Weld Reinforcement Research Articles

Low-cycle fatigue properties and fracture location transition mechanism of dissimilar steel welded joints in towers of wind turbines

This study investigates the low-cycle fatigue (LCF) behavior of two types of dissimilar steel welded joints (DSWJs): AISI 1035 & S550Q and AISI 1020 & S550Q. Digital image correlation (DIC) and finite element analysis (FEA) were used to analyze the heterogeneous strain distribution. The results reveal that the location of maximum strain, which is load-dependent and related to strength mismatch, corresponds to the fracture location of the LCF specimens. Specifically, the crack initiation site shifts from the weld toe to the base metal as strain increases. Moreover, the weld reinforcement of the DSWJs significantly affects the failure site transition, introducing strain concentration at lower stress levels while enhancing deformation resistance at higher stress levels, as evidenced by DIC strain measurements and FEA. These findings highlight the importance of joint reinforcement profile, strength mismatch and external load level in designing DSWJs for wind turbine towers against LCF failure.

Effect of slag recycling on bead geometry, dilution and microstructure in submerged arc cladding of stainless steels

The submerged arc welding (SAW) process generates a large quantity of slag, which, when disposed-of, harms the environment and wastes valuable ingredients. A technology was developed to recycle the SAW slag generated in stainless steel cladding, enabling its reuse as flux. Bead geometry and dilution play crucial roles in weld cladding. Dilution determines the minimum number of layers needed to achieve the desired chemistry, while bead width dictates the fewest passes required to cover the entire surface area. Additionally, bead geometry influences the mechanical strength of the clad layers. The microstructure and solidification mode also significantly affect clad quality. Therefore, understanding the impact of recycled slag on bead geometry, dilution, and microstructure is essential. This paper presents a systematic investigation into the effects of process variables and recycled slag on bead geometry and dilution in clad welding. It includes a comparison of microstructures obtained using fresh flux versus recycled slag. The results indicate that increasing the welding current (I) by 37.5% enhances weld penetration (p), bead width (w), reinforcement (r), and dilution (d) by 50.9%, 14.4%, 69.5%, and 5.5%, respectively. Conversely, increasing the travel speed (V) by 90%, decreases p, w, and r by 19.29%, 11.9%, and 25.3%, respectively; however, dilution (d) increases by 17.6%. On the other hand, increasing the open-circuit voltage (V) by 26.7% increases bead width (w) and dilution (d) by 10.4% and 5.4%, respectively, while reinforcement (r) decreases by 7.5%. Both single and multilayer claddings prepared with fresh flux and recycled slag exhibit similar microstructures.

Underlying mechanisms for the effect of Nb micro-alloying on the elemental distribution and precipitation behavior in the X70 weld metal

Niobium (Nb) is a widely recognized micro-alloying element due to its low cost and substantial impact on steel properties. While the effect of Nb in processed steels has been well investigated, studies on its elemental distribution and precipitation behavior in weld metal remain scarce. This study focuses on the weld metal of specially designed Nb-rich X70 pipeline steel by scanning transmission electron microscopy (STEM) and energy-dispersive X-ray spectroscopy (EDS) characterization, complemented with thermodynamic and kinetics modeling analysis. In the majority of the weld, Nb was essentially uniformly distributed. This suggests that Nb primarily exists in the solid solution form in the weld metal, which is also supported by precipitation kinetics modeling results. This is primarily due to the short thermal history associated with the welding process, which leads to insufficient time for the uniform precipitation of Nb. Two instances of Nb precipitates were observed at the weld centerline and reinforcement region. The low partition coefficient of Nb results in an elevated local concentration along the weld centerline. However, precipitation kinetics calculations suggest that this enhancement alone is not adequate to induce precipitate formation. The occurrence of MnS and the prior formation of Ti precipitates may provide heterogeneous nucleation sites for Nb, facilitating the nucleation of Nb precipitates in the weld centerline and reinforcement region.

Enhancing of low-temperature deformation compatibility of pure titanium welded tube by laser welding and cold-worked in welded zone

This study is aimed to improve the low-temperature deformation behaviour of titanium heat exchange tubes by optimizing welding method and weld treatment processes. The various welding processes and cold-worked in welded zone process are adopted, and the effects of macro-morphology, microstructure and mechanical properties on low-temperature deformation behaviour are studied. The results show that the width of the laser welded joint and welded zone is 3.8 mm and 2.9 mm respectively, which is 40% and 63% of TIG welded joint. Especially, the width of heat affected zone and the grain size of laser welded joint are obviously reduced due to its concentrated energy density. The cold-worked process in welded zone can relieve the macroscopical and microstructural discontinuity between base metal, heat affected zone and welded zone. The inner weld reinforcement is eliminated to improve smooth transition and the columnar α grains in welded zone are remarkable fragmented with plenty of twins. The hardness of the welded zone after cold-worked is significantly higher than that of the base metal, resulting in base metal being the main deformation area of the welded tube at low temperature, which is beneficial to improve the deformation performance of the whole welded tube. By adapting the cold-worked and laser welding process with smooth transition and narrower weld width, the pure titanium welded tube can meet the requirement of three times low-temperature deformations.

