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Vanadium microalloying concepts for Quenching and Partitioning Steels

Friday (28.09.2018)
09:45 - 10:00 S1/01 - A4
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Quenching and Partitioning (Q&P) steels represent one of the most promising concepts for automotive third generation advanced high strength steels. The predominantly martensitic base microstructure of these steels provides both higher yield and tensile strength compared to conventional high strength dual phase steels, while retained austenite imparts significantly improved ductility compared to low carbon martensitic steels of comparable tensile strength. One of limitations of these steels is the partitioning process itself, which is typically performed between 400°C and 500°C. Partitioning both reduces the carbon content of the martensite matrix via diffusion to austenite, and the dislocation density of the martensite by recovery, leading to considerable strength loss compared to low temperature tempered martensite of comparable bulk composition. In this work, we explore opportunities for increasing the yield and tensile strength of Q&P steels via secondary precipitation hardening during two step Q&P processes, such as those performed in continuous annealing lines. To do this, a reference 0.2C-2Mn-1.5Si Q&P steel composition was microalloyed with combinations of V and V-N and processed at laboratory scale using dilatometry. We show that a useful secondary hardening response can be obtained in low carbon martensite at partitioning temperatures over 450°C, and discuss the effects of V microalloying on the kinetics of partitioning and retained austenite content during two step Q&P processing of this steel.

David Martin
Additional Authors:
  • Dr. Jacek Komenda
    Swerea KIMAB AB