Effect of Alloying Elements on Heat Treatment Behavior of Hypoeutectic High Chromium Cast Iron

Abstract

The relationship between hardness and volume fraction of retained austenite (Vy) was investigated in heat-treated 16mass% and 26 mass%Cr hypoeutectic cast irons with and without addition of a third alloying element of Ni, Cu, Mo and V. In as-hardened state, hardness changed remarkably depending on the Vy. Overall, Ni and Cu decreased hardness but Mo increased it. Hardness increased in 16 mass%Cr cast iron but decreased in 26 mass%Cr cast iron by V addition. The Vy increased with Ni, Cu and Mo addition but diminished with V addition in 16 mass%Cr cast iron. In 26 mass%Cr cast iron, Ni and Mo increased the Vy but Cu and V reduced it. Higher austenitization caused more Vy. Curves of tempered hardness showed an evident secondary hardening due to precipitation of special carbides and transformation of destabilized austenite into martensite. High tempered hardness was obtained in the specimens with high Vy in as-hardened state. Maximum tempered hardness (H Tmax ) was obtained when Vy was less than 20% and it increased with an increase in Mo content. The H Tmax slightly increased with V content in 16 mass%Cr cast iron and decreased in 26 mass%Cr cast iron. Ni and Cu did not show significant effects on H Tmax . The highest value of H Tmax was obtained in both series of cast irons containing Mo.