Differential electrode parameter optimization-based dissimilar steel resistance spot welding process

Abstract

A dissimilar steel resistance spot welding process based on differential electrode parameter optimization belongs to the technical field of welding, a carbon steel plate and a stainless steel plate are used as workpieces to be assembled and fixed on a fixture in a lap joint mode, a chromium zirconium copper electrode is selected as a welding electrode, the diameter of the end face of the electrode is 5mm-9mm, and the diameter of the end face of the electrode is 5mm-9mm; the end surface diameter of the electrode on the carbon steel plate side is smaller than that of the electrode on the stainless steel plate side; completely contacting the end face of the electrode with the surface of the workpiece, and pre-pressing; welding is conducted in a resistance spot welding mode, during welding, the electrode pressure ranges from 7 kN to 10 kN, the welding current ranges from 7 kA to 10 kA, and the welding time ranges from 0.2 s to 0.4 s; after electrifying is finished, removing the current, continuously keeping the electrode pressure, and naturally cooling; and thus, resistance spot welding of the carbon steel plate and the stainless steel plate dissimilar steel is completed. According to the method, the electrodes with different sizes are adopted on the two sides of the stainless steel and the low-carbon steel, so that nugget deviation and nugget sizes are effectively controlled, and the spot welding quality and stability are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of welding, and in particular, relates to a resistance spot welding process for dissimilar steels based on differentiated electrode parameter optimization. Background Art

[0002] 301L austenitic stainless steel cold-rolled series plates are the main materials for manufacturing rail vehicles. In addition to the welding of 301L stainless steel, there are also many dissimilar steel welding structures of 301L stainless steel and low carbon steel. At present, the dissimilar steel welding of 301L stainless steel and low carbon steel still has the following problems:

[0003] 1. The arc welding and plug welding currently used not only have low production efficiency and high cost, but also need to be improved in strength, stiffness and fatigue reliability.

[0004] 2. The traditional spot welding process usually directly welds two plates and cannot be changed according to changes in steel properties.

[0005] 3. Due to the differences in resistivity, thermal conductivity and expansion coefficient between 301L stainless steel and low carbon steel, the welding nugget will shift, affecting the welding strength.

[0006] 4. Since the welding of dissimilar steels of 301L stainless steel and low carbon steel is widely used in automobile manufacturing, the following problems may occur during welding:

[0007] (1) The diameter and depth of the weld nugget on the stainless steel side are greater than those on the low carbon steel side.

[0008] (2) The high temperature zone of the temperature field shifts toward the 301L stainless steel side.

[0009] 5. The patent document "A three-layer steel plate resistance spot welding process and electrodes used therein" (publication number: CN116586732A, publication date: 2023.08.15) adopts upper and lower differentiated electrodes to solve the problem that the outer low-resistance steel plate of the three-layer steel plates of unequal thickness cannot form a qualified welding nugget with the high-resistance steel plate. However, this solution is applicable to multiple layers of unequal thickness steel plates. It uses spherical electrodes and is only suitable for resistance spot welding of soft steel and high-strength steel. It optimizes the weldability, but is not suitable for resistance spot welding of thick steel plates such as stainless steel / low-carbon steel. There is no clear data on the improvement of weldability and the problem of nugget offset in resistance spot welding of dissimilar steels is not solved.

[0010] The above methods are of great reference significance to the present invention. For the resistance spot welding of dissimilar steels, not only the defects caused by the differences in resistivity, thermal conductivity and expansion coefficient should be considered, but also the problem of nugget displacement should be considered.

[0011] Therefore, the prior art urgently needs a new technical solution to make full use of the welding characteristics of stainless steel and low-carbon steel, and to cleverly use electrodes with different sizes to optimize the problems existing in welding during the welding of stainless steel and low-carbon steel. Summary of the invention

[0012] The purpose of the present invention is to provide a resistance spot welding process for dissimilar steels based on differentiated electrode parameter optimization. By adopting electrodes with different sizes on both sides of stainless steel and low carbon steel, effective control of the nugget offset and the nugget size is achieved, thereby improving the quality and stability of spot welding.

