發(fā)布時(shí)間：2018-05-31 09:29

  本文選題：鈦微合金鋼 + 鐵素體相變��； 參考：《東北大學(xué)》2015年博士論文

【摘要】：我國(guó)經(jīng)濟(jì)、社會(huì)的快速增長(zhǎng)帶動(dòng)了鋼鐵行業(yè)的高速發(fā)展,同時(shí)也對(duì)鋼鐵材料的品種和質(zhì)量等提出了更高的要求,新一代鋼鐵材料向著高強(qiáng)度、高韌性、低成本、減量化的方向發(fā)展。特別是隨著人們對(duì)環(huán)境污染和礦產(chǎn)資源枯竭等問(wèn)題的重視,微合金高強(qiáng)度鋼的開(kāi)發(fā)和研究受到了越來(lái)越多的關(guān)注,細(xì)晶強(qiáng)化和析出強(qiáng)化作為改善鋼材綜合力學(xué)性能的主要途徑已經(jīng)廣泛的應(yīng)用在微合金高強(qiáng)度鋼的開(kāi)發(fā)和生產(chǎn)中,因此,如何充分發(fā)揮微合金元素在細(xì)化晶粒和析出強(qiáng)化方面的作用成為控軋控冷工藝開(kāi)發(fā)的一個(gè)關(guān)鍵問(wèn)題。在中央高校基本科研業(yè)務(wù)費(fèi)項(xiàng)目研究生科研創(chuàng)新項(xiàng)目(N110607006)的經(jīng)費(fèi)支持下,本文以添加Ti、Nb、Mo等元素的微合金鋼為研究對(duì)象,利用熱模擬實(shí)驗(yàn)系統(tǒng)研究了奧氏體高溫變形行為、連續(xù)冷卻相變行為、鐵素體相變及納米析出行為,豐富了鈦微合金鋼研究的一些基礎(chǔ)理論,討論了析出形式對(duì)鐵素體相微觀力學(xué)性能的影響,同時(shí)利用熱軋實(shí)驗(yàn)研究了控軋控冷工藝參數(shù)對(duì)鈦微合金鋼力學(xué)性能和析出行為的影響,為現(xiàn)場(chǎng)工業(yè)生產(chǎn)提供了理論基礎(chǔ)。本文的主要工作和研究成果如下： (1)通過(guò)單道次壓縮實(shí)驗(yàn)研究了鈦微合金鋼奧氏體高溫變形行為,分析了微合金元素以及變形參數(shù)對(duì)奧氏體動(dòng)態(tài)再結(jié)晶的影響,同時(shí)建立了實(shí)驗(yàn)鋼的變形抗力模型。結(jié)果表明,Ti、Nb、Mo的加入能夠提高奧氏體的流變應(yīng)力和熱變形激活能,抑制奧氏體的動(dòng)態(tài)再結(jié)晶,計(jì)算得到C-Mn、Ti、Ti-Nb、Ti-Nb-Mo實(shí)驗(yàn)鋼的奧氏體熱變形激活能分別為351kJ/mol、458kJ/mol、483kJ/mol、497kJ/mol。 (2)通過(guò)連續(xù)冷卻相變實(shí)驗(yàn)研究了奧氏體在連續(xù)冷卻中的相變行為,繪制了實(shí)驗(yàn)鋼的CCT曲線,分析了微合金元素、冷卻速率以及變形在奧氏體相變過(guò)程中的作用。結(jié)果表明,Ti、Nb、Mo的加入能夠提高奧氏體在連續(xù)冷卻過(guò)程中的穩(wěn)定性,抑制鐵素體和珠光體相變,促進(jìn)貝氏體相變；變形降低了奧氏體的穩(wěn)定性,提高了相變開(kāi)始溫度,促進(jìn)了鐵素體相變,使鐵素體相變的C曲線向左移動(dòng)。 (3)利用熱模擬技術(shù)系統(tǒng)研究了微合金元素、等溫時(shí)間、卷取前冷卻速率、卷取溫度、卷取后冷卻速率以及變形對(duì)鈦微合金鋼鐵素體相變和納米析出行為的影響。研究結(jié)果表明,在卷取溫度為640℃時(shí),Ti、Nb、Mo等元素的加入能細(xì)化鐵素體晶粒,同時(shí)在鐵素體中形成大量的納米析出相,顯著提高鐵素體的硬度；640℃等溫時(shí),隨著等溫時(shí)間的增加,鐵素體的尺寸和體積分?jǐn)?shù)逐漸增加,鐵素體中相間析出的面間距增大；隨著卷取前冷卻速率的增大,鐵素體的晶粒尺寸和鐵素體中納米析出的粒子尺寸減小,鐵素體的顯微硬度逐漸增大；隨著卷取溫度的降低,實(shí)驗(yàn)鋼的組織從鐵素體+珠光體向貝氏體轉(zhuǎn)變,鐵素體的晶粒尺寸逐漸減小,基體的顯微硬度先升高后降低,卷取溫度為640℃基體的顯微硬度最大,在卷取溫度為640℃和700℃時(shí),鐵素體中發(fā)現(xiàn)了排列規(guī)則的相間析出,卷取溫度越高,相間析出的粒子尺寸和面間距越大；640℃卷取后,隨著冷卻速率的增大,實(shí)驗(yàn)鋼的顯微組織從鐵素體+珠光體向貝氏體轉(zhuǎn)變,實(shí)驗(yàn)鋼基體的顯微硬度呈現(xiàn)降低的趨勢(shì),卷取后采用較小的冷卻速率同樣能獲得尺寸細(xì)小的鐵素體,而且能夠促進(jìn)微合金碳氮化物在鐵素體中的析出；隨著變形程度的增加,鐵素體的顯微硬度先升高后降低,變形為22%時(shí)鐵素體的顯微硬度最大,變形的增加使相間析出的面間距增大。 (4)利用納米壓痕實(shí)驗(yàn)研究了鐵素體中析出對(duì)其微觀力學(xué)性能的影響。結(jié)果表明,相同工藝下,C-Mn實(shí)驗(yàn)鋼和Ti-Nb實(shí)驗(yàn)鋼鐵素體的納米硬度分別為2.64GPa和4.19GPa,鐵素體中納米析出相將鐵素體的納米硬度提高了1.55GPa；卷取溫度為600℃、640℃和700℃時(shí)鐵素體的納米硬度分別為3.90GPa、4.19GPa和3.60GPa。存在相間析出的鐵素體晶粒的載荷-深度曲線在壓入的初始階段會(huì)出現(xiàn)一個(gè)平臺(tái),平臺(tái)的長(zhǎng)度與相間析出面間距的大小有關(guān)。不同卷取溫度下鐵素體晶粒內(nèi)部納米硬度的變化規(guī)律不同,600℃時(shí)鐵素體晶界附近納米硬度最大,晶粒內(nèi)部納米硬度變化不大；640℃時(shí)鐵素體晶粒內(nèi)部的納米硬度基本不變；700℃時(shí)由于先形核的析出的消失和粗化,納米硬度隨離晶界距離的增加逐漸降低。 (5)控軋控冷工藝研究結(jié)果表明,隨著終軋溫度的升高,抗拉強(qiáng)度和屈服強(qiáng)度先升高后降低,840℃終軋時(shí)實(shí)驗(yàn)鋼的強(qiáng)度最高；卷取溫度從460℃升高到675℃時(shí),強(qiáng)度先降低后升高,在675℃卷取時(shí),由于析出強(qiáng)化作用的加強(qiáng),具有很好的綜合力學(xué)性能；冷卻速率的增大能夠同時(shí)提高細(xì)晶強(qiáng)化和析出強(qiáng)化作用從而提高實(shí)驗(yàn)鋼的強(qiáng)度：Mo的加入細(xì)化了鐵素體晶粒和納米析出粒子,從而將屈服強(qiáng)度提高了25-35MPa；與卷取后石棉冷卻相比采用保溫+爐冷工藝屈服強(qiáng)度提高了94MPa,抗拉強(qiáng)度提高了54MPa。在國(guó)內(nèi)某鋼廠成功試制了不同厚度規(guī)格的600MPa和700MPa級(jí)別微合金高強(qiáng)度鋼,具有較好的綜合力學(xué)性能,其中析出強(qiáng)化作用可以超過(guò)300MPa。
