Influence of processing route and section size on tensile stress–strain and work hardening behaviour of 9Cr–1Mo ferritic steel

Abstract

True stress–true plastic strain behaviour of 9Cr–1Mo steel in two different product forms, i.e. 20-mm plate and thick section tubeplate forging has been examined in the temperature range 300–873 K in the framework of various flow relationships. The analysis suggested that a combination of Ludwigson and Hollomon equations describes stress–strain behaviour most accurately in both plate and tubeplate forging. Two-stage work hardening has been observed in the variations of instantaneous work hardening rate with stress. The variations in stress–strain, flow parameters and work hardening rate as a function of stress with respect to temperature exhibited three distinct temperature regimes. Signatures of dynamic strain ageing at intermediate temperatures and dominance of dynamic recovery at high temperatures have been observed. The differences in tensile flow and work hardening behaviour obtained between plate and tubeplate forging has been attributed to the affects associated with the initial microstructures obtained for the two product forms in 9Cr–1Mo steel.