抄録
Corrosion fatigue crack growth tests in low ΔK region in 3%NaCl solution and in distilled water have been carried out on 13Cr stainless steels at various stress ratios (R=-1.0, 0.1, 0.4, 0.8). The effect of frequency on corrosion fatigue crack growth in 3%NaCl solution was also investigated. The results are summarized as follows.
(1) The corrosive environment studied here had little effect on crack growth rate in ΔK≥ΔKth (ΔKth: threshold value in air) for R=-1.0 and 0.1, but it slightly increased the crack growth rate for R≥0.4.
(2) As critical crack growth rate dropped from (2∼5)×10-10m/cycle in air to (2∼5)×10-11m/cycle in 3%NaCl, ΔKthCF(ΔKthCF: threshold value in corrosive environment) decreased 0.4 times (R=-1.0) to 0.6 times (R=0.1) of ΔKth. ΔKthCF in distilled water was (0.65∼0.70) time (R=-1.0 and R=0.1) of ΔKth.
(3) Corrosion pits often occurred at the corrosion fatigue crack tip in the region below da/dN=(2∼8.7)×10-11m/cycle. Therefore, the ΔK value required to reinitiate crack growth from those pits was about 1.5 times higher than that of ΔKthCF.
(4) The crack growth law derived previously by considering the effects of waveform and frequency was also found valid as the first approximation for the materials tested.
