Fundamental Study on Wet Corrosion Fatigue of Mild Steel by Electrochemistry

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In this study, fundamental experiments were conducted in order to simulate a real corrosive environment in the laboratory and to understand the long life properties through comparatively short time test. First, Noting that the phenomena of wet-corrosion may be analyzed by the theory of electrochemistry, corrosion rates of test specimens were obtained under various environments. Second, experimental weight loss of corrosion were compared with theoretical values. The results provide basic data to obtain the limit of acceleration of corrosion rate without disturbing the corrosion process. Finally, ordinary fatigue tests in air and corrosion fatigue tests were performed to compare with both results. In the corrosion fatigue tests, specimens were attached to cell for corrosion by a 3% salt solution saturated by air. Then the fractured section of them were observed with scanning electron microscope. Main conclusion is as follows ;(1) The corrosion rate of mild steel is higher in salt water than in fresh water and is strongly affected by the dissolved oxygen in both cases. (2) In sea water, the mild steel appear to show continuously decreasing ability to withstand cyclic stress as the number of cycles of applied stress increases. (3) The corrosion fatigue strength in a sea water is less than the allowable strength in air. (4) The long life fatigue tests are required to determine the S-N curve for corrosion fatigue. This kind of tests can easily be electrochemistry performed. (5) In the surfaces that suffered corrosion fatigue, the area of brittles surface has a tendency to be larger than that of the fatigue test in air and, in addition, the percentage of brittle surface are increases as the stress level decreases. (6) Dynamic analyses of cable subjected to a fluid force were carried out, due to developing a study of fatigue strength of cable in sea water.