Crack growth in stainless steel 304 at 538 degrees C under fatigue loading with and without hold time

Abstract

The crack growth behavior in stainless steel 304 is investigated at 538 degreesC in air. The effects of frequency (f), load level (P) and hold time on the crack growth rate are examined. It is shown that fracture mechanics parameters DeltaK and DeltaJ can correlate crack growth rates reasonably well beyond the regime of small scale yielding for no hold time tests. Depending on the values of f x P-max, three (f-P-max) domains are suggested for characterization of the da/dN-DeltaK relation. The crack tends to grow faster at low values of f x P-max for DeltaK < 25Mpa<root>m. The trend is reversed for DeltaK > 25MPa rootm. The SEM fractographs and optical micrographs of fracture surfaces indicate that oxidation plays a significant role on crack growth. The mode of crack propagation is transgranular for loading without hold time, and it becomes intergranular for loading with hold time. The crack growth rate is found to be much higher for loading with hold time.