Steels

Steels are iron alloys whose main alloying element is carbon, typically up to about 2.1% by weight. The carbon content governs hardness, strength, and ductility, while other elements such as chromium, nickel, vanadium, molybdenum, and tungsten are added to tailor properties. Low-carbon steels (approximately 0.04–0.3% C) are ductile and weldable; medium-carbon steels (0.3–0.6% C) balance strength and formability; high-carbon steels (0.6–1.0%+ C) are harder but less ductile. Alloy steels include stainless steels (chromium ≥ 10.5%), tool steels, and high-strength low-alloy steels, among others. Stainless steels vary by microstructure: ferritic, austenitic, martensitic, or duplex.

Manufacturing and processing: modern steel is produced from iron ore and recycled scrap in basic oxygen furnaces or electric arc furnaces, refined in ladles, and solidified by continuous casting. Downstream processing includes hot rolling, forging, and heat treatments to achieve target properties.

Heat treatment and microstructure: heat treatment such as annealing, normalizing, quenching, and tempering alters microstructures—ferrite, pearlite, cementite, and martensite—controlling hardness and toughness.

Applications: widespread in construction, transportation, energy, machinery, and household items. Common examples include rebar, gears, pipes, cutlery, and structural components.

History: steel production advanced rapidly in the 19th century with Bessemer, open-hearth, and later basic oxygen and electric methods, enabling large-scale, economical steelmaking.