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Shielding gas plays a vital role in customising the weld bead characteristics. This study explores the effect of shielding gases at different heat inputs of welding considering wire arc additive manufacturing (WAAM) of Inconel 718 on its bead geometry characteristics, microstructure evolution and mechanical properties. Bead-on-plate experiments were fabricated using the cold metal transfer (CMT) technique of gas metal arc welding (GMAW) using Taguchi's L9 orthogonal array. ANOVA and S/N ratio approaches were used to analyse factor effects, their contribution and optimum level. For heat input determination, the dynamic characteristics of the welding power source are recorded and processed. Higher bead geometry characteristics and wider heat affected zone (HAZ) area were observed with increased heat input. The increase in CO2 concentration in the Ar + CO2 mixture changed the weld texture from silver metallic (with pure Ar) to grey with 2.5% CO2 and light yellow with 20% CO2. Higher bead width, reinforcement, penetration and dilution were observed when 20% CO2 was mixed with Ar. With 2.5% CO2, beads were continuous and smoother with all heat inputs. While with 100% Ar shielding environment, higher hardness is obtained compared to welds prepared with 2.5% CO2 and 20% CO2 mixed with Ar. The presence of a higher concentration of Nb-riched precipitates, observed from SEM-EDS analysis, resulted in higher strength. The findings of this experimental investigation will empower the WAAM researchers and practitioners to enhance the weld quality and optimize its geometrical characteristics. [ABSTRACT FROM AUTHOR]

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This study aims to clarify the effect of oxygen in shielding gas on weldability in the plasma-GMA (Gas Metal Arc) hybrid welding process of high-tensile strength steel plates. The difference in keyhole profile and bead formation, when the GMA shielding gas was pure Ar, Ar + 2% O2, or Ar + 20% CO2, was investigated for plate thicknesses of 6 and 9 mm for the first time. It was found that the weld beads were in good condition for 6 mm thickness plates for all shielding gases, which implied that the window of welding conditions for this thickness is wide. In contrast, for 9 mm thickness plates, a fully penetrated weld bead was achieved only in Ar + 20% CO2, and weld bead penetration in Ar + 20% CO2 is higher than in pure Ar and Ar + 2% O2 in the same welding condition. Due to decreased surface tension caused by sufficiently increased oxygen absorbed into the weld pool, the keyhole diameter increased to penetrate the bottom side of the plate, and the depressing weld pool surface under GMA allowed the heat input from the GMA to be directly applied to a deeper position. Consequently, the plasma-GMA hybrid welding process with Ar + 20% CO2 achieved a complete penetration for a plate of 9 mm thickness, owing to the effects of both phenomena. It proved a potential to increase penetrability in welding thicker plates by controlling oxygen content in shielding gas of GMA adequately. [ABSTRACT FROM AUTHOR]

Plume are common physical phenomena in fiber laser keyhole welding and have serious negative effects on the welding process. Based on this, this paper explores the regulation law of conventional shielding gas flow on plume. The results show that the shielding gas has a very significant effect on the suppression of the slender part of the plume, and the greater the gas flow rate, the better the plume removal effect. The addition of the shielding gas makes the welding process more stable, the molten pool flows stably, and the frequency of spatter eruption is reduced. Under the experimental conditions, the optimal shielding gas flow rate is around 15 l/min, and the penetration depth and width are increased by about 10% and decreased by about 22%, respectively, compared with that without adding the shielding gas. Based on the gas flow simulation, the gas flow pressure (about 132 Pa) generated by an appropriate amount of shielding gas (about 15 l/min) can press the liquid column and spatter near the keyhole mouth into the molten pool to avoid the spatter eruption. Excessive shielding gas flow will interfere with the flow of the molten pool excessively, and the weld surface will show a serious undercut phenomenon. [ABSTRACT FROM AUTHOR]

The main objective of this work was to propose and evaluate a methodology for shielding-gas selection in additive manufacturing assisted by wire arc additive manufacturing (WAAM) with an austenitic stainless steel as feedstock. To validate the proposed methodology, the impact of multi-component gases was valued using three different Ar-based blends recommended as shielding gas for GMA (gas metal arc) of the target material, using CMT (cold metal transfer) as the process version. This assessment considered features that potentially affect the building of the case study of thin walls, such as metal transfer regularity, deposition time, and geometrical and metallurgical characteristics. Different settings of wire-feed speeds were conceived to maintain a similar mean current (first constraint for comparison's sake) among the three gas blends. This approach implied different mean wire-feed speeds and simultaneously forced a change in the deposition speed to maintain the same amount of material deposited per unit of length (second comparison constraint). The composition of the gases affects the operational performance of the shielding gases. It was concluded that by following this methodology, shielding-gas selection decision-making is possible based on the perceived characteristics of the different commercial blends. [ABSTRACT FROM AUTHOR]

