JP2642284B2 - High strength and high ductility alloyed hot-dip galvanized steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength, high-ductility alloyed hot-dip galvanized steel sheet.

[0002]

2. Description of the Related Art Recently, as a part of measures to reduce the weight of automobiles, demand for high-strength steel sheets of 40 to 80 kg class for bodies, lower parts, underbody parts and the like has been increasing. From the viewpoint of corrosion resistance, it is effective to apply hot-dip Zn plating or hot-dip Zn plating and alloying hot-dip galvanizing to these steel sheets. In the case of a steel sheet having a high Si content, the surface of the steel sheet tends to have an oxide film, so that a small non-plated portion occurs during hot-dip Zn plating, or the plating adhesion of the processed portion after alloying is reduced. There is a problem such as inferiority and the like, and at present, a high Si-based high tensile high ductility alloyed hot-dip galvanized steel sheet which has excellent adhesion to a processed portion and excellent corrosion resistance has not been put to practical use.

[0003]

On the other hand, the present inventors have disclosed Japanese Patent Application Nos. 03-146541 and 03-1946.
No. 30226 proposes a method for hot-dip pre-Ni plating followed by rapid low-temperature heating and hot-dip Zn plating followed by alloying treatment as a method for alloying hot-dip coating of high-Si high-strength steel sheets. This method is an excellent method, and when applied to a high-tensile-high-ductility steel sheet containing high Si, the hot-dip galvanizing property is greatly improved, and the production of an alloyed hot-dip galvanized steel sheet is easy.
After that, the structure of the alloyed hot-dip galvanized layer obtained by the present method was analyzed in detail, and various experiments were repeated to form a high-strength, high-ductility alloy excellent in plating adhesion and corrosion resistance of the processed portion, which is the above problem. We studied to develop a hot-dip galvanized steel sheet.

[0004]

Means for Solving the Problems The present inventors have firstly filed Japanese Patent Application Nos. 03-146541 and 03-130226.
Detailed analysis of the structure of the plated layer of the alloyed hot-dip galvanized steel sheet obtained by the method proposed in the above issue revealed that the structure of the alloy layer at the interface with the base iron was clarified. Furthermore, as a result of preparing a plating layer composed of various steel sheet compositions, plating layer compositions, and structures, and continuing to study, it is clear that the plating layer structure and composition have the highest corrosion resistance and the highest plating adhesion of the processed portion for high Si steel. Lead to the discovery of a high-strength, high-ductility alloyed hot-dip galvanized steel sheet having excellent corrosion resistance and excellent plating adhesion at the processed portion, comprising a base steel sheet composition, a coating layer structure, and an alloyed hot-dip Zn coating layer having the composition of the present invention. The present invention described below has been completed.

[0005] That is, C 0.02-0.2%, Si
0.2-2.0%, Mn 0.15-2.5%, So
l. The remaining has free and Al 0.08% or less has an alloy layer consisting of gamma ₁ phase dispersed on a steel sheet consisting of an unavoidable component _{(Fe 5 Zn 21), Fe8~15} % thereon, al 1
%, A high-strength high-ductility alloyed molten Z excellent in plating adhesion and corrosion resistance in a processed portion, characterized by having a Zn alloy layer comprising 0.01% to 2% Ni and unavoidable impurities.
n-plated steel sheet and C 0.02-0.2%, Si
0.2-2.0%, Mn 0.15-2.5%, So
l. The remaining has free and Al 0.08% or less between Γ1 phase dispersed on a steel sheet consisting of an unavoidable component Ni-Al-S
i-Fe-Zn compound phase, and Fe8
-15%, Al 0.05-1% or less, Ni 0.01-
A high-strength, high-ductility alloyed hot-dip galvanized steel sheet having a Zn alloy layer consisting of 2% and unavoidable impurities and having excellent plating adhesion and corrosion resistance in a processed part, and an An alloy layer of these steel sheets. S b, P as an alloy component
A high-strength, high-ductility alloyed hot-dip galvanized steel sheet having excellent plating adhesion and corrosion resistance in a processed part, wherein b and Mg are contained individually or in a composite within 3%.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram schematically showing a plating layer structure of a hot-dip galvanized steel sheet according to claim 1 of the present invention. Base steel interface alloy layer composed of dispersed gamma ₁ phase, their upper layer Fe8~15%, Al 1%, a Zn alloy layer consisting of Ni 0.01 to 2% and unavoidable impurities.

[0008] Figure 2 represents the plated layer structure of claim 2 of the present invention, N between the alloy layer consisting of gamma ₁ phase dispersed on a steel sheet
It has an i-Al-Si-Fe-Zn compound layer, and 8-15% of Fe, 0.05-1% of Al, Ni
The Zn alloy layer is composed of 0.01 to 2% and inevitable impurities.

[0009] Figure 3 is a diagram illustrating a plating layer structure when gamma ₁ for comparison is continuous.

[0010] Table 1 shows the results of examining the plating adhesion of the processed portions of the plated steel sheet of the present invention and the comparative material.

