JP2002045904A - Rolling method for suppressing surface defect of steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling method for suppressing a surface defect caused by the movement of ruggedness located at the side faces of a material to be rolled to the upper and lower surfaces. SOLUTION: In a method by which, after heating the material to be rolled with a heating furnace and after performing broadside rolling for rolling the material in the width direction of a product, the material is turned 90 deg. and longitudinal rolling for rolling the material in the length direction of the product is performed, this method is a rolling method for suppressing the surface defect of the steel sheet, by which edger rolling for forming the shape of the side faces equivalent to the front and rear end parts in the longitudinal rolling of the material to be rolled into a taper shape which is inclined to the side of a face where heating temperature is higher in the thickness direction of the material to be rolled is performed befor the longitudinal rolling.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of a rolling method for suppressing the occurrence of surface flaws generated at the front and rear ends of a steel sheet in a rolling process.

[0002]

2. Description of the Related Art Conventionally, during rolling of a steel sheet, irregularities causing flaws existing on the side surface of the material to be rolled are wrapped around the upper and lower surfaces of the material to be rolled by rolling. A surface flaw called a seam flaw extending in the rolling direction is generated at an end in the width direction. There is no major problem when this seam flaw is in the truncated part of the product, but if it is in the product part, care work is required, and if it can not be done, the product will be rejected and the product yield will be reduced .

[0003] As a measure for reducing the seam flaw, for example,
As disclosed in JP-A-8-1205 and JP-A-8-150402, the leading end of the material to be rolled is made thinner at the time of tentative rolling, and finish rolling (longitudinal rolling) is performed from the side in the width direction. There is known a method of reducing the amount of flaw wraparound to reduce the occurrence of seam flaws. If the flaws are generated in the rolling direction at the width direction ends of the upper and lower surfaces of the steel sheet, it can be reduced by this method, but the surface mechanism generated at the leading end and the rear end of the steel sheet by the same mechanism, It cannot be reduced.

At the time of longitudinal rolling, the material to be rolled hardly extends in the width direction, which is a direction perpendicular to the rolling direction, and therefore, the leading end of the material to be rolled in the width direction is made thinner. In the subsequent longitudinal rolling, the amount of wraparound from the side surface in the width direction can be reduced, and the amount of the seam flaws entering the product side can also be reduced. However, as shown in FIG. 7, in the longitudinal rolling, since the material to be rolled is extended in the rolling direction, the amount of wraparound to the upper and lower surfaces of the front and rear end side surfaces of the material to be rolled increases.
The surface flaws generated at the front and rear ends of the steel sheet largely enter the product side. Also, in vertical rolling, the rolling ratio is large, so even a slight temperature difference between the upper and lower surfaces of the material to be rolled, the higher temperature surface is extended, and the amount of surface flaws entering the product side also differs between the front and back surfaces. In addition, the amount of surface flaws penetrating into the low temperature surface increases. For this reason, the product yield is affected by the amount of surface flaws, that is, the surface with a large amount of wraparound to the upper and lower sides of the side surface. The black circles in the drawing indicate the corner positions of the front and rear ends of the material to be rolled, and schematically show the process in which the black circles before vertical rolling are wrapped around the upper and lower surfaces by vertical rolling.

[0005]

SUMMARY OF THE INVENTION As a result, the present inventors have studied, and as a result, in order to reduce the amount of surface flaws generated at the front and rear end portions of a steel sheet into the product side and improve the product yield. It has been found that it is effective to make the amount of surface flaws penetrating into the product side symmetrical in the vertical direction.

The present invention has been made in order to solve the above-mentioned problems, and takes into account the temperature difference between the upper and lower surfaces of the material to be rolled and the amount of wrap around to the upper and lower surfaces due to the temperature difference. After rolling, the side surface of the material to be rolled corresponding to the leading and trailing ends in longitudinal rolling is formed into a tapered shape, and then longitudinal rolling is performed, so that the amount of surface flaws entering the leading and trailing ends of the product is symmetrical in the upper and lower planes. It is an object of the present invention to provide a rolling method capable of suppressing surface flaws of a steel sheet.

