Narrow Welding Research Articles

Insight on microstructure and mechanical properties of 40 mm thick-walled ferromagnetic super-MSS by magnetic-field-assisted narrow gap GTAW

In this work, the welding of 40 mm thick-walled ferromagnetic super martensitic stainless steels (super-MSS) welded by magnetic-field-assisted (MFA) narrow gap-gas tungsten arc welding (NG-GTAW) is reported and a defect-free joint is successfully obtained. The variations trends of microstructure and mechanical properties at different positions along the thickness direction of the joint are analyzed. The results show that there are obvious differences in microstructure and properties between different layers of the MSS joint. The strength level of the joint is comparable to that of the base metal. The impact toughness of the middle and bottom layers is much higher than that of the base metal. This is mainly due to the differences in microstructure, such as austenite content, refinement and grain boundary characteristics of martensite observed by OM, SEM, and EBSD. A two-pass filling test is employed to understand the evolution of microstructure and properties of thick-walled super-MSS joint and clarify the self-heat-treatment (SHT) effect between the weld passes by simulation. It is found that during the welding process of thick-walled super-MSS, the adjacently later pass can exert an obvious SHT effect on the bottom layer, which leads to significant refinement of martensitic lath in the weld. Finally, the relation between microstructure and properties of the thick-walled super-MSS joint is revealed.

A comparison of the swing and non-swing arc behavior in arc ultrasonic assisted narrow gap GMAW

The arc ultrasonic technology was applied to the swing arc narrow gap GMA welding process of aluminum alloy. The ultrasonic energy acts on the welding process by superimposing an ultrasonic current on the basis of pulsed welding current. The arc behavior will be significantly different from that in the conditions of non-narrow gap and non-swing due to influences from the narrow gap groove constraint and the arc swing. In this paper, the behavior of swing arc and non-swing arc at different positions in narrow gap groove are compared, and the influence mechanism of arc ultrasonic on arc behavior is analyzed. Results indicate that the arc expands after superposition of ultrasonic current, and that the arc behavior is different at different positions of the narrow gap groove. In the sidewall, the expansion degree of the non-swing arc is obviously greater than that of the swing arc. The swing arc area increases by 50.33% at most, and the non-swing arc area increases by 117.94% at most. In the groove bottom, the expansion degree of the swing arc is greater than that of the non-swing arc. The average area and width of the swing arc in the groove are nonlinear relationships with the ultrasonic current amplitude and a linear positive correlation with the ultrasonic frequency, respectively. Arc swing and ultrasonic action make the arc length longer. The difference in speed between arc expansion and contraction and the oscillation of arc plasma under the arc ultrasonic action together promote arc expansion.

Effect of thickness on mechanical properties of modified 9Cr 1Mo steel welds made by narrow gap hot wire gas tungsten arc welding process

Hot wire Gas Tungsten Arc Welding (GTAW) process is selected for fabrication of thick section modified 9Cr 1Mo steel components of Steam Generators (SGs) for 500MWe Prototype Fast Breeder Reactor (PFBR) at Kalpakkam, India. During the welding procedure qualification for fabrication of SGs, the 30 mm and 62 mm thick modified 9Cr 1Mo steel welds were subjected to chemical analysis, visual examination, liquid penetrant examination, radiography examination, micro-hardness tests, longitudinal and transverse tensile tests (at ambient temperature and 525 °C), bend tests, drop weight tests and impact tests (at 0 °C and +18 °C). Literature reveals both positive and negative view on the welding of thick section steel components. Limited information is available in open literature on the effect of thickness on material properties of modified 9Cr 1Mo steel welds made by hot wire GTAW method. In view of the above, authors attempted to systematically investigate the influence of thickness on mechanical properties of modified 9Cr 1Mo steel welds made by hot wire GTAW process. In this paper, the chemical compositions, hardness, tensile strength, bending strength and impact properties of 30 mm and 62 mm thick welds produced by narrow gap hot wire GTAW process are characterized and compared. It is found that the mechanical properties of 30 mm and 62 mm thick welds are comparable except the impact properties at 0 °C. The impact strength at 0 °C for 62 mm thick weld was found inferior in comparison with 30 mm thick weld.

