Austenitic stainless steels stress amplitude

As austenitic stainless steels are widely used, their fatigue and fatigue-relaxation behavior has been studied for more than three decades [106—112]. Their stress—strain behavior differs from that of martensitic steels. As mentioned concerning creep, the initial microstructures differ strongly and therefore hardening is observed in austenitic stainless steels, whereas softening is observed in martensitic steels. The evolution of the stress amplitude with the number of cycles is shown in Fig. 6.34(a) for various strain... 

Fig. 1.13 S-N curve obtained for austenitic stainless steel type 304 B. S is the equivalent ideally elastic stress amplitude. Open circles are experimental data points...

CF tests on smooth specimens were performed at room temperature on a 316 L austenitic stainless steel in a 0.5 N H2SO4 solution at different electrochemical potentials and for a prescribed plasfic strain amplitude of 4 x 10 (s = 10 s ). The depassivation-repassivation process occurs in a very regular way, well before any microcracks can form [11]. It is of particular interest to follow the evolution of the maximum flow stress in the corrosive solution at free potential and at imposed cathodic potential and to compare this evolution with that observed in air (Figure 12.9). It clearly appears that (a) a cyclic softening effect occurs at the free potential in comparison with the behavior in air (b) this softening effect disappears when the cathodic potential is applied (and the anodic dissolution is markedly reduced), after about 150 cycles (c) the softening effect then occurs in the same way when... 

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