Modified constitutive analysis and activation energy evolution of a low-density steel considering the effects of deformation parameters

• The modified hyperbolic sine equations can accurately predict the flow behavior.
• The solid solution hardened steel exhibit relatively high activation energy.
• The activation energy is found to be a function of deformation parameters.
• Solute drag effect is responsible for higher activation energy at low strain rates.
• The activation energy is being reduced as dynamic recrystallization occurs.

In the present study, typical hyperbolic sine equation was found inappropriate to model the flow behavior of a Fe-18Mn-8Al-0.8C low-density steel in warm to hot deformation regime. This is related to the fact that the materials constants do not actually remain constant during deformation. Considering the effects of deformation parameters, a modified model was derived and used to accurately predict the flow behavior of the steel. The 3D activation energy map showed that the activation energy would decrease at high temperature due to the thermally activated nature of dislocation motion. However, the calculated activation energies are higher than those for conventional austenitic steels since the present highly alloyed steel is considered to be strongly strengthened by solid solution. The solute drag effect of alloying elements is found to be the main reason for obtaining higher activation energy values at relatively low strain rates. The subsequent calculations showed that the activation energy would decrease by about 50 kJ.mol−1 by increasing the strain due to the occurrence of dynamic recrystallization at above 1073 K. In contrast, the accumulation of deformation energy in the absence of dynamic recrystallization (below 1073 K) would lead to activation energy increase by increasing the amount of deformation.

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