JP2000192175A - Copper alloy for cold working and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To particularly improve the cold forgeability of an alloy and to make better its corrosion resistance and stress corrosion cracking resistance by controlling an apparent Zn content to a specified range and controlling an Sn content to a specified range. SOLUTION: In an alloy, an apparent Zn content is controlled to 10 to 35 wt.%, and an Sn content is controlled to 1 to 1.6 wt.%. The apparent Zn content is expressed by (B+t.Q)/(A+B+t.Q)×100, A denotes a Cu content (wt.%), B denotes a Zn content (wt.%), (t) denotes a Zn equivalent of the 3rd element to be added (such as Sn), and Q denotes the content (wt.%) of the 3rd element. As to this alloy, after cold drawing, annealing is executed for controlling the internal pressure, and the annealing temp. is controlled to <=450 deg.C, preferably to <=380 deg.C. Moreover, as to the one in which cold drawning and annealing are repeatedly executed, the final annealing temp. is controlled to <=450 deg.C, preferably to 380 deg.C, and the annealing temp. on the way is suitably controlled to about 550 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a copper alloy for cold working, particularly for cold forging, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, as a copper alloy having excellent cold workability (forgeability), brass (JIS C2600, JIS C2
700) are known. In addition, copper bronze (JIS C22
00) is used for cold working (forging) in some cases.

[0003]

However, since brass (JIS C2600, JIS C2700) is inferior in corrosion resistance and stress corrosion cracking resistance, its use place is limited. On the other hand, in copper (JIS C2200), the cold workability (forgeability) is not always good, and there are problems such as forging defects.

Further, in a conventional method for producing a copper alloy for cold working, the hardness distribution of the material (the difference in hardness between the surface and the center).
It is hard to say that sufficient measures have been taken for the optimization of the thickness and the adhesion of the oxide film, and this has caused a reduction in cold workability.

An object of the present invention is to provide a copper alloy which is excellent in cold workability, particularly cold forgeability, and has good corrosion resistance and stress corrosion cracking resistance.

Another object of the present invention is to eliminate the cause of deterioration in cold workability in a method of manufacturing a copper alloy for cold working.

[0007]

In the present invention, the apparent Zn content is 10 to 35 wt%, preferably 15 to 30 wt%, and the Sn content is 1 to 1.6 wt%.
By having a composition that is wt.%, not only characteristics excellent in corrosion resistance and stress corrosion cracking resistance, but also cold workability,
In particular, characteristics excellent in cold forgeability can be obtained.

That is, when the apparent Zn content is 10 w
With a copper alloy of about t%, corrosion resistance is originally good, but S
Since the addition of n increases the hardness and lowers the friction coefficient, adhesion to the mold is suppressed, and forging defects such as galling of the mold are reduced.

The apparent Zn content is 10 wt%.
If it is less than the above, the hardness is also improved by the addition of Sn, but the cold ductility is too low, so that it is not suitable for cold working (forging).

On the other hand, the apparent Zn content is 35 wt%.
In some copper alloys, the addition of Sn improves the corrosion resistance and stress corrosion cracking resistance.

The apparent Zn content is 35 wt%.
In super-copper alloys, the apparent Zn content is large,
In order to ensure corrosion resistance, the amount of Sn must be increased,
As a result, the cold ductility decreases.

Here, the term "apparent Zn content" means that A is Cu content [wt%], B is Zn content [wt%], and t is a third element (for example, Sn). Z
When n equivalents and Q are the content of the third element [wt%], “{(B + t · Q) / (A + B + t · Q)} × 10
0 ”is used.

[0013] The present invention also provides a method for producing a copper alloy for cold working, in particular, for cold forging, in which annealing for internal stress adjustment is performed after cold drawing, wherein the annealing temperature is 450 ° C or less.
It is characterized in that the temperature is preferably 380 ° C. or lower.

According to this manufacturing method, the hardness of the material surface is increased and the friction coefficient is reduced, so that adhesion to the mold is suppressed, and forging defects such as mold galling are reduced.

