JP6402043B2 - High strength copper alloy tube - Google Patents

Description

  The present invention relates to a copper alloy tube used as a heat transfer tube for a heat exchanger such as an air conditioner or a water heater.

  In general, a copper alloy tube excellent in heat conductivity and workability is applied to a heat transfer tube through which a heat medium of a heat exchanger flows. For example, a heat exchanger of an air conditioner has a structure in which a large number of plate-like aluminum fins are stacked and a copper alloy tube meandering is passed therethrough. In order to manufacture such a heat exchanger, first, a copper alloy tube is bent into a hairpin shape to form a U-shaped copper alloy tube, and both ends are passed through through holes formed in aluminum fins. The tube is expanded and brought into close contact with the fin collar formed at the edge of the through hole of the aluminum fin. A plurality of U-shaped copper alloy pipes penetrated by aluminum fins are connected to each other by expanding the end (open end) and inserting the end of another U-shaped copper alloy pipe (return bend copper pipe), The connecting portion is joined by brazing with a brazing material such as phosphor copper brazing (for example, JISZ3264, BCuP-2).

In addition, a natural refrigerant heat pump water heater known by the nickname of Ecocute (registered trademark of Kansai Electric Power Co., Inc.) is a copper alloy pipe (CO) for circulating CO ₂ as a refrigerant in a pipe (water pipe) through which water flows. ₂ refrigerant pipes) are spirally wound. Accordingly, first, a copper alloy tube is processed into a spiral shape, a water pipe is passed through it, and the water pipe with the CO ₂ refrigerant pipe wound is processed into a U-shape, and then in a furnace with a phosphor copper braze or the like. By brazing together by brazing, the water pipe and the CO ₂ refrigerant pipe are brought into close contact with each other. Further, it is manufactured by connecting a water pipe, a CO ₂ refrigerant pipe, and the like by brazing with an accumulator, a compressor, and the like using an in-machine pipe of a copper alloy pipe.

  Thus, the copper alloy tube used in the heat exchanger is required to have good bending workability in addition to thermal conductivity and brazing. On the other hand, in recent years, from the viewpoint of resource saving, copper alloy pipes have been required to be thin and have a long life, and in order to satisfy these requirements, copper alloy pipes having a strength that can withstand severe internal pressure for a long period of time have been developed. It has been demanded.

  For example, Patent Document 1 contains a predetermined amount of Co, P, Sn, and Zn, and the balance is made of Cu and inevitable impurities. The Co content [Co], the P content [P], and the Sn content Between the amount [Sn] and the Zn content [Zn] 2.4 ≦ ([Co] −0.02) / [P] ≦ 5.2 and 0.20 ≦ [Co] +0.5 [P ] A heat-resistant copper alloy material having a relationship of +0.9 [Sn] +0.1 [Zn] ≦ 0.54 is described. Patent Document 1 describes that the heat-resistant copper alloy material is a seamless copper alloy tube.

  Patent Document 2 contains a predetermined amount of Co, P, Sn, and O, the balance is made of Cu and inevitable impurities, and 2. between the Co content [Co] and the P content [P]. A high-strength, high-conductivity copper alloy tube having a relationship of 9 ≦ ([Co] −0.007) / ([P] −0.008) ≦ 6.1 and made by a process including hot extrusion is described. Has been. Patent Document 2 discloses that when a high-strength, high-conductivity copper alloy tube is observed with a transmission electron microscope (TEM), fine precipitates are uniformly dispersed in crystal grains, and the average of the intra-grain precipitates. It is described that the particle diameter is 1.5 to 20 nm, or 90% or more of all intragranular precipitates are 30 nm or less.

International Publication No. 2004/079026 International Publication No. 2009/119222

In conventional copper alloy tubes, the tensile strength obtained by a tensile test can be increased by controlling the component composition and intragranular precipitates. However, in the conventional copper alloy pipe, since the grain boundary precipitates are not controlled, the elongation obtained by the tensile test was small. Therefore, the thinned copper alloy tube has a problem that cracking or the like occurs when it is bent into a hairpin shape or a spiral shape.
Therefore, the present invention was devised to solve such problems, and the problem is that even when the wall thickness is reduced, cracks and the like do not occur during bending, and the high-strength copper alloy has excellent bending workability. To provide a tube.

