JP3781055B1 - Hot dip galvanizing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a good plating film containing no harmful Pb and having high fluidity in a hot dip galvanizing bath composition for forming a galvanizing film on the surface of a steel material by an immersion method. A hot dip galvanizing bath composition is provided.
A hot-dip galvanizing bath composition for forming a galvanized film on the surface of a steel material by a dipping method, wherein Ni is 0.01 to 0.05% by weight and Al is 0.001 to 0.01. It is a hot dip galvanizing bath composition containing Pb in an amount of 0.01% by weight, Bi of 0.01 to 0.08% by weight, the balance Zn and inevitable impurities.
[Selection] Figure 5

Description

The present invention relates to a hot dipping process for forming a galvanized coating on the surface of the steel material by dipping method, and more particularly those concerning the galvanized methods that do not contain Pb.

  Conventionally, hot dip galvanizing is well known as a method for imparting corrosion resistance to steel materials for power transmission towers and road facilities, and further to steel materials for building structures. This hot dip galvanizing can be performed by a simple dipping method in which a flux-treated steel material is dipped in a plating bath and pulled up, and is an excellent treatment for enhancing the corrosion resistance of the steel material. In the hot dip galvanizing process, in order to make the plating bath composition easily penetrate into the minute gaps of the steel material and to improve the liquid drainage when pulling up, a small amount of Pb is added to the plating bath composition to reduce the viscosity of the plating bath. The liquidity is raised by lowering.

  Conventionally, hot dip galvanizing treatment of steel materials and steel plates has been widely used. For example, in Patent Document 1, Al 0.1 to 0.3 wt%, Pb or Sb type 1 0.02 to 0.2 wt. In addition, a hot dip galvanizing bath composition containing 0.001 to 0.2 wt% of one or two of Ni and Co, and the balance Zn and Fe as an inevitable impurity is disclosed. Yes. Patent Document 2 contains one or more selected from Ni, Co, and Ti, in total 0.001 to 0.5 wt%, Al 0.1 to 0.5 wt%, and Pb 1 wt% or less. In addition, a hot dip galvanizing bath composition having the balance Zn and inevitable impurities is disclosed. Patent Document 3 discloses a hot dip galvanizing bath composition containing Al: 0.001 to 4%, Ni: 0.001 to 3%, Pb: 0.001 to 1% and the like in addition to Zn. Furthermore, this plating bath composition contains many other elements including Cr: 0.001 to 0.05%, Cd: 0.001 to 3%.

  Thus, for a long time, a small amount of Pb was added to the hot dip galvanizing bath composition to improve the efficiency of the plating process and improve the appearance of the plating film. It has come to regulate the use. In particular, there is a RoHS directive issued in the EU on February 13, 2003. The RoHS Directive restricts the use of certain hazardous substances in electrical and electronic equipment distributed in EU member states. Since July 1, 2006, the EU has four heavy metals (lead, mercury, cadmium, hexavalent). Chromium) and two brominated flame retardants (polybrominated biphenyls, polybrominated diphenyl ethers) will not be able to sell products that contain more than the allowable amount. The target range is consumer products such as electrical and electronic equipment, but it is possible that steel materials and steel plates that have been subjected to hot dip galvanizing treatment are used as their parts or as casings or mounts.

On the other hand, in the field of information electronic equipment such as computers, whiskers are generated from the electrogalvanized film in the housing and pedestal, and the whiskers fly and accumulate on the microelectronic circuit formed on the electronic substrate, thereby short-circuiting the circuit. This causes problems such as malfunctions and circuit destruction. In this way, it has been considered to change to hot dip galvanizing treatment, which has been difficult to generate whiskers in parts used in electrical and electronic equipment, which has been electrogalvanized in the past, and hot dip galvanizing treatment has attracted more and more attention. It was.
JP 05-098407 A Japanese Patent Laid-Open No. 08-060329 Japanese Patent No. 3631710

  The aforementioned RoHS Directive is in the EU member countries, but due to the globalization of the industry, products are distributed all over the world and Japan can no longer be ignored. In addition, an increasing number of companies in Japan have their own environmental standards, and there is a movement to enact laws that are more stringent in Japan.

