KR100299436B1 - Reactive solution for surface treatment and method for treating steel sheet using the same - Google Patents

Abstract

PURPOSE: A reactive solution for surface treatment and method for treating steel sheet using the same are provided to improve weldability, processability, adhesiveness of electrostatic painting, corrosion resistance and paintability of panels for automobile uses. CONSTITUTION: The absolute solution for surface treatment essentially consists of Mn 2.9-4.1wt.%, Ni 2.0-4.0wt.%, Cl 1.2-1.4wt.%, Fe 0.5-0.9wt.%, a balance of phosphate, and the mole ratio of (Ca+Mg)/P2O7 ranges from 0.4 to 0.8. The absolute solution, for the application, is diluted to 2.4-5wt.%·absolute solution/L·water. The diluted solution of which temperature is 30-60deg.C is reacted with electrolytic galvanized iron or hot dipped galvanized iron to regulate an amount of diluted solution on above steel sheet to 1.0-2.0g/m¬2. Phosphates formed on the surface treated steel sheet consist of phosphophyllite and hopeite.

Description

[Name of invention]

Reaction type surface treatment stock and surface treatment method of steel sheet using the same

Detailed description of the invention

[Purpose of invention]

[Technical field to which the invention belongs and the prior art in that field]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment technology for automotive steel sheets, and more particularly, to form a reactive alloy layer on a surface treated steel sheet to improve the weldability, processability, electrodeposition adhesion, anticorrosion effect, and paintability of the steel sheet. And it relates to a surface treatment method of the steel sheet using the same.

Generally, steel sheets used in automobiles are used by surface treatment on hot-dip galvanized steel sheets or electroplated steel sheets. Such automotive surface treated steel sheets are first of all inexpensive and have excellent weldability, electrodeposition adhesion, paintability, corrosion resistance and processability. Various characteristics such as these are required.

In order to improve these characteristics, in addition to the general steel company, the automobile company used a steel sheet formed with a coated phosphate coating on a cold rolled steel sheet, but the steel sheet is not only subjected to post-processing treatment such as press, but also uneven surface before deformation and coating. Due to the state has a variety of problems, such as color changes, the fundamental disadvantage is not solved. Moreover, in addition to the phosphate treatment, automobile companies are applying various technologies to improve the anti-corrosion properties and paintability in surface treatment lines, but ultimately these methods are not applicable to steel companies, so they are cheap steel plates. There is a drawback that this cannot be supplied. Therefore, various attempts have been made in the steel industry to improve the characteristics of automotive steel sheets. The typical conventional automotive steel sheets are instantaneous electric double plating, that is, flash plating on alloyed steel sheets after hot dip galvanizing treatment. Flash steel sheets for performing the above have been mainly used. However, the flash plated steel sheet is excellent in general characteristics as a steel sheet for automobiles, but most of all, it is vulnerable in cost competitiveness because its cost is very high in manufacturing such as electroplating after hot dip plating.

Meanwhile, a method for forming a phosphate surface treatment film on a steel sheet has been developed as a method for enabling production at low cost while maintaining the characteristics of the flash plated steel sheet.

That is, Japanese Laid-Open Patent Publication No. 7-138764 discloses a Mn content of 3.4-4.1 wt%, a Ni content of 0.5-1.7 wt%, and the remaining phosphoric acid during post-treatment in order to produce a zinc-containing metal plated steel sheet composite having excellent high-speed press formability. A method using the treatment solution containing the same is proposed, which has a disadvantage in that paintability is deteriorated when applied to an actual automobile line.

As another attempt, Hankel, Germany, suggests that a surface treatment film of excellent properties can be obtained by using a solution containing 7.0-8.5 wt% Mn, 3.6-4.0 wt% Ni and remaining acid. However, this method also has a problem in that the paintability is deteriorated by high manganese.

[Technical problem to be achieved]

Therefore, the present invention has been proposed to solve the above-mentioned problems, and the present invention is suitable by controlling various components based on phosphoric acid, the film formed by reacting with the steel sheet to achieve the characteristics equivalent to or more than the conventional flash-plated steel sheet It is an object to provide a reactive surface treatment stock solution to have.

Still another object of the present invention is to provide a surface-treated steel sheet which improves the weldability, workability, electrodeposition adhesion, anticorrosion effect, and paintability of the steel sheet by forming a reactive alloy layer on the surface-treated steel sheet using the surface treatment stock solution. have.

[Configuration and Function of Invention]

The present invention for achieving the above object, in weight%, Mn: 2.9-4.1%, Ni: 2.0-4.0%, C1: 1.2-1.4%, Fe: 0.5-0.9% and the rest is composed of phosphoric acid, and It relates to a reactive surface treatment stock solution having a molar ratio of (Ca + Mg) / P ₂ O ₇ of 0.4-0.8.

In addition, the present invention by diluting the treatment stock solution to the surface treatment solution of the concentration of 2.4-5% by weight and the temperature of the solution in the range of 30-60 ℃ to react the solution with a steel sheet for 3-5 seconds solution The surface treatment of a steel plate is carried out so that the adhesion amount of may be set to 1.0-2.0 g / m <^2> .

