“Colossal” interstitial supersaturation in delta ferrite in stainless steels—I. Low-temperature carburization

Wang, D.; Chen, C. W.; Dalton, J. C.; Yang, Fan; Sharghi-Moshtaghin, Reza; Kahn, H.; Ernst, F.; Williams, Robert E.A.; McComb, David W.; Heuer, A. H.

doi:10.1016/j.actamat.2014.12.013

Cited by 19 publications

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“…2e) from a ferrite grain undergoing transformation to a weak-contrast appearance deeper in the case shows diffuse streaks along [0 0 1] bcc directions and no sign of any nitride formation, indicating that it is at an early stage of weak-contrast ferrite formation [14]. However, this diffraction pattern is significantly different from the one obtained from the original ferrite grain in the bulk material shown in Fig.…”

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confidence: 84%

Section: Introductionmentioning

confidence: 99%

“…Although NiAl particles form in the ferrite grains in the bulk material during low-temperature carburization or nitridation, NiAl cannot be readily observed in the near-surface carburized or nitrided weak-contrast ferrite grains. This is apparent by the absence of NiAl reflections in all the diffraction patterns acquired from weak-contrast grains after both low-temperature carburization and low-temperature nitridation [14,15,18].…”

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confidence: 94%

“…The ferrite phase in the alloy responds to such interstitial hardening in a very unique and unusual manner, leading to a weak-contrast appearance in conventional transmission electron microscopy (TEM) images. Nanometer-scale NiAl precipitates were observed in the ferrite grains in the bulk but absent in the weak-contrast grains [14].In the present work, we investigate the effect of lowtemperature carburization and nitridation on the formation of NiAl precipitates in the ferrite phase of 17-7 PH stainless steel. 17-7 PH stainless steel in condition A [1] was provided by AK steel in the form of 3 mm thick plates.…”

mentioning

confidence: 96%

“…Interestingly, a thin carbidic layer formed on the carburized surface. However, there was no report of NiAl formation.Low-temperature carburization and nitridation have also been successfully applied to 17-7 PH stainless steel [14,15]. The ferrite phase in the alloy responds to such interstitial hardening in a very unique and unusual manner, leading to a weak-contrast appearance in conventional transmission electron microscopy (TEM) images.…”

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NiAl precipitation in delta ferrite grains of 17-7 precipitation-hardening stainless steel during low-temperature interstitial hardening

et al. 2015

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a b s t r a c tInterstitial hardening via low-temperature carburization and nitridation has been studied in 17-7 precipitation-hardening stainless steel. During such interstitial hardening, nanometer-scale NiAl precipitates form in delta ferrite in the bulk, but not in the hardened surface layer. In the carburized ferrite grains, regions of NiAl stoichiometry could be identified, but cannot be identified as regions with a different crystal structure. In the nitrided grains, NiAl particles could neither be detected by corresponding changes in local composition nor by their crystal structure.Precipitation-hardening (PH) stainless steels are a family of stainless steels that combine high strength, ductility, and good corrosion resistance. They are widely used as structural materials in various industrial applications. Depending on the thermal history, alloys can contain variable amounts of austenite, ferrite, and martensite. Precipitation hardening in these steels is achieved by homogeneously dispersed fine precipitates formed during aging.PH stainless steels containing Ni and Al (like 17-7 and 13-8 Mo) can be age-hardened by the formation of NiAl particles (space group Pm 3m). The lattice parameter of stoichiometric NiAl at room temperature is 0.2887 nm, which is very close to the lattice parameter of the ferrite matrix (0.2881 nm in this study). The aging temperature of 17-7 PH stainless steel is above 773 K [1].Age hardening by NiAl was studied previously in several stainless steels. In the initial stage of NiAl precipitation, there are significant fractions of Cr, Mo, and Fe present in the precipitates [2-6]. As aging proceeds, the fractions of Ni and Al increases and the Ni-to-Al ratio approaches unity [2,3]. The NiAl precipitates are nanometer-sized, spherical, and coherent with the ferrite-or martensite matrix [6].Low-temperature carburization or nitridation are effective ways to improve surface properties and corrosion resistance of stainless steels [7][8][9][10][11][12][13]. For PH 13-8 Mo stainless steel, a significant increase of surface hardness and corrosion resistance was achieved after low-temperature carburization [13]. Interestingly, a thin carbidic layer formed on the carburized surface. However, there was no report of NiAl formation.Low-temperature carburization and nitridation have also been successfully applied to 17-7 PH stainless steel [14,15]. The ferrite phase in the alloy responds to such interstitial hardening in a very unique and unusual manner, leading to a weak-contrast appearance in conventional transmission electron microscopy (TEM) images. Nanometer-scale NiAl precipitates were observed in the ferrite grains in the bulk but absent in the weak-contrast grains [14].In the present work, we investigate the effect of lowtemperature carburization and nitridation on the formation of NiAl precipitates in the ferrite phase of 17-7 PH stainless steel. 17-7 PH stainless steel in condition A [1] was provided by AK steel in the form of 3 mm thick plates. The nominal composition is 17-19 at.% Cr, ...

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confidence: 84%

Section: Introductionmentioning

confidence: 99%

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confidence: 94%

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confidence: 96%

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confidence: 99%

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NiAl precipitation in delta ferrite grains of 17-7 precipitation-hardening stainless steel during low-temperature interstitial hardening

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Low-Temperature Nitridation of 2205 Duplex Stainless Steel

Dalton

Ernst

Heuer

2019

Metall Mater Trans A

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“Colossal” interstitial supersaturation in delta ferrite in stainless steels: (II) low-temperature nitridation of the 17-7 PH alloy

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Low-temperature gas-phase nitridation has been studied in interstitially-hardened 17-7 precipitationhardening stainless steel. After nitridation, conventional transmission electron microscopy reveals that delta ferrite grains in such alloys show a uniform weak diffraction contrast. Chemical analysis reveals that the weak-contrast ferrite grains contain an enormous interstitial nitrogen supersaturation (> 20 at.%). Surprisingly, there is no significant tetragonality in these weak-contrast ferrite grains. Such weak diffraction contrast is attributed to a nanometer-scale nitridation-induced spinodal decomposition of delta ferrite grains. In addition, nitride nanoparticles are observed in the steel, and were identified as rocksaltstructured MN nitride (M: Fe, Cr, Ni, and Al). Further, platelets of hexagonal M 2 N 1-x are observed at low nitriding temperatures (623 and 653 K), but are absent during nitridation at a higher temperature (713 K).

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“Colossal” interstitial supersaturation in delta ferrite in stainless steels—I. Low-temperature carburization

Cited by 19 publications

References 43 publications

NiAl precipitation in delta ferrite grains of 17-7 precipitation-hardening stainless steel during low-temperature interstitial hardening

NiAl precipitation in delta ferrite grains of 17-7 precipitation-hardening stainless steel during low-temperature interstitial hardening

Low-Temperature Nitridation of 2205 Duplex Stainless Steel

“Colossal” interstitial supersaturation in delta ferrite in stainless steels: (II) low-temperature nitridation of the 17-7 PH alloy

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