Keywords: 
• 稀土 /
• 分配 /
• Fe3C /
• 第一性原理

Abstract: With the active physical and chemical properties of rare earth (RE), the segregation and solution behaviors of RE elements in steel have still not been very clear to date. Thus, the first-principles method based on the density functional theory is employed to address this problem. The partitioning behaviors of RE elements, including Sc, Y, Ce and La, betweenα-Fe and Fe3C are studied by partitioning enthalpy, and the average overlap population, density of states (DOS) of rare earth alloyed cementite are also discussed. Moreover, the ferromagnetic (FM) and non-magnetic (NM) cementite with RE element substitutions are both considered in this work. The results show that all the RE elements in theα-Fe and Fe3C align anti-ferromagnetic, which is in good agreement with the experimental result. The partitioned enthalpies of these rare earth elements are all negative for the FM and NM cementite, indicating that they tend to partition and solubilize in the cementite phase. Furthermore, the partitioned enthalpies of Y, Ce and La substituting the general position (8d) Fe atom for FM or NM cementite are lower than those of the special position (4c), which indicates that Y, Ce and La prefer to substitute the 8d Fe site. However, Sc partitioning 4c site of FM and NM cementite is energetically favorable compared with the 8d site. The calculated average overlap populations of Fe—C covalent bond and Fe—Fe metallic bond in Y-, La- and Ce-substituted cementite are all larger than that of cementite, showing that the binding strength and the stability of RE-introduced cementite increase. In addition, compared with the 4c Fe site of cementite, Y, La, and Ce substituting the 8d Fe site exhibits larger average overlap population, suggesting that the stability of cementite is enhanced after the introduction of Y, La and Ce, proving again that these elements tend to replace the 8d Fe site of cementite. By comparing the DOSs of the alloyed cementite, we find that the density of states at Fermi level of alloyed cementite with Y, La, and Ce substitutions at 8d Fe site are smaller than those of alloyed cementite with Y, La, and Ce substitutions at 4c Fe site, this further suggests that Y, La, and Ce partitioning at 8d Fe site result in more stable structures, which agrees well with the analysis results of the partitioned enthalpy.