JPS6033897B2 - Manufacturing method of lead-tin alloy plated steel sheet with excellent corrosion resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a lead-tin alloy plated steel sheet.

Surface-treated steel sheets are made by melt-plating steel sheets with an alloy of lead and tin.
Due to its excellent corrosion resistance, processability, and solderability, it is used in many everyday items such as automobile gasoline tanks and radiators.

However, in lead-tin alloy plated steel sheets, lead does not easily react with iron and is relatively easily oxidized, so there is a problem that pinholes occur when adjusting the amount of plating deposited using plating methods such as rolls or high-pressure gas. Ta. Furthermore, since the lead-tin alloy plated steel sheet is a soft metal, it has the disadvantage that it is easily scratched to reach the base metal during transportation or press processing. A lead-tin alloy plated steel plate having pinholes or scratches as described above has a problem in that it generates red rust due to a corrosive environment, and its anti-corrosion effect is significantly reduced. Recently, as a solution to this problem, many lead-tin alloy plated steel plates, in which a steel plate is underplated with Ni, Co, or an alloy thereof, are commercially available and in use.

Such a lead-tin alloy plated steel sheet with a base plating such as Ni is prepared by electrolytically degreasing, pickling, and water washing cold rolled steel sheets, which are subjected to a base treatment such as Ni plating, and then being washed with water. It is manufactured using a process of immersing the bond in a molten metal. The lead-tin alloy plated steel sheet manufactured in this manner has extremely excellent corrosion resistance and does not pose any problem in use. Furthermore, the present inventors conducted many experiments with the aim of exploring a manufacturing method for lead-n-tin alloy plated steel sheets that could stably obtain even better corrosion resistance.
, Co, or any of these alloys is pickled with hydrochloric acid, washed with water or treated with diluted cherry salt, and hot-dipped with a lead-tin alloy to produce the desired steel sheet. I learned that it is possible.

The present invention was constructed based on this knowledge. In other words, the gist is that Ni,
Co, and their alloys are electroplated with molten lead in a wet state after being washed with water and pickled with hydrochloric acid, or in a wet state after being further washed with water, further washed with water, and treated with an aqueous solution containing chloride. - A method for producing a lead-tin alloy plated steel sheet with excellent corrosion resistance, which is characterized by tin alloy plating. The present invention will be explained in detail below.

Cold-rolled steel sheets manufactured through the normal cold-rolling manufacturing process,
After going through the usual surface cleaning process of electrolytic depointing, pickling, and water rinsing, Ni, Co, or alloy plating thereof is applied.

Ni electroplating is NiS04/7 ratio ○, NiC12,
Plating is performed using a commonly used electrolytic plating grade such as a finishing bath consisting of 3803. Similarly, for Co electroplating or Ni-Co alloy plating, CoC1
2. Mother's day 20, N ratio CI, day 3B03 or COS04
・7th 20, NiS04 ・7th 20, NjC12, Sun 3
It is plated with a commonly used electrolytic plating grade such as B03. The thickness of the electroplated layer of Ni, Co, or an alloy thereof is 0.01 to 1 mm, preferably 0.03 to 1 mm, from the viewpoint of improving corrosion resistance by reducing pinholes, workability, and economical efficiency. A range of 0.5 French is used. In this way, the steel plate coated with Ni, Co, or an alloy thereof is washed with water, then pickled with hydrochloric acid, and then washed with water or treated with an aqueous solution containing chloride, and then hot-dipped with lead-tin alloy. be done.

This hydrochloric acid pickling dissolves and removes oxides, hydroxides, and other films that inhibit the reactivity of the plating layer surface that are generated on the surface layer of the base plating layer during or after washing with water after base electroplating such as Ni plating. It is something to do. In other words, after base electroplating such as Ni plating, to reduce the amount of plating grade removed from the electrolytic tank and to prevent the plating grade attached to the surface of the plating layer from being carried into the molten lead-tin alloy plating bath. After plating, a wiping process using roll squeezing, which is commonly used for plating, and a water washing process are performed. Oxides, hydroxides, etc. are generated on the surface of the underlying electroplated layer such as the Ni plating layer during this water washing treatment or after the water washing treatment and before being immersed in the molten lead-tin alloy plating bath. , hydroxide, etc. are generated on the surface of the base electroplating layer, the reaction with Sn in the molten lead-tin alloy plating layer is inhibited, and Ni, Co, Nj-C
The amount of the alloy layer produced by the reaction between the o-alloy and Sn is small, and its uniform density is poor, and the amount of pinholes produced in the alloy tends to increase. Therefore, by removing the oxides and hydroxides on the surface of the base electroplating layer through hydrochloric acid pickling after the base electroplating and water washing, the surface of the plating layer is activated and the molten lead-tin alloy plating layer is removed. The increased reactivity with tin promotes the alloy layer formation reaction between the base plating layer and Sn, increasing the amount, uniformity and denseness of the alloy layer, and reducing pinholes in the alloy layer.

