JP2776151B2 - Method for producing two-layer alloyed hot-dip galvanized steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a two-layer alloyed hot-dip galvanized steel sheet used for an automobile body, underbody parts and the like.
In particular, the present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet which has excellent outer surface suitability, resistance to ED bumps, and powdering resistance during press forming, and has stable friction characteristics in a coil.

[0002]

2. Description of the Related Art A two-layer alloyed galvanized steel sheet having an Fe-based coating layer on an alloyed hot-dip galvanized layer has excellent corrosion resistance after painting and coating compatibility. Has recently increased, and in recent years, in particular, the thickness of the galvanized film tends to be increased in order to ensure corrosion resistance. This type of plated steel sheet is required to have excellent press formability and resistance to film peeling during press forming, so-called powdering resistance. Particularly in recent years, more stringent performance has been demanded for these, and in particular, as the thickness of the film as described above increases, securing powdering resistance is becoming a major issue.

As a technique for improving such powdering resistance, a technique is known in which a coated steel sheet is firstly heated by rapid heating to alloy a part of the coating, and then subjected to secondary heating by batch annealing. Although this method is effective for improving powdering resistance, it has a drawback of high manufacturing cost. On the other hand, as a technique for improving the powdering resistance in-line, Japanese Patent Application Laid-Open No. 1-279738 discloses that after plating in a bath of Al: 0.04 to 0.12%, the temperature of 470 ° C. A method for producing an alloyed hot-dip galvanized steel sheet mainly composed of a δ ₁ phase by rapidly heating to a temperature and rapidly cooling it to a temperature of 420 ° C. or less after completion of alloying in 2 seconds or less.

[0004]

However, in this method, the alloying treatment is performed at a relatively high temperature, so that the alloying proceeds rapidly, the Γ phase grows thickly, and the powdering resistance tends to deteriorate. There is. In this regard, Japanese Unexamined Patent Publication No.
No. 8 discloses that the alloy is rapidly cooled from the alloy completion temperature range to a temperature range of 420 ° C. or less in 2 seconds or less in order to prevent over-alloying. However, due to changes in the basis weight and line speed, an appropriate alloying pattern is obtained. In order to implement this method, it is necessary to arrange the heating source and the cooling source in multiple stages in the line direction to cope with the problem, and there is a major problem that the equipment cost increases.

[0005] Further, in a commonly used gas-fired heating type alloying furnace, the temperature of the furnace tends to fluctuate in the width and length directions of the steel sheet, so that it is difficult to strictly control the film structure as described above. In some cases, the resulting alloyed galvanized film partially has an overalloy or a ζ phase remaining. Therefore, the resulting plated steel sheet is δ
The amount of _one phase is non-uniform, that is, the powdering resistance is non-uniform. In addition, since the amount of the ζ phase is closely related to the friction characteristics, if the ζ phase remains, the friction coefficient of the portion locally increases, so that the press formability becomes unstable.

On the other hand, in order to improve the coverage of the upper plating of a two-layer alloyed hot-dip galvanized steel sheet having an Fe-based plating in the upper layer, the roughness of the skin pass work roll has been conventionally controlled. Since the furnace is a gas heating furnace system, the alloyed galvanized film cannot be stably smoothed, and there is a limit in improving the coatability of the upper plating only by controlling the skin pass roll. In particular, since the elongation rate of the skin pass roll is determined by the material and application,
The transfer rate cannot be improved by increasing the draft rate unnecessarily.

In the case where the upper layer plating is applied in a state where the smoothness of the alloyed zinc plating film is insufficient to secure the suitability for the outer surface, the coverage of the upper layer plating is inferior. The amount of plating had to be increased, resulting in the following problems. a) Hydrogen in the upper plating film opens a mouth during electrodeposition coating by a user (such as an automobile manufacturer), which causes a defect called so-called ED spot. b) Equipment and operating costs for increasing the amount of deposition of the upper plating are increased.

