Shielding Gas Composition Research Articles

Characterisation of microstructure, mechanical and corrosion properties of pulsed MIG welded modified P91 steel weld metal

Varying the shielding gas composition with argon and carbon dioxide influences the properties of the weldments which are evaluated using microstructural, micro-hardness and corrosion studies. The modified P91 steel samples are welded by Pulsed Metal Inert Gas welding process with different shielding gas mixture, i.e., 95%Ar-5%CO2, 80%Ar-20%CO2 and 60%Ar- 40%CO2. The welded steels are studied metallographically by observing microstructures at three different regions namely at the base metal, Heat Affected Zone (HAZ) and the Weld zone. Hardness measurements are also done using Vicker’s micro-hardness tester. Corrosion studies in acidic media (sulphuric and nitric acid media of four different normalities 0.5, 1.0,1.5 and 2.0) are done in the welded region and the parent metal to compare the corrosion resistance. Of all the welded samples, welds made with the shielding gas composition of 95%Ar-5%CO2 exhibits good corrosion resistance over the other two welds while the weld made with the shielding gas composition of 60%Ar -40%, shows very poor corrosion resistance.

Effect of flow rate and argon-hydrogen shielding gas mixture on weld bead morphology of inconel 718

Shielding gas composition plays an important role in the weldment characteristics of Gas tungsten arc welding process (GTAW).Argon is the commonly used shielding gas which is used in the GTAW of the super alloy Inconel 718, which combines high strength with good creep and corrosion resistant properties up to 650°C.In the present work a comparative study by bead on plate GTA welds were made using pure Argon (Ar) and Argon-hydrogen (Ar-H2) mixture in continuous and pulsed modes while changing the gas flow rates on Inconel 718. Addition of hydrogen to the argon shielding gas has affected the bead morphology. Results from the experiment indicate that the maximum penetration was achieved using pulsed Ar-H2 combination and there is an increase in the bead area, bead width and heat affected zone (HAZ) size compared to pure argon. The arc pulsing caused a considerable increase in bead profile and the flow rate influence on the bead morphology was not significant.

A contribution to the study of negative polarity in GMA welding

Gas metal arc welding (GMAW) using the electrode with negative polarity (DCEN) has been frequently suggested as a potential means of increasing production capacity. The objective of this work was to further study the performance of negative polarity in GMAW of carbon steels. In this project phase, bead-on-plate welds were carried out in flat position to assess the effect of different potential shielding gas compositions on bead geometry, finishing and spattering. The characteristics were compared with DCEP at the same current, but depositing the same volume of material per unit of length (more industrial related comparison). The arc length was kept the same by adjusting voltage to reach shortest arcs, yet with suitable non short-circuiting metal transfer mode. An approach to measure bead convexity was also proposed and assessed. The results showed that DCEN is feasible as a means of increasing GMAW production capacity. However, to become DCEN applicable with GMAW, the results suggest an Ar-based blend with around 6.5% of O2 is the most appropriate shielding gas, as much as that there is a demand for a standard electronic controlled power source able to work in constant current mode.

Optimization of shielding gas composition in narrow gap GMA welding based on response surface methodology

In gas metal arc (GMA) welding, metal melting behaviors and the weld geometry are affected by shielding gas composition. Helium has special properties, and it can provide a wider weld profile which is benefit for increasing sidewall penetration in narrow gap GMA welding. In this paper, helium was added to shielding gas for narrow gap GMA welding to ensure the sidewall penetration. The shielding gas includes argon, carbon dioxide, and helium. The statistical models for narrow gap GMAW weld bead sidewall penetration were developed using response surface methodology (RSM) based on central composite design (CCD). The developed models were checked for their adequacy and significance by analysis of variance (ANOVA), and the effects of shielding gas composition on sidewall penetration were studied. Finally, the optimal ternary shielding gas for tandem narrow gap GMA welding were obtained by numerical optimization using RSM. The largest sidewall penetration can be obtained under 79%Ar–10%CO2–11%He.

Effects of shielding gas composition on arc characteristics and droplet transfer in tandem narrow gap GMA welding

ABSTRACTThe effects of shielding gas composition in tandem narrow gap gas metal arc welding were studied. The shielding gas included argon, carbon dioxide and helium. The arc characteristics and droplet transfer process were analysed. The results show that in the same welding parameters, the trail wire welding current is higher than the lead wire welding current. With the increase of carbon dioxide content, the welding currents of two wires decrease, and the trail wire droplet transfer mode transforms from spray transfer to projected transfer. With the increase of helium content, the welding currents increase and the lead wire droplet transfer mode transforms from projected transfer to spray transfer. The weld width is the largest when the shielding gas mixture is 80%Ar10%CO210%He.

