Dynamic strain aging of dual phase steels in forming applications

Bayramin, Berkay
Sheet metals are subjected to certain temperatures (25-200oC) and strain rates (1-10 s-1) during forming applications. These thermomechanical conditions may cause dynamic strain aging (DSA) in various grades of steels including dual phase (DP) steels. DSA represent itself as serrations in the stress-strain curves. Two grades of DP steels (DP590 and DP800) were studied systematically at different strain rates (10-3s-1-1s-1) and temperatures (25oC-400oC) to investigate the DSA effects on the mechanical properties and formability. Test results show that DSA controls the deformation behavior between 200oC - 300°C through serrations in the stress-strain curves of both grades. Increasing strain rates between these temperatures result in severe drops of uniform and total strain. Also with increasing negative strain rate sensitivity (NSRS) these drops in the ductility state weak formability. Besides the tests to identify DSA, a simple microstructural model on dislocation motion is developed to explain the responsible mechanisms for DSA and its effects on the jerky-serrative flow behavior. 


Dynamic strain aging in DP steels at forming relevant strain rates and temperatures
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Mechanical testing of dual phase (DP) steels at low strain rates (10(-3) s(-1)) have shown that they are susceptible to dynamic strain aging (DSA) between 100 degrees C-400 degrees C. During industrial forming processes at intermediate strain rates (1-10(2) s(-1)), the local temperatures may rise to the DSA range due to deformation heating which may disturb the exceptional formability of these steels. In this study, two grades of DP steel (DP590 and DP800) are tested at thermomechanical conditions relevant ...
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Citation Formats
B. Bayramin, “Dynamic strain aging of dual phase steels in forming applications,” M.S. - Master of Science, Middle East Technical University, 2017.