This study investigates the influence of the shielding gas composition on the microstructural and mechanical properties of wire arc additive manufactured duplex stainless steel. The choice of shielding gas influences the quality and performance of these steels in various industries. Three shielding gases, namely Ar, Ar + 2wt%O2 (Ar–O), and Ar + 2wt%N2 (Ar–N) were used for the deposition of walls with 2209 duplex stainless steel wire. Extensive microstructural analysis and mechanical property evaluations were performed. Based on microscopic observations, the walls produced under different gases exhibited varying inclusion levels, primarily composed of silicon-rich oxide inclusions, with the Ar–O sample exhibiting the highest inclusion concentration at 1.5 vol%. Moreover, the microstructure of all samples consisted of ferrite and austenite phases with different austenite morphologies, with intergranular austenite dominating in the Ar–O sample. In three samples, different degrees of preferred orientation were found in both the ferrite and austenite phases. In this regard, the Ar and Ar–O samples had the strongest and weakest texture, respectively, owing to the influence of inclusions on the formation of a random texture. The microhardness mapping revealed the highest hardness of 250 HV in the Ar–N sample and the lowest hardness of 220 Hv in the Ar–O sample. Nitrogen's strengthening effect on austenite in the Ar–N sample and the higher austenite content in the Ar–O sample were believed to be responsible for these variations. Nanohardness indentations confirmed the lower hardness of austenite compared to ferrite, corroborating the overall lower hardness observed in the Ar–O sample. The Ar–N sample exhibited the highest tensile strength and yield strength of 826 and 539 MPa, respectively in the horizontal direction, which is consistent with the observed hardness results. On the other hand, the Ar sample exhibited the highest elongation of all samples at 39%, which is consistent with its lower inclusion content. [ABSTRACT FROM AUTHOR]

[Objective] This paper seeks to address shortcomings in the conventional structural design of welding torch nozzles, such as prolonged development cycles, high costs, and uncertainty regarding the efficacy of shielding gas fow field protection. [Methods] The fuid dynamics computational software Fluent was utilized for numerical simulations, concentrating on critical parameters like shielding gas fow rates, welding torch nozzle structures, and nozzle-to-bevel spacings. The simulation results were subsequently verified and analyzed through gas dyeing experiments and practical welding operations. [Results] In the gas metal arc welding(GMAW) process context involving narrowgap bevels, a shielding gas fow rate of 20 L/min yielded effective protection to pipes. The conical nozzle and the fat conical nozzle presented ideal results in which the fat conical nozzle structure helped the shielding gas fow field obtain minimal conicity and straighter fow, fostering stable welding conditions by efficiently resisting crosswind disturbances at lower fow rates. Ensuring a nozzle-to-bevel spacing of less than 15 mm produced a shielding gas fow field with enhanced protection. The subsequent gas dyeing experiment and welding operations mirrored the simulation results on the fow field and welding performance of the conical nozzle and fat conical nozzle, affirming the feasibility of simulation methods for optimizing shielding gas fow fields. [Conclusion] The study findings showcase the effectiveness of fuid dynamic computation simulation technology in optimizing the structural design of welding torch nozzles and accelerating the development cycles, significantly improving the utilization efficiency of shielding gas in the GMAW welding process with narrow-gap bevels, and enhancing the stability of welding quality.By emphasizing the important role of simulation in welding process improvement, this paper offers new insights and technical references for the structural design of welding torch nozzles and the regulation of shielding gas fow fields.

In this paper, the ER5356 aluminum alloy wire was used for cold metal transfer (CMT) welding of the 5083-H111 base metal with 20 mm thickness. The effects of four shielding gases, which were 100%Ar, 75%Ar+25%He, 50%Ar+50%He and 100%He on the weld formation, microstructure and mechanical properties were investigated using optical microscope, scanning electron microscope (SEM), x-ray diffraction (XRD) and mechanical testing. The results showed that with the increase of He in the shielding gas, the weld penetration and width increased, and the porosity in the weld zone decreased significantly; the microstructure changed from coarse dendrites to fine equiaxed crystals, and the microstructure was gradually refined; the tensile strength of deposited metal increased from 220 MPa to 270 MPa, with an increase of 22.7%, the tensile fracture was quintessential ductile fracture, and the hardness increased from 64.2 HV to 68.4 HV. The addition of He in the shielding gas can effectively inhibit the generation of pores and promote the β-Al3Mg2 phase in the weld microstructure, thus improving the mechanical properties of the deposited metal.

Blue light emitted during arc welding is known to potentially cause photoretinopathy. To help prevent retinal injury, it is important to identify the hazards associated with various welding conditions. The present work conducted experiments involving gas metal arc welding of mild steel under various conditions, and measured the spectral radiance of the arcs. The effective radiance values, as used by the American Conference of Governmental Industrial Hygienists (ACGIH) to quantify exposure level of blue light, were subsequently calculated from the data. The resulting values were in the range of 5.0-118 W/cm²/sr, corresponding to hazardous levels according to ACGIH guidelines. The effective radiance was increased at higher welding currents and when pulsed currents were used rather than steady currents. The blue light hazard was also affected by the type of shielding gas employed. These data confirm that it is very hazardous to stare at arcs during gas metal arc welding of mild steel. As such, appropriate eye protection is necessary during arc welding, and directly staring at the arc should be avoided. [ABSTRACT FROM AUTHOR]

SMAW (Shielded Metal Arc Welding) and GMAW (Gas Metal Arc Welding) are two of the most prominent welding processes commonly utilized in almost all types of modern industries. Among various aspects of these processes, some of the important parameters that govern the quality of the final weld product are the skill level of welders, welding consumables, and the role of shielding gases (in GMAW). Currently, the role of these parameters in determining the quality of the welded product is examined by evaluating the final weld produced and not by investigating how these factors affect the welding process. This is an indirect way to evaluate such welding parameters, which are both time-consuming and expensive. During the actual welding process, random variations in arc signals (voltage and current) take place. These dynamic variations are so short and rapid that ordinary ammeters and voltmeters cannot monitor the rate of such variations. However, the reliable acquisition of such variations and its subsequent analysis can provide very useful information in determining the quality of the final weld product. In this study, arc voltage and current were acquired at 100,000 samples/sec, filtered and subsequently analyzed using Continuous Wavelet Transform based on Fast Fourier Transform (CWT-FFT) technique to evaluate welding skill, welding electrodes (in SMAW process), and the effect of shielding gases (in GMAW process). Results thus obtained clearly differentiated the skill level of different trainee welders and welding electrodes in the SMAW process and the effect of shielding gases and arc current in the GMAW process. Very good correlation among the obtained results, its weld bead and its weld pool images were observed. Hence, this research proposes a simple yet effective methodology to evaluate the arc welding process parameters using CWT-FFT analysis of the welding signals. [ABSTRACT FROM AUTHOR]

