Prediction of forming limits and microstructural evolution during warm stretch forming of DP590 steel

Dual-phase (DP) steel has an excellent blend of various mechanical properties; hence it is used immensely in the automotive industries. It is challenging to form high strength DP steel into desirable complex shapes because of their limited formability at room temperature conditions. One of the proven alternatives is warm/hot forming. In-detail investigation of forming limits over DP590 steel has been carried out in present work. Firstly, various constitutive models and yield criteria have been formulated for DP steel at different temperatures and strain rates. The modified Arrhenius (m-A) constitutive model and Barlat 1989 yielding function displayed the best prediction of flow stress and anisotropic yielding behavior, respectively. The experimental forming limits (FLD) were evaluated at 300, 473 and 673 K temperatures using Nakazima tests. The forming limits of the material are improved by approximately 24% on increasing the temperature from 300 to 673 K. The textural analysis of the deformed surface has been done using electron back scattered diffraction (EBSD) studies, and γ fibers are found to be responsible for improvement in the formability of the material. Additionally, Marciniak and Kuczynski (MK) model was used to predict the theoretical FLD using all the possible combinations of constitutive models and yield criteria. Finally, the m-A constitutive model, along with Barlat 1989 yielding function has shown the best prediction for forming limits at all the temperatures. The finite element study has also been performed using mentioned material models for accurate prediction of dome height, surface strain and thickness distribution across the specimens.

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Opracowanie rekordu ze środków MEiN, umowa nr SONP/SP/546092/2022 w ramach programu "Społeczna odpowiedzialność nauki" - moduł: Popularyzacja nauki i promocja sportu (2022-2023)