bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of repair welding procedures for 2.25Cr–1Mo and 9Cr–1Mo steel welds
Authors: Bhaduri A.K. , Rai S.K. , Gill T.P.S. , Sujith S. , Jayakumar T.
Published: June 2004

Chromium–molybdenum steels are extensively used in the steam generator circuits of power plants. These components may require welding of the cracks that can develop during fabrication, storage, and transportation stages, or during the service life of the plant. This investigation compares repair welding methods for Cr–Mo steels, using 2.25Cr–1Mo and 9Cr–1Mo materials. To simulate aging during service, welds were heat treated at 873 K for 5000 h. Simulated repair welding of the aged welds was carried out at the weld/base metal interface, i.e. at the location at which cracks are usually reported to occur during service. Two repair welding methods (half bead and butter bead temper bead methods) conforming to the ASME Boiler and Pressure Vessel Code were used. Tensile properties, hardness profiles, and X-ray diffraction based residual stress distributions were determined for both the Cr–Mo steel welds to evaluate the simulated repair welds. Analysis of the test results showed that both the repair welding methods can be used for 2.25Cr–1Mo steel welds, although the butter bead temper bead method is much more suitable for both the 2.25Cr–1Mo and 9Cr–1Mo steel welds.
Arc stability estimation and fuzzy control for arc stabilisation in short circuit transfer mode of CO2 arc welding
Authors: Kang M.J. , Rhee S.
Published: June 2004

The purpose of the present work is to evaluate and control the arc stability in the short circuit transfer mode of CO2 arc welding. The arc stability was investigated under different welding conditions, using the arc stability index developed by Mita et al., and a fuzzy control algorithm was developed. The correct parameters for the subset of fuzzy input/output variables were determined from the experimental results using a regression model. Simulations using the fuzzy controller with the selected parameters were performed. Application of the arc stability control in real welding showed convergent performance, similar to the result of the simulations. Also, when a step change in contact tip to work distance (CTWD) was introduced, the arc was initially unstable; however, it became stable within 6 s. Furthermore, when the CTWD was varied continuously, a stable arc was maintained even under conditions where the CTWD increased.
Study of weld strength variability for capacitor discharge welding process automation
Authors: Paul B.K. , Wilson D.D. , McDowell E. , Benjarattananon J.
Published: June 2004

The capacitor discharge welding (CDW) process is an autogenous, rapid solidification joining process ideal for joining small parts incorporating dissimilar metals. Potential applications include welding of solderless electrical contacts, cutting tool inserts, and automotive valves. Because of high cooling rates, in excess of 106 K s-1, the production rate for CDW processes is potentially very high. However, potential industrial users are hesitant to use the CDW process, owing largely to the unavailability of automated process control. The objective of the present study was to investigate the source of weld strength variability in CDW as a foundation for process automation and control. Results show that welding time significantly affects weld strength variability for both high thermal conductivity and high gas content materials, independent of the tw/2RC ratio.
Neural network analysis of strength and ductility of welding alloys for high strength low alloy shipbuilding steels
Authors: Metzbower E.A. , deLoach J.J. , Lalam S.H. , Bhadeshia H.K.D.H.
Published: June 2004

There are considerable demands for the development of weld metals for high strength low alloy steels. To assist in meeting such demands, a neural network was trained and tested on a set of data obtained on weld metals for steels of the type used for shipbuilding. The input variables for the network were the chemical elements and the weld cooling rate. The outputs consisted of the yield and ultimate tensile strengths, elongation, and reduction of area. Many models were created using different network configurations and initial conditions. An appropriate committee of models was then assembled by testing the ability of the models to generalise on unseen data. The neural network technique used is due to MacKay, with a Bayesian framework, and hence allows the estimation of error bars, which warn the user when data are sparse or locally noisy. The method revealed significant trends describing the dependence of mechanical properties on weld composition and cooling rate.
Empirical model of effects of pressure and temperature on electrical contact resistance of metals
Authors: Babu S.S. , Santella M.L. , Feng Z. , Riemer B.W. , Cohron J.W.
Published: June 2004

An important input property in the development of process models for resistance spot welding is electrical contact resistance. A model for the pressure and temperature dependence of electrical contact resistance was developed from established concepts of contact resistance. The key to developing the desired relationship is determining surface roughness characteristics, which is experimentally problematic. To overcome this difficulty the electrical resistance of contacting interfaces was measured as a function of the pressure applied across the interfaces. Using known information about the temperature dependence of bulk resistivity and mechanical properties, a curve fitting procedure was used to establish the desired relationship of contact resistance to pressure and temperature. This empirical model agrees well with experimental measurements in the regime of low applied pressure. At high pressures, predictions underestimate contact resistance, and this was attributed to strain hardening of asperities at the contacting interface. The model also predicts that the competing effects of bulk resistance and contact resistance will produce a peak in the variation of contact resistance with temperature. The model provides a suitable means for incorporating the pressure and temperature dependence of contact resistance into process models of the resistance spot welding process.
Finite element simulation of material flow in friction stir welding
Authors: Xu S. , deng X. , Reynolds A.P. , Seidel T.U.
Published: June 2004

