Showing papers on "Submerged arc welding published in 2022"

TiO2-Assisted Microstructural Variations in the Weld Metal of EH36 Shipbuilding Steel Subject to High Heat Input Submerged Arc Welding

Abstract: Two simple yet comparable fluxes, CaF2 and CaF2–40 wt pct TiO2, have been employed to engineer shipbuilding steels under high heat input submerged arc welding, aiming to clarify the unique functions demonstrated by incurring TiO2 addition. Compared with pure CaF2, TiO2-containing flux could increase columnar austenite width from 119.2 ± 18.1 to 201.5 ± 32.2 μm. Furthermore, TiO2 could significantly enhance acicular ferrite fraction, which has been primarily enabled by the formation of Ti-bearing inclusions.

Chemical Interaction of Cr-Al-Cu Metal Powders in Aluminum-Assisted Transfer of Chromium in Submerged Arc Welding of Carbon Steel

Abstract: In submerged arc welding (SAW) of chromium containing steels, the chromium in the weld metal is usually sourced from weld wire. Manufacturing of precise weld wire compositions for alloying of the weld metal is expensive. In addition, alloying of weld metal with high levels of copper via weld wire is hindered by work hardening of the weld wire. In the SAW process, a large quantity of oxygen is added to the weld pool. Because chromium has a high affinity for oxygen, the oxygen partial pressure at the weld pool-molten flux interface must be controlled to ensure high recovery of chromium to the weld metal. This study illustrates the application of copper as stabilizer, in conjunction with aluminum, to enhance chromium transfer to the weld pool. The stabilizer effect occurs because the Cr-Al-Cu alloy liquidus temperatures are much lower than the pure Cr liquidus temperature. The result is an increase in the total quantity of Cr, Al, and Cu powder melted into the weld pool. The application of Al powder additions to control the partial oxygen pressure at the molten flux-weld pool interface is confirmed in the presence of Cr and Cu metal powders to ensure the weld metal ppm O content is maintained at the acceptable level of 300 ppm.

In Situ Modification of CaF2-SiO2-Al2O3-MgO Flux Applied in the Aluminium-Assisted Transfer of Titanium in the Submerged Arc Welding of Carbon Steel: Process Mineralogy and Thermochemical Analysis

Abstract: Flux formulations are specified to target chemical and physico-chemical parameters. Chemical parameters set flux element transfer behaviours and weld metal oxygen contents. Physico-chemical parameters such as slag viscosity, surface tension and melting range are targeted to ensure an acceptable weld bead profile and surface appearance. Slag detachability is an important physico-chemical property required to ensure high welding productivity, smooth weld bead surface and no slag entrapment. Here, bead-on-plate welding tests were made with and without metal powder additions, including aluminium powder as a de-oxidiser. Difficult slag detachability was observed in weld runs made with metal powder additions. Mineralogy of the post-weld slags, and thermochemical calculations, show that the flux was modified due to the aluminothermic reduction of MnO and SiO2 from the slag to form alumina. Increased quantities of spinel phase were identified in the post-weld slag samples, at the weld pool–slag interface. The combined effect of increased slag viscosity, from increased spinel in the slag, and lowered weld pool solidus temperature, resulted in the formation of a rough bead surface morphology, which, in turn, caused mechanical fixation of the slag to the weld bead. Flux modification to higher CaF2 content should ensure that higher quantities of spinel phase can be tolerated in the slag.

Aluminium-Assisted Alloying of Carbon Steel in Submerged Arc Welding: Application of Al-Cr-Ti-Cu Unconstrained Metal Powders

Abstract: Al assisted alloying of carbon steel in Submerged Arc Welding (SAW) by Al-Cr-Ti-Cu unconstrained metal powders is applied. A base case without metal powder additions is compared to two metal powder addition schedules, Al-Cu-Ti and Al-Cu-Ti-Cr. Al powder is used as a deoxidiser element to control the oxygen partial pressure at the weld pool–molten flux interface to ensure that most of the Ti and Cr metal powder is transferred into the weld pool and that the weld metal ppm O is controlled within acceptable limits of 200 to 500 ppm O. The likely sequence of alloy melt formation is deduced from the relevant alloy phase diagrams. The effect of Fe addition into the initial Al-Cu-Ti and Al-Cu-Ti-Cr alloy melt is illustrated in thermochemical calculations. Increased metal deposition productivity with metal powder addition in SAW is confirmed. The metal deposition rates increased by 19% and 40% when Al-Cu-Ti and Al-Cu-Ti-Cr powders were applied at the same weld heat input used in the absence of metal powder additions.

