JPH0719786A - Corrosion-resistant copper alloy pipe - Google Patents

Abstract

PURPOSE:To obtain a corrosion-resistant copper alloy pipe having a high resistance to ant-nest-shaped corrosion and being suitable for a refrigerant piping by a method wherein an oxide film containing a prescribed additive element in a prescribe amount is formed on the surface of the main body of the pipe. CONSTITUTION:A corrosion-resistant copper alloy pipe has the main body of the pipe which contains one or two or more kinds of additive elements of which the standard enthalpy of formation of an oxide is -169kj/mol or less, in a range shown by the formula, and of which the residual part is constituted of Cu and unavoidable impurities, and an oxide film which is formed in a thickness of 40 to 2000Angstrom on the surface of the main body of the pipe by subjecting this main body to heat treatment. According to an analysis by an X-ray photoelectron spectroscopy at the surface of the oxide film, the ratio between the main peak intensity of the additive element and the main peak intensity of Cu is 0.10 or above. In the formula, Ax denotes the content (at.%) of the additive element (x), In a natural logarithm and DELTAH<0>f(x) the standard enthalpy of formation (kj/mol) of the oxide of the additive element (x).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corrosion resistant copper alloy pipe used as a copper alloy pipe for a refrigerant pipe or a copper alloy pipe for a heat exchanger, and particularly to an ant nest which rarely occurs in a refrigerant pipe or a heat exchanger pipe. The present invention relates to a corrosion-resistant copper alloy tube having improved corrosion resistance against corrosive corrosion.

[0002]

2. Description of the Related Art Conventionally, phosphorus deoxidized copper pipes have been widely used for refrigerant pipes or heat exchanger pipes because of their good bending workability and brazing property.

[0003]

However, in these pipes, organic substances such as lubricating oil or processing oil and organic solvents, which are unavoidably left in the pipe making process and the assembling process, are repeatedly adsorbed and evaporated by the refrigerant. In addition, when exposed to the unique temperature and humidity formed by the structure and the environment of aeration, it decomposes and contains carboxylic acid, causing a unique corrosion that locally presents an ant nest shape. There is.

Although a lot of lubricating oil is used in the heat exchanger assembling process, degreasing cleaning with an organic solvent tends to be avoided because of recent environmental problems, and a volatile lubricating oil is used instead of the organic solvent. Tend to be used. in this case,
Despite the fact that the base oil is volatile, some oily additives remain on the surface of copper pipes.

Therefore, as compared with the case where degreasing is performed with an organic solvent, it is considered that the risk of ant nest-like corrosion is increased as the volatile lubricating oil is used in the future. Under these circumstances, countermeasures against ant nest corrosion have recently attracted attention as a major problem. Therefore, as a pipe material for a refrigerant pipe or a heat exchanger, development of a copper alloy pipe having better corrosion resistance than a conventional phosphorus deoxidized copper pipe has been desired.

The present invention has been made in view of the above problems, and is exposed to a phenomenon peculiar to a refrigerant pipe or a heat exchanger pipe, that is, repeated adhesion and evaporation of water, and a specific temperature and humidity condition and Corrosion resistant copper that has excellent corrosion resistance against ant nest corrosion even when used under aeration conditions and can increase its reliability and life for refrigerant piping or heat exchanger piping. The purpose is to provide an alloy tube.

[0007]

The corrosion-resistant copper alloy tube according to the present invention has a standard enthalpy of oxide formation of -169 kJ.
/ Mol or less of one or more kinds of additional elements within the range shown by the following formula (1), and the balance consisting of Cu and inevitable impurities, and the surface of the tube body by heat treating the tube body And an oxide film formed to a thickness of 40 to 2000 Å, and a main peak intensity (Ix) of the additive element and a main peak intensity of Cu (Ix) in an analysis by X-ray electron spectroscopy on the surface of the oxide film. A corrosion-resistant copper alloy pipe having a ratio (Ix / ICu) of 0.10 or more. 0.04 ≦ Σ [Ax · ln (ΔH ⁰ f (x) /-169)] ≦ 4.2 (1) where Ax: content of additive element x (atomic%) ln; natural logarithm ΔH ⁰ f (X); standard enthalpy of formation of oxide of additive element x (kJ / mol) Σ; Ax · ln (ΔH ⁰ f (x) for each additive element
/ -169) value sum.

[0008]

The present inventors conducted various experimental studies to improve the corrosion resistance of copper alloy tubes. As a result, on the surface of the pipe body, the standard enthalpy of oxide formation is Cu oxide (C
u ₂ O) standard enthalpy of formation (-169 kJ / mo)
It was found that by providing an oxide film containing a predetermined amount of an oxide of an element smaller than 1) when the Kelvin temperature is 298.15K), the corrosion resistance against ant nest corrosion is significantly improved. Such an oxide film has a standard enthalpy of oxide formation of −169 kJ / mol or less and contains one or more additive elements and the balance consisting of Cu and inevitable impurities, for example, in an inert atmosphere. Alternatively, it can be formed by annealing in an atmosphere containing an extremely small amount of oxygen.