Effect of nitrogen in shielding gas of keyhole GTAW on properties of duplex and superduplex welds

Keyhole gas tungsten arc welding (GTAW) is a relatively new variant used for fabrication of pressure equipment where up to 10-mm-thick material can be autogenously welded in one pass. As the shielding gas used for keyhole mode is typically Ar + 5% H2, the suitability of this method for welding of duplex stainless steels has been investigated. Duplex UNS S31803 and superduplex UNS S32750 schedule 40 seamless pipe was welded using a closed square butt joint configuration. Shielding gas compositions were applied with increasing nitrogen content in argon or argon-hydrogen mixtures. An investigation of the completed welds included examinations of the microstructure, corrosion and mechanical properties of the weld metal. All shielding gases resulted in high-quality welds free from defects, showed high strength and excellent corrosion resistance. Hydrogen additions increased the weld metal nitrogen loss and resulted in lower austenite formation. Ar + 5% H2 showed up to 20 vol.% less austenite than the gas types containing nitrogen and also showed the lowest impact toughness. At least 2% nitrogen would be recommended for optimizing the phase balance and impact toughness. Taking all aspects into account, Ar + 2% N2 is the preferred shielding gas for welding duplex and superduplex with the keyhole GTAW process.

Role of Ambient Gas Composition on Cold Physical Plasma-Elicited Cell Signaling in Keratinocytes

A particularly promising medical application of cold physical plasma is the support of wound healing. This is presumably achieved by modulating inflammation as well as skin cell signaling and migration. Plasma-derived reactive oxygen and nitrogen species (ROS/RNS) are assumed the central biologically active plasma components. We hypothesized that modulating the environmental plasma conditions from pure nitrogen (N2) to pure oxygen (O2) in an atmospheric pressure argon plasma jet (kINPen) will change type and concentration of ROS/RNS and effectively tune the behavior of human skin cells. To investigate this, HaCaT keratinocytes were studied in vitro with regard to cell metabolism, viability, growth, gene expression signature, and cytokine secretion. Flow cytometry demonstrated only slight effects on cytotoxicity. O2 shielding provided stronger apoptotic effects trough caspase-3 activation compared to N2 shielding. Gene array technology revealed induction of signaling and communication proteins such as immunomodulatory interleukin 6 as well as antioxidative and proproliferative molecules (HMOX1, VEGFA, HBEGF, CSF2, and MAPK) in response to different plasma shielding gas compositions. Cell response was correlated to reactive species: oxygen-shielding plasma induces a cell response more efficiently despite an apparent decrease of hydrogen peroxide (H2O2), which was previously shown to be a major player in plasma-cell regulation, emphasizing the role of non-H2O2 ROS like singlet oxygen. Our results suggest differential effects of ROS- and RNS-rich plasma, and may have a role in optimizing clinical plasma applications in chronic wounds.

Benefits from H2 and CO2 additions in argon gas mixtures in GMAW

The effects of shielding gas composition on wire melting rate, deposition efficiency, and geometry of the welds were studied. Commercial shielding gases were evaluated, among them pure Ar, pure CO2, Ar+CO2 mixtures and Ar+5% H2. The Ar+8% CO2 mixture exhibited superior deposition efficiency and weld bead wettability. In contrast, the wire melting rate obtained with Ar+5% H2 mixture was significantly higher than all other tested gases. In order to simultaneously obtain the advantageous characteristics produced by the CO2 and H2 additions, further tests were performed with ternary mixtures consisting of Ar+5% H2 with various CO2 contents. The best results were obtained with Ar+5% H2+7% CO2 mixture, which yielded an increase in wire melting rate with deposition efficiency and weld bead wettability similar to those of the Ar+8% CO2.

