Electro-gas Welding Research Articles

조선용 B Gr. 강의 용접부 미세조직과 기계적 성질에 미치는 용접기법의 영향

The microstructurale and mechanical properties of B Gr. steel were evaluated for shipbuilding according to a welding process. The following conclusions were drawn. In tandem submerged arc welding(TSAW), compared to single submerged arc welding(SAW), the grain boundary ferrite was coarsened, and the fraction was higher owing to the high heat input and low flux basicity ; conversely, the volume fraction of acicular ferrite was lower. Fine intragranular acicular ferrite and polygonal ferrite were observed in the weld metal of the electrogas welding (EGW), which had the highest heat input. In the microstructure near the fusion line, as the amount of heat input increased, the prior austenite grain boundary became coarse. Further, both the intergranular grainboundaryferrite and intragranular bainite became coarse, and the heat-affected zone became wider. The hardness of weld metal was independent of the amount of heat input and was demonstrated to be high in the order of EGW, single SAW, and TSAW owing to the microstructure difference caused by the chemical composition of the filler material and the dilution rate of the base metal. Furthermore, the tensile strength of all three welding processes resulted in stable satisfaction with the class society rules.

Comparative study of electrogas and shielded metal arc welding processes on steel A537 welded joints

In this research, the electro-gas welding process was compared with a shielded metal arc welding process for welding steel A573 from a mechanical properties point of view. Visual and radiographic inspections confirmed the soundness of weldments produced by electro-gas welding and shielded metal arc welding techniques. Various assessments were performed, including hardness, tensile strength, V-notch impact toughness, macrostructure, microstructure, and electrochemical tests. The mechanical properties of the two welding processes were closely matched, with an average tensile strength of 590 MPa for electro-gas welding and 585 MPa for shielded metal arc welding. Furthermore, the influence of welding variables, such as groove design and heat input, on the welded joints’ quality, mechanical properties, and electrochemical behavior was thoroughly examined. Dilution estimates, particularly for the electro-gas welding process, were around 35%, and a significant similarity was observed between the chemical composition determined through dilution calculations and that obtained from chemical analysis using an arc spark emission spectrometer. Notably, the electro-gas welding process demonstrated exceptional productivity, surpassing the shielded metal arc welding process by more than elevenfold. The optimum welding parameters for the electro-gas welding process were identified to achieve superior mechanical properties, low corrosion rates, and reduced consumption of the welding electrodes. This included adopting a single V type and groove angle of 30° instead of 60°, resulting in a 23% reduction in economic costs. Selecting an appropriate heat input within the range of 12 to 14 kJ/mm further contributed to enhancing overall welding efficiency.

Modification of electro gas weld metal microstructure reflecting mechanical property specifications in cruise vessel shipbuilding

AbstractTo identify the microstructural factors effecting the electro gas welding (EGW) weld metal properties, this study investigated the influence of different prototype welding consumables and shielding gases on the microstructural composition and mechanical-technological properties. The aim was to adjust the weld metal properties as a trade-off between strength, ductility, and impact toughness to fulfill typical weld metal material specifications in cruise vessel shipbuilding under consideration of the manufacturing conditions at European shipyards. The microstructure is analyzed by quantitative metallography of the ferritic matrix, martensite-retained austenite (M/A) constituents, and non-metallic inclusions (NMI). The influence of the Ni content, the deoxidation concept by variation of Si and Ti contents, and different shielding gas activity by variation of the Ar proportions is discussed. The interaction of ferritic matrix with high acicular ferrite content of about 70 ± 10%, the existence of larger grain boundary ferrite formations, and the M/A morphology plus distribution are considered as the determining factors for the material properties.

