Method for improving strength of molybdenum material welding joint

Abstract

The invention relates to the technical field of alloy welding, in particular to a method for improving the strength of a molybdenum material welding joint. Comprising the steps that cobalt and nickel are added in the welding process of the molybdenum material, and the molybdenum material comprises molybdenum or molybdenum alloy. According to the method, Co and Ni elements are added into a molybdenum and molybdenum alloy welding joint, the effects of second phase strengthening, grain boundary purification and grain refinement are exerted, then the welding seam strength of molybdenum and molybdenum alloy is improved, and through tests, the room-temperature tensile strength of a welding seam prepared through the method is 220%-300% of that of a welding seam in the prior art, and no pore defect exists.

Description

Technical Field

[0001] The invention relates to the technical field of alloy welding, and in particular to a method for improving the strength of a molybdenum material welding joint. Background Art

[0002] With the transformation of the global energy structure, nuclear energy has significant advantages such as high energy density, high stability and low carbon emissions. In this process, improving the long-term service stability of key equipment within the nuclear system to better cope with the increasingly harsh service environment has become an important issue. Molybdenum (Mo) and its alloys are often used in nuclear reactor components, including internal structures, fuel cladding and control rods, due to their strong high-temperature strength, radiation resistance and corrosion resistance, to improve the operational safety and stability of these facilities.

[0003] However, due to the intrinsic brittleness, non-intrinsic brittleness and manufacturing technology of molybdenum alloys, molybdenum alloys are still very easy to generate porosity defects and embrittlement in fusion welding joints, resulting in low strength of welded joints. Specifically, the brittleness of molybdenum is mainly affected by its atomic structure and the segregation of impurity elements (C, N, O) at the grain boundaries. Among them, O plays the greatest role in enhancing the brittleness of molybdenum, because the combination of O and molybdenum produces MoO 2 It will reduce the grain boundary strength. The formation of pores is mainly related to the reaction between Mo and O.

[0004] In order to solve the above problems, some scholars have proposed a method to reduce the brittleness of molybdenum alloy grain boundaries and improve the bonding strength of molybdenum grain boundaries by regulating metallurgical elements. The existing element regulation methods mostly use single element regulation methods, which cannot completely solve the problems of porosity defects and the formation of brittle compounds in the molybdenum alloy welding process. Summary of the invention

[0005] In order to solve the above problems, the present invention provides a method for improving the strength of a molybdenum material welding joint. The method provided by the present invention solves the problem of pore defects in the molybdenum alloy welding process and improves the strength of the joint.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a method for improving the strength of a molybdenum material welding joint, comprising the following steps: adding cobalt and nickel during the welding process of the molybdenum material, wherein the molybdenum material comprises molybdenum or a molybdenum alloy.

[0008] Preferably, the dimensions of the molybdenum material are: 50 mm in length, 50 mm in width, and 1 mm in height.

[0009] Preferably, the cobalt and nickel are added in the form of powder or foil.

[0010] Preferably, when the cobalt and nickel are added in powder form, the cobalt powder and nickel powder are applied to the surface of the welding surface of the molybdenum material and then welded, the atomic ratio of the nickel powder to the cobalt powder is 4:3, and the total thickness is 400 to 800 μm.

[0011] Preferably, when the cobalt and nickel are added in the form of foil, the cobalt foil and the nickel foil are alternately stacked to obtain a composite intermediate layer, and the composite intermediate layer is fixed to the molybdenum material and then welded;

[0012] The number of the cobalt foil and the nickel foil is more than 5;

[0013] The dimensions of the cobalt foil and the nickel foil are: thickness of 20-60 μm, length of 50 mm, and width of 1 mm.

[0014] Preferably, the welding is performed by a laser welding method, and the parameters of the laser welding method are: laser welding power 2500W to 4000W, and welding speed 0.8m / min to 2m / min.

[0015] Preferably, the welding form includes any one of butt weld, lap weld, T-weld and fillet weld.

[0016] Preferably, the pre-treatment of the molybdenum material before welding comprises the following steps:

[0017] The molybdenum material is polished with sandpaper in sequence to remove the oxide film to obtain a polished material;

[0018] The polished material was immersed in acetone for ultrasonic cleaning and then dried.

[0019] Preferably, 400# sandpaper, 800# sandpaper and 1200# sandpaper are used in sequence for grinding for 5 to 10 minutes.

[0020] Preferably, the ultrasonic cleaning is performed more than 3 times, the duration of each ultrasonic cleaning is more than 10 minutes, and the power of the ultrasonic cleaning is 120W to 240W.

