JP2020164947A - Surface-treated base material for brazing and heat exchanger - Google Patents

Abstract

To provide a surface-treated base material for brazing that is excellent in corrosion resistance after brazing.SOLUTION: A surface-treated base material for brazing comprises a base material, a first layer formed on the base material and composed of a first material having a melting point of 1100°C or higher, and a second layer formed on the first layer and composed of a second material containing a Ni-P alloy and having a melting point lower than that of the first material by 300°C or higher, in which the relationship between the thickness t1 of the first layer and the thickness t2 of the second layer satisfies either a thickness condition (1): t1≥3 μm and t2≥5 μm or a thickness condition (2): 1 μm≤t1<3 μm and t2≥20 μm.SELECTED DRAWING: Figure 3

Description

The present invention relates to a surface-treated substrate for brazing and a heat exchanger.

Conventionally, as a heat exchanger that requires corrosion resistance, stainless steel plates having irregularities formed by press molding or the like are laminated by brazing, and a gap formed by the irregularities of the stainless steel plates is used as a flow path for a refrigerant or the like. Plate heat exchangers are known.

As a brazing stainless steel sheet for manufacturing such a plate heat exchanger, for example, Patent Document 1 describes a ferritic stainless steel sheet in which a nickel-phosphorus alloy plating layer as a brazing material is formed on the surface. It is disclosed.

Japanese Unexamined Patent Publication No. 2000-61627

However, in the stainless steel sheet for brazing described in Patent Document 1, the nickel-phosphorus alloy plating layer, which is a brazing material, flows due to the heat during brazing, and the stainless steel sheet as a base material is exposed on the surface. As a result, there is a problem that the corrosion resistance when used as a heat exchanger is lowered.

An object of the present invention is to provide a surface-treated base material for brazing, which has excellent corrosion resistance after brazing.

The present inventors have found that the above object can be achieved by forming a specific first layer and a specific second layer on a base material in this order, and have completed the present invention.

That is, according to the present invention, the first material comprises a base material, a first material having a melting point of 1100 ° C. or higher, a first layer formed on the base material, and a Ni-P alloy. melting point is a low 300 ° C. or more second material than, and a second layer formed on the first layer, the thickness t ₁ of the first layer, the thickness t ₂ of the second layer Will satisfy either the thickness condition (1) "t ₁ ≥ 3 μm and t ₂ ≥ 5 μm" or the thickness condition (2) "1 μm ≤ t ₁ <3 μm and t ₂ ≥ 20 μm". A surface-treated substrate for brazing is provided.

In braze surface-treated substrate of the present invention, the thickness t ₁ of the first layer, the relationship between the thickness t ₂ of the second layer, if it meets the thickness condition (1), the thickness condition (3 ) It is preferable to further satisfy "t ₂ > t ₁ ".
In the surface-treated base material for brazing of the present invention, it is preferable that the base material is stainless steel.
In the surface-treated base material for brazing of the present invention, the first material is a Ni, Ni alloy (Ni alloy in which the content ratio of elements other than Ni is 10 atomic% or less), Co, Co alloy (elements other than Co). It is preferable to contain a Co alloy) having a content of 10 atomic% or less, or a Ni—Co alloy.
The surface-treated base material for brazing of the present invention is preferably used in contact with salt water.

Further, according to the present invention, there is provided a heat exchanger provided with any of the above-mentioned surface-treated base materials for brazing.

In the present invention, it is possible to provide a surface-treated base material for brazing, which has excellent corrosion resistance after brazing.

It is a perspective view which shows one Embodiment of the plate type heat exchanger provided with the heat transfer plate formed by using the surface treatment base material for brazing which concerns on this invention. It is sectional drawing of the heat transfer plate provided in the plate type heat exchanger shown in FIG. It is sectional drawing which shows the other example of the plate type heat exchanger in this embodiment. It is sectional drawing of the surface treatment base material for brazing which concerns on one Embodiment of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The surface-treated base material for brazing according to the present invention can be brazed by applying heat treatment, and can be used for parts that can be formed by laminating by brazing, particularly parts that require corrosion resistance. For example, the brazing surface-treated substrate according to the present invention can be used to form the heat transfer plate 23 constituting the plate heat exchanger 2, as shown in FIGS. 1 and 2. In the following, the present invention will be described in an embodiment using the surface-treated base material for brazing according to the present invention as the heat transfer plate 23 of the plate heat exchanger 2.

