Steel production
Steel is an iron alloy with up to 2.14 % carbon (in practice usually below 1.5 %); making it from cast iron means reducing most of the carbon and the harmful impurities (S, P, Si, Mn). Oxygen is blown into molten cast iron: first some iron is oxidised: 2Fe + O₂ → 2FeO, then FeO oxidises the impurities: FeO + C → Fe + CO↑, 2FeO + Si → 2Fe + SiO₂, FeO + Mn → Fe + MnO, 5FeO + 2P → 5Fe + P₂O₅. The oxides go into the slag; sulfur is bound by FeS + CaO → CaS + FeO, phosphorus by 3CaO + P₂O₅ → Ca₃(PO₄)₂. Today steel is made mainly in basic oxygen converters and electric arc furnaces; these have almost entirely replaced the open-hearth furnaces that were once widespread. By composition steel is carbon or alloy steel; alloying additions are Cr, Ni, Mo, V, W, Ti. By purpose we distinguish structural steel (machine parts, bridges, buildings), tool steel (cutting tools) and special steels (stainless, heat-resistant); heating and cooling (hardening) change the hardness of steel. In chemistry problems we often find a formula: from the mass of water lost on heating a crystal hydrate we find n, and from the dissolving of a metal oxide in acid we find the atomic mass of the metal.
Make a table: for cast iron and steel give carbon content, properties, uses and production. Sort steel objects (tool, bridge, knife, medical instrument) into groups: structural, tool, stainless. Hardening of steel is done only by an instructor in suitable conditions; do not heat or burn anything as an experiment at home.