CHARACTERIZATION OF METAL KINGS IN SLAG AFTER DESULFURIZATION CAST IRON ACCORDING TO THE REAGENT CO-INJECTION SCHEME

Abstract

The results a study of the distribution by fractions and composition of metal drops removed from the cover slag formed along the ladle desulfurization of hot metal according to the reagent co-injection scheme in the conditions of the converter shop of Dneprovsky Metallurgical Plant PJSC are presented. It is proposed to classify metal drops according to size and shape by groups «A», «B» and «C». Drops are assigned to group «A», mostly of irregular shape, which are formed mainly due to bursts of metal in the zone of the «eye» on the surface of the metal bath and are larger than10 mm; to group «B» – drops of spherical shape with a size of 2.5 ...10 mmand to group «C» – drops of both spherical and irregular shape with a size of less than2.5 mm, respectively. A characteristic size distribution of drops was established, which, for the conditions of co-injection lime and magnesium, amounted to: 0.5 ...2.5 mm– 10 ... 16%; 6 ...8 mm– 10 ... 20%; >10 mm– 30 ... 45%, respectively. It was found that with a decrease in the diameter of the drops from2.5 mmor less, there is a trend towards an increase in the sulfur content in the latter, and the sulfur content in the fraction <0.5 mmreaches, and in most cases, exceeds this figure for the coating slag. The substantiation of a high degree influence physicochemical state of the coating slag on the conditions for the transition sulfur from slag to metal droplets in its volume is given. It was established that both the dimensions and the total mass metal drops in the coating slag substantially depend on the thickness of the slag coating layer, which is formed during processing, the diameter gas-metal bubbles that pop up and collapse at the slag-metal and gas-slag boundaries, the degree of turbulization bath and size «eye» on the surface of the bath. Schemes formation and accumulation metal drops group «B» in the slag layer are proposed. In accordance with the first scheme, with increasing viscosity coating slag more than 0.3 Pa.s metal drops in the slag are crushed. In accordance with the second, the formation groups of drops is ensured by grinding metal drops «A» group, which are carried out into the space above the surface of the bath, as a result of the explosion latter during the course their decarburization reaction with the release CO. A scheme is proposed for the transition sulfur from coating slag into metal droplets, which consists in the following. As it rises to the interfacial boundaries, the surface bubbles is covered with a metal shell, which contains surface-active sulfur, which, in addition, diffuses from the volume metal to the surface bubble. If the bubble floats to the “slag-metal” boundary, and the slag is dry, heterogeneous, then the bubble with a metal film on the surface is destroyed with the formation of liquid metal droplets saturated with MgS, and the slag, respectively, is enriched with sulfur. Depending on the physicochemical state slag, both rounded or oval drops and irregular particles are formed. Within the «eye», at the intersection gas-metal boundary, the metal shell from the surface bubbles at the moment their destruction is ejected at different angles into the surrounding space, is crushed and forms metal droplets group «A», which under certain conditions are decarburized with destruction, followed by subsidence on the surface slag and the formation groups drops «B» and «C». Moreover, depending on the period of desulfurization, the metal shell and the metal droplets formed from it contain various amounts sulfur in the slag. Thermodynamic calculations confirmed the possibility of a spontaneous reaction formationFeSin the slag over the entire temperature range ladle desulfurization hot metal under the conditions co-injection lime and magnesium.