Applicability of the one-internal-variable Kocks-Mecking approach for tensile flow and work hardening behaviour of modified 9Cr-1Mo steel

Tensile flow and work hardening behaviour of modified 9Cr-1Mo steel in normalised and tempered (N+T) and additional three different simulated post-weld heat treatments (PWHTs of 993, 1013 and 1033 K for 1 h) conditions have been examined in the framework of the one-internal-variable Kocks-Mecking (K-M) approach in the temperature range 300-873 K. The steel exhibited two-stage work hardening behaviour characterised by a rapid decrease in instantaneous work hardening rate, θ (θ=dσp/dεp, where σp is the plastic flow stress component and εp is the true plastic strain) with σp at low stresses (transient stage) followed by a gradual and linear decrease at high stresses (stage-III). The variations in work hardening parameters with temperature exhibited three distinct temperature regimes. The influence of PWHT is reflected in systematic variations in work hardening parameters with increasing PWHT temperature from 993 to 1033 K due to microstructural softening.