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Submerged arc welding (SAW), renowned for its high deposition rate and superior weld quality, is the go-to method for joining thick metals in heavy structures. However, industry beams and columns welded with SAW can exhibit detrimental defects like undercut, porosity, and burn-through, significantly impacting weld properties. This study addresses this challenge by presenting a multi-objective optimization approach for SAW parameters on AISI 1020 mild steel. Aiming to optimize tensile strength, hardness, and bead width, the study employs Taguchi's design of experiments and couples the multi-objective Jaya algorithm with an artificial neural network (ANN). This synergistic combination yielded optimal process parameters: 417 A welding current, 20.7 mm electrode stick-out, 33.7 V voltage, and 505.8 mm/min transverse speed. These settings translated into exceptional weld characteristics, with ultimate tensile strength reaching 427 MPa, hardness of 73.9 HRB, and bead width of 14.29 mm. Confirmation tests further validated these findings, demonstrating minimal error and solidifying the effectiveness of the optimization approach. This research paves the way for enhanced weld quality and process control in heavy structural applications. [ABSTRACT FROM AUTHOR]

EH36-shipbuilding steel has been welded by CaF2-ZrO2 fluxes with designed ZrO2 additions. Possible chemical and electrochemical reactions have been postulated to analyze alloying element transfer behaviors. The decomposition of ZrO2 during SAW has been validated by applying the gas–slag–metal equilibrium model and the O supply capacity of ZrO2 has been quantified. For the entire compositional range, O content has been controlled within a well-maintained range from 220 to 400 ppm, and the transferred quantity of Zr content reaches to the maximum value of 120 ppm. It is further demonstrated that ZrO2 addition incurs appreciable Si loss within the weld metal. [ABSTRACT FROM AUTHOR]

Owing to its low operating costs and high productivity, submerged arc welding (SAW) is a widely utilized machine in various sectors, particularly industry. However, achieving optimal bead width (BW) remains a challenge due to the process being intricate and non-linear. This research is devoted to proposing a novel nature-inspired meta-heuristic optimization algorithm based on the whale optimization algorithm (WOA), called the improved whale optimization algorithm (IWOA), an inertia weight is included, which imitates the social behavior of hunting humpback whales. This parameter controls the influence of the current best solution on the search process during the exploitation phase, allowing an exhaustive search near the optimal solution. Today, due to its competitiveness and efficiency, this algorithm has been widely used to solve complex optimization problems in various fields, including manufacturing and engineering. The proposed algorithm was used to adjust four parameters of the SAW process, including arc voltage (V), welding current (I), welding speed (S), and wire feed (F). The objective function is minimizing the bead width, which is an essential factor in order to maximize weld quality and neatness (consistency). The obtained results have revealed that the IWOA can effectively optimize the SAW process parameters. When compared to other optimization algorithms, which include particle swarm optimization (PSO) and WOA, the suggested method exceeds them all in terms of fast convergence time and solution quality. [ABSTRACT FROM AUTHOR]

Duplex stainless steel (DSS) mainly consists of ferrite and austenite. DSS finds wide uses in offshore applications, due to its admirable mechanical properties and great corrosion resistance. The chemical and physical characteristics of the weld metal (WM) are significantly impacted by the flux compositions. In the present work, the submerged arc welding (SAW) of DSS was achieved by using an electrode wire (ER-308L). The resulting physiochemical compositions, C, Mn, Ni, Cr, Mo and W of the WM, have been examined by utilizing 21 designed fluxes. The SAW fluxes in the current study are formulated using the limited mixture design approach. Using the extreme vertices design method, 21 compositions of flux are designed and the effect of flux mixtures has been studied. Regression models were developed for the submerged arc weld of DSS-2205 by considering the different flux constituents and their binary combinations. From the study, it has been concluded that among the individual flux mixtures, Al2O3 is the most significant mixture and SiO2 is the second most significant flux mixture. The most significant binary mixture to change the content of WM's composition is SiO2MgO. Regression mathematical models have been checked at a 95% significance level by using an analysis of variance (F test). [ABSTRACT FROM AUTHOR]

In this work, the effects of the mixing water loss capacity of hydrated lime mortars with different dosages were analysed—type O (mix 1:2:9), type N (mix 1:1:6), and type M (mix 1:0.5:4.5), with additions of submerged arc welding (SAW) slag. Infrared thermography tests and optical and scanning electronic microscopy analyses of the mortars were also carried out. The experimental results showed that the mortar samples with additions of SAW slag type M, using low-cost materials, proved to be in economic and technical terms (adhesion strength) the best solution, even more so if a spatter dash layer is used, a fact that increases the adhesion strength even more. Also, the infrared thermographic results revealed that the ability of the mortar paste to yield water to the ceramic substrate in the interface regions is a relevant factor in the adhesion of these coatings. Finally, the analyses by scanning electron microscopy and optical microscopy revealed that the ability to release water to the substrate is related to the hydration of the mortar and its anchoring capacity. Furthermore, the analyses carried out demonstrated that the adhesion of the mortars is influenced and increased with the application of a layer of splashes, as the pores of the substrate become more refined and better filled with the applied mortar. [ABSTRACT FROM AUTHOR]

High-manganese steel (high-Mn) is valuable for its excellent mechanical properties in cryogenic environments, making it essential to understand its deformation behavior at extremely low temperatures. The deformation behavior of high-Mn steels at extremely low temperatures depends on the stacking fault energy (SFE) that can lead to the formation of deformation twins or transform to ε-martensite or α′-martensite as the temperature decreases. In this study, submerged arc welding (SAW) was applied to fabricate thick pipes for cryogenic industry applications, but it may cause problems such as an uneven distribution of manganese (Mn) and a large weldment. To address these issues, post-weld heat treatment (PWHT) is performed to achieve a homogeneous microstructure, enhance mechanical properties, and reduce residual stress. It was found that the difference in Mn content between the dendrite and interdendritic regions was reduced after PWHT, and the SFE was calculated. At cryogenic temperatures, the SFE decreased below 20 mJ/m2, indicating the martensitic transformation region. Furthermore, an examination of the deformation behavior of welded high-Mn steels was conducted. This study revealed that the tensile deformed, as-welded specimens exhibited ε and α′-martensite transformations at cryogenic temperatures. However, the heat-treated specimens did not undergo α′-martensite transformations. Moreover, regardless of whether the specimens were subjected to Charpy impact deformation before or after heat treatment, ε and α′-martensite transformations did not occur. [ABSTRACT FROM AUTHOR]

