The behaviour of steels in the continuous casting process depends significantly on the steel composition, the associated phase transitions and the corresponding thermophysical properties. Particularly "peritectic steels", where the peritectic phase transformation (L+δ→γ+δ) coincides with the final solidification apply as critical. These steels exhibit unfavourable process behaviour and show a lower product quality. If peritectic steels are identified in the production program, they can be produced under controlled conditions through targeted operational requirements. While the peritectic range is exactly known in the binary system Fe-C, the influence of alloying elements such as Mn, Si, Al and their combinations are not completely clear. Therefore, the investigation of the effect of alloying elements on the peritectic phase transformation in steels is of particular importance. The literature part of this thesis shows that thermal analytical laboratory methods have the greatest potential to characterise the phase transformation behaviour of peritectic steels in equilibrium and that the CALPHAD method is the ideal calculation method to describe the effect of alloying elements. Practical evaluation of selected laboratory tests shows that the Dynamic-Heat-Flow-Differential-Scanning-Calorimetry (DSC) enables a clear identification of peritectic steels. Additional studies were carried out with the Dilatometry and the High-Temperature-Laser-Confocal-Microscopy. Systematic DSC measurements of model alloys of the ternary systems Fe-C-Si, Fe-Mn-C and Fe-C-Al were carried out and preliminary tests of the quaternary systems Fe-C-Si-Al and Fe-C-Si-Mn were performed. The findings on the effect of Al and the interaction of Si with Mn with respect to the Fe-C system represent a new scientific ground.