[0013] The technical solution adopted by the present invention to achieve the above-mentioned purpose is: the present invention proposes a dissimilar steel resistance spot welding process based on differentiated electrode parameter optimization, comprising:

[0014] Step 1: Clean and polish the carbon steel plate with a thickness of 1.5 mm to 3 mm for later use;

[0015] Step 2: Clean and polish the stainless steel plate with a thickness of 2 mm to 3.5 mm for later use;

[0016] Step 3: The carbon steel plate and the stainless steel plate are assembled and fixed on the fixture in an overlapping manner as workpieces, and a chromium-zirconium-copper electrode is selected as a welding electrode. The electrode end face diameter is 5 mm to 9 mm, and the electrode end face diameter on the carbon steel plate side is smaller than the electrode end face diameter on the stainless steel plate side;

[0017] Step 4: Make the electrode end face completely contact with the workpiece surface, set the electrode pressure, and perform pre-pressing treatment;

[0018] Step 5: resistance spot welding is used for welding, the electrode pressure during welding is 7kN-10kN, the welding current is 7kA-10kA, and the welding time is 0.2s-0.4s;

[0019] Step 6: After the power supply is turned off, remove the current, continue to maintain the electrode pressure, and allow it to cool naturally;

[0020] At this point, the resistance spot welding of dissimilar steel plates, carbon steel plates and stainless steel plates, is completed.

[0021] According to a specific embodiment of the present invention, the carbon content of the carbon steel plate is less than 0.25.

[0022] According to a specific embodiment of the present invention, the stainless steel plate is composed of an alloy having Fe as a main component and containing Cr in a mass fraction of 10.5% or more.

[0023] Among them, when the thicknesses of the carbon steel plate and the stainless steel plate are 1.5 mm and 2 mm respectively, the diameter of the electrode end surface on the carbon steel plate side is 5 mm; and the diameter of the electrode end surface on the stainless steel plate side is 7 mm.

[0024] When the thicknesses of the carbon steel plate and the stainless steel plate are 2 mm and 2 mm respectively, the diameter of the electrode end surface on the carbon steel plate side is 6 mm; and the diameter of the electrode end surface on the stainless steel plate side is 7 mm.

[0025] When the thicknesses of the carbon steel plate and the stainless steel plate are 2 mm and 2.5 mm respectively, the diameter of the electrode end surface on the carbon steel plate side is 6 mm; and the diameter of the electrode end surface on the stainless steel plate side is 8 mm.

[0026] When the thicknesses of the carbon steel plate and the stainless steel plate are 2 mm and 3 mm respectively, the diameter of the electrode end surface on the carbon steel plate side is 6 mm; and the diameter of the electrode end surface on the stainless steel plate side is 8 mm.

[0027] When the thicknesses of the carbon steel plate and the stainless steel plate are 3 mm and 3 mm respectively, the diameter of the electrode end surface on the carbon steel plate side is 6 mm; and the diameter of the electrode end surface on the stainless steel plate side is 8.5 mm.

[0028] Among them, when the thicknesses of the carbon steel plate and the stainless steel plate are 3 mm and 3.5 mm respectively, the diameter of the electrode end surface on the carbon steel plate side is 7 mm; and the diameter of the electrode end surface on the stainless steel plate side is 9 mm.

[0029] Wherein, in step 4, the electrode pressure is set to 7 kN to 10 kN.

[0030] Through the above-mentioned design scheme, the present invention can bring the following beneficial effects: The present invention proposes a dissimilar steel resistance spot welding process based on differential electrode parameter optimization, which effectively controls the nugget offset and nugget size by adopting size-differentiated electrodes on both sides of stainless steel and low-carbon steel, thereby improving the quality and stability of spot welding. Differentiated electrodes are used to optimize current distribution, adjust pressure distribution, control heat-affected zones, adapt to differences in plate characteristics, effectively improve the organizational structure of welds, and balance thermal stresses during welding. The electrode size can be flexibly adjusted to accommodate workpieces of different materials and thicknesses.

[0031] Furthermore, the process method is simple to operate and can be widely used in the spot welding production of stainless steel and low carbon steel. By using the process method of the present invention, the quality and production efficiency of the product can be improved, the production cost can be reduced, and strong support can be provided for the sustainable development of the enterprise. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to understand the present invention and do not constitute improper limitations of the present invention. In the drawings:

[0033] Figure 1 This is the process flow chart of resistance spot welding of dissimilar steels based on differentiated electrode parameter optimization.

[0034] Figure 2It is a schematic diagram of the position of the weld nugget using the same electrode according to an embodiment of the present invention.

