Abstract:In this work, the influence of working pressure on the characteristics of the layers produced by the nitriding treatment on the AISI 316 austenitic stainless steel surface using the Cathodic Cage Plasma Nitriding technique (CCPN) is assessed. The treatments were carried out at a temperature of 723 K for 5 hours under working pressures of 120, 250 and 500 Pa. The morphology, microstructure and corrosion resistance were studied through optical microscopy, x-ray diffraction, and electrochemical potential curves. … Show more
“…At 450 and 500 ºCthe peaks corresponding to the austenite phase disappear and the peaks corresponding to CrN and Fe 3 N phases appear. At these temperatures, the expanded austenite decomposes to form CrN and Fe 3 N phases [29]. Moreover, the extent to which the CrN forms at 500 ºChas been found to be higher than that formed at 450 ºC.…”
“…At 450 and 500 ºCthe peaks corresponding to the austenite phase disappear and the peaks corresponding to CrN and Fe 3 N phases appear. At these temperatures, the expanded austenite decomposes to form CrN and Fe 3 N phases [29]. Moreover, the extent to which the CrN forms at 500 ºChas been found to be higher than that formed at 450 ºC.…”
“…The dissolution of a large amount of active atomic nitrogen and carbon into the crystal lattice results in distortion and expansion of the austenite and leads to increase in lattice constant. Supersaturated with nitrogen and carbon austenite (Fe-γ N, C ) decomposes into Fe-α N, C , Cr(N, C) and Fe 4 (N, C) phases when treatment temperature exceeds 450°C [1][2][3][4][5][6][7][8]10,21]. A high density of the defects of the crystal structure contributes to great and deep diffusion processes under surface saturation of metals with interstitials [1,7,12,13].…”
Section: Resultsmentioning
confidence: 99%
“…Ion-plasma treatment (IPT) allows to reduce treatment temperature (below 600°C) and processing time as compared to diffusion saturation in gases. Surface IPT-assisted properties are strongly dependent on process parameters (treatment temperature [2,3], processing time [4], pressure [5], etc. ), the initial microstructure [7], chemical and phase composition [8] of saturated material.…”
Section: Introductionmentioning
confidence: 99%
“…IPT-processing is accompanied with diffusion alloying of steel surface with nitrogen and carbon and can facilitate series of phase transformations with different resultant products -precipitates (based on Fe, Cr, V, Mn, etc. ), austenite supersaturated with nitrogen or carbon (so-called expanded austenite γ N, C or S-phase) and ferrite [1][2][3][4][5][6][7][8][9][10][11]. Initial microstructure of the material is one of the key parameters during IPT.…”
The effect of pre-deformation by cold-rolling on phase composition and nanohardness of a surface layer and resultant tensile properties of Fe-17Cr-13Ni-2.7Mo-1.7Mn-0.6Si-0.01C (wt.%, 316L-type) austenitic stainless steel subjected to an ion-plasma treatment was investigated. The ion-plasma treatment facilitates a formation of inhomogeneous surface layers of ≈18 -25 μm in thickness in steel specimens. Independently of type of initial microstructure, coarse-grained or highly defective deformationassociated one, the surface layers of the steel specimens undergo similar phase transformations under ion-plasma treatment. Solid-solution strengthening of austenite (Fe-γ N, C ) and dispersion hardening by different phases (Fe 4 (N, C), Cr(N, C), Fe-α N, C ) both increase surface nanohardness and tensile strength characteristics of austenitic stainless steel. X-ray diffraction data show that morphology and distribution of dispersed phases in the surface layers could be strongly dependent on prior microstructure of the steel. In ion-plasma treatment, specimens with coarse-grained structure are prone to accumulate and save interstitials in austenite (solid-solution). After surface treatment, higher strength properties (nanohardness) of the composition layer and more extended diffusion zone both provide higher tensile strength characteristics of pre-deformed specimens as compared to coarse-grained one. The experimental results clearly show that surface hardening of specimens of 316L-type austenitic stainless steel during ion-plasma treatment strongly depends on its initial microstructure.
“…phase (γ N ) with a peak nitrogen concentration up to 35 at.% on the austenitic stainless steel. 1 It was verified that the γ N phase layer on austenitic stainless steel has superior pitting corrosion resistance and equivalent general corrosion resistance in comparison with that of original austenitic stainless steel in NaCl, [2][3][4][5][6][7][8][9][10][11][12][13][14] and Na 2 SO 4 15 and H 2 SO 4 2,6,10,16,17 aqueous solutions. However, a few reports have described the corrosion resistance of the γ N phase layer on austenitic stainless steel in borate solution, 18,19 although different nitrogenmodified austenitic stainless steel has been made in an effort to increase hardness and wear resistance of austenitic stainless steel for use in nuclear power systems.…”
The corrosion behavior of a high nitrogen face-centered-cubic (f.c.c.) phase (γ N ) formed on plasma-based low-energy nitrogen ion implanted AISI 304L austenitic stainless steel in a borate buffer solution with a pH value of 8.4 was investigated by using anodic polarization, electrochemical impedance spectroscopy, Mott-Schottky analysis and Auger electron spectroscopy/x-ray photoelectron spectroscopy. Compared with original austenitic stainless steel, the γ N phase layer on austenitic stainless steel possessed a significant improvement in corrosion resistance in the borate buffer solution with an apparent decrease of passivation current density and an increase of corrosion potential. A larger electrochemical impedance with a maximal phase angle of the 83 • over low frequency range was obtained for the γ N phase layer. The donor and acceptor densities of the γ N phase layer and the corresponding flat band potential decreased, relative to that of original austenitic stainless steel. The protective passive film on the γ N phase layer was observed as n-type and p-type semiconductors in the potential range above and below the flat band potential, respectively. It was composed of hydroxide/oxides of iron and chromium in the outer region and oxides of chromium and iron in the inner region both accompanied by chromium and iron nitrides, unlike original stainless steel which had pure iron and chromium on outermost surface. The calculated passive film thickness of 2.82 ± 0.67 nm on the γ N phase layer by the power law distribution was compared with the measured thickness of 6.5 nm by AES/XPS. The improvement mechanism of nitrogen atoms in the γ N phase layer on corrosion properties in the borate buffer solution was proposed by means of an applied point defect model.In order to improve combined properties in wear and corrosion resistance of Fe-Cr-Ni austenitic stainless steel, a series of nitrogenmodified processes has been successfully used to form the modified layer composed of a single high nitrogen face-centered-cubic (f.c.c.) phase (γ N ) with a peak nitrogen concentration up to 35 at.% on the austenitic stainless steel. 1 It was verified that the γ N phase layer on austenitic stainless steel has superior pitting corrosion resistance and equivalent general corrosion resistance in comparison with that of original austenitic stainless steel in NaCl, 2-14 and Na 2 SO 4 15 and H 2 SO 4 2,6,10,16,17 aqueous solutions. However, a few reports have described the corrosion resistance of the γ N phase layer on austenitic stainless steel in borate solution, 18,19 although different nitrogenmodified austenitic stainless steel has been made in an effort to increase hardness and wear resistance of austenitic stainless steel for use in nuclear power systems. 20 Moreover, corrosion fatigue cracking in borate solution is one of the typical failure types for Fe-Cr-Ni austenitic stainless steel applied in nuclear power equipment, which is always initiated by destruction and dissolution of the passive film on austenitic stainless steel. 2...
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