As a preferred embodiment, in the case where the cold drawing and the annealing are repeatedly performed, the final annealing temperature is 450.
° C or lower, preferably 380 ° C or lower, and the annealing temperature during the process is preferably about 550 ° C.

Thus, the hardness of the material can be lowered after annealing in the middle, so that the working ratio can be increased in the subsequent cold drawing.

As an embodiment of the composition, the apparent Zn content is 10 to 35 wt%, preferably 15 to 30 wt%.
It is desirable to have a composition in which the content of Sn and the content of Sn is 1 to 1.6 wt%.

The present invention is further characterized in that in the method for producing a copper alloy for cold forging produced through hot extrusion, the hot extrusion temperature is 800 ° C. or less.

According to this manufacturing method, surface defects associated with oxide films and the like are suppressed, and defects during cold working are reduced. Therefore, not only the workability such as the cold forging but also the pre-processability such as the cold drawing is improved, and the effect of reducing the number of times of the cold drawing is also exerted.

In a preferred embodiment, the hot extrusion temperature is set to 650 ° C. or less, and preferably, the cross-sectional reduction rate is set to 90% or more to suppress the coarsening of the crystal grain size and make the crystal grain size smaller. Defects are further suppressed.

When extruding at 800 ° C. or less as described above, the apparent Zn content is 10 to 35 wt%.
Preferably, the content of Sn is 15 to 30% by weight and the content of Sn is 1 to 1.
It is desirable to have a composition of 6 wt%. because,
This is because, in such a composition range, the hot ductility is good, and the extrusion moldability is good even at a low temperature.

[0022]

Embodiments of the present invention will be described below. First, FIG. 1 shows the apparent Zn content,
It shows the relationship between cold ductility, hardness and corrosion resistance.

Referring to FIG. 1, first, the characteristics without Sn will be described. If the apparent Zn content is 10 wt% corresponding to copper (JIS C2200), the corrosion resistance is good because the Zn content is small. However, it is inferior in cold ductility and hardness and inferior in cold workability. When the apparent Zn content is 5 wt%, the cold workability is further reduced.

On the other hand, brass (JIS C2600, JIS
C2700), an apparent Zn content of 30,
35% by weight has excellent cold ductility and hardness and good cold workability, but is inferior in corrosion resistance and stress corrosion cracking resistance. When the apparent Zn content is 40 wt%, the cold ductility is slightly lowered, and the cold workability is slightly lowered.

Next, referring to FIG. 1, the characteristics in the presence of Sn will be described.
The alloy containing 0 wt% has excellent corrosion resistance and cold workability as a result of the improvement in corrosion resistance due to the addition of Sn.

With an apparent Zn content of 35 wt%, the corrosion resistance is similarly improved by the addition of Sn, but a large amount of Sn must be added to secure the corrosion resistance, so that the cold ductility is slightly reduced. However, there is no problem in practical use.
When the apparent Zn content reaches 40 wt%, S
The decrease in cold ductility due to the addition of n is large, and practical use is difficult.

In the case of an apparent Zn content of 10 wt%, the hardness is improved by adding Sn. In addition, when the apparent Zn content becomes 5 wt%, although the hardness is improved by the addition of Sn, the cold ductility remains poor.
Practical is difficult.

As described above, an apparent Zn content of 10
Brass having a composition range of up to 35 wt% can satisfy both cold workability and corrosion resistance by adding an appropriate amount of Sn.

Next, a specific composition will be described with reference to FIG. FIG. 2 is a comparison table of the composition and characteristics of Examples and Comparative Examples 1 to 3.

In FIG. 2, the cold forgeability (workability) was evaluated from the cold ductility and hardness, and the corrosion resistance (dezincification corrosion resistance) was evaluated.
In the dezincification corrosion test according to the Japan Copper and Brass Association technical standard (JBMA T-303), the maximum corrosion depth is 100 μm or less when parallel to the processing direction, and 70 μm or less when it is perpendicular to the processing direction. , Those that do not meet these criteria are marked as x.

