8 research outputs found
Ferrite recrystallization and austenite formation during annealing of cold-rolled advanced high-strength steels: In situ synchrotron X-ray diffraction and modeling
Ferrite recrystallization and austenite formation occurring during annealing of cold-rolled advanced high-strength steels are key mechanisms as they largely determine the ïŹnal microstructure and mechanical properties. However, the inïŹuence of processing parameters on these mechanisms and their interactions is still not fully understood. This is particularly the case for Dual-Phase steels having an initial cold-rolled microstructure con-sisting of ferrite and martensite before annealing, which were scarcely investigated compared to ferrite-pearlite initial microstructures. In situ synchrotron X-ray diïŹraction experiments together with post-mortem metallo-graphic analysis allowed clarifying both ferrite recrystallization and austenite formation during annealing of a ferrite-martensite initial microstructure depending on the process parameters of the annealing cycle. Results showed a major inïŹuence of recrystallization state on austenite formation, leading to an unexpected eïŹect of heating rate on austenite formation kinetics. A modeling approach was undertaken to rationalize the inïŹuence of heating rate on austenite formation by taking into account the bi-phased ferrite-martensite initial microstructure and the eïŹect of ferrite recrystallization state
Phase transformations and recrystallization in Dual Phase steels microalloyed with Ti and Nb : experimental study and modeling
Les aciers multiphasĂ©s Ă trĂšs haute rĂ©sistance mĂ©canique destinĂ©s Ă lâindustrie automobile font lâobjet dâimportantes activitĂ©s de recherche et dĂ©veloppement dans le contexte de lâallĂšgement des structures. Lâobtention de meilleurs compromis entre rĂ©sistance et ductilitĂ© nĂ©cessite de comprendre lâinfluence du couple composition chimique nominale â paramĂštres du procĂ©dĂ© dâĂ©laboration sur la formation des microstructures.La prĂ©sente Ă©tude sâinscrit dans cette dĂ©marche de comprĂ©hension et porte en particulier sur les mĂ©canismes se produisant lors du recuit des nuances dâaciers Dual Phase de haut grade microalliĂ©s au Ti et au Nb, dont la microstructure initiale laminĂ©e Ă froid est composĂ©e de bainite et de martensite. Ces mĂ©canismes (prĂ©cipitation des Ă©lĂ©ments de microalliage Ti, Nb et Mo, recristallisation de la ferrite et formation de lâaustĂ©nite) prĂ©sentent des interactions complexes. Le scĂ©nario des Ă©volutions microstructurales lors du recuit est caractĂ©risĂ© Ă lâaide dâune Ă©tude expĂ©rimentale sâappuyant sur des techniques dâanalyses complĂ©mentaires Ă diffĂ©rentes Ă©chelles (DRX in situ, MEB, MET, SAT). Lâinfluence respective des Ă©lĂ©ments de microalliage Ti, Nb et Mo et des paramĂštres du recuit sur ce scĂ©nario est clarifiĂ©e Ă lâaide dâune caractĂ©risation systĂ©matique des Ă©volutions microstructurales couplĂ©e Ă la mise en Ćuvre dâune dĂ©marche de modĂ©lisation des mĂ©canismes et de leurs interactions.To meet the need for weight reductions in the automotive industry, new advanced high-strength steels are being developed. The achievement of a better balance between high strength and high formability requires a deep understanding of both the effect of chemical composition and processing parameters on the formation of microstructures. The present work contributes to such an objective and deals with the mechanisms occurring during annealing of Dual Phase steels microalloyed with Ti and Nb. Microstructural changes during this stage include precipitation of microalloying elements, ferrite recrystallization and austenite formation. These mechanisms are investigated using complementary experimental techniques at different scales such as in situ XRD, SEM, TEM and APT in various Dual Phase steel grades having the same bainite-martensite initial cold-rolled microstructure. Using combined experimental and modeling approaches, the present work clarifies the separate influence of microalloying elements Ti, Nb and Mo and heating rate on the mechanisms occurring during annealing and their interactions
Effect of Minor Alloying Elements (Ag, Mg, Zn) and Temperature on Natural Ageing Kinetics of Al-Cu-Li Alloys
International audienc
Influence of Microalloying Elements Ti and Nb on Recrystallization during Annealing of Advanced High-Strength Steels
International audienc
Influence of Microalloying Elements Ti and Nb on Recrystallization during Annealing of Advanced High-Strength Steels
International audienc