焊接接头材料低周疲劳断口的分形分析

对16MnR压力容器用钢焊接接头应变控制的低周疲劳试验,运用计算机视觉系统测量疲劳断裂粗糙表面,用二维变差法(Variation Method)计算了断口(焊缝金属和焊接热影响区)的Hausdorff维数,发现其随循环滞回能的增加而降低,焊接热影响区断口的Hausdorff维数的变化比焊缝金属断口的Hausdorff维数变化大;建立了疲劳寿命同Hausdorff维数的关系,说明分形维数愈大疲劳寿命愈长。     

焊接力学非均匀体低周疲劳循环滞回能实验研究

通过16MnR压力容器用钢焊接接头的低周疲劳实验,研究了母材、焊缝和热影响区的循环滞回环特性及其变化规律提出了焊接接头疲劳失效的定义,建立了循环滞回能及总耗散能与疲劳寿命之间的实验关系式;讨论了焊接力学非均匀性对疲劳损伤的影响.     

钟罩型电子束焊接接头的疲劳寿命分析

利用MSC公司的系列软件,模拟试验加载条件,将TC4钛合金钟罩型电子束焊接试件划分成焊缝、热影响区和母材3个区域,同时考虑热影响区材料强度的梯度分布,建立有限元模型,详细分析了焊件中的应力和疲劳寿命分布,沿不同观察路径考察了应力分布的规律,并将疲劳寿命分析结果与试验结果进行了比较.结果表明,焊缝对焊件的受力分布有明显影...     

镍基高温合金电子束焊接接头疲劳性能

对GH4169高温合金板材电子束焊接试样进行了金相分析和高、低周疲劳试验,分析GH4169合金的高、低周疲劳性能及疲劳断口形貌.结果表明,GH4169合金电子束焊接接头焊缝区的特点是树枝晶比较明显,为比较发达的树枝晶和明显的二次枝晶.在较高放大倍数下发现,母材和热影响区也为树枝晶结构.接头低周疲劳性能不低于母材,随应变幅降低,相同应变幅下焊接接头疲劳寿命变得略高于母材.接头高周中值疲劳强度比母材高约80 MPa.     

Fatigue properties of ferrite/bainite dual-phase X80 pipeline steel welded joints

Fatigue properties are important parameters for the safety design and security evaluation of pipelines. In this work, fatigue life and fatigue crack propagation of full-thickness X80 pipeline steel joints compared with the base metal (BM) was investigated. Full-thickness BM specimens showed superior fatigue life compared with that of welded joints. The fatigue crack initiation of full-thickness X80 welded joint specimens occurred at the outside weld toe and then grew inward until a fracture was formed. During fatigue crack growth in the heat-affected zone (HAZ), crack growth rate linearly increased with increased ΔK in each HAZ subregion. However, the change rate of fatigue crack growth rate (da/dN) differed among HAZ subregions. This difference was related to the variation in crack path and fracture mode because of the possible microstructural sensitivity of fatigue crack propagation behaviour.     

A6N01-T5合金FSW和MIG焊接头疲劳裂纹扩展行为的对比

研究了6N01-T5铝合金搅拌摩擦焊(FSW)和氩弧焊(MIG)接头不同部位的疲劳裂纹扩展性能, 并对疲劳断口和接头组织进行了分析. 结果表明,对于FSW和MIG焊接头, 其裂纹扩展速率从高到低的部位依次为焊缝(核)区、热影响区和母材. 裂纹在FSW和MIG焊接头相同区域的扩展速率无明显差别, 然而裂纹在FSW接头细晶组织中开始扩展所需的门槛值ΔK要比对应的MIG焊接头高, 总体上其裂纹在FSW焊核区的抗疲劳裂纹扩展性能要优于对应的MIG焊缝区. 裂纹在FSW和MIG焊接头焊核(缝)区扩展的疲劳断口表现为脆性断裂, 而在热影响区则以规则和光滑的疲劳条纹形式扩展.     

