JPH1112712A - Manufacture of high tensile strength galvannealed steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in a P-containing high tensile strength steel sheet that alloying reaction after hot dip galvanizing is slow and resultantly productivity is deteriorated and to provide a method of manufacture of a galvannealed steel sheet improved in a plating-layer-alloying velocity and excellent in plating adhesion. SOLUTION: A high tensile strength steel sheet, containing 0.02-0.2 wt.% P, or a high tensile strength steel sheet, containing one or more kinds among, by weight, 0.02-2.5% Si, 0.3-2.5% Mn, and 0.1-6.0% Cr, is coated with (0.002 to 2.0) g/m<2> of Cu or Cu alloy and subjected to heating reduction treatment. Subsequently, the steel sheet is hot-dip galvanized in a galvanizing bath containing 0.05-0.25 wt.% Al and, if necessary, 0.1-1.0 wt.% Mg. After wiping, alloying heating treatment is applied at 460-550 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a high-tensile alloyed hot-dip galvanized steel sheet.

[0002]

2. Description of the Related Art Conventionally, galvannealed steel sheets have been widely used in automobiles, building materials and the like because of their excellent corrosion resistance after coating and plating adhesion. Recently, as part of measures to reduce the weight of automobiles, expectations for the application of a high-strength steel sheet of 340 to 590 MPa class to the inner plate of the body, the lower peripheral parts, the suspension parts, and the like are increasing.

[0003]

As one of surface-treated steel sheets for automobiles, alloying treatment is generally performed after hot-dip galvanizing from the viewpoint of corrosion resistance after coating such as coating swelling when a coating is scratched. An alloyed hot-dip galvanized steel sheet is used, but a high-tensile steel sheet containing 0.02 to 0.2% by weight of P, Si: 0.02 to 2.5% by weight, and Mn: 0.3 to 0.3%
Among high-strength steel sheets containing at least one of 2.5% by weight and Cr: 0.1 to 6.0% by weight, in the conventional non-oxidation-reduction (annealing) hot-dip galvanizing method, Due to the fact that elements added for high strength such as P in the previous annealing step are concentrated at the grain boundaries and the like, the Zn-Fe alloying reaction rate of the plating layer is slow, and compared with other steel types. The problem is that productivity is extremely poor.
An object of the present invention is to solve such problems and to provide a method for producing a high-tensile alloyed hot-dip galvanized steel sheet with high productivity by increasing the alloying speed in hot-dip galvanizing of a P-added high-tensile steel sheet. It is in.

[0004] The present inventors have already found that the Zn-F
Japanese Patent Laid-Open No. 4-33535 discloses a method for increasing the e-alloying speed.
No. 52 and JP-A-4-346644. These methods for producing an alloyed hot-dip galvanized steel sheet using pre-Ni plating and rapid low-temperature heating include, for example, P: 0.02 to 0.2% or Si: 0.02 to 2.5%.
%, The alloying speed in the alloying process at the time of alloying treatment is improved as compared with the conventional high-temperature hot-oxidation-reduction hot-dip galvanizing method. However, in this method, rapid low-temperature heating is essential after pre-Ni plating. Therefore, the production line is subject to significant equipment limitations, and is also subject to a non-oxidation-reduction method performed at a normal high temperature, In the hot-dip galvanizing line of the reduction system, the pre-Ni layer diffuses into the base iron during the heating, so that there are many practical problems such as its effect being reduced. Therefore, development of a more effective pretreatment method that can be applied to a normal plating line has been desired.

[0005] The present inventors have conducted further intensive studies to solve the above-mentioned problems.
High strength steel sheet containing 0.2% or Si: 0.02 to 2.5
Wt% Mn: 0.3 to 2.5 wt%, Cr: 0.1 to
After coating the surface of a high-strength steel sheet containing at least one of 6.0% by weight with Cu or a Cu alloy in advance, hot-dip galvanizing by a normal high-temperature heating reduction method, and then performing an alloying treatment. As a result, the Zn-
The rate of Fe alloying is remarkably improved, for example, usually Zn-F
(e) Even with 0.06% P steel in which the reaction does not easily proceed, the Fe reaction amount can be increased by about 30 to 50% under a constant alloying condition, and a plating layer having high plating adhesion can be obtained. Was found.

