Laser welding method for ultrathin ferritic stainless steel

Abstract

The invention is applicable to the technical field of welding and connection, and provides a laser welding method for ultrathin ferritic stainless steel, which comprises the following steps: selecting an ultrathin ferritic stainless steel material; a powder mixture is prepared from, by mass, 15%-20% of TiC, 5%-10% of nickel powder, 10%-15% of chromium powder, 2%-5% of silicon powder and the balance iron powder. A laser welding device is adopted, the incident angle of a laser head is set to be 60 degrees, and the included angle between a powder conveying device and a weldment is 30 degrees. During welding, a laser beam heats a molten pool, and powder is synchronously conveyed to the molten pool for reaction to generate refined grains and a strengthening phase. And after welding, the workpiece is recovered to be in a flat state through heating and mechanical force leveling treatment. Through surface treatment, a specific powder ratio and process parameters, the tensile strength and corrosion resistance of a welding material can be remarkably improved, and the flatness of a welded workpiece can be guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of welding and connection, and in particular relates to a laser welding method for ultra-thin ferritic stainless steel. Background Art

[0002] Ultra-thin ferritic stainless steel has been widely used in many fields such as automobile, construction, electronics and energy due to its excellent corrosion resistance, oxidation resistance and excellent formability. However, with the growing demand for high-performance materials, this material has encountered challenges in the mechanical properties and corrosion resistance of the welded joints, especially during laser welding. Laser welding is an ideal choice for joining thin sheet materials due to its high precision and high efficiency, but when processing ultra-thin ferritic stainless steel, the mechanical properties of the welded joints are significantly reduced due to grain coarsening and uneven microstructure in the heat-affected zone.

[0003] The high heat input during welding causes rapid grain growth in the weld area, which weakens the strength and toughness of the welded joint, especially in the heat affected zone (HAZ) and weld area. These problems not only cause uneven mechanical properties, but also reduce corrosion resistance, making these areas prone to stress corrosion cracking and intergranular corrosion in corrosive environments.

[0004] Although the existing technologies such as patent CN 118664079 A have achieved certain results in optimizing the organizational structure of welded joints by adjusting process parameters such as laser power, welding speed and cooling rate, they still cannot completely solve the problem of grain coarsening, and have limited effect in improving the corrosion resistance of welded joints. In addition, traditional methods often focus on improving the hardness or strength of the joint, but pay insufficient attention to the refinement of the microstructure of the joint, especially in dealing with high temperature and corrosive media environments, showing poor long-term performance.

[0005] In order to further enhance the mechanical properties and corrosion resistance of ultra-thin ferritic stainless steel welded joints, it is particularly important to refine the grain size of the welded joints. This can not only effectively improve the strength and hardness of the material, but also improve its plasticity and crack resistance. By controlling the welding heat input and introducing reinforcing ceramic and alloy powders, the goal of grain refinement can be achieved while improving corrosion resistance. For example, adding TiC ceramic powder can not only refine the grain size, but also enhance wear resistance; alloy powders such as nickel powder and iron powder can help improve corrosion resistance and oxidation resistance.

[0006] In summary, in view of the problems encountered in the laser welding process of ultra-thin ferritic stainless steel, optimizing the welding process parameters and rationally selecting additives are effective ways to improve the comprehensive performance of the welded joint. Therefore, in view of the above status quo, it is urgent to develop a laser welding method for ultra-thin ferritic stainless steel to overcome the shortcomings in current practical applications. Summary of the invention

[0007] The object of the present invention is to provide a laser welding method for ultra-thin ferritic stainless steel, aiming to solve the problems mentioned in the above background technology.

[0008] The present invention is achieved by a laser welding method for ultra-thin ferritic stainless steel, comprising the following steps: Step 1: Select ultra-thin ferritic stainless steel material with a thickness of 0.1mm-0.3mm; before laser welding, use mechanical cleaning and chemical cleaning methods to treat the surface of the material to remove oil, oxides and other contaminants on the surface; Step 2: According to the performance requirements of the welded joint, prepare the powder mixture required for welding; the powder mass percentage is as follows: TiC powder 15%-20%, nickel powder 5%-10%, chromium powder 10%-15%, silicon powder 2%-5%, and the rest is iron powder; Step 3: The laser welding device consists of a laser welding head, a powder conveying device, a welding table and a control system; the incident angle of the laser welding head is set to 60°, and the angle between the powder conveying device and the sample to be welded is adjusted to 30° to ensure that the powder feeding position and the laser focus are at the same point; Step 4: When laser welding starts, the laser welding head irradiates the welding joint area, and the laser beam heats the welding area to a molten state; at the same time, the prefabricated powder mixture is fed into the molten pool area through a powder conveying device; the powder reacts with the metal in the molten pool to form refined grains and strengthening phases; Step 5: After welding is completed, the ultra-thin ferritic stainless steel material is leveled. The leveling process includes heating the welded workpiece and restoring it to a flat state through mechanical force to complete the welding operation.

