Effect of bainitic transformation on bake hardening in TRIP assisted steel

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2012-02, Vol.534, p.485-494
• Main Authors: Das, S., Timokhina, I., Singh, S.B., Pereloma, E., Mohanty, O.N.
• Format: Article
• Language: English
• Subjects: 3-D atom probe; Bainite; Bake hardening; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Defects and impurities in crystals; microstructure; Dilatation; Dislocation; Exact sciences and technology; Linear defects: dislocations, disclinations; Martensitic transformations; Materials science; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Structure of solids and liquids; crystallography; XRD
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.11.097

► Bainitic transformation in TRIP-assisted steel can lead to a very good bake hardening response as demonstrated by other researchers also. ► No extra deformation is needed. Dislocations can be generated in situ during the transformation itself. ► Detail characterisation and theoretical treatments showed bainite plates are sufficiently enriched with extra carbon atoms which can migrate and lock the dislocations. Bake hardening is a phenomenon where freshly generated dislocations get pinned down by the migrating carbon atoms under the influence of temperature employed in paint baking shop. Experimentally, a minimal 2% deformation is given to generate such new dislocations. On the other hand, after bainitic transformation, steel contains a large number of dislocations as well as excess carbon atoms in bainite, a combination of which is capable of producing bake hardening effect. In the current analysis, one grade of transformation induced plasticity aided steel was chosen to study the effect of isothermal bainitic transformation on subsequent bake hardening response, without giving any deformation assuming that the previous treatment would have generated sufficient dislocations which could be pinned down by the migrating carbon atoms under the influence of thermal treatment of the bake hardening process. The final microstructure was characterised by many techniques, using Thermo-Calc, optical microscopy, XRD analysis and 3-DAP. A good agreement was observed amongst all the techniques employed.