Showing papers on "Shielding gas published in 2022"

Laser treatment of 430 ferritic stainless steel for enhanced mechanical properties

Abstract: Thin AISI 430 ferritic stainless steel sheets containing 18% Cr were hardened by continuous-wave laser beams under different conditions. A symmetric double laser treatment platform was developed to operate two lasers simultaneously in order to achieve a homogenous microstructure through the specimen and avoid the overheating associated with single laser treatments on one surface. The influence of linear energy density and shielding gas on microstructure and hardness is investigated for both single and double laser treatments. Tensile behavior and oxidation effect during treatment are also studied. With a peak temperature around Tm, the single-track laser yields local microhardness that is 90% higher than the base material, while samples completely treated by the multi-track laser present a 60% increase in yield stress and 45.8% in ultimate tensile stress. These improvements in mechanical behaviors are driven by the formation of martensite and chromium carbides upon rapid cooling despite poor carbon content and dramatic grain coarsening. These results could be useful in order to locally modify the behavior of medium chrome ferritic stainless steel to meet industrial

Investigation of the TIG Welding Process for Joining AA6082 Alloy Using Grey Relational Analysis

Abstract: The goal of this project is to find optimization parameters in the TIG weld bead. To ensure the success of this research project, a semiautomatic TIG was developed. Samples are made in a single bead on top of a substrate (base metal) in a horizontal position. Aluminum 6082 is used as the substrate, and AA5356 filler wire with a diameter of 2.4 mm is used as the filler wire. This research project employs argon as the shielding gas. Welding current (A), travel speed (mm/min), and gas flow rate (lit/min) have all been identified as influencing parameters for welding. The Taguchi orthogonal array L9 (Minitab 19) was used to calculate the amount of runoff and analyze the samples. Tensile and hardness tests were performed on the welded samples. According to the test results, as the current value increases, the tensile strength and the hardness values decrease. As a result of this experiment, it is possible to conclude based on grey relational analysis that the best parameters for welding Al 6082 alloy are 150 A of welding current, 200 mm/min of travel speed, and a gas flow rate of 14 lit/min.

Influence of shielding gas nitrogen content on the microstructure and mechanical properties of Cu-reinforced maraging steel fabricated by wire arc additive manufacturing

Abstract: This study investigated the effects of using shielding gases with different nitrogen concentrations on the microstructures and mechanical properties of SHER-120G maraging steel fabricated by wire arc additive manufacturing (WAAM). With increases in the nitrogen concentration, the contents of nitrogen and austenite in the bulk specimens increased significantly, while δ-ferrite formation was inhibited. In addition, nitrogen was absorbed by the molten pool and decomposed into N atoms during WAAM. Some N atoms formed a solid solution with the matrix and the rest reacted with Cr to form Cr2N, which plays an important role in the process of martensite lath refinement. The optimal shielding gas composition was 94% Ar + 2% O2 + 4% N2, which resulted in a tensile strength and micro-hardness of 1324 MPa and 441 HV, respectively. These values are 12.3% and 12.5% higher, respectively, than those of samples fabricated without nitrogen in the shielding gas.

Microstructure and Corrosion Properties of Austenitic and Duplex Stainless Steel Dissimilar Joints

Abstract: In several applications duplex stainless steels should be joint welded to conventional austenitic stainless steels. In this research LDX 2101 lean duplex stainless steel sheets were welded to conventional 304 austenitic stainless steels, using gas tungsten arc welding. For the welded joints three different welding rods were used: ER 308L, ER 309LSi, and ER 2209. For gas shielding two different shielding gases were used: argon and argon +2% nitrogen. It was found that the nitrogen addition to the shielding gas promoted austenite formation in the weld metal. It was also found Schaeffler-diagram modified by Outokumpu showed a very good estimation to the ferrite content and chemical composition of the weld metal. The ferrite content estimated by the Outokumpu-diagram, showed a close correlation to measured ferrite contents, the highest error was 30%. In case of the chemical composition of the weld metal, the Cr- and Ni-contents were estimated with a maximum of 15% error. In terms of the corrosion resistance, the best pitting corrosion resistance was achieved using the 308L welding rod with argon shielding gas, where the weight loss was 1.6% after the 24 hours immersion test.

