JPH0726229B2 - Molten salt electroplating method for steel materials - Google Patents

Description

TECHNICAL FIELD The present invention relates to a molten salt electrolytic plating method for steel materials, and more particularly to a molten salt electrolytic Al plating method having excellent plating adhesion.

(Prior Art) Conventionally, molten salt electrolytic plating has been known as a plating method such as aluminum plating on steel materials, but it has hardly been put to practical use. This is because the steel material (steel strip, steel wire, etc.) had to be previously treated with an appropriate means to be activated before electrolytic plating in the AlCl ₃ mixed molten salt. In particular, it is difficult to completely remove the surface oxide film for activation, and development of an efficient means therefor is desired. On the other hand, the molten salt electroplating bath easily deteriorates when water is mixed in, and the water management in the plating line must be strictly controlled together with the management of the plating atmosphere.

Therefore, first, from the viewpoint of removing the oxide film, it is necessary to dry and preheat the steel material through alkali degreasing, followed by pickling and water washing, and then the water washing step, followed by a drying step and a preheating step. The drying process removes most of the water adhering to the steel material, and the preheating process elevates the temperature of the steel material to or near the molten salt plating temperature to prevent the molten salt bath from lowering its temperature and removes it by low-temperature drying. The purpose is to promote the removal of adsorbed water from the surface of steel that cannot be carried out. However, when preheated to a high temperature (eg 180 ° C.) in the atmosphere, the plating adhesion of the molten salt electrolytic plating performed thereafter will be significantly reduced.

Conventionally, when wet pretreatment such as degreasing, pickling, and water washing is performed and molten steel electrolytic plating is performed on steel material with a water film, even drying and preheating conditions of the steel material are sufficient. It was unavoidable that something with poor plating adhesion was not made clear.

(Problems to be solved by the invention) Therefore, various investigations have been made on the cause of such a decrease in plating adhesion, and an oxide film and adsorption of oxygen are formed on the surface of the steel during heating and drying of the steel. I knew that.

In order to prevent the formation of such an oxide film and the adsorption of oxygen, it is necessary to dry the steel material after washing with water at a low temperature, and to raise the temperature in an inert gas even in the preheating step. On the other hand, however, the oxide film that has once been formed must be removed by some means.

With respect to this point, an anodic electrolytic treatment in a molten salt bath has been separately proposed by the applicant of the present invention as an activation treatment of the steel material prior to the molten salt electrolytic plating. The steel to be treated is used as an anode for electrolytic treatment to promote the dissolution of the surface.

Therefore, the degree of surface oxidation of the steel material changes depending on the drying conditions after washing with water, and the anodic electrolysis conditions must be changed accordingly, which complicates the operation.

Here, an object of the present invention is to perform a wet pretreatment, and in performing molten salt electrolytic plating on a steel sheet to which a water film is attached, by drying the steel sheet and defining preheating conditions, An object of the present invention is to provide a method for producing a plated material with stable quality.

Still another object of the present invention is to perform electroplating using a molten salt, particularly Al-based alloy plating in an AlCl ₃ mixed salt of about 150 to 220 ° C. to stabilize the quality of the plating film,
It is to provide a means for extending bath life.

(Means for Solving Problems) Thus, in order to achieve such an object, the present inventors have variously studied drying and / or preheating conditions in a drying and / or preheating step after washing with water, The present invention has been completed, knowing that there are various heating and drying conditions.

Here, at the time of the gist of the present invention, in a molten salt electroplating method of steel material comprising a pre-washing step of steel material, a water washing step, a drying step, a preheating step, an activation step, and a molten salt electrolytic plating step, in the atmosphere The molten salt electroplating method for steel materials is characterized in that the drying or preheating conditions in the drying step and / or the preheating step are performed at Tm ≦ 44.4logR + 120 when the ultimate temperature of the steel material exceeds 100 ° C.

However, Tm is the maximum temperature (° C) that the steel material reaches in the atmosphere, and R is the average heating rate (° C / S) of the steel material in the atmosphere during the drying and preheating processes after washing with water.