  In order to solve the above problems, a high-strength copper alloy tube according to the present invention contains Co: 0.05 to 0.40 mass%, P: 0.02 to 0.10 mass%, with the balance being Cu and A high-strength copper alloy tube made of a copper alloy that is an unavoidable impurity, the average diameter of the grain boundary precipitates at the center of the tube thickness in a plane parallel to the side surface of the tube being 150 nm or less, The average number per grain boundary length is 5000 pieces / mm or less.

  Thus, the high-strength copper alloy tube of the present invention contains a predetermined amount of Co and P, and the average number of grain boundary precipitates and the average number per grain boundary length are high. Even an alloy tube having a tensile strength can maintain its elongation. Thereby, the bending workability of the high-strength copper alloy tube of the present invention is improved.

  In the high-strength copper alloy tube according to the present invention, the copper alloy contains Ni: 0.005 to 0.100 mass%, Zn: 0.005 to 1.000 mass%, and Sn: 0.05 to 1.00 mass%. It is preferable to further contain at least one of%. In the high-strength copper alloy tube according to the present invention, the copper alloy further contains one or more selected from Fe, Mn, Mg, Cr, Ti, Zr and Ag in total less than 0.10% by mass. It is preferable.

  Thus, in the high-strength copper alloy tube of the present invention, the copper alloy further contains a predetermined amount of any one or more of Ni, Zn and Sn, and the copper alloy is Fe, Mn, Mg, Cr. By further including a predetermined amount of one or more selected from Ti, Zr and Ag, the tensile strength is further improved even in the case of a thinned alloy tube.

  According to the high-strength copper alloy tube according to the present invention, even when it is thinned, it does not generate cracks during bending and has excellent bending workability.

It is a figure which shows typically the grain boundary precipitate in a transmission electron micrograph. It is a figure which shows the process flow of the manufacturing method of the high intensity | strength copper alloy pipe | tube which concerns on this invention. It is a figure which shows typically the procedure which produces the thin film for a grain boundary precipitate measurement.

An embodiment of a high-strength copper alloy tube (hereinafter referred to as a copper alloy tube) according to the present invention will be described.
The copper alloy tube of the present invention is made of a copper alloy having a predetermined component composition and has a predetermined alloy structure.
First, the component composition of the copper alloy pipe of the present invention will be described.
The first component composition contains a predetermined amount of Co and P, and the balance consists of Cu and inevitable impurities. The reason for limiting the numerical values of each component will be described below.

(Co: 0.05-0.40 mass%)
Co forms a compound with P (suitably referred to as a Co—P compound) in a copper alloy, and precipitates in crystal grains and in grain boundaries. In particular, the Co—P compound precipitated in the crystal grains has an effect of increasing the tensile strength of the copper alloy tube. In addition, the Co—P compound acts as pinning particles that suppress the coarsening of crystal grains in the heat treatment for brazing, and therefore suppresses the decrease in tensile strength due to the heat treatment, particularly brazing at a high temperature of 800 ° C. or higher. Ensure tensile strength after treatment.

  These effects are improved as the amount of intra-granular precipitation of the Co—P compound increases. When the Co content is less than 0.05% by mass, the amount of intra-granular precipitation is small, and the above effect cannot be obtained sufficiently. On the other hand, if the Co content exceeds 0.40% by mass, the Co—P compound is excessively precipitated in the crystal grains and at the grain boundaries, so that the tensile strength becomes excessive or the elongation decreases and bending occurs. There is a possibility that the workability is insufficient or the deformation resistance becomes excessive due to hot extrusion or the like, resulting in cracks. Therefore, the Co content is 0.05 to 0.40 mass%. The Co content is preferably 0.15% by mass or more from the viewpoint of improving the tensile strength, and preferably 0.30% by mass or less from the viewpoint of improvement of elongation and the like.

(P: 0.02-0.10 mass%)
P is generally added for deoxidation of copper alloys. Moreover, P produces | generates the compound (Co-P compound) with Co in a copper alloy, precipitates in a crystal grain and a grain boundary, and has the effect of improving tensile strength as above-mentioned. When the P content is less than 0.02 mass%, the amount of intra-grain precipitation of the Co—P compound is small, and the above effects cannot be obtained sufficiently. In addition, deoxidation becomes insufficient, oxide is caught in the ingot, the soundness of the ingot is lowered, and the bending workability of the manufactured pipe is lowered. On the other hand, if the content of P exceeds 0.10% by mass, cracks may occur in hot working or cold working. Therefore, the content of P is set to 0.02 to 0.10% by mass. The P content is preferably 0.03% by mass or more from the viewpoint of improving tensile strength and the like, and preferably 0.07% by mass or less from the viewpoint of preventing cracking.

