Creep constitutive equations for a 0.5Cr 0.5 Mo 0.25V ferritic steel in the temperature range 565 °C-675 °C

A two damage state variable model is used to describe the softening mechanisms, damage initiation and growth for a low alloy ferritic steel 1/2Cr-1/2Mo-1/4V at 565 and 590 °C within the Continuum Damage Mechanics framework. The level of complexity of the constitutive equations and the degree of coupling through damage is high and it is difficult to calibrate values of the constitutive constants without recourse to optimisation techniques. A methodology for the analysis of uni-axial experimental data, coupled with a traditional gradient-based optimisation technique, is presented for the unique determination of the constitutive constants. Two sets of experimental data on parent material are used for inversion purposes: at 565 °C, c.f. Cane [Cane BJ. Collaborative programme on the corelation of test data for high temperature design of welded steam pipes. Presentation and analysis of the material data. Note No. RD/L/2101N81, March, CEGB Laboratory; 1981]; and, at 590 °C, c.f. Miller [Miller DA. Private communication: “Creep rupture testing of Cr M V pipe steel. ERA Project 63-01-040320009”. Barnwood, Gloucs, UK: British Energy; 2000]. The variation of the constitutive parameters with temperature in the range 565-590 °C has been deduced by considering the values of constitutive parameters for the same alloy deduced by Perrin and Hayhurst [Perrin IJ, Hayhurst DR. Creep constitutive equations for a 0.5Cr-0.5Mo-0.25V ferritic steel in the temperature range 600-675 °C. J Strain Anal 1996;31:299-314] in the temperature range 620-675 °C.