How Steel Is Manufactured

Steel is the quiet winner of modern civilization. It is not the newest material, nor the rarest, nor the most glamorous, but it is the one that shows up everywhere the modern economy needs strength at scale: in bridges and towers, ports and pipelines, cars and railways, ship hulls and cranes, wind turbines and warehouses. When you zoom out far enough, steel is less a “material” than a physical platform that lets countries build, move, and manufacture.

Two facts capture why steel remains so dominant.

First, the world makes an extraordinary amount of it. Global crude steel production was 1,885 million tonnes in 2024 and 1,849.4 million tonnes in 2025.

Second, steel use tracks living standards. In 2024, 214.7 kg of steel was used in new products per person globally (finished steel products).

Those numbers are not abstract. They translate directly into how many apartments can be framed, how many kilometers of rail can be laid, how many factories can be built, how many trucks can be manufactured, and how quickly supply chains can expand. Steel sits at the intersection of density (it packs a lot of strength into a compact cross-section), cost (it is affordable relative to performance), manufacturability (it can be melted, cast, rolled, and welded in endless forms), and circularity (it can be recycled repeatedly).

But steel’s story is also a chemistry story: the transformation of iron atoms locked inside rock into a precisely engineered alloy. A structural beam in a building is not “iron shaped into a beam.” It is a carefully controlled mixture of iron and small amounts of carbon and alloying elements, processed through furnaces and mills to build a specific microstructure that delivers strength, ductility, and weldability.

What follows is the steelmaking journey from mine to mill to beam: step-by-step, with the chemical logic that makes each step necessary.

Why Steel Still Runs the Modern World

Steel’s dominance comes from a combination of properties that are hard to match simultaneously:

• Strength and stiffness at scale. The steel frame of a high-rise, the girder of a bridge, and the chassis of a truck all rely on predictable load-bearing performance.

• Formability and joining. Steel can be rolled into sheet, drawn into wire, forged, machined, and welded at industrial scale. That matters as much as raw strength.

• Durability and fatigue resistance. Infrastructure is not a one-time purchase. It must survive decades of cycling loads, vibration, weather, and impacts.

• Standardization. Construction, automotive, and machinery industries depend on consistent grades and specifications, enabling global sourcing and design reuse.

• Recyclability. Steel is magnetically separable and routinely recycled. The steel industry’s second major production route is built around scrap (and increasingly around low-carbon “manufactured iron” like DRI).

Even upstream, the steel economy is anchored by a simple truth: almost all iron ore exists to make steel. The USGS notes that 98% of iron ore is used in steelmaking, and that Australia and Brazil each account for about one-third of global iron ore exports.

That sets up the basic steelmaking equation:
Iron ore + energy + carbon (or electricity + reducing gas) → iron → steel → engineered shapes

The Two Main Steelmaking Routes

At a high level, modern steel is produced via two dominant industrial routes:

Route 1: Blast Furnace + Basic Oxygen Furnace (BF–BOF)

This is the classic integrated route: turn iron ore into molten iron (hot metal) in a blast furnace, then refine that hot metal into steel in a basic oxygen furnace.

World Steel Association (Worldsteel) estimates that around 70% of global steel production comes from the BF–BOF route.

Route 2: Electric Arc Furnace (EAF), Primarily Scrap-Based

This route melts scrap (and/or DRI, pig iron, or hot metal) in an electric arc furnace, then refines chemistry to target grades.

Worldsteel estimates global EAF output accounts for about 30% of global steel production.

Those two routes are not simply “old vs new.” They are two different resource logics:

• BF–BOF is ore-and-coal intensive (it makes new iron from rock).

• EAF is scrap-and-electricity intensive (it turns existing iron back into steel, often topped up with manufactured iron units to control impurities and chemistry).

Worldsteel provides a useful mass-and-energy snapshot:

• To produce 1 tonne of pig iron from a blast furnace, it “typically” takes 1.6 tonnes of iron ore and around 450 kg of coke.

• For an average recycled steel EAF route producing 1,000 kg of crude steel, worldsteel lists inputs of 710 kg recycled steel, 586 kg iron ore, 150 kg coal, 88 kg limestone, and 2.3 GJ of electricity.

