应用Jacksonα指数控制低SiO2(0-6%)电渣重熔渣系晶体形貌和改善润滑性基础研究

Large scale nickel base alloy ingots are the main material of large engine tunbine disk . It has not been solved regarding of smelting the large-scale nickel base alloy base ingot up to now, since during the production of large nickel base alloy ingots by means of withdrawing electric slag remelting(ESR) technology, the amount of SiO2 in the ESR slag should be as few as possible to limit the easy oxidized elements Al and Ti losses which are the key alloyed elements due to the oxidation reaction, but low SiO2 content ESR slag has poor lubrication due to its strong crystallization ability, which increases the ESR ingot surface crack risk. As a result, it is significant to improve the lubrication of low SiO2 content ESR slag. In this project, a new idea to promote the lubrication of ESR slag by controlling its primary crystal morphology. Jackson α factor is being introduced to low SiO2 content(0-6%) CaF2-CaO-Al2O3 based ESR slag to quantifiedly study the crystal morphology control. Crystallization experiments of ESR slags are performed by applying platinum crucible welding sealing technique and the effects of SER component and cooling rate on ESR crystal morphology is investigated. The purpose of this project is to enhance the rgular-shape crystal precipitation with suitable size to improve the total lubrication of the slag film in manner of ESR slag composition and cooling rate adjustment. On the basis of the foregoing research, it provides theoretical and technique basis for development the new ESR slag and parameters that meets the requirements of production of large size nickel base alloys by the withdrawing ESR technique.

大型镍基高温合金锭是生产大型发动机涡轮盘的最主要材料，但我国目前还未解决镍基合金锭大型化的冶炼问题。主要问题之一为使用抽锭式电渣重熔工艺冶炼大型镍基合金时，为防止合金中关键合金元素Al、Ti的过度烧损，渣中尽量少加SiO2，但低SiO2重熔渣结晶能力强、润滑性差，导致电渣锭表面质量缺陷增加，故提高低SiO2重熔渣的润滑性是解决这一问题的有效方法。本课题提出通过控制重熔渣结晶相形貌来改善其润滑性的新思路，拟引入Jackson α指数对低SiO2含量（0-6%）的CaF2-CaO-Al2O3基重熔渣系晶体形貌控制进行定量研究，并使用铂坩埚焊接密封技术进行结晶实验，研究重熔渣组分和冷却速率变化对晶体形貌的影响规律，通过调整合适的渣成分和控制冷却制度促进尺寸适中且形貌规则的晶体析出，降低渣膜界面粗糙度以提高其润滑性。旨在为我国开发合适的大型高温合金重熔渣系以及冶炼参数优化提供理论和技术参考。

本项目针对电渣重熔生产大型镍基合金面临的控制关键合金元素Al,Ti烧损和改善电渣锭表面质量的矛盾难题，本研究本文通过使用热力学模拟软件Factsage，结合DSC实验，SEM-EDS 和XRD观察分析来确定析晶行为。引入经典的晶体学模型 Jackson α 指数来预测晶体形态。通过改变炉渣成分来改善炉渣的结晶形貌。并结合生产实践，计算了炉渣成分变化对炉渣各组分活度的影响，同时取样探究渣皮结晶形貌及成分变化。研究表明：（1）TiO2和SiO2的添加改变了电渣重熔炉渣的析出相类型，含量和析出顺序。随着SiO2含量从2 wt.%增加到6 wt.%，ESR炉渣结晶温度基本不变。ESR炉渣样品中各析出相的结晶温度随着冷却速率的增加而降低。（2）直接观察到电渣重熔中各析出相在晶体/熔体界面上的生长情况，如CaF2晶体/熔体界面是粗糙的，CaF2晶体呈指纹状。CaAl4O7，CaO，CaTiO3等析出相晶体/熔体界面是平坦的。晶体形貌均符合Jackson α指数的预测。（3）渣皮中的结晶相主要是CaF2和Al2O3,存在少量的CaO·6Al2O3，渣皮中各物质按熔点高低成分含量有明显的分层变化，不同的位置受生产过程影响大，选分结晶现象显著。（4）离子分子共存理论表明在电渣重熔炉渣中添加少量的SiO2对炉渣组分活度影响很大，添加5wt.%左右的SiO2是对生产较为合理的选择。（5） 一定量的TiO2可以抑制炉渣中的CaF2晶体的生长，使CaF2晶体倾向于球形。随着SiO2的增加，样品中CaF2的晶体形态从主要是树枝状主要是球状改变。（6）根据现有的实验结果，认为在电渣重熔炉渣添加5 wt.%的TiO2和4 wt.%的SiO2并经过预熔，加大冷却速率，有利于改善炉渣润滑性能。

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