Similar Welds Research Articles

Development of laser beam welding of advanced high-strength steels

Advanced high-strength steels have been extensively used in automobile construction, although a more complete understanding of their weld microstructure and mechanical behavior is needed. This work aims to contribute to the understanding of these basic features as well as propose the fiber laser processing conditions. Similar and dissimilar welds of dual-phase or transformation-induced plasticity (TRIP) steels present similarities in terms of microstructure features with the presence of martensite, proeutectoid ferrite, and bainite in the fusion zone and in the heat-affected zone. However, the more important microconstituent is bainite under regular and coalesced morphologies. The tensile behavior could be considered acceptable as most of the welded coupons broke in the base material and far from the weld. Fatigue curves presented a limit at approximately 350 MPa for dual-phase steels and 450 MPa for the TRIP steel.

STUDY OF MICROSTRUCTURE AND STRESS CORROSION CRACKING BEHAVIOR IN WELDING TRANSITION ZONE OF Ni–BASED ALLOYS

Welding technique is generally used in nuclear power plant for manufacturing and machining important components such as steam generator. The similar metal weld and dissimilar metal weld were commonly involved to connect and fixup tubings in steam generators. However, in recent years large amounts of cracking accidents have been observed in the welded joints. A concern has been raised about the integrity and reliability in the joint transition zone due to the high susceptibility of heat affected zone (HAZ) and fusion zone (FZ) to stress corrosion cracking (SCC). In this study, the similar metal and dissimilar metal joints were investigated and compared, focusing on the correlation between microstructure, residual strain and SCC behavior. The microstructures of transition zone in Ni-based Alloys 690 and 52 similar metal joint and Alloys 182 and A533B low alloy steel dissimilar metal joint were investigated comprehensively by SEM, EBSD, TEM. The residual strain distribution in the HAZ of 690-52 similar metal joint was quantitatively measured. The SCC behavior of 182-A533B dissimilar metal joint in high temperature oxygenated water were simulated by creviced bent beam specimen. The HAZ in the similar joint exhibits higher residual strain, sensitive microstructure and high susceptibility to SCC, therefore, the HAZ region deserve more attention during the inspection and examination of components. The FZ of the dissimilar metal joint exhibits complicated microstructure and chemical

Sub-surface stress measurement of cross welds in a dissimilar welded pressure vessel

Manufacturing process of pressure vessels used in high-temperature applications normally needs employing dissimilar metal welds (DMWs) between austenitic and ferritic steel. However, high amount of thermal stresses at the welds are induced due to differences in coefficient of thermal expansion between the types of steel. This study investigates the evaluation of welding residual stresses in a pressure vessel manufactured by DMW of 316 L stainless steel shell to A106 carbon steel caps as well as similar welding of stainless steel shells. By using longitudinal critically refracted (LCR) ultrasonic waves, the residual stresses are experimentally measured. The ultrasonic method is based on acoustoelasticity law by which the ultrasonic wave velocity could be connected to the material stress. By changing the frequency in which the ultrasonic transducers are working, the LCR waves are able to penetrate in various depths of the material in order to measure the sub-surface residual stresses. Hence, four main aspects are considered in this study: (I) stress evaluation of the DMW; (II) sub-surface stress measurement; (III) stress evaluation of longitudinal weld and (IV) stress measurement in cross weld. It is demonstrated that the residual stresses of the DMW pressure vessel could be comprehensively evaluated by using the LCR method.