Structural galvanized steel SGC440, known for its high tensile strength, is commonly used in the manufacturing of vehicle bodies, especially for cars and buses. The Gas Metal Arc Welding (GMAW) method is considered most suitable for connecting SGC440 plates. Despite its effectiveness, GMAW welding often faces challenges such as bending deformation and excessive burning, which can lead to damage in the welded areas. The use of shielding gas and the electric current need to be adjusted to achieve optimal joint quality. Therefore, an investigation into the parameters of shielding gas flow rate and the magnitude of the electric current is necessary to determine the quality of the joints. This study aims to determine the tensile strength of SGC 440 steel resulting from GMAW welding with variations in shielding gas consumption and the electric current used. Tensile strength testing of the samples was carried out following the JIS Z 2201 standard. The welding results indicate that variations in the shielding gas flow rate and the magnitude of the electric current affect the tensile strength. Additionally, microstructure observations show differences in the material's phase structure due to the influence of the electric current magnitude and shielding gas consumption. [ABSTRACT FROM AUTHOR]

A rotary tungsten inert gas (TIG) torch has been developed to enhance the quality and complexity of fabrications in wire and arc additive manufacturing (WAAM). This study explores the influence of arc length on deposition characteristics within a rotary TIG torch by adjusting the wire feed speed, travel speed, and shielding gas type. The findings reveal that the unique vertical wire feeding mechanism of the rotary TIG torch prevents the wire-feeding position shift typically observed in conventional TIG processes. However, extended arc lengths in the rotary TIG setup tend to induce arc deflection and molten metal scattering due to the employment of a tilted electrode. Specifically, at high wire feed and travel speeds, bead continuity is compromised by molten metal scattering. Conversely, at low travel speeds relative to wire feed speeds, defect-free deposition is achievable across a broad arc length spectrum from 4 to 20 mm using rotary TIG. Furthermore, decreasing the wire feed speed in proportion to the current and increasing the heat input per material input minimizes the contact time between the wire and the molten pool, thus mitigating arc deflection. Employing helium-mixed gas as a shielding gas facilitates defect-free deposition over an extensive range of arc lengths, even under conditions that typically induce humping with pure argon.

Ar–N2-O2 ternary shielding gas is employed in dissimilar welding between high nitrogen steel and low alloy steel. The effect of O2 and N2 is investigated based on the systematical analysis of the metal transfer, nitrogen escape phenomenon, weld appearance, nondestructive detection, nitrogen content distribution, microstructure and mechanical properties. There are two nitrogen sources of the nitrogen in the weld: high nitrogen base material and shielding gas. The effect of shielding gas is mainly reflected in these two aspects. The change of the droplet transfer mode affects the fusion ratio, N2 in the shielding gas can increase nitrogen content and promote the nitrogen uniform distribution. The addition of 2% O2 to Ar matrix can change the metal transfer from globular transfer to spray transfer, high nitrogen base material is thereby dissolved more to the molten pool, making nitrogen content increase, ferrite decrease and the mechanical properties improve. When applying N2-containing shielding gas, arc stability becomes poor and short-circuiting transfer frequency increases due to the nitrogen escape from droplets and the molten pool. Performance of the joints is improved with N2 increasing, but internal gas pores are easier to appear because of the poor capacity of low alloy steel to dissolve nitrogen, The generation of pores will greatly reduce the impact resistance. 4–8% N2 content in shielding gas is recommended in this study considering the integrated properties of the dissimilar welded joint.

Gas protection is a crucial part of quality control in laser welding, especially for titanium alloy, which oxidizes easily at high temperatures. Substantial experiments concerning shielding gas characteristics in the welding process have been implemented. However, the common analysis conducted is simplistic and lacks a theoretical basis. This paper presented an investigation of the shielding gas behaviors based on numerical simulation and a titanium alloy laser welding experiment. The numerical model was established and validated by experiment. Subsequently, the temperature field and gas flow fields were calculated. By combining the two fields, the threshold temperature of gas protection was determined, and the influence of shielding gas parameters on the protection effect was examined. The results revealed that the protection of the high-temperature zone was primarily influenced by the nozzle height, nozzle inner diameter, and nozzle angle, while the plasma suppression effect was mainly correlated with the nozzle inner diameter and gas flow rate. These initial findings provide scientific guidance for the better quality production of laser beam welded components made of not only titanium alloy but also other metallic materials. [ABSTRACT FROM AUTHOR]

