Binary and ternary interstitial alloys - II. The iron-carbon-nitrogen system

Abstract

Chemical and X-ray investigation of the reaction of carbon monoxide with iron nitrides and of the reaction of ammonia with iron carbides discloses the existence of iron carbonitrides— a series of new ternary interstitial alloys containing iron, carbon and nitrogen. ζ-phase carbonitrides, with structures similar to those of ζ-iron nitrides, have a range of homogeneity extending approximately from Fe 8 N 4 to Fe 8 C 3 N. The latter is isomorphous with Fe 2 N. Є-phase carbonitrides, which are isomorphous with Є-iron nitrides, have a composition range of approximately 25 to 33 atomic % nitrogen plus carbon, i.e. from Fe 3 X to Fe 2 X , in which the higher carbon concentration limit is not less than 16 atomic %. Probable phase fields for part of the iron-carbon-nitrogen system are given on a ternary diagram. Prolonged reaction of carbon monoxide with iron nitrides results in complete elimination of nitrogen. Below 500° C the product is a carbide of iron, now called iron percarbide, the narrow composition range of which includes Fe 20 C 9 . Above 500° C the product of the same reaction is cementite.