JP2011153326A - Hot-dip galvanization - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot-dip galvanizing bath which has fluidity almost similar to that of a hot-dip galvanizing bath obtained from a distilled zinc base-metal though its Pb content is controlled to 0.1% or less, in hot-dip galvanization for a precision component. <P>SOLUTION: The hot-dip galvanizing bath includes, by mass%, 0.1% or less Pb, 0.2-0.4% Bi, 0.2-0.3% Sn, 0.6% or less Bi plus Sn, and the balance Zn with unavoidable impurities. In some cases, 0.02 mass% or less Al is added. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to hot dip galvanizing, and more particularly, to a hot dip galvanizing bath having good fluidity while suppressing the Pb content and a method for producing a plated steel material by hot dip galvanizing using the hot dip galvanizing bath.

Conventionally, a hot dip galvanizing bath in which a distilled zinc bullion is dissolved is generally used for hot dip galvanization, and this bullion usually contains about 1 to 2% by mass of a Pb component. On the other hand, in the RoHS Directive issued for environmental protection in the EU, since regulations regarding electrical and electronic equipment with Pb content exceeding 1000 ppm (0.1% by mass) were announced, The demand to reduce the content of is increasing.
However, Pb in hot dip galvanizing has the effects of increasing fluidity, suppressing sagging defects, and finishing the plating neatly. Therefore, when the content of Pb is simply reduced, it is not practical.
For such a problem, Bi, which is an element belonging to Pb, is used as an alternative.
In Patent Document 1 below, Pb is 0.1 mass% or less and Bi is contained in an amount of 0.5 mass% to 7% by mass as a hot dip galvanizing having excellent plating appearance and corrosion resistance and good throwing power. In addition, it is shown that 0.001 to 0.1% by mass of Sn and / or 0.01 to 0.1% by mass of Cu is added.
The following Patent Document 2 shows that a hot dip galvanizing bath containing Pb of 0.1% by mass or less and Bi of 0.4 to 1.5% by mass is used to suppress the occurrence of non-plating. .
In Patent Document 3 below, in order to suppress the occurrence of non-plating, Pb is 0.1% by mass or less, Sb is 0.5% by mass or more, Bi is 0.3% by mass or more, and Sb and Bi. It is shown that a hot dip galvanizing bath containing 1.5% by mass or less in total is used.
In the following Patent Document 4, a hot dip galvanizing bath containing 0.5 to 10% by weight of Al and 0.4 to 5% by weight of Sn, Bi, Tl or Cl is used in order to suppress the occurrence of non-plating. It is shown.
In Patent Document 5 below, Ni is 0.01 to 0.05% by weight, Al is 0.001 to 0.01% by weight, Bi as hot dip galvanizing that ensures fluidity and is excellent in appearance and corrosion resistance. Has been shown to use a hot dip galvanizing bath containing 0.01-0.08 wt.

Japanese Patent No. 4163232 JP 2009-221604 A JP 2009-221605 A JP-A-3-173754 Japanese Patent No. 3781055

By the way, when hot dip galvanizing is applied to precision parts such as screws, if the hot dip galvanizing bath does not have a significant fluidity, excess zinc remains in the screw grooves, etc., even if the hot dip galvanizing is performed. There is a problem that the probability of occurrence of the plating becomes high and the yield of the plated product is deteriorated.
In order to solve such problems, the present inventors have conducted various tests. In hot dip galvanizing for precision parts, a hot dip galvanizing bath in which only Bi is mixed with pure zinc is obtained from distilled zinc metal. As compared with the hot dip galvanizing bath, sufficient fluidity could not be secured. Furthermore, the inventors of the present application have tried a hot dip galvanizing bath in which various metals are mixed with a focus on Bi. When Bi and Sn are mixed at a certain ratio, the conventional distilled zinc ingot is dissolved. It has been found that fluidity almost the same as that of a hot dip galvanizing bath can be secured.
Based on this knowledge, the present invention can obtain fluidity almost the same as that of a hot dip galvanizing bath obtained from distilled zinc bullion while maintaining the Pb content to 0.1% or less in hot dip galvanizing for precision parts. The challenge is to do so.

In order to solve the above problems, the present invention has the following configuration.
According to the first aspect of the present invention, Pb is 0.1% by mass or less, Bi is 0.2 to 0.4% by mass, Sn is 0.2 to 0.3% by mass, and Bi and Sn are combined. It is a hot dip galvanizing bath with a balance of .6 mass% or less and the balance being Zn and inevitable impurities.
In the invention according to claim 2, Pb is 0.1 mass% or less, Al is 0.02 mass% or less, Bi is 0.2 to 0.4 mass%, and Sn is 0.2 to 0.3 mass%. , Bi and Sn together are 0.6% by mass or less, and the balance is a hot dip galvanizing bath containing Zn and inevitable impurities.
Invention of Claim 3 is a manufacturing method of the hot dip galvanized steel material which forms the hot dip galvanization coating on the steel material surface using the hot dip galvanization bath of Claim 1 or 2.