In the present invention, no reference is made to the case where Tm is 100 ° C. or less, but it is 10 at a normal line speed.
This is because if the temperature is 0 ° C. or lower, the surface of the steel material will not be excessively oxidized, and there is no need to limit it.

The average heating rate is the average heating rate in the temperature range above 70 ° C. However, when the temperature of the washing water is higher than 70 ° C, the average heating rate is in the range above the washing water temperature.

The pre-cleaning step in the present invention refers to a pre-treatment step such as so-called degreasing, pickling (including electrolysis), and water washing.

Also, the plating metal is typically Al, but other Al-M
Alloy plating of n, Al-Ti, etc. may be mentioned.

(Operation) The present invention will now be described in further detail with reference to the accompanying drawings.

FIG. 1 of the accompanying drawings is a schematic explanatory view of a molten salt electrolytic Al plating apparatus for steel materials for carrying out the method according to the present invention.

In the figure, the steel strip 2 from the recoiler 1 is passed through a degreasing tank 3, a water washing tank 4, and a pickling tank 5 that perform a pretreatment process, and a water washing tank 6 that performs a water washing process, and then a drying process of a drying chamber 7. It is sent continuously. In this drying chamber 7, first, heating gas,
For example, the steel strip 2 is heated by being blown with heated air,
To be dried. Next, the steel strip 2 is subjected to a preheating step, heated and dried in an inert atmosphere 9 which is shielded from the outside by a seal roll 8, and then fed into the anode electrolytic cell 10 in the same atmosphere, where, for example, AlCl ₃ molten salt is used. Anodic electrolysis is performed in the electrolytic bath. This is an activation process. Sign
Reference numeral 11 indicates a conductor roll for anode electrolysis, and reference numeral 12 indicates a sink roll.

The steel strip 2 thus pretreated exits from the inert gas atmosphere through the compartment rolls 13, enters the molten salt electrolytic plating tank 14, and is subjected to predetermined plating.

It should be noted that molten salt electrolytic plating, for example, molten salt electrolytic plating of Al itself is already known and well understood by those skilled in the art, and therefore further description is omitted for the sake of simplicity.

Here, according to the present invention, the drying and preheating conditions performed in the atmosphere, the temperature of the steel material, that is, the steel surface temperature is 100
If it exceeds ℃, Tm ≦ 44.4logR + 120.

However, Tm is the maximum temperature (° C) of the steel material in the atmosphere, and R is the average temperature rise (° C / S) of the steel material in the atmosphere during drying and preheating after washing with water. Specifically, it is an average temperature gradient between the temperature at the time of washing with water, for example, the temperature of the washing water and the maximum attainable temperature.

That is, since it takes time for an oxide film to be formed at a low heating temperature in the air of 100 ° C or less, it does not cause any problem at normal steel material conveying speed, but if it exceeds 100 ° C, it easily oxidizes. Since the film is formed, the heating conditions are adjusted as described above.

In the case of the illustrated example, the drying / preheating conditions can be determined from the maximum temperature reached by the steel strip 2 before the preheating step of the inert atmosphere 9 and the temperature rising rate up to that. When the rate of temperature increase is high, the highest temperature can be increased accordingly. On the other hand, when the heating rate is low, the maximum temperature reaches a low value because it takes a long time to heat. In other words, this limits the amount of heating energy above 100 ° C in the atmosphere to a certain amount. That is, the surface oxidation of the steel material is made to be about the same.

Thus, according to the present invention, electrolytic anodic treatment in the activation step can be made necessary and minimal, and continuous treatment can be performed efficiently. From the results shown in FIG. 2, if the average temperature rise rate of the steel sheet is set sufficiently high and Tm is set low,
It is even possible that the electrolytic anodization could be omitted.

Next, the present invention will be further described with reference to examples.

Example 1 In order to simulate the implementation of the method of the present invention by an apparatus as shown in FIG. 1, a flow cell (SUS316) dedicated to molten salt is used.
Made by L). An Al plate having a purity of 99.8% was installed as an anode in this flow channel. SPCD grade as treated steel
The present invention was carried out by electroplating in a molten salt under the conditions shown in Table 1 using a 0.8 mm thick mild steel plate.

