Environmental Fatigue Testing of Type 316 Stainless Steel in 310 °C Water

Low cycle fatigue tests were conducted to investigate fatigue behaviors of Type 316 stainless steel in 310 °C low oxygen water. In the tests, strain rates were 4 × 10⁻⁴, 8 × 10⁻⁵ s⁻¹ and applied strain amplitudes were 0.4, 0.6, 0.8, and 1.0%. The test environment was pure water at a temperature of 310 °C, pressure of 15 MPa, and dissolved oxygen concentration of < 1 ppb. Type 316 stainless steel underwent a primary hardening, followed by a moderate softening for both strain rates in 310 °C low oxygen water. The primary hardening was much less pronounced and secondary hardening was observed at lower strain amplitude. On the other hand, the cyclic stress response in room temperature air exhibited gradual softening and did not show any hardening. The fatigue life of the studied steel in 310 °C low oxygen water was shorter than that of the statistical model in air. The reduction of fatigue life was enhanced with decreasing strain rate from 4 × 10⁻⁴ to 8 × 10⁻⁵ s⁻¹.