  When hot dip galvanization is performed using the hot dip galvanizing bath as described above, the fluidity comparable to that of the hot dip galvanizing bath obtained from distilled galvanizing is achieved while keeping the Pb content to 0.1% or less. The hot-dip galvanized product for precision parts with a reduced Pb content can be produced with high yield.

It is a front view which shows the shape and measurement point of a test body. It is a table | surface which shows a test result. It is a graph which shows a test result.

Hereinafter, embodiments of the present invention will be described. In the hot dip galvanizing, the present invention includes components of a hot dip galvanizing bath in which Pb is 0.1 mass% or less, Bi is 0.2 to 0.4 mass%, Sn is 0.2 to 0.3 mass%, The total amount of Bi and Sn is 0.6% by mass or less, with the balance being Zn and inevitable impurities.
As a result, when hot-dip galvanizing is applied to precision parts such as screws, even the parts where zinc is likely to remain, such as screw grooves, can flow out to the extent that it can be discharged to the extent that it is comparable to distilled zinc. Sex can be secured.
Here, the Pb component may not be included, but the fluidity increases as the Pb component increases in the above range.

  In addition, in a conventional hot dip galvanizing bath in which distilled zinc is dissolved, adding 0.02% by mass or less of Al can reduce zinc oxide adhering to the plating surface and make the plating surface beautiful. Although it is known, even if 0.02 mass% or less of Al is mixed with the hot dip galvanizing bath according to the present invention having the above components, the plating surface can be made beautiful without affecting the fluidity. it can.

(Fluidity test)
Below, the result of the fluidity | liquidity test of the hot dip galvanizing bath by the mixing ratio of Bi and Sn is shown. In the fluidity test, a thickness of 1 mm shown in FIG. 1 is obtained for each hot dip galvanizing bath in which Bi and Sn are mixed in a melted electrozinc ingot (Zn: 99.99% or more). A test body T made of SS400 having a width of 50 mm and a length of 100 mm was hung from a hanging hole H and dipped for a predetermined time. Specifically, after dipping and cooling the test specimen, the film thickness A at the five measurement points a at the upper 15 mm position and the film thickness B at the five measurement points b at the lower 15 mm position are measured with a film pressure gauge. The ratio of the difference between the average value of the film thickness B and the average value of the film thickness A to the average value of the film pressure A was calculated as the thickness ratio. This test was performed three times for each hot dip galvanizing bath having the same component ratio, and the average value of the ratios was calculated. Detailed test conditions are as follows.
(Test conditions)
Bath temperature: 465 ± 2 ° C
Immersion time: 10 seconds Lifting speed: 0.6 m / min
Cooling: Water-cooled 24 ° C
Test steel SS400
The reason why the immersion time is as short as 10 seconds is that in a precision part such as a screw, the sagging is necessary for the upper layer part not involved in the alloy layer, and the fluidity of this part is compared.
As a benchmark, a similar test was performed on a hot dip galvanizing bath in which one kind of distilled zinc metal (Zn: 98.5% or more) was melted.

The test results are shown in FIG. 2, and the test results are graphed in FIG. In the hot dip galvanizing bath obtained from distilled zinc bullion, the thickness ratio was 20.0%. In FIG. 3, it is found that when more than 16% which is considered to be relatively close to the test result of the distilled galvanizing bath is extracted, it is concentrated in the range surrounded by the thick line in FIG. 2. Moreover, it is estimated from the result that the sum of Bi and Sn is not good for fluidity.
From the above, Bi is 0.2 to 0.4 mass%, Sn is 0.2 to 0.3 mass%, and the total of Bi and Sn does not exceed 0.6 mass%. It is considered that fluidity close to that of hot dip galvanization obtained from gold can be secured.
Actually, when hot dip galvanizing is applied to a screw of M10 screw in a hot dip galvanizing bath having a component ratio in this range, the yield is comparable to that of a hot dip galvanizing bath obtained from distilled galvanized metal. Could get.
Even when a hot dip galvanizing bath with a component ratio in the above range is mixed with about 0.01% by mass of Al and hot galvanizing is similarly applied to the M10 screw, the distilled galvanized metal A yield comparable to that obtained by mixing about 0.01% by mass of Al with the hot dip galvanizing bath obtained from No. 1 was obtained.
Furthermore, when 0.1 mass% or less of Pb is added to these hot dip galvanizing baths, the fluidity does not change or tends to increase somewhat.

Claims (3)

  Pb is 0.1% by mass or less, Bi is 0.2 to 0.4% by mass, Sn is 0.2 to 0.3% by mass, Bi and Sn are combined and 0.6% by mass or less, and the balance Is a hot dip galvanizing bath in which Zn and inevitable impurities are present.   Pb is 0.1 mass% or less, Al is 0.02 mass% or less, Bi is 0.2 to 0.4 mass%, Sn is 0.2 to 0.3 mass%, and Bi and Sn are combined to 0 A hot dip galvanizing bath with a balance of 6% by mass or less and the balance being Zn and inevitable impurities.   A method for producing a hot dip galvanized steel material, wherein a hot dip galvanized coating is formed on the surface of the steel material using the hot dip galvanizing bath according to claim 1.

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