JP2016078026A - Rolling method for hot rolled steel plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolling method for a hot rolled steel plate that can reduce a warpage generated by rolling by a rough rolling mill, stabilize accuracy of a cutting position of a crop and achieve stable passing of a steel sheet at a finish-rolling mill group.SOLUTION: A rolling method for a hot rolled steel sheet performs a rough rolling step in which a final rolling pass for reducing a thickness of a plate is performed in a reversible rough rolling mill on the downmost stream side of at least one reversible rolling mill, and then a pass for flattening which changes a roll gap during passing of a plate is performed, of a pass from an upstream side toward a downstream side or reciprocatory passes from a downstream side toward an upstream side and from the upstream side toward the downstream side, in the rolling mill.SELECTED DRAWING: Figure 5

Description

The present invention relates to a method for rolling a hot-rolled steel sheet having a rough rolling step and a finish rolling step,
In particular, the present invention relates to a rolling method for stably producing a high-strength thick hot-rolled steel sheet having a sheet bar thickness after rough rolling exceeding 50 mm.

In a general hot-rolled steel plate manufacturing process, as shown in FIG. 1, a steel slab is heated to about 1200 ° C. by a continuous heating furnace 1 and then forged in the plate width direction by a sizing press 2 to adjust the plate width. After that, the hot rolling is performed by the rough rolling mill group 3 to form a semi-finished steel plate called a sheet bar of about 30 to 50 mm, and then this sheet bar can be rolled continuously for 6 to 7 stands. 6 is hot rolled to finish a hot rolled steel sheet having a thickness of 1.2 to 25 mm. Subsequently, the finish-rolled steel sheet is cooled by a runout table cooling device 7 and then wound by a coiler (winding device) 8.
Usually, a crop shear 5 is provided between the rough rolling mill group 3 and the finish rolling mill group 6 to cut the crop portion of the steel sheet after the rough rolling.

  In rolling in rough rolling, rolling warpage often occurs at the front end or rear end of the steel sheet. When warping occurs at the front end or rear end of the steel sheet in the rough rolling process, a finish rolling mill in the next process When rolling in the group 7, a biting defect occurs and a stable threading plate cannot be secured.

Thus, although the manufacturing process of a hot-rolled steel sheet includes a rough rolling process and a finish rolling process, rolling warpage often occurs at the front end portion or the rear end portion of the steel plate during rough rolling.
When warping occurs at the leading end and the trailing end of the steel sheet due to rolling in the rough rolling process, when rolling is performed by the finish rolling mill group 6 in the next process, it becomes impossible to secure a stable sheeting due to biting failure.

  Further, the steel plate (sheet bar) that has been subjected to the rough rolling is subjected to finish rolling by a finishing mill group in the next step after the crop portion is cut by a crop shear. In cutting the crop portion, the sheet bar 10 If a large warp is generated at the front and rear ends, not only a cutting failure is caused, but there is a risk that the cutting cannot be performed at the target cutting position.

In the production line for hot-rolled steel sheets shown in FIG. 1, the sheet width is adjusted by a width reducing device such as a sizing press 2 or an edger 4, but when the width is reduced, the thickness in the vicinity of the end in the width direction of the slab is increased. As a result of the subsequent horizontal rolling, the front end and the rear end in the longitudinal direction of the steel sheet have a planar shape called a fish tail, as shown in the top view of FIG.
When warping occurs at the front and rear end portions of the steel plate (sheet bar) 10, as shown in the side view of FIG. 4B, the crop portion is sheared obliquely by the crop shear blade 15 with respect to the sheet bar. As a result, tracking errors are likely to occur, the shear position is not stable, and only a part of the fishtail is cut. Become.
If the warp of the steel plate leading end generated in the rough rolling step is left as it is, it may cause various troubles if it is conveyed to the next step.

Although the cause of warpage will be described later, there are those caused by one-side heat of the slab and those caused by an error in the pass line when the rolling mill is engaged.
Therefore, in order to avoid warpage of the steel sheet, it is necessary to strictly control the pass line in the rough rolling process so that the thickness center of the steel sheet (sheet bar) matches the center of the roll gap. As the plate thickness decreases with progress, it is necessary to change the level of the table roller in each rolling pass. It is difficult to operate such a mechanism stably because large equipment such as steel facilities cannot avoid variations in machine accuracy.

  The temperature deviation between the upper and lower surfaces of the material to be rolled can be adjusted by heating or cooling the upper or lower surface of the sheet bar. However, it is necessary to accurately measure the upper and lower surface temperatures. In a steelmaking process line, when a radiation thermometer is installed under the table roller where the sheet bar is transported, the scale generated on the sheet bar contaminates the radiation thermometer due to peeling, dropping, water vapor, etc., and measuring accuracy over a long period of time. It is difficult to ensure. For this reason, it is difficult to accurately adjust the output of the cooling device or the heating device installed in the conveyance path of the sheet bar.

Conventionally, the following techniques have been disclosed as means for improving the rolling warp generated at the front and rear end portions of the sheet bar during rough rolling.
The technique described in Patent Document 1 is a technique for correcting the shape of the sheet bar by installing a first warp correction device immediately after the rough rolling mill and a second warp correction device before the finishing mill. A roller leveler type that can be repeatedly bent by a roll is described as a warp correction device.
Patent Document 2 describes a technique for correcting a rolling warp by installing a warp correction roll on the exit side of a roughing mill as shown in FIG.

