Ultrapure ferritic stainless steel brazing method and tool assisted by pulsed magnetic field

Abstract

The invention discloses a pulsed magnetic field assisted ultra-pure ferritic stainless steel brazing method and tool, and the method comprises the following steps: arranging the cleaned and dried ultra-pure ferritic stainless steel and a welding position of a welded part on the tool with a pulsed magnetic field for brazing, and driving molten brazing filler metal to directionally flow by utilizing Lorentz force, the magnetic field intensity is controlled to be 50-1000 mT, the magnetic field frequency is controlled to be 10-500 Hz, the temperature rising speed of the brazing filler metal is controlled to be 10-100 DEG C / min, and the brazing temperature is controlled to be 700-1100 DEG C; after brazing is completed, a workpiece formed by the welded ultra-pure ferrite stainless steel and the welded part is subjected to heat preservation, and the heat preservation time is controlled to be 2-20 min; and after heat preservation is finished, gradient cooling is conducted on the welded workpiece, a pulsed magnetic field is started during cooling, after the temperature of the welded workpiece is reduced to be below the melting point of brazing filler metal, the pulsed magnetic field is closed, heat preservation is conducted after the workpiece is rapidly cooled to the set temperature, furnace cooling is conducted after heat preservation, and the brazed workpiece is obtained. According to the invention, the brazing filler metal can be uniformly distributed at the joint, and a high-quality brazed joint is formed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of stainless steel welding, in particular to a pulse magnetic field assisted ultra-pure ferritic stainless steel brazing method and tooling. BACKGROUND

[0002] When ultra-pure ferritic stainless steel is widely used in the fields of household appliances, automobiles, chemical equipment, etc., due to the advantages of high production efficiency and low cost, the same material parts, austenitic stainless steel or copper and other dissimilar materials are often connected by brazing process. However, due to the existence of protective oxide film on the surface of the stainless steel, the wetting property of the filler metal is usually poor. In order to ensure that the filler metal is fully melted and wetted in the gap between the connecting parts, and to ensure the sealing performance and mechanical properties of the welded joint, the ultra-pure ferritic stainless steel usually needs to be heated at about 1000 degrees Celsius for about 30 minutes. However, due to the characteristics of easy grain growth of ferrite, the base material and the weld of the ultra-pure ferritic stainless steel after brazing are severely coarsened, which leads to the rapid increase of brittleness of the weld and the base material, and the deterioration of the elongation and fatigue performance. At the same time, it also has a serious adverse effect on the corrosion resistance of the base material and the weld of the ultra-pure ferritic stainless steel, which eventually leads to the failure of the product in use, such as base material cracking and corrosion.

[0003] In order to avoid the above-mentioned shortcomings, in the prior art, on the one hand, a higher content of Nb, W and other elements is added to the ultra-pure ferritic stainless steel to improve the high temperature performance of the base material and the weld of the ultra-pure ferritic stainless steel, and at the same time, the pulse magnetic field assisted ultra-pure ferritic stainless steel generates LAVES phase and other second phases to inhibit grain coarsening. On the other hand, a silver-based filler metal with higher wettability is used to reduce the high temperature heating time to prevent the grain coarsening of the ultra-pure ferritic stainless steel. However, both of the above-mentioned methods in the prior art greatly increase the cost of raw materials and processing, which seriously affects and restricts the development and application of ultra-pure ferritic stainless steel. SUMMARY

[0004] In order to solve the above-mentioned technical problems in the prior art, the present application provides a pulse magnetic field assisted ultra-pure ferritic stainless steel brazing method and tooling, which can use ultra-pure ferritic stainless steel raw materials and filler metals without adding noble metal elements, greatly reduce the high temperature brazing time of ultra-pure ferritic stainless steel and inhibit grain coarsening, ensure good mechanical properties and corrosion resistance of the base material, and at the same time, can make the filler metal uniformly distributed at the connecting part to form a high-quality brazed joint.

