BR1500HS高强度钢板高温流变模型研究

以高强度硼钢板BR1500HS为研究对象,在Gleeble1500热模拟试验机上进行高温热拉伸试验,对高强度钢板BR1500HS分别在500、600、700、800、900、1000℃,应变速率0.1、1、10 s-1时进行拉伸试验,获得了真应力-真应变曲线,根据理论分析及实验数据得到其高温流变模型。结果表明,所得流变模型可较好反映材料真实高温流变行为。     

高强钢B340LA与B1500HS钢激光拼焊板热冲压淬火性能

用质子光谱仪、光学显微镜、维氏硬度计等手段研究低合金高强钢B340LA与超高强硼钢B1500HS激光拼焊板焊接后的热冲压淬火特性。结果表明,拼焊板母材B340LA钢随着冷却速度的增加其相变点发生偏移,维氏硬度略有增加。拼焊板母材B1500HS钢随着冷速的增加硬度迅速提高。光学显微镜观察,当冷速超过30 K/s时母材B1500HS钢基本转化为马氏体组织。通过维氏硬度计测量,发现焊缝至母材过渡区硬度值平滑过渡,保证母材及焊缝力学性能良好的连续性。由于热冲压淬火后母材及焊缝区域显微硬度平滑过渡,应力应变分别更趋均匀,可显著提高低合金高强钢与超高强硼钢激光拼焊板拉深成形性。     

热冲压用硼钢B1500HS的高温热力学性能实验

采用Gleeble 3500热/力模拟实验机,对宝钢生产的冷轧硼钢B1500HS进行热冲压过程的模拟;通过不同的工艺参数,包括加热温度、保温时间和冷却速率对B1500HS试样最终力学性能的影响进行测试,提出了合理的工艺参数取值建议。获得了B1500HS在不同温度和不同应变速率下的流动应力曲线。结果表明,温度和应变速率对B1500HS高温流动性能有显著影响,并就其中的一些典型特点与22MnB5进行了对比。实验结果可为利用B1500HS开展热冲压生产与研究提供参考。     

热冲压用硼钢B1500HS高温非等温变形性能研究

由于非等温高温变形流程与实际的直接热冲压过程相似,利用Gleeble 3500热/力模拟试验平台,对硼钢B1500HS的高温非等温变形性能进行了研究,获得了B1500HS在不同变形温度和应变速率下的流动应力曲线。研究结果显示:硼钢B1500HS高温非等温变形时的峰值应力明显高于等温变形时的峰值应力。随着变形温度的升高和应变速率的减小,B1500HS的高温流动性能增强。当变形温度高于800℃时,材料成形时的加工硬化率降低,成形性较好;应变速率高于10 s-1时,材料成形时的加工硬化率也降低。     

硼钢B1500HS奥氏体状态下Arrhenius本构模型

在550~850℃内(温度间隔50℃),应变速率0.1、1.0、10 s~(-1)时使用Gleeble-1500D热模拟试验机对硼钢B1500HS试样进行了等温单向拉伸试验,并用试验得到的真应力-真应变数据研究Arrhenius方程,引入Zener-Hollomon参数建立流动应力模型。结果表明:该模型的计算结果与试验数据吻合度较好。     

热成形用硼钢热膨胀性能测试及应用

硼钢热冲压生产过程中投料的准确性和可靠性对生产效率有重要影响。采用自行研制的热膨胀实验装置,对B1500HS硼钢的热膨胀性能进行研究,使用Pamstamp模拟与实验相结合的方法获得B1500HS硼钢的热膨胀变化规律,准确预测B1500HS在加热膨胀后轮廓线的变化。结果表明:Pamstamp模拟的膨胀结果与实验结果非常接近,可以用于硼钢热膨胀模拟研究;板料膨胀后其纵向尺寸膨胀量大于宽度方向;板料内孔不仅形状发生改变,更为重要的是孔的中心位置产生较大变化。可以为板料定位装置的设计提供依据,提高生产过程中板料投放的准确性和工作效率,同时也能提高零件的制造精度与稳定性。     

