Corrosion fatigue crack propagation in a heat affected zone of high-performance steel in an underwater sea environment

Abstract

Fatigue crack propagation in high-performance steel, HSB800, was investigated in air and seawater environments using three-point single-edge notched bending fatigue tests. Two types of heat affected zones (HAZ) resulting from welding processes, coarse grained and inter-critically reheated coarse grained zones, together with as-received metal were used to analyze the behavior. A 3.5% sodium chloride solution was used as the seawater, and several types of loading conditions, according to the stress ratio and loading frequency, were applied. The fatigue crack propagations were then assessed using the da/dN-Delta K curves. The results showed that the corrosion fatigue crack in seawater was more rapidly propagated than was that in the air environment. The third region of crack propagation was not observed in the da/dN-Delta K curve for the seawater environment, particularly in base metal. Generally, high stress ratio and load frequency shows a low threshold value in the stress intensity factor range. Furthermore, a different microstructural aspect of the crack propagation behavior in HAZs, as compared with that of the base metal, has been identified according to the crack propagation mechanisms.