In order to forecast and regulate the quality of the weld with improved mechanical qualities while automating the welding process for an increased production rate, a relationship between the process parameters must be developed. The relationship between the welding parameters and the mechanical properties can be easily tracked using the response surface methodology. The aim of this study is to optimize the parameters in the submerged arc welding of AISI 1055 steel using Box–Behnken design in response surface methodology. The metal deposition rate is more influenced by the current, which simultaneously improves the mechanical properties of the weld. The optimized process parameters are 349.94A for current, 52.90V for voltage, and 0.6m/min for carrier speed. These optimized performance parameters are 461.72N/mm2 for ultimate tensile strength, 35.26J for impact strength, and 41.95HRC for hardness. The desirability of 0.718 is obtained for the developed optimization model, which proves the reliability of the model in the actual experimentation. [ABSTRACT FROM AUTHOR]

A new process of continuous and synchronous calibration process of ovality and straightness for LSAW (Longitudinally Submerged Arc Welding, LSAW) pipes with three rollers is proposed. Specifically, the process is introduced from three aspects: roller-shape, loading parameters and axial and circumferential deformation paths. The process is verified by numerical simulation and physical experiments. Further, the stress-strain in the Sections Ⅱ and Ⅳ is analyzed. The relationship between the process parameters and the residual ovality and residual straightness by experiments is discussed. The calibration scheme of LSAW pipes is put forward by using the control variable method. The results show that the shear stress is the principal stress direction in the Sections Ⅱ and Ⅳ. The residual ovality and residual straightness decrease with the increase of the radial reduction and times of reciprocating bending. The reciprocating bending process can eliminate the difference of the initial curvature, make the curvature of each section tend to be uniform. After calibration, the residual straightness is less than 0.2% and the residual ovality is less than 1%, demonstrating a good feasibility of this process. [ABSTRACT FROM AUTHOR]

The submerged arc welding (SAW) process involves a complex relationship between controllable input parameters and measurable output characteristics. Several research works based on statistical methods, nature-inspired algorithms, and Multicriteria decision-making methods have been carried out to optimise submerged arc welding process parameters for effective utilization of resources and improved weld quality. Past researches suffer from limitations like the tendency to get trapped into local minima, lack of repeatability of optimised output, subjective nature of the methods, mathematical complexity, rank reversal, or bias in determining user-dependent weights. In the present work, a hybrid Fuzzy-MABAC approach has been employed that can overcome the difficulties of the previous approaches to optimise submerged arc welding process parameters. The 27 numbers of experiments have been conducted based on 3 level 5 factor L27 Taguchi orthogonal array where arc voltage, welding current, welding speed, electrode stick out, and reuse of flux are considered as input parameters and weld quality has been assessed through the combined effect of measured output characteristics such as, weld hardness (H), weld bead width (BW), and heat affected zone (HAZ) respectively. The triangular Fuzzy method has been used to determine the weights of output parameters. Further, Multi-Attributive Border Approximation Area Comparison (MABAC) utilized the weights to determine optimised SAW output. The highest overall score of 0.6144 indicates optimum weld quality with 84 HRB, 11.1 mm, and 11.4 mm for H, BW, and HAZ respectively. Corresponding input parameters are 175A, 26 V, 1.2 m/min, 45 mm, and 30% for welding current, arc voltage, welding speed, electrode stick-out length, and reuse of flux respectively. Optimised weld quality has been achieved by moderate current, low arc voltage, moderate welding speed, adequate electrode stick out, and percentage reuse of flux. Welding voltage is found to affect the overall weld quality most significantly. The sensitivity analysis has been carried out with adequate details. The performance of the proposed Fuzzy-MABAC method corroborates well with the popular Fuzzy-TOPSIS method. [ABSTRACT FROM AUTHOR]

This article presents a study on the influence of the intensity of the welding current on the properties of the mechanical strain strength of welded joints made by using submerged arc welding technology. The influence of the welding current on the microstructure of the welded joints was also observed in different regions of the cross-section of the welding seam. Also subject to observation was the mode of influence of the welding current on the geometry and dimensions of the welding seams. The welded samples were obtained using five different welding regimes whose main variable was the intensity of the welding current, which had values between 300 A and 700 A. The criterion used as a reference for comparing the effects produced by the studied welding regimes was a standard welding regime that is used in the industry for welding railway tank wagons, with a welding current intensity of 480 A. The base material used in the experiments was a fine-grained carbon steel specially intended for the manufacture of pressure vessels identified as P355 N; the semi-finished product from which the samples were made consisted of 6 mm thick laminated sheets used in the manufacture of the covers of the vessels that make up the railway tank wagon. The aim of this study was to highlight the differences that may appear through varying the current welding parameter and identify welding regimes that can provide welded joints with superior mechanical properties compared to what is currently employed in the industry. This study focused on the most widespread technology of welding pressure vessels: the submerged electric arc welding method. [ABSTRACT FROM AUTHOR]

In this study, a novel TIP–TIG (TT) automatic welding method was used to weld the girth seams of liquefied natural gas (LNG) tanks composed of 9% nickel steel. The microstructure of the joints was characterized via electron microscopy and x-ray diffraction. The tensile strength and ductility of the joints were evaluated via tensile testing. The low-temperature toughness of the joints was investigated via low-temperature impact testing at - 196 °C. This increased the toughness and strength of the TT-welded joint compared to the corresponding values of joints welded using conventional submerged arc welding (SAW). A comparison with the SAW-welded joints revealed that the TT-welded joint presented high strength and excellent low-temperature toughness, which can be primarily attributed to the low heat input. Compared with SAW, TT welding resulted in a lower joint dilution ratio, smaller heat-affected zone, and lower degree of grain coarsening. In addition to fine austenite, as the joint microstructure and several uniformly distributed carbides in the weld seam. These properties hindered the dislocation slip. However, they promoted precipitation strengthening and grain refinement and provided excellent low-temperature toughness to the TT-welded joints. Notably, TT welding does not require weld-bead cleaning between passes. Additionally, owing to improvements in the degree of automation for TT welding, the welding time can be further matched with that of SAW. TT welding with narrow-gap grooves reduces the required amount of filler metal by more than 50%. Therefore, the TT welding process is significantly advantageous and can replace SAW for girth–seam welding of LNG storage tanks. [ABSTRACT FROM AUTHOR]

