Study on mechanical and micro structural properties of spin arc welding in Hastelloy C-2000

: Nickel-based Hastelloy C-2000 is widely used in the aerospace, chemical, and medicinal sectors. Investigating the potential efficacy of the spin arc welding process on Hastelloy C-2000 was the main focus of this study. In spin arc welding the centrifugal force has been obtained in the fusion zone, thus the weldbead quality increases. Weld current, rotating speed, and spin diameter are all separate parameters used in the welding procedure. The microstructural investigation was carried out using optical microscopy, X-Ray Diffraction (XRD), and field emission scanning electron microscopy (FESEM). The mechanical characteristics of the welded specimens were examined closely. Spin Arc Welding ultimate tensile strength (UTS), hardness value (HV), and impact experiments were compared to those of the Multi-pass Pulsed Current Gas Tungsten Arc welding method (MPCGTAW). In 27 tests, increasing the current and rotating speed resulted in greater penetration depth and weld height. The width of the weld was found to be a little high, with a spinning diameter of 2 mm. In comparison, samples 5 and 15 were found to have better hardness, tensile strength, and toughness, especially with suitable welding parameters such as current (120 I and 140 I), speed (1800 rpm), and spin diameter (2 mm and 3 mm). A microstructural study showed no grain segregation, contributing to the material’s increased hardness and tensile strength. The novel findings of the present study suggest that spin arc welding might be superior for various Hastelloy C-2000 connections that might have great applications in industries.


INTRODUCTION
Hastelloy C-2000 is widely used in the chemical industries, aeronautical, oil refining, industrial food sectors and anti-pollution systems.Alloy C-2000 outperforms common alloys like C-276 and can be used in place of alloy C-276 in many applications.It contains 1.6% copper, which is not present in alloy C-276 (Vara Prasad et al., 2018).Hastelloy C-2000 has stronger mechanical and corrosion-resistant qualities, which allow it to be used for more applications (Hao et al., 2021).Nickel, chromium, molybdenum, and a trace of copper compose the majority of the elemental composition of alloy C-2000C- (Arulmurugan et al., 2021a)).The C-2000 alloy's outstanding corrosion resistance was due to its high Mo concentration, which can hinder corrosion growth and spread (Zhang et al., 2013).Previous study indicated that the evaporation rate of Mo oxides is extremely fast over 725 °C, resulting in Mo element consumption in the composite (Birks et al., 2006).Due to its remarkable performance in highly corrosive environments, the Hastelloy C-2000 alloy is a particularly interesting candidate material for high-temperature flue gas filters (Mcdaniel et al., 2011;Li et al., 2013).A vessel constructed of the alloy C-2000 may carry both oxidizing and reducing elements at the same time.It resists cracking, pitting, and stress corrosion cracking well (Pathak et al., 2020).Alloy C-2000 may be welded using standard welding techniques.When traditional arc welding procedures such as TIG and MIG welding are performed, an excessive amount of heat is provided, greatly increasing the area of the heat-affected zone.More heat input results in a lesser depth of penetration (Prajapthi et al., 2018).The mechanical qualities of a weldment are impacted not only by the composition of the parent metal but also by the weld bead geometry (Ma et al., 2011).The bead on plate weld is a crucial feature of weld geometry, influencing chemical composition and the flux consumption rate of the weld zone and then determining the different mechanical properties of the weldment (Naffakh et al., 2009).
The width of the weld bead is well recognised as a critical element influencing the geometrical characteristics of the weldment.The quality of the weldment is determined by satisfying requirements such as the geometry of the weld bead, which is impacted by various welding process parameters (Qiu et al., 2020).It is probable that, for the examined set of input parameters, as current depths of penetration and reinforcement height grow, the weld bead width will increase to compensate for the increasing volume (Choudhary et al., 2011).The intermetallics topologically close pack (TCP) phases, also known as Frank-Kasper (FK), promote hot cracking and early failure in weldments.The observed TCP phases are predominantly caused by the segregation of the alloying elements Mo and Cr (Manikandan et al., 2014).From the observed research, the alloy C-2000 has good weld mechanical characteristics and microstructure, utilising autogenous and Morich filler (ERNiCrMo-4) (Liu et al., 2022).In both cases, the Cr-rich secondary TCP phases were found near the interdendritic area of the weld joints.As a result, mechanical characteristics deteriorated (Singh et al., 2023).The production of secondary, brittle, and TCP phases during solidification is the main disadvantage of combining Ni-Cr-Mo alloys.During a eutectic reaction, most pure alloying elements surpass their solubility limits, causing the interdendritic area to separate (Arulmurugan et al., 2021b).Improving the welding speed minimises the decomposition of the filler metal and the heat input per unit length of the weldment, resulting in smaller weld bead widths and weld reinforcement (Khanna and Maheshwari, 2016).Because of the heat energy transmitted to the base metal from the arc, weld bead width shrinks as welding speed increases (Mistry, 2016).Hastelloy C-2000 has superior properties and has undergone a variety of welding procedures.Gas tungsten arc welding (TIG) is an arc-based joining technology that creates an arc between a workpiece and a non-consumable tungsten electrode (Arulmurugan and Manikandan, 2018;Han et al., 2020).Spin arc welding is used to increase the productivity and quality of welding methods; it is also known as rotational arc welding.It is a welding technique that employs a one-of-a-kind welding gun and control system (Pathak et al., 2020).The welding procedure is mostly carried out using gas metal arc welding (GMAW) with solid wires.In the industrial aspects of Hastelloy C-276, welding techniques such as gas metal arc welding (GMAW), gas tungsten arc welding (GTAW) and activated flux-TIG (A-TIG) welding are widely utilised (Yuquan et al., 2014;Singh et al., 2013).To enhance the microstructure of the welding zone, the process parameters are modified.To improve the quality of weldments with no secondary phases visible in the welding zone microstructure, electron beam welding and pulsed laser welding are used (Ahmad et al., 2005).The spin arc welding technology intend to increase productivity by reducing the process duration and energy consumption in a corrosive environment (Câmpurean et al., 2023).
To eliminate hot cracking, many methods such as pulsed current GTA, laser beam welding, and electron beam welding are utilised.Nonetheless, Spin Arc welding is a promising method in terms including both cost and effectiveness.The spin arc welding with bead on weld of Hastelloy C-2000 in-depth experiments were executed at minimal level to the researchers' knowledge.This research looks at the macro and microstructures of the weld interface, heat-affected zone (HAZ), and base metal.Several testing methods have been used to determine mechanical qualities such as hardness, tensile strength, and impact.The grain distribution in the weld zone and HAZ was analysed using FESEM.Also, the weld samples high intensity peak was determined using X-ray diffraction (XRD) analysis.The operations were performed with the following distinct parameter variations: speed, current, and spin diameter.Tensile strength, hardness, and impact strength were evaluated, and metallurgical characteristics were examined using an optical microscope and a FESEM.
Investigating the potential efficacy of the spin arc welding process on Hastelloy C-2000 was the main objective of this study.