A brief summary of recent finite element simulation results for the friction stir welding process is presented. The focus of the present study is on the characterisation of material flow around the rotating tool pin. Material flow patterns predicted by finite element simulations are found to compare favourably with experimental observations. The simulation results also reveal that material particles tend to pass and move behind the rotating pin from the trailing side, rather than both sides, of the pin. Possible variations in the material flow pattern due to variations in process parameters are discussed.
Laser spot welding of bearing protective washers
Authors: Fedosov S.
Published: June 2004

Laser spot welding has been applied for the fastening of protective bearing washers. The technology and laser welding plants employed are described. A correlation between the appearance of the spot welds and their quality has been discovered. The mechanism of welding deformation has been revealed and ways of reducing this are discussed.
Modification of welding stresses by flexural vibration during welding
Authors: Munsi A.S.M.Y. , Waddell A.J. , Walker C.A.
Published: June 2004

Flexural vibration was applied to specimens during the welding process to observe its effect on welding residual stresses. The study was carried out in three phases, namely, (i) investigation of the effect of amplitude of vibration, (ii) investigation of the effect of time of vibration, and (iii) investigation of the effect of high frequency vibration. The results of the present study provide a basis for relieving the residual stresses in practice. It has been shown that there is an optimum applied stress that will maximise the reduction in both longitudinal and transverse residual stresses. The effect of time of vibration on residual stresses was found to be negligible. After high frequency vibration, the change in longitudinal and transverse residual stresses showed no consistent trend.
Assessing metal transfer stability and spatter severity in flux cored arc welding
Authors: Bauné E. , Bonnet C. , Liu S.
Published: June 2004

Five experimental basic type flux cored arc welding consumable wire electrodes were manufactured from the same base formulation. The composition of these electrodes was adjusted in an attempt to improve the operating performance. This involved additions of various ratios of alkali oxides, namely, lithium, magnesium, sodium, and potassium containing ingredients, in the flux formulations. The operating behaviours of these experimental electrodes and two reference products (i.e. one commercial basic T–5 and one commercial rutile T–1 electrode) were thoroughly investigated by recording welding arc signals using a high speed data acquisition system. By comparing these electrodes among themselves, the experimental electrodes were reported to exhibit extremely stable arcs, some showing electrical arc signals even smoother than those for the reference rutile grade electrode. Despite their improved metal transfer consistency, however, basic electrodes were characterised by somewhat higher spatter levels.
Effect of pulsed gas tungsten arc welding on angular distortion in austenitic stainless steel weldments
Authors: Tseng K.H. , Chou C.P.
Published: June 2004

The effect of the parameters of the pulsed gas tungsten arc welding (GTAW) process on the angular distortion in austenitic stainless steel weldments was investigated. Autogenous GTAW was conducted on types 304 and 310 stainless steels to produce a bead on plate weld. The weldment thermal cycle was recorded during pulsed GTAW to investigate the influence of thermal stress. Angular distortion was determined by using the mean vertical displacement method. The experimental results indicate that higher pulse frequency, smaller pulse spacing, greater amplitude ratio, and greater duration ratio can reduce the angular distortion. The angular distortion of type 310 stainless steel weldments was greater than that of type 304 weldments under the same welding conditions because of the lower thermal conductivity and thermal diffusivity of type 310.
Plasma arc cutting torch tracking control
Authors: Wang J. , Kusumoto K. , Nezu K.
Published: June 2004

The present paper is concerned with a tracking system for cutting torch height in the plasma arc process. The computer based control system consists of the sensing and detection unit, controller, and servo actuator. The use of arc and laser sensors to detect the torch height is presented, and their applied characteristics are investigated in detail. A feedforward compensation of workpiece position is introduced to improve tracking properties. Moreover, to address the non-linear characteristics of the arc sensor, deviation classification and adaptive control approaches are also proposed. Tracking experimental results show acceptable tracking precision and strong noise restraining capability for the system. These demonstrate the effectiveness of the sensing and detection, and the proposed control algorithms. It is also shown that the arc sensing approach is more attractive, owing to its merits of synchronous sensing, high reliability, and low cost.
Development of base materials for welding
Authors: de Meester B.
Published: June 2004

The various aspects of weldability, seen as a material property, are introduced. These are illustrated by considering examples, in particular the recent advances in structural C–Mn and microalloyed steels. Important issues for the further development of the weldability of these materials are outlined. In concluding, the growing importance of mathematical modelling as a tool for the design of new weldable materials is emphasised.
Microstructural evolution in seven 2.25Cr–1Mo superheater outlet headers resulting from service exposure
Authors: Mitchell D.R.G. , Small R.
Published: June 2004

