电渣重熔含Al、Ti高温合金的多元反应动力学及质量控制研究

The improvements of homogeneous composition along the height of ingot and surface defects on ingot during electroslag remelting (ESR) with superalloy containing aluminum and titanium are typical difficulties in the process. Especially for superalloy containing high titanium and low aluminum, slag-metal reaction in the first slag-temperature-rising period of electroslag remelting process would cause the macrosegregation of aluminum and titanium elements along the height of ingot and reduce the superalloy ingot yield, which has not been resolved well till today. Therefore, the debate over alloying elements and surface quality of ingot control during ESR with superalloy containing aluminum and titanium elements will be investigated based on the thermodynamics and kinetics. Firstly, the thermodynamic equilibrium of titanium’s reaction with alumina in the systems of superalloy and CaF2-CaO-MgO-Al2O3-TiO2 slags containing different CaO content will be investigated, and the concentrations of alumina and titania in slag containing different CaO content can be determined based on thermodynamic equilibrium with aluminum and titanium in superalloy. After the slag physical properties (melting temperature, viscosity and crystallization) measured, the optimum proportion of slag used for improving surface quality of ESR ingot will be selected. Secondly, mass transfer model of slag-metal multiphase reaction will be established to illustrate the effect of adding titania into molten slag in the first slag-temperature-rising period during ESR process on macrosegregation of aluminum and titanium along the height of ingot, which is proposed in this research for the first time. At last, mass transfer model of slag-metal-inclusion multiphase reaction will be established to illustrate the evolution and control mechanisms of inclusion during ESR process. The research results will enrich and develop the process and theory of electroslag remelting with high performance superalloy, and promote the development of the new varieties of superalloy in China.

含Al、Ti高温合金电渣锭的成分均匀性及表面质量改善一直是电渣重熔该品种的技术难点。尤其是“高钛低铝”高温合金，电渣重熔初期渣-金反应易引起成分不均匀，电渣锭收得率显著降低，国内外尚无有效解决方案。为此，本项目以电渣重熔含Al、Ti高温合金为对象，利用冶金热力学与动力学，揭示不同CaO含量的CaF2-CaO-MgO-Al2O3-TiO2熔渣中(Al2O3)、(TiO2)与合金中[Al]、[Ti]的热力学平衡关系，获得多组不同CaO含量的平衡渣系，并测定其基础物性，为优选渣系和改善电渣锭表面质量提供了新方法；首次提出重熔初期升温段补加TiO2方法，并构建电渣重熔渣-金多元反应动力学模型，为改善Al、Ti沿电渣锭轴向的均匀分布提供了新思路；构建熔渣-合金液-夹杂物三相反应体系动力学模型，揭示夹杂物的演变机理与控制方法。研究成果将提升高品质高温合金的电渣重熔制备技术，促进我国高温合金新品种研发。

高温合金在600℃以上服役时，Ni3(Al,Ti)相对强化基体起着重要的作用，其生产方法主要有：真空感应炉+电渣重熔、真空感应炉+电渣重熔+真空自耗。两种生产方法均要求电渣重熔中控制铸锭的表面质量、内部质量、合金元素均匀性分布。为此，本项目开展了高温合金的专用低熔点渣系CaF2-CaO-MgO-Al2O3-TiO2以获得表面光滑的电渣锭、其次开发了电渣重熔中的合金元素含量控制技术实现电渣锭中合金元素的均匀分布、此外开发了电渣重熔中水汽烘烤制度、脱氧剂加入技术和夹杂物控制技术获得了低氧、低氢、夹杂物细小的铸锭。研究成果包括：（1）企业用预熔渣的标准化，开发了A+B含钛预熔渣，将A、B两组预熔渣混合配入使用，满足不同钛铝比的高温合金生产需要，且具有低熔点特性，改善了电渣锭表面质量，其中A预熔渣配比为CaF2:CaO:MgO:Al2O3=47:25:3:25、B预熔渣配比为CaF2:CaO:MgO:Al2O3:TiO2=47:25:3:15:10；（2）基于渣-金反应动力学开发了电渣重熔中的合金元素成分预测模型，当确定冶炼工艺后，能够动态预测电渣锭中的合金元素分布，进而优化工艺参数；（3）开发了电渣炉水汽烘烤制度、脱氧剂加入装置和加入制度，已经广泛应用于工业生产，获得了低氧、低氢的电渣锭，具有良好的经济效益；（4）构建了电渣重熔中的熔渣-钢液-夹杂物多相反应动力学模型，提出了高CaO渣系能够改善铸锭洁净度、提高铸锭含镁夹杂物MgO·Al2O3的特点；（5）基于含镁夹杂物MgO·Al2O3与TiN的错配度低、可作为TiN的基底促进形核的原理，引入镁处理技术细化夹杂物、改善铸锭洁净度，提升了高温合金产品性能。上述研究成果提升了高品质高温合金的电渣重熔制备技术，改善电渣锭表面质量和内部质量，对我国高温合金的产品质量以及高温合金新品种研发具有重要的现实和科学意义。