JPH11200004A - Galvannealed steel sheet excellent in slidability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a galvannealed steel sheet excellent in slidability. SOLUTION: On the surface of the galvannealed layer, crystals consisting essentially of Ti and Al are recognized at >=5 pieces/mm<2> of 2-10 μm dimension of one side thereof. In this galvannealed layer, it is desirable to contain >=0.001 wt.% Ti and >=0.05 wt.% Al and further, >=5 wt.% Fe.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a galvannealed steel sheet having excellent slidability and, more particularly, to a galvannealed steel sheet having good plating peeling resistance.

[0002]

2. Description of the Related Art In a galvannealed steel sheet, Zn in the hot-dip galvanized layer and Fe of the base steel sheet are diffused by immediately performing a reheating treatment after the hot-dip galvanizing of the steel sheet. It is obtained by changing into an alloy layer. This alloyed hot-dip galvanized steel sheet has coating adhesion,
Because of its excellent weldability and corrosion resistance, it is widely used for automotive products, home electric appliances, building materials and the like.

[0003] However, alloyed hot-dip galvanized steel sheets generally have a high coefficient of friction. Therefore, in actual forming, it is necessary to take appropriate measures to improve the friction. For example, a method such as applying thin flash plating to the surface layer can be used. Have been.

On the other hand, alloyed hot-dip galvanized steel sheets have recently been expanded and applied to the field of deep drawing products and the like. Is growing. In order to meet such required characteristics, it is necessary to further improve the workability, and there is an urgent need to improve the slidability of the plating layer.

[0005] In general, it is known that in order to improve the slidability, it is effective to increase the Fe concentration in the plating layer by promoting alloying of the plating layer and to make the plating layer hard. However, when the Fe concentration in the plating layer is high, the growth of the extremely hard and brittle Γ phase becomes remarkable, so that the plating layer cannot follow the deformation of the base material during processing or further undergoes compression deformation. As a result, so-called powdering, in which the plating layer becomes powdery and peels off, is likely to occur, which may cause surface defects of the press-formed product.

[0006]

As described above, when the Fe concentration in the plating layer is increased in order to enhance the slidability, powdering easily occurs. Therefore, the slidability and the powdering resistance (plating resistance) are increased. It can be seen that the peeling property) is an opposite property. According to the conventional method, in order to obtain an alloyed hot-dip galvanized steel sheet excellent in any of these properties, the Fe concentration in the coating layer must be controlled to a narrow range of about 9 to 13%, There were various problems in actual operation.

[0007] The present invention has been made in view of the above circumstances, and the object thereof is to reduce not the Fe concentration in the plating layer but the T concentration.
To provide an alloyed hot-dip galvanized steel sheet having excellent slidability by focusing on i and Al.
It is an object of the present invention to provide an alloyed hot-dip galvanized steel sheet which is excellent not only in sliding property but also in peeling resistance.

[0008]

SUMMARY OF THE INVENTION The alloyed hot-dip galvanized steel sheet having excellent slidability according to the present invention, which can solve the above-mentioned problems, comprises:
The gist lies in that at least 5 / mm < ² > crystals of ^{2 to} 10 [mu] m on a side mainly composed of Ti and Al exist on the surface of the alloyed plating layer. In order to form a predetermined number of such Ti.Al-based crystals having a specific size, the contents of Ti and Al in the alloyed plating layer are each 0.001% or more of Ti (% by weight, hereinafter the same).
And Al: 0.05% or more, and more preferably, the Fe content is 5% or more.

Further, if the ratio of Fe in the alloyed plating layer is suppressed to 13% or less, plating peeling resistance can be imparted in addition to slidability.

[0010] The surface roughness Ra of the alloyed plating layer in the steel sheet of the present invention described above is 1.5 to 3 µm.
Since it is larger than Ra (about 1 μm) in the steel sheet without additives, the effect of retaining lubricating oil such as rust-preventive oil and processing oil attached to the surface of the plating layer during processing is increased. The slidability can be improved as compared with a steel plate.

In the steel sheet of the present invention, the area ratio of the δ ₁ phase in the alloyed plating layer is 40% or more, and
Since the area ratio of the phase is suppressed to 3% or less, it can be confirmed that the steel sheet of the present invention has excellent slidability and plating-peeling resistance also from the viewpoint of the alloying layer.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors considered that it is effective to promote alloying of a plating layer in order to improve the slidability. Focused on Ti instead of Fe. T during plating bath
It is the first finding by the present applicant that the alloying rate is significantly improved by adding a small amount of i. Japanese Patent Publication Nos. 6-27316 and 6-27317 each disclose the addition of Ti in the plating bath. A method for producing an alloyed hot-dip galvanized steel sheet is disclosed.

