Unified description of tensile work hardening behaviour of P92 steel

Tensile work hardening behaviour of P92 steel has been examined over wide range of temperatures (300-923 K) and strain rates (3.16×10−5-1.26×10−3 s−1) in terms of the variations of instantaneous work hardening rate (θ) with true stress (σ) and true plastic strain rate (ε̇p). At all the temperatures and applied strain rates, θ vs. σ exhibited two-stage work hardening behaviour characterised by a rapid decrease in θ at low stresses (transient stage) followed by a gradual decrease at high stresses (stage-III). θ vs. σ also exhibited three distinct temperature regimes along with signatures of dynamic strain ageing at intermediate temperatures and dominance of dynamic recovery at high temperatures. Analysis in terms of the variations of θ with ε̇p displayed a unified curvilinear behaviour independent of temperature. For a given applied strain rate, a linear correlation between θ and the reciprocal of plastic strain rate (1/ε̇p) was observed. As a consequence, the rate of change of true stress was observed to be directly proportional to plastic strain rate independent of temperature. Further, a unified description of tensile work hardening in terms of a master curve between work hardening rate (θ) and plastic strain rate normalised by applied strain rate (ε̇p/ε̇a) has been obtained for the range of strain rates and temperatures examined.