Plasma Arc Welding Research Articles

Effects of Nitrogen on Microstructure and Properties of SDSS 2507 Weld Joints by Gas Focusing Plasma Arc Welding.

Regulating the phase ratio between austenite and ferrite in welded joints is crucial for welding super duplex stainless steel. Nitrogen plays a significant role in maintaining an optimal phase ratio. In this study, the focusing gas channel of gas-focused plasma arc welding was utilized to introduce nitrogen into the arc plasma, which was then transferred to the weld pool. Experiments with and without nitrogen addition were designed and conducted to examine the effects of nitrogen on the microstructure and properties of SDSS 2507 weld joints. The results show that nitrogen addition increased the austenite content in the weld metal from 22.2% to 40.2%. Nitrogen also altered the microstructure of the austenite, changing it from thin grain boundary austenite and small intragranular austenite to a large volume of coarse, side-plate Widmanstätten austenite. The ferrite in the weld metal exhibited a preferred orientation during growth, while the austenite showed a disordered orientation. Additionally, the maximum texture intensity of the ferrite decreased with nitrogen addition. Nitrogen addition led to an increase in the microhardness of the austenite in the weld metal, attributed to the solid solution strengthening effect of nitrogen and increased dislocation tangling, while it decreased the microhardness of the ferrite. This study enhances the welding theory of 2507 super duplex stainless steel and guides the practical application of gas-focused plasma arc welding for 2507 super duplex stainless steel.

A Review of Welding Process for UNS S32750 Super Duplex Stainless Steel.

Super duplex stainless steel UNS S32750 is widely used in marine industries, pulp and paper industries, and the offshore oil and gas industry. Welding manufacturing is one of the main manufacturing processes to make material into products in the above fields. It is of great importance to obtain high-quality welded UNS S32750 joints. The austenite content and ferrite content in UNS S32750 play an important role in determining UNS S32750 properties such as mechanical properties and corrosion resistance. However, the phase proportion between the ferrite phase and austenite phase in the welded joint will be changed during welding. Lots of research has been done on how to weld UNS S32750 and how to obtain welded joints with good quality. In this work, the recent studies on welding UNS S32750 are categorized based on the welding process. The welding process for UNS S32750 will be classified as gas tungsten arc welding, submerged arc welding, plasma arc welding, laser beam welding, electron beam welding, friction stir welding, and laser-MIG hybrid welding, and each will be reviewed in turn. The microstructure and properties of the joints welded using different welding processes will also be discussed. The critical challenge of balancing the two phases of austenite and ferrite in UNS S32750 welded joints will be discussed. This review about the welding process for UNS S32750 will provide people in the welding field with some advice on welding UNS S32750 super duplex stainless steel.

Comparative investigation on the microstructure and corrosion properties of surfacing cobalt alloys by various methods

This study applies three different welding methods, namely tungsten inert gas (TIG) welding, laser welding, and plasma arc welding, to perform cobalt alloy surfacing on austenitic stainless steel substrates, and compares their microstructure and corrosion properties. The results reveal that samples obtained through all three methods exhibit excellent metallurgical bonding between the austenitic stainless steel substrate and the cobalt alloy surfacing layer, with no observed defects such as cracks, pores, or inclusions. Among them, the cobalt alloy surfacing layer produced by laser welding shows a finer and more uniform microstructure, displaying a distinct growth direction along the surfacing direction away from the interface. Additionally, electrochemical polarization curve testing demonstrates that the corrosion resistance of the laser-welded surfacing layer surpasses that of TIG welding and plasma arc welding, exhibiting a lower corrosion rate. This study offers valuable insights into the selection of cobalt alloy surfacing welding methods on austenitic stainless steel substrates and the evaluation of the corrosion properties for the cobalt alloy surfacing layer, providing essential guidance for engineering practices in the power plant valves.

