Showing papers on "Shielded metal arc welding published in 2018"

Wire arc additive manufacturing of Al-6Mg alloy using variable polarity cold metal transfer arc as power source

Abstract: A variable polarity cold metal transfer (VP-CMT) arc power source with different arc modes was employed in additive manufacturing Al-6Mg alloy parts. The microstructures were characterized using scanning electron microscopy with electron back-scattered diffraction. Even equiaxed grains in size of 20.6–28.5 µm with random orientation were obtained under VP-CMT mode, while a large number of columnar grains in bigger size exist in samples under other arc modes. Tensile strength of the VP-CMT sample with a maximum of 333 MPa is higher than that of the Al-6Mg wrought alloys due to fine-grain strengthening. However, the tensile strength of the VP-CMT sample in different tensile direction was anisotropic, with a percentage of 8–27%. The comprehensive analysis of defects and grain orientation showed that the micro pores in interlayer pore region lead to the anisotropy.

Effect of Weld Consumable Conditioning on the Diffusible Hydrogen and Subsequent Residual Stress and Flexural Strength of Multipass Welded P91 Steels

Abstract: P91 steel weld joint was prepared using the shielded metal arc welding process and four different conditions of weld consumable that provide the different levels of diffusible hydrogen in deposited metal. In the present research, the effects of diffusible hydrogen content on the flexural strength, lower critical stress, and tensile strength of P91 steel welds were also determined with respect to different electrode conditions. To investigate the effect of diffusible hydrogen on multipass welding, top and root side flexural tests were performed. The residual stresses (axial stress and transverse stress) were also measured using the blind hole drilling method for different conditions of welding consumable. The peak value of residual stresses was measured at the center of the weld fusion zone. The maximum value of transverse stress was measured to be 355 MPa for case II (6.21 mL/100 g of diffusible hydrogen), while the maximum axial stress was about 218 MPa for case IV (12.43 mL/100 g of diffusible hydrogen). A three-dimensional finite element simulation was also performed to predict the residual stress distribution and thermal profile along the welded joint. The experimentally determined residual stresses correlated well with the numerically estimated residual stresses. The diffusible hydrogen content was not observed to have any significant effect on the residual stresses. The corrected residual stress values were also predicted by considering the plasticity-induced error. However, the flexural performance of the welded joint was affected by the diffusible hydrogen content. The top and root flexural strength was measured to be optimum for the low level of diffusible hydrogen content, and the values decreased with an increase in diffusible hydrogen content.

Repairing casting part using laser assisted additive metal-layer deposition and its mechanical properties

Abstract: Generally, it is known that a welding technology is not suitable for repairing casting parts due to metallurgical issues and high carbon contents. So, the repairing of cast iron by welding has not been satisfactorily realized yet, resulting in microstructure changes in the welding area, which greatly impacts on crack initiation and growth as well as Martensite formation in the repaired area and heat affected zone (HAZ). In this study, we evaluated how the HAZ affected the mechanical properties of gray cast iron after it was repaired by the traditional welding process (shielded metal arc welding) and by the additive metal-layer deposition (AMD) process using a laser. The results indicated that the ultimate strength of each repaired part reduced by up to 16% when compared to that of the original specimen composed of only cast iron, FC300. However, the elongations of the specimens varied according to the repair methods. In the case of repair welding, the elongation decreased by approximately 20%. However, in the case of repairing by AMD, the elongation increased dramatically to approximately 60%. Hence, the proposed repairing method based on AMD appears to be a promising method for repairing castings.

Hot wire-assisted gas metal arc welding of hypereutectic FeCrC hardfacing alloys: Microstructure and wear properties

Abstract: The deposition welding of hypereutectic FeCrC hardfacing alloys requires low dilution rates in order to ensure the specified chemical composition and thus the precipitation of primary M7C3 (M = Fe, Cr) carbides, which affect the abrasive wear resistance of the hardfacing. Because dilution is critical in determining the above mentioned criteria during surfacing, the development of deposition welding processes with reduced thermal impact and hence reduced dilution of the base material is a main focus of current research. For the purpose of improving the processing properties of gas metal arc welding (GMAW) in hardfacing applications, the potential of an additional hot wire (HW-GMAW) was investigated. The application of a hot wire enabled the independent adjustment of the deposition and dilution rates. Furthermore, the dilution and microstructural properties could be adjusted independently of the deposition rate. HW-GMAW enabled hypereutectic solidification in the first layer, even at very high deposition rates of 9 kg/h. In this manner, a primary M7C3 carbide content reaching 17% by area (A%) was achieved in the first layer. In comparison to single-layer GMAW overlays the wear properties were improved.