Therefore, the conditions for hydrochloric acid pickling in this case are a hydrochloric acid concentration of 0.1
~30% (preferably 0.5-10%), liquid temperature at room temperature ~9
5o0 (preferably 40oo~8000), processing time 0
．． Processing under pickling conditions of 1 to 10 seconds (preferably 0.3 to 3 seconds) is preferred. Especially for hydrochloric acid concentration, 0.1
If it is less than 30%, the activation treatment of the surface of the Ni undercoat electroplated layer, which is the object of the present invention, will not be sufficiently effective.
%, the effect tends to be saturated. Although there is no restriction on the pickling temperature, if the temperature exceeds 960°C, it is undesirable in terms of generation of steam during pickling and damage to the pickling tank. When the processing time is 0.1 seconds or less, the activation effect on the surface of the base plating layer is small, and when the processing time exceeds 1.0 seconds, the melting of iron from the pinholes in the base plating layer tends to increase.
After the above-mentioned hydrochloric acid pickling treatment, a wet state where the hydrochloric acid aqueous solution remains on the surface of the base electroplated layer, or a wet state where the hydrochloric acid aqueous solution is wiped off by roll squeezing and washing with water, or a wet state where hydrochloric acid, zinc chloride, etc. After being treated with an aqueous solution containing chlorine ions, it is introduced into a molten lead-tin alloy plating in a wet state, and lead-tin alloy plating is applied.

In this case, molten lead-tin alloy plating is carried out by floating flux (generally zinc chloride-based flux, ZnC12, ZnC12-NACI-based flux, ZnC12-NaCI-based flux) on the plating surface, especially on the introduction part of the steel plate. This is done using a wet flux method. For this reason, it is important to activate the reaction between the underlying electroplated layer and the flux at the point where it is introduced into the plating process.
This is necessary to obtain iron alloy plating, and when the steel plate surface is wetted with an aqueous solution, the reaction between the flux and the aqueous solution takes place actively in the plating layer introduction area, and the surface cleaning effect of the flux is activated. It can be done.

Therefore, in the present invention, it is important that after the hydrochloric acid pickling, the aqueous solution is introduced into the molten lead-tin alloy plating layer while the surface of the base electroplating layer is wet.

Further, immediately before being introduced into the plating bath, the steel plate is heated by heat radiation from the plating process, since molten lead-tin plating is normally carried out at a temperature of 300 to 400 degrees Celsius. Therefore, in order to prevent the base electroplating layer activated by hydrochloric acid pickling from being oxidized by this heating immediately before being introduced into the plating layer, an aqueous solution is added until it is introduced into the molten lead-tin plating process. It is important that the underlying electroplated coating layer is protected. This aqueous solution includes water from water washing after hydrochloric acid pickling, aqueous solution remaining on the surface of hydrochloric acid pickling, and chloride newly supplied after hydrochloric acid pickling (for example, ZnC12,
Any aqueous solution containing HC1, NaCI, etc.) may be used, and it is necessary to introduce these aqueous solutions in a wet state into the molten lead-tin alloy plating. Here, the newly supplied aqueous solution was limited to chloride because the flux generally used as a wet flux is chloride, and the aqueous solution mixed with this flux contains other components (for example, S
04-2 etc.), the aging of the flux is accelerated, so it is necessary to use a chloride with few inclusions. In particular, after pickling the base electroplating layer/surface with hydrochloric acid and wiping off the hydrochloric acid solution by roll squeezing, apply a hydrochloric acid aqueous solution with a lower concentration than the hydrochloric acid pickling solution to the base electroplating layer/surface.
By supplying it to the surface and introducing it into the molten lead-tin alloy plating in a wet state, it is possible to reduce the amount of the hydrochloric acid pickling solution taken out of the pickling tank and to use a solution with a low concentration of hydrochloric acid as the solution supplied to the steel plate. This method is most desirable from the viewpoint of effectiveness and economy, since even if the temperature of the steel sheet rises before it is introduced into the plating process, the activation effect of the base electroplating layer and surface by hydrochloric acid can be utilized. The steel plate with the base electroplating layer treated as described above is immersed in a molten lead-tin alloy plating bath, and the plating is adjusted to a predetermined amount by wiping with a roll or high-pressure gas. be done.

