JPS5996237A - Copper alloy for welded tube - Google Patents

Abstract

PURPOSE:To obtain a Cu alloy for a welded tube having superior corrosion resistance at its weld zone and low weld crack sensitivity by adding specified amounts of Zn, P, Sn and Al to Cu. CONSTITUTION:A Cu alloy for a welded tube is composed of, by weight 25-40% Zn, 0.005-0.070% P, 0.015-1.0% Sn, 0.05-1.0% Al and the balance Cu. The grain size of the alloy is regulated to <= about 0.015mm. by final annealing. When a thin-walled welded tube or the like is manufactured by high-frequency resistance or induction welding using the resulting alloy, a product having superior corrosion resistance at its weld zone and causing hardly weld crack can be 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 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. This is a major constraint on the use of balanced fully welded pipes, considering the deterioration of the usage environment in recent years. For example, when cylindrical frequency induction welding or high frequency resistance welding is used as a welding method when manufacturing alloy welded pipes, due to the characteristics of the welding method, weld cracking is particularly likely to occur. . Under these circumstances, there is a demand for materials that have low corrosion resistance in welded parts and are less susceptible to weld cracking.

The present invention was developed as a result of research conducted in light of this situation.
Zinc 25-40 wt, phosphorus 0.005-0.07
Owt section, tin 0.05~1. Owt section, aluminum [105-1. Copper alloy for welded pipes with improved corrosion resistance consisting of Owt% and balance copper and unavoidable impurities and zinc 25-40wt%, phosphorus o, oos~0.07
0 wt%, /14 G, 05-1. Owt%
, aluminum 0.05-1. We have developed a steel alloy for welded pipes with improved corrosion resistance and improved weld cracking resistance, which is adjusted so that the grain size is 0.015n+m or less in the final annealing, which contains Owt4 and the balance is copper and unavoidable impurities. .

The effects and additions of the alloy components in the copper alloy for welded pipes of the present invention and reasons for limiting the crystal grain size will be explained.

Copper and zinc are the basic materials of the alloy of the present invention, and have excellent corrosion resistance, workability, mechanical strength, and thermal conductivity. The reason why the amount of zinc added was limited to the above range was as follows.
This is because if the zinc content is less than 25 wt%, workability deteriorates, and if the zinc content exceeds 4 wt%, precipitation of β phase is observed in the copper-zinc alloy, resulting in poor corrosion resistance and cold workability. The amount of phosphorus added is o, o o s~0.070
The reason for choosing Wtqb is that the amount of phosphorus added is 0.005.
No improvement in corrosion resistance was observed below the wt ratio, and 0, 0
If it exceeds 70 W14, the corrosion resistance will improve, but signs of intergranular corrosion will be seen. The amount of tin added is α05~1
, the reason why it is in charge of Owt is (the amount of addition is 0.05 w
With tφ Miki, there is no improvement in corrosion resistance, especially in the welded parts when welded, and if it exceeds 1.0% by weight, the effect of improving corrosion resistance is saturated. The reason why the amount of aluminum added is set to 0.05 to wt% is as follows.
When the amount of aluminum added is Q, 05wt%, no improvement in corrosion resistance, especially in the welded part, is observed when the groove is not grooved.
In addition, 1. This is because the effect of improving corrosion resistance is saturated when Owt exceeds 96.

As mentioned above, the addition of phosphorus adds corrosion resistance to the material.
By adding aluminum and aluminum, corrosion resistance is added to the welded part when the materials are welded. Furthermore, the reason why the crystal grain size was limited to 0.015- or less will be described.

As a result of investigating the causes of weld cracking caused by high-frequency induction welding or high-frequency resistance welding, the present inventors found that:
It was discovered that the grain boundaries become brittle when in contact with molten base metal, and weld cracking occurs when subjected to a light impact. As a result of investigating such phenomena, we found that the effect of crystal grain size is significant and that such phenomena can be largely suppressed by reducing the crystal grain size.

