JP5602707B2 - High strength copper tube with excellent strength after brazing - Google Patents

Description

  The present invention relates to a copper tube used in a heat exchanger such as an air conditioner or a water heater, and more particularly to a copper tube having high strength even after brazing at a high temperature.

  In general, a copper pipe (referred to as a pipe made of copper or a copper alloy) having excellent thermal conductivity and workability is applied to the pipe through which the heat medium of the heat exchanger flows. For example, a heat exchanger of an air conditioner has a structure in which a large number of plate-like aluminum fins are stacked and a copper pipe meandering is passed therethrough. In order to manufacture such a heat exchanger, first, a copper tube is bent into a hairpin shape to form a U-shaped copper tube, both ends of which are passed through through holes formed in aluminum fins, and expanded from the inside with a jig. Then, it is brought into close contact with the fin collar formed at the edge of the through hole of the aluminum fin. A plurality of U-shaped copper pipes penetrating through the aluminum fins are connected to each other by expanding the end (open end) and inserting the end of another U-shaped copper pipe (return bend copper pipe). Are joined by brazing with a brazing material such as phosphor copper brazing.

Further, a natural refrigerant heat pump water heater known by the nickname of Ecocute (registered trademark of Kansai Electric Power Co., Inc.) has a copper pipe (CO ₂ ) for circulating CO ₂ as a refrigerant in a pipe (water pipe) through which water is circulated. The refrigerant pipe is spirally wound. Therefore, first, a copper pipe is processed into a spiral shape, a water pipe is passed through the copper pipe, a water pipe around which a CO ₂ refrigerant pipe is wound is processed into a U shape, and then a phosphor copper braze (for example, JISZ3264, BCuP The water pipe and the CO ₂ refrigerant pipe are brought into close contact with each other by performing the brazing in the furnace according to -2). Further, it is manufactured by connecting a water pipe, a CO ₂ refrigerant pipe, and the like by brazing with an accumulator, a compressor, and the like, using a copper pipe inside the machine.

  Thus, the copper tube used for the heat exchanger is required to have good brazing properties in addition to thermal conductivity and bending workability. Therefore, phosphorus deoxidized copper having good characteristics and appropriate strength is widely used. On the other hand, in recent years, from the viewpoint of resource saving, thinning and long life of copper pipes are required, and in order to satisfy these demands, copper pipes having strength that can withstand severe internal pressure for a long period of time are required. ing.

  For example, Patent Documents 1 to 3 include a predetermined amount of Co, Sn, Zn, Ni and the like in addition to P, and are formed of a copper alloy that regulates inevitable impurities such as O and H. In particular, a copper tube with improved strength after brazing is disclosed. Further, Patent Documents 1 to 3 use a copper tube with controlled structure. That is, in Patent Documents 1 and 2, bending workability is improved by setting the crystal grain size to a predetermined value or less. In Patent Document 3, fatigue strength is obtained by having recrystallized grains having a predetermined grain size in which fine precipitates are dispersed. Has improved.

Japanese Patent No. 3794971 JP 2008-255379 A Japanese Patent No. 4228166

  On the other hand, in recent years, brazing is performed at a higher temperature than before in order to improve workability. However, even a copper tube made of a Cu—Co—P copper alloy having excellent heat resistance has a problem that the strength is greatly reduced, particularly when brazing is performed at a high temperature of 800 ° C. or higher.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide a high-strength copper tube that has a sufficient strength even after being thinned and brazed at a high temperature of 800 ° C. or higher. It is to provide.

  In order to solve the above problems, a high-strength copper tube excellent in strength after brazing according to the present invention has Co: 0.13-0.30 mass%, P: 0.03-0.10 mass%. And the content of Co is 2.5 times or more of the content of P, and the balance is made of Cu and inevitable impurities. As the inevitable impurities, S: 0.005% by mass or less, O : Extrusion molding of copper alloy regulated to 0.005 mass% or less, H: 0.0002 mass% or less. And the average crystal grain diameter in the cross section along a pipe axis is 30 micrometers or less, and the precipitate calculated from specific resistance is 0.20-0.30 mass%, Comprising: It is said with respect to all the said precipitates. A precipitate having a circle-equivalent diameter of 3 to 50 nm in the central portion in the thickness direction of the cross section is 50% or more in area ratio. Furthermore, the copper alloy may contain Ni: 0.005 to 0.20% by mass. In this case, the content of Ni is not more than the content of Co, and the total of Co and Ni It is sufficient that the content of is 2.5 times or more of the content of P.

  Thus, Co and P, or further containing Ni in a predetermined range, and further forming a Co-P compound or (Co, Ni) by using a copper alloy containing Co and Ni in a predetermined ratio or more with respect to P. An appropriate amount of the -P compound can be precipitated, and further, by restricting the amount of precipitation and the size of the precipitate, the strength and further the strength after brazing at a high temperature can be increased. And by restricting the allowable amount of S, O, and H inevitably contained in the copper alloy and limiting the crystal grain size to a predetermined value or less, it is possible to prevent cracking during extrusion or bending. .

  Further, the copper alloy may contain one or more selected from Fe, Mn, Mg, Cr, Ti, Zr, and Ag in total less than 0.10% by mass. By containing these metals in a predetermined range in total, the precipitates improve the strength including after brazing as in the case of the Co-P compound.

