US Steel’s boss warned that the company would shut down mills and move its headquarters out of Pittsburgh if its planned sale to Nippon Steel is blocked.CEO David Burritt said US Steel is banking on a $3 billion investment from Nippon to survive as part of a nearly $15 billion acquisition. The multi-billion dollar investment will help the steel company avoid making job cuts, he said. 6 US Steel’s CEO said the company would shut down mills and move its headquarters out of Pittsburgh if its planned sale to ...