Mechanical and microstructural behaviour of ferritic/martensitic steels low-cycle fatigued between room temperature and 550ºC

MF GIORDANA; I ALVAREZ; M SAUZAY; A ARMAS

Brno

Conferencia; 6th International Cnference on Materials Structure & Micromechanics of Fracture; 2010

Institute of Physics of Metrials - Academy of Science of the Czech Republic

Components built from reduced activation ferritic/martensitic steels (like EUROFER 97 and F82H) are of interest within the development of the future fusion power plants. The cyclic behavior of these steels as a function of the imposed plastic strain amplitude and temperature has been analyzed in detail between room temperature and 5500C. At all temperatures and strain levels, a cyclic softening behavior following a linear (in a log-log scale) stage is observed. At each temperature, the cyclic softening rate and final average subgrain size appear to be independent on the plastic strain range. From the analysis of the peak tensile stress of the hysteresis loops and its respective correlation with transmission electron microscopy observations can be concluded that the cyclic softening observed could be attributed, principally at low temperatures, to the progressive annihilation of dislocations located in the interior of the subgrains and, under the synergic effect of temperature, to the disappearance of the subgrain dislocation walls. Precipitate fences decoration the disappeared dislocation walls become visible at high temperatures. Cyclic softening rates increase linearly with temperature up to temperatures at which self-diffusion mechanisms can operate enhancing the dislocation annihilation process.