JP2006322059A - Lead-free free-cutting brass alloy and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead-free free-cutting brass alloy having machinability equal to that of conventional lead free-cutting brass alloys, being free from leaching of lead when brought into contact with water and having excellent dezincification corrosion resistance, hot forgeability and other physical properties and also to provide its manufacturing method. <P>SOLUTION: The lead-free free-cutting brass alloy has a metallic composition consisting of, by weight, 60.0 to 62.50% copper (Cu), 0.4 to 2.0% bismuth (Bi), ≤0.10% lead (Pb), 0.2 to 1.0% tin (Sn), 0.01 to 0.05% phosphorus (P), ≤0.1% iron (Fe) and the balance zinc (Zn) with inevitable impurities and also has a metallic structure in which a β-phase is surrounded by an α-phase by heat treatment and is in an isolated state. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a lead-free free-cutting brass alloy excellent in dezincification corrosion resistance, hot forgeability and the like, and a method for producing the same.

  For water fittings and other water contact instruments that can come into contact with water, conventionally, free-cutting brass C3604 excellent in machinability based on the standard of “JIS H 3250” and brass for forging C3771 excellent in machinability and hot forgeability. Free-cutting brass alloys such as are widely used.

  The free-cutting brass alloy contains a large amount of lead (Pb) so that it can be easily machined. The lead thus added does not dissolve in the alloy matrix, and the inside and outside of the crystal grains. In the form of fine particles, thereby ensuring good machinability of the material.

  However, as described above, the lead-free free-cutting brass alloy to which lead is added exhibits excellent machinability, but tends to cause dezincification corrosion on contact with water and tends to leach lead into water. There was concern about environmental pollution and health damage caused by lead damage. In this regard, the standard of tap water quality for lead was established in accordance with the “Ministerial Ordinance to Revise Part of the Ministerial Ordinance on Structure and Material Standards for Water Supply Equipment” enforced on April 1, 2003 (Ministry of Health, Labor and Welfare Ordinance 138) In response to this revision, the lead leaching performance standard for water supply systems has also been revised to a strict standard value.

  Therefore, the conventional leaded brass alloy cannot be practically used for drinking water supply devices, and the development of a lead-free free-cutting brass alloy that satisfies the revised standard for lead leaching is awaited. It was.

  In order to solve the above problem, for example, JP-A-5-255778, JP-B-5-63536, and Japanese Patent No. 3335002 describe that bismuth (Bi), which is non-toxic instead of lead (Pb), is a copper alloy. There has been proposed a lead-free free-cutting brass alloy that can be prevented from leaching of lead into water while being added while being able to ensure cutting performance.

However, the brass alloy according to JP-A-5-255778 is inferior in dezincification corrosion resistance, and the brass alloy according to JP-B-5-63536 has a problem in hot workability, and the brass according to Japanese Patent No. 3335002. Although the alloy is said to have improved the problems of the brass alloy, it still has problems in dezincification corrosion resistance, wear resistance and the like.
JP-A-5-255778 Japanese Patent Publication No. 5-63536 Japanese Patent No. 3335002

  It is an object of the present invention to have a machinability comparable to that of a conventional leaded free-cutting brass alloy, and since there is no leaching of lead when in contact with water, there is no fear of lead damage, and furthermore, dezincification corrosion resistance Another object of the present invention is to provide a lead-free free-cutting brass alloy excellent in hot forgeability and other physical properties and a method for producing the same.

  The lead-free free-cutting brass alloy according to the invention of claim 1 is 60.0 to 62.50 wt% copper (Cu), 0.4 to 2.0 wt% bismuth (Bi), 0.10 wt% or less. Lead (Pb), 0.2 to 1.0 wt% tin (Sn), 0.01 to 0.05 wt% phosphorus (P), 0.1 wt% or less iron (Fe), and the balance zinc (Zn) ) And inevitable impurities, and the β phase has a metal structure surrounded by the α phase and isolated by heat treatment.

  The lead-free free-cutting brass alloy according to claim 2 is the lead-free free-cutting brass alloy according to claim 1, wherein the metal composition is 60.0 to 61.0 wt% of copper (Cu), 0 .4 to 2.0 wt% bismuth (Bi), 0.10 wt% or less lead (Pb), 0.5 to 0.7 wt% tin (Sn), 0.01 to 0.05 wt% phosphorus (P ) And 0.1 wt% or less of iron (Fe), the remaining zinc (Zn), and inevitable impurities.