[0005] The technical scheme of the present application is as follows:

[0006] In a first aspect, a pulse magnetic field assisted ultra-pure ferritic stainless steel brazing method is provided, comprising:

[0007] The cleaned and dried ultra-pure ferritic stainless steel and the welding position of the welded part are arranged on a tooling with a pulsed magnetic field for brazing, the molten filler metal is driven to flow directionally by using the Lorentz force, the magnetic field intensity is controlled to be 50-1000 mT, the magnetic field frequency is controlled to be 10-500 Hz, the brazing temperature is controlled to be 700-1100℃, and the brazing temperature is controlled to be 700-1100℃.

[0008] After the brazing is completed, the welded ultra-pure ferritic stainless steel and the workpiece formed by the welded part are subjected to heat preservation, and the heat preservation time is controlled to be 2-20 min.

[0009] After the heat preservation is completed, the welded workpiece is subjected to gradient cooling, the pulsed magnetic field is turned on during the cooling, the pulsed magnetic field is turned off after the temperature of the welded workpiece is reduced to below the melting point of the filler metal, then the workpiece is rapidly cooled to a set temperature, and the workpiece is subjected to heat preservation for 2-5 min, and after the heat preservation is completed, the workpiece is cooled in the furnace to obtain a brazed workpiece.

[0010] Further, in the above-mentioned brazing method of the ultra-pure ferritic stainless steel assisted by the pulsed magnetic field, the filler metal comprises a hard brazing filler metal.

[0011] Further, in the above-mentioned brazing method of the ultra-pure ferritic stainless steel assisted by the pulsed magnetic field, the filler metal comprises a nickel-based brazing filler metal, a copper brazing filler metal or a silver-based brazing filler metal.

[0012] Further, in the above-mentioned brazing method of the ultra-pure ferritic stainless steel assisted by the pulsed magnetic field, a protective gas is introduced or the brazing is performed in a vacuum environment during the brazing.

[0013] Further, in the above-mentioned brazing method of the ultra-pure ferritic stainless steel assisted by the pulsed magnetic field, the welded part is arranged in a direction perpendicular to the alternating magnetic field, which comprises:

[0014] For a pipe, a transverse pulsed magnetic field and a longitudinal pulsed magnetic field are turned on respectively, and heat preservation is performed for 2-10 min.

[0015] For a plate, the magnetic field in the corresponding direction is turned on according to the direction in which the brazing filler metal is arranged perpendicular to the alternating magnetic field.

[0016] Further, in the above-mentioned brazing method of the ultra-pure ferritic stainless steel assisted by the pulsed magnetic field, the gradient cooling of the welded workpiece after the heat preservation is completed comprises: after the pulsed magnetic field is turned off, the workpiece is rapidly cooled to 200-400℃ at a rate of 20-200℃ / s, heat preservation is performed for 2-10 min, and then the workpiece is rapidly cooled to room temperature after the heat preservation is completed.

[0017] In a second aspect, a brazing tooling for the ultra-pure ferritic stainless steel assisted by the pulsed magnetic field is provided, which comprises:

[0018] A furnace shell is located at the outermost layer of the tooling as a tooling body, and is hollow inside;

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

[0020] A magnetic field coil is filled in the gap.

[0021] Further, in the pulse magnetic field assisted super-pure ferritic stainless steel brazing tooling described in the above, the furnace shell comprises a rectangular furnace shell.

[0022] Further, in the pulse magnetic field assisted super-pure ferritic stainless steel brazing tooling described in the above, the magnetic field coil is arranged in the four side walls of the rectangular furnace shell.

