The effects of microstructure and temperature on fatigue crack growth behavior of type 347 stainless steels

The effect of the microstructure and temperature on the fatigue crack growth behavior of AISI type 347 stainless steels(SS) has been studied. The isothermal FCGR (fatigue crack growth rate) of the type 347 SS increased as the temperature increased. The FCGRs of the type 347 SS at various temperatures were slightly lower than those presented in the ASME code. Even though the effect of the microstructure on the crack growth rate was not significant in the steady-state FCGR region, it was observed that the Delta K-th of a specimen with a high precipitate density was higher than that of a specimen with a low precipitate density. It was deduced that the difference in Delta K-th resulted from a difference in the mean free path length of a dislocation movement. The FCGRs were higher than the isothermal FCGR when a thermal stress and a mechanical stress were imposed on the type 347 SS coincidently.