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We have studied the corrosion-fatigue crack initiation and propagation of different types of steels: two austenitic, one austenitic-ferritic, and one ferritic. The testing program had been established in order to define, particularly, the part in corrosion fatigue of electrochemical effects and mechanical damage. Tests were carried out on smooth specimens in rotating bending and on precracked specimens in tension in air, and in a 3 percent aerated solution of sodium chloride. The capacity of the metal for dissolution and repassivation seems largely responsible for the behavior of the metal in the corrosive solution. This capacity varies notably with the composition of the metal, the loading conditions of the specimens, and the characteristics of the corrosive medium.

Load-controlled experiments on 304L stainless steel were run in Air and PWR water, at 150°C and 300°C, with and without a mean stress of 100MPa. These experiments were run to determine the influence of temperature, environment, and mean stress on the 107 Cycle Fatigue Limit stress amplitude. A 100MPa mean stress was found to have different effects at the different temperatures and environments. In contrast to all the conventional models used to describe the effects of mean stress, when the testing was done at 300°C (for both air and PWR water), a 100MPa mean stress was found to raise the 107 Cycle Fatigue Limit relative to that observed without a mean stress. This was ascribed to the effect of the hardening due to the initial straining and to secondary hardening, both of which are more pronounced at 300°C than at 150°C. The increased initial and secondary hardening resulted in the development of less non-elastic strain, thereby improving the fatigue behavior. In PWR water at 150°C, a 100MPa mean stress reduced the 107 Cycle Fatigue Limit by more than that predicted by conventional mean stress models, but in air at 150°C, the decrease in the endurance limit was more in keeping with the predictions of these models. This difference was ascribed to the effect of the PWR water, in the absence of significant initial straining and secondary hardening.