<p>To optimize the forging process parameters of as-cast TC4 (Ti–6Al–4V) titanium alloy, the hot deformation behavior and microstructure evolution of the alloy were investigated within the temperature range of 1073–1323&#xa0;K and strain rates from 0.001 to 10&#xa0;s⁻¹ using an isothermal compression testing system. Based on the experimental data, a strain-compensated Arrhenius constitutive model was developed. Microstructure analysis revealed that in the dual-phase region, the primary softening mechanism is dynamic recrystallization, whereas in the single-phase region, dynamic recovery predominates. Two types of dynamic recrystallization were observed: continuous dynamic recrystallization and discontinuous dynamic recrystallization. Power dissipation, instability, and thermal processing maps were constructed using the dynamic material model to elucidate the material’s rheological behavior and microstructure evolution under various deformation conditions. By combining the hot processing map with microstructural observations, the optimal hot working window for as-cast TC4 titanium alloy was determined to be a deformation temperature range of 1133–1173&#xa0;K and a strain rate of 0.001–0.01&#xa0;s⁻¹. In this range, the alloy exhibits a high degree of dynamic recrystallization. The instability zone primarily occurs at a strain rate of 10&#xa0;s⁻¹, where cracking and flow localization take place. Thus, to prevent material failure, deformation should be avoided in the instability zone during forging.</p> Graphical Abstract <p></p>