A method for inhibiting the formation of brittle borides in nickel-based brazing filler metals and its use

Abstract

This invention discloses a method for suppressing the formation of brittle borides in nickel-based brazing filler metals and its application. The method involves compounding a certain amount of metallic Cu powder onto a commercially available BNi-2 nickel-based brazing filler metal. The content of the reinforced BNi-2 nickel-based brazing filler metal is 95-99 wt.%, and the content of Cu element is 1-5 wt.%. The elemental composition of the BNi-2 nickel-based brazing filler metal by mass percentage is as follows: Cr: 6-8 wt.%, Si: 4-5 wt.%, Fe: 2.5-3.5 wt.%, B: 2.75-3.5 wt.%, with the balance being Ni. The Cu-reinforced nickel-based brazing filler metal is applied between the surfaces of two stainless steel base materials and bonded using organic adhesive, resulting in a sandwich structure of stainless steel / Cu-reinforced BNi-2 brazing filler metal / stainless steel. The components are then brazed under vacuum conditions. The reinforcement method provided by this invention effectively suppresses the brittle phase at the weld center, which has a significant impact on performance. The joint forms a complete nickel-based solid solution, further improving the shear strength of the joint and overcoming the inherent shortcomings of nickel-based brazing filler metals.

Description

Technical Field

[0001] This invention belongs to the field of brazing stainless steel manufacturing, specifically relating to a method for suppressing the formation of brittle borides in nickel-based brazing fillers and its application. Background Technology

[0002] Stainless steel products have mature manufacturing processes and excellent comprehensive properties, making them widely used in various industries. Currently, the forming and manufacturing process of stainless steel components relies heavily on welding technology. Commonly used welding methods include brazing, fusion welding, and pressure welding. Among these, brazing technology has become the preferred method for stainless steel welding due to its advantages such as low heating temperature, minimal deformation of the weldment, and high production efficiency.

[0003] Currently, widely used stainless steel brazing filler metals in industrial production include silver-based, copper-based, and nickel-based filler metals. Silver-based filler metals offer advantages such as a moderate melting point and excellent performance, but their cost is relatively high. Copper-based filler metals are inexpensive and have good plasticity, but their high melting point results in poor corrosion resistance at the joint. Nickel-based filler metals offer advantages such as low cost, moderate melting point, high temperature resistance, and corrosion resistance, but they are prone to forming brittle phases in the weld center, affecting joint performance. Considering the advantages and disadvantages of various filler metals, silver-based filler metals, due to their moderate melting point and excellent mechanical properties, have become the most widely used filler metal in industry. However, the high cost of silver-based filler metals still restricts the development of stainless steel brazing technology.

[0004] Therefore, it is necessary to invent a new type of composite brazing alloy that can replace the silver-based brazing alloy widely used in industrial production while meeting the performance requirements of stainless steel, thereby reducing the cost of stainless steel brazing technology. Summary of the Invention

[0005] The purpose of this invention is to provide a method for suppressing the formation of brittle borides in nickel-based brazing filler metals and its application. This method aims to replace the widely used silver-based brazing filler metals in industry, thereby reducing the cost of stainless steel brazing and promoting the transformation and upgrading of the stainless steel manufacturing industry. Based on the three commonly used brazing filler metals for stainless steel brazing, this invention proposes to use nickel-based brazing filler metals instead of silver-based filler metals. However, the presence of melting point degrading elements Si, B, and P in commonly used nickel-based brazing filler metals easily leads to the formation of brittle phases in the weld center, affecting the joint's service performance. To regulate the precipitation of brittle phases, this invention incorporates a certain amount of Cu element into the nickel-based brazing filler metal, utilizing the infinite solid solution strengthening properties of Cu and Ni to achieve the goals of lowering the melting point, reducing brittle phases, and improving joint strength.

[0006] The specific technical solution is as follows:

[0007] A Cu-reinforced nickel-based solder is composed of BNi-2 nickel-based solder and Cu. The content of BNi-2 nickel-based solder is 95-99 wt.%, and the content of Cu is 1-5 wt.%. The elemental composition of BNi-2 nickel-based solder by mass percentage is as follows: Cr: 6-8 wt.%, Si: 4-5 wt.%, Fe: 2.5-3.5 wt.%, B: 2.75-3.5 wt.%, with the balance being Ni.

[0008] The preparation method of the above-mentioned Cu-reinforced nickel-based solder includes the following steps:

[0009] 1) Weighing and quantitative determination: Weigh the required element powders, mix them according to the mass ratio, put them into a ball mill jar and add acetone;

[0010] 2) Ball milling and mixing: The composite brazing filler metal powder is wet-milled using zirconia balls in a ball mill jar;

[0011] 3) Powder drying: The composite brazing alloy powder after ball milling is filtered and sieved, poured into a glass container, and then placed in a drying oven to dry. After drying, the powder is manually crushed using a mortar and pestle.

[0012] Furthermore, in step 3), the drying temperature is 50-70℃ and the drying time is 6 hours.