[0011] The plating adhesion of the processed portion was evaluated by a 5-point method according to the degree of chemical conversion after conducting a 60-degree V bending test and performing a tape test. All original sheets were hot rolled steel sheets containing 1.2% Si.

Evaluation of plating adhesion (bending test at 60 ° V) of processed part Tape test blackness (%) 5 ... 0-10 4 ... less than 10-20 3 ... less than 20-30 2 ... less than 30-40 1 ... 40 or more (3 or more passed)

[0013]

[Table 1]

In the case of having the plating layer structure of the present invention, the plating adhesion of the processed portion is extremely good.

The plated steel sheet of the present invention has a dispersing or Ni-Al-Si-Fe- Zn compound phase gamma ₁ phase of base steel interface, the coating adhesion of the processed portion is greatly improved. FIG. 4 is a diagram showing the relationship between Ni% (% by weight) in the plating layer and corrosion resistance. After pickling, using a hot-rolled steel sheet containing 1.2% Si polished with emery paper, pre-N
After applying i-plating of 0.1-2 g / m ² ,
After heating at 0 ° C./s, plating was performed for 3 seconds in a hot-dip Zn plating bath in which the bath temperature was 450 ° C., Al 0.25% was constant, and the Ni content in the bath was changed, and immediately after wiping, the plating was performed for 50 seconds.
An alloying treatment was performed at 0 ° C. for 5-20 s. The coating weight was 60 g / m ² . The corrosion resistance was evaluated based on the occurrence of red rust in a salt spray test (SST 120 hr) in an unpainted state. Further, after the end face punched material was electrodeposited, the occurrence of red rust on the end face was evaluated by a corrosion cycle test (CCT) for 10 weeks.

[0016] Corrosion resistance (SST120hr) Edge corrosion resistance (CCT 10 weeks) Rating Score 5 No red rust 5 No red rust 4 Trace rust (yellow rust) 4 Trace rust (yellow rust) 3 Trace rust (red rust) 3 Trace rust (red rust) 2) Many red rusts 2 Many red rusts 1 Full red rust 1 Full red rust (3 or more passed) When the Ni content in the plating layer is 0.01% or more, bare corrosion resistance is improved.

If the Ni content in the plating layer exceeds 2%, the corrosion resistance of the end face deteriorates. It is considered that the potential becomes too noble when the corrosion of Zn progresses, and local corrosion such as end faces and scratches is likely to occur. S b in the plating layer, Pb, were similar results when it contains 3% or less alone or a composite of Mg.

The reason why the Fe content in the plating layer is set to 8% or more is that when the Fe content is less than 8%, chemical conversion treatment (phosphate treatment) coating film adhesion becomes good. Further, the Fe content is set to 1
The reason for setting the content to 5% or less is that if the content exceeds 15%, the alloy becomes overalloy and the plating adhesion of the processed portion deteriorates.

The reason why the content of Al in the plating layer is set to 1 or less is that when Al in the bath exceeds 1%, A segregated in the plating layer.
This is because 1 constitutes a local battery and the corrosion resistance is deteriorated.

The thickness of the Zn plating layer is not particularly limited, but is preferably 0.1 μm or more from the viewpoint of corrosion resistance and 50 μm or less from the viewpoint of workability.

The results in FIGS. 1 and 2 show that as a high-strength steel sheet as a base, C is 0.02-0.2% and Si is 0.2-0.2%.
2.0%, Mn 0.15 to 2.5%, Sol. Al
Containing 0.08% or less was similar in the steel plate consisting of the remaining rehabilitation unavoidable component. The lower limits of the amounts of C, Si, and Mn in the steel were taken into consideration that if the upper limit is greater than this, workability is deteriorated in order to ensure strength. In addition, Sol. A
The purpose of adding l is to serve as a deoxidizing element. The reason why the upper limit is set to 0.08% is that if the excessive addition is made, cracks are likely to occur when manufacturing a steel sheet. As a high-tensile steel sheet, both a hot-rolled steel sheet and a cold-rolled steel sheet can be used. As material, tensile strength 40-80 kg / m ² , elongation 20-3
A hot-dip galvanized steel sheet with high strength and high ductility of about 5% is possible.

The method for producing the plated steel sheet of the present invention is not particularly limited. As a method of manufacturing the plating layer having the structure shown in FIG. 1, the surface of a steel sheet is plated with Ni plating in a small amount of less than 0.2 g / m < ² >, and after heating at a low temperature in a reducing atmosphere, Al 1% or less.
Below, containing 0.01 to 2% of Ni, with the balance being Zn
A method of immersing in a hot-dip Zn plating bath made of unavoidable impurities, plating, and alloying can be applied. As a method of manufacturing a plating layer having the structure shown in FIG. 2, a steel plate proposed by the present inventors is subjected to pre-Ni plating at 0.2 to ² g / m ² , and after rapid low-temperature heating in a non- oxidizing or reducing atmosphere , Al 1% or less
Below, containing 0.01 to 2% of Ni, with the balance being Zn
Immersion and plating in hot-dip Zn plating bath consisting of inevitable impurities
An alloying method is preferred. The plating of claim 3
The steel sheet is made of the above-mentioned Al, Ni
In addition, Sb, Pb, and Mg may be used alone or in combination.
It can be manufactured by adopting one containing 3% or less.

