JP2011168846A - Copper tube for heat exchanger having excellent fracture strength and bending workability - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper tube for a heat exchanger having excellent workability, which can be, e.g., cold-worked into the heat transfer tube of a heat exchanger even when being thinned and increased in strength, and a method for producing the same. <P>SOLUTION: The β fiber orientation grains particularly in a rolled texture in the texture of a P based copper tube or an Sn-P based copper tube having a specified composition are suppressed by devising production conditions such as process annealing to increase a ratio between fracture strength and tensile strength, thus, even when its wall thickness is thinned, the balance between the fracture strength and bending workability of the steel tube is improved. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a copper tube for a heat exchanger excellent in fracture strength and bending workability. Here, the breaking strength is a pressure breaking strength and has a high breaking pressure. In the present invention, the term “copper pipe” includes a copper pipe made of a copper alloy.

  For example, a heat exchanger of an air conditioner is mainly composed of a U-shaped copper tube bent into a hairpin shape and fins made of aluminum or an aluminum alloy plate (hereinafter referred to as aluminum fins). Specifically, the heat transfer part of the heat exchanger is obtained by passing a copper tube bent into a U shape through a through hole of an aluminum fin, inserting a jig into the U shape copper tube, and expanding the copper tube. And aluminum fins are in close contact. Further, the open end of the U-shaped copper pipe is expanded (flared), and a bent copper pipe bent into a U-shape is inserted into the expanded open end, and a brazing material such as phosphor copper braze is used. The heat exchanger is manufactured by connecting the bend copper pipe to the open end of the copper pipe by brazing.

  For this reason, copper pipes used in heat exchangers are required to have good workability (bending, expansion / flare, contraction / drawing, etc.) and brazing. Accordingly, phosphorous deoxidized copper having good characteristics, good thermal conductivity, and appropriate strength is widely used.

  HCFC (hydrochlorofluorocarbon) fluorocarbons have been widely used as refrigerants for heat exchangers such as air conditioners. However, HCFC has a low ozone depletion coefficient, so its value is small in terms of protecting the global environment. HFC (hydrofluorocarbon) -based fluorocarbons have been used. Moreover, CO2 which is a natural refrigerant has come to be used for heat exchangers used in water heaters, automotive air conditioners, vending machines and the like. In the heat exchanger, the pressure at which these refrigerants are used (pressure flowing in the heat transfer tubes of the heat exchanger) is the maximum in the condenser (gas cooler in CO2), for example, 1.8 MPa for R22 of HCFC-based Freon. The HFC-based fluorocarbon R410A is about 3 MPa and the CO2 refrigerant is about 7 to 10 MPa (supercritical state), and the operating pressure of the newly adopted refrigerant is increased to 1.6 to 6 times that of the conventional refrigerant R22. Yes.

  The operating pressure of the refrigerant flowing in the heat transfer tube is P, the outer diameter of the heat transfer tube is D, the tensile strength of the heat transfer tube (longitudinal direction of the heat transfer tube) is σ, and the thickness of the heat transfer tube is t (in the case of an internally grooved tube) (Thickness of the bottom wall), there is a relationship of P = 2 × σ × t / (D−0.8t) between them. When the above formula is arranged with respect to the wall thickness t, t = (D × P) / (2 × σ + 0.8P), and it can be seen that the wall thickness can be reduced as the tensile strength of the heat transfer tube is increased. Actually, when selecting a heat transfer tube, a heat transfer tube having a tensile strength and a wall thickness calculated for a pressure obtained by multiplying the above-mentioned P by a safety factor S (usually about 2.5 to 4) is used.

  In the case of a phosphorous deoxidized copper heat transfer tube, since the tensile strength is small, it is necessary to increase the thickness of the tube in order to cope with an increase in the operating pressure of the refrigerant. In addition, when assembling the heat exchanger, the brazed part is heated to a temperature of 800 ° C. or higher for several seconds to several tens of seconds. Therefore, it is necessary to make the wall thickness thicker. Thus, when phosphorous deoxidized copper is used as a heat transfer tube, the mass of the heat exchanger increases and the price increases, so the tensile strength is high, workability is excellent, and good thermal conductivity is achieved. There has been a strong demand for heat transfer tubes.

  In order to meet the demands for reducing the thickness of such heat transfer tubes, instead of phosphorous deoxidized copper, the strength is higher than that of phosphorous deoxidized copper, and a copper alloy such as a Co—P based copper alloy or a Sn—P based copper alloy is used. Various copper pipes have been proposed. Sn—P based copper alloy contains Sn: 0.1 to 1.0%, P: 0.005 to 0.1%, restricts impurities such as O and H, and selectively adds Zn There has been proposed a copper tube for a heat exchanger having a composition as described above and having an average crystal grain size of 30 μm or less (see Patent Documents 1, 2, 3, and 4).

  In addition, as control of the texture, in the Sn-P copper pipe (meaning a copper pipe made of a Sn-P copper alloy), the strength in the circumferential direction is controlled by controlling the integration rate of the Goss orientation to 4% or less. And a method of appropriately controlling the balance of elongation and improving the breaking pressure (see Patent Document 5).

  Moreover, in Sn-P type copper pipe, compared with phosphorus deoxidized copper, it is high by making ratio of fracture strength and tensile strength (fracture strength / tensile strength) larger than phosphorous deoxidized copper. A copper tube for a heat exchanger that has both a burst pressure and good bending workability has also been proposed (see Patent Document 6).

