EFFECT OF STEEL’S THERMAL CONDITION ON THE TRANSFORMATION TEMPERATURES OF TWO HOT-WORK TOOL STEELS WITH INCREASED THERMAL CONDUCTIVITY

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.