By the way, in recent years, the demand for high-strength thick-walled hot-rolled steel sheets has increased, but in high-strength thick-walled hot-rolled steel sheets with high toughness specifications, in order to ensure toughness, the reduction rate during finish rolling at a temperature of 950 ° C. or less. May be controlled and rolled under rolling conditions at a high pressure reduction rate of 60% or more. In such a case, the thickness of the sheet bar at the end of rough rolling is 50 mm or more and a maximum of 100 mm.
However, when warping occurs at the leading end and the trailing end of the thick sheet bar in this way, it is substantially difficult to correct the warping by applying the techniques described in Patent Documents 1 and 2. is there.
As a correction device such as a roller leveler described in Patent Document 1, if a roller leveler capable of imparting a sufficient correction reaction force is introduced, a sufficient effect for reducing warpage can be exhibited. In the case where the thickness of the sheet bar is about 50 mm or more to a maximum of about 100 mm, it is necessary to introduce a roller leveler having a very high correction reaction force with a load resistance exceeding 200 tons. Such equipment is accompanied by modification of the equipment for installation, and the equipment itself is expensive.
The correction means described in Patent Document 2 is also usually equipped with sensors that greatly affect the final product, such as thickness gauges and width gauges, in the vicinity of the rolling mill. To do this, it is difficult to secure a space, and it is necessary to modify the equipment to install this apparatus, and a large correction reaction force is required. Therefore, the equipment itself is quite expensive.

JP 2004-351484 A Japanese Patent Laid-Open No. 5-57317

  Therefore, in order to solve the above-described problems, the present invention utilizes the reversible rolling mill 31 and the nonreversible rolling mill of the rough rolling mill group without using a warp straightening machine such as a roller leveler, and performs rough rolling. Provided is a method of rolling a hot-rolled steel sheet that can be satisfactorily cut by a crop shear and can be stably threaded in rolling in a finish rolling mill group by reducing warpage that occurs during rolling in the mill group 3. It is for the purpose.

The present invention has the following means.
[1] A rough rolling step of roughly rolling a heated steel slab by a rough rolling mill group including at least one reversible rolling mill and a finish rolling step of finish rolling the steel plate after the rough rolling by a finish rolling mill group. A method of manufacturing a hot-rolled steel sheet having a final rolling pass for reducing a sheet thickness in a rough rolling process, in a reversible rolling mill located downstream of the at least one or more reversible rolling mills. Next, in the same rolling mill, from the upstream side to the downstream side, the top end of the steel plate is passed through a wide roll gap so that the upper and lower rolling rolls do not contact the steel plate at the same time. Then, before the rear end portion of the steel plate passes, the roll gap is narrowed, and the rear end portion is passed to perform a flattening pass for passing the steel plate, thereby rolling the hot rolled steel plate.
[2] A rough rolling process in which a heated steel slab is roughly rolled by a group of rough rolling mills including at least one reversible rolling mill and a finish rolling process in which a steel sheet after the rough rolling is finish rolled by a finish rolling mill group. A method of manufacturing a hot-rolled steel sheet having a final rolling pass for reducing a sheet thickness in a rough rolling process, wherein the upstream of the at least one or more reversible rolling mills in a reversible rolling mill located downstream. The odd-numbered path from the side to the downstream side, and following the final path, in the rolling mill, both the even-numbered path from the downstream side to the upstream side and the odd-numbered path from the upstream side to the downstream side, Pass the leading edge of the steel sheet through a wide gap so that the upper and lower rolling rolls do not touch the steel sheet at the same time, then narrow the roll gap before the trailing edge of the steel sheet passes, and pass through the trailing edge. Let the steel Rolling method for hot-rolled steel sheet and performing Tsuban to at least once the round-trip path to flatten path.
[3] The flattening pass sets a roll gap within a range of +50 mm to +300 mm with respect to the steel plate thickness and passes the leading end of the steel plate, and before the plate of the rear end of the steel plate with respect to the steel plate thickness. The method of rolling a hot-rolled steel sheet according to [1], wherein the roll gap is set within a range of +1 mm or more and less than +50 mm, the rear end portion is passed, and the steel sheet is passed. .
[4] The flattening pass sets a roll gap within the range of +50 mm to +300 mm with respect to the steel plate thickness, passes the tip of the steel plate, and passes through the steel plate thickness before passing the rear end of the steel plate. The rolling method for hot-rolled steel sheets according to [2], wherein the roll gap is set within a range of +1 mm or more and less than +50 mm and the rear end is passed through to pass the steel sheet. .
[5] The rough rolling mill group includes at least one or more irreversible rolling mills on the downstream side of the reversible rolling mill at the most downstream of the reversible rolling mills, and the at least one or more irreversible rolling mills. In any of the rolling mills, a roll gap is set within a range of +50 mm to +300 mm with respect to the steel sheet thickness, and the leading end of the steel sheet is allowed to pass through. On the other hand, any one of [1] to [4] is characterized in that a roll gap is set within a range of +1 mm or more and less than +50 mm, and a flattening pass for passing the steel plate through the rear end portion is performed. A method for rolling a hot-rolled steel sheet according to claim 1.
[6] The method for rolling a hot-rolled steel sheet according to any one of [1] to [5], wherein the thickness of the steel sheet at the completion of rough rolling is 50 mm to 100 mm.

  As described above, according to the method for rolling a hot-rolled steel sheet according to the present invention, it is possible to reduce warpage occurring at the front end and the rear end of the steel sheet during the rough rolling process, and in subsequent processes, crop cutting. Stabilization of position accuracy and stable threading in the finish rolling mill group can be realized, and a hot-rolled steel sheet can be manufactured stably. Moreover, in this invention, since the rolling mill of a rough rolling mill group is utilized, it is not necessary to install curvature correction apparatuses, such as a roller leveler, in order to reduce curvature, and can use the existing installation.

