Multiscale investigation of crack path and microstructural changes during liquid metal embrittlement of 304L austenitic steel in liquid sodium

Fracture micro-mechanisms and crack path of embrittled austenitic steel 304L by liquid sodium strained at 4.2 × 10−7 m s−1 and 573 K are investigated underneath the fracture surface by transmission electron microscopy down to the nanoscale. Automated crystal orientation and phase mapping analyses show that abundant martensitic transformation (γ austenite → α' martensite) as well as mechanical twinning occur during the deformation of austenite and play a major role in the fracture process. A correlation between the fracture surface features and the underlying microstructural interfaces is evidenced, strengthening the conclusion that liquid metal embrittlement by sodium of austenitic steels is basically an interfacial cracking phenomenon.