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 investigation, analysis, and optimisation of weld reinforcement during powder-fed gas metal arc welding of AISI 1023

ABSTRACT The main aim of the present study is to perform a comparative investigation, experimental analysis, and optimisation of weld reinforcement in the specific domain of powder-fed gas metal arc welding in relation to AISI 1023 steel. The study conducted a comprehensive analysis of several parameters, encompassing statistical methodologies (i.e. Genetic Algorithm and artificial neural networks) and response surface methodology (RSM). The study shows that the advance gas metal arc welding provides maximum of 95% more reinforcement and current and powder feed rate has emerged as the most influential parameter for bead reinforcement. Based on the results obtained, it can be concluded that the Levenberg-Marquardt (5-14-1) model demonstrates the highest level of suitability as an ANN model for the purpose of forecasting output data. As per R value positive correlation of 0.9674 between the empirical data and the forecasts produced by the LM (5-14-1) model. Genetic algorithm suggested that the optimal point is situated within the predetermined range of process variables. According to validation experimentation the ANN model exhibited superior performance compared to the RSM model and then come GA. ANN has shown the maximum error of 0.06 when compared to experimental results.

Dynamic behavior regulation of droplet transfer based on arc-bubble control by ultrasound-induced during underwater wet welding

In comparison to welding in air, the periodic formation of unstable arc bubbles is a significant factor contributing to the unstable mass transfer process during underwater wet welding (UWW). Up to now, there is no ideal method to control droplet transfer and improve arc stability. In this study, the ultrasound-induced method (UIM) was used to regulate the droplet transition behavior and improve the process stability. The behavior features and key mechanisms of arc-bubble and droplet transfer induced by ultrasound were revealed with the employment of highspeed camera and X-ray observation, respectively. The incident angle of ultrasound was taken as a variable to reveal its effects and mechanism of action on the behaviors of arc bubble and droplet transfer, weld formation quality, microstructure, and property of weld joint. The results show that ultrasound-induced a new rising mode of arc bubble, which can significantly reduce the repulsive resistance that come from the bubble rising on the droplet transfer process. Compared with underwater wet welding without ultrasound, the average diameter of molten droplets reduces from 3.2 mm to 1.7 mm, and the droplet transfer frequency increases from 7.8 Hz to 13 Hz as the incident angle of ultrasound increases to 60°. In addition, the weld seam without obvious defects could be produced by UWW with UIM, of which the Variation coefficient of weld reinforcement is reduced from 21.3 to 11.6 and 17.4 at an ultrasonic incident angle of 30° and 45°. With increasing of ultrasound incident angle, it showed that the microhardness of the weld joint has a slight increase. In the heat-affected zone, the microhardness for the joint increased from 290 HV to 320 HV while the incident angle increased to 60°. This research shows that an appropriate incident angle of ultrasound can obtain good-quality joints which has a stable metal transfer process in underwater wet welding.

Effect of strain rate on tensile characteristics and failure behavior of Al/steel welded joint producing by a laser-MIG composite heating source

Studies on dynamic tensile characteristics for Al/steel dissimilar materials are crucial to ensure the integrity and dependability of light-weight structures. In this study, the tensile characteristics and failure behaviors of Al/steel laser-MIG welded-brazed joints were studied. The dynamic fracture mechanisms of the joints are discussed. With the increase in strain rate, the fracture mode and tensile properties of Al/steel joints with reinforcement changed. The joints exhibited two failure modes of heat-affected zone failure at lower strain rates and interface failure at higher strain rates. When the strain rate was 1000 s−1, the increase in dislocation density in the weld reinforcement and diversion of cracks in the intermetallic compound layer significantly enhanced the joint’s properties. The tensile and yield strengths reached 222.6 and 166.6 MPa, 6.5 % and 17.9 % higher than those at a stain rate of 1 s−1, respectively. For Al/steel joints without reinforcement, as the strain rate increased, the crack gradually grew to the Al8Fe2Si phase, leading to a notable enhancement in the joint’s performance. At a strain rate of 500 s−1, the maximum strength of the joint reached 238.3 MPa, representing an increase of 58.9 % in comparison to the strain rate of 1 s−1.

