| Problems such as electrochemical corrosion and physical corrosion seriously affect the service life of large offshore steel structures such as offshore resource extraction platforms.How to improve the corrosion resistance of mining platforms and other devices at low cost and high efficiency is a problem that scholars have been keen to study today.The effective strategy of the moment is the incorporation of rare earth elements into offshore steel,which has more significant theoretical benefits compared to other measures such as surface coating.The incorporation of rare earth elements exhibits good desulfurization and deoxidation properties and further improves the corrosion resistance of the samples.The Y element in rare earths has the advantage of small radius and low density compared to elements such as La and Ce,which would be more beneficial to improve the corrosion resistance of offshore steels.In this paper,the changes of micro and macro morphology and corrosion resistance of marine steel after incorporation of Y element in marine steel cast billets with different contents,heat treatment tests and electrochemical corrosion tests are investigated as follows:1.The adsorption energy between the marine steel and Cl-in artificial seawater was calculated by the first nature principle,as a way to analyze the effect of Y element doping on the corrosion resistance of the specimens.The results show that Cl-will only occur in the top-site adsorption phenomenon on the Fe（100）surface during the whole corrosion process.The best corrosion resistance was achieved when the doping amount of element Y was 0.2wt%,and the corrosion resistance of the specimens decreased significantly when the doping amount continued to increase.Based on the preheating regime of industrial production,the effects of different Y-element doping amounts and different heat treatment temperatures on the inclusions in the cast billets of marine steel and the changes in corrosion resistance of the final samples were investigated within a specific heat treatment time.The results show that spherical or ellipsoidal Y-containing inclusions are generated in all samples doped with Y elements,while the precipitation of manganese sulfide is suppressed.The inclusions size of the samples increased with the increase of temperature during the heat treatment of the samples.At 800°C,the grain size of the specimens had the smallest grain spacing and the densest organization.The corrosion resistance behavior of the specimens was further analyzed by electrochemical corrosion tests,and the incorporation of element Y further inhibited the cracking phenomenon of the corrosion layer and reduced the corrosion rate.2.Based on the international standard proportioned artificial seawater solution as the medium for the electrochemical corrosion test,the electrochemical test and the morphological characterization and composition analysis of corrosion products were carried out on 0.2wt%marine steel,so as to investigate the electrochemical corrosion behavior of the samples under different conditions.The results show that the immersion corrosion rate increases and then slows down for all samples.The decrease of p H in the solution will lead to the increase of corrosion rate of the samples,the original corrosion layer closely associated with the substrate produces cracks,leading to more seawater entry,the corrosion degree is increased and the corrosion resistance is reduced.The corrosion potential(Ecorr)of the specimen increases from-0.704Vsce to-0.685Vsce,and the corrosion current density(Icorr)increases from 5.93±0.02×10-6A/cm2 to 8.37±0.02×10-6A/cm2.When the temperature of the experimental environment increases,the thickness and composition of the corrosion layer changes,and some Mn elements and Fe elements diffused outward,and Cl elements gradually enriched in the inner layer of corrosion.The Ecorr of the specimen increased from-0.841Vsce to-0.825Vsce,and the Icorr increased from4.59±0.02×10-6A/cm2 to 6.83±0.02×10-6A/cm2.The presence of two corrosion products（α-Fe OOH andα-Fe2O3）was verified throughout the experiment,and theα-Fe OOH andα-Fe2O3 percentage fluctuates with the change of p H value. |
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