JP3097472B2 - Alloyed hot-dip galvanized steel sheet excellent in press formability 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 galvannealed steel sheet excellent in press formability and suitable for use as a rustproof steel sheet for automobiles, and a method for producing the same.

[0002]

2. Description of the Related Art Alloyed hot-dip galvanized steel sheets have good paintability,
Because of its excellent weldability and corrosion resistance, it is widely used for steel sheets for automobile bodies, steel sheets for household appliances, steel sheets for furniture, and the like. In recent years, since much higher corrosion resistance has been required, thicker galvannealed steel sheets have come to be used.

However, in an alloyed hot-dip galvanized steel sheet, since the alloying treatment is performed by thermal diffusion, the iron concentration gradient in the alloyed hot-dip galvanized layer increases as the basis weight increases. As a result, a brittle phase having a high iron concentration is likely to be generated at the interface between the plating layer and the base steel sheet, while a low iron concentration is present near the surface of the plating layer.
Easy to form phase.

[0004] When the Γ phase is thick, the brittle 破 壊 phase is destroyed during press working, and powdering occurs in which the alloyed hot-dip galvanized layer is separated into powder. On the other hand, when the ζ phase exists near the surface of the plating layer, the ζ phase has a relatively low melting point, so that the mold and the ζ phase adhere to each other during press working, and the sliding resistance increases. As a result, mold galling and press cracking occur.

[0005] In order to solve the above-mentioned problems, as a method for improving the structure of the galvannealed layer and improving the plating characteristics, Japanese Patent Publication No. 3-55543 and Japanese Patent Application Laid-Open No. Hei 6-55543 have been proposed.
Japanese Patent No. 17221 discloses a method of controlling the thickness of the Γ phase or the Γ1 phase so that the surface layer of the plating layer is mainly composed of the δ1 phase (hereinafter referred to as prior art 1).

As a method for improving the press formability of an alloyed hot-dip galvanized steel sheet, for example, Japanese Patent Application Laid-Open No. 4-353 discloses a method in which a very thick additive is added to the surface of an alloyed hot-dip galvanized layer. (Hereinafter referred to as prior art 2) for applying a rust preventive oil or a solid lubricant.

Further, as disclosed in JP-A-1-319661, for example, a relatively hard iron-based or iron-group-based alloy plating film is formed on the surface of the galvannealed layer. Alternatively, as disclosed in JP-A-3-243755, a method of forming an organic coating on the surface of an alloyed hot-dip galvanized layer and thereby improving the press formability of the alloyed hot-dip galvanized steel sheet (hereinafter referred to as a method). , Prior art 3) is known.

Further, JP-A-2-190483 and JP-A-5-148605 disclose the formation of an oxide layer on the surface of an alloyed hot-dip galvanized layer so as to press an alloyed hot-dip galvanized steel sheet. A method for improving moldability (hereinafter referred to as
Prior art 4) is disclosed.

On the other hand, as a means for improving the wear resistance of steel parts used under severe wear conditions, a technique of performing a sulfurizing treatment is described in, for example, "Metal Surface Technology Handbook" (Metal Surface Technology Association). (Ed.), P. 1152, which is introduced as "sulfurization treatment of steel" (hereinafter referred to as prior art 5).

[0010]

However, as described in Prior Art 1, simply improving the structure of the galvannealed layer and controlling the thickness of the Γ-phase or Γ1 phase requires the plating as described above. As a result of mold seizure and press cracking caused by the ζ phase present near the surface of the layer, a sufficient effect of improving press formability cannot be obtained.

In the method of applying rust-preventive oil or the like to the surface of an alloyed hot-dip galvanized layer as in prior art 2, the applied rust-preventive oil or the like flows down from shipping to pressing. Alternatively, the non-uniform portion called “thirsty unevenness” is generated by evaporation, so that press molding becomes unstable. Also, when various high-viscosity rust-preventive oils and solid lubricants are applied, their degreasing properties are inferior, so they are less likely to be degreased than in the past. The problem of worsening the environment occurs.

Prior art 3 in which a relatively hard alloy plating film of, for example, iron or iron group is formed on the surface of the alloyed hot-dip galvanized layer exhibits an excellent effect of improving press formability. However, in order to form the above-mentioned iron-based or iron-group-based alloy plating film or organic film on the surface of the alloyed hot-dip galvanized layer, a large-scale facility is required, resulting in high cost. However, there is a problem that workability and productivity are poor.

