Microwave hybrid process-based fabrication of super duplex stainless steel joints using nickel and stainless steel filler materials

1 Introduction

Industries need more adaptable, rapid, and environmentally friendly methods to enhance production rates and attain superior physical and mechanical properties. The microwave joining method serves as a substitute for traditional techniques, enabling a solution that meets the needs of current industrial uses [1,2]. In this method, microwaves interact at the molecular level with the specimen material, enabling energy conversion through ionic conduction and dipole rotation [3,4]. MHH represents a likely, environmentally friendly, and energy-efficient process of joining that ensures constant and volumetric heating nature of the weld area, thereby reducing heat loss and time [5,6]. The investigation of welded joints of super duplex stainless steel (SDSS) is highly significant due to its extensive applications. SDSSs are famous for their exceptional mechanical strength and outstanding corrosion resistance [7]. These properties are largely due to the balanced presence of ferrite and austenite, along with substantial amounts of chromium and nickel in their composition, as well as favourable grain boundary morphologies [8,9]. The ferrite phase contributes to high strength and corrosion resistance, while the austenite part provides uniform corrosion resistance and enhances ductility [10]. SAF2507 demonstrates superior corrosion resistance compared to earlier grades of duplex stainless steel (DSS). These alloys exhibit exceptional corrosion resistance, particularly in chloride-rich environments, making them suitable for applications involving seawater. They also demonstrate excellent resistance to pitting corrosion and possess high mechanical strength [11,12]. The joining of iron-based alloys holds significant industrial relevance, extending to applications in power plant steam lines, chemical and marine industries, vehicle manufacturing, and aerospace [13,14]. The various techniques utilized for welding stainless steel plates include friction stir welding method, gas metal arc welding method, laser beam welding method, pulsed-fibre welding method, laser-metal inert gas hybrid welding method, and gas tungsten arc welding. Ye et al. [15] fabricated a butt joint of Inconel600 with a thick sheet of 2 mm using the friction stir welding method. A shielding agent like argon gas was selected to avoid joint oxidation. During this process, tool rotation at 400 rpm and a welding speed of 1.67 mm·s⁻¹ were used. The authors did not observe softening in the heat-affected zone. Vickers hardness testing showed slightly higher hardness compared to that of the base metal. Furthermore, the ultimate strength of the stir region was found to exceed that of the joint. Mohammed et al. [16] employed a pulsed-fibre welding method for the joining of SS2205–SS304. Microstructural examination revealed the presence of fine-grain and dendritic structures in the joining area, with ferritic microstructures detected next to SS304. Austenitic–ferritic microstructures were also recognized along the boundary of SS2205. Mechanical testing of dissimilar welds revealed increased tensile strength and microhardness was found in comparison to parent metals. Bhattacharya and Kumar [17] employed gas metal arc welding to create dissimilar welds of SS2205–SS304 plates. Their study focused on the effects of welding current, shielding gas, filler material, flow rate, and welding voltage on the properties of the joints. They found that using CO₂ as a secondary shielding gas in a double-shielding configuration significantly improved the toughness and tensile strength of the welds while also reducing distortion. The welding of inconel625-SS304 plates with gas tungsten arc-welding method using ERNiCrMo-3 as interface powder was proposed by Mithilesh et al. [18]. A plate of dimensions 125 × 50 × 5 mm³ was selected for joining in the butt form. A hardness value of 236.4 HV was observed on the joint area and 249.5 HV on the inconel625 side. Tensile examinations revealed that fractures occur at the SS304 side. Correspondingly, Ramkumar et al. [19] discussed the tungsten inert gas (TIG) welding process involving Inconel718-SS316L dissimilar materials with 4 mm-thick plates. They conducted welding without using activated flux. The study demonstrated the feasibility of achieving complete penetration in multi-pass welding. Optical microscopy and SEM analysis revealed the growth of the unmixed area and heat-affected area. Additionally, the authors employed EDS analysis to determine the chemical composition of both joints. Singh et al. [20] conducted a comprehensive literature review on various MIG welding variants. Their focus was to determine the effects of different input factors on the physical and mechanical properties of weldments. Hong et al. [21] investigated dissimilar material welding of SAF2507 and 316L using plasma arc welding (PAW). Optimal values of input factors for joints were observed by a combination of response surface methodology, finite element modelling, and experiments. Li et al. [22] reviewed the various types of welding techniques used for joining the UNS S32750 material. The various techniques utilized for welding UNS S32750 material include friction stir welding method, PAW method, laser beam welding method, submerged arc welding method, electron beam welding method, laser-MIG hybrid welding method, and gas tungsten arc welding. The dissimilar joining of SAF2507 and 316L material was studied analytically and verified experimentally by Hong et al. [23]. They also assessed the process factors, current, and speed of PAW that affect the deformation and residual stress of welded joints. Mabuwa et al. [24] investigated the mechanical and physical characteristics of welds prepared through the hybrid technique of friction stir-processed TIG joints. A fine grain structure was presented by the weld zone prepared through the hybrid technique. Lawal and Afolalu [25] reviewed the current developments in TIG and MIG advanced welding techniques. The process improvements introduced in these methods have contributed to decreasing manufacturing expenses, enhancing welding speed, and simplifying the procedure, ultimately