Relationship between fatigue limit of austenitic stainless steels and existence of micro-cracks

摘要

Fatigue tests have been performed to investigate the effect of strain aging on the fatigue limit and fatigue crack behavior about two kinds of austenitic stainless steels, SUS 304 and nitrogen contained SUS 304 (SUS 304 N). From the testingresults, the fatigue limits of SUS 304 and SUS 304 N increase by 5 and 30 MPa, respectively by the low temperature annealing (300℃×2 h) during fatigue test by the specified cyclic ratio under constant higher stress amplitude than their original fatiguelimits. It is considered that the effect of strain aging by nitrogen in SUS 304 N increases its fatigue limit. However, the specimens, in which the fatigue micro-cracks in the length of 1~2 grains sizes exist under the higher stress amplitude than thefatigue limit of each material, propagate to he a final fracture before 1×10{sup}7 cycles under the same original stress amplitude of fatigue limit, even if the specimens were annealed in the vacuum at low temperature.