Dissimilar Metal Welds Research Articles

Atypical Attack of the Dissimilar Metal Welds of a Water–Water Energetic Reactor Nuclear Power Plant Secondary Circuit: Possible Mechanisms of Failure

ABSTRACTDissimilar metal welds are utilized in the energy industry to connect two materials with different material characteristics. In the case of nuclear power plants, the connected materials tend to be low‐alloyed steel and high‐alloyed material. Despite different material and corrosion properties, under the proper environmental conditions, the used construction materials and weld metals are protected either by a passive layer or by a high‐temperature oxide. Although dissimilar metal welds are used in both primary and secondary circuits, the most frequently documented damage is in the secondary circuit, where, in addition to material heterogeneities, local environmental heterogeneities may form. For dissimilar metal welds in WWER nuclear power plants, a water–water energetic reactor, a subtype of pressure water reactor, we note two main types of attack near the dissimilar fusion boundary: on the carbon steel side or on the high‐alloyed weld metal side (X10CrNiMoN16‐25‐6). The possible causes of the latter “atypical” corrosion attack are debated and can be generalized as a consequence of change of the grain boundary condition.

Microstructural features and mechanical properties of in-situ remelting welding of TC4 titanium alloy and T2 copper welded joint by electron beam

In order to achieve high-quality welding of titanium copper dissimilar metals, the in-situ remelting welded joints of TC4 and T2 were obtained by using a time-sharing dual electron beam(TDEB). A welded joint consisting of the IMCs layer, FZ zone, copper weld zone, and titanium side HAZ is formed in the TC4/T2 interface area. The microstructure and morphology of IMCs layers in welded joints with TDEB welding and copper offset welding were observed by using SEM and TEM. Multiple forms of IMCs were observed in the IMCs layer, including columnar Ti2Cu, granular Ti3Cu4, and sheet-like TiCu4, clarifying the orientation relationship between some precipitates and matrix phases. The TC4/T2 joint welded with TDEB welding achieved micro zone remelting of the IMCs layer. The thickness of the IMCs layer has significantly decreased, and the number of copper-rich phases in the IMCs layer has increased, which improves the mechanical properties of the welded joint. The TC4/T2 joint welded by time-sharing dual beam electron beam has a tensile strength of 215.9MPa and an elongation of 6.14%. The joint exhibits brittle quasi dissociation fracture. The main factor causing fracture is the high brittleness and hardness of titanium-rich phases such as TiCu and Ti2Cu. This study provide a new welding method for titanium copper dissimilar metals, as well as research ideas for dissimilar metal welding.

Evaluation of Tensile Strength of Dissimilar Metals SS 316-pure Zn Joining by Friction Welding Method

Welding of dissimilar metals has always been a challenge in industrial applications. In this study, the joining of SS 316 and 99.9% pure zinc by continuous drive friction welding has been carried out. The welding process is carried out with parameters such as rotation speed, friction pressure, forging pressure, and burn length being kept constant for all weld joint samples. This friction time is selected through the process parameter approach carried out on aluminium alloy material. The experimental results were analysed by tensile test and microstructure using a scanning electron microscope (SEM) to characterise the microstructure. Tensile test results from friction welding with variations in friction time from 30 to 80 seconds obtained a higher tensile strength of the joint in the 30 to 50 seconds friction time range. In this experiment, the maximum joint tensile strength is obtained at 53.93 MPa, and the maximum modulus elasticity of 128.60 GPa at 35 seconds of friction. Solid-state welding makes it possible to join SS 316 and pure zinc, which is difficult to join in conventional fusion welding methods.

Microstructure and mechanical properties of ultrasonically welded aluminum to Zn–Mg–Al coated and uncoated mild steels

The gaining popularity of aluminum alloys in the automotive industry demand the development of energy efficient joining methods of Al with other metals such as steel. Among such joining methods, ultrasonic welding is advantageous because it is cost effective and prevents metallurgical defects because of the low welding energy involved. This study evaluates the microstructural changes and mechanical properties of dissimilar ultrasonic welding of Al to Zn–Mg–Al-coated and uncoated mild steels. Various intermetallic compounds (IMCs), such as FeAl3, and Fe2Al5 with different thicknesses and morphologies were observed at the joint interfaces. The Al-to-Zn-Mg-Al-coated steel exhibited mechanical properties that are superior to those of Al-to-uncoated mild steel. The results are discussed in terms of microstructure evolution, joint characteristics, and interfacial reactions in the welds. This study contributes to the understanding of the mechanisms behind strong ultrasonic welding of dissimilar metals.