A coupled ray-tracing based CFD and cellular automaton model for predicting molten pool formation and microstructure evolution in narrow gap laser welding

Laser beam reflection plays a significant role in the temperature development history during various laser material processes. Different from other processes where laser beam reflection main happens inside the keyhole, in narrow gap laser welding (NGLW), the laser beam would interact with the sidewalls multiple times before existing the narrow groove, which would have a great impact on the defect formation as well as the grain structure development. However, the underlying mechanism of this process remains unknown in multi-pass NGLW. In this study, an integrated ray-tracing based CFD and cellular automaton (CA) modelling framework is established to investigate the impact of laser beam reflection on molten pool formation and microstructure evolution in multi-pass NGLW. From the CFD simulation, it is found that the overall laser beam absorption of NGLW is greater than laser metal deposition (LMD) while smaller than laser powder bed fusion (LPBF) process. Besides, the overall absorptivity in NGLW is increased 28% when considering the ray reflection during the first welding pass. The absorptivity would increase and then stabilise through the multi-pass welding process, which is attributed to the change in incident angle and number of reflections. Additionally, it is found that the undercut defect is more likely to occur with ray reflection due to the excessive temperature rise on the sidewalls, while lack of fusion is observed in the case without ray reflection. By incorporating the thermal history of each welding pass with CA, the impact of laser beam reflection on grain structure development is evaluated. Columnar grains would govern the microstructure evolution in the case with ray reflection, which grow epitaxially from the fusion line to the molten pool centre. Grain coarsening would occur around the lack of fusion region in the case without ray reflection. Moreover, the analysis on grain size distribution is conducted and a greater maximum grain size is obtained in the case without ray reflection as a result of lower cooling rate caused by lack of fusion. However, a higher grain size increase is obtained in the case with ray reflection during multiple welding passes, and larger grains are expected to form if more welding passes are to be conducted. The simulated molten pool morphology and grain structure are compared with the experimental observation, and a good agreement is achieved.

Evaluation of strength in stainless steel weld joints using ball indentation technique

In the present study, strength variations across the type 316LN stainless steel weld joints processed by advanced hot wire tungsten inert gas, activated tungsten inert gas, and hybrid laser metal inert gas welding processes were evaluated using automated ball indentation technique. The secondary dendrite arm spacing (SDAS) associated with welding heat input and welding thermal cycles strongly influenced the strength properties across the weld joints. The strength properties were lower at 823 K compared to 298 K because of thermally activated deformations. The hybrid laser metal inert gas welding process exhibited significantly narrower weld and higher strength in the weld and heat-affected zone due to finer SDAS and grain size, respectively, than the other weld joints.

The evaluation on performance of narrow- gap welding thick steel plates under the influence of main welding parameters

This work presents the experimental results of narrow gap butt welding of steel plates with large thickness by using the Metal Active Gas (MAG) welding method.The typical defects are accompanied with this process such as the infusion in the side wall and the porosity due to the narrow gap which affect on the melting process. Thus, some publications noted the results of welding for the thickness up to 20−30 mm and the chamfer angle about 30° using GMAW/MIG, GTAW/TIG, SMAW and new development such as laser – arc hybrid, laser multi- pass technique, super -TIG welding etc. But the production requires the solution to save the costs by the reduction of time, labour and investment keeping the standard quality. That is the aim of this study. In order to improve the quality of weld joint and increase the productivity of the process, is it suggested to develop the innovative welding process, in which the welding voltage – Uw, the translational velocity of the tip – Vt, and rotational velocity of the tip – Vr, are changing. This helped to increase the thickness of steel plates up to 50 mm and the chamfer angle decreased at 15°, providing the satisfied quality of the weld. The micrography study serve as the preliminary proof of this hypothesis.
 The microstructures in 4 regions, such as the weld center zone, heat-affected zone (HAZ), parent metal region, and the boundary between the weld metal and the HAZ were examined. The microstructures of 13 positions from different experiments are investigated using the optical microscope (Axiovert 25).These experiments covered all specific points (node) locating accordingly to three layers from bottom to top of the weld joint . The findings proved the welding quality is similar in case of narrow gap but the chamfer angle is twice lower and the thickness is increased. The result of the study enhances the productivity due to saving the labour cost and the welding materials. It is recommended to consider the effect of other factors (such as cooling conditions, dwell time when the arc approaching the side walls) to optimize the weld quality. There is the huge volume of the heavy steel constructions with the thick steel construction and specific narrow gap in industry. The results of this study with the optimization and more deeper evaluation the influence of main parameters of welding process to eliminate the typical defects will be the valuable reco mmendation for the managers and engineers in the production of metallic constructions