Effect of N2- and CO2-Containing Shielding Gases on Composition Modification and Carbonitride Precipitation in Wire Arc Additive Manufactured Grade 91 Steel

Abstract: Additive manufacturing (AM) represents a promising technique to fabricate metallic alloys with greater control of the resulting material features as compared to traditional manufacturing routes. Recently, there is greater interest in AM research on 9 wt% Cr ferritic/martensitic (F/M) steels, which are commonly studied for use in the nuclear energy industry. This research aims to prove that wire arc AM can manufacture F/M steels with adequate mechanical properties in multiple processing atmospheres and aims to study how shielding gas composition can be leveraged during fabrication to induce specific precipitation pathways. The effect of shielding gas composition on MX (M=Nb and/or V, XC and/or N) carbonitride precipitation in a 9 wt% Cr ferritic/martensitic (F/M) steel alloy known as Grade 91 was studied using N2 and CO2 gas additions to an inert Ar shielding gas atmosphere during wire arc AM. The N and C atoms present in the processing atmospheres were absorbed into the melt pools during fabrication. Due to their differing affinities for precipitate-forming reactions, the varying levels of C and N between the samples contributed to differences in final carbonitride composition and morphologies. Such precipitate behavior is of interest as carbonitrides have been shown to contribute to increased mechanical performance. This increased performance was studied via electron microscopy and tested for strength, ductility, and fracture properties.

Metal Transfer Behavior of Metal-Cored Arc Welding in Pure Argon Shielding Gas

Abstract: The metal transfer behavior of gas metal arc welding in a pure argon shielding gas was evaluated through experiments using a standard solid wire and a metal-cored wire. The investigation was conducted using observation techniques based on recording images by a high-speed camera equipped with laser assistance and bandpass filters in a range of welding currents. It was observed that the metal transfer mode became a streaming transfer mode when the welding current increased in the solid wire. Meanwhile, in the metal-cored wire, the droplet transfer frequency increased, and the droplet diameter decreased without changing the metal transfer mode in the globular transfer mode. We surmised that the streaming transfer in the solid wire would be caused by the spread of argon plasma at the wire tip, which decreases the effect of the electromagnetic force on droplet detachment. Conversely, due to the presence of flux inside the metal-cored wire, the argon plasma could not spread and was attached close to the iron vapor plasma at the overhead of the droplet. Hence, the electromagnetic force acting on the side of the unmelted flux was ineffective at promoting droplet detachment, preventing the transition to a streaming transfer mode. Furthermore, weld bead formation in the metal-cored wire was better than that in a conventional solid wire.

The Toughness of High-Strength Steel Weld Metals

Abstract: Low-temperature phase transformation (LTPT) welding consumables are a new class of welding wires developed to mitigate hydrogen-induced cracking in the welding of high-strength steels without preheating or postweld heat treatment. LTPT weld metals have a high strength, but their toughness needs further investigation. LTPT weld metals predominately contain a martensite microstructure, which is necessary to achieve high strength; however, martensitic weld metals containing oxide inclusions have relatively poor toughness. Three welding processes — gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), and hot wire GTAW — were investigated. Optical microscopy, scanning electron microscopes, and transmission electron microscopes were employed for characterization. The role of the shielding gas in the formation of oxide inclusions in LTPT weld metals was investigated. The formation of oxide inclusions in the weld metals was related to the CO2 in the shielding gas. When 100% Ar or a pure inert shielding gas mixture was used for all three welding processes, oxide inclusions were greatly reduced, and the weld metal toughness improved considerably, matching the base metal toughness. The mechanism by which inclusions promote fracture propagation in the weld metal was proposed.

Taguchi-based experimental investigation into weld cladding of Ni-WC MMC overlays by CMT process

Abstract: Abstract In the search for versatile and effective weld cladding processes to deposit ultra-wear-resistant Ni-WC MMC (Ni-based tungsten carbide metal matrix composite) overlays for mining applications, there is an increasing interest in exploring advanced low-heat-input cold metal transfer (CMT) method. Depositions of single weld bead tracks of Ni-WC MMCs on steel plates were performed by employing the CMT process; Taguchi’s design of experiments was used to plan the experimental investigation. All weld tracks exhibit continuous and uniform bead profile and sound metallurgical bonding to the substrate. Retained WCs are present in the overlay tracks relatively uniformly. The formation of primary WC and secondary carbides is observed depending on the level of dilution. In contrast to standard gas metal arc welding processes, the volume fraction of retained WC, which is negatively correlated with dilution level, is not directly interrelated with heat input for the CMT process and can reach a high level together with improved weld bead appearance at high deposition rate. Deposition rate has a positive correlation with average instantaneous power, which is, in turn, positively correlated with wire feed speed. The addition of oxygen into shielding gas mixtures promotes carbide transfer from cored feed wire to the weld track and increases the volume fraction of retained WC. Analysis of signal-to-noise ratios shows that it is difficult to find a single set of optimized processing parameters, and trade-offs are needed in engineering practice. The present investigation demonstrates that the Taguchi method is a powerful tool in process improvement for weld cladding of Ni-WC MMC overlays.