[0008]

In order to solve the above-mentioned conventional problems, the present inventors first studied the alloying reaction of a hot-dip galvanized steel sheet.
5 ° C. generated by the following reaction, more by not occur, therefore, cause a major reaction (reaction to molten zinc phase is eliminated) at temperatures above 495 ° C., if then cooled, [delta] ₁ main phase It was clarified that a film could be formed. FIG. 1 and FIG. 2 show an example of a phase change due to a constant temperature alloying reaction at 450 ° C. and 500 ° C. of a hot-dip galvanized steel sheet. ζ phase is alloyed with are hardly occurs, a film of [delta] ₁ main phase.

However, as described above, in such a method of alloying at a relatively high temperature, the plating film is easily overalloyed, and the powdering resistance is apt to deteriorate. Furthermore, when alloying under the above conditions using a normal direct-fired heating type alloying furnace, it is difficult to burn uniformly over time and place,
Baking unevenness is likely to occur. Then, due to such unevenness in firing, a non-uniform alloy layer is formed, and only a non-uniform product having different powdering resistance and friction characteristics depending on the position of the steel sheet can be obtained. Therefore, the smoothness of the surface also differs depending on the position of the steel sheet, the coverage of the Fe-based upper plating is poor, and it is not possible to obtain excellent external suitability with a small amount of adhesion.

[0010] From the above, as a result of repeated studies on a method capable of stably obtaining both powdering resistance and press moldability and obtaining good coverage of the Fe-based upper plating. The following findings were obtained. Suppress alloying reaction (generation of ζ phase) in plating bath,
Moreover by carrying out the subsequent alloying treatment using a heating furnace of high frequency induction heating method, the width direction of the alloying phase consisting mainly of [delta] ₁ phase strip, is uniformly formed film in the longitudinal direction is obtained In addition, the alloyed plating film thus obtained not only has the macroscopic uniformity as described above, but also has an excellent alloying reaction even microscopically. And press formability

[0011] Strict control of the film is possible by specifying the bath conditions and the plate temperature conditions on the exit side of the heating furnace of the high-frequency induction heating method.
By plating at a lower penetration plate temperature defined by the relationship with the amount, or by plating at a higher penetration plate temperature defined by the relationship with the Al amount in the bath in a high Al bath, By forming the alloying suppressing phase Fe ₂ Al ₅ thickly in the bath, it is possible to appropriately suppress the alloying reaction (formation of the ζ phase) in the bath. Is performed by controlling the sheet temperature at the exit side of the heating furnace to a temperature higher than 495 ° C. to 520 ° C. to obtain a film as described above. As described above, a smooth bulk crystal mainly composed of δ ₁ phase is uniformly formed on the surface of the steel sheet, and the surface of the alloyed hot-dip galvanized layer is extremely smooth by subjecting it to skin pass rolling under predetermined conditions. Fe-based upper layer even with a small amount of adhesion That the present invention may significantly improve the coverage of Kki has been made based on such findings, the configuration is as follows.

(1) After plating in a hot-dip galvanizing bath containing Al and the balance of Zn and unavoidable impurities, the basis weight is adjusted, and the Fe content in the film is 8 to 12% in a heating furnace. In a method for producing a two-layer alloyed hot-dip galvanized steel sheet in which an alloying treatment is performed so as to provide a skin pass, and then an Fe-based upper plating is applied, the amount of Al in the bath is set to 0.1.
05% or more, less than 0.13%, bath temperature: 460 ° C. or less, and the amount of Al in the bath and the plate temperature of the steel sheet entering the plating bath are 437.5 × [Al%] + 428> T ≧ 437.5x
[Al%] + 408, where [Al%]: Al content in bath (%) T: Infiltration plate temperature (° C.)
-Suppress the Zn alloying reaction, after plating, heat in a high-frequency induction heating furnace so that the sheet temperature on the exit side of the heating furnace is more than 495 ° C to 520 ° C, hold for a predetermined time, cool down, and then surface roughness Ra: a two-layer alloyed hot-dip galvanized steel sheet characterized by applying a skin pass with a work roll of 0.4 to 0.9 μm with a rolling force of 0.2 Ton / mm or more, and then applying an Fe-based upper layer plating. Production method.