Microstructures and Mechanical Properties of Thick Ti–6Al–3Nb–2Zr–1Mo Joint by Magnetron-Controlled Narrow Gap TIG Welding

Microstructures and Mechanical Properties of Thick Ti–6Al–3Nb–2Zr–1Mo Joint by Magnetron-Controlled Narrow Gap TIG Welding

Narrow Weld Joint Recognition Method Based on Laser Profile Sensor

Intelligent manufacturing technology has recently experienced rapid development, where robot welding systems are an essential component. A laser profile sensor is commonly utilized in intelligent robot welding systems. However, when the laser stripe is projected onto a narrow weld joint, the deformation of the laser stripe is not sufficiently apparent, and the traditional weld joint recognition methods based on the laser profile sensors cannot detect the narrow weld joint position. Meanwhile, the strong arc and spatter noise during welding and the expansion of weld joint width caused by welding thermal expansion are likely to interfere with weld joint recognition. In addition, many common weld seam recognition methods can only recognize certain weld joints and have limited flexibility and robustness for other types of weld joints. This study proposes a wide range of weld joint recognition algorithms based on the laser profile sensor to overcome these challenges. The gray value histogram analysis method, the adaptive threshold method, the internal propulsion center and boundary extraction (IPCBE) method, the coordinate analysis method, and the stripe end center detection method proposed in this study are used primarily in the algorithm. The algorithm solves the problem of identifying narrow weld joints and allows for the identification of larger conventional weld joints. Furthermore, the algorithm has good a anti-spatter and anti-arc interference ability and a fast speed, allowing it to meet the demand for real-time welding identification.

Numerical analysis modeling of temperature field in swing-arc narrow gap GMA welding with additional wire

Numerical analysis modeling of temperature field in swing-arc narrow gap GMA welding with additional wire

Development of resistance spot welding technology applying multi-stage adaptive control for narrow pitch spot welding of high strength steel sheets

Development of resistance spot welding technology applying multi-stage adaptive control for narrow pitch spot welding of high strength steel sheets

Overlapping Features and Microstructures of Coarse Grain Heat-Affected Zones in Swing Arc Narrow Gap GMA Welded EH40 Grade Steels

Swing arc narrow gap GMA welding experiments were carried out with a Box–Behnken response surface design. Weld metal and heat-affected sizes were measured from the joints obtained, and an ANOVA was performed to obtain well-fitting models for definition of the heat-affected length. Overlapping patterns and microstructures were analyzed and observed in zones within the heat-affected length through the thickness direction. In addition, thermal processes in typical zones of HAZs were calculated by FEM and analyzed to explain the patterns in the typical coarse grain heat-affected zones (CG-HAZs) with thermal simulated microstructures attached. It was realized that a single pass could only be confused with an austenitized process by two passes. The coarse grain heat-affected zone of a single pass could be divided into an unaltered coarse grain heat-affected zone (UACG-HAZ), a supercritically reheated coarse grain heat-affected zone (SCRCG-HAZ) and an intercritically reheated heat-affected zone (IRCG-HAZ). It is likely that there would be an intercritically reheated UACG-HAZ upon the UACG-HAZ. The microstructures in the CG-HAZs and the UACG-HAZ were mainly lath bainite and a little acicular ferrite; the microstructures in the SCRCG-HAZ were short lath bainite, granular bainite and acicular ferrite and the microstructures in the IRCG-HAZ were massive textures and secondary austenite decomposition products. The cooling times in the typical bainite transformation procedures were similar to one another in a secondary austenitized process and significantly longer than those in a single austenitized thermal cycle, which caused similar patterns in reheated CG-HAZs and an increase in acicular ferrite compared to CG-HAZs. The prior austenite grain sizes caused differences among the reheated CG-HAZs.

