JP2008174785A - Copper alloy tube for heat exchanger - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper alloy tube for heat exchanger having a ratio of burst pressure to tensile strength (PFa)/(σa) more than the ratio of burst pressure to tensile strength (PFd)/(σd) for a phosphorus-deoxidized copper tube, and superior in bending property and heat resistance. <P>SOLUTION: The copper alloy tube for heat exchanger has a composition containing 0.1-2.0 mass% of Sn, 0.005-0.1 mass% of P, 0.005 mass% or lower of S, 0.005 mass% or lower of O, 0.0002 mass% or lower of H and balance Cu with inevitable impurities. This copper alloy tube has a tensile strength of 255 N/mm<SP>2</SP>or higher, and an average crystal particle size of 30 μm or lower measured in the direction vertical to the wall thickness direction of the tube in the section crossing the tube axis at a right angle. When the tensile strength and the burst pressure of the copper alloy tube are represented by σa and PFa respectively, and the tensile strength and burst pressure of the phosphorus-deoxidized copper tube having the same outer diameter and wall thickness as the copper alloy tube are represented by σd and PFd respectively, the relation of (PFa)/(σa)>(PFd)/(σd) is satisfied. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a copper alloy tube for a heat exchanger having excellent pressure fracture strength and workability.

  For example, a heat exchanger for an air conditioner has a U-shaped copper tube bent into a hairpin shape (hereinafter referred to as a copper tube also includes a copper alloy tube) of a fin made of aluminum or an aluminum alloy plate (hereinafter referred to as an aluminum fin). Through the through hole, the copper tube is expanded by inserting a jig into the copper tube, thereby bringing the copper tube and the aluminum fin into close contact with each other, and further expanding the open end of the copper tube. A U-shaped bend copper tube is inserted into the U-shaped copper tube, and the bend copper tube is brazed to the expanded open end of the U-shaped copper tube with a brazing material such as phosphor copper brazing. Connected by a bend copper tube, a heat exchanger is manufactured.

  For this reason, it is requested | required that the copper tube used for a heat exchanger should have favorable heat conductivity, bending workability, and brazing property. Therefore, phosphorus deoxidized copper having good characteristics 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. In addition, CO ₂ that is a natural refrigerant has been used in 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 through the heat transfer tubes of the heat exchanger) is maximum in the condenser (gas cooler in CO ₂ ). 8 MPa, the R410A of HFC-based fluorocarbons 3 MPa, also in CO ₂ refrigerant is about 7 to 10 MPa (supercritical state), the operating pressure of the newly adopted refrigerant is increased to 1.6 to 6 times that of the conventional refrigerant R22 is doing.

  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. Also, 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, so that the crystal grains are coarsened and softened in the brazed part and its vicinity in comparison with other parts. 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 such a demand, as a copper alloy tube excellent in 0.2% proof stress and fatigue strength, for example, Co: 0.02 to 0.2 mass%, P: 0.01 to 0.05 mass% , C: 1 to 20 ppm, the remainder is made of Cu and inevitable impurities, and oxygen of impurities is 50 ppm or less, and a seamless copper alloy tube for heat exchanger has been proposed (Patent Document 1). Also, Sn: 0.1 to 1.0 mass%, P: 0.005 to 0.1 mass%, O: 0.005 mass% or less and H: 0.0002 mass% or less, with the balance being Cu And the copper alloy pipe | tube for heat exchangers which has the composition which consists of unavoidable impurities and whose average crystal grain diameter is 30 micrometers or less is proposed (patent document 2).

JP 2000-199023 A JP 2003-268467 A

  However, although the copper alloy disclosed in Patent Document 1 has improved tensile strength by precipitation strengthening with Co phosphide, the pressure fracture strength does not increase for the strength increase (copper of Patent Document 1). When the fracture pressure of the alloy tube is PF1 and the tensile strength is σ1, σ1> σd (σd is the tensile strength of the phosphorous deoxidized copper tube). Since the phosphide dissolves at the brazing temperature, the strength decreases after brazing. Therefore, when used for a heat transfer tube, there is a problem that the wall thickness cannot be reduced so much that a desired effect cannot be obtained.

