Single-pass Welding Research Articles

Microstructure Evolution and Mechanical Properties of Underwater Dry Welded Metal of High Strength Steel Q690E Under Different Water Depths

Abstract Q690E high strength low alloy (HSLA) steel has been intensively applied in maritime engineering. Also, the underwater dry welding (UDW) technique has been widely used to repair important offshore facilities. In this paper, joints of Q690E steel were fabricated through single-pass underwater dry welding at three pressures (0, 0.2, and 0.4 MPa). To study the effect of the pressure on the microstructure and mechanical properties of the UDW joint, an optical microscope (OM) and scanning electron microscope (SEM) were used to observe the microstructure and fracture morphology of the welded joints. The electron backscattered diffraction (EBSD) technique was used to analyse the crystallographic features and the crystallographic grain size of the ferrites. The proportion of acicular ferrite (AF) in the UDW joints and the density of low-angle boundaries increase dramatically with the increasing depth of water. The weld metal of UDW-40 shows higher strength because more fine ferrites and low-angle boundaries within UDW-40 impede the dislocation movement.

Single-pass laser welding of TC4 Ti alloy to 304 SS with V interlayer and V/Cu bilayer

Two novel single-pass laser welding methods were performed to join TC4 Ti alloy and 304 SS using V interlayer and V/Cu bilayer. In order to avoid the formation of brittle Ti-based IMCs, two hybrid joints based on different welding mechanisms were created. The joint using the V interlayer with a fusion weld and a diffusion weld was obtained. The fusion weld was formed on Ti alloy, diffusion weld was formed at the Ti alloy-SS interface. The joint using the V/Cu bilayer with a fusion weld, a diffusion weld, a braze weld was obtained. The fusion weld was formed on Ti alloy, V and Ti alloy were joined by atomic interdiffusion, SS and Cu were joined by brazing. The tensile strength and quality of joints was evaluated.

Residual Stress and Deformation of Butt-Welded Joint of Low Carbon Steel to Stainless Steel

This paper investigates and determines residual stress and deformation of butt welded joint between two plates of low carbon steel and stainless steel. Based on the theoretical basis of the virtual force method [1-3], this study has constructed the formulas to calculate the residual stress and deformation in fusion welding of two dissimilar materials for butt joint and single-pass weld. The residual stresses and deformations in the butt-welded joint of two plates of 5 mm thickness, beveled edge, single-pass weld between low carbon steel and stainless steel are determined and compared to show the difference of residual stress and deformation in each plate. These results are also compared with the butt welded joint of two low carbon steel plates.

Narrow gap laser welding (NGLW) of structural steels—a technological review and future research recommendations

Advanced welding processes for structural materials are gaining increasing importance for strategic applications in nuclear, aerospace, automobile, and defence sectors. These processes have been designed keeping in view the criterion of minimal stress generation, microstructure retentivity, and process reproducibility. Narrow gap laser welding (NGLW) is one such advanced welding technique that has been developed in the past decade owing to its fabricate-ability of thick-section steels at high welding speeds. Of the many advantages, several characteristics of the process outperform the traditional arc welding processes as well as single-pass autogenous laser welding, including process flexibility, increased welding productivity, excellent weld properties, and the potential for automation. This paper provides a state-of-the-art technological review on the NGLW process primarily for structural steels covering several topics including the effect of process parameters, structure-property relationship, and induced defects and residual stresses of NGLWed joints. A list of future research recommendations based on several research gaps is also reported in this article.

Effect of enhanced weld cooling on the mechanical properties of a structural steel with a yield strength of 700\xa0MPa

In this study, we present the effect of enhanced cooling on the mechanical properties of a high-strength low-alloy steel (having a yield strength of 700 MPa) following a single-pass weld process. The properties evaluated in this study include uniform elongation, impact toughness, yield, tensile and fatigue strengths alongside the cooling time of the weld. With the steel used in this study, the enhanced cooling resulted in a weld joint characterized with excellent cross-weld uniform elongation, yield and fatigue strength. The intensified cooling reduced the time it takes for the weld to reach 100 °C by around 190 s. Not only the fusion line of the weld was less pronounced, but also the grain size of the CGHAZ was greatly refined as a result of the enhanced cooling. The results indicate that combining external cooling to the welding processes can be beneficial for the studied high-strength steel.

