Carbide-Free Bainite Transformations Above and Below Martensite Start Temperature Investigated by In-Situ High-Energy X-Ray Diffraction
Résumé
Carbide-Free Bainitic AHSS exhibit multiphase microstructures made of fine ferrite and retained austenite. The carbon partition between these constituting phases during the bainitic transformation is studied above and below MS by in-situ High Energy X-Ray Diffraction experiments. The timeresolved analysis of the phase fraction, austenite lattice parameter and ferrite tetragonality offer the possibility to establish phase-scaled consistent and precise carbon balances.
In the studied steel, the carbon content in ferrite ranges between 0.1 and 0.15 wt.% after isothermal treatments meaning that the available carbon for austenite stabilization is reduced. The stasis conditions are close to the T0’ criterion below 400 °C but are not reached at higher temperatures.
Our multi-step experiments also prove that the transformation below MS is very sensitive to the carbon content in austenite and auto-catalytic nucleation processes inherited from prior transformations (martensite and bainite at higher temperature). The bainitic transformation thus does not follow additivity rules.
Domaines
MatériauxOrigine | Fichiers produits par l'(les) auteur(s) |
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