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 1600.    ---------------.  [JACK, K. H.]  [X-Ray Structural Investigations of the Iron-Carbon and Iron-Nitrogen Systems and of Related Interstitial Alloys.]  Acta Cryst., vol. 3, 1950, pp. 392-393; British Abs., 1951, I, A, p. 41.

        Three tempering stages of C martensite are discussed.  The loss of tetragonality of martensite during the 1st tempering stage is due to the precipitation of a close-packed hexagonal Fe carbide, structurally similar to ε-Fe3N.  The unit-cell dimensions are a 2.73 , c 4.33 .  The behavior of N martensite on tempering is quite different from that of the corresponding C alloys.  At temperature <250 a new phase, a, is formed as an intermediate in the decomposition a-γ.  This a phase is relatively stable, with a 5.72, c 6.29 .  The structures of ε-Fe nitrides and the ε-ζ transitions are discussed.  The hexagonal structure of Ni3N is confirmed, the unit-cell dimensions being a 2.6677 ű0.0005 , c 4.3122 ű0.0005 .  There appears to be no evidence as yet for the existence of a hexagonal allotrope of Ni.

        See abs. 578a, 1218.

        JACOB, K.  See abs. 2434.

        JACOBS, J.  See abs. 1255.