Accuracy and reliability of numerical simulation of hot rolling processes are dependent on a suitable material model, which describes metal flow behavior. In the present study, Gleeble hot compression tests were carried out at high temperatures up to 1300 °C and varying strain rates for a medium carbon micro-alloyed steel. Based on experimental results, a Johnson-Cook model (JC) and a Zerilli-Armstrong (ZA) model were developed and exhibited limitation in characterizing complex viscoplastic behavior. A combined JC and ZA model was introduced and calibrated through investigation of strain hardening, and the coupled effect of temperature and strain rate. Results showed that the combined JC and ZA model demonstrated better agreement with experimental data. An explicit subroutine of the proposed material model was coded and implemented into a finite element model simulating the industrial hot rolling. The simulated rolling torque was in good agreement with experimental data. Plastic strain and stress distributions were recorded to investigate nonlinear mass flow behavior of the steel bar. Results showed that the maximum equivalent plastic strain occurred at 45° and 135° areas of the cross section. Stress increased with decreasing temperature, and the corresponding rolling torque was also increased. Due to the extent of plastic deformation, rolling speed had limited influence on the internal stress of the bar, but the relative rolling torque was increased due to strain rate hardening.