FV520B钢十字焊接接头的疲劳性能

用金相显微镜和扫描电镜观察了FV520B钢焊接接头母材、焊缝及热影响区的微观组织;并通过透射电镜给出了母材和焊缝的微观形貌。结果表明:母材组织为细小均匀的回火马氏体、弥散分布的析出相及高密度位错,而焊缝为粗大的板条马氏体及少量的析出相,说明母材力学性能优于焊缝。利用疲劳实验获得了高平均拉应力下接头的疲劳强度及S-N曲线等。通过对疲劳断口的观察,发现疲劳断裂主要有两种形式:破坏于焊趾处和焊接缺陷处,由于这里严重的应力集中,加速了疲劳裂纹的萌生。     

Microstructure and Fatigue Properties of Laser Welded DP590 Dual-Phase Steel Joints

In this paper, cold-rolled DP590 dual-phase steel sheets with 1.5 mm thickness were butt-welded by a fiber laser, and the evolution and effect on microhardness, tensile property and fatigue property of the welded joint microstructure were studied. The results showed that the base metal is composed of ferrite and martensite, with the martensite dispersed in the ferrite matrix in an island manner. The microstructure of the weld zone was lath-shaped martensite that can be refined further by increasing the welding speed, while the heat-affected zone was composed of ferrite and tempered martensite. The microhardness increased with increasing welding speed, and the hardness reached its highest value—393.8 HV—when the welding speed was 5 m/min. Static tensile fracture of the welded joints always occurred in the base metal, and the elongation at break was more than 16%. The conditional fatigue limits of the base metal and the weld joints were 354.2 and 233.6 MPa, respectively, under tension–tension fatigue tests with a stress rate of 0.1. After observation of the fatigue fracture morphology, it was evident that the fatigue crack of the base metal had sprouted into the surface pits and that its expansion would be accelerated under the action of a secondary crack. The fatigue source of the welded joint was generated in the weld zone and expanded along the martensite, forming a large number of fatigue striations. Transient breaking, which occurred in the heat-affected zone of the joint as a result of the formation of a large number of dimples, reflected the obvious characteristics of ductile fracture.     

Fatigue life assessment of weld joints manufactured by GMAW and CW-GMAW processes

The fatigue strength of weld joints manufactured using gas metal arc welding and cold wire GMAW (CW-GMAW) was evaluated under stress-controlled cyclic loading. The material used in this study was class ASTM 131 grade A steel, joined using ER70S wire filler metal. The addition of cold wire led to a decrease in the amount of intergranular ferrite and an increase in hardness in the heat-affected zone. The assessment of fatigue life was performed by using the Weibull distribution and the results revealed that with a 99% reliability the joints produced using the CW-GMAW process have a longer fatigue life, especially as the stress amplitude increases.     

UNS S32304双相不锈钢等离子弧焊接头的组织及其耐点蚀性能

采用恒电位临界点蚀温度(CPT)法,利用OM,SEM,EDX和恒电位极化技术等研究了等离子弧焊接对双相不锈钢UNSS32304焊接接头微观组织及其耐点蚀性能的影响.结果表明,焊接接头热影响区和熔合区微观组织较母材相比发生了显著变化,两相比例严重失衡,铁素体所占比例均大于70%;两区域微观组织形态发生明显变化.且在铁素体晶粒内及两相相界处析出大量氮化物;焊接接头的耐点蚀性能明显下降,点蚀优先发生在高温热影响区所在的铁素体晶粒内.     

DE-GMAW高速电弧焊工艺机理的研究

通过大量的工艺实验,找出了DE-GMAW双焊枪组合的匹配参数,测试了焊接电流波形,拍摄了熔滴过渡图像,并获得了无成型缺陷的焊缝照片.基于实验结果解释了高速焊接工艺的机理.建立了适用于DE-GMAW焊接工艺的有限元模型,并对该工艺条件下的温度场、应力-应变场进行了数值模拟.结果表明:计算出的DE-GMAW焊缝横断面形状尺寸与实验结果吻合良好;在通过焊丝的总电流相同时,DE-GMAW焊接时焊缝尺寸、热影响区宽度、应力、应变及变形均小于常规GMAW焊时的结果.这为DE-GMAW焊接工艺参数优化提供了基础数据.     

