Steel

Steel is an alloy made from iron and carbon. It is stronger and more useful than pure iron, so it is used everywhere. You can find steel in buildings, bridges, cars, ships, trains, tools, and many other everyday items.

The amount of carbon in steel changes how it works. For example, stainless steels contain chromium and do not rust easily. Other types of steel are coated with zinc to keep them safe from weather damage.

People have been making steel for thousands of years, but it became widely used after new, better ways of producing it were invented in the 17th century. Today, China makes more steel than any other country. Even though making steel uses a lot of energy, it is also one of the most recycled materials in the world.

Definitions and related materials

See also: Steel grades

The word "steel" comes from an old word meaning "made of steel" or "standing firm."

Steel is made mostly of iron with a little bit of carbon, usually between 0.02% and 2.14%. Sometimes other elements like manganese, nickel, chromium, and others are added to change how strong or flexible the steel is. These extra elements make what we call alloy steel.

When iron is melted with coke or charcoal, it becomes pig iron, which has too much carbon. To make it into steel, the carbon level is lowered by blowing oxygen through the melted iron. Today, we can check the exact ingredients of steel using special tests.

In the past, steel was poured into blocks called ingots. Now, steel is usually made continuously and shaped right away into things like sheets, bars, or I-beams.

See also: List of countries by steel production

Material properties

Iron is found in the Earth as a rock called an ore, such as magnetite or hematite. We get iron from iron ore by heating it with carbon. This process is called smelting and was first used for metals that melt more easily, like tin and copper. As ways to make heat better were invented, we could make iron with more carbon in it.

Steel’s qualities depend on how much carbon and iron it has. At room temperature, pure iron is soft and can only hold a very small amount of carbon. When steel with about 0.8% carbon cools, it forms layers called pearlite, which makes steel strong. Cooling it faster makes martensite, a hard but breakable form of steel. Heating and cooling methods like annealing, quenching, and tempering help change steel’s qualities, making it stronger or more bendable when needed.

History

Main articles: History of ferrous metallurgy and History of the steel industry (1850–1970)

Steel has been known for thousands of years and was made in special furnaces. The earliest pieces of steel come from a site in Anatolia that is almost 4,000 years old, from around 1800 BC.

Wootz steel was made in Southern India and Sri Lanka as early as the first millennium BC. People in these areas used wind to power their furnaces, making steel with a lot of carbon. In Britain, steel was made from 490 to 375 BC, and in the Netherlands from the 2nd to 4th centuries AD. The Roman writer Horace wrote about steel weapons in the Iberian Peninsula, and the Romans used a type of steel called Noric steel.

The Chinese made steel during the Warring States period (403–221 BC) and the Han dynasty (202 BC – AD 220). They mixed melted iron with cast iron to make steel. There is evidence that a type of steel called carbon steel was made in Tanzania by the ancestors of the Haya people as long ago as 2,000 years.

Main articles: Wootz steel and Damascus steel

Wootz steel was made in parts of South Asia like Tamil Nadu, Telangana, and Karnataka in India, and in Sri Lanka. This steel was famous for being strong and keeping a sharp edge. It was exported around the world and was called the best steel of its time.

The method of making steel was passed from South India to Sri Lanka by about the 5th century AD. In Sri Lanka, they used wind furnaces to make high-carbon steel.

Since the 1600s, steel has been made by heating iron ore in a special furnace called a blast furnace. At first, charcoal was used, but later, coke became the common material because it was cheaper.

In the 1800s, new ways to make steel were invented, such as the Bessemer process in 1855. This process made it cheaper to produce steel in large amounts. Later, other methods like the Gilchrist-Thomas process and the Siemens-Martin process were developed. Today, most steel is made using the basic oxygen steelmaking method, which is faster and makes cleaner steel. Another common way to make steel today is using electric arc furnaces, which melt down old metal to make new steel.

Industry

See also: History of the steel industry (1850–1970), History of the steel industry (1970–present), Global steel industry trends, Steel production by country, and List of steel producers

The steel industry shows how strong a country's economy is because steel is needed to build many things. In 1980, more than 500,000 people worked in steel factories in the United States. By 2000, this number fell to 224,000.

Big growth in places like China and India increased the need for steel. Between 2000 and 2005, the world needed 6% more steel. Large steel companies in India and China grew to meet this demand, like Tata Steel, which bought Corus Group in 2007, and others such as Baosteel Group and Shagang Group. As of 2017, ArcelorMittal was the largest steel maker in the world.

