Brass alloy with excellent resistance to stress corrosion cracking

Abstract

To provide a yellow copper alloy having excellent stress corrosion cracking resistance.SOLUTION: A yellow copper alloy contains, in mass%, Cu: 57.0-64.0%, Bi: 0.8-2.2%, Fe: more than 0.03% and 0.30% or less, Sn: more than 0.5% and 1.5% or less, Sb: 0.02-0.12%, Ni of less than 0.05%, with the balance being Zn and inevitable impurities.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a brass alloy having excellent stress corrosion cracking resistance, and in particular to a leadless brass alloy that is substantially free of lead. [Background technology]

[0002] A lead-free brass alloy having improved stress corrosion cracking resistance is disclosed in, for example, Patent Document 1. However, all of the alloys actually used in the evaluation of stress corrosion cracking resistance in this publication contain 0.1% or 0.2% Ni. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4550154 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present invention is to provide a brass alloy having excellent stress corrosion cracking resistance. [Means for solving the problem]

[0005] The brass alloy having excellent stress corrosion cracking resistance according to the present invention is characterized by the following, in mass%, Cu: 57.0 to 64.0%, Bi: 0.8 to 2.2%, Fe: more than 0.03% and not more than 0.30%, Sn: more than 0.5% and not more than 1.5%, Sb: 0.02 to 0.12%, Ni: less than 0.05%, and the balance being Zn and unavoidable impurities.

[0006] The brass alloy according to the present invention is a lead-free brass alloy in which the Pb content is suppressed to the impurity level, and is characterized by improved stress corrosion cracking resistance, particularly in that in addition to setting the component ranges of Bi, Sn, and Sb, Fe content is added. In the present invention, the Ni component is not an essential component. Preferably, in terms of mass %, Cu: 60.0 to 63.0%, Bi: 0.8 to 2.2%, Fe: 0.06 to 0.30%, Sn: 0.6 to 1.5%, Sb: 0.04 to 0.1%, and the balance is Zn and inevitable impurities.

[0007] In the brass alloy according to the present invention, the reasons for setting the component ranges are as follows. <Cu component> The Cu component is an essential component together with the Zn component in the brass alloy. In, for example, the typical alloy C6804B described in JISH3250, the Cu component is defined as 57.0 to 64.0%. In consideration of the workability during hot and cold working, the component range of Cu may be set in the range of 60.0 to 63.0%. <Sn component> The brass alloy according to the present invention is also excellent in formability and has good elongation and drawability. When the Sn component is 0.5% or less, the effect of improving stress corrosion cracking resistance is small. When the Sn component exceeds 1.5%, the elongation decreases and it becomes difficult to form hexagonal bars and the like. Therefore, the Sn component is set to exceed 0.5% and be 1.5% or less. Preferably, it is in the range of 0.6 to 1.5%. <Sb component> The Sb component can improve the corrosion resistance by dissolving more in the γ phase. When the Sb component exceeds 0.12%, on the contrary, the stress corrosion cracking resistance decreases. Therefore, the range of Sb: 0.02 to 0.12% is set. Preferably, it is in the range of 0.04 to 0.1%. <Bi component> The Bi component is added to improve the machinability as an alternative to the conventional Pb component. In the brass alloy according to the present invention, the range of Bi: 0.8 to 2.2% is set. When Bi exceeds 2.2%, the elongation characteristics deteriorate. <Fe component> The Fe component promotes the refinement of crystals in the metal structure. When Fe exceeds 0.03%, the stress corrosion cracking resistance is improved. Since no improvement in stress corrosion cracking resistance was observed even when added at more than 0.30%, the Fe content was set in the range exceeding 0.03% and not exceeding 0.30%. Preferably, it is in the range of 0.06 to 0.30%. <Ni component> In the present invention, the Ni component is not essential, but is suppressed to less than 0.05%. Currently, in the water quality standard system diagram of Japan, Ni is a water quality management target setting item and is set at 0.02 mg / L or less. In the future, if Ni is standardized in water quality, the leaching standard value of the end faucet fitting is likely to be 0.002 mg / L or less. From the results of the leaching test described later, the Ni component needs to be less than 0.05%. <Other components> In the present invention, it is allowed to contain P at 0.1% or less, and other components are inevitable impurities.

Effect of the invention

[0008] The brass alloy according to the present invention can improve stress corrosion cracking resistance by containing Fe in addition to Bi, Sn and Sb, and can meet strict environmental regulations by making the content of the Ni component less than 0.05%.

Brief description of the drawings

[0009] [Figure 1] The alloy composition used for evaluation and its evaluation results are shown. [Diagram 2] The influence of Sn on SCC resistance (maximum crack length) is shown. [Diagram 3] The influence of Sn on elongation is shown. [Figure 4] The influence of Fe on SCC resistance (maximum crack length) is shown. [Diagram 5] The influence of Sb on SCC resistance (corrosion fracture surface rate) is shown. [Figure 6] The test method for SCC resistance (corrosion fracture surface rate) is shown. [Figure 7] A photograph of the corrosion fracture surface is shown. [Figure 8] Shows the leaching test results of Ni.