leading to improved productivity. Dagur et al. [26] compared TIG and activated flux tungsten inert gas (A-TIG) welding methods used for the joining of SAF2507 material with 6 mm thickness plates. Physical and mechanical properties were detected after welding the specimen material. The welding of 317L austenitic stainless steel and 2507 SDSS plates with the help of the friction stir welding method was proposed by Song et al. [27]. During this process, tool rotation at 400 rpm and a welding speed of 20 mm·min⁻¹ were used to examine the surface and mechanical properties of dissimilar joints. Qi et al. [28] performed the joining of the SAF2507 material with a laser beam welding procedure. The dissimilar joining of AISI 904L and AISI 2507 materials with the help of laser welding procedures by changing laser speeds and powers was achieved by Köse [29]. Šimeková et al. [30] examined the effect of different factors like shielding gas, focusing, power, joining rate, and head oscillation on the physical and mechanical properties of SAF2507 joints made by the laser beam welding method. Wang et al. [31] investigated the keyhole PAW of the SAF2507 material with a 10 mm thickness. They evaluated the properties and the microstructure of welded joints. Cao et al. [32] studied the microstructural inhomogeneity in the SAF2507 joints fabricated by the friction stir welding method and its influence on corrosion resistance and mechanical properties. Previously, numerous investigators have used MHH to form different types of metallic joints. Singh et al. [33] conducted a review of different types of material joints fabricated using microwave energy. Nickel filler welding of SS304 and Inconel625 was performed by Kamble et al. [34] utilizing SiC as a susceptor. The study revealed that the average microhardness value was 303 ± 17 HV. XRD analysis confirmed the presence of Cr₂₃C₆, NbC, Fe₃Ni₂, Cr₂Ni₃, and Ni₈Nb phases in the joint area. Additionally, the joints showed a flexural strength value of 435 MPa and a tensile strength value of 448.6 MPa. A novel experimental set-up was utilized by Handa et al. [35] for joining Inconel625 plates by MHH at a joining time of 360 s. A microwave oven working at 2.45 GHz at 900 W was used for joining without any type of filler material. The average microhardness of 325.1 HV was measured in the joint area, indicating a 10.32% increase compared to the base material. The average UTS of 319.9 MPa was found, which was lower than that of the parent alloy. Sahota et al. [36] created SS316 butt joints with the help of the SS316 filler material by the MHH method. The microhardness of the joint was found to be 450 ± 45 HV, which was 2.05 times higher than that of the parent metal. A flexural strength of 763.59 MPa and a tensile strength of 495 MPa were found. An analytical and experimental research was conducted by Thakur et al. [37] for joining pipes of MS, with nickel filler powder at a process time of 900 s. SEM examination showed the presence of uniform and fully dense microstructure, demonstrating robust metallurgical bonding. Vickers microhardnesses of 262 ± 10 HV were found at the weld area and 240 ± 10 HV at HAZ. The ultimate tensile strength of 217 ± 8 MPa was determined. Gamit et al. [38] studied the procedure of the MHH for the purpose of joining mild steel pipes. They introduced an interface layer comprising nickel filler powder between the mild steel pipes, enabling exposure to microwave radiation. The investigation yielded the formation of dense joints, primarily attributed to the favourable metallurgical bonding that occurred between the mild steel pipes and the nickel filler powder, as evident from the SEM results. Elemental examination confirmed the presence of both nickel and an iron-rich joint. Observations of microhardness values indicated a mean value of 572 HV for the joint area, 519 HV value for the interface area, and 397 HV value for the parent material, respectively. Notably, the joint’s efficiency was found to be predominantly dependent on the duration of exposure during microwave heating. Joints developed over a processing time of 480 s exhibited higher efficiency in comparison to those formed during process times of 420 and 510 s. The dissimilar joining of SS304 and SS2205 plates utilizing SS304 filler was examined by Kumar et al. [39]. XRD examination detected the presence of various intermetallics and carbides in the weld area. SEM examination revealed that the whole melting of filler particles at the specimen interface caused strong metallurgical bonding among the joined area. The average microhardness of 515.2 HV was observed at the joint centre and was found to be higher than the joining specimens. Ultimate tensile strength of 584.15 MPa was observed. Likewise, the parametric evaluation was performed by Kumar and Sehgal [40] for the dissimilar joining of SS304 and SS2205 alloys through MHH utilizing nickel filler powder and rods of graphite act as a susceptor material. The input factors included a microwave oven functioning with 900 W, 2.45 GHz, and 16 graphite rods with a diameter of 2 mm and a length of 30 mm. Mechanical characterization results revealed an average microhardness value of 494.52 HV and a UTS value of 407.83 MPa. XRD investigation unveiled the presence of numerous carbides and intermetallics, such as FeNi₃, FeNi, CrNi₃, Ni₃C, Fe₃C, and C₂Cr₃. Physical characterization showed a strong metallurgical bond on interface surfaces without any interfacial cracking. Singh and Sehgal [41] evaluated and comprehensively reviewed the computational aspect of microwave hybrid heating (MHH), considering the various steps involved in fabricating, modelling, and simulation of the process. Singh and Sehgal [42] described in detail the heating mechanism of material classification based on microwave processing, materials utilized in joining, experimental configurations, and operating parameters of the MHH-based processing and joining of metallic samples. The microwave joining of mild steel pipes was studied analytically and confirmed experimentally by Singh and Sehgal [43], who also assessed the input factors that affect the electric field generated and operating duration. An in-depth analysis of the processing of analytical modelling was also performed.

