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 A degrees C to 600 A degrees C). Detailed analysis in terms of the variations of instantaneous work hardening rate, theta (theta = d sigma/d epsilon (p) = d sigma (p)/d epsilon (p), where sigma is the true stress, sigma (p) is the plastic flow stress component, and epsilon (p) is the true plastic strain) with sigma and sigma (p) indicated two-stage work hardening behavior, and three distinct temperature regimes in the variations of work hardening parameters, theta - sigma and theta - sigma (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 A degrees C to 600 A degrees 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.