Bimetallic Welds Research Articles

Influence of heat input on bead geometry, microstructure and hardness characteristics of dissimilar 410 martensitic stainless steel weld deposits on 304L substrate

ABSTRACT Examining the impact of heat-input (QHI) on the characteristics of dissimilar welds of 410 and 304L is essential for improving the structural integrity, longevity, and functionality of bimetallic welds and components produced through additive manufacturing. The study delved into key variables influencing deposited bead and fusion zone (FZ) characteristics. An increase in QHI from 170J/mm to 530J/mm caused an exponential bead width (W) rise, expanding the weld bead width from 5mm to 13mm. Despite this, both bead height and penetration depth rose, resulting in a reduction of aspect ratios at higher QHI values. Aspect ratios remained low within the range of 300-480J/mm. Furthermore, the research demonstrated that an increased QHI value caused a reduction in the Cr-Ni equivalent ratio from 1.91 to 1.77, promoting the γ-phase in the FZ. The γ-phase further transformed into α’-martensite upon cooling. The lowest QHI increased the γ-phase metastability, fostering the formation of α’ and γ-FeNi in the FZs, gradually elevating the deposition hardness up to 13.9 % compared to the highest QHI. Various linear and non-linear models were developed to anticipate the correlations for predicting crucial parameters such as Ms temperature, Mεs temperature, SFE, α’-martensite volume fraction, γ-FeNi volume fraction, and hardness.

Electrical and thermal stability of Al-Cu welds: Performance benchmarking of the hybrid metal extrusion and bonding process

Advances in joining processes for aluminum and copper are sought after to facilitate the greater adoption of aluminum in electrical applications. Aluminum's chemical affinity to copper causes the joining and lifetime of Al-Cu welds to be vulnerable to the formation of various intermetallic compounds. Intermetallic compounds and the resulting weld structure are known to reduce the structural integrity and increase the electrical resistance of Al-Cu welds. In this study we evaluate the novel joining process, Hybrid Metal Extrusion and Bonding, for butt welding aluminum and copper. The weld structure was examined using scanning and transmission electron microscopy, and the weld resistance was measured using four-point measurements forecast to the weld interface. Energy dispersive spectroscopy and electron diffraction zone axis patterns were analysed to identify intermetallic compounds. Weld samples were examined pre and post heat treatment at 200 °C, 250 °C and 350 °C for total durations of over 1000 h. The results are compared to existing Al-Cu joining processes, and a new metric, weld interface resistivity, is proposed to compare the electrical properties of bimetallic welds. The Hybrid Metal Extrusion and Bonding process was found to form a thin, consistent and straight intermetallic layer with negligible impact on electrical resistance in the as-welded condition. Artificial ageing of samples by heat treatment established the overall growth rate of intermetallic compounds. The growth rate was used to evaluate the weld's operational lifetime versus temperature. The intermetallic growth rate of Hybrid Metal Extrusion and Bonding was quantified at 200 °C and compared to alternative processes. The Hybrid Metal Extrusion and Bonding process showed a significant performance advantage requiring the longest time to reach 2 μm thickness. Furthermore, the growth of intermetallic compounds did not increase the electrical resistance of the weld interface. The negligible impact on electrical resistance and slow intermetallic growth are promising results of the potential functional performance. This study is the first characterisation of the Hybrid Metal Extrusion and Bonding process for electrical applications showcasing its exciting potential for the joining of aluminum and copper.

