Hydrogen-Free Active Screen Plasma Nitriding of AISI 316 L Stainless Steel

The paper discusses active screen plasma nitriding (ASPN) of AISI 316 L austenitic stainless steel without the use of hydrogen. It is shown that hydrogen-free plasma nitriding with double-folded active screen provides the formation of hard diffusion layers at 570 °С. In the case of conventional plasma nitriding without the use of the active screen, the diffusion layers are obtained at 600 °С and have lower length and hardness. The increase in the ASPN process time from 30 to 360 min results in the thickness growth of the nitrided layers from 10 to 90 μm and the growth in the S phase (expanded austenite) content. The time increase of the ASPN process is accompanied by the reduction in the corrosion resistance of 316 L austenitic stainless steel. But at a relatively short process time (30 min), when the thickness of diffusion layers does not exceed 10–20 μm, the corrosion resistance even slightly improves at a simultaneous hardness growth and wear rate reduction. As a result, high-temperature and high-speed hydrogen-free plasma nitriding is demonstrated for 316 L austenitic stainless.