Investigation of the effect of the types and densities of grain boundary carbides on grain boundary cavitation resistance of AISI 321 stainless steel under creep–fatigue interaction

The effect of MX (where X=C, N) and M₂₃C₆ and their densities at the grain boundaries on creep–fatigue behavior of AISI 321 stainless steel are investigated. The creep–fatigue lives of fine MX and coarse MX aged alloys were longer than those of M₂₃C₆ aged alloy under the same test conditions. In order to better understand the difference in the creep–fatigue lives between the tested alloys, microstructural observations are conducted by scanning electron microscope (SEM) and transmission electron microscope (TEM). The differences in the creep–fatigue lives of the alloys are due to the stronger cavitation resistance of MX carbides compared with that of M₂₃C₆ carbides. From the microstructural observations, it is verified that formation and growth of grain boundary cavities in MX carbides are more retarded than in M₂₃C₆ carbides. Therefore, it is suggested that the types of carbides are a more prominent factor than the density of carbides for grain boundary cavitation in austenitic stainless steels.