[0007]

The gist of the present invention is that after the material to be rolled is heated in a heating furnace, rolling is performed in the width direction of the product, followed by rotation by 90 ° and rolling in the length direction of the product. In a rolling method of performing vertical rolling, before the vertical rolling,
A steel sheet characterized by performing edger rolling in which a side surface shape corresponding to the front and rear end portions in the longitudinal rolling of the material to be rolled is formed into a tapered shape inclined to a surface side having a higher heating temperature in a thickness direction of the material to be rolled. This is a rolling method that suppresses surface flaws.

In the above-mentioned edger rolling, there is provided a rolling method for suppressing surface flaws of the above-mentioned steel sheet, which is rolled by a vertical roll in which the diameter of a vertical roll of an edger rolling machine changes in a tapered shape in a thickness direction of a material to be rolled. .

In the above-mentioned edger rolling, there is provided a rolling method for suppressing surface flaws of the above-mentioned steel sheet, which is rolled by a vertical roll in which a vertical roll axis of an edger rolling mill is inclined in a thickness direction of a material to be rolled.

The temperature difference between the upper and lower surfaces of the material to be rolled, the amount of wrap around the front and rear ends of the material to be rolled into the upper and lower surfaces in the longitudinal rolling, and the tapered shape imparted to the side surface of the material to be rolled by edger rolling are determined in advance. In actual rolling, the temperature difference between the upper and lower surfaces of the material to be rolled before the longitudinal rolling is obtained by actual measurement or calculation, and the obtained temperature difference and the previously obtained temperature difference are obtained. The rolling method for suppressing surface flaws of a steel sheet according to any one of the above, wherein an optimum taper shape to be imparted to the side surfaces of the front and rear ends of the material to be rolled in longitudinal rolling is determined from the correlation.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The material to be rolled in a heating furnace tends to be easily heated at the upper surface due to the structure of the heating furnace, and the temperature of the upper surface tends to be higher than that of the lower surface. For this reason, in the vertical rolling with a high rolling ratio, the upper surface side with a higher temperature is extended, and the side surface on the lower surface side with a lower temperature is more likely to wrap around to the lower surface side. Further, in the rolling of a steel sheet, when the material to be rolled is thick, if warpage occurs, a problem such as conveyance on a roller table occurs, so that the steel sheet is generally rolled slightly downward. For this reason, surface flaws tend to enter the lower surface side of the product.

Therefore, the rolling method according to the present invention for suppressing the surface flaws of a steel sheet takes into account the temperature difference between the upper and lower surfaces of the material to be rolled, and after rolling, after rolling, corresponds to the front and rear ends of the vertical rolling. The side of the material is formed into a tapered shape. That is, the amount of wraparound of the side surface due to the temperature difference between the upper and lower surfaces of the material to be rolled is predicted, and in order to shorten the length of the side with the higher temperature, the side of the material to be rolled is It is formed into a tapered shape inclined toward the side (thickness direction).

[0013] The side surface of the material to be rolled is formed into a tapered shape by an edger rolling mill having a function of tilting a vertical roll, whereby the vertical roll is tilted in the thickness direction of the material to be rolled, and is subjected to edger rolling. Furthermore, by changing the diameter of the vertical roll of the edger rolling machine in the thickness direction of the material to be rolled from small to large, or from large to small, the roll surface of the vertical roll can be tapered. Therefore, the inclination angle of the vertical roll shaft in the thickness direction of the material to be rolled can be small. Needless to say, the vertical roll diameter at this time is changed from large to small from the surface side where the temperature of the material to be rolled is high to the surface side where the temperature is low.