The reason why the grain size is limited to 0.015+a or less is that if the grain size exceeds 0.015 Tjn, weld cracking is likely to occur.

Examples Alloys having the various compositions shown in Table 1 were melted and cooled, hot-rolled and appropriately annealed, and then cold-rolled into plates with a thickness of 1 mm, and finally drilled to various degrees. After adding salt, it was tested. The welded parts to be subjected to the corrosion resistance test were fabricated by butting T-welding and G-welding alloys having the compositions shown in Table 1 and having one thickness. The corrosion resistance test was carried out by dissolving 1.59/l of sodium bicarbonate, 1.59/l of sodium sulfate, and 1.69/l of sodium chloride in 1 ton of water, maintaining the liquid temperature at 88°C, and blowing air at 100 g/min. It was blown into the solution and submerged in this solution for 240 hours. The depth of dezincification corrosion that occurred at that time was measured for the welded part and the base metal part, and the corrosion resistance was evaluated based on this. The results are shown in Table 2.

A test sample for resistance to weld cracking caused by embrittlement of grain boundaries when in contact with molten base metal, t, is shown in Figure 1 for a 1-meter thick alloy with the various compositions shown in Table 1. It is processed into a pipe shape so that it is melted, and then immersed in a molten metal having the same composition held at point D + 50℃ for 3 seconds, and then taken out and placed in a holding furnace so that the metal being cleaned is molten. So, as shown in Figure 2, is the bladder f? added. The cross section of the ring deformed at that time was observed with a microscope to confirm the presence or absence of single grain boundary fracture, and this was used to evaluate resistance to weld cracking. The results are shown in Table 3.

As shown in Tables 2 and 6, it was found that the alloy of the present invention has excellent corrosion resistance against dezincification corrosion in both the base metal and the welded part, and the weld cracking resistance has been improved. .

That is, in the comparative alloys (sample numbers 1 to 6.19 to 21), the base metal part had a diameter of 70 to 125μ, and the weld part had a diameter of 165 to 413μ.
1 invention alloy (sample numbers 4 to 18)
The minimum value of 8μ to the maximum value of 15μ in the base metal part, and the minimum value of 15μ to only 63μ in the welded part, indicating that the dezincification corrosion resistance is excellent.

As shown in Table 5, among the alloys of the present invention with excellent dezincification corrosion resistance, those with a grain size of 0.015 m or less have a higher resistance to molten base metal than those with a grain size of more than 0.015 m. It can be seen that the material has excellent weld cracking resistance because it does not cause intergranular fracture but grain boundary embrittlement when impact is applied when it comes into contact with the material.

Table 1 (Unit wt%) Table 2 'jrJ Table 3

[Brief explanation of drawings]

FIG. 1 is a sectional view of a pipe to be subjected to a weld crackability test, and FIG. 2 is a schematic explanatory diagram of a plate for testing the weld crackability of a pipe by dropping a heavy object in a heating and holding furnace. 1... Test pipe 2... Support stand 3... Falling heavy object (200S'w)
4・・・・・・Heating and holding furnace a・・・・・・Inner diameter (20a+)b・・・・・・
...Outer diameter (22r-Jn)C...Free fall distance! 'J(50+r,g)d・・・・・・・・・
Fall Direction Patent Applicant Nippon Koken Co., Ltd. Agent Patent Attorney (7569) Keishi Junyo 11th Uni U, 2, 2i-, =

Claims (2)

[Claims] (1) Zinc 2525-4o%, phosphorus Q, OO5-1
1070wt, tin 0.05~1. Owtφ, aluminum 0.05-1. A copper alloy for welded pipes, which contains Owt and the remainder is brocade and unavoidable external impurities. (2) Zinc 25-40wt, phosphorus 0, . 00
5~0.07'Owt, tin 0.05~1. Copper alloy for welded pipes containing 0.05 to 0 wt% of Owt tip 7/L/minium and the remainder consisting of sawdust and unavoidable impurities.