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34                     METALLURGY   OF   CAST. IRON.
In re-melting iron, whatever phosphorus the fuel or flux may contain will largely go to the iron, and hence phosphorus has a tendency to be increased every time iron is re-melted, Its influence in effecting changes in the other elements is to favor the reduction of silicon, sulphur and manganese, owing to the quality of phosphorus which causes iron to have greater fluidity and life.
Total carbon is, as a general thing, increased by re-melting. The amount is chiefly dependent upon the percentage of fuel used, and the length of time the iron is in the cupola. Little fuel and quick melting may at times cause a slight reduction of the carbon. In the case of excessive fuel which can give hot iron and cause slow melting carbon may be increased. It is also, to some degree, dependent upon the silicon and manganese present. The former retards, while the latter promotes the increase of carbon.
Combined carbon with the silicon above four per cent., and sulphur not over .01, may sometimes be slightly reduced. After silicon has decreased to 4.00 with the sulphur above .02, every re-melt will surely increase the combined carbon until the silicon is so decreased and the sulphur increased that '' white iron" will be produced, giving an iron which may have its carbon almost wholly in a combined form.
Graphitic carbon is increased accordingly as combined carbon is decreased, and the elements best calculated to promote its formation are silicon about 3.50 and phosphorus not above 1.25, with low sulphur.
In a general way it can be said that with iron melted in the cupola, the silicon, manganese and graphitic carbon are decreased, while the sulphur, phosphorus and combined carbon are increased.y eliminated.sile strength of 50,000 to 60,000 pounds per square inch is claimed. The author has endeav-give a softer re-melt than gray parts of the same casting, see pages 338 and 339.