The Tool Desk
Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Short answer: A blast furnace is the ironmaking stage of an integrated blast-furnace/basic-oxygen-furnace (BF-BOF) route. It reduces iron ore with coke, after which a basic oxygen furnace (BOF) converts the hot iron into steel. An electric arc furnace (EAF) melts and refines a metallic charge—often recycled scrap, but also direct-reduced iron (DRI), hot metal, or a blend—using electric arcs. The meaningful comparison is therefore between complete production routes, their feedstocks, energy sources, emissions and economics, not between two interchangeable furnace vessels.
For construction buyers, the distinction affects embodied-carbon estimates, recycled-content claims, supply resilience and the way an environmental product declaration (EPD) should be interpreted. Scrap-EAF generally uses less energy and produces fewer greenhouse-gas emissions than ore-based BF-BOF, but an EAF is not automatically low-carbon: its electricity mix and charge composition matter.
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BF-BOF and EAF at a glance
| Dimension | BF-BOF route | EAF route |
|---|---|---|
| Primary function | The blast furnace reduces iron ore to iron; a BOF then refines that iron into steel. | An electric arc melts and refines metallic inputs into steel. |
| Typical metallic inputs | Iron ore (sinter, pellets or lump ore), with coke, coal, limestone and some recycled steel in the integrated route. | Usually recycled steel scrap; DRI, hot metal or combinations can be added. |
| Main energy source | Coal and coke dominate the route’s energy input; electricity and natural gas are supplementary. | Electricity powers melting. Coal, natural gas and chemical energy vary with the charge and furnace practice. |
| Material pathway | Ore → hot metal (blast furnace) → crude steel (BOF) → finished products. | Scrap/DRI/hot metal → EAF steel → secondary metallurgy and finished products. |
| Typical emissions profile | Higher route emissions because carbon is used to reduce ore and supply heat. | Scrap-EAF is usually much lower-emitting; DRI-EAF retains emissions from making the DRI, and electricity generation adds indirect emissions. |
| What must be specified in a comparison | Include both blast-furnace ironmaking and BOF steelmaking, and state the system boundary. | State whether it is scrap-EAF or DRI-EAF, the charge mix and the electricity emissions factor. |
These definitions follow the World Steel Association’s descriptions of raw materials and production routes (raw-materials overview and climate and production page).
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1. Preparing ore and fuel
Iron ore is processed into a size and chemistry suitable for the furnace, commonly as sinter or pellets. Coke made from metallurgical coal provides both heat and a chemical reducing agent. Limestone and other fluxes help capture unwanted elements in a molten slag. Recycled steel may be added to the integrated route, but the route’s defining input is newly reduced ore.
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2. Reducing ore in the blast furnace
Hot air is blown through tuyeres near the furnace base. Coke combustion creates heat and carbon monoxide; the gas removes oxygen from iron oxides as the burden descends. Molten iron collects at the hearth, while slag absorbs gangue and flux constituents. The resulting hot metal contains more carbon and impurities than finished steel.
3. Refining in the basic oxygen furnace
The hot metal is transferred to a BOF, where high-purity oxygen is blown through the melt. Oxygen oxidizes excess carbon, silicon, manganese, phosphorus and other elements; scrap is commonly added as a coolant and metallic source. Fluxes form a refining slag. After sampling and temperature adjustment, the steel goes to continuous casting and rolling or other finishing operations.
Calling the blast furnace itself a “steel furnace” hides this sequence: the blast furnace makes iron, while the BOF makes crude steel. Energy and emissions comparisons must include both stages and the associated coke, sinter, transport and finishing operations when those are inside the chosen boundary.
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How an electric arc furnace makes steel
1. Charging the furnace
A roof-mounted bucket or conveyor charges prepared scrap into the vessel. A scrap-based shop may use obsolete products, manufacturing off-cuts and internally recycled returns. An EAF can also charge DRI or hot briquetted iron, hot metal from another furnace, or a deliberate blend. Therefore, “EAF” does not mean “100% scrap.”
2. Melting with electric arcs
Graphite electrodes are lowered into the charge and an arc is struck between the electrodes and the metal. The arc’s heat melts the burden; oxygen injection, carbon injection, burners and foamy slag practice improve thermal efficiency and protect the arc. Electricity is the dominant purchased energy input for a 100% scrap EAF, although auxiliary fuels and chemical energy are also used.
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3. Refining and tapping
Operators adjust chemistry with oxygen, carbon, alloys and slag-forming materials. Once temperature and composition meet the grade, the furnace is tapped into a ladle. Ladle metallurgy, vacuum treatment where required, continuous casting and rolling then determine much of the final product quality. EAFs can make a wide range of construction grades, but the ability to meet a specification depends on scrap cleanliness, dilution strategy, refining equipment and mill controls—not on the furnace label alone.
