Influence of Beam Power on Structures and Mechanical Characteristics of Electron-Beam-Welded Joints of Copper and Stainless Steel

Abstract

In this study, we present the results of electron-beam welding of joints with 304-L stainless steel and copper. The influence of the beam’s power on the structures and mechanical properties of the welded joints was studied; the experiments were realized at a beam deflection of 0.3 mm to the Cu plate and beam powers of 2400, 3000, and 3600 W. The phase compositions of the obtained welded joints were studied by using X-ray diffraction (XRD); the microstructure and chemical composition were investigated by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), respectively. The mechanical properties were studied by using tensile experiments and microhardness investigations. The phase compositions of the welded joints were in the forms of substitutional solid solutions between Fe, Cu, and pure copper and remained unchanged in terms of power. It was found that the microstructures changed gradually with the application of different values of the power of the electron beam. The results of the tensile tests showed higher tensile strengths at lower beam powers (i.e., 2400 and 3000 W) that dropped at 3600 W. The relative elongations rose with increases in the power of the electron beam. Moreover, it was found that the microhardnesses strongly depended on the applied technological conditions (defined by the electron beam’s power) and the corresponding microstructures of the welded joints.

1. Introduction

Copper and copper alloys, as well as all varieties of stainless steel, are materials widely used for many applications. Cu and its alloys are widely used in aerospace, microelectronics, etc. due to their excellent thermal and electrical conductivities and good ductilities. At the same time, stainless steel has a high strength and durability and can be applied in a number of industrial branches, such as automotive and aircraft construction, shipping containers, and refuse vehicles. Additionally, stainless steel is a non-corrosive and rust-resistant type of steel. In this sense, the welding of these dissimilar materials can be beneficial and can have a number of practical applications. Joints of Cu and stainless steel are characterized by high electric and thermal conductivities, light weights, and uses in the fields of heat exchange and the nuclear and chemical industries, etc. [1,2] However, the joining of the discussed metals and alloys has many problems related to their different physical and chemical properties, including their melting points, thermal expansion coefficients, thermal conductivities, and so on. Furthermore, joints between Cu- and Fe-based materials can have deteriorated mechanical properties [3,4,5,6].

Different technological methods are used for welding and joining dissimilar materials [7,8], such as laser-beam welding [9,10], arc welding [11,12], friction-stir welding [13,14], and electron-beam welding [15,16,17]. Electron-beam welding (EBW) has a number of advantages over other techniques for welding dissimilar materials. Such advantages include the ability to obtain a homogeneous molten pool due to a high rate of heating materials and quickly reaching the different melting temperatures of the dissimilar metals; a lack of gases in welds due to vacuum technology, which leads to good plastic properties; and a narrow and deep weld, which allows for the welding of dissimilar materials with great thicknesses [18]. In a study [19], an overview of the possibilities for welding dissimilar materials using the EBW method was presented. It was reported that the weldability of copper and iron is “probably acceptable (complex structure may exist)” [19].

Results on electron-beam-welded joints of copper and steel as well as steel and copper alloys at different EBW parameters were reported [15,16,17,20,21]. We successfully obtained samples of electron-beam-welded copper and stainless steel at various technological conditions while studying the levels of residual stresses in these samples using the neutron-diffraction method [22]. The authors of [16] reported results on the electron-beam welding of Cu with three different austenitic stainless steels, namely 304-L, 304, and 316-L, using different technological conditions for the welding procedure. The conditions were optimized in order to achieve full penetration. The results showed heterogeneous microstructures in all cases due to a poor mixability of the materials caused by a high cooling rate [16]. Kar et al. [20] applied beam oscillation during the EBW of Cu and 304 SS. They evaluated the effects of beam oscillation with different diameters through analyses of microstructure, hardness, and tensile property tests. The authors found a better mixing of copper with SS under beam oscillation, which led to an improvement in some of the mechanical characteristics of such joints. In another study [21], the microstructures of electron-beam-welded specimens of Cu and 304L SS were investigated. The technological conditions were optimized to obtain full penetration welds. The authors did not find any pores or cracks but obtained non-equilibrium copper-rich phases that may pass toward an equilibrium microstructure during service and worsen the mechanical characteristics and behaviors of the joints. Guo et al. [15] studied the influence of beam offset on the characteristics of joints of copper and stainless steel carried out via EBW. The results showed that a small beam offset leads to the formation of a strong joint with a narrow heat-affected zone (HAZ) and a fusion zone with few defects. A large offset leads to a low joint performance. Our previous investigation [23] showed that the electron-beam welding of Cu and 304-L stainless steel with a beam offset of 0.3 mm toward a Cu plate leads to the best plastic properties of such a welded joint.

