Specific Features of Forming Surface Phases under Chemical Heat Treatment of Iron-Base Alloys

The article gives a detailed analysis of specific features of forming surface phases in the samples of ingot iron after chemical heat treatment at the temperature of 850 °C during 2, 4 and 6 hours of saturation in two different media — vacuum carburizing in acetylene and liquid boriding in the melt which contains sodium tetraborate and amorphous boron. Micro images of the surface cross sections of the samples were obtained. The X-ray-phase analysis conducted allowed us to compare phase structure of the near-surface layers resulted from chemical heat treatment with samples microstructures. Findings of the research show that after carburizing there appear Fe₃C и Fe-α phases in the surface layer of the samples of ingot iron. After boriding FeB, Fe₂B и Fe₃B phases were found and characteristic peaks of Fe-α and Fe-y were not detected on X-ray diffraction pattern. The analysis of the microstructure provided us with data on the penetration depth for the saturating elements, and, consequently, allowed us to identify the dependence of thickness of a strengthened layer on saturation time. Results suggest that this dependence is parabolic, which suggests the major role of the diffusion mass transfer in saturation

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