Microstructure-Linked Mechanical Properties of P91-Incoloy 800HT Dissimilar Metal Welds

Dissimilar metal welds (DMWs) between P91 steel and Incoloy 800HT® using shielded metal arc welding (SMAW) with ENiCrCoMo-1 filler electrode were characterized in detail. The impact of multiple weld passes on microstructure in the heat-affected zone (HAZ) and weld fusion zone (WFZ) was thoroughly investigated. Postweld heat treatment (PWHT) impacts on mechanical characteristics and microstructure were also observed. The DMW was observed with heavy C, Cr, and Mo microsegregation in the WFZ, which deteriorated mechanical strength. The microstructural changes directly affected the mechanical behavior of the DMW. The ultimate tensile strength of the weld fusion zone was low at 576 MPa compared to the base metals’ strength. The tensile specimens failed in the IN 800HT base metal and WFZ. The WFZ had significant microsegregation near the solidified grain boundaries (SGBs). The metallurgical heterogeneity in the WFZ caused the formation of localized stress zones, which directly affected the mechanical behavior of the WFZ. The carbide particles influenced the microhardness in the WFZ and P91 HAZ regions. The PWHT successfully homogenized the microhardness in the WFZ and P91 HAZ regions. The impact toughness decreased to 64 J from 82 J after PWHT due to precipitation at SGBs and its coarsening. The SMAW process involves multiple thermal cycles during welding. The deposition of filler metal in multiple welding passes created uncontrolled variations in the solidification behavior of the WFZ. Microsegregation had a detrimental impact on the microstructure and mechanical properties of the P91 and IN 800HT dissimilar metal welds.

DISSIMILAR HARDOX AND LOW-ALLOY STEEL IN EXCAVATOR STRUCTURES

In the structure of excavators and other transport vehicles, it is observed that there is an increasing necessity to weld elements from the Hardox steels. The paper verifies the possibility to obtain accurate DMW (dissimilar metal welds from totally different grades of Hardox 450 steel with S355J2 steel). The microstructure and mechanical tests of the obtained various welds were analysed. Argon-based shielding gases with micro nitrogen additions were used for MAG welding. Gas mixtures with micro nitrogen additions of up to even 2000 ppm and their use in welding are an absolute novelty. The purpose of the manuscript was to find the correct parameters of making dissimilar joints with such modern mixtures and to determine the most suitable mixture for welding Hardox steel and low-alloy steel for use in the automotive industry.

Optimizing tool offset in static shoulder friction stir welding of Al6061 to Ti6Al4V for enhanced joint integrity

The precise control of tool offset in static shoulder friction stir welding (SSFSW) is vital for enhancing the mechanical properties and overall effectiveness of dissimilar metal joints. The present study investigates the impact of tool offset on the development of microstructural features, intermetallic compound formation, texture analysis, and mechanical characteristics of SSFSWed Al6061 to Ti6Al4V joints. The results demonstrate that a 2.5 mm tool offset results in an average grain size of 2.65 μm, compared to larger grains of about 4.76 μm and 7.31 μm observed at 2.0 mm and 1.5 mm offsets, respectively. The percentage of low-angle grain boundaries also varies, reaching up to 42.2% at a 2.5 mm offset compared to 48.6% at 2.0 mm and 64.1% at 1.5 mm, indicating enhanced homogeneity in the microstructural properties. Moreover, the ultimate tensile strength at the 2.5 mm tool offset reaches 279 MPa, which is 5.7% higher than at the 2.0 mm offset and 13.4% higher than at the 1.5 mm offset. This improvement is attributed to more uniform distribution of Ti particles over the stir zone. Texture analysis further supports these findings, with the development of alpha fibre at 2.5 mm offset enhancing ductility, thereby underscoring the critical role of tool offset in achieving sound dissimilar metal weldments.

