Showing papers on "Shielded metal arc welding published in 1999"

An analysis of heat transfer and fume production in gas metal arc welding. III

Abstract: A two–dimensional dynamic theory for predictions of arc and electrode properties in arc welding has been used to investigate heat transfer phenomena in the welding wire in gas metal arc welding (GMAW). The theory is a unified treatment of the welding wire, the plasma and the workpiece and includes a free surface treatment for the welding drops, accounting for the effects of inertia, gravity, surface tension, arc pressure, magnetic forces, and viscous drag by the gas flow around the drop. Also, the theory accounts for the variation of the surface tension coefficient with temperature and includes thermal and dynamic phenomena within the solid and liquid phases of the wire, together with a detailed treatment for the electrode sheath regions. Calculations are made for arcs in argon with wires of mild steel at currents between 150 and 325 A. Results of calculations for heat fluxes within the wire suggest that evaporation from the surface of the droplet during droplet growth has an important influence on the he...

The classification of metal weld deposits in terms of the amount of oxygen

Abstract: In analogy to the classification of metal weld deposits and arc welding processes of low-carbon and low-alloy steel in terms of the amount of hydrogen in metal weld deposits, a similar classification was given in terms of the amount of oxygen. Different methods of arc welding processes were chosen, such as welding with coated electrodes (basic, rutile, acid, oxide electrodes), shielded arc welding process MIG/MAG, submerged arc welding process (various wires, fluxes, shielded gases). The amount of oxygen and the percentage of acicular ferrite of metal weld deposits were mainly analysed and the impact toughness of it. Metallographical structures and fractography tests of metal weld deposit with varied amount of acicular ferrite were presented by putting attention to non-metallic inclusions and their morphology presented in metal weld deposit. Additional inclusions observation and measurements were done using a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer. The studies were also made on the classification of metal weld deposits and arc welding processes of low carbon and low alloy steel in terms of the amount of oxygen in metal weld deposits on the following processes: low-oxygen processes, medium-oxygen processes, high-oxygen processes.

Laser welding superalloy articles

Abstract: A process is provided for laser welding a nickel or cobalt based superalloy article to minimize cracking by preheating the entire weld area to a ductile temperature, maintaining such temperature during welding and solidification of the weld, with the welding utilizing a powder alloy feed and the speed of the laser controlled to less than 10 inches per minute.

Effects of welding parameters and electrode atmospheric exposure on the diffusible hydrogen content of gas shielded flux cored arc welds

Abstract: Gas-shielded flux cored arc welding (FCAW-G) has been in use for many years. However, some major issues still exist regarding the ability of the FCAW-G process to deposit sound welds on high-integrity applications, even though it offers significant economies due to its high deposition rate. One of the major issues when welding high-strength steels with FCAW-G is the diffusible hydrogen potential of various electrodes. There have been questions regarding the moisture content of various types and classifications of FCAW-G electrodes, especially after atmospheric exposure. Few studies have been performed to establish the effects of electrode classification electrode use, moisture absorption from atmospheric exposure and weld parameters on weld metal diffusible hydrogen content. Low-hydrogen shielded metal arc welding (SMAW) electrodes, for example, must be stored at 250°F per ANSI/AWS D1.1 and have a permissible atmospheric exposure up to 9 h before rebaking is required. The objectives of this investigation were to determine the effects of weld parameters on the results of the diffusible hydrogen test per AWS A4.3-93 for FCAW-G electrodes, develop an atmospheric exposure test procedure and evaluate the atmospheric exposure test procedure on mild steel and Cr-Mo FCAW-G electrodes. The moisture resistance of E71T-1, E70T-1, E71T-5 and ER70S-3 mild steel electrodes and E81 T-B2, E91T-B3 and E80C-B2 Cr-Mo electrodes was investigated using the atmospheric exposure test. Three wire feed speeds and three contact tube-to-work distances were used to study the effects of current and electrode extension on the weld diffusible hydrogen content of an E71T-1 mild steel electrode. Weld voltage and travel speed were adjusted to maintain a constant arc length of in. (6.35 mm) and weld deposit area, respectively. Diffusible hydrogen content of the weld deposit was found to increase almost linearly as the weld current increased for the E71T-1 electrode. The weld diffusible hydrogen content increased from 2.3 mL/100 g at 140 A to approximately 11.6 mL/100 g at 345 A. Contrary to published literature, the effects of electrode extension were small at a constant current and arc length with this electrode. Increased contact tube-to-work distance decreased current and, hence, the weld diffusible hydrogen content at a constant wire feed speed. Diffusible hydrogen content of the weld deposit decreased with increasing time in the electrode extension column. The diffusible hydrogen content was higher in welds made with a longer contact tube-to-work distance when comparing tests that had equal time in the electrode extension column. This was believed to be a result of the higher wire feed speeds, which change the temperature profile in the electrode extension. The atmospheric exposure test evaluated the moisture resistance of several mild steel and Cr-Mo FCAW-G electrodes from different suppliers. The test used a single layer of FCAW-G electrode that was carefully wound on a painted wire spool. The spool was exposed to moisture inside a forced air humidity cabinet. Diffusible hydrogen tests were performed on welds made with these electrodes in the as-received and after a one-week exposure condition. The atmospheric exposure environment was controlled at 80°F (27°C) and 80% relative humidity. These humidity cabinet parameters were based on the absorbed moisture test described in AWS A5.1-91 sections 16.2 through 16.6 for SMAW electrodes.

