GENERAL
Magnesium is essentially insoluble in solid steel and is not used as an alloying constituent per se. However, like calcium, magnesium is very useful as a desulfurizer, and large quantities have been consumed in steelmaking for this purpose. (For a further discussion of this topic, see Sulfur.) Magnesium is a powerful inoculant in cast iron. When added in concentrations exceeding 0.04%, it produces a spheroidal form of graphite that improves the iron's strength and ductility.
Magnesium is an abundant metal with a price roughly comparable to that of aluminum, albeit usually higher. The US is a leading world supplier.