The Anisotropic Stress-Induced Diffusion and Trapping of Nitrogen in Austenitic Stainless Steel during Nitriding

Galdikas, Arvaidas; Moskaliovienė, Teresa

doi:10.3390/met10101319

Cited by 6 publications

(9 citation statements)

References 55 publications

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“…Coarse carbides are formed in the carbide-lacking area. A previous study reported that FCC materials have various carbon (and nitrogen) diffusion reactions depending on the crystal orientation, such as the (111) and (100) planes [ 25 , 26 ]. Comparing the two types of surfaces, because the activation energy of the dense (111) surface is larger than that of the more open (100) surface, it is relatively difficult to cause the reactions by carbon diffusion on the dense (111) surface [ 25 ].…”

Section: Resultsmentioning

confidence: 99%

Effect of Grain Size on Carburization Characteristics of the High-Entropy Equiatomic CoCrFeMnNi Alloy

Nam

Kim²,

Kim

et al. 2021

Materials

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In this study, the carburization characteristics of cast and cold-rolled CoCrFeMnNi high-entropy alloys (HEAs) with various grain sizes were investigated. All specimens were prepared by vacuum carburization at 940 °C for 8 h. The carburized/diffused layer was mainly composed of face-centered cubic structures and Cr7C3 carbide precipitates. The carburized/diffused layer of the cold-rolled specimen with a fine grain size (~1 μm) was thicker (~400 μm) than that of the carburized cast specimen (~200 μm) with a coarse grain size (~1.1 mm). In all specimens, the carbides were formed primarily through grain boundaries, and their distribution varied with the grain sizes of the specimens. However, the carbide precipitates of the cast specimen were formed primarily at the grain boundaries and were unequally distributed in the specific grains. Owing to the non-uniform formation of carbides in the carburized cast specimen, the areas in the diffused layer exhibited various carbide densities and hardness distributions. Therefore, to improve the carburization efficiency of equiatomic CoCrFeMnNi HEAs, it is necessary to refine the grain sizes.

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Section: Resultsmentioning

confidence: 99%

Effect of Grain Size on Carburization Characteristics of the High-Entropy Equiatomic CoCrFeMnNi Alloy

Nam

Kim²,

Kim

et al. 2021

Materials

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“…In addition, the γ N phase has a mixture of lattice parameters, as this phase is formed with different stoichiometries. The grains might contain crystalline structures with different lattice parameters, as the nitriding process is dependent on the crystalline orientation [40,41]. The broadening of the XRD peaks is caused by the strains induced in the crystal lattice due to the introduction of nitrogen in the solid solution, while the peaks overlapping correspond to the various non-stoichiometric Fe-N concentrations in the austenite CFC structure [14,27,42].…”

Section: Samplementioning

confidence: 99%

Identification of Expanded Austenite in Nitrogen-Implanted Ferritic Steel through In Situ Synchrotron X-ray Diffraction Analyses

Schibicheski Kurelo,

Lepienski,

de Oliveira

et al. 2023

Metals

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The existence and formation of expanded austenite in ferritic stainless steels remains a subject of debate. This research article aims to provide comprehensive insights into the formation and decomposition of expanded austenite through in situ structure analyses during thermal treatments of ferritic steels. To achieve this objective, we employed the Plasma Immersion Ion Implantation (PIII) technique for nitriding in conjunction with in situ synchrotron X-ray diffraction (ISS-XRD) for microstructural analyses during the thermal treatment of the samples. The PIII was carried out at a low temperature (300–400 °C) to promote the formation of metastable phases. The ISS-XRD analyses were carried out at 450 °C, which is in the working temperature range of the ferritic steel UNS S44400, which has applications, for instance, in the coating of petroleum distillation towers. Nitrogen-expanded ferrite (αN) and nitrogen-expanded austenite (γN) metastable phases were formed by nitriding in the modified layers. The production of the αN or γN phase in a ferritic matrix during nitriding has a direct relationship with the nitrogen concentration attained on the treated surfaces, which depends on the ion fluence imposed during the PIII treatment. During the thermal evolution of crystallographic phase analyses by ISS-XRD, after nitriding, structure evolution occurs mainly by nitrogen diffusion. In the nitrided samples prepared under the highest ion fluences—longer treatment times and frequencies (PIII 300 °C 6 h and PIII 400 °C 3 h) containing a significant amount of γN—a transition from the γN phase to the α and CrN phases and the formation of oxides occurred.

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“…Cr atoms are hypothesized to have a "trapping effect" on N atoms in the octahedral sites nearby, causing short-range ordering, while additional N atoms can be "detrapped" and diffuse rapidly through the expanded austenite layer [166][167][168]. A further phenomenon, which may influence the diffusion of interstitial atoms, is the high compressive residual stresses which are produced in the modified layer as a consequence of the expansion of austenite lattice, and may become an additional component of the driving force for the interstitial atoms transport [169][170][171].…”

Section: Formation Of Expanded Austenitementioning

confidence: 99%

The “Expanded” Phases in the Low-Temperature Treated Stainless Steels: A Review

Borgioli

2022

Metals

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Low-temperature treatments have become a valuable method for improving the surface hardness of stainless steels, and thus their tribological properties, without impairing their corrosion resistance. By using treatment temperatures lower than those usually employed for nitriding or carburizing of low alloy steels or tool steels, it is possible to obtain a fairly fast (interstitial) diffusion of nitrogen and/or carbon atoms; on the contrary, the diffusion of substitutional atoms, as chromium atoms, has significantly slowed down, therefore the formation of chromium compounds is hindered, and corrosion resistance can be maintained. As a consequence, nitrogen and carbon atoms can be retained in solid solutions in an iron lattice well beyond their maximum solubility, and supersaturated solid solutions are produced. Depending on the iron lattice structure present in the stainless steel, the so-called “expanded austenite” or “S-phase”, “expanded ferrite”, and “expanded martensite” have been reported to be formed. This review summarizes the main studies on the characteristics and properties of these “expanded” phases and of the modified surface layers in which these phases form by using low-temperature treatments. A particular focus is on expanded martensite and expanded ferrite. Expanded austenite–S-phase is also discussed, with particular reference to the most recent studies.

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The Anisotropic Stress-Induced Diffusion and Trapping of Nitrogen in Austenitic Stainless Steel during Nitriding

Cited by 6 publications

References 55 publications

Effect of Grain Size on Carburization Characteristics of the High-Entropy Equiatomic CoCrFeMnNi Alloy

Effect of Grain Size on Carburization Characteristics of the High-Entropy Equiatomic CoCrFeMnNi Alloy

Identification of Expanded Austenite in Nitrogen-Implanted Ferritic Steel through In Situ Synchrotron X-ray Diffraction Analyses

The “Expanded” Phases in the Low-Temperature Treated Stainless Steels: A Review

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