JPH07278794A - Automobile high strength zn-ti plated steel sheet - Google Patents

Abstract

PURPOSE:To produce an automobile high strength Zn-Ti plated steel sheet excellent in surface appearance, corrosion resistance and workability. CONSTITUTION:This automobile high strength Zn-Ti plated steel sheet is the one in which, on the surface of a steel sheet contg., by weight, <=0.02% C, <=1.0% Sr, 0.1 to 1.0% Mn, 0.02 to 0.2% P, <=0.01 N, <=0.10% Al and Ti alone or the combination of Ti and Nb by <=0.1% in total, a Zn Ti allay plated layer contg. 3 to 60% Ti, and the balance Zn is formed by 1 to 60g/m<2>. The substrate of the Zn-Ti plated layer may be applied with Ni preplating treatment by 0.05 to 3g/m<2> and the upper layer of the Zn-Ti plated layer with galvanizing by 0.1 to 10g/m<2>.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a high strength Z which is required to have excellent surface appearance and corrosion resistance like automobile steel sheets.
It relates to an n-based plated steel sheet.

[0002]

2. Description of the Related Art Zn plating has hitherto been considered to be the most economical and effective method for preventing corrosion of steel products in the atmosphere.

In recent years, the requirements for rust prevention have become more stringent, and alloying hot-dip galvanizing, Zn--Ni electroplating, and Zn having already improved corrosion resistance
-Various Zn alloy plated steel sheets such as Fe electroplating are disclosed.

Further, when these Zn alloy-plated steel sheets are applied to automobile bodies, high press formability is required. Therefore, ultra-low carbon steel to which Nb, Ti, etc. are added is used as a plating original sheet.

Further, in order to reduce the weight of the automobile body,
Higher strength is sought by adding P, Mn and the like.

[0006]

However, the ultra-low carbon steel sheet to which Ti or Ti and Nb are added is a so-called difficult plating material, and non-plating or poor alloying occurs after galvannealing, resulting in surface appearance quality. Is significantly impaired and causes a drop in yield.

Further, the addition of P, Mn and the like to the original plating plate for enhancing the strength further amplifies this tendency.

[0008] Although electroplated steel sheets such as Zn-Ni do not have the problem of galvannealing, they cannot secure sufficient corrosion resistance due to the light weight, and the cost becomes higher if the weight is increased. I have a problem.

The present invention has excellent corrosion resistance and excellent surface appearance by using as a base material a high-strength ultra-low carbon steel sheet obtained by further adding P, Mn, etc. to the above-mentioned ultra-low carbon steel sheet which is said to be difficult to plate. A high-strength steel sheet for automobiles is provided.

[0010]

The first of the present invention, which has solved the above-mentioned problems, is C: 0.02 wt% or less, Si: 1.0 w.
t% or less, Mn: 0.1 to 1.0 wt%, P: 0.02
.About.0.2 wt%, N: 0.01 wt% or less, Al: 0.
3-60w on the surface of a steel sheet containing 10 wt% or less and Ti alone or 0.1 wt% or less in total of Ti and Nb.
High-strength Zn for automobiles in which a Zn—Ti alloy plating layer containing t% Ti and the balance Zn is formed in an amount of 1 to 60 g / m ²
-Ti-plated steel sheet.

In a second aspect of the present invention, in the above Zn—Ti plated steel sheet, N is used as a base of the Zn—Ti plated layer.
A high-strength Zn-Ti-plated steel sheet for automobiles, characterized by being subjected to i pre-plating treatment in an amount of 0.05 to 3 g / m ² .

A third aspect of the present invention is characterized in that, in the Zn—Ti plated steel sheet according to the first or second aspect of the invention, Zn plating is applied to the upper layer of the Zn—Ti plated layer in an amount of 0.1 to 10 g / m ^2. It is a high strength Zn-Ti plated steel sheet for automobiles.

[0013]

In order to solve the above-mentioned problems, a search has been made for a plating species that does not impair the appearance of the plating surface and a plating species that has corrosion resistance that can withstand use as a steel sheet for automobiles. The inventors have found that Ti plating is optimal for solving problems, and completed the present invention.

The details will be described below.

First, the inventors have noted that electroplated steel sheets such as Zn-Ni plating have a satisfactory surface appearance, although their corrosion resistance is insufficient.

