JPS59159994A - Surface-treated steel sheet withsuperior suitability to chemical conversion treatment - Google Patents

Abstract

PURPOSE:To obtain the titled steel sheet having favorable properties by which the formation of nuclei of crystals of a film and the growth of the crystals are not hindered during chemical conversion treatment, that is, superior suitability to chemical conversion treatment by depositing a prescribed amount of an Ni-P alloy contg. a prescribed amount of P on the surface of a rolled steel sheet. CONSTITUTION:At least one side of a rolled steel sheet is plated with 1-100mg/ m<2> Ni-P alloy contg. 0.01-5% P by electroplating, chemical plating, vacuum deposition or other method. The resulting plated steel sheet has superior suitability to chemical conversion treatment.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface-treated steel sheet with excellent chemical conversion treatment properties.

In general, when steel sheets for automobiles are actually used, they are processed by press forming, etc., and then subjected to chemical conversion treatment (for example, phosphate treatment) as a coating base, and then, for example, cationic electrodeposition coating is applied on top of that. However, in order to obtain good coating corrosion resistance from the electrodeposition coating, it is essential to first obtain a good chemical conversion coating in the surface treatment. In order to obtain this good chemical conversion coating, the surface of the material must have good properties that do not inhibit the nucleation and growth of the chemical conversion coating crystals (properties that are excellent in chemical conversion treatment). Ru.

Now, cold-rolled steel sheets used as steel sheets for automobiles have conventionally been cooled after continuous annealing by methods such as gas jet cooling in a non-oxidizing atmosphere, which is considered to be advantageous for forming chemical conversion coatings, such as LMn, etc. It was a steel sheet with extremely good chemical conversion treatment properties, such as the presence of a surface concentration layer. However, recently, in order to rationalize the heat cycle in the continuous annealing described above, there is a tendency to adopt water cooling or air/water cooling instead of gas jet cooling in a non-oxidizing atmosphere.

In this case, since the cooling process creates an oxidizing atmosphere, an oxide film is formed on the surface, and therefore, pickling treatment is required to remove this oxide film. The cold-rolled mesh sheet subjected to this pickling treatment is
The chemical conversion properties have deteriorated due to removal of the mountain concentration layer and surface adsorption of pickling residue (iron hydroxide).

In addition, when cold-rolled steel sheets are used for automobile bodies, body corrosion becomes a major safety problem.In particular, one side of the automobile exterior plate, which is susceptible to corrosion, is coated with a highly corrosion-resistant surface such as a Zn-plated surface or a Zn-Ni alloy. Single-sided plated steel sheets have come into use, with gold plating or Fe-Zn composite plating on one side, and the other side left as a steel plate to reduce car body corrosion. There are two manufacturing methods for single-sided plated steel sheets: electroplating and hot-dip plating, but in the case of electroplating, pickling is performed as a pretreatment, and in many cases the process is still carried out in an acidic electroplating bath. Because it passes through, it is subjected to the pickling effect, which reduces the chemical conversion treatment properties of the non-plated surface. In addition, in the case of the hot-dip plating method, since the material comes out of the hot-dip plating bath in a high-temperature state, oxidation of the non-plated surface is unavoidable.Therefore, pickling treatment is required after completion of plating, and chemical conversion treatment properties are similarly reduced. In recent years, Fe-based or Fe-Znn-based alloys have become particularly popular, and in this case, a large amount of Fe is used in the acidic plating bath.
Because the 3+ ions are applied, the non-plated surface exhibits a pitting state during acid annealing, resulting in extremely poor chemical conversion properties. There is also an electric Zn plating method, but as the trend toward high current density operation progresses, highly corrosive chloride baths are used in this case, and the unplated side of single-sided plated steel sheets is subject to extreme dissolution. Therefore, chemical conversion treatment properties are also extremely poor.

In addition, especially when using a vertical plating tank with a long immersion time in the plating bath, the deterioration of chemical properties is much more severe than in the case of a horizontal plating tank, which can lead to serious problems. There is.

