JP2011079038A - Method for controlling operation of tandem rolling machine and method for manufacturing hot-rolled steel sheet using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for controlling the operation of a tandem rolling machine which can manufacture an ultrafine grain steel and to provide a method for manufacturing a hot-rolled steel sheet using the same. <P>SOLUTION: In the method, an output side sheet thickness determination step of determining an output side sheet thickness in each stand comprises a first output side sheet thickness determination step (S11) that determines an output side sheet thickness of an Nth stand from a first stand when a stationary part of the rolling material is rolled and a second output side sheet thickness determination step (S12) that determines an output side sheet thickness of the Nth stand from the first stand when a front end rolling part of the rolling material is rolled. Until at least the leading edge of the rolling material is bitten into each stand, the rolling material is rolled to an output side sheet thickness determined in the second output side sheet thickness determination step without use of a rolling lubricant in each of the stands, and the stationary part of the rolling material is rolled to an output side sheet thickness determined in the first output side sheet thickness determination step using a rolling lubricant. It should be noted that, in the second output side sheet thickness determination step, the output side sheet thickness is larger than that in the first output side sheet thickness determination step. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an operation control method for a tandem rolling mill and a method for producing a hot-rolled steel sheet using the same. The present invention is, for example, an operation control method for a tandem rolling mill in which the exit side plate thickness of each stand constituting a tandem finishing rolling mill for a hot rolling line is changed after the leading end of the material to be rolled, and a hot-rolled steel plate using the same. It relates to the manufacturing method.

  When rolling a material to be rolled by a tandem rolling mill having a plurality of rolling mills (stands) such as a finish rolling mill in a hot rolling line, the operation of each stand depends on the thickness of the material to be rolled and the plate on the final stand exit side. The width and the like are determined so as to satisfy the target condition. The operating condition of each stand is called a draft schedule (pass schedule), and greatly affects the quality and productivity of the product. Therefore, it is required to determine an appropriate draft schedule according to the product.

  The draft schedule of the tandem finish rolling mill in the hot rolling line is generally better in the surface quality of the product by reducing the surface roughness of the work roll surface as the stand closer to the final product (downstream in the moving direction of the material to be rolled). Therefore, the rolling load is determined to be light. Here, even if the reduction ratio of the first stage (upstream side in the moving direction of the material to be rolled) stand and the second stage stand is set to be the same, the latter stage stand that rolls the material to be rolled with a small thickness requires a large rolling load. There are rolling characteristics. Therefore, in the normal draft schedule, the rolling reduction is smaller as the latter stage stand.

  On the other hand, steel materials used for automobiles and structural materials are required to have excellent mechanical properties such as strength, workability, and toughness. To improve these mechanical properties comprehensively, It is effective to refine the grains. Further, if the crystal grains are refined, it is possible to produce a high-strength hot-rolled steel sheet having excellent mechanical properties even if the addition amount of the alloy element is reduced.

  As a method for refining the crystal grains of the hot-rolled steel sheet, particularly in the latter stage of hot finish rolling, high pressure rolling (finish rolling with a higher reduction ratio of the latter stage stand) is performed to refine the austenite grains and within the grains. There is known a method for accumulating rolling strain and quenching immediately after finish rolling to refine the ferrite grains obtained. In order to manufacture a hot-rolled steel sheet having fine crystal grains (hereinafter referred to as “fine-grained steel”) by this method, the reduction ratio of the rear stage stand of the tandem finish rolling mill in the hot rolling line is made higher than before. Need to increase. Therefore, in order to manufacture fine-grained steel, it is necessary to determine a draft schedule different from the conventional one and to control the operation of the tandem finish rolling mill in a form different from the conventional one. In particular, the use of a rolling lubricant is effective in order to reduce the load (rolling load, rolling torque, etc.) of the rear stage stand, which has a higher reduction ratio than before, within the upper limit of the equipment and to reduce the surface roughness of the work roll. However, if the friction coefficient between the work roll and the material to be rolled decreases due to the use of rolling lubricant, the biting performance of the material to be rolled into the work roll deteriorates. become.

