JP2009214161A - Method and finishing rolling mill for manufacturing hot-rolled steel strip - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a finishing rolling mill for manufacturing a hot-rolled steel strip and a finishing rolling mill by which the hot-rolled steel strip is manufactured while keeping down the amount of meandering in the finishing rolling mill when a sheet bar is high strength steel such as a high tensile strength steel and even when rolling load is largely varied by slight irregularity of material. <P>SOLUTION: When manufacturing the hot-rolled steel strip 1 by finish-rolling a rough rolled sheet bar 2 with the finishing rolling mill 3, the hot-rolled steel strip 1 is manufactured by using a rolling stand 4G in which the peripheral surface parts of work rolls are formed of cemented carbide as a rolling stand the work rolls 5 of which are crossed among a plurality of rolling stands 4A-4G of the finishing rolling mill 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a hot-rolled steel strip and a finish rolling mill used when producing a hot-rolled steel strip.

Generally, a hot-rolled steel strip is obtained by roughly rolling a steel slab (steel material) heated to about a few hundred degrees to a sheet bar having a thickness of about 20 to 50 mm with a rough rolling machine of a hot rolling line. It is manufactured by rolling a sheet bar thinly and finishing it into a strip steel with a finishing mill composed of about seven continuous rolling stands.
The quality required for such a hot-rolled steel strip includes plate thickness accuracy in the longitudinal direction and width direction (plate thickness distribution in the width direction is referred to as plate crown), flatness (also referred to as shape), surface quality, and the like. In order to maintain a good sheet crown and flatness, it is important to perform rolling while considering roll bending due to a rolling load in finish rolling and roll wear accompanying the progress of rolling.

As a method for reducing the influence of roll deflection, a method of hot rolling a sheet bar by crossing a work roll of a latter stage of a finishing mill is known. Moreover, as a technique for fundamentally improving roll bending and roll wear, a technique is known in which the peripheral surface of the work roll is formed of a cemented carbide such as tungsten carbide (see, for example, Patent Document 1).
JP 2001-321804 A

  However, when the work roll is crossed, a force for pushing the sheet bar in the width direction acts on the front and back surfaces of the sheet bar. In this case, if the force acting on the surface of the seat bar and the force acting on the back surface of the seat bar antagonize, the seat bar goes straight without meandering, but the force acting on the surface of the seat bar and the back surface of the seat bar There are a number of factors present in the finishing stand of a finishing mill that make a difference between the forces acting on the rolling mill. Examples of the factors that cause a difference between the force acting on the surface of the seat bar and the force acting on the back surface of the seat bar include, for example, generation of a seat bar approach angle caused by a pass line being pushed up by a louver, Examples include a difference in friction coefficient due to a difference between the side scale state and the back side scale state, and a difference in lubrication state on the front and back surfaces of the sheet bar due to the supply of rolling oil. For this reason, when a large variation in rolling load occurs due to slight material unevenness (for example, a hardness difference between the operator side and the drive side of the work roll), the difference in the contact state between the front and back surfaces of the sheet bar is caused between the work rolls. As a result, there is a problem that it is difficult to roll the sheet bar without meandering.

Further, when the seat bar is made of high strength steel such as high tension steel (high tensile steel), the rolling load becomes large, so that the deflection and wear due to the rolling load become large. In order to compensate for the larger deflection of the roll, it is necessary to increase the cross angle. In this case, if there is a load difference in the width direction such as material unevenness, the amount of meandering in the finishing mill increases. There was a problem.
Further, when the work rolls are crossed, the gap between the work rolls is larger as the distance from the end of the roll is closer than when the work rolls are not crossed. In particular, when only the work roll is crossed, the support by the backup roll at the end of the roll is less than when the work roll is crossed with the backup roll. It becomes difficult.

  The present invention has been made in view of the above points, and the sheet bar meanders in the finishing mill even when the sheet bar is made of high-strength steel such as high tensile steel or when the rolling load varies greatly due to slight material unevenness. It aims at providing the manufacturing method and finish rolling mill of a hot-rolled steel strip which can manufacture a hot-rolled steel strip, keeping quantity small.

