Brazing paste for flux-free brazing of stainless steel, its manufacturing method and use

Abstract

The present invention discloses a brazing paste for flux-free brazing of stainless steel, which is mainly composed of water, sodium silicate, nanosilica and copper-based brazing material, and the raw materials of the brazing paste are 70-80 parts by weight of copper-based brazing material, 3-5 parts by weight of nanosilica, 1-3 parts by weight of sodium hydroxide and 10-15 parts by weight of water. The brazing paste is a paste containing water, sodium silicate and nanosilica, which is dehydrated at high temperature during brazing to form a thin film, and the nanosilica can build a three-dimensional network structure, which has a huge surface area and extremely high activity, and strengthens the strength and high temperature resistance of the thin film, forming a high temperature resistant thin film. The thin film blocks air, protects the brazing surface and the molten brazing material from oxidation, and realizes flux-free brazing of stainless steel in an air atmosphere. At the same time, the nanosilica particles are pinned to the brazing joint, which helps to strengthen the strength of the stainless steel joint. The present invention also discloses a method for producing the brazing paste, its use and a copper manganese nickel cobalt brazing material.

Description

[Technical Field]

[0001] The present invention relates to the technical field of brazing filler metals, and more particularly to a brazing filler metal paste for flux-free brazing of stainless steel and its manufacturing method, a copper-manganese-nickel-cobalt brazing filler metal and its use. [Background technology]

[0002] Stainless steel has excellent high-temperature and corrosion resistance, making it widely used in the manufacture of heat exchanger piping. In recent years, stainless steel heat exchangers have become a commonly used heat exchanger in industries such as metallurgy, chemicals, energy, transportation, light industry, and food. Brazing is an important part of the manufacture of stainless steel heat exchanger piping and determines the heat exchanger's service life. As people's quality of life improves, the requirements for the welding quality of stainless steel heat exchangers are becoming increasingly higher. The welding quality of stainless steel heat exchangers largely depends on the brazing filler metal used.

[0003] H1CuNi30-2-0.2 (Ni 27-30, Si 1.5-2.0, B 0.2, Cu balance) is widely used in the aviation industry. Its melting temperature range is 1080-1200°C, and its operating temperature reaches 600°C (Zou Xi, "Brazing", high-temperature copper-based brazing filler metal). Its advantages include good high-temperature performance, low cost, and good compatibility with stainless steel. It is often used for brazing stainless steel in protective atmosphere furnaces. However, conventional H1CuNi30-2-0.2 brazing filler metal lacks self-brazing properties. When brazing stainless steel in an atmosphere furnace, brazing temperatures below 1000°C make it difficult to remove the dense oxide film on the stainless steel surface. Temperatures above 1000°C cause stainless steel grain growth, both of which affect the weld quality and increase costs. H1CuNi30-2-0.2 copper-based brazing filler metal can provide good joints when brazing stainless steel in an air atmosphere, but most brazing filler metals contain fluorides, which are easily vaporized during brazing, polluting the environment and endangering human health. Residual brazing filler metal residues are highly corrosive and can easily corrode stainless steel pipes, causing leaks and shortening the service life of stainless steel heat exchangers. Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a brazing filler paste for flux-free brazing of stainless steel that can realize flux-free brazing of stainless steel in an air atmosphere and improve joint strength.

[0005] A second object of the present invention is to provide a method for producing the brazing filler paste for flux-free brazing of stainless steel.

[0006] A third object of the present invention is to provide a copper-manganese-nickel-cobalt brazing filler metal for brazing stainless steel.

[0007] A fourth object of the present invention is to provide a use of the brazing filler paste in induction brazing stainless steel. [Means for solving the problem]

[0008] In order to achieve the above object, the brazing paste for flux-free brazing of stainless steel of the present invention employs the following technical means.

