Integrated Modelling of Microstructure Evolution and Mechanical Properties Prediction for Q&P Hot Stamping Process of Ultra‑High Strength Steel

High strength steel products with good ductility can be produced via Q&P hot stamping process,while the phase transformation of the process is more complicated than common hot stamping since two-step quenching and one-step carbon partitioning processes are involved.In this study,an integrated model of microstructure evolution relating to Q&P hot stamping was presented with a persuasively predicted results of mechanical properties.The transformation of diffusional phase and non-diffusional phase,including original austenite grain size individually,were considered,as well as the carbon partitioning process which affects the secondary martensite transformation temperature and the subsequent phase transformations.Afterwards,the mechanical properties including hardness,strength,and elongation were calculated through a series of theoretical and empirical models in accordance with phase contents.Especially,a modified elongation prediction model was generated ultimately with higher accuracy than the existed Mileiko’s model.In the end,the unified model was applied to simulate the Q&P hot stamping process of a U-cup part based on the finite element software LS-DYNA,where the calculated outputs were coincident with the measured consequences.

Research status and progress of hot stamping

In this article,current application,materials,key equipments,finite element(FE) simulation and parts properties of hot stamping are introduced.The investigations of all processes and further excellent processes are described.The survey of existing works,especially key equipments has revealed several gaps.Some new ideas and programs are proposed on the basis of traditional process.This article aims at providing an insight into a whole process backgrounds and pointing out the great potential for further investigations and innovations of hot stamping.

Microstructure Evolution and Simulation in 22MnB5 Steel during Hot Stamping

Hot stamping components with 1500 MPa ultra-high strength are obtained by press hardening during hot stamping, and the properties depend on the microstructures. It is very important that the microstructure evolution rule is found out during hot stamping process. To characterize the microstructure evolution during hot stamping, a method combining finite element and experiment is carried out. Samples were heated to 950°C and held for 300 second at a induction heating furnace, then taken out from the furnace and stayed in the air at different time (7 s, 11 s, 13 s, 22 s), respectively, finally the specimens were formed and quenched at a die. Microstructural observation as well as surface hardness profiling of formed specimens was performed. And the numerical simulation to predict the austenite transformation into ferrite, pearlite, bainite, and martensite and the volume fraction of each phase during the hot stamping process was made with ABAQUS software. The results show that the ferrite is observed when the specimen stays in the air for 22 s, and the temperature drops to 325°C when the dwell time increases from 7 s to 22 s. The results of numerical simulation and experimental results are in good agreement. So the method finite element can be used to guide the optimization of hot stamping process parameters.

热成形钢22MnB5的Q&P工艺

采用盐浴法对热成形钢22MnB5进行了Q&P工艺(quenching and partitioningprocess)处理,研究了淬火终点温度、分配温度和分配时间对试验钢的显微组织、力学性能和残余奥氏体含量的影响。结果表明:Q&P工艺处理22MnB5钢的显微组织主要为马氏体和残余奥氏体组织,同时有一定量的碳化物析出,随着淬火终点温度和分配温度的升高或分配时间的延长,马氏体和碳化物的微观形貌会发生变化;在淬火终点温度和分配温度为325℃,分配时间为60s时得到的试样强塑积最高,达到20435MPa.%;试样的拉伸断口都显示出良好的韧性断裂特征;XRD分析表明,在Q&P工艺处理后试验钢的残余奥氏体含量可达5.5%。

Low‑Carbon‑Emission Hot Stamping:A Review from the Perspectives of Steel Grade,Heating Process,and Part Design

Hot stamping steels have become a crucial strategy for achieving lightweighting and enhancing crash safety in the automo-tive industry over the past two decades.However,the carbon emissions of the materials and their related stamping processes have been frequently overlooked.It is essential to consider these emissions during the design stage.Emerging materials and technologies in hot stamping pose challenges to the automotive industry's future development in carbon emission reduc-tion.This review discusses the promising materials for future application and their special features,as well as the emerging manufacturing and part design processes that have extended the limit of application for new materials.Advanced heating processes and corresponding equipment have been proven to improve heating efficiency and control temperature uniformity.The material utilization and the overall performance of the components are improved by tailored blanks and an integrated part design approach.To achieve low-carbon-emission(LCE)hot stamping,it is necessary to systematically consider the steel grade,heating process,and part design,rather than solely focusing on reducing carbon emissions during the manufacturing process stage.This review aims to present the latest progress in steel grade,heating process,and part design of hot stamping in the automotive industry,providing solutions for LCE from a holistic perspective.

