JPH04198492A - Organic composite coated steel sheet - Google Patents

Abstract

PURPOSE:To supply a coated sheet excellent in corrosion resistance by having a chromate film layer on a galvannealed steel sheet, having an organic resin layer on it and incorporating Fe and Al and especially a specified amount of Mg, Sn in the Zn plated film. CONSTITUTION:A steel sheet is dipped in the hot dip galvanizing bath having a specified bath composition to form a galvannealing. Fe in the plated film is 7-20wt.% for all film and the film prepared to be 0.05-0.8% Al, 0.1-1.2% Mg, 0.1-1.2% Sn and the balance is Zn and the inevitable impurity. But Al, Mg, Sn and the balance of Zn are a weight% based on that the total amount being omitted Fe in the film is 100. Next after a chromate film layer of 10-200mg/m<2> at Cr calculated amount is formed on the galvannealed sheet, the organic resin film layer is formed on it. The steel is excellent in corrosion resistance and it is fitted well to the corrosion resistant steel plate for car, building, houshold electric products, etc.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a surface-treated steel sheet with excellent corrosion resistance suitable for use in automobiles, building materials, and home appliances. This invention relates to a so-called organic composite coated steel sheet on which a chromate film layer and an organic resin film layer are disposed.

(Prior Art) Various types of surface-treated steel sheets are used in many industrial fields, including automobiles, and the amount thereof tends to increase year by year. Along with this, the required quality has also become more sophisticated. In particular, there is a demand for further improvement in rust prevention ability. This tendency is very strong in surface-treated steel sheets for automobiles used in North America, where snow-melting salt is sprayed to prevent roads from freezing in winter. There is a demand for anti-rust properties that can withstand corrosion over a long period of time.

Conventionally, surface-treated steel sheets such as electrogalvanized steel sheets, Ni-Zn electroalloy-plated steel sheets, Fe-Zn electroalloy-plated steel sheets, and hot-dip galvanized steel sheets have been used as measures to strengthen the rust prevention ability of automobile bodies. However, it is said that these surface-treated steel sheets have insufficient anti-corrosion ability despite their ``10-year guarantee against perforation''. Generally, these surface-treated steel sheets have a coating weight of 20 to 30 g/m.
However, it is said that the amount of plating deposited must be more than double that amount in order to satisfy the ``10-year guarantee against perforation''.

However, in the case of electroplated steel sheets, the manufacturing cost increases significantly as the coating weight increases, so it is extremely difficult to apply this method from a cost standpoint.

In addition, "porosity" refers to corrosion of the steel plate that progresses from paint defects, plating defects or scratches, or areas where the coating is insufficient, pitting corrosion occurs in the steel plate, and in some cases, penetrating corrosion occurs. This is a phenomenon.

For these reasons, in recent years, efforts have been made to improve rust prevention through the following two methods.

(a) A method for increasing the coating weight of hot-dip galvanized steel sheets, which has a relatively small cost limit due to an increase in coating weight, compared to electroplated steel sheets.

(b) A method of forming a composite coated steel sheet by disposing a chromate film layer and a thin resin film layer on a zinc or zinc alloy coated steel sheet.

Method (a) refers to hot-dip galvanized steel sheets, which are rarely used in automobiles as they are from the viewpoint of weldability, and are alloyed with a coating weight of 45 g/m. Since galvanized steel sheets are widely used, the amount of coating applied is increased to, for example, about 60 g/m'' per side in order to increase the rust prevention ability.

However, alloyed hot-dip galvanized steel sheets have traditionally been considered to be a material with many difficulties in press formability, and in fact,
There is a problem in which the plating film peels off from the steel sheet during press forming, which is called flaking or powdering. This problem becomes more serious as the amount of plating increases, leading to more troubles in the molding process than in the past. Furthermore, there is also the problem that increasing the thickness reduces spot weldability.

In method (b), the base plated steel sheet has a coating weight of 20 to 30, which is generally said to have good corrosion resistance.
g/m2 Ni-Zn electroalloy plated steel sheet is used and exhibits generally good corrosion resistance.

However, since the underlying old-Zn alloy plating layer has poor sacrificial anticorrosion ability, there is a problem in that the corrosion resistance is particularly poor at the end faces. This problem can be improved by increasing the amount of plating deposited, but as described above, in the case of a single electroplated copper plate, there is a problem that the cost increases as the amount of plating increases.

