Similar Welds Research Articles

Titanium Alloys Thin Sheet Welding with the Use of Concentrated Solar Energy

The present study deals with the welding of titanium alloys thin sheets 1.3 mm thick, with the use of concentrated solar energy. The experimental part of the work took place at a medium size solar furnace at the installation of the Centre National de la Recherche Scientifique, at Odeillo, in Southern France, where similar and dissimilar defect-free welds of titanium Grades 4 and 6 were achieved, in the butt joint configuration. After the determination of the appropriate welding conditions, the optimum welded structures were examined and characterized microstructurally, by means of light optical microscopy, scanning electron microscopy, and microhardness testing. In addition, test pieces extracted from the weldments were tested under uniaxial tensile loading aiming to the estimation of the strength and the ductility of the joint. The analysis of the experimental results and the recorded data led to the basic concluding remarks which demonstrate increased hardness distribution inside the fusion area and severe loss of ductility, but adequate yield and tensile strength of the welds.

Development of Creep Damage in Similar Weld Joints of P92 Steel Pipe

The microstructure and creep behaviour of the welded joints of P92 steel pipe were investigated in order to determine the influence of orbital heat welding technology on the creep resistance. Creep specimens were machined from the welded joints. Tensile creep tests of welded joints were performed at 873 K using different stresses. The microstructure of tested specimens was investigated by scanning electron microscope Tescan equipped with an electron-back scatter diffraction. The creep results showed that the creep fracture strain of the welded joints decreases with decreasing value of applied stress. Microstructure investigation showed that fracture behaviour of welded joints is influenced by an enhanced cavity formation at grain boundaries in the heat-affected zone causing lower fracture ductility.

Dissimilar and Similar Laser Beam and GTA Welding of Nuclear Fuel Pin Cladding Tube to End Plug Joint

The end plug to cladding tube of fast reactor fuel pin is normally welded using Gas Tungsten Arc Welding (GTAW) process. The GTAW process has large heat input and wide heat-affected-zone (HAZ) than high energy density process such as laser welding. In the present study Laser Beam Welding (LBW) is being considered as an alternative welding process to join end plug to clad tube. The characteristics of autogenous processes such as GTAW and pulsed Nd-YAG laser welding on fuel cladding tube to end plug joints have been investigated in this study. Dissimilar combinations of modified stainless steel (SS) alloy D9 cladding tube to SS316L end plug, and similar combinations of SS316L cladding tube to SS316L end plug were successfully welded using the above two welding processes. The laser welding was performed at the butting surfaces of the cladding tube and the end plug, and also by shifting the laser beam by 0.2 mm towards the end plug side to compensate the heat balance and for improving the Creq/Nieq ratio in the molten pool. Helium Leak Test (HLT) and Radiography Test (RT) were carried out to validate the quality of the welds. The microstructures of the weld joints were analysed using optical microscope. In the present study, it has been demonstrated that it is possible to obtain welds free from hot cracks by shifting the laser beam by 0.2 mm towards end plug side, while the weld produced using the beam positioned at the interface shows cracks in the weld.

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 0.2–0.3mm 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.

Accurate analytical structural stress and stress intensity factor solutions for similar and dissimilar spot welds in lap-shear specimens

New analytical closed-form structural stress solutions for a rigid inclusion in a finite square thin plate under counter bending, central bending, in-plane shear and tension are developed. The new solutions are used to derive new analytical structural stress and stress intensity factor solutions for similar and dissimilar spot welds in lap-shear specimens. The new analytical solutions can predict the stress intensity factor solutions for similar and dissimilar magnesium/steel spot welds in lap-shear specimens of equal thickness under pinned loading conditions with less than 6% differences when compared with the results of three-dimensional finite element analyses.

Similar and dissimilar joining of AA6061-T6 and copper by single and multi-spot friction stirring

Similar and dissimilar friction stir spot welding (FSSW) between AA6061-T6 aluminum alloy and copper with single and multi-spots are prepared with pinless tool and variation of joint lap shear, cross tensile strength are investigated and presented. Finite element models for lap shear and cross tensile loading conditions are created considering the stir zone, thermo-mechanically affected zone, base metal, shoulder penetration and flash region. For similar FSSW joints, failure from joint circumference is mostly observed under lap shear test whereas plug type and interface fracture is observed in cross tensile test. Finite element results predicted maximum stress and strain near these regions. In dissimilar joints failure and separation of the sheets are mostly observed from the joint interface. Formation of intermetallic compound is observed in dissimilar joints having maximum thickness near the joint periphery. Significant amount of grain refinement as compared to the base metal is observed in stir zones due to the dynamic recrystallization. Observation of failure surfaces showed presence of numerous dimples all thought out the surface in similar joints and presence of micro-cracks, rupture in dissimilar joint.

