Gaseous processes for low temperature surface hardening of stainless steel

Somers, Marcel A. J.; Christiansen, Thomas

doi:10.1533/9780857096524.4.581

Cited by 12 publications

(11 citation statements)

References 28 publications

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“…For gas-based treatments the employed gaseous atmospheres are not usually able to remove the passive film, so that activation pre-treatments are required. Some activation treatments have been recently reviewed by Somers and Christiansen [86]. Stripping the passive film and replacing it with a thin metallic layer (nickel [57,87] or iron [88]) allow to prevent surface repassivation and can catalytically promote the dissociation of gaseous species at the surface.…”

Section: Activation Of the Surface Of Austenitic Stainless Steels And Pre-treatment Processesmentioning

confidence: 99%

“…Stripping the passive film and replacing it with a thin metallic layer (nickel [57,87] or iron [88]) allow to prevent surface repassivation and can catalytically promote the dissociation of gaseous species at the surface. The passive film can also be removed using chemical etching [89], or with the addition of reactive compounds, as halogen-based ones, to the gaseous atmosphere [90], or using reducing gases as mixtures of acetylene-hydrogen atmospheres at high temperatures [86], or with ion sputtering [89,91]. Baranowska [89] and Baranowska et al [91] pointed out that the activation process influences the N adsorption in gas nitriding treatment.…”

Section: Activation Of the Surface Of Austenitic Stainless Steels And Pre-treatment Processesmentioning

confidence: 99%

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From Austenitic Stainless Steel to Expanded Austenite-S Phase: Formation, Characteristics and Properties of an Elusive Metastable Phase

Borgioli

2020

Metals

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Austenitic stainless steels are employed in many industrial fields, due to their excellent corrosion resistance, easy formability and weldability. However, their low hardness, poor tribological properties and the possibility of localized corrosion in specific environments may limit their use. Conventional thermochemical surface treatments, such as nitriding or carburizing, are able to enhance surface hardness, but at the expense of corrosion resistance, owing to the formation of chromium-containing precipitates. An effective alternative is the so called low temperature treatments, which are performed with nitrogen- and/or carbon-containing media at temperatures, at which chromium mobility is low and the formation of precipitates is hindered. As a consequence, interstitial atoms are retained in solid solution in austenite, and a metastable supersaturated phase forms, named expanded austenite or S phase. Since the first studies, dating 1980s, the S phase has demonstrated to have high hardness and good corrosion resistance, but also other interesting properties and an elusive structure. In this review the main studies on the formation and characteristics of S phase are summarized and the results of the more recent research are also discussed. Together with mechanical, fatigue, tribological and corrosion resistance properties of this phase, electric and magnetic properties, wettability and biocompatibility are overviewed.

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Section: Activation Of the Surface Of Austenitic Stainless Steels And Pre-treatment Processesmentioning

confidence: 99%

Section: Activation Of the Surface Of Austenitic Stainless Steels And Pre-treatment Processesmentioning

confidence: 99%

From Austenitic Stainless Steel to Expanded Austenite-S Phase: Formation, Characteristics and Properties of an Elusive Metastable Phase

Borgioli

2020

Metals

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“…Since the mid-eighties of the previous century, surface hardening of primarily austenitic stainless steel by the dissolution of nitrogen, carbon atoms, or both has developed into a commercially successful remedy against galling and wear and has further improved the corrosion performance, in particular with respect to localized corrosion, i.e., pitting and crevice corrosion. For a description of the historical development, the process variants, and the obtainable properties and performance improvement, the reader is referred to recent comprehensive reviews of the topic [1][2][3][4][5]. The microstructure developing during low temperature surface hardening of stainless steel consists of a zone of a supersaturated solid solution of interstitial atoms (N, C, or both) in austenite, called expanded austenite.…”

