JPH05125485A - High-tension galvannealed steel sheet having excellent plating adhesion and production thereof - Google Patents

Abstract

PURPOSE:To provide the high-tension galvannealed steel sheet having excellent plating adhesion. CONSTITUTION:The steel sheet contains 0.01 to 0.3% C, 1.5 to 3.0% Mn, <=0.15% Si, <=0.1% P, and 0.01 to 0.1% Al, satisfies a relation Mn/Si>=3.0, contains, if necessary, one or >=2 kinds of <=1.0% Mo, <=0.01% B, <=0.1% Ti, <=0.1% Nb, <=0.1% Zr, <=1.0% Cr, <=1.0% Cu, <=1.0% Ni, <=0.1% V, and <=0.1% W, and consists of the balance Fe and unavoidable impurities. This steel sheet is produced by passing a plating bath at 400 to 460 deg.C bath temp. at the time of subjecting the steel consisting of the above-mentioned chemical components to hot rolling or cold rolling after the hot rolling, then passing the steel through a galvanizing line. The steel sheet is suitable for an ultra-high strength material, such as steel sheet for bumper members and door guard bars of automobiles for which high workability is needed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an alloyed high-strength hot-dip galvanized steel sheet excellent in plating adhesion suitable for ultra-high strength materials such as automobile bar bar members and steel sheets for door guard bars which require high workability. The present invention relates to a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, demands for weight reduction, safety and corrosion resistance of automobiles have increased, and galvanized steel sheets having higher strength than ever have been used. Since increasing the strength of this steel plate deteriorates workability, various measures for preventing workability deterioration have been attempted. For example, Japanese Patent Publication No. 62-4
No. 0405 and the like are intended to obtain strength and workability by a ferrite / martensite two-phase structure.

On the other hand, in hot-dip galvanized high-strength steel sheets, various workability improvements have been studied in association with higher strength. Si added in order to obtain high-ductility high-strength steel sheets,
P or the like deteriorates alloying characteristics and generates a hard phase called Γ phase, which deteriorates powdering resistance characteristics.
Adhesion between galvanizing and steel sheet base and deterioration of alloying characteristics have been problems.

[0004]

As described above, in the alloyed hot-dip galvanized steel sheet, a problem may occur in the adhesion between the galvanization and the steel sheet substrate and the alloying characteristics in some cases. In the production, even though the strength and processing characteristics were good, galling (powdering) and uneven alloying occurred. In particular, when elements are added as the strength increases, adverse effects such as Si are large.

An object of the present invention is to solve the above-mentioned problems of the prior art, to provide an alloyed hot-dip galvanized steel sheet having high tensile strength and improved plating characteristics, and to provide a method for producing the same. Is.

[0006]

In order to solve the above-mentioned problems, the present inventor has conducted earnest studies on the steel composition and manufacturing conditions, and as a result, the composition of the alloyed high-strength hot-dip galvanized steel sheet, especially the reduction of Si. Regulates the Mn / Si ratio with
The inventors have found that this is possible by adjusting the temperature of the plating bath appropriately and completed the present invention.

That is, the present invention uses C: 0.01 to 0.3.
%, Mn: 1.5 to 3.0%, Si: 0.5% or less, P ≦ 0.1
%, Al: 0.01 to 0.1%, and Mn / Si ≧
Satisfies the relationship of 3.0, and if necessary, Mo: 1.0% or less, B: 0.01% or less, Ti: 0.1% or less, Nb: 0.1%.
Below, Zr: 0.1% or less, Cr: 1.0% or less, Cu: 1.0
% Or less, Ni: 1.0% or less, V: 0.1% or less, W: 0.1
% Or less of 1 or 2 or more and the balance is Fe
And an alloyed high-strength hot-dip galvanized steel sheet excellent in plating adhesion, characterized by comprising unavoidable impurities.

Further, the manufacturing method is such that, when the steel having the above-described composition is hot-rolled or hot-rolled and then cold-rolled and passed through a hot dip galvanizing line, the plating bath temperature is 400 to 460 ° C. It is characterized by doing.

The present invention will be described in more detail below.

[0010]

[Action]

First, the reasons for limiting the chemical composition of steel in the present invention will be explained.

C: C is an element that has a large effect on the strength of steel, can change the amount and form of the second phase transformation product, and affects local elongation and flanging characteristics. Therefore, it is the most important element for obtaining an alloyed high-strength hot-dip galvanized steel sheet. However, it does not significantly affect the plating characteristics,
From the small addition amount of 0.01% to the addition amount of 0.3% necessary for obtaining the ultra high strength steel, the plating adhesion and the alloying rate are not deteriorated (see FIG. 1). Further, if C is added in an amount exceeding 0.3%, the welding characteristics are deteriorated, which is not preferable. Therefore, the amount of C is set to the range of 0.01 to 0.3%.