钛合金激光焊接接头的组织和力学性能

对2.5mm厚BT20钛合金激光焊接接头各区域(包括焊缝和热影响区)的组织特征进行了观察,并测试了焊接接头各区域的显微硬度分布以及室温条件下的接头拉伸、弯曲、疲劳及断裂韧度等力学性能.研究结果表明,焊接接头各区域的微观组织均以"网篮状"马氏体组织为特征,接头各区域显微硬度均高于母材.接头静抗拉强度基本与母材相当,塑性略低于母材.接头中值疲劳寿命与应力水平有很大的关系.在低应力水平下,接头中值疲劳寿命与母材相当,而在高应力水平下,接头中值疲劳寿命远低于母材.接头焊缝金属的断裂韧度显著低于母材,而热影响区断裂韧度则介于母材和焊缝金属之间.     

07MnNiCrMoVDR低温钢的焊接及其低温冲击韧性分析

从制定低温钢07MnNiCrMoVDR的焊接及焊后热处理工艺着手,并对其母材、焊缝区和热影响区进行了低温冲击试验、不同温度断口纤维率的计算、断口宏观与微观观察及显微组织观察.结果表明,各区的低温冲击功均符合07MnNiCrMoVDR钢力学性能的要求,采取的焊接及焊后热处理工艺合理;通过断口纤维率的计算得知母材断口的纤维率高于热影响区的断口纤维率,焊缝区的最低,表明母材的低温冲击韧性最高,热影响区的低温冲击韧性高于焊缝区的,对各区显微组织的观察结果也证明了这一点.     

Analysis of acoustic and optical signals used as a basis for controlling laser‐welding processes

Stud joints of 2017 aluminium alloy were friction welded and its joint strength was examined. A stair zone was formed at the weld interface. Although the hardness of the stair zone was almost the same as base metals, the heat-affected zone of the bar and the plate was softened. The tensile strength of joints tended to increase with a pressure and a friction time, and the highest tensile strength was 275 MPa (63.1% joint efficiency for the bar base metal). In the bending testing, joints were cracked in the weld zone at a bending angle of less than 5°. In the fatigue testing, joints fractured near the weld interface and the fatigue strength of joints increased as the tensile strength of joints was high.     

方波加载对20CrMo钢焊缝疲劳裂纹扩展的影响

利用拉-拉疲劳法和金属磁记忆检测法研究了20CrMo钢焊缝在方波加载方式下疲劳裂纹扩展与自发射磁信号的相关性,用扫描电镜对疲劳断口特征进行了研究.结果表明,裂纹到达焊缝中心前,随着疲劳寿命的增加,焊缝处的自发射磁信号也随着增加,疲劳裂纹扩展速率先增加后减小,当裂纹越过焊缝后,随着疲劳寿命的增加,焊缝处的自发射磁信号开始减小,疲劳裂纹的扩展速率却迅速增加.在焊接接头的不同区域,疲劳裂纹扩展速率也不相同,其中热影响区扩展速度较快,而在其它区域扩展速率相对较慢.断口扫描分析表明方波加载方式下的疲劳断口为类解理断裂.     

Microstructure and mechanical properties of laser welded dissimilar DP600/DP980 dual-phase steel joints

The use of dual phase (DP) steels in the automobile industry unavoidably involves welding and dynamic loading. The aim of this investigation was to evaluate the microstructural change and mechanical properties of laser welded dissimilar DP600/DP980 steel joints. The dissimilar joints showed a significant microstructural change from nearly full martensite in the fusion zone (FZ) to the unchanged ferrite-martensite dual-phase microstructure in the base metal. The welding resulted in a significant hardness increase in the FZ but the formation of a soft zone in the heat-affected zone (HAZ). The dissimilar welded joints were observed to exhibit a distinctive unsymmetrical hardness profile, yield-point-like phenomenon, and single-stage work hardening characteristic, with yield strength and work hardening rate lying in-between those of DP600 and DP980 base metals, and ultimate tensile strength equivalent to that of DP600 base metal. Although the welded joints showed a lower fatigue limit than the base metals, the fatigue life of the welded joints at higher stress amplitudes was almost the same as that of the DP600 base metal. The welded joints failed in the soft zone at the DP600 side under tensile loading and fatigue loading at the higher stress amplitudes. Fatigue crack initiation occurred from the specimen surface and crack propagation was characterized by typical fatigue striation together with secondary cracks.     

