A new approach to evaluating the chemical micro-heterogeneity of a continuously cast steel slab: Nov način ocenjevanja kemijske mikroheterogenosti kontinuirno ulitih slabov

The paper deals with a new approach to measuring and evaluating the chemical micro-heterogeneity of the elements in solidified poly-component metallic systems. The original approach is based on experimental measurements made on the samples taken from characteristic places in a casting and the subsequent application of an original mathematical model for determining the element-distribution profile, characterizing the most probable distribution of an element concentration in the frame of a dendrite, and an original mathematical model for determining the effective partition coefficients of these elements in the structure of the analyzed alloy. The paper also describes an application of this method in the research of the chemical heterogeneity on a cross-section of a CC steel slab and presents the selected results (indices of the heterogeneity and effective partition coefficients of seven analyzed elements) characterizing the chemical micro-heterogeneity on one-half of the cross-section of this CC steel slab. The following main results were obtained: (i) the dendritic heterogeneity of the accompanying elements and impurities is comparatively high; (ii) all the analyzed elements segregate during the solidification into an inter-dendritic melt, and their partition coefficient is smaller than one; (iii) the effective partition coefficients calculated in this new way inherently include both the effect of segregation in the course of an alloy solidification, and the effect of the homogenization occurring during the solidification as well as during the cooling of an alloy. Članek obravnava nov način merjenja in ocenjevanja kemijske mikroheterogenosti elementov v večkomponentnih kovinskih sistemih. Izviren način temelji na eksperimentalnih meritvah, narejenih na vzorcih, vzetih iz značilnih mest ulitka, in uporabi izvirnega matematičnega modela za določanje profila razporeditve elementov, kar omogoča oceno najbolj verjetne razporeditve koncentracije elementov v dendrite in določanje efektivnega koeficienta razporeditve teh elementov v strukturi analizirane zlitine. Članek opisuje tudi uporabo te metode pri raziskavi kemijske heterogenosti prečnega prereza kontinuirno ulitega slaba in predstavlja izbrane rezultate (indeks heterogenosti in koeficiente razporeditve sedmih analiziranih elementov) značilne kemijske mikroheterogenosti polovice prereza kontinuirno ulitega slaba. Glavni rezultati so: (i) heterogenost spremljajočih elementov in nečistoč je razmeroma velika; (ii) vsi analizirani elementi izcejajo med strjevanjem v meddendritno talino, njihov koeficient razporeditve je manjši odena; (iii) na nov način izračunani koeficienti razporeditve vključujejo v sebi oba učinka, to je učinek izcejanja med potekom strjevanja in učinek homogenizacije, ki se pojavi med strjevanjem, in nadaljnjim ohlajanjem zlitine.