JP2002004018A - High strength hot-dip galvanized steel sheet having good corrosion resistance after coating and good press- workability, and coated steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high strength hot-dip galvanized steel sheet sufficiently securing both of the strength and the corrosion resistance of the steel sheet and having good press-workability obtaining 530-880 MPa tensile strength TS. SOLUTION: The high strength hot-dip galvanized steel sheet having good corrosion resistance and press-workability after coating, has the peculiarity, in which the hot-dip galvanized layer of Zn-Al alloy plating, Zn-Al-Si alloy plating, Zn-Al-Mg alloy plating or Zn-Al-Mg-Si alloy plating, containing Ni and/or Cu, is coated on the high strength steel sheet composed by mass% of 0.05-0.15% C, 0.3-2.0% Si, 1.5-2.8% Mn, <=0.03% P, <=0.02% S, 0.005-0.5% Al, <=0.006% N and the balance Fe with unavoidable impurities and further, satisfying (%Mn)/(%C)>=15 and (%Si)/(%C)>=4, in the case of using %C, %Si, %Mn for C, Si, Mn content, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a high-strength hot-dip galvanized steel sheet, and more particularly to a galvanized steel sheet having excellent corrosion resistance after painting and applicable to various uses, for example, a steel sheet for building materials and automobiles. It is.

[0002]

2. Description of the Related Art Hot-dip galvanized steel sheets are known as coated steel sheets having good corrosion resistance. This hot-dip galvanized steel sheet is usually preheated in a non-oxidizing furnace after degreasing the steel sheet, subjected to reduction annealing in a reducing furnace to clean the surface and secure the quality of the steel sheet, immersed in a hot-dip zinc bath, It is manufactured by performing control. It is widely used mainly in automobiles, building materials and the like because of its excellent corrosion resistance and plating adhesion.

In recent years, in particular, in the field of automobiles, it has become necessary to increase the strength of plated steel sheets in order to ensure a function of protecting an occupant in the event of a collision and to achieve a reduction in weight for the purpose of improving fuel efficiency.

In order to increase the strength of a steel sheet without deteriorating the workability, it is effective to add elements such as Si, Mn, and P. However, the addition of these elements generally reduces the wettability of the steel sheet surface. However, it is difficult to perform hot-dip galvanizing. Therefore, in order to perform hot-dip galvanizing on a steel sheet to which elements such as Si, Mn, and P are added, for example, Japanese Patent Laid-Open No.
A method proposed in JP-A-5-122865 to improve the plating adhesion by suppressing the formation of an oxide layer of an element such as Si, Mn, or P by setting the oxide film thickness of iron to an appropriate range is used. ing. Further, as a high-strength galvanized steel sheet manufactured by using such a plating method, JP-A-6-192807 and JP-A-6-192854 are exemplified.

[0005] Further, since hot-dip galvanized steel sheets are generally used after being coated from the viewpoint of design and corrosion resistance, corrosion resistance after coating is important.

[0006]

However, in the above-mentioned and other high-strength galvanized steel sheets disclosed above, neither the strength nor the corrosion resistance of the steel sheet is sufficiently ensured.

Accordingly, the present invention solves the above-mentioned problems and has a metal structure in which martensite and retained austenite are mixed in ferrite, and a tensile strength TS of 530 to 880 MPa by strengthening the composite structure. It is intended to provide a hot-dip galvanized steel sheet having good workability.

[0008]

Means for Solving the Problems The present inventors disclosed in Japanese Patent Laid-Open No.
Japanese Patent Application Publication No. 1-279691 proposes a high-strength galvannealed steel sheet having good workability and a method for producing the same.

Further, the present inventors have conducted intensive studies on the plating treatment of a high-strength steel sheet. As a result, the surface of the Si-containing high-strength steel sheet was plated with Zn-Al alloy containing one or two or more kinds of Ni or Cu. Zn-Al-Si alloy plating, Zn-Al-Mg alloy plating, Zn-Al-Mg-
The present invention has been found to be able to obtain a high-strength hot-dip galvanized steel sheet and a coated steel sheet having good corrosion resistance after coating and good press workability by forming a Si alloy plating.

That is, the gist of the present invention is as follows.
It is as shown below.

