Showing papers in "Science and Technology of Welding and Joining in 2000"
TL;DR: In this article, material flow in friction stir welds has been visualised using embedded marker materials and the fidelity of the visualisation technique has also been demonstrated, showing that the friction stir welding process can be roughly described as an in situ extrusion process wherein the tool shoulder, the weld backing plate, and the cold base metal outside the weld zone form an extrusion chamber which moves relative to the workpiece.
Abstract: Material flow in friction stir welds has been visualised using embedded marker materials. The fidelity of the visualisation technique has also been demonstrated. Results from the flow visualisation show that the friction stir welding process can be roughly described as an in situ extrusion process wherein the tool shoulder, the weld backing plate, and the cold base metal outside the weld zone form an ‘extrusion chamber’ which moves relative to the workpiece. Deviation from this description occurs primarily at the top surface of the weld where significant material transport occurs owing to the action of the rotating tool shoulder. The transport caused by the shoulder leads to a small amount of circulation about the longitudinal axis of the weld with material moving primarily from trailing to leading sides at the top of the weld and primarily from leading to trailing near the middle and bottom of the weld.
242 citations
TL;DR: The most dominant mechanism for increased penetration is considered to be arc constriction rather than a change in the surface tension of the molten pool as mentioned in this paper, which is the most common mechanism used in tungsten inert gas welding.
Abstract: Mechanisms by which active fluxes increase the penetration of conventional tungsten inert gas (TIG) welds (so called A-TIG welds) are reviewed. The most dominant mechanism for increased penetration is considered to be arc constriction rather than a change in the surface tension of the molten pool. An experimental programme of work was carried out using A-TIG flux in combination with a number of welding processes. The plasma process was investigated as it gives greater penetration than conventional TIG welding by increasing current density. The CO2 laser and electron beam processes which do not rely on a current carrying arc as the heat source for welding were also investigated. Macrosections taken from the welds made by these processes showed that the A-TIG flux was only effective when the weld pool was produced by an arc or plasma. Where there was no arc or plasma present, the flux had little effect.
183 citations
TL;DR: Aluminium alloys AA 5083 and AA 6082 have been friction stir welded and the mechanical properties and micro-structures of the welds have been evaluated as mentioned in this paper.
Abstract: Aluminium alloys AA 5083 and AA 6082 have been friction stir welded and the mechanical properties and microstructures of the welds have been evaluated. Alloy AA 5083 mainly fractured near t...
168 citations
TL;DR: In this article, a constricted anode root was found in the gas tungsten arc (GTA) process with activating fluxes consisting of oxides and halides.
Abstract: Dramatic increases in the depth of weld bead penetration have been demonstrated by welding stainless steel using the gas tungsten arc (GTA) process with activating fluxes consisting of oxides and halides. However, there is no commonly agreed mechanism for the effect of flux on the process. In order to clarify the mechanism, behaviour of the arc and weld pool in the GTA process with activating flux was observed in comparison with a conventional GTA process. A constricted anode root was found in the GTA process with activating flux, while a diffuse anode root was found in the conventional process. Furthermore, it is suggested that these anode roots are strongly related to metal vapour from the weld pool, which is also related to temperature distributions on the weld pool surface.
158 citations
TL;DR: In this paper, the effects of CO2 and Nd-YAG laser beam processing parameters and the properties of the most common wrought aluminium alloys on the characteristics of welded joints are discussed.
Abstract: Laser beam welding is now a common manufacturing method for a wide range of steel products from automobiles to razor blades. However, the process has only recently been approved for critical applications involving aluminium alloys, notably in the aerospace and automotive industries. The properties of aluminium alloys influence the interaction between the beam and the material to a far greater extent than for steels. The challenge of developing industrial welding procedures has therefore been considerable. The present review describes the effects of CO2 and Nd–YAG laser beam processing parameters and the properties of the most common wrought aluminium alloys on the characteristics of welded joints. Porosity, solidification cracking, and poor weld bead geometry are shown to be the most frequently encountered imperfections. These can be eliminated through the use of appropriate filler materials, process gases, material preparation, and in some instances, adaptive control systems. Very little work has...
89 citations
TL;DR: In this article, microstructure and fracture properties relationships have been investigated in the heat affected zones (HAZs) of a high strength low alloy steel used for offshore applications.
Abstract: Microstructure and fracture properties relationships have been investigated in the heat affected zones (HAZs) of a high strength low alloy steel used for offshore applications. Metallograph...
88 citations
TL;DR: In this paper, the microstructural characteristics and mechanical properties of welds in 20 mm thickness high strength low alloy steel HSLA 80, of Australian manufacture were evaluated using colour etching techniques.
