SR処理後の再加熱によって2 1/4Cr-1Mo鋼HAZに生じる焼もどし脆化

Cr-Mo鋼熱影響部の焼もどし脆化に関する研究(第4報)

抄録

Temper embrittlement, which occurs in the HAZ of 2 1/4Cr-1Mo steel subjected to SR treatment and subsequent reheating, was investigated by using the synthetic HAZ specimen, and it was compared with the embrittlement observed in the specimens tempered in the same temperature range without the SR treatment (direct tempering). With a suitable SR treatment (975 K for 5 hours) the synthetic HAZ specimen became the de-embrittled state. However, the subsequent reheating at 775 to 925 K produced in the specimens four different types of embrittlement. Those were the second, third, fourth and fifth types, which had already been recognized in the direct tempered specimens. The first type of embrittlement which arose in the direct tempering in the shortest time range did not appear after the SR treatment. The second type (the short time type), which occurred in a wide time-temperature range in the direct tempering, arose only in a narrow one after the SR treatment. The third and fourth types (the long time types) arose intensively as the case of direct tempering. The fifth type (the high temperature type) appeared also after the SR treatment. It will be concluded that the embrittlement in the short time range is suppressed to some extent by the SR treatment, but those arising in the long time range and the high temperature one arose after the SR treatment as well. It was found that "the step-cooling process" also could reveal the temper embrittlement of this steel. However, an essential advantage of this process over the isothermal tempering shown above was not recognized from the view point of promoting the embrittlement.