Application of Hot Forming High Strength Steel Parts on Car Body in Side Impact

Lightweight structure is an important method to increase vehicle fuel efficiency. High strength steel is applied for replacing mild steel in automotive structures to decrease thickness of parts for lightweight. However, the lightweight structures must show the improved capability for structural rigidity and crash energy absorption. Advanced high strength steels are attractive materials to achieve higher strength for energy absorption and reduce weight of vehicles. Currently, many research works focus on component level axial crash testing and simulation of high strength steels. However, the effects of high strength steel parts to the impact of auto body are not considered. The goal of this research is to study the application of hot forming high strength steel（HFHSS） in order to evaluate the potential using in vehicle design for lightweight and passive safety. The performance of HFHSS is investigated by using both experimental and analytical techniques. In particular, the focus is on HFHSS which may have potential to enhance the passive safety for lightweight auto body. Automotive components made of HFHSS and general high strength steel（GHSS） are considered in this study. The material characterization of HFHSS is carried out through material experiments. The finite element method, in conjunction with the validated model is used to simulate the side impact of a car with GHSS and HFHSS parts according to China New Car Assessment Programme（C-NCAP） crash test. The deformation and acceleration characteristics of car body are analyzed and the injuries of an occupant are calculated. The results from the simulation analyses of HFHSS are compared with those of GHSS. The comparison indicates that the HFHSS parts on car body enhance the passive safety for the lightweight car body in side impact. Parts of HFHSS reduce weight of vehicle through thinner thickness offering higher strength of parts. Passive safety of lightweight car body is improved through reduction of crash deformation on car body by the application of HFHSS parts. The experiments and simulation are conducted to the HFHSS parts on auto body. The results demonstrate the feasibility of the application of HFHSS materials on automotive components for improved capability of passive safety and lightweight.

Investigation of Surface Damage in Forming of High Strength and Galvanized Steel Sheets

Powdering/exfoliating of coatings and scratching galvanized steels and high strength steels （HSS）, are the main forms of surface damage in the forming of which result in increased die maintenance cost and scrap rate. In this study, a special rectangular box was developed to investigate the behavior and characteristics of surface damage in sheet metal forming （SMF） processes. U-channel forming tests were conducted to study the effect of tool hardness on surface damage in the forming of high strength steels and galvanized steels （hot-dip galvanized and galvannealed steels）. Experimental results indicate that sheet deformation mode influences the severity of surface damage in SMF and surface damage occurs easily at the regions where sheet specimen deforms under the action of compressive stress. Die corner is the position where surface damage initiates. For HSS sheet, surface damage is of major interest due to high forming pressure. The HSS and hot-dip galvanized steels show improved ability of damage-resistance with increased hardness of the forming tool. However, for galvannealed steel it is not the forming tool with the highest hardness value that performs best.

Microstructure design and feasibility of hot stamping for new generation high strength multi-phase steels

Optimization of microstructure for new generation advanced high strength steels(AHSS ) for automobiles was briefly reviewed.Two different heat treatments(quenching partitioning austempering/QPA and quenching partitioning tempering/QPT) have been investigated to obtain optimal microstructures,which are made up of martensite(hard phase),retained austenite(soft phase),and carbide or nano-bainite.Combination of hot stamping and newly developed heat treatments is discussed.

Research on welding technology of hot-rolled extra-high-strength steel developed by Baosteel

In this study, the welding technology of the hot-rolled extra-high-strength steel, BS960QC, has been comprehensively investigated. Analysis has been made on the weldability ,the different welding procedures ,the mechanical properties, and the fatigue properties, and a set of recommendation guidelines have been proposed for evaluating the welded joints of the extra-high-strength steel. The research and results indicate that the hot-rolled extra-high-strength steel, BS960QC,has good weldability and an excellent adaptability to welding procedures. Further,the excellent mechanical properties and fatigue properties of the welded joints ,which can be achieved by using optimized welding procedures, can completely meet the technical requirements of the construction machinery industry.

Effect of Quenching Parameters on Mechanical Property of Ultra High Strength Steel BR1500HS Based on Response Surface Methodology

Hot stamping of high strength steels is defined as a process in which blank is heated to the temperature of the austenite stabilization region for a definite time and then formed and quenched simultaneously in a mold with cooling channels. During this process,the processing parameters of austenite temperature and soaking time have strong effects on the mechanical properties such as quenching hardness,tensile strength and elongation. Hence,it is necessary to investigate the relationship between the mechanical properties and the two processing parameters. In this paper,the orthogonal experiment with two factors and five levels was applied, and the experimental data based on the orthogonal experiment was acquired. Based on the data,regression models were set up and the results of the analysis of variance( ANOVA) showed that it is reliable to predict the quenching hardness,tensile strength and elongation by the regression models. Besides,the optimal results of each single object were obtained based on response surface methodology( RSM),and global optimums was gained by employing ideal point method in which the quenching hardness,and tensile strength and elongation were considered simultaneously.