[0023] The main advantages of the technical scheme of the present application are as follows:

[0024] The pulse magnetic field assisted super-pure ferritic stainless steel brazing method and tooling provided by the embodiment of the present application solve the problems of poor wettability of brazing filler metal, excessive grain size of base material, deterioration of material brittleness mechanical properties, and poor sealing of brazed joints in the brazing process of super-pure ferritic stainless steel. By integrating a pulse magnetic field generating device in the brazing furnace, the holding time in the high-temperature section is greatly reduced, and the grains of super-pure ferritic stainless steel are prevented from growing excessively large. By combining magnetic field assistance and gradient cooling, the wettability of conventional brazing filler metal during brazing of super-pure ferritic stainless steel is improved, and the sealing and connection strength of the brazed joint are improved. The influence of the surface passivation film of the existing super-pure ferritic stainless steel and elements such as Ti and Al is overcome, and the strength and sealing of the finished product after brazing are qualified. BRIEF DESCRIPTION OF DRAWINGS

[0025] The drawings described herein are used to provide further understanding of the embodiments of the present application, and form a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0026] Figure 1 A flowchart of a pulse magnetic field assisted super-pure ferritic stainless steel brazing method provided by an embodiment of the present application is shown;

[0027] Figure 2 A structural schematic diagram of a pulse magnetic field assisted super-pure ferritic stainless steel brazing tooling provided by an embodiment of the present application is shown.

[0028] Explanation of reference signs:

[0029] 1, magnetic field coil; 2, stainless steel pipe; 3, brazing filler metal; 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 embodiments of the present application, the filler metal comprises hard filler metal, and preferably the filler metal is any one of nickel-based filler metal, copper filler metal or silver-based filler metal.

[0037] In order to avoid oxidation of the parts to be welded during welding, inert gas or other protective gas is continuously introduced during brazing welding, or welding is performed in a vacuum environment, so as to guarantee the strength and performance requirements of the workpiece after welding, wherein the protective gas comprises inert gas.

[0038] In order to further guarantee the welding quality and welding effect during welding, the direction of the magnetic field set when welding the parts is different according to the shape of the welded parts, and specifically the brazed part weld is placed in a direction perpendicular to the alternating magnetic field, comprising:

[0039] For pipe materials, the transverse pulse magnetic field and the longitudinal pulse magnetic field are respectively turned on and kept for a certain time, and the preferred holding time is 2-10 min.

[0040] For plate materials, the magnetic field in the corresponding direction is turned on according to the direction in which the brazed part brazing weld is placed perpendicular to the alternating magnetic field.

[0041] Step S2: After brazing, the workpiece formed by the welded ultra-pure ferritic stainless steel and the welded parts is kept for a certain time, and the holding time is controlled to be 2-20 min.

[0042] Step S3: After the holding is completed, the welded workpiece is gradiently cooled, the pulse magnetic field is turned on during the cooling, the pulse magnetic field is turned off after the temperature of the welded workpiece is reduced to below the melting point of the filler metal, then the workpiece is rapidly cooled to a set temperature, kept for 2-5 min, and then cooled in the furnace after the holding is completed, to obtain the brazed workpiece.

[0043] Specifically, the gradient cooling of the welded workpiece after the holding is completed comprises: after the pulse magnetic field is turned off, the workpiece is rapidly cooled to 200-400℃ at a rate of 20-200℃ / s, kept for 2-10 min, and then rapidly cooled to room temperature after the holding is completed.

[0044] Embodiment 1:

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

[0046] (1) The pipe shell of the ultra-pure ferritic stainless steel SUS445J2 pipe material and SUS316L is cleaned by using low-alkalinity water to remove the oil stains on the inner and outer surfaces, and then cleaned with clean water, and after drying, the pipe shell is slightly polished by using a sand belt.

[0047] (2) Put the copper-based filler metal at the connection between the SUS316L tube shell and the SUS445J2 pipe, assemble the parts to be brazed, and then place and fix them on the tool;

[0048] (3) Close the furnace door and continuously input argon as a protective gas, and raise the temperature in the brazing furnace to 900 DEG C; then push the tool with the parts to be brazed into the brazing furnace, and close the furnace door. Open the horizontal and vertical pulse magnetic fields respectively for 3 min, and set the magnetic field intensity to be 500 mT and the frequency to be 50 Hz.