[0006]

The present invention has been completed based on this finding, and the gist thereof is as follows. (1) A high-tensile steel sheet containing 0.02 to 0.2% by weight of P is coated with 0.002 to 2.0 g / m ² of Cu or a Cu alloy and subjected to a heat reduction treatment. .05
Hot-dip galvanizing in a galvanizing bath containing up to 0.25% by weight, and after wiping, performing an alloying heat treatment at 460 to 550 ° C., characterized by excellent galvanic adhesion, Manufacturing method of plated steel sheet.

(2) Si: 0.02 to 2.5% by weight, M
n: 0.3 to 2.5% by weight, and Cr: 0.1 to 6.0% by weight.
After coating with ^{2 to} 2.0 g / m ² of Cu or Cu alloy, performing a heat reduction treatment, hot-dip galvanizing in a zinc plating bath containing 0.05 to 0.25% by weight of Al, and after wiping, A method for producing a high-tensile alloyed hot-dip galvanized steel sheet having excellent plating adhesion, comprising performing an alloying heat treatment at 460 to 550 ° C. (3) The plating adhesion as described in (1) or (2) above, wherein the zinc plating bath contains 0.05 to 0.25% by weight of Al and 0.1 to 1.0% by weight of Mg. It is a method for producing an excellent high-tensile alloyed hot-dip galvanized steel sheet.

[0008]

Embodiments of the present invention will be described below in detail. The present inventors preliminarily applied Cu treatments having different thicknesses (0.002 to 2 g /
m ² ) by displacement plating using an immersion method, followed by hydrogen 10
%-Reduced at a heating temperature of 780 ° C for 60 seconds in a nitrogen atmosphere,
3 in a 450 ° C. Zn-Al (0.05-0.25%) bath
Secondly hot-dip galvanized, and a predetermined plating thickness (60 g / m ² ) was obtained by wiping. Then, using an alloying furnace,
Alloying treatment is performed at 60 to 550 ° C, and Fe in the plating layer is
By measuring the reaction amount, the degree of promotion of Zn—Fe alloying was investigated in detail. Based on the results, the reasons for limiting each condition in the present invention will be described below.

P is the most representative element for increasing the tensile strength. First, the range of the P content in the target steel is set to 0.0
The reason for setting the content within the range of 2 to 0.2% is that if the content of P is 0.02% or more, a delay in the alloying speed occurs in a normal method for producing a galvannealed alloy, and also the strength of the material is secured. The reason why the upper limit of P in steel is set to 0.2% is that if it is added more than that, it becomes too hard. When P is not used as a high-tension additive element, Si, Mn,
A high-tensile steel sheet to which one or more of Cr is added is used.

The reason why the range of the Si content is set in the range of 0.02 to 2.5% is that when the content of Si is 0.02% or more, the plating wettability decreases in a normal alloyed hot-dip galvanizing production method, and This is for the purpose of delaying the formation speed and ensuring strength in terms of material. The upper limit of the content of Si in steel is set to 2.5% because if the content is further increased, the material becomes too hard. The reason that the range of the Mn content is in the range of 0.3 to 2.5% by weight is that the strengthening effect appears at 0.3% or more, and that the upper limit of 2.5% is that the elongation increases when added more. This is because it has an adverse effect.

The reason that the range of the Cr content is in the range of 0.1 to 6.0% by weight is that the effect of strengthening appears at 0.1% or more;
The upper limit of 6.0% is because no further improvement is observed in the addition of Nb. The high-strength galvanized steel sheet of the present invention can be manufactured by exactly the same method regardless of the components of the high-strength steel sheet to be processed.

