Transferprojekt T4: Einfluss der Mikrostruktur auf die Wasserstoffversprödung in Cr-haltigen hoch Mangan Stählen

Dr. T. Hickel, Prof. Dr. rer. nat. J. Neugebauer (Max-Planck Institut für Eisenforschung, Düsseldorf)

Abb. 1 T4 Wasserstoff-Karbid-Wechselwirkung
Abb. 1 T4 Wasserstoff-Karbid-Wechselwirkung

It is known that the addition of alloying elements such as Al, Si and Cr to high-Mn (TWIP) steels influences both their microstructure and deformation properties as well as the significant effect on the delayed cracking due to hydrogen embrittlement. Thus, it was observed experimentally that the change of Mn- and especially C-addition can lead to the formation of Fe-containing carbides in the form of intercrystalline precipitates, which unfavorably affect the mechanical properties of TWIP and TRIP steels. The relationship between Al on the one hand and Mn and C on the other hand seems to play a central role. Accordingly, Al not only suppresses the aforementioned carbide formation in austenitic grain boundaries, but also significantly reduces the tendency to delayed crack formation. This observation provides a possible key to the question of how Al affects the hydrogen embrittlement, namely indirectly via the prevention of intercrystalline carbide formation.

The microstructure in high-Mn steels is also noticeably influenced by the change in the Cr content, which is relevant for applications because of the corrosion resistance achieved. Alloying with Cr  stabilizes the ferrite on the one hand and therefore produces a two-phase microstructure. On the other hand, the formation of Fe-containing carbides is significantly reduced by Cr in favor of a large number of Cr carbides. The latter can arise both within the austenite as well as in the ferrite-austenite phase boundary. However, little is known about the influence of these carbides on the tendency to delayed crack formation in the context of hydrogen embrittlement.

 

 

 

Abb. 2 T4 Wasserstoff-Karbid-Wechselwirkung
Abb. 2 T4 Wasserstoff-Karbid-Wechselwirkung

 

Within the scope of this transfer project, the influence of Al and Cr on hydrogen embrittlement in the context of carbide formation is to be investigated for industrial alloys. Such a project is benefiting, on the one hand, from the previous ab initio-based investigation into carbide formation in high-Mn steels and, on the other hand, the calculations for the interaction of the steels with hydrogen. It compiles these preliminary investigations within a new question. The following aspects should be considered theoretically and experimentally:

• The influence of Al, Cr and Si on the phase stability and deformation mechanisms (TRIP, TWIP) in high-Mn steels.

• The suppression of the formation of (intercrystalline) carbides by Al and Cr.

• The interaction of these carbides with hydrogen and the resulting influence on the delayed crack formation.

SZMF supports the project with sample material, experimental characterization and loading tests. Above all, SZMF brings the experience and current problems of industrial implementation into research.