Cast Iron Metallurgy

Cast iron (CI) is one of the oldest materials in commercial use. It has excellent compressive strength and is commonly used for structures that require this property, as well as for water and sewer lines. This article explains CI metallurgy and why the understanding of this metallurgy is key to understanding other ferrous materials and alloys. The composition of cast iron (CI) varies significantly depending upon the grade of pig iron used in its manufacture. CI contains carbon in the range of ~2 to 4 wt%. The mode and concentration of carbon in the CI is controlled to produce various grades of CI, which differ significantly in their mechanical properties and weldability. The carbon equivalent (CE) of a CI helps to distinguish the gray irons, which cool into a microstructure containing graphite, and the white irons, where the carbon is present mainly as cementite. The CE is defined in Equation (1).