Now let’s walk through the process in the order steel actually experiences it.

Step 1: Mining Iron Ore, Then Making It “Furnace-Ready”

Ore Is Not “Iron”

In nature, iron is rarely found as metallic iron. It is chemically bound to oxygen as iron oxides. The USGS highlights the two primary forms:

• Magnetite (Fe₃O₄)

• Hematite (Fe₂O₃)

Steelmaking begins by extracting ore from open-pit or underground mines. But the mine’s output is typically not ready to be fed directly into a blast furnace or direct reduction plant. The ore must be upgraded and shaped into a form that behaves predictably at high temperatures.

Beneficiation: Upgrading the Ore

Most ores need processing to increase iron concentration and reduce unwanted gangue (silica, alumina, and other non-iron minerals). Techniques include crushing, grinding, magnetic separation (especially for magnetite), flotation, and other separation methods depending on deposit geology.

Agglomeration: Sinter and Pellets

A blast furnace cannot be fed with only fine powder. It needs a burden with permeability so hot gases can rise and react efficiently. That is why iron ore is often transformed into:

• Sinter: fused lumps made by heating fine ore with fluxes and fuel fines, creating porous agglomerates.

• Pellets: marble-sized balls made from concentrated ore fines with binders, then fired for strength.

This step looks “mechanical,” but it has large downstream impact: burden permeability, reducibility, and chemistry control can make the difference between a stable furnace and a furnace that fights operators every hour.

Step 2: Turning Metallurgical Coal Into Coke

The blast furnace needs carbon for two jobs: heat and chemistry.

• Heat: to reach the extreme temperatures needed for reduction and melting.

• Chemistry: to create carbon monoxide (CO), which strips oxygen from iron oxides.

This is where metallurgical coal enters.

The University of Kentucky’s Kentucky Geological Survey describes the coking process as heating coal without air in an oven at temperatures as high as 2,060°F, driving off volatile matter; the coal softens, liquefies, and resolidifies into a hard porous material called coke.

They also summarize coke’s three classic blast furnace roles:

1. Fuel for added heat

2. Chemical reducing agent for iron oxides

3. Permeable support that helps burden materials flow and react inside the furnace

Not all coal can do this. Metallurgical coals are selected (and blended) for coking behavior and impurity limits, because impurities like sulfur and phosphorus can migrate into iron and degrade steel properties.

Step 3: Building the Blast Furnace Burden: Ore + Coke + Flux

A blast furnace is a tall counter-current reactor: solids descend; hot gases rise. To work, it needs more than ore and coke. It also needs fluxes, typically limestone (CaCO₃) or lime (CaO), to capture impurities into slag.

Worldsteel describes the core BF feed logic directly: iron ore as the iron-bearing raw material, coke (from coking coal) as fuel and reductant, and lime/limestone as flux.

Step 4: Blast Furnace Ironmaking: Reducing Rock Into Hot Metal

What a Blast Furnace Produces

The blast furnace’s job is not to produce steel. It produces:

• Hot metal (molten iron with high carbon content and other dissolved elements)

• Slag (a molten oxide layer that captures impurities)

• Top gas (CO, CO₂, N₂, H₂, and other components, often cleaned and reused as fuel on site)

Steeluniversity’s blast furnace module frames the objective: produce hot metal of consistent quality for downstream basic oxygen steelmaking. It cites typical hot metal targets such as 0.3–0.7% Si, 0.2–0.4% Mn, 0.06–0.13% P, and tapping temperature 1480–1520°C.

The Chemistry: How Oxygen Leaves Iron Oxide

Iron ore is iron plus oxygen. Steelmaking starts by removing oxygen.

Inside the blast furnace, coke burns near the bottom where hot air is blown in (the “blast”). The furnace creates large volumes of carbon monoxide (CO), which is the workhorse reducing gas.