Therefore, in view of the above-described situation, the present invention intends to solve the problem in the hot dip galvanizing method for forming a galvanized film on the surface of a steel material by a dipping method, which does not contain harmful Pb and has fluidity. The present invention provides a hot dip galvanizing method capable of forming a high and good plating film.

In order to solve the above-mentioned problems, the present invention provides 0.01 to 0.05% by weight of Ni, 0.001 to 0.01% by weight of Al, 0.01 to 0.08% by weight of Bi, and the balance Zn. And a hot dip galvanizing method characterized in that a hot dip galvanizing film is formed on the surface of a steel material by a one bath method using a hot dip galvanizing bath which is an inevitable impurity and does not contain Pb. 1).

Further, Ni is 0.01 to 0.05% by weight, Al is 0.001 to 0.01% by weight, In is 0.05 to 0.1% by weight, the balance is Zn and inevitable impurities, and does not contain Pb. A hot dip galvanizing method characterized in that a hot dip galvanizing film is formed on the surface of a steel material by a one bath method using a hot dip galvanizing bath (claim 2).

Furthermore, Ni is 0.01 to 0.05% by weight, Al is 0.001 to 0.01% by weight, Bi is 0.01 to 0.08% by weight, In is 0.01 to 0.1% by weight, Using a hot dip galvanizing bath that is the balance Zn and inevitable impurities and does not contain Pb, a hot dip galvanizing method was formed by forming a hot dip galvanized film on the surface of the steel material by a one bath method ( Claim 3).

According to the hot dip galvanizing method of the present invention as described above, there is no concern about environmental pollution because it does not contain any specific hazardous substance specified by the RoHS directive, including Pb, and contains Pb corresponding to the RoHS directive. Not hot dip galvanized steel can be supplied. In addition, during the hot dip galvanizing treatment, Bi is added to the plating bath composition in an amount of 0.01 to 0.08 in order to facilitate the penetration of the plating bath composition into the minute gaps of the steel material and to improve the drainage when the steel is pulled up. In addition, 0.05% to 0.1% by weight of In or 0.05% to 0.1% by weight, or 0.01% to 0.08% by weight of Bi and 0.01% to 0.1% by weight of In are added. It has the same good fluidity as the hot-dip galvanizing bath composition it contains, and the hot-dip galvanized film applied on the surface of the steel has excellent appearance and corrosion resistance, and has excellent overall film properties. It is. Moreover, since 0.001 to 0.01% by weight of Al is contained to suppress the formation of the Fe—Zn alloy phase, the adhesion of the plating film is good and the Al is contained. In addition, since the plating temperature can be lowered by using a normal flux liquid mainly composed of ammonium chloride, thermal deformation of the steel material can be suppressed.

Further, by using the hot dip galvanizing method of the present invention to form a base layer for forming a Zn-Al alloy plating film on the steel surface by a two-bath method, a hot dip galvanized aluminum alloy plated steel material having particularly excellent corrosion resistance is obtained. Can be supplied.

Next, details of the present invention will be described in more detail based on embodiments. The present invention relates to steel materials related to power communication facilities such as power transmission towers and overhead hardware, steel materials related to road facilities such as bridges, guardrails and gratings, steel materials related to buildings such as steel frames and emergency stairs, and automobile related materials such as body steel plates. This is a hot dip galvanizing method for forming a galvanized film on the surface of steel materials for general consumer products such as steel materials, electrical and electrical equipment casings, and pedestals in order to enhance corrosion resistance. The feature of the plating bath composition used in the hot dip galvanizing method of the present invention is that it does not contain any specific harmful substances specified by the RoHS directive including Pb. In addition, the plating bath composition used in the present invention is one for forming a hot-dip galvanized film on the surface of a steel material by one bath and for forming a Zn-Al alloy plated film on the surface of a steel material by a two-bath method. It can also be applied when used in a bath.