In this case, if the thickness of the oxide film is less than 40Å, the effect of improving the corrosion resistance cannot be sufficiently obtained. On the other hand, when the thickness of the oxide film exceeds 2000Å, the effect of improving corrosion resistance is saturated, and further effect cannot be expected, and the brazing property is deteriorated.
Therefore, the thickness of the oxide film needs to be 40 to 2000 liters.

As for the additive element, the smaller the standard enthalpy of formation of oxide, the greater the effect of improving the corrosion resistance. In addition, the higher the content of the additional element, the higher the corrosion resistance against ant nest corrosion. However, if the content of the additive element exceeds a certain value, the workability of the copper alloy tube is significantly reduced. Therefore, the lower limit of the content of the additional element is limited from the viewpoint of corrosion resistance, and the upper limit is limited from the viewpoint of workability. As a result of various experimental studies, the inventors of the present application have found that an oxide film having excellent corrosion resistance to ant nest corrosion can be obtained by setting the content of the additional element within the range shown by the following mathematical formula 1. It was

[0011]

## EQU1 ## 0.04 ≦ Σ [Axln (ΔH ⁰ f (x) /
-169)] ≦ 4.2, where Ax; content (atomic%) of additional element x ln; natural logarithm ΔH ⁰ f (x); standard formation enthalpy of oxide of additional element x (kJ / mol) Σ; Ax · ln (ΔH ⁰ f (x) for each additive element
/ -169) value sum.

That is, the corrosion resistance due to the oxide film is related to the standard enthalpy of formation and content of the oxide of the additional element,
The value obtained by calculating Equation 2 below can be used as an index of corrosion resistance.

[0013]

2 [Ax · ln (ΔH ⁰ f (x) /-169)]

That is, when the oxide film on the surface of the copper alloy tube contains an element having an affinity for oxygen larger than that of copper (that is, an additive element having a small standard enthalpy of oxide formation), the oxide of the additive element is the main constituent. Becomes In general, adsorbed water exists as hydroxyl groups on the oxide surface, and an oxide having a smaller standard enthalpy of formation tends to have more adsorbed water. Therefore, when the standard enthalpy of formation of the oxide of the additional element is represented by ΔH ⁰ f (x), the oxide of Cu (Cu ₂
O) standard enthalpy of formation (-169 kJ / mol)
It can be said that an alloy containing an element having a larger ratio [ΔH ⁰ f (x) /-169] with the surface is covered with more hydroxyl groups than pure copper. In the alloy having many hydroxyl groups on the surface, when dew condensation occurs on the surface, water droplets spread in a film shape, so that unevenness of the surface state is unlikely to occur and ant nest corrosion is less likely to occur. That is, the value of Equation 2 described above can be used as a measure of the corrosion resistance against ant nest corrosion. Further, the effect becomes more remarkable as the content of these additional elements increases, but the present inventors have found that the content Ax and [ΔH ⁰ f
There is a correlation with the value of (x) / − 169], and the corrosion resistance improving effect is the product of the natural logarithm of [ΔH ⁰ f (x) /-169] and Ax, that is, Ax · ln (ΔH ⁰ f (X) /-1
69), and when more than two kinds of additional elements are contained, Ax.ln (ΔH ⁰ f (x) / − 16
It was experimentally found that the value of 9) is additive.

Therefore, when a plurality of kinds of elements are added, it is necessary to add the values obtained by the mathematical formula 2 for each element. That is, it becomes as shown in the following formula 3.

[0016]

[Equation 3] Σ [Ax · ln (ΔH ⁰ f (x) /-169)]

If the value obtained by the mathematical formula 3 is less than 0.04, the effect of improving the corrosion resistance due to the oxide film cannot be sufficiently obtained. Further, when the value obtained by the mathematical formula 3 exceeds 4.2, the effect of improving the corrosion resistance is saturated, and further improvement of the corrosion resistance cannot be expected, and the workability of the copper alloy pipe is deteriorated by the additive element. Will end up. Therefore, the content of the additional element needs to be within the range shown in the above-mentioned formula 1.

The characteristics of the oxide film formed on the tube surface can be easily judged by the main peak intensity in X-ray electron spectroscopy (XPS) analysis. That is, when the ratio (Ix / ICu) of the main peak intensity (Ix) of the additive element and the main peak intensity (Cu) of Cu is 0.10 or more, a remarkable effect of improving the corrosion resistance against ant nest-like corrosion can be obtained. Obtainable. The ratio between the main peak intensity (Ix) of the additive element and the main peak intensity (Cu) of Cu will be described in more detail below.