  Moreover, the copper alloy of Patent Document 2 has improved strength due to solid solution strengthening of Sn, and the softening after brazing is also smaller than that of Patent Document 1, and when used in a heat transfer tube, the thickness of the tube can be reduced. Although it becomes possible, when U-shaped bending is performed to make a heat exchanger, wrinkles or cracks are likely to occur in the bent part, and the part starts to break at an unexpectedly low strength. It turns out that there is a point.

  By the way, when hydrostatic pressure is applied to a copper pipe having a tensile strength σ and the breaking pressure when the pipe breaks is PF, PF and σ are normally in a proportional relationship, and PF / σ = α (α Is a proportionality constant). PFd / σd = αd, where σd is the tensile strength of the soft phosphorous deoxidized copper tube and PFd is its breaking pressure. When a light drawing process is applied to the soft phosphorous deoxidized copper pipe, the tensile strength increases, and σd ′ (σd ′> σd) is obtained. Accordingly, the breaking pressure also increases, and PFd ′ (PFd ′> PFd). However, the ratios PFd / σd and PFd ′ / σd ′ of PF and σ are both αd, and the tensile strength of the phosphorous deoxidized copper pipe is improved by drawing the annealed soft material and the like. However, if the tensile strength is increased, the ductility is drastically reduced, and cracks and wrinkles are likely to occur at the bent part of the heat transfer tube. It breaks at low pressure.

  Therefore, if a heat transfer tube exceeding the ratio αd of the fracture pressure to the tensile strength of phosphorous deoxidized copper is obtained, the pressure strength can be secured without increasing the tensile strength of the tube, and the tube can be processed. It is advantageous to ensure the property. Moreover, even if the wall thickness of the tube is reduced, it is possible to ensure a predetermined pressure resistance.

  The present invention has been made in view of such a problem, and a ratio of the breaking pressure / tensile strength (PFa) exceeding the ratio (PFd) / (σd) between the breaking pressure and the tensile strength for the phosphorous deoxidized copper pipe. An object of the present invention is to provide a copper alloy tube for a heat exchanger having / (σa) and excellent bending workability and heat resistance.

The copper alloy tube for a heat exchanger according to the present invention has Sn: 0.1 to 2.0 mass%, P: 0.005 to 0.1 mass%, S: 0.005 mass% or less, O: 0.005. Less than mass%, and H: 0.0002 mass% or less, with the balance being composed of Cu and unavoidable impurities, with a tensile strength of 255 N / mm ² or more. A copper alloy tube having an average crystal grain size of 30 μm or less measured in a direction perpendicular to the thickness direction of the copper alloy tube, wherein the tensile strength of the copper alloy tube is σa, the fracture pressure is PFa, When the tensile strength of the diameter and thickness of the phosphorous deoxidized copper pipe is σd and the breaking pressure is PFd, (PFa) / (σa)> (PFd) / (σd).

  This copper alloy tube for a heat exchanger can further contain Zn: 0.01 to 1.0% by mass.

  Furthermore, it is possible to contain a total of less than 0.07% by mass of one or more elements selected from the group consisting of Fe, Ni, Mn, Mg, Cr, Ti and Ag.

  Furthermore, the copper alloy tube for heat exchanger may be drawn.

  The copper alloy tube for a heat exchanger according to the present invention preferably has an average crystal grain size of 100 μm or less measured in a direction perpendicular to the thickness direction of the tube in a cross section perpendicular to the tube axis after heating at 800 ° C. for 15 seconds. The average crystal grain size is determined by measuring the crystal grain size in the direction perpendicular to the wall thickness by a cutting method defined in JISH0501 in a cross section orthogonal to the axial direction of the tube, It is the average value of the measured values when measured at a location.

  Furthermore, this copper alloy tube for heat exchangers is, for example, an internally grooved tube.

  Hereinafter, the present invention will be described in more detail. As a result of various experimental studies by the present inventors, the Sn content, the P content, the S content, and the average crystal grain size in the direction perpendicular to the thickness in the cross section perpendicular to the tube axis are appropriately defined. It discovered that the copper alloy tube for heat exchangers which can solve a subject could be obtained.

