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.

Effect of carbon (C) content on heat treatment behavior of multi-alloyed white cast irons with basic alloy composition was investigated. The multi-alloyed white cast irons with varying C content of 1.732.34% were prepared. After annealing, the test specimens were austenitized at 1323 and 1373 K, and then hardened by fan air cooling. The hardened specimens were tempered between 673 and 873 K. It was found that the hardness in as-hardened state increased first and then decreased as C content increased. The volume fraction of retained austenite (V£) increased with increasing C content. In tempered state, each hardness curve showed secondary hardening due to the precipitation of secondary carbides as well as the transformation of decomposed austenite to martensite during post cooling. The V£ began to decrease greatly when the tempering temperature was elevated over 723 K. The maximum tempered hardness (H Tmax ) was obtained in the specimens tempered between 798 K and 823 K where the V£ ranged from 8 to 12%. The highest value of H Tmax was obtained in the 2.00% C specimen hardened from 1373 K austenitizing and in the 2.34% C specimen hardened from 1323 K austenitizing.

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