Why feedstock determines the EAF comparison
Scrap-EAF and DRI-EAF should be treated as separate pathways in carbon and energy calculations.
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Scrap-EAF
Scrap already contains iron in metallic form, so the furnace mainly supplies the energy to melt and refine it. This avoids the blast furnace’s ore-reduction step. Contaminants accumulated in scrap—such as copper or tin—can be difficult to remove, so sorting, dilution with clean iron units and tight chemistry control are important. Scrap availability also depends on the stock of steel products reaching end of life; it cannot expand instantly to satisfy every increase in demand.
DRI-EAF
DRI is made by removing oxygen from ore in a shaft furnace or similar reactor using a reducing gas. The DRI is then melted in an EAF, sometimes while hot. Because ore reduction still occurs upstream, DRI-EAF is not equivalent to scrap-EAF. Natural-gas DRI has a different footprint from hydrogen-based DRI, and the result changes with the electricity used in the EAF and the emissions assigned to hydrogen production.
Hot-metal EAF charging
Some plants combine an EAF with hot metal from a blast furnace or another ironmaking unit. This can increase productivity and dilute residual elements in scrap, but it also carries the upstream emissions of making that hot metal. A route description that says only “EAF” is incomplete unless the metallic charge is stated.
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Energy use: which route is more efficient?
For the common comparison of remelting scrap in an EAF with making new steel from ore through BF-BOF, the U.S. Department of Energy states: Remelting steel scrap in Electric Arc Furnaces (EAF) requires less than half the energy to make steel vs. production from iron ore using Blast Furnaces and Basic Oxygen Furnaces.
The statement is a general route comparison, not a guarantee for every plant or product grade (U.S. Department of Energy, Iron and Steel Manufacturing).
World Steel Association benchmarking data show the composition of energy inputs, not energy consumed per tonne:
| Route | Coal or coke share of energy inputs | Electricity share | Natural-gas share | How to read the figures |
|---|---|---|---|---|
| BF-BOF | 70–80% | 10–15% | 5–15% | Indicative route shares; they are not an energy-intensity value. |
| 100% scrap EAF | 5–15% | 50–70% | 10–25% | Indicative shares for a scrap route; actual values vary by plant and operating practice. |
See the World Steel Association’s energy-use page for the benchmark context. The percentages should not be confused with the DOE’s “less than half” energy comparison: one describes the mix of energy carriers, while the other compares total energy requirements for two production pathways.
Emissions: numbers, boundaries and what they mean
Route-level intensities
The U.S. International Trade Commission reproduces World Steel Association 2023 global-average sustainability indicators with these route-level intensities:
| Route | Reported intensity | Qualification |
|---|---|---|
| BF-BOF | 2.33 tCO2e per tonne of steel | 2023 global route average reproduced in USITC Publication 5584; retain the source year and route boundary. |
| Scrap-EAF | 0.68 tCO2e per tonne of steel | 2023 global route average reproduced in USITC Publication 5584; this is the scrap pathway, not every EAF. |
| DRI-EAF | 1.37 tCO2e per tonne of steel | 2023 global route average reproduced in USITC Publication 5584; upstream DRI emissions are included in the reported route context. |
The source is the U.S. International Trade Commission’s Publication 5584, which cites the World Steel Association’s 2023 Sustainability Indicators Report. These are global averages, not an EPD for a particular mill. An EPD may use a different product scope, allocation method, electricity factor, recycled-content rule or life-cycle module.
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Industry-wide average versus route average
World Steel Association reported an average of 2.18 tonnes of CO2e per tonne of steel in 2024, counting scopes 1, 2 and 3 across the reporting scope. That figure is an association-wide average, not the intensity of either BF-BOF or EAF alone (World Steel Association, 2025 reporting page). It should not be blended with the route-specific 2023 values as though the year and boundaries were identical.
Why EAF is not zero-carbon
An EAF has no ore-reduction emissions when it uses only metallic scrap, but it still consumes electricity. Emissions from generating that electricity are counted in the relevant indirect-emissions boundary. Electrode manufacture, fluxes, alloying additions, scrap preparation, transport and any DRI or hot metal in the charge can add further emissions. A low-carbon grid or verified low-emissions power procurement can materially improve a scrap-EAF’s footprint; a carbon-intensive grid narrows the advantage.
