通过OM, SEM, EBSD观察和EIS谱、动电位极化曲线测试等手段分析了不同应变下冷拔珠光体钢的腐蚀形貌、组织演变及点蚀在其演变组织中的分布和铁素体取向差分布, 研究了冷拔珠光体钢的横纵截面组织演变对其点蚀行为的影响. 结果表明, 由于横截面和纵截面组织演变规律的不同, 不同应变下冷拔珠光体钢的横截面和纵截面的耐蚀性分别表现出不同的变化规律: 随着应变的增加, 横截面耐蚀性持续下降, 而纵截面耐蚀性先降低后回升. 通过表征点蚀在冷拔演变组织中的分布规律, 发现珠光体组织的晶界、珠光体团界面、相界面对点蚀敏感性高, 是点蚀倾向于萌生和生长的区域, 冷拔变形造成界面面积增加, 使横截面和处于第一阶段应变ε ≤1.2的纵截面的耐蚀性显著下降. 铁素体<110>织构形成导致晶体取向差分布规律的改变会使纵截面在第二阶段ε =1.6的耐蚀性改善.
Heavily cold drawing pearlitic steel wires are widely used for aerospace, tire cord, suspension bridge cable, and architecture due to the high strength with acceptable level of ductility. For marine steel wires, which are widely applied in the marine and offshore structures enduring the effect of stress and corrosion, the corrosion performance is significant. Corrosion is a primary cause of structural deterioration for marine and offshore structures, which results in structural failure, leakage, product loss, environmental pollution and the loss of life. Numerous studies have been devoted to the microstructure evolution or cementite dissolution induced by cold drawing. With respect to the effect of microstructure evolution on the performance of pearlitic steel, the views were mainly focused on the mechanical performance, and only a little attention was paid to the effect of microstructure evolution on the corrosion behavior of pearlitic steel. Hence, it is still unclear whether and how the cold drawing influences the corrosion resistance of pearlitic steel. In this work, the effect of microstructure evolution on the pitting corrosion of pearlitic steel was investigated. The electrochemical measurements were carried out by electrochemical impedance spectroscopy and potentiodynamic measurement. Meanwhile, the corrosion morphology after immersion for 5 d was observed by standard visual techniques. The results indicate that corrosion resistance of cross section decreases with increasing the strain of cold drawing, while the corrosion resistance of longitudinal section decreases in the first stage of cold drawing (strain ε ≤1.2) but increases in the second step of cold drawing (ε =1.6). By characterizing the distribution of pits in the evolutionary microstructure induced by cold drawing, the grain boundary, the pearlite colony boundary and the phase boundary where the pits are inclined to initiate and propagation, are sensitive to pitting. Thus, the decrease of corrosion resistance of cross section and longitudinal section in the first stage of cold drawing (ε ≤1.2) is due to the multiplication of interface, which increases the pitting sensibility of microstructure. Electron backscattered scattering detection was used to quantify the content of <110> texture of pearlitic steels with different strains. The result showed that the improvement of corrosion resistance of the longitudinal section in the second stage of cold drawing (ε =1.6) is due to the variation of misorientation angle distribution caused by the formation of <110> texture.
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