In method (b), an alloyed hot-dip galvanized steel sheet that is relatively inexpensive and has sacrificial anticorrosion ability may be used as the base plated steel sheet, but in the case of an alloyed hot-dip galvanized steel sheet, - The reality is that the excellent corrosion resistance of the old Zn alloy plated steel sheet is not exhibited. Also, AF! disclosed in Japanese Patent Application Laid-open No. 63-48945! ,
Although alloyed hot-dip galvanized steel sheets to which Mn and Mg are added have somewhat better corrosion resistance than conventional alloyed hot-dip galvanized steel sheets, their performance is not fully satisfactory.

(Problem to be Solved by the Invention) The object of the present invention is to provide a surface that does not have the above-mentioned problems, that is, has characteristics that are sufficiently satisfactory from a comprehensive standpoint, such as sacrificial corrosion resistance of the end face, corrosion resistance, formability, and economic efficiency. Our goal is to provide treated steel sheets.

(Means for Solving the Problems) In order to solve the above problems, the present inventors have made repeated studies and have first developed an organic composite coated steel sheet using an alloyed hot-dip galvanized steel sheet as a base steel sheet. (filed on October 12, 2013). This steel plate contains 7 to 20% by weight of Fe and a small amount of 8! and Mg, or even Mn.

It has a chromate film layer and an organic resin film layer on an alloyed hot-dip galvanized steel sheet containing St, and has excellent properties in various aspects such as corrosion resistance, formability, and economic efficiency.

Therefore, the present inventors further investigated an organic composite coated steel sheet using an alloyed hot-dip galvanized steel sheet as a base steel sheet, and found that Mg and Sn were added in combination to the galvanized film of the base galvanized steel sheet. It has been found that the corrosion resistance of organic composite coated steel sheets is significantly improved.

The present invention has been made based on the above findings, and its gist lies in the following organic composite coated steel sheets.

■ On top of the alloyed hot-dip galvanized steel sheet, 1
The alloyed hot-dip galvanized steel sheet has a chromate film layer of 0 to 200 mg/m2 and an organic resin film layer thereon, and the Pe content in the plating film of the alloyed hot-dip galvanized steel sheet is 7 to 20% by weight.
An organic composite coated steel sheet in which the other components except e are as follows.

8f: 0.05~0.8% by weight Mg: 0.1~
1.2% by weight Sn 20, 1 to 1.2% by weight Zn and unavoidable impurities: Remaining ■ The organic resin film layer contains 5 to 30% by weight metal-based particles. The organic composite coated steel sheet described above.

■ Second, the Fe concentration of the alloyed hot-dip galvanized steel sheet is 50.
% by weight or more and has an iron-based plating film layer with an adhesion amount of I~log/m'', and on top of this an iron-based plating film layer with an amount of 10 to 200 mg in terms of Cr.
/m'' chromate film layer, and further has an organic resin film layer thereon, Fe in the plating film of the alloyed hot-dip galvanized steel sheet is 7 to 20% by weight, and other than this Fe An organic composite coated steel sheet whose components are as follows.

8N: 0.05-0.8% by weight Mg: 0.
1 to 1.2% by weight Sn: 0.1 to 1.2% by weight Zn and unavoidable impurities: Remaining (■) The organic resin film layer contains 5 to 30% by weight of nonmetallic particles. The organic composite coated steel sheet described above.

(effect) The present invention will be explained in detail below.

The organic composite coated steel sheet of the present invention uses an alloyed hot-dip galvanized steel sheet that is relatively inexpensive and has excellent end face corrosion resistance as a base plated steel sheet. The reason why the coating composition of this plated steel sheet is limited as described above is as follows.

In the present invention, Fe in the plating film, F at the boundary between the steel sheet and the plating film during alloying treatment after hot-dip plating.
F flows into the coating from the steel plate due to mutual diffusion of e and Zn.
It is e. If this Fe content is less than 7% by weight, the weldability and corrosion resistance (especially corrosion resistance after coating) will be poor, and if it exceeds 20% by weight, the corrosion resistance at the notch or end face after coating will be significantly deteriorated, so the plating film The content of Fe therein was 7 to 20% by weight.

