The Justice Department has opened up an in-depth antitrust investigation of Nippon Steels $14.1 billion takeover of U.S. Steel‚ according to two people with direct knowledge of the matter.The move escalates U.S. government scrutiny of the controversial deal‚ which has drawn fire from lawmakers‚ labor unions and others who argue the storied U.S. industrial titan should not be owned by a foreign company even one based in Japan‚ one of Americas closest allies. It also follows a preliminary...