Aluminium to steel resistance spot welding with cold sprayed interlayer

Abstract: Studies on bonding of aluminium alloys to steels are popular because these are structural materials widely used in a variety of industries. However, joining these dissimilar materials is difficult mainly because of the formation of brittle intermetallic compounds. This paper presents a study on welding aluminium to steel by resistance spot welding. Before the welding, steel surface was covered by cold spraying with the layer of aluminium, nickel and nickel–aluminium. This way, instead of the welding of dissimilar materials, the welding of aluminium to aluminium (or nickel) layer pre-deposited on the steel sample was performed. The feasibility of using interlayers for improving the welding of dissimilar materials was tested using SEM, EDX and XRD. Mechanical properties of welds were investigated by microhardness and shear strength tests. The results showed that the coating allowed to decrease hardness in the welding zone and to increase the shear strength of the weld.

RBF-NN-based model for prediction of weld bead geometry in Shielded Metal Arc Welding (SMAW)

Abstract: Welding processes are considered as an essential component in most of industrial manufacturing and for structural applications. Among the most widely used welding processes is the shielded metal arc welding (SMAW) due to its versatility and simplicity. In fact, the welding process is predominant procedure in the maintenance and repair industry, construction of steel structures and also industrial fabrication. The most important physical characteristics of the weldment are the bead geometry which includes bead height and width and the penetration. Different methods and approaches have been developed to achieve the acceptable values of bead geometry parameters. This study presents artificial intelligence techniques (AIT): For example, radial basis function neural network (RBF-NN) and multilayer perceptron neural network (MLP-NN) models were developed to predict the weld bead geometry. A number of 33 plates of mild steel specimens that have undergone SMAW process are analyzed for their weld bead geometry. The input parameters of the SMAW consist of welding current (A), arc length (mm), welding speed (mm/min), diameter of electrode (mm) and welding gap (mm). The outputs of the AIT models include property parameters, namely penetration, bead width and reinforcement. The results showed outstanding level of accuracy utilizing RBF-NN in simulating the weld geometry and very satisfactorily to predict all parameters in comparison with the MLP-NN model.

Evaluating the Properties of Dissimilar Metal Welding Between Inconel 625 and 316L Stainless Steel by Applying Different Welding Methods and Consumables

Abstract: The current work was carried out to characterize welding of Inconel 625 superalloy and 316L stainless steel In the present study, shielded metal arc welding (SMAW) and gas tungsten arc welding (GTAW) with two types of filler metals (ERNiCrMo-3 and ERSS316L) and an electrode (ENiCrMo-3) were utilized This paper describes the selection of the proper welding method and welding consumables in dissimilar metal joining During solidification of ERNiCrMo-3 filler metal, Nb and Mo leave dendritic cores and are rejected to inter-dendritic regions However, ERSS316L filler metal has small amounts of elements with a high tendency for segregation So, occurrence of constitutional super-cooling for changing the solidification mode from cellular to dendritic or equiaxed is less probable Using GTAW with lower heat input results in higher cooling rate and finer microstructure and less Nb segregation The interface between weld metal and base metal and also unmixed zones was evaluated by scanning electron microscopy and energy dispersive X-ray (EDX) analysis Microhardness measurements, tensile test, and Charpy impact test were performed to see the effect of these parameters on mechanical properties of the joints

Mechanical properties and microstructure of SMAW welded and thermically treated HSLA-80 steel

Abstract: This paper aims to present a comparison on the use of different heat treatment conditions in association with welding of a HSLA-80 steel. This investigation was carried out by multipass welding using the coated electrode process in different heat treatment conditions, with or without pre- or post-weld heating, in order to compare effects on the mechanical properties and microstructure for each condition. After welding was performed, procedures to identify microstructural phases and characterize the mechanical behavior were carried out. The results of mechanical tests and metallographic analysis were conclusive that heat treatments are not necessary to complement welding procedures of this steel. This is especially the case of the post-welding heat treatment. In fact, the application of these treatments did not significantly affect neither the microstructure nor the mechanical characteristics of the material.

