Kocks–Mecking approach to tensile work hardening behaviour of normalised and tempered and post-weld heat-treated modified 9Cr–1Mo steel

Abstract

Detailed analysis performed on modified 9Cr–1Mo steel in normalised and tempered (N+T) and three different post-weld heat treatment (PWHT) conditions indicated that the work hardening behaviour can be adequately described by Kocks–Mecking approach in the temperature range 300–873 K. The steel in all test conditions exhibited two-stage work hardening behaviour in the variation of instantaneous work hardening rate (θ) with true stress (where θ = dσ/dε, σ is true stress and ε is true plastic strain). The variations of work hardening parameters and θ–σ with temperature exhibited three distinct temperature regimes. The influence of additional PWHTs is discussed in terms of the systematic variations in flow and work hardening parameters due to microstructural softening observed with increasing PWHT temperature in modified 9Cr–1Mo steel. Comparison of work hardening parameters obtained using Voce equation and Kocks–Mecking approach demonstrated an analogy between two approaches for the steel.

Keywords:

• modified 9Cr–1Mo steel
• work hardening behaviour
• post weld heat treatment
• Kocks–Mecking approach