[0035] Figure 3 It is a schematic diagram of the position of the weld nugget using different electrodes according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The present invention provides a dissimilar steel resistance spot welding process based on differentiated electrode parameter optimization. By adjusting the size of the electrode, the size-differentiated electrode can change the distribution of current in the welding area. When the large-sized electrode contacts one plate and the small-sized electrode contacts another plate, the current will flow more concentratedly to the thick plate or the plate with low resistivity. The plate corresponding to the large-sized electrode will obtain a relatively uniform and moderate current to avoid local overheating, while the plate corresponding to the large-sized electrode can obtain a higher current density. This targeted current distribution helps to improve the welding quality and reduce the generation of welding defects. Electrodes of different sizes can achieve different pressure distribution. In the resistance welding process, the pressure applied by the electrode is crucial to the welding quality. Large-sized electrodes can provide more stable and uniform pressure, while small-sized electrodes can apply higher pressure in local areas. For the welding of stainless steel and carbon steel plates, this pressure differentiation can better adapt to the different characteristics of the two plates. For example, stainless steel may require less local pressure to avoid excessive deformation, while carbon steel plates can withstand greater overall pressure to ensure good contact. By reasonably adjusting the electrode size, the best pressure distribution can be achieved, and the strength and sealing of the welded joint can be improved. Differentiated electrodes help control the size and properties of the heat-affected zone. During welding, the heat-affected zone is the area around the weld joint where the heat of welding causes changes in structure and properties. By selecting the right electrode size, the heat input and heat dissipation during welding can be adjusted. Large electrodes can dissipate heat faster and reduce the range of the heat-affected zone; while small electrodes can concentrate heat in local areas to achieve precise welding. This can reduce the adverse effects of the heat-affected zone on the properties of the parent material and improve the overall performance of the welded joint. Stainless steel and carbon steel plates differ in physical properties and welding characteristics. Stainless steel generally has higher resistivity and thermal conductivity, while carbon steel plates have lower resistivity and thermal conductivity than stainless steel plates. Differentiated electrodes can be optimized according to the characteristics of the two plates. For example, for stainless steel with high resistivity, small electrodes can be used to increase current density and increase welding temperature; for carbon steel plates with high thermal conductivity, large electrodes can be used to increase heat dissipation and prevent overheating. This targeted design can better adapt to the different characteristics of the two plates and improve welding efficiency and quality. The effective control of nugget offset and nugget size is achieved, which improves the quality and stability of spot welding. By rationally designing the electrode size ratio and position, the welding parameters can be flexibly adjusted to adapt to workpieces of different materials and thicknesses.

[0037] The present invention proposes a dissimilar steel resistance spot welding process based on differentiated electrode parameter optimization. According to different plate thickness combinations of stainless steel and carbon steel plates, electrodes of appropriate sizes are selected to improve the dissimilar steel resistance spot welding. Due to the differences in resistivity, thermal conductivity and expansion coefficient between stainless steel and carbon steel, the welding nugget is offset, affecting the welding strength.

[0038] like Figure 1 As shown, a dissimilar steel resistance spot welding process based on differentiated electrode parameter optimization includes:

[0039] Selection of carbon steel plate and stainless steel plate:

[0040] The composition of the carbon steel plate is not particularly limited. Considering the practicality of rail vehicles, the carbon content is less than 0.25. The thickness should also be selected based on practicality, so 1.5 mm to 3 mm is selected.

[0041] The composition of the spot-welded stainless steel plate is not particularly limited. For example, austenitic stainless steel, ferritic stainless steel, duplex stainless steel and martensitic stainless steel are used, the main component of which is Fe and is composed of an alloy containing more than 10.5% Cr by mass. According to practicality, the thickness of the stainless steel plate is 2 mm to 3.5 mm.

[0042] Electrode selection:

[0043] Considering the welding performance of carbon steel plate and stainless steel plate, the welding electrode material should be chromium zirconium copper electrode, which has higher strength and hardness, good electrical conductivity and thermal conductivity. In the spot welding of dissimilar steels, it can withstand higher current and pressure, is not easy to deform and wear, can effectively conduct current, and generate enough heat to make the plate. According to the selection of plate thickness, the electrode end face diameter is selected to be 5mm~9mm.

