Plate Welding Research Articles

Microstructure and Mechanical Properties of the Ternary Gas Shielded Narrow-Gap GMA Welded Joint of High-Strength Steel

An 80%Ar-10%CO2-10%He ternary gas mixture was used as the shielding gas during the narrow-gap welding of thick Q690E high-strength steel plates. Complete and defect-free welded joints were obtained, and the microstructure and mechanical properties of the welded joint were investigated. The weld zone consists of a solidification area and interlayer zone, and the heat-affected zone consists of a coarse-grain heat-affected zone (CG-HAZ) and a fine-grain heat-affected zone (FG-HAZ). The microstructures of the weld zone are mainly lath bainite (LB), acicular ferrite (AF), and granular bainite (GB). The microstructure of the CG-HAZ is lath martensite (LM) and the microstructure of FG-HAZ is GB. Methods with different heat inputs were used to study their effects on the mechanical properties of the welded joint. It was found that the microstructure and mechanical properties of the welded joints are better with lower heat input. With tandem wire narrow-gap GMA welding, the tensile strength of the joints declined from 795.3 to 718.3 MPa and the impact toughness at −40 °C resulted in a weak position in the weld zone, which declined from 76~81 J to 55~69 J, when the welding speed reduced from 350 to 250 mm/min. With oscillating-arc narrow-gap GMA welding, the tensile strength achieved 853.4 MPa and the impact toughness at −40 °C was around 69~87 J. The results indicated that, under the appropriate heat input, the tensile strength of the joint exceeds 770 MPa and the low temperature impact toughness at −40 °C exceeds 69 J. A 155 mm-thick Q690E steel welded joint was obtained and the mechanical properties of the welded joint meets the requirements of the offshore drilling platforms.

Cover plate welding sequence and shape rationality simulation analysis on wall cracks of stainless steel spent fuel pool

The wall of spent fuel pools is prone to pitting or electrochemical corrosion owing to a long-term service in acidic media, where a penetrating cracking may occur in severe cases. Moreover, totally replacing the spent fuel pool causes huge economic losses. Thus, cover plate welding is used to repair the cracked region of spent fuel pools using the ‘fitness for service’ principle. The finite element method is used to simulate and analyse the temperature and stress fields during the repair process of cover plate welding to guarantee that the repair process does not cause new dangerous effects on the cracked region. In this study, we used self-fusion gas tungsten arc welding (GTAW) to cover defects with square and circular patch plates. The modified double-ellipsoid heat source model is derived for cure welding. The effects of two patch plate shapes and different welding sequences on the temperature and stress fields during the welding process were compared using numerical analyses. Finally, a reasonable patch board shape and welding sequence were determined.

Multi-pass butt welding of thick AISI 316L plates by gas tungsten arc welding: Microstructural and mechanical characterization

Austenitic stainless steels exhibit excellent properties such as outstanding formability even at cryogenic temperatures, high mechanical properties and good corrosion performance. This makes them attractive for use in various industries ranging from petro-chemical industries, food industry, medical-dental equipments, and pressure vessels to LNG tanks and welding is often required in most of these applications. Especially with the increase in energy crisis in recent years, the production of LNG tanks using conventional arc welding processes is important. In this study, the weldability of 10 mm thick 316 L stainless steel plates used in the production of LNG tanks by gas tungsten arc welding was investigated. The effect of multi-pass welding on the microstructural evolution and thus on mechanical behavior of the joint produced was studied. Optical microscopy and scanning electron microscopy as well as energy dispersive spectroscopy were employed to investigate the microstructural evolution in the weld region of the joint fabricated. In addition, microhardness measurements and tensile testing were conducted to mechanical characterization. As a result of the study, a slight hardness increase was observed within the weld region of the joint compared to that of the base material. The welded joint exhibited higher yield and tensile strength values, namely 329 and 630 MPa respectively, than the base plate which displayed a yield strength of 308 MPa and a tensile strength of 603 MPa.

