During the design of critical steel infrastructures and structures—such as bridges, high-rise buildings, offshore platforms, and cranes—it is essential to account for mechanical resistance and robustness under exceptional conditions. Ensuring safety is paramount to preventing material damage, environmental contamination, and loss of life. Consequently, understanding the behaviour of structural steel under high strain rates is vital. Modern steel manufacturing has adopted processes like quenching and self-tempering to produce high-strength steels. These steels exhibit martensitic grains in their outer layers and ferritic grains in their core, necessitating detailed studies of individual layers under high strain rates to gain accurate insights into their behaviour. This paper presents a comparative analysis of tensile tests on homogeneous layers of S690QL and S960QL steels, focusing on the effects of elevated temperatures and high strain rates on material properties. Additionally, it discusses SEM images of fracture surfaces subjected to varying strain rates and temperatures. Experiments were conducted under combined extreme loading conditions across a wide temperature range (up to 900 °C) and at three distinct high strain rates using a Split Hopkinson Tensile Bar equipped with a water-cooled induction heating system. Based on these experimental findings, new reduction factors were proposed for dynamic loading conditions. Moreover, two constitutive models were calibrated to enable reliable predictions, offering practical guidance for designing high- and very-high-strength steel structures.