Stress Corrosion Behavior Of T91and316L Steels In Liquid Lead-Bismuth Eutectic

Lead-Bismuth Eutectic (LBE) is one kind of promising materials as the coolant of the lead-based reactor and spallation target in the Accelerator Driven Sub-critical System (ADS), because of its low chemical activity with water and air, good neutron properties and thermal conductivity, etc.. Martensitic steel T91and austenite steel316L have been selected as the main candidate structure materials for ADS projects. Liquid metal embrittlement (LME) effect may occur when the structure materials suffer from stress and LBE, which would pose a threat to the reactor safety. Therefore, the stress corrosion embrittlement of T91and316L steels in LBE had been studied in the thesis. The main research progresses are as follows:1) To assess the LME susceptibility of T91and316L steels in LBE qualitatively, the wetting of LBE-T91and LBE-316L at the temperatures among200℃and600℃was investigated with the sessile drop tests. The results showed that the T91and316L steels were not wet with LBE under the inert gases. The contact angles decreased with the increasing of the temperature above400℃, but they remained constant at the temperature below400℃. Moreover, the contact angle of LBE-T91(100～121°) was much less than that of LBE-316L (107～145°) at the same temperature, this indicated that the interaction between T91steel and LBE was much larger, and then the LME of T91in LBE was more susceptibility.2) Withing the slow strain rate testing device, the tensile tests for T91and316L steels in oxygen saturated LBE and air were conducted at the temperature of200℃to450℃, respectively. The results indicated the mechanical properties of316L steel were not affected by LBE, but the total elongation of T91steel increased at above400℃. To study the effects of oxygen content in LBE and surface flaws, and given the toughness recovery temperature (above400℃) of T91steel, the tensile tests of the pre-wet and notched specimens were conducted at350℃. The total elongations of T91specimens decreased about15%and25%when pre-exposed in LBE with the oxygen concentration of10-6wt%and10-8wt%, respectively. And the accelerated rupture occurred after the elastic deformation. The ductile of the pre-wet316L specimens was not affected. And the result of the T91notched specimens showed that the non-wet specimen was ductile fracture. The total elongation of the pre-wet notched one reduced about40%, and the fracture surface was brittle.3) In order to study the service behavior of relevant structure components with the static load in LBE, the content strain stress corrosion tests of the C-ring specimens for T91and316L steels in saturated oxygen (～5×10-4wt%) and low oxygen content (～10-8wt%) LBEs were conducted in corrosion device, respectively. The stress cracking was not observed for the T91and316L specimens both in saturated oxygen and low oxygen environments. One of the reasons was that the oxide scales prevented the direct contact of liquid LBE and the matrixes, and the other might be the surface cracks did not generate with the stress below the yield strength.The above results of the thesis revealed the LME of T91steel in LBE was more susceptibility than that of316L steel, and the direct contact of the solid-liquid and the plastic deformation of the steel have an important role on the occurrence of LME, which is very useful for the engineering design and materials selection for CLEAR-I.