热冲压钢B1500HS的淬后综合力学性能研究

通过开展单向拉伸试验、三点弯曲试验和夏比冲击试验,对硼钢B1500HS热冲压后的拉伸、弯曲、冲击韧性等综合力学性能进行了系统研究,并讨论了不同淬火速度对B1500HS综合力学性能的影响。结果表明:B1500HS热冲压后具有强度高、塑性较差的特点;当B1500HS在高于临界全马氏体转变的淬火冷速冷却时,淬火速度对B1500HS的综合力学性能仍有一定影响。淬火冷速越快,其抗拉强度越高,吸能性越好;但冷弯性能越差,延伸率越低。     

BR1500HS硼钢热冲压表面涂层研究

超高强度硼钢板热冲压是加热、冲压和淬火相结合的新型成形工艺。但是硼钢板在加热后容易生成氧化皮,耐腐性能降低,影响零件的使用性能。为了解决这个问题,研制了BR1500HS硼钢耐高温防氧化的保护涂层。并在加热950℃保温6 min的热冲压工艺条件下,分析了有无涂层试件的表面形态和组织变化。结果表明:该光滑涂层均匀覆盖在基体表面,对其无影响,满足硼钢板热冲压过程中的高温防氧化要求。     

不同间隙下硼钢板-模具界面换热系数的反演

确定不同条件下板料-模具界面的换热系数对控制硼钢板在热成形中的局部冷却速率、获得组织性能呈区域性分布的构件具有重要意义,还可为热成形过程精确数值仿真提供可靠的热边界条件。设计了简单、有效的实验装置以模拟硼钢板热成形中不同单边间隙下板料与模具间的传热状态,其中测温点处的温度变化仅与板料-模具界面换热系数相关,从而为界面换热系数的准确反演提供了保障。建立了界面换热系数的有限元优化模型,反演获得了不同间隙下B1500HS板与H13模具钢之间的换热系数,发现其随间隙的增大呈指数函数式减小,并对反演获得的界面换热系数进行了实验验证。     

基于Dynaform的SUV汽车B柱热冲压成形仿真分析与工艺研究

研究了采用B1500HS钢制成的某款SUV汽车B柱加强板的热冲压变形过程,利用中心差分法得到热冲压硼钢变形时单元体的温度公式,通过有限元模拟软件Dynaform建立B柱热-力-相耦合模型,研究B柱典型U形截面受力情况和温度场分布,同时分析B柱厚度、减薄率、屈服应力、硬度变化情况。有限元分析表明,B柱热冲压变形时,凸模圆角区和直壁区受到较大的拉应力及厚压应变的作用,易发生减薄。进行了B柱热冲压成形试验,结果表明,热冲压B柱的微观组织均为板条状马氏体,维氏硬度达到457 HV以上,屈服强度达到1200 MPa以上,满足热冲压零件淬火强化性能要求,验证了热冲压数值模拟的可靠性。     

FE Simulation Models for Hot Stamping an Automobile Component with Tailor-Welded High-Strength Steels

Ultra-high-strength in sheet metal parts can be achieved with hot stamping process. To improve the crash performance and save vehicle weight, it is necessary to produce components with tailored properties. The use of tailor-welded high-strength steel is a relatively new hot stamping process for saving weight and obtaining desired local stiffness and crash performance. The simulation of hot stamping boron steel, especially tailor-welded blanks (TWBs) stamping, is more complex and challenging. Information about thermal/mechanical properties of tools and sheet materials, heat transfer, and friction between the deforming material and the tools is required in detail. In this study, the boron-manganese steel B1500HS and high-strength low-alloy steel B340LA are tailor welded and hot stamped. In order to precisely simulate the hot stamping process, modeling and simulation of hot stamping tailor-welded high-strength steels, including phase transformation modeling, thermal modeling, and thermal-mechanical modeling, is investigated. Meanwhile, the welding zone of tailor-welded blanks should be sufficiently accurate to describe thermal, mechanical, and metallurgical parameters. FE simulation model using TWBs with the thickness combination of 1.6 mm boron steel and 1.2 mm low-alloy steel is established. In order to evaluate the mechanical properties of the hot stamped automotive component (mini b-pillar), hardness and microstructure at each region are investigated. The comparisons between simulated results and experimental observations show the reliability of thermo-mechanical and metallurgical modeling strategies of TWBs hot stamping process.     