Seven 2.25Cr–1 Mo superheater outlet headers with service exposures ranging from as fabricated through to 190 kh (21.7 years) have been examined using analytical TEM. Parent plate, heat affected zone, and weld regions have been characterised to understand the influence of service exposure on the microstructure and the carbide make-up. Post-weld stress relief heat treatment in a virgin header produced a starting microstructure devoid of M3C, and consisting of M7C3and M23C6in the bainite and M2C in the ferrite. Service induced aging produced coarsening of M2C and the development of denuded zones along prior austenite grain boundaries. The carbide compositions in the bainite shifted towards thermodynamically stable phases, rich in Mo and Cr. One header exhibited anomalous behaviour; parent plate compositional effects may have contributed to this, along with fabrication and/or operational differences. Most of the individual carbide phases studied were found to undergo compositional changes with parabolic kinetics. These microstructural and compositional changes may find application in the assessment of effective time at temperature.
Determination of optimal brazing frequency by solution of thermal and electromagnetic models
Authors: Durand D. , Coupard D. , Goetz C. , Girot F.
Published: June 2004

Control of the thermal cycles in induction heating has now been achieved, as a result of the use of software that simulates electrical and thermal phenomena. In brazing, however, the results are more disappointing. This is because, in comparison with the classical cases of heating before forging, or of thermal processing, the charge consists of at least three more or less separate parts and the thermal cycles of these must be simultaneous. First, relying on the resolution of Maxwell equations applied to a homogeneous cylinder, the present paper describes the problem of determining the optimal brazing frequency, which is a fundamental parameter in solving the multiple charge heating problem. Then a model is presented that will allow solution in the general case of both electromagnetic and thermal equations in a coupled manner. The general method is illustrated with the example of brazing carbide blades onto a tempered steel body.
Experimental study of laser welding with applied electrical potential
Authors: Hamatani H. , Miyazaki Y. , Ohara M. , Tanaka T.
Published: June 2004

The objective of the present study is to develop laser welding with an applied voltage potential, to increase the weld bead root size in laser welding and thereby to improve the welding speed and the butt joint gap tolerance. The influences of the experimental conditions, namely, input laser power, applied voltage between plate and backside electrode, welding speed, plasma operating gaseous species (air, argon, or argon–helium), and the butt joint gap, on the plasma stability and the weld bead were investigated. The weld beads are evaluated from the point of view of the bead appearance, the penetration depth, the ratio of the widths of the weld bead root and weld bead face, and the smoothness of the bead surface. It is found that to stabilise the plasma, it is preferable to set the plate polarity as the cathode (electrode positive), and to use argon or helium gas as a plasma operating gas. Also, it is concluded that this novel method is effective in increasing the bead root/face width ratio, and the melting area. Although it is necessary to optimise the experimental conditions to avoid overheating and melting of the plates, the present method is applicable for higher speed and wider gap butt joint welding than in conventional laser welding.
Significant system parameters influencing HAZ properties in 9%Ni steel
Authors: Price A.H.
Published: June 2004

The relative influence of welding system parameters on the properties of the heat affected zone (HAZ) in 9%Ni steel has been investigated via a fractional factorial experiment. The HAZ properties evaluated were the dimensions in two locations, the hardness, and the impact strength. The independent variables were bevel preparation method, welding process, heat input, plate thickness, joint design, and position of the weldment. The study indicated that heat input, bevel preparation method, and an aliased interaction between the bevel preparation method and the joint design must be controlled to minimise the extent of the HAZ at the plate surface. The width of the HAZ measured at plate mid-thickness is a function of plate thickness, heat input, and two aliased interactions: between welding process and joint design; and that determined for the surface HAZ (interaction between joint design and bevel preparation method). Hardness was significantly affected by thickness, welding process, position, and heat input as well as by an aliased interaction between thickness and joint design. Impact strength was most influenced by two aliased interactions, both including the bevel preparation method. Weld position was found to affect HAZ impact values significantly.
Hydrogen distribution in multipass submerged arc weld metals
Authors: Kasuya T. , Hashiba Y. , Ohkita S. , Fuji M.
Published: June 2004

Hydrogen distribution in multipass submerged arc weld metal has been measured and analysed. The measurement of initial hydrogen content in a molten pool by obtaining samples directly from the pool shows that the effect of dilution on the initial hydrogen content can be neglected. The transient hydrogen distribution in multipass weld metal has also been measured. This can be fairly well explained by the present hydrogen diffusion model using the two-dimensional source solution.
Quality and productivity improvement in aluminium alloy thin sheet welding using alternating current pulsed metal inert gas welding system
Authors: Tong H. , Ueyama T. , Harada S. , Ushio M.
Published: June 2004

