Flux Cored Arc Welding Process Research Articles

The Efficiency of Thermite-Assisted Underwater Wet Flux-Cored Arc Welding Process: Electrical Dependence, Microstructural Changes, and Mechanical Properties

Alumino-thermic additions to the flux-cored wire can be utilized to enhance welding heat input, improve welding productivity, and minimize the dependency on power sources in the air environment. In this article, the influence of Al/Fe2O3 thermite on electrical dependency, microstructural characteristics, and mechanical performance during the underwater wet welding of Q235 steel was investigated. The results revealed that adding exothermic flux enhanced the underwater wet welding appearance. The basicity of the slag steadily decreased from 1.77 to 0.73 because of the formation of Al2O3. Thermite increased the quantity and diameter of inclusions in the underwater wet weld metal. The excessive addition of Al/Fe2O3 thermite resulted in agglomerated inclusions in the weld metal. Significant microstructural changes from grain boundary ferrite to acicular ferrite were mainly caused by the de-oxidation products of the thermite process. When thermite was added to the flux-cored wire, the ultimate tensile strength first increased and then decreased, while the microhardness of the underwater wet welds showed an obviously increasing trend. The addition of exothermic flux additions to the flux-cored wire can help generate chemical heat and increase the energy required to melt the wire. This study established a link between thermite addition and joint performance, paving the way for the development and application of thermite-assisted self-shielded flux-cored wire.

Tribological performance under abrasive wear of Fe-Cr-C+Nb coating deposited by FCAW process

This paper aims to investigate the abrasion resistance performance of Iron-Crhomium-Carbon + Niobium (Fe-Cr-C + Nb) coatings deposited by Flux-Cored Arc Welding (FCAW) process. Two coatings conditions were prepared in a 1-layer setup, with a selfshielded tubular wire over SAE 1020 carbon steel substrate, varying the FCAW parameterization levels, searching to reproduce different conditions of welding energy and their respective effects on the coatings' properties. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) were employed in the microstructure and wear micromechanism analysis. X-ray Energy Dispersive Spectroscopy (EDS) was used for chemical composition assessment and Vickers microdurometer for hardness evaluation. In the tribological attempt, it was used the dry/sand rubber wheel apparatus according to ASTM G65. From the results, in neither sample of the two coating conditions, deleterious defects were observed on the surfaces, as well as in the cross-sections, such as lack of fusion and process interruptions. Dilutions were sufficient to ensure metallurgical bond without compromising layer geometry. Cold cracking characteristics of the process and material were observed, which did not significantly influence the performance of the coatings. The microstructure of both coatings showed CrC and NbC carbides dispersed in the Fe-matrix, whose volume fraction and mean free path between them varied as a function of dilution. The greater Nb-content and less intense heat input in the lower dilution coating provided greater refining of the CrC, NbC, and Fe-matrix strength, which was reflected in higher hardness, lower wear rate, and less severe abrasive wear micromechanism.

Experimental and Numerical Predictions of Cryogenic Leakages in Welded Steel Plates

This study presented experimental and numerical research to investigate the effect of cryogenic leakage on a plate structure of AH36-grade steel containing welded joints. To simulate the cryogenic leakage conditions, the welded plate was exposed to a temperature of −196 °C by supplying liquid nitrogen (LN2) to the center of the steel plate. The time-dependent temperature history and strain variation were measured by using thermocouples and strain gauges attached to the plate surface. Additionally, the residual stress of the middle surface section before and after the cryogenic leakage process was measured by X-ray diffraction analysis (XRD). A three-dimensional finite element model was created with the use of a commercial finite element analysis (FEA) program to simulate the flux-cored arc welding process and cryogenic leakage process. The steel surface temperature dropped sharply and reached approximately −196 °C at 160 s after LN2 supplement. After the first 650 s of the LN2 leakage experiment, the outside of the trough reached approximately −75 °C and −25 °C, depending on the location of the thermal couples. Although there was a relative difference in the results, the experiment and numerical simulation results for temperature and stress distribution showed good agreement. The results could be utilized in the ship design stage adopting welded structures as a basic database.

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.