FIG. 1 is a perspective view showing an embodiment of a plate heat exchanger 2 including a heat transfer plate 23 formed by using the surface-treated base material for brazing according to the present invention.

The plate heat exchanger 2 shown in FIG. 1 is provided with a heat transfer plate 23 shown in FIG. 2 inside, and a fluid such as a refrigerant flows from the fluid inlet 21 along the direction of the arrow shown in FIG. After flowing into the inside of 2 and passing through the fluid flow path 24 formed between the plurality of heat transfer plates 23, it flows out from the fluid outlet 22 from the plate heat exchanger 2 along the direction of the arrow shown in FIG. It is configured to go on.

The heat transfer plate 23 constituting the plate heat exchanger 2 can be obtained by molding the surface-treated base material for brazing according to the present invention into a desired shape by a molding method such as a press, for example. It can have a corrugated shape like the heat transfer plate 23 shown in FIG. In the present embodiment, a plurality of such heat transfer plates 23 are prepared, and as shown in FIG. 2, the heat transfer plate 23 and the intervening member are subjected to heat treatment in a state of being overlapped with each other via the intervening member 25. At the portion where the heat transfer plate 23 is in contact, the outermost layer of the heat transfer plate 23 is melted and brazed, whereby the heat transfer plate 23 and the intervening member 25 are joined, and the heat transfer plate 23 and the intervening member 25 are joined. The fluid flow path 24 can be formed in the gap with the 25. Further, in the present embodiment, as shown in FIG. 3, the heat transfer plate 23 formed into a desired shape is brazed to the outer layer member 26 constituting the outer layer of the plate heat exchanger. A fluid flow path 24a may be formed between the heat transfer plate 23 and the outer layer member 26 to manufacture a plate heat exchanger. Hereinafter, the configuration of the brazing surface-treated base material (surface-treated base material 1) according to the present invention will be described with reference to FIG.

FIG. 4 is a cross-sectional view of the surface-treated base material 1 used for manufacturing the heat transfer plate 23 shown in FIGS. 2 and 3. In the surface-treated base material 1 of the present embodiment, as shown in FIG. 4, a first layer 12 made of a first material and a second layer 13 made of a second material are formed on the base material 11 in this order. It becomes.

In the surface-treated base material 1 of the present embodiment, the melting point of the first material constituting the first layer 12 is 1100 ° C. or higher. Further, in the surface-treated base material 1 of the present embodiment, the melting point of the second material constituting the second layer 13 contains a Ni-P alloy and is 300 ° C. or more lower than the melting point of the first material. .. Further, in the surface-treated base material 1 of the present embodiment, the relationship between the thickness t ₁ of the first layer and the thickness t ₂ of the second layer is the thickness condition (1) “t ₁ ≧ 3 μm and t ₂ ≧”. It satisfies either "5 μm" or the thickness condition (2) "1 μm ≦ t ₁ <3 μm and t ₂ ≧ 20 μm". As a result, the surface-treated base material 1 of the present embodiment has excellent corrosion resistance after brazing even when the outermost layer (second layer 13) is melted and brazed.

<Base material 11>
The base material 11 of the present embodiment is not particularly limited as long as it has excellent moldability, but it is preferable to use a stainless steel plate. Examples of the stainless steel sheet include martensitic, ferrite, and austenitic stainless steel sheets. Among them, austenitic stainless steel sheets are preferable, and SUS304 and SUS316 are particularly preferable.

When a stainless steel plate is used as the base material 11, the hot-rolled stainless steel plate is pickled to remove surface scale (oxide film), then cold-rolled, and then electrolytically washed, then annealed and tempered. A rolled product, or a product obtained by cold rolling, electrolytic cleaning, and temper rolling without annealing can be used.

