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

为了实现高密度氧化物颗粒结合的新型钢，本研究主要集中在以下三个方面：(a)改善钢熔体和氧化物颗粒之间的润湿性，这是氧化物颗粒在液相加工中分散所必需的；(b)发展数值模拟技术，为氧化物颗粒分散提供定量指导，以获得细晶粒钢；(c)研究氧化物颗粒形成细铁素体形核的机制，以获得细微观结构钢。在润湿性方面，钢熔体中加入Ti后，在原氧化物上形成富钛纳米级氧化物，改善了熔体-氧化物的润湿性。为了模拟氧化物弥散对钢晶粒细化的影响，建立了有限差分法和蒙特卡罗法相结合的混合数值模型，其中有限差分法用于传热传质，蒙特卡罗法用于晶核和生长模拟。利用该模型，定量地明确了氧化颗粒在不同热循环过程中对奥氏体晶粒生长的钉住作用，这表明分散的氧化颗粒的钉住力与修正的齐纳理论所预测的相同，并提出了在焊接结构钢中达到理想晶粒尺寸所需的分散量。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氧化薄膜，研究了氧化物-钢界面奥氏体向铁素体的转变行为。结果表明，氧化铁和氧化镁等nacl型氧化物优先形成铁素体，这是由于氧化物与铁素体的晶格匹配良好所致。研究还表明，界面组成对氧化物中铁氧体的形成和生长也有影响。这两方面的研究结果将为氧化分散钢的组织控制提供依据。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