Profiling inclusion characteristics in submerged arc welded metals of EH36 shipbuilding steel treated by CaF2–TiO2 fluxes

Abstract: EH36 shipbuilding steel has been submerged arc welded under 6 kJ mm−1 heat input employing CaF2–TiO2 fluxes. Ensuing weld metals have been examined with an emphasis on inclusion characteristics. Compositional-wise, the inclusion ensemble is largely categorised as a complex Ti-containing type. It is demonstrated that, as a function of TiO2 content, the average Ti content in the inclusions is gradually enhanced, which is compensated by the simultaneous reduction of Al and Mn. Meanwhile, inclusion size distribution curves show log-normal patterns with the frequency peaks ranging from 0.3 to 0.4 μm. Furthermore, inclusion number density and volume fraction show a definitive increasing trend, which are concurrent to the O uptake from 110 to 210 ppm enabled by TiO2 decomposition.

Effect of the Cooling Rate of Thermal Simulation on the Microstructure and Mechanical Properties of Low-Carbon Bainite Steel by Laser-Arc Hybrid Welding

Abstract: A new kind of low-carbon bainite steel with excellent strength and toughness was developed, serving as the bogie of the next-generation high-speed train. However, the softening of the heat-affected zone (HAZ) in laser-arc hybrid welding (LAHW) needs to be overcome. In this study, the effect of the cooling rate of the LAHW process on the microstructure and mechanical properties in the HAZ was explored via thermal simulation. The results showed that with increased cooling rate, the grain size increased, the content of lath martensite decreased, and the lath bainite gradually changed to a granular shape in the thermal simulation specimen. With the decrease in the cooling rate, i.e., with the increase of t8/5, the strength–toughness matching of the material showed a downward trend. The thermal simulation specimen with a t8/5 of 6~8 s had higher strength and good toughness, which can be considered a potential welding parameter reference. The content of martensitic austenite (M-A) constituents was the main factor that determined the strength and toughness of the joint. During the tensile test, the axial force caused the material to tighten, and the transverse stress as obvious in the part of the M-A constituents that are prone to microcracks and many defects, resulting in cracks, paths, and multi-component layers in the center. As a result, the thermal cycle specimens had mixed fracture characteristics.

Facilitating flux design process geared towards submerged arc welding via thermodynamic approach: Case study into CaF2–SiO2–Na2O–Al2O3–TiO2 agglomerated flux

Abstract: Submerged arc welding is a metallurgical process with temperature of 2000°C, during which complex chemical reactions occur. Due to an incomplete understanding of flux thermodynamic properties and welding process, experiments are required for the flux design, thereby consuming significant resources. Within this study, thermodynamic software, FactSage, is employed to facilitate the flux design subject to CaF2–SiO2–Na2O–Al2O3–TiO2 agglomerated flux. Then, experiments are performed with designed fluxes, and transfer behaviors of the essential elements have been quantified by Δ values. The measured data indicates that the thermodynamic approach proposed in present study is capable of facilitating the flux design process and developing the selection strategies for the welding materials. Additionally, the elemental transfer mechanisms have been evaluated, and assumptions made in previous studies have been discussed from the perspective of thermodynamics. The limitations of the thermodynamic approach are also given.

Spectroscopic Approach for the On-Line Monitoring of Welding of Tanker Trucks

Abstract: The appearance of defects during the manufacture of tanker trucks via arc-welding is a significant problem in the industry. A reliable low-cost and non-destructive on-line method could aid the discovery of solutions to overcome productivity problems. Plasma optical spectroscopy was employed in this study to correlate the presence of several elemental emission lines with certain quality-related events, such as the appearance of porosities. Results obtained through field trials and also during in-line production show that the convenient processing of acquired process signals facilitates not only the detection of defects, but also the identification of their causes. Output monitoring signals have been compared with X-ray inspections of the seam welds performed. It has been demonstrated that the spectroscopic monitoring variables obtained are good indicators for evaluating contamination in the process and therefore the occurrence of welding defects.

