Thick Steel Research Articles

Analysis of Steel Cutting Results Using a Semi-Automatic Oxy-LPG Gas Cutting Machine

The manufacturing industry, steel is one of the main materials in making every tool. Steel itself has different thicknesses according to its use, ranging from 1 mm-20 mm. The thicker the steel used, the more difficult the fabrication process, especially cutting the steel, will be. In general, the tool used to cut thick steel is Gas Cutting with the type of gas used being Oxygen and LPG (Liquified Petroleum Gas), or you can also use Oxygen and Acytelene gas, this is more effective when compared to cutting steel or steel using cutting grinder. However, the operator who operates the cutting gas greatly influences the neatness of the cut results. Given these problems, this research aims to analyze the results of cutting steel or steel using semiautomatic Oxy-LPG cutting gas, and then the results of this research are compared with the results of cutting steel or steel using conventional Oxy-LPG cutting gas.

Improving Welding Penetration and Mechanical Properties via Activated-Flux Smearing by Tungsten Inert Gas Arc Welding

For the welding process of thick-walled structural components in liquid rocket engines, the activated-flux TIG method can effectively address issues such as the formation of intermetallic phases in the weld seams, thereby enhancing mechanical performance. The present study investigates the activated-flux TIG welding technique on 10mm thick 1Cr21Ni5Ti duplex stainless steel plates. Various activated-flux, including -SiO2, TiO2, V2O5, NiO, MnO2, CaO, AlCl3, CaF2, B2O3 Cr2O3, and Al2O3, were examined to understand their impact on the weld-bead geometry. The aim was to determine the optimal activator ratio for the effective welding of 1Cr21Ni5Ti duplex stainless steel. The weld-shift experiment confirmed that the deep penetration observed in flux-assisted welding is attributed to Marangoni convection in the molten pool. Comprehensive evaluations and analyses were performed on the microstructure and mechanical properties of the normal welded joint and the A-TIG welded joint. Finally, the study delves into a discussion on the factors influencing changes in the weld penetration, microstructure, and mechanical properties of the weld.

Finite Element Analysis of Axial Compression Performance of Stainless Steel -Steel Tube Sandwich Concrete Columns

A finite element analysis software, ABAQUS, was used to numerically analyze nine specimens with varying inner steel tube thickness and slenderness ratio to study the axial compression performance of stainless steel - steel tube sandwich concrete columns. The influence of each parameter on the axial compression behavior was explored. The simulation results aligned closely with the experimental results, with the ultimate bearing capacity prediction error within 5%. Bulging deformation consistently occurred on the upper outer steel tube. Increasing the inner steel tube thickness improved the ultimate bearing capacity up to 20%, with the 4-6 mm wall thickness range providing the most effective capacity increase. The ultimate bearing capacity deteriorated up to 5% as the slenderness ratio increased, but the axial compression stiffness markedly decreased due to overall instability. A relationship between the stability coefficient and slenderness ratio was proposed, and the calculation results showed excellent agreement.

Assessment of fabrication completeness for curved plates in ships and offshore plants using lightweight models and point cloud data

The bow sections of ships and offshore structures incorporate curved surfaces designed to minimize propulsive resistance and enhance fuel efficiency. These surfaces are fabricated from thick steel plates. While extensive research has been undertaken to explore the manufacturing and dimensional verification of such curved plates, traditional methods remain prevalent in most shipyards. This research introduces a methodology for evaluating the dimensional quality of fabricated curved plates comprehensively. Reference design data were generated through lightweight models, and point cloud data for the curved plates were acquired using a three-dimensional scanner. A grid framework was employed to eliminate noise from the extensive point cloud and to create the measured surface. Dimensional discrepancies were determined by contrasting the measured surface with the design data, and the quality of the fabrication was appraised by allocating weighted scores based on spatial location. The efficacy of the proposed methodology was confirmed through its application to various curved plates within a shipyard setting.

