Abstract
Thin films of iron carbides were heated in vacuo and their phase transition was studied. It was found that the carbides transform irreversibly as ε→χ→θ. Diffraction patterns of the carbides transformed by heating are not different from those of the carbides produced by cementation of iron films. High temperature electrton diffraction showed that the phase transition ε→χ takes place at 380∼400° and the transition χ→θ at about 550°. θ carbide decomposes gradually into iron and carbon by prolonged heating above 550°. Since any trace of precipitation of iron or carbon could not be observed in the patterns after the phase transition, it is presumed that the carbides transform with no composition change. The 380° Curie point of ε carbide found by Hofer et al. is the transition temperature of ε→χ. Measurement of the thermal change of axial ratio of ε carbide showed that the carbide has considerable anisotropy.