With the advancement of the manufacturing industry, performing submerged arc welding subject to varying welding heat inputs has become essential. However, traditional thermodynamic models are insufficient for predicting the effect of welding heat input on elemental transfer behavior. This study aims to develop a model via CALPHAD technology to predict the influence of heat input on essential elements such as O, Si, and Mn when typical SiO2-bearing fluxes are employed. The predicted data demonstrate that the proposed model effectively forecasts changes in elemental transfer behavior induced by varying welding heat inputs. Furthermore, the study discusses the thermodynamic factors affecting elemental transfer behavior under different heat inputs, supported by both measured compositions and thermodynamic data. These insights may provide theoretical and technical support for flux design, welding material matching, and composition prediction under various heat input conditions subject to submerged arc welding processes when SiO2-bearing fluxes are employed. [ABSTRACT FROM AUTHOR]

The submerged arc welding (SAW) process is operated at high temperatures, up to 2500 °C, in the arc cavity formed by molten oxy-fluoride flux (slag). These high arc cavity temperatures and the complex interaction of gas–slag–metal reactions in a small space below the arc render the study of specific chemical interactions difficult. The importance of gas phase reactions in the arc cavity of the SAW process is well established. A low-temperature (1350 °C) experimental method was applied to simulate and study the vaporisation and re-condensation behaviour of the gas species emanating from oxy-fluoride flux. Energy dispersive X-ray spectroscopy (EDX) analyses and reaction thermochemistry calculations were combined to explain the role of Al as a de-oxidiser element in gas phase chemistry and, consequently, in nano-strand formation reactions. EDX element maps showed that the nano-strands contain elemental Ti only, and the nano-strand end-caps contain Co-Mn-Fe fluoride. This indicates a sequence of condensation reactions, as Ti in the gas phase is re-condensed first to form the nano-strands and the end-caps formed from subsequent re-condensation of Co-Mn-Fe fluorides. The nano-strand diameters are approximately 120 nm to 360 nm. The end-cap diameter typically matches the nano-strand diameter. Thermochemical calculations in terms of simple reactions confirm the likely formation of the nanofeatures from the gas phase species due to the Al displacement of metals from their metal fluoride gas species according to the reaction: yAl + xMFy ↔ xM + yAlFx. The gas–slag–metal equilibrium model shows that TiO2 in the flux is transformed into TiF3 gas. Formation of Ti nano-strands is possible via displacement of Ti from TiF3 by Al to form Al-fluoride gas. [ABSTRACT FROM AUTHOR]

P92 heat-resistant steel has been successfully submerged arc welded by employing designed CaF2–Cr2O3 fluxes. It has been demonstrated that δ-ferrite is retained in the weld metal, the area fraction of which is found an approximately 3.7-fold enhancement as the Cr2O3 content in the fluxes is raised from 5 to 25 wt pct. Such phenomenon has been elucidated through governing element transfer behaviors incurred by the decomposition of Cr2O3. Our findings possibly offer a viable solution towards developing welding fluxes geared towards durable heat-resistant steel grades. [ABSTRACT FROM AUTHOR]

The paper presents the experimental results into the development of a multi-channel system for monitoring and quality assurance of the multi-wire submerged arc welding (SAW) process for the manufacture of large diameter pipes. Process signals such as welding current, arc voltage and the acoustic signal emitted from the weld zone are recorded and processed to provide information on the stability of the welding process. It was shown by the experiments that the acoustic pattern of the SAW process in a frequency range between 30 Hz and 2.5 kHz contains the most diagnostic information. The on-line quality assessment of the weld seam produced is carried out in combination with methods of artificial intelligence (AI). From the results obtained, it can be concluded that the use of the latest concepts in welding and automation technology, combined with the high potential of AI, can achieve a new level of quality assurance in pipe manufacturing. [ABSTRACT FROM AUTHOR]

In the present work, the effect of electrode negative (EN) ratio on bead cross-section, mechanical properties and microstructure was analysed. The welding was performed on MC-600 steel of 12.5 mm thickness by two passes in butt configuration at three different EN ratios varying from 0.25 to 0.75. Out of different types of power sources, alternating current (AC) with the square wave was selected here for the experiment. Penetration depth and bead width decreased with an increase in EN ratio, but reinforcement height increased with an increase in EN ratio. There is no notable effect on yield strength but ultimate tensile strength increased slightly due to an increase in the EN ratio. Vickers hardness of weld at lowest and highest EN ratios is almost similar and slightly higher than that of the middle one. The impact toughness of all three locations improved with an increase in the EN ratio. [ABSTRACT FROM AUTHOR]

Descaling roll is a key component used to remove iron oxide on billet surface in hot rolling production lines, and its surface properties have a significant effect on the quality of hot rolling products. The descaling roll is in bad service condition and subjected to the dynamic impact caused by high-pressure water erosion and high temperature billet descaling process for a long time. Under the action of high temperature, strong wear, multi-cycle heat, force, flow and multi-field strong coupling, the surface is prone to wear and corrosion failure, which affects the continuous rolling production. Submerged arc welding provides an effective way to repair and strengthen the descaling roll surface. The content of WC hard phase has a significant effect on welding quality. At the same time, direct submerged arc welding of Ni based WC wire on the descaling roll surface is easy to cause cracks, and a gradient synergistic strengthening effect can be formed by setting the transition bottom layer in welding. At present, there is a lack of experiments related to the preparation of flux-cored wire with different contents and the overlaying for the bottom submerged arc welding. Relevant studies are urgently needed to further reveal the welding process mechanism to provide significant theoretical support for the preparation of wire materials and the improvement of welding quality. In this paper, 30% and 60% WC flux-cored wires were prepared by employing Ni-Cr-B-Si alloy powder as the base powder, and submerged arc welding tests were conducted on the descaling roll, preparing three welding layers, namely 70% NiCrBSi + 30% WC without the bottom layer, 70% NiCrBSi + 30% WC with the bottom layer, and 40% NiCrBSi + 60% WC with the bottom layer. The properties of the welding layer were evaluated by SEM, XRD, EDS, hardness, friction and wear, corrosion and impact experiments. The results show that the WC hard phase added in the filler metal has dissolved and formed a new phase with other elements in the melting pool. The surfacing layer mainly contains Fe-Ni, Cr-C, Fe3Si, Ni3C and other phases. The surfacing layer prepared by a different amount of WC flux-cored wire and the surfacing layer with or without the bottom layer have great differences in microstructure and properties. This study lays a significant theoretical foundation for optimizing the submerged arc welding process and preparing welding materials for the descaling roll and has significant practical significance and application value. [ABSTRACT FROM AUTHOR]

