What is ductile iron?
Although chemically similar to Gray Iron of low phosphorous content, Ductile Iron incorporates significant casting refinements, additional metallurgical processes, and superior quality control. After a desulfurizing treatment, magnesium is added, which in turn is followed by a post-inoculation treatment with a silicon base alloy. These steps cause a profound change in the manner that the carbon, as a graphite, is formed during the solidification of the iron. Instead of the interlaced flake form found in Gray Iron, the graphite develops myriads of isolated spheroids. The matrix becomes relatively continuous, thereby greatly increasing the strength, ductility and impact resistance of the metal. The strength of the Ductile Iron used in commercial piping (minimum yield strength = 42,000 psi and minimum tensile strength = 60,000 psi) is comparable to one of the higher grades (X42 API 5L) of steel pipe commonly specified for snowmaking piping.
