Pulse magnetic field assisted brazing method and tooling for ultra-pure ferritic stainless steel

Abstract

The application discloses a pulse magnetic field assisted ultra-pure ferrite stainless steel brazing method and tool, and the method comprises the following steps: placing the cleaned and dried ultra-pure ferrite stainless steel and the welding position of a welded part on a tool with a pulse magnetic field to perform brazing, driving the directional flow of molten filler metal by using Lorentz force, controlling the magnetic field intensity to be 50-1000 mT, controlling the magnetic field frequency to be 10-500 Hz, controlling the brazing temperature to be 700-1100 DEG C, and controlling the brazing temperature to be 700-1100 DEG C; after the brazing is completed, the brazed ultra-pure ferrite stainless steel and the workpiece formed by the welded part are subjected to heat preservation, the heat preservation time is controlled to be 2-20 min; after the heat preservation is completed, the brazed workpiece is subjected to gradient cooling, the pulse magnetic field is turned on during the cooling, the pulse magnetic field is turned off after the temperature of the brazed workpiece is reduced to below the melting point of the filler metal, the brazed workpiece is rapidly cooled to a set temperature and then is subjected to heat preservation, and the brazed workpiece is obtained after the heat preservation and furnace cooling. By the application, the filler metal can be uniformly distributed at the joint, and a high-quality brazed joint can be formed.

Description

Technical Field

[0001] This invention relates to the field of stainless steel welding technology, and in particular to a pulsed magnetic field-assisted brazing method and tooling for ultrapure ferritic stainless steel. Background Technology

[0002] Ultra-pure ferritic stainless steel is widely used in home appliances, automobiles, chemical equipment, and other fields. Due to its advantages such as high production efficiency and low cost, it is often brazed to connect components of the same material, dissimilar materials such as austenitic stainless steel, or copper. However, due to the protective oxide film on the surface of stainless steel, the wettability of the brazing filler metal is usually poor. In order to ensure that the brazing filler metal melts fully and wets the gap between the joints, and to ensure the sealing of the joint and the mechanical properties of the welded joint, ultra-pure ferritic stainless steel usually needs to be heated in an environment of about 1000 degrees Celsius for about 30 minutes. However, due to the characteristic of ferrite grains growing easily, severe grain coarsening occurs in both the ultra-pure ferritic stainless steel base material and the weld after brazing. This leads to a sharp increase in the brittleness of the weld and the base material. While the elongation and fatigue performance deteriorate, it also has a serious adverse effect on the corrosion resistance of the ultra-pure ferritic stainless steel base material and the weld, ultimately causing the product to fail during use due to cracking and corrosion of the base material.

[0003] To avoid the aforementioned drawbacks, existing technologies employ two approaches: firstly, by adding higher levels of elements such as Nb and W to ultra-pure ferritic stainless steel to improve the high-temperature performance of the base material and weld; and secondly, by using a pulsed magnetic field to assist in the formation of a second phase, such as the Laves phase, to suppress grain coarsening. Thirdly, by using silver-based brazing filler metals with high wettability to reduce high-temperature heating time and prevent grain coarsening in ultra-pure ferritic stainless steel. However, both of these existing methods significantly increase raw material and processing costs, severely impacting and restricting the development and application of ultra-pure ferritic stainless steel. Summary of the Invention

[0004] To address some or all of the technical problems existing in the prior art, this invention provides a pulsed magnetic field-assisted brazing method and tooling for ultrapure ferritic stainless steel. This method can use ultrapure ferritic stainless steel raw materials and brazing filler metals without the addition of precious metal elements, while greatly reducing the high-temperature brazing time of ultrapure ferritic stainless steel and suppressing grain coarsening, ensuring good mechanical properties and corrosion resistance of the base material. At the same time, it can make the brazing filler metal evenly distributed at the joint, forming a high-quality brazed joint.

[0005] The technical solution of the present invention is as follows:

[0006] In a first aspect, a pulsed magnetic field-assisted brazing method for ultrapure ferritic stainless steel is provided, comprising:

[0007] The cleaned and dried ultrapure ferritic stainless steel is placed on a tooling with a pulsed magnetic field at the welding position of the part to be welded. The molten filler metal is driven to flow in a directional manner by the Lorentz force. The magnetic field strength is controlled at 50-1000mT, the magnetic field frequency is controlled at 10-500Hz, the filler metal heating rate is controlled at 10-100℃ / min, and the brazing temperature is controlled at 700~1100℃.

