69.    ARBUZOV, M.  [Crystal Structure and Particle Size of the Carbide Phase in Tempered Steel.]  Doklady Akad. Nauk S. S. S. R., vol. 73, 1950, pp. 83-86; Chem. Abs., vol. 45, 1951, p. 3217.

               X-ray line widths were measured photometrically for carbide residues from 1% C steels tempered at 50° intervals from 100° to 700°.  The calculated size and shape of the carbide particles showed that in the range 200°-350° the c dimension of the carbide is only about 10 lattice spacings and is about 1/3 as large as the a or b dimension.  Growth in all dimensions occurred above 350°, and the difference between c and a or b decreased.  Some X-ray lines present above 400° disappeared below this temperature.  No lines were present in the pattern of carbides from the steel tempered at 150°.  Even in steels tempered at low temperatures the carbide phase, Fe_xC, has the lattice of Fe₃C.  The difference in diffraction patterns between Fe_xC and Fe₃C is caused by the platelet form and the small dimensions of Fe_xC.  The change that occurs in the range 300°-400° is partly caused by changes in the interaction of the carbide and the solid solution.