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

The resistance to corrosion and embrittlement of T91 steel in stagnant Pb-Bi eutectic was studied in the temperature interval 150-650 deg C. The degradation of the corrosion resistance manifested itself above 350 deg C, with Pb-Bi sticking at surface inclusions at 600 deg C and with localized corrosion effects visible at 650 deg 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 carried out in situ in Pb-Bi in the temperature interval 300-400 deg 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%H2 cover gas, whereas almost no LME effect was detected in Pb-Bi under vacuum. A maximum reduction in energy to rupture (around 30%) was found for notched specimens tested in Pb-Bi under He-4%H2 cover gas at a cross-head displacement rate of 6 x 10-4 mm/s at 350 deg C. (authors)