The production line of a general hot-rolled steel sheet is shown. The rolling at the front-end | tip part of a steel plate is shown. The rolling at the rear end of the steel sheet is shown. The fishtail shape of a steel plate is shown. The production line of the hot rolled sheet steel of embodiment of this invention is shown. Roll to steel plate gap is shown. 4 shows a method for correcting warpage of an end portion of a sheet bar according to an embodiment of the present invention. The manufacturing line of the hot rolled sheet steel of other embodiment of this invention is shown. 6 illustrates sheet bar end curvature correction according to another embodiment of the present invention. The manufacturing line of the hot rolled sheet steel of other embodiment of this invention is shown. The manufacturing line of the hot rolled sheet steel of other embodiment of this invention is shown.

Since rolling of a reversible rolling mill is utilized in the present invention, the rolling pass in reversible rolling will be briefly described.
A general hot-rolled steel sheet production line has already been shown in FIG. The hot-rolled steel sheet manufacturing facility shown in FIG. 1 includes a reversible rolling mill 31 in which the rough rolling mill group can perform reverse rolling and a non-reversible rolling mill 32 capable of rolling only in the conveying direction downstream. An arrow (solid line) shown at the bottom of the machine represents a reduction pass (a rolling pass for reducing the plate thickness). And, in the reversible rolling mill 31, normally, a reduction pass of about 5 to 11 passes is performed in a reversible direction (from the upstream side to the downstream side, or from the downstream side to the upstream side). In this pass, since rolling and transport to the next rolling mill are performed simultaneously, the number of rolling passes of the reversible rolling mill 31 is always an odd number, and the sheet bar 10 is transported to the rolling mill on the downstream side while rolling. To do. Therefore, the rolling direction of the final pass in the reversible rolling mill always matches the conveying direction of the sheet bar 10 to the next rolling mill.
In addition, the above “upstream side to downstream side” refers to the direction from the heating furnace 1 to the coiler 9 in the hot-rolled steel sheet production line as shown in FIG. 1, and “downstream side to upstream side” 1 indicates the direction from the coiler 9 to the heating furnace 1 as shown in FIG. 1, and the same applies to the following.

Before describing the embodiment of the present invention, the warp occurring at the leading end and the trailing end of the sheet bar during rolling in the rough rolling step will be described in detail.
A major cause of warpage occurring during rolling is warpage of the steel sheet tip due to an error in a pass line when the rolling mill is engaged.
In FIG. 2, the curvature which generate | occur | produces in the front end side of a steel plate (sheet bar) with respect to the rolling direction at the time of rough rolling is shown typically.
FIG. 2A shows a state in which the steel plate (sheet bar) 10 is conveyed from the left to the right and is bitten by the upper and lower rolling rolls (work rolls) 33 and 33. Moreover, FIG.2 (b) has shown the state which rolling of the front-end | tip part of the steel plate advanced after the steel plate was bitten by the up-and-down rolling roll. The rolling direction is from left to right.

  As can be seen from FIG. 2 (a), the pass line of the steel plate 10 is lower than the roll gap center of the upper and lower rolling rolls, and the plate thickness center of the steel plate is in a position lower than the center of the roll gap. Since the steel plate is being conveyed, the lower end of the steel plate tip first comes into contact with the lower rolling roll 33 first. Therefore, the front end of the steel plate 10 is pushed upward by the lower rolling roll 33, and is bitten into the rolling mill in a bent state. As a result, as can be seen from FIG. 2 (b), the steel plate tip after rolling is warped.

FIG. 3 schematically shows a state in which the rolling shown in FIG. 2 proceeds and the rear end side of the steel sheet is rolled.
FIG. 3A shows a state in which rolling proceeds and the rear end portion of the steel plate 10 is rolled onto upper and lower rolling rolls. Moreover, FIG.3 (b) has shown the state which rolling progresses further and the rear end of the steel plate 10 is going out from the roll gap of an up-and-down work roll.
As can be seen from FIG. 3 (a), on the rear end side, rolling proceeds in a state where the center of the roll gap and the center of the sheet thickness of the sheet bar 10 substantially coincide with each other, and as can be seen from FIG. 3 (b). In addition, no vertical force is generated on the steel plate 10 and no warp occurs at the rear end portion, or even if it occurs, the degree of warpage is small and the rolled shape becomes substantially flat.

As a second cause of the occurrence of the warp, there is a temperature deviation between the upper surface and the lower surface of the seat bar.
Usually, a skid is disposed on the lower surface of the slab in order to support the slab in the heating furnace, but since the radiant heat in the furnace is blocked by the skid, the temperature on the lower surface of the slab tends to be low. In addition, the rolling line after slab extraction has a table roller for conveying the slab and sheet bar of the material to be rolled, and the lower surface of the material to be rolled is less likely to escape heat, so the temperature of the upper surface is lowered. Become a trend. Therefore, at the beginning of rolling, the upper surface of the material to be rolled becomes higher than the lower surface, and the temperature of the lower surface of the material to be rolled tends to increase with the progress of rolling time. As described above, when rolling is performed in a state where there is a temperature deviation between the upper and lower surfaces, the deformation resistance on the upper surface side and the lower surface side of the sheet bar is different, so warpage occurs because the surface is well extended on the surface with high temperature and low deformation resistance .
In general, the amount of warpage due to the deviation of the pass line when the rolling mill is engaged, which is the first cause, is larger than the amount of warpage caused by the temperature deviation, which is the second cause.