In the method of forming an oxide layer on an alloyed hot-dip galvanized layer as in the prior art 4, an oxide layer applied to a sliding surface between a steel sheet surface and a press die during press forming is used. The effect of reducing the impulse resistance of the material layer is small, so that a sufficient effect of improving press formability cannot be obtained.

Prior art 5 is a technique applied to parts such as bearing steel, and cannot be applied to galvannealed steel sheets because it requires high-temperature and long-time treatment. .

Accordingly, an object of the present invention is to solve the above-mentioned problems, to have a stable and excellent press formability, to have good productivity and not to impair the working environment, and to reduce the cost and efficiency. It is an object of the present invention to provide an alloyed hot-dip galvanized steel sheet that can be manufactured in a specific manner and a method for manufacturing the same.

[0016]

An alloyed hot-dip galvanized steel sheet according to claim 1 of the present invention comprises: a steel sheet; an alloyed hot-dip galvanized layer formed on at least one surface of the steel sheet; It is characterized by comprising a sulfide layer formed on the galvannealed layer in an amount of 5 to 1000 mg / m ² in terms of sulfur. And the alloyed hot-dip galvanized steel sheet according to claim 2, wherein the alloyed hot-dip galvanized layer has an average thickness of 1 μm or less,
It is characterized in that it comprises a Γ1 phase having an average thickness of 2 µm or less, and substantially the δ1 phase for the rest.

According to a third aspect of the present invention, in the manufacturing method, the steel sheet is passed through a hot-dip galvanizing bath, the steel sheet is subjected to a hot-dip galvanizing treatment, and a hot-dip galvanizing treatment is performed on at least one surface of the steel sheet. Forming a galvanized layer, and then heating the steel sheet on which the hot-dip galvanized layer is formed, alloying the hot-dip galvanized layer and a surface portion of the steel sheet, and thus at least one of the steel sheets In the method of forming an alloyed hot-dip galvanized layer on the surface, after performing the alloying treatment, the steel sheet is subjected to a sulfurizing treatment, and the sulfur content is reduced on the surface of the alloyed hot-dip galvanized layer. It is characterized by forming a sulfide layer in an amount of 5 to 1000 mg / m ^{2 in} terms of conversion.

According to a fourth aspect of the present invention, there is provided the steel sheet having the hot-dip galvanized layer formed thereon, wherein the surface of the steel sheet is sprayed with a sulfur-containing solution, and the sulfur-containing solution is sprayed. There is subjected to alloying processing to spray steel sheet, on the surface of the hot dip galvanized layer, characterized in that to form the sulfide layer in an amount of 5 to 1000 mg / m ² in terms of sulfur content Have

[0019] In the production method according to the fifth aspect of the present invention, the surface of the steel sheet may be previously converted to a sulfur amount by 10 to 2000.
forming a sulfide layer in an amount of mg / m ^2, to form steel plate in such a sulfide layer, was subjected to annealing by performing molten zinc plating treatment and alloying treatment, galvannealed It is characterized in that a sulfide layer is formed on the surface of the plating layer in an amount of 5 to 1000 mg / m ² in terms of the amount of sulfur.

[0020]

In the galvannealed steel sheet of the present invention, a sulfide layer is formed on the surface of the galvannealed layer. The presence of a sulfide layer on the surface of the galvannealed layer prevents direct contact between the press mold and the metal of the plated layer during press forming, thereby suppressing the adhesion or welding phenomenon. As a result, the sliding resistance decreases. In addition, the sulfide layer is soft and easily plastically deforms during the sliding process, so that even when subjected to large deformation, the sulfide layer completely covers the surface following the elongation of the galvannealed steel sheet. Thus, the effect of reducing the sliding resistance is maintained.

On the other hand, when an oxide layer is present on the surface of the galvannealed layer,
Since the alloyed hot-dip galvanized steel sheet is deformed due to its hardness as compared with the sulfide layer, the plated layer is exposed by cracking or destruction and falling off. As a result, the press die and the metal of the plating layer come into direct contact with each other, and the effect of reducing the sliding resistance cannot be expected. Therefore, when the sulfide layer is formed on the alloyed hot-dip galvanized layer as in the present invention, compared to the case where the oxide layer is formed as in Prior Art 4,
Excellent press formability is exhibited.

