Three - dimensional mathematical model of fusion of cubical steel scrap in the converter melt was developed. The model was solved using modified implicit Brian’s method. The obtained algorithm was programmed in ASCII FORTRAN for the computer SPERRY 1106. In the model temperature dependent thermo-physical properties of material were incorporated. That gives to the model a nonlinearity. On the basis of the model it was concluded that addition of 1% of low - carbon steel scrap decreases the temperature of a middle carbon steel melt for cca 23 °C. This is in good agreement with experimental data from literature. At the same time a new formula for the fusion time of steel scrap was developed, which enables to calculate the fusion time on the basis of the volume of the steel scrap in the converter melt.Trodimenzijski matematički model taljenja čeličnog otpatka u konvertorskoj talini. Razvijen je trodimenzijski matematički model taljenja kockastog čeličnog otpatka u konvertorskoj talini. Model je riješen korištenjem modificirane implicitne Brianove metode. Dobiveni algoritam prograimiran je u ASCII FORTRAN za računalo SPERRY 1106. U model su ugrađena temperaturno ovisna toplofizička svojstva materijala, što modelu daje nelinearnost. Na temelju modela zaključeno je da 1 % niskougljičnog čeličnog otpatka smanji temperaturu srednje ugljične taline za cca 23 °C, što se dobro slaže s eksperimentalnim podacima iz literature. Istodobno, dobivena je nova formula za vrijeme taljenja čeličnog otpatka, koja omogućuje računanje vremena taljenja u ovisnosti o volumenu čeličnog otpatka u konvertorskoj talini