A in the plating film! ^l added to the plating bath is transferred to the film r1]. Af in plating film
If the bath composition has an i content of less than 0.05% by weight, the reaction between the steel plate and the plating bath will be intense, the amount of bottom dross generated will increase, the operability will be reduced, and the processability of the plating film (
The powdering resistance of the alloyed material also decreases. Also,
Eight in the plating film! If Mg exceeds 0.8% by weight, the alloying rate decreases, and the uniformity of the surface properties of the plating film in which Mg and Sn coexist is impaired, so the upper limit is set to 0.8% by weight. In addition, since 8L is enriched in the plating film during plating, in order to obtain a plating film with a 2 content of 0.05 to 0.8% by weight, 0.03 to 0.35% of the weight is usually required. A plating bath containing 1 is used.

Mg is an element that has the effect of improving the corrosion resistance of the plating film, but if it is less than 0.1% by weight, the corrosion resistance is poor.

On the other hand, in a bath composition in which Mg in the plating film exceeds 1.2% by weight, the oxidation reaction of Mg in the bath becomes intense, and the AN content in the plating film becomes 0.8% by weight or less as described above. It's like taking a bath! Addition (for example, An content in the bath of 0.35% by weight) cannot suppress this oxidation reaction, making it difficult to ensure normal bath characteristics. Therefore, the Mg content in the plating film is 0.1 to 1.
It was bound at 2% by weight.

When Sn is contained in the plating film in combination with Mg, it very effectively affects the corrosion resistance of the organic composite coated steel sheet based on the alloyed hot-dip galvanized steel sheet.

However, if it is less than 0.1%, it will not have much of an effect on improving corrosion resistance, and if it exceeds 1.2%, it will adversely affect corrosion resistance.

In other words, this plating film hardly improves the corrosion resistance of the alloyed hot-dip galvanized steel sheet without coating with organic resin, but rather, the coexistence of Sn improves the corrosion resistance of the alloyed hot-dip galvanized steel sheet. However, corrosion resistance is developed by forming an organic composite. The effect of this Sn is 0.1% by weight as mentioned above.
If it is less than 1.2% by weight, it is not very large, whereas if it exceeds 1.2% by weight, it will adversely affect the corrosion resistance, so the Sn content in the plating film was set to 0.1 to 1.2% by weight.

In addition, "%" of the above components refers to the "weight percentage J" of the entire coating of the alloyed plated steel sheet, and A
2. Regarding Mg, Sn, and the remaining Zn, the weight percentages are based on 100 excluding Fe in the film.

The alloyed hot-dip galvanized steel sheet having the above-mentioned plating film composition is A! Usually 0.03 to 0.35% by weight,
A plating bath with a composition consisting of 0.1 to 1.2% by weight of Mg, 0.1 to 1.2% by weight of Sn, and the remainder Zn and unavoidable impurities is used, and the steel plate after pretreatment is immersed in this plating bath. After plating, adjust the amount of adhesion, and then
It is obtained by alloying at a temperature of 00°C so that the Fe content in the film is 7 to 20% by weight.

The organic composite coated steel sheets of (1) and (2) are those in which a chromate film layer and an organic resin film layer are arranged on the second side of this alloyed hot-dip galvanized steel sheet. The above-mentioned organic composite coated steel sheets (1) and (2) have an iron-based plating film layer interposed in the middle.

The chromate film may be formed by a coating method, a reaction method, or an electrolytic method.
The converted amount is preferably 10 to 200 mg/m''.

If it is less than 10 mg/m2, corrosion resistance is insufficient and the surface of the underlying alloyed galvanized steel sheet cannot be uniformly covered. If it exceeds 200 mg/m'', the workability of Cr is poor, so the plating film tends to peel off during processing, and weldability also deteriorates.

The organic resin film to be applied on the chromate film may be any film as long as it has good adhesion to the chromate film layer and can form a uniform elastic film on the surface.

For example, epoxy resin, acrylic resin, polyester resin, melamine resin, alkyd resin, polyhydroxy polyether resin, etc. can be used. These resins are applied onto the chromate film by a roll coater method, a spray method, a brushing method, or the like. The coating thickness is preferably about 0.2 to 3 μm.

If this organic resin film contains one or more types of nonmetallic particles such as silica, titania, magnesia, molybdenum oxide, antimony oxide, tungsten oxide, iron phosphide, and poorly soluble chromium compounds, the organic The corrosion resistance of the composite coated steel sheet is further improved.

Among these, silica has the greatest effect.

The above-mentioned inventions (1) and (2) are inventions in which a film layer containing non-metallic particles as described above is used as the organic resin film layer of the organic composite coated steel sheet of the inventions (1) and (2), respectively.

