JP4818179B2 - Copper alloy tube - Google Patents

Description

  The present invention relates to a copper alloy tube that has excellent pressure fracture strength and workability and is useful as a heat exchanger.

  For example, a heat exchanger of an air conditioner passes a U-shaped copper tube bent into a hairpin shape (hereinafter referred to as a copper tube also includes a copper alloy tube) through an aluminum fin through-hole and expands the copper tube with a jig. Then, the copper tube and aluminum fin are brought into close contact with each other, and the open end of the copper tube is expanded, and a copper tube (return bend) bent into a U-shape is inserted into the expanded portion, and a solder such as phosphor copper braze A heat exchanger in which a plurality of hairpin-shaped copper tubes are connected by a return bend copper tube is manufactured by brazing the copper tube (return bend) to the expanded portion of the hairpin-shaped copper tube with a material.

  In-machine piping connecting the heat exchanger and various components such as a four-way valve and an accumulator is also connected by expansion and brazing. 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. Further, CO ₂ that is a natural refrigerant has come to be 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.

  When the burst pressure of the heat transfer tube is P, the outer diameter of the heat transfer tube is D, the tensile strength of the heat transfer tube is σ, and the wall thickness of the heat transfer tube is t (in the case of an internally grooved tube), Has a relationship of P = 2 × σ × t / (D−0.8t). 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 thickness calculated with respect to the pressure obtained by multiplying the above P by a safety factor S (usually about 2.5 to 5) 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 the heat transfer tube, the mass of the heat exchanger is increased and the price is increased. There has been a strong demand for heat tubes.

  In order to meet such demands, for example, Co: 0.02 to 0.2 mass%, P: 0.01 to 0.05 mass%, as a copper alloy tube having excellent 0.2% proof stress and fatigue strength , C: 1 to 20 ppm, the remainder being made of Cu and inevitable impurities, and oxygen of impurities is 50 ppm or less, and a seamless copper alloy tube for a heat exchanger (Patent Document 1) has been proposed. Further, Co: 0.03 to 0.15 mass%, P: 0.02 to 0.05 mass% is contained so as to be Co / P: 4 or less, and the balance is made of Cu and inevitable impurities, and is unavoidable. It has a composition in which the oxygen content contained as impurities is regulated to 50 ppm or less, and further has recrystallized grains having an average crystal grain size of 20 μm or less, and the recrystallized grains have a fine average grain size of 1 to 30 nm. A copper alloy tube (Patent Document 2) in which precipitates are dispersed has been proposed.

JP2000-1728 JP 2001-316742 A

  However, the copper alloy of Patent Document 1 is excellent in 0.2% proof stress and fatigue strength due to precipitation strengthening by Co phosphide, but since the emphasis is on strength, the 0.2% proof stress value is high, and the heat exchanger At the time of assembling, when it was bent into a hairpin tube, cracking was likely to occur, resulting in a decrease in yield. In addition, Co phosphide, which is a strengthening mechanism of precipitation strengthening, is heated at a temperature higher than that of phosphor copper brazing, or even if the heating temperature is about the brazing temperature of phosphor copper brazing. There is a problem that the strength such as tensile strength, proof stress and breaking pressure after heating is lowered.

  In addition, the copper alloy of Patent Document 2 is excellent in fatigue strength by precipitation strengthening by fine precipitates of Co phosphide, as in Patent Document 1, but in the examples, the crystal grain size is 10 μm or less. Naturally, the tensile strength and 0.2% proof stress are large, the elongation is small, and there is a risk of cracking when bending into a hairpin tube, as in the case of Patent Document 1. There were problems such as occasional equipment failures. On the other hand, as described above, if the brazing temperature of the phosphor copper brazing is high or the brazing time is long, the phosphide of Co in the precipitation strengthening mechanism is dissolved, and the strength after heating is low. It was.

  The present invention has been made in view of such a problem, and is a copper alloy tube having high tensile strength and 0.2% proof stress and superior in strength, and has improved hairpin bending workability and tube expandability. An object of the present invention is to provide a copper alloy tube useful for a high-strength heat exchanger.