(2) After plating in a hot-dip galvanizing bath containing Al and the balance of Zn and unavoidable impurities, the basis weight is adjusted, and the Fe content in the coating is 8 to 12% in a heating furnace. In a method for producing a two-layer alloyed hot-dip galvanized steel sheet in which an alloying treatment is performed so as to provide a skin pass, and then an Fe-based upper plating is applied, the amount of Al in the bath is set to 0.1.
13% or more, bath temperature: 470 ° C or less, and Al in the bath
571 × [Al%] + 416 ≧ T ≧ 571 × [Al%]
+396 However, [Al%]: Al amount in bath (%) T: Plating is performed under conditions that satisfy the following conditions:
-Suppress the Zn alloying reaction, after plating, heat in a high-frequency induction heating furnace so that the sheet temperature on the exit side of the heating furnace is more than 495 ° C to 520 ° C, hold for a predetermined time, cool down, and then surface roughness Ra: a two-layer alloyed hot-dip galvanized steel sheet characterized by applying a skin pass with a work roll of 0.4 to 0.9 μm with a rolling force of 0.2 Ton / mm or more, and then applying an Fe-based upper layer plating. Production method.

[0014]

Conventionally, a technique of alloying a plated steel sheet by high-frequency induction heating is disclosed in, for example, Japanese Patent Publication No. 60-82.
No. 89, JP-A-2-37425 and the like. However, the techniques disclosed therein merely use high-frequency induction heating as a means of rapid heating.

On the other hand, the present invention suppresses the alloying reaction in the bath as much as possible, and performs alloying treatment by high-frequency induction heating on the plating film in which the alloying is suppressed under specific conditions. by performing, gamma phase is small, and smooth alloying phase consisting mainly of [delta] ₁ phase in the steel sheet each section is uniformly formed, yet excellent powdering resistance as a whole by the microscopic uniformity of coating structure has further the coated steel sheet is also excellent in press formability can be obtained, furthermore, the plating conditions and alloying treatment by high-frequency induction heating, smooth massive galvannealed coating [delta] ₁ main phase It has been found that an upper layer plating excellent in coverage can be achieved with a small amount of coating by applying a skin pass under predetermined conditions to a crystal.

First, in the manufacturing method of the present invention, it is presumed that the plating conditions and the alloying treatment by high-frequency induction heating provide a plated steel sheet having the above-mentioned excellent characteristics for the following reasons. Is done. First, first,
By using the high-frequency induction heating method in the alloying treatment, the steel sheet itself can be directly heated, and the interface in contact with the plating film is heated most. Therefore, the Fe-Zn reaction at the interface is shorter than in the atmosphere heating method. It occurs uniformly in time and regardless of the position on the strip, and as a result, there is no partial overalloy or 鋼板 phase remaining on the steel sheet, and a uniform δ ₁ phase is formed. It is estimated that uniform powdering resistance and press moldability can be obtained.

Second, since the high-frequency induction heating is heating from the steel plate side as described above, it is presumed that a uniform alloying reaction occurs microscopically. That is, in the conventional alloying treatment by gas heating,
Since heat is applied from the outside of the film, the heating is likely to be non-uniform, and the alloying reaction is likely to be microscopically non-uniform. In particular, since the crystal grain boundaries are highly reactive, the so-called outover
A strike reaction is likely to occur, and when an outburst structure is generated in this way, a Γ phase starts to grow from this portion, and the formation of the Γ phase deteriorates the powdering resistance. On the other hand, since high-frequency induction heating is heating from the steel plate side, there is little local variation in the alloying as described above,
Oxide on steel plate surface and alloying inhibitor (Fe ₂
Since Al ₅ ) is also easily diffused, it is considered that a uniform alloyed film can be obtained even from a microscopic viewpoint.

Third, high-frequency induction heating can alloy the plating in a short time, so that the growth time of the Γ phase is short. In the present invention, since the generation of the Γ phase in the bath can be suppressed, the final formation amount of the 少 な く phase is small, which is also considered to contribute greatly to the improvement of the powdering resistance.

Fourth, as an advantage of high-frequency induction heating, uniform heating can be performed in the width and length directions of the steel sheet, so that strict control of the sheet temperature at the exit side of the heating furnace is possible. Unlike an atmosphere heating method such as a furnace, there is no rise in the heated atmosphere gas (draft effect), so it is considered that overalloy hardly occurs even without special cooling.