Parametric study in similar ultrasonic spot welding of A5052-H32 alloy sheets

Ultrasonic spot welding (USW) is a solid-state joining process highly applicable to lightweight alloy materials with high diffusivity rates in the melt state. To improve the understanding of the USW process and to enhance the weld strength in similar Al alloy welding, this work focused on a parametric study using some process parameters such as vibration amplitude and welding time. Experiments were conducted using lateral-drive USW machine operating in time control mode. Weld quality of USWed joint was analyzed based on the weld strength obtained by lap-shear tests and the fracture pattern subsequently characterized. Mixed fracture pattern of shear and pull-out exhibited a higher lap-shear failure load, while solely shear and pull-out was a distinct fracture pattern in lower lap-shear failure load. Shorter welding time was needed for higher vibration amplitude to generate enough temperature and to prevent over welding. Joint microstructures revealed that longer welding time produced over welding which gave short but intensified weld interface waviness, resulting to a shorter fracture path. The horn and anvil tip surface patterns influenced on the variation in temperature rise measured at the weld part and the extent of part marking/sticking. The temperature rise measured on the weld surface was useful to determine over welding condition. Weldability map of USWed Al alloy sheets could be constructed from the results of weld strength and fracture type, and an effective welding energy input was determined from welding process parameters combination.

Analysis of weld defects in similar and dissimilar resistance seam welding of aluminium, zinc and galvanised steel

In the present investigation, a microstructural characterisation of welds performed by resistance seam welding was carried out, with special focus on weld defect analysis. In order to perform a comparative weldability analysis, the welds were performed using similar welding procedures. Similar welds in aluminium (5754-H22) and zinc (Zintek) alloys, as well as dissimilar welds between galvanised steel and zinc, were studied. The defective aluminium welds were found to be characterised by important grain growth inside an inhomogeneous nugget and by the presence of important voids and cracks. The zinc welds showed a well defined nugget, but with porosities and some cracks. In the dissimilar steel–zinc welds, important macroscopic defects were observed. Microstructural analysis evidenced the occurrence of melting at the zinc side of the welds; meanwhile, no microstructural modifications could be observed for the steel side. Defect formation, as well as weld morphologies, was related to the variation in welding parameters.

Microstructure and mechanical properties of Al/Ti joints welded by resistance spot welding

Resistance spot welding of commercial pure titanium and aluminium alloy 6061-T6 is carried out. The microstructure and tensile shear properties of the weld joints are studied. There is a critical range of welding current at which the reaction between liquid aluminium and solid titanium changes to a reaction between liquid aluminium and liquid titanium. The microstructure in the aluminium side is a type of transition structure, which is considered to be the same microstructure that connects the columnar dendrite and equiaxed dendrite in similar aluminium alloy resistance spot welding. The welding current has the largest influence upon the tensile shear properties of the Al/Ti weld joint, while the welding time has a small effect and the electrode force has virtually no effect.

Effect of material properties and mechanical tensioning load on residual stress formation in GTA 304-A36 dissimilar weld

Using a finite element analysis (FEA) model, the residual stress (RS) formation in an autogenous GTA dissimilar weld between austenitic stainless steel (304) and low carbon steel (A36) are analyzed. The effect of material properties on RS formation was determined by first considering a similar weld of 304 plates, and then changing only a selected mechanical property of the 304 plate on one side of weld to that corresponding to an A36 plate. Enforcing one set of mechanical property to be different at a time helped to isolate the role of these individual properties on the RS formation in the dissimilar weld. The effect of mechanical tensioning on dissimilar welds is then investigated. Results show that the longitudinal RS in both the similar and dissimilar welds can be reduced in the weld zone (WZ) by an amount equal to the stress corresponding to the applied mechanical tensioning load, as the tensioning load is removed after cooling. The mechanism of RS formation in dissimilar weld, and its mitigation by mechanical tensioning are determined by comparing the longitudinal stress evolution on a cross-section of the dissimilar weld plates under the mechanically tensioned and free conditions.

Emerging Friction Stir Welding for Aluminium and its Applications

Friction Stir Welding (FSW) was invented by Wayne Thomas at TWI (The Welding Institute), and the first patent applications were filed in the UK in December 1991. FSW offers numerous benefits in the fabrication of all aluminum products. Friction Stir Welding (FSW) has become a major joining process in the aerospace, railway and ship building industries especially in the fabrication of aluminum alloys. The process uses a spinning non-consumable tool to generate frictional heat in the work piece. Heat is generated between the tool and material then mechanically intermixes the two pieces of metal at the place of the join, then the softened metal (due to the elevated temperature) can be joined using mechanical pressure. This paper looks at the review, on friction stir welding process, various welding variables, generation and flow of heat, Microstructural features and material flow during FSW. The study indicates that Friction stir welding is most suitable joining technique for similar and dissimilar aluminum alloy. It is found that weld quality of FSW joint is excellent than other joining process. The estimated thermal profiles are compared with experimental results at similar welding conditions, thus validating the developed heat transfer model.

