JP2002030364A - High-strength free-cutting brass - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce the Pb content and to provide excellent machinability.
Provided is high-strength free-cutting brass that has machinability and dezincification corrosion resistance and is advantageous in cost. SOLUTION: Cu: 69.0 to 76.0%, Si:
1.5 to 4.0%, P: 0.02 to 0.10%, Bi and / or Pb: more than 0.4% to 1.0%, with the balance being Zn and unavoidable impurities And (Cu% −2.8 × Si%) ≧ 64
Is satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention has excellent properties unique to brass, high strength and free cutting properties,
The present invention relates to brass having excellent dezincification corrosion resistance.

[0002]

2. Description of the Related Art Conventionally, brass obtained by adding Pb to a Cu-Zn alloy is excellent in castability, hot and cold workability, and machinability, so that brass fittings, valve parts, and home electric appliances are connected. Used as parts.

In recent years, various devices, especially home appliances, have been required to have high performance and energy saving. From this viewpoint, the brass parts have also been required to be reduced in weight and thickness. Reduction is a problem, and improvement in the strength of the material itself is required.

[0004] For example, the alternative refrigerant R410A used for a package air conditioner is required to have a pressure resistance several times higher than that of a conventionally used R22 refrigerant, and a material having a higher strength than the current material is required. Conventionally, free-cutting phosphor bronze has been known as a copper alloy material with excellent strength and free-cutting properties.However, at the time of manufacture, inexpensive brass-based return scrap cannot be used, so the amount of scrap used is limited and costs are reduced. Inevitably, it is disadvantageous in terms of cost, and becomes more expensive than free-cutting brass containing Pb based on 46-brass.

Recently, as high-strength brass with excellent machinability,
Brass with a significantly reduced Pb content and brass without Pb have been proposed (JP-A-2000-1197).
74, JP-A-2000-119775). These brass are considered to be harmful substances that have an adverse effect on the human body and the environment in recent years, and their use has been restricted.
It has been proposed in response to the problem, and both contain Cu and Si. However, in this composition range, the β phase becomes relatively excessive depending on the hot working temperature, and the cutting resistance is reduced. In some cases, the surface roughness may increase and the surface roughness may deteriorate. Further, since the β phase is hard and brittle, the cold workability is impaired if it is present in excess. Although there is a method of reducing the β phase generated during hot working by post heat treatment, the number of steps is increased, which is disadvantageous in cost.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems in Pb-containing free-cutting brass. Another object of the present invention is to provide a high-strength free-cutting brass which has excellent machinability, machinability and dezincification corrosion resistance and is advantageous in cost.

[0007]

In order to achieve the above object, a high-strength free-cutting brass according to claim 1 of the present invention comprises Cu:
69.0-76.0%, Si: 1.5-4.0%, P:
0.02 to 0.10%, and further contains Bi and / or Pb: more than 0.4% and 1.0% or less, and has a composition consisting of a balance of Zn and unavoidable impurities.
−2.8 × Si%) ≧ 64.

The high-strength free-cutting brass according to claim 2 is characterized in that, in claim 1, Sn as an impurity is 0.05% or less, and
1 is limited to 0.016% or less.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The significance of the components contained in the present invention and the reasons for limitation will be described. Si content increases the apparent Zn content.
Because it is as large as 0.0, the γ phase is precipitated by adding a small amount,
Since the γ phase is hard, an increase in strength due to precipitation hardening is obtained.

[0010] Precipitation of the β phase also contributes to an increase in strength, but since the hardness of the β phase is lower than the hardness of the γ phase, the increase in strength is reduced as compared with the case where only the γ phase is precipitated. Since the precipitation amount of the γ phase decreases according to the phase diagram when the β phase precipitates, it is desirable to reduce the precipitation amount of the β phase as much as possible in order to obtain the strength improvement effect. In the range of 69.0 to 76.0%, (Cu% -2.8 ×
It is preferable to include Si in a range satisfying the relationship of (Si%) ≧ 64.

In order to precipitate the γ phase only by hot working without post-heat treatment after hot working, the Si content must be reduced to 1.5 in consideration of hot working (hot extrusion) conditions.
% Or more is preferable. By containing Si, the effect of improving the flowability of the molten metal and preventing casting defects in the ingot can also be obtained. If the content of Si exceeds 4.0%, the abundance ratio of the γ phase is increased, and the γ phase particles are coarsened to significantly impair cold workability. Therefore, the preferable content range of Si is set to 1.5 to 4.0%.

By setting the Cu content in the range of 69.0 to 76.0% and the Si content in the range of 1.5 to 4.0%, regardless of the hot working temperature, the matrix has an α + β phase, an α + γ phase,
Alternatively, the structure becomes α + β + γ phase. As a result of conducting a more detailed experiment on the relationship between the composition and the hot working temperature and the structure, the relationship between the Cu amount and the Si amount becomes (Cu% −2.8).
When xSi%) <64, depending on the hot working temperature, the β phase becomes relatively excessive, and good machinability may not be obtained, and the β phase is hard and brittle. It was found that the cold workability was sometimes reduced.

