A previous report by the authers states that carbon and oxygen in molten iron attract each other. As the -
ΔF value for the reaction C+S
2=CS
2 is larger at higher temperature, sulfur and carbon in molten iron may also attract each other. In that respect the effect of oxygen and sulfur on the spheroidal graphite formation may be similar.
Considering the above situation, the mechanism of spheroidal graphite formation was studied tharaughly and the following results were obtained.
(1) Spheroldal graphite was formed, when the precipitation velocity of carbon was very rapid, without the presence of any special nuclei. It was concluded that the tendency of spheroidal graphite formation was an intrinsic nature of carbon in molten iron.
(2) The cooperative effect of silicon on the formation of spheroidal graphite was thermodynamically interpreted.
(3) Consideratins on the activity of carbon afforded an understanding of the spheroidal graphite formation in deoxidized melt.
(4) Calcium and magnesium exhibited a favorable effect, “filter effect”, on the formation of spheroidal graphite.
(5) The difference between calcium and magnesium in their effects on the formation of spheroidal graphite was related to the difference in their solubility in molten iron, and hence to the difference of their “filter effects”.
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