Research on the mechanical properties and fracture mechanism of ultrasonic vibration enhanced friction stir welded aluminum/steel joint

Friction stir welding (FSW) and ultrasonic vibration enhanced friction stir welding (UVeFSW) were used to connect 3 mm thick 2024-T3 Al alloy and Q235 carbon structural steel. The weld forming quality, mechanical properties, fracture location and interface behavior of the whole and layered joints were compared and analyzed, and the different mechanisms of the ultrasonic vibration to improve the tensile strength of the joint were summarized. As the results show, the ultrasonic vibration promoted the plastic flow ability of materials and improved the welding seam forming quality. Moreover, the ultrasonic vibration made the plastic deformation of the material in the nugget zone more uniform, which improved the strength of the nugget zone. In the middle layer of the joint, the ultrasonic vibration reduced the thickness of intermetallic compound layers (IMCLs), eliminated the laminated structure that harmed the connection quality of the joint, and formed a micromechanical interlocking structure in which IMCLs was inserted into the steel, which improved the interfacial bonding strength and improved the tensile strength by 11.1%. The ultrasonic vibration optimized the macro-mechanical interlocking structure in the joints of the lower layer, which enhanced its mechanical bonding ability with Al alloy.

Evolutions of temperature field and stress field in narrow gap oscillating laser welding process based on equivalent heat source

With the increased demand for high-performance thick high-strength steel structures in high-end offshore equipment, narrow gap oscillating laser welding with the advantage of high power density and satisfied penetration depth has attracted considerable attention. A thermal-elastic-plastic finite element model was established to calculate the narrow gap oscillating laser welding process of 30-mm-thick high-strength steel, which requires a large amount of computational time cost. To increase the computational efficiency, two equivalent heat source models were founded to replace the laser oscillation. The temperature field and stress-strain field were analyzed. The accuracy of the equivalent heat source model was verified from the weld seam profile and residual stress distribution curves. Results showed that the simulated results were in good agreement with the actual results. With the number of welding passes increasing, the cross-section shape of the molten pool changed from an elongated shape to an arc shape, and the groove gap on the top surface was reduced from 4.82 mm before welding to 3.18 mm after welding. The maximum equivalent residual stress, with the value of 669 MPa, was distributed in the middle and upper parts of the weld seam as well as the root. The longitudinal residual stresses exhibited tensile stresses in the weld seam zone. Due to the upward bending of the workpiece, the transverse residual stresses showed compressive stresses on the top surface of the weld seam and maximum tensile stresses with the value of 806 MPa at the bottom of the weld seam.

High-damping fiber-reinforced elastomeric seismic isolator in different boundary conditions: An experimental insight

Seismic isolation reduces structural vulnerability and is an effective retrofitting solution. The commonly used steel-reinforced elastomeric isolators (SREIs) consist of several rubber pads interspersed with steel laminas for vertical reinforcement. However, SREIs are expensive, making them economically-unjustified for ordinary residential buildings, especially in developing countries. Fiber-reinforced elastomeric isolators (FREIs) offer a lighter alternative with thin fiber layers instead of steel laminas. FREIs can be applied to the structure in bonded (traditional), unbonded, or partially bonded configurations. Unbonded FREIs (UFREIs) are cost-effective as they are not bonded or fastened to thick connection steel plates. Furthermore, they are inherently more flexible in lateral directions and thus require relatively less rubber material to offer the same seismic isolation performance as traditional elastomeric isolators. However, UFREIs cannot resist tensile forces and may slip under certain loads, limiting their use in situations with overturning or high vertical accelerations. To address these limitations, partially bonded applications (PBFREIs) bond only a reduced area of the rubber device to the connection steel plates. PBFREIs retain beneficial characteristics of both unbonded and bonded applications, such as improved lateral flexibility, and resistance to uplift forces and slip. The possibility of UFREI applications remains promising, particularly in developing countries, due to their low cost, ease of fabrication and installation. This paper proposes a FREI made of high-damping rubber and glass fiber fabrics, and examines its performance in bonded, partially bonded, and unbonded applications. As a unique feature, the material and geometrical characteristics of the FREIs are identical. A comparative analysis, including experimental testing, highlights the strengths and weaknesses of each application typology. The paper also provides a detailed explanation of the design process, encompassing rubber compound development, fabrication, and experimental characterization of the device.

