高强钢局部加热辊压成形技术研究与应用

发布时间：2018-02-26 23:26

本文关键词： 高强钢辊压成形局部感应加热成形特性　出处：《北京科技大学》2017年博士论文　论文类型：学位论文

【摘要】：随着全球的能源危机、严峻的环境压力以及工业用钢结构安全性能设计的提高,开发和应用先进高强钢是当今钢铁行业的改革趋势,也是汽车工业和桥梁工程领域共同关注的主题。开发先进高强钢及其在结构轻量化中的应用,正符合当代经济社会低碳、节能、安全、可持续发展的理念。而实现这该理念的三大关键技术是:高强钢种类的开发和应用、结构轻量化设计及优化和新型制造及成形工艺技术的创新。尽管高强钢的诸多优点在汽车工业和桥梁工程领域备受人们的青睐,但是高强钢不同于传统普碳钢,高强钢室温下强度高、成形困难、成形过程中力学行为和微观组织变化更加复杂,对成形设备及工艺提出了更高的要求,所以采用传统工艺制备高强钢辊压件难度很大或根本无法完成。为解决高强钢引入传统辊压工艺所带来的难题,本文提出了高强钢局部感应加热辊压成形技术。即在传统辊压变形前,对其塑性形变区感应加热到特定的温度,降低其成形抗力,提高其成形性能,保证变形后工件强度没有损失以及变形区无明显的硬化效应,从而克服高强钢引入辊压工艺所面临的难题。本文从感应加热基础理论、辊压成形机理和组织演化机制以及热辊压过程中的有限元算法方面系统地分析了高强钢局部加热辊压工艺特点;以汽车用高强钢方管和桥梁用新型UTU肋两个产品为例,进行了较全面的有限元模拟分析,明确了不同工艺参数对热辊压工艺的影响以及与传统成形工艺特点进行了对比;然后对这两个实例产品进行了装备开发和试验研究来阐述高强钢局部感应加热辊压成形工艺技术实际应用领域。通过对高强钢方管辊压工艺的有限元分析和试验研究,在温度场中方管获得了较为理想的温度分布,且自主设计的线型复合线圈很好满足了辊压工艺局部加热的需求。在对比的"直接成方"和"圆成方"工艺中,方管圆角处应力均超过1000 MPa;而在"方成方"热辊压工艺中,角部应力仅100 MPa左右,且截面形状尺寸精度更高,辊压成形力更小。在实验研究中,随着成形温度的升高,方管圆角处成形性能得到了明显改善;当成形温度为650 ℃时,方管角部冷作硬化效应明显减弱,方管压扁过程中也没有裂纹出现及其角部应力集中也获得了释放。通过微观组织观察,650 ℃成形时,圆角处的微观组织为由板条状贝氏体向粒状贝氏体发展,拉伸断口出现大量抛物线韧窝,说明在断裂前发生了明显的塑性形变。在对UTU肋热辊压成形数值模拟研究中,给出了两种孔型设计方案,分别从金属流动规律、截面形状尺寸和轧辊受力特点进行了对比。综合分析认为,"近终型"成形方案更合适辊压成形工艺;从不同工艺参数的模拟结果来看,当成形温度为900 ℃、单道次压下量为9 mm时,热辊压成形工艺结果相对较好。结合试验研究,与室温辊压成形的UTU肋相比,热辊压成形后的UTU肋抗疲劳性能大大提高;当辊压温度在900 ℃～1000 ℃之间,UTU肋端部力学性能得到一定程度上的改善,微观组织从初始粗大的铁素体-珠光体组织转变成等轴超细化晶粒且弥散分布的细小的贝氏体和渗碳体颗粒;随着温度的升高,(Nb,Ti)(C,N)析出物数量增加且分布地更加均匀,位错密度急剧下降;微观断口形貌出现大尺寸韧窝且伴随着小尺寸撕裂棱,这与UTU肋具有良好的强韧性能相互印证。
[Abstract]:With the global energy crisis, the design of safety performance of steel structure with increasing serious environmental pressures as well as industry, development and application of advanced high strength steel is the reform trend of the steel industry, is also a common concern of automobile industry and the field of bridge engineering subject. The development of advanced high strength steel and its application in lightweight structure, is in line with modern economy low carbon society, energy saving, safety, the concept of sustainable development and the realization of this idea. The three key technologies: the development and application of high strength steel types, innovative design and optimization of lightweight structure and new manufacturing and forming technology. Despite the many advantages of high strength steel has been popular in the field of automobile industry and bridge engineering, but different from the traditional carbon steel high strength steel, high strength steel high strength at room temperature, the difficulty of forming, forming mechanics behavior and microstructure change of more complex Put forward higher requirements for the equipment and the process of forming, so the traditional preparation process of high strength steel rolling parts is very difficult or impossible to complete. In order to solve the problem of high strength steel into the traditional rolling process caused by the proposed high strength steel induction heating roll forming technology. The traditional rolling deformation, the plastic deformation zone of induction heating to a certain temperature, reduce the forming resistance, improve the forming performance, ensure the workpiece strength without loss and no obvious deformation hardening effect, so as to overcome the problem of high strength steel by rolling faces. This paper from the basic theory of induction heating, roll forming finite element algorithm evolution mechanism and organization mechanism the hot rolling process and the systematic analysis of high strength steel, local heating and rolling process characteristics; to automotive high strength steel square and bridge with the new UTU two rib As an example, makes a comprehensive analysis of finite element simulation, the influence of different parameters on the hot rolling process and traditional forming process characteristics were compared; then the equipment development and Experimental Research on these two examples to explain the products of high strength steel induction heating roll forming technology application field. Through the finite element analysis of the pipe rolling process of high strength steel analysis and experimental research, in the temperature field in tube temperature distribution in the ideal, and the linear composite coil designed can meet the demand of heating and rolling department. In contrast to the "direct" and "self" in the process of square tube the fillet stress was more than 1000 MPa; and in the "prescription" hot rolling process, the stress in the corner is only about 100 MPa, and the cross section shape of high dimensional accuracy, rolling force smaller. In the experimental study, with the The forming temperature, tube fillet forming performance has been significantly improved; when the forming temperature is 650 degrees centigrade, square corner cold hardening effect significantly weakened, in the process of flattening square no cracks and corner stress concentration was also released. Through the microstructure observation, forming 650 DEG C, the microstructure of the fillet on the lath bainite to granular bainite tensile fracture development, the emergence of a large number of parabolic dimples, indicating the obvious plastic deformation before fracture. The UTU fin heat roll forming a numerical study on simulation, gives two kinds of design pass respectively from the laws of the metal flow. Section size and roll force characteristics were compared. The comprehensive analysis, near the end of "forming scheme more suitable roll forming process; simulation results from different process parameters, when the forming temperature is 900 DEG C, single pass The amount of pressure is 9 mm, hot rolling process results is relatively better. Based on experimental study, compared to the UTU rib and room temperature pressure forming roller, anti fatigue performance of UTU rib rolling after heat is greatly improved; when the rolling temperature is between 900 to 1000 DEG C, the end of the mechanical properties of the UTU get a rib the degree of improvement, the microstructure from the initial coarse ferrite and pearlite transformation into bainite and cementite particles of fine and ultra fine grain axial dispersion; with the increase of temperature (Nb, Ti) (C, N) the number of precipitation increases and the distribution is more uniform, dislocation the density decreased sharply; Microfractograph large size dimples and tear ridges with small size, the UTU rib has good strength and toughness properties confirm each other.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG306

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