Welded Steel Plates Research Articles

High power laser welding of thick steel plates in a horizontal butt joint configuration

In this investigation, two laser-based welding techniques, autogenous laser welding (ALW) and laser welding assisted with a cold wire (LWACW), were applied to join thick plates of a structural steel (A36) in a horizontal narrow gap butt joint configuration. The main practical parameters including welding method and laser power were varied to get the sound weld with a requirement to achieve a full penetration with the reinforcement at the back side of weld in just one pass. The weld-bead shape, cross-section and mechanical properties were evaluated by profilometer, micro-hardness test and optical microscope. In order to investigate the stability of laser-induced plasma plume, the emitted optical spectra was detected and analyzed by the spectroscopy analysis. It was found that at the laser power of 7kW a fully penetrated weld with a convex back side of weld could be obtained by the LWACW. The microstructural examinations showed that for the ALW the acicular ferrite and for the LWACW the pearlite were formed in the heat affected zone (HAZ). The prediction of microstructure based on continuous cooling transformation (CCT) diagram and cooling curves obtained by thermocouple measurement were in good agreement with each other. According to the plasma ionization values obtained from the spectroscopy analysis the plume for both processes was recognized as dominated weakly ionized plasma including the main vaporized elemental composition. At the optimum welding condition (LWACW at the laser power of 7kW) the fluctuation of the electron temperature was reduced. The spectroscopy analysis demonstrated that at the higher laser power more of the elemental compositions such as Mn and Fe were evaporated.

A simplified FE simulation method with shell element for welding deformation and residual stress generated by multi-pass butt welding

In order to propose a simplified simulation method using finite element (FE) model for predicting deformation and residual stress generated by multi-pass butt welding, a series of experiments and numerical analyses were carried out. 3-pass butt welding of steel plates was simulated by the thermal elasto-plastic analysis with shell elements and with solid elements respectively. A heat input model for considering the temperature distribution in the thickness direction in shell elements was proposed. The validity of the heat input model was verified by comparing analytical results with experimental results or other analytical results using solid elements. Furthermore, the effectiveness for saving computing time by using shell elements was confirmed from the comparison with the case using solid elements. It was confirmed that the welding out-of-plane deformation and residual stress could be predicted with high accuracy by the proposed method. The computing time was around 14% of that by the precise model with solid elements.

Comparison of residual stress in relaxed and non-relaxed weldments of steel plates

In this study, two methods, X-ray diffraction (nondestructive) and hole-drilling (destructive) are applied to measure the residual stress of gas metal arc welded steel plate. Both non-relaxed and relaxed (local heating, furnace annealing and bead blasting) weldments are examined to understand the residual stress distributions before and after elimination of residual stresses. Results show that the heat affected zone of gas metal arc welding method is about 10 mm from the weld centerline. The local heating method is very effective in reducing the residual stress caused by the cold work of the original steel plate. The furnace annealing method reduces the residual stress to compressive but not uniformly distributed. The detrimental fluctuation of residual stress is successfully reduced and uniformly relaxed to be beneficially compressive in the bead blasting. Most importantly, X-ray diffraction shows more precise and better handling than hole-drilling method in terms of data error.

Relationship between penetration and porosity in horizontal fillet welding by a new process “hybrid tandem MAG welding process”

In the shipbuilding and bridge construction industries, shop primer paint is coated to the surface of steel plates in order to protect them from rusting during a long fabrication period. However, when arc welding is applied to the primer-coated plates, the arc heat may decompose and vaporize the coating. Then, the generated gas will be enclosed in the weld metal during the solidification process, causing the porosity defects, such as blowholes and the pits. In this study, the effects of penetration depth and non-penetrated joint root length on the generation of blowholes were clarified with various welding parameters. A new horizontal fillet welding process called ‘hybrid tandem MAG (HTM)’ was developed, a combination of a solid wire for the leading electrode and a flux-cored wire for the trailing electrode. The process features deep penetration and excellent porosity resistance. In order to reduce porosity in the fillet welding of primer-coated steel plate, it was found that the following measures are effective: (a) increasing the penetration depth and (b) decreasing the non-penetrated joint root length. The reduction of porosity by increasing the penetration depth is achieved by the formation of consistent ejection passage for vaporized gas. The phenomena mentioned above were verified by observing the interior of the weld pool directly by using an X-ray video camera. It is effective to reduce the leading electrode torch angle and to use a combination of high current and low voltage to create a buried arc to realize these measures. The MAG (HTM) procedure reduced the porosity formation to one tenth of that produced with the conventional tandem MAG process even at travel speeds up to 1600 mm/min.

