Interfacial microstructure evolution of 12Cr1MoV/TP347H dissimilar steel welded joints during aging

The interfacial microstructure evolution of 12Cr1MoV/TP347H dissimilar steel welded joints with a nickel-based filler metal during aging was studied in detail to elucidate the mechanism of premature failures of this kind of joints.The results showed that not only a band of granular Cr_(23)C_(6)carbides were formed along the fusion boundary in the ferritic steel during aging,but also a large number of granular or plate-like Cr_(23)C_(6)carbides,which have a cube-cube orientation relationship with the matrix,were also precipitated on the weld metal side of the fu-sion boundary,making this zone be etched more easily than the other zone and become a dark etched band.Stacking faults were found in some Cr_(23)C_(6)carbides.In the as-welded state,deformation twins were observed in the weld metal with a fully austenitic structure.The peak micro-hardness was shifted from the ferritic steel side to the weld metal side of the fusion boundary after aging and the peak value increased signific-antly.Based on the experimental results,a mechanism of premature failures of the joints was proposed.

Influence of Creep Strength of Weld on Interfacial Creep Damage of Dissimilar Welded Joint between Martensitic and Bainitic Heat-Resistant Steel

The mechanical properties, creep rupture strength, creep damage and failure characteristics of dissimilar metal welded joint （DMWJ） between martensitic （SA213T91） and bainitic heat-resistant steel （12Cr2MoWVTiB（G102）） have been investigated by means of pulsed argon arc welding, high temperature accelerated simulation, mechanical and creep rupture test, and scanning electronic microscope （SEM）. The results show that there is a marked drop of mechanical properties of undermatching joint, and low ductility cracking along weld/G102 interface is induced due to creep damage. Creep rupture strength of overmatching joint is the least. The mechanical properties of medium matching joint are superior to those of overmatching and undermatching joint, and creep damage and failure tendency along the interface of weld/G102 are lower than those of overmatching and undermatching joint after accelerated simulation for 500 h, 1 000 h, 1 500 h, and the creep rupture strength of medium matching joint is the same as that of undermatching joint. Therefore, it is reasonable that the medium matching material is used for dissimilar welded joint between martensitic and bainitic steel.

Numerical Investigation on Fracture Initiation Properties of Interface Crack in Dissimilar Steel Welded Joints

Fracture toughness property is of significant importance when evaluating structural safety.The current research of fracture toughness mainly focused on crack in homogeneous material and experimental results.When the crack is located in a welded joint with high-gradient microstructure and mechanical property distribution,it becomes difficult to evaluate the fracture toughness behavior since the stress distribution may be affected by various factors.In recent years,numerical method has become an ideal approach to reveal the essence and mechanism of fracture toughness behavior.This study focuses on the crack initiation behavior and driving force at different interfaces in dissimilar steel welded joints.The stress and strain fields around the crack tip lying at the interfaces of ductile-ductile,ductile-brittle and brittle-brittle materials are analyzed by the numerical simulation.For the interface of ductile-ductile materials,the strain concentration on the softer material side is responsible for ductile fracture initiation.For the ductile-brittle interface,the shielding effect of the ductile material plays an important role in decreasing the fracture driving force on the brittle material side.In the case of brittle-brittle interface,a careful matching is required,because the strength mismatch decreases the fracture driving force in one side,whereas the driving force in another side is increased.The results are deemed to offer support for the safety assessment of welded structures.

Microstructure characteristics and mechanical properties of steel stud to Al alloy by CMT welding-brazing process

Cold metal transfer （CMT） welding of nickel-coated Q235 steel studs with 606l Al alloy was carried out using ER4043 as filler metal. The welding process was stable, and appearance of weld formed well without surface defect under the parameters of welding current 121 A, welding voltage 15.4 V and welding speed 6 r/min. The microstructure of fiUer metal was analyzed by means of scanning electron microscopy. The filler metal and 6061 Al alloy were fused to form fusion welding interface, the fusion zone had a good bonding without any micro defect. The steel stud did not melt and brazing interface was formed between the filler metal and steel stud. Two different reaction layers existed in the brazing interface, the Fe2Al5 layer about 10 -12 p^m formed near the steel stud side, and the other layer was mainly composed of FeAl3. Nickel-rich zone was formed in the root toe area of the fillet weld, which was mainly composed of Al3Ni2. The tensile tests showed that the maximum shearing strength of the joints was 129 MPa. The joint was brittle fractured in the intermetallic compound layer where plenty of FeAl3 were distributed continuously.

