本文選題：稀土 + 微合金��； 參考：《北京科技大學》2017年博士論文

【摘要】：通過微合金化與控軋控冷技術的有機結合,依靠碳氮化物析出與形變再結晶的交互作用使鋼獲得良好的強韌性,是有效提高鋼鐵材料性能的重要手段。在Ti、Nb、V、B、稀土等微合金元素中,Nb因具有顯著抑制奧氏體晶粒長大、提高非再結晶溫度、細化相變組織、提高鋼的強韌性等作用,在高強低合金鋼領域得到了廣泛應用,稀土因其在鋼中的凈化、抗氧性、提高耐蝕性等作用而引起材料研究者廣泛關注。我國白云鄂博礦擁有豐富的稀土資源,前期研究表明,包頭鋼鐵公司使用白云鄂博鐵礦原料生產(chǎn)的鋼中含有一定量的殘余稀土,其含量達到微合金化要求。如何充分發(fā)揮稀土的有益作用,不僅需要關注稀土本身的微合金化效果,還應著眼于稀土的存在形式及其與微合金元素Nb等的交互作用。然而,由于稀土理化性質(zhì)的特殊性以及研究手段的限制,目前稀土在鋼中的微合金化作用尚缺乏系統(tǒng)的研究。本文基于稀溶液固溶體,計算了鋼中常用稀土元素La、Ce、Y在Fe基合金中形成穩(wěn)定第二相的形成焓與溶解焓,獲得了稀土在Fe中固溶度隨溫度的變化曲線。此外,Fe-RE系合金在升溫與降溫過程中的內(nèi)耗變化規(guī)律表明,當稀土原子溶于基體時,在高溫區(qū)段會出現(xiàn)溶質(zhì)原子在晶界偏聚的阻尼峰,當稀土含量增加到超過基體最大固溶量時,會與其他合金元素反應形成化合物;進一步地,從電子結構層次深入分析了稀土原子的占位傾向及對晶界的強韌化作用機理�；谙⊥僚c其他微合金元素的相互作用系數(shù),計算了稀土作用下NbC的固溶度積,分析了稀土元素對高溫奧氏體化狀態(tài)下NbC溶解行為的影響,建立了 NbC在奧氏體區(qū)的析出動力學模型。此外,設計了奧氏體區(qū)的等溫析出實驗,結合等溫析出后的組織觀察與硬度測試結果表明,稀土元素會提高NbC在奧氏體中的固溶度積,降低其固溶溫度,促進NbC在奧氏體中的溶解。通過系列等溫實驗與熱變形實驗,結合物理化學相分析與析出物統(tǒng)計,對添加稀土前后實驗鋼中NbC的析出行為進行了定量定性表征。根據(jù)差熱分析曲線中第二相析出峰的變化,利用JMA模型討論了稀土對微合金鋼中NbC析出動力學的影響。結果表明,稀土添加后,NbC在奧氏體區(qū)的激活能由75.32kJ/mol升高到90.15kJ/mol,在鐵素體中的激活能則由176.98kJ/mol降低為65.47kJ/mol。此外,利用第一性原理分析了稀土與Nb原子的交互作用,以及對Nb原子擴散激活能的影響,從微觀角度深入解釋了稀土對奧氏體與鐵素體區(qū)NbC析出行為的影響機理。通過設計系列擴散偶實驗,討論了稀土 La對鐵鈮互擴散行為的影響。在此基礎上,得出稀土 La作用下Nb在鐵素體中的擴散系數(shù)。結果表明,添加稀土后,Nb在鐵素體中的擴散系數(shù)增加�；谖诲e形核機制,建立了 NbC在鐵素體中的形核與析出模型,結合NbC析出動力學實驗,闡明了稀土對鐵素體區(qū)NbC析出行為的影響機理。實驗與計算結果均表明,稀土加入后會加快NbC在鐵素體區(qū)的析出,增加鐵素體中析出相密度與彌散強化效果。借助系列熱變形工藝下的平均流變應力實驗,確定了實驗鋼的未再結晶溫度,從形變儲能作用下回復與再結晶之間的競爭關系討論了稀土對形變再結晶行為的影響機理。根據(jù)應變誘導析出NbC顆粒的體積分數(shù)和分布形態(tài),在考慮釘扎和拖曳效應的情況下,預測了再結晶晶粒等溫長大動力學�；谏鲜龅睦碚撆c實驗研究,對白云鄂博含稀土鐵礦生產(chǎn)鋼材的可行性和經(jīng)濟性進行評估,并給出了合金成分設計與熱機軋制工藝設計的思路。
[Abstract]:Through the organic combination of microalloying and controlled rolling and controlled cooling technology, the interaction of carbides precipitation and deformation recrystallization makes the steel get good strength and toughness. It is an important means to effectively improve the properties of steel materials. In Ti, Nb, V, B, rare earth and other micro alloy elements, Nb has a significant inhibition of austenite grain growth and the increase of non recrystallization temperature. It has been widely used in the field of high strength and low alloy steel, which has been widely used in the field of high strength and low alloy steel. The rare earth is widely concerned because of its purification, anti oxygen and corrosion resistance in the steel. The Baiyunebo mine has rich rare earth resources. The previous research shows that the use of the Baotou Steel Corp has been used. There is a certain amount of remainder rare earth in the steel produced from Baiyunebo iron ore raw material, and its content reaches the requirement of microalloying. How to give full play to the beneficial effect of rare earth should not only pay attention to the microalloying effect of rare earth itself, but also focus on the existence of rare earth and its interaction with the microalloying element Nb, however, due to the rare earth theory. The microalloying effect of rare earth in steel is still lack of systematic study at present. Based on the solution solid solution, the formation enthalpy and dissolution enthalpy of the stable second phase of the rare earth elements La, Ce, Y in the Fe based alloy are calculated in this paper, and the solid solubility of rare earth in Fe is obtained with the temperature change. In addition, the variation of internal friction of Fe-RE alloy during heating and cooling shows that when the rare earth atoms dissolve in the matrix, the damping peak of the solute atoms will appear at the grain boundary in the high temperature zone. When the content of rare earth increases to the maximum solid solution, it will