Influence of Hydrogen on Deformation and Embrittlement Mechanisms in a High Mn Austenitic Steel: In-Situ Neutron Diffraction and Diffraction Line Profile Analysis

Abstract

Austenitic steels have relatively high resistance to hydrogen embrittlement and play a critical role in hydrogen service applications. In particular, high Mn austenitic steels are considered economically viable alloy alternatives for these applications. The current study employed in-situ and ex-situ neutron diffraction techniques combined with diffraction line profile analysis (DLPA) to investigate the influence of hydrogen on deformation and embrittlement mechanisms in a high Mn (approximately 30 wt pct) austenitic steel. Investigation using both neutron diffraction and electron backscatter diffraction revealed the presence of extensive deformation twins and stacking faults within the steel microstructure after tensile deformation in the non-charged condition. These microstructural features suggest planar deformation behavior, which is expected from the relatively low stacking fault energy (SFE) of the alloy (approximately 29 mJ/m2). Hydrogen pre-charging resulted in apparent increases of both dislocations and stacking faults, contributing to macroscopic hardening and embrittlement mechanisms. It is interpreted that hydrogen embrittlement was facilitated by the enhanced planar deformation behavior, likely associated with the hydrogen-induced reduction in SFE. Overall, numerical parameters obtained through neutron DLPA were used to elucidate the underlying mechanisms associated with hydrogen effects on the mechanical behavior, i.e. macroscopic strengthening, strain hardening rate, and embrittlement.

Keywords: High Mn Steel, Neutron diffraction, hydrogen embrittlement, Austenite, Stacking fault energy