  Several techniques related to operation control of a rolling mill have been disclosed so far. For example, in Patent Document 1, in a hot finishing rolling mill composed of a plurality of stands, widening is performed so that the roll gap of the work roll of at least one stand is extended in the thickness direction of the rolled plate. In the hot finish rolling method, the first step of starting the widening of the roll gap of the work roll when the leading end of the conveyed rolled plate reaches the work roll of the stand that performs the widening, and the first step The second step of rolling the leading end of the rolled plate into a taper shape by performing the widening started in step 1 to the preset roll gap over time, and the roll gap preset in the second step A third step of rolling the steady portion of the rolled plate with a constant thickness by keeping the roll gap constant after widening to There has been disclosed. Further, in Patent Document 2, after the leading end of the rolled material has bitten into the work roll, application of rolling lubricating oil to the work roll is started, and lubrication rolling is performed until rolling of the trailing end of the rolled material is completed. The rolling lubricating oil adhering to the work roll is removed during the rolling of the preceding rolled material after the rolling of the preceding rolled material is finished and the subsequent rolled material is bitten into the work roll. A hot lubrication rolling method is disclosed.

Japanese Patent No. 4266185 JP 2002-178011 A

  When the technique disclosed in Patent Document 1 and the hot lubricated rolling method disclosed in Patent Document 2 are combined, the thickness of the tip portion of the material to be rolled is thinner than the thickness of the steady portion of the material to be rolled. Hot lubricated rolling will be performed. However, in such a form, it becomes difficult to increase the rolling reduction of the latter stage stand of the tandem finish rolling mill as compared with the conventional case, and particularly refers to ultrafine crystal grains (for example, crystal grains having an average grain size of 2 μm or less. In the following, there is a problem that it becomes difficult to produce a hot-rolled steel sheet (hereinafter, sometimes referred to as “ultrafine grained steel”).

  Then, this invention makes it a subject to provide the operation | movement control method of the tandem rolling mill which can manufacture ultrafine-grained steel, and the manufacturing method of a hot-rolled steel plate using the same.

  The present invention will be described below. In order to facilitate understanding of the present invention, reference numerals in the accompanying drawings are appended in parentheses, but the present invention is not limited to the illustrated embodiments.

  The first aspect of the present invention includes N (N is an integer of 2 or more) stands (1, 2,..., 7) and N-m + 1 stands (m is an integer of 1 to N) to the Nth stand. A method of controlling the operation of a tandem rolling mill (10) provided with lubricant supply means (5d, 6d, 7d) for supplying rolling lubricant to the first stand (1) to the Nth stand (7) The exit side plate thickness determination step (S1) for determining the exit side plate thickness of each stand of the stand, the exit side plate thickness determination step from the first stand when rolling the steady portion of the material to be rolled (8) Nth A first delivery side thickness determining step (S11) for determining the delivery side plate thickness of the stand, and a second delivery for determining the delivery side plate thickness of the Nth stand from the first stand when rolling the tip rolling portion of the material to be rolled. Side plate thickness determination step (S12), and at least the most advanced part of the material to be rolled is The rolled material is rolled to the outlet thickness determined in the second outlet thickness determining step without using the rolling lubricant of each stand until it is bitten by the stand, and the steady portion of the rolled material is N- From the (m + 1) th stand to the Nth stand, the rolling lubricant is used to roll to the exit side plate thickness determined in the first exit side plate thickness determining step, and the (N−m + 1) th stand to the Nth stand determined in the second exit side plate thickness determining step. This is an operation control method for a tandem rolling mill, characterized in that the outlet side plate thickness is thicker than the outlet side plate thickness of the same stand determined in the first outlet side plate thickness determining step.