Effect of nano-sized precipitates on the crystallography of ferrite in high-strength strip steel

For strip steel with the thickness of 1.6 ram, the yield and tensile strengths as high as 760 and 850 MPa, respectively, were achieved using the compact strip production technology. Precipitates in the steel were characterized by scanning and transmission electron microscopy to elucidate the strengthening mechanism. In addition, intragranular misorientation, Kernel average misorientafion, and stored energy were measured using electron backscatter diffraction for crystallographic analysis of ferrite grains containing precipitates and their neighbors without precipitates. It is found that precipitates in specimens primarily consist of TiC and Ti4CzS2. Ferrite grains containing pre- cipitates exhibit the high Taylor factor as well as the crystallographic orientations with {012}, {011}, {112}, or {221} plane parallel to the rolling plane. Compared with the intragranular orientation of adjoining grains, the intragranular misorientation of grains containing precipi- tates fluctuates more frequently and more mildly as a function of distance. Moreover, the precipitates can induce ferrite grains to store a rela- tively large amount of energy. These results suggest that a correlation exists between precipitation in ferrite grains and grain crystallographic properties.

Experimental Investigation of the Effect of the Material Damage Induced in Sheet Metal Forming Process on the Service Performance of 22MnB5 Steel

The use of ultra-high strength steels through sheet metal forming process offers a practical solution to the lightweight design of vehicles.However,sheet metal forming process not only produces desirable changes in material properties but also causes material damage that may adversely influence the service performance of the material formed.Thus,an investigation is conducted to experimentally quantify such influence for a commonly used steel（the 22MnB5 steel） based on the hot and cold forming processes.For each process,a number of samples are used to conduct a uniaxial tensile test to simulate the forming process.After that,some of the samples are trimmed into a standard shape and then uniaxially extended until fracture to simulate the service stage.Finally,a microstructure test is conducted to analyze the microdefects of the remaining samples.Based on the results of the first two tests,the effect of material damage on the service performance of 22MnB5 steel is analyzed.It is found that the material damages of both the hot and cold forming processes cause reductions in the service performance,such as the failure strain,the ultimate stress,the capacity of energy absorption and the ratio of residual strain.The reductions are generally lower and non-linear in the former process but higher and linear in the latter process.Additionally,it is found from the microstructure analysis that the difference in the reductions of the service performance of 22MnB5 by the two forming processes is driven by the difference in the micro damage mechanisms of the two processes.The findings of this research provide a useful reference in terms of the selection of sheet metal forming processes and the determination of forming parameters for 22MnB5.

Influence of Hot Press Forming Techniques on Properties of Vehicle High Strength Steels

Based on the combination of materials science and mechanical engineering,hot press forming process of the vehicle high strength steels was analyzed. The hot forming process included：heating alloys rapidly to austenite microstructures,stamping and cooling timely,maintaining pressure and quenching. The results showed that most of austenite microstructure was changed into uniform martensite by the hot press forming while the samples were heated at 900 ℃ and quenched. The optimal tensile strength and yield strength were up to 1530 MPa and 1000 MPa,respectively,and the shape deformation reached about 23%. And springback defect did not happen in the samples.

Influences of hot stamping parameters on mechanical properties and microstructure of 30MnB5 and 22MnB5 quenched in flat die

The influences of hot stamping parameters such as heating temperature,soaking time,deformation temperature and cooling medium on the phase transformation,microstructure and mechanical properties of 30MnB5 and 22MnB5 are investigated and analyzed in this work.The quenching experiment,tensile testing,hardness measurement and microstructure observation were conducted to obtain the mechanical and microstructural data.The results indicate that 30MnB5 possesses a higher tensile strength but a lower elongation than 22MnB5,if hot stamped at the same process parameter.The tensile strength and hardness of the hot stamped specimens decrease under inappropriate heating conditions for two reasons,insufficient austenitization or coarse austenite grains.The austenitic forming rate of 30MnB5 is higher than that of 22MnB5,because more cementite leads to higher nucleation rate and diffusion coefficient of carbon atom.More amount of fine martensite forms under the higher deformation temperature or the quicker cooling rate.

