The steel scrap was carburized by electrode-carbon, charcoal, coke or charcoal plus CaC
2, and the irons containing 3.10∼3.39% C were made. Using specimens cast in dry sand mould 14 mm in diameter, the effect was investigated of the carburizing method on the spheroidization of graphite in these irons by the addition of 0.1∼0.5% Mg in the form of Mg-Ni-Si-Fe-Cu-Al alloy containing 10% Mg, and the following results were obtained: (1) The sulphur-content in electrode-carbon-, charcoal- or coke-treated irons was higher than that in the original steel scrap, while the sulphur-content in charcoal plus CaC
2-treated iron was remarkably lower than that in the original steel scrap. (2) Charcoal plus CaC
2-treated iron was most suitable for the spheroidization of graphite by the magnesium-addition on account of the pig-making with the basic and reducing atmosphere accompanying the strong desulphurization. (3) In the case of charcoal plus CaC
2-treated iron, the spheroidizing effect of magnesium appeared with but few addition of 0.1% Mg. While, in iron treated with charcoal, the spheroidizing effect was seen at 0.15% Mg-addition, and in irons treated with electrode-carbon or coke, it was seen at 0.2% Mg. (4) Though in iron treated with charcoal plus CaC
2 the spheroidization of graphite can be completed by the magnesium-addition, the spheroidal form is gradually disintegrated in irons of the other carburizing method even by abundant addition of magnesium in the following order: charcoal, electrode-carbon, coke. This fact signifies that some elements except common ones in irons have fatal effect on the spheroidization of graphite and the so-called inherrent properties of irons caused by the pig-making method have the intimate relation with the spheroidizing of graphite.
View full abstract