The molten lead-tin alloy coated steel sheet manufactured by the method of the present invention as described above has a significantly activated base electroplated layer/surface, and the reactivity with Sn in the plating layer increases. Electroplated layer and Sn alloy layer, Ni-S
The amount of N-based alloy layer, Co-Sn-based alloy layer, Ni-Co-Sn-based alloy layer is increased, and the pinholes in the alloy layer are reduced due to the improved uniform densities of the alloy layer, resulting in a reduction in molten lead-tin alloy. The corrosion resistance of gold-plated steel sheets is significantly improved. Next, examples of the present invention will be described.

Example 1 A 0.8 Yanagi cold-rolled steel plate whose surface had been surface cleaned by degreasing and pickling was coated with 300/so NiS04, 7 days 20-30/and Ni
Current density 10 using C12-30 evening/sunset 3803 common
Ni plating with a thickness of 0.1 mm was applied at A/d.

Next, after roll squeezing and water washing, hydrochloric acid pickling treatment was performed for 1 second at a temperature of 70 oo in a 1% HCI aqueous solution, and after the roll squeezing, a 0.5% HCI aqueous solution was sprayed and N
40% Z while keeping the i plating layer/surface in a wet state.
Molten P with nC12 aqueous solution suspended as flux
b-Immerse in 8% Sn glazing bath at 360qo for 7 seconds,
A molten lead-tin alloy plated steel plate having a plating amount of 60 mm/pillow per side was obtained by a high-pressure gas squeezing method. Further, as a comparative example, Ni plating was performed under the same conditions, followed by water washing and molten lead-tin plating to obtain a plated steel plate with almost the same coating weight, which was designated as Comparative Example 1. Example 2 A 1.0 Yanagi cold-rolled steel plate whose surface was cleaned by degreasing and pickling was coated with 240 yen/ku CoC12/fine 20-40 yen/soN.
Current density 2 using RCI-15 evening/day 3B03 general
Co plating with a thickness of 0.05 mm was applied at 0 A/d.

Next, after roll squeezing and water washing, a hydrochloric acid pickling treatment was carried out for 3 seconds at room temperature in a 3% HCI aqueous solution, and after water washing, a 30% ZnC12-10% NaCI based aqueous solution was suspended as a flux while being kept in a wet state with a water washing solution. Molten Pb-12%
A molten lead-tin alloy plated steel plate having a plating amount of 45 qo per side was obtained by dipping the Sn plating at 350 qo for 5 seconds and using a high-pressure gas squeezing method. In addition, as a comparative example, Co plating was performed under the same conditions, followed by molten lead-tin plating after washing with water.
Comparative Example 2 was obtained by obtaining a plated steel plate with almost the same amount of coating. Example 3 A 1.2-wall cold-rolled steel plate whose surface had been cleaned by degreasing and pickling was coated with 200 Yen/SoNjCl2, Navy 20-150 Yen/SoCoCi2, Navy 20-30 Yen/Sohi 3B03 Soy. Using Ni-Co with a current density of 7.5 A/d and a thickness of 0.5
Alloy plated.

Next, after roll squeezing and water washing, hydrochloric acid pickling treatment was performed in an 8% HCI aqueous solution at a temperature of 5000 for 0.5 seconds, and after roll squeezing and water washing, a 1% ZnC12 aqueous solution was sprayed to form the Ni-Co plating layer. While keeping the surface moist, it was immersed in a molten Pb-5% Sn plating with a 35% ZnC12-5% SnC12 aqueous solution suspended as a flux at 3800° for 3.5 seconds, and plated using a high-pressure gas squeezing method. Amount of molten lead-tin alloy plated steel sheet was obtained: 37.5 min per side.

