Analysis of Tensile Stress-Strain and Work-Hardening Behavior in 9Cr-1Mo Ferritic Steel

Abstract

Detailed analysis on tensile true stress (σ)-true plastic strain (e) and work-hardening behavior of 9Cr-1Mo steel have been performed in the framework of the Voce relationship and Kocks-Mecking approach for wide range of temperatures, 300 K to 873 K (27 °C to 600 °C) and strain rates (6.33 × 10−5 to 6.33 × 10−3 s−1). At all test conditions, σ-e data were adequately described by the Voce equation. 9Cr-1Mo steel exhibited two-stage work-hardening behavior characterized by a rapid decrease in instantaneous work-hardening rate (θ = dσ/de) with stress at low stresses (transient stage) followed by a gradual decrease in θ at high stresses (stage III). The variations of work-hardening parameters and θ-σ as a function of temperature and strain rate exhibited three distinct temperature regimes. Both work-hardening parameters and θ-σ displayed signatures of dynamic strain aging at intermediate temperatures and dominance of dynamic recovery at high temperatures. Excellent correlations have been obtained between work-hardening parameters evaluated using the Voce relationship and the respective tensile properties. A comparison of work-hardening parameters obtained using the Voce equation and Kocks-Mecking approach suggested an analogy between the two for the steel.