JP4604327B2 - Cold rolling method of raw steel sheet for hot metal plating and manufacturing method of alloyed hot metal plating steel sheet - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for cold rolling a raw steel sheet for hot metal plating using a tandem rolling mill and a method for producing an alloyed hot metal plated steel sheet using the cold rolling method.
[0002]
[Prior art]
During coil handling in the state of a hot rolled coil before cold rolling, there are many cases in which minute surface defects having irregularities are generated on the surface of the steel sheet due to a phenomenon such as rubbing or fusion between the steel sheets.
Minute dent defects before cold rolling often occur at the time of feeding the hot rolled coil to the pickling equipment, at the time of winding the steel plate after the pickling, and at the time of feeding the coil to the cold rolling equipment, Scratches due to rubbing between the steel plates during handling in the hot rolled coil state are likely to occur not only when the coil is discharged or when the steel plate is wound.
[0003]
The size of the defect described above varies depending on the size, but has a depth of about 10 μm.
In the above-described defect dents, the rolling oil is sealed with the roll during cold rolling, and remains as an unrolled part, generating an oil pit.
On the other hand, this inventor peeled the plating of the part in which the alloying unevenness generate | occur | produced at the time of manufacture of an galvannealed steel plate, and measured the profile of the raw steel plate surface.
[0004]
The obtained results are shown in FIGS.
As shown in FIGS. 1 to 3, a dent scratch having a depth of about 10 μm was observed in the uneven part of alloying.
Conventionally, this level of dents has not been a problem in cold rolling, but from the above survey results, when the cold-rolled steel sheet is a material for hot-dip metal plating, It was found that the unevenness of the plating adhesion was amplified at the part, and when the alloying treatment was performed after plating, the unevenness of the alloying occurred at the dents and remained as a pattern.
[0005]
That is, the present inventors have found that the presence of dents in the cold-rolled steel sheet results in uneven coating coverage in molten metal plating and uneven alloying in the alloyed molten metal-plated steel sheet. It has been found that this is a major factor in reducing the yield in manufacturing.
[0006]
[Problems to be solved by the invention]
The present invention solves the above-described problems of the prior art, prevents uneven coating amount on the molten metal plated steel sheet, and prevents molten alloy plating of the alloyed molten metal plated steel sheet from occurring. An object of the present invention is to provide a method for cold rolling a material steel sheet and a method for producing a galvannealed steel sheet using the cold rolling method.
[0007]
[Means for Solving the Problems]
The inventor of the present invention has focused on the fact that the dent scratches generated before cold rolling remain as oil pits even after cold rolling, and unevenness of the amount of molten metal plating in the oil pits causes unevenness of alloying.
As a result, the work roll has grooves in the roll circumferential direction that have the same depth as the recesses in the steel sheet, and more preferably has a groove-shaped part in the roll circumferential direction that has a depth and length that is not buried in the recesses in the steel sheet. By cold rolling the material steel sheet for hot metal plating using a work roll, the groove shape of the roll surface is transferred to the shoulder of the dent wound, oil discharge is promoted, oil pits are not generated, and rolling It was found that the dent defect can be erased.
[0008]
Furthermore, after cold rolling the steel sheet for molten metal plating using the above-mentioned work roll, by performing molten metal plating, the occurrence of uneven coating amount of the molten metal plating is prevented. The present inventors have found that it is possible to prevent unevenness in alloying in alloyed molten metal plating such as galvanizing, and have arrived at the present invention.
[0009]
That is, the first invention, when rolling the molten metal plating steel sheet in cold rolling using the data tandem rolling mill has a groove formed in the roll circumferential direction, the depth of the grooved roll A cold rolling method for a raw steel sheet for hot metal plating, wherein a work roll having a surface roughness R _Z of 10 μm or more and a groove length L (μm) satisfying the following formula (1) is used.