Next, the lower limit of the adhesion amount of the Cu treatment layer is set to 0.0
The reason why it was set to 02 g / m ² was that the minimum adhesion amount for improving the alloying treatment speed of the hot-dip galvanized steel sheet was 0.002 g / m ^2.
m ² . Further, when the upper limit is more than 2.0 g / m ² , the amount of Cu eluted into the hot-dip galvanizing bath is considered to be too large, and the effect of improving the alloying speed is saturated. In addition, in consideration of economical aspects in terms of manufacturing cost, the range of the amount of the Cu treatment layer of the present invention to be applied is set to 0.002 to 2.0 g / m ² . In addition, a case where a Cu alloy containing Ni, Fe, P, Co, Zn, Cr, or the like was used as a coating material was also examined.
The effect of promoting Zn-Fe alloying by Cu was exactly the same.

Although the details of the reason why the alloying is promoted by the Cu coating treatment is unknown, it is difficult for Cu to penetrate into the base iron, and remains at the plating-base iron boundary even after high-temperature heating and reduction. Fe-Al-Z, which is considered to be the largest factor in determining the Zn-Fe alloying rate of the layer
This is probably because the formation of the n-type barrier layer is suppressed in some way. The reason why the lower limit of Al in the plating bath is set to 0.05% is that if it is less than this, the Zn—Fe alloying proceeds too much during the alloying treatment, and a brittle alloy layer develops too much at the interface of the base iron, so that the plating adhesion is poor. This is due to deterioration. The reason why the upper limit of Al is set to 0.25% is that if it exceeds 0.25%, an Fe—Al—Zn-based barrier layer is easily formed at the time of plating and alloying does not proceed at the time of alloying treatment.

When Mg is further contained in the plating bath, the lower limit of Mg is set to 0.1%, because the alloying is promoted and the red rust resistance of the coating flaw is improved. Was also recognized. The upper limit is set to 1% because the amount of dross generated in the bath exceeding the upper limit is greatly increased. Further, in the plating bath, Ni, Sb, P which is usually added as a trace additive element is added.
Even if b and Fe are contained, the effects of the present invention are not particularly affected.

The optimum temperature for the alloying treatment is 460 to 550 ° C. If the temperature is lower than 460 ° C., the alloying is difficult to proceed, and
If the temperature exceeds ℃, the alloying proceeds too much, the base iron interface alloy layer develops too much, and the plating adhesion deteriorates. The alloying time is not particularly defined, but is determined by the balance with the alloying temperature, and a range of 10 to 40 seconds is appropriate for actual operation. Although there is no particular limitation on the amount of plating, it is preferable that the plating amount is 10 g / m ² or more from the viewpoint of corrosion resistance and 150 g / m ² or less from the viewpoint of workability. As the P-added high-strength steel sheet, both hot-rolled steel sheets and cold-rolled steel sheets can be used, and ordinary ultra-low carbon Ti, Nb, B
The method for producing a high-tensile alloyed hot-dip galvanized steel sheet of the present invention can also be effectively applied to a high-tensile steel sheet further added with such.

[0016]

The present invention will be described in more detail with reference to the following examples.
explain. (Example 1) Extra low carbon type 0.03-0.18% P added cold
Cu coating treatment is applied to the rolled steel sheet by various methods to change the adhesion amount.
Let's go. As shown in Table 1, the plating conditions and
Under the conditions of heat treatment for metallization, plated steel sheets were produced. Coating
As a physical solution, sulfuric acid Cu10g / liter, pH about 0-3
Immersion and spray treatment time is 1
The amount of Cu adhesion was adjusted by changing the amount in the range of ３０30 seconds.
Reduction treatment is 10% H_Two-N_Two780 ° C in atmosphere
And then cooled to 460 ° C, bath temperature 460 ° C, Al
Hot-dip galvanizing bath containing Mg and Mg in the amounts shown in Table 1.
Plated with N _Two60g / m of adhesion amount by wiping^TwoTo
It was adjusted. After that, the alloying process is performed for 20 seconds in the alloying furnace.
Performing, about the obtained plated steel sheet, Zn-
The degree of Fe alloying and plating adhesion were compared. Evaluation method
Indicates the Fe reaction in the plating layer depending on the appearance
The amount and plating adhesion were peeled by a 60 degree V bending test.
The degree of release was determined by a tape test. Evaluation is shown below
According to the standard, a five-point scoring method was used.