The MHH-based experimental arrangement traditionally consists of susceptor powder (usually vertical charcoal feeder setup), refractory bricks (with different alumina content), and a separator sheet (usually graphite) as its main components. In this study, the arrangement used minimizes the level of craftsmanship essential in the conventional vertical charcoal feeder set-up. This novel configuration incorporates graphite rods as the susceptor medium, a departure from the use of charcoal powder and utilizing ceramic wool instead of refractory bricks. The utilization of graphite rods as the susceptor material obviates the necessity for a separator medium as well. Initial findings indicate a reduction in the carbon content within the weld area with the implementation of this arrangement, leading to enhanced joint properties. Ceramic wool effectively maintains higher heat than refractory bricks close to the joining area, thus reducing the processing time. The combined use of graphite rods and ceramic wool facilitates better heat generation and retention, resulting in a significant reduction in exposure time.

Furthermore, the joining set-up is better in terms of ease of assembly, reduced exposure time, reduced labour, and cleanliness. A similar experimental setup has successfully been utilized for the effective joining of Inconel625, SS304, and SS2205. Furthermore, this redesigned setup reduces the fabrication cost of the joining by eliminating the need for susceptor material. The joining of iron-based alloys holds significant industrial relevance, extending to applications in power plant steam lines, chemical and marine industries, vehicle manufacturing, and aerospace. While DSS demonstrates favourable weldability characteristics, the specific alloy SAF2507 has not undergone MHH joining previously. Consequently, in this era of rapid industrial advancement, employing MHH for joining SAF2507 could emerge as a highly advantageous process. Although various techniques have been employed for joining SAF2507, MHH joining has not been extensively explored. As a result, SDSS SAF2507 was chosen as the foundational specimen for this current investigation, aiming to explore novel opportunities for joining. Thus, the major novelty of this work lies in the first-time exploration of applying the MHH technique for joining the industry relevant SAF2507 material specimens with environmentally friendly hybrid processing by utilizing two different filler powders, namely, Ni and SS304. Furthermore, the physical properties of the joints were also examined using SEM and EDS methods, while mechanical properties were assessed through tensile and microhardness tests.

