Copper alloy tube with excellent high-temperature brazeability and manufacturing method therefor

Abstract

Provided is a copper alloy tube that is a drawn tube made from a CuCrZr alloy which suppresses the deterioration of mechanical strength and, in particular, the coarsening of crystal grains even in a temperature zone of a solutionizing treatment, and is thus excellent in high-temperature brazeability, as well as the manufacturing method therefor. The manufacturing method comprises a solutionizing step of heating and holding a tubular extrusion material at a solutionizing temperature of 900 C. or greater and then water-quenching the tubular extrusion material; a main process step comprising a set of steps including a drawing process step of drawing the tubular extrusion material, and an intermediate annealing step of heating at an annealing temperature and then water-quenching the drawn material; and an adjusting process step of further drawing the drawn material and setting average crystal grain sizes in a vertical cross section along an axis as well as a horizontal cross section orthogonal to the axis to 50 m or less each. The average crystal grain sizes of the vertical cross section and the horizontal cross section are each set to 100 m or greater and the annealing temperature is set to 900 C. or greater after the solutionizing step, thereby making it possible to make the average crystal grain sizes of the vertical cross section and the horizontal cross section 100 m or less after the adjusting process step, even if heating is performed at at least 980 C. for 30 minutes followed by air-cooling.

Claims

1. A method for manufacturing a copper alloy tube, the method comprising: a solutionizing step of heating and holding a tubular extrusion material, made from a chromium-zirconium-copper alloy having a component composition consisting of 0.5 to 1.5 mass % Cr, 0.02 to 0.20 mass % Zr, impurities, and Cu, at a solutionizing temperature of 900 C. or greater, and then water-quenching the tubular extrusion material, wherein the average crystal grain sizes of the vertical cross section and the horizontal cross section are each set to 100 micrometers or greater; thereafter a main process step comprising a set of steps including a drawing process step of drawing the tubular extrusion material to obtain a drawn material at a surface area reduction rate of 40% or greater of the horizontal cross section, and an intermediate annealing step of heating at an annealing temperature, wherein the annealing temperature is set to 900 C. or greater, and then water-quenching the drawn material; and an adjusting process step of further drawing the drawn material and setting average crystal grain sizes in a vertical cross section along an axis as well as a horizontal cross section orthogonal to the axis to 50 micrometers or less each.

2. The method for manufacturing a copper alloy tube according to claim 1, wherein the drawing process step performs the drawing process at a surface area reduction rate of 50% or greater of the horizontal cross section.

3. The method for manufacturing a copper alloy tube according to claim 2, wherein the adjusting process step performs the drawing process a plurality of times.

4. The method for manufacturing a copper alloy tube according to claim 3, wherein the drawing process step performs the drawing process a plurality of times.

5. The method for manufacturing a copper alloy tube according to claim 4, wherein the main process step performs the set of steps a plurality of times.

6. The method for manufacturing a copper alloy tube according to claim 5, wherein the solutionizing step further includes heating the tubular extrusion material after pre-processing in a drawing process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a table showing a component composition of a copper alloy used for a copper alloy tube according to the present invention.

(2) FIG. 2 is a flowchart showing a manufacturing method according to the present invention.

(3) FIG. 3 is a cross-sectional view for describing a method of a drawing process.

(4) FIGS. 4A and 4B are cross-sectional views for describing a processing rate.

(5) FIG. 5 is a diagram illustrating cutting directions of observed samples.

(6) FIG. 6 is a flowchart showing a method for installing the copper alloy tube to a device.

(7) FIG. 7 is a table showing processing conditions of examples and a comparative example of the copper alloy tube according to the present invention.

(8) FIG. 8 is a table showing crystal grain sizes of the examples and the comparative example of the copper alloy tube according to the present invention.

(9) FIGS. 9A and 9B are structural images of cross-sectional observations of the copper alloy tube of Example 2.

(10) FIGS. 10A and 10B are structural images of cross-sectional observations of the copper alloy tube of FIGS. 9A and 9B after heat treatment.

(11) FIG. 11 is a graph showing the relationship between processing rate and crystal grain size in an adjusting process step.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(12) In the following, one example of a method for manufacturing a copper alloy tube according to the present invention will be described using FIGS. 1 to 6.

