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How does slag form during blast-furnace ironmaking?

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How iron is turned into steel — iron processing Iron ore is one of the most abundant elements on Earth, and one of its primary uses is in the production of steel. When combined with carbon, iron changes character completely and becomes the alloy steel.

In blast-furnace ironmaking, slag is a vital by-product formed through the chemical interaction of impurities and additives at high temperatures. As the furnace burden—consisting of iron ore, coke, and a fluxing agent like limestone—descends through the furnace, it is subjected to intense heat.1

The slag is specifically produced by the combination of the following components:
* Flux: The limestone or other fluxing substances added to the furnace.21
* Impurities: Various substances present in the iron ore that react with the flux.21
* Ash: Residue derived from the coke used as fuel.21

These materials melt and react to form a liquid mixture that accumulates in the furnace hearth. Because it is less dense than the molten iron, the slag floats on the surface of the metal. This layer serves a protective function by shielding the molten iron from oxidation and keeping it clean during the smelting process. The slag is eventually removed from the furnace through a dedicated slag hole or the same taphole as the iron.123