[0009] The brazing filler metal paste for flux-free brazing of stainless steel is mainly composed of water, sodium silicate, nanosilica, and a copper-based brazing filler metal. The raw materials of the brazing filler metal paste are 70 to 80 parts by weight of the copper-based brazing filler metal, 3 to 5 parts by weight of nanosilica, 1 to 3 parts by weight of sodium hydroxide, and 10 to 15 parts by weight of water. The copper-based brazing filler metal has the following components by mass: 26.0 to 30.0% Mn, 26.0 to 30.0% Ni, 4.0 to 6.0% Co, 0.1 to 0.5% B, 0.1 to 0.6% Li, 0.1 to 0.2% Na, 0.01 to 0.3% K, and the balance Cu.

[0010] The brazing filler metal paste of the present invention is a paste containing water, sodium silicate, and nano-silica, which dehydrates at high temperatures during brazing to form a thin film, and the nano-silica can form a three-dimensional network structure with a large surface area and extremely high activity, enhancing the strength and high-temperature resistance of the thin film. This thin film blocks air and protects the brazing surface and molten brazing filler metal from oxidation, enabling flux-free brazing of stainless steel in an air atmosphere. At the same time, the nano-silica particles are pinned in the brazing seam, helping to strengthen the strength of the stainless steel joint.

[0011] In the present invention, the improved copper-based brazing filler metal is based on the H1CuNi30-2-0.2 brazing filler metal. By adding Mn and Co and lowering the Cu content, the brazing filler metal melting temperature is adjusted to between 930 and 970°C, thereby lowering the brazing temperature. At the same time, a certain amount of B and Li elements is added to the brazing filler metal, resulting in self-brazing properties. This is because B and Li reduce oxides on the stainless steel surface, such as Cr2O3. The melting point of the reduction product is lower than the brazing temperature, and the reduction product floats as a liquid thin film on the surface of the base metal and molten brazing filler metal, providing protection. However, the high viscosity of B oxides hinders the spreading of the brazing filler metal. Therefore, trace amounts of Na and K elements are further added. The low viscosity of Na and K oxides reduces the viscosity of the reduction product, promoting wetting of the coating and spreading of the brazing filler metal, thereby enhancing the self-brazing properties of the brazing filler metal.

[0012] To enhance the strength of stainless steel joints, the raw materials for the brazing filler metal paste preferably comprise 74 to 80 parts by weight of copper-based brazing filler metal, 3 to 5 parts by weight of nanosilica, 1 to 3 parts by weight of sodium hydroxide, and 12 to 15 parts by weight of water. More preferably, the copper-based brazing filler metal comprises 28.0 to 30.0 mass% of Mn, 28.0 to 30.0 mass% of Ni, 4.0 to 6.0 mass% of Co, 0.3 to 0.5 mass% of B, 0.4 to 0.6 mass% of Li, 0.1 to 0.2 mass% of Na, 0.15 to 0.3 mass% of K, and the balance being Cu.

[0013] Preferably, the particle size of the nanosilica is 30 to 50 nm.

[0014] The copper-manganese-nickel-cobalt brazing filler metal for brazing stainless steel of the present invention employs the following technical means.

[0015] The copper-manganese-nickel-cobalt brazing filler metal for brazing to stainless steel has the following composition: 26.0 to 30.0 mass% Mn, 26.0 to 30.0 mass% Ni, 4.0 to 6.0 mass% Co, 0.1 to 0.5 mass% B, 0.1 to 0.6 mass% Li, 0.1 to 0.2 mass% Na, 0.01 to 0.3 mass% K, and the balance Cu.

[0016] The copper-manganese-nickel-cobalt brazing filler metal for stainless steel brazing of the present invention has a lower brazing temperature (which is advantageous for suppressing the growth of stainless steel crystal grains) and a stronger wetting and spreading ability than the H1CuNi30-2-0.2 brazing filler metal, and therefore it is possible to reduce the amount of flux used or to eliminate the use of flux when compared to the conventional use of flux for matching.

[0017] Preferably, the copper manganese nickel cobalt brazing filler metal for brazing to stainless steel has a composition of 28.0 to 30.0 mass% Mn, 28.0 to 30.0 mass% Ni, 4.0 to 6.0 mass% Co, 0.3 to 0.5 mass% B, 0.4 to 0.6 mass% Li, 0.1 to 0.2 mass% Na, 0.15 to 0.3 mass% K, and the balance Cu.

