Solubility of nitrogen in ferrite; the Fe–N phase diagram

Stein, Jendrik; Schacherl, R. E.; Jung, Minsu; Meka, Sai Ramudu; Rheingans, Bastian; Mittemeijer, E. J.

doi:10.3139/146.110968

Cited by 44 publications

(55 citation statements)

References 11 publications

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“…In an ideal case, thus, a local equilibrium at the surface of the specimen is achieved. Often, however, a steady state [10,12,61] prevails at the surface.…”

Section: Methodsmentioning

confidence: 99%

“…Experimentally determined data from recent works [32,61] and the temperature of the invariant reaction U 2 (if a type I model is assumed) or the temperature range for the invariant reactions E 2 and e 4 (if a type II model is assumed) as determined in the present work are given in Table II. Matches of the experimental and calculated data have been marked with an asterisk.…”

Section: Compatibility Of Experimental Data With the Models From Tmentioning

confidence: 99%

“…As discussed elsewhere, [7,12] whereas local solid-solid equilibria can occur at each depth, corresponding to the local gross (laterally averaged) composition, within the compound layer, this may not occur at the gas-solid interface, i.e., at the surface of the compound layer, where moreover at most a stationary state may be established. [10,61] Then, recognizing that in gaseous nitrocarburizing, as compared to gaseous nitriding, distinctly more reactions participate at the gas/solid interface, [59,60] it may be understood that the microstructures obtained upon nitriding are more uniform than those obtained upon nitrocarburizing (cf. Sections IV-A and IV-B).…”

Section: B Nitriding Of Fe-c Alloysmentioning

confidence: 99%

“…[32] (Invariant Reactions c, e 2 , E 1 ; and U 1 ), Ref. [61] [33] Kunze [34] Du/Hillert [35] Du [36] Kunze [37] SGTE [38] Experimental Data I II I I II I I/II c No error margin given.…”

Section: B Comparison Of Thermodynamic Descriptions: Invariant Reactmentioning

confidence: 99%

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The $$\upalpha +\upvarepsilon $$ Two-Phase Equilibrium in the Fe-N-C System: Experimental Investigations and Thermodynamic Calculations

Göhring

Leineweber

Mittemeijer

2016

Metall Mater Trans A

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The present work is dedicated to investigating the occurrence of the a þ e equilibrium at temperatures typically applied for nitrocarburizing treatments. To this end, pearlitic Fe-C specimens were treated between 823 K and 863 K (550°C and 590°C) in gaseous nitriding and gaseous nitrocarburizing atmospheres, allowing control of the chemical potentials of N and C. Subsequently, the resulting compound-layer microstructures were investigated using light microscopy and X-ray diffraction. Thermodynamic calculations, adopting several models for the Fe-N-C system from the literature, were performed, showing significantly different predictions for both the sequence of the invariant reactions and their temperatures. Comparison of the experimental data and the theoretical calculations led to the conclusion that none of the models from the literature is able to realistically describe the experimentally observed constitution in the Fe-N-C system in the considered temperature range. Values/value ranges for the temperatures of the invariant reactions were obtained.

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“…In an ideal case, thus, a local equilibrium at the surface of the specimen is achieved. Often, however, a steady state [10,12,61] prevails at the surface.…”

Section: Methodsmentioning

confidence: 99%

Section: Compatibility Of Experimental Data With the Models From Tmentioning

confidence: 99%

Section: B Nitriding Of Fe-c Alloysmentioning

confidence: 99%

“…[32] (Invariant Reactions c, e 2 , E 1 ; and U 1 ), Ref. [61] [33] Kunze [34] Du/Hillert [35] Du [36] Kunze [37] SGTE [38] Experimental Data I II I I II I I/II c No error margin given.…”

Section: B Comparison Of Thermodynamic Descriptions: Invariant Reactmentioning

confidence: 99%

See 2 more Smart Citations

The $$\upalpha +\upvarepsilon $$ Two-Phase Equilibrium in the Fe-N-C System: Experimental Investigations and Thermodynamic Calculations

Göhring

Leineweber

Mittemeijer

2016

Metall Mater Trans A

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“…It is important to realize that establishment of this equilibrium requires that thermal dissociation of NH 3 can be ignored and that the recombination of nitrogen atoms adsorbed at the surface is negligible (if the latter would not hold, a stationary state, instead of an equilibrium situation, would occur at the surface of the substrate; for full discussion see References 1,19 [20] r…”

Section: Thermodynamics Of Gas Nitriding and Pore Formationmentioning

confidence: 99%

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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Reducing Iron Oxide with Ammonia: A Sustainable Path to Green Steel

Bae

Kim

et al. 2023

Advanced Science

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Iron making is the biggest single cause of global warming. The reduction of iron ores with carbon generates about 7% of the global carbon dioxide emissions to produce ≈1.85 billion tons of steel per year. This dramatic scenario fuels efforts to re‐invent this sector by using renewable and carbon‐free reductants and electricity. Here, the authors show how to make sustainable steel by reducing solid iron oxides with hydrogen released from ammonia. Ammonia is an annually 180 million ton traded chemical energy carrier, with established transcontinental logistics and low liquefaction costs. It can be synthesized with green hydrogen and release hydrogen again through the reduction reaction. This advantage connects it with green iron making, for replacing fossil reductants. the authors show that ammonia‐based reduction of iron oxide proceeds through an autocatalytic reaction, is kinetically as effective as hydrogen‐based direct reduction, yields the same metallization, and can be industrially realized with existing technologies. The produced iron/iron nitride mixture can be subsequently melted in an electric arc furnace (or co‐charged into a converter) to adjust the chemical composition to the target steel grades. A novel approach is thus presented to deploying intermittent renewable energy, mediated by green ammonia, for a disruptive technology transition toward sustainable iron making.

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Solubility of nitrogen in ferrite; the Fe–N phase diagram

Cited by 44 publications

References 11 publications

The $$\upalpha +\upvarepsilon $$ Two-Phase Equilibrium in the Fe-N-C System: Experimental Investigations and Thermodynamic Calculations

The $$\upalpha +\upvarepsilon $$ Two-Phase Equilibrium in the Fe-N-C System: Experimental Investigations and Thermodynamic Calculations

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

Reducing Iron Oxide with Ammonia: A Sustainable Path to Green Steel

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