Toshiba said Thursday it had formally signed a deal to sell its memory chip business to a group led by U.S. investor Bain Capital for around $18 billion.

The sale to the consortium - which includes U.S. tech giants Apple and Dell as well as South Korean chipmaker SK Hynix - is seen as crucial to keeping the struggling Japanese conglomerate afloat.

THursday's signing caps a months-long saga that saw heated courtroom battles, rival bids and the near-delisting of one of Japan's best-known firms. The Japanese firm had already said last week it would sell the business to the Bain-led group and aims to complete the sale by March. Toshiba is the world's number-two chipmaker behind Samsung and the division's products are found in many smartphones and electronic gadgets.

The chip unit accounts for around a quarter of Toshiba's total annual revenue and is the crown jewel in a vast range of businesses ranging from home appliances to nuclear reactors. Toshiba narrowly averted a delisting this year, but it still faces the humiliating prospect of being yanked from Japan's premier stock exchange if the sale does not raise enough money.

Selling the chip division is seen as key to Toshiba's survival, as it battles to recover from multi-billion-dollar losses at its US nuclear operation Westinghouse Electric.