Unexpected thermal aging effect on brittle fracture and elemental segregation in modern dissimilar metal weld

A full-scale dissimilar metal weld safe-end mock-up, precisely replicating a critical component of a modern nuclear power plant, was investigated. The brittle fracture behavior, carbide evolution and nanoscale elemental segregation in the heat-affected zone (HAZ) of low alloy steel (LAS) were analyzed under both post-weld heat-treated and thermally-aged conditions (400 °C for 15,000 h, equivalent to 90 years of operation) using analytical electron microscopy and atom probe tomography. The observed increase in grain boundary (GB) decohesion and intergranular cracking on the fracture surface and the decrease of fracture toughness are primarily attributed to P and Mn segregation to GBs and the coarsening of carbides upon long-term thermal aging. The direct observations of significant elemental segregation to GBs and the consequent reduction in fracture toughness in the HAZ are unexpected for modern low-phosphorus LASs, highlighting potential concerns for evaluating the structural integrity of modern nuclear power plants.

Development of a hybrid ANFIS method for optimising laser beam welding of dissimilar metals: a virtual prototype approach

Development of a hybrid ANFIS method for optimising laser beam welding of dissimilar metals: a virtual prototype approach

Fracture toughness and microstructural analysis of rotary friction welded S355J2 and SS316L steels for critical applications

Dissimilar metal welding is seeing growing adoption across industries to enhance structural functionality and efficiency. Achieving high-quality, defect-free dissimilar weld joints requires a comprehensive understanding of the interrelationships between the welding-induced microstructural changes and the material's performance characteristics, particularly its fracture-related properties. This study investigates the impact of microstructural changes on the fracture toughness of dissimilar welds between structural low-carbon steel (S355J2) and austenitic stainless steel (SS316L) prepared using the Rotary Friction Welding (RFW) technique. Welding preforms were created from respective pipe pup pieces. The evaluation involves microstructural analysis, tensile testing, hardness testing, and fracture toughness testing using compact tension specimens derived from various zones of the weld joints. Results revealed significant microstructural differences across the weld joint. The weld region exhibited stable hardness with a maximum of 208 HV1 in S355J2′s thermo-mechanically affected zone (TMAZ). High tensile strength (Ultimate Tensile Strength 540 MPa, Yield Strength 367 MPa) with failures mainly on the S355J2 side. The fracture toughness (KQ) matched parent metal values, with the RFW weld centre line (WCL) showing superior crack tip opening displacement (CTOD) of 0.35 mm. Fractography generally indicates ductile failure.

The formation control and microstructure evolution of macrosegregation in laser offset welding on steel-nickel dissimilar alloy

To precisely control the melting of two base metals, laser offset welding is an effective method for managing the interfacial microstructure in dissimilar metal welds. Macrosegregation exhibits a markedly different morphology near the steel-nickel fusion line, which plays an important role in premature creep failure. In this study, it was found that an offset of the laser beam towards the nickel correlated with an increase in macrosegregation. When the laser beam was biased towards the steel, the partially mixed zone (PMZ) and transition zone (TZ) of 9Cr steel were identifiable within the macrosegregation, displaying a distinct solidification mode. Lath martensite and fine austenite formed in the PMZ, with alternating distributions of martensite and austenite observed in the TZ. Conversely, when the laser beam was biased towards the nickel, the unmixed zone (UMZ) of 9Cr steel was observed within the macrosegregation. Nanoindentation tests revealed that the maximum nanohardness in macrosegregation reached 5.90 GPa in the PMZ due to the formation of lath martensite, while the minimum nanohardness was 1.30 GPa in the TZ due to reduced martensite formation. Additionally, the TZ exhibited a significant reduction in resistance to plastic deformation. The various microstructures of macrosegregation were attributed to the solidification process and the dilution rate of 9Cr steel. When the liquidus temperature of WM exceeded 1455℃, a wide TZ formed in the macrosegregation due to adequate mixing. In contrast, when the WM had a significantly lower liquidus temperature than the 9Cr steel, only UMZ and PMZ formed in the macrosegregation due to preferential solidification and insufficient mixing. To minimize macrosegregation and eliminate the softening TZ, a laser beam offset towards the steel between 0.1 mm and 0.2 mm is recommended.