  The lead-free free-cutting brass alloy according to the invention of claim 3 is 61.0 to 62.50 wt% copper (Cu), 0.4 to 2.0 wt% bismuth (Bi), 0.10 wt% or less. Lead (Pb), 0.5 to 1.0 wt% tin (Sn), 0.01 to 0.05 wt% phosphorus (P), 0.1 wt% or less iron (Fe), and 0.02 to 0 .25 wt% of antimony (Sb) and the balance of zinc (Zn) and an inevitable impurity metal composition, and the β phase is surrounded by the α phase by heat treatment and has a metal structure in an isolated state It is characterized by.

  According to a fourth aspect of the present invention, there is provided a lead-free free-cutting brass alloy manufacturing method by melting and holding a molten copper-base alloy having a metal composition according to claim 1, 2 or 3 by horizontal continuous casting. A step of casting and drawing the ingot, a step of hot-extruding the obtained ingot at a temperature of 600 to 730 ° C., or a step of hot-extruding and cold-drawing at the temperature, and an extrusion or drawing obtained And annealing the material at a temperature of 350 to 550 ° C. for 1 to 8 hours and gradually cooling the material, so that the β phase is surrounded by the α phase by the heat treatment so as to have an isolated metal structure. It is characterized by that.

  In the metal composition, copper (Cu) has a brass alloy metal structure having two phases of α phase and β phase in any temperature range, and always includes β phase in the temperature range of hot working, In the brass alloy according to claim 1, in order to make the α phase mainly contain the α phase and to make the β phase surrounded by the α phase and isolated by heat treatment. 50 wt%, preferably in the range of 60.0 to 61.0 wt% as described in claim 2, and in the brass alloy according to claim 3, it is managed in the range of 61.0 to 62.50 wt.

  Bismuth (Bi) is added in the range of 0.4 to 2.0 wt% mainly for improving machinability. This component, like lead (Pb), does not dissolve in the alloy matrix but is dispersed as fine particles, thereby improving the machinability of the material. In addition, when this addition amount is less than 0.4 wt%, a required effect is not acquired, and when it exceeds 2.0 wt%, the hot forgeability will be reduced.

  About lead (Pb), the presence of 0.10 wt% or less is allowed as an impurity. It is advantageous to use scrap as part of the bullion in order to reduce the price of the product. In the present invention, as long as the lead content is within the allowable range, the bullion from which scrap is used is suitable. Can be used for Even if the brass alloy contains 0.10 wt% or less of lead, the brass alloy can sufficiently satisfy the revised standard related to lead leaching, so that it can be regarded as substantially lead-free. Note that lead as an impurity as described above is also useful for improving machinability in combination with the bismuth (Bi).

  Antimony (Sb) contributes to improvement of machinability and suppression of dezincification corrosiveness similarly to bismuth (Bi), and in the brass alloy according to claim 2, in the range of 0.02 to 0.25 wt%. Added. In addition, when this addition amount is less than 0.02 wt%, the required effect cannot be obtained, and when it exceeds 0.25 wt%, segregation to the grain boundary becomes remarkable, especially with respect to hot workability. When the β phase is large, the adverse effect on the hot workability is small, but when the amount of the α phase is increased, the hot workability is easily inhibited.

  Tin (Sn) improves the dezincification corrosion resistance of the α phase and β phase, and in particular, provides greater dezincification corrosion resistance to the β phase, which is more susceptible to dezincification corrosion than the α phase. The brass alloy according to item 1 is added in an amount of 0.2 to 1.0 wt%, preferably 0.5 to 0.7 wt% as described in claim 2, and the brass alloy according to claim 3 is added in an amount of 0.2 to 1.0 wt%. It is added in the range of 5 to 1.0 wt%. When the added amount of tin is in the range of 0.2 to 0.5 wt%, tin is dissolved in the alloy matrix, and when the added amount exceeds 0.5 wt%, a hard γ phase is precipitated. Although the machinability is improved, when the amount added exceeds 1.0 wt%, the cold workability is adversely affected.