On the Moving of Neutral Point for Mn Subject to Submerged Arc Welding under Various Heat Inputs: Case Study into CaF2-SiO2-Na2O-MnO Agglomerated Fluxes

Abstract: Neutral Point indicates the flux formula where no transfer of alloying element between the flux and weld metal occurs. For the submerged arc welding process, Neutral Point is an essential definition for flux design and specification since it helps to identify the flux microalloying ability. The scientific hypothesis that the Neutral Point is only a function of the flux formula is considered as the basis of the Mitra kinetic model. Within this framework, by performing submerged arc welding with CaF2-SiO2-Na2O-MnO agglomerated fluxes under various heat inputs, the moving of Neutral Point has been captured, indicating the scientific hypothesis proposed in Mitra kinetic model may be revised under high heat input welding. Additionally, although some studies have incorporated the consideration of the gas-slag-metal equilibrium, only the effective equilibrium temperature of 2000 or 2100 °C is utilized, which may be insufficient to constrain Mn content in the weld metal. In this study, we have incorporated all possible effective equilibrium temperatures that may be attained in the submerged arc welding process to simulate the transfer behavior of Mn. Then, a novel thermodynamic approach is proposed to detect the moving direction of Neutral Point for Mn from both slag-metal and gas-slag-metal equilibrium considerations, which may pave a vital way for the flux design and the setting of welding parameters. The factors responsible for the deviation between real and predicted data are discussed. The mechanism responsible for the moving of Neutral Point regarding the Mn element is evaluated from the perspective of both slag-metal and gas-slag-metal equilibrium considerations.

Waste to wealth: Recycling of steel slag as flux for the submerged arc welding process and its effect on mechanical and metallurgical properties of welds

Abstract: A novel technology has been developed to recycle steel slag as a flux for the submerged arc welding process. The chemical, mechanical, and metallurgical properties of welds produced using recycled slag have been evaluated and compared with that of fresh flux available in the market. The tensile strengths of weld metal prepared with recycled slag and fresh flux are 462.25 MPa and 471.49 MPa, which are comparable. The impact strength of welds produced using recycled slag is 83.66 J which is acceptable in accordance with AWS SFA 5.17 specifications. The welds produced were subjected to non-destructive tests such as radiography and also dye-penetration test apart from visual inspection to ascertain the soundness of welds produced. Metallurgical investigations were carried out, and a favorable microstructure containing acicular ferrite was obtained in welds deposited using recycled slag. Similar trends of microhardness survey have been observed in both the welds produced.

Effect of electrode negativity ratio and heat input on bead and arc characteristics in submerged arc welding

Abstract: The effect of electrode negativity (EN) ratio, current and welding speed on bead profile and arc stability in case of constant current square wave power source were investigated by conducting bead on plate (BOP) welding experiments on API X80 steel. In addition to this, effects of heat input on prior austenite grain (PAG) size, microstructure and hardness of coarse grain heat affected zone (CGHAZ) were also studied. Deleterious hump angle created due to EN ratio variation, decreased with increase in EN ratio and welding current. Average PAG size and spacing between bainite laths increased from 17.09 µm to 62.66 µm and 0.67 µm to 50 µm respectively with increase in heat input from 0.69 kJ/mm to 3.6 kJ/mm, which altered CGHAZ hardness. Arc stability and metal transfer mode for different EN ratios and currents were analyzed by means of probability density distribution (PDD) graphs of current and voltage transients recorded using a digital storage oscilloscope. PDD graph show better arc stability at higher currents and during the electrode positive (EP) part of current waveform.

Element Transfer Behavior for CaF2-Na2O-SiO2 Agglomerated Flux Subject in Submerged Arc Welding Process

Abstract: From a thermodynamic perspective, the present study has been performed to investigate the effect of SiO2 level in agglomerated fluxes on the element transfer behavior of essential elements, by applying CaF2-Na2O-SiO2 agglomerated fluxes with varying SiO2 contents. Element transfer behavior is quantified by the Δ value. The impact of SiO2 and heat input upon element transfer behavior is interpreted. Additionally, a possible thermodynamic approach to predict high basicity flux O potential and weld metal composition is proposed and evaluated. It is revealed that the consideration of the gas-slag-metal equilibrium is able to place constraints on the transfer behaviors (of O, Si, and Mn) and formation of gases. In submerged arc welding metallurgy, the empirically determined basicity index models proposed by Tuliani have been applied for more than 50 years to predict flux O potential and weld metal oxygen content. However, it is well known by welding practitioners that the flux basicity index model can only predict the changing trend of flux O potential when the flux basicity index is lower than 2.0. The present study has proposed a new thermodynamic method to identify the flux O potential for fluxes with a basicity index higher than 2.0. Additionally, the experimental evidence for the Mitra kinetic model has been provided.