The thickness of the base material 11 is not particularly limited, but is preferably 0.1 to 1.0 mm, from the viewpoint that the strength and processability of the obtained surface-treated base material 1 can be more balanced. It is preferably 0.2 to 0.8 mm, more preferably 0.3 to 0.5 mm.

<First layer 12>
The first layer 12 is a layer formed as a lower layer of the second layer 13 described later, and is composed of a first material having a melting point of 1100 ° C. or higher. In the present embodiment, when the outermost layer (second layer 13) is melted by heat treatment in a state where a plurality of surface-treated base materials 1 are stacked so as to partially contact each other, the second layer 13 becomes a brazing material. By acting, it can be joined to the contact portion of another member (another surface-treated base material 1 or a member made of another material). According to the present embodiment, even if the second layer 13 flows due to the heat of brazing, the corrosion resistance of the surface-treated base material 1 is due to the presence of the first layer 12 as the lower layer of the second layer 13. Can be improved.

The first material may have a melting point of 1100 ° C. or higher, and is not particularly limited. For example, a Ni-Ni alloy (for example, a Ni alloy in which the content ratio of an element other than Ni is 10 atomic% or less). , Co, Co alloys (for example, Co alloys in which the content of elements other than Co is 10 atomic% or less), or Ni—Co alloys (for example, alloys in which the content of Ni and Co is more than 10 atomic%, respectively). ), Etc., and among them, Ni, Ni—Zn alloy, Ni—Fe alloy, Ni—Zn—Co alloy are preferable, and Ni is particularly preferable. That is, it is preferable that the first layer 12 is composed of a first material substantially composed of only Ni.

The method for forming the first layer 12 is not particularly limited, but a method of plating the base material 11 using the plating bath containing the first material described above is preferable.

When the first layer 12 containing Ni as the first material is formed by plating, the first layer 12 can be formed on the base material 11 by plating using a nickel plating bath. As the nickel plating bath, a plating bath usually used for nickel plating, that is, a watt bath, a sulfamic acid bath, a boron fluoride bath, a chloride bath and the like can be used. For example, the first layer 12 containing Ni as the first material uses a watt bath having a bath composition of nickel sulfate 200 to 350 g / L, nickel chloride 20 to 60 g / L, and boric acid 10 to 50 g / L. Formed at pH 3.0 to 4.8 (preferably pH 3.6 to 4.6), bath temperature 50 to 70 ° C., and current density 10 to 40 A / dm ² (preferably 20 to 30 A / dm ² ). can do.

Further, when the first layer 12 containing Co as the first material is formed by plating, the first layer 12 can be formed on the base material 11 by plating using a cobalt plating bath. it can. For example, the first layer 12 containing Co as the first material is a cobalt-plated bath having a bath composition of cobalt sulfate: 200 to 300 g / L, cobalt chloride: 50 to 150 g / L, and sodium chloride: 10 to 50 g / L. It can be formed under the conditions of pH: 2 to 5, bath temperature: 40 to 80 ° C., and current density: 1 to 40 A / dm ² .

Alternatively, when the first layer 12 containing the Ni-Co alloy as the first material is formed by plating, for example, the nickel-cobalt alloy plating bath contains nickel sulfate, nickel chloride, cobalt sulfate and boric acid. The first layer 12 can be formed on the base material 11 by performing plating using a plating bath based on the watt bath. The nickel-cobalt alloy plating is preferably performed under the conditions of a bath temperature of 40 to 80 ° C., a pH of 1.5 to 5.0, and a current density of 1 to 40 A / dm ² . When a Ni-Co alloy is used as the first material, examples of the Ni-Co alloy include alloys in which the content ratios of Ni and Co each exceed 10 atomic%. Further, the Ni—Co alloy may contain other metals, and for example, a Ni—Zn—Co alloy or the like can be used. In this case, the first layer 12 can be formed on the base material 11 by performing plating using a plating bath containing a metal (Ni, Zn, Co, etc.) that constitutes the first material. it can.