(Inevitable impurities)
Inevitable impurities are inevitably contained in the copper alloy ingot and are contained to such an extent that they do not impair the various characteristics of the copper alloy tube. Inevitable impurities are S, As, Bi, Sb, Pb, Se, Te, O, and the like. The content is S: 0.005 mass% or less, the total (total amount) of As, Bi, Sb, Pb, Se, Te is 0.0015 mass% or less, and O: 0.003 mass% or less. preferable. In addition, when the amount of H taken into the molten metal at the time of melting and casting increases, the amount of H that has decreased in solid solution during solidification precipitates at the grain boundaries of the ingot, forming a large number of pinholes and cracking during hot extrusion. May occur. Therefore, the H content is preferably 0.0002% by mass or less.

  The second component composition preferably further contains a predetermined amount of at least one of Ni, Zn and Sn in addition to the first component composition. Hereinafter, the reason for limiting the numerical value of each component will be described.

(Ni: 0.005-0.100 mass%)
Ni forms a ternary compound with Co and P (suitably referred to as (Co, Ni) -P compound) in a copper alloy and precipitates in crystal grains and in grain boundaries. This ternary compound (precipitate) improves the tensile strength of the copper alloy tube, like the Co-P compound. Further, the (Co, Ni) -P compound acts as pinning particles in the heat treatment and has an action of securing the tensile strength after brazing. Therefore, Ni can further improve the tensile strength without increasing the Co content.

  In order to sufficiently precipitate the (Co, Ni) -P compound and obtain the above effect, the Ni content is preferably 0.005% by mass or more. On the other hand, if the Ni content exceeds 0.100% by mass, the (Co, Ni) -P compound precipitates excessively, so that the tensile strength becomes excessive and the elongation decreases, resulting in insufficient bending workability. Therefore, the Ni content is preferably 0.005 to 1.000% by mass.

When the Ni content is increased beyond Ni, the precipitated ternary compound tends to be a (Ni, Co) -P compound having a composition with more Ni than Co. The ternary compound is closer to the nature of the lower Ni-P compounds of the solid solution temperature (Ni 2 _P), liable melted at the brazing process, the effect of the pinning particles is reduced. Therefore, the Ni content is more preferably 0.100% by mass or less and the Co content or less.

(Zn: 0.005 to 1.000% by mass)
Zn has the effect of improving the tensile strength, heat resistance, and fatigue strength of the copper alloy tube. Further, by containing Zn, the wettability of a brazing material such as phosphor copper brazing is improved in brazing a copper alloy tube. Furthermore, containing Zn has the effect of reducing the wear of tools used for cold rolling, drawing, rolling, etc., extending the life of drawing plugs and grooved plugs, etc., contributing to the reduction of production costs To do. In addition, when assembling copper alloy tubes into heat exchangers, the wear of the mandrel during bending is reduced, and the wear of the expanded burette is reduced during tube expansion when contacting the fin collar of the through hole of the aluminum fin. can do. In order to obtain these effects, the Zn content is preferably 0.005% by mass or more. On the other hand, when the Zn content exceeds 1.000 mass%, the stress corrosion cracking sensitivity increases. Therefore, the content of Zn is preferably 0.005 to 1.000% by mass.

(Sn: 0.05 to 1.00% by mass)
Sn improves the tensile strength by solid solution strengthening in the copper alloy. Moreover, Sn suppresses the coarsening of the crystal grain size and improves the heat resistance against the thermal effect due to annealing and brazing of the copper alloy tube. In order to obtain these effects, the Sn content is preferably 0.05% by mass or more. On the other hand, if the Sn content exceeds 1.00% by mass, solidification segregation in the ingot becomes severe, and segregation may not be completely eliminated in normal hot extrusion or thermomechanical processing. , Mechanical properties and bending workability, texture after brazing and mechanical properties become non-uniform. In addition, hot deformation resistance in hot extrusion becomes high, and there is a possibility that an extruded material cannot be produced. In order to obtain the same extrusion pressure as that of a copper alloy having a Sn content of 1.00% by mass or less, hot extrusion is performed. It is necessary to increase the temperature, the surface oxidation of the extruded material increases at a high temperature, and the productivity decreases and the surface defects of the copper alloy tube increase. Therefore, the Sn content is 0.05 to 1.00% by mass.