Comparison of the Stress Corrosion Cracking Behaviour of AISI 304 Pipes Welded by TIG and LBW

The stress corrosion cracking (SCC) behaviour of AISI 304 pipe girth welds which were welded by a single-pass laser beam welding (LBW) and a multi-pass tungsten inert gas welding (TIG), respectively, was studied by the slow strain rate tests combined with the electrochemical corrosion tests. The results show that fracture of both the TIG joint and LBW joint occurs in the heat-affected zone (HAZ). According to the electron-backscattered diffraction observation of the microstructures, comparison of potentiodynamic polarization curves and X-ray photoelectron spectroscopy analysis of corrosion products on HAZs of the two joints after the electrochemical tests, the LBW joint exhibits better SCC resistance than the TIG joint in corrosion environments, due to the synthetic effect of more Cr2O3 in corrosion products, finer grains, lower residual strain and higher δ-ferrite content in its HAZ. Although the TIG joint has better mechanical property, considering lower SCC susceptibility and higher production efficiency of the LBW joint, the LBW promisingly replaces the TIG for welding of AISI 304 pipes in the nuclear power industry.

Optimization of electron beam butt welding of 32 mm CLF-1 steel T-joints of Test Blanket Module (TBM) in ITER

• Well-formed CLF-1 steel T-joints with no weld defects could be obtained by electron beam welding without a base plate. • The mean values of impact-absorbing energy of the welds were 296 J and 297 J, which higher than that of CLF-1 base metal. • The average tensile strengths of two joints at room temperature were 620 MPa, while those at 550℃ were 350 MPa. Reduced-Activation Ferrite/Martensitie (RAFM) CLF-1 steel thick plates currently exhibit extensive applications in helium cooled ceramic breeder Test Blanket Module (TBM) building. This study conducted electron beam welding (EBW) of T-joints without base plates, and achieved the single-pass welding and double-sided forming welding of CLF-1 thick steel plates via the optimization of technological parameters. Moreover, the microstructure and mechanical properties of two welded joints were systematically investigated. The welds in both joints were well-formed with no defects, such as pores, incomplete fusion, and cracks. The weld zone (WZ) was mainly composed of tempered martensite laths. No obvious δ-ferrites appeared in the weld, and numerous MX carbides were dispersed in the martensite laths. The coarse-grain heat-affected zone (CG-HAZ) near the fusion zone mainly included slender batten-shaped martensites and a few carbides. The fine-grain heat-affected zone (FG-HAZ) near the base metal (BM) mainly consisted of dual-phase mixed structures of tempered sorbite and martensite. The tensile strengths of the two welded joints at room temperature were 621 MPa and 623 MPa, while at 550℃, they were 350 MPa and 363 MPa, respectively. The fracture positions of both joints were located in the BM. The microhardness of the WZ slightly exceeded that of the BM, while HAZ exhibited no apparent softening. The mean impact absorbed energy values of the welds in two joints were 296 J and 297 J, being much higher than that of the BM. Accordingly, the welded joints fully satisfied the service requirements.

Effect of welding processes and heat input on corrosion behaviour of Ferritic stainless steel 409M

In the present work, Ferritic stainless steel 409M is welded with shielded metal arc welding (SMAW), gas metal arc welding (GMAW) and gas tungsten arc welding (GTAW) of welding current 90A, 100A and 110A. Four mm thick plates were used as base material and single V-joint was prepared for welding. Single pass welding was carried out. Microstructures in the transverse section were observed for base metal, Heat Affected Zone (HAZ) and weld joint. Corrosion rate of welded joints have been evaluated by weight loss method in sodium chloride (NaCl) solution. In this investigation results reveal that, corrosion rate of welded joint is more than the base metal. It is also found that corrosion rate increases on increasing welding current. It is observed that corrosion rate is more in SMAW than GMAW and GTAW weld joint. Results are discussed in the light of microstructure. Increased corrosion rate is attributed to welded structure and formation of HAZ due to variable welding heat input.

