Steel is made through one of two dominant industrial routes. The integrated blast-furnace/basic-oxygen-furnace (BF-BOF) route first removes oxygen from iron ore to make liquid hot metal, then refines that metal into crude steel. The electric-arc-furnace (EAF) route melts mainly recycled steel with electricity, sometimes adding direct-reduced iron (DRI) or hot metal. In both routes, crude steel is continuously cast, reheated, rolled and finished into products such as coil, plate, rebar, wire rod, tubes and rails.
What steel is, and what “crude steel” means
Steel is an alloy whose main ingredients are iron and carbon. World Steel Association definitions describe steel as containing less than 2% carbon; other elements are added or controlled to give each grade its required strength, toughness, corrosion resistance, formability or heat resistance.
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Crude steel is the output of the primary steelmaking furnace before it is cast and transformed into commercial shapes. It is not unfinished ore or a low-quality material. It is liquid or newly solidified steel with a controlled chemical composition that still needs casting and downstream processing. “Finished steel” means the material after those later operations have produced a form and surface suitable for a specific use.
The phrase “from iron ore to finished steel” describes the complete chain, but it does not describe every plant. An integrated BF-BOF works from ore-derived iron, while an EAF mill can begin chiefly with recycled steel and may use little or no newly mined ore in its metallic charge.
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The two main steelmaking routes
| Feature | BF-BOF (integrated route) | EAF (electric-arc route) |
|---|---|---|
| Primary metallic feed | Iron ore is reduced to liquid hot metal in a blast furnace; recycled steel is also charged in the BOF. | Usually recycled steel; DRI and/or hot metal can supplement scrap, depending on the plant and supply. |
| Main energy or reducing agent | Coke made from coking coal supplies heat and removes oxygen from ore; oxygen is then used in the BOF. | Electric arcs melt the metallic charge. Electricity demand depends on the charge, furnace and operating practice. |
| Scrap flexibility | Can use up to 30% scrap in the BOF charge, according to World Steel Association guidance. | Can operate with 100% recycled steel when suitable scrap is available; many plants blend in DRI or hot metal. |
| Primary refining purpose | The blast furnace makes hot metal; the BOF lowers carbon and removes impurities to make crude steel. | The EAF melts the charge, then operators adjust chemistry with oxygen, carbon and alloy additions as required. |
| Global production share | About 70% of global steel production, a rounded industry estimate. | About 30%, a rounded industry estimate. |
| After the furnace | Casting into slabs, billets or blooms, followed by reheating, rolling and finishing, is broadly similar for both routes. | |
The route shares are not an exact, exhaustive partition. World Steel Association material separately reports open-hearth production at about 0.4% of global output, so the 70% and 30% figures should be read as rounded global proportions rather than a precise census of every furnace type.
How the BF-BOF route makes steel from iron ore
1. Prepare the ore, fuel and fluxes
An integrated plant prepares iron-bearing material, coking coal and fluxes before they enter the furnaces. Coking coal is heated without oxygen to make coke. Coke is strong enough to support the burden in a tall blast furnace and porous enough to allow gases to pass through it. It serves two essential functions: it is a fuel that supplies heat, and it is a reducing agent that helps remove oxygen from iron oxides.
Limestone and other fluxing materials are added to help collect unwanted minerals into a separate molten slag. The exact burden can include prepared ore forms such as sinter or pellets, but the proportions vary with plant equipment, ore quality and product requirements.
2. Reduce iron ore to liquid hot metal
In the blast furnace, layers of iron-bearing material, coke and flux descend while hot gases rise. Carbon monoxide and other reducing gases remove oxygen from the iron oxides. At the high temperatures near the tuyeres, the reduced iron melts and absorbs carbon, producing liquid iron known as hot metal or pig iron. Slag captures much of the non-iron mineral matter and is tapped separately.
Hot metal is not yet the steel grade ordered by a customer. Its carbon content and impurity levels are too high for most steel products, so it must be refined in a basic oxygen furnace.
3. Refine hot metal in the basic oxygen furnace
The BOF receives hot metal, a measured amount of steel scrap and fluxes. A water-cooled lance blows high-purity oxygen at high speed onto the molten bath. Oxygen reacts with excess carbon and with elements such as silicon, manganese and phosphorus. The resulting oxides move into the slag or leave as dust and gas, while the bath becomes crude steel with a controlled carbon level.
