Effect of laser heating on the microstructure and hardness of TRIP590advanced high strength steel used for roll forming

TRIP590 advanced high strength steel sheets were heated by laser with different powers.Changes of the microstructure and the hardness of TRIP590 steel under laser heating with different powers were investigated by metallographic microscope,scanning electron microscope,and hardness tester.The purpose was to study the effect of laser power on microstructure and hardness of TRIP590 steel.It is shown that the power of laser plays an important role on the microstructure and hardness of heated steel sheets.The results are helpful to determine suitable power for the laser auxiliary forming of Trip590 steel in order to obtain uniform microstructure and high hardness.

Yield Loci of TRIP590 Advanced High Strength Steel Based on Biaxial Loading Test

The main purpose of the paper is to obtain the experimental yield loci of TRIP590 advanced high strength steel,and to compare it with the theoretical loci in order to obtain the best yield criterion for this material.First,the biaxial loading tests under different loading paths in the method of load control are carried out.Then,the experimental yield loci of different deformation stages are obtained.Finally,the experimental yield loci are compared with the theoretical loci of Mises criterion and Hill48 criterion,the parameters of which are calculated based on the r?value and the yield stress method,respectively.The results show that the accuracy of the theoretical yield loci of Hill48 based on the yield stress is higher than that of Mises criterion and Hill 48 criterion based on r?value method.

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.

Delayed fracture of tensile strength 980 MPa grade steels for automotive applications

Three different types of tensile strength （TS） 980 MPa grade advanced high-strength steels used in automotive applications, namely, 980MS （ martensite steel ）, 980DP （ dual phase ） and 980QP （ quenching and partitioning） steels were examined. The delayed fracture resistance of the steels was evaluated using a U-bend test, slow strain rate test（SSRT） and a constant load tensile test. The results indicated that all the steels could pass the 300 h HC1 solution immersion test and none of the U-bend specimens was fractured in the test. However,the steels exhibited different susceptibilities to delayed fracture under SSRT and the constant load tensile tests. 980DP exhibited the highest resistance to delayed fracture among all the samples, while 980MS was found to be the most susceptible to delayed fracture.

Tensile and Spring-Back Behavior of DP600 Advanced High Strength Steel at Warm Temperatures

In recent years, the use of advanced high strength steels in automotive industry has been increased remarkably. Among advanced high strength steels, dual phase （DP） steels have gained a great attention owing to a combination of high strength and good formability. However, high strength usually increases the spring-back behavior of the material, which creates problems for the parts during the assembly. Thus, the uniaxial tensile deformation and spring-back behaviors of DP600 advanced high strength steel were investigated in rolling （0°）, diagonal （45°） , and transverse （90°） directions in the temperature range from room temperature （RT） to 300 ℃. All tests were performed at a deformation speed of 25 mm/min. A V-shaped die （60°） was used for the spring-back measurements. The results indicated that the formability and spring-back of the material were decreased with increasing the temperatures. The material showed complex behaviors in different directions and at different temperatures.

Strain Hardening and Strain Rate Sensitivity Behaviors of Advanced High Strength Steels

The mechanical properties of commercial dual phase （DP）, transformation induced plasticity （TRIP）, and high strength low alloy （HSLA-340） steel sheets are investigated and compared at various strain rates ranging from 0.001 7to 0.17 s-1 at ambient temperature.TRIP steel outperforms the other two materials , having comparable ductility and twice as large strength relative to DP steel.TRIP has larger strength and much larger ductility than HSLA-340.The exceuent ductility of TRIP800is due to its high strain hardening capability , which promotes stable plastic deformation.It is observed that the strain hardening rate in TRIP800does not decrease to zero at failure , as common in most materials in which failure is preceded by necking.

Shear Fracture of Advanced High Strength Steels

Failure experiments were carried out through a stretch-bending test system for advanced high strength steels, i.e. dual-phase （DP） steels and martensitic steels （MS）. The die radius in this system was designed from 1 to 15 mm to investigate the failure mode under different geometries. Two failure modes were observed during the ex- periments. As a result, critical relative radii （the ratio of inner bending radius R to sheet thickness t） for DP590 and DP780 steels were obtained. The stretch-bending tests of DP980 display some trends unlike DP590 and DP780 steels, and curve of DP980 in different thicknesses does not coincide well. High blank holder force exhibits more possibility of shear fracture tendency than low blank holder force. The unique character of high strength martensitic steel （1500MS） is that no shear fracture is found especially over small bending radius （R =2 mm） under the same experi- mental conditions. Microstructure analysis indicates that there are obviously elongated grains on shear fracture sur- face. It shows smaller diameter and shallower depth of the dimples than the necking failure.