  Here, the “Nth stand (7)” means the final stand of the tandem rolling mill (10), that is, the downstream end in the moving direction of the material to be rolled (8) rolled by the tandem rolling mill (10). This refers to the stand (7) of the tandem rolling mill. The “first stand (1)” refers to a tandem mill stand (1) disposed at the upstream end in the moving direction of the material (8) to be rolled by the tandem mill (10). In the present invention, the “tip rolling portion of the material to be rolled (8)” refers to a tip side portion of the material to be rolled (8) that is rolled without using a rolling lubricant. In the present invention, the “steady portion of the material to be rolled (8)” refers to a portion of the material to be rolled (8) that is rolled using a rolling lubricant. Further, “the N-m + 1 stand to Nth stand outlet thickness determined in the second outlet thickness determination step is thicker than the outlet thickness of the same stand determined in the first outlet thickness determination step” Is that the exit side plate thickness of each stand from the (N−m + 1) th stand to the Nth stand is determined in the first exit side plate thickness determination step in the exit side plate thickness determined in the second exit side plate thickness determination step. It means that it is determined to be thicker than the thickness of the exit side plate.

  In the first aspect of the present invention, the load of each stand when rolling the tip rolling portion of the material to be rolled (8) is substantially the same as the load of the same stand when rolling the steady portion of the material to be rolled. It is preferable that the outlet side plate thicknesses of the first stand to the Nth stand are determined in the second outlet side plate thickness determining step (S12) so as to be equal.

  Here, “the load of each stand when rolling the tip rolling portion of the material to be rolled (8) is substantially equal to the load of the same stand when rolling the steady portion of the material to be rolled” is tandem rolling. When attention is paid to any one stand constituting the machine, it means that the rolling load when rolling the tip rolling part of the material to be rolled is substantially equal to the rolling load when rolling the steady part of the material to be rolled. Further, “substantially equal” is a concept that allows a difference of 1MN that can be regarded as a minute change in the shape of the material to be rolled due to a change in the amount of bending of the roll, in addition to the case where they are completely equal.

  According to a second aspect of the present invention, a steel plate (8) is rolled using a hot finish rolling mill row (20) whose operation is controlled by the operation control method for a tandem rolling mill according to the first aspect of the present invention. It is the manufacturing method of a hot-rolled steel plate characterized by having the process to do.

  In the first aspect of the present invention, the steady portion of the material to be rolled (8) is rolled using a rolling lubricant, whereas the rolling lubricant is not used at the tip rolling portion of the material to be rolled (8). It becomes possible to stabilize the plate of the most advanced part of the rolled material (8). Further, in the first aspect of the present invention, the outlet side plate thickness of the rear stage stand (5, 6, 7) in the tandem rolling mill (10) is more than that when the steady portion of the material (8) is rolled. Since it is determined to be thicker when rolling the tip rolling portion of the rolled material (8), even during rolling of the tip rolling portion without using the rolling lubricant, the rear stand (5, 6, 7) It is possible to prevent the load (load, torque, etc.) from exceeding the upper limit value of the facility or roughening the surface of the work roll. Moreover, in the 1st aspect of this invention, since the stationary part of a to-be-rolled material (8) is rolled using a rolling lubricant, the finishing which raised the reduction | decrease rate of the back | latter stage stand (5,6,7) rather than before. Even if rolling is performed, it becomes possible to reduce the rough surface of the work roll surface of the rear stage stand within the load constraints (load resistance constraint, torque constraint, etc.) of the rear stage stands (5, 6, 7). It becomes possible to suppress the quality defect of (8). Therefore, by applying the first aspect of the present invention to the hot finish rolling mill row (20), it is possible to provide an operation control method for a tandem rolling mill capable of producing ultrafine grain steel. it can. Moreover, the 2nd aspect of this invention uses a hot finishing rolling mill row | line | column (20) by which operation | movement is controlled by the operation | movement control method of the tandem rolling mill concerning the 1st aspect of this invention, and uses a steel plate (8). It has the process of rolling. Therefore, according to the 2nd aspect of this invention, the manufacturing method of a hot-rolled steel plate which can manufacture an ultra fine grain steel can be provided.