Prediction and Validation for Welding Deformation of the Upper Port Stub

The vacuum vessel (VV) as an ultrahigh vacuum pressure vessel is one of the essential components of the Chinese Fusion Engineering Test Reactor (CFETR) device. VV has strict position tolerance. The VV port stub is a typical large-scaled welded structure manufactured by electron beam welding (EBW) technique. Welding has the most significant influence on deformation. Therefore, it is essential to analyze welding deformation. A systematic welding simulation method aimed at welding deformation controlling for a large EB welded structure is proposed in this article. First, the dynamic process of EBW of 50-mm-thick ultralow carbon austenitic stainless steel was simulated based on the thermal elastoplastic theory. The weld forming mechanism of high energy density welding of the thick plate was revealed. Then the inherent strain extracted from the results of the simulation of local welding was introduced to the simulation of tailor welding of the port stub. Finally, optimal welding sequence and clamping conditions were obtained, and the reliability of the simulation was verified by the profile measurement results of the inner shell of the upper port stub.

입열량 변화에 따른 용접부 충격강도에 관한 기초 수치해석 연구

The welding of thick steel plates is an important process in the manufacture of pressure vessels, and submerged arc welding (SAW) is mainly used as the welding method. In this study, the impact strength according to welding conditions of SAW was confirmed through numerical analysis. Numerical analysis was performed using the ANSYS mechanical. Thermal analysis was carried out by applying heat input for each welding condition, and the impact strength was confirmed by applying residual stress to the numerical analysis of the impact test. As a result of the numerical analysis, it is considered that it can be used as basic data for analyzing the impact strength of welded steel.

Effects of Preheating on Microstructural and Mechanical Properties of Friction Stir Welded Thin Low Carbon Steel Joints

Abstract Friction stir welding of a low carbon thin steel plate was performed with preheating the base material to increase the joining performance. The rotational speed of the tool was set from 1500 to 2000 rpm with a constant travel speed of 15 mm/min and preheating temperature of 50 to 150 °C. The tensile strength of 340 MPa was achieved for the preheated specimen compared with 310 MPa for the non-preheating specimen at the welding speed of 15 mm/min. Electron microscopic images of the preheated joint revealed a remarkable plasticized material flow and dynamic recrystallization, which resulted in the grain refinement that had increased the joining strength. The weld thinning issue was almost eliminated in the preheated welded specimen. However, by increasing the preheat temperature further, the tensile strength decreases due to the formation of defects from excessive heat. The preheated sample fractured at the base metal, revealing a ductile fracture mode.

Investigations on laser beam welding of thick steel plates using a high-power diode laser beam source

For joining of thick steel plates, commonly arc welding and partially laser-arc hybrid welding are used. Both techniques offer individual disadvantages besides their advantages. Arc welding processes are typically characterized by low welding speeds, high heat inputs, high distortions, and high filler material consumptions. Laser-arc hybrid welding processes are limited to weldable material thicknesses regarding weld imperfections as well as the ability to bridge gaps. Therefore, the investigations presented are about high-power diode laser beam welding of steel with plate thicknesses t between 15 and 30 mm using output powers PL of up to 60 kW and welding speeds v between 0.5 and 1.0 m/min. The welding experiments contain butt welds by using weld backing materials. Among other things, influence of energy per unit length (laser beam power PL, welding speed v), focal position z, and plate thickness t are analyzed for different reproducible processes. The evaluation of weld seams includes visual inspection, metallographic analyses regarding geometric characteristics, and weld imperfections as well as radiographic inspections. The investigations show achievable qualities and characteristics of the weld seams depending on the plate thickness t by using high-power diode laser beam sources. Weld seams on plates with thicknesses t of 15 and 22 mm were welded without cracks or other weld imperfections according to metallographic analyses and radiographic testing by using a laser beam power PL of 40 kW and the suitable process parameters developed. As a result, relatively high plate thicknesses t can be welded in a single layer with high quality as well as comparatively high welding speed v.

The joining of CP-vanadium and Ti–6Al–4V using the Electron Beam Melting Additive Manufacturing method

The use of electron beam welding for dissimilar welding (DW) of commercially pure (CP) vanadium to Ti–6Al–4V has been investigated via ARCAM S12, an additive manufacturing powder-bed system. Investigations of bead-on-plate welds for Ti–6Al–4V were first conducted to identify the process parameters for full penetration welds with a minimum energy input of 37 mA at a traverse speed of 7 mm/s. Vanadium bead on plate welds produced a penetration of approximately 75%, which was enough to proceed onto DW experiments. Defect-free full penetration welds were produced. The DW weld zone microstructure revealed an elongated dendritic structure comprised of bulky βTi grains and a fine substructure of α' laths. Thermal imaging (TI) showed an increment in radiance temperature ahead of the melt pool, indicating that there is a minimum energy required before keyhole welding is present, confirming mathematical calculations. Mechanical characterisation finds a fair range of hardness across both base metals (BM), heat affected zones (HAZ) and fusion zones (FZ). With no yield plateau in tensile test curves, the material is confirmed to fail on the side with lower mechanical properties, i.e., vanadium, which draws a fair process window for dissimilar welding between Ti6Al4V and vanadium alloys.

