Steel Joints Research Articles

Low‐Cycle Fatigue Performance of Directed Energy Deposited and Conventionally Manufactured Hybrid Gas Tungsten Arc‐Welded Duplex Stainless Steel Joints

Arc‐directed energy deposition (DED‐Arc) is a technology for the production of complex and large‐scaled components. It benefits from high deposition rates and low investment costs. However, to further expand the applications of additively manufactured parts, the possibility for implementation in conventionally manufactured assemblies is crucial. Therefore, this study focusses on the structural integrity of welded joints of DED‐Arc and as‐rolled duplex stainless steels and the welded and nonwelded as‐rolled benchmark. While the fraction of the constituents is almost balanced in the as‐rolled condition, the amount of austenite in the DED‐Arc specimens exceeds 60%. The similar weldment is predominantly ferritic and the hybrid welded joint contains ≈30% austenite, which is discussed based on the nickel concentration. Results from microstructure characterization are correlated to the superior yield and ultimate tensile strength of the as‐rolled condition. Under total strain‐controlled fatigue experiments, the hybrid welded joints exhibit enhanced fatigue lives at various strain amplitudes while the base material shows lowest fatigue resistance. Computed tomography and fractography conclude that the structural integrity is not governed by inherent defects, but instead the phase ratio and distribution yield significant differences in the cyclic deformation response as well as an asymmetry of the hysteretic stress–strain behavior.

High-temperature creep rupture behavior of dissimilar welded joints of RAFM steel and 316L steel by friction stir welding

High-temperature creep rupture behavior of dissimilar welded joints of RAFM steel and 316L steel by friction stir welding

Comparative study of marine steel and welding joint in artificial seawater based on stress corrosion cracking and crack growth

In this work, the environmental fracture behavior of marine steel and its welding joint were compared in artificial seawater. The electrochemical measurement, slow strain rate tensile test, and low-frequency cyclic loading test were conducted. The results showed that the corrosion current density and stress corrosion cracking susceptibility of welding joints were higher than those of base metal, caused by high dislocation density and residual stress in the heat-affected zone. The acidification and ion concentration occurred at the crack tip of the welding joint and basic metal. pH value and Cl− concentration at the crack tip reached 4.1 and 3.8 mol/L, respectively. The crack growth rate of the welding joint was higher than that of base metal. The crack growth behavior was controlled by the mechano-electrochemical effect at the crack tip, and hydrogen embrittlement was the main factor.

Experimental evaluation of multiple-component residual stress distribution in a dissimilar metal repair joint of ferritic/martensitic steel using the asymmetric-cut and the symmetric-cut contour method

A thick multi-pass butt-welded ferritic/martensitic steel (P91) joint is prepared and the local region of the weld is repaired with an ENiCrFe-3 nickel-based alloy using the manual metal arc welding method. The repair weld including part of the base metal is then subjected to ultrasonic impact treatment (UIT). A three-cut contour method, including two asymmetric cuts and one symmetric cut, is developed in the present study to obtain the two-dimensional residual stress distributions at different locations, and the stress release after multiple cuts is considered to get the original stress distribution before cuts. The measurement procedure is introduced in detail. The longitudinal stresses in the repair weld and the initial weld of the P91 steel joint, as well as the transverse stress at the weld center, are finally obtained. The effects of the dissimilar metal repair weld at the local region on the longitudinal and transverse welding residual stresses are investigated. In addition, the applicability of UIT to mitigate the surface stress in nickel-based alloy repair weld is analyzed. The results show that the transverse and longitudinal stresses in the nickel-based alloy repair weld are both tensile stresses, the maximum longitudinal stress is close to the yield strength of the B91 weld metal and occurs in the heat-affected zone of the repair weld located in the initial weld. Repair welding causes the internal transverse compressive stress region to be narrower than in the original weld. UIT can be used to introduce compressive stress to the surface layer of the nickel-based alloy repair weld.