[0044] Matching of base material and electrode:

[0045] The resistivity of stainless steel is 5 times that of carbon steel, and its thermal conductivity is 1 / 3 of that of carbon steel plate. Therefore, small-sized electrodes should be used on the carbon steel plate side, and large-sized electrodes should be used on the stainless steel plate side. In rail vehicles, common plate thickness combinations are: 1.5mm thick carbon steel plate and 2mm thick stainless steel plate, 2mm thick carbon steel plate and 2mm thick stainless steel plate, 2mm thick carbon steel plate and 2.5mm thick stainless steel plate, 2mm thick carbon steel plate and 3mm thick stainless steel plate, 3mm thick carbon steel plate and 3mm thick stainless steel plate, 3mm thick carbon steel plate and 3.5mm thick stainless steel plate. For the above plate thickness combinations, the electrode end face diameters on the carbon steel plate side are selected as: 5mm, 6mm, 6mm, 6mm, 6mm, 7mm, and the electrode end face diameters on the stainless steel plate side are: 7mm, 7mm, 8mm, 8mm, 8.5mm, 9mm. That is: when the thickness of the carbon steel plate and the stainless steel plate are 1.5mm and 2mm respectively, the diameter of the electrode end face on the carbon steel plate side is 5mm; the diameter of the electrode end face on the stainless steel plate side is 7mm. When the thickness of the carbon steel plate and the stainless steel plate are 2mm and 2mm respectively, the diameter of the electrode end face on the carbon steel plate side is 6mm; the diameter of the electrode end face on the stainless steel plate side is 7mm. When the thickness of the carbon steel plate and the stainless steel plate are 2mm and 2.5mm respectively, the diameter of the electrode end face on the carbon steel plate side is 6mm; the diameter of the electrode end face on the stainless steel plate side is 8mm. When the thickness of the carbon steel plate and the stainless steel plate are 2mm and 3mm respectively, the diameter of the electrode end face on the carbon steel plate side is 6mm; the diameter of the electrode end face on the stainless steel plate side is 8mm. When the thickness of the carbon steel plate and the stainless steel plate are 3mm and 3mm respectively, the diameter of the electrode end face on the carbon steel plate side is 6mm; the diameter of the electrode end face on the stainless steel plate side is 8.5mm. When the thicknesses of the carbon steel plate and the stainless steel plate are 3 mm and 3.5 mm respectively, the diameter of the electrode end face on the carbon steel plate side is 7 mm; and the diameter of the electrode end face on the stainless steel plate side is 9 mm.

[0046] Resistance spot welding:

[0047] For carbon steel plates, a soft specification of long time and small current should be adopted, and for stainless steel plates, a hard specification of short time and large current should be adopted. Considering the weldability of carbon steel plates and stainless steel plates comprehensively, a hard specification of large current and long time is adopted. According to the plate thickness in the above steps, the electrode pressure is 7kN~10kN, the welding current is 7kA~10kA, and the welding time is between 0.2s~0.4s. In spot welding, increasing the electrode end face diameter, pressurizing, increasing the current or power-on time can increase the diameter of the molten core and the depth of the weld. Therefore, adjust the electrode end face diameter, pressurizing, power-on time and power-on current according to the plate thickness and component composition of the steel plate.

[0048] At this point, the process steps for optimizing differentiated electrode parameters for resistance spot welding of dissimilar steels are completed.

[0049] The technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments are conventional methods in the art unless otherwise specified.

[0050] Example 1

[0051] Select 2mm thick 301L stainless steel and 2mm thick Q235 low carbon steel materials and process them into a size of 100mm×25mm. The specific steps are as follows:

[0052] Step 1: Immerse 2mm thick 301L stainless steel in an ultrasonic cleaning machine, use sodium hydroxide solution for ultrasonic cleaning, then immerse the stainless steel in a pickling tank, use a mixed solution of HCL, H2SO4, and HNO3 as an HCL acid deoxidizer for pickling, and finally put the stainless steel into a polishing machine;

[0053] Step 2: Immerse the Q235 low-carbon steel with a thickness of 2 mm in a solvent cleaning tank, use petroleum ether for cleaning, then immerse the low-carbon steel in a pickling tank, use a mixed solution of HCL and hexamethylenetetramine as an acidic deoxidizer for pickling, and finally put the low-carbon steel into a polishing machine;

[0054] Step 3: Stainless steel and low carbon steel are assembled and fixed on the fixture in an overlapping manner. A conical electrode with an end face diameter of 6 mm is selected as a small-sized electrode, and a conical electrode with an end face diameter of 7 mm is selected as a large-sized electrode. The large-sized electrode corresponds to the stainless steel side, and the small-sized electrode corresponds to the low carbon steel side.

