Chemical composition of steel – the influence of carbon

The chemical composition of steel is what defines the properties of steel. Based on this characteristic, the different grades of steel are differentiated.

Steel in general is an alloy of carbon and iron, but it contains many other elements. Some of these are retained from the steelmaking process, while other elements are added to produce specific properties.

The most common chemical elements in the chemical composition of steel, besides iron, are: carbon, manganese, silicon, phosphorus, sulfur, chromium, molybdenum, nickel, aluminum, and vanadium.

Each element added to the base composition of steel has certain effects on the properties of steel and how it reacts to manufacturing processes.

The carbon content ranges between 0.02% and 2.11%.

Chemical composition of steel – the influence of carbon

Carbon is the most important element in steel. It is essential in steels that need to be hardened through quenching, and the carbon grade controls the hardness and strength of the material, as well as its response to heat treatment (hardenability).

The carbon content ranges between 0.02% and 2.11%.

Ductility, forgeability, and machinability will decrease if the carbon amount increases, as will the welding properties of steel.

The higher the carbon content of steel, the greater the hardness, strength, and wear resistance after heat treatment. Hardness and strength increase proportionally as the carbon content rises up to approximately 0.85%.

As the carbon content of steel increases, the yield strength and tensile strength increase, but the plasticity and impact properties decrease. In addition, carbon can increase the steel's sensitivity to heat and aging.

Also, when the carbon content exceeds 0.23%, the welding performance of the steel will deteriorate.

Based on carbon content, we can make the following classification:

• low-carbon steel, up to 0.3% carbon;

• medium-carbon steel, between 0.3 and 0.6% carbon;

• high-carbon steel, between 0.6 – 1% carbon;

• very high-carbon steel, 1 – 2%.

Compared to other elements found in steel (with the exception of boron), small variations in carbon content can radically change its properties and uses.

Thus, if the steel has a carbon content lower than 0.7% C, it can be used as construction steel. On the other hand, if the carbon content exceeds this value, it can be used as tool steel.