JPH02101200A - Cold-rolled steel sheet with excellent phosphating properties and corrosion resistance - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides a cold-rolled steel sheet with improved phosphating properties and corrosion resistance, particularly a method in which metallic nickel and non-metallic nickel are precipitated in the form of particles on the surface. The present invention relates to a cold-rolled steel sheet with improved phosphating properties and corrosion resistance.

[Conventional technology]

Cold-rolled steel sheets, which are used in large quantities for automobiles or home appliances, are often painted before use, and in that case, phosphate treatment is often performed as a pre-painting treatment. This treatment is performed for the purpose of increasing paint adhesion and corrosion resistance when painting is applied on the surface of the steel plate by precipitating and adhering phosphate crystals to the surface of the steel sheet. The method consists of applying the following to the steel plate to be treated.

Basically, the precipitation mechanism of phosphate crystals in this case is that iron is eluted at the anode site by phosphate treatment, and on the other hand, the pH increases due to the reduction reaction of hydrogen ions at the anode site. It is said that this causes phosphate to precipitate and grow on the cathode site.

On the other hand, phosphatizability, i.e., due to phosphate treatment, °ζ
The formability of the chemical conversion film that is generated is evaluated from the viewpoint of the precipitation rate and crystal morphology of phosphate crystals, and the film formation should proceed uniformly and as quickly as possible on the steel plate surface.
Furthermore, because the crystal form is dense and fine,
It has been evaluated as having excellent phosphate treatment properties.

Therefore, in the second type of surface preparation in the steps of the phosphate treatment method, titanium-based colloids are adsorbed onto the steel sheet surface, or heavy metal ions such as Ni and Go are added to the phosphate treatment solution to improve the surface of the steel sheet. Processing methods have been extensively researched and improved on methods for uniformly and as quickly as possible substitution precipitation.

On the other hand, as a conventional technique for treating steel sheets to improve phosphate treatment properties, for example, Japanese Patent Publication No. 5,643,392 discloses that jV, Ti, Cr, Mn, Co, Ni, Zn, Zr,
A steel plate is electrolytically treated at a cathode or an anode with an alkaline aqueous solution containing a complexing agent containing one or more of Mo and Sn, and a film made of a metal or a metal compound is converted into metal ions in an amount of 5 to 500 mg/n (steel plate). A method is disclosed in which a steel plate is formed on the surface and then subjected to a chemical conversion treatment.

Among them, application of an electrolytic cleaning process before annealing is indicated as a method for manufacturing steel sheets.

Furthermore, JP-A No. 56-116883 discloses that 0.3 to 10 mg/dn (deposition of metallic nickel) on the surface of a cold-rolled steel sheet, and JP-A No. 56-116887 discloses that Ti is deposited on the surface of a cold-rolled steel sheet. Mn.

A cold-rolled steel sheet containing one or more metals selected from Ni+Go+Cu+Mo and H in an amount of 0.001 to Q, 5 g/m2 is disclosed. In these cases, the metal deposited on the surface of the steel plate becomes the cathode or anode part.
The aim is to promote the precipitation of phosphate crystals as a result of increasing the reactivity of the steel plate surface. That is, it aims to increase the reactivity of the surface by utilizing the potential difference between the cathode site and the anode site, and on the other hand, to improve the crystal morphology of the precipitated phosphate crystals by regulating the distribution state of the cathode site and the anode site. It is.

[Problem to be solved by the invention]

However, in the conventional technique described in Japanese Patent Publication No. 56-43392 mentioned above, an effect was observed when applied immediately before phosphate treatment, but when applied to alkaline cleaning before annealing, a stable improvement effect was not achieved. I was not able to admit.

This is particularly noticeable when impurities such as rolling oil and iron are mixed into the plating solution.Moreover, when the processing solution is new, the metal or metal compound undergoes changes such as diffusion due to post-treatment annealing, making it difficult to use industrially. It was impossible to stably obtain phosphate treatability.