Scrap has a thermal as well as a material role: it absorbs some of the heat released by oxidation and contributes iron units. Operators sample the bath, adjust the endpoint and add alloying materials to meet the required chemistry. The finished heat is tapped from the BOF into a ladle for secondary treatment and casting.
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4. Tune the steel in the ladle
Between the primary furnace and the caster, ladle metallurgy can fine-tune temperature and composition. Depending on grade and plant design, the steel may be deoxidized, desulfurized, alloyed, stirred with inert gas or treated under vacuum. These operations improve cleanliness and consistency; they do not change the basic fact that the BOF has produced crude steel.
How the EAF route makes steel
1. Select and prepare metallic feedstock
EAF plants commonly charge shredded or sorted recycled steel. Sorting matters because copper, tin and other residual elements can accumulate when scrap is repeatedly recycled. A plant may also add DRI, hot-briquetted iron or blast-furnace hot metal when it needs more iron units or tighter control of residuals. The proportion depends on local scrap availability, the desired grade and the furnace design.
2. Melt with electric arcs
A graphite-electrode EAF creates intense electric arcs above and through the charge. The arcs and the hot molten bath melt the scrap and other metallic feed. Oxygen, carbon injection and slag-forming additions help deliver heat, protect the arc, capture impurities and improve melting efficiency. Unlike a blast furnace, the EAF does not need coke to reduce iron ore when its charge is already metallic steel.
3. Adjust chemistry and temperature
Once the charge is molten, operators sample it and add alloying elements or other materials to reach the ordered grade. Oxygen can remove unwanted carbon and impurities; carbon and alloys can be added when the target chemistry requires them. Electrical power and oxygen injection are adjusted to reach the casting temperature without overheating the steel.
An EAF can therefore use exclusively recycled steel, but “EAF” does not automatically mean “scrap only.” DRI, hot metal and other iron units are legitimate parts of the route when scrap quality or availability makes them useful.
Representative material and energy inputs
World Steel Association figures illustrate the scale of the two routes. They are representative route averages, not a recipe that every mill follows. Actual charges change with ore grade, scrap chemistry, furnace configuration, product mix and regional supply.
| Input for 1,000 kg of crude steel | BF-BOF route average | Recycled-steel EAF route average |
|---|---|---|
| Iron ore | 1,370 kg | 586 kg |
| Recycled steel | 125 kg | 710 kg |
| Metallurgical or other coal | 780 kg metallurgical coal | 150 kg coal |
| Limestone | 270 kg | 88 kg |
| Electricity | Not stated in this route-average comparison | 2.3 GJ |
The BF-BOF column represents the World Steel Association’s current raw-materials average accessed in 2026. The EAF column is specifically its recycled-steel EAF route average, also current as accessed in 2026. The numbers should not be interpreted as a mass balance in which every kilogram becomes steel: oxygen, process gases, slag, dust and other by-products account for the difference.
From liquid crude steel to a cast shape
Continuous casting
Steel from either route is transferred in a ladle to a tundish and then flows through water-cooled copper molds in a continuous caster. The outer shell solidifies first while liquid steel remains inside. Spray cooling completes solidification as the strand is withdrawn, straightened and cut to length.
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- Slabs: wide, relatively thin sections for flat products such as plate and coil.
- Billets: smaller square or rectangular sections commonly used for bars, wire rod and rebar.
- Blooms: larger sections used for heavy structural shapes, rails and some seamless-tube feedstock.
Reheating and hot rolling
Cast slabs, billets and blooms are reheated to a controlled temperature so they can be deformed without cracking. Rolling stands squeeze the steel between rotating rolls, reducing thickness or changing the cross-section. A slab may become plate or strip; a billet may become bar, rebar or wire rod; a bloom may become an I-section, rail or another heavy shape.
Finishing operations
Downstream processing determines the dimensions, surface and final properties. Typical operations include:
- Cold rolling to achieve tighter thickness tolerances, a smoother surface and specific mechanical properties.
- Coating, such as metallic coating or painting, to improve corrosion resistance or appearance.
