JP2001316742A - Copper alloy tube excellent in fatigue strength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper alloy tube having superior fatigue strength. SOLUTION: The copper alloy tube excellent in fatigue strength has a composition which contains, by mass, 0.03-0.15% Co and 0.02-0.05% P within the range satisfying Co/P<=4 and has the balance Cu with inevitable impurities and in which the content of oxygen among the inevitable impurities is controlled to <=50 ppm. Further, the copper alloy tube has recrystallized grains of <=20 μm average grain size, and fine precipitates are uniformly dispersed in the recrystallized grains and the average grain size of the fine precipitates is 1-30 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a heat exchanger tube, a refrigerant tube, a kerosene tube, a fire system line, a control copper tube, a four-way valve, an ice heat storage copper tube, a show case copper tube, and the like. The present invention relates to a copper alloy tube having excellent fatigue strength and particularly to a seamless copper alloy tube having excellent fatigue strength.

[0002]

2. Description of the Related Art In general, a seamless copper tube made of phosphorous deoxidized copper has been used as a heat exchanger tube of a heat exchanger. However, in recent years, in order to prevent coarsening of crystal grains during brazing, phosphorus removal is performed. A copper alloy tube in which crystal grains are hardly coarsened by adding Fe to copper oxide is used. As a conventional copper alloy tube having excellent fatigue strength containing Fe as an essential component in the conventional phosphor deoxidized copper, for example, Fe: 0.005 to 0.8%, and P: 0.01 to 0.
026%, Zr: 0.005 to 0.3%, O ₂ : 3 to 3
Copper alloy tube containing 0 ppm and the balance: Cu (see Japanese Patent Publication No. 58-39900); and Fe: 0.
01-1.0%, Cr, Si, Mn, As, Ni, Co
One or more of the following: 0.005 to 0.6%,
One or more of P, Ca and Mg: 0.004
Copper alloy pipes having a composition of about 0.04%, with the balance being Cu, are known (see JP-A-52-156718).

However, when HFC-based fluorocarbons without depletion of the ozone layer are used as the heat medium for the heat exchanger,
Since it is necessary to further increase the condensing pressure when HFC-based chlorofluorocarbon is used as the heat medium of the heat exchanger, there has been a demand for an even more excellent high-strength copper alloy tube. For these requirements, Co: 0.03 to 0.
15%, P: 0.02-0.05%, the balance being C
There has been proposed a copper alloy tube made of a copper alloy composed of u and unavoidable impurities and having a composition in which the oxygen content contained as the unavoidable impurities is regulated to 50 ppm or less (Japanese Patent Application Laid-Open No. 200-200200).
0-1728).

[0004]

In recent years, due to the problem of resource saving, there has been an increasing tendency to reduce the thickness of a copper alloy tube as much as possible and to use a device incorporating the copper alloy tube for a longer period of time. In order to satisfy these demands, there is a demand for a copper alloy tube having more excellent fatigue strength that can withstand repeated loads such as severe internal pressure and external vibration for a long period of time.

[0005]

Means for Solving the Problems Accordingly, the present inventors have
As a result of conducting research to obtain a copper alloy tube having more excellent fatigue strength than before, it was found that (a) Co: 0.03 to
0.15%, P: 0.02 to 0.05% (however, Co
/ P: 4 or less), and the balance consists of Cu and inevitable impurities. The composition is adjusted so that the oxygen content contained as the inevitable impurities is 50 ppm or less, and furthermore, an appropriate working heat treatment is applied thereto to generate a structure. Average recrystallized grain size: 2
When the thickness is adjusted to 0 μm or less and a structure in which fine precipitates are uniformly precipitated in the recrystallized grains is further provided, the fatigue strength is further improved. (B) It is uniformly dispersed in the recrystallized grains. It has been found that the fine precipitate is more preferably a fine precipitate of 1 to 30 nm.