Temperature Field and Flow Field of Molten Pool in SRA EGW

This study investigates the temperature field and flow field of molten pool in seven-wire rotating arc (SRA) electrogas welding (EGW) with the methods of numerical simulations and experiments. The results show that the welding heat source swings back and forth, and the welding heat source starts to heat from the back of the welding workpiece and gradually swings to the front of the welding workpiece with the swing welding arc. The high temperature area of the molten pool and the sidewall penetration are large due to more heat on the molten pool and the sidewall from the unique rotating force, the large arc heating area, and the non-axial droplet transfer. The isotherm distribution of the molten pool is relatively uniform, and the temperature gradient gradually decreases. The simulated welding morphology is generally consistent with the experimental welding morphology with the same welding parameters, which indicates the correctness of the numerical analysis model of the welding temperature field and flow field.

Methods to reduce residual welding stresses in mining excavator metal structures

Residual stresses in metal structures of mining machinery caused by welding occur due to simultaneous uneven heating and cooling of local sections of structures, variable cooling rates in the different areas of the weld and deformations caused by metallurgical phase transformations. Residual stress in the welded joint can significantly increase the external load that can lead to structural failure. Research on the calculation, measurement and relief of residual stresses under welding is an important issue when predicting the service life of metal structure units of mining machinery and equipment. An accurate quantitative estimation of residual stresses in welded products, repair welds included, as well as the search for the fundamental principles of the elimination methods of residual deformations are of considerable practical interest, which is relevant for the authors of this paper. The study involved a general review of the latest researches in the field of estimation and measurement of residual stresses caused by electrogas welding. It has been proposed to use various techniques and analytical methods for quantitative estimation of welded joint residual stresses on the basis of fracture mechanics, which enabled to take preventative measures at early stages to reduce the cost of repair and maintenance of welded metal structures of mining excavators. The conducted study resulted in formulating the proposals on relief of residual welding stresses in the metal structures of mining excavators.

A Comparison of Vertical Electro-Gas Welding and Submerged arc Welding Methods on the Corrosion Behaviors of Crude Oil Storage Tank Steel in Simulated Seawater

A Comparison of Vertical Electro-Gas Welding and Submerged arc Welding Methods on the Corrosion Behaviors of Crude Oil Storage Tank Steel in Simulated Seawater

Effect of Defects on Structural Integrity in High-Heat-Input Weldment

With the rapid increase in the size of container ships, the steel plates used for ship hulls have increased in thickness. The use of thick plates leads to an increase in welding. Alternative welding processes such as electro gas welding (EGW), with high heat input have been replacing the multi-pass flux cored arc welding process. Shipbuilding companies have tended to use EGW increasingly to improve productivity. However, because the toughness of steel tends to decrease for thicker plates, brittle fracture requireded more attention. Although some research on high-heat-input EGW weld joints has been performed, much less attention has been paid to estimating the integrity of defective high-heat-input weld joints. The purpose of this study was to determine the reliability of EGW weld joints for thick plates. To do so, the fracture toughness of EGW weld joints was investigated. In addition, to estimate the integrity of defective welds, the fatigue characteristics of experimentally reproduced defective welds were examined. Based on these investigations, an engineering critical assessmentwas conducted. As a result, a standard for the allowable defect size for field application according to the defect type is proposed.

Effect of Ti/N Ratio on Grain Growth Inhibition in the Coarse-Grained Heat-Affected Zone of Low Carbon Steels Simulated for Ultra-High Heat Input and Tandem Electro-Gas Welding

Effect of Ti/N Ratio on Grain Growth Inhibition in the Coarse-Grained Heat-Affected Zone of Low Carbon Steels Simulated for Ultra-High Heat Input and Tandem Electro-Gas Welding

The Effect of Heat Source Path on Thermal Evolution during Electro-Gas Welding of Thick Steel Plates.