In contrast to conventional components made from a single material, hybrid multi-material components allow the production of load-adapted parts with different materials in different structural and functional areas. Hardenable and forgeable steels with a high carbon content are suitable for increasing fatigue and wear resistance and thus an extension of component life. However, materials with an equivalent carbon content of more than 0.6 are considered difficult to weld due to their tendency to crack. This study investigates the influence of the shielding gas coverage on the laser hot-wire cladding process with high carbon cladding material AISI 52100. For this reason, welding tests were carried out with different parameter combinations in a process chamber flooded with argon. The oxygen content in the chamber was less than 500 ppm during the welding process. The claddings welded in the process chamber are compared to the claddings welded in a previous investigation with a commercial shielding gas nozzle for laser deposition welding with wire. The tests conducted showed reduced pore formation and very little sparking. By using a process chamber, the average degree of dilution was reduced from 16.9% to 8.5% and burn-off of alloying elements was reduced. In most cases, high hardness values of 700 HV0.1 to 850 HV0.1 were achieved. The use of the process chamber demonstrates that the shielding gas coverage and therefore the remaining oxygen content have a high influence on the process stability and seam quality when welding high carbon steel. Such a considerable effect has not yet been observed with other commercially available cladding steels. [ABSTRACT FROM AUTHOR]

Stellite is a cobalt-chromium alloy that is widely used for hard facing of the industrial valves' internal components, including the seat and closure member, to prevent erosion and cavitation. Although previous studies have emphasized using stellite to avoid erosion and wearing of substrates, most of them do not focus on applying this material for the valve industry in oil and gas projects. Thus, the present study mainly aims to provide a method to qualify the stellite 6 hardfacing applied on the low-temperature carbon steel (LTCS) valve body contact surface with disks and ensure that the weld overlay is used correctly. This study has developed a weld overlay qualification method including various tests such as Non-destructive test (NDT), Charpy V-Notch test, chemical composition, hardness test, and finally micro examination. The results of the trials and interpretation and evaluation are also included in this research. [ABSTRACT FROM AUTHOR]

Laser-based powder bed fusion is an additive manufacturing process in which a high-power laser melts a thin layer of metal powder layer by layer to yield a three-dimensional object. An inert gas must remove process byproducts formed during laser processing to ensure a stable and consistent process. The process byproducts include a plasma plume and spatter particles. An NC sensor gantry is installed inside a bespoke open-architecture laser-based powder bed fusion system to experimentally characterize the gas velocity throughout the processing area. The flow maps are compared to manufactured samples, where the relative density and melt pools are analyzed, seeking a potential correlation between local gas flow conditions and the components. The results show a correlation between low gas flow velocities and increased porosity, leading to lower part quality. Local flow conditions across the build plate also directly impact components, highlighting the importance of optimizing the gas flow subsystem. The experimental flow analysis method enables optimization of the gas flow inlet geometry, and the data may be used to calibrate the computational modeling of the process. [ABSTRACT FROM AUTHOR]

Regarding porosity formation and gas content, choosing the appropriate shielding gas for laser welding is essential for achieving high-quality joints. Keyhole-induced porosity formation tendency and nitrogen content in SS 304 stainless steel welds were investigated based on the nitrogen content in shielding gases during fiber laser welding. Beads-on-plate autogenous welds were made at 5 kW continuous wave (CW) fiber laser in N2 and Ar mixtures. Optical metallography, micro-focused X-ray, X-ray radiography, and high-speed images of the molten pool were used to investigate the porosity formation. In addition, a gas analyzer was used to study the weld metal nitrogen content. The results show that nitrogen significantly impacts the reduction of porosity in the melting zone and increases the dissolved nitrogen in the solidified weld metal, as using pure nitrogen leads to an increase in dissolved nitrogen by 36% higher than the nitrogen content in the base metal. In contrast, it has almost no significant effect on the keyhole mode. [ABSTRACT FROM AUTHOR]

The effect of shielding gas composition and welding current on the mechanical-physical properties of plug welding joint stainless steel SUS 304L has been investigated. Metal Inert Gas (MIG) welding was used to join SUS304L with a thickness of 3 mm. The variations of welding current were 80 A, 100 A, and 120 A, while variations of shielding gas composition were 100% Ar; 92,5% Ar-7,5% CO2; 85% Ar-15% CO2; 77,5% Ar-22,5% CO2; 100% CO2. Macro and microstructural tests were conducted to determine welded joints physical properties. Tensile-shear testing and micro hardness Vickers were done to determine welded joints physical properties. The results show that the higher level of welding current and CO2 content in the shielding gas, the more tensile-shear load bearing capacity and decreased hardness. The welding current of 120 A and shielding gas 77,5% Ar-22,5% CO2 produced welded joints with the highest tensile-shear load bearing capacity. The nugget size increased as the higher level of welding current and the CO2 content in the shielding gas due to the increase of heat input.

• Exploring the inhibition of moisture intrusion and the protection of perovskite solar cells in a CO 2 and N 2 sealed environment. • Established the model of moisture intrusion under the environment of N 2 , CO 2 and SF 6 , and simulated the degree of moisture intrusion under the three gas environments. • In the practical application of perovskite solar cells, on the premise of considering sealing and cost, it provides guidance for the selection of shielding gas. The stability and reliability of perovskite solar cells (PSCs) are severely affected by moisture. Therefore, it is very meaningful to study the barrier effect of gases with different compositions on moisture in a sealed environment. In this work, the stability of PSCs in a sealed environment filled with N 2 , CO 2 with an external environment of 45 °C and 85% RH was investigated. After 240 h treatment, the PCE of the PSCs in the CO 2 sealed environment decayed to 71.1% of the initial value. The PCE of the PSCs in the N 2 sealed environment decayed to 51.8% of the initial value, while in the air environment as a control, the PCE decayed to 36.3% of the initial value. Through SEM, XRD film characterization and finite element simulation, it is found that both CO 2 and N 2 can be used as shielding gases to inhibit moisture intrusion, thereby slowing down the decay rate of perovskite solar cells. And CO 2 is more effective than N 2 in inhibiting moisture intrusion. On the one hand, CO 2 molecules are larger than N 2 molecules. When tiny gaps appear in the sealed environment, N 2 molecules can escape, but CO 2 cannot escape, which will lead to less moisture intrusion in the CO 2 sealed environment. On the other hand, when there are large gaps in the sealed environment, both N 2 and CO 2 can escape, because the diffusion coefficient of moisture in the N 2 sealed environment is larger, resulting in more moisture intrusion in the N 2 sealed environment. [ABSTRACT FROM AUTHOR]

