Fatigue Behavior of Stainless Steels with Different Ferrite and Austenite Volume Fraction in 3%NaCl Solution

Fatigue tests in 3%NaCl solution have been performed on stainless steels with different volume fraction of ferritic (α)/austenitic (γ) phases in order to clarify the influence of corrosive environment on crack initiation and growth behavior. Specimens with five different volume fractions of ferritic/austenitic phases, i.e. SUS304 (100%γ), SUS329J4L (50%γ, 28%γ, 12%γ), SUS444 (100%α), were prepared. Cracks were generated predominantly from slip band within γ grains in SUS304 and SUS329J4L and within α grains in SUS444, which was the same behavior as in laboratory air. Fatigue strengths in 3%NaCl solution slightly decreased for all materials compared to those in laboratory air. In early crack growth region, crack growth rates in 3%NaCl solution were faster than in laboratory air. In SEM observation, the brittle feature was seen on the fracture surfaces near the crack initiation site. Environmental effect was also found in high ΔK region for long cracks, where crack growth was enhanced in 3%NaCl solution.