One of the methods for obtaining a uniform δ ₁ phase in the present invention is to suppress the Fe—Zn reaction by forming Fe ₂ Al ₅ as an alloying suppressing phase in a bath,
It is to form a [delta] ₁ phase in the heat treatment to continue.
Regarding this method, since the high-frequency induction heating is heating from the steel plate side as described above, Fe ₂ Al ₅
Readily diffuse to form the δ ₁ phase. That is, Fe-Zn
Even if Fe ₂ Al ₅ is formed thick to properly suppress the reaction, it can be diffused reliably and uniformly during alloying. As a result, the alloying becomes microscopically uniform, and the formation of a thick Fe ₂ Al ₅ suppresses the generation of a Γ phase in the bath, which results in a uniform alloy phase and excellent powdering resistance. It is considered that the property can be obtained.

Hereinafter, the configuration of the present invention and the reasons for the limitation will be described. In the present invention, in order to minimize the alloying reaction in the plating bath, the amount of Al in the plating bath, the sheet temperature of the steel sheet when entering the plating bath, and the bath temperature are specified. In the present invention, the following two plating conditions can be adopted in order to suppress the alloying reaction in the plating bath. It is a low penetration plate temperature defined in the low Al bath and in relation to the amount of Al in the bath. It is a high penetration plate temperature defined by the relationship between the high Al bath and the amount of Al in the bath. Hereinafter, the reasons for limiting the respective plating conditions will be described.

Under the above conditions, plating is carried out in a low Al bath at a low penetration plate temperature in order to suppress the alloying reaction (generation of the ζ phase) in the plating bath.
If it is less than 0, there is no effect of suppressing alloying by Fe ₂ Al _5, so that an outburst reaction occurs in the bath, and the powdering resistance is deteriorated. Therefore, the Al content in the bath is set to 0.05% or more. On the other hand, when the Al content is 0.13% or more, F
Since the e-Zn alloying reaction is excessively suppressed, it is necessary to cause a rapid alloying reaction in the subsequent alloying treatment, and such a rapid alloying reaction causes uniformity and smoothness of the plating film and resistance to plating. Deteriorates powdering properties. Therefore, the Al content in the bath is set to less than 0.13%.

It is necessary that the penetration plate temperature satisfies the condition of the following relational expression in relation to the amount of Al in the bath. 437.5 × [Al%] + 428> T ≧ 437.5 ×
[Al%] + 408 where [Al%]: Al amount in bath (%) T: Penetration plate temperature (° C.) When the penetration plate temperature exceeds the above upper limit in relation to the Al amount in bath,
Ζ phase occurs alloying reaction in the bath is formed, not eventually alloyed phase mainly composed of [delta] ₁ phase which is an object of the present invention can be obtained. On the other hand, if the penetration plate temperature falls below the lower limit, Fe ₂ A
l ₅ is to be unevenly generated, localized uniformity and smoothness and powdering resistance of the plating film to produce the alloying reaction deteriorates.

If the plating bath temperature is high, the alloying reaction in the bath is accelerated, so that the bath temperature is set to 460 ° C. or lower.
On the other hand, if the bath temperature is too high, structures immersed in the bath are eroded, causing problems such as the generation of dross.

Next, under the above conditions, A in the plating bath
1 forms Fe ₂ Al ₅ on the surface of the steel sheet immediately after entering the bath,
-Suppress generation of Zn alloy. If the Al content is less than 0.13%, such an effect is small, and a ζ phase is formed in the bath, and an alloyed phase mainly composed of the δ ₁ phase, which is the object of the present invention, cannot be finally obtained. Therefore, the amount of Al in the bath is 0.13%
Above.

In a bath containing 0.13% or more of Al, when the temperature of the intruding plate is increased, the reaction temperature immediately after entering the steel plate increases,
Fe ₂ Al ₅ is formed to be thick. As a result, the reaction of the Fe—Zn alloy in the bath is suppressed. However, the penetration plate temperature needs to satisfy the condition of the following relational expression in relation to the Al content in the bath. 571 × [Al%] + 416 ≧ T ≧ 571 × [Al%]
+396 where [Al%]: amount of Al in bath (%) T: Temperature of penetration plate (° C)

The above-mentioned method is based on a high Al bath and a high penetration plate temperature.
If the upper limit is exceeded in relation to the amount, the diffusion rate of Fe increases, so that the suppression effect of Fe ₂ Al ₅ becomes insufficient, and an outburst structure is partially generated in the bath. In addition, the uniformity and the powdering resistance deteriorate. On the other hand, if the penetration plate temperature falls below the lower limit, Fe
_The amount of ₂ Al ₅ formed is not sufficient, and the effect of suppressing the reaction of the Fe—Zn alloy in the bath cannot be obtained properly.