The hot dip galvanizing bath composition used in the present invention has a Ni content of 0.01 to 0.05 wt%, an Al content of 0.001 to 0.01 wt%, a Bi content of 0.01 to 0.08 wt%, and the balance Zn. And inevitable impurities. Alternatively, 0.05 to 0.1% by weight of In is added instead of Bi. Alternatively, 0.01 to 0.08 wt% Bi and 0.01 to 0.1 wt% In are mixed and added.

Here, when the steel material is immersed in a hot dip galvanizing bath, Al suppresses the growth of a Fe—Zn alloy phase having a hard and brittle property at the interface with the steel material, and improves the adhesion of the plating film. When the Al content is less than 0.001% by weight, the effect of suppressing the Fe—Zn alloy phase is poor, and when it is more than 0.01% by weight, non-plating occurs . Therefore, the Al content is set to 0.001 to 0.01% by weight. More preferably, the Al content is 0.001 to 0.005% by weight.

Moreover, when Ni immerses steel in a hot dip galvanizing bath, Ni forms an Fe—Ni alloy phase on the surface of the steel and suppresses growth of the Fe—Zn alloy phase together with Al . When the Ni content is less than 0.01% by weight, the effect of suppressing the Fe—Zn alloy phase is poor, and when it is more than 0.05% by weight, the effect is saturated and it is not economical. Therefore, the Ni content is set to 0.01 to 0.05% by weight.

  Bi increases the fluidity of the plating bath composition to improve the wettability and has the effect of suppressing non-plating. If it is less than 0.01% by weight, the effect is poor, and 0.08% by weight. If it is more, problems such as spangles and blackening occur. Therefore, the Bi content is set to 0.01 to 0.08% by weight. More preferably, the Bi content is 0.01 to 0.05% by weight, and the amount of expensive Bi used is reduced.

  Moreover, In has the effect | action which raises the fluidity | liquidity of a plating bath composition and improves wettability similarly to Bi, but there are few effects than Bi. Therefore, the addition amount of In is larger than Bi, and 0.05 to 0.1% by weight is added. If the amount of In is less than 0.05% by weight, the effect is poor, and if it is more than 0.1% by weight, the effect is saturated.

  Increasing the amount of Bi increases the size of spangles, while increasing the amount of In tends to decrease the size of spangles, so add Bi and In together. As a result, an even better hot-dip galvanized film can be obtained. In that case, since the fluidity of the plating bath composition is ensured by addition of Bi, it is only necessary to reduce the amount of addition compared to the case of using In alone and to expect the effect of suppressing the size of spangles. Therefore, 0.01 to 0.08% by weight of Bi and 0.01 to 0.1% by weight of In are mixed and added.

In order to form a hot dip galvanized film on the surface of a steel material using the above hot dip galvanizing bath composition, first, the steel material is degreased, pickled, washed with water, and then only a mixed aqueous solution of zinc oxide and ammonium chloride or ammonium chloride. Is immersed in a hot dip galvanizing bath set at a predetermined temperature for a predetermined time, then pulled up at a predetermined speed, air-cooled or water-cooled, and a hot dip galvanized film with a predetermined thickness on the surface of the steel material Is formed.

The Example which formed the hot dip galvanization film | membrane on the surface of steel materials using the hot dip galvanization bath composition which concerns on this invention was demonstrated below, and the effect which added Bi was confirmed. The plating conditions are shown in Table 1 below.

  The test steel material is a low silicon steel material of C: 0.035 wt%, Si: 0.01 wt%, Mn: 0.17 wt%, P: 0.012 wt%.