Abstract: An evaluation is presented of the microstructural characteristics and mechanical properties of welds in 20 mm thickness high strength low alloy steel HSLA 80, of Australian manufacture. In total, nine butt joints were prepared using the double tandem (four wire) submerged arc welding process in which both heat input and travel speed were varied. The inclusion size distribution was determined for selected welds and showed that heat input had a major effect. Colour etching techniques were used to reveal the solidification structure, which in turn correlated with welding parameters. As the heat input increased, the cooling rate decreased resulting in a larger cellular dendritic cell spacing, decreased acicular ferrite content, and coarser acicular ferrite laths. The effect of travel speed on delta ferrite cell spacing and prior austenite grain size was found to be co-dependent on the heat input and the thermal profile resulting from multiple electrode welding. These results show that increased deposi...
77 citations
TL;DR: In this article, the formation mechanisms for the vermicular and lacy ferrite observed in the weld metals were clarified by both the crystallographic orientation relationship between ferrite and austenite established at the stage of ferrite nucleation and the relationship between the welding heat source direction and the preferential growth directions of ferritic-austenite.
Abstract: Solidification and subsequent transformation of austenitic stainless steel weld metals that solidified in the ferritic–austenitic mode were investigated from the viewpoint of crystallography. The formation mechanisms for the vermicular and lacy ferrite observed in the weld metals were clarified. The ferrite morphology is determined by both the crystallographic orientation relationship between ferrite and austenite established at the stage of ferrite nucleation and the relationship between the welding heat source direction and the preferential growth directions of ferrite and austenite. In particular, for the formation of continuous lacy ferrite, it is necessary that the ferrite continues to grow with the Kurdjumov–Sachs orientation relationship with austenite that is established at the stage of ferrite nucleation.
58 citations
54 citations
TL;DR: In this paper, the yield strength and ultimate tensile strength of ferritic steel weld metal have been expressed as functions of chemical composition, the heat input during welding, and the heat treatment given after welding is completed.
Abstract: The yield strength and ultimate tensile strength of ferritic steel weld metal have been expressed as functions of chemical composition, the heat input during welding, and the heat treatment given after welding is completed. The method involved a neural network analysis of a vast and fairly general database assembled from publications on weld metal properties. The outputs of the model have been assessed in a variety of ways, including specific studies of model predictions for the so called C–Mn and 2.25Cr–1Mo systems. Where possible, comparisons have also been made with corresponding methods which use simple physical metallurgical principles. The models created are believed to have been trained on the largest weld metal database to date, and are shown to capture vital metallurgical trends. The computer programs associated with the work have been made freely available on the World Wide Web.
44 citations
TL;DR: In this paper, a neural network system for process monitoring and quality evaluation in gas metal arc welding is presented, which is based on measured and statistically processed data for welding voltage and short circuiting time.
Abstract: To ensure product quality, it is essential to ensure process quality. Thus, early monitoring and detection of process disturbances in welding production lines are of great significance. The present paper introduces a neural network system for process monitoring and quality evaluation in gas metal arc welding. The system is based only on the measured and statistically processed data for welding voltage and short circuiting time. It is a self-organising feature map Kohonen network which can automatically recognise and classify process disturbances occurring during welding.
TL;DR: In this paper, the authors identify weld metal compositions and microstructures capable of meeting high strength and toughness requirements for X100 seam welded linepipe for single pass, multi-pass, and single-pass linepipe.
Abstract: Research has been carried out to identify weld metal compositions and microstructures capable of meeting high strength and toughness requirements for X100 seam welded linepipe. Single pass, multiwi...
TL;DR: In this article, the authors presented models which can be used to estimate the yield and ultimate tensile strength of ferritic steel welds, but they dealt with properties that are much more difficult to predict: the elongation and Charpy impact toughness.
Abstract: Previous work presented models which can be used to estimate the yield and ultimate tensile strengths of ferritic steel welds. The present paper deals with properties that are much more difficult to predict: the elongation and Charpy impact toughness. While the models are found to be useful and emulate expectations from current physical metallurgy principles, it is clear that much more systematic experimental data are needed before the predictability becomes as good as the strength models of Part 1.
TL;DR: In this article, the authors present a method which can be used to estimate the creep rupture strength of ferritic steel weld metals, from a knowledge of the creep strength of wrought plates.