In recent years, the shipbuilding industry has experienced a growing demand for tighter control and higher strength requirements in thick steel plate welding. Electro-gas welding (EGW) is a high heat input welding method, widely used to improve the welding efficiency of thick plates. Modelling the EGW process of thick steel plates has been challenging due to difficulties in accurately depicting the heat source path movement. An EGW experiment on 30 mm thickness E36 steel plates was conducted in this study. A semi-ellipsoid heat source model was implemented, and its movement was mathematically expressed using linear, sinusoidal, or oscillate-stop paths. The geometry of welding joints, process variables, and steel composition are taken from industrial scale experiments. The resulting thermal evolutions across all heat source-path approaches were verified against experimental observations. Practical industrial recommendations are provided and discussed in terms of the fusion quality for E36 steel plates with a heat input of 157 kJ/cm. It was found that the oscillate-stop heat path predicts thermal profile more accurately than the sinusoidal function and linear heat path for EGW welding of 30 mm thickness and above. The linear heat path approach is recommended for E36 steel plate thickness up to 20 mm, whereas maximum thickness up to 30 mm is appropriate for sinusoidal path, and maximum thickness up to 35 mm is appropriate for oscillate-stop path in EGW welding, assuming constant heat input.

Microstructure features and formation mechanism in a newly developed electroslag welding

Electroslag welding (ESW) is known to show higher heat input than electrogas welding (EGW), resulting in poor low-temperature toughness. However, a newly developed ESW (dev. ESW) method using low-resistivity slag bath exhibited excellent low-temperature toughness as a result of lower effective heat input than conventional EGW, as demonstrated by the faster cooling rates measured in weld metals and estimated using finite element method analyses. This led to much shallower molten pool in the dev. ESW, resulting in much finer columnar grains and thinner centerline axial grains. High cooling speed in the dev. ESW method appeared to contribute to increased acicular ferrite proportion. The uniform microstructure with large acicular ferrite proportion and small number of inclusions in the weld metal permitted the dev. ESW weld metal to possess little variation in Charpy impact energy across the center of weld metal.

Heterogeneous Microstructure-Induced Mechanical Responses in Various Sub-Zones of EH420 Shipbuilding Steel Welded Joint Under High Heat Input Electro-Gas Welding

Heterogeneous microstructure-induced mechanical responses in EH420 shipbuilding steel welded joint by electro-gas welding processed have been systematically studied by scanning electron microscopy, electron backscatter diffraction and mechanical testing. Comparing with the coarse-grained heat-affected zone (CGHAZ), the weld metal presents higher toughness (129.3 J vs. 37.3 J) as it contains a large number of acicular ferrites with high-angle grain boundaries (frequency 79.2%) and special grain boundary ∑3 (frequency 55.3%). Moreover, coarse austenite grains in CGHAZ and slender martensite–austenite constituents between bainite laths may likely facilitate crack propagation. Polygonal ferrites and tempered pearlites formed at the junction of the fine-grained heat-affected zone and the intercritical heat-affected zone induced a softened zone with an average hardness of 185 HV0.5, which is the main reason for the occurrence of tensile fracture.

The decoupling behavior of arc coupling and rotating in seven-wire rotating arc EGW

Abstract In the present study, the decoupling behavior of the arc coupling and rotating in the seven-wire rotating arc electrogas welding (EGW) is studied. It is found that the arc motion processes is composed of the arc axial motion process, arc coupled motion process, and arc circumferential rotation process. The arc is moving up and down along the axial direction. Moreover, it is observed that as the welding current increases, the arc axial motion frequency accelerates while the corresponding motion amplitude decreases. The arc coupled motion process does not always exist, and the arc coupled motion time and arc coupled forces increase as the welding current increases. Obtained results show that the arc axial motion hinders the arc coupled motion and the arc circumferential rotation. Meanwhile, the arc coupled motion and circumferential rotation are more obvious as the welding current increases.

Droplet formation and motion characteristics in seven-wire rotating arc electrogas welding

This paper investigates the droplet formation and motion characteristics in seven-wire rotating arc electrogas welding. A high-speed video camera was used to observe the droplet formation and motion behaviors. The forces on the droplet in different welding parameters were analyzed to explain the droplet formation and motion processes. The results show that the small droplets at the end of six peripheral wires accumulate and grow toward the small droplet at the end of the center wire under the action of the electromagnetic force, and the coupled droplet forms under the action of electromagnetic force and surface tension at the end of the center wire. Gravity, plasma flow force, and rotating force affect the fall of the coupled droplet through the arc space and show non-axial motion and axial motion with different welding currents.

