Development of inelastic constitutive equations for modified 9Cr-1Mo steel. 3. Extension of the constitutive model for cyclic deformation under isothermal and nonisothermal conditions

A series of cyclic deformation tests was conducted on modified 9Cr-1Mo steel at various temperatures, including nonisothermal conditions to investigate inelastic behavior of the material. The material showed cyclic softening behavior under temperatures between 200degC and 600degC, and its degree got larger as the temperature was increased. As for a dependency of cyclic response on temperature variations, it seemed that it was relatively small in the steel. Based on the test results, the unified constitutive model proposed in the previous report was extended for cyclic deformations, including under nonisothermal conditions. To evaluate the validity of the constitutive model, it was applied to analysis of inelastic behavior under monotonic tension, stress relaxation, creep, isothermal cyclic deformations including stress relaxation and nonisothermal cyclic deformations. It was found that the present constitutive model was successful in describing the inelastic behavior of the steel adequately. (author)