Rapid brazing connection method for tungsten and steel

Abstract

The invention discloses a rapid brazing connection method for tungsten and steel, which comprises the following steps: step 1, pretreatment: machining a to-be-welded surface of a tungsten block and a to-be-welded surface of a steel substrate, so that the roughness of the two to-be-welded surfaces is less than or equal to Ra6.4; secondly, cleaning is conducted, specifically, the pretreated tungsten block is soaked in absolute ethyl alcohol to be subjected to ultrasonic cleaning for 5-10 min and dried, and meanwhile the to-be-welded face of the pretreated steel base body is subjected to alcohol spraying cleaning and then dried; (3) spraying is conducted, specifically, brazing filler metal powder is sprayed on the cleaned to-be-welded face of the tungsten block and the cleaned to-be-welded face of the steel base body, and a uniform coating with the thickness ranging from 0.05 mm to 0.3 mm is formed; and fourthly, brazed connection is conducted, specifically, the sprayed to-be-welded face of the tungsten block and the sprayed to-be-welded face of the steel base body are tightly laminated and heated to 900-1300 DEG C under the protective atmosphere, heat preservation is conducted for 1-30 min, and brazed connection is completed.

Description

Technical Field

[0001] The invention belongs to the technical field of heterogeneous material welding, and in particular relates to a method for quickly brazing tungsten and steel. Background Art

[0002] The cladding component faces the high-temperature plasma in a fusion reactor and is crucial for achieving nuclear fuel self-sustaining, heat removal, and radiation shielding. Therefore, the cladding is an essential core component in future commercial fusion reactors. The cladding's first wall is the portion of the cladding component that directly faces the high-temperature plasma. Its structure and function are similar to those of the divertor's first wall. Currently, tungsten and its alloys are preferred materials, typically in a mosaic-like tile structure. The cladding's first wall material is welded to the underlying structural material via hot isostatic pressing or brazing. Because the cladding portion experiences lower thermal radiation energy and higher neutron doses, the selection of the cladding's structural material prioritizes the neutron activity of the material elements, often using low-activation steels such as RAFM and CLAM. Poor welding between the cladding's first wall and the structural material increases the risk of the first wall detaching during extended service. This can expose the low-melting-point, sputtering-prone structural material to the high-temperature plasma, seriously impacting the safe and stable operation of the device. Therefore, joining tungsten to steel is a core process in cladding component manufacturing.

[0003] There are several problems with welding between tungsten and steel:

[0004] (1) The thermal expansion coefficients of the two are very different. The thermal expansion coefficient of steel is about 14×10 -6 K -1 , while the thermal expansion coefficient of tungsten is 4.5×10 -6 K -1 The difference of 3 times in thermal expansion coefficient between tungsten and steel will lead to stress-induced interfacial cracking during welding and long pulse cycle thermal shock conditions.

[0005] (2) The plastic deformation energy of steel is poor, and it cannot coordinate the strain through plastic deformation dislocation movement, leading to cracking;

[0006] (3) Long-term high-temperature diffusion between Fe and W will produce FeW and Fe2W brittle metal compounds at the interface, affecting the bonding strength;

[0007] (4) The melting points of the two are very different, making it difficult to weld them using conventional fusion welding methods.

[0008] Existing welding processes for tungsten and steel primarily fall into two categories: hot isostatic pressing (HIP) and brazing. HIP welding presents challenges such as limited equipment space, high processing costs, technically complex ferrule design and fabrication, and long production cycles. Traditional brazing processes, on the other hand, suffer from high brazing foil preparation costs. The wetting between the liquid brazing material and the solid substrate is easily affected by factors such as temperature uniformity and surface quality, resulting in poor weld spread uniformity and liquid brazing overflow. Furthermore, brazing processes typically use only a single layer of brazing material, making its thickness difficult to control and leading to unstable weld joint quality.

