Chemical symbol C, atomic weight 12, atomic number 6
We all know what carbon is, that it exists as charcoal, coal, coke, and after millions of years under extreme pressure, diamonds. But for the most part it’s a dirty, messy, shapeless mass that seems good for nothing apart from being burned or reducing iron ore to iron. Admittedly, throughout most of the world, it’s used to generate electricity. The fact is it’s the very basis of steel, together with iron, and more than any other element controls the properties of steel.
Carbon may be a shapeless mass, but it exists in steel as a compound of iron and carbon known as iron carbide. A basic carbon steel consists of pure iron – otherwise known as ferrite – and iron carbide. Ferrite is soft, iron carbide is hard, hence the more carbon in steel the more iron carbide and the harder the steel. So, we’d expect a steel with 0.20% carbon, in say the forged condition, to be harder than a steel with 0.08% carbon in the same condition, and we’d be right to expect that. We know from this example that if we want a structural steel with a higher hardness, as opposed to a mild steel, we’ll choose a steel with say 0.20/0.25% carbon, even higher. Steels that are required to hold a cutting edge, cutlery or shears for example, we’ll opt for a steel with up to 1% carbon, in some cases slightly higher.
The Role Of Carbon In Steel
It should be mentioned here that carbon alone is not responsible for many of steels’ properties, and that a good number of alloying elements all have their parts to play in the steel story. Carbon effectively controls the hardness of steel, and for the most part, the other elements are its chemical partners. Once carbon is in steel, particularly higher carbon steels, it’s important to keep it there. When steels are heated to high temperatures in a non-protected atmosphere, the carbon at the steel surface is oxidized away leaving a layer denuded in carbon, hence much softer, less wear-resistant than the general body of the steel. Certain steels undergo a carburizing treatment whereby the carbon content of the steel surface is increased. This increases surface hardness, at the same time retaining lower carbon, hence lower hardness and greater toughness in the body of the steel.
Years and years of experience have demonstrated the effects of carbon on the subsequent properties and uses of the thousands of grades of this startlingly impressive alloy we call steel. But it’s not the carbon alone that leads the way here, rather the effect that the percentage of carbon has during hot working and heat treatment of the steels. That’s another chapter in this interesting story of carbon and steel.
All Metals & Forge Group carries several common carbon steels, such as 1020, 1025, 1045, and 1060 for open die forgings and seamless rolled ring manufacturing. Carbon steel is used in a variety of industries for many forged part shapes.