Phosphorus (P) promotes refinement of crystal grains in the metal structure and suppresses dezincification corrosion, and is added in the range of 0.01 to 0.05 wt%. If the added amount is less than 0.01 wt%, the required effect cannot be obtained, and if it exceeds 0.05 wt%, the produced Cu ₃ P fine particles are dispersed in the alloy matrix and cold worked. It will inhibit sex. Further, when phosphorus coexists with the antimony in the brass alloy, crystal grain refinement and dezincification corrosion resistance are synergistically improved.

Iron (Fe) is effective for refining crystal grains in the ingot, and is added in a range of 0.1 wt% or less. In order to obtain a more healthy ingot, it is preferable to add iron to some extent. However, if the added amount is too large, hard and brittle Fe ₃ P, Fe ₃ Sn, etc. are generated and cold workability is inhibited. Therefore, from the viewpoint of securing a sound ingot and maintaining cold workability, it is preferable to add iron in the range of 0.02 to 0.04 wt%.

  The remaining zinc (Zn) is solid-dissolved in the alloy matrix to improve castability and solubility and strengthen.

  The Cu—Zn—Bi alloy material according to the present invention is liable to cause ingot cracking due to segregation of Bi during casting. In the method for producing a lead-free free-cutting brass alloy according to the present invention, in order to obtain a good quality and sound ingot without the ingot cracking, it was melted by a low frequency groove type melting furnace or the like and held by a cage. A method is employed in which an ingot is cast from a molten copper-base alloy having the metal composition according to claim 1 by horizontal continuous casting and drawn. The drawing after the casting is preferably performed at a speed of 50 mm / min or less in order to obtain a higher quality and sound ingot without cracking of the ingot. In addition, for cooling after drawing, for example, primary cooling by water cooling and secondary cooling by air cooling or light water cooling are employed.

The ingot obtained as described above is inspected for the homogenized state of bismuth and the like in the fine columnar crystal structure and the presence or absence of ingot surface cracks (2 mm or less), hydrogen (H ₂ ) gas and internal defects. Is called.

  A good and sound ingot after the inspection is subjected to hot extrusion at a temperature of 600 to 730 ° C., preferably 600 to 650 ° C. in order to suppress the amount of β phase by a hydraulic single-acting direct extruder or the like. It is subjected to hot extrusion at temperature and subsequent cold drawing. The ingot is preferably extruded in the range of 3 to 10% of cold work, and the extruded material after extrusion is preferably gradually cooled by air cooling, thereby preventing cold work cracks. This is because bismuth in the extruded material is melted at 271 ° C. or higher, and is easily wetted by the β phase, thereby preventing cracks from occurring. As for cooling after extrusion, it is preferable that the extruded material is gradually cooled by air cooling until the surface temperature becomes 180 ° C. or less, and rapid cooling by water cooling is avoided.

  In the extruded material obtained as described above, the metal structure is composed of an α phase and a β phase, and most of the β phase is continuously extruded by hot extrusion and further by cold drawing. Exists in a state. The extruded or drawn material in such a state is subjected to annealing at a temperature of 350 to 550 ° C. for 1 to 8 hours and subsequent annealing, thereby transforming a part of the β phase into the α phase. As a result, the abundance ratio of the α phase increases, and a metal structure is formed in which the remaining β phase is wrapped in the α phase, and the dezincification corrosion resistance is improved. As for the annealing conditions, in order to improve the α single phase structure and obtain better dezincing corrosion resistance, the brass alloy according to claim 1 is annealed at a temperature of 350 to 550 ° C. for 1 to 5 hours. Preferably, the brass alloy according to claim 2 is preferably annealed at a temperature of 450 to 550 ° C. for 2 to 5 hours. In the brass alloy according to the present invention, since the copper content is as large as 60.0 to 62.50 wt%, the abundance ratio of the β phase is relatively small, which is extremely advantageous for ensuring high dezincing corrosion resistance. It is a condition.

  As described above, according to the first, second, and third aspects of the invention, it has a machinability comparable to that of a conventional leaded free-cutting brass alloy and is safe because there is no leaching of lead when in contact with water. It is possible to provide a lead-free free-cutting brass alloy which is free from fear of lead damage and further excellent in dezincification corrosion resistance, hot forgeability and other physical properties. In particular, the invention according to claim 3 provides a lead-free free-cutting brass alloy having a synergistic improvement in crystal grain refinement and dezincification corrosion resistance due to the coexistence of phosphorus and antimony in the brass alloy. It is done.

