Short-range order influences H distribution in Fe-Ni-Cr austenitic stainless steels

TL;DR

This study investigates how short-range order influences hydrogen distribution in Fe-Ni-Cr austenitic stainless steels, revealing that pre-existing SRO promotes local H enrichment, which may facilitate slip localization and embrittlement.

Contribution

The paper introduces a combined spin cluster expansion and Monte Carlo simulation approach to analyze H-SRO interactions, providing new insights into their influence on hydrogen embrittlement mechanisms.

Findings

H slightly alters intrinsic alloy ordering preferences.

H-Ni and H-Cr pairs show stronger ordering tendencies.

Pre-existing SRO promotes local H enrichment in specific domains.

Abstract

Hydrogen embrittlement (HE) in austenitic stainless steels is advanced by hydrogen enhanced localized plasticity (HELP), typically accompanied by a transition from homogeneous to localized slip. Short-range order (SRO) in face-centered cubic (FCC) alloys is known to promote slip planarity, and recent studies suggest that H may amplify this localization behavior linked to inherent SRO. However, the manner in which the introduction of H affects SRO properties and, conversely, the manner that pre-existing SRO may affect H behavior, are not fully understood. In this work, a spin cluster expansion model combined with Monte Carlo simulation is employed to study the interplay between H and SRO in Fe-Ni-Cr alloys. Chemical order is quantified using Warren-Cowley SRO parameters, and the model predictions are validated against experimental data. We find that the presence of H only slightly alters the intrinsic ordering preference of the Fe-Ni-Cr alloys. As temperature decreases and the alloy evolves from disordered to ordered thermodynamic states, distinct H-metal correlations emerge. In particular, H-Ni and H-Cr pairs exhibit stronger ordering tendencies than H-Fe pairs, suggesting a selective affinity of H for certain atomic environments. On the other hand, we also find that compared to random alloys, when pre-existing SRO is present, it significantly affects the resulting H distribution by promoting local H enrichment in SRO domains. Such SRO-driven local H accumulation may facilitate slip localization and contribute to the early onset of embrittlement. These findings provide thermodynamic and structural insights into the interaction between H and SRO in austenitic stainless steels, highlighting possible implications on how the interaction between HELP and SRO brings about hydrogen embrittlement in austenitic stainless steels.