Recent progress in the development and application of the new Gen.AHSS at Baosteel

In recent years,despite the global economic recession and steel oversupply,the demand for high strength steel( HSS) and advanced high strength steel( AHSS) sheets has robustly increased. To supply the materials needed for automotive manufacturing,various AHSS products and application technologies have been developed by Baosteel,including the 1st,2nd,and 3rd Gen. AHSS,which makes Baosteel the world’s first steel maker to commercially provide all three generations of AHSS. Recently,the new Gen.( the 2nd and 3rd Gen. combined)AHSS products,which feature ultra-high strength and enhanced ductility,have drawn great attention from both steel makers and the automotive industry as these products can be used to produce auto parts with complicated shapes by cold forming and have great potential for manufacturing car bodies that are lighter in weight and have higher crash resistance. In this article,the concepts,properties,and applications of Baosteel’s new Gen. AHSS products,including quenching and partitioning( QP) steels,twinning-induced-plasticity( TWIP) steels,and Medium-Mn( Mn-TRIP)steels,are described and reviewed. Moreover,the progress of the Baosteel light-weight steel car body( BCB) was reported.

FEM simulation of flexible roll forming based on different material models

Flexible roll forming is a new roll forming process that produces parts with variable cross sections. This forming process is proposed to meet the demand of weight reduction of automobile industry. In order to study the mechanisms and material flow rules in this new forming process,the finite element mothod( FEM) model of a nine-step flexible roll forming of an ultra-high-strength steel bumper is established based on deep understanding and reasonable simplification of the process.Given that the material model is an important factor that influences the simulation accuracy,three material models which consist of different yield criteria and hardening models are adopted in the FEM models. Sheet thickness and springback amount calculated with three material models are studied comparatively. According to sheet thickness reduction and springback amounts,it is found that the MKi( Mises yield criterion and kinematic hardening law) model's result is larger than MI( Mises yield criterion and isotropic hardening law) model and HI( Hill's yield criterion and isotropic hardening law) model. Therefore,it is concluded that material models do have influences on the flexible roll forming simulation and need to be determined carefully.

The development of surface treatment products and technologies of steel sheets in Baosteel

The surface treatment technology can improve the corrosion resistance of steel sheets and increase the value of steel application.The surface treated steel sheets in Baosteel include zinc galvanized steel sheets,sin galvanized steel sheets,chromium galvanized steel sheets,and colour coating steel sheets with the application in the area from construction to automobiles,appliance,package,etc.The development,application and manufacturing technique of these products have become the core competition power of Baosteel. The article reviews the developments of surface treated steel sheets and surface treatment technologies in Baosteel in 10 years,especially hot dip galvanized high strength steel products used in vehicles.The article also looks forward into further developments of surface treatment steel products and technologies in Baosteel,which will focus on:①the new products of hot dip galvanized advanced high strength steels;②more environmental friendly products or functional coating products;③the development of surface treatment technologies to meet the requirement of higher surface quality in the marcket;④new type of surface treatment and coating technologies.

Study of front bumper process on the basis of hot stamping

The fitting method is used for obtaining the constitutive relation of ultra-high strength steel in this paper. At the same time, the forming limit of material is researched under different de/brmation conditions. Through experiments, the paper obtains stress-strain curve under different deformation temperatures and strain rates. On the basis of experimental data, the constitutive relation model is established which can reflect the de- fomlation capacity of ultra-high strength steel during process of hot stamping. Combining with finite element simulation results of hot stamping by the commercial software AUTOFORM, transfer path of load and matching law of strength, the paper determines the design criteria and forming process requirements of parts manufactured by hot stamping. Through setting different process parameters, such as punch velocity and friction coefficient, and blank shape, the paper finds that process parameters and blank shape have an essential effect on the quality of parts.

嵌套加强的LQ550高强冷弯薄壁C型钢连续檩条受力性能研究

为提高LQ550级高强冷弯薄壁C型钢连续檩条的承载能力,采用在支座处嵌套的方法来加强连续檩条。对未加强和采用两种嵌套方式加强的檩条共7组试件进行三点受弯试验,得到了试件的承载性能和破坏形态,试验结果表明加强后的试件出现跨中局部屈曲和嵌套端部局部屈曲两种破坏形态。采用ABAQUS软件建立了非线性有限元模型对嵌套加强的檩条进行数值模拟,有限元分析得到的承载力和破坏形态与试验结果吻合良好,验证了有限元模型的准确性。基于验证的有限元模型,分析了两种嵌套方式和不同嵌套长度对檩条承载力的提升,且表明嵌套檩条的长度宜取为连续檩条跨度的1/5~1/4。

