Fawey, M. H. / Abd El-Rahman, A.M. / El-Hossary, F. M. / Hashem, T. (2023)

Natural Sciences Publishing, 2023, 12, 1, 135-148, doi 10.18576/isl/120110

Abstract

Nitriding, annealing, and carbonitriding processes are conducted to modify the surface of AISI 304 austenitic stainless steel via radio frequency plasma. A ~20 μm thick nitride layer is obtained in ten minutes at a plasma power of 450 W. Hence, all nitrided samples are annealed under vacuum for one hour at 400 ̊C. The nitrided-annealed samples are carbonitrided via the identical technique at various C2H2/N2 gas pressure ratios. Numerous analytical techniques, including X-ray diffractometry, glow discharge optical spectroscopy (GDOS), Talysurf Intra Profilemeter, optical microscopy (OM), scanning electron microscopy (SEM), and Vickers microhardness tester, were employed to investigate the triple-treated specimens. Microstructure analysis of the triple-treated samples reveals the formation of N2 expanded austenite phase (γN), γʹ-Fe4N, CrN, Fe3C, and Fe7C3. The results indicate that the elemental composition, microhardness, and thickness of the triple-treated layers are all depending on the gas composition. After carbonitriding, the total thickness of the compound layer grew from ~20 to ~34.5 μm. The surface microhardness of the triple-treated samples increased as the C2H2/N2 gas composition ratio increased up to 70%, reaching 1,497±33.5 HV0.1, which is ~6.8 and ~1.42 folds higher than the untreated and prenitrided samples, respectively.

Download