An alternating current (ac) pulsed metal inert gas (MIG) welding power source has been developed for welding thin sheets of aluminium alloys and the process features are investigated. Advantages such as high wire melting coefficient, low heat input, shallow penetration, and increased reinforcement height are obtained at high values of electrode negative ratio (ratio of electrode negative current integration to electrode negative plus electrode positive current integration over one pulse cycle). These features successfully counteract the problem of burnthrough in welding of thin sheet joints and greatly improve the bridging ability for wide gap joints. Thin sheet joints can be welded at high speed and with low distortion. By integrating the present welding power source with a welding robot, welding process and current waveform parameters can be defined by key operations in the teach pendant. It is possible to switch between welding processes such as ac pulsed MIG, direct current (dc) pulsed MIG, low frequency modulated ac pulsed MIG, and low frequency modulated dc pulsed MIG during a continuous welding run, so that the optimum welding process can always be selected.
New measurement technique and model for friction torque in continuous drive friction welding: Engineering oriented voltage–current floating evaluation measurement method and exponential function model of friction torque
Authors: Luo J.
Published: June 2004

Friction torque has been measured successfully using a voltage–current floating evaluation measurement technique. The friction heating process is divided into two stages and analysed. A model of friction torque in continuous drive friction welding at the transition–steady stage is presented and the model can be used to monitor and control the continuous drive friction welding process. The results can be used for numerical simulation of the friction welding process.
Thermal analysis of horizontal fillet joints by considering bead shape in gas metal arc welding
Authors:   Cho S.-H.,   Kim J.-W.
Published: June 2004

In gas metal arc (GMA) welding, the weld size, that is, the locally melted area of a workpiece, is one of the most important factors determining the strength of a welded structure. Variations in the welding power and the welding heat flux may affect the weld pool formation and ultimately the size of the weld. Therefore, an accurate prediction of the weld size requires a precise analysis of the weld thermal cycle. In the present study, a model that can estimate the weld bead geometry and a method for thermal analysis, including the model, are suggested. To analyse the weld bead geometry, a mathematical model was developed with transformed coordinates to apply to horizontal fillet joints. A heat flow analysis was performed using a two-dimensional finite element model that was adopted to compute the base metal melting zone. The reliability of the proposed model and the thermal analysis was evaluated through experiments, and the results showed that the proposed model was highly effective in predicting the weld bead shape, and that the predicted melting zone of the base metal also corresponded well with the experimental profile.
Characteristics of dissimilar welding of alloy 690 to 304L stainless steel
Authors: Lee H.T. , Jeng S.L.
Published: June 2004

The object of the present work is to research the dissimilar welding of nickel based 690 alloy and SUS 304L stainless steel using two alternative Inconel filler metals, namely, 82 (I–82) and 52 (I–52). Gas tungsten arc welding with identical parameters and procedures was used to carry out single V groove butt welding with six passes in four layers on nickel based alloy 690 and 304L stainless steel. Mechanical and corrosion resistance tests were performed. Metallographical, fractographical, and compositional analysis were used to study filler metal dissimilarities. Mechanical tests show that the I–82 weldment, owing to its denser dendrites and formation of abundant niobium enriched precipitates, has a higher strength and hardness than the I–52 weldment. Rupture occurred in the alloy 690 base metal. In comparison, the I–52 weldment, with coarse dendrites and no niobium enriched precipitates, exhibits superior corrosion resistance to the I–82 weldment but has a lower tensile strength and ruptured in the fusion zone. Microstructural investigation reveals that I–52 is a mixture of cellular dendrites and columnar dendrites whereas I–82 is mainly columnar dendrites with niobium enriched precipitates.
Search for filler metal for welding of ferrous alloys to titanium
Authors: Marya M. , Liu S.
Published: June 2004

The use of a filler metal to facilitate the gas tungsten arc (GTA) welding of ferrous alloys to titanium alloys has been investigated. Semi-empirical rules have been applied to identify alloying elements that would resolve the important problems of brittle intermetallic formation and weld cracking. Vanadium was found appropriate. The GTA welds between a low carbon steel and Ti–15V–3Cr–3Sn–3Al made with a vanadium filler wire resisted cracking better than comparable autogenous welds. However, the presence of a hard, brittle eutectic microconstituent along the ferrous side of the fusion boundary drastically limited the gain in weldability. As anticipated, analysis of GTA welds produced with vanadium filler wire suggested the presence of a ternary (Fe,Ti,V) single phase. Although cracking was reduced with vanadium, the practical benefit of a vanadium filler wire for GTA welding is small because the weld metals remain very hard and brittle.
Importance of filler material chemistry for optimising weld metal mechanical properties in modified 9Cr–1Mo steel
Authors: Sireesha M. , Albert S.K. , Sundaresan S.
Published: June 2004

Although modified 9Cr–1Mo (grade 91) steel is considered weldable using conventional procedures, the attainment of optimum weld metal properties often causes concern. In the current work, plates of grade 91 were manual metal arc welded using electrodes with slightly different compositions provided by two manufacturers. Post-weld tempering was performed at 730 and 760°C for 2 and 6 h in each case. The weld fusion zones were metallographically examined in detail and hardness, tensile properties, and toughness were estimated. The results showed that the weld metal produced from one of the two electrodes was distinctly superior in terms of ductility and toughness for any given welded or heat treated condition. This was attributed to the slightly higher silicon, niobium, and chromium contents in the inferior electrode, which resulted in both retention of some high temperature ferrite and a greater degree of precipitation. In this electrode, additionally, the alloying elements were introduced through the flux coating, which produced inhomogeneities in the microstructure that degraded the mechanical properties.
Effect of surface condition and bonding pressure on quality of diffusion bonded high purity copper for linear collider accelerator structures
Authors: Elmer J.W. , Klingman J. , van Bibber K.
Published: June 2004

