TRACE-ELEMENT EMBRITTLEMENT IN A 2.25-PERCENT-CR-1-PERCENT-MO STEEL

Creep and Charpy impact tests have been performed on 2.25%Cr-1%Mo stee l, containing trace additions of P, As, Sb or Sn in an attempt to asse ss their influence on intergranular embrittlement. The effects of the impurity elements differ in creep and impact testing. At 580 degrees C , the effect of P is to increase creep ductility compared to a high pu rity cast of the material, whereas Sb and Sn have an embrittling effec t. As has little influence. The impact test data obtained at an ambien t temperature shows that P causes embrittlement; Sb and Sn increase th e ductility and As has a negligible effect. Auger analysis of post cre ep test samples shows that segregation of the trace elements is select ive: P is observed on the grain boundary facets whereas Sb and Sn segr egate to the inside of the creep cavities. Examination of the post tes t Charpy specimens which exhibited intergranular embrittlement reveale d only the segregation of P; As, Sb and Sn were not detected. As appea rs to have no influence at any temperature, whereas at 580 degrees C, Sb and Sn appear to segregate preferentially to cavities at the grain boundaries.