Steel makers U.S. Steel (X) and smaller AK Steel (AKS) are slated to report results Tuesday, opening a window on prospects for the sector and the global economy this year. Nucor (NUE) was the first steel company to report, announcing first-quarter results Thursday. Shares dropped 6% in two days after the company said profit slipped 16% to 42 cents a share on pricing and margin weakness, and increasing competition from foreign rivals. The company