Microstructure and mechanical properties of fibre laser welded medium manganese TRIP steel

Fibre laser welds of Fe-0.15C-10Mn-1.5Al medium-Mn transformation induced plasticity (TRIP) steel and its dissimilar combination with high strength low alloy (HSLA) and dual-phase (DP980) steel was assessed with respect to microstructure, microhardness, formability, and tensile properties. The fusion zone (FZ) of the medium-Mn TRIP steel weldment was consist of predominantly martensite with some interdendritic austenite due to high manganese concentration which stabilizes austenite. The FZ of dissimilar combinations to HSLA and DP980 steel consisted of mostly martensite. Microhardness profiles of the medium-Mn TRIP steel showed no indications of detrimental heat-affected zone (HAZ) softening despite the high base metal (BM) hardness (396HV). Laser welds containing medium-Mn TRIP displayed similar FZ hardness values (413–438HV). Failure of medium-Mn TRIP laser welds under uniaxial tension occurred adjacent to the FZ where localized strain accumulated. The tensile results showed consistent failure in the weaker BM of dissimilar joints at high joint efficiency (95–100%) with respect to the weaker material of the joint. Biaxial stretch formability of TRIP-TRIP similar welds was determined to be severely limited by the brittle FZ. Strain accumulation in the BM of HSLA and DP980 steel in dissimilar combinations improved formability of laser welded blanks containing medium-Mn TRIP steel.

Optimization of hybrid laser–TIG welding of 316LN stainless steel using genetic algorithm

ABSTRACTDetermination of optimum hybrid laser–TIG welding process variables for achieving the maximum depth of penetration (DOP) in type 316LN stainless steel has been carried out using a genetic algorithm (GA). Nd:YAG pulsed laser and the TIG heat source were coupled at the weld pool to carry out hybrid welding. Design of experiments approach was used to generate the experimental design matrix. Bead-on-plate welds were carried out based on the design matrix. The input variables considered were laser power, pulse frequency, pulse duration, and TIG current. The response variable considered was the DOP. Multiple-regression model was developed correlating the process variables with the DOP using the generated data. The regression model was used for evaluating the objective function in GA. GA-based model was developed and it produced a set of solutions. Tournament and roulette wheel selection methods were used during the execution of GA. It was found that both the selection methods identified similar welding process parameters for achieving the maximum DOP. Excellent agreement was observed between the target DOP and the DOP values obtained in the validation experiments during hybrid laser–TIG welding.

Stress intensity factor solutions for similar and dissimilar spot welds in lap-shear specimens under clamped loading conditions

In this paper, analytical stress intensity factor solutions for similar and dissimilar spot welds in lap-shear specimens under pinned and clamped loading conditions are derived. Closed-form solutions for similar welds in lap-shear specimens of equal thickness under pinned and clamped loading conditions are derived to show explicitly the effects of the clamped edges on the stress intensity factor solutions. Finite element analyses are also employed to obtain the stress intensity factor solutions for similar and dissimilar spot welds in lap-shear specimens under pinned and clamped loading conditions. Both computational and analytical solutions indicate that the clamped loading reduces the stress intensity factor solutions for the given specimen geometries by up to 7% for similar welds and by about 20% for dissimilar magnesium/steel welds.

