發(fā)布時(shí)間：2018-04-01 11:34

  本文選題：Nb-N微合金化　切入點(diǎn)：貝氏體　出處：《昆明理工大學(xué)》2017年碩士論文

【摘要】：鈮微合金化技術(shù)是鋼筋獲得綜合力學(xué)性能、優(yōu)良抗震性能、經(jīng)濟(jì)安全的一種生產(chǎn)技術(shù)。目前,關(guān)于鋼中合金元素的配比對(duì)組織和變形行為影響的研究報(bào)道集中于N-V、Nb-V復(fù)合微合金化,而對(duì)Nb-N復(fù)合微合金化的研究不足�；�于此,本文設(shè)計(jì)了七種不同Nb、N含量的試驗(yàn)鋼,研究Nb/N的變化對(duì)鋼筋組織和變形行為的影響規(guī)律。同時(shí),通過(guò)拉伸試驗(yàn)SEM原位觀察具有不同組織的試驗(yàn)鋼筋在不同變形量下的組織演變規(guī)律,研究組織對(duì)變形行為的作用機(jī)理,并進(jìn)行裂紋萌生與擴(kuò)展分析。通過(guò)對(duì)七種不同Nb、N含量的鋼筋的顯微組織及抗震性能進(jìn)行分析,結(jié)果表明,試驗(yàn)鋼的組織均為鐵素體+珠光體+少量貝氏體。Nb含量的增加抑制珠光體的形成,但能促進(jìn)貝氏體含量的增加,同時(shí)細(xì)化組織。N含量的增加有利于屈服強(qiáng)度和抗拉強(qiáng)度的提高,使強(qiáng)屈比增大,抗震性能得到改善。試驗(yàn)鋼的鈮氮比(Nb/N)為4.29左右時(shí),鋼筋的抗拉強(qiáng)度和屈服強(qiáng)度均達(dá)到最大值,且有利于強(qiáng)屈比的提高。鋼筋鈮氮比越接近于理想化學(xué)配比值6.63,析出相量越多,且更為細(xì)小。擬合得到鐵素體晶粒尺寸與其顯微硬度之間的定量關(guān)系式。對(duì)具有鐵素體、珠光體和極少量貝氏體的鋼筋的SEM原位拉伸觀察結(jié)果表明,鐵素體和珠光體變形明顯,鐵素體優(yōu)先變形,鐵素體變形到一定程度之后引起臨近珠光體內(nèi)滑移系的開(kāi)動(dòng),最后導(dǎo)致珠光體的斷裂。對(duì)具有不同貝氏體含量的試驗(yàn)鋼筋原位拉伸變形過(guò)程的研究結(jié)果表明,貝氏體的引入使變形機(jī)制發(fā)生變化。貝氏體體積分?jǐn)?shù)為10%左右時(shí),試驗(yàn)鋼的強(qiáng)度和塑韌性配合最好,變形以鐵素體和珠光體為主。貝氏體在變形過(guò)程中對(duì)其它組織有阻礙作用,變形初期僅發(fā)生一定程度的偏轉(zhuǎn)。變形控制的主因?yàn)殍F素體和珠光體的滑移運(yùn)動(dòng)、貝氏體的轉(zhuǎn)動(dòng)。貝氏體含量超過(guò)50%時(shí),試驗(yàn)鋼中出現(xiàn)大量的針狀鐵素體。變形初期以鐵素體變形為主,珠光體變形不明顯的原因可能是貝氏體作為硬質(zhì)相對(duì)其變形的阻礙作用。貝氏體和鐵素體承擔(dān)主要的變形。隨著變形量的增加,珠光體逐漸斷裂,貝氏體沿平行于拉伸軸方向排列,使得變形難以繼續(xù)。對(duì)斷裂過(guò)程的研究結(jié)果表明,顯微裂紋主要萌生于鐵素體/鐵素體晶界、鐵素體/貝氏體和珠光體/貝氏體相界等這些應(yīng)力集中的地方,并沿晶界或相界處進(jìn)一步擴(kuò)展,最終導(dǎo)致斷裂。
[Abstract]:Niobium microalloying technology is a kind of production technology which can obtain comprehensive mechanical properties, excellent aseismic performance and economic safety of steel bars. The study on the effect of alloying element ratio on microstructure and deformation behavior of steel was focused on N-VN Nb-V composite microalloying, but not on Nb-N composite microalloying. Based on this, seven kinds of experimental steels with different NbN content were designed. The effect of the change of Nb/N on the microstructure and deformation behavior of steel bar was studied. At the same time, through the tensile test SEM in situ, the evolution law of the steel bars with different structures was observed, and the mechanism of the effect of the structure on the deformation behavior was studied. By analyzing the microstructure and seismic behavior of seven kinds of steel bars with different NbN content, the results show that, The microstructure of the test steel is that the increase of ferrite pearlite bainite. NB content can inhibit the formation of pearlite, but it can promote the increase of bainite content, at the same time, the increase of microstructure and N content is beneficial to the increase of yield strength and tensile strength. When the NB / N ratio of test steel is about 4.29, the tensile strength and yield strength of steel bar reach the maximum. The ratio of niobium to nitrogen is close to the ideal chemical ratio 6.63, the precipitated phase is more and smaller. The quantitative relation between the grain size of ferrite and its microhardness is obtained by fitting the quantitative relation between ferrite grain size and microhardness. The SEM in-situ tensile observation of pearlite and a very small amount of bainite bars shows that the deformation of ferrite and pearlite is obvious, the deformation of ferrite is preferred, and the deformation of ferrite to a certain extent leads to the start of slip system near pearlite. The results show that the deformation mechanism is changed by the introduction of bainite. When the volume fraction of bainite is about 10%, the deformation mechanism is changed. The strength and ductility of the test steel are the best, and the deformation is mainly ferrite and pearlite. Bainite hinders other microstructure during deformation. Only a certain degree of deflection occurs in the early stage of deformation. The main causes of deformation control are the slip movement of ferrite and pearlite, the rotation of bainite. There are a large number of acicular ferrite in the test steel. The reason why the pearlite deformation is not obvious is that bainite acts as an obstacle to its deformation. Bainite and ferrite bear the main deformation. With the increase of deformation amount, pearlite gradually breaks. The bainite is arranged along the direction parallel to the tensile axis, which makes it difficult to continue the deformation. The results of the fracture process show that the microcracks mainly occur at the grain boundary of ferrite / ferrite. These stress concentration areas such as ferrite / bainite and pearlite / bainite phase boundary extend further along grain boundary or phase boundary and eventually lead to fracture.
【學(xué)位授予單位】：昆明理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TG142.1

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