Structure and corrosion behaviour of stainless steels after plasma and gas nitriding

Spies, H.‐J.; Eckstein, C.; Zimdars, H.

doi:10.1179/026708402225006286

Cited by 19 publications

(8 citation statements)

References 4 publications

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“…Spies [120] reported a significant increase of corrosion potential and decrease in the corrosion rate for AISI 430 steel samples nitrided at 300 • C for 60 h or at 350 • C for 26 h and tested in a 0.05 M H 2 SO 4 solution, in comparison with the untreated alloy. A similar behavior was observed for AISI 430 samples nitrided at 250 • C for 39 h or 420 • C for 36 h [127]. On the contrary, Gontijo et al [128] reported only a slight increase in corrosion potential and a marked increase in anodic current density for AISI 409 samples nitrided in the range of 350-500 • C and tested in a 0.1 M H 2 SO 4 solution, in comparison with the untreated steel.…”

Section: Corrosion Resistance Of the Modified Surface Layerssupporting

confidence: 63%

“…When AISI 430 was nitrided at 420 • C, the pitting potential increased with respect to that of the untreated steel in a 0.5 M NaCl solution, but when the treatment was prolonged up to 20 h, a marked decrease in corrosion and pitting potentials was observed [120]. When a large volume fraction of Cr nitrides was able to form, a marked decrease in corrosion resistance was reported [114,123,127].…”

Section: Corrosion Resistance Of the Modified Surface Layersmentioning

confidence: 99%

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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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Section: Corrosion Resistance Of the Modified Surface Layerssupporting

confidence: 63%

Section: Corrosion Resistance Of the Modified Surface Layersmentioning

confidence: 99%

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

Borgioli

2022

Metals

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“…Possibly, the enhanced reactivity of upper layers is due to microstructural non-homogeneity of the nitrided samples. Spies et al 47 showed that the resistance of Cr18Ni10 (AISI 304) steel to pitting corrosion increased by nitriding up to 420uC, but deteriorated for higher nitriding temperatures. Annealing decreased the resistance of nitrided samples owing to redistribution of 13 Polarisation curves in 0?1M Na 2 SO 4 modified to pH 3?0, 6?0 and 9?0 for unnitrided and nitrided (425uC, 30 h) 304L steel 37 14 Current transients for nitrided 316L steel in 0?1M Na 2 SO 4 of pH 3?0 at 2300 mV(MSE) after abrasion to various depths: corresponding nitrogen concentration at depths of 0, 1?3, 5?0, 10?0 and 17?1 mm are 14?2, 10?5, 7?2, 5?9 and 1?0 wt-%N respectively 40 nitrogen and promotion of chromium nitride precipitation.…”

Section: Discussionmentioning

confidence: 99%

Corrosion and passivation of plasma nitrided stainless steels

Flis

2010

Surface Engineering

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Corrosion behaviour of nitrided steels was examined in chloride free and chloride containing sulphate solutions acidified to pH 3?0. Conventional nitriding (550-600uC) strongly deteriorates the corrosion resistance, however, high reactivity of nitrided layers enables the formation of thick conversion coatings to protect against corrosion (oxidation and phosphating) or to improve lubrication (phosphating). Low-temperature nitriding (380-450uC) produces thin layers of a supersaturated solid solution of nitrogen in austenite (S phase) of high resistance to pitting corrosion in chloride containing solutions. After nitriding at 450uC for 30 h, the near-surface parts of layers with .7 wt-%N have a deteriorated resistance to general corrosion in the acidified solution, but deeper parts with lower nitrogen contents have the resistance comparable with that of untreated steels. It is proposed that the improved pitting resistance is due mainly to the accumulation on corroding surface of large amounts of passivating products and of Cr-N species.

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“…25 The progressive darkening of the modified layer reflects the homogeneous depletion of Cr from solid solution during annealing which gave rise to reduced corrosion resistance. 26,27 However, cross-sections of annealed 904L PN were less affected by the preparation procedure, with only locally darkened areas (not shown). These preliminary findings of γ N decomposition on corrosion resistance are consistent with our previous studies on oxidation in humid air.…”

Section: Decomposition Of Expanded Austenite By Isothermal Annealingmentioning

confidence: 96%

Thermal decomposition of N-expanded austenite in 304L and 904L steels

Maistro

Pérez‐García

Norell

et al. 2017

Surface Engineering

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In this study, expanded austenite was prepared by an industrial low-temperature plasma nitriding process in 304L and 904L austenitic stainless steels. The current investigation focuses on the assessment of the thermal stability and related phase evolution of the expanded austenite layer during isothermal annealing in protective argon atmosphere at temperatures ranging from 450 to 600°C for 24 and 168 h. Characterisation of the original expanded austenite and the decomposed surface layers was performed. Denitriding, inward N-diffusion and Cr-compounds precipitation occurred at different extent, depending on annealing conditions and alloy composition. Expanded austenite in 304L exhibited a near complete eutectoid decomposition after a short annealing time, while 904L showed significantly better thermal stability. A fine dispersion of small CrN precipitates resulting from expanded austenite decomposition at relatively low annealing temperature or short duration could further positively affect the surface hardness of both materials. Precipitate growth reduces hardness at higher annealing temperatures/times.

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Structure and corrosion behaviour of stainless steels after plasma and gas nitriding

Cited by 19 publications

References 4 publications

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

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

Corrosion and passivation of plasma nitrided stainless steels

Thermal decomposition of N-expanded austenite in 304L and 904L steels

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