  Hereinafter, the reason for adding components and the reason for limiting the composition of the heat exchanger tube for heat exchanger according to the present invention will be described.

“Sn: 0.1 to 2.0 mass%”
Sn has the effect of improving the tensile strength of the copper alloy tube and suppressing the coarsening of crystal grains. When Sn is contained in the copper alloy of the heat transfer tube using various refrigerants, the phosphorus deoxidized copper tube It becomes possible to reduce the wall thickness of the tube as compared with the above. If the Sn content of the copper alloy tube exceeds 2.0% by mass, solidification segregation in the ingot becomes severe, and segregation may not be completely eliminated by normal hot extrusion and / or thermomechanical treatment. The metal structure, mechanical properties, bending workability, structure after brazing, and mechanical properties are not 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. Increased productivity decreases and surface defects of the copper alloy tube increase. 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.

“P: 0.005 to 0.1 mass%”
When the P content of the copper alloy tube exceeds 0.1% by mass, cracking is likely to occur during hot extrusion, and the stress corrosion cracking sensitivity is increased, and the thermal conductivity is greatly decreased. When the P content is less than 0.005% by mass, the amount of oxygen increases due to insufficient deoxidation, Sn oxide is generated, the soundness of the ingot is lowered, and the bending workability as a copper alloy tube is lowered. To do.

“S: 0.005 mass% or less”
In the copper alloy tube of the present invention, S in the copper alloy tube 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 and the S content increases, ingot cracking and hot extrusion cracking during ingot increase. Even if hot extrusion cracking does not occur, when the extruded material is cold-rolled or drawn, the Cu—S compound inside the material expands in the axial direction of the tube, and the copper alloy matrix and Cu—S Cracks are likely to occur at the compound interface, resulting in surface defects and cracks in the semi-finished product being processed and the product after processing, thereby reducing the product yield. Even when cracks do not occur at the Cu-S compound interface, when bending the alloy pipe of the present invention, it becomes a starting point of crack generation, and the frequency of occurrence of cracks at the bent portion increases. In order to improve such problems, the S content in the copper alloy tube of the present invention should be 0.005% by mass or less, desirably 0.003% by mass or less, more desirably 0.0015% by mass or less. There is. S is relatively simpler than copper metal, raw materials such as scrap, oil adhering to scrap, melting casting atmosphere (charcoal / flux covering molten metal, SOx gas in furnace atmosphere, furnace material, etc.) In order to reduce the S content to 0.005% by mass or less, the amount of low-grade Cu ingots and scrap used is reduced, the SOx gas in the melting atmosphere is reduced, and an appropriate furnace material is used. Measures such as adding a trace amount of an element having a strong affinity for S, such as Mg and Ca, to the molten metal are effective. In addition, the impurity elements As, Bi, Sb, Pb, Se, and Te other than S are similarly reduced in the soundness of the ingot, the hot extruded material, and the cold work material, and the bending workability of the pipe is improved. Therefore, the total content 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: 0.005 mass% or less”
In the copper alloy pipe of the present invention, when the content of O exceeds 0.005 mass%, Cu or Sn oxide is caught in the ingot, and the soundness of the ingot is lowered, and the manufactured pipe Bending workability tends to decrease. For this reason, it is necessary to make content of O 0.005 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% or less.

“H: 0.0002 mass% or less”
When the amount of hydrogen taken into the molten metal at the time of melt casting increases, the hydrogen whose solid solution amount has decreased at the time of solidification precipitates at the grain boundary of the ingot, forms a large number of pinholes, and generates cracks at the time of hot extrusion. In addition, when a copper alloy tube that has been rolled and drawn after annealing is annealed, H is concentrated at the grain boundaries during annealing, and blistering is likely to occur due to this, resulting in a decrease in product yield. For this reason, in the copper alloy pipe | tube of this invention, it is necessary to make content of H 0.0002 mass% or less. In order to further improve the product yield, the H content is desirably 0.0001% by mass or less.