Development and Qualification of Materials for Indian Advanced Ultra-Supercritical Coal-Fired Power Plant

Abstract India has embarked on an ambitious program of setting up efficient advanced ultra-supercritical (AUSC) technology with steam temperature and pressure of 993 K and 31 MPa, respectively. This article deals with the testing and qualification of indigenously produced materials for the Indian AUSC mission project, the research and development phase of which is currently in the advanced stage of completion. As part of this, exhaustive database pertaining to various mechanical properties including creep, low cycle fatigue (LCF), creep-fatigue interaction (CFI), high cycle fatigue (HCF), fracture toughness, and crack growth has been generated covering important candidate materials such as alloy 617M tubes and forgings, 304HCu stainless steel tubes, and alloy 625 castings. Tubes of both alloy 617M and 304HCu stainless steels are to be used in the boilers, whereas alloy 617M forgings would be used as turbine rotor and alloy 625 castings as turbine casings. The data have been subsequently used to establish design curves identifying safe regimes of operation with respect to creep, LCF, HCF, CFI, and fatigue and creep crack growths. The properties were seen to be comparable with those derived from internationally developed equivalent grades. The bimetallic weld joints between alloy 617M and 10Cr steels were also evaluated to derive the appropriate strength reduction factors under creep and cyclic loadings. Additionally, the influence of thermal aging at service temperature on the microstructural evolution and mechanical properties was investigated based on tensile and fracture properties to account for the service exposure induced degradation and associated embrittlement.

Combining CaO–SiO2–TiO2 and CaO–SiO2–Al2O3 ternary phase systems for design of bimetallic welds

The bimetallic welds are frequently utilized for pipeline transport system of the nuclear power plants. The occurrences of welding defects generally depend on the filler electrode as well as the electrode coatings during shielded metal arc welding process. This study involves the design of austenitic stainless steel welding electrodes for SS304L–SA516 bimetallic welds. The objective of research work includes the novel design of Al2O3–TiO2–CaO–SiO2 coatings by combining two ternary phase systems using extreme vertices mixture design methodology to analyze the effect of key coating constituents on the weld metal chemistry and mechanical properties of the welds. The significant effect of electrode coating constituent CaO on weld metal manganese content is observed which further improves the toughness of bimetallic weld joints. Various regression models have been developed for the weld responses and multi objective optimisation approach using composite desirability function has been adopted for identifying the optimized set of electrode coating compositions. The role of delta ferrite content in promoting the favourable solidification mode has been studied through microstructural examination.

Weldability and mechanical properties of AA5052 and AA7075 dissimilar joints developed by GTAW process

Study of the weldability and mechanical behavior of bimetallic welds of AA5052 and AA7075 obtained from gas tungsten arc welding process was done. Two filler wires viz., ER4043 and ER5356 were employed to join the dissimilar metals. The process parameters and welding conditions were used same in both filler weldments. Non-destructive testing was carried out to confirm the weldability of dissimilar joint with fusion welding process. The mechanical tests such as tension, hardness and impact test were conducted as per ASTM standards to evaluate the weld properties. Weldments obtained using ER4043 filler has exhibited superior quality with UTS of 182 MPa. It was found that the welds of ER 4043 have shown higher impact strength of 62 J whereas weldment obtained by ER 5356 has given toughness value of 24 J. The micro-porous and voids were observed in weld zone when ER5356 filler was employed.

Comparative study of TIG and MIG welding for Bi-metallic weld of AISI 304 and monel 400

The use of combination of two different advanced categorized metals are always being considered by industries as of its versatile properties as well as the benefits of two metals could be extracted out of single joined bi-metal at competitive price. These hardened steels have applications from general use articles to aerospace machinery. In order to achieve such useable tempered steel many techniques have been tried and found that welding is the one that could be resulting best. Though there are many procedures in the vast field of welding could be performed. To find the optimal as well as adequate technique, physical macrostructural as well as microstructural strength of joint is highly recommended to check the quality as well as the reliability [1] of the joint.

Microstructural investigation and mechanical properties evaluation using miniature specimen testing of various constituents of dissimilar weld joint

Microstructural evolution in P91 (modified 9Cr–1Mo) steel and 316LN Stainless Steel (SS) bi-metallic weld joints fabricated by arc welding technique using Inconel-182 electrode has been studied in as-welded and post weld heat treated (PWHT) conditions. The PWHT brought about significant changes in the microstructure which altered the strength gradient especially in the ferritic steel side. The differences in weld thermal cycling which occurred in various regions of the P91 steel side caused M23C6 precipitates to evolve in varying sizes. The size variation in these precipitates was the paramount cause for the variation in strength in this region which could be probed by miniature specimen testing. Using this testing it could be established that PWHT resulted in offsetting the strength variation in the HAZ of the ferritic steel side. It could also be understood that PWHT generates a weak region in the P91 side making it most susceptible to damage.

