JP3498466B2 - High workability alloyed hot-dip coated steel sheet and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet, and more particularly to an alloyed hot-dip galvanized steel sheet excellent in workability suitable as a steel sheet for automobiles and a method for producing the same.

[0002]

2. Description of the Related Art Alloyed hot dip plated steel sheets are used as steel sheets for automobiles because of their excellent corrosion resistance after coating, but they have a drawback called powdering during press forming, in which powdery plating peeling easily occurs. Powdering is Z
This is a phenomenon in which a Γ-phase layer having a high Fe content in the n-Fe alloy and having a brittle property is formed between the steel sheet and the base material, so that peeling occurs from the portion during press working. Γ
Since the phase is more likely to be formed when the Fe content in the plating layer is higher, powdering is more likely to occur as the Fe content in the plating layer is higher.

In order to suppress powdering of alloyed hot-dipped steel sheet and improve workability, a technique of adding several kinds of metal elements to a plating bath has been proposed. JP-A-6
No. 2-23948 discloses that Ti is 0.1 to 2% and Al is
Is 0.08 to 5.0%, Mg is 0.01 to 0.8%, and one or more of Mn, Ni, and Co in addition to Fe or Fe is 0.1 to 1. It has been reported that the addition of 6% improves the corrosion resistance and workability, and the effect obtained by adding Ni is described therein. It is because the Ti compound is uniformly dispersed and deposited, and
The fact that the crystal grains of the alloy itself become finer, the action of Mn that suppresses the initial generation of white rust in a corrosive environment, and the corrosion resistance of Ni can be combined to obtain remarkably excellent corrosion resistance. Further, as a means for improving workability, Al
And, if necessary, by adding Si, Fe—Zn, Fe between the plating layer and the base material, which causes plating separation,
It is described that the formation of the —Ti alloy layer is significantly suppressed.

Further, in Japanese Patent Laid-Open No. 7-3417, a Zn—Fe alloy layer is formed as a first layer on a steel sheet, 8 to 15% of Fe, 0.1 to 2% of Ni, and Al as a second layer. An alloyed hot-dip Zn-plated steel sheet composed of a Zn-Fe-Ni-Al alloy layer containing 1% or less of Al is disclosed. And second
An alloyed hot-dip galvanized steel sheet containing Sb, Pb, and Mg alone or in combination within 1% is disclosed in the layer, and it is described that it exhibits excellent red rust resistance.

[0005]

However, in JP-A-62-23948, in a zinc bath, Ti, Al,
Mg and one or more of Fe, Mn, Co, and Ni are added, and the characteristics obtained by adding Ni are only improvement in corrosion resistance, not improvement in workability. Further, Japanese Patent Laid-Open No. 7-3417 discloses that a steel sheet is subjected to Ni pre-plating, then hot-dip galvanizing, and further subjected to alloying treatment. It easily becomes a plated part, which adversely affects the surface appearance.

It is an object of the present invention to provide a high workability alloyed hot-dip galvanized steel sheet and a method for producing the same which solves the above problems.

[0007]

Therefore, the present inventors
Ni is added to a hot dip galvanizing bath containing 1 and at least one of Pb, Sb, Bi and Sn is added to perform hot dip plating, and the galvanized steel sheet is alloyed. However, even though the Fe content in the plating layer was high, the amount of plating peeling during processing was Ni, Pb, Sb, B.
i, Sn compared with alloyed hot-dip galvanizing of a bath without addition of Sn, and by performing hot-dip galvanizing in a hot-dip galvanizing bath containing Ni, Ni can be concentrated at the interface between the plating and the steel sheet. The present invention has been completed by finding that it is possible and that the oxide of Ni is not formed and does not adversely affect the surface appearance of the galvannealed steel sheet.

The present invention is based on the above findings.
1 to 0.1 to 0.25% by weight, Fe to 6.0 to 18.0
% By weight, 0.05 to 0.3% by weight of Ni, and further Pb,
0.001 to at least one of Sb, Bi, and Sn
Provided is a high workability alloyed hot-dip galvanized steel sheet having a plating layer containing 0.01% by weight and the balance being zinc and inevitable impurities.

According to the method of the present invention for producing such a steel sheet, Al is 0.1 to 0.2% by weight and Ni is 0.01 to 0.01%.
0.2 wt% and further 0.001 to 0.01 wt% of at least one of Pb, Sb, Bi and Sn, and the balance is hot-dip galvanized in a zinc plating bath consisting of zinc and a trace amount of unavoidable impurities. After being applied, the method is a method for producing a high workability alloyed hot-dip galvanized steel sheet, which comprises heating at a heating rate of 20 ° C./s or less and performing heat alloying treatment at 480 to 600 ° C.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The action of each composition component constituting the plating layer of galvannealing and the galvanizing bath according to the present invention, the reason why the content is set as described above, and the alloying treatment conditions are as follows. An embodiment will be described. (1) Al When Al is not contained in the zinc bath in hot dip plating, the steel sheet is immersed in the zinc bath and Zn-
Since the Fe alloying reaction proceeds, a Zn-Fe alloy layer with a high Fe content is formed at the interface between the plating layer and the steel sheet at the completion of hot dip plating, and the Zn-Fe alloy layer grows by further alloying treatment. , Increase the thickness. The alloy layer is composed of a hard and brittle alloy phase called a Γ layer (Fe: 22% by weight), so that peeling easily occurs during processing.