Experimental and numerical study on extended endplate beam-column joints after high temperature to resist progressive collapse

This paper presents experimental and numerical investigations on the collapse-resisting behavior of extended endplate beam-column joints after high temperatures. The failure patterns and structural responses of extended endplate (EP) joints after high temperature to resist progressive collapse were first described, and then the effects of fire temperature and temperature duration on their collapse resistance mechanisms were also analyzed in detail. The test results demonstrate that all specimens withdrew from work owing to the serious deformation of endplate bolt holes or the brittle fracture of high-strength bolts, resulting in the catenary mechanisms of EP joints not being adequately developed. Compared with previous studies, it is shown that the fire temperature exerts the most significant effects on the carrying capacities and deformability of EP joints, and the collapse resistance of corresponding assemblies is most sensitive to the fire temperature. However, the temperature durations have an insignificant influence on the development of flexural mechanism resistance, especially for those after 600 °C and 800 °C. Moreover, the corresponding refined FE models in consideration of the damage and fracture of ductile metals have been established to reproduce the structural response of specimens after high temperature. To improve the post-fire collapse-resisting performance of assemblies, both the lateral plate reinforcement and welding reinforcement methods were proposed and compared with the assistance of validated FE models. From a practical viewpoint, the reinforcement with lateral plates is determined as a superior technique for post-fire EP joints against progressive collapse.

On reinforcing the friction stir weld joints of AA5086-H116 using the plasma spray coatings

The fatigue properties of friction stir weld joints of AA5086-H116 alloy, reinforced with Al2O3 particles using the plasma spray coating method, were investigated after single and double weld passes. A relatively uniform distribution of reinforced particles was achieved with superior properties, even higher than that of the parent alloy. The reinforced joints had enhanced hardness as well as joint efficiency, the double pass being superior to the single pass, but at the cost of reduced total elongation. Furthermore, the reinforced double-pass joints exhibited a remarkable ∼ 55%, ∼ 14%, and ∼ 89% increase in fatigue strength compared to the as-weld, the base material, and single-pass joints, respectively. The fractographic examination mainly revealed a defect-free crack initiation mechanism with a few cases of the ones induced by defects. The superior fatigue performance was mainly attributed to the uniform spatial and size distribution of fine Al2O3 particles within the weld nugget zone, thanks to the novel weld reinforcement method used in this study, which provides a promising avenue for improving the fatigue properties of weld joints.

Decoupling the role of microstructure and geometric discontinuity introduced by weld reinforcement height on corrosion behavior of SA106B/316L SS welded joint in the flowing 0.5 M NaCl solution

The flow-influenced corrosion (FIC) behavior of SA106B/316L stainless steel (SS) welded joints with SS located upstream and downstream is investigated experimentally and numerically. The damage components of microstructure heterogeneity and geometric discontinuity are quantified. The FIC of the welded joint is affected by the combination of galvanic corrosion, mass transfer, and charge transfer. The electrochemical measurements indicate that the corrosion is aggravated by a flow disturbance component of 18.70∼26.96%. The corrosion of SA106B carbon steel is more severe than 52M and 316L SS due to galvanic effect, which is further promoted by flow disturbance. The FIC mechanism is also discussed.

Corrosion of welding reinforcement height under dynamic conditions

The presence of welding reinforcement height (WRH) within oil and gas pipelines can lead to micro-turbulence in localized areas during transportation, resulting in corrosion failure. This study employed a modular reconstruction method to simulate and reconstruct X80 steel welded joints, and investigated the erosion-corrosion behavior at the WRH using wire beam microelectrode, electrochemical impedance spectroscopy, and computational fluid dynamics simulations. The results show that the galvanic current density (GCD) in the weld metal exhibits cathodic behavior, while the GCD in the base metal and heat-affected zone shows anodic behavior. The top of WRH is susceptible to corrosion failure. As the radius of WRH increases, the corrosion rate also increases. Additionally, the corrosion rate increases similarly with an increase in flow velocity. The galvanic corrosion intensity factor (g) is 0.24, and the local corrosion is moderate. This work has scientific significance in ensuring the long-term safe operation of pipelines and reducing the risk of corrosion failure.

