Abstract:
Eutectic and hypoeutectic cast irons containing 16% and 26%Cr were prepared in order to investigate their heat treatment characteristics. In as-hardened state, hardness does not change much but volume fraction of retained austenite (V gamma) varies greatly depending on carbon content at the same chromium level. The V gamma is high in the iron hardened from higher austenitizing temperature. It gradually decreases with an increase in Cr/C value of iron. In tempered state, curve of tempered hardness shows a secondary hardening but the degree is smaller compared with multi-component white cast iron. The precipitation hardening is greater in the iron hardened from higher austenitizing temperature, in other words, in the iron with more V gamma. The tempering temperature to obtain the maximum hardness (H[subscript Tmax]) shifts to the long time side when the austenitizing temperature rises. The H[subscript Tmax] is uniformly related to the V gamma value in as-hardened state irrespective of austenitizing temperature and it increases gradually up to the highest value of around 800 HV30 at 30% V gamma, and the H[subscript Tmax] is settled even if the V gamma increases over 30%. The difference in macro-hardness between 16%Cr and 26%Cr cast irons is due to the difference in morphology of eutectic carbide at the same eutectic ratio, thick or large massed and more interconnected eutectic carbides in 16%Cr cast irons, and thin and less interconnected ones in 26%Cr cast irons
