Studium vybraných termodynamických vlastností kovových systémů metodami termické analýzy

Abstract

Steel are studied for many decades, despite it there are very little accurate data available for exact chemical composition of the real steel grades. For studying steels can be used data available for important ternary systems (i.e. Fe-C-Cr, Fe-C-Ni) or higher systems (i.e. Fe-C-Cr-Ni). However, these systems represent only approach to the complex behaviour of real steel grades, so properties of these systems and real steel grades are often very different. For this reason, the investigation of the properties of real steel grades is still a highly topical issue. Many thermophysical and thermodynamical properties of real steel grades can be obtained by thermal analysis methods, i.e. using the differential thermal analysis (DTA), differential scanning calorimetry (DSC), thermomechanical analysis (TMA). Using these (and other) methods can be obtained many thermophysical and thermodynamical data, i.e. temperatures and latent heats of phase transformations, density, heat capacity and their temperature dependence. This dissertation is focused onto experimental and theoretical study of thermophysical and thermodynamical properties of real steel grades using thermal analysis methods and dependence of these properties on temperature. For three real steel grades, temperatures of phase transformations (start of eutectoid transformation, Curie temperature, end of αγ transformation, temperature of solidus, temperature of peritectic transformation and temperature of liquidus) and corresponding latent heats were studied. Moreover, heat capacity of steels was determined in the temperature interval from 200 to 1600 °C, thus not only in the solid state, but also in the melt. Linear coefficient of thermal expansion and density were determined in the temperature region from 200 to 1400 °C. Also, surface tension of steel melts was determined in the temperature region from 1540 to 1600 °C. All the above mentioned thermophysical and thermodynamical properties of real steel grades were theoretically determined using Thermo-Calc software and obtained theoretical values were compared and discussed with experimental results. Chemical composition of real steel grades differs mainly in the carbon content, so that possibility of dependence of thermophysical and thermodynamical properties of real steel grades to the amount of this element was verified.