Analytical models for predicting the moment‒rotation relationships of steel hub joints with bolted steel side plates in single-layer wood reticulated domes

A very popular and efficient pattern of joints adopted for wood reticulated domes is steel hub joints featuring end-bearing and bolt-connected wood members (EBBC joints). This type of joint shows clear semi-rigidity, which affects the rigidity and overall stability of the structures. This study developed analytical models for predicting the moment‒rotation curves of EBBC joints, considering the effect of axial compression. Specifically, two models termed the WR and WEP models, were developed assuming rigid and elastic-plastic constitutive behaviour, respectively, of the wood in the compression zone of the joint. A tri-linear model for the lateral force-slip relationship of bolt connections was derived. A formula for calculating the deformation modulus and predicting the shear failure of wood members under local compression was proposed and verified. The moment–rotation relationship of the joint was established with equilibrium and compatibility conditions. The accuracy of the analytical models was verified by comparison with a series of experimental results as well as the parametric study results obtained using a refined finite element model. It was revealed that both the WR and the WEP models can predict the moment–rotation relationships accurately for joints without axial compression, whereas for the case of non-negligible axial compression loads, the WEP model offers more accurate predictions. The analytical WEP model proposed in the current paper provides a versatile tool for general design practice to predict moment–rotation curves for traditional or novel EBBC joints.

Resistance of the welded joint of X70 steel for main gas pipelines against corrosion-mechanical cracking under cathodic polarization in near-neutral pH solutions

ABSTRACT Resistance of welded joint of X70 steel welded using Sv-08G1NMA and OK 10-74 flux wire against stress-corrosion cracking in near-neutral pH solution NS4 was investigated by slow-strain rate method, voltammetry, optical and scanning electron microscopy, electrolytic permeation of hydrogen. It was established that the stress-corrosion cracking of welded joint occurs through the base metal in the range of potentials more positive than −0.921 V by the anodic dissolution mechanism, more negative than −1.050 V is consistent with a hydrogen embrittlement mechanism, and in the potentials' range from −0.921 V to −1.050 V – both by the anodic dissolution and hydrogen embrittlement mechanism. The susceptibility to stress-corrosion cracking coefficient KS increases with the polarization potential shift −0.750 V → −0.950 V → −1.050 V as follows: for the welded joint – 1.1 → 1.16 → 1.35, for X70 steel as 1.0 → 1.12 → 1.0.

Achieving excellent properties of laser tailor-welded thin Al-Si coated press-hardened steel joint via controlling dilution rate

In laser tailor welded traditional 25 μm thick Al-Si coated press-hardened steel (PHS), a lot of ferrite was easily formed in the weld, so filling with expensive high-alloys wire is usually necessary. In this work, a new thin Al-Si coated PHS with 18 μm thickness was laser tailor welded, and a cheap low alloy wire was attempted to fill into the weld to via control the dilution rate. At a high dilution rate of 94%, the weld contained a ferrite fraction of 38%, resulting in the fracture occurring in the weld during tension and bending. At a medium dilution rate of 85%, the ferrite fraction in the weld decreased to 18%, obtaining excellent tensile and bending properties. The tensile strength and elongation of the joint reached 1528 MPa and 5.6%, respectively, with fracture being in the base metal (BM). The maximum bending load and displacement were 1291 N and 7.0 mm, respectively, and cracks initiated and propagated in the BM. This is attributed to the small amount of ferrite and stress concentration in the narrow weld. At a low dilution rate of 76%, the ferrite reduced to 6%, and the bending cracks initiated and propagated in the BM. However, the tensile specimen fractured in the weld, which should be related to the relatively low C concentration and the stress concentration at the weld toe due to the weld reinforcements.

Comparative analysis of filler metals on microstructure and mechanical performance of TIG-welded AISI 201 austenitic stainless steel joints

In this study, 4-mm thick AISI 201 austenitic stainless steel butt joints were fabricated using the tungsten inert gas (TIG) process with ER309L, ER316L and ER2209 filler rods. TIG welding was performed using a current of 100 A, voltage of 14 V, with pure argon as the shielding gas at a flow rate of 10 L/min, and filler rod diameters of 2.4 mm. The microstructural and mechanical properties were analysed. ER2209 and ER316L promote an austenitic structure in the fusion zone. ER316L filler produced the finest grain structure (9.39 μm) and the lowest δ-ferrite content (25.85%) in the weld zone. Welds made of ER316L exhibited the highest hardness (314 HV), ultimate tensile strength (857 MPa) and yield strength (448 MPa). ER316L welds also demonstrated superior strain-hardening capacity (0.91) and impact toughness (19.8 GPa). Fracture analysis revealed finer dimples in the ER316L welds, indicating improved ductility and strength compared to other welded joints.