The copper alloy tube according to the present invention has Co: 0.03 to 0.15 mass%, Sn: 0.1 to 1.0 mass%, P: 0.004 to 0.08 mass%, and S: 0.005. mass% or less, O: 0.005 wt% or less, and H: 0.0002 mass% or less, have a composition the balance being Cu and unavoidable impurities, the average crystal grain size is 10 to 35μm It is characterized by that.

Further, in the present invention, it is preferable that the tensile strength of the tube 250 to 300N / mm ^2, elongation of the 40% or more.

Furthermore, in the present invention, it is preferable that the tensile strength after heating at 800 ° C. for 15 seconds is 235 N / mm ² or more and the average crystal grain size is 100 μm or less.

  Furthermore, the copper alloy is, for example, an internally grooved tube in which grooves are formed on the tube inner surface.

The present invention is described in detail below. As a result of various experimental studies by the present inventors, a copper alloy tube capable of solving the problems of the present invention by appropriately defining Co content, Sn content, P content, S content, tensile strength, etc. Found that can be obtained.

  Next, regarding the composition of the copper alloy tube useful for the heat exchanger of the present invention, the reason for adding the component and the reason for limiting the composition will be described.

“Co: 0.03 to 0.15 mass%”
Co is a component that improves the tensile strength by forming precipitates with a compound with P in the copper alloy tube of the present invention. If the Co content exceeds 0.15% by mass, the strength becomes too high and the elongation decreases, which adversely affects workability. Moreover, desired intensity | strength cannot be obtained as Co content of the copper alloy of this invention is less than 0.03 mass%. Therefore, the Co content needs to be 0.03 to 0.15 mass%.

“Sn: 0.1 to 1.0 mass%”
Sn improves the tensile strength by solid solution hardening and suppresses the coarsening of the crystal grain size against the heat effect of brazing such as phosphor copper brazing, thereby improving the heat resistance. If the Sn content exceeds 1.0% by mass, solidification segregation in the ingot becomes severe, and segregation may not be completely eliminated by normal hot extrusion and / or thermomechanical treatment. It leads to mechanical properties, bendability, texture after brazing and non-uniformity of mechanical properties. Also, in order to increase the extrusion pressure and make the same extrusion pressure as that of an alloy having Sn of 1% by mass or less, it is necessary to raise the extrusion temperature, thereby increasing the surface oxidation of the extruded material and reducing the productivity. And the surface defects of the copper alloy tube increase. Further, if the Sn content in the alloy of the present invention is less than 0.1% by mass, sufficient tensile strength cannot be obtained after annealing and brazing heating, and a fine crystal grain size cannot be obtained. Moreover, the effect which suppresses that a intensity | strength falls at the time of brazing heating by a phosphor copper brazing etc., and the effect which prevents that a crystal grain coarsens will become inadequate. Therefore, it is necessary that the Sn content be 0.1 to 1.0 mass%.

“P: 0.004 to 0.08 mass%”
In the alloy of the present invention, P is a component that improves the tensile strength by forming a precipitate CoP with a compound with Co as described above. When the P content in the copper alloy of the present invention exceeds 0.08% by mass, the electrical conductivity is lowered, and hot workability and cold workability are inhibited. On the other hand, when the P content is less than 0.004% by mass, the predetermined strength due to the CoP precipitate cannot be obtained, and deoxidation becomes insufficient, and the oxide is caught in the ingot. While soundness falls, the bending property of the manufactured pipe | tube becomes easy to fall. Therefore, it is necessary to make the P content 0.004 to 0.08 mass%.

“S: 0.005 mass% or less”
S is present in the matrix by forming a compound with Cu in the alloy of the present invention. When 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 and drawn, the Cu-S compound inside the material stretches in the axial direction of the tube and cracks occur at the Cu-S compound interface. It easily causes surface flaws and cracks during product processing and in the product, which reduces 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 copper alloy tube of the present invention needs to have an S content of 0.005% or less, desirably 0.003% or less, and more desirably 0.0015% or less. 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 because of being incorporated into the steel, the amount of low-grade Cu ingots and scrap used is reduced, the SOx gas in the melting atmosphere is reduced, the selection of appropriate furnace materials, Mg, Measures such as adding a trace amount of an element having strong affinity for S, such as Ca, to the molten metal are effective.

