JP2016140881A - Hot finish rolling method, manufacturing method of hot rolled steel sheet, and hot finish rolling mill - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hot finish rolling method and a hot finish rolling mill capable of maintaining high surface quality of a rolled material and a rolling roll even when heavy-load and high-speed rolling is carried out at a rear-stage stand.SOLUTION: The hot finish rolling method tilts, by using the hot finish rolling mill having a plurality of finish rolling mills continuously arranged in the moving direction of a target material, the target material from a spray header disposed immediately before at least one finish rolling mill installed on the downstream side of the moving direction to the entrance side of the finish rolling milli installed immediately after a vertical direction, and rolls the target material while spraying water by pressure of 1.5 MPa or more to 15 MPa or less. The hot finish rolling mill includes the plurality of finish rolling mills continuously arranged in the moving direction of the target material, and the spray header disposed immediately before at least one finish rolling mill installed on the downstream side of the moving direction so that the target material can be tilted to the entrance side of the finish rolling mill installed immediately after the vertical direction and water can be sprayed by the above-mentioned pressure.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a hot finish rolling method, a method for producing a hot rolled steel sheet using the hot finish rolling method, and a hot finish rolling mill. Specifically, it suppresses the rough surface and the damage of rolling rolls (work rolls and backup rolls, the same applies hereinafter) involving oxide coatings called the scales of steel plates, and especially the material to be rolled even under conditions of high load and high speed rolling. The present invention relates to a hot finish rolling method, a method for producing a hot-rolled steel sheet, and a hot finish rolling mill that efficiently perform hot rolling while suppressing damage to a rolling roll without impairing the surface properties of the steel sheet.

  In recent years, the strength of steel materials used as automobiles and structural materials has increased. In addition, the production amount of such a steel material with increased strength (hereinafter sometimes referred to as “high-strength steel”) is also increasing.

  High-strength steel usually contains a lot of alloy components other than iron, so the strength of the material when manufacturing in the hot rolling process is also high, and the rolling load such as the load acting on the rolling mill is increased overall. Yes.

  In addition, improvement of mechanical properties such as workability and toughness of high-strength steel is also demanded. In order to improve mechanical properties comprehensively, in the hot finishing mill equipped with a plurality of finishing mills, the downstream side (in the following, the moving direction (rolling direction) of the material to be rolled in the hot finishing mill) For example, when the hot finishing mill is provided with 5 to 7 finishing mills, 2 to 3 machines arranged on the downstream side in the moving direction of the material to be rolled are referred to as “ "Hot finish rolling mill in the latter stage" (or called "rear stand"). Rolling with a high rolling load may be performed in the later stage of the hot finish mill, such as increasing the rolling reduction ratio. The rolling load is further increased.

  When manufacturing such a high-load material, in order to avoid deterioration of the surface properties of the material to be rolled, in particular, in the rear stage stand of a hot finishing mill with a high rolling speed, the rolling speed is reduced. Has been done normally.

  As described above, when high-load rolling is performed at the subsequent stage of a hot finish rolling mill, rough surface of the material to be rolled and rough surface of the rolling roll, which do not occur under normal operating conditions, are problematic. It was.

  It is considered that the above rough surface is caused by complicated action of rolling load, rolling speed, rolling reduction, rolling temperature, temperature of the material to be rolled, scale thickness before rolling of the material to be rolled, and the like.

  The scale thickness before rolling of the material to be rolled tends to be thick when high-load rolling is performed at the subsequent stage stand of a hot finish rolling mill. In other words, when high-load rolling is performed in the latter stage stand, in order to perform the operation with a reduced rolling speed as a whole, after rolling in the upstream side rolling mill and before rolling in the latter stage stand, Time increases. Moreover, when a rolling speed is made slow, a to-be-rolled material will become easy to be cooled. In order to maintain the delivery temperature of the hot finish rolling mill at a constant value, when high-load rolling is performed in the latter stage stand, the temperature of the material to be rolled during rolling is set higher. Under such conditions, the scale of the surface of the material to be rolled easily grows between passes, and the scale thickness immediately before rolling of the latter stage stand where high load rolling is performed may be about double the normal.

  As the scale grows thicker, the ability to deform with the material during rolling decreases. As a result, it is considered that parting and peeling occur and the surface properties of the material to be rolled and the roll are deteriorated.

