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Zhao Z.Z.,University of Science and Technology Beijing | Zhao Z.Z.,Beijing Laboratory of Metallic Materials | Yin H.X.,University of Science and Technology Beijing | Yin H.X.,Beijing Laboratory of Metallic Materials | And 9 more authors.
Materials Science and Engineering A | Year: 2014

The transformation behavior, mechanical properties and stretch-flangeability of an ultra-high-strength TRIP-assisted bainitic-ferritic sheet steel 0.2C-2Si-1.8Mn were investigated at different austempering temperatures for automotive applications. Increasing the austempering temperature was found to partially transform the uniform fine lath structure matrix and film-type metastable retained austenite into blocky martensite or austenite. The investigated steel exhibits good stretch-formability, particularly when austempered at temperatures lower than or slightly higher than the Ms point, accompanied by an excellent combination of strength and ductility. The good stretch-flangeability is related to a certain number of film-type metastable retained austenite structures. Blocky martensites, which blocky austenite transforms into during the cooling process or subsequent tensile test, deteriorate the stretch-flangeability. © 2014 Elsevier B.V.

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