the industrial study of metal alloys is a large part of materials science. of all the metallic alloys in use today, the alloys of iron (steel, stainless steel, cast iron, tool steel, alloy steels) make up the largest proportion both by quantity and commercial value. iron alloyed with various proportions of carbon gives low, mid and high carbon steels. an iron carbon alloy is only considered steel if the carbon level is between 0.01% and 2.00%. for the steels, the hardness and tensile strength of the steel is related to the amount of carbon present. increasing carbon levels leads to lower ductility and toughness. heat treatment processes such as quenching and tempering can significantly change these properties however. cast iron is defined as an iron-carbon alloy with more than 2.00% but less than 6.67% carbon. stainless steel is defined as a regular steel alloy with greater than 10% by weight alloying content of chromium. nickel and molybdenum are also found in stainless steels.