Macroscopic and microscopic element distribution in transition zones of GTAW Alloy 52M weld joint and its PWSCC growth behaviour

The microstructure and element distribution in the transition zone (TZ) of Alloy 52M buttering (52Mb) layer near the fusion boundary to the SA508III low alloy steel in a dissimilar metal weld joint with post-weld heat treatment (PWHT) is characterized. Two macroscopic TZs in the heat-affected zone have lower Cr and Ni contents than the bulk Alloy 52Mb. The first TZ near the fusion boundary has the lowest Cr and Ni compositions, accompanying the highest Fe content. Cr depletion and Ni enrichment along with slight Fe enrichment at the dendrite boundaries in the TZs, are more significant than those in the bulk Alloy 52Mb. The number and the maximum depth of local oxidation penetrations at the alloy-inner oxide interface based on the oxidation tests, the number and the maximum length of locally interdendritic cracks, as well as the average crack growth rate (CGR) in terms of the stress corrosion cracking (SCC) band based on the SCC tests in the first TZ are higher than those in the second TZ. The average SCC CGR is enhanced by macroscopic element dilution, while local oxidation penetration, as well as locally interdendritic SCC, are thought to be enhanced by both the macroscopic dilution of Cr in the TZs and the microscopic Cr depletion at dendrite boundaries.

Hastelloy C276/AISI SS304 dissimilar metal welding: A comparative review of the effective application of laser and Micro-GTAW

Hastelloy C276, known for its high temperature strength and corrosion resistance, is essential in the manufacture of medical devices and aerospace components. This study developed a micro-controlled GTA welding technology capable of precisely welding 0.4 mm thick dissimilar metals, Hastelloy C276 and SS304. This technology utilizes advanced digital signal processing (DSP) to control the arc time with precision up to 1/100 of a second and improves the welding quality through spot stitch and cold-welding functions. Moreover, the use of 300A inverter-type GTA welding equipment and 2 kW fiber laser welding equipment in this study improved the precision of the welding process. The effectiveness of this technology has been validated through macro-inspections and heat-affected zone (HAZ) analysis. The new welding technique demonstrates the potential to overcome existing welding limitations on thin Hastelloy C276 plates by integrating digital signal processing and rapid response control mechanisms.

Failure Analysis of Dissimilar Metal Welds between Ferritic Heat Resistant Steels and Austenitic Stainless Steels in Power Plant

This study analysed the failure of dissimilar metal welds (DMWs) between ferritic heat resistant steels and austenitic stainless steels and investigated its influencing factors by means of numerical simulation, microstructure characterization and mechanical property test. Under the long-term high-temperature service condition in practical power plant, the DMW failure mode was along the interface between nickel-based weld metal (WM) and ferritic heat resistant steel, and the failure mechanism was stress/strain concentration, microstructure degradation and oxidation coupling acting on the interface. The numerical simulation results show that interface stress/strain concentration was due to the differences in coefficient of thermal expansion and creep strength, and the degree of stress/strain concentration was related to service time. The ferrite band formed at the WM/ferritic steel interface was prone to cracking, attracting the fracture along the interface. The interface crack allowed oxidation to develop along the WM/ferritic steel interface. During long-term service, the interface stress/strain concentration, microstructure and oxidation all evolved, which synergistically promoted interface failure of DMW. However, only under the long-term service of low stress conditions could trigger the interface failure of DMW. Meanwhile, long-term service would reduce the mechanical strength and plasticity of DMW.

