Elion Method of Nitriding of High-Chromium Stainless Steel: Structure and Properties

The work is aimed at analyzing the structure and properties of high-chromium austenitic steel AISI 310S, subjected to nitriding in a low-pressure gas discharge plasma. Nitriding was carried out on the «ELION» setup at 723, 793, and 823 K temperatures and 1, 3, and 5 hours duration. For effective heating of the samples, the electronic component of the gas discharge plasma was used. This treatment mode is called the elion mode, that is, it includes the action of both the electronic and ion components of a non-self-sustained arc discharge plasma with a glowing cathode. It was established that the hardness of the surface layer of steel is maximum (10.8 GPa) at a nitriding temperature of 793 K, regardless of the process duration. The thickness of the hardened layer reaches $60\ \mu\mathrm{m}$ and weakly depends on the process temperature. It is shown that the minimum (≈200 times less than the wear parameter of the initial steel) value of the wear parameter (maximum wear resistance) is achieved after 3 hours of nitriding at temperature of 793 K. It was found that nitrogen saturation of AISI 310S austenitic high-chromium steel in a low-pressure gas discharge plasma is accompanied by the formation of a multiphase structure. The hardening phases of the layer are chromium and iron nitrides, the particle sizes vary within a few tens of nanometers. It was shown for the first time that with the elion nitriding method for AISI 310S steel, a plate-like structure with alternating plates of austenite and iron nitride of the composition Fe4N is formed in the modified layer; the austenite plates transverse dimensions vary in the range of 10–60 nm, nitride layers transverse sizes vary in the range of 10–23 nm.