Study on the Weldability of Copper—304L Stainless Steel Dissimilar Joint Performed by Robotic Gas Tungsten Arc Welding

Abstract: The welding process of dissimilar metals, with distinct chemical, physical, thermal, and structural properties, needs to be studied and treated with special attention. The main objectives of this research were to investigate the weldability of the dissimilar joint made between the 99.95% Cu pipe and the 304L stainless steel plate by robotic Gas Tungsten Arc Welding (GTAW), without filler metal and without preheating of materials, and to find the optimum welding regime. Based on repeated adjustments of the main process parameters—welding speed, oscillation frequency, pulse frequency, main welding current, pulse current, and decrease time of welding current at the process end—it was determined the optimum process and, further, it was possible to carry out joints free of cracks and porosity, with full penetration, proper compactness, and sealing properties, that ensure safety in operating conditions. The microstructure analysis revealed the fusion zone as a multi-element alloy with preponderant participation of Cu that has resulted from mixing the non-ferrous elements and iron. Globular Cu- or Fe-rich compounds were developed during welding, being detected by Scanning Electron Microscope (SEM). Moreover, the Energy Dispersive X-ray Analysis (EDAX) recorded the existence of a narrow double mixing zone formed at the interface between the fusion zone and the 304L stainless steel that contains about 66 wt.% Fe, 18 wt.% Cr, 8 wt.% Cu, and 4 wt.% Ni. Due to the formation of Fe-, Cr-, and Ni-rich compounds, a hardness increase up to 127 HV0.2 was noticed in the fusion zone, in comparison with the copper material, where the average measured microhardness was 82 HV0.2. The optimization of the robotic welding regime was carried out sequentially, by adjusting the parameters values, and, further, by analyzing the effects of welding on the geometry and on the appearance of the weld bead. Finally, employing the optimum welding regime—14 cm/min welding speed, 125 A main current, 100 A pulse current, 2.84 Hz oscillation frequency, and 5 Hz pulse frequency—appropriate dissimilar joints, without imperfections, were achieved.

Augmentation in depth of penetration of hastelloy C-22 by FATIG welding

Abstract: Flux assisted tungsten inert gas welding (FATIG) welding is a modified version of tungsten inert gas (TIG) welding to achieve a higher depth of penetration. In the present work, nanoparticles SiO2, Al2O3, Fe2O3, and CuO mix with acetone and coated on the joint before welding. Bead on plate welding using different variants of FATIG welding performed on Hastelloy C-22. A comparative study of these variants called Activated tungsten inert gas (ATIG) and Flux bound tungsten inert gas (FBTIG) welding was conducted to find out their effects on depth of penetration, depth to width (D//W) ratio, surface appearance, and slag detachability. In addition, the influence of acidic and basic nature of flux on weld bead geometry and surface appearance are analyzed. Acidic fluxes produce a smoother weld surface than basic oxide fluxes; additionally, acidic flux slag is less sticky than basic flux slag. activated TIG (ATIG) welding with SiO2 flux increases penetration and D/W ratio by 125% and 190%, respectively compared to normal TIG welding.

Effect of Arc Length on Oxygen Content and Mechanical Properties of Weld Metal during Pulsed GMAW

Abstract: Pulsed gas metal arc weld (GMAW) was widely used for the advantages of controllable heat input, all-position welding, and no spatter. In order to obtain an ideal welding process, the stability of the arc length was studied in many researches, but the influence of arc length on the properties of weld metal was ignored. In this paper, the effect of arc length on oxygen content and mechanical properties of weld metal during pulsed GMAW was studied. Q690 high strength steel was selected as the base metal, and ER69-G solid wire, with a diameter of 1.2 mm, was used as the electrode wire. Additionally, the shielding gas and the wire feed rate were 82% Ar + 18% CO2 and 4 m/min, respectively. The results showed that as the arc length raised from 2.9 mm to 9.2 mm, the oxidation reacted more completely in the droplet transfer zone, and the oxygen content of the weld metal increased significantly. The tensile strength of the weld metal reduced but the −40 °C impact energy heightened. Due to the longer arc, the proportion of acicular ferrite (AF) in the microstructure decreased, but the proportion of lath bainite (LB) and granular bainite (GB) decreased. The higher oxygen content of weld metal was useful for the formation of inclusions, which promoted the nucleation of acicular ferrite and dimples, contributing to the growth of plasticity and toughness of weld metal.

