Use of Large Scale Facilities to Understand the Physical Metallurgy of Fe-based Alloys: Session I
Program Organizers: Sebastien Allain, Institut Jean Lamour; Alexis Deschamps, Genoble Institute of Technology; MingXin Huang, University of Hong Kong; Amy Clarke, Los Alamos National Laboratory; C. Tasan, Massachusetts Institute of Technology
Monday 10:00 AM
February 24, 2020
Room: Mission Hills
Location: Marriott Marquis Hotel
Session Chair: Sébastien Allain, Institut Jean Lamour
10:00 AM
Precipitation Kinetics and Chemistry Evolution of Oxide Dispersion Strengthened Steels throughout their Consolidation Process Evaluated by In-situ Anomalous Small-angle X-ray Scattering: Gabriel Spartacus1; Joël Malaplate1; Frédéric De Geuser2; Denis Sornin1; Alexis Deschamps2; 1CEA Saclay; 2SIMaP, Grenoble Alpes University
Oxide Dispersion Strengthened (ODS) steels are candidate for nuclear reactor applications. ODS steels are made by powder metallurgy processes involving ball milling of Fe-Cr, Y2O3 and TiH2 powders to dissolve Y, Ti and O into the matrix. These species precipitate as Y-Ti-O nano-oxides during the subsequent high temperature consolidation at 1100°C.Acquiring experimental data on the precipitation kinetics and chemical evolution is invaluable to further control and optimize the elaboration. For this purpose, we have performed in-situ observations up to 1100°C on cold-compressed powders during heat treatments representative of the real process route, using synchrotron anomalous small angle x-ray scattering. These measurements elucidate the precipitation kinetic path showing a coarsening start around 400°C, as well as a chemical and structural shift near 800°C probably linked to the precipitates transformation from non-stoichiometric clusters to Y2Ti2O7 pyrochlore. These oxides show outstanding stability with almost no ripening even after 12 hours at 1100°C.
10:20 AM
Nucleation and Evolution of Sigma Phase and Nitrides during Heat Treatment and Welding of Duplex Stainless Steels: Shirin Nouhi1; Niklas Pettersson; Lars Höglund1; Amer Malik1; Jan Jonsson1; Staffan Hertzman1; Sten Wessman1; Andreas Stark1; David Lindell1; 1Swerim AB
Duplex stainless steels have unique properties in terms of strength, ductility, fatigue, and corrosion resistance. During heat treatment or welding, the molten phase solidifies into ferritic phase and austenite precipitates while cooling. The holding time and cooling cycles, however, require a delicate choice of time and rate to avoid the formation of intermetallic phases, such as sigma phase, and allow nitrogen diffusion which promotes austenite formation. For optimizing production processes and developing the application of duplex steels, understanding the conditions where the intermetallic phases precipitate is a key challenge. In this project, we have used Wide-Angle X-ray Scattering (WAXS) and Small-Angle X-ray Scattering (SAXS) in order to explore the phase tranformation, probe the nucleation and follow the kinetics of sigma phase and nitrides formation, and quantify the precipitates during heating and cooling processes relevant to e.g. welding. The results are compared to the simulations using DICTRA software.
10:40 AM Invited
HEXRD and SAXS to Unveil the Dynamics of Phase Transformation in Steels: From Carbide-free Bainite To Mapping of Compositionally Graded Samples: Imad-Eddine Benrabah1; Z. Tournoud2; Frédéric Bonnet3; Frederic De Geuser1; Alexis Deschamps1; D. Huin3; P. Donnadieu1; Hugo Van Landeghem1; 1Université Grenoble Alpes, CNRS, Grenoble INP, SIMaP; 2Université Grenoble Alpes, CNRS, Grenoble INP, SIMaP; ArcelorMittal; 3ArcelorMittal
This presentation will illustrate how the use of synchrotron in-situ experiments helps to reach a quantitative characterization of phase transformations in steels. First, in-situ high energy X-ray diffraction (HEXRD) and in-situ small-angle X-ray scattering (SAXS) will be applied to follow how the bainite transformation in TRIP-aided bainitic steels is modified by the addition of microalloying (V or Nb). HEXRD is used to follow the austenite and ferrite phase fractions as well as the carbon content of austenite. SAXS is used to follow the formation of nanometer-scale transition carbides. In the second part of this talk, we will show that the in-situ HEXRD experiments can be extended to be spatially-resolved on compositionally-graded steels, in order to achieve by a combinatorial approach a map of phase transformation kinetics in compositional space. Fe-X1-X2-C alloys with composition gradients have been obtained, where Xi=(Mn, Mo, Cr, Si). The evolution of austenite and ferrite phase fractions have been followed in these gradients in-situ during inter-critical annealing, in order to evaluate the solute drag effect when several substitutional species are involved.