Induction assisted autogenous plasma arc welding of HSLA steel

In this work, a high frequency induction heating (HFIH) assisted plasma arc welding (IPAW) technique is proposed to weld 6 mm thick S690QL high strength low alloy steel plates in square butt joint configuration and without using any filler material. A 3D finite element based coupled electromagnetic-thermal analysis is carried out to ascertain the weld's thermal characteristics. Microstructure evolution and mechanical performance are investigated using scanning electron microscopy, electron back scattered diffraction, transmission electron microscopy, tensile test, Charpy impact test and micro hardness test. The results demonstrate that 15 s initial static heating using a co-directional current coil with magnetic flux concentrator predominantly improves the weld penetration by 48 % and joint efficiency reaches 90 % to the base plate strength. Microstructural study shows that the addition of HFIH promotes low angle grain boundaries (LAGB) with bainite ferrite and granular bainite micro-constituents in the fusion zone, which causes localised yielding and failure in this zone during tensile test. Further investigation reveals that the HFIH encourages the formation of BI-type bainite ferrite laths of 1.3–2.2 μm width, combined with slender martensite-austenite (M-A) island at the bainite ferrite lath boundaries. The results also reveal that the induction heating promotes the formation of M23C6 precipitates and B2 structured Cu-enrich nano precipitates in the fusion zone (FZ). The microhardness distribution indicates that the FZ and coarse grain heat affected zone are significantly reduced due to the assistance of the HFIH. The impact test result shows a lower energy absorption by the IPAW weldments due to dominance of the LAGB with unfavourable strain distribution.

Crucial effects of plasma gas on the weld and microstructural characteristics of plasma arc welded aero engine Ti6Al4V alloy joints

This study explores the influence of plasma gas flow rate (PGFR) on the defects, microstructure evolution and mechanical properties during plasma arc welding of Ti6Al4V titanium alloy thin sheets using microscopic analysis, spectroscopic analysis, tensile and microhardness tests. The variation in PGFR affects the welding arc in terms of its stability, pressure and constriction which results in transformation of arc from conduction mode to keyhole mode and changes in microstructure as well. All the other welding process parameters were kept constant except for PGFR which was varied to investigate its significance. Excess weld metal was observed under the weld bead is an attribute of keyhole formation. Macrographs exhibits increments in weld geometry measurements whereas weld defects such as lack of penetration and porosity decreased with increased PGFR. The microstructural examination showed a variety of phase formations that includes majorly with acicular α and Widmanstätten α morphologies. Tensile strength and hardness at the weld region of the welded joints increases with increase in PGFR. An oxygen rich brittle subsurface layer called α-case morphology was observed at the weld region of 1 L/min joint causes significant reduction in ductility.

Mechanical properties and corrosion resistance of TC4 titanium alloy joints by plasma arc welding + gas tungsten arc welding combination welding

Mechanical properties and corrosion resistance of TC4 titanium alloy joints by plasma arc welding + gas tungsten arc welding combination welding

Structure and mechanical properties of Ti2AlNb-based alloy welded joints using keyhole plasma arc welding with subsequent heat treatment

Using keyhole plasma arc welding, welded joints of a Ti2AlNb-based alloy, VTI-4, were obtained, and their structure and mechanical properties were studied. It has been established that the dynamic effect of a keyhole arc had a positive effect on the quality of the welded joint; namely, lack of penetration, porosity, and microcracks were eliminated. The welded joint consisted of a fusion zone (FZ), a heat-affected zone (HAZ), and a base metal (BM). Depending on the phase composition and morphology of the obtained phases, the HAZ can be divided into four zones: HAZ1 with large β-phase grains near the melting line, HAZ2 with large β-phase grains + α2, HAZ3 with more fragmented β-phase grains retaining more α2-phase, and HAZ4 with the phase composition β + α2 + O. Subsequent heat treatment (HT: quenching at 920 °C for 2 h, cooling in air, followed by aging at 800 °C for 6 h, cooling in air) preserved the zone structure of the weld but led to the formation of the O-phase within β-grains. The microhardness of the weld in the zone corresponds to 360±15 HV0.2, but after HT, it increased to 382±20 HV0.2. The strength properties of the welded joint after HT were above 90 % of the base metal (σucs = 1120 MPa, σ0.2 = 1090 MPa), while elongation to failure is close to the initial condition (δ = 2.1 %).