When a Ni alloy (a Ni alloy having an element content other than Ni of 10 atomic% or less) is used as the first material, for example, a Ni—Zn alloy, a Ni—Fe alloy or the like can be used. Further, when a Co alloy (a Co alloy in which the content ratio of an element other than Co is 10 atomic% or less) is used as the first material, a Co—Fe alloy or the like can be used. In this case, by performing plating using a plating bath containing a metal (Ni, Zn, Fe, Co, etc.) that constitutes the first material, the above-mentioned Ni is used as the first material on the base material 11. The first layer 12 containing the alloy or the first layer 12 containing the Co alloy as the first material can be formed.

The melting point of the first material constituting the first layer 12 may be 1,100 ° C. or higher, but is preferably 1,200 ° C. or higher, more preferably 1,400 ° C. or higher. If the melting point of the first material is too low, when the outermost layer (second layer 13) of the surface-treated base material 1 is melted and brazed, the heat of the brazing causes not only the second layer 13 but also the first layer. The layer 12 also melts, which may cause the first layer 12 to flow and expose the base material 11, which may reduce the corrosion resistance of the surface-treated base material 1. The upper limit of the melting point of the first material is not particularly limited, but is usually 1,600 ° C. or lower, preferably 1,500 ° C. or lower.

The thickness t ₁ of the first layer 12 is not particularly limited, but is preferably 0.5 to 10 μm, more preferably 1 to 8 μm, and further preferably 3 to 5 μm. By setting the thickness t ₁ of the first layer 12 to the above range, the corrosion resistance of the obtained surface-treated base material 1 can be further improved. In particular, when the first layer is composed of a plating layer, if it exceeds 10 μm, the entire surface may bend due to strain during plating, surface irregularities may easily occur, or plating unevenness may occur between the edges and the center of the base material. As a result, when the second layer is formed, particularly when the Ni-P alloy is formed by plating, the uniformity of the thickness of the Ni-P alloy layer may be easily lost. Therefore, 10 μm or less is preferable.

<Second layer 13>
The second layer 13 is composed of a second material containing a Ni—P alloy. As the second material, a material having a melting point lower than the melting point of the first material described above by 300 ° C. or more is used. In the surface-treated base material 1 of the present embodiment, the Ni-P alloy contained in the second layer 13 acts as a brazing material by performing a heat treatment after laminating a plurality of surface-treated base materials 1, and the like. Can be joined to the contact portion of the member (another surface-treated base material 1 or a member made of another material).

The second material may contain a Ni-P alloy and has a melting point lower than the melting point of the first material by 300 ° C. or more, and is not particularly limited, but the Ni-P alloy alone (that is, the first material). However, it may be substantially composed of only a Ni-P alloy), or may contain, for example, Si or Cr in addition to the Ni-P alloy. In order to ensure brazing property, Si is preferably 10% by weight or less and Cr is preferably 30% by weight or less. This is because Si is a melting point lowering element, but if it is too much, the Ni-P alloy becomes brittle and the brazing property is lowered. Cr is an element for improving corrosion resistance, but if it is too much, the fluidity of the brazing material deteriorates and the brazing property deteriorates.

The Ni-P alloy contained in the second material has a P content of preferably 7 to 15% by weight, more preferably 9 to 14% by weight, and even more preferably 11 to 12% by weight. By setting the content ratio of P in the Ni-P alloy to the above range, the melting point of the second material can be controlled to a more appropriate range, and the second layer 13 formed by using the second material can be formed. It can be made more suitable as a brazing material.

The method for forming the second layer 13 is not particularly limited, but a method of plating on the first layer 12 using the plating bath containing the second material described above is preferable.

When the second layer 13 is formed by electroplating, for example, as a nickel-phosphorus alloy plating bath, a plating bath containing a nickel salt such as nickel sulfate and a phosphorus component such as sodium phosphite is used. By plating the base material 11 on which the first layer 12 is formed, the second layer 13 can be formed on the first layer 12. The nickel-phosphorus alloy plating is preferably performed under the conditions of a bath temperature of 40 to 80 ° C., a pH of 1.5 to 5.0, and a current density of 1 to 20 A / dm ² . In addition, in this embodiment, by forming the first layer and the second layer by electroplating, it is industrially productive, and a constant width (width 10 to 150 cm) and a length 10 to 40,000 m are obtained by continuous treatment. It is possible to obtain a continuous metal band of the above surface-treated base material, and the surface-treated base material obtained from such a continuous metal band is suitable for brazing.