Further, since the sulfide layer is uniformly distributed on the surface of the galvannealed layer, it has excellent lipophilicity. Therefore, unlike prior art 2, the rust-preventive oil does not flow down or evaporate between shipping and pressing, so that an uneven portion called “thirst unevenness” does not occur. Also, even if an uneven portion occurs, the press formability does not become unstable due to the action of the sulfide uniformly distributed on the surface of the plating layer.

The amount of the sulfide layer formed on the surface of the galvannealed layer should be limited to the range of 5 to 1000 mg / m ² in terms of sulfur. If the amount of the sulfide layer is less than 5 mg / m ² in terms of the amount of sulfur, the effect of improving press formability cannot be obtained. On the other hand, the amount of sulfide layer
If it exceeds 00 mg / m ² , not only the effect of improving the press formability will be saturated, but also a problem will occur in that the powdering resistance and the chemical conversion property deteriorate.

An alloyed hot-dip galvanized layer on which a sulfide layer is formed is composed of a Γ phase having an average thickness of 1 μm or less, a ζ phase having an average thickness of 2 μm or less, and substantially the δ1 phase remaining. With such a configuration, further excellent press moldability and powdering resistance are exhibited. The alloyed hot-dip galvanized layer having the above structure can be obtained by a known method for controlling hot-dip galvanizing conditions and alloying treatment conditions, as disclosed in, for example, JP-A-4-232565.

It is necessary that the average thickness of the phase (1) is 1 μm or less, and the average thickness of the phase (1) is 2 μm or less. The average thickness of the phase (1) exceeds 1 μm and the average thickness of the phase (1) If it exceeds 2 μm, the powdering resistance deteriorates. From the viewpoint of such powdering resistance, a more preferable average thickness of the Γ phase is 0.5 μm or less, and a more preferable average thickness of the Γ phase is 1 μm or less.

Measurement of the amount of sulfur in the sulfide layer formed on the surface of the galvannealed layer is performed by ICP (Inductively
It can be performed by quantitative analysis by Coupled Plasma (high frequency induction plasma) emission spectroscopy. That is, the sulfide layer of the test material is dissolved with dilute hydrochloric acid together with the galvannealed layer, and the sulfur content is measured by the ICP method. When the sulfide layer was made of an acid-insoluble compound, the sulfide layer of the test material was dissolved with dilute hydrochloric acid together with the galvannealed layer, and the residue in the solution was filtered and filtered. The residue is further dissolved using a mixed melting agent (borax: sodium carbonate: potassium carbonate = 4: 3: 3), and the sulfur content is measured by an ICP method using dilute hydrochloric acid.

When the composition of the sulfide layer formed on the surface of the galvannealed layer is subjected to X-ray diffraction, peaks of FeS, FeS ₂ and ZnS are detected. However, since the sulfide amount is as small as 1000 mg / m ² or less in terms of the sulfur amount, the diffraction intensity is low and it cannot be completely identified. Therefore, the sulfide may be an alloy containing S and bonded to Fe or Zn, or a composite oxide containing these elements.

The alloyed hot-dip galvanized layer of the plated steel sheet of the present invention contains, in addition to the main elements Fe and Zn, Al, As, Bi, Cd, Ce, and Co for the purpose of improving corrosion resistance and the like. , C
r, In, La, Li, Mg, Mn, Ni, O, P, Pb, S, Sb, Sn, T
Even if one or more kinds of i, Zr, etc. are contained, the effect of the present invention is not changed.

The method for producing the galvannealed steel sheet according to the present invention will be described. Claim 3 of the present invention
According to the method of the first embodiment, the galvannealed steel sheet of the present invention is manufactured as follows. The steel sheet is passed through a hot-dip galvanizing bath in a continuous hot-dip galvanizing line, the steel sheet is subjected to a hot-dip galvanizing treatment, and a hot-dip galvanized layer is formed on at least one surface of the steel sheet. Next, the hot-dip galvanized steel sheet is heated to perform an alloying treatment on the hot-dip galvanized layer and the surface portion of the steel sheet, thereby forming an alloyed hot-dip galvanized layer on at least one surface of the steel sheet.

