This work predicts the temperature ranges for dynamic strain aging (DSA) activation in C45 steel at various strain rates through constitutive modeling and finite element (FE) simulations. DSA is often defined by a sudden increase in a metal’s strength when subjected to specific combinations of strain rates and temperatures due to the interaction of the diffused solute atoms with dislocations, and there is currently no effective constitutive model in the literature that can explain DSA physically. The current study offers a modification to the Voyiadjis–Abed (VA) model, which is used to predict DSA activation in C45 steel, in order to address this limitation. The modified constitutive model considers the diffusion kinetics and concentration of solute atom along the dislocation cores. The developed model was able to capture the activation of DSA in C45 steel at strain rates of 0.0015/s-0.15/s and temperature ranges of 500 K-750 K, which was found to be caused by carbon solute atoms. Additionally, FE simulations were carried out in ABAQUS through subroutine coded as VUMAT to validate the modified VA model’s prediction abilities. The results obtained compare effectively with the available experimental data. By integrating physical and microstructural features, the modified constitutive VA model can effectively capture the increase in flow stress due to the activation of DSA. This enables further investigation and progress in understanding the behavior of metals under specified temperature and strain rate conditions.