JP3209389B2 - Heat-resistant copper alloy sheet for heat exchanger having a small expansion coefficient after hard brazing heating and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-resistant copper alloy sheet for a heat exchanger which has a small decrease in strength and fatigue properties even after hard brazing and has a small expansion coefficient after hard brazing. And its manufacturing method.

[0002]

2. Description of the Related Art Since cans and pipes of heat exchangers such as bath kettles or water heaters are assembled by welding or brazing, the materials used for the cans and pipes may have good weldability and brazing properties. In addition, phosphorus deoxidized copper is generally used, since it is necessary to have good thermal conductivity because it is a component of the heat exchanger.

[0003] However, in the case of deoxidized copper, it is known that when thermal stress is repeatedly applied to a brazed portion and a welded portion, fatigue fracture occurs from this portion. this is,
Due to the heat at the time of brazing, the crystal grains in that part coarsen,
This is because the resistance to fatigue fracture decreases. In order to prevent fatigue failure due to thermal stress, in conventional heat exchangers, measures have been taken to make it difficult for thermal stress to be generated from the structural surface by inserting bellows in the pipe part. Provision of the heat exchanger has the disadvantage that the structure of the heat exchanger becomes complicated and the production cost increases.

[0004] Therefore, the heat exchanger has the same excellent corrosion resistance as deoxidized copper, prevents crystal grains from being coarsened by heat such as brazing and welding, and has high durability against fatigue fracture due to thermal stress. A dexterous copper alloy has been desired. Under such circumstances, the present applicant has proposed a copper alloy having improved durability against fatigue fracture as Fe: 1.3 to 2.1% by weight, P: 0.001 to 0.1% by weight, Co: 0.2 to 1.0% by weight, and Zn: 0.01 to 1.0% by weight, and the total of the Fe content and the Co content is 2.5% by weight or less; A copper alloy having the remainder consisting of Cu and unavoidable impurities has been previously proposed (JP-A-4-272148).

[0005] This copper alloy is used, for example, in the heat exchanger shown in FIG. 3 for the flange portion 1 in the can body which requires particularly high durability. In this case, the copper alloy is formed from the flange portion 1 and deoxidized copper. The brazing of the pipe 3 is often performed in a state where the burner case 2 is tightened with bolts, and this hard brazing heating (for example, heating at 830 ° C. for 10 minutes in nitrogen) as shown in FIG. In addition, there is a problem that the flange portion 1 made of the copper alloy expands and, after cooling, a flexure 5 is generated between the burner case 2 made of deoxidized copper and the burner case 2 based on a dimensional difference. In FIG. 3, 4
Is a fin.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the conventional copper alloy, and has been developed by using a copper alloy having the same composition as the conventional copper alloy during hard brazing and welding. In addition to having the same excellent characteristics as before, such as suppression of coarsening of crystal grains due to heat and high durability against fatigue fracture caused by repetition of thermal stress, expansion after hard brazing heating is equivalent to that of deoxidized copper. It is an object of the present invention to provide a heat-resistant copper alloy sheet for a heat exchanger that has a low level.

[0007]

Means for Solving the Problems The above copper alloy has been subjected to precipitation annealing (575 ° C. × 2Hr +) during cold rolling.
(500 ° C. × 4 hours, then slowly cooled in a furnace), and in the slow cooling process, Fe was intentionally precipitated to improve the heat conductivity and conductivity required for the heat exchanger can. F of the subsequent studies of the present inventors, the thus treated copper alloy is subjected to a brazing heat, such as Fe and Fe ₂ P
e The precipitates form a solid solution during the process of hard brazing and heating, so that the expansion of the copper alloy becomes larger than that of deoxidized copper, and the cooling process is air-cooled (rapid air-cooling). , And as a result, it was found that the length after the hard brazing was not restored to the original length and was larger than the length before the heating.

The present inventors conducted various experiments and investigations on the basis of this finding, and by preliminarily dissolving Fe precipitates in the parent phase before heating by hard brazing, the hard brazing heating process was carried out. It has been found that the solid solution and the expansion accompanying it can be suppressed, the elongation after heating by hard brazing can be suppressed, and the above-mentioned properties of the copper alloy are not impaired, and the following invention has been completed.