Process advantages of laser hybrid welding compared to conventional arc-based welding processes for joining thick steel structures of wind tower

The most common welding processes when joining thick-walled steels in the industry are arc-based welding processes such as GMAW or SAW. For this purpose, the sheets are joined in multi-layer technique, which can lead to productivity losses due to high welding times. The process-specific challenges in welding thick steels using multi-layer technique relate to the high heat input from the process. Therefore, alternative welding processes are being actively sought. A suitable alternative is provided by beam-based welding processes such as the laser hybrid welding processes, which are characterized by deep penetration welds and lower heat input. With implementation of the laser hybrid welding process in the heavy industry, such as the wind tower industry, economic benefits can be reached such as the increase in productivity by reducing the layer number, and the lower consumption of filler material and energy. When comparing SAW welded 25 mm thick steels in five to six layers and single-pass laser hybrid welding, the welding time can be reduced more than 80 % and the costs of filler material, flux and energy can be saved up to 90 %. However, the industrial use of the laser hybrid welding process is still limited to applications, where the material thickness does not exceed 15 mm due to some process-specific challenges such as the sagging, sensitivity to manufacturing tolerances such as gaps and misalignment, limited filler wire mixing, and deteriorated mechanical properties resulting from high cooling rates. To overcome these challenges, a contactless electromagnetic backing based on an externally applied AC magnetic field was used. Eddy currents are induced due to the oscillating magnetic field, and an upward-oriented Lorentz force is generated to counteract the droplets formed due to gravitational forces. It allows to weld up to 30 mm thick structural steels in a single-pass with a 20-kW fiber laser system. Additionally, the gap bridgeability and the misalignment of edges were increased to 2 mm when welding 20 mm thick steels. With the aid of the AC magnetic field, a vortex was formed in the weld root, which had a positive effect on the filler wire mixing. A further significant advantage of the EM backing was the possibility to expand the process parameter window to maintain desired cooling times and mechanical properties, without suffering adverse effects concerning the root quality of the weld.

Influence of shielding gas on filler wire mixing at laser hybrid welding of thick high strength steels

The laser hybrid welding process offers many advantages during welding of thick-walled steels, such as the increased penetration depth and, thus, reduced number of layers, reduced heat input and decreased distortion compared to arc-based welding processes. Especially, when welding high-strength steels (HSS), the reduced heat input plays an essential role. However, a major challenge when laser hybrid welding of thick-walled steels is the limited filler wire mixing over the entire seam thickness, which can lead to changed mechanical properties over the depth. To overcome this issue, the add of oxygen into the shielding gas and its influence on the filler wire mixing and finally to the mechanical properties were investigated within this work. Therefore, 20 mm thick S690QL steels were laser hybrid welded in a single-pass. A contactless electromagnetic backing was used to avoid sagging. The admixture of oxygen was performed by a gas mixer, where the oxygen content was varied between 0 % and 7.2 %. The experiments were also accompanied by laser beam welding tests in steel/glass configuration, where the melt pool geometry as well as the melt flow characteristics were captured by a high-speed camera. It can be concluded, that adding of approx. 4 % oxygen into the shielding gas had a positive effect on the filler wire mixing, were up to a depth of 18 mm elements of the filler wire could be observed.

Numerical modelling of high-power laser spot melting of thin stainless steel

Numerical modelling is an important scientific tool in laser materials processing to study different melting, evaporation, and solidification phenomena. It can assist in understanding why certain defects are formed, and thus may provide solution paths for how to decrease certain defects and to increase the quality of a product. Laser spot melting in heat conduction mode represents a simple case and is an excellent first step to build and test solvers prior to moving on to more complicated cases such as laser keyhole welding of thick plates. Modelling of laser spot melting requires only a limited computational domain and allows more complex physics to be added gradually. In this work, a thin 3.0 mm thick stainless steel plate was melted with high-power fiber laser and numerically simulated using a native and custom-build solver based on the VOF method within OpenFOAM. The process was captured with a high-speed imaging camera and simulation results are compared with the experimental results. It was found that temperature-dependent surface tension plays a vital role in controlling melt flow directions within melt pool.

