DP980钢及DP980钢激光焊接接头的高周疲劳性能

摘要：为了研究DP980钢的高周疲劳性能,采用疲劳试验机对DP980钢和DP980钢激光焊接接头进行高周疲劳试验,得到Basquin方程,并利用光学金相显微镜和扫描电镜进行组织和断口分析。结果表明：DP980钢激光焊接接头的焊缝根部和顶部出现形状凹陷,焊接接头的质量为中等。DP980钢疲劳极限为341MPa,DP980钢激光焊接接头的疲劳极限为148MPa,激光焊接接头的疲劳极限较母材的疲劳极限降低约50%。对于DP980钢而言,铁素体/马氏体晶界是裂纹萌生的主要位置,疲劳断口为准解理断口。对于DP980钢激光焊接接头而言,疲劳裂纹源位于焊缝凹陷处,而非热影响区及母材,疲劳断口为解理断口。DP980钢和DP980钢激光焊接接头的疲劳裂纹扩展区均有明显的疲劳条带,并伴随有二次裂纹。     

热输入对DP980激光焊组织和力学性能的影响

为了研究DP980钢的焊接性能,采用3种不同的激光焊接工艺进行焊接试验。结果表明,熔融区为板条马氏体,热影响区为马氏体、铁素体和回火马氏体,随着热输入增加,上下表面的熔宽逐渐增大,强塑积逐渐减小,热影响区的软化程度逐渐恶化。从熔融区到母材,显微硬度的变化趋势是先降低后升高。焊接接头静态拉伸失效位置均在亚临界热影响区,拉伸断口为韧性断口,随着热输入增加,杯状韧窝逐渐转变为较大的抛物线状韧窝,通过分析不同热输入条件下焊接接头的静态拉伸应变场云图,可知在塑性变形阶段,熔融区两侧呈双峰形貌,随着热输入的增加,软化区的面积逐渐增大,颈缩易出现在熔融区两侧的软化区部位。     

Comparative study of resistance spot welding performance between cold-rolled DP980 and Q&P980 steels

Advanced high strength steel (AHSS) has been widely used in the automobile industry.The resistance spot welding performance of DP980 and Q&P980 steels was studied through comparing the two steels’welding current range,tensile shear strength (TSS),cross tension strength (CTS),weld spots’microhardness,etc.The following conclusions were achieved:It is easy for both DP980 and Q&P980 steels to get a nugget size bigger than 4 mm,they all have welding current ranges exceeding 2 kA and high weld strength.     

激光拼焊异种超高强钢组织和力学性能

 汽车轻量化后对安全性和碰撞吸能性提出了更高要求,从而促进了高强、吸能材料及其拼接技术的发展。以汽车安保件之一的汽车B柱为研究对象,采用能满足要求的DP980双相钢和22MnB5热冲压成型钢异种材料进行激光拼焊,研究焊接热输入对焊接接头显微组织与力学性能的影响。通过保持激光输出功率不变(1.3 kW)改变焊接速度的方法控制焊接热输入,考察焊接热输入与拼焊接头组织和力学性能之间的关系。利用光学显微镜、扫描电子显微镜、显微硬度测试仪和拉伸试验机研究接头不同亚区的组织和性能。结果表明,当焊接速度为16~26 mm/s时,均获得了完整而无缺陷的熔化区组织;随着焊接速度的提高,不仅焊缝表面凹陷逐步改善,并且焊接热影响区宽度也随之减小。硬度测试表明,接头中存在明显的软化区域,主要分布在DP980侧热影响区的回火区和不完全相变区,而DP980侧热影响区的细晶区、粗晶区、22MnB5侧热影响区以及焊缝金属区的硬度则有所增加,形成了焊接接头的硬化区。拼焊接头在能形成完整接头的条件下抗拉强度保持为576~597 MPa,断裂均发生在22MnB5侧的母材区,断裂时有明显的颈缩现象;接头断后伸长率为11.9%~15.5%,介于DP980母材(11%)和22MnB5(22%)母材的断后伸长率之间;研究还表明,焊接热输入越大,焊接接头相同区域的组织越粗大。     

热输入对DP600激光焊组织和力学性能的影响

摘要：为了研究DP600钢的焊接性能，采用5种不同的激光焊接工艺进行焊接试验。结果表明，焊接接头表面成形质量良好，随着热输入的增加，上下熔宽逐渐增大；熔融区均为板条状马氏体组织，当热输入高于33J/mm时热影响区组织为马氏体、铁素体和少量的回火马氏体；当热输入低于33J/mm时，热影响区组织为马氏体和铁素体。在低热输入条件下，回火时间很短，马氏体未发生分解；在高的热输入条件下，回火时间较长，马氏体分解显著，热影响区中出现M3C型碳化物，碳化物形貌以球状和片状为主。从熔融区到母材，显微硬度值逐渐降低；焊接接头静态拉伸失效位置均在母材，拉伸断口为韧性断口，DP600钢激光焊接接头不存在软化现象。     