The melting point of the second material may be 300 ° C. or higher lower than the melting point of the first material, but is preferably 400 ° C. or higher lower than the melting point of the first material, and 500 ° C. or higher lower than the melting point of the first material. Is more preferable. By setting the melting point of the second material in the above range, the second layer 13 formed by using the second material can be made more suitable as a brazing material.

In the present embodiment, the thickness t ₂ of the second layer 13 is related to the thickness t ₁ of the first layer described above, and the thickness condition (1) “t ₁ ≧ 3 μm and t ₂ ≧ 5 μm” or It satisfies any of the thickness conditions (2) "1 μm ≦ t ₁ <3 μm and t ₂ ≧ 20 μm".

In the thickness condition (1) described above, the thickness t ₂ of the second layer 13 may be t ₂ ≧ 5 μm when the thickness t ₁ of the first layer is t ₁ ≧ 3 μm, but is preferably t. ₂ ≧ 10 μm, more preferably t ₂ ≧ 20 μm. In the thickness condition (1) described above, the upper limit of the thickness t ₂ of the second layer 13 is not particularly limited, but is usually t ₂ ≤ 10 μm, preferably t ₂ ≤ 20 μm. Further, when the above-mentioned thickness condition (1) is satisfied, it is preferable to further satisfy the thickness condition (3) "t ₂ > t ₁ ". When the thickness t ₁ of the first layer is t ₁ ≧ 3 μm, the thickness t ₁ of the first layer is preferably 4 μm ≦ t ₁ ≦ 6 μm, preferably 4.5 μm ≦, from the viewpoint of being more excellent in corrosion resistance. More preferably, t ₁ ≤ 5.5 μm.

On the other hand, in the thickness condition (2) described above, the thickness t ₂ of the second layer 13 may be t ₂ ≧ 20 μm when the thickness t ₁ of the first layer is 1 μm ≦ t ₁ <3 μm. In the thickness condition (2) described above, the upper limit of the thickness t ₂ of the second layer 13 is not particularly limited, but is usually t ₂ ≦ 40 μm.

In the present embodiment, the thickness t ₂ of the second layer 13, and a thickness t ₁ of the first layer, by a satisfies the above relationship, the outermost layer of the surface treated substrate 1 (second layer 13 ) Is melted and brazed, even if the second layer 13 flows due to the heat of brazing, the first layer 12 remains on the base material 11, and the surface-treated base material 1 Corrosion resistance can be further improved.

In the present embodiment, the first layer ratio of the thickness _{t 1} of the relative thickness _{t 2} of the second layer 13 (thickness _{t 2} of the first layer thickness _{t 1} / second layer 13) is preferably 0. It is 05 to 1.0, more preferably 0.1 to 1.0, and even more preferably 0.2 to 1.0. By setting the ratio of the thickness t ₁ of the first layer to the thickness t ₂ of the second layer 13 within the above range, when the surface-treated base material 1 is laminated by brazing, the second layer 13 is affected by the heat of brazing. Even if it flows, the first layer 12 remains as the lower layer of the second layer 13, and the corrosion resistance of the surface-treated base material 1 can be further improved.

The surface-treated base material 1 of the present embodiment is configured as described above.

Since the surface-treated base material 1 of the present embodiment is formed by forming the above-mentioned specific first layer 12 and the specific second layer 13 on the base material 11 in this order, a plurality of surface-treated groups. When the outermost layer (second layer 13) is melted by heat treatment in a state where the materials 1 are overlapped so as to partially contact each other, the second layer 13 acts as a brazing material and other members (other surfaces). It can be joined to the contact portion of the treated base material 1 or a member made of another material). According to the surface-treated base material 1 of the present embodiment, even if the second layer 13 flows due to the heat of brazing at this time, the surface surface is due to the presence of the first layer 12 as the lower layer of the second layer 13. The corrosion resistance of the treated base material 1 can be improved.