2 Experimental process and materials

Under ambient conditions, the similar joining of SAF2507 was conducted by an MHH-based method using a Samsung microwave oven operational at 2.45 GHz and 900 W. During experiments, the environmental conditions included a temperature of 37°C and a humidity of 58% under atmospheric working conditions. Nickel and SS304 filler powders were selected as filler materials. Nickel was selected due to its significant role in the joining specimens and its compatibility with specimen materials, as indicated in the literature review. On the other hand, SS304 was chosen as a filler powder because it shares the same composition as one of the specimens being joined. Upon receiving the SAF2507 plates, an ATOM COMP 81 direct analysis spectrometer was employed to determine the alloy compositions. The chemical composition of the SAF2507 material is shown in Table 1. The slurry was prepared using epoxy resin (Blumer 1450-XX) and filler powder (50-μm) in a 75:25 ratio. XRD images of the as-received nickel and SS304 filler powders are shown in Figures 1 and 2. SEM images of the as-received nickel and SS304 filler powders are shown in Figures 3 and 4. Nickel and SS304 filler powders showed a spherical morphology. Samples were cut from the received plates using (Model: Electronica Sprintcut-win) a wire-cut electric discharge machine to dimensions of 3.5 mm in width, 18 mm in gauge length, and 3 mm in thickness, ensuing ASTM E8/E8-09 standards, as shown in Figure 5. Following the cutting of the material, a similar joining of SAF2507 plates was performed.

Figure 1

XRD image of the as-received Ni-based powder.

Figure 2

XRD image of the as-received SS304 powder.

Figure 3

SEM image of the nickel (50 μm) filler powder.

Figure 4

SEM image of the SS304 (50 μm) filler powder.

Figure 5

Specimen dimensions in mm.

3 Joining process

The input parameters of MHH used in this study were as follows: 900 W microwave oven operated on 2.45 GHz, 600 s processing time, six graphite rods (as susceptor material), and 100 × 60 × 60 mm³ ceramic wool. A visual representation of the recommended strategy and the precise sequential steps integral to the ongoing study are depicted in Figure 6. In the joining process, first, the specimens were exposed to acetone cleaning and then dried in open air. Then, a paste-like slurry was made, mixing the filler material with Blumer 1450-XX. The slurry was applied uniformly as a layer among the joining surfaces arranged in a butt joint configuration. After applying the slurry on the specimen interfaces, the specimens were positioned atop the ceramic wool of 100 × 60 × 60 mm³ dimension. The graphite rods were arranged along the joining region, acting as a susceptor to initiate the interaction between microwaves and the metallic material. Additionally, another piece of ceramic wool was employed as a layer above the metallic material to fulfil both masking and insulation functions. The MHH-based joining arrangement is shown in Figure 7, and the entire setup is introduced into the microwave cavity, enabling the passage of microwaves while insulating the generated heat required for the joining process.

Figure 6

Flow chart of the microwave hybrid process.

Figure 7

Microwave oven setup for joining.

In the initial stages, the graphite rods ignited rapidly, instigating heat transfer to the workpiece through conventional means of thermal conduction. Subsequently, upon reaching the critical temperature, the metal’s skin depth expands, leading to the direct absorption of microwaves. When the skin depth of powder particles equals or surpasses their diameter, the filler powder assumes microwave absorption. As microwaves are absorbed, the powder particles undergo heating, initiating their melting phase. The molten powder particles then impart heat energy to the base metal interface. This marks the initiation of a diffusion process involving a slender section of the metallic parent material and liquefied filler powder. The audible cracking noise emerging from the microwave provided a distinct indication that the joining specimens had undergone melting, thus affirming their successful joining. Subsequently, the experimental setup was carefully extracted from the microwave oven, aided by a protective hand glove to avert any risk of burns. The heated setup was then situated in an ambient environment to initiate the cooling process and thoroughly cleaned and polished.

Determining the appropriate processing time is a crucial factor in achieving successful microwave-based material joining. Microwave processing factors used for joining are revealed in Table 2, selected based on literature review and trial experiments. Multiple trials were conducted across varying process times to establish an optimal range guided by the resultant joint quality. The microstructure of the joint area was examined for physical characterization and subjected to mechanical checks, including microhardness and tensile strength evaluation.

4 Results and discussion

Similar butt joints of SAF2507 were formed and evaluated through physical and mechanical characterization. To prepare the specimen for polishing, a range of emery paper with various grades was utilized. These grades included 220, 400, 600, 800, 1,000, 1,500, and 2,000, with 220 being the coarsest and 2,000 being the finest grade. For the attainment of a reflective finish resembling a mirror, the ultimate stage of polishing was executed using velvet cloth infused with alumina solution. To unveil microstructural characteristics, the polished workpieces were etched using Carpenter 300 series SS etchant, as shown in Figure 8.

