Abstract

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

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