  According to the invention which concerns on Claim 4, the lead-free free-cutting brass alloy which combines the said effect of Claims 1-3 can be manufactured reliably.

Hereinafter, the present invention will be specifically described based on Examples and Comparative Examples.
[Preparation of brass alloy specimen]
Based on the metal composition shown in Table 1 below, while preparing the specimens 1 and 2 of the present invention as lead-free free-cutting brass alloys according to the examples of the present invention, the conventional leaded free-cutting brass alloys according to the comparative examples Comparative specimens 1 and 2 were prepared as follows.

  As the specimen 1 of the present invention, the metal composition described in the column of the specimen 1 of the present invention in Table 1 obtained by melting, casting and drawing with a low frequency groove melting furnace, a cage and a horizontal continuous casting apparatus is used. The ingot of the copper-based alloy is subjected to hot extrusion at a temperature of 600 to 670 ° C. by a hydraulic single-acting direct extruder, and after slow cooling, it is subjected to cold drawing with a drawing rate of 0.5 to 0.8 mm, The obtained drawn material was manufactured by annealing at a temperature of 500 to 550 ° C. for 90 to 120 minutes and gradually cooling. Further, as the specimen 2 of the present invention, an ingot of a copper-based alloy having the metal composition described in the column 2 of the specimen of the present invention in Table 1 obtained by melting, casting, and drawing as described above, In the same manner as above, it is subjected to hot extrusion at a temperature of 680 to 720 ° C., and after slow cooling, it is subjected to cold drawing with a drawing rate of 0.3 to 0.6 mm, and the obtained drawing material is heated to a temperature of 500 to 550 ° C. It was manufactured by a step of annealing for 90 to 150 minutes and annealing.

Further, as the comparative specimen 1, an ingot of a copper base alloy having the metal composition described in the comparative specimen 1 column of Table 1 obtained by melting, casting and drawing as described above is the same as described above. The sample is subjected to hot extrusion at a temperature of 690 to 750 ° C., and after slow cooling, it is subjected to cold drawing with a drawing rate of 1 mm, and the obtained drawing material is annealed at a temperature of 520 ° C. for 100 minutes and slowly cooled. A drawn material made of free-cutting brass C3604BD-F based on the standard of “JIS H 3250” was manufactured. Further, as the comparative specimen 2, an ingot of a copper-based alloy having the metal composition described in the comparative specimen 2 column of Table 1 obtained by melting, casting and drawing as described above is the same as described above. Then, it was subjected to hot extrusion at a temperature of 600 to 670 ° C. to produce an extrusion material made of forging brass C3771BD-F based on the standard of “JIS H 3250”.

[Test on mechanical properties]
Measure the mechanical properties of tensile strength (N / mm ² ), elongation (%), proof stress (N / mm ² ) and hardness (Hv) for specimens 1 and 2 of the present invention and comparative specimens 1 and 2 did. The tensile strength (N / mm ² ) and elongation (%) were measured by preparing a No. 4 test piece based on the standard of “JIS Z 2201”, and the hardness (Hv) was measured according to “JIS Z 2244”. ”And the Vickers hardness test method based on the standard.

The test results regarding the mechanical properties of each specimen are shown in Table 2 below. For reference, a micrograph (× 500) showing the metal structure of the brass alloy according to the specimen 1 of the present invention and a micrograph (× 500) showing the dispersion state of bismuth in the metal structure are shown in FIG. Shown in (B).

  According to the test results relating to the mechanical properties, the specimens 1 and 2 of the present invention exhibited substantially the same or higher mechanical properties as the comparative specimens 1 and 2.

[Machinability test]
Under the test conditions shown in Table 3 below, a cutting test with a lathe and a drilling test with a drilling machine were performed on the specimens 1 and 2 of the present invention and the comparative specimen 1 as an evaluation reference material. The cutting test results for each specimen are shown in Table 4 below.

In Table 4, the machinability 1 indicates the machinability when cutting with a lathe, and the machinability 2 indicates the machinability that combines the machinability when cutting with a lathe and when drilling with a drilling machine. The machinability was calculated by the following formula: machinability index (%) = (cutting resistance value of comparative specimen 1 being an evaluation reference material / cutting resistance value of each material) × 100.

