JP5366498B2 - Cu-plated ferritic stainless steel sheet and multi-turn steel pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Cu-plated ferritic stainless steel sheet which remarkably suppresses the coarsening of crystal grains in fusion bonding treatment between Cu-plated layers, and is suitable for a multiple-wound steel pipe. <P>SOLUTION: The Cu-plated stainless steel sheet uses a ferritic stainless steel sheet as its substrate, which includes, by mass%, 0.03% or less C, 3% or less Si, 2% or less Mn, 0.05% or less P, 0.03% or less S, 11-30% Cr, 0.15-0.8% Nb, 0.03% or less N, optionally, 0.4% or less in total of one or more of Ti and Al, 4% or less in total of one or more of Mo, Cu, V and W, 5% or less in total of one or more of Ni and Co, and the balance Fe with unavoidable impurities; has a value A of 0.1 or more, which is determined by A=Nb-(C&times;92.9/12+N&times;92.9/14) when Ti&le;N, and A=Nb-C&times;(92.9/12)/2 when Ti&gt;N; and contains precipitates of which the maximum particle diameter is 0.25 &mu;m or smaller and of which the area rate is 0.05% or more. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a Cu-plated ferritic stainless steel plate suitable for a multi-turn steel pipe for forming a pipe by forming a Cu fusion layer, and a multi-wind stainless steel pipe using the same.

  Conventionally, pipes of copper or copper alloys (hereinafter referred to as “Cu pipes”) that have good workability and brazing properties and relatively good corrosion resistance are used for refrigerant pipes and water pipes of heat exchangers. It is used a lot.

  On the other hand, a multi-winding stainless steel pipe using extremely soft austenitic stainless steel is known as a metal pipe excellent in workability and corrosion resistance (Patent Document 1).

JP-A-5-33103

Recently, hot water supply equipment using a heat pump is becoming widespread. In addition to air conditioners, home appliances using heat pumps such as washing and drying machines have appeared. The heat pump can obtain a heat amount exceeding the input power from the atmosphere, and the heat pump will become more widespread in the future, and a great effect on CO ₂ emission reduction is expected.

  In order to improve the efficiency of the heat pump, it is advantageous to increase the refrigerant pressure. However, the conventional Cu tube, which is frequently used, has a problem that it is difficult to cope with an increase in refrigerant pressure because of its low strength. If it is going to improve the intensity | strength of Cu pipe | tube, it will be forced to employ | adopt thickness increase and a high intensity | strength copper alloy, and will involve a great cost increase. In addition, the recent increase in copper prices has also increased the cost of Cu tubes. Therefore, it is desired to apply a new piping material in place of the copper-based material.

  A stainless steel pipe is mentioned as a material which has the intensity | strength and corrosion resistance which exceed a Cu pipe | tube. However, in the case of a mere stainless steel pipe, it is necessary to employ “silver brazing” as a brazing material used for brazing. Silver brazing is several times more expensive than “phosphorous copper brazing” conventionally used for brazing Cu pipes, so it is difficult to substitute a simple stainless steel pipe.

  On the other hand, there is the above-described multi-winding stainless steel pipe as a stainless steel pipe to which phosphor copper brazing can be applied. Since the multi-winding stainless steel pipe is made of a Cu-plated stainless steel plate, it has a Cu plating layer on the outer surface, and a copper-based brazing material can be applied. However, the multi-winding stainless steel pipe that is currently in practical use uses austenitic stainless steel. Since austenitic stainless steel is expensive, the cost merit for Cu pipe is small. In order to achieve both high strength and cost reduction, it is desired to use a multi-winding steel pipe using inexpensive ferritic stainless steel.

  However, it is technically difficult to manufacture a multi-winding steel pipe excellent in strength characteristics using ferritic stainless steel, and at the present time, an alternative to a Cu pipe that can cope with an increase in refrigerant pressure has not been put into practical use. The reason for this is that ferritic stainless steel is a ferrite crystal grain of the base matrix in the “Cu plating layer fusion treatment” (ie, brazing treatment using the Cu plating layer as a brazing material) in the production of a multi-turn steel pipe. Can easily be coarsened.

  An object of the present invention is to overcome such problems and provide a Cu-plated ferritic stainless steel plate suitable for a multi-turn steel pipe and a multi-wind steel pipe using the same.