That is, a galvanized steel sheet having a beautiful surface appearance can be produced even with an extremely low carbon steel or a high strength steel sheet as long as it does not involve a chemical reaction with the base steel sheet as in hot dipping.

However, it is difficult to produce an alloy of metals having different deposition potentials from an aqueous solution when producing an electroplated steel sheet, and it is difficult to obtain high corrosion resistance because the plating species are limited. Also, thickening the weight by electroplating is costly and not practical.

Therefore, the present inventors have paid attention to the vapor phase plating method, which has less chemical reaction with the base steel sheet when forming the film, as compared with the hot dip coating, and proceeded to study the plating species.
It was found that the plating did not react with the base steel sheet and had excellent corrosion resistance.

Zn-Ti plating is mainly prepared by a vacuum deposition method, an ion plating method, and a sputtering method. Zn and Ti react with each other when forming a film to form an amorphous alloy or an intermetallic compound, and a base steel sheet. There is no reaction with
It is a very small amount. That is, there is no reaction with the base steel sheet that affects the surface appearance.

In addition, from the study results of Zn-Ti plating,
It was found that the Ti concentration should be ³ to 60 wt% and the basis weight should be 1 to 60 g / m ² .

If the Ti concentration is less than 3 wt%, the effect of adding Ti is not seen and the corrosion resistance is insufficient.
The potential of n-Ti becomes nobler than that of the base steel sheet, and the sacrificial anticorrosion effect is lost.

If the basis weight is less than 1 g / m ² , corrosion resistance to the base steel sheet is insufficient, and if it exceeds 60 g / m ² , the plating peels off during processing, so-called powdering phenomenon occurs, which is not preferable as a plated product. Range 1-6
It is defined as 0 g / m ² .

Further, 0.0 is used as a base for Zn-Ti plating.
By applying a Ni pre-plating treatment of 5 to ³ g / m ² , strong adhesion can be imparted.

The lower limit of the Ni pre-plating should be 0.05 g / m ² , although it is sufficient if the Ni pre-plating is attached. Upper limit, be deposited beyond the 3 g / m ^2, since its performance comes saturated, the upper limit was set to 3 g / m ^2.

In addition, the upper layer of Zn--Ti plating is
The upper layer Zn plating of 10 g / m ² can be applied to improve the chemical conversion treatability.

The Zn adhesion amount was set to 0.1 to 10 g / m ² as an amount capable of sufficient reaction with the chemical conversion treatment liquid.

By performing the above-mentioned Ni pre-plating treatment as the base and the upper Zn plating at the same time,
A Zn-Ti plated steel sheet with high performance is obtained overall.

Next, the base material components of the high-strength ultra-low carbon steel sheet on which the Zn--Ti plating is applied will be described.

C is preferably as low as 0.02 wt% or less because it is more preferable from the viewpoint of deep drawability and ductility. 0.0020 wt% for extremely severe deep drawing and overhang forming
The following is preferable, and 0.0010 wt% or less is optimal.

Si is effective as an element for strengthening the steel sheet, but if it is too much, the plating peeling and workability are deteriorated, so the content is made 1.0 wt% or less. When added as a strengthening element, 0.1 to 0.6 wt% is preferable.

Mn also has the function of strengthening the steel sheet, but has a lower strengthening function than other strengthening elements, and even if added in a large amount, plating peeling and workability are significantly impaired rather than the strengthening function. It is set to 0.0 wt% or less.

On the other hand, from the viewpoint of securing the function of Mn, 0.1w
t% or more. 0.3 to 0.7 wt% as a strengthening element
It is preferable to add in the range of%.

P is an element having the highest strengthening function and is positively applied for strengthening. However, if it is too much, notable plating peeling occurs and brittle cracking occurs remarkably at low temperature, so P is 0.2 wt% or less. To do.

On the other hand, the lower limit is 0.02 wt% in order to exert the strengthening function of P. As a strengthening element 0.03-
It is preferable to appropriately select the addition amount according to the required strength within the range of 0.12 wt%.

If N exists in a solid solution state, it ages and deteriorates workability, so it is necessary to fix it as a nitride by Ti, Nb, or Al described later.

Therefore, if the amount of N is too large, a large amount of the nitride-forming element required for fixing is required, so N is 0.01 w.
t% or less.

Since N is preferably as small as possible,
0.0050 wt% or less, further 0.0020 wt%
It is preferable if the following can be done.

Al is added for deoxidizing the steel, but 0.10 wt% or less is sufficient for that purpose.