Limit state design of steel columns reinforced with welded steel plates

I-shape steel columns in many old bridges can be rehabilitated by welding steel plates to the flanges of the existing columns. However, the effect of welding residual stresses, initial imperfections, and column load at the time the reinforcing plates are welded to the column can significantly affect the column strength. Currently there are no guidelines available for the design of columns reinforced under load with welded cover plates. This paper presents a numerical study to determine the appropriate column curve, whether SSRC column curve 1 or 2, i.e. n=2.24 or 1.34 in the Canadian steel design standard, to use for design of columns reinforced with steel cover plates welded to the flange tips, either parallel to the web or parallel to the flanges. A validated finite element model is used to conduct a parametric study to investigate several parameters that affect the strength of the reinforced column. Considering the variation in the resistance, a detailed statistical analysis, which provides a uniform level of safety, is conducted based on the results obtained from the parametric study to determine appropriate resistance factor to use for limit state design of columns reinforced with welded steel plates. A reliability analysis indicated that steel columns reinforced with plates welded under load should be designed using SSRC column curve 2 (n=1.34) with a resistance factor of 0.90.

Effect of B2O3 containing fluxes on the microstructure and mechanical properties in submerged arc welded mild steel plates

This paper represents a study on the effect of B2O3 additions in fluxes on the microstructure and mechanical properties of the weld metal formed during Submerged Arc Welding of Mild Steel plates. Five fluxes with about 2.5, 5, 7.5, 10 and 12.5% B2O3 were used with a low carbon electrode. Welding process parameters were kept constant for all the conditions. The microstructure of weld metal for each flux consisted mainly of acicular ferrite, polygonal ferrite, grain boundary ferrites and equiaxed pearlite. It was noted that the Vicker's hardness value was a function of boron content and shows a mixed trend. Impact Energy and Tensile Strength were increased with the increase in boron content in welds this can be attributed to relation with the higher acicular ferrite percentage. However an optimum level of toughness and tensile strength was available with 7.5% and 5% of B2O3 respectively. A qualitative comparison has also be done with fresh flux by means of full metallography and mechanically.

Effect of CaF2, FeMn and NiO additions on impact strength and hardness in submerged arc welding using developed agglomerated fluxes

This experimental study was conducted to evaluate the effects of CaF2, FeMn and NiO additives on impact strength and hardness of low carbon steel plate welds using submerged arc welding. Fluxes containing CaO, SiO2 and Al2O3 as base fluxes were designed and developed through agglomeration technique. CaF2, FeMn and NiO were added to these fluxes in the varying amounts of (2–8) %. Mathematical models were developed using design expert and these models were correlated with the Mn, Ni and C transfer to the bead. The mechanical properties also have been correlated with the microstructure developed and the oxygen content in the welds. CaF2 and FeMn are found significant factors for the impact strength while the interaction of CaF2 and NiO is significant for hardness of the weld. The optimum ranges for Mn and Ni contents that produce optimum impact strength and hardness also have been suggested. The basicity index of flux and the carbon equivalent of the welds also have been correlated with the mechanical properties of the welds. The impact strength was found minimum for those welds which were welded by fluxes having CaF2, FeMn and NiO each at mid-level of 5%, though the Δ Mn quantities for these welds were low.

High-power Laser Welding of Thick Steel-aluminum Dissimilar Joints

According to the Intergovernmental Panel on Climate Change (IPCC), a worldwide reduction of CO2-emissions is indispensable to avoid global warming. Besides the automotive sector, lightweight construction is also of high interest for the maritime industry in order to minimize CO2-emissions. Using aluminum, the weight of ships can be reduced, ensuring lower fuel consumption. Therefore, hybrid joints of steel and aluminum are of great interest to the maritime industry.In order to provide an efficient lap joining process, high-power laser welding of thick steel plates (S355, t = 5mm) and aluminum plates (EN AW-6082, t = 8mm) is investigated. As the weld seam quality greatly depends on the amount of intermetallic phases within the joint, optimized process parameters and control are crucial. Using high-power laser welding, a tensile strength of 10 kN was achieved. Based on metallographic analysis, hardness tests, and tensile tests the potential of this joining method is presented.