MATERIALS AND METHODS
The Spin Arc welding was used for welding a Hastelloy C-2000 hot-rolled plate at a thickness of 2 mm.And the dimensions of the plate are 130×55×2 mm 3 by using the filler ERNiCrMo-04 with a diameter of 1.2 mm.Table 1 show the welding parameters used during the procedure.Throughout the weld shown in Table 1, a constant travel speed of 300 mm•min -1 was maintained.The Argon gas was delivered at a flow rate of 15 litres per minute for shielding and the back purging procedure.On each pass, a metal wire brush was utilized to remove the contaminated oxide layer on the welding zone.Figure 2 in the ASTM standard for mechanical and metallurgical characterization depicts similar workpieces cut in the EDM process.

Metallurgy and Microstructure
The weld dimension of 10x10x2 mm was metallographically characterised, along with the normal direction of the weld joint.The polishing was carried out through three stages, with the first stage including the use of an emery sheet with grades ranging from 220 to 2000 grid.The second stage was completed using a disc polishing machine with water and alumina powder.The final stage of polishing used electrolytic cleaning with an oxalic acid solution.The Optical Microscope (OM) and FESEM (Carl ZeisEigma TM equipment with 5kV and 10X -1,000,000X magnification) were used to evaluate the microstructure of beads on welds.The X-Ray Diffraction test was used to identify crystal structural refinement and second phase and in the normal area of the fusion zone.Figure 1 depicts the entire experimental setup, which includes a wire feeder, shielding gas feeder, spin arc torch, and current supply.

Mechanical properties
The Vickers hardness test, the ultimate tensile strength test, and the Charpy impact test were used to determine mechanical strengths such as hardness, tensile strength, and toughness.Together with the weld bead, the testing coupons were moving in the cross-sectional direction.The tensile strength was determined using the Universal testing machine (UTM) and an extensometer.Table 2 shows the mechanical characteristics of the base metal.
The hardness of the weldment zone was measured using the Wolpert Wilson Vickers 452-SVD machine.The indenter was constructed of a diamond in the shape of a square pyramid.A conventional load of 500 g of force was given to a square pyramidal diamond indenter over the course of 20 seconds, at regular intervals of 2 mm.The experiment was repeated for each of the 27 samples.Figure 3 (a-b) also depicts the bead on plate weld joint workpiece that was utilised in this study.The Charpy V-notch test was employed to determine the overall energy absorbed in a weldment bead during the breakage.The V-notch was designed with a 45 o angle to carry the impact weight.The arm length in this test was 825 mm, the pendulum weight was 20.932 kg, and the pendulum release angle was maintained at 140 o .In the merely supported state, the specimen's notch was positioned opposite the striking edge.To confirm the outcome and compute the average data, the measurements were tested several times.

