Nippon Steel and U.S. Steel said Wednesday they have finalized their “historic partnership,” a year-and-a-half after the Japanese company first proposed its deal to buy the iconic American steelmaker for nearly $15 billion.

Nippon Steel Corp. closed its $14.1 billion takeover of United States Steel Corp., bringing to an end an 18-month effort to combine the American and Japanese steelmakers, the companies said in a Wednesday statement.