Investigation of Single Pass Welding of Thick AH36 Steel Plates in a Square Groove Butt Joint Configuration During AC-GMAW

Investigation of Single Pass Welding of Thick AH36 Steel Plates in a Square Groove Butt Joint Configuration During AC-GMAW

Characterization of wire arc additive manufactured products: A comparison between as-deposited and inter-layer cold worked specimens

The presence of large dendrites and alloy segregation in as-deposited wire arc additive manufacturing (WAAM) products results in a wide range of mechanical properties that are often inferior to wrought ones. In this study, the effect of inter-layer cold working on the microstructure and mechanical properties of AISI 347 samples manufactured by WAAM has been investigated. The average hardness of single-pass welding, as-deposited, and cold worked WAAM samples were 190 HV, 249 HV, and 323 HV, respectively. Inter-layer cold working has led to an increase in ultimate tensile strength from 576 MPa to 803 MPa and yield strength from 395 MPa to 697 MPa. Also, Inter-layer cold working and thermal energy due to the deposition of subsequent layers have resulted in microstructural evolution and grain refinement through recrystallization. Besides, a semi-quantitative analysis has shown that increasing the amount of cold working by four times resulted in 64 % decrease in average recrystallized grain size.

Development of ANN modelling for estimation of weld strength and integrated optimization for GTAW of Inconel 825 sheets used in aero engine components

Nickel-based superalloys are widely used in fabrication of components in aero space and nuclear sectors due to excellent strength, corrosion resistance, good ductility and high-temperature resistance. Inconel 825 superalloy is predominantly used for making aircraft engine components. This work investigates single pass welding of Inconel 825 strips employing gas tungsten arc welding. Four weld parameters, viz. welding speed (V), welding current (I), arc length (N) and gas flow rate (GFR), were used to investigate ultimate tensile strength (UTS) of weld employing Box–Behnken design having 27 experiments. The welding current is found the most dominating factor followed by welding speed (V). Higher heat input with low welding speed increases deposition rate that ensures more strength in weldment. Microstructural analysis shows two different grain boundaries, i.e., solidification sub-grain boundaries and solidification grain boundaries, in fusion zone. Artificial neural network (ANN) modelling for UTS is developed, and its predictive capability is compared with multiple regression analysis. A new integrated ANN–TLBO-based soft computing modelling and optimization approach is proposed for obtaining optimum weld parameters to maximize weld strength. The proposed optimization methodology obtained maximum UTS of 701.73 MPa at optimal weld parameters I = 120 A, V = 180 mm/min, GFR= 12 l/min and N = 2.24 mm. Validation result was found highly encouraging with 0.60% error with confirmation experiment. The proposed method has better convergent capability with minimum number of iterations.

Laser-arc hybrid welding of 12- and 15-mm thick structural steel

High-power lasers are very effective in welding of plates thicker than 10 mm due to the keyhole mode. High-power intensity generates a vapor-filled cavity which provides substantial penetration depth. Due to the narrow and deep weld geometry, there is susceptibility to high hardness and weld defects. Imperfections occur due to keyhole instability. A 16-kW disk laser was used for single-pass welding of 12- to 15-mm thick plates in a butt joint configuration. Root humping was the main imperfection and persisted within a wide range of process parameters. Added arc source to the laser beam process may cause increased root humping and sagging due to accelerated melt flow. Humping was mitigated by balancing certain arc and other process parameters. It was also found that lower welding speeds (< 1.2 m/min) combined with lower laser beam power (< 13 kW) can be more positive for suppression of humping. Machined edges provided more consistent root quality and integrity compared with plasma cut welded specimens. Higher heat input (> 0.80 kJ/mm) welds provided hardness level below 325 HV. The welded joints had good Charpy toughness at − 50 °C (> 50 J) and high tensile strength.

A novel laser welding method for the reliable joining of NiTi/301SS

In this paper, a novel laser welding method with Nb/Cu multi-interlayer was developed for improving the mechanical properties of NiTi/301SS joint. A hybrid joint consisting three metallurgical joining zones was obtained based on different welding mechanisms through a single pass welding. The self-fusion welding was formed on the Nb interlayer, and the fusion zone was composed of Nb-based solution. NiTi and Nb were well bonded by eutectic reaction, and the NiTi/Nb interface contained Nb-based solution, NiTi phase and Nb-NiTi eutectic structure. Nb and 301SS were joined by brazing because of the melting of Cu, and the Nb/Cu/301SS interface consisted of Nb-, Cu-, and Fe-based solutions and a little Fe7Nb6 intermetallic. The strength and ductility of the joints with interlayer were 126% and 188% higher than the joints without interlayer, respectively. The use of Nb/Cu multi-interlayer completely prevented the formation of Ti-Fe and TixNiy IMCs, which can improve significantly mechanical properties of joints.