[0018] The method for producing a brazing paste for flux-free brazing of stainless steel according to the present invention employs the following technical means.

[0019] The method for producing a brazing paste for stainless steel flux-free brazing includes the following steps. 1) Sodium hydroxide and water are mixed to form an alkaline aqueous solution. 2) The alkaline aqueous solution obtained in step 1) is reacted with nanosilica under conditions of atmospheric pressure or higher to obtain a suspension. 3) The suspension and copper-based brazing powder are mixed to form a uniform paste, thereby obtaining a brazing paste.

[0020] The method for producing a brazing filler paste for flux-free brazing of stainless steel according to the present invention has a simple production process, the obtained brazing filler paste has high stability, and can effectively improve the brazing effect of stainless steel brazing.

[0021] Preferably, in step 2), the condition of atmospheric pressure or higher is a steam pressure of 0.3 to 0.5 MPa, and the reaction time is 3.0 to 5.0 hours.

[0022] A technical means of using brazing paste is the use of the brazing paste in induction brazing stainless steel.

[0023] Preferably, at the time of use, the stainless steel is brazed in an air atmosphere without flux.

[0024] When brazing stainless steel, the brazing paste can be used to realize rapid induction brazing of stainless steel in an air atmosphere without using flux, which is environmentally friendly and does not pollute the environment. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a schematic diagram illustrating the production of the brazing paste of the present invention. FIG. [Figure 2] This is the spreading pattern when a flux-free spreading performance test was conducted in an air atmosphere for a conventional H1CuNi30-2-0.2 brazing filler metal. [Figure 3] 10 shows the spreading form of the brazing filler metal paste obtained in Example 5 of the present invention when a flux-free spreading performance test was carried out in an air atmosphere. DETAILED DESCRIPTION OF THE INVENTION

[0026] In the present invention, the reaction between nanosilica and sodium hydroxide is SiO2 + 2NaOH = Na2SiO3 + H2O.

[0027] During the reaction, the amount of nanosilica is relatively excessive, and some of the nanosilica is consumed by reacting with sodium hydroxide, while the other part remains in the liquid, forming a suspension. This suspension is then dehydrated at high temperature to form a thin film layer, and the excess nanosilica has a three-dimensional network structure, a huge surface area, and extremely high activity, which enhances the strength and high-temperature resistance of the thin film, forming a high-temperature resistant thin film. This thin film blocks air and protects the brazing surface and molten brazing material from oxidation. The nanosilica particles are pinned in the brazing seam, helping to strengthen the strength of the stainless steel joint.

[0028] In summary, the suspension can dehydrate the mucilage to enhance the high temperature resistance of the formed thin film, while the nanosilica can be pinned into the brazed joint to enhance the strength of the joint.

[0029] Furthermore, by combining with improvements in copper-based brazing filler metals, it is possible to more effectively realize rapid flux-free induction brazing of stainless steel in an air atmosphere, resulting in high-strength joints.

[0030] 1. Specific Examples of the Method for Producing Brazing Filler Metal Paste for Flux-Free Brazing of Stainless Steel of the Present Invention Example 1 In the manufacturing method of the brazing filler metal paste for flux-free brazing of stainless steel in this example, the composition of the raw materials used is 70 parts by weight of copper-based brazing filler metal powder, 3 parts by weight of nanosilica, 3 parts by weight of sodium hydroxide, and 10 parts by weight of deionized water, and the components in the copper-based brazing filler metal powder are 26.0 mass % of Mn, 26.0 mass % of Ni, 4.0 mass % of Co, 0.1 mass % of B, 0.1 mass % of Li, 0.1 mass % of Na, 0.01 mass % of K, and the balance is Cu.

[0031] Step (1) of weighing out the components in proportion and dissolving sodium hydroxide in deionized water to form an alkaline aqueous solution for use; Step (2) is a step in which nanosilica (30-50 nm) is added to the alkaline aqueous solution of step (1), placed in a high-pressure reactor, and reacted for 3.0 hours at a steam pressure of 0.3 MPa to form a suspension (transparent gel-like liquid + a small amount of silica), the reaction process of which is shown in Figure 1; The brazing paste is obtained by adding copper-based brazing powder to the suspension of step (2) and mixing and stirring the mixture to form a uniform paste (step (3)).

