Multi-component white cast irons containing 2.13mass% and 2.41mass% carbon with single additions of 5mass% chromium(Cr), molybdenium(Mo), tungsten(W) and vanadium(V) were employed to investigate the effect of tempering conditions on hardness and volume fraction of retained austenite(Vγ). After hardening the specimens from 1373K, they were tempered at the temperatures between 753K and 873K for 150s to 7×105s. Regardless of tempering temperature, the hardness increases to maximum value and decreases with an increase in holding time. The holding time when a maximum hardness is obtained sifts to a short time side as the tempering temperature is elevated. When holding time increases, on the other hand, Vγ lowers gradually in the first stage and then decreases steeply irrespective of tempering temperature. The holding time at which the Vγ begins to reduce critically moves to a short time side with increasing the tempering temperature. It was found that the hardness and Vγ after tempering could be consistently connected to a tempering parameter (P＝T(20 ＋ log t))). In addition, the hardness increases with a decreasing of Vγ and the maximum hardness is obtained when the Vγ lies at 5 to 10%.