Review and Analysis of Modern Laser Beam Welding Processes.

Laser beam welding is the most modern and promising process for the automatic or robotized welding of structures of the highest Execution Class, EXC3-4, which are made of a variety of weldable structural materials, mainly steel, titanium, and nickel alloys, but also a limited range of aluminum, magnesium, and copper alloys, reactive materials, and even thermoplastics. This paper presents a systematic review and analysis of the author's research results, research articles, industrial catalogs, technical notes, etc., regarding laser beam welding (LBW) and laser hybrid welding (LHW) processes. Examples of industrial applications of the melt-in-mode and keyhole-mode laser welding techniques for low-alloy and high-alloy steel joints are analyzed. The influence of basic LBW and LHW parameters on the quality of welded joints proves that the laser beam power, welding speed, and Gas Metal Arc (GMA) welding current firmly decide the quality of welded joints. A brief review of the artificial intelligence (AI)-supported online quality-monitoring systems for LBW and LHW processes indicates the decisive influence on the quality control of welded joints.

Effects of Cooling Media on Microstructure and Mechanical Properties in Friction Stir Welded SA516 Gr.70 Cryogenic Steel Joints.

SA516 Gr.70 steels were welded by friction stir welding (FSW) under various media of air, water, and water + CO2 cooling, and the effect of the cooling media on the microstructure and mechanical properties of joints was systematically analyzed. The nugget zone (NZ) under the air-cooling condition contained coarse bainite + martensite. Martensite was obtained by decreasing the cooling media temperature. Furthermore, tensile fracturing of the joints occurred in the basal metal (BM), and the ultimate tensile strength of the joints under various cooling media was similar to that of the BM. However, with decreasing cooling media temperature, the total elongation of the joints noticeably increased. Good strength (545 MPa) and elongation (16.8%) were obtained in the joints under the water + CO2 cooling condition since the fine martensite microstructure enhanced the plastic deformation capacity of the joints. In addition, in the NZ under water + CO2 cooling condition, good toughness of 110 J/cm2 was obtained due to a high fraction of high-angle boundaries and fine martensite.

Effect of Surface Treatment on Tensile Strength of Steel Single Lap Joints Bonded with Double-Sided Acrylic Foam Tapes for Naval Applications

This study investigated single lap joints in steel used for naval carpentry. The surface was mechanically treated, and then a double-sided acrylic foam tape was applied with varying surface preparation conditions. Specifically, three different conditions were examined. Tensile tests revealed that changing the type of surface preparation significantly affects the mechanical strength of the joints. The best mechanical properties were achieved when a primer was used. Our results demonstrate that this method can be effectively employed in naval applications as an alternative to welding for non-structural applications, such as the installation of brackets for mounting electrical devices (e.g., sockets).

Effect of Zr on microstructure and mechanical properties of 304 stainless steel joints brazed by Ag–Cu–Sn–In filler metal

Effect of Zr on microstructure and mechanical properties of 304 stainless steel joints brazed by Ag–Cu–Sn–In filler metal

Mechanical and Metallurgical behavior of Manual Metal Arc Welded P91 Ferritic Martensitic Steel Joints

In the nuclear power plant industry, Cr-Mo ferritic steels are indispensable due to their high-temperature tensile strength, creep strength, and resistance to stress corrosion cracking. This study evaluated and analyzed the mechanical properties and metallurgical behavior of indigenously developed filler (over matched with base metal) manual metal arc welded Cr-Mo ferritic steel (hereafter referred as P91 steel). The analysis revealed that the ultimate tensile properties of the weld joint exceed those of the unwelded metal, being 6% higher than the base metal. Consequently, the joint efficiency for the weld joint is 106%. However, the impact toughness of the weld pad is significantly lower compared to the unwelded metal, nearly 2.5 times less than the base metal. The weld metal region’s microstructure is characterized by untempered lath martensite pinned with dense dislocations, which is attributed to rapid cooling from the liquidus range. Furthermore, a distinct Heat-Affected Zone (HAZ) was identified adjacent to the weld metal region, which results from the elevated temperature experienced in this area.

