(ECCC-31)Evaluation of Lime-Silica and Lime-Alumina Mold Powders Developedfor Casting High Aluminum TRIP Steel Grades

摘要

When continuously casting Advanced High Strength Steels, such as high aluminum Transformation InducedPlasticity (TRIP) steelgrades, conventional lime-silica based mold powders have shown an inherent instability dueto gross reduction of the SiO2. The extent of the silica reduction in the base mold powder leads to an aluminaincrease of as much as 30% in the “working” mold slag composition. The magnitude and inconsistency of thischange adversely impacts the physical properties of the slag which can affect mold heat removal, slagconsumption and in mold behavior. In combination, these factors lead to an as-cast slab surface containingtransverse and longitudinal depressions and cracks. As a result, efforts were focused on developing lime-aluminamold powders which would be less reactive for casting high aluminum TRIP steelgrades. The development work atArcelorMittal Global R&D – East Chicago Center (ECC) and Stollberg USA resulted in production trials of two moldpowders at ArcelorMittal USA (AM-USA). This paper describes work done to assess the effectiveness of thesenew mold powders in comparison to traditional lime-silica based powders for casting high aluminum TRIPsteelgrades. Optical microscopy, Cathode Luminescence Microscopy and SEM were used to examine slag filmssecured during the production casts to determine the nature and distribution of precipitates found in the film. Theuse of lime-alumina based mold powders resulted in significant changes in the steel/slag chemical interaction andimproved the as-cast slab surface quality.