In order to efficiently produce an alloyed hot-dip galvanized steel sheet, it is necessary to increase the alloying speed of Zn and Fe. However, in the Zn—Fe alloy layer, the hard and brittle Zn
Since the -Fe alloy layer (so-called Γ phase) remarkably inhibits the adhesion of the plating layer, it is necessary to suppress the formation of the 層 phase as much as possible. 05-0.3% is added. In order to change the entire plating layer to an Fe—Zn alloy layer while maintaining the alloying suppression effect by adding a small amount of Al, it is necessary to add Ti in the plating bath.
It is the above-mentioned inventions based on the finding that it is effective to add C. and that the alloying speed can be remarkably increased.

Further studies have found that the addition of a small amount of Ti to the plating bath also contributes to the improvement of powdering resistance, and has already disclosed it (Japanese Patent Publication No. 6-3967).
9).

The present inventors have further studied the above-mentioned alloying accelerating action or powdering resistance improving action by Ti in relation to the slidability, and as a result, it has been found that the surface of the alloyed plating layer has a certain size. The present inventors have found that the slidability is significantly improved by the presence of a predetermined amount of the Ti / Al-based crystal, thereby completing the present invention. Hereinafter, each requirement constituting the present invention will be described in detail.

[0016] As described above, the present invention provides a method for producing a small amount of Ti and A
The most important point is where the Ti.Al-based crystal having a predetermined size and number is present by adding l in a complex manner. FIG. 1 shows that 0.2% T in the alloyed plating layer.
It is a micrograph (1500 times) showing the surface of the galvannealed steel sheet containing i and 0.13% Al. From the figure, it can be seen from the figure that the surface of the galvanized layer mainly contains Ti and Al. It can be seen that many extremely hard crystals having a side of 2 to 10 μm are formed. In contrast, FIG.
It is a microscope photograph (1500 times) showing the surface of the galvannealed steel sheet containing 0.13% of Al without containing Ti in the alloyed plating layer. Crystals or bulk crystals are formed. These crystals are formed by the T
Since the main component of the crystal is different from that of the i-Al-based crystal, the size of the diameter is also different, and the form is very irregular, so that it does not have a specific hardness. Therefore, as in the present invention, Ti and A
Fig. 3 shows the surface roughness (Ra) of the plating layer when a steel sheet containing l and a steel sheet not containing Ti (Ti-free steel sheet) were used and the Fe concentration in the alloyed plating layer was variously changed. As shown in the figure, Ra (1 μm
It can be seen that Ra of the steel sheet of the present invention is as large as 1.5 to 3 μm as compared with (before and after). In the figure, ○ indicates 0.2% T
i, a steel sheet of the present invention to which 0.13% Al was added, and △ indicates a steel sheet to which no Ti was added and 0.13% Al was added. As described above, according to the steel sheet of the present invention, Ra is 1.5 to
Since it is as large as 3 μm, it is considered that the effect of retaining lubricating oil such as rust-preventive oil and processing oil adhered to the plating layer surface during processing is increased, and as a result, slidability is improved. . In a conventional steel sheet to which Ti is not added, a preferable Ra for improving the slidability was considered to be about 1 μm. On the other hand, according to a Ti-added steel sheet as in the present invention,
Since the preferable range of Ra is 1.5 to 3 μm,
From the viewpoint of Ra, the steel sheet of the present invention is clearly different from the conventional steel sheet.

In order to effectively exert the effect of improving the slidability by forming such Ti / Al-based crystals, it is necessary to average 5 crystals / mm ² in which the size of each side satisfies 2 to 10 μm.
It is necessary that these exist. If the diameter and the number are not satisfied, the hardening effect due to the formation of the Ti / Al-based crystal cannot be obtained. As for the size of the diameter, the size of each side constituting the crystal needs to be 2 to 10 μm, preferably 2 to 8 μm, more preferably 2 to 6 μm. In the present invention, it is sufficient that the size of each side satisfies the above range, and the shape is not particularly limited. The present invention is applicable to any of rectangular, rectangular, and elliptical shapes. Are included in the range. Further, in order to effectively exert the above-described hardening effect, the average number of Ti.Al-based crystals having such a diameter is at least 5 / m 2.
m ² must be present or more. Preferably 7 pieces / m
m ² or more. However, if the number of Ti.Al-based crystals is too large, Ra becomes large, and conversely, the slidability is remarkably reduced. Therefore, it is preferable to set the upper limit to 15 crystals / mm ² or less. More preferably, the number is 12 / mm ² or less.