[0049] (4) Close the heating device, input cooling gas, rapidly reduce the temperature in the furnace to 350 DEG C at a rate of 50 DEG C / s, and close the pulse magnetic field. Open the heating device, keep the temperature at 350 DEG C for 2 min, then input cooling gas, and cool to room temperature.

[0050] Cut the base material and the weld sample from the brazed parts, prepare metallographic and mechanical samples, observe the grain size of the base material, the density of the brazing part and the mechanical properties of the welded joint, and the analysis results are shown in Table 1.

[0051] Example 2:

[0052] Taking the pulse magnetic field assisted brazing of the ultra-pure ferritic stainless steel SUS444 pipe and the SUS441 fin as an example, the above-mentioned assisted welding method of the embodiment of the application is used for welding, which comprises the following steps:

[0053] (1) Remove the oil stains on the inner and outer surfaces of the ultra-pure ferritic stainless steel SUS444 pipe and the SUS441 fin by using low-alkalinity water, and clean them with clean water, and then dry and slightly polish them by using a sand belt.

[0054] (2) Put the nickel-based filler metal at the connection between the SUS444 pipe and the SUS441 fin, assemble the parts to be brazed, and then place and fix them on the tool;

[0055] (3) Close the furnace door and continuously input argon as a protective gas, and raise the temperature in the brazing furnace to 900 DEG C; then push the tool with the parts to be brazed into the brazing furnace, and close the furnace door, open the horizontal and vertical pulse magnetic fields respectively for 2 min, and set the magnetic field intensity to be 450 mT and the frequency to be 50 Hz.

[0056] (4) Close the heating device, input cooling gas, rapidly reduce the temperature in the furnace to 350 DEG C at a rate of 40 DEG C / s, and close the pulse magnetic field. Open the heating device, keep the temperature at 350 DEG C for 2 min, then input cooling gas, and cool to room temperature.

[0057] The base material and weld sample are cut from the brazed parts, and the metallographic and mechanical sample preparation is carried out, the base material grain size, brazing density and mechanical properties of the welded joint are observed, and the analysis results are shown in Table 1 below.

[0058] Comparative Example 1

[0059] Taking the conventional brazing of ultrapure ferritic stainless steel SUS444 pipe and SUS441 fin as an example, the conventional welding means of the prior art is used for welding, including:

[0060] (1) The ultrapure ferritic stainless steel SUS444 pipe and SUS441 fin are cleaned with low-alkalinity water to remove oil stains on the inner and outer surfaces, and then washed with clean water, dried, and then lightly polished with a sand belt.

[0061] (2) The nickel-based filler metal is placed at the connection between the SUS444 pipe and the SUS441 fin, and after assembling the brazing parts, it is placed on the fixture and fixed;

[0062] (3) Close the furnace door and continuously introduce argon as a protective gas, and raise the temperature in the brazing furnace to 1100°C; then push the fixture with the brazing parts into the brazing furnace, and close the furnace door. Keep warm for 30 min

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

[0064] The base material and weld sample are cut from the brazed parts, and the metallographic and mechanical sample preparation is carried out, the base material grain size, brazing density and mechanical properties of the welded joint are observed, and the analysis results are shown in Table 1 below.

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

[0066] Case Parent material average grain size Presence of porosity at the brazing Brazed joint yield strength Example 1 53 μm No 251 MPa Example 2 52 μm No 247 MPa Comparative Example 1 180 μm Yes 100 MPa

