The effect of phosphorous and arsenic on the fracture behaviour of a 2,25% Cr-1% Mo Steel

Creep and Charpy impact tests have been performed on specially melted casts of 2.25%Cr - 1%Mo steel, containing trace additions of P, As and (P + As), and on a high purity melt of this steel. Creep testing at 580°C and 160 MPa revealed that casts containing either P or (P + As) had improved ductility compared to that of the high purity alloy. The creep behaviour of material containing only the addition of As was similar to the high purity data. Conversely, the presence of P was associated with brittle intergranular fracture in Charpy impact tests at ambient temperature, while the high purity and As bearing alloys were indistinguishable and ductile. Furthermore, intergranular fracture of the P-containing material was obtained at both lower and upper energy positions. Auger Electron Spectroscopy (AES) analysis of post creep test and Charpy test samples showed that segregation of P to grain boundaries had occurred. No evidence was detected for the segregation of As to these boundaries.