US miner Peabody Energy and the world's biggest steel maker, ArcelorMittal, have agreed to improve their joint $4.7 billion takeover bid for Queensland-based coal miner Macarthur Coal.

US miner Peabody Energy and the world's biggest steel maker, ArcelorMittal, have agreed to improve their joint $4.7 billion takeover bid for Queensland-based coal miner Macarthur Coal.