Welded Steel Plates Research Articles

Experimental Study on High Power Laser Welding of Ship Steel Plate

This article puts forward adopting the fast-flow axis high power CO2 laser to weld the ship steel plate and mainly studies the influences of technical parameters to the seam. This article also analyzes and tests the welded products which are in the conditions of laser power of 8 kW, welding speed of 1m/min and focus position below 3mm of the workpiece. The results indicate that the distortion of laser welding is small, the ratio of depth and width are bigger than 2:1, and the structure is compact and has no deficiency and presents tiny martensite and few remnants austenite. Laser welding of ship steel plate can realize shaping double sides up one time with single side welding by choosing reasonable welding technical parameters. Therefore, the laser welding ship steel plate technique possesses high practical values.

선급 극후물 강재 용접부 취성균열 정지특성

선박의 고강도화 및 극후물화가 진행됨에 따라 선체 구조물의 파괴 특성에 대한 관심이 높아지고 있으며, 최근 균열정지의 관점에서 취성균열 정지특성에 대한 연구가 활발히 이루어지고 있다. 기존의 연구결과에 따르면 65mmt 이상의 극후물 용접부에 대해서 취성균열 정지특성의 저하가 발생할 가능이 있다고 보고되고 있으며, 취성균열 정지특성이 우수한 강재의 개발 이외에 용접부 보강재의 부착, 보수 용접 실시 등 개선 방안을 마련하기 위한 다양한 연구가 진행되고 있다. 그러나 극후물 용접부 취성균열 전파기구에 관한 규명은 현재 전무한 실정이며, 강재 두께의 영향 이외에 용접 입열량 용접부 잔류응력 등의 효과가 복합적으로 검토되어야 한다. 아울러 극후물 용접부 균열정지 파괴인성의 평가, 대형파괴시험을 대체할 소형시험법의 개발 및 검증 등에 관한 연구가 요구된다.

Nd:YAG 레이저 필렛 용접의 비드형상 예측에 관한 유한요소해석

Nd:YAG pulse laser fillet welding of stainless steel plate was simulated to find welding condition by using commercial finite element code MARC. Full model of AISI 304 stainless steel plate was considered and user subroutines were applied to boundary condition for the heat transfer. Material properties such as conductivity, specific heat, mass density and latent heat were given as a function of temperature. As results, Three dimensional heat source model for pulse laser beam conditions of fillet welding has been designed by the comparison between the finite element analysis results and experimental data on AISI 304 stainless steel plate. Nd:YAG laser welding for AISI 304 stainless steel was successfully simulated and it should be useful to determine optimal welding condition.

Nondestructive Image Evaluation of Welded Zone of Steel Plate using Photoacoustic Microscope

The nondestructive evaluation (NDE) of welded steel plates was performed using photoacoustic microscope (PAM). Specimens were prepared by changing the maximum welding current to 5, 6.5, and 8 kA. A noncontact inspection without having to assemble a transducer was performed, and the results were compared with those of destructive inspection using an optical microscope. The agreement of NDE using a PAM and results from an actual shear fracture destructive test was good. The large fluctuation in the PA signal measured for the steel plates welded at the small current suggests the inhomogeneity of the inside welded region. Furthermore, visualization of the welded region suggests the feasibility of obtaining information on the status or uniformity of the inner welded region, which is difficult to measure by the other methods.

Study of influencing factors and joint performance of laser brazing on zinc-coated steel plate

Laser brazing is applied to the zinc-coated steel plate welding for its superior processing property. The delivery stability of filler metal such as the position of filler wire tip relative to laser focal point centre and the existence time of liquid filler metal are the key technologies in laser brazing. Also, due to the addition of the filler metal, the changeable factors increase in the process of brazing, so matching and optimizing of the processing parameters are important. In this paper, different influencing factors of laser brazing such as wire feeding stability, laser power distribution and galvanized layer, and parameters affecting the laser brazing process including the laser system, base material, filler metal and processing conditions were analysed and tested by experiments. Optimizing parameters were also acquired and used to laser braze lap joint of zinc-coated steel plate. Joint performance and quality were tested by micro-hardness testing, macro-metallographic analysis and SEM analysis. The results proved that laser brazing joints have good intensity and corrosion resistance.

