螺旋喷吹包覆纳米粒子在钢液中的运动行为及机理研究

Grain refinement, as a strengthening method to improve both strength and toughness of steel, can be realized by externally adding nanoparticles, which offers technical simpleness and flexible particle type, size, and quantity. However, the bottleneck of this technique is how to make the particles distribute homogeneously in steel. This project aims to solve this question by proposing a pattern of spiral injecting coated nanoparticles with a core-shell structure into Q235 and GCr15 molten steel. Based on thermodynamics and kinetics, and using modern analyzing and detecting methods of high temperature laser confocal microscope, high resolution scanning electron microscope, transmission electron microscope, and insitu analysis system, etc., this project will conduct systematic research on shell melting, release, and stress pattern of the particles, on building varying-volume and varying-density motion model for the particles, on motion behaviors of the particles with hot experiments, on relationship between spiral blowing parameters and particle distribution, and on blowing conditions for homogeneous particle distribution. Motion rules of the released particles during solidification will be studied, and metallurgy conditions of inhibiting particle motion and aggregation will be analyzed. Control strategies of coating, spiral blowing, and solidifying for homogeneous particle distribution will be proposed to provide theoretical direction and technical support for industrial grain refining process with nano particle addition.

晶粒细化是同时提高钢的强度和韧性指标的强化手段。实验室研究表明，外部添加纳米粒子能细化钢的晶粒，且添加粒子的种类、尺寸和数量灵活，工艺简单。但该技术的瓶颈是使纳米粒子在钢中均匀分散，为解决该瓶颈问题，本项目提出以螺旋喷吹的方式向钢液加入具有核壳结构的包覆铁层的纳米粒子，以热力学和动力学为基础，借助高温激光共焦显微镜、高分辨扫描电镜、透射电镜、原位分析系统等现代分析检测手段，系统研究包覆层熔化、粒子释放和粒子受力规律，建立包覆纳米粒子在Q235普碳钢及GCr15轴承钢的液态钢中变体积、变密度的运动模型，探讨纳米粒子分散度与螺旋喷吹参数、钢液原始条件（如温度、粘度）等之间的关系。研究释放后的粒子在凝固过程运动规律，分析抑制纳米粒子在凝固过程运动及聚集的冶金学条件。综合提出实现纳米粒子在钢中的均匀分散的包覆、螺旋喷吹和凝固过程控制策略，为今后外加纳米粒子细化晶粒工业化生产提供理论指导和技术支持。

外加纳米粒子是提高钢材性能的手段，限制该工艺的瓶颈是粒子的均匀分布，本项目提出在钢中以螺旋喷吹的方式加入包覆纳米粒子，来更好的实现粒子在钢中的均匀分布。针对该问题，采用理论计算、数值模拟和热态实验相结合的方法，研究了纳米粒子在钢液中与铁元素的相互作用规律，释放并分散后的纳米粒子在钢液凝固过程的运动及团聚行为，分析了冶金工艺参数及粒子性质对包覆纳米粒子分散的影响规律，探讨添加包覆纳米粒子对钢材组织性能的影响机制。得到了拥有自主知识产权的制备铁包覆纳米粒子的新工艺方法和螺旋喷吹包覆纳米粒子的工艺方法。研究得出在氧化物（Al2O3、Ti2O3、ZrO2和SiO2）基底上随Fe原子或Fe团簇的增多，体系的总能量与束缚能均降低，氧化物与Fe的界面稳定性ZrO2＞Ti2O3＞Al2O3＞SiO2；氧化物与Fe界面的结合力Ti2O3＞Al2O3＞ZrO2＞SiO2。添加经过预分散处理的尺寸100纳米和20纳米二氧化锆的森下氏分散指数分别为0.94，0.91，经过预分散处理的纳米二氧化锆粒子能够在钢中分散均匀；添加经过预分散处理纳米二氧化锆比未经过预分散处理纳米二氧化锆的钢试样晶粒细化了37.5%，洛氏硬度提高了21.7%，抗拉强度提高了13.9Mpa，延伸率提高了8.35%。