同軸複層ワイヤを用いた純Ar-GMAWの9%Ni鋼共金溶接への適用検討

同軸複層ワイヤを用いた純Ar-GMAWの9%Ni鋼共金溶接への適用検討

Grain size distribution after similar and dissimilar gas tungsten arc welding of a ferritic stainless steel

In this study, gas tungsten arc welding of ferritic stainless steel and grain size distribution in heat affected zone of the welded samples were investigated. Both similar and dissimilar arc welding operations were considered where in dissimilar welding joining of stainless steel to mild steel was examined. In the first stage, a three-dimensional model was developed to evaluate temperature field during and after arc welding while the model was performed using finite element software, ANSYS. Then, the effects of welding heat input and dissimilarity of the joint on the weld pool shape and grain growth in HAZ of stainless steel was investigated by means of model predictions and experimental observations. The results show that the similar joint produces wider HAZ and considerably larger grain size structure while in the dissimilar welds, the low carbon part acts as an effective heat sink and prevents the grain growth in the stainless steel side as well reduces the welding maximum temperature.

Weldability and mechanical properties of similar and dissimilar resistance spot welds of three-layer advanced high strength steels

Similar and dissimilar combinations of a 1000 MPa galvanised dual phase (DP) steel, a 980 MPa transformation induced plasticity (TRIP) steel and a 980 MPa twinning induced plasticity (TWIP) steel were resistance spot welded under different welding parameters. The macrostructure, splash situation, nugget size and mechanical properties of the spot welds were evaluated systematically. The results showed that the different heat conductivities, melting points and surface electric resistances of the DP, TRIP and TWIP steels resulted in the asymmetric weld nuggets of the dissimilar spot welds and the increase in the splash occurring current in order of DP/DP/DP, TRIP/DP/TWIP, TWIP/TRIP/DP, TRIP/TWIP/DP (TRIP/TRIP/TRIP), TWIP/TRIP/DP and TWIP/TWIP/TWIP. For the dissimilar spot welding of galvanised DP1000, uncoated TRIP980 and uncoated TWIP980, the TRIP/TWIP/DP combination can obtain better weld quality than the TRIP/DP/TWIP and TWIP/TRIP/DP combinations.

Heat transfer analyses in friction stir welding of aluminium alloy

This work is aimed to develop a heat transfer model of friction stir welding process and subsequently to utilize the same for transient thermal analysis under differential influence of process parameters. The heat generation is assumed due to friction and plastic deformation at the tool–workpiece interface. A contact state variable is defined to estimate the amount of heat generation due to plastic deformation. The symmetric heat flux at the interfaces of flat tool shoulder surface, tool pin side, and bottom surfaces acts as heat input to the system by neglecting the effect of transverse tool speed. The heat generation from both the side and bottom surfaces of pin plays a significant role for the development of the temperature. Thermal history of friction stir welded AA1100 and AA6061 is estimated by developed numerical model and is compared with experimental results under similar welding conditions, thus validating the developed model. The experiments reveal that the temperature distributions are not symmetric with respect to welding line and maximum temperature occurs behind the tool pin. With the addition of heat generation due to plastic deformation, the heat transfer model precisely predicts the maximum temperature and time–temperature profiles at different welding conditions.

Orbital friction welding as an alternative process for blisk manufacturing

Linear friction welding (LFW) is used for the production of compressor blisks in modern turbine engines. Orbital friction welding (OFW) performs a circular motion in contrast to the linear motion applied during LFW. In order to display the influence of the different kinetics on the heat generation, both processes were compared using identical process parameters. The tests were performed on multi-orbital friction welding machine in the force–displacement mode. In a frequency range from 28 to 56Hz the time necessary to achieve a displacement of 5mm was measured for both processes. Using Ti–6Al–4V as the test material, it is shown that with similar welding parameters, shorter welding times are achieved with OFW. The reason for the faster heat generation is a continuous relative speed, higher contact pressure and a larger distance covered within one cycle of the process.

