Cr-Mo鋼HAZの焼もどし脆化におよぼす冶金学的因子の影響

Five types of temper embrittlement arose in HAZ of Cr-Mo steel in the temperature range of 775K to 875K. The metallurgical factors affecting those types of embrittlement were discussed from the view point of the precipitation and growth of carbide, the size and shape of ferrite grains and the segregation of impurity elements. The first and the second types of embrittlement are induced by the secondary hardening brought about by the coherent precipitation of M2C. The third type is induced by the segregation of impurity elements in the grain boundary. The fourth type is possibly induced by the coarsening of M2C and M7C3. The fifth type is induced mainly by the coarsening of ferrite grains