[0013] The application of the aforementioned Cu-reinforced nickel-based brazing filler metal in brazing stainless steel includes the following steps: applying the Cu-reinforced nickel-based brazing filler metal between the surfaces of two stainless steel base materials, bonding them with organic adhesive to obtain a sandwich structure of stainless steel / Cu-reinforced nickel-based brazing filler metal / stainless steel, and brazing the parts under vacuum conditions.

[0014] Furthermore, during the brazing process, the temperature is raised to 1050-1100℃ by program-controlled heating, held for 10-30 minutes, and finally cooled to room temperature by program-controlled cooling.

[0015] Compared with the three commonly used stainless steel brazing filler metals, this invention has the following advantages:

[0016] 1. The Cu-reinforced nickel-based solder provided by the present invention uses nickel-based solder as the matrix, which has the advantages of high temperature resistance, high strength and corrosion resistance of nickel-based solder. Compared with the initial nickel-based solder, its melting point is lower, which plays a role in reducing the melting point.

[0017] 2. Compared with conventional nickel-based brazing filler metals for stainless steel, this method eliminates the brittle phase in the weld center that has a significant impact on performance, and forms a complete nickel-based solid solution at the joint. This further improves the shear strength of the joint, overcomes the inherent shortcomings of nickel-based brazing filler metals, and is expected to replace the widely used silver-based brazing filler metals in industry, greatly reducing the cost of brazing. Attached Figure Description

[0018] Figure 1 The present invention provides various DSC test curves for brazing filler metals;

[0019] Figure 2 This is a SEM micrograph of the original BNi-2 powder brazed with SS304 according to the present invention;

[0020] Figure 3 This is a SEM micrograph of SS304 brazed with 99wt% BNi-2+1wt% Cu powder of the present invention;

[0021] Figure 4 This is a SEM micrograph of SS304 brazed with 95wt% BNi-2+5wt% Cu powder according to the present invention. Detailed Implementation

[0022] The present invention will be further described below with reference to specific embodiments and accompanying drawings, but the scope of protection of the present invention is not limited thereto.

[0023] Comparative Example 1

[0024] The solder used in this comparative example is BNi-2, with a mass percentage of [missing information] and the composition is as follows:

[0025] Cr: 7 wt.%, Si: 4.5 wt.%, Fe: 3 wt.%, B: 3 wt.%, balance Ni.

[0026] preparation:

[0027] 1) Weighing and quantitative determination: Weigh the required element powders, mix them according to the mass ratio, put them into a ball mill jar and add acetone;

[0028] 2) Ball milling and mixing: The composite brazing filler metal powder is wet-milled using zirconia balls in a ball mill jar;

[0029] 3) Powder drying: The composite brazing alloy powder after ball milling is filtered and sieved, poured into a glass container, and then placed in a drying oven at 70°C for 6 hours. The dried powder is then manually pulverized using a mortar and pestle.

[0030] The liquidus temperature of the prepared solder was 1017.62℃, and the DSC curve is shown below. Figure 1 As shown.

[0031] A Cu-reinforced nickel-based brazing filler metal is applied between the surfaces of two stainless steel base materials and bonded with organic adhesive to obtain a sandwich structure of stainless steel / Cu-reinforced nickel-based brazing filler metal / stainless steel. The components are then brazed under vacuum conditions at a temperature of 1050℃ for 10 minutes.

[0032] During the brazing process, the vacuum level is controlled at 1-9×10⁻⁶. -3 For assembled parts to be welded, a molybdenum block is used as a pressure block to ensure close contact between the base material and the brazing filler metal during the brazing process. The specific process of programmed temperature control is as follows: the temperature is increased to 300℃ at a heating rate of 10℃ / min, held at 300℃ for 30min, then increased to the brazing temperature of 1050℃ at a heating rate of 10℃ / min, held at the brazing temperature for 10min, and then cooled to room temperature at a cooling rate of 6℃ / min.

[0033] The electron micrograph of the stainless steel brazed joint in this comparative example is as follows: Figure 2 As shown, a large number of black boride phases exist in the joint, and the brittle borides have an adverse effect on the joint performance.

[0034] Example 1

[0035] In this embodiment, the Cu-reinforced nickel-based solder has the following composition by mass percentage:

[0036] BNi-2: 99 wt.%, Cu: 1 wt.%, the elemental composition of BNi-2 nickel-based solder by mass percentage is as follows: Cr: 7 wt.%, Si: 4.5 wt.%, Fe: 3 wt.%, B: 3 wt.%, balance Ni.

[0037] The preparation method in this embodiment is the same as that in Comparative Example 1. The liquidus temperature of the prepared Cu-reinforced nickel-based solder is 1014.84℃, and the DSC curve is shown below. Figure 1 As shown.

[0038] The brazing process in this embodiment is the same as in Comparative Example 1. The electron microscope morphology of the stainless steel brazed joint is as follows: Figure 3 As shown, the joint forms a nickel-based solid solution, meaning that the addition of Cu eliminates the boride phase.

[0039] Example 2:

[0040] In this embodiment, the solder mass percentage is as follows:

[0041] BNi-2: 95 wt.%, Cu: 5 wt.%, the elemental composition of BNi-2 nickel-based solder by mass percentage is the same as in Example 1.