  Furthermore, the said copper alloy may contain at least 1 sort (s) of Sn: 0.05-1.0 mass% and Zn: 0.005-1.0 mass%. Thus, strength and heat resistance are improved by including Sn and Zn in a predetermined range in the copper alloy.

  According to the high-strength copper pipe excellent in strength after brazing according to the present invention, it is thinned and has sufficient strength even after brazing treatment at a high temperature of 800 ° C. or higher, thus saving resources. And the brazing workability is improved, and since it can withstand long-term use as a heat exchanger, the cost is reduced.

Hereinafter, the high-strength copper pipe excellent in strength after brazing according to the present invention will be described in detail.
A high-strength copper pipe excellent in strength after brazing according to the present invention (hereinafter simply referred to as a high-strength copper pipe) is applied to a heat exchanger, for example, a pipe for circulating a heat medium of an air conditioner or a heat pump water heater, Although it is set as the shape and dimension according to uses, such as a smooth tube and an internal grooved tube, it does not specifically limit. First, the copper alloy forming the high-strength copper tube according to the present invention will be described.

〔Copper alloy〕
The copper alloy forming the high-strength copper tube according to the present invention contains Co: 0.13 to 0.30 mass%, P: 0.03 to 0.10 mass%, and the Co content is P. More than 2.5 times the amount, and the balance is made of Cu and inevitable impurities, and as the inevitable impurities, S: 0.005 mass% or less, O: 0.005 mass% or less, H: 0.0002 It is regulated to less than mass%. Hereinafter, each element which comprises this copper alloy is demonstrated.

(Co: 0.13-0.30 mass%)
Co produces and precipitates a compound with P (suitably referred to as a Co—P compound) in a copper alloy. This compound (precipitate) has the effect of improving the strength such as the tensile strength of a high-strength copper tube, and also acts as pinning particles that suppress the coarsening of crystal grains in heat treatment for brazing. Therefore, strength reduction due to heat treatment is suppressed, and in particular, strength after brazing treatment at a high temperature of 800 ° C. or higher is ensured. In addition, the Co—P compound is precipitated even during hot extrusion and intermediate annealing, and the crystal grain size of the high-strength copper tube before brazing may be set to a predetermined value or less in order to suppress coarsening of crystal grains. it can. These effects improve as the amount of precipitation of the Co—P compound increases. When the Co content is less than 0.13% by mass, the amount of precipitation is small, and the above effects cannot be obtained sufficiently. On the other hand, if the Co content exceeds 0.30% by mass, the Co—P compound is excessively precipitated, resulting in excessive strength, resulting in a decrease in elongation and insufficient workability, hot extrusion, etc. There is a possibility that the deformation resistance becomes excessive and cracking occurs. Therefore, the Co content is set to 0.13 mass% or more and 0.30 mass% or less.

(P: 0.03-0.10 mass%)
P is generally added for deoxidation of copper alloys. Furthermore, in the high-strength copper pipe according to the present invention, P has an effect of generating and precipitating a compound with Co (Co—P compound) in a copper alloy and improving the strength as described above. If the P content is less than 0.03 mass%, the amount of Co-P compound deposited is small, and the above effects cannot be obtained sufficiently. On the other hand, when the content of P exceeds 0.10% by mass, workability is deteriorated, and there is a possibility that cracking may occur in hot working or cold working. Therefore, the P content is set to 0.03% by mass or more and 0.10% by mass or less.

(Co / P mass ratio: 2.5 or more)
As described above, in the high-strength copper tube according to the present invention, the compound of Co and P (Co—P compound) is sufficiently precipitated, so that the strength is improved even after brazing at a high temperature. As a result of detailed observation of TEM (transmission electron microscope) and extraction residue analysis of high strength copper tube with high strength after brazing treatment at high temperature in particular, Co ₂ P (dicobalt phosphide) was precipitated. It became clear that. The mass ratio of Co to P in Co ₂ P (Co / P) is about 3.8. For the Co and P contained in the copper alloy, when the mass ratio (Co / P) is greatly reduced from 3.8 to less than 2.5, even if each content of Co and P is within the above range, Co is insufficient with respect to P, and Co ₂ P is not sufficiently precipitated, so that the above effect cannot be obtained sufficiently. Therefore, the Co content is 2.5 times or more, preferably 3.0 times or more the P content. As will be described later, when Ni is contained in the copper alloy, the total content of Co may be 2.5 times or more of the content of P with Ni.

(S: 0.005 mass% or less)
S exists in the parent phase as a compound with Cu in the copper alloy. When the S content increases, ingot cracking during the casting of the copper alloy and cracking during hot extrusion increase. And even if these cracks do not occur, when a copper alloy extruded material containing a large amount of S is cold-rolled and drawn, the Cu-S compound inside the material expands in the axial direction of the tube, and Cu Cracking is likely to occur at the -S compound interface. As a result, surface flaws, cracks, etc. occur in the product (copper pipe) during and after processing, thereby reducing the product yield. Or when bending a copper pipe, it becomes a starting point of a crack generation | occurrence | production and a crack is easy to generate | occur | produce in a bending part. Therefore, the S content is regulated to 0.005 mass% or less, preferably 0.003 mass% or less, and more preferably 0.0015 mass% or less.

