Correlation between the carbide morphology and cavity nucleation in an austenitic stainless steels under creep-fatigue

It is well known that grain boundary cavitation at carbides is one of the detrimental damaging processes for the degradation of austenitic stainless steels that reduces the creep-fatigue life at high temperatures. In the case of the 316 and 304 austenitic stainless steels, it is found that grain boundary is considerably serrated with the modified heat treatments to the change of carbide morphology from triangular to planar shape. And it is found that the interfacial mismatch between the neighboring matrix and modified planar carbides has been reduced to have less incoherency than that between the neighboring matrix and triangular carbides, so that the creep-fatigue resistance has been remarkably increased. These results imply that the modified carbides, whose interface energy is lower, have higher cavitation resistance, resulting in the retardation of cavity nucleation and growth to increase creep-fatigue life. Therefore, it is suggested that the cavity nucleation factor is regarded as the material constant related with the carbide characteristics. (C) 2004 Elsevier B.V. All rights reserved.