The interaction of N with atomically dispersed Ti, V, Cr, Mo, and Ni in ferritic steel

• Published in: Journal of computer-aided materials design Vol. 10; no. 1; pp. 1 - 11
• Main Authors: KAMMINGA, J.-D, KLAVER, T. P. C, NAKATA, K, THIJSSE, B. J, JANSSEN, G. C. A. M
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer 2003
• Subjects: Anelasticity, internal friction, stress relaxation, and mechanical resonances; Applied sciences; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; Mechanical and acoustical properties of condensed matter; Metals. Metallurgy; Other surface treatments; Physics; Production techniques; Surface treatment; Ferritic steels; Moessbauer effect; Internal friction; Plasma assisted processing; Vanadium; Mechanical properties; Nitriding; Steel; Molybdenum; Alloying elements; Precipitation; Trapping; Nitridation; Mossbauer spectroscopy; Density functional method; Chromium; Titanium; Density functional theory; Nickel; Diffusion; Concentration distribution
• ISSN: 0928-1045; 1573-4900
• DOI: 10.1023/B:JCAD.0000024188.42120.e0

Since long, the nitriding process has been used to improve the mechanical properties of the surface of steel. However, results from the prevailing model for the nitriding of steel are still not in perfect agreement with experimental data. It is investigated if this can be attributed to the model assumption that there is no interaction between nitrogen atoms and alloying atoms in solution in the iron matrix. To this end, the interaction of N with atomically dispersed Ti, V, Cr, Mo, and Ni alloying element atoms in ferritic steel is calculated using Density Functional Theory. Results of the Density Functional Theory calculations agree well with experimental lattice parameter, Mossbauer spectroscopy, and internal friction data taken from literature. Deficiencies in prevailing atomistic models for Fe-Me-N configurations in steel (Me denotes the alloying element considered) are revealed and the initial stages of MexN precipitation in alloyed iron are elucidated. For all elements but Ti, the interaction with N is negligible or repulsive. Significant attractive interaction exists only if Ti is a second nearest neighbour of N (-0.22 eV). It is shown that this interaction is too small to significantly influence nitriding at typical nitriding temperatures ( > 500 deg C). Consequently, in modelling the nitriding of steel at typical nitriding temperatures, interaction between the atomically dispersed alloying elements and nitrogen can be disregarded. Internal friction experiments evidence nitrogen in solution in the steel bonded with higher binding energy, also for the other alloying elements. We suggest that this nitrogen is bound in Fe-Me-N accumulations consisting of more than one alloying atom and one or more nitrogen atoms. For the modelling of nitriding of steel, these interactions must be taken into account.