JPS6143419B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a copper-based alloy with excellent corrosion resistance and machinability. Conventionally, when copper-based alloys are used as materials for main components of valves, such as valve seats and stems, free-cutting brass rods and forged brass rods with good machinability have often been used. However, these have problems in corrosion resistance and are particularly susceptible to dezincification corrosion in the presence of chloride ions. As a copper-based alloy with good corrosion resistance,
There are naval brass rods, high-strength brass rods, and special aluminum bronze rods, but on the other hand, these have poor machinability. For this reason, copper-based alloys with excellent corrosion resistance and machinability have long been desired as materials of this type. An object of the present invention is to provide a copper-based alloy that meets this requirement. For this purpose, the present inventors conducted various test studies and found that Cu; 58 to 63% by weight, Pb; 1.0 to 2.0% by weight, Sn; 0.4 to 1.5% by weight,
It has been found that a copper-based alloy consisting of P: 0.01 to 0.1% by weight, the balance being Zn and unavoidable impurities, exhibits excellent properties in both corrosion resistance and machinability. The copper-based alloy of the present invention is as shown in the examples below.
Corrosion resistance properties include dezincification ratio (r value) and total corrosion amount (Δ
One of the characteristics is that the resistance to dezincification corrosion shown by T) is significantly improved, and this is mainly due to the addition of P within a predetermined range. In addition, it has very good machinability in turning tests and drilling tests, and has high elongation and good workability. Such properties that combine excellent corrosion resistance, machinability, and workability can be obtained by appropriately balancing the amounts of Cu, Pb, Sn, and Zn, and by adding an appropriate amount of P. The reason why the chemical composition values of each of these alloy components are determined as in the claims is as follows. Cu: 58% by weight or more of Cu is required to maintain appropriate tensile strength, elongation, and hardness. However, if it exceeds 63% by weight, the α phase increases and hot workability decreases rapidly, and from an economical point of view,
Since it is desirable to reduce the amount of Cu used as much as possible, the Cu content is set to 58 to 63% by weight. Pb: Pb is an element that provides the effect of improving machinability. If the amount is less than 1.0% by weight, the improvement in machinability will not be sufficient, and if it is added more than 2.0% by weight, the hardness will decrease as seen in samples No. 3 and No. 5 in Table 2 below. If the amount increases, elongation decreases and workability deteriorates, so the content is set in the range of 1.0 to 2.0% by weight. Sn: Sn is an element that improves corrosion resistance and increases tensile strength and hardness. However, if it is less than 0.4% by weight, No. 3, No. 4 in Table 3 below and
As seen in sample No. 5, the corrosion resistance improvement effect was not sufficient. On the other hand, if it is added in an amount exceeding 1.5% by weight, it becomes hard and brittle and has poor hot workability. Furthermore, from an economic point of view, it is advantageous to reduce the amount of Sn used as much as possible. For this reason
The Sn content is in the range of 0.4 to 1.5% by weight. P: As shown in Table 3 below, P is added in an appropriate amount without impairing machinability and workability.
It is an element that has a great effect on the corrosion resistance of the alloy of the present invention, particularly on suppressing dezincification corrosion. However, 0.01% by weight
With less addition, as seen in No.2,
The effect of suppressing dezincification corrosion is not sufficiently exhibited. on the other hand,
Addition of more than 0.1% by weight results in brittleness and increased stress corrosion cracking susceptibility. Therefore, for the purpose of the present invention, it is important to add P content in the range of 0.01 to 0.1% by weight. The characteristics of the alloy of the present invention will be specifically explained below with reference to typical examples. Alloy No. 1 to No. 5 whose chemical composition is shown in Table 1
were prepared and their mechanical properties, machinability, corrosion resistance and hot forgeability were investigated. The results are shown in Tables 2 and 3. Alloy No. 1 is a copper-based alloy of the present invention, No. 2 is a comparative alloy with P reduced from the range of the present invention, and No. 3 is a comparative alloy with Pb reduced to 3
Commercially available copper-based alloy for cutting with addition of more than % by weight,
No. 4 is a commercially available copper-based alloy for forging, and No. 5 is a commercially available copper-based alloy that has both machinability and forgeability. Among the machinability tests in Table 2, the machinability was measured when each sample was cut on a lathe using a cutting tool (SKH) (cutting conditions, rotation speed: 1000 rpm, depth of cut;
The principal force and feed force at a feed rate of 0.1 mm/rev) were measured and evaluated using a cutting tool dynamometer. The perforability was measured when each sample was perforated with an automatic drilling machine using a drill with a diameter of 6 mm (drilling conditions, rotation speed;
1480r.pm, drilling depth: 20mm, feed 0.116mm/
rev) thrust and rotational torque were measured and evaluated using a rotating tool dynamometer. The corrosion resistance test shown in Table 3 was carried out in accordance with the dezincification corrosion test method described below, since selective dezincification corrosion is more important than overall corrosion loss when it comes to corrosion of brass. The outline of the method is to immerse a specimen in a 5% hydrochloric acid aqueous solution at 60°C with the dissolved oxygen level constant through air saturation for 72 hours, and measure the change in weight of the specimen as well as the concentration of copper ions and zinc ions in the solution. Figure 1 shows an outline of the equipment used in the test. Specifically, as shown in the figure, 250 ml of 5% hydrochloric acid aqueous solution 3 is placed in a three-necked flask 2 (500 ml capacity) equipped with a reflux device 1, a sample 4 is inserted into the flask 2, and a plastic thread 5 is inserted. hang it by
This flask was placed in a constant temperature bath 6 kept at 60°C.
Leave it for a while. 7 is water, 8 is a heater, 9 is a temperature regulator, 10 is a thermometer, and 11 is a heat insulating material. After this test, the specimen 4 is taken out and the change in weight before and after immersion is measured, and the concentrations of Cu ²⁺ ions and Zn ²⁺ ions eluted into the aqueous hydrochloric acid solution are quantified. Then, the weight ratio of zinc and copper contained in this aqueous hydrochloric acid solution was determined, and r = weight ratio of zinc and copper contained in the aqueous hydrochloric acid solution/weight of zinc and copper contained in the original test piece. Calculate the r value expressed as a ratio. When the r value is 1, it means that there is no dezincification corrosion, and as the r value becomes larger than 1, it means that the dezincification corrosion becomes more significant. The dezincing ratio (r) in Table 3 indicates this r value. Furthermore, the amount of copper corresponding to the amount of Zn ²⁺ ions eluted into the liquid is the sum of the amount of Cu ²⁺ ions eluted into the liquid and the amount of Cu present in the dezincing layer on the surface of the brass. The amount of brass per unit surface area changed by the leaching test is: ΔT = {amount of copper contained in the original specimen / amount of zinc contained in the original specimen × [Zn ²⁺ ] + [ Zn ²⁺ ]×(V/S). However, the symbols in the formula are as follows. ΔT: Total corrosion amount (mg/cm ² ) [Zn ²⁺ ]: Zn ²⁺ ion concentration in the liquid (mg/) V: Test liquid amount () S: Specimen surface area (cm ² ) Total in Table 3 The amount of corrosion ΔT is a value determined by this formula, and the larger the ΔT value, the more significant the dezincification corrosion is. Further, the depth of the dezincing layer in Table 3 is determined by observing the cross section of the specimen after the test using an optical microscope, and determining the distance of the dezincing corrosion layer from the surface. In addition to the above corrosion resistance test, hot forgeability was also investigated, which was determined by the constant load upsetting rate at 700°C. This constant load upsetting rate is the maximum upsetting rate that can be obtained by free forging using a 150-ton press, and its magnitude indicates the hot deformation resistance. The results are shown in Table 3.