  As a result of detailed research, the inventors have used the drag effect of solid solution Nb and the pinning effect of precipitates to suppress the coarsening of the crystal grains in the Cu plating layer fusion process. We have found that suitable materials can be realized.

That is, in the present invention, by mass, C: 0.03% or less, Si: 3% or less, Mn: 2% or less, P: 0.05% or less, S: 0.03% or less, Cr: 11-30 %, Nb: 0.15 to 0.8%, N: 0.03% or less, and optionally contains one or more of Ti and Al in a total range of 0.4% or less, or Mo 1 or more of Cu, V, and W in a total range of 4% or less, or further, 1 or more of Ni and Co in a range of 5% or less in total, with the balance being Fe and inevitable impurities Yes, preferably the total content of C and N is 0.01% or more, and the relationship of Ti content (mass%) ≤ N content (mass%) is satisfied (including the case where Ti is not contained) If the relationship of the following formula (1) and Ti content (mass%) > N content (mass%) is satisfied, the following formula (2) The base material is a ferritic stainless steel plate having a chemical composition with an A value determined to be 0.1 or more, and a Cu plating layer is provided on at least one surface thereof, and precipitates are distributed in the steel substrate of the base material. A Cu-plated stainless steel sheet for fusion bonding of a Cu plating layer is provided in which the maximum particle diameter dmax of the precipitate determined by cross-sectional SEM observation is 0.25 μm or less and the area ratio f of the precipitate is 0.05% or more.
A = Nb− (C × 92.9 / 12 + N × 92.9 / 14) (1)
A = Nb−C × (92.9 / 12) / 2 (2)

Here, the content of the element represented by mass% is substituted for the element symbol in the formulas (1) and (2). It means if the Ti content in wt% and "Ti content (mass%) ≦ N content when the relationship is satisfied (mass%)" does not exceed the N content, "Ti content (wt% ) > When the relationship of > N content (% by mass) is established, it means the case where the Ti content exceeds the N content in mass% .

  In the present invention, the above-mentioned Cu-plated stainless steel sheet is wound in multiple layers, and the Cu plating layer interposed between the substrates is melted and solidified to form a Cu fusion layer, thereby joining adjacent substrates together. A multi-winding stainless steel pipe having a Cu plating layer on the outer surface of the pipe is provided.

Even if the Cu plated ferritic stainless steel sheet of the present invention is subjected to a Cu plating layer fusion treatment, coarsening of crystal grains is suppressed. When this steel plate is used, a multi-winding steel pipe excellent in strength characteristics using a ferritic stainless steel as a base material can be obtained. This multi-turn steel pipe can be wire brazed with a phosphor copper brazing material and can be used as an alternative to a conventional Cu pipe. In particular, since the base material is stainless steel, the corrosion resistance is excellent, and the strength can be improved without increasing the cost. Therefore, the present invention can cope with an increase in fluid pressure in heat pumps and other piping members, and can contribute to a reduction in CO ₂ emissions and a reduction in equipment costs.

  FIG. 1 schematically illustrates a cross-sectional structure of a multi-turn steel pipe that is a subject of the present invention. The multi-winding steel pipe 10 is formed by spirally winding a Cu-plated stainless steel plate having the Cu plating layer 1 on the surface of the stainless steel base material 2 into a tubular shape, and heat-treating it at a temperature equal to or higher than the melting point of Cu. Are fused and solidified to form a Cu fusion layer 3, and adjacent stainless steel substrates 2 are joined together. The thing of this FIG. 1 is an example of a double wound steel pipe. In this specification, the heat treatment is referred to as “Cu plating layer fusion treatment”, and the joining of the base materials 2 via the Cu fusion layer 3 formed by the Cu plating layer fusion treatment is referred to as “Cu plating layer fusion joining”. " The Cu plating layer fusion bonding is a kind of brazing bonding using a Cu plating layer as a brazing material. However, in the present specification, the term “brazing” simply means brazing applied when the multi-turn steel pipe 10 is bonded to another member, and is distinguished from bonding by Cu plating layer fusion treatment. .

