Improving Sulfide Shape Control in High-Quality Heavy Plate Steel Grades at ArcelorMittal Coatesville

摘要

Low sulfur content, sulfide shape control, and the absence of excessive oxide inclusions in heavy steels plates are well recognized features of high toughness, high formability and resistance to hydrogen induced cracking (HIC). Poor sulfide shape control in plate grade steels can lead to product failures and downgrades affecting a steelmaker's yield, productivity, and reputation. This study was undertaken to establish steelmaking parameters to assure sulfide shape control without undue MnS stringers and oxide inclusions. New tools were used to characterize sulfide and oxide inclusions in steel grades and plate products, and results of trials conducted in steel refining and casting to improve cleanliness and shape control are presented. The trial data were examined with inclusion analysis achieved using an automated SEM applied to tundish and plate steel samples. It was shown that to control sulfide shape it is necessary to desulfurize the steel to very low levels, < 10 ppm S in this case, and prevent steel reoxidation during easting. Specific ratios among Sulfur, Oxygen and Calcium were found to be necessary to ensure adequate shape control. Successful implementation of modified practices has not only resulted in improved shape control in certain plate products, but application of these practices to other steel grades has significantly improved overall cleanliness, thus improving overall customer satisfaction.