[0055] Step 4: Make the electrode end face effectively contact with the workpiece surface, and set the electrode pressure to 8kN for pre-pressing treatment;

[0056] Step 5: Perform spot welding, set the welding current to 9.5kA, the electrode pressure to 9kN, and the welding time to 0.3s;

[0057] Step 6: After the power is turned on, remove the current and continue to maintain the 9kN electrode pressure to allow it to cool naturally. Perform a shear strength test on the welded joint. The shear strength of the welded joint reaches 1850N.

[0058] Example 2

[0059] Select Q215 low carbon steel with a thickness of 1.5mm and 304 stainless steel with a thickness of 2mm and process them into a size of 100mm×25mm. The specific steps are as follows:

[0060] Step 1: Immerse 2mm thick 304 stainless steel in an ultrasonic cleaning machine, use sodium hydroxide solution for ultrasonic cleaning, then immerse the stainless steel in a pickling tank, use a mixed solution of HCL, H2SO4, and HNO3 as an HCL acid deoxidizer for pickling, and finally put the stainless steel into a polishing machine;

[0061] Step 2: Immerse the Q215 low-carbon steel with a thickness of 1.5 mm in a cleaning tank, clean it with petroleum ether, then immerse the low-carbon steel in a pickling tank, use a mixed solution of HCL and hexamethylenetetramine as an acidic deoxidizer for pickling, and finally put the low-carbon steel into a polishing machine;

[0062] Step 3: Fix the low carbon steel and stainless steel on the fixture. The stainless steel and low carbon steel are assembled and fixed on the fixture in an overlapping manner. Select a conical electrode with an end face diameter of 5 mm as a small-sized electrode and a conical electrode with an end face diameter of 7 mm as a large-sized electrode. The large-sized electrode corresponds to the stainless steel side, and the small-sized electrode corresponds to the low carbon steel side.

[0063] Step 4: Make effective contact between the electrode and the workpiece surface, and set the electrode pressure to 7kN for pre-pressing treatment;

[0064] Step 5: Perform spot welding, set the welding current to 8kA, the electrode pressure to 8kN, and the welding time to 0.2s;

[0065] Step 6: After the power is turned on, remove the current and continue to maintain the 8kN electrode pressure to allow it to cool naturally. Perform a shear strength test on the joint and the shear strength of the joint reaches 1633N.

[0066] According to the above embodiments, Figure 2 and attached Figure 3It can be seen that in the resistance spot welding of dissimilar steels, due to the differences in resistivity, thermal conductivity and expansion coefficient between stainless steel and low carbon steel, the welding nugget will be offset, affecting the welding strength. Differentiated electrodes are used on both sides of the dissimilar steel plates, and then resistance spot welding is performed. The size difference electrodes can change the distribution of current in the welding area. When the large-sized electrode contacts the stainless steel plate and the small-sized electrode contacts the low carbon steel plate, the current will flow more concentratedly to a specific area. The large electrode will obtain a relatively uniform and moderate current to avoid local overheating, while the small electrode can obtain a higher current density at a specific location to promote the fusion of the welding part. This targeted current distribution helps to improve the welding quality and reduce the occurrence of welding defects. Electrodes of different sizes can achieve different pressure distribution. In the resistance welding process, the pressure applied by the electrode is crucial to the welding quality. Large-sized electrodes usually provide more stable and uniform pressure, while small-sized electrodes can apply higher pressure in local areas. For the welding of stainless steel and carbon steel plates, this pressure differentiation can better adapt to the different characteristics of the two plates. Stainless steel requires less local pressure to avoid excessive deformation, while carbon steel plates can withstand greater overall pressure to ensure good contact. By properly adjusting the electrode size, the best pressure distribution can be achieved, improving the strength and sealing of the welded joint. Electrodes with different sizes help control the size and performance of the heat-affected zone. It can effectively improve the problem of nugget displacement and improve welding quality. Figure 2 and Figure 3 By comparison, it can be clearly seen that the nugget offset is reduced and the nugget size is more reasonable. Figure 2 and Figure 3 In the figure, A represents stainless steel, B represents low carbon steel, and C represents the nugget.

