铌微合金化高强度抗震钢筋的组织和拉伸变形行为研究

发布时间：2018-04-01 11:34

本文选题：Nb-N微合金化　切入点：贝氏体　出处：《昆明理工大学》2017年硕士论文

【摘要】：铌微合金化技术是钢筋获得综合力学性能、优良抗震性能、经济安全的一种生产技术。目前,关于钢中合金元素的配比对组织和变形行为影响的研究报道集中于N-V、Nb-V复合微合金化,而对Nb-N复合微合金化的研究不足。基于此,本文设计了七种不同Nb、N含量的试验钢,研究Nb/N的变化对钢筋组织和变形行为的影响规律。同时,通过拉伸试验SEM原位观察具有不同组织的试验钢筋在不同变形量下的组织演变规律,研究组织对变形行为的作用机理,并进行裂纹萌生与扩展分析。通过对七种不同Nb、N含量的钢筋的显微组织及抗震性能进行分析,结果表明,试验钢的组织均为铁素体+珠光体+少量贝氏体。Nb含量的增加抑制珠光体的形成,但能促进贝氏体含量的增加,同时细化组织。N含量的增加有利于屈服强度和抗拉强度的提高,使强屈比增大,抗震性能得到改善。试验钢的铌氮比(Nb/N)为4.29左右时,钢筋的抗拉强度和屈服强度均达到最大值,且有利于强屈比的提高。钢筋铌氮比越接近于理想化学配比值6.63,析出相量越多,且更为细小。拟合得到铁素体晶粒尺寸与其显微硬度之间的定量关系式。对具有铁素体、珠光体和极少量贝氏体的钢筋的SEM原位拉伸观察结果表明,铁素体和珠光体变形明显,铁素体优先变形,铁素体变形到一定程度之后引起临近珠光体内滑移系的开动,最后导致珠光体的断裂。对具有不同贝氏体含量的试验钢筋原位拉伸变形过程的研究结果表明,贝氏体的引入使变形机制发生变化。贝氏体体积分数为10%左右时,试验钢的强度和塑韧性配合最好,变形以铁素体和珠光体为主。贝氏体在变形过程中对其它组织有阻碍作用,变形初期仅发生一定程度的偏转。变形控制的主因为铁素体和珠光体的滑移运动、贝氏体的转动。贝氏体含量超过50%时,试验钢中出现大量的针状铁素体。变形初期以铁素体变形为主,珠光体变形不明显的原因可能是贝氏体作为硬质相对其变形的阻碍作用。贝氏体和铁素体承担主要的变形。随着变形量的增加,珠光体逐渐断裂,贝氏体沿平行于拉伸轴方向排列,使得变形难以继续。对断裂过程的研究结果表明,显微裂纹主要萌生于铁素体/铁素体晶界、铁素体/贝氏体和珠光体/贝氏体相界等这些应力集中的地方,并沿晶界或相界处进一步扩展,最终导致断裂。
[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.
【学位授予单位】：昆明理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.1

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