[0009]

The heat-resistant copper alloy sheet for a heat exchanger according to the present invention, which has a small coefficient of expansion after heating by hard brazing, contains Fe: 1.3 to 2.1% by weight, P: 0.001 to 0.1% by weight, C
o: 0.2 to 1.0% by weight, and Zn: 0.01 to 1.0% by weight, and the total of the Fe content and the Co content is 2.5% by weight or less. Yes, the balance is a copper alloy plate composed of Cu and unavoidable impurities, and has a conductivity of 20 to 50% IACS before brazing and heating.
And a crystal grain size of 1 to 50 μm.

Further, the method for producing a heat-resistant copper alloy sheet for a heat exchanger according to the present invention, which has a small coefficient of expansion after heating by hard brazing, comprises: 1.3 to 2.1% by weight of Fe, and 0.001 to 0% of P. 0.1% by weight, Co: 0.2 to 1.0% by weight, and Zn: 0.01 to 1.0% by weight,
The total of the content of e and the content of Co is not more than 2.5% by weight, and the remainder is Cu alloy and an ingot of Cu and inevitable impurities. , then heated over 10 seconds at a temperature of 500 to 830 ° C., and cooled at 5 ° C. / sec or more cooling rate, the following equation
An expansion coefficient R (%) after the defined hard brazing heating is 0.0
It is characterized by producing a heat-resistant copper alloy plate for a heat exchanger having a content of 5% or less . R = (L1−L0) ÷ L0 × 100 where L1: length after brazing, L0: length before brazing.

This manufacturing method can be applied to precipitation hardening type alloys such as Cu-Fe-Ti and Cu-Ni-Ti other than the above composition.

[0013]

First, a heat-resistant copper alloy for a heat exchanger according to the present invention.
The reasons for adding the components of the metal plate, the reasons for limiting the composition, and the reasons for limiting the properties will be described.

Fe Fe is an element that contributes to improving the strength of the copper alloy. When the Fe content is less than 1.3% by weight, the strength after hard brazing is insufficient. On the other hand, if the Fe content exceeds 2.1% by weight, the solid solution in Cu becomes saturated, and the crystal grains of Fe that have become huge tend to crystallize and internal defects are likely to occur. Manufacturing becomes difficult. Therefore, the Fe content is set to 1.3 to 2.1% by weight, more preferably 1.6 to 2.0% by weight.

Co Co is an element essential for suppressing the coarsening of crystal grains. Further, even in the brazing process at a temperature of 800 to 900 ° C., it has the effect of suppressing the growth of secondary recrystallized grains, keeping the structure fine, and improving the thermal fatigue resistance. If the Co content is less than 0.2% by weight, such effects cannot be sufficiently obtained. Further, the Co content is 1.0% by weight.
If the amount exceeds, the effect of adding Co corresponding to the increase in the content cannot be improved, which is wasteful. Therefore, the Co content is O.O. 2 to 1.0% by weight, more preferably 0.3 to 0.7% by weight. When the content of Fe and Co described above exceeds 2.5% by weight, internal defects due to the large crystallized Fe are likely to occur. Therefore, the total content of Fe and Co needs to be 2.5% by weight or less.

PP has a deoxidizing effect in the molten copper alloy. If the P content is less than 0.001% by weight, the deoxidizing effect in the molten metal cannot be obtained. Further, when the P content is 0.1.
If it exceeds 1% by weight, the hot workability is degraded and the conductivity is lowered. Therefore, the P content is 0.001 to 0.1.
% By weight.

Zn Zn has the effect of improving the plating adhesion of a plating layer such as Sn plating or solder plating and also improving the solder wettability. When the Zn content is less than 0.01% by weight, such an effect is insufficient. On the other hand, when the Zn content exceeds 1.0% by weight, the brazing property and the conductivity are reduced. Therefore, the Zn content is set to 0.01 to 1.0% by weight.

Incidentally, it is conceivable that elements such as B, Cr, Ti, Zr, Mg, Ni and Sn are inevitably mixed into the copper alloy from the scrap material or the like. If the total content of these elements is 0 or 2% by weight or less, there is no possibility that the physical properties of the alloy of the present invention will be adversely affected.

Expansion coefficient The expansion coefficient after hard brazing is a characteristic relating to the dimensions and strength of the can body. In the case of a heat exchanger can, various measures have been taken to reinforce the can, such as reinforcing the can in order to improve the resistance to thermal fatigue. The effect is significantly reduced. If the expansion rate defined by the above equation exceeds 0.05%, it is difficult to correct the dimensions of the can body in a later step, so the expansion rate is set to 0.05% or less.

