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Ab initio study of the phase stability in paramagnetic duplex steel alloys
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
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2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 2Article in journal (Refereed) Published
Abstract [en]

Duplex stainless steels have many superior properties compared to conventional steels, this being mainly due to their microstructure containing approximately equal amount of ferrite and austenite phases formed by iron, chromium (or Cr equivalent), and nickel (or Ni equivalent). Using computational methods based on first-principles theories, the phase stability of paramagnetic Fe1-c-nCrcNin alloys (0.12 <= c <= 0.32 and 0.04 <= n <= 0.32) at high temperatures (greater than or similar to 1000 K) is addressed. It is shown that the stabilization of the ferrite-austenite two-phase field in duplex steels is a result of complex interplay of several competing phenomena. Taking into account only the formation energies yields a complete phase separation, strongly overestimating the two-phase region. The formation energies are calculated to be lower for the austenite than for the ferrite, meaning that the configurational entropy has a more significant impact on the stability field of the austenitic phase. The magnetic and vibrational free energies have opposite effects on the phase stability. Namely, the magnetic entropy favors the ferrite phase, whereas the vibrational free energy stabilizes the austenite phase. Combining the formation energies with the magnetic, vibrational, and configurational free energies, a region of coexistence between the two phases is obtained, in line with former thermodynamic assessments as well as with experimental observations.

Place, publisher, year, edition, pages
APS , 2009. Vol. 79, no 2
Keyword [en]
ab initio calculations, alloy steel, austenitic stainless steel, crystal microstructure, entropy, free energy, magnetic structure, magnetic transitions, paramagnetic materials, phase separation, regular solution model, potential model, stainless-steel, approximation, perovskite
National Category
Physical Sciences
URN: urn:nbn:se:kth:diva-18142DOI: 10.1103/PhysRevB.79.024108ISI: 000262978100033ScopusID: 2-s2.0-59249108238OAI: diva2:336188
See Erratum: Physical Review B. Condensed Matter and Materials Physics, Vol 79, 2009. QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2012-02-22Bibliographically approved

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Ropo, MattiJohansson, BörjeHertzman, Staffan N.Vitos, Levente
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