JPS639573B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a special brass that has excellent properties peculiar to brass and also has dezincification corrosion resistance and free machinability, and a method for producing the same. Conventionally, brass is made by adding Pb to a copper-zinc alloy.
It has excellent casting and processability and is used for valve parts, etc., but dezincification corrosion occurs when used in corrosive water environments or under hot water. Among brasses, alpha brass can be prevented from dezincification corrosion by adding As, P, Sb, etc. However, α-brass theoretically requires 67.5% or more of Cu. Furthermore, alpha brass has a higher melting temperature and hot extrusion temperature than alpha+beta brass, and therefore has higher energy costs. Furthermore, α-brass has a tendency for chips to remain long during machining, making it unsuitable for automatic lathe processing. On the other hand, α+β brass does not have sufficient dezincification corrosion resistance even if As, P, and Sb are added. A certain amount (54.5 ~
α+β brass containing 67.5% Cu is easy to hot-work, and especially those containing 61 to 67.5% Cu can be transformed into α brass by applying appropriate heat treatment. Therefore, by adding As, P, Sb, etc. to this α+β brass to alphanize it, hot working can be easily performed and dezincification corrosion can be prevented. However, this brass has poor machinability and requires a long time to undergo heat treatment to become alpha. The present invention aims to improve the above-mentioned conventional drawbacks of Pb-containing brass, and aims to create a special brass that is easy to hot work, has dezincification corrosion resistance, and free machinability. This is determined by the heat treatment time. That is, the first invention is Cu60.0~63.0%,
Consists of Pb2.0~3.7%, P0.02~0.06%, balance Zn,
This is dezincification corrosion-resistant free-cutting brass characterized by a brass structure that is made up of α+β phases due to heat treatment, and the β phase is separated by the α phase. Since Cu is more expensive than Zn, its usage is reduced to 60.0%.
~63.0%, and the effects of other additive elements and heat treatment provide dezincification corrosion resistance and free machinability. Among these, a range of 61.0 to 62.0% is most preferable. Pb is added to improve machinability. 2.0%
If the amount is less than 3.7%, sufficient machinability will not be obtained, and if it is added too much, the mechanical properties will deteriorate, especially brittleness, so the upper limit is set at 3.7%. Among these, 2.8 to 3.1% is particularly suitable. P is added to improve dezincification corrosion resistance. As, Sb, Sn, etc. may be added as other elements to improve dezincification and corrosion resistance, but due to their toxicity and the need to add trace amounts within a range that does not impair processability or mechanical properties, etc. , P is selected in the present invention. When P is added in an amount of 0.02 to 0.06%, it exhibits sufficient dezincification corrosion resistance. When added in such a small amount, P exhibits dezincification corrosion resistance and also has the effect of reducing the grain size. If it is less than 0.02%, these effects will not be exhibited. However, since a part of P exists in the alloy as a hard and brittle Cu ₃ P phase, it is not preferable to add a large amount. The content is up to 0.06% without major changes in mechanical properties.
Among these, a range of 0.03 to 0.05% is particularly suitable. It is better for the alloy of the present invention to have as few impurities as possible, but since Fe and Sn are unavoidable in the manufacturing process, it is preferable to suppress both to 0.1% or less. Especially Fe,
It is preferable that the total amount of unavoidable impurities including Sn does not exceed 0.2%. The alloy of the present invention exhibits a state in which the β phase of the brass structure is separated by the α phase by heat treatment. To explain this with the help of drawings, Fig. 1 shows the structure of an extruded material made of the alloy of the present invention.
However, some are in the β phase, and the others are in the α phase 2. Most of this β phase 1 exists as a continuous phase. Figure 2 is a diagram showing the structure of the alloy of the present invention, which is obtained by annealing the extruded material in Figure 1 under special conditions, where the continuous β phase 1 is separated by the α phase 2. It's summery. The second invention is a method suitable for producing the alloy of the first invention. That is, the second invention is
Cu60.0~63.0%, Pb2.0~3.7%, P0.02~0.06%,
Extrusion or extrusion of an alloy ingot consisting of the remainder Zn
After drawing, it is annealed at 350 to 550°C for preferably 1 to 6 hours, so that the brass structure consists of α + β phase, and the β phase is α
This is a method for producing free-cutting brass that is resistant to dezincification and corrosion, and is characterized in that the brass is divided into phases. The above-mentioned alloy ingot has a low Cu content, so it is easy to extrude, and after extrusion, it consists of α+β phases, and the β phase exists in a continuous state. However, due to annealing under the above specific conditions, part of the β phase in the brass structure changes to the α phase according to the principle shown in the phase diagram, so the ratio of the α phase in the structure increases, and as a result, the remaining β phase It becomes a shape divided by the α phase,
It is enveloped in the α phase, making it difficult for dezincification corrosion to proceed, thereby improving the dezincification corrosion effect. The annealing temperature is
If the temperature is less than 350°C, a sufficient effect of dividing the β phase cannot be obtained, and if the temperature exceeds 550°C, the β phase increases, resulting in poor corrosion resistance. Hereinafter, the present invention will be explained in more detail by giving Examples and Comparative Examples. Table 1 shows the alloy components, heat treatment conditions, and test results.

