JP2895596B2 - Manufacturing method of brass material excellent in stress corrosion cracking resistance - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a brass material having excellent resistance to stress corrosion cracking.

[Prior art] Brass has excellent mechanical properties and plastic workability and is inexpensive.
It is widely used in electronic components and wiring devices, as well as in objects and heat exchangers.

However, brass has a drawback in that it is susceptible to seasonal cracking (so-called stress corrosion cracking) due to interaction with stress in a corrosive environment. Therefore, other copper-based materials having low susceptibility to stress corrosion cracking, such as phosphor bronze, have been used for applications requiring reliability.

As a method of improving the stress corrosion cracking resistance of brass materials,
There are also known methods of reducing the residual stress of the material, refining the structure, and adding Sn, Si, or the like.

However, even with these methods, the improvement effect is insufficient, and is not an essential solution.

On the other hand, a method of improving by providing a layer having a high copper content on the surface of a brass material has also been attempted. As a method of providing a layer having a high copper content, a method of copper plating, a method of evaporating zinc by heating in a vacuum, and the like have been proposed.

However, when a layer having a high copper content is provided on the surface of the brass material by the above-described method, the cost is high and the characteristic of the brass material, which is an inexpensive material, is impaired. Therefore, it is desired to improve the stress corrosion cracking resistance of brass by a low cost method.

[Problems to be Solved by the Invention] The present invention has been made in view of this demand, and an object of the present invention is to provide a method of manufacturing a brass material excellent in stress corrosion cracking resistance at a low cost. Aim.

[Means for Solving the Problems] A feature of the method for producing a brass material having excellent resistance to stress corrosion cracking according to the present invention is that the brass is immersed in a solution having a dezincification corrosive property. After forming a layer having a higher copper content than the inside on the surface of the steel sheet, cold rolling and annealing are performed.

[Operation] Hereinafter, the operation of the present invention will be described together with the knowledge and detailed configuration obtained when the present invention is performed.

First, the inventor studied various methods for forming a layer having a high copper content on the surface of a brass material. As a result, it has been found that a layer having a high copper content can be formed also by a method of dipping a brass material in a solution having a dezincification corrosion property (wet method). Moreover, this method was found to be the most economical and practical. That is, the brass material immersed in a solution having a dezincification corrosion property, either after the surface is dissolved, only the copper component is reprecipitated, or only the zinc component is selectively ionized and eluted. The mechanism forms a layer with high copper content on the surface. The solution having such a dezincification corrosion, for example, although a mixed solution of CuSO ₄ and CH ₃ COONa and CH ₃ COOH and KCl is preferred reaction speed, CuCl ₂ solution, and CuCl ₂ and HCl Or a mixed solution of CuSO ₄ and FeCl ₃ is also applicable.

In addition, since the above-mentioned solution is a solution having dezincification corrosion property, it is not preferable that this solution remains on the surface of the brass material. Therefore, after the brass material is immersed in the above solution to form a layer having a high copper content, it is desirable to neutralize the layer with a weak alkali such as NaHCO ₃ .

On the other hand, the present inventor has found that, when observed microscopically, the layer with a high copper content formed by the above method has a porous structure with many defects such as voids, porosity and gas. It has been found that such a structure cannot improve the stress corrosion cracking resistance of the internal brass portion even with a layer having a high copper content. Therefore, the present inventor has studied a method of improving internal defects of a layer having a high copper content formed by the above wet method, and after forming the layer, performing cold rolling and further annealing. It has been found that internal defects are improved and stress corrosion cracking resistance is improved, and the present invention has been accomplished.

As the brass targeted in the present invention, those containing 20 to 40 wt% of Zn are preferable.

Here, the area reduction rate in cold rolling is preferably 5 to 20%. Internal defects are pressed by cold rolling at such a reduced area,
The stress corrosion cracking resistance is further improved. If the annealing after the cold rolling is performed at a temperature of 200 ° C. to 400 ° C. for 20 seconds or more, the removal of the internal defects becomes more complete. That is, defects such as voids, porosity, and gas are diffused by heat and disappear, and the stress corrosion cracking resistance is further improved.