High Power Laser Beam Welding of Thick-walled Ferromagnetic Steels with Electromagnetic Weld Pool Support

The development of modern high power laser systems allows single pass welding of thick-walled components with minimal distortion. Besides the high demands on the joint preparation, the hydrostatic pressure in the melt pool increases with higher plate thicknesses. Reaching or exceeding the Laplace pressure, drop-out or melt sagging are caused.A contactless electromagnetic weld support system was used for laser beam welding of thick ferromagnetic steel plates compensating these effects. An oscillating magnetic field induces eddy currents in the weld pool which generate Lorentz forces counteracting the gravity forces. Hysteresis effects of ferromagnetic steels are considered as well as the loss of magnetization in zones exceeding the Curie temperature. These phenomena reduce the effective Lorentz forces within the weld pool. The successful compensation of the hydrostatic pressure was demonstrated on up to 20mm thick plates of duplex and mild steel by a variation of the electromagnetic power level and the oscillation frequency.

Research on the Characteristics of Double-Sided Hybrid Laser-GMAW Synchronous Horizontal Welding of High-strength Thick Steel Plates

Research on the Characteristics of Double-Sided Hybrid Laser-GMAW Synchronous Horizontal Welding of High-strength Thick Steel Plates

FINITE ELEMENT MODEL FOR PREDICTING RESIDUAL STRESSES IN SHIELDED MANUAL METAL ARC WELDING OF MILD STEEL PLATES

This paper investigates the prediction of residual stresses developed in shielded manual metal arc welding of mild steel plates through Finite Element Model simulation and experiments. The existence of residual stresses that cause fatigue and distortion in welded structures has been responsible for failure of machine parts in service. These stresses if not properly controlled can lead to loss of lives and property. The highlight is that various trial and error welding runs have to be carried out while hoping for the best performance during operation. This is wasteful of time, material and finance. Thus the need to incorporate Finite Element Analysis prediction of residual stresses by computational methods to first determine satisfactory welding conditions before actual production. The geometry of the butt welded Low Carbon (ASTM A36) steel plates was modeled and the residual stresses simulated using ANSYS Multiphysics V14. Three experimental samples of similar geometry were also produced using the shielded manual metal arc welding process to verify the result. Low carbon steel (ASTM A36) was used as the parent metal, E066 electrodes were used to complete the weld. The generated residual stresses were measured using an X-Ray Diffractometer (XRD 6000). From the Finite Element Model Simulation, the transverse residual stress in the x-direction (σ x ) had a maximum value of 375MPa (tensile) and minimum value of -183MPa (compressive) while in the y-direction (σ y ), the maximum value of 172MPa (tensile) and minimum value of zero. The longitudinal stress in the x-direction (σ x ) indicated a maximum value of 355MPa (tensile) and a minimum value of -10MPa (compressive) while in the y-direction (σ y ), the maximum value was 167MPa and the minimum value of the residual stress was -375MPa. The experimental values as measured by the X-Ray diffractometer were of reasonable correlation as transverse residual stress (σ x ) along the weld line in the transverse x-direction varied from 353MPa (tensile) to -209MPa (compressive) while in the y-direction, stress (σ y ) along the weld line varied from 177MPa (tensile) to zero. The longitudinal stress measured by the X-Ray diffractometer in the x-direction (σ x ) varied from 339MPa (tensile) to zero (compressive) while in the y-direction (σ y ) varied from 171MPa (tensile) to -366MPa (compressive). These results shows that the residual stresses obtained by prediction from the finite element method are in fair agreement with the experimental results. Based on this, it can be concluded that Finite Element Model can be used to replicate and determine the expected residual stresses that would be generated before an actual welding process is carried out. http://dx.doi.org/10.4314/njt.v35i1.14

