Resistance to corrosion an embrittlement of T91 steel in stagnant Pb-Bi of eutectic composition

Abstract
The resistance to corrosion and embrittlement of T91 steel in stagnant Pb-Bi eutectic was studied in the temperature interval 150-650°C. The degradation of the corrosion resistance manifested itself above 350°C, with Pb-Bi sticking at surface inclusions at 600°C and with localized corrosion effects visible at 650°C. Nevertheless, the specimens aged in Pb-Bi did not exhibit any degradation of mechanical properties during ex situ testing in air at room temperature. On the contrary, a liquid metal embrittlement (LME) effect was observed, when the tensile tests were camed out in situ in Pb-Bi in the temperature interval 300-400°C. The LME effect depends on temperature, strain rate, existence of stress concentrators and especially on the chemical composition of the cover gas. This effect was observed in Pb-Bi under He-4% H ₂ cover gas, whereas almost no LME effect was detected in Ph-Bi under vacuum. A maximum reduction in energy to rupture (around 30%) was found for notched specimens tested in Pb-Bi under He-4% H ₂ cover gas at a crosshead displacement rate of 6x10 ^-4 mm/s at 350°C.