  In the Cu plating layer fusion treatment, the steel material is normally subjected to high temperature heating of 1100 ° C. or higher. When the base material is ferritic stainless steel, the crystal grains are likely to be coarsened by such a high temperature holding. If the ferrite crystal grains of the base material are coarsened in a multi-winding steel pipe, cracks are likely to occur during the forming process, and during use as a product, vibration, external impact, internal It is easy to be damaged by the pulsation of the fluid flowing through. As a result of various studies, in order to avoid such a problem, it is important that the average grain size of the ferrite crystal grains does not exceed 500 μm. In the present invention, the drag effect and the pinning effect are utilized in order to impart to the ferritic stainless steel the property that the crystal grains are difficult to coarsen when subjected to the Cu plating layer fusion treatment.

[Drag effect]
When a crystal grain grows, it is accompanied by movement of a crystal grain boundary. When solid solution elements and impurity elements that are likely to accumulate at the grain boundaries are contained in the matrix, the grain boundaries move with the elements, and it is accompanied by diffusion of these solute atoms. (Drug effect). As a result of detailed studies, the inventors have found that solute Nb is extremely effective in suppressing the growth of crystal grains of ferritic stainless steel at high temperatures. Since Nb is an element that easily binds to C and N, it can be understood that, among Nb added to steel, the remainder consumed as carbide / nitride is solute Nb. However, when Ti is added, Ti also easily bonds with C and N, so the amount of solid solution Nb is affected by the Ti content.

When Ti is not added, the A value determined by the following equation (1) can be adopted as an index representing the amount of solid solution Nb (% by mass).
A = Nb− (C × 92.9 / 12 + N × 92.9 / 14) (1)

When Ti is added, it is necessary to consider that Ti is likely to bond with N preferentially over Nb to form TiN. As a result of the examination, it was found that the above formula (1) may be applied when the relationship of Ti content (% by mass) ≦ N content (% by mass) is established . Strictly speaking, since part or all of N is fixed by Ti, the A value according to the equation (1) estimates the amount of solute Nb slightly lower, but from the viewpoint of influence on the drag effect, the equation (1) May be applied. On the other hand, when the relationship of Ti content (mass%) > N content (mass%) is established, the A value according to the following equation (2) is used as an index of the solid solution Nb content.
A = Nb−C × (92.9 / 12) / 2 (2)
Strictly speaking, the actual solute Nb amount slightly varies from the A value according to the formula (2) depending on the Ti content, but as an index representing the influence on the drag effect within the range of the Ti content described later. Equation (2) can be applied.

  When the index A value reflecting the solid solution Nb amount represented by the above formula (1) or (2) is 0.1 or more, the drag effect to suppress the grain boundary movement due to high temperature heating of the ferritic stainless steel is The effect | action which works effectively and suppresses the crystal grain coarsening in Cu plating layer fusion | melting process is acquired. It is more effective that the A value is 0.2 or more.

[Pinning effect]
When precipitates are finely dispersed in the metal matrix, they interfere with dislocation movement and cause a so-called precipitation strengthening phenomenon. Such precipitates can also interfere with grain boundary migration during high-temperature heating ( Pinning effect). The pinning effect increases as the particle size of the individual precipitates decreases and the total volume ratio increases. The inventors examined in detail the influence on the coarsening of the grains when the particle size of the precipitates was variously changed in the ferritic stainless steel sheet having the total volume fraction of the precipitates of 0.02 to 0.20%. . As a result, when the maximum particle diameter dmax of the precipitate is 0.25 μm or less and the area ratio f of the precipitate is 0.05% or more, after the Cu plating layer fusion treatment due to the synergistic effect with the above-described drag effect. It has been found that the average crystal grain size can be maintained at 500 μm or less.

Precipitates effective for the pinning effect are mainly Nb-based precipitates, and examples thereof include Nb carbide, Nb nitride, Nb carbonitride, Fe ₂ Nb (Laves phase), Fe ₃ NbC, and the like. Precipitates of alloy elements other than Nb are also effective. The maximum particle diameter dmax of the precipitate may be determined by measuring the particle diameter (major axis) of each precipitate appearing in the cross section of a sample obtained by polishing a steel cross section from an SEM image or the like. However, the area of the observation visual field may be 2 × 10 ⁻² mm ² or more. The area ratio f of the precipitate corresponds to the total volume ratio of the precipitate. In the sample obtained by polishing the steel cross section, the total area of the precipitate appearing in the cross section is measured, and this is the area of the observation field. It can be obtained by dividing it and converting it to a percentage. Also in this case, the area of the observation visual field may be the same as described above. The total area of the precipitate can be obtained by identifying the precipitate containing Nb, Ti, Mo, Cu, V, W by EDX and processing an image in which the detected intensity in the observation field is recorded.
The distribution form of precipitates can be controlled by the chemical composition and production conditions.