As described above, in the alloyed hot-dip galvanized steel sheet of the present invention, a predetermined amount of the Ti / Al-based crystal is present on the surface of the alloyed plating layer. Zn.Fe-based crystal, etc.) may be contained, and the number thereof is not particularly limited, and may be contained within a range that does not impair the function of the present invention.

In the plating layer, Ti and Al are respectively contained in the content of Ti: 0.001 to 0.5% and Al: 0.05 to 0.5%.
It is preferable to contain 5%. FIG. 4 is a diagram showing the change in the coefficient of friction when the steel sheet of the present invention containing Ti and Al and the steel sheet not containing Ti (Ti-free steel sheet) are used and the Fe concentration in the alloyed plating layer is variously changed. It is.
This coefficient of friction serves as an index for evaluating slidability,
The surface pressure is about 30N /
It is calculated based on the obtained pulling load when pressed at a pressure of mm ² and pulled out at a pulling speed of about 150 mm / min.

From FIG. 4, it can be seen that the alloy with a combined addition of Ti and Al as in the present invention has a significantly lower coefficient of friction than a steel sheet without the addition of Ti. This decrease in the coefficient of friction means an improvement in the slidability, and the coefficient of friction (0.16-0.2) required to obtain the desired sliding effect.
(Near 0) was conventionally required to be added with an Fe concentration of 9% or more.
It is understood that it is sufficient to add the e concentration of 5% or more. As described above, since excellent slidability can be imparted even when the Fe concentration in the plating layer is reduced, it is possible to suppress the generation of the hard and brittle Γ phase which adversely affects the slidability described above. Very useful in.

In order to effectively exert the effect of improving the slidability by the addition of Ti, the alloyed plating layer preferably contains 0.001% of Ti. More preferably, it is 0.05% or more. In addition, even if the content exceeds 0.5%, the above-mentioned effect is saturated, and the cost is increased, which is not practical. Therefore, the upper limit is preferably set to 0.5%. It is more preferably at most 0.3%.

It is preferable that the plating layer contains 0.05% or more of Al in order to effectively exert the above-described alloying suppressing action (specifically, the Γ layer formation suppressing action). It is more preferably at least 0.08%. Note that 0.5
%, The effect is saturated, and the cost is increased, which is not practical. Further, in producing an alloyed hot-dip galvanized steel sheet, the Al concentration in the plating bath and the Al concentration in the alloyed plating layer become substantially equal, so that the Al in the alloyed plating layer exceeds 0.5%. Then, since the Al concentration in the plating bath becomes high, floating dross such as FeAl ₅ is easily generated on the surface of the plating bath, which may cause surface defects such as dents. More preferably 0.3%
It is as follows.

Further, in the present invention, in order to impart excellent slidability, it is preferable that the Fe concentration in the plating layer is 5% or more. As described above, it is well known that Fe is an element that affects the slidability and plating peeling resistance of an alloyed plating layer, but conventionally, a steel sheet excellent in both of these properties is obtained. For this purpose, the Fe concentration in the plating layer should be 9-1.
It had to be controlled around 3%. However, by using the above-described hot-dip galvanized steel sheet containing the Ti / Al-based crystal, the lower limit of the Fe content contained in the plating layer can be increased from about 9% of the related art to 5%, This is very useful because the allowable range of the Fe content is expanded. When it is desired to impart powdering resistance in addition to slidability, the upper limit of the Fe content in the plating layer may be controlled to 13%. That is, in order to obtain an alloyed hot-dip galvanized steel sheet having excellent slidability and powdering resistance, the Fe content in the plating layer is reduced to about 9 to 13% of the conventional value.
Thus, according to the present invention, it can be expanded to 5 to 13%. More preferably, it is 7% or more and 11% or less.

The components contained in the alloyed plating layer in the present invention are basically as described above, with the balance being Zn
And Pb, Sb, etc., depending on the use of the plated steel sheet. For example, when it is desired to actively grow a spangle like a non-alloyed material such as a regular spangled material, and when the non-alloyed material is manufactured in the same plating bath as another alloyed material, the spangle is preferably used. For the purpose of growth, up to 1% of Pb or Sb is usually added to the plating bath. Therefore, Pb (about 1%) of substantially the same level is contained in the plating layer. However, when the regular spangle material is not manufactured in the same bath, it is not necessary to add Pb or Sb to the plating bath, so that the content of these elements in the plating layer becomes zero.

