TW201335391A - Lead-free brass alloy for hot processing - Google Patents

Abstract

Provided is a lead-free brass alloy for hot processing having excellent hot-processing characteristics and mechanical properties. The alloy comprises 28.0-35.0 wt% of zinc, 0.5-2.0 wt% of silicon, 0.5-1.5 wt% of tin, 0.5-1.5 wt% of bismuth, and 0.10 wt% or less of lead, the remainder comprising copper and unavoidable impurities. The zinc equivalent is 40.0 to 43.0, and the area ratio of the kappa phase after hot processing is 20% or less.

Description

Lead-free brass alloy for thermal processing

The present invention relates to a lead-free brass alloy for hot working which has excellent hot workability and mechanical properties and is excellent in dezincification resistance and corrosion/corrosion resistance.

In tap water faucet metal parts, water pipes for general piping, or various valves, copper alloys such as bronze or brass have been used since they have used their excellent material properties. These copper alloys are required to have good machinability for product processing, and therefore, it is generally possible to impart necessary machinability by containing lead. For example, a bronze alloy such as JIS H5120 CAC406 or CAC407 excellent in machinability, or a brass alloy such as JIS H3250 C3604 or C3771 contains 1 to 6 wt% of lead.

However, since lead evaporates during the melting/casting process of the alloy or dissolves into drinking water when used as a water-containing appliance, it is considered to be a harmful element that adversely affects human body or environmental sanitation in recent years. There is also a tendency to impose strict restrictions on its content. Therefore, development of a fast-cutting copper alloy that does not contain lead is required.

In the case of the bismuth-zinc bronze-based alloy, a Cu-Zn-Si-based alloy in which ruthenium is added without a lead to obtain a fast-cutting property is proposed and used (see Patent Documents 1 and 2). In addition, a Cu-Zn-Si-Sn-based alloy to which tin is added in order to improve the corrosion resistance of the Cu-Zn-Si-based alloy has also been proposed (see Patent Document 3). Also, in order to further improve the Cu-Zn-Si alloy A Cu-Zn-Si-Bi-based alloy to which tantalum is added (see Patent Document 4) and a Cu-Zn-Si-Sn-Bi alloy to which tin is added for the purpose of improving corrosion resistance (refer to the patent literature) 5) Also proposed. These alloys are excellent in mechanical properties and lead-off resistance, and have excellent machinability when bismuth is added, and excellent hot workability in alloys to which bismuth is not added. Further, when ruthenium is added to the Cu-Zn-Si-based alloy, there is an advantage that the use amount of the waste material for dissolving the raw material is wide.

Patent Document 1: Japanese Patent No. 3917304

Patent Document 2: Japanese Laid-Open Patent Publication No. 2001-64742

Patent Document 3: Japanese Patent Laid-Open Publication No. 2002-12927

Patent Document 4: Japanese Laid-Open Patent Publication No. 2009-7657

Patent Document 5: Japanese Patent Application No. 2010-84231

The alloys disclosed in the above documents are mainly for the purpose of removing the harmfulness of lead. Therefore, maintaining the rapid cutting property in the case where lead is not contained is the most important problem in performance, and a certain degree of machinability is ensured.

However, in the above alloy, when ruthenium is not contained, the effect of improving the machinability is obtained by the lanthanoid compound, but it may not be sufficient. Therefore, in order to improve the machinability, it is necessary to add a certain The degree of ambiguity. Moreover, it is preferable to use bismuth from the viewpoint of waste utilization.

On the other hand, a lead-free brass alloy containing niobium is hot-processable in a forming process with a small amount of deformation, but a forming process with a large amount of deformation is performed. In the case where the amount of ruthenium added and the forging conditions are not strictly managed, problems such as forging rupture are likely to occur. Hot forging of brass alloys is known to vary depending on the processing temperature. The processing temperature that can be processed without causing cracking has an upper limit and a lower limit, and it is necessary to heat and forge in this temperature range (hereinafter referred to as a processing temperature range). For example, in the alloy of Patent Document 5 containing about 0.7% by weight, the processing temperature must be increased, and the processing temperature range is extremely narrow, so that temperature management is difficult, and there is a problem in terms of energy usage. Further, although the alloy of Patent Document 3 describes that the addition of niobium is effective as an element having good hot forgeability, in the examples, the data on the hot workability of niobium is not described, and the processing temperature is only one level of 750 ° C. The evaluation of the temperature range is not clear.

