The Iron and steel magazine . ilarity betweenthe structure of this metal and that of the metallic matrix ofgray cast iron free from combined carbon (Fig. 1) will be appar-ent. The ferrite which necessarily forms the totality of carbon-less iron exhibits the network structure seen also in the matrix ofthe gray cast iron. Both are made up of irregular, polyhedric 122 The Iron and Steel Magazine ferrite grains. There is much structural resemblance, therefore,between perfectly gray cast iron and carbonless iron — and stilltheir properties differ widely. Gray cast iron, free from com-bined carbon,
The Iron and steel magazine . ilarity betweenthe structure of this metal and that of the metallic matrix ofgray cast iron free from combined carbon (Fig. 1) will be appar-ent. The ferrite which necessarily forms the totality of carbon-less iron exhibits the network structure seen also in the matrix ofthe gray cast iron. Both are made up of irregular, polyhedric 122 The Iron and Steel Magazine ferrite grains. There is much structural resemblance, therefore,between perfectly gray cast iron and carbonless iron — and stilltheir properties differ widely. Gray cast iron, free from com-bined carbon, lacks strength, ductility and malleability, whilecarbonless iron is strong, ductile and malleable. The reason forthis difference must be ascribed to the presence of graphite inthe gray cast iron, which by breaking the continuity of themetallic mass (the strong, malleable ferrite) greatly weakens itand destroys its original ductility and malleability, rather thanto the weakness and brittleness of the graphite particles them-. Fig. 3. Highly Graphitic Cast Iron. Magnified50 diameters (not etched). lelves. If all the particles of graphite could be removed bodily,seaving in the iron the small cavities which they once occupied,it does not seem probable that the properties of the cast ironwould be materially modified. It will be apparent from these considerations that the morenumerous the particles of graphite the more will they weaken andotherwise affect the properties of the ferrite in which they areembedded, and it will also be apparent that the shape anddimensions of the graphite particles must also have their influ-ence. If the graphite could be made to occur in small, roundedparticles it would probably affect the ferrite to a much less extentthan when present, as is generally the case, in irregular and Metallography Applied to Foundry Work 123 curved plate. (See Fig. 3.) [ndeed, this is strikingly borne outby the strength and ductility of malleable cast-iron castings inwhich
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