  As with S, impurity elements As, Bi, Sb, Pb, Se, and Te other than S also reduce the soundness of ingots, hot extruded materials, and cold worked materials, and bend pipes. Therefore, the total content of these elements is preferably 0.0015% or less, desirably 0.0010% or less, and more desirably 0.0005% or less.

“O: 0.005 mass% or less”
In the copper alloy pipe of the present invention, when the O content exceeds 0.005 mass%, one or more of Cu, Sn and Co oxides are caught in the ingot, and the soundness of the ingot is improved. In addition to the decrease, the bending workability of the manufactured pipe tends to decrease. For this reason, it is necessary to make content of O into 0.005 mass%. 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 more hydrogen is taken into the molten metal during melt casting, it is present in the ingot in a state of pinhole and grain boundary enrichment, and cracks are generated during hot extrusion. Further, even after the extrusion, blistering of H is likely to occur at the grain boundaries during annealing, and the product yield decreases. 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 (2 ppm) or less, the raw material is dried at the time of melting and casting, the red heat of the molten metal is reduced, the dew point of the atmosphere in contact with the molten metal is reduced, and the molten metal before phosphorus is added. It is effective to take measures such as oxidizing

“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. Also, in the heat exchanger assembly process, wear of the expanded burette during tube expansion when the heat transfer tube is brought into close contact with the mandrel or aluminum fin during bending of the hairpin can also be reduced.

  When the Zn content exceeds 1.0% by mass, the stress corrosion cracking sensitivity becomes high. Further, when the Zn content is less than 0.01% by mass, the above-described effects are not sufficient. Therefore, the Zn content is set to 0.01 to 1.0% by mass.

“Total of less than 0.05% 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. If the total content of these elements exceeds 0.05% by mass, the extrusion pressure will increase, so if you try to extrude with the same pressing force as those without adding these elements, increase the hot extrusion temperature. Is required. 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 of Fe, Ni, Mn, Mg, Cr, Ti, Zr, and Ag be less than 0.05% by mass. Further, the total content is more preferably less than 0.03%, and further preferably less than 0.02% by mass.

“Tensile strength: 250 to 300 N / mm ² ”
Tensile strength is an important indicator of tube strength. As described above, the tensile strength of a tube is related to the fracture strength, and the higher the tensile strength, the thinner the tube. . When the tensile strength is less than 250 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. If the tensile strength exceeds 300 N / mm ² , cracks in the bending process of the hairpin tube and tube expansion force becomes too high during tube expansion, and the tube cannot be expanded or the bar to which the burette of the tube is fixed breaks. There is a risk of problems such as these. Therefore, the tensile strength needs to be 250 to 300 N / mm ² . The tensile strength here is the tensile strength in the tube axis direction of the copper alloy tube having the composition of the present invention that is annealed to be a soft material.

“Elongation: 40% or more”
Elongation indicates the workability of the tube. If the elongation is less than 40%, the tube does not extend sufficiently at the time of hairpin bending, cracking occurs in the bent portion, and inconvenience occurs at the time of processing the piping in the machine. Accordingly, the elongation needs to be 40% or more.

“Crystal grain size: average crystal grain size is 10 to 35 μm”
The grain size plays an important role in the strength and workability of the material. In general, if the crystal grain size is small, the strength is high but the workability is lowered, and if the crystal grain size is large, the strength is lowered and the workability is improved. When the crystal grain size exceeds 35 μm, the strength decreases, the pressure resistance when incorporated in a heat exchanger such as an air conditioner becomes insufficient, and the strength after brazing cannot be sufficiently maintained. On the other hand, if the grain size is lower than 10 μm, it is too hard to cause cracks in the bending process of the hairpin tube, the tube expansion force becomes too high at the time of tube expansion processing, and the tube cannot be expanded, or there is a bar to which the expanded burette is fixed There is a high possibility that problems such as breaking will occur.

  For the average crystal grain size, the average crystal grain size in the thickness direction was measured for the cross section parallel to the axial direction of the copper alloy tube by the cutting method defined in JISH0501, and this was measured at any 10 locations in the pipe axis direction. The average of these was measured as the average grain size.