Design and construction of fatigue-prone detail retrofits for Interstate 79 Neville Island interchange bridges

The Interstate 79 Neville Island Interchange Bridge complex located north of Pittsburgh, Pennsylvania, carries four through lanes of the Interstate over Neville Island and the main and back channels of the Ohio River. The mainline bridge consists of a tied through arch span and 26 dual parallel approach spans. These mainline dual approach spans are continuous units comprised two welded steel plate deck girders, welded steel plate floorbeams and rolled steel wide-flange stringers. In addition, the complex includes eight ramp bridges consisting of both straight and curved continuous dual welded steel plate girders, welded steel plate or rolled wide-flange floorbeams and rolled steel wide-flange stringers. These structures, built and opened to traffic during the early to mid-1970s, are owned and maintained by District 11-0 of the Pennsylvania Department of Transportation. All nine bridges are considered fracture-critical (FCM) owing to the two-girder floorbeam system used on the mainline approach spans and a...

Improvement of HAZ Toughness for High Heat Input Welding by using Boron Diffusion from Weld Metal

In high heat input welding, such as 1-pass electrogas arc welding (EGW) of thick steel plates, HAZ toughness is deteriorated because HAZ microstructure coarsens significantly. TiN precipitates dispersed in steel plates are effective to suppress coarsening HAZ microstructure by pinning effect. However TiN precipitates resolve in high temperature region near the fusion line, where deterioration of HAZ toughness is unavoidable near the fusion line. As a solution of this problem, the authors paid attention to boron in the weld metal. Boron is known to be effective to prevent coarse ferrite formation at prior austenite grain boundaries, and to diffuse rapidly in steel. In this research, boron diffusion from weld metal to HAZ during EGW process was confirmed by SIMS analysis. It was certified that diffused boron in HAZ improved HAZ toughness because boron suppressed microstructure coarsening, and fixed free nitrogen originated by TiN resolution as BN near the fusion line. These research results proposed a new HAZ structure control technology considering combination of high boron bearing weld metal and TiN-treated steel plates.

The effect of process parameters on keyhole welding with a 400 W Nd : YAG pulsed laser

A low average power pulsed Nd : YAG laser is used for bead-on-plate welding of low carbon steel plate. The criterion for welding in the conduction and keyhole regime together with the effect of laser process parameters on weld quality is studied. It is established that for a weld with full penetration and velocities viable for industrial applications, welding in the conduction mode would not be suitable. The formation of a keyhole is found to be highly dependent on laser pulse parameters. With an average power in the range 220–240 W and a peak power of 1.8 kW, full penetration through keyhole generation of a 0.7 mm thick st14 sheet metal is achieved.

Effect of water-shower cooling during welding on tensile residual stress improvement in multi-layer welding of austenitic stainless steel plates

Effect of water-shower cooling during welding on tensile residual stress improvement in multi-layer welding of austenitic stainless steel plates

Corrosion detection in welds and heat-affected zones using ultrasonic Lamb waves

Measurements are reported on the amplitude of ultrasonic Lamb waves reflected from a single 20 mm-diameter flat-bottomed hole located adjacent to the weld of a 6 mm-thick butt welded steel plate. The hole was introduced to simulate the presence of corrosion defects in the heat-affected zone, and served to assess the suitability of using the fundamental So Lamb waves as a means for remote detection of corrosion in fluid-filled storage tanks. Measurements were made using a prototype, omnidirectional multi-element transducer developed at Imperial College, and also using a single edge-mounted transducer. Detection of a hole was only possible when using the plate tester at oblique incidence angles, because of the inability to discriminate weld echoes from those due to the hole at normal or near-normal incidence. Detection of holes was also limited to those with a minimum depth of approximately 3 mm by the presence of coherent background noise. Measurements using a single edge-mounted transducer demonstrated that preferential waveguide propagation of the So mode occurred along the weld, in a manner coined 'weld-guided waves'. This permitted easy detection of a 2 mm deep-hole located adjacent to the weld at a distance of 1 m from the transducer. It is likely that a practical surface-mounted transducer based on the S 0 waveguide mode of operation could be developed for the inspection of corrosion defects within the heat-affected zone of fluid-filled tanks. It is probable that such a device would have a range of many metres, be simple in construction, and that the method would be relatively unaffected by the presence of fluid and inherently sensitive because of the suppression of other propagation modes.

