For Hitachi, which currently owns 53% of Hitachi Metals, the deal is the latest divestiture in a decade-long business overhaul to pivot the business from electronics hardware to digital services.
The Bain-led consortium, which includes two Japanese funds, will offer 2,181 yen per share to buy the 47% of Hitachi Metals not owned by Hitachi at a premium of 15.8% to Tuesday's closing price. It will spend a further 382 billion yen acquiring Hitachi's 53% stake.
Hitachi Metals will be delisted from the Tokyo Stock Exchange.
Hitachi is expecting to book extraordinary profit of 328 billion yen in the current financial year, it said in a separate statement.
Hitachi has sought buyers since last year for the business which has posted net losses for two consecutive years in a deteriorating business environment.
In recent years it has also sold chemical unit Hitachi Chemical Co to Showa Denko and diagnostic imaging business to Fujifilm Holdings Corp.
($1 = 108.9800 yen)
(Reporting by Takashi Umekawa, editing by Louise Heavens and Elaine Hardcastle)