Structure peculiarities of cementite and their influence on the magnetic characteristics

Source: arXiv


The iron carbide $Fe_3C$ is studied by the first-principle density functional theory. It is shown that the crystal structure with the carbon disposition in a prismatic environment has the lowest total energy and the highest energy of magnetic anisotropy as compared to the structure with carbon in an octahedron environment. This fact explains the behavior of the coercive force upon annealing of the plastically deformed samples. The appearance of carbon atoms in the octahedron environment can be revealed by Mossbauer experiment.

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Available from: A. K. Arzhnikov, Oct 29, 2013
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    ABSTRACT: The role of cementite in the formation of the H c of carbon steels after quenching and tempering is determined based on analysis of dependences of the coercive force of У9A steel in the measurement temperature range from the temperature of liquid nitrogen to the cementite Curie point. It is shown that the key contribution to the formation of the maximum in the H c (T temp) dependence measured at room temperature is due to the magnetic hardness of cementite, whose maximum lies at T temp = 500°C. The coercive force measured at 250°C is mainly related to the interaction of the domain walls of the ferrite matrix with nonferromagnetic inclusions of cementite, the maximum of which is at T temp = 400°C, thus causing a shift of the maximum in the H c (T temp) dependence measured at the temperature above the cementite Curie point toward lower tempering temperatures.
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    ABSTRACT: The effect of alloying elements Mn, Cr, and Si on the magnetic hysteresis properties of cementite and model steels with a carbon concentration of 0.6 wt % has been studied. It has been shown that alloying with carbide-forming elements (Mn, Cr) reduces the coercive force and the Curie temperature of cementite. Measurements of the temperature dependences of the coercive force of the model steels with carbon content of 0.6 wt % alloyed with manganese, chromium, or silicon have been performed in the temperature range of −196 to +300°C. It has been established that the local maximum of the coercive force of these steels in this temperature range coincides with the Curie point of the precipitates of the carbide phases. Based on an analysis of the temperature dependences of the coercive force, the content of the alloying element in the precipitates of cementite of steels tempered at different temperatures has been estimated. It has been shown that the character of the dependence of the coercive force of alloy steels on the temperature of tempering in the temperature range of 250–700°C is mainly determined by the coercivity and by the kinetics of the formation of cementite precipitates.
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