2010 July Issue
Full Table of Contents

Continuous Casting Technologies

This paper postulates the mechanisms of spinel formation in LCAK steel produced via the EAF route. The effective modification of solid spinel inclusions into liquid inclusions by Ca treatment is also demonstrated.

The increase in barrel refractory brick erosion that occurred at the Nucor Crawfordsville meltshop was mitigated by implementing a combination of operational practices and ladle preheating practices.

Transient fluid flow phenomena in a 60-ton continuous casting tundish were investigated using mathematical models and industrial trials. The study provides useful information to help improve steel cleanliness during continuous casting.

Mathematical process models — including fully online, semi-online, offline and literature models — can induce beneficial changes to process operation. Examples are taken from the author’s experience in modeling the continuous casting of steel and related processes.

A comprehensive model for recommending the required ladle exit temperatures to achieve consistent superheats in the tundish has been developed. The model is universal and can easily be modified to suit any casting process.

Modernization projects can offer notable operating and maintenance improvements for a reasonable capital investment. This paper describes the design concepts and benefits of projects in the strand containment zone, from the mold through the final segment.

In the production of Al-killed steels, calcium treatment is a common practice for modification of solid alumina inclusions to liquid/partially liquid calcium aluminates. Alumina inclusions may contain some MgO (5–40%). Because the MgO is not soluble in Al2O3, the presence of any non-zero amount of MgO causes spinel inclusion to form; the resulting Al-Mg spinels are more stable than alumina and may be more difficult to modify. Recently, some authors have shown successful modification of spinels by calcium and have also proposed that MgO in inclusions may help in the liquefaction of inclusions. The present work studies the modification of spinels by calcium. A vacuum induction furnace is used for melting iron in a MgO crucible, followed by addition of aluminum (Al or Al-Mg alloys) and calcium. Reduction of the MgO crucible by aluminum was an ineffective source of MgO in inclusions in the melt, so Al-Mg alloys were used for deoxidation, to produce Al2O3-MgO inclusions. The effectiveness of calcium treatments was evaluated by tracking the compositions of inclusions in steel samples taken from the melt. Just after calcium treatment, inclusions were found to be dual-phased, with pure CaS in contact with unmodified oxide inclusion. Equilibrium calculations showed that this phase combination is not stable and CaS can react with the oxide inclusion to yield modified (CaO-Al2O3) inclusions. At longer times after calcium treatment, inclusions were found to be inhomogeneous in composition, with areas richer in Ca being depleted of Mg and vice versa. This two-phase structure is as expected for equilibrium at steelmaking temperature: the MgO-rich region is unmodified spinel, and the CaO-rich region is liquid oxide (modified spinel), containing some of the MgO from the spinel.