  S is relatively easily taken into the molten metal from raw materials such as copper bullion and scrap and oil adhering to the scrap, and from the melt casting atmosphere (flux, SOx gas in the atmosphere in contact with the molten metal, furnace material, etc.) It is. Therefore, in order to keep the S content in the copper alloy to 0.005% by mass or less, the amount of low-grade Cu metal and scrap is reduced, the SOx gas in the melting atmosphere is reduced, and the appropriate furnace material And measures such as adding a trace amount of an element having strong affinity for S, such as Mg and Ca, to the molten metal are effective.

  In addition, impurity elements As, Bi, Sb, Pb, Se, and Te other than S also reduce the soundness of the ingot, the hot extruded material, and the cold work material, and impair the bending workability of the copper tube. It is preferable to reduce as much as possible. These elements can also be reduced in the same manner as S, and the total content is preferably 0.0015% by mass or less, more preferably 0.0010% by mass or less, and further preferably 0.0005% by mass. It is as follows.

(O: 0.005 mass% or less)
When O (oxygen) is present in the copper alloy, Cu or Sn oxides are produced when they are contained, and these oxides are rolled into the ingot to reduce the soundness of the ingot. There is a possibility that the bending workability of the copper pipe is lowered. Therefore, the O content is limited to 0.005% by mass or less, and in order to further improve the bending workability of the high-strength copper tube, it is preferably 0.003% by mass or less, more preferably 0.0015% by mass or less. And In order to suppress the incorporation of O into the copper alloy, a reducing atmosphere may be used at the time of dissolution of the raw electrolytic copper.

(H: 0.0002 mass% or less)
H (hydrogen) is taken into the molten metal at the time of copper alloy melting and casting, and when it increases, pinholes are formed in the ingot, or H is present in a concentrated state at the grain boundaries, causing cracks during hot extrusion. generate. And even if a crack does not generate | occur | produce at the time of hot extrusion, the extrusion material of the copper alloy containing much H tends to generate | occur | produce the H of a grain boundary at the time of annealing, and a product yield falls. Therefore, the H content is limited to 0.0002 mass% or less, and is preferably 0.0001 mass% or less in order to further improve the product yield. In order to suppress the incorporation of H into the copper alloy, the raw material during melting and casting is dried, the dew point of the atmosphere in contact with the molten metal is reduced, or the molten metal before the addition of P (Cu-P alloy) is oxidized. Measures such as making it effective are effective.

  The copper alloy forming the copper alloy tube according to the present invention may further contain Ni: 0.005 to 0.20% by mass in the above components. At this time, the total content of Ni and Co is P. The content is 2.5 times or more. In addition, the copper alloy forming the copper alloy tube according to the present invention further contains one or more selected from Fe, Mn, Mg, Cr, Ti, Zr, and Ag in addition to the above components in total less than 0.10% by mass. Or you may contain at least 1 sort (s) of Sn: 0.05-1.0 mass% and Zn: 0.005-1.0 mass%.

(Ni: 0.005 to 0.20% by mass and less than Co content)
((Co + Ni) / P mass ratio: 2.5 or more)
Ni generates and precipitates a ternary compound with Co and P (appropriately referred to as (Co, Ni) -P compound) in a copper alloy. This (Co, Ni) -P compound has the effect of improving the strength of a high-strength copper tube and ensuring the strength after brazing by acting as pinning particles in the heat treatment, like the Co-P compound. Therefore, Ni can further improve the strength without increasing the Co content. Result of detailed observation of TEM (transmission electron microscope) and extraction residue analysis of high strength copper tube made of copper alloy containing Co, Ni, P, especially high strength after brazing at high temperature , (Co, Ni) ₂ P was found to be precipitated. That is, by including Ni, Co in the Co ₂ P is partially substituted with Ni. Further, since Ni has an atomic weight close to that of Co, it can be said that the total mass ratio ((Co + Ni) / P) of Co and Ni to P in (Co, Ni) ₂ P is about 3.8. Therefore, as in the case of the copper alloy containing Co and P, when the mass ratio ((Co + Ni) / P) is greatly reduced from 3.8 to less than 2.5, the contents of Co, Ni, and P are increased as described above. Even within this range, Co and Ni are insufficient with respect to P, and Co ₂ P and (Co, Ni) ₂ P are not sufficiently precipitated, so that the above effect cannot be obtained sufficiently.

In order to sufficiently precipitate the (Co, Ni) -P compound and obtain the above effect, the Ni content is preferably 0.005% by mass or more. On the other hand, if the Ni content exceeds 0.20% by mass, the (Co, Ni) -P compound is excessively precipitated, so that the strength is excessive and the elongation is lowered, resulting in insufficient workability. Further, when Ni increases beyond Co, the resulting ternary compound of P is likely to be a (Ni, Co) -P compound having a composition with more Ni than Co, and the precipitate has a low solid solution temperature. The effect as pinning particles is small because it approaches the properties of the -P compound (Ni ₂ P) and is easily melted by brazing. Therefore, the Ni content is 0.20% by mass or less and the Co content or less, and the total content with Co is 2.5 times or more the P content, preferably 3.0%. It is more than double.