(1) In mass%, C: 0.05 to 0.1
5%, Si: 0.3 to 2.0%, Mn: 1.5 to 2.8
%, P: 0.03% or less, S: 0.02% or less, Al:
0.005 to 0.5%, N: 0.006% or less, with the balance being Fe and unavoidable impurities.
When C,% Si, and% Mn are respectively C, Si, and Mn contents, (% Mn) / (% C) ≧ 15 and (% Si) /
On a high-strength steel sheet satisfying (% C) ≧ 4, Al:
0.2 to 12% by mass, and Ni: 0.1 to 1
0% by mass, Cu: 0.05 to 3% by mass, having a hot-dip galvanized layer composed of Zn and unavoidable impurities, the balance being good, and having good corrosion resistance after painting and press working High strength hot-dip galvanized steel sheet.

(2) In mass%, C: 0.05-0.1
5%, Si: 0.3 to 2.0%, Mn: 1.5 to 2.8
%, P: 0.03% or less, S: 0.02% or less, Al:
0.005 to 0.5%, N: 0.006% or less, with the balance being Fe and unavoidable impurities.
When C,% Si, and% Mn are respectively C, Si, and Mn contents, (% Mn) / (% C) ≧ 15 and (% Si) /
(% C) ≧ 5 on a high-strength steel sheet satisfying ≧ 4.
-70% by mass, Si: 0.01-2% by mass, Ni: 0.1-10% by mass, Cu: 0.05-3% by mass, the balance being Zn A high-strength galvanized steel sheet having good corrosion resistance after painting and good press workability, characterized by having a hot-dip galvanized layer composed of unavoidable impurities.

(3) In mass%, C: 0.05-0.1
5%, Si: 0.3 to 2.0%, Mn: 1.5 to 2.8
%, P: 0.03% or less, S: 0.02% or less, Al:
0.005 to 0.5%, N: 0.006% or less, with the balance being Fe and unavoidable impurities.
When C,% Si, and% Mn are respectively C, Si, and Mn contents, (% Mn) / (% C) ≧ 15 and (% Si) /
(% C) Al: 2 on a high-strength steel plate satisfying ≧ 4
-12% by mass, Mg: 1-10% by mass, Ni: 0.1-10% by mass, Cu: 0.05-3% by mass
A high-strength hot-dip galvanized steel sheet having good corrosion resistance after coating and good press workability, characterized by having a hot-dip galvanized layer containing one or two of the following, and the balance being Zn and unavoidable impurities.

(4) In mass%, C: 0.05-0.1
5%, Si: 0.3 to 2.0%, Mn: 1.5 to 2.8
%, P: 0.03% or less, S: 0.02% or less, Al:
0.005 to 0.5%, N: 0.006% or less, with the balance being Fe and unavoidable impurities.
When C,% Si, and% Mn are respectively C, Si, and Mn contents, (% Mn) / (% C) ≧ 15 and (% Si) /
(% C) ≧ 5 on a high-strength steel sheet satisfying ≧ 4.
70% by mass, Mg: 1 to 10% by mass, Si: 0.01
Hot-dip galvanized layer containing 0.1 to 10% by mass of Ni, one or two types of 0.05 to 3% by mass of Cu, and the balance consisting of Zn and unavoidable impurities A high-strength hot-dip galvanized steel sheet having good corrosion resistance after painting and good press workability, characterized by having:

(5) By mass%, B: 0.0002-
The high-strength hot-dip galvanized steel sheet according to any one of (1) to (4) above, wherein the steel sheet contains 0.002% and has good corrosion resistance after coating and good press workability.

(6) The steel sheet is composed of the chemical component according to any one of (1) to (5), and its metal structure contains martensite and retained austenite in a volume ratio of 3% or more and 20% or less. High strength hot-dip galvanized steel sheet with good corrosion resistance after coating and good press workability.

(7) On the plated layer of the plated steel sheet according to any one of the above (1) to (6), a chromate film layer is provided as an intermediate layer, and 0.5 to 100 is further provided as an upper layer.
A high-strength hot-dip galvanized coated steel sheet having an organic coating layer having a thickness of μm and having good corrosion resistance after coating and good press workability.

(8) The high-strength hot-dip galvanized steel sheet according to the above (7), wherein the organic coating is a thermosetting resin coating and has good corrosion resistance after coating and good press workability.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
In addition, all the percentages shown below represent mass%.

First, C, Si, Mn, P, S, Al,
The reasons for limiting the numerical values of N and B will be described.