As a result of investigations by the inventors of the present invention, it has been found that when the Cu-Zn-Si-Sn-based alloy contains niobium, the processing temperature range becomes extremely narrow. Therefore, in order to perform the forming process with a large amount of deformation in the present alloy system, it is necessary to strictly control the forging conditions, and thus it is easy to cause an obstacle in work. In other words, in order to apply the excellent corrosion resistance and machinability of the present alloy to most parts, it is important to increase the processing temperature range.

Further, in the Cu-Zn-Si-Sn-Bi alloy, since tin is added in order to improve dezincification resistance and corrosion corrosion resistance, elongation is likely to be lowered. In this alloy system, a κ phase or a γ phase is precipitated, and mechanical properties are easily deteriorated depending on the precipitation state. Further, since the precipitation conditions are easily affected by the thermal experience during production, etc., it is important to accurately grasp the relationship between the form of the structure and the mechanical value to perform appropriate control. That is, the mechanical properties of the Cu-Zn-Si-Sn-Bi alloy, particularly the elongation control, is the second problem.

The present invention has been made to solve the above problems, and an object thereof is to provide a lead-free brass alloy for hot working which has excellent hot workability and mechanical properties.

The gist of the present invention will be described.

The invention relates to a lead-free brass alloy for hot working, which is characterized in that it contains zinc: 28.0~35.0wt%, 矽: 0.5~2.0wt%, tin: 0.5~1.5wt%, 铋: 0.5~1.5wt%, lead: 0.10 wt% or less, the remainder is composed of copper and unavoidable impurities, and the zinc equivalent is in the range of 40.0 to 43.0, and the area ratio of the kappa phase after hot working is 20% or less.

Further, the lead-free brass alloy for hot working as described in claim 1 has an elongation of 10% or more.

Since the present invention is constituted as described above, it can be a lead-free brass alloy for hot working which has excellent hot workability and mechanical properties. That is, good hot workability can be obtained by containing 28.0 to 35.0% by weight of zinc. In the same manner as zinc, it is effective to add 0.5 to 2.0% by weight for an essential element for obtaining good hot workability. Tin helps to improve dezincification resistance and erosion/corrosion resistance. Tantalum is added to improve machinability. The zinc equivalent is determined by the balance of zinc, antimony and other elements, in particular, the parameters for maintaining the balance between hot workability and mechanical properties, and the properties of both can be satisfied in the range of 40.0 to 43.0. Moreover, by making the area ratio of the κ phase 20% or less, Good mechanical properties.

Embodiments of the present invention which are preferred in view of the present invention show the effects of the present invention for simplicity.

The present invention provides a lead-free brass alloy for hot working, which contains zinc: 28.0 to 35.0% by weight in order to maintain good dezincification resistance, corrosion resistance/corrosion resistance, and to ensure excellent hot workability and mechanical properties.矽: 0.5~2.0wt%, tin: 0.5~1.5wt%, 铋: 0.5~1.5wt%, lead: 0.10wt% or less, the balance is composed of copper and unavoidable impurities, and the zinc equivalent is 40.0~43.0 Within the scope.

The reason why the above-described component composition and mechanical characteristics are specified in the present invention and the effects of the present invention will be briefly described below.

Zinc (Zn)

The zinc system is solid-melted in a matrix of a Cu-Zn-Si-based copper alloy, and has an effect of improving mechanical strength. Further, the melting point of the alloy can be lowered, and the fluidity of the melt can be improved to improve the castability. Further, in order to obtain such effects, it is necessary to contain 28.0% by weight or more of zinc in accordance with the relationship between the amount of ruthenium added and the zinc equivalent described later.

On the other hand, when the amount of zinc exceeds 35.0% by weight, the hot workability is deteriorated due to the relationship between the amount of niobium added and the zinc equivalent described later, and the hard phase is required to be precipitated, so that the mechanical properties are deteriorated. For this reason, the zinc content is 28.0 to 35.0% by weight.