Fatigue properties of friction stir welded butt joint and base metal of MB8 magnesium alloy

The fatigue properties of friction stir welded(FSW) butt joint and base metal of MB8 magnesium alloy were investigated.The comparative fatigue tests were carried out using EHF-EM200K2-070-1A fatigue testing machine for both FSW butt joint and base metal specimens.The fatigue fractures were observed and analyzed using a scanning electron microscope of JSM-6063 LA type.The experimental results show that the fatigue performance of the FSW butt joint of MB8 magnesium alloy is sharply decreased.The conditional fatigue limit(2 × 10~6) of base metal and welded butt joint is about77.44 MPa and 49.91 MPa,respectively.The conditional fatigue limit(2 × 10~6) of the welded butt joint is 64.45%of that of base metal.The main reasons are that the welding can lead to stress concentration in the flash area,tensile welding residual stress in the welded joint(The residual stress value was 30.5 MPa),as well as the grain size is not uniform in the heat-affected zone.The cleavage steps or quasi-cleavage patterns present on the fatigue fracture surface,the fracture type of the FSW butt joint belongs to a brittle fracture.     

Effect of Laser Welding Process Parameters on Microstructure and Mechanical Properties on Butt Joint of New Hot-Rolled Nano-scale Precipitation-Strengthened Steel

A 4 kW fiber laser was chosen to weld the new hot-rolled nano-scale precipitation-strengthened steel with a thickness of 4.5 mm. The effect of laser power, defocusing distance, and welding speed on the welded joint appearance was examined, and the microstructure and mechanical properties on the typical butt joints were investigated. Results showed that increasing laser welding power may cause faster downward flow of molten metal to produce greater root humping. With the welding speed increasing, the average welding seam （WS） width decreased, and the average WS and heat-affected zone （HAZ） hardness increased. The microstructures of WS, fusion line, and coarse grain heat-affected zone were lath martensite, but the growth direction of the original austenite grain boundaries was significantly different. The microstructures of fine grain heat-affected zone were ferrite and martensite, and the microstructure of mixed grain heat- affected zone contained ferrite, massive M/A island, and a small amount of martensite. The micro-hardness values of WS, HAZ, and base metal （BM） were 358, 302, and 265 HV, respectively. The butt joint fracture at the BM far from the WS and the welded joint tensile strength are observed to follow proportional relationship with hardness.     

Effect of welding heat input on HAZ character in ultra-fine grain steel welding

In this essay, we studied how heat input affected the microstructure, hardness, grain size and heat-affected zone (HAZ) dimension of WCX355 ultra-fine grain steel which was welded respectively by the ultra narrow-gap welding (UNGW) process and the overlaying process with CO2 as protective atmosphere and laser welding process. The experimental results show when the heat input changed from 1.65 kJ/cm to 5.93 kJ/cm, the width of its HAZ ranged from O. 6 mm to 2. 1 ram. The average grain size grew up from 2 ~ 5 pln of base metal to 20～70 um and found no obvious soften phenomenon in overheatedzone. The width of normalized zone was generally wide as 2/3 as that of the whole HAZ, and the grain size in this zone is smaller than that in base metal. Under the circumstance of equal heat input, the HAZ width of UNGW is narrower than that of the laser welding.     

S355钢T形接头高周疲劳性能

在工程领域中焊接构件极易产生疲劳断裂,引起各行业广泛关注。文中以T形接头为研究对象,采用MIG焊对S355钢板进行T形接头焊接试验,并对焊接接头进行金相组织和硬度分析。结果表明,焊缝主要为先共析铁素体、珠光体、粒状贝氏体和少量针状铁素体;熔合区成分和组织不均匀,晶粒大小不一致;过热区晶粒较粗大且不均匀;正火区组织主要为铁素体和珠光体,晶粒细小均匀。焊接接头的硬度高于母材,最高硬度出现在热影响区。对T形接头焊接试样进行轴向高周疲劳试验,通过最小二乘法拟合试验数据,得到疲劳S-N曲线。