Furthermore, in a P-based copper pipe made of a P-based copper alloy containing P, the intermediate annealing is performed to remove cracks and strain of the copper pipe, thereby improving workability such as improving cracks during tube expansion processing. A method has been proposed (see Patent Document 7).
JP 2000-199023 A Japanese Patent No. 3794971 JP 2004-292917 A JP 2006-274313 A JP 2009-102690 A JP 2008-174785 A Japanese Patent No. 4150585

  However, in the said patent documents 1-4, tensile strength (tensile strength) will also increase with fracture strength. When the tensile strength is increased, the ductility is lowered and cracks and wrinkles are likely to occur at the bent portion of the heat transfer tube, and the portion becomes a base point and breaks at a pressure lower than a predetermined breaking pressure.

  In Patent Document 5, since the strength and elongation in the circumferential direction of the tube are controlled, it is possible to provide a copper tube excellent in fracture strength and workability such as tube expansion and contraction. However, since the strength and elongation in the axial direction of the tube are not controlled, cracks and wrinkles are generated during bending.

  In addition, including the above-mentioned Patent Documents 6 and 7, methods for providing copper pipes with improved strength and bending workability or workability such as pipe expansion have been proposed, but recently, copper for heat exchangers has been proposed. The demand for thinner pipes is becoming more severe, and there is a demand for higher strength and better bending workability. However, the material copper pipe thinned in this way is further deteriorated in bending workability as compared with a thick material copper pipe.

  This invention is made | formed in view of this problem, Comprising: It aims at providing the copper tube for heat exchangers excellent in fracture strength and bending workability.

  For the above purpose, the gist of the copper tube for a heat exchanger of the present invention is a copper tube containing P: 0.005 to 0.1% by mass, with the balance being composed of Cu and inevitable impurities, As a result of measurement by the SEM-EBSP method, the average crystal grain size is 40 μm or less, and the sum of the average area ratios of the Cu orientation, S orientation, and Brass orientation belonging to the β fiber of the rolling texture is 10 to 25%. It is assumed that it is a range.

  Moreover, when the copper pipe of the said summary further contains Sn: 0.1-3.0 mass%, the said average crystal grain diameter is 30 micrometers or less, Cu direction which belongs to the beta fiber of the said rolling texture, S direction , The sum of the average area ratio of each direction of the Brass orientation is in the range of 10 to 20%. These copper tubes may further contain Zn: 0.01 to 1.0% by mass in addition to P or P and Sn. In addition to the addition of P or P and Sn, and Zn added thereto, the copper tube is further selected from one or two selected from the group consisting of Fe, Ni, Mn, Mg, Cr, Ti, Zr and Ag. You may contain the element more than a seed | species less than 0.07 mass% in total (however, 0% is not included).

  When pressure is applied to the in-machine piping of the heat exchanger, a tensile force acts in the circumferential direction of the copper pipe, causing cracks parallel to the drawing direction and breaking. Therefore, it is important to suppress the occurrence of cracks in order to improve the fracture strength. Usually, a tensile force acts in the circumferential direction of the copper tube (at right angles to the rolling direction). In this state, it is important that the strain is not concentrated locally on the copper tube in order to suppress cracking. is there.

  In contrast, the present inventors paid attention to the relationship between local strain concentration and texture in a P-based copper tube or a Sn-P-based copper tube. That is, the characteristics of crystal grains in each orientation with respect to the local strain concentration were different, and it was thought that local strain concentration of the copper tube could be prevented by controlling these textures.

  From the characteristics of the crystal grains in each orientation, in particular, the Cu orientation, S orientation and Brass orientation belonging to the β fiber of the rolling texture are limited in the active slip system. Strain tends to concentrate locally on the copper tube. For this reason, it has been found that the fracture strength can be increased by suppressing the area ratio of these oriented grains low.

  The Cu orientation, S orientation, and Brass orientation belonging to the β fibers of these rolling textures are textures generated during the rolling of the extruded element pipe, and an extruded element pipe made of a P-based copper alloy or a Sn-P-based copper alloy, As long as the copper tube is manufactured by rolling or drawing, it is unavoidable to produce it.

  If there are many crystal grains in each orientation of the rolling texture, the strength of the copper tube in the tube axis direction parallel to the rolling direction is higher than the strength in the tube circumferential direction perpendicular to the rolling direction. For this reason, in order to improve the fracture strength, by suppressing these orientation grains, it is possible to suppress the tensile strength from becoming higher than necessary and to improve the bending workability.

  In this respect, as described above, in Patent Document 5 as well, by focusing on the texture and controlling the time until the completion of hot extrusion in the production of the extruded element tube, Goss orientation grains are suppressed, and the fracture strength is increased. is doing. However, in a general method for manufacturing a copper tube, as described above, rolling and drawing with a high area reduction of 95% or more are performed after extrusion, and therefore β-fiber orientation grains, which are rolling textures, are inevitably generated. That is, unless the β fiber orientation grain which is a rolling texture is intentionally suppressed, it is difficult to suppress the area ratio of the β fiber orientation grain. For this reason, in Patent Document 5, even if Goss orientation grains are suppressed, the area ratio of β fibers is inevitably high, and due to this, the fracture strength and bending workability intended by the present invention have been reduced. .

  That is, in the conventional texture control such as Patent Document 5, attention is not paid to the β fiber oriented grains, and the effect of the β fiber oriented grains on the fracture strength and bending workability is not clear in the past. It is speculated that there was.