It is a flowchart which shows the form example of the operation | movement control method of the tandem rolling mill concerning this invention. It is a figure which shows the example of a form of the tandem rolling mill 10 by which operation | movement is controlled by the operation | movement control method of the tandem rolling mill concerning this invention. It is a figure which shows the example of the form of the production line 100 of the hot rolled sheet steel provided with the finishing mill row | line | column 20 by which operation | movement is controlled by the operation | movement control method of the tandem rolling mill concerning this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a flowchart showing an example of an operation control method for a tandem rolling mill according to the present invention (hereinafter sometimes referred to as “the operation control method of the present invention”). The operation control method of the present invention shown in FIG. 1 includes an exit side plate thickness determination step (hereinafter, also referred to as “step S1”), and the step S1 includes a first exit side plate thickness determination step (hereinafter referred to as “step S1”). And a second delivery side plate thickness determination step (hereinafter also referred to as “step S12”). That is, in the operation control method of the present invention, the operation of the tandem rolling mill is controlled using the step S1 having the steps S11 and S12.

  FIG. 2 is a diagram showing a form example of the tandem rolling mill 10 whose operation is controlled by the operation control method of the present invention. In FIG. 2, the form of the tandem rolling mill 10 is shown in a simplified manner. As shown in FIG. 2, the tandem rolling mill 10 has seven stands, a first stand 1, a second stand 2,..., And a seventh stand 7, and the first stand 1 to the seventh stand 7. By the seven stands up to, the material to be rolled 8 (hereinafter, sometimes referred to as “steel plate 8”) can be continuously rolled. These seven stands 1, 2,..., 7 are each provided with a pair of work rolls and a pair of backup rolls, and their operations are controlled by a control device. That is, for example, the first stand 1 includes a pair of work rolls 1a and 1a and a pair of backup rolls 1b and 1b. The operations of the work rolls 1a and 1a and the backup rolls 1b and 1b are performed by the control device 1c. It is controlled. Similarly, for example, the seventh stand 7 includes a pair of work rolls 7a and 7a and a pair of backup rolls 7b and 7b. The operations of the work rolls 7a and 7a and the backup rolls 7b and 7b are performed by the control device 7c. Is controlled by. 2, in the tandem rolling mill 10, the fifth stand 5 includes lubricant supply means 5d and 5d, the sixth stand 6 includes lubricant supply means 6d and 6d, and the seventh stand 7 Lubricant supply means 7d and 7d are provided. Lubricant supply means 5d, 6d, and 7d are devices that inject a rolling lubricant (for example, rolling lubricating oil or rolling lubricating oil aqueous solution) toward the work rolls 5a, 6a, and 7a, respectively, and are pressurized. A pipe for supplying the rolling lubricant and a nozzle for injecting the rolling lubricant toward the work roll are provided. Hereinafter, the operation control method of the present invention will be specifically described with reference to FIGS. 1 and 2 in the case of N = 7 and m = 3, which is an embodiment of the present invention.

<Exit side plate thickness determining step S1>
Step S1 is a step of determining the exit side plate thickness of each stand from the first stand to the Nth stand (N is an integer of 2 or more). That is, when N = 7 and m = 3, step S1 is a step of determining the exit side plate thicknesses of the seven stands from the first stand 1 to the seventh stand 7, respectively. In the operation control method of the present invention, the form of step S1 is not particularly limited as long as it includes step S11 and step S12 described later.

<First Outlet Plate Thickness Determination Step S11>
Step S11 is a step of determining the outlet side plate thickness of the Nth stand from the first stand when rolling the steady portion of the material 8 to be rolled. That is, when N = 7, step S11 is a step of determining exit side plate thicknesses h1 to h7 from the first stand 1 to the seventh stand 7 when rolling the steady portion of the material 8 to be rolled. In the operation control method of the present invention, the steady portion of the material 8 to be rolled refers to a portion of the material 8 to be rolled using a rolling lubricant, and obtains the original product specifications (plate thickness, particle size). It refers to the part that is rolled under the rolling conditions.

