Effects of pre-exposure and simulated corrosion “pits” on liquid metal embrittlement of T91 steel exposed to liquid lead-bismuth eutectic at 350 °C

Abstract

In this paper, the effects of pre-exposure and simulated uneven corrosion “pitting” on liquid metal embrittlement (LME) of T91 ferritic/martensitic (F/M) steel exposed to liquid lead-bismuth eutectic (LBE) at 350 °C have been studied by oxygen-specific pre-exposure test, tensile test and ANSYS stress simulation. The results show that a “pit” with a size of 0.8 mm in diameter and 0.4 mm in depth on a cylindrical tensile specimen with a diameter of 3 mm and a gauge length of 15 mm can greatly promote occurrence of LME, regardless of the oxygen concentration dissolved in LBE, leading to the formation of typical quasi-cleavage on the whole fracture surface. ANSYS stress simulation shows that the presence of such a “pit” can give rise to a strong stress concentration effect and the stress level at the “pit” region before yielding is thus increased by a factor of ∼1.7, which is responsible for the premature failure of oxide scales and earlier LME crack initiation. The results also alarm that the LME enhancement effect of uneven corrosion should not be ignored during reactor system design especially for thin-walled tubes and under transient conditions, when taking this steel as a candidate material.