Abstract: Recent changes in the design of steam turbine power plant have necessitated the replacement of bolted flanges with welded joints. The design process therefore requires a knowledge of the creep rupture strength of the weld metal consumed in the welding process. This paper presents a method which can be used to estimate the creep rupture strength of ferritic steel weld metals, from a knowledge of the creep strength of wrought plates. The method is validated using published data.
TL;DR: In this article, the application of variable polarity plasma arc welding (VPPAW) to two medium-to high-strength 6·35 mm thickness aluminium alloys is described, where automated computer controlled equipment is used to produce single pass, full penetration keyhole welds of even bead width.
Abstract: The application of the variable polarity plasma arc welding (VPPAW) process to two medium to high strength 6·35 mm thickness aluminium alloys is described. Automated computer controlled equipment was used to produce single pass, full penetration keyhole welds of even bead width. The paper covers the development and optimisation of the welding parameters and different material preparation procedures, providing macrographs, electrical transient traces, hardness profiles, and tensile results from some of the welds made. Repeatable procedures were obtained more easily by welding in the vertical up position, using the plasma gas flowrate in conjunction with the welding current to generate the desired bead profile. Autogenous welded joints were found to provide adequate root reinforcement with a slight degree of undercutting at the top bead. Example skimmed and as welded tensile tests were carried out on 2024 alloy, resulting in a typical overall ultimate tensile welded performance of 66% of the parent ...
TL;DR: In this article, it was found that when the interpass temperature was controlled to below 150°C, the average ferrite content increased in the weld metal and in the heat affected zone (HAZ).
Abstract: Butt welds of duplex stainless steel plate (grade 2205) have been produced using grade 2209 consumables for a variety of welding processes employed in the shipbuilding industry. The welding processes were used initially with interpass temperatures in the range 250–350°C. When the interpass temperature was controlled to below 150°C, the average ferrite content increased in the weld metal and in the heat affected zone (HAZ). Controlling the interpass temperature did not dramatically affect the properties in the mechanical tests performed. Heat inputs were in some instances higher than those used previously, but this did not adversely affect weld metal and HAZ properties. No evidence of intermetallic phase precipitation was found, by TEM of thin foils, in any of the weld metal in the processes used. There was evidence of fine particle precipitation of M23C6 in the HAZ regions. The level of precipitation observed is acceptable for the final application as all the mechanical test and corrosion test req...
TL;DR: In this article, the authors report the development of a prototype which takes arc voltage data as online input, and applies the data to a neural network, which can be used for direct feedback control of the welding equipment.
Abstract: Modern welding equipment often features a rather complex operator interface that can make it somewhat difficult, even for an experienced welder, to determine optimum settings for a given welding job. For example, the joint fitup may vary, or some form of unexpected contamination may occur. In addition, in welding tasks for which a procedure has been specified, and in automated welding, changes in welding conditions may mean that some adjustment to the pre-established welding parameters is desirable. With online signal inputs from the welding process, artificial neural networks offer the possibility of providing signals that can be used for control, either indirectly by advising the operator of problems when the system conditions have deviated from satisfactory operation, or by direct feedback control of the welding equipment. This paper reports the development of a prototype which takes arc voltage data as online input, and applies the data to a neural network. The neural network has been trained ...
TL;DR: In this article, solidification cracking in austenitic stainless steel welds was considered based on the solidification modes and the nickel and chromium equivalents in welding processes where the cooling rate was evaluated.
Abstract: Solidification cracking in austenitic stainless steel welds has been considered based on the solidification modes and the nickel and chromium equivalents in welding processes where the cooling rate...
TL;DR: In this paper, a tungsten insert at the tip of conventional circular face electrodes has been used to enhance the effective electrode life in resistance spot welding of galvanized steels.
Abstract: Rapid electrode wear is the major concern in resistance spot welding of galvanised steels. The electrode life in such instances is tremendously influenced by the continuous alloying reactions that occur between the molten free zinc and the copper electrodes. It is shown in the present work that the use of compound electrodes can considerably enhance the effective electrode life. The compound electrodes are fabricated by introducing a tungsten insert at the tip of conventional circular face electrodes. The performance of these new electrodes has been investigated under laboratory conditions during multispot welding. It is observed that the compound tip electrodes can offer superior electrode life only for a small insert size. A finite element method based numerical simulation has simultaneously been carried out. The results of the numerical calculation also indicate that the optimum design of the compound tip electrode depends on the insert size.
TL;DR: In previous evaluations, of GTA welding stainless steel plates, the surfactant content in the workplace has been assumed to be in a state of equilibrium as mentioned in this paper, but this assumption was not always the case.