Key reaction logic (simplified):

1. Carbon combustion (heat generation):
   C + O₂ → CO₂

2. CO generation (creating the reducing agent):
   CO₂ + C → 2CO

3. Iron oxide reduction (turning oxide into metal):
   Fe₂O₃ + 3CO → 2Fe + 3CO₂
   FeO + CO → Fe + CO₂

As the burden descends and temperatures rise, iron transitions from solid reduced iron to molten hot metal that drips to the hearth.

Slag: The “Garbage Truck” of the Furnace

Limestone decomposes at high temperature:
CaCO₃ → CaO + CO₂

That CaO combines with silica and other oxides to form slag. This matters because slag does two crucial jobs:

• It removes impurities from the metal by absorbing oxides.

• It protects the molten iron from re-oxidation and helps manage sulfur and phosphorus behavior depending on slag chemistry.

At tapping, operators draw off hot metal and slag separately.

At this point, the iron is still too dirty and too high in carbon to be structural steel. That refinement happens next.

Step 5: Basic Oxygen Furnace: Burning Carbon Out of Iron, Fast

If the blast furnace is about reduction, the basic oxygen furnace (BOF) is about controlled oxidation.

A BOF takes:

• Hot metal from the blast furnace

• Often some scrap steel (to cool the process and recycle)

• Fluxes (lime/dolomite)

Then it blows high-purity oxygen into the melt. The oxygen reacts with:

• Carbon (forming CO gas and stripping carbon down toward steel levels)

• Silicon, manganese, phosphorus (forming oxides that report into slag)

• Some iron (forming FeO in slag, which also participates in refining reactions)

Why so violent? Because oxidation reactions release huge heat. A BOF can refine a heat of metal in a short time precisely because chemistry supplies much of the energy once oxygen is introduced.

Why Carbon Matters So Much

Steel is defined by carbon control. Worldsteel summarizes steel as an alloy consisting primarily of iron and less than 2% carbon.

Hot metal from a blast furnace contains far more carbon than that. The BOF’s job is to pull carbon down into steel range while managing other elements, producing a composition that can be cast and shaped without cracking, embrittlement, or weld failure.

Step 6: Electric Arc Furnace Steelmaking: Steel From Scrap (Plus “Manufactured Iron”)

If BF–BOF is the route of primary iron, EAF steelmaking is the route of circular iron.

Steeluniversity’s EAF module states that electric arc furnaces are used to produce carbon and alloy steels “primarily by recycling ferrous scrap,” melting scrap (and/or DRI, pig iron, iron carbide) using high-power electric arcs. It also provides concrete operating-scale details: scrap is “about 80% of all EAF metal feedstock,” a modern EAF “typically makes 150 tonnes in each melt,” and a melt “takes around 90 minutes.”

Why EAF Steel Still Uses Ore (Sometimes)

A pure scrap melt can be limited by:

• Impurities like copper (from wiring in obsolete scrap), which can cause hot shortness and surface cracking.

• Chemistry constraints for high-spec products.

• Availability and price of quality scrap grades.

That is why EAF shops often supplement scrap with “virgin” or manufactured iron units such as:

• DRI (Direct Reduced Iron): solid iron made by reducing ore with reducing gas (often derived from natural gas, and increasingly discussed in the context of hydrogen).

• Pig iron or hot metal: to dilute tramp elements and stabilize chemistry.

Worldsteel’s raw materials page explicitly includes DRI/hot metal as part of the EAF route input mix and quantifies a representative EAF route material set (including iron ore and coal) for 1,000 kg of crude steel.

EAF Refining: Oxidation, Slag, and Alloying

An EAF is not just a “big toaster.” It is a metallurgical reactor. Alongside electrical energy, EAF steelmaking often uses:

• Oxygen lancing to oxidize carbon and other elements

• Carbon injection to create foamy slag (improving thermal efficiency and protecting the arcs)

• Flux additions to form slag that captures impurities

• Ferroalloy additions to hit target chemistry

Steeluniversity notes that during melting “other metals (ferro-alloys) are added to the steel to give it the required chemical composition.”

Step 7: Secondary Metallurgy: The Ladle as a Precision Chemistry Lab

Primary furnaces (BOF or EAF) can get you close. Secondary metallurgy gets you right.

