Study on Improving the Corrosion Resistance of BT490XT Steel via Rare Earth Ce Modification of TiN Inclusions AITranslate

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Chinese Library Classification Number:TG142.13[一般工业技术]

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The morphology,quantity and size of TiN inclusions in BT490XT automotive body steel exert a significant influence on its corrosion resistance.In this work,a combined approach of experiments and firstprinciples calculations was adopted to systematically investigate the modification mechanism of rare earth Ce on TiN inclusions in BT490XT steel.The evolution laws governing the occurrence state,micromorphology,elemental distribution,and size of TiN inclusions before and after Ce addition were explored.Meanwhile,the effect of Ce-modified TiN inclusions on the corrosion resistance of the steel was evaluated via computational analysis,and the electrochemical corrosion behavior of the steel with and without Ce addition was comparatively characterized.The results show that in the absence of rare earth Ce,the dominant inclusions in the steel are single TiN inclusions and Al₂O₃-TiN composite inclusions,which are large in number and irregular in blocky shape.After the addition of 0.0019%(mass fraction)rare earth Ce,the two types of TiN inclusions in the steel are transformed into CeAlO₃-TiN composite inclusions,accompanied by a reduction in quantity and a decrease in average size from 2.72μm to 2.32μm.The modification mechanism of Ce on TiN inclusions is as follows:Al tends to combine preferentially with Ce to form CeAlO₃,which precipitates prior to Al₂O₃.The precipitated CeAlO₃ serves as heterogeneous nucleation sites,inducing the precipitation of TiN phase at its periphery and further facilitating the growth of CeAlO₃-TiN composite inclusions with a core-shell structure and reduced particle size.First-principles calculations reveal that the electron work functions of different TiN crystal planes are not identical.When the exposed surfaces of TiN inclusions are the(100)and(110)crystal planes,as well as the Ti-atom-terminated surface of the(111)crystal lographic plane,TiN inclusions act as the anode and are susceptible to corrosion.In contrast,when the exposed surface is the N-atom-terminated surface of the(111)crystal lographic plane,the steel matrix surrounding the inclusions acts as the anode and undergoes preferential corrosion.After Ce addition,the electron work function of CeAlO₃ formed in the steel is closer to that of the steel matrix,and both the potential energy difference and fluctuation degree between CeAlO₃ and the steel matrix are lower than those between TiN and the matrix.Consequently,the smaller-sized CeAlO₃-TiN composite inclusions are less likely to induce pitting corrosion than pure TiN inclusions,thus effectively improving the corrosion resistance of the steel.Electrochemical corrosion tests confirm that the steel with Ce addition exhibits a lower self-corrosion current density and superior corrosion resistance,which is in good agreement with the results derived from first-principles calculations.