[0008] After brazing, the welded ultrapure ferritic stainless steel and the workpiece formed by the welded parts are kept at a temperature for 2 to 20 minutes.

[0009] After the heat preservation is completed, the welded workpiece is subjected to gradient cooling. During the cooling process, the pulsed magnetic field is turned on. After the temperature of the welded workpiece drops below the melting point of the brazing filler metal, the pulsed magnetic field is turned off. Then, the workpiece is rapidly cooled to the set temperature and held for 2 to 5 minutes. After the heat preservation is completed, the workpiece is cooled with the furnace to obtain the brazed workpiece.

[0010] Furthermore, in the above-mentioned pulsed magnetic field assisted brazing method for ultrapure ferritic stainless steel, the brazing filler metal includes hard brazing filler metal.

[0011] Furthermore, in the above-mentioned pulsed magnetic field assisted brazing method for ultrapure ferritic stainless steel, the brazing filler metal includes nickel-based brazing filler metal, copper brazing filler metal, or silver-based brazing filler metal.

[0012] Furthermore, in the above-mentioned pulsed magnetic field assisted brazing method for ultrapure ferritic stainless steel, a protective gas is introduced during the brazing process or the process is carried out in a vacuum environment.

[0013] Furthermore, in the above-mentioned pulsed magnetic field-assisted brazing method for ultrapure ferritic stainless steel, placing the weld seam of the brazed parts in a direction perpendicular to the alternating magnetic field includes:

[0014] For pipes, the transverse pulse magnetic field and the longitudinal pulse magnetic field are turned on respectively, and the temperature is maintained for 2 to 10 minutes respectively;

[0015] For plates, the magnetic field in the corresponding direction is turned on according to the direction of the brazing weld seam of the brazed parts being perpendicular to the alternating magnetic field.

[0016] Furthermore, in the above-mentioned pulsed magnetic field assisted brazing method for ultrapure ferritic stainless steel, the gradient cooling of the welded workpiece after the heat preservation includes: rapidly cooling to 200-400℃ at a rate of 20-200℃ / s after the pulsed magnetic field is turned off, holding for 2-10 minutes, and then rapidly cooling to room temperature after the heat preservation is completed.

[0017] Secondly, a pulsed magnetic field-assisted brazing fixture for ultrapure ferritic stainless steel is provided, comprising:

[0018] The furnace shell, which serves as the main body of the tooling, is located on the outermost layer of the tooling, and the interior of the furnace shell is a hollow structure;

[0019] A furnace body insulation layer is disposed inside the furnace shell and connected to the furnace shell, with a gap between the furnace body insulation layer and the furnace shell;

[0020] A magnetic field coil, which fills the gap.

[0021] Furthermore, in the brazing fixture for pulsed magnetic field-assisted ultrapure ferritic stainless steel described above, the furnace shell includes a rectangular furnace shell.

[0022] Furthermore, in the brazing fixture for ultrapure ferritic stainless steel assisted by the pulsed magnetic field described above, the magnetic field coil is disposed within the four side walls of the rectangular furnace shell.

[0023] The main advantages of the technical solution of this invention are as follows:

[0024] The present invention provides a pulsed magnetic field-assisted brazing method and tooling for ultrapure ferritic stainless steel, which solves the shortcomings of poor wettability of brazing filler metal, excessively coarse grains in the base material, embrittlement and deterioration of mechanical properties, and poor sealing of brazed joints during the brazing process of ultrapure ferritic stainless steel. By integrating a pulsed magnetic field generator into the brazing furnace, the holding time in the high-temperature section is significantly reduced, avoiding excessive grain growth in ultrapure ferritic stainless steel. By combining magnetic field assistance and gradient cooling, the wettability of conventional brazing filler metal during the brazing of ultrapure ferritic stainless steel is improved, as well as the sealing and connection strength of the brazed joint. The invention overcomes the influence of the passivation film on the surface of existing ultrapure ferritic stainless steel and elements such as Ti and Al, achieving qualified strength and sealing of the finished brazed parts. Attached Figure Description

[0025] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and constitute a part of this invention, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings:

[0026] Figure 1 This is a schematic flowchart of a pulsed magnetic field-assisted brazing method for ultrapure ferritic stainless steel according to an embodiment of the present invention.