Mn: Mn is an element that stabilizes the γ phase by changing the amount of solid solution C in ferrite or austenite, and is effective in controlling the characteristics of the second phase transformation product formed during cooling. is there. Therefore, in order to obtain various properties of the high-strength steel sheet, a minimum addition amount of 1.5% is necessary.
Furthermore, this element accelerates the alloying rate and brings about a good effect on the plating adhesion (see FIG. 2). The amount of this element added is
By adding in an amount that satisfies Mn / Si ≧ 3.0 in relation to the amount of Si described below that deteriorates the plating characteristics,
The plating adhesion can be improved (see FIG. 6). However, if added in excess of 3.0%, the Fe concentration in the galvanization becomes excessively high, and on the contrary, the rust preventive property of the galvanization is deteriorated and the generation of the Γ phase is promoted. Therefore, the amount of Mn is 1.5-
The range is 3.0%.

Si: Si is an element that forms a solid solution in ferrite to increase the strength, and the effect of solid solution strengthening is the second largest after P. Therefore, it is one of the most effective elements for securing strength. However, when added in a large amount, an oxide film is formed on the surface and the alloying rate of zinc plating is also slowed, which causes uneven plating and non-plating. The upper limit is 0.5% (see FIG. 3). Below 0.5%, the above Mn
When added in an amount satisfying Mn / Si ≧ 3.0 in relation to the amount, the plating adhesion and alloying rate are not deteriorated.

P: P is an element which, like Si, forms a solid solution in ferrite to increase strength and has the largest solid solution strengthening ability. However, if added in a large amount, uneven plating or non-plating may occur as in Si. However, Mn
If the amount is 1.5% or more, even if it is added up to 0.1%, the plating characteristics are not deteriorated. Therefore, the amount of P is 0.
1% or less.

Al: Al is used as a deoxidizing agent and is usually added in an amount of 0.01% or more. However, if more than 0.1% is added, inclusions are formed in the steel and the ductility is deteriorated, so the Al content is made 0.01 to 0.1%.

In addition to the above components, in the present invention, one or more of the following elements can be added in appropriate amounts, if necessary, to improve the plating characteristics.

Mo, B: Mo and B are segregated in a small amount at grain boundaries in the steel, prevent zinc plating from penetrating from the grain boundaries in the steel, and prevent cracking and workability deterioration due to hot dip galvanization. In particular, M
The addition of n changes the solid solubility limit of these elements and promotes segregation, and is mainly formed by the grain boundary portion appearing on the steel surface as a nucleus.
Prevent the formation of phases. When added, if the Mo content is 1.0% or less and the B content is 0.01% or less, the above effect is obtained.

Ti, Nb, Zr: Ti, Nb, Zr have a considerable effect of improving the galvanizing characteristics when the amount of C is about 80 ppm or more. When these elements are added to Mn-added steel, in addition to the improvement of zinc plating adhesion by Mn, the alloying rate is improved by expanding the solid solution limit and diffusion of these elements. However, when the amount of Mn is very small or when these elements are excessively added, carbides are generated and the C concentration in the ferrite grain boundary is lowered, so that zinc plating infiltration from the grain boundary or generation of Γ phase causes plating. Deteriorate the characteristics. Therefore, the amounts of Ti, Nb, and Zr are each set to 0.1% or less.

Cr, Cu, Ni, V, W: Cr, Cu, Ni,
When V and W are added in combination with Mn, they have the effect of suppressing the formation of the Γ phase and increasing the adhesion of the plating. Further, since these are also elements that improve corrosion resistance, they are effective elements for improving rust resistance. For that purpose, Cr, C
The u and Ni amounts may be 1.0% or less, and the V and W amounts may be 0.1% or less.

Next, the manufacturing conditions of the present invention will be described.

The steel sheet having the above chemical composition is hot-rolled, or hot-rolled and then cold-rolled, and is manufactured in a hot dip galvanizing line. However, when the temperature of the plating bath is high, rapid alloying is performed in the bath. It is easy to cause a reaction and generate a Γ phase at the steel sheet interface. For this reason, it is preferable to deposit the plating at a low temperature and then alloy it after raising the temperature. However, if the temperature is lower than 400 ° C, zinc is not completely melted, and in some cases, uneven adhesion occurs during plating adhesion, which causes uneven alloying. Therefore, the temperature of the hot dip galvanizing bath is limited to 400 to 460 ° C. The heating rate is not particularly limited, but is preferably about 100 ° C./s or less. Other galvannealing conditions are not particularly limited.

The alloyed high-strength hot-dip galvanized steel sheet thus obtained is free from galling and uneven alloy. Moreover,
The steel sheet structure is composed of bainite and ferrite or bainite, ferrite and martensite, and has high strength and good workability.

Next, examples of the present invention will be described.

[0025]

【Example】

[Table 1] After cold rolling to a thickness of 2.0 mm using a steel sheet having the chemical composition shown in Table 1, after annealing using a galvanizing experimental device, galvanizing is performed at 420 ° C. and alloying treatment is performed to 55
Performed at 0 ° C. The plating applied 60 mg / mm ² on one side to both sides.

