JP2013234362A - Brass alloy excellent in high temperature brittleness resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Bi-based brass alloy which suppresses the lowering of brittleness at high temperature range, even if containing Pb in the range of about 0.1%.SOLUTION: A Bi-based brass alloy is characterized by containing, by mass%, 58.0 to 64.0% of Cu, 0.9 to 2.0% of Bi, 0.4 to 0.8% of Mg, 0.2 to 0.7% of Al, no more than 0.15% of Pb, no more than 0.5% of Fe, and no more than 0.5% of Sn, the remainder comprising Zn and unavoidable impurities.

Description

  The present invention relates to a brass alloy with improved brittleness in a high temperature range.

As a brass alloy excellent in machinability, a free-cutting alloy to which a Pb component is added has been generally used so far.
However, in recent years, Pb-less brass alloys have been studied in consideration of environmental impact, and while maintaining the material properties required for conventional brass alloys such as strength and slidability, free-cutting properties are comparable to Pb-based brass alloys. Bi-based brass alloys have been developed (Patent Documents 1 and 2).
However, it has been clarified that the conventional Bi-based brass alloy has a brittleness near room temperature that is almost the same as that of the Pb-based brass alloy, but the brittleness may suddenly decrease in a high temperature range of about 150 ° C. .
The inventor of the present application explains in detail why the brittle region decreases to about 150 ° C. when bismuth is added instead of Pb even though the conventional lead-containing brass alloy does not significantly decrease brittleness to about 250-300 ° C. An experimental investigation was conducted.
As a result, the copper material and the zinc material used for the casting of the brass alloy contain a small amount of Pb, and a slight amount of Pb is mixed even when casting using the melting furnace. The amount of the component is Pb: 0.05 to 0 It was 1 mass%.
Although the melting point of Bi itself is 271 ° C., it has been clarified that the melting point decreases to around 125 ° C. even if Pb is mixed at a ratio of 5 to Bi100.
Therefore, when Pb and Bi contained in a very small amount are alloyed and segregated at the grain boundaries, if the temperature is higher than 150 ° C., it is presumed that high temperature brittleness occurs due to the fracture starting from the segregated particles. The
For this reason, a Bi-based brass alloy with good high-temperature brittleness resistance in which the Pb component is suppressed so that the component ratio Pb / Bi is 0.005 or less has been proposed (Patent Document 3).
Patent Document 4 discloses a copper-based alloy in which the amount of Pb is suppressed to suppress the formation of a Bi—Pb eutectic phase and the deterioration of mechanical properties at high temperatures is improved.
However, in order to reduce the amount of Pb to the limit of 0.01% or less, there is a problem that the cost is high because it is manufactured from a high purity metal such as electrolytic copper, electrolytic zinc, or metallic bismuth.
In the RoHS regulation and ELV regulation by the European Union, the amount of Pb is set to 0.1% or less. Therefore, it is preferable that Pb is allowed to be mixed within a range that can satisfy this regulation.

JP 7-310133 A JP 2001-059123 A JP 2004-359968 A JP 2006-111925 A

  An object of the present invention is to provide a Bi-based brass alloy that suppresses a decrease in brittleness in a high temperature range even when Pb is mixed in a range of about 0.1%.

The brass alloy excellent in high temperature brittleness resistance according to the present invention is, by mass, Cu: 58.0 to 64.0%, Bi: 0.9 to 2.0%, Mg: 0.4 to 0.8%. , Al: 0.2 to 0.7%, Pb: 0.15% or less, Fe: 0.5% or less, Sn: 0.5% or less, with the balance being Zn and inevitable impurities Features.
The present invention is characterized in that Mg is added to preferentially form an intermetallic compound of Bi and Mg as a means for preventing the eutectic of Bi and Pb when Pb is mixed. .
Since Pb is 0.1% or less in the RoHS regulation and the ELV regulation, the present inventor has studied to suppress the influence of Pb even when the amount of Pb mixed slightly exceeds 0.1%. It has been clarified that the addition amount of Mg needs to be increased in accordance with the addition amount of Bi, and the addition amount is preferably not less than [Bi] × 0.4 in mass%.
In addition, it is preferable to suppress the mixing amount of the Pb component to 0.1% or less.

The present invention is characterized in that Mg is added so as to allow the Pb component to be mixed up to about 0.1% in the Bi-based brass alloy, and other components depending on the use of the brass alloy. May be added.
For example, in mass%, Cu: 58.0-64.0%, Bi: 0.9-2.0%, Mg: 0.4-0.8%, Al: 0.2-0.7%, Pb: 0.15% or less, Fe: 0.5% or less, Sn: 0.5%, P: 0.03-0.1%, Se: 0.01-0.5%, Sb: It is good also as a brass alloy which contains any one or more among 0.01-0.5%, Te: 0.01-0.5%, and remainder consists of Zn and an unavoidable impurity.
Also in this case, the amount of Pb mixed is preferably 0.1% or less.

