Fundamentals of Magnesium Addition to Ductile Iron 640802
Although ductile iron production is increasing rapidly, the methods of adding magnesium are still inefficient, expensive, and result in both undesirable dross and large amounts of carrier elements such as silicon in the treated metal.
The object of this research was to determine the maximum amount of magnesium which could be dissolved in ductile iron under different conditions of temperature, pressure, and chemical analysis.
By constructing a pressure chamber with an argon atmosphere and remote controls, melts of liquid cast iron with an upper layer of liquid magnesium were produced and analyzed. The solubility of magnesium in pure liquid iron at 2900 F is less than 0.5% but carbon and silicon both increase the solubility markedly. In a 4%C, iron alloy, the maximum solubility is 1.80% at 2600 F. Silicon is surprisingly less effective than carbon since the addition of 3% Si to the above alloy raises the solubility to 2.3% Mg.
Some high (2%) Mg iron silicon carbon alloys were frozen and then used as addition material. Magnesium recoveries of up to 70% were obtained.
The general results should be useful to operating as well as research groups because the conditions for the addition and recovery of a volatile, as well as easily oxidized element, are not generally well understood.