[0009] Therefore, there is an urgent need for a method for connecting tungsten and steel with high efficiency, low cost and excellent welding quality. Summary of the Invention

[0010] The purpose of the present invention is to overcome the above-mentioned deficiencies of the prior art and provide a method for rapid brazing connection of tungsten and steel to solve the problems of uneven spreading of the brazing material, low welding efficiency and high cost in the prior art.

[0011] In order to solve the technical problem, the technical solution of the present invention is: a method for quickly brazing tungsten and steel, comprising the following steps:

[0012] Step 1: Preprocessing:

[0013] The welding surface of the tungsten block and the welding surface of the steel substrate are machined to make the roughness of both welding surfaces ≤Ra6.4;

[0014] Step 2: Cleaning:

[0015] Immerse the pretreated tungsten block in anhydrous ethanol for ultrasonic cleaning for 5 to 10 minutes and dry it. At the same time, spray the pretreated steel substrate to be welded with alcohol and then dry it.

[0016] Step 3: Spraying:

[0017] Spray solder powder on the cleaned tungsten block to be welded and the steel substrate to be welded to form a uniform coating with a thickness of 0.05mm to 0.3mm;

[0018] The coating thickness is 0.05mm~0.3mm, and the thickness deviation does not exceed ±0.02mm;

[0019] Step 4: Brazing connection:

[0020] The sprayed tungsten block to be welded surface and the steel substrate to be welded surface are tightly overlapped and heated to 900-1300°C in a protective atmosphere and kept warm for 1-30 minutes to complete the brazing connection.

[0021] Preferably, the tungsten block in step one is made of pure tungsten, W-Al-K alloy, W-La alloy, W-Re alloy, W-ZrC alloy, W-TiC alloy or W-HfC alloy; the steel substrate is made of RAFM steel, CLAM steel or ODS steel; and the machining includes milling, turning, grinding, wire cutting or laser machining.

[0022] The selection of tungsten block material and steel substrate material can effectively reduce the stress concentration caused by the difference in thermal expansion coefficient.

[0023] Preferably, the solder powder composition in step three includes copper-based, iron-based, nickel-based or vanadium-based alloys, and the powder particle size is 10 μm to 100 μm.

[0024] Preferably, the number of layers of solder powder sprayed in step three is a single layer or a multi-layer structure.

[0025] Preferably, the solder powder in step three is selectively sprayed on the following positions: only on the surface to be welded of the tungsten block, only on the surface to be welded of the steel substrate, or sprayed on both the surface to be welded of the tungsten block and the steel substrate simultaneously.

[0026] Preferably, the method of spraying the solder powder in step three includes atmospheric plasma spraying, vacuum plasma spraying, cold spraying or supersonic flame spraying.

[0027] Preferably, the method for spraying the solder powder in step three adopts atmospheric plasma spraying, the spraying power is 20-60kW, the spraying distance is 20-50mm, the spraying path is spiral covering, and the interlayer temperature is controlled at ≤150°C to ensure that the solder powder is evenly spread and forms a dense coating.

[0028] Preferably, the heating method in step 4 includes induction heating, resistance heating, laser heating or electron beam heating.

[0029] Preferably, in step 4, the protective atmosphere includes nitrogen, argon, helium or vacuum; the purity of nitrogen is ≥99.99%, the purity of argon is ≥99.99%, the purity of helium is ≥99.99%, and the vacuum degree is ≤1×10-3Pa.

[0030] Preferably, after the brazing connection in step 4, the brazing connection is furnace cooled to below 200° C. and then air cooled, or forced cooled by helium with a cooling rate of ≤5° C. / s to reduce residual stress and improve the strength and plasticity of the welded joint.

