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为了从原子层面上了解钢中铌元素对奥氏体转变的作用,采用基于密度泛函理论(DFT)的第一性原理方法,计算了在奥氏体和铁素体中铌原子或碳原子分别占据间隙位置或者置换位置几种构型的体系总能量和结合能,由此判断铌及碳的固溶形式。结果表明,在奥氏体中,铌原子只能以置换固溶形式存在,碳原子可以以间隙固溶或者置换固溶的形式存在;在铁素体中,铌原子和碳原子均不能够固溶。进一步计算了在奥氏体中碳原子的迁移扩散能量,考察铌原子的存在对碳原子迁移的影响。在奥氏体中,以置换固溶形式存在的铌原子可导致碳原子的迁移激活能提高和系统能量出现较大波动,正是铌的这个效应使奥氏体向铁素体的转变温度降低,并且造成铁素体晶粒细化。
In order to understand the effect of niobium in austenite on the atomic level, a first-principles method based on density functional theory (DFT) was used to calculate the effect of niobium or austenite in austenite and ferrite The total energy and the binding energy of several configurations occupying the gap position or the displacement position, respectively, are used to determine the solid solution forms of niobium and carbon. The results show that in the austenite, the niobium atoms exist only in the form of substitutional solid solution, and the carbon atoms can be dissolved or replaced by interstitial solid solution. In the ferrite, niobium atoms and carbon atoms can not be solidified Soluble. The migration and diffusion energies of carbon atoms in austenite are further calculated, and the effect of niobium atoms on the migration of carbon atoms is investigated. In austenite, niobium atoms in the form of substitutional solid solution lead to the increase of carbon atom migration activation energy and large fluctuation of system energy, which is the effect of niobium to reduce the transformation temperature of austenite to ferrite , And causes ferrite grain refinement.