Considering the above literature review, it is obvious that the electron-beam welding of copper with stainless steel is a very promising technology for joining these materials, for which the applied technological conditions are of major importance. However, the electron-beam welding of 304-L stainless steel with Cu at different powers of electron beams and at a constant offsets to copper sides are currently less well investigated than other methods. Therefore, the aim of the present study was to investigate the influence of electron-beam power on the structures and mechanical properties of welded joints of 304-L stainless steel and copper formed by electron-beam welding at constant offsets toward Cu substrates. The results obtained in this study give new knowledge on the influence of the technological conditions of the welding procedure on the resultant structure of such a weld as well as on the structures–mechanical property relationship.

2. Materials and Methods

Plates of copper (with impurities of 99.5%) and AISI 304-L stainless steel were welded. The chemical composition of the steel was as follows (wt %): 0.03% C, 1.52% Mn, 0.19% Si, 0.03% P, 0.03% S, 17.70% Cr, 8.30% Ni, 0.10% N, and Fe–Bal. The dimensions of the plates were 100 mm $\times$ 50 mm $\times$ 8 mm. Before welding, the Cu and the 304-L SS plates were mechanically polished, and the flatnesses of the welded surfaces were in the range from 0.01 to 0.02 mm.

The scheme of the EBW is shown in Figure 1. EBW was carried out on the Evobeam Cube 400 welding machine (Evobeam GmbH, Nieder-Olm, Germany). The technological conditions of the EBW process were the following: accelerating voltage U = 60 kV; welding speed v = 0.5 cm/s; and beam currents I₁ = 40 mA (Sample 1), I₂ = 50 mA (Sample 2), and I₃ = 60 mA (Sample 3), corresponding to beam powers of 2400 W, 3000 W, and 3600 W. In this study, a beam offset of 0.3 mm to a copper side was used. The discussed technological conditions were optimized in order to reach a welded joint with sufficient penetration and strength. The experiments were realized in a high-vacuum state. The working pressure was 4 × 10⁻² Pa. During the welding procedure, the specimens were welded along the y-axis.

The X-ray diffractometer Bruker D8 Advance (Bruker Corporation, Billerica, MA, USA) was used for phase analysis of the welded joints. The applied analysis method was coupled two theta using Co Kα radiation with wavelength of 1.78897 Å and line focus orientation. The range of the research was from 40° to 125°. The X-ray generator current was 40 mA, and the voltage was 35 kV. The step size and the time for the step were 0.05° and 0.25 s, respectively.

The structures of the welded specimens were investigated by using scanning electron microscopy (SEM, LYRA3 I XMU, Brno, Czech Republic) with back-scattered electron scattering. Energy-dispersive X-ray spectroscopy (EDX, Quantax 200, Bruker, Billerica, MA, USA) was used for the determination of the distribution of chemical elements in the fusion zone and near it.

The mechanical properties were examined by using a machine for static and dynamic tests: Zwick Vibrophore 100 (Zwick/Roell, Ulm, Germany). The test was performed in accordance with the ISO requirements 6892-1 Method B. Tensile specimens welded at different powers of the beam were tested, and for comparison, samples made of pure copper and 304-L SS were investigated.

The microhardness experiment was executed on a semi-automatic microhardness tester: Zwick/Indentec–ZHVμ-S (Zwick/Roell, Ulm, Germany). Metallographic cross-sections of specimens were made of welded materials in the transverse directions of the welds. The line along which each microhardness was measured was located at the middle depth of the weld seam. A load force of 0.49 N was used for all experimental points.

3. Results and Discussion

According to a binary Fe–Cu phase diagram, both materials can exist in the forms of a limited solid solubility of iron in copper and of copper in iron above 600 °C. No intermetallic phases exist. This limited solid solubility can be explained due to very close lattice parameters, atomic radii, and the same types of crystalline lattices [24].

