Deoxidation of Liquid Iron with Silicon

The mechanism of the deoxidation of liquid iron with Si was studied on the basis of the various facts obtained by the following experiments A, B, and C. Experiment A ; An investigation was made of the change in the oxygen content in liquid iron and the shape and the size distribution of the inclusion after the addition of metallic Si. Experiment B ; The process of growth and the composition of the deoxidation products were studied after the prompt and homogeneous dissolution of deoxidizer Si or Si-Al. Experiment C ; The mechanism of dissolution of oxygen from the SiO_2 crucible into liquid iron was studied. (1) The formation of SiO_2 is not completed immediately after the addition of Si, and consequently, the supersaturation in liquid iron occurs until the equilibrium is reached. (2) It was concluded that the growth of oxide particle or the deoxidation reaction was not controlled by the diffusion of the solute atom, but the reaction rate at the particle surface, and in general, the local equilibrium was not maintained there even at steelmaking temperatures. (3) The ratio of the rate constants for the reactions Si+2O→SiO_2 and 2Al+3O→2Al_2O_3 was estimated by means of the composition of the products obtained by the Si-Al deoxidation in experiment B. The ratio was constant in a wide range of the concentration of aluminium, silicon and oxygen in liquid iron. (4) In experiment A, a great part of the primary inclusion float out rapidly and the total oxygen agrees nearly with the dissolved oxygen in 5 minutes after the addition of silicon. (5) The mechanism of the formation of the inclusion during solidification was discussed from the point of the nucleation and growth of oxide particle