Abstract
A series of cyclic deformation tests was conducted on modified 9 Cr-1 Mo steel at various temperatures, including nonisothermal conditions to investigate inlastic behavior of the material. The material showed cyclic softening behavior under temperatures between 200°C and 600°C, and its degree got larger as the temperature was increased. Temperature history effect was scarcely found except the case where the test temperature was changed from high to low after large cyclic softening at the high temperature. Peak stress under thermomechanical conditions showed approximately the same value as those observed under corresponding isothermal condition. Furthermore, internal state variables used in the authors' unified constitutive model were experimentally measured. An aging stress, which corresponds to resistance by dynamic strain aging effect, and an effective stress were almost constant under cyclic deformation conditions, while a back stress showed eminent cyclic softening behavior.