[0010]
L> 10 / (tan α) (μm) ………… (1)
2nd invention has the groove | channel surface roughness which has the groove | channel formed in the roll circumferential direction when rolling the raw steel plate for molten metal plating in the cold rolling using a tandem rolling mill, and is the depth of a groove | channel. A cold rolling method for a steel sheet for hot metal plating, characterized in that a work roll having a R _Z of 10 μm or more and a groove length L (μm) satisfying the following formula (2) is used.
[0011]
L> R _Z / (tan α) (μm) (2)
In the above formulas (1) and (2), α is the contact angle between the roll and the steel sheet for molten metal plating that is the material to be rolled, that is, the arc portion where the steel sheet and the roll are in contact with the roll center. Indicates the angle.
In the first invention - the second invention described above, the work rolls, it is not preferable is a work roll of a previous stand from the final stand of the formed tandem mill from multiple stand.
[0012]
First invention-second inventions described above is more preferably applied as cold rolling method of molten metal plating for steel sheet is steel sheet for hot-dip galvanizing.
A third invention is, after being subjected to molten metal plating to the above first invention - molten metal plating steel plate obtained by the second inventions of the cold rolling method, it is subjected to a heat alloying treatment It is the manufacturing method of the galvannealed steel plate characterized by the above.
[0013]
The above-described third invention is more preferably applied as a method for producing an alloyed hot-dip galvanized steel sheet in which the hot-dip metal plating material steel sheet is a hot-dip galvanizing material steel sheet.
The surface roughness R _Z in the first to third inventions described above represents the two-dimensional surface roughness R _Z measured in the roll axis direction, and is a ten-point average roughness specified in JIS B 0601-1994. It shows.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail.
The inventor of the present invention has a work roll having a groove having a depth similar to that of a dent flaw in the steel sheet in the roll circumferential direction, more preferably a groove-shaped part having a depth and length not embedded in the dent flaw of the steel plate in the roll circumferential direction. The roll shape of the roll surface is transferred to the shoulders of the dents and the oil drainage is promoted, the oil pits can be prevented, and the dents can be erased. I found.
[0015]
Furthermore, by cold rolling the material steel plate for molten metal plating using the work roll described above and applying the molten metal plating to the obtained steel plate, the occurrence of uneven coating amount of the molten metal plating is prevented, and as a result, The present inventors have found that it is possible to prevent uneven alloying in alloyed molten metal plating.
Hereinafter, the present invention will be described in the order of I. Cold rolling method and II. Alloyed molten metal plating.
[0016]
[I. Cold rolling method:]
As the material steel plate for molten metal plating in the present invention, it is preferable to use a steel plate made of plain steel having a carbon content of 0.02% by mass or less (hereinafter referred to as% by mass) .
[0021]
The first invention, when rolling the steel sheet for molten metal plating, preferably in front stand of the tandem rolling mill has a groove formed in the roll peripheral direction due grinding roll surface, the grooves of This is a cold rolling method using a work roll in which the roll surface roughness R _Z which is the depth is 10 μm or more and the groove length L (μm) satisfies the following formula (1).
[0022]
L> 10 / (tan α) (μm) (1)
In the above formula (1), α represents a contact angle between the roll and the plating material steel plate that is the material to be rolled, that is, an angle formed by the arc portion where the steel plate and the roll are in contact with the roll center.
The length L of the groove on the roll surface can be measured by microscopic observation with a replica of the roll surface.
[0023]
Α can be measured from the relationship between the roll bit length of the material to be rolled and the roll diameter.
That is, α can be obtained from the relationship between the length of the roll bite portion (contact arc length) and the roll diameter by actually measuring the surface shape of the steel sheet that has been in contact with the roll after rolling is stopped.
[0024]
Further, tan α can be approximately obtained from the roll radius and the amount of reduction as shown in FIG.
In FIG. 4, 1 is a work roll, 2 is a rolling end portion of the hot-dip metal plating material steel plate, and 3 is an indented portion of the hot-metal plating material steel plate.