C is an essential element in the case where the steel sheet is to be strengthened by strengthening the structure by martensite or retained austenite. The reason why the content of C is set to 0.05% or more is that if C is less than 0.05%, cementite or pearlite is difficult to be rapidly cooled from the annealing temperature by using mist or jet water as a cooling medium in a galvanizing line. This is because it is easy to produce and it is difficult to secure the required tensile strength. On the other hand, the reason why the content of C is 0.15% or less is that if C exceeds 0.15%, it becomes difficult to form a sound welded portion by spot welding, and at the same time, segregation of C becomes remarkable and workability is increased. Is deteriorated.

Si is added in an amount of 0.3 to 2.0% as an element for increasing the strength without significantly impairing the workability of the steel sheet, particularly, the elongation, and is set to be at least 4% by mass of the C content. The reason why the content of Si is set to 0.3% or more is that if the content of Si is less than 0.3%, it is difficult to secure the required tensile strength, and the content of Si is set to 2.0% or less. The reason for this is that if the content of Si exceeds 2.0%, the effect of increasing the strength is saturated and the ductility is reduced. By setting the content by mass to 4 times or more of the C content, the progress of the pearlite and bainite transformation is remarkably delayed by reheating for the alloying treatment performed immediately after plating, and the volume ratio is 3 to 3 even after cooling to room temperature.
A metal structure in which 20% of martensite and retained austenite are mixed in ferrite can be obtained.

Mn is added in an amount of 1.5% or more to stabilize austenite before immersing the steel strip in the plating bath in order to reduce the free energy of austenite together with C. By adding 15% by mass or more of the C content, the progress of the pearlite and bainite transformation is remarkably slowed by reheating for the alloying treatment performed immediately after plating, and the volume ratio becomes 3% even after cooling to room temperature. A metal structure in which about 20% of martensite and retained austenite are mixed in ferrite can be obtained. However, if the amount is too large, the slab is liable to crack and the spot weldability deteriorates, so the upper limit is 2.8%.

P is generally contained in steel as an unavoidable impurity, but if its content exceeds 0.03%, spot weldability is significantly deteriorated and the tensile strength as in the present invention is 4%.
In a high-strength steel sheet exceeding 90 MPa, not only the toughness but also the cold-rolling property is significantly deteriorated.
% Or less.

Although S is generally contained in steel as an unavoidable impurity, if its amount exceeds 0.02%, the presence of MnS elongated in the rolling direction becomes remarkable, which adversely affects the bendability of the steel sheet. The content is 0.02% or less.

Al is used as a deoxidizing element in steel and is used in order to improve the material quality by suppressing the grain size of the hot rolled material by AlN and the coarsening of the crystal grains in a series of heat treatment steps.
It is necessary to add at least 05%. However, if it exceeds 0.5%, not only the cost is increased, but also the surface properties are deteriorated, so the content is made 0.5% or less.

N is also generally contained in steel as an unavoidable impurity, but if its amount exceeds 0.006%, the brittleness is deteriorated along with the elongation, so the content is 0.006%.
The following is assumed.

B is generally known as an element that increases hardenability, and delays the transformation of pearlite and bainite during reheating for alloying treatment, so that after cooling to room temperature, 3 to 20% by volume of 0.0002% or more is added for the purpose of facilitating the formation of a metal structure in which sites are mixed in ferrite. However, if the addition amount exceeds 0.002%, the ferrite does not grow to a sufficient volume ratio even when the temperature is slowly cooled from the temperature range of two phases of ferrite and austenite to 650 ° C, and the ferrite and austenite do not grow from 650 ° C to the plating bath. Austenite is transformed into martensite during the cooling process, and then martensite is tempered by reheating for alloying treatment to precipitate cementite. Therefore, it is difficult to achieve both high strength and good press workability.

In addition, Nb, T
Even if i, Mo, Cu, Sn, Zn, Zr, W, Cr, and Ni are contained in a total amount of 1% or less, the effect of the present invention is not impaired, and depending on the amount, the corrosion resistance may be improved.

Next, the hot-dip galvanized layer will be described.

In the present invention, the Al of the Zn—Al plating layer
The reason why the composition is limited to 0.2 to 12% is that when a normal hot-dip plating process is performed with an Al amount of less than 0.2%, a Zn—Fe alloying reaction occurs during the plating process, and the interface is brittle at the base iron interface. This is because the alloy layer develops and the plating adhesion deteriorates, and if it exceeds 12%, the growth of the Fe—Al alloy layer becomes remarkable and the plating adhesion is impaired.