The present invention has been made based on such findings, and (1) Co: 0.03% by mass%.
0.15%, P: 0.02 to 0.05%, Co / P: 4
And the remainder is composed of Cu and unavoidable impurities, has a composition in which the oxygen content contained as the unavoidable impurities is adjusted to 50 ppm or less, and further has recrystallized grains having an average particle size of 20 μm or less. A copper alloy tube having excellent fatigue strength and having a structure in which fine precipitates are uniformly dispersed in the recrystallized grains.

The fine precipitates uniformly dispersed in the recrystallized grains are more preferably fine precipitates of 1 to 30 nm. Therefore, the present invention provides (2)
Co: 0.03 to 0.15%, P: 0.02 to 0.05
% Co / P: 4 or less, with the balance being Cu
And an unavoidable impurity, having a composition in which the oxygen content contained as the unavoidable impurity is adjusted to 50 ppm or less, and further having recrystallized grains having an average particle size of 20 μm or less, and having fine particles in the recrystallized grains. A copper alloy tube having excellent fatigue strength, which is a fine precipitate having an average particle size of 1 to 30 nm in which the precipitate is uniformly dispersed, is characterized.

In order to produce the copper alloy tube having excellent fatigue strength according to the present invention, first, ordinary electrolytic copper, oxygen-free copper, tough pitch copper, phosphorus deoxidized copper, high-grade copper scrap, etc. are melted in a reducing atmosphere. Then, a low-oxygen copper melt having an oxygen content of 50 ppm or less is produced, and a Co-metal and a Cu-P master alloy are added to the obtained low-oxygen copper melt, followed by casting to produce a cylindrical ingot.

The cylindrical ingot is heated to 850 ° C. to 950 ° C., extruded in water, cold-worked, and then heated to 570 to 670 ° C., which is higher than usual, to 15 to 120 ° C.
Annealing is carried out under the condition of holding for one minute, thereby sufficiently recrystallizing and adjusting the particle size of the precipitates precipitated in the recrystallized grains.

Next, the reason why the component composition, the recrystallized grain size, and the grain size of the precipitate of the copper alloy constituting the copper alloy tube having excellent fatigue strength of the present invention are limited as described above will be described.

[I] Ingredient Composition (a) Co Co is a component that forms a solid solution or a phosphorus compound phase in a phosphorus-deoxidized copper base to improve the proof stress and fatigue strength of the material. If it exceeds 15%, coarse crystals remain and fatigue strength and workability decrease, which is not preferable. On the other hand, if the Co content is less than 0.03%, the desired effect cannot be obtained. Therefore, the Co content is 0.03-
Each was determined so as to be in the range of 0.15%. A more preferable range of the Co content is 0.04 to 0.12%.

(B) PP coexists with Co to refine crystal grains, thereby improving proof stress and fatigue strength. However, if the content exceeds 0.05%, precipitates become coarse. On the other hand, if the content is less than 0.02%, the desired effect cannot be obtained. Therefore, the content of P is 0.1.
It was set to 02-0.05%. A more preferable range of the P content is 0.025 to 0.045%.

(C) Co / P Co and P contained in the copper alloy of the present invention are Co: 0.0
3 to 0.15%, P: 0.02 to 0.05% and Co
It is necessary that the ratio of Co and P (Co / P) be 4 or less in order to further improve the fatigue strength and workability.
More preferably, P is in the range of 1.5-3.

(D) Oxygen Oxygen is contained as an unavoidable impurity.
If the content exceeds the above range, a coarse oxide is formed, which impairs the strength and processability, which is not preferable. Therefore, the oxygen content is set to 50 ppm or less (preferably 10 ppm or less).

[II] Recrystallized grain size and precipitate size (e) Recrystallized grain size The finer the recrystallized grain obtained by annealing after cold working, the better the size. The average grain size is 20 μm. Exceeding this is not preferred because the fatigue characteristics are reduced. Therefore,
The average grain size of the recrystallized grains obtained by annealing was set to 20 μm or less. A more preferred range is 10 μm or less.