Acoustic Signature Based Weld Quality Monitoring for SMAW Process Using Data Mining Algorithms

The quality of weld depends upon welding parameters and exposed environment conditions. Improper selection of welding process parameter is one of the important reasons for the occurrence of weld defect. In this work, arc sound signals are captured during the welding of carbon steel plates. Statistical features of the sound signals are extracted during the welding process. Data mining algorithms such as Naive Bayes, Support Vector Machines and Neural Network were used to classify the weld conditions according to the features of the sound signal. Two weld conditions namely good weld and weld with defects namely lack of fusion, and burn through were considered in this study. Classification efficiencies of machine learning algorithms were compared. Neural network is found to be producing better classification efficiency comparing with other algorithms considered in this study.

High power disk laser-metal active gas arc hybrid welding of thick high tensile strength steel plates

In this study, welding with hybrid heat sources combined with a high power disk laser and a metal active gas (MAG) arc was carried out on 780 MPa high strength steel plates of 12 mm in thickness. The effects of respective welding conditions, such as laser power, root gap and welding speed on the penetration, geometry, and defects of weld beads, were investigated. The results showed that the process window of welding conditions for the production of good welded joints was narrow. Also, the laser keyhole behavior, the molten pool geometry, and the melt flows inside the molten pool were observed by the high-speed x-ray transmission real-time imaging system. It was confirmed that the melt flows inside the molten pool during hybrid welding were different between humping and good weld beads. The melt flowed from the bottom tip of a keyhole to the humping portion and did not flow forward to the keyhole bottom tip, resulting in the formation of the humping defect. On the other hand, in the case of good weld beads, the tungsten particle flowed to the back part of the molten pool but then flowed to the forward keyhole. It was clarified that a good weld bead without humping nor underfilling could be produced due to the forward melt flow.

Finite Element Simulation Research on Medium Plate Multi-Pass Welding Temperature Field

V-grooved steel plate 30mm in thickness has been taken into consideration to research on the distribution of temperature field for the multi-pass welding of steel plate with intermediate thickness in the whole process of welding and cooling. With the establishment of a reasonable three-dimensional solid model, the utility of ANSYS software for finite element analysis, the usage of birth-death elements and the setting of normal Gauss heat source, steps have been undertaken to achieve the goal that the process of multi-pass welding about steel plate in intermediate thickness is simulated and the law of distribution about welding temperature field is obtained. The research results indicate the following: the temperature in every point of base metal changes constantly when the steel plate 30mm in thickness is being welded, the heat input position and position behind heat source are the integral parts which have the highest temperature during the process that welded joints are welded, the temperature gradient in front of welding arc is pretty large as well as that behind welding arc is relatively small. The calculation results are consistent with actual observations providing exactly reliable references for stress field of the welding on steel plates.

Experimental investigations on the SiO2 flux-assisted GTA welding of super-austenitic stainless steels

This study addressed the use of activated flux SiO2 for the gas tungsten arc (GTA) welding of super-austenitic stainless steel plates of 5 mm thickness. Trials were carried out to investigate the effect of flux and the welding current to determine the depth of penetration. Bead-on-plate trials were carried out on the AISI 904L with and without flux. It was inferred from the macrostructure studies that with a welding current of 180 A, complete penetration could be achieved using flux-assisted GTA welding. The optimal process parameters were validated by conducting the experimental investigations to ascertain the structure–property relationships of flux-assisted GTA weldment. Experimental results corroborated that the average tensile strength and impact toughness of SiO2 flux-assisted GTA weldments of AISI 904L were observed as 553 MPa and 49.3 J. It was inferred from the studies that defect-free welds of super-austenitic stainless steel could be obtained on employing flux-assisted GTA welding process.

Aspects Regarding the Achievement of Vertical Welding Joints

The vertical MAG welding procedure is a difficult position to be executed because the trend of the molten bath flowing. This article aims to present the achievement of vertical welding joints with a linear device with a radial oscillation system that should achieve automatic vertical welds and the correlation of the welding parameters with the movement of the welding torch in order to obtain these, using the MAG procedure, protective gas M 21 (82% argon + 18% CO2), welding wire SG2, the material of the welded pieces S 355 JR. Samples will be cut from the welded steel plates and they will be characterized from the mechanical point of view (hardness, microstructure and macrostructure).