A study on sidewall penetration of cable-type welding wire electrogas welding

Cable-type welding wire (CWW) electrogas welding (EGW) is an innovative process in which CWW is used as the consumable electrode. Seven wires can be melted simultaneously with only one welding power source, one wire feeder, and one welding torch. This paper reports a study of the sidewall penetration of CWW EGW. The results showed that all the mechanical properties of CWW EGW welded joints met the standards of the China Classification Society (CCS). The arc heating area of CWW EGW was large and that the unique rotating arc of CWW EGW had a strong stirring effect, enhancing convective motion of the molten pool and accelerating heat transfer between the superheated molten pool and the sidewall. The droplet of the CWW EGW appeared to be non-axial transfer due to the rotating force. The superheated droplet transferred to the sidewall or the molten pool near the sidewall directly, promoting the heating and melting of the base metal.

Corrosion behavior of the high strength low alloy steel joined by vertical electro-gas welding and submerged arc welding methods

Abstract The high strength low alloy (HSLA) steel used as a large crude oil storage tank (LCOST) was often welded by vertical electro-gas welding (VEGW) and submerged arc welding (SAW). The VEGW specimen was produced by single-pass weld with high heat input (about 100 KJ/cm), and the SAW specimen was manufactured by mutil-pass weld with low heat input (about 30 KJ/cm). The corrosion behaviors of both samples were studied by electrochemical techniques and surface methods. The research results achieved in this investigation disclosed that the welding process played an important role in obtaining satisfactory corrosion property. In comparison with the SAW joint, the VEGW joint showed uniform microstructure and coarse micro-phase. The scanning vibrating electrode technique (SVET) results demonstrated that the corrosion of the VEGW joint majorly took in the heat effect zone (HAZ) and the attack for the SAW joint mainly occurred in the fusion zone (FZ). In addition, the scanning electron microscopy (SEM) results exhibited that the VEGW joint exhibited a light local attack and the SAW joint demonstrated a heavy uniform corrosion. The electrochemical results showed that the VEGW joint showed lower corrosion rate than the SAW joint. In summary, it can be discovered that the corrosion rates of welded specimens were associated with the welding-pass and the corrosion forms of welded specimens were related to the heat input energy.

극후물재 용접부 내부잔류응력 측정기술 및 특성

Abstract Recent keywords of the heavy industries are large-scale structure and productivity. Especially, the sizes of the commercial vessels and the offshore structures have been gradually increased to deliver goods and explore or produce oil and natural gas in the Arctic. High heat input welding processes such as electro gas welding (EGW) have been widely used for welding thick steel plates with flux-cored arc welding (FCAW),especially in the shipbuilding industries. Because high heat input welding may cause the detrimental effects on the fracture toughness of the welded joint and the heat affected zone, it is essential to obtain the sufficienttoughness of welded joint. There are well known that the fracture toughness like CTOD, CVN, and KIC were very important factors in order to secure the safety of the structures. Furthermore, the welding residual stress should be considered to estimate the unstable fracture in both EGW and FCAW. However, there are no references on the welding residual stress distribution of EGW and FCAW with thick steel plates. Therefore the welding residual stresses were very important elements to evaluate the safety of the welded structure. Based on the measurement results, the characteristics of residual stress distribution through thicknesswere compared between one-pass electron gas welding and multi-pass flux-cored arc welding. The longitudinal residual stress in the multi-pass flux-cored arc welding is tensile through all thicknesses in the welding fusion zone. Meanwhile, longitudinal residual stress of EGW is tensile on both surfaces and compressive at the insideof the plate. The magnitude of residual stresses by electron gas welding is lower than that by flux-cored arc welding.Key Words : Welding residual stress, Thick steel plate, Heat input, Fracture toughnessISSN 2466-2232Online ISSN 2466-2100