Figure 2 presents the XRD patterns of three welded samples and of the separate initial materials. Due to the close atomic radii of copper and iron, a substitutional solid solution between both materials was formed during the solidification of the molten materials. These results were consistent with those obtained by the authors of [15,25], which showed the welded joint between Cu and 304-l SS is mostly in the form of a solid solution. During the electron-beam procedures, the cooling rates were very high and the solid solutions formed during the welding remained stable at room temperature as well. The peaks corresponding to the phase of γ-iron and copper were clearly visible at around 51°. The next peak at about 52.5° corresponded to α-iron. Both γ-iron and Cu are characterized by a face-centered cubic (fcc) structure, while α-Fe a body-centered cubic (bcc) structure. The formation of an α phase of iron during the EBW process is associated with dendritic liquation. The affinities of the alloys to dendritic liquation can be influenced by changes in and the types of the elements within the alloys or the cooling rates during the manufacturing, heat treatment procedures, etc. [26]. In the present case in particular, the EBW process was characterized by a very high cooling rate, which could be a reason for the dendritic liquation and the formation of the alpha phase. No peaks corresponding to intermetallic phases could be observed, meaning that the welded joints were in the forms of solid solutions between Cu and Fe as main phases as well as second-phase structures of copper in all considered cases. The experimentally obtained diffraction patterns did not show changes in the phase compositions of the considered specimens, meaning that beam power does not lead to a transformation of this structural characteristic. Therefore, some dissolution between both materials occurred in the melted states, and during the solidification and cooling, some copper particle precipitated from the steel as well as some fine steel particles formed in the copper regions [27]. In addition, each of the three samples had a different ratio between the peak associated with the γ-iron and that associated with the copper. For Sample 1, the copper peak as higher; for Sample 2, the γ-iron peak was higher; and for Sample 3, both peaks were equal in height. The application of the lowest beam power of 2400 W led mostly to the melting of the copper, and a very small amount of molten steel could be observed. In this case, the beam power was not high enough to melt a large amount of the SS, and therefore, a very small quantity of a Fe–Cu solid solution was expected to form within the welded joint. It would consist mostly of pure Cu. At the higher values of power of 3000 and 3600 W, a significant amount of the SS material was melted, meaning that the amount of the solid solution between Fe and Cu was expected to increase. Therefore, the peaks corresponding to (111) of gamma-Fe would rise with an increase in the beam power. These statements were consistent with our results, in which the diffraction maximum of γ-Fe had the lowest intensity in the case of the electron-beam welding at 2400 W, and it rose with increases in the beam power of 3000 and 3600 W. Moreover, a shift in the diffraction maxima to a lower Bragg angle position could be observed, which could be associated with the presence of residual stresses as a result of the welding process [28]. Nevertheless, in all the considered cases (i.e., the welded joints and non-welded Cu plate), the peak positions of (111) Cu were in the range from 50.9659 to 51.0660. Similarly, the locations of the (111) γ-Fe peaks for all the investigated samples (i.e., the welded joints and non-welded SS plate) were from 51.3665 to 51.4666 at the 2θ scale. This very small deviation in the positions of the discussed diffraction maxima corresponded to the presence of a very small amount of residual stress. It should be noted that the existence of residual stresses, etc. are typical for welds formed by high-energy fluxes, such as electron-beam welding, due to the non-equilibrium character of such processes.

Cross-sectional SEM images of the sample welded by a beam power of 2400 W are shown in Figure 3. The specimen was cut along the z-axis perpendicular to the y-axis. The chemical composition of the obtained joint was studied by using EDX experiments, and the results are presented in Figure 3d and

Table 1. Chemical composition of each point marked on SEM images of Sample 1.

Element, wt. %	Point 1	Point 2	Point 3	Point 4	Point 5
Cu	89.53 ± 2.4	56.71 ± 1.3	13.39 ± 0.4	93.34 ± 2.5	92.78 ± 2.6
Fe	5.61 ± 0.2	30.58 ± 0.7	65.44 ± 1.5	3.51 ± 0.1	4.15 ± 0.1
Cr	2.56 ± 0.1	8.85 ± 0.2	16.37 ± 0.4	1.11 ± 0.1	1.14 ± 0.1
Ni	2.30 ± 0.1	3.86 ± 0.1	6.05 ± 0.2	2.05 ± 0.1	1.93 ± 0.1

. A detailed SEM image with a higher magnification (Figure 3b) of the interface between the fusion zone (FZ) and the stainless steel (SS) exhibits a narrow area of a solid solution between the Fe and Cu as well as undissolved Cu particles. Moreover, a wide area of molten copper can be observed within the fusion zone. This means that the joint consisted almost entirely of copper and a very small amount of SS. This could be attributed to the relatively low beam power, which was not high enough for the melting of the steel [29]. The SEM image presented in Figure 3c shows the structure of the copper after the welding process, in which a large number of pores are observable. The aforementioned attribution was confirmed by using the EDX experiments, in which it was shown that the amount of copper within the fusion zone remained relatively unchanged in comparison with that in the welded Cu plate. The measured average grain size within the welded joint was 1.640 ± 0.438 μm.