[0021] Beneficial effects:

[0022] The present invention adds Co and Ni elements to the molybdenum and molybdenum alloy welding joints to play the role of second phase strengthening, grain boundary purification and grain refinement, thereby improving the weld strength of molybdenum and molybdenum alloys. According to tests, the room temperature tensile strength of the weld prepared by the present invention is 220%-300% of the prior art, and there is no pore defect. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments are briefly introduced below.

[0024] Figure 1 Adjust the tensile curve of the weld joint for powder;

[0025] Figure 2 X-ray flaw detection results: (a) Mo alloy welded joint; (b) Mo+CoNi welded joint;

[0026] Figure 3 Comparison of weld joint morphology: (a) Mo alloy weld joint; (b) Mo+CoNi weld joint;

[0027] Figure 4 The distribution of elements after adding the composite intermediate layer;

[0028] Figure 5 The measurement location and specific value of the element content;

[0029] Figure 6 Regulating the tensile curve of welded joints for foils. DETAILED DESCRIPTION

[0030] The present invention provides a method for improving the strength of a molybdenum material weld joint, comprising the following steps: adding cobalt and nickel during the welding process of the molybdenum material, wherein the molybdenum material comprises molybdenum or a molybdenum alloy. The present invention has no special restrictions on the metal elements contained in the molybdenum alloy, and a conventional molybdenum alloy can be used.

[0031] The present invention has no special requirements on the size of the molybdenum material, and those skilled in the art can select conventional sizes when welding. In a specific embodiment of the present invention, the size of the molybdenum material is preferably: 50 mm in length, 50 mm in width, and 1 mm in height.

[0032] In the present invention, the cobalt and nickel are preferably added in the form of powder or foil. In the present invention, when the cobalt and nickel are preferably added in the form of powder, the cobalt powder and nickel powder are applied to the surface of the welding surface of the molybdenum material (if welding along the length direction, they are applied to the length × height surface) and then welded, wherein the atomic ratio of the applied nickel powder to the cobalt powder is 4:3, and the total thickness is 400-800 μm. In the present invention, when the cobalt and nickel are preferably added in the form of foil, cobalt foil and nickel foil are alternately stacked to obtain a composite intermediate layer, and the composite intermediate layer is fixed to the molybdenum material and then welded. In the present invention, the number of cobalt foil and nickel foil is preferably more than 5. In the present invention, the sizes of the cobalt foil and nickel foil are preferably: 20-60 μm in thickness, 50 mm in length, and 1 mm in width.

[0033] The present invention has no special limitation on welding, and those skilled in the art can use conventional welding methods. In the present invention, the welding preferably adopts a laser welding method, and the parameters of the laser welding method are preferably: laser power 2800-4000W, welding speed 0.8-2m / min. In the present invention, the form of the welding preferably includes any one of butt weld, lap weld, T-weld and fillet weld.

[0034] In the present invention, the pretreatment of the molybdenum material before welding preferably includes the following steps: the molybdenum material is polished with sandpaper in sequence to remove the oxide film to obtain a polished material; the obtained polished material is soaked in acetone for ultrasonic cleaning, and then dried. The present invention preferably uses 400# sandpaper, 800# sandpaper and 1200# sandpaper for polishing for 5 to 10 minutes in sequence. In the present invention, the number of ultrasonic cleaning is preferably more than 3 times, the time of each ultrasonic cleaning is preferably more than 10 minutes, and the power of the ultrasonic cleaning is preferably 120 to 240W.

[0035] In order to further illustrate the present invention, the present invention is described in detail below in conjunction with embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1

[0037] A method for improving the strength of a molybdenum material welded joint, comprising the steps of:

[0038] Step 1: Take pure molybdenum plate as an example, cut the pure molybdenum plate according to 50mm (length) × 50mm (width) × 1mm (height), and grind the cut sample with 400#, 800# and 1200# sandpaper for 5 minutes in turn to remove the oxide film;

[0039] Step 2: Soak the polished sample in acetone and use 240W ultrasonic cleaning for at least 3 times, with each cleaning time not less than 10 minutes. Blow dry the cleaned sample and set aside for later use;

[0040] Step 3: One group of plates are directly welded without adjustment, and the other group is adjusted by adding elements using the pre-set powder addition method. Cobalt powder and nickel powder are pre-applied to the welding surface of the pure molybdenum plate, and the application amount of the two powders should be controlled so that the atomic ratio of the two powders is 4:3 and the total application thickness is 600μm;

[0041] Step 4: Fix the two sets of plates in the form of butt joints, and use conventional laser welding methods for welding, where the laser power is 3200W and the welding speed is 1.5m / min. After setting the parameters, weld and obtain a welded joint;

[0042] Step 5: Use the obtained weld joint to make a standard tensile part, and obtain the following Figure 1The tensile curve is shown in Figure 2. The results show that the joint performance of the molybdenum welded joint is 160.2MPa before regulation and reaches 362.2MPa after regulation, an increase of 226%.

