President Donald Trump is set to announce Monday that a $15 billion steel mill billed as the largest ever built in the United States will go up in Iowa. White House officials said the Oval Office event is scheduled for 2 p.m. ET. Mesabi Metallics is expected to name the Iowa site at that briefing. The administration said the plant would be the first U.S. “mega-steel” facility constructed since the 1960s. Production is targeted to begin in 2030. Officials said the mill would turn out about 7.5 million tons of steel a year in its first phase and as much...