The welding community faces a challenging problem in choosing the best welding methods since they are multi-input processes. Modern manufacturing industries have requirements to get fast and optimum process parameters to utilize complete resources in an optimum way. This work attempts to improve the performance of submerged arc welding (SAW), friction welding (FW), and gas tungsten arc welding (GTAW) processes by optimizing their parameters. The newly developed Rao algorithms and their modified versions known as quasi-oppositional Rao (QO Rao), self-adaptive multi-population elite Rao (SAMPE Rao), and improved Rao (I-Rao) are used. This paper contains four multi-objective optimization case studies of SAW, FW, and GTAW processes. A weighted approach is employed to tackle the multi-objective optimization problems effectively. The outcomes achieved using the Rao, QO Rao, SAMPE Rao, and I-Rao algorithms are compared with those obtained by the established optimization algorithms such as accelerated cuckoo optimization algorithm (ACCOA), cuckoo optimization algorithm (COA), plant propagation algorithm (PPA), teaching–learning-based optimization (TLBO) algorithm, Jaya algorithm, quasi-oppositional Jaya (QO Jaya) algorithm, genetic algorithm (GA), particle swarm optimization (PSO) algorithm, and heat transfer search (HTS) algorithm. The effectiveness of the Rao algorithms and their modified versions has been clearly demonstrated as these algorithms have provided superior solutions while requiring fewer generations to achieve them. [ABSTRACT FROM AUTHOR]

Hot-rolled backup rolls are widely used in steel rolling and usually need to be repaired by arc hardfacing after becoming worn. However, a corrugated-groove defect commonly occurs on the roll surface due to the uneven hardness distribution in the hardfacing layers, affecting the proper usage of the roll. Accordingly, a new swing-arc submerged arc welding (SA-SAW) process is proposed to attempt to solve this drawback. The microstructure and hardness are then investigated experimentally for both SAW and SA-SAW hardfacing layers. It is revealed that a self-tempering effect occurs in the welding pass bottom and the welding pass side neighboring the former pass for both processes, refining the grain in the two areas. In all the zones, including the self-tempering zone (STZ), heat-affected zone (HAZ), and not-heat-affected zone in the welding pass, both SAW and SA-SAW passes crystallize in a type of columnar grain, where the grains are the finest in STZ and the coarsest in HAZ. In addition, the arc swing improves the microstructure homogeneity of the hardfacing layers by obviously lowering the tempering degree in HAZ while promoting the even distribution of the arc heat. Accordingly, the hardness of the SA-SAW bead overall increases and distributes more uniformly with a maximum difference of < 80 HV0.5 along the horizontal direction of the bead. This hardness difference in SA-SAW is accordingly decreased by ~38.5% compared to that of the SAW bead, further indicating the practicability of the new process. [ABSTRACT FROM AUTHOR]

In this paper, the effect of ER2209 multi-stranded wire compared to single wire on the microstructure and pitting resistance of 2205 duplex stainless steel submerged arc welded joints was studied using electron backscatter diffraction, scanning electron microscopy, energy spectrum analysis, electrochemistry and other detection techniques. Compared with single-wire welding of duplex stainless steel, the multi-stranded wire deposited more metal and doubled the welding efficiency with the same heat input, while increasing the elemental concentration of Ni in the weld metal and the proportion of austenite in the heat-affected zone. Compared with single-wire welding, multi-stranded wire welding promotes the diffusion of the main alloying elements (Cr, Mo, Ni, N) in the welded joint and improves the mechanical properties and pitting resistance of the welded joint. [ABSTRACT FROM AUTHOR]

Because of the inefficiency of the existing production process for large diameter longitudinal submerged arc welded (LSAW) pipe, a roll bending process is proposed, but it is difficult to control the pipe straightness with large length and small diameter to thickness (D/T) ratio. A method of deflection compensation with reverse bending top roll is proposed to solve the problem. The mechanical model of the roll bending process is established, and the forces on the plate and the roll, the deflection of the top roll and the torque are analyzed systematically. A set of roll bending machines was designed and developed, and the process parameters of different specifications of products were tested. The results show that the straightness of the pipe is less than 0.1 % of full length, and the error between theoretical analysis and test data is less than 15 %. The theoretical analysis method can be used to direct the production. [ABSTRACT FROM AUTHOR]

TiO2 inclusion formation in the weld pool is required to produce potent nucleation sites for acicular ferrite microstructure formation. Weld metal oxygen content must be limited to ensure acceptable materials properties, although sufficient oxygen is required for inclusion formation. Weld pool oxygen is sourced from the decomposition of flux oxides. Weld metal oxygen is controlled with flux chemistry formulation by CaF2 dilution of oxides. In conventional submerged arc welding (SAW), the flux is the source of weld metal Ti. Transfer of Ti from the slag appears to be limited to 400 parts per million (ppm). SAW modification by metal powder additions changes the element transfer reactions. Thermochemical analysis is applied to explain the limitations in Ti transfer from the slag, compared to improved reaction conditions for Ti element transfer in the aluminum‐assisted Ti alloying of weld metal. Low TiO2 activity due to low flux TiO2 content from CaF2 dilution and Ti loss from Ti‐fluoride gas formation limits Ti transfer from slag. Aluminum‐assisted alloying of the weld metal shifts the gas composition from Ti‐fluoride formation to Al‐fluoride formation and lowers the system partial oxygen pressure to increase the weld metal Ti content, with acceptable ppm O remaining in the weld metal. [ABSTRACT FROM AUTHOR]

Microstructural characteristics has been investigated along the weld metal penetration of EH36 shipbuilding steel processed by CaF2–30 wt. pct TiO2 flux under 60 kJ·cm−1 submerged arc welding. It is demonstrated that microstructures have been significantly refined from equiaxed to columnar grain zone, where acicular ferrite morphology varies from plate to lath. Concurrently, the fraction of acicular ferrites is enhanced while that of polygonal ferrites shrinks, enabling a bimodal misorientation distribution towards auspicious properties. [ABSTRACT FROM AUTHOR]

A high-strength low-alloy (HSLA) steel plate of 10 mm thickness underwent submerged arc welding with enhanced fluxes containing additional titanium oxide (TiO2) or vanadium oxide (V2O5). The addition of TiO2 led to the development of a finer acicular ferrite structure but coarsening the carbide and martensite/austenite (M/A) constituents, which marginally improved the hardness, tensile strength, and ductility of weld metal. Conversely, incorporating V2O5 facilitated a substantial vanadium absorption (0.7 wt. %) in the weld metal, giving rise to a distinctive acicular microstructure less reliant on ferrite nucleation at non-metallic inclusions than conventional acicular ferrite. The distinctive microstructure, unique to vanadium steels, combined lath bainite with irregularly shaped granular bainite. The resultant dual-mode bainitic structure, coupled with a more uniform distribution of refined microphase constituents, outperformed the conventional acicular ferrite, delivering more than 20% and 13% improvements in yield and tensile strengths respectively, as evidenced by transverse tensile tests on the weld metals.

