Liquid-metal-induced fracture mode of martensitic T91 steels

The liquid-metal-induced fracture mode of T91 martensitic steel was investigated by using transmission electron microscopy techniques to characterize the microstructure and crack network in specimens obtained from focused-ion beam machining at and immediately below the fracture surface. Contrary to previous claims of quasi-cleavage fracture, the dominant fracture mode is intergranular cracking at martensite laths and prior austenite grain boundaries. These fracture mode results clarify an outstanding issue in liquid-metal embrittlement of steels that generally occur in a heavily-deformed microstructure. Several cracks were arrested at intergranular carbides, suggesting a metallurgical strategy for impeding liquid-metal-induced crack propagation.