  In order to make the H content 0.0002% by mass or less, drying of the raw material at the time of 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 the molten metal before the addition of phosphorus seem to be oxidized Measures such as making it effective are effective.

“Zn: 0.01 to 1.0 mass%”
By adding Zn, the strength, heat resistance and fatigue strength can be improved without greatly reducing the thermal conductivity of the copper alloy tube. In addition, the addition 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. When the Zn content exceeds 1.0% by mass, the stress corrosion cracking sensitivity becomes high. Further, if the Zn content is less than 0.01% by mass, the above effects cannot be obtained sufficiently. Therefore, the Zn content needs to be 0.001 to 1.0 mass%.

  Next, the reasons for limitation such as the characteristics of the copper alloy tube for heat exchanger of the present invention will be described.

“Tensile strength: 255 N / mm ² or more”
When the tensile strength of the copper alloy tube is less than 255 N / mm ² , the strength when incorporated in a heat exchanger such as an air conditioner is insufficient, and the strength after brazing cannot be sufficiently maintained. The tensile strength referred to here is the tensile strength in the tube axis direction of a copper alloy tube annealed and made into a soft material.

“Average crystal grain size in the direction perpendicular to the thickness direction in the cross section perpendicular to the tube axis: 30 μm or less”
When hydrostatic pressure is applied to the inside of the pipe, a force is applied in the direction orthogonal to the pipe circumferential direction and the wall thickness direction in the cross section perpendicular to the pipe axis, surface defects on the inner and outer surfaces of the pipe, inclusions such as sulfides inside the pipe, and the inner surface of the pipe Alternatively, a crack is generated based on a defect such as an internal fine crack, and the crack propagates to break. The present inventors have found that it is effective to reduce the average crystal grain size in the direction perpendicular to the thickness direction in the cross section perpendicular to the tube axis to 30 μm or less in order to prevent such a problem leading to destruction. . If the average crystal grain size in the direction perpendicular to the thickness direction in the cross section perpendicular to the tube axis exceeds 30 μm, cracks are likely to occur in the bent portion when bent into a heat exchanger such as an air conditioner. In this case, the average crystal grain size in the direction orthogonal to the thickness direction is more preferably 20 μm or less.

  The average crystal grain size may be either a state recrystallized by annealing or a state in which plastic processing such as drawing is performed.

“When the tensile strength of the copper alloy pipe is σa, the pressure breaking pressure is PFa, the tensile strength of the phosphorus-deoxidized copper pipe having the same outer diameter and thickness as the copper alloy pipe is σd, and the pressure breaking pressure is PFd ( PFa) / (σa)> (PFd) / (σd). ”
The copper alloy tube of the present invention has a ratio (Pfa) / (σa) between the pressure breaking pressure Pfa and the tensile strength σa (PFd) of the pressure breaking pressure PFd and the tensile strength σd of the phosphorous deoxidized copper tube. Since it is larger than / (σd), for example, even when a pipe having the same tensile strength and the same thickness is used, the copper alloy pipe of the present invention can guarantee a higher pressure strength. Also, if the tensile strength of the phosphorus-deoxidized copper tube and the copper alloy tube of the present invention is the same, the copper alloy tube of the present invention has a larger elongation, so that cracking due to bending of the tube is less likely to occur. Severe bending (bending with a small bending radius) can be performed.

  In addition, since the ratio between the pressure fracture pressure and the tensile strength is the same alloy, even if the tempering (softened state by annealing and the processing rate after annealing) changes, it shows almost the same value. It can be determined by measuring the tensile strength and the pressure fracture strength of the phosphorous deoxidized copper tube and the copper alloy tube of the present invention.