A Comparison of Gas Metal Arc Welding with Flux-Cored Wires and Solid Wires Using Shielding Gas

Abstract: In the present work, gas metal arc welding (GMAW) with flux-cored wires and solid wires using shielding gas has been adopted for welding stainless steel. Five different compositions of shielding gas are used with flux-cored wire and three with solid wire. Spatter rates, chemical compositions, tensile strength and elongation tests have been performed and are reported. The spotter rates of the sample made using flux-cored wires are less than that for the sample made using solid wire. The ultimate tensile strength and elongation are not influenced by the composition of the shielding gas.

Universal shielding gas for GMAW and FCAW welding and process

Abstract: A universal shielding gas mixture contains, by volume, about 96.0% argon, 3.0% carbon dioxide, and 1.0% oxygen. This single shielding gas composition can be used for welding ferrous metals, including both carbon steel and stainless steel using a variety of gas metal arc welding (GMAW) processes including short circuit arc, pulse arc, spray arc, metal transfer modes and flux core metal arc welding (FCAW) when welding carbon steel, stainless steel, hardfacing and metal core wires. This universal shielding gas composition will not substantially alter the carbon content of the weld metal chemistry. In a second embodiment, suitable for use with carbon steel materials but not stainless steel, the shielding gas mixture contains, by volume, about 95.0% argon, 3.0% carbon dioxide, and 2.0% oxygen. Another aspect of the invention is a single tank containing the premixed universal shielding gas, and improved gas metal arc welding processes that utilize the disclosed shielding gas mixture.

Numerical modelling and experimental determination of temperature distribution during manual metal arc welding

Abstract: Welding is a highly reliable and efficient metal joining process. Manual metal arc (MMA) welding is very widely used in industry. The temperature distribution that occurs during welding affects the material microstructure, hardness, and the residual stresses present in the material after welding. In the present work, the temperature distribution during bead on plate welding using MMA welding was experimentally determined for AISI type 304 stainless steel plates and low carbon steel plates of thickness 6 and 12 mm. A three-dimensional computer model based on the control volume method has been developed to predict the temperature distribution in the heat affected zone (HAZ) and in the base plate region of the bead on plate welds, using the weld parameters as input data to the computer model. In this computer model, the heat energy used to melt the electrode is considered as a separate heat flux term and the remaining heat supplied by the welding arc is considered as another heat flux term. A good match between the experimental results and the theoretical predictions was obtained. Using the computer model, the time taken to cool from 800 to 500°C in the coarse grained HAZ (close to the fusion line) of low carbon steel specimens was calculated. From this cooling time and the chemical composition of the material, the maximum hardness in the coarse grained HAZ was predicted. Microhardness measurement in the same region of the welded plates was carried out. The experimentally measured values and predicted results match closely.

