Laser Welding Of Steel Research Articles

Effect of beam wobbling on microstructure and hardness during laser welding of X70 pipeline steel

Laser welding with beam wobbling was employed to weld X70 pipeline steel. The influence of beam wobbling on weld surface morphology, fusion zone microstructure, and microhardness was investigated. The formation of spatter was suppressed by beam wobbling using a beam with higher energy density. At a welding speed of 1.0 m min−1, the weld metal produced with a circular laser wobble pattern contained more martensite but less ferrite, compared to that of static spot welded joint. The presence of more martensite led to the increase in fusion zone hardness. A softened region was found in the inter-critical heat-affected zone. The hardness of the softened region could be improved by increasing the welding speed (from 1.0 to 1.5 m min−1).

Melt flowing behaviors and microstructure evolution during laser offset welding of dissimilar metals between AH36 and 304 steels

The study aimed to reveal the mechanism of microstructure evolution in the fusion zone of dissimilar AH36 and 304 steel laser welds and provide a feasible method for controlling austenite/martensite phase balance via adjusting laser offset (defined 304 side (-) and AH36 side (+)). The results suggested that asymmetrical fusion line boundaries were observed when centerline of dissimilar joints was irradiated by laser beam (L = 0 mm). Besides, fraction of austenite phase in weld center was decreased from 10.8% to 0.01% and broader inherited lathy martensite grain was obtained when laser offset shifted from 304 stainless steel side of 0.5 mm (L = −0.5 mm) to AH36 steel side of 0.5 mm (L = 0.5 mm). Microstructural difference of fusion zone under varying laser offset was determined by Gibbs free energy of the martensite transformation and growth time of matrix-austenite grain, which were related with element distribution and cooling rate from austenitic temperature to Ms temperature. The inhomogeneous element distribution was observed due to inadequate mixing of two liquid steels when L = −0.5 mm while strong mixing was obtained at L = 0 mm and L = 0.5 mm. The phenomenon was attributed to different dilution of base metal irradiated by laser beam and driving force for melt flowing. Therefore, more martensite grains resulted in increasing average hardness with laser offset shifting from −0.5 to 0.5 mm while impact absorbed energy was lower, due to weaker deformation capacity of coarse martensite grain.

Numerical Simulation and Experimental Analysis of Thermal Cycles and Phase Transformation Behavior of Laser-Welded Advanced Multiphase Steel

This work presents the results of the comparison between simulations and experiments of the laser welding of advanced multiphase steel. The numerical simulations of welding with different parameters were carried out using the Sysweld software. The geometry of the weld and structural constituents as well as stress distributions were analyzed. The simulated thermal cycles were incorporated in the JMatPro software to determine the phase transformation kinetics during cooling. The experimental tests were performed to compare the simulations with the real results. According to them, the shape of the weld and its width were symmetrical according to the weld axis. The simulated values were higher compared to the real one at heat inputs higher than 0.048 kJ/mm. The microstructure investigations conducted with scanning electron microscopy showed a good agreement in the fusion zone. Some differences in the microstructure of heat-affected zone and transition zone were identified. According to the phase transformation simulations, the weld should be composed of only martensite. The real microstructure was composed of martensite and some fraction of bainite in the heat affected zone. The more complex microstructure consisting of ferrite, bainite and retained austenite was present in the transition zone. The results of measured and simulated hardness indicated the good agreement with the difference of 17 HV0.1.

Investigation of Weld Root Defects in High-Power Full-Penetration Laser Welding of High-Strength Steel

The currently available high-power laser shows promising opportunities for the welding of thick plates in a single pass. However, weld-root defect frequently occurs when a high-power laser is used to join thick plates in a full-penetration mode, which has a significantly adverse effect on the serviceability of the weld joint. The purpose of this work is to understand the defect formation mechanism and reduce these defects through controlling welding parameters. In this study, the characteristics of weld root defects were investigated using a 10 kW fiber laser using a program of experiment and theoretical analysis. The corresponding defect formation mechanisms were discussed based on the bottom molten pool behaviors observed by the high-speed camera. The results showed that there were four types of weld-root appearances as follows with an increase of linear heat input from 300 J/mm to 1000 J/mm: weld-root humping (30 mm/s), sound weld (25 mm/s), weld sagging (20 mm/s) and excessive weld sagging. The remedies for reducing weld-root defects were also presented to obtain sound weld bead by optimizing welding parameters. Weld-root humping was formed due to the quasi-full-penetration keyhole. Weld sagging resulted from the imbalance of the hydrostatic pressure and surface tension in the condition of a through keyhole. It was also found that the sound weld was formed when a through keyhole and a proper molten pool size were obtained. Thus, the state of the keyhole and molten pool geometry were the major factors that affect weld-root defects.