The welding of carbon steel for boiler structures poses significant challenges that remain an open problem for researchers. Welded joints in boiler applications are subjected to harsh conditions involving exposure to both fire and water environments, complicating material sustainability. This study focuses on the unique challenges arising from the interaction of welds with chloride-rich environments. The combustion of fuel and the presence of chloride in the aqueous zone are particularly influential factors, as highlighted by research on fire side columns. The weld zone experiences severe deterioration, resulting in substantial material loss. To address this issue, the current research involved subjecting the weld material to a chloride environment, with a comprehensive evaluation of the weldment's behaviour through electrochemical corrosion studies. Material characteristics were further analysed using electron microscopy, EDS spectra, and X-ray diffractometry. The corrosion results form the basis for recommendations and suggestions aimed at enhancing the resilience of weldments in carbon steel boiler structures, offering valuable insights for the improvement of material performance in challenging operational conditions. [ABSTRACT FROM AUTHOR]

An investigation into the evolution of temperature and stress fields, as well as the phase transformation in marine steel EH36 during multi-pass welding, and their subsequent effects on Charpy impact toughness, remains in great lack. In this study, submerged arc welding (SAW) was employed to carry out multi-pass welding on EH36 steel plates, followed by the low-temperature toughness test of weldments. Comsol software version 6.2 and finite element analysis are utilized to simulate the evolution of the microstructure, temperature, and residual stress fields throughout the multi-pass welding process. As welding progressed, the heat absorption along the vertical direction was enhanced; in contrast, a decrease is observed in the horizontal direction away from the heat source. This complicated temperature history favors the bainite transformation in the vicinity to the heat source, whereas areas more remote from the weld zone exhibit a higher prevalence of acicular ferrite due to the reduced cooling rate. The concentration of residual stress is predicted to occur at the boundary of the melt pool and at the interface between the weld and the heat-affected zone, with the greatest deformation observed near the fusion line at the top surface of the model. Furthermore, multi-pass welding may alleviate the residual stress, especially when coupled with the formation of acicular ferrite upon cooling, leading to improved low-temperature impact toughness in regions remote from the heat source. These findings offer valuable insights for the design and optimization of multi-pass welding in future applications. [ABSTRACT FROM AUTHOR]

This document is a summary of two journal articles in the field of materials science. The first article discusses the importance of microstructure design in achieving desired material properties, with a focus on metals and alloys in aeronautical and aerospace applications. It includes a list of related articles covering topics such as welding and phase transformation. The second article is a compilation of various research studies in materials science, covering topics such as the effects of boron additions on alloy microstructure and the properties of porous alloys. Both articles provide valuable insights into the behavior and properties of different materials. The document acknowledges the contributions of the authors and reviewers and expresses gratitude to the publisher, MDPI. [Extracted from the article]

A series of CaF2-Al2O3-TiO2 welding fluxes with TiO2 content from 20 to 60 wt.% were applied to join EH36 shipbuilding steel under high heat input submerged arc welding. The effect of TiO2 content on Charpy impact energy, inclusion characteristics, microstructure features, and chemical compositions of weld metals were systematically investigated. A maximum Charpy impact energy of 81.67 J was detected for the weld metal treated by the flux with 50 wt.% TiO2. Such unusual behavior was consistent with the initially increased and subsequently decreased changing trend for the faction of acicular ferrite, which is closely related to the formation, number density, and size distribution of significantly populated TiO2-containing inclusions that were largely dictated by the transfer of O and Ti. Current findings may serve as a viable way of tuning weld metal properties enabled by optimized flux designs. [ABSTRACT FROM AUTHOR]

The confinement boundaries of spent nuclear fuel (SNF) canisters are typically fusion welded. Welded microstructures, strain hardening, and residual stresses combined with a chemically aggressive, chloride-rich environment led to concerns that the welded canister may be susceptible to chloride-induced stress corrosion cracking (CISCC). A comprehensive understanding of the modification of stainless steel (SS) metallurgical and mechanical properties by fusion welding could accelerate the predictive analysis of CISCC susceptibility. This paper describes a submerged arc welding (SAW) procedure that was developed and qualified on 12.7 mm (0.5 in.) thick AISI 304/304L SS to produce joints in a way similar to actual SNF canister manufacturing. This procedure has the potential to reduce the production cost and weld CISCC susceptibility by using fewer welding passes and lower heat input than current industrial applications. Global and local mechanical behaviors and properties, as well as residual stress distributions on the welded joint, were studied. The results indicate that hardness values in the fusion zone (FZ) and heat-affected zone (HAZ) are slightly higher than that of the base metal. Strain localization was presented in the HAZ before the tensile stress reached its maximum value, and then it shifted to the FZ. The specimen finally broke in the FZ. High tensile residual stresses exhibited in the FZ and the nearby HAZ suggest the highest CISCC-susceptible spots. The maximum tensile residual stresses were along the welding direction, indicating that if cracks occur, they would be perpendicular to the welding direction. This study involved developing and qualifying a SAW procedure for SNF canister production. The new procedure yielded cost savings (SAW working efficiency increased by about 80%), improved mechanical properties, and presented moderate residual stresses. Analysis revealed that the welded joint's low-stress and high-stress damage assessments may be affected by shifts in the strain localization spot under loading. [ABSTRACT FROM AUTHOR]

The effect of heat treatment on microstructure, mechanical properties, and corrosion resistance of 410NiMo super martensitic stainless steel applied by Submerged Arc Welding on 21CrMoV5-11 sublayer has been investigated. The cladded steel was heat treated at different cycles which were; single stage heat treatment (600 °C-6 h), double stage heat treatment (700 °C-2 h & 600 °C-6 h), and austenitizing followed by double stage heat treatment cycles. Results revealed that austenitizing at 1000 °C followed by a double stage treatment improved the impact energy (75j) more than other cycles, due to the formation of austenite and dissolution of carbides and delta ferrite, while the lowest hardness was observed for the welded specimens heat-treated at 600 °C (318HV). It was further shown that the best corrosion resistance (icorr (A/cm2) = 1.02E−9 ± 5E−11 and Ecorr(Vvs Calomel) = − 0.132 ± 0.007) for the cladded steel was obtained by austenitizing the specimen at 1150 °C followed by the double stage treatment, due to the complete dissolution of the delta ferrite phase, chromium carbides, and homogeneous chrome distribution in the clad layer. [ABSTRACT FROM AUTHOR]

