Determination of the solidus and liquidus temperatures of the real-steel grades with dynamic thermal-analysis methods: Določanje solidusnih in likvidusnih temperatur realnih jekel z metodami dinamične analize

The knowledge of the solidus and liquidus temperatures of the real-steel grades is one of the most important technological factors - especially when dealing with the processes of casting and solidification. These temperatures are critical parameters for proper settings of the models (physical or numerical) or in the final stage of an applied research of a real process. A correct setting of a production technology is significantly affecting the final quality of the as-cast steel (billets or ingots). Therefore, this paper is devoted to discussing the findings obtained during a utilization of dynamicthermal-analysis methods to identify the solidus and liquidus temperatures applicable to commercially produced steels. The results obtained with a differential thermal analysis (DTA) for three steel grades and with 3D differential scanning calorimetry (3D DSC) for two steel grades are compared with the results of the selected equations commonly used for liquidus and/or solidus temperature calculations. The calculations obtained with the Computherm SW for the discussed steels were also realized. It can be stated that the equilibrium liquidus and solidus temperatures obtained with the above-mentioned methods for each steel grade differ. The differences between the calculated results, the thermodynamic calculations and thermal-analysis results are very unpredictable and vary individually for different steels. These differences are not marginal (tens of Celsius degrees). So, it is sometimes suitable to combine several methods for a proper determination of the liquidus and solidus temperatures for a correct setting of a steel-making process or its modelling. The best solution for a technological process is to obtain the liquidus and solidus temperatures for a concrete-steel grade from agiven steelmaking practice - a thermal analysis of a concrete-steel grade is a possible way. Poznavanje solidusnih in likvidusnih temperatur realnih jekel je med najpomembnejšimi tehnološkimi dejavniki - še posebno pri obravnavi procesov med ulivanjem in strjevanjem. Te temperature so kritični parametri za pravilno postavitev modela (fizikalnega ali numeričnega) ali pri končni stopnji raziskav realnega procesa. Pravilna postavitev proizvodne tehnologije pomembno vpliva na končno kvaliteto ulitega jekla (gredic in ingotov). Zato je ta članek namenjen razpravi o ugotovitvah, dobljenih med uporabo metod dinamične termične analize za ugotavljanje solidusne in likvidusne temperature pri komercialno proizvedenih jeklih. Rezultati, dobljeni z diferenčno termično analizo (DTA) za 3 jekla in s 3D diferenčno vrstično kalorimetrijo (3D DSC) za 2 vrsti jekel, so bili primerjani z rezultati iz izbranih enačb, ki se navadno uporabljajo za izračun temperature solidusa in likvidusa. Za obravnavana jekla so bili tudi izdelani izračuni s Computherm SW. Ugotovljeno je bilo, da se ravnotežne likvidusne in solidusne temperature, dobljene z omenjenimi metodami, razlikujejo. Razlike med izračunanimi rezultati, termodinamičnimi izračuni in rezultati termične analize so nepredvidljivi in se različno spreminjajo pri različnih jeklih. Te razlike niso nepomembne (desetine stopinj Celzija). Zato je včasih pomembno kombinirati več metod za pravilno določitev likvidusne in solidusne temperature pri procesu proizvodnje jekla ali njegovem modeliranju. Najboljša rešitev za tehnološki proces je ugotavljanje likvidusne in solidusne temperature pri konkretnem jeklu iz dane jeklarske prakse - mogoča pot pa je tudi s termično analizo konkretnega jekla.