Analysis of welding solidification crack in narrow gap laser welding of high-strength steel

Analysis of welding solidification crack in narrow gap laser welding of high-strength steel

Research progress of transition layer and filler wire for laser welding of steel and aluminum dissimilar metals

Research progress of transition layer and filler wire for laser welding of steel and aluminum dissimilar metals

Effects of reduced ambient pressure on the OCT-based weld depth measurement signal in laser welding of aluminum and steel

For the process monitoring during laser deep penetration welding, optical coherence tomography (OCT) has emerged as a promising method for the in-situ measuring of the keyhole depth or, as a result, of the weld penetration depth. Prior research on this topic with steel substrates has shown that reducing the ambient pressure significantly improves the detectability of keyhole bottoms. In addition to OCT measurements, high-speed recordings of the process zone enable the evaluation of the keyhole opening behavior in this study. Bead-on-plate welds in steel demonstrate that the reduction of the ambient pressure improves the measurements unambiguity and decreases the average keyhole diameter while the keyhole opening stability seems to remain mainly unchanged. Therefore, it can be concluded that the higher measurement unambiguity at lower ambient pressure is not caused by a higher keyhole accessibility of the OCT probe beam but rather by changed conditions inside the keyhole. Experiments with aluminum substrates validated the beneficial effects of the reduced ambient pressure on the detectability of the keyhole bottom.

Developing Laser Welding of Steel to Aluminum for Body Weight Reduction of Transportation Equipment

Developing Laser Welding of Steel to Aluminum for Body Weight Reduction of Transportation Equipment

Dynamic Behavior of Keyhole and Molten Pool Under Different Oscillation Paths for Galvanized Steel Laser Welding

Dynamic Behavior of Keyhole and Molten Pool Under Different Oscillation Paths for Galvanized Steel Laser Welding

Estimation of Residual Hydrogen in Laser Weld by Two-dimensional Differential Calculation

It has been reported that hydrogen dissolves in the weld bead in laser welding. If the hydrogen concentration in the weld bead is high, there is concern that the weld bead may fracture during press forming of tailored blanks. Therefore, assuming that 1ppm of hydrogen is dissolved in the weld bead at welding, the change in hydrogen concentration over time is estimated by a two-dimensional difference calculation. In the calculations, hydrogen is assumed to follow the Fick’s diffusion equation, and the diffusion coefficient at room temperatures is the value determined by the authors for a 980MPa steel laser welds in the past. The diffusion coefficients at high temperatures were determined from several references. As a result, it was estimated that about 30% of the hydrogen had effused from the surface by the time the weld bead cooled to room temperature. The mechanical properties of the weld bead are considered to be governed by the maximum hydrogen concentration at the center of the weld bead cross-section, but this value cannot be measured directly. Therefore, assuming that all the hydrogen contained in the entire model is in the weld bead and considering the average hydrogen concentration in the weld bead, the ratio of the maximum hydrogen concentration to the average hydrogen concentration is around 1 up to 6h after welding, indicating that the average hydrogen concentration is a good indicator of the maximum hydrogen concentration. It was also confirmed that the logarithm of the average hydrogen concentration is proportional to time as time passes after welding and that the hydrogen concentration distribution in the thickness direction behaves as a solution of a one-dimensional diffusion equation. These results suggest that the hydrogen concentration in the laser weld bead can be considered as an analytical solution of the one-dimensional diffusion equation.

Evaluation of the effect of filler metal interlayer on the weld joint quality in fiber laser welding of alloy steel (A516)

Laser welding of A516 steel was performed using the filler metal to serve as the interlayer. The effects of laser welding parameters on the melt pool microstructure, weld bead shape, dimensions of the melt pool, and temperature field around the melt pool were investigated. The results indicated that the nozzle distance had the most significant influence on the temperature around the molten pool. As the maximum energy of the laser beam was irradiated on the center of the filler, the highest value of the temperature near the fusion zone was about 360°C. The welding speed, determining the overlap factor, had a considerable effect on the weld bead shape. The laser power, therefore, could determine laser beam line energy to melt the filler volume effectively. Enhancing the laser power up to 450 W increased the temperature to about 300 °C; also, the melting rate of the filler used was almost completed and the weld bead appearance was clearly improved; therefore, the width of the melt pool was increased by about 10%. Increasing the nozzle distance from 3 to 7 mm also reduced the width of the molten pool by about 75% and 40% with and without the filler, respectively. By using the filler metal, the geometry of the welding bead changed from a concave one to a convex one. The major fusion zone microstructure of the fusion zone was an acicular ferrite characterized by needle-shaped ferrite crystallites.

