高强度抗震钢筋在不同温度下的拉伸变形行为研究

发布时间：2018-05-10 19:53

  本文选题：高强抗震钢筋 + 贝氏体　； 参考：《昆明理工大学》2015年硕士论文

【摘要】：高强度抗震钢筋在各种大型、高层建筑的复杂结构中承担着重要作用,高强度、高韧性和高强屈比的钢筋能够更大限度的吸收地震能量,是保障建筑物结构安全的最重要材料之一。本文采用万能试验机、金相显微镜、显微硬度计、高温试验机、扫描电镜(SEM)、透射电子显微镜(TEM)等,对试验钢筋进行室温和高温拉伸变形,探讨了不同温度下显微结构与抗震性能的变化规律。针对5种不同贝氏体含量(3%、8%、15%、20%和50%)的试验钢筋,进行室温拉伸试验。研究表明,不同贝氏体含量的试验钢筋的各项抗震指标符合500MPa抗震钢筋的要求,随着贝氏体含量的增加,强屈比呈现升高趋势。分析贝氏体含量对屈服平台的影响,结果显示,当贝氏体含量达到20%时,试验钢筋屈服平台消失：导致无屈服现象的主要原因有两个：(1)溶质原子在位错上的偏聚,起钉扎位错的作用,位错运动受阻,派纳力增大,进一步运动需要应力增大,在曲线上表现为上升的趋势。(2)贝氏体中的板条铁素体中含有较高的位错密度,在变形过程中高的位错密度使得位错之间容易发生缠结,需要增大应力才能使位错运动,实现继续变形。通过对比贝氏体含量为8%和50%的试验钢筋的显微结构在不同变形阶段的变化。研究结果表明,贝氏体含量50%的钢筋,贝氏体承担主要的变形,贝氏体中的亚板条中的位错密度随变形的进行先增大后减小；贝氏体含量为8%的试验钢筋中铁素体的位错密度随变形的进行急剧增大,珠光体发生较大的变形,甚至断裂,铁素体和珠光体承担主要的变形。五种贝氏体含量的试验钢筋在200～600℃高温拉伸试验。研究结果表明,在200～400℃,试验钢筋均出现明显的加工硬化现象,并随温度的升高加工硬化现象越发不明显。当温度上升到500～600℃,试验钢筋的加工硬化现象基本消失,应力应变曲线甚至趋于水平直线。高温拉伸试验中的屈服强度和抗拉强度在不同温度下的变化规律,结果表明：在200～600℃,试验钢筋的屈服强度和抗拉强度都随温度升高呈下降趋势；在400～600℃,屈服强度和抗拉强度下降的程度比200～400℃内剧烈得多。在200～600℃,抗拉强度随温度的升高而下降的幅度比屈服强度的大。高温试验钢筋的强屈比,研究结果显示：当温度不超过500℃时,试验钢筋的强屈比都高于1.25,满足抗震要求；不同贝氏体含量的试验钢筋的强屈比都随温度的升高呈现先升高后降低的规律。试验钢筋的高温抗震性能是通过与室温性能的对比来确定,对比发现,试验钢筋具有较高的强屈比；而且不超过500℃时,高温下的屈服强度都高于室温屈服强度2/3,试验钢筋具有较好的高温抗震性能。
[Abstract]:High-strength aseismic reinforcement plays an important role in complex structures of large and high-rise buildings. The reinforcement with high strength, high toughness and high yield ratio can absorb seismic energy to a greater extent. It is one of the most important materials to ensure the safety of building structure. In this paper, a universal testing machine, a metallographic microscope, a microhardness tester, a high temperature tester, a scanning electron microscope (SEM), a transmission electron microscope (TEM), etc, were used to deform the tested steel bars at room and high temperature. The variation of microstructure and seismic performance at different temperatures is discussed. Tensile tests at room temperature were carried out for 5 kinds of test steel bars with different bainite content of 20% and 50% respectively. The results show that the seismic indexes of the tested steel bars with different bainite content meet the requirements of 500MPa seismic reinforcement. With the increase of bainite content, the ratio of strength to yield increases. The effect of bainite content on the yield platform is analyzed. The results show that when the bainite content reaches 20%, the yield platform of the tested steel bar disappears. The main cause of the non-yielding phenomenon is the segregation of solute atoms on dislocation. As a result of pinning dislocation, the dislocation movement is blocked, the Pina force increases, and the further movement requires an increase in stress. In the curve, the lath ferrite in the bainite has a higher dislocation density, and the lath ferrite in the bainite has a higher density of dislocation. In the process of deformation, the high density of dislocation makes it easy to tangle between the dislocations, and it needs to increase the stress to make the dislocation move and continue to deform. The microstructure of steel bars with bainite content of 8% and 50% was compared in different deformation stages. The results show that when the bainite content is 50%, the bainite bears the main deformation, and the dislocation density in the bainite sublath increases first and then decreases with the deformation. When the bainite content is 8%, the dislocation density of ferrite increases sharply with the deformation, and the pearlite is deformed, even fracture, and the ferrite and pearlite bear the main deformation. Five kinds of bainite content test steel bar at 200 鈩，

本文编号：1870647