TY - JOUR
T1 - Precipitation and reverted austenite formation in maraging 350 steel
T2 - Competition or cooperation?
AU - Feitosa, A. L. M.
AU - Ribamar, G. G.
AU - Escobar, J.
AU - Sonkusare, R.
AU - Boll, T.
AU - Coury, F.
AU - Ávila, J.
AU - Oliveira, J. P.
AU - Padilha, A. F.
N1 - Funding Information:
We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for providing the experimental facilities. Parts of this research were carried out at PETRA III, and we would like to thank Emad Maawad and Norbert Schell for their assistance in using the P07 beamline. Beamtime was allocated for proposal I-20191506. The authors thank the Laboratory of Structural Characterization (LCE/DEMa/UFSCar) for the general facilities. This research used facilities of the Brazilian Nanotechnology National Laboratory (LNNano), part of the Brazilian centre for Research in Energy and Materials (CNPEM), a private non-profit organization under the supervision of the Brazilian Ministry for Science, Technology, and Innovations (MCTI). The Microscopia eletrônica staff is acknowledged for the assistance during the experiments (proposal # TEM-C1 - 27214). The authors thank the Karlsruhe Nano and Micro Facility (KNMFi), a Helmholtz Research Infrastructure at Karlsruhe Institute of Technology (KIT) for the usage of Atom Probe Tomograph (APT) equipment and the assistance of Marina Weinhard and Delphine Chassaing in producing the samples for APT. Authors from the USP Polytechnic School would like to thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) - Programa de Excelência Acadêmica (PROEX) - Brasil for Financial Support. We especially acknowledge Felipe Moreno Siqueira Borges de Carvalho for conducting the cold rolling process at the IPT – USP. J. Avila is a Serra Hunter fellow and a CNPq fellow. JPO acknowledges funding by national funds from FCT - Fundação para a Ciência e a Tecnologia, I.P., in the scope of the projects LA/P/0037/2020, UIDP/50025/2020 and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication – i3N.
Publisher Copyright:
© 2024
PY - 2024/5/15
Y1 - 2024/5/15
N2 - Aged maraging steels offer unique strength and toughness via the presence of finely dispersed precipitates, allowing the material to reach values of up to 2400 MPa in yield strength in the case of 18Ni350. However, when aging heat treatments above 550 °C are conducted, simultaneous precipitation and austenite reversion can occur changing the mechanical behavior of the material. Although many studies related to the physical metallurgy of maraging steels have already been published, less attention has been given to a detailed understanding of the initial formation of austenite and its relationship with the precipitates. In this study, undeformed and cold rolled commercial 18Ni350 maraging steel samples were submitted to short aging heat treatments of 1800s at 600, 650, and 700 °C. The influence of the initial microstructure on subsequent phase evolution was studied using in-situ synchrotron X-ray diffraction and final microstructural products using transmission electron microscopy and atom probe tomography. Results show that cold rolled samples did not present faster kinetics of transformation of reverted austenite as expected, but this condition presented austenite in a different morphology than the undeformed condition. However, cold rolling changed the morphology of reverted austenite from elongated (undeformed case) to equiaxed; and induced a higher density of smaller Ni3Ti and Fe2Mo precipitates, especially after low-temperature aging. Besides, the deformation extinguished retained austenite, which influenced the reverted austenite formation, concluding that the simple increase in dislocation density is not a unique and direct factor to increase the reverted austenite kinetics.
AB - Aged maraging steels offer unique strength and toughness via the presence of finely dispersed precipitates, allowing the material to reach values of up to 2400 MPa in yield strength in the case of 18Ni350. However, when aging heat treatments above 550 °C are conducted, simultaneous precipitation and austenite reversion can occur changing the mechanical behavior of the material. Although many studies related to the physical metallurgy of maraging steels have already been published, less attention has been given to a detailed understanding of the initial formation of austenite and its relationship with the precipitates. In this study, undeformed and cold rolled commercial 18Ni350 maraging steel samples were submitted to short aging heat treatments of 1800s at 600, 650, and 700 °C. The influence of the initial microstructure on subsequent phase evolution was studied using in-situ synchrotron X-ray diffraction and final microstructural products using transmission electron microscopy and atom probe tomography. Results show that cold rolled samples did not present faster kinetics of transformation of reverted austenite as expected, but this condition presented austenite in a different morphology than the undeformed condition. However, cold rolling changed the morphology of reverted austenite from elongated (undeformed case) to equiaxed; and induced a higher density of smaller Ni3Ti and Fe2Mo precipitates, especially after low-temperature aging. Besides, the deformation extinguished retained austenite, which influenced the reverted austenite formation, concluding that the simple increase in dislocation density is not a unique and direct factor to increase the reverted austenite kinetics.
KW - Atom-probe tomography
KW - Phase transformation kinetics
KW - Reverted austenite
KW - Transmission electron microscopy
KW - X-ray synchrotron radiation
UR - http://www.scopus.com/inward/record.url?scp=85189665286&partnerID=8YFLogxK
U2 - 10.1016/j.actamat.2024.119865
DO - 10.1016/j.actamat.2024.119865
M3 - Article
AN - SCOPUS:85189665286
SN - 1359-6454
VL - 270
JO - Acta Materialia
JF - Acta Materialia
M1 - 119865
ER -