After tapping steel into a ladle, producers perform ladle refining steps such as:

• Deoxidation (removing dissolved oxygen to prevent porosity and inclusions)

• Desulfurization (improving toughness and weldability)

• Alloy trimming (adding Mn, Si, Cr, Ni, Mo, V, Nb, Ti, etc.)

• Temperature control (critical for casting and downstream rolling)

• Inclusion engineering (modifying non-metallic inclusions so they are less harmful)

• Vacuum degassing (for low-hydrogen, low-nitrogen steels and high-toughness grades)

This is where steel shifts from “liquid metal” to “engineered alloy.” The ladle stage determines whether a steel will behave cleanly in continuous casting and whether it can meet structural toughness requirements without brittle failure.

Step 8: Continuous Casting: Freezing Liquid Steel Into Semi-Finished Shapes

Once chemistry and temperature are set, steel is cast, most commonly by continuous casting.

Instead of pouring into individual ingot molds (the historic method), continuous casting flows molten steel through a water-cooled mold, forming a solid shell that thickens as the strand is withdrawn and cooled.

Continuous casting produces semi-finished shapes such as:

• Slabs (for plate and sheet)

• Blooms (for heavy sections, rails, structural shapes)

• Billets (for rebar, wire rod, and smaller sections)

The choice depends on what products the mill intends to roll next. Structural beams typically start from blooms or beam blanks designed for efficient shape rolling.

Step 9: Rolling: Turning Cast Steel Into Structural Beams

Rolling is where steel becomes geometry.

A cast slab, bloom, or billet is reheated to a temperature where it can be plastically deformed and then passed through a sequence of rolling stands. Each pass changes thickness and shape, progressively pushing the metal toward the target section.

For structural beams (like wide-flange sections), mills often use specialized roll passes and universal stands that form the flange and web geometry with high dimensional control.

Rolling is also where “high-strength” becomes practical: controlled deformation and controlled cooling are how mills manipulate grain size and microstructure. A beam’s strength is not only a function of chemistry; it is a function of how the microstructure is built during thermomechanical processing.

Step 10: The Chemistry of “Steel”: Carbon, Alloying, and Strength Mechanisms

Carbon: The Master Dial

If iron is the base, carbon is the dial that changes steel’s personality.

• Low carbon generally improves weldability and ductility.

• Higher carbon increases hardness and strength potential but reduces weldability and often toughness.

Worldsteel’s definition captures the boundary: steel is primarily iron with less than 2% carbon.

But structural steels are typically far below that maximum. Structural beams need a blend of:

• Strength (to carry loads)

• Ductility (to deform rather than snap)

• Toughness (to resist brittle fracture, especially in cold conditions)

• Weldability (construction depends on welding and fabrication)

That combination pushes producers toward relatively low carbon, with strength delivered by microstructure and microalloying rather than simply “more carbon.”

Alloying Elements: Small Additions, Big Effects

Steelmakers add alloying elements for targeted reasons:

• Manganese (Mn): improves strength and hardenability; also ties up sulfur.

• Silicon (Si): deoxidizer; affects strength.

• Chromium (Cr): improves hardenability and corrosion resistance (critical in stainless and alloy steels).

• Nickel (Ni): improves toughness.

• Molybdenum (Mo): improves hardenability and high-temperature strength.

• Vanadium (V), Niobium (Nb), Titanium (Ti): microalloying elements that enable precipitation strengthening and grain refinement.

In modern high-strength low-alloy (HSLA) steels, precipitation strengthening is a core mechanism: nanometer-scale carbides/nitrides form and impede dislocation motion, raising strength without extreme carbon content.

Microstructure: Strength Is “Designed” by Phases

Steel’s mechanical behavior is governed by microstructure: ferrite, pearlite, bainite, martensite, and the distribution of precipitates and grain boundaries.

Structural steels commonly aim for refined ferrite-based microstructures with controlled pearlite and microalloy precipitates, delivering strength with ductility.

From Generic Steel to Structural Beam Steel: What Changes

A high-strength structural beam is not only about meeting a yield strength number. It must also be weldable, consistent across thick sections, and resistant to brittle fracture.

