Laser Welding Of Stainless Steel Research Articles

Modeling of laser welding of stainless steel using artificial neural networks

Laser Welding (LW) is a process which is used to effectively weld metal, alloy or thermoplastics. Laser Welding uses a high concentrated beam of laser to melt the material and to perform welding. Its demand is increasing rapidly in automation as it is fast, more precise, have a deep penetration capacity and have less heat affected zone (HAZ), reduced tendency to spiking thus suitable for Ultra-Narrow Gas Laser Welding (UNGLW). Due to the high cost and time-consuming nature of laser welding experiments, repetition of one experiment in a wide range of data is not feasible. Artificial neural networks have been introduced as an effective tool for predicting values of outcomes and input parameters of various machining processes. In this work, the effect of laser power, welding speed and wire feed rate on the weld quality, i.e., tensile strength and overlap factor is investigated by ANN. Modelling of laser welding of stainless steel is performed using feed forward back propagation trained neural network. The projected outcomes are found to be in good agreement with the previous experimental findings.

Experimental and numerical studies of laser-welded slender stainless steel I-section columns

Stainless steel has extensive applications in the construction industry because of its attractive appearance, unique corrosion resistance, durability, and superior mechanical properties. Laser-welding is a manufacturing process that is suitable for connecting various steel and stainless steel. High precision and low heat input characteristics make it have smaller heat-affected zones than the traditional welding process, resulting in lower thermal distortions and residual stress to give it increased load-carrying capacity. The present paper focuses on investigating the structural response of laser-welded slender stainless steel I-section columns to address the lack of test data. Nine stub columns tests and ten long columns tests were analysed for slender I-sections of austenitic laser-welded stainless steel of two stainless steel alloys (austenitic EN 1.4301 and EN 1.4307). Additionally, the material tensile coupon tests, residual stress measurements, and initial geometric imperfection measurements were performed. The observed results verified a representative residual stress pattern. The finite element model was validated based on the test results and parametric analysis was carried out on laser-welded slender stainless steel I-section axially compressed members. Further, the study evaluated the cross-sectional and column buckling resistances for European code EN 1993-1-4, American Design Guide AISC 27, and Continuous Strength Method. Interestingly, the continuous strength method reflected significantly better buckling behaviour of slender I-sections. Although this method gives more accurate results than the code predictions, slight conservatism predictions were still found for slender I-section columns with room for improvement.

Laser Welding of AISI 316L Stainless Steel Produced by Additive Manufacturing or by Conventional Processes

Among all the additive manufacturing techniques, Laser Powder Bed Fusion (LBPF), also called Selective Laser Melting (SLM), is the most common technique due to its high capability of building complex parts with generally improved mechanical properties. One of the main drawbacks of this technique is the sample size limitation, which depends on elaborating chamber dimensions. In this study, we investigate the viability of obtaining large parts with the laser welding of additive manufactured plates. A comparison of the microstructure and the tensile mechanical properties of SLM-welded plates and cold-rolled welded plates was performed. This paper shows the possibility of obtaining defect-free parts. Even if welding has a low impact on the microstructure of the SLM samples, fractures are located on the fusion zone, and a decrease in ductility of around 30% compared to the base metal is observed.

A Study on the Fiber YAG Laser Welding of 304L Stainless Steel

This work aims to optimize the main YAG fiber laser parameters to weld 304L stainless steel plates of 3 mm thick. Different laser powers (2500, 2000, and 1500 W) and speeds (60, 40, and 20 mm/s) were used and merged in heat input, maintaining the defocusing distance at –2 mm to get full penetration. The weld quality and the effect of the laser heat input on the microstructures of the weld and heat-affected zones were investigated. Besides, the fracture strength of the welded joints and hardness distribution through the cross-sections were evaluated. The weld width has a direct relationship with heat input. The laser power of 2800 W produced full penetration joints without any macro defects while reduction in laser power pronounced partial penetration defects. The size of the heat-affected zone in all the processing parameters was very small. The microstructure of the weld zone shows columnar dendrite austenite grains with small arm spacing in most of the welded zone. The size of the dendrites became finer at lower heat input. At a higher heat input, a reasonable amount of lathy equiaxed grains with some delta ferrite occurred. A small amount of delta ferrite was detected in the heat-affected zone, which prevented the crack formation. The hardness of the weld metal was much higher than that of the base metal in all processing parameters and it has a reverse relationship with the heat input. The fracture strength of the welded joints was very close to that of the base metal in the defect-free samples and it increased with decreasing the heat input.