[0067] In summary, the present invention conducts a large number of experiments and summarizes the matching relationship between the differentiated electrodes and the plate thickness based on the experimental results to solve the above-mentioned problems in the spot welding of rail vehicles.

Claims

1. A resistance spot welding process for dissimilar steels based on differentiated electrode parameter optimization, characterized in that: include: Step 1: Clean and polish the carbon steel plate with a thickness of 1.5 mm to 3 mm for later use; Step 2: Clean and polish the stainless steel plate with a thickness of 2 mm to 3.5 mm for later use; Step 3: The carbon steel plate and the stainless steel plate are assembled and fixed on the fixture in an overlapping manner as workpieces, and a chromium-zirconium-copper electrode is selected as a welding electrode. The electrode end face diameter is 5 mm to 9 mm, and the electrode end face diameter on the carbon steel plate side is smaller than the electrode end face diameter on the stainless steel plate side; Step 4: Make the electrode end face completely contact with the workpiece surface, set the electrode pressure, and perform pre-pressing treatment; Step 5: resistance spot welding is used for welding, the electrode pressure during welding is 7kN-10kN, the welding current is 7kA-10kA, and the welding time is 0.2s-0.4s; Step 6: After the power supply is turned off, remove the current, continue to maintain the electrode pressure, and allow it to cool naturally; At this point, the resistance spot welding of dissimilar steel plates, carbon steel plates and stainless steel plates, is completed.

2. The dissimilar steel resistance spot welding process based on differentiated electrode parameter optimization according to claim 1 is characterized in that: The carbon content of the carbon steel plate is less than 0.

25.

3. The dissimilar steel resistance spot welding process based on differentiated electrode parameter optimization according to claim 1, characterized in that: The stainless steel plate is composed of an alloy having Fe as a main component and containing 10.5% by mass or more of Cr.

4. The resistance spot welding process for dissimilar steels based on differentiated electrode parameter optimization according to claim 1, characterized in that: When the thicknesses of the carbon steel plate and the stainless steel plate are 1.5 mm and 2 mm respectively, the diameter of the electrode end face on the carbon steel plate side is 5 mm; and the diameter of the electrode end face on the stainless steel plate side is 7 mm.

5. The resistance spot welding process for dissimilar steels based on differentiated electrode parameter optimization according to claim 1, characterized in that: When the thicknesses of the carbon steel plate and the stainless steel plate are 2 mm and 2 mm respectively, the diameter of the electrode end face on the carbon steel plate side is 6 mm; and the diameter of the electrode end face on the stainless steel plate side is 7 mm.

6. The dissimilar steel resistance spot welding process based on differentiated electrode parameter optimization according to claim 1, characterized in that: When the thicknesses of the carbon steel plate and the stainless steel plate are 2 mm and 2.5 mm respectively, the diameter of the electrode end face on the carbon steel plate side is 6 mm; and the diameter of the electrode end face on the stainless steel plate side is 8 mm.

7. The resistance spot welding process for dissimilar steels based on differentiated electrode parameter optimization according to claim 1, characterized in that: When the thicknesses of the carbon steel plate and the stainless steel plate are 2 mm and 3 mm respectively, the diameter of the electrode end face on the carbon steel plate side is 6 mm; and the diameter of the electrode end face on the stainless steel plate side is 8 mm.

8. The process for optimizing differential electrode parameters for resistance spot welding of dissimilar steels according to claim 1, characterized in that: When the thicknesses of the carbon steel plate and the stainless steel plate are 3 mm and 3 mm respectively, the diameter of the electrode end face on the carbon steel plate side is 6 mm; and the diameter of the electrode end face on the stainless steel plate side is 8.5 mm.

9. The process for optimizing differential electrode parameters for resistance spot welding of dissimilar steels according to claim 1, characterized in that: When the thicknesses of the carbon steel plate and the stainless steel plate are 3 mm and 3.5 mm respectively, the diameter of the electrode end face on the carbon steel plate side is 7 mm; and the diameter of the electrode end face on the stainless steel plate side is 9 mm.

10. The process for optimizing differential electrode parameters for resistance spot welding of dissimilar steels according to claim 1, characterized in that: In step 4, the electrode pressure is set to 7 kN to 10 kN.

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