JPH0995748A - Corrosion resistant copper alloy excellent in high temperature ductility and annealing brittleness resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a copper alloy at low material cost and production cost by using a cupro nickel alloy improved in annealing brittleness resistance as the base and regulating the combination of alloy compsns, the amt. of impurities or the like. SOLUTION: This copper alloy has a compsn. contg., by weight, 29 to 33% Ni, 0.4 to 2.3% Fe, 0.2 to 2.5% Mn and 0.001 to 0.05% Zr, in which the content of Zn as an impurity is regulated to <=0.5%, and the balance Cu, the quantitative relation between Mn and Fe satisfies Fe%-1.5<=Mn%<=Fe%+1.5, and the total content of Cu, Ni, Fe and Mn is regulated to >=99.5%. This copper alloy is excellent in high temp. ductility, is free from the generation of cracks caused by annealing brittleness during the process of the production, is furthermore excellent in corrosion resistance and is satisfactory in the case of valued from the total view point of the production cost, the improvement of the productility or the like.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a corrosion resistant copper alloy excellent in high temperature ductility and resistance to annealing brittleness, and more specifically, to a corrosion resistant copper alloy having no cracks due to annealing brittleness during the manufacturing process and excellent corrosion resistance. Regarding nickel alloys.

[0002]

2. Description of the Related Art A cupronickel alloy containing about 30% Ni (JIS H 3300 C7150, BS2871, CN107) and a high Fe high Mn cupronickel alloy (JIS H 3300 C7164, BS2871, Since CN108) has excellent seawater corrosion resistance, it has been applied as a heat transfer tube for multi-tube heat exchangers or multi-stage evaporative seawater desalination equipment that uses seawater as cooling water, such as in power plants and chemical plants.

The production of these cupro nickel alloy tubes is as follows.
Generally, it is performed by continuous casting, hot working (hot rolling, hot extrusion) of the ingot, and then cold working (cold rolling, cold drawing) and heat treatment. Medium, especially when hot working the ingot, cracks easily occur due to the decrease in ductility, and also during the ingot heating before performing hot working,
Fine cracks are likely to occur in the process of relaxing the stress remaining in the ingot, which causes work cracks in the subsequent hot working or cold working. These phenomena are called annealing brittleness, which is an obstacle to the production of cupro nickel pipes.

As a measure for preventing the annealing brittleness, the grain size of the ingot is made finer, and the working degree at the time of hot working is limited. Although it is possible to some extent by lowering the pouring temperature or increasing the cooling rate, the casting rate is greatly reduced, and the productivity is reduced. There is also a problem that casting defects such as shrinkage cavities are likely to occur. Although it is possible to make the crystal grains finer by performing electromagnetic stirring during casting, an expensive electromagnetic stirring device is required, resulting in an increase in production cost. Further, annealing brittleness cannot be completely prevented only by refining ingot crystal grains. Limiting the workability during hot working lowers the production efficiency.

The alloy composition is adjusted to, for example, 24 to 38%.
Ni, containing 2.3-3.8% Cr and less than 2% M
a copper-nickel alloy containing n, 0.02% or less of carbon, 0.8% or less of Zr, the balance being substantially copper, and having improved hot workability (Japanese Patent Publication No. 51-44089), 29-33%
Ni, 0.01-1% Fe, 0.01-1.5% Mn,
A cupronickel alloy (British Patent No. 1,144,334) containing 0.05 to 0.5% Zr and the balance being substantially copper and having improved annealing brittleness resistance has been proposed, but in addition to the annealing brittleness resistance, It is not always sufficient when evaluated from a comprehensive viewpoint such as corrosion resistance, production cost, and improvement of productivity.

[0006]

DISCLOSURE OF THE INVENTION The present invention is based on the above cupro-nickel alloy having improved resistance to annealing and brittleness.
In order to obtain a comprehensively excellent alloy, it was made as a result of various experimental studies on the combination of alloy compositions, the amount of impurities, etc. It does not cause cracks during ingot heating or hot working, and has excellent corrosion resistance such as pitting corrosion resistance, crevice corrosion resistance, and erosion resistance. Material cost and production cost are reduced compared to the above cupro nickel alloy. Another object of the present invention is to provide a corrosion-resistant copper alloy excellent in high temperature ductility and resistance to annealing and brittleness that can also improve productivity.

[0007]

The corrosion resistant copper alloy excellent in high temperature ductility and annealing brittleness according to the present invention for achieving the above object is Ni: 29-33%, Fe: 0.4-2.
3%, Mn: 0.2 to 2.5%, Zr: 0.001% or more and less than 0.05%, and Zn as an impurity is less than 0.1%.
5% or less, the balance Cu and unavoidable impurities,
The quantitative relationship between Mn and Fe is Fe% -1.5 ≦ Mn ≦ Fe
% + 1.5, and the total amount of Cu, Ni, Fe and Mn is 99.5% or more.

