Abstract
The recrystallization technique has been adapted to observe directly the plastic zones around creep and fatigue cracks at 650°C in Type 304 stainless steel. It is found that creep crack growth from notches occurs after an incubation period of ∼ 70%t f, whereas fatigue crack propagation occurs easily in the test. During the incubation period the plastic zone at the tip of the notch increases in size. However, when the creep and fatigue plastic zones are compared at almost the same time, they are seen to be of comparable size. It is shown that the strain gradients in the creep and fatigue plastic zones are different, in spite of their comparable size, and the easier initiation of fatigue cracks suggests that fatigue damage accumulates more quickly than creep damage in the plastic zones.
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