JP3372853B2 - Alloyed hot-dip galvanized steel sheet with excellent slidability - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alloyed hot-dip galvanized steel sheet having excellent slidability, and further relates to an alloyed hot-dip galvanized steel sheet which also has good resistance to peeling of plating.

[0002]

2. Description of the Related Art An alloyed hot-dip galvanized steel sheet is subjected to a reheating treatment immediately after hot-dip galvanizing, whereby Zn in the hot-dip galvanized layer and Fe of the base steel sheet are diffused, and the entire galvanized layer is Zn-Fe. It is obtained by changing to an alloy layer. This galvannealed steel sheet has coating adhesion,
Due to its excellent weldability and corrosion resistance, it is widely used for automobile products, household electrical products, building materials, etc.

However, since the alloyed hot-dip galvanized steel sheet generally has a high friction coefficient, it is necessary to take appropriate measures for improving friction in actual forming. For example, a method such as applying a thin flash plating to the surface layer is used. Has been.

On the other hand, recently, alloyed hot-dip galvanized steel sheets have been expanded and applied to the field of deep-drawing products and the like, and there is a demand that the above-mentioned friction improving measures are omitted as much as possible and the products are manufactured at low cost. Is increasing. It is necessary to further improve the workability in order to meet such required characteristics, and it is earnestly desired to improve the slidability of the plating layer.

In general, in order to improve slidability, it is known that it is effective to increase the Fe concentration in the plating layer and harden the plating layer by promoting alloying of the plating layer. However, when the Fe concentration in the plating layer becomes 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, and further the compressive deformation is added. As a result, so-called powdering in which the plating layer becomes powdery and peels off easily occurs, which may lead to surface defects of the press-formed product.

[0006]

As described above, if Fe concentration in the plating layer is increased in order to improve slidability, powdering is likely to occur. Therefore, slidability and powdering resistance (plating resistance) It can be seen that this is a property that is contradictory to (peelability). According to the conventional method, in order to obtain an alloyed hot-dip galvanized steel sheet excellent in any of these characteristics, the Fe concentration in the plating layer must be controlled within a narrow range of approximately 9 to 13%, There were various problems in actual operation.

The present invention was made in view of the above circumstances, and its purpose is not the Fe concentration in the plating layer but the T concentration.
It is to provide an alloyed hot-dip galvanized steel sheet excellent in slidability by paying attention to i and Al.
An object of the present invention is to provide an alloyed hot-dip galvanized steel sheet which is excellent in sliding resistance as well as plating resistance.

[0008]

The alloyed hot-dip galvanized steel sheet having excellent slidability according to the present invention which can solve the above-mentioned problems,
The gist is that there are 5 to 15 crystals / mm ² having a side of ² to 10 μm and containing Ti and Al as main components on the surface of the alloyed plating layer. In order to form a predetermined number of Ti / Al-based crystals having such a specific size, the content of Ti and Al in the alloyed plating layer is Ti: 0.001% or more (weight%, the same applies hereinafter).
And Al: 0.05% or more, and further, the Fe content is preferably 5% or more.

Further, if the proportion of Fe in the alloyed plating layer is suppressed to 13% or less, not only sliding property but also plating peeling resistance can be imparted.

The surface roughness Ra of the alloyed plating layer in the above-mentioned steel sheet of the present invention is 1.5 to 3 μm.
Since it is larger than Ra (about 1 μm) in the additive-free steel sheet, the effect of retaining lubricating oil such as rust-preventing oil and processing oil adhering to the surface of the plating layer during processing increases It is possible to improve slidability as compared with a steel plate.

Further, the area ratio of the δ ₁ phase in the alloyed plating layer in the steel sheet of the present invention is 40% or more, and Γ
Since the area ratio of the phases is suppressed to 3% or less, it can be confirmed that the steel sheet of the present invention is excellent in slidability and resistance to delamination even from the viewpoint of the alloyed layer.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Based on the viewpoint that it is effective to promote alloying of a plating layer in order to improve slidability, the present inventors have proposed a conventional alloying promoting element in the plating layer. Attention was paid to Ti instead of Fe. T in the plating bath
It is a finding first discovered by the applicant of the present invention that the alloying rate is remarkably improved by adding a small amount of i. In Japanese Patent Publication Nos. 6-27316 and 6-27317, Ti is added to the plating bath, respectively. A method for producing an alloyed hot-dip galvanized steel sheet is disclosed.

In order to efficiently produce a galvannealed steel sheet, it is necessary to increase the alloying rate of Zn and Fe. However, among the Zn--Fe alloy layers, hard and brittle Zn
Since the -Fe alloy layer (so-called Γ phase) significantly impairs the adhesion of the plating layer, it is necessary to suppress the formation thereof as much as possible. For the purpose of suppressing the growth of the Γ phase, Al is usually added to the plating bath at about 0. 05-0.3% is added. In order to change the entire plating layer into a Fe-Zn alloy layer while maintaining the alloying suppressing effect by the addition of such a small amount of Al, Ti in the plating bath is changed.
Each of the above inventions has been made based on the finding that it is effective to add the alloying alloy and the alloying speed can be remarkably increased.

