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.

Corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding in alkaline solution

This study was done to evaluate the nugget zone(NZ)corrosion behavior of dissimilar copper/brass joints welded by friction stir lap welding(FSLW)in a solution of 0.015 mol/L borax(pH 9.3).To this end,dissimilar copper/brass plates were welded with two dissimilar heat inputs(low and high)during the welding procedure.The high and low heat inputs were conducted with 710 r/min,16 mm/min and 450 r/min,25 mm/min,respectively.Using open circuit potential(OCP)measurements,electrochemical impedance spectroscopy(EIS)and Tafel polarization tests,the electrochemical behavior of the specimens in borate buffer solution was assessed.With the help of scanning electron microscope(SEM),the morphology of welded specimen surfaces was examined after immersion in the test solution.According to the results,the NZ grain size and resistance improvement reduced due to the nugget zone corrosion with a decreased heat input.The results obtained from Tafel polarization and EIS indicated the improved corrosion behavior of the welded specimen NZ with a decrease in the heat input during the welding process unlike the copper and brass metals.Furthermore,an increased heat input during the welding process shows a reduction in the conditions for forming the passive films with higher protection behavior.

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.

Investigation on Electron Beam Welded Copper to AISI 316 Stainless Steel Joints

Joints of copper and stainless steels are used in a er ospace applications. Production of these joints by fusion welding faces many dif ficulties. This may be due to the differences in their physical, metallurgical a nd mechanical properties. Electron Beam Welding (EBW) process has been found to be especially well suited in this area. Selection of the appropriate welding par ameters needs thorough investigations. These parameters include: preheat tempera ture (℃), welding current (I w), focusing current (I F), welding spee d (V), height between the gun and workpiece surface (H), scan width (S w) and shift distance (S). The present work aims firstly, setting the pr oper welding conditions to get sound joint between commercially pure copper (C10 200) and AISI 316 stainless steel plates 8 mm thickness. Secondly, investigate t he effect of Electron Beam (EB) shift, single-sided and double-sided welds on the mechanical, metallurgical and chemical properties of the weld bead. Due to t he high difference in thermal conductivity between copper and stainless steel, E lectron Beam (EB) was shifted towards copper with different values. These values were ranged from 0.3 to 0.9 mm in welding without preheating of copper plate an d from 0.1 to 0.4 mm with preheating. Number of joints were welded using variabl e EBW parameters in view to obtain the sound weld bead. These parameters are as follows: gradual reduction I w=51 to 49 mA, I F=845 mA, V=8 mm/sec , H=130 mm, S w=500 μm and S=0.4 mm. The investigation has shown t hat, the copper (C10200) plate must be preheated to get sound welded joint with AISI 316 stainless steel using the EBW process. The tensile fracture in all wel ded samples occurred in copper plate away from the weld bead. This reflects that the weld bead tensile strength is greater than the copper strength. The EB shif t has slight effect on hardness distribution through weld bead. The hardness val ue (H v) reduces in gradual manner from stainless steel hardness to copper one. The EB shift distance has no significant effect on the impact toughness.

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.

Electron beam welding of 304 stainless steel to QCr0.8 copper alloy with copper filler wire

Electron beam welding （EBW） of 304 stainless steel to QCr0.8 copper alloy with copper filler wire was carried out. Orthogonal experiment was performed to investigate the effects of process parameters on the tensile strength of the joints, and the process parameters were optimized. The optimum process parameters are as follows：beam current of 30 mA, welding speed of 100 mm/min, wire feed rate of 1 m/min and beam offset of-0.3 mm. The microstructures of the optimum joint were studied. The results indicate that the weld is mainly composed of dendriticαphase with little globularεphase, and copper inhomogeneity only occurs at the top of the fusion zone. In addition, a melted region without mixing exists near the weld junction of copper side. This region with a coarser grain size is the weakest section of the joints. It is found that the microhardness of the weld decreases with the increase of the copper content in solid solution. The highest tensile strength of the joint is 276 MPa.

Microstructural evolution and mechanical properties of friction stir-welded C71000 copper–nickel alloy and 304 austenitic stainless steel

Dissimilar joints comprised of copper–nickel and steel alloys are a challenge for manufacturers in modern industries, as these metals are not thermomechanically or chemically well matched. The present study investigated the effects of tool rotational speed and linear speed on the microstructure and mechanical properties of friction stir-welded C71000 copper–nickel and 340 stainless steel alloys using a tungsten carbide tool with a cylindrical pin. The results indicated that a rotational-to-linear speed ratio of 12.5 r/mm did not cause any macro defects, whereas some tunneling defects and longitudinal cracks were found at other ratios that were lower and higher. Furthermore, chromium carbide was formed on the grain boundaries of the 304 stainless steel near the shoulder zone and inside the joint zone, directing carbon and chromium penetration toward the grain boundaries. Tensile strength and elongation percentages were 84% and 65% of the corresponding values in the copper–nickel base metal, respectively.

Gas tungsten arc welding of CP-copper to 304 stainless steel using different filler materials

The dissimilar joining of CP-copper to 304 stainless steel was performed by gas tungsten arc welding process using different filler materials. The results indicated the formation of defect free joint by using copper filler material. But, the presence of some defects like solidification crack and lack of fusion caused decreasing tensile strength of other joints. In the optimum conditions, the tensile strength of the joint was 96% of the weaker material. Also, this joint was bent till to 180° without any macroscopic defects like separation, tearing or fracture. It was concluded that copper is a new and good candidate for gas tungsten arc welding of copper to 304 stainless 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.

Mechanical Properties of Laser Welded Joint of Copper and Steel Dissimilar Metals

In this research project,copper and stainless steel were connected by two laser welding methods:straight seam welding and swing welding.Then,electronic tensile test machine,X-ray diffractometer,scanning electron microscope and metallographic microscope were used to analyze the tensile properties,macroscopic and microscopic structure morphology and phase of the welded joint.Based on the experimental results,we determined that the strength of the straight seam welded joint was higher.Because of the intermetallic compound near the weld in the swing welding process,it leads to stress concentration,crack cracking and strength reduction.In addition,the oscillating laser beam also leads to the disorderly direction of columnar crystal and coarse structure,which makes the joint strength decrease.

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。

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.

Impact wear properties of dissimilar joints between bainitic frogs and pearlite rails

The impact wear behavior and damage mechanism of dissimilar welded joints between U26Mn frog and U75 V rail before and after normalizing treatment were studied by cyclic impact tests.The experiment indicated that the impact wear volume of the joints increased with the increasing number of impact cycles.The main wear mechanisms include pitting wear,mild fatigue wear,delamination wear,and fatigue wear,and plastic deformation was the primary impact wear mechanism.Among them,fatigue wear had the greatest influence on wear volume,while other wear mechanisms had limited effect.The impact wear resistance of the base material was better than that of the heat-affected zone.Normalizing treatment was beneficial to improving the impact wear resistance of welded joints owing to its effect to promote pearlite recovery,grain refinement,and uniform distribution of grains.The martensite generated in the rail welded joints aggravated the impact wear damage to the materials,which should be avoided.

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。