高强度钢板热冲压成形工艺的改进

热成形技术因结合热锻和冲压的技术优势,已经在汽车零部件制造工艺中获得了广泛的关注和应用。在热成形生产中,产品在高温下成形伴随非等温淬火过程容易出现起皱、破裂等成形质量缺陷。本文围绕高强度热成形钢板22MnB5材料相变过程、机械性能进行了相关研究,基于深冲盒试验进行热成形工艺改进优化,在热成形生产工艺过程中增加相应的转运冷却环节,使完全奥氏体化后的板料在冲压淬火前降低至优化冲压温度。实验表明:改进后的热成形工艺对冲压产品的成形性有明显改善,可有效降低和消除起皱、破裂等缺陷,材料微观马氏体转化更加细致充分,可获得抗拉强度达到1500MPa以上,硬度达到450HV以上的热成形产品,满足连续热冲压成形自动化生产过程工艺改进要求。     

热冲压成形车门防撞梁组织和性能研究

使用宝钢生产的热冲压用钢B1500HS,热冲压成形某车车门防撞梁.运用金相分析、拉伸试验、硬度测试和C-NCAP等手段,测试了成形件的组织、力学性能和侧面刚性,并特别测试了防撞梁5个典型位置的硬度.结果表明,成形件的微观组织为理想的板条状马氏体,抗拉强度达到1500 MPa以上,5个典型位置硬度都在450 HV以上,组...     

高强度板热冲压成形模具设计

通过对高强度22MnB5硼镁合金板材热冲压成形工艺和关键技术分析、热冲压成形模具热平衡分析,建立了高强度板材热冲压成形热平衡模拟方程,提出高强度板材热冲压成形模具设计方法,对热冲压成形模具冷却系统作了详细的设计.     

热冲压工艺参数对22MnB5马氏体钢汽车B柱性能影响的有限元模拟

通过有限元仿真软件Autoform分析了热冲压过程中工艺参数的变化对22MnB5马氏体钢B柱起皱、回弹、减薄、马氏体量以及强度的影响。结果表明:22MnB5马氏体钢B柱热冲压最优化工艺参数为加热温度930 ℃,冷却速率80 ℃/s。该工艺参数下,热冲压过程各处均完成马氏体转变,硬度分布均匀,材料减薄率较低,热冲压成形效果好,尺寸精度高,冲压件强度均大于1400 MPa。     

基于PAMS-TAMP的高强钢板热成形工艺研究

在22MnB5高强钢板的力学及热物理性能的实验数据基础上,建立了汽车U形梁零件的有限元模型,并运用PAMS-TAMP软件进行了热冲压成形以及成形后的淬火冷却全过程的模拟分析.根据模拟参数进行了物理试验验证.结果表明,模拟结果与试验结果一致.这能为高强钢板的热冲压工艺提供了有效的科学依据.     

38MnB5热轧钢板热成形温度参数与力学性能探索

装甲车辆的轻量化发展对高强钢的成形工艺和材料性能提出了更高的要求,为提升材料的装甲防护性能,以8 mm厚38MnB5热轧钢板为研究对象,对不同加热温度和保温时间条件下的微观组织、晶粒尺寸进行研究,以得到合理的热成形温度参数,并通过室温拉伸、冲击及穿甲破坏试验对材料的相关性能进行检测和分析。结果表明:加热温度950℃、保温12 min为试验材料合理的热成形温度参数,在此条件下组织完全奥氏体化,晶粒尺寸基本一致、分布均匀;在选定参数条件下,材料水淬后的塑性、韧性极差,晶间脆性严重;采用通有冷却水的平整模具进行热成形试验,得到钢板的抗拉强度为1925 MPa,断后伸长率为9. 1%,表面硬度为52 HRC,塑性、冲击韧性有了较大改善,射击试验弹坑深度在2～3 mm,钢板弹坑背面平整,无明显凸起,抗弹性能较好。     

钛合金曲面类零件的热冲压工艺

为了解决钛合金钣金件成形困难、易起皱、易破裂等问题,以异形曲面钛合金钣金件为研究对象,给出了热成形工艺方案。首先采用热冲压预制零件的主体部分,然后采用热校形工艺调整头部折弯边角度;进一步通过正交试验方法建立了正交试验组,采用极差分析法确定了各因素影响程度的主次关系,并得到了最优的工艺参数水平组合;最后,通过试验验证了工艺参数的有效性。研究结果表明：成形温度对钣金件成形质量的影响较大,温度过低,容易起皱,温度过高,软化严重,成形精度不高,TA15钛合金的最优成形温度为670℃;最优工艺参数组合下,钣金件厚度较均匀,最大偏差仅为0.1 mm,说明热冲压成形工艺可以满足钛合金曲面类零件的厚度要求。     