“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, the copper alloy tube is affected by heat due to brazing. Simulating the thermal effect of this brazing, the strength after heating to 800 ° C. for 15 seconds is examined. If the tensile strength after heating at 800 ° C. for 15 seconds is less than 235 N / mm ² , fatigue failure tends to occur when the HFC-based refrigerant and carbon dioxide refrigerant have high operating pressure.

“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”
When processed into a heat exchanger, the crystal grain size becomes coarse after heating for 15 seconds at 800 ° C., which simulates the thermal effect of brazing. However, if the value exceeds 100 μm, the decrease in pressure resistance at the brazed part is large. When used in a heat exchanger for HFC-based chlorofluorocarbon refrigerant and carbon dioxide refrigerant having a high operating pressure, the reliability decreases. Therefore, the average crystal grain size in the thickness direction of the tube axis parallel section is preferably 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 it has a higher tensile strength and a smaller crystal grain size than a phosphorous deoxidized copper tube. In particular, because the tensile strength is high, it is difficult to stretch in the drawing direction during rolling, so the groove of the grooved plug can be smoothly filled with the alloy tube meat, and the inner surface grooved tube with a good fin shape can be filled at high speed. It becomes possible to process with. If the tensile strength of the copper alloy tube is insufficient, the copper alloy tube will stretch in the drawing direction during rolling, and even if the groove of the grooved plug presses the inner surface of the copper alloy tube, Since the inner surface portion does not sufficiently enter the groove of the grooved plug, it is difficult to process the groove, and the processing speed must be reduced.

Next, the method for producing a copper alloy tube of the present invention will be described below by taking the case of a smooth tube and an internally grooved tube as an example.
(A) Melting casting After electrolytic copper is melted in the atmosphere and copper is melted, Co and Sn are added, and further the P component is adjusted by adding Cu-15 mass% P intermediate alloy. After adjusting to a predetermined component, it is cast into a billet of a predetermined size.
(B) Heating The billet is heated to 650 to 850 ° C.
(C) Hot extrusion A hot billet is perforated and hot extruded at 750 to 950 ° C. The processing rate of hot extrusion ([cross-sectional area of the perforated billet−cross-sectional area of the raw tube after hot extrusion] / [cross-sectional area of the perforated billet] × 100%) is desirably 80% or more. , More preferably 90% or more.
(D) Quenching treatment In order for the copper alloy tube of the present invention to exhibit predetermined characteristics, it is necessary to dissolve Co after extrusion and to prevent coarsening of crystal grains due to recrystallization. For example, the hot extruded material is rapidly cooled by a method such as water cooling. After hot extrusion, cooling is performed so that the cooling rate until the surface temperature of the extruded tube reaches 300 ° C. is 10 ° C./second or more, preferably 15 ° C./second or more, more preferably 20 ° C./second or more. Is preferred.
(E) Rolling The extruded element tube is rolled. By reducing the rolling process rate to 95% or less, preferably 90% or less in terms of cross-sectional reduction, product defects can be reduced.
(F) Drawing process A rolling process is performed on the rolled blank to produce a blank having a predetermined size. Usually, drawing is performed using several drawing machines, but surface defects and internal cracks can be reduced by setting the processing rate (cross-sectional reduction rate) by each drawing machine to 40% or less.
(G) Annealing The drawing tube is annealed under conditions where recrystallization and Co—P compound precipitation occur. Elongation is restored by recrystallization, the workability of the tube is improved, and the desired tensile strength and yield strength can be maintained by precipitation of the Co-P compound. In order to produce the copper alloy tube of the present invention, it is desirable to hold the drawing tube at a substantial temperature of 400 to 700 ° C. for about 5 to 120 minutes. 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. Normally, continuous annealing with a roller hearth furnace is performed, but high-frequency heating, short-time heating, high-speed cooling, and short-time heating annealing may be performed using a high-frequency induction heating furnace. The smooth tube is manufactured through the above steps.
(H) Internal grooved processing In the case of an internally grooved tube, a grooved rolling process is further performed on the inner surface of the annealed smooth tube.
(I) Annealing Thereafter, the processed inner grooved tube is annealed as necessary. The annealing conditions are the same as in the above (g). Thereby, an internally grooved tube is processed.