As described above, a large warp tends to occur after rolling on the front end side of the steel sheet, which is on the rolling roll biting side with respect to the rolling direction.
By the way, in a general operation in the rough rolling process, rolling of a steel plate (sheet bar) is performed by the reversible rolling mill 31 or the nonreversible rolling mill 32.
In a reversible rolling mill, rolling is always completed in a path (odd path) from the upstream side to the downstream side of the rolling mill, so that warpage always occurs at the end of the steel sheet on the downstream side.
Further, in the non-reversible rolling mill, rolling is completed in one pass from the upstream side to the downstream side of the rolling mill, so that warpage also occurs at the end of the steel sheet on the downstream side of the rolling mill.
Thus, in any type of rolling mill, warping occurs at the downstream end, so that warping is likely to occur at the front end of the steel sheet after the rough rolling.
Further, in reversible rolling, rolling is performed from the downstream side to the upstream side in the even-numbered pass, so that the warp occurs at the upstream side of the steel plate, but as described in FIG. The warpage of the end of the steel plate on the upstream side tends to be reduced by the rolling of the odd-numbered pass.

A first embodiment of the present invention will be described with reference to FIGS.
FIG. 5 shows a hot-rolled steel sheet manufacturing facility in which this embodiment is performed.
In the hot rolling facility of this embodiment, the rough rolling mill group is composed of at least one or more reversible rolling mills and at least one or more irreversible rolling mills. Both are not essential because rough rolling is possible. FIG. 5 shows only one reversible rolling mill 31 and one non-reversible rolling mill 32 downstream thereof.
Further, a cooling device 7 and a coiler 8 provided on a runout table for cooling the crop shear 5, the finishing rolling mill group, and the steel plate are provided downstream of the rough rolling mill group.

The path pattern in the first embodiment is shown by arrows in FIG. 5, but the solid arrow indicates a rolling path for rolling the plate to a small thickness, and the broken arrow indicates a flattening path. The flattening pass will be described later.
In this embodiment, the heated slab is first reversibly rolled by one or more reversible rolling mills to reduce the thickness of the steel sheet (sheet bar) (that is, the sheet thickness is thin). In the reversible rolling mill 31 located downstream (i.e., closest to the coiler 8 side), the even-numbered pass reduction pass (i.e., the rolling pass for reducing the plate thickness) is completed. Therefore, this final reduction pass is performed in the direction in which the steel plate (sheet bar) 10 is directed from the downstream side to the upstream side (see the solid line arrow shown below the roughing mill 31 in FIG. 5).
In addition, when one or more reversible rolling mills are composed of only one, this one rolling mill is the reversible rolling mill located on the most downstream side among the reversible rolling mills.
Then, following the final reduction pass, in the reversible rolling mill 31 on the most downstream side, the steel plate 10 is called a flattening pass with the roll gap wider than the plate thickness from the upstream side to the downstream side. The sheet passing is performed as follows, and the steel sheet is conveyed downstream (see the broken arrow shown below the roughing mill 31 in FIG. 5).

FIG. 7 shows the state of plate passing in the final reduction pass and the flattening pass performed after the final reduction pass, which are performed in the reversible rolling mill 31 on the most downstream side.
FIG. 7A shows a final reduction pass, and FIGS. 7B to 7E show a flattening pass performed following the final reduction pass.

  In the sheet pass called flattening pass, the roll gap is set to +50 mm or more with respect to the plate thickness of the steel plate, that is, 50 mm or more than the plate thickness so that the steel plate 10 does not contact the upper and lower rolling rolls simultaneously. A steel plate is passed through a roll gap set to be thicker, and its tip is passed (see FIG. 7B). And before the rear end of the steel plate passes through the roll gap, the roll gap is set to +1 mm to less than 50 mm with respect to the plate thickness of the steel plate, the rear end is passed through, and the steel plate is passed through [ See FIGS. 7C and 7D].

  FIG. 6 shows the relationship between the roll gap of the upper and lower rolling rolls and the plate thickness. Setting the roll gap to +50 mm or more with respect to the plate thickness of the steel sheet means setting the roll gap to be 50 mm or more thicker than the plate thickness, and setting “roll to steel plate gap” in FIG. 6 to 50 mm or more. It is.

  Due to this flattening pass, the warp of the steel sheet tip that occurred in the final reduction pass in the previous reversible rolling mill, that is, the part where the warp occurs in the rear end of the steel plate in this flattening pass, It is corrected by coming into contact with the upper and lower rolling rolls, and the warpage is reduced and flattened (see FIGS. 7D and 7E).

Here, it is the reason why the roll gap is set to +50 mm or more with respect to the plate thickness when the leading end is passed. However, if the roll gap is narrowed, the leading end becomes the table roller when the sheet bar 10 is passed. There is a risk of colliding with the upper roll and colliding with the upper roll to promote warpage. In particular, since there is a case where the sheet bar 10 bounces greatly on the rolling mill entrance side when the rolling speed is high, the thickness of the sheet bar 10 is ensured in order to ensure a sufficient roll gap so that there is no collision between the sheet bar and the rolling roll. Is set to +50 mm or more.
However, if the roll gap is too wide, if the sheet bar length is short or the rolling speed is high, the roll gap setting time after passing through the sheet bar leading end becomes long and appropriate at the sheet bar trailing end. Since it becomes impossible to make a roll gap, about 300 mm or less is preferable. In view of the above, it is preferable to set approximately 100 to 150 mm.

