钢中氧化物与溶质原子的相互作用及其对铁素体形成的影响

发布时间：2018-08-11 12:21

【摘要】：非金属夹杂物一直被认为是钢中的有害杂质,但钢中的溶质原子如Mn、B、C等能和钢中适当种类、形态、大小和分布的氧化物夹杂如Ti2O3、ZrO2和Al2O3发生相互作用,通过置换、间隙、化学反应等不同的途径形成各种缺陷氧化物,部分缺陷氧化物周围溶质原子的含量会减少,降低了奥氏体稳定性,有助于铁素体的形成。本课题通过第一性原理计算得到各种缺陷氧化物的形成能,揭示出溶质原子和氧化物相互作用的机理,深入探讨铁素体的形成机制及其对强韧性的影响规律。本课题采用双重热压连接的方法制备试样,分别研究了钢中Mn、B和C三种溶质原子与Ti2O3、ZrO2和Al2O3三种氧化物的相互作用。通过金相显微镜观察铁素体形成的效果,使用电子探针显微分析(EPMA)定量分析氧化物周围元素含量的变化,用第一性原理计算相关物质的能量、磁性、态密度等性质,达到实验和理论计算相结合、相互印证的目的。结合理论研究成果,对于工业规模锆钛复合脱氧钢和铝脱氧钢的微观组织结构和力学性能等进行了比较、讨论和分析,工业生产的钢进一步验证了实验室结果。论文主要研究结论如下:(1)第一性原理计算结果表明Ti2O3是阳离子空位氧化物,Zr O2是阴离子空位氧化物,而Al2O3不易形成空位氧化物。使用Gibbs2将第一性原理计算的结果扩展到高温状态下,高温状态下的计算结果和基态下的结果相差约5%。(2)实验表征和计算数据表明:Mn能作为掺杂原子进入到Ti2O3和ZrO2的空位中,在这两种氧化物的周围形成了明显的贫锰区。通过结构分析发现,Mn离子与Zr离子半径相近,使得Mn离子易于掺杂进入ZrO2,晶体结构更加稳定。由于锰是奥氏体扩大化元素,因此贫锰区的存在,能降低铁素体形成的阻力,促进铁素体的形成。(3)第一性原理计算结果表明硼与氧化物掺杂形成能为正值,在奥氏体晶界偏聚的硼与氧化物(Ti2O3、ZrO2和Al2O3)颗粒发生相互作用时,硼不会进入到氧化物颗粒中。但是,活度较大的硼可以和阳离子空位的Ti2O3中富余的氧发生反应,生成氧化硼,阳离子空位氧化物向完整氧化物转变。硼是奥氏体稳定化元素,硼的存在会抑制铁素体的形成,生成了氧化硼后将不再抑制铁素体的形成。(4)奥氏体中含碳量大于铁素体的含碳量,第一性原理计算结果表明,对于仅仅含有碳的钢而言,碳与氧化物(Ti2O3、ZrO2和Al2O3)颗粒发生相互作用时,碳不会进入到氧化物颗粒中,而是和阳离子空位的Ti2O3中富余的氧发生反应,生成一氧化碳,阳离子空位氧化物向完整氧化物转变。碳含量的降低,有助于奥氏体向铁素体的转变。(5)通过第一性原理计算的数据分析了Ti、Zr、Al的氧化物(MxOy)和Mn掺杂氧化物(MnMx-1Oy)的稳定性、电性能和磁性能,结果表明:Ti2O3具有较多的阳离子空位,Ti3MnO6的形成能最低。态密度显示Ti2O3有一定的导电性,而ZrO2和Al2O3为绝缘体。Mn掺杂氧化物中Mn的化学环境发生变化,导致掺杂氧化物的态密度不对称,因此掺杂氧化物有磁矩。(6)基于以上理论研究,采用Zr-Ti脱氧方式,研制了高强度焊接结构钢。实验结果发现:钢中形成细小弥散分布的Zr-Ti复合氧化物,为MnS的析出提供了形核质点,引起MnS球化,并在钢中均匀、细小、弥散分布,使钢的组织和力学性能均匀。与传统的Al脱氧相比,强度、延展性和低温韧性改善,尤其是力学性能的稳定性明显提高。该结果验证了以上理论计算结果,说明第一性原理计算对于研制高性能钢铁材料,特别是制定成分体系,具有较好的理论指导作用。通过以上研究,基于溶质原子与氧化物形成能计算及优化结构,从量子力学角度提出两种溶质原子与氧化物在钢中的相互作用机制:溶质原子掺杂形成溶质贫乏区和溶质原子与氧化物中富余氧反应降低溶质原子含量。在理论上解释了与溶质原子作用后的氧化物对于铁素体形成的促进作用,为研究其它溶质原子与氧化物的相互作用及其对相变的影响,提供了研究思路、手段和方法。
[Abstract]:Nonmetallic inclusions have long been considered as harmful impurities in steel. However, solute atoms such as Mn, B, C in steel interact with oxide inclusions such as Ti2O3, ZrO2 and Al2O3, forming various defective oxides and some defective oxides through different ways such as substitution, gap and chemical reaction. The formation energies of various defective oxides are obtained by first-principles calculation. The mechanism of interaction between solute atoms and oxides is revealed. The formation mechanism of ferrite and its influence on strength and toughness are discussed. The interaction of three solute atoms Mn, B and C in steel with three oxides Ti2O3, ZrO2 and Al2O3 was studied. The effect of ferrite formation was observed by metallographic microscope, and the content of elements around oxides was quantitatively analyzed by electron probe microanalysis (EPMA). The properties of energy, magnetism and density of states of the related substances are calculated by the principle of property, so as to achieve the purpose of combining experiment with theoretical calculation and verifying each other. The main conclusions are as follows: (1) First-principles calculations show that Ti2O3 is a cationic vacancy oxide, Zr O2 is an anionic vacancy oxide, and Al2O3 is not easy to form a vacancy oxide. The results show that Mn ions can enter the vacancies