The test device for heat friction coefficient of high strength steel

Using high strength steel and ultra-high strength steel in hot stamping and automobile parts is one of the most important ways of the automobile lightweight,which is the development trend of automobiles currently.In this paper, the development of test device for heat friction coefficient by high strength steel can provide important technical parameters for hot stamping process,making the right selection of equipment types,mold design,technology optimization,and research and development of lubrication medium of press forming.At the same time,the experiments indicate that the instrument has not only accurate test result but also good repeatability.     

高强度钢板热成形性预测研究进展

高强度钢板热冲压成形是实现车身轻量化、保证安全性的重要途径,近年来得到汽车和钢铁工业的广泛关注与应用。由于高温工况的引入,高强度钢板的力学行为表现出明显的应变率和温度相关性,为准确评价板料的热成形性带来了挑战。概述了热冲压技术的工艺特点,从热成形极限实验和理论预测两方面展开讨论,介绍了国内外学者的相关研究工作,分析了应变成形极限方法存在的不足,引出了基于损伤力学理论的板材成形性评价方法,分别介绍了连续介质损伤和细观损伤理论在板材成形性方面的若干研究,以及材料损伤参数的识别方法。结合热冲压技术的工艺特点,指出热冲压高强度钢的损伤研究应采用实验、理论及数值仿真相结合的方式,并充分考虑温度、加载速率以及应力状态对损伤演化的影响。本研究可为完善损伤理论在金属板材热冲压中的应用提供借鉴。     

超高强度硼钢B1500HS的热冲压工艺试验

摘要： 研究了奥氏体化加热温度和保温时间对厚1.8 mm的冷轧硼钢B1500HS的淬火组织、原奥氏体晶粒尺寸和力学性能的影响,制定了B1500HS钢的奥氏体化加热规程,并采用带冷却流道的V型弯曲模具进行了B1500HS钢的热冲压和纯马氏体钢M1200的冷冲压对比试验.结果表明：B1500H钢的热冲压成形零件强度高达1.530 GPa,其型面精度较高且基本无回弹;而M1200钢冷冲压成形所需最大成形力约为750 kN,是热冲压成形所需最大成形力的2倍,且出现了明显的回弹现象,回弹角约为9°.     

火车用C级钢的高温流动应力

C级钢因其优越的机械性能而广泛应用于火车车轮、车钩等重要零部件上。该材料零部件通常经热锻成形,因此对该材料在高温下的流动应力进行研究具有重要意义。该文采用Gleeble热力学模拟机对C级钢在温度为1 050～1 250℃、应变速率为0.01～10 s-1条件下的流动应力进行测试,获得C级钢的流动应力数据以及C级钢在不同热变形条件下的峰值及稳态流动应力。实验结果预测了C级钢存在动态再结晶现象,得到了变形温度、应变速率和变形程度对C级钢流变应力的影响规律。基于Sellers-Tegart方程拟合本构参数,包括应力水平参数、应力指数、变形激活能和结构因子,建立了C级钢的本构关系式,可作为C级钢零部件热成形加工工艺选择和参数确定的依据,同时也可作为C级钢零部件锻造工艺数值模拟的基础数据。     

Optimization of yield criterion and simulation based on QP980 high strength steel

QP980 is an ultra high strength steel. First, uniaxial and biaxial tension tests have been done in different loading paths. Then QP980 basic mechanical properties have been obtained. And the stress and strain graph has been drawn. Second, according to the equal principle of the unit volume plastics work and yield stress, QP980 plastic work contour map has been drawn. Third, through comparing Mises, Hill'48, Hosford and Barlat89 yield criterion theoretical curves with the experimental plastic work contour map, the result shows that the Hill'48 yield criterion is in good conformity with the QP980 material. Fourth, Hill'48 yield criterion is optimized by introducing an equivalent plastic strain parameter. The result shows that average error of optimized Hill'48 theoretical yield trajectory is reduced by 8.4%. Last, finite element model about variable cross-section roll forming is established, then applying the optimized Hill'48 parameter yield criterion to the ABAQUS for finite element simulation. The simulation result shows that the forming quality is good, and in agreement with the actual forming parts. Therefore, the optimized Hill'48 yield criterion can be used to precisely describe QP980 ultra high strength steel.     

齿轮钢SAE8620 H高温变形行为及热加工图

通过高温压缩试验研究齿轮钢SAE8620H在950~1100℃、应变速率0．01~10 s-1条件下的高温变形行为.该合金钢的流动应力符合稳态流变特征,流变应力随变形温度升高以及应变速率降低而减小,其本构方程可以采用双曲正弦方程来描述.基于峰值应力、应变速率和温度相关数据推导出SAE8620H高温变形激活能Q=280359．9 J·mol-1.根据变形量40%和60%下应力构建该齿轮钢的热加工图,通过热加工图中耗散值及流变失稳区确定其热变形工艺参数范围. SAE8620H钢在在变形程度较小时宜选取低的应变速率进行成形,而在变形程度大时则要选取低温低应变速率或者高温高应变速率.     