  In addition to the first or second component composition, the third component composition preferably further contains a predetermined amount in total of one or more selected from Fe, Mn, Mg, Cr, Ti, Zr and Ag. . The reason for limiting the numerical values of components such as Fe will be described below.

(Fe, Mn, Mg, Cr, Ti, Zr and Ag: less than 0.10 mass% in total)
Each of Fe, Mn, Mg, Cr, Ti, Zr and Ag is precipitated as a single compound or as a P compound such as Fe ₂ P and Mn ₃ P _{2 in the} crystal grains and in the grain boundaries, thereby allowing the Co—P Like a compound etc., there exists an effect which improves the tensile strength of a copper alloy pipe, and the tensile strength after brazing. On the other hand, when these elements are contained in a total of 0.10% by mass or more, P compounds such as Fe ₂ P and Mn ₃ P ₂ are excessively precipitated, so that the elongation is lowered and bending workability is insufficient. In addition, the hot deformation resistance in hot extrusion becomes high, and in order to obtain the same extrusion pressure as that of the copper alloy not containing the element, it is necessary to increase the hot extrusion temperature. It increases, resulting in decreased productivity and increased surface defects in copper alloy tubes. Accordingly, the total content of one or more selected from Fe, Mn, Mg, Cr, Ti, Zr, and Ag is less than 0.10% by mass.

Next, the alloy structure of the copper alloy tube of the present invention will be described.
In the copper alloy pipe of the present invention, the average diameter of grain boundary precipitates at the center of the pipe thickness in a plane parallel to the pipe side surface is 150 nm or less, and the average number of grain boundary precipitates per grain boundary length is 5000. It has an alloy structure that is not more than pieces / mm. Here, the tube thickness center portion refers to a range corresponding to a total of 100 nm, 50 nm in both thickness directions centering on a portion in the tube thickness direction 1/2. In addition to the component composition, the alloy structure is adjusted by controlling the intermediate annealing when manufacturing the copper alloy tube shown below.

  In the present invention, the grain boundary precipitate is the above-described Co—P compound, (Co, Ni) —P compound, simple substance such as Fe, or a compound of Fe and the like and P. The grain boundary precipitates are measured using a transmission electron microscope. As shown in FIG. 1, the precipitates deposited on the grain boundaries 2 of the crystal grains 1 are separated from the grain boundaries 2 by a predetermined distance. Together with the precipitate deposited in the vicinity of the grain boundary 2, the grain boundary precipitate 3 is obtained. Specifically, the grain boundary precipitate 3 is a precipitate deposited in a region having a width of 200 nm with the grain boundary 2 of the crystal grain 1 as the center. Here, the grain boundary 2 is a boundary between crystal grains 1 in which the orientation difference between adjacent crystal grains 1 measured by a crystal orientation analysis method is 15 ° or more. Hereinafter, the reason for limiting the numerical values of the average diameter and the average number of grain boundary precipitates will be described.

(Average diameter: 150 nm or less)
If the average diameter of the grain boundary precipitates exceeds 150 nm, the grain boundary breakage tends to occur, the elongation of the copper alloy tube is lowered, and the bending workability is lowered. Therefore, in the copper alloy tube of the present invention, the average diameter of the grain boundary precipitate is 150 nm or less, preferably 80 nm or less. In addition, the lower limit of the diameter of the grain boundary precipitate is 5 nm, which is the measurement limit with a transmission electron microscope. In the present invention, the diameter of the grain boundary precipitates is the diameter of the same circle as the particle area of the precipitates, that is, the equivalent circle diameter.

(Average number: 5000 pieces / mm or less)
When the average number of grain boundary precipitates exceeds 5000 / mm, grain boundary breakage tends to occur, the elongation of the copper alloy tube is lowered, and the bending workability is lowered. Therefore, in the copper alloy tube of the present invention, the average number of grain boundary precipitates is set to 5000 pieces / mm or less, preferably 3000 pieces / mm or less. The number of grain boundary precipitates is the value obtained by dividing the number (number) of grain boundary precipitates deposited in the field of view of the transmission electron microscope by the total length of the grain boundaries of the crystal grains present in the field of view. It shall be converted into the number per 1 mm.