선체구조용 EH36 TMCP 후판의 FCAW 및 EGW 조합 용접부 기계적 성질에 미치는 개선조건의 영향

Characterization of microstructures and mechanical properties of 83mm thickness EH36-TM welds produced by the combined flux cored arc (FCA) and electro gas (EG) welding processes has been studied with the two different groove conditions, single-V (SV) and double-V (DV) bevels. The welding consumables used for FCA and EG welding processes were ASME/AWS A5.29 (E81T1-K2) and A5.26 (EG72T), respectively. Experimental results showed that all the mechanical properties of welds such as tensile property, CVN toughness and Vickers hardness met IACS requirements. The tensile strength of EG welded plates were reduced by approximately 4% (DV: 3.8%, SV: 4.2%) compared to the base metal. The hardness value of SV-beveled weld metal was slightly lower than that of DV-beveled one. There were no significant differences as per welding groove conditions except for the weld metal. In addition, at the fusion line, the toughness of SV condition was 20J lower and the weld metal was 40J lower than DV condition, respectively. On the basis of microstructural analysis, grain boundary ferrite (GBF) structures for SV condition were 2 times higher volume fraction than for DV condition and their packet sizes were coarsened to almost double. It was thus suggested that the GBF volume fractions and packet sizes in the weld metal of EH36-TM steel plates are the most important factors affecting the mechanical properties of the combined FCA and EG welded joint. Nevertheless, all the results of welds with both DV and SV conditions were found to be excellent.

Finite element analysis of residual stress distribution in a thick plate joined using two-pole tandem electro-gas welding

Abstract A computational approach considering moving heat sources was introduced to predict the residual stress distribution produced by electro-gas welding (EGW) joints. Considering the two-pole tandem of EGW, a finite element analysis (FEA) was suggested to evaluate the thermal behavior of EGW applied to a joint of ultra-thick plates. Based on a thermo-mechanical FEA, the profiles of the residual stresses are investigated for EH40 thermo-mechanical control process (TMCP) steel plates with a thickness of 80 mm. In order to simulate the weaving motion of two weldment poles, a quasi-steady heat flux model is introduced based on Goldak’s double ellipsoidal heat source model. The X-ray diffraction methods were used to measure the residual stress field on the surface treated by chemical polishing. The residual stress profiles determined by the FEA and measurement showed quite good agreement, as regards the values both peaks and of the profile. Residual stresses relieved by post-weld treatments, particularly by ultrasonic peening and toe grinding, is also presented.

Numerical analysis on the welding residual stress and fracture toughness of the heavy thick steel welded joints by welding processes

This study examined the welding residual stress and fracture toughness of 78mm thick steel electro gas welding (EGW) and flux cored arc welding (FCAW) welded joints by numerical analyses of the thermal elasto-plastic behavior and fracture toughness(KIC). The residual stress, fracture toughness characteristics and production mechanism on the welded joints were clarified. Moreover, the effects of the welding process (EGW and FCAW) on the welding residual stresses and fracture toughness of welded joints were evaluated. The results showed that the new welding process (EGW) appears to be an effective substitute for the existing welding process (FCAW) in a thick steel plate with high strength.

Structural Integrity Assessments by Measuring of Residual Stresses and Brittle Crack Toughness: A Thick Large-Scale Welding Study

Residual stresses inherently occur in welds and through-thickness distributions in an extra thick weld is unclear to date, though it is important in various steel, plant, and shipbuilding industries. Here introduce a recent complementary technique to determine residual stress measurement methods. Spatial variations of residual stresses were determined through the thickness of 70-mm thick ferritic steel welds created using low heat-input (1.7 kJ/mm) one-pass electro-gas welding (EGW) and high heat-input (56 kJ/mm) multi-pass flux-cored arc welding (FCAW). The results show that significant tensile stresses (about 90% of yield strength) occur along the weld centerline near the top surface (within 10% of the depth) in the FCAW specimen. Meanwhile, in the EGW weld, the peak stress moved towards the heat-affected zone at a depth of about 40% of the thickness due to the high heat-input. Secondly, large-scale (1 x 1 m) brittle fracture experiments have been performed to examine the brittle crack-arrest toughness and crack propagation path in each case. The fracture behavior compares to the observations of the grain size, hardness, and Charpy impact energy of the localized crack region in each weld. This study provides an insight in terms of the relevance between residual stresses and the brittle fracture behavior.