Monitoring of high-speed laser welding process based on vapor plume

The increase of welding speed can improve the productivity of laser welding. The behavior of vapor plume is an important indicator reflecting the state of the laser welding process. However, the behavior of vapor plume in high-speed laser welding (whose welding speed is higher than 10 m/min) has not been studied adequately. In this research, images of the vapor plume in high-speed laser welding of SUS304 austenitic stainless steel are captured through high-speed imaging for the monitoring of the welding process. Characteristics of the vapor plume are extracted with image processing, and the influences of laser power and welding speed on these characteristics are analyzed. The relationships between the behavior of vapor plume and melt pool are discussed, and three ejection regimes of the vapor plume are proposed. In order to predict the occurrence of humping, which is a typical defect in high-speed laser welding, samples are built by applying a time sliding window and then a classification model is built with the random forest. In addition, the importance of features in the classification is analyzed. The test results show that the proposed method can predict the humping defect in high-speed laser welding accurately.

Dissimilar Laser Welding of Austenitic Stainless Steel and Abrasion-Resistant Steel: Microstructural Evolution and Mechanical Properties Enhanced by Post-Weld Heat Treatment.

In this study, ultra-high-strength steels, namely, cold-hardened austenitic stainless steel AISI 301 and martensitic abrasion-resistant steel AR600, as base metals (BMs) were butt-welded using a disk laser to evaluate the microstructure, mechanical properties, and effect of post-weld heat treatment (PWHT) at 250 °C of the dissimilar joints. The welding processes were conducted at different energy inputs (EIs; 50–320 J/mm). The microstructural evolution of the fusion zones (FZ) in the welded joints was examined using electron backscattering diffraction (EBSD) and laser scanning confocal microscopy. The hardness profiles across the weldments and tensile properties of the as-welded joints and the corresponding PWHT joints were measured using a microhardness tester and universal material testing equipment. The EBSD results showed that the microstructures of the welded joints were relatively similar since the microstructure of the FZ was composed of a lath martensite matrix with a small fraction of austenite. The welded structure exhibited significantly higher microhardness at the lower EIs of 50 and 100 J/mm (640 HV). However, tempered martensite was promoted at the high EI of 320 J/mm, significantly reducing the hardness of the FZ to 520 HV. The mechanical tensile properties were considerably affected by the EI of the as-welded joints. Moreover, the PWHT enhanced the tensile properties by increasing the deformation capacity due to promoting the tempered martensite in the FZ.

Prediction of temperature field and residual stress of oscillation laser welding of 316LN stainless steel

The finite element (FE) analysis in this study is used to predict the effect of oscillation parameters on the temperature field and residual stress and as-welded distortion of 316 LN stainless steel weld joint. The simulated results indicate the simulation temperature field is good in agreement with the geometry morphology of actual weld metal (WM), and with the increase of oscillation frequency, the simulation temperature of WM gradually decreases. However, the temperature first decreases and then increases with the increase of amplitude. The residual stress concentrates on the WM and the surrounding heat-affected zone (HAZ). With the increase of oscillation frequency and amplitude of laser beam, the compressive stress converts to tensile stress, and the residual stress and the as-welded distortion gradually present a decreasing trend. The oscillation laser welding can alleviate the stress concentration phenomenon.

Influence of scan line spacing on nanosecond pulse laser welding of 6063 Al to steel thin sheets

Nanosecond pulsed laser welding of 316L stainless steel and 6063 aluminum alloy thin sheets was performed. The influence of scan line spacing on the joining process was clarified. Large explosive hole and hot cracking defects including radial cracks and arc-shaped cracks occurred in the joint caused by excessive heat accumulation when the line spacing was 0.02 mm. The joints without oxidation were obtained. The thermal-induced penetration increment (TIPI) decreased with the increase of line spacing and reached the maximum value of about 162.24% with the line spacing of 0.02 mm. Fe2Al5 and FeAl phases probably were produced at all the line spacings. However, FeAl and α-Fe phases in the form of banding structures were possibly generated only with the line spacing of no less than 0.06 mm. The shear force test results indicated that the maximum shear load of 158.8 N was achieved at the line spacing of 0.06 mm due to the large bonding area and fewer defects. Three fracture paths, namely, button pullout failure (BPF), interfacial failure (IF) and mixed fracture (MF) mode of BPF and IF were produced. The heat affected zone was the origin of BPF mode. Local deformation, pores and Fe-Al brittle phases led to the fracture paths of IF and MF.

