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Restitution de la microtexture parente à partir de la microtexture héritée mesurée par EBSD : une application aux aciers faiblement alliés

Abstract : The metallurgical state of the austenite before the last cooling (grain size, texture, strain hardening ...) cannot be directly characterized because the austenite transforms during the last cooling. However, it influences remarkably the in use properties of steels. This thesis proposes an indirect automatic method to restore the austenitic microtexture from the microtexture of the inherited phases (martensite, bainite) at low temperature, measured by EBSD. This method requires three prerequisites: 1) the presence of an orientation relationship between the parent austenite and the transformation product, 2) the inherited phase has to be formed in the grain with which it is related and 3) there is a sufficient number of variants. Its validation has been performed both on numerical examples and for low alloyed steels. The restitution of austenitic grain boundaries is efficient but sensitive to variants in orientation relationship with several adjacent parent grains. These ambiguous situations are mainly generated by the presence of twins in austenite grains or by selection of variants at the austenitic grain boundaries. In this case, it is possible to improve the quality of the restitution of the parent contours (especially the twins boundaries) by taking into account topological information. These restitution methods consequently allow to identify twins or variant selection at grain boundaries and thus to better analyze local texture inheritance mechanisms. Therefore, the developed methods can be generalized to other phase transformations
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Submitted on : Monday, June 21, 2021 - 11:28:32 AM
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Pierre Blaineau. Restitution de la microtexture parente à partir de la microtexture héritée mesurée par EBSD : une application aux aciers faiblement alliés. Matériaux. Université Paul Verlaine (Metz), 2010. Français. ⟨NNT : 2010METZ042S⟩. ⟨tel-03265772⟩

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