It is possible to generate a desirable form (soft, pliable) of sulfide inclusions in magnesium-treated case irons. Thermodynamically, MnS and MoS.sub.2 are not stable in the presence of magnesium. However, by adding magnesium to a cast iron melt containing manganese sulfide/molybdenium sulfide as late as possible, and preferably when the molten cast iron has been dispensed into the mould, such sulfide inclusions may be preserved in magnesium-treated cast iron. Alternatively, said cast iron can also be formed by adding said sulfides directly to the iron after the magnesium reaction has taken place and an in situ equillibrium has been established between magnesium, oxygen and sulfur. Another option is to begin with a sulfur content in excess of the stoichiometric amount required to combine with the added magnesium, thus ensuring an amount of left-over sulfur to promote the formation of the desired sulfide inclusion.