In order to improve the workability of the alloyed hot-dip plated steel sheet, it is necessary to suppress the alloying reaction of Zn-Fe, which can be achieved by incorporating Al in the zinc bath. When a steel sheet is immersed in a zinc bath, a Fe-Al alloy layer (Al-enriched layer) is formed on the surface of the steel sheet, and the alloying reaction between the plating layer (Zn) and the steel sheet (Fe) is suppressed. If the Zn-Fe alloy layer is not formed and further alloying treatment is performed, the Al-rich layer is pierced and Zn-Fe alloying starts from the grain boundaries of the steel sheet and proceeds. Z
The thicker the Al-rich layer is, the later the timing at which the alloying of n-Fe starts becomes, and the formation of the Γ layer, which causes deterioration of workability, can be suppressed.

However, if the Al-rich layer is too thick, Zn-Fe alloying reaction does not occur in the alloying process, resulting in uneven alloying or the inability to obtain an alloyed hot-dip plated steel sheet. Therefore, the content of Al in the zinc bath is limited to 0.1 to 0.2% by weight. If it is less than 0.1% by weight, Zn-Fe alloying will start early, and if alloying treatment is performed, brittle Γ phase will be formed in large numbers and peeling will easily occur during processing. This is because the Fe alloying reaction is unlikely to occur and it becomes difficult to control the Fe content in the plated layer within the target range during the production of the alloyed steel sheet.

(2) Mechanism of Adhesion Improvement by Ni, Pb, Sb, Bi, Sn (2-a) Ni Ni contained in the zinc bath causes Fe-on the surface of the steel sheet when the steel sheet is immersed in the zinc bath. A Ni alloy layer is formed. That Fe
The -Ni alloy layer is more noticeable as the Ni content in the plating layer is higher, and has the function of suppressing Zn-Fe alloying together with the Al-rich layer. When the hot dip plated steel sheet is heated and alloyed, Ni diffuses from the surface of the steel sheet into the plating layer to form a Zn-Fe-Al-Ni quaternary alloy layer. System alloy (F
e content 22% by weight) Formation of Γ phase is suppressed.

However, when the Ni content in the plating layer exceeds 0.1% by weight, the Al—Ni alloying reaction becomes remarkable, so that the formation of the Fe—Ni alloy layer and the Al-rich layer becomes insufficient. However, there is a problem that the alloying suppressing function is reduced and the plating adhesion is deteriorated. Further, if only Ni is added, a Ni content of 0.05 wt% or more is necessary to obtain a sufficient Zn-Fe binary alloy Γ phase suppressing effect. Therefore, in order to improve the adhesion by adding only Ni, 0.0
It is necessary to set the Ni content to 5 to 0.1% by weight.
It becomes difficult to control the concentration.

(2-b) Ni and Pb, Sb, Bi, S
Synergistic effect with n Here, Pb, S
When at least one of b, Bi and Sn is contained in an amount of 0.001% by weight or more, Fe-N rather than Al-Ni alloying reaction
Since the i-alloying reaction is promoted, the allowable range of the Ni content is widened, and the concentration control is facilitated. Also, Pb, Sb,
Other effects of Bi and Sn include improvement of wettability and suppression of non-plating, but P in the plating layer
If the contents of b, Sb, Bi and Sn exceed 0.01% by weight, problems such as deterioration of corrosion resistance and blackening occur.

Therefore, the Ni content in the plating layer is 0.
05 to 0.3% by weight, and further Pb, Sb, Bi, S
0.001 to 0.01% by weight of at least one of n
Is contained in the plating layer. Further, when Ni is added to the hot dip galvanizing bath to obtain the above-mentioned plated layer, the Ni content exceeds 0.1% by weight, depending on the amount of Al added at the same time.
Dross (Ni ₂ Al ₃ ) begins to be generated depending on the content, and when the content exceeds 0.2% by weight, the dross amount remarkably increases,
It causes plating surface defects. On the other hand, Ni in the plating layer is
Before the heat-alloying treatment, the average concentration of Ni in the plating layer is the same as the Ni concentration in the plating bath, as it has concentrated on the surface of the steel sheet.
Higher than concentration. Therefore, in order to obtain a plating layer having the above-mentioned Ni composition, it is possible to manufacture even if the Ni content in the plating bath is slightly lower, and the Ni content in the plating bath is 0.2% by weight or less in consideration of dross suppression. And More preferably, it is 0.1% by weight or less. Further, in order to realize the effect of Ni in the plating bath, Ni: 0.01 wt% or more is contained in the plating bath.

