Fatigue Behavior of Stainless Steels with Different Fern tie and Austenite Volume Fractions in Laboratory Air

摘要

Fatigue crack initiation and growth behavior of stainless steels with different volume fraction of ferritic (alpha)-austenitic (gamma) phases were studied. Materials with five different volume fractions of alpha/gamma phases, i.e. SUS304 (100 percent gamma), SUS329J4L (50 percent gamma, 28 percent gamma, 12 percent gamma), and SUS444 (100 percent alpha), were prepared. Fatigue tests were conducted in laboratory air using electro-hydraulic fatigue testing machine. Cracks initiated predominantly from slip bands within gamma grains for SUS304, and SUS329J4L, and within alpha grains for SUS444, i.e. transgranular crack initiation was found. Fatigue lives decreased in the order of SUS329J4L, SUS444 and SUS304. The same tendency was also seen in fatigue limits. In early crack growth region, while no remarkable differences were found in all materials, for three materials in SUS329J4L crack growth rates were faster in the order of 50 percent gamma, 28 percent gamma, and 12 percent gamma, i.e. early crack growth was influenced by the phase boundary. Moreover, the early crack growth was enhanced in comparison with the long crack in all materials. After allowing for crack closure, long cracks exhibited a similar growth behavior in all materials. Based on these results, the transition from small to large crack and the effect of alpha/gamma phase fraction were discussed.