For the appearance and sagging inspection, a test piece 1 (70 mm × 150 mm outer shape) made of the aforementioned steel material having a pentagonal thickness of 2.3 mm with a sharpened lower end as shown in FIG. 1 was used. And the external appearance of this test piece 1 was observed visually. Further, as shown in FIG. 2, the degree of sagging is the total thickness t ₁ including the upper plating film 2 formed with a substantially uniform thickness of the plating film 2 attached to the test piece 1, and the lower end. The difference (t ₂ −t ₁ ) in the total thickness t ₂ including the plating film 2 of the most swollen part was evaluated as the sagging thickness t.

In addition, as shown in FIG. 3, the permeability test is performed on the lower surface of the 70 mm × 150 mm × 2.3 mm ^t substrate 3 made of the above-described steel material, with a thickness of 20 mm × 30 mm × leaving the lower end portion. Stainless steel plates 4 and 4 of 1.0 mm ^t are arranged on both sides as spacers, 70 mm × 30 mm × 2.3 mm ^t of the short plate 5 made of the above-mentioned steel material is stacked thereon, and metal clips 6 and 6 are placed on both sides. A test member held in step 1 was prepared. As a result, a gap having a width of 30 mm, a vertical length of 30 mm, and a gap of 1.0 mm in thickness of the stainless steel plate 4 was formed between the substrate 3 and the short plate 5. Then, the permeability of the hot dip galvanizing bath composition into the gap was evaluated by the adhesion rate of zinc penetrating into the gap (ratio of the area of the zinc adhesion portion to the area of 30 mm × 30 mm).

  Table 2 shows the results of the appearance, sagging, and permeability evaluated by the test piece and the test member.

  As a result of Table 2, when Zn of one kind of distilled zinc was used, a satisfactory result was obtained even when the Bi concentration was 0%, but Pb having a concentration that cannot be ignored as an impurity in one kind of distilled zinc. Is presumed to be contained. Taking this point into consideration, the overall appearance, sauce, and permeability are evaluated, and the Bi concentration is preferably in the range of 0.01 to 0.08% by weight, and particularly in the range of 0.01 to 0.05% by weight. It turned out to be optimal.

  Next, an experiment in which In was added instead of Bi and an experiment in which Bi and In were added at the same time were performed for the purpose of improving the fluidity of the galvanizing bath and the permeability into the gap. The plating conditions are shown in Table 3.

  Table 4 shows the results obtained with respect to appearance (presence or absence of spangles), sagging, and penetration into gaps when Bi and In are added at various concentrations. Here, the method for inspecting the penetration and the penetration into the gap is the same as described above.

  As a result, it was found that the flowability was improved by adding a predetermined amount of In similarly to Bi. The details are shown in FIGS.

  That is, FIG. 4 shows the relationship between the Bi concentration and the size of the spangle. Increasing the Bi concentration increases the fluidity of the galvanizing bath, but tends to increase the size of the spangle and reduce the appearance. It shows that there is.

  FIG. 5 shows the relationship between the concentration and the sagging thickness when Bi and In are added alone. In FIG. 5, the result by the conventional hot dip galvanization is compared and displayed as PW. Here, usually, in hot dip galvanizing, a good plating film is obtained when the sagging thickness is less than 0.8 mm, and when the sagging thickness is more than 0.8 mm, the plating is defective. As a result, Bi satisfies the sacrificial thickness standard when the additive concentration is 0.01 wt% or more, and the sacrificial thickness decreases as the concentration increases, but the effect tends to be saturated at approximately 0.08 wt%. On the other hand, the sagging thickness gradually decreases as the additive concentration increases, but the sagging thickness does not satisfy the standard of 0.8 mm unless it is 0.05 wt% or more.