In the first invention described above, as shown in FIGS. 1 to 3, the dent scratch having a depth of about 10 μm is caused by uneven coating amount of molten metal plating and uneven alloying in alloyed molten metal plating. Roll surface roughness R _Z (ten-point average roughness) having a groove-shaped portion in the roll circumferential direction is 10 μm or more and the groove length L (μm) satisfies the above formula (1). Is used for cold rolling.
[0025]
The work roll described above can be obtained by shot dull processing and / or discharge dull processing.
According to the first invention described above, a roll whose depth d is a depth of a groove with respect to a dent defect having a depth d of about 10 μm, which causes uneven plating coverage of molten metal plating and uneven alloying in alloyed molten metal plating. By using a work roll having a surface roughness R _Z of 10 μm or more and a groove length L (μm) satisfying the above formula (1), the shape of the groove portion on the roll surface is formed on the shoulder portion of the steel plate recess. The oil is further transferred, the oil discharge is further promoted, oil pits can be prevented, and the dent defect can be eliminated (FIG. 5).
[0026]
As a result, the steel sheet for molten metal plating is cold-rolled using the work roll described above, and the resulting steel sheet is subjected to molten metal plating, thereby preventing the occurrence of uneven coating amount of the molten metal plating and the alloy. It is possible to prevent uneven alloying in the hot dip galvanizing.
When the length L of the groove does not satisfy the above formula (1), the oil discharge groove is not formed in the shoulder portion of the dent and the oil is not completely discharged and the oil pit is formed.
[0027]
In the first invention described above, it is preferable that the surface roughness R _Z of the roll described above is 50 μm or less and the groove length L is 10 mm or less.
This is because, when the surface roughness R _Z of the roll exceeds 50 μm, the length L of the groove exceeds 10 mm, the dent defect erasing effect is saturated in practical use, and man-hours are required for the roll processing. Because.
[0028]
Moreover, in the above-described first invention, it is preferable that the above-described work roll is disposed on a stand before the final stand of the tandem rolling mill.
This is because even if the above-mentioned work roll is arranged as the work roll of the stand before the final stand, the dent defect is erased by the front stand and the oil cannot be completely discharged from the front stand, the discharge groove has already been formed. This is because the oil is discharged from the rear stage stand and the dent defect portion disappears by rolling.
[0029]
That is, in the case of a five-stand cold rolling tandem mill, for example, a work roll satisfying the above formula (1) is used for the first stand and / or the second stand, and other stands are generally used in cold rolling. A grinding roll having an R _Z of about 2 to 5 μm is used.
In addition, since the work roll of the last stand (in the case of 5 stands, the 5th stand) uses a roll having a surface roughness corresponding to the target plate surface roughness, a grinding roll, a shot dull roll, a discharge dull are appropriately used. A processing roll can be selected.
[0030]
FIG. 6 shows the oil pit remaining rate when R _Z is changed under the condition satisfying the above-described formula (1).
In addition, the oil pit residual rate was calculated | required from the number of the dent flaws per unit area of the unrolled part and the part by which rolling was complete | finished to the 2nd stand about the to-be-rolled material which implemented the biting prevention during rolling.
[0031]
As shown in FIG. 6, it can be seen that the oil pit residual ratio can be remarkably reduced by setting R _Z to 10 μm or more and using a work roll satisfying the above formula (1).
As described above, the cold rolling method of the present invention has been described. In the present invention, in order to more reliably transfer the shape of the groove portion of the roll surface to the shoulder portion of the steel plate dent and erase the dent defect by rolling. A work roll having grooves formed in the roll circumferential direction, the roll surface roughness R _Z being the groove depth being 10 μm or more, and the groove length L (μm) satisfying the following formula (2): It is more preferable to use ( second invention).
[0032]
L> R _Z / (tan α) (μm) (2)
[II. Alloyed molten metal plating:]
In the present invention, after the molten metal plating material steel plate obtained in the first to second inventions described above is subjected to molten metal plating, a heat alloying treatment is performed to produce an alloyed molten metal plated steel plate. .