  On the other hand, the present invention is to elucidate and control the influence of the β fiber orientation grain on the fracture strength and bending workability. In the present invention, by suppressing the β fiber orientation grain, the fracture strength is controlled. And tensile strength ratio (breaking strength / tensile strength or breaking pressure / tensile strength) can be increased. Even if the thickness of the copper tube is reduced, the tensile strength is not increased so much. It becomes possible to ensure the breaking strength of the. For this reason, the bending workability of the tube can be improved by the margin of this tensile strength. That is, the present invention can improve the balance between fracture strength and bending workability by increasing the ratio of fracture strength and tensile strength (tensile strength), and the copper tube having excellent fracture strength and bending workability. Can be provided.

  Therefore, for example, even if the P-type copper pipe or Sn-P-type copper pipe thinned to 1.0 mm or less and having a high strength is used, the breaking strength as the heat transfer pipe of the heat exchanger and the transmission of the material pipe are not limited. Good bending workability to the heat pipe can be combined.

  Hereinafter, the embodiments of the present invention will be specifically described for each requirement in order from the structure of the copper tube.

Copper tube structure:
(Average crystal grain size)
In copper pipes, it is known that the smaller the average crystal grain size, the better the fracture strength and bending workability balance. Also in the present invention, this mechanism is used to refine the average crystal grain size together with texture control described later. That is, in a Cu-Sn-P alloy containing both Sn and P as a result of measurement by the SEM-EBSP method described later, the average crystal grain size of the copper tube is 30 μm or less, and Cu—containing P without containing Sn. In the P alloy, the average crystal grain size is set to 40 μm or less, and the balance between fracture strength and bending workability is improved.

  Incidentally, when the thickness of the copper tube is relatively thick, the average crystal grain size has little influence on the fracture strength and the bending workability balance. However, when the thickness of the heat transfer tube is reduced to 1.0 mm or less due to demands for weight reduction and thinning, the influence of the crystal grain size on the fracture strength and bending workability balance is significant. growing. If the average crystal grain size is too large beyond the above-mentioned upper limits, “strain concentration” when cracks are generated by the tensile force applied to the heat transfer tubes cannot be avoided, and cracks are likely to occur in the heat transfer tubes. For this reason, when a copper pipe is used for the heat exchanger for HFC type | system | group fluorocarbon refrigerant | coolant and carbon dioxide refrigerant with a high operating pressure, reliability falls. In addition, when the crystal grain size becomes coarse, there is a problem that when the copper tube is bent when incorporated in a heat exchanger such as an air conditioner, a crack is easily generated in the bent portion.

  Furthermore, when the copper tube is processed into a heat exchanger, the crystal grain size of the heated portion of the heat transfer tube is necessarily increased due to the heat effect of brazing. On the other hand, if the average crystal grain size of the copper tube is not refined in the above-mentioned range in advance, the average crystal grain size is likely to exceed 100 μm due to coarsening, or the pressure strength at the brazed portion is high. Decrease increases.

Copper tube texture:
(Area ratio of β fiber orientation grains)
As described above, since the copper tube is reduced by 95% or more by rolling and drawing after hot extrusion, it belongs to the β fiber which is a rolling texture at the time of rolling or drawing. However, in the Sn-P copper pipe containing both Sn and P, this rolling texture is less likely to develop than in the P copper pipe containing P without containing Sn, and Sn-P copper pipe, In each P-based copper pipe, the range of texture to be controlled is slightly different.

  Specifically, in the Sn-P-based copper pipe, the sum of the average area ratios of the Cu orientation, S orientation, and Brass orientation belonging to the β fiber that is the rolling texture is controlled within a range of 10 to 20%. Thus, as described above, the ratio between the breaking strength and the tensile strength can be increased. For this reason, even if the wall thickness of the copper pipe is reduced, it is possible to ensure a predetermined breaking strength without increasing the tensile strength so much, and bending the pipe by the margin of this tensile strength. Can be improved. That is, by increasing the ratio between the breaking strength and the tensile strength, the balance between the breaking strength and the bending workability can be improved, and both high breaking strength and good bending workability can be achieved. When the sum of the average area ratios exceeds 20%, local strain is liable to occur, the ratio of fracture strength to tensile strength is lowered, and the balance between fracture strength and bending workability is lowered. On the other hand, if the sum of the average area ratios is less than 10%, the work hardening by drawing is insufficient and the fracture strength is lowered.

  On the other hand, in the P-based copper pipe, β fiber orientation grains are likely to develop as compared with the Sn-P-based copper pipe as described above. For this reason, in the Cu-P copper pipe, by controlling the sum of the average area ratios of the Cu, S, and Brass orientations belonging to the β fiber, which is a rolling texture, to a range of 10 to 25%. The above-described mechanism combines high fracture strength and good bending workability. When the sum of the average area ratios exceeds 25%, local strain is likely to occur, the ratio between fracture strength and tensile strength is lowered, and the balance between fracture strength and bending workability is lowered. . On the other hand, if the sum of the average area ratios is less than 10%, the work hardening by drawing is still insufficient, and the fracture strength is lowered.

(Measuring method of average grain size and texture)
By using a crystal orientation analysis method in which a backscattered electron diffraction image (EBSP: Electron Back Scattering (Scattered) Pattern) system is mounted on a field emission scanning electron microscope (FESEM), For the cross section parallel to the drawing direction of the alloy, the texture from the tube outer surface to the tube inner surface is measured, and the average crystal grain size is measured.

  In the EBSP method, an electron beam is irradiated onto a sample set in a FESEM column and the EBSP is projected onto a screen. This is taken with a high-sensitivity camera and captured as an image on a computer. In the computer, the orientation of the crystal is determined by analyzing this image and comparing it with a pattern obtained by simulation using a known crystal system. The calculated crystal orientation is recorded as a three-dimensional Euler angle together with position coordinates (x, y) and the like. Since this process is automatically performed for all measurement points, tens of thousands to hundreds of thousands of crystal orientation data can be obtained at the end of measurement.