Furthermore, in the subsequent research, it was found that the addition of a trace amount of Ti to the plating bath also contributes to the improvement of powdering resistance, and it has already been disclosed (Japanese Patent Publication No. 6-3967).
9).

The present inventors further studied the alloying promoting action or the powdering resistance improving action of Ti described above in relation to the slidability, and as a result, a certain size was found on the surface of the alloyed plating layer. The inventors have found that the slidability is remarkably improved by the presence of a predetermined amount of a Ti / Al-based crystal, and have completed the present invention. Hereinafter, each requirement that constitutes the present invention will be described in detail.

As described above, according to the present invention, trace amounts of Ti and A are used.
The most important point is where Ti / Al-based crystals of a predetermined size and number are made to exist by the combined addition of l. Figure 1 shows 0.2% T in the alloyed plating layer.
2 is a photomicrograph (1500 times) showing the surface of a galvannealed steel sheet containing i and 0.13% Al, which shows that the surface of the galvanized layer contains Ti and Al as main components. It can be seen that a large number of extremely hard crystals having a side of 2 to 10 μm are formed. On the other hand, in FIG.
It is a photomicrograph (1500 times) showing the surface of the galvannealed galvanized steel sheet containing 0.13% of Al but not Ti in the galvannealed layer, which is rod-shaped with Fe and Zn as the main components. Crystals or lump crystals are formed. These crystals are T formed by the steel sheet of the present invention.
The i-Al type crystal does not have a specific hardness because the main component of the crystal is different from that of the i-Al type crystal and the size of the diameter is also different and the morphology is very irregular. Therefore, as in the present invention, Ti and A
Using a steel sheet containing 1 and a steel sheet not containing Ti (Ti-free steel sheet), the surface roughness (Ra) of the plated layer was investigated when the Fe concentration in the alloyed plated layer was variously changed. As shown in, the 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, ○ is 0.2% T
i is the steel sheet of the present invention to which 0.13% Al is added, and Δ is the Ti-free steel sheet to which Ti is not added and 0.13% Al is added. Thus, 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 holding the lubricating oil such as rust preventive oil and processing oil adhering to the surface of the plating layer during the processing is enhanced, and as a result, the slidability is improved. . In addition, in the conventional steel sheet to which Ti is not added, the preferable Ra for improving the slidability was considered to be about 1 μm, whereas according to the Ti-added steel sheet according to the present invention,
Since the preferable range of Ra is 1.5 to 3 μm,
From the viewpoint of Ra as well, the steel sheet of the present invention is clearly differentiated from the conventional steel sheet.

In order to effectively exert the slidability improving effect by forming such a Ti / Al type crystal, the average number of the crystals satisfying the size of each side of 2 to 10 μm is 5 to 15 /
It is necessary that mm ^{2 be} present. 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. Regarding the size of the diameter, it is necessary that the size of each side forming the crystal is 2 to 10 μm,
The thickness is 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 thereof is not particularly limited, and the present invention may be any of rectangular, rectangular, and elliptical shapes. Within the range of. Further, in order to effectively exhibit the above-mentioned hardening effect, at least 5 Ti / Al-based crystals having such a diameter are used on average.
It must be at least mm ² . Preferably 7 /
mm ² or more. However, if the number of Ti / Al-based crystals is too large, Ra becomes large and conversely the slidability is remarkably deteriorated. Therefore, the upper limit is set to 15 / mm ² or less. It is preferably 12 pieces / mm ² or less.

As described above, the alloyed hot-dip galvanized steel sheet of the present invention has a predetermined amount of the Ti / Al-based crystal on the surface of the alloyed-plated layer. Zn.Fe-based crystals, etc.) may be contained, and the number thereof is not particularly limited, and may be contained within a range not impairing the action of the present invention.

In the plated layer, Ti and Al are contained in the amount of Ti: 0.001 to 0.5% and Al: 0.05 to 0.
It is preferable to contain 5%. FIG. 4 is a diagram showing changes in the friction coefficient when various Fe concentrations in the alloyed plating layer are changed using the steel sheet of the present invention containing Ti and Al and the steel sheet not containing Ti (Ti-free steel sheet). Is.
This coefficient of friction is an index for slidability evaluation,
The surface pressure on both sides of the test piece is about 30 N / with a flat tool of 20 mm square.
It is calculated on the basis of the pulling load obtained by pressing at mm ² and pulling out at a pulling speed of about 150 mm / min.

