Reobservations on ordering, precipitation and polymorphic phase transformation phenomena during annealing of a severely cold rolled magnetic Fe-Co-10V alloy
Kamali, Mohammad R.; Mashreghi, Ali R.; Karjalainen, L. Pentti; Hasani, Saeed; Javaheri, Vahid; Saukko, Sami; Kömi, Jukka (2020-06-12)
Mohammad R. Kamali, Ali R. Mashreghi, L. Pentti Karjalainen, Saeed Hasani, Vahid Javaheri, Sami Saukko, Jukka Kömi, Reobservations on ordering, precipitation and polymorphic phase transformation phenomena during annealing of a severely cold rolled magnetic Fe-Co-10V alloy, Materialia, Volume 12, 2020, 100765, ISSN 2589-1529, https://doi.org/10.1016/j.mtla.2020.100765
© 2020 Acta Materialia Inc. Published by Elsevier B.V. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/.
https://creativecommons.org/licenses/by-nc-nd/4.0/
https://urn.fi/URN:NBN:fi-fe2020062545748
Tiivistelmä
Abstract
Despite extensive investigations conducted on magnetic Fe-Co-V alloys, some aspects of microstructural evolution during annealing of cold rolled sheets have not yet been clarified yet. Various techniques such as dilatometry, X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM, SEM) as well as ThermoCalc predictions were employed to study ordering, precipitation and austenite transformation in an 86% cold-rolled 40Fe-50Co-10 V alloy. Dilatometric results revealed atomic ordering initiated from disordered martensite at 350 °C, while XRD patterns ascertained the completion of the process at 600 °C and its disappearance close to 750 °C. X-ray and electron diffraction patterns exhibited the B2 type ordered structure in this temperature range. Rod-shaped precipitates with HCP crystalline structure and the constant composition of (Co,Fe)₃ V were detected by SEM within the deformed ferrite grains after annealing in the temperature range of 500–700 °C. The percentage of the precipitates decreased by raising the annealing temperature and they vanished above 700 °C, in accordance with ThermoCalc prediction. Austenite grains formed below 750 °C had an ordered L1₂-type structure as revealed by TEM and XRD patterns. A combination of different techniques demonstrated that the two-phase ferrite-austenite region exists in the temperature range of 495–840 °C. Vanadium partitioning into austenite during isothermal holding in addition to austenite grain size were evaluated as the main parameters affecting austenite stability during quenching from temperatures between 500 and 800 °C. As a final result, most of the existing disagreements and ambiguities in previous works could be explained.
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