Microstructure, Mechanical Properties, and Wear Behavior of Dissimilar Metallic Coatings for Steel Discs of Butterfly Valves

Abstract In the present work, coating materials that can be welded to the EN 1.6220 low-alloy steel disc of a butterfly valve and are also compatible with the seal material, i.e., 17–4 PH steel, are studied. 312 duplex stainless steel, 316 austenitic stainless steel, and Stellite 6 are identified as potential coating materials for the disc based on Cobweb analysis and are welded to the disc using metal active gas (MAG) welding (312 and 316 steel coatings) and powder plasma arc welding (Stellite 6 coating). Microstructural analyses and Vickers hardness measurements of the weld joints are performed. The surface roughness and wear behavior of the coatings are also studied. Nanoscale wear phenomena and consequent phase transformations are studied using molecular dynamics simulations. The results show that 312 and 316 stainless steels are suitable coating materials for the disc.

Microstructure, Mechanical Properties, and Corrosion Resistance of ER2209 Duplex Stainless Steel Manufactured by Plasma Arc Welding

Microstructure, Mechanical Properties, and Corrosion Resistance of ER2209 Duplex Stainless Steel Manufactured by Plasma Arc Welding

Joining Behaviour of Thick Plate Using High-Frequency Induction Assisted Arc Welding

Combining a preheating source with conventional arc welding is a promising method to study the weld quality and improvement of strength for high-strength super-alloy materials. The present research used an induction preheating source with plasma arc welding (PAW) to weld Inconel 625 thick plates. The investigation was performed at a constant induction current of 600 A, welding speed of 100 mm/min and a plasma welding current of 135 A. The induction-assisted plasma arc welding (IAPAW) demonstrated that a weld joint was possible with static induction preheating and a high plasma welding current at low welding speed. The microstructural observation showed various dendritic structures in the fusion zone (FZ). The FESEM and EDX analysis confirmed the formation of Laves phase in the interdendritic structure of the FZ. The ultimate tensile strength of the IAPAW joint reached to 658 MPa. The tensile fracture surface of the welded sample revealed a lower number of dimples, indicating the reduction of ductility. The XRD analysis was carried out at various zones and it confirmed the peak shifting towards the higher 2-theta value of the FZ.

Deposition of Functionally Graded Material Fabricated by Robot Plasma Arc Welding

Functionally graded materials (FGMs) are a new type of composite materials capable of facilitating the dependable bonding of dissimilar materials. A double‐wire plasma welding process is used to manufacture Stainless steel 316 L (SS316L)/Inconel 625 FGM. Subsequently, two thin‐walled structures with 5% gradient and non‐gradient are fabricated to investigate the morphology, microstructure, and properties in different gradients, focusing on the 67% SS316L region. In the findings, it is indicated that two depositions exhibit well‐formed structures with varying gradients and no macroscopic defects. The composition experiences an abrupt transition at the interface between depositions with a non‐gradient, whereas deposition with a 5% gradient does not exhibit this issue and demonstrates a higher effective deposition rate. The analysis of the energy dispersive spectrum indicates the presence of Nb elements at the grain boundary in the 67% SS316L region, with no observed cracks. This suggests resistance to cracking and impediment to the segregation of Nb. Additionally, the hardness and tensile strength in various regions exhibit a gradual increase with a 5% gradient of Inconel 625 content, while the tensile anisotropy is not noticeable. Consequently, the 5% gradient transition demonstrates a more favorable performance in comparison to the non‐gradient sample, resulting in the avoidance of the 75% SS316L region due to its poor performance.