[0009] In a further technical solution, in step 2, the particle size of the powder is controlled to be 20 μm-50 μm, and the powder mixing process is carried out using a vacuum ball milling device, and the vacuum degree is maintained at 10 -3 Pa, mixing time is 4-6 hours.

[0010] According to a further technical solution, in step three, the welding parameters are set as follows: laser power is 600 W, welding speed is 10 mm / s, laser welding frequency is 10 Hz, and duty cycle is 20%.

[0011] According to a further technical solution, in step four, the powder conveying device has a powder conveying speed of 5-8 g / min.

[0012] According to a further technical solution, in step five, the welded workpiece is heated to 100°C-150°C, and a leveling device is used to apply mechanical force, the magnitude of which is controlled at 1000N-3000N, to level the welded workpiece by gradually applying force.

[0013] The laser welding method for ultra-thin ferritic stainless steel provided by the present invention has the following beneficial effects: Through surface treatment, specific ratio of powder mixture (including TiC powder 15%-20%, nickel powder 5%-10%, chromium powder 10%-15%, silicon powder 2%-5%, and the rest is iron powder), precise laser parameter setting and leveling treatment, it has been verified through experiments that compared with the control ratio without added elements, the tensile strength of the welding material can be significantly improved and the corrosion current density can be reduced; and as the content of elements such as TiC and nickel increases, the tensile strength continues to increase and the corrosion current density decreases, which effectively improves the mechanical properties and corrosion resistance of the material, while ensuring the flatness and dimensional accuracy of the welded workpiece. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of a laser welding device for ultra-thin ferritic stainless steel; Figure 2 This is the weld microstructure diagram of the ultra-thin ferritic stainless steel laser welded joint without and with mixed powder. Figure 2 (a) is the weld microstructure diagram of the ultra-thin ferritic stainless steel laser welded joint without adding mixed powder; Figure 2 (b) is the weld microstructure of the ultra-thin ferritic stainless steel laser welded joint with mixed powder added; Figure 3 It is the electrochemical corrosion polarization curve of the weld of the ultra-thin ferritic stainless steel laser welded joint without and with mixed powder added; Figure 4 The tensile curves of ultra-thin ferritic stainless steel laser welded joints without and with mixed powder added are shown in Figure 2. Figure 4 (a) is the tensile curve of the ultra-thin ferritic stainless steel laser welded joint without adding mixed powder; Figure 4 (b) is the tensile curve of the ultra-thin ferritic stainless steel laser welded joint with mixed powder added.

[0015] In the figure: 1-laser welding head, 2-mixed powder, 3-powder feeder, 4-welding fixture. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0017] The specific implementation of the present invention is described in detail below in conjunction with specific embodiments.

[0018] like Figure 1 As shown, it is a schematic diagram of the laser welding device of ultra-thin ferritic stainless steel, which includes a laser welding head 1, a powder conveying device (including a powder feeder 3 for conveying mixed powder 2) and a welding fixture 4 (an accessory of the welding table). The welding fixture 4 clamps and fixes the ultra-thin ferritic stainless steel material, and the powder feeder 3 conveys the mixed powder 2 and cooperates with the laser welding head 1 to perform welding operations.

[0019] An embodiment of the present invention provides a laser welding method for ultra-thin ferritic stainless steel, comprising the following steps: Step 1: Select ultra-thin ferritic stainless steel material with a thickness of 0.1mm-0.3mm. Before welding, treat the surface of the material to remove oil, oxides and other contaminants on the surface. The surface treatment method can be mechanical cleaning (such as sandpaper polishing) or chemical cleaning (such as pickling) to ensure that there are no impurities in the welding area and ensure the welding quality.