The present invention has been made in order to eliminate the deterioration in heat treatment properties of the non-plated surface of cold rolled steel sheets or single-sided plated steel sheets that have been subjected to pickling treatment etc. as described above. The purpose of this invention is to improve the surface properties of rolled steel sheets and to provide surface-treated steel sheets with excellent chemical conversion treatment properties that promote the reaction rate of chemical conversion treatment.

In order to improve the surface of cold-rolled steel sheets with deteriorated chemical conversion treatment properties, metallic Ni was added to the surface of cold-rolled steel sheets at α3 to 10 q.
/dm2 is disclosed in Japanese Patent Laid-Open No. 116883/1983. According to this invention, chemical conversion properties (crystal size,
The effect of improving coating film adhesion amount) and paint corrosion resistance can be obtained. However, in actual chemical conversion treatment processes, continuous processing is carried out online, and in order to improve productivity in such processes, it is necessary to increase the reaction rate of chemical conversion treatment and further increase the line speed. There has been a desire for a cold-rolled steel sheet that can improve the surface of a steel sheet with deteriorated chemical conversion treatment properties and also improve the reaction rate of chemical conversion treatment.

In view of the above, the present inventors have conducted various experimental studies with the intention of developing a surface-treated steel sheet with excellent chemical conversion treatment properties that can provide a good chemical conversion coating and improve the chemical conversion reaction rate. As a result, we discovered a new fact that chemical conversion treatability can be dramatically improved by depositing an appropriate amount of N1-P alloy containing a small amount of P on the surface of a cold-rolled steel sheet.

The mechanism by which chemical conversion treatment properties are improved by adhering N1-P alloy to the surface of a steel sheet has not yet been properly elucidated, but at this stage it is considered as follows. In other words, products such as iron hydroxide and water rust that inhibit chemical conversion treatment are formed on the surface of steel sheets after pickling. It is thought that when electrolyzed, this Ni is dispersed on the surface of the steel sheet and precipitated in a state that protrudes from the product layer. Therefore, during chemical conversion treatment, this precipitated Ni force;
It acts as a nucleus for chemical conversion crystals and becomes a starting point for the crystal growth of chemical conversion coatings, and can be expected to form fine and dense chemical conversion coatings.・Increasing the chemical conversion reaction rate - by adding a small amount of P to Ni. The academic reason for this is not clear, but one possible hypothesis is as follows. That is, N
i performs the movement of crystal nucleation as described above, and rcP acts as an autocatalytic active site when reacting with mono-nonacid in the chemical conversion treatment solution, promoting the reaction rate of the chemical conversion treatment. It is presumed that this is the case.

The present invention has been made based on the above findings, and the gist thereof is to apply 0.01 P on the surface of a cold-rolled steel sheet.
~5.0% N1-P alloy containing 1-100”g/m
There is a separate surface treatment board that is characterized by chemical conversion treatment properties.

Next, a method for attaching the 1'Ji-P alloy will be explained.

The deposition method is not particularly limited, and may be any method such as electroplating (the plating bath may be an aqueous solution, non-aqueous solvent, molten salt bath, etc.), electroless plating, or vacuum deposition. However, from the viewpoint of equipment scale, operating cost, etc., it is most preferable to apply the conventional electroplating method using an acidic aqueous solution or the electroless plating method. It is as follows.

(2) Electroplating method: For example, it is preferable to use a phosphorous acid-added bath based on a known wand bath having the following bath composition.

Bath composition: NiSO4-6) (20240?#NiCA
2-6H2045fi'#I H3BO33of/111 Temperature 60'C Current rating 1-10 A/dm' Above bath KH3P
O3 is added in i form in the range of 0.1-10 fi'#), and the N1-P alloy is adhered to the surface of the steel sheet while adjusting the P content. The amount of N1-P deposited is adjusted by appropriately changing the electrolysis time x current density.

■Electroless plating method A bath consisting of a secondary composition is used.