热冲压成形22MnB5钢板的组织和性能

采用扫描及透射电镜观察和力学性能实验研究了22MnB5钢板热冲压成形件的组织形貌和力学性能。结果表明,加热温度930℃,保温4.5 min,初始成形温度850℃,冲压速度75 mm/s条件下,22MnB5钢板热冲压成形完成完全马氏体转变,得到均匀板条马氏体组织,组织内产生高密度位错,强度大幅提升,抗拉强度达到1550 MPa。形变有助于动态再结晶并获得更为细小的马氏体组织,促进细晶强化。硼元素在晶界发生偏聚,延长奥氏体转变孕育期,提高了22MnB5钢的淬透性,同时引起点阵畸变,促进相变强化。     

汽车B柱高强度钢热冲压工艺

采用数值模拟与试验相结合的方法,研究了汽车B柱22Mn B5高强度钢热冲压成形工艺。根据对B柱零件结构的分析,设计模具型面,并合理添加压料板。建立B柱热冲压有限元模型,设置板料加热温度、模具温度、压料板的压力、冲压速度、淬火保压压力等工艺参数,确定工艺参数方案。对B柱热冲压进行全过程数值模拟,得到了热冲压件的厚度、微观组织、硬度等性能分布情况,并与试验结果进行对比。热冲压件性能检测结果表明:零件的厚度分布较均匀,最大减薄率小于25%,平均硬度达到470 HV以上,平均抗拉强度达到1400 MPa以上,显微组织为均匀板条状马氏体。成形后的B柱各项性能均满足热冲压技术规范要求,表明了该B柱热冲压成形工艺的可靠性。     

22MnB5钢相变特性和热成形工艺研究

采用热膨胀仪研究了22Mn B5钢连续冷却转变特性,并对热冲压零件的力学性能以及显微组织进行了研究。结果表明,880℃及以上温度奥氏体化,快速冷却后主要发生奥氏体向马氏体的转变,但当奥氏体化加热温度降低到820℃时,冷却后的组织中存在明显的铁素体。热冲压方式制造的22Mn B5钢试样具有良好的力学性能,抗拉强度能够达到1 500 MPa,屈服强度能够达到1 000 MPa。显微硬度达到450HV以上。     

Effect of oxide scale on temperature-dependent interfacial heat transfer in hot stamping process

An optimization-based numerical procedure was developed to determine the temperature-dependent interfacial heat transfer coefficient (IHTC). The effects of temperature, pressure and oxide scale thickness were analyzed, for oxide thickness between 9 μm and 156 μm and pressure from 8 MPa to 42 MPa. Oxide scales and contact pressure both show distinctive effects on IHTC in the cooling process. The average IHTC decreases about 2461 W/(m² °C) with the increase of oxide scale thickness and increases 2620 W/(m² °C) with the increase of pressure. Based on the two-way ANOVA, the effect of contact pressure influences the IHTC most. Their mutual interaction is negligible. The IHTC decreases when the average temperature between the blank and die surface is above 250 °C and increases when the latent heat release.     

Thermal behavior of aluminum-coated 22MnB5 in hot stamping under dry and lubricated conditions

The hot stamping of aluminum-coated 22MnB5 has usually been conducted under dry condition, for which the forming load is high since the coefficient of friction is over 0.5. In order to decrease the forming load, the authors previously proposed the use of a lubricant to decrease so that the coefficient of friction from over 0.5 to 0.3. However, it is necessary to understand the heat transfer property in hot stamping under lubricated condition. The purpose of this paper is to examine the heat transfer property of aluminum-coated 22MnB5 in hot stamping under dry and lubricated conditions. In this study, the die and specimen temperatures were measured during compression and compression-sliding tests under dry and lubricated conditions using the hot flat drawing test simulator. In the compression test, the die and specimen temperatures measured under dry and lubricated conditions were the same. On the other hand, in the compression-sliding test up to a sliding distance of 70 mm, the die temperature under lubricated condition was lower than that under dry condition, and it was found that the heat transfer under lubricated condition is superior to that under dry condition. Consequently, there is a difference between the specimen temperatures under dry and lubricated conditions. However, from the results of the tensile test, there is no difference between the tensile strengths under dry and lubricated conditions.     

