中锰钢温成形技术探讨

使用Gleeble-3800热模拟试验机研究了中锰钢(温成形钢)和22MnB5钢(热成形钢)的微观组织、力学性能和高温拉伸性能.结果表明:与22MnB5钢相比,在获得1 500 MPa级的抗拉强度时,中锰钢的加热温度可从950℃降低到800℃,钢的组织明显细化并且没有发生表面脱碳,断后伸长率从7.5％提高到10％.高温拉伸试验结果表明:中锰钢比22MnB5钢具有更高的延伸率和硬化指数,可以减小成形过程中局部减薄过高导致的样件破裂.     

热成形加热速率对22MnB5钢组织和性能的影响

22MnB5是常见的热成形高强钢，广泛应用于汽车车身，可减轻车身质量，提高汽车抗冲击和防温性。随着用户对热成形零件生产效率要求的不断提高，特别是感应力加热，火焰直燃加热等快速加热技术的推广应用，热减形加热速率快速提升到120℃/s。为了考察不同加热速率对22MnB5钢热成形后的组织和性能的影响规律，利用淬火膨胀仪、扫描电子显微镜(SEM)和拉伸试验机，分别对加热冷却过程中的热膨胀曲线、热成形后的微观组织和力学性能进行了测定。结果表明，随加热温度升高，试样冷却组织由铁素体向马氏体、贝氏体转变，且150℃/s加热速率下组织中贝氏体和铁素体含量要高于10℃/s加热速率的试样；且当加热速率从10℃/s提高到150℃/s时，22MnB5钢在950℃仍然能够完全奥氏体化，但是冷却试样的条件屈服强度、抗拉强度、断后伸长率都有所下降，分别降低了334 MPa、56 MPa、0.9%。     

加热温度对热成形中锰钢氢脆敏感性的影响

对0.1C–5Mn中锰钢在不同温度(850、950和1000℃)加热后进行热成形处理,利用电化学预充氢、慢应变速率拉伸及氢渗透实验等研究了加热温度对其氢脆敏感性的影响.结果表明,试验钢在不同温度加热后进行热成形处理,其组织全部为马氏体,同时因自回火而生成一定量的ε-碳化物,且随着加热温度的升高,原奥氏体晶粒尺寸增加,而试验钢的强度和塑性逐渐降低.当加热温度为850℃时获得了较好的强度与塑性配合,强塑积为22 GPa·%.随着加热温度升高,充氢样中的可扩散氢含量明显降低而非可扩散氢含量有所增加,而以相对缺口抗拉强度损失表征的氢脆敏感性指数及有效氢扩散系数呈现先升高后显著降低的变化趋势,当加热温度为1000℃时,氢脆敏感性最低.进一步断口分析表明,试验钢充氢断口起裂区均为沿着原奥氏晶界的沿晶断裂.试验钢的这种氢脆断裂行为主要与热成形中锰钢的强度水平及自回火析出的ε-碳化物有关.与常用的传统热成形钢22MnB5相比,试验钢的氢脆敏感性较高,这主要与其M_s点(马氏体转变开始温度)较低而使得自回火程度较低等有关.     

Ti-V-Mo微合金化22MnB5钢中析出相及其强化作用

使用温成形替代热成形可以避免热成形过程中表面氧化等问题,但热成形常用22MnB5钢在高温回火后出现明显的软化现象.而通过向钢中添加Ti、V、Mo等微合金元素可以在钢中形成细小的析出相以及细化晶粒,起到提高强度的作用,从而可以解决该问题.因此,通过在22MnB5钢中添加Ti、V、Mo微合金元素,利用OM(光学显微镜)、F...     

变强度22MnB5热成型钢热处理工艺研究

利用Gleeble-3500型热模拟试验机研究了冷却速率和等温温度对22MnB5热成型钢的力学性能和组织转变的影响.结果表明,将22MnB5由室温加热到930℃保温5 min后,以2℃/s冷却到500～550℃范围内进行等温淬火,显微组织为铁素体和珠光体,屈服强度为430～450 MPa,抗拉强度为650～680 MP...     

一种Si-Mn系超高强度钢板的热冲压成形试验研究

 采用弯曲件热冲压成形试验研究了板料加热温度、保温时间及移送时间等工艺参数对一种Si-Mn系超高强度钢板热成形零件的力学性能及微观组织的影响规律。结果表明,通过控制热成形工艺参数,在所设计的模具上可实现Si-Mn系超高强度钢板热成形零件的有效淬火,在合适的工艺参数下,可获得细小均匀的马氏体组织,从而获得抗拉强度1700MPa以上,伸长率10%以上的性能,达到原始板料抗拉强度的3倍左右,并明显高于传统的Mn-B系超高强度钢板。     