Next, the steel sheet having the galvannealed layer formed on at least one of its surfaces is subjected to a sulfurizing treatment, and the surface of the galvannealed layer is converted to a sulfur amount by 5%. forming a sulfide layer in an amount of 1000 mg / m ^2.

In the above-mentioned sulfurizing treatment, for example, sodium thiosulfate (Na ₂ S ₂ O ₃ ): 100 g / l, boric acid (H ₃ BO ₃ ): 30 g / l,
In an aqueous solution of pH: 5 to 8, current density: 0.003 to 0.1.
Under the conditions of 02 A / cm ² , electrolysis voltage: 0.5 to 3 V, processing temperature: room temperature, electrolysis time: several seconds, it can be performed relatively easily by an aqueous solution electrolysis method in which a steel plate is used as an anode and electrolysis is performed. For activation, it is more effective to perform the first electrolytic treatment using the steel sheet as a cathode and then perform the second electrolytic treatment under the above conditions using the steel sheet as an anode.

The amount of sulfur in the sulfide layer can be controlled by adjusting the above electrolysis conditions, the concentration of sulfur in the aqueous solution, and the like. The sulfurizing treatment is not limited to the above method, and may be performed by any method such as an aqueous solution sulfurizing method, a molten salt sulfurizing method, and a gas sulfurizing method. The sulfide layer may be formed on the surface of the substrate.

According to the method of the second embodiment described in claim 4 of the present invention, the galvannealed steel sheet of the present invention is manufactured as follows. The steel sheet is passed through a hot-dip galvanizing bath in a continuous hot-dip galvanizing line, the steel sheet is subjected to a hot-dip galvanizing treatment, and a hot-dip galvanized layer is formed on at least one surface of the steel sheet. Next, a sulfur-containing solution is sprayed on the steel sheet on which the hot-dip galvanized layer is formed, on the surface of the hot-dip galvanized layer.

Next, the steel sheet sprayed with the sulfur-containing solution is heated to perform an alloying treatment on the hot-dip galvanized layer and the surface portion of the steel sheet, so that at least one surface of the steel sheet is alloyed. While forming a hot-dip galvanized layer, a sulfide layer is formed on the surface of the alloyed hot-dip galvanized layer in an amount of 5 to 1000 mg / m ² in terms of sulfur amount.

The sulfur-containing solution may be sulfur or a sulfur compound (eg, sodium thiosulfate, thiourea, etc.)
Is used by dissolving it in water or alcohols or mixing them. The amount of sulfur in the sulfide layer can be controlled by adjusting the spray amount of the solution or the sulfur concentration in the solution.

According to the method of the third embodiment of the present invention, the galvannealed steel sheet of the present invention is manufactured as follows. On the surface of the steel sheet, a sulfide layer is formed in advance in an amount of 10 to 2000 mg / m ² in terms of the amount of sulfur. Next, an annealing treatment is performed on the steel sheet on which such a sulfide layer is formed. As a result, the sulfide layer formed on the surface of the steel sheet diffuses and alloys to form an Fe-S alloy layer on the surface of the steel sheet.

The steel sheet having the Fe-S alloy layer formed on its surface in this way is passed through a hot-dip galvanizing bath to subject the steel sheet to hot-dip galvanizing treatment, so that at least one surface of the steel sheet Form a hot-dip galvanized layer, then
The steel sheet on which the hot-dip galvanized layer is formed is heated to perform an alloying treatment on the hot-dip galvanized layer and the surface portion of the steel sheet, thereby forming an alloyed hot-dip galvanized layer on at least one surface of the steel sheet.

As a result, Fe- formed on the surface of the steel sheet
The S alloy layer diffuses and moves to the surface of the hot-dip galvanized layer during the alloying process. That is, the Fe—S alloy layer or the sulfur is diffused by the alloying treatment and exists on the surface layer of the galvannealed layer. By this Fe-S alloy layer,
Adhesion and welding with the press die during press molding are less likely to occur, and therefore, press moldability is improved.

As a means for forming the sulfide layer on the surface of the steel sheet, any method such as an electroplating method, an electroless plating method and a solution coating method may be used. It is sufficient that a sulfide layer is formed on the substrate.

