• Galler, Matthew
• Traxler, Ines
• Warchomicka, Fernando Gustavo
• Ahmed, Hamdi Ahmed Elsayed
• Vallant, Rudolf
• Sommitsch, Christof
• Drexler, Andreas
• Domitner, Josef

Abstract

<p>Multiphase ultra-high strength steels (UHSS) containing retained austenite (RA) appear to be among the most interesting steels for the automotive industry. Developments in the last decades have allowed obtaining a very good combination of mechanical strength and ductility. Quenching and partitioning (Q&amp;P) steels have been proposed as third-generation UHSS, reaching ultimate tensile strength up to 1300 MPa along with excellent fracture elongations of more than 15%. However, the use of Q&amp;P steels is mainly limited by their susceptibility to hydrogen embrittlement (HE). The present work investigates the influence of the Q&amp;P heat treatment parameters on the mechanical properties and on the HE resistivity of 20Mn-Si wire rod steel. The HE resistivity was measured using incremental step load testing with in situ electrochemical hydrogen charging according to ASTM F1624-12 standard. A comprehensive microstructure characterization was performed to examine volume fraction, nucleation sites and morphologies of RA. Although the mechanical properties were similar after Q&amp;P heat treatment, an increase in the partitioning time revealed a significant increase in the HE threshold stress of more than 200 MPa.</p>

Topics

• impedance spectroscopy
• microstructure
• resistivity
• strength
• steel
• Hydrogen
• tensile strength
• susceptibility
• ductility
• wire
• quenching