[0027] Figure 2 This is a schematic diagram of a pulsed magnetic field-assisted brazing fixture for ultrapure ferritic stainless steel, provided in an embodiment of the present invention.

[0028] Explanation of reference numerals in the attached figures:

[0029] 1. Magnetic field coil; 2. Stainless steel pipe; 3. Brazing material; 4. Furnace body insulation layer; 5. Furnace shell. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0031] The following is in conjunction with the appendix Figure 1 -Appendix Figure 2 The technical solutions provided in the embodiments of the present invention will be described in detail.

[0032] As attached Figure 1 As shown, this invention provides a pulsed magnetic field-assisted brazing method for ultrapure ferritic stainless steel. This method, based on Lorentz force-driven filler metal flow, utilizes a short-process flow, combined with magnetic field assistance and gradient cooling, to improve the wettability of conventional filler metals during ultrapure ferritic stainless steel brazing, thereby improving the sealing performance and connection strength of the brazed joint. When brazing ultrapure ferritic stainless steel using the method provided in this invention, it overcomes the influence of existing passivation films on the surface of ultrapure ferritic stainless steel, as well as the influence of elements such as Ti and Al, and the dependence on high temperatures and long durations. It solves the shortcomings of poor filler metal wettability, excessively coarse base metal grains, material embrittlement and deterioration of mechanical properties, and poor sealing performance of the brazed joint during the brazing process of ultrapure ferritic stainless steel. The method includes the following steps S1-S3:

[0033] Step S1: Place the cleaned and dried ultrapure ferritic stainless steel and the welding position of the part to be welded on a fixture with a pulsed magnetic field for brazing. Use Lorentz force to drive the molten brazing filler metal to flow in a directional manner. Control the magnetic field strength to be 50-1000mT, control the magnetic field frequency to be 10-500Hz, control the brazing filler metal heating rate to be 10-100℃ / min, and control the brazing temperature to be 700~1100℃.

[0034] Specifically, in this embodiment of the invention, in order to ensure the welding effect, the oil stains on the inner and outer surfaces of the ultrapure ferritic stainless steel (plate, pipe, etc.) to be brazed and the brazing material need to be cleaned and dried before welding. The surface cleaning method includes using physical methods such as chemical treatment and surface grinding, or a combination of both.

[0035] For example, chemical treatment methods include using low-alkalinity water to remove oil stains from the inner and outer surfaces, while physical treatment methods include using sandpaper for light polishing.

[0036] In some optional implementations of the present invention, the brazing filler metal includes hard brazing filler metal, and preferably the brazing filler metal is any one of nickel-based brazing filler metal, copper brazing filler metal or silver-based brazing filler metal.

[0037] To prevent oxidation of the parts to be welded during the welding process, inert gases or other protective gases are continuously introduced during brazing, or welding is carried out in a vacuum environment to ensure the strength and performance requirements of the welded workpiece. The protective gas includes inert gases.

[0038] During the welding process, in order to further ensure welding quality and effect, the direction of the magnetic field is set differently depending on the shape of the parts being welded. Specifically, the weld seam of the brazed parts is placed in a direction perpendicular to the alternating magnetic field, including:

[0039] For pipes, the transverse pulse magnetic field and the longitudinal pulse magnetic field are turned on respectively, and the heat is maintained for a certain period of time, preferably 2 to 10 minutes;

[0040] For plates, the magnetic field in the corresponding direction is turned on according to the direction of the brazing weld seam of the brazed parts being perpendicular to the alternating magnetic field.

[0041] Step S2: After brazing, the welded ultrapure ferritic stainless steel and the workpiece formed by the welded parts are kept at a constant temperature for 2 to 20 minutes.