  In addition, the scale has a heat insulating effect that inhibits heat transfer between the work roll and the material to be rolled. There is also a survey result that the thermal conductivity of the scale is about 1/2 to 1/10 of the thermal conductivity of the steel plate itself existing inside the scale. There is a heat insulation effect that inhibits heat transfer to the work roll. Moreover, in the latter stage stand of a hot finishing mill, the rolling speed is fast and the contact time between the work roll and the material to be rolled is short. Therefore, the heat transfer from the material to be rolled to the work roll refers to a finish rolling mill that is disposed upstream of the front stage stand of the hot finish rolling mill (in the moving direction (rolling direction) of the material to be rolled relative to the rear stage stand). The same is true in the following), and it becomes a more insulated state. On the other hand, when high-load rolling is performed, frictional heat is generated between the work roll and the material to be rolled. The heat generated at the interface between the scale and the work roll grown on the surface of the material to be rolled is also distributed to the material to be rolled through the scale. As mentioned above, the scale has low thermal conductivity, so if the scale is thick and the insulation is high, the heat is difficult to disperse, and the outermost surface temperature of the work roll and the scale itself will rise significantly. become. The temperature rise due to such frictional heat generation may cause roughing of the rolling roll, scale division / pushing of the surface of the material to be rolled, etc., resulting in deterioration of the surface properties of the rolling roll or material to be rolled. It is done.

  If the rolling speed is lowered in order to suppress such frictional heat generation, the scale is generated thicker and the outlet temperature of the hot finish rolling mill cannot be maintained at a constant value. Therefore, simply reducing the rolling speed is not sufficient.

  Regarding reducing the temperature rise due to frictional heat generation during high-load high-speed rolling, which is a cause of rough skin, for example, Patent Document 1 describes cooling to a hot-rolled material immediately before the hot-rolled material is bitten by a work roll. A hot rolling method is disclosed in which a medium is brought into contact and hot rolling is performed in a state where the surface of the hot rolled material is cooled.

Further, in Patent Document 2, when the scale thickness of the steel sheet surface exceeds 10 μm on the entrance side of the pre-finishing stand in the hot continuous rolling mill, the surface of the steel sheet has a collision pressure of 0.15 kgf / cm ² or more. A method of rolling a hot-rolled steel sheet that is rolled with the above-mentioned pre-finishing stand within 1 second after spraying spray water is disclosed.

Japanese Patent Laid-Open No. 4-200903 JP-A-7-171610

  With the technique described in Patent Document 1, it is possible to lower only the surface temperature of the steel sheet, but the ability to remove scale is extremely low. Since the amount of water is about 20 L / min per rolling mill (hereinafter sometimes referred to as “stand”), the scale cannot be sufficiently removed due to insufficient water amount and insufficient water pressure. Therefore, it is insufficient as a countermeasure for rough skin when high-load rolling and high-speed rolling are performed at a subsequent stage stand of a hot finish rolling mill. Moreover, in the technique of patent document 1, the location and conditions which inject | pour a cooling water on the surface of a to-be-rolled material are not prescribed | regulated in particular. Therefore, when the cooling water comes into contact with the material to be rolled quickly, not only the surface of the material to be rolled but also the inside is cooled, so that there is a possibility that the finish rolling temperature cannot be maintained. Further, when the pressure or amount of cooling water is low, there is a problem that the cooling capacity is insufficient and rough skin cannot be suppressed.

The technique described in Patent Document 2 is an effective countermeasure against rough skin when the temperature of the material to be rolled is high and the plate thickness is relatively thick at the front stage stand of the hot finishing mill. However, when this technique is applied to a subsequent stage stand of a hot finish rolling mill, there is an excess or deficiency in the cooling of the material to be rolled, and the structure of the material to be rolled changes or the cooling is insufficient when cooled excessively. There was a problem that the surface temperature drop was insufficient. Here, in the rear stage stands of a hot finishing mill and is rolled at a low temperature close to A ₃ transformation point compared to the previous stage stand of the hot finish rolling mill. For this reason, there has been a problem that the structure of the material to be rolled changes when it is cooled excessively. On the other hand, if the cooling is insufficient, the plate thickness of the latter stage of the hot finish rolling mill is thin, so that the material to be rolled is soaked quickly. There was a problem of heat. It should be noted that the time between the rear stands in the hot rolling finishing mill (rolling in the second rear stand after the rolling in one rear stand of the two rear stands arranged continuously in the moving direction of the material to be rolled is completed. Is about 0.5 seconds when it is short, the time of 1 second does not represent “immediately before” in the subsequent stage stand of the hot finishing mill.

  Therefore, the present invention can maintain the surface property of the material to be rolled and the surface property of the rolling roll well even when a high load and high-speed rolling are performed in the latter stage stand of the hot finishing mill. It is an object to provide a hot finish rolling method, a method for producing a hot rolled steel sheet, and a hot finish rolling mill.

