Dissimilar welding of high nitrogen stainless steel and low alloy high strength steel under different shielding gas composition:Process,microstructure and mechanical properties

Ar-N_(2)-O_(2)ternary shielding gas is employed in dissimilar welding between high nitrogen steel and low alloy steel.The effect of O_(2)and N_(2)is investigated based on the systematical analysis of the metal transfer,nitrogen escape phenomenon,weld appearance,nondestructive detection,nitrogen content distribution,microstructure and mechanical properties.There are two nitrogen sources of the nitrogen in the weld:high nitrogen base material and shielding gas.The effect of shielding gas is mainly reflected in these two aspects.The change of the droplet transfer mode affects the fusion ratio,N2in the shielding gas can increase nitrogen content and promote the nitrogen uniform distribution.The addition of 2%O_(2)to Ar matrix can change the metal transfer from globular transfer to spray transfer,high nitrogen base material is thereby dissolved more to the molten pool,making nitrogen content increase,ferrite decrease and the mechanical properties improve.When applying N2-containing shielding gas,arc stability becomes poor and short-circuiting transfer frequency increases due to the nitrogen escape from droplets and the molten pool.Performance of the joints is improved with N_(2)increasing,but internal gas pores are easier to appear because of the poor capacity of low alloy steel to dissolve nitrogen,The generation of pores will greatly reduce the impact resistance.4-8%N2content in shielding gas is recommended in this study considering the integrated properties of the dissimilar welded joint.

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.

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.

Microstructural Evolution on the T91 Dissimilar Metal Joints during Creep Rupture Tests

T91 steel is one of the new materials presently employed in power plant pipe components. The creep rupture strength and microstructure of the T91+10CrMo910 and T91+13CrMo44 welded joints were analyzed during creep rupture tests. Creep transgranular ductile rupture occurred at the 10CrMo910 matrix in the T91+10CrMo910 welded joints and creep intergranular brittle rupture occurred at the 13CrMo44 HAZ in the T91+13CrMo44 joints. Microhardness measurements showed high hardness at the heat affected zone (HAZ) of T91 and a sharply drop at the 13CrMo44 HAZ during creep rupture. The metallographic tests showed that no obvious microstructure degradation was observed in the 10CrMo910 HAZ and matrix, while creep cracks appeared at the 13CrMo44 HAZ. T91 steel had relatively high creep resistant strength in the welded joints tested. Recovery occurred in the T91 HAZ with the growth of subgrain size and the decrease of dislocation density during creep. It was concluded that the dissimilar joints of T91 and low alloy heat-resistant steel should have close creep strength matching to increase the service life of the overall joints at elevated temperature.

蒸汽发生器异种钢焊接接头疲劳裂纹扩展研究

钠冷快堆是我国发展第4代先进核能系统的主力堆型,蒸汽发生器是钠冷快堆重要部件.为了保证蒸汽发生器的安全性和可靠性,对异种钢焊接接头进行疲劳裂纹扩展行为研究.异种钢焊接接头共有6个不同微区,分别为F22母材、F22侧热影响区、隔离层、堆焊层、对接焊缝及316H母材.对异种钢焊接接头进行硬度测试、显微组织观察、疲劳裂纹扩展试验,利用光学显微镜和扫描电子显微镜(SEM)进行微观组织观察.F22母材组织主要为铁素体、珠光体和贝氏体,F22侧热影响区组织主要为铁素体和珠光体,隔离层、堆焊层、对接焊缝主要组织为奥氏体和δ铁素体,316H母材组织主要为奥氏体.F22母材的显微硬度最小,隔离层显微硬度最大,堆焊层、对接焊缝、316H母材的显微硬度逐渐下降,F22侧热影响区显微硬度变化较大.在低ΔK时,F22母材的疲劳裂纹扩展速率最快,隔离层、堆焊层、对接焊缝、316H母材的疲劳裂纹扩展速率逐渐变缓,随着ΔK的增加,隔离层的疲劳裂纹扩展速率变化最快,这是因为隔离层裂纹逐渐向F22母材侧偏转,使得其抵抗疲劳裂纹扩展能力逐渐降低.δ铁素体会影响隔离层、堆焊层、对接焊缝的抗疲劳裂纹扩展能力.F22母材和F22侧热影响区的疲劳裂纹断口撕裂最严重,隔离层、堆焊层、对接焊缝的断口平坦度逐渐增加,316H母材的疲劳裂纹断口形貌最平坦,与抗疲劳性能相对应.