“Totally less than 0.07% by mass of one or more elements selected from the group consisting of Fe, Ni, Mn, Mg, Cr, Ti and Ag”
Fe, Ni, Mn, Mg, Cr, Ti, Zr, and Ag all improve the strength, pressure breakdown strength, and heat resistance of the copper alloy of the present invention, and refine crystal grains to improve bending workability. When the content of one or more elements selected from the above elements exceeds 0.07% by mass, the extrusion pressure rises. Therefore, when extrusion is performed with the same pressing force as that in which these elements are not added, 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 alloy tube of the present invention, and the product yield decreases. For this reason, it is desirable that the total of one or more elements selected from the group consisting of Fe, Ni, Mn, Mg, Cr, Ti, Zr and Ag be less than 0.07% by mass. The content is more preferably less than 0.05% by mass, and still more preferably less than 0.03% by mass.

“Tensile strength after heating to 800 ° C. for 15 seconds: 235 N / mm ² or more”
When a copper alloy tube is processed into a heat exchanger, it is affected by heat from brazing. Usually, phosphor copper brazing (JIS BCuP-2: Cu-6.8 to 7.5% by mass P, brazing temperature: 735 to 840 ° C.) is frequently used for brazing. If the tensile strength after heating at 800 ° C. for 15 seconds, which is equivalent to the thermal effect of brazing, is less than 235 N / mm ² , fatigue is caused when the operating pressure is high for HFC-based fluorocarbon refrigerant and carbon dioxide refrigerant. Destruction is likely to occur. Therefore, it is preferable that the tensile strength of the copper alloy tube after heating at 800 ° C. for 15 seconds is 235 N / mm ² or more.

“Average crystal grain size in the direction perpendicular to the wall thickness direction of the tube axis orthogonal section after heating to 800 ° C. for 15 seconds: 100 μm or less”
As described above, when a copper alloy tube is processed into a heat exchanger, it is affected by heat due to brazing. The crystal grain size becomes coarse due to the heat effect of brazing. After heating to 800 ° C. for 15 seconds, which is equivalent to the heat effect of brazing, the average crystal in the direction perpendicular to the thickness direction of the cross section perpendicular to the tube axis If the particle size exceeds 100 μm, the pressure strength is greatly reduced in the brazed part, and the reliability decreases when copper alloy tubes are used in heat exchangers for HFC-based refrigerants and carbon dioxide refrigerants with high operating pressure. . Accordingly, it is desirable that the average crystal grain size in the direction perpendicular to the thickness direction of the cross section perpendicular to the tube axis is 100 μm or less, more preferably 60 μm or less.

“The copper alloy tube is an internally grooved tube.”
The copper alloy tube of the present invention is suitable for the production of an internally grooved tube by rolling because the tensile strength and elongation can be increased and the crystal grain size can be reduced as compared with a phosphorous deoxidized copper tube. In particular, because the tensile strength is large, it is difficult to stretch in the drawing direction during rolling, so the groove of the grooved plug can be smoothly filled with the meat of the alloy tube, and the inner surface grooved tube with a good fin shape can be filled at high speed. It becomes possible to process with.

  Next, an example of the method for producing a copper alloy tube of the present invention will be described below by taking a smooth tube or an internally grooved tube as an example.

  First, the raw electrolytic copper is dissolved in a charcoal-coated state, and after the copper is dissolved, a predetermined amount of Sn and Zn is added, and further P is added as a Cu-15 mass% P intermediate alloy for deoxidation. . After the component adjustment is completed, a billet having a predetermined size is 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. In order to manufacture the copper alloy pipe of the present invention, it is essential to eliminate the segregation of Sn and to refine the structure of the product pipe. For this purpose, the cross-sectional reduction rate ([perforated billet Donut-shaped area-cross-sectional area of tube after hot extrusion] / [doughnut-shaped area of perforated billet] × 100%) is 88% or more, preferably 93% or more, and further after hot extrusion The raw tube is cooled by a method such as water cooling so that the cooling rate until the surface temperature reaches 300 ° C. is 10 ° C./second or higher, preferably 15 ° C./second or higher, more preferably 20 ° C./second or higher. Is preferred.

  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.