  In the operation control method of the present invention, if the step S11 is a step of determining the exit side plate thicknesses h1 to h7 of the first stand 1 to the seventh stand 7 when rolling the steady portion of the material 8 to be rolled, Although a form is not specifically limited, From a viewpoint of making ultrafine grain steel into a form which can be manufactured easily etc., especially 3 back | latter stages (5th stand 5, 6th stand 6, 7th stand 7) Is preferably determined in consideration of at least the accumulated strain to be accumulated in the steel plate 8 by the three stands and load constraints (load bearing constraint, torque constraint, etc.) of each of the subsequent-stage stands 5, 6, 7. .

<Second Outlet Plate Thickness Determination Step S12>
In step S12, the exit side plate thickness of each subsequent stage of the N-th stand from the (N−m + 1) th stand (m is an integer of 1 or more and N or less) when rolling the tip rolled portion of the material 8 to be rolled 8 It is the process of determining the delivery side plate thickness of the 1st stand to the Nth stand so that it may become thicker than the delivery side plate thickness of the same stand when rolling the stationary part. That is, when N = 7 and m = 3, the process S12 determines the exit side plate thicknesses of the respective rear stands of the fifth stand 5 to the seventh stand 7 determined in the process S12 by h5 ′, h6 ′, h7 ′, respectively. , The exit side plate thicknesses h1 ′ to h7 ′ of the respective stands from the first stand 1 to the seventh stand 7 are determined so that h5 ′> h5, h6 ′> h6, and h7 ′> h7. It is a process to do. In the operation control method of the present invention, the tip rolling portion of the material to be rolled 8 refers to the tip side portion of the material to be rolled 8 that is rolled without using a rolling lubricant.

  In the operation control method of the present invention, the process S12 includes steps 1-12 for rolling the tip rolling portion of the material 8 to be rolled so that h5 ′> h5, h6 ′> h6, and h7 ′> h7. 7, the form is not particularly limited. For example, the rolling load of each stand 1 to 7 when rolling the tip rolling part of the material 8 to be rolled is It is preferable that the exit side plate thickness of each of the stands 1 to 7 is determined so as to be substantially equal to the rolling load of the same stand when the steady portion of the rolled material 8 is rolled. By adopting such a configuration, it is possible to prevent a change in the amount of bending of the work rolls 1a, 1a,..., 7a, 7a of the stands 1 to 7 when changing from the exit side plate thickness of the tip rolling portion to the exit side plate thickness of the steady portion. Therefore, it becomes possible to stabilize the shape of the material 8 to be rolled.

Here, the operation of the tandem rolling mill 10 for rolling the material to be rolled 8 is as follows. First, the tandem rolling mill 10 is operated by operating the control devices 1c to 7c so that the outlet side plate thicknesses of the first stand 1 to the seventh stand 7 become the outlet side plate thicknesses h1 ′ to h7 ′ of the tip rolling portion determined in step S12. Set up and start rolling. At this time, the lubricant supply means 5d, 5d, ..., 7d, 7d do not supply rolling lubricant. The lubricant supply means 5d, 5d,..., 7d, 7d start supplying the rolling lubricant at a predetermined timing after the leading edge has been bitten, and the first stand 1 to the seventh stand 7 exit. The control devices 1c to 7c are operated so that the side plate thickness becomes the outlet side plate thickness h1 to h7 of the stationary part determined in step S11, and the process proceeds to rolling of the stationary part. As a specific method, for example, the so-called absolute value AGC for calculating the output side thickness from the rolling load and the actual value of the reduction position and operating the reduction position so that the output side thickness matches the target plate thickness can be calculated. What is necessary is just to apply to a stand and to change the target board thickness from h1'-h7 'to h1-h7, respectively.
In addition, as the timing for starting the supply of rolling lubricant for each of the subsequent-stage stands 5, 6 and 7, any timing is possible as long as the stand has bitten the most advanced portion of the material to be rolled. For example, in each of the rear stage stands 5, 6, and 7, the time from when the most advanced portion is bitten to when the supply of rolling lubricant is started may be designated in advance, or the seventh stand 7 that is the final stand may be designated. You may make it start supply of the rolling lubricant of all the back | latter stage stands 5, 6, and 7 after the most advanced part is bitten.