Similar and dissimilar resistance spot welding of advanced high strength steels: welding and heat treatment procedures, structure and mechanical properties

Similar and dissimilar combinations of a 1000 MPa galvanised dual phase (DP) steel and a 980 MPa transformation induced plasticity (TRIP) steel were resistance spot welded under different welding and heat treatment parameters. The microstructure and mechanical properties of spot welds were evaluated using metallographic technique, microhardness and tensile shear tests. The results showed that the tendency to fail in the pullout mode increased in the order of DP/DP, TRIP/TRIP and DP/TRIP welds, which was caused by the different hardness distribution, carbon equivalent and susceptibility to shrinkage void formation of spot welds for different combinations. In the study of the effects of heat treatments on the DP/TRIP welds, the pre-heating procedure improved the splash of welding to some extent. When the cooling time was larger than or equal to 1000 ms, the post-heating procedure improved the mechanical properties of spot welds owing to the temper of spot weld microstructure.

Picosecond laser welding of similar and dissimilar materials.

We report picosecond laser welding of similar and dissimilar materials based on plasma formation induced by a tightly focused beam from a 1030nm, 10ps, 400kHz laser system. Specifically, we demonstrate the welding of fused silica, borosilicate, and sapphire to a range of materials including borosilicate, fused silica, silicon, copper, aluminum, and stainless steel. Dissimilar material welding of glass to aluminum and stainless steel has not been previously reported. Analysis of the borosilicate-to-borosilicate weld strength compares well to those obtained using similar welding systems based on femtosecond lasers. There is, however, a strong requirement to prepare surfaces to a high (10-60nm Ra) flatness to ensure a successful weld.

Weldability assessment and high temperature properties of advanced creep resisting austenitic steel DMV304HCu

The modern (USC PP) applying the 600 °C technology require advanced austenitic stainless steels in superheater/reheater systems in order to cope with the increased steam parameters. Different grades of austenitic stainless steels have been developed by increasing Cr contents, alloying with stabilizing and precipitating elements as well as thermomechanical heat treatments resulting in high creep rupture strengths and improved oxidation/corrosion resistance. In the context of a collaborative research project, DMV304HCu (X10CrNiCuNb18-9-3) has been selected. The main focus of the research project was on characterization and weldability assessment. As a result, the base metal under investigation was compared with governing code cases and specifications. Base metal chemical composition, microstructures, mechanical properties, reheat cracking sensitivity, hot ductility as well as creep rupture strengths have been investigated. A weldability assessment, including thermal simulation and welding procedure qualifications, has been performed to establish parameter windows for similar and dissimilar welding. Dissimilar welding between Grade 92 and austenitic stainless steel tubes has been performed. The project also took the opportunity to investigate the behavior of a recently developed gas tungsten arc welding (GTAW) P87 consumable for dissimilar welding. Cross-weld creep rupture testing has been conducted for both similar and dissimilar welding, and aging tests addressed microstructural stability.

Microstructure-properties correlation in fiber laser welding of dual-phase and HSLA steels

Similar and dissimilar welds of dual-phase (DP) and high strength low alloy (HSLA) steels were made by fiber laser welding (FLW). The welds were characterized with respect to microstructure, micro- and nano-hardness, and tensile properties. The fusion zone (FZ) in the DP welds consisted of fully martensitic structure; whereas HSLA and dissimilar weld FZ microstructure were mixture of martensite and bainite. Analytical transmission electron microscopy (TEM) confirmed bainite structures containing bainitic ferrite laths with intralath and interlath cementite. Precipitation of single variant carbides inside the bainitic ferrite laths were confirmed by measuring the interplanar spacing. The cooling rate in the FZ, estimated using Rosenthal equation, and continuous-cooling-transformation diagrams corroborated the microstructure formed. Nanoindentation was used to verify the hardness of these individual microconstituents, since a much lower nano-hardness for bainite (4.11GPa) was observed compared to martensite (6.57GPa) phase. Tensile failure occurred in the tempered area of the heat affected zone (HAZ) in the DP steel welded, which was confirmed by typical cup-like dimple fracture; likewise failure in the HSLA base metal, which occurred in dissimilar and HSLA welds, indicated distinctive dimple and shear dimple ductile morphology.