高含硫气田压力容器异种钢焊接接头失效泄漏原因分析

对国内某高含硫气田酸性湿气增压项目压缩机进气洗涤罐进行“酸敏试验”,试验过程中上封头与长高颈法兰连接角焊缝处即异种钢焊接部位连续出现了两次介质泄漏事故。通过宏观形貌观察、化学成分分析、金相组织分析、硬度测试、断口宏观与微观形貌分析等方法,对现场试样进行系统分析,再结合焊接冶金学机理分析,确定了异种钢焊接接头失效泄漏的原因。在硫化物应力腐蚀开裂敏感环境中,在残余应力与外加应力的共同作用下,裂纹沿最薄弱的熔合线分布,从内侧启裂,并向外侧扩展,最终穿透管壁,导致泄漏发生。

铝/钢异种金属焊接接头腐蚀行为及其影响因素综述

铝/钢异种金属焊接接头结合了两种材料优异的性能,在各行各业具有较为广泛的应用.由于铝、钢两种金属之间理化性能的巨大差异以及极小的固溶度,导致铝/钢接头容易出现脆性金属间化合物、气孔等缺陷,严重影响着接头的力学性能.然而,随着铝/钢接头越来越广的应用范围和复杂多样的应用环境,接头的耐腐蚀性能也得到了更多的关注.对近些年铝/钢异种金属焊接接头的耐腐蚀方面研究工作做了系统的汇总,旨在从接头腐蚀机理出发,提升接头的耐腐蚀性.综述了接头腐蚀形式规律,并从焊接工艺、腐蚀环境、微观组织和金属间化合物等影响因素的角度出发,详细地讨论了腐蚀行为与各因素之间的关系及影响机理.同时,指出了接头腐蚀机理,从各影响因素方面提出了改善接头耐腐蚀性能的措施,减小铝/钢接头实际服役过程中腐蚀所带来的影响.

经长时服役的超临界锅炉T91/TP347H异种钢接头性能分析

对某超临界锅炉运行7.5万小时的T91/TP347H异种钢接头,采用金相显微镜、万能材料试验机和扫描电镜等仪器设备,研究长时服役后T91/TP347H异种钢接头的性能。结果表明:该异种钢接头薄弱区在T91熔合线处,该位置链状孔洞和脱碳层的形成大大弱化了力学性能,氧化缺口的形成加速了接头的开裂。异种钢接头各区域的冲击性能显著降低,其中焊缝冲击性能最低,实测仅为66 J。

制氢转化炉上尾管加强接头频繁开裂原因分析及对策

某炼化企业制氢转化炉2010年升级改造后,不同炉管的加强接头与上尾管焊口位置先后出现了5次开裂,造成制氢装置非计划停工。通过对运行环境、高温氢腐蚀、热膨胀应力、结构应力、异种钢焊接、弹簧支吊架等多方面开展深入分析,发现泄漏的原因主要是加强接头与上尾管连接焊缝局部高应力区发生了应力松弛开裂,同时,工艺参数控制不严格加遽了开裂速度。2021年通过实施炉管材质升级、稳定工艺运行环境、严控施工质量等措施,没有再出现过开裂的情况,彻底消除了炉管运行过程中的安全隐患,保障了设备的本质安全和装置的长周期运行。

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。

焊后热处理对SA-182F1和SA-106C钢接头显微组织和力学性能的影响

采用钨极氩弧焊和焊条电弧焊焊接SA-182F1和SA-106C钢.对焊接接头进行了615℃保温8h的消除应力处理.检测了焊接接头热处理前、后的显微组织和力学性能.结果表明:热处理前、后焊接接头的拉伸和冲击性能均满足要求,消除应力处理使接头拉伸性能降低、冲击韧度提高;热处理前后焊接接头的显微组织没有差异.