- Cutting, slitting and leveling to supply coils, sheets, plates or bars in usable sizes.
- Tube production, either by welding strip or by piercing and rolling suitable solid feedstock to make seamless tube.
- Heat treatment and inspection where the grade requires controlled hardness, strength, grain structure or cleanliness.
Finished products include plate and coil; rebar, bars and wire rod; welded and seamless tubes; structural sections; and rails. The product’s name refers to its final geometry and specification, not to a different primary steelmaking route.
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Metallic feedstock
BF-BOF depends on a continuous flow of ore-derived iron. EAF plants are more dependent on the quantity and quality of scrap available in their region, although DRI and hot metal can supplement it. Because scrap supply is finite and grades vary, an EAF may not be able to make every steel grade from 100% scrap at every location.
Energy and reducing chemistry
The defining chemical task in the integrated route is reducing iron oxide to iron, which is why coke and coal are central inputs. The EAF’s defining task is melting metallic feed with electricity. Both routes still use oxygen, fluxes and alloy additions, and both require electricity for motors, casting, rolling and plant services.
Emissions context
World Steel Association reports an industry-average footprint of 2.18 tonnes of CO2e per tonne of steel produced in 2024, covering scopes 1, 2 and 3. That figure is not a BF-BOF or EAF-specific result. The association says most steel-sector emissions are associated with making iron from ore and that ore-based and scrap-based profiles differ substantially. An EAF’s footprint therefore depends strongly on its electricity source and metallic charge, while an ore-based route’s profile is dominated by ironmaking and the reducing agents used.
Process diagrams showing the common routes of the 2020s do not include every developing low-carbon technology. Hydrogen-based direct reduction, carbon capture and other approaches are evolving, but they do not replace the established BF-BOF and EAF sequence described here unless a plant has actually adopted them.
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- “Iron” and “steel” are not interchangeable. Blast-furnace hot metal is an iron product with too much carbon and too many impurities for most steel applications. The BOF or EAF produces the crude steel composition.
- “Recycled steel” does not mean the route has no emissions. Melting scrap avoids the ore-reduction step, but electricity generation, electrode use, alloy production, transport and downstream operations still have impacts.
- “Crude” does not mean crude quality. It identifies the stage before casting and rolling.
- Every EAF is not identical. Scrap-only, scrap-and-DRI and scrap-and-hot-metal furnaces have different chemistry, energy use and emissions.
- Finished steel is not one product. A rail, a galvanized sheet and reinforcing bar can all originate as crude steel but require different rolling, dimensions and finishing.
The complete chain in one view
- Choose the route: prepare ore, coke and fluxes for BF-BOF, or sort scrap and other metallic feed for EAF.
- Make or melt iron: reduce ore to hot metal in a blast furnace, or melt metallic feed with electric arcs.
- Refine the bath: blow oxygen in a BOF, or adjust EAF chemistry with oxygen, carbon, slag and alloy additions.
- Control the heat: tune temperature, cleanliness and composition in ladle treatment.
- Cast semi-finished shapes: produce slabs, billets or blooms by continuous casting.
- Roll and finish: reheat, hot-roll, cold-roll, coat, cut and inspect the steel for its application.
The essential distinction is at the front of the chain: BF-BOF makes iron from ore before refining it, whereas EAF primarily melts existing metallic steel. After crude steel is made, casting, rolling and finishing bring the two routes together.
Frequently Asked Questions
Can an electric arc furnace use 100% scrap steel?
Yes. An EAF can use exclusively recycled steel when suitable scrap is available, although plants may add DRI or hot metal to control chemistry, residual elements or iron-unit supply.
How much scrap does a blast-furnace/basic-oxygen plant use?
World Steel Association says the BF-BOF route can use up to 30% scrap in the BOF charge. The exact proportion depends on the plant, hot-metal condition and product requirements.
What are slabs, billets and blooms?
They are the three principal continuously cast semi-finished shapes: slabs feed flat products, billets commonly feed bars and wire rod, and blooms feed heavy sections, rails and some tube products.
Is crude steel the same as finished steel?
No. Crude steel is the furnace output before casting and downstream forming. Finished steel has been cast, rolled and possibly cold-worked, coated, cut or heat-treated into a specified commercial product.
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