Effect of zinc vapor forces on spattering in partial penetration laser welding of zinc-coated steels

A three-dimensional thermal-fluid numerical model considering zinc vapor interaction with the molten pool was developed to study the occurrence of zinc vapor-induced spatter in partial penetration laser overlap welding of zinc-coated steels. The zinc vapor effect was represented by two forces: a jet pressure force acting on the keyhole rear wall as the vapor bursts into the keyhole and a drag force on the upper keyhole wall as the vapor escapes upwards. The numerical model was calibrated by comparing the predicted keyhole shape with the keyhole shape observed by high-speed X-ray imaging and applied for various weld schedules. The study showed that large jet pressure forces induced violent fluctuations of the keyhole rear wall, resulting in an unstable keyhole and turbulent melt flow. A large drag force pushed the melt adjacent to the keyhole surface upward and accelerated the movement of the melt whose velocities reached 1 m/s or even higher, potentially inducing spatter. Increased heat input facilitated the occurrence of large droplets of spatter, which agreed with experimental observations captured by high-speed camera.

Investigation of the gap bridgeability at high-power laser hybrid welding of plasma-cut thick mild steels with AC magnetic support

One of the challenges of the high-power hybrid laser welding of thick steels is the sensitivity of the process of the process to manufacturing tolerances. This usually leads to a time-consuming preparation of the welding edges, such as milling. The study deals with the influence of the edge quality of milled and plasma-cut steel made of S355J2 with a wall thickness of 20 mm on the laser hybrid welded seam quality. Furthermore, the gap bridgeability and the tolerances towards edge misalignment was investigated. An AC magnet was used as backing support to prevent sagging and positioned under the workpiece, to generate an upwards directed electromagnetic pressure. The profiles of the edges and the gap on the top and root side were measured using a digital camera. Single-pass laser hybrid welds of plasma-cut edges could be welded using a laser beam power of just 13.7 kW. A gap bridgeability up to 2 mm and misalignment of edges up to 2 mm could be achieved successful. Additionally, the independence of the cutting side and the welding side was shown, so that samples were welded to the opposite side to their cutting. For evaluation of internal defects or irregularities, X-ray images were carried out. Charpy impact strength tests were performed to determine the toughness of the welds.

Microstructure and mechanical properties of laser welding of AZ31B magnesium alloy and DP590 dual-phase steel with concave groove joint

A novel connection method has been explored for laser welding of AZ31B magnesium alloy and DP590 dual-phase steel, where lap joint with concave groove was added by Sn powder. The influence of groove width on the interface reaction and mechanical properties of the joint was also studied. The result show that the boundary surface of the concave groove was mainly divided into two regions. One was the laser directly irradiated area which was mainly composed of FeAl + Mg2Sn + α-Mg. As the width of the concave groove increased, the phase composition of the interface changed from FeAl + Mg2Sn + α-Mg to FeAl + FeSn + Mg2Sn + α-Mg. The other was the side boundary area of the concave groove, where a large amount of Sn was transferred from the directly irradiated area, thus the columnar Mg2Sn + α-Mg crystal grains were larger than the directly irradiated area. This interface was mainly composed of FeAl + Mg2Sn + α-Mg. The calculation results of the atomic chemical potential were shown that the Al atoms from the base material diffused to the Fe side in the Mg-Al-Sn-Fe system, which made it easier to form the FeAl phase at the interface. At the Fe interface, Fe and Sn atoms were attracted by Al atoms, which promoted the reaction between Fe atoms and Sn atoms. The maximum load value reaches 1711 N with 1.5 mm width of concave groove, representing twice enhancement compared with that with no-concave groove.

Laser welding of 4330V steel with a micro-additive of vanadium

This article presents the results of a test of laser welding of high-strength low-alloy steel with a micro-additive of vanadium. Steel 4330V is a delivery material after heat treatment. Welded joint was made by laser welding using a TruDisk 12002 disc laser. As a result of welding, a joint was formed which was subjected to visual and penetration tests from the face side, as well as macro and microscopic tests. Impact tests were carried out at reduced temperature in the weld and in the heat affected zone (HAZ). The resulting joint was also subjected to the Vickers hardness test, bend test and the tensile strength test. This research show how the low-alloy high-strength material behaves during welding without processing before and after welding. In results after welding show incomplete penetration from the root side. No cracks on the weld face. In HAZ hardness was of 520HV0.5 and tensile strength of joint was on level1077MPa.