(13) As shown in FIG. 1, a CuCrZr alloy, which is a precipitation-hardening type copper alloy excellent in electrical conductivity, thermal conductivity, and mechanical properties at high temperatures, is used as the copper alloy for a copper alloy tube. Typically, the copper alloy C18150, containing 0.5 to 1.5 mass % Cr and 0.02 to 0.20 mass % Zr, is used for this tube. Such a copper alloy is generally subjected to a solutionizing treatment at 900 C. or greater, machined into shapes of various electric parts and the like, subsequently subjected to an aging treatment (heat treatment) that disperses a precipitation phase, and then used. Here, on the other hand, the copper alloy is plastic-formed into a copper alloy tube, typically drawn, aged, and then used. It should be noted that, while the brazing treatment onto various devices may follow the aging treatment, high-temperature treatments, particularly brazing treatments in which the metal is exposed to temperatures of 900 C. or greater, which is comparable to the temperature of a solutionizing treatment, are preferably performed prior to the aging treatment. This will be described later.

(14) As illustrated in FIG. 2, a tubular extrusion material made from the CuCrZr alloy described above is heated and held at a solutionizing temperature, and then water-quenched (S11: solutionizing step). This tubular extrusion material is drawn to obtain a drawn material (S12: drawing process step), the drawn material is heated to a temperature higher than the annealing temperature for conventional process-induced distortion removal, such as an annealing temperature of 900 C. or greater, for example, and water-quenched after the distortion is annealed (S13: intermediate annealing step). Subsequently, the drawing process is performed, and the average crystal grain size is adjusted to 50 m or less (S14: adjusting process step). It should be noted that this set of processing including the drawing process step S12 and the intermediate annealing step S13 is preferably repeated as appropriate (S21).

(15) At least in the case of CuCrZr alloy, the distortion of the drawing process, in which plastic forming is performed with the tubular shape retained as is, is corrected in the intermediate annealing step S13. After the annealing temperature at this time is increased to the high temperature of 900 C. or greater, water-quenching is performed so as to control recrystallization during the temperature drop, allowing the distortion introduced in the adjusting process step S14 to then function so as to suppress the average crystal grain size to 100 m or less, even under the high-temperature conditions of the subsequent brazing treatment, such as the temperature conditions of heating at 980 C. for 30 minutes and then air-cooling, for example.

(16) Further, this set of processing that includes the drawing process step S12 and the intermediate annealing step S13 is repeated, allowing the distortion introduced in the adjusting process step S14 to function so as to further suppress crystal growth under the high-temperature conditions of the subsequent brazing treatment.

(17) More specifically, in the solutionizing treatment step S11, the tubular extrusion material obtained from an alloy ingot having a component composition such as shown in FIG. 1 is heated to and held at the solutionizing temperature and subsequently water-quenched. Here, while consideration may be given to the heating temperature, heating duration, and the like from the perspective of efficiently homogenizing the tubular extrusion material at a macro level, the internal heat gradient in a copper alloy excellent in thermal conductivity can be reduced, making the copper alloy not largely dependent on shape and the need to consider such factors minimal. It should be noted that when the solutionizing temperature is too high, the component composition may change. Therefore, even in the atmosphere or, more typically, in an inert gas atmosphere or a reducing gas atmosphere (the same for other heating treatment as well, unless otherwise noted), the tubular extrusion material is heated to a solutionizing temperature between 900 C. and 1,050 C., held for about 30 minutes to one hour, and then water-quenched. With the water-quenching, recrystallization during the temperature drop is suppressed and the coarsened crystal grains are cooled as is, thereby unavoidably obtaining an average crystal grain size of 100 m or greater.

(18) It should be noted that, prior to the solutionizing treatment step S11, performing plastic forming such as a drawing process (pre-processing) on the tubular extrusion material to a predetermined size makes it possible to lower the necessary processing rate resulting from the subsequent drawing process, and is thus preferred in terms of manufacturing efficiency.