  According to the results of the machinability test, the specimens 1 and 2 of the present invention exhibited excellent machinability of 80% or more of the comparative specimen 1 when cutting with a lathe and drilling with a drilling machine.

[Test for chip condition]
The state of the chips produced when the specimens 1 and 2 of the present invention and the comparative specimen 1 were subjected to the lathe cutting test in the cutting test as described above were the cutting depths 0.2 mm, 0.4 mm and 1.0 mm. A comparative observation was made in the case of.

  FIGS. 2A, 2B and 2C show photographs of chips produced in each case of the depth of cut of 0.2 mm, 0.4 mm and 1.0 mm in the specimen 1 of the present invention, respectively. 3 (A), (B), and (C), respectively, show photographs of chips produced in each case where the cutting depth in the specimen 2 is 0.2 mm, 0.4 mm, and 1.0 mm, and the cutting in the comparative specimen 1 FIGS. 4A, 4B, and 4C show photographs of chips produced in each case of amounts 0.2 mm, 0.4 mm, and 1.0 mm, respectively.

  According to the test results relating to the chip state, the specimens 1 and 2 of the present invention are slightly larger than the comparative specimen 1 in the case of the depth of cut of 0.2 mm and 0.4 mm. Good chips with fine needle tip shape were produced. In addition, in the case of the cutting depth of 1.0 mm, the test specimen 1 of the present invention was slightly larger than the comparative test specimen 1, but produced good chips with the same fine needle tip shape. In the specimen 2 of the present invention, generation of curled and spiral chips was observed.

[Forgeability test]
The specimen 1 of the present invention and the comparative specimen 2 as the evaluation reference material are subjected to the most severe flat forging as an evaluation test method, and the diameter from the original size to the spread without cracks is measured, and the temperature is 600 ° C. to 800 ° C. The forging rate at each heating temperature (= expanded diameter without cracks / original diameter) was calculated. In the evaluation of hot forgeability, the case where the forging rate is 1.5 or less is defective (x), the case where the forging rate is 1.5 to 2.5 is conditional half-defect (△), and the case where it is 2.5 or more is good (◯ ).

Table 5 below shows the forgeability test results and the evaluation of hot forgeability for each specimen. As a reference, a cross-sectional photograph showing a flattened state without cracks in the specimen 1 and comparative specimen 2 of the present invention subjected to the forging test conducted at each heating temperature of 600 ° C. to 800 ° C. Are shown in FIGS. 5A and 5B, respectively.

  According to the forgeability test results, the specimen 1 of the present invention exhibited good hot forgeability substantially equal to that of the comparative specimen 2 at a temperature of 700 ° C. or higher.

[Dezincing corrosion resistance test]
With respect to the specimen 2 of the present invention and the comparative specimen 1 as the evaluation reference material, three test pieces (Nos. 1 to 3) were respectively added to a 75 ± 3 ° C. CuCl ₂ solution (CuCl ₂ ) according to the standard of “ISO 6509”. ₂ -2H ₂ O 12.7g / L) was immersed for 24 hours, dezincification corrosion maximum depth of the exposed surface ([mu] m) was measured. In the evaluation of dezincification corrosion resistance, a case where the depth of dezincification corrosion was 100 μm or less was accepted as practically acceptable, and a case where the depth exceeded 100 μm was rejected. In addition to the measurement of the dezincification corrosion depth, the amount of zinc eluted (mg / L / 100 mm ² ) per 100 mm ² exposed area after 24 hours immersion was measured.

Tables 6 and 7 show the measurement results of the dezincification corrosion depth and the eluted zinc amount for each specimen. For reference, a micrograph (× 100) showing the dezincification corrosion state of the specimen 2 of the present invention subjected to the dezincification corrosion resistance test is shown in FIG.

  According to the results of the dezincification corrosion resistance test, the specimen 2 of the present invention exhibited a dezincification corrosion resistance much superior to that of the comparative specimen 1.

[Abrasion resistance test]
With respect to the specimen 1 of the present invention and comparative specimens 1-1 and 1-2 as evaluation reference materials, an abrasion resistance test was carried out under the following test conditions, and the width (mm) of the wear scar at each wear rate. Was measured. The comparative specimen 1-1 is a sample that is processed at a right angle to the longitudinal direction of the material, and the comparative specimen 1-2 is the comparative specimen 1 with respect to the longitudinal direction of the material. A sample processed in parallel was used. Table 8 shows the measurement results of the width of the wear scar at each wear rate for each specimen.

