Factors Affecting Fatigue Strength of Hot-Rolled Steel Sheets Corroded with Salt-Water

Abstract

In order to investigate the corrosion effect on the fatigue strength of steel sheets used in automobile suspension members, plane bending fatigue tests were carried out. The materials used were 0.075%C and 0.15%C hot-rolled steel sheets. One group of specimens were intermittently dipped in 5% salt-water at room temperature and another group continuously in 20% HCl aqueous solution at 50°C. The fatigue strength of the corroded specimens was correlated with the feature of the corroded surfaces.
The main factors affecting the degradation of fatigue strength due to corrosion were the reduction of the sectional area and the increase of surface roughness. The corrosion products and charged hydrogen did not decrease the fatigue strength of the corroded specimen in a dry condition.
The following equation was proposed for estimation of the bending fatigue strength σ_wap of the specimens after the corrosion products were removed.
σ_wap=(Z_c/Z₀)·(1-ηΔd_max^0.4)·σ_w0
where Z: section modulus, η: 0.45 for 0.075C steel and 0.65 for 0.15 steel, Δd_max: maximum depth of roughness due to corrosion, suffix 0: Electropolished specimens, suffix C: Corroded specimens.