Predicting residual stress in a 316L electron beam weld joint incorporating plastic properties derived from a crystal plasticity finite element model

Electron beam welding is an advanced joining technique which induces narrow weld region with minimal heat affected zone and weld-induced distortion. This reduces residual stresses in the joints which can be detrimental to structural performance of components in safety critical industries. Being an autogenous process, electron- beam welding generates a highly textured, columnar microstructure in the weld zone which have distinct properties when compared to the parent material region. Determining mechanical properties of the weld material assists in accurate assessment of the joint. However, extracting weld material specimens to determine plastic properties becomes increasingly cumbersome in thinner weld joints. An alternate approach has been demonstrated in this work wherein mechanical properties were derived using the weld microstructure in a crystal plasticity finite element (CPFE) framework. The initial calibration of the CPFE parameters was done using experimental data from thick weldment. These calibrated values were used to obtain the elastic and elastic-plastic properties of thinner weld materials by deforming corresponding synthetic microstructures whose attributes were determined by Electron Backscatter Diffraction analysis. The resultant properties were incorporated in a finite element (FE) based weld simulation to determine the residual strain. These results were compared with the residual strain data obtained using X-ray diffraction and good agreement was observed.

Interlaminar Microstructure and Mechanical Properties of Narrow Gap Laser Welding of 40-mm-Thick Ti-6Al-4V Alloy.

Narrow gap laser welding (NGLW) is a common solution for the welding of thick structures. NGLW was carried out on narrow-gap butt joints of 40 mm-thick Ti-6Al-4V alloy plates with a U-shaped groove. The distribution characteristics of the interlaminar microstructure in different height ranges of the joint were investigated, and the evolution behavior and formation mechanism of the interlaminar microstructure of the joint were also revealed. This showed that a large amount of short needle martensite nucleated and grew up near the fusion line and the upper boundary of the remelting zone. The "softening" phenomenon occurred in all welds except the cover layer weld. The microstructure evolution and defect migration, induced by multiple welding thermal cycles in the upper weld forming process, were the main reasons for the "softening" of the lower weld. The tensile strength of each sample changed in the range of 920~990 MPa; the fracture mode of the sample belongs to a transgranular ductile fracture. In addition, compared with the upper part of the joint, the plasticity and toughness of the weld area in the lower part of the joint was improved.

Investigation of Distribution of Residual Stress in Swing arc Narrow Gap MAG Welding by Numerical Simulation and Experiments

Investigation of Distribution of Residual Stress in Swing arc Narrow Gap MAG Welding by Numerical Simulation and Experiments

Effect of heat source parameters on weld formation and defects of oscillating laser-TIG hybrid welding in horizontal position

In this paper, a comparison study of the narrow gap horizontal welding characteristics of tungsten inert gas (TIG) welding, non-oscillating laser-TIG hybrid welding, and oscillating laser-TIG hybrid welding is presented. Weld forming tests were performed using various heat source mode parameters. The plasma behavior, the molten pool flow, and the keyhole behavior of these different heat source modes were observed. In addition, filling welding operations were performed, and the defect generation mechanism was analyzed. The results show that oscillating laser-TIG hybrid welding can improve weld formation effectively and suppress defects such as weld porosity and incomplete fusion. The coupling effect of the laser-TIG arc weakens as the oscillation amplitude and the distance between the laser and the tungsten electrode increase. The hybrid plasma generates periodic changes with the laser oscillation, which results in a more uniform energy distribution that improves the sidewall fusion and prevents the formation of large numbers of bubbles. The keyhole stirs the molten pool and drives the molten pool to scour the groove sidewall, which helps to improve the sidewall fusion and suppress pore formation. The oscillating laser-TIG hybrid welding process with an oscillation amplitude of 4 mm and a distance of 3 mm between the laser and the tungsten electrode obtained high-quality welds with good weld morphology.

Effect of preheating and preplaced filler wire on microstructure and toughness in laser-arc hybrid welding of thick steel

Acicular ferrite (AF) is the most important microstructural constituent to achieve high toughness at low temperatures in weld metal of steels. This is due to the relatively small grain size and large misorientation angles. AF is known to form at non-metallic inclusions (NMIs), but under high cooling rates, as in deep and narrow laser-arc hybrid welding (LAHW), this phenomenon is scarcely studied. In deep and narrow LAHW, insufficient transportation of filler wire to the root results in low amount of NMIs, thus bainite-martensite mainly forms due to fast cooling. In this work, a 45 mm thick high strength low alloy steel was welded by double-sided LAHW using different groove preparations. The effect of different cooling times on the microstructure in the weld metal and the heat-affected zone was studied. A low fraction of AF and high hardness were achieved in the root of weld metal when using standard LAHW. This was related to a rapid cooling time (Δt8/5 < 1.0 s) and a low population of NMIs due to lack of filler wire. Micro X-ray computed tomography revealed centerline solidification cracks and porosity. Two external methods were conducted to assist the formation of AF and to reduce hardness, base plate preheating and preplaced metal-cored filler wire into the weld groove prior to welding. Preheating reduced hardness and increased the AF fraction due to increased cooling time. In addition, preheating showed to mitigate porosity. Preplaced filler wire provided an enhanced population of NMIs in the root thus significantly increased the fraction of AF. It was found that the diameter and chemical composition of NMIs has a strong correlation with the cooling time Δt8/5. High impact toughness (> 35 J) was achieved at −50 °C by combining preheating and preplaced filler wire, and up to 45 % fraction content of AF was reached. However, many NMIs were still inactive due to a small diameter (< 200 nm) and unfavorable chemical composition related to the high cooling rate. The external methods had no influence on the occurrence of weld centerline cracks in the root, which will require further attention to secure mechanical properties and integrity.