Investigation of Microstructural Features Determining the Toughness of 980 MPa Bainitic Weld Metal

The microstructural features that control the impact toughness of weld metals of a 980 MPa 8 pct Ni high-strength steel are investigated using instrumented Charpy V tester, optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM), electron back-scattered diffraction (EBSD), and finite-element method (FEM) calculation. The results show that the critical event for cleavage fracture in this high-strength steel and weld metals is the propagation of a bainite packet-sized crack across the packet boundary into contiguous packets, and the bainitic packet sizes control the impact toughness. The high-angle misorientation boundaries detected in a bainite packet by EBSD form fine tear ridges on fracture surfaces. However, they are not the decisive factors controlling the cleavage fracture. The effects of Ni content are essential factors for improving the toughness. The extra large cleavage facets seriously deteriorate the toughness, which are formed on the interfaces of large columnar crystals growing in welding pools with high heat input.     

Fatigue Assessment of Cruciform Joints Welded with Different Methods

The advantages of the relatively new laser welding method are low welding distortions and high productivity, and it opens new opportunities for welding of steel structures in the automotive and heavy machinery industries. There is a need for understanding the fatigue strength and to develop fatigue design curves for laser welded joints. In this paper fatigue testing and weld quality of Hybrid Nd: YAG laser/MAG and MAG welded non‐load carrying cruciform joints is examined. Four batches were produced, tested and the results were compared. The local weld geometry of the cruciform welded joints was measured and analysed. The measured parameters were used to calculate the stress concentration factors by implementing FE‐models, in order to anticipate the influence of size of weld geometrical parameters on the stress concentrations. Residual stress measurement was carried out close to the toe region using the X‐ray diffraction method and weld defects (cold laps) in the cracked specimens was measured.     

Characteristics of Welding Crack Defects and Failure Mode in Resistance Spot Welding of DP780 Steel

The mechanical properties of welded joints in resistance spot welding of DP780 steel were tested,and three dif-ferent types of welding cracks in welded joints were investigated by optical microscopy,scanning electron microscopy and electron back-scattered diffraction.Finally,the failure mode of the welded joints in shear tensile test was dis-cussed.It is found the shear tensile strength of welded joints can be greatly improved by adding preheating current or tempering current.The surface crack in welded joint is intergranular fracture,while the inner crack in welded joint is transgranular fracture,and the surface crack on the edge of the electrode imprint can be improved by adding prehea-ting current or tempering current.The traditional failure mode criterion advised by American Welding Society is no longer suitable for DP780 spot welds and the critical nugget size suggested by Pouranvari is overestimated.     

DP980钢的动态力学性能及本构模型构建

随着汽车轻量化事业的不断推进,先进高强DP钢得到了快速的发展和应用.而汽车碰撞过程安全性的模拟仿真,对DP钢提出了动态力学性能数据的迫切需求.利用万能拉伸试验机和高速拉伸试验机系统研究了高强度DP980钢不同应变速率下的力学性能,构建并修正了基于JC模型的动态本构数学模型,并进行了模型计算结果与试验数据的对比分析.试验...     

超声冲击对P355NL1钢焊接接头超高周疲劳性能影响

 通过超声疲劳试验探究超声冲击对P355NL1钢焊接接头超高周疲劳性能的影响。结果表明,由疲劳[S-N]曲线可知,在105～109寿命区间内,冲击态试样的疲劳性能要高于焊态试样,在1.0×108的疲劳寿命下,焊态试样的疲劳强度为139 MPa,冲击态的疲劳强度为217 MPa,冲击态疲劳强度相较于焊态提高了56%,这表明超声冲击可以明显提高焊接接头的疲劳强度。利用扫描电镜（SEM）观察断口形貌可以发现,裂纹源位于焊接接头焊根区表面。P355NL1钢焊接接头疲劳断裂为准解理断裂,超声冲击可以提高焊接接头的疲劳强度,但不会改变其疲劳失效机理。超声冲击可以降低焊根处应力集中,引入有益压应力和表面晶粒细化,从而提高焊接接头的疲劳强度。     