  Next, examples of the present invention will be described in comparison with comparative examples that are out of the scope of the present invention.

(First embodiment)
First, an example of a smooth tube will be described.

  After adding Co and Sn to the molten metal obtained by melting electrolytic copper, and further adding Zn as necessary, a Cu-P master alloy is added to produce a molten metal having a predetermined composition and having a diameter of 300 mm. Cast into billets.

  Next, after the billet was heated to 820 to 950 ° C., the center of the billet was pierced, and an extruded element tube having an outer diameter of 100 mm and a wall thickness of 10 mm was produced by hot extrusion. This cross-sectional reduction rate is 90% or more. The raw tube after extrusion was rapidly cooled, and the average cooling rate up to 300 ° C. was estimated to be 20 ° C./second or more from the time from immediately after extrusion to water cooling and the surface temperature of the extruded raw tube after water cooling.

  Next, the extruded element tube was rolled and drawn to produce an element tube having an outer diameter of 9.52 mm and a wall thickness of 0.80 mm. The cross-sectional reduction rate in rolling was 90% or less, and the processing rate per pass in drawing was 40% or less.

  Next, the drawing tube is heated to 560 to 620 ° C. (substance temperature) (average temperature increase rate of 10 to 25 ° C./min) in a roller hearth furnace in a reducing gas atmosphere and held at that temperature for 30 to 90 minutes. Then, it was cooled to room temperature to obtain a test material.

(Second embodiment)
Next, an embodiment of the internally grooved tube will be described. The process from melting to drawing is the same as in the case of the smooth tube described above. The smooth tube after drawing was used as a tube for rolling with grooves, and this tube was subjected to intermediate annealing with an induction heater.

  Groove-rolling processing is performed on the intermediate annealed grooved rolling element tube, and the inner surface grooved tube has an outer diameter of 7 mm, a bottom wall thickness of 0.23 mm, a fin height of 0.16 mm, a lead angle of 35 °, and a groove number of 55 Was made.

  The inner grooved tube was passed through a heating zone at an ambient temperature of 600 ° C. in a reducing gas atmosphere for 120 minutes in an annealing furnace, and then gradually cooled to room temperature through a cooling zone.

(Test methods for Examples and Comparative Examples)
The bending test was performed as follows. Ten tubes having a length of 1000 mm were sampled from the test material, and the first example was hairpin bent at a pitch of 25 mm and the second example was pitched 20 mm, and the presence or absence of cracks in the bent portion was confirmed. FIG. 1 is a diagram showing the bending pitch of the test tube. As shown in FIG. 1, the bending pitch is the center interval of the tube 1 in the parallel part after bending.

  The stress corrosion cracking test was conducted as follows. A 75 mm long test piece was cut out from the tube, degreased and dried, and then the desiccator containing 11.8% or more of ammonia water diluted with an equal amount of pure water as defined in JISK8085 was placed 50 mm from the liquid surface. Separated 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. No cracking is indicated by ○, and cracking is indicated by ×.

  The tool wear test was performed as follows. Examples and comparative pipes having an outer diameter of 12 mm and a wall thickness of 0.9 mm were manufactured. When 100 tons of the test material was cold drawn to an outer diameter of 9.52 mm and a wall thickness of 0.8 mm, the outer diameter of the copper tube processed part before and after the machining of the cemented carbide floating plug was measured, and the outer diameter decreased. The amount was tool wear.

Table 1 below shows the composition, mechanical strength and bending test results of the first example. Examples 1 to 7 satisfying the claims of the present application were all excellent in tensile strength, elongation, 0.2% proof stress, bending workability, and tensile strength after heating at 800 ° C. for 15 seconds. On the other hand, in Comparative Examples 1 to 12, which are out of the scope of the present invention, any of the above characteristics is inferior.

