| WU Xing-jun,CHEN Yue-liang,BIAN Gui-xue,ZHANG Yong,WANG An-dong,HUANG Hai-liang,WEI Zi-lin.Initial Corrosion Behavior and Electrochemical Property Evolution of 40CrNiMo Steel in Salt Spray Environment[J],51(5):234-244 |
| Initial Corrosion Behavior and Electrochemical Property Evolution of 40CrNiMo Steel in Salt Spray Environment |
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| DOI：10.16490/j.cnki.issn.1001-3660.2022.05.024 |
| KeyWord:40CrNiMo steel salt spray test rust layer electrochemical properties micro area electrochemistry |
| Author | Institution |
| WU Xing-jun |
Naval Aviation University Qingdao Campus, Shandong Qingdao , China |
| CHEN Yue-liang |
Naval Aviation University Qingdao Campus, Shandong Qingdao , China |
| BIAN Gui-xue |
Naval Aviation University Qingdao Campus, Shandong Qingdao , China |
| ZHANG Yong |
Naval Aviation University Qingdao Campus, Shandong Qingdao , China |
| WANG An-dong |
Naval Aviation University Qingdao Campus, Shandong Qingdao , China |
| HUANG Hai-liang |
Naval Aviation University Qingdao Campus, Shandong Qingdao , China |
| WEI Zi-lin |
Naval Aviation University Qingdao Campus, Shandong Qingdao , China |
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| Abstract: |
| In order to study the initial evolution of rust layer and electrochemical properties of 40CrNiMo steel in simulated marine environment, in this paper, the neutral salt spray test method was used to simulate the marine atmospheric environment. The changes of microstructure and composition of inner and outer rust layer of 40CrNiMo steel were characterized by Optical Microscope (OM) and XRD, the redistribution process of Cr element in rust layer was studied by EDS line scanning, the evolution of electrochemical properties were studied by potentiodynamic polarization and EIS, the Volta potential and its distribution on the sample surface were studied by scanning Kelvin probe (SKP). The initial corrosion behavior (0-11 d) of 40CrNiMo steel in neutral salt spray environment with NaCl content of 5% gradually developed from pitting corrosion to uniform corrosion, the evolution law of the maximum corrosion pit depth is d=87.787t0.325, the corrosion kinetic characteristics accord with the law of power function, the fitting result is ΔW=6.091t0.738, which show that the rust layer have a certain protective effect on the metal matrix. The rust layer was obviously stratified after 4 days of salt spray, and the inner rust layer was significantly thickened after 7 days. XRD results show that the yellow loose outer rust layer is mainly composed of γ-FeOOH; the black dense inner rust layer is mainly composed of α-FeOOH and Fe3O4, and the EDS line scanning test results show that Cr element enrichment occurs at the interface with the matrix. The polarization curves show that the corrosion process was controlled by cathodic reaction, and the corrosion current density first increase, then decrease and finally increase. The EIS measurement results show that the charge transfer resistance first decrease, then increase and finally decrease. The polarization curves have a good correlation with the EIS measurement results, which show that the corrosion rate of 40CrNiMo steel first increase, then decrease and finally increase in the neutral salt spray environment. The SKP measurement results show that the cathode and anode regions were rapidly formed on the sample surface in salt spray environment, the Volta potential range on the surface of the non corroded sample was 225 mV, which increase to 884 mV after 7 days of salt spray and decrease to 609 mV after 11 days of salt spray. Therefore, it is concluded that after 1 day of salt spray, the rust layer of 40CrNiMo steel was loose and porous, which provide a humid environment for the reaction and speeds up the corrosion rate. With the increase of salt spray time, the rust layer gradually thickened and densified, meanwhile Cr element were enriched in inner rust layer, which lead to the inhibition of oxygen reduction reaction and the protective effect on the matrix became more and more prominent; after 7 days of salt spray, the activity of γ-FeOOH reduction reaction in the rust layer gradually increased, and two parallel cathodic reactions of oxygen reduction and corrosion product reduction occurred at the same time. the reaction rate tended to be stable after increasing. |
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