It can be seen from FIG. 4 that the composite addition of Ti and Al as in the present invention has a remarkably smaller friction coefficient than that of a Ti-free steel sheet containing no Ti. This reduction of the friction coefficient means improvement of slidability, and the friction coefficient (0.16 to 0.2) required to obtain a desired sliding effect.
In order to secure (about 0), it was necessary to add Fe concentration of 9% or more in the past, but according to the present invention, F
It is understood that it is sufficient to add the e concentration of 5% or more. Thus, even if the Fe concentration in the plating layer is reduced, excellent slidability can be imparted, so that it is possible to suppress the generation of the hard and brittle Γ phase which adversely affects slidability. Very useful at.

In order to effectively exhibit the slidability improving effect by adding Ti, it is preferable that the alloyed plating layer contains 0.001% of Ti. It is more preferably at least 0.05%. Even if the content exceeds 0.5%, the above effect is saturated and the cost is increased, which is not practical. Therefore, the upper limit is preferably 0.5%. It is more preferably 0.3% or less.

The plating layer preferably contains 0.05% or more of Al in order to effectively exert the alloying suppressing effect (specifically, the Γ layer formation suppressing effect) described above. It is more preferably 0.08% or more. In addition, 0.5
Even if it is added in excess of%, the above effect is saturated and the cost becomes high, which is not practical. Further, in producing an alloyed hot-dip galvanized steel sheet, since the Al concentration in the plating bath and the Al concentration in the alloyed plating layer are almost equal, Al in the alloyed plated 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 lead to surface defects such as blemishes. More preferably 0.3%
It is the following.

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 of the alloyed plating layer and the resistance to delamination, but conventionally, a steel sheet excellent in both properties is obtained. To achieve this, the Fe concentration in the plating layer should be 9 to 1
I had to control it to around 3%. However, by using the above-described hot-dip galvanized steel sheet containing Ti / Al-based crystals, the lower limit of the Fe content contained in the plated layer can be expanded from about 9% of the prior art to 5%, It is very useful because the allowable range of Fe content is expanded. Furthermore, in order 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 excellent in slidability and powdering resistance, the Fe content in the plating layer is set to about 9 to 13% of the conventional value.
Therefore, according to the present invention, it can be expanded to 5 to 13%. It is more preferably 7% or more and 11% or less.

The components contained in the alloyed plating layer in the present invention are basically as described above, and the balance is Zn.
Although it is an unavoidable element, Pb, Sb, etc. may be appropriately contained in addition to the above, depending on the application of the plated steel sheet. For example, when it is desired to positively grow spangle like a non-alloyed material such as regular spangled material, and the non-alloyed material is manufactured in the same plating bath as another alloyed material, spangle For the purpose of growth, a maximum of 1% Pb or Sb is usually added to the plating bath. Therefore, the plating layer also contains approximately the same level of Pb (about 1%). 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 the content of these elements in the plating layer becomes zero.

The alloyed plating layer thus obtained is
Area ratio of δ ₁ phase is 40% or more, and area ratio of Γ phase is 3%
Below, the Γ phase that adversely affects the powdering resistance is significantly suppressed, and many δ ₁ phases useful for improving the slidability and the powdering resistance are formed. Therefore, it can be confirmed that the alloyed hot-dip galvanized steel sheet of the present invention is excellent in slidability and powdering resistance also from the viewpoint of the alloyed layer.

Explaining this point in detail, in general, in the alloyed plating layer of the galvannealed steel sheet, Fe and Zn diffuse as the alloying time becomes longer.
As the concentration increases, η phase (Zn) 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 resistance to peeling of plating, but the alloy phase in this case is δ ₁ Phase and Γ phase are the main components, and a large amount of Γ phase, which causes plating peeling, is also included, so 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 reduced as compared with the conventional steel sheet, the slidability is remarkably improved due to the formation of the Ti / Al type crystal. Since the δ ₁ phase is the main constituent and the Γ phase is hardly formed, it becomes possible to improve the slidability and further the plating peel resistance.

As the area ratio of each phase, the δ ₁ phase is preferably 40% or more from the viewpoint of making the entire plated layer relatively hard and improving slidability. More preferably 60
% Or more. Also, since the Γ phase is extremely hard and brittle,
In order to improve the resistance to peeling of plating, it is desirable to reduce the amount as much as possible, and it is preferably 3% or less. It is more preferably 2% or less.

Next, a method for manufacturing the above-mentioned steel sheet of the present invention will be described. In order to produce the steel sheet of the present invention, the plating conditions and alloying conditions may be appropriately controlled so that the 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 so that a predetermined amount of element is contained in the plating layer and the plating bath temperature and A method of controlling the plating conditions such as the penetration plate temperature and the alloying conditions (alloying temperature, alloying time, heat cycle for alloying, etc.) and the like can be adopted.