[0031] Compared with the prior art, the advantages of the present invention are:

[0032] (1) The present invention adopts a solder powder spraying method to evenly spread the solder powder on the surface to be welded, and form a certain metallurgical bond or mechanical bond between the solder and the tungsten block or the solder and the steel substrate. In the subsequent heating and welding process, the wetting process of the solder and the tungsten block or the solder and the substrate is ignored, thereby accelerating the brazing speed and improving the efficiency. At the same time, the formation of brittle intermetallic compound phases caused by atomic interdiffusion and the increase of solid-solution atoms in the solder are avoided, thereby improving the plastic deformation ability of the solder layer to coordinate stress and strain, thereby improving the welding quality.

[0033] (2) The present invention adopts a solder powder spraying method to evenly spread the solder powder on the surface to be welded, forming a uniform coating with controllable thickness, thereby avoiding the problem of uneven powder thickness when manually applying solder flux or powder in traditional brazing, which in turn causes uneven solder spreading during brazing, and significantly improves welding quality and welding accuracy.

[0034] (3) The present invention directly adopts solder in powder form, eliminating the need for traditional solder foil. The foil prepared by powder sintering / melting, casting, multi-pass rolling, shearing and other processes is used as the preparation process of the solder, which significantly shortens the welding cycle, improves production efficiency, reduces brazing costs, and is easy to realize industrial production.

[0035] (4) The solder sprayed in the present invention can be selected as a single-layer or multi-layer solder structure as needed, which is suitable for connecting tungsten and steel of different thicknesses and shapes, expanding the scope of application. The reasonable design of the multi-layer solder plays a role in reducing residual stress, reducing the generation of brittle phase, and improving the overall plastic deformation capacity of the transition layer.

[0036] (5) The present invention is applicable to a variety of tungsten alloys (such as pure tungsten, W-Al-K alloy, W-La alloy, etc.) and steel substrates (such as RAFM steel, CLAM steel, ODS steel), and the spraying position can be flexibly selected, and only the tungsten block, only the steel substrate, or both can be sprayed at the same time, which is suitable for welding complex structures.

[0037] (6) By optimizing the spraying and brazing processes, the shear strength of the welded joint obtained by the present invention is significantly improved, and there are no defects such as cracks and pores on the interface, and the welded joint performance is excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 , a schematic flow chart of a method for rapid brazing connection of tungsten and steel according to the present invention;

[0039] Figure 2 , Interface characterization detection diagram after welding steel and tungsten copper in Example 3 of the present invention. DETAILED DESCRIPTION

[0040] The specific implementation of the present invention is described below with reference to the accompanying drawings and embodiments:

[0041] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions under which the present invention can be implemented. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in the present invention without affecting the efficacy and purpose that can be achieved by the present invention.

[0042] At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments to their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0043] like Figure 1 As shown, a method for quickly brazing tungsten and steel comprises the following steps:

[0044] Step 1: Preprocessing:

[0045] The welding surface of the tungsten block and the welding surface of the steel substrate are machined to make the roughness of both welding surfaces ≤Ra6.4;

[0046] Step 2: Cleaning:

[0047] Immerse the pretreated tungsten block in anhydrous ethanol for ultrasonic cleaning for 5 to 10 minutes and dry it. At the same time, spray the pretreated steel substrate to be welded with alcohol and then dry it.

[0048] Step 3: Spraying:

[0049] Spray solder powder on the cleaned tungsten block to be welded and the steel substrate to be welded to form a uniform coating with a thickness of 0.05mm to 0.3mm;

[0050] Step 4: Brazing connection:

[0051] The sprayed tungsten block to be welded surface and the steel substrate to be welded surface are tightly overlapped and heated to 900-1300°C in a protective atmosphere and kept warm for 1-30 minutes to complete the brazing connection.

[0052] Here are a few specific examples

[0053] Example 1

[0054] A method for quickly brazing tungsten and steel, comprising the following steps:

[0055] (1) Pretreatment: Pure tungsten block and CLAM steel were selected as welding objects. The surface to be welded of the pure tungsten block was ground to a roughness of Ra0.6; the surface to be welded of the CLAM steel substrate was milled to a roughness of Ra1.6.