Comparison of two-body abrasive wear resistance of high chromium boron-containing Fe–C B–13wt.%Cr Ti alloy with incomplete replacement of Cr for Cu the Fe C B 4wt.%Cr 7wt.%Cu–Ti alloy

Hardfacing process commonly employed because of its low cost and high efficiency. The microstructure of an two sample of deposited metal by X-ray diffraction, scanning electron microscope (SEM). In this research, the mechanical and tribological properties of two deposited metal of Fe–C–Cr–B–Ti alloying systems, high chromium 140Cr13Si1MnBTi alloy, and low chromium and high copper 110Cr4Cu7TiVBAl alloy hradfecing by flux-cored arc welding process (FCAW) was studied. It provided a low content of chromium (4 wt.%) and a high content of copper (7 wt.% Cu). Results of the studies had showed that the introduction of exothermic addition (CuO‒Al) to the core filler of the flux‒cored wire electrode, change melting characteristic and provides the highest resistance of the deposited metal to abrasion wear due to additional alloying by copper and reduction in grain size.

Effects of welding parameters on the angular distortion of welded steel plates

Abstract In a welding process, distortion is inevitable and causes a significant problem. Distortion could be minimized up to a specific limit by controlling the welding parameters. The expansion and contraction of the welding metal and the adjacent base metal during the heating and cooling cycles of the welding process create thermal stresses and angular distortion in a welding joint. The welding parameters determine the geometry of a weld bead. The form of the weld bead is vital in the angular distortion of butt welded plates. This article discusses the influence of some flux-cored arc welding process parameters such as shielding gas flow rate, weaving motion of welding electrodes, and torch angle on bead profile and angular distortion of St 37 steel plates of 10 mm thickness. The angular distortion decreases with the torch angle, but it increases with the gas flow rate. The electrode weaving motion consists of three components: the designed weld width, the vertical motion period in the welding direction, and the lateral motion speed normal to the welding direction. The angular distortion decreases with the weld width and the vertical motion period but decreases with the lateral speed.

Effect of austenitic stainless steel weld clad layers on conduction heat transfer across the walls of pressure vessels

Cladding austenitic stainless steels are popular nowadays in pressure vessels to enhance surface qualities. In this work, austenitic stainless-steel clad layers deposited by flux cored arc welding process on structural steel plates used in boiler construction are investigated in the direction of heat energy conservation. This study is vital, as the low thermal conductivity of austenitic stainless-steel clad layer is capable of reducing heat transfer across walls of pressure vessels. Heat transfer studies were performed using theoretical approach, computational simulations and experimental approach. Results of these studies exhibit a heat conservation of 10.6% owing to the stainless-steel clad layers with optimum clad thickness. The results of theoretical and computational method are having good agreement with the experimental results. These dual-benefit findings of the present work could be supportive to impart corrosion resistance and energy conservation, thereby, in energy efficient design of the thermal equipment.

Long-term metal fume exposure assessment of workers in a shipbuilding factory

This study aims to assess the metal fume exposure of welders and to determine exposure rates for similar exposure groups in a shipyard through the use of Near-field/Far-field (NF/FF) mathematical model and Bayesian decision analysis (BDA) technique. Emission rates of various metal fumes (i.e., total chromium (Cr), iron (Fe), lead (Pb), manganese (Mn), and nickel (Ni)) were experimentally determined for the gas metal arc welding and flux cored arc welding processes, which are commonly used in shipyards. Then the NF/FF field model which used the emission rates were further validated by welding simulation experiment, and together with long-term operation condition data obtained from the investigated shipyard, the predicted long-term exposure concentrations of workers was established and used as the prior distribution in the BDA. Along with the field monitoring metal fume concentrations which served as the likelihood distribution, the posterior decision distributions in the BDA were determined and used to assess workers’ long-term metal exposures. Results show that the predicted exposure concentrations (Cp) and the field worker’s exposure concentrations (Cm) were statistically correlated, and the high R2 (= 0.81–0.94) indicates that the proposed surrogate predicting method by the NF and FF model was adequate for predicting metal fume concentrations. The consistency in both prior and likelihood distributions suggests the resultant posterior would be more feasible to assess workers’ long-term exposures. Welders’ Fe, Mn and Pb exposures were found to exceed their corresponding action levels with a high probability (= 54%), indicating preventive measures should be taken immediately. The proposed approach provides a universal solution for conducting exposure assessment with usual limited number of personal exposure data.

