In this research, two different 1800 MPa grades of press-hardening steel were investigated;​ one with 0.30 wt% and the other 0.32 wt% of Carbon. The suitability of an austenite decomposition model after cooling and the effect of short tempering times after quenching on the final mechanical properties was examined. To assess the austenite decomposition model, both materials were subject to a variety of constant cooling and resulted in a mixed-phase of bainite, martensite, and ferrite. The Gleeble experiments were simulated using LS-Dyna and a thermalmechanical-microstructural model. In the second investigation (Part II – Short Cycle Tempering), both steels were fully quenched in the Gleeble to produce a fully martensitic microstructure and tempered at temperatures ranging from 100 to 700 °C and times of 0.5 to 15 s For both experiments microhardness tests were conducted on the specimens and a FESEM was used to characterize and quantify the resultant mixed-phase microstructures.