SKM 2021 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 2: Topical Session Interface-Dominated Phemomena - Moving Interfaces / Functional Properties
MM 2.1: Talk
Monday, September 27, 2021, 11:15–11:30, H8
Theory and modeling of the austenite-martensite interface structure and glissile transformation in steels — •Francesco Maresca1 and William Curtin2 — 1University of Groningen, Groningen, Netherlands — 2EPFL, Lausanne, Switzerland
The austenite-martensite (fcc-bcc) transformation controls the formation of microstructures in a wide range of high strength steels. Recent progress in the physical metallurgy of steels has shown that nanolaminate austenite/martensite microstructures contribute to high material toughness and resistance to hydrogen-embrittlement. Despite its relevance for applications, there is no established theory for the transformation capable to predict the contribution of the austenite-martensite phase transformation to ductility. To clarify the mechanism of transformation, we have performed atomistic simulations of the interface reproducing the major experimental TEM and HRTEM observations in Fe alloys. The atomistic model reveals for the first time the structure and motion of the athermal and glissile fcc austenite/bcc martensite interface in steels. The interface structure consists of [-101](111)fcc screws, as envisioned by previous theories, and [1-11](-101)bcc screws with kinks, which was not envisioned before. The atomistic findings have guided the formulation of a new, parameter-free double-shear predictive theory of martensite crystallography. Theory predictions show that the fcc/bcc lattice parameter ratio is the key factor controlling the shape deformation (i.e. the in-situ transformation strain), which can achieve more than 90%, namely three times the existing experimental estimates. The theory can be used to guide design of tougher AHSS.