回火工艺对热成形AHSS力学特性的影响

热成形22MnB5高强钢板在提高其强度的同时，塑性及韧性急剧降低。基于强度、塑性和韧性指标，通过拉伸力学性能测试、Kahn撕裂实验等方法，获得硼钢淬火前后的基本力学参数，研究其在不同回火温度条件下的断裂韧性特征，获得了其力学性能变化规律。结果表明：回火温度在100～200℃范围内时，其单位面积裂纹扩展能（UPE）和撕裂强度（粥）随着回火温度的升高而增大；回火温度在200～350℃范围内时，单位面积裂纹扩展能和撕裂强度随着回火温度的升高而降低。合理的回火处理工艺可显著改善热成形硼钢的力学性能。

预变形对AHSS及UHSS高强钢边缘开裂的影响研究

选取不同料厚和强度等级的AHSS和UHSS材料,对其不同预变形量的料片进行扩孔试验,通过数据拟合分析,总结预变形量对AHSS和UHSS高强钢边缘开裂的影响,为后续边缘开裂研究及前期CAE预测边缘开裂状态提供参考。

周期载荷作用下单涂层AHSS双曲板的热弹性动力学行为

利用分离变量法得到局部热载荷作用下单涂层先进高强度钢(AHSS)双曲板的三维瞬态温度场.在此温度场下,通过在空间域上应用有限差分法和在时间域上应用Newmark法求解板的三维瞬态热动力控制方程,研究机械载荷幅值和周期、热载荷作用区域和板的几何参数对单涂层AHSS双曲板的无量纲位移和正应力的影响.结果表明:无量纲位移和正应力的变化形式与载荷的变化形式相同;随着机械载荷的增大、热载荷作用区域的增大和曲率半径的减小,AHSS层无量纲正应力和涂层无量纲正应力的绝对值均增大;热载荷对无量纲正应力的影响较大,对位移的影响较小.

AHSS汽车钢板用高强度钢的连续退火工艺研究

研究了DP双相钢在连续退火工艺中加热温度、退火时间、缓冷温度和过时效温度对其组织和力学性能的影响。结果表明,随着临界区加热温度的升高,DP钢组织中的马氏体逐步转化为由铁素体和贝氏体组成的混合组织,其抗拉强度先升高后降低。随着退火时间的增加,抗拉强度升高而屈服强度和伸长率降低。随着缓冷温度的降低或过时效温度的升高,DP钢抗拉强度和屈服强度呈下降趋势,而伸长率增加。

AHSS拉弯矫直机辊系配置与传动方案探讨

结合拉弯矫直机在先进高强度带钢中的应用,介绍了拉弯矫直机的功能组成,重点分析并阐述了不同辊系配置的功能及应用场景,并对比分析了电机直联与差动传动两种传动方案的特点。

Effect of Deformation during Stamping on Structure and Property Evolution in 3^rdGeneration AHSS

Over the past decade extensive development of advanced high strength steel (AHSS) was driven by the demand from the automotive industry for stronger materials that can enable lightweighting to meet increasing fuel efficiency requirements. However, achievement of higher strength in many AHSS grades comes with reductions in ductility, leading to geometric constraints on formability and limiting their application. In this paper, a 3rd Generation AHSS with a compelling property combination of high tensile strength of ~1200 MPa and total elongation > 40% was used for laboratory and stamping studies. Various auto related laboratory tests were done including tensile testing, 180 degree bending, bulge testing, and cup drawing to estimate the steel’s formability under different applied conditions. Additionally, since laboratory testing provides only an estimation of the potential stamping response, the 3rd Generation AHSS sheet was stamped into B-pillars under industrial stamping conditions. Non-destructive and destructive analysis of the resulting stampings were done to evaluate the microstructural and property changes occurring during stamping. Significant strengthening of material in the stamped part is attributed to the structural changes through the complex Nanophase Refinement and Strengthening mechanism.

Feasibility of 0.02% Nb-Based Microalloyed Steel for the Application of One-Step Quenching and Partitioning Heat Treatment

To attain an enhanced combination of mechanical properties for low alloyed steel, the current study has been made to fulfill that growing need in the industry. Its results are introduced within this paper. One step Quenching and Partitioning (Q&P) heat treatment has been applied on Niobium-based microalloyed steel alloy with 0.2 %C, in the form of 2 mm thickness sheets. The target of this study is to investigate the viability of applying that significantly recommended, results-wise, heat treatment on the highly well-suited alloy steel samples, to achieve the main target of enhanced properties. A single temperature of 275°C was used as quenching and Partitioning temperature. Four Partitioning periods (30, 200, 500, and 1000 Seconds) were used for soaking at the same temperature. The results were analyzed in the light of microstructural investigation and mechanical testing. All applied cycles did not enhance the strength but moderately improved the ductility and toughness, mainly caused by the slightly high soaking temperature used. Niobium impact of grain refining was apparent through all cycles. The cycle of 500 Seconds Partitioning time obtained optimum values at that particular temperature. The 1000 Seconds Cycle obtained the worst combination of properties. A set of recommendations are set. More research is required at this point, where a lower Partitioning temperature is advised. In the light of the applied combination of parameters, the Partitioning period at such temperature is advised to be between 500 and 1000 Seconds. A high probability that periods closer to 500 than 1000 Seconds will produce better results. More research is needed between those two values of Partitioning time to precisely determine the optimum time at that temperature on that specific alloy.