Figure 8

Specimen surface exposed to the etching agent.

This etchant consists of 8.5 g of ferric chloride, 122 ml of hydrochloric acid, 122 ml of methanol, 2.4 g of cupric chloride, and 6 ml of nitric acid. EDS and SEM analyses were selected to physically characterize the welded joints. Microhardness and tensile investigations were also used to evaluate the mechanical characterization of the welded joints.

4.1 SEM observation

SEM micrographs were captured from multiple locations using the JSM-IT500 model and inspected at varying magnifications to analyse the grain boundary microstructure within the weld area. Figure 9 presents the SEM micrograph illustrating the fused joint region of the joint formed using nickel filler powder. The joint region displays the filler powder’s grain structure boundaries, evenly distributed and fully melted, diffusing seamlessly with the joining material. This uniform integration is attributed to the consistent and volumetric heating of the material. Both the base alloy and filler material demonstrate robust, uniform metallurgical bonding, causing the development of dense, homogeneous joints with no cracks, while the filler blends with the base material. When exposed to microwave radiation, Ni powder melts along with the thin layer at the interfaces of the joining materials. This process enables the dispersion of elements throughout the joining region, leading to the formation of metal carbide bonds that effectively bind the components together. These carbide phases are formed because of the affinity of chromium and nickel towards carbon at elevated temperatures. Thus, a specific interval of exposure to high temperatures and, subsequently slow cooling promotes the development of chromium and nickel carbides.

Figure 9

SEM image of the weld area of joint formed using nickel powder (600 s processing time and six graphite rods).

Figure 10 presents the SEM micrograph depicting the fused joint region of the joint formed using SS304 filler powder. The filler powders, evenly distributed along the grain structure boundaries, were fully melted and diffused with the parent material within the weld area. The base alloy and filler material were asserted to display robust and consistent metallurgical bonding. Consequently, when the filler is thoroughly mixed with the base specimen, it results in the formation of dense, homogeneous joints that are devoid of cracks. When exposed to microwave radiation, the SS304 powder melts simultaneously with the thin layer at the specimen interfaces. This procedure enables the dispersion of elements throughout the joining region, leading to the formation of metal carbide bonds that effectively bind the components together. Chromium carbide formation at the grain boundary zone is observed because chromium exhibits a strong affinity towards carbon at higher temperatures. These types of carbides are likely to be formed because of the distinctive cooling pattern associated with MHH. The rapid heating, facilitated by the spherical shape of the filler material, promotes the dispersion of various elements of the filler material into the joining interface.

Figure 10

SEM image of the weld area of joint formed using SS304 powder (600 s processing time and six graphite rods).

4.2 EDS analysis

Figures 11 and 12 show the joint area EDS spectrum of nickel and SS304 filler powder joint, respectively. The EDS spectra reveal the presence of various elements in the weld area, including iron, chromium, carbon, molybdenum, manganese, and nickel. These elements indicate that the base alloys underwent complete melting during the joining process, and the elements from the joining specimens were shifted to the weld area through joining.

Figure 11

EDS graph of the weld area of the nickel powder joint.

Figure 12

EDS graph of the weld area of the SS304 powder joint.

This confirmed the successful fusion of the filler powder interlayer with base metals. Notably, the percentage of carbon content in the weld area increased compared to the joining specimens. The utilization of graphite rods, acting as a susceptor, contributed significantly to this increase in carbon content, thereby enhancing the joint’s hardness by facilitating the transfer of carbon to the joint zone.

4.3 Mechanical characterization

The welded specimens were subjected to Vickers microhardness testing using a 1 kgf load for 10 s. The results, shown in Figure 13, demonstrated a notable increase in hardness values in the weld area when using Ni-based and SS304 filler powders. The average microhardness of the three joints in each category was measured, resulting in 432 HV for the Ni-based filler powder joint and 461 HV for the SS304 filler powder joint, respectively, exceeding the hardness of the base alloy. The average microhardness value for SAF2507 was found to be 255 HV.

Figure 13

Comparison of microhardnesses of welded joints.

