Effect of cast wall thickness, composition and austempering temperature on microstructure and properties of ductile cast iron

Abstract

In this study, two ductile irons were prepared: the first cast was unalloyed with a chemical composition of 3·65C–2·58Si–0·31Mn–0·045Mg, and the second one was alloyed with 0·5%Cr. The solidification rate was changed by casting four different cast thicknesses of 5, 10, 20 and 30 mm. The austempering treatment was carried out by austenitising the samples at 900°C for 1 h and then rapidly quenched into two different salt baths with temperatures of 325 and 375°C for 1 h each. The austempering temperature of 325°C showed higher mechanical properties than of 375°C. An addition of 0·5%Cr enhanced the tensile strength and hardness on the account of impact toughness. Maximum abrasion resistance was reported for the iron containing 0·5%Cr and austempered at 325°C for the cast thickness of 5 mm. This is due to the formation of fine ausferrite matrix and existing Cr carbides imbedded in the matrix that resist well the abrasion resistance. Minimum abrasion resistance was obtained for the unalloyed iron austempered at 375°C due to the formation of coarse ausferritic structure and existence of a higher amount of retained austenite.