When the invading plate temperature exceeds 520 ° C., F
Since e ₂ Al ₅ tends to be locally excessively generated, baking unevenness occurs, and the uniformity and the powdering resistance of the plating film deteriorate. In addition, an increase in the amount of heat input to the pot requires additional equipment such as a bath temperature cooling unit, and further, increases the amount of dross generated in the bath and causes problems such as frequent occurrence of surface defects. For this reason, it is preferable that the penetration plate temperature be 520 ° C. or less regardless of the amount of Al in the bath. Further, similarly to the above method, the bath temperature is set to 470 ° C. or less.

The plated steel sheet is subjected to heat treatment for alloying in a high-frequency induction heating furnace. In the present invention, in addition to the provision of the bath conditions as described above, the heat treatment by this high-frequency induction heating furnace is a great feature. No plating film is obtained. In this alloying treatment, the sheet is heated so that the sheet temperature on the outlet side of the furnace becomes more than 495 ° C. to 520 ° C., and is cooled after holding for a predetermined time. As described above, δ ₁
In order to form a phase, heating at a temperature exceeding 495 ° C. is necessary, and the plating in which the alloying in the bath is suppressed is alloyed here, and the bulk alloy phase mainly composed of the δ ₁ phase is formed. Let it form. However, if the heating temperature exceeds 520 ° C., the Γ phase is formed, and the powdering resistance deteriorates. Therefore, the upper limit of the heating temperature is 520 ° C. In the present invention, the reason why the sheet temperature on the exit side of the high-frequency induction heating furnace is controlled is that the temperature becomes the highest sheet temperature in the alloying heat cycle. In addition, since the growth rate of the alloy phase becomes maximum in this vicinity, it is possible to cause an alloying reaction at that temperature by controlling the outlet sheet temperature.

According to the present invention, the Fe content in the coating is 8 to 12%.
The purpose is to produce galvannealed steel sheets.
If the Fe content in the coating exceeds 12%, the coating becomes hard and the powdering resistance deteriorates. If alloying is promoted from the exit side of the high-frequency induction heating furnace, the Fe content in the coating will increase due to the diffusion reaction in the solid. On the other hand, when the Fe content is 8
%, The η phase (pure zinc phase) remains on the surface,
A phenomenon called baking (flaking) occurs during press molding, which is not preferable.

Conventionally, it has been thought that the film structure is uniquely determined by the Fe content in the film. However, as in the present invention, the bath conditions are appropriately selected, and the alloying treatment is performed by high-frequency induction heating. Thereby, regardless of the Fe content in the film, a specific film structure as intended by the present invention is obtained. The alloyed plating film thus obtained is
The plating structure has a δ ₁ phase which is a uniform and smooth bulk crystal in the surface layer and an extremely thin Γ phase in the lower layer.

The alloyed hot-dip galvanized film thus obtained is subjected to a skin pass under predetermined conditions.
Since the plating film is a smooth bulk crystal mainly composed of δ ₁ phase, a smooth plating film having a small surface roughness (surface roughness ≦ 1.0 μm) can be obtained by the skin pass.

The skin pass has a surface roughness Ra: 0.4 to 0.4.
It is applied by a 0.9 μm work roll with a rolling force of 0.2 Ton / mm or more. Work roll surface roughness is R
If a exceeds 0.9 μm, the surface roughness of the plating film after the skin pass cannot be reduced to the target Ra: 1.0 μm or less. On the other hand, when the roll surface roughness is Ra: 0.4 μm
If it is less than m, the coefficient of friction of the product decreases, causing problems such as generation of scratches due to slip when used in a consumer and a decrease in cutting length accuracy due to slip during blanking. Also, with a skin pass having a rolling force of less than 0.2 Ton / mm, the surface of the plating film cannot be sufficiently smoothed.

