Temper embrittlement of type 13Cr-4Ni cast steel.

Abstract

The mechanism of toughness degradation by temper embrittlement is studied in 13Cr-4Ni martensitic stainless cast steel. The variation of toughness, brittle fracture mode and fraction of retained austenite are examined as a function of tempering temperature and the subsequent isothermal treatment in the range 550-450°C. Temper embrittlement is referred to as increases in FATT and fraction of intergranular fracture after tempering at lower temperatures and subsequent isothermal treatment at higher temperatures. The embrittlement is found to be related to the intergranular fracture and precipitation of carbide along prior austenite grain boundary. The degree of the embrittlement is found to be substantially independent of the segregation of phosphorous at prior austenite grain boundary. The precipitation of intergranular carbides is resulted from the decrease of carbon solubility in the reverted austenite during tempering. Susceptibility to temper embrittlement in this steel is suppressed as tempering temperatures are raised.