Also, JP-A-56-116883 and JP-A-561
The prior art of No. 16887 only states that the above-mentioned distribution state of the precipitated metal must be distributed discontinuously on the iron plate because it is necessary to form an anode part and a cathode part with respect to the iron of the steel. The range of adhesion amounts is very wide. Accordingly, when various experiments were actually attempted based on the prior art, the conditions under which the effect of improving phosphate treatability was observed were limited to a fairly narrow range. Moreover, steel sheets manufactured under conditions that provide excellent phosphate treatment properties tend to have surfaces that rust easily during storage. This is because the surface of the cold-rolled steel sheet to which metallic nickel has adhered has a very strong local cell effect of the precipitated metallic nickel, which not only affects the phosphating property but also affects the surface of the cold-rolled steel sheet during storage. It also acts on the oxidation of iron, that is, on the generation of surface rust, resulting in extremely poor corrosion resistance.

Therefore, an object of the present invention is to provide a cold-rolled steel sheet that solves the above-mentioned problems and exhibits excellent phosphate treatment properties and corrosion resistance.

[Means and effects for solving the problem] The present inventors:
By changing various plating conditions, especially nickel plating conditions,
We investigated the manufacturing conditions for cold-rolled steel sheets that exhibit stable phosphating properties and have sufficient corrosion resistance. That is,
The relationship between surface conditions such as the amount, distribution, and composition of nickel coating the surface of cold-rolled steel sheets, phosphate treatability, and corrosion resistance was investigated. As a result, when nickel and nickel oxide, which are metals more harmful than iron, precipitate on the surface of the steel sheet, the precipitation rate and crystal morphology of phosphate crystals change depending on the particle size and distribution of nickel and nickel oxide, which are the cathode sites. It was found that the uniformity of phosphate crystals was strongly influenced by the amount of adhesion and the distribution density. Furthermore, cold-rolled steel sheets made of metallic nickel and a nickel oxide film have better not only surface corrosion resistance but also better crystal morphology of phosphate crystals than cold-rolled steel sheets made of metallic nickel only. We also obtained the following knowledge.

This invention was made based on two consecutive findings, and it is found that the surface of a cold rolled steel sheet has a nickel particle density of 1 x 1012 to 5 XIO' particles per IM, and a total nickel content of 1 to 50 ■/Po nickel plating film is formed, the nickel particles are composed of metallic nickel and non-metallic nickel with a thickness of 0,0009~Q,Q3J!In attached to the surface layer, and the nickel particles The diameter of
．． 0.001 to 0.3 pm.

Next, the cold rolled steel sheet of the present invention will be explained with reference to the drawings.

FIG. 1 is a transmission electron micrograph of a steel sheet showing nickel particles on the cold-rolled steel sheet of the present invention, and FIG. 2 is an ESCA (Electron 5pectros
copyfor Chemical Analysis
) is a graph showing the results measured by.

As shown in FIG. 1, nickel particles are observed in the form of particles, and uniformly cover the surface of the steel sheet, albeit discontinuously. Moreover, this nickel particle is ES shown in Figure 2.
As can be seen from the CA results, the surface layer is made of non-metallic nickel and the inner layer is made of metallic nickel. To explain in more detail, the outermost layer of nonmetallic nickel is nickel oxide, and the inner layer is made up of nickel oxide.

The reason why the total amount of nickel in the nickel particles consisting of metallic nickel and non-metallic nickel was limited to a range of 1 to 50 mg/rrf is as follows. If the total amount of nickel in the nickel particles is less than 1 nickel/po, the number of nickel particles of 1 x 10'2 per 1M will not be secured, and the role as a cathode will be insufficient on the steel plate surface, resulting in poor phosphate treatment. You won't be able to have sex.

On the other hand, if the total amount of nickel in the nickel particles exceeds 50 mg/%, even if the diameter of the nickel particles is increased, the surface of the steel sheet will be almost completely covered with nickel, so the entire surface of the steel sheet will become a cathode site, making it difficult to Phosphate treatment properties cannot be obtained.

The amount of nonmetallic nickel on the surface of nickel particles is 0.0009~
The reason why the thickness was limited to 0.03 μm is as follows.