Sound absorption analysis of carbon steel varied in density and microstructures

In many factories, noise is an important issue considering workers' health and safety; and metal blocks of the machinery is the main source of noise generated while running. Hence, the acoustical characteristics of the metal parts of machineries need to be considered in design. This study aims to determine the effect of metal density to sound absorption (α) in order to reduce noise impact, including its correlation to the metal microstructures. The αvalues of specimen were measured on 5mm thick carbon steel -varies in carbon densities and well-known in metal industries as ST 30, ST 42, and ST 60 standards. Through 5000x magnification of Scanning Electron Microscopic (SEM), the microstructures of carbon steel are identified. The results showed that in the high-frequency range (1200-1400 Hz) the highest α values occurred on ST 60 steel, while in the low-frequency range (200-400 Hz), the α values were relatively similar for all specimen with a small discrepancy on ST 42. Homogenous metal grains with less gaps are clearly shown on ST 30 microstructures, while for ST 60 the grains seem varied in size and types, dominate with carbon particles, making the steel more rigid and better for sound absorptive function.

The effect of weld bead heat input on the performance of thick 3CR12 stainless steel welds

3CR12 is a low cost special stainless steel containing 12% chromium. It is widely used in material handling, road transport, rail transport, power generation and petrochemical applications due to its favorable corrosion performance. 3CR12 is a weldable material, but it has challenges such as poor ductility, poor toughness of 3CR12 stainless steel welds, unfavorable microstructure and cross-sectional properties of the weld bead. This is due to the welding heat input and heat transfer across beads, which causes cracking due to property changes. When welding a thick stainless steel section, the hardest heat affected zone (HAZ) is created due to uneven heating and cooling in the weld metal and base material, which is susceptible to cold cracks and residual stresses, resulting in welding defects and unfavorable material properties. Welding thick 3CR12 stainless steels can be accomplished by using a variety of welding techniques. In order to restore undesirable material qualities, the majority of welds require a post-weld heat treatment (PWHT). However, critical PWHT factors such as duration, weld geometry, and unsupported loads during the hot phase of the weld do not always allow the process to be effective. This process results in prolonged downtime since the holding time in the PWHT cycle can be very long, especially with thick-walled 3CR12 steel members. There are other methods that are currently used to weld or repair thick 3CR12 steels. Among these other methods, the use of controlled temper bead welding technique which potentially could mitigate the above mentioned problems is mentioned. The approach involves using the heat input of the weld bead as a way of introducing the heat into the previous weld bead. This is achieved by varying the heat input in order to improve the mechanical performance of the previous weld bead and thus the overall weld integrity. Welding procedures for 3CR12 recommend the use of minimum heat to avoid weld defects and unfavorable material properties. This study was carried out to investigate the effect of the heat input of the weld bead on the mechanical properties of thick welds made of 3CR12 stainless steel. By utilizing inert gas (MIG) welding, two heat input levels were used in the process: low heat input averaged at 1.53 kJ/mm and high heat input averaged at 2.1kJ/mm. The heat input was varied by changing the welding parameters, for example the average welding voltage ranging from 28V to 30V, the average welding current from 120 A to 150 A and the average feed rate between 1.77mm/sec to 2.0mm/sec.

Iron ore wires as consumable electrodes for the hydrogen plasma smelting reduction in future green steel production

In this work we investigate the feasibility and optimisation pathways for using oxide-filled consumable electrodes as both ore feeding system and reducing/melting arc carrier in the hydrogen plasma smelting reduction process. Similar in nature to Söderberg-type electrodes, but free of C-containing substances, this approach has the potential advantage of eliminating the carbon emissions stemming from conventional electric arc furnace electrodes while drastically simplifying the ore feeding into the process. Using a commercial welding setup with a 1.2 mm thick oxide-cored steel wire, area investigations indicate that approximately 50% of the introduced iron ore could be reduced to metallic iron at 100 A arc current under an Ar-10% H2 atmosphere independent from deposition time. The reduction efficiency was negatively affected by increasing arc current and it was increased by using the wire as the anode. Based on the performed variation of deposition parameters, microstructural characterisation results, high speed footage and first upscaling trials, the key scientific questions and engineering pathways for technological optmisiation towards future green steel production technology are outlined and discussed.