[Examples] Next, the present invention will be described in more detail with reference to examples.

(Example 1) An alloy having a composition shown in Table 1 was melted in a charcoal-coated atmosphere in a charcoal-coated atmosphere to produce an ingot of 50 mmt x 80 mmw x 200 mml. After cutting the ingot 2.5 mm each on the front and back sides, hot rolling at a temperature of 740 ° C. to 780 ° C. to form a 10 mmt plate, then removing the scale on the surface, repeating cold rolling and annealing, and repeating No. For Nos. 1 to 4, plates were 0.35 mmt, and for Nos. 5 and 6, plates were 0.3 mmt. No. 6 was subjected to the test as bare material.

Next, the plates No. 1 to No. 5 were degreased, immersed in a dezincification corrosive solution, and neutralized with a 10% NaHCO ₃ solution. No.5
Was subjected to a test without performing cold rolling and annealing.

Further, for No. 1 to No. 4, the sheet thickness was 0.3 mmt by cold rolling. No. 4 was subjected to the test without annealing. No.1
About No. 3, after cold rolling, it was heated at a temperature of 300 ° C. for 40 seconds.

 The composition and immersion conditions of the dezincification corrosive solution are shown below.

[Composition of _{solution] CuSO 4 · 5H 2 O 125gr} / 1 CH 3 COONa · 5H 2 O 45gr / 1 CH 3 COOH 38gr / 1 KCl 25gr / 1 0.3mmt from the immersion conditions] Temperature 30 ° C. Time 40 seconds above the plate × 10mmw × 150mml test piece was cut out and stress corrosion cracking test was performed by Thompson's method (Material
s Research & Standards (1961) 1081). That is, the test piece was made into a loop shape as shown in Fig. 1 and then exposed to a desiccator filled with saturated steam at a temperature of 40 ° C containing 14 wt% of aqueous ammonia, and the time until the test piece was broken was measured. did. The results are shown in Table 1.

As is clear from Table 1, the brass materials No. 1 to
It can be seen that No. 3 shows much better stress corrosion cracking resistance than bare material No. 6.

On the other hand, Comparative material No. 5 has a layer with a high surface copper content by immersion in a dezincification corrosive solution, but since the cold rolling and annealing were not performed, the layer was porous and had internal defects. And the effect of improving stress corrosion cracking resistance is small.

Further, Comparative Material No. 4 has a layer having a high surface copper content by immersion in a dezincification corrosive solution, and is cold-rolled, but is not annealed because it has not been annealed. The effect of improving the stress corrosion cracking resistance is less than that of Nos. 1 to 3.

The samples of No. 1 to No. 3 and No. 6 were directly plated with Sn and left at room temperature for one month, and then examined for solder wettability.
No. 1 to No. 3 showed good solder wettability of 95% or more as in the case of Sn plating after Cu base plating.

On the other hand, in the sample of No. 6, zinc in the base metal was reduced because there was no Cu layer.
It diffused to the surface of the Sn plating layer, and the solder wettability was rejected.

[Effects of the Invention] As described above, according to the present invention, a brass material having excellent stress corrosion cracking resistance can be manufactured at low cost,
When used in electric / electronic parts, wiring devices, heat exchangers, and the like, it has the effect of greatly improving the reliability.

In addition, in applications where Sn plating is performed and used, it has an effect that it can be used instead of Cu underplating and can be omitted.

[Brief description of the drawings]

 FIG. 1 is a conceptual diagram showing the shape of a stress corrosion cracking test piece.

Continuation of front page (56) References JP-A-59-173251 (JP, A) JP-A-54-69518 (JP, A) JP-A-51-46310 (JP, A) JP-A-62-284088 (JP, A) , A) JP-A-63-43024 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23F 1/00, 1/18 C22C 1/00

Claims (1)

(57) [Claims] The present invention is characterized in that a brass is immersed in a solution having a dezincification corrosive property, a layer having a higher copper content than the inside is formed on the surface of the brass, and then cold rolling and annealing are performed. A method for producing brass with excellent stress corrosion cracking resistance.