In order to solve the above-mentioned problem, a method for producing a hot-rolled steel strip according to the first aspect of the present invention comprises hot rolling a rough-rolled sheet bar by a finish rolling mill having a plurality of rolling stands. When manufacturing a rolled steel strip, the hot rolled steel strip is manufactured using a rolling stand having a work roll peripheral surface portion formed of cemented carbide as a rolling stand in which a work roll is crossed among the plurality of rolling stands. It is characterized by that.
A method for producing a hot-rolled steel strip according to the invention described in claim 2 is the method for producing a hot-rolled steel strip according to claim 1, wherein the work roll peripheral surface portion is formed of cemented carbide, and The hot-rolled steel strip is manufactured using a rolling stand having a cross angle of a work roll of 0.3 degrees to 1 degree.

A finishing mill according to a third aspect of the present invention is a finishing rolling mill used when manufacturing a hot-rolled steel strip, wherein work rolls of at least one rolling stand among a plurality of rolling stands cross each other. And the surrounding surface part of the said work roll is formed with the cemented carbide.
A finishing mill according to a fourth aspect of the present invention is the finishing mill according to the third aspect, wherein a work roll of at least one rolling stand among the plurality of rolling stands has a cross angle of 0.3 to 1 degree. And the peripheral surface of the work roll is formed of a cemented carbide.

  According to the inventions of claims 1 and 3, by using a rolling stand in which the work roll peripheral surface portion is formed of cemented carbide as a rolling stand in which the work roll is crossed among the plurality of rolling stands of the finish rolling mill, The Young's modulus of the work roll is larger than that of the steel work roll. As a result, roll deflection due to rolling load can be kept small, so even when the sheet bar is high-strength steel such as high tensile steel, a hot-rolled steel strip is manufactured while keeping the meandering amount of the sheet bar in the finish rolling mill small. Can do.

In addition, since the roll deflection is suppressed to a small extent, the difference in contact state between the front and back surfaces of the sheet bar is less likely to occur between the work rolls. Therefore, even when the rolling load varies greatly due to slight material unevenness, A hot-rolled steel strip can be produced while keeping the meandering amount of the bar small.
According to the second and fourth aspects of the invention, the amount of meandering of the sheet bar can be reduced compared with that of a work roll made of steel, and the cross angle of the work roll is less than 0.1 degrees. The accuracy of the crown and flatness can be increased.

Hereinafter, with reference to FIGS. 1-3 and Table 1, the finishing rolling mill used for the manufacturing method and method of the hot rolled steel strip which concerns on this invention is demonstrated.
FIG. 1 is a view for explaining a method for producing a hot-rolled steel strip according to the present invention. As shown in FIG. 1, the hot-rolled steel strip 1 is a sheet roughly rolled by a roughing mill (not shown). The bar 2 is manufactured by finish rolling with a finish rolling mill 3. Here, the finish rolling mill 3 is configured by arranging, for example, four-stage rolling stands 4A to 4G along a pass line, and each rolling stand 4A to 4G includes a pair of upper and lower work rolls 5 and 5 and these work rolls. 5 and a pair of upper and lower backup rolls 6 and 6 for backing up the motor 5.

Among the rolling stands 4A to 4G, the work rolls 5 of the rolling stand (final stand) 4G arranged at the position farthest from the roughing mill cross each other, and the backup roll 6 of the final stand 4G is the same as the work roll 5. Cross each other.
The cross angle of the work roll 5 is not less than 0.3 degrees and not more than 1 degree, preferably not less than 0.3 degrees and not more than 0.5 degrees. Here, the reason for setting the cross angle of the work roll 5 to 0.3 degrees or more and 1 degree or less is that when the cross angle is less than 0.3 degrees, the accuracy of the plate crown or flatness is lowered, and when it exceeds 1 degree, the meandering is performed. It is because it becomes easy to do.

