Shares of U.S. Steel Corp. tumbled 5.7% in midday trade Wednesday, after UBS went back to being bearish on the steel maker, citing concerns that blast oxygen furnace (BOF) operators will continue to lose market share to electric arc furnace (EAF) operators. Analyst Andreas Bokkenheuser downgraded U.S. Steel to sell, after upgrading it to neutral in early December. He slashed his price target to $10, which is 35% below current levels and the lowest target he's had on the stock since February 2016, from $22. Meanwhile, Bokkenheuser upgraded EAF operator Steel Dynamics Inc. to buy from neutral, and raised his price target to $47.00 from $37.50. "With U.S. steel demand in structural decline, EAF product quality rapidly improving and imports remaining somewhat resilient, we believe the war for market share will be fought on price," Bokkenheuser wrote in a note to clients. With an average of 66% higher [earnings before interest, taxes, depreciation and amortization per ton] than the BOFs, we assess the EAFs are best positioned to compete on price." Shares of EAF operator Nucor Corp. are up 1.2% in midday trade while BOF operator AK Steel Holding Corp.'s stock was down 1.4%. Meanwhile, the S&P 500 has up 0.1%.