Effect of Heat Input on Microstructure and Corrosion Behavior of Duplex Stainless Steel Shielded Metal Arc Welds

Abstract: In the present work, UNS S32750 super duplex stainless steel sheets were welded by shielded metal arc welding process with E2595 electrode using two different heat inputs, 0.54 and 1.10 kJ/mm. Microstructural investigations (optical and scanning electron microscopy) showed very small differences in the heat affected zone for both the heat inputs. The weld metals showed presence of three different morphologies of austenite—Widmanstatten, intra-granular and grain boundary austenite along with ferrite. Ferrite content in the weld region was also nearly same and did not change significantly with the increase in heat input. Both the weldments showed similar mechanical properties (ultimate tensile strength, impact strength and hardness) and failed in a ductile manner. Electrochemical studies in 3.5% NaCl solution showed the degree of sensitization to less than 1% and nearly same pitting potential for both heat inputs. Since the effect of heat input on the weld behavior was negligible, low heat input may be preffered for welding UNS S32750 super duplex stainless steel.

Study of the sensitivity of high-strength cold-resistant shipbuilding steels to thermal cycle of arc welding

Abstract: Structure and properties of welded joints of low-alloy thermomechanically processed (09G2FB) and quenched and tempered shipbuilding steels (10XN2MD, 08XN3MD, and 12XN3MF), welded with manual metal arc welding (MMA) and submerged arc welding (SAW), were studied. Effects of specific energy input on the microstructure, mechanical properties, and impact energy of the heat-affected zone (HAZ) have been investigated, and probable reasons for crack formation in welded joints have been found. It was found that welding heat input increase leads to a significant increase in grain size near the fusion boundary and the formation of martensite with high hardness. Therefore, the heat input is recommended to be limited to 2.5–3.5 kJ/mm for these specific steel grades. The study indicates that microalloying elements can be used to limit the grain growth when the steel is subjected to high temperatures during welding thermal cycle. Carbon content and alloying level reduction tend to increase the steel ductility and lower the HAZ toughness.

Influence of welding parameters on diffusible hydrogen content in high-strength steel welds using modified spray arc process

Abstract: In order to satisfy the growing requirements towards lightweight design and resource efficiency in modern steel constructions, e.g., mobile cranes and bridges, high-strength steels with typical yield strength ≥ 690 MPa are coming into use to an increasing extent. However, these steels require special treatment in welding. The susceptibility for degradation of the mechanical properties in the presence of hydrogen increases significantly with increasing yield strength. In case of missing knowledge about how and the amount of hydrogen that is uptaken during welding, hydrogen-assisted cracking (HAC) can be a negative consequence. Moreover, modern weld technology like the modified spray arc process enables welding of narrower weld seams. In this context, a reduced number of weld beads, volume, and total heat input are technical and economical benefits. This work presents the influence of welding parameters on the diffusible hydrogen content in both (1) single-pass and (2) multi-layer welds. Different hydrogen concentrations were detected by varied contact tube distance, wire feed speed, arc length, and varied arc type (transitional arc and modified spray arc). The results show that all welding parameters have significant influence on the diffusible hydrogen concentration in the single-pass welds. By increasing the number of weld beads in case of multi-layer welding, the hydrogen concentration has been reduced. Whereby, differences in hydrogen concentrations between both arc types are present.

Cancer risk assessment for occupational exposure to chromium and nickel in welding fumes from pipeline construction, pressure container manufacturing, and shipyard building in Taiwan.

