The influences of impurity elements on the creep embrittlement were investigated for synthetic heat affected zone (HAZ) of l 1/4 Cr-1/2 Mo and C-1/2 Mo steels.
The creep embrittlement, the decrease in creep rupture elongation was greater with larger CEF (Creep Embrittlement Factor), which was proposed by Gooch and his coworkers for the effect of impurity elements on the propagation rate creep cracking.
CEF=P+2.4As+3.6Sn+8.2Sb (wt%)
Addition of a small amount of rare earth metals or Ca to l1/4 1/2 Mo steel decreased remarkably the creep embrittlement of the synthetic HAZ due to decrease of impurity elements segregation to the grain boundaries.
Commercial 1 1/4 Cr- 1/2 Mo steel added with 0.004% Ca indicated an excellent resistance to the creep embrittlement in the synthetic HAZ. While it maintained the mechanical properties of the original material. Furthermore, the influence of hydrogen atomosphere on the creep embrittlement was investigated for the synthetic HAZ of C- 1/2 Mo steel. It was found that hydrogen decreased markedly the notch creep rupture strength, another indicator of the creep embrittlement, unless it was subjected to a post weld heat treatment. The decrease was more remarkable increase in hydrogen pressure.
