Effect of Carbon Content and Heat-treating Condition on Retained Austenite and Hardness of Multi-component White Cast Iron

摘要

Multi-component white cast irons with varying carbon content from 1.4 to 2.4 mass percent and with about the same amount (5 mass percent) of each alloying elements Cr, Mo, W, V and Co respectively were prepared to determine the effect of carbon content and heat-treating condition on the heat treatment behaviors. Hardness of as-hardened specimens rise with an increase in carbon up to a certain or critical carbon content and then decrease. Volume fraction of retained austenite (V7) increases as carbon content and austenitizing temperature rise. Each specimen tempered after hardening shows a tempered hardness curve with remarkable secondary hardening, which is due to the precipitation of MC and M6C carbides with extremely high hardness, and V7 decreases rapidly over a given tempering temperature. It was found that the maximum value of tempered hardness in high carbon iron is obtained from the specimens austenitized at low temperatures and at high temperature in low carbon iron, and that their tempering temperatures range between 773 K and 823 K.