Plane bending fatigue tests of steel sheet specimens corroded with salt-water were carried out in order to examine the relation between the feature of the corroded surface and the fatigue strength of the corroded specimens. The material used was quenched and tempered spring steel sheet SUP6 (Hv470).
The main factors affecting the degradation of fatigue strength due to corrosion were the reduction of sectional area and the increase in surface roughness, as is the case of 0.075%C and 0.15%C hot-rolled steel sheets.
The following equation for estimation of the bending fatigue strength σwap of the corroded specimens, proposed in our previous report, has been ascertained to hold also for a high strength steel such as spring steel SUP 6.
Where Z is the section modulus, η=0.45 for 0.075%C steel, 0.65 for 0.15%C steel and 1.1 for SUP 6 (Hv470), and Δdmax is the maximum depth of roughness (mm).
The value of η increased as the hardness of steel sheet became higher, and was well related to the notch sensitivity of the material.