Medium-Mn steels for hot forming application in the automotive industry

Advanced high-strength steels have been widely used to improve the crashworthiness and lightweight of vehicles.Different from the popular cold stamping,hot forming of boron-alloyed manganese steels,such as 22MnB5,could produce ultra-high-strength steel parts without springback and with accurate control of dimensions.Moreover,hot-formed medium-Mn steels could have many advantages,including better mechanical properties and lower production cost,over hot-formed 22MnB5.This paper reviews the hot forming process in the automotive industry,hot-formed steel grades,and medium-Mn steel grades and their application in hot forming in depth.In particular,the adaptabilities of medium-Mn steels and the presently popular 22MnB5 into hot forming were compared thoroughly.Future research should focus on the technological issues encountered in hot forming of medium-Mn steels to promote their commercialization.     

Medium-Mn steels for hot forming application in the automotive industry

Advanced high-strength steels have been widely used to improve the crashworthiness and lightweight of vehicles. Different from the popular cold stamping, hot forming of boron-alloyed manganese steels, such as 22MnB5, could produce ultra-high-strength steel parts without springback and with accurate control of dimensions. Moreover, hot-formed medium-Mn steels could have many advantages, including better mechanical properties and lower production cost, over hot-formed 22MnB5. This paper reviews the hot forming process in the automotive industry, hot-formed steel grades, and medium-Mn steel grades and their application in hot forming in depth. In particular, the adaptabilities of medium-Mn steels and the presently popular 22MnB5 into hot forming were compared thoroughly. Future research should focus on the technological issues encountered in hot forming of medium-Mn steels to promote their commercialization.     

Effect of hot stamping parameters on the mechanical properties and microstructure of cold-rolled 22MnB5 steel strips

Thermomechanical experiments were carried out to reproduce the hot stamping process and to investigate the effects of process parameters on the microstructure and mechanical properties of stamped parts. The process parameters, such as austenitizing temperature, soaking time, initial deformation temperature and cooling rate, are studied. The resulting microstructures of specimens were observed and analyzed. To evaluate the mechanical properties of specimens, tensile and hardness tests were also performed at room temperature. The optimum parameters to achieve the highest tensile strength and the desired microstructure were acquired by comparing and analyzing the results. It is indicated that hot deformation changes the transformation characteristics of 22MnB5 steel. Austenite deformation promotes the austenite-to-ferrite transformation and elevates the critical cooling rate to induce a fully martensitic transformation.     

Numerical simulation of hot stamping of side impact beam

Ls-DYNA software is adopted to conduct research of numerical simulation on hot stamping of side impact beam to calculate the temperature field distribution,stress field distribution,forming limit diagram(FLD) figure,etc.in the course of hot stamping so as to predict and analyze the formability of parts.ProCAST software is employed to conduct research of numerical simulation on solid quenching course concerning hot stamping to calculate temperature field distribution of tools and component of multiple stamping cycles.The results obtained from numerical simulation can provide significant reference value to hot stamping part design,formability predication and tools cooling system design.     

抛物面形零件冲压成形悬空侧壁圆锥台变形区的应力应变计算

应力和应变的分布情况可以反映出零件在成形过程中的变形特点,它是研究零件冲压成形的基础.采用主应力法推导出了冲压成形过程中旋转抛物面形零件悬空侧壁圆锥台变形区的应力和应变计算公式,以材料为SS304不锈钢的抛物面形零件为算例,得出其应力和应变分布趋势.另外,还计算出了抛物面形零件冲压成形时的应力分界圆直径和应变分界圆直径,其中,应变分界圆直径的计算结果与已有实验数据一致.通过对旋转抛物面形零件冲压成形过程中悬空侧壁圆锥台变形区应力和应变分布的研究,明确零件的成形过程和变形特点,为其冲压成形时内皱曲极限的预报与控制奠定了基础.     

高强度钢板热塑性行为及在车身轻量化中的应用

为深入研究板材热塑性变形机理以及促进热成形工艺在汽车结构件生产制造中的应用,采用理论、试验与仿真相结合的方式,基于高强度钢板热-力-相变耦合本构关系,结合弹塑性非线性大变形分析建立了热塑性成形动力显式有限元列式,开发了高强度钢板热成形数值仿真有限元分析软件,对一款U型试件的热成形过程进行数值模拟,模拟结果与试验一致,且通过拉伸试验获得了成形后零件的力学性能,屈服极限在1 100 MPa以上,强度极限可达1 500 MPa以上. 并通过数值仿真对比一款热成形前保险杠与原始冷成形保险杠的碰撞过程,得出保险杠采用热成形件可减重36.5%,比吸能比原始模型增加16.0%.     

