モリブデン鋼中の炭化物について

抄録

Carbides isolated electrolytically from molybdenum steels were studied by X-ray, chemical and thermo-magnetic analyses, and by electron-microscopic observations, with the objects to elucidate the nature of carbides in the steels, and to determine the carbide-phase diagram of molybdenum steel below the eutectoid temperature. In the case of thermal treatment at 700°C for 24 hrs, the carbides formed by tempering are quite different from those formed by isothermal transformation. But, after a prolonged treatment at 700°C, carbides in both the structures tend to approximate each other gradually, and five kinds of carbides, M₃C, M₂₃C₆, ξ, M₂C and M₆C appear, as the atomic ratio Mo: C in the steel increases. Among these carbides, M₃C and M₂₃C₆ are ferromagnetic, of which the Curie points are 215∼181°C and 312∼183°C, respectively. The composition ranges of carbides in molybdenum steels at 700°C are as follows. M₃C: 6.67%C, 0∼2.5%Mo; M₂₃C₆: 5.0∼6.0%C, 5.5∼13.5%Mo; ξ: 5.5∼6.0%C, 30∼37%Mo; M₂C: about 6%C, 70%Mo; M₆C: 2.5∼2.8%C, 45∼62%Mo.