The aim of our study was to investigate how different thermal conditions affect the transformation temperatures of two hot-work steels with high thermal conductivity. We focused on two conditions: ...soft annealing, and quenching and tempering. Soft annealing results in a ferritic steel matrix with spherical carbides, while quenching and tempering result in a fully hardened and tempered martensitic matrix with secondary and tempering carbides. We analysed samples using a simultaneous thermal analysis (STA) and differential scanning calorimetry (DSC) to determine the transformation temperatures. Controlled heating and cooling allowed us to observe the energy changes associated with the phase transformations. The equilibrium temperatures were calculated using the CALPHAD method. Our study investigated the influence of thermal conditions on different transformation temperatures, including solidus/liquidus temperatures, austenite solid transformation temperatures (A1 and A3), austenite solidification temperatures and bainite and/or martensite transformation temperatures. A DSC analysis was used to quantitatively measure the transformation temperatures and energy absorption during the endothermic processes (austenite solid transformation and melting) and to study the energy release during the exothermic processes (solidification and transformation). The results showed that soft annealing reduced the solidification interval and the solidus temperature, while energy absorption increased during melting. Conversely, quenching and tempering reduced the austenite solid transformation temperatures and energy release during solidification, including δ-ferrite solidification.
The aim of this experimental work was to design a modified test with which it will be possible to determine the fluidity of ductile cast iron. First, we planned the conceptual verification of the ...designed experiment, which was done by numerical simulations of the casting processes, followed by rapid mould fabrication using 3D printing. A measurement cell was placed in the mould cavity of the experimental chamber for further investigation of the cooling and solidification during casting. From the matrix of data obtained with the experiment, we defined the fluidity of the ductile iron EN-GJS-500-7. Also, we analysed the mechanical properties of the studied alloy, the microstructure, the chemical composition, and the results of the thermal analysis. In accordance with the expectations and theory from the literature, the fluidity in the experimental sample cast at a higher temperature was better than that cast at a lower temperature. Because of the faster cooling rate at the end of the channel of the experimental casting, the microstructure is fine, moreover, we obtain white solidification, ledeburite in the microstructure of the samples etched with Nital. At lower cooling rates, fewer graphite nodules appear in the microstructure, which are larger, and the portion of ferrite is greater.
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