[0056] (2) Cleaning: The pretreated pure tungsten block was immersed in anhydrous ethanol for ultrasonic cleaning for 5 minutes and then dried. At the same time, the pretreated CLAM steel substrate to be welded was sprayed with alcohol for cleaning and then dried.

[0057] (3) Spraying: The iron-based Fe-Si-B brazing filler metal powder is sprayed on the cleaned CLAM steel surface to be welded by supersonic flame spraying, with a spraying thickness of 0.19 mm to 0.23 mm. The iron-based Fe-Si-B brazing filler metal powder is selected because of its moderate melting point and good wettability with the steel matrix, which can effectively improve the strength of the welded joint.

[0058] (4) Brazing connection: The surface to be welded of the pure tungsten block and the surface to be welded of the steel substrate sprayed with brazing filler metal are tightly pressed together and heated to 1280°C in a protective atmosphere for 10 minutes in a vacuum atmosphere. This achieves a brazing connection between the pure tungsten block and the CLAM steel substrate with a shear strength of ≥200 MPa.

[0059] After brazing, the parts are furnace cooled to below 200°C and then air cooled.

[0060] Example 2

[0061] A method for quickly brazing tungsten and steel, comprising the following steps:

[0062] (1) Pretreatment: W-Al-K alloy and CLF-1 steel were selected as welding objects. The surface to be welded of the W-Al-K alloy block was subjected to wire cutting, with a roughness of Ra3.2; the surface to be welded of the CLF-1 steel substrate was subjected to milling, with a roughness of Ra3.2;

[0063] (2) Cleaning: The pretreated W-Al-K alloy block was immersed in anhydrous ethanol for ultrasonic cleaning for 5 min and then dried. At the same time, the pretreated CLF-1 steel substrate to be welded was sprayed with alcohol for cleaning and then dried.

[0064] (3) Spraying: Pure Cu spherical powder was sprayed on the cleaned W-Al-K alloy block to be welded by supersonic flame spraying method, with a spraying thickness of 0.3mm~0.35mm; Copper-based BCu84MnNi solder powder was sprayed on the cleaned CLF-1 steel substrate to be welded by cold spraying method, with a spraying thickness of 0.2mm~0.25mm.

[0065] (4) Brazing connection: The tungsten block to be welded sprayed with brazing filler metal and the steel substrate to be welded sprayed with brazing filler metal are tightly superimposed together and heated to 980°C in an atmosphere for 5 minutes. The protective atmosphere is argon, that is, the brazing connection between the W-Al-K alloy block and the CLF-1 steel substrate has a shear strength of ≥120 MPa.

[0066] After brazing, helium is used for forced cooling, with a cooling rate of ≤5℃ / s.

[0067] Example 3

[0068] A method for quickly brazing tungsten and steel, comprising the following steps:

[0069] (1) Pretreatment: Pure tungsten and CLF-1 steel were selected as welding objects. The surface to be welded of the pure tungsten block was milled to a roughness of Ra3.2; the surface to be welded of the CLF-1 steel substrate was milled to a roughness of Ra6.4.

[0070] (2) Cleaning: The pretreated pure tungsten block was immersed in anhydrous ethanol for ultrasonic cleaning for 5 min and then dried. At the same time, the pretreated CLF-1 steel substrate to be welded was sprayed with alcohol for cleaning and then dried.

[0071] (3) Spraying: BNi-2 powder is sprayed on the cleaned pure tungsten block to be welded by atmospheric plasma spraying method, with a spraying thickness of 0.15mm~0.2mm; pure Fe spherical powder is sprayed on the cleaned CLF-1 steel substrate to be welded by cold spraying method, with a spraying thickness of 0.05mm~0.1mm;

[0072] (4) Brazing connection: The surface of the tungsten block to be welded after spraying treatment and the surface of the steel substrate to be welded after spraying with brazing filler metal are tightly superimposed together, and heated to 1000℃ in an atmosphere for 10 minutes. The protective atmosphere is vacuum, that is, the brazing connection between the pure tungsten block and the CLF-1 steel substrate has a shear strength of ≥180MPa.