Heterogeneous creep deformation in Dissimilar Metal Welds (DMWs)

Dissimilar Metal Welds (DMWs) made between ferritic low alloy steels and austenitic alloys are widely used in high temperature components of nuclear and fossil energy power plants. Literature shows that these bimetallic welds fail prematurely by creep mechanism close to the interface of the ferritic (BCC) and austenitic regions (FCC), with lifetimes much less than the creep lives of both materials. These creep failures are associated with cavity formation close to BCC/FCC interfaces. However, the spatial and temporal variations of creep strain rates in these DMWs have not been measured. In this research, DMW coupons were fabricated between 2.25Cr-1Mo steel and Alloy 800 H base material using a Ni base Inconel weld consumable. These samples were aged at 600 ℃ for 2000 h and 4000 h to induce two different sizes and distributions of Type I interfacial carbides and further subjected to a short term (~1 month) creep testing. Surface strains were measured with Digital Image Correlation (DIC) technique to extract local creep strain rates. In both samples, creep strain concentration occurred in the BCC matrix. The location of creep strain concentration from the BCC/FCC interface, changed from 5 µm (2000 h aged condition) to 400 µm (4000 h aged condition) depending on the initial carbide distributions in these regions.

Corrosion protection of low-cost carbon steel with SS-309Mo and Inconel-625 bimetallic weld overlay

The dissimilar weld overlay coatings of components can lead to corrosion. In the present work, two different weld overlay layers (SS-309Mo and Inconel-625) are deposited on IS2062 grade B carbon steel, in order to avoid distortions and improve corrosion resistance. The microstructural investigations revealed that the intermediate layer SS-309Mo on carbon steel prevents the dilution by aiding crack-free weld overlay of Inconel-625 on the top. The corrosion behaviour of the coatings is studied using Linear Polarization Resistance and the Electrochemical Impedance Spectroscopy. The corrosion rate of the coatings decreased by two orders of magnitude compared to that of low carbon steel substrate. The corrosion rate of the deposited Inconel-625 along with intermediate SS-309Mo is 1.16 × 10−3 and is comparable to that of bare Inconel-625 (1.12 × 10−3 mmpy). Further, the immersion tests for 14 days show that, the depositions are stable with the formation of the passive film.

Metallurgical Investigations on Bimetallic Weld Joints in Austenitic/Ferritic Stainless Steels for Paper-Pulp Industries

Metallurgical Investigations on Bimetallic Weld Joints in Austenitic/Ferritic Stainless Steels for Paper-Pulp Industries

Investigations on weld metal chemistry and mechanical behaviour of bimetallic welds using CaO–CaF2–SiO2–Ni based electrode coatings

The bimetallic welds between ferritic low alloy steels and austenitic stainless steels are widely used in the heat piping transport systems of nuclear power plants for connecting the heavy section low alloy steel components with those of high temperature stainless steel pipes. The operating experience of major nuclear power plant components has recently shown that bimetallic joints can jeopardize the plant availability and safety because of increased incidences of failure. In shielded metal arc welding process, the occurrence and severity of weld defects mainly depend upon the type of electrode filler wire and the electrode coating ingredients used. The use of nickel based filler metals is no longer considered as the final solution for unexpected failures of bimetallic welds due to incidences of hot cracking. In the present paper, an attempt has been made to design and develop an intermediate electrode based on CaO–CaF2–SiO2 ternary phase diagram system and nickel as an additional electrode coating ingredient using mild steel as a filler wire for the bimetallic weld joint. The extreme vertices methodology has been used to design 21 electrode coating formulations. The quadratic regression models for weld metal chemistry, ultimate tensile strength, impact toughness, macrohardness, diffusible hydrogen content, and corrosion rate in terms of electrode coating ingredients, have been developed and checked for adequacy using analysis of variance. The work aims at studying the individual as well as combined effect of electrode coating ingredients on the measured weld responses and microstructures of the weld. Also, the electrode coating formulations suggesting multiobjective optimized solutions have been proposed.