Test conditions Test machine name: Ogoshi type rapid wear tester Wear distance: 100,000mm (100m)
Final load: 2.1kgf
Wear rate: 0.17, 0.61, 1.14, 1.64, 2.37, 4.36 m / sec
Mating material: SUS304 (ring)

  According to the results of the abrasion resistance test, the specimen 1 of the present invention exhibited excellent abrasion resistance substantially equal to or higher than that of the comparative specimens 1-1 and 1-2.

[Other physical property comparison tests]
The Young's modulus and other physical properties of the inventive specimens 1 and 2 and the comparative specimens 1 and 2 were measured, and the measurement results are shown in Table 9 below.

  According to the physical property comparison test results, the specimens 1 and 2 of the present invention exhibited substantially the same physical properties as the comparative specimens 1 and 2.

FIG. 1 (A) is a micrograph (× 500) showing a metal structure of a brass alloy according to the specimen 1 of the present invention, and FIG. 1 (B) is a micrograph (× 500) showing a dispersion state of bismuth in the metal structure. It is. 2 (A), (B) and (C) are photographs of chips produced in each case of the depth of cut of 0.2 mm, 0.4 mm and 1.0 mm in the specimen 1 of the present invention. 3 (A), (B) and (C) are photographs of chips produced in each case of the depth of cut of 0.2 mm, 0.4 mm and 1.0 mm in the specimen 2 of the present invention. 4 (A), (B) and (C) are photographs of chips produced in each case of the cutting depth of 0.2 mm, 0.4 mm and 1.0 mm in the comparative specimen 1. FIG. 5 (A) and 5 (B) were flattened in a crack-free spread state in the specimen 1 of the present invention and the comparative specimen 2 subjected to a forging test conducted at each heating temperature of 600 ° C. to 800 ° C. It is a cross-sectional photograph which shows a state. FIG. 6 is a micrograph (× 100) showing the dezincification corrosion state of the specimen 2 of the present invention subjected to the dezincification corrosion resistance test.

Claims (4)

60.0-62.50 wt% copper (Cu), 0.4-2.0 wt% bismuth (Bi), 0.10 wt% or less lead (Pb), 0.2-1.0 wt% tin ( Sn), 0.01-0.05 wt% phosphorus (P), 0.1 wt% or less iron (Fe), the balance zinc (Zn), and a metal composition consisting of inevitable impurities, and β phase is formed by heat treatment. A lead-free free-cutting brass alloy excellent in dezincification corrosion resistance and hot forgeability, characterized by having an isolated metal structure surrounded by an α phase. Metal composition is 60.0-61.0 wt% copper (Cu), 0.4-2.0 wt% bismuth (Bi), 0.10 wt% or less lead (Pb), 0.5-0.7 wt% 2. Tin resistance (Sn), 0.01-0.05 wt% phosphorus (P), 0.1 wt% or less iron (Fe), and the balance zinc (Zn) and inevitable impurities. Lead-free free-cutting brass alloy with excellent dezincification corrosion resistance and hot forgeability. 61.0-62.50 wt% copper (Cu), 0.4-2.0 wt% bismuth (Bi), 0.10 wt% or less lead (Pb), 0.5-1.0 wt% tin ( Sn), 0.01-0.05 wt% phosphorus (P), 0.1 wt% or less iron (Fe) and 0.02-0.25 wt% antimony (Sb) and the balance zinc (Zn) and inevitable Excellent anti-dezincing corrosion resistance and hot forgeability, characterized by having a metal composition consisting of impurities and having a metal structure in which the β phase is surrounded by the α phase and isolated by heat treatment Lead-free free-cutting brass alloy. A step of casting and drawing an ingot by horizontal continuous casting from a molten copper-base alloy having the metal composition according to claim 1, 2 or 3, and drawing the obtained ingot to 600 to 730 A step of hot extrusion at a temperature of ° C or a hot extrusion at that temperature and cold drawing, and a step of annealing the obtained extruded or drawn material at a temperature of 350 to 550 ° C for 1 to 8 hours and gradually cooling The β-phase has an isolated metal structure surrounded by the α-phase by heat treatment thereof, and is excellent in dezincification corrosion resistance and hot forgeability A method for producing a lead-free free-cutting brass alloy.