22MnB5热成形工艺及应用技术

出于节能减排、增加燃油经济性和满足日益严厉的安全法规的需要，超高强度钢热冲压成形零部件在汽车上身的应用比例逐年增加。详细介绍了22MnB5钢热冲压工艺参数的设计规范，及裂纹失效问题的控制。为保证淬火后零件微观组织中马氏体含量≥95%,抗拉强度≥1 500 MPa的要求，奥氏体化加热温度应控制在900～950℃、淬火冷却速度≥30℃/s;模具设计时需进行导热量计算及导热系统结构设计，保证热冲压零件的成形减薄率<15%、弯曲角圆弧半径R≥13 mm;为抑制应力集中导致的开裂，系统导热量在整个零件表面分布应均衡一致，导热水管外壁距模具型腔表面的垂直散热距离应均匀一致为10 mm,零部件热处理后显微组织中应减少马氏体粗大化，避免混晶。     

热处理工艺对22MnB5车用超高强度马氏体钢的组织性能影响

本试验使用金相显微镜、拉伸试验仪,配合Jmatpro及Imageproplus等软件对22MnB5超高强度马氏体钢板材在不同温度下的水淬组织以及相关力学性能进行了测试分析。结果表明:22MnB5综合性能在920℃时最优,马氏体转变量在860℃时达到最值,马氏体转变量与22MnB5的力学性能无直接相关性,且水淬性能优于油淬性能。综合考量,1.2mm厚22MnB5钢板材的最佳淬火工艺参数为:920℃保温后水淬至室温。     

提高汽车安全性的先进高强钢高效成形技术

先进高强钢与高效成形技术相结合并通过部件整合,可减轻部件质量或减少部件的使用,在提高汽车碰撞安全性的同时减轻车体结构的质量。总结了先进高强钢的激光拼焊板、定制钢材、热成形、拼焊板热成形、连续变截面板热成形、定制回火、定制热成形等高效成形技术的研究和开发现状。展望未来,顺应汽车轻量化、提高汽车碰撞安全性能、降低制造成本和未来钢制汽车发展的需求,兼顾汽车轻量化和提高汽车碰撞安全性的先进高强钢高效成形技术必将获得深入研究和广泛应用。     

回火温度对淬火后30MnB5热成形钢组织与性能影响

将30MnB5热成形钢进行淬火和回火处理,利用扫描电镜、透射电镜、能谱仪和拉伸性能检测等方法研究了不同回火温度后的显微组织和力学性能变化.经200℃保温2 min回火后热成形钢的综合力学性能最佳,抗拉强度为1774 MPa,总伸长率为8%,强塑积达14 GPa·%以上,该性能满足热成形后作为汽车结构件的使用要求;并且随着回火温度的升高,力学性能呈非单调性变化.200℃低温回火后,主要为板条马氏体和ε碳化物,位错密度略有降低,析出的ε碳化物粒子呈针状分布在马氏体板条内,长度方向大小为100 nm左右,并与位错发生钉扎作用.随着回火温度的升高,板条马氏体发生回复和再结晶,板条边界逐渐模糊,并向等轴状铁素体转变,位错密度显著降低,ε碳化物逐渐向低能态的近球形渗碳体转变并粗化至200 nm左右,对位错的钉扎作用也随之减弱.      

Modeling of Microstructure Evolution in 22MnB5 Steel during Hot Stamping简

Automobile manufacturers have been inereasingl~r adopting hot-stamped parts for use in newly designed ve- hicles to improve crash worthiness and fuel efficiency. However, the simulation of hot stamping is rather complex and challenging, and further research still needs to be done on hot stamping hardening mechanism. The microstruc- ture evolution and hardening mechanisms during hot stamping of 22MnB5 steel were thoroughly investigated, using information provided in the literatures as well as experimental results. New models were developed to predict the grain growth during heating and the flow stress of a manganese boron steel （22MnB5） with high hardenability by the Gleeble simulation experimental results. The deformed austenite decomposition during stamping and quenching was emphatically quantified based on the transformation thermodynamic and kinetic theories, and the relationship of mi- crostructure to properties was analyzed. The results showed that the optimal process to obtain homogeneous and small lath martensite is heating at 900--950 ℃ for 5 min and then auenching at 50 ℃/s with a Dressing time about 8 s.     

Determination of Thermal and Mechanical Material Properties of Ultra‐High Strength Steels for Hot Stamping

Direct and indirect hot stamping presently constitutes one of the most innovative forming technologies in the automotive industry through the combination of forming and hardening in one process step or line. Thus, structural components with strength up to 1600 MPa can be accomplished with the quench hardenable ultra‐high strength steel 22MnB5. With respect to the numerical investigation of the feasibility of different parts the knowledge of various thermal and mechanical material characteristics determined under process relevant conditions are required. Within the scope of this paper different experimental methods will be introduced for the determination of material properties according to the typical time‐temperature characteristics of the hot stamping process, as well as the modelling of it as input data for the FE analysis.     