Hysteretic behavior of prestressed high-strength bolt joint subject to combined flexure and axial forces for prefabricated prestressed spatial structures

A novel prestressed high-strength bolt (PHSB) joint applied in the prefabricated large-span ridge tube cable dome with annular struts (PLRTCDAS) was proposed. Firstly, the hysteretic behavior of the PHSB joint under combinations of bending moment and axial compression was studied by experiments. Four parameters of the PHSB joint, including the disc thickness, perforated cross plate thickness, perforated angle steel thickness, and outer sleeve height, were considered in the test. The effects of these parameters on the hysteretic curves, skeleton curves, bearing capacity, failure modes, energy dissipation behavior, and ductility were analyzed and discussed in detail. Secondly, a three-dimensional finite element (FE) model of the PHSB joint considering geometric, material, and interaction nonlinearities was established by ABAQUS. The accuracy of FE model was verified by comparing the test and numerical results. Finally, the hysteretic behavior of the PSHB joint under different combinations of axial forces and bending moments was investigated by the proposed FE model. The research indicates that the PHSB joint exhibits perfect energy dissipation capacity and higher ductility. Reducing the perforated angle steel thickness or increasing the outer sleeve height can improve the hysteretic behavior of the PHSB joint without significantly reducing its bearing capacity. The verified FE model is an effective method to simulate PHSB joint hysteretic behavior.

Probabilistic fatigue analysis on a central holed thick steel plate of C1 Wedge Connection for wind turbine tower assembling

Hole patterns are common in engineering design for connections and/or assembly purposes. Geometrical discontinuities can cause stress concentration in localized areas, making them more prone to fatigue crack initiation and influencing the fatigue life of the overall unit. In the past, much effort has been exerted on fatigue modelling of holed plates from both experimental and theoretical perspectives. However, most studied objects were aluminium or titanium thin plates for aviation purposes. In this work, the fatigue performance of a downscaled holed thick steel plate, extracted from a novel C1 Wedge Connection for wind turbine tower assembling, was tested and categorized according to commonly used industry codes. In particular, the influence of the surface size effect was experimentally observed and computationally discussed. Finally, a probabilistic fatigue model was proposed, which gives a favourable prediction on the fatigue behaviour of the surface polished holed thick steel plate with the help of the Smith–Watson–Topper (SWT) model.

Agile robotic inspection of steel structures: A bicycle‐like approach with multisensor integration

AbstractThis paper introduces an innovative and streamlined design of a robot, resembling a bicycle, created to effectively inspect a wide range of ferromagnetic structures, even those with intricate shapes. The key highlight of this robot lies in its mechanical simplicity coupled with remarkable agility. The locomotion strategy hinges on the arrangement of two magnetic wheels in a configuration akin to a bicycle, augmented by two independent steering actuators. This configuration grants the robot the exceptional ability to move in multiple directions. Moreover, the robot employs a reciprocating mechanism that allows it to alter its shape, thereby surmounting obstacles effortlessly. An inherent trait of the robot is its innate adaptability to uneven and intricate surfaces on steel structures, facilitated by a dynamic joint. To underscore its practicality, the robot's application is demonstrated through the utilization of an ultrasonic sensor for gauging steel thickness, coupled with a pragmatic deployment mechanism. By integrating a defect detection model based on deep learning, the robot showcases its proficiency in automatically identifying and pinpointing areas of rust on steel surfaces. The paper undertakes a thorough analysis, encompassing robot kinematics, adhesive force, potential sliding and turn‐over scenarios, and motor power requirements. These analyses collectively validate the stability and robustness of the proposed design. Notably, the theoretical calculations established in this study serve as a valuable blueprint for developing future robots tailored for climbing steel structures. To enhance its inspection capabilities, the robot is equipped with a camera that employs deep learning algorithms to detect rust visually. The paper substantiates its claims with empirical evidence, sharing results from extensive experiments and real‐world deployments on diverse steel bridges, situated in both Nevada and Georgia. These tests comprehensively affirm the robot's proficiency in adhering to surfaces, navigating challenging terrains, and executing thorough inspections. A comprehensive visual representation of the robot's trials and field deployments is presented in videos accessible at the following links: https://youtu.be/Qdh1oz_oxiQ and https://youtu.be/vFFq79O49dM.