Tests have been carried out to assess the feasibility of diffusion bonding as a fabrication technology for vacuum tight joints in linear accelerator cells for the Next Linear Collider. High purity copper specimens were diffusion bonded over a range of temperatures from 400 to 1000°C, under high (3.45 MPa) and low (3.45 kPa) bonding pressures, and at two different diamond machined surface finishes. Experiments showed that diffusion bonds with strengths equal to, or greater than, that of silver brazed joints could be made at temperatures ≥700°C at the 3.45 MPa bonding pressure, or ≥800°C at the 3.45 kPa bonding pressure. Partial strength diffusion bonds were made at temperatures as low as 400°C at the high bonding pressure, whereas no bonding (zero strength) was observed at temperatures below 700°C at the low bonding pressure. Observations of the fracture surfaces of the diffusion bonded specimens showed that bonding begins by point asperity contact. At low bonding pressures, surfaces created by diamond turning of annealed copper specimens produce higher strength bonds than those created by diamond flycutting of unannealed surfaces, whereas at higher bonding pressures the effect of surface finish was less important.
Factors affecting initiation of pitting corrosion in super martensitic stainless steel weldments
Authors: Enerhaug J. ,   Grong Ø., Steinsmo U.M.
Published: June 2004

In the present investigation optical microscopy, in combination with sputtered neutral mass spectrometry (SNMS), has been used to examine the conditions for initiation of pitting corrosion in the heat affected zone (HAZ) of two super martensitic (SM) stainless steel weldments. It is shown that the corrosion resistance depends mainly on the nature of the surface oxide, as determined by the oxygen potential in the shielding gas and the HAZ temperature–time relationship, and less strongly on the underlying microstructure. In the absence of H2S the initiation is associated with spalling of the iron enriched chromium oxide within a narrow region approximately 6 mm from the fusion line, where the contaminated oxide layer is thinnest. As H2S is introduced, the region close to the fusion boundary becomes susceptible to localised corrosion because of the more extensive metal oxidation. Thus, the high temperature oxidation and iron oxide scale formation accompanying the welding operation appear to be the main factors affecting pitting corrosion initiation in SM stainless steel weldments.
Comparative study of small scale and ‘large scale’ resistance spot welding
Authors: Chang B.H. , Li M.V. , Zhou Y.
Published: June 2004

An incrementally coupled electrical–thermal–mechanical model is developed to simulate small scale resistance spot welding (SSRSW) using the finite element method. This numerical model is then employed to study the differences between SSRSW and ‘large scale’ resistance spot welding (LSRSW). The variations in contact area, current distribution, and temperature profile at the workpiece/workpiece interfaces are compared. The computation shows that the difference in electrode force could be the essential reason for other differences between SSRSW and LSRSW. Compared with LSRSW, a much lower electrode force (pressure) applied in SSRSW results in a relatively small contact area and hence a much higher current density, which in turn leads to a greater heating rate and higher temperature at the workpiece/workpiece interface. This small contact area also results in a relatively small nugget diameter in SSRSW, which is only about 30% of the electrode tip diameter. In contrast, the nugget diameter in LSRSW is comparable to the electrode tip diameter. The predicted nugget diameters in both SSRSW and LSRSW of mild steel sheets compare well with experimental results.
Experimental determination of weld pool geometry in gas tungsten arc welding
Authors: Gao J. , Wu C.
Published: June 2004

Based on the analysis of the gas tungsten arc welding (GTAW) arc spectrum, a composite light filter is designed. This filter and a normal charge coupled device camera form a vision sensor, which observes the GTAW weld pool from the topside of the workpiece. During the welding process, the captured image brightness is adjusted according to the magnitude of the welding current using software, and comparatively distinct images of the weld pool are obtained. The weld pool geometry is measured through an image processing algorithm developed by the present authors. The algorithm requires less than 70 ms to process an image frame in a 100 MHz main frequency computer, and therefore meets the requirements of real time measurement.
Proposed specimen for reheating cracking susceptibility and mechanical behaviour assessment in 2.25Cr–1Mo steel pressure vessel weld joint
Authors:   Bang H.-S.,   Kim J.-M.
Published: June 2004