[0020] Step 2: Prepare the powder mixture required for welding. The mixture contains iron powder, nickel powder, chromium powder (Cr) and TiC powder. The mass percentage (wt%) of the powder is as follows: TiC powder 15%-20%, nickel powder 5%-10%, chromium powder 10%-15%, silicon powder 2%-5%, and the rest is iron powder. The particle size of the powder should be controlled at 20μm-50μm to ensure that it can be evenly distributed during the welding process and fully react with the base metal. Use a vacuum ball mill to mix the powder, and the vacuum degree should be maintained at 10 -3 Pa, the mixing time is 4-6 hours to ensure that the powder is uniform and free of large particles.

[0021] Step 3. Configure the laser welding device, including the laser welding head 1, the powder conveying device, the welding table and the control system. The incident angle of the laser welding head 1 is set to 60° to ensure that the laser beam can accurately irradiate the welding joint. The laser power is set to 600W, the welding speed is 10mm / s, the welding frequency is 10Hz, and the duty cycle is 20%. These parameters can ensure proper heat input and avoid excessive melting or excessive heat-affected zone. The angle between the powder conveying device and the sample to be welded is adjusted to 30°, so that the powder feeding position and the laser focus are the same point, ensuring that the prefabricated powder mixture is evenly delivered into the welding area.

[0022] The incident angle of the laser welding head 1 is set to 60°, which changes the distribution pattern of laser energy on the weld surface. Compared with the traditional 90° incident angle, its energy distribution is more uniform, which reduces local overheating, optimizes the molten pool temperature field, inhibits abnormal grain growth, refines the weld structure grains, and makes the weld structure more uniform and dense. Figure 2 (a) and Figure 2 The difference can be clearly seen in the comparison of (b). At the same time, reasonable energy distribution improves the fluidity of the molten pool, facilitates gas escape, reduces the probability of defects such as pores, and improves the quality of the weld.

[0023] The angle between the powder conveying device and the sample to be welded is adjusted to 30°, combined with the 60° incident angle of the laser welding head 1, which can ensure that the powder feeding position coincides precisely with the laser focus. This allows the prefabricated powder mixture to quickly and evenly enter the molten pool under the action of the laser, fully mix with the molten pool metal and react efficiently. The functions of TiC powder to refine the grains, and nickel powder and chromium powder to enhance corrosion resistance can be better played. Overall, the tensile strength of the welded joint is improved, the corrosion current density is reduced, and the comprehensive performance of the welded joint is effectively improved.

[0024] Step 4: Start the laser welding process. The laser welding head 1 irradiates the laser beam to the welding joint area, so that the metal material in the welding area is quickly heated to a molten state. At the same time, the prefabricated powder mixture is accurately delivered to the molten pool area through the powder conveying device, and the powder feeding speed is adjusted to 5-8g / min. The powder reacts with the metal in the molten pool through the conveying device to form a strengthening phase. TiC powder participates in the grain refinement process, and nickel powder and iron powder can improve the oxidation resistance and corrosion resistance of the welded joint.

[0025] Step 5. After welding is completed, leveling is performed to improve the flatness of the workpiece. First, heat the welded workpiece to 100℃-150℃ to eliminate some of the internal stress in the material. Then, use a dedicated leveling equipment to apply mechanical force, usually controlled between 1000N-3000N, to perform gradual leveling to ensure that the welded workpiece is restored to flatness. During the leveling process, the force should be applied smoothly and evenly to avoid secondary deformation caused by excessive local force. This step ensures the shape and dimensional accuracy of the welded joint, so that the ultra-thin ferritic stainless steel workpiece can meet the high flatness standards.

[0026] Experimental Section like Figure 2-Figure 4 As shown, according to the laser welding method for ultra-thin ferritic stainless steel recorded above, under the premise of consistent overall process parameters, powder mixtures of components in different proportions were prepared to obtain Comparative Example 1 and Examples 1 to 6, and their tensile strength and corrosion current density were tested. The test results are shown in Table 1 below.

[0027] Table 1 Tensile strength and corrosion current density test of powder mixtures with different ratios ; in, Figure 2 (a) is the weld microstructure diagram of ultra-thin ferritic stainless steel laser welded joint; Figure 2 (b) is the weld microstructure diagram of the ultra-thin ferritic stainless steel laser welded joint with added mixed powder. Figure 3 It is the electrochemical corrosion polarization curve of the weld of ultra-thin ferritic stainless steel laser welded joint without and with mixed powder added. Figure 4 (a) is the tensile curve of the ultra-thin ferritic stainless steel laser welded joint without adding mixed powder; Figure 4 (b) is the tensile curve of the ultra-thin ferritic stainless steel laser welded joint with mixed powder added.