[0067] From the above table 1, it can be seen that the average grain size of the workpiece base material brazed by the method provided by the embodiment of the present application is obviously smaller than that of the conventional brazing base material, about 30%, and when the workpiece is brazed by the method provided by the embodiment of the present application, there is no gap at the brazing position, while when brazed by the prior art, there is a gap at the brazing position, the yield strength of the brazed joint of the ultra-pure ferritic stainless steel when brazed by the method provided by the embodiment of the present application is 2.5 times that of the brazed joint when brazed by the prior art, thus the welding performance of the ultra-pure ferritic stainless steel when brazed by the method provided by the embodiment of the present application is far superior to the mechanical performance when brazed by the prior art, and the method provided by the embodiment of the present application can be combined with magnetic field assistance, the traditional holding time is shortened from 10-15 minutes to 3-5 minutes, the high-temperature heating time is shortened by 40%-60%, the grain size is controlled within the range of 10-50 μm, and in the embodiment of the present application, gradient cooling control is used to further inhibit grain growth and reduce stress at the weld, thereby improving the brazing strength, in addition, the content of noble metal elements such as Nb and W does not need to be intentionally increased in the ultra-pure ferritic stainless steel used in the embodiment of the present application, thereby reducing the cost while ensuring the brazing quality of the workpiece and the overall quality of the workpiece.

[0068] In summary, the pulse magnetic field assisted ultra-pure ferritic stainless steel brazing method provided by the embodiment of the present application solves the problems of poor brazing material wettability, excessively coarse base material grains, deterioration of material brittleness mechanical properties and poor brazed joint sealing during the brazing process of the ultra-pure ferritic stainless steel; by integrating a pulse magnetic field generating device in the brazing furnace, the high-temperature holding time is greatly reduced, thereby avoiding excessive grain growth of the ultra-pure ferritic stainless steel; by combining magnetic field assistance and gradient cooling, the wettability of the conventional brazing material during brazing of the ultra-pure ferritic stainless steel is improved, and the sealing and connection strength of the brazed joint are improved; the influence of the surface passivation film of the existing ultra-pure ferritic stainless steel and elements such as Ti and Al is overcome, and the strength and sealing of the finished product after brazing are qualified.

[0069] In a second aspect, the embodiment of the present application further provides a pulse magnetic field assisted ultra-pure ferritic stainless steel brazing tool, comprising: a furnace shell 5, a furnace body insulation layer 4 and a magnetic field coil 1, wherein:

[0070] The furnace shell 5 serves as the main body of the tool and is located at the outermost layer of the tool, and the furnace shell 5 has a hollow structure inside; the furnace body insulation layer 4 is arranged inside the furnace shell 5, and the furnace body insulation layer 4 is connected with the furnace shell 5, and a gap is arranged 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 the embodiments of the present application, the furnace shell 5 comprises a rectangular furnace shell 5. When the furnace shell 5 is arranged as a hollow rectangular structure, the magnetic field coil 1 is arranged in the four side walls of the rectangular furnace shell 5.

[0072] Exemplarily, as shown in Figure 2 Fig. 4, a brazing tool for pulse magnetic field assisted ultra-pure ferritic stainless steel provided by the embodiments of the present application adopts a hollow rectangular structure. When the tool of the embodiments of the present application is used to braze ultra-pure ferritic parts, the ultra-pure ferritic parts to be welded, the filler metal and the parts to be welded with the ultra-pure ferritic parts are assembled according to the method shown in Figure 2 Fig. 4, and then the ultra-pure ferritic stainless steel pipes 2 with different diameters shown in Figure 2 Fig. 5 are sleeved and set, the centers of the two ultra-pure ferritic stainless steel pipes 2 are overlapped, the filler metal 3 is filled in the gap between the two ultra-pure ferritic stainless steel pipes 2, and the ultra-pure ferritic stainless steel pipes 2 are fixed and placed in the middle hollow position of the furnace shell 5. Then, the ultra-pure ferritic stainless steel pipes 2 are brazed by using the above-mentioned brazing method and the corresponding parameters of the method. As a result, the ultra-pure ferritic stainless steel raw materials and the filler metal without adding noble metal elements can be used, the high-temperature brazing time of the ultra-pure ferritic stainless steel is greatly reduced, the grain coarsening is inhibited, the mechanical properties and corrosion resistance of the base metal are ensured to be good, the filler metal can be uniformly distributed at the connection, and a high-quality brazed joint is formed.

