Low cycle fatigue behavior of a modified 9Cr–1Mo ferritic–martensitic steel in lead–bismuth eutectic at 350 °C – Effects of oxygen concentration in the liquid metal and strain rate

• Fatigue endurance of T91 steel in LBE was significantly degraded due to LME.
• Oxygen concentration effect was strain amplitude and strain rate dependent.
• Fatigue crack initiation was delayed by the protection of surface oxides.
• Fatigue crack propagation was unaffected by oxygen concentration.
• A new LME mechanism was proposed to explain quasi-cleavage.

The synergistic effects of oxygen concentration and strain rate on the low cycle fatigue behavior of a 9Cr–1Mo steel have been investigated in lead–bismuth eutectic (LBE) at 350 °C. The results showed substantial fatigue life reduction due to liquid metal embrittlement (LME), compared to vacuum. Nevertheless, no evident life degradation was observed under a combination of low strain amplitude, high oxygen concentration in LBE and slow strain rate. This is because fatigue crack initiation was delayed by surface oxide films, rather than because LME disappeared. Fatigue crack propagation remained unaffected by oxygen concentration. A new LME mechanism is proposed.