Conventionally, a surface-treated base material for brazing obtained by forming a copper plating layer or a nickel plating layer as a brazing material by plating on a base material on which irregularities such as a fluid flow path are formed in advance has been used. , Is used as a member of heat exchangers. However, in such a conventional surface-treated base material for brazing, when a plurality of surface-treated base materials are stacked and heat-treated to melt the brazing material on the surface of the surface-treated base material for brazing. There is a problem that the brazing material on the surface flows due to the heat of brazing, which exposes the base material on the surface of the surface-treated base material and lowers the corrosion resistance of the surface-treated base material.

On the other hand, according to the surface-treated base material 1 of the present embodiment, the base material 11 can be prevented from being exposed on the surface by forming the first layer 12 as the lower layer of the second layer 13. Therefore, even when used in a harsh environment where it comes into contact with salt water after brazing, it is possible to appropriately suppress corrosion. Therefore, the surface-treated base material 1 of the present embodiment can be particularly preferably used as a material for a heat exchanger that uses seawater as a refrigerant (fluid), such as an oil cooler used for ships such as marine jets. ..

Further, especially when the thickness of each layer is controlled by using Ni, Ni-Co alloy, or an alloy based on Ni as the first material, brazing by Ni-P of the second layer is not hindered. While maintaining the bondability between the brazing layers, the adhesion between the base material and the brazing layer after brazing can be sufficiently maintained, and it can be preferably used.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

<< Example 1 >>
First, as a base material, a SUS304 stainless steel sheet (thickness (0.3) mm) having the following chemical composition was prepared.
C: 0.08% by weight, Si: 1.00% by weight, Mn: 2.00% by weight, P: 0.04% by weight, S: 0.03% by weight, Ni: 8 to 10.5% by weight, Cr: 18.0 to 20.0% by weight, balance: Fe and unavoidable impurities

Then, the prepared base material was subjected to alkaline electrolytic degreasing and pickling by immersion in sulfuric acid, and then nickel-plated under the following conditions, and the first layer (thickness 3 μm nickel plating layer) using Ni as the first material. ) Was formed. The thickness of the first layer was determined by measuring the amount of nickel adhering with a fluorescent X-ray analyzer (Rigaku Fluorescent X-ray analyzer ZSX100e) and using the specific gravity of nickel of 8.9. In Example 1, the amount of nickel adhered was 26.7 g / m ² . Further, when the melting point of the formed nickel plating layer was measured using a thermogravimetric differential thermal analyzer TG-DTA (TG8210, manufactured by Rigaku Co., Ltd.), a peak of endothermic reaction was observed between about 1455 ° C. (1445-1465 ° C.). Exists).
<Nickel plating>
Bath composition: nickel sulfate 250 g / L, nickel chloride 45 g / L, boric acid 30 g / L
pH: 3.5-5.0
Bath temperature: 60 ° C
Current density: 10A / dm ²