Crystal Grain The crystal grain size is related to the strength and thermal fatigue resistance of the heat exchanger can. The smaller the crystal grain size, the higher the heat resistance, the smaller the decrease in mechanical properties even after hard brazing heating, and the higher the durability against fatigue fracture due to repeated thermal stress. However, when the crystal grain size is less than 1 μm, the moldability deteriorates and cracks occur during molding. On the other hand, when the crystal grain size exceeds 50 μm, the mechanical properties after hard brazing are heated. In addition, the thermal fatigue characteristics are reduced. Therefore, the crystal grain size is 1 to 50 μm.

Conductivity The coefficient of expansion of the copper alloy sheet is related to the amount of solid solution of Fe which is a contained element. In order to suppress the coefficient of expansion, an Fe precipitate is dissolved in a parent phase in advance before heating by brazing. There is a need. On the other hand, F
The solid solution amount of e appears in the conductivity, and the higher the solid solution amount of Fe, the lower the conductivity. Therefore, in this copper alloy sheet , the expansion coefficient after brazing and heating can be evaluated based on the electrical conductivity before brazing and heating. It is necessary to keep the conductivity before heating.

FIG. 1 shows that a cold-rolled material of a copper alloy described in Table 1 in the Examples section described below was adjusted to various electric conductivity (before brazing and heating) according to the procedure described in the same section. The expansion coefficient after brazing and heating is determined by the method described in the same column, and the relationship between the conductivity before brazing and the expansion coefficient after brazing is graphed. As shown in FIG.
It can be seen that in order to make the copper alloy 5% or less, the conductivity of the copper alloy before the brazing heating should be made 50% IACS or less.
However, it is desired that the heat exchanger can be excellent in thermal conductivity and electrical conductivity, and it is necessary that the electrical conductivity be 20% IACS or more. Therefore, the conductivity is 20-50% IACS before brazing.

Next, the heat exchanger heat copper case according to the present invention
The reason for limiting the processing conditions for the method of manufacturing a metal plate will be described.

In the method of the present invention, for the cold-worked material,
The heating at a temperature of 500 to 830 ° C. for 10 seconds or more is performed so that the Fe precipitates form a solid solution in the mother phase. If Fe is precipitated as in the prior art, it starts to form a solid solution at around 500 ° C. due to heating during hard brazing,
The expansion of the copper alloy sheet is greater than that of deoxidized copper, and the cooling process during hard brazing is air cooling (rapid air cooling), so once dissolved Fe is cooled in a solid solution state and precipitates again. They cannot be traced, resulting in a length greater than the initial length.

When the heating temperature is lower than 500 ° C., the Fe precipitate does not form a solid solution in the matrix, so that the expansion rate increases. On the other hand, when the heating temperature exceeds 830 ° C., the recrystallized grains become coarse and the material strength decreases. Therefore, the heating temperature is 500 to 83
0 ° C. In particular, heating in the temperature range of 550 to 650 ° C. reduces the strength reduction after brazing,
Is preferable because the solid solution reduces the expansion coefficient. Also,
When the heating time is less than 10 seconds, the solid solution of Fe is insufficient even when heating in the above temperature range, so the heating time is 10 seconds or more.

The reason why the cooling rate is set to 5 ° C./sec or more is that if the cooling rate is less than 5 ° C./sec,
_{This is because 2} P and Fe are precipitated. Note that these precipitates generated during cooling do not contribute to the enhancement of the heat resistance and mechanical properties of the copper alloy. Therefore, the cooling rate is 5 ° C
/ Sec or more.

[0027]

EXAMPLE Next, a heat-resistant copper alloy sheet for a heat exchanger having a small expansion coefficient after hard brazing according to an example of the present invention was manufactured.
The results of testing the characteristics will be described in comparison with comparative examples that are outside the scope of the claims of the present application.

First, a copper alloy and a deoxidized copper (Cu-0.
02 wt% P) was melted under a charcoal coating in the atmosphere using a kryptor furnace, and then cast to obtain an ingot having a thickness of 50 mm, a width of 75 mm and a length of 180 mm.

[0029]

[Table 1]

The front and back surfaces of the ingot are 5 m
After m-face milling, the steel sheet was held at 940 ° C. for 1 hour using a Kanthal furnace, and then hot-rolled to a thickness of 15 mm, and these rolled materials were put into water and quenched. next,
After removing the oxide scale on the surface of these hot-rolled materials, the hot-rolled materials were cold-rolled to obtain cold-rolled materials having a thickness of 0.8 mm.

