JPH11140568A - Production of brass, brass, production of metallic material, and metallic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To refine grain size by applying extrusion in two times to a brass rod stock of specific composition and also regulating reduction of area to a specific value or above. SOLUTION: Dynamic recrystallization is allowed to occur in a brass rod stock having 37-46 wt.% apparent Zn content by means of extrusion to refine grain size. Then, dynamic recrystallization is allowed to occur by similar extrusion to refine grain size. The reduction of area by the two-time extrusion is regulated to >=90%. Resultantly, extrusion pressure per time can be minimized. It is preferable to perform extrusion at 400-650 deg.C. As to the time interval between the first extrusion and the second extrusion, a time not shorter than that capable of covering a slight time lag until the above dynamic recrystallization is completed suffices, and it must not be longer than is needed in order to prevent the occurrence of grain growth. When the average grain size of the brass rod stock is <=50 μm, the brass having <=15 μm average grain size can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a metal material, a method for producing a metal material, particularly brass, and brass.

[0002]

2. Description of the Related Art The applicant of the present invention has developed brass materials having excellent hot ductility and machinability, which are properties at the time of processing, and corrosion resistance, SCC resistance, and brass materials having excellent strength at the time of using products.
It has been previously proposed in PCT / JP97 / 03152.

As an embodiment for obtaining such characteristics, precise control such as optimizing the crystal grain size, optimizing the area ratio and arrangement of α, β, and γ phases is performed. As a means for realizing an appropriate particle size, a cross-section reduction rate control during extrusion molding is proposed.

[0004]

SUMMARY OF THE INVENTION The present invention is to improve an extrusion molding method for refining a crystal grain size.

[0005]

The method for producing brass according to the present invention comprises: a first step of preparing a brass rod having an apparent Zn content of 37 to 46 wt%;
A second step of subjecting the brass bar prepared in the first step to dynamic recrystallization by extrusion molding to reduce the crystal grain size, and a brass bar passed through the second step And a fourth step of subjecting the brass bar material prepared in the third step to dynamic recrystallization by extrusion to reduce the crystal grain size. In addition, the cross-sectional reduction rate obtained by combining the second and fourth steps is 90% or more, and the following reduction is made as compared with the case where the cross-section reduction rate is made 90% or more in one extrusion molding step. Has advantages.

That is, in order to reduce the cross-sectional reduction rate to 90% or more in one extrusion molding process, a considerable extrusion pressure is required. However, if the extrusion process is divided into two as in the present invention, one extrusion process is required. The extrusion pressure per unit can be small.

[0007] The principle of refining the crystal grain size during extrusion molding is based on the use of dynamic recrystallization of a crystal structure subjected to an external force. Since there is a slight time delay, the recrystallization actually continues after the extrusion. In the present invention, paying attention to this, by increasing the number of extrusion molding steps to two, the chance of continuing recrystallization after extrusion is increased to twice.
As a result, the crystal grain size can be reduced with a small extrusion pressure.

Here, the term "apparent Zn content" means that A is Cu content [wt%], B is Zn content [wt%], and t is the 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.

In the second and fourth steps, 400 to 65
It is desirable to perform extrusion molding in a temperature range of 0 ° C. This is because in a higher temperature range, there is a high possibility that the crystal once refined will cause grain growth after extrusion molding.

[0010] As an embodiment of the third step, by maintaining the temperature range of 400 to 650 ° C from the second step to the fourth step, the second and fourth steps can be performed in one manufacturing facility.
The two extrusions in the step can be performed successively. In this case, the time between the second and fourth steps should satisfy at least a slight time delay until the completion of the dynamic recrystallization described above, and an unnecessarily long time is required to prevent grain growth. No need to empty.

As another embodiment of the third step, the second step
After completion of the step, it can be cooled to a temperature below the temperature range of 400 to 650 ° C. and then heated to this temperature range. However, this can be carried out by extruding twice with different equipment or extruding by different manufacturers. It is suitable for molding.