When these nonmetallic particles are contained in the resin film layer, they are contained in an amount of 5 to 30% by weight of the entire solidified organic resin film. If it is less than 5% by weight, no effect of improving corrosion resistance can be obtained, and there is almost no difference from that containing no nonmetallic particles.

Even if the content exceeds 30% by weight, the effect of improving corrosion resistance is saturated and spot weldability deteriorates.

In the inventions of (1) and (2), the Fe-based plating film layer (hereinafter referred to as the upper plating layer) interposed between the alloyed hot-dip galvanized steel sheet and the chromate film layer mainly has the effect of reducing the coefficient of friction and improves formability. Contribute to the improvement of Fe-based plating includes pe-Zn, Fe-Ni, Fe-
Although various platings such as Mn, Fe-P, and Pe-B are used in practice, any plating film may be used as long as the Fe concentration in the plating film is 50% by weight or more. If the Pe concentration in the plating film is less than 50% by weight, the effect of reducing the coefficient of friction will be small. The adhesion amount of Pe-based plating is 1 g/m
If it is less than 2, the effect of reducing the friction coefficient is insufficient;
/m2 rather leads to a decrease in corrosion resistance.

Note that the two-layer plating layer is not limited to Fe-based, for example, 1
It may also be a former Zn plating layer containing 2% by weight or more of Ni.

(Example) In weight%, C: 0.002%, Si: 0.01%
, Mn: 0.25%, P 70.011%, S: 0
．． 012%, So 1 , Al: 0.025%,
Ultra-low carbon-IF steel containing Nb: 0.08% and Ti: 0.036% (Interstitial
A test material with a width of 100 mm and a length of 250 mm was cut out from an unannealed material (thickness: 0.8 mm) of Free Steel).
After aqueous solvent cleaning and electrolytic cleaning in a NazCO3+Na0II aqueous solution, hot-dip plating was performed using a hot-dip plating simulator.

For hot-dip plating, the sample after cleaning is subjected to reduction annealing at a temperature of 850°C for 60 seconds in an atmosphere of 25% H20 Nz, and then immersed in a hot-dip galvanizing bath having a predetermined bath composition. This was done by adjusting the adhesion amount to 50 to 60 g/m2, and then alloying the test material after plating at a temperature of 500°C. For some test materials, a 2% Na0II aqueous solution (75 °C) for 10 seconds, and P
e-Zn-based and Fe-layer electroplating (upper layer plating) was performed.

[Fe-Zn electroplating] Anode: Pb Bath composition: FeSO4.71+20; 60-120
g/lZnSO4・711go; 0~40g/
lNa2SO4; 75 g/(! [Fe"] = 2800 ppm, pH = 1.8. Temperature 50°C (however, the amounts of FeSO4 and ZnSO4 added were varied within the above range in order to change the plating film composition. ) Liquid flow rate: 0.66 m/s Current density: 658/dm" [Pe-Ni plating] Anode: Pb Bath composition: FeSO4'711zO; 360 g/
1NiS04・7+1゜0; 40~80g/lNa
2SO4; 75g/1 [Fe”] = 150ppm, pH = 1.9. Temperature 5
0°C (However, the amount of NiSO4 added was varied within the range indicated in "-" in order to change the plating film composition.) Liquid flow rate: 1 m/s Current density: 65 A/dm" - Upper layer plating in h A chromate film layer and an organic resin film layer were formed under the following conditions on the test material subjected to the above treatment and the test material only subjected to the alloying treatment.

[Formation conditions of chromate film layer]

Fine Cleaner 433 manufactured by Nippon Barker Rising Co., Ltd.
After washing the sample material in Step 6, reducing the Cr (h: 120 g/1 solution with ethylene glycol, diluting it by adding a chromic acid aqueous solution and adjusting the ratio of Cr''/total Cr), add it to the chromate film layer solution. Colloidal silica 40g7N, glycerin 11.5g, #!, citric acid 6.5g/1., γ-
Glycidoxypropyltrimethoxysilane 15g/l
, and apply the suspension with a bar coater.

After application, bake at a temperature of 140″C for 30 seconds.

[Formation conditions of organic resin film layer]

Solid resin content: Powdered polyhydroxy polyether resin (
Union Carbide Co., Ltd. PK +11+)...20% by weight inorganic filler:
Uses cross-linking materials, plasticizers, conductive pigments and anti-corrosion pigments.

Non-metal particles: Uses colloidal silica.

Add a predetermined amount of inorganic filler to the resin liquid, or add a predetermined amount of inorganic filler and metal particles, stir and disperse, and then apply with a bar coater.