On the other hand, in the method for surface treatment of the steel sheet, the steel sheet is preferably an electrogalvanized steel sheet or a hot dip galvanized steel sheet.

In addition, in the surface-treated steel sheet, the phosphate coating structure formed after the coating treatment is composed of a phosphoprite and a phosphite lattice structure, the phosphoprite lattice structure is formed on the phosphate coating structure consisting of the phosphophyllite and a phosphite It is preferable that 80% or more be produced | generated.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

First, manganese contained in the surface treatment stock solution of the present invention forms Zn ₃ Ni _x Mn _y (PO ₄ ) H ₂ O and the like to improve alkali resistance of the film together with the Ni component and to improve the water-resistant secondary adhesion. Do it. At this time, too much Mn component in the stock solution of the present invention inhibits the anticorrosive action of the base zinc having Ni component, and too little is undesirably high film loss. Therefore, the Mn content in the stock solution is preferably limited to 2.9-4.1% by weight.

In addition, the Ni component reacts with the base iron to selectively produce a protective film of zinc zinc to suppress corrosion to improve corrosion resistance as well as to improve the coating performance. At this time, if the amount of Ni in the stock solution of the present invention is too small, the above-described film forming effect is small, and the corrosion width is increased. Ni content is preferably limited to 2.0-4.0% by weight.

In addition, the chlorine component forms a role of 4Zn (OH) ₂ ZnC1 ₂ to act as a protective coating, as well as to improve adhesion to the base iron, when the content is less than 1.2% by weight of the amount of the film formation If it is insufficient, the protective effect is small, and when contained in more than 1.4% by weight, it remains on the surface and acts as a nucleus of corrosion, which is not preferable.

In addition, the Fe component in the stock solution of the present invention serves to precipitate the by-products generated in the treatment solution as sludge by the formation of Fe (PO) ₄ 2H ₂ O as follows.

In this case, when the Fe content is less than 0.5% by weight, the film forming effect is lowered, and when the content is more than 0.9% by weight, the presence of Fe itself is rather adversely affected, which is not preferable.

In addition, in the present invention, when the molar ratio of (Ca + Mg) / P ₂ O ₇ in the stock solution is maintained at 0.4-0.8, excellent coating adhesion and coating property can be obtained by the surface adjustment effect. Here, the surface adjustment effect refers to the application of colloids on the surface of the material steel sheet during the chemical conversion process (post-treatment process) to help the formation of microcells during the chemical reaction and to refine the precipitation film, but the molar ratio is 0.4. If it is less than the effect is on the contrary 0.8 or more is not preferable because the particle size of the colloid is increased to cause agglomeration rather adversely.

On the other hand, phosphate ions contained in the process stock solution of the present invention is a main component that reacts with the steel sheet to form a phosphate film, and is present in the solution as follows.

_{H 3 P0 4 ↔ H 2 PO} 4 - + H +, K 1 = 7.52 x 10 -3

H ₂ PO ₄ ^- ↔ HPO ₄ ^2- + H ⁺ , K ₂ = 6.23 x 10 ^-8

HPO ₄ ^2- ↔ PO ₄ ^3- + H ⁺ , K ₃ = 4.8 x 10 ^-13

The phosphate ion is the pH of the steel sheet material activation by the acid is raised to thereby the precipitation precipitation of the acid salt is made. In other words,

Fe + 2H ⁺ → Fe ²⁺ + H ₂ ↑

Zn + 2H ⁺ → Zn ²⁺ + H ₂ ↑

When using the undiluted solution of the present invention, the phosphate coating structure formed after the coating treatment is composed of chemically stable phosphophyllite and hopite lattice structures, and the phosphoprite lattice structure. Since is produced in a ratio of about 80% or more with respect to the phosphoprite and hophite lattice structure, it is excellent in acid resistance and alkali resistance, thereby maintaining good paintability. At this time, the phosphophyllite and the hopitite formed are reacted as follows by reference.

_{^{3Zn 2+ + 2H 2 PO 4 -}} + 40H - → Zn 3 (PO 4) 2 4H 2 O ↓ (hopeite)

_{^{3Zn 2+ + Fe 2+ + 2H 2}} PO 4 - + 40H - → Zn 2 (PO 4) 2 4H 2 O ↓ (phosphophyllite)

The reactive surface treatment stock solution prepared as described above is used to form a reaction film by reacting with a steel sheet through a spray method or dipping, wherein the stock solution is preferably diluted with water and used at a concentration of 2.4-5% by weight. Do.

In addition, it is preferable to maintain the temperature of the solution at 30-60 ℃ during the reaction, because the reaction force is weak when the temperature of the reaction solution is less than 30 ℃, the reaction effect is almost the same as below if the temperature is above 60 ℃ to be.

In addition, the reaction time is an important factor because it relates to the amount of adhesion of the treatment solution, in the present invention, it is preferable to perform the time of contact with the steel sheet for about 3-5 seconds. If the reaction time is less than 3 seconds, the amount of coating is relatively small. On the contrary, if it exceeds 5 seconds, the amount of adhesion is too high. Rather, it is not preferable in terms of manufacturing cost.

