Obrabotka Metallov 2019 Vol. 21 No. 2

OBRABOTKAMETALLOV Vol. 21 No. 2 2019 107 MATERIAL SCIENCE Effect of Low-Temperature Carburization in Electron Beam Plasma on the Hardening and Surface Roughness of the Metastable Austenitic Steel Polina Skorynina 1, a,* , Aleksey Makarov 1, 2,3, b , Andrey Men’shakov 4, c , Alevtina Osintseva 1, d 1 Institute of Engineering Science, Ural Branch of Russian Academy of Sciences, 34 Komsomolskaya str., Yekaterinburg, 620049, Russian Federation 2 M.N. Miheev Institute of Metal Physics of the Ural Branch of the Russian Academy of Sciences, 18 S. Kovalevskaya str., Yekaterinburg, 620108, Russian Federation 3 Ural Federal University named after the first President of Russia B.N. Yeltsin, 19 Mira str., Yekaterinburg, 620002, Russian Federation 4 Institute of Electrophysics of the Ural Branch of the Russian Academy of Sciences, 106 Amundsena str., Yekaterinburg, 620016, Russian Federation a https://orcid.org/0000-0002-8904-7600, polina.skorynina@mail.ru, b http://orcid.org/0000-0002-2228-0643, avm@imp.uran.ru , c https://orcid.org/0000-0003-3715-7741, menshakovandrey@mail.ru , d https://orcid.org/0000-0003-0043-8435, osintseva@imach.uran.ru Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2019 vol. 21 no. 2 pp. 97–109 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2019-21.2-97-109 Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov ARTICLE INFO Article history : Received: 24 March 2019 Revised: 08 April 2019 Accepted: 11 April 2019 Available online: 15 June 2019 Keywords : Austenitic stainless steel Plasma carburization Electron beam Microhardness Roughness Funding: The reported studywas funded byRFBR according to the research project № 18- 38-00561_mol_a. It was done within the state assignment for IESUBRAS, theme No. AAAA-A18-118020790148-1, and the assignment for IMP UB RAS, theme “Structure” No. AAAA-A18- 118020190116-6. The studies were performedattheCentersofCollaborative Access “Plastometry” of the Institute of Engineering Science, Ural Branch, Russian Academy of Sciences. ABSTRACT Introduction. Low-temperature plasma carburization is an effective way to increase the hardness of thermally unhardened austenitic chromium-nickel steels. Usage of low-energy (up to 1 Kev) electron beams for plasma surface modification allows not only to generate plasma efficiently, but also to heat objects placed in the plasma to a high temperature without using additional external heating. However, in the literature there is no information about the carburization of austenitic stainless steels using plasma generated by an electron beam. The carburization temperature has a significant impact on the level of characteristics and the phase composition of austenitic steels. It is also important to take into account that the usage of ion-plasma chemical-thermal treatments can lead to a change in the roughness of the treated surface. The aim of the work is to study the effect of the temperature carburization in the plasma of a low-energy electron beam in the range T C =350-500 °C on the phase composition, roughness, depth and hardening of the carburized layer of austenitic steel AISI 321. The research methods are microhardness measurement, X-ray phase analysis, scanning electron microscopy and optical profilometry. Results and discussion. Carburization in the plasma generated by the electron beam at T C =350-500 °C provides an increase in the microhardness of the surface of austenitic steel by 5.5 times (up to ~ 1100 HV 0.025). It is found that the depth of the hardened layer strongly depends on the temperature of carburization and is 25 μm at T C =350 °C, and with further increase in the temperature of carburization increases up to 200 μm at T C =500 °C. The effective hardening of the surface layer of stainless steel is associated with the formation of carbon-supersaturated austenite γ C and carbides Cr 23 C 6 at T C =350-500 °C, as well as carbides Cr 7 C 3 at T C =500 °C. It is shown that the carburization of the electropolished steel surface at temperatures of 400-500 °C is accompanied by an increase in the roughness parameter Ra to 0.73-1.06 μm. The decrease in the carburization temperature to T C =350 °C leads to the formation of a surface with a significantly lower roughness parameter Ra=0.15 μm. Thus, carburization in the plasma of a low-energy electron beam at temperatures T C =350-500 °C is an effective way to increase the hardness of thermally unhardened austenitic Cr-Ni steel, and carbon modification at a minimum temperature T C =350 °C also provides a low roughness of the carburised surface. This allows us to consider that this technology is a promising finish hardening treatment of precision products made of austenitic stainless steel. For citation: Skorynina P.A., MakarovA.V., Men’shakovA.I., OsintsevaA.L. Effect of low-temperature carburization in electron beam plasma on the hardening and surface roughness of the metastable austenitic steel. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science , 2019, vol. 21, no. 2, pp. 97–109. DOI: 10.17212/1994-6309-2019-21.2-97-109. (In Russian). ______ * Corresponding author Skorynina Polina A. , Junior researcher Institute of Engineering Science, Ural Branch of Russian Academy of Sciences, 34 Komsomolskaya str., Yekaterinburg, 620049, Russian Federation Tel.: 8 (343) 362-30-33, e-mail: polina.skorynina@mail.ru