The stress corrosion cracking resistance (SCC resistance) is such that when a cylindrical sample is exposed to an ammonia atmosphere on a 14% aqueous ammonia solution for 24 hours while applying a load, the maximum stress at which the sample does not crack is 50 N / mm ^2. ○, 50N / m
less than m ² was ×.

As shown in FIG. 3, the SCC resistance test was performed by exposing the cylindrical sample 53 to a NH3 vapor atmosphere for 24 hours while applying a vertical load to the cylindrical sample 53 in the glass dicator 52. Was investigated.

Returning to FIG. 2, the embodiment shows that the addition of Sn
Cold forging (working), corrosion resistance (dezincification corrosion resistance), S resistance
Comparative Examples 1 and 2 have good cold forgeability, but are inferior in corrosion resistance (dezincification corrosion resistance) and SCC resistance, while exhibiting excellent properties in all CC properties.

In Comparative Example 3, the corrosion resistance (anti-zinc corrosion resistance) and the SCC resistance were good, but the cold forgeability was slightly inferior.

In addition to the above comparisons, in the examples, the strength is improved by adding Sn. The amount of Sn added is preferably in the range of 1 to 1.6 wt%.

Subsequently, a comparison of the manufacturing process between the example and the comparative example 3 will be made. FIG. 4 shows a manufacturing process of Comparative Example 3, in which after melting and casting, hot extrusion is performed at 900 ° C., then drawing and shaving are repeated twice, and then annealing is performed at 550 ° C. for 2 hours. After that, after pickling, shaving, squeezing, straightening,
After annealing at 550 ° C. for 2 hours again, pickling and straightening are performed to obtain a bar product.

In FIG. 4, the reasons why the drawing is performed three times and the annealing is performed twice are as follows. That is, since the hot extrusion step was performed at 900 ° C., surface and subcutaneous defects were generated due to adhesion of an oxide film and coarsening of crystal grain size.

If the number of defects is large as described above, the reduction rate of the cross section in one drawing cannot be increased, so that the number of drawing steps is increased to three. Also, in the middle of the three drawing steps, intermediate annealing is required to eliminate defects and to soften the material to facilitate drawing, and the annealing is performed twice.

In the example of FIG. 4, the final annealing temperature is 55
Since the temperature is 0 ° C., the surface of the bar is annealed to have a hardness distribution as shown in FIG. With such a hardness distribution, in the case of cold working (forging), the coefficient of friction of the material surface is large, and adhesion with a mold occurs during working, and forging defects such as mold galling occur.

As described above, the manufacturing method of Comparative Example 3 requires a long manufacturing process, and the manufactured bar has a problem in cold workability (forgeability).

On the other hand, the manufacturing method of the embodiment described below solves this problem. That is, FIG. 6 shows a manufacturing process of the embodiment, in which after melting and casting, after hot extrusion at 650 ° C., drawing and shaving, and then 550
Anneal for 2 hours at ° C. Then, after pickling, shaving, squeezing, and straightening, annealing at 370 ° C. for 30 minutes, followed by pickling,
After straightening, it becomes a bar product.

As described above, in the example of FIG. 6, since the hot extrusion step is performed at 650 ° C., adhesion of an oxide film and coarsening of crystal grain size are reduced, and surface and subcutaneous defects are reduced.
When the number of defects is small as described above, the reduction rate of the cross section in one drawing can be increased, so that the number of drawing steps can be reduced to two.

With respect to the concern about the lowering of the extrudability due to lowering the hot extrusion temperature, the apparent Zn content is 10 to 35 wt%, preferably 15 to 30 watts.
By having a composition in which the content of t% and Sn is 1 to 1.6 wt%, the hot ductility is good and the extrusion moldability is good even at a low temperature.

In the example of FIG. 6, the final annealing temperature is 37.
Since the temperature is 0 ° C., the surface of the bar is not excessively annealed, and the hardness distribution is as shown in FIG. With such a hardness distribution, when cold working (forging) is performed, the coefficient of friction of the material surface is small, and adhesion to the mold is less likely to occur during working, and forging defects such as mold galling are reduced.