If the amount of nonmetallic nickel in the nickel particles is less than 0.0009, the nonmetallic nickel layer becomes too thin, and the local battery effect between metallic nickel and the iron of the plate is extremely strong, resulting in poor phosphate treatment. In addition to this, it also acts on the oxidation of iron on the surface of cold-rolled steel sheets during storage, that is, on the generation of surface rust, resulting in extremely poor corrosion resistance. On the other hand, the amount of nonmetallic nickel is Q, Q3. If Bm is exceeded, even if the nickel oxide has semiconducting properties, the effect of the local battery between the metal nickel and the iron of the steel sheet will be weakened, and good phosphate treatment properties will not be obtained. Also, although the cause is unknown,
As the amount of nonmetallic nickel increases, the workability of cold-rolled steel sheets tends to deteriorate.

Next, the reason for limiting the diameter of the nickel particles and the density of the particles will be described below.

The size and density of nickel particles are determined by the surface condition of the cold-rolled steel sheet before Ni-Nkel plating, such as the composition and amount of oxide on the surface, the type of nickel plating solution, and the treatment time such as electrolysis time. However, outside of a limited diameter and particle density, phosphatability becomes significantly inferior. Therefore, the diameter of the nickel particles is between 0.001 and 0.001.
It was limited to a range of 3 μm. In particular, when the density of nickel particles is less than 1 x 10'2, the effect of the local battery between the nickel particles at the cathode and the iron of the steel plate at the anode becomes weak, resulting in the growth of dense phosphate crystals. will no longer be recognized. On the other hand, if it exceeds 5 x 10'4, the occupancy of the anode site will decrease, suppressing the formation of phosphate crystals, causing unevenness in the film such as sagging (insufficient amount of adhesion), and the growth of dense crystals. It will no longer be recognized.

Next, an example of a method for attaching nickel particles will be described.

The material used is a cold-rolled strip of killed continuous cast aluminum material that is annealed on a continuous annealing line and then temper-rolled. It goes without saying that the present invention is applicable not only to those described here, but also to cold-rolled steel sheets in general that are widely used for automobiles and home appliances. Therefore, for example, when normal continuous annealing is performed, final cooling is performed in a reducing atmosphere, so nickel plating can be directly applied without plating pretreatment. In addition, when manufacturing cold-rolled steel sheets in which cooling is performed in an oxidizing atmosphere such as water-cooled hot water cooling or air-water cooling, cathodic electrolysis treatment in an acidic solution containing sulfuric acid or oxycarboxylic acid is performed as a pretreatment. After applying
Nickel plating can also be applied. Nickel plating can be applied using any of the known nickel plating methods, such as electroplating and displacement plating, but electroplating has smaller particle diameters and higher density, and is less efficient in high-speed productivity than displacement plating. It is advantageous in this respect.

Furthermore, an important factor of the present invention is that the nickel particles consist of metallic nickel and non-metallic nickel. For this purpose, after nickel plating, wash with water and immediately immerse or anodize in a weakly alkaline solution such as alkali phosphate or alkali carbonate, or after nickel plating, wash thoroughly with water and heat at a temperature of 90°C or higher. May be dried. Furthermore, in electroplating, the pH of the cathode interface during electrolysis is
Nickel plating may be carried out using a p++ plating solution to which a p++ control agent, such as nitrate ions or nitrates, is added to increase the p++ and precipitate hydrated oxides.

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

[Example 1] A cold rolled strip of killed aluminum cast material was annealed on a continuous annealing line and then temper rolled at a rolling reduction of 1% to a thickness of 1.0.
After degreasing and pickling a cold-rolled steel sheet of mrnl in the usual manner, nickel plating was performed under the conditions described below.

Bath composition: 120 g/E Ni
SO4・6 I+ 2020 g/l NtC
! 2.6H2015g/E IIJO3 pH: 3.1 Bath temperature: 50°C Current density: 3A/d Bo Treatment time: 0.3 sec Subsequently, after washing with water, 5g/! at 50°C. N a O
5A/drrf in a mixed aqueous solution of H and Na3PO4
After performing anodic electrolytic treatment, washing with water, and drying, the following tests were conducted, and the results are shown in Table 1.