Mode for Carrying Out the Invention

[0010] Prototype brass alloys with each component composition shown in the table of Fig. 1 were made and evaluated.

[0011] In the table of Fig. 1, the maximum crack length and corrosion fracture rate are shown as stress corrosion cracking resistance (SCC resistance), and the elongation by a tensile test is shown. Test pieces for evaluation were cast from φ60 billets of the brass alloy shown in the table of Fig. 1, extruded to φ16.5 and cold-worked to φ16.0, and then heat-treated at 420 °C for 2 hours. <Evaluation of SCC Resistance and Maximum Crack Length> Seal tape was wound around the Rc1 / 4 thread part, a stainless steel plug was screwed in with a torque of 5 Nm, and it was left in a desiccator filled with aqueous ammonia with an ammonia concentration of 14% for 24 hours for testing. After a predetermined time had passed, each test material was taken out from the desiccator, washed with dilute sulfuric acid, and then observed under a 20-fold magnification to measure the maximum crack length. <Evaluation of SCC Resistance and Corrosion Rate of Fracture Surface> Test pieces with the size and shape shown in Fig. 6 were fabricated and left in a desiccator filled with an aqueous solution with an ammonia concentration of 14% for 16 hours with a torque of 10 Nm applied. After that, the test pieces were destroyed and the corrosion fracture rate was measured. <Evaluation of Elongation> No. 4 test pieces in JIS Z 2241 Metallic Materials - Tensile Test Method were fabricated and measured with a tensile testing machine. For the test for measuring elongation, those extruded from a φ60 billet to a φ10 round bar were used. <Leaching Test of Ni> It was carried out based on the leaching performance test method for plumbing fixtures specified in JIS S3200-7. Leaching solution at 40 °C was left standing for 16 hours so that the wetted surface area ratio became 1600 cm 2 / L, and the leaching amount of Ni in mg / L was measured by ICP mass spectrometry. The results are shown in the table in Figure 8. The column for material indicates the amount of Ni contained in the alloy used in the test. Ni (raw data) indicates the measured leaching amount in the above test, and 1L correction is the value converted per 1L of water. From these results, when Ni is contained in the brass alloy, if the Ni content is 0.10% or less, preferably less than 0.05%, it is possible to clear the strict environmental regulations that are expected in the future.

[0012] In brass alloys, the quality characteristics are influenced by the additive components. Based on the results shown in the table in Figure 1, the influence of each component was examined, and the results are explained below.

[0013] In Figure 2, the horizontal axis represents the amount of Sn, and the vertical axis represents the measurement results of maximum crack length as SCC resistance. The addition of Sn improves SCC resistance. The brass alloy containing 0.8% Sn has a larger SCC resistance than the brass alloy containing 0.5% Sn, and has improved SCC resistance. From this, it can be said that Sn has an effect of improving SCC resistance, and it is good to add a large amount of Sn, at least exceeding 0.5%. FIG. 3 shows how the elongation (%) changes with the addition of Sn. When the amount of Sn added is large, the elongation decreases. In the present invention, since the target elongation is 30% or more, the upper limit of the Sn content is set to 1.5% or less.

[0014] FIG. 4 shows the effect of the Fe content on SCC resistance (maximum crack length). In the table of FIG. 1, these are the values ​​for Comparative Example 4, and Examples 2, 6, 7, 8, and 9. From the results shown in FIG. 4, it can be seen that the addition of Fe improves SCC resistance. From these results, it is preferable that the Fe content is added in an amount exceeding 0.03%, and preferably 0.06% or more. In this respect, the use of an Fe component to improve SCC resistance has not been considered in conventional brass alloys, and this is one of the features of the present invention.

[0015] Figure 5 shows the results of examining the effect of the amount of Sb added on SCC resistance. The corrosion fracture surface rate (%) was used to evaluate SCC resistance. Figure 7 shows example photographs of fracture surfaces, and the evaluation was based on the area ratio of the corroded fracture surface. From the results shown in FIG. 5, it is clear that the addition of Sb improves SCC resistance, but if the amount added is too large, the SCC resistance decreases. In the present invention, the target corrosion fracture rate is set to 60.0% or less, so the Sb content is set in the range of 0.02 to 0.12%.

Claims

[Claim 1] A brass alloy having excellent stress corrosion cracking resistance, characterized in that, in mass%, Cu: 57.0 to 64.0%, Bi: 0.8 to 2.2%, Fe: more than 0.03% and not more than 0.30%, Sn: more than 0.5% and not more than 1.5%, Sb: 0.02 to 0.12%, Ni is less than 0.05%, and the balance is Zn and unavoidable impurities.

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