In the actual rolling, the temperature difference between the upper and lower surfaces of the material to be rolled, the amount of the front and rear end sides of the material to be rolled into the upper and lower surfaces of the material to be rolled in vertical rolling, and the side surface of the material to be rolled are given by edger rolling. It is important to investigate the correlation between the tapered shapes. That is, by knowing the relationship between the temperature difference between the upper and lower surfaces of the material to be rolled and the amount of wraparound of the side surface to the upper and lower surfaces of the material to be rolled, it is possible to determine the taper shape to be imparted to the side surface of the material to be rolled. This makes it possible to make the amount of surface flaws entering the product side due to the side surface wrapping around the upper and lower surfaces of the product symmetrical in the upper and lower surfaces, and to minimize the amount of surface flaws entering the product side.

For this purpose, the temperature difference between the upper and lower surfaces of the material to be rolled before longitudinal rolling is obtained by actual measurement or calculation, and based on the temperature difference, the correlation between the above three factors is used to determine the side surface of the material to be rolled. The amount of wrap around the upper and lower surfaces can be predicted, and the taper shape to be applied to the side surface of the material to be rolled can be determined. When calculating the temperature difference between the upper and lower surfaces of the material to be rolled by calculation, the temperature difference can be obtained from the temperature distribution in the heating furnace, the heating time, the elapsed time after leaving the heating furnace, and the like, using the heat conduction equation.

FIG. 1 is a schematic diagram showing a change in the shape of a longitudinal section when a material to be rolled having a temperature difference between upper and lower surfaces is longitudinally rolled. In the drawing, an asterisk on the lower surface of the material to be rolled indicates the lower corner position of the material 3 to be rolled before longitudinal rolling, and the temperature of the material to be rolled at this time is higher at the upper surface than at the lower surface. As shown in FIG. 1 (a), when the conventional rolling method, that is, the upper surface side of the material 3 to be rolled has a high temperature and the side surface is not tapered, the lower surface side of the material to be rolled is also extended by longitudinal rolling. But
Since the upper surface where the temperature is higher is extended more than the lower surface, the amount of wraparound from the upper surface to the lower surface of the side surface is increased. Therefore, in the product 4, the distance to the front and rear end portions based on the lower surface corner position (star mark) of the material 3 to be rolled before longitudinal rolling is large.

FIG. 1B shows a case where a tapered shape having a small inclination angle is provided on the side surface of the material 3 to be rolled. By forming the tapered shape on the side surface of the material to be rolled, the extension on the upper surface side, that is, The wraparound of the side surface from the upper surface side to the lower surface side is reduced, and in the product 4, the distance to the front and rear end portions based on the lower surface corner position (star mark) of the material 3 to be rolled before longitudinal rolling is larger than (a). It is getting smaller.

FIG. 1 (c) shows a case where a tapered shape having a large inclination angle is provided on the side surface of the material 3 to be rolled in consideration of the temperature difference between the upper and lower surfaces. By forming, the wraparound from the upper surface side to the lower surface side of the side surface is reduced, and in the product 4, the distance from the front and rear end portions based on the lower surface corner position (star mark) of the material to be rolled before longitudinal rolling is ( a) and (b).

As described above, when there is a temperature difference between the upper and lower surfaces of the material to be rolled, a taper shape is formed on the side surface of the material to be rolled, so that the amount of wraparound from the upper surface of the side surface to the lower surface is reduced. As a result, in the product, the distance to the front and rear end portions based on the lower surface corner position (star mark) of the material to be rolled before longitudinal rolling is shortened.

In the above method, it is necessary to determine an optimum taper shape angle based on various sheet thicknesses, temperature differences, and rolling pass schedules. However, in reality, it is difficult to experimentally determine all cases. Therefore, the relationship between the amount of wraparound to the upper and lower surfaces of the side surface and the taper shape angle by the rolling pass schedule including the temperature difference between the upper and lower surfaces of the material to be rolled can be obtained by numerical simulation and given as a table for each rolling pass schedule. It is. The specific method is described below.