  An example of the work roll 5 of the rolling stand 4G is shown in FIG. As shown in the figure, the work roll 5 of the rolling stand 4G includes, for example, a steel shaft member 7 formed by forging Cr steel having a Cr content of 5 mass%, and a body portion of the steel shaft member 7. The cemented carbide joining sleeve 8 is shrink-fitted in the region corresponding to the rolled portion, and two steel side end rings 9 and 9 fixed to both ends of the cemented carbide joining sleeve 8 are configured.

  The cemented carbide joining sleeve 8 is formed by, for example, machining an outer diameter of 650 mm and a barrel length of 2050 mm after joining six sleeve members 11 in the roll axis direction. The sleeve member 11 of the cemented carbide joining sleeve 8 is formed, for example, by rubber molding a powder obtained by adding 20% by mass of Co to tungsten carbide (WC) by the CIP method (cold isostatic pressing method). .

  The joining method of the sleeve member 11 is not particularly limited. For example, a method of joining the sleeve member 11 by the HIP method (hot isostatic pressing method) under the conditions of joining temperature: 1260 ° C. and joining atmosphere: 10 atm. it can. When the sleeve member 11 is formed by rubber molding by the CIP method, it is preferable to add an appropriate amount of Ni to the material of the sleeve member 11 because the wear resistance is improved.

As described above, when the hot rolled steel strip 1 is manufactured by finishing and rolling the roughly rolled sheet bar 2 with the finish rolling mill 3, the upper and lower work rolls 5 of the rolling stands 4A to 4G of the finishing mill 3 are used. When a rolling stand whose work roll peripheral surface portion is formed of a cemented carbide is used as a rolling stand crossed, the Young's modulus of the work roll 5 becomes larger than that of a steel work roll. As a result, the roll deflection due to the rolling load can be suppressed to be small, and the contact length and cross angle of the roll tool can be made smaller than those of the steel work roll, so that the meandering amount of the sheet bar 2 can be suppressed to a smaller value.
Further, since the roll deflection is suppressed to be small, a difference in contact state between the front and back surfaces of the sheet bar 2 is less likely to occur between the work rolls. Therefore, even in the case where the rolling load greatly fluctuates due to slight material unevenness, The hot-rolled steel strip 1 can be produced while keeping the meandering amount of the sheet bar 2 at a small value.

  590 MPa class high tensile steel is used as the sheet bar 2 that is finished and rolled by the finishing mill 3, and the work bar diameter is 650 mm, the backup roll diameter is 1600 mm, and the weight per coil is 2.4 mm. Table 1 shows the results of measuring the rolling speed, meandering amount, crown, and flatness at the final rolling stand when rolled to the finished thickness, together with the roll material and the cross angle.

  In Table 1, Examples 1-3 show the case where the rolling stand in which the upper and lower work rolls cross each other and the work roll peripheral surface portion is formed of cemented carbide is used as the final stand of the finishing mill, and is a conventional example. 1 shows a case where a rolling stand in which a work roll peripheral surface portion in which upper and lower work rolls do not cross each other is formed of cemented carbide is used as a final stand of a finishing mill. Further, Conventional Example 2 and Conventional Example 3 show a case in which the upper and lower work rolls cross each other and the work roll material made of steel is used as the final stand of the finishing mill.

Comparing Conventional Examples 2 and 3 shown in Table 1 with Examples 1 to 3 of the present invention, Conventional Examples 2 and 3 had a crown of 8 μm or more and a flatness of 0.6% or more. In Examples 1 and 2 of the invention, the crown was 5 μm or less, and the flatness was 0.5% or less.
Therefore, as in Examples 1 to 3 shown in Table 1, when using a rolling stand in which the upper and lower work rolls cross each other and the work roll peripheral surface portion is formed of cemented carbide as a rolling stand of a finishing mill, Compared with the one where the upper and lower work rolls cross each other and the work roll material is made of steel (conventional examples 2 and 3), the rolling load is increased due to high strength steel such as high tensile steel or slight material unevenness. Even when it fluctuates greatly, it is possible to produce a hot-rolled steel strip with stable quality while suppressing the meandering amount of the sheet bar in the finishing mill.

