Creep behaviour of 15-15Ti(Si) austenitic steel in air and in liquid lead at 550°C

Abstract: This work aims at studying the creep behaviour of 15-15Ti(Si) austenitic steel, under uniaxial stress and its interaction with liquid lead. Creep tests were performed at 550 °C in an engineering stress range of 300-560 MPa. The 15-15Ti(Si) stainless steel is one of the best candidates for the nuclear reactor components of IV generation Lead-cooled fast reactor (LFR) and was tested in air and in stagnant liquid lead to simulate its behaviour in operating thermal and mechanical stress conditions and to verify its sensitivity to Liquid Metal Embrittlement (LME). Only few data can be found in the literature on 15-15Ti(Si) characterization, therefore the performed tests provided important information to use this material in the nuclear field, allowing to obtain the characteristic curve simulating the creep behaviour in air at all stress values, based on the Norton law and experimental data. The results of the specimens in air were compared with those obtained in lead, providing important information on creep corrosion: the liquid metal embrittlement effect takes place in lead and it produces a decrease of creep-rupture time, a reduction of creep strain and then the loss of steel ductility. Moreover, Scanning Electron Microscope (SEM) micrographs highlighted that lead changes both the mode and the type of specimen fracture. In addition, it was analyzed the lead action time, as the time after which the corrosion appears with macroscopic effects. These tests are still in progress: up to the current value of time (800h), they showed similar creep behaviour of the specimens tested in air and in lead. It can be assumed that liquid metal embrittlement takes place after a long time of steel/lead contact. However, since these tests are ongoing, these results will be object of our future studies.