Stainless steels have been increasingly used for agricultural and food processing, biogas, architecture, automotive, machine-manufacturing, biomedicine, chemical, and petrochemical industry due to their corrosion resistance and sanitary qualities. Dissimilar stainless steels may need to be utilized together in various fields due to their different properties. Therefore, it is important to weld dissimilar stainless steel, which are employed in these fields, with strong mechanical properties. However, the requirement to join many metals, each of which has different properties, on the same construction may result in the emergence of some problems. The properties of the weld zone as well as the quality of the welded joints depend on the selection of the optimal welding parameters and the kind of shielding gas. Therefore, estimating the quality and service life of dissimilar stainless steel joints requires to understand the weld zone's properties better. Therefore, it is important to investigate the effect of shielding gases and gas combinations on the welding of dissimilar stainless steels in the welding process. In this study, AISI 316 austenitic stainless steel and AISI 430 ferritic stainless steel were joined utilizing the metal inert gas (MIG) welding with different shielding gas combinations. In welding processes, 100% Ar, 97% Ar+3% H2, and 93% Ar+7% H2 gas combinations were used. The welded sheets were subjected to hardness, tensile, and bending tests in addition to metallographic testing. The effects of the shielding gas combinations on the mechanical and microstructural properties of AISI 316 austenitic and AISI 430 ferritic stainless steel connections were investigated through these tests. [ABSTRACT FROM AUTHOR]

The paper presents the study results of the parameters influence of arc welding with a consumable electrode with two-jet gas shielding in CO2 on the structure and microhardness of high-strength steel 45 welded joints with slotted edges. Controlling the dynamic impact of the internal shielding gas jet on the processes in the welding zone changes the heat and mass transfer processes in the welding zone and results in the intensive mixing of the molten electrode metal with the base metal in the weld pool. The results of the studies determined the dynamic effect of the active shielding gas jet on the structure and microhardness of multilayered steel 45 welded joints with slotted edges using the method of full factorial experiment, developed dependences of chemical elements (carbon, silicon, manganese) content in the weld metal of multilayered steel 45 welded joints on the controlled parameters of the welding mode (Q, Iw, U). Due to uneven heat introduction into each of the welded plates during edge slotting, the asymmetric distribution of microhardness in the cross sections of welded joints relative to the weld axis indicates some differences in the structure and properties of the heat-affected zone (HAZ) and the weld. According to the results of the studies, consumable electrode arc welding with two-jet gas shielding provides faster distribution and equalization of heat on the product surface and reduces its instantaneous overheating, which improves the structural phase state of the welded joint made of steel 45 and reduces the microhardness gradient in the HAZ. An increase in the heat input of welding (a simultaneous increase in the welding current and voltage of the welding arc) leads to a decrease and smoothing of the microhardness peak in the HAZ. [ABSTRACT FROM AUTHOR]

High nitrogen steel (HNS) have been widely used in many industrial fields in place of stainless steels. As we know, the welding is the main fabricating method of the HNS structural components. In this article, the recent investigations of joining methods of HNS, such as tungsten inert gas welding, melt inert-gas welding, laser welding, laser-arc hybrid welding, friction stir welding (FSW), and brazing method are summarized. First, the effect of nitrogen content in shielding gas, welding wire, and base metal on the evolution of microstructure, mechanical properties, and corrosion susceptibility of fusion welded joints are discussed systemically. Then the existing problem during FSW and brazing process of HNS are analyzed. Additionally, the key issues and future trends in the joining of HNS are proposed. The main purpose of this review is to provide a technical reference and theoretical basis for research and technological development during the welding of HNS.

In this study, the parameters of Metal Inert Gas (MIG) and Metal Active Gas (MAG) were investigated of AISI 316L/ER 316L. A quaternary shielding gas mixture consisting of Argon (Ar), Helium (He), Carbon Dioxide (CO _2 ), and Nitrogen (N _2 ) was chosen. The Taguchi orthogonal array (OA-L9) methodology was employed to explore optimal welding settings, including arc current (120A, 160A, 200A), wire feed rate (3, 3.5, 4 m min ^−1 ), and shielding gas combination (G1, G2, G3). The findings highlighted the importance of shielding gas in influencing the ultimate tensile strength (UTS), elongation percentage (EL%), and material toughness of welding joints. Notably, the highest UTS (515.77 MPa), EL% (20.85%), and material toughness (133J) were achieved by the specific group gas combination shown as G1. It is recommended to configure welding parameters to an arc current of 160A, a wire feed rate of 4 m min ^−1 , and the G1 gas combination. Welded specimens using a G1 gas mixture showcased the best UTS and EL%. Additionally, it was found that the fusion zone (FZ) and heat-affected zone (HAZ) hardness are most profoundly influenced by the choice of gas combination (G2), resulting in the best hardness values of 253.79 HV and 239.68 HV, respectively. The optimal parameters for achieving the desired material hardness were precisely identified as (120A, 3 m min ^−1 , G2). These insights offer a pathway to enhance welding performance and, in turn, elevate the quality and efficiency of industrial applications.