(Fe, Mn, Mg, Cr, Ti, Zr, Ag: less than 0.10% in total)
Each of Fe, Mn, Mg, Cr, Ti, Zr, and Ag precipitates as a single substance or as a compound with P such as Fe ₂ P, Mn ₃ P ₂ , and the like, similarly to the Co—P compound and the like. There is an effect of improving the strength of the high-strength copper tube and the strength after brazing. On the other hand, when these elements are contained in a total of 0.10% by mass or more, the hot deformation resistance in hot extrusion increases, and in order to obtain the same extrusion pressure as that of the copper alloy not containing the elements, It is necessary to increase the extrusion temperature, and the surface oxidation of the extruded material increases at a high temperature, resulting in a decrease in productivity and a surface defect of the copper tube. Accordingly, the total content of one or more selected from Fe, Mn, Mg, Cr, Ti, Zr, and Ag is less than 0.10% by mass.

(Sn: 0.05 to 1.0% by mass)
Sn improves the tensile strength by solid solution hardening in a copper alloy, and also suppresses the coarsening of the crystal grain size against the thermal effects of annealing and brazing of a high-strength copper tube, thereby improving the heat resistance. In order to obtain these effects, the Sn content is preferably 0.05% by mass or more. On the other hand, if the Sn content exceeds 1.0% by mass, solidification segregation in the ingot becomes severe, and segregation may not be completely eliminated in normal hot extrusion or processing heat treatment, Mechanical properties, bending workability, texture after brazing, and non-uniformity of mechanical properties occur. In addition, the hot deformation resistance in hot extrusion is increased, and in order to obtain the same extrusion pressure as a copper alloy having a Sn content of 1.0 mass% or less, it is necessary to increase the hot extrusion temperature. As a result, the surface oxidation of the extruded material increases, resulting in decreased productivity and surface defects on the copper tube. Therefore, the Sn content is 1.0% by mass or less.

(Zn: 0.005 to 1.0 mass%)
Zn has the effect of improving the strength, heat resistance, and fatigue strength of the copper alloy. In addition, inclusion of Zn improves the wettability of a brazing material such as phosphor copper brazing when brazing a high-strength copper tube. Furthermore, containing Zn has the effect of reducing the wear of tools used for cold rolling, drawing, rolling, etc., extending the life of drawing plugs and grooved plugs, etc., contributing to the reduction of production costs To do. In addition, when assembling a high-strength copper tube into a heat exchanger, the wear of the mandrel during bending is reduced, and the wear of the expanded burette during expansion of the tube when closely contacting the fin collar of the aluminum fin through-hole is also reduced. Can be reduced. In order to obtain these effects, the Zn content is preferably 0.005% by mass or more. On the other hand, when the Zn content exceeds 1.0 mass%, the stress corrosion cracking sensitivity becomes high. Therefore, the Zn content is 1.0% by mass or less.

[High-strength copper tube structure]
The high-strength copper pipe according to the present invention has an average crystal grain size of 30 μm or less in a cross section along the pipe axis. Moreover, the precipitation amount of the precipitate calculated from the specific resistance is 0.20 to 0.30% by mass, and the equivalent circle diameter of 3 to 50 nm in the central portion in the thickness direction of the cross section with respect to all the precipitates. The deposit is 50% or more in area ratio.

(Average crystal grain size: 30 μm or less)
In bending a copper tube into a U shape, the plastic strain applied to the outer periphery of the U shape increases as the bending radius decreases and the thinner the copper tube. In a copper tube, when large crystal grains are present at a portion corresponding to the outer periphery, the crystal grain boundary is the starting point of fracture, and cracking is likely to occur. Moreover, when a copper pipe is assembled in a heat exchanger and hydrostatic pressure is applied to the inside, a force is applied in the circumferential direction in the cross section perpendicular to the pipe axis, that is, in the direction perpendicular to the wall thickness. As a result, in the thinned copper pipe, cracks can occur starting from defects such as wrinkles and fine cracks on the inner surface, fine cracks inside, or inclusions such as sulfides, If the grain is large, cracks propagate and break. If the average crystal grain size in the cross section including the pipe axis direction and the thickness direction of the copper pipe, that is, the cross section along the pipe axis exceeds 30 μm, cracks may occur during bending due to particularly large crystal grains, or There is a risk that it will become larger during the brazing process and cause damage after being assembled into a heat exchanger. Therefore, the high-strength copper tube has an average crystal grain size in a section along the tube axis of 30 μm or less, preferably 20 μm or less. The crystal grain size can be controlled by the method for producing a high-strength copper tube described below, with the components of the copper alloy within the above range. The average crystal grain size is the average grain size of all the crystal grains in the thickness direction. For example, a high-strength copper tube is cut on the surface including the tube axis and the cross section is polished to obtain an observation surface. A plurality of visual fields are selected along with the optical microscope and observed with an optical microscope, the crystal grain size is measured by a comparison method described in JISH0501, and an average value is calculated.