32Cr3MoVE轴承钢旋弯疲劳特性及裂纹萌生扩展行为

摘要：采用光滑漏斗状试样对32Cr3MoVE轴承钢进行旋转弯曲疲劳测试，研究了32Cr3MoVE轴承钢旋转弯曲疲劳性能及裂纹萌生扩展行为。采用升降法测得其疲劳极限为860MPa，疲劳断口SEM观察并统计破断试样结果表明：疲劳破坏68.7%是由于非金属夹杂起裂，18.8%由表面加工缺陷起裂，125%为表面粗糙度起裂。当加载应力低于980MPa时，疲劳断裂主要是由于内部非金属夹杂引起的，高于980MPa时，疲劳断裂主要是由于表面粗糙度引起的。表面加工缺陷和表面粗糙度引起的最大应力强度因子分别为3.05和2.97MPa·m1/2，容易引发疲劳裂纹。非金属夹杂物尺寸在5.30～5.90μm范围内，局部应力从859.35MPa升至977.75MPa时，疲劳寿命从1.96×105降低到1.58×105；非金属夹杂物局部应力在840～900MPa范围内，夹杂物尺寸从2.28μm升至5.83μm时，疲劳寿命从1.10×106降低到1.96×105。     

高强度无取向电工钢疲劳性能及断裂机制

测试了高强无取向电工钢的S-N曲线,并借助光学显微镜、扫描电子显微镜、透射电子显微镜分析了实验钢组织,疲劳断口形貌和位错结构.结果 表明:室温条件下,频率为20 Hz,应力比R为0.1,循环107周次时,实验钢的疲劳强度为360 MPa,疲劳裂纹萌生于实验钢的次表面,裂纹萌生点附近有沿晶开裂现象,疲劳裂纹扩展区域有解理台阶与疲劳条纹,瞬间断裂区是韧性断裂,有大量韧窝.实验钢在循环应力作用下基体中产生了大量位错,并有驻留滑移带终止在晶界位置.     

1800 MPa热成形钢与CR340LA低合金高强钢激光焊接性能

采用光纤激光焊接设备对1800 MPa级热成形钢与CR340LA低合金高强钢进行对接激光拼焊,研究了不同激光焊接功率和焊接速度下焊接接头的组织演变规律及热冲压成形性能,并对焊接接头的力学性能和硬度进行了分析。结果表明,3种焊接工艺下激光拼焊原板综合力学性能相差较小,由焊接接头造成的伸长率和抗拉强度的损失均在母材的28.3%和9.1%以内。激光焊接后焊缝区均为粗大、高硬度的马氏体结构;两侧热影响区组织主要为铁素体和马氏体,接头未出现明显的软化区。激光拼焊原板拉伸试样均断裂于CR340LA母材区,距离焊缝12 mm左右,且存在焊缝隆起现象。选取焊接功率和焊接速率分别为4000 W和0.18 m·s?1的焊接试样在高温下进行热冲压成形检测,未出现焊缝开裂,热成形后拼焊板具有良好性能,满足汽车激光拼焊板使用要求,拉伸结果表明,试样断裂位置与未热冲压成形前一致,均位于CR340LA母材区,拉伸过程中,焊缝向高强度母材侧偏移,在弱强度母材侧产生应力集中并缩颈断裂。      

Properties of the welded joints of manganese steel made by low-frequency pulsed arc welding

The structure, the mechanical properties, the impact toughness, and the fracture mechanisms of the welded joints made of steel 09G2S plates by direct current welding and pulsed arc welding with a modulated arc current in the frequency range 0.25–5.0 Hz are studied. The application of low-frequency pulsed arc welding allowed us to form welded joints with a fine-grained structure in the weld metal and the heat-affected zone and to achieve a higher impact toughness and a longer cyclic fatigue life as compared to the welded joints fabricated by direct current welding. The achieved effect manifests itself over the entire testing range from 20 to–60°C.     

Spot weldability comparison of high strength steel DP590 with different chemical composition

This paper introduces the cold-rolled DP590 high strength automotive steel sheets produced by Sougang Steel,which involve two different composition systems,one with high Al content and the other with C-Si-Mn.These two materials are pot-welded and the optimized welding current range and the best welding current are obtained.Both the two kinds of materials welding current’s scope is 1 800 A,but the current of C-Si-Mn system DP590 is 1 400 A higher then the high Al content one’ s;when these two kind of materials are welded with the optimal current,the nugget can be get by no defect.There have some difference in these two base materials.High Al DP590 has a bandy metallurgical structure compose with ferrite and martensite,the volume fraction of martensite is 8%,the grain size is 10.5.C-Si-Mn system DP590 compose with ferrite and martensite also while the volume fraction of martensite is 9%,the grain size is 9.5.Weld structure of high Al DP590 are bainite and lath martensite when C-Si-Mn system DP590’s is lath martensite only.The variation of HV is same for these two materials nugget,the length of the are both 10 mm,there have no soft zone in the weld scope.The HV of the both materials are the same of 210 -220.The HV of high Al DP590 weld scope is 280,when C-Si-Mn system DP590 is much more then it with 425.After test these two welded sample get the same failure modes,the maximum shearing resistance and maximum positive tension of high Al DP590 are both less than the C-Si-Mn system DP590.     