  After that, when the pipe is bent by the customer or when the inner surface grooved pipe is manufactured using the drawing pipe, the drawing pipe is annealed. In order to continuously anneal the copper alloy tube of the present invention, a roller hearth furnace usually used for annealing a copper tube coil or the like, or heating by a high frequency induction coil that passes the copper tube through the coil while energizing the high frequency induction coil Can be used. In order to manufacture the copper alloy tube of the present invention using a roller hearth furnace, it is desirable to anneal the drawing tube so that the actual temperature of the drawing tube is 400 to 600 ° C., and the drawing tube is heated for about 1 to 120 minutes at that temperature. . Moreover, it is desirable to heat so that the average rate of temperature increase from room temperature to a predetermined temperature is 5 ° C./min or more, preferably 10 ° C./min or more.

  When the actual temperature of the drawing tube is lower than 400 ° C., a complete recrystallized structure is not obtained (a fibrous processed structure remains), and it becomes difficult for a customer to bend and process an internally grooved tube. In addition, when the temperature exceeds 600 ° C., the crystal grains are coarsened, the bending workability of the pipe is lowered, and the tensile strength of the pipe is reduced in the inner surface grooving process. It is large and it becomes difficult to form the fin on the inner surface of the tube into a correct shape. For this reason, it is desirable to anneal the drawing tube in the range of 400 to 600 ° C. Further, when the heating time in this temperature range is shorter than 1 minute, the above-mentioned problem occurs because a complete recrystallization structure is not obtained. 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. Therefore, the heating time in the temperature range is suitably 1 minute to 120 minutes. In order not to make the crystal grains coarse, it is desirable that the average temperature increase rate from room temperature to a predetermined temperature is high. If the rate of temperature rise is slower than 5 ° C./min, the crystal grains are likely to be coarsened even when heated to the same temperature, which is undesirable from the viewpoint of pressure breakdown strength and bending workability, and also hinders productivity. Therefore, the average rate of temperature rise from room temperature to a predetermined temperature is preferably 5 ° C./min or more.

  In place of the continuous annealing by the roller hearth furnace, a high-frequency induction heating furnace may be used to perform high-temperature heating, high-speed cooling, and short-time heating annealing. The above is the smooth tube manufacturing method. Moreover, it is good also as a processed pipe which improved the tensile strength by performing the drawing process of various processing rates as needed to the smooth pipe annealed in this way.

  In the case of an internally grooved tube, grooved rolling 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.

  Hereinafter, test results for demonstrating the effects of the present invention will be described.

(Example 1: Smooth tube)
(A) Using electrolytic copper as a raw material, predetermined Sn was added to the molten metal, and Zn was added as necessary, and then a Cu-P master alloy was added to prepare a molten metal having a predetermined composition. At this time, a Cu—Sn—P master alloy may be used instead of Sn and the Cu—P master alloy.
(B) An ingot having a diameter of 320 × length of 6500 mm was semi-continuously cast at a casting temperature of 1200 ° C.
(C) A billet having a length of 450 mm was cut out from the resulting ingot.
(D) After heating the billet to 650 ° C. with a billet heater, the billet is heated to 950 ° C. with an induction heater, and after reaching 950 ° C., after 2 minutes, piercing with a diameter of 80 mm is performed at the center of the billet with a hot extruder Thereafter, an extruded element tube having an outer diameter of 96 mm and a wall thickness of 9.5 mm was produced by hot extrusion (cross-sectional reduction rate: 96.6%). The average cooling rate up to 300 ° C. of the extruded element tube was 40 ° C./second.
(E) The extruded element tube was rolled to produce a rolled element tube having an outer diameter of 35 mm and a wall thickness of 2.3 mm.
(F) The drawing tube was repeatedly drawn and drawn so that the cross-sectional reduction rate in one drawing process was 35% or less, and a copper alloy tube having an outer diameter of 9.52 mm and a wall thickness of 0.80 mm was obtained. .
(G) In an annealing furnace, the drawing tube is heated to 450 to 580 ° C. in a 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.

  Table 1 below shows the characteristics of the annealed material of a smooth tube having an outer diameter of 9.52 mm and a wall thickness of 0.80 mm. The conventional product shown in Table 1 is a phosphorus deoxidized copper tube of JISH3300C1220T. The types of the conventional products are common in Tables 2 to 8 below.