The amount of the sulfide layer formed on the surface of the steel sheet should be limited to the range of 10 to 2000 mg / m ² in terms of the amount of sulfur. The amount of the sulfide layer is 10 mg / m
^If it is less than ² , a part of the sulfide is diffused into the furnace during annealing or reacts with the steel sheet base and the sulfur content is taken into the steel sheet.As a result, the amount of sulfur is reduced on the surface of the galvannealed layer. It becomes impossible to form a sulfide layer in an amount of 5 mg / m ² or more in conversion. On the other hand, the amount of the sulfide layer is more than 2000 mg / m ² in terms of sulfur content and reacts with the steel sheet base material
Too much the amount of Fe-S diffusion alloy layer, on the surface of the hot dip galvanized layer, results sulfide layer in an amount in terms of sulfur content greater than 1000 mg / m ² is produced, the material of the deterioration Problem arises.

[0041]

Next, the present invention will be described with reference to examples and comparative examples. [Example 1] A cold-rolled steel sheet having a thickness of 0.8 mm was used as a base plate for plating, and was subjected to a continuous hot-dip galvanizing line (CGL).
Hot dip galvanizing and alloying are applied to the cold-rolled steel sheet, and an alloyed hot-dip galvanized layer is formed on the surface of the cold-rolled steel sheet in an amount of 60 g / m ² per one side of the steel sheet. A steel sheet was prepared. At this time, a sulfide layer was formed on the surface of the alloyed hot-dip galvanized layer by the method according to the first to third embodiments of the present invention described below. Hereinafter, the test piece of the present invention) and a test piece out of the scope of the present invention (hereinafter, referred to as a comparative test piece).
Was prepared.

[0042]

[Table 1]

First Embodiment: A steel sheet subjected to an alloying treatment is subjected to a sulfurizing treatment (hereinafter, referred to as production method 1). Second Embodiment: A steel sheet having a hot-dip galvanized layer formed thereon is sprayed with a sulfur-containing solution on its surface, and the steel sheet sprayed with the sulfur-containing solution is subjected to alloying treatment. (Hereinafter, referred to as Production Method 2). Third Embodiment: A sulfide layer in an amount of 10 to 2000 mg / m ² in terms of the amount of sulfur is previously formed on the surface of a steel sheet, and the steel sheet on which such a sulfide layer is formed is annealed. , A hot-dip galvanizing process and an alloying process are performed (hereinafter, referred to as manufacturing method 3).

In the case of production method 1, a steel plate was used as an anode, sodium thiosulfate (Na ₂ S ₂ O ₃ ): 100 g / l, boric acid (H ₃ B
O ₃ ): In an aqueous solution of 30 g / l and pH: 5 to 8, electrolysis is performed under the conditions of current density: 0.02 A / cm ² and electrolysis voltage: 2 V, and by changing the electrolysis time at this time, sulfurization is performed. The amount of sulfur in the material layer was adjusted.

In the case of Production Method 2, a solution containing sodium thiosulfate (Na ₂ S ₂ O ₃ ): 2 g / l was sprayed on the surface of the hot-dip galvanized steel sheet. The amount of sulfur in the sulfide layer was adjusted by changing the spray amount of the solution at this time.

In the case of Production method 3, sodium thiosulfate (Na ₂ S ₂ O ₃ ): 2 g / l and thiourea (CH ₄
N ₂ S): A solution containing 2 g / l was sprayed, and the amount of sulfur in the sulfide layer was adjusted by changing the spray amount of the solution at this time.

The amount of sulfur in the sulfide layer formed on the surface of the alloyed hot-dip galvanized layer was determined by using a special grade concentrated hydrochloric acid (12 mol /
Liters) is immersed in hydrochloric acid (hereinafter referred to as dilute hydrochloric acid) diluted with 5 times distilled water, the sulfide layer is dissolved together with the galvannealed layer, and quantitatively analyzed by ICP emission spectroscopy. ,Were determined.

When the sulfide layer is an acid-insoluble compound, the test piece is immersed in dilute hydrochloric acid to dissolve the sulfide layer together with the galvannealed layer, and the residue in the dissolved solution is filtered. The filtered residue was mixed with borax (Na ₂ B ₄ O ₇ ), sodium carbonate (NaCo ₃ ) and potassium carbonate (K ₂ Co ₃ ) as a mixed melting agent (borax: sodium carbonate: potassium carbonate = 4:
3: 3) and then dissolved in dilute hydrochloric acid and IC
It was determined by quantitative analysis using the P method.