Further, since Pb, Sb, Bi and Sn are contained in the plating layer in an amount substantially equal to that of the plating bath,
1 to 0.01 wt% is contained in the plating bath. Taking the above into consideration, the Ni content in the plating bath is 0.01 to 0.2.
%, Preferably 0.01 to 0.1% by weight, and at least one of Pb, Sb, Bi, and Sn is 0.1% by weight.
001 to 0.01% by weight contained in the plating bath.

Further, as already described, Ni is concentrated on the interface between the plating and the base iron by plating with the hot dip galvanizing bath containing Ni. Since it is possible to manufacture by the same method as the conventional hot-dip galvanized steel plate manufacturing without needing to adhere, Pb, Sb, B in the zinc bath described above can be manufactured.
In addition to the effect of improving the wettability of i and Sn, the unplated portion of the steel sheet is reduced, and the surface appearance after alloying is improved.

(3) The temperature rising rate during the alloying treatment is 20 ° C. /
The reason why the temperature is set to s or less is that when the heating rate exceeds 20 ° C./s, a Γ phase is formed between the plating layer and the steel sheet and workability deteriorates, and the alloying temperature is 480 to 600 ° C. The reason is that when the temperature exceeds 600 ° C, the Zn-Fe alloying reaction proceeds considerably and the Γ phase is easily formed, so that the workability deteriorates, and when the temperature is less than 480 ° C, the alloying reaction does not proceed and the surface layer is formed. This is because zinc remains.

[0020]

EXAMPLES Next, examples of the galvannealed steel sheet of the present invention will be described in comparison with comparative examples. Examples 1 to 6 show alloyed hot-dip galvanized steel sheets of the present invention having the composition of components in the zinc bath and plating layer shown in Table 1, and comparative examples thereof are shown in Comparative Examples 1 to 6. The methods for evaluating the workability of the steel sheet and the surface appearance of the steel sheet are shown below. (90 ° C. bending test) After shearing the sample to 40 × 50 mm, a knit tape was attached, 90 ° compression bending was performed, and bending back was performed, then the knit tape was peeled off, and the plating powder adhering to the tape was measured by a fluorescent X-ray device ( Made by Rigaku; Model37
0) was used to measure zinc counts.

If the Zn count number is less than 50, it is ⊚, 50 to
100 was evaluated as ◯ and 101 or more was evaluated as x. (Steel plate surface appearance) In the sample of the alloyed hot dip galvanized steel plate,
The surface appearance was evaluated in the area of 500 mm square as shown below.

[0022] ◯: No plating or alloying unevenness ×: No plating or uneven alloying

[0023]

[Table 1]

As shown in Table 1, in Examples 1 to 6 according to the concentration of each component in the bath and the alloying conditions according to the present invention, the bending test results are excellent and the surface appearance is also excellent. On the other hand, Comparative Example 1 in which the amount of Al in the bath is insufficient, Comparative Example 2 in which Ni is not added to the bath, and Comparative Example 4 not containing any of Pb, Sb, Bi and Sn have poor bending workability, In Comparative Example 3 in which Al in the bath is excessive, the surface appearance is deteriorated. Ni in the bath
In Comparative Example 6 in which the amount is too large, both the workability and the appearance are inferior. Further, in Comparative Examples 5, 7, and 8 in which the alloying conditions are not appropriate, bending characteristics or appearance defects are generated.

[0025]

EFFECTS OF THE INVENTION From the comparative example of Table 1, when the Fe content in the plating layer exceeds 10% by weight, the workability deteriorates.
In the example in which the alloying hot-dip galvanizing was performed in the added zinc bath, the workability was less deteriorated than the comparative example even when the Fe content in the plating layer greatly exceeded 10% by weight. It was clarified that the property is maintained, and further, by adding at least one of Pb, Sb, Bi, and Sn, no plating is formed on the steel sheet, and the appearance appearance is not deteriorated. It has become possible to manufacture galvannealed steel sheets.

─────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-4-13855 (JP, A) JP-A-8-20854 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (2)

(57) [Claims] 1. Al of 0.1 to 0.25% by weight, Fe of 6.0 to 18.0% by weight, Ni of 0.05 to 0.3% by weight, and further Pb, Sb, Bi and Sn. At least one
A high workability alloyed hot-dip plated steel sheet containing 0.001 to 0.01% by weight of a seed , and the balance having a plating layer made of zinc and unavoidable impurities. 2. Al: 0.1 to 0.2% by weight, Ni: 0.01 to 0.2% by weight, and further Pb, Sb, Bi, S.
0.001 to 0.01% by weight of at least one of n
After hot-dip galvanizing in a galvanizing bath containing zinc and a trace amount of unavoidable impurities, the temperature rising rate is 20 ° C /
A method for producing a high-workability alloyed hot-dip galvanized steel sheet, which comprises heating at s or less and heat alloying at 480 to 600 ° C.