11/4Cr-1/2Mo鋼熱影響部の焼もどし脆化におよぼす焼もどし条件の影響

Cr-Mo鋼熱影響部の焼もどし脆化に関する研究(第2報)

抄録

The temper embrittlement arising in the heat affected zone (HAZ) of 1 1/4Cr-1/2Mo steel was studied in the tempering temperature-time range of 775 to 900 K and 5 to 10000 hours. The temper embrittlement was detected as the rise of energy transition temperature. Three types of embrittlement were recognized; they are the second, third and fourth types of embrittlement which have been observed in 2 1/4Cr-lMo steel. The third type of embrittlement is same as the reversible temper embrittlement (RTE), but other two types are new ones observed by the authors. They are characterized by their own shapes of transition curves and appearances of the fracture surfaces. The third and fourth types in this steel appear later than in the case in 2 1/4Cr-1Mo steel. The third type in this steel continues to appear at a higher temperature than in the case in 21/4Cr-1Mo steel. The influence of stress in the tempering process was examined. It increases the magnitude of the third type of embrittlement, but does not affect the second type. Examinations were also made on the SR-treated specimen. SR treatment turns the HAZ specimen into the de-embrittled state, but reheating it at 825K induces two different types of embrittlement. One of them is the third type of embrittlement (RTE) which exhibits the intergranular fracture. The other type exhibits the cleavage fracture; it is not yet known whether it belongs to the third type or not.