After the skin pass as described above, an Fe-based upper plating is applied to improve coating compatibility. The alloyed hot-dip galvanized steel sheet is liable to cause a defect called cratering during electrodeposition coating, which affects the appearance after final coating. The upper plating prevents the occurrence of such coating defects and enhances the coating compatibility of the coated steel sheet. In order to improve coating compatibility, it is preferable that the upper layer plating be an α single phase.
Since it is a single phase, the Fe content of the upper plating is 50%
It is preferable to make the above.

In the present invention, since the surface roughness of the plating film after the skin pass can be made extremely smooth such that Ra ≦ 1.0 μm, good coatability can be obtained even when the amount of the upper layer plating is small. . When the heating after hot-dip plating is performed by high-frequency induction heating as in the present invention, the plating surface is not oxidized, so that the upper plating can be appropriately deposited on the alloyed plating layer, and therefore, the alloying treatment is performed by gas heating. In this case, the amount of adhesion of the upper layer plating can be reduced as compared with the case where the coating is performed.

In the present invention, since the coatability of the upper layer plating is improved, even plating can be performed with an upper layer coating amount of 4.0 g / m ² or less. However, the adhesion amount of 2.0 g / m ²
If it is less than 1, the coating of the upper plating may not be sufficient even according to the present invention, and therefore, the adhesion amount is 2.0 g / m2.
Preferably, the lower limit is ² .

[0037]

EXAMPLES Examples of the present invention are shown in Tables 1 to 8. In this example, the IF steel (0.0024% C-0.06%
Sol. A cold-rolled steel sheet manufactured from Al-0.06% Ti-0.007% Nb) was used as a material and subjected to hot-dip galvanizing, alloying heat treatment, skin pass and upper layer plating under the conditions shown in Tables 1 to 4. Was. The alloying heat treatment was performed by a gas heating method or a high-frequency induction heating method. Tables 5 to 8 show the properties of the obtained galvannealed steel sheet.

In the present embodiment, the temperature at which the steel sheet enters the plating bath is the surface temperature of the steel sheet immediately before immersion measured by a radiation thermometer. The sheet temperature on the exit side of the heating furnace is the surface temperature of the steel sheet measured by a radiation thermometer. In addition, A
The 1 amount is the effective Al concentration defined by the following equation. [Effective Al concentration] = [Total Al concentration in bath] − [Iron concentration in bath] +0.03

The Fe% in the film depends on bath conditions, heating conditions and cooling conditions. The cooling conditions hardly affect the macro or micro uniformity of the film structure, which is one of the features of the present invention, but affect the characteristics by changing the degree of alloying (Fe% in the film). Therefore, in this embodiment, the air volume of the cooling blower and the amount of mist are adjusted,
Fe% in the film was controlled.

The basis weight of the lower layer plating was measured using an in-line plating coating weight meter (fluorescent x-ray method). At the center of the coil width direction, five arbitrary points were extracted in the coil longitudinal direction and averaged. Value. The upper-layer plating weight is a value obtained by measuring five samples at the center in the coil width direction by an electrolytic peeling method and averaging the measured values. Tests and evaluation methods for each characteristic are as follows.

○ Amount of phase in product film: X obtained film
And ray diffraction, for ζ phase peak of d = 1.900 - click strength Iζ the _(421), also peak of d = 1.990 for [delta] ₁ Phase - takes click intensity i? ₁ a _(249), respectively, under The amount of ζ phase in the film was represented by the peak strength ratio shown in the equation. In addition,
Ibg is a background, and if Z / D is 20 or less, substantially no ζ phase exists. Z / D = (Iζ ( ₄₂₁ ) −Ibg) / (Iδ ₁ ( ₂₄₉ ) −
Ibg) × 100

○ Powdering resistance: rust-proof oil (powder
-Kog Kosan Co., Ltd. Knoxlast 530F) at 1 g /
m ^TwoAfter coating, bead radius R: 0.5 mm, pressing
Bead at load P: 500kg, indentation depth h: 4mm
Perform a pull-out test, and after tape peeling, change in weight before and after molding.
The peeling amount was calculated from the conversion. The figures in the table are for multiple measurements.
It is an average value of fixed values (5 × 5 = 25).