[0028] Through performance index testing, compared with Comparative Example 1 (without adding TiC, nickel, chromium, silicon and other elements), after adding these elements in the embodiment, the tensile strength of the material is significantly improved (from 249Mpa to 494Mpa and above), and the corrosion current density is reduced (from 24.09μA・cm⁻² to 11.16μA・cm⁻² and lower), indicating that the addition of these elements can improve the mechanical properties and corrosion resistance of the material.

[0029] In Examples 1-6, with the increase of TiC, nickel, chromium and silicon content, the tensile strength of the material showed an increasing trend (from 494Mpa to 600Mpa), and the corrosion current density showed a decreasing trend (from 11.16μA・cm⁻² to 10.51μA・cm⁻²), indicating that the increase of the content of each element has a positive effect on improving the tensile strength and reducing the corrosion current density.

[0030] The above embodiment of the present invention provides a laser welding method for ultra-thin ferritic stainless steel. Through surface treatment, a powder mixture with a specific ratio (containing 15%-20% TiC powder, 5%-10% nickel powder, 10%-15% chromium powder, 2%-5% silicon powder, and the rest is iron powder), precise laser parameter setting and leveling treatment, it is experimentally verified that compared with the control ratio without adding elements, the tensile strength of the welding material can be significantly improved (from 249Mpa to more than 494Mpa), and the corrosion current density can be reduced (from 24.09μA・cm⁻² to less than 11.16μA・cm⁻²); and as the content of elements such as TiC and nickel increases, the tensile strength continues to increase (up to 600Mpa) and the corrosion current density decreases (down to 10.51μA・cm⁻²), which effectively improves the mechanical properties and corrosion resistance of the material, while ensuring the flatness and dimensional accuracy of the welded workpiece.

[0031] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0032] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A laser welding method for ultra-thin ferritic stainless steel, characterized in that: The following steps are involved: Step 1: Select ultra-thin ferritic stainless steel material with a thickness of 0.1mm-0.3mm; before laser welding, use mechanical cleaning and chemical cleaning methods to treat the surface of the material to remove oil, oxides and other contaminants on the surface; Step 2: According to the performance requirements of the welded joint, prepare the powder mixture required for welding; the powder mass percentage is as follows: TiC powder 15%-20%, nickel powder 5%-10%, chromium powder 10%-15%, silicon powder 2%-5%, and the rest is iron powder; Step 3: The laser welding device consists of a laser welding head, a powder conveying device, a welding table and a control system; the incident angle of the laser welding head is set to 60°, and the angle between the powder conveying device and the sample to be welded is adjusted to 30° to ensure that the powder feeding position and the laser focus are at the same point; Step 4: When laser welding starts, the laser welding head irradiates the welding joint area, and the laser beam heats the welding area to a molten state; at the same time, the prefabricated powder mixture is fed into the molten pool area through a powder conveying device; the powder reacts with the metal in the molten pool to form refined grains and strengthening phases; Step 5: After welding is completed, the ultra-thin ferritic stainless steel material is leveled. The leveling process includes heating the welded workpiece and restoring it to a flat state through mechanical force to complete the welding operation.

2. The laser welding method for ultra-thin ferritic stainless steel according to claim 1, characterized in that: In step 2, the particle size of the powder is controlled to be 20 μm-50 μm, and the powder mixing process is carried out using a vacuum ball mill. The vacuum degree is maintained at 10 -3 Pa, mixing time is 4-6 hours.

3. The laser welding method for ultra-thin ferritic stainless steel according to claim 1, characterized in that: In step three, the welding parameters are set as follows: laser power is 600 W, welding speed is 10 mm / s, laser welding frequency is 10 Hz, and duty cycle is 20%.

4. The laser welding method for ultra-thin ferritic stainless steel according to any one of claims 1 to 3, characterized in that: In step 4, the powder conveying device has a powder conveying speed of 5-8 g / min.

5. The laser welding method for ultra-thin ferritic stainless steel according to claim 4, characterized in that: In step five, the welded workpiece is heated to 100°C-150°C, and a leveling device is used to apply mechanical force, the magnitude of which is controlled at 1000N-3000N, to level the welded workpiece by gradually applying force.

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