Effect of chromium content on heat treatment behavior of multi-alloyed white cast iron for abrasive wear resistance

Abstract

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 (£ +MC) along with (£ +M 2 C). The (£ +M 7 C 3 ) 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 (V£) 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 (H Tmax ) was obtained at 773798 K tempering. The V£ values decreased continuously as the tempering temperature increased and they were overall less than 5% at H Tmax . The degree of secondary hardening (¦Hs) increased proportionally with a rise of V£ in as-hardened state. The H Tmax increased first and then decreased as the Cr content increased. The highest values of H Tmax were obtained in 5 mass%Cr specimen regardless of austenitizing temperature.