Analysis of process parameters effects on dissimilar friction stir welding of AA1100 and A441 AISI steel

A prominent benefit of friction stir welding process is to join plates with dissimilar material. In this study, an attempt is made to find effects of tool offset, plunge depth, welding traverse speed and tool rotational speed on tensile strength, microhardness and material flow in dissimilar friction stir welding of AA1100 aluminium alloy and A441 AISI steel plates. Here, one factor at a time experimental design was utilised for conducting the experiments. Results indicated the strongest joint obtained at 1·3 mm tool offset and 0·2 mm plunge depth when the tool rotational speed and linear speed were 800 rev min− 1 and 63 mm min− 1 respectively. The maximum tensile strength of welded joints with mentioned optimal parameters was 90% aluminium base metal. Fracture locations in tensile test at all samples were in aluminium sides. Owing to the formation of intermetallic compounds at high tool rotational speed, the microhardness of joint interface goes beyond that of A441 AISI steel.

Study of sub-shoulder tool wear on friction stir welded steel plates using two modes of metal transfer phenomenon

Tool wear study is undertaken with IS 3039, grade II steel plates and analysed by two modes of the metal transfer phenomenon. The first mode of metal transfer takes place by the direct contact of the tool shoulder on the work plate, generating heat owing to friction, and the second mode of metal transfer takes place around the pin. This study is aimed at knowing the formation of a weld for every 300-mm length, which indirectly reflects the effect of the pin profiles on producing a better weld. The individual contribution of two modes of metal transfer has been studied, and it was observed that the higher the area of the first mode of metal transfer, the more the strength of the weld. The variations in the distribution of hardness along the first mode of metal transfer were found to be higher, because the compaction offered by the tool shoulder is more than that in the second mode of metal transfer. Microstructure and macrostructural analyses were performed on the weld, based on the two modes of the metal transfer phenomenon. The ultimate tensile strength gets reduced, if the percentage formation of the first mode of metal transfer is less.

Multi-objective Optimization of Welding Parameters in Submerged Arc Welding of API X65 Steel Plates

Submerged arc welding (SAW) is one of the main welding processes with high deposition rate and high welding quality. This welding method is extensively used in welding large-diameter gas transmission pipelines and high-pressure vessels. In welding of such structures, the selection process parameters has great influence on the weld bead geometry and consequently affects the weld quality. Based on Fuzzy logic and NSGA-II (Non-dominated Sorting Genetic Algorithm-II) algorithm, a new approach was proposed for weld bead geometry prediction and for process parameters optimization. First, different welding parameters including welding voltage, current and speed were set to perform SAW under different conditions on API X65 steel plates. Next, the designed Fuzzy model was used for predicting the weld bead geometry and modeling of the process. The obtained mean percentage error of penetration depth, weld bead width and height from the proposed Fuzzy model was 6. 06%, 6. 40% and 5. 82%, respectively. The process parameters were then optimized to achieve the desired values of convexity and penetration indexes simultaneously using NSGA-ll algorithm. As a result, a set of optimum vectors (each vector contains current, voltage and speed within their selected experimental domains) was presented for desirable values of convexity and penetration indexes in the ranges of (0. 106, 0. 168) and (0. 354, 0. 561) respectively, which was more applicable in real conditions.

Flexural Buckling of Columns Strengthened under Load

This paper refers to behaviour and capacity of axially loaded columns strengthened under load using welded steel plates. This method of strengthening is fast, simple and widely used but no universal and reliable analytical solution has been presented yet. In the paper, focus is put on flexural buckling. The approach using cross-section properties of strengthened member and the modified buckling reduction factor was used to calculate the ultimate resistance. In buckling theory, the resistance of column subjected to compression load is reached when the most stressed fibres start to yield. However, some researchers allow certain amount of yielding for base material of columns strengthened under load. In the paper, the new modified buckling reduction factor based on Eurocodes is derived. Two types of column strengthening under various preload magnitudes are investigated using finite element study in ANSYS code and transient analysis type. Birth and death of elements is used to simulate strengthening welded plates. The results are compared with analytical solutions.