Computational Modeling of Thermo-Metallurgical Behavior During the TIG Welding Process

Welding is widely used in the aerospace, naval and automotive industries. Since high temperatures are involved in this process, solid state metallurgical changes are expected. These metallurgical changes can induce deformations and residual stresses in welded parts. The objective of this work is to develop a finite element calculation code, under the MATLAB environment, to predict the evolution of the various metallurgical transformations during TIG welding of C50 steel plates. In the proposed calculation procedure, we used Leblond’s equation and Waeckel’s model to characterize the metallurgical transformations during respectively heating and cooling stage. We also taken into account the effect of austenitic grain size on metallurgical transformations evolution. Thermal properties are introduced according temperature and phase proportions present during welding operation. Simulation results show that the metallurgical structure in the heat affected zone (HAZ) is largely related to welding thermal power and the plate preheating temperature. We compared simulation results to experimental measurements and the efficiency of the developed computational code was confirmed.

Thermal analysis of thin P91 steel using FlexPDE and SYSWELD

In this paper investigation of FEM based thermal analysis of Gas Tungsten Arc welding of 2 mm thick plate ferritic martensitic steel plate was carried out. Three dimensional thermo-elastic model based on FEA was carried using two different softwares SYSWELD and FlexPDE. In the initial part of the work, heat source fitting (HSF) was carried out using Grade 91 steel bead on plate welding. Predicted weld profile using heat source fitting tool was compared with predicted models. In both the softwares step-by-step modeling has been carried out using HSF analysis tool. In the second step square butt joint welding of Grade 91 steel was carried.

The effect of conformal cooling channels on welding process in parts produced by additive manufacturing, laser powder bed fusion

Given the excellent performance in making lighter, customizable, strong, and aesthetically attractive components at a reduced time and cost, additive manufacturing (AM) presents an unparalleled approach to extending and developing industrial applications. A conformal cooling channel (CCC) is one application that is gaining traction in many vital industries, including mold production, aerospace, healthcare, automotive, and electronics. In this study, the laser powder bed fusion (LPBF) based AM approach is utilized experimentally and numerically to incorporate a CCC network to improve the performance of a weld joint of 316 L SS plates. The study demonstrates a substantial improvement in welding performance by expediting heat dissipation during the TIG welding process using a specifically constructed CCC network on weld plates. Furthermore, CCC-based computational models reported better hardness around the weld joint and lowered residual stress levels.

Controlling Welding Residual Stress and Distortion of High-Strength Aluminum Alloy Thin Plates by a Trailing Hybrid High-Speed Gas Fluid Field

This paper presents an investigation of the welding residual stress and distortion of LY12 high-strength aluminum alloy (6061) by improving the local welding thermal and mechanical fields. A trailing hybrid high-speed gas fluid method was proposed and applied to decrease the welding residual stress and distortion of 6061 aluminum alloy efficiently. Firstly, the temperature and stress fields were calculated using the finite element simulation method, considering a trailing hybrid high-speed gas fluid field. The distance between the aerodynamic load and the heat source action was a key factor determined by the simulation method. In addition, the reasonable effective range of gas pressure was obtained. Subsequently, welding and distortion tests were conducted on the self-developed device under conventional welding and high-speed gas fluid field conditions. The results showed that an aerodynamic load under 30 MPa of gas pressure was available near the area at a distance of 20–28 mm from the heat source for thin plate welding distortion. The peak longitudinal residual tensile stresses in the weld’s mid-length section decreased by 77.73%, the peak residual compressive stresses decreased by 69.23% compared with conventional welding, and the deflection distortion disappeared almost entirely. The maximum deflection of the distortion was only 1.79 mm, which was 83.76% lower than the 11.02 mm of the conventional welding distortion. This validates that the method can simultaneously and greatly eliminate the welding residual stress and distortion.