980MPa级先进高强钢的发展

选用轻量化汽车材料时应综合考虑材料的性能、质量和成本。目前,先进高强钢被广泛用于汽车工业。先进高强钢有双相钢、相变诱导塑性钢、马氏体钢、复相钢、淬火-配分钢、DH钢等。综述了980 MPa及以上高强钢的分类和主要钢种,汽车用高强钢的化学成分、显微组织、力学性能和使用性能,并结合实际零件的制造过程对这些高强钢的焊接和成形性能作了较深入的探讨,简述了其发展现状和研究进展。

汽车用冷轧先进高强钢（AHSS）标准研究

主要介绍10种汽车用先进高强钢的特点及应用，重点研究了我国、美国、欧洲、日本汽车用冷轧先进高强钢标准及标准间的差异性，同时也介绍了VDA、GM等汽车制造商制定的材料标准。

汽车用先进高强钢本构模型与韧性断裂模型研究进展

轻量化是当前汽车行业全产业链共同面对的课题,提高先进高强钢使用比例是实现汽车轻量化的有效手段。对先进高强钢本构模型与韧性断裂模型的充分研究有助于提高先进高强钢开裂分析和预测的准确性,从而推动先进高强钢工程的应用进程。目前,在先进高强钢的研究过程中,学者们通常通过多种应变强化模型的线性组合,或结合微观结构与宏观力学行为进行多尺度分析来建立本构模型;通过多种应力状态下的准静态拉伸实验以及使用仿真与实验混合的方法来标定韧性断裂模型的参数。以第三代先进高强钢中的淬火配分(QP)钢为重点讨论对象,介绍了制备工艺与材料特性及其相关研究进展,并介绍了QP钢本构模型的研究现状、新近发展的非耦合韧性断裂模型以及考虑了应力三轴度和罗德角参数影响的韧性断裂模型在先进高强钢上的应用现状,最后指出了先进高强钢本构模型和韧性断裂模型未来的研究方向。

烘烤对980MPa先进高强钢RSW接头性能的影响

以DP980-DP980,DP980-QP980和QP980-QP980焊接组合在5√t熔核直径条件下的电阻点焊接头为研究对象,通过170℃保温20 min的烘烤处理,对接头进行拉剪试验、十字拉伸试验、扫描电镜观察及显微硬度测试等,分析了烘烤对980 MPa先进高强钢RSW接头性能的影响。结果表明,烘烤使各组合的抗拉剪峰值载荷进一步提升,接头吸收能量提升均超过10%;在十字拉伸方面,3种组合接头在烘烤后具有相近的能量吸收,对于DP980-QP980和QP980-QP980接头,烘烤后十字拉伸强度分别提升了56%和63%,吸收能量分别提升了27%和67%;3种组合的拉剪失效模式在烘烤前后没有显著变化,而经烘烤后,DP980-QP980的十字拉伸失效模式呈现QP980侧的裂纹扩展路径从熔合线向母材偏移的趋势;烘烤使点焊接头的金相组织呈现一定的回火特性,熔核硬度有一定的降低,但是并不显著。

先进高强度双相钢板料成形极限研究

随着先进高强度双相钢的工业需求量日益增加,亟需实现双相钢板料成形极限曲线的精确预测,由于根据国标采用的胀形试验较难准确获取FLC_(0)点使FLC不准确。本文基于DP590、DP780、DP980、DP1180在常温下的胀形试验结果,结合MMC断裂模型的数值模拟,建立了4种板料的胀形断裂预测模型,通过模拟准确求出FLC_(0),结合试验数据,建立了基于MMC断裂准则的成形极限曲线(FLC),并进行参数化研究。结果表明,基于MMC准则的成形极限曲线拥有较好的准确性。

先进高强双相钢DP780温度相关应力⁃应变关系

为了研究先进高强度双相钢DP780的温热成形力学行为,通过不同温度(300℃、400℃、500℃、600℃)及不同应变率(10-4~10-3 s-1)下的单向温拉伸试验获得了先进高强度双相钢DP780在相应条件下的基本力学性能指标和应力⁃应变曲线,并对试验结果进行了分析;为描述温热成形DP780板料应力⁃应变曲线,求解、修正了Grosman本构模型的相关参数;以单向拉伸试样为例,基于Fortran语言通过编写Abaqus⁃Vumat子程序进行了数值模拟验证。结果表明,所用Grosman模型预测值与试验数值拟合较好,验证了所求模型的有效性。