Probing Element Transfer Behavior during the Submerged Arc Welding Process for CaF2-SiO2-Na2O-Cr2O3 Agglomerated Fluxes: A Thermodynamic Approach

Abstract: Submerged arc welding joins metal by the heating of the electrode, base metal, and flux in the arc plasma, while the weld pool is protected under the granular flux and molten slag. Due to complex chemical reactions occurring between the arc plasma, weld pool, and molten slag (flux), flux essentially affects the weld metal composition, which, in turn, dictates the mechanical properties of the weldment. Therefore, fine-tuning the weld metal composition is essential to ensure a sound weld, and efforts worldwide have been focused on the control mechanism of flux on the weld metal composition. Recently, agglomerated fluxes have been widely applied due to low energy consumption during manufacture. The Cr2O3-bearing agglomerated flux is one of the most commonly used flux types in fields of heavy industrial applications. However, few works concern the element transfer behavior when Cr2O3-bearing agglomerated fluxes are used. Within this framework, typical agglomerated CaF2-SiO2-Na2O-Cr2O3 fluxes with varying Cr2O3 content from 10 to 50 wt.% are designed and applied to Q345A steel. The influence of Cr2O3 content upon the transfer behaviors of essential elements, including O, Cr, and Mn, is quantified and interpreted from the point of thermodynamics. By incorporating a gas-slag-metal equilibrium consideration, the assumptions made in previous studies are justified. Additionally, evidence regarding the loss of Cr and Mn to the arc plasma is provided, and a possible thermodynamic approach to predict element transfer levels is proposed. It is revealed that the gas-slag-metal equilibrium consideration is able to qualitatively analyze the transfer behaviors involved in the submerged arc welding system, even under high temperatures. Based on the quantitative data, the practical implications as well as limitations of the gas-slag-metal equilibrium model are proposed.

Corrosion Effects on Fracture Toughness Properties of Wire Arc Additively Manufactured Low Carbon Steel Specimens

Abstract: The emerging wire + arc additive-manufacturing (WAAM) technique has significant potential to improve material design, as well as manufacturing cost and efficiency of structural components such as offshore wind turbines and subsequently reduce the levelised cost of energy (LCoE). Welded joints in offshore structures are usually considered potential spots for crack initiation due to the combination of high stress concentration at the weld toes, residual stresses introduced by the welding process and cyclic loading conditions in harsh, corrosive marine environments. The WAAM technique is a deposition method consisting of repetitive welding process that can be used as an alternative manufacturing technique for fabrication or repair of structural components. An important issue that needs to be understood in structural-integrity assessment of WAAM-built components is fracture-toughness behaviour. In particular, the sensitivity of fracture-toughness properties to corrosive environments must be examined in order to extend the application of the WAAM technique to offshore wind structures. Therefore, in this study, fracture-toughness tests were conducted on WAAM-built compact-tension specimens made of ER70S-6 and ER100S-1 steel that were initially exposed to a seawater corrosive environment prior to testing. All fracture-toughness tests were performed at room temperature, and crack length was estimated using the compliance method with a clip gauge attached onto the knife edge of the specimens. The obtained results, which include load vs. load-line displacement and J-integral vs. crack extension, were analysed and compared with the results of tests in air, without any exposure to seawater. The conclusions of this study show that corrosive environments affect the yield stress and R-curves of the selected materials and contribute to the overall understanding of the design requirements for functionally graded structures fabricated by means of WAAM technique for offshore applications.

Investigation of distinct welding parameters on mechanical and corrosion properties of dissimilar welded joints between stainless steel and low carbon steel

Abstract: The tensile strength and corrosion behavior of dissimilar welded joints are currently a subject of concern. In this work, gas metal arc welding (GMAW) and distinct welding parameters (welding current, arc voltage, and welding speed) were used to join 304 stainless steel (SUS304) and SS400 low carbon steel, and the ultimate tensile strength (UTS) of the dissimilar welded joints was investigated. A corrosion test was conducted by immersion in 3.5 wt.% sodium chloride (NaCl) solution for 7, 14, and 21 days. Based on tensile strength and Tafel testing, the welding parameters “Item 4” (welding current: 170 A, arc voltage: 20 V, welding speed: 40 cm/min) yielded good mechanical strength and low corrosion characteristics. The microstructure characterization showed that the area around the welded joints and SUS304 had more granular corrosion and corrosion tubercles with increasing immersion time. The chromium content gradually decreased. When exposed to the chloride environment, these welded joints easily underwent corrosion due to the loss of passivity. However, high-velocity oxygen-fuel (HVOF) spray used on the welded joints reduced the corrosion current density. Compared with the non-thermal spray sample (corrosion current density:7.49e − 05 A/cm2) while the corrosion current density (7.89e − 10 A/cm2) is five orders of magnitude lower. This spray effectively slowed down the corrosion rate of the welded joints and gave the structural objects good protection in the sodium chloride solution.