  Next, FIGS. 6 and 7 show the case where Bi and In are mixed and added simultaneously. Here, the addition concentration of Bi was fixed at 0.05% by weight, and the In concentration was changed to examine the spangle size (see FIG. 6) and the sagging thickness (see FIG. 7). From FIG. 6, it was found that the size of spangles decreased as the additive concentration of In increased, and the appearance improved. Further, FIG. 7 shows that the sagging thickness hardly changes when the In concentration is in the range of 0 to 0.1 wt%. This indicates that the addition of 0.05% by weight of Bi sufficiently increases the fluidity, and the addition of some In does not cause a significant change in the action. In other words, since the main purpose of adding In is to reduce the size of spangles, the additive concentration at which the effect can be expected is lower than the concentration added to increase the fluidity of In alone. is there. Therefore, when adding In simultaneously with Bi, the addition concentration of In is set to 0.01 to 0.1% by weight.

Finally, FIG. 8 shows a salt spray test result (based on JIS). Figure 8 is a molten zinc plating bath according to the present invention: a (Bi 0.05 wt%) Galvanized coating according to one bath method using (indicated by in the figure "diamonds"), molten zinc according to the present invention 5% Al—Zn alloy plating formed by a two-bath method (two baths, Bi: 0.1% by weight) on an underlayer formed using a plating bath (one bath, Bi: 0.05% by weight). 5% formed by the two-bath method on the coating (indicated by “square” in the figure), the conventional hot-dip galvanized film (indicated by “triangle” in the figure), and the base layer of the conventional hot-dip galvanized film The salt spray test results with the Al—Zn alloy plating film (indicated by “circle” in the figure) are shown simultaneously.

Under this result, the corrosion resistance of the galvanized coating according to one bath method using a molten zinc plating bath according to the present invention, superior corrosion resistance of the conventional hot dip plating film also formed by hot-dip galvanizing method of the present invention The corrosion resistance of the 5% Al—Zn alloy plating film formed on the base layer by the two bath method is the same as that of the 5% Al—Zn alloy plating film formed by the two bath method on the base layer of the conventional hot dip galvanizing film. It was found to be superior to the corrosion resistance of.

It is a front view of a test piece for appearance and sagging evaluation. It is sectional drawing of the state which formed the hot dip galvanization membrane | film | coat in the test piece of FIG. The test member for evaluation of permeability is shown, (a) is an exploded perspective view, (b) is a perspective view in a set state. It is a graph of the relationship between Bi density | concentration and the magnitude | size of a spangle. It is a graph of the relationship between Bi and In density | concentration and sauce thickness. It is a graph of the relationship between In addition concentration and spangle (Bi: 0.05% addition). It is a graph of the relationship between In addition concentration and sauce thickness (Bi: 0.05% addition). It is a graph showing the salt spray test result of various plating films.

Explanation of symbols

1 Test piece 2 Plating film 3 Substrate 4 Stainless steel plate 5 Short plate 6 Clip

Claims (3)

Molten zinc containing 0.01 to 0.05 wt% of Ni, 0.001 to 0.01 wt% of Al, 0.01 to 0.08 wt% of Bi, the balance Zn and inevitable impurities, and containing no Pb A hot dip galvanizing method comprising forming a hot dip galvanized film on the surface of a steel material by a one bath method using a plating bath. Molten zinc containing 0.01 to 0.05% by weight of Ni, 0.001 to 0.01% by weight of Al, 0.05 to 0.1% by weight of In, remaining Zn and inevitable impurities, and containing no Pb A hot dip galvanizing method comprising forming a hot dip galvanized film on the surface of a steel material by a one bath method using a plating bath. Ni is 0.01 to 0.05% by weight, Al is 0.001 to 0.01% by weight, Bi is 0.01 to 0.08% by weight, In is 0.01 to 0.1% by weight, and the balance is Zn. And a hot dip galvanizing method comprising forming a hot dip galvanized film on the surface of a steel material by a one bath method using a hot dip galvanizing bath which is an inevitable impurity and does not contain Pb.

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