超高强度钢热变形方程

热冲压成形工艺是将冲压成形工艺和淬火工艺集成在同一工序中进行的新型成形工艺。根据热冲压工艺的时间-温度特征,采用Gleeble3800热模拟系统,在温度600℃~900℃、应变速率0.01/s~0.5/s下,对热冲压钢板USIBOR1500进行热拉伸实验,获得了相应的应力-应变曲线。结果表明,USIBOR1500钢的热变形行为符合应变硬化加动态回复机制,变形温度和应变速率对其力学性能有很大的影响;计算了USIBOR1500钢的热变形激活能,并通过对变形激活能及Zener-Hollomon参数的研究,建立了超高强度硼钢热变形稳态流变应力模型和热变形方程,为估算成形时所需的最大载荷及设备选取提供参考。     

Fractional Cooling Strategy of the Hot-Stamping Process and Its Influence on Formability and Mechanical Properties of Ultra-High-Strength Steel Parts

The effects of forming temperature on the formability and product properties of hot-stamping boron steel B1500HS were investigated. Based on the fractional cooling strategy, boron steel sheets were heated to achieve full austenitization before they were removed from the furnace and cooled to the forming temperature using different cooling methods. Subsequently,they were simultaneously press-formed and quenched inside the tool until the martensitic transformation was finished. A series of thermal tensile tests were conducted to study the effects of forming temperatures on the stamping performance indices, including elongation, yield ratio, and hardening exponent. Then, the mechanical properties and microstructures of the hot-stamped products were characterized. Finally, an irregular part was formed using different fractional cooling strategies, while its formability and springback phenomena were discussed. The results show that using a fast-cooling method to reach 650 °C as the forming temperature optimizes the formability of the tested B1500HS boron steel. The best mechanical properties and smallest springback values were achieved using this optimal strategy.     

Hot deformation behavior of EA4T steel

The compressive deformation behavior of EA4T steel was investigated at temperatures ranging from 950 to 1150 C and strain rates from 0.1 to 20 s 1 on Gleeble-1500 thermo-simulation machine. The work hardening rate versus stress curves were used to determine the characteristic points of flow curves. The application of constitutive equations to determine the hot working constants of this material was discussed. Furthermore, the effect of Zener-Hollomon parameter (Z) on the characteristic points of flow curves was studied using the power law relation. The deformation activation energy of this steel was determined as 309.5 kJ/mol. Some behaviors were compared to other steels.     

超高强度钢热流变行为

热冲压成形工艺是将冲压成形工艺和淬火工艺集成在同一工序中进行的新型成形工艺。根据热冲压工艺的时间-温度特征,采用Gleeble3800热模拟系统,在温度600℃~800℃和应变速率0.01/s~0.5/s下,对热冲压钢板USIBOR1500进行热拉伸实验,获得了相应的应力-应变曲线,并利用最小二乘法进行多元线性回归,建立USI-BOR1500钢板的热变形抗力数学模型。结果表明,USIBOR1500钢的热变形行为符合应变硬化加动态回复机制,变形温度和应变速率对其力学性能有很大的影响,变形温度的影响更为强烈。在热变形情况下,USIBOR1500钢板的抗拉强度大幅下降。建立的数学模型与实验数据吻合较好。     

高强度硼钢22MnB5的热变形方程及其模拟应用

利用Gleeble-3500热模拟试验机,在温度为700℃～950℃、应变速率为0.01/s～0.4/s的条件下,对高强度硼钢22MnB5的热变形行为进行研究。结果表明,随着变形温度的升高,硼钢的延伸率升高,变形抗力降低;随着应变速率的提高,硼钢22MnB5的变形抗力和延伸率增大。根据高温拉伸实验得出的数据,构建硼钢22MnB5的稳态流变应力模型和热变形方程,并将试验结果和构建的本构方程输入ABAQUS软件进行U型件热弯曲成形的回弹模拟,数值模拟结果与实验结果吻合较好,验证了模型的可靠性和正确性,为成形所需的最大载荷及设备选择提供依据。     

