Metal Profile: Steel

Steel, the world's foremost construction material, is an iron alloy that contains between 0.2% and 2% carbon by weight and sometimes small amounts of other elements, including manganese. In addition to buildings, it is used in the manufacture of appliances, cars, and airplanes.

History

The advent of commercial steel production came in the late 19th century and was a result of Sir Henry Bessemer's creation of an efficient way to lower the carbon content in cast iron. By lowering the amount of carbon, the much harder and more malleable metal product of steel is produced.

Steel has been around since the Iron Age, which lasted from about 1200 BCE to 550 BCE, though beginning and end dates vary by geographical area. The Hittites—who lived in modern-day Turkey—may have been the first people to create steel by heating iron with carbon.

Production

Today, most steel is produced by basic oxygen methods (also known as basic oxygen steelmaking or BOS). BOS derives its name from the process that requires oxygen to be blown into large vessels containing molten iron and scrap steel.

Although BOS accounts for the largest share of global steel production, the use of electric arc furnaces (EAFs) has been growing since the early 20th century and now accounts for about two-thirds of U.S. steel production. EAF production involves melting scrap steel with an electrical current.

Grades and Types

According to the World Steel Association, there are over 3,500 different grades of steel, encompassing unique physical, chemical, and environmental properties. These properties include density, elasticity, melting point, thermal conductivity, strength, and hardness. To make different grades of steel, manufacturers vary the types and quantities of alloy metals, the amounts of carbon and impurities, the production process, and the manner in which the resulting steels are worked.

Commercial steels are also generally classified into four groups that differ according to their metal alloy content and end-use applications:

1. Carbon steels include low carbon (less than 0.3% carbon), medium carbon (as much as 0.6% carbon), high carbon (as much as 1% carbon), and ultra-high-carbon (as much as 2% carbon) steels. Low carbon steel is the most common and the weakest of the three types. It's available in a wide array of shapes, including sheets and beams. The higher the carbon content, the more difficult the steel is to work with. High carbon and ultra-high-carbon steels are used in cutting tools, radiators, punches, and wires.
2. Alloy steels contain other metals such as aluminum, copper, or nickel. They may be used in auto parts, pipelines, and motors.
3. Stainless steels always contain chromium and maybe also nickel or molybdenum. They are shiny and generally resistant to corrosion. The four main types of stainless steel are ferritic, which is similar to carbon steel and strongly resistant to stress corrosion cracking but is not good for welding; austenitic, which is the most common and good for welding; martensitic, which is moderately resistant to corrosion but high in strength; and duplex, which consists of half ferritic and half austenitic steels and is stronger than either of those two types. Because stainless steels are easily sterilized, they are often used in medical equipment and instruments and food production equipment.
4. Tool steels are alloyed with hard metals such as vanadium, cobalt, molybdenum, and tungsten. As their name suggests, they are often used to make tools, including hammers.

Additional Uses

Steel's versatility has made it the most widely used—and most recycled—metal material on Earth. In addition, its high strength and relatively low production cost make it suitable for use in countless applications, including in railways, boats, bridges, cooking utensils, packaging, and electrical transformers.