Subsequently, the roll gap is set to be +1 mm or more and less than +50 mm with respect to the plate thickness, and the rear end portion is passed. However, when the roll gap is set to be less than +1 mm, there is an error in the plate thickness during rolling. If there is, there is a risk of light reduction on the reversible rolling mill. At this time, if there is a temperature deviation between the upper and lower surfaces of the seat bar, the warpage may be promoted.
Further, when the roll gap setting is set to +50 mm or more with respect to the thickness of the sheet bar 10, the warp correction effect is reduced.
In order to increase the correction effect, the roll gap should be set as narrow as possible. Therefore, it is preferable that the roll bar is set to +5 mm or less with respect to the sheet bar thickness. Therefore, the roll gap is preferably set to +1 mm to +5 mm.

Further, in the hot rolling production facility shown in FIG. 5, the irreversible rolling mill 32 is provided on the downstream side of the reversible rolling mill 31, but as described above, at least one or more irreversible rolling mills are provided. In any of the irreversible rolling mills, a further straightening effect may be aimed at by setting a roll gap similar to the above and performing a flattening pass.
If correction by the irreversible rolling mill 32 is not required, the roll gap may be opened to a plate thickness of +50 mm or more and passed (hereinafter referred to as an empty pass).
After the flattening pass, the sheet bar that has been subjected to the rough rolling is conveyed to the next step, and after the crop portion is cut by a crop shear, continuous rolling is performed in the finishing mill group.
Further, when there is no irreversible rolling mill on the downstream side of the reversible rolling mill 31, the rough rolling is finished in the flattening pass in the reversible rolling mill 31, and then the crop part is cut in the crop shear, Continuous rolling is performed in the finishing mill group.

Next, a second embodiment of the present invention will be described with reference to FIGS.
In FIG. 8, the manufacturing equipment of the hot-rolled steel plate in 2nd embodiment of this invention was shown typically. In the figure, the path pattern is indicated by an arrow as in FIG.
Even in the hot rolling equipment of this embodiment, the rough rolling mill group is composed of at least one or more reversible rolling mills and at least one or more irreversible rolling mills. Rough rolling is possible without installation. FIG. 8 shows only one reversible rolling mill 31 and one non-reversible rolling mill 32 downstream thereof.
Further, a cooling device 7 and a coiler 8 provided on a runout table for cooling the crop shear 5, the finishing rolling mill group, and the steel plate are provided downstream of the rough rolling mill group.

Similar to the first embodiment, in the second embodiment, the heated slab is first subjected to reversible rolling with at least one or more reversible rolling mills to reduce the thickness. In the reversible rolling mill, the rolling to reduce the sheet thickness is completed by the reduction pass of the reversible rolling mill 31 which is the most downstream (that is, closest to the coiler 8 side), but unlike the first embodiment, The final rolling pass for rolling to reduce the plate thickness is completed in the odd-numbered pass. Therefore, the final reduction path is a path from the upstream side toward the downstream side, and in FIG. 8, the third reduction path shown by a solid line corresponds to this.
Then, following the final reduction pass, in the reversible rolling mill 31 located on the most downstream side, a flattening pass for moving the steel sheet 10 from the downstream side to the upstream side, and subsequently, downstream from the upstream side in the rolling mill. A reciprocating path consisting of a flattening path toward the side is performed at least once, and then the steel sheet is conveyed downstream.

FIG. 9 shows a schematic diagram of the shape of the seat bar 10 after the final reduction pass in the second embodiment.
In the final rolling pass for rolling to reduce the plate thickness, the rolling direction is directed toward the downstream side, and a relatively large warp occurs at the end of the sheet bar on the rolling biting side, that is, the downstream side.
On the other hand, a relatively small warp occurs at the upstream end [FIG. 9 (a)]. This is the result of remaining warpage that occurred during the reduction pass from the downstream side to the upstream side before the final reduction pass.

Subsequently, the roll gap of the reversible rolling mill 31 is made wider than the plate thickness to perform a flattening pass.
First, the roll gap of the reversible rolling mill 31 is set to +50 mm or more sufficiently larger than the plate thickness so that the sheet bar 10 does not contact the upper and lower rolling rolls at the same time, and then the sheet bar 10 is conveyed upstream [ FIG. 9 (b)].
And after the front-end | tip part of a sheet bar passes the reversible rolling mill 31, the roll gap of the reversible rolling mill 31 is set to +1 mm or more and less than +50 mm with respect to plate | board thickness, and the rear-end part of a sheet bar is allowed to pass through. The portion where the warpage is generated on the downstream side of the sheet bar 10 is flattened by bending correction because it is in contact with the upper and lower rolling rolls (FIG. 9C).

  Thereafter, the roll gap of the reversible rolling mill 31 is set again to +50 mm or more which is sufficiently larger than the plate thickness so that the sheet bar 10 does not contact the upper and lower rolling rolls at the same time, and then the sheet bar 10 is conveyed downstream [ FIG. 9 (d)]. And after the front-end | tip part of a sheet bar passes the reversible rolling mill 31, the roll gap of the reversible rolling mill 31 is set in the range of +1 mm or more and less than +50 mm with respect to plate | board thickness, and the rear-end part of a sheet bar [Fig. 9 (e)]. The portion where the warp is generated on the upstream side of the sheet bar 10 is flattened by bending correction because it contacts the upper and lower rolling rolls (FIG. 9F).

In the second embodiment, the reciprocating flattening pass is performed in the most downstream of the reversible rolling mills, so that both ends in the rolling direction of the sheet bar 10 can be warped under substantially the same conditions. In addition, it is possible to manufacture the seat bar 10 having a better shape as compared with the first embodiment.
In the description of this embodiment, an example has been described in which the flattening path is performed once for each of the even-numbered path and the odd-numbered path, but may be performed a plurality of times. In the flattening pass, when the even-numbered pass and the odd-numbered pass reciprocating pass are performed a plurality of times, a method of sequentially narrowing the roll-steel plate gap within the scope of the present invention may be used.