The alloyed plating layer thus obtained is
The area ratio of δ ₁ phase is 40% or more, and the area ratio of Δ phase is 3%
Or less, the powdering resistance to adversely affect Γ phase is suppressed significantly, are formed many useful [delta] ₁ phase to the improvement of the sliding property and powdering resistance. Therefore, it can be confirmed that the alloyed hot-dip galvanized steel sheet of the present invention has excellent slidability and powdering resistance also from the viewpoint of the alloyed layer.

To explain this point in detail, generally, the diffusion of Fe and Zn progresses as the alloying time increases in the alloyed galvanized steel sheet.
As the concentration increases, η phase (Zn) changes to ζ phase, δ ₁ phase, Γ phase.
It changes into a phase. As described above, in the conventional steel sheet, the Fe content is controlled in the range of about 9 to 13% in consideration of the balance between the slidability and the plating resistance, but in this case, the alloy phase is δ _1. Since the main phase is a phase and a phase, and also contains a large amount of a phase which causes plating peeling, good characteristics cannot be obtained.

On the other hand, according to the present invention, even if the Fe concentration in the alloyed plating layer is made lower than that of the conventional steel sheet, the slidability is remarkably improved by the formation of the Ti.Al-based crystal. [delta] ₁ phase mainly constituting the result Γ phase is hardly formed, thereby, improving the sliding property, even it is possible to remarkably improve also the resistance to plating peeling resistance.

As for the area ratio of each phase, the δ ₁ phase is preferably 40% or more from the viewpoint of making the entire plating layer relatively hard and improving the slidability. More preferably 60
% Or more. The Γ phase is extremely hard and brittle,
In order to improve the plating peeling resistance, it is desirable to minimize it, and it is preferable that it is 3% or less. It is more preferably at most 2%.

Next, a method for producing the steel sheet of the present invention will be described. In order to produce the steel sheet of the present invention, plating conditions and alloying conditions may be appropriately controlled so that desired Ti / Al-based crystals are formed on the surface of the plating layer.
Specifically, in addition to Ti and Al, if necessary, elements such as Pb and Sb are added to the plating bath, and the plating bath temperature and plating bath are adjusted so that a predetermined amount of element is contained in the plating layer. It is possible to adopt a method of controlling the plating conditions such as the temperature of the invading plate and controlling the alloying conditions (alloying temperature, alloying time, heat cycle to alloying, etc.) and the like.

Hereinafter, the present invention will be described in detail with reference to examples.
However, the following examples do not limit the present invention,
All modifications and alterations without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

[0031]

EXAMPLE First, a general Al-killed cold-rolled steel sheet (0.8 mm thick x 100 mm wide x 210 mm long) was used as an original sheet, and hot-dip galvanizing was performed while variously changing the Ti concentration and the Al concentration in the plating bath. went. Next, an alloying treatment was performed by changing the alloying time in various ways to obtain an alloyed hot-dip galvanized steel sheet having an alloyed hot-dip coating layer of about 100 g / m ² per one side of the steel sheet.

Using the alloyed hot-dip galvanized steel sheet thus obtained, the area ratio of each phase in the alloyed galvanized layer, slidability, and plating peeling resistance were examined by the following methods. Further, the surface of the obtained steel sheet was visually observed, and a crystal formed on the surface of the plating layer was observed under a microscope (1500 times).

[Ratio of each phase in plating layer] The ratio was determined by a constant current anodic electrolysis method. The experimental conditions are as follows. Electrolyte: ZnSO of 200g / L ₄ · 7H ₂ O and 10
0 g / L NaCl Current density: 200 mA / cm ² room temperature

[Slidability] FIG. 5 is a schematic view of a friction coefficient measuring method performed for evaluating the slidability. In the figure, 1 indicates a test piece, 2 indicates a flat tool, and F indicates a pulling load. First,
After pressing both sides of the test piece at a surface pressure of about 30 N / mm ² using a 20 mm square flat tool, the drawing speed is about 150 mm.
/ Min. At this time, a pulling load F was measured, and a friction coefficient: μ = F /
The index of slidability evaluation was obtained by calculating 2P.

[Plating Peeling Resistance] FIG. 6 is a schematic diagram of a V-bending test conducted to evaluate plating peeling resistance.
In the figure, 3 indicates a test piece, 4 indicates a punch, and 5 indicates a die. As shown in the figure, a V-bending test was performed using a V-shaped punch having a bending angle of 60 ° and a bending diameter of 1 mm, and the amount of plating peeling inside the bending was measured. Table 1 shows the results.