react with his alloy element to form a compound; further, from the alloy element, the compound will be formed. The occupying tendency of rare earth atom and the mechanism of strengthening and toughening of grain boundary are analyzed in depth by electronic structure. Based on the interaction coefficient of rare earth and other microalloying elements, the solid solubility product of NbC under the action of rare earth is calculated. The effect of rare earth elements on the dissolution behavior of NbC under austenitizing condition is analyzed, and NbC is established in austenite. In addition, the isothermal precipitation experiment of austenite area is designed. The results of microstructure observation and hardness test after isothermal precipitation show that the rare earth elements can increase the solid solubility product of NbC in austenite, reduce the solution temperature and promote the dissolution of NbC in austenite. The precipitation behavior of NbC in the experimental steel before and after the addition of rare earth was qualitatively characterized by physical and chemical phase analysis and precipitation. According to the change of the precipitation peak in the second phase of the differential heat analysis curve, the effect of rare earth on the precipitation kinetics of NbC in microalloy steel was discussed by JMA model. The results showed that after the addition of rare earth, the NbC was in austenite. The activation energy of the region is increased from 75.32kJ/mol to 90.15kJ/mol, and the activation energy in the ferrite is reduced from 176.98kJ/mol to 65.47kJ/mol.. The interaction between rare earth and Nb atoms and the effect on the activation energy of Nb atom diffusion are analyzed by the first principle, and the NbC analysis of the austenite and ferrite region is explained from the microscopic angle. By designing series of diffusion couple experiments, the effect of rare earth La on the interdiffusion of iron and niobium is discussed. On this basis, the diffusion coefficient of Nb in ferrite under the action of rare earth La is obtained. The result shows that the diffusion coefficient of Nb in ferrite is added after adding rare earth. Based on the dislocation nucleation mechanism, the NbC in ferrite is established. The nucleation and precipitation model in the body, combined with the NbC precipitation kinetic experiment, clarifies the influence mechanism of rare earth on the precipitation behavior of NbC in ferrite region. The experiment and calculation results show that the addition of rare earth will accelerate the precipitation of NbC in the ferrite region, increase the precipitation density and dispersion strengthening effect in the ferrite. The non recrystallization temperature of the experimental steel was determined by mean rheological stress experiment. The influence mechanism of re on the deformation recrystallization behavior was discussed from the relationship between the recovery and recrystallization under the action of deformation energy storage. The volume fraction and distribution of NbC particles precipitated by strain induced precipitation and the effect of nailing and towing were predicted. The kinetics of isothermal growth of crystalline grains. Based on the theoretical and experimental studies mentioned above, the feasibility and economy of the steel produced by rare earth iron ore in Baiyunebo are evaluated, and the design of the alloy composition and the design of the hot machine rolling process are given.

【學位授予單位】：北京科技大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TG142.1

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