Uniform hard metals like Fe and Cr carbides and a compact microstructure formation in the weld areas were responsible for the increase in the hardness values. The dense microstructure, rich in Cr and Fe carbides, resisted the load indentation. As observed from EDS analysis, an increase in the content of various element compositions like Cr, Ni, Mn, and Mo was also responsible for higher hardness. The EDS results indicated that the heightened hardness resulted from an increased carbon concentration in the weld area, consistent with an earlier study. Chromium, nickel, and iron carbide formation [44,45] also supported this justification. Previous research results also showed that increased carbon content was responsible for higher hardness [46,47]. To evaluate the tensile strength, a Tinius Olsen machine with a 50 kN capacity was utilized. The examination was conducted using a strain rate of 0.2 mm·min⁻¹. These micro-tensile strength assessments were performed using ASTM designation E8/E8-09 standards, using specimens of 3 mm thickness, 3.5 mm width, and 50 mm length, as illustrated in Figure 5. Each category was evaluated using three samples, and their mean value was taken into consideration. The average ultimate tensile strength was found to be 442 MPa for the Ni-based joint and 534 MPa for the SS304 joint. A comparison of Figures 11 and 12 confirms that the SS304 joint exhibits lower carbon content, which results in their enhanced ductility. The increase in the carbon increases the chance of chromium and iron carbide formation within the joint zone, consequently leading to a reduction in ductility. The presence of carbides in the joint structure hinders the flow of grains during tensile loading, resulting in decreased ductility [10].

4.4 Fractography results

After conducting tensile tests on the specimens, an additional examination was performed using SEM. Photographs of the fractured specimens of joints fabricated using various filler powders are shown in Figures 14 and 15. The test results revealed that all joints failed in the joint area. Hardness results indicated increased values in the interface area as a result of carbide precipitation, which contributed to joint failure. The specimens exhibited a mixed mode of fracture, revealing a mixture of brittle and ductile failure. The ductile fracture is detectable through its fibrous pattern with dimples marked at different sites. The existence of tear ridges is symptomatic of shear failure and displays a cleavage fracture. Initially, the load is supported by the ductile nature of the filler powder; however, as the load increases, the joint undergoes significant plastic deformation, causing the growth of micro-cracks. The brittle metallic phases at the grain boundaries perform as initiation points for these cracks. Moreover, tensile stress within the joint contributes to the propagation and expansion of these cracks. The existence of these hard phases obstructs the material from undergoing plastic deformation under load, causing shearing at the weld joint section and abrupt material failure in that portion. Brittle failure in the joint area may be particularly marked in regions where complete melting of filler material particles occurs in the interface layer during microwave joining, followed by subsequent re-solidification.

Figure 14

SEM image of the tensile fractured joint formed using nickel powder.

Figure 15

SEM image of the tensile fractured joint formed using SS304 powder.

5 Conclusion

This study involved the development of similar joints of SAF2507 using an innovative joining method based on MHH with nickel and SS304 filler powder. Furthermore, the mechanical and physical characterization of the welded joints were tested. The principal findings are the following:

• The suggested method offers a clean process compared to the former MHH method, as it does not involve the use of charcoal powder. The combined utilization of ceramic wool and graphite rods enhances heat capacity and holding, respectively, leading to a notable reduction in the processing time. This shortened joining time increases productivity and reduces energy consumption.

• SEM investigation showed the successful fusion of the specimen joints, revealing the weld area with no cracks. Both the base alloy and filler material demonstrate robust, uniform metallurgical bonding, resulting in the formation of dense, homogeneous joints devoid of any cracks, while the filler blends with the specimen base material.

• The EDS spectra reveal the presence of various elements in the weld area: iron, chromium, molybdenum, manganese, nickel, and carbon. These elements indicate that the base alloys underwent complete melting during the joining process, and the elements from the specimens were transported to the weld area through joining. Notably, the carbon content in the weld area increased compared to the joining specimens. Hardness values increased in the weld area because of high carbon content, as inferred from the EDS results. Higher carbon content results in the formation of several carbide phases of Cr, Ni, and Fe during joining.

• The joint region revealed an average value of microhardness of 432 HV for the Ni-based joint and 461 HV for the SS304 joint, which is better than that of the parent alloy. The elevated carbon content in the weld area was responsible for the increased microhardness. Also, the average tensile strength was calculated to be 442 MPa for the Ni-based joint and 534 MPa for the SS304 joint. The hardness of SS304 filler joints was 6.71% higher than that of the Ni-filler joints. Furthermore, the tensile strength of the SS304 filler joints was 20.81% better than that of the Ni-filler joints.