Explaining the significance and the reason for limiting the addition of alloying components in the present invention, Ni is necessary for ensuring the corrosion resistance of the alloy, and the preferable content range is 29-.
33%. If the Ni content is less than 29%, the corrosion resistance is not sufficient, and if it exceeds 33%, the solid solubility of hydrogen increases and annealing embrittlement easily occurs.

Fe improves the erosion resistance of the Cu-Ni alloy. The effect is particularly remarkable when 0.4% or more is added. The preferable content is in the range of 0.4 to 2.3%, and when it exceeds 2.5%, the pitting corrosion resistance and the crevice corrosion resistance decrease. Mn also gives the alloy the same effect as Fe. The preferable content range is 0.2 to 2.5%, and when Mn exceeds 2.5%, the pitting corrosion resistance and the crevice corrosion resistance are reduced as in the case of Fe.

Zr is an important component for improving the high temperature ductility of the alloy and improving the annealing embrittlement resistance in combination with other components in the alloy. The preferred content is 0.0
The content is in the range of 01% or more and less than 0.05%, and the content of this range makes the crystal grains finer and also functions to capture sulfur (S) and segregated hydrogen in the grain boundaries that cause annealing brittleness. Have. In addition, intermetallic compounds (N
i, Cu) ₅ Zr is crystallized to act to increase the grain boundary bonding force.

If Zr is less than 0.001%, the effect is small, and if it is 0.05% or more, the recrystallization temperature of the alloy becomes high, and precipitation hardening occurs due to the precipitation of Zr in the heat treatment step of the alloy, so that the high temperature is high. Therefore, softening treatment for a long time is required, resulting in a decrease in productivity and an increase in production cost. Moreover, since Zr itself is expensive, the material cost increases. A more preferable content range of Zr is 0.01 to 0.
It is 03%.

Zn as an impurity needs to be limited to 0.5% or less, and if it exceeds 0.5%, crevice corrosion resistance tends to deteriorate. As other impurities, sulfur (S) is 0.001% or less and hydrogen (H) is 0.0005.
% Or less, and carbon is preferably limited to 0.16% or less from the viewpoint of annealing brittleness resistance.

Regarding the quantitative relationship between Fe and Mn, Fe%
The relational expression of −1.5 ≦ Mn ≦ Fe% + 1.5 is satisfied to ensure that corrosion resistance is obtained. If this relational expression is not satisfied, erosion and crevice corrosion are likely to occur. Further, in order to ensure the high temperature ductility, the annealing brittleness resistance and the corrosion resistance in consideration of the above-mentioned components and impurities, the total amount of Cu, Ni, Fe and Mn is 99.5%.
As described above, it is necessary to reduce impurities as much as possible.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The copper alloy of the present invention is used as a pipe material or a plate material as a member such as a heat exchanger. It is carried out by carrying out cold rolling or hot extrusion, cold rolling or cold drawing, and heat treatment.

[0015]

Hereinafter, examples of the present invention will be described in comparison with comparative examples. Example 1 A Cu-Ni alloy having the composition shown in Table 1 was used in a vacuum melting furnace, the pressure inside the furnace was reduced to about 1.3 Pa, and the ingot was replaced with argon gas to be melted, and an ingot having a diameter of 100 mm and a length of 150 mm was formed. Was manufactured, and the following tests and measurements were performed for each ingot. Table 2 shows the results.

(1) Measurement of grain size (2) Hot forging test: Test pieces each having a diameter of 25 mm and a height of 25 mm were cut out from each ingot, and these test pieces were set in an electric furnace set at 800 to 1000 ° C. After holding for 1 hour, a forging process with a compression rate of 70% was performed within 10 seconds, and the hot ductility was evaluated from the presence or absence of cracking of the test piece. Test temperature is 800 ℃, 850
℃, 900 ℃, 950 ℃ and 1000 ℃. (3) High temperature tensile test: In accordance with JIS Z 2201 from each ingot
Cut out the No. 4 test piece and use an Instron tester,
Each test piece was heated to 850 ℃ in an electric furnace attached to the tester and held for 15 minutes, then subjected to tensile deformation at a strain rate of 1.4 × 10 ^-2 s ^-1 until it broke, and from the elongation and cross-section reduction rate. The hot ductility and the annealing brittleness were evaluated. (4) Measurement of softening temperature: Compared with conventional alloys, in order to see the necessity of changing the heat treatment conditions in actual production, for each ingot, standard processing in actual production (hot working ratio 80%,
Cold workability (75%) was added, and then heat treatment was performed for 10.5 minutes in an electric furnace set at 500 to 800 ° C, Vickers hardness was measured, and the temperature at which the measured value suddenly dropped was defined as the softening temperature. .

