Multiscale Investigation of Microcracks and Grain Boundary Wetting in Press-Hardened Galvanized 20MnB8 Steel
Martin Arndt,
Philipp Kürnsteiner,
Tia Truglas,
Jiri Duchoslav,
Kurt Hingerl,
David Stifter,
Christian Commenda,
Johannes Haslmayr,
Siegfried Kolnberger,
Josef Faderl,
Heiko Groiss
Affiliations
Martin Arndt
Voestalpine Stahl GmbH, Voestalpine-Straße 3, 4020 Linz, Austria
Philipp Kürnsteiner
Christian Doppler Laboratory for Nanoscale Phase Transformations, Center for Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz, Austria
Tia Truglas
Christian Doppler Laboratory for Nanoscale Phase Transformations, Center for Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz, Austria
Jiri Duchoslav
Center for Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz, Austria
Kurt Hingerl
Center for Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz, Austria
David Stifter
Center for Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz, Austria
Christian Commenda
Voestalpine Stahl GmbH, Voestalpine-Straße 3, 4020 Linz, Austria
Johannes Haslmayr
Voestalpine Stahl GmbH, Voestalpine-Straße 3, 4020 Linz, Austria
Siegfried Kolnberger
Voestalpine Stahl GmbH, Voestalpine-Straße 3, 4020 Linz, Austria
Josef Faderl
Voestalpine Stahl GmbH, Voestalpine-Straße 3, 4020 Linz, Austria
Heiko Groiss
Christian Doppler Laboratory for Nanoscale Phase Transformations, Center for Surface and Nanoanalytics (ZONA), Johannes Kepler University Linz, Altenberger Straße 69, 4040 Linz, Austria
Grain boundary wetting as a preliminary stage for zinc-induced grain boundary weakening and embrittlement in a Zn-coated press-hardened 20MnB8 steel was analyzed using electron backscatter diffraction, Auger electron spectroscopy, energy dispersive X-ray analysis, atom probe tomography and transmission electron microscopy. Microcracks at prior austenite grain boundaries were observed. Structures that developed after microcrack formation were identified: for example, Zn/Fe intermetallic phases with grain sizes smaller than 100 nm were present at the crack surfaces and the wedge-shaped crack tips. An electrolytically coated reference sample that underwent the same heat treatment as the press-hardened material but without the application of tensile stress was investigated in order to find the initial cause of the microcracks. On this sample, Zn, in the order of one atomic layer, was found along prior austenite grain boundaries several micrometers away from the actual Zn/Fe phases in the coating. The resulting grain boundary weakening with the Zn wetting of prior austenitic grain boundaries during austenitization and/or hot forming is a necessary precondition for microcrack formation.