The strength of carbon steel is affected by many factors, some of which deal with how the steel is alloyed and others that deal with what happens after the steel is created. One of the main factors affecting the strength of carbon steel is the amount of carbon added to iron before steel is made, because carbon serves both to create and to harden steel. While carbon steel typically does not have much of any other elements included in the steel alloy, these inclusions can change the strength, hardness and other attributes of steel. After the steel is alloyed, it then can be subjected to heat, which can increase its strength.
Carbon steel is a type of steel that generally contains a low amount of carbon, but there are some grades that have more carbon than others. A large factor in determining the strength of carbon steel is the amount of carbon itself. This is needed to make steel in the first place, and it is heated along with iron until the two melt and merge into one another. Carbon is a hardener, so more carbon means stronger and harder steel. While tempering will be able to strengthen the steel more after it is made, carbon often dictates the total hardness of steel.
Inclusions are uncommon in carbon steel, unlike some other types of steel alloys, but even a small amount of other metals has the capability of changing the strength of carbon steel. These metals are added in when the steel is being alloyed; otherwise, the steel has to be melted down later for these metals to be introduced. Most metals, such as manganese, phosphorus and nickel, are added to carbon steel to increase its strength. Other metals, such as lead and copper, weaken steel but can help make it easier to machine or weld, which can be beneficial.
Most steel is heat-treated after it is alloyed to help increase the strength of carbon steel, though the steel sometimes is used as is. There are many different methods available for tempering steel, and each serves to increase different attributes. The steel commonly is placed in a furnace or similar area, where the steel is heated enough to make it a blue color but not enough to melt it. After repeating this process several times, the strength of carbon steel tends to dramatically increase.