The aim of the research is to study the possibility of the accelerated formation of a highly-rigid carbide coating on the surface of steel products. The use of the microarc thermochemical treatment technology is proposed. A steel article is placed into the black coal powder and is heated by transmission of the electric current. The formation of the microarc discharges in the powder environment leads to the carbon saturation of a surface, and the simultaneous diffusion in metal allows forming a highly rigid carbide layer. The possibility of ferroalloys usage as a source of the carbide forming metal under the formation of a highly rigid coating with the help of the microarc chemical heat treatment is established. The electrical conductivity of ferroalloys is higher than chemical combinations, and it allows obtaining acceleration of diffusion saturation due to the intensive formation of the fissile atoms of metals under the influence of microarcs. The application of ferroalloys is more favorable in terms of power, as restitution of metal oxides to an atomic state requires additional energy cost. When using ferrochrome, ferromolybdenum and ferrotungsten, a surface carbide layer up to 160 microns thick and with microhardness to 18 hPa is formed.
surface hardening, microarc thermochemical treatment, formation of highly-rigid coating on the surface of steel products.
The modern mechanical engineering imposes increased requirements to reliability and durability of the used materials. In many cases these requirements can be provided with increase of details of machines and the tool blanket properties. Chemical heat treatment changes a chemical composition and structure of a material surface and allows to increase the hardness, wear resistance, corrosion resistance, heat resistance and other mechanical and physic- chemical properties of responsible details [1]..
The methods of chemical heat treatment applied in the industry are based on diffusion saturation of metals and alloys blankets by one element or a complex of elements that allows obtaining the required properties on a surface of the processed product [1-3]. Usually it is necessary to form very hard surface coatings. For example, to apply a saturation of the surface with
chromium, molybdenum and tungsten in powder mixtures. Treatment is performed within several hours in the pressurized containers in the protective atmosphere or in vacuum [1].
However, these methods have a number of shortcomings including: the long duration of saturation process, surface decarburization, a possibility of a layer without carbide phase formation, dependence of layer hardness on duration and temperature of diffusion. Insufficient sealing of containers accelerates depletion of the saturating mixture, and it worsens stability of results and can cause powder agglomeration. Besides, it is difficult to automate such methods of treatment and therefore they require application of a manual work.
1. Voroshnin, L.G., Mendeleyeva, O. L., Smetkin, V. A. Teoriya i tekhnologiya khimiko-termicheskoy obrabotki. [Theory and technology of thermochemical treatment.] Moscow: Novoe znanie; Minsk: Novoe znanie, 2010, 304 p. (in Russian).
2. Mehrer, H. Diffusion in Solids. Fundamentals, Methods, Materials, Diffusion-Controlled Processes. Springer-Verlag Berlin Heidelberg, 2007, 645 p.
3. Antczak, G., Ehrlich, G. Surface diffusion . Cambridge University Press, 2010, 779 p.
4. Dombrovsky, Yu.M., Stepanov, M.S. Mikrodugovaya tsementatsiya stal´nykh izdeliy v poroshkovykh sredakh. [Microarc carburizing of the steel parts in powder environments.] Strengthening Technologies and Coatings, 2013, no. 12, pp. 25–29 (in Russian).
5. Dombrovsky, Yu.M., Stepanov, M.S. Novye vozmozhnosti poverkhnostnogo legirovaniya stali v poroshkovykh sredakh. [New facilities of surface alloyage of steels in powder environments.] Vestnik Mashinostroeniya, 2015, no. 8, pp. 79–81(in Russian).
6. Stepanov, M. S., Dombrovsky, Yu.M. Formirovanie karbidnogo pokrytiya pri mikrodugovom khromirovanii stali. [The formation of carbide coating at the microarc chromizing of steel.] Strengthening Technologies and Coatings, 2015, no. 1, pp. 35–38 (in Russian).
7. Stepanov, M.S., Dombrovsky, Yu.M. Formirovanie karbidnogo pokrytiya pri mikrodugovom molibdenirovanii stali. [The formation of carbide coating at the microarc molybdenizing of steel.] Strengthening Technologies and Coatings, 2015, no. 10, pp. 34–38 (in Russian).
8. Stepanov, M.S., Dombrovsky, Yu.M. Thermodynamic Analysis of Carbide Layer Formation in Steel with Microarc Saturation by Molybdenum. Steel in Translation, 2016, vol. 46, no. 2, pp. 79–82.
9. Dombrovsky, Yu.M., Stepanov, M.S., Davidyan, L.V. K voprosu o tekhnologicheskikh parametrakh mikrodugovoy khimiko-termicheskoy obrabotki (MDKhTO). [Revisiting technological parameters of microarc thermochemical treatment (MTCT).] Izvestia VSTU, 2015, no. 5(160), pp. 130-131 (Series “Problems of materials science, welding and strength in machine building”) (in Russian).
10. Dombrovsky, Yu.M., Stepanov, M.S. Osobennosti molibdenirovaniya stali v rezhime mikrodugovogo nagreva. [Features of molybdenizing of steel under conditions of microarc heating.] Izvestiya VSTU, no. 5(160), pp. 135–138 (Series “Problems of materials science, welding and strength in machine building”) (in Russian).