  Here, in the case of a normal copper alloy sheet, mainly a texture composed of many orientation factors called Cube orientation, Goss orientation, Brass orientation, Copper orientation, S orientation, etc. as shown below is formed, and according to them Crystal planes exist. These facts are described in, for example, edited by Shinichi Nagashima, “Aggregate” (published by Maruzen Co., Ltd.) and “Light Metal”, Vol. 43, 1993, P285-293, published by the Japan Institute of Light Metals. The copper pipe of the present invention is manufactured by extrusion / drawing. In the case of a copper pipe by extrusion / drawing, the extrusion surface and the extrusion direction (extrusion base pipe) of the extrusion raw pipe are the same as in the case of the texture of the plate material by rolling. In the case of rolling, the rolling surface and rolling direction). The extrusion surface is expressed by {ABC}, and the extrusion direction is expressed by <DEF>. Based on this expression, the respective directions are expressed as follows.

Cube orientation {001} <100>
Goss orientation {011} <100>
Rotated-Goss orientation {011} <011>
Brass orientation (B orientation) {011} <211>
Copper orientation (Cu orientation) {112} <111>
(Or D direction {4 4 11} <11 11 8>
S orientation {123} <634>
B / G direction {011} <511>
B / S orientation {168} <211>
P direction {011} <111>

  In the present invention, basically, deviations of orientation within ± 15 ° from these crystal planes belong to the same crystal plane (orientation factor). Further, a boundary between crystal grains in which the orientation difference between adjacent crystal grains is 5 ° or more is defined as a crystal grain boundary.

  In addition, in the present invention, the number of crystal grains measured by the crystal orientation analysis method is set to n by irradiating an electron beam at a pitch of 1.0 μm with respect to the measurement area, tube axis direction 1000 × tube circumferential direction 800 μm. When the measured crystal grain size is x, the average crystal grain size is calculated as (Σx) / n.

  In the present invention, the electron beam is irradiated at a pitch of 1.0 μm with respect to the tube axis direction 1000 × tube circumferential direction 800 μm, the crystal orientation areas measured by the crystal orientation analysis method are respectively measured, and the measurement area is measured. The area ratio (average) in each direction was determined.

  Here, the crystal orientation distribution may be distributed in the tube axis direction. It is preferable to obtain some points arbitrarily in the tube axis direction by taking an average.

Copper alloy composition:
Hereinafter, the copper alloy component composition of the copper pipe of the present invention, the reason for adding the additive element, the reason for limiting the composition, and the like will be described.

“P: 0.005 to 0.1 mass%”
For Sn-P copper pipes containing both Sn and P, and P copper pipes containing P without containing Sn, in common, the P content of the copper pipe exceeds 0.1% by mass. In addition, cracking is likely to occur during hot extrusion, the stress corrosion cracking susceptibility increases, and the thermal conductivity decreases greatly. Further, if the P content is less than 0.005% by mass, the amount of oxygen is increased due to insufficient deoxidation, Sn oxide is generated, the soundness of the ingot is lowered, and the bending workability as a copper pipe is reduced. descend. Therefore, the range of P content shall be 0.005-0.1 mass%.

“Sn: 0.1 to 3.0% by mass”
Sn is essential in the Sn-P-based copper pipe, has the effect of improving the tensile strength of the copper pipe and suppressing the coarsening of the crystal grains, and in the copper alloy of the heat transfer pipe using various refrigerants. When it is contained, the thickness of the tube can be made thinner than that of the phosphorus-deoxidized copper tube. If the Sn content of the copper tube exceeds 3.0% by mass, solidification segregation in the ingot becomes severe, and segregation may not be completely eliminated by normal hot extrusion and / or processing heat treatment. The structure, mechanical properties, bendability, structure after brazing and mechanical properties become non-uniform. Further, in order to perform extrusion molding at the same extrusion pressure as that of a copper alloy having an Sn content of 2% by mass or less, the extrusion temperature needs to be raised, thereby causing surface oxidation of the extruded material. Increases and decreases the productivity and surface defects of the copper tube. On the other hand, if Sn is less than 0.1% by mass, sufficient tensile strength and fine crystal grain size cannot be obtained after annealing and after brazing heating. Therefore, the range of Sn content shall be 0.1-3.0 mass%.

Zn: 0.01-1.0 mass%
In the Sn-P-based copper pipe and the P-based copper pipe, in common, by selectively containing Zn, the strength, heat resistance and fatigue strength can be increased without greatly reducing the thermal conductivity of the copper pipe. Can be improved. In addition, the inclusion of Zn can reduce the wear of tools used for cold rolling, drawing, rolling, etc., and has the effect of extending the life of drawing plugs, grooved plugs, etc., contributing to the reduction of production costs To do. If the Zn content is less than 0.01% by mass, the above effects cannot be obtained sufficiently. On the other hand, if the Zn content exceeds 1.0% by mass, the tensile strength in the longitudinal direction of the tube and the circumferential direction of the tube is lowered, and the fracture strength is lowered. In addition, the stress corrosion cracking sensitivity is increased. Therefore, the Zn content when selectively contained is 0.001 to 1.0 mass%.