Optimising the welding conditions to determine the influence of shielding gas on fume formation rate and particle size distribution for gas metal arc welding

An automatic voltage control technique, to optimise gas metal arc welding (GMAW) conditions for minimised fume generation, was compared to conventional constant-voltage operation on the influence of shielding gas on fume formation rate (FFR) and particle size distribution. Significant reductions in FFR were attributed to reductions in the arc length and current and to improved metal transfer stability, achieved by promoting the ‘drop-spray’ transfer condition and reducing repelled globular transfer. A general decrease in average particle size was observed when using the automatic control technique for the O2-bearing shielding gases, which is significant, as finer particulates are more likely to be inhaled into the lungs. The proposed mechanism to explain this behaviour was lower arc temperatures combined with an increase in the availability of oxygen, leading to nucleation of large amounts of extremely fine fume particles when the supercooling of the vapour was large. FFR increased as CO2 content increased due mainly to the dominant influence of CO2 on metal transfer and arc characteristics. It is recommended that the influence of shielding gas on FFR should be investigated using optimised welding conditions for each shielding gas composition for GMAW, especially when operating in the spray regime.

Effects of shielding gas composition on arc properties and wire melting characteristics in narrow gap MAG welding

At constant current, the arc voltage increases with increasing helium or CO2 content. At constant wire feed speed and constant voltage, as the helium or CO2 content increases, the welding current decreases. The arc length decreases significantly with the increase of CO2 content and arc core expands with the increase of helium content. When the shielding gas composition changes, arc properties and wire melting characteristics both change and the arc works at a new equilibrium point to keep the wire melting rate equal to wire feed speed. Shielding gas with the addition of helium presents a bowl weld bead profile. The depth of sidewall fusion increases as helium content increases. The welding process and weld quality are good when the shielding gas is 80%Ar10%CO210%He.

Effects of shielding gas composition on arc behaviors and weld formation in narrow gap tandem GMAW

In narrow gap gas metal arc welding (GMAW), it is useful to understand the arc behaviors to ensure the weld quality. Arc behaviors are strongly affected by the shielding gas composition. In this study, a three-component shielding gas mixture was used in tandem narrow gap pulsed GMAW, and the effect of its composition on arc behaviors and weld formation were investigated. The shielding gas included argon, carbon dioxide, and helium. The arc behaviors and electrical characteristics were recorded by a high-speed camera and an electrical signal acquisition system. The results show that the arc behaviors in different shielding gas are different. The arc expands and the arc length decreases with the increase of CO2 content or helium content. The arc is the widest when the shielding gas is 80%Ar10%CO210%He. The weld shape was observed, and it was found that the weld width increases first and then decreases with increasing of the CO2 content. When the helium content is below 15%, the weld width increases as the helium content increases, but when the helium is 15%, the weld width drops due to the decrease of arc length. When the helium content is above 15%, the weld width continues to increase as the helium content increases. The largest weld width can be obtained in 80%Ar10%CO210%He.

Influence of shielding gas on the mechanical and metallurgical properties of DP-GMA-welded 5083-H321 aluminum alloy

In the present research, 6-mm-thick 5083-H321 aluminum alloy was joined by the double-pulsed gas metal arc welding (DP-GMAW) process. The objective was to investigate the influence of the shielding gas composition on the microstructure and properties of GMA welds. A macrostructural study indicated that the addition of nitrogen and oxygen to the argon shielding gas resulted in better weld penetration. Furthermore, the tensile strength and bending strength of the welds were improved when oxygen and nitrogen (at concentrations as high as approximately 0.1vol%) were added to the shielding gas; however, these properties were adversely affected when the oxygen and nitrogen contents were increased further. This behavior was attributed to the formation of excessive brown and black oxide films on the bead surface, the formation of intermetallic compounds in the weld metal, and the formation of thicker oxide layers on the bead surface with increasing nitrogen and oxygen contents in the argon-based shielding gas. Analysis by energy-dispersive X-ray spectroscopy revealed that most of these compounds are nitrides or oxides.

Influence of microstructure and elemental partitioning on pitting corrosion resistance of duplex stainless steel welding joints

