Influence of strain rate and temperature on tensile stress–strain and work hardening behaviour of 9Cr–1Mo ferritic steel

True stress (σ)–true plastic strain (ɛ) behaviour examined in the framework of various flow relationships for wide range of temperatures (300–873 K) and strain rates (6.33 × 10−5 to 6.33 × 10−3 s−1) suggested that a combination of Ludwigson and Hollomon equations describes σ–ɛ behaviour most accurately in 9Cr–1Mo steel. The variations of instantaneous work hardening rate (θ = dσ/dɛ) and θσ with stress indicated two-stage behaviour characterised by a rapid decrease at low stresses (transient stage) followed by a gradual decrease at high stresses (stage-III). The variations of work hardening parameters and work hardening rate in terms of θ vs. σ and θσ vs. σ with respect to strain rate and temperature exhibited three distinct temperature regimes. σ–ɛ, work hardening parameters along with θ–σ and θσ–σ exhibited signatures of dynamic strain ageing at intermediate temperatures. Rapid decrease in flow stress and work hardening parameters and rapid shift in θ–σ and θσ–σ towards low stresses with decrease in strain rate and increase in temperature indicated dominance of dynamic recovery at high temperatures.

► A combination of Ludwigson and Hollomon equations described σ–ɛ behaviour.
► Two-stage work hardening behaviour has been observed.
► 9Cr–1Mo steel exhibited three distinct temperature regimes.
► Signatures of dynamic strain ageing at intermediate temperatures have been obtained.
► Dominance of dynamic recovery has been observed at high temperatures.