[0042] The preparation method in this embodiment is the same as that in Comparative Example 1. The liquidus temperature of the prepared Cu-reinforced nickel-based solder is 1013.73℃, and the DSC curve is shown below. Figure 1 As shown.

[0043] The brazing process in this embodiment is the same as in Comparative Example 1. The electron microscope morphology of the stainless steel brazed joint is as follows: Figure 4 As shown, black boride is redeposited in the joint.

[0044] Brazing filler metal performance comparison test:

[0045] 1. The shear strength of the 304 stainless steel joints obtained in Comparative Example 1, Example 1 and Example 2 above was tested on a universal testing machine, and the results are shown in Table 1.

[0046] Table 1. Shear strength of brazed joints in Comparative Examples 1, 1, and 2

[0047] Brazed joint Shear strength / MPa Error / MPa Comparative Example 1 599.8 45.1 Example 1 713.9 16.4 Example 2 423.5 49

[0048] The results of the shear test show that the brazed joint strength obtained in Example 1 is significantly improved compared with Comparative Example 1, but the brazed joint strength obtained in Example 2 is much lower than that of Comparative Example 1.

[0049] 2. Through SEM microstructure analysis and EDS energy dispersive spectroscopy analysis of the joints in Comparative Example 1, Example 1, and Example 2, it can be seen that: when the Cu addition amount is 1 wt%, a complete nickel-based solid solution is formed at the joint, and the joint strength is significantly improved; however, when the Cu addition amount is 5 wt%, a large number of fine boride phases precipitate at the joint, filling the entire joint, causing the joint strength to decrease compared to the original solder. Therefore, the addition of an appropriate amount of Cu can eliminate boride and improve the joint strength, but the addition of excessive Cu is not conducive to improving the joint strength.

[0050] Based on the above data and SEM and EDS analysis of the brazed joints, the following conclusions can be drawn:

[0051] (1) For BNi-2 nickel-based brazing filler metal with 1wt% Cu, during the brazing process, the diffusion of Cu element causes the brazing filler metal and the base metal to dissolve at the contact point. Since element diffusion is more likely to occur at the grain boundaries, dissolution will first occur at the grain boundaries of the stainless steel brazing surface, forming a downward-depressed groove-shaped defect, thereby promoting the diffusion of B element and eliminating borides in the weld.

[0052] (2) For BNi-2 nickel-based brazing filler metal with 5wt% Cu, due to the infinite solid solubility of Cu and Ni, the addition of excessive Cu element reduces the solubility of elements such as B and Cr in the nickel-based solid solution, and borides are re-precipitated in the weld.

[0053] This invention successfully suppresses the formation of brittle phases in nickel-based brazing fillers by adding Cu, overcoming the inherent shortcomings of nickel-based stainless steel brazing fillers and further expanding the application range of nickel-based brazing fillers. It is expected to replace the silver-based brazing fillers widely used in stainless steel brazing, thereby saving stainless steel brazing costs, promoting industrial upgrading, and improving product competitiveness.

[0054] The above description outlines the basic principles and main advantages of this invention. Those skilled in the art should understand that this invention is not limited to the above embodiments; the embodiments are merely illustrative of the principles of the invention. Various changes and modifications can be made without departing from the scope of this invention, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A Cu-reinforced nickel-based solder, characterized in that... It is composed of BNi-2 nickel-based solder and Cu. The content of BNi-2 nickel-based solder is 99 wt.% and the content of Cu is 1 wt.%. The elemental composition of BNi-2 nickel-based solder by mass percentage is as follows: Cr: 6-8 wt.%, Si: 4-5 wt.%, Fe: 2.5-3.5 wt.%, B: 2.75-3.5 wt.%, with the balance being Ni.

2. A method for preparing Cu-reinforced nickel-based solder as described in claim 1, characterized in that... Includes the following steps: 1) Weighing and quantitative determination: Weigh the required element powders, mix them according to the mass ratio, put them into a ball mill jar and add acetone; 2) Ball milling and mixing: The composite brazing filler metal powder is wet-milled using zirconia balls in a ball mill jar; 3) Powder drying: The composite brazing powder after ball milling is filtered and sieved, poured into a glass container, and then placed in a drying oven to dry. After drying, the powder is manually crushed using a mortar and pestle.

3. The preparation method according to claim 2, characterized in that... In step 3), the drying temperature is 50-70℃ and the drying time is 6 hours.

4. The application of a Cu-reinforced nickel-based brazing filler metal as described in claim 1 in brazing stainless steel, characterized in that... The process includes the following steps: applying Cu-reinforced nickel-based brazing filler metal between the surfaces of two stainless steel base materials, bonding them with organic adhesive to obtain a sandwich structure of stainless steel / Cu-reinforced nickel-based brazing filler metal / stainless steel. The components are then brazed under vacuum conditions. During the brazing process, the temperature is raised to 1050-1100℃ using a programmed heating method, held for 10-30 minutes, and finally cooled to room temperature using a programmed cooling method.

Images