Improvement of Mechanical Properties of Automotive Components Using Hot Stamping With Integrated Q-P Process

Cold forming of high strength materials is accompanied by an undesirable spring-back effect and therefore the automotive industry prefers to produce components from high strength steels by hot stamping.Hot deformation and cooling in a die are applied to obtain shaped components with martensitic microstructure and high yield strength and ultimate tensile strength.This article presents new applications of this forming technology by incorporating another innovative heat treatment by the Q-P process,which improves both strength and ductility of obtained structures at the same time.Ultimate strengths over 2000 MPa with ductility above 10% can be achieved by this processing.To test microstructure development,thin sheet was hot formed and a corresponding FEM simulation was created.This processing was applied to low alloyed AHS steel with 0.42% of carbon and with an alloying strategy based on Mn,Si and Cr.Martensitic microstructure with retained austenite was obtained by this processing with a strength of around 2000 MPa and ductility of 10%.

大面积微结构辊对板热压印装置研发及工艺优化

目的研发一种模块化辊筒对平板类型的微结构热压加工装置,研究不同模具结构下的辊压工艺参数对光学聚合物微结构成形的影响,研究大尺寸的PMMA样品的翘曲规律。方法使用一种基于线接触的扫描连续辊压工艺,分别使用线槽模具、不锈钢网孔模具进行辊压实验,根据实验结果确定最佳工艺参数范围。结果在辊筒温度为150~180℃、平板温度为25℃、辊压压力为200~500 N和辊压速度为1 mm/s的工艺条件下,甲基丙烯酸甲酯平板(PMMA)微槽阵列的线槽宽复制度最高可达90%,微圆柱结构在40 mm×40 mm PMMA衬底的覆盖率高达95%。结论优化辊压工艺参数后,可以实现聚合物的大面积槽阵列和圆孔微透镜的稳定连续辊压成形。针对大面积光学聚合物翘曲的问题,进行了双面热辊压实验,发现二次成形后微透镜样品的最大高度偏差小于0.16 mm,翘曲现象得到了有效抑制。

摩擦因数对超薄316L不锈钢双极板热冲压数值模拟的影响

构建了一个高温摩擦实验装置,用于测量厚度仅为0.1 mm的超薄316L不锈钢双极板在5种不同温度下的名义摩擦因数。实验结果表明,在200℃时,超薄不锈钢板的名义摩擦因数为1.05,远高于室温条件下的摩擦因数(0.29)。基于摩擦因数随温度变化的实验结果,建立了双极板热冲压过程的有限元模型,并利用温度相关摩擦因数模拟了0.1 mm厚316L不锈钢双极板在热冲压成形后的微流道厚度分布。结果显示,相比于使用恒定摩擦因数的模型,采用摩擦因数随温度变化的有限元模型可以更准确地预测微流道截面的厚度分布,其预测准确性提高了192%。

Microstructure and performance evaluations on Q&P hot stamping parts of several UHSS sheet metals

Hot stamping(press hardening) is widely used to fabricate safety components such as door beams and B pillars with increased strength via quenching. However, parts that are hot-stamped from ultra-high-strength steel(UHSS) have very limited elongation,i.e., low ductility. In the present study, a novel variant of hot stamping technology called quenching-and-partitioning(Q&P) hot stamping was developed. This approach was tested on several UHSS sheet metals, and it was confirmed that this method can be used to overcome the drawbacks associated with conventional hot stamping. The applicability of Q&P hot stamping to each of these steels was also assessed. The part properties and performances of three widely used ultra-high-strength sheet metals, B1500 HS,27 SiMn, and TRIP780, were evaluated through tensile testing and microstructural observations. The results demonstrated that the ductility of Q&P hot-stamped sheet metals was notably higher than that of the conventionally hot-stamped parts because Q&P hot stamping gives rise to a dual-phase structure of both martensite and austenite. Further, material tests demonstrated that the Q&P treatment had positive effects on all three selected materials, of which TRIP780 had the best ductility and the highest value of the product of strength and plasticity. Scanning electron microscopy images indicated that the silicon in the steels could limit the formation of cementite and would, therefore, improve the mechanical properties of Q&P hot-stamped products.

