Effect of the segregation of embrittling impurities on the local strength of grain boundaries in a martensitic steel

Abstract

The finite element method and the results of delayed fracture tests of Charpy specimens are used to determine the local strength of grain boundaries in 18Kh2N4VA steel at various contents of phosphorus, antimony, and tin impurities. The embrittlement of grain boundaries is attributed to the adsorption enrichment of grain boundaries in impurities in initial austenite, which leads to weakening of the intergranular cohesion. Phosphorus is found to have the highest susceptibility to intergranular segregation: during the same heat treatment, its grain-boundary concentration is higher than that in steel with antimony or tin. However, the segregation of antimony is more dangerous than the segregation of phosphorus, since, at its lower intergranular concentration, the local strength of grains of quenched steel decreases as in the case of phosphorus segregation