Mod. 9Cr-1MO Steel is a candidate material of the steam generator pipe and IHX tubes in SFR reactor. Those piping components are subjected to repeated thermal stress as a results of temperature gradients during plant cooling down or heating. It makes ratcheting and creep-fatigue behavior and cause failure to piping components. Therefore simulation of inelastic behavior is needed to investigate inelastic and ratcheting behavior for structure integrity evaluation and lifetime prediction.
To investigate the inelastic behavior of a modified 9Cr-1Mo steel, uniaxial stress controlled ratcheting tests and strain controlled cyclic tests were conducted at $500\degC$, $550\degC$, $600\degC$. Modified 9Cr-1Mo steel exhibits cyclic softening and ratcheting behaviors at the temperature ranges tested. Based on the cyclic test results, isotropic hardening behavior and kinematic hardening behavior depending on the temperature were incorporated into the constitutive model. An inelastic behavior simulation is conducted using the Chaboche three-decomposed constitutive model. From the parameter identification simulation, each kinematic parameter and isotropic parameter are obtained. And ratcheting simulation are verified from the ratcheting test and strain controlled cyclic test result.