Figure 4a,b presents cross-sectional SEM images of the joint obtained by using a beam power of 3000 W. The specimen was cut along the z-axis perpendicular to y-axis. Figure 4a shows the whole weld, while Figure 4b exhibits a higher-magnification micrograph of the fusion zone. The chemical composition within the fusion zone was studied by using EDX, and the results are shown in Figure 4c and

Table 2. Chemical composition of each point marked on SEM images of Sample 2.

Element, wt. %	Point 6	Point 7
Cu	90.15 ± 2.2	31.13 ± 0.7
Fe	5.75 ± 0.2	51.41 ± 1.0
Cr	1.53 ± 0.1	12.41 ± 0.3
Ni	2.57 ± 0.1	5.04 ± 0.1

. It was found that the joint was mostly in the form of a solid solution between iron and copper as well as globular particles of undissolved copper. In this case, the beam power of 3000 W was enough to melt a significant amount of the stainless steel, and after the solidification of the molten material, a solid solution between iron and copper was formed [29]. The obtained results show that the Cu particles were relatively homogeneously distributed within the fusion zone, confirming the higher degree of homogeneity of the welded joint. At the electron-beam welding, an intense Marangoni convection existed for which higher values of the beam power lead to greater temperature gradients within the molten material and better melt homogenizations [30]. A higher-magnification SEM micrograph of the weld (Figure 4b) shows an absence of cracks, pores, and other structural defects. The average grain size measured within the welded joint was 2.052 ± 0.687 μm.

Cross-sectional SEM images of the specimen electron-beam welded at a beam power of 3600 W are presented in Figure 5. The specimen was cut along the z-axis perpendicular to the y-axis. The chemical composition of the fusion zone was studied by using EDX experiments at different points, which are indicated in Figure 5b,c, and the results are summarized in

Table 3. Chemical composition of each point marked on SEM images of Sample 3.

Element, wt. %	Point 8	Point 9	Point 10	Point 11
Cu	90.25 ± 2.0	21.07 ± 0.5	93.00 ± 2.5	35.96 ± 0.9
Fe	5.98 ± 0.2	60.12 ± 1.3	4.12 ± 0.2	48.58 ± 1.1
Cr	1.80 ± 0.1	14.23 ± 0.4	1.10 ± 0.1	11.59 ± 0.3
Ni	1.97 ± 0.1	4.58 ± 0.2	1.78 ± 0.1	3.87 ± 0.1

. Moreover, the element distribution from the SS to the copper side within the fusion zone was studied, and the results are presented in Figure 5d. It is obvious that the fusion zone consisted of two separate zones, indicated as A and B (Figure 5a). According to the results obtained by using the EDX experiments, both areas were in the form of a double-phase structure. Considering zone A (i.e., the zone near the stainless steel), one can see it consisted of a double-phase structure of a solid solution between Fe and Cu and of undissolved Cu particles. The average grain size measured within zone A of the welded joint was 2.200 ± 0.610 μm. Considering zone B, one can see it was in the form of a double-phase structure of pure copper (point 10 from Figure 5 and Table 3) and a solid solution between Fe and Cu (point 11 from Figure 5 and Table 3). The formation of two distinguished areas within the fusion zone can be attributed to the differences in the thermophysical properties of the welded materials. The beam power of 3600 W was enough to melt the stainless steel and copper, during which Cu melted first, and when the temperature of the molten materials reached the melting point of SS, the steel also started melting. The two different zones obtained within the fusion zone solidified for different times due to their different thermophysical properties, which could be the main reason for the formation of two separated areas. The rise in the power of an electron beam leads to an increase in the heat input and a higher temperature achieved. This leads to a higher miscibility between the elements within the welded joint. Furthermore, the temperature gradient is much higher, causing intense convective Marangoni flows, which are responsible for the distribution and homogenization of the elements within a fusion zone. A larger amount of a Cu element was introduced in zone A of the joint. The previous statements are in agreement with the results obtained. It is obvious that the application of the highest beam power led to a more homogeneous elemental distribution within zone A and a larger amount of Cu precipitates within the Fe–Cu solid solution.

