Studium reálných jakostí ocelí metodami termické analýzy

Abstract

One of the most important binary systems of engineering practise is Fe-C system, which is the base of iron alloys. Results of phase diagrams modelling, thermophysical and thermodynamical properties modelling for real steel grades is still only approaching the results of experiments. Therefore, it is necessary to study Fe-C based systems (steels), precise phase diagrams, thermophysical and thermodynamical data and so enhance the quality of SW databases and calculation relations. Proper material data are necessary for many of technological processes – for their optimal adjustment (e.g. for heat treatment and casting). Thermal behaviour of Fe-C based systems can be characterized by thermal analysis methods, such as by differential thermal analysis (DTA) and differential scanning calorimetry (DSC). Using these methods it is possible to obtain temperatures and latent heats of phase transformations, heat capacity and its temperature dependence. A significant effect on the obtained data can have the experimental conditions that should be eliminated by calibration and methodological measurements. The thesis is focused on the study of temperatures, latent heats of phase transformations and thermal capacity (in dependence on temperature) of two real steel grades. In the low-temperature region were observed temperatures of start (Tα→γ,S) and end (Tα→γ,E) of α→γ transformation and latent heats of this transformation (ΔHα→γ). In the high temperature region were observed temperatures of solidus (TS), liquidus (TL), peritectic transformation (TP) and latent heats of fusion (ΔHtav.). Heat capacities were observed in the temperature range 150 – 1320°C. Temperatures and latent heats were obtained using differential thermal analysis (DTA) by heating rate of 10°C/min and the heat capacity using differential scanning calorimetry (DSC) by heating rate of 5°C/min. and "continuous" method. Calibration and methodological experiments were performed in the frame of this work. Phase transformation temperatures were approximated to “equilibrium conditions”. Repeated experiments were performed and basic statistics was done. Experimental data were compared and discussed with calculation results using SW Thermo-Calc and liquidus temperature also with results obtained by empirical equations.