SW400钢预热闪光对焊接头组织及性能的研究

发布时间：2017-12-30 23:50

本文关键词：SW400钢预热闪光对焊接头组织及性能的研究　出处：《吉林大学》2016年硕士论文　论文类型：学位论文

【摘要】：随着人们环保意识的提高,低能耗、环境友好型经济模式逐渐成为未来发展的潮流。在汽车行业,各大生产商都在积极寻求节能发展的新方向。在影响汽车油耗的各个因素中,车体自重占有很大的比例,车体轻量化成为车辆开发的热点。作为车身的重要部件,车轮在车体轻量化中占据着重要地位。国内车辆,尤其是中低端车型和商用车型,车轮依旧以使用钢材为主。提高、优化车轮钢材强度等级和结构设计,成为国内车轮生产商实现轻量化的发展方向。SW400钢是本钢新研制的一种车轮生产专用钢,具有良好的承载性能与安全性能优势,是生产轮辋的主要材料之一。轮辋焊接常使用闪光对焊,但SW400钢闪光对焊接头仍面临很多问题。轮辋焊缝易在随后的加工中开裂,很难修补,导致车轮生产废品率居高不下。预热工艺可以有效改善接头组织,提高轮辋的力学性能,是优化车轮生产工艺的的一种有效手段。本文主要研究了SW400钢预热闪光对焊的热循环特征及预热工艺参数对热循环的影响;预热闪光对焊接头的宏、微观组织特点;预热参数对接头组织及力学性能的影响和闪光留量对接头组织及力学性能的影响。研究结果表明,预热可以改变焊接过程中接头的热循环,预热电流和预热时间共同决定预热阶段接头的热输入量,增加两者或其中之一均会增大热输入,导致接头温度梯度变缓,各区域峰值温度和加热速度升高,冷却速度降低,焊缝激冷效应减弱。闪光对焊接头可分为界面区(WZ)、过热区(OZ)、重结晶区(RZ)和不完全重结晶区(PZ)。SW400钢对焊接头界面区由于脱碳、高温和热变形等因素主要由块状铁素体、上贝氏体和针状铁素体组成;过热区主要是粗大的上贝氏体,并有少量珠光体生成;重结晶区晶粒得到细化,主体为块状铁素体和珠光体;不完全重结晶区组成与重结晶区一致,但晶粒大小不均。随着预热电流和预热时间的增加,SW400钢接头加热速度上升,冷却速度下降;接头的微观组织经历了块状铁素体增多、长大,上贝氏体和针状铁素体粗化,微观组织均匀化这一过程。合适的预热电流和预热时间有利于改善接头组织,但其一或两者过大会导致接头晶粒粗化严重,明显降低接头力学性能。这个规律在接头力学性能测试中得到验证。闪光对焊过程中的闪光留量对接头组织及力学性能具有明显影响,加入预热工艺后,应适当采用较小的闪光留量值,否则,接头组织会因预热工艺带来的额外热输入而严重粗化,力学性能降低。降低闪光留量同时可以节省钢材,节约闪光时间。
[Abstract]:With the improvement of people's awareness of environmental protection, low energy consumption, environment-friendly economic model has gradually become the trend of future development, in the automotive industry. Major manufacturers are actively looking for a new direction of energy conservation development. In the various factors that affect the fuel consumption of cars, the weight of the car body occupies a large proportion. As an important part of the body, the wheel occupies an important position in the body lightweight. Domestic vehicles, especially low-end models and commercial models. The wheel still mainly uses steel. Improves, optimizes the wheel steel strength grade and the structure design. SW400 steel, which has become the development direction of domestic wheel manufacturer to realize lightweight, is a new kind of special steel for wheel production in Benxi Iron and Steel Co., which has the advantages of good bearing capacity and safety performance. Flash butt welding is often used in rim welding, but the SW400 steel flash butt welding joint still faces many problems. The weld seam of rim is easy to crack in the subsequent processing, and it is difficult to repair. The preheating process can effectively improve the joint structure and improve the mechanical properties of the rim. This paper mainly studies the thermal cycle characteristics of SW400 steel preheating flash butt welding and the influence of preheating process parameters on thermal cycle. Macrostructure and microstructure of preheated flash butt welding joint; The effect of preheating parameters on the microstructure and mechanical properties of the joints and the effect of flash retention on the microstructure and mechanical properties of the joints. The results show that preheating can change the thermal cycle of the joints during welding. Preheating current and preheating time jointly determine the heat input of the joint in the preheating stage. Increasing both or one of them will increase the heat input, resulting in the joint temperature gradient becoming slower, and the peak temperature and heating speed of each region increasing. The flash butt welding joint can be divided into interfacial zone (WZ) and superheated zone (OZ). Recrystallization zone (RZ) and incomplete recrystallization zone (PZN. SW400) are mainly composed of bulk ferrite, upper bainite and acicular ferrite due to decarburization, high temperature and hot deformation. The superheated zone is mainly composed of coarse upper bainite and a small amount of pearlite. The grains in recrystallization region are refined, and the main grains are block ferrite and pearlite. The composition of the incomplete recrystallization zone is consistent with that of the recrystallization zone, but the grain size is uneven. With the increase of preheating current and preheating time, the heating rate increases and the cooling rate decreases with the increase of preheating current and preheating time. The microstructure of the joints experienced a process of increasing and growing up, coarsening of upper bainite and acicular ferrite, and homogenization of microstructure. Proper preheating current and preheating time were beneficial to improve the microstructure of the joints. But one or both of them lead to serious grain coarsening. The mechanical properties of the joints were obviously reduced. This rule was verified in the testing of the mechanical properties of the joints. The flash retention during flash butt welding had a significant effect on the microstructure and mechanical properties of the joints, and the preheating process was added. The smaller flash retention should be used properly, otherwise, the microstructure of the joint will be coarsened seriously because of the extra heat input brought by the preheating process, and the mechanical properties will be reduced, and the steel and flash time can be saved by reducing the flash retention at the same time.
【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：U466

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