Laser welding of new austenitic cryogenic corrosion-resistant steels alloyed with nitrogen

The article proposes a method for improving the thermal performance of walking beam reheating furnaces using a statistical mathematical model of metal heating. The main part of the study refers to the creation of a metal heating model based on a comprehensive analysis of 15 industrial experiments carried out on the Russian continuous furnaces. The first stage of statistical model creation consists of factors’ selection, construction of regression model, correlation analysis and assessment of the variables’ significance, adjustment of factors and obtaining regression equations. As a result, a quasi-dynamic statistical mathematical model of a five-zone walking beam reheating furnace has been created and adapted, that actually makes it possible to trace the heating process in dynamics. The adaptation of the statistical model and error calculation has been carried out using the results of industrial experiments on the investigated furnaces of mills 2000 and 5000. The article contains graphs comparing real temperatures and temperatures calculated on the basis of mathematical and statistical models for one of the experiments. The second stage of quasidynamic statistical model creation has shown that temperature of the combustion products of neighboring zones is a significant factor, that enhances calculation accuracy by 1-3%. The main conclusions are formulated based on the results of the research done. For the first time in metallurgical practice, a quasi-dynamic statistical model has been developed and adapted which describes the process of metal heating in a walking beam reheating furnaces. Since the regression function is defined, interpreted and justified, and the assessment of the accuracy of the regression analysis meets the requirements, it can be assumed that the model and predicted values have sufficient reliability.

Effects of Heat Input on Microstructure and Mechanical Properties of Dissimilar Laser-Welded Dual-Phase and Boron Steel Joints

Effects of Heat Input on Microstructure and Mechanical Properties of Dissimilar Laser-Welded Dual-Phase and Boron Steel Joints

Laser welding of ultra-high strength steel with different oscillating modes

To obtain high-quality welded joints with low heat input and high welding efficiency, a laser oscillating mode was proposed for welding D406A ultra-high strength steel (UHSS). The effect of four oscillating modes on morphology, microstructure and mechanical properties of the 3.5 mm-thick UHSS welded joints were discussed, including transverse, longitudinal, circular and without oscillation. The morphologies of the welded joints with different oscillating modes were significantly different. Among them, circular oscillation obtained the deepest weld penetration, and an asymmetric phenomenon of cross-section was observed. Furthermore, both transverse and circular oscillation obtained equiaxed grains, while circular oscillation had the finest columnar grains and the largest equiaxed grain area. Subsequently, mechanical properties of the welded joints with circular oscillation were improved obviously, which has the highest tensile strength of 809.44 MPa and the largest ductility of 21.8%. In comparison to without oscillation, the tensile strength and ductility were increased by 9.58% and 11.4% respectively. This study provides guidance for the selection of optimal oscillating modes for laser welding of UHSS.

Effect of beam oscillating pattern on laser welding of steel to PMMA

Laser welding of 1 mm-thick steel and PMMA was employed via beam oscillating. Three modes of beam oscillation, transverse, longitudinal and circular were explored. Due to the stirring effect, the beam oscillation improves the weld formation and promotes the flow of bubbles in the molten layer. The circular oscillation gives the strongest weld homogeneous without overheat discoloration defect. The bonding strength was 38% more than the weldment without beam oscillation. The weld strength improvement was attributed to the variation of the oscillating speed varies the time-frequency distribution of the beam energy. This technology reduces the morphological defects and increases the uniformity of the weld. The improvement mechanism of beam oscillation on bubble behavior and melt flow behavior is also discussed.

Laser welding of new austenitic cryogenic corrosion-resistant steels alloyed with nitrogen

There were studied structures and properties of welded joints of laboratory melted austenitic steels: Fe-0.04C-18Cr-9Ni-0.2N and new-developed Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo and Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo-2Cu. Correct choice of composition and deformation-heat treatment leads the new-developed steels are high-strength corrosion-resistant ones with stable austenite. Computer simulation shows that enough quality of welded seam can be provided by laser welding of plates of up to 4 mm in thick at the room temperature. For bigger thicknesses preliminary heating is necessary. Microstructure, phase compositions, lattice periods, X-ray diffraction peak broadening, microhardness, bending strength and ductility, resistance against intercrystalline, pitting and total corrosion was studied for bulk metal and laser welded joints of high-temperature thermomechanically treated hot-rolled plates, including tests after 1000 thermal cycles in range –163…+20 °C were investigated. It was shown that welded seams are 300…1000 μm in wide and have no porosity and no thermal affected zone. The welded seam strength is the same as for bulk metal, 180° bend test shows no cracks in the seam. The resistances of welded seam and bulk of Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo and Fe-0.1C-19Cr-10Mn-6Ni-0.3N-2Mo-2Cu steels against total corrosion in the sea water (3 % NaCl) and in acid environment (0,5M H2SO4, including additional blowdown by H2S), pitting and intercrystalline corrosion in standard environments are practically equal. The structures, phase compositions, hardnesses and corrosion resistances of welded joints of both new-developed steels are constant after the thermocycling.