High strength dual phase (DP) steels have been increasingly used in car body structure for reducing weight and increasing safety performance. Bake hardening process is widely applied for improving final mechanical properties of formed components by means of carbide precipitation and occurred Cottrell cloud. In this work, effects of bake hardening on mechanical behavior of coarse and fine grain DP steels are investigated. Initially, fine grain ferritic-pearlitic structure is produced from a low carbon steel by constrained groove pressing (CGP) based on severe plastic deformation. Ferrite grains with a submicro size of 470 nm can be hereby achieved. DP microstructures are generated afterward by intercritical annealing. Finally, bake hardening at the temperature of 160 8C for 20 min is performed under consideration of various pre-strains between 0 and 10%. It is found that bake hardenability of the DP steels can be significantly increased due to the fine grain structure induced by the CGP, which provide enhanced heterogeneous nucleation sites for precipitates and accelerated carbon diffusion.[ Ã ] Prof.

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