The work experimentally examined the effect of temperature on the change in the physical and microstructural properties of steel exposed to high temperatures in order to determine the variable and temperature-dependent strength parameters. The article presents the experimental results obtained during a uniaxial tensile test (elastic modulus, yield strength and tensile strength were determined) in variable thermal conditions. The heating process took place in an infrared oven at temperatures up to 1100^oC. An MTS extensometer adapted to tests at high temperatures was used to measure strains. Microstructural tests and microhardness measurements were carried out for samples heated at various temperatures. Based on the obtained results, a numerical model of the static tensile test was developed in the Abaqus CAE software.