Effect of water-shower cooling during welding on tensile residual stress improvement in multi-layer welding of austenitic stainless steel plates

A new welding method that uses a water shower behind the welding torch has been developed in order to reduce tensile residual stress in a welded region. When this method is applied to the welding of austenitic stainless steel, the welding and cooling conditions mainly determine how much the residual stress can be reduced. To optimize these conditions, we first used the robust design technique to determine the effects of the interpass temperature, the heat input quantity and the water-shower area on the residual stress distribution of bead-on-plate. We found that, to decrease the tensile residual stress, the interpass temperature should be high, the heat input low, and the water-shower area large. Effect of the water-shower cooling on multi-layer welding was examined analytically and experimentally. It was found that the residual stresses were tensile without water-shower cooling, but compressive with water-shower cooling under the optimized conditions. It can therefore be concluded that the new welding method is appropriate for reducing tensile residual stress in multi-layer welding of austenitic stainless steel.

Residual Stress Improvement in Multi-Layer Welded Plates Using Water-Shower Cooling During Welding Process

To reduce tensile residual stress in a welded region, we developed a new welding method that applies a water-shower behind the welding torch. When this method is applied to welding of austenitic stainless steel plates, cooling conditions mainly determine how much the residual stress can be reduced. To determine the conditions, we first used FEM to evaluate the effects of interpass temperature on the residual stress. And we found effective conditions for reducing tensile residual stress. To verify the validity of the conditions, specimens welded with or without water shower cooling were manufactured. Residual stresses of the specimens were experimentally measured. It was found that tensile residual stresses were generated on the surface of the welds and those were reduced in the case that the water-shower was applied. These measurement results agree well with the FEM analyses. It can therefore be concluded that the water-shower cooling during welding is appropriate for reducing tensile residual stress in austenitic stainless steel welding.

Automatic Welding System Using Speed Controllable Autonomous Mobile Robot

A prototype of autonomous mobile robot with two vision sensors for automatic welding of steel plates was constructed. The robot can move straight, steer and turn around the robot center by controlling the driving speed of the two wheels respectively. At the tip of the movable arm, two CCD cameras are fixed. A local camera observes the welding line near the welding torch and another wide camera observes relatively wide area in front of the welding part. The robot controls the traveling speed in accordance with the shape of the welding line. In the case of straight welding line, the speed of the robot is accelerated and the welding efficiency is improved. However, if the robot finds a corner of welding line, the speed is decelerated in order to realize the precise seam tracking and stable welding. Therefore, the robot can realize precise and high speed seam-tracking by controlling the travel speed. The effectiveness of the control system is confirmed by welding experiments.

Laser beam welding of steel plates using consumable inserts

Summary The aim of this study was to identify the appropriate parameters for laser welding of steel plates. The mechanical characteristics and metallurgical microstructures of the joints were analysed experimentally. Welded joints were made using two different types of steel (Cr–Mo low-alloy steel and austenitic stainless steel). Samples were cut from the welds and examined macrographically and micrographically; tensile and microhardness tests were also performed. Observation of these samples showed the beneficial effects of narrower molten and heat-affected zones and the consequent advantageous reductions in distortions and residual stresses. On the basis of these experimental results we conclude that both ferritic and austenitic steels can be properly welded, with good mechanical and metallurgical results, using consumable inserts pre-fitted to the edges before welding, provided that suitable welding parameters are chosen.

Non-Vacuum Electron Beam Welding

The electron beam has, for decades now, proven to be a most efficient and reliable tool for joining tasks in different application fields. Vacuum electron beam welding (EBW) has, for many years now, been a standard method for a great variety of industrial application fields. However, even out-of-vacuum (NV-EBW), the electron beam has become a high-productivity joining tool. The substantial weld depths which characterise vacuum electron beam welding are not achievable with the NV-EBW method – those weld depths characterise the vacuum electron beam and are a result of its power density. The strong points of NV-EBW lie, mainly, in high-speed production. The achievable welding speeds reach up to 60 m/min when welding aluminium sheets and up to 25 m/min when welding steel plates.