The present invention will be described in detail below based on examples.
However, the following examples do not limit the present invention,
All changes and modifications made without departing from the spirits of the preceding and the following are included in the technical scope of the present invention.

[0031]

EXAMPLES First, a general Al-killed cold-rolled steel plate (0.8 mm thick × 100 mm wide × 210 mm long) was used as a base plate, and hot dip galvanizing was performed while variously changing the Ti concentration and Al concentration in the plating bath. went. Next, alloying treatment was performed while changing the alloying time variously to obtain an alloyed hot-dip galvanized steel sheet having an alloyed hot-dip coating layer of about 100 g / m ² formed on each surface of the steel sheet.

Using the alloyed hot-dip galvanized steel sheet thus obtained, the area ratio of each phase in the alloyed plated layer, the slidability and the resistance to peeling of plating were investigated by the following methods. Furthermore, the surface of the obtained steel sheet was observed with the naked eye, and the crystals formed on the surface of the plating layer were observed under a microscope (1500 times).

[Ratio of each phase occupying in the plating layer] It was determined by the 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

[Sliding Property] FIG. 5 shows a schematic diagram of a friction coefficient measuring method carried out for evaluating slidability. In the figure, 1 is a test piece, 2 is a flat tool, and F is a drawing load. First,
After pressing both sides of the test piece with a surface pressure of about 30 N / mm ² using a 20 mm square flat tool, the drawing speed is about 150 mm.
/ Min. The pulling load F at this time is measured, and the friction coefficient: μ = F /
It was used as an index for slidability evaluation by calculating 2P.

[Peeling Resistance to Plating] FIG. 6 is a schematic view of a V-bending test carried out to evaluate resistance to plating peeling.
In the figure, 3 is a test piece, 4 is a punch, and 5 is a die. As shown in the figure, a V-bending test was carried out with a V-shaped punch having a bending angle of 60 ° and a bending diameter of 1 mm, and the amount of plating peeling on the inside of the bending was measured. The results are shown in Table 1.

[0036]

[Table 1]

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

No. 1 is also excellent in the above characteristics,
Since the amount of Ti is too large, the cost is high. No. 5 is excellent in both slidability and resistance to peeling of plating, but Al
Since the amount is too large, the plating surface properties are inferior. Also N
No. 9 has very good slidability, but the Fe concentration is too high, the ratio of the Γ phase becomes large, and the plating peeling resistance is deteriorated.

On the other hand, in No. 4, since the upper limit of the Fe concentration in the plating layer satisfies the preferable requirement, the plating peeling resistance is good, but since Ti is not added at all, the plating surface Hard Ti / Al type crystals are not formed and the slidability is poor.

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

[0041]

Since the steel sheet of the present invention is constructed as described above, it has excellent slidability, and further, a steel sheet having improved plating peeling resistance and plating surface properties can be obtained at low cost. . Since the above-mentioned slidability and resistance to peeling of plating are the most important characteristics for press working of galvannealed steel sheet, the use of the steel sheet 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 such as being able to be molded into.

[Brief description of drawings]

FIG. 1 is a photograph (1500 times) showing the surface of a plated layer of a galvannealed 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 plated layer of a galvannealed steel sheet containing 0.13% Al in the plated layer (without Ti).

FIG. 3 is a graph showing the relationship between the Fe concentration in the 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 friction coefficient.

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

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

[Explanation of symbols]

1,3 test piece 2 flat tools 4 punch 5 dice

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koji Irie 1 Kanazawa Town, Kakogawa City, Hyogo Prefecture Kobe Steel Works, Ltd. Inside the Kakogawa Steel Works (56) Reference JP-A-8-60329 (JP, A) JP-A-8 -20854 (JP, A) JP 4-21753 (JP, A) JP 62-174360 (JP, A) JP 3-191045 (JP, A) (58) Fields investigated (Int.Cl) . ⁷ , DB name) C23C 2/00-2/40

Claims (6)

(57) [Claims] 1. Ti and Al on the surface of the alloyed plating layer
5 to 15 crystals with a side of 2 to 10 μm containing
An alloyed hot-dip galvanized steel sheet with excellent slidability characterized by being present in mm ² . 2. Ti: 0.001 in the alloyed plating layer.
% Or more (weight%, the same below) and Al: 0.05% or more are contained, The hot-dip galvannealed steel sheet of Claim 1. 3. The galvannealed steel sheet according to claim 1, wherein Fe is contained in the alloyed plating layer in an amount of 5% or more. 4. The galvannealed steel sheet according to claim 3, wherein excellent galvannealing resistance is imparted by suppressing the proportion of Fe in the alloyed plating layer to 13% or less. 5. The surface roughness Ra of the alloyed plating layer is 1.5.
The hot-dip galvannealed steel sheet according to claim 4, which has a thickness of 3 μm. 6. The alloy 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.