The maximum deviation in the sheet width direction of the powdering resistance:
5 points in coil length direction, 5 points in coil width direction (both edges, 1/4 position and center
Part), the powdering resistance was measured, and the difference between the maximum value and the minimum value was determined.

Coefficient of friction: After applying 1 g / m ² of rust-preventive oil (Knoxlast 530F, manufactured by Parker Kosan Co., Ltd.) to the test piece, an indenter made of tool steel SKD11 was pressed with a load of 400 kg, and 1 m / m 2 The drawing was performed at a drawing speed of min, and the ratio between the drawing load and the pressing load was defined as the friction coefficient. The numerical values in the table represent a plurality of measured values (5 × 5 = 25).
).

The maximum deviation of the coefficient of friction in the width direction of the plate: The coefficient of friction was measured at the same location as the powdering resistance, and the difference between the maximum value and the minimum value was determined.

ＥＤ Resistance to ED bumps After a phosphate film was formed on each surface of the material of the present invention and the comparative material by dipping treatment, a cationic type electrodeposition coating was applied under the following conditions. Voltage: 300 V Bath temperature: 26.5 ° C. Specimen area / anode area: 1/1 Coating thickness: 20 μm Baking temperature: 170 ° C. Baking time: 20 minutes Specimen subjected to electrodeposition coating as described above The spot-like defects generated in the coating film were visually inspected, and the number of spot-like defects in 48 mmφ was evaluated as follows. : No bump-like defects ○ ○ △: Two or less bump-like defects △: More than two bump-like defects and five or less ×: More than five bump-like defects

Cratering resistance After a phosphate film was formed on each surface of the material of the present invention and the comparative material by immersion treatment, a cationic type electrodeposition coating was applied under the following conditions. Voltage: 300 V Bath temperature: 26.5 ° C. Specimen area / anode area: 1/1 Coating thickness: 20 μm Baking temperature: 170 ° C. Baking time: 20 minutes Specimen subjected to electrodeposition coating as described above Of the crater-like defects generated in the coating film was visually inspected, and the number of crater-like defects in 48 mmφ was evaluated as follows. ○: 5 or less crater-like defects △: more than 5 crater-like defects to 20 or less ×: more than 20 crater-like defects

○ P ratio This is an evaluation of the suitability of the outer surface of the plated steel sheet (mainly, the coating property of the upper layer of the Fe system). A phosphate film is formed by immersion treatment, and this film is analyzed by X-ray diffraction. The peak values of the crystal and the whipite crystal were measured, and the P ratio was defined by the following equation. P ratio = (Phosphophyllite crystal diffraction peak height) /
[(Phosphophyllite crystal diffraction peak height) + (Hopite crystal diffraction peak height)] The P ratio was evaluated as follows. : P ratio of 0.8 or more △ to Ｐ: P ratio of 0.7 to less than 0.8 △: P ratio of 0.5 to less than 0.7 ×: P ratio of less than 0.5

[0049]

[Table 1]

[0050]

[Table 2]

[0051]

[Table 3]

[0052]

[Table 4]

[0053]

[Table 5]

[0054]

[Table 6]

[0055]

[Table 7]

[0056]

[Table 8]

Remarks * 1 Since Fe ₂ Al ₅ is formed unevenly, the powdering resistance is poor. * 2 A phase is formed in the bath, and the coating quality of the upper plating is reduced. Poor external suitability. * 3 The Γ phase partially remains due to uneven baking. Poor powdering resistance. * 4: The ζ phase partially remains due to uneven baking. Lowering of upper plating coverage. Poor external suitability. * 5: The ζ phase partially remains due to uneven baking. Lowering of upper plating coverage. Poor external suitability. * 6 Surface roughness and coefficient of friction increase. Lowering of upper plating coverage. External suitability deteriorates. * 7 Surface roughness and coefficient of friction increase. * 8 Powdering resistance is poor because Fe ₂ Al ₅ is formed unevenly. * 9: The ζ phase is formed in the bath, and the coatability of the upper plating is reduced. Poor external suitability. * 10 Partial Γ phase remains due to uneven firing. Poor powdering resistance. * 11 Due to uneven baking, the ζ phase partially remains. Lowering of upper plating coverage. Poor external suitability. * 12 Due to uneven baking, the ζ phase partially remains. Lowering of upper plating coverage. Poor external suitability. * 13 Surface roughness and coefficient of friction increase. Lowering of upper plating coverage. External suitability deteriorates. * 14 Surface roughness and friction coefficient increase. * 15 Since Fe ₂ Al ₅ is formed unevenly, the powdering resistance is poor. * 16 Poor powdering resistance due to outburst in bath. * 17 Partial Γ phase remains due to uneven firing. Poor powdering resistance. * 18 Due to uneven baking, the ζ phase partially remains. Lowering of upper plating coverage. Poor external suitability. * 19 Low phase temperature at the exit plate of the alloying furnace. Lowering of upper plating coverage. Poor external suitability. * 20 Surface roughness and coefficient of friction increase. Lowering of upper plating coverage. External suitability deteriorates. * 21 Surface roughness and friction coefficient increase. Lowering of upper plating coverage. External suitability deteriorates.

