[en] This paper aims to simulate the behavior of some alloys in high temperature fatigue-relaxation (creep), for a long hold time (one month for each cycle) when laboratory experiments are difficult to realize. The first part presents an estimation of the internal intergranular stresses. The second part deals with the recovery occurring during the hold time. (A.L.B.)

[en] This study aims at foreseeing the behaviour of some alloys during high temperature fatigue-relaxation (creep) conditions when the maximum deformation is maintained during long times (about a month for each cycle). Such experiments can hardly be performed with laboratory tests. A simple modeling of the restoration occurring during the keeping of the conditions of deformation can explain the absence of dislocation microstructures. Abstract only. (J.S.)

[en] The aim of this work is to give a general comparison of the swelling behaviours of two Ti-stabilized austenitic steels (type 316 and 15 Cr-15 Ni). The irradiation of samples at 500⁰C shows that 15-15Ti SS swells less than 316 Ti SS only when irradiated in the cold-worked state. The irradiation of these two cold-worked alloys as fuel pin cladding shows that the higher swelling resistance of 15-15 Ti steels is only clearly established in the temperature range 450-550⁰C. Moreover this steel may exhibit large swelling variability from cast to cast. Transmission electron microscopy examinations are used to understand the origin of the swelling variability of cold worked 15-15 Ti steel and its difference of behaviour with cold worked 316 Ti steel in the upper range of irradiation temperature. (author)

[en] In the past, a lot of experimental studies have been devoted to creep-fatigue interactions in austenitic stainless steels. Tests have been carried mainly at temperatures of at least 600 deg. C and at high applied strains, which are supposed to be the most damaging. The present work is dedicated to mechanical tests, TEM observations and lifetime predictions at 550 deg. C which corresponds to the real industrial temperature in Liquid Metal Fast Breeder Reactors. It is shown that if pure fatigue test results are close to those performed at 600 deg. C, some of the creep-fatigue results are different, particularly for small applied strains which correspond once more to the industrial conditions. In the 0.25-0.3% strain amplitude range, the stress is larger with hold time than without whatever is the hold time up to 5 h. The numbers of cycles to failure are greatly reduced and no saturation with the hold time is observed, contrary to higher temperature results. The stress-strain behaviour is discussed considering several high temperature mechanisms such as ageing, recovery and viscoplasticity and using TEM observations and stress partitioning into kinematic, isotropic and thermal stresses. Finally, a simple linear damage accumulation model is applied to the 550 deg. C and 600 deg. C tests, using the measured stresses. The stress dependence on hold time can partly explain the observed failure results on fatigue life