Tempering embrittlement of 2.25Cr-1Mo steel for, a long term of service

The microstructures and mechanical properties are investigated in this paper for a hydrogenation reactor steel 2.25Cr-1Mo after long-term service. The material exposed at 427 degreesC for 10 years as a testing block in reactor vessel show appreciable temper embrittlement. The fracture toughness K(IC) at room temperature is lower because of tempering situation and hydrogen absorption. Coarse grain and impurity segregation at grain boundary are observed from micrography. The results show that fracture mode changes from quasi-cleavage to intergranular when temper embrittlement becomes more serious. It also shows that the ratio of intergranular fracture-to transgranular fracture will be bigger after cathodical hydrogen charging.