Next, the base material on which the nickel plating layer is formed is subjected to a plating treatment using the nickel-phosphorus alloy plating bath shown below under the following conditions, whereby Ni-P as a second material is applied on the first layer. A surface-treated base material was obtained by forming a second layer (a nickel-phosphorus alloy plating layer having a thickness of 5 μm) using the above. The amount of Ni and the amount of P were measured by using a fluorescent X-ray analyzer as in the first layer. Specifically, first, the total amount of nickel adhered and the amount of phosphorus adhered after plating with a nickel-phosphorus alloy are measured, and the amount of nickel adhered to the first layer is subtracted from the total amount of nickel adhered to the second layer. The amount of nickel adhered was calculated. Next, the total amount of nickel adhesion and phosphorus adhesion in the obtained second layer was calculated and calculated as the nickel-phosphorus alloy plating adhesion amount, which was 40 g / m ² . The phosphorus content was determined from the phosphorus adhesion amount / nickel-phosphorus alloy plating adhesion amount and found to be 10% by weight. Since the specific gravity of Ni-10% P is 8.0, the plating thickness can be determined to be 5 μm from the amount of nickel-phosphorus alloy plating adhered. However, the thickness does not depend on the above method, and can be measured, for example, by observing a cross section. Further, when the melting point of the formed nickel-phosphorus alloy plating layer was measured using a thermogravimetric differential thermal analyzer TG-DTA (TG8210, manufactured by Rigaku Co., Ltd.), heat was absorbed between about 907 ° C. (897 to 917 ° C.). There is a peak of). In each of the Examples and Comparative Examples, the plating amount and the plating thickness were calculated by the same method.
<Electrodeposited nickel-phosphorus alloy plating bath>
Bath composition: Nickel sulfate 200 g / L, nickel chloride 10 g / L, boric acid 30 g / L, phosphorous acid 40 g / L, disodium hydrogen phosphate 110 g / L
pH: 2.0
Bath temperature: 60 ° C
Current density: 10A / dm ²

Then, the surface-treated base material thus obtained was cut into a size of 100 mm in length × 30 mm in width to obtain a test piece, and the obtained test piece was subjected to conditions of 1,100 ° C. for 1 minute. Heat-treated in. In this heat treatment, the second layer of the surface-treated base material is used as a brazing material, and it is assumed that a plurality of surface-treated base materials are brazed to each other or brazed to other materials. The heat treatment was performed under the same conditions as the heat treatment. Next, the heat-treated test piece was subjected to a corrosion resistance test in accordance with JIS H8502. Specifically, a sodium chloride aqueous solution having a concentration of 5% by weight was used as a test solution, and salt spray (35 ° C., 2 hours), drying (60 ° C., 25% RH, 4 hours) and wetting (50 ° C., 98%). RH, 2 hours) cycle was performed 100 cycles. Then, the surface of the test piece after the corrosion resistance test was visually observed, and the salt damage resistance of the surface-treated substrate was evaluated by judging according to the following criteria. The results are shown in Table 1. In the following criteria, if it is 1 or 2, it is judged that the surface-treated base material has excellent salt damage resistance.
1: No corrosion was confirmed on the test piece.
2: Although corrosion occurred on the test piece, all the corrosion that occurred was generated from the cut surface (the part where the base material was exposed) at the end of the test piece.
3: Corrosion was confirmed on areas other than the cut surface at the end of the test piece.

<< Examples 2 to 7 >>
The plating conditions for forming the first layer and the plating conditions for forming the second layer were changed so that the thickness of the first layer and the thickness of the second layer are as shown in Table 1, respectively. A surface-treated base material was prepared in the same manner as in Example 1 except for the above, and evaluated in the same manner. The results are shown in Table 1.

<< Comparative Example 1 >>
Example 1 except that a copper plating layer having a thickness of 20 μm was formed in place of the second layer by directly performing copper plating on the base material without forming the first layer under the following conditions. A surface-treated base material was prepared in the same manner as in the above, and evaluated in the same manner. The results are shown in Table 1.
<Copper plating>
Bath composition: Copper sulfate / pentahydrate 200 g / L, sulfuric acid 45 g / L
pH: 1 or less Bath temperature: 50 ° C
Current density: 20A / dm ²

<< Comparative Examples 2 to 4 >>
The surface was the same as in Example 1 except that the second layer was formed directly on the substrate without forming the first layer by adjusting the plating conditions so that the thickness was as shown in Table 1. A treated substrate was prepared and evaluated in the same manner. The results are shown in Table 1.

<< Comparative Examples 5 to 7 >>
The plating conditions for forming the first layer and the plating conditions for forming the second layer were changed so that the thickness of the first layer and the thickness of the second layer are as shown in Table 1, respectively. A surface-treated base material was prepared in the same manner as in Example 1 except for the above, and evaluated in the same manner. The results are shown in Table 1.