Ti has C and N fixed and deep drawability and ductility,
It is an element necessary to secure non-aging property.

In order to obtain these functions, it is desirable to add Ti which is stoichiometrically equivalent to C or N.
However, if it is too much, the plating peeling will occur remarkably, so the content is made 0.1 wt% or less.

Nb is also an element having the same function as Ti, and it is effective to add Nb in combination.

The amount of addition is the same as Ti alone and N
The total of b is 0.1 wt% or less.

[0043]

EXAMPLES The present invention will be described in more detail below with reference to examples.

Various cold-rolled base steel sheets having a plate thickness of 0.7 mm shown in Table 1 were subjected to Zn--Ti alloy plating by vacuum deposition or ion plating. Table 2 shows the prepared Zn-Ti plated steel sheet.

The performance of the various Zn-Ti plated steel sheets obtained was evaluated by the following methods.

1) The surface appearance was visually judged. The case where even a slight pattern due to non-plating or poor alloying was observed was marked with X, and the case where no pattern was observed was marked with ◯.

2) Plating adhesion was evaluated by a tape peeling test after bending. 18 so that the plated surface is on the inside
Bending was performed at 0 degree (adhesive tape was previously attached to the bent portion), and a tape peeling test was performed.

No peeling of the plating was marked with ⊚, peeling width of less than 1 mm was marked with ◯, peeling width of 1 mm or more and less than 3 mm was marked with Δ, and peeling width of 3 mm or more was marked with x.

3) Bare corrosion resistance is determined by salt spray test (JIS
According to Z 2371), the time until the occurrence of initial red rust was measured, and 1000 hours or more was regarded as good.

4) The chemical conversion treatment is B manufactured by Nippon Parker Co., Ltd.
It was dipped at t3080 (trade name) at 45 ° C. for 3 minutes and dried.

5) The corrosion resistance after coating was evaluated using a test piece that had been subjected to dip-type phosphate treatment and cationic electrodeposition coating. Phosphate treatment was carried out with Bt3080 manufactured by Nippon Parker Co., Ltd., and standard cold-rolled steel sheet with a coating amount of 2.5 to 3.0 g / m ² and a P treatment ratio of 85% or more.

For the electrodeposition coating, Nippon Paint's cationic type electrodeposition coating U-80 was used, and the film thickness after baking was 20 μm.
It was adjusted to be m.

For the post-painting corrosion resistance test, a cross-cut (5 cm × 5 cm) reaching the base material was put in this test piece, and a salt spray test (in accordance with JIS Z 2371) was conducted.
The swelling width of the coating film on the cut portion after the time lapse was measured. When the swelling width of the coating film was less than 3 mm, the corrosion resistance after coating was judged to be good.

Table 2 shows the performance evaluation results of surface appearance, corrosion resistance, chemical conversion treatment property, and adhesion. It can be seen that the Zn-Ti plating configured as in the present invention exhibits excellent performance.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

EFFECTS OF THE INVENTION By adopting the constitution of the present invention, even if an extremely low carbon steel sheet containing a large amount of P, Mn, etc. is applied as a base material, it has excellent surface appearance, corrosion resistance, and excellent plating adhesion. It is possible to obtain a high strength Zn-Ti plated steel sheet for automobiles, which is capable of imparting the properties and chemical conversion treatability.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location C22C 38/14

Claims (3)

[Claims] 1. C: 0.02 wt% or less, Si: 1.0
wt% or less, Mn: 0.1 to 1.0 wt%, P: 0.0
2 to 0.2 wt%, N: 0.01 wt% or less, Al:
3 to 6 on the surface of a steel sheet containing 0.10 wt% or less and Ti alone or 0.1 wt% or less in total of Ti and Nb.
A high-strength Zn-Ti plated steel sheet for automobiles, wherein a Zn-Ti alloy plated layer containing 0 wt% Ti and the balance Zn is formed in an amount of 1 to 60 g / m ² . 2. N as a base of the Zn—Ti alloy plating layer
The high-strength Zn-Ti-plated steel sheet for automobiles according to claim 1, wherein the i-pre-plating treatment is performed at 0.05 to 3 g / m ² . 3. The high-strength Zn—Ti plated steel sheet for automobiles according to claim 1 or 2, wherein Zn plating is applied on the upper layer of the Zn—Ti alloy plated layer in an amount of 0.1 to 10 g / m ² .