[0036]

[Table 1]

From the table, it can be considered as follows.
First, in Nos. 2, 3, 6, 7, and 10 to 13, the Ti / Al-based crystal on the surface of the plating layer and the Ti, Al and Fe concentrations in the alloyed plating layer satisfy the requirements of the present invention. It is excellent not only in slidability but also in plating resistance,
Further, it can be seen that a steel sheet having good surface properties can be manufactured at low cost.

No. 1 is also excellent in the above characteristics,
The cost is high because the amount of Ti is too large. No. 5 is excellent in both slidability and plating peeling resistance.
Since the amount is too large, the plating surface properties are inferior. Also N
In the case of O.9, the slidability was very good, but the Fe concentration was too high, the ratio of the Γ phase increased, and the plating peeling resistance was deteriorated.

On the other hand, in No. 4, the upper limit of the Fe concentration occupying the plating layer satisfies the preferable requirement, and the plating peeling resistance is good, but since no Ti is added, the plating surface is not added. No hard Ti.Al-based crystal is formed on the surface of the sample, and the sliding property is poor.

In Nos. 8, 14 to 17, the upper limit of the Fe concentration in the plating layer satisfies the preferable requirement.
In this example, the plating resistance is good, but the desired hard Ti / Al-based crystal is not formed on the plating surface and the sliding property is poor. For example, No. 8 is an example in which a desired crystal size cannot be obtained because Al is not added at all.
For Nos. 4 to 17, Fe concentration and alloying conditions are inappropriate,
In this example, a predetermined number is not formed (No. 14, 17), and the crystal size is too large (No. 15) or too small (No. 16).

[0041]

The steel sheet of the present invention is excellent in slidability since it is constituted as described above, and furthermore, a steel sheet having improved plating peeling resistance and plating surface properties can be obtained at low cost. . The above-mentioned slidability and plating-peeling resistance are the most important characteristics in press-working galvannealed steel sheets, so using the steel sheets of the present invention makes it easy to form difficult-to-form products such as deep drawing. It can be expected to be applied to various uses, for example, it can be formed into a thin film.

[Brief description of the drawings]

FIG. 1 is a photograph (1500 times) showing the surface of a plated layer of an alloyed hot-dip galvanized steel sheet containing 0.2% Ti and 0.13% Al in the plated layer.

FIG. 2 is a photograph (1500 times) showing the surface of a plating layer of an alloyed hot-dip galvanized steel sheet containing 0.13% Al (without adding Ti) in the plating layer.

FIG. 3 is a graph showing the relationship between the Fe concentration in an alloyed plating layer and the surface roughness (Ra) of the plating layer.

FIG. 4 is a graph showing the relationship between the Fe concentration in the alloyed plating layer and the coefficient of friction.

FIG. 5 is a schematic view showing a method of measuring a coefficient of friction.

FIG. 6 is a schematic view showing a measuring method of a V-bending test.

[Explanation of symbols]

 1,3 test piece 2 plane tool 4 punch 5 die

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koji Irie 1 Kanazawa-cho, Kakogawa-shi, Hyogo Kobe Steel Works Kakogawa Works

Claims (6)

[Claims] 1. The method according to claim 1, wherein Ti and Al are formed on the surface of the alloyed plating layer.
5 / mm ² crystals having a side of ^{2 to} 10 μm whose main component is
An alloyed hot-dip galvanized steel sheet having excellent slidability, characterized in that it exists as described above. 2. The method according to claim 1, wherein Ti: 0.001 is contained in the alloyed plating layer.
2. The galvannealed steel sheet according to claim 1, containing at least 0.05% by weight (% by weight, the same applies hereinafter) and at least 0.05% of Al. 3. The galvannealed steel sheet according to claim 1, wherein the alloyed plating layer contains 5% or more of Fe. 4. The galvannealed steel sheet according to claim 3, wherein excellent galvanic separation resistance is imparted by suppressing the ratio of Fe in the alloyed plating layer to 13% or less. 5. An alloyed plating layer having a surface roughness Ra of 1.5
The galvannealed steel sheet according to claim 4, which has a thickness of from 3 to 3 m. 6. The method according to claim 4, wherein the area ratio of the δ ₁ phase in the alloyed plating layer is 40% or more, and the area ratio of the Γ phase is suppressed to 3% or less. Alloyed hot-dip galvanized steel sheet.