The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Tiziano Bacci - One of the best experts on this subject based on the ideXlab platform.
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low temperature nitriding of aisi 300 and 200 series austenitic stainless steels
Vacuum, 2016Co-Authors: Francesca Borgioli, Emanuele Galvanetto, Tiziano BacciAbstract:Abstract In this study the effects of low temperature plasma nitriding on the characteristics of different austenitic stainless steels, CrNi-based (AISI 304L and AISI 316L) and CrMn-based (AISI 202), were compared. Samples were Nitrided at 400 and 430 °C, at 1000 Pa for 5 h, and their microstructure, phase composition, microhardness and corrosion resistance were evaluated. The characteristics of modified surface layers depended on both treatment parameters and alloy composition. For all the steels modified surface layers had a double layer microstructure. In the outer modified layer, mainly consisting of S phase, deformation (or shear) bands were observed in the grains, and nitrogen induced h.c.p. martensite, e′ N , formed. The tendency to form shear bands and e′ N was higher for AISI 202 samples, and decreased for AISI 304L and then for AISI 316L ones, influencing the modified layer thickness. When nitriding was performed at 430 °C, Nitrides formed, and their amount was affected by steel composition. Nitriding treatments allowed to markedly increase surface microhardness and corrosion resistance, in comparison with the untreated alloys. When Nitrides did not form, as for the 400-°C Nitrided samples, the corrosion behaviour of the considered steels was comparable. Nitride precipitation affected corrosion resistance, increasing corrosion phenomena.
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glow discharge nitriding of aisi 316l austenitic stainless steel influence of treatment pressure
Surface & Coatings Technology, 2006Co-Authors: Francesca Borgioli, Emanuele Galvanetto, Tiziano Bacci, Andrea Fossati, G PradelliAbstract:Abstract The influence of treatment pressure on the characteristics of the modified surface layers produced by low-temperature d.c. glow discharge nitriding on AISI 316L austenitic stainless steel samples is investigated. Glow discharge nitriding treatments were performed at 703 K for 5 h at working pressures in the range of 1.5–20 hPa. Morphology and microstructure of the untreated and Nitrided samples were studied by means of microscopy techniques, energy dispersion spectroscopy and X-ray diffraction analysis; microhardness measurements and corrosion resistance tests were also performed. The nitriding treatments produce a hardened surface layer consisting mainly of the so-called S phase. The presence of Nitrides and the thickness of the modified layer depend on the used treatment pressure. When treatments are performed at 2.5 hPa, a fairly large amount of Nitrides is observed in the modified layer, while when the nitriding pressure is lower or higher than 2.5 hPa, the Nitride amount decreases and the layer becomes thinner. When the treatments are performed at 10 or 20 hPa, only a very small amount of chromium Nitride is present as small surface precipitates. Metallographic analysis shows that many slip lines are present both at the surface and in the cross-section of the modified layer, presumably due to high stresses occurring during the formation of the layer. X-ray diffraction analysis of the S phase shows that its diffraction peaks are shifted from those of a perfect f.c.c. lattice; the observed shifts may be explained assuming that the S phase has an f.c.c. structure with a high density of stacking faults. Corrosion resistance tests, performed in 5% NaCl aerated solution with the potentiodynamic method, show that with the used treatment parameters nitriding at a pressure of 10 hPa or higher allows to obtain a significant improvement of the corrosion resistance in respect of the untreated alloy, reducing the anodic currents up to about 4 orders of magnitude.
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glow discharge nitriding of aisi 316l austenitic stainless steel influence of treatment temperature
Surface & Coatings Technology, 2005Co-Authors: Francesca Borgioli, Emanuele Galvanetto, Andrea Fossati, Tiziano BacciAbstract:Abstract Nitriding treatments of austenitic stainless steels can be performed only at relatively low temperatures in order to avoid a decrease of corrosion resistance due to chromium Nitride formation. These conditions promote the formation of the so-called S phase, which shows high hardness and good corrosion resistance. In the present paper, the influence of the treatment temperature of glow-discharge nitriding process on the microstructural and mechanical characteristics of AISI 316L steel samples was evaluated. Glow-discharge nitriding treatments were performed at temperatures in the range 673–773 K for 5 h at 10 3 Pa. The modified surface layer of the Nitrided samples consists mainly of the S phase and, according to metallographic technique analysis, it seems to be essentially a modification of the austenite matrix. All the Nitrided sample types show a peculiar surface morphology due to both plasma etching during nitriding and the presence of slip steps and relieves at grain boundaries, the latter features presumably due to the formation of the Nitrided layer. X-ray diffraction analysis shows that for the samples Nitrided at temperatures up to 723 K, besides the S phase, small chromium Nitride precipitates are present at the surface, while using higher treatment temperatures both chromium (CrN) and iron (γ'-Fe 4 N) Nitrides precipitate along the grain boundaries and in the middle of the grains, and their amount increases as treatment temperature increases. High hardness values (from ∼1450 to ∼1550 HK 0.01 , depending on nitriding conditions) are observed in the modified layer with a steep decrease to matrix values. Preliminary corrosion resistance tests, carried out in 5% NaCl aerated solution with the potentiodynamic method, show that with the used treatment parameters a substantial improvement of corrosion resistance can be achieved when glow-discharge nitriding treatments are performed at temperatures in the range 703–723 K.
