EFFECT OF CARBIDE COATINGS ON CORROSION OF IRON-BASED COMPOSITE MATERIALS

Summary: Increasing the properties of iron-based abrasive composition materials by volume and surface alloying is of scientific and technical importance. Since increasing the properties of composite materials by volume alloying causes a number of difficulties, surface alloying is often used to improve the properties of this type of materials. Therefore, in order to increase the properties, successive saturation processes of their surface layer with one or more carbide-forming elements are carried out. It was found that the properties enhancement with one-component coatings differs from the properties of multi-component coatings. It is clear that as a result of the saturation of the surface layer of the abrasive composition materials with certain elements, coatings with different composition are created in them. Carbide, nitride, boride and other coatings allow to obtain the necessary results. Therefore, the improvement of the structure and properties of iron-based abrasive composition materials directly depends on the coatings formed as a result of hammering the surface layer of construction materials with various elements. In the article, the effect of carbide, nitride and boride-containing coatings on the structure and properties of iron-based abrasive composition materials was considered. The distribution of chromium in the depth of the diffusion layer was studied by the method of micro-X-ray spectral analysis. The greatest concentration of chromium is observed on the surface, which increases as the degree of carbonization of the material increases. The change of the amount of chromium on the depth of the carbide zone obeys a linear law. At the boundary of the carbide zone, its concentration is approximately the same in the studied materials and is 58-61% In connection with the increase in the initial carbonization degree of the surface zone, the increase in the concentration of chromium is accompanied by the increase in the microhardness of the carbide coating. Based on the data of X-ray structural studies, the studied carbide coatings have the same phase composition (Cr, Fe) C 23 6, (Cr,Fe) C 7 3. The structure of the transition zone and its layers is determined by the degree of carbonization of the material during the initial processing. At relatively low temperatures (875 and 925 °C) in cementitized iron, as in the case of JQr 0.5 composition, a weakly tanned zone (20-25 μm thick) of an extremely saturated γ-solid solution with a microhardness H100 = 6100-7000 MPa, formed in the process of cooling from the air chroming temperature directly under the carbide layer is located. Behind it is a zone of high etching ability, which is caused by the eutectoid decomposition of the solid solution of chromium and carbon in γ-iron. The intermediate zone of annealed iron cementitized at 975-1025 °C undergoes eutectoid decomposition during cooling in air and metallographically is detected as a band with high etching ability.