As a result of intensive studies, the inventors removed the scale from the surface of the material to be rolled immediately before the material to be rolled in the subsequent stage stand of the hot finish rolling mill, and the material to be rolled from which the scale was removed. While maintaining the state where the scale is not easily formed on the surface of the material, by rolling the material to be rolled in the latter stage stand, even when high load and high speed rolling is performed in the latter stage stand of the hot finish rolling mill, It has been found that the surface properties of the material to be rolled and the surface properties of the rolling roll can be kept good.
The present invention has been completed based on such findings. The present invention will be described below.

  The first aspect of the present invention is a hot finishing method in which a material to be rolled is hot-rolled using a hot finishing rolling mill having a plurality of finishing rolling mills arranged continuously in the moving direction of the material to be rolled. A rolling method, comprising: a spray header for injecting medium-high pressure water immediately before at least one finishing rolling mill disposed downstream of the moving direction among the plurality of finishing rolling mills, wherein the spray header From the vertical direction, tilting to the entry side of the finishing mill placed immediately after the spray header, rolling the material to be rolled while injecting water at an injection pressure of 1.5 MPa or more and 15 MPa or less. This is a hot finish rolling method.

  In the present invention, "immediately before" refers to the position on the material to be rolled that is very close to the roll bite on the upstream side in the direction of movement of the rolled material from the roll bite of the rolling mill. A place closer to the roll tool than the work roll radius of the machine. The “medium / high pressure water” is water sprayed at a pressure capable of removing the scale from the surface of the material to be rolled, and is sprayed to remove the scale from the surface of the material to be rolled in the prior art. Water sprayed at a pressure lower than the pressure of the water. More specifically, it refers to water having a water pressure (header pressure) of 1.5 MPa to 15 MPa. The “entry side” refers to the upstream side in the moving direction (rolling direction) of the material to be rolled.

  Medium and high pressure water sprayed from the spray header tilted to the entry side of the finishing mill placed immediately after it collides with the material to be rolled, then flows downstream in the moving direction of the material to be rolled and hits the work roll. . Immediately before the finishing mill, the medium-high pressure water collides with the material to be rolled, so that the material to be rolled can be efficiently cooled immediately before rolling. It becomes possible to suppress the temperature rise. As described above, by cooling the material to be rolled very shortly before, it is possible to solve the problem in the case of using the conventional technique that the material to be rolled is excessively cooled or the cooling is insufficient. Also, by making medium-high pressure water collide with the material to be rolled, the scale that existed on the surface of the material to which the medium-high pressure water collided can be peeled off, so the scale thickness should be made thinner than before. Is possible. Moreover, since the water which collided with the to-be-rolled material flows toward the work roll side after that, the surface of the to-be-rolled material just before rolling with a finish rolling mill is covered with water. By covering the surface of the material to be rolled with water, generation of a new scale on the surface of the material to be rolled can be suppressed. By reducing the thickness of the scale and suppressing the generation of a new scale, it is possible to suppress the division and peeling of the scale, so that the surface properties of the material to be rolled and the rolling roll can be kept good. .

  Further, in the first aspect of the present invention, the portion where water sprayed from the spray header collides with the material to be rolled is a roll bite of a finishing mill disposed immediately after the spray header, and the roll bite. It is preferable to perform rolling while spraying water from the spray header so as to be between the upstream position in the moving direction by the radius of the work roll of the finishing mill.

  Here, the “roll bite of the finish rolling mill” refers to a portion where the work roll of the finish rolling mill that rolls the material to be rolled and the material to be rolled are in contact (portion where the material to be rolled is bitten by the work roll). . Usually, the radius of the work roll of the rolling mill of the latter stage stand of the hot rolling finishing mill is at most about 0.4 m. Moreover, the plate | board speed of the to-be-rolled material between the back | latter stage stands of a hot rolling finishing rolling mill is 150 m / min at the latest. Therefore, water is removed at a location between the roll bit of the finishing mill arranged immediately after the spray header and the upstream position in the moving direction by the radius of the work roll of the finishing mill from the roll bit. Is caused to collide with the surface of the material to be rolled, so that the material to be rolled is rolled by the work roll within 0.2 seconds at the latest after the surface of the material to be rolled is cooled. By setting it as such a form, only the surface of a to-be-rolled material can be cooled immediately before rolling. As a result, the temperature of the material to be rolled on the exit side of the hot finish rolling mill can be easily controlled to the target value, and in addition to the above effects, it becomes easy to manufacture high-strength steel having target properties.