Analysis of Microstructure and Mechanical Properties of Different Hot Stamped B‐bearing Steels

Hot stamping is a technique to produce ultra high strength automobile components. The common material used in hot stamping process is coated and/or uncoated 22MnB5 boron alloyed steel. Ferritic‐pearlitic microstructure in as‐delivered sheets is transformed to fully lath martensitic after hot stamping. In the present research, hot stamping under water or nitrogen cooling media was investigated using different boron alloyed steel grades. Microstructural analyses, linear and surface hardness profiling as well as tensile tests of hot stamped samples were performed. Various microstructures of fully bainitic and/or fully martensitic were produced. The resulting microstructures provided yield strengths of 650–1370 MPa and tensile strengths of 850–2000 MPa. There is an optimum carbon equivalent content for which the highest formability index value, UTS × A₂₅, is achieved. Using a nitrogen cooled punch resulted in higher yield strength without significant changes in ultimate tensile strength. It is concluded that a wide range of B‐bearing steels having an extended carbon equivalent range with an acceptable formability index value can be used by increasing the cooling rate in the die assembly.     

A Numerical and Experimental Investigation into Hot Stamping of Boron Alloyed Heat Treated Steels

Hot stamping of steel sheets using water or nitrogen cooling media was studied on a laboratory scale. Sheets of grade 22MnB5 boron steels in three different thicknesses were investigated and the results of experimental hot stamping tests were considered. Microstructural analysis, linear and surface hardness profiling as well as tensile tests of formed samples were carried out. After hot stamping, mostly fully martensitic microstructures, which yield ultra high strength levels, were produced. It is concluded that die cooling media, i.e., water or nitrogen, have a significant effect on material properties after hot stamping. Using liquid nitrogen as coolant in the punch instead of water increases yield strength by 50 to 65MPa. Moreover, the evolution of the temperature and force during the hot stamping process was simulated by using a coupled thermomechanical FEM program. The results of numerical simulation and experimental results are in good agreement.     

BZ37汽车车轮用冷冲压钢板的开发

BZ37热轧钢板主要用于冷冲压加工汽车车轮。该钢要求抗拉强度波动范围窄,塑性指标高,冷冲压加工性能良好,因此要严格控制影响钢板强度、塑性、冲压性能的元素含量,生产过程中要求纯净钢质．组织和性能均匀,保证钢板的冲成率。     

Optimization Evaluation Test of Strength and Toughness Parameters for Hot-Stamped High Strength Steels

Use of hot-stamped high strength steels (HSHSS) not only reduces the vehicle weight, but also improves the crash safety, therefore more and more mentioned steels are used to produce automobile parts. However, there are several problems especially the low ductility and toughness, which have restricted the application of HSHSS in automobile body. Suitable process parameters are very crucial to improve strength and toughness. In order to study the effect of austenization temperature, soaking time and start deformation temperature on strength and toughness of boron steel 22MnB5, an L9 (3⁴) orthogonal experiment which was analyzed by means of comprehensive evaluation was carried out based on Kahn tear method to obtain the value of fracture toughness. The results indicate that the excellent formability, high strength and toughness of boron steel 22MnB5 with 1.6 mm in thickness are obtained when the austenization temperature is in the range of 920 — 950 °C, the soaking time is 1 min and the start deformation temperature is in the range of 650 — 700 °C. The optimal parameters were used for typical hot stamping structural parts tests. Properties of samples such as tear strength, unit initiation energy and ratio of strength to toughness (RST) were improved by 10.91%, 20.32% and 22.17%, respectively. Toughness was increased substantially on the basis of a small decrease of strength.     

热成形工艺参数对AC1500HS钢板性能的影响

以鞍钢热成形用钢ACl500HS为研究对象．采用热模拟试验机测定了ACl500HS的CCT曲线并模拟了热成形工艺,确定了ACl500HS钢热成形工艺参数：对钢板进行热成形汽车零件试制,结果表明,该钢热成形性良好,零件尺寸精度达到要求。抗拉强度达到1500MPa以上,满足汽车零件装车要求。     

Fracture morphologies of a hot stamped steel and comparisons with several sheet metals

Hot stamping has been widely used in car industry to produce safety components.Most existing researches focused on the stamping and quenching process,but less on the mechanical properties of stamped parts.The fracture behaviors of hot stamped boron steel B1500 HS have been studied,and other four commonly used sheet metals with different strengths,including Q235,TRIP780,QP980 and MS1300,were also introduced for comparison.Both uniaxial tests and mechanical trimming tests were performed,and the fracture surfaces under different stress states were observed and discussed.The SEM observations showed that the fracture models are closely related to the stress states,i.e.,the tensile surfaces have ductile rupture characters while the trimming surfaces have brittle rupture characters.Compared with other steels,the quenched boron steel has smaller dimple size accompanied by shear planes in the tensile surface,and has smaller burnish zone in the trimming surface,and its cutting surface with‘S'like shape is also very different with others.Furthermore,two fitted empirical models were derived to describe the quantitative correlations between the average dimple diameter and the steel strength and between the percentage of burnish zone and the steel strength.