[0023]

[Action] reason for plating adhesion of the processed portion of the steel sheet of the present invention is excellent very is not yet clear, gamma ₁ of base steel interface of the plating layer is entered cracks to gamma ₁ during processing to have dispersed Is difficult to propagate, and Ni-Al-Si-F
It is considered that the e-Zn compound phase plays a role of a kind of binder. It is considered that the reason why the bare corrosion resistance is improved by adding a small amount of Ni in the plating layer is to stabilize basic zinc hydroxide among corrosion products of Zn, as is well known.

[0024]

EXAMPLES Table 2 shows examples of the plated steel sheet of the present invention. *
Marks are comparative materials other than the present invention. As a base, a hot-rolled high-tensile steel sheet shown in Table 3 was used. As a manufacturing method of plating,
A pre-Ni plating method in which the amount of the pre-Ni plating applied was changed and a method in which Ni was dissolved in the bath by changing the content ratio were used. 3s hot-dip plating was performed in a 450 ° C. Zn plating bath in which the amount of Al changed, and 470-55 after N ₂ wiping.
An alloying treatment was performed at 0 ° C. for 5 to 40 s. 60
g / m ² . The corrosion resistance of the resulting plated steel sheet is
In addition to the above-mentioned evaluation of bare corrosion resistance, taking into account the local corrosion of the end face and the adhesion of the coating film, a comprehensive evaluation was made in four steps, and a result of 〇 or more was evaluated as acceptable. Further, the plating adhesion of the processed portion was also examined by the above-described 60-degree V bending test.

No. Nos. 2 to 6; 8-17 and N
o. As shown in Nos. 19 to 21, the plated steel sheet having the plated layer structure and composition of the present invention has excellent plating adhesion and corrosion resistance in the processed portion, and exhibits high strength and high ductility.

In contrast, when the plating layer structure and composition deviate from the scope of the present invention (Nos. 1, 7, 18,
No. 22) is inferior in bare corrosion resistance and plating adhesion of the processed portion as compared with the steel sheet of the present invention.

[0027]

[Table 2]

[0028]

[Table 3]

[0029]

As described above, the present invention is a high-strength, high-ductility alloyed hot-dip galvanized steel sheet excellent in plating adhesion and corrosion resistance in a processed part, which is not available in the past, and is useful for vehicle bodies and building material applications. Therefore, its industrial significance is extremely large.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a plating layer structure of a hot-dip galvanized steel sheet of the present invention.

FIG. 2 is a view schematically showing a plating layer structure of a hot-dip galvanized steel sheet of the present invention.

FIG. 3 is a diagram showing a plating layer structure of a comparative material.

FIG. 4 is a graph showing the relationship between Ni% (% by weight) in a plating layer and bare corrosion resistance.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical display location C23C 2/40 C23C 2/40 28/02 28/02 (72) Inventor Masahiko Oda 1 Fujimachi, Hirohata-ku, Himeji-shi Address Nippon Steel Corporation Hirohata Works (72) Inventor Fujiwa Muramoto 1 Fujimachi, Hirohata-ku, Himeji City Nippon Steel Corporation Hirohata Works (56) References JP-A-4-314848 (JP) JP-A-4-333552 (JP, A) JP-A-4-346644 (JP, A) JP-A-5-59513 (JP, A)

Claims (3)

(57) [Claims] 1. C 0.02 to 0.2%, Si 0.2 to 2.0%, Mn 0.15 to 2.5%, Sol. The remaining has free and al 0.08% or less has an alloy layer consisting of gamma ₁ phase dispersed on a steel sheet consisting of an unavoidable component, Fe 8 to 15% on their upper,
A high-strength, high-ductility alloyed hot-dip galvanized steel sheet having a Zn alloy layer composed of inevitable impurities of Al 1% or less and Ni 0.01 to 2% and having excellent plating adhesion and corrosion resistance in a processed portion. 2. C 0.02 to 0.2%, Si 0.2 to 2.0%, Mn 0.15 to 2.5%, Sol. The remaining has free and Al 0.08% or less has a Ni-Al-Si-Fe- Zn compound layer between the alloy layer consisting of gamma ₁ phase dispersed on a steel sheet consisting of an unavoidable component, those of the upper layer 8-15% Fe, Al
A high-strength, high-ductility alloyed hot-dip galvanized steel sheet having a Zn alloy layer comprising 1% or less, 0.01 to 2% of Ni and inevitable impurities, and having excellent plating adhesion and corrosion resistance in a processed portion. 3. A as claimed in claim 1 or further alloying element Zn alloy layer in 2 S b, Pb, processing unit plating adhesion and that is characterized by containing less than 3% of Mg alone or a composite corrosion Excellent high strength and high ductility alloyed hot-dip galvanized steel sheet.