The progress of dephosphorization of liquid Fe-Cr-Ni alloys under strong reducing conditions

Some aspects of dephosphorization of liquid alloys (18 wt.% Cr-8 wt.% Ni) c ontaining different contents of phosphorus and oxygen under strong reducing conditions (P-O2 less than or equal to 1.10(-17) atm) were a main purpose of the present work. CaF2-Ca-met. solution in the molar proportion 1:1 and synthetic slag 25 wt.% CaO-75 wt. % CaF2 were used as the refining material s. The investigations have been carried out under elevated pressure of argo n (p(Ar) = 0.6 MPa) at 1743 and 1823 K in the resistance laboratory furnace . The changes of the phosphorus, total oxygen T [O] and calcium contents T [Ca] in the metal phase vs. refining time were determined. It was shown, that the dephosphorization reaction may be regarded as a reve rsible reaction which proceeds at the two characteristic regions. The 1-st region is characterized by an intensive decrease of P-content in alloy to t he minimal value [%P](min.). At the 2-nd region an increase in P-concentrat ion takes place, which is greater at higher temperature. Location of [%P](m in.) in the coordinate system tau; [%P](tau), where tau-refining time, is s ubordinated by the total oxygen concentration in the alloy at the moment of calcium adding. The effect of the time factor "tau" or a change in another physical factor e.g. temperature increase cause a definite loss of the act ive mass of calcium, thus also a change of its activity at the refining pha se due to partial evaporation of calcium. The result will be observed chang e in the direction of the dephosphorization reaction progress. Location of [%P](min.) in the coordinate system tau; [%P](tau) where tau-re fining time, is subordinated by the total oxygen concentration T [O] in the alloy at the moment of calcium adding. The integration method to estimatio n of the kinetic run of the dephosphorization reaction in the 1-st region w as applied. The calculation were made using the computer programme named ST ATISTICA. It was shown that the increase of phosphorus concentration in the metal pha se after reaching the point with the coordinates (tau(min.); [%P](min.)) is characteristic for all time courses and it does not depend on the initial content of phosphorus in the investigated alloys. The changes in the conten t of total calcium T[Ca] for different refining time in the examined alloys may help to explain above mentioned regularities.