Direct observation of the accumulated plastic zone (i.e., a zone with accumulated plastic strain > 0.02) around a fatigue crack in Type 304 stainless steel has been made using the recrystallization phenomenon. Annealing at 950°C for 24 h followed by electrolytic etching in Morris solution was used to reveal the accumulated plastic zone. It is shown that the larger the zone, the larger the crack-growth rate, and that the fatigue crack growth rate is proportional to the second power of the accumulateci plastic zone size.
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