【table】

【table】

[Table] From the results in Table 2, the present invention alloy No. 1 is a commercially available copper-based cutting alloy containing 3% by weight or more of Pb.
It can be seen that compared to No. 3 and the commercially available copper-based alloy No. 5, which has improved machinability and forgeability, the feeding force on the lathe is lower and the turning performance is better. In addition, in terms of perforability, Thrust has a good perforability that is equivalent to that of the copper-based alloys No. 3 and No. 5. In addition, No. 1 and No. 2 with P added
It can be seen that the alloys have lower hardness and improved elongation than alloys No. 3 to No. 5 without P addition, and are excellent in workability. In addition, from the results in Table 3, copper-based alloys without P addition
Compared to No. 3 to No. 5, P-added copper-based alloy No. 1 to
In No. 2, both the dezincification corrosion (r) and the total corrosion amount (ΔT) are reduced, and the dezincification layer depth is also low, indicating that the dezincification corrosion resistance is significantly improved.
However, the improvement effect was not sufficient in the No. 2 copper-based alloy with a P content of less than 0.01%, and as seen in the No. 1 copper-based alloy, adding P of 0.01% by weight or more improved the improvement. It is clear that dezincification can significantly improve corrosion resistance, especially the dezincification ratio. In addition, the P-added copper-based alloy of the present invention has forgeability equal to or better than commercially available copper-based alloy No. 3 for forging. As described above, the copper-based alloy of the present invention has both good machinability and corrosion resistance, and also has good workability and hot forgeability, so it is suitable for valve parts and similar fields. It is a very suitable material.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing test equipment for a dezincification corrosion test. 3...5% hydrochloric acid aqueous solution, 4...test piece, 6... constant temperature bath.

Claims (1)

[Claims] 1 Cu; 58-63% by weight, Pb; 1.0-2.0% by weight,
A copper-based alloy with excellent corrosion resistance and machinability, consisting of Sn: 0.4 to 1.5% by weight, P: 0.01 to 0.1% by weight, and the balance being Zn and unavoidable impurities.