The influences of microstructure and elemental partitioning on pitting corrosion resistance of duplex stainless steel joints welded by gas tungsten arc welding (GTAW) and flux-cored arc welding (FCAW) with different shielding gas compositions were studied by optical microscopy, electron backscatter diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, electron probe microanalysis, and potentiostatic and potentiodynamic polarization methods The adding 2% N2 in shielding gas facilitated primary austenite formation in GTAW weld metal (WM) and suppressed Cr2N precipitation in GTAW weld root. In the HAZ, the banded microstructure disappeared while the coarse ferrite grains maintained same orientation as the banded ferrite in the BM. In the WM, the ferrite had one single orientation throughout a grain, whereas several families of austenite appeared. The austenite both in BM and WM enriched in Ni and nitro`gen, while Cr and Mo were concentrated in the ferrite and thus no element showed clear dendritic distribution in the WM (ER2209 and E2209T1). In addition, the secondary austenite had higher Ni content but lower Cr and Mo content than the primary austenite. The N2-supplemented shielding gas promoted nitrogen solid-solution in the primary and secondary austenite. Furthermore, the secondary austenite had relatively lower pitting resistance equivalent number (PREN) than the ferrite and primary austenite, thereby resulting in its preferential corrosion. The Cr2N precipitation led to relatively poor resistance to pitting corrosion in three HAZs and pure Ar shielding GTAW weld root. The N2-supplemented shielding gas improved pitting corrosion resistance of GTAW joint by increasing PREN of secondary austenite and suppressing Cr2N precipitation. In addition, the FCAW WM had much poorer resistance to pitting corrosion than the GTAW WM due to many O-Ti-Si-Mn inclusions. In the BM, since the austenite with lower PREN compared to the ferrite, the pitting corrosion occurred at the ferrite and austenite interface or within the austenite.

Influence of Metal Transfer Stability and Shielding Gas Composition on CO and CO2 Emissions during Short-circuiting MIG/MAG Welding

Abstract: Several studies have demonstrated the influence of parameters and shielding gas on metal transfer stability or on the generation of fumes in MIG/MAG welding, but little or nothing has been discussed regarding the emission of toxic and asphyxiating gases, particularly as it pertains to parameterization of the process. The purpose of this study was to analyze and evaluate the effect of manufacturing aspects of welding processes (short-circuit metal transfer stability and shielding gas composition) on the gas emission levels during MIG/MAG welding (occupational health and environmental aspects). Using mixtures of Argon with CO2 and O2 and maintaining the same average current and the same weld bead volume, short-circuit welding was performed with carbon steel welding wire in open (welder’s breathing zone) and confined environments. The welding voltage was adjusted to gradually vary the transfer stability. It was found that the richer the composition of the shielding gas is in CO2, the more CO and CO2 are generated by the arc. However, unlike fume emission, voltage and transfer stability had no effect on the generation of these gases. It was also found that despite the large quantity of CO and CO2 emitted by the arc, especially when using pure CO2 shielding gas, there was no high level residual concentration of CO and CO2 in or near the worker’s breathing zone, even in confined work cells.

Electrophysical characteristics of arc and formation of welded joints for welding with a non-consumable electrode

The influence of non-consumable electrode design and shielding-gas composition on the arc force effects on a welded metal is studied here, due to their impact in improving the quality of welding processes at high currents and speeds. A physical model of the welding arc in inert gases is proposed; this model includes consideration for the working area shape of the non-consumable electrode, the dependence of the materials’ thermal-physical properties on temperature, the interaction of the magnetic field produced by the electrode with the discharge self-magnetic field, and the correlation of these parameters with the force effect of the arc on the weld pool. The physical model helps to clarify the main correlations of the electrode working area construction, history of cathode processes, shielding-gas composition, and magnetic-field configuration near the cathode spot with the arc thermal-force effect on the weld pool. Experiments involving different electrode constructions and shielding-gas compositions demonstrate that, in order to avoid seam-formation defects at high welding currents and speeds, such electrodes should be used while ensuring the existence of the arc with a diffused cathode spot, and the helium concentration should be increased in the shielding gas when welding with a conical electrode.

Effect of Shielding Gas Mixture on Gas Metal Arc Welding (GMAW) of Low Carbon Steel (LR Grade A)

The aimed of this research is to determine the feasibility and effect of the mixture of the shielding gas in the physical and mechanical properties. Low carbon steel LR grade A in a thickness 12 mm were joined in butt joint types using GMAW (Gas Metal Arc Welding) with groove’s gap 5 mm and groove angle’s 400 with variation of shielding gas composition. The composition of shielding gas that used were 100% Ar, 100 % CO2 and 50% Ar + 50 % CO2. The measured of mechanical properties with regard to strength, hardness and toughness using, tensile test, bending test, Vickers hardness Test, and Charpy impact test respectively. The physical properties examined with optical microscope. Results show that tensile strength of welding metals are higher than raw materials. Welds metal with mixing Ar + CO shielding gas has the highest tensile strength. Hardness of weld metals with the shielding gas 100% Ar, 100 % CO2 and 50% Ar + 50 % CO2 are 244.9; 209.4; and 209.4 VHN respectively. The temperature of Charpy test was varied to find the transition temperature of the materials. The temperature that used were –60°C, -40°C, -20°C, 0°C, 20°C , and room temperature. Weld metals with various shielding gas have similar trends of toughness flux that was corellated with the microstructure of weld .

