Metallurgy Of Cast Iron

CHEMICAL AND PHYSICAL PROPERTIES, ETC
215
simply as a de-oxidizing agent, the manganese seizing any oxygen which has combined with the iron, forming manganic oxide, which, being lighter than the molten metal, rises to the surface and floats off with the scoria. When a casting which has been artificially softened by this novel treatment is re-melted, the effects of the ferro-manganese disappear and hard iron results.
In the experiments conducted by the author (seen in Chapter XXXII.) he found that, in iron above 2.00 silicon, the addition of manganese to molten metal had a tendency to hold the carbon more in a combined form, which is the reverse of its action in low silicon irons, and partly in keeping with the above experience of Mr. Outerbridge.
Phosphorus is the element which differentiates " Bessemer" from "Foundry" iron, and generally ranges from a trace to i^ per cent, in ordinary pig" metal. In foundry iron it generally varies from 25 to i.oo, and it can be found in iron as high as 7 per cent. If iron exceeds . 10 in phosphorus it is no longer regular Bessemer, and may be often classed as Foundry. To make this distinction between Bessemer and Foundry iron clear, Table 30 is presented:
TABLE 30 — CHEMICAL ANALYSES OF FOUNDRY AND BESSEMER IRONS.
No. i Foundry. No. 3 Foundry. No. 4 Bessemer. No. 7 Bessemer.
Phosphorus ....... . ............... .60 .50 .09 .09
Graphitic Carbon •2 CQ 300 3-5° -i OO
Combined Carbon ........... .15 •3° •35 .65
3-OO 2.25 2.00 1.25
.01 .02 .025 .050
Manganese 3° 40 •5° •45

As can be seen by the above table, excepting phosphorus, the four analyses could pass as Foundry iron. Further comments on Foundry versus Bessemer will be found in Chapter XXII.