Analysis of microstructure and mechanical properties of different high strength carbon steels after hot stamping

Usage of high strength steels may reduce the weight of automobiles and improve the crash safety and low down the gas emissions. Besides cold forming, hot stamping has gained much interest for the production of car body components. Boron alloyed steels have been the point of focus for the materials choice in hot stamping. In this paper, four high strength non-boron alloyed steels were hot stamped using water and nitrogen cooling media. Microstructural analyses, lateral and surface hardness profiling as well as tensile tests of hot stamped samples were performed. These steels provided yield strength (Y.S.) values of 600-1100 MPa and ultimate tensile strength (U.T.S.) values of 900-1400 MPa. Increasing cooling rates, i.e. by using nitrogen cooled punch (NCP) during hot stamping resulted in mostly martensitic microstructure and maximum strength, while hot stamping using water cooled punch (WCP) resulted in maximum formability index due to presence of some ferrite phase.     

热冲压快速冷却工艺对22MnB5钢组织与性能的影响

基于RCP（Rapid Cooling Process）快速冷却工艺+不同模具温度淬火热处理工艺,对22MnB5钢板材的淬火力学性能及微观组织进行了研究,探讨了冷速、强度硬度之间的关系,建立了三者之间的硬度指数模型。结果表明,采用加入淬火前快速冷却过程及改变淬火模具温度的方式可以有效实现梯度冷却速率控制,冷却速率实现了从6 ~40 ℃/s的变化,微观组织从铁素体与珠光体、上、下贝氏体逐渐向“残留奥氏体+马氏体”组织过渡,对应的强度区间范围为700~1600 MPa。建立的冷速、强度硬度模型与试验数据拟合良好。     

Investigation on induction heating for hot stamping of boron alloyed steels

Within hot stamping of quenchenable steels the blank is heated up to austenitization temperature, transferred to the tool, formed rapidly and quenched in the cooled tool. Essential for the complete process is the heating of the blank which is currently carried out with roller hearth furnaces. As a consequence of rising energy costs new and more time and energy effective heating systems are needed. The paper presents investigations on induction heating as an alternative heating technology. Results concerning the process windows as well as material characteristics and grain structure will be presented and discussed.     

新型模具制取变强度制件及其力学性能研究

设计出利用感应加热方式形成变强度制件的热冲压新型分区模具,进行了热-流-固耦合场的理论分析,建立了热-力耦合有限元模型,得到了板料在热冲压过程中温度和维氏硬度的分布。仿真结果表明,当模具感应加热端温度升至400℃时,加热端的冷却速度为13.6℃·s~(-1),冷却速度决定了板料不同温区的微观组织和维氏硬度。利用该模具进行了热冲压实验,对不同温区的微观组织和维氏硬度进行检测。结果表明:该模具可冲压不同高温区(低强度)形状的制件。制件高温区已经基本转化为贝氏体组织,过渡区转化为马氏体、贝氏体和铁素体多相混合组织,低温区转化为板条状马氏体组织。设计出的新型分区模具可以获得变强度制件,为成形复杂变强度零件和工艺参数的优化提供了依据。     

22MnB5热成形钢变厚度轧制及退火工艺

基于离散化思路建立变厚度轧制的厚度控制系统;在实验四辊轧机上进行了单厚度过渡区的22MnB5热成形钢变厚度板轧制,对轧后的板材进行模拟退火试验,使用光学显微镜、扫描显微镜观察及拉伸试验分析了变厚度板退火后不同厚度位置的组织和力学性能。结果表明,在50 mm变厚度区中：厚度偏差为0.08 mm,长度偏差为0.3 mm。变厚度板在退火快速冷却过程中不同厚度区存在较大的温度差,薄区温度跟随性差,其他退火过程的温度跟随性好,偏差不大;不同厚度区的力学性能区别小;快速冷却退火后的组织为层状珠光体+铁素体;结合工艺可行性并有效保证组织性能控制,建议根据厚区的厚度来制定退火工艺,并采用低冷却速度的罩式退火或半连续退火。