The term carbon steel may also be used in reference to steel which is not stainless steel; in this use carbon steel may include alloy steels. High carbon steel has many different uses such as milling machines, cutting tools (such as chisels) and high strength wires. These applications require a much finer microstructure, which improves the toughness.
Carbon steel is a popular metal choice for knife making due to its high amount of carbon, giving the blade more edge retention. To make the most out of this type of steel it is very important to heat treat it properly. If not the knife may end up being brittle, or too soft to hold an edge.