We all use steel
Steel is a material that people in the modern world encounter every day. Steel is known for its strength
, and stiffness
. This unique combination of properties makes it ideal for building vehicles, structures, and tools. However, steel’s contribution to our world does not just stop there. You can find steel in countless household items including refrigerators, microwaves, paper clips and even the cans you might buy food in at the grocery store. Because of its wide-ranging uses, 1.3 billion tons of steel is produced every year. That is enough to make 21 trillion steel food cans, which, if stacked on top of one another, could reach the moon and back 7,000 times! Together, we will explore the chemistry of steel and find out why this material has such useful properties.
Steel’s key properties are strength, toughness, and stiffness
Steel is more than just a gray, shiny metal. It is also strong, tough and stiff — a combination of properties
that makes steel ideal for many uses. When describing the properties of a material, the words strong, tough, and stiff have particular meanings. Let’s look at these properties one by one.
If a material has the property of being strong
, that means it can stand up to a lot of force. You exert a force on an object by either pushing or pulling on it. If you push on an object, it is under compression. If you pull on an object, it is under tension. Steel is strong under both tension and compression. Its strength makes steel an ideal material for things that have to support a lot of weight, like the columns and beams used in construction.
If a material is tough
, it can deform, or permanently change shape, without fracturing or breaking. With materials, the opposite of being tough is being brittle. A brittle material will break without first deforming under stress. A material can be strong and tough, like steel, or strong and brittle like a ceramic mug. A ceramic mug is strong. For example, you can put a lot of heavy items on top of a ceramic mug and it won’t break. But if you accidentally knock it off a counter, it will probably break when it hits the floor. A mug made out of steel, on the other hand, will not break if you knock it off the counter, although it might get a dent in it. This ability to deform without breaking makes steel handy for things like camping mugs and dishes. Toughness is also a critical property for things like car frames, which are designed to crumple to protect passengers. Toughness is also the property that makes steel an ideal material for things like staples, which are designed to bend and then hold that shape.
If a material is stiff
, it is not very stretchy. With materials, the opposite of being stiff is being flexible. If something is very flexible, that means it’s going to stretch under pressure, like when you pull on a rubber band. A material can be strong and stiff, like steel, or strong and flexible, like rubber. Rubber might be able to support a lot of weight, but you would not want to use it to build a bridge. A rubber bridge would bend under the weight of its users and maybe even under the force of just its own weight. Steel, on the other hand, is ideal for building large structures like bridges because it can support the force of the weight of its users without stretching down. Strong, tough and stiff, steel has a unique combination of properties, making it an ideal material for a wide range of uses, from staples to bridges.
Carbon makes steel strong and tough
Steel is an alloy
, which is a material made up of a metal plus something else. That something else can be another metal or can be nonmetal. The two key elements of steel are iron, a metal, and carbon, a nonmetal. There are different types of steels, which depend on the amount of carbon and other elements present in the alloy. To understand steel’s behavior, we must look more closely at iron and carbon.
Steel is mostly iron, with a very small amount of carbon. Yet, thanks to carbon, steel can be 1,000 times stronger than pure iron! Adding carbon to iron makes steel stronger and tougher, but only up to a point. Iron with too much carbon will be strong, but instead of being tough, it will turn brittle
. Different types of steel contain different amounts of carbon. An engineer, builder, or manufacturer must use the type of steel that has the right amount of carbon and therefore the right amount of strength and toughness for what she is building.
The other elements in steel also affect steel’s properties
Although all steels contain carbon and iron, some steels also contain other elements that affect the steel’s properties. Many steels contain the elements nickel, manganese, chromium, and vanadium, which change the properties of the steels. For example, by adding a large amount of chromium, stainless steel can be made. Stainless steel has a very shiny finish and is highly resistant to corrosion
, a gradual wearing away of a material. Stainless steel is used to make jewelry, silverware, surgical instruments, and other objects where the finish and non-corrosive attributes of stainless steel are desired. Stainless steel has even been used on the outside of some of the world’s tallest skyscrapers!
Steel has only been in wide usage for less than 200 years
Steel made its earliest appearance around 1800 BCE. Ancient Rome, Greece, India, and China all used steel. In ancient times, steel was largely used for making weapons. Since steel is strong and can bend without breaking, a steel sword could be used in a sword fight without snapping. However because the methods used to manufacture steel were not very advanced, steel was not widely used prior to the 1800s.
Although steel was known in the ancient world, it started becoming widely used in the late 1800s. In 1856, Henry Bessemer patented the Bessemer process for manufacturing steel, which revolutionized the steel industry. The Bessemer process allowed steel to be mass-produced at low costs.
Today’s steel manufacturers can precisely control the amount of carbon in steel
To start the steelmaking process, iron must first be extracted from iron ore. An ore is a natural formation like a rock, which is partly made up of a mineral like iron. The process of getting a mineral out of rock is called smelting. When iron ore is smelted, the result is iron in a metallic form. This iron contains a high amount of carbon from the smelting process. But remember, the alloy of iron and carbon is only considered steel if the alloy has a particular range of carbon, typically under about 2%. Too much carbon and the metal will be brittle and therefore not steel. So the second step of making steel is to reduce the amount of carbon in the iron to the desired amount. Carbon is removed by blowing oxygen through molten, or melted, iron. The melting point of iron is 2800 °F (1538 °C), so the steelmaking process requires some pretty intense heat.
Today’s steel manufacturers are able to control exactly how much carbon remains in the steel. Thus, they can make different steels for almost any project and know precisely how each steel will behave. Whether we need steel with a tiny percentage of carbon for making car bodies or a steel with a larger percentage of carbon for making tools, steel manufacturers have the ability to produce it.
Steel is a defining material of the modern world
From eating with stainless steel utensils, to driving around in vehicles built with steel parts, to going to school or work in buildings made with steel columns and beams, we benefit from steel every day. The ability to cost-effectively manufacture high-quality steel, with its unique combination of strength, toughness and stiffness has been critical to the development of our modern world. Our lives would simply not be the same without it.