Effect of wire deposition rate on macro and microscopic characteristics of laser weld-brazed AA5083 aluminum alloy to galvanized steel joints and their corrosion response

ABSTRACT In this study, dissimilar metals, such as aluminium (AA5083) and galvanised interstitial free steel, were laser-brazed in a flange configuration using eutectic filler aluminium wire (4047, Al-12%Si). To investigate the effects of wire deposition rate on the characteristics of laser-brazed joints and to understand the factors contributing to corrosion in these joints. The wire deposition rates were varied while keeping other laser parameters constant. Changes in wire deposition rate were observed to affect the flow behaviour of molten metal leading to variations in the geometrical characteristics of the brazed joints and interfacial reactions as revealed by macroscopic examination. A series of corrosion tests, including electrochemical, immersion, and salt spray tests, were conducted on the laser-brazed joints. It was demonstrated by Immersion corrosion tests that the wire rate influenced the corrosion results for the laser-brazed joints. However, the salt spray test showed no substantial effect on corrosion with respect to different wire deposition rates. Furthermore, the electrochemical results indicated significant changes in the corrosion response of the brazed zone due to the presence of chemically dissimilar phases. A correlative discussion between laser parameters, observed microstructure, and their effects on the corrosion performance of the brazed samples is presented.

Effect of Ni interlayer on microstructures and mechanical properties of 2205 duplex stainless steel joint by laser oscillating welding

Effect of Ni interlayer on microstructures and mechanical properties of 2205 duplex stainless steel joint by laser oscillating welding

Multi-angle analysis of Mo on martensite–austenite component and toughness in SCGHAZ of X80 pipeline automatic ring welding

In order to solve the embrittlement problem of welded joint of pipeline steel, this paper proposes to study the influence of Mo on M-A component of the subcritically reheated coarse-grained HAZ (SCGHAZ), and Mo on bainite transformation. Through the welding thermal simulation experiment, two kinds of X80 pipeline steel with different Mo content were set different secondary thermal cycle peak temperatures to simulate the heat affected zone (HAZ). Samples in the SCGHAZ were selected to observe the microstructure, M-A component, microalloy-element distribution and fracture crack trend, and comprehensively analyze the reasons for the deterioration of impact toughness caused by the changes of Mo content. The results show that the increase of Mo content leads to the formation of twinning martensite, which is one of the reasons for the deterioration of toughness. Mo is enriched at the interface of ferrite and M-A component, reducing the binding energy at the interface, resulting in the desorption of M-A component from the matrix, the formation of pores and becoming the nucleation site of cracks, resulting in the generation of micro-cracks and the decrease of toughness.

The High-Cycle Tensile-Shear Fatigue Properties and Failure Mechanism of Resistance Spot-Welded Advanced High-Strength Steel with a Zn Coating.

Advanced high-strength steels (AHSSs) with Zn coatings are commonly joined by the resistance spot welding (RSW) technique. However, Zn coatings could possibly cause the formation of liquid metal embrittlement (LME) cracks during the RSW process. The role of a Zn coating in the tensile-shear fatigue properties of a welding joint has not been systematically explored. In this study, the fatigue properties of tensile-shear RSW joints for bare and Zn-coated advanced high-strength steel (AHSS) specimens were comparatively studied. In particular, more severe LME cracks were triggered by employing a tilted welding electrode because much more stress was caused in the joint. LME cracks had clearly occurred in the Zn-coated steel RSW joints, as observed via optical microscopy. On the contrary, no LME cracks could be found in the RSW joints prepared with the bare steel sheets. The fatigue test results showed that the tensile-shear fatigue properties remained nearly unchanged, regardless of whether bare or Zn-coated steel was used for the RSW joints. Furthermore, Zn mapping adjacent to the crack initiation source was obtained by an electron probe micro-analyzer (EPMA), and it showed no segregation of the Zn element. Thus, the failure of the RSW joints with the Zn coating had not initiated from the LME cracks. It was concluded that the fatigue cracks were initiated by the stress concentration in the notch position between the two bonded steel sheets.

