Fatigue crack growth behavior in a harmonic structure designed austenitic stainless steel

摘要

Heterogeneous nanograined structures have been proposed to achieve unprecedented mechanical properties. The objective of the present work is to investigate fatigue crack growth behavior of harmonic structure designed austenitic stainless steels at room temperature. The harmonic structured SUS316L steels were produced by mechanical milling and subsequent hot isostatic pressing. Fatigue crack propagation tests were carried out under load ratio from 0.1 to 0.5. Results show that the change in fatigue crack growth rates of harmonic structured SUS316L steels is insignificant even as grain size decreases. The load ratio has little influence on the fatigue crack growth rates for harmonic structured SUS316L steels compared to their coarse-grained counterparts. It is worth mentioning that fatigue crack growth is impeded by embedded coarse grains, which results in fatigue crack deflection and secondary cracks. The continuously network shell (UFG structure) provides increased tensile strength, enhancing the fatigue crack nucleation resistance. Simultaneously, the embedded core (CG structure) restrains crack growth. Therefore, the harmonic structure design is proposed to be an effective method to achieve good balance of high strength and high ductility as well as good fatigue resistance.