Unified tensile work hardening behaviour of 9Cr–1Mo ferritic steel

Abstract

Tensile work hardening behaviour of 9Cr–1Mo ferritic steel has been examined in terms of the variations in instantaneous work hardening rate (θ = dσ/dϵ_p, where σ is true stress and ϵ_p is true plastic strain) with stress and plastic strain rate for a wide range of temperatures (300–873 K) and strain rates (6·33×10⁻⁵–6·33×10⁻³ s⁻¹). Both θ–σ and θσ–σ exhibited two stage work hardening behaviour and distinct three temperature regimes with signatures of dynamic strain aging at intermediate temperatures and dominance of dynamic recovery at high temperatures. The variations in θ with for 300–873 K exhibited unified work hardening in terms of separate master curves for different strain rates. At all the strain rates, θ varied linearly with reciprocal of plastic strain rate independent of temperature. As a consequence, direct proportionality between rate of change in true stress and plastic strain rate is obtained.

Keywords:

• 9Cr–1Mo steel
• Unified tensile work hardening
• Work hardening rate
• Plastic strain rate