What Is Steel? Composition, History, Manufacturing, and Types

Steel surrounds us: it frames the skyscrapers that mark the skyline of nearly every major city and forms the bodies of the vehicles we drive. So what exactly is steel, and how is it produced? In short, it is a strong alloy of iron and carbon, with carbon typically making up about 0.2% to 2.1% of the weight.

This article explores the science, history and technology behind steel — its composition, mechanical properties, the main manufacturing routes, the different grades available, and the enormous influence it has had on human progress.

What Is Steel?

Steel is an alloy of iron and carbon, normally holding between 0.04% and 2.0% carbon by weight. Other elements are frequently added to fine-tune its behaviour: manganese raises strength and wear resistance, chromium improves corrosion resistance, nickel adds toughness, and vanadium boosts strength.

The Effect of Carbon Content on Steel

Type of Steel	Carbon Content	Properties	Applications
Low-Carbon (Mild Steel)	<0.2%	Ductile, malleable and easily welded	Structural components, pipes and pipelines, machinery parts
Medium-Carbon	0.2 – 0.6%	Higher strength, still ductile, responds well to heat treatment	Automotive parts such as gears, axles and crankshafts
High-Carbon	0.6 – 1.5%	Very hard, maximum strength, good wear and corrosion resistance	Dies, machinery components and ball bearings

Raising the carbon content makes steel harder and stronger, but it also becomes less ductile and more brittle.

What Is the History of Steel?

Steel’s earliest origins were accidental. Blacksmiths discovered that iron heated in the presence of high-carbon material turned into a markedly stronger metal, and the technique spread by word of mouth through Turkey, Greece and neighbouring lands before reaching the Roman Empire. In those early days it was used mainly for tools and weapons.

Before the mid-19th century steel was expensive to produce and relatively uncommon. In 1751 Benjamin Huntsman devised the crucible method, melting blister steel to obtain a far higher-quality product.

The next milestone was the Bessemer process of 1856. Henry Bessemer’s converter forced air through molten pig iron, rapidly burning off impurities through oxidation. It was the first inexpensive way to mass-produce steel, and it opened the door to the material’s widespread use.

By the late 1800s the United States had become the world’s leading steel producer, with large-scale projects such as bridges, skyscrapers and steel-hulled ships. Progress continued into the 20th century, when the electric arc furnace made high-quality steel production economically viable.

How Is Steel Made?

Ironmaking in the Blast Furnace

• Raw Materials: Iron ore, coke (derived from high-carbon coal) and limestone.
• Combustion and Reduction: Hot air burns the coke to generate carbon monoxide, which reduces the iron ore to molten iron, known as pig iron.
• Fluxing: The limestone binds impurities into a slag that floats on the molten iron, making it easy to skim off.
• Tapping: The molten iron and slag are drawn off, ready for the steelmaking stage.

Steelmaking Route A: Basic Oxygen Furnace (BOF)

• Raw Materials: Molten iron from the blast furnace together with scrap steel.
• Oxygen Blowing: Pure oxygen is blown in, oxidising impurities such as carbon, silicon, phosphorus and sulfur, which leave as gases or enter the slag.
• Refining: Other elements are added to reach the desired properties.
• Tapping: The steel is poured into moulds, where it cools and takes shape for further processing.

Steelmaking Route B: Electric Arc Furnace (EAF)

• Raw Materials: Mainly scrap steel, sometimes supplemented with direct-reduced iron or pig iron.
• Melting: Electric arcs between graphite electrodes melt the scrap rapidly.
• Refining: Oxygen and fluxes remove impurities and adjust the composition.
• Tapping: The steel is poured out, cooled and shaped into forms.

BOF vs EAF at a Glance

Feature	BOF Route	EAF Route
Main Raw Materials	Iron ore, coke, limestone	Scrap steel, DRI, pig iron
Process	A high-velocity jet of pure oxygen oxidises and removes impurities such as carbon from the molten iron	High-power electric arcs melt the scrap steel
Energy Source	Chemical reaction	Electricity
Flexibility	Less flexible, large scale	Highly flexible, scalable

Secondary Steelmaking and Shaping

• Ladle Metallurgy: Fine-tuning the temperature and composition of the melt.
• Continuous Casting: Molten steel is cast into billets, blooms and slabs for downstream processing.
• Finishing: Hot and cold rolling, coating, machining and fabrication turn the semi-finished steel into finished products.

The Mechanical Properties of Steel Explained

Steel is widely used across industry because of its mechanical properties, which shift with the alloying elements. It is simultaneously strong and comparatively lightweight, yet stiff, ductile, rigid and easy to weld.

• Corrosion Resistance: The right grade keeps its integrity in harsh environments without rusting.
• Ductility: The ability to deform under tensile stress without fracturing.
• Hardness: Resistance to dents, scratches and wear; heat treatment can tailor hardness for specific uses.
• Strength: High tensile, compressive and shear strength make it ideal for load-bearing structures, machinery and tools.
• Weldability: Steel components join easily through welding.

What Types of Steel Are There?

Steel comes in many grades, each with its own properties and uses. The main families are:

• Carbon Steel: Strong and durable, cheap and easy to produce, with varying carbon content.
• Stainless Steel: Contains chromium, giving excellent resistance to rust and corrosion.
• Alloy Steel: Alloying elements such as nickel, chromium or molybdenum create stronger steel that withstands wear.
• Tool Steel: Remains hard and strong even at elevated temperatures.
• Electrical Steel: Optimised for electromagnetic devices, offering better efficiency and lower energy loss.
• High-Strength Low-Alloy (HSLA) Steel: An excellent strength-to-weight ratio with improved weldability and enhanced corrosion resistance.
• Steel Superalloys: Exceptional resistance to corrosion, oxidation and fatigue, capable of withstanding extreme temperatures.

FAQs

What exactly is steel?
Steel is an alloy of iron and carbon, typically containing 0.04–2.0% carbon by weight, with other elements sometimes added to adjust its properties.

Does steel rust?
It can rust, but how quickly depends on the grade of steel and the environment. Regular maintenance and protective coatings help prevent or slow corrosion.

Is steel magnetic?
Yes — steel is attracted to magnets, a property that comes from the iron in its composition.

Which industries use steel?
Steel is used in construction, automotive, aerospace, machinery and infrastructure development, among many other sectors.

Which SHBD Metal capabilities work with steel?
At SHBD Metal, precision CNC machining and sheet metal fabrication both process steel parts.