Bryansk State Technical University (Bryansk, Russia):

S. V. Davydov, Dr. Eng., Prof., Dept. of Tribotechnical Materials Science and Materials Technology, e-mail: fulleren_grafen@mail.ru

Within the limits of the existing diagram of “iron-carbon” alloys it is impossible to explain some of the effects, for example, the separation of “sings” from blast furnace cast irons and the impossibility of existing metallurgical technologies to obtain iron-carbon alloys containing more than 5.0 %C. In addition, the “white” spot on the diagram is the carbide area lying on the right cement line. Significant progress made now in the study of iron carbides and the behavior of ironcarbon alloys at extreme parameters makes it possible to update and refine the “iron-carbon” diagram, and above all in the area of phase transformation of iron carbides, to a concentration of 9.7 %C, corresponding to the chemical composition of ε-carbide Fe2C. In the present work the complete diagram of the system “iron-carbide ε-Fe₂C” in the concentration range of 0...9,7 %C is offered. The following phase transformations are introduced in the diagram: Cementite θ-Fe3C crystallization follows the reaction of the peritectic type of nonvariant three-phase synthetic equilibrium; Hegg carbide χ-Fe₅C₂ crystallization is described in the framework of transformation following the reaction of nonvariant three-phase peritectic equilibrium; low-temperature peritectoid-type carbide transformation in which the solid solutions of ferrite and cement form a solid solution of a wide area of homogeneity based on bertollide ε-karbide Fe₂C. It is shown that the carbide phases are a single isomorphic quasi-carbide solid solution, and structurally, according to the proposed diagram variant, the carbide phase is crystallized as a mixture of carbide phases as a quasi-eutectic.

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