In the case where cooling is performed after the second step as described above, it is desirable that the cooling rate after the completion of the second step until the temperature becomes 400 ° C. or less is 0.4 K / sec or more.
This is because if the cooling rate is low, the crystal grain size becomes coarse during cooling. Similarly, after the fourth step, the cooling rate until the temperature becomes 400 ° C. or less after the end of the fourth step is 0.4
It is desirably at least K / sec.

According to the method for producing brass described above, the brass bar prepared in the first step has an average crystal grain size of 50 μm.
In the following cases, brass having an average crystal grain size of 15 μm or less can be obtained. However, when the cross-sectional reduction rate combining the second and fourth steps is 97% or more, brass having an average crystal grain size of 10 μm or less is obtained. Can be obtained.

As a specific crystal structure, in the hot or warm working temperature range after reheating, the area ratio of α + β phase and β phase is 30 to 80%, and the average crystal grain size is 15 μm or less, preferably A crystal structure of 10 μm or less and in which α and β phases are uniformly dispersed can be realized. According to this crystal structure, hot or warm working temperature range, preferably 480
In a temperature range of ７750 ° C., a strain of 160% is given at a strain rate of 0.00083 / sec and there is no breakage.
At least one of the following characteristics can be satisfied: 50% strain at a strain rate of 083 / sec, no breakage, and 30% strain at a strain rate of 0.083 / sec, no breakage. .

In another embodiment of the specific crystal structure, the area ratio of the α + β phase and the β phase is 15% or more, preferably 20% or more, and the average crystal grain size of the α and β phases is 15 μm or less. Preferably, a crystal structure of 10 μm or less can be realized. According to this crystal structure, 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 180 N / mm 2 or more. Satisfies at least one of the following two characteristics: a cutting resistance index based on a free-cutting brass bar according to C-3604 of 80 or more and a 0.2% proof stress or a yield stress of 250 N / mm2 or more. Can be.

In the above brass manufacturing method, when the brass rod prepared in the first step contains 0.9 to 7 wt% of Sn, hot or warm working after reheating is performed. Temperature range,
Alternatively, in the temperature range of 300 to 500 ° C., preferably 400 to 500 ° C., the area ratio of α + β + γ phase and α phase is 44 to 65.
%, The area ratio of the β phase is 10 to 55%, the area ratio of the γ phase is 1 to 25%, and the average crystal grain size of the α, β, and γ phases is 15 μm or less, preferably 10 μm or less. , Γ phase can be realized. According to this crystal structure, at 450 ° C., 0.0008
No damage at 50% strain at 3 / sec strain rate, no damage at 25% strain at 0.0083 / sec strain rate, 30 at 0.083 / sec strain rate. % At least one of the following characteristics can be satisfied.

In particular, when the cooling rate after completion of the fourth step until the temperature falls to 400 ° C. or lower is 5 to 1000 K / sec, the area ratio of α + β phase and β phase is 15% or more, preferably 20% or more. As described above, it is possible to realize a crystal structure in which the average crystal grain size of the α and β phases is 15 μm or less, preferably 10 μm or less, and the Sn concentration in the β phase is 1.5 wt% or more.

When the cooling rate after the completion of the fourth step until the temperature becomes 400 ° C. or less is 0.4 to 5 K / sec, the area ratio of the α + γ phase and the γ phase is 3 to 30%, preferably 5 to 30%, and the average crystal grain size of the α phase is 1
5 μm or less, preferably 10 μm or less, the average crystal grain size (minor diameter) of the γ phase is 8 μm or less, preferably 5 μm or less, and further, the Sn concentration in the γ phase is 8 wt% or more, A crystal structure in which a γ phase is scattered at the grain boundaries can be realized.