  When Examples 1-3 shown in Table 1 are compared with Conventional Example 1, Examples 1-3 have a crown of 5 μm and flatness of 0.5%, whereas Conventional Example 1 has a crown of 6 μm, The flatness was 0.55%. In Examples 1 to 3, the cemented carbide work rolls cross each other, whereas in Conventional Example 1, the cemented carbide work rolls do not cross each other or the cross angle is less than 0.1. This is because.

Next, when Example 1 shown in Table 1 and Examples 2 and 3 were compared, Example 2 and 3 had a smaller amount of meandering of the sheet bar than Example 1. In Examples 2 and 3, the cross angle of the cemented carbide work roll is 0.3 to 0.5 °, whereas in Example 1, the cross angle of the cemented carbide work roll is 0.9. This is because it is °.
Therefore, as in Examples 2 and 3 shown in Table 1, as a finishing mill rolling stand, the work roll peripheral surface portion is formed of cemented carbide, and the cross angle of the work roll is 0.3 ° or more and 0.5 °. When the following rolling stands are used, the accuracy of the crown and flatness can be increased.

In addition, although the rolling stand of 4 steps was shown in FIG. 1 as a rolling stand of the finish rolling mill used for the manufacturing method of the hot rolled steel strip according to the present invention, the number of rolling stands and the number of stands are particularly limited. It is not a thing.
1 shows the final stand 4G of the finishing mill 3 as a rolling stand in which the work rolls are crossed. However, it is not always necessary that only the work rolls 5 of the final stand 4G are crossed. The work roll of the stand may be crossed.

  Furthermore, as a work roll having a roll peripheral surface portion formed of cemented carbide, in FIG. 2, a steel shaft member 7, a cemented carbide joining sleeve 8 shrink-fitted to the body portion of the steel shaft member 7, and cemented carbide Although what consists of the two steel side end rings 9 fixed to the both ends of the alloy joining sleeve 8 was shown, it is not restricted to this. For example, as a work roll having a roll peripheral surface portion formed of a cemented carbide, as shown in FIG. 3, the steel shaft member 7 and the outer peripheral surface of the steel shaft member 7 are shrink-fitted through a steel cushioning material 10. A work roll 5 including the cemented carbide joining sleeve 8 and two steel side end rings 9 fixed to both ends of the cemented carbide joining sleeve 8 may be used.

It is a figure for demonstrating the manufacturing method of the hot rolled steel strip which concerns on this invention. It is a figure which shows an example of the work roll in which the roll peripheral surface part was formed with the cemented carbide. It is a figure which shows the other example of the work roll in which the roll peripheral surface part was formed with the cemented carbide.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Hot rolled steel strip 2 Sheet bar 3 Finishing mill 4A-4G Rolling stand 5 Work roll 6 Backup roll 7 Steel shaft member 8 Cemented carbide joining sleeve 9 Steel side end ring 10 Steel shock absorbing member 11 Sleeve member

Claims (4)

  When producing a hot-rolled steel strip by finishing and rolling the roughly rolled sheet bar with a finishing mill having a plurality of rolling stands, as a rolling stand in which upper and lower work rolls of the plurality of rolling stands are crossed, A method for producing a hot-rolled steel strip, comprising producing the hot-rolled steel strip using a rolling stand having a work roll peripheral surface portion made of a cemented carbide.   It is a manufacturing method of the hot rolled steel strip of Claim 1, Comprising: The said work roll surrounding surface part is formed with a cemented carbide, and the cross angle of the said work roll is 0.3 degree or more and 1 degree or less. A method for producing a hot-rolled steel strip, characterized by using the hot-rolled steel strip.   A finish rolling mill used in manufacturing a hot-rolled steel strip, wherein work rolls of at least one rolling stand among a plurality of rolling stands cross each other, and a peripheral surface portion of the work roll is made of cemented carbide. A finishing mill characterized by being formed.   4. The finishing mill according to claim 3, wherein work rolls of at least one rolling stand among the plurality of rolling stands cross each other at a cross angle of 0.3 degrees or more and 1 degree or less, and a peripheral surface portion of the work rolls A finishing mill characterized by being formed of cemented carbide.

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