Steel

Steel Definitions and Properties

• Steel is an alloy of iron and carbon with improved strength and fracture resistance compared to other forms of iron.
• Stainless steels, which are resistant to corrosion and oxidation, typically need an additional 11% chromium.
• Iron is the base metal of steel and can take two crystalline forms: body-centred cubic and face-centred cubic.
• Small amounts of carbon, other elements, and inclusions within the iron act as hardening agents in steel.
• The carbon content of steel can vary and may contribute up to 2.14% of its weight.
• Steel is known for its hardness, quenching behavior, need for annealing, tempering behavior, yield strength, and tensile strength.
• The increase in steel's strength compared to pure iron is achieved by reducing its ductility.
• Steel has a density ranging between 7,750 and 8,050 kg/m or 7.75 and 8.05 g/cm.
• Different metallurgical structures can form in steel with different properties.
• Pure iron exists as alpha iron (BCC structure) at room temperature.
• Carbon can be included in iron as ferrite or austenite.
• Annealing relieves local internal stresses in steel.
• Quenching creates a hard but brittle martensitic structure.
• Tempering reduces brittleness and transforms martensite into cementite or spheroidite.
• Heat treatment improves ductility and fracture resistance in steel.
• The temperature required for annealing depends on the type and alloying constituents.

Steel Origins and Production

• Iron is commonly found in the Earth's crust as an ore, usually an iron oxide.
• Iron is extracted from iron ore through smelting, which involves removing the oxygen by combining it with carbon.
• Smelting results in an alloy called pig iron, which retains too much carbon to be called steel.
• Other materials, such as nickel, manganese, chromium, and vanadium, are added to the iron/carbon mixture to produce steel with desired properties.
• Stainless steel is created by adding at least 11% chromium to inhibit corrosion and form a hard oxide on the metal surface.
• Steel production on a large scale began in the 17th century with the introduction of blast furnaces and crucible steel.
• The Bessemer process, developed in the mid-19th century, revolutionized mass-produced steel.
• The open-hearth furnace and basic oxygen steelmaking (BOS) further improved the production process.
• Mild steel replaced wrought iron, and major steel production centers emerged in cities like Pittsburgh and Cleveland.
• Refinements in production methods have lowered costs and increased the quality of the final steel product.

Steel Alloying Elements

• Common alloying elements in steel include manganese, nickel, chromium, molybdenum, boron, titanium, vanadium, tungsten, cobalt, and niobium.
• Phosphorus, sulfur, silicon, and traces of oxygen, nitrogen, and copper are also important, albeit often considered undesirable.
• Cast iron, with a carbon content higher than 2.1%, is not malleable but can be formed through casting.
• Cast iron can be heat treated to produce malleable iron or ductile iron objects.
• Steel is distinguishable from wrought iron, which contains a small amount of carbon but large amounts of slag.

Steel History and Industry

• Steel production has ancient origins, with bloomeries and crucibles used in antiquity.
• The earliest known production of steel dates back to 1800 BC in Anatolia.
• Steel weapons like the falcata were used in the Iberian Peninsula.
• Noric steel was utilized by the Roman military.
• Seric iron (wootz steel) from India gained a reputation worldwide.
• Bethlehem Steel in Pennsylvania was one of the largest steel manufacturers before its closure in 2003.
• The steel industry is considered an indicator of economic progress.
• The number of U.S. steelworkers decreased from 500,000 in 1980 to 224,000 in 2000.
• China and India's economic boom increased steel demand.
• Indian and Chinese steel firms expanded to meet demand.
• ArcelorMittal is the world's largest steel producer as of 2017.
• China was the top steel producer in 2005 with one-third of the world share.
• Japan, Russia, and the US followed as top steel producers.
• Steel production capacity results in significant carbon dioxide emissions.
• Around 7% of global greenhouse gas emissions come from the steel industry.
• Reduction of emissions expected through a shift in production route and carbon capture technology.

Steel Uses and Applications

• Steel plays a critical role in infrastructural and economic development.
• Steel demand increased by 6% between 2000 and 2005.
• Tata Steel, Baosteel Group, and Shagang Group expanded to meet demand.
• Steel is widely used in the construction, automotive, and manufacturing industries.
• Steel is still the main material for car bodies, despite the growth of aluminum usage.
• It is used in shipbuilding, pipelines, mining, aerospace, and heavy equipment.
• Other applications include office furniture, steel wool, tools, and armor.
• Steel is one of the most-recycled materials globally, with a recycling rate of over 60%.
• In the United States, over 82,000,000 metric tons of steel were recycled in 2008, with an overall recycling rate of 83%.
• The amount of recycled raw materials in steel production is about 40% of the total steel produced.
• In 2016, 630,000,000 tonnes of steel were recycled out of a total of 1,628,000,000 tonnes produced globally.

Steel Data Sources