Technology to Improve the Performance Properties of Heterogeneous Boronized Layers

Abstract The aim of this work is to develop a technology for obtaining heterogeneous boronized layers of considerable thickness on structural steels to ensure higher wear resistance. Typically, boronized layers are obtained at different temperatures (1,150–550°C) by the diffusion and diffusion-crystallization mechanisms of mass transfer. The heterogeneous layers with a dispersed distribution of borides in the α-solid solution are obtained by the diffusion-crystallization mechanism, with the liquid-crystalline state of the treated surface. This aim is achieved by stepwise temperature treatment. At the beginning, the borating is carried out in the liquid-crystalline state of the surfaces, and then in the crystalline state. To efficiently determine the processing temperature in the crystalline and liquid crystal states of the surface, for the first time, the five-component scheme diagram of the state iron-chromium-nickel-manganese-boron in the traditional temperature–concentration coordinates was built. At the base of this scheme diagram is a pentagon with a divergent concentration grid. The amount of liquid phase during the processing in the liquid crystal state of the surface should not exceed 20 %. After this treatment, the boronized layers consist on the surface of a compact single-phase structure of iron boride (Fe2B) or a two-phase structure (FeB + Fe2B). The thickness of this zone is not more than 0.2 mm. Next, there is an extensive zone (0.5–1.5 mm) with a heterogeneous structure (α—solid solution with alloy borides). This structure ensures a smooth distribution of hardness from the surface to the core of the part. The resulting boronized layers provide higher wear resistance. The choice of a particular layer structure depends on the operating conditions. Under the conditions of the experiment performed, the layer with the combination of borides on the surface and the pseudoeutectic structure in the sublayer became the best.