The Iron and steel magazine . tion of picric acid in alcohol, in order to distin-guish the ferrite from the pearlite, one may make use of theirdifferent mineralogical hardness. Ferrite is scratched by a steelneedle, but not cementite. The pearlite also is scratched, al-though only the projecting cementite laminations are touchedby the needle. Since these are extremely thin and brittle, theyare simply broken by the needle. 202 The Iron and Steel Magazine Photograph 15 shows such a scratch, which scratches thepearlite but not the cementite. The graphite runs through thestructure in the form of w
The Iron and steel magazine . tion of picric acid in alcohol, in order to distin-guish the ferrite from the pearlite, one may make use of theirdifferent mineralogical hardness. Ferrite is scratched by a steelneedle, but not cementite. The pearlite also is scratched, al-though only the projecting cementite laminations are touchedby the needle. Since these are extremely thin and brittle, theyare simply broken by the needle. 202 The Iron and Steel Magazine Photograph 15 shows such a scratch, which scratches thepearlite but not the cementite. The graphite runs through thestructure in the form of wormlike veins; often it forms largerareas according as the cut separates the layers of graphite. Inthe last case the graphite is carried away by polishing the sampleand one sees then in indistinct outline the structure of the neigh-boring fields. The immediate transition from white to graypig iron of the same composition is shown by photograph 16,just mentioned above. As we have already seen, during the cooling at 7000 C. the. Fig. 19. Magnified 750 diameters mother metal, consisting of per cent carbon, changes into anintimate mixture of ferrite and cementite. This process isreversible; thus at this temperature the cementite dissolves inferrite with formation of solid solution, which as a structuralform has received the name of martensite.* If we fix the formof these crystals by sudden cooling (chilling) we obtain a regularstructure which has the character of crystal clusters (places ofcleavage, crystalline granulation). Photograph 17 shows a whitecast iron chilled at 9900 C. The white fields are unalteredcementite, broken through by a ground mass whose structure is * Austenite (?). — Editor. Iron-t arbon . \llo 203 given m photograph [8. We see thai it consists of a light ground mass wliicli is dotted with dark needles crossing each oilier m sharp corners or in triangles; and also of Mack irregular areaswithout recognizable form. In order to understand the meaning of th
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Keywords: ., bookcentury1800, bookdecade1890, bookidironsteel, booksubjectiron