Effect of Salt Spray Corrosion Performance on Variable Polarity Plasma Arc Welding of Aerospace Aluminum Alloy

Effect of Salt Spray Corrosion Performance on Variable Polarity Plasma Arc Welding of Aerospace Aluminum Alloy

Computational investigation of plasma arc welding process for aluminium alloys

Thermal stress is a very common phenomenon that occurs at the welded joint. Determination of the same at the joint is however difficult due to inhomogeneity of the weld joint metals and spreading of heat to the surroundings from the Heat Affected Zone (HAZ). Thermal stress induced at the welded joint changes the microstructure of grains which affects the mechanical properties of the welded material. Due to this, cracks may appear in the joint leading to failure of the weld. In the present study, three-dimensional model of two types of welded joint, i.e., Tee Joint and lap joint of two plates having dimensions 100 mm × 75 mm × 5 mm are prepared using ANSYS Workbench 2020 R2. Hex dominant meshing is chosen in order to have clear picture of the spread of temperature over the entire region. The change of Residual stress with variation of welding current and keeping welding voltage constant is also observed for weld joint made of Aluminium Alloy. In this study, conduct steady-state thermal analysis and structural analysis on an aluminium alloy 6063 to assess von Mises stress, von Mises strain, and deformation distribution induced by heating. Evaluate various welding joints to identify the most effective technique.

Assessing the pros and cons of wire-arc additive manufacturing for material production

A promising new method for mass-producing metal components and structures for a range of industries, including shipbuilding, automotive, aviation, and other technical sectors, is wire arc additive manufacturing (WAAM). Additive manufacturing (AM) called 3D printing, it is a disruptive manufacturing technique that starts with digital design data and manufactures products layer by layer. WAAM has been utilized to create parts from a variety of materials, such as alloy wires based on aluminium (Al), titanium (Ti) and nickel. This review article focuses on the most important facets of the WAAM process, including the technology utilized, the drawbacks encountered, the steps taken during and after the process, the tools used to monitor the process, the gases involved, and the materials. The comparison of WAAM with other additive manufacturing technologies is also emphasized in the article. Moreover, it compares and analyses several WAAM techniques, including plasma arc welding (PAW), gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) in terms of material deposition rate, the method GMAW have higher material deposition rate when compared to other approach. Material manufacturing using WAAM has great potential. The accuracy of the manufacturing and smoothness of WAAM-made parts can be enhanced in the future to better suit tight-tolerance uses.

Effect of groove angle on the residual stress and deformation of nuclear waste container cylinder body welded by plasma arc welding

AbstractAs an important barrier for high‐level radioactive waste transportation and deep burial disposal, the welding quality of nuclear waste container is particularly important. At present, nuclear waste container is usually manufactured by plasma arc welding. Therefore, in order to manufacture nuclear waste container parts with high quality, based on the finite element simulation software simufact welding, this paper uses a combination of numerical simulation and experimental verification to simulate the temperature field, stress field and deformation of the longitudinal weld of 316L nuclear waste container cylinder body by selecting different welding groove angles. The test results show that the groove angle of the V‐groove increases, the residual stress distribution and size increase, and the deformation increases. The stress value of the I‐shaped groove is between the V‐shaped groove angle of 30° and 45°, but the deformation is the smallest. In practical engineering applications, residual stress and deformation need to be considered comprehensive. Reasonable groove angle plays an important role in controlling residual stress and deformation after welding.

Development of a melt pool characteristics detection platform based on multi-information fusion of temperature fields and photodiode signals in plasma arc welding

Development of a melt pool characteristics detection platform based on multi-information fusion of temperature fields and photodiode signals in plasma arc welding

Interaction Mechanism of Arc, Keyhole, and Weld Pool in Keyhole Plasma Arc Welding: A Review.