[Abstract]:The rapid growth of China's economy and society has led to the rapid development of the iron and steel industry. At the same time, it has also raised higher requirements for the variety and quality of steel materials. The new generation of steel materials is developing towards the direction of high strength, high toughness, low cost and reduction, especially with the attention of people to environmental pollution and the depletion of mineral resources. More and more attention has been paid to the development and research of microalloy high strength steel. As the main way to improve the mechanical properties of steel, the main way to improve the comprehensive mechanical properties of steel has been widely used in the development and production of microalloy high strength steel. Therefore, how to make full use of the microalloying elements in refining grain and precipitation strengthening is made. With the support of the graduate scientific research and innovation project (N110607006) for the basic scientific research business fee project of the Central University, this paper takes the microalloy steel adding Ti, Nb and Mo as the research object, and studies the high temperature deformation behavior of austenite and continuous cooling phase by the thermal simulation experiment system. Change behavior, ferrite transformation and nanometer precipitation have enriched the basic theory of titanium microalloyed steel and discussed the influence of precipitation form on the micromechanical properties of ferrite phase. At the same time, the influence of controlled rolling and controlled cooling process parameters on the mechanical energy and precipitation behavior of titanium microalloy steel was studied by hot rolling experiment. The main work and research results in this paper are as follows:
(1) the high temperature deformation behavior of austenite in titanium microalloy steel was studied by single channel compression test. The influence of Microalloy Elements and deformation parameters on the dynamic recrystallization of austenite was analyzed, and the deformation resistance model of the experimental steel was established. The results showed that the addition of Ti, Nb and Mo could increase the rheological and thermal deformation activation energy of austenite, and suppress the activation energy of the austenite. The dynamic recrystallization of austenite is made and the activation energy of the austenite thermal deformation of C-Mn, Ti, Ti-Nb, Ti-Nb-Mo experimental steels is 351kJ/mol, 458kJ/mol, 483kJ/mol, 497kJ/mol., respectively.
