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Effect of Triple Treatment on the Surface Structure and Hardness of 304 Austenitic Stainless Steel |
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PP: 135-148 |
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doi:10.18576/isl/120110
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Author(s) |
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Mohammed H. Fawey,
A. M. Abd El-Rahman,
F. M. El-Hossary,
Tawheed Hashem,
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Abstract |
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| 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.
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