Abstract: OBJECTIVE We assessed the cancer risks resulting from the exposure to chromium, hexavalent chromium (Cr (VI) ), oxidic nickel (Ni), and soluble Ni in welding fumes during pipeline and shipyard construction and pressure container manufacturing in Taiwan. We also determined the roles of welding performance and demographic characteristics during the exposure to Cr and Ni. METHODS Personal air samples were collected for the analysis of Cr and Ni, and the concentrations of Cr (VI), oxidic Ni, and soluble Ni were quantified. We assessed cancer slope factors for Cr, Cr (VI), oxidic Ni, and soluble Ni, and we used the Incremental Lifetime Cancer Risk model proposed by the United States Environmental Protection Agency to calculate excess risk. RESULTS The risks of exposure to Cr and Cr (VI) in welding fumes exceeded the acceptable level of occupational exposure (10-3). We ranked the excess cancer risk in three industries in decreasing order as follows: pipeline construction, shipyard construction, and pressure container manufacturing. The most sensitive parameters for the risk assessment were Cr and Ni concentrations. Statistically significant determinants of Cr (VI), oxidic Ni, and soluble Ni concentrations were the following: stainless steel as the base metal and the filler metals of shielded metal arc welding (SMAW) and of gas tungsten arc welding (GTAW). CONCLUSION The study revealed that welders belong to a high cancer-risk group. Furthermore, we demonstrated the roles of filler metals and stainless steel in exposure to Cr and Ni.

Shielded metal arc welding of UNS S32750 steel: microstructure, mechanical properties and corrosion behaviour

Abstract: In the present investigation, ER2594 (conventional) and ER2595 (consisting of additional Cu and W) electrodes were used to produce butt joints of 5.5 mm thick super duplex stainless steel (UNS S32750) sheets using shielded metal arc welding (SMAW) process. During SMAW process, the heat input was 0.81 kJ mm−1 for ER2594 electrode and 0.75 kJ mm−1 for ER2595 electrode. Optical microscope and scanning electron microscope were used to observe the microstructures of different zones, namely, fusion zone (FZ), heat affected zone (HAZ) and base metal (BM). Tensile test, impact test and micro-hardness measurements were carried out for both the weldments on samples cut across the weld. The microstructures of the FZ consisted of inter-granular austenite (IGA), grain boundary austenite (GBA) and Widmanstatten austenite (WA). There was minor change in the width of the HAZ of the weldments with the change in electrode. This is expected to be due to the minor change in the heat input during SMAW process. The weld zone (cap pass) of both the weldments predominantly showed WA and mode of solidification was found to be ferritic (F mode). The tensile strength of both the weldments was approximately same as that of base metal and both the samples fractured through the BM. Cr, Fe and Mo rich precipitates were found in the FZ (weld region), which are expected to be formed due to pick of gaseous content from the atmosphere during welding. The FZ of the weldments produced by ER2595 electrode showed better pitting corrosion resistance than those produced by ER2594 electrode.

Enhancement of mechanical properties of low carbon steel joints via graphene addition

Abstract: Steel base metal laps or welding electrode surfaces were coated using graphene suspensions with various concentrations, and then the steel plates were welded using the shielded metal arc welding process. Microstructural observations showed that the addition of graphene to the weldment significantly refines the microstructure and promotes the formation of fine acicular ferrite. The results of mechanical testing indicated that with lower concentrations of graphene in the weldment, both the strength and ductility improve, but the hardness remains unchanged in comparison to the unreinforced weld metal. However, reinforcing with a higher concentration of graphene gives rise to the significant enhancement of the hardness and strength without deterioration of the ductility.

Effect of Ti Addition on the Microstructure and Mechanical Properties of Weld Metals in HSLA Steels