Optimum Design of Welded Steel Plate Girder Bridges Using a Genetic Algorithm with Elitism

The genetic algorithm (GA) is a general optimization technique that has some unique features that are especially suitable for structural engineering problems. This work uses a simple GA with elitism to find the optimum design of welded steel plate girder bridges. The objectives are to minimize the weight and the cost of the girders. Two types of plate-girder bridges are studied: a single-span bridge and a two-equal-span continuous bridge. Bridges with various span lengths, in increments of 20 ft , are investigated; results are tabulated, parametric studies are made, and meaningful conclusions are drawn.

Artificial neural networks – an aid to welding induced ship plate distortion?

A preliminary study on the potential application of artificial neural networks in welded structures was expanded to metal inert gas welding of steel plates of grades D and DH 36. The main controllable variables were plate thickness, steel grade, plate cutting process, and heat input. A series of welded plates of each grade was manufactured, covering plate thicknesses of 6 and 8 mm. The topography of each welded plate was evaluated after tacking the plates together and after welding, allowing the actual distortion to be calculated. It was established that a multilayer perceptron network architecture configuration accurately represented the distortion for the 6 mm thickness plate, and for the 8 mm thickness plate after treatment of the data. The data generated were used to develop the PREDICTOR software package, which allows a distortion prediction to be produced, and to carry out a sensitivity analysis. Heat input was found to be the most sensitive factor related to distortion, with carbon content of the plates, yield/tensile strength ratio, carbon equivalent, and steel grade also having significant effects. Some test plates were modelled using finite element method software packages: the initially poor agreement was improved via the addition of significant detail, but the finite element model by its nature will normally predict symmetrical distortion from a symmetric weld, whereas the artificial neural network model developed was capable of predicting the asymmetric distortion observed in reality.

High-power CO2 laser-MIG hybrid welding for increased gap tolerance. Hybrid weldability of thick steel plates with a square groove

High power enhancement of laser processors has recently led to laser welding being used for the joining of thick steel plates. For example, the literature includes a study on the practical application of a 45 kW CO2 laser for the welding of thick steel plates,1 although few such applications have thus far been documented. The limited application of lasers to welding of thick steel plates is attributable to the narrow gap tolerance provided and the small laser beam diameter that leads to unacceptable welding defects, such as underfills, melt-through, and porosities.

Scanning Acoustic Microscope/Photoacoustic Microscope Operating on a Unified Software Environment

A scanning acoustic microscope (SAM) and a photoacoustic microscope (PAM) operating on a unified software environment was designed and fabricated. Welded steel plates, in which the welding condition was changed by varying the amount of current and its duration, were used as specimens. SAM and PAM measurements for this specimen were carried out, and the obtained images were compared. This system has the advantage of complementary measurement using both SAM and PAM.

Effect of Initial Deflection Shape on the Ultimate Strength Behavior of Welded Steel Plates Under Biaxial Compressive Loads

The shape of weld-induced initial distortion in steel plates bounded by support members is normally very complex. It must be recognized that it is not only the magnitude of initial distortion, but also its shape that can significantly affect the plate collapse behavior. In this paper, some typical plate initial deflection shapes are selected from measurements for merchant ship plating between stiffeners. The influence of such initial deflection shapes on the ultimate strength behavior of steel plates subjected to biaxial compression as well as uniaxial thrust is then investigated applying nonlinear finite element analyses. It is confirmed that an initial deflection shape that approximates the buckling mode, with its maximum amplitude selected to be the same as the measured maximum initial deflection, is a good representation for the purposes of somewhat pessimistic evaluation of the ultimate strength of plating between stiffeners under biaxial compression as well as under uniaxial compression. Also, it appears that the influence of initial deflection shape on the plate collapse behavior under predominantly transverse axial compression or biaxial compression can be quite different from that under predominantly longitudinal axial compression. As another contribution, the ultimate strength interaction relationship of plating under biaxial compressive loads is presented. The results and insights developed from the present study are summarized.