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Guide

Explore the Elements: Steel

Explore the Elements: Steel

Steel underpins almost every industry, but at over 1.8 billion tonnes a year it accounts for around 8% of global emissions. This guide introduces steel's raw materials, the two main production routes, the green steel technologies emerging, and the role of LCA.

Steel underpins almost every industry, but at over 1.8 billion tonnes a year it accounts for around 8% of global emissions. This guide introduces steel's raw materials, the two main production routes, the green steel technologies emerging, and the role of LCA.

Tara Ryan

IN SUMMARY

Understanding steel, and the challenge of decarbonising it

Understanding steel, and the challenge of decarbonising it

Steel is one of the most essential materials of modern society, produced at over 1.8 billion tonnes a year and providing structure, directly or indirectly, to virtually every industry, from construction and transport to wind turbines and machinery. That scale comes at a cost: the steel industry contributes around 8% of total global emissions, making its decarbonisation one of the most important challenges in heavy industry. Steel is an alloy of iron and carbon, tailored to different uses by adding elements like chromium, nickel and manganese. This guide, a special edition of Minviro's "Explore the Elements" series, introduces steel's raw materials, production routes, emerging green technologies and the role of LCA.

  • Steel is everywhere, and high-emitting. At more than 1.8 billion tonnes a year, steel underpins construction, transport, energy and manufacturing, but accounts for roughly 8% of global greenhouse gas emissions.

  • Two routes dominate production. The blast furnace-basic oxygen furnace (BF-BOF) route makes around 70–75% of global steel from iron ore and coke, while the electric arc furnace (EAF) route makes 25–30%, mainly from recycled scrap, with a lower carbon footprint.

  • Green steel is coming, but constrained. Hydrogen-based direct reduction (H₂-DRI-EAF) offers a promising decarbonised route when powered by green hydrogen and renewables, though it currently depends on high-grade iron ore.

What steel is, and why it matters

Steel is an alloy made primarily of iron and carbon, with carbon content typically between 0.02% and 2.14% by weight, a composition that gives it its mechanical strength, durability and versatility. Different varieties are tailored to specific applications by adding elements such as chromium, nickel, molybdenum, vanadium and manganese, producing carbon steel, alloy steel, stainless steel and more. Its importance is hard to overstate: at an annual production level exceeding 1.8 billion tonnes, steel provides structure to every industry imaginable, buildings in construction, turbines in energy, trains in transport, and machines in manufacturing. But that combination of enormous volume and currently carbon-intensive production makes decarbonisation critical, since the industry contributes around 8% of total global emissions.

Raw materials and where they come from

The primary raw material for steel is iron, sourced from iron ore, mainly hematite (Fe₂O₃) and magnetite (Fe₃O₄). Hematite is favoured for its higher iron content and easier processing, while magnetite is denser and strongly magnetic but needs more intensive beneficiation. Global iron ore extraction is dominated by Australia, Brazil, China and India: as of 2023, Australia led with over 900 million tonnes a year (mostly hematite from the Pilbara), followed by Brazil at 400–450 million tonnes (around 90% hematite, including from the Carajás mine), China at 300–350 million tonnes, and India at 200–250 million tonnes. Two other raw materials are essential: metallurgical coal, used to produce the coke that acts as both fuel and reducing agent (with major reserves in the US, Russia, China and Australia), and limestone, used as a flux to remove impurities (abundant globally). Further downstream, alloying elements like chromium, nickel, molybdenum, vanadium and manganese feed a complex supply chain spanning multiple continents.

The two main production routes

Steel production typically follows one of two routes. The blast furnace-basic oxygen furnace (BF-BOF) route accounts for around 70–75% of global production and is concentrated in regions with abundant iron ore and coking coal, such as China, India and the US. Iron ore, coke and limestone are fed into the blast furnace and heated to extreme temperatures; the coke acts as fuel and reducing agent, stripping oxygen from the ore to produce molten pig iron, while limestone forms a slag that carries off impurities, with large quantities of CO₂ released in the process. The electric arc furnace (EAF) route, around 25–30% of production, primarily melts recycled steel scrap using electrical energy, with alloying elements added after melting; it can also take supplementary feedstocks like direct reduced iron (DRI), hot briquetted iron and pig iron. The EAF route is more flexible and environmentally friendly, relying on recycling and producing fewer emissions, and it is more common in Europe and North America where recycling infrastructure and electricity are readily available. Molten steel from either route is then cast into slabs or billets and finished by rolling, coating and other processes.

Steel production typically follows one of two routes. The blast furnace-basic oxygen furnace (BF-BOF) route accounts for around 70–75% of global production and is concentrated in regions with abundant iron ore and coking coal, such as China, India and the US. Iron ore, coke and limestone are fed into the blast furnace and heated to extreme temperatures; the coke acts as fuel and reducing agent, stripping oxygen from the ore to produce molten pig iron, while limestone forms a slag that carries off impurities, with large quantities of CO₂ released in the process. The electric arc furnace (EAF) route, around 25–30% of production, primarily melts recycled steel scrap using electrical energy, with alloying elements added after melting; it can also take supplementary feedstocks like direct reduced iron (DRI), hot briquetted iron and pig iron. The EAF route is more flexible and environmentally friendly, relying on recycling and producing fewer emissions, and it is more common in Europe and North America where recycling infrastructure and electricity are readily available. Molten steel from either route is then cast into slabs or billets and finished by rolling, coating and other processes.

Green steel and the role of LCA

Sustainability is a central concern given steelmaking's energy use and carbon footprint, and the industry is innovating new routes in response. The major opportunity is "green" steel using hydrogen-based direct reduction (DRI), which replaces carbon-rich fuels with hydrogen to reduce iron; linked to an EAF and supplied with green hydrogen and renewable electricity, this H₂-DRI-EAF route offers a genuinely decarbonised pathway, though it is constrained by high-grade iron ore requirements and is not yet fully commercially proven. Other future routes include hydrogen DRI to electric smelting furnace (ESF) to BOF, which qualifies more of the iron ore supply and minimises emissions, while carbon capture and storage, renewable-powered EAFs, and more scrap recycling all add further levers. Upstream matters too, low-carbon mining fleets and high-quality iron concentrates make downstream processing less energy-intensive. Life cycle assessment is the tool that ties this together, pinpointing the stages that contribute most to emissions and other impacts, and as frameworks like the Carbon Border Adjustment Mechanism (CBAM) and product passports gain prominence, the industry is increasingly using LCA to quantify and reduce its footprint.

Sustainability is a central concern given steelmaking's energy use and carbon footprint, and the industry is innovating new routes in response. The major opportunity is "green" steel using hydrogen-based direct reduction (DRI), which replaces carbon-rich fuels with hydrogen to reduce iron; linked to an EAF and supplied with green hydrogen and renewable electricity, this H₂-DRI-EAF route offers a genuinely decarbonised pathway, though it is constrained by high-grade iron ore requirements and is not yet fully commercially proven. Other future routes include hydrogen DRI to electric smelting furnace (ESF) to BOF, which qualifies more of the iron ore supply and minimises emissions, while carbon capture and storage, renewable-powered EAFs, and more scrap recycling all add further levers. Upstream matters too, low-carbon mining fleets and high-quality iron concentrates make downstream processing less energy-intensive. Life cycle assessment is the tool that ties this together, pinpointing the stages that contribute most to emissions and other impacts, and as frameworks like the Carbon Border Adjustment Mechanism (CBAM) and product passports gain prominence, the industry is increasingly using LCA to quantify and reduce its footprint.

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