[0032] Example 2 In the manufacturing method of the brazing filler metal paste for flux-free brazing of stainless steel in this example, the composition of the raw materials used is 72 parts by weight of copper-based brazing filler metal powder, 4 parts by weight of nanosilica, 2 parts by weight of sodium hydroxide, and 11 parts by weight of deionized water, and the components in the copper-based brazing filler metal powder are 27.0 mass% Mn, 27.0 mass% Ni, 5.0 mass% Co, 0.2 mass% B, 0.2 mass% Li, 0.1 mass% Na, 0.1 mass% K, and the balance is Cu.

[0033] The specific production method was almost the same as in Example 1, except that in step (2), the steam pressure was 0.4 MPa and the reaction time was 4.0 hours.

[0034] Example 3 In this example, the method for producing a brazing filler metal paste for flux-free brazing of stainless steel uses 74 parts by weight of copper-based brazing filler metal powder, 5 parts by weight of nanosilica, 1 part by weight of sodium hydroxide, and 12 parts by weight of deionized water. The components of the copper-based brazing filler metal powder are 28.0 mass% Mn, 28.0 mass% Ni, 6.0 mass% Co, 0.3 mass% B, 0.4 mass% Li, 0.2 mass% Na, 0.15 mass% K, and the balance Cu.

[0035] The specific production method was almost the same as in Example 1, except that in step (2), the steam pressure was 0.5 MPa and the reaction time was 5.0 hours.

[0036] Example 4 In this example, the manufacturing method of the brazing filler metal paste for flux-free brazing of stainless steel uses a composition of raw materials: 76 parts by weight of copper-based brazing filler metal powder, 3 parts by weight of nanosilica, 3 parts by weight of sodium hydroxide, and 14 parts by weight of deionized water. The components of the copper-based brazing filler metal powder are: 29.0 mass% Mn, 29.0 mass% Ni, 4.0 mass% Co, 0.4 mass% B, 0.5 mass% Li, 0.1 mass% Na, 0.2 mass% K, and the balance Cu. The specific manufacturing method is the same as in Example 1.

[0037] Example 5 In this example, the manufacturing method of the brazing filler metal paste for flux-free brazing of stainless steel uses a composition of raw materials: 80 parts by weight of copper-based brazing filler metal powder, 5 parts by weight of nanosilica, 2 parts by weight of sodium hydroxide, and 15 parts by weight of deionized water. The components of the copper-based brazing filler metal powder are: 30.0 mass% Mn, 30.0 mass% Ni, 5.0 mass% Co, 0.5 mass% B, 0.6 mass% Li, 0.2 mass% Na, 0.3 mass% K, and the balance Cu. The specific manufacturing method is the same as in Example 1.

[0038] In another embodiment of the method for producing a brazing filler metal paste for flux-free brazing of stainless steel according to the present invention, in step (3), the reaction is carried out under a pressure of 0.3 to 0.5 MPa for 3.0 to 5.0 hours, for example, at 0.5 MPa for 3.0 hours or at 0.4 MPa for 5.0 hours, and the reaction effect is almost the same as that in Example 1.

[0039] 2. Specific examples of the brazing filler paste for flux-free brazing of stainless steel according to the present invention correspond to the brazing filler pastes obtained by the manufacturing methods of Examples 1 to 5 above, and will not be described in detail here.

[0040] 3. Specific examples of the copper-manganese-nickel-cobalt brazing filler metal for brazing stainless steel according to the present invention correspond to the copper-based brazing filler metals of Examples 1 to 5 above, respectively, and will not be described in detail here.

[0041] 4. Experimental example: Instructions for using brazing paste (Experimental Example 1) Using the H1CuNi30-2-0.2 brazing filler metal and the brazing filler paste of Example 5, a flux-free spreading performance test was conducted on a 304 stainless steel plate (length 40 mm × width 40 mm × thickness 3 mm). The plate was rapidly induction heated to 1000°C in an air atmosphere, and the wetting and spreading morphology of the two joints was compared. The test results are shown in Figures 2 and 3.