Impact and Measurement Techniques of Residual Stress in Welding of Bimetallic Material

Objectives: The welding techniques are being developed at a very fast pace with novel and efficient techniques coming up for unconventional cases such as dissimilar metal joints between plates of various types, which have various practical applications, like in nuclear power plants. Methods/Statistical Analysis: A few strategies and procedures have been proposed furthermore have been connected for measuring residual stress (σR) in a few metals. Some of such strategies are: stress relaxation procedures, X-Ray Diffraction methods, Techniques utilizing stress touchy properties and Cracking systems. In addition, endeavors have additionally been made to use ultrasonic and hardness strategies to decide remaining burdens in metals by measuring stress sensitivity properties. Finding: Failure investigations of many dissimilar joints and literature review have revealed that several failures of the dissimilar welded joints have taken place in the Heat Affected Zone [HAZ]. One of the major reasons for failure of dissimilar welded joints is the untreated left residual stresses. In the present paper a brief description of the ideology of bimetallic weld processes, their capabilities and restrictions, phenomenon and types of σR and their treatment techniques is presented. The overall impact of σR and their measurement techniques have also been discussed. Application/Improvements: There are numerous applications of dissimilar metal joints such as in automotive industry, power generation industry etc.

Linear Friction Welding of IN718 to Ti6Al4V

Linear friction welding (LFW), an emerging automated technology, has potential for solid-state joining of dissimilar materials (bi-metals) to enable tailoring of the mechanical performance, whilst limiting the assembly weight for increased fuel efficiency. However, bi-metallic welds are quite difficult to manufacture, especially when the material combinations can lead to the formation of intermetallic (brittle) phases at the interface, such as the case with assembly of Ti base alloys with Ni base superalloys. The intermetallic phase, once formed, lowers the performance of the as-manufactured properties and its growth during elevated temperature service can lead to unreliable performance. In this project, it was demonstrated that linear friction welding can be applied to join Ti-6%Al-4%V (workhorse Ti alloy) to INCONEL® 718 (workhorse Ni-base superalloy) with minimized interaction at the interface. Of particular merit is that no intermediate layer (between the Ti alloy and Ni-base superalloy) was needed for bonding. Characterization of the bi-metallic weld included macro-and microstructural examination of the flash and interface regions and evaluation of the hardness.

Experimental Analysis of Thermal Fatigue in Bimetallic Welds

The bimetallic weld joints are widely utilized in the pressurized water reactors, boiling water reactors, heat exchangers in process industries, heat transport piping system utilized in nuclear plants, etc. The present study is aimed at analyzing the bimetallic weld strength degradation due to thermal fatigue. For generating thermal fatigue like conditions, an experimental test rig has been developed. The bimetallic weld between low alloy steel SA 516 grade 70 and stainless steel 304 L was prepared. The experimental results show that, heating time, notch radius and number of cycles have the effect on tensile properties of bimetallic welds.

Analysis of Mechanical Behaviour of Heat Affected Zone on Ferritic Side of Bimetallic Welds under Thermal Fatigue Conditions

In this paper the effect of thermal fatigue on mechanical behaviour of the heat affected zone on ferritic side of bimetallic weld was investigated. The bimetallic weld coupons between ferritic steel SA516 Grade 70 and stainless steel 304L were fabricated using TIG (Tungsten Inert Gas) welding process. In this investigation, an experimental test rig was developed and used to simulate the thermal fatigue conditions at laboratory scale. The thermal fatigue factors selected were heating time, notch radius and number of cycles.