The corrosion resistance of a copper alloy is
It is widely known that it largely depends on the film formed on the surface. In the present invention, excellent corrosion resistance is obtained not only by limiting the thickness of the oxide film formed on the surface but also by defining the elements forming the oxide film.
In order to further enhance the effect of an alloy containing an additive element with a small standard enthalpy of oxide formation, the oxide film formed on the surface of the alloy contains an additive element in an amount more than the ratio of the alloy composition of the pipe body. It is necessary to perform the surface analysis by XPS analysis as the index, which is the most practical from the technical and economical viewpoints. The inventors of the present invention have found that the main peak intensity (Ix) of the additive element and the main peak intensity (Ix) of Cu
As a result of repeating various experiments to investigate the relationship between the corrosion resistance and the ratio (Ix / ICu) with Cu), the ratio (Ix / ICu) of the main peak intensity (Ix) of the additive element and the main peak intensity (ICu) of Cu ) Is 0.10 or more, it was found that the effect of improving the corrosion resistance becomes remarkable. Main peak intensity (Ix) of additive element and main peak intensity (IC) of Cu
The means for making the ratio (Ix / ICu) with respect to u) 0.10 or more is not particularly limited. For example, in the annealing step for softening the copper alloy tube, oxygen and C in the atmosphere are used.
By controlling the ratio of the reducing gas such as O, the main peak intensity ratio (Ix / ICu) can be set to 0.10.

[0020]

EXAMPLES Next, examples of the present invention will be described in comparison with comparative examples.

First, a pipe material having a composition shown in Table 1 (O material;
An outer diameter of 9.5 mm × thickness of 0.3 mm) was produced by the steps of melt casting → hot extrusion → cold drawing → heat treatment. In addition, Table 1
In, the numerical value below the element symbol column is 298.15.
It is a standard enthalpy of formation (unit: kJ / mol) of an oxide of the element at a temperature of K. The values calculated by Equation 3 (column for the value of Σ []), the thickness of the oxide film, and the main peak strength ratio (Ix / ICu) for each copper alloy tube (or copper tube) of these Examples and Comparative Examples. ) Are also shown in Table 1. The thickness of the oxide film is AES (Auger Electron
It was determined from the etching time by Spectroscopy) analysis. The main peak intensity measured by XPS analysis is Mg
Output is 300W using X-ray (Kα) output from
(Voltage is 15 kV, current is 20 mA), analysis area is 10
The measurement was performed under the condition of 00 μm ² .

The corrosion resistance, the brazing property and the hot workability against ant nest corrosion of these Examples and Comparative Examples were evaluated by the following methods.

Corrosion resistance to ant nest corrosion The test piece was exposed to the environment of formic acid, which is a typical carboxylic acid, and the maximum corrosion depth after corrosion was measured. The test conditions are shown below. -Corrosion medium: 100 ml of 1% formic acid.・ Exposure condition: A test piece (length 1
00 mm) and the beaker is placed in a container having a volume of 1 liter containing the corrosive medium and sealed. -Temperature conditions and test period: The temperature was kept at 40 ° C for 20 days.

Brazing Property The brazing property was evaluated by assembling the fins coil, brazing the return bend part, and checking the presence or absence of leakage. The brazing conditions are that the brazing material is BCuP-2, the temperature is 850 ° C., and the brazing time is 30 seconds. Then, after brazing, an air tightness test was performed at an air pressure of 2.94 MPa.

The hot workability ingot diameter from 15mm, samples the specimen落槌test 15mm length, deformation rate of 50% at a temperature of 850 ° C.
And the presence or absence of cracks was examined.

The results are summarized in Table 2 below.
However, the brazing property was indicated by x when a leak occurred and by o when there was no leak. Further, the hot workability is indicated by x when cracks occur and by o when cracks do not occur.

[0027]

[Table 1]

[0028]

[Table 2]

As is clear from Table 2, Examples 1 to 1
No. 12 had a very small corrosion depth of 0.03 mm or less, and had good brazability and hot workability. On the other hand, in Comparative Examples 1, 2, 3, 8 and 12, in which the value of Equation 3 (column for the value of Σ []) is 0.02 or less, the corrosion depth is 0.19.
Comparative Examples 6, 9 and 11 having a large value of mm or more and a value of Formula 3 of 4.42 or more had poor hot workability.
Further, in Comparative Examples 4, 8 and 11 in which the oxide film had a thickness of 2500 Å or more, the brazing property was poor. Further, Comparative Examples 1, 5, 7, 10, and 12 having a small peak intensity ratio (Ix / ICu) of 0.07 or less had insufficient corrosion resistance.