The powdering resistance was evaluated by bending the steel sheet subjected to the alloying treatment for 60 seconds at 90 °, applying a tape to the bent portion, and measuring the amount of plating adhered to the tape. The alloying speed was evaluated by changing the alloying time within the range of 30 to 90 seconds and the concentration of iron dissolved in the plating layer. This result is

[Table 2] Shown in.

In Table 2, steel No. 1 to No. 4 show the effect of the C concentration, and No. 5 to No. 10 show the effect of the Mn / Si ratio. Further, No. 11 to No. 21 show the influence of other additive elements. As is clear from Table 2, the present invention examples having the chemical components within the scope of the present invention and obtained under the production conditions within the scope of the present invention (plating bath temperature 420 ° C.) all show excellent plating adhesion. The strength and elongation are also good. FIG. 4, FIG. 5, and FIG. 6 summarize the effects of the Mn / Si ratio on the alloying rate.

For steel No. 2, No. 10 and No. 17,
The results when the plating bath temperature was changed in the range of 400 to 470 ° C

[Table 3] ,

[Table 4] ,

[Table 5] Are shown respectively. The plate thickness is 2 mm, and the coating weight is 60 mg / mm ² on both sides. From each table, it is understood that the appropriate plating bath temperature is 420 to 460 ° C.

[0029]

[Table 6] Figure 2 shows the difference in the generation state of the Γ phase due to the added elements. In order to clarify the difference in the generation state of the Γ phase, the plating adhesion temperature (500 ° C) and the alloying temperature (600 ° C) were set high, and the alloying time (3 minutes) was set long. Based on the criteria shown, it was judged as 1 (excellent) → 5 (poor). As a result, as shown in the table, when there is much Si (No. 7), there is much unplating,
It is understood that the addition element within the range of the present invention can prevent the generation of the Γ phase.

[0030]

As described in detail above, according to the present invention,
It is possible to provide a galvannealed steel sheet having excellent plating adhesion and high tension.

[Brief description of drawings]

FIG. 1 is a diagram showing the effect of C on the alloying rate,
The manufacturing conditions are a plate thickness of 1.2 mm and a plating bath temperature of 450 ° C.

FIG. 2 is a diagram showing the effect of Mn on the alloying rate, and the manufacturing conditions are a plate thickness of 1.2 mm and a plating bath temperature of 450 ° C.

FIG. 3 is a diagram showing the influence of Si on the alloying rate, and the production conditions are a plate thickness of 1.2 mm and a plating bath temperature of 450 ° C.

FIG. 4 is a diagram showing the effect of the Mn / Si ratio on the alloying rate.

FIG. 5 is a diagram showing the effects of the Mn / Si ratio and the additive elements (Mo, Ti, Cr) on the alloying rate.

FIG. 6 is a diagram showing the effect of the Mn / Si ratio on the alloying rate.

FIG. 7 is a diagram illustrating a criterion for determining a Γ-phase occurrence state,
(A) is the case without the Γ phase (rank 1), (b) is the case where the Γ phase is locally generated (rank 3), and (c) is the case where the Γ phase is continuously generated at 1.0 μm or more (rank 5). ).

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C23C 2/06 2/40

Claims (5)

[Claims] 1. By weight% (hereinafter the same), C: 0.01-
0.3%, Mn: 1.5 to 3.0%, Si: 0.5% or less, P ≦
0.1%, Al: 0.01 to 0.1%, and Mn / S
An alloyed high-strength hot-dip galvanized steel sheet having excellent plating adhesion, which satisfies the relation of i ≧ 3.0 and the balance is Fe and inevitable impurities. 2. The steel further comprises Mo: 1.0% or less and B:
0.01% or less, Ti: 0.1% or less, Nb: 0.1% or less,
Zr: less than 0.1%, Cr: less than 1.0%, Cu: less than 1.0%, Ni: less than 1.0%, V: less than 0.1%, W: less than 0.1% The alloyed high-strength hot-dip galvanized steel sheet according to claim 1, which contains one or more types. 3. The alloyed high-strength hot-dip galvanized steel sheet according to claim 1, wherein the steel sheet structure comprises bainite and ferrite or bainite, ferrite and martensite. 4. C: 0.01 to 0.3%, Mn: 1.5 to 3.
0%, Si: 0.5% or less, P ≦ 0.1%, Al: 0.01 to
Steel containing 0.1% and satisfying the relationship of Mn / Si ≧ 3.0 and the balance Fe and unavoidable impurities is hot-rolled or cold-rolled after hot-rolling to form a hot dip galvanizing line. A method for producing an alloyed high-strength hot-dip galvanized steel sheet having excellent plating adhesion, which comprises passing a plating bath at a temperature of 400 to 460 ° C. when passing. 5. The steel further comprises Mo: 1.0% or less and B:
0.01% or less, Ti: 0.1% or less, Nb: 0.1% or less,
Zr: less than 0.1%, Cr: less than 1.0%, Cu: less than 1.0%, Ni: less than 1.0%, V: less than 0.1%, W: less than 0.1% The method according to claim 4, which contains one or more kinds.