. Transactions. Fig. 19.—Low-carbon steel held 30 Mm. in vacuo at 760° C, copper-plated AND ETCHED WITH 4 PER CENT. HNO3, SHOWING CROSS-SECTIONAL VIEW WITH PEARLITEEXTENDING PRACTICALLY TO THE SURFACE. Fig. 20.— oikel heated for 30 min. at 740° C, etched for 30 sec WITH 4 PER CENT. HNO3, PEARLITIC CRYSTALS BEGINNING TO APPEAR. X500. 406 SURFACE CHANGES OF CARBON STEELS HEATED IN VACUO its crystalline structure will change to that of the lower allotropes and thevaporization and deposition which must still continue, but at a slowerrate, will tend to develop these new boundaries
. Transactions. Fig. 19.—Low-carbon steel held 30 Mm. in vacuo at 760° C, copper-plated AND ETCHED WITH 4 PER CENT. HNO3, SHOWING CROSS-SECTIONAL VIEW WITH PEARLITEEXTENDING PRACTICALLY TO THE SURFACE. Fig. 20.— oikel heated for 30 min. at 740° C, etched for 30 sec WITH 4 PER CENT. HNO3, PEARLITIC CRYSTALS BEGINNING TO APPEAR. X500. 406 SURFACE CHANGES OF CARBON STEELS HEATED IN VACUO its crystalline structure will change to that of the lower allotropes and thevaporization and deposition which must still continue, but at a slowerrate, will tend to develop these new boundaries. On the other hand, if thesample is never taken above the Az point, only the crystalline boundariesof the lower allotropes can be developed. Below the A3 range, the vapor that condenses will build up a layer ofpure iron of almost infinitesimal thickness, since carbides are no longersoluble in alpha and beta iron. In steels of higher carbon content, wherethe Az and A2 points are gradually merged with the Ai point, it is to beexpected that the ferrite layer would be reduced in thickness. Takingas an example a steel of this composition, on being cooled from 1000° C,the iron vapors, when redeposited,
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