Further, when the cooling rate until the temperature becomes 400 ° C. or less after completion of the fourth step is 0.4 to 10 K / sec, the area ratio of α + β + γ phase and α phase is 40 to 94.
%, Β, and γ phase have an area ratio of 3 to 30%, the α, β phase has an average crystal grain size of 15 μm or less, preferably 10 μm or less, and the γ phase has an average crystal grain size (minor axis) of 8 μm.
Hereafter, a crystal structure in which the Sn concentration is preferably 5 μm or less, the Sn concentration in the γ phase is 8 wt% or more, and the γ phase surrounds the β phase can be realized.

According to the above crystal structure, one cylindrical sample is
When exposed to an ammonia atmosphere over a 4% aqueous ammonia solution for 24 hours while applying a load, the maximum stress that does not crack the sample can satisfy the characteristic of 180 N / mm 2 or more.

The 0.2% proof stress or the yield stress is 250
Characteristics of N / mm2 or more, Japanese Industrial Standard JIS C-36
The cutting resistance index based on a free-cutting brass bar according to No. 04 is 80
The above characteristics, Japan Copper and Brass Association Technical Standard JBMA T-30
When performing the dezincification corrosion test according to 3, when the maximum dezincification depth direction is parallel to the processing direction, the maximum dezincification depth is 100 μm or less, or when the maximum dezincification depth direction is perpendicular to the processing direction. Can satisfy at least two of the three properties of the properties satisfying the corrosion resistance having a maximum dezincing depth of 70 μm or less.

The present invention also includes a plurality of extrusion steps for reducing the crystal grain size by causing dynamic recrystallization, and a metal having a cross-sectional reduction rate of 90% or more obtained by combining the plurality of extrusion steps. A method for producing a material is provided.

According to this, 1 is obtained by dividing the extrusion process.
Not only can the extrusion pressure per operation be reduced as much as possible, but also the chance of continuing dynamic recrystallization after the extrusion is increased to a plurality of times, so that the crystal grain size can be efficiently reduced at the time of extrusion.

In a preferred embodiment, in a step between a plurality of extrusion steps, by maintaining a temperature range during the plurality of extrusion steps, the extrusion step can be efficiently performed by a single facility.

According to another embodiment, in a step between a plurality of extrusion steps, the material is cooled to a temperature lower than the temperature range of the plurality of extrusion steps, and then heated to this temperature range, thereby extruding twice with different equipment. It is suitable when performing molding or when performing extrusion molding by different manufacturers.

As an embodiment of the metal material, a copper alloy, particularly brass, is preferable, and further, a brass having an apparent Zn content of 37 to 46 wt% is preferable.

When the metal material is brass, specifically,
When the average grain size of the metal material prepared before the plurality of extrusion steps is 50 μm or less, the average grain size is 15 μm or less.
A crystal structure of not more than μm can be realized, and when the cross-sectional reduction rate of a plurality of extrusion steps is 97% or more, a crystal structure having an average crystal grain size of not more than 10 μm can be realized.

[0028]

Embodiments of the present invention will be described in detail below. FIG. 1 shows the relationship between the cross-sectional reduction rate and the average crystal grain size when Examples 1 to 4 are extruded in two stages. In all of Examples 1 to 4, the composition ratio was Cu ... 5
8.3 wt%, Sn: 1.87 wt%, Pb: 1.91
wt%, Zn ... remainder, and the average crystal grain size before extrusion molding is 50 μm. During the two-stage extrusion, the temperature was maintained at 400 to 650 ° C.

In the above Examples 1 to 4, the relationship between the cross-sectional reduction rate and the average crystal grain size is the same as that obtained by the single extrusion, except that the difference in the first stage of the extrusion. The cross-sectional reduction rate is 66%, the cross-sectional reduction rate at the time of the first extrusion is 75 to 85%, and the cross-sectional reduction rate per operation is small.

According to this, 1 is obtained by dividing the extrusion process.
Not only can the extrusion pressure per operation be reduced as much as possible, but also the opportunity to continue dynamic recrystallization after the extrusion is increased to a plurality of times, and the crystal grain size can be efficiently refined during extrusion molding. .