Stress distribution in a 316L(N) steel narrow gap TIG model weld for Gen IV nuclear applications

The stress distribution in a model weld developed for nuclear application has been determined non-destructively by means of neutron diffraction, in the frame of the Horizon 2020 Project Generation IV Materials Maturity (GEMMA). The investigated sample is a narrow gap Tungsten Inert Gas (TIG) austenitic 316L(N) steel weld, prepared following RCC-MRx Code specifications. Two lines perpendicular to the welding direction, at the middle of the sample, were scanned at 6 mm and 14 mm depth; additional measurements were carried out in the middle of the weld, down to 16 mm depth. At 6 mm depth and within ± 5 mm distance from the weld centre, marked tensile stress gradients are found, with the residual stresses reaching maximum values up to 400 MPa in the longitudinal direction. At 14 mm depth, the stresses decrease to around 200 MPa for the longitudinal component and get compressive for the transverse and normal components, down to −200 MPa for the transverse one, with smoother stress gradients around the weld. The in-depth measurements inside the weld confirm that the main integrity concern for the investigated sample may arise from the tensile longitudinal stresses. Additional micro-structural information has been obtained by qualitative comparison of diffraction line profiles in the weld and in the base metal. These experimental results are discussed with reference to the expected service conditions of such welds and to their capability to fulfill Gen IV safety goals and requirements.

Infrared Visual Sensing Detection Approach of Swing Arc Narrow Gap Weld Deviation Based on Outlier Data Filtering

Narrow gap arc welding interferences pose notable challenges to accurate weld deviation detection in infrared visual sensing. An outlier data filtering (ODF) approach is proposed to precisely detect weld deviation between the groove and the torch centers after eliminating the welding-induced intense disturbances in images. The ODF approach develops a global pattern recognition (GPR) based algorithm to detect the groove center, and an optimal-estimation based position consistency filtering (PCF) algorithm to locate the torch center. In addition, ODF also modifies a welding image processing procedure to prepare the groove and the wire edges for the center detections. Experimental results show that the GPR algorithm removes the simulated welding spatters of ≤ 2.48 mm diameters on the groove edge, and the PCF algorithm accurately gains the torch center with the detection error of−0.022 ~ +0.035 mm. Finally, the ODF approach realizes a precise detection of the weld deviation with the detection error of−0.107 ~ +0.079 mm, demonstrating the effectiveness of the proposed approach regardless of welding interferences.

A vision-based method for narrow weld trajectory recognition of arc welding robots

A vision-based method for narrow weld trajectory recognition of arc welding robots

Effects of sidewall grain growth on pore formation in narrow gap oscillating laser welding

How to suppress the pores is one of the most important challenges in narrow gap laser welding of aluminum alloys. In order to solve this question, narrow gap oscillating laser welding (O-NGLW) of dissimilar AA6061 and AA2024 aluminum alloys was carried out. With the increase of the laser oscillation frequency (f), the pores changed from the dense and linear chain at weld center to the scattered distribution segregating at AA2024 side, and disappeared when f ≥ 400 Hz. The normalized calculated stirring Reynolds number of O-NGLW was 1369 when suppressing the pores totally, 1.39–1.75 times that of the welding without narrow gap, indicating that a stronger stirring effect induced by laser oscillation was needed to capture the bubbles. The theoretical analysis suggested that this phenomenon was closely related to the effect of columnar grains growth on bubble interception (ECGGBI). Based on the interaction between ECGGBI and the stirring effect induced by laser oscillation, the pore formation was discussed, and the reason why stronger stirring effect was needed to suppress the pores was revealed.