A cold-rolled material having the composition shown in Table 1 was immersed in a salt bath furnace adjusted to 525 to 800 ° C., held for 30 seconds, and cooled in water at a rate of about 10 ° C./sec to 100 ° C. or less. These were used as test materials of Examples 1 to 5. Table 2 shows their characteristics.

Further, a cold-rolled material having the composition shown in Table 1
After immersing in a salt bath furnace adjusted to 0 to 850 ° C and holding for 30 seconds, the temperature is reduced to 100 ° C or less by about 10 ° C / sec or 2 ° C.
/ Sec, and these were used as test materials of Comparative Examples 1 to 3, and a cold-rolled material having a composition shown in Table 1 was cooled in a salt bath furnace for 5 minutes.
Precipitation annealing of 75 ° C x 2Hr + 500 ° C x 4Hr,
It was cooled at a rate of 2 ° C./sec to 100 ° C. or less, and this was used as a test material of Comparative Example 4 (corresponding to a conventional example). After one
(0% cold rolling) was used as the test material of Comparative Example 5. Table 3 shows their characteristics.

[0033]

[Table 2]

[0034]

[Table 3]

Subsequently, Examples 1 to 5 manufactured as described above were used.
5 and each of the test materials of Comparative Examples 1 to 5 at a temperature of 830 ° C. in nitrogen, assuming actual hard brazing heating conditions.
Heating was performed for 0 minutes, and the characteristics after heating were examined (only the expansion coefficient depends on the heating conditions of the following test method). The results are shown in Tables 4 and 5.

[0036]

[Table 4]

[0037]

[Table 5]

However, in Tables 2 to 5, each characteristic was measured by the following test methods. (1) In the tensile test, a JIS No. 5 test piece cut out from each test material in parallel with the rolling direction was used to measure tensile strength, proof stress, and elongation. (2) The hardness of each test material was measured using a Vickers hardness meter under a load of 2 kg. (3) The conductivity was measured using a test piece having a width of 10 mm and a length of 300 mm using a double bridge, and calculating the average cross-sectional area method. (4) The crystal grain size was measured with an optical microscope.

(5) Regarding the measurement of the coefficient of expansion, the thickness was set to 0.
Using a test material having a length of 8 mm, a width of 8 mm, and a length of 20 mm, using an expansion length measuring device, 850 corresponding to the heating temperature for hard brazing.
After cooling to 10 ° C at 10 ° C / min, cool (air cooling, about 63
° C / min), and the length change (expansion coefficient) was measured. (6) In the fatigue test, use a thin plate fatigue tester,
A repetitive oscillating stress was applied to a test piece having a width of 10 mm cut out from each test material under the conditions of a cycle of 60 Hz, a stress amplitude of 2.5 mm, and an average stress of 15 kgf / mm ² . Then, the number of times until the test piece was broken by the repeated stress was measured.

In Examples 1 to 5, heating was performed at a temperature of 525, 550, 600, 650, and 800 ° C. for 30 seconds, respectively, before heating was performed assuming hard brazing.
It is a test material produced by cooling in water at a rate of ° C / sec. In contrast, Comparative Examples 1 and 2 were 400 and 850, respectively.
The test material heated at ℃ and the comparative example 3 was a test material having a cooling rate after heating of 2 ° C./sec, all of which fall outside the scope of the claims of the present invention. Comparative Example 4
Is a test piece obtained by a method corresponding to a conventional production method, and Comparative Example 5 is a test piece of conventional deoxidized copper (corresponding to -1 / 4H).

As is clear from Tables 2 to 5, Example 1
5 have a value close to that of Comparative Example 5 (deoxidized copper) after the hard brazing assumed heating, which is smaller than that of Comparative Example 4 corresponding to the conventional manufacturing method. This is because Fe is dissolved in the mother phase before heating for hard brazing, and the conductivity before heating is within the range of 20 to 50% IACS specified in the present invention. Further, the crystal grain size was determined in Comparative Example 5 (deoxidized copper).
, So that it has excellent mechanical properties and fatigue properties, and particularly has a proof strength of 9.5 times.

On the other hand, in Comparative Example 1, the heating temperature was 400
Due to the low temperature of ° C., Fe could not form a solid solution in the parent phase, so that the electrical conductivity was as high as 55% IACS, and the expansion rate after hard brazing assumed heating was as large as 0.07%. In Comparative Example 2, since the heating temperature was as high as 850 ° C., the crystal grains were 80 μm.
Therefore, the mechanical properties and fatigue properties after brazing are inferior. In Comparative Example 3, the cooling rate after heating was 2 ° C.
/ Sec, Fe is precipitated, and the conductivity before heating is 60% IACS, which is higher than the range specified in the present invention.
Therefore, the expansion coefficient after the heating for the brazing assumption is as large as 0.08%.