[0073] It should be noted that, in the present document, relational terms such as "first" and "second", and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. Furthermore, the terms "front", "rear", "left", "right", "up", "down", and the like in the present document are used with reference to the positions shown in the drawings.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than limit the present application; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can make modifications to the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some technical features; and these modifications or replacements 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 application.

Claims

1. A brazing method of pulse magnetic field assisted ultra-pure ferritic stainless steel, characterized by, The method comprises the following steps: The cleaned and dried ultra-pure ferritic stainless steel and the welding position of the welded part are placed on a tooling with a pulsed magnetic field for brazing, the molten filler metal is driven to flow directionally by Lorentz force, the magnetic field intensity is controlled to be 50-1000 mT, the magnetic field frequency is controlled to be 10-500 Hz, the brazing temperature is controlled to be 700-1100 ℃, and the brazing temperature is controlled to be 10-100 ℃ / min; After brazing, the brazed ultra-pure ferritic stainless steel and the welded part form a workpiece, and the workpiece is heat treated, and the heat preservation time is controlled to be 2-20 min; After the heat preservation is completed, the brazed workpiece is gradiently cooled, the pulsed magnetic field is turned on during the cooling, the pulsed magnetic field is turned off when the temperature of the brazed workpiece is reduced to below the melting point of the filler metal, then the brazed workpiece is quickly cooled to a set temperature, and the brazed workpiece is heat treated for 2-5 min after the heat treatment is completed, and the brazed workpiece is cooled in the furnace after the heat treatment is completed.

2. The method of claim 1, wherein the method is a method of pulse magnetic field- assisted super-pure ferritic stainless steel brazing. The filler metal comprises hard brazing filler metal.

3. The method of brazing of an ultra-pure ferritic stainless steel with pulsed magnetic field assistance according to claim 2, characterized in that, The filler metal comprises nickel-based filler metal, copper filler metal or silver-based filler metal.

4. The method of claim 1, wherein the ultra-pure ferritic stainless steel is a pulse magnetic field-aided brazing method, characterized by, In the brazing process, a protective gas is introduced or brazing is carried out in a vacuum environment.

5. The method of brazing pulse magnetic field assisted ultra-pure ferritic stainless steel according to claim 1, characterized in that, The brazed part weld is placed in a direction perpendicular to the alternating magnetic field, which comprises the following steps: For a pipe, a transverse pulsed magnetic field and a longitudinal pulsed magnetic field are turned on respectively, and heat preservation is carried out for 2-10 min respectively; For a plate, the magnetic field in the corresponding direction is turned on according to the brazing position of the brazing part.

6. The method of brazing a pulse magnet field assisted ultra-pure ferritic stainless steel according to claim 1, characterized in that, After the heat preservation is completed, the brazed workpiece is gradiently cooled, which comprises the following steps: after the pulsed magnetic field is turned off, the brazed workpiece is quickly cooled to 200-400 ℃ at a rate of 20-200 ℃ / s, heat preservation is carried out for 2-10 min, and then the brazed workpiece is quickly cooled to room temperature.

7. A pulse magnetic field-aided super-pure ferritic stainless steel brazing jig according to any one of claims 1 to 6, characterized by The method comprises the following steps: A furnace shell is used as a tooling main body and is located at the outermost layer of the tooling, and the furnace shell is internally hollow; A furnace body heat preservation layer is arranged in the furnace shell, and the furnace body heat preservation layer is connected with the furnace shell, and a gap is arranged between the furnace body heat preservation layer and the furnace shell; A magnetic field coil is filled in the gap.

8. The pulse magnetic field-aided super-purity ferritic stainless steel brazing kit according to one of claims 7, characterized by The furnace shell comprises a rectangular furnace shell.

9. The pulse magnetic field-aided super-purity ferritic stainless steel brazing kit according to one of claims 8, characterized by The magnetic field coil is arranged in the four side walls of the rectangular furnace shell.

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