Effect of V Content on Microstructure and Heat Treatment Behavior of Multi-component White Cast Iron used for Hot Work Roll Applications

Multi-component white cast irons in which microstructures consist of multiple types of hard eutectic carbides embedded in a strong matrix have been developed for hot work roll materials. Their hard eutectic carbides contribute to improving the abrasive wear resistance of roll materials. The basic alloy composition is 5 wt% of Cr, Mo, W, V each and 2 wt% of C and Co. In this work, the effect of V content on heat treatment behavior of multi-component white cast irons with basic alloy composition was investigated. The V content of prepared cast irons varied from 2.01 to 6.64 wt%. After annealing, the specimens were hardened from 1050 °C and 1100 °C by fan air cooling and subsequently tempered between 350 and 600 °C. The results indicated that regardless of austenitizing temperature, the hardness in the as-hardened state increased to the maximum value and then decreased as V content rose. The volume fraction of retained austenite in the as-hardened state ( Vγ -As) decreased greatly with a rise of V content at both austenitizing temperatures. In the tempered state, the hardness curves showed secondary hardening due to the precipitation of carbides and the transformation of decomposed austenite to martensite. The Vγ value began to decrease greatly at 450-500 °C tempering and then decreased gradually as the tempering temperature was elevated. The maximum tempered hardness ( H Tmax ) was obtained in each specimen tempered between 500 and 520 °C for 1050 °C and 500–600 °C for 1100 °C austenitizing where the Vγ ranged from 1 to 15%. The highest H Tmax, values near 1000 HV30 were obtained at 4 wt%V for 1050 °C and 5 wt%V for 1100 °C austenitizing, respectively.