One or more selected from the group consisting of Fe, Ni, Mn, Mg, Cr, Ti, Zr and Ag:
In the Sn-P-based copper pipe and the P-based copper pipe, in common, Fe, Ni, Mn, Mg, Cr, Ti, Zr, and Ag are selectively contained, whereby the strength of the copper alloy and the pressure breakdown strength. In addition, the heat resistance can be improved, and the crystal grain can be refined to improve the bending workability. However, if the content of one or more elements selected from these elements exceeds 0.07% by mass in total, the extrusion pressure rises, so the same pressing as that without adding these elements. When extrusion is performed with output, it is necessary to increase the hot extrusion temperature. Thereby, since the surface oxidation of the extruded material increases, surface defects frequently occur in the copper tube of the present invention, and in particular, the fracture strength of the thinned copper tube as a heat transfer tube cannot be improved. For this reason, when it is selectively contained, one or more elements selected from the group consisting of Fe, Ni, Mn, Mg, Cr, Ti, Zr, Zr, and Ag are contained. The total content is less than 0.07% by mass (however, 0% by mass is not included). The content is desirably less than 0.05% by mass, and more desirably less than 0.03% by mass.

impurities:
Other elements are impurities, and it is preferable that the content of Sn-P copper pipe and P copper pipe be as small as possible in order to improve the breaking strength of the thinned copper pipe as a heat transfer pipe. However, there is also a trade-off with the cost for reducing these impurities, and the practical allowable amounts (upper limit amounts) of typical impurity elements are shown below.

S:
In both the Sn-P copper pipe and the P copper pipe, S forms a compound with Cu and exists in the parent phase. When the blending ratio of low-grade copper ingots and scraps used as raw materials increases, the S content increases. S promotes ingot cracking and hot extrusion cracking during ingots. Further, when the extruded material is cold-rolled or drawn, the Cu—S compound expands in the axial direction of the tube, and cracks are likely to occur at the interface between the copper alloy matrix and the Cu—S compound. For this reason, it is easy to become a surface flaw, a crack, etc. in the half-finished product and the product after processing, and especially the fracture strength as a heat transfer tube of the thinned copper tube is reduced. Further, when the pipe is bent, it becomes a starting point of occurrence of cracks, and the frequency of occurrence of cracks at the bent portion increases. Therefore, the S content is 0.005% by mass or less, desirably 0.003% by mass or less, and more desirably 0.0015% by mass or less. In order to reduce the S content, reduce the amount of low-grade Cu ingots and scrap used, reduce the SOx gas in the melting atmosphere, select appropriate furnace materials, and have an affinity for S such as Mg and Ca. Measures such as adding trace amounts of strong elements to the molten metal are effective.

As, Bi, Sb, Pb, Se, Te etc .:
Similarly for Sn-P copper pipes and P copper pipes, impurity elements other than S, such as As, Bi, Sb, Pb, Se, Te, etc. The fracture strength of the thinned copper tube as a heat transfer tube is reduced. Therefore, the total content (total amount) of these elements is preferably 0.0015% by mass or less, desirably 0.0010% by mass or less, and more desirably 0.0005% by mass or less.

O:
For both Sn-P copper pipe and P copper pipe, if the O content exceeds 0.005% by mass, Cu or Sn oxide is caught in the ingot, and the soundness of the ingot is reduced. Reduces the breaking strength of thinned copper tubes as heat transfer tubes. For this reason, the content of O is preferably 0.005% by mass or less. In order to further improve the bending workability, the O content is desirably 0.003% by mass or less, and more desirably 0.0015% by mass or less.

H:
In both Sn-P copper pipes and P copper pipes, when the amount of hydrogen (H) taken into the molten metal at the time of melting and casting increases, hydrogen whose solid solution amount has decreased during solidification precipitates at the grain boundaries of the ingot, and many pins Holes are formed and cracks are generated during hot extrusion. In addition, when a rolled and drawn copper tube is annealed even after extrusion, H is concentrated at the grain boundary during annealing, and this tends to cause blistering, particularly as a heat transfer tube of a thinned copper tube. Reduces fracture strength. For this reason, it is preferable to make content of H 0.0002 mass% or less. In order to further improve the fracture strength including the product yield, the H content is preferably 0.0001% by mass or less. In order to reduce the H content, measures such as drying of the raw material during melting and casting, red hotness of the molten-coating charcoal, reduction of the dew point of the atmosphere in contact with the molten metal, and making the molten metal before the addition of phosphorus feel oxidized It is valid.

(Manufacturing method of copper pipe)
Next, the method for producing a copper pipe of the present invention will be described below by taking the case of a smooth pipe as an example. The copper tube of the present invention can be manufactured by a conventional method for both the Sn-P-based copper tube and the P-based copper tube, but in order to keep the texture of the copper tube within the above-mentioned provisions of the present invention, It is necessary to particularly control the annealing process. Each step will be specifically described below. Unless otherwise specified, the conditions of each step and their significance are common to the Sn-P-based copper tube and the P-based copper tube.

  First, the raw electrolytic copper is dissolved in a charcoal-covered state, and after the copper is dissolved, a predetermined amount of alloy elements are added so as to obtain a predetermined Sn-P-based copper alloy and P-based copper alloy composition. At this time, it is preferable to add P as a Cu-15 mass% P intermediate alloy also for deoxidation. In addition, in the Sn—P based copper alloy, a Cu—Sn—P master alloy can be used instead of the Sn and Cu—P master alloy. After these component adjustments are completed, billets having predetermined dimensions are produced by semi-continuous casting. The obtained billet is heated in a heating furnace and homogenized. Before hot extrusion, it is desirable to improve segregation by homogenization by holding the billet at 750 to 950 ° C. for about 1 minute to 2 hours.

