High-manganese steels gain more and more importance in lightweight automotive constructions because of their excellent strength properties and crash safety. These steels are industrial manufactured by the continuous casting process. For a precise configuration of this process and an accurate casting, exact thermodynamic data and the knowledge of the phase transformation in the high temperature range is of great importance. A recent study [1] has shown, that the present thermodynamic databases are using outdated or unreliable values for these steel grades. In this thesis, the binary system Fe - Si up to 12,5 wt.-% Si as well as a section of the ternary system Fe - Si - Mn with 3 wt.-% Si and manganese contents up to 30 wt.-% Mn were investigated experimentally. Additional emphasis was put on the determination of the α→γ transformation of different Fe - C - Mn - Si alloys. The investigated alloys were melted under argon atmosphere and the phase transformation temperatures were measured using differential thermal analysis (DTA) or differential scanning calorimetry (DSC). A comparison of the experimental data from this thesis with values from the literature and latest thermodynamic databases shows significant differences. In case of the binary system Fe - Si, the differences of the solidus and liquidus temperatures amount up to +10 °C and +18 °C, respectively. In the ternary system Fe - 3 % Si - high Mn, the deviations are even higher, because the actual solidus and liquidus temperatures are up to 85 °C and 37 °C higher than the previously reported. Furthermore, the stability area of the ferrite phase in the high temperature area is much bigger and the peritectic range is located at higher Mn amounts.