Effects of tempering conditions on temper embrittlement of the HAZ in 1 1/4Cr-1/2Mo steel: Study of temper embrittlement of the HAZ in Cr-Mo steels (2nd Report)

Summary

This paper describes an investigation of the temper embrittlement of the heat affected zone (HAZ) in 1 1/4Cr-1/2Mo steel in the tempering temperature-time range 775–900 K and 5–10 000 hours. The temper embrittlement is detected as an increase in energy at the transition temperature. Three types of embrittlement -the second, third, and fourth types of embrittlement observed in 2 1/4Cr-1 Mo steel - are identified. The third type of embrittlement is the same as reversible temper embrittlement (RTE), whereas the other two are new types, being characterised by their own transition curve shapes and fracture surface appearances. The third and fourth types of embrittlement in this steel appear later than in 2 1/4Cr-1 Mo steel. The effect of stress on the tempering process is examined in this investigation. It increases the magnitude of the third type of embrittlement but does not affect the second type. SR-treated specimens are also examined in this investigation. When specimens de-embrittled by SR treatment are reheated, they are re-embrittled. Reaching this de-embrittled state at 825 K induces two different types of re-embrittlement. One is the third type of embrittlement (RTE) exhibiting intergranular fracture. The other type exhibits cleavage fracture, but it is not known whether or not this type belongs to the third type.