Next, the reason for setting each component range will be described.
<Cu>
The Cu component is a component that serves as a base of the brass material, and Cu: 58.0 to 64.0%, preferably 60.0 to 62.0%.
<Bi>
The purpose is to improve the free-cutting property starting from Bi in the brass material structure, and it serves as an alternative to conventional Pb.
In order to exhibit such an effect, Bi needs to be 0.9% or more, and when it exceeds 2.0%, the effect is saturated.
Therefore, Bi is preferably in the range of 0.9 to 2.0%, and preferably Bi: 1.0 to 1.8%.
<Mg>
Mg has an action to suppress the formation of a Bi—Pb eutectic phase in the brass material, and Mg is Mg: 0.4 to 0.8% within the above Bi component range. Is preferably not less than the value of [Bi] × 0.4 by mass%.
Mg forms Bi-Mg intermetallic compounds.
When the amount of added Mg increases, surface defects due to the formation of magnesium oxide tend to occur during casting, so the upper limit was made 0.8%.
In order to confirm that the Pb component may be mixed up to 0.1%, which is a general upper limit, the Pb component may be mixed up to 0.15%. For this purpose, an experiment was conducted to arrive at the present invention.
Therefore, if the Pb component is 0.1% or less, the amount of Mg added may be in the range of 0.4 to 0.65%.
<Al>
The purpose of the Al component is to ensure fluidity during casting, and the range of 0.2 to 0.7% is preferable.
Preferably, it is 0.2 to 0.5% of range.
<Zn>
The Zn component is a component serving as a base of the brass material together with the Cu component, and based on the fact that the ratio of Cu: Zn is about 6: 4, in this specification, it is expressed as the balance with respect to the sum of Cu and other additive components. .
<Sn>
The Sn component is effective in improving mechanical properties such as tensile strength. However, since the hard Mg-rich phase is easily generated when the amount of the Sn component is increased, 0.5% or less is preferable.
<Other ingredients>
In the present invention, the Fe component should be 0.5% or less, preferably 0.2% or less as an impure component, P and Sb contribute to the improvement of dezincification corrosion resistance, and Se and Te contribute to the improvement of free-cutting properties. To do.
When adding, the range of P: 0.03-0.15%, Sb: 0.01-0.5%, Se: 0.01-0.5%, Te: 0.01-0.5% Good.

  According to the present invention, since a predetermined amount of Mg is added to the Bi-based brass alloy, the appearance of a Bi—Pb eutectic phase can be suppressed, and the brittleness in the high temperature region due to the mixing of Pb can be prevented.

The alloy components used in the evaluation of the present invention and the evaluation results are shown. The SEM image of a casting material is shown. The evaluation standard of chips is shown. The evaluation method of castability is shown.

  A brass alloy having each chemical composition shown in the table of FIG.

  As the evaluation method, those that passed the following evaluation criteria were judged to be acceptable.

The impact test piece was a JIS Z 2202 V notch test piece.
The normal temperature impact value was tested at 23 ° C., and impact absorption energy of 15 J or more was evaluated as “◯” (passed), and less than 15 J was evaluated as “x” (failed).
The high temperature impact value was tested at 200 ° C., and impact absorption energy of 10 J or more was evaluated as “◯” (passed), and less than 10 J was evaluated as “x” (failed).
The Charpy test method conformed to JIS Z 2242.
As for the chip shape, the feed rate (mm / rev) was set to 0. 5 mm at a cutting depth of 0.5 mm (cutting speed: 99 m / min) and a cutting depth of 1.0 mm (cutting speed 94.2 m / min) as shown in FIG. Chips were collected as 064, 0.128, 0.192, 0.256, 0.320.
The shape of chips was observed at a total of 10 levels.
Among the 10 levels, even when one piece of A chips was present, it was set as x (failed), and when it was only chips of other shapes, it was marked as ◯ (passed).
In the hot water flow test using a mold as shown in FIG. 4 and cast at 1000 ° C., the hot water flowability was evaluated as ○ (passed) when the total length was 150 mm or more, and X (failed) when the total length was 150 mm or less.

The evaluation results of each prototype alloy are shown in the table of FIG.
Alloy No. 1 to 10 correspond to examples of the present invention, in which the Cu component is 58.0 to 64.0%, the Bi component is 0.9 to 2.0%, and the Al component is 0.2 to 0.7%. Since the Fe component is 0.5% or less and the Sn component is 0.5% or less, even if the Pb component is intentionally mixed in an amount of 0.09 to 0.15%, the Mg component is 0.4 to 0.00. By adding 8%, the impact value at a high temperature of 200 ° C. was able to clear the target, and the machinability (chip shape) and castability (hot water flow) could also be cleared.
For reference, FIG. 2 shows an SEM image of the structure of the cast material.
From the surface analysis, it can be seen that the positions of Mg and Bi overlap.
On the other hand, in the comparative example, as a result of intentionally mixing the Pb component to the same extent as described above, the comparative example alloy No. No. 21 has a Mg component less than 0.4%. Since 30 and 31 did not add the Mg component, the high temperature impact value did not clear the target.
Comparative Example Alloy No. In No. 23, 0.68% of the Mg component was added, but since the Bi component amount exceeded 2.0%, the high temperature impact value could not be cleared.
Comparative Example Alloy No. In Nos. 21-24 and 26-29, the addition amount of the Al component was less than the target, so the hot water flowability did not clear the target.

Claims (2)

  In mass%, Cu: 58.0 to 64.0%, Bi: 0.9 to 2.0%, Mg: 0.4 to 0.8%, Al: 0.2 to 0.7%, Pb: A brass alloy excellent in high temperature brittleness resistance, characterized in that it is 0.15% or less, Fe: 0.5% or less, Sn: 0.5% or less, and the balance is made of Zn and inevitable impurities. In mass%, Cu: 58.0 to 64.0%, Bi: 0.9 to 2.0%, Mg: 0.4 to 0.8%, Al: 0.2 to 0.7%, Pb: 0.15% or less, Fe: 0.5% or less, Sn: 0.5% or less,
Any one or more of P: 0.03-0.1%, Se: 0.01-0.5%, Sb: 0.01-0.5%, Te: 0.01-0.5% A brass alloy having excellent high-temperature brittleness resistance, which contains Zn and inevitable impurities.