2 1/4Cr-1Mo鋼溶接部の脆化および延性低下におよぼす顕微鏡組織の影響

The low ductility creep fracture (LDCF) and the temper embrittlement (TE) arised in the heat affected zone (HAZ) when the welded constructions of Cr-Mo steels were used at their service temperatures around 800K. The former was reproduced in the laboratory by the creep-rupture test at the temperature range of 775K to 875K on the synthetic HAZ specimens. The latter was reproduced by the impact test on the specimens tempered at those temperatures. Four types of LDCF (LDCF 1 to 4) and four types of temper embrittlement (TE 1 to 4) were recognized. LDCF 1,2,3 and 4, respectively appear in the same time-temperature ranges as those in which TE 1,2,3 and 4 arise. Common metallurgical causes of the LDCF and TE were discussed. LDCF 1,2 and TE 1,2 which arise in the short-term range, will be induced both by the loss of ductility in ferrite matrix and the segregation of impurities in grain boundaries. LDCF 3 and TE 3, which arises in the long-term range, will be induced by the segregation of impurities in grain boundaries. LDCF 4 and TE 4, which appears in the high temperature range, will be brought about by the coarsening of carbide particles in ferrite matrix