The numerical simulation uses an analysis by the FEM (finite element method). In the FEM, the shape of the initial material to be rolled, in which the side surfaces of the front and rear ends in the longitudinal rolling of the material to be rolled before the longitudinal rolling are tapered, is given as a two-dimensional section, and the temperature difference between the upper and lower surfaces (deformation resistance) Is given arbitrarily. The initial shape model is analyzed by a two-dimensional unsteady elasto-plastic (or rigid-plastic) finite element method to determine the amount of wrap around the side surface.

Hereinafter, an example in which FEM (finite element method) analysis is performed will be described. In this calculation example, the taper shape angle is 0 ° (without forming the taper shape) to 15 °,
Upper and lower surface temperature difference is 100 ° C (upper surface 1100 ° C, lower surface 100
0 ° C). Table 1 shows the rolling pass schedule at this time.

[0023]

[Table 1]

FIG. 2 shows a deformation diagram of the material to be rolled after the rolling is completed as a calculation result. 2 (a) is 0 ° (no tapered shape is formed), (b) is 5 °, (c) is 10 °, (d)
Is 15 °. As shown in FIG. 2, when the angle of the taper shape is increased, the shape of the front and rear ends approaches a rectangular shape in balance with the temperature difference between the upper and lower surfaces. That is, it is understood that the amount of the material to be rolled into the upper and lower surfaces of the front and rear end side surfaces is reduced. The numbers in the figure indicate the amount of wraparound to the upper and lower surfaces, and the unit is mm.

FIG. 3 shows the numerical value of the amount of wraparound from the side surface to the upper and lower surfaces as a result of the above calculation. (A), (b), (c), and (d) in FIG.
(B), (c), and (d), each of which corresponds to the taper angle formed on the side surface of the material to be rolled.
(A) shows that the taper shape is not formed, and (b) shows that the taper shape angle is 5 °. As shown in FIG. 4, the wraparound amount is determined by the product 4 on the side surface of the material 3 to be rolled by longitudinal rolling.
At the upper surface side or the lower surface side.

As shown in FIG. 3, when the taper shape angle increases, the amount of wraparound of the side surface toward the lower surface side decreases, and when the taper shape angle is 5 °, the amount of wraparound toward the upper surface side begins to increase. When it becomes larger and becomes 15 °, the amount of wrap around to the upper and lower surfaces becomes substantially symmetric.

As described above, the tapered shape is formed on the side surface of the material to be rolled in consideration of the temperature difference between the upper and lower surfaces of the material to be rolled, thereby minimizing the amount of wraparound to the upper and lower surfaces of the side material. it can. Therefore, by adopting this rolling method, the amount of surface flaws generated by wrapping around to the upper and lower surfaces of the side surfaces can be reduced, so that the product yield can be improved.

[0028]

Embodiments will be described below with reference to embodiments. The thickness (rolled material) after completion of tentative rolling in vertical rolling is 100 mm
Then, rolling was performed in 16 passes at a rolling reduction of about 5.4 mm per pass to complete the plate thickness to 13.2 mm. At this time, the temperature difference between the upper and lower surfaces of the slab is 30 ° C., the upper surface side is 1100 ° C., the lower surface side is 1070 ° C., and the tapered shape is as shown in FIG.
No taper molding, 100: 10, 100: 30
There are three types that have a tapered shape. FIG. 6 shows the result of longitudinal rolling at this time.

As shown in FIG. 6, when the tapered shape is not formed on the front and rear end side surfaces of the slab of the comparative example, the amount of wrap around the lower surface side of the side surface is 65 mm.
When a taper shape of 10 is provided, the wraparound amount is 5
It is reduced by about 10 mm at 0 mm. One of the aspects of the present invention
When the tapered shape of 00:30 is provided, the wraparound to the upper and lower surfaces of the side surface occurs, and the amount of wraparound to the lower surface side is 4
The wraparound amount to the upper and lower surfaces of the product is 2 mm, the wraparound amount to the upper surface side is 46 mm, and the wraparound amount to the upper and lower surfaces of the product is reduced by about 20 mm compared to the comparative example which is not formed into a tapered shape. As a result, the amount of cut-off at the front and rear ends of the product can be reduced, and the product yield can be improved. Since the initial slab thickness of 100 mm corresponds to the slab thickness at the start of vertical rolling in actual rolling, by giving a tapered shape of 100: 30 at the start of vertical rolling,
Surface flaws caused by the wraparound of the side surface to the surface can be prevented.

