A steel containing various percentages of carbon.  The classification “carbon steel” is generally accepted  for all commercial irons and plain steels. Low-carbon

steel is defined as having a maximum of 0.15% carbon  content. Mild steel is described as having 0.15 to  0.35% carbon. Medium-carbon steel contains 0.35 to 0.60% carbon, and high-carbon steel contains from 0.60 to 1.0% carbon.

Carbon primarily controls the response of steel to  hardening heat treatments; however, other alloying  elements such as manganese, silicon, sulfur, and copper may be added. These elements may impart properties to the steel that are also important.