Influence of CMT welding parameters on microstructural and properties investigation of dissimilar weld joint for aluminum bronze and carbon steel

Cold Metal Transfer (CMT) welding technology has improved the appearance of weld beads and revolutionized the welding of thicker materials and dissimilar metals with precise metal deposition and reduced heat input. Cold Metal Transfer welding is predominantly used in a variety of industry applications, including aerospace, shipbuilding, automotive and marine industries. In this study, aluminum bronzes and carbon steel were joined by using CMT welding, a variant of the Gas Metal Arc Welding process, with ERCuAl-A2 as the filler metal. Optical microscopy was used to examine the microstructure of the CMT weld joint between aluminum bronze and carbon steel. Results have indicated that dissimilar metals such as aluminum bronze, and carbon steel could be successfully joined by CMT under various processing parameters. The tensile and bending strengths of the dissimilar joint were 490 MPa and 822 MPa, respectively. A variety of intermetallic compounds and solid solutions were generated in the weld zone and fusion zone. The micro-hardness in the carbon steel side of the fusion zones increased sharply, which was 164 HV in the welded condition. The dissimilar joint was stronger than the carbon steel, as the ductile fracture occurred on the carbon steel during the transverse tensile test of the welded specimen. The microstructure interpretation of welded dissimilar joints was analyzed by scanning electron microscopy and transmission electron microscopy.

Investigation on fracture resistance behaviour of dissimilar metal weld joint of modified 9Cr–1Mo steel and AISI 316LN SS

Fracture behavior of dissimilar metal weld joint consisting of mod. 9Cr–1Mo steel, AISI 316LN stainless steel, Inconel 82 butter layer and Inconel 182 weld has been investigated through experiments and FE simulations. The metallographic studies on weld joint and its interfaces have been carried out to determine the influence of microstructure on tensile and fracture properties. Tensile properties of different weld regions viz., weld metal, butter layer and HAZ have been evaluated using sub-size specimens. Fracture resistance behavior of weld joint has been studied through testing of compact type specimens with initial cracks machined at different locations. The plastic η factors for estimation of J-R curve have been obtained using FE analysis for crack in different regions viz., weld metal, butter layer and HAZ. Crack in weld metal exhibits lower fracture resistance as compared to butter layer and HAZ. Further, the constraint acting on crack and its susceptibility for deviation have been discussed in terms of stress triaxiality ahead of crack tip.

Improve the impact property in a novel butt joint of Ti/Al dissimilar metals

The dissimilar metal welding joint is connected by the metallurgical bond of intermetallic compounds at the interface, which easily causes stress concentration at the interface and cracks continuously along the interface, resulting in low reliability in impact environments. A novel multi-layer plug and bolt connection for TC4/7A52 dissimilar metal butt joints is proposed in this manuscript and analyzes the influence mechanism of the structural design on impact toughness. The impact toughness of the Ti/Al composite butt joint is 30.3 J/cm2, which is 2.6 times that of the 7A52 BM. The layered toughening design significantly reduces stress concentrations for the butt joint at impact for the Ti/Al composite butt joint. Upon impact, the Ti/Al composite butt joint does not fracture continuously at the V-notch and exhibits significant macroscopic plastic deformation. For the microstructure of each TC4 and 7A52 layer in the impact fracture, more intragranular slip systems are activated and show a higher dislocation density. Therefore, this structural design can enable dissimilar metals to absorb more impact energy during the impact process.

Estimation of residual stress in dissimilar metals welding using deep fuzzy neural networks with rule-dropout

Welding processes are used to connect several components in nuclear power plants. These welding processes can induce residual stress in welding joints, which has been identified as a significant factor in primary water stress corrosion cracking. Consequently, the assessment of welding residual stress plays a crucial role in determining the structural integrity of welded joints. In this study, a deep fuzzy neural networks (DFNN) with a rule-dropout method, which is an artificial intelligence (AI) method, was used to predict the residual stress of dissimilar metal welding. ABAQUS, a finite element analysis program, was used as the data collection tool to develop the AI model, and 6300 data instances were collected under 150 analysis conditions. A rule-dropout method and genetic algorithm were used to optimize the estimation performance of the DFNN model. DFNN with the rule-dropout model was compared to a deep neural network method, known as a general deep learning method, to evaluate the estimation performance of DFNN. In addition, a fuzzy neural network method and a cascaded support vector regression method conducted in previous studies were compared. Consequently, the estimation performance of the DFNN with the rule-dropout model was better than those of the comparison methods. The welding residual stress estimation results of this study are expected to contribute to the evaluation of the structural integrity of welded joints.

