Flow stress modeling and microstructural characteristics of a low carbon Nb-V microalloyed steel

Abstract

Hot and warm deformation behaviors of a Nb-V added low carbon microalloyed steel have been examined in the present study. The deformation was performed in 700–1100 °C temperature range with 100 °C interval in 0.01–10 s-1 strain-rate range. The total deformation was subjected to a0.7 true strain in compression by employing a Gleeble-3800® thermomechanical simulator. The plastic flow behavior during hot and warm deformation was characterized from the analysis of generated flow curves. The flow stress decreased when the strain-rate was reduced or increased in temperature. The plastic deformation was majorly governed by the strain hardening and dynamic recovery (DRV) behavior over dynamic recrystallization (DRX). To predict the flow stress, the constitutive models equations were developed using activation energy (Q) and various material constants to anticipate the impact of strain-rate and deformation temperature on flow stress in ferrite+austenite and austenite phases, separately. The Q was estimated to be 367.3 kJ/mol and 411.5 kJ/mol for ferrite+austenite and austenite phases, respectively, with a respective stress exponent (n) value of 14.2 and 5.9. The model’s flow stress was correlated with the experimental value for both ferrite+austenite and austenite phase regions with a worthy fitting value (R) of 0.988 and 0.969, respectively. The micromechanical behavior of the deformed samples has been demonstrated through the correlation of the flow stress with microstructural validity. Texture analysis of the deformed samples shows that the formation of the cube component was weak in the analyzed samples indicating the formation of grains through DRV over DRX. A detailed analysis of activation energy, stress exponent and flow stress for DRV and DRX using the constitutive models suggested that the warm and hot deformation processes were governed by dislocation climb and glide mechanisms.