Post-welding heat treatment (PWHT) is carried out on 2.25Cr–1Mo steel used in pressure vessels, to relieve welding residual stress and diffused hydrogen and to soften the weld joint. However, it is known that reheating cracks often occur during PWHT. A standard specimen is available to pre-estimate the existence of cracks in pressure vessels according to rules such as those in Japanese Industrial Standard WES 3005. However, these specimens do not reflect the shape of the pressure vessels and do not reproduce the actual cracks correctly because of non-cylindrical welding. In the present paper, a numerical analysis has been conducted for various models, which can reproduce the occurrence of reheating cracks in the welded joint of a pressure vessel nozzle. The present paper also investigates mechanical behaviour such as the relief history of welding residual stress as well as the accumulated history of creep strains. Through the above processes, the mechanical behaviour of the welded pressure vessel nozzle joints has been elucidated and a model of reheating crack initiation has been selected. In addition, experiments on reheating crack initiation have been carried out for the WES 3005 specimen, and a new susceptibility assessment specimen has been proposed and developed to pre-estimate the existence of actual reheating cracks correctly.
Observations on welding of α2+O+β titanium aluminide
Authors: Madhusudhan Reddy G. , Mohandas T. , Chandreshekar K.
Published: June 2004

The weldability characteristics of an α 2+O+ β titanium aluminide of nominal composition Ti–24Al–15.5Nb (at.-%) have been investigated. Conventional gas tungsten arc (GTA) and electron beam (EB) welds exhibited columnar fusion zone grains. Pulsed current and arc oscillated GTA welds exhibited predominantly equiaxed fusion zone grains. The microstructure of GTA welds and pulsed current GTA welds exhibited α 2+O phases, whereas arc oscillated GTA welds and EB welds contained α 2+O+ β 0/ β 2; however, β 0/ β 2 is predominant in EB welds. The EB welds, which contained α 2+ β 0/ β 2 microstructure, exhibited high strength and ductility compared with GTA welds. The observed microstructural variations are explained on the basis of possible weld thermal cycles and convective currents in the weld pool.
Weld pool shape prediction in plasma augmented laser welded steel
Authors: Vitek J.M. , David S.A. , Richey M.W. , Biffin J. , Blundell N. , Page C.J.
Published: June 2004

A welding process that combined plasma arc welding with laser welding was used to make autogenous bead on plate welds on a sheet stock of a carbon steel. A wide range of welding parameters (arc current, laser power, weld speed) was employed. The experimental weld pool shapes were analysed and the data were used to train a neural network to predict weld pool shape as a function of process conditions. The predictions of the neural network model showed excellent agreement with the experimental results, indicating that a neural network model is a viable means for predicting weld pool shape. Using the model, a parametric study was carried out to examine the influence of process conditions on the final weld pool profile.
Comments on spread of plasticity from edge crack close to interface of dissimilar metal joint
Authors: Wu S.J. , Knott J.F.
Published: June 2004

The situation encountered by a crack in a dissimilar metal joint is analysed using a weight function method applied to a Dugdale crack model. The stress intensity factor at an effective crack tip located in the vicinity of the interface can be calculated from the weight function for a constant pressure load system, based on the principle of elastic stress superposition. The effects on the stress intensity factor and the crack tip opening displacement of a hard transitional zone, which is developed near the interface, are discussed.
Effect of slag variations on ANSI/AWS A5.1–91 E6013 electrode properties: Replacement of TiO2 in electrode coating with MnO, FeO, CaO, MgO, K2O, or Na2O
Authors: Ramini de Rissone N.M. , Surian E.S. , Conde R.H. , de Vedia L.A.
Published: June 2004

The present work is part of a research programme to study the effect of variation of the coating composition of covered rutile manual electrodes on both operational and deposited weld metal properties. According to previous results obtained for rutile electrodes, an increase of slag basicity, achieved through modifications in the coating, produces an improvement of the impact properties of the deposited weld metal, as well as a decrease in the diffusible hydrogen, along with beneficial changes in the operational properties of the electrode. The aim of the present work is to study the influence of the replacement of titanium oxide with oxides of alkali metals (sodium and potassium), alkaline earth metals (calcium and magnesium), and iron and manganese oxides in the coating of an ANSI/AWS A5.1–91 E6013 type electrode on the operational characteristics of the electrode and the microstructure, mechanical properties, and diffusible hydrogen content of the electrode weld metal. Tensile strength and Charpy V notch impact properties were measured in the all weld metal samples produced using each of the seven electrodes designed for the present study. A cross-section from each coupon was used to determine the chemical composition of the deposit and to carry out a metallographic study using a light microscope. As a result of the addition of different oxides, changes in the operational properties were observed using both direct and alternating current, as well as a decrease in the diffusible hydrogen content in the weld metal. Also, electrodes in which rutile was substituted by sodium oxide in the coating showed an improvement in the impact properties of the deposit.
Effect of high energy density welding processes on inclusion and microstructure formation in steel welds
Authors: Babu S.S. , Reidenbach F. , David S.A. , Böllinghaus T. , Hoffmeister H.
Published: June 2004