Finite Element Modeling of Beam-to-Column Steel Timber Composite Joints with Different Parameters

This study presents a comprehensive three-dimensional finite element modeling and parametric analysis of composite beam-to-column joints in steel–timber composite structures. The investigation encompassed a variety of shear connector configurations, end plate designs, and bolt dimensions, aiming to elucidate their respective influences on the structural performance and behavior of these joints. Through meticulous numerical simulation, this research sought to enhance the understanding of the interactions and load transfer mechanisms within composite connections, thereby contributing to the optimization of design practices in the field of structural engineering. The load–displacement relationship for timber–steel composite joints subjected to monotonic loading was investigated using ABAQUS 6.14 software. This study systematically analyzed the effects of various parameters, including different configurations of shear connectors, end plate thicknesses, and bolt dimensions, on the overall performance of the joints. Through this comprehensive numerical analysis, the research aimed to provide deeper insights into the mechanical behavior and structural integrity of these composite connections under the applied loading conditions. A non-linear finite element model of timber was developed and verified with the results of the experiment in this study. The findings are discussed in detail, highlighting the intricate relationships between the selected parameters and their respective effects on the performance and overall stability of the composite connections. This thorough evaluation aimed to enhance the understanding of how these variables interact within the context of composite joint design and behavior. Finally, design recommendations for composite structures, such as the dimensions of the bolt, end plate thickness, and different sizes of shear connectors are provided.

Moment Capacity of Bolted-Side Plate for the Eaves Joint of Nested Tapered Box Beam Portal Frame

The joints of cold-formed steel (CFS) portal frames with box sections are primarily formed either through stiffened welded connections or by bolted end plates, which typically involve costly full penetration butt welds. In New Zealand, CFS portal frames with nested tapered box beam (NTBB) sections are popular, and the joints of these portal frames are also formed through a bolted end plate system. In literature, it was found that welds in these joints are prone to cracking in the heat-affected zone (HAZ) under bearing opening moments (tension). Therefore, this paper focuses on proposing an alternative connection system (bolted-side plate) for eaves joints without any weld, aiming to reduce the overall cost of construction and increase construction speed. The performance (strength and stiffness) of these joints is mainly dependent on the geometric details of the bolted-side plate, which is limited in Australia/New Zealand standards (AS/NZ 4600). Herein, a non-linear finite element (FE) model was developed for the NTBB portal frame and validated against the experimental test results from the literature. Firstly, the validated FE model was used to investigate the feasibility of using bolted-side plates for NTBB portal frames and found that the bolted-side plate can increase the ultimate capacity of NTBB portal frame by 9%. A parametric study was then conducted by considering different geometric details of the bolted-side plates under both closing (gravity) and opening (wind uplift) moments. Finally, unified design equations for the moment capacity of bolted-side plates were proposed based on the results of the parametric study, and their accuracy was assessed through reliability analysis.

Lateral stiffness of modular steel joint with semi-rigid bolted intra-module connection

In contrast to the beam-column joints found in traditional assembled steel structures, modular steel structures feature inter-module and intra-module connections within their joints. While existing research has largely focused on the mechanical properties of inter-module connections, the impact of intra-module connection stiffness on the performance of modular steel joints remains unclear. This study introduces a novel corner-fitting-reinforced fully bolted joint specifically designed for modular steel structures. A series of experiments were conducted, including a flexural test on bolted intra-module connection to determine its initial rotational stiffness, and four groups of lateral static tests on full-scale modular steel joints with varying intra-module connection stiffnesses. These tests aimed to characterize mechanical properties such as load-carrying capacity, lateral stiffness, strain development, and ductility. The study elucidates the influence of intra-module connection stiffness on the lateral stiffness of modular steel joints. Furthermore, a refined finite-element (FE) model of the corner-fitting-reinforced fully bolted joint was developed. Simulation results showed good agreement with experimental findings., with an average error of less than 10 % for ultimate load-carrying capacity prediction. The FE model also, analyzed the stress-strain development of the corner fitting throughout the process. The study establishes a theoretical analysis model for the corner-fitting-reinforced fully bolted joint and derives a theoretical formula for the initial lateral stiffness of the modular steel joint, considering semi-rigid intra-module connections. This formula aligns well with both experimental and FE results, with a maximum error of 15 %. Finally, the study delves into the force-transfer mechanism of the corner-fitting-reinforced fully bolted joint, providing valuable insights for its design.