The Iron and steel magazine . ntain freecarbide as cementite and pearlite, the normal union of carbideand iron. Photograph 12 shows such an iron magnified 50diameters. It consists of white fields which are dotted withnumerous dark spots. Magnified still more (photograph 13)the latter prove to be a number of fine laminations which showthe characteristic structure of the mixture, the pearlite. The 11 on ( (ii hoi . [Hoys 20I cementite is extremely hard and is not attacked by dilute acid . 11 a polished piece of such iron is treated with dilute acid, thecementite remains unattacked in relief whil
The Iron and steel magazine . ntain freecarbide as cementite and pearlite, the normal union of carbideand iron. Photograph 12 shows such an iron magnified 50diameters. It consists of white fields which are dotted withnumerous dark spots. Magnified still more (photograph 13)the latter prove to be a number of fine laminations which showthe characteristic structure of the mixture, the pearlite. The 11 on ( (ii hoi . [Hoys 20I cementite is extremely hard and is not attacked by dilute acid . 11 a polished piece of such iron is treated with dilute acid, thecementite remains unattacked in relief while the separate ferriteplates of the pearlite between the cementite laminations areeaten away. In this way the pearlite plates act as a netting andgive rise to the peculiar light effects which distinguish mother-of-pearl ; hence the name pearlite. In gray cast iron a part of the carbon is separated out asgraphite and so there will appear beside cementite and pearliteblack particles of graphite, which are generally torn away in. Fig. 18. Magnified 750 diameters polishing. Photograph 14 shows such a structure magnified500 diameters. It often happens, especially with very slow cool-ing, that the cementite plates of the pearlite are very far apartwith a free field of ferrite between them. Since the ferrite isattacked but not stained by the agent used in this experiment,a 4 per cent solution 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 largerar
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Keywords: ., bookcentury1800, bookdecade1890, bookidironsteel, booksubjectiron