  A specific example of the exit side plate thickness [mm] of the first stand 7 to the seventh stand 7 when rolling the steady portion of the material 8 to be rolled, which is determined by the step S1 including the step S11, is the reduction ratio of each stand, The deformation resistance [MPa], friction coefficient, and load [MN] are shown in Table 1. Table 1 shows that the entry side plate thickness of the first stand 1 is 32 mm for the purpose of producing ultrafine-grained steel having an average particle size of 2 μm or less, which has been rolled so that the plate thickness of the stationary part is 2 mm. It is a draft schedule of the tandem rolling mill 10 when rolling the steady part of the material 8 to be rolled having a plate width of 1250 mm, and F1 to F7 in Table 1 correspond to the first stand 1 to the seventh stand 7, respectively. ing.

  Moreover, the specific example of exit side board thickness [mm] of the 1st stand 1 to the 7th stand 7 when rolling the front-end rolling part of the to-be-rolled material 8 determined by process S1 containing the said process S12 is shown for each stand. Table 2 shows the rolling reduction, deformation resistance [MPa], coefficient of friction, and load [MN]. The rolling conditions of the tip rolling part of the first stand 1 to the fourth stand 4 are exactly the same including the rolling condition of the stationary part and the rolling load. Table 2 shows the steady part of the draft schedule shown in Table 1 for the purpose of producing ultrafine-grained steel having an average grain size of 2 μm or less, which has been rolled so that the thickness of the steady part is 2 mm. FIG. 2 is a draft schedule of the tandem rolling mill 10 when rolling the tip rolling portion of the material 8 to be rolled having a thickness of 32 mm and a width of 1250 mm before the rolling of the first stand 1 is started. F1 to F7 correspond to the first stand 1 to the seventh stand 7, respectively.

  As shown in Table 1, when the steady portion of the material to be rolled 8 is rolled using a rolling lubricant, the friction coefficient from the fifth stand 5 to the seventh stand 7 becomes 0.15. Under such conditions, even if the rolling reduction ratio from the fifth stand 5 to the seventh stand 7 is increased, the material 8 to be rolled can be rolled within the range of the load constraint of the fifth stand 5 to the seventh stand 7. Become. Therefore, in step S11 in the operation control method of the present invention, the exit side plate thicknesses of the fifth stand 5 to the seventh stand 7 when rolling the steady portion of the material 8 to be rolled are 4.082 mm, 2.857 mm, It was determined to be 2,000 mm. When the outlet side plate thicknesses of the fifth stand 5 to the seventh stand 7 are determined in this way, the reduction ratios of the fifth stand 5, the sixth stand 6 and the seventh stand 7 can all be set to 0.300. Since it can be rolled under high pressure, it becomes possible to produce ultrafine-grained steel.

  On the other hand, as shown in Table 2, when the tip rolling portion of the material to be rolled 8 is rolled without using a rolling lubricant, the friction coefficient from the fifth stand 5 to the seventh stand 7 becomes 0.40. Under this condition, when the outlet side plate thickness of the fifth stand 5 to the seventh stand 7 is set to the outgoing side plate thickness equivalent to the outgoing side plate thickness (see Table 1) when rolling the steady portion of the material 8 to be rolled, The load restrictions of the fifth stand 5 to the seventh stand 7 will be exceeded. Therefore, in step S12 in the operation control method of the present invention, the fifth stand 5 to the fifth stand 5 when rolling the tip rolling portion of the material 8 to be rolled so as not to exceed the load constraints of the fifth stand 5 to the seventh stand 7 are used. The exit side plate thickness of 7 stands 7 was determined to be 4.670 mm, 3.746 mm, and 2.997 mm, respectively. By determining the outlet side plate thickness in this way, it becomes possible to roll the tip rolling portion of the material 8 to be rolled without using a rolling lubricant within the load constraints of the respective rear stage stands 5, 6, 7. .