Flow enhanced corrosion of tee in gas transmission pipeline

A tee failed due to flow enhanced corrosion at an oil field was investigated and analyzed by macroscopic analysis, nondestructive tests, material tests (including chemical composition, metallurgical analysis) and microstructure analysis (including microtopography, SEM, EDS and XRD) in this paper. It was concluded that the chemical composition and metallurgical properties of the tee accord with related standards, and the anti-corrosion coating on the inner wall peeled off is considered as one of the main failure factors of tee. The corrosion failure mechanism analysis results shows that the change of flow pattern caused the sudden change of the inner diameter between weld reinforcement and nickel based coating results in water gathering and flow enhanced corrosion at the concave area. Also, galvanic corrosion occurs at the concave area formed by weld reinforcement and nickel based coating between the carbon steel tee and nickel based coating due to high electrode potential difference. The galvanic corrosion further accelerated the corrosion process. Under the combined action of erosion, galvanic corrosion and flow enhanced corrosion, perforation leakage finally occurs.

Optimization of welding parameters on weld deposits area in pulsed gas metal arc welding

This paper presents a methodology for optimising pulsed gas metal arc welding parameters on Stainless Steel GRADE 410. Most sectors favour the economic welding technique for its favourable outcomes, such as enhanced strength and reduced corrosion. Compared to conventional welding methods, pulsed gas metal arc welding has the advantage of reducing current consumption and increasing the rate at which metal is deposited. An optimisation technique is employed to forecast the weld bead's accurate geometry, penetration depth, and reinforcement height, considering the welding input parameters such as welding speed, current rate, and frequency level. The Taguchi technique uses experimental analysis by considering input and output parameters. A multiple regression analysis model has been developed for SS Grade 410 Stainless steel to determine the bead geometry's correctness.

Method of reinforcing defects in field welds of unique buildings and structures

Introduction. The article presents a new method of reinforcing field welds with defects, impermissible according to the regulation requirements. This method allows reinforcement works to be carried out while maintaining the functional purpose of a building or structure without closing for the repair.Aim. To develop a technology of reinforcing defective welds, which preserves the functional purpose of a structure during repair works without its closure.Materials and methods. Reinforcement is carried out using a sheet of high-strength steel. The reinforcing sheet must be attached to connected field elements, which excludes the defective weld from the operation. Welders are permitted to perform works after testing on control welded joints. Welds, made by a candidate welder, is cut and sent to a specialized laboratory for determining weld strength properties, impact strength of weld macro- and microstructures, as well as the order and dimensions of legs for multi-pass welds. If the obtained weld data meets the standard indicators, the candidate welder is permitted to connect the reinforcement sheets of defective field welds. After making welded joints, they must be checked by visual, instrumental and ultrasonic testing.Results. A method of reinforcing defective welds was developed and implemented. Defects in the welds appeared during the connection of field elements, whose dimensions were less than the transport size, into a single spatial system, for example, the inner contour of a dome cover. This type of reinforcement can be made without closing the building or structure for repair works.Conclusion. The method of weld reinforcement can be used to remedy impermissible derects, detected by visual, instrumental and ultrasonic testing, in any buildings and structures, including unique long-span ones, therefore ensuring their reliable and safe operation after the construction.

Mitigating Stress Corrosion Cracking of 304L and 316L Laser Welds in a Salt Spray through Micro-Shot Peening

Two austenitic stainless steel (ASS) plates, 304L and 316L, were cold-rolled (304R and 316R) with a 10% reduction in thickness and then subjected to laser welding. Cold rolling caused slight surface hardening and introduced residual tensile stress into the ASS plates. The susceptibility to stress corrosion cracking (SCC) of the welds (304RW and 316RW) was determined using the U-bend test pieces in a salt spray. To highlight the stress concentration at the weld’s fusion boundary (FB), the top weld reinforcement was not ground off before bending. Moreover, micro-shot peening (MSP) was performed to mitigate the SCC of the welds by imposing high residual compressive stress and forming a fine-grained structure. Cold rolling increased the susceptibility of the 304R specimen to pitting corrosion and intergranular (IG) microcracking. Moreover, pitting corrosion and SCC were found more often at the FBs of the 304RW. The corrosion pits of the peened 304RW (304RWSP) were finer but greater in amount than the those of the un-peened one. The results also indicated that the 316L ASS welds with MSP were resistant to the incidence of pitting corrosion and SCC in a salt spray. The better reliability and longer service life of dry storage canisters could be achieved by using 316L ASS for the construction and application of MSP on it.