  The stress corrosion cracking test is a desiccator containing 11.8% or more of ammonia water obtained by cutting a 75 mm long test piece from a tube, degreasing and drying, and then diluting the ammonia water specified in JIS K8085 with an equal amount of pure water. The sample was placed 50 mm away from the liquid surface and kept in this ammonia atmosphere at room temperature for 2 hours. Then, the test piece was crushed to 50% of the original outer diameter, and the crack was visually determined. The case where there was no crack was indicated by ○ and the case where there was a crack was indicated by ×.

  Moreover, after heating a test piece at 850 degreeC for 30 minute (s) in hydrogen stream, it polish-etched and expanded 100 times with the microscope, and confirmed the presence or absence of embrittlement. The case where there was no embrittlement was indicated by ○, and the case where there was embrittlement was indicated by ×.

  Comparative Example No. No. 2 has a high extrusion pressure and cannot be extruded. 3, no. No. 7 was cracked during hot extrusion and could not be processed.

  As shown in Table 1, Examples 1 to 11 had high tensile strength and high fracture pressure, and no cracks occurred in the stress corrosion cracking test and the hydrogen embrittlement test. On the other hand, Comparative Examples 4 and 5 each have a P and Zn content greater than the specified range of the present invention, so that cracking occurred in the stress corrosion cracking test, and Comparative Example 6 had an O content of the present invention. Cracking occurred in the hydrogen embrittlement test because it was larger than the specified range. Conventional products have low tensile strength and low breaking pressure.

  Table 2 below shows characteristics after heating an annealed material of a smooth tube having an outer diameter of 9.52 mm and a wall thickness of 0.80 mm to 800 ° C. for 15 seconds.

  Comparative Example No. 2, No. 3, no. No sample 7 was prepared, and Comparative Example No. 3, no. 4 and no. No. 5 was not tested because a failure occurred in the stress corrosion cracking test and the hydrogen embrittlement test.

  As shown in Table 2, Examples 1 to 11 had high tensile strength and breaking pressure even after annealing the annealed material to 800 ° C. for 15 seconds. On the other hand, in Comparative Example 1, these were low.

(Example 2: Semi-hard material)
The steps (a) to (g) are the same as in the case of the smooth tube.
(H) Next, the annealed material was blanked by a die at a processing rate of 10% to be drawn to an outer diameter of 8.50 mm and a wall thickness of 0.82 mm to obtain a test material.

  Table 3 below shows the characteristics of a semi-hard material having an outer diameter of 8.50 mm and a wall thickness of 0.82 mm, and Table 4 below shows the result after heating this semi-hard material to 800 ° C. for 15 seconds. Show properties.

  As shown in Table 3, also in this semi-rigid material, Examples 12 to 15 have high tensile strength and fracture pressure, and no cracks are generated in the stress corrosion cracking test and the hydrogen embrittlement test. Further, as shown in Table 4, the tensile strength and breaking pressure after heating the semi-hard annealed material to 800 ° C. for 15 seconds were sufficiently high. In contrast, Comparative Example 8 had low tensile strength and breaking pressure.

(Example 3: internally grooved tube)
The steps (a) to (e) are the same as in the case of the smooth tube.
(I) Next, the rolled blank was drawn to produce a rolled rolled blank.
(J) A base tube for grooved rolling was subjected to intermediate annealing with an induction heater.
(K) The grooved rolling element tube subjected to intermediate annealing was subjected to grooved rolling to produce an internally grooved tube having an outer diameter of 7 mm and a bottom wall thickness of 0.23 mm. This inner surface groove has a fin height of 0.16 mm, a lead angle of 35 °, and a fin crest number of 55.
(L) The inner grooved tube was passed through a heating zone in a reducing gas atmosphere at an atmospheric temperature of 550 to 650 ° C. for 60 to 120 minutes in an annealing furnace, and then gradually cooled to room temperature through a cooling zone. .

  Table 5 below shows the characteristics of the annealed copper alloy tube having an inner diameter of 7.00 mm and a bottom wall thickness of 0.23 mm. Table 6 shows the result of heating the annealed material to 800 ° C. for 15 seconds. It is a characteristic.

