Influence of Temperature on Tensile Stress–Strain and Work Hardening Behaviour of Forged Thick Section 9Cr–1Mo Ferritic Steel

Abstract

True stress (σ)–true plastic strain (e) behaviour examined for temperatures ranging from 300 to 873 K suggested that a combination of Ludwigson and Hollomon equations describes σ–e behaviour most accurately in forged thick section 9Cr–1Mo steel. Alternatively, the flow behaviour for temperature range 300–873 K can be described adequately using single Voce equation. Good correlations have been obtained between work hardening parameters evaluated using Voce equation and the respective tensile properties. The variations of instantaneous work hardening rate (θ = dσ/de) and θσ with stress displayed 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, θ versus σ and θσ versus σ with temperature exhibited three distinct temperature regimes along with signatures of dynamic strain ageing at intermediate temperatures and dominance of dynamic recovery at high temperatures. Comparison of work hardening parameters obtained using Voce equation and Kocks–Mecking approach suggested an analogy between the two for the steel.