  Thereafter, the billet is perforated by piercing and hot extruded at 750 to 950 ° C. At this time, in particular, it is necessary to eliminate the segregation of Sn at the time of manufacturing the Sn-P-based copper pipe and to achieve the refinement of the structure in the product pipe common to the P-based copper pipe. For this purpose, both the Sn-P-based copper pipe and the P-based copper pipe are reduced in cross-sectional area by hot extrusion ([the donut-shaped area of the perforated billet−the cross-sectional area of the base tube after the hot extrusion] / [perforated]. The dough-shaped area of the billet] × 100%) is 88% or more, preferably 93% or more, and the raw tube after hot extrusion is cooled to a surface temperature of 300 ° C. by a method such as water cooling. It is preferable to cool so that the speed is 10 ° C./second or more, desirably 15 ° C./second or more, and more desirably 20 ° C./second or more.

  Next, the extruded element tube is rolled to reduce the outer diameter and thickness. By setting the processing rate at this time to 92% or less in terms of the cross-sectional reduction rate, product defects during rolling can be reduced. In addition, a drawn tube is manufactured by drawing the rolled tube. Usually, drawing is performed using a plurality of drawing machines, but surface defects and internal cracks in the raw pipe can be reduced by setting the processing rate (cross-sectional reduction rate) by each drawing machine to 35% or less.

  Thereafter, intermediate annealing is performed for 2 min to 1 hr. At this time, it is performed at a temperature range of 350 ° C. or higher and lower than 700 ° C. for a Sn—P copper tube and at a temperature range of 300 ° C. or higher and lower than 650 ° C. Further, the temperature increase rate of the intermediate annealing is preferably 20 ° C./min or more, more preferably 40 ° C./min or more.

  Here, in the Sn-P-based copper pipe, when the intermediate annealing temperature is lower than 300 ° C. or the rate of temperature increase is lower than 20 ° C./min, β-fiber, which is a rolling texture, develops to 20% or more and breaks. The ratio between the pressure and the tensile strength (breaking strength / tensile strength or breaking pressure / tensile strength) becomes smaller than before. Similarly, in a P-based copper pipe, when the intermediate annealing temperature is lower than 250 ° C. or the rate of temperature increase is lower than 20 ° C./min, β-fiber, which is a rolling texture, develops to 25% or more, The ratio of tensile strength will be below the conventional level. Therefore, the balance between the breaking strength and the bending workability is lowered, and the copper pipe excellent in breaking strength and bending workability cannot be provided.

  On the other hand, when the intermediate annealing temperature is 700 ° C. or higher in the Sn—P-based copper pipe, the crystal grain size becomes as coarse as 30 μm or more, and the converted stress of the fracture pressure becomes too low at 230 MPa or less. Similarly, in the P-based copper tube, when the intermediate annealing temperature is 650 ° C. or higher, the crystal grain size is as coarse as 40 μm or more, and the converted stress of the fracture pressure is too low as 190 MPa or less.

  Thereafter, a smooth tube and an internally grooved tube are manufactured by drawing or grooved rolling. At this time, the cross-sectional area reduction ratio after intermediate annealing is set to 35% or more and 80% or less for both the Sn-P copper pipe and the P copper pipe.

  When the area reduction is lower than 35%, the amount of accumulated strain is small, and the grain size of the recrystallized grains in the subsequent annealing is 30 μm or more for Sn-P type copper pipes and 40 μm or more for P type copper pipes. The ratio of the burst pressure to the converted stress is below the conventional level. On the other hand, if the area reduction rate is higher than 80%, β-fiber, which is a rolling texture, develops, and the tensile strength and fracture pressure are 20% or more for Sn-P copper pipes and 25% or more for P copper pipes. The ratio with the converted stress is below the conventional level.

  Thereafter, a final annealing process is performed on the drawn element tube. In order to continuously anneal the copper pipe of the present invention, a high-frequency induction coil in which a drawing element pipe is passed through the coil while energizing a high-frequency induction coil or a roller hearth furnace usually used for annealing a copper pipe coil or the like. Heating by can be used.

  In order to manufacture the copper tube of the present invention using a roller hearth furnace, annealing is performed so that the actual temperature of the drawn element tube is 350 to 700 ° C., and the drawn element tube is heated for about 1 to 120 minutes at that temperature. Is desirable.

  When the body temperature of the drawn element tube is lower than 350 ° C., a complete recrystallized structure is not formed, and a fibrous processed structure remains, which makes it difficult for a customer to perform bending. Moreover, when the temperature exceeds 700 ° C., the crystal grains become coarse, and the bending workability of the tube is lowered. Therefore, it is desirable to anneal the drawing tube at a solid temperature of 350 to 700 ° C.

  In addition, when the heating time in this temperature range is shorter than 1 minute, a complete recrystallized structure is not obtained, and thus the above-described problem occurs. Further, even if annealing is performed for more than 120 minutes, the crystal grain size does not change, and the effect of annealing is saturated. For this reason, the heating time in the temperature range is suitably 1 minute to 120 minutes.

  In this respect, Patent Document 7 performs intermediate annealing for the purpose of improving workability such as tube expansion. However, the aim of intermediate annealing is to remove strain and reduce wrinkles, and does not focus on the control of β fiber, which is the technical point of the present invention. For this reason, compared with the present invention, the temperature increase rate of the intermediate annealing and the area reduction rate after the intermediate annealing are not strictly controlled, the β fiber area ratio is large, and the ratio between the fracture resistance and the tensile strength is compared. It is estimated that it is small. In particular, the rate of temperature increase during intermediate annealing is up to about 10 ° C./min at the maximum in the normal manufacturing method, and the rate of temperature increase (20 ° C./min or more) as required in the present invention described above. I never dared to adopt it.