(Precipitate: calculated value based on specific resistance 0.20 to 0.30 mass%)
The precipitate in the high-strength copper pipe according to the present invention mainly refers to a Co—P compound. When the copper alloy contains Ni, the (Co, Ni) —P compound is further included, and the copper alloy is Fe, Mn, Mg. , Cr, Ti, Zr, and Ag further refer to a single element of these elements or a compound with P, and the amount of precipitate (precipitation amount) refers to the total amount of all of these. As described above, these precipitates improve the strength of the high-strength copper tube, particularly the strength after brazing, as the amount of precipitation increases. In the present invention, not only the components of the copper alloy but also the amount of precipitation in the high-strength copper tube is reduced to the specific resistance as will be described later. By calculating and managing based on this, a high-strength copper tube with sufficient strength is obtained. If the amount of precipitation is less than 0.20% by mass, the effect of improving the strength after brazing cannot be sufficiently obtained. On the other hand, when the amount of precipitation exceeds 0.30 mass%, strength will become excessive and elongation will fall and workability will become insufficient. Therefore, the precipitate in the high-strength copper tube is 0.20 mass% or more and 0.30 mass% or less. Precipitates can be controlled in accordance with the production conditions of the high-strength copper tube, which will be described later, with the contents of the copper alloy components, particularly the contents of Co, Ni, and P, including the mass ratio within the above range.

Linde et al. Have reported the relationship between the specific resistance of copper alloy and the solid solution elements in the copper alloy, and the amount of change (increase) in the specific resistance of copper (unit: Ω · cm) depending on the concentration of the solid solution element. ) Δρ can be expressed by the following equation (1).
Δρ = Σ (Ci · Δρi) (1)
Ci is the concentration (mass%) of the i-th solid solution element. Δρi is the contribution to the electric resistance of the i-th solid solution element. For Co, Ni, P, Sn, Zn, Fe, Mn, Mg, Cr, Ti, and Ag, Δρ _Co = 6.0, Δρ _Ni = 1.1, Δρ _P = 7.0, Δρ _Sn = 3.1, Δρ _Zn = 0.3, Δρ _Fe = 9.3, Δρ _Mn = 2.9, Δρ _Mg = 0.8, Δρ _Cr = 4 0.0, Δρ _Ti = 16.0, Δρ _Ag = 0.6 (unit: × 10 ⁻⁶ Ω · cm / mass%). Note that Zr can be ignored in the calculation of the specific resistance change Δρ because it hardly affects the conductivity in the range of the components of the copper alloy forming the high-strength copper tube according to the present invention.

Here, in the range of the components of the copper alloy that forms the high-strength copper tube according to the present invention, Sn and Zn do not form a compound, so the content of Sn and Zn in the copper alloy (addition amount at the time of casting) The solid solution Sn amount (C _Sn ) and the solid solution Zn amount (C _Zn ) are obtained as they are. On the other hand, for Co, Ni, and P that form a compound (precipitate), the value obtained by subtracting the precipitation amount from the content in the copper alloy is the solid solution amount (C _Co , C _Ni , C _P ). In addition, Fe, Mn, Mg, Cr, Ti, Zr, and Ag are partially dissolved, but the content is small in the range of the components of the copper alloy that forms the high-strength copper tube according to the present invention. In any case, it can be calculated by approximating that 20% of the content is dissolved. Therefore, in the high-strength copper tube according to the present invention, the specific resistance change Δρ can be expressed by the following equation (2).
Δρ = (Co content−Co precipitation amount) · Δρ _Co + (Ni content−Ni precipitation amount) · Δρ _Ni + (P content−P precipitation amount) · Δρ _P + C _Sn · Δρ _Sn + C _Zn · Δρ _Zn + 0.2 × [(Fe content), Δρ _Fe + (Mn content), Δρ _Mn + (Mg content), Δρ _Mg + (Cr content), Δρ _Cr + (Ti content), Δρ _Ti + (Ag content) ・ Δρ _Ag ] (2)

The change Δρ in specific resistance is obtained as the difference between the specific resistance of pure copper and the specific resistance measured from a copper tube made of a copper alloy. Δρi is a known constant. Each content of Co, Ni, P and each solid solution amount of Sn, Zn, Fe, Mn, Mg, Cr, Ti, and Ag are clear from the components of the copper alloy. As described above, from the composition of the precipitates Co ₂ P and (Co, Ni) ₂ P, the Co / P or (Co + Ni) / P ratio is 3.8 with respect to the mass ratio of Co, Ni, and P in these compounds. And Ni / Co in (Co, Ni) ₂ P can be assumed to be 1/8. From the above, it is possible to calculate the respective solid solution amounts and precipitation amounts of Co, Ni, and P, and obtain the sum of the precipitation amounts as the precipitation amounts of the Co—P compound and (Co, Ni) —P compound in the copper pipe. it can. Furthermore, since Fe, Mn, Mg, Cr, Ti, Zr, and Ag can be assumed to precipitate 80% of their contents, the amount of precipitation can be approximated by multiplying these contents by 0.8. . Since these elements produce relatively few compounds with P, P contained in the compounds can be ignored. As mentioned above, if the precipitation amount obtained is added, the precipitation amount of all the precipitates is calculated.