An Analysis of Laser Welding Technology used for Joining Dissimilar Metals, Computational Parameters and Challenges

Welding particularly joining dissimilar metals is new technology. Laser welding is a challenging task and most essential and reliable method of joining dissimilar metal used in various industrial area. Out of the modern welding laser welding is gaining its popularity due to its various unique features. Laser welding, is modern method of joining similar or dissimilar parts metal/non-metal by laser beam of very high power, high temperature source. Very good control on input factors, very small heat affected zone, precise accurate welding joint and high speed are some attractive features of this technique. This technology gives more flexibility to design engineer. Various kind of lasers such as Nd:YAG, Co2 laser, Diode laser, disk laser m/c are used in welding of automobile, aerospace and ships. All concept of laser welding depends on the key-hole phenomena. It is a cavity formed by recoil pressure and energy absorption is due to high temperature multi reflection of laser rays. So this gives deep Penetration of weld joint. This paper shows various Challanges of dissimilar metal welding and technique to over come this. In our use study We are going to use dissimilar metal plates of 3.5 mm thick of 16MnCr5 and 316 SS. This metal jonts are used in production of automotive cylindrical part in large quantity.

Microstructure and mechanical properties of a dissimilar metal welded joint of Inconel 617 and P92 steel with Inconel 82 buttering layer for AUSC boiler application

The application of the novel dissimilar metal welded (DMW) joint, utilizing Inconel 617 and P92 steel, was showcased in the advanced ultra-supercritical (AUSC) boiler. The work has been performed to investigate the effect of Inconel 82 (ERNiCr-3) buttering layer on microstructure and mechanical properties (high-temperature tensile strength, impact strength and microhardness) of gas tungsten arc welded (GTAW) dissimilar joint between Inconel 617 and P92 steel fabricated using the Inconel 617 (ERNiCrCoMo-1) filler. For optical microscopy and scanning electron microscopy (SEM), samples were machined along a transverse direction which comprised the butter layer, weld metal, and heat-affected zone of both sides. The energy-dispersive X-ray spectroscopy (EDS) was used to map the interface of the buttering layer and weld metal and butter layer and P92 steel. The high-temperature tensile testing and Charpy impact testing at room temperature were conducted for the integrity assessment of the welded joint. The examination of microstructure and hardness revealed that the buttering layer of Inconel 82 filler successfully mitigated a significant portion of the brittle martensitic microstructure from the coarse-grained heat-affected zone (CGHAZ), along with hardness peaks on the side of P92 steel. The conventional method of DMW joint fabrication, without the use of a buttering layer, has been demonstrated to be less favourable compared to the new fabrication method, which incorporates a buttering layer. The TiC/NbC carbides were identified in the Inconel 82 buttering layer, whereas M23C6 and Mo6C carbides were found in the Inconel 617 filler weld. Near the interface of the Inconel 82 buttering layer and P92 steel, the formation of peninsula and island structures, as well as Type I and Type II boundaries, were confirmed. Additionally, element diffusion of Ni, Cr, and Fe was observed. The tensile test results indicated an ultimate tensile strength of 620 ± 4 MPa and % elongation of 19 ± 4 % at room temperature, with fracture occurring in the buttering layer near the interface of the buttering layer and P92 steel. At temperatures of 550 °C and 650 °C, the ultimate tensile strength decreased to 448 MPa and 326 MPa, respectively, with fractures occurring in the P92 steel, irrespective of temperature. The hardness of the Inconel 82 buttering layer and Inconel 617 filler weld were 219 ± 10 HV and 248 ± 11 HV, respectively. The Charpy impact toughness of the Inconel 82 buttering layer and Inconel 617 filler weld were 138 ± 6 J and 115 ± 4 J, respectively. The study comprehensively investigates and discussed the correlations between microstructure and mechanical properties.