  The smooth tube manufacturing method has been described above. However, the annealed smooth tube may be subjected to drawing processing at various processing rates as necessary to obtain a processed tube having improved tensile strength. Moreover, in the case of an internally grooved tube, a grooved rolling process is performed on the annealed smooth tube. Thus, after manufacturing an internally grooved pipe | tube, normally it anneals further. Further, the annealed inner surface grooved tube may be subjected to a drawing process at a light processing rate as necessary to improve the tensile strength.

  Examples of the present invention will be described below. As shown in Table 1, various P-type copper pipes and Sn-P-type copper pipes having various chemical compositions and production conditions and different textures in the structure were produced as smooth tubes.

  For the cross section (structure) parallel to the tube axis of these copper tubes, the average crystal grain size and texture density were measured, and the tensile strength and fracture strength of these copper tubes were also measured and evaluated. These results are shown in Table 2. Specific manufacturing methods, measurements, and evaluation methods for these Sn-P-based copper tubes and P-based copper tubes (smooth tubes) are as follows.

(Smooth tube manufacturing conditions)
(A) Using electrolytic copper as a raw material, Sn—P-based copper pipe is to add a predetermined Sn to the molten metal, and optionally add additional additive elements, and then add a Cu—P master alloy. Thus, a molten metal having a predetermined composition was produced. For the P-based copper tube, a predetermined Cu-P master alloy was added to the molten metal, and a selective additive element was added as necessary to prepare a molten metal having a predetermined composition. The component composition of these molten copper alloys was defined as the component composition of the copper tube.

(B) An ingot having a diameter of 300 mm and a length of 6500 mm was semi-continuously cast at a casting temperature of 1200 ° C., and a billet having a length of 450 mm was cut out from the obtained ingot.

(C) After heating the billet to 650 ° C. with a billet heater, the billet is heated to 950 ° C. with a heating furnace (induction heater). After reaching 950 ° C., after 2 minutes, the billet is taken out from the heating furnace, Immediately after the piercing process with a diameter of 80 mm at the center of the billet (without delay), an extruded element tube having an outer diameter of 96 mm and a wall thickness of 9.5 mm was produced with the same hot extruder (cross-sectional reduction rate: 96.6). %). The average cooling rate to 300 ° C. of the extruded tube after hot extrusion was 40 ° C./second.

(D) The extruded element tube is rolled to produce a rolled element tube having an outer diameter of 35 mm and a wall thickness of 2.3 mm, and the rolling element tube has a cross-sectional reduction rate of 35% or less in one drawing process. Then, drawing and drawing were performed to obtain an outer diameter of 22 mm, a wall thickness of 1.2 mm to an outer diameter of 12 mm, and a wall thickness of 0.95 mm.

(E) Heated to 300 to 700 ° C. in a heating furnace (induction heater), held at this temperature for 30 minutes, passed through a cooling zone, gradually cooled to room temperature, and used as a test material.

(G) In this case, in the inventive examples, the heating rate of these intermediate annealings was set to the fastest possible cooling rate of 20 ° C./min or more. These intermediate annealing temperatures and heating temperatures in the intermediate annealing are shown in Table 1.

(H) Drawing and drawing were performed to obtain a copper tube having an outer diameter of 9.52 mm, a wall thickness of 0.80 mm, and various cross-sectional area reduction rates. Table 1 shows the cross-sectional area reduction ratio.

(I) In an annealing furnace, the drawing tube is heated to 450 to 580 ° C. in an reducing gas atmosphere (average rate of temperature increase of 12 ° C./min), maintained at this temperature for 30 to 120 minutes, and a cooling zone is formed. The sample was allowed to pass through and slowly cooled to room temperature to obtain a test material.

  Mean crystal grain size of these manufactured copper tubes (outer diameter: 9.52 mm, wall thickness: 0.80 mm), structures such as area ratios of Cu orientation, S orientation and Brass orientation belonging to β fiber, tensile strength, Table 2 shows mechanical properties such as fracture strength. As reference data, the area ratio of Goss orientation grains is shown in Table 2. In Table 1, the S content of the copper tube is 0.005% by mass or less in common with each of the examples of the invention and the comparative example, and the total content of As, Bi, Sb, Pb, Se, Te The (total amount) was 0.0005% by mass or less, the O content was 0.003% by mass or less, and the H content was 0.0001% by mass or less.

(Gathering organization)
The average grain size, the Cu orientation belonging to the β fiber, the area ratio of each orientation of the S orientation and the Brass orientation, etc. in the texture of the manufactured copper tube are measured by the crystal orientation analysis method in which the EBSP system is mounted on the SEM. did.

(Tensile test)
A tensile test (MPa) was performed on the specimen under the conditions of room temperature, test speed 10.0 mm / min, GL = 50 mm, using a JIS No. 11 test piece and a 5882 type Instron universal testing machine. ) Was measured. Three test pieces under the same conditions were tested, and the average value thereof was adopted.