[0042] Step S3: After the heat preservation is completed, the welded workpiece is subjected to gradient cooling. During the cooling process, the pulse magnetic field is turned on. After the temperature of the welded workpiece drops below the melting point of the brazing filler metal, the pulse magnetic field is turned off. Then, the workpiece is rapidly cooled to the set temperature and held for 2 to 5 minutes. After the heat preservation is completed, the workpiece is cooled with the furnace to obtain the brazed workpiece.

[0043] Specifically, after the heat preservation is completed, the welded workpiece is subjected to gradient cooling, which includes: after the pulse magnetic field is turned off, it is rapidly cooled to 200-400℃ at a rate of 20-200℃ / s, held for 2-10 minutes, and then rapidly cooled to room temperature.

[0044] Example 1:

[0045] Taking the pulsed magnetic field assisted brazing of ultra-pure ferritic stainless steel SUS445J2 pipe and SUS316L pipe shell as an example, the above-mentioned assisted welding method of the present invention is used for welding, including:

[0046] (1) Use low-alkalinity water to remove oil stains from the inner and outer surfaces of the ultra-pure ferritic stainless steel SUS445J2 pipe and SUS316L pipe shell, and wash with clean water. After drying, use sanding belt to lightly polish.

[0047] (2) Place the copper-based brazing filler metal at the connection between the SUS316L tube shell and the SUS445J2 tube, assemble the brazing parts, place them on the tooling and fix them.

[0048] (3) Seal the furnace door and continuously introduce argon gas as a protective gas, raising the temperature inside the brazing furnace to 900℃; then push the fixture with the parts to be brazed into the brazing furnace and close the furnace door. Turn on the transverse and longitudinal pulsed magnetic fields for 3 minutes each, setting the magnetic field strength to 500mT and the frequency to 50Hz.

[0049] (4) Turn off the heating device, introduce cooling gas to rapidly reduce the furnace temperature to 350°C at a rate of 50°C / s, and then turn off the pulse magnetic field. Turn on the heating device, maintain the temperature at 350°C for 2 minutes, and then introduce cooling gas to cool to room temperature.

[0050] Samples of the base material and weld were taken from the brazed parts and metallographic and mechanical samples were prepared to observe the grain size of the base material, the density of the brazed joint, and the mechanical properties of the weld joint. The analysis results are shown in Table 1 below.

[0051] Example 2:

[0052] Taking the pulsed magnetic field assisted brazing of ultra-pure ferritic stainless steel SUS444 tubing and SUS441 fins as an example, the above-mentioned assisted welding method of the present invention is used for welding, including:

[0053] (1) Use low-alkalinity water to remove oil stains from the inner and outer surfaces of ultra-pure ferritic stainless steel SUS444 pipes and SUS441 fins, rinse with clean water, dry, and then lightly polish with sandpaper.

[0054] (2) Place the nickel-based brazing filler metal at the connection between the SUS444 tube and the SUS441 fin, assemble the brazing parts, place them on the tooling and fix them.

[0055] (3) Seal the furnace door and continuously introduce argon gas as a protective gas, and raise the temperature inside the brazing furnace to 900℃; then push the fixture with the parts to be brazed into the brazing furnace, close the furnace door, and turn on the transverse and longitudinal pulse magnetic fields for 2 minutes each, with a magnetic field strength of 450mT and a frequency of 50Hz.

[0056] (4) Turn off the heating device, introduce cooling gas to rapidly reduce the furnace temperature to 350°C at a rate of 40°C / s, and then turn off the pulse magnetic field. Turn on the heating device, maintain the temperature at 350°C for 2 minutes, and then introduce cooling gas to cool to room temperature.

[0057] Samples of the base material and weld were taken from the brazed parts and metallographic and mechanical samples were prepared to observe the grain size of the base material, the density of the brazed joint, and the mechanical properties of the weld joint. The analysis results are shown in Table 1 below.

[0058] Comparative Example 1:

[0059] Taking the conventional brazing of ultra-pure ferritic stainless steel SUS444 tubing and SUS441 fins as an example, the welding is performed using existing conventional welding methods, including:

[0060] (1) Use low-alkalinity water to remove oil stains from the inner and outer surfaces of ultra-pure ferritic stainless steel SUS444 pipes and SUS441 fins, rinse with clean water, dry, and then lightly polish with sandpaper.