of Ti2O3 and ZrO2 as doping atoms, and the Mn-depleted regions are formed around the two oxides. The structure analysis shows that the radius of Mn ions and Zr ions is similar, which makes Mn ions easily doped into ZrO2, and the crystal structure is more stable. As manganese is an austenitic enlarged element, the existence of Mn-poor zone can reduce the resistance of ferrite formation and promote the formation of ferrite. (3) The first-principles calculation results show that the formation energy of boron and oxide doping is positive. Boron does not occur when the boron segregated at the austenitic grain boundary interacts with oxide particles (Ti2O3, ZrO2 and Al2O3). Boron is an austenitic stabilizing element. The presence of boron inhibits the formation of ferrite and the formation of boron oxide will not inhibit the formation of ferrite. (4) Carbon content in austenite is higher than that in ferrite. First-principles calculations show that for steel containing only carbon, when carbon interacts with oxide particles (Ti2O3, ZrO2 and Al2O3), carbon does not enter into oxide particles, but reacts with excess oxygen in cationic vacancy Ti2O3 to form carbon. (5) The stability, electrical and magnetic properties of Ti, Zr, Al oxides (MxOy) and MnMx-1Oy doped oxides (MnMx-1Oy) were analyzed by first-principles calculation data. The results show that Ti2O3 has more cations. The formation energy of vacancy and Ti_3MnO_6 is the lowest. The density of States indicates that Ti_2O_3 has certain conductivity, while ZrO_2 and Al_2O_3 are insulators. The chemical environment of Mn in Mn-doped oxides changes, resulting in the asymmetry of the density of states of the doped oxides. Therefore, the doped oxides have magnetic moments. (6) Based on the above theoretical study, the Zr-Ti deoxidization method was used to develop high strength. Welded structural steels. The results show that the formation of fine dispersed Zr-Ti composite oxides in steels provides nucleation particles for the precipitation of MnS and causes spheroidization of MnS. The microstructure and mechanical properties of the steels are uniform, fine and dispersed. Compared with traditional Al deoxidation, the strength, ductility and low temperature toughness are improved, especially the mechanical properties. The results show that the first-principles calculation has a good theoretical guidance for the development of high-performance steel materials, especially for the formulation of composition systems. Based on the above studies, the structure of solute atoms and oxides can be calculated and optimized from the perspective of quantum mechanics. The interaction mechanism of two solute atoms with oxides in steel is proposed: solute atoms doping to form solute depleted zone and solute atoms reacting with oxides to reduce solute atoms content. The interaction with oxides and their effects on phase transition provide research ideas, means and methods.
【学位授予单位】：武汉科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG142.1

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