In Comparative Example 4 corresponding to the conventional production method, Fe was intentionally precipitated, so that the conductivity before heating was 70%.
% IACS, which is high, and therefore, the expansion coefficient after heating for the brazing assumption is as large as 0.09%. In Comparative Example 5 (deoxidized copper), the crystal grain size was coarsened to 200 μm by hard brazing, and the mechanical properties and fatigue properties after hard brazing assumed heating were inferior.

FIG. 2 shows the measurement results of the expansion length of the test pieces (Example 1, Comparative Examples 1, 4, and 5).
“a” indicates a change in the body temperature, and “b”, “c”, “d”, and “e” indicate changes in the expansion lengths (and elongation percentages) of Example 1 and Comparative Examples 1, 4, and 5, respectively. As shown here, Comparative Examples 1 and 4
In this case, Fe precipitated in the parent phase began to form a solid solution at around 500 ° C., and the expansion was larger than that of Comparative Example 5 (deoxidized copper). The dissolved Fe does not precipitate again, and as a result, does not return to its original state after cooling, and is considerably larger than the length before heating. On the other hand, in Example 1, since Fe was dissolved before heating, the coefficient of expansion (= elongation after cooling) after cooling was as low as that of Comparative Example 5 (deoxidized copper).

[0045]

The heat-resistant copper for a heat exchanger according to the present inventionAlloy plate
(Claim 1) is characterized by heat during hard brazing and welding.
Grain growth is suppressed and mechanical properties after hard brazing
Excellent quality and fatigue properties,Conductivity before hard brazing
By limiting, the expansion rate after hard brazing is small,example
For example, as a flange of the heat exchanger can, a bag made of deoxidized copper
Hard brazing, for example, when used in combination with
Deflection after heating is suppressed, and even if
It can be easily corrected in the process.

According to the method for producing a heat-resistant copper alloy sheet for a heat exchanger of the present invention ( claim 2 ), the mechanical properties and the fatigue properties after hard brazing are not deteriorated as compared with the material produced by the conventional production method. Thus, a heat-resistant copper alloy for a heat exchanger having a small expansion coefficient after hard brazing can be obtained. Therefore, the present invention is extremely useful for improving the reliability of the heat exchanger.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the conductivity of a test material before hard brazing and heating and the expansion coefficient after hard brazing and heating.

FIG. 2 shows an expansion history of a test material when hard brazing is performed.

FIGS. 3A and 3B are schematic diagrams showing the structure of a heat exchanger, wherein FIG. 3A is a front view and FIG. 3B is a side view.

FIG. 4 shows a copper alloy and a (flange portion) according to a conventional manufacturing method.
FIG. 4 is a side view showing the internal structure of the heat exchanger after hard brazing using a deoxidized copper (burner case portion) (when bending occurs).

[Explanation of symbols]

 1 Flange part 2 Burner case part 5 Flexure part

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C22C 1/00-49/14 C22F 1/00-3/02 F28F 21/08

Claims (2)

(57) [Claims] 1. Fe: 1.3 to 2.1% by weight, P:
0.001 to 0.1% by weight, Co: 0.2 to 1.0
% By weight, and Zn: 0.01 to 1.0% by weight, and the total of the Fe content and the Co content is 2.5% by weight or less, with the balance being Cu and unavoidable impurities. A copper alloy plate comprising, before brazing heating, a conductivity of 20 to 50% IACS and a crystal grain size of 1 to 50 μm, after hard brazing heating. Heat-resistant copper alloy plate for heat exchanger with small expansion coefficient. 2. Fe: 1.3 to 2.1% by weight, P:
0.001 to 0.1% by weight, Co: 0.2 to 1.0
% By weight, and Zn: 0.01 to 1.0% by weight, and the total of the Fe content and the Co content is 2.5% by weight or less, with the balance being Cu and unavoidable impurities. After hot working, quenching, and then cold working, then heating at 500 to 830 ° C for 10 seconds or more, and cooling at a cooling rate of 5 ° C / sec or more. A method for producing a heat-resistant copper alloy sheet for a heat exchanger, having an expansion coefficient R (%) after hard brazing and heating defined by the following formula of 0.05% or less. R = (L1−L0) ÷ L0 × 100 where L1: length after brazing, L0: length before brazing.