Study Of Effect And Mechanism Of Rare Elements On Corrosion Behavior Of Ultrahigh Strength Steel

Low-alloying Ultrahigh-strength Steel (LUHS) with ultra high specific strength,excellent fatigue property and good processability characteristics, have been applied tovessel, offshore work platform, amphibious armored equipment and other field. Marineatmospheric corrosion occurred easily on vessel, offshore platform and armoured vehicleand reduced their service life, because of the combination of marine atmosphere withhigh temperature, high humidity and high salt fog characteristics. In order to improve themarine atmospheric corrosion performance and the service life, I have studied thecorrosion processes and regular of LUHS in marine atmosphere and analyzed theinfluence mechanism of rare earth by adding rare earth into LUHS from a steel factory inChina, which may takes full advantage of local RE resources and provides someexperimental evidence and theoretical basis of corrosion protection to LUHS.This work investigated the effect and its mechanism of RE and its content on thecorrosion resistance of LUHS to marine atmospheric corrosion by cycle immersioncorrosion test model. We have characterized the influence of RE on microstructure andinclusions of test steel by metallographic microscope and SEM, analyzed the effect of REon the surface morphology of the samples by digital camera, calculated the corrosion ratethrough weightlessness method and researched the corrosion kinetics of test steel, testeddynamic polarization curves and electrochemical impedance spectroscopy byelectrochemical workstation, analyzed the electrochemical behavior and properties of thesample with corrosion products.The results show that: RE adding into Low-alloying Ultrahigh-strength Steel refinedthe microstructure and changed the nature of the inclusions. Compared with test steelwithout RE, the width of lath martensite of test steels with0.008%RE and0.08%REdecreased11%and17%, the inclusions are smaller and more round. The test steels withand without RE in marine atmosphere occurred uniform corrosion, the main corrosionproducts of them are α-FeOOH, γ-FeOOH, Fe3O4, γ-Fe2O3, β-FeOOH. The addition of REin Low-alloying Ultrahigh-strength Steel enhansed the content of protective α-FeOOH ofcorrosion products, produced a more densest, continuous and attached layer of rust,reduced the corrosion current density and corrosion rate of weight loss, improved significantly marine atmospheric corrosion resistance. The corrosion resistance ofLow-alloying Ultrahigh-strength Steel with0.08%RE was best in this study.