It is effective to increase the Al composition of the Zn-Al plating layer to obtain a plated steel sheet having better corrosion resistance. However, as described above, when the Al composition exceeds 12% by weight, the Fe-Al alloy layer is formed. Growth becomes remarkable and plating adhesion is impaired. Therefore, in order to increase the Al composition of the Zn—Al plating layer, it is necessary to add Si to suppress the growth of the Fe—Al alloy layer.

In the present invention, the reason why the Al composition of the Zn—Al—Si plating layer is limited to 5 to 70% is that if the amount of Al is less than 5%, the adhesion is sufficient without adding Si. , 70%, the effect of improving corrosion resistance is saturated.

The reason why the Si composition is limited to 0.01 to 2% is that if it is less than 0.01%, the effect of suppressing the growth of the Fe—Al alloy layer during plating is not sufficient. This is because the effect of improving the adhesion is saturated. The amount of Si added for the purpose of suppressing the reaction between Al and Fe in the steel sheet is preferably 1% or more of the Al content.

As a method of obtaining a plated steel sheet having good corrosion resistance, a method of adding Mg to a Zn—Al plating layer is also effective.

In the present invention, the reason why the Al composition of the Zn—Al—Mg plating layer is limited to 5 to 12% is that when Mg is added to a plating bath having an Al content of less than 5%, a large amount of dross is generated, which is satisfactory. This is because plating cannot be performed, and if it exceeds 12%, the growth of the Fe-Al alloy layer becomes remarkable, and the plating adhesion is impaired.

The reason for limiting the Mg composition to 1 to 10% is as follows.
If it is less than 1%, the effect of improving corrosion resistance is insufficient, and if it exceeds 10%, the plating bath is easily oxidized, and a large amount of Mg oxide is generated on the bath surface, making plating difficult. is there.

Further, in the Zn—Al—Mg plating layer, increasing the Al composition of the plating layer is effective in improving the corrosion resistance. However, as described above, when the Al composition exceeds 12%, the Fe—Al alloy layer becomes The growth becomes remarkable and impairs plating adhesion. Therefore, in order to increase the Al composition of the Zn—Al plating layer, it is necessary to add Si to suppress the growth of the Fe—Al alloy layer.

In the present invention, the reason why the Al composition of the Zn—Al—Mg—Si plating layer is limited to 5 to 70% is as follows.
If the amount of Al is less than that, sufficient adhesion can be obtained without adding Si, and if it exceeds 70%, the effect of improving corrosion resistance is saturated.

The reason for limiting the Mg composition to 1 to 10% is as follows.
If it is less than 1%, the effect of improving corrosion resistance is insufficient, and if it exceeds 10%, the plating bath is easily oxidized, and a large amount of Mg oxide is generated on the bath surface, making plating difficult. is there.

The reason for limiting the Si composition to 0.01 to 2% is that if it is less than 0.01%, the effect of suppressing the growth of the Fe—Al alloy layer during plating is not sufficient. This is because the effect of improving the adhesion is saturated. The amount of Si added for the purpose of suppressing the reaction between Al and Fe in the steel sheet is preferably 1% or more of the Al content.

Further, for the purpose of improving corrosion resistance after painting, N
One or two of i: 0.1 to 10% and Cu: 0.05 to 3% are added. The reason why the corrosion resistance after painting is improved by adding these elements is considered as follows. 1. The thin film formed on the surface of the plating layer further exhibits a passivation tendency and slows the corrosion of the plating layer under the coating film. 2. The passivation tendency described above suppresses the reaction at the interface between the plating layer and the coating film, and contributes to the stabilization of the coating film. 3. It is considered that the plating layer surface has an anchoring effect on the coating film due to the presence of fine irregularities. 4. It is considered that Ni and Cu improve plating wettability and suppress generation of minute non-plating.

The effect of improving corrosion resistance after painting is as follows: Ni,
The effect starts to be remarkable at 0.1% and 0.05% or more in Cu, respectively, and the effect is almost saturated by adding more than Cu. However, when the amount of addition increases, the appearance after plating becomes coarse, and poor appearance occurs due to, for example, dross or oxide attachment. Therefore, the upper limit of each element is 10% and 3%.

There is no particular limitation on the method of adding Ni and Cu to the plating, and there is no particular limitation on the method of adding Ni or Cu to the plating bath, or the method of adding these metals or Zn containing these metals to the surface in advance. A method of dipping in a hot-dip Zn plating bath and mixing can be used. In addition, the plating layer may further contain Sb, Pb, Fe, etc., alone or in combination, within 0.5%. The amount of hot-dip galvanized coating is not particularly limited, but is not less than 20 g / m ² from the viewpoint of corrosion resistance and 150 g from the viewpoint of economy.
/ M ² or less.