Thermo-mechanical study of single and multi-pass welding of CSEF steel for residual stresses and deformations considering solid state phase transformation

The present study involves thermo-mechanical modelling of submerged arc welding of CSEF (Creep Strength Enhanced Ferritic) steel plate of thickness 10 mm as single pass and multi-pass welding. A square butt joint with no edge preparation and a V-butt joint with 15° included angle are considered for SAW welding. The martensitic-austenitic transformation phenomenon in P91 steel was also implemented with specific changes in the properties of the weld and base material. It is observed that SAW process with single pass demonstrates stable residual stress distribution, whereas in multi-pass weld, the residual stresses show uneven distribution across the weld. The longitudinal residual stresses are higher in magnitude comparing to transverse residual stresses for both the welding cases. The single pass SAW weld fusion zone has shown compressive stress throughout the thickness of the plate with maximum value at the top side. However, in multi pass weld, the compressive residual stresses have multiple peak values along the weld thickness. The deflection pattern is not effectively altered with multi pass with slight difference from single pass. Therefore, it is suggested that if possible, single pass weld can be preferred over multi pass weld.

LMD coatings as filler material for laser beam welded 30 mm thick plates

The development of high energy laser sources enables single-pass welds of thick plates up to 30 mm, but often additional materials are needed to influence the properties of the weld seams. However, the homogenous distribution of filler materials in form of e.g. electrodes is only possible up to 7 mm while the elements are only traceable up to a depth of 14 mm. To overcome this problem a two-step process is used where first the edges of the weld partners are coated with the filler material by laser metal deposition (LMD) and afterwards are welded by laser beam. Single-pass welds with electromagnetic weld pool support of 30 mm thick S355 J2+N-plates with austenitic AISI 316L-coatings were investigated as well as the influence of the coatings to the penetration depth of the laser beam without electromagnetic weld pool support in double-sided joints. The weld seams were tested by X-ray inspection and cross sections.

Rail surfacing repairing technique with self-shielded flux-cored wires

A newly self-protecting flux-cored wire was used for simulated U75V rail repairing and five welding process parameters were applied. The influence of welding parameter on the hardness and microstructure of the wire and solder layers was investigated. The single-pass welding process with different preheating parameters and post-treatment parameters were also taken into research. The results showed that the welding process parameters have a significant influence on the weld quality, and mismatched parameters will increase the welding defects. The number of welding layers has a great influence on the hardness and structure. Increasing preheating temperature and a post-heat treatment at a high-temperature can enhance the hardening effect.

Measurement of residual stresses in submerged arc welded P91 steel using surface deformation

In an arc welded joint, welding induced residual stresses significantly affect the overall strength of the weld components. Determination of residual stresses before the actual welding not only prevents the failure of the weld structure but also helps in its mitigation before and during the welding process. In this study, a single pass double sided submerged arc welded P91 steel square butt weld joint is considered to determine welding induced residual stress. Strain associated to trapped stresses in a component can trace its distribution. The corresponding deformation was determined for the welded plate. The weld sample was cut across the weld length into two equal halves using wire EDM (Electrical Discharge Machine). The surface deformations were recorded onCoordinate Measuring Machine (CMM). The positioning of sample on CMM bed, non-uniformity in cutting process etc., may affect the deformation data and so, data conditioning was performed. The conditioned deformation values were imposed as the structural load on the same weld joint FE model in ANSYS software package. The FE analysis structural results generate the residual stress distribution in longitudinal direction or say perpendicular to the targeted surface. A compressive residual stress distribution was observed in weld-zone unlike other steels weld. The single pass welding is justified for stable residual stress distribution in both weld zone and Heat Affected Zone (HAZ).