超临界电站锅炉马氏体/奥氏体异种钢焊接接头失效模式分析

某350 MW超临界循环流化床机组T91+TP347HFG异种钢焊接接头发生开裂泄漏。本文采用宏观检查、化学成分分析、力学性能测试、硬度测定、金相组织形貌观察等方法对焊接接头试样进行研究,分析其开裂原因。试验结果表明:该异种钢焊接接头泄漏的原因是焊接质量不过关,且未按照要求进行焊后热处理工作。

桥式起重机箱形梁异种钢焊接接头疲劳损伤的声发射表征

文中通过声发射技术对桥式起重机箱形梁Q345B/Q235B异种钢焊接接头疲劳损伤过程进行表征,发现了声发射特征参数变化取决于疲劳裂纹扩展不同阶段的特点,得以利用声发射动态监测桥式起重机循环载荷下的疲劳损伤状态,从而实现及早预警的目的。另外,通过对异种钢焊接接头焊缝和热影响区2种不同缺陷位置疲劳实验各阶段典型声发射信号的对比分析,获知热影响区比焊缝位置更易发生疲劳断裂,故箱形主梁在服役过程中应重点关注异种钢焊接接头热影响区位置并及早发现危险。

Microstructure and properties in dissimilar/similar weld joints between DP780 and DP980 steels processed by fiber laser welding

The microstructure and mechanical properties（strength, fatigue and formability） of dissimilar/similar weld joints between DP780 and DP980 steels were studied. The microstructure in fusion zone（FZ） was lath martensite（LM）, and alloying elements in the FZ were uniformly distributed. The hardness in the FZ of dissimilar weld joint was similar to the average value（375 HV） of the two similar weld joints. The microstructural evolution in heat affected zone（HAZ） of dissimilar/similar weld joints was as follows：LM（coarse-grained HAZ） →finer LM（fine-grained HAZ） →M-A constituent and ferrite（intercritically HAZ） →tempered martensite（TM） and ferrite（sub-critical HAZ）. Lower hardness in intercritically HAZ and sub-critical HAZ（softening zones） was observed compared to base metal（BM） in dissimilar/similar weld joints. The size of softening zone was 0.2-0.3 mm and reduction in hardness was ~7.6%-12.7% of BM in all the weld joints, which did not influence the tensile properties of weld joints such that fracture location was in BM. Formability of dissimilar weld joints was inferior compared to similar weld joints because of the softening zone, non-uniform microstructure and hardness on the two sides of FZ. The effect of microstructure on fatigue life was not influenced due to the presence of welding concavity.

超超临界锅炉末级过热器异种钢焊接接头断裂原因分析与预防

对某电厂开裂的超超临界锅炉末级过热器F91/TP310HNbN异种钢焊接接头进行分析,包括宏观形貌检查、几何尺寸测量、金相组织检验、扫描电镜断口形貌分析和维氏硬度试验。结果表明:异种钢焊接接头开裂是焊缝的化学成分、组织、力学性能和物理性能与不锈钢侧母材差异较小,而与F91侧母材差异较大,导致F91侧焊缝熔合线附近成为整个接头的薄弱环节,再加上多种应力作用共同造成的。预防异种钢焊接接头早期失效应选用更为合适的焊材进行焊接,并在机组停机时加强金属监督检验。

F92/Super304H异种钢接头镍基填充焊缝裂纹分析

通过显微组织观测和裂纹形貌观察,分析ERNiCr-3焊丝填充的F92/Super304H异种钢接头焊缝裂纹性质与原因。结果表明,裂纹位于第4和5层焊道焊缝中心或近中心的树枝晶晶间或亚晶间,沿晶分布,裂纹面上可观察到方向性一致的树枝晶和自由凝固面形成的晶胞,裂纹具有典型的镍基焊缝金属凝固裂纹的形貌特征,为焊接凝固裂纹。该裂纹产生的原因是接头第4和5层焊道宽度达16~21 mm,每层单道焊道,焊道摆动宽度大,焊缝金属高温停留时间长,使以奥氏体结晶模式凝固的焊缝金属生成方向性极强的粗状发达的树枝晶,Ni,Nb,Si和Ti等元素偏析于树枝晶晶间或亚晶间,形成Ni-Nb,Ni-Si等低熔点共晶,在凝固收缩应变作用下,沿枝晶界或亚晶界开裂,镍基填充焊缝固有的凝固裂纹敏感性和接头焊接工艺因素是导致该裂纹产生的主要原因。