Investigation on microstructure evolution and properties of duplex stainless steel joint multi-pass welded by using different methods

We investigated the microstructure, impact toughness, and pitting corrosion resistance of duplex stainless steel (DSS) welding joints fabricated by using gas tungsten arc welding (GTAW) and flux-cored arc welding (FCAW) with different shielding gas compositions. N2-supplemented shielding gas during the GTAW process significantly facilitated austenite formation and reduced amounts of chromium nitride (Cr2N) precipitation tendency, thereby resulting in an improvement in impact toughness. The heat-affected zone (HAZ) had relatively low toughness because of an insufficient austenite content and Cr2N and σ-phase precipitation. Dimple fracture was the main fracture mode of the weld metal. Large irregular inclusions resulting in discontinuous dimple fractures mainly contributed to the lowest level of toughness in the FCAW weld metal. The HAZ fracture mode was dominated by the ferrite quasi-cleavage fracture. The base metal exhibited a mixed fracture mode of alternating dimple and quasi-cleavage. Furthermore, the pitting resistance of the whole joint was predominated by the HAZ. The N2-supplemented shielding gas significantly improved the pitting resistance of the GTAW joint. The pits were prone to form in the secondary austenite and around Cr2N. Moreover, an abundance of inclusions in the FCAW weld metal resulted in adverse effects on the pitting resistance.

Influence of Argon-Nitrogen Gas to Balance the Microstructure in the Welding of Super Duplex Stainless Steel

Super duplex stainless steel is steel that has a corrosion resistance and good mechanical strength so that used in industry especially in oil and gas and petrochemical industry. In use in the field is often used for the connection process by welding methods. To produce good welds, it should be noted that the welding procedures and parameters used , especially the heat input. In this study is used the heat input variables shielding gas composition to determine how much influence on the balance of ferrite - austenite phase structure in the weld stainless steels SAF 2507 super duplex with tungsten inert gas welding method (TIG). Heat input varied by applying different welding speed 1,3,4 and 5 mm /sec while the shielding gas is used 100 % argon, 98 % argon + 2 % nitrogen and 95 % argon + 5 % nitrogen. The result showed that at different welding speeds generated depth and width of the weld metal which is different. Likewise the use of protective gas will produce a different ratio wide and deep of weld metal which is different. By using protective gas 95 % argon + 5 % nitrogen squeak - ausenit phase, resulting in weld metal that is relatively balanced than others. On a slow welding in addition to produce a large heat input also produces weld metal hardness at high and affect the growth of the austenite phase. The higher the heat input ( 2,280 kJ / mm ) , the lower the austenite phase in the weld metal.

Fiber laser-MIG hybrid welding of 5 mm 5083 aluminum alloy

Aluminum and its alloys are difficult to weld due to their specific characteristics. New joining methods such as high power fiber laser-MIG can provide higher overall productivity compared to the arc welding or laser beam welding. There is huge lack of information on how the specific welding parameters in laser-arc hybrid welding affect quality of welds such as torch arrangement, distance between heat sources and shielding gas composition while other parameters were kept at constant. Laser-arc hybrid welds with short separation distance between sources produced severe porosity in one pass 5mm thick aluminum alloy sheets welding due to unstable interactions and keyhole frequent collapses. Higher process stability and lower porosity level can be achieved by applying trailing torch arrangement. Addition of significantly more expensive helium to the shielding gas did not provide any benefits in terms of porosity decrease, process stability and mechanical properties of welds overall as was expected with selected welding parameters.

Environmental Criteria for Shielding Gas Selection during Arc Welding of Stainless Steels

Gas-shielded arc welding of stainless steels belongs to processes which are characterized by the highest concentration of chromium (VI) and nickel in welding fume. These substances are carcinogenic to humans. Material and technological conditions of gas-shielded arc welding of stainless steels influence fume emission rates and chemical composition of welding fume. This fact creates the possibility of process optimization in aspect of emission rates and chemical composition of welding fume including carcinogenic compounds. This paper presents the correlation between shielding gas compositions and fume emission rates and carcinogenic substances contents during gas-shielded arc welding of stainless steels using MIG/MAG, Cold Arc and CMT methods.