T91+TP347H异种钢焊接接头失效分析

某电厂超临界锅炉运行中发现高温再热器出口T91/TP347H异种钢焊接接头发生断裂致使锅炉泄漏。对失效焊接接头进行宏观形貌观察、化学成分分析、金相检验、硬度测试等一系列检验,结合该锅炉的运行情况和历史故障情况,综合分析该锅炉异种钢焊接接头的失效原因。结果显示,焊缝成形差、焊接质量不合格是导致出现接头开裂的直接原因;异种钢接头本身化学成分差异大,性能不均匀,在长期的高温和应力作用下发生元素迁移,造成交界面性能下降,这是焊接接头出现开裂的根本原因;机组的深度调峰、频繁启停调峰则进一步加速了裂纹的产生。经过失效原因分析,并借鉴异种钢焊接接头的管理标准及实践经验,建议加强焊接质量控制和优化金属监督策略,提高无损检测的抽样率,并注意控制机组调峰速率。可为同类型电厂异种钢焊接接头管理提供参考。

Q235/304不锈钢异种钢焊接接头超声相控阵检测研究

异种钢焊接接头具备高强度、高耐腐蚀性以及低成本等特性,已经被广泛应用于锅炉、管道和压力容器等特种设备中。然而由于异种钢焊接接头的材料组织、力学性能以及残余应力不均匀,在制造和服役后极易出现开裂等缺陷,采用常规无损检测存在检测精度低、扫查范围小等缺点,导致缺陷难以检出。针对上述问题,以Q235/304不锈钢两种典型异种钢焊接接头为研究对象,推导了超声相控阵检测异种材料聚焦延时计算法则,制作Q235和304不锈钢焊接试块,并利用汕超SUPOR32P/32PT检测仪结合延时法则检测含有预制未熔合、未焊透和裂纹的人工缺陷,然后通过射线检测对比分析。检测结果表明:相较于传统超声检查技术,采用超声相控阵检测技术检测的定位误差小于5mm,长度定量误差均小于10%,定性分类准确度达到100%,能够较好地满足异种钢焊接接头质量检测要求。

42CrMo与06Cr19Ni10异种钢焊接工艺研究

为了解决42CrMo和06Cr19Ni10异种钢焊接熔深不足的问题,进行异种钢焊接工艺研究。采用氩弧焊的焊接方法,焊接材料选择不锈钢焊材,并进行必要的焊前处理,焊接完成后对42CrMo与06Cr19Ni10异种钢焊接接头进行金相和硬度试验。结果表明:选用铬镍含量更高的不锈钢焊材,并对42CrMo母材进行焊前预热处理,可以获得熔合更好的焊接接头,焊缝区域硬度更加均匀。

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。

316L和2205异种不锈钢等离子弧焊接头的微观组织和性能

采用等离子弧对3 mm厚的316L奥氏体不锈钢和2205双相不锈钢板进行对接焊,分析了焊接接头微观组织、力学性能以及耐腐蚀性能。结果表明,316L/2205异种不锈钢等离子弧焊焊缝组织总体均匀细小,但各区域具有一定方向性,焊缝组织随转弧电流增大而粗化,焊缝区的奥氏体和铁素体较粗大。不同大小电流下的异种不锈钢接头的显微硬度分布总体的变化趋势基本一致,焊缝平均抗拉强度达到533~571 MPa,且均断裂在316L侧。转弧电流较小时,焊缝细小均匀的组织保证了其较高的硬度和拉伸强度。两种母材和焊缝的自腐蚀电位从高至低为75 A焊缝>85 A焊缝>316L母材>2205母材>95 A焊缝。增大转弧电流可使焊缝中奥氏体含量增加且破坏晶界,从而影响晶间腐蚀速率。