Macrostructural examination
The macro structural evaluation gave the penetration depth, width, height, and excess penetration, which are displayed in Fig. 4 (a-d) and Table 3.The grain size measurement and macrostructural analysis of comparable joints showed that all of the joints were effectively welded.Various welding parameters were employed to generate a similar weld, and the results were compared to another sample.Out of 27 samples, the Sample 5, and sample 15 had better penetration depth 2.493 and 2.450 mm, bead width 6.943 and 7.959 mm, bead height 4.687 and 4.887 mm and excess penetration 0.399 mm and 0.367mm with a current 120 and 140 I, speed 1800 r.p.m and spin diameter of 2 and 3 mm at constant travel speed of 300 mm•min -1 .There are no defects or cracks in the fusion zone or heat-affected zone of the weldments, and there is minimal excess penetration.The image and Table 3 shows the macrostructure and macrostructure interpretation of comparable weldments.A Dyni-lite digital microscope was used to capture macrostructure features of weldments.Additionally, the filler rod indicated that we employed the ERNiCrMo-04 filler material to accomplish   improved fusion and full penetration, resulting in a good base metal.The microstructure displayed the weldment's breadth and depth based on the various factors.A microscope was used to capture the macrostructural features of the weldments.

Optimal microstructure examination
The image depicts the optical microstructure analysis of Hastelloy C-2000 similar bead on plate welded joints.The weld zone microstructure is made up of equivalent dendrites, cellular grains, columnar dendrites, and columnar grains.The weld zone microstructure has fine equiaxed dentrities.The grain rough located adjacent to the heat-affected zone will be seen in the microstructure of alloy C-2000.Figure 5(a-m) depicts four distinct zones: base metals, heat-affected zones (HAZ), weld interfaces, and weld zones.The different tested sample microstructures are depicted in Fig. 5, with details exhibited at 100X magnification.The tiny grain size and dentition will be plainly seen under the microscope.The bead on plate welding will be performed using various parameters such as current, spinning speed, spinning diameter, and travel speed.In comparison to the other examples, samples 5 and 15 were picked as the best since they were devoid of faults and cracks.The macrostructure examination (refer to Fig. 4) and macrostructure interpretation (refer to Table 2) were similar to the optical microstructure (OM) images.Additionally, it is consistent with improved grain size and dispersion being seen up to samples 5 and 15.Beyond samples 5 and 15, there are columnar dendrites and uneven grain development.As a result, it largely decreases the mechanical strength of joints.

Hardness test
The fusion zone has a somewhat greater average hardness rating than the basic metals.The enhancement is due to the presence of finer equiaxed grains in the weld zone.This is due to the fact that filler wire contains additional alloy elements that drive the solution-strengthening impact.The mean hardness values of the alloy C-2000 were determined and compared to the welded samples' least and highest values.Samples 5 and 15 have a higher hardness value because of their finer equiaxed grains.Also, it has higher tensile and impact strength compared to the remaining samples.Similarly, sample 22 hardness rating was deter-mined to be an intermediate value, with fine equiaxed grains.Table 4 shows that sample 3 has a lower hardness value due to its inadequate equiaxed grain size.These changes in hardness value are generated by varying welding parameters (shown in Table 1).The hardness of the weld bead is steadily increases in the HAZ, reaching its maximum value at the weld FZ.The hardness value is measured at a certain distance (2 mm) from the left, right, and FZ (fusion zone) of bead on plate weldments.

Tensile test
In this research, the tensile test results of weldments were achieved in this study by employing universal testing equipment under certain loading condi-tions.By establishing a weld microstructure with an equiaxed grain pattern, the mechanical properties of various coordinate axes of X, Y, and Z will be similar in all three directions.It also maintains isotropic characteristics.Because of the existence of a high quantity of fine equiaxed grains size in the FZ of bead on weld, the tensile strength has been improved.Similarly, the spacing between dendrite arms is maintained equally in all directions.Fine equiaxed grains are more ductile than columnar grains.As a result, fine equiaxed grains can deform rapidly while resisting contraction stresses.As a result, equiaxed grains prevent FZ failure and can sustain tensile loads well.In this study, of the 27 samples, sample 5 and sample 15 had the highest UTS (refer Fig. 6).Because of the higher hardness values of the samples the ultimate