In practicing the present invention, it is necessary to impart a tapered shape to the side surface of the slab (rolled material) corresponding to the front and rear ends in the vertical rolling. For this purpose, the edger rolling mill is provided with the function of tilting the vertical rolls, and
In accordance with the temperature distribution in the slab thickness direction, the vertical roll is inclined to form a tapered shape on the slab side surface corresponding to the front and rear ends of the vertical rolling. Also, by changing the diameter of the vertical roll to a tapered shape in the length direction, the inclination angle of the vertical roll can be small.

[0031]

As is apparent from the above description,
According to the rolling method of the present invention, even in longitudinal rolling with a high rolling ratio, the amount of wraparound of the material to be rolled into the upper and lower surfaces of the front and rear end side surfaces can be reduced, so that the amount of surface flaws entering the product side Can be suppressed. Therefore, according to the rolling method of the present invention, the yield of the product steel sheet can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a relationship between a wraparound of a material to be rolled on an upper surface side and a tapered shape formed on a side surface of the material to be rolled.

FIG. 2 is a view for explaining deformation of front and rear end portions of a material to be rolled after completion of rolling analyzed by a finite element method.

FIG. 3 is a diagram showing the relationship between the amount of wrap around the upper and lower surfaces of the material to be rolled and the taper angle formed on the side surface of the material to be rolled by FEM analysis.

FIG. 4 is a diagram illustrating the definition of a wraparound amount.

FIG. 5 is a diagram showing an initial slab cross-sectional shape in the example.

FIG. 6 is a diagram illustrating the amount of wraparound to the upper and lower sides of the side surface in the embodiment.

FIG. 7 is a view for explaining the cause of the occurrence of surface flaws generated during conventional vertical rolling.

[Explanation of symbols]

1 vertical roll, 2 horizontal roll, 3 rolled material, 4 product.

Claims (4)

[Claims] 1. A rolling method comprising: heating a material to be rolled in a heating furnace, performing tentative rolling for rolling in a product width direction, and then rotating by 90 ° and performing vertical rolling for rolling in a product length direction. Prior to the vertical rolling, edger rolling is performed in which a side surface shape corresponding to the front and rear end portions in the vertical rolling of the material to be rolled is formed into a tapered shape that is inclined in a thickness direction of the material to be rolled toward a surface having a higher heating temperature. A rolling method for suppressing surface flaws on a steel sheet. 2. An edger rolling machine according to claim 1, wherein the vertical roll of the edger rolling mill is tapered in the thickness direction of the material to be rolled.
3. A rolling method for suppressing surface flaws of a steel sheet according to item 1. 3. The roll for suppressing surface flaws of a steel sheet according to claim 1, wherein the edger rolling is performed by a vertical roll in which a vertical roll axis of an edger rolling mill is inclined in a thickness direction of a material to be rolled. Method. 4. The temperature difference between the upper and lower surfaces of the material to be rolled, the amount of wrap around the front and rear ends of the material to be rolled to the upper and lower surfaces in longitudinal rolling, and the taper shape given to the side surface of the material by edger rolling in advance. Investigating the correlation between the three
At the time of actual rolling, the temperature difference between the upper and lower surfaces of the material to be rolled before the vertical rolling is obtained by actual measurement or calculation, and the material to be rolled in the vertical rolling is obtained from the obtained temperature difference and the previously obtained correlation. The rolling method for suppressing surface flaws of a steel sheet according to any one of claims 1 to 3, wherein an optimum taper shape to be imparted to the side surfaces of the front and rear ends is determined.