For each of the test pieces of the present invention and the comparative test pieces prepared as described above, the following method was used.
Press formability and powdering resistance were examined, and the results are shown in Table 1.

The coefficient of friction of the steel sheet surface for evaluating press formability was measured using a friction coefficient measuring device shown in FIG. That is, the test piece 2 is fixed to the sample table 3 on the roller 4, the sample table 3 is pulled out along the rail 7 at a pressing load N: 400 kg, and the drawing speed: 1 m / min.
Is pressed against the test piece 2, and from the pulling load F and the pressing load N measured by the load cells 5 and 6,
The friction coefficient F / N of the test piece 2 was calculated.

The bead 1 has a contact area of 3 mm ×
A 10 mm × 12 mm, 4.5R shape was used. As a lubricating oil, “NOXLAST 530F” manufactured by Nippon Parkerizing Co., Ltd. was used and applied to the surface of the test piece 2. Based on the friction coefficient thus obtained, press formability was evaluated according to the following criteria. Good: coefficient of friction is less than 0.150 Bad: coefficient of friction is 0.150 or more

The powdering resistance of the plating layer was determined as follows by a draw bead test using a draw bead test apparatus shown in a schematic front view in FIG. 2 and an enlarged schematic sectional view of a bead and a die portion in FIG. Was evaluated. First, width
The plating layer on the non-target surface of the test piece 10 having a size of 30 mm × length 120 mm was dissolved and peeled off with dilute sulfuric acid, then degreased and its weight was measured. Next, the test piece 10 is mounted between the bead 8 and the die 9 of the draw bead tester, and the die 9 is pressed by the hydraulic device 12 at a pressure P = 500 Kg through the test piece 10 onto the bead 8. P was measured by the load cell 11.

Next, the test piece 10 thus sandwiched between the bead 8 and the die 9 was drawn upward at a drawing speed V = 200 mm / min. “Noxlast 530F” manufactured by Nippon Parkerizing Co., Ltd. was used as a lubricating oil, and the lubricating oil was applied to the surface of the test piece 10. Next, the test piece 10 was degreased, a tape was stuck to the surface to be measured and peeled off, and degreased again, the weight of the test piece 10 was measured, and the amount of powdering was determined from the weight difference between the test pieces before and after the test. Was. Based on the powdering resistance obtained in this way,
The powdering resistance was evaluated according to the following criteria. Good: Those with a powdering amount of less than 5 g / m ² Poor: Those with a powdering amount of 5 g / m ² or more

As is clear from Table 1, the comparative test piece No. 1 in which the sulfide layer was not formed on the surface of the galvannealed layer, the sulfide layer was formed on the surface of the plated layer. However, Comparative Test Specimens Nos. 2, 12, and 22 whose amounts were out of the range of the present invention were low in friction coefficient and poor in press formability. Even if a sulfide layer is formed on the surface of the plating layer, the amount of the sulfide layer out of the range of the present invention is large. The ring properties were poor.

On the other hand, test pieces Nos. 3 to 10, Nos. 13 to 20 of the present invention in which a sulfide layer having an amount within the range of the present invention was formed on the surface of the galvannealed layer. In Nos. 23 to 30, press formability and powdering resistance were excellent irrespective of the means of forming the sulfide layer (production methods 1 to 3). In particular, in the test pieces Nos. 22 to 30 of the present invention in which the sulfide layer was formed by the production method 3, the amount of peeling by the draw bead test was much smaller, and the powdering resistance was extremely excellent.

