航空用超高强度钢超纯净特种熔炼新技术和理论基础

On the bases of the existing special melting equipment in domestic special steel companies, this project is proposed to make the research of ultra-pure special melting technology for the typical steel grade of Aermert 100 and S53. A new process (EAF+LF+MC) has been put forward for producing ultra-pure metal materials containing Cr and V alloys for VIM smelting application, and the new technology will solve the key issues of excessive impurity elements in Chinese ferroalloy. Then the thermodynamic conditions of the preparation of raw metal material with ultra-low impurity elements will be studied and especially the problem of selective oxidation of Cr, V and Al, Ti will be discussed during the alloying process in LF. Using the 200 kg VIM and VAR equipment in our laboratory, the new pure purification smelting technology of vacuum carbon deoxidation and bottom blowing argon gas mixing will be developed during VIM process. Then the mechanism of denitrification for ultra-high strength steel in VIM smelting process is revealed, and the theory and method for ultra-low nitrogen content smelting are put forward. By using the rare earth treatment technology, the deoxidation, desulfurization and inclusions control in VIM smelting process is cleared, finally the ultra-low oxygen and ultra-low sulfur steel smelting theory are proposed. At the same time, the influence mechanism of VAR process parameters on deoxidation, denitrification and removal of inclusions in ultra-high strength steel is studied. Through the whole process of the systematic research and optimization, a process theory on ultra-purity special melting of ultra-high strength steel will be created, so that the significant constraints problem of China's ultra-high strength steel for aviation development will be solved.

项目基于国内特钢企业现有的特种熔炼装备，以Aermert 100和S53为代表钢种开展超纯净特种熔炼技术研究。创造地提出采用EAF+LF+MC新工艺生产含Cr、V等合金的VIM用超纯净金属原料，以解决铁合金杂质元素超标的关键问题。据此，分析超低杂质元素含量金属原料制备的热力学条件，重点解决LF精炼合金化过程中元素Cr、V和Al、Ti的选择性氧化问题。同时，利用实验室的200kgVIM和VAR设备，开发VIM熔炼过程碳脱氧和底吹氩气搅拌等纯净化熔炼新技术，揭示超高强度钢VIM过程脱氮机理，提出超低氮的熔炼理论。采用稀土处理技术，研究VIM熔炼脱氧、脱硫和夹杂物控制机理，提出超低氧和超低硫钢熔炼理论。同时，研究VAR工艺参数对超高强度钢脱氧、脱氮和夹杂物去除的影响机理。通过对全流程的系统研究和优化，形成超高强度钢超纯净特种熔炼工艺理论，解决制约我国航空用超高强度钢发展的重大瓶颈问题。

项目以Aermert 100和S53等为代表钢种开展超纯净特种熔炼技术研究，提出EAF+LF+MC新工艺生产含Cr、V等合金的VIM用超纯净金属原料，解决铁合金杂质元素超标问题。主要开展以下工作：. （1）铁基金属料Al、Ti、Cr/V选择性氧化的热力学计算和实验研究。（2）含Cr VIM用纯净原料工业试验研究。（3）稀土对超高强度钢脱硫、脱氧以及夹杂物控制的影响研究。（4）不同坩埚材质和真空条件对钢洁净度和夹杂物的影响作用。（5）脱氧、脱硫以及钢液碳脱氧沸腾搅拌对S53钢深脱氮的影响规律。（6）采用新工艺含Cr超纯净精钢材+VIM+VAR生产S53铸态钢锭与原有工艺对比分析，考察了不同洁净度对钢性能的影响。. 渣金平衡实验发现：渣中（FeO）以及渣金比对Al、Ti、Cr和V的质量分数有显著的影响，合适的（FeO）和渣金比都是必要的。在渣金比为10%而渣中（FeO）为18.4%时，终点[Al]和[Ti]都小于0.005%，同时Cr的收得率达99.16%。含V金属原料去Al、Ti保V需要更高的氧位，降低渣金比。在渣金比为10%而渣中（FeO）为24%时，终点[Al]和[Ti]都小于0.005%，V收得率达99.11%。采用EAF+LF+模铸的工艺流程，成功实现了含Cr纯净金属原料的冶炼。在[Cr]= 11.08%前提下，杂质元素控制水平完全满足高纯净超高强度钢的生产需要。 VIM超纯净化冶炼实现深脱氧和深脱氮，钢中全氧质量分数最低T.O为0.0002%，最低[N]达0.0002%。可通过控制钢中的T.O和自由镧量实现对夹杂物类型、数量和尺寸的控制。真空感应炉不同坩埚材质的研究表明：稳定性顺序依次为CaO（C）坩埚>MgOAl2O3（MA）坩埚>MgO（M）坩埚。S53钢中的氮、硫、氧、Al等元素，可以形成夹杂物。由于变形可以在夹杂物尖端处产生应力集中，萌生裂纹源，并且加速裂纹生长。采用新工艺纯净化熔炼后的钢组织中的夹杂物含量大大降低，在拉伸断口几乎看不到夹杂物的存在，通过合适热处理后，得到交错度高的回火马氏体和弥散分布的碳化物，材料的力学性能得到很大提升，接近美国S53钢水平。. 项目提出的超高强度钢纯净熔炼新工艺经已经应用推广到超高强度钢及部分镍基高温合金的纯净化生产中。