After application, bake at a temperature of 130°C.

The organic composite coated steel sheet thus obtained (organic resin film layer thickness: 1.2 μm) was subjected to the following electrodeposition coating, and then subjected to a corrosion test.

[Electrodeposition coating]

Paint: Cationic electrodeposition paint I+-80 (manufactured by Nippon Paint ■) Voltage: 200 V, electrodeposition time: 3 minutes Baking: 30 minutes at 180°C Film thickness: 20 μm In the corrosion test, there were 1 to 1 cross cuts on the electrodeposition coating surface. After making the scratches, drying and wetting were repeated 60 times under the following conditions, the perforation depth of the cut portion was measured, and the corrosion resistance was evaluated based on the maximum depth.

[Corrosion test] Immersion in saline solution (5% NaCff1, 25°C, 0.25 hours) → Dry (25”C, 1.25 hours) → Wet (60°
C9 relative humidity 95% or more.

22.5 hours) as one cycle.

On the other hand, an organic composite-coated steel sheet without electrodeposition coating was subjected to molding with changing the blank hold pressure to determine the friction coefficient.

These results are shown in Table 1. The table also lists the composition and coating weight of the alloyed hot-dip galvanized film, the coating weight and Fe content of the upper plating layer, the coating weight of Cr, and the content of nonmetallic particles (colloidal silica).

As is clear from Table 1, the organic composite coated steel sheet of the present invention exhibits good corrosion resistance with a corrosion depth of 0.16 mm or less.

In addition, No. 14 to No. 17, which were subjected to upper layer plating.

19 and 20, No. 28 to 33 organic composite coated steel sheets are No. 8 to 12, No. 22, N without upper layer plating.
The coefficient of friction was smaller than that of O, 24, N026 and 27.

On the other hand, steel plates No. 1 to 4 (which also do not have a chromate film layer) and No. 34 to 36, which do not contain Mg or Sn in the plating film, have a high Pe content in the plating film. Too much N023, same <Sn content too high N
025, even if the plating film composition is within the range defined by the present invention, it does not have a chromate film layer, or even if it does have a C
The steel plates of No. 005 to 7, which had a small amount of r coating, and No. and I8, which had an upper layer coating amount that exceeded the range of the present invention, had a large corrosion depth and had poor corrosion resistance. In addition, No. 21, in which the Fe concentration in the upper plating film is outside the range defined by the present invention,
The steel plate had a large friction coefficient for a system with an upper plating layer, and no effect of the upper plating layer was observed.

Note that the steel plate N013 in which the silica content in the organic resin film exceeds the range of the present invention had good corrosion resistance and friction coefficient, but poor weldability.

(Hereinafter, blank spaces) (Effects of the Invention) The organic composite coated steel sheet of the present invention has excellent corrosion resistance, and is most suitable as a rust-proof steel sheet in industrial fields such as automobiles, architecture, and home appliances. Furthermore, since this organic composite coated steel sheet uses an alloyed hot-dip plated steel sheet as the base plated steel sheet, it has the advantage of being inexpensive.

Claims (4)

[Claims] (1) Having a chromate film layer of 10 to 200 mg/m^2 in terms of Cr on the alloyed hot-dip galvanized steel sheet,
An organic composite coated steel sheet having an organic resin film layer thereon, wherein Fe in the plating film of the alloyed hot-dip galvanized steel sheet is 7 to 20% by weight, and other components other than Fe are as follows. Al: 0.05-0.8% by weight Mg: 0.1-1.2% by weight Sn: 0.1-1.2% by weight Zn and inevitable impurities: Remaining (2) The organic composite coated steel sheet according to claim (1), wherein the organic resin film layer contains 5 to 30% by weight of nonmetallic particles. (3) Fe concentration 50 on top of alloyed hot-dip galvanized steel sheet
% by weight or more and has an iron-based plating film layer with a coating amount of 1 to 10 g/m^2, and on top of this, 10 to 200 m of Cr equivalent amount.
The alloyed galvanized steel sheet has a chromate film layer of 7 to 20% by weight, and has an organic resin film layer thereon. An organic composite coated steel sheet having the following components except for: Al: 0.05 to 0.8% by weight Mg: 0.1 to 1.2% by weight Sn: 0.1 to 1.2% by weight Zn and Unavoidable impurities: remainder (4) The organic composite coated steel sheet according to claim (3), wherein the organic resin film layer contains 5 to 30% by weight of nonmetallic particles.