Estimation of Some Mechanical Properties for Similar & Dissimilar Welded Joints

This research deals with the choice of the suitable filler metal to weld the similar and dissimilar metals (Low carbon steel type A516 & Austenitic stainless steel type 316L) under constant conditions such as, plate thickness (6 mm), voltage (78 v), current (120 A), straight polarity. This research deals with three major parts.
 The first parts Four types of electrodes were used for welding of dissimilar metals (C.St A516 And St.St 316L) two from mild steel (E7018, E6013) and other two from austenitic stainless steel (E309L, E308L) various inspection were carried out include (Visual T., X-ray T., δ- Ferrite phase T., and Microstructures T.) and mechanical testing include (tensile T., bending T. and micro hardness T.)
 The second parts done by used the same parameters to welding similar metals from (C.St A516) Or (St.St 316L).
 The third parts deals with welding of dissimilar weldments (C.St And St.St) by two processes, gas tungsten are welding (GTAW) and shielded metal are welding (SMAW).
 The results indicated that the spread of carbon from low carbon steel to the welding zone in the case of welding stainless steel elect pole (E309L) led to Configuration Carbides and then high hardness the link to high values ​​compared with the base metal. In most similar weldments showed hardness of the welding area is higher than the hardness of the base metal. The electrode (E309L) is the most suitable to welding dissimilar metals from (C.St A516 With St.St 316L). The results also showed that the method of welding (GTAW) were better than the method of welding (SMAW) in dissimilar welded joints (St.St 316L with C.St A516) in terms of irregular shape and integrity of the welding defects, as well as characterized this weldments the high-lift and resistance ductility good when using the welding conditions are similar.

Comparative study on dissimilar welding of Inconel 718 and Udimet 500 precipitation strengthened nickel based superalloys

Microstructural, mechanical and weldability aspects in the similar and dissimilar welds of alloy 718 and alloy 500 nickel based superalloys have been investigated. Alloy 500 weld metal showed high tendency of titanium to the segregation. Coalescence of the microvoids led to propagation of hot solidification microfissures. The alloy 718 weld metal displayed the formation of Nb rich low melting eutectic type morphologies, which can reduce the weldability. The microstructure of dissimilar weld metal with dilution of 65 wt-% displayed semideveloped dendritic boundaries. The less segregation and decrease in the low melting eutectics caused less susceptibility of dissimilar weld to solidification cracking. The segregation elimination phenomenon has occurred in the heat affected zone of alloy 500. In the partially melted zone, remelted and resolidified regions have been observed. These locations provided sites for nucleation of liquation cracks. For the alloy 718 heat affected zone, dissolution of γ″-Ni3Nb needle-like precipitations has taken place. It was the chief reason for sharp decline of the microhardness. The heat affected zone of alloy 500 revealed intense liquation cracking, in which the crack is initiated at the partially melted zone. The hot liquation cracking in the heat affected zone of Alloy 718 was observed as a result of γ″-Ni3Nb dissolution.

Comparing bond formation mechanism between similar and dissimilar aluminium alloy friction welds

Friction welding of high strength aluminium alloys was considered in the current study. The mechanism of bond formation in dissimilar alloy welding was compared to similar alloy welding. The differences in flow properties between two different alloys of aluminium lead to uneven deformation behaviour while welding. Since flow behaviour directly affects bond formation and strength, it is important to understand its behaviour. Rods of aluminium alloys AA 2024 and AA 6061 were welded to themselves and to each other denoting similar and dissimilar weld systems. Burn-off length, which is one of the important parameters in friction welding was varied in steps to see how it affects the bond formation. The flash geometry of the welds was observed to interpret the flow differences. Reasons for variations in bond formation were discussed with the help of fracture surfaces.