Corrosion-fatigue crack growth and the threshold characteristics of a high-tension steel HT55 (σ_B = 580 MPa) have been investigated in 1% NaCl solution by using an automated microcomputer-controlled K-device.

Crack growth rates are significantly reduced in 1% NaCl solution at 5 Hz and R = 0.1, with a threshold value above the air values. The corrosion-products-induced wedge effect results in a reduced ΔK-value, thereby reducing growth rates. Therefore crack growth rates in 1% NaCl solution exceed those in air, with a lower threshold value than in air when considered in terms of ΔK_eff.

Supposing a linear summation hypothesis in terms of ΔK_eff given by (da/dN)_CF = (da/dN)_F + (da/dN)_D, the crack growth that proceeds by stress-assisted dissolution (da/dN)_D is derived. A proposal to estimate long-term corrosion-fatigue crack growth characteristics is presented, where ΔK_eff is assumed to be identical to ΔK since the crack tip is blunted and the crack is much thickened in long-term corrosion fatigue. The long-term corrosion-fatigue crack growth curves are finally derived at various stress cycle frequencies.