As described above, a post-heat treatment method is effective to reduce the β phase generated during hot working. However, the conventional free-cutting brass is required because the number of steps is increased and the production cost is increased. Is not desirable as a substitute for Therefore, in the present invention, it is preferable that the composition satisfy the relationship of (Cu% −2.8 × Si%) ≧ 64.

[0014] Bi and Pb function to improve the machinability. When the α-phase particles are fine and the γ-phase is uniformly dispersed, the γ-phase acts as a chip breaker without adding Bi and Pb, and it is possible to cut off cuttings. In order to obtain such an effect, temperature control for controlling the structure at the time of hot working or post heat treatment is required, and concentration control at the time of casting must be strictly performed.

Bi and / or Pb exceeding 0.4%
, Ie, more than 0.4% of B
i or Pb, or both Bi and Pb in total of 0.4
%, It is possible to obtain good machinability without requiring the above-mentioned concentration control, temperature control, and post-heat treatment. However, Bi,
Since Pb precipitates in the matrix inconsistently and makes the material brittle, in the present invention in which the strength is improved by precipitation hardening of the γ phase, if the content exceeds 1.0%, the cold workability is impaired. This may cause breakage. Furthermore, addition of a large amount of Pb is not preferable from the viewpoint of regulation of elution into drinking water.
Considering that i is a rare metal, it is desirable to minimize the addition of Bi and Pb, and Bi and / or P
The preferable content of b is more than 0.4% and 1.0% or less, more preferably 0.50 to 0.80%.

P functions to improve the dezincification corrosion resistance. In particular, it is effective in suppressing the dezincification corrosion of the α phase.
In the present invention, (Cu% −2.8 × Si%) ≧ 64
In the composition range that satisfies the relationship, the precipitation of β phase, in which the occurrence of dezincification corrosion is remarkable, is relatively small, the structure is surrounded by the α phase, and the γ phase itself hardly causes dezincification corrosion. In order to suppress dezincification corrosion in the invention,
The addition of P is effective.

The content of P effective for dezincification corrosion resistance is 0.0
Although it is 2% or more, a part of P exists as a hard and brittle Cu ₃ P phase, and when a particularly large Cu ₃ P phase is formed, it inhibits cold workability and causes breakage. It is not preferable to add them. Considering these, the preferable content of P is in the range of 0.02 to 0.10%, and the more preferable content range is 0.03 to 0.08%.

[0018] Sn and Al as impurities increase the apparent Zn content.
Since n is as high as 2.0 and Al is as high as 6.0, when Sn and Al are contained, the concentration control of the essential components becomes complicated.
Although it is desirable not to contain Sn and Al, scrap and distilled zinc cannot be used, which is disadvantageous in terms of production cost. Sn and A for controlling the concentration of Si
The upper limit of 1 is 0.05% or less and 0.016, respectively.
% Or less.

The brass of the present invention is usually supplied as a rod, and its production is performed by ingoting an alloy having the above-described composition, subjecting the obtained ingot to hot extrusion, and further usually cold drawing. Processing is performed, and correction and finishing are performed as necessary.

[0020]

EXAMPLES Examples of the present invention will be described below in comparison with comparative examples, and the effects thereof will be demonstrated based on them.
It should be noted that these examples are for describing a preferred embodiment of the present invention, and the present invention is not limited thereto.

Example 1 New ingot of Cu, Zn, Bi, Pb, Si and Cu-1
Table 1 in which the concentration of component elements was adjusted by mixing 5% P master alloy
Was melted, cast and ingot into a billet having a diameter of 294 mm.

The obtained billet was hot-extruded into a rod having a diameter of 17.0 mm at a temperature of 580 to 620 ° C.
Cold drawing was performed at a cross-sectional reduction rate of 10%, followed by straightening.

The workability, dezincification corrosion resistance, and machinability of the bar (test material) after the corrective finishing were evaluated by the following methods, and the tensile strength was measured. Workability: In hot extrusion and cold drawing, those that did not break or crack were accepted (o), and those that broke or cracked were rejected (x).

Dezincification corrosion resistance: 12.7 g of CuCl ₂ .2H ₂ O at 75 ± 3 ° C. according to the ISO method
/ L solution for 24 hours, measure the dezincification corrosion depth,
Evaluation was made according to the following criteria. Dezincification corrosion depth 100μm
The following (depth that does not cause a problem of dezincification corrosion in practical use) are acceptable (（), and those with a dezincification corrosion depth exceeding 100 μm are unacceptable (x).

Cutting performance: rotation speed 1000-2000 rpm
m, depth of cut 0.01 to 2.5 mm, feed amount 0 to 0.
25 mm / rev. The cutting process was performed using cutting tools of various shapes, and the cutting chips were finely divided under any conditions and the cutting performance was excellent (O): The cutting chips were continuous under any one of the conditions Those that were judged as failed (x). Tensile strength: A Pb-containing free-cutting brass (JIS C360) subjected to a tensile test in accordance with JIS and subjected to the same cold working.
Compared with the tensile strength of 4), those that were more excellent were evaluated as pass (○), and those that were equal to or lower were evaluated as unacceptable (x).