[0073] After brazing, the steel and tungsten copper are cooled in the furnace to below 200℃ and then air-cooled. The interface between steel and tungsten copper after welding is then characterized and tested, such as Figure 2 As shown, it can be seen that the interface has good formability and no obvious defects. Figure 2 (a) is the macroscopic morphology at the interface; (b) is the microstructure at the interface; (c) is the SAT nondestructive testing of the interface.

[0074] The present invention adopts a spraying method to evenly spread the solder powder on the surface to be welded, thereby avoiding the problem of uneven solder spreading in traditional brazing and improving the welding quality; the present invention reduces the complex process of solder preparation and reduces the cost; the present invention is suitable for connecting various tungsten alloys and steel substrates and has broad application prospects.

[0075] The preferred embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in this field without departing from the scope of the present invention.

[0076] Many other changes and modifications can be made without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments, and the scope of the present invention is defined by the appended claims.

Claims

1. A method for rapid brazing connection of tungsten and steel, characterized in that: The following steps are involved: Step 1: Preprocessing: The welding surface of the tungsten block and the welding surface of the steel substrate are machined to make the roughness of both welding surfaces ≤Ra6.4; Step 2: Cleaning: Immerse the pretreated tungsten block in anhydrous ethanol for ultrasonic cleaning for 5 to 10 minutes and dry it. At the same time, spray the pretreated steel substrate to be welded with alcohol and then dry it. Step 3: Spraying: Spray solder powder on the cleaned tungsten block to be welded and the steel substrate to be welded to form a uniform coating with a thickness of 0.05mm to 0.3mm; Step 4: Brazing connection: The sprayed tungsten block to be welded surface and the steel substrate to be welded surface are tightly overlapped and heated to 900-1300°C in a protective atmosphere and kept warm for 1-30 minutes to complete the brazing connection.

2. The method for rapid brazing connection of tungsten and steel according to claim 1, characterized in that: The tungsten block in step 1 is made of pure tungsten, W-Al-K alloy, W-La alloy, W-Re alloy, W-ZrC alloy, W-TiC alloy or W-HfC alloy; the steel substrate is made of RAFM steel, CLAM steel or ODS steel; and the machining includes milling, turning, grinding, wire cutting or laser machining.

3. The method for rapid brazing connection of tungsten and steel according to claim 1, characterized in that: The solder powder in step three comprises copper-based, iron-based, nickel-based or vanadium-based alloys, and the powder particle size is 10 μm to 100 μm.

4. The method for rapid brazing connection of tungsten and steel according to claim 1, characterized in that: The number of layers of solder powder sprayed in step three is a single layer or a multi-layer structure.

5. The method for rapid brazing connection of tungsten and steel according to claim 1, characterized in that: In step 3, the solder powder is selectively sprayed on the following positions: only on the surface to be welded of the tungsten block, only on the surface to be welded of the steel substrate, or simultaneously on the surfaces to be welded of the tungsten block and the steel substrate.

6. The method for rapid brazing connection of tungsten and steel according to claim 1, characterized in that: The method of spraying the solder powder in step three includes atmospheric plasma spraying, vacuum plasma spraying, cold spraying or supersonic flame spraying.

7. The method for rapid brazing connection of tungsten and steel according to claim 1, characterized in that: The heating method in step 4 includes induction heating, resistance heating, laser heating or electron beam heating.

8. The method for rapid brazing connection of tungsten and steel according to claim 1, characterized in that: In step 4, the protective atmosphere includes nitrogen, argon, helium or vacuum.

9. The method for rapid brazing connection of tungsten and steel according to claim 1, characterized in that: After the brazing connection in step 4, the furnace is cooled to below 200° C. and then air-cooled, or forced cooling is performed using helium, with a cooling rate of ≤5° C. / s.

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