An improved simulation of temperature field in PMHW of Ti-6Al-4V alloy

This article describes a coaxial plasma–MIG hybrid welding (PMHW) method to improve the welding quality of titanium alloy plates. Aiming at the temperature field analysis of a Ti-6Al-4V alloy plate in the PMHW process, an improved hybrid heat source model capable of accurately characterising the heat input of a hybrid arc on workpieces and the arc deflection phenomenon, is proposed. Experiments were conducted on 4-mm Ti-6Al-4V plates in PMHW surfacing, and a corresponding simulation analysis was performed. To calculate the weld geometry, a weld pool shape was used in accordance with the experimental results. The results showed that, as plasma current increased from 60 to 80 A, the weld reinforcement and offset decreased, and the size of the weld pool increased. Plasma arc power had a greater effect on the length than on the width of the molten pool. Hybrid arcs had a stronger penetrating ability; hence, achieving deep penetration welding and high welding efficiency in the PMHW of the Ti-6Al-4V alloy was easier. Microstructure analysis showed that the Ti-6Al-4V alloy base metal zone was organised by α- and β-phase transformations; β grains in the weld zone were internally formed by a mixture of Weischer tissue and net basket tissue; and the size of β grains in the heat-affected zone decreased with the increase in the distance from the weld.

Properties study on Ti/Al butt joining by GMAW/GTAW hybrid welding-brazing

For adjusting the distribution of welding heat to obtain sound Ti/Al butt joints, Gas Metal Arc Welding (GMAW)/Gas Tungsten Arc Welding (GTAW) hybrid welding-brazing was introduced to join 5A06 to TC4. Then two kinds of tensile strength was tested. And the weld microstructure was observed by Scanning Electron Microscope (SEM), X-ray diffraction (XRD) and Energy Dispersive Spectrometer (EDS). Effects of welding parameters on weld reinforcement and interface characteristics were investigated. Results revealed TiAl3 IMCs layer was formed in the weld area of the titanium alloy side. The other area of weld was composed of α-Al matrix and Mg2Si+Al+Si eutectic. The back welding reinforcement was improved with the welding heat of the joint back increasing. But this may lead to a large number of molten metal flowing to the back of weld, the face reinforcement of the weld became poor. However, effects of welding parameters on the interface bonding strength was different. It was depended on the thickness and morphology of IMCs. When serrated IMCs of 2–6μm thickness were formed, the highest tensile strength without reinforcement was 240.3 MPa. Through comprehensive analyzing, when the welding parameters were welding speed of 15 mm s−1, GTAW current of 80–90 A and GMAW/GTAW position of −1 mm, the weld reinforcement and interface bonding strength were also high. So the excellent butt joints of TC4/5A06 were achieved. The maximum average value of TC4/5A06 joints tensile strength with reinforcement was 265 MPa with fracture inside the weld far from IMCs layer.

Microstructure and mechanical properties of 7075-T6 aluminum alloy plates by welding with weld reinforcement rolling

The welding with weld reinforcement rolling (WR) process was proposed to improve the deteriorated mechanical properties of traditional arc welded (TW) joints of the 7075-T6 aluminum alloy. In this novel process, the welding process and joint strengthening process were performed simultaneously. A comprehensive investigation of the microstructure evolution during the WR process was conducted. Ultimate tensile strength and elongation determined from tensile testing of the joints were 427.4 MPa, 5.5 % for WR joint and 301.3 MPa, 3.4 % for TW joint. The microhardness of the fusion zone (FZ) and heat-affected zone 1 (HAZ1, the dissolution zone) in the WR joint exceeded that of the TW joint. These results suggest that the application of rolling force not only affected the FZ but also simultaneously strengthened the HAZ1 through deformation while having a comparatively less effect on the heat-affected zone 2 (HAZ2, the over-ageing zone). Quantitative assessments of the effects of different strengthening mechanisms on the strength were conducted, and dislocation strengthening was found to be the predominant factor in increasing the strength of the WR joint. Deformation within both the FZ and HAZ1 during the WR process was mainly due to dislocation slip, while sub-grain rotation was also observed.

Welding reinforcement between silica glass and stainless steel using nanosecond fiber laser with chromium interlayer

Modern manufacturing industries need high strength and stable joint between glass and steel. Laser welding is an efficient technique to meet the requirement, but strength still needs to be improved. In this work, a welding reinforcement method of Cr addition was proposed to improve shear strength. The two materials were added with Cr metal film and Cr3+ solution in the interface, and welded by an nanosecond fiber laser. A maximum shear strength of 41.4 MPa was obtained, 40 % higher than that without Cr addition. The surface morphology and elemental distribution of the welds were observed. With Cr addition, the elemental diffusion in the interface was extended. Fe-O-Si and Cr-Si bonds were greatly increased in the welds. And microcracks were significantly reduced. In addition, the Cr layer also reduced the adverse effects caused by the different thermal expansion, making it more reliable in various industrial production fields.