Stress corrosion cracking (SCC) in EUROFER RAFM steel subjected to Li-ceramics at 550 °C

• EUROFER steel exhibits stress corrosion cracking (SCC) under low elastic preloads when exposed to Li 4 SiO 4 /Li 2 TiO 3 breeder ceramics at 550 °C. • Crack initiation occurs at the oxide/metal interface, where a duplex Fe-rich/Cr-rich oxide forms together with a Cr-depleted subsurface. • Transgranular crack propagation is promoted by local stress accumulation in martensitic laths and the presence of dispersed MX-type carbides. • Lithium ingress from the ceramic pebbles penetrates into the substrate, further reducing cohesion and enhancing susceptibility to SCC. • A transition from crack nucleation to growth is observed over exposure time, with tensile–compressive asymmetry that diminishes at longer times. This study investigates the susceptibility of EUROFER reduced-activation ferritic-martensitic (RAFM) steel to stress corrosion cracking (SCC) when exposed to lithium ceramic breeder materials (HCPB environment) at 550 °C. A standardized experimental methodology based on the U-bend configuration was employed to apply well-defined stresses while preserving microstructural integrity. Specimens were subjected to prolonged exposure (up to 4300 h) in direct contact with lithium ceramics, and the resulting damage was characterized using scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). Complementary finite element simulations were performed to ensure the applied load remained within the elastic regime, evaluate the stress distribution, and identify the region experiencing maximum stress. The results reveal that SCC is promoted by the formation of a thin, brittle, chromium-depleted surface layer, resulting from high-temperature oxidation. Cracks nucleate within this chemically and structurally degraded zone and propagate transgranularly under residual stress. A quantitative analysis of crack density and size demonstrates a clear correlation with exposure time and stress level, confirming the critical role of mechanical load in accelerating crack initiation and growth. These findings identify a significant degradation mechanism affecting EUROFER in breeder blanket operating conditions, underscoring the need to control both surface chemistry and residual stresses to ensure long-term structural reliability.