PET柱镜光栅材料的转印适性研究

目的通过对PET柱镜光栅的表面改性,并调整印刷参数和烫金参数,改良PET柱镜光栅材料转印质量。方法通过调整PET-UV水晶油墨厚度、UV光固化机传送速度,以及烫金技术上的烫印速度、烫金压力及电热温度,用实验对比总结出最佳的工艺参数。结果在室内温度为18~25℃,丝网印刷压力为22 N/cm^2,PET-UV水晶油墨厚度为35μm,UV光固化机传送速度为10~30 m/min,烫印速度为0.6 s/张,烫金压力为42 N/cm^2,电热温度为180℃条件下,水晶油墨的附着力牢度、定位烫印效果最理想。结论该工艺条件下PET柱镜光栅凹槽表面达到的转印效果最好,全息定位电化铝具有的立体触摸感与柱镜光栅虚拟的立体图像有机结合在一起,取得了很好的应用效果。

低成本600 MPa级热冲压桥壳用钢的开发

通过低碳当量和Nb、V复合微合金化成分体系设计,采用高洁净钢冶炼工艺、高品质铸坯生产技术和控轧控冷工艺,成功以短流程开发出12~16 mm厚度600 MPa级桥壳钢。其微观组织为铁素体+珠光体,晶粒度达到12.0~13.0级,带状组织为1.5级,满足了钢板加工成型性、焊接性能等工艺要求。

基于热加工图和NURBS曲线的伺服热冲压工艺设计

考虑热冲压成形过程中工艺流程和材料变形行为的复杂性以及温度分布的时变性,提出一种基于热加工图和NURBS曲线的伺服热冲压工艺设计。以常用B1500HS热成形试样为研究对象,通过高温拉伸实验测得了不同热变形参数下B1500HS硼钢的真应力-真应变曲线,基于DMM原理构建了不同应变量下的B1500HS硼钢热加工图,计算了该材料在伺服热冲压过程中成形阶段最优速度和温度区间。根据典型热冲压模式的各阶段工艺特征和NURBS曲线数学模型,规划和建立了符合各约束条件的伺服热冲压工艺曲线,实现了对伺服热冲压工艺曲线的设计。借助CAE分析软件,开展了汽车中立柱伺服热冲压对比仿真实验。综合分析表明,与常规热冲压工艺相比,采用所提出的伺服热冲压工艺曲线模型成形时中立柱样件应力和温度分布更均匀,最大减薄率降低约8.5%,最大起皱度为4.002×10-3,主应变降低约12.5%,表明所提出的伺服热冲压工艺对危险位置破裂趋势有明显的抑制作用。

热烫印制品耐温水性失效分析及工艺优化

热烫印工艺是一种常见的表面处理技术,它通过将热敏箔或热熔胶与印刷材料结合,利用热力和压力将图案转移至基材表面。然而,在实际应用中,热烫印产品耐温水性差的问题突出。文章对热烫印耐温水性失效进行原因分析,发现热烫印原材料性能、热烫印硬件和热烫印工艺三个方面可能存在问题,故从这些方面提出了热烫印耐温水性的改善方案,经验证满足了性能要求。

热冲压模具钢激光熔覆Stellite6钴基粉末的工艺研究

利用激光熔覆技术改善热冲压模具的表面性能,在H13热作模具钢表面熔覆Stellite6钴基合金粉末,进行一定范围内的梯度数值的工艺参数单道和多道熔覆工艺研究。研究了工艺参数对钴基熔覆层的高度、宽度、熔深和稀释率的影响。采用金相显微观察、硬度测试和XRD检测分析方法,研究了Stellite6钴基合金熔覆层的组织、硬度和物相组成。结果表明:在激光输出功率1200 W、扫描速度500 mm/min、送粉速率12 g/min、搭接率40%的激光熔覆工艺下,可得到理想几何形貌、组织细化、硬度较高的熔覆层。熔覆层主要物相是γ-Co和高硬度硬化碳化物组成,显微硬度较基体有了较大提高,表明激光熔覆Stellite6合金能有效改善H13钢的表面性能。