(Precipitate size distribution: precipitates with equivalent circle diameter of 3 to 50 nm are area ratios of 50% or more)
As described above, precipitates such as Co-P compounds and (Co, Ni) -P compounds act as pinning particles that suppress the coarsening of crystal grains in the heat treatment for brazing, thereby reducing the strength due to the heat treatment. Suppresses and improves the strength after brazing. However, a fine precipitate, specifically, a precipitate having an equivalent circle diameter of less than 3 nm in a cross section along the tube axis (a cross section including the tube axis direction and the thickness direction), that is, the area of a circle having a diameter of 3 nm. The precipitate having a small cross-sectional area melts in the brazing process and therefore does not act as pinning particles. On the other hand, when the number of precipitates having a diameter exceeding 50 nm is large, the number is small and the distribution is insufficient, so that the effect of suppressing the coarsening of the crystal grains decreases. Therefore, in the precipitates in the central part in the thickness direction, the equivalent circle diameter of 3 to 50 nm is more than half, that is, the area ratio in the central part in the thickness direction of the cross section is 50% or more, preferably 60% or more. Specifically, the central portion in the thickness direction refers to a range corresponding to 55 to 70% of the thickness centering on a portion in the thickness direction 1/2. The size distribution of such precipitates can be controlled by the manufacturing conditions of the high-strength copper tube described later.

  The size distribution of the precipitates is determined by cutting a high-strength copper tube on the surface including the tube axis, polishing the cross section, and preferably selecting a plurality of fields of view from the range of the central portion in the thickness direction. ). Then, the TEM image is analyzed by image analysis software, the area of each precipitate is measured, the diameter (equivalent circle diameter) is derived from the area in terms of a circle, and the total of all the precipitates in the analysis range is calculated. What is necessary is just to calculate the ratio of the total area of the precipitates having an equivalent circle diameter of 3 nm to 50 nm with respect to the area.

[Method of manufacturing high-strength copper pipe]
Next, an example of the manufacturing method of the high intensity | strength copper pipe which concerns on this invention is shown. The high-strength copper pipe according to the present invention can be manufactured by casting, hot extrusion, rolling, drawing, and final annealing, as well as known copper pipes, but in order to control crystal grains and precipitates, The following conditions are preferable.

  First, electrolytic copper as a raw material is dissolved. After copper is dissolved, a predetermined amount of Co, Ni, Sn, Zn, etc. is added, and a copper alloy containing about 15% by mass of P for deoxidation. After adding and adjusting the components of the molten metal, billets having predetermined dimensions are produced by semi-continuous casting. Next, the billet is heated to 680 to 800 ° C., and if necessary, is maintained for about 0.1 to 2 hours to improve segregation and homogenization is performed.

  The heated billet is subjected to perforation, and is formed into an extruded raw tube by hot extrusion at 750 to 980 ° C., and then rapidly cooled by water cooling or the like. The high-strength copper tube according to the present invention has a cooling rate of 10 ° C./until the surface temperature of the extruded element tube reaches 300 ° C. in order to dissolve Co after extrusion and prevent coarsening of crystal grains due to recrystallization. It is preferable to rapidly cool in seconds. The cooling rate is preferably 15 ° C./second or more, more preferably 20 ° C./second or more. The processing rate of hot extrusion, that is, (cross-sectional area of perforated billet−cross-sectional area of extruded pipe) / cross-sectional area of perforated billet × 100 (%) is preferably 80% or more, More preferably, it is 90% or more.

  The extruded element tube is rolled into a rolled element tube. The processing rate at this time is preferably 95% or less, more preferably 90% or less in terms of the cross-sectional reduction rate, in order to reduce product defects during processing.

  The rolling raw pipe is drawn to obtain a drawn pipe (smooth pipe) having a predetermined size. Here, first, rough drawing is performed, and the intermediate is annealed at 400 to 700 ° C. for 5 minutes to 1 hour to disperse the precipitates. If the intermediate annealing temperature is less than 400 ° C., the amount of precipitation is insufficient. On the other hand, if it exceeds 700 ° C., the precipitates become coarse and the number is insufficient. After that, a drawing process is performed to obtain a drawing tube. Here, several drawing machines are usually used for the drawing process, but surface defects and internal cracks can be reduced by setting the processing rate (cross-sectional reduction rate) by each drawing machine to 40% or less. Then, by holding the drawing tube at 500 to 750 ° C. for about 5 minutes to 1 hour and performing final annealing, in addition to softening the work-hardened drawing tube and enabling bending, etc., further precipitates To disperse. Instead of the drawing process after the intermediate annealing, a grooved rolling process may be performed to form an internally grooved tube.

  Thus, it can be set as a desired precipitation state by performing annealing twice. In particular, the intermediate annealing in the drawing process is not performed in the normal manufacturing method, or is performed for the purpose of reducing distortion in order to facilitate the drawing, so that the temperature and time are insufficient to disperse the precipitate. There is. In order to continuously anneal a rolling raw tube and a drawing tube, a high-frequency induction coil is passed through the drawing tube while energizing a roller hearth furnace or a high-frequency induction coil normally used for annealing a copper tube coil, etc. Heating by induction coil can be used.