When the reaction is carried out under such conditions, a film of about 1.0-2.0 g / m ² is formed on the steel sheet, thereby obtaining a surface-treated steel sheet having excellent coating performance as well as workability.

On the other hand, the steel sheet to which the treatment solution of the present invention can be applied can be used as long as it is a plated steel sheet, but preferably an electrogalvanized steel sheet or a hot dip galvanized steel sheet.

Hereinafter, the present invention will be described in detail through examples.

Example 1

First, the surface treatment solution having the composition shown in Table 1 was diluted to prepare a surface treatment solution having a concentration of 5% by weight. Subsequently, under the conditions as shown in Table 1, an electroplated steel sheet having a zinc plating adhesion amount of 20/20 g / m ² and a thickness of 0.75 mm was immersed in the solution to form a film on the surface of the steel sheet. A draw bead test, a cylindrical deep drawing test, a limit machining test, an electrodeposition coating resistance, and a water-resistant secondary adhesion test were performed on the coated steel sheet. The results are shown in Table 2 below.

The draw bead test was conducted at room temperature with a specimen size of 300 mm X 300 mm, a drawing speed of 260 mm / min, and a drawing distance of 100 mm.

In addition, the planar sliding test was evaluated as a drawing force in a scratch-free planar sliding state when the blank holding force was 1.4 tons, which means that the greater the drawing force, the better the lubricity of the plane.

In addition, the limit machining test was performed at room temperature with a punch diameter of 50 mm, a die diameter of 52.5 mm / 5.0 mm, a punch speed of 30 mm / min, a punch shoulder of 5 mmR, and a bead height of 4 mm.

The electrodeposition coating property was evaluated by a temperature resistant salt water test. The salt water test was a paint used by automobile companies. After electrodeposition coating, the surface of the steel sheet was cut to 1-2 mm, and then immersed in a 55 ° C. and 5% NaCl solution for 240 hours. The corrosion site of the coating film at that time was peeled off with a vertical plate tape, and then the corroded width of the cross section was measured. For reference, the cross section width required for automotive steel sheet is 4mm or less.

In addition, the coating adhesion test, after reacting the surface treatment solution, and subjected to phosphate treatment, top, middle and electrodeposition coating carried out by the automobile company, and then immersed in pure water at 40 ℃ 240 hours, interval 1-2mm After cutting by 100 division and peeling with vertical tape, the peeling degree of coating was indexed.

As shown in Table 2, Inventive Example (1-3) in which a film was formed by reacting an electroplated steel sheet using an inventive solution that satisfies the composition range of the present invention is not only excellent in workability but also very excellent in coating performance. It was found to be excellent.

On the other hand, in the case of Comparative Example (1-5) using a solution outside the composition range of the present invention, it was found that the processability is deteriorated compared to the example of the present invention but the coating performance is deteriorated.

Example 2

Except for using a hot-dip galvanized steel sheet having a 45/45 g / m ² zinc coating thickness of 0.75 mm, a film was formed on the surface of the steel sheet in the same manner using the comparative solution and the inventive solution shown in Table 1 in Example 1. Tensile tests, planar wettability, limit processing tests, electrodeposition coating properties, and water-resistant secondary adhesion tests were performed on the coated steel sheets. The results are also shown in Table 3 below.

As shown in Table 3, Inventive Example (4-6) in which a film was formed by reacting a molten plated steel sheet using an inventive solution that satisfies the composition range of the present invention is not only excellent in workability but also very high in coating performance. It was found to be excellent.

On the other hand, in the case of Comparative Example (6-10) using a solution outside the composition range of the present invention, compared to the present invention it was found that the workability is maintained at the same level, but the coating performance deteriorated.

[Effects of the Invention]

As described above, the present invention forms a film on the steel sheet by reacting a reactive surface treatment solution with appropriate control of various components based on phosphoric acid to form a film on the steel sheet, thereby not only having characteristics equivalent to those of the conventional flash-plated steel sheet, but also having weldability, Processability, electrodeposition adhesion, anticorrosive effect, as well as improved coating properties can be provided at low cost.

Claims (4)

By weight, Mn: 2.9-4.1%, Ni: 2.0-4.0%, C1: 1.2-1.4%, Fe: 0.5-0.9% and the rest are composed of phosphoric acid, and (Ca + Mg) / P ₂ O ₇ Reaction surface treatment stock solution, characterized in that the molar ratio of 0.4-0.8. After diluting the treatment solution of claim 1, a surface treatment solution having a concentration of 2.4-5% by weight is prepared, and the solution is allowed to react with the steel sheet for 3-5 seconds with the temperature of the solution in the range of 30-60 ° C. Surface treatment method of the steel sheet, characterized in that to be 1.0-2.0g / m ² . 3. The method of claim 2, wherein the steel sheet is an electrogalvanized steel sheet or a hot dip galvanized steel sheet. 4. The surface-treated steel sheet according to claim 2 or 3, wherein the surface-treated steel sheet has a phosphate structure composed of phosphorphyllite and hopeite; And at least 80% of the phosphor phosphite lattice structure.