高温锅炉管T22/TP347H异种钢焊接接头早期失效原因

采用化学成分分析、力学性能测试、金相检验和硬度测试等方法,分析了T22/TP347H异种钢焊接接头早期失效的原因。结果表明:在T22钢侧熔合区发现了氧化缺口;T22钢与焊缝的边界附近存在元素浓度梯度,产生了马氏体脆化层。建议选用合金元素含量更高的焊材或者镍基焊材,避免早期失效的发生。

5083铝合金与304不锈钢异种材料涡流搅拌摩擦搭接焊工艺研究

为解决铝/钢常规搅拌摩擦焊中搅拌头的磨损和断裂问题,对5083铝合金和304不锈钢进行涡流搅拌摩擦搭接焊工艺试验。通过焊缝表面形貌、接头力学性能和横截面界面组织分析,研究倾角、转速和焊速对涡流搅拌摩擦搭接焊接头质量的影响规律。结果表明:在低转速和低焊速条件下,获得了较好的焊缝表面成形;在转速不变的条件下,随着焊速的提高,界面可承受的拉剪载荷逐渐降低;在焊速不变的条件下,随着转速的提高,界面可承受拉剪载荷先略微增大后减小并维持稳定;搅拌工具以2.5°倾角进行涡流搅拌摩擦焊接时,相较于无倾角条件,可以获得更大的焊缝成形工艺参数窗口和更好的冶金结合强度;5083铝合金和304不锈钢界面结合的主要方式为Al原子向不锈钢中扩散,低转速-低焊速组合下形成的扩散层相对更厚。

基于深度敏感压痕研究高温时效对HR3C/T92异种钢焊接接头局部力学性能的影响

应用深度敏感压痕技术(DSI)研究了高温时效对HR3C/T92焊接接头局部力学性能的影响。通过引入压痕特征参量来表征焊接接头各区域的强度、塑性与韧性,采用Oliver和Pharr方法计算弹性模量,并结合微观组织结构演化对时效后HR3C/T92焊接接头局部力学性能的变化进行了分析。结果表明:高温时效后,HR3C侧与焊缝的强度增强,塑性与韧性下降,但在T92一侧,力学性能的变化与之相反;高温时效后,HR3C侧与焊缝中析出大量的第二相粒子;在T92一侧,马氏体板条出现回复,位错出现湮灭。

TP304H/T22异种钢焊接接头微观组织特性对焊缝失效的影响分析

异种钢焊接接头在锅炉再热器与过热器中具有广泛的应用,但长期服役于高压高温等工况易萌生裂纹导致早期失效。通过对某运行已超过20万小时的TP304H/T22异种钢焊接接头的焊缝、母材与垫板交界区域,近熔合线侧的热影响区及远离焊缝的母材区域的微观组织及裂纹萌生与扩展进行研究,考察分析接头裂纹区域与非裂纹区域的组织特征对焊缝失效的影响。结果表明:焊缝、母材及垫板三者的交界处的微观晶粒分布密集呈无规则排列且随着服役时间的增长存在明显的粗化现象,导致该区域易萌生裂纹并扩展延伸;非裂纹区域的显微组织结构排列均匀有序并存有大量孪晶,钢材热稳定性提高,不易产生裂纹。本研究能够为开发高性能异种钢焊接接头工艺以及现有焊接接头性能检测和维护提供研究基础。

高压储氢罐封头与接管的焊接工艺

在高压储氢罐焊接工艺中,Q345R低合金钢的封头与S31603奥氏体不锈钢的接管进行焊接时,由于材质不同及大尺寸的原因,容易产生裂纹。针对此问题开展了异种钢焊接工艺的研究和试验,主要包括裂纹产生原因的分析、对焊接工艺方法和参数进行研究以及焊接试验。结果表明,采用焊条电弧焊对封头过渡层进行焊接,然后采用钨极氩弧焊打底、焊条电弧焊填充的焊接方案,可有效防止裂纹的产生。

核电异种钢内坡口镍基焊缝全位置对接焊技术研究

为了解决核电异种钢接管类焊接接头由于结构尺寸限制而无法正常从接管外壁进行焊接的技术难题以及提高该结构焊缝质量及焊接效率,在基于多年核电一回路核主设备焊接制造工艺的基础上,进行了材料、焊接设备、坡口形状尺寸、焊接位置等的合理选择并开展相关工艺试验及焊接工艺评定、产品模拟件焊接验证等工作。最终实现了从管内壁进行镍基焊缝全位置对接焊,并且按照NB/T 20002.3—2013《核电厂核岛机械设备无损检测》标准及技术条件进行了相关焊接工艺评定试验,结果均满足指标要求。该技术在产品制造中进行了成功应用,将焊接制造周期缩短为横焊位焊接周期的1/n(n为焊缝数量),焊缝一次性无损探伤合格率达96.9%,实现了提质增效的目的。

