JPS59126742A - 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, P, Ni and Sn to Cu. CONSTITUTION:A Cu alloy consisting of, by weight, 25-40% Zn, 0.005-0.070% P, 0.05-2.0% Ni, 0.05-1.0% Sn and the balance Cu with ineviatable 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 noticeable for tubes used in radiators. 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 becomes a major constraint 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 welding a copper alloy welded pipe, weld cracking tends to occur, which is a manufacturing drawback. Under these circumstances, there is a demand for materials that have excellent corrosion resistance in welded areas and have low weld cracking susceptibility.

The present invention was developed as a result of research conducted in view of the above circumstances.
Zinc 25-40wt, phosphorus 0005-α070wt
%, Nickel C, 05-2, Owt4.

Copper alloy for welded pipes containing 0.05 to 1 Owt% of tin and improved corrosion resistance due to the balance copper and unavoidable impurities, and zinc 25-25-4O, phosphorus Q, 005-0.070
wt%, nickel 0.05-2. Owt%.

Tin α05~1. Copper alloy for welded pipes with improved corrosion resistance and improved weld cracking resistance, which is adjusted so that the grain size is 0.015 cm or less in the final annealing, containing Owt% and residual copper and unavoidable impurities. was developed.

The effects of the alloy 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 components of the alloy of the present invention, and have excellent workability, mechanical strength, and thermal conductivity.

The reason why the amount of zinc added was limited to the above range is that zinc
If it is less than wt%, the processability will be poor and the zinc content will be less than 40%.
This is because when the content exceeds wt4, precipitation of β phase in the copper-zinc alloy is observed, resulting in poor corrosion resistance and cold opening workability. The reason why the amount of phosphorus added is 0.005 to α070 wt% is that if the amount of phosphorus added is less than o, o o s wt%, no improvement in corrosion resistance is observed.

In addition, corrosion resistance improves when α070 wt4 is exceeded, but 1
This is because signs of grain boundary disease are observed. The amount of nickel added is α05~2. The reason for setting it as Owt% is that when the amount of nickel added is less than 0.05 wt%, no improvement in the corrosion resistance of the welded part is observed when welding.

2. If the content exceeds Owt%, the effect of improving corrosion resistance is saturated. The amount of tin added is 0.05-1.0wt%
The reason for this is that if the amount of tin added is less than 0.05 wt%, no improvement in the corrosion resistance of the welded part will be observed, and if it exceeds 1.0 wt%, the effect of improving corrosion resistance will be saturated. . As described above, by adding phosphorus, corrosion resistance is added to the material, and by adding nickel and tin, corrosion resistance is added to the welded part when welded to the material.

Furthermore, the reason why the crystal grain size is limited to αO15m 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 when contact with molten base metal, the grain boundaries become brittle and cracking due to a light impact causes weld cracking. I found out that. As a result of conducting various investigations into such phenomena, it was found that the influence of crystal grain size is significant, and by reducing the crystal grain size, the susceptibility to such phenomena is significantly reduced.

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

This is because if the grain size exceeds 0.01j+gm, weld cracking is likely to occur.

Examples Alloys having the various compositions shown in Table 1 were melted, hot rolled and appropriately annealed, then cold rolled to form a plate with a thickness of 1 m, and finally annealed at various temperatures to form the sheets shown in Table 1. The crystal grain size was adjusted to the one shown in , and used for the test. The welded parts to be subjected to the corrosion resistance test were manufactured by butting 1 m+thick alloys having various compositions shown in Table 12 and performing T-welding and G-welding.

The corrosion resistance test was carried out by dissolving 1 t of sodium bicarbonate, 1.5 f/L of sodium sulfate, and 1.6 f/L of sodium chloride in 1 ton of distilled water.
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 results are shown in Table 2.

A test for resistance to weld cracking caused by embrittlement of grain boundaries when in contact with molten base metal was conducted using alloys of one thickness and the compositions shown in Table 1 in pipes as shown in Figure 1. This is processed into a shape, immersed for 3 seconds in molten metal of the same composition maintained at +50°C, melting point, and then taken out in a holding furnace with the attached metal melted, as shown in Figure 2. It was shocking. 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, for the comparison alloys (sample numbers 1 to 5), the maximum dezincification corrosion depth of the welded part was 347μ to 603μ, but only one crack occurred. In the light alloys (sample numbers 6 to 20), the maximum dezincification corrosion depth was 48μ to 104μ in the welded area, indicating that the dezincification corrosion resistance of the alloy of the present invention is extremely excellent.

In addition, the alloys of the present invention have excellent dezincification corrosion resistance as described above, but those with crystal grain sizes of 0.015 or less (sample numbers 7 to 11, 14, 18 to 20) are shown in Figure 2. In the weld cracking test NC shown in Figure 3, there is only ductile deformation, no cracking occurs, and the weld cracking resistance is improved. On the other hand, crystal grains with a grain size exceeding 0.015 mm are not preferable because they cause grain boundary fracture.

Therefore, the grain size is adjusted depending on the use of the pipe.The alloy of the present invention has extremely excellent properties as a copper alloy for welded pipes.

Table 1 M2 table Table 3

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a one-piece thick alloy pipe used in the weld cracking resistance test, and FIG. 2 is a schematic explanatory diagram of the weld cracking resistance testing apparatus. 1: 1 piece thick alloy pipe (length 10mm) 2: Free falling body (tt2 o gw) 3: Support stand 4: Heating and holding furnace a; Pipe inner diameter (20 m) b = Pipe outer diameter (◇22 mm) ) C: Falling distance of falling object 2 (50 wins) Patent applicant Nippon Mining Co., Ltd. Agent Patent attorney (7569) Keishi Namiyo 206-

Claims (2)

[Claims] (1) Zinc 25-40wt, phosphorus α005-0
．． 070wt%, nickel a O5~2. Owtq6
．． A copper alloy for welded pipes, containing tin [105 to 4 wt4, with the remainder being steel and unavoidable impurities. (2) Zinc 25 to 40 wt., phosphorus (1
005-0,070wt%, = Tsukel [LO5~2.
Owt person, tin α05~1. Copper alloy for welded pipes, containing copper and the remainder copper and unavoidable impurities.