Analysis of Ni interlayer effects on laser beam welding of dissimilar pure Mo alloy to stainless steel

The effect of Ni interlayer thickness on chemical composition, microstructure and mechanical properties of laser welding of Mo and stainless steel was analyzed systematically. Experimental results indicated that with the increase in thickness of Ni interlayer, the number of MoFe IMCs, the hardness at the Mo-FZ interface, the width and grain size in the heat affected zone of Mo side and the thickness of MoFe IMCs layer decreased significantly. The maximum tensile strength attained 351 MPa for joints with 0.1 mm thick Ni interlayer. With excessive (>0.1 mm) Ni addition in the welded joint, the mechanical properties deteriorated due to the formation incomplete fusion, void and crack defects. The tensile investigation showed that the weakest area of the joint was MoFe IMCs layer. When an appropriate thickness of Ni interlayer is used, the MoFe IMCs layer can be strengthened by increasing diffusion ability of Mo to FZ and Ni concentration in the MoFe IMCs and restraining of MoFe IMCs, consequently producing high-quality welded joints.

Design criteria for pin-ended hot-rolled and laser-welded stainless steel equal-leg angle columns

This paper explores an attempt to investigate the structural behaviour and design of equal-leg stainless steel angle columns fabricated by the laser-welding of individual hot-rolled plates and by hot-rolling process. The studies cover columns with pin-ended boundary conditions exposed to pure axial compression. An advanced and realistic finite element model able to replicate the buckling features of stainless steel angle columns is developed and validated against available experiments collected in the literature. Employing the validated finite element model, quantitative numerical parametric studies, considering minor-axis flexural buckling, as well as flexural–torsional buckling, are performed. Based on comprehensive benchmark data, the accuracy, safety and applicability of the existing column design procedures provided in the European and North American structural stainless steel codes are assessed. The evaluation results reveal that the North American codified design procedures lead to conservative and scattered resistance predictions, thereby demonstrating a need for their improvement. As a result of conducted studies, the new criteria for design of pin-ended hot-rolled and laser-welded stainless steel equal-leg angle columns are proposed. Their suitability for inclusion in the European structural stainless steel design code is confirmed by statistical reliability analyses in accordance with EN 1990.

The microstructures and mechanical properties of dissimilar laser welding of copper and 316L stainless steel with Ni interlayer

To improve the quality of welded joints between copper and 316L stainless steel, laser welding with Ni interlayer was carried out. A sound welded joint was obtained and the microstructures as well as mechanical properties were investigated. Results indicate that no welding defects or spherical particles were formed in the fusion zone. The microstructures in the fusion zone were characterized as dendritic grains, and no macroscopic segregation was observed. The welded joint failed at copper base material with an average tensile strength of 408 MPa at 77 K, and ductile fracture mode with dimples on the fracture surface were presented. Moreover, the addition of Ni interlayer prevents formation of welding defects and spherical particles and improves mechanical properties of the joint.

Dynamic behavior of molten pool flow field for active laser welded-thick stainless steel plates

By combining numerical simulation and experimental investigation, this paper intensively investigated the influence rules of adding three active agents (SiO2, TiO2 and NaF) on the dynamic behaviors of flow field in the laser welding 304 stainless steel thick plate pool. First of all, the mathematical model of the activating laser welding stainless steel thick plate was constructed to numerically investigate the impact of active agents on the fluid flow in the pool. Secondly, based on the tungsten particle tracing principle test, the high speed camera system was adopted for real-time monitoring to investigate the mechanism of action of the active agents on the flow field in the pool. The results suggested that, the active agents partially affected the mode of fluid flow. The velocity vector from both sides of the pool to the center occurred on the pool surface, while vortex from the pool margin to the center occurred on the pool cross section. The phenomenon that the tracing tungsten particles moving from the pool margin to the center, it shows that the flow direction of the fluid changed after coating with the active agent, the fluid flew from the pool margin to the center. At the same time, the coating of active agents changed the flow velocity of fluid inside the pool, and SiO2 active agent has the most significant increase effect, the maximum velocity of fluid flow on the upper surface, the longitudinal and cross sections at the same position of the SiO2 active agent coated specimen increased by 25.8%, 8% and 33.8%, respectively, compared with that without the active agents.

