2006 Volume 47 Issue 1 Pages 72-81
The relationship between hardness and volume fraction of retained austenite (Vγ) was investigated in heat-treated 16 mass% 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 Vγ. 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 Vγ 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 Vγ but Cu and V reduced it. Higher austenitization caused more Vγ. 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 Vγ in as-hardened state. Maximum tempered hardness (HTmax) was obtained when Vγ was less than 20% and it increased with an increase in Mo content. The HTmax 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 HTmax. The highest value of HTmax was obtained in both series of cast irons containing Mo.