[0061] (2) Place the nickel-based brazing filler metal at the connection between the SUS444 tube and the SUS441 fin, assemble the brazing parts, place them on the tooling and fix them.

[0062] (3) Seal the furnace door and continuously introduce argon gas as a protective gas to raise the temperature inside the brazing furnace to 1100℃; then push the fixture with the parts to be brazed into the brazing furnace and close the furnace door. Hold at this temperature for 30 minutes.

[0063] (4) Turn off the heating device and let the furnace cool to room temperature.

[0064] Samples of the base material and weld were taken from the brazed parts for metallographic and mechanical analysis. The grain size of the base material, the density of the brazed joint, and the mechanical properties of the welded joint were observed. The results of the mechanical property analysis of the welded workpiece are shown in Table 1 below.

[0065] Table 1. Welding performance data of microstructure between ultrapure ferritic stainless steel base material and weld after brazing using different brazing processes.

[0066] Example 1 53μm none 251MPa Example 2 52μm none 247MPa Comparative Example 1 180μm have 100MPa

[0067] As shown in Table 1 above, the average grain size of the base material of the workpiece brazed with ultra-pure ferritic stainless steel using the method provided in this embodiment of the invention is significantly smaller than the average grain size of the base material brazed using conventional techniques, by approximately 30%. Furthermore, when brazing the workpiece using the method provided in this embodiment of the invention, there are no voids at the brazed joint, whereas voids exist when brazing using conventional techniques. The yield strength of the brazed joint when brazing ultra-pure ferritic stainless steel using the method provided in this embodiment of the invention is 2.5 times that of the brazed joint using conventional techniques. Therefore, the method provided in this embodiment of the invention is effective for brazing ultra-pure ferritic stainless steel. The welding performance far exceeds the mechanical properties of brazing using existing technologies. Furthermore, the method provided in this invention, combined with magnetic field assistance, can shorten the traditional holding time from 10-15 minutes to 3-5 minutes, reduce the high-temperature heating time by 40%-60%, and control the grain size within the range of 10-50 μm. In this invention, gradient cooling control is used to further suppress grain growth and reduce stress at the weld, thereby improving the brazed joint strength. In addition, the ultra-pure ferritic stainless steel used in this invention does not require the addition of precious metal elements such as Nb and W, reducing costs while ensuring the brazing quality and overall quality of the workpiece.

[0068] In summary, the pulsed magnetic field-assisted brazing method for ultrapure ferritic stainless steel provided by this invention solves the shortcomings of poor solder wettability, excessively coarse base metal grains, material embrittlement and deterioration of mechanical properties, and poor sealing of brazed joints during the brazing process of ultrapure ferritic stainless steel. By integrating a pulsed magnetic field generator into the brazing furnace, the holding time in the high-temperature section is significantly reduced, avoiding excessive grain growth in ultrapure ferritic stainless steel. By combining magnetic field assistance with gradient cooling, the wettability of conventional solders during the brazing of ultrapure ferritic stainless steel is improved, thereby improving the sealing and connection strength of the brazed joints. The method overcomes the influence of the passivation film on the surface of existing ultrapure ferritic stainless steel and elements such as Ti and Al, achieving qualified strength and sealing performance of the finished brazed parts.

[0069] Secondly, embodiments of the present invention also provide a brazing fixture for ultrapure ferritic stainless steel assisted by a pulsed magnetic field, comprising: a furnace shell 5, a furnace insulation layer 4, and a magnetic field coil 1, wherein:

[0070] The furnace shell 5 serves as the main body of the tooling and is located on the outermost layer of the tooling. The interior of the furnace shell 5 is a hollow structure. The furnace body insulation layer 4 is set inside the furnace shell 5 and is connected to the furnace shell 5. A gap is provided between the furnace body insulation layer 4 and the furnace shell 5. The magnetic field coil 1 is filled in the gap.

[0071] In some optional implementations of this invention, the furnace shell 5 includes a rectangular furnace shell 5. When the furnace shell 5 is configured as a rectangular hollow structure, the magnetic field coil 1 is disposed within the four side walls of the rectangular furnace shell 5.

