Liquid Pb-Bi embrittlement effects on the T91 steel after different heat treatments

The present work aims to investigate the susceptibility of ferritic/martensitic steels of different strength to the embrittlement of liquid Pb-Bi eutectic (LBE). Slow strain rate tensile (SSRT) tests on specimens of the T91 steel in three tempering conditions at 500, 600 and 760 °C were conducted in Ar and in LBE at temperatures between 150 and 500 °C. For the specimens tempered at 760 °C (the normal tempering condition) the susceptibility of the steel to LBE embrittlement appeared at temperatures between 300 and 450 °C. With increasing the strength of specimens by lowering the tempering temperature, specimens tempered at 600 and 500 °C demonstrated more pronounced embrittlement effects, reflected by wider and deeper ‘ductility-troughs’. The results suggest that ferritic/martensitic steels with higher strength are more susceptible to LBE embrittlement. The LBE embrittlement effects can be attributed to the decrease of fracture stress resulted from the ‘weakening inter-atomic bond’ by LBE contacting at crack tips.