Experimental investigation of the effect of laser parameters on the weld bead shape and temperature distribution during dissimilar laser welding of stainless steel 308 and carbon steel St 37

Fiber laser fusion welding of two applicable alloys including 308 stainless steel and low carbon steel (St 37) was performed to assess the formation mechanism of the weld bead and temperature field near the fusion zone. In this research, some parameters including welding speed, laser power, nozzle distance, and beam deviation of the laser beam were determined as the main parameters. The results showed that the effect of the nozzle distance on the temperature field was higher than that of the welding speed and laser power. It was also observed that increasing the nozzle distance caused more absorption of the beam in the parts and there was an almost two-fold increase in the dimensions and volume of the weld bead. The measured temperature near melt pool was decreased about 120 °C for st37 while a reduction about 30 °C for stainless steel according to increasing nozzle distance from 3 to 7 mm. Unlike carbon steel, the temperature of the stainless steel was clearly decreased at the nozzle distance to the highest point. By increasing the welding speed, the temperature around the molten area was decreased. The beam deflection parameter showed the effect of the temperature gradient index on changes and a temperature decrease was observed by creating a distance from the location of thermocouples. Increasing laser power from 300 to 400 W created wider weld bead about 40% and higher temperature about 40 °C for stainless steel in comparison to st37.

Experimental study of laser-welded stainless steel angle columns

Substantial research has been conducted in the last years into the structural responses of cold-formed and hot-rolled stainless steel equal-leg angle columns, whereas there is no experimental data on laser-welded stainless steel angle columns despite these sections being increasingly used in the modern construction industry. To fill this gap and provide benchmarks for design, a comprehensive experimental investigation into the structural strength and stability of laser-welded austenitic stainless steel equal-leg angle columns under pure axial compression was performed and described in this paper. A series of laboratory tests, performing on two test groups of specimens with nominal dimensions of 60 ×60× 6 mm and 100 ×100× 10 mm and different lengths, involved 6 stub column tests and 20 global buckling tests together with measurements on material properties, initial geometric imperfections and residual stresses. The experimental observations reveal that the column ultimate capacity and prevalent failure mode – major-axis flexural–torsional buckling and minor-axis flexural buckling – are highly dependent on the column slenderness and initial imperfections. The full load-lateral displacement, load-torsional rotation and load-axial strain responses of the specimens were fully reported and discussed. The results were employed to evaluate the accuracy of the current European and North American stainless steel design standards. The evaluation results revealed that the codified design procedures yield conservative resistance predictions of laser-welded stainless steel equal-leg angle columns, showing a prospective for their modification and improvement by providing more optimized and realistic results in design considering the actual residual stress distributions, material nonlinearity and strain hardening.

Pulsed laser welding and microstructure characterization of dissimilar brass alloy and stainless steel 308 joints

The laser welding of stainless steel and brass is difficult due to their different physical properties, including thermal conductivity and melting point. In this study, the laser welding of stainless steel 308 and brass was experimentally investigated. To systematically investigate the effects of different thermophysical properties, including the heat transfer rate, thermal conductivity, and laser beam interaction in relation to the beam absorption coefficient, the temperature of the melt pool zone was measured while changing welding conditions. Different temperature gradients were obtained by changing different parameters including the laser peak power, nozzle distance, and laser beam deviation. The results showed that an asymmetric melt pool formed, to which the melting of brass made a higher contribution. Due to the lower melting temperature and the higher thermal conductivity of brass, the measured temperature and the melt size of brass were higher. The microstructure of the melt pool consisted of intermetallic compounds. Variation of melt pool size (width and depth) and temperature could be affected by laser peak power and reductions in the nozzle distance than the other parameters. For instance, 1 mm increase in the nozzle distance reduced the melt pool zone temperature by approximately 20 °C for stainless steel. Furthermore, an increase in the laser peak power raised the maximum measured temperature to about 225 and 160 °C for brass and stainless steel sides, respectively. At the same time, the amount of temperature reduction at a period of 20 s for stainless steel is almost half that of brass.

On the interaction of microstructural morphology with residual stress in fiber laser welding of austenitic stainless steel