The pretreatment of the steel plate to be plated was performed by electrolytically cleaning the steel plate sample in a 5% sodium orthosilicate solution as an anode at 10 A / dm ² for 15 S, then washing with water, and then pickling with a 10% HCl aqueous solution for 20 S for 20 S. . The steel sheet thus pretreated in this manner was then washed again with water in a water washing step to remove most of the water film with the air blower at room temperature. Immediately after that, set the heating rate and maximum heating temperature in the infrared heater that can be set in advance, heat in the air atmosphere, and immediately after heating, immediately
It was rapidly cooled in N ₂ gas. The cooling rate at this time is 30 ° C./S, and the holding time at the highest temperature reached is 0 s. Then, the steel plate was taken out from the heater and electroplated by the plating method. However, prior to plating, 10 A / dm ² × 2S or 25 A / dm ² × 2S of anodic dissolution was performed in the plating solution using the steel sheet as the anode. The plated sample was washed with water, dried and then subjected to the DuPont impact test (ball head diameter 1/2 inch, potential energy 0.8
The adhesion of the plating film was evaluated with kgf-m). The results are summarized in the graph in FIG.

Tm ≦ 44.4l in the region where the temperature reached by the steel sheet exceeds 100 ℃
It can be seen that when the condition of ogR + 120 is satisfied, the steel material to be treated can be activated by electrolytic anodizing within 2 seconds.

Example 2 Next, substantially repeating Example 1, variously changing the steel plate heating rate, and selecting several highest attainable temperatures at that time, the adhesion of the plating film was evaluated for each, and at each heating rate. It was investigated how many times it was allowable as the ultimate temperature.

The results are shown graphically in FIG. In the figure, ● indicates anodic electrolysis 25A /
If the plating adhesion is poor even with dm ² × 2S, then ○
Shows the case where the plating adhesion is good under the same conditions. The points ● and ○ are the points where the temperature rise was stopped. In the illustrated example, the region above the broken line must be heated under an inert gas atmosphere. In other words, the region under the broken line can be heated under the atmosphere.

It can be seen that when the rate of temperature rise is high, the maximum temperature attainable can be increased, and when the rate of temperature rise is low, the maximum temperature reached cannot be raised too high. Therefore, if the temperature rising rate is increased, the electrolytic anodization can be directly performed without performing the preheat treatment in the inert atmosphere.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view of an apparatus for carrying out the method according to the present invention, and FIG. 2 is a graph showing the relationship between the temperature rising rate after washing with water, the maximum heating temperature in the atmosphere and the plating adhesion; And FIG. 3 is a graph showing the relationship between the heat pattern of heating in the air after washing with water and the plating adhesion. 1: Recoiler, 2: Steel strip 3: Degreasing tank, 4: Washing tank 5: Pickling tank, 6: 〃 7: Drying room, 8: Seal roll 10: Anode electrolysis tank

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Junichi Uchida 1-3-3 Nishi-Nagasumoto-dori, Amagasaki City, Hyogo Prefecture Sumitomo Metal Industries, Ltd. Research Institute (72) Hirohisa Seto Nishi-Nagasumoto, Amagasaki City, Hyogo Prefecture Sumitomo Metal Industries, Ltd. General Technical Research Institute (72) Inventor Yuji Furusawa 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries Ltd. Hiroshima Research Institute (72) Inventor Yukio Kanda Hiroshima 4-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture Mitsubishi Heavy Industries Ltd. Hiroshima Works

Claims (1)

[Claims] 1. A steel material pre-washing step, water washing step, drying step,
In the molten salt electroplating method for steel materials consisting of a preheating step, an activation step, and a molten salt electroplating step, the drying temperature and / or the drying or preheating conditions in the preheating step, which are performed in the air, are set so that the ultimate temperature of the steel material exceeds 100 ° C. In the case of, the molten salt electroplating method for steel material is characterized in that Tm ≦ 44.4logR + 120. However, Tm: the maximum temperature of the steel material reached in the atmosphere (° C), R: the average temperature rise rate (° C / S) of the steel material in the atmosphere during the drying and preheating processes after washing with water.