[Example 2] As a plating original plate, a plate thickness of 0.8 m
m, using a cold-rolled steel sheet made of Ti-IF steel, and subjecting the cold-rolled steel sheet to a hot-dip galvanizing treatment and alloying treatment under the following conditions by a continuous hot-dip galvanizing line (CGL). On the surface, a Δ phase having an average thickness of 1 μm or less, preferably 0.5 μm or less, a Δ1 phase having an average thickness of 2 μm or less, preferably 1 μm or less, and the remainder substantially comprising δ
An alloyed hot-dip galvanized steel sheet having one phase and having an alloyed hot-dip galvanized layer in an amount of 60 g / m ² per one side of the steel sheet was prepared. Inlet sheet temperature: 474 ° C Line speed: 100 mpm Al concentration in plating bath: 0.12 wt.% Outlet sheet temperature in alloying furnace: 505 ° C Heating method in alloying furnace: induction heating

Further, by appropriately changing the exit side sheet temperature in the alloying heating furnace, the Γ phase and the Γ phase
An alloyed hot-dip galvanized layer in which the thickness of one phase and the rest of the alloy phase structure were adjusted was formed, and then a sulfide layer was formed on the surface of the plated layer by the manufacturing method 1. And a comparative test piece were prepared.

[0058]

[Table 2]

The thickness of the Γ phase and the Γ1 phase were measured as follows.
The cross section of the plating layer was mirror-polished and then etched with a dilute nital solution of about 0.01%, and the cross section of the obtained plating layer was photographed with a scanning electron microscope photograph at a magnification of 3000 times. FIG. 4 shows the microstructure of the cross section of the plating layer taken by the scanning electron microscope photograph.

In the electron micrograph shown in FIG.
at 11 points where the length of m is divided at a pitch of 2 μm,
The thickness of the phase and the # 1 phase were measured. FIG. 5 shows an example of the measurement result. In FIG. 5, the thicknesses of the Γ phase and the Γ1 phase were calculated as follows. ＝= (a ₁ + a ₂ + a ₃ + a ₄ + a ₅ + a ₆ + a ₇ + a ₈ + a ₉ + a ₁₀ +
a ₁₁ ) / 11Γ1 = (b ₁ + b ₂ + b ₃ + b ₄ + b ₅ + b ₆ + b ₇ + b ₈ + b ₉ + b ₁₀ +
b ₁₁ ) / 11

The remaining alloy phase structure of the alloyed hot-dip galvanized layer was analyzed by X-ray diffraction to obtain ζ (−4, 2, 1), that is, d = 2.
12 angstrom height (I [ζ]) and δ1
(2, 4, 9), that is, the height of d = 1.99 angstroms (I [δ1]) was measured, and it was judged from the ratio. That is,
When I [ζ] / I [δ1] is 0.4 or less, substantially ζ
It can be regarded as a plating layer having no phase and consisting of the δ1 phase.

With respect to each of the test pieces of the present invention and the comparative test pieces prepared as described above, press formability and powdering resistance were examined by the above-described methods. The results are shown in Table 2. .

As is clear from Table 2, the comparative test piece No. 32 in which the sulfide layer was not formed on the surface of the galvannealed layer, the sulfide layer was formed on the surface of the plated layer. However, the comparative test piece No. 33, whose amount was out of the range of the present invention, had a high coefficient of friction and was inferior in press moldability. Even if a sulfide layer is formed on the surface of the plating layer, the amount of the sulfide layer is out of the range of the present invention, and the comparative test piece N is large.
o.42 had a large amount of peeling in the draw bead test and was inferior in powdering resistance.

Comparative specimen No. 48 in which the thickness of the Γ phase of the alloyed hot-dip galvanized layer is too thick beyond the range of the present invention, and the thickness of the Γ1 phase is too thick beyond the range of the present invention The test piece No. 54 had a large amount of peeling by the draw bead test. Comparative test piece No. 55 in which the remaining phase structure other than the Γ phase and the Γ1 phase was the ζ phase had a high coefficient of friction.

On the other hand, on the surface of the alloyed hot-dip galvanized layer composed of the Γ phase and the Γ1 phase having a thickness within the range of the present invention, and the remainder substantially consisting of the δ1 phase, Test pieces No. 34 to 41 of the present invention in which an amount of sulfide layer is formed, N
In o.43 to 47 and No.49 to 53, the press formability and the powdering resistance were excellent.

[0066]

As described above, according to the present invention,
An industrially useful alloyed hot-dip galvanized steel sheet that has stable and excellent press formability, has good productivity, does not deteriorate the working environment, and can be efficiently manufactured at low cost. The effect is brought.

[Brief description of the drawings]

FIG. 1 is a schematic front view of a friction coefficient measuring device for evaluating press formability.

FIG. 2 is a schematic front view of a draw bead testing device for evaluating powdering resistance.

