Therefore, steel contains no graphite and no slag but has only the small percentage of carbon which was purposely put back to give to it its valuable properties.
No. 92d. Semi-Steel, a Stronger Gray Cast Iron
Photomicrograph No. 22c is typical for steel which contains .50 per cent (½ per cent) of carbon. The irregular patches containing the carbon are much larger and more frequent. It will be seen, therefore, that through metallography the various iron alloys, to a considerable extent, may be analyzed as well as classified.
Photomicrographs Nos. 74 and 92d represent soft and stronger grades of ordinary gray cast iron respectively. It will be noted at once that both much resemble pig iron in structure, as of course they should, for simple remelting in the cupola does not effect much modification in composition or structure.
Occasionally castings are made from molten iron direct from the blast furnace, but such practice is not very satisfactory and is little done. It forms probably the only exception to the statement made above that pig iron has no useful purpose in the commercial world except as something to be transformed by some refining process into another material.
No. 132. Gray Cast Iron 200 Years Old
No. 109. Malleable Cast Iron Before Annealing