MALLEABLIZING OF CAST IRON TREATED WITH MAGNESIUM

Abstract

The graphitizing phenomena were studied by annealing the magnesium-treated (0.1%-1.0%Mg) and sandcast iron having the composition of C 2.56%, Si 1.13%, Mn 0.421%, P 0.118%, S 0.149%, Cr 0.01%, Cu 0.312%, and the following resulta obtained.
(1) The sand cast iron castings treated with small amount of magnesium (0.1%-0.3%) in the form of Mgalloys have mottled structures including flaky graphite, although they are white if not treated with Mg-alloys. The above phenomenon is caused by the strong desulphurization effect of magnesium as well as by alloying of the graphitizationpromoting elements in the Mgalloys.
(2) If the added amount of magnesium exceeds 0.6%, the structure becomes white or mottled, the graphite in the iron being spherulitic and not flaky. This phenomenon is caused by strong desulphurization of the molten iron and by alloying of the magnesium in its amount sufficient to apheroidize graphite.
(3) The magnesium aiioyed has not only a tendency to chill the molten iron, but also re tards the graphitization in the annealing slightly.
(4) Temper carbon in the iron treated with magnesium is rounder in form than that in the iron not treated with magnesium.
(5) Quick malleablizing will surely be achieved by annealing the magnesiumtreated iron containing a dequate amount of carbon and silicon, and the iron casting malleablized has, for example, tensile strength 50kg/mmmm2 and elongation 8% By this method even the high phosphor iron (-0.1%P) can be used for making ductile iron, and the castings of larger section size than the maximum size applied up to the present in malleable iron products can be manufactured.