Corrosion behavior of 300M ultra-high strength steel in simulated gap water environment

The gap water produced in an airplane's structural parts during its service usually leads to the corrosion of structure materials. In this paper, the corrosion behavior of 300M ultra-high strength steel in simulated gap water is studied by evaluating the corrosion products, their morphology, weight loss, corrosion rate, damage area, pH of the solution, and the ratio of the corrosion media volume to the exposed area of 300M steel, etc. The results show that the corrosion initiates with pitting, and gradually developes into general corrosion with the pits scaling out and merging. As corrosion time extends, both corrosion weight loss and damage area ratio increase, while the corrosion damage area ratio exhibits a trend of power function. The pH in the simulated gap water first increases from 4.2 to 5.2 and then decreases to 4.8-5.0. The average corrosion rate decreases linearly from 0.289 g/(m²·h) to 0.120 g/(m²·h). The results of electrochemical impedance spectroscopy indicate that the size of the capacitive reactance arc increases with the extension of corrosion time. It illustrates that the corrosion products formed in the surface of steel seem to protect the matrix, which agree with the regular pattern of corrosion rate. In addition, the increase in area-to-volume ratio, i.e., the ratio of corrosion media volume to the exposed area of 300M steel, results in an increase in corrosion weight loss and corrosion rate.