Section: Introductionmentioning

confidence: 99%

“…The microstructure developing during low temperature surface hardening of stainless steel consists of a zone of a supersaturated solid solution of interstitial atoms (N, C, or both) in austenite, called expanded austenite. 4 Expanded austenite refers to an expansion of the crystal lattice as a consequence of the (colossal) interstitial content in supersaturated solid solution, which, expressed as the number of interstitials per metal atom, amounts to up to 0.61 or 0.22 for nitrogen and carbon, respectively [6,7]. As a consequence of the lattice expansion, which with the highest nitrogen content reaches 11 % for the lattice parameter, huge compressive residual stresses develop.…”

Section: Introductionmentioning

confidence: 99%

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Residual Stress in Expanded Austenite on Stainless Steel; Origin, Measurement, and Prediction

Somers

Kücükyildiz

Ormstrup

et al. 2018

Materials Performance and Characterization

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Expanded austenite is a supersaturated solid solution of nitrogen/carbon in austenite that forms as a case by the diffusion of nitrogen/carbon into austenitic stainless steel. Expanded austenite has a high level of hardness that provides resistance against galling and wear, superior resistance against localized corrosion, and contributes to improvement of the fatigue performance. This latter characteristic is a consequence of the huge compressive residual stresses in the expanded austenite case. Such stresses are induced by the high interstitial content in the austenite lattice and are accommodated elasto-plastically. The experimental assessment of the elastic lattice strains is complicated by the presence of steep composition-depth and stress-depth profiles, which necessitate special measurement or correction procedures to unravel the influence of composition and stress on the lattice spacing and avoid artifacts arising from (steep) lattice-spacing gradients. In the present work the sin 2 ψ method was combined with grazing incidence X-ray diffraction to keep the information depth during measurement shallow, independent of the (effective) tilt angle ψ. The plastic strains in the expanded austenite 27 zone were estimated from the lattice rotations, as determined with electron backscatter diffraction. It is demonstrated that the level of elastic lattice strains in expanded austenite can be adjusted by retracting part of the dissolved nitrogen. The experimental results for elastic and plastic strains are compared to those predicted by a comprehensive numerical Manuscript

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On the Nitrogen-Induced Lattice Expansion of a Non-stainless Austenitic Steel, Invar 36®, Under Triode Plasma Nitriding

Tao

Matthews

Leyland

2019

Metall Mater Trans A

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Chromium, as a strong nitride-forming element, is widely regarded to be an ''essential'' ingredient for the formation of a nitrogen-expanded lattice in thermochemical nitrogen diffusion treatments of austenitic (stainless) steels. In this article, a proprietary ''chrome-free'' austenitic iron-nickel alloy, Invar Ò 36 (Fe-36Ni, in wt pct), is characterized after triode plasma nitriding (TPN) treatments at 400°C to 450°C and compared with a ''stainless'' austenitic counterpart RA 330 Ò (Fe-19Cr-35Ni, in wt pct) treated under equivalent nitriding conditions. Cr does indeed appear to play a pivotal role in colossal nitrogen supersaturation (and hence anisotropic lattice expansion and superior surface hardening) of austenitic steel under low-temperature (£ 450°C) nitrogen diffusion. Nevertheless, this work reveals that nitrogen-induced lattice expansion occurs below the nitride-containing surface layer in Invar 36 alloy after TPN treatment, implying that Cr is not a necessity for the nitrogen-interstitial induced lattice expansion phenomenon to occur, also suggesting another type of c N .

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Gaseous processes for low temperature surface hardening of stainless steel

Cited by 12 publications

References 28 publications

From Austenitic Stainless Steel to Expanded Austenite-S Phase: Formation, Characteristics and Properties of an Elusive Metastable Phase

From Austenitic Stainless Steel to Expanded Austenite-S Phase: Formation, Characteristics and Properties of an Elusive Metastable Phase

Residual Stress in Expanded Austenite on Stainless Steel; Origin, Measurement, and Prediction

On the Nitrogen-Induced Lattice Expansion of a Non-stainless Austenitic Steel, Invar 36®, Under Triode Plasma Nitriding

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