本文選題：氧化物冶金 + 晶內(nèi)鐵素體��； 參考：《北京科技大學(xué)》2017年博士論文

【摘要】：進(jìn)入二十一世紀(jì)以后,機(jī)械工程結(jié)構(gòu)的巨型化和高參量發(fā)展對鋼鐵材料的抗形變能力與塑性均提出了更高要求。研究證明,細(xì)化晶粒組織是使鋼鐵材料達(dá)到此要求的最有效方法。當(dāng)前最有前景的兩種細(xì)晶技術(shù)是脈沖磁場處理技術(shù)和氧化物冶金技術(shù),它們分別在凝固的液態(tài)相變和固態(tài)相變階段有效細(xì)化晶粒組織,并均取得了很大發(fā)展。在深入理解氧化物冶金技術(shù)細(xì)化晶粒組織的理論基礎(chǔ)上,有機(jī)結(jié)合脈沖磁場處理技術(shù)來研究晶粒的雙重細(xì)化將具有重要的理論意義和極大的工程應(yīng)用價值。本文采用熱動力學(xué)計算等手段以及高溫激光共聚焦顯微鏡技術(shù)、透射和掃描電子顯微鏡技術(shù)、電子衍射技術(shù)等實驗方法來研究45鋼中的氧化物冶金行為及脈沖磁場對其的影響,并利用計算機(jī)模擬技術(shù)研究等效處理的脈沖磁場對凝固過程中組織演變的影響,主要研究結(jié)果如下：(1)隨著氧含量降低,Ti203變的較難析出；鋁元素可以抑制Ti203的析出,但錳元素的影響不大；45鋼中能夠促使鐵素體在晶內(nèi)優(yōu)先析出的夾雜物類型多是以高熔點氧化物為核心,與其錯配度為有效形核且析出溫度較低的MnS和i/VN/C等在其周圍附著析出的復(fù)合型夾雜物;復(fù)合夾雜物內(nèi)部存在大量位錯,在錯配應(yīng)力作用下向鐵素體內(nèi)部擴(kuò)展。(2)脈沖磁場有利于夾雜物上浮,上浮過程中夾雜物之間相互碰撞長大,導(dǎo)致夾雜物形狀因子降低；脈沖磁場作用抑制溫度場和流場對夾雜物的作用,使夾雜物在液相區(qū)的遷移速率降低,在整個液-固相變過程中分布更加均勻；脈沖磁場作用使凝固前沿的夾雜物受到一個更大的,指向固相區(qū)的壓力.,驅(qū)使夾雜物更容易被凝固前沿吞沒,并最終均勻分布在固相區(qū),細(xì)化凝固組織。(3)在本課題的脈沖磁場參數(shù)調(diào)控范圍內(nèi),脈沖磁場強(qiáng)度增加或作用時間延長都能夠使晶粒尺寸減��；當(dāng)冷卻速率為100℃/分鐘左右,電壓為100v,PMF周期為1.5s時,可以使45鋼最有效的細(xì)品化。(4)在CA-FE法模擬中,等效處理后的脈沖磁場可以改變凝固過程中的晶區(qū)分布,有利于中心等軸晶區(qū)比例增加和晶粒尺寸減小。
[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，

本文編號：1840540