[0072] For example, such as Figure 2 As shown, this is a pulsed magnetic field-assisted brazing fixture for ultrapure ferritic stainless steel provided in an embodiment of the present invention. The fixture adopts a hollow rectangular structure. When brazing ultrapure ferritic parts using the fixture of this embodiment, the ultrapure ferritic material to be welded, the brazing filler metal, and the parts to be welded to the ultrapure ferritic material are arranged according to... Figure 2 After assembly as shown ( Figure 2 The diagram shows two ultra-pure ferritic stainless steel tubes 2 with different diameters. During brazing assembly, the two tubes 2 are nested together, with their centers coinciding. Brazing filler metal 3 is filled into the gap between the two tubes 2. The tubes are then fixed in the hollow center of the furnace shell 5. The method described above, using a pulsed magnetic field-assisted brazing technique for ultra-pure ferritic stainless steel and its corresponding parameters, allows the use of ultra-pure ferritic stainless steel raw materials and brazing filler metal without added precious metals. This significantly reduces the high-temperature brazing time and suppresses grain coarsening, ensuring good mechanical properties and corrosion resistance of the base material. Simultaneously, it ensures uniform distribution of the brazing filler metal at the joint, forming a high-quality brazed joint.

[0073] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Additionally, the terms "front," "back," "left," "right," "upper," and "lower" in this document refer to the placement shown in the accompanying drawings.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A pulsed magnetic field-assisted brazing method for ultrapure ferritic stainless steel, characterized in that, include: The cleaned and dried ultrapure ferritic stainless steel is placed on a tooling with a pulsed magnetic field at the welding position of the part to be welded. The molten filler metal is driven to flow in a directional manner by the Lorentz force. The magnetic field strength is controlled at 50-1000mT, the magnetic field frequency is controlled at 10-500Hz, the filler metal heating rate is controlled at 10-100℃ / min, and the brazing temperature is controlled at 700~1100℃. After brazing, the welded ultrapure ferritic stainless steel and the workpiece formed by the welded parts are kept at a temperature for 2 to 20 minutes. After the heat preservation is completed, the welded workpiece is subjected to gradient cooling. During the cooling process, the pulsed magnetic field is turned on. After the temperature of the welded workpiece drops below the melting point of the brazing filler metal, the pulsed magnetic field is turned off. After the pulsed magnetic field is turned off, the workpiece is rapidly cooled to 200-400℃ at a rate of 20-200℃ / s. The temperature is then maintained for 2-10 minutes. After the heat preservation is completed, the workpiece is rapidly cooled to room temperature to obtain the brazed workpiece. Depending on the shape of the parts being welded, the direction of the magnetic field used during welding varies, ensuring that the weld seam is placed perpendicular to the alternating magnetic field. This includes: For pipes, activate the transverse pulse magnetic field and the longitudinal pulse magnetic field respectively, and keep them heated for 2~10 minutes respectively; For plates, the magnetic field in the corresponding direction is turned on according to the direction of the brazing weld of the brazed parts being perpendicular to the alternating magnetic field. The tooling includes: The furnace shell, which serves as the main body of the tooling, is located on the outermost layer of the tooling, and the interior of the furnace shell is a hollow structure; A furnace body insulation layer is disposed inside the furnace shell and connected to the furnace shell, with a gap between the furnace body insulation layer and the furnace shell; A magnetic field coil, which fills the gap.

2. The method for brazing ultrapure ferritic stainless steel assisted by a pulsed magnetic field according to claim 1, characterized in that, The brazing filler metal includes hard brazing filler metal.

3. The method for brazing ultrapure ferritic stainless steel assisted by a pulsed magnetic field according to claim 2, characterized in that, The brazing filler metal includes nickel-based brazing filler metal, copper brazing filler metal, or silver-based brazing filler metal.

4. The method for brazing ultrapure ferritic stainless steel assisted by a pulsed magnetic field according to claim 1, characterized in that, The brazing process can be carried out by introducing a protective gas or in a vacuum environment.

5. The method for brazing ultrapure ferritic stainless steel assisted by a pulsed magnetic field according to claim 1, characterized in that, The furnace shell includes a rectangular furnace shell.

6. The method for brazing ultrapure ferritic stainless steel assisted by a pulsed magnetic field according to claim 5, characterized in that, The magnetic field coils are disposed inside the four side walls of the rectangular furnace shell.

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