THE INFLUENCE OF LOW-TEMPERATURE PLASMA MODIFICATION WITH CARBON AND NITROGEN ON THE HARDENING AND SURFACE ROUGHNESS OF AUSTENITIC STAINLESS STEEL

Low-temperature plasma carburization and low-temperature plasma nitriding are the effective methods for hardening of thermally nonhardenable austenitic chromium-nickel steels. However, the ion-plasma methods of surface modification can lead to the roughness parameter increase. Previously, the authors identified that the level of surface roughness strongly depends on the temperature of plasma treatment. The hot topic of the research is the reduction of temperature of chemical and thermal treatment to ensure the effective hardening and low surface roughness of austenitic chromium-nickel steel. In this paper, using the X-ray phase analysis, microhardness measurements at various loads and optical profilometry, the authors studied the influence of carburization and nitriding in the electron beam plasma at the temperature of T =350 °C on the phase composition, microhardness and surface roughness of 04Cr17Ni8Ti austenitic steel. It is established that carburization and nitriding in the plasma generated by low-energy electron beam provides an increase in microhardness of the surface of austenitic steel in 5-6 times (from 220 to 1100 HV and 1390 HV 0.025, respectively). The effective hardening of the surface layer of austenitic steel is associated with the formation as a result of low-temperature plasma modification of carbon-supersaturated austenite γ_C and chromium carbides Cr₂₃C₆ during carburization, as well as S-phase (nitrogen-supersaturated austenite γ_N), ε-phase (Fe_2-3N) and γ¢-phase (Fe₄N) during nitriding. The study identified that stainless austenitic steel after carburization is characterized by the greater depth of a hardened layer than in the case of plasma nitriding. Low-temperature (at the temperature of T =350 °C) treatment in the plasma electron beam by carburization and nitriding provides the formation of a high-quality 04Cr17Ni8Ti steel surface with low values of roughness parameter Ra (185-265 nm) and, therefore, can be considered as a finishing operation during the surface hardening of austenitic steel.

austenitic stainless steel, plasma carburization, plasma nitriding, low-energy electron beam, microhardness, surface roughness