The impact toughness of a nitride-strengthened martensitic heat resistant steel

The nitride-strengthened martensitic heat resistant steel is precipitation strengthened only by nitrides. In the present work, the effect of nitride precipitation behavior on the impact toughness of an experimental steel was investigated. Nitrides could hardly be observed when the steel was tempered at 650°C. When the tempering temperature was increased to 700°C and 750°C, a large amount of nitrides were observed in the matrix. It was surprising to reveal that the impact energy of the half-size samples greatly increased from several Joules to nearly a hundred Joules. The ductile-brittle transition temperature (DBTT) was also discovered to decrease from room temperature to −50°C when the tempering temperature was increased from 650°C to 750°C. The nitride precipitation with increasing tempering temperature was revealed to be responsible for the improved impact toughness.