矽(Si)

When it is dissolved, it acts as a deacidifying material, and improves the fluidity of the melt to improve the castability. Further, a part of the material is solid-melted to the substrate to improve the mechanical strength, and a part of it acts on the zinc to function as a chip breaker during cutting to form a hard phase to improve machinability.

Furthermore, as a result of an investigation by the inventors of the present invention, it was found that the processing temperature range of the Cu-Zn-Sn-Si alloy containing bismuth (the upper limit of the processing temperature which can be hot forged without rupture minus the lower limit) is leap. The following facts of the ground uplift.

In the heating stage at the time of hot working, the crystal grain boundary has a property of being easily aggregated, which is presumed to be a factor that hinders hot workability. However, by adding an appropriate amount of ruthenium, it is possible to prevent agglomeration of the ruthenium and to prevent the forging from being broken. In order to obtain such effects, it is necessary to contain 0.5% by weight or more of ruthenium. On the other hand, when the content exceeds 2.0% by weight, the hot workability is deteriorated even if the zinc equivalent is maintained optimally, and the mechanical properties are deteriorated due to the occurrence of a hard phase of a necessary amount or more. For this reason, the content of strontium is 0.5 to 2.0% by weight.

Tin (Sn)

Tin is effective for improving dezincification resistance and erosion/corrosion resistance. In particular, it is effective to improve corrosion resistance/corrosion resistance, and in order to obtain such effects, it is necessary to add 0.5% by weight or more. On the other hand, if it contains more than 1.5% by weight, the mechanical properties are deteriorated. For this reason, the tin content is 0.5~1.5 Wt%.

铋(Bi)

When the enthalpy is less than 0.5% by weight, the improvement in machinability is hardly confirmed, and by the addition of 0.5% by weight or more, the machinability is improved by the amount of addition. However, since it is a cause of deterioration of hot workability, it is not preferable to add a large amount. Moreover, not only the hot workability but also the deterioration of mechanical properties is caused, so it is added up to 1.5% by weight.

Lead (Pb)

Lead, by making it a content of 0.10% by weight or less, can substantially avoid evaporation during alloy melting/casting, or dissolution to drinking water, etc., when used as a water-containing component, for human or environmental sanitation. Lead damage. For this reason, the content of lead is specified to be 0.10% by weight or less.

Copper (Cu)

The copper system weakens the dezincification corrosion susceptibility, and the element which improves the corrosion resistance or the mechanical property is determined by the balance of the zinc and strontium content in the alloy of the present invention, and the content is substantially 59.0~71.0wt. %.

Zinc equivalent

Zinc equivalent is an important parameter used in the alloy of the present invention to maintain a wide range of processing temperatures. As described above, by appropriately adding the crucible, the processing temperature can be kept wide, but only the management is not sufficient, and then the management is limited. The zinc equivalent calculated by the balance of bismuth and zinc can more reliably maintain a wide processing temperature range. As a result of investigation by the inventors of the present invention, the zinc equivalent in the alloy of the present invention is 40.0 or more, and the processing temperature range can satisfy the industrial range. On the other hand, if the zinc equivalent exceeds 43.0, there is a risk of deterioration of mechanical properties. Due to this background, the zinc equivalent is 40.0 to 43.0.

Further, the zinc equivalent is determined by the formula of guilett (zinc equivalent = 100 × (B + Σ tq) / (A + B + Σ tq)), and the zinc equivalent of Bi is calculated by a coefficient of 1 (see Fig. 1).

The ratio of the amount of κ phase or heat treatment

The alloy of the present invention exhibits excellent performance by the addition of each of the above elements and the imparting of hot working, but the ductility is slightly insufficient depending on the cooling rate or the processing rate at the time of hot working. In order to improve the ductility of the alloy of the present invention, it is necessary to control the metal structure, and the ductility can be ensured by setting the area ratio of the κ phase in the alloy of the present invention to 20% or less. Therefore, the area ratio of the κ phase is 20% or less. Further, the method of organizing the control may be controlled by a method of heat treatment, heat treatment, or the like, and the method is not particularly limited.

[Examples]

Specific embodiments of the invention are illustrated in accordance with the drawings.

