Characterisation of Corrosion Damage in T91/F91 steel exposed to Liquid Lead-Bismuth Eutectic

TL;DR

This study investigates how T91 steel corrodes in liquid lead-bismuth eutectic at high temperatures, revealing microstructural intrusion patterns and chromium depletion as key corrosion mechanisms.

Contribution

It provides detailed microstructural analysis of corrosion patterns and identifies chromium dissolution as the main corrosion process in T91 steel exposed to LBE.

Findings

Networks of LBE intrusion beneath surfaces identified.

Corrosion patterns vary under oxidising and reducing conditions.

Chromium depletion occurs near intrusion sites.

Abstract

T91 samples were exposed to static liquid lead-bismuth eutectic (LBE) at 700{\deg}C for 250-500 hours in either an oxidising or reducing environment. Corrosion damage was characterised using electron microscopy techniques, which identified networks of LBE intrusion beneath LBE-wetted surfaces. Under reducing conditions these networks are uniformly distributed, while they appear patchier and deeper under oxidising conditions. The individual intrusions preferentially follow microstructural features, initially along prior-austenite grain boundaries, followed by penetration down martensite lath boundaries. Local depletion of Cr was observed within 4 {\mu}m of the intrusions and along intersecting boundaries, suggesting local Cr dissolution as the main corrosion mechanism.