[0033]
Hereinafter, alloyed hot dip galvanizing which is a typical alloyed hot metal plating will be described.
In the present invention, the cold-rolled steel sheet obtained by the rolling method described above is preferably subjected to pickling treatment, for example, after heat reduction in a reducing atmosphere in a heating furnace provided in a continuous hot dip galvanizing line. Apply hot dip galvanizing.
[0034]
As the hot dip galvanizing bath, a plating bath containing 0.08 to 0.2% Al is suitable, and the bath temperature is suitably 450 to 500 ° C.
Next, after controlling the coating amount of the hot dip galvanized steel sheet pulled up from the hot dip galvanizing bath by the gas wiping method, in the alloying furnace, preferably under the condition of the highest plate temperature: 460-530 ° C Heat alloy.
[0035]
The amount of Fe diffusion into the plating layer during the alloying treatment is preferably 8 to 11% as the Fe content in the resulting plating layer.
[0036]
【Example】
Hereinafter, the present invention will be described more specifically based on examples.
Example 1
The hot-rolled steel sheet was cold-rolled using a 5-stand cold-rolled tandem mill.
As the steel plate, a steel plate made of plain steel having a carbon content of 0.005% was used.
[0037]
As the work roll of the first stand, a work roll having a groove with a surface roughness R _Z of 14 μm formed by shotdal processing is used. As the work rolls of the second stand to the fifth stand, a work roll of R _Z of 2.5 μm is used. A roll (grinding roll) was used.
The resulting cold-rolled steel sheet had an oil pit residual rate as low as 3%, and it was found that the dents formed before cold-rolling disappeared.
[0038]
Next, the obtained cold-rolled steel sheet was passed through a continuous hot dip galvanizing line, and pickling, heat reduction annealing, hot dip galvanizing, and alloying treatment were performed.
Hot dip galvanization and alloying were performed under the following conditions.
[Hot galvanizing:]
Bath temperature: 465 ℃
Al concentration in bath: 0.13%
[Alloying treatment:]
Maximum plate temperature: 490 ℃
Note that the coating amount of hot dip galvanizing was 40 g / m ^{2 on} both sides.
[0039]
The resulting alloyed hot-dip galvanized steel sheet was visually judged for unevenness in alloying, and as a result of investigating the defective product rate due to unevenness of alloying from the weight ratio of the spotted pattern, the defective product rate was 0.4%. The number of defective products could be reduced.
(Example 2)
An alloyed hot-dip galvanized steel sheet was produced in the same manner as in Example 1 except that a work roll having a groove with a surface roughness R _Z of 13 μm formed by electric discharge dull machining was used as the work roll of the first stand.
[0040]
Next, as a result of investigating the defective product generation rate due to alloying irregularities by the same method as in Example 1, the defective product generation rate was as low as 0.5%, and defective products could be reduced.
(Example 3)
The hot-rolled steel sheet was cold-rolled using a 5-stand cold-rolled tandem mill.
As the steel plate, a steel plate made of plain steel having a carbon content of 0.005% was used.
[0041]
As the work roll of the first stand, a work roll having the following specifications in which grooves are formed in the circumferential direction of the roll by grinding is used. As the work rolls of the second to fifth stands, R _Z is a work roll having 2 μm (grinding roll). )It was used.
[Specifications of the work roll of the first stand:]
Roll diameter: 600mm
Roll axis direction surface roughness R _Z : 13μm
Groove length (L): 550 μm
Contact angle between roll and steel plate for plating (α): 1.7 °
L> 10 / (tan α) = 337 μm
Note that the length L of the groove-shaped portion on the roll surface is measured by microscopic observation with a replica of the roll surface, and α is a cross-sectional shape of the steel sheet that has been in contact with the roll after rolling is stopped. It was determined from the relationship between the length of the bite part (contact arc length) and the roll diameter.
[0042]
The oil pit remaining rate of the obtained cold-rolled steel sheet was as extremely low as 1%.