(19) The drawing process step S12 is a cold forming step at room temperature and, as illustrated in FIG. 3, is performed using a plug 11 inserted into an alloy tube 1, and a die 12. While the thickness of the alloy tube 1 can be determined by the difference between the die diameter and the plug diameter, preferably the mode of introduction of process distortion is varied over a plurality times to obtain a predetermined diameter size.

(20) Here, as illustrated in FIG. 4, the processing rate is expressed by a reduction rate of the cross-sectional area of a horizontal cross section. That is, given S.sub.1 (outer diameter R.sub.1, inner diameter r.sub.1) and S.sub.2 (outer diameter R.sub.2, inner diameter r.sub.2) as the cross-sectional areas before processing and after processing, respectively, then:
Processing rate =(S.sub.1S.sub.2)/S.sub.1={(R.sub.1.sup.2r.sub.1.sup.2)(R.sub.2.sup.2r.sub.2.sup.2)}/(R.sub.1.sup.2r.sub.1.sup.2)

(21) The intermediate annealing step S13 is a step in which the tubular extrusion material is heated and held at a predetermined temperature, recrystallization during temperature drop is controlled, and water-quenching is performed. The distortion introduced in the drawing process step S12 is alleviated, and the distortion introduced in the adjusting process step S14 is then introduced so as to suppress the growth of the crystal grains in a subsequent brazing treatment S32 (described later). Thus, the temperature to which the tubular extrusion material is heated and held is 1,050 C. or less, and should be a temperature of at least 800 or greater, preferably 850 C. or greater, and more preferably 900 C.

(22) It should be noted that the set of steps including the drawing process step S12 and the intermediate annealing step S13 may be performed a plurality of times (S21). In this case, the distortion introduced in the adjusting process step S14 can be introduced so as to further suppress the growth of crystal grains in the subsequent brazing treatment S32.

(23) The adjusting process step S14, similar to the drawing process step S12, is a cold forming step that uses the plug 11 and the die 12 (refer to FIG. 3). As illustrated in FIG. 5, in this adjusting process step S14, a drawing process is performed so as to set the average crystal grain sizes in a vertical cross section A1 along an axis 2 of the alloy tube 1 and a horizontal cross section A2 orthogonal to the axis 2 to 50 m or less each. Here as well, the process may be performed over a plurality of times to obtain a predetermined diameter size. In the drawing process, the process is performed over a plurality of times even when the same processing rate is applied, and thus the mode of introduction of process distortion may become more complex.

(24) With the above, it is possible to obtain a copper alloy tube with excellent high-temperature brazeability prior to the aging treatment.

(25) It should be noted that, as illustrated in FIG. 6, the copper alloy tube obtained via the adjusting process step S14 is installed to a predetermined device that uses the copper alloy tube (assembly step: S31), brazed using a brazing material that contains a metal having a high melting point such as nickel, chromium or tungsten which is highly reliable at high temperatures (brazing treatment step: S32), and lastly heated in its entirety, thereby precipitating deposits and adjusting the mechanical strength (aging treatment step: S33).

(26) As described above, the alloy tube obtained via the adjusting process step S14 can suppress deterioration of mechanical strength without significantly increasing the average crystal grain size, even when heating is performed at the temperature zone of the solutionizing treatment of 900 C. or greater. For example, even if heating is performed at at least 980 C. for 30 minutes followed by air-cooling, the average crystal grain sizes in the vertical cross section A1 and the horizontal cross section A2 can be set to 100 m or less.

EXAMPLES

(27) As shown in FIG. 7, a copper alloy tube was created by the manufacturing method described above, and the crystal grain size was measured and observed before and after heat treatment modeled on the brazing treatment step S32.

(28) First, a tubular extrusion material was drawn (pre-processed) at a processing rate of =31.7% to obtain a tube having an outer diameter of 57 mm and a thickness of 4 mm. The tube was then heated and held at 980 C. for 30 minutes and water-quenched to obtain a tubular material.

(29) In Examples 1 and 2, the material was drawn at a processing rate of =52.4% over three times as the drawing process step S12, subsequently heated and held at 980 C. for 30 minutes as the intermediate annealing step S13, and then water-quenched. Subsequently, the material was adjusted at a processing rate of =42.0% over two times as the adjusting process step S14 in Example 1, and adjusted at a processing rate of =76.3% over six times as the adjusting process step S14 in Example 2.