After the second stage extrusion, it is desirable to cool at a cooling rate of 0.4 K / sec or more until the temperature becomes 400 ° C. or less. This is because if the cooling rate is low, the crystal grain size becomes coarse during cooling.

In each embodiment, when the crystal grain size is reduced by cooling, the crystal ratio control of the α, β, and γ phases,
By controlling the Sn concentration in the γ phase, a crystal structure excellent in machinability, corrosion resistance, SCC resistance, strength and the like can be realized. Some examples of such a crystal structure are shown below.

The composition ratio is not limited to the above specific values, and an example using brass having an apparent Zn content of 37 to 46 wt% is shown. Here, the term "apparent Zn content" means that A is Cu content [wt%], B is Zn content [wt%], Zn equivalent of a third element (for example, Sn) to which t is added, When Q is the content of the third element [wt%], “{(B + t · Q) / (A + B + t · Q)} × 1
00 ”.

[Crystal structure 1] In the temperature range of hot or warm working after reheating, the area ratio of α + β phase and β phase is 30 to 8
0%, average crystal grain size is 15 μm or less, preferably 10 μm
m or less, and a crystal structure in which α and β phases are uniformly dispersed can be realized. According to this crystal structure, hot or warm working temperature range, preferably 480 to 750 ° C.
At a strain rate of 0.00083 / sec.
No damage by giving 0% strain, 0.0083 / s
At least one of the following characteristics can be satisfied: applying 50% strain at an ec strain rate and giving no damage, and applying 30% strain at a 0.083 / sec strain rate and giving no damage. The shape of the test piece for this property,
Figure 2 shows the dimensions (distance between gauges 12 mm, outer diameter φ2.5 mm)
FIG. 3 shows the test conditions. The tensile tester used was a mechanical type, the heating was an electric heater, and the atmosphere was air.

[Crystal Structure 2] A crystal structure in which the area ratio of the α + β phase and the β phase is 15% or more, preferably 20% or more, and the average crystal grain size of the α and β phases is 15 μm or less, preferably 10 μm or less. Can be realized. According to this crystal structure, (1) 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 that the sample does not crack is 180 N / mm 2 or more; 2) Japanese Industrial Standard JI
A cutting resistance index based on a free-cutting brass bar according to SC-3604 is 80 or more, and a 0.2% proof stress or a yield stress is 2
At least one of the two characteristics of 50 N / mm2 or more can be satisfied.

The cutting resistance index will be described in detail with reference to FIG. 4. In the cutting test, the peripheral surface of the round bar-shaped sample 1 is turned on a lathe at two different speeds of 100 [m / min] and 400 [m / min]. , And the main component force Fv was measured. The cutting resistance index is a free-cutting brass rod (Japanese Industrial Standard JIS C-36), which is said to have the best machinability for the main component force.
04) is the percentage of the main component. (The cutting resistance index for each cutting speed was averaged.)

Next, an example using brass having an apparent Zn content of 37 to 46 wt% and an Sn content of 0.9 to 7 wt% as a composition ratio will be described.

[Crystal Structure 3] Temperature range of hot or warm working after reheating, or 300 to 500 ° C., preferably 40 ° C.
In the temperature range of 0 to 500 ° C., the area ratio of α + β + γ phase and α phase is 44 to 65%, the area ratio of β phase is 10 to 55%, γ
The phase area ratio is 1 to 25%, and the average crystal grain size of the α, β, and γ phases is 15 μm or less, preferably 10 μm or less,
A crystal structure in which α, β, and γ phases are dispersed can be realized. According to this crystal structure, at 450 ° C., 50% strain was given at a strain rate of 0.0008 / sec to give no damage, and 25% strain was given at a strain rate of 0.0083 / sec to give a breakage. Nothing, 0.08
It is possible to satisfy at least one of the characteristics of giving a 30% strain at a strain rate of 3 / sec and not causing breakage. The test method for this characteristic is the same as that shown in FIGS.