Microstructure and mechanical properties of high strength TMCP steel hybrid disk laser-MAG welded joint

Hybrid laser-arc welding (HLAW) was carried out on high strength thermo-mechanical controlled process (TMCP) steel of 14 mm thickness using single-pass welding (SPW) and multi-pass welding (MPW) processes. Well-formed weld joints with good performance were successfully obtained. The results showed that the microstructure of weld was pre-eutectoid ferrite, acicular ferrite and some granular bainite. There were mainly lath bainite, granular bainite and acicular ferrite in the heat-affected zone. The grain sizes of SPW were thicker than MPW, and the bainite content of MPW was higher than SPW. The average hardness value of the fusion zone was lower than that of the Heat affected zone, but higher than that of the base material. The weld was divided into upper arc domain zone (ADZ) and lower laser domain zone (LDZ). The ADZ was harder than the LDZ. The average absorbed energy of SPW and MPW in the fusion zone at −40[Formula: see text]C was 125.5 and 92 J/cm2, respectively. The influences of microstructure on impact toughness were summarized by analyzing the hardness distribution and microstructure of the welded joint. The brittle transition temperatures of the two processes obtained by the energy criterion and the morphology criterion were close to each other.

Additive manufacturing using fine wire-based laser metal deposition

PurposeUsing wire as feedstock has several advantages for additive manufacturing (AM) of metal components, which include high deposition rates, efficient material use and low material costs. While the feasibility of wire-feed AM has been demonstrated, the accuracy and surface finish of the produced parts is generally lower than those obtained using powder-bed/-feed AM. The purpose of this study was to develop and investigate the feasibility of a fine wire-based laser metal deposition (FW-LMD) process for producing high-precision metal components with improved resolution, dimensional accuracy and surface finish.Design/methodology/approachThe proposed FW-LMD AM process uses a fine stainless steel wire with a diameter of 100 µm as the additive material and a pulsed Nd:YAG laser as the heat source. The pulsed laser beam generates a melt pool on the substrate into which the fine wire is fed, and upon moving the X–Y stage, a single-pass weld bead is created during solidification that can be laterally and vertically stacked to create a 3D metal component. Process parameters including laser power, pulse duration and stage speed were optimized for the single-pass weld bead. The effect of lateral overlap was studied to ensure low surface roughness of the first layer onto which subsequent layers can be deposited. Multi-layer deposition was also performed and the resulting cross-sectional morphology, microhardness, phase formation, grain growth and tensile strength have been investigated.FindingsAn optimized lateral overlap of about 60-70% results in an average surface roughness of 8-16 µm along all printed directions of the X–Y stage. The single-layer thickness and dimensional accuracy of the proposed FW-LMD process was about 40-80 µm and ±30 µm, respectively. A dense cross-sectional morphology was observed for the multilayer stacking without any visible voids, pores or defects present between the layers. X-ray diffraction confirmed a majority austenite phase with small ferrite phase formation that occurs at the junction of the vertically stacked beads, as confirmed by the electron backscatter diffraction (EBSD) analysis. Tensile tests were performed and an ultimate tensile strength of about 700-750 MPa was observed for all samples. Furthermore, multilayer printing of different shapes with improved surface finish and thin-walled and inclined metal structures with a minimum achievable resolution of about 500 µm was presented.Originality/valueTo the best of the authors’ knowledge, this is the first study to report a directed energy deposition process using a fine metal wire with a diameter of 100 µm and can be a possible solution to improving surface finish and reducing the “stair-stepping” effect that is generally observed for wires with a larger diameter. The AM process proposed in this study can be an attractive alternative for 3D printing of high-precision metal components and can find application for rapid prototyping in a range of industries such as medical and automotive, among others.

Influence of Keyhole Mode of Plasma Arc Welding on Microstructure and Mechanical Properties of Similar Butt-Welded Incoloy 800H

The keyhole mode of plasma arc welding (K-PAW) was employed to weld Incoloy 800H plates of 6 mm thickness. A nickel–chromium-based superalloy, Incoloy 800H is a fully austenitic face-centered cubic structure and imparts better tensile strength, fatigue strength, and creep properties at higher temperatures. Full-penetration weld was achieved by a single-pass welding, and no defects were observed in X-ray radiography testing. Microstructural studies revealed fine equiaxed dendritic structure present in the weld metals due to the steep temperature gradient induced by the K-PAW. Due to fine grain structure, no solidification cracking was observed in the weldment. Mechanical properties studies confirmed that weldments attained the minimal requirements of tensile strength, hardness, ductility, and toughness as per the boiler pressure vessel fabrication requirement norms.