  In the first aspect of the present invention, a plurality of the spray headers may be provided immediately before the finishing mill.

  By adopting such a form, a spray header that sprays water whose main purpose is to peel off the scale, and a spray header that sprays water whose main purpose is to cool the material to be rolled from which the scale has been peeled off. Can be placed immediately before the finishing mill. As a result, it is possible to control the peeling of the scale and the cooling of the material to be rolled separately, so that in addition to the above effects, it is easy to expand the applicable manufacturing conditions.

  Further, in the first aspect of the present invention, the spray pressure when spraying water from the spray header is 1.5 MPa or more and 10 MPa or less, and the amount of water sprayed from the spray header to the material to be rolled is It is preferably 100 L / min or more and 200 L / min or less per finishing mill.

  By spraying water in such a form, it becomes easy to maintain the surface properties of the material to be rolled and the roll.

  A second aspect of the present invention is a method for producing a hot-rolled steel sheet, comprising a step of finish-rolling a steel sheet using the hot-rolling finish rolling method according to the first aspect of the present invention.

  As described above, according to the hot rolling finish rolling method according to the first aspect of the present invention, it is possible to maintain the surface properties of the material to be rolled and the surface properties of the roll. Therefore, it becomes possible to manufacture the high strength steel which has the outstanding surface property by having the process of finish-rolling a steel plate using the hot-rolling finish rolling method which concerns on the 1st aspect of this invention.

  A third aspect of the present invention is a hot finish rolling mill having a plurality of finish rolling mills arranged continuously in the moving direction of the material to be rolled, and among the plurality of finish rolling mills, the moving direction A spray header for injecting medium-high pressure water immediately before at least one finish rolling mill arranged downstream of the vertical rolling mill, to the entry side of the finishing mill arranged immediately after the spray header rather than in the vertical direction. It is a hot finish rolling mill characterized in that a spray header is arranged so that water is injected at an injection pressure of 1.5 MPa or more and 15 MPa or less.

  By adopting such a form, as in the first aspect of the present invention, it is possible to suppress an increase in the temperature of the surface layer portion due to frictional heat generated by rolling, and to reduce the scale thickness, and , Generation of a new scale can be suppressed. As a result, since division and peeling of the scale can be suppressed, the surface properties of the material to be rolled and the rolling roll can be kept good.

  Further, in the third aspect of the present invention, the portion where water sprayed from the spray header collides with the material to be rolled is a roll bite of a finishing mill disposed immediately after the spray header, and the roll bite. It is preferable that it is between the upstream position in the moving direction by the radius of the work roll of the finishing mill.

  By setting it as such a form, only the surface of a to-be-rolled material can be cooled immediately before rolling. As a result, the temperature of the material to be rolled on the exit side of the hot finish rolling mill can be easily controlled to the target value, and in addition to the above effects, it becomes easy to manufacture high-strength steel having target properties.

  In the third aspect of the present invention, a plurality of the spray headers may be provided immediately before the finishing mill.

  By adopting such a form, a spray header that sprays water whose main purpose is to peel off the scale, and a spray header that sprays water whose main purpose is to cool the material to be rolled from which the scale has been peeled off. Can be placed immediately before the finishing mill. As a result, it is possible to control the peeling of the scale and the cooling of the material to be rolled separately, so that in addition to the above effects, it is easy to expand the applicable manufacturing conditions.

  According to the present invention, it is possible to keep the surface properties of the material to be rolled and the surface properties of the rolling rolls even when a high load and high speed rolling are performed at the subsequent stage of the hot finish rolling mill. A hot finish rolling method, a method for producing a hot rolled steel sheet, and a hot finish rolling mill can be provided.

It is a figure explaining one embodiment of the present invention. It is a figure which expands and shows finishing mill 15, spray header 22x, 22y, and finishing mill 16, and explains one embodiment of the present invention. It is a figure explaining other embodiment of this invention. It is a figure explaining other embodiment of this invention.

  Embodiments of the present invention will be described below. In addition, the following description is an illustration of this invention and this invention is not limited to the form demonstrated below.

