Development of Next-generation Steels combined with High-density Oxide Particles assisted by Interfacing

为了获得与高密度氧化物颗粒相结合的新型钢材，本研究集中在以下三个方面：(A)改善钢液与氧化物颗粒之间的润湿性，这是通过液相工艺实现氧化物颗粒弥散所必需的；(B)开发数值模拟技术，为氧化物颗粒的分散提供定量的指导，以获得细晶粒钢；(C)研究氧化物颗粒中细小铁素体形核的机理，以获得细小的组织钢。在润湿性方面，研究发现，在钢液中加入钛可以在原氧化物上形成富钛纳米氧化物，从而改善了熔体-氧化物的润湿性。为了模拟氧化物弥散对钢中晶粒细化的影响，建立了有限差分法和蒙特卡洛法相结合的混合数值模型，其中传热传质采用有限差分方法，n…采用蒙特卡罗方法更多的成核和生长模拟。利用该模型定量地揭示了氧化物颗粒在钢中不同热循环过程中对奥氏体晶长大的钉扎作用，表明弥散分布的氧化物颗粒的钉扎力与修正的齐纳理论所预测的一致，并提出了达到焊接结构钢所需晶粒度所需的弥散量。在第三个研究课题中，利用电子束物理气相沉积技术在钢板上沉积了一层薄的氧化膜，并研究了奥氏体铁素体从氧化物-钢界面的转变行为。结果表明，铁氧体是由氧化钛和氧化镁等氯化钠类氧化物优先生成的，这是由于氧化物与铁氧体之间良好的晶格匹配所致。研究还表明，界面成分对氧化物中铁素体的形成和长大也有影响。这两个发现将为氧化物弥散钢的组织控制提供依据。较少

To achieve new steels combined with high-density oxide particles, this study focuses on the following three subjects : (a)improvement of the wettability between steel melts and oxide particles which is necessary for the oxide particle dispersion through liquid phase processing, (b)development of numerical simulation techniques to give quantitative guideline for oxide particle dispersion to achieve fine grain steels, and (c)investigation of the mechanism of fine ferrite nucleation from oxide particles to achieve fine microstructure steels. As for the wettability, it was found that the addition of Ti to steel melts improved the melt-oxide wettability by forming Ti-rich nano-scale oxide on the original oxide. For the simulation of the effect of oxide dispersion on grain refinement in steels, a hybrid numerical model combining finite difference method and Monte Carlo method was developed, where the finite difference method is used for heat and mass transfer and the Monte Carlo method for n … More ucleation and growth simulation. Using the model, the pinning effect of oxide particles against austenite grain growth during various thermal cycles in steels was made quantitatively clear, which indicated that the pinning force of the dispersed oxide particles was the same as what the modified Zener theory predicted and suggested necessary amount of the dispersion to achieve desired grain size in steels used for welded structure. In the third research subject, a thin oxide film was deposited on a steel plate using electron-beam physical vapor deposition technique, and austenite-to-ferrite transformation behavior from the oxide-steel interface was investigated. It was found that ferrite was preferentially formed from the NaCl-type oxide such as TiO and MgO and this was attributed to good lattice matching between the oxide and ferrite. The investigation also suggested that the interface composition also exerted an influence on the formation and growth of ferrite from the oxide. Both findings would be the basis of the microstructure control in oxide-dispersed steels. Less