Failure Analysis on Bulging of 30CrMo Pipe during Hot Processing

Failure reason of bulging on a 30CrMo pipe was analyzed by means of macroscopic examination, chemical composition analysis, metallographic examination, SEM and EDS analysis. The results showed that the over high temperature was caused by unstable temperature of stove or the friction of pipe in hot processing, the oxygen intruded into the grain boundary and the defect such as crack, and caused oxidation decarbonization and overburnning, then embrittlement was happened in the pipe. On the other hand, the loose of hot spinning scraper led to the uneven forces during pipe deformation. Finally, the wall of pipe was bulged and folded at the embrittlement area during hot processing.