High Temperature Low Cycle Fatigue of 2 1/4 Cr1Mo Steels : Role of Microstructure and Effect of Environment(Special Issue on Creep and Fatigue at Elevated Temperatures)

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The paper aims to analyse the high temperature low cycle fatigue behaviour of 2.25Cr1Mo steels that have been exposed in service at 565℃ for about 110 000 h and 160 000 h. The volumic fraction of ferrite and bainite and the effect of the in-service long term ageing are analysed. Under strain controlled tests at 565℃ in air, cyclic hardening is promoted by a large volumic fraction of ferrite. With a volumic fraction of 35% ferrite, a softening is favoured but the intensity and the rate are controlled by the state of bainite. Long term aged bainite promotes a softening of the steel. However, fatigue resistance did not appear to depend strongly on the microstructure because of the marked oxidation. Tests carried out in vacuum at a reduced pressure of 10^-4 Pa result in much longer fatigue lives than in air. At low strain amplitude, the fatigue resistance in vacuum is increased with a 65% bainite volumic fraction.
2002-01-15