(2) the phase transition behavior of austenite in continuous cooling was studied by continuous cooling phase transformation experiment. The CCT curve of experimental steel was plotted. The effect of Microalloy Elements, cooling rate and deformation on the phase transformation of austenite was analyzed. The results showed that the addition of Ti, Nb and Mo could improve the stability of austenite during continuous cooling and restrain iron. The phase transition of the prime body and pearlite promotes the bainite phase transformation, and the deformation reduces the stability of the austenite, improves the starting temperature of the phase transition, promotes the ferrite transformation, and moves the C curve of the ferrite transformation to the left.
(3) the effects of microalloying elements, isothermal time, cooling rate before coiling, coiling temperature, cooling rate and deformation on the phase transition and nano precipitation of titanium microalloy were investigated by thermal simulation. The results showed that the addition of Ti, Nb, Mo and other elements could refine ferrite grain when the coiling temperature was 640. At the same time, with the increase of isothermal time, the size and volume fraction of ferrite gradually increased with the increase of isothermal time, and the interphase separation between ferrite in ferrite increased. With the increase of cooling rate before coiling, the grain size of ferrite and the content of ferrite in ferrite increased with the increase of cooling rate before coiling. With the decrease of the particle size and the microhardness of the ferrite, the microstructure of the experimental steel is changed from ferrite and pearlite to bainite with the decrease of coiling temperature. The grain size of the ferrite decreases gradually. The microhardness of the matrix increases first and then decreases. The microhardness of the matrix is maximum at 640 C, and the coiling temperature is at the coiling temperature. At 640 C and 700 C, the arrangement rules are found in the ferrite. The higher the coiling temperature is, the larger the particle size and the surface spacing are. The microstructure of the experimental steel turns from ferrite + pearlite to bainite with the increase of cooling rate at 640 C, and the microhardness of the experimental steel matrix decreases. After coiling, small size of ferrite can be obtained with smaller cooling rate, and it can promote the precipitation of microalloy carbonitride in ferrite. With the increase of the deformation degree, the microhardness of ferrite first increases and then decreases, and the microhardness of ferrite is the largest when the deformation is 22%, and the increase of deformation makes the interphase precipitated between each other. The distance increases.
(4) the effect of precipitation on micromechanical properties of ferrite in ferrite was studied by nano indentation test. The results showed that the nano hardness of C-Mn experimental steel and Ti-Nb experimental steel was 2.64GPa and 4.19GPa under the same process. The nano precipitation of ferrite in ferrite increased the nanoscale hardness of ferrite by 1.55GPa, and the coiling temperature was 600, 640. The nanoscale hardness of ferrite at 700 C is 3.90GPa, and the load depth curve of ferrite grain that precipitates between 4.19GPa and 3.60GPa. will appear a platform in the initial stage of pressure entry. The length of the platform is related to the size of the interphase gap between the phases. The change law of the hardness of the ferrite grain inside the ferrite grain under different coiling temperatures At 600, the nanoscale hardness in the ferrite grain boundary is the largest and the nano hardness in the grain is not changed. At 640 C, the nano hardness in the ferrite grain is basically unchanged, and the nano hardness decreases gradually with the increase of the distance from the grain boundary at 700 C.
(5) the research results of controlled rolling and controlled cooling process show that the tensile strength and yield strength increase first and then decrease with the increase of final rolling temperature. The strength of the experimental steel is the highest at the end of 840 degrees centigrade. When the coiling temperature rises from 460 to 675 C, the strength decreases first and then increases. At 675 centigrade, it has good comprehensive strength due to the strengthening of precipitation strengthening. The increase of cooling rate can increase the strength of the fine grain and precipitate to increase the strength of the experimental steel at the same time. The addition of Mo has refined the ferrite grain and the nano precipitated particles, thus increasing the yield strength by 25-35MPa, and increasing the yield strength of 94MPa by using the yield strength of the asbestos cooling process after the coiling. The tensile strength is improved by 54MPa. in a steel plant in China, which has successfully developed 600MPa and 700MPa grade microalloy high strength steel with different thickness specifications. It has better comprehensive mechanical properties, and the precipitation strengthening effect can exceed 300MPa..
【學(xué)位授予單位】：東北大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TG142.1

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本文編號(hào)：1959148