Spoluautoři SCHINDLER Ivo, PETREK Tomáš, KAWULOK Petr, VANČURA Filip, KAWULOK Rostislav, RUSZ Stanislav

High-grade medium-carbon steel C45 with content of carbon 0.42 – 0.50 % and manganese 0.50 – 0.80 %, intended for hardening and tempering, has been often used for production of die forgings and the less exposed machine components. The hot stress-strain curves of this steel were investigated by uniaxial compression tests using the Hot Deformation Simulator HDS-20 within a wide strain range (up to 1.0). The testing temperatures were 1000 – 1100 – 1200 °C and nominal strain rates were 0.1 – 1.0 – 10 – 100 1/s. The unique computing method was developed which enabled to correct the shape of the experimentally obtained stress-strain curves, influenced by the samples’ spreading at high strains. The value of the activation energy at hot forming was calculated (290 kJ/mol) using the peak stress values and the dynamic recrystallization kinetics was described. The mathematical model was developed which considered the predicted peak strains and described mathematically the influence of strain, strain rate and temperature on the flow stress. Reliability of this model was verified in comparison with the experimental data and compared with the stress-strain curves calculated according to the software FORGE material database. Thanks to its physical fundamentals the developed model is more accurate than the FORGE-based calculations, at the highest strain rates in particular.