Table 2 below shows the results of the stress corrosion cracking test and the tool wear amount test of the first example. Real施例No. The test material 2 , comparative example No. of J ISC1220T equivalent product. 1, Comparative Example No. 1 in which Zn is below the lower limit of the claims. Comparative Example No. 8 containing Zn and 8 exceeding the upper limit of the scope of claims. I chose 9. In Comparative Example 4 in Table 1, the extrusion pressure was high and extrusion was not possible, and in Comparative Example 12, cracking occurred during hot extrusion and processing was not possible.

FIG. 2 is a diagram showing a state of wear of the floating plug. When the die 2 is provided outside the test tube 4, the plug 3 is arranged in the test tube 4 at a position aligned with the die 2, and the test tube 4 is pulled out in the direction of the arrow, the test tube 4 is connected to the die 2 and the floating plug 3. The diameter is reduced between. At this time, the force in the direction of the arrow acts on the plug 3 due to the frictional force generated by pulling out the test tube 4, and the wear at the boundary portion between the approach portion 3b and the bearing portion 3a of the plug 3 is the most severe. Table 2 shows the wear of the boundary portion between the approach portion 3b and the bearing portion 3a of the plug 3. Stress corrosion cracking tends to occur when the Zn content is high, and tool wear is improved as the Zn content increases . As shown in Tables 1 and 2, since the second embodiment of the present invention do not contain Zn, although the tool wear amount is relatively large, stress corrosion cracking did not occur. Since Comparative Example 1 is phosphorous-deoxidized copper (not containing Co and Sn), tool wear is not so great, but strength is low. Since Comparative Example 8 contains Co and Sn, the amount of tool wear is large, and the Zn content is smaller than the range of claim 2 of the present application, so the effect of reducing the amount of tool wear is not obtained. Since Comparative Example 9 had a high Zn content, the amount of tool wear was small, but stress corrosion cracking occurred. In Comparative Example 8, since the components other than the Zn content satisfy the claims of the present invention, the same effects as those of Example 2 are shown, and the effect of the lower limit of the Zn content is obtained. Table 2 is provided for illustrative purposes.

  Table 3 below shows the mechanical strength and bending test results of the second example. In the second embodiment, among the smooth tubes of the first embodiment, those having the compositions of Example 2 and Comparative Examples 1 and 2 were subjected to inner surface groove rolling. As shown in Table 3, Example 2 was superior in tensile strength and tensile strength after heating at 800 ° C. for 15 seconds as compared with Comparative Examples 1 and 2. In addition, the stress corrosion cracking test result and the tool wear test result of Example 2 are as shown in Table 2.

  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 Refrigerant pipes and in-machine pipes connecting the condenser and the condenser, and parts of the heat exchanger can be used for four-way valves and accumulators. Moreover, since the copper alloy pipe of the present invention has an excellent pressure fracture strength even after brazing heating, it can be used for a heat transfer pipe having a brazed portion, an in-machine pipe, a refrigerant pipe, a heat pipe, and the like. Moreover, since the copper alloy tube of this invention is high intensity | strength and is excellent in hairpin bending workability and pipe expansion workability, it can be applied also to uses, such as kerosene piping, water piping, and a control copper tube.

It is a figure which shows the bending pitch of a copper pipe. It is a figure which shows the wear condition of a floating plug.

Explanation of symbols

2 Dies 3 Floating plug 4 Test tube 3a Bearing part 3b Approach part 5 part

Claims (4)

Co: 0.03 to 0.15 mass%, Sn: 0.1 to 1.0 mass%, P: 0.004 to 0.08 mass%, S: 0.005 mass% or less, O: 0.005 mass%, and H: 0.0002 mass% or less, have a composition the balance being Cu and unavoidable impurities, the copper alloy tube, wherein the average crystal grain diameter of 10 to 35 [mu] m. Copper alloy tube according to claim 1, the tensile strength of the tube 250 to 300N / mm ^2, elongation, characterized in that a on 40% or more. The copper alloy tube according to claim 1 or 2, wherein the tensile strength after heating at 800 ° C for 15 seconds is 235 N / mm ² or more and the average crystal grain size is 100 µm or less. The copper alloy tube according to any one of claims 1 to 3, wherein the tube is an internally grooved tube in which a groove is formed on the tube inner surface.

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