Abstract: Acicular ferrite (AF) can significantly improve the mechanical properties of steel welds. One practical approach to enhance the formation of AF is to provide the heterogonous nucleation sites such as Ti oxides. In this study, Ti was added to different conventional welding processes including shield metal arc welding (SMAW), submerged arc welding (SAW) and tandem SAW (T-SAW). In the SMAW process, TiO2 particles as a source of Ti were inserted into the weld groove, while in the SAW and the T-SAW processes, the Ti-enriched S2MoTB wire was used as the filler metal. The microstructural evolution of weldments was characterized by employing optical and scanning electron microscopes. In addition, microhardness (Vickers, HV), Charpy impact and tensile tests were carried out to investigate the mechanical properties of weldments. Although the microhardness measurements of all weldments did not vary significantly and were in the range of 205-252 HV, there was a considerable difference in tensile and impact properties of the SAW and the T-SAW weldments. In the SMAW process, the addition of TiO2 results in no significant enhancement in tensile and impact toughness. This can be attributed to the inhomogeneous distribution of TiO2 particles as well as the formation of large inclusions in the structure. On the other hand, Ti addition to WM increased the yield strength from 489 to 552 MPa for the SAW process, and in contrast, it decreased the impact toughness from 75 to 33 J. This detrimental effect can be related to the higher deposition of other alloying elements in the WM and the formation of more ferrite side plate phase. By applying the T-SAW process, more Ti in WM led to a higher content of AF in the microstructure and increased both yield strength and impact toughness from 528 to 595 MPa and 100 to 180 J, respectively.

Effect of welding process parameters on hybrid GMAW-GTAW welding process of AZ31B magnesium alloy

Abstract: MIG-TIG double arc welding of magnesium alloy was studied in this paper. The effects of different welding process parameters (bypass current, wire extension, distance between the tungsten electrode, and the workpiece) on weld forming were analyzed, and the craft parameters were obtained through the technology experiment. The favorable forming weld was obtained at the total current of 225 A, bypass current of 140 A, welding voltage of 21 V, welding speed of 2.8 m/min, distance between end of tungsten electrode, and the workpiece of 5 mm. The effect of the process parameters on welding process and weld was analyzed to provide a theoretical basis for further improving the stability of double arc welding of magnesium alloy and obtaining the weld which was in high quality and good forming.

An improved model for cold metal transfer welding of aluminium alloys

Abstract: An improved model is proposed for automated cold metal transfer (CMT) welding based on a time-dependent double-ellipsoidal volumetric heat flux distribution. Equations are evaluated numerically within COMSOL Multiphysics for CMT welding of a 3-mm-thick AA5754 Al–Mg alloy plate. The simulation calculates transient and steady-state temperature distributions within the weld seam and heat-affected zone (HAZ). Validation of the model is achieved by comparing simulated temperatures with measured values from thermocouples in the HAZ during welding experiments, as well as through comparison of the calculated fusion zone and microscope images of the weld seam. Under steady-state conditions, large differences between the peak and average calculated temperatures in the weld pool highlight the underlying phenomenon responsible for improvements in weld quality for thin sheets with CMT compared to conventional joining processes. The developed simulation provides opportunities for process optimisation and sensitivity analysis in many applications.

Microstructural Evolution and Mechanical Properties of CSEF/M P92 Steel Weldments Welded Using Different Filler Compositions

Abstract: In the present investigation, P92 steel weld joints were prepared using a shielded metal arc welding (SMAW) process for two different fillers, E911 and P92. A comparative study was performed on the microstructural evolution, tensile strength, microhardness, and Charpy toughness across the P92 steel weldments in the as-welded and post-weld heat-treated (PWHT) conditions. The PWHT was performed at 760 °C for 2 hours. To study the effect of the different filler metals and PWHT on the mechanical properties, longitudinal and transverse tensile tests were carried out at room temperature for a constant cross-head speed of 1 mm/min. In the longitudinal direction, the tensile strength of the P92 steel welds was measured as 958 ± 35 and 1359 ± 38 MPa for the E911 and P92 filler, respectively. In the as-welded condition, the transverse tensile specimens were fractured from the fine-grained heat-affected zone or inter-critical heat-affected zone (FGHAZ/ICHAZ) and, after PWHT, the fracture location was shifted to over-tempered base metal from the FGHAZ/ICHAZ. After the PWHT, the tempering reaction resulted in lowering of the hardness throughout the weldment. After PWHT, the Charpy toughness of the weld fusion zone and heat-affected zone (HAZ) of the E911 filler weldments was measured as 66 ± 5 and 142 ± 8 J, respectively. The minimum required Charpy toughness of 47 J (EN1557: 1997) was achieved after the PWHT for both E911 and P92 filler.