Steel

Steel is an iron alloy typically containing carbon, usually between 0.02% and 2.0% by weight, and often other elements such as chromium, nickel, vanadium, or molybdenum to tailor properties. Carbon content and alloying determine strength, hardness, toughness, and weldability. Stainless steels contain at least 10.5% chromium and resist corrosion; tool steels include elements that harden at high temperatures.

Most steel is produced by reducing iron ore in a blast furnace to produce pig iron, then converting it in a basic oxygen or electric arc furnace to refine the composition. Scrap steel is a common feedstock for electric furnaces. After melting, steel can undergo heat treatments such as annealing, normalizing, quenching and tempering, or carburizing to adjust microstructure and properties.

Steel grades are broad: carbon steels, alloy steels, stainless steels, and tool steels. Carbon steels are widely used in construction and infrastructure; alloy steels are selected for strength and toughness in automotive and machinery; stainless steels are used where corrosion resistance is essential.

Applications include construction (rebar, beams), transportation (vehicles, ships), machinery, tools, energy, and consumer products. The industry emphasizes recycling; steel is one of the most recycled materials, and recycled steel can be melted and reused with relatively low energy input compared with primary production.

Historically, iron was worked in ancient times, but modern steelmaking emerged in the 19th century with processes such as the Bessemer converter and open-hearth furnaces, followed by basic oxygen and electric arc furnaces that enabled large-scale production and standardized grades.