[Crystal structure 4] The cooling rate until the temperature becomes 400 ° C. or less after the second stage extrusion molding is 5 to 1000 K.
/ Sec, the area ratio of α + β phase and β phase is 15% or more, preferably 20% or more.
The average crystal grain size of the α and β phases is 15 μm or less, preferably 1 μm or less.
0 μm or less, and the Sn concentration in the β phase is 1.5 wt%
The above crystal structure can be realized.

[Crystal Structure 5] The cooling rate until the temperature becomes 400 ° C. or lower after the second stage extrusion molding is 0.4 to 5 K /
In the case of sec, the area ratio of the α + γ phase and the γ phase is 3 to 3
0%, preferably 5 to 30%, and the average crystal grain size of the α phase is 15 μm or less, preferably 10 μm or less,
The average crystal grain size (minor diameter) of the γ phase is 8 μm or less, preferably 5 μm or less, and the Sn concentration in the γ phase is 8 w
At least t%, it is possible to realize a crystal structure in which the γ phase is scattered at the grain boundary of the α phase.

[Crystal structure 6] The cooling rate until the temperature becomes 400 ° C. or less after the second stage extrusion molding is 0.4 to 10 K
/ Sec, the area ratio of the α + β + γ phase and the α phase is 40 to 94%, and the area ratio of both the β and γ phases is 3 to 30.
% And the average grain size of the α and β phases is 15 μm
Or less, preferably 10 μm or less, the average crystal grain size (minor axis) of the γ phase is 8 μm or less, preferably 5 μm or less, furthermore, the Sn concentration in the γ phase is 8 wt% or more, and the γ phase is β A crystal structure surrounding the phase can be realized.

According to the above crystal structures 4 to 6, when the cylindrical sample was 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 was not cracked was 180 N / mm 2 or more. Can satisfy the characteristics excellent in SCC resistance. In this SCC resistance test, as shown in FIG. 5, after the cylindrical sample 3 was exposed to an NH 3 vapor atmosphere for 24 hours in a state where a load was applied vertically to the cylindrical sample 3, cracks were generated. investigated.

Also, (1) the characteristic that the 0.2% proof stress or the yield stress is 250 N / mm 2 or more; (2) the Japanese Industrial Standard JI
A characteristic in which a cutting resistance index based on a free-cutting brass bar in accordance with SC-3604 is 80 or more. When the depth direction is parallel to the processing direction, the maximum dezincing depth is 100 μm or less, or when the maximum dezincing penetration depth direction is perpendicular to the processing direction, the maximum dezincing depth is 7
Of the three characteristics of satisfying the corrosion resistance of 0 μm or less, at least two characteristics can be satisfied.

[Brief description of the drawings]

FIG. 1 shows a relationship between an average crystal grain size and a cross-sectional reduction rate according to an embodiment of the present invention.

FIG. 2 shows the shape of a high-temperature tensile test piece of the embodiment.

FIG. 3 is a high-temperature tensile test condition of the embodiment.

FIG. 4 is an explanatory diagram of a cutting test of the embodiment.

FIG. 5 is an explanatory view of a stress corrosion cracking resistance test of the same embodiment.

[Explanation of symbols]

 1: Sample for cutting property test 2: Glass digitizer 3: Sample for stress corrosion cracking resistance test

────────────────────────────────────────────────── ─── front page continued (51) Int.Cl. ⁶ identifications FI C22F 1/00 640 C22F 1/00 640A 683 683 684 684A 684C 685 685A 686 686Z 692 692A 694 694B 694A

Claims (31)