Abstract: In previous evaluations, of GTA welding stainless steel plates the surfactant content in the workplace has been assumed to be in a state of equilibrium. However surfactant concentration usually had ...
TL;DR: In this article, a quasi-steady state heat conduction model considering phase change for laser welding of sheet metals is presented, where the method of least squares is used to solve the governing equation in the liquid phase.
Abstract: A quasi-steady state heat conduction model considering phase change for laser welding of sheet metals is presented. The method of least squares was used to solve the governing equation in the liquid phase. The solution provides the weld pool shape and the temperature distribution in the weld pool. Results for stainless steel were compared with experimental data and fairly good agreement was obtained between the theoretical predictions and the experimental data.
TL;DR: Gas tungsten arc welding was performed on 18Ni (250 grade) maraging steel sheet using two different filler wires: one of the same composition as the base material and the other containing more cobalt and aluminium and less molybdenum and titanium as mentioned in this paper.
Abstract: Gas tungsten arc welding was performed on 18Ni (250 grade) maraging steel sheet using two different filler wires: one of the same composition as the base material and the other containing more cobalt and aluminium and less molybdenum and titanium. Weld specimens were then aged under four different sets of conditions. After metallographic characterisation, mechanical properties including hardness, tensile strength and ductility, and fracture toughness were evaluated. Results showed that use of the matching filler material led to lower strength but higher ductility than in the other case; this was attributed to the presence of reverted austenite in the former (caused by segregation, especially of molybdenum) at the fusion zone substructure boundaries. In both types of weld metal, a re-solution treatment followed by aging at 480°C resulted in optimum tensile properties. Fracture toughness of the aged weldments was in general close to that of the parent material aged at 480°C; some deterioration occur...
TL;DR: In this paper, the authors compared the relative merits of the two tests for evaluating cracking susceptibility and found that the transvarestraint test is preferred over the LVT for study of weld metal cracking.
Abstract: The longitudinal varestraint test (LVT) and transvarestraint test (TVT) are widely used for assessment of weld metal cracking susceptibility. The TVT is preferred over the LVT for study of weld metal cracking. However, few reports exist that discuss the relative merits of the two tests for evaluating cracking susceptibility. This investigation was carried out to compare weldability assessments using the two tests and the relevant criteria for weldability evaluation. Several stainless steels solidifying in the austenitic and ferritic solidification modes were tested. The study shows that the LVT can be used for evaluation of fusion zone cracking through a maximum cracking distance criterion. This parameter correlated well with the maximum crack length in the TVT, traditionally used to derive the brittleness temperature range (BTR). The study further indicates that the total crack length can be related to the BTR by considering the area density of cracking.
TL;DR: In this article, the results from tests of spray coating to impart corrosion resistance and from creep cracking tests in the heat affected zones of heat resistant steels are also briefly introduced, as part of the Japanese STX21 project involving welding of 800 MPa high strength steels with reduced carbon equivalents achieved through grain refinement.
Abstract: Research activities, as part of the Japanese STX21 project, involving welding of 800 MPa high strength steels with reduced carbon equivalents achieved through grain refinement are described. Results from tests of spray coating to impart corrosion resistance and from creep cracking tests in the heat affected zones of heat resistant steels are also briefly introduced.
TL;DR: In this paper, a methodology for the construction of transfer mode maps for stainless steel gas metal arc welding, with argon and argon-oxygen shielding gases, is presented.
Abstract: A methodology for the construction of transfer mode maps for stainless steel gas metal arc welding, with argon and argon–oxygen shielding gases, is presented. A back lighting laser and high speed video camera were used for visualisation and measurement of droplets and electrode extension. The reasons for the use of a groove, instead of the traditional bead on plate method, and of same volume beads are discussed and the results assessed. Unlike in other mapping procedures, mapping was conducted as a function of welding current and arc length. In addition, transfer rate v. welding current or wire feedrate curves were plotted. The results show the importance of the use of both maps and curves for identification and quantification of the shielding gas effects on the transfer mode. The results also suggest that an increase in oxygen content in the shielding gas reduces the values of transition current and transition wire feedrate (as expected), but also that it reduces the transfer rate and droplet siz...
TL;DR: In this article, a formula for weld induced angular distortion, in terms of weld parameters such as heat input and plate thickness, is developed analytically using an infinite laminated plate theory to consider an elliptical cylindrical inclusion with an eigenstrain.
