The Effect of V/C Ratio on the Phase Formation Behavior in Vanadium Carbide‐Based Tool Steel Fabricated through Powder Metallurgy

Abstract

This study investigates phase formation behavior by considering the vanadium (V) to carbon (C) ratio in vanadium carbide‐based tool steel. The V/C ratios are controlled by changing the V content. The samples with the V/C ratio of 4.78 and 6.12 are first prepared through gas atomization with a form of powder and then turned into bulk forms through hot isostatic pressing. The bulk samples are annealed at 1070 °C and then quenched. The hardness values of the 4.78V/C and 6.12V/C samples are 50.7 and 17.3 HRC, respectively. Phases of each sample are analyzed to confirm the reason for the hardness difference. The α′‐martensite phase is formed in the matrix of the 4.78V/C sample, whereas the matrix of the 6.12V/C sample is the α‐ferrite phase. Thermodynamic calculations and high‐temperature phase analysis are performed to examine the difference in the phase formation. In the 4.78V/C sample, the γ‐austenite phase is formed at 1070 °C, which transforms to the α′‐martensite phase during cooling in the heat treatment process. Meanwhile, the 6.12V/C sample has no austenite phase at 1070 °C, so martensitic transformation does not occur. These analyses confirm that it is crucial to control the phase formation by controlling the contents of V and C with an appropriate ratio.