JPS59126743A - Copper alloy for welded pipe - Google Patents

Abstract

PURPOSE:To obtain a Cu alloy for a welded pipe with superior corrosion resistance and weld crack resistance at the weld zone by adding specified percentages of Zn and P to Cu. CONSTITUTION:A Cu alloy consisting of 25-40wt% Zn, 0.005-0.070wt% P and the balance Cu with inevitable impurities is prepd. so that the grain size is regulated to 0.015mm. by final annealing. A Cu alloy for a welded pipe with improved corrosion resistance and weld crack resistance is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a copper alloy for welded pipes having excellent corrosion resistance and weld cracking resistance in welded parts.

In recent years, thin-walled copper alloy pipes have come to be welded by high-frequency resistance welding or high-frequency induction welding.

This tendency is particularly remarkable for radiator tubes.

Traditionally, lock-seam tubes have been used for radiators, but due to demands for cost reduction and increased production efficiency, welded tubes made by high-frequency resistance welding or high-frequency induction welding are increasingly being adopted. However, copper alloy welded pipes have the disadvantage that the welded part has significantly lower corrosion resistance than other parts due to the uniqueness of its welded structure. Considering the deterioration of the usage environment in recent years, this is a major restriction on the use of copper alloy welded pipes.

Furthermore, when high-frequency induction welding or high-frequency resistance welding is used as a welding method when manufacturing copper alloy welded pipes, there is a manufacturing difficulty in that weld cracking is particularly likely to occur due to the characteristics of the welding method.

Under these circumstances, the welded parts have excellent corrosion resistance.

In addition, materials with low weld cracking susceptibility are required.

The present invention was developed as a result of research conducted in view of these circumstances.
Zinc 2525-4o%, phosphorus cL005-0.07
Copper alloy for welded pipes with improved corrosion resistance, containing 0 wt% and the balance consisting of copper and unavoidable impurities, and zinc 25~
40 wt%, phosphorus 0.005 to 0.070 wt%, the balance is copper and unavoidable impurities, and the grain size is adjusted to α015 or less in the final annealing. We have developed a steel alloy for welded pipes with improved weld cracking resistance.

The effects of the alloying components in the copper alloy for welded pipes of the present invention, the amount added, and the reason for limiting the crystal grain size will be explained.

Copper and zinc are the basic materials for the alloy of the present invention, and have excellent workability and mechanical strength.

It also has excellent thermal conductivity. Zinc content 25-40'w
The reason why the zinc content is less than 25 wt% is that workability deteriorates and 40. This is because if the content exceeds vyt%, precipitation of β phase in the copper-zinc alloy will occur, resulting in poor corrosion resistance and cold workability. Phosphorus content 0.00'
5~l 07 The reason why it is classified as Owt is that the phosphorus content is O.
, 0.070 wt.
%, corrosion resistance improves, but signs of intergranular corrosion are seen. By adding phosphorus in this way, corrosion resistance is added to the welded part when welding with the raw material. Furthermore, the reason why the crystal grain size was limited to 0.015 m+n or less will be described. As a result of investigating the cause of weld cracking caused by high-frequency induction welding or high-frequency resistance welding, the inventors found that the grain boundaries become brittle when in contact with molten base metal, and weld cracking occurs when subjected to a light impact. I found out that. As a result of investigating such phenomena, it was found that the effect of crystal grain size is large and that such phenomena can be significantly suppressed by reducing the crystal grain size.

The reason why the crystal grain size was limited to 0.015 mm or less.

This is because weld cracking is likely to occur if the grain size exceeds 0.015 m.Alloys with the various compositions shown in Table 1 of Examples were melted, hot rolled and appropriately annealed, and then cold rolled to 1+ mn. The plates were made into plates of various thicknesses, and finally annealed at various temperatures to adjust the grain size shown in Table 1 and used for testing. The welded parts to be subjected to the corrosion resistance test were manufactured by butting 1wn thick alloys having the various compositions shown in Table 1 and welding them using T-welding and G-welding. Corrosion resistance test was carried out using 1 ton of distilled water, 1.3 y of sodium bicarbonate, 1.5 y of sodium sulfate, and 7 y of sodium chloride. /) The solution in which each of r/z was dissolved was maintained at a temperature of 88℃, and the speed was
/ of air was blown into the sample, and the sample was immersed in this liquid for 240 hours.

The maximum dezincification corrosion depth that occurred at that time was measured for the welded part, and the corrosion resistance was evaluated based on this. The second result is
Shown in the table.

Test for resistance to weld cracking caused by embrittlement of grain boundaries when in contact with molten base metal.Alloys with the compositions shown in Table 1 and the thickness of 1.5 mm were made into pipes as shown in Figure 1. This is immersed in a molten metal of the same composition with a melting point + 50'CK: held for 3 seconds, and then taken out and placed in a holding furnace with the attached metal melted as shown in Figure 2. added a shock. The cross section of the deformed pipe was then observed under a microscope to confirm the presence or absence of intergranular fracture, and this was used to evaluate resistance to weld cracking. The results are shown in Table 3.

As can be seen from Tables 2 and 3, it was found that the alloys of the present invention have excellent corrosion resistance against dezincification corrosion of welded parts and have improved weld cracking resistance.

That is, in the comparison alloys (sample numbers 1 to 5), the maximum dezincification corrosion depth at the weld zone was 321μ to 567μ, whereas in the two invention alloys (sample numbers 6 to 15), the maximum dezincification corrosion depth was at the weld zone. It can be seen that the dezincing corrosion resistance of the alloy of the present invention is extremely excellent.

The alloy of the present invention has excellent dezincification corrosion resistance as described above, but also has a grain size of 0.015.
Table 3

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an alloy pipe with a thickness of 1 used for the weld cracking resistance test, and FIG. 2 is a schematic explanatory diagram of the weld cracking resistance testing apparatus. 1° thickness 1+W alloy pipe (length 10mm) 2: Free falling object (weight 200 gw) 5: Support stand 4; Heating and holding furnace a: Pipe inner diameter (c 120 mm) b: Pipe outer diameter (rice cake 22 m+) C : Falling distance of falling object 2 (50+m) Patent applicant Nippon Mining Co., Ltd. Agent Patent attorney (7569) Keishi Namikawa Figure 2

Claims (2)

[Claims] (1) Zinc 25-40 wt%, phosphorus o,
A copper alloy for welded pipes containing from 0.070 wt% to 0.070 wt%, with the remainder consisting of copper and unavoidable impurities. (2) Grain size is 0.01511111 in final annealing
Zinc 25-40 vrt%, adjusted to:
A copper alloy for welded pipes, containing 0% phosphorus, OO5~0.070 wt, and the remainder consisting of copper and unavoidable impurities.