[Chemical composition]
In the following, “%” in the content of constituent elements of steel means “% by mass” unless otherwise specified.
C and N are elements that combine with Nb to consume Nb added to the steel and reduce the abundance of solute Nb. If the amount of dissolved Nb is insufficient, the above-described drag effect cannot be obtained sufficiently, and the coarsening of crystal grains during the Cu plating layer fusion treatment cannot be suppressed. As a result of various studies, the C content needs to be 0.03% or less, and more preferably 0.025% or less. The N content also needs to be 0.03% or less, and more preferably 0.025% or less. On the other hand, Nb bonded to C or N forms Nb carbide, Nb nitride, Nb carbonitride (hereinafter collectively referred to as “Nb carbon / nitride”), and these precipitates have a pinning effect. Exhibits the effect of suppressing crystal grain coarsening during the Cu plating layer fusion treatment. In order to sufficiently exhibit the pinning effect by Nb charcoal / nitride, it is more effective to make the total content of C and N 0.01% or more, and the C content 0.005% or more, The N content is more preferably 0.005% or more.

  Si is an element effective for improving the corrosion resistance of ferritic stainless steel. In order to obtain the effect sufficiently, it is more effective to secure a Si content of 0.2% or more. However, containing a large amount of Si hardens the ferrite phase and causes deterioration of workability. As a result of various studies, the Si content is limited to 3% or less, and more preferably 2.5% or less.

  Mn is effective as a deoxidizer for stainless steel, but may reduce the Cr concentration in the passive film and inhibit corrosion resistance, so in the present invention, the Mn content is limited to 2% or less.

  P is undesirable because it impairs the toughness of the base material and brazed portion of the ferritic stainless steel. As a result of various studies, the present invention allows P content up to 0.05%.

  S is an element that forms MnS that tends to be a starting point of pitting corrosion and inhibits corrosion resistance. Moreover, when S content is high, it becomes easy to produce a hot crack in a brazing part. The S content is limited to 0.03% or less.

  Cr is an essential element for securing the corrosion resistance as stainless steel. Considering application to piping members constituting heat exchangers and refrigerant piping, a Cr content of 11% or more is necessary. On the other hand, when the Cr content increases, it becomes difficult to reduce C and N, which becomes a factor that impairs mechanical properties and toughness. As a result of the study, the Cr content is limited to a range of 30% or less.

  Nb is an important element in the present invention. That is, as described above, solute Nb in steel is effective for the drag effect, and Nb-based precipitates are effective for the pinning effect. In order to remarkably suppress the grain coarsening in the Cu plating layer fusion process by utilizing these effects, the Nb content is 0.15% after limiting the C and N contents to the above ranges. That is important. It is more preferable to ensure the Nb content of 0.3% or more, and it is more effective to set it to 0.4% or more. It may be controlled to 0.5% or more. However, when the Nb content is increased, the hot workability and the surface quality characteristics of the steel material are adversely affected. As a result of various studies, the Nb content is limited to a range of 0.8% or less.

  Of Ti and Al, Ti has a strong affinity with C and N like Nb, and forms fine Ti-based charcoal / nitride to increase the grain size at the time of Cu plating layer fusion treatment by pinning effect. It exhibits an inhibitory action. Al is effective as a deoxidizer. Therefore, one or two of these elements can be added as necessary, and it is more effective to make the total content of Ti and Al 0.03% or more. However, Ti and Al are easily oxidizable elements, and if their content is large, a strong oxide film is likely to be formed during finish annealing. This oxide film may not be sufficiently removed by pickling. In this case, the Cu plating layer cannot be uniformly formed (non-plated part is generated), so that the bonding strength at the non-plated part in brazing using phosphor copper braze is high. It became clear that it could be a problem. When one or more of Ti and Al are added, the total content of Ti and Al must be suppressed to 0.4% or less in order to avoid the problems caused by the oxide film as described above. More preferably, it is as follows.