Austenitic/ferrite two phase stainless steel welding material, and high chromium steel welding method using it

Abstract: PROBLEM TO BE SOLVED: To provide a welding material and a welding method which do not cause delayed crack even in welding without preheating or post heat treatment. SOLUTION: This invention relates to a two phase stainless steel welding material to weld a stainless steel including 0.03 wt.% or less C and 727 wt.% Cr, where the product of hydrogen content (Hw, ppm) in the steel of the welding material and the ferrite volume (ω, volume %) of the deposit metal of the welding material is 135 or less. Also, a gas shield arc welding method is provided, wherein the product of the ferrite volume (δw, volume %) of the welding metal part and Hw is adjusted to be 154 or less using the welding material. It is preferable that the welding material includes 0.08% or less C, 1.0% or less Si, 2.5% or less Mn, 0.03% or less P, 0.02% or less S, 18-27% Cr, 5-11% Ni, 4% or less Mo, 2.5% or less W, 0.35% or less N, and the balance of Fe and inevitable impurities.

Method for laser beam welding of steel plate

Abstract: PROBLEM TO BE SOLVED: To decrease an amount of generation of spatter in the case of laser beam welding of steel plates. SOLUTION: The method comprises a process of forming through holes on a welding part to form through holes 11 on a steel plate W1 of one side alogn a welding line L connecting a weld part of the steel plate W1 of the one side, a steel plates setting process to fix both the steel plates W1, W2 on condition that the steel plate W1 of one side comes into contact with the other steel plate W2, and a welding process in which from a steel plate W1 of one side out of both the fixed steel plates W1, W2 a laser beam B is irradiated along the welding line L and both the steel plates W1, W2 are welded.

Hot working method for austenitic stainless steel containing b

Abstract: PROBLEM TO BE SOLVED: To work to a specific plate thickness without reheating during hot working and without causing edge cracks by providing a coating layer of stainless steel buildup welding containing a specific ratio in a total of one or more types of Ti, Nb, Zr and V, to a side face of an austenitic stainless steel containing B at specific ratio. SOLUTION: Austenitic stainless steel containing 0.3 to 2.5 weight% B contains 0.01 to 2 weight% in total of one or more types of Ti, Nb, Zr and V. The composition of the stainless steel of a coating layer of buildup welding is not defined in particular, and it may be Cr stainless steel or Cr-Ni stainless steel containing 12% or more Cr. As the method of providing the coating layer of buildup welding, TIG welding, coated arc welding, band arc welding, etc., can be used. The thickness of the coating layer of buildup welding is preferably 3 mm or more from the point of workability, though thickness of 2 mm or more can prevent edge cracks.

Effects of niobium on microstructure, mechanical properties, and corrosion behaviour in weldments of alloy 690

Abstract: 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 tensi...

Performance of repair welds on aged Cr-Mo piping girth welds

Abstract: This article documents the results of an industry survey of weld repair practices and describes the results of experimental evaluations performed on service-aged 21/4 Cr-1Mo steel piping using SMAW with both conventional postweld heat treatments and temper bead repair techniques. The overall results of this program provide substantial evidence that service-aged piping systems can be successfully weld repaired with and without postweld heat treatments and that life extension by several decades is achievable under the right design and repair conditions. Weld repairs performed on degraded exservice welds resulted in restoration or improvement of tensile and creep properties. Microhardness test results within the heat-affected zone of each weldment indicated that the temper bead weld repairs produced only slightly higher peak hardness values than those measured for the fully postweld heat treated repairs. Finally, in terms of toughness, temper bead weld repairs consistently produced higher impact properties than those measured for the postweld heat treated weldments. Gas tungsten arc weld repairs with postweld heat treatment resulted in the best combination of tensile strength, uniform microhardness distribution across the weld, Charpy toughness, and creep rupture life.

Recent Developments on the Weldability of a New High Nitrogen Stainless Steel

Abstract: There is no other class of metallic materials offering a similar combination of strength, toughness. corrosion resistance and non magnetic properties as nitrogen alloyed austenitic stainless steels. However, welding characteristics of these materials still have to be quantified. In the present paper recent developments on the weldability of a new high nitrogen austenitic stainless steel are presented. Due to an approximate nitrogen content of 0.6% by weight, careful welding procedures are required to retain as much nitrogen as possible in the weld. Different are welding techniques such as shielded metal are welding (SMAW), gas metal are welding (GMAW) and gas tungsten are welding (GTAW) were used. To investigate the influence on the microstructure and the resulting mechanical properties different filler materials and gas compositions were used. The welding performance tests were carried out according to EN 288-3. All weld tests were successful. For the SMAW process the microstructure showed fusion zones without pores or any other defects. In the GMA and GTA welds the addition of nitrogen to the shielding gas promotes the formation of pores. It has been shown that a content of 8 vol.-% of nitrogen in the shielding gas is too high. An optimum can be expected around 4 vol.-% of nitrogen. Hardness tests exhibited lower values in the fusion zone. Lower values could also be observed in the ultimate tensile strength with a loss in the range of 15%. These results are due to a lower nitrogen content in the weld metal. The Charpy V values in the fusion zone are high. A weighting factor of 18 for nitrogen was used in the Schaeffler diagram and showed a good correlation.