[0042] As can be seen from Figures 2 and 3, the H1CuNi30-2-0.2 brazing filler metal was almost completely oxidized without spreading on the steel sheet, whereas the brazing filler metal paste of Example 5 spread on the steel sheet and wetted it, showing good wetting performance.

[0043] (Experimental Example 2) The purpose of this experiment is to compare the shear strength of brazed joints made with different brazing filler metals. The test base material is a stainless steel plate with a thickness of 3 mm, a width of 20 mm, and a length of 80 mm. First, a 304 stainless steel plate is brazed in a gas atmosphere using H1CuNi30-2-0.2 brazing filler metal (the gas atmosphere brazing temperature must be maintained between 1170°C and 1200°C). Then, a 304 stainless steel plate is brazed in an air atmosphere using the brazing filler metal pastes of Examples 1 to 5 (the brazing temperature is 1050°C to 1100°C). Six types of joints are processed into standard shear specimens (in accordance with the provisions of GB / T11364-2008), and the shear strength of the joints is tested and compared. The results are shown in Table 1.

[0044] [Table 1]

[0045] As can be seen from Table 1, the average shear strength of the brazed joints of the brazing filler pastes of Examples 1 to 5 was all higher than the average shear strength of the brazed joints of H1CuNi30-2-0.2, indicating high joint strength.

[0046] (Addendum) (Appendix 1) A brazing paste for flux-free brazing of stainless steel, comprising: The brazing filler metal paste is mainly composed of water, sodium silicate, nanosilica, and a copper-based brazing filler metal, and raw materials of the brazing filler metal paste are 70 to 80 parts by weight of the copper-based brazing filler metal, 3 to 5 parts by weight of nanosilica, 1 to 3 parts by weight of sodium hydroxide, and 10 to 15 parts by weight of water, and the components of the copper-based brazing filler metal are 26.0 to 30.0 mass% of Mn, 26.0 to 30.0 mass% of Ni, 4.0 to 6.0 mass% of Co, 0.1 to 0.5 mass% of B, 0.1 to 0.6 mass% of Li, 0.1 to 0.2 mass% of Na, 0.01 to 0.3 mass% of K, and the balance is Cu. A brazing paste for flux-free brazing of stainless steel, characterized in that

[0047] (Appendix 2) The raw materials of the brazing paste are composed of 74 to 80 parts by weight of copper-based brazing filler metal, 3 to 5 parts by weight of nanosilica, 1 to 3 parts by weight of sodium hydroxide, and 12 to 15 parts by weight of water. 2. The brazing filler paste for flux-free brazing of stainless steel according to claim 1.

[0048] (Appendix 3) The copper-based brazing filler metal has a composition of 28.0 to 30.0 mass% Mn, 28.0 to 30.0 mass% Ni, 4.0 to 6.0 mass% Co, 0.3 to 0.5 mass% B, 0.4 to 0.6 mass% Li, 0.1 to 0.2 mass% Na, 0.15 to 0.3 mass% K, and the balance Cu. 3. The brazing filler paste for flux-free brazing of stainless steel according to claim 2.

[0049] (Appendix 4) The particle size of the nanosilica is 30 to 50 nm. 4. The brazing filler paste for flux-free brazing of stainless steel according to any one of appendices 1 to 3.

