The current status of developing a self-consistent thermodynamic database for tramp elements (Fe-C-Cu-Sn-S) and impurities (Fe-C-P) in steel is presented. The binary and ternary subsystems were modeled according to the CALPHAD-approach, enabling precise calculations of phase diagrams and thermodynamic properties of multicomponent steel. The Modified Quasichemical Model (MQM) was used to formulate the Gibbs energy of the liquid phase to consider the strong short-range ordering (SRO) tendency between metal M (M = Fe, Cu, Sn) and nonmetal (S and P) in melts. Ferrite (α-Fe, BCC) and austenite (γ-Fe, FCC) solid solutions and intermediate phases were treated by the Compound Energy Formalism (CEF). Numerous compounds, e.g. phosphides and higher-order sulfides, were modeled stoichiometrically. In the first part, the modeling of the selected quaternary Fe-C-Cu-Sn subsystem is presented and applications in calculating solid/liquid phase equilibria with respect to liquid metal embrittlement are shown. Based on the previously assessed Fe-C-P system, the approach of linking of thermodynamic databases to an in-house developed solidification model for continuous casting is introduced. It is demonstrated how to extract relevant data from computational thermodynamics for microsegregation modeling of steel. Finally, future requirements on experimental research and modeling work in the field of tramp element containing steel will be critically discussed.