Degree of alloying (three points or more passed) Rating Appearance Iron reaction amount in plating layer (%) 5 Uniform Less than 11-12% 4 Almost uniform Less than 10-11% 3 Almost uniform Less than 8-10% 2 Not good Uniform less than 7-8% 1 Uneven less than 7%

[0018] The evaluation was carried out by a five-point scoring method according to the criteria shown in the lower margin of the table.

[0019]

[Table 1]

As shown in Table 1, the alloying of the high-strength plated steel sheet produced by the production method of the present invention is promoted. Both the degree of conversion and the plating adhesion were good with a rating of 3 or more. On the other hand, in the comparative example, alloying was slow because the underlined conditions were out of the range of the present invention, and the degree of alloying or plating adhesion was evaluated as 2 or less, indicating poor plating. .

(Example 2) Cu treatment was performed on various types of cold-rolled ultra-low carbon steel sheets reinforced with additional elements other than P as shown in Table 2 by changing the amount of Cu. The plated steel sheet according to the present invention was manufactured under the plating conditions and alloying heat treatment conditions shown in Table 2. As a coating treatment solution, a sulfuric acid acid solution having a sulfuric acid concentration of 10 g / liter and a pH of about 0 to 3 was used, and the immersion or spraying treatment time was changed within a range of 1 to 30 seconds to adjust the Cu adhesion amount. Reduction process is 1
In an atmosphere of 0% H ₂ —N ₂ at 780 ° C. for 60 seconds, after cooling to 460 ° C., bath temperature 460 ° C., Al and Mg
Was plated in a hot-dip galvanizing bath containing the amount shown in Table 2, and the amount of adhesion was adjusted to 60 g / m ² by N ₂ wiping. After that, alloying treatment is performed for 20 seconds in an alloying furnace,
About the obtained plating steel plate, the Zn-Fe alloying degree of a plating layer and plating adhesion were compared. The evaluation method was such that the degree of alloying was evaluated by the amount of Fe reaction in the plating layer depending on the appearance, and the degree of peeling was determined by a 60 ° V bending test with a tape test for the plating adhesion. The evaluation was performed according to the same standard as in Example 1 by a five-point scoring method.

[0022]

[Table 2]

As shown in Table 2, the alloying of the high-strength plated steel sheet produced by the production method of the present invention is promoted, and the alloying treatment is performed in a relatively short time of 20 seconds. Both the degree of conversion and the plating adhesion were good with a rating of 3 or more. On the other hand, in the comparative example, alloying was slow because the underlined conditions were out of the range of the present invention, and the degree of alloying or plating adhesion was evaluated as 2 or less, indicating poor plating. .

[0024]

According to the production method of the present invention, a high-tensile alloyed hot-dip galvanized steel sheet having excellent plating adhesion and used for applications such as automobiles and building materials can be produced very efficiently. Therefore, it can be said that the present invention is an industrially valuable invention.

Claims (3)

[Claims] 1. A high-tensile steel sheet containing 0.02 to 0.2% by weight of P is coated with 0.002 to 2.0 g / m ² of Cu or a Cu alloy, and subjected to a heat reduction treatment. , Al
A high-tensile alloy excellent in plating adhesion, characterized in that hot-dip galvanizing is performed in a zinc plating bath containing 0.05 to 0.25% by weight, and after wiping, an alloying heat treatment is performed at 460 to 550 ° C. Manufacturing method of galvannealed steel sheet. 2. A high-strength steel sheet containing one or more of Si: 0.02 to 2.5% by weight, Mn: 0.3 to 2.5% by weight, and Cr: 0.1 to 6.0% by weight. , 0.002
-2.0 g / m ² of Cu or Cu alloy, after heat reduction treatment, Al 0.05-0.25 wt%
A hot-dip galvanized steel sheet excellent in plating adhesion, characterized in that hot-dip galvanizing is performed in a zinc plating bath containing, and after wiping, an alloying heat treatment is performed at 460 to 550 ° C. 3. The galvanizing bath has an Al content of 0.05 to 0.25.
3. The method for producing a high-tensile alloyed hot-dip galvanized steel sheet having excellent plating adhesion according to claim 1, comprising 0.1% by weight of Mg and 0.1 to 1.0% by weight of Mg.