The article discusses the future trends and technologies in the welding industry, focusing on the vision of DNIPROMETYZ TAS, a leading manufacturer of welding wire in Ukraine. The article highlights the significant growth predicted in the welding materials market over the next six years, driven by industries such as automotive, fuel and energy, and pipeline construction. The main challenges faced by the industry include unstable raw material supplies, price fluctuations, and a shortage of skilled welders. DNIPROMETYZ TAS addresses these challenges by collaborating with educational institutions, investing in training, and providing technical assistance. The company also aims to expand its presence in the European market, particularly in Germany, and focuses on diversifying its products and introducing new technologies. The article emphasizes the importance of automation and innovation in the industry, as well as the integration of digital technologies. DNIPROMETYZ TAS offers a wide range of welding wire products and strives to be a strategic partner for its customers. The company is committed to producing high-quality products and has obtained various certifications to ensure compliance with international standards. In the future, DNIPROMETYZ TAS plans to continue investing in new technologies and expanding its product range to meet customer needs. The company aims to create innovative solutions that enhance the quality, reliability, and environmental friendliness of welding technologies. [Extracted from the article]

At present, a large amount of rice straw ash is being dumped as waste creating soil and water pollution. The manufacturing of welding fluxes requires minerals which are mined out from the earth's crust creating environmental ill effects. This paper presents a novel methodology for utilizing rice straw ash in the manufacturing of submerged arc welding (SAW) fluxes. The chemical composition of the joints produced with the developed flux is well within the acceptable range of American Welding Society (AWS) specifications. Their tensile strength and joint efficiency are 8% and 9% more than the joints produced with a commercial flux respectively. Their bead geometries are comparable to the beads deposited with the commercial flux. The joints are sufficiently ductile and could easily pass the bend test. The weld metal exhibits a desired microstructure containing acicular ferrite. This technology may turn the rice straw ash into a blessing in disguise. [ABSTRACT FROM AUTHOR]

API X70 steel requires high strength and toughness for safety in extreme environments like high pressure and low temperature. Submerged Arc Welding (SAW) is effective for manufacturing thick steel pipes. However, the welding heat input during SAW alters the microstructure and mechanical properties of the heat affected zone (HAZ). Therefore, investigating the correlation between microstructure and mechanical properties in welded X70 pipes is important to address potential degradation of HAZ and weld metal (WM). In this study, post weld heat treatment (PWHT) was performed to improve mechanical properties of HAZ and WM and to reduce residual stress caused by the welding process. We performed PWHT at 640°C for 15 hours and followed by air cooling. After heat treatment, we observed the microstructure through OM and SEM analysis, and investigated the mechanical properties through tensile test, hardness test, and Charpy impact test. [ABSTRACT FROM AUTHOR]

In submerged arc welding, evaluating elemental transfer behaviors is critical for selecting and designing welding materials. Accurate assessment of O, Si, and Mn transfer behavior is essential for ensuring process quality, particularly when silicon-manganese fluxes are applied. Traditional quantification methods, however, focus only on chemical reactions in the weld pool zone, potentially overlooking the cross-zone elemental transfer behavior and leading to significant predictive inaccuracies. This study investigates the CaO-SiO2-MnO flux, a prevalent silicon-manganese flux, focusing on O, Si, and Mn, which exhibit notable transfer behaviors of O, Si, and Mn. By employing a multi-zone approach and integrating various scientific principles, the research aims to improve the accuracy of predicting elemental transfer behaviors and deepen the understanding of the metallurgical processes in submerged arc welding when silicon-manganese fluxes are employed. The study proposes strategic enhancements to traditional quantification methods, which may offer valuable insights for the improvement of industry standards. This study demonstrates that considering only the local thermodynamic equilibrium of the weld pool zone when quantifying the transfer behavior of elements may lead to predictive errors, especially for easily evaporating metallic elements. By incorporating a cross-zone assessment for submerged arc welding process, i.e., introducing new quantifying parameters (Δd and Δw), the predictive accuracy of the transfer behavior of elements and their cross-zone actions can be enhanced. [ABSTRACT FROM AUTHOR]

The cable-type welding wire (CWW) submerged arc surfacing (SAS) is an innovative welding process with the advantages of high efficiency, energy saving, and good welding quality. At present, this welding process has been applied to repair the large structure. This study investigate the arc heat efficiency and arc heat distribution of CWW SAS using the mathematical calculation method. The deposition rate and the surfacing layer area of CWW SAS increases with the increasing welding current. The deposition rate and the surfacing layer area of CWW SAS are larger than those in single-wire SAS. The ratio of the surfacing layer area between CWW SAS and single-wire SAS is similar to the ratio of the surfacing deposition rates between CWW SAS and single-wire SAS. The efficiency of the arc heat on melting wire in CWW SAS is larger than that in single-wire SAS. The arc heat working on base metal in CWW SAS is lower than that in single-wire SAS, leading to a smaller molten base metal area. The arc heat working on droplet transfer in CWW SAS is greater than that in single-wire SAS, leading to a larger surfacing area. [ABSTRACT FROM AUTHOR]

The low-temperature fracture toughness of double-V weld seams is a well-known challenge due to the essential increased heat input for heavy-wall pipelines. A thorough investigation was conducted to explore the impact of the heat input on the grain size and precipitate coarsening, correlating the microstructure with the heat-affected-zone (HAZ) toughness. The results indicated that the actual weldments showed a toughness transition zone at −20 °C, with considerable scattering in Charpy V-notch (CVN) tests. Gleeble thermal simulations confirmed the decreased toughness of the coarse-grained HAZ (CGHAZ) with increasing heat input and prior austenite grain size (PAGS). A specially designed thermal treatment demonstrated its potential for enhancing the toughness of the CGHAZ, with the recommended thermal cycle involving peak temperatures of 700 and 800 °C, holding for 1 s, and rapid cooling. The toughness of the intercritically reheated CGHAZ (ICCGHAZ) improved with higher intercritical reheating temperatures and the removal of necklace-type M–A constituents along the PAG. Despite various thermal treatments, no significant improvements were observed in the toughness of the ICCGHAZ. Future work was suggested for optimising the use of tack welds to reduce the effective heat input (HI) associated with double-sided submerged arc welding (SAW). [ABSTRACT FROM AUTHOR]