In the current experiment, the fiber laser parameters were optimized for welding P91 steel using the Box–Behnken design (BBD). Bead-on-plate welds were produced with an 8000 W fiber laser welding machine, with the focal point, power, and welding speed of the laser varied under various shielding atmospheres. The input parameters were optimised to achieve the desired depth of penetration (Dp), underfill (U), top bead width (Tw), and heat-affected zone width (Hw), and their impact on output responses were analyzed using the analysis of variance (ANOVA). The results of bead-on-plate trial welds and analysis of variance demonstrated that welding speed has the most decisive influence on the depth of penetration (Dp), the width of top bead (Tw), and HAZ (Hw), while laser power has the most significant influence on underfill (U). The optimal solution for argon shielding resulted in a weld with a penetration depth of 5.5 mm, compared to full penetration weld with a narrow top bead and heat affected zone achieved in CO2 shielding atmosphere. The results of validation trials utilising the optimal parametric combination were found to be highly correlated with the expected values, confirming the mathematical model's adequacy. The high laser intensity used in CO2 shielding resulted in the formation of underfill with a depth of 0.456 mm. In both shielding atmospheres, the fusion zone microstructure exhibited untempered martensite in as-welded condition with a columnar lath structure and was devoid of δ-ferrite. [ABSTRACT FROM AUTHOR]

Direct energy deposition with arc and wire (DED-AW) is a versatile, low-cost, and energy-efficient technology for additive manufacturing of medium- and large-sized metallic components. In this study, the effects of arc energy and shielding gas in cold metal transfer (CMT) welding of walls and blocks on cooling time, mechanical properties, and macro- and microstructure have been studied using precipitation-hardenable Ni-based superalloy Haynes® 282®. The arc energy and consequently the cooling rate were varied by changing the wire feed rate and the travel speed. As expected, increasing the arc energy leads to higher cooling times for the walls. Due to the 2D thermal conduction, the thin walls cool down much slower than multi-layer welded blocks, but this reduces the strength values only very slightly. While the walls have no sensitivity to the occurrence of unacceptable seam irregularities, the multi-layer blocks show isolated seam defects, such as hot cracks or lack of fusion. Despite shielding gas variation, the as-welded blocks show acceptable strength properties at room temperatures (RT) and impact values at RT and −196 °C. However, the use of an N-containing shielding gas results in lower elongation and notched bar impact energy. Precipitation-hardened specimens tested at 871 °C exhibit a similar strength level to transverse tensile specimens of gas metal arc welding (GMAW) welded joints on 12.7 mm thick plates with fracture in the weld metal. [ABSTRACT FROM AUTHOR]

As improving fuel economy and performance through weight reduction in vehicles are recognized as important tasks, the defense industry is researching ways to reduce the weight of armor plates for combat vehicles and increase bulletproof performance and durability. Most armor plates in combat vehicles are manufactured using weld joints. High-hardness armor (HHA) is used to make armor plates; however, its mechanical properties deteriorate because of hydrogen embrittlement and high-temperature softening during welding. Welding defects, such as pores and cracks, occur frequently. In this study, HHA steel was subjected to single-pulse gas metal arc welding (GMAW), and the welding performance of the shielding gas and heat input was analyzed by the United States army tank-automotive and armaments command (TACOM) standard. The specimen cross-section was visually examined, and hardness, tensile, and impact tests were used to identify the mechanical properties based on the welding conditions. Additionally, flux cored arc welding (FCAW) and GMAW were used and compared, and spatter image analyses were used to assess the integrity of the welding process of the HHA plate applied to a combat vehicle. As a result of the experiment, as the CO2 content and heat input increased, the mechanical strength of the welded zone and the integrity of the welding process deteriorated. [ABSTRACT FROM AUTHOR]

Welding fume exposure at work is recognized as a known concern for public health. This study aims to assess the welding fumes produced during welding using two different extraction patterns and to compare their influences. A thorough assessment of domestic arc welders in the erode district of India was done to assess their exposure to welding gases. The survey results chose the gas metal arc welding (GMAW) process for future investigation. The stainless-steel grade SS 316 L was used in this study. To weld 3-mm, 5-mm, and 6-mm-thick stainless-steel specimens, ER316 L filler wire and four shielding gas compositions were used. Two distinct, cost-effective welding hoods with a square duct section and a conical duct section were constructed to examine welding gases. The produced fume was collected on a 240 mm glass fibre filter and re-weighted during welding. Gas flow rates of 5, 10, and 15 LPM were investigated, with current intensities of 150A, 200A, and 275A. A novel attempt has been made to compare fume formation rates (FFR) obtained using two extraction patterns. According to this investigation, weld fume hoods with conical duct sections extract more welding gases than square duct sections. The extraction rate using two extraction patterns was compared. Furthermore, the addition of CO2 to any shielding gas mixture results in a higher fume formation rate. The experimental FFR values were quite close to the American Welding Society (AWS) specifications. This finding also revealed that welders' socio-demographic characteristics, such as age, marital status, level of education, and work experience, influenced their awareness of occupational hazards and personal protection equipment (PPEs). As a result, there should be a strong emphasis on hazard identification education and strict enforcement of proper PPEs use among small-scale welders in and around the erode district to protect welders from a variety of hazards. [ABSTRACT FROM AUTHOR]

