Effects of Heat-Treatment on the Microstructure and Wear Resistance of a High-Chromium Cast Iron for Rolls

Abstract

The variations of microstructure and mechanical properties of a high-chromium cast iron for rolls were studied from as-cast to the final heat treatments. Results show that the as-cast microstructure of the HCCI consists of M 7 C 3 carbide, M 23 C 6 carbide, martensite matrix, and retained austenite. The large dendritic M 7 C 3 carbide surrounds the matrix, and the M 23 C 6 carbide is mainly distributed in the matrix. Part of M 23 C 6 carbide transforms to M 7 C 3 carbide and is dissolved in austenite during austenization at 1020°C. Thus, the amount of M 23 C 6 carbide decreases, whereas that of M 7 C 3 carbide increases after quenching; the highest hardness is also obtained. After tempering, the martensite transforms to a tempered martensite, and some carbide precipitates in the martensite matrix. The hardness also changes from HRC62.1, which corresponds to quenching, to HRC55.2 and HRC56.3, which correspond to once and twice tempering, respectively. However, tempering could improve the impact toughness and wear resistance of the HCCI.