Test material No. 1 to 9 indicate that the matrix is β
Β-phase becomes α even if there is no phase-existing tissue or β-phase
It shows the structure morphology divided by phase, is excellent in workability, dezincification corrosion resistance, and machinability, and has higher tensile strength than Pb-containing free-cutting brass (JIS C3604) cold-worked with the same workability. .

[0027]

[Table 1]

Example 2 A return scrap of 65/35 brass and a return scrap of free-cutting brass containing Pb were used as main raw materials.
An alloy having a composition shown in Table 2 was prepared by mixing a new ingot of i and Si and a Cu-15% P mother alloy to adjust the concentration of the constituent elements, and the resulting alloy was cast into a billet having a diameter of 294 mm. Sn and Al as impurities are mixed from return scrap.

After the obtained billet was hot-extruded into a bar having a diameter of 17.0 mm at a temperature of 610 ° C., it was cold-drawn at a cross-sectional reduction rate of 10%, and further subjected to a straightening finish.
Example 1 about bars (test materials) after straightening finish processing
Workability, dezincification corrosion resistance, and machinability were evaluated in the same manner as described above, and tensile strength was measured.

Test material No. Nos. 10 to 11 show a structure in which the matrix does not have a β phase or a structure in which the β phase is separated by the α phase even if the β phase exists, and is excellent in workability, dezincification corrosion resistance, machinability, and equivalent. P cold-worked at a working degree of
It has higher tensile strength than brass containing b (JIS C3604).

[0031]

[Table 2]

Comparative Example 1 A return scrap of 65/35 brass and a return scrap of free-cutting brass containing Pb were used as main raw materials, and copper wire scrap and B
An alloy having the composition shown in Table 3 was prepared by mixing a new ingot of i and Si and a Cu-15% P master alloy to adjust the concentration of the component elements, casting and ingot into a billet having a diameter of 294 mm. Sn and Al as impurities are mixed from return scrap.

After the obtained billet was hot-extruded into a rod having a diameter of 17.0 mm at a temperature of 580 to 620 ° C.,
Cold drawing at a cross-section reduction rate of 10%, straightening and finishing, and bars (test materials) after straightening
Workability, dezincification corrosion resistance, and machinability were evaluated in the same manner as in Example 1, and tensile strength was measured. Table 4 shows the results. In Table 3, those outside the conditions of the present invention are underlined.

[0034]

[Table 3]

[0035]

[Table 4]

As shown in Table 4, the test material No. 12 is C
u content is low, and the test material No. In No. 15, since the Si content was large, the abundance of the precipitated γ phase was high, or the γ phase was coarsened, and fracture occurred in the drawing process.
Test material No. No. 13 has a large amount of Cu, and test material No. 1
In No. 4, since the Si content was small, the abundance of the precipitated γ phase was low, and the hardening of Bi and Pb was not sufficiently obtained, and the cutting chips were not divided.

Test material No. In No. 16, since the contents of Bi and Pb were small, the cutting chips were not connected continuously in a spiral shape depending on the cutting conditions, and sufficient cutting properties could not be obtained. Test material No. 17 has a large content of Bi and Pb,
Cold workability was impaired, and fracture occurred during cold drawing.

Test material No. Test Material No. 18 was inferior in zinc removal resistance because of low P content. No. 19 had a large P content, so that fracture occurred during drawing from Cu ₃ P as a starting point. Test material No. Test material No. 20 has a large amount of Sn.
Since No. 21 had a large amount of Al, the abundance ratio of the precipitated γ phase was high, or the γ phase was coarsened, and fracture occurred in the drawing process. Test material No. No. 22 does not satisfy the relational expression between Cu and Si, and the amount of Si is larger than the amount of Cu.
Cracks occurred due to insufficient ductility during drawing.

[0039]

According to the present invention, there is provided a high-strength free-cutting brass having a reduced Pb content, excellent cutability, machinability, and dezincification corrosion resistance, and which is advantageous in cost. You.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tetsuro Atsumi 5-11-3 Shimbashi, Minato-ku, Tokyo Sumitomo Light Metal Industries, Ltd. (72) Inventor Yoshihiro Yoshikawa 4-1 Kashiwara, Ishioka-shi, Ibaraki Shin Nitto Metal Co., Ltd.

Claims (2)

[Claims] 1. Cu: 69.0 to 76.0% (% by mass,
The same applies hereinafter), Si: 1.5 to 4.0%, P: 0.02 to
0.10% and additionally Bi and / or Pb:
It has a composition of more than 0.4% and not more than 1.0%, the balance being Zn and unavoidable impurities, and (Cu% -2.8 ×
A high-strength free-cutting brass that satisfies the relationship of (Si%) ≧ 64. 2. Sn as an impurity of 0.05% or less,
2. The high-strength free-cutting brass according to claim 1, wherein Al is limited to 0.016% or less.