超高强度钢防撞梁热成形改冷冲压工艺设计及优化

安装在车门内的防撞梁是提高轿车侧碰撞安全性的关键部件,国外高安全性轿车都采用超高强度钢板制造防撞梁,但超高强度钢板成形困难,普遍采用成本高的加热成形方法。笔者介绍了采用有限元分析软件Dynaform对某高级进口型轿车超高强度钢防撞梁热成形改冷冲压工艺过程进行模拟仿真,并优化成形工艺,主要研究了温度对超高强度板内部组织变化起的作用。通过模拟和实际对比研究工艺补充面对零件成形及回弹的影响,并设置凸顶得到了优化的工艺型面,为同类相关高强度钢零件的生产起到了指导作用。     

多工位级进冲压全工序数值模拟关键技术研究

综合运用UG、HyperMesh和Dynaform建立了某高强钢板汽车安装座件的13工位级进冲压全工序数值模拟排样条料模型,采用多工位多工序级进冲压法对冲压成形全工序进行了有限元数值模拟,并对关键的第三、四工位的正、反拉深进行了详细分析,通过对毛坯及凸包形状进行修正后重新建模获得了理想的模拟结果,据此设计制造出了该零件的13工位级进冲模,成功冲制出了左右对称的一套两件的某汽车安装座零件,成形质量经过检具检测满足使用要求,现该级进模已投入批量生产.     

虚拟仪器的超高强混凝土结构性能测试

虚拟仪器技术在工程结构测试中的应用越来越广泛,结合预应力混凝土结构性能研究平台,以LabVIEW为平台设计了载荷、挠度、钢筋应变、混凝土应变的实时测试系统,并阐述了基于虚拟仪器的测试系统的硬件组成、数据采集和程序框图设计。基于该测试系统,对超高性能混凝土———混凝土界面性能、超高强预应力混凝土结构性能进行了测试。结果表明,基于LabVIEW编程的虚拟仪器测试表现出精度高、性价比高、界面友好、智能化的优势,特别是能够实时观测,避免了传统测试方法中的数据后处理,是混凝土结构试验的理想选择。     

Comparative analysis by simulating and testing pole impact for hot stamping front crossbeam of automobile

Hot stamping 22MnB5 steel plate with ultra-high strength has been widely used for body structural members in consideration of automobile safety and lightweight.This paper presents a verification program of simulating and testing pole impact in order to verify if the front crossbeam reinforcement assembly can meet the design requirements,reduce the overall vehicle simulation and test cost and shorten the operation period.In the same condition,the simulation proved conforming to the design requirements;however,the bumper cracked at the impacting point in the course of pole impact test.The analysis of the crack by optical microscope,Vickers and scanning electron microscope indicates that mixture of ferrite,bainite and martensite was produced in the weld heat-affected zone of the 340/590DP tow hook holder and the 22MnB5 front crossbeam;therefore,their hardness and mechanical property were reduced obviously,so that they fractured when impacted.No welding process with continuous weld but spot welding or other bonding method may be employed for the reason that the capacity of the 22MnB5 steel plate in the weld heat-affected zone was reduced obviously.     

全载体车身结构件级进冲压成形排样设计

为复杂构形的车身结构件级进冲压成形排样设计提供参考,以全载体形式车身结构件为例,首先提出排样存在的主要设计问题,明确了设计任务;然后分析了制件的级进冲压成形工艺,设计了制件的排样图;最后通过实冲试验验证了排样工艺的合理性。试验所获产品零件无开裂、起皱等成形性问题,且关键成形部位达到了零件图的形位精度设计要求。     

Ti微合金化Q390高强钢热变形行为研究

通过单道次压缩实验,研究了屈服强度390 MPa级Ti微合金化高强钢的热变形行为,并建立了实验钢的变形抗力模型和动态再结晶数学模型.结果表明:随着变形温度的降低,变形抗力逐渐增大;随着应变速率的增大,应力-应变曲线由动态再结晶型转变为动态回复型.Q390钢的动态再结晶激活能为257.142 k J/mol.建立的高精度的数学模型可表征Ti微合金化Q390钢的高温变形行为.与常规成分体系相比,Ti微合金化成分设计的实验钢轧制时所需的轧制力较小,更容易发生动态再结晶,有利于奥氏体晶粒的细化,可有效地提高钢材强韧性.     

CSP热连轧再结晶临界应变模型研究

通过THERMOMASTER-Z型热／力模拟试验机对CSP生产线上冷轧冲压基板（SPHD）进行了热变形实验，建立了该钢种的临界应变模型以及流动应力-应变模型；分析了试验过程中工艺参数对临界应变、流动应力的影响。结果表明，变形温度、变形速率是影响临界应变的主要因素，当热变形达到临界应变时，将发生动态再结晶，同时造成变形抗力的波动。     

汽车内板用冷热冲压薄板成形性对比

因生产工艺不同,薄板坯连铸连轧所生产的0.8～3.o mm的热轧产品与待统冲压用冷轧产品存在着一定的差异.从材料的化学成分、力学性能、扩孔性能等方面与冷轧冲压薄板进行对比研究.研究结果表明,两种材料化学成分相近,热轧SPHE薄板因屈服强度过高,r值过小,致使成形性低于冷轧产品.与汽车用冲压材料要求对比结果表明,SPHE板满足汽车用板冲压要求,可在汽车内板采用热轧材料进行“以热代冷”冲压生产.