Fatigue tests were carried out on fatigue crack growth properties of small as well as large surface cracks in SUS 304 stainless steel at 538°C, by using plate specimens with surface notches of various shapes and small plate specimens with a small artificial pit. All the data of the fatigue crack growth rate obtained in the present tests were correlated with the stress intensity factor range ΔKI, so that the applicability of linear fracture mechanics to the fatigue crack growth of surface cracks at elevated temperature was investigated and discussed in comparison with the data of through cracks at elevated temperature and those at room temperature.
It was found that the fatigue crack growth properties of surface cracks followed the same properties of through cracks even at 538°C and depended on test frequency in the same manner as through cracks. And it was observed that the fatigue crack growth properties of small surface cracks in plastic regime depended slightly on applied stress level. The data points, however, fell within a relatively narrow scatter band for a wide range of the applied stress levels and almost agreed with the data of through cracks. Therefore, under the present experimental conditions, linear fracture mechanics is to some extent applicable to the fatigue crack growth behavior of surface cracks at 538°C.