大尺寸均质化M50轴承钢坯的构筑成形

针对大尺寸M50轴承钢锭中液析碳化物粗大的问题,提出采用金属构筑成形技术制备大尺寸均质化M50轴承钢坯的新思路。通过基元加工、真空封焊、高温变形、保温扩散和多向锻造工艺制备了80 mm×80 mm×1000 mm的M50轴承钢构筑坯料。拉伸和疲劳性能的试验结果表明,M50轴承钢构筑界面实现了完全冶金结合,其力学性能达到与基体相当的水平,通过构筑成形技术制备的均质化M50轴承钢坯的疲劳性能显著优于采用一体化冶炼工艺制备的大尺寸M50轴承钢坯。

新型汽车覆盖件钢板性能研究

UF340作为一种新型超细晶高强钢,在汽车外覆盖件的应用上具有替代HC180BD的潜力,研究了UF340力学性能和成形性能。结果表明,在塑性、加工硬化指数和各向异性方面,UF340与HC180BD具有相似的力学性能,与HC180BD相比UF340没有明显的烘烤硬化性,2种材料的成形性能基本一致。通过Keeler模型计算获得UF340的成形极限曲线与成形试验结果存在一定差异,采用线性分段拟合方式获得的成形极限图与试验结果吻合度更高,采用该方法获得的成形极限曲线可为新材料的成形应用提供参考。

High strength and ductility of 34CrNiMo6 steel produced by laser solid forming

Because of the excellent mechanical properties of 34 CrNiMo6 steel, it is widely used in high-value components. Many conventional approaches to strengthening-steels typically involve the loss of useful ductility.In this study, 34 CrNiMo6 Steel having high strength and ductility is produced by laser solid forming(LSF)with a quenching-tempering(QT) treatment. Tempering of bainite is mainly by solid phase transformation in the previous LSF layers during the LSF process. The stable microstructure of LSF consists of ferrite and fine carbides. The microstructure transfers to tempered sorbite after heat-treatment. The tensile properties of the LSF steel meet those of the wrought standard. The UTS and elongation of LSF sample at 858 MPa, 19.2%, respectively, are greater than those of the wrought. The QT treatment enhanced the ultimate tensile strength and yield strength of the LSF sample. The ultimate tensile strength, yield strength, reduction in area, and elongation of the LSF+QT sample at 980 MPa, 916 MPa, 58.9%, and 13.9%,respectively, are greater than those of the wrought standard. The yield strength of the LSF+QT sample is approximately 1.27 times that of the wrought. The LSF samples failed in a ductile fracture mode, while the LSF+QT samples showed mixed-mode failure. The defects have only a small effect on the tensile properties owing to the excellent ductility of the LSF sample.

退火温度对淬火配分后热轧高强钢显微组织和力学性能的影响

将热轧高强钢升温至不同温度(780,810,840,870℃)保温退火600s后进行200℃×60s淬火+410℃×300s配分处理,研究了退火温度对其显微组织和力学性能的影响。结果表明:随着退火温度升高,淬火配分后试验钢中铁素体和马奥岛含量减少,回火马氏体、残余奥氏体和贝氏体含量增加;随着退火温度升高,抗拉强度先减小后增大,屈服强度、断后伸长率、屈强比和冲击吸收功均先增大后减小;840℃退火温度下淬火配分后试验钢的强度、塑性和韧性匹配优异,抗拉强度(830MPa)较大,屈服强度(585MPa)、断后伸长率(39.6%)、屈强比(0.70)和冲击吸收功(-20,-40℃环境下分别为28.35,27.69kJ)最大。

长材轧机热轧钢筋类产品生产概述

结合国家标准对长材轧机热轧钢筋类产品的生产工艺、产品特点等进行解读,并介绍高强螺纹钢筋的几种生产工艺。可供工程技术人员、产品用户等理解各类热轧钢筋的生产工艺、产品特点等。

Development of Ti-Microalloyed 600 MPa Hot Rolled High Strength Steel

A high strength steel with yield strength on the order of 600 MPa was developed successfully with only addition of titanium alloying element based on a low-carbon steel. The results showed that the hot deformation accelerated ferrite and pearlite transformation and retarded bainite transformation under continuous cooling condition. The microstructure of this steel was mainly composed of fine grained ferrite and carbides distributing along the ferrite grain boundaries. The yield and tensile strengths of steels were about 620--650 MPa and 720--740 MPa, respectively, and the values of strain hardening exponent and plastic strain ratio were 0.12 and 0.80, respectively, thereby providing a good combination of strength with toughness. In short, the fine grained ferrite and TiC precipitation strengthening contributed to a high strength.