The Keyhole Plasma Arc Welding (KPAW) process utilizes arc plasma highly constricted by a water-cooled cupper nozzle to produce great arc pressure for opening a keyhole in the weld pool, achieving full penetration to the thick plate. However, advanced control of welding is known to still be difficult due to the complexity of the process mechanism, in which thermal and dynamic interactions among the arc, keyhole, and weld pool are critically important. In KPAW, two large eddies are generally formed in the weld pool behind the keyhole by plasma shear force as the dominant driving force. These govern the heat transport process in the weld pool and have a strong influence on the weld pool formation process. The weld pool flow velocity is much faster than those of other welding processes such as Tungsten Inert Gas (TIG) welding and Gas Metal Arc (GMA) welding, enhancing the heat transport to lower the weld pool surface temperature. Since the strength and direction of this shear force strongly depend on the keyhole shape, it is possible to control the weld pool formation process by changing the keyhole shape by adjusting the torch design and operating parameters. If the lower eddy is relatively stronger, the heat transport to the bottom side increases and the penetration increases. However, burn-through is more likely to occur, and heat transport to the top side decreases, causing undercut. In order to realize further sophistication of KPAW, a deep theoretical understanding of the process mechanism is essential. In this article, the recent progress in studies regarding the interaction mechanism of arc, keyhole, and weld pool in KPAW is reviewed.

Structural design and adaptive tracking control of automatic welding robot for liquefied natural gas containment system

Liquefied natural gas (LNG) is commonly transported by LNG carriers and stored in cargo containment systems. The primary barrier of the MARK III cargo containment system is welded to a closed space with corrugated stainless steel plates. To meet the requirements of excellent sealing and thermal insulation for cargo containment, the welding process of the corrugated plate need to be strictly controlled, which poses a challenge to the development of related welding equipment. In this paper, we present a new five-axis automatic welding robot system used for plasma arc welding on corrugated surfaces. The moment transfer scheme of the dual linkage mechanism makes the rotary movement of the robot more accurate and stable which gives the system with simpler control algorithm and better overall force characteristics. To ensure tracking accuracy, a novel sensing method based on a LASER sensor, two contact sensors, and an angle sensor is proposed to implement multiple functions such as tracking the welding arc length, identifying corrugation shapes, and detecting welding gun posture. Based on the devised tracking sensor system and welding robot, a servo-control system with a surface-tracking welding control algorithm is established. The experimental results show that the robot system's welding speed is about 7 times that of hand welding and the welding qualification rate was 99%, significantly improving welding efficiency and quality as a critical equipment technology in the process of corrugated plate welding.

A novel optimizing Pulsed Plasma Gas Variable Polarity Plasma Arc Welding (PPG-VPPAW) method for improving weld quality

To enhance the reliability of aluminum alloy welding quality, a novel Pulsed Plasma Gas Variable Polarity Plasma Arc Welding (PPG-VPPAW) system is proposed. This system enables independent control and rapid adjustment of the plasma gas, allowing for flexible modulation of arc pressure output under constant thermal conditions, thereby reducing porosity and refining grain structure. The research analyzed the impact of parameters of different plasma gas on arc characteristics, welding porosity, and welding microstructure. The results reveal that the periodic changes in pulsed plasma gas induce corresponding variations in arc temperature, arc shape, arc pressure, arc voltage, and the morphology of the weld pool keyhole. The magnitude of the difference between the base value and peak value of pulsed plasma gas determines the extent of arc pressure fluctuations and the behavior of the backside keyhole. The maximum oscillation amplitude of the backside keyhole can reach up to 4.5 mm². Additionally, the oscillation of pulsed plasma gas within the molten pool has been demonstrated to effectively reduce weld porosity and refine grain size. Under this process, the grain size of the weld metal can be reduced by up to approximately 25%. Current work provides an important direction for fabricating highly reliable aluminum alloy weldments.

Plasma Arc Welding of 780CP High Strength Steel Sheet Lap Joint for Tensile Strength of 100% Compared to Base Metal

Plasma Arc Welding of 780CP High Strength Steel Sheet Lap Joint for Tensile Strength of 100% Compared to Base Metal