取向硅钢中铜硫化物析出形式及其固溶的基础研究

【作者】 何寒；

【导师】 曹建春；

【作者基本信息】 昆明理工大学 ， 材料学， 2010， 硕士

【摘要】 取向硅钢沿轧制方向具有极佳的磁性能,是制造变压器铁芯必不可少的材料。它是钢铁工业中唯一运用二次再结晶现象生产的产品。在日益追求环保、节能以及降低成本的现代钢铁业中,传统的取向硅钢铸坯高温加热技术已不符合这些要求。铜硫化物(CuxS)作为一种可以实现铸坯低温加热的晶粒抑制剂,其具体的析出形式对取向硅钢的生产起着重要作用。目前,取向硅钢中作为晶粒抑制剂的铜硫化物究竟以哪种形式析出,还存在争议。因此,本文采用Materials Studio软件中基于量子力学密度泛函理论的CASTEP和DMOL3两个计算模块,分别对取向硅钢中可能存在的铜硫化物(Cu1.8S、Cu2S和CuS)的态密度、能带结构、形成热及结合能进行第一性原理研究,探讨在含铜取向硅钢中最有可能析出的铜硫化物的形式。并且对含铜的取向硅钢中析出的第二相颗粒进行透射电镜实验研究。同时,在第一性原理理论研究和实验研究基础上,对铜硫化物在铁基体中的固溶度积公式进行相关热力学推导。通过计算得到Cu1.8S、Cu2S和CuS的平均结合能及形成热。Cu1.8S、Cu2S和CuS的平均结合能分别为-10.12416 eV、-10.16943 eV和-6.91536eV,三种铜硫化物的相结构稳定性按Cu2S、Cu1.8S、CuS的顺序依次降低；Cu1.8S、Cu2S和CuS的形成热值均为负,分别为-97.7594 eV、-1.2055 eV和-0.9699 eV,表明它们都是热力学稳定相,并且Cu1.8S具有最负的形成热即其具有最强的形成能力。态密度计算结果表明,Cu2S、Cu1.8S和CuS在费米能级处的态密度均大于0,分别约为1.65electrons/eV、2.58electrons/eV、2.52electrons/eV。可见,Cu2S具有最稳定的结构是由于其在费米能级处的态密度N(EF)最小的缘故。通过对Cu含量(约0.48%)相对较高的取向硅钢中第二相进行透射电镜实验研究表明,沿晶界析出的细小颗粒状第二相为具有立方晶体结构的Cu1.8S。用热力学方法推导得到CuS和Cu2S在铁素体和奥氏体中的平衡固溶度积公式,并且对CuS和Cu2S在铁素体和奥氏体中的平衡固溶度积绘图比较得出,Cu2S在铁素体和奥氏体中的平衡固溶度均要小于CuS的,在富含Cu元素的情况下,Cu2S在取向硅钢中的析出数量要多于CuS。但是,由于相互竞争的结果,很难发生CuS的析出。从三种铜硫化物的第一性原理研究结果及固溶度积的比较可以推断出,在富含Cu元素的情况下,取向硅钢中更容易优先析出结构相对较稳定的Cu1.8S或Cu2S作为晶粒抑制剂。但是,取向硅钢中铜硫化物是在热轧或高温常化过程中(温度均约为1100℃左右)析出的。因此,在取向硅钢中真正起晶粒抑制作用的铜硫化物为高温立方结构的Cu1.8S。更多还原

【Abstract】 The grain oriented silicon steel which has excellent magnetic properties along the rolling direction, is essential material for manufacturing the core of transformer. It is the only products manufacted by using the phenomenon of secondary recrystallization in iron and steel industry. The traditional high temperature slab reheating technology for grain oriented silicon steel no longer meets these requirements such as environmental protection, energy conservation and reducing costs in the modern steel industry. Copper sulfide (CuxS) is a kind of grain inhibitor which can decrease the reheating temperature of slab. There is still controversial currently about the precipitation form of copper sulfide grain inhibitors in grain oriented silicon steel. Therefore, it is very important to investigate the specific form of CuxS precipitate playing an important role in grain oriented silicon steel. In this paper, the density of states, band structure, formation energy and binding energy of copper sulfides such as.Cu1.8S, CU2S and CuS which may exist in grain oriented silicon steel with copper are calculated and analysed using the first principles calculation module of CASTEP and DMOL3 of Materials Studio based on the density functional theory of quantum mechanics, and the most possible form of the precipitation of copper sulfides is investigated. Furthermore, the precipitated second phase particles in tested grain oriented silicon steel with copper are investigated by TEM. Meanwhile, based on the studies of first principles and experiment, the formulas of solubility of copper sulfides in the iron matrix are derivated by thermodynamic method.The calculation results show that the average binding energy of Cu1.8S,Cu2S and CuS are-10.12416 eV,-10.16943 eV and-6.91536eV, respectively.It can be seen that the phase stability of three kinds of copper sulfide is decrease by the order of Cu2S,Cu1.8S,CuS. The formation energy of Cu1.8S,Cu2S and CuS are negative, and their value are-97.7594 eV,-1.2055 eV,-0.9699 eV, respectively.The results show that they are thermodynamically stable phase,and the formation energy of Cu1.8S is the most negative value which indicates that Cu1.8S has the highest forming ability.The calculation results of density of states show that the density of states of Cu1.8S,Cu2S and CuS at fermi level are all higer than zero,1.65 electrons/eV for Cu2S,2.58 electrons/eV for Cu1.8S and 2.52 electrons/eV for CuS, respectively. The Cu2S with the most stable structure is due to that it has the minimum value of density of states at fermi level.The results of TEM eperiments for the second phase in the tested grain oriented silicon steel which contains relatively high content about 0.48%Cu show that the fine particle precipitations along the grain boundaries is Cu1.8S with cubic crystal structure.The balance solubilities of CuS and Cu2S in iron matrix have be deduced by using thermodynamic method. Futhermore, it can make conclusions by comparison of the figures of the balance solubility in the iron matrix that the balance solubilities of Cu2S in ferrite and austenite are less than that of CuS, and the precipitation amount of Cu2S in grain oriented silicon steel is more than that of CuS in the case of Cu-rich. However, it is difficult for precipitating CuS in the grain oriented silicon steel because of the results of competition.It can be inferred by the results of the first principle study and comparison of solubility product that it is easier that the relatively stable structure of Cu1.8S or Cu2S as grain inhibitor precipitate in grain oriented silicon steel. However, the copper sulfides in grain oriented silicon steel often precipitate in the hot rolling process or during the normalizing annealing(about 1100℃). Therefore, the really effective grain inhibitor of copper sulfides precipitated at high temperature is the Cu1.8S with cubic crystal structure.更多还原