In the present invention, the method for producing a plated steel sheet is not particularly limited, and a usual hot-dip plating method using a non-oxidizing furnace can be applied. However, when annealing in a continuous hot-dip galvanizing equipment of an in-line annealing method, the annealing temperature is in a region where two phases of ferrite and austenite coexist.

In the present invention, the coated steel sheet is a steel sheet in which layers composed of hot-dip plating, a chromate film, and an organic film are sequentially applied. The chromate film as the intermediate layer of the coated steel sheet may be applied by any method such as electrolytic chromating, coating chromate, and reactive chromate. The role of the chromate film is to improve the adhesion between the plating and the organic film, which is also effective in improving the corrosion resistance.

Next, examples of the upper organic film of the coated steel sheet include polyester resin, amino resin, epoxy resin, acrylic resin, urethane resin, fluororesin and the like, and are not particularly limited. When used for a product that requires severe processing, a thermosetting resin coating film is most preferable. Examples of the thermosetting resin coating film include polyester paints such as epoxy polyester paints, polyester paints, melamine polyester paints, urethane polyester paints, and acrylic paints.

Polyester paints in which melamine resin or polyisocyanate resin is used as a curing agent in combination with an alkyd resin in which a part of the acid component of the polyester resin is replaced with a fatty acid, an oil-free alkyd resin which is not modified with oil, and various crosslinks Acrylic paint combined with the agent,
This is because the workability is better than other paints, so that the coating film does not crack even after severe processing.

The appropriate film thickness is 0.5 μm to 100 μm. The reason for setting the film thickness to 0.5 μm or more is that the film thickness is 1 μm.
This is because if it is less than m, corrosion resistance cannot be ensured. The reason for setting the film thickness to 100 μm or less is that if the film thickness exceeds 100 μm, it is disadvantageous in terms of cost. Desirably, it is 20 μm or less. The organic coating layer may be a single layer or multiple layers.

The organic coating used in the method of the present invention may optionally contain additives such as a plasticizer, an antioxidant, a heat stabilizer, inorganic particles, a pigment, and an organic lubricant.

[0051]

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

(Example 1) The test materials shown in Table 1 were annealed in a pretreatment furnace of a continuous galvanizing line.
The plating treatment shown in Table 4 was performed.

The hot-dip galvanizing is performed at a plating bath temperature of 460-6.
Plating was performed in a hot-dip galvanizing bath containing one or more of Al, Mg, and Si at 00 ° C., and the amount of plating was adjusted to 60 g / m ² by wiping with nitrogen gas. Cu during plating,
The addition of Ni was performed by using a steel sheet plated with these metals in advance and diffusing it into the plating during the plating process.

The tensile strength and elongation were determined by cutting a JIS No. 5 test piece from the plated steel strip produced in this way and performing a tensile test at room temperature. Tensile strength is 530
MP and below were rejected, and press workability was set as rejection when elongation was less than 25%.

Next, the plated steel sheets shown in Tables 2 to 4 were immersed in a coating type chromate treatment solution to perform chromate treatment. The adhesion amount of the chromate film was 50 mg / m ^{2 in} terms of Cr. On top of this, an epoxy polyester paint was applied as a primer with a bar coater and baked in a hot air drying oven to adjust the film thickness to 5 μm.
For the top coat, a polyester coating was applied with a bar coater and baked in a hot air drying oven to adjust the film thickness to 20 μm. Corrosion resistance after painting is measured by cutting the painted plate with a shear,
The occurrence of red rust on the cut end face after 30 cycles of CT was judged by the following rating. CCT is SST2hr →
One cycle of dry 4 hr → wet 2 hr was defined as one cycle. Score 3
The above was passed. 5: Less than 5% 4: 5% or more and less than 10% 3: 10% or more and less than 20% 2: 20% or more and less than 30% 1: 30% or more

Tables 2 to 4 show the evaluation results.