FIG. 3 is an enlarged schematic cross-sectional view of a bead and a die portion in a draw bead test device.

FIG. 4 is a scanning electron microscope photograph showing a structure of a cross section of a plating layer.

FIG. 5 is a diagram showing an example of a measurement result of thicknesses of a Γ phase and a Γ1 phase of a plating layer.

[Explanation of symbols]

 1 bead, 2 test pieces, 3 sample stage, 4 rollers, 5 load cells, 6 load cells, 7 rails, 8 beads, 9 dies, 10 test pieces, 11 load cells, 12 hydraulic equipment.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Toyofumi Watanabe 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (56) References JP-A-2-38549 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) C23C 2/00-2/40 C23C 28/00

Claims (5)

(57) [Claims] 1. A steel sheet, an alloyed hot-dip galvanized layer formed on at least one surface of the steel sheet, and 5 to 5% in terms of sulfur amount formed on the alloyed hot-dip galvanized layer. An alloyed hot-dip galvanized steel sheet excellent in press formability, comprising a sulfide layer in an amount of 1000 mg / m ² . 2. The galvannealed layer comprises a Γ phase having an average thickness of 1 μm or less, a Γ1 phase having an average thickness of 2 μm or less, and the remainder substantially having a δ1 phase.
The galvannealed steel sheet according to claim 1. 3. A steel sheet is passed through a hot-dip galvanizing bath, the steel sheet is subjected to a hot-dip galvanizing treatment, and a hot-dip galvanized layer is formed on at least one surface of the steel sheet.
Next, the steel sheet on which the hot-dip galvanized layer is formed is heated to alloy the hot-dip galvanized layer and the surface portion of the steel sheet, and thus the alloyed hot-dip galvanized layer is formed on at least one surface of the steel sheet. In the method for producing an alloyed hot-dip galvanized steel sheet for forming a plated layer, after performing the alloying treatment, the steel sheet is subjected to a sulfurizing treatment, and a sulfur content is formed on the surface of the alloyed hot-dip galvanized layer. in terms of forming a sulfide layer in an amount of 5 to 1000 mg / m ^2,
A method for producing an alloyed hot-dip galvanized steel sheet excellent in press formability, comprising manufacturing the galvannealed steel sheet according to claim 1 or 2. 4. Passing a steel sheet through a hot-dip galvanizing bath, subjecting the steel sheet to a hot-dip galvanizing process, forming a hot-dip galvanized layer on at least one surface of the steel sheet;
Next, the steel sheet on which the hot-dip galvanized layer is formed is heated to alloy the hot-dip galvanized layer and the surface portion of the steel sheet, and thus the alloyed hot-dip galvanized layer is formed on at least one surface of the steel sheet. In the method for producing an alloyed hot-dip galvanized steel sheet that forms a plated layer, the steel sheet on which the hot-dip galvanized layer is formed is sprayed with a sulfur-containing solution on the surface thereof, and the sulfur-containing solution is to spray steel sheet, subjected to the alloying treatment, on the surface of the hot dip galvanized layer, in terms of sulfur content to form a sulfide layer in an amount of 5 to 1000 mg / m ^2, wherein Item 3. A method for producing an alloyed hot-dip galvanized steel sheet having excellent press formability, comprising manufacturing the galvannealed steel sheet according to item 1 or 2. 5. A steel sheet is passed through a hot-dip galvanizing bath, the steel sheet is subjected to a hot-dip galvanizing treatment, and a hot-dip galvanized layer is formed on at least one surface of the steel sheet.
Next, the steel sheet on which the hot-dip galvanized layer is formed is heated to alloy the hot-dip galvanized layer and the surface portion of the steel sheet, and thus the alloyed hot-dip galvanized layer is formed on at least one surface of the steel sheet. In a method for producing an alloyed hot-dip galvanized steel sheet for forming a plating layer, in advance, on the surface of the steel sheet, 10 to 2000
mg / m ² to form a sulfide layer, the steel sheet on which such a sulfide layer is formed, after annealing, subjected to the hot-dip galvanizing treatment and the alloying treatment, the alloy On the surface of the galvannealed galvanized layer, 5-10
Forming a sulfide layer in an amount of 00 mg / m ² and producing the alloyed hot-dip galvanized steel sheet according to claim 1 or 2; Production method.