CaF2-SiO2-CaO-TiO2 fluxes have been designed and employed to submerged arc weld EH36 shipbuilding steel. Pathways for O gain and loss of weld metal have been quantitatively evaluated. Results revealed that O gain and loss increase with higher TiO2 content, but the value of O gain is slightly greater than that of O loss, resulting in a net increase for weld metal O. Such findings yield a fine-tuned strategy for formulating fluxes with lower O potential. [ABSTRACT FROM AUTHOR]

Fused CaF2-TiO2 fluxes are formulated to clarify the role of TiO2 upon columnar austenite grains within the weld metal of EH36 shipbuilding steel subjected to high heat input submerged arc welding. As the TiO2 content varies from 0 to 40 wt pct, weld metal geometries are significantly altered. Additionally, the volume fraction of columnar grains is found to experience a maximum value at 30 wt pct TiO2, which is inversely concurrent to the width variation. [ABSTRACT FROM AUTHOR]

This paper focuses on optimizing the submerged arc welding encapsulation for domestic steel mills producing bridge stainless steel composite plates. It utilizes a combination of numerical simulation and experimental methods to investigate the changes in temperature field and stress field at the weld joint of the Q370qE/31603 stainless steel composite plate using submerged arc welding. The submerged arc welding of Q370qE/31603 stainless steel composite plate is modeled by the ABAQUS software. The submerged arc welding heat source model is represented by double ellipsoidal heat source model and written in Fortran language. The correctness of the stress field was verified by a layer-by-layer electrolytic polishing method based on the X-ray diffraction method to measure the residual stress at different locations after welding. The simulation and experimental results show that the finite element model is very effective for predicting the temperature and stress of submerged arc welding. By changing the parameters of the submerged arc welding process, the effects of different welding process parameters on the temperature field during the welding process, and the distribution state and pattern of post-weld residual stress were studied. Additionally, the research on the thermo-mechanical coupling for the submerged arc welding process of stainless steel composite plate has been carried out; it was found that there is a strong interaction between temperature and stress fields. The hot rolling tests of the stainless steel composite plates were conducted after welding encapsulation to verify the effectiveness of the submerged arc welding encapsulation model. [ABSTRACT FROM AUTHOR]

The work is aimed at studying the effect of additions of oxides K2O, Na2O, MgO, Al2O3 on slag density and viscosity, as well as the separability and covering capacity of slag of the CaO–MnO–SiO2 system obtained by melting the fused flux during automatic arc welding of low-carbon steels. The subject of research is physicochemical and technological properties of slags, mechanical properties of welded joints obtained as a result of the process of automatic submerged arc welding. It is shown that with an increase in K2O and Na2O content slag density and viscosity, as well as the separability of the slag crust, decrease, and an increase in MgO and Al2O3 content increases slag density and viscosity. Based on results of the work, a composition of the slag base of fused flux is developed on the basis of oremineral raw materials of the Republic of Uzbekistan, selected on the basis of the CaO–MnO–SiO2 ternary system melting diagram. The results obtained make it possible to increase welded joint strength properties by 10–12%. [ABSTRACT FROM AUTHOR]

The influence of welding repair technology on structural and phase composition and mechanical properties of longitudinal pipe joints within the area of stopping the process of submerged arc mechanical welding during manufacture of pipes made of steels of strength categories K60, K65 is investigated. [ABSTRACT FROM AUTHOR]

The influence of chemical composition of steels of strength classes K65 and K80 on austenite decomposition kinetics, impact strength, and hardness of the overheating zone for cooling rates typical for multiarc submerged arc welding and manual arc welding is investigated. The range of cooling rates within which the mechanical properties meet standard requirements for the welding methods considered is determined. Welding production parameters are determined using an analytical calculation method providing a selected range of cooling rates. [ABSTRACT FROM AUTHOR]

The physical phenomena of submerged arc welding (SAW) conducted with a 1.6 mm flux-cored wire were investigated using X-ray imaging technique. Three kinds of metal transfer modes were confirmed in this paper, namely the front flux wall-guided droplet transfer, back flux wall-guided droplet transfer, and repelled droplet transfer, of which the corresponding percentages were 47.65%, 45.29%, and 7.06%, respectively. Although the average sizes of the droplets for SAW and FCAW (flux-cored wire welding) were 2.0 mm and 1.9 mm with an average droplet transfer time of 90.3 ms, it required 36.4% more time for the droplet of SAW to finish one metal transfer than it did in FCAW. In addition, the volume of the cavity was not constant but repeated a cycle mode of "expansion and contraction" during the whole process. Thus, the dynamics of the cavity and viscous resistance caused by the flux collectively slowed down the velocity of the droplets from the wire to the weld pool in SAW. Compared with FCAW, a smoother weld without pits and pores was manufactured during the SAW process. Due to the compression effect of the flux, the 14.5 mm average weld width of SAW was 2.9 mm shorter than that of the FCAW. Furthermore, the thickness of slag with a porous structure in SAW was 2.7 times of that in FCAW, indicating that it could provide better protection to the weld of SAW. [ABSTRACT FROM AUTHOR]

The present study aims to explore experimental investigations and numerical simulations for temperature distributions at heat-affected zones within SA 387-Gr.11-Cl.2 steel during the submerged arc welding (SAW) process. Experimental endeavors entailed welding steel plates under controlled conditions, precisely measuring temperatures at key locations by thermocouples. A special program based on 3D Goldak’s double ellipsoidal model was developed in ANSYS Parametric Design Language for moving heat source calculations in the finite-element analysis (FEA). For welding an 8 mm thick plate with one pass, the suitable parameters were found to be 600 A current, 31 V voltage, and 10 mm·s−1 welding speed. The experimental cooling periods were found to be slower than predicted by FEA. When temperature distributions were compared between experimental and FEA results, an average variation of 1.88% at peak temperatures and 11.8% at completion time was observed. The results showed the temperature distribution at various time steps, illustrating the transient nature of the welding process. The results highlight the capacity of the FEA model to predict temperature profiles during SAW accurately, presenting a potent tool for optimizing welding parameters without extensive trial and error.