(30) In Example 3, the material was drawn at a processing rate of =52.4% over three times as the drawing process step S12, subsequently heated and held at 980 C. for 30 minutes as a first intermediate annealing step S13, and then water-quenched. Furthermore, the material was drawn at a processing rate of =56.1% over three times as the second drawing process step S12, subsequently heated and held at 900 C. for 30 minutes as the intermediate annealing step S13, and then water-quenched. The resulting tube was then adjusted at a processing rate of =46.1% over two times as the adjusting process step S14.

(31) On the other hand, in Comparative Example 1, the material was drawn at a processing rate of =52.4% over three times as the drawing process step S12, subsequently heated and held at 600 C. for 30 minutes as the intermediate annealing step S13, and then water-quenched. Furthermore, the resulting tube was then adjusted at a processing rate of =74.9% over six times as the adjusting process step S14.

(32) Portions of these materials were cut out, the vertical cross section A1 and the horizontal cross section A2 (refer to FIG. 5) were observed under a microscope, and the crystal grain sizes were measured. The remainder was subjected to heat treatment modeled on the brazing treatment step S32, that is, heated and held at 980 C. for 30 minutes and then air-cooled. Then, in the same way, the vertical cross section A1 and the horizontal cross section A2 were observed under a microscope, and the crystal grain sizes were measured. The results are shown in FIG. 8. It should be noted that the crystal grain sizes were measured in accordance with ASTM E 112-96 (2004), and the average crystal grain sizes were indicated.

(33) As shown in FIG. 8, the average crystal grain sizes before heat treatment in Examples 1 to 3 as well as Comparative Example 1 were 50 m or less. In contrast, after heat treatment, the average crystal grain sizes in Examples 1 to 3 were 100 m or less and crystal grain growth could be suppressed, while the average crystal grain size in Comparative Example 1, in which the heat treatment in the intermediate annealing step S13 was performed at 600 C., was 100 m or greater and abnormal grain growth was observed. That is, the observation was made that performing the intermediate annealing step S13 at a higher temperature made it possible to suppress crystal grain growth. It should be noted that, in Example 3, it was confirmed that the average crystal grain size could be maintained at 100 m or less even under the temperature conditions of heating and holding the tube at 985 C. for three hours and then air-cooling.

(34) FIGS. 9A to 10B show microphotographs of the vertical cross section A1 and the horizontal cross section A2 of Example 2 before and after heat treatment. In FIGS. 9A and 9B, it is clear that the crystal grains became distorted, and distortion intricately accumulated in the interior of the crystal grains as well. On the other hand, in FIGS. 10A and 10B, the sizes of the crystal grains in both the vertical cross section and the horizontal cross section are relatively very uniform, and sub-grains are also clearly observed.

(35) Further, in FIG. 9A, the crystal grains are observed extending in a drawing direction T. On the other hand, FIG. 10A shows that, while the size of the crystal grain is substantially constant, the crystal grains are aligned in the drawing direction T, and these are recrystallized grains resulting from heat treatment. According to the heat treatment at a higher temperature in the intermediate annealing step S13 described above, recrystallization of the crystal grains is prioritized over crystal growth in the brazing treatment step S32, and a relatively fine crystal grain is considered to be obtained.

(36) In Examples 1 and 2, the processing rates of the adjusting process step S14 are different. FIG. 11 shows the processing rate and measurement results of the crystal grain size after heat treatment, along with other measurements. That is, as long as the processing rate of the adjusting process step S14, as indicated by P1 in FIG. 11, is 30% or greater, and preferably 40% or greater, it is possible to suppress the crystal grain size to 100 m or less.

(37) While the above has described examples according to the present invention and modifications based on these, the present invention is not limited thereto, and those skilled in the art may conceive various alternative examples and modified examples, without departing from the spirit or the appended claims of the present invention.

DESCRIPTIONS OF REFERENCE NUMERALS

(38) 1 Tube 2 Axis 11 Plug 12 Die A1 Vertical cross section A2 Horizontal cross section