The alloy shown in the present invention (the alloy of the present invention) and the comparative alloy were used as samples, and the tests shown below were carried out.

1) Thermal processing test

The chemical composition of the sample supplied for the hot working test is shown in FIG. It is melted by a carbon bar furnace for experimental melting, and is adjusted to a molten metal having a chemical composition as shown in Fig. 2, and cast in a die having an outer diameter of 88 mm and a length of 120 mm, and machined to have an outer diameter of 78 mm and a length of 90 mm. The machined steel blank was extruded into a diameter of 22 mm, and the resulting extruded rod was processed into a test piece shape as shown in FIG. The test pieces were forged at a processing rate of 80% at a processing temperature. The processing rate here is calculated by the following formula.

Processing rate = 100 × (sample height before forging - height of sample after forging) / height of sample before forging

The test piece (sample) after forging was visually observed, and the upper limit to the lower limit of the forging was determined without causing cracking, and the processing temperature range was defined and evaluated. Also, the heating time was 20 minutes for all tests. The processing temperature amplitudes of the respective samples are shown in Figs. 4 to 6.

(a) Regarding the validity of the addiction

The effect of adding bismuth to the alloy of the present invention is shown in Fig. 5. It can be seen that when there is no added enthalpy, the processing temperature amplitude is small, and the processing temperature amplitude increases with the addition of cerium. The effect of these can be achieved by adding 0.5 wt% or more. On the other hand, when the amount added exceeds 2.0% by weight, the processing temperature range tends to decrease, and it is known that 矽 is effective at 0.5 to 2.0% by weight.

(b) validity of zinc equivalent

Next, the effectiveness of the zinc equivalent is shown in Fig. 6. In order to maintain the processing temperature range in the alloy of the present invention to be good, it is known that the zinc equivalent must be in the range of 40.0 to 43.0, and it is confirmed that the zinc equivalent control is appropriately controlled together with the above-mentioned effect of expanding the processing temperature range caused by the addition of niobium. necessity.

2) Tensile test of hot processed materials

The chemical composition of the test piece supplied for the tensile test is shown in Fig. 7. The mold was cast in a mold having a diameter of 45 mm and a length of 100 mm, and was machined into a steel embryo having a diameter of 40 mm and a length of 75 mm. Next, the steel embryo was heated at 650 to 750 ° C, and after being extruded to a diameter of 10 mm, it was machined into a test piece of JIS Z2201 14A, and a tensile test was performed by a universal testing machine. The results are shown in Figures 8-10.

When focusing on the influence of the amount of ruthenium added, it was confirmed that the elongation tends to decrease with the amount of ruthenium added, particularly when the zinc equivalent is high. Tensile strength, when the zinc equivalent is in the vicinity of 4.06, the enthalpy is in the vicinity of 1.0 wt%, and in the vicinity of 42.5, it is temporarily lowered in the vicinity of 2.0 wt%, but there is a tendency to increase thereafter.

3) Metal structure and mechanical properties

The alloy of the present invention has excellent hot workability as described above, and it is important to appropriately control the amount of addition of Si and the equivalent of zinc. However, when the zinc equivalent is high, the elongation tends to be lowered, and the control of the structure becomes a problem.

In the alloy of the present invention, the k phase and the α phase are the main constituent structures, and the ratio of the amount of the kappa phase affects the mechanical properties, and the structure is observed. Using a sample supplied with the aforementioned tensile test, with an optical microscope The images of 500 times of the five parts were taken, and the ratio of the amount of the κ phase was measured by the image processing software (an example of the photograph taken is shown in FIG. 23). The results of these are shown in Figures 11-14. The inventors of the present invention found the following facts by the observation of the organizations. It has been found that the elongation of the alloy system of the present invention has a very strong correlation with the area ratio of the κ phase. When the elongation is to be increased, the area ratio of the κ phase must be suppressed to be low.

The relationship between the area ratio of the κ phase and the amount of strontium added is increased by the amount of strontium added (see Fig. 13). Further, the relationship between the area ratio of the κ phase and the elongation is 10% or more and 10% or more (see Fig. 14). Therefore, the area ratio of the κ phase in the alloy of the present invention must be 20% or less.