  As mentioned above, although the form for implementing this invention has been described, the Example which confirmed the effect of this invention is demonstrated concretely compared with the comparative example which does not satisfy | fill the requirements of this invention below. It should be noted that the present invention is not limited by this embodiment, and can be implemented with appropriate modifications within the scope of the claims, all of which are included in the technical scope of the present invention. The

[High strength copper tube production]
A copper tube was produced as a test material by the following steps.
In accordance with the components shown in Table 1 and Table 2, in the molten metal made from electrolytic copper, after adding Ni or the like, a Cu-P alloy is added, and the casting temperature is 1200 ° C., the diameter is 300 mm, and the length is 3000 mm. The ingot was semi-continuously cast. A billet having a length of 475 mm was cut out from the ingot, and the billet was heated in the range of 680 to 800 ° C. and held for 1 hour as a homogenization process, and then hot extruded to obtain an extruded element tube having an outer diameter of 100 mm and a wall thickness of 10 mm. This was rapidly cooled at a cooling rate of 20 ° C./second or more until the surface temperature reached 300 ° C. by water cooling. After this extruded raw tube was rolled and further subjected to rough drawing, specimen No. 1 was used as intermediate annealing. Nos. 1 to 17 and 20 to 31 are 600 ° C. Nos. 18, 19, 33 and 34 were held at the temperatures shown in Table 2 for 1 hour. After the intermediate annealing, drawing was further performed to produce a smooth tube having an outer diameter of 9.52 mm and a wall thickness of 0.80 mm. The test material No. About 32, it draws continuously, without performing intermediate annealing, and the intermediate annealing temperature of Table 2 is represented by "-". The smooth tube was held at 600 ° C. for 30 minutes as the final annealing to produce a copper tube. Moreover, what interrupted production by the malfunction in the process in the middle does not perform the following measurement and evaluation, and represents the column of the measured value etc. of Table 1 by "-". In addition, the test material No. 9 is also shown in Table 2.

  With respect to the produced copper tube, the average crystal grain size, the precipitation amount of the precipitate, and the area ratio of the equivalent circle diameter of 3 nm to 50 nm in the precipitate are measured by the following methods and are shown in Tables 1 and 2.

(Average crystal grain size)
The copper tube was cut along the surface including the tube axis, and the cross section was polished to obtain an observation surface. Three visual fields from the whole in the thickness direction were observed with an optical microscope, the crystal grain size was measured by the comparative method described in JISH0501, and the average value was calculated.

(Measurement of precipitates based on specific resistance)
The specific resistance of the copper pipe was measured with “Hocking Autosigma 3000” manufactured by GE Inspection Technologies, and the specific resistance change Δρ was calculated by setting the specific resistance of pure copper to 1.68 × 10 ⁻⁶ Ω · cm. From the obtained specific resistance change Δρ and the copper alloy component, the amount of each precipitation of Co, Ni, and P (amount in the Co—P compound or (Co, Ni) —P compound) based on the formula (2) Was calculated. The contribution of each solid solution element of Co, Ni, P, Sn, and Zn to the electric resistance is represented by Δρ _Co = 6.0, Δρ _Ni = 1.1, Δρ _P = 7.0, Δρ _Sn = 3.1. , Δρ _Zn = 0.3, Δρ _Fe = 9.3, Δρ _Mn = 2.9, Δρ _Mg = 0.8, Δρ _Cr = 4.0, Δρ _Ti = 16.0, Δρ _Ag = 0.6 ( (Unit: × 10 ⁻⁶ Ω · cm / mass%). Further, regarding the mass ratio of Co, Ni, and P in the compound, Co / P or (Co + Ni) / P is set to 3.8, and when Ni is further contained, Ni / Co is 1/8, however, the content of Ni It was assumed that the specimen with more than Co had the same value as the ratio of Ni and Co contents. Further, assuming that 80% of the content of Fe, Mn, Mg, Cr, Ti, Zr, and Ag is precipitated, the total amount of these elements and each of Co, Ni, and P was defined as the amount of precipitation.

(Size distribution of precipitates)
The copper tube was cut along the surface including the tube axis, and the cross section was polished to obtain an observation surface. Observed with a TEM at a magnification of × 150,000, and from a range corresponding to 70% of the thickness centering on a portion in the thickness direction 1/2, three fields of view along the thickness direction, 700 nm × 800 nm, and an image photograph I took a picture. Analyze the image with image analysis software, measure the area of each precipitate, derive the equivalent circle diameter from the area, and the equivalent circle diameter of 3 nm or more with respect to the total area of all the precipitates in the image The ratio of the total area of precipitates of 50 nm or less was calculated, and the average value of three fields of view was calculated.

[Evaluation]
About the produced copper pipe, bending workability, tensile strength as strength, tensile strength after heat treatment as strength after brazing, and stress corrosion cracking resistance were evaluated as follows.

(Bending workability)
The copper tube was bent into a U shape with a bending pitch of 25 mm (bending radius at the tube axis was 12.5 mm), and the bent portion on the outer surface was visually observed. The test was conducted for 10 specifications, and if 5 or less cracks or cracks were observed, the test was accepted. All 10 specimens were “O”, and one or more cracks were observed. Tables 1 and 2 show “X” with 5 or less as “Δ” and 6 or more as “failed”.

(Strength)
The copper tube was cut out to produce two JIS No. 11 tensile test pieces. The test piece was subjected to a tensile test at room temperature according to JISZ2241. Specifically, the tensile strength was measured at a test speed of 10.0 mm / min and GL = 50 mm using a 5882 type Instron universal testing machine. The average of the two times is shown in Tables 1 and 2. The acceptance criterion is a tensile strength of 240 MPa or more.