  In addition, as shown in FIG. 8, when there is a nonreciprocal rolling mill 32 on the downstream side of the reversible rolling mill 31, the path in the nonreciprocating rolling mill 32 is flattened for further correction effect. As above, the roll gap setting similar to the above may be performed. When correction is not necessary with the irreversible rolling mill 32, a pass (hereinafter referred to as an empty pass) for completing the sheet passing with the roll gap opened to 50 mm or more may be performed.

FIG. 10 schematically shows a hot rolling facility and a path pattern in which a third embodiment of the present invention different from the first and second embodiments is performed. The equipment downstream from the rough rolling process is the same as the hot rolling equipment to which the first and second embodiments are applied.
In the hot rolling facility in this embodiment, the rough rolling mill group 3 is composed of a plurality of reversible rolling mills 31. In FIG. 10, the form at the time of comprising with three reversible rolling mills is shown.
In this embodiment, in any of the reversible rolling mills except the reversible rolling mill at the most downstream of the reversible rolling mills, the reduction pass for reducing the plate thickness of the steel sheet is performed an odd number of times, and the reversible rolling is performed as described above. The final pass of the odd number in the reversible rolling mill located at the most downstream side of the mill is the flattening pass. The planarization pass here is the same as that performed in the first and second embodiments.
Therefore, the third embodiment corresponds to the case where the rough rolling mill group does not include the irreversible rolling mill 32 in the first embodiment.
The steel sheet that has finished the rough rolling process is subjected to finish rolling after the cropped portion has been cut, as in the first and second embodiments.

FIG. 11 schematically shows a hot rolling facility and a path pattern in which the fourth embodiment of the present invention, which is different from any of the first to third embodiments, is performed. The equipment downstream from the rough rolling process is the same as the hot rolling equipment to which the first and second embodiments are applied.
In the present embodiment, at least one or more irreversible rolling mills 32 are provided upstream and downstream of at least one or more reversible rolling mills 31. In FIG. 11, the rough rolling mill group 3 is composed of one reversible rolling mill 31 and four irreversible rolling mills 32, one upstream of the one reversible rolling mill and one downstream. An example in which three irreversible rolling mills are respectively installed on the side is shown.

In this embodiment, the heated slab is first subjected to a reduction reduction pass to reduce the plate thickness of one pass with one or more non-reversible rolling mills, and then subjected to reversible rolling with a reversible rolling mill to obtain a steel plate. Although the thickness is reduced, in the reversible rolling mill 31 at the most downstream of the reversible rolling mills, the rolling for reducing the plate thickness is completed in the even-pass reduction pass. Therefore, this final reduction pass is performed in a direction in which the steel plate (sheet bar) 10 is directed from the downstream side to the upstream side (see the solid line arrow shown below the roughing mill 31 in FIG. 11).
In addition, when one or more reversible rolling mills are composed of only one, this one rolling mill is the reversible rolling mill located on the most downstream side among the reversible rolling mills.

Then, following the final reduction path, in the reversible rolling mill 31 (second rolling mill from the left in FIG. 11) on the most downstream side, the steel sheet 10 is rolled gap from the upstream side toward the downstream side. Is made wider than the plate thickness, and the same flattening pass as in the first embodiment is performed (see the broken arrow shown below the roughing mill 31 in FIG. 11).
Subsequently, the steel plate that has finished this flattening pass is the same as that of the first embodiment in at least one non-reversible rolling mill provided downstream of the reversible rolling mill 31 on the most downstream side. The steel sheet that has undergone the flattening pass and finished the rough rolling process is subjected to finish rolling after the cropped portion is cut, as in the first and second embodiments.

  Even in this embodiment, the flattening pass is also performed in the non-reversible rolling mill downstream from the most downstream reversible rolling mill, but this is an empty pass, that is, a pass where the steel sheet does not contact the upper and lower rolls simultaneously. ) To finish rough rolling. Furthermore, as in the first embodiment, the flattening pass may be performed by only one of the irreversible rolling mills 32.

Although the example which applied the embodiment of this invention to the manufacturing equipment of the hot-rolled steel plate shown by FIG.5 and FIG.7,8,10,11 was demonstrated, not only these equipment but this invention is a group of rough rolling mills As long as it is a facility for producing a hot-rolled steel sheet having a rough rolling process for rough rolling and a finish rolling process for finishing and rolling the steel sheet after the rough rolling by a finish rolling mill group, the present invention can be applied.
In addition, the present invention is based on the technical idea of the invention, and is only for producing a high strength thick hot rolled steel sheet in which the thickness of the steel sheet after completion of rough rolling is 50 mm or more and the thickness of the steel sheet after finish rolling is 20 mm or more. Obviously, the present invention can also be applied to the production of ordinary hot-rolled steel sheets.