Directed energy deposition-arc (DED-arc) manufactured duplex stainless steel (DSS) has shown great potential for use in marine propellers. However, challenges remain in achieving phase-balanced DSS deposits through the DED-arc process. To overcome this, we conducted a study that involved regulating the deposition energy and shielding gas with the use of ER2205 wire. The results show that the austenite content in DSS deposits increases with the increase of deposition energy, and the content in the Ar+2%N 2 -protected deposits is significantly higher than that of Ar+2%CO 2 -protected deposits. Ultimately, DSS deposits with balanced phase content (austenite content of ∼48.4 %) are obtained at a line energy of 600 J/mm for DED-arc under Ar+2%N 2 protection. Unlike the N loss in Ar+2%CO 2 -protected samples, more nitrogen elements are introduced into the DSS samples by Ar+2%N 2 shielding gas. Ar+2%N 2 -protected samples contain more austenite and exhibit a more homogeneous microstructure, which results in the solid solution strengthening and a significant reduction in the anisotropy of the tensile properties. Furthermore, a more systematic evolution of the microstructure and tensile properties of DSS deposits under the influence of deposition energy and shielding gas is revealed. This study preliminarily obtains the relationship between the DED-arc parameters, microstructure, and tensile properties of DED-arc-fabricated DSS, which will provide an important reference for tailoring microstructure and properties in additive-manufactured DSS. [ABSTRACT FROM AUTHOR]

In this article, the effect of shielding gas combinations on gas tungsten arc-welded dissimilar AISI 310 steel and AISI 2205 steel joints was investigated. Two gases such as nitrogen and carbon dioxide were substituted in argon shielding gas and its corresponding improvement in the mechanical, microstructural, machining, and wear aspects of the dissimilar AISI 310–AISI 2205 joints was studied. Weld bead studies, tensile, and weld region microhardness were conducted. X-ray diffraction studies revealed joint intermetallics, and microstructural evaluation was conducted. Machining studies were conducted using drilling experiments. Using local analysis and global analysis, the cutting force variations in the feed direction and cutting direction were studied. Wear tests revealed that the variations in traction force, specific wear rate, coefficient of friction and tribo wear mass loss were studied. A considerable improvement in wear characteristics of AISI 310–AISI 2205 joints was observed by substituting CO2 and N in shielding gas.

An 80%Ar-10%CO2-10%He ternary gas mixture was used as the shielding gas during the narrow-gap welding of thick Q690E high-strength steel plates. Complete and defect-free welded joints were obtained, and the microstructure and mechanical properties of the welded joint were investigated. The weld zone consists of a solidification area and interlayer zone, and the heat-affected zone consists of a coarse-grain heat-affected zone (CG-HAZ) and a fine-grain heat-affected zone (FG-HAZ). The microstructures of the weld zone are mainly lath bainite (LB), acicular ferrite (AF), and granular bainite (GB). The microstructure of the CG-HAZ is lath martensite (LM) and the microstructure of FG-HAZ is GB. Methods with different heat inputs were used to study their effects on the mechanical properties of the welded joint. It was found that the microstructure and mechanical properties of the welded joints are better with lower heat input. With tandem wire narrow-gap GMA welding, the tensile strength of the joints declined from 795.3 to 718.3 MPa and the impact toughness at −40 °C resulted in a weak position in the weld zone, which declined from 76~81 J to 55~69 J, when the welding speed reduced from 350 to 250 mm/min. With oscillating-arc narrow-gap GMA welding, the tensile strength achieved 853.4 MPa and the impact toughness at −40 °C was around 69~87 J. The results indicated that, under the appropriate heat input, the tensile strength of the joint exceeds 770 MPa and the low temperature impact toughness at −40 °C exceeds 69 J. A 155 mm-thick Q690E steel welded joint was obtained and the mechanical properties of the welded joint meets the requirements of the offshore drilling platforms. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Laser-based powder bed fusion is an additive manufacturing process in which a high-power laser melts a thin layer of metal powder layer by layer to yield a three-dimensional object. An inert gas must remove process byproducts formed during laser processing to ensure a stable and consistent process. The process byproducts include a plasma plume and spatter particles. An NC sensor gantry is installed inside a bespoke open-architecture laser-based powder bed fusion system to experimentally characterize the gas velocity throughout the processing area. The flow maps are compared to manufactured samples, where the relative density and melt pools are analyzed, seeking a potential correlation between local gas flow conditions and the components. The results show a correlation between low gas flow velocities and increased porosity, leading to lower part quality. Local flow conditions across the build plate also directly impact components, highlighting the importance of optimizing the gas flow subsystem. The experimental flow analysis method enables optimization of the gas flow inlet geometry, and the data may be used to calibrate the computational modeling of the process.