  As shown in Table 5, the inner surface grooved pipes of Examples 16 to 19 have high tensile strength and breaking pressure, and no cracks are generated in the stress corrosion cracking test and the hydrogen embrittlement test. Further, as shown in Table 6, the tensile strength and breaking pressure after heating the semi-hard annealed material to 800 ° C. for 15 seconds were sufficiently high. In contrast, Comparative Example 9 had low tensile strength and breaking pressure.

(Example 4: Casting type rolling method (cast and roll method))
(M) Using electrolytic copper as a raw material, predetermined Sn was added to the molten metal, Zn was further selectively added, and then a Cu-P master alloy was added to prepare a molten metal having a predetermined composition. Thereafter, a raw pipe was produced by continuous casting into a horizontal mold, and further, a rolled raw pipe having an outer diameter of 35 mm and a wall thickness of 2.3 mm was produced while rotating the roll.

  Thereafter, a copper alloy tube was manufactured in the same step as the step (f) after the smooth tube or the step (i) after the inner grooved tube.

  Table 7 below shows the characteristics of an annealed material of a cast-type rolling method (cast and roll method) smooth tube having an outer diameter of 9.52 mm and a bottom wall thickness of 0.80 mm. Table 8 also shows the annealing material at 800 ° C. The characteristic after heating for 15 seconds.

  As shown in Table 7, the smooth tube of Example 20 has high tensile strength and fracture pressure, and no cracks are generated in the stress corrosion cracking test and the hydrogen embrittlement test. Further, as shown in Table 8, the tensile strength and breaking pressure after heating the annealed material of the smooth tube to 800 ° C. for 15 seconds were sufficiently high. In contrast, Comparative Example 10 had low tensile strength and breaking pressure.

  Since the copper alloy tube of the present invention has excellent pressure fracture strength, the heat transfer tube (smooth tube and inner grooved tube) of the heat exchanger using a refrigerant such as carbon dioxide and chlorofluorocarbon, the evaporator of the heat exchanger Can be used for refrigerant piping or in-machine piping connecting the condenser and the condenser. Moreover, since the copper alloy pipe of the present invention has excellent pressure fracture strength even after brazing heating, it is used for a heat transfer pipe having a brazed portion, a water pipe, a kerosene pipe, a heat pipe, a four-way valve, a control copper pipe, and the like. be able to.

Claims (6)

Sn: 0.1 to 2.0 mass%, P: 0.005 to 0.1 mass%, S: 0.005 mass% or less, O: 0.005 mass% or less, and H: 0.0002 mass% An average measured in a direction perpendicular to the thickness direction of the pipe in a cross section perpendicular to the pipe axis, having a composition comprising the following, the balance consisting of Cu and inevitable impurities, and having a tensile strength of 255 N / mm ² or more A copper alloy tube having a crystal grain size of 30 μm or less, wherein the tensile strength of the copper alloy tube is σa, the fracture pressure is PFa, and the tensile strength of the phosphorus-deoxidized copper tube having the same outer diameter and thickness as the copper alloy tube A copper alloy tube for a heat exchanger, wherein (PFa) / (σa)> (PFd) / (σd) where σd is the strength and PFd is the breaking pressure. Furthermore, Zn: 0.01 thru | or 1.0 mass% is contained, The copper alloy pipe for heat exchangers of Claim 1 characterized by the above-mentioned. The total content of one or more elements selected from the group consisting of Fe, Ni, Mn, Mg, Cr, Ti and Ag is less than 0.07% by mass in total. Copper alloy tube for heat exchanger. The copper alloy tube for a heat exchanger according to any one of claims 1 to 3, wherein a drawing process is performed. 5. The average crystal grain size measured in a direction perpendicular to the thickness direction of the tube in a cross section orthogonal to the tube axis after being heated at 800 ° C. for 15 seconds is 100 μm or less. A copper alloy tube for a heat exchanger as described in 1. The copper alloy tube for heat exchanger according to any one of claims 1 to 5, wherein the copper alloy tube is an internally grooved tube.