【table】

[Table] In Table 1, alloy materials No. 1 to No. 7 are extruded from a 250 mm diameter billet into a 20 mm diameter rod at 640°C.
After drawing with a cross-section reduction rate of 14%, it was annealed, further drawn by 14%, and straightened and finished. No.8 is the well-known JIS C
3604 alloy, No. 10, corresponds to JIS C 2700 alloy, and all were extruded, drawn, and straightened by known methods. No. 9 is a JIS C 3771 alloy as extruded. Annealing was performed by holding the sample at a predetermined temperature for a predetermined time using an electric furnace, followed by slow cooling. After annealing, the structure was examined using a microscope in a longitudinal section to determine whether the β phase was continuous or segmented. In Table 1, β indicates a continuous state and β' indicates a divided state. In the dezincing test, each specimen was immersed in a 1% CuCl ₂ solution at 75±3° C. for 150 hours, and the dezincing depth was measured. If the dezincing depth was 200μ or less, it was considered acceptable (marked with an ○) since no problem of dezincification corrosion would occur in practice, and if it exceeded 200μ, it was marked as a failure (marked with an x). In the cutting test, cutting is performed under certain conditions, and if the chips are finely divided and have excellent machinability, it is considered a pass (○ mark), and if the chips are continuous, it is considered a fail (x mark). did. In Table 1, No. 1 has a large amount of Cu and has an α structure, so its machinability is poor. No. 2 has a low P content and does not have sufficient dezincification corrosion resistance. No. 3 has a low annealing temperature,
Since the β phase of the α+β structure is in a continuous state, dezincification corrosion resistance is poor. No. 6 has a high annealing temperature and a large amount of β phase, so the dezincing corrosion resistance effect is small. No.7 is Cu
Since the amount is small and the β phase is large, dezincification corrosion resistance is poor. All of the known alloys No. 8 to No. 10 have an α+β structure and have poor dezincification corrosion properties. On the other hand, alloys No. 4 and No. 5 of the present invention have a structure in which the β phase is separated by the α phase, and are excellent in both dezincification corrosion resistance and machinability.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the state of the structure of the alloy composition of the present invention after extrusion, and FIG. 2 is a diagram showing the state of the structure after heat treatment. 1...β phase, 2...α phase.

Claims (1)

[Claims] 1 Cu60.0-63.0%, Pb2.0-3.7%, P0.02-0.06
%, with the remainder being Zn, and is characterized by having a brass structure made up of α+β phases by heat treatment, and in which the β phase is separated by the α phase. 2 Cu60.0~63.0%, Pb2.0~3.7%, P0.02~0.06
%, the balance is Zn, and the alloy ingot is extruded or annealed at 350 to 550℃ after extrusion and drawing, and the brass structure becomes α+.
A method for producing dezincification corrosion-resistant free-cutting brass comprising a β phase, the β phase being separated by an α phase.