Copper plating on bonding properties of aluminium/steel explosive welded composite plate

In order to reduce critical impact velocity and enlarge weldability window of aluminium/steel explosive welding, a chemical copper plating layer as interlayer was proposed to carry out aluminium/steel explosive welding. The results showed that the interface of the 1060/Q235 composite plate had good bonding performance, and no obvious defects such as cracks and pores were found. Copper plating as intermediate layer could enlarge aluminium/steel weldability window. The thickness of solidified melt was much thicker than that of diffusion zone. The molten copper particles participated in the formation of re-entry jet, which rotated under the action of initial jet. The presence of the Cu layer reduces the occurrence of excessive melting during welding and improves the properties of the interface.

Heat Transfer Modelling of Friction Stir Lap Welding of PP Plastics and 6061 Aluminium Alloy

Structures with dissimilar materials can make full use of the advantages of each material. However the welding of the aluminum alloy plate and plastic plate are difficult due to high difference in melting point. The friction stir lap welding method is selected in this paper. The numerical model was built to study the heat transfer behavior inside the plates, as the temperature plays an important role in determine the weld quality. The model was validated through experimentally measured temperature results. The influence of welding process parameters such as welding speed, tool rotating speed and downward feed was analyzed. It was found that under the welding speed of 100r/min and downward feed of 0.3mm/s, sound weld was produced.

Numerical evaluation of welding residual stress of X80 pipeline steel under the influence of various welding process parameters

This work aims to improve the durability of the deep-sea transportation pipeline’s weld, prolong the pipeline’s service life, and ensure the safe and efficient operation of the transportation work. By analyzing the influence of welding parameters on the welding residual stress (WRS) of X80 pipeline steel, the welding process is improved to improve the durability of the welded joint. The WRS of the plate butt joint was measured by the hole-drilling method and X-ray diffraction method; the WRS of the pipe butt joint was measured by the hole-drilling method. The experimental results are compared with the numerical simulation results. The relationship between process parameters and welding residual stress is obtained by simulating WRS of flat plate and circular pipe butt joint under different welding process parameters. The results show that the experimental data measured by X-ray diffraction and the hole-drilling method agree with the results of numerical simulation. The WRS of the two plates decreases with the increase in welding speed and backing thickness, increasing with laminate thickness, welding line energy, and groove angle. The WRS value can be obtained by changing the butt plate welding process, and the WRS value of the tube can be inferred under the same condition.

OPTIMIZATION OF PROCESS PARAMETERS FOR THE A-TIG WELDING OF INCONEL 617 USING PARTICLE SWARM OPTIMIZATION AND GENETIC ALGORITHM

Inconel 617 alloy has been included in the boiler and pressure vessel (BPV) code of the American society of mechanical engineers (ASME) for its effectiveness in nuclear applications due to its ability to maintain strength at elevated temperatures. This study is based on the optimization of process parameters for activated flux tungsten inert gas (A-TIG) welding of 10-mm thick Inconel 617 material. Process parameters considered in this study include weld current (A), weld torch travel speed (mm/min), arc gap (mm) and flux powder (silicon dioxide (SiO[Formula: see text] and titanium dioxide (TiO[Formula: see text] combination. The bead on plate welding experiment was carried out by varying the combination of process parameters in each experimental trial. The Taguchi L16 orthogonal array was the design matrix used for the design of experiments (DOE). In the bead on plate welding experiment, a total of 16 experimental trials, each having a different set of process parameters was conducted. The weld bead samples corresponding to each trial were prepared for measurement of the responses which were measured from each of the 16 weld bead samples and included depth of penetration (DOP), bead width (BW), depth to width ratio (DWR), weld cross-sectional area (WA), and bead height (BH). The objective of this work was to maximize DOP, DWR, WA, BH and minimize BW. Analysis of variance (ANOVA) was used to identify the significance of process parameters. Optimization techniques including particle swarm optimization (PSO) and genetic algorithm (GA) were used in the study. The optimized process parameters and optimal solutions attained from each optimization technique were compared. It was found from the study that weld current was the most significant process parameter for all responses followed by weld torch travel speed, flux powder combination and arc gap. Optimal process parameters to achieve maximum DOP, DWR and WA were found to be weld current of 290 A, weld torch travel speed of 50[Formula: see text]mm/min along with an arc gap of 1[Formula: see text]mm and 100% TiO2 as flux. The optimal solution for DOP, DWR and WA was found to be 7.04[Formula: see text]mm, 0.437 and 7.619[Formula: see text]mm2 respectively. The optimal solution for BW and BH was 6.302 and 0.677[Formula: see text]mm, respectively. A confirmation test was conducted to validate the optimal solution obtained from this study. The results from the confirmation test agreed with the solution obtained by optimization techniques.