Inclusion formation and microstructure development in autogenous laser and electron beam welds made on a submerged arc weld deposit were investigated. Oxygen loss from the submerged arc weld metal deposit to the atmosphere occurred during electron and laser beam welding owing to the low pressure and helium shielding, respectively. Rapid weld cooling rates and changes in oxygen concentration resulted in different inclusion characteristics in these welds. The measured inclusion characteristics were compared with calcu lations obtained using an inclusion model. Acicular ferrite and bainitic microstructures were observed in electron beam welds, and predominantly martensitic microstructures were observed in laser welds.
Resistance spot welding of steel and aluminium sheet using insert metal sheet
Authors: Oikawa H. , Ohmiya S. , Yoshimura T. , Saitoh T.
Published: June 2004

The present paper reports the resistance spot welding of steel and aluminium sheets using aluminium clad steel sheets as insert metals. Intermetallic compound layers were formed in the weld zones in direct spot welding of steel sheets to aluminium sheets. Thus, the strength of these joints was lower than that of aluminium to aluminium joints. Intermetallic compound layers were also formed at the steel/aluminium interfaces of the insert metal in welding of steel to aluminium using an insert metal sheet. However, the strength of these joints was of the same order as that of the aluminium joints. The fracture mode of these joints varied with the welding current. The suitable welding current for steel to aluminium joints varied between the values suitable for steel to steel and aluminium to aluminium joints. The fatigue strength of joints using insert metals was somewhat lower than that of the aluminium joints.
Residual strength of aluminium alloy Afnor 7020
Authors: Sharma V.M.J. , Diwakar V. , Arumugham S. , Lakshmanan T.S.
Published: June 2004

Surface crack tension specimens of Afnor 7020 aluminium alloy (parent metal and weldment) were used to evaluate the residual strength in panels 5 mm thick and 125 mm wide. The reduction in the ultimate tensile strength (UTS) was in the range 9–15% in the parent metal for cracks up to about 4 mm deep. For similar crack depths in weldments the reduction in UTS was in the range 14–30%. The results have a significant bearing on the quality and reliability of welded components that are to be subjected to non-destructive evaluation.
Depth of penetration in gas metal arc welding
Authors: Murray P.E. , Scotti A.
Published: June 2004

A model is presented of the depth of penetration in gas metal arc welding. This model is based on the assumption that the heat and mass transfer to the weld pool and the depth of penetration may be correlated by a dimensionless relation. This correlation leads to an analytical expression for depth of penetration, which involves empirical constants that are related to the efficiency of heat and mass transfer to the pool. The accuracy of the model is examined by comparing the theoretical depth of penetration and the measured depth of the weld pool for a range of processing variables encompassing short arc and free flight mass transfer. Measurements are obtained from bead on plate welds of stainless steel using a stainless steel electrode and a shielding gas that is rich in argon. The results confirm that the depth of penetration is affected by variations in the rate of mass transfer.
Relationships between coating composition, all weld metal properties, operational behaviour, and diffusible hydrogen in weld metal from rutile electrodes of types ANSI/AWS A5.1–91 E6013 and E7024
Authors: Surian E.S. , de Rissone N.M.R.
Published: June 2004

Manual rutile electrodes of types ANSI/AWS A5.1– 91 E6013 and E7024, which represent the highest percentage by weight of the total production of manual electrodes, have been manufactured for many years. Nevertheless, there are few publications of systematic studies to relate coating composition, operating behav iour, all weld metal properties, and diffusible hydrogen in the deposit. It is only recently that information of this kind has become available (as, for example, for E7018 electrodes). The present work is intended to summarise and review all studies on manual rutile electrodes presented in Subcommission II–A of the International Institute of Welding from 1994 to 1997. The aim is to contribute to a better understanding of the metallurgy of weld metal deposited by C–Mn steel welding electrodes.
Characterisation of inclusions found in C–Mn steel welds containing titanium
Authors: Blais C. , L'Espérance G. , Evans G.M.
Published: June 2004

The main goal of the present study was to identify the chemistry of the phases on the surface of inclusions found in steel welds, to enable a better understanding of their role in the formation of acicular ferrite. Transmission electron microscopy and parallel electron energy loss spectrum imaging of specimens prepared by ultramicrotomy have been used to characterise inclusions found in C–Mn welds having different titanium concentrations. The results indicate that, for a weld containing 28 ppm titanium, which is the tough est weld studied, a phase comprising MnTi2O4 is present on the surface of the inclusions. As the concentration of titanium in the weld is increased to 120 ppm, the MnTi2O4 phase is found more towards the centre of the inclusions. It is partially enveloped by a slag of MnO. SiO2. The presence of TiO, often cited as a phase promoting the formation of acicular ferrite, was found only in the specimen that contained 410 ppm titanium. Thermodynamic calculations using databases for oxide solutions corroborate the experimental findings. They show that, below 112 ppm titanium, the first phase to solidify in the liquid inclusions is MnO. SiO2, followed by MnTi2O4. Above a concentration of 112 ppm titanium, the calculations indicate that there should be a reversal in the solidification sequence, i.e. MnTi2O4 should solidify first, followed by MnO. SiO2. Further more, these calculations indicate that the inclusions are still liquid after the solidification of the steel matrix.
Use of magnetic arc oscillation for grain refinement of gas tungsten arc welds in α–β titanium alloys
Authors: Sundaresan S. , Ram G.D.J.
Published: June 2004