The American Iron and Steel Institute explains the role of electricity and charge materials in its steel-production overview. Always ask the mill for the product-specific EPD or verified emissions data when a construction specification sets a carbon limit.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Global scale, investment and the emerging DRI-EAF option
BF-BOF remains the dominant global route. The International Energy Agency says it accounts for about 70% of global steel production on its 2025 Breakthrough Agenda steel page (IEA, Steel—Breakthrough Agenda Report 2025). Existing integrated sites have large blast furnaces, coke ovens, sinter plants, BOFs and downstream mills; replacing that capital takes decades.
Hydrogen-based DRI feeding an EAF is an emerging lower-emissions option in regions with suitable ore, abundant low-emissions electricity and competitively priced hydrogen. The IEA estimates that early commercial plants using 100% hydrogen blends could cost 50–140% more than BF-BOF plants, with variation by region. That estimate applies to the described hydrogen-based DRI-EAF transition, not to EAFs in general and not to every future project. Natural-gas DRI, partial hydrogen substitution and scrap-EAF projects have different economics.
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Economics and operating constraints for construction supply
Feedstock and price exposure
- BF-BOF: costs track iron ore, coking coal, coke-making, limestone, carbon controls and the substantial fixed capital of an integrated site.
- Scrap-EAF: costs track regional scrap grades, collection and sorting, electricity, electrode consumption and alloy additions. Electricity price and peak-demand charges can be decisive.
- DRI-EAF: costs add the DRI plant and reducing gas or hydrogen, plus electricity for melting. DRI can provide a cleaner iron unit when high-quality scrap is scarce, but it is not a free substitute for scrap.
Product and quality considerations
Both routes can supply structural sections, plate, bar, wire rod and sheet when the mill’s equipment and quality system are designed for the grade. Construction buyers should specify the required standard, toughness, weldability, residual-element limits and certification rather than assuming route alone determines performance. For a project with a declared recycled-content or embodied-carbon target, request the heat or product documentation that supports the claim.
Reliability and regional availability
BF-BOF capacity is concentrated in large integrated complexes and can provide stable volumes of ore-based steel. EAF capacity is often more modular and can be built near scrap supplies or rolling mills, but it is exposed to local scrap availability and grid constraints. Neither route is automatically more reliable: the answer depends on the region, plant maintenance, energy contracts, transport and the product being ordered.
How to compare steel offers without misleading carbon claims
- Identify the route and charge. Ask whether the steel is BF-BOF, 100% scrap-EAF, DRI-EAF, or a mixed EAF charge. “Electric furnace” alone is insufficient.
- Define the accounting boundary. Confirm whether the figure covers scopes 1 and 2 only or also relevant scope 3 emissions, and whether it is cradle-to-gate or another life-cycle module.
- Check the year and geography. Emissions factors and grid intensity change. Record the reporting year, plant location and electricity assumptions beside the number.
- Request an EPD or verified plant data. Compare like-for-like product categories and standards; do not compare a global route average with a product-specific EPD without explaining the difference.
- Verify recycled-content language. “Contains scrap” does not mean 100% scrap, and a mass-balance or allocation claim may not describe the physical heat you receive. Ask how the percentage was calculated.
- Check technical compliance. Confirm grade, dimensions, tolerances, toughness, weldability, coating or treatment, mill test certificates and delivery schedule before selecting on carbon alone.
- Document assumptions in the project carbon model. Keep route, intensity, scope, year and source together so later substitutions do not silently change the baseline.
Common misconceptions
“A blast furnace makes steel and an EAF only melts scrap.”
The blast furnace makes iron that a BOF refines into steel. An EAF is a melting and refining furnace that can use scrap, DRI, hot metal or blends.
“Every EAF has the same carbon footprint.”
No. Scrap-EAF, natural-gas DRI-EAF and hydrogen DRI-EAF have different upstream emissions. Electricity generation and the charge mix can change the result substantially.
“The route with the lowest average is always best for a project.”
Average route values are useful for orientation, but a construction decision also requires the actual product’s grade, EPD boundary, delivery distance, availability and compliance documentation.
“Energy percentages tell me how many megajoules a tonne requires.”
They do not. World Steel Association’s coal, electricity and natural-gas figures are shares of route energy inputs. Total energy intensity requires a separate, explicitly defined measurement.
Practical verdict for construction professionals
If the comparison is between conventional ore-based BF-BOF and a well-supplied scrap-EAF using relatively low-emissions electricity, the scrap-EAF route normally has the advantage in energy use and greenhouse-gas intensity. The DOE’s less-than-half energy statement and the route averages reproduced by the USITC support that direction, while the exact result depends on boundaries and plant data.
Do not extend that verdict to every EAF. DRI-EAF includes ore reduction, and a carbon-intensive grid can raise an EAF’s indirect emissions. For procurement, the defensible question is: Which route and charge produced this specific steel, under which accounting boundary, in which year, and does it meet the project’s technical requirements?
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