Studium termofyzikálních a termodynamických vlastností systémů na bázi Fe-C-O-X(Y),(X, Y = Cr, Ni) v pevné a kapalné fázi

Abstract

Chromium and nickel are important alloying elements for steels. Knowledge of simpler systems such as Fe C Cr, Fe C Ni and Fe C Cr Ni are necessary for the accurate thermodynamic and thermophysical description of polycomponent systems (steels) and similar alloys used in practice. There is still a lack of accurate experimental results in this area, which can serve as input data for the creation and refinement of Fe-based databases (for e.g. SW JMatPro and Thermo Calc) and can also be used in simulation software (e.g. SW Procast). For these reasons, the study of systems based on Fe C Cr, Fe C Ni and Fe C Cr Ni is still an actual topic. The thermal behaviour of Fe C based systems can be among other things described by thermal analysis methods, which include differential thermal analysis (DTA), differential scanning calorimetry (DSC), dilatometry and others. Using these methods, it is possible to obtain temperatures and heats of phase transformations, heat capacity, enthalpy change, coefficient of thermal expansion, density and their dependence on temperature. In order to obtain accurate data, it is necessary to eliminate experimental conditions through calibration and methodological measurements. Within the solution of the dissertation, valuable original fundamental data and knowledge about the studied systems were obtained. The dissertation is focused on the study of temperatures and heats of phase transformations, heat capacities, enthalpy change, coefficient of thermal expansion and density (depending on temperature) of alloys based on Fe C O Cr, Fe C O Ni and Fe C O Cr Ni. In the low-temperature area, the start (Tα→γ,S) and end (Tα→γ,E) temperatures of the phase transformation α→γ and the heats of this transformation were studied. Solidus (TS), liquidus (TL), start (TP,S) and end (TP,E) of peritectic transformation temperatures and heats of melting were studied in the high temperature region. Heat capacities and enthalpy change were obtained in the temperature range 30 – 1580 °C. The coefficient of thermal expansion and density were studied in the range of 200 – 1600 °C. Phase transformation temperatures were obtained using three methods: differential thermal analysis (DTA), differential scanning calorimetry (DSC) and dilatometry. The heat capacities from which the enthalpy change was subsequently calculated were obtained by differential scanning calorimetry (DSC) using the "continuous" method. Dilatometric curves, from which the coefficient of thermal expansion and density were calculated, were obtained by dilatometry. Within the experiments, calibration and additional methodological measurements were performed. The resulting temperatures were approximated to the "equilibrium conditions". Based on the repetition of the experiments, a basic statistical analysis was performed. The experimentally obtained data were compared and discussed with the results of SW calculations Thermo Calc, JMatPro and IDS and with the values available in the literature. Selected studied alloys were subjected to structural and phase analysis. Based on the obtained results, corresponding conclusions were drawn. Furthermore, by means of a linear regression from the results of these measurements, they were supplemented by other results obtained within the GAČR project reg. no. 17 18668S obtained new models for calculating liquidus temperature, heat capacity and enthalpy change taking into account the influence of chemical composition, especially chromium and nickel, and temperature on the studied thermophysical properties in the form of empirical relationships.