Strategies to increase austenite FCC relative phase stability in High-Mn steels

• Published in: Journal of alloys and compounds Vol. 854; p. 156971
• Main Authors: Guerrero, L.M., La Roca, P., Malamud, F., Butera, A., Baruj, A., Sade, M.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15-02-2021; Elsevier BV
• Subjects: Antiferromagnetism; Austenite; Austenite stabilization; Austenitic stainless steels; Body centered cubic lattice; Crystal defects; Deformation effects; Face centered cubic lattice; FCC magnetic ordering; FCC-HCP martensitic transition; Ferrous alloys; Grain size; High Mn steels; Magnetic measurement; Manganese; Manganese steels; Martensite; Martensitic transformations; Nucleation; Phase stability; Plastic deformation; Stability analysis; Temperature; Thermal cycling; Austenite stabilization; FCC-HCP martensitic transition; High Mn steels; FCC magnetic ordering; Thermal cycling
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2020.156971

Several strategies to increase the FCC austenite stability compared to BCC and HCP martensites have been tested and are discussed. The relative stability of the different phases was analyzed by studying the effects of: a) grain size, b) antiferromagnetic ordering of the austenite, c) thermal cycling through the FCC-HCP transition, d) plastic deformation of the austenite and e) combined effects. As a first step, the effect of decreasing the grain size was analyzed in Fe–Mn alloys for Mn contents smaller than 18 wt.%, where BCC and HCP martensites compete in stability. Formation of the BCC phase is inhibited for 15 wt.% and 17 wt.% of Mn for grain sizes smaller than 2 μm. This enabled, for the first time at these compositions, the measurement of the Néel temperature of the austenite using specific heat and magnetic measurements. A comparison of the obtained transition temperatures with accepted models is discussed. The effect of modifying the grain size on the FCC-HCP transition temperatures was also analyzed for 15 wt.% and 17 wt.% Mn contents showing a complete HCP inhibition for grain sizes smaller than 200 nm. A nucleation model for the HCP martensite is considered which includes an additional resistance to the transformation term depending on the austenitic grain size. Additional combined effects on the FCC stabilization are discussed like the interaction between the antiferromagnetic ordering and the introduction of defects by thermal cycling through the martensitic transformation. The analysis can be easily applied to systems with a larger number of components. Results obtained in the Fe–Mn–Cr system are also presented.
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•Several strategies to increase the FCC austenite stability in High-Mn steels have been presented.•For grain size of 2 μm the suppression of the BCC martensite was found in binary alloys.•Néel temperatures show some discrepancies with models presented in the literature.•The effect of grain size on the FCC-HCP transition was analyzed.•Thermal cycling combined with magnetic ordering can be used to stabilize the austenite.