  Further, in the operating conditions (draft schedule) shown in Tables 1 and 2, the first stand 1 is used for both the rolling of the tip rolling part of the material 8 and the steady part of the material 8. The same rolling conditions including the rolling load are used up to 4 stands 4, the rolling load of the fifth stand 5 is constant at 16.99 MN, the rolling load of the sixth stand 6 is constant at 16.68 MN, The rolling load of the stand 7 was constant at 16.58MN. By operating the tandem rolling mill 10 under such conditions, it is possible to eliminate the change in rolling load in each of the stands 1 to 7, so that the change in the amount of bending of the work roll of each of the stands 1 to 7 is eliminated, and the exit side plate It becomes possible to stabilize the shape of the material 8 to be rolled during the thickness change.

  In the operation control method of the present invention in which the operation of the tandem rolling mill 10 is controlled by the above-described step S1, the output of the rear stands 5, 6, 7 when rolling the tip rolling portion of the material 8 to be rolled without using a rolling lubricant. The exit side plates of the rear stand 5, 6, 7 so that the side plate thickness is thicker than the exit side plate thickness of the rear stand 5, 6, 7 when rolling the steady portion of the material 8 to be rolled using a rolling lubricant. Determine the thickness. Therefore, based on a draft schedule in which the rolling reduction of the plurality of subsequent stages including the final stand is set higher than before, the tip rolling portion can be stably passed without using a rolling lubricant. Further, in the stationary part, it is possible to produce ultrafine-grained steel by increasing the rolling reduction ratio of a plurality of subsequent stages including the final stand as compared with the conventional one. Therefore, according to the present invention, ultrafine-grained steel is produced. It is possible to provide an operation control method for a tandem rolling mill.

FIG. 3 is a diagram showing an example of a form of a hot-rolled steel sheet production line 100 provided with a finish rolling mill row 20 whose operation is controlled by the operation control method of the present invention. In FIG. 3, only a part of the production line 100 for hot-rolled steel sheets is extracted, and descriptions of a control device, a lubricant supply means, and the like provided in the finishing rolling mill row 20 are omitted. As shown in FIG. 3, the hot-rolled steel sheet production line 100 includes a rough rolling mill row 30 including rough rolling mills 30 a, 30 b,..., 30 f and a finishing rolling mill including finishing rolling mills 20 a, 20 b,. The cooling device 40 has a row 20 and a cooling device 40 so that the steel plate 8 rolled by the final stand 20g of the finish rolling mill row 20 can be rapidly cooled (specifically, rolling by the final stand 20g). (The steel plate 8 can be rapidly cooled at a cooling rate of 600 ° C./s or more within 0.2 seconds from the end). The finish rolling mill row 20 has seven stands from the first stand 20a to the seventh stand 20g, and the operation of the finish rolling mill row 20 is controlled through the step S1 having the steps S11 and S12. The Therefore, the finishing rolling mill row 20 has, for example, a reduction ratio of the subsequent three stands (the fifth stand 20e, the sixth stand 20f, and the seventh stand 20g) when producing a steel plate other than the ultrafine-grained steel. It is possible to operate in a form higher than the rolling reduction, thereby making it possible to refine the austenite grains of the steel plate 8 and accumulate rolling strain in the grains. And since the cooling device 40 is arrange | positioned so that the steel plate 8 rolled by the last stand 20g of the finishing rolling mill row | line | column 20 can be rapidly cooled, according to the production line 100 of a hot-rolled steel plate, a steel plate immediately after finish rolling. By rapidly cooling 8, it becomes possible to produce ultrafine-grained steel. As described above, by controlling the operation of the finishing rolling mill 20 in the hot-rolled steel sheet production line 100 by the operation control method of the present invention, it becomes possible to produce ultrafine-grained steel.
From the above, according to the present invention, there are provided an operation control method for a tandem rolling mill capable of producing ultrafine-grained steel, and a method for producing a hot-rolled steel sheet capable of producing ultrafine-grained steel. be able to.