Investigations on Design and Formulation of Buttering Layer Electrode Coatings for Bimetallic Welds

The bimetallic welds (BMWs) between ferritic low alloy steels and austenitic stainless steel are used widely in steam generators of the power plants. The adoption of these welds in wide industrial applications provides feasible solutions for the flexible design of the products by using each material efficiently and economically. The present paper is an effort towards studying the development of austenitic stainless steel buttering filler material for bimetallic weld joint. The work aims at the design and development of buttering layer electrode coatings for shielded metal arc welding process using extreme vertices design methodology suggested by McLean and Anderson to study the effect of electrode coating ingredients on the buttering layer metal composition and delta ferrite content to prevent solidification cracking.

Investigation of TiO2–SiO2–CaO–CaF2 based electrode coatings on weld metal chemistry and mechanical behaviour of bimetallic welds

The use of nickel base alloy as filler metal is no longer considered as the final solution for unexpected failures due to incidences of hot cracking of bimetallic welds under cyclically shifted temperature environment. The present paper is a novel attempt to study the development of austenitic stainless steel filler material for bimetallic weld joint. The present work aims at the design and development of shielded metal arc welding (SMAW) electrode coatings using extreme vertices design methodology to study the effect of electrode coating ingredients on the mechanical properties such as tensile strength, percentage elongation, impact toughness, micro-hardness of the weld metal. The work also attempts to study the weld metal chemistry along with the control of ferrite number and microstructural evolution to prevent hot cracking in stainless steel welds with variation in coating ingredients. It has been found from the study that the addition of SiO2 content in the coating tends to increase the weld metal silicon content whereas the effect of CaO content is to decrease it. The ultimate tensile strength of welds is increased with the TiO2, SiO2 and CaF2 content in the electrode coating while higher SiO2 content shows decreasing effect on impact toughness and microhardness values of the weld. The microstructures of welds comprise of austenite with varying amount of delta ferrite and inclusions which are further responsible for varying mechanical properties in welds.

MECHANICAL PROPERTIES OF BIMETALLIC WELD JOINT BETWEEN SA 516 GRADE 65 CARBON STEEL AND SS 304 L FOR STEAM GENERATOR APPLICATION

For a long time now, bimetallic welds (BMWs) have been a necessity within the pressurized water reactors (PWR) and boiling water reactor (BWR) designs, where the heavy section low alloy steel components are usually connected to stainless steel (SS) primary piping systems. For PWRs, the BMWs, which are of particular interest, are those attaching the systems to the various nozzles of the reactor pressure vessel (RPV), steam generators (SG) and pressuriser. The scope of this paper is to study of mechanical behavior in bimetallic welds used in nuclear power plant. We intended to summarize the understanding of weld behavior that may be applicable in the design of welded components for nuclear power plant systems.

Simulation of ultrasonic wave propagation in welds using ray-based methods

Austenitic or bimetallic welds are particularly difficult to control due to their anisotropic and inhomogeneous properties. In this paper, we present a ray-based method to simulate the propagation of ultrasonic waves in such structures, taking into account their internal properties. This method is applied on a smooth representation of the orientation of the grain in the weld. The propagation model consists in solving the eikonal and transport equations in an inhomogeneous anisotropic medium. Simulation results are presented and compared to finite elements for a distribution of grain orientation expressed in a closed-form.

Optimization of Process Parameters for Friction Welding of Bimetallic Welds

Bimetallic welds made between ferritic steels and austenitic stainless steels are conventionally fabricated using arc welding procedures such as Tungsten Inert Gas, Metal Inert Gas, Shielded Metal Arc Welding and Submerged Arc Welding. However friction welding provides a new and unique solid state approach for joining many similar and dissimilar materials, which may not be possible to join by other welding techniques available without adding any external filler metal. This approach is mostly used in joining of dissimilar materials. The reason for increased utility being the absence of any external filler material which may otherwise add to the heterogeneity of the weld structure. In this paper, the fabrication and effect of friction welding parameters on mechanical-micro structural changes of bimetallic weld joints has been discussed. An attempt has also been made to relate the effect of friction welding parameters on the peak temperature values taken near faying surface and micro hardness changes measured in various zones of weld.