稀土元素铈对钢中非金属夹杂物改性和腐蚀影响的第一性原理研究

通过原位腐蚀观察和基于密度泛函理论的第一性原理计算方法，从微观角度研究了稀土元素铈（Ce）对J5不锈钢中夹杂物的改性和夹杂物诱导腐蚀的机理。采用扫描电子显微镜与能谱分析了稀土元素Ce改性夹杂物的过程中夹杂物成分和类型的变化，观察到的代表夹杂物为CeAlO₃?Ce₂O₂S、Ce₂O₃?Ce₂O₂S、MnS等。根据形成能计算，经稀土元素Ce处理后，生成了稳定的Ce₂O₃、Ce₂O₂S、CeAlO₃夹杂物。通过表面能判断了晶面的稳定性，Fe(100)-2面的表面能经收敛测得为2.4374 J·m?2，该晶面的功函数为4.7352 eV。通过对比夹杂物与钢基体的功函数与计算电势差，分析了不同含Ce夹杂物诱导点蚀的趋势，探讨了不同原子位置、原子数量和不同slab模型对功函数的影响。研究表明，与Fe (100)-2面的电子功函数相比，MnS以及改性后3种夹杂物CeS、Ce₂O₃和Ce₂O₂S电势差大多小于0，CeAlO₃的电势差在0 eV左右。夹杂物不同晶面对功函数影响很大，O、S等非金属原子数量多的晶面功函数平均值较高，添加稀土元素Ce可以有效降低晶面功函数。5种夹杂物和钢基体的平均功函数大小顺序为CeAlO₃>Fe>MnS>CeS>Ce₂O₂S>Ce₂O₃。结合不锈钢中复合夹杂物的实验结果可知，Ce₂O₃诱导点蚀发生的概率最高，CeAlO₃可以有效提高钢的耐腐蚀能。 

First-principle study of the effect of cerium on the modification and corrosion of nonmetal inclusions in steel

Nonmetallic inclusions in steel significantly influence the steel life, quality, toughness, and corrosion resistance. Pitting corrosion is the most common type of localized corrosion in stainless steel. Rare-earth elements, which are key materials in the metallurgical sector, largely influence the modification of sulfur (S) and oxygen (O) inclusions in steel. Numerous experimental studies have been conducted on the corrosion of the rare-earth metal cerium (Ce); however, studies on the microscopic-scale mechanism are few. In this study, in situ corrosion observation and the first-principle calculations based on density functional theory were applied to investigate the effects of the rare-earth element cerium on inclusions in J5 stainless steel and the inclusion-induced corrosion process. The changes in the inclusion composition and the primary types of inclusions in the steel were investigated by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The results show that CeAlO₃?Ce₂O₂S, Ce₂O₃?Ce₂O₂S, and MnS are representative inclusions. MnS and other oxide inclusions in stainless steel were treated with Ce to generate stable Ce₂O₃, Ce₂O₂S, and CeAlO₃ inclusions, according to formation energy calculations. The surface energy of the Fe (100)-2 plane is measured as 2.4374 J·m?2, and the work function of this crystal plane is predicted to be 4.7352 eV. The crystal plane stability was examined according to the surface energy. The work functions and potential differences between the inclusion and the steel matrix were analyzed to compare the trend of pitting corrosion induced by different Ce-containing inclusions, and the influences of different atomic positions, atomic numbers, and different slab models on the work function were explored. Compared with the electronic work function of the Fe (100)-2 surface, the potential difference between MnS and the three modified inclusions CeS, Ce₂O₃, and Ce₂O₂S is typically less than zero, and the potential difference of CeAlO₃ is about 0 eV. The average work function of the crystal plane with a large number of nonmetal atoms such as O and S is higher. Ce addition reduces the work function of the crystal plane, and the molecular mechanism of pitting corrosion according to different crystal planes and termination planes of inclusions is revealed. The five types of inclusions and the steel matrix are in the following order: CeAlO₃>Fe>MnS>CeS>Ce₂O₂S>Ce₂O₃. The experimental findings on composite inclusions in stainless steel reveal that Ce₂O₃ has the highest chance of pitting corrosion, and CeAlO₃ can significantly improve steel corrosion resistance.