Effects of quenching and partitioning process on mechanical properties of TRIP780 steel

A transformation-induced plasticity (TRIP) steel was applied to test its mechanical properties in quenching and partitioning (Q&P) process. A series of Q&P experiments followed by tensile tests, Charpy impact tests, fracture morphology analyses and microstructure observations were conducted. The experimental results showed that the Q&P treatment could increase the mechanical properties of TRIP steel evidently. The strength of tested TRIP780 after Q&P process reaches more than 1500 MPa with elongation of 17.8%, which is obviously greater than that of 22MnB5 after hot stamping. The microstructure observations indicate that the good combination of high strength and plasticity of TRIP steel after Q&P process is attributed to the multi-phase microstructure of hard martensite matrix and soft retained austenite.

汽车B柱内板热冲压成形工艺优化的模拟分析

针对某品牌汽车B柱内板的成形工艺问题,研究了零件22MnB5高强度钢的热冲压成形参数对成形质量的影响,以最大减薄率、最大增厚率和最大回弹量为评价目标,通过正交实验和极差分析,获得零件热冲压成形的最优工艺参数,并完成最优工艺参数的成形仿真和回弹分析,仿真结果表明零件的厚度分布均匀,零件最大减薄率为10.1%,最大增厚率为7.1%,零件的回弹量小,最大回弹量为0.714 mm,该零件成形质量符合设计要求,表明了该零件热冲压成形优化方案的可行性。

热冲压工艺参数对超高强热成形钢组织及性能的影响

本文结合工业生产实际,采用光学显微镜与维氏硬度计,研究加热温度、保温时间和合模温度对超高强热成形钢组织及性能的影响。结果表明:当保温时间为3 min时,加热温度对试验钢性能影响较大,随着加热温度的升高,马氏体转变量不断增加,同时马氏体板条长度及束条宽度不断增大,试验钢的硬度也不断增加。当加热温度为900℃、保温时间为4 min时,合模温度在650~730℃范围内,组织均为马氏体+铁素体,随着合模温度的升高,铁素体的含量逐渐减少,马氏体含量逐渐增加,试验钢的硬度大幅增加。

浅谈汽车一体式门环热冲压成形工艺技术

分别从零部件造型设计特征、斜度、圆角方面,探讨零件结构工艺性设计合理性;从工艺形面构建及设置方面,提出其工艺面设计的注意事项;从激光落料排样阐述了坯料设计解决材料利用率低的问题;从计算机辅助工程仿真过程阐述了热冲压成形性分析涉及的开发风险与管控。从以上4方面探讨一体式门环开发过程涉及的热冲压成形工艺技术,为一体式门环工艺技术开发提供了借鉴经验,以便解决开发过程中存在的相关问题,同时也能更好地降低开发成本及缩短开发周期。

可淬火硼钢板热冲压成形实验研究

为研究淬火加热温度、保温时间及冷却水流速等热冲压工艺参数对热冲压零件力学性能及微观组织的影响规律,通过在不同工艺参数条件下进行弯曲件热冲压工艺试验,测量弯曲件的力学性能并观察其金相组织.结果表明,在所设计的模具上可实现高强硼钢热成形零件的有效淬火,热冲压弯曲件的抗拉强度可达到1500MPa以上,主要形成均匀细小的马氏体组织.确定了热冲压工艺参数的选择范围.

超高强钢热成形奥氏体化加热参数的优化

以汽车用高强钢22MnB5为研究对象,采用金相显微镜、激光共焦扫描显微镜、洛氏硬度仪等分析手段对热成形中加热参数进行研究。结果表明:对于2mm厚的22MnB5板材在热成形过程中,奥氏体化最佳的加热温度为950℃,保温时间为5min。采用优化后的加热工艺参数进行汽车防撞梁热成形试验,试验件的微观组织为均匀的马氏体组织,抗拉强度达到1500MPa以上,显微硬度在450HV以上,完全满足实际要求。