Hardfacing deposition processes were carried out using unalloyed S1-EL12 welding wire and submerged arc welding fluxes produced by agglomerated method containing 4-16 wt.% ferrochromium and 2 wt.% ferroboron to achieve wear-resistant of hardfacing deposits on common steel substrates via submerged arc welding. Typical parameters such as slag detachment behaviour, measurements of weld seam widths and heights, microstructural examinations, and hardness and wear tests of hardfacing deposits were characterized. End of the characterization processes, with the increase of chromium, carbon, and boron transition from welding fluxes to hardfacing deposits, the welding seam widths, and heights were determined to increase from 14.12 mm to 15.65 mm and 6.14 mm to 6.50 mm, respectively. Besides; carbide and boro-carbide ratios in the microstructures increased, the hardness values increased from 43 HRC to 61 HRC and the wear losses decreased from 5.79 to 4.43. (10 –7 mm 3 (N m) –1).

One large-current high-power full-bridge DC-DC converter is often used to cater several multi-characteristic welding loads. The load could be a welding arc or a conductive molten flux. The contour of operating point (voltage-current) of each load type is different. The converter often operates under complex light-load conditions. The design of such high power continuous-duty converter needs to meet three objectives – desired control performance, high across-the-load efficiency, and superior thermal management. To address the thermal issues, this article proposes to use parallel-connected converter modules. It helps distribute the power loss over larger component base; increased surface area would assist the heat removal process. For high operating efficiency, this article proposes superior component engineering in each module. And, for high across the load efficiency, this article proposes to enable or disable an efficient converter module based on the current demand. It means each converter module is equipped to feed the connected load in stand-alone mode. For reduction of power loss, this article elaborates the role of each critical component. The distribution of heat loss would be optimally shared if the current sharing by converter modules is equal, but it needs to be compatible to the dynamic behavior of multi-input process loads. This research proposes and practically validates that single PWM-controller driven parallel-connected converter-modules are not only compatible to process dynamics, the idea would achieve proper current sharing among similar components.

The 18 mm thick Q235A low carbon steel plates were welded via the ultra-narrow gap metal active gas arc welding (ultra-NGMAGW) and narrow gap submerged arc welding (NGSAW), and the microstructure and mechanical properties of the welded joints' area were characterized. The results showed that there is acicular ferrite (AF) in the weld zone of the joint obtained via the ultra-NGMAGW. The AF grains are fine and have a great difference in growth direction, resulting in high local dislocation density. However, there is no AF in the welded joint obtained via the NGSAW. Using numerical simulation analysis of the temperature field distribution and the thermal cycle curve in the welding process of the ultra-NGMAGW, it was found that the mechanism of microstructure evolution is that during the welding process of the ultra-NGMAGW, the heat input is low, the cooling rate is quick, and the residence time in the high temperature region is short. Therefore, pearlite with coarse grains is basically not formed. AF nucleates in different directions with inclusions as the core. The tensile strength of the weld joint obtained via the ultra-NGMAGW is 643 MPa, which corresponds to 139% of that of the base metal, and 132% of that obtained via the NGSAW. The ultra-NGMAGW joints exhibited better tensile strength and higher microhardness than the NGSAW joints, which is mainly due to the existence of AF. [ABSTRACT FROM AUTHOR]

This study focuses on the metallurgical characterization of single and multi‐layer martensitic hard surfacing onto non‐standardized low‐chromium alloy steel with a single buttering layer using an automatic submerged arc welding process as a standard reference. The metallurgical properties of hard surfaced samples are examined using an optical microscope, energy dispersive x‐ray spectroscopy, and x‐ray diffractometer. Micro‐Vickers hardness testing is also conducted to analyze and confirm the metallographic results of hard surfacing. The current study finds that the microstructure of each region is influenced by three key factors: chemical composition, heat input, and dilution. The structural type is determined by the chemical composition of materials, heat input influences the structural characteristics in the heat‐affected zone (needle‐shape martensite and tempered martensite), and dilution affects the structural characteristics of the hard surfacing layers (martensite with retained austenite). Comparing multi‐layer hard surfacing to single‐hard surfacing, the hardness values of the heat‐affected zone of the multi‐layer hard surfacing are greatly reduced, while the hardness values of the hard surfacing layers are raised. [ABSTRACT FROM AUTHOR]

The impact toughness, microstructure and break features of low-alloy steel weld samples produced by automatic submerged arc welding have been compared. It has been established that when a notch is applied along the weld axis, fracture occurs along large grains of grain-boundary ferrite 80–140 μm in size with an unfavorable cleavage planes orientation {001}. The combination of such grains with non-metallic inclusions 3–5 μm in size facilitates the transcrystalline cleavage initiation. The effect of austenite grain size, crystallographic texture, and intergranular fracture on the impact toughness value is shown. Continuous chains of grain-boundary ferrite at the front of the main crack line up along the notch-parallel boundaries of columnar grains of axial orientation, which increases the tendency to transcrystalline cleavage. At the same time, with the lateral orientation of the columnar grains of the former austenite, the front line of the main crack intersects only certain separate areas of the grain-boundary ferrite. Offset notch results in an increase in both impact toughness and plasticity of weld metal. [ABSTRACT FROM AUTHOR]

In this paper, the influence of the silicon (Si) content on microstructure and impact property of submerged arc weld metals (WMs) for weathering bridge steel was clarified. Actual submerged arc welding (SAW) was carried out to produce WMs with 0.18 wt.%, 0.36 wt.%, 0.51 wt.%, and 0.60 wt.% of Si. The low temperature impact property of weld metal was detected, and the weld microstructures were characterized by optical microscopy (OM), scanning and transmission electron microscope (SEM and TEM), and electron backscatter diffraction (EBSD). The results indicate that WMs consist of polygon ferrite (PF), acicular ferrite (AF), granular bainitic ferrite (GBF), and martensite/austenite (M/A) constituents in each Si content. With increasing Si, the proportion of PF increased, while AF and GBF coarsened, the area fraction, fM/A, and the mean size, dM/A, of M/A constituents increased, the number of inclusions decreased, but the size increased. Further, the fraction of high-angle grain boundaries (HAGBs) with the misorientation tolerance angles (MTAs) greater than 15° reduced, while the mean equivalent diameter, MEDMTA≥15°, of ferrite grains with HAGBs increased. Accordingly, the impact toughness of WM was degraded from 108.1 J to 39.4 J with the increase in Si. The increase in M/A constituents and inclusions size reduced the critical fracture stress, thereby formation of larger microcracks and cleavage planes occurred. The reduced HAGBs exhibited a low hindering effect on crack propagation, and, consequently, the impact toughness decreased with increasing Si content. [ABSTRACT FROM AUTHOR]