Next, a method for producing the copper alloy tube will be described.
As shown in FIG. 2, the copper alloy tube manufacturing method includes a casting step S1, a homogenization heat treatment step S2, a hot extrusion step S3, a rolling drawing step S4, an intermediate annealing step S5, and a processing step. S6 and final annealing step S7 are included. Hereinafter, each step will be described.

(Casting process)
The casting step S1 is a step of melting and casting the copper alloy having the above component composition to form an ingot. As the melting method and conditions and the casting method and conditions, conventionally known methods and conditions are used.

(Homogenization heat treatment process)
The homogenization heat treatment step S2 is a step of improving the segregation of the ingot by subjecting the ingot to a homogenization heat treatment. Conventionally known methods and conditions are used as the method and conditions for the homogenization heat treatment, and the homogenization heat treatment temperature is preferably 680 to 800 ° C. and the holding time is preferably 1 minute to 2 hours.

(Hot extrusion process)
The hot extrusion step S3 is a step of hot extruding the ingot that has been subjected to the homogenization heat treatment to obtain an extruded material. Conventionally known methods and conditions are used for the hot extrusion method and conditions. The extrusion temperature is preferably 680 to 800 ° C., and the cross-sectional reduction rate by hot extrusion is preferably 80% or more. Moreover, it is preferable to rapidly cool the extruded material after hot extrusion at a cooling rate of 10 ° C./second or more until the surface temperature of the extruded material reaches 300 ° C. by a method such as water cooling.

(Rolling drawing process)
Rolling drawing process S4 is a process which performs cold rolling and drawing processing on the extruded material to obtain a drawing tube. Conventionally known methods and conditions are used for the cold rolling method and conditions, and the drawing method and conditions, but the cold rolling processing rate is reduced in cross section to reduce product defects during processing. Is preferably 95% or less, and more preferably 90% or less. Moreover, it is preferable that the processing rate of a drawing process shall be 40% or less. Usually, several drawing machines are used for drawing, but surface defects and internal cracks can be reduced by making the processing rate (cross-sectional reduction rate) by each drawing machine 40% or less.

(Intermediate annealing process)
The intermediate annealing step S5 is a step of annealing the drawing pipe. Conventionally known methods are used for the annealing method. And intermediate annealing process S5 controls the grain-boundary precipitate of a copper alloy pipe | tube by adjusting annealing conditions.

  In order to control the grain boundary precipitates, that is, to control the average diameter of the grain boundary precipitates to 150 nm or less and the number per grain boundary length to 5000 pieces / mm or less, the drawing tube is set to 800 to 950 ° C., It is necessary to carry out the annealing treatment for 10 seconds or more and 5 minutes or less, the temperature increase rate to the treatment temperature is 50 ° C./second or more, and the cooling rate to room temperature is 100 ° C./second or more. And it becomes possible to enlarge elongation of a copper alloy pipe | tube by controlling a grain boundary precipitate.

(Processing temperature: 800-950 ° C)
When the treatment temperature is less than 800 ° C., the average diameter of the grain boundary precipitates increases and the elongation of the copper alloy tube decreases. For this reason, the bending workability of the copper alloy tube is lowered. On the other hand, when the processing temperature exceeds 950 ° C., the crystal grain size increases, so that the processed structure remains in the copper alloy tube after the final annealing. Therefore, the elongation of the copper alloy tube is reduced and the bending workability is lowered. Therefore, the processing temperature in the intermediate annealing step S5 is set to 800 to 950 ° C. Further, from the viewpoint of improving the elongation of the copper alloy tube, the upper limit value of the processing temperature is preferably 900 ° C.

(Retention time: 10 seconds to 5 minutes)
When the holding time is less than 10 seconds, the average number of grain boundary precipitates increases and the elongation of the copper alloy tube decreases. For this reason, the bending workability of the copper alloy tube is lowered. On the other hand, when the holding time exceeds 5 minutes, the average diameter of the grain boundary precipitates increases and the elongation of the copper alloy tube decreases. For this reason, the bending workability of the copper alloy tube is lowered. Accordingly, the holding time in the intermediate annealing step S5 is set to 10 seconds or more and 5 minutes or less. Further, from the viewpoint of improving the elongation of the copper alloy tube, the upper limit value of the holding time is preferably 3 minutes.