Effect of Shielding Gas on the Microstructure and Properties of Laser-MAG Hybrid Welded Joint for Nickel-Saving Stainless Steel

Abstract: Laser-MAG (metal active gas) hybrid welding of nickel-saving 08Cr19Mn6Ni3Cu2N stainless steel was carried out by using 98%Ar + 2%N2 and 95%Ar + 5%CO2 as shielding gases. The effect of different shielding gases on the microstructure and properties of the welded joints was investigated. The results showed that arc shrinkage was significant with the addition of nitrogen, weld spatter increased with the expansion of arc volume, and arc stability deteriorated. The ferrite content in the weld decreased by about 60%, the ferrite dendrite also gradually became finer, and the secondary dendrite arm was shorter. Only a small amount of δ and γ phases existed in the weld, and no precipitation of the σ phase and nitride was found. Observing four crystal planes, we found that size of the austenite grains decreased with the addition of nitrogen. The average tensile strength of the welded joints decreased from 712 MPa to 704 MPa, but with improved corrosion resistance, the pitting corrosion rate increased from 19.45 g·m2/h to 18.72 g·m2/h, and the hardness of weld was slightly reduced.

A Novel Approach of Microstructure Refinement of TiAl in Laser Beam Welding

Abstract: Grain refinement through borides is known to be suppressed when TiAl is welded with a laser beam. As β grains do not primarily nucleate on boride at a high cooling rate, a mixture of nitrogen and argon is applied as a protecting gas for the formation of TiN during solidification. The phase transformation is changed correspondingly from Liquid → Liquid + β → β → α + β → α + γ+ β → α2 + γ + B2 to Liquid → TiN + Liquid → β+ TiN → α + γ + TiN → α2 + γ+ TiN. It is found that β grains prefer to nucleate heterogeneously on the suspending TiN in the melt with orientation relationship {111}TiN// {110}β, leading to refined β grains. α2 colonies that were thus modified into fine non-dendritic grains. The effects of nitrogen as a shielding atmosphere on the microstructure evolution of TiAl are elaborately studied.

Investigation the effect of welding parameters on mechanical properties of AISI 316L by Metal Inert Gas (MIG)

Abstract: Abstract The purpose of this research is to study the behavior of AISI 316L steel during the Metal Inert Gas (MIG) welding process. Three welding parameters are adjusted at three levels of voltage, wire feed, and shielding gas combination (6V, 8V, 10V), (3, 3.5, 4), and (G4, G5, G6). The welding properties are investigated by tensile test strength and Charpy impact test. Ordering parameters are performed based on Taguchi's orthogonal array (L9). The data was analyzed using an analysis of variance (ANOVA) and signal-to-noise (S/N) to determine the optimal welding parameter sets. According to the results of this study, the most influential welding parameter is the gas combination on tensile strength; followed by voltage, wire feed, and gas combination (10V, 3.5, G4). The most influential parameter on maximum elongation is shielding gas. The welding parameter sets the voltage, wire feed, and gas combination (10V, 3.5, G4). The voltage has the most influential parameter on toughness. The welding parameter sets the voltage, wire feed, and gas combination (8V, 3.5, G5). A quaternary shielding gas is used in this study, which gives new insights into the mechanical properties of AISI 316L stainless steel and selects an appropriate shielding gas combination. The results assist engineers and technicians in making more effective welding parameter selections.

Effect of shielding gas on microstructure and mechanical properties in AA6061-T6 alloy MIG welding

Abstract: Due to its properties such as high strength/weight ratio, enhanced corrosion resistance, low density, AA6061T6 aluminum alloy welding is widely used in structural, automotive and rail industry. In this study, AA6061T6 alloy was welded with robotic metal inert gas technique using ER5356 filler wire. The effects of different shielding gas composition ratios (argon/helyum) on the macro / microstructre, mechanical properties (hardness, tensile strength) of the weld joint were investigated. Welding porosity decreased with the addition of helium gas to argon gas. Accordingly, the tensile strength of welded joints increased from 190 MPa to 221 MPa with the addition of helium gas. The strength of the welded joints (190-221 MPa) was obtained lower than that of the base material (290 MPa) due to the changes in the microstructure as a result of the weld thermal cycle and grain coarsening in the heat affected zone. Dentritic, columnar and coarse shaped grains were observed along the weld section, respectively in the weld bead, partially melted zone and heat affected zone. The differentiation of the shielding gas composition did not cause these regions to change, but the heat affected zone expanded with the increase in the helium content. The change in hardness of the cross section of welded joint has increased from around 60 HV to 90 HV from the welding area to the base material. 25% Argon-75% Helium gas mixtures provided optimum combination in terms of microstructure, mechanical properties and cost.