<< Comparative Examples 8 to 12 >>
A base material on which the first layer was formed was prepared in the same manner as in Example 1 except that the plating conditions for forming the first layer were changed so that the thickness of the first layer was as shown in Table 1. did. Next, the same copper plating as in Comparative Example 1 was performed on the base material on which the first layer was formed by adjusting the plating conditions to form a copper plating layer having a thickness as shown in Table 1. By doing so, a surface-treated base material was prepared. Then, the prepared surface-treated base material was evaluated in the same manner as in Example 1. The results are shown in Table 1.

<< Comparative Example 13 >>
The above corrosion resistance test was carried out on the base material as it was without forming the first layer and the second layer. The results are shown in Table 1.

As shown in Table 1, a second layer containing a first layer made of a first material having a melting point of 1100 ° C. or higher and a Ni-P alloy on the base material and having a melting point of 300 ° C. or higher lower than that of the first material. A surface-treated base material obtained by forming a second layer made of a material in this order and having the thickness of the first layer and the thickness of the second layer satisfy the predetermined relationship described above has corrosion resistance (salt damage resistance). ) Was excellent (Examples 1 to 7).

On the other hand, as shown in Table 1, the surface-treated base material on which neither the first layer nor the second layer was formed was inferior in corrosion resistance (salt damage resistance) (Comparative Example 1). Similarly, even if the second layer containing the Ni-P alloy was formed, the surface-treated base material that did not form the first layer was inferior in corrosion resistance (salt damage resistance) (Comparative Examples 1 to 3). ).
Further, on the base material, a first layer made of a first material having a melting point of 1100 ° C. or higher and a second material containing a Ni-P alloy and having a melting point lower than that of the first material by 300 ° C. or higher are formed. Even if the layers were formed in this order, the surface-treated base material in which the thickness of the second layer was too thin was inferior in corrosion resistance (salt damage resistance) with respect to the thickness of the first layer being less than 3 μm. (Comparative Examples 5 to 7).
Further, even if the first layer is formed, the surface-treated base material having a Ni-P alloy-free layer (copper plating layer) formed on the first layer is inferior in corrosion resistance (salt damage resistance). (Comparative Examples 8 to 12).
Further, the base material itself on which the plating layer was not formed was inferior in corrosion resistance (salt damage resistance) (Comparative Example 13).

1 ... Surface-treated base material 11 ... Base material 12 ... First layer 13 ... Second layer 2 ... Plate heat exchanger 21 ... Fluid inlet 22 ... Fluid outlet 23 ... Heat transfer plate 24, 24a ... Fluid flow path 25 ... Intervention Member 26 ... Outer layer member

Claims (6)

With the base material
A first layer made of a first material having a melting point of 1100 ° C. or higher and formed on the base material,
It is composed of a second material containing a Ni-P alloy and having a melting point lower than that of the first material by 300 ° C. or more, and includes a second layer formed on the first layer.
Wherein the thickness _{t 1} of the first layer, the second layer relationship between the thickness _{t 2} of the thickness condition (1) _{"t 1} ≧ 3 [mu] m and,, _{t 2} ≧ 5 [mu] m" or thickness condition (2) "1 [mu] m, A surface-treated base material for brazing that satisfies any of ≦ t ₁ <3 μm and t ₂ ≧ 20 μm ”. The thickness t ₁ of the first layer, the relationship between the thickness t ₂ of the second layer, if it meets the thickness condition (1), the thickness condition (3) further satisfy the "t _2> t _1" according Item 2. The surface treatment base material for brazing according to Item 1. The surface-treated base material for brazing according to claim 1 or 2, wherein the base material is stainless steel. The first material is a Ni, Ni alloy (Ni alloy in which the content ratio of elements other than Ni is 10 atomic% or less), Co, Co alloy (Co alloy in which the content ratio of elements other than Co is 10 atomic% or less). ), Or the surface-treated base material for brazing according to any one of claims 1 to 3 containing a Ni—Co alloy. The surface-treated base material for brazing according to any one of claims 1 to 4, which is used in contact with salt water. A heat exchanger comprising the surface-treated base material for brazing according to any one of claims 1 to 5.

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