Examples of the present invention will be described below. The target material is a high-strength, high-toughness hot-rolled steel sheet having a sheet bar thickness of 64 mm after rough rolling, which is difficult to improve the shape of the sheet bar warp by a general straightening machine.
As shown in FIG. 5, the production line for hot-rolled steel sheets to which the following examples and comparative examples are applied includes one reversible rolling mill 31 and one non-reversible rolling mill from the upstream side to the downstream side. 32, and a crop shear 5, a finish rolling mill group 6, a run-out table cooling device 7, and a coiler 8 are provided downstream thereof.
In this case, since there is one reversible rolling mill, this reversible rolling mill corresponds to a reversible rolling mill located on the most downstream side of at least one or more reversible rolling mills.
In this line, a steel bar having a thickness of 250 mm, a width of 1850 mm, and a length of 9090 mm was rolled to a thickness of 64 mm by the rough rolling group 3 of the hot rolling line to produce a sheet bar 10.
The steel plate (sheet bar) after the rough rolling is in an oscillation standby state for the sheet bar 10 before the finish rolling process, and when the surface temperature of the sheet bar 10 becomes 900 ° C. or lower, the crop portion of the sheet bar is cut by the crop shear 5. Then, the steel sheet was finish-rolled by a finish rolling mill group 6 to finish a steel plate having a thickness of 25 mm, cooled to 480 ° C. by a cooling device 7 of a run-out table, and then wound by a coiler 8.

Example 1
Table 1 shows the pass schedule during rough rolling in Example 1 of the present invention. Note that the number of rolling passes is from the start of rough rolling, and the rolling mill No. is described in order from the most upstream side (hereinafter the same).
Further, “roll to steel plate gap” in this table indicates a value obtained by subtracting the value of the sheet bar thickness from the value of the roll gap formed by the upper and lower rolling rolls, as can be seen from FIG. 6. In addition, when “the gap between the roll and the steel plate” is 0 (zero) mm, it indicates that a rolling pass (pass for reducing the plate thickness) is performed in rolling (hereinafter the same).

In Example 1, as shown in Table 1, in the reversible rolling mill 31 of the rough rolling mill group 3, a pass for reducing the plate thickness up to the eighth pass was performed.
In the 9th pass in which the rolling direction continues downstream, in the reversible rolling mill 31, the roll to steel plate gap is set to +100 mm (that is, the roll gap is set to a value obtained by adding 100 mm to the plate thickness), and the leading end of the sheet bar Before the rear end of the sheet bar passes through the roll gap, the roll to the steel plate gap is narrowed to +40 mm (that is, the roll gap is set to a value obtained by adding 40 mm to the plate thickness) A flattening path through which the end portion is passed is used. Further, in the non-reversible rolling mill 32, the same roll gap as that in the flattening pass performed in the reversible rolling mill 31 was set and passed.

(Example 2)
Table 2 shows the pass schedule during rough rolling in Example 2 of the present invention.
In Example 2, in the reversible rolling mill 31 of the rough rolling mill group 3, the rolling pass was performed up to the ninth pass. That is, the rolling pass in the rough rolling process was completed in the ninth pass.
In the subsequent 10th pass (even-numbered pass) and 11th pass (odd-numbered pass), in the reversible rolling mill 31, the roll to steel plate gap is set to +100 mm with respect to the plate thickness and the leading end of the sheet bar is passed, and then the sheet Before the rear end portion of the bar passes through the roll gap, the roll to steel plate gap is narrowed to +40 mm with respect to the plate thickness, and the rear end portion is passed through to obtain a flattening path for passing the sheet bar. . Therefore, the 10th pass and the 11th pass are performed by a flattening pass in a round trip.
Further, in the irreversible rolling mill 32, the final pass of the twelfth pass is an empty pass through which the roll to steel plate gap is set to +200 mm so that the roll does not contact the steel plate at the same time .

(Comparative Example 1)
Table 3 shows a pass schedule during rough rolling in Comparative Example 1.
In Comparative Example 1, in the rough rolling mill group 3, nine reduction passes were performed in the reversible rolling mill 31 of the rough rolling mill group 3, and then one reduction pass was performed in the irreversible rolling mill 32.

(Example 3)
Table 4 shows the pass schedule during rough rolling in Example 3 of the present invention.
In Example 3, as can be seen from Table 4, in the reversible rolling mill 31 of the rough rolling mill group 3, the sheet bar 10 is squeezed down to the eighth pass, and in the ninth pass of the reversible rolling mill 31, roll to steel plate A flattening path for passing the sheet bar with a gap of +100 mm with respect to the plate thickness and then passing the sheet gap with a roll gap of +4 mm with respect to the plate thickness and further narrower than the roll gap of Example 1. did. Further, the non-reversible rolling mill 32 was passed by the same roll gap setting method as the flattening pass performed by the reversible rolling mill 31.

Example 4
Table 5 shows the pass schedule during rough rolling in Example 4 of the present invention.
In Example 4 of the present invention, as shown in Table 5, in the reversible rolling mill 31 of the rough rolling mill group 3, a reduction pass is performed up to the ninth pass, and in the 10th to 11th passes in the same reversible rolling mill, The roll steel plate gap is set to +100 mm with respect to the plate thickness, and the leading end of the sheet bar is allowed to pass. Thereafter, before the trailing end of the sheet bar passes through the roll gap, the roll to steel plate gap is narrowed to +4 mm with respect to the plate thickness. Thus, a flattening path for passing the rear end of the sheet bar was formed. Moreover, in the irreversible rolling mill 32, the roll to the steel plate gap was set to +200 mm, and the plate was passed by an empty path.

Table 6 shows the results of the cutting conditions of the crop shear in Examples 1 to 4 and Comparative Example 1 of the present invention and the sheet passing conditions in the finishing mill group.
As shown in Table 6, in the pass schedule of the rough rolling mill group 3 in Example 1 of the present invention, the warp of the downstream end of the sheet bar 10 was 6 mm, and the warp of the upstream end was 35 mm. The warp on the upstream side was relatively small at 35 mm, and the warp at the downstream end (that is, the front end) on the finish rolling mill biting side was as good as 6 mm. Subsequent crop shear cutting and biting during finish rolling could be performed satisfactorily.
In Example 2 of the present invention, since the final reduction path is the ninth odd-numbered path, the warp at the downstream end (ie, the front end) is relatively small at 30 mm, and the warp at the upstream side (ie, the rear end) is It was as good as 6 mm. Subsequent crop shear cutting and biting during finish rolling could be performed satisfactorily.

