Growth Characteristics of Surface Fatigue Cracks of High-Tensile Strength Steel in Synthetic Seawater

Abstract

Growth rates of surface fatigue cracks of high-tensile strength steels have been measured in ASTM synthetic seawater at a state of free corrosion and under a cathodic potential. The aspect ratio in synthetic seawater at a state of free corrosion was larger than that in air, while under a cathodic potential it was almost fixed and the same as that in air, while under a cathodic potential it was almost fixed and the same as that in air. At a state of free corrosion and at R=0.1, the crack growth rate to the inside exists under a plane-strain condition, and the O₂ concentration is lower than that near the surface. Following the initial growth, the da/dN and dc/dN were the same as that of a compact tension type specimen, both at a state of free corrosion and under a cathodic potential. Under a cathodic potential, the threshold values were remarkably high because the Ca⁺² and Mg²⁺ deposit-induced wedge effect was conspicuous.