The development of compressive residual stress is governed by the metallurgical transformation and associated microstructure, which in turn influences the mechanical properties of a welded structure. In the present work, the microstructural interaction with the thermo-mechanical performance of Yb-Fiber laser-welded austenitic stainless steel (SS304) is evaluated at different heat inputs and varying defocus distances. The interrelation between microstructural morphology and the typical pattern of residual stress is systematically investigated. The development of the thermal-metallurgical-mechanical model particularly considers the effect of solid-state phase transformation (SSPT) such that the model predicts the phase fraction and its influence on residual stress distribution. The present study exclusively focuses on the mechanism of residual stress generation as a consequence of dual-phase microstructural evolution during solidification. Low heat input (45J/mm) leads to a high cooling rate, excellent tensile strength, and low tensile residual stress. The finite element-based thermo-mechanical model predicts the residual stress with a maximum deviation of ±50 MPa compared to the experimental value. The Ferritic-austenitic (FA) mode of solidification results in the combination of skeletal and lathy δ-ferrite morphology. Increasing peak intensity of δ {110} with a cooling rate confirms the enhancement of δ-phase within the austenite matrix and restricts the complete transformation to the austenitic phase. A relatively high amount of δ-ferrite due to enriched Cr and lean Ni content at the dendritic core with fine or acicular morphology at a high cooling rate reduces the longitudinal and transverse residual stress significantly. Besides, the increasing trend of primary dendritic arm-size of δ-ferrite yields a gradual increase in residual stress.

Investigation of dissimilar laser welding of stainless steel 304 and copper using the artificial neural network model

In this study, to accurately predict the temperature and melting ratio at low time and cost, the process of dissimilar laser welding of stainless steel 304 and copper was simulated based on artificial neural network (ANN). Among various ANN models, the Bayesian regulation backpropagation training method was utilized to model the current problem. This method was used considering the two temperatures of copper and steel and the two melting ratios of steel and copper as the four outputs, and the four parameters, pulse width, pulse frequency, welding speed, and focal length, as the inputs. According to the results, regression values had a good accuracy in all cases and the histogram diagrams indicated that the error distribution was mainly concentrated at the center; in other words, the major errors of the network were not very large. It was also observed that the error concerning the trained neural networks was acceptable in the experiment phase. Finally, this neural network could be used as a numerical model to estimate the four outputs of steel temperature, copper temperature, steel melting ratio, and copper melting ratio for all input values of pulse width, pulse frequency, welding speed, and focal length in the studied range, without any need to rerun the experiment.

Effect of welding speed, pulse frequency, and pulse width on the weld shape and temperature distribution in dissimilar laser welding of stainless steel 308 and brass alloy

Laser welding of brass and stainless steel alloys is of special importance due to its wide application in the industries related to energy production. In this study, laser welding of heterogeneous metals was performed in a laboratory. Measurements of the temperature around the molten pool showed changes in the welding conditions. By changing different parameters such as welding speed, frequency, and pulse width, different thermal gradients were obtained. The results showed that the formation of the molten pool was asymmetric, and it was mostly done by melting the brass alloy. Due to the lower melting temperature and the high heat transfer rate of the brass alloy, the measured temperature and the molten volume of this alloy were higher. The microstructure of the molten pool also included intermetallic compounds. Increasing the dimensions of the molten pool (width and depth) by raising the peak power and reducing the welding speed was more effective than other parameters. The microhardness results also indicated the higher weld strength of the brass alloy with stainless steel rather than pure copper. At the range of the investigated process parameters, the adjacent temperature near the molten pool was about 20% (30 °C) higher for the brass alloy, in comparison to stainless steel, when the pulse frequency and pulse width were changed.

Investigation of dissimilar fiber laser welding of low carbon steel and stainless steel by numerical simulation

A three-dimensional numerical simulation model is developed in this paper to analyze the symmetry of weld geometry and the homogeneity of alloy distribution in the molten pool during the dissimilar fiber laser welding of low carbon steel and stainless steel during different welding conditions. The simulated results are compared with the experimental results and good agreement has been obtained. The characteristics of weld geometry, flow field and alloy distribution are analyzed based on the numerical calculation. The obtained results indicate that the weld morphology is asymmetric and the weld width is increasing gradually with the laser power increasing. The convection formed in the molten pool is enhanced under high laser power welding condition, which results in that the alloy distribution in the molten pool is more homogeneous and the difference between the upper and lower widths of the weld is decreasing. The weld morphology and alloy distribution in the dissimilar fiber laser welding can be predicted. It is clearly seen that the proposed model is effective for optimal welding process parameters selection to obtain the desired welded joints with excellent performance, which demonstrates guiding significance for improving the quality of dissimilar laser welding.

Laser Welding of Stainless Steel 321 in Different Welding Positions

It was revealed that spatial position during laser welding of AISI 321 stainless steel influences the processes in the weld pool and the process of its crystallization. The geometry, structure, distribution of chemical elements depend on the cooling rate of the welded joint, which varies in different spatial positions during laser welding of stainless steel AISI 321. To achieve the lowest variance of results and the maximum values of mechanical characteristics of the welded joints of AISI 321 stainless steel it is recommended to produce laser welding in a vertical position.