Lie Shen - One of the best experts on this subject based on the ideXlab platform.
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plasma nitriding of aisi 304 austenitic stainless steel with pre shot peening
Surface & Coatings Technology, 2010Co-Authors: Yi Zuo Wang, Lie Shen, Liang Wang, Chunhua WangAbstract:AISI 304 austenitic stainless steel was plasma Nitrided at the temperature ranging from 410 to 520 °C with pre-shot peening. The structural phases, micro-hardness and electrochemical behavior of the Nitrided layer were investigated by optical microscopy, X-ray diffraction, micro-hardness testing and anodic polarization testing. The effects of shot peening on the Nitride formation, Nitride layer growth and corrosion properties were discussed. The results showed that shot peening enhanced the nitrogen diffusion rate and led to a twice thicker Nitrided layer than the un-shot peening samples under the same plasma nitriding conditions (410 °C, 4 h). The Nitrided layer was composed of single nitrogen expanded austenite (S-phase) when nitriding below 480 °C, which had combined improvement in hardness and corrosion resistance.
Francesca Borgioli - One of the best experts on this subject based on the ideXlab platform.
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low temperature nitriding of aisi 300 and 200 series austenitic stainless steels
Vacuum, 2016Co-Authors: Francesca Borgioli, Emanuele Galvanetto, Tiziano BacciAbstract:Abstract In this study the effects of low temperature plasma nitriding on the characteristics of different austenitic stainless steels, CrNi-based (AISI 304L and AISI 316L) and CrMn-based (AISI 202), were compared. Samples were Nitrided at 400 and 430 °C, at 1000 Pa for 5 h, and their microstructure, phase composition, microhardness and corrosion resistance were evaluated. The characteristics of modified surface layers depended on both treatment parameters and alloy composition. For all the steels modified surface layers had a double layer microstructure. In the outer modified layer, mainly consisting of S phase, deformation (or shear) bands were observed in the grains, and nitrogen induced h.c.p. martensite, e′ N , formed. The tendency to form shear bands and e′ N was higher for AISI 202 samples, and decreased for AISI 304L and then for AISI 316L ones, influencing the modified layer thickness. When nitriding was performed at 430 °C, Nitrides formed, and their amount was affected by steel composition. Nitriding treatments allowed to markedly increase surface microhardness and corrosion resistance, in comparison with the untreated alloys. When Nitrides did not form, as for the 400-°C Nitrided samples, the corrosion behaviour of the considered steels was comparable. Nitride precipitation affected corrosion resistance, increasing corrosion phenomena.
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glow discharge nitriding of aisi 316l austenitic stainless steel influence of treatment pressure
Surface & Coatings Technology, 2006Co-Authors: Francesca Borgioli, Emanuele Galvanetto, Tiziano Bacci, Andrea Fossati, G PradelliAbstract:Abstract The influence of treatment pressure on the characteristics of the modified surface layers produced by low-temperature d.c. glow discharge nitriding on AISI 316L austenitic stainless steel samples is investigated. Glow discharge nitriding treatments were performed at 703 K for 5 h at working pressures in the range of 1.5–20 hPa. Morphology and microstructure of the untreated and Nitrided samples were studied by means of microscopy techniques, energy dispersion spectroscopy and X-ray diffraction analysis; microhardness measurements and corrosion resistance tests were also performed. The nitriding treatments produce a hardened surface layer consisting mainly of the so-called S phase. The presence of Nitrides and the thickness of the modified layer depend on the used treatment pressure. When treatments are performed at 2.5 hPa, a fairly large amount of Nitrides is observed in the modified layer, while when the nitriding pressure is lower or higher than 2.5 hPa, the Nitride amount decreases and the layer becomes thinner. When the treatments are performed at 10 or 20 hPa, only a very small amount of chromium Nitride is present as small surface precipitates. Metallographic analysis shows that many slip lines are present both at the surface and in the cross-section of the modified layer, presumably due to high stresses occurring during the formation of the layer. X-ray diffraction analysis of the S phase shows that its diffraction peaks are shifted from those of a perfect f.c.c. lattice; the observed shifts may be explained assuming that the S phase has an f.c.c. structure with a high density of stacking faults. Corrosion resistance tests, performed in 5% NaCl aerated solution with the potentiodynamic method, show that with the used treatment parameters nitriding at a pressure of 10 hPa or higher allows to obtain a significant improvement of the corrosion resistance in respect of the untreated alloy, reducing the anodic currents up to about 4 orders of magnitude.