[0043] Example 2

[0044] A method for improving the strength of a molybdenum material welded joint, comprising the steps of:

[0045] Step 1: Taking a molybdenum alloy containing 5% Re by mass as an example, the molybdenum alloy is cut into pieces according to 50 mm (length) × 50 mm (width) × 1 mm (height), and the cut samples are polished with 400#, 800# and 1200# sandpapers for 5 minutes in turn to remove the oxide film;

[0046] Step 2: Soak the polished sample in acetone and use 240W ultrasonic cleaning for at least 3 times, with each cleaning time not less than 10 minutes. Blow dry the cleaned sample and set aside for later use;

[0047] Step 3: The element adding method uses the foil adding method. 50μm thick pure cobalt foil and pure nickel foil are made into 50mm×1mm size, 5 pieces of each foil are stacked alternately to form a composite middle layer;

[0048] Step 4: Place the composite intermediate layer in the middle of the butt welding surface, fix the plate to be welded, and the joint form is butt welding;

[0049] Step 5: The welding method adopts a vacuum laser welding method, the ambient pressure is 10Pa, the laser power is 2800W, the welding speed is 1.5m / min, and welding is performed after setting the welding parameters to obtain a welded joint;

[0050] Step 6: Use X-ray to detect the weld joints without the composite intermediate layer and the weld joints with the composite intermediate layer, and obtain the following Figure 2 The results are shown in Figure 2. After adding the CoNi intermediate layer, no porosity defects are generated in the weld.

[0051] Step 7: The welded joints without the composite intermediate layer and the welded joints with the composite intermediate layer were cut into 10 mm × 5 mm metallographic parts by wire cutting machine for microstructure observation. Figure 3 As shown in the figure, it can be seen that after adding CoNi, the structure of the molybdenum-rhenium alloy weld joint is refined and there is no porosity defect. After observing the element distribution in the weld joint, the following is obtained: Figure 4 , Figure 5 The results shown in the figure show that the introduced Co and Ni elements are evenly distributed in the weld joint. After the tensile test was carried out using a 20kN tensile testing machine, the following results were obtained: Figure 6The results shown show that the tensile strength increased from 145 MPa to 430 MPa, an overall increase of 297%.

[0052] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for improving the strength of a molybdenum material welded joint, characterized in that: The following steps are involved: Cobalt and nickel are added during the welding process of the molybdenum material, and the molybdenum material includes molybdenum or a molybdenum alloy.

2. The method according to claim 1, characterized in that: The dimensions of the molybdenum material are: 50 mm in length, 50 mm in width, and 1 mm in height.

3. The method according to claim 1, characterized in that The cobalt and nickel are added in the form of powder or foil.

4. The method according to claim 2 or 3, characterized in that: When the cobalt and nickel are added in powder form, the cobalt powder and nickel powder are applied to the surface of the molybdenum material for welding, and then welding is performed. The atomic ratio of the nickel powder to the cobalt powder is 4:3, and the total thickness is 400-800 μm.

5. The method according to claim 2 or 3, characterized in that: When the cobalt and nickel are added in the form of foil, the cobalt foil and the nickel foil are alternately stacked to obtain a composite intermediate layer, and the composite intermediate layer is fixed to the molybdenum material and then welded; The number of the cobalt foil and the nickel foil is more than 5; The dimensions of the cobalt foil and the nickel foil are: thickness of 20-60 μm, length of 50 mm, and width of 1 mm.

6. The method according to claim 1, characterized in that The welding adopts a laser welding method, and the parameters of the laser welding method are: laser welding power 2500W to 4000W, and welding speed 0.8m / min to 2m / min.

7. The method according to claim 1, characterized in that The welding form includes any one of butt weld, lap weld, T-weld and fillet weld.

8. The method according to claim 1, characterized in that: The pre-treatment of the molybdenum material before welding comprises the following steps: The molybdenum material is polished with sandpaper in sequence to remove the oxide film to obtain a polished material; The polished material was immersed in acetone for ultrasonic cleaning and then dried.

9. The method according to claim 8, characterized in that Use 400# sandpaper, 800# sandpaper and 1200# sandpaper in turn to polish for 5 to 10 minutes.

10. The method according to claim 8, characterized in that The number of ultrasonic cleaning is more than 3 times, the time of each ultrasonic cleaning is more than 10 minutes, and the power of the ultrasonic cleaning is 120W-240W.

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