Impact test
The Charpy V-notch test was used to determine the impact toughness of the weldments.These ex-periments were carried out to determine the impact values for a bead on plate weld of alloy C-2000.The impact values in Joules (J) were acquired from the test.Moreover, this test was carried out at ambient temperature.Of the 27 samples, samples 5 and 15 are the best; as compared to alloy C-2000, the toughness of welded FZ is 23.68% lower.This is because to a lack of alloying element microsegregation at both bead weld interfaces and FZ.It also withstands impact loads well because to the existence of equiaxed grains with fine microstructures.As compared to the MPCGTAW-ERNiCrMo-17 approach, the toughness of samples 5 and sample 15 is 5.9% higher.It has high impact strength, as demonstrated in Fig. 7, and performs better in all other strength tests, including the tensile strength test and the hardness test (see Fig. 6 and Table 3).It also contains fine equiaxed grains.The observed tensile and impact strength data have been compared to earlier studies, as shown in Table 5.     age grain size of the bead on weld of sample 5.The XRD analysis will reveal the high-intensity peaks (Ni-Cr-Co-Mo) and (CoCx) of the welded zone.The elemental development and precipitates (Ni, Cr, Co, and Mo) will increase the performance of the bead on the weld and prevent cracks from forming in the fusion zone.These precipitates keep them from expanding and shattering.The segregation of molybdenum and chromium-rich precipitates is not apparent in XRD results.The XRD investigations are repeated for the twenty-seven samples and compared to one another in order to choose more effective work settings.In comparison to the other twenty-seven samples, samples 5 had average grain size and phase composition values.

XRD analysis
The results reveal that a crack-free weld increases the strength of the samples.It is believed that the Spin Arc Welding parameter does not allow for the segregation of molybdenum and chromium-rich components in interdendritic areas.This is due in part to the Spin Arc Welding minimal heat input, rapid cooling rate, and considerable thermal gradient.

FESEM analysis
The FESEM analysis is carried out at the best magnification ratio possible, and a grid matrix is started to obtain current FESEM pictures in various areas.The Fig. 9(a-h) shows a higher magnification FESEM micrograph of the bead weld fusion zone used in the investigation.Figure is shown bead weld FZ with exquisite equiaxed dendritic structure.The necessary elemental values (Ni, Cr, Co, Mo, and CoCX) are found at the bead on weld unique zone, and the welding zone has a fine columnar and equiaxed dendritic structure.FESEM was used to examine the lack of a secondary topologically closed packed (TCP) phase at the weld centre.There is no evidence of a significant secondary TCP phase in the interface region between the similar alloy C-2000 and the bead on the weld.This indicates that there is no hot cracking and no defects are present in the bead on plate welds.Samples 5 and 15 are chosen as the best in Spin Arc Welding because of their low level currents (120 I and 140 I), medium spinning speed (1400 rpm), and small spin diameters (2 and 3 mm), which have greater mechanical qualities and more evenly distributed grains than the other welding parameters.The spin arc energy may be successfully exploited to join the targeted region in a short period by conductivity into the base metal.Due of the decreased rapid cooling rate and heat input, the weld interface and fusion zone do not have enough time to separate the alloying components.

CONCLUSION
Selective parameters including current, spinning speed, and spin diameter were used to create a defect-free weld on a Hastelloy C-2000 bead using spin

Figure 1
Figure 1 Experimental set-up of Spin Arc Welding.

Figure 3 .
Figure 3. (a) C-2000 Bead on plate weld joints; (b) Different zones in C-2000 Bead on plate weld joint.

Figure 5 .
Figure 5. C-2000 Microstructural Examination in interface of right side, left side and weld zone in the sample 3 (a, b, c); sample 5 (d, e, f); sample 15 (g, h, i) and sample 22 (j, k, m).
be enhanced upto 7.9% compared to MMPCGTAW-ERNiCrMo-17 weldment.The fusion zone tensile properties will be improved by the reduced heat input, increased cooling rate, and the absence of microsegregation, resulting in a finer microstructure.The development of Mo-rich secondary phases in the interdendritic zones indicates a reduction in the strength and flexibility of the weld joints during spin arc welding FESEM fractography has revealed the ductility of the tensile fractures by exhibiting a significant number of micro-voids with ductile tearing ridges that should have failed due to crystallisation mechanism failure.Moreover, the development of more micro-voids with long dimples and lower cleavage facets indicates a ductile mode of failure.The dimension of the ductile dimple varies in each sample used for fractography.

Figure 8
Figure 8 depicts the use of X-ray diffraction (XRD) to assess the phase study composition and the aver-

Figure 8 .
Figure 8.The XRD analysis of the sample 5

Table 1 .
Parameters of welding

Table 5 .
Comparative análysis of Tensile and impact strength