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

GUERRERO, L.M.; BUTERA, A.; LA ROCA, P.; BARUJ, A.; MALAMUD, F.; SADE, M.

JOURNAL OF ALLOYS AND COMPOUNDS

ELSEVIER SCIENCE SA

Año: 2021 vol. 854 p. 156971 - 156971

0925-8388

Several strategies toincrease the FCC stability compared to BCC and HCP martensites are discussed.Particular attention is paid on several methods used to affect the relativephase stability among the involved structures like controlling the effect of: a)grain size, b) antiferromagnetic ordering of the austenite, c) thermal cyclingthrough 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 wasanalyzed in Fe-Mn alloys for Mn contents smaller than 18 wt.%, wheremartensites BCC and HCP compete in stability. Formation of BCC is inhibited for15 wt.% and 17 wt.% of Mn for grain size smaller than 2 µm. This enabled, forthe first time at these compositions, the measurement of the Néel temperatureof the austenite using specific heat and magneticmeasurements. A comparison of the obtained transition temperatures withaccepted models is discussed. The effect of modifying the grain size on the FCC-HCPtransition temperatures was also analyzed for several Mn contents showing acomplete HCP inhibition for grain size smaller than 200 nm. A nucleation modelfor the HCP martensite is considered which includes an additional resistance tothe transformation term depending on the austenitic grain size. Additionalcombined effects on the FCC stabilization are discussed like the interactionbetween the antiferromagnetic ordering and the introduction of defects bythermal cycling through the martensitic transformation. The analysis can beeasily applied to systems with a larger number of components. Results obtainedin the Fe-Mn-Cr system are also presented.