(destruction strength)
A copper tube having a length of 300 mm was collected for testing from the manufactured copper tube, and one end of the copper tube was closed in a pressure-resistant manner with a metal jig (bolt). Then, from the other open side end, the water pressure loaded into the pipe by the pump is gradually increased (pressure increase rate: about 1.5 MPa / second), and the water pressure (MPa) when the pipe completely ruptures. Was read with a Bourdon tube pressure gauge and used as the breaking strength (pressure resistance, pressure resistance, breaking pressure) of the heat transfer tube. This test was performed five times on the same copper tube (for five test tubes), and the average value of each water pressure (MPa) was taken as the fracture strength. Moreover, the conversion stress which remove | eliminated the influence of the thickness and outer diameter of a copper pipe from fracture strength was calculated | required. Here, the converted stress σ was obtained from the following equation when the fracture strength was P, the outer diameter of the copper tube was D, and the thickness of the copper tube was t.
σ = P × (D−0.8t) / (2 × t)

(Evaluation of strength-workability balance)
As disclosed in Patent Document 6, it is presumed that the higher the ratio between fracture strength and tensile strength, the better the balance between strength and workability. Therefore, the larger the ratio between the converted stress obtained from the fracture strength and the tensile strength, the better the strength-workability balance.

(Invention example)
(Sn-P copper pipe)
As shown in Tables 1 and 2, since Invention Examples 1 to 13 have appropriate chemical compositions and production conditions within the scope of the present invention, the sum of the area ratios of the Cu, S, and Brass orientations belonging to the β fiber. Is controlled in the range of 10 to 20%. Therefore, the ratio between the breaking strength and the tensile strength is 0.90 or higher, which is higher than that of the comparative example.

(Comparative example)
(Sn-P copper pipe)
Although Comparative Examples 1, 2, 4, and 5 are alloys within the composition range of the present invention, since the manufacturing conditions are not in an appropriate range, each of the Cu orientation, S orientation, and Brass orientation belonging to the β fiber. The sum of the area ratios is as high as 20% or more. For this reason, the ratio between the breaking strength and the tensile strength is less than 0.90, which is lower than that of the invention example.

  In Comparative Examples 3 and 6, since the sum of the area ratios of the Cu orientation, S orientation, and Brass orientation belonging to the β fiber is in an appropriate range, the manufacturing conditions are not in an appropriate range. Becomes 30 μm or more, and the converted stress becomes as low as 230 MPa or less.

  In Comparative Examples 7 and 8, the Sn and P contents are too much greater than the specified range, so that extrusion cannot be performed (extrusion is impossible) or cracks are generated during extrusion. In Comparative Example 9, since the P content is too much less than the specified range, the converted stress is too low at 230 MPa or less.

  Moreover, since the Zn content is too high in Comparative Example 10, the sum of the area ratios of each of the Cu, S, and Brass orientations belonging to the β fiber is 20% or more. Therefore, the ratio between the fracture strength and the tensile strength. Is as low as less than 0.90.

(Invention example)
(P-type copper pipe)
As shown in Tables 1 and 2, since the inventive compositions 14 to 25 have appropriate chemical compositions and production conditions within the scope of the present invention, the sum of the area ratios of the Cu, S, and Brass orientations belonging to the β fiber. Is controlled in the range of 10 to 25%. For this reason, the ratio of the breaking strength and the tensile strength is 0.85 or higher, which is higher than that of the comparative example.

(Comparative example)
(P-type copper pipe)
Although Comparative Examples 11 to 14 are alloys within the composition range of the present invention, since the manufacturing conditions are not in an appropriate range, the sum of the area ratios of the Cu, S, and Brass orientations belonging to the β fiber. Is as high as 25% or more. For this reason, the ratio of fracture strength to tensile strength is less than 0.85, which is lower than that of the inventive examples. Further, although Comparative Example 15 is an alloy within the composition range of the present invention, the area reduction rate is too low, so the crystal grain size is 40 μm or more, and the fracture strength is smaller than 190 MPa.

  In Comparative Example 16, as in Comparative Example 8, since the P content is too much than the specified range, cracks occur during extrusion. In Comparative Example 17, as in Comparative Example 9, since the P content is too much less than the specified range, the crystal grain size is larger than 40 μm, and the fracture strength is smaller than 190 MPa.

  From the above results, the component composition, strength, and texture of the present invention for obtaining a copper tube excellent in fracture strength and workability balance that can be used even when thinned due to a high operating pressure of a new refrigerant. Further, the significance of preferable production conditions for obtaining this texture is supported.

  As described above, according to the present invention, it is possible to provide a material Sn-P-based copper pipe that is excellent in bending workability and is thinned and strengthened and a method for manufacturing the same. As a result, the material Sn-P-based copper pipe can be suitably applied to a heat exchanger heat transfer pipe used by cold working.

Claims (4)

  P: A copper tube containing 0.005 to 0.1% by mass, with the balance being composed of Cu and inevitable impurities, and the average crystal grain size is 40 μm or less as measured by the SEM-EBSP method. Yes, excellent in fracture strength and bending workability, characterized in that the sum of the average area ratios of Cu orientation, S orientation, and Brass orientation belonging to β fiber of rolling texture is in the range of 10-25% Copper tube for heat exchanger.   The copper tube further contains Sn: 0.1 to 3.0% by mass, the average crystal grain size is 30 μm or less, and each of Cu orientation, S orientation, and Brass orientation belonging to the β fiber of the rolled texture. The copper tube for a heat exchanger according to claim 1, wherein the sum of the average area ratios of the orientations is in the range of 10 to 20%.   The copper pipe for heat exchangers according to claim 1 or 2, wherein the copper pipe further contains Zn: 0.01 to 1.0 mass%. The copper pipe further contains one or more elements selected from the group consisting of Fe, Ni, Mn, Mg, Cr, Ti, Zr and Ag in total less than 0.07% by mass (provided that 0% is included) The copper tube for heat exchangers of any one of Claims 1 thru | or 3 to contain.