  Mo, Cu, V, and W are effective elements for preventing ferrite crystal grain coarsening during the Cu plating layer fusion treatment. That is, Mo, V, and W exhibit a drag effect by solid solution and a pinning effect by precipitate formation. Cu exhibits a pinning effect by precipitating as an ε-Cu phase. For this reason, in this invention, 1 or more types of these elements can be added as needed. In particular, it is more effective to set the total content of these elements to 0.05% or more. However, when the content of these elements increases, the hot workability is adversely affected. As a result of various studies, when adding one or more of Mo, Cu, V, and W, it is necessary to add them in a range where the total content thereof is 4% or less.

  Ni and Co are effective elements for suppressing a decrease in toughness when ferrite crystal grains are coarsened by a Cu plating layer fusion treatment or the like. The effect of suppressing the decrease in toughness is enjoyed even when the average crystal grain size is 500 μm or less. For this reason, in this invention, 1 or more types of Ni and Co can be added as needed. In order to sufficiently exhibit such an action, it is more effective to set the total content of Ni and Co to 0.5% or more. However, excessive addition of Ni and Co is not preferable because it causes formation of an austenite phase in a high temperature range. When adding 1 or more types of Ni and Co, it is necessary to carry out in the range from which the total content will be 5% or less.

[Manufacture of Cu plated stainless steel sheet]
After melting the steel having the above chemical composition, it is made into a steel plate using a general ferritic stainless steel plate manufacturing process, and then subjected to electric Cu plating in the same manner as a conventional Cu plated stainless steel plate manufacturing method. The Cu plated stainless steel sheet of the present invention can be obtained. However, in order to prevent crystal grain coarsening when it is subjected to the Cu plating layer fusion treatment, it is important to obtain the above-mentioned precipitate distribution form so that the pinning effect is sufficiently exhibited. .

In order to obtain such a distribution form of precipitates, it is extremely effective to adopt conditions satisfying the following [1] and [2] in a process including hot rolling → cold rolling → finish annealing. .
[1] In hot rolling, the coiling temperature is set to less than 750 ° C.
[2] In finish annealing, the average temperature increase rate from 600 ° C. to the maximum temperature T _{M is set} to 10 ° C./sec or more in the temperature rising process, and the average cooling rate from T _M to 600 ° C. is set to 10 ° C. in the cooling process. The heat pattern is controlled to be at least / sec.
By performing the treatment satisfying the above [1] and [2] on the steel satisfying the above chemical composition, the maximum particle diameter dmax of the precipitate is 0.25 μm or less and the area ratio f of the precipitate is 0.05. % Or more of the precipitation form can be realized.

  The average thickness of the Cu plating layer can be adjusted in the range of 1 to 10 μm per side, but it is practical to set the thickness to about 2 to 5 μm.

[Multi-wrapped steel pipe]
The multi-winding stainless steel pipe of the present invention can be obtained by the same method as that for manufacturing a conventional multi-winding stainless steel pipe. The Cu plating layer fusion treatment can be performed by holding a pipe in which steel plates are wound in multiple layers, for example, in a vacuum atmosphere at a temperature equal to or higher than the melting point of Cu. Specifically, the holding temperature may be 1100 to 1175 ° C. and the holding time may be 10 to 60 minutes. The obtained multi-winding steel pipe has an average crystal grain size of the substrate matrix of 500 μm or less, and is excellent in workability and strength characteristics. Moreover, it has a Cu plating layer on the outer surface, and can be used for brazing using a copper-based brazing material such as a phosphor-copper brazing material in the same manner as a conventional Cu pipe.

Stainless steel having the chemical composition shown in Table 1 is melted, hot rolled to a plate thickness of 3 mm, pickled, cold rolled to a plate thickness of 1 mm, and finish annealing at the highest temperature T _M : 1000 to 1000 It was performed in a range of 1070 ° C. and holding time of 1 to 60 sec. Hot rolling and finish annealing were performed under the conditions satisfying the above [1] and [2] except for Nos. 37 and 38. For No. 37, steel having the same chemical composition as No. 10 was used, and the coiling temperature in hot rolling was 880 ° C. In No. 38, steel having the same chemical composition as No. 15 was used, and the average cooling rate from T _M to 600 ° C. was 1 ° C./sec in the cooling process of finish annealing.

About each steel plate except No. 21, electric Cu plating was given. The average thickness of the Cu plating layer was 2 μm per side, and a plating layer under the same conditions was formed on both sides to obtain a test steel plate. No. 34 is a test steel plate corresponding to the No. 10 plating base plate (stainless steel plate before plating). No. 36 is a test steel plate obtained by applying Cu plating to an austenitic stainless steel plate.
The following characteristics were examined for each test steel plate.

