Tensile Work Hardening Behavior of Thin-Section Plate and Thick-Section Tubeplate Forging of 9Cr-1Mo Steel in the Framework of One-Internal-Variable Kocks–Mecking Approach

Comparative tensile flow and work hardening behavior of normalized and tempered plate and quenched and tempered tubeplate forgings of 9Cr-1Mo steel have been examined in the framework of one-internal-variable Kocks–Mecking approach at temperatures ranging from 300 K to 873 K (27 °C to 600 °C). Detailed analysis in terms of the variations of instantaneous work hardening rate, θ (θ = dσ/dε _p = dσ _p/dε _p, where σ is the true stress, σ _p is the plastic flow stress component, and ε _p is the true plastic strain) with σ and σ _p indicated two-stage work hardening behavior, and three distinct temperature regimes in the variations of work hardening parameters, θ − σ and θ − σ _p, with temperature. The influence of initial microstructures associated with different product forms of the steel is reflected in the systematic variations in work hardening parameters at temperatures ranging from 300 K to 873 K (27 °C to 600 °C). Tubeplate forging exhibited improved work hardening characteristics in terms of higher plastic component of flow stress because of microstructural softening than that of the plate material in the steel.