The effect of repeated loadings on the stress relaxation properties of 2.25Cr–1Mo steel at 550 °C and the influence on the Feltham ‘a’ and ‘b’ parameters

This paper describes studies undertaken to evaluate the stress relaxation behaviour of 2.25Cr–1Mo steel, a material used extensively in high temperature steam components. Repeated stress relaxation loadings were conducted on normalised and tempered 2.25Cr–1Mo steel at 550 °C, under constant strain, in a closed loop testing system. Detailed analysis of stress relaxation curves is presented. Application of the data to the Feltham equation for subsequent use in life assessment procedures is discussed and analysed.