Influence of the formulation of a flux-cored wire on the microstructure and hardness of welded metal

For this paper, the microstructure and hardness of the weld metal were investigated by conducting experiments with the flux cored arc welding process in underwater and air conditions. A rutile/oxidizing tubular wire was used, manufactured by the Robotics, Welding and Simulation Laboratory at Minas Gerais Federal University, especially for underwater wet welding. Underwater welds had a lower volumetric fraction of acicular ferrite in the weld metal compared to air welds. In the thermally affected zone, for both welds, there was a predominant formation of martensite. However, the grain size and width of the thermally affected zone of underwater welds are smaller. The hardness values shown correspond to the microstructure formed in the weld metal. On the other hand, in the region of the thermally affected zone, the hardness values were higher underwater welds, due to the smaller martensite grains presented.

Analytical method using SEM-EDS for metal elements present in particulate matter generated from stainless steel flux-cored arc welding process

Welding fumes (WFs) can cause occupational pneumonoconiosis and other diseases in workers. WFs have complex chemical composition and morphology depending on the welding conditions. The WF surface is a key factor affecting those diseases. The objective of this study was to establish an analytical method focused on characterizing individual WFs and welding slags (WSs) formed during CO2 arc welding processes for knowledge acquisition of risk assessment. Especially, the characterization was focused on the elemental distributions near the surfaces obtained using fluxing agents and size of the WFs. WFs were collected using personal samplers. After welding, WS was also collected. The fluxing elemental distribution (e.g., Bi) near the surfaces WS and WFs were analyzed through scanning electron microscopy and energy-dispersive X-ray spectroscopy. As a result, some of the micron-sized spherical particles (SPs) grew by incorporating nanosized primary particles composed of other metal species. The fluxing agents formed elemental distribution patterns on the SP surface. Bi were dotted in an agglomerate. Mn amount in WS depends on Mn amount in the WFs. These results obtained through the analysis of both the WS and WF surface as well as the particle sizes will facilitate the establishment of exposure assessment models.

A Study on the Weldment Hardening Discrimination Procedure and Improvement of Flux Cored Arc Welding Process of ASTM A553-1 (9% Nickel Steel) Material Using Bead Geometry Distribution

As a result of strengthened sulfur content standards for ship fuel oil in IMO regulations, major domestic and foreign carriers have a high and growing demand for liquefied natural gas (LNG) powered ships and related equipment. For LNG operation in a cryogenic environment, a storage tank and fuel supply system that uses steel with excellent brittleness and fatigue strength is required. Ships that use LNG have a high vulnerability to explosion and fire. For this reason, 9% Ni is typically used, since a ship requires high quality products with special materials and structural technologies that guarantee operability at cryogenic temperatures. However, there is an urgent need for research to derive a uniform welding quality, since high process difficulty and differences in welding quality related to a welder’s skills can cause a deterioration of the weld quality in the 9% Ni steel welding process. For 9% Ni steel, the higher the dilution ratio of the base metal, the lower the strength. In order to secure the required strength, excessive dilution of the base metal should be avoided, and the relationship between dilution ratio and strength should be investigated. According to previous research, if it exceeds 25% it may be lower than the API standard of 363 MPa for hardening welds. Therefore, in this study, the flux cored arc welding process is performed by establishing criteria that can be evaluated based on the SVM method in order to determine the structure of the weld to be cured according to the dilution rate of the base metal. We would like to propose a multipurpose optimization algorithm to ensure uniform quality of 9% Ni steel.

Real-Time Weld Gap Monitoring and Quality Control Algorithm during Weaving Flux-Cored Arc Welding Using Deep Learning

In the flux-cored arc welding process, which is most widely used in shipbuilding, a constantexternal weld bead shape is an important factor in determining proper weld quality; however, thesize of the weld gap is generally not constant, owing to errors generated during the shell formingprocess; moreover, a constant external bead shape for the welding joint is difficult to obtain whenthe weld gap changes. Therefore, this paper presents a method for monitoring the weld gap andcontrolling the weld deposition rate based on a deep neural network (DNN) for the automationof the hull block welding process. Welding experiments were performed with a welding robotsynchronized with the welding machine, and the welding quality was classified according to theexperimental results. Welding current and voltage signals, as the robot passed through the weldseam, were measured using a trigger device and analyzed in the time domain and frequency domain,respectively. From the analyzed data, 24 feature variables were extracted and used as input for theproposed DNN model. Consequently, the offline and online performance verification results for newexperimental data using the proposed DNN model were 93% and 85%, respectively

