Essar Steel, the Indian steel producer, is to buy American steel firm Esmark, in a $778m (£392m) deal which includes a $110m long-term loan.
Esmark accepted a cash purchase price of $17 per share, a 13.5% premium on Tuesday's closing share price.
Esmark chief executive James Bouchard said it needed a strategic partner as raw material and transport costs rose.
The global market for steel has been growing, with strong demand from developing countries such as China.
Last year, Essar bought Minnesota Steel for an undisclosed sum, only days after it also agreed to acquire Canadian firm Algoma Steel for $1.6bn.
Essar supplies steel to India, Canada, the United States, the Middle East and Asia.