Creep-rupture tests of T91 and 15-15 Ti(Si) steels in Pb at 550° C

This is a preliminary study of  uniaxial creep-to-rupture tests were performed on T91 (ferritic martensitic stainless steel) and 15-15 Ti(Si) (austenitic stainless steel)  in air and in lead. This material will have to be used for nuclear reactor components of IV generation “LFR” (Lead-cooled fast reactor). A key problem in development of heavy liquid metal cooled nuclear energy and transmutation reactors is the corrosion of structural and fuel. Corrosion experiments of T91 steel were carried out in air and static Pb at 550°C  and compared with those of 15-15Ti in Pb at the same exposure conditions. The T91 compared to specimens tested in air, the specimens tested in liquid–metal show: (i) strain and strain rate increase (strain rate); (ii) time-to-rupture decrease; (iii) rapid transition into the third creep stage at high stress. The analysis of the test results revealed several important surface phenomena, which lead to different behaviour of the specimens tested in lead compared to those tested in air. Under high stress, and therefore high strain, the crack propagation process is mostly controlled by the reduction of the surface energy due to Pb adsorption on the steel surface. Under low stress (140 and 160 MPa) and low strain, this process is delayed due to the competing mechanism of healing the oxide scale cracks. The 15-15 Ti(Si) compared to specimens tested in air, the specimens tested in liquid–metal show: (i) strain and strain rate increase (strain rate); (ii) time-to-rupture decrease. Creep-rupture tests of T91 in lead at 550°C reveal significant reduced creep strength of non-modified T91 and 15-15Ti(Si) test specimens.