[Distribution form of precipitates]
The surface of each test steel sheet electropolished was observed by SEM, and the largest precipitate diameter (major axis) observed in the total area of 2 × 10 ⁻² mm ² in the observation field was the maximum particle diameter of the precipitate. dmax. In addition, the visual field is analyzed by EDX with respect to the visual field, and the portion where the detection intensity of Nb, Ti, Mo, Cu, V, and W is higher than the matrix is regarded as a precipitate, and the total area of the precipitate is determined by image processing. The area ratio f of the precipitate was determined by dividing the value by the area of the observation field and converting it to a percentage. These results are listed in Table 1.

[Crystal grain size after heat treatment equivalent to Cu plating layer fusion treatment]
Each sample steel test piece 30 mm × 80 mm was taken from the plate, as a heat treatment comparable to the Cu plating layer fusion process in manufacturing the multi-turn stainless steel tube, 1 × 10 ^-3 torr (about 1.3 × 10 ^- A heat treatment of 1150 ° C. × 30 min was performed in a vacuum of ¹ Pa). The cross section of the steel plate after the heat treatment was polished, etched with a mixed acid of hydrofluoric acid and nitric acid, observed with an optical microscope, and the average crystal grain size was determined by a section method. A having an average crystal grain size of 200 μm or less is A (coarseening suppression effect; excellent), B is 200 μm or more to 500 μm or less B (coarseening suppression effect; good), and C is 500 (coarseening suppression effect; It was considered that the B evaluation was obtained and the B evaluation was obtained, so that it was considered that it exhibited practically no problem in many uses of the multi-winding steel pipe. Therefore, the A evaluation and the B evaluation were determined to be acceptable.

[Wire brazing with phosphor copper brazing material]
A test piece of the same kind of 30 mm × 80 mm that has been subjected to the heat treatment under the above conditions corresponding to the Cu plating layer fusion treatment is placed in a state where the overlap is 4 mm as shown in FIG. 2, and wire brazing is performed using flux. Attempts were made to braze the surfaces of the two steel plates at the overlap. A flux of H ₃ BO ₄ —K ₂ B ₄ O ₇ —KF—KBF ₄ was used, and a BCuP-3 (Cu-6P-5Ag alloy) wire was used as the phosphor copper brazing material. By this brazing, the two steel plates are joined only by the phosphor copper brazing material (no fusion by the Cu plating layer). The test piece that was brazed and integrated was subjected to a shearing test in which the test piece was pulled in the longitudinal direction to break by a tensile tester. If the specimen having this thickness is brazed well, it will theoretically break at the base metal part. Therefore, what was fractured at the base metal part was evaluated as ◯ (brazing property: good), and the material fractured at the brazing material part was evaluated as x (brazing property: poor), and the evaluation was determined as acceptable.

[Outer surface corrosion resistance]
In order to evaluate the corrosion resistance of the outer surface of the steel pipe in the case of a multi-winding steel pipe, each steel plate and Cu plate subjected to heat treatment under the above conditions corresponding to the above Cu plating layer fusion treatment were prepared, and “salt spray; 5 % NaCl, 35 ° C. × 15 min → drying; 60 ° C., 30% R.H. × 1 h → wet; 50 ° C., 95% R.H. × 3 h ”10 cycles of salt dry-wet test, end face ○ (external surface corrosion resistance: excellent) where corrosion is not observed on the surface, except for 、 (external surface corrosion resistance: good) where the surface area ratio is equal to or less than that of the Cu plate, and the surface area ratio is larger than the Cu plate Was evaluated as x (external corrosion resistance; poor), and Δ or higher was determined to be acceptable.
These results are shown in Table 2.

  In the case of the present invention example, the ferrite crystal grains are prevented from being coarsened even when subjected to the Cu plating layer fusion treatment, the brazing property using the phosphor copper brazing material is good, and the outer surface corrosion resistance is also good. Was confirmed.

