Trace element embrittlement in a 2.25%Cr-1%Mo steel

Creep and Charpy impact tests have been performed on 2.25%Cr-1%Mo steel, containing trace additions of P, As, Sb or Sn in an attempt to assess their influence on intergranular embrittlement. The effects of the impurity elements differ in creep and impact testing. At 580 °C, the effect of P is to increase creep ductility compared to a high purity cast of the material, whereas Sb and Sn have an embrittling effect. As has little influence. The impact test data obtained at an ambient temperature shows that P causes embrittlement; Sb and Sn increase the ductility and As has a negligible effect. Auger analysis of post creep test samples shows that segregation of the trace elements is selective: P is observed on the grain boundary facets whereas Sb and Sn segregate to the inside of the creep cavities. Examination of the post test Charpy specimens which exhibited intergranular embrittlement revealed only the segregation of P; As, Sb and Sn were not detected. As appears to have no influence at any temperature, whereas at 580 °C, Sb and Sn appear to segregate preferentially to cavities at the grain boundaries.