By Rob Lenihan If your view of steel mills is smokestacks belching soot, U.S. Steel’s chief sustainability officer, Rich Fruehauf, would like a word with you. When you think of a steel mill, you most likely conjure images of rows of smokestacks churning out black clouds of soot. Sustainability is probably one of the last things you think about. Well, Rich Fruehauf would like to change all that. He’s chief strategy and sustainability officer at U.S. Steel (X) – Get United States Steel Corporation Report, the iconic American company founded more than a century ago by the legendary executives And…