The plate specimens of two-phase stainless steel were fatigued by a cyclic bending fatigue test machine. The surface morphology and the dislocation structure just beneath the specimen surface were examined through a transmission electron microscope operated at 200kV. Tensile tests were also performed to understand the basal deformation behavior of two-phase stainless steel. Based on these experimental results, the behavior of fatigue crack initiation was discussed.
The main results obtained are as follows;
(1) When the specimens were stretched, sharp slip bands were observed in austenite phase, whereas in ferrite phase they were not clearly detected because of the occurrence of fine wavy slips.
(2) When the specimens were fatigued, persistent slip bands were observed in both phases. The fatigue cracks leading to failure, which were expected to be formed preferentially in austenite phase from the above experimental results, however, were observed only in ferrite phase of both solution treated and aged specimens.
(3) The reason why persistent slip bands in austenite phase could not be developed into fatigue cracks may be due to the finer grain diameter of austenite phase than that of ferrite phase and the high strength of austenite phase containing a significant amount of nitrogen.