(F) Precipitate diameter If the precipitates uniformly dispersed in the recrystallized grains obtained by the annealing are fine precipitates of less than 1 nm, the effect of improving the fatigue strength is not sufficient. If the particle size exceeds 30 nm, the fatigue strength is rather reduced, which is not preferable. Therefore, the average particle size of the precipitate uniformly dispersed in the recrystallized grains was set to 1 to 30 nm. A more preferred range is from 1 to 10 nm.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Electrolytic copper is prepared as a raw material, and electrolytic copper is dissolved in a reducing atmosphere to produce a low-oxygen copper melt having an oxygen content of 50 ppm or less. After adding a 15% P mother alloy, it was cast into a mold to produce a cylindrical ingot having a diameter of 320 mm and a length of 710 m and having the component composition shown in Table 1.

This columnar copper alloy ingot is heated by a billet heater at a temperature of 900 ° C. for 10 minutes, and then extruded in water to simultaneously form a solution with a diameter of 100 mm and a thickness of 10 mm. A tube having dimensions was produced.

The solution-treated tube is further cold-worked to form a seamless copper alloy tube having an outer diameter of 12.7 mm and a wall thickness of 0.7 mm. The alloy tube was further charged into a light-volume annealing furnace and annealed under the conditions shown in Table 1, and copper alloy tubes 1-6 having excellent fatigue strength according to the present invention (hereinafter referred to as the present tube) and comparative copper alloy tubes ( Hereinafter, referred to as a comparative tube).

The tubes 1 to 6 of the present invention and the comparative tubes 1 to 3
The average grain size of the recrystallized grains was measured by observing the cross section of each with an optical microscope, and the average grain size of the precipitates precipitated in the recrystallized grains was further measured by a TEM (transmission electron microscope). Are shown in Table 1.

Further, a nominal tensile / compressive stress of 120 MPa was repeatedly applied to the tubes 1 to 6 of the present invention and the comparative tubes 1 to 3 by a hydraulic servo pulser 1 × 10 ⁸ times, and the number of repetitions at the time of breakage was measured. The results are shown in Table 1 to evaluate the fatigue strength.

[0022]

[Table 1]

[0023]

According to the results shown in Table 1, the pipes 1 to 5 of the present invention are shown.
Nominal tensile-compression stress of 120 MPa for 1 × 1
Although there was no rupture even when the load was repeated ⁸ times,
Since all of the comparative tubes 1 to 3 are broken by a repetitive load of less than 1 × 10 ⁷ times, it can be understood that the tubes 1 to 6 of the present invention have better fatigue strength than the comparative tubes 1 to 3. ,
Therefore, it is understood that the copper alloy pipe of the present invention can be used for a longer period as a pipe in a portion where a high repetitive load is applied.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroharu Ogawa 1975-2 Shimoishito, Kitamoto City, Saitama Prefecture Inside Mitsubishi Materials Co., Ltd. Kitamoto Works (72) Inventor Ryoji Shibuya 1975-2 Shimoishitogami, Kitamoto City, Saitama Prefecture Mitsubishi Materials Corporation Kitamoto Works (72) Inventor Tetsuo Yamamichi 1-297 Kitabukurocho, Omiya City, Saitama Prefecture Mitsubishi Materials Corporation Research Laboratory

Claims (2)

[Claims] (1) Co: 0.03 to 0.15% by mass%;
P: 0.02 to 0.05% is contained so as to be Co / P: 4 or less, and the rest consists of Cu and unavoidable impurities,
The oxygen content contained as the inevitable impurities is 50 ppm
Fatigue strength having a composition adjusted as follows, further having recrystallized grains having an average particle size of 20 μm or less, and having a structure in which fine precipitates are uniformly dispersed in the recrystallized grains. Excellent copper alloy tube. 2. The copper alloy tube having excellent fatigue strength according to claim 1, wherein the fine precipitates uniformly dispersed in the recrystallized grains are fine precipitates of 1 to 30 nm.