[Claims] 1. An apparent Zn content of 37 to 46 wt.
% Of a brass rod prepared in the first step, and a second step of subjecting the brass rod prepared in the first step to dynamic recrystallization by extrusion to reduce the crystal grain size. And a third step of preparing a brass rod that has passed through the second step; and causing the brass rod prepared in the third step to undergo dynamic recrystallization by extrusion. A method for producing brass, comprising: a fourth step of refining the crystal grain size; and a cross-sectional reduction rate of 90% or more, combining the second and fourth steps. 2. The method according to claim 1, wherein the second and fourth steps are performed in a range of 400 to 6 times.
The method for producing brass according to claim 1, wherein the brass is extruded in a temperature range of 50 degrees. 3. The method for producing brass according to claim 2, wherein, in the third step, the temperature range is maintained from the second step to the fourth step. 4. The method for producing brass according to claim 2, wherein, in the third step, after the second step is completed, the brass is cooled to a temperature lower than the temperature range and then heated to the temperature range. 5. The method for producing brass according to claim 4, wherein a cooling rate until the temperature becomes 400 ° C. or less after completion of the second step is 0.4 K / sec or more. 6. The method for producing brass according to claim 1, wherein a cooling rate until the temperature becomes 400 ° C. or less after completion of the fourth step is 0.4 K / sec or more. 7. The brass produced by the method for producing brass according to claim 1, wherein the brass rod prepared in the first step has an average crystal grain size of 50 μm or less. Brass having a particle size of 15 μm or less. 8. The brass according to claim 7, wherein a cross-sectional reduction rate obtained by combining the second and fourth steps is 97% or more and an average crystal grain size is 10 μm or less. 9. A brass produced by the method for producing brass according to claim 6, wherein in a temperature range of hot or warm working, α + β phase,
β-phase area ratio is 30-80%, average crystal grain size is 15μ
m or less, preferably 10 μm or less, having a crystal structure in which α and β phases are uniformly dispersed. 10. Brass produced by the method for producing brass according to claim 6, wherein the temperature range is hot or warm working, preferably 480 to 750.
In a temperature range of ° C., no damage is caused by giving 160% strain at a strain rate of 0.0008 / sec, and no damage is caused by giving 50% strain at a strain rate of 0.0083 / sec. A brass that satisfies at least one of the following characteristics: a 30% strain at a strain rate of 083 / sec, and no breakage. 11. Brass produced by the method for producing brass according to claim 6, wherein the area ratio of the α + β phase and the β phase is 15% or more, preferably 20% or more, and the average crystal of the α and β phases. Brass having a crystal structure with a particle size of 15 μm or less, preferably 10 μm or less. 12. A brass produced by the method for producing brass according to claim 6, wherein the cylindrical sample is not cracked when exposed to an ammonia atmosphere on a 14% aqueous ammonia solution for 24 hours while applying a load. A maximum stress of 180 N / mm2 or more; a characteristic of a cutting resistance index of 80 or more based on a free-cutting brass bar according to Japanese Industrial Standard JIS C-3604 and a 0.2% proof stress or a yield stress of 250 N / mm2 or more; Brass that satisfies at least one of the two properties described above. 13. The brass bar prepared in the first step contains Sn in an amount of 0.9 to 7% by weight.
The method for producing brass according to any one of the above. 14. Brass which has been subjected to the method for producing brass according to claim 6 and 13, wherein the temperature is in a hot or warm working temperature range, or in a temperature range of 300 to 500 ° C., preferably 400 to 500 ° C., α + β + γ phase, α phase area ratio is 44 to 65%, β phase area ratio is 10 to 55%, γ phase area ratio is 1 to 25