4) Corrosion test (a) Erosion/corrosion test

The chemical composition of the test material supplied for the erosion/corrosion test is shown in FIG. The melt was melted in a silica gel furnace for test melting, and the melt was adjusted to a composition as shown in Fig. 15, and was cast in a mold having a diameter of 40 mm and a length of 100 mm, and processed into a test piece shape as shown in Fig. 16. Using these test pieces, the test was carried out under the test conditions of Fig. 17. The test results are shown in Fig. 18. From these results, it was judged that the alloy of the present invention was slightly inferior to CAC406, but it was greatly improved as compared with the fast-cut brass.

(b) Dezincification corrosion test

The sample was used in the same manner as the aforementioned erosion and corrosion test. The test was carried out in accordance with the method of ISO 6509. The test results are shown in Fig. 19. this The alloys of the invention gave good results with a maximum corrosion depth of 100 μm or less.

5) Machinability test

The chemical composition of the test piece supplied for the cutting test is shown in Fig. 20. The melt was melted in a carbon bar furnace for test melting, and the melt was adjusted to the composition shown in Fig. 20, and was cast in a mold of JIS H5120E. The outer diameter of the test piece was processed under the cutting conditions shown in Fig. 21, and the measurement was performed. The cutting resistance. The test results are shown in Fig. 22. When the alloy of the present invention is improved in resistance as compared with lead-containing bronze or lead-containing brass, it is confirmed to be of the same grade as lead-free bronze.

From the above, it was confirmed that zinc was contained: 28.0 to 35.0% by weight, 矽: 0.5 to 2.0% by weight, tin: 0.5 to 1.5% by weight, 铋: 0.5 to 1.5% by weight, lead: 0.10% by weight or less, and the balance being copper and not A lead-free brass alloy for hot working with a zinc equivalent of 40.0 to 43.0, which has a good hot workability and mechanical properties.

Figure 1 is an explanatory diagram of zinc equivalent.

Figure 2 is a table showing the chemical composition of a sample for thermal processing.

Fig. 3 is an explanatory view showing the shape of a test piece of a hot working test.

Figure 4 is a table showing the results of the forging test.

Fig. 5 is a graph showing the relationship between the amount of addition of Si and the magnitude of processing temperature.

Figure 6 is a graph showing the relationship between Zn equivalent and processing temperature amplitude.

Figure 7 is a table showing the chemical composition of a tensile test specimen.

Fig. 8 is a table showing the test results of the tensile test.

Fig. 9 is a graph showing the relationship between the amount of Si added and the mechanical properties at a low Zn equivalent.

Fig. 10 is a graph showing the relationship between the amount of Si added and the mechanical properties at a high Zn equivalent.

Fig. 11 is a table showing the chemical composition of a sample in which the relationship between the Si addition amount and the area ratio of the κ phase and the elongation is investigated.

Fig. 12 is a table showing the relationship between the area ratio of Si added and the κ phase and elongation.

Fig. 13 is a graph showing the relationship between the amount of Si added and the area ratio of the κ phase.

Fig. 14 is a graph showing the relationship between the area ratio of the κ phase and the elongation.

Figure 15 is a table showing the chemical composition of a sample for the erosion/corrosion test and the dezincification corrosion test.

Fig. 16 is an explanatory view showing the shape of a test piece of an erosion/corrosion test.

Figure 17 is a table showing the test conditions.

Figure 18 is a table showing the results of the test.

Fig. 19 is a table showing the test results of the dezincification corrosion test.

Fig. 20 is a table showing the chemical composition of a sample to be subjected to a cutting test.

Figure 21 is a table showing the test conditions.

Figure 22 is a table showing the results of the test.

Fig. 23 is a photograph showing an example of a micro tissue photographed.

Claims (2)

A lead-free brass alloy for hot working, characterized by containing zinc: 28.0~35.0wt%, 矽: 0.5~2.0wt%, tin: 0.5~1.5wt%, 铋: 0.5~1.5wt%, lead: 0.10wt% Hereinafter, the remainder is composed of copper and unavoidable impurities, and the zinc equivalent is in the range of 40.0 to 43.0, and the area ratio of the kappa phase after hot working is 20% or less. The lead-free brass alloy for hot working as in the first application of the patent scope has an elongation of 10% or more.