Chromium – Iron – Nitrogen

Perrot, Pierre

doi:10.1007/978-3-540-74199-2_10

Cited by 2 publications

(1 citation statement)

References 54 publications

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“…(i) The (metastable) equilibrium amount of dissolved nitrogen in the ferrite matrix of nitrided iron-based Fe-Al and Fe-Cr alloys can in principle be larger than that for nitrided pure iron, due to (a) a higher nitrogen solubility in iron-based Fe-Al [31] and Fe-Cr alloys [32] as compared to pure iron and (b) the presence of so-called excess nitrogen taken up in the strain fields surrounding the MeN-precipitates. [33][34][35] (ii) Moreover, the development of AlN and CrN precipitates in Fe-Al and Fe-Cr alloys upon nitriding competes with the development of N 2 gas containing pores.…”

Section: A Pore Formation In Nitrogen Ferrite and The Role Of Alloyimentioning

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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