A widely used example in the United States is ASTM A992/A992M, commonly specified for wide-flange shapes. The American Institute of Steel Construction (AISC) notes that A992 is preferred for W-shapes and highlights two performance-related constraints:

• A maximum yield-to-tensile ratio of 0.85 (ductility definition)

• A maximum carbon equivalent of 0.45 (0.47 for thicker flanges), improving weldability

That carbon-equivalent constraint is a quiet but crucial idea: it recognizes that weldability is not about carbon alone. It is about how carbon and alloying elements together influence hardenability and heat-affected zone behavior.

In practice, achieving “high strength structural steel” usually involves a package deal:

1. Low-to-moderate carbon for weldability

2. Microalloying (Nb/V/Ti) for precipitation strengthening and grain refinement

3. Thermomechanical controlled processing (TMCP) during rolling

4. Controlled cooling to lock in microstructure

5. Tight chemistry and inclusion control via secondary metallurgy

That is how mills make beams that can be fabricated, shipped, welded, and trusted in a bridge or tower.

Scrap, Circularity, and the New Center of Gravity in Steel

Scrap is not a side story. It is the foundation of the EAF route and a major lever for cost and emissions.

Steeluniversity emphasizes scrap’s dominance in EAF feedstock, estimating about 80% of EAF metal feed is scrap.

Worldsteel’s raw materials framing also reflects the broader shift: the EAF route is explicitly defined around recycled steel and electricity, and it increasingly incorporates DRI/hot metal to manage chemistry at scale.

The Carbon and Energy Reality: Why Route Choice Matters

Steel’s future is being shaped by a constraint that older industrial eras could ignore: emissions intensity.

Worldsteel’s Sustainability Indicators (with route-level breakdowns) provide a clear comparison for 2024:

• Global average CO₂ emissions intensity: 1.92 tonnes CO₂ per tonne of crude steel

• BF–BOF: 2.34 tonnes CO₂ per tonne of crude steel

• Scrap–EAF: 0.69 tonnes CO₂ per tonne of crude steel

• DRI–EAF: 1.47 tonnes CO₂ per tonne of crude steel 

Energy intensity shows a similar split in 2024:

• Global average: 20.95 GJ per tonne of crude steel

• BF–BOF: 23.88 GJ/tonne

• Scrap–EAF: 9.84 GJ/tonne

• DRI–EAF: 23.30 GJ/tonne 

Those numbers explain why the industry is pursuing multiple pathways at once:

• More scrap-EAF capacity where scrap and electricity conditions allow

• More DRI as a way to create cleaner iron units (and potentially decarbonize further with low-carbon hydrogen over time)

• Continued optimization of blast furnaces, including higher efficiency and carbon reduction practices where BF infrastructure remains dominant

Even in a decarbonizing world, steel demand does not disappear. It shifts toward “cleaner steel,” meaning the same beam in a building, but produced with a different upstream carbon equation.

The Beam’s Real Journey: From Rock to Skyline

If you trace a single wide-flange beam backward, you can see the entire industrial machine it implies:

• An iron ore deposit, blasted and crushed

• Beneficiation plants turning ore into a concentrate

• Coke ovens turning metallurgical coal into porous carbon

• A blast furnace reducing oxides into hot metal near 1500°C

• A BOF burning carbon down into steel range

• Or, alternatively, an EAF melting scrap and refining chemistry in 90-minute heat cycles

• Ladle treatment dialing composition, cleanliness, and temperature

• Continuous casting freezing liquid steel into beam-ready shapes

• Rolling mills shaping and strengthening steel through deformation and cooling

• Standards that demand not just strength, but weldability and ductility (as A992 illustrates)

Steelmaking is often described as heavy industry, and it is. But it is also, at its core, a precision discipline: controlling chemistry at parts-per-thousand (and sometimes parts-per-million), controlling temperature in narrow windows, and controlling microstructure so the final product behaves predictably in the real world.

That is why steel remains the backbone material. It is not simply “strong.” It is engineerable. It can be mass-produced and still tuned. And it can be melted down and reborn as new steel again and again, while continuing to hold up the physical economy.