%, The average grain size of the α, β, and γ phases is 15 μm or less, preferably 10 μm or less, and brass having a crystal structure in which α, β, and γ phases are dispersed. 15. A brass produced by the method for producing brass according to claim 6 or 13, wherein at 450 ° C., a strain of 50% is given at a strain rate of 0.00083 / sec and there is no breakage. Brass that satisfies at least one of the following characteristics: 25% strain at a strain rate of 0083 / sec, no breakage, and 30% strain at a strain rate of 0.083 / sec, no breakage. 16. The method for producing brass according to claim 13, wherein a cooling rate until the temperature becomes 400 ° C. or less after the completion of the fourth step is 5 to 1000 K / sec. 17. Brass produced by the method for producing brass according to claim 16, wherein the area ratio of the α + β phase and the β phase is 15% or more, preferably 20% or more, and the average crystal of the α and β phases. Brass having a crystal structure with a particle size of 15 μm or less, preferably 10 μm or less, and a Sn concentration in the β phase of 1.5 wt% or more. 18. The method for producing brass according to claim 13, wherein a cooling rate until the temperature becomes 400 ° C. or less after the fourth step is 0.4 to 5 K / sec. 19. Brass produced by the method for producing brass according to claim 18, wherein the area ratio of the α + γ phase and the γ phase is 3 to 30.
%, Preferably 5 to 30%, and the average crystal grain size of the α phase is 15 μm or less, preferably 10 μm or less, γ
The average crystal grain size (minor diameter) of the phase is 8 μm or less, preferably 5 μm or less.
μm or less, and the Sn concentration in the γ phase is 8 wt.
% Or more, and a brass having a crystal structure in which a γ phase is scattered at a grain boundary of an α phase. 20. The method for producing brass according to claim 13, wherein a cooling rate until the temperature becomes 400 ° C. or less after the fourth step is 0.4 to 10 K / sec. 21. Brass produced by the method for producing brass according to claim 20, wherein the area ratio of α + β + γ phase and α phase is 40.
９４94%, the area ratio of β and γ phases are both 3 to 30%, the average crystal grain size of α and β phases is 15 μm or less, preferably 10 μm or less, and the average crystal grain size (minor axis) of γ phase Is 8 μm or less, preferably 5 μm or less, further has a Sn structure in the γ phase of 8 wt% or more, and has a crystal structure in which the γ phase surrounds the β phase. 22. Brass produced by the method for producing brass according to claim 6 or 13, wherein when the cylindrical sample is exposed to an ammonia atmosphere on a 14% aqueous ammonia solution for 24 hours while applying a load, the sample becomes: Brass that satisfies the characteristic that the maximum stress that does not crack is 180 N / mm2 or more. 23. Brass produced by the method for producing brass according to claim 6 or 13, wherein 0.2% proof stress or yield stress is 250 N / mm2 or more, free-cutting brass according to Japanese Industrial Standard JIS C-3604. When the dezincification corrosion test according to the Japan Copper and Brass Association Technical Standard JBMA T-303 is performed and the maximum dezincing penetration depth direction is parallel to the processing direction, When the maximum dezincing depth is 100 μm or less or the maximum dezincing penetration depth direction is perpendicular to the processing direction, the property satisfies the corrosion resistance of the maximum dezincing depth of 70 μm or less. brass. 24. A method for producing a metal material having a plurality of extrusion steps for causing dynamic recrystallization to reduce the crystal grain size, and combining the plurality of extrusion steps with a cross-sectional reduction rate of 90% or more. . 25. The method for manufacturing a metal material according to claim 24, wherein in the step between the plurality of extrusion steps, a temperature range during the plurality of extrusion steps is maintained. 26. The method for producing a metal material according to claim 24, wherein in the step between the plurality of extrusion steps, the metal material is cooled to a temperature lower than a temperature range of the plurality of extrusion steps, and then heated to the temperature range. . 27. The metal material is a copper alloy.
27. The method for producing a metal material according to any one of items 26. 28. The method according to claim 27, wherein the metal material is brass. 29. The method according to claim 28, wherein the metal material is brass having an apparent Zn content of 37 to 46 wt%. 30. The metal material prepared before the plurality of extrusion steps has an average crystal grain size of 50 μm or less.
9. A metal material obtained through the method for producing a metal material according to item 9,
A metal material having an average crystal grain size of 15 μm or less. 31. A cross-sectional reduction rate obtained by combining the plurality of extrusion steps is 97% or more, and an average crystal grain size is 10 μm.
31. The metal material according to claim 30, wherein: