Nickel brazing material having excellent wetting spreadability

Abstract

Provided is a nickel brazing material capable of brazing various stainless steel members at a relatively low temperature, having excellent corrosion resistance, and used for brazing of heat exchangers and the like. The melting temperature is 1000°C or lower, excellent wetting and spreading are exhibited, and corrosion resistance against acids is possessed, characterized by comprising 8.0 to 19.0 mass% of Cr, 7.0 to 10.5 mass% of P, 0.1 to 1.5 mass% of B, 2.0 to 8.0 mass% of Cu, the content of Mo being 10.0 mass% or lower, the content of Si being 2.5 mass% or lower, and the balance being composed of Ni and unavoidable impurities. In addition to the above, one or more elements selected from the group consisting of Co, Fe, and Mn can also be contained, in which case the content of Co is 5.0 mass% or lower, the content of Fe is 3.0 mass% or lower, the content of Mn is 3.0 mass% or lower, and the total content of these elements is 8.0 mass% or lower.

Description

Technical Field

[0001] This invention relates to a brazing filler metal for use in general heat exchangers, water heaters, and waste heat recovery devices, suitable for joining various stainless steel components. It relates to a nickel brazing filler metal with good corrosion resistance, particularly with a lower melting temperature compared to general nickel brazing fillers, and excellent wetting and spreading properties. Background Technology

[0002] Traditionally, nickel brazing fillers have been used in stainless steel heat exchangers for applications such as refrigerant evaporation, condensation, and hot water supply, where oxidation and corrosion resistance are required. Among general-purpose nickel brazing fillers for joining various stainless steel components, in addition to BNi2 and BNi5 as specified in JIS Z 3265:1998 "Nickel Brazing Fillers," there are, for example, Ni-Cr-P-Si brazing fillers as described in Patent Document 1 below.

[0003] In recent years, there has been a strong push to reduce energy costs and lower brazing temperatures during brazing operations. Therefore, there is a demand for nickel brazing filler metals with a melting temperature lower than that of general-purpose products. However, given this situation, the melting temperatures of BNi2, BNi5, and the Ni-Cr-P-Si brazing filler metals described in Patent Document 1 are all above 1000°C. Lowering the brazing temperature would result in insufficient wetting and spreading properties.

[0004] To address this issue, the application of BNi6 and BNi7 as specified in JIS Z 3265:1998 "Nickel Brazing Alloys" and BNi12 in AWS A5.8 / A5.8M:2004, which have low melting temperatures, is being investigated. In addition, in recent years, new brazing alloys with low melting temperatures, such as those described in Patent Documents 2-7, have also been proposed.

[0005] However, both BNi6 and BNi7 suffer from insufficient corrosion resistance. While BNi12 exhibits excellent corrosion resistance and a liquidus temperature below 1000°C, it lacks wetting and spreading properties compared to BNi6 and BNi7. In the embodiments described in Patent Documents 2-7, although a brazing filler metal with a melting temperature lower than that of general nickel brazing fillers is presented, its characteristics still include a liquidus temperature above 1000°C, or even if the melting temperature is low, insufficient wetting and spreading properties, and, in addition, insufficient corrosion resistance.

[0006] Therefore, the commonly used brazing filler metals and the nickel brazing filler metals described in Patent Documents 1-7 have the above-mentioned problems. Currently, there is no nickel brazing filler metal that has good corrosion resistance and can also achieve the characteristic of reducing the brazing temperature (sufficient wetting and spreading properties).

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent No. 3168158

[0010] Patent Document 2: Japanese Patent Application Publication No. 2007-75867

[0011] Patent Document 3: Japanese Patent Application Publication No. 2009-202198

[0012] Patent Document 4: Japanese Patent Application Publication No. 2011-110575

[0013] Patent Document 5: Japanese Patent Application Publication No. 2012-55914

[0014] Patent Document 6: WO2015 / 156066

[0015] Patent Document 7: Japanese Patent Application Publication No. 2017-131968 Summary of the Invention

[0016] The problem that the invention aims to solve

[0017] In recent years, there has been a strong demand for energy cost reduction in brazing operations on stainless steel heat exchangers used in applications such as refrigerant evaporation, condensation, and hot water supply. Therefore, the development of low-melting-point nickel brazing fillers with good corrosion resistance and a melting temperature that can lower the brazing temperature has become a research topic.

[0018] The objective of this invention is to provide a nickel brazing filler metal that solves the aforementioned problems in the prior art, exhibits excellent corrosion resistance, and displays sufficiently high wetting and spreading properties even at brazing temperatures lower than those of existing products.

[0019] Problem-solving methods

[0020] In this invention, in order to develop a nickel brazing filler metal that has a melting temperature and wettability that can reduce the brazing temperature, and has excellent corrosion resistance, the following objectives are set and fully satisfied when studying the alloy composition.

[0021] (Target value)

[0022] (1) Melting temperature (liquidline temperature) → below 1000℃

[0023] (2) Wetting and spreading properties (solder diffusion coefficient) → 10 or above

[0024] (3) Corrosion resistance (loss of corrosion in sulfuric acid) → 0.50 mg / m 2 ·s and below

[0025] The alloy (nickel brazing filler metal) of the present invention, which satisfies all the above-mentioned target values, is characterized by having a melting temperature below 1000°C and possessing acid corrosion resistance. Its composition includes 8.0–19.0% by mass of Cr, 7.0–10.5% by mass of P, 0.1–1.5% by mass of B, 2.0–8.0% by mass of Cu, and a Mo content of 10.0% by mass or less, a Si content of 2.5% by mass or less, with the balance being Ni and unavoidable impurities.

[0026] Here, "unavoidable impurities" refers to impurities that are not intentionally added but are unavoidably mixed in during the manufacturing processes of various raw materials. Examples of such impurities include Al, C, Ti, Mg, S, O, N, V, Zr, Sn, etc., and their total amount is usually less than 0.3% by mass, which is a level that will not affect the function of the present invention.

[0027] Furthermore, the nickel brazing filler metal of the present invention is characterized in that, as an element that does not adversely affect the properties, the nickel brazing filler metal having the above-described characteristics also contains one or more elements selected from the group consisting of Co, Fe, and Mn, and the content of Co is 5.0% by mass or less, the content of Fe is 3.0% by mass or less, the content of Mn is 3.0% by mass or less, and the total content of Co, Fe, and Mn is 8.0% by mass or less.

[0028] The following will explain the reasons for the limitations of each component range described in this invention.

[0029] Cr dissolved in Ni solid solution improves the corrosion resistance of the alloy, but this effect is insufficient when the Cr content is below 8.0% by mass. Furthermore, if the Cr content exceeds 19.0% by mass, the melting temperature increases, and the wettability and spreadability of the substrate during brazing decreases, reducing brazing operability. Therefore, the Cr content is set in the range of 8.0–19.0% by mass.

[0030] P undergoes a eutectic reaction with Ni, which lowers the melting temperature of the alloy and improves its fluidity, thus enhancing its wetting and spreading properties on stainless steel substrates. However, below 7.0% by mass, this effect is not fully realized. Conversely, above 10.5% by mass, it becomes a hypereutectic composition, resulting in an increased melting temperature and decreased wetting and spreading properties. Therefore, the P content is set in the range of 7.0% to 10.5% by mass.

[0031] Like phosphorus (P), boron (B) lowers the melting temperature of the alloy through a eutectic reaction with Ni. Besides this effect, it also acts as a flux, improving brazing operability; however, its effect is not fully realized below 0.1% by mass. Furthermore, if the content exceeds 1.5% by mass, it forms a compound with Cr, significantly increasing the melting temperature. Therefore, the B content is set in the range of 0.1% to 1.5% by mass.

[0032] Cu dissolves in Ni solid solution, which helps to lower the melting temperature. In addition, it also improves corrosion resistance. However, this effect is not sufficient when the content is below 2.0% by mass, and the melting temperature rises when the content is above 8.0% by mass. Therefore, the Cu content is set in the range of 2.0% to 8.0% by mass.

[0033] Mo is dissolved in Ni solid solution, which helps to lower the melting temperature. In addition, it also improves corrosion resistance. It can be added arbitrarily. If it is higher than 10.0% by mass, the melting temperature will rise and the wetting and spreading properties will decrease. Therefore, the content of Mo is set to be below 10.0% by mass.

[0034] Like P and B, Si lowers the melting temperature of alloys through a eutectic reaction with Ni. In addition to this effect, it also acts as a flux, improving brazing operability. It can be added arbitrarily; however, if Si exceeds 2.5% by mass, it becomes a hypereutectic composition, increasing the melting temperature and reducing wettability and spreadability. Therefore, the Si content is set below 2.5% by mass.

[0035] Furthermore, in the nickel solder of the present invention, elements that do not adversely affect the properties can include 5.0% by mass or less of Co, 3.0% by mass or less of Fe, and 3.0% by mass or less of Mn. These components can be blended individually or together, but the blending ratio of each component is limited to the above-mentioned range because if Co, Fe, and Mn exceed the upper limit of the range, the wettability and spreadability decrease. In addition, in the present invention, in order to satisfy all the target values ​​for corrosion resistance, material strength, and melting temperature, the upper limit of the total content of Co, Fe, and Mn is set to 8.0% by mass. In the present invention, the upper limit of the above total content is particularly preferably 4.0% by mass or less.

[0036] The nickel solder of this invention contains 60-80% by mass of Ni.

[0037] The effects of the invention

[0038] The nickel brazing filler metal of the present invention has excellent wetting and spreading properties due to its liquidus temperature being below 1000°C, which can reduce brazing temperature (energy cost) and is effective in stainless steel heat exchangers used for applications such as refrigerant evaporators, condensers, and hot water supply. Attached Figure Description

[0039] Figure 1 This is a schematic diagram used to illustrate brazing tests of brazing filler alloys. Detailed Implementation

[0040] The nickel brazing filler metal of the present invention can be obtained by adjusting and combining Ni as a base and additives Cr, P, B, Cu, Mo, and Si according to a specified mass percentage, and adding Co, Fe, Mn, etc. in a specified amount as needed. The resulting ingot is completely melted in the crucible of a furnace, and the molten alloy is turned into powder by atomization or melt pulverization, or cast into rod or plate shape in a specified mold.

[0041] In particular, alloy powder manufactured by atomization, after being adjusted to a particle size suitable for the target construction method, can be used as a method for setting the nickel brazing filler metal of the present invention on a stainless steel base material. Various methods can be freely selected, such as: spraying (spreading) adhesive and powder on the surface of the base material; mixing adhesive and powder into a paste for coating; processing into sheet or foil form; and setting by thermal spraying powder.

[0042] Example

[0043] The nickel brazing filler metal of the present invention (example alloy) adjusted and formulated as described above, and the nickel brazing filler metal having a composition deviating from the composition range specified in the present invention (comparative example alloy), were melted and evaluated by measuring the liquidus temperature, the brazing filler metal diffusion coefficient, and the corrosion reduction in sulfuric acid according to the method shown below.

[0044] (1) Liquidus temperature measurement: Using an electric furnace, 100g of ingots containing the alloy composition are heated to approximately 1500°C in an argon gas flow to melt them. The ingots are then allowed to cool naturally within the furnace while the melting temperature is measured using a thermal analysis method that continuously measures the alloy temperature. Specifically, a recorder connected to a thermocouple inserted into the center of the molten metal plots a thermal analysis curve, from which the liquidus temperature is read.

[0045] (2) Measurement of brazing filler metal diffusion coefficient: The alloy of the example was melted in an electric furnace under an argon atmosphere. The molten metal was cast in a graphite mold to obtain a φ5mm rod-shaped casting. This rod was cut to approximately 0.5g in weight and used as a brazing filler metal sample. Next, as... Figure 1 As shown in (a), the brazing filler metal sample was placed on SUS304 stainless steel base material and heated to 980°C for 10 minutes. －2 ~10 －1 The brazing heat treatment is carried out in a vacuum of Pa for 30 minutes (hereinafter referred to as brazing).

[0046] After brazing, as Figure 1 As shown in (b), the area S of the solder melting and spreading is measured, and the value of dividing this area S by the cross-sectional area So of the sample before brazing is obtained. That is, the solder diffusion coefficient W (=S / So) is used as an indicator of the wettability of the solder alloy to the SUS304 stainless steel base material.

[0047] (3) Measurement of corrosion loss in sulfuric acid: The ingot was melted using the same method as in (1) above. After casting the molten metal in a shell mold, the casting was machined into a piece approximately 10×10×20mm as a test piece. Next, a 1% sulfuric acid aqueous solution was prepared in a 300cc beaker, and the test piece was placed inside for a full immersion corrosion test. The test conditions were: test temperature 80℃, test time 6 hours. Then, the mass reduction per unit area per unit time before and after the test was calculated as the corrosion loss (mg / m²). 2 •s), to evaluate resistance to sulfuric acid corrosion.

[0048] The evaluation indicators are shown below.

[0049] Corrosion loss ≤ 0.50 mg / m³ 2 ·s:○”

[0050] "Corrosion loss > 0.50 mg / m" 2 ·s:×”

[0051] Table 1 shows embodiments of the present invention, and Tables 2 and 3 show comparative examples.

[0052] Table 1

[0053]

[0054] Table 2

[0055]

[0056] Table 3

[0057]

[0058] Alloys No. 1 to 18 shown in Table 1 are embodiments of the present invention, and their liquidus temperatures are all below 1000°C. Furthermore, it can be seen that the solder diffusion coefficients all show values ​​above 10, and the alloys of the embodiments of the present invention also exhibit excellent wettability during brazing.

[0059] Furthermore, regarding the resistance to sulfuric acid corrosion, it is known that the corrosion loss under the test conditions was 0.50 mg / m³. 2 Below ·s, the alloys of the embodiments of the present invention have good resistance to sulfuric acid corrosion.

[0060] On the other hand, among the alloys shown in Table 2, (a) to (n) are solders whose composition deviates from the scope of the alloys of this invention, and at least one of the properties—liquidothermal temperature, solder diffusion coefficient, and sulfuric acid resistance—does not meet the target value. Specifically, the Cr content of (a) and (b) deviates from the scope of this invention; the P content of (c) and (d) deviates from the scope of this invention; the B content of (e) and (f) deviates from the scope of this invention; the Cu content of (g) and (h) deviates from the scope of this invention; the Mo content of (i) exceeds the upper limit of the scope of this invention; and the Si content of (j) exceeds the upper limit of the scope of this invention. These alloys do not meet at least one target property. (k), (l), and (m) are respectively Co, Fe, and Mn exceeding the upper limit of the scope of this invention; and (n) is the sum of Co, Fe, and Mn exceeding the upper limit of the scope of this invention, thus not meeting at least one target property.

[0061] Table 3 shows comparative example solders (A), (B), and (C), which are nickel solder compositions as specified in existing JIS and AWS standards. Comparative example solders (D) to (J) are nickel solders described in existing documents in Japanese Patent No. 3168158, Japanese Unexamined Patent Publication No. 2007-75867, Japanese Unexamined Patent Publication No. 2009-202198, Japanese Unexamined Patent Publication No. 2011-110575, Japanese Unexamined Patent Publication No. 2012-55914, WO2015 / 156066, and Japanese Unexamined Patent Publication No. 2017-131968.

[0062] None of the solders shown in Table 3 meet at least one of the target values ​​for liquidus temperature, solder diffusion coefficient, and sulfuric acid corrosion resistance.

[0063] Furthermore, the nickel brazing filler metal (example alloy) of the present invention exhibits good wetting properties for various stainless steel base materials, and also shows good brazing properties in reducing hydrogen atmosphere and inert argon atmosphere, except that the brazing atmosphere is a vacuum.

[0064] Industrial availability

[0065] As detailed above, the nickel brazing filler metal of the present invention has excellent wetting and spreading properties during brazing because its melting temperature is below 1000°C. In addition, it also exhibits good corrosion resistance to acids such as sulfuric acid. Therefore, it is suitable for joining (brazing) various stainless steel components and is not limited to applications such as refrigerant evaporation, condenser, and hot water supply. Rather, it can be widely used in heat exchangers related to the environment and energy.

[0066] Symbol Explanation

[0067] So: Cross-sectional area of ​​the brazing filler metal sample

[0068] S: Alloy spread area after brazing

[0069] W: Solder diffusion coefficient (S / So)

[0070] 1. Base material (SUS304 stainless steel)

[0071] 2: Sample filler metal (φ5mm, approximately 0.5g) before brazing

[0072] 3: The molten brazing alloy after brazing

Claims

1. A nickel brazing material, characterized by, It is a nickel brazing filler metal with a melting temperature below 1000℃, exhibiting excellent wetting and spreading properties with a solder diffusion coefficient of 10 or higher at 980℃, and possessing acid corrosion resistance. This filler metal contains 8.0 to 19.0% by mass of Cr, 7.0 to 10.5% by mass of P, 0.1 to 1.5% by mass of B, 2.0 to 8.0% by mass of Cu, 1.1 to 10.0% by mass of Mo, and less than 2.5% by mass of Si, with the balance being Ni and unavoidable impurities.

2. The nickel braze of claim 1, wherein, As an element that does not adversely affect the properties, it also contains one or more elements selected from the group consisting of Co, Fe, and Mn, and the content of Co is 5.0% by mass or less, the content of Fe is 3.0% by mass or less, the content of Mn is 3.0% by mass or less, and the total content of Co, Fe, and Mn is 8.0% by mass or less.

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