  On the other hand, in Comparative Example 1, as shown in Table 3, in the rough rolling mill group 3, the final pass is a reduction pass from the upstream side to the downstream side of the irreversible rolling mill, and the flattening pass is performed. Therefore, the warp of the upstream end of the sheet bar 10 after the rough rolling was as good as 2 mm or less, but a large warp of 200 mm occurred at the downstream end (that is, the tip). For this reason, the fishtail was partially cut at the time of cutting the crop shear, and could not be rolled without being bitten when entering the finishing mill. This confirmed the warp reduction effect of the present invention.

In Example 3 of the present invention, the warp at the downstream end was 6 mm, and the warp at the upstream end was 4 mm, both of which were small. Similarly, in Example 4, the warp at the downstream end was 4 mm and the warp at the upstream end was 4 mm, both of which were small.
In particular, when the flattening pass is performed in both the even-numbered pass and the odd-numbered pass of the reversible rolling mill as in Example 4, both the downstream and upstream end warpage amounts are as small as 4 mm. It was.
Moreover, also in any of Examples 1-4, crop shear cutting was able to cut | disconnect a target site | part favorably, and the subsequent plate of the finishing mill group 6 was also favorable.

  As described above, regardless of whether the rolling mills of the rough rolling mill group are reversible or reversible rolling mills and irreversible rolling mills, the reversible rolling mills in the rough rolling mill group are By utilizing in such a manner, it was not necessary to install a sheet bar straightening machine, and the warp that occurred during rough rolling could be reduced.

DESCRIPTION OF SYMBOLS 1 Continuous heating furnace 2 Sizing press 3 Rough rolling mill group 4 Edger 5 Crop shear 6 Finish rolling mill group 7 Cooling device 8 Coiler 10 Sheet bar (steel plate)
15 Cropshire blade 31 Reversible rolling mill 32 Non-reversible rolling mill 33 Rolling roll

Claims (6)

Hot rolling comprising a rough rolling process in which a heated steel slab is roughly rolled by a group of rough rolling mills including at least one reversible rolling mill and a finish rolling process in which a steel sheet after the rough rolling is finish rolled by a finish rolling mill group A method of manufacturing a steel sheet,
In the rough rolling step, the final pass of rolling to reduce the plate thickness is performed from the downstream side to the upstream side in the reversible rolling mill at the most downstream of the at least one reversible rolling mill, and then In the rolling mill, from the upstream side to the downstream side, the top end of the steel plate is passed through a roll gap that is set broadly so that the upper and lower rolling rolls do not contact the steel plate at the same time, and then before the rear end of the steel plate passes. A rolling method of a hot-rolled steel sheet, characterized by performing a flattening pass in which a roll gap is narrowed and the rear end portion is passed to pass a steel sheet. Hot rolling comprising a rough rolling process in which a heated steel slab is roughly rolled by a group of rough rolling mills including at least one reversible rolling mill and a finish rolling process in which a steel sheet after the rough rolling is finish rolled by a finish rolling mill group A method of manufacturing a steel sheet,
In the rough rolling step, the final pass of rolling to reduce the sheet thickness is performed by an odd-numbered pass from the upstream side to the downstream side in the reversible rolling mill at the most downstream of the at least one reversible rolling mill. After the final pass, in the same rolling mill, both the even-numbered pass from the downstream side to the upstream side and the odd-numbered pass from the upstream side to the downstream side so that the upper and lower rolling rolls do not touch the steel plate at the same time. A flattening path for passing the steel plate through the wide gap, and passing the steel plate through the rear end, narrowing the roll gap before the rear end of the steel plate passes. A method of rolling a hot-rolled steel sheet, comprising performing at least one reciprocating pass.   The flattening pass sets a roll gap within the range of +50 mm to +300 mm with respect to the steel sheet thickness and passes the front end of the steel sheet, and +1 mm or more with respect to the steel sheet thickness before passing through the rear end of the steel sheet The method for rolling a hot-rolled steel sheet according to claim 1, wherein the roll gap is set within a range of less than ~ + 50 mm and the rear end portion is passed to pass the steel sheet.   The flattening pass sets a roll gap within the range of +50 mm to +300 mm with respect to the steel sheet thickness and passes the front end of the steel sheet, and +1 mm or more with respect to the steel sheet thickness before passing through the rear end of the steel sheet The method for rolling a hot-rolled steel sheet according to claim 2, wherein the roll gap is set within a range of less than ~ + 50 mm and the rear end is passed through to pass the steel sheet.   The rough rolling mill group includes at least one or more irreversible rolling mills on the downstream side of the reversible rolling mill at the most downstream of the reversible rolling mills, and the at least one or more irreversible rolling mills In any of the rolling mills, a roll gap is set within a range of +50 mm to +300 mm with respect to the steel plate thickness, and the leading end of the steel plate is allowed to pass through, and +1 mm with respect to the steel plate thickness before passing through the trailing end of the steel plate. 5. A flattening pass for setting a roll gap within a range of less than +50 mm and passing the rear end portion and passing a steel plate is performed. 5. Rolling method for hot rolled steel sheets. The method for rolling a hot-rolled steel sheet according to any one of claims 1 to 5, wherein the thickness of the steel sheet at the completion of the rough rolling is set to 50 mm to 100 mm.