Influence of Vanadium Content on Hot Deformation Behavior of Low-Carbon Boron Microalloyed Steel

Single-pass compression tests were performed to investigate the hot deformation behavior of low-carbon boron microalloyed steel containing three various vanadium contents at 900-1100℃ and strain rate of 0.01-10 s~(-1) using the MMS-300 thermal mechanical simulator.The flow stress curves of investigated steels were obtained under the different deformation conditions,and the effects of the deformation temperature and strain rate on the flow stress were discussed.The characteristic points of flow stress were obtained from the stress dependence of strain hardening rate;the activation energy of investigated steels was determined by the regression analysis;the flow stress constitutive equations were developed;the effect of vanadium content on the flow stress and dynamic recrystallization(DRX) was investigated.The result showed that the flow stress and activation energy(3-6.5 kJ mol~(-1)) of the steel containing 0.18 wt% V were significantly higher than those of the steels with0.042 wt% and 0.086 wt% V,which was related to the increase in solute drag and precipitation effects for higher vanadium content.DRX analysis showed that the addition of vanadium can delay the initiation and the rate of DRX.     

B1500HS高强钢连续轧制变截面板的高温本构关系

为了研究B1500HS高强钢连续轧制变截面板热冲压时的流变力学行为,采用Gleeble-3500热拉伸机,对厚度在1.2~1.7 mm、初始温度在650~850℃的试样,分别以0.2,0.5,2和5 s~(-1)的应变速率进行单向等温拉伸试验,经过测量和计算得到高温下材料的应力-应变试验曲线。然后研究不同板料厚度、热拉伸初始温度以及应变速率对高温下材料的流变应力的影响规律,基于热成形过程材料的加工硬化-动态软化这一特点,建立了加入厚度修正因子的Norton-Hoff本构关系,并通过拟合试验数据求取了本构关系的相关系数。最后将建立的本构关系模型预测应力值与试验结果进行线性回归分析,评估两者之间的线性相关系数、均方根误差和平均相对误差。结果表明,修正的Norton-Hoff本构关系与试验结果吻合较好。     

基于Kriging模型的超高强度钢板热冲压工艺参数优化

为了改善超高强度钢板冲压件的加工质量,以某方形槽热冲压件为对象,以板料淬火温度、模具初始温度、冲压速度和模具间隙为设计变量,以冲压件成形温降、回弹量和成形减薄率3个质量指标为响应量,构建了热冲压加工质量指标的Kriging模型。在此基础上,以构建的Kriging模型为目标函数,建立超高强度钢板热冲压工艺参数多目标优化模型。应用第二代非支配遗传算法进行寻优计算,获得了优化的热冲压工艺参数:B1500HS超高强度钢板零件热冲压的最佳淬火温度为898.3℃,模具的初始温度为67.1℃,冲压速度为39.64 mm·s-1,模具间隙为2.2 mm。工艺参数优化后的验算结果表明,工艺参数优化后,成形温度更加均匀,回弹量减少25.6%,最大减薄率下降23%。     

Prediction of Forming Limit Diagrams for 22MnB5 in Hot Stamping Process

Hot stamping of ultra-high strength steels possesses many superior characteristics over conventional room temperature forming process and is fairly attractive in improving strength and reducing weight of vehicle body product. However, the mechanical and failure behavior of hot stamping boron steel 22MnB5 are both strongly affected by strain hardening, temperature, strain rate, and microstructure. In this paper, the material yield and flow behavior of 22MnB5 within the temperature and strain rate range of hot stamping are described by an advanced anisotropic yield criterion combined with two different hardening laws. The elevated temperature forming limit diagram (ET-FLD) is constructed using the M-K theoretical analysis. The developed model was validated by comparing our predicted result with experimental data in the literature under isothermal conditions. Based on the verified model, the influence of temperature and strain rate on the forming limit curve for 22MnB5 steel under equilibrium isothermal condition are discussed. Furthermore, the transient forming limit diagram is developed by performing a transient forming process simulation under non-isothermal transient condition.