How does blast-furnace iron differ from steel in carbon content?

Blast-furnace iron, also known as pig iron or hot metal, typically contains a high carbon content ranging from 4 to 4.5 percent. This high concentration is a result of the reduction process occurring within the blast furnace, where iron ore is processed with coke.12

In contrast, steel is an engineered material created by refining this iron to contain significantly lower amounts of carbon. While the specific carbon content of steel can vary based on its intended application, it is generally much lower than that of pig iron; for example, common steel compositions often feature carbon levels well below 2 percent, such as 0.25 percent or 0.77 percent. The addition of these smaller, controlled amounts of carbon is the primary method used to strengthen iron and convert it into useful steel.3