. Bulletin - United States National Museum. Science. THE METALDOGRiAiPHY OF METEO'RIC IROiN' 57 Vogel's theory.—The foregoing outline of the process reflects the current prevailing views of metallographers and is consistent Vvith the early iron-nickel equilibrium diagram of Osmond and Cartaud (fig. 4), upon which the now generally accepted diagrams are based, which postulated the existence of two phases although at that time two phases had not been produced in artificial alloys. That was accomplished first by Benedicks (1910), who succeeded in producing characteristic Widmanstatten structures,
. Bulletin - United States National Museum. Science. THE METALDOGRiAiPHY OF METEO'RIC IROiN' 57 Vogel's theory.—The foregoing outline of the process reflects the current prevailing views of metallographers and is consistent Vvith the early iron-nickel equilibrium diagram of Osmond and Cartaud (fig. 4), upon which the now generally accepted diagrams are based, which postulated the existence of two phases although at that time two phases had not been produced in artificial alloys. That was accomplished first by Benedicks (1910), who succeeded in producing characteristic Widmanstatten structures, in some cases visible to the eye. A macroscopic structure of great perfection was recently produced by Mehl and Derge (1937). Vogel, however (1925, 1927), did not accept the production of an artificial Widmanstatten struc- ture as confirmation of Cartaud's hypothesis, arguing that the exist- r o o a: a: UJ Q. LU 1500 1400. 20 PER CENT 30 NiCKEL Figure 9.—The delta-gamma transformation in nickel-iron. ence of a eutectoid horizontal line extending from 6 to 30 percent nickel, which he deemed essential to that theory, had not been estab- lished. He ascribed the origin of the structure (both natural and artificial) not to the gamma-alpha transformation but to an earlier delta-gamma transformation. J^igure 9 shows the range in which this transformation takes place, which is brief and at a very high temperature. The Vogel mechanism.—In artificial irons containing carbon the delta range between the melt and gamma phase is small and its effects are negligible; but in iron-nickel alloys its width is greater and it extends to about 30 percent nickel. If the percentage of nickel is more than that, the alloy passes directly from the melt to the gamma phase. 507394—44 5. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original
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