2019 Volume 60 Issue 2 Pages 346-354
The effect of chromium (Cr) content on heat treatment behavior of multi-alloyed white cast iron with basic alloy composition of 5 mass% Mo, W and V each and 2 mass%C was investigated. Cast iron with varying Cr content from 3 to 9% was prepared. Specimens were annealed at 1223 K and then hardened using fan air cooling from 1323 and 1373 K austenitizing. Hardened specimens were tempered between 673 and 873 K with 50 K intervals. In the as-cast state, the microstructure of specimens with Cr content less than 5 mass% consisted of primary austenite and eutectic structure of (γ+MC) along with (γ+M2C). The (γ+M7C3) was observed in specimens with Cr content of more than 5 mass%. In as-hardened state, the hardness increased to the highest value at 5 mass%Cr and subsequently decreased with an increase in the Cr content. The volume fraction of retained austenite (Vγ) also behaved in the same way with reference to hardness. In the tempered state, evident secondary hardening was observed in all specimens. Maximum tempered hardness (HTmax) was obtained at 773–798 K tempering. The Vγ values decreased continuously as the tempering temperature increased and they were overall less than 5% at HTmax. The degree of secondary hardening (ΔHs) increased proportionally with a rise of Vγ in as-hardened state. The HTmax increased first and then decreased as the Cr content increased. The highest values of HTmax were obtained in 5 mass%Cr specimen regardless of austenitizing temperature.