[0030]

As described above, in the corrosion-resistant copper alloy pipe according to the present invention, since the oxide film containing the predetermined amount of the predetermined additive element is formed on the surface of the pipe body, the conventional phosphorus-deoxidized copper pipe Ant-like corrosion that occurs uniquely in refrigerant pipes or refrigerant pipes for heat exchangers, that is, ant-like corrosion that occurs under conditions of unique temperature and humidity and aeration environment due to repeated adhesion and evaporation of water. The present invention is extremely useful because it has excellent corrosion resistance and can increase its reliability and life as a refrigerant pipe or a heat exchanger pipe.

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[Procedure amendment]

[Submission date] August 19, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 1

[Correction method] Change

[Correction content]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction content]

[0007]

The corrosion-resistant copper alloy tube according to the present invention has a standard enthalpy of oxide formation of -169 kJ.
/ Mol or less of one or two or more additive elements within the range shown by the following formula (1), and the balance consisting of Cu and inevitable impurities, and the surface of the tube body by heat treating the tube body And an oxide film formed to a thickness of 40 to 2000 Å, and a main peak intensity (Ix) of the additive element and a main peak intensity of Cu (Ix) in an analysis by X-ray electron spectroscopy on the surface of the oxide film. A corrosion-resistant copper alloy pipe having a ratio (Ix / ICu) of 0.10 or more. 0.04 ≦ Σ [Ax · ln { ΔH ⁰ f (x) / ( −16
9) } ] ≤ 4.2 (1) where Ax; content of additive element x (atomic%) ln; natural logarithm ΔH ⁰ f (x); standard formation enthalpy of oxide of additional element x (kJ / mol) Σ; Ax · ln { ΔH ⁰ f (x) for each additive element
The sum of the values of / ( -169) } .

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

[0011]

## EQU1 ## 0.04 ≦ Σ [Axln { ΔH ⁰ f (x) /
( −169) } ] ≦ 4.2 where Ax; content of additive element x (atomic%) ln; natural logarithm ΔH ⁰ f (x); standard enthalpy of formation of oxide of additional element x (kJ / mol) Σ; Ax · ln { ΔH ⁰ f (x) for each additive element
Sum of the values of / ( -169) } .

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction content]

[0013]

[2] [Ax · ln { ΔH ⁰ f (x) / ( -169) } ]

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

That is, when the oxide film on the surface of the copper alloy tube contains an element having an affinity for oxygen larger than that of copper (that is, an additive element having a small standard enthalpy of oxide formation), the oxide of the additive element is the main constituent. Becomes In general, adsorbed water exists as hydroxyl groups on the oxide surface, and an oxide having a smaller standard enthalpy of formation tends to have more adsorbed water. Therefore, when the standard enthalpy of formation of the oxide of the additional element is represented by ΔH ⁰ f (x), the oxide of Cu (Cu ₂
O) standard enthalpy of formation (-169 kJ / mol)
It can be said that the alloy containing an element having a larger ratio { ΔH ⁰ f (x) / ( -169 )} with the surface is covered with more hydroxyl groups than pure copper. In the alloy having many hydroxyl groups on the surface, when dew condensation occurs on the surface, water droplets spread in a film shape, so that unevenness of the surface state is unlikely to occur and ant nest corrosion is less likely to occur. That is, the value of Equation 2 described above can be used as a measure of the corrosion resistance against ant nest corrosion. Also,
The effect becomes more remarkable as the content of these additional elements increases, but the inventors of the present application have found that the content Ax and { ΔH ⁰ f
There is a correlation with the value of (x) / ( -169 )} , and the corrosion resistance improving effect is { ΔH ⁰ f (x) / ( -16
9 )} natural logarithm and Ax, that is, Axln { ΔH ⁰
f (x) / ( -169 )} can be evaluated, and further 2
If more than one kind of additive element is contained, Ax · ln { ΔH
It was experimentally found that the value of ⁰ f (x) / ( -169) } is additive.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

[0016]

Σ [Ax · ln { ΔH ⁰ f (x) / ( -169) } ]

Claims (1)

[Claims] 1. The standard enthalpy of formation of oxide is -16.
A tube body containing one or more additive elements of 9 kJ / mol or less in the range represented by the following formula (1) and the balance consisting of Cu and inevitable impurities, and a heat treatment of the tube body An oxide film formed to a thickness of 40 to 2000 Å on the surface, and the main peak intensity (Ix) of the additive element and the main peak intensity of Cu by analysis by X-ray electron spectroscopy on the surface of the oxide film. A corrosion-resistant copper alloy tube having a ratio (Ix / ICu) with respect to (ICu) of 0.10 or more. 0.04 ≦ Σ [Ax · ln (ΔH ⁰ f (x) /-169)] ≦ 4.2 (1) where Ax: content of additive element x (atomic%) ln; natural logarithm ΔH ⁰ f (X); standard enthalpy of formation of oxide of additive element x (kJ / mol) Σ; Ax · ln (ΔH ⁰ f (x) for each additive element
/ -169) value sum.