Next, the obtained cold-rolled steel sheet was passed through a continuous hot dip galvanizing line, and pickling, heat reduction annealing, hot dip galvanizing, and alloying treatment were performed.
Hot dip galvanization and alloying were performed under the following conditions.
[Hot galvanizing:]
Bath temperature: 465 ℃
Al concentration in bath: 0.13%
[Alloying treatment:]
Maximum plate temperature: 490 ℃
Note that the coating amount of hot dip galvanizing was 40 g / m ^{2 on} both sides.
[0043]
Next, as a result of investigating the occurrence rate of defects due to uneven alloying by the same method as in Example 1, the occurrence rate of defective products was as low as 0.2%, and defective products could be reduced.
(Comparative example)
An alloyed hot-dip galvanized steel sheet was produced in the same manner as in Example 1 except that a work roll having the following specifications, which was a grinding roll, was used as the work roll of the first stand.
[0044]
[Specifications of the work roll of the first stand:]
Roll diameter: 600mm
Roll axis direction surface roughness R _Z : 8 μm
Groove length (L): 50 μm
Contact angle between roll and steel plate for plating (α): 1.7 °
L <R _Z / (tan α) = 270 μm
Next, as a result of investigating the defective product generation rate due to uneven alloying by the same method as in Example 1, the defective product generation rate was 1.2%.
[0045]
【The invention's effect】
According to the present invention, it is possible to prevent the occurrence of uneven plating coverage in a hot-dip galvanized steel sheet by making the dent defect generated before cold rolling defect-free in cold rolling. It has become possible to prevent the occurrence of uneven alloying in alloyed molten metal plating and improve the yield of alloyed molten metal plated steel sheets.
[Brief description of the drawings]
FIG. 1 is a graph showing a profile of a surface of a raw steel plate in an uneven alloying portion.
FIG. 2 is a graph showing a profile of the surface of a raw steel plate at an uneven alloying portion.
FIG. 3 is a graph showing a profile of the surface of a raw steel plate in an uneven alloying portion.
FIG. 4 is an explanatory view showing a contact angle between a work roll and a material to be rolled.
FIG. 5 is a cross-sectional view (schematic diagram) showing a groove-like portion of a work roll and a steel plate recess.
FIG. 6 is a graph showing the relationship between the work roll surface roughness R _Z and the oil pit residual rate of the cold rolled steel sheet.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Work roll 2 Rolling completion | finish part of the raw steel plate for molten metal plating 3 Inferred part of the raw steel plate for molten metal plating 4 Groove of a work roll 5 Indentation crack of a steel plate

Claims (4)

When rolling a steel sheet for hot metal plating in cold rolling using a tandem rolling mill, it has grooves formed in the circumferential direction of the roll, and the roll surface roughness R _Z that is the groove depth is 10 μm or more. A cold rolling method for a steel sheet for hot metal plating, wherein a work roll having a groove length L (μm) satisfying the following formula (1) is used.
L> 10 / (tan α) (μm) ………… (1)
In the above formula (1), α represents a contact angle between the roll and the material steel plate for molten metal plating that is the material to be rolled. When rolling a steel sheet for hot metal plating in cold rolling using a tandem rolling mill, it has grooves formed in the circumferential direction of the roll, and the roll surface roughness R _Z that is the groove depth is 10 μm or more. A cold rolling method for a steel sheet for hot metal plating, characterized in that a work roll having a groove length L (μm) satisfying the following formula (2) is used.
L> R _Z / (tan α) (μm) (2)
In the above formula (2), α represents the contact angle between the roll and the steel sheet for hot metal plating that is the material to be rolled. The method for cold rolling a raw steel sheet for hot metal plating according to claim 1 or 2 , wherein the work roll is a work roll of a stand before a final stand of a tandem rolling mill. An alloyed hot-dip galvanized steel sheet, which is obtained by subjecting a hot-dip metal plating material steel plate obtained by the cold rolling method according to any one of claims 1 to 3 to hot alloying treatment. Manufacturing method.

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