In an effort to refine the weld metal grain structure in α–β titanium alloys, gas tungsten arc welding was carried out, during which transverse oscillations of the arc were induced through the use of an alternating external magnetic field. At optimum values of oscillation amplitude and frequency in both the alloys investigated, considerable refinement of the fusion zone grain structure was achieved. This could be attributed to factors that include enhanced fluid flow, reduced temperature gradients, and a continually changing weld pool size and shape owing to the action of the imposed magnetic field. The reduction in the prior β grain size was shown to result in a notable increase in fusion zone tensile ductility. Post-weld annealing increased ductility in all cases, but the magnetically treated material continued to show a higher elongation than that of the untreated material even after post-weld heat treatment.
Modelling of grain boundary liquation in Al–Zn–Mg weldments
Authors: Bjørneklett B.I. , Grong Ø. , Myhr O.R. , Kluken A.O.
Published: June 2004

The present investigation is concerned with the modelling of grain boundary liquation (i.e. local melting) within the subsolidus region of the heat affected zone (HAZ) during welding of Al–Zn–Mg alloys. As a starting point, the low melting grain boundary constit uents in two commercial extrusions have been identified and documented by means of optical and transmission electron microscopy. Based on a closer examination of the kinetics of particle dissolution during continuous heating, a mathematical formulation of the underlying diffusion problem is presented. The results from the numerical simulations show that the occurrence of local melting depends on the interplay between two main variables, i.e. the heating rate and the initial size of the grain boundary precipitates. In an actual welding situation, these variables are interrelated to the applied heat input and the thermal history of the base material, respectively.
Residual stress and its effect on corrosion behaviour of butt jointed Cu–Al alloys
Authors: Wang S.H. , Shan S.H. , Pan Y.C.
Published: June 2004

Residual stresses in dissimilar metal joints of copper and aluminium alloys have been measured using an X-ray diffraction technique and estimated by finite element analysis. The effects of local tensile and com pressive residual stresses in the joints on corrosion in artificial seawater have been investigated, using a potentiodynamic polarisation method. Galvanic cor rosion at the dissimilar metal weld region may be enhanced by the additional effect of differential stress induced by welding.
Application of wetting research to joining and to fabrication of composite materials
Authors: Fujii H.
Published: June 2004

To assist in selection of suitable wetting materials and control of wetting in various situations, previous results for ceramic–aluminium systems have been readdressed. Wetting systems can be categorised into three types (A, B, and C), characterised by original wettability and equilibrium wettability. In pure systems at 1373 K, AlN–Al and Si3 N4–Al are categorised as system A, a non-wetting system, and Al2O3–Al as system C, a wetting system. However, h-BN–Al, graphite–Al, MgO–Al, and SiC–Al belong to system B, changing from a non-wetting to a wetting system through interfacial reactions. From the present results, it was found that the contact angle for h-BN is far lower than the contact angles for typical ceramics. In fact, the contact angle decreased to 0° in phase IV (equilibrium phase) at and above 1273 K. This indicates that, from the viewpoint of wetting, h-BN and aluminium are an ideal combination for joining and, even more so, for the manufacture of a metal matrix composite. To demon strate the efficiency of joining or fabricating a composite material using this combination, a simple experiment was set up. The composite material is expected to have high wear resistance and good lubricating properties.
Effects of niobium on microstructure, mechanical properties, and corrosion behaviour in weldments of alloy 690
Authors: Lee H.T. , Kuo T.Y.
Published: June 2004

The present work investigates the effects of adding different quantities of Nb (0·1, 1·03, 2·49, and 3·35 wt-%) to the flux of electrodes used in welding Inconel alloy 690 on the microstructure, mechanical properties, and corrosion behaviour of the resulting weldments. Inconel filler metal I–52 coated with flux was used as the welding electrode. Weldments were butt welded using a manual shielded metal arc welding process. The experimental results indicated that the subgrain structure of the fusion zone was primarily dendritic. Niobium was depleted at the dendritic cores and enriched in the interdendritic regions. A small heat affected zone with typical coarse grains, which subsequently formed ghost grain boundaries, was present. With increasing Nb, the welds tended to show a finer subgrain structure and smaller dendritic spacing. Niobium rich segregants in the form of small particles formed in interdendritic spaces, providing the sites for microvoid formation by rupture. Correspondingly, the tensile strength and microhardness of the fusion zone appeared to increase slightly whereas the ductility decreased significantly. However, corrosion tended to initiate on the interdendritic sites, and was worse with increasing Nb. With increasing Nb, the tensile rupture mode changed from slant (ductile) to flat (brittle) fracture.