(Temperature increase rate: 50 ° C / second or more)
When the heating rate is less than 50 ° C./second, the average number of grain boundary precipitates increases and the elongation of the copper alloy tube decreases. For this reason, the bending workability of the copper alloy tube is lowered. Therefore, the temperature increase rate in the intermediate annealing step S5 is set to 50 ° C./second or more. Further, from the viewpoint of improving the elongation of the copper alloy tube, the temperature rising rate is preferably 100 ° C./second or more.

(Cooling rate: 100 ° C / second or more)
When the cooling rate is less than 100 ° C./second, the average diameter of the grain boundary precipitate is increased and the elongation of the copper alloy tube is decreased. For this reason, the bending workability of the copper alloy tube is lowered. Therefore, the cooling rate in the intermediate annealing step S5 is set to 100 ° C./second or more. Further, from the viewpoint of improving the elongation of the copper alloy tube, the cooling rate is preferably 500 ° C./second or more.

(Processing process)
The processing step S6 is a step in which the annealed drawing tube is processed to form a processed tube. Here, when a smooth tube is used as the copper alloy tube of the present invention, the processed tube is a drawn tube, and the drawn drawing tube is further subjected to drawing to reduce the tube outer diameter to the product outer diameter. Reduce diameter. Further, when an internally grooved tube is used as the copper alloy tube of the present invention, the processed tube is a rolled tube, and the annealed drawing tube is subjected to a rolling process so that a predetermined shape is formed on the tube inner surface. Groove. The drawing method and conditions are the same as those in the rolling drawing step S4, and conventionally known methods and conditions are used as the rolling method and conditions.

(Final annealing process)
The final annealing step S7 is a step of annealing the processed tube. As the annealing method and conditions, conventionally known methods and conditions are used, but the processing temperature is preferably more than 450 ° C. and less than 700 ° C., and the annealing time is preferably 5 minutes to 1 hour. By performing this annealing step S7, the average diameter and number density of the intragranular precipitates in the processed tube are controlled, and the processed and hardened processed tube is softened and can be bent.

Next, examples of the present invention will be described.
Using electrolytic copper as a raw material, a predetermined amount of other components such as Co, P, Ni, Zn, Sn, and Fe was added as necessary to prepare molten metal having the composition shown in Table 1. An ingot having a diameter of 300 mm and a length of 3000 mm was semi-continuously cast from the produced molten metal at a casting temperature of 1200 ° C., and a billet having a length of 475 mm was cut out from the obtained ingot. After heating the billet in the range of 680 to 800 ° C. and holding it for 1 hour, immediately, an extruded element tube having an outer diameter of 100 mm and a wall thickness of 10 mm is produced by a hot extruder, and the surface temperature becomes 300 ° C. by water cooling. Until cooled. A drawn tube having an outer diameter of 10 mm and a wall thickness of 0.41 mm was produced by subjecting the extruded tube to cold rolling and drawing. The drawn pipe was subjected to the intermediate annealing shown in Table 1, and then subjected to a rolling process with a cross-section reduction rate of 40% to produce a rolled pipe having an outer diameter of 7 mm and a groove bottom thickness of 0.36 mm. The rolled tube was subjected to a final annealing at 650 ° C. for 30 minutes to prepare copper alloy tubes (test tubes No. 1 to 15). In Table 1, “-” indicates that no component is contained.

  About the produced test tube, the average diameter and average number of grain boundary precipitates were measured by the following procedure. The results are shown in Table 1.

(Average diameter and average number of grain boundary precipitates)
As shown in FIG. 3, the sample 11 is cut out from the side surface of the test tube 10, and mechanically polished from above and below in the tube thickness t direction, both thicknesses are centered on a portion in the tube thickness t direction 1/2 (1/2 t). After setting the thickness to 0.05 mm (total 0.1 mm), the thin film 12 having a thickness of 100 nm was formed by twin jet electrolytic polishing. A surface parallel to the side surface of the test tube of the thin film 12 was used as an observation surface. Observation was carried out with a transmission electron microscope (TEM) at a magnification of 30,000, and four fields of view of about 5 μm × 4 μm were taken and image photographs were taken. The image photograph is analyzed by image analysis software Image-Pro Plus, and as shown in FIG. 1, the length of the grain boundary 2 of the crystal grain 1 and the vicinity of the grain boundary 2 above the grain boundary 2, that is, the grain boundary The number of grain boundary precipitates 3 centering on 2 and precipitated in a range of 200 nm in width was counted. The number of grain boundary precipitates 3 is divided by the total length of the grain boundary 2 photographed in the field of view to calculate the number of grain boundary precipitates 3 per length of the grain boundary 2, and the unit length (1 mm) Converted to per. Further, the particle area of the grain boundary precipitate 3 was measured, and the equivalent circle diameter was calculated from the particle area. Furthermore, the average value of 4 visual fields was calculated. The results are shown in Table 1.