(Strength after brazing)
Simulating the brazing treatment, the tensile strength of a copper tube subjected to heat treatment for 10 minutes at two temperatures of 800 ° C. and 850 ° C. was measured in the same manner as in the tensile test. Tables 1 and 2 show the average values of the two times for each heat treatment temperature. The acceptance criterion is a tensile strength of 230 MPa or more.

(Stress corrosion cracking resistance)
The stress corrosion cracking test was carried out by the following method. A copper tube is cut out to a length of 75 mm to make a test piece. After the test piece is degreased and dried, a desiccator containing 11.8% or more of ammonia water diluted with an equal amount of pure water as defined in JIS K8085. And fixed at a height of 50 mm away from the liquid surface and stored in an ammonia atmosphere at room temperature for 2 hours. Thereafter, the test piece was crushed in the radial direction to 50% of the original outer diameter of the copper tube. The test piece was visually observed to determine the presence or absence of cracks on the outer peripheral surface. Tables 1 and 2 show “O” when the crack is not passed and “X” when the crack is generated.

  As shown in Table 1 and Table 2, the test material No. Nos. 1 to 19 are examples in which the components of the copper alloy, the crystal grain size, and the distribution of precipitates are all within the scope of the present invention, and the strength, bending workability, and stress corrosion cracking resistance are all good. A decrease in strength due to brazing at a high temperature of 850 ° C. was suppressed.

  On the other hand, the test material No. 20 to 31 are comparative examples in which the components of the copper alloy are outside the scope of the present invention. Specimen No. In Nos. 20 and 22, since Co and P were insufficient, the Co—P compound was insufficient, and there were many small precipitates having an equivalent circle diameter of less than 3 nm. In particular, the specimen No. No. 22 was low in strength, further decreased by heat treatment, and further, there were few precipitates that became pinning particles even during hot extrusion or intermediate annealing, so the crystal grains became coarse. Specimen No. No. 20 was greatly reduced in strength by heat treatment at 850 ° C. On the other hand, the test material No. In No. 21, since Co was excessive, a Co—P compound was precipitated even at a high temperature, and the deformation resistance was excessively increased by hot extrusion to cause cracking. Specimen No. No. 23 was cracked by hot extrusion because P was excessive.

  Specimen No. Nos. 24 and 25 contain Ni in excess of Co, so that Co is within the scope of the present invention. Even if the precipitation amount is within the range of the present invention, including 25, the precipitated (Co, Ni) -P compound becomes Ni-excess and does not act as pinning particles in the heat treatment at 850 ° C., and the strength after that is large. Declined. Specimen No. In No. 26, Sn was excessive, so that the hot deformation resistance was high and hot extrusion could not be performed. Specimen No. In No. 27, since Zn was excessive, the stress corrosion cracking sensitivity was high. Specimen No. In No. 28, since Cr is excessive, the strength is excessive due to excessive precipitates, and bending workability is deteriorated.

  Specimen No. Nos. 29 and 31 contained unavoidable impurities S and H in excess of the specifications, and thus cracks were generated by hot extrusion. Specimen No. No. 30 contained inevitable impurities O exceeding the specified range, so that bending workability was lowered.

  Specimen No. Nos. 32-34 are the components of the copper alloy, specimen No. This is a comparative example that is the same as 9 and within the scope of the present invention, but the distribution of precipitates or the crystal grain size is outside the scope of the present invention. Specimen No. No. 32 does not perform intermediate annealing during the drawing process. No. 33 was a general intermediate annealing for removing strain in the drawing process, and the temperature was low. Therefore, each of the (Co, Ni) -P compounds was not sufficiently precipitated, and the strength was initially high, but by heat treatment at 850 ° C. It was greatly reduced. On the other hand, the test material No. In No. 34, since the intermediate annealing temperature was high, the crystal grains and precipitates were coarsened, and the strength decreased.

Claims (4)

A high-strength copper tube formed by extruding a copper alloy,
The copper alloy contains Co: 0.13-0.30 mass%, P: 0.03-0.10 mass%, and the Co content is 2.5 times or more of the P content. And the balance consists of Cu and inevitable impurities, and the inevitable impurities are regulated to S: 0.005 mass% or less, O: 0.005 mass% or less, H: 0.0002 mass% or less,
The average crystal grain size in the cross section along the tube axis is 30 μm or less, and the precipitate calculated from the specific resistance is 0.20 to 0.30 mass%, and the cross section of the cross section with respect to all the precipitates A high-strength copper tube excellent in strength after brazing, wherein a precipitate having an equivalent circle diameter of 3 to 50 nm in the central portion in the thickness direction is 50% or more in area ratio.   The copper alloy further contains Ni: 0.005 to 0.20 mass%, the Ni content is equal to or less than the Co content, and the total content of the Co and the Ni is the P content. The high-strength copper tube having excellent strength after brazing according to claim 1, wherein the strength is 2.5 times or more.   The copper alloy further contains at least one selected from Fe, Mn, Mg, Cr, Ti, Zr, and Ag in a total amount of less than 0.10% by mass. High strength copper tube with excellent strength after brazing.   The copper alloy further contains at least one of Sn: 0.05 to 1.0 mass% and Zn: 0.005 to 1.0 mass%. A high-strength copper tube excellent in strength after brazing according to claim 1.