Glossary

Pig iron is the crude, high-carbon form of iron that is produced as the first product of smelting iron ore in a blast furnace. It serves as the primary raw material for making both cast iron and steel. The term “pig iron” comes from the traditional shape of the ingots cast in sand molds: molten iron was poured into a central channel (the “runner”) with smaller branching molds that resembled piglets nursing from a sow—hence the name.

Pig iron typically contains 3.5–4.5% carbon, along with 1–3% silicon, 0.5–1% manganese, and small amounts of sulfur and phosphorus. This high carbon content makes pig iron hard and brittle, meaning it cannot be used directly for most structural or mechanical applications. However, it’s an essential intermediate material—a starting point for refining into more useful forms of iron and steel.

The process of producing pig iron begins with the blast furnace, where a mixture of iron ore (usually hematite or magnetite), coke (carbon source), and limestone (flux) is heated to temperatures of around 1,500–2,000°C (2,700–3,600°F). Inside the furnace, several key reactions take place:

1.The coke burns in the presence of air, producing carbon monoxide (CO):

C+O2​→CO2​

and then

CO2​+C→2CO

2. The carbon monoxide reduces the iron ore (Fe₂O₃ or Fe₃O₄) to metallic iron:

Fe2​O3​+3CO→2Fe+3CO2

3. The limestone (CaCO₃) acts as a flux, combining with impurities like silica to form slag, which floats on top of the molten iron.

The result is a molten pool of pig iron at the bottom of the furnace, which is periodically drained and cast into ingots or transported in molten form for further processing.

There are several grades of pig iron, depending on composition and intended use:

- Basic pig iron, for conversion into steel in basic oxygen furnaces.

- Foundry pig iron, used directly for making cast iron products.

- High-phosphorus pig iron, used in certain specialized chemical processes.

Pig iron on its own is too brittle for shaping or forming, but when remelted and refined to reduce carbon and impurities, it becomes steel; when remelted with additional carbon and silicon, it becomes cast iron.