The formation of undissolved particles and inhomogeneous structures during electron-beam welding can be attributed to the applied technological conditions of the welding procedure. Convective flows, which are formed due to the high-temperature gradient within a molten material, are the main mechanisms by which the homogenization of the structure and element distributions in a welded joint occur. However, the results obtained in the present study show large numbers of Cu particles as well as copper-rich and iron-rich areas within the fusion zones. This means that the solidification of the molten materials occurred before complete homogenizations. The temperature needed for the dissolution of the elements and the formation of solid solutions without second-phase particles (i.e., undissolved fractions) was not reached with the technological conditions of electron-beam welding used in the present study. The grains of the obtained solid solutions within the considered welded joints were much smaller in the cases of electron-beam welding by using beam powers of 2400 and 3000 W. It is well known that during the welding procedure, a higher cooling rate corresponds to a finer microstructure. As already mentioned, the application of a higher beam power leads to higher heat input and strong temperature gradient convection. Such a convection flow is responsible for the melt homogenization of a welded joint and a lower cooling rate. Therefore, in the case of welding by using 3600 W, the convective mixing flows within the molten material became predominant [31], which led to a decrease in the cooling rate and therefore to an increase in the grain size [32]. The previous statements are in agreement with the results obtained in this study; at a beam power of 2400 W, the average size was about 1.64 μm. It increased to about 2.00 μm at a beam power of 3000 W and to 2.20 μm at 3600 W.

The mechanical properties of the electron-beam-welded specimens were studied in terms of their tensile strengths and elongations. The results are presented in Figure 6 and

Table 4. Tensile test results.

Welded Joint	Tensile Strength, MPa	Elongation, %
Sample 1 (2400 W)	228	13.6
Sample 2 (3000 W)	232	16.1
Sample 3 (3600 W)	207	23.1

. Samples of pure Cu and 304-L stainless steel were also subjected to the above-mentioned mechanical tests for comparison purposes.

The obtained results show that values of the tensile strengths of the specimens welded by using beam powers of 2400 and 3000 W (i.e., Samples 1 and 2, respectively) were comparable. With an increase in the power of the electron beam to 3600 W, the tensile strength decreased. The results obtained for the relative elongation of the weld formed by using 2400 W show a value of 13.6%. The rise in the power of the electron beam led to an increase in the considered mechanical property to 16.1 and 23.1% at 3000 and 3600 W, respectively. Therefore, this means that the rise in the beam power during the electron-beam welding led to an increase in elongation.

A number of aspects can influence the mechanical properties of the materials. According to the authors of [33], the impacts of microstructure and grain size on mechanical properties and strengthening effects are significant. In the case of a finer microstructure, the amount of grain boundaries is higher in comparison with larger and coarser grains. This larger surface area boundary plays a role in obstacles to dislocation movement, which result in increases in strengths [34,35]. At the same time, elongation increases with an increase in beam power during the welding procedure. As already mentioned, higher values of beam power lead to the formation of joints with larger grain sizes. In this case, dislocations can move significantly more freely within larger grains. Obviously, how freely the dislocations can move can define the ductile properties of a material, and therefore, materials with larger grain sizes correspond to higher ductilities and greater fracture extensions. These statements are in agreement with the results obtained in the present study. It was found that the microstructure of the solid solution formed between the copper and the stainless steel was the finest in the case of electron-beam welding at a beam power of 2400 W, which corresponded to the highest measured values of the materials’ strengths. Furthermore, the elongation increased with an increases in the beam power and grain sizes of the welded joints. Moreover, the highest beam power led to a wider welded joint, which corresponded to an increase in plasticity. From another point of view, the application of 3600 W led to the highest amount of undissolved Cu as a second-phase structure, which could be another reason for the highest plasticity of the considered specimen. It is well known that Cu material is characterized as more plastic than stainless steel. An increase in the plasticity of the material leads to a reduction in the strength of the welded joint. These statements are again consistent with the results of this study; with a rise in the beam power, the elongations increased and the tensile strengths decreased.

