Low cycle fatigue of 2.25Cr1Mo steel with tensile and compressed hold loading at elevated temperature

Abstract

A series of uniaxial strain-controlled fatigue and creep-fatigue tests of the bainitic 2.25Cr1Mo steel forging were performed at 455°C in air. Three different hold periods (30s, 120s, 300s) were employed at maximum tensile strain and compressive strain under fully reversed strain cycling. Both tensile and compressive holds significantly reduce the fatigue life. Fatigue life with tensile hold is shorter than that with compressive hold. A close relationship is found between the reduction of fatigue life and the amount of stress relaxation. Microstructural examination by scanning electron microscope reveals that strain hold introduces more crack sources, which can be probably ascribed to the intensified oxidation and the peeling-off of oxide layers. A modified plastic strain energy approach considering stress relaxation effect is proposed to predict the creep-fatigue life, and the predicted lives are in superior agreement with the experimental results.