The formation of intermediate reaction products after calcium addition to aluminum-killed steel was studied. Steel samples were taken from laboratory and industrial heats before and at various times after calcium treatment. Inclusions were characterized by automated and manual scanning electron microscopy and X-ray microanalysis of polished cross sections and inclusions extracted by dissolution of the steel. Industrial and laboratory melts containing more than 40 parts per million (by mass) of dissolved sulfur showed calcium sulfide as the main reaction product after calcium injection, with calcium aluminates appearing later. It is proposed that the calcium aluminates are formed by reaction between the calcium sulfide and the alumina. A laboratory heat containing 7 parts per million of sulfur showed calcium oxide as the main initial calcium reaction product. A simple mechanism is proposed for the modification of alumina inclusions by calcium, considering transient CaO and CaS formation.

In aluminum-killed steels, modification of solid alumina inclusions is often carried out by calcium treatment, converting the alumina to liquid calcium aluminates. When calcium treatment is performed, calcium can either react with sulfur in the melt or with solid alumina. Calcium sulfide inclusions are solid at steel casting temperatures and thus would be detrimental to castability if they remained in the steel after calcium treatment. The aim was to study the transient evolution of inclusions after calcium treatment, testing the hypothesis that calcium sulfide may form as an intermediate reaction product, which can subsequently react with alumina to form modified calcium aluminates. The first part gives the project background and describes the experimental and quantification techniques adopted, including the effect of sampler size in laboratory melts. Results of the formation of intermediate calcium reaction products in laboratory and industrial heats are presented in the second part.

The kinetics of the oxidation of graphite, metallurgical coke, and glassy carbon by CO 2 and H 2 O were investigated at temperatures between 1300 ЊC and 1500 ЊC. The experimental technique employed a lance-crucible geometry with continuous gas analysis to measure the reaction rate. The experiments were designed to ensure that the carbon reaction behavior was in the limited mixed regime, where only a small volume of material close to the surface is reacting, and external gas phase mass transfer was fast. The results demonstrated the importance of internal pore structure, particularly as it develops in the reacted layer during the course of the reaction. This was believed to be responsible for the higher rates measured in graphite than in coke and the time-dependent rate increase that was observed in nonporous glassy carbon during experiments. For a commercial grade graphite and metallurgical coke, the rate constants depended strongly upon the carrier gas species, indicating that molecular diffusion was the primary transport mechanism in the pores of these materials. In contrast, for a specially purified graphite, the rate constant was found to be independent of the carrier gas species, which suggested Knudsen diffusion control dominates in this carbon. The results are in good agreement with extrapolations of previous work carried out at lower temperatures.

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was the leader in developing our understanding of the kinetics of metallurgical reactions. Selected recent kinetic studies, based on this understanding and the application of the results to actual processes, are presented in this article. In particular, the rates of reaction of carbon and carbon in iron with CO 2 and H 2 O gases and FeO in slag are reviewed and applied to the iron smelting process. In addition, our basic understanding of the kinetics of the nitrogen reaction with iron is reviewed, and the results are used in comprehensive models, which can predict the nitrogen content in steel as a function of operating variables in the basic oxygen furnace, electric arc furnace (EAF), and vacuum degassing.