Synergistic Effects of Temperature and Dissolved Oxygen on Liquid Metal Embrittlement of a Si-alloyed 12cr Ferritic/martensitic Steel in Lead-Bismuth Eutectic

The liquid metal embrittlement (LME) behavior of a Si-alloyed 12Cr ferritic/martensitic (F/M) steel (0.6 wt.% Si) in lead-bismuth eutectic (LBE) was investigated via slow-strain-rate tensile tests at 250-550°C and dissolved oxygen concentrations of 10-9-10-5 wt.%. The steel exhibits a distinct ductility trough under moderate-oxygen (10-8-10-7 wt.%) at 250-450°C, with maximum embrittlement at 350°C. This temperature window is independent of Si content (0-1.09 wt.%). At 350°C, high oxygen (10-6-10-5 wt.%) suppresses LME via a protective oxide layer, while moderate and low oxygen (10-9-10-7 wt.%) cause severe embrittlement (embrittled area fractions of 96 % and 91 %, respectively), with no significant difference between the two, revealing a threshold effect. A comparison with literature further shows that Si content does not shift the temperature window, but strongly affects fracture toughness degradation (nearly 71 %) versus a modest effect on elongation reduction (18-42 %), indicating that Si influences crack propagation more significantly than crack initiation. These findings provide new insights into the coupled roles of temperature, oxygen, and Si in LME, with implications for oxygen control strategies in LBE-cooled reactors.