Experimental and Finite Element Analysis of Butt Weld of Double-layer Steel Plates

This paper aims to study the weldability of butt weld of double-layer steel plates. Experiments for three groups of specimens subjected to various parameters are first conducted to obtain angular deformation, residual stress and temperature data. Then, 3-D finite element (FE) thermal simulation of butt welding is carried out to obtain the load-displacement curves under different included angles and weld length. Moreover, the butt welded steel plate welds were parametric analyzed for the stress concentration factor and the formula for the stress concentration factor was fitted according to the data. The analytical results have shown that double-layer butt welded steel plates with better performance compared to single-layer butt welded steel plates, and the proposed stress concentration factor formula predicts well and thus has certain reference value.

Combined experimental/theoretical approach to residual stresses within multiplicative elasto-plasticity

The study is devoted to geometrically non-linear modelling of viscoplastic structures with residual stresses. We advocate and develop a special approach to residual stresses based on the transition between reference configurations. The finite strain kinematics of the viscoplastic material is modelled by the multiplicative decomposition of the deformation gradient tensor. Numerical algorithms originally developed for unstressed materials are extended to materials with pre-stresses. Owing to the weak invariance of constitutive equations, the incorporation of pre-stresses happens without additional costs. Thus, the advocated approach is especially efficient. A novel experimental/theoretical method for assessment of residual stresses in welded structures is presented; the method combines advantages of purely experimental and theoretical approaches. To demonstrate the applicability of the proposed procedure, we simulate plate welding. As an example we show that the procedure allows extrapolation of the field of residual stresses away from the measurement points. As another example, we address the reduction of weldment-related residual stresses by mechanical treatment.

Effect of welding current on properties of activated gas tungsten arc super duplex stainless steel welds

Abstract A comparative evaluation of the influence of welding current on Tungsten Inert Gas (TIG) welding and Activated Tungsten Inert Gas (ATIG) welding on the depth of penetration and microstructure properties was performed. Various super duplex stainless steel (SDSS) beads on plate weld joints were studied. Visual observation showed that lower welding current resulted in partial weld penetration in the case of both TIG and ATIG weldments. Weld joints obtained by the ATIG process have a higher depth of penetration and depth/width ratios than weld joints obtained in the conventional TIG process at comparatively lower welding currents. Further, microstructural characterizations were performed using optical microscopy. The weld zone microstructure consists of grain boundary austenite (GBA), widmanstätten austenite (WA) and intragranular austenite (IGA). Ferrite percentage in bulk material and each weldment was measured using ferrite scope. The TIG-welded heat affected zone (HAZ) joints showed higher ferrite content than activated flux TIG-welded HAZ joints for various welding current conditions. Ferrite content measured in the weld-zone, HAZ and base material was within the ranges of the standard values. The TIG weld zone showed higher hardness than that of the ATIG weld zone.

Numerical modeling on formation of periodic chain-like pores in high power laser welding of thick steel plate

The porosity with chain-like shape is found in high power laser welding of thick steel plate, which are periodically distributed at the lower and middle parts of the weld and parallel to bottom fusion line. A 3D numerical model is developed to reveal the effect of laser energy absorption and transfer, keyhole fluctuation, molten pool flow and solidification behavior on the formation process of chain-like pores. It is found that the chain-like pores are mainly determined by the unique profile of molten pool concaved inward at middle part on its rear wall. The periodic distribution of chain-like pores is resulted of the periodic variation of molten pool profile influenced by simultaneous periodic change of keyhole collapse frequency, heat accumulation at lower part, heat transfer through clockwise vortex as well as solidification latent heat accumulation at middle part. With the increasing of weld speed, the distribution of pores changes to form in the same height from the bottom fusion line due to the unchanged molten pool profile, which is resulted from insufficient solidification latent heat accumulation at middle part and less heat transferred by weaken upward flow in clockwise vortex. While the bubbles tend to reach a relatively higher position or escape from molten pool for more heat input, slower solidification speed and violent upward flow in clockwise vortex when weld speed decreases.