中碳钢中的氧化物冶金行为及脉冲磁场对其的影响

发布时间：2018-05-03 23:20

  本文选题：氧化物冶金 + 晶内铁素体　； 参考：《北京科技大学》2017年博士论文

【摘要】：进入二十一世纪以后,机械工程结构的巨型化和高参量发展对钢铁材料的抗形变能力与塑性均提出了更高要求。研究证明,细化晶粒组织是使钢铁材料达到此要求的最有效方法。当前最有前景的两种细晶技术是脉冲磁场处理技术和氧化物冶金技术,它们分别在凝固的液态相变和固态相变阶段有效细化晶粒组织,并均取得了很大发展。在深入理解氧化物冶金技术细化晶粒组织的理论基础上,有机结合脉冲磁场处理技术来研究晶粒的双重细化将具有重要的理论意义和极大的工程应用价值。本文采用热动力学计算等手段以及高温激光共聚焦显微镜技术、透射和扫描电子显微镜技术、电子衍射技术等实验方法来研究45钢中的氧化物冶金行为及脉冲磁场对其的影响,并利用计算机模拟技术研究等效处理的脉冲磁场对凝固过程中组织演变的影响,主要研究结果如下：(1)随着氧含量降低,Ti203变的较难析出；铝元素可以抑制Ti203的析出,但锰元素的影响不大；45钢中能够促使铁素体在晶内优先析出的夹杂物类型多是以高熔点氧化物为核心,与其错配度为有效形核且析出温度较低的MnS和i/VN/C等在其周围附着析出的复合型夹杂物;复合夹杂物内部存在大量位错,在错配应力作用下向铁素体内部扩展。(2)脉冲磁场有利于夹杂物上浮,上浮过程中夹杂物之间相互碰撞长大,导致夹杂物形状因子降低；脉冲磁场作用抑制温度场和流场对夹杂物的作用,使夹杂物在液相区的迁移速率降低,在整个液-固相变过程中分布更加均匀；脉冲磁场作用使凝固前沿的夹杂物受到一个更大的,指向固相区的压力.,驱使夹杂物更容易被凝固前沿吞没,并最终均匀分布在固相区,细化凝固组织。(3)在本课题的脉冲磁场参数调控范围内,脉冲磁场强度增加或作用时间延长都能够使晶粒尺寸减小；当冷却速率为100℃/分钟左右,电压为100v,PMF周期为1.5s时,可以使45钢最有效的细品化。(4)在CA-FE法模拟中,等效处理后的脉冲磁场可以改变凝固过程中的晶区分布,有利于中心等轴晶区比例增加和晶粒尺寸减小。
[Abstract]:After entering the 21 century, the development of giant mechanical engineering structures and the development of high parameters put forward higher requirements for the deformation resistance and plasticity of iron and steel materials. It is proved that refinement of grain structure is the most effective method for iron and steel materials to meet this requirement. At present, the two most promising fine crystal technologies are pulsed magnetic field treatment and oxide metallurgy, which refine the grain structure effectively in the solidified liquid phase transformation and solid phase transformation stage, respectively, and have made great progress. On the basis of deeply understanding the theory of oxide metallurgical technology to refine grain structure, it will be of great theoretical significance and great engineering application value to study the double grain refinement by organic combination of pulsed magnetic field processing technology. In this paper, the metallurgical behavior of oxide in 45 steel and the effect of pulsed magnetic field on it are studied by means of thermodynamics calculation, high temperature laser confocal microscopy, transmission and scanning electron microscopy and electron diffraction. The effect of the equivalent pulsed magnetic field on the microstructure evolution during solidification was studied by computer simulation. The main results are as follows: 1) it is difficult to precipitate with the decrease of oxygen content in Ti203, and aluminum can inhibit the precipitation of Ti203. However, the type of inclusions which can promote the preferential precipitation of ferrite in the crystal is mostly the high melting point oxide as the core. There are a lot of dislocations in the complex inclusions, such as MnS and i/VN/C, which are attached to the complex inclusions with effective nucleation and low precipitation temperature, the mismatch degree is effective nucleation and the precipitation temperature is lower, and a large number of dislocations exist in the complex inclusions. The pulse magnetic field extends to the ferrite interior under mismatch stress. The pulse magnetic field is favorable to the inclusion floating. During the floating process, the inclusions collide and grow, which results in the decrease of the inclusion shape factor. The effect of pulse magnetic field on inclusions is inhibited by temperature field and flow field, and the migration rate of inclusions in liquid phase region is decreased, and the distribution of inclusions is more uniform in the whole liquid-solid phase transformation process. The pulsed magnetic field causes the inclusion at the solidification front to be subjected to a greater pressure pointing to the solid region, which drives the inclusion to be swallowed more easily by the solidification front and eventually uniformly distributed in the solid zone. The grain size can be reduced by increasing the pulse magnetic field intensity or prolonging the working time in the range of the parameters of the pulse magnetic field, and when the cooling rate is about 100 鈩，

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