Rhein-Westfalia Technical University RWTH (Aachen, Germany):

Bleck W., Dr. Eng., Prof., Head of Dept. in the IEHK Steel Institute, e-mail: bleck@iehk.rwth-aachen.de

Three generations of advanced high strength steels have been developed that provide an extraordinary balance of strength and formability. These can be distinguished by their combination of crystallographic phases, their alloying contents and the deformation mechanisms. The processing of these strip steels requires stringent hot rolling schedules and heat treatments after cold rolling for microstructure adjustment. Special emphasis is laid on the control of phase transformations, the partitioning of alloying elements during processing, and the segregation eff ects. AHHS of 1st generation are multiphase steels with a ferritic matrix. Their properties result from a mixture of phases that need to be adjusted during cooling after hot rolling or during continuous heat treatment after cold rolling. AHHS 0f 2nd generation are austenitic high manganese steels that are characterized by continuous adaptive microstructural refi nement during straining. The full exploitation of their properties requests for a basic understanding of the various involved deformation phenomena. AHSS of 3rd generation are medium manganese steels with a multiphase microstructure of which one phase is metastable austenite. The processing of these steels needs the close control of phase transformations, of partitioning of carbon between concurrent phases with diff erent solubilities and the control of segregation effects. Characteristic for the new steels is a microstructure that has to be adjusted on the nm scale. Part of this work was supported by the Deutsche Forschungsgemeinschaft within the collaborative research centre SFB 761 “steel – ab initio” which is gratefully acknowledged.

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