Mechanical properties and constitutive models of butt-welds in Q345GJ thick steel plates

GJ steel is a high-performance steel manufactured in China, and its thick plates are widely used in building structures. The first companion study examined the material properties of the thick GJ steel plates (t ≥ 60 mm). This study focuses on the mechanical properties of butt welds in thick GJ steel plates (t ≥ 60 mm). Monotonic and cyclic tests were conducted on butt-weld specimens made of 60-mm and 100-mm thick Q345GJ steel plates in the longitudinal and transverse directions. In addition, the layered specimens obtained from five different thickness locations were tested. Based on the cyclic test results, the Chaboche constitutive parameters were calibrated and verified via the finite element analysis (FEA). Moreover, the differences in the static and cyclic mechanical properties of the base metal and butt welds were analysed. Compared with the base metal, the static tensile strength and hysteretic energy dissipation under the same cyclic loading protocol were better in the weld specimens; however, their ductility was significantly lower. Furthermore, the distribution of the mechanical properties along the thickness direction was more uniform in the weld specimens. Moreover, the weld specimens had higher yield surface reduction ratios. However, their initial and final yield surface sizes were larger than those of the base metals.

Validation of a New Analytical Formula to Predict the Steel Temperature of Heavily Insulated Cross-Sections

Fire protection is a popular solution to slow down the temperature increase in steel elements subjected to fire, and simple equations, such as the mass lumped formula proposed in EN1993-1-2, may be employed to estimate the steel temperature in the cross-section. The EN1993-1-2 formula assumes that the temperature of the exposed insulation surface and the surrounding gas are equal. This simplification may provide inaccurate results for heavily insulated steel sections. Therefore, a new mass lumped formula was derived, accounting for more accurate boundary conditions considering the heat flux impinging the insulation. On these premises, this work evaluates how the new simple formula fares with respect to the EN1993-1-2 formula. In this respect, a comprehensive comparison with the results of 1-D and 2-D analyses considering several insulation materials and thicknesses of insulation and steel is thoroughly presented. The proposal results in being always safe and better estimates steel temperatures relevant in the structural fire engineering context. Its use is particularly recommended for heavily insulated sections, where the ratio between the insulation and the steel heat capacities is higher than 14, and the EN1993-1-2 formula gives unsafe predictions.

Response Surface Methodology (RSM) Approach for Optimizing the Processing Parameters of 316L SS in Directed Energy Deposition

Directed energy deposition (DED) is a crucial branch of additive manufacturing (AM), performing repairs, cladding, and processing of multi-material components. 316L austenitic stainless steel is widely used in applications such as the food, aerospace, automotive, marine, energy, biomedical, and nuclear reactor industries. Nevertheless, there is need for process parameter optimization and a comprehensive understanding of the individual and complex synergistic effects of process parameters on the geometry, microstructure, and properties of the deposited material or component. This is essential for ensuring repeatable manufacturing of parts across a single or series of platforms over time, or for minimizing defects such as porosity. In this study, the response surface methodology (RSM) and central composite design (CCD) were employed to investigate the effects of laser power, laser scan speed, and powder mass flow rate on layer thickness, density, microstructure, and microhardness of 316L steel processed by Laser Engineered Net Shaping (LENS®) DED. Polynomial empirical prediction models correlating the applied processing parameters and the studied responses were developed.

Measurement of neutron spectra for various thicknesses of concrete and steel shielding at 24-GeV/c proton beam facility using Bonner sphere spectrometer

ABSTRACT Neutron energy spectra down to thermal energy were measured using a Bonner sphere spectrometer (BSS) for various thicknesses of concrete and steel shielding at the CERN/CHARM facility, where high-energy neutrons were produced by 24-GeV/c protons incident on a thick copper target. The thicknesses of the concrete and steel shielding blocks ranged from 40 cm to 200 cm and from 20 cm to 80 cm, respectively. The BSS consisted of a spherical 3He proportional counter and five polyethylene moderators with diameters of 7.62 cm, 10.2 cm, 12.7 cm, 17.8 cm, and 24.1 cm, respectively. In addition, polyethylene moderators combined with a lead or copper inner shell were used to increase the sensitivity to high-energy neutrons. The neutron energy spectra were deduced using an unfolding method. The initial guesses were obtained using the PHITS code for each experimental geometry. The response function for the BSS was determined using the MCNP6.2 code with JENDL-4.0/HE. The neutron energy spectra over the entire energy region from 10−4 eV to 10 GeV were successfully obtained for the different shielding conditions. The validity of the response function and the contribution of each moderator are discussed referring to previous studies and tests at the standard neutron fields of AIST.