I worked in a steel mill for about 9 months and was on the pouring platform once when they made killed steel.. These were old timers which did not offer much in the way of explanations. They said it took out the oxygen. To see a guy walking around with an arm load of soap bar sized Aluminum ingots, and, tossing 2 or 3 into each just poured steel mold was amazing. The Aluminum would just go "poof" and be gone. Watching closely, it seemed that a thin flow of liquid was spread across the top of the steel. Not much in relevant facts, just amazing that Aluminum would disappear so quickly.