In addition, as a comparative example, Ni--Co plating was performed under the same conditions, and after washing with water, molten lead-tin plating was performed to obtain a plated steel plate with almost the same coating amount, and this was designated as Comparative Example 3. Example 4 A cold-rolled steel plate of 0.7 ribs whose surface had been surface-cleaned by degreasing and pickling was subjected to a current density of 120 pm/ku NiS04 and 7 days 20-150 pm/soNiC12-45 pm/Yuhi 3803 general. Ni plating was applied to a thickness of 0.15 mm with a finish of 1 pine/d.

Next, after roll squeezing and water washing, a hydrochloric acid pickling treatment was performed in a 1.5% HCI aqueous solution at a temperature of 80 degrees for 0.5 seconds,
While keeping the surface of the Ni plating layer wet with the residue of the hydrochloric acid aqueous solution, it was immersed in a molten Pb-7% Sn plating in which a 50% ZnC12 aqueous solution was suspended as a flux at 36,000 for 8 seconds, and then exposed to high pressure gas. A molten lead-tin alloy plated steel plate having a plating amount of 55 mm/force per side was obtained by the drawing method. In addition, as a comparative example, Ni plating was performed under the same conditions, followed by molten lead-tin plating after washing with water, to obtain a plated steel plate with almost the same coating weight, which was designated as Comparative Example 4. For the molten lead-tin alloy plated steel plate obtained by the method of the present invention and the molten lead-tin alloy plated steel plate obtained in the comparative example, Fig. 1 shows the analysis results of the Sn content in the alloy layer, and Fig. 2 shows the results of the analysis of the Sn content of the alloy layer. As shown in the measurement results of the couple current value between the alloy layer and Sn, in the example, a large amount of alloy layer was formed due to the increased reactivity with Sn in the plating layer, and the alloy layer was uniform with few pinholes. It has excellent sensitivity.

Figure 1 shows the Sn content in the alloy layer of the product produced by the method of the present invention, and the Sn content measurement method in the alloy layer is 5% NaOH
Only the plating layer was electrolytically peeled off in an aqueous solution to expose the alloy layer, and the strength of the SMQ was determined from the surface of that surface using EPMA.

FIG. 2 shows the results of a pinhole test on the alloy layer of a product produced by the method of the invention. Pinholes in the alloy layer were determined by measuring the couple current value between the Sn metal and the alloy layer (Nj-Sn, Co-Sn, Ni-Co-Sn alloy layer) from which the turn metal was peeled off in a tomato juice solution. Part of Fe(S
The current value between the n metal, the alloy layer, and Fe in the pinhole portion (which is the most base in terms of potential) and the Sn metal (of the above, the most direct in terms of potential) was measured as a representative value of the number of pinholes. As a result, as shown in Table 1, which shows the corrosion resistance test results of the flat plate and after processing by the salt spray test (JIS2371), the corrosion resistance of the molten lead-tin alloy plated steel plate obtained by the method of the present invention is extremely excellent. Table 1 Corrosion resistance of products produced by the method of the present invention by salt spray test (S.S.T.) Note 1. ◎．・Remarkably good 〇． ．． - Relatively good△・・
・Slightly inferior ×. ... Significantly inferior 2. *...Blank diameter 500 x 50 mm, drawing depth 12 mm 200
×200 square tube aperture with flat bottom shape

[Brief explanation of the drawing]

FIG. 1 shows the Sn content in the alloy layer of a product produced by the method of the present invention, and FIG. 2 shows the pinhole test results of the alloy layer of the product produced by the method of the present invention. Kaya Zuzu Z diagram

Claims (1)

[Claims] 1 Electroplating of Ni, Co, and their alloys on the surface of a surface-cleaned steel plate, washing with water, and pickling with hydrochloric acid, in a wet state, or after further washing with water, and after washing with water, and treating with an aqueous solution containing chloride. Lead with excellent corrosion resistance, characterized by being plated with a molten lead-tin alloy in a wet state.
Manufacturing method of tin alloy plated steel plate.