In 2005, China made the most steel, about one-third of all the steel in the world. Japan, Russia, and the United States were next. By the end of 2008, the steel industry had a hard time and needed to reduce work. Making steel can also harm the environment, creating about 7% of the world's greenhouse gases as of 2024. Some ways to help reduce these gases include using hydrogen instead of coal, recycling more steel, and using carbon capture and storage technology.

Recycling

Main article: Ferrous metal recycling

Steel is one of the most recycled materials in the world. A lot of steel is recycled everywhere.

Even though more steel is made than recycled, a big part of the steel produced comes from recycled materials.

Contemporary

See also: Steel grades

Carbon

Main article: Carbon steel

Modern steel is made with different mixes of metals for many uses. Carbon steel, made from iron and carbon, is 90% of all steel made. Low alloy steel has extra elements like molybdenum, manganese, chromium, or nickel to stay strong in thick pieces. High strength low alloy steel adds small amounts of manganese to make it stronger without costing more.

New rules about saving fuel created a special steel called Advanced High Strength Steel (AHSS). This steel is strong and flexible, so car parts can be safe but use less material. There are different kinds of AHSS, like dual-phase steel, which is treated with heat to be easy to shape and very strong.

Carbon steels are often coated with zinc to stop rust. This coating can be put on by dipping the steel in hot zinc or using electricity.

Alloy

Main article: Alloy

Stainless steel has at least 11% chromium, often with nickel, to resist rust. Some stainless steels can be pulled by a magnet, while others cannot.

Alloy steels are basic steels with small amounts of extra elements like chromium and vanadium. Some newer steels, called tool steels, have large amounts of tungsten and cobalt to keep their edges sharp and lasting long. These are used in tools like axes and drills. Other special steels, like weathering steels, form a protective rust layer and can be used without painting. Maraging steel is made with nickel and other elements but has very little carbon, making it very strong yet easy to shape.

Some steels are made for special jobs. Eglin steel uses many different elements to make a low-cost steel for strong weapons. Hadfield steel, named after Robert Hadfield, contains manganese that hardens when rubbed, making it great for parts that need to wear well, like tank tracks or bulldozer blades.

Standards

Most common steel types are grouped into different grades by groups that set rules. The Society of Automotive Engineers has grades for many steels used in cars. The American Society for Testing and Materials has its own set of rules, including for A36 steel, the most used building steel in the United States. The JIS sets rules for steel grades used a lot in Japan and nearby countries.

Uses

Iron and steel are used in many places, like roads, railways, and buildings. Big structures such as stadiums, bridges, and airports depend on steel for support. Even buildings made of concrete use steel to make them stronger. Steel is also found in major appliances and cars. Even though aluminium is used more now, steel is still the main material for car bodies. It is also used to make bolts, nails, screws, and many household items.

Steel is used in many other ways, such as in shipbuilding, pipelines, mining, and offshore construction. It is also important in aerospace, in white goods like washing machines, heavy machines like bulldozers, office furniture, steel wool, tools, and for protection like vests and helmets.

Before modern ways of making steel were invented, it was expensive and only used for special things like the edges of knives, razors, swords, and springs in clocks and watches. Today, steel is easier to make and cheaper, so it is used for many more things. Some items now use plastics instead of steel because they are lighter and cheaper to make. Carbon fibre is also starting to replace steel in some places because it is stronger, but it costs more.

Steel is used in many forms:

• As reinforcing bars and mesh in reinforced concrete
• Railroad tracks
• Structural steel in modern buildings and bridges
• Wires
• Input to reforging applications

• Major appliances
• Magnetic cores
• The inside and outside body of automobiles, trains, and ships.

Weathering (COR-TEN)

Main article: Weathering steel

• Intermodal containers
• Outdoor sculptures
• Architecture

Stainless

Main article: Stainless steel

See also: List of applications of stainless steel

• Cutlery
• Surgical instruments
• Watches
• Rail passenger vehicles
• Jewellery
• Components of spacecraft and space stations

Low-background

Main article: Low-background steel

Steel made after World War II can have small amounts of radioactive material because of testing of nuclear weapons. Steel made before 1945 is used in special tools like Geiger counters and for protecting against radiation.