Bath composition: Nickel sulfate 0.1M Sodium nitrate Q5NVA Ammonium sulfate Q5A4//1 pH9 Temperature 90'C Sodium hypophosphite was added to the above bath at αo1~0.05M/
It is added by changing it within the range of A to adjust the P content in the N1-P alloy. Further, the amount of N1-P deposited is adjusted by changing it by controlling the immersion time.

Next, the reasons for limiting the numerical values of each requirement in the present invention will be explained.

The reason why the P content in the 1" Ji-P alloy was limited to α01~5.OS is that if it is less than 0.01%, the effect of accelerating the chemical conversion reaction rate is insufficient; if it exceeds 50%, This is because the N1-P component with low solubility increases and conversely suppresses the chemical conversion reaction rate.When P exceeds 50%, the reason why the reaction rate decreases is that N1-P component increases.
This seems to be because the ratio of the amorphous component increases between the crystalline component and the amorphous component of the 1-P alloy.

The amount of N1-P alloy still adheres to 1-1001! '? /m2
The one limited to 12n? This is because if the amount is less than 100 "P/rn", the amount of adhesion is too small and sufficient improvement effect on chemical conversion treatment properties and paint corrosion resistance cannot be achieved.
This is because if the amount exceeds 1, the amount of adhesion will be too large, and the effect of improving chemical conversion treatment property will be reduced, and problems such as unevenness or sagging (insufficient amount of adhesion) will occur in the chemical conversion film, resulting in unfavorable results.

Note that the structure of the surface-treated steel sheet with excellent chemical conversion properties based on the present invention does not always have to be applied to both sides of the steel sheet, but this structure is adopted only for one side, and the other side is For example, there is no problem in implementing the plated surface with a different structure, and such a form also belongs to the scope of the surface-treated steel sheet of the present invention.

Next, the present invention will be described in detail with reference to Examples.

Example 1 An aluminum killed continuous cast slab was cold rolled to a thickness of 08, then annealed on a continuous annealing line, cooled to room temperature with air water cooling (N2 + water), and then pickled. Tests of examples of the present invention were carried out by depositing N1-P alloy on cold-rolled steel sheets by electroless plating with varying amounts of pNi-P alloy deposited and P content in the N1-P alloy within the range of the present invention. Materials (2) to (5) and (8) to 0■ were obtained.

For comparison, an aluminium-killed cold-rolled steel sheet that had been annealed, vented, water-cooled, and pickled was treated with Ni in a range outside the scope of the present invention.
-P alloy adhesion amount is still N1-P content in P alloy is N1-
Comparative example test materials (1) (6) (7) with P alloy attached
) (14) was obtained. Similarly to the above, the conventional specimen α0 has been annealed with water cooled and pickled, and the conventional specimen α0 has been cooled with gas jet cooling in a non-oxidizing atmosphere according to the conventional cooling method after annealing.・I got it.

Subsequently, each of these test materials (1) to α0 was subjected to phosphate treatment and cationic electrodeposition coating under the chemical conversion treatment conditions and cationic electrodeposition conditions shown below, and the quality of chemical conversion treatment and paint corrosion resistance was investigated. did.

■Chemical treatment conditions G) Degreasing: Fine Cleaner 4326T (product name manufactured by Tamoto Parker Rising Co., Ltd.) Immersion for 12 minutes at a liquid temperature of 50°C (B)] Surface conditioning: Percolene ZT (product name manufactured by Nippon Parker Rising Co., Ltd.) ] 20 seconds immersion e-) Zinc phosphate treated Nihon Prite BT-3030 (
Product name: Nippon Parker Rising (manufactured by Nippon Parker Rising) Liquid temperature: 50°
c, immersion for 2 minutes ■Electrodeposition coating conditions (K) Paint: Cationic electrodeposition paint of SBI No. 1000 (manufactured by Shinto Toyo Co., Ltd.) (B) Voltage: 250V, v → Bath temperature: 30°C, (B) Current application time = The chemical conversion treatment property is 3 minutes, but the chemical conversion film phosphofluorite (
Ratio P/P+1 (denoted by P) and hopite (denoted by H)
was determined from Xi diffraction, the size of the Si crystal was determined using a scanning electron microscope, and the amount of film attached was determined using a gravimetric method.
Evaluation was made based on these values.

