Effect of Tempering Condition on Toughness Degradation in 13Cr-3.8Ni Cast Steel

Abstract

It is known that the toughness of 13Cr-3.8Ni cast steel decreases when the steel is tempered at around 550°C and cooled at slow rate. Effects of tempering temperature, holding time and repetition of tempering on toughness deterioration of the steel are investigated by means of metallurgical observation and mechanical test. It is found that toughness decreases with increase of yield strength which accompanies the increase of corrosion loss in 6.0% HNO₃ solution. Fracture appearance transition temperature and yield strength tend to decrease with the increase of the degree of tempering, while the amount of austenite increases. Toughness is recovered when the steel is tempered at higher temperatures such as 630°C. From these results it is considered that the deterioration of toughness during tempering is ascribed to the rejection of carbon from reverted austenite during slow cooling and the formation of carbide.