[0017]

[Table 1]

[0018]

[Table 2]

As shown in Table 2, in all the test materials according to the present invention, the crystal grain size of the ingot is as fine as 1 mm or less, cracks do not occur in the hot forging test, and the elongation in the high temperature tensile test is not generated. Also, it has excellent hot ductility with a cross-section reduction rate of 30% or more, and has a softening temperature of 600 to 640 ° C, so there is no need to change conventional heat treatment conditions.

Comparative Example 1 A Cu-Ni alloy having the composition shown in Table 3 was cast by the same method as in Example 1, and the obtained ingot was subjected to the same tests and measurements as in Example 1. The results are shown in Table 4. In Table 3, those that do not satisfy the conditions of the present invention are underlined.

[0021]

[Table 3]

[0022]

[Table 4]

As shown in Table 4, the test material No. 6 is Ni
Since the content of hydrogen is high, the concentration of solid solution hydrogen is high and sufficient hot ductility cannot be obtained. Since the Zr content of Test Material No. 7 was too small, the crystal grain size was large and the high temperature ductility was poor, and the fracture surface of the test piece after the high temperature tensile test was observed and showed brittle fracture. Since the test material No. 8 has a large amount of Zr, the softening temperature becomes high, and the general heat treatment (780 ℃
(× 10.5 minutes) does not show sufficient softening, and requires high heat treatment temperature for a long time, resulting in lower productivity and higher production cost.

Example 2, Comparative Example 2 A Cu-Ni alloy having the composition shown in Table 5 was melted using an electric furnace (charge amount: 2 ton), and was ingot-cast by continuous casting. A tube material with a diameter of 30 mm and a thickness of 1 mm was manufactured by hot extrusion, cold drawing and softening treatment. These pipes were subjected to the jet test and crevice corrosion test shown below to evaluate erosion resistance and crevice corrosion resistance. Table 6 shows the results. In Table 5, those outside the conditions of the present invention are underlined.

(1) Jet test: Seawater mixed with 1 to 2 vol% of air bubbles was sprayed on the inner surface of the halved pipe material at 8 m / s for 7 days, and the erosion depth was measured and tested simultaneously. JIS H
The erosion resistance of 3300 C7150 alloy tubing and C7164 alloy tubing was compared. (2) Crevice corrosion test: Teflon sheet of 20 mm x 20 mm x 1 mm is laid on the inner surface of a pipe material with a length of 55 mm, and it is pressed with a vinyl chloride tube with an outer diameter of 22 mm and stopped with a rubber band, then for 20 days. It was immersed in seawater, the corrosion depth was measured, and it was compared with JIS H3300 C7150 alloy pipe material and C7164 alloy pipe material tested at the same time.

[0026]

[Table 5]

[0027]

[Table 6] <Table Note> ○: JIS H 3300 C7150, C7164 equivalent or above
×: Inferior to JIS H3300 C7150, C7164.

As shown in Table 6, test material N according to the present invention
All of o.9 to No.11 have sufficient corrosion resistance as heat exchanger members. On the other hand, the test material No. 12 has a large amount of Zn and thus is inferior in crevice corrosion resistance, and the test material No. 13 has a low content of Ni and therefore has poor erosion resistance. Test Material No.14
Has a high Fe content, and the test material No. 17 has a high Mn content, and thus both have poor crevice corrosion resistance. The test material No. 15 has a low Fe content and the test material No. 16 has a low Mn content. Poor erosion resistance. Test material No. 18 is inferior in crevice corrosion resistance because it does not satisfy the relational expression between Fe and Mn.

[0029]

As described above, according to the present invention, Ni2
In a cupro nickel alloy containing 9-33%,
Excellent corrosion resistance, it is possible to prevent the occurrence of cracks due to annealing embrittlement during the manufacturing process, reduce material cost, manufacturing cost, improve productivity, and high temperature ductility and annealing brittleness. A corrosion resistant copper alloy is provided.

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[Procedure amendment]

[Submission date] November 6, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

Fe improves the erosion resistance of the Cu-Ni alloy. The effect is particularly remarkable when 0.4% or more is added. The preferable content is in the range of 0.4 to 2.3% , and when it exceeds 2.3% , the pitting corrosion resistance and the crevice corrosion resistance decrease. Mn also gives the alloy the same effect as Fe. The preferable content range is 0.2 to 2.5%, and when Mn exceeds 2.5%, the pitting corrosion resistance and the crevice corrosion resistance are reduced as in the case of Fe.

Claims (1)

[Claims] 1. Ni: 29 to 33% (weight%, the same hereinafter), Fe: 0.4 to 2.3%, Mn: 0.2 to 2.5.
%, Zr: 0.001% or more and less than 0.05%,
The content of Zn as an impurity is 0.5% or less, the balance is Cu and unavoidable impurities, and the quantitative relationship between Mn and Fe satisfies Fe% −1.5 ≦ Mn% ≦ Fe% + 1.5. , Cu, Ni, Fe and Mn total amount is 99.5%
Corrosion resistant copper alloy excellent in high temperature ductility and annealing brittleness characterized by the above