Microstructure, Mechanical and Corrosion Properties of UNS 32205 Duplex Stainless Steel Weldment Joints by Multipass FCAW

Abstract In this study, the effect of multipass welding on the microstructure, mechanical and corrosion properties of the UNS 32205 duplex stainless steels (DSS) is investigated. The UNS 32205 DSS is welded in 3 or 7 passes by flux-cored arc welding (FCAW) using E2209 T1 – 1/4 flux cored wire. The weldments are characterized by light optical microscopy (LOM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Feritscope analysis, Charpy impact tests and electrochemical corrosion tests. The results suggest that the multipass FCAW process induces the formation of γ2 in the weld seam. The mechanical and the corrosion properties of the weld joints are affected by the heat input variation and the phase transformations. Especially, the formation of the γ2 in the weld seam results in a decrease in the corrosion resistance of the joint samples.

Study of arc welding stability in flux cored arc welding process and pulsed continuous current

ABSTRACT In the execution of a welding process, there are a large number of variables that need to be adjusted by the operator/welder to improve stability of the process. The quality of the welding process is closely linked to the stability that has been carried out. In this work, the coating welding process in pulsed direct current with Gas-Shielded Flux Cored Arc Welding (FCAW-G) was used, having SAE 1020 steel as base metal and martensitic stainless steel 410NiMo with 1.2 mm in diameter as additional metal. Current and voltage data were analysed to verify, using computational tools and the Vilarinho Regularity Index (IVcc ), the performed process. It was observed that the effectiveness of the tools was used as a way of detecting the phenomena of voltage signal variation, which serve as indications of drop detachment. Five samples were extracted from the test, where the occurrence of voltage peaks was noted, indicating the occurrence of drop detachment in a stable manner, according to the result observed by the Vilarinho Regularity Index (IVcc ).

Research for the Optimal Flux-Cored Arc Welding Process of 9% Nickel Steel Using Multi Object Optimization with Solidification Crack Susceptibility.

The environment of the global shipbuilding market is changing rapidly. Recently, the International Maritime Organization (IMO) has tightened regulations on sulfur oxide content standards for marine fuels and tightened sulfur oxide emission standards for the entire coastal region of China to consider the environment globally and use LNG as a fuel. There is a tendency for the number of vessels to operate to increase significantly. To use cryogenic LNG fuel, various pieces of equipment, such as storage tanks or valves, are required, and equipment using steel, which has excellent impact toughness in cryogenic environments, is required. Four steel types are specified in the IGG Code, and 9% Ni steel is mostly used for LNG fuel equipment. However, to secure safety at cryogenic temperatures, a systematic study investigating the causes of quality deterioration occurring in the 9% Ni steel welding process is required and a discrimination function capable of quality evaluation is urgent. Therefore, this study proposes a plan where the uniform quality of 9% Nickel steel is secured by reviewing the tendency of the solidification crack susceptibility among the quality problems of cryogenic steel to establish the criteria for quality deterioration and to develop a system capable of quality discrimination and defect avoidance.

Metal Transfer Mapping for Flux-Cored Arc Welding Process by Using Near-Infrared Filming

In the flux-cored arc welding (FCAW) process, the transfer of filler metal to the base material to accomplish the weld bead, determines the weld quality. It must be pointed out that the radiation emitted from the weld arc, fumes and particles (spattering) in this process represent a barrier for these studies based on the process visualization. The objective of this study is to assess metal transfer during the FCAW process of ASTM 1020 steel by filming the phenomena with assistant of near-infrared visualization, contributing to a better understanding of this process and to evaluate characteristics of metal transfer. It can clearly be seen that how the droplet is created and transferred in this process and also identify the different modes of metal transfer by changing the parameters of voltage and wire feed speed in metal transfer maps. Finally, having achieved the metal transfer maps, the suitable condition and approach for developing arc control strategies for the FCAW process were introduced.