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glow discharge nitriding of aisi 316l austenitic stainless steel influence of treatment temperature
Surface & Coatings Technology, 2005Co-Authors: Francesca Borgioli, Emanuele Galvanetto, Andrea Fossati, Tiziano BacciAbstract:Abstract Nitriding treatments of austenitic stainless steels can be performed only at relatively low temperatures in order to avoid a decrease of corrosion resistance due to chromium Nitride formation. These conditions promote the formation of the so-called S phase, which shows high hardness and good corrosion resistance. In the present paper, the influence of the treatment temperature of glow-discharge nitriding process on the microstructural and mechanical characteristics of AISI 316L steel samples was evaluated. Glow-discharge nitriding treatments were performed at temperatures in the range 673–773 K for 5 h at 10 3 Pa. The modified surface layer of the Nitrided samples consists mainly of the S phase and, according to metallographic technique analysis, it seems to be essentially a modification of the austenite matrix. All the Nitrided sample types show a peculiar surface morphology due to both plasma etching during nitriding and the presence of slip steps and relieves at grain boundaries, the latter features presumably due to the formation of the Nitrided layer. X-ray diffraction analysis shows that for the samples Nitrided at temperatures up to 723 K, besides the S phase, small chromium Nitride precipitates are present at the surface, while using higher treatment temperatures both chromium (CrN) and iron (γ'-Fe 4 N) Nitrides precipitate along the grain boundaries and in the middle of the grains, and their amount increases as treatment temperature increases. High hardness values (from ∼1450 to ∼1550 HK 0.01 , depending on nitriding conditions) are observed in the modified layer with a steep decrease to matrix values. Preliminary corrosion resistance tests, carried out in 5% NaCl aerated solution with the potentiodynamic method, show that with the used treatment parameters a substantial improvement of corrosion resistance can be achieved when glow-discharge nitriding treatments are performed at temperatures in the range 703–723 K.
Chunhua Wang - One of the best experts on this subject based on the ideXlab platform.
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plasma nitriding of aisi 304 austenitic stainless steel with pre shot peening
Surface & Coatings Technology, 2010Co-Authors: Yi Zuo Wang, Lie Shen, Liang Wang, Chunhua WangAbstract:AISI 304 austenitic stainless steel was plasma Nitrided at the temperature ranging from 410 to 520 °C with pre-shot peening. The structural phases, micro-hardness and electrochemical behavior of the Nitrided layer were investigated by optical microscopy, X-ray diffraction, micro-hardness testing and anodic polarization testing. The effects of shot peening on the Nitride formation, Nitride layer growth and corrosion properties were discussed. The results showed that shot peening enhanced the nitrogen diffusion rate and led to a twice thicker Nitrided layer than the un-shot peening samples under the same plasma nitriding conditions (410 °C, 4 h). The Nitrided layer was composed of single nitrogen expanded austenite (S-phase) when nitriding below 480 °C, which had combined improvement in hardness and corrosion resistance.
Wang Liang - One of the best experts on this subject based on the ideXlab platform.
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surface modification of aisi 304 austenitic stainless steel by plasma nitriding
Applied Surface Science, 2003Co-Authors: Wang LiangAbstract:Abstract Plasma nitriding of austenitic stainless steel samples has been carried out using pulse dc glow discharge plasma of NH3 gas at substrate temperature ranging from 350 to 520 °C. A nitriding time of only 4 h has been found to produce a compact surface Nitride layer composed of γN′ phase with a thickness of around 7–12 μm as processing temperature remained between 420 and 450 °C. The thickness of γN phase was found to be very thin only about 2 μm after plasma nitriding at temperature below 400 °C. Microhardness measurements showed significant increase in the hardness from 240 HV (for untreated samples) up to 1700 HV (for Nitrided samples at temperature of 460 °C). For nitriding at higher temperature, i.e. above 460 °C, the chromium Nitrides precipitated in the Nitrided layer and caused austenite phase transform into ferrite phase or iron Nitrides (γ′ or e). The consequent result of chromium Nitride precipitation is the reduction of corrosion resistance of Nitrided layer. Compressive residual stresses existed in the Nitrided layer due to nitrogen diffusion into austenitic stainless steel.