  Roll the tip rolling part with the draft schedule in Table 2 without using rolling lubricant, and after 1 second has passed since the most advanced part is bitten into the seventh stand, rolling lubricant from the fifth stand to the seventh stand The steady portion was rolled on the draft schedule shown in Table 1 and the steel sheet was cooled to 680 ° C. at a cooling rate of 830 ° C. to 1000 ° C./s after 0.2 seconds of finish rolling. The particle size was 2 μm, and ultrafine-grained steel could be produced (Example of the present invention). In addition, since the rolling load of the fifth stand to the seventh stand in the subsequent stage was kept low in both the tip rolled portion and the steady portion, in the present invention example, the surface quality of the steel sheet due to the rough surface of the work roll did not occur.

  On the other hand, as a comparative example, the rolling load from the fifth stand to the seventh stand was made equal to that in Table 2 without using a rolling lubricant, and rolled according to the draft schedule shown in Table 3 below. When the same cooling conditions were applied, the average ferrite grain size was 2.6 μm, and ultrafine grain steel could not be produced. As described above, according to the method of the present invention, ultra-fine-grained steel can be produced by rolling under high pressure at a subsequent stage stand using a rolling lubricant in a stationary part, and a rolling lubricant is used. By reducing the rolling reduction at the tip rolling part including the most advanced part where the biting property of the rolled material deteriorates, the rolling load exceeds the upper limit value and the surface of the work roll surface becomes rough without using a rolling lubricant. No threading is possible.

  The operation control method for a tandem rolling mill and the method for producing a hot-rolled steel sheet according to the present invention can be used for producing a hot-rolled steel sheet having ultrafine crystal grains. Moreover, the hot-rolled steel sheet having ultrafine crystal grains can be used as a material used for applications such as automobiles, household appliances, machine structures, and buildings.

DESCRIPTION OF SYMBOLS 1 ... 1st stand 2 ... 2nd stand 3 ... 3rd stand 4 ... 4th stand 5 ... 5th stand 5d ... Lubricant supply means 6 ... 6th stand 6d ... Lubricant supply means 7 ... 7th stand 7d ... Lubrication Agent supply means 8 ... Rolled material (steel plate)
DESCRIPTION OF SYMBOLS 10 ... Tandem rolling mill 20 ... Finish rolling mill row 30 ... Rough rolling mill row 40 ... Cooling device 100 ... Hot-rolled steel plate production line

Claims (3)

Operation of a tandem rolling mill provided with lubricant supply means for supplying rolling lubricant from N stands (N is an integer of 2 or more) and N-m + 1 stand (m is an integer of 1 to N) to the Nth stand A method of controlling
There is an exit side plate thickness determining step for determining the exit side plate thickness of each stand from the first stand to the Nth stand, and the exit side plate thickness determining step includes the first stand when rolling the steady portion of the material to be rolled. A first outlet side thickness determining step for determining the outlet side plate thickness of the Nth stand, and the outlet side plate thickness of the Nth stand from the first stand when rolling the tip rolling portion of the material to be rolled. A second exit side plate thickness determining step,
Until at least the foremost part of the material to be rolled is caught in each stand, the material to be rolled is rolled to the outlet side thickness determined in the second outlet side thickness determining step without using the rolling lubricant of each stand. And the steady portion of the material to be rolled is rolled from the (N−m + 1) th stand to the outlet side thickness determined in the first outlet side thickness determining step using the rolling lubricant in the Nth stand,
The outlet side plate thickness of the Nth stand from the (N−m + 1) th stand determined in the second outlet side plate thickness determining step is larger than the outlet side plate thickness of the same stand determined in the first outlet side plate thickness determining step. An operation control method for a tandem rolling mill. The second delivery side plate thickness determination is performed so that the load of each stand when rolling the tip rolling portion of the material to be rolled is substantially equal to the load of the same stand when rolling the steady portion of the material to be rolled. 2. The operation control method for a tandem rolling mill according to claim 1, wherein an outlet side plate thickness of the Nth stand is determined from the first stand in the process. A method for producing a hot-rolled steel sheet, comprising the step of rolling a steel sheet using a hot finish rolling mill whose operation is controlled by the operation control method for a tandem rolling mill according to claim 1 or 2.

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