[0050] (Appendix 5) The composition is 26.0 to 30.0 mass% of Mn, 26.0 to 30.0 mass% of Ni, 4.0 to 6.0 mass% of Co, 0.1 to 0.5 mass% of B, 0.1 to 0.6 mass% of Li, 0.1 to 0.2 mass% of Na, 0.01 to 0.3 mass% of K, and the balance is Cu. A copper-manganese-nickel-cobalt brazing filler metal for brazing stainless steel, characterized in that

[0051] (Appendix 6) A method for producing a brazing paste for flux-free brazing of stainless steel according to any one of appendices 1 to 4, Step 1) of preparing an alkaline aqueous solution from sodium hydroxide and water; Step 2) of reacting the alkaline aqueous solution obtained in step 1) with nanosilica under conditions of atmospheric pressure or higher to obtain a suspension; and 3) mixing the suspension and the copper-based brazing powder to form a uniform paste to obtain a brazing paste. 1. A method for producing a brazing paste for flux-free brazing of stainless steel, comprising:

[0052] (Appendix 7) In step 2), the condition of atmospheric pressure or higher means that the steam pressure is 0.3 to 0.5 MPa. 7. A method for producing a brazing paste for flux-free brazing of stainless steel according to claim 6.

[0053] (Appendix 8) In step 2), the reaction time is 3.0 to 5.0 hours. 8. A method for producing a brazing paste for flux-free brazing of stainless steel according to claim 7.

[0054] (Appendix 9) Use of the brazing filler paste for flux-free brazing of stainless steel according to any one of appendices 1 to 4 in induction brazing stainless steel.

[0055] (Appendix 10) Brazing stainless steel in an air atmosphere without flux. 10. The use according to claim 9, characterized in that

Claims

1. A brazing paste for flux-free brazing of stainless steel, comprising: The brazing filler metal paste is made of water, sodium silicate, nanosilica particles, and a copper-based brazing filler metal, and raw materials of the brazing filler metal paste are made of 70 to 80 parts by weight of the copper-based brazing filler metal, 3 to 5 parts by weight of nanosilica, 1 to 3 parts by weight of sodium hydroxide, and 10 to 15 parts by weight of water. The copper-based brazing filler metal has components of 26.0 to 30.0 mass% of Mn, 26.0 to 30.0 mass% of Ni, 4.0 to 6.0 mass% of Co, 0.1 to 0.5 mass% of B, 0.1 to 0.6 mass% of Li, 0.1 to 0.2 mass% of Na, 0.01 to 0.3 mass% of K, and the balance being Cu. A brazing paste for flux-free brazing of stainless steel, characterized in that

2. The raw materials of the brazing paste are composed of 74 to 80 parts by weight of copper-based brazing filler metal, 3 to 5 parts by weight of nanosilica, 1 to 3 parts by weight of sodium hydroxide, and 12 to 15 parts by weight of water.

2. The brazing paste for flux-free brazing of stainless steel according to claim 1.

3. The copper-based brazing filler metal has a composition of 28.0 to 30.0 mass% Mn, 28.0 to 30.0 mass% Ni, 4.0 to 6.0 mass% Co, 0.3 to 0.5 mass% B, 0.4 to 0.6 mass% Li, 0.1 to 0.2 mass% Na, 0.15 to 0.3 mass% K, and the balance Cu.

3. The brazing paste for flux-free brazing of stainless steel according to claim 2.

4. The particle size of the nanosilica particles is 30 to 50 nm; The brazing paste for flux-free brazing of stainless steel according to any one of claims 1 to 3.

5. A method for producing a brazing paste for flux-free brazing of stainless steel according to any one of claims 1 to 3, Step 1) of preparing an alkaline aqueous solution from sodium hydroxide and water; Step 2) of reacting the alkaline aqueous solution obtained in step 1) with nanosilica under atmospheric pressure or higher to obtain a suspension; and 3) mixing the suspension and the copper-based brazing powder to form a uniform paste to obtain a brazing paste.

1. A method for producing a brazing paste for flux-free brazing of stainless steel, comprising:

6. In step 2), the condition of atmospheric pressure or higher means that the steam pressure is 0.3 to 0.5 MPa.

6. The method for producing a brazing paste for flux-free brazing of stainless steel according to claim 5.

7. In step 2), the reaction time is 3.0 to 5.0 h; 7. The method for producing a brazing paste for flux-free brazing of stainless steel according to claim 6.

8. 4. Use of the brazing filler paste for flux-free brazing of stainless steel according to claim 1 in induction brazing of stainless steel.

9. Brazing stainless steel in an air atmosphere without flux.

9. Use according to claim 8.

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