Tent shielding is an effective and flexible method to provide inert protective atmosphere during wire arc additive manufacturing of titanium alloy. In this study, five deposited walls were fabricated by CMT-WAAM process with different oxygen levels in the tent shielding, and the influences of oxygen levels on the microstructure and mechanical properties were analyzed. The results showed that, the oscillated path provided enough time for the molten pool to absorb oxygen out of atmosphere. With the increase in oxygen level, the thickness of α-case with higher micro-hardness became larger, the amount of β phase gradually decreased, the ratio of length to width for α lamellar was increased, and the boundary α phase became coarser. The higher oxygen level in the tent shielding caused an increase in tensile strength and a decrease in elongation. An ultimate tensile strength higher than 900 MPa and an elongation higher than 6% could be obtained when the oxygen level in the tent was lower than 2000 ppm. [ABSTRACT FROM AUTHOR]

Growing awareness for occupational safety in the welding environment needs a sustainable welding system. Welding gases releases toxic tiny particles and gases that inflict severe health consequences in the weld zone are unsolicited. Some of the other main adverse effects are lung disease, hemoptysis, pulmonary inflammation, pneumoconiosis, etc. GMAW procedure has been used for welding 316L stainless steel plates of 3 mm, 5 mm, and 6 mm. Various current configurations with gas flow rate of 5 LPM, 10 LPM and 15 LPM were also used to achieve optimum butt joint performance and to reduce the production rate of fume contributing to cost-effectiveness. In this research a cost-effective fume extraction hood was fabricated for measuring Emission factor produced during welding. Various shielding gas compositions including Pure Argon, Pure CO2, 92% Ar+8% CO2 and 88% Ar+12% CO2 were used to determine the best operating parameters in the GMAW method. To satisfy the latest Permissible Exposure Limit (PEL) legislation, optimum technical parameters for efficient welding were acknowledged with the lowest emission factor. A maximum reduction of Emission factor can be achieved by using Pure Argon. The inclusion of CO2 as a shielding gas mixture gives higher emission factor when compared to Pure Argon. Very low emission factor were witnessed in this research when compared to previous investigations. Lower emission factor of 2941.17 mg /kg of electrode, 4411.76 mg/kg of electrode and 7352.94 mg/kg of electrode were obtained for pure argon as shielding gas with 150 A welding current.

The paper presents the study results of the parameters influence of arc welding with a consumable electrode with two-jet gas shielding in CO2 on the structure and microhardness of high-strength steel 45 welded joints with slotted edges. Controlling the dynamic impact of the internal shielding gas jet on the processes in the welding zone changes the heat and mass transfer processes in the welding zone and results in the intensive mixing of the molten electrode metal with the base metal in the weld pool. The results of the studies determined the dynamic effect of the active shielding gas jet on the structure and microhardness of multilayered steel 45 welded joints with slotted edges using the method of full factorial experiment, developed dependences of chemical elements (carbon, silicon, manganese) content in the weld metal of multilayered steel 45 welded joints on the controlled parameters of the welding mode (Q, Iw, U). Due to uneven heat introduction into each of the welded plates during edge slotting, the asymmetric distribution of microhardness in the cross sections of welded joints relative to the weld axis indicates some differences in the structure and properties of the heat-affected zone (HAZ) and the weld. According to the results of the studies, consumable electrode arc welding with two-jet gas shielding provides faster distribution and equalization of heat on the product surface and reduces its instantaneous overheating, which improves the structural phase state of the welded joint made of steel 45 and reduces the microhardness gradient in the HAZ. An increase in the heat input of welding (a simultaneous increase in the welding current and voltage of the welding arc) leads to a decrease and smoothing of the microhardness peak in the HAZ.

Electricity produced in power plants is essential in our everyday life. In general, the energy transfer takes place after processing the energy source in boilers or steam generators. Steam is generated through this process, that operates the turbines and they generate electricity through the generators. As such equipment operates in a high pressure, corrosive and high temperature environment, these circumstances may damage the tubes in the heat exchangers. Our research examines the potential of corrosion of heat exchanger tubes after welding. The typical corrosion process is pitting. The corrosion resistance of stainless steel depends on a protective, passive film formed on the surface of the steel exposed to the service environment. The use of fusion welding for fabrication leads to local variations in the chemical composition inside the material, which may significantly alter the stability of the passive layer and hence the corrosion behavior. The impact of welding parameters (shielding gas, amperage) was examined on corrosion resistance of X6CrNiTi18-10 austenitic stainless steel. The corrosion test was performed according to ASTM G48 standard. The weight loss was measured in Fe(III)-chloride solution by the first corrosion test. The results showed that the corrosion resistance of stainless steel was better at 50 A and 10 l/min welding parameters. During the second test, a potentiodynamic corrosion test was made, and the potentiodynamic curve was measured in 9% saline solution. In this solution, the stainless steel had a better corrosion property because it was measured in a less aggressive medium. [ABSTRACT FROM AUTHOR]

Wire arc additive manufacturing (WAAM) is the process by which large, metallic structures are built, layer-by-layer, using a welding arc to melt wire feedstock. In this process, the proper selection of the shielding gas plays a vital role in the achievement of structurally acceptable part geometries and quality surface finishes. In this study, the authors used either a ternary mix (He, Ar and CO2) or a binary mix (Ar and CO2) of shielding gases to deposit wall geometries using an open loop-controlled WAAM system developed at Oak Ridge National Laboratory's Manufacturing Demonstration Facility. The binary blend produced a wider and shorter geometry, while the ternary blend resulted in a narrower build that was more equivalent to the CAD geometry. The data indicated that the binary blend provided a higher oxygen concentration in the weld as compared to that of the ternary blend. The results imply that the arc characteristics and heat input had a significantly higher impact on the weld penetration than the surface tension effect of surface active elements. This was further verified by developing and applying a high-fidelity computational fluid dynamics (CFD) model of the thermophysical properties of gas mixtures. The results from the model showed that, while the influence of increased oxygen concentration on the surface tension for the binary blend led to a deeper penetration, the ternary blend gave rise to heat flux to the workpiece. [ABSTRACT FROM AUTHOR]