Effects Of Alloying Elements On The Corrosion Behavior Of High-Strength Hull Steel In High-Humidity Marine Environment

The South China Sea is crucial to China’s economic growth and security because it is the country’s maritime strategic position.In the South China Sea’s harsh atmospheric environment,corrosion loss of low-alloy high-strength hull steel and other materials is significantly higher than it is in other sea regions.The study of high-performance steel’s corrosion resistance mechanism in a marine atmosphere with high humidity is still in its early stages.In view of the above problems,this paper constructs a simulated corrosion environment of the high-humidity marine atmosphere in the South China Sea based on the dry-wet alternate cycle experimental equipment,and studies the effects of alloy elements such as Ni,Cu and Sb on the corrosion behavior of Cu-containing high-strength hull steel in such environments.The rust layer morphology,corrosion products,element distribution and electrochemical characteristics of the experimental materials were characterized and analyzed by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,electron probe（EPMA）and electrochemical tests.The influence mechanism of Ni,Cu and Sb on the corrosion of experimental steel in high-humidity marine atmospheric environment was clarified.The results are as follows:（1）The experimental steel’s resistance to air corrosion is enhanced by the addition of Ni.The rate of steel corrosion is reduced by 25%when the Ni content rises from 1.5 weight percent to 2.5weight percent.The majority of the Ni in steel is present in the rust layer as Ni Fe₂O₄,which can encourage the conversion ofγ-FeOOH to the stable phaseα-FeOOH in the rust layer and increase rust layer density.The rust layer is electronegative and repellent to Cl^-due to the crystal structure of Ni Fe₂O₄,which lessens the harm that Cl^-can cause to the rust layer.Additionally,Ni enrichment in the rust layer can improve electrochemical protection by raising the corrosion potential and charge transfer resistance.（2）The experimental steel’s resistance to air corrosion can be enhanced by the addition of Cu.The corrosion rate of the 2.0 wt%Cu experimental steel in the 360 h corrosion experiment was52.67%lower than that of the 1.3 wt%Cu experimental steel.The high concentration of Cu in the rust layer produced a lot of Cu O during the corrosion process,which enriched at the rust layer/substrate interface,inhibiting the in-depth development of the corrosion reaction and promoting uniform substrate dissolution,thereby slowing the corrosion rate.The relative amount ofγ-FeOOH in the rust layer falls noticeably as Cu content rises,and the rust layer’s protective coefficientα/γ*rises noticeably as well as its density.According to the electrochemical test results,the experimental steel rust sample has a higher self-corrosion potential and a lower corrosion current density the higher the Cu content.The impedance spectroscopy test further reveals that Cu greatly enhances charge transfer resistance and rust layer resistance,and that its protective effect on the experimental steel’s rust layer increases noticeably when the corrosion cycle is prolonged.（3）The experimental steel’s corrosion rate is decreased by adding Sb,and a 0.5 weight percent increase has the same effect.Sb has an 8%reduction in corrosion rate.Sb can decrease the amount of active phase in the rust layer,stimulate the conversion ofγ-FeOOH to Fe₃O₄ andα-FeOOH there,and increase the stability of the rust layer.Sb is mostly present in the rust layer as Sb₂O₅,which boosts rust layer density and the matrix’s capacity for protection.The electrochemical test results demonstrate that an increase in Sb content significantly improves the corrosion resistance of the experimental steel while decreasing the current generated by corrosion density,increasing the charge transfer resistance,and decreasing the electrochemical reaction rate of the rusted sample.