Control of droplet transfer using a filler-wire in tandem arc welding

In this paper, the tandem flux-cored arc welding process was enhanced to improve weld productivity. Additional filler-wire of opposite polarity was used to prevent deterioration of weld quality that occurred due to arc interaction at two electrodes. Droplet transfer is one of the main factors which determine the quality of the weldment. In the tandem process, it is difficult to control droplet transfer due to arc interaction. In the hybrid welding process developed for stabilising the molten pool, the arc interaction and droplet transfers of the two electrodes in the hybrid process were investigated according to the feeding location and applied current of the filler-wire. This presented a method for improving the penetration depth and bead appearance of the weldment.

Robust regression analysis for the relationship between welding parameters and microhardness of 410 NiMo martensitic steel deposits on SAE 1020 steel

The objective of this study was to analyze the flux-cored arc welding (FCAW) welding parameters and microhardness levels on surface quality of 410 NiMo martensitic stainless-steel coatings. The parameters of the FCAW process applied to the coating, included pulsation frequency, voltage, welding speed, average current and contact tip to work distance. The welding was carried out by the pulsed tubular wire process with pulsed current, constant voltage, Ar+2% O2 shielding gas and short-circuit metal transfer for the deposition of EC410 NiMo Martensitic Steel Deposits alloy coatings on a SAE 1020 steel substrate. For the statistical analysis, the Taguchi experimental planning was applied to test the influence of the parameters of the FCAW process (average current, CTWD, pulsation current and welding speed) on the coating properties. The best configuration with respect to the increased microhardness of the fusion zone in the coating welding process is: Average Current 200 A; CTWD 40 mm; Pulsation Frequency 26.31 Hz and Welding Speed 300 mm min.-1. The lowest microhardness of the melting zone in the coating welding process is: Average Current 170 A; CTWD 30 mm; Pulsation Frequency 23.26 Hz and Welding Speed 400 mm min.-1.

Multi-objective optimization of FCA welding process: trade-off between welding cost and penetration under hardness limitation

Flux-cored arc welding (FCAW) is an innovative semi-automatic assembly process that is increasingly used in the industrial sector. However, the achievement of quality welds on steels with a low weldability index often and inevitably rhymes with high production costs. Therefore, the optimization of welding conditions in order to find a compromise between economic and technological criteria is of great interest. This document proposes the determination of optimal welding parameters, which minimize the total welding cost and maximize weld penetration simultaneously under maximum allowable hardness limitation in the heat-affected zone (HAZ) of high-strength low alloy steel (HSLA) grade S460. The decision variables chosen are welding current, welding speed, voltage and preheating temperature. For this purpose, a mathematical model of the total welding cost for the FCAW process has been developed. Then, the optimization problem is implemented with Matlab™ software and solved using a non-dominated sorting genetic algorithm (NSGA-II). The near optimal solutions are presented as a Pareto front. The choice of optimal welding parameters according to the operator’s objective is made simple and practical. The study highlighted the major role of preheating in reducing the total welding cost and preserving the quality of the weld joint for HSLA steel.

Thermodynamic Stacking Fault Energy, Chemical Composition, and Microstructure Relationship in High-Manganese Steels

Stacking fault energy (SFE) is related to activating complex high strength and ductility mechanisms such as transformation-induced plasticity and twinning-induced plasticity effects. This type of energy can be estimated by many different methods and its importance is in its ability to predict microstructure and phase transformation behavior when the material is submitted to stress/strain. In order to study the SFE, chemical composition, and microstructure relationships, eleven different welding parameters were chosen to obtain a large range of dilution levels. A new tubular wire electrode of high-manganese steel (21 wt pct Mn) was used as the consumable and an SAE 1012 steel plate (0.6 wt pct Mn) as the base metal in a flux-cored arc welding process. These welding parameters were related to the phases formed and phase transformation behavior in the fusion zone. The SFE of the austenite phase was calculated using a thermodynamic model. The welding parameters produced SFE values in the range of − 5 to 7 mJ/m2. $$\epsilon $$ -martensite and austenite were observed in all samples, but $$\alpha $$ ′-martensite was only found in those that presented negative SFE values, i.e., those with lower Mn content. Chemical Gibbs Free energy was the component with the most influence on the SFE. Nanoindentation detected the phase transformations during hardness testing for the medium and low dilution levels used, while the high dilution levels presented the highest hardness and modulus of elasticity values, and the lowest elastic and plastic deformation values. The results provide an improved method to develop high-manganese steels with microstructure control through welding parameters.