Nitrogen strengthening of a stable austenitic stainless steel

An ultra-fine-grained AISI 301LN austenitic stainless steel has been achieved by heavy cold rolling, to induce the formation of martensite, and subsequent annealing at 800°C, 900°C, and 1000°C, from 1 to 100 seconds. The microstructural evolution was analyzed using transmission electron microscopy and the yield strength determined by tension testing. Ultra-fine austenite grains, as small as~0.54 lm, were obtained in samples annealed at 800°C for 1 second. For these samples, tensile tests revealed a very high yield strength of~700 MPa, which is twice the typical yield strength of conventional fully annealed AISI 301LN stainless steels. An analysis of the relationship between yield strength and grain size in these submicron-grained stainless steels indicates a classical Hall-Petch behavior. Furthermore, when the yield dependence on annealing temperature is considered, the results show that the Hall-Petch relation is due to an interplay between fine-grained austenite, solid solution strengthening, precipitate hardening, and strain hardening.

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“…At 1000°C, the nitrides dissolve due to the high solubility of nitrogen in austenite. [24] B. Grain Size Measurements…”

Section: A Microstructurementioning

confidence: 99%

Hall–Petch Behavior in Ultra-Fine-Grained AISI 301LN Stainless Steel

Rajasekhara

Ferreira

Karjalainen

et al. 2007

Metall Mater Trans A

175

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“…[26] which is valid at a temperature of 295 K (22°C). For higher temperatures, the tensile yield strength becomes significantly smaller and is above 450°C nearly constant [27] . The relative decrease of the yield strength from RT to 450°C is almost independent of the nitrogen content in austenitic steels.…”

Section: ½6mentioning

confidence: 98%

“…Also in this case, the equilibrium N 2 gas pressure exceeds 2/3 of the austenite (uniaxial) tensile yield strength which equals about 570 MPa**. [26,27] Hence, as for ferrite upon nitriding, in view of the inequality, [6] the austenite matrix already yields well before the equilibrium N 2 gas pressure in a pore is reached.…”

Section: ½6mentioning

confidence: 99%

“…The relative decrease of the yield strength from RT to 450°C is almost independent of the nitrogen content in austenitic steels. [27] Therefore, the calculated value for the tensile yield strength at 295 K (22°C) was multiplied with this factor to estimate the tensile yield strength of austenite containing 9.5 at. pct nitrogen at 923 K (650°C).…”

Section: ½6mentioning

confidence: 99%

“…[28] E. Light Microscopy Specimens for light microscopical analysis were cut perpendicular to the nitrided surface and embedded in Struers Polyfast to obtain cross-sections. The embedded cross-sections were ground, polished (final stage 1 lm diamond paste) and etched with 2 vol pct Nital for [21] Where p i is the Nitrogen Gas Pressure in the Pore and r y is the (Uniaxial) Tensile Yield Strength of Ferrite [24] or Nitrogen Austenite [26,27] ) 30 seconds. A Zeiss Axiophot microscope, equipped with an Olympus Color View IIIu digital camera, was used to record the microstructures.…”

Section: X-ray Diffractionmentioning

confidence: 99%

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Pore Formation Upon Nitriding Iron and Iron-Based Alloys: The Role of Alloying Elements and Grain Boundaries

Schwarz

Göhring

Meka

et al. 2014

Metall Mater Trans A

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Pure iron and a series of iron-based Fe-Me alloys (with Me = Al, Si, Cr, Co, Ni, and Ge) were nitrided in a NH 3 /H 2 gas mixture at 923 K (650°C). Different nitriding potentials were applied to investigate the development of pores under ferrite and austenite stabilizing conditions. In all cases, pores developed in the nitrided microstructure, i.e., also and strikingly pure ferritic iron exhibited pore development. The pore development is shown to be caused by the decomposition of (homogeneous) nitrogen-rich Fe(-Me)-N phase into nitrogen-depleted Fe(-Me)-N phase and molecular N 2 gas. The latter, gas phase can be associated with such high pressure that the surrounding iron-based matrix can yield. Thermodynamic assessments indicate that continued decomposition, i.e., beyond the state where yielding is initiated, is possible. Precipitating alloying-element nitrides, i.e., AlN, CrN, or Si 3 N 4 , in the diffusion zone below the surface, hinder the formation of pores due to the competition of alloying-element nitride (Me x N y ) precipitation and pore (N 2 ) development; alloying elements reducing the solubility of nitrogen enhance pore formation. No pore formation was observed upon nitriding a single crystalline pure iron specimen, nitrided under ferrite stabilizing conditions, thereby exhibiting the essential function of grain boundaries for nucleation of pores.

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Low‐Cycle Fatigue at Room Temperature

Alvarez‐Armas

2013

Duplex Stainless Steels

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Nitrogen strengthening of a stable austenitic stainless steel

Cited by 251 publications

References 20 publications

Hall–Petch Behavior in Ultra-Fine-Grained AISI 301LN Stainless Steel

Hall–Petch Behavior in Ultra-Fine-Grained AISI 301LN Stainless Steel

Pore Formation Upon Nitriding Iron and Iron-Based Alloys: The Role of Alloying Elements and Grain Boundaries

Low‐Cycle Fatigue at Room Temperature

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