Strength and failure analysis of similar and dissimilar friction stir spot welds: Influence of different tools and pin geometries

Tool and pin geometries play significant roles in material flow, stirring and weld quality in friction stir spot welding (FSSW) process. The present work investigates the influence of tool pin length (0mm i.e. pinless, 0.2mm and 0.4mm) and pin diameter (3.3mm and 4.95mm) on lap shear strength during the FSSW of similar and dissimilar aluminum and copper alloy. Pinless tools are differently designed from H13 die steel single material and embedded aluminum and/or copper rods in H13. Results indicate that the maximum lap shear strength is achieved with pinless tools (single material). However, when tools with pins are used lap shear strength decreases with increase in tool plunge depth but increases with pin diameter. For pinless tool obscure hook formation is noted and crack is initiated from the joint interface. Asymmetric strain distributions as observed from the finite element analysis and hook formation observed during microscopic analysis may be responsible for quick failure when higher plunge depth of pin is used. Shear fracture in presence of micro-voids/dimples elongated along the loading direction are observed in similar FSSW whereas in case of Cu-Al dissimilar joints, formation of intermetallic compounds and quasi-cleavage fracture is observed.

Study of Weld Integrity and Nugget Development in Seam-Welded Cold-Rolled High-Strength Steels

Production processes like continuous annealing and continuous galvanizing/galvannealing rely on welding of two strips across their width, for continuous operation. The operational stability of these lines depends highly on the consistency of the welding process. Any failure of weld joint during processing is detrimental to production as the recovery times are very high (~1–3 days). Two instances of similar weld failures having identical chemical composition and dimensions of the strips were investigated to identify the root cause and establish adequate countermeasures. A systematic approach to evaluate weld performance using metallographic examination was carried out. The examinations revealed that poor nugget formation was the root cause of failure. The nugget formation, its orientation and size were also evaluated after carrying out a series of trials with different welding process parameters, and an optimum condition was arrived at. In summary, the weld failure occurred due to insufficient and unbalanced nugget formation which could be rectified by modifying the welding parameters such as current, pressure and speed.

Investigation of transient/residual strain and stress in dissimilar weld

Optimizing welding parameters to achieve low residual stress (RS) with the aid of stress reduction techniques usually relies on the study of residual strain distribution in weldment. However, investigating transient strains using experimental methods such as strain gauges gives an additional view on how RS is reduced. In this work, the transient strain and stress on the surface of dissimilar plate during gas-tungsten arc (GTA) welding process have been studied using non-destructive strain gauge method. It is demonstrated that strain gauge measurements during dissimilar welding processes can be used to indicate residual elastic strain and stress. Moreover, three- dimensional (3D) finite element (FE) model has been developed and verified with experimental work (neutron diffraction measurement), and was employed to examine the formation of RS upon cooling of a 304-1018 dissimilar weldment. The strain gauge (SG) measurement method shows good agreement with FE model and neutron diffraction measurements. The assumptions and limitations associated with strain measurement and determination of the stress state are explored. Lastly, curvature due to dissimilar weld and its effects on strain measurement, which is in contrast with similar weld, was measured and discussed.

Study on weld pool behaviors and ripple formation in dissimilar welding under pulsed laser

A three-transient numerical model is developed to study the dissimilar metal welding under pulsed laser. The melting, resolidification and vaporization inducing recoil pressure are considered in this model. Their effects on molten pool dynamic and the weld bead formation are studied. The similar metal welding and dissimilar metal welding under pulsed laser are respectively simulated by using this model. It is found that surface ripples are caused mainly by the periodical laser and molten pool solidification. In the first, this model is validated by the weld bead geometry comparison between the simulated and experimental results in similar metal welding. Then, this model is applied to simulate the dissimilar metal welding under pulsed laser. The results show that the distributions of the temperature, melt-flow velocity and surface ripples are asymmetric due to the differences in physical properties of the materials. The higher pulse overlapping factor decreases the solidification rate, leading to the more uniform penetration depths and the finer ripples. Good agreements between the experimental observations and simulation results are obtained by the proposed model.

Fatigue Strength Estimation Based on Local Mechanical Properties for Aluminum Alloy FSW Joints.

Overall fatigue strengths and hardness distributions of the aluminum alloy similar and dissimilar friction stir welding (FSW) joints were determined. The local fatigue strengths as well as local tensile strengths were also obtained by using small round bar specimens extracted from specific locations, such as the stir zone, heat affected zone, and base metal. It was found from the results that fatigue fracture of the FSW joint plate specimen occurred at the location of the lowest local fatigue strength as well as the lowest hardness, regardless of microstructural evolution. To estimate the fatigue strengths of aluminum alloy FSW joints from the hardness measurements, the relationship between fatigue strength and hardness for aluminum alloys was investigated based on the present experimental results and the available wide range of data from the references. It was found as: σa (R = −1) = 1.68 HV (σa is in MPa and HV has no unit). It was also confirmed that the estimated fatigue strengths were in good agreement with the experimental results for aluminum alloy FSW joints.