  On the other hand, Comparative Example No. 31 had a low Cr content in the base material and was inferior in corrosion resistance to the Cu plate. In Nos. 32 and 33, the Nb content of the base material was insufficient, and the coarsening of crystal grains could not be suppressed. No. 32 was insensitive to corrosion because of its high C content, resulting in sensitization. In Nos. 33 and 35, since the total content of Ti + Al was large, unevenness of Cu plating occurred, and brazing with a phosphor copper brazing material was insufficient at a portion where Cu plating did not adhere, resulting in poor bonding strength. Since No. 34 was not subjected to Cu plating, brazing with a phosphor copper brazing material was impossible. In Nos. 37 and 38, the distribution form of the precipitates did not satisfy the provisions of the present invention, and the pinning effect was not sufficiently exhibited, resulting in coarsening of crystal grains.

The figure which illustrated typically the section structure of a multiplex winding steel pipe. The figure which showed typically arrangement | positioning of the test piece in a wire brazing test.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cu plating layer 2 Stainless steel base material 3 Cu melt | fusion layer 10 Multiple winding steel pipe

Claims (7)

In mass%, C: 0.03% or less, Si: 3% or less, Mn: 2% or less, P: 0.05% or less, S: 0.03% or less, Cr: 11-30%, Nb: 0 A ferritic stainless steel sheet having a chemical composition of 0.15 to 0.8%, N: 0.03% or less, the balance being Fe and inevitable impurities, and an A value determined by the following formula (1) being 0.1 or more The substrate has a Cu plating layer on at least one surface thereof, and precipitates are distributed in the steel substrate of the substrate, and the maximum particle diameter dmax of the precipitates determined by cross-sectional SEM observation is 0.25 μm or less. Cu-plated stainless steel sheet for fusion-bonding of Cu plating layer having an area ratio f of 0.05% or more.
A = Nb− (C × 92.9 / 12 + N × 92.9 / 14) (1)
Here, the content of the element represented by mass% is substituted for the element symbol in the formula (1). In mass%, C: 0.03% or less, Si: 3% or less, Mn: 2% or less, P: 0.05% or less, S: 0.03% or less, Cr: 11-30%, Nb: 0 .15~0.8%, N: and 0.03% or less, further Ti, contained in a range of total 0.4% or less of one or more Al, a balance being Fe and unavoidable impurities, Ti Ferrite having a chemical composition in which the relationship of content (mass%) ≦ N content (mass%) (including the case where no Ti is contained) is established and the A value determined by the following formula (1) is 0.1 or more A stainless steel plate is used as a base material, and a Cu plating layer is provided on at least one surface thereof. Precipitates are distributed in the steel substrate of the base material. Hereinafter, Cu plating stainless steel for fusion bonding of Cu plating layer whose area ratio f of the precipitate is 0.05% or more Less steel plate.
A = Nb− (C × 92.9 / 12 + N × 92.9 / 14) (1)
Here, the content of the element represented by mass% is substituted for the element symbol in the formula (1). In mass%, C: 0.03% or less, Si: 3% or less, Mn: 2% or less, P: 0.05% or less, S: 0.03% or less, Cr: 11-30%, Nb: 0 .15~0.8%, N: and 0.03% or less, further Ti, contained in a range of total 0.4% or less of one or more Al, a balance being Fe and unavoidable impurities, Ti A ferritic stainless steel sheet having a chemical composition in which the relationship of content (mass%)> N content (mass%) is established and the A value determined by the following formula (2) is 0.1 or more is used as a base material. At least one side has a Cu plating layer, precipitates are distributed in the steel substrate of the base material, the maximum particle diameter dmax of the precipitates obtained by cross-sectional SEM observation is 0.25 μm or less, and the area ratio f of the precipitates is Cu-plated stainless steel sheet for fusion-bonding of Cu plating layer of 0.05% or more.
A = Nb−C × (92.9 / 12) / 2 (2)
Here, the content of the element represented by mass% is substituted for the element symbol in the formula (2). The Cu-plated stainless steel sheet according to any one of claims 1 to 3, wherein the substrate further contains one or more of Mo, Cu, V, and W in a total range of 4% or less. The Cu-plated stainless steel sheet according to any one of claims 1 to 4 , wherein the substrate further contains one or more of Ni and Co in a total range of 5% or less. The Cu-plated stainless steel sheet according to any one of claims 1 to 5 , wherein a total content of C and N is 0.01% or more. And the Cu-plated stainless steel sheet according to multi-turn to any one of claims 1 to 6 adjacent by forming a Cu bonding layer is melted and solidified a Cu plating layer interposed between the substrate each other group A multi-winding stainless steel pipe having a Cu plating layer on the outer surface of a pipe formed by joining materials.

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