The results of the microhardnesses measured in the cross-sections of the welding seams are shown in Figure 7. On the side of the 304-L steel, as we approached the welding area, the microhardness increased in all cases. It should be noted that the materials located near the welded joints (the so-called heat-affected zones) were characterized by finer microstructures in comparison to regions more distant from the fusion zones. According to the authors of [36,37], finer microstructures correspond to higher values of microhardness. Considering the specimen welded by using a beam power of 2400 W (i.e., Sample 1, Figure 7a), one can see that the values at the interface between the welded joint and the SS part were about 250 HV and dropped to 150 HV within the fusion zone. This could be attributed to the structure of the welded joint obtained by using a beam power of 2400 W. As already mentioned, the fusion zone of this specimen consisted of a very narrow Fe–Cu solid-solution area and pure copper. The previous statement is in agreement with the results concerning the microhardness, in which a value of about 250 HV was measured at the formed solid solution and dropped to 150 HV at the Cu part of the welded joint. Considering the sample welded by using a beam power of 3000 W (i.e., Sample 2, Figure 7b), one can see that the microhardness measured at the welded joint was relatively unchanged from the near-stainless-steel part to the copper region as it was about 200 HV. The previous statement is again in agreement with the results concerning the microstructure of the welded joint formed by using a beam power of 3000 W. As already mentioned, the whole fusion zone was in the form of a solid solution between iron and copper as well as homogeneously distributed formations of undissolved copper. The microhardness measured at the joint of the specimen welded by using a beam power of 3600 W was about 200 HV near the stainless steel and dropped to 120 HV in the region near the copper. As already mentioned, the fusion zone consisted of two distinguished zones. The first one (near the stainless steel) consisted of a double-phase structure of a solid solution between Fe and Cu and of Cu particles as a second phase, for which values of about 200 HV were measured. The second zone (near copper) was in the form of a double-phase structure of pure copper as a main phase and some formations of a solid solution between Fe and Cu as a second phase, for which the measured microhardness was about 120 HV. It is obvious that the discussed mechanical characteristics decreased from the side of the SS to the Cu due to the formation of two separate structural zones. The observed drop could be attributed mainly to the decrease in the amount of Fe and increase in Cu within the second structural region (near the copper, indicated as area B in Figure 5a).

This work presents the results of electron-beam welding Cu and stainless steel samples. The influence of beam power on the phase compositions, the microstructures, and the sizes of the welding seams was examined. A correlation between beam power and grain size was established; it indicates that with an increase in electron-beam power, grain size increases, leading to an increase in the plasticity of materials, which in turn leads to a decrease in the strength of a welded joint [34,35]. The highest beam power led to a wider welded joint and a higher plasticity. The joint formed by using a beam power of 3600 W was characterized by the highest amount of undissolved Cu as a second-phase structure, which is considered another reason for the highest plasticity of the considered specimen. The increase in plasticity corresponded to a reduction in the strength of the welded joint. These results can be used for the optimization of the technological conditions used during the electron-beam welding of copper and stainless steel for the formation of dissimilar joints with specific microstructures and mechanical characteristics.

4. Conclusions

In this study, we present results on the possibility of the electron-beam welding of 304-L stainless steel with Cu at an offset of 0.3 mm to a Cu plate. The influence of beam power on the structures and mechanical properties of welded joints was studied. The fusion zone at the lowest beam power (2400 W) consisted of molten copper and a narrow zone of a solid solution between Cu and Fe. An increase in the beam power to 3000 W led to the formation of a solid solution of copper and iron within the molten materials, and at the highest beam power (3600 W), the materials were divided into two separate zones: the first one was a solid solution of Cu and Fe with an amount of undissolved copper; the second one consisted of molten Cu with a small amount of a solid solution between Fe and Cu. The welded joints showed higher tensile strengths at beam powers of 2400 and 3000 W, and the strength dropped with an increase in the power to 3600 W. The relative elongation rose with an increase in the beam power. The microhardness of the specimen welded by using 2400 W was about 250 HV at the narrow zone of the Fe–Cu solid solution in the SS part and dropped to 150 HV within the molten Cu zone. The sample welded by using 3000 W exhibited relatively unchanged values within the fusion zone of about 200 HV. The microhardness of the specimen welded by using 3600 W was about 200 HV near the stainless steel and dropped to 120 HV in the region near the copper.