Steel is made of iron and a small amount of carbon, under 2% by weight, plus around 1% manganese and traces of silicon, phosphorus, sulfur and oxygen. The iron comes from iron ore or recycled steel scrap. Other elements such as chromium and nickel are added on purpose to make special grades like stainless steel.
Those small additions matter a lot. A fraction of a percent of carbon is the difference between soft iron and a structural beam. This guide covers what goes into steel, how it is made in the US today, and what the ingredients change.
The Basic Recipe: Iron Plus Carbon
The World Steel Association defines steel as an alloy of iron and carbon containing less than 2% carbon and 1% manganese, with small amounts of silicon, phosphorus, sulfur and oxygen (worldsteel “About steel”, checked October 2026). It also says there are more than 3,500 grades of steel, each with different physical, chemical and environmental properties.
| Ingredient | Typical amount | What it does |
|---|---|---|
| Iron (Fe) | The balance, by far the largest share | The base metal |
| Carbon (C) | Less than 2% | Raises strength and hardness; too much makes it brittle and harder to weld |
| Manganese (Mn) | Around 1% | Adds strength and helps deal with sulfur during steelmaking |
| Silicon, phosphorus, sulfur, oxygen | Small amounts | Silicon helps remove oxygen; phosphorus and sulfur are mostly impurities kept low |
| Chromium, nickel, molybdenum and others | Only in alloy grades | Corrosion resistance, toughness, heat resistance |
Where the line sits between steel and cast iron is about carbon. The Los Alamos National Laboratory periodic table notes that cast iron contains 3-5% carbon, compared with under 2% for steel. That extra carbon is why cast iron is hard but brittle. A cast iron pipe can crack if dropped, while a steel beam bends and yields first.
Where the Iron Comes From
Steel is made by two main routes, and both can use recycled scrap. The American Iron and Steel Institute describes them on its steel production page (checked October 2026).
Blast furnace and basic oxygen furnace (BF-BOF)
This is the integrated route that starts from ore. A blast furnace melts iron ore with coke (a fuel made from metallurgical coal) and limestone to make molten pig iron. Pig iron has too much carbon to be steel. It goes to a basic oxygen furnace with some recycled scrap, and oxygen blown through the melt burns off the extra carbon.
Electric arc furnace (EAF)
An electric arc furnace melts mostly scrap steel with electric current. It can also take direct reduced iron or pig iron. worldsteel notes that the EAF route can run on recycled steel alone. These plants are often called minimills.
In the US, the electric route now dominates. The USGS Mineral Commodity Summaries 2026, Iron and Steel chapter reports:
- About 82 million metric tons of raw steel made in the US in 2025 (estimated).
- EAF steel made by 47 companies at 102 minimills.
- Integrated mills, the blast furnace route, at about 28% of domestic steel production.
- Construction as the largest market, at an estimated 31% of net shipments.
So most American steel, including most structural shapes, starts as melted scrap rather than fresh ore. Steel does not lose its basic properties when it is remelted, which is why it recycles so well.
From Liquid Steel to a Beam
Once the chemistry is right, the liquid steel is cast. USGS reports that 99.7% of US raw steel is continuously cast into semi-finished pieces. Those are then rolled. Structural shapes like W-beams, channels and angles are hot rolled, which leaves the dark oxide skin called mill scale. Thinner sheet and some bar is cold rolled afterward for tighter tolerances and a smoother surface. Our comparison of hot rolled vs cold rolled steel covers what each process does to the finished product.
If you want to see the shapes that come out of the rolling mill, the types of steel beams guide walks through W, S, HP, channel and angle sections.
How the Ingredients Change the Steel
Carbon steels
Most steel in buildings is plain carbon steel with modest carbon and manganese. Keeping carbon low makes the steel ductile and weldable, which matters more in a frame than raw hardness. Higher-carbon steels are used for tools, springs and wear parts. They are harder but need more care, such as preheat, when welded.
Structural grades
Structural steel is ordered to an ASTM specification that caps the chemistry and sets minimum strength. Wide flange beams in the US are mostly rolled to ASTM A992. Our page on ASTM A992 vs A572 Grade 50 explains what those two specs require and why A992 replaced older grades for W-shapes.
Alloy and stainless steels
Adding other elements changes the steel’s behavior. worldsteel notes that nickel and chromium are added to make stainless steel, which helps prevent rust. Small amounts of copper, chromium and nickel produce weathering steel, which forms a protective rust layer outdoors. See where weathering steel works and where it fails. If you are choosing between a stainless part and a coated carbon steel part, our galvanized vs stainless steel comparison covers the trade-offs.
Steel vs Iron vs Other Metals at a Glance
| Material | Made of | Typical use in building |
|---|---|---|
| Wrought or pure iron | Iron with almost no carbon | Historic ironwork; rarely produced today |
| Carbon steel | Iron, under 2% carbon, about 1% manganese | Beams, columns, rebar, plate, decking |
| Stainless steel | Steel with chromium and nickel added | Railings, fasteners, exposed or wet locations |
| Cast iron | Iron with 3-5% carbon | Pipe, valves, older columns |
| Aluminum | A different metal, not iron-based | Light framing, trim, aluminum I-beams |
Why It Matters When You Buy or Build
- Ask for the grade, not just “steel.” Two beams with the same dimensions can have different strengths if they are rolled to different specs. The mill test report lists the actual chemistry and strength.
- Old steel is not the same as new steel. Beams in older buildings may be an older grade, or even cast or wrought iron. An engineer has to identify the material before any new load is added.
- Chemistry affects welding. Higher carbon and alloy content raise the risk of cracking without the right procedure.
Composition is only one input to a design. A licensed structural engineer has to size and check any steel member that carries load, using its grade, section properties and the actual loads.
What Is Steel Made Of: FAQ
What are the two main ingredients of steel?
Iron and carbon. Steel is iron with less than 2% carbon, usually with about 1% manganese and small amounts of other elements.
Is steel a metal or an alloy?
Both. It is a metal alloy: a mixture of iron, the metal, with carbon and other elements.
What is the difference between steel and iron?
Carbon content. Steel holds under 2% carbon, while cast iron holds roughly 3-5%. The lower carbon makes steel tougher and able to bend instead of cracking.
Is most steel made from recycled scrap?
In the US, yes. Most is made in electric arc furnaces that melt mainly scrap. USGS puts integrated blast furnace mills at about 28% of domestic production. Both routes use some scrap.
What is stainless steel made of?
Iron and carbon like other steels, with chromium and usually nickel added. The chromium forms a thin protective film on the surface that resists rust.
Reference information only, not engineering advice. Disclaimer.