Abstract: The problems of distortion and residual stresses in and around a welded joint are of major concern in heavy industry. In the present work, a formula for weld induced angular distortion, in terms of weld parameters such as heat input and plate thickness, is developed analytically using an infinite laminated plate theory to consider an elliptical cylindrical inclusion with an eigenstrain. The source of angular distortion in weldments is the plastic strains that are caused by non-uniform temperature gradient. The distributions of the plastic strain corresponding to the eigenstrain are determined using Rosenthal's solution, which describes temperature distributions. Comparison of the calculated results with the experimental data shows the accuracy and validity of the proposed method.
TL;DR: In this article, the influence of sulphur on microfissuring was studied by characterising the hot ductility and heat affected zone (HAZ) micro-fissures in welded wrought Inconel 718.
Abstract: The influence of sulphur on microfissuring has been studied by characterising the hot ductility and heat affected zone (HAZ) microfissuring in welded wrought Inconel 718. A series of Inconel 718 base alloys, with sulphur concentrations in the range 7–110 wt-ppm and with the lowest possible concentrations of carbon, boron, and phosphorus were used in the study. The hot ductility of the alloys was measured using a Gleeble 1500 system, and their weldability was evaluated by bead on plate electron beam welding. The effect of sulphur on microfissuring in the weld HAZ was compared with that of boron in boron containing, but sulphur free, alloys. Sulphur reduced the weldability of the material, but its influence was very moderate in comparison with that of boron. The rate of increase of the brittle temperature range hot ductility parameter with increasing sulphur concentration was significantly smaller compared with that with increasing boron concentration. This may be because sulphur and boron seem to i...
TL;DR: In phase thermomechanical fatigue (TMF) in the temperature range 573-973 K (300-700°C) and isothermal fatigue behaviour at 973 K in air were studied for type 316 stainless steel using smooth cylindrical specimens machined from base metal, weld metal, and the weld joint as mentioned in this paper.
Abstract: In phase thermomechanical fatigue (TMF) in the temperature range 573–973 K (300–700°C) and isothermal fatigue behaviour at 973 K in air were studied for type 316 stainless steel using smooth cylindrical specimens machined from base metal, weld metal, and the weld joint (cross-weld) In all joint specimens, fatigue failure occurred in the weld metal region The lifetimes of weld metal and joint specimens were almost equal and were always inferior to those of base metal specimens In the base metal, the effect of strain rate on the isothermal fatigue life was not very significant Although TMF lifetimes were always a little shorter than the isothermal fatigue lifetimes in base metal, the difference was small for the same mechanical strain range and similar strain rate This may be because the fracture mode for both types of loading was of a similar mixed type Conversely, a dramatic reduction in lifetime was observed in weld metal and joint specimens under TMF in comparison with isothermal fatigue
TL;DR: In this article, the basic characteristics of electron beam welding of high strength aluminium alloys for express train applications were evaluated, including cracks, cold shuts, porosities, and spikes; the tendency to form weld discontinuities was strongly dependent on the EB process parameters and chemistry.
Abstract: The basic characteristics of electron beam (EB) welding of high strength aluminium alloys for express train applications were evaluated. The aluminium alloys tested were non-heat treatable A5083–O, heat treatable A6N01–T6, and A7N01–T6. Principal welding process parameters, such as accelerating voltage, beam current, welding speed, and chamber pressure were investigated. The dimensions and microstructures of welds were evaluated using optical light microscopy and SEM (EDAX). In addition, variation in weldability (in terms of formation of cracking and porosity) owing to process parameters was evaluated. Electron beam welds showed discontinuities such as cracks, cold shuts, porosities, and spikes; the tendency to form weld discontinuities was strongly dependent on the EB process parameters and chemistry. Although the three aluminium alloys were welded using the same conditions, alloying elements had an important effect on the dimensions of the weld and thus on weldability. Alloy A6N01 showed a lower...
TL;DR: In this article, a quasi-steady state heat conduction model is developed for laser welding of sheet metals, where the heat flux at the surface of the workpiece is considered to be due to a moving Gaussian laser beam.
Abstract: A three-dimensional quasi-steady state heat conduction model is developed for laser welding of sheet metals. The heat flux at the surface of the workpiece is considered to be due to a moving Gaussian laser beam. An analytical expression is obtained for the temperature distribution by solving the conduction problem using the Fourier integral transform technique. This expression is used to locate the melting temperature isotherm, and thereby determine the weld depth and width. Experimental and theoretical results for the weld depths and widths are illustrated for different welding parameters such as the laser power, absorptivity, welding speed, and shielding gas speed. The theory and experiment are found to agree reasonably well. The effects of absorptivity, shielding gas speed, and heat loss due to different contact media at the bottom surface of the workpiece are also investigated, and are found to be significant for thin metal laser welding.