In Nos. 1 to 8, the strength was rejected because the C content of the steel sheet A was outside the range of the present invention. Number 9-16
For the steel sheet B, the strength was rejected because the Si content of the steel sheet B was outside the range of the present invention. In Nos. 57 to 64, the strength was rejected because the Mn content of the steel sheet E was out of the range of the present invention.
In Nos. 153 to 160, the press formability was rejected because the B content of the steel sheet K was outside the range of the present invention. Number 17
In Nos. 7 to 184, the press formability was rejected because the ratio of the Mn content to the C content of the steel sheet M was out of the range. Number 18
In Nos. 5 to 192, the press formability was rejected because the ratio of the Mn content to the Si content of the steel sheet N was out of the range. Number 2
In Nos. 17 to 224, the press formability was rejected because the Mn content of the steel sheet P was outside the range of the present invention. Number 225
In No. 232, the press formability was rejected because the Si content of the steel sheet Q was out of the range of the present invention. Other than these, good results were obtained in press workability, strength, and corrosion resistance after painting.

[0058]

[Table 1]

[0059]

[Table 2]

[0060]

[Table 3]

[0061]

[Table 4]

(Example 2) First, a test material shown in H of Table 1 was prepared, and a hot-dip galvanized steel sheet having a plating composition shown in Table 5 was prepared using a continuous hot-dip galvanizing equipment of an in-line annealing method. Manufactured. For hot-dip galvanizing, the plating bath temperature is 460
Plating was performed in a hot-dip galvanizing bath containing at least one of Al and Si at ~ 600 ° C, and the coating weight was adjusted to 60 g / m ² by wiping with nitrogen gas. Cu, N during plating
The addition of i was carried out by using a steel sheet plated with these metals in advance and diffusing it into the plating during the plating process. The tensile strength and elongation were determined by cutting out a JIS No. 5 test piece from the plated steel strip produced in this way and performing a tensile test at room temperature. Tensile strength is 5
30MP or less is rejected, press workability is 25% elongation
Less than was rejected. The plating adhesion was determined by attaching the tape to a plated steel sheet, bending it 180 degrees, bending it back, peeling off the tape, and rating the width of the plating adhered to the tape by the following rating. As for the score, x was rejected. ○: less than 1 mm △: 1 mm or more and less than 3 mm ×: 3 mm or more

Next, the plated steel sheets shown in Table 5 were immersed in a coating type chromate treatment solution to perform chromate treatment. The adhesion amount of the chromate film was 50 mg / m ^{2 in} terms of Cr. On top of this, an epoxy polyester paint was applied as a primer with a bar coater and baked in a hot air drying oven to adjust the film thickness to 5 μm. For the top coat, a polyester coating was applied with a bar coater and baked in a hot air drying oven to adjust the film thickness to 20 μm. The corrosion resistance after painting was measured by cutting the painted plate with a shear and applying CCT18.
The swollen width from the cut end face after 0 cycles was determined by the following rating. The CCT is a salt spray test using 0.5% salt water for 4 hours → drying for 4 hours → wet for 4 hours → drying for 4 hours
Was one cycle. The score was 3 or more. 5: less than 2 mm 4: 2 mm or more and less than 5 mm 3: 5 mm or more and less than 8 mm 2: 8 mm or more and less than 15 mm 1:15 mm or more

Table 5 shows the evaluation results.

For Nos. 1, 6, and 7, the adhesion was rejected because the Al and Si contents in the plating were outside the range of the present invention. Numbers 10, 16, 24, and 30 are Ni, C during plating.
Since the u content was out of the range of the present invention, the corrosion resistance was rejected.

[0066]

[Table 5]

(Example 3) First, test materials shown in H of Table 1 were prepared, and a hot-dip galvanized steel sheet having a plating composition as shown in Table 6 was prepared using an in-line annealing continuous hot-dip galvanizing equipment. Manufactured. For hot-dip galvanizing, the plating bath temperature is 460
Plating was performed in a hot-dip galvanizing bath containing at least one of Al, Mg, and Si at ~ 600 ° C, and the coating weight was adjusted to 60 g / m ² by wiping with nitrogen gas. C during plating
The addition of u and Ni was performed by using a steel sheet plated with these metals in advance and diffusing it into the plating in the plating process.