Tool kit for shielded metal-arc welding

Abstract: Welding device to enable a welder to maintain an upright position when welding at floor level. The device is a rigid handle having a pistol-type handgrip and telescoping tubes. The telescoping tubes can be easily adjusted and interlocked, thus providing a handle that is adjustable to a plurality of lengths. The handgrip is angled approximately 90° to the longitudinal axis of the handle and provides for a comfortable and secure grip. The electrode holder used in the welding process can be releasably attached to the distal end of the device. In the Preferred Embodiment, the telescoping tubes and handgrip are hollow, so that a power cable can be fed through the device and connected to the electrode holder. Mounted on the device is a welding shield made of welder's glass, that shields the welder's eyes from the welding flame and protects the welder from sparks arising from the welding site, thus eliminating the need on the part of the welder to wear a welding hood with mask. The device provides for increased safety and comfort of the welder.

One-side welding method for steel for low-temperature use

Abstract: PROBLEM TO BE SOLVED: To achieve the welding of a steel plate for low-temperature use high in efficiency and excellent in low-temperature toughness by welding a first layer using a flux-cored wire of a specified Ni content, and achieving the submerged arc welding of second and subsequent layers using the flux of the specified alkalinity and the wire of the specified composition. SOLUTION: A pair of steel plates to be welded are butted to each other preferably with the groove gap of 2 to 10 mm, and a refractory backing is tightly attached to the groove from its back side. A first layer is welded using a flax-cored wire containing, by weight, 0.5-3.5% Ni from its face side to form an excellent back bead. The submerged arc welding is achieved to form second to final layers with the heat input of <=60 kJ/cm using a wire having the composition consisting of the flux of 1.2 to 1.7 in alkalinity L defined by the formula, 0.01-0.l% C, 0.8-1.5% Mn, 2-4% Ni, <=0.1% Si, and the balance Fe with impurities. The one-side welding of a thick steel plate excellent in low-temperature toughness in a welded part and a heat affected part can be achieved thereby.

Welding electrode holder for coated electrodes

Abstract: Welding electrode holder comprising an electrically conducting body with positioning seats of electrodes and welding cable connection position, an insulating tubular handle where the back part of the body is encaged, a lever pivotably assembled with the body and having insulated lever arm, a compression spring seated on the electrode holder body or on the handle and pushing the lever arm thus forcing the lever to be turned and to exert force onto the positioning seats of electrodes, and an insulating head covering the parts of the body and those of the lever located in front of the handle or even covering and part of the handle and allowing the clamping of electrodes on the body. It is characterized in that the welding cable connection position is located outside the handle and inside the insulating head, behind or/and underneath the positioning seats of electrodes, and in that the rest electrode holder body, i.e. behind the welding cable connection position, is encaged in a separate receptacle located above the longitudinal though hole of the handle and outside or inside the insulating head. It is used for manual metal arc welding with coated electrodes, it develops low temperature on the external surface of the handle held by the welder and moreover it has low weight.

Method of magnetically impelled arc butt welding

Abstract: A press welding process which can be used in such industries as car-making, production of hot-water boilers, industrial and civil construction, in construction of pipelines using small and medium diameter pipes, for welding parts with a solid and developed cross-section, as well as for joining parts to form a T-joint. A magnetically impelled arc butt welding is achieved, that, during heating, the controlled continuous displacement of the parts being welded is performed where the gap between the parts edges is kept constant. The value of the welding arc voltage is used as the parameter for the gap size adjustment, and the moment of achievement of the required temperature on the edges of parts being welded, is determined by the length of the relative displacement of the parts, and when the assigned values of displacement have been reached, the speed of the arc movement along the edges of the parts being welded, is programmed. An improved quality of the welded joints produced by magnetically impelled arc butt welding is obtained.

