Thermodynamics of nozzle blockage in continuous casting of calcium-containing steels

Abstract

Calcium-bearing material is added commercially to remove sulfur and to control sulfide shape. Few steelmakers, however, have used calcium additions to cast aluminum-killed steels successfully through metering nozzles. In a development program to cast aluminum-killed steels at Inland's No. 1 Electric Furnace and Billet Caster Shop, calcium-silicide injection at first resulted in nozzle blockage in both aluminum-killed and silicon-killed steels. This paper discusses the thermodynamics of iron containing silicon, aluminum, calcium, oxygen, and sulfur, as well as analyses of the nozzle deposits. The thermodynamic calculations show that, in iron containing aluminum, the calcium content can be too high, so that solid calcium sulfides form. In iron containing silicon without aluminum, with similar calcium contents, solid calcium silicates and calcium sulfides can form. The results of the analyses from plugged nozzles were in agreement with these thermodynamic predictions.