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Lecture

WEB Measurement and Prediction of the Transformation Strain in High Strength Steels

Friday (25.09.2020)
11:20 - 11:35 M: Modelling and Simulation 2
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Metastable austenite in steels is at the origin of a number of desirable mechanical properties, such as larger ductility and remarkable fatigue resistance. This is intimately connected to strain and consequent stress fields developing during the martensitic phase transformation. It is therefore essential to predict and tailor deformation due to phase transformation in order to design better-performing alloys.

Here, we combine High-Resolution Digital Image Correlation (HR-DIC) to obtain fine-accuracy in-plane deformation fields with a new, predictive theory of martensite crystallography [Maresca and Curtin (2017) Acta Materialia 134, 302] to determine the full 3D in-situ transformation strain (“shape deformation”) in a model Fe-20.2Ni-5.4Mn (wt%) alloy.

Neutron diffraction and TEM are used to determine the austenite and martensite alloy lattice parameters. Crystallographic orientation of both austenite and martensite are measured and they serve as input for the crystallographic theory of martensite, along with the alloy lattice parameters. Tensile tests are then performed until martensite transforms, and HR-DIC yields 3 in-plane strain measurements.

The crystallographic theory predicts within experimental accuracy 2 of the 3 in-plane measurements [Maresca, Polatidis, Smid, Van Swygenhoven, Curtin (2020) Under review]. The third measured is captured by including contribution of crystallographic slip, which is observed experimentally.

This work validates the crystallographic theory proposed by Maresca and Curtin. Furthermore, combined experimental-theoretical analysis reveals for the first time the full, 3D in-situ transformation strain associated with austenite-martensite transformation in Fe-Ni-Mn. The theory, which is general for face-centered-cubic to body-centered-cubic transformation in steels, can be then used to predict new alloys with exceptional transformation strains.

Speaker:
Dr. Francesco Maresca
University of Groningen
Additional Authors:
  • Dr. Efthymios Polatidis
    Paul Scherrer Institute
  • Dr. Miroslav Smid
    Paul Scherrer Institute
  • Prof. Dr. Helena Van Swygenhoven
    Paul Scherrer Institute
  • Prof. Dr. William Curtin
    EPFL