The total amount of Nira gel deposited was measured by fluorescent X-ray method.

The amount of nonmetallic nickel was estimated using ESCA from the Ar sputtering time until the 2P, 7□ peak of NiO or N1(Oft)z disappeared.

The size and density of nickel particles were examined by transmission electron microscopy after nickel particles were extracted by extraction replica method.

Phosphate treatment properties were determined using a commercially available phosphate treatment solution (Bt3o:3oM, manufactured by Nippon Bariki Rising Co., Ltd.). The crystal size of each completed phosphate film was examined by scanning electron microscopy.

Corrosion resistance was determined by stacking plated cold-rolled steel sheets in a size of 15 x 15 cJ, sandwiching them between wooden boards and tightening them at a moderate temperature, and then leaving them in an atmosphere at a temperature of 30°C and relative humidity of 85% for one month.
Evaluation was made based on the state of rust occurrence.

Workability was determined by measuring the friction coefficient of the plated cold-rolled steel sheet using a conventional friction coefficient measuring method.

[Example 2] Same as Example 1 until nickel plating, after washing with water, 80%
It was immersed in a sodium phosphate degreaser (cL-342 manufactured by Nihon Pariki Rising Co., Ltd.) at a temperature of °C and washed with water.

After drying, the same test as in Example 1 was conducted, and the results were reported in the first example.
Shown in the table.

[Example 3] The cold-rolled steel sheet used in Example 1 was subjected to displacement nickel plating under the conditions described below, washed with water, and then heated and dried for 10 minutes in a dryer at a temperature of 100°C. A test was conducted and the results are shown in Table 1.

Plating bath composition: pH Bath temperature: Processing time: 60 g/E NiCf□・6H2040g/
NH,BO3 100g/l N11aGR 4,0 80℃ sec [Example 4] The cold rolled steel sheet used in Example 1 was nickel plated under the following conditions, washed with water, dried, and then subjected to the same test as Example 1. The results are shown in Table 1.

Plating bath composition: 60 g/f! , NiSO4・6II2010
g/N de ICp, ・6H2030g/N
Ntl a CR3g/I! HNO3 pH: 4.7 Current density: 5A/dirf Treatment time: 0.2 sec [Comparative Example 1] The same test as in Example 1 was conducted without nickel plating on the cold rolled steel sheet used in Example]. The results are shown in Table 1.

[Comparative Example 2] After nickel plating in Example I, the product was washed with water, dried, and immediately subjected to the same test as in Example 1. The results are shown in Table 1.

[Comparative Example 3] The cold rolled steel sheet used in Example 1 was subjected to normal degreasing and pickling, and then nickel plating was performed under the conditions described below. After washing with water and drying, the same test as in Example 1 was conducted, and the results are shown in Table 1.

Bath composition: pH: Bath temperature: Current density: Treatment time: 240 g/l N15O<・6 I+ 204
5 g / l N1 (J!z ・611203
0 8 / fi H, BO3 3,5 50°C 5 A/d po 0.3 sec As is clear from Table 1, the steel sheet of the present invention has excellent phosphate treatment properties, corrosion resistance, and workability, unlike the comparative example. It can be seen that it is excellent.

[Effects of the Invention] As explained above, according to the present invention, two useful effects can be obtained in the industry in which a cold rolled steel sheet having excellent phosphate treatment properties and corrosion resistance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a transmission electron micrograph of a steel sheet showing nickel particles on the cold-rolled steel sheet of the present invention, and FIG.
pyfor C1+emical Analysis)
It is a graph showing the results measured by.

Claims (1)

[Claims] 1 A nickel plating film with a total nickel content of 1 to 50 mg/m^2 on the surface of a cold-rolled steel sheet, with a density of nickel particles of 1 x 10^1^2 to 5 x 10^1^4 per 1 m^3. The nickel particles are composed of metallic nickel and non-metallic nickel with a thickness of 0.0009 to 0.03 μm attached to the surface layer thereof, and the diameter of the nickel particles is 0.001 to 0.03 μm. A cold-rolled steel sheet with excellent phosphate treatment properties and corrosion resistance, characterized by a thickness of .3 μm.