Creep-to-rupture tests of T91 steel in flowing Pb-Bi eutectic melt at 550 °C

Uniaxial creep-to-rupture tests were performed on T91 in air and in flowing lead-bismuth eutectic melts. Compared to specimens tested in air, the specimens tested in liquid-metal show: (i) strain and strain rate increase up to a factor of about 50 (strain rate); (ii) time-to-rupture decrease; (iii) rapid transition into the third creep stage at high stress (above 180 MPa). The analysis of the test results revealed several important surface phenomena, which lead to different behavior of the specimens tested in lead-bismuth eutectic melts 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 and Bi 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.