Design of cold rolled and continuous annealed carbide-free bainitic steels for automotive application

► Design of cold rolled and annealed bainitic steels for automotive application. ► Cost effective lightweight steel solution for future vehicles. ► Solving the lack of formability of advanced high strength steel sheets. ► Microstructure consisting of ferrite laths and thin films of retained austenit...

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Bibliographic Details
Published in:Materials in engineering 2013-08, Vol.49, p.667-680
Main Authors: Caballero, F.G., Allain, S., Cornide, J., Puerta Velásquez, J.D., Garcia-Mateo, C., Miller, M.K.
Format: Article
Language:English
Subjects:
Annealing
Automotive components
Carbide-free bainite
Constants
Continuous annealing
Ductility
Ferrite
Formability
Heterogeneity
Microstructure
Steel
Structural steels
Ultimate tensile strength
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Summary:► Design of cold rolled and annealed bainitic steels for automotive application. ► Cost effective lightweight steel solution for future vehicles. ► Solving the lack of formability of advanced high strength steel sheets. ► Microstructure consisting of ferrite laths and thin films of retained austenite. ► Reaching optimum combination of strength, ductility, and formability. Advanced high strength steels for automotive applications were designed to achieve a carbide-free bainitic microstructure after conventional thermo-mechanical processing and a continuous annealing treatment. The microstructure obtained consists of ferrite laths interwoven with thin films of untransformed retained austenite. The sufficiently tough matrix and the control of the heterogeneity in the microstructure will allow an optimum combination of strength, ductility, and formability to be achieved. The designed steels reached far higher uniform elongations than that in commercial dual phase steels and martensitic steels with the same range of ultimate tensile strengths. Their formability was found to be appropriate for the production of final parts after cold-stamping or cold-forming. On the other hand, the yield strength/ultimate tensile strengths ratio was found to remain roughly constant (∼0.7). The reduction of area value did not seem to change as a function of overaging temperature, but the V-bending angle and the hole expansion ratio (cut-edge stretching ability) decreased significantly at the bainite holding temperature increases.
ISSN:0261-3069
DOI:10.1016/j.matdes.2013.02.046