[Brief description of the drawings]

FIG. 1 shows an example of a phase change due to a constant temperature alloying reaction at 450 ° C. of a hot-dip galvanized steel sheet.

FIG. 2 shows an example of a phase change due to a constant temperature alloying reaction at 500 ° C. of a galvanized steel sheet.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akihiko Nakamura 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (56) References JP-A-2-173250 (JP, A) JP-A-4 JP-A-187751 (JP, A) JP-A-4-235265 (JP, A) JP-A-4-232240 (JP, A) JP-A-4-232239 (JP, A) JP-A-4-176853 (JP, A) JP-A-2-254146 (JP, A) JP-A-4-193938 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 28/00-30/00 B21B 1 / 22 B21B 27/02 C23C 2/00-2/26

Claims (2)

(57) [Claims] 1. After plating in a hot-dip galvanizing bath containing Al and the balance of Zn and unavoidable impurities,
After adjusting the weight per unit area, the Fe content in the film was 8 to
In the method for producing a two-layer alloyed hot-dip galvanized steel sheet in which an alloying treatment is performed so as to be 12%, a skin pass is performed, and an Fe-based upper layer is plated, the Al content in the bath is 0.05%.
Above, less than 0.13%, bath temperature: 460 ° C. or less, and the amount of Al in the bath and the temperature of the steel sheet entering the plating bath are 437.5 × [Al%] + 428> T ≧ 4337. 5x
[Al%] + 408, where [Al%]: Al content in bath (%) T: Infiltration plate temperature (° C.)
-Suppress the Zn alloying reaction, after plating, heat in a high-frequency induction heating furnace so that the sheet temperature on the exit side of the heating furnace is more than 495 ° C to 520 ° C, hold for a predetermined time, cool down, and then surface roughness Ra: a two-layer alloyed hot-dip galvanized steel sheet characterized by applying a skin pass with a work roll of 0.4 to 0.9 μm with a rolling force of 0.2 Ton / mm or more, and then applying an Fe-based upper layer plating. Production method. 2. After plating in a hot-dip galvanizing bath containing Al and the balance of Zn and unavoidable impurities,
After adjusting the weight per unit area, the Fe content in the film was 8 to
In the method for producing a two-layer alloyed hot-dip galvanized steel sheet in which an alloying treatment is performed so as to be 12%, a skin pass is performed, and an Fe-based upper layer is plated, the Al content in the bath: 0.13%
As described above, the bath temperature is 470 ° C. or less, and the amount of Al in the bath and the plate temperature of the steel sheet entering the plating bath are 571 × [Al%] + 416 ≧ T ≧ 571 × [Al%]
+396 However, [Al%]: Al amount in bath (%) T: Plating is performed under conditions that satisfy the following conditions:
-Suppress the Zn alloying reaction, after plating, heat in a high-frequency induction heating furnace so that the sheet temperature on the exit side of the heating furnace is more than 495 ° C to 520 ° C, hold for a predetermined time, cool down, and then surface roughness Ra: A method for producing a two-layer alloyed hot-dip galvanized steel sheet, wherein a skin pass is performed with a work roll of 0.4 to 0.9 μm with a rolling force of 0.2 Ton / mm or more, and an Fe-based upper layer is plated.