The corrosion resistance of the coating is still confirmed by CelloTef after 960 hours of a salt spray test on a cross-cut area where the electrodeposited coating has cuts reaching the plated surface in a goblin pattern at intervals of two.

Evaluation was made during peeling.

The above survey results are summarized in Table 1.

The ○ mark in the appearance of the chemical conversion coating in Table 1 indicates a good quality product.As shown in Table 1, Comparative Example (1) has a small amount of Ni-P alloy deposited, resulting in coarse crystals and uneven coating. In Comparative Example (6), the amount of N1-P adhesion was too high, the improvement effect of chemical conversion treatment decreased to 75, and the amount of adhesion was small.
Unevenness and sagging occurred on the film, and the remaining 11-width was the size of a crab.In comparison 91 (7), the P content was too small, so the desired rate of sludge collection could not be obtained, and the amount of adhesion was also insufficient. Enough, coating-
Comparative Example α4) had a large P content, S, and the rate of reaction for forming the film was low, and the coating strength was extremely low. Corrosion resistance after treatment, treatment and painting was poor. On the other hand, (2) to (5) and (8) to q■ of the present invention examples are all appropriate within the N1-P alloy deposition amount and the P content in the i'Ji-P alloy of 75 balls within the present invention range. Because of this, the chemical conversion treatment rate was fast, and an appropriate amount of film was obtained.The thickness of the crystals was fine, and the film appearance was completely free of unevenness and scratches, showing good conversion processability and coating film. The peeling width was also less than 12 threshold, indicating good paint corrosion resistance.

Conventional example α is still a cold-rolled plate that has been pickled, so the surface quality is poor, and the chemical conversion coating crystals are coarse, the coating appearance is uneven and uneven, and the chemical conversion treatment is poor, and the coating peels off. The corrosion resistance of the paint on the inside was also poor. On the other hand, since Conventional Example α was a cold-rolled steel sheet that was cooled in a non-oxidizing atmosphere after annealing and was not pickled, both chemical conversion treatment properties and paint corrosion resistance were extremely good.

Example 2 An aluminum killed cold-rolled steel sheet with a thickness of O, & up, which had been annealed and cooled to room temperature by water cooling and then pickled in the same manner as in Example 1, was coated with N1-P@-gold medium by electroless plating. The test materials, in which the P content was varied in the range of 0 to 10, and the N1-P alloy was deposited at 15 to 10/rn', were subjected to Rin Kairyu under the same conditions as shown in Example 1. A chemical conversion treatment using lead was performed, and the completion time of the chemical conversion treatment reaction (the time required until the amount of chemical conversion film produced was saturated) was measured.

The measurement results are shown in FIG. FIG. 1 is a diagram showing the relationship between the P content (wt%) in the N1-P alloy and the chemical conversion reaction completion time using a characteristic curve P.

As shown in the figure, all of the sample materials with a P content within the range of the present invention, which is 0.01 to 50%, had extremely fast chemical conversion reaction rates, with a chemical conversion reaction completion time of about 1 to 12 minutes. However, when the P content is less than 0.01% or exceeds 50%, the reaction rate of chemical conversion treatment decreases rapidly, and the time required to complete the reaction of chemical conversion treatment increases rapidly. It was shown to have a significant effect.

As is clear from the above description, the surface-treated steel sheet of the present invention has excellent chemical conversion treatment properties comparable to conventional cold-rolled steel sheets without pickling, and has excellent paint corrosion resistance in cationic electrodeposition coating. It is not just a spoof that makes it possible to obtain a coated coating with a high chemical conversion rate, but it also has the extremely advantageous property of having a fast chemical conversion reaction rate. Some 0

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the P content in the N1-P alloy and the chemical conversion reaction completion time.

Claims (1)

[Claims] (1) N containing 001 to 50% P on at least one side
A surface-treated steel sheet excellent in chemical conversion treatment, characterized in that a 1-P alloy is adhered at a thickness of 1 to 100"?/rl.