The reason why the forging defects are suppressed as described above may be that the work hardening coefficient (n value) has been optimized. According to the example of FIG. 6, there is also an advantage that the forging load is reduced by reducing the deformation resistance and the friction coefficient.

FIG. 8 shows a manufacturing process as a modification of the embodiment of FIG. 6, in which after melting and casting, hot extrusion at 650 ° C., drawing and shaving, and then 37
After annealing at 0 ° C. for 30 minutes, pickling and straightening are performed to obtain a bar product.

As described above, in the example of FIG. 8, based on the reduction of the surface and subcutaneous defects due to the reduction of the hot extrusion temperature, the cross-section reduction rate in one drawing is made as large as possible. I have to.

In order to realize the manufacturing method shown in FIG. 8, the crystal grain size is reduced and the surface and subcutaneous defects are further reduced by setting the cross-sectional reduction rate in the hot extrusion step to 90% or more. Is preferred. Further, when the cross-section reduction rate is increased in this manner, the diameter can be made smaller at the end of hot extrusion, so that the load in the drawing step is reduced, and it is possible to cope with even a single drawing step.

In the example of FIG. 8, as described above, the drawing step is performed once, so that the annealing step can be performed only once.

Further, in the example of FIG. 8, since the annealing step is performed only once, the hardness distribution is as shown in FIG. In such a hardness distribution, forging defects such as mold galling are further reduced because the surface hardness is higher.

As described above, in the embodiment and its modifications,
Since the manufacturing process is simplified, not only can the manufacturing cost be significantly reduced, but also cold workability (forgeability) can be ensured.

[Brief description of the drawings]

FIG. 1. Relationship between cold ductility, hardness and corrosion resistance with respect to apparent Zn content

FIG. 2 shows an example as an embodiment of the present invention and Comparative Example 1.
Comparison table of composition and characteristics of 3

FIG. 3 shows stress corrosion cracking resistance (SCC resistance) of the embodiment.
Illustration of test

FIG. 4 is an explanatory view of a manufacturing process of Comparative Example 3.

FIG. 5 is an explanatory diagram of a hardness distribution of Comparative Example 3.

FIG. 6 is an explanatory diagram of a manufacturing process of an example as an embodiment of the present invention.

FIG. 7 is an explanatory diagram of a hardness distribution of the embodiment.

FIG. 8 is an explanatory view of a manufacturing process according to a modification of the embodiment.

FIG. 9 is an explanatory diagram of a hardness distribution according to a modification of the embodiment.

[Explanation of symbols]

 52: glass digitizer, 53: cylindrical sample

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Claims (8)

[Claims] 1. An apparent Zn content of 10 to 35 watts
A copper alloy for cold working wherein the content of t% and Sn is 1 to 1.6 wt%. 2. A method for producing a copper alloy for cold forging, in which annealing for adjusting internal stress is performed after cold drawing, wherein the annealing temperature is 450 ° C. or lower, preferably 380 ° C. or lower. Copper alloy manufacturing method. 3. The production of a copper alloy for cold working according to claim 2, wherein the cold drawing and the annealing are repeatedly performed, and a final annealing temperature is 450 ° C. or lower, preferably 380 ° C. or lower. Method. 4. The method for producing a copper alloy for cold working according to claim 3, wherein the intermediate annealing temperature is higher than the final annealing temperature. 5. An apparent Zn content of 10 to 35 watts.
The method for producing a copper alloy for cold working according to any one of claims 2 to 4, wherein the content of t% and Sn has a composition of 1 to 1.6 wt%. 6. A method for producing a copper alloy for cold forging produced through hot extrusion, wherein the hot extrusion temperature is 8%.
A method for producing a copper alloy for cold working having a temperature of 00 ° C. or lower. 7. The method for producing a copper alloy for cold working according to claim 6, wherein the hot extrusion temperature is 650 ° C. or lower. 8. An apparent Zn content of 10 to 35 watts.
The method for producing a copper alloy for cold working according to claim 6 or 7, having a composition of t%.