高强度焊丝WER80的应用研究

介绍了以高强度、高韧性气保护焊丝WER80为材料,对焊丝熔敷金属及武钢HG785钢、HG980钢对接进行气保护焊接试验研究。采用富氩气体保护熔敷金属抗拉强度达到了810 MPa,-30℃冲击功达到106 J;匹配HG785钢气保护焊焊接接头抗拉强度达到815 MPa,-30℃冲击功大于90 J;匹配HG980钢气保护焊...     

DP590/DP780高强钢管液压成形的性能

为对生产进行指导,研究了DP590/DP780高强钢焊管在液压成形过程中的变形行为;使用场发射扫描电镜观察管材周向的横截面以确定基体的组织,通过VMHT30M显微硬度计确定管材的焊缝及热影响区的大小,以便研究液压成形破裂行为;采用液压成形试验机对两种管件进行液压成形研究。实验结果表明:管材在胀形过程中的破裂压力比理论计算公式得到的破裂压力大,破裂位置全部位于靠近焊缝及热影响区的母材区域;随着管径的增大和长径比的增大,管材的极限膨胀率呈现下降趋势;在自由胀形过程中,管材的焊缝区域基本上不发生减薄,最小壁厚位于管材的热影响区和基体的过渡区域,并且壁厚的减薄率在胀形最高点所在截面最大,越靠近管材夹持区,壁厚的减薄率越小。最终得到以下结论:管材液压成形实验是准确获得管材力学性能参数的途径;提高焊接质量有助于控制失效破裂位置;合理选择管材的长径比有利于管材性能的充分发挥;通过合理控制各处的减薄有利于降低液压成形件的破裂风险。      

High- temperature fatigue property of 18CrNbTi ferritic stainless steel

In order to determine the influence of dwell time and atmosphere environment on high- temperature fatigue properties of 18CrNbTi ferritic stainless steel, the high- temperature fatigue behaviors of 18CrNbTi steel with 10s dwell time at maximum stress in argon and simulated automobile exhaust gas were investigated under axial tension- tension stress- controlled mode at 800??, and compared with its high- temperature fatigue behavior in air without dwell time. The fracture surfaces of fatigued specimens were observed with scanning electron microscope. The results show that: the fatigue limit of 18CrNbTi steel in air is 25MPa; the fatigue resistance and fatigue life of 18CrNbTi steel significantly reduce after introducing 10s dwell time; in comparison with those in argon, the fatigue resistance and fatigue life have a further decrease in the simulated automobile exhaust gas; the fatigue cracks both initiate and propagate in a transgranular mode under all testing conditions.     

铈和铌改性对DP780双相钢焊缝冲击性能的影响

 双相钢中铁素体马氏体两相性能差异会导致焊接接头软化,在使用过程中温度较低时,冲击功下降,使材料由韧性状态变为脆性状态。为研究铈和铌添加量对改善DP780焊缝低温脆性的问题,利用低温冲击试验与拉伸试验,开展了不同铈和铌添加量对DP780焊缝的力学性能的研究。利用金相显微镜、SEM等方法阐明了试验钢在添加不同铈和铌后的焊缝组织与形貌变化。结果表明,在-40 ℃时,无铈和铌添加时组织中出现部分残余奥氏体,焊缝冲击功为0.465 J,解理台阶面出现大量河流花样,属于脆性断裂;随铈与铌质量分数变化,焊缝冲击功与铈和铌的添加量呈现非线性关系。当铈与铌占熔敷金属质量分数分别为0.35%和0.15%时焊缝的综合性能最佳,冲击功达到3.9 J,熔敷金属组织晶界紧密,撕裂棱周围出现韧窝,呈混合断裂特征。试验研究表明,加入的适量的铈与铌,焊缝中形成的稀土化合物可增加断裂变形阻力与消耗能量,从而有效阻碍裂纹的扩展,显著提高DP780的低温冲击韧性而不会大幅降低其抗拉强度,保证双相钢焊接质量。但铈与铌影响焊缝性能无固定函数关系可循且试验样本量少,无法精确到任意添加量探究。在后续研究中可引入算法对DP780焊缝力学性能进行预测,在生产之前建立模型,寻找最佳铈和铌添加量,提高安全性能。     

Microstructural Evolution of DP980 Steel during Friction Bit Joining

The authors study a new solid-state spot joining process, friction bit joining (FBJ), which relies on the use of a consumable joining bit. It has been reported that FBJ is feasible for the joining of steel/steel and aluminum/steel, but the metallurgical characteristics of the joint for enhancement of the properties and reliability remain unclear. Therefore, this study produced friction bit joints in DP980 steel and then examined the microstructures in the joint precisely. In this article, the microstructure distribution associated with hardness in the friction-bit-joined DP980 steel and the microstructural evolution during FBJ are reported.