Dissimilar metal welds between 9Cr creep strength enhanced ferritic steel and advanced stainless steels—creep rupture test results and microstructural investigations

Modern and future power plants will use more complex materials to withstand the higher steam temperatures and pressures as well as thermal cycling. As such, dissimilar metal welds (DMWs) will be more widespread in new design than before and will need to demonstrate resistance to combinations of severe creep, corrosion/oxidation, and low cycle fatigue. The DMWs between different steels or alloys are an underestimated topic. Experienced and documented premature failures reveal the criticality of DMWs. This study focused on the DMWs between 9Cr martensitic creep strength enhanced ferritic steels and advanced austenitic stainless steels. Two collaborative projects related to 18%Cr and 25%Cr austenitic creep resisting stainless steel delivered data concerning base metal characterization and weldability of similar and dissimilar welding. The specific features of dissimilar welding are further approached in more detail in this analysis. Two main methodologies, i.e., direct welding and buttering techniques using different filler metals were investigated and characterized via uniaxial creep rupture testing and metallographic examination particularly focusing on the fusion line carbide formation and morphology. For the limited exposure times of 10 kh in this project, the results show that aligned and coarse type I carbide formation is occurring at the 9Cr fusion line between A617 type weld metal. The selection of P87 or A82 type filler metals demonstrated isolated to partly aligned carbides, respectively, at the fusion line. To mitigate the risk to corrosion and achieve a marginal increase in creep performance, buttering techniques are recommended.

Dissimilar metal welds between martensitic and advanced austenitic high temperature creep resisting steels: Creep rupture test results and fusion line investigation

Modern and future power plants will use more elaborated and complex materials to withstand the higher steam temperatures and pressures as well as thermal cycling. As such, dissimilar metal welds (DMWs) will be much more widespread in new design than before and will need to demonstrate resistance to combinations of severe creep, corrosion/oxidation and low cycle fatigue. The DMWs between different steels or alloys are an underestimated topic. Experienced and documented premature failures reveal the criticality of DMWs. This study focused on the DMWs between martensitic and advanced austenitic stainless steels. Two collaborative projects related to a 18%Cr and 25%Cr austenitic creep resisting stainless steel delivered data concerning base metal characterization and weldability of similar and dissimilar welding. The specific features of dissimilar welding are further approached in more detail in this analysis. Two main methodologies i.e. direct welding and buttering techniques using different filler metals were investigated and characterized via uni-axial creep rupture testing and metallographic examination particularly focusing on the fusion line carbide formation and morphology. For the limited exposure times of 10kh in this project, the results show that aligned and linked up type I carbide formation is occurring when A617 type filler metals are used. The selection of P87 or A82 type filler metals demonstrated isolated to partly aligned carbides respectively at the fusion line. Due to a risk for corrosion and the somewhat better creep rupture strengths at comparable conditions, buttering techniques seem to be recommended above direct welding.

PREDICTION OF STRENGTH REDUCTION FACTOR FOR WELDED JOINTS OF REDICTION OF STRENGTH REDUCTION FACTOR FOR WELDED JOINTS OF TURBINES WITH ULTRA SUPERCRITICAL STEAM PARAMETERS URBINES WITH ULTRA SUPERCRITICAL STEAM PARAMETERS