Identification of dominant factors determining droplet temperature in gas metal arc welding

Abstract: Abstract In this study, to identify dominant factors of droplet temperature in a gas metal arc welding, the effects of polarity on droplet temperature were investigated. In particular, the droplet temperature, the wire heat input, and the wire melting rate with electrode positive (EP) polarity and electrode negative (EN) polarity using 100% Ar gas and 100% CO2 gas were measured. As a result, the droplet temperature with EP polarity was higher than EN polarity’s one using 100% Ar gas within the range of 130–230 A. This result showed the reverse tendency compared with the case of 100% CO2. Moreover, the wire heat input and the wire melting rate with EN polarity were larger than EP polarity’s ones regardless of the shielding gas type. The simplified calculation suggested that this was because the ion current ratio was about 80% or more. Besides, especially with EP polarity, the wire melting rate using 100% CO2 was larger than 100% Ar’s one. It was suggested that this was because the wire melting rate was made a difference by the wire preheating effect depending on the droplet frequency determined by the specific heat of the shielding gas. These results identified the dominant factors of droplet temperature as the welding current, the ion current ratio, and the specific heat of the shielding gas.

Properties of Additively Manufactured Deposits of Alloy 718 Using CMT Process Depending on Wire Batch and Shielding Gas

Abstract: Wire + arc additive manufacturing (WAAM®) is a versatile, low-cost, energy-efficient technology used in metal additive manufacturing (AM). This process uses arc welding to melt a wire and form a three-dimensional (3D) object using a layer-by-layer deposit. In the present study, the effect of heat input and shielding gas during CMT-WAAM welding on cooling time, mechanical properties at room temperature, and macro- and microstructure was investigated based on different part geometries (wall, block) using two S Ni 7718 wire batches. The heat input and consequently the cooling rate were varied by changing the wire feed and the travel speed. As expected, increasing the heat input leads to higher cooling times. Due to the 2D-heat conduction, the thin walls cool significantly slower than the multi-pass block welds. Nevertheless, the influence on mechanical properties is only marginal. Both the AM batch of S Ni 7718 with the lower Nb/C and the multi-pass block welds with the higher thermomechanical reactions exhibit a high susceptibility to unacceptable seam defects, such as hot cracks or lacks of fusion. But even the standard batch causes hot cracks. An influence of the shielding gas on microstructure, mechanical properties, and occurrence of the seam defects cannot be detected.

Gas tungsten arc process optimization and assessment for robotized position welding of austenitic stainless steel edge joints

Abstract: Gas tungsten arc welding (GTAW) is a common joining method for austenitic stainless steel sheets. Edge joint is frequently used configuration when the aim is to produce weldments e.g., between the tube sheets and the tubes and to other hollow structures needing tight sealing welds and sound joints. In those applications all positions for welding is usually needed. Robotized welding is utilized, when manual welding is not possible, e.g., in maintenance for nuclear power applications. In automatic welding a strict control of location of arc and welding parameters are extremely important. In this work the aim was to find suitable welding parameters, as pulse parameters, welding speed and shielding gas composition and study their effects on weld joint penetration and weld quality in different welding positions. In addition, the inaccuracy in the alignment of the arc and its effects was tested in different cases. It was found that it was possible to find the optimal parameters in different positions, flat (PA), overhead (PE), and vertical-up position (PF). However, the vertical-down position (PG) was giving a lower joint penetration in the cases which allow sound welds. Therefore, it was considered that the fabrication of the circumferential joint was best done in two steps to avoid the PG position, which ensures that a sound weld with the set 2.6 mm penetration requirement is achieved over the entire circumference. The use of a shielding gas mixture containing argon and 2% hydrogen showed significant advantages over the other three shielding gas compositions tested, which was observed as deeper penetration of the welds.

Process Comparison of Friction Stir Welding, MIG, Laser Beam Welding and Laser Hybrid Welding in Joining Aluminium EN AW-6063 T6

Abstract: Four different welding processes had been investigated and compared to each other in joining aluminium extrusion for a battery tray panel in the automotive industry. Friction Stir Welding (FSW), Metal Inert Gas Welding (MIG), Laser Beam Welding (LBW) and Laser MIG Hybrid Welding (LMH). Weld properties had been analysed by metallographic cross sections, tensile tests and fatigue tests after initial visual inspection. Simultaneously to the mechanical properties data for a carbon footprint evaluation had been gathered as well. The energy consumption, feed rates for welding consumables and shielding gas flow which had been analysed were appropriate. The GaBi software database for life cycle assessment was used for final evaluation. Significant differences had been identified proving tremendous differences for a carbon neutral production.