** BMO raises U.S. steelmakers Steel Dynamics STLD.O and Nucor Corp NUE.N

** Brokerage says past price increases are expected to drive steady earnings growth for sheet steel producers

** BMO notes that current sheet prices will stay elevated for longer, with stronger momentum

** Both Steel Dynamics and Nucor posted a rise in first-quarter profit in April, helped by higher steel prices resulting from tighter supply due to mill outages and imports falling to multi-year lows

** As of last close, STLD up 62.4% and NUE rose 58% YTD