The tensile strength and elongation were determined by cutting out a JIS No. 5 test piece from the plated steel strip thus prepared and performing a tensile test at room temperature. Tensile strength is 530
MP and below were rejected, and press workability was set as rejection when elongation was less than 25%. The plating adhesion was determined by attaching the tape to a plated steel sheet, bending it 180 degrees, bending it back, peeling off the tape, and rating the width of the plating adhered to the tape by the following rating. As for the score, x was rejected. ○: less than 1 mm △: 1 mm or more and less than 3 mm ×: 3 mm or more

Next, the plated steel sheets shown in Table 6 were immersed in a coating type chromate treatment solution to perform a chromate treatment. The adhesion amount of the chromate film was 50 mg / m ^{2 in} terms of Cr. On top of this, an epoxy polyester paint was applied as a primer with a bar coater and baked in a hot air drying oven to adjust the film thickness to 5 μm. For the top coat, a polyester coating was applied with a bar coater and baked in a hot air drying oven to adjust the film thickness to 20 μm. After painting, the corrosion resistance was measured by cutting the painted plate with a shear and using CCT16.
The swollen width from the cut end face after 0 cycles was determined by the following rating. The CCT was performed in a cycle of a salt spray test using 0.5% salt water for 6 hr → dry 4 hr → wet 4 hr → frozen 4 hr. The score was 3 or more. 5: less than 2 mm 4: 2 mm or more and less than 5 mm 3: 5 mm or more and less than 8 mm 2: 8 mm or more and less than 15 mm 1:15 mm or more

Table 6 shows the results of the evaluation.

For Nos. 7 and 8, adhesion was rejected because the Al and Si contents in the plating were outside the range of the present invention.
Nos. 4, 11, 14, 20, 27, and 33 indicate M in plating.
Since the contents of g, Ni and Cu were out of the range of the present invention, the corrosion resistance was rejected.

[0072]

[Table 6]

(Example 4) First, test materials shown in H of Table 1 were prepared, and a hot-dip galvanized steel sheet having a plating composition as shown in Table 7 was prepared using an in-line annealing continuous hot-dip galvanizing equipment. Manufactured. For hot-dip galvanizing, the plating bath temperature is 460
Plating was performed in a hot-dip galvanizing bath containing at least one of Al, Mg, and Si at ~ 600 ° C, and the coating weight was adjusted to 60 g / m ² by wiping with nitrogen gas. C during plating
The addition of u and Ni was performed by using a steel sheet plated with these metals in advance and diffusing it into the plating in the plating process.

Next, these plated steel sheets were immersed in a coating type chromate treatment solution to perform a chromate treatment. The adhesion amount of the chromate film was 50 mg / m ^{2 in} terms of Cr.

The coating was performed by coating each with an epoxy polyester coating, a polyester coating, a melamine polyester coating, a urethane polyester coating, and an acrylic coating with a bar coater and baking in a hot air drying furnace to adjust the film thickness as shown in Table 5.

As a comparative example, the test materials shown in H of Table 1 were subjected to Fe annealing using an in-line annealing continuous hot-dip galvanizing equipment.
An alloyed hot-dip galvanized steel sheet having a plating composition of 10% was produced. For plating, hot-dip plating is performed for 3 seconds in a plating bath in a bath at 460 ° C., and the coating weight is reduced by 60% on one side by N ₂ wiping.
g / m ² . Thereafter, alloying treatment was performed in an alloying furnace for 20 seconds. The addition of Cu and Ni during plating was carried out by using a steel sheet plated with these metals in advance and diffusing it with Fe in the alloying process.

The coated steel sheet prepared as described above was cut with a shear, and the occurrence of red rust at the cut portion after 30 cycles of CCT was evaluated according to the following rating. CCT is SST
One cycle was 2 hr → dry 4 hr → wet 2 hr.
The score was 3 or more. 5: Less than 5% 4: 5% or more and less than 10% 3: 10% or more and less than 20% 2: 20% or more and less than 30% 1: 30% or more

Table 7 shows the evaluation results. Numbers 1, 6, 1
1, 16, 21, 26, 31, 36, and 41 were out of the range of the present invention, and thus the end face corrosion resistance after coating was rejected.
All of the other materials of the present invention showed good corrosion resistance after painting.

[0079]

[Table 7]

[0080]

As described above, the plated steel sheet according to the present invention is characterized in that one or two or more types of Ni and Cu are formed on the surface of a high-strength steel sheet having a metal structure in which martensite and retained austenite are mixed in ferrite. Containing Zn-
Al alloy plating, Zn-Al-Si alloy plating, Zn-
Al-Mg alloy plating or Zn-Al-Mg-Si
This is a steel plate that has been subjected to alloy plating and has excellent strength, press workability, and corrosion resistance, which are not found in conventional materials, and has an extremely large industrial effect.