超声振动辅助铝/钢激光–MIG熔钎焊外观成形、组织以及拉伸性能研究

目的利用超声振动改善铝/钢对接接头界面的微观结构,降低气孔缺陷并提高接头力学性能。方法通过超声振动辅助激光–MIG焊接方法实现铝/钢异种金属连接,采用光学显微镜观察焊缝形貌,采用金相显微镜和扫描电子显微镜观察焊缝和界面微观结构,利用拉伸试验机测试接头的拉伸强度。结果超声振动的施加提高了熔融金属的润湿铺展性能,减少了焊缝中的气孔缺陷,并降低了界面层金属间化合物的厚度。带有余高和去除余高的接头拉伸强度由未加超声的175 MPa和154 MPa分别提高到189 MPa和172 MPa。结论利用超声振动的声流、空化效应有效改善了熔融金属的润湿铺展性能和界面微观结构,并在一定程度上消除了气孔缺陷,进而提高了接头的力学性能。

1000 MW超超临界发电机组过热器管T91/HR3C钢焊接接头开裂原因分析

某1000 MW超超临界发电机组运行了约7万小时后其过热器管T91/HR3C钢焊接接头开裂。对开裂的过热器管进行了宏观分析、硬度检验、金相检验和力学性能试验。结果表明:过热器管异种钢焊接时焊缝金属溢流至T91钢侧母材形成扇形异常区,且未焊后热处理,导致接头T91钢侧熔合线部位组织和性能极不均匀,长时间高温运行过程中产生氧化缺口。在内应力、交变应力和拘束应力等的共同作用下,氧化缺口根部产生裂纹,裂纹沿熔合线扩展导致接头开裂。

Microstructure and Mechanical Properties of RAFM-316L Dissimilar Joints by Friction Stir Welding with Different Butt Joining Modes

Dissimilar welded joints of reduced activation ferritic/martensitic(RAFM)steel and 316 L austenitic stainless steel were prepared by friction stir welding with different butt joining modes and welding parameters.The weld quality of the joint was improved by placing the 316 L steel on the advancing side and the RAFM steel on the retreating side,and using a relatively high rotational speed of 400 rpm.The microstructure of the stir zone on the 316 L steel side consisted of single-phase austenite,and the microstructure of the stir zone on the RAFM steel side mainly consisted of lath martensite and equiaxed ferrite.A mechanical mixture of the two steels and diffusion of Cr and Ni could be detected near the bonding interface.Diffusion of Ni from the 316 L steel to the RAFM steel resulted in the formation of a dual-phase structure consisting of austenite and ferrite.The as-welded joints showed good strength and ductility at room temperature and 550°C,which were nearly equal to those of the 316 L base material.The heat-affected zone on the RAFM side had the lowest impact toughness throughout the weld with a value of 13.2 J at-40°C,~52%that of the RAFM base material.

T92/Super304H异种钢焊接接头的组织结构和力学性能

采用钨极氩弧焊(GTAW)技术,采用ERNiCr-3和ERNiCrMo-3两种镍基焊丝实施T92/Super304H异种钢焊接,并对接头的显微组织结构及力学性能进行测试分析。结果表明:T92侧热影响区(HAZ)中粗晶区析出大量的第二相颗粒,细晶区则为细小的索氏体组织;Super304H侧HAZ奥氏体晶粒长大,晶界析出明显;ERNiCr-3焊接的焊缝组织呈胞状结构,晶粒粗大;ERNiCrMo-3焊接的焊缝组织呈柱状晶组织特征。ERNiCrMo-3焊接的接头强度、塑性及硬度较大,拉伸断裂位于Super304H母材;而ERNiCr-3焊接的接头强度、硬度较低,但冲击韧性较高,拉伸断裂位于焊缝。

T92/Super304H异种钢焊接接头的性能研究

根据新型耐热钢T92和Super304H钢的焊接特点制定了适宜的焊接工艺,研究了焊制的T92/Su-per304H异种钢焊接接头的力学性能。结果表明,T92/Super304H异种钢接头的各项力学性均能满足使用要求。焊缝金属的韧性远低于T92钢侧热影响区,焊缝金属的结晶形态对焊缝韧性有很大的影响。焊接接头中焊缝金属的硬度值最高,而T92钢侧热影响区硬度最低,并且不同热影响区部位显微硬度变化较大,Super304H钢侧热影响区硬度变化不大。