  Next, the prepared test tube was measured for tensile strength and elongation by the following procedure, and evaluated for bending workability according to the following criteria. The results are shown in Table 1.

(Tensile strength and elongation)
A JIS No. 11 test piece was cut out from the test tube. Using the test piece, a tensile test was performed under the conditions of room temperature, tensile speed: 10.0 mm / min, and gauge distance: 20 mm, and tensile strength (MPa) and elongation (%) were measured. Two test pieces under the same conditions were tested, and the average value was adopted. The results are shown in Table 1.

(Bending workability)
The test tube was bent into a U shape with a bending pitch of 25 mm (bending radius at the tube axis was 12.5 mm), and the bent portion on the outer surface was visually observed. Ten test tubes were used for each test tube, and all of the ten tubes had no cracks, etc., were accepted as “◯”, and one in which even one crack was observed was rejected as “x”.

  From the results in Table 1, the test tube No. satisfying the requirements of the present invention was obtained. Nos. 1 to 9 (Examples) had large tensile strength and elongation and good bending workability. On the other hand, test tube No. which does not satisfy the requirements of the present invention. 10-15 (comparative example) had small elongation and bending workability was poor.

  Specifically, the test tube No. In No. 10 (Comparative Example), since the treatment temperature of the intermediate annealing was low, the average diameter of the grain boundary precipitates was larger than the upper limit value. As a result, the test tube No. No. 10 (Comparative Example) had a small elongation and a poor bending workability.

  Test tube No. No. 11 (Comparative Example) had a low intermediate annealing treatment temperature, a long holding time, and a slow cooling rate, so the average diameter of the grain boundary precipitates was larger than the upper limit. Moreover, since the temperature increase rate of the intermediate annealing was slow, the average number of grain boundary precipitates exceeded the upper limit. As a result, the elongation was small. As a result, the test tube No. No. 11 (comparative example) had poor bending workability.

  Test tube No. In No. 12 (Comparative Example), since the Ni content exceeded the upper limit, the elongation was small and the bending workability was poor. Test tube No. In No. 13 (Comparative Example), the Sn content was higher than the upper limit, so that an extruded material could not be produced in the hot extrusion process. Test tube No. No. 14 (Comparative Example) had a large Cr content exceeding the upper limit, so the elongation was small and the bending workability was poor.

  Test tube No. No. 15 (Comparative Example) was produced by the manufacturing method described in Patent Document 2, and since the intermediate annealing treatment temperature is low, the holding time is long, and the cooling rate is slow, the average diameter of the grain boundary precipitates is It was larger than the upper limit. Moreover, since the temperature increase rate of the intermediate annealing was slow, the average number of grain boundary precipitates exceeded the upper limit. As a result, the test tube No. No. 15 (Comparative Example) had low elongation and poor bending workability.

DESCRIPTION OF SYMBOLS 1 Crystal grain 2 Grain boundary 3 Grain boundary precipitate S1 Casting process S2 Homogenization heat treatment process S3 Hot extrusion process S4 Rolling drawing process S5 Intermediate annealing process S6 Processing process S7 Final annealing process 10 Test tube 11 Sample 12 Thin film

Claims (3)

Co: 0.05 to 0.40% by mass, P: 0.02 to 0.10% by mass, and the balance is a high strength copper alloy tube made of a copper alloy with Cu and inevitable impurities,
The average diameter of grain boundary precipitates at the center of the tube thickness in a plane parallel to the pipe side surface is 150 nm or less, and the average number per grain boundary length of the grain boundary precipitates is 5000 pieces / mm or less. High strength copper alloy tube.   The copper alloy further contains at least one of Ni: 0.005 to 0.100 mass%, Zn: 0.005 to 1.000 mass%, and Sn: 0.05 to 1.00 mass%. The high-strength copper alloy tube according to claim 1, wherein   The copper alloy further contains at least one selected from Fe, Mn, Mg, Cr, Ti, Zr, and Ag and less than 0.10% by mass in total. High strength copper alloy tube as described.

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