Creep fracture mechanism map and creep damage of Cr-Mo-V turbine rotor steel

Abstract

Specimens of a Cr-M-V rotor steel with creep rupture lives of up to 100 000h were examined metallographically to clarify their creep fracture mechanisms and to construct creep fracture mechanism maps showing the dominant regions of each mechanism. The creep fracture mechanism maps were constructed with stress on the y-axis and time to rupture on the x-axis, and also with stress on the y-axis and testing temperature on the x-axis. The maps included three different creep fracture mechanism fields: transgranular creep fracture, intergranular creep fracture with cavitation, and rupture with dynamic recrystallization. The maps indicate that the steel in the service of power plants is being used under conditions within the field of intergranular creep fracture with cavitation. This means that long term use of this steel under the conditions could cause extensive cavitation and low ductility fracture due to the cavitation. © 2006 ISIJ.