An integrated steel mill has all the functions for primary steel production:

• iron making (conversion of ore to liquid iron),
• steelmaking (conversion of pig iron to liquid steel),
• casting (solidification of the liquid steel),
• roughing rolling/billet rolling (reducing size of blocks)
• product rolling (finished shapes).

The principal raw materials for an integrated mill are iron ore, limestone, and coal (or coke). These materials are charged in batches into a blast furnace where the iron compounds in the ore give up excess oxygen and become liquid iron. At intervals of a few hours, the accumulated liquid iron is tapped from the blast furnace and either cast into pig iron or directed to other vessels for further steelmaking operations. Historically the Bessemer process was a major advancement in the production of economical steel, but it has now been entirely replaced by other processes such as the basic oxygen furnace.

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