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

摘要

The relationship between hardness and volume fraction of retained austenite (V_gamma) was investigated in heat-treated 16mass percent and 26 mass percent 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 V_gamma. Overall, Ni and Cu decreased hardness but Mo increased it. Hardness increased in 16mass percent Cr cast iron but decreased in 26mass percent Cr cast iron by V addition. The V_gamma increased with Ni, Cu and Mo addition but diminished with V addition in 16mass percent Cr cast iron. In 26mass percent Cr cast iron, Ni and Mo increased the V_gamma but Cu and V reduced it. Higher austenitization caused more V_gamma. 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 V_gamma in as-hardened state. Maximum tempered hardness (H_Tmax) was obtained when V_gamma was less than 20 percnet and it increased with an increase in Mo content. The H_Tmax slightly increased with V content in 16 mass percent Cr cast iron and decreased in 26 mass percent 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.