JPS6056775B2 - Copper alloy for welded pipes - Google Patents

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. Conventionally, lock seam tubes have been used for radiators, but due to the demand 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, due to the uniqueness of the weld structure, copper alloy welded pipes have the disadvantage that the corrosion resistance of the welded part is significantly inferior to that of other parts. This is a major restriction on the use of copper alloy welded pipes, considering the deterioration of the usage environment in recent years. 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, there is a demand for materials that have excellent corrosion resistance in welded parts and are low in susceptibility to weld cracking. The present invention was developed as a result of research conducted in view of the above situation.
Copper alloy for welded pipes with improved corrosion resistance, containing 0.05 to 1.0 wt% of aluminum and the balance copper and unavoidable impurities, and 25 to 40 wt% of zinc and 0.00 wt% of phosphorus.
5 to 0.070 wt%, tin 0.05 to 1.0 wt%, aluminum 0.05 to 1.0 wt%, the balance is copper and unavoidable impurities, crystal grain size is O, 0l5Tfgf
We have developed a copper alloy for welded pipes that has excellent corrosion resistance and weld cracking resistance.

Incidentally, the crystal grain size indicated by J in the specification means the crystal grain size after final annealing. 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 materials 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 is 25W.
If it is less than t%, the workability will be poor and the zinc content will be 40Wt.
%, precipitation of β phase is observed in the copper-zinc alloy, resulting in poor corrosion resistance and cold workability. The reason why the amount of phosphorus added is 0.005 to 0.070 Wt% is as follows.
This is because if the amount of phosphorus added is less than 0.005 wt%, no improvement in corrosion resistance is observed, and if it exceeds 0.070 wt%, corrosion resistance is improved but signs of intergranular corrosion are observed. The reason why the amount of tin added is set to 0.05 to 1.0 Wt% is that if the amount of tin added is less than 0.05 Wt%, no improvement in corrosion resistance is observed, especially in the welded part when welded. .0
This is because when the content exceeds Wt%, the effect of improving corrosion resistance is saturated. The reason why the amount of aluminum added is set to 0.05 to 1.0 Wt% is that if the amount of aluminum added is less than 0.05 Wt%, no improvement in corrosion resistance, especially of the welded part when welded, is observed; %, the effect of improving corrosion resistance is saturated. As described above, by adding phosphorus, corrosion resistance is added to the material, and by adding tin and aluminum, corrosion resistance is added to the welded part when the materials are welded. Furthermore, the grain size was increased to 0.015TW.
The reason for limiting it to i or less will be explained. As a result of investigating the cause of weld cracking caused by high-frequency induction welding or high-frequency resistance welding, the present inventors found that it is caused by contact with molten base metal. It was discovered that weld cracking occurs when the grain boundaries become brittle and receive a light impact.

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 largely suppressed by reducing the crystal grain size. The grain size is 0.015? The reason why it is limited to the following is that if the grain size exceeds 0.015, welding cracks are likely to occur.

Example Alloys having various compositions shown in Table 1 were melted and hot rolled at 800°C to a thickness of 8mm. It was made into a board.

Next, after pickling treatment, it was cold rolled into a plate with a thickness of 2 gourds. Furthermore, after annealing at 500° C. for 1 hour, a plate having a thickness of 1 wn was obtained by cold rolling. Finally, the samples were annealed for 1 hour at various temperatures shown in Table 1, and then tested. The welded parts to be subjected to the corrosion resistance test were prepared by butting and TIG welding alloys having the compositions shown in Table 1 and having a thickness of 1 mm. Corrosion resistance test was conducted using sodium bicarbonate in 1' water.
1.3v1e Sodium sulfate 1.5y
A solution in which 1.6yIe of sodium chloride (No. Ie) was dissolved was maintained at a temperature of 88° C., air was blown in at a rate of 100 ml per minute, and the samples were immersed in this solution for 24 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 for resistance to weld cracking due to embrittlement of grain boundaries when in contact with molten base metal was conducted using alloys with a thickness of 1 Tgn having various compositions shown in Table 1.
As shown in the figure, it is processed into a vibrator shape, immersed in molten metal of the same composition maintained at +50°C, melting point, for 3 seconds, then taken out and placed in a holding furnace, where the attached metal is melted. Then, a shock was applied as shown in Figure 2.

The cross section of the deformed ring was then observed using a microscope, and
The presence or absence of intergranular fracture was confirmed, and resistance to weld cracking was evaluated based on this. The results are shown in Table 3. As shown in Tables 2 and 3, 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 has improved weld cracking resistance.

That is, the comparative alloys (sample numbers 1 to 3, 19 to 21) have a base material of 70 to 125 μm and a welded part of 165 to 413 μm.
In contrast, the alloys of the present invention (sample numbers 4 to 18)
The minimum value is 8μ to the maximum value 15μ in the base metal part, and the minimum value is 15μ to the maximum value 63μ in the welded part, indicating that the steel has excellent dezincification corrosion resistance.

Furthermore, as shown in Table 3, among the alloys of the present invention that have excellent dezincification corrosion resistance, those with a grain size of 0.015Tr0fL or less are more likely to contact the molten base metal than those with a grain size of more than 0.015TIrIn. It can be seen that when subjected to impact, grain boundary embrittlement, which causes intergranular fracture, is less likely to occur, and the weld cracking resistance is excellent.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a vibrator used for a weld crackability test, and FIG. 2 is a schematic illustration of an apparatus for testing the weld crackability of a vibrator by dropping a heavy object in a heating and holding furnace. 1... Test vibrator, 2... Support stand,
3... Falling heavy object (200yw), 4...
...Heating and holding furnace, a...Inner diameter (2C) m), b.
...Outer diameter (in 22 order), c...Free fall distance (50T!Rm), d...Falling direction.

Claims (1)

[Claims] 1. Zinc 25-40wt%, phosphorus 0.005-0.07
0wt%, tin 0.05-1.0wt%, aluminum 0
．． A copper alloy for welded pipes, which contains 0.05 to 1.0 wt%, with the remainder being copper and unavoidable impurities. 2 Zinc 25-40wt%, phosphorus 0.005-0.07
0wt%, tin 0.05-1.0wt%, aluminum 0
．． A copper alloy for welded pipes, containing 0.05 to 1.0 wt%, the balance consisting of copper and unavoidable impurities, and having a crystal grain size of 0.015 mm or less.