During long-term operation heat-resistant ferrite and martensitic steel welds have type IV cracking in a so-called ‘soft layer’, which contains part of fine grain region and inter-critical region of heat-aff ected zone (HAZ). The rupture of dissimilar welds occurs in the carbonless soft layer near fusion line. Therefore the strength reduction factor of welds decreases significantly with increasing lifetime and operating temperature. Based on experimental investigations the design model is constructed to predict the welds strength reduction coefficient at the design stage, taking into account different structural and technological factors, also changes creep and fracture mechanisms. Creep strength tests of martensitic steel P91 welds and dissimilar welds P91 + Cr-Mo-V steel were performed at temperature of 620°С. The HAZ metal investigation was performed after the thermal welding cycle simulation at the «IMETCKTI» and «Gleeble-3800» units. In addition, numerical modeling was carried out, using the Kachanov-Rabotnov constitutive equations, taking into account the three stages of creep, the influence of complex stress state, changes creep and fracture mechanisms. Based on the calculation results, the life time of P91 welds depends from the soft layer relative width and the creep rate ratio the base metal vs. the soft layer metal. A quantitative evaluation of the dissimilar welds creep strength is obtained using a sample model with two soft layers. Both have the same properties corresponding to the weakened region HAZ metal of the similar weld. According to the calculation results, the dissimilar welded samples rupture location moves to carbonless zone at lower stress level. Calculation results have good agreement with the experimental data. The obtained dependences are in good agreement with the theoretical and experimental studies of L. M. Kachanov, D. R. Hayhurst, V. N. Zemzin, R. Z. Schron et al.

Similar and Dissimilar Ultrasonic Spot Welding of 5754 Aluminum Alloy for Automotive Applications

Aluminum (Al) alloys are increasingly used in the transportation industry to reduce the weight of vehicles due to their high strength-to-weight ratio. These applications unavoidably involve similar and dissimilar joining of an automotive grade 5754 Al alloy to manufacture multi-material vehicle body structures and parts. Ultrasonic spot welding (USW), an emerging and promising solid-state joining technology, can be suitably applied to join Al alloys. In this study, 5754 Al alloy was welded in similar (Al5754-Al5754) and dissimilar (Al5754-ZEK100 Mg alloy, Al5754-HSLA steel) configurations at varying levels of welding energy. It was observed that USW had a strong effect on the interface microstructure, with fine grains present at the weld interface via dynamic recrystallization in the similar welding, while an interface diffusion layer formed in the dissimilar welding. The tensile lap shear strength increased with increasing welding energy, reached its optimum value, and then decreased with further increasing welding energy. The strength of dissimilar Al5754-ZEK100 and Al5754-HSLA steel joints was about 55% and 88% of that of the similar Al-Al joints, respectively. The dissimilar Al5754-HSLA steel joints exhibited the longest fatigue life due to the reduced stress concentration and additional strengthening arising from the brazing effect of the squeezed-out Al-Zn eutectic structure at the nugget edge.

Welded, pickled stainless steel reinforcements: corrosion results after 9 years in mortar

The corrosion behaviour of mortar samples reinforced with three different types of ribbed stainless steel (SS) was tested after 9 years. The reinforcements had been both similar welded (SS–SS) and dissimilar welded to carbon steel (SS–CS). After welding, the bars were cleaned by pickling, although this treatment was unable to remove the welding oxides completely. The prepared reinforcements were then embedded in carbonated mortar with chlorides and exposed to high relative humidity. Corrosion potential and electrochemical impedance spectroscopy measurements were used to monitor the spontaneous corrosion behaviour of the samples over 8 years. The welded bars were then anodically polarised in order to force attack. Exposure was continued for a further year to allow progression of the pits. For the SS–SS welded samples, S20430–S20430 showed poor corrosion resistance under these conditions, whereas S32205–S32205 reinforcements demonstrated excellent corrosion behaviour.

Friction stir welding of similar and dissimilar aluminium alloys for automotive applications

Aluminium alloys are lightweight materials relatively used in automotive industries. However, welding using the conventional welding methods is known to be difficult. In this study, the friction stir welding (FSW) known as the solid state joining process was extensively used for joining similar and dissimilar 5 mm aluminium alloy plates. The butt-joint type of similar joints (AA5083-AA5083) and dissimilar joints (AA5083- AA6061) were carried out under the same welding parameters; 1000 rpm (rotational speed) and 100 mm/min (transverse speed). Macro- and microstructural observations were acquired at the cross-section of the weld regions by stereo and optical microscopes. The microstructural study showed that the formation of ‘onion ring’ structure was detected in the nugget zone of similar joints, while wavy and distorted patterns appeared in dissimilar joints. All tensile specimens of similar welding joint showed similar fracture patterns where all fractures occurred in the thermo-mechanically affected zone (TMAZ). However, tensile specimens of dissimilar welding joint broke up at the TMAZ region as well as at Al6061 base metal at the retreating side. The tensile strength of similar joint and dissimilar joint was 22% and 19% lower compared to the base metal of Al5083 and Al6061.