EUROPEAN STEEL TECHNOLOGY AND APPLICATION DAYS 2017 - ESTAD 2017

ArcelorMittal USA Indiana Harbor plant is making large quantity of high Al TRIP and DP grades to meet the needs from automobile industry for high strength and high deformability steel products. During steelmaking process of these high Al TRIP and Dual Phase steel grades, it has been observed that the nitrogen behaves very differently from regular Al-killed steels. Nitrogen will drop along the way of the process for high Al steels. In order to understand the mechanism, industrial heats were sampled and detailed inclusion characterizations were performed. Meanwhile, lab heats were also made under well controlled conditions to study the formation of AlN and the absorption of nitrogen in regular Al killed steel and high Al steel. This paper is attempting to document some of the preliminary findings of these studies. The basic conclusion is that the AlN inclusions form at steelmaking temperature in high Al steels and float out quickly. The floatation of AlN inclusion out of steel bath drives the nitrogen down in the bulk chemistry of the steel. The plant trials were done at Ladle Metallurgy Furnace with argon injecting facility through a lance and primary steelmaking is done at Basic Oxygen Furnace. Trials were done because steel was tapped from BOF with high Nitrogen (more than maximum allowable chemistry) because of a recycled (any off chemistry or heats which could not be cast due to operating/maintenance problem) are produced in BOF with very less Hot Metal and tends to be higher on Nitrogen (above 70 ppm ).