An analysis of direct tensile tests conducted on round samples of S690QL and S960QL steels is presented in this paper, which investigates how elevated temperatures and high strain rates affect the mechanical properties of these steels. Additionally, SEM imaging was used to examine fracture surfaces, revealing variations across different strain rates and temperatures. Experiments were carried out using a Split Hopkinson Tensile Bar with a water-cooled induction heating system, subjecting the materials to extreme loading conditions over a wide temperature range (up to 900°C) and two distinct high strain rates. Based on the experimental findings, new reduction factors were proposed for dynamic loading conditions. Furthermore, two constitutive models were calibrated to enhance predictive accuracy, offering valuable insights for the design of high- and very-high-strength steel structures.