Continued on the front page (72) Inventor Koji Sakuma 1 Kimitsu, Kimitsu-shi Nippon Steel Corporation Kimitsu Works F-term (reference) 4K027 AA02 AA23 AB02 AB09 AB26 AB44 AC82 AE03

Claims (8)

[Claims] 1. A mass% of C: 0.05 to 0.15%,
Si: 0.3 to 2.0%, Mn: 1.5 to 2.8%,
P: 0.03% or less, S: 0.02% or less, Al: 0.
005-0.5%, N: 0.006% or less, the balance consisting of Fe and unavoidable impurities,
When Si and% Mn are C, Si and Mn contents, respectively, (% Mn) / (% C) ≧ 15 and (% Si) / (%
C) On a high-strength steel sheet satisfying ≧ 4, Al: 0.2
Hot-dip galvanized layer containing one or two of Ni: 0.1 to 10% by mass and Cu: 0.05 to 3% by mass, with the balance being Zn and unavoidable impurities A high-strength hot-dip galvanized steel sheet having good corrosion resistance after painting and good press workability, characterized by having: 2. C: 0.05 to 0.15% by mass%,
Si: 0.3 to 2.0%, Mn: 1.5 to 2.8%,
P: 0.03% or less, S: 0.02% or less, Al: 0.
005-0.5%, N: 0.006% or less, the balance consisting of Fe and unavoidable impurities,
When Si and% Mn are C, Si and Mn contents, respectively, (% Mn) / (% C) ≧ 15 and (% Si) / (%
C) On a high-strength steel sheet satisfying ≧ 4, Al: 5 to 7
0% by mass, Si: 0.01 to 2% by mass, Ni: 0.1 to 10% by mass, Cu: 0.05 to 3% by mass
A high-strength hot-dip galvanized steel sheet having good corrosion resistance after coating and good press workability, characterized by having a hot-dip galvanized layer containing one or two of the following, and the balance being Zn and unavoidable impurities. 3. C: 0.05 to 0.15% by weight,
Si: 0.3 to 2.0%, Mn: 1.5 to 2.8%,
P: 0.03% or less, S: 0.02% or less, Al: 0.
005-0.5%, N: 0.006% or less, the balance consisting of Fe and unavoidable impurities,
When Si and% Mn are C, Si and Mn contents, respectively, (% Mn) / (% C) ≧ 15 and (% Si) / (%
C) On a high-strength steel sheet satisfying ≧ 4, Al: 2-1
2% by mass, Mg: 1 to 10% by mass, and further N
i: 0.1 to 10% by mass, Cu: 0.05 to 3% by mass, after coating, characterized by having a hot-dip galvanized layer composed of Zn and unavoidable impurities. High strength galvanized steel sheet with good corrosion resistance and good press workability. C: 0.05 to 0.15% by mass%,
Si: 0.3 to 2.0%, Mn: 1.5 to 2.8%,
P: 0.03% or less, S: 0.02% or less, Al: 0.
005-0.5%, N: 0.006% or less, the balance consisting of Fe and unavoidable impurities,
When Si and% Mn are C, Si and Mn contents, respectively, (% Mn) / (% C) ≧ 15 and (% Si) / (%
C) On a high-strength steel sheet satisfying ≧ 4, Al: 5 to 7
0 mass%, Mg: 1 to 10 mass%, Si: 0.01 to 2
% Ni, 0.1 to 10% by mass Ni, C
u: contains one or two kinds of 0.05 to 3% by mass, and has a hot-dip galvanized layer composed of Zn and unavoidable impurities, with the balance being excellent in corrosion resistance after painting and good in press workability. High-strength galvanized steel sheet. 5. B: 0.0002 to 0.00% by mass
The high-strength hot-dip galvanized steel sheet according to any one of claims 1 to 4, wherein the steel sheet contains 2% of the steel. 6. A steel sheet comprising the chemical component according to any one of claims 1 to 5, wherein the metal structure has a volume fraction of 3% or more and 2% or more.
A high-strength galvanized steel sheet having good corrosion resistance after painting and good press workability, characterized by containing 0% or less of martensite and retained austenite. 7. The plating layer of the plated steel sheet according to any one of claims 1 to 6, further comprising a chromate film layer as an intermediate layer, and further having an organic film layer having a thickness of 0.5 to 100 μm as an upper layer. A high-strength hot-dip galvanized coated steel sheet with good corrosion resistance after coating and good press workability, characterized by the following features. 8. The high-strength hot-dip galvanized steel sheet according to claim 7, wherein the organic coating is a thermosetting resin coating.