 and 5% were added to a 12%Cr–3%C white iron, and their effects on the microstructure, hardness and sliding wear were analyzed. The experimental irons were melted in a 10 kg capacity vacuum induction furnace and cast into wedge metallic molds to analyze different solidification thicknesses. The alloys were characterized by optical and electronic microscopy, and X-ray diffraction. Bulk hardness was measured in the as-cast conditions and after a destabilization heat treatment at 900 °C for 30 min. Sliding wear tests (block-on-ring) were undertaken for different thicknesses according to the ASTM G77 standard in both as-cast and heat-treated conditions under a load of 52 N. The results show that, high titanium additions caused a decrease in the carbon content in the alloy and that some carbon was also consumed to form primary TiC during solidification; this in turn decreased the eutectic M7C3 carbide volume fraction and promoted a more martensitic matrix. Bulk hardness changed from 53 HRC (as-cast) to 65 HRC (as-heat treated); however, the best wear behavior was observed for the 3%Ti iron. It was found that for such amount of titanium, a good combination of austenite/martensite matrix reinforced with primary TiC carbides was obtained. While for higher titanium amounts (5%) large agglomerates of TiC particles were segregated to the eutectic zone leaving the matrix unprotected; this phenomenon was particularly observed for thicker sections. After heat treatment, the precipitation of secondary carbides occurred within the matrix, which improved the wear resistance of most irons; however, the best behavior was observed again 3%Ti iron. These results are explained in terms of the obtained microstructure; particularly in the well distribution of primary TiC carbides within the matrix.