Variation of the Corrosion Behavior Prior to Crack Initiation of E690 Steel Fatigued in Simulated Seawater with Various
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Variation of the Corrosion Behavior Prior to Crack Initiation of E690 Steel Fatigued in Simulated Seawater with Various Cyclic Stress Levels Tianliang Zhao, Zhiyong Liu, Liu Chao, Chunduo Dai, Cuiwei Du, and Xiaogang Li (Submitted July 23, 2017; in revised form June 6, 2018) The electrochemical process and corrosion behavior prior to crack initiation of E690 steel fatigued in simulated seawater are investigated under different cyclic stress levels by methods of electrochemical impedance spectroscopy, cyclic current response, electrochemical noise and morphology observation. The results show that the electrochemical behavior changes with the peak stress of cyclic loading and the corrosion behavior transforms as the peak stress increases over the proof strength. The charge transfer resistance (Rct) decreases with elevated peak stress. Continuous decreasing Rct with cycling number under peak stress of 1.02 rp0.2 indicates that continuous fresh metal induced by work-softening is exposed to the seawater, which is also proved by cyclic current response induced by cyclic stress and contact angle test. As a result, the corrosion type of E690 steel changes from general corrosion to pitting corrosion with the peak stress close to and above the proof strength. That induces the corrosion fatigue crack initiation mechanism to change correspondingly. Keywords
corrosion fatigue, corrosion type, cyclic stress, low-carbon bainite steel, simulated seawater
1. Introduction It is extensively realized that corrosion can dramatically shorten fatigue crack initiation life by up to 90% than that in air (Ref 1). The corrosion is mainly attributed to the synergistic effect of the corrosive medium and cyclic load, which can be theoretically explained with the well-known mechanochemical and chemomechanical effects (Ref 2, 3). However, due to different material properties, loading and environmental conditions, the synergistic effect usually behaves complicatedly, making corrosion prior to crack complex and inducing a different corrosion fatigue crack initiation (CFCI) mechanism. Numerous studies (Ref 4-17) concluded that cyclic load had a great effect on corrosion or electrochemical behaviors of metals in media and hence exerted an effect on the crack initiation behaviors and mechanisms. Guan et al. (Ref 9) found that cyclic stress with peak value above yield strength evidently promoted occurrence of the metastable pitting and decreased the pitting potential, while those with peak values below the yield strength had barely no effect on corrosion behavior. Ebara (Ref 4) monitored the corrosion process prior to crack initiation of 12Cr stainless steel by the electrochemical noise method and Tianliang Zhao, Zhiyong Liu, Liu Chao, Chunduo Dai, and Cuiwei Du, Corrosion and Protection Center, University of Science and Technology Beijing, Beijing 100083, China; and Xiaogang Li, Key Laboratory of Chinese Ministry of Education for Corrosion and Prevention, University of Science and Technology Beijing, Beijing 1000
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