Effect of welding process on fatigue crack growth behaviour of ASTM 517 ‘F’ grade steel weld metals

Abstract: The fatigue crack growth behaviours of two weld metals deposited by shielded metal arc welding (SMAW) and flux cored arc welding (FCAW) processes have been compared. Load carrying cruciform joints, with a lack of penetration (LOP) defect, were fabricated from high strength, quenched and tempered steel of ASTM 517 ‘F’ grade. Fatigue crack growth experiments were carried out in a vertical pulsator (Schenck 200 kN capacity) with a frequency of 30 Hz under constant amplitude loading (stress ratio R = 0). It was found that the fatigue crack growth resistance of the weld metal deposited by the SMAW process is superior, compared to the weld metal deposited by the FCAW process. The high heat input involved in the FCAW process probably contributes to the changes in weld metal properties, which result in a change in fatigue crack growth behaviour.

Laser assisted plasma arc welding

Abstract: Experiments have been performed using a coaxial end-effecter to combine a focused laser beam and a plasma arc. The device employs a hollow tungsten electrode, a focusing lens, and conventional plasma arc torch nozzles to co-locate the focused beam and arc on the workpiece. Plasma arc nozzles were selected to protect the electrode from laser generated metal vapor. The project goal is to develop an improved fusion welding process that exhibits both absorption robustness and deep penetration for small scale (< 1.5 mm thickness) applications. On aluminum alloys 6061 and 6111, the hybrid process has been shown to eliminate hot cracking in the fusion zone. Fusion zone dimensions for both stainless steel and aluminum were found to be wider than characteristic laser welds, and deeper than characteristic plasma arc welds.

Ductile fracture mechanisms in shielded metal-arc and gas tungsten-arc welds of Type 347 stainless steels

Abstract: The ductile fracture behavior of two different welds of Type 347 stainless steel, which are made by SMAW (shielded metal arc welding) and GTAW (gas tungsten arc welding) processes was characterized by J-integral testing and microstructural evaluation techniques. Both welds by SMAW and GTAW processes showed significantly low fracture toughness compared with that of the base metal. Metallographic and fractographic examinations revealed that different micromechanisms are operative in the fracture process of the two welds. In the SMAW weld, the fracture was dominated by void initiation and growth at the inclusions that are homogeneously distributed in the matrix. On the other hand, in the GTAW weld, a large number of Nb(CN) particles precipitated on the austenite/ferrite interface as long rod shapes and the fracture proceeded by void initiation at these particles and accompanying decohesion of the interface. It is recommended that the C and Nb contents be reduced in weld metal itself as well and that the welding atmosphere be controlled.

Weld Repair of 2-1/4Cr-1Mo Service-Aged Header Welds

Abstract: The objective of this investigation was to evaluate the efficacy of different weld repair techniques as applied to service-aged 2-1/4Cr-1Mo steel weldments. A header which had been in service for 244,000 h at 1,050 F (565 C) was utilized for the study. Three girth welds were partially excavated and subjected to repairs using gas tungsten arc welding (GTAW), shielded metal arc welding (SMAW) with postweld heat treatment (PWHT), and without postweld heat treatment using a temperbead technique. Results show that all the weld repairs improved the creep rupture lives of the ex-service weldments and that remaining lives of several decades could be achieved in the repaired condition. The SMAW-temperbead repairs resulted in increase of future life, tensile strength, and impact toughness compared to the SMAW-PWHT repairs. The GTAW-PWHT repairs also produced a superior combination of mechanical properties. Remaining creep rupture lives were a function of the extrapolation procedure and specimen size. These results are described here and discussed in comparison with results previously reported for a less severely degraded condition of the steel in order to delineate the effect of prior degradation on weld repair performance.

The Effect of Welding Speed on the Microstructure and Penetration in Arc Welding

Abstract: The effect of welding speed on the microstructure and penetration in MAG, SMAW and MMA welding was investigated in a low carbon steel. Experimental results revealed that the penetration decreased when the welding speed was lower or higher than the optimum speed. It was also observed that when the welding speed was high, undercuttings occurred at the edge of welding bead and microstructure of weld metals consisted of fine grains, but when the welding speed was low, at the edge of welding bead weld metal piled up and the microstructure of weld metal consisted of large grains.