stôl

Stål, or steel, is an alloy of iron with carbon and other elements. It usually contains carbon up to about 2.1% by weight; the rest is iron, with alloying elements such as chromium, nickel, vanadium, molybdenum, and tungsten used to tailor properties. Carbon content and additives determine strength, hardness, ductility, toughness, and weldability.

Production and processing: Steel is produced from iron ore in furnaces to make pig iron, which is refined in basic oxygen or electric arc furnaces to adjust carbon content and introduce alloys. Scrap steel is widely recycled, especially in electric furnaces. Through heat treatment and processing, steels are produced in a wide range of grades for different uses.

Properties and applications: Steel offers high strength and ductility at relatively low cost. Strength and hardness rise with carbon content and via quenching and tempering, but ductility and weldability can fall. Stainless steels contain chromium and offer corrosion resistance; other alloys improve wear resistance and high-temperature performance. Common applications include construction, transportation, machinery, tools, pipelines, and consumer goods.

Types and standards: Major families include carbon steels, alloy steels, stainless steels, and weathering steels. Tool steels and high-strength low-alloy steels are important special grades. Standards set by national and international bodies define composition, properties, and testing methods.

History: Modern steel production expanded in the 19th century with methods such as the Bessemer process and the open-hearth furnace, later replaced by basic oxygen and electric arc techniques. Steel remains a foundational material in engineering and industry.