SECONDARY METALLURGICAL TREATMENT FOR THE PRODUCTION OF PLATE STEELS

Objective. The present article sets out to show the secondary metallur gical treatment possibilities necessary nowadays in a ladle tank degas sing facility to produce plate grades which have to satisfy the highes t cleanness requirements. The aim, essentially, is to illustrate the a dvantages of vacuum-treating the steel in conjunction with a lime-satu rated slag phase. Summary. The levels of phosphorus, sulphur, nitrogen , hydrogen and oxygen achievable while making optimum use of the prope r plant and process routes are: discussed. Phosphorus concentrations l ower than 70 ppm are realisable only by utilization of the heat from t he exothermic reaction between oxygen and aluminium. The use of a lime -saturated lime-alumina slag allows steel grades with sulphur concentr ations lower than 10 ppm to be produced. The degassing efficiency for nitrogen and hydrogen as a function of the total amount of stirring ga s and treatment time is considered. It is described how the total oxyg en concentration develops during the steelmaking process; levels lower than 10 ppm in the final product can be attained for continuous casti ng in vertical-bending lines where bending takes place after complete solidification. A final operation that is performed during the seconda ry metallurgical treatment is the addition of calcium for inclusion sh ape control, which simultaneously helps to improve the castability.