  FIG. 1 is a diagram illustrating a hot finish rolling mill 10 according to the present invention. The hot finish rolling mill 10 shown in FIG. 1 has seven finish rolling mills 11, 12,..., 17, and these 7 finish rolling mills 11, 12,. The material 1 is hot rolled. Each finish rolling mill 11, 12,..., 17 includes a pair of work rolls 11a, 12a,..., 17a and backup rolls 11b, 12b,. Of the seven finishing mills 11, 12,..., 17, spray headers 21x and 21y are disposed immediately before the finishing mill 15 arranged on the downstream side in the moving direction of the material 1 to be rolled. Spray headers 22x and 22y are disposed immediately before the end, and spray headers 23x and 23y are disposed immediately before the finish rolling mill 17, respectively. The spray headers 21x and 21y inject water with a pressure of 1.5 MPa or more and 15 MPa or less (preferably 1.5 MPa or more and 10 MPa or less; the same applies hereinafter) inclined toward the entry side of the finishing mill 15 from the vertical direction. Arranged to be able to. Similarly, the spray headers 22x and 22y are arranged so that water having a pressure of 1.5 MPa or more and 15 MPa or less can be sprayed by being inclined toward the entrance side of the finishing mill 16 from the vertical direction. 23y is arranged so that water having a pressure of 1.5 MPa or more and 15 MPa or less can be injected while being inclined toward the entry side of the finishing mill 17 from the vertical direction.

  FIG. 2 is a diagram for explaining a state in which the material to be rolled 1 is hot-rolled using the hot finish rolling mill 10. The finish rolling mill 15, the spray headers 22 x and 22 y, and the finish rolling mill 16 are shown in FIG. It is shown enlarged. As shown in FIG. 2, when the material to be rolled 1 is hot-rolled using the hot finish rolling mill 10, the spray header 22 x disposed on the upper surface side of the material 1 to be rolled and the material 1 to be rolled 1 The material to be rolled 1 is rolled while spraying the medium-high pressure water 2 from the spray header 22y arranged on the lower surface side to incline toward the entry side of the finishing mill 16 from the vertical direction. In addition, although the figure which showed a mode that water was injected was abbreviate | omitted, when hot-rolling the to-be-rolled material 1 using the hot finishing mill 10, from spray headers 21x and 21y, it is from a perpendicular direction. In addition, the material to be rolled 1 is rolled while inclining toward the entry side of the finishing mill 15 and spraying medium-high pressure water, and is inclined from the spray headers 23x and 23y toward the entry side of the finishing mill 17 from the vertical direction. The material to be rolled 1 is rolled while jetting high-pressure water.

  The medium-high pressure water 2 that is sprayed from the spray headers 22x and 22y toward the entrance side of the finish rolling mill 16 collides with the material 1 to be rolled, and then flows downstream in the moving direction of the material 1 to be rolled. It hits the work roll 16a of the machine 16. Similarly, the medium-high pressure water sprayed from the spray headers 21x and 21y to the entrance side of the finishing mill 15 collides with the material 1 to be rolled, and then flows downstream in the moving direction of the material 1 to be rolled. The medium-high pressure water that hits the work roll 15a of the finishing mill 15 and is sprayed from the spray headers 23x and 23y toward the entrance of the finishing mill 17 collides with the material 1 and then moves the material 1 to be rolled. It flows downstream in the direction and hits the work roll 17a of the finishing mill 17. Immediately before the finish rolling mills 15, 16, 17, by causing the medium-high pressure water to collide with the material to be rolled 1, it becomes possible to efficiently cool the material to be rolled 1 immediately before rolling. It is possible to suppress the temperature rise of the surface layer portion due to the frictional heat generated. Thus, by cooling the material 1 to be rolled very shortly before, it is possible to solve the problem in the case of using the conventional technique that the material 1 is excessively cooled or the cooling is insufficient. Further, since the medium-high pressure water 2 collides with the material 1 to be rolled, the scale existing on the surface portion of the material 1 to which the medium-high pressure water 2 collided can be peeled off. It becomes possible to reduce the thickness. Moreover, since the water which collided with the to-be-rolled material 1 flows over the surface of the to-be-rolled material 1 toward the work rolls 15a, 16a, and 17a after that, the to-be-rolled material just before being rolled by the finish rolling mills 15, 16, and 17 The surface of the rolled material 1 is covered with water. By covering the surface of the material 1 to be rolled with water, a new scale is hardly generated on the surface of the material 1 to be rolled. By reducing the thickness of the scale and suppressing the generation of a new scale, it is possible to suppress the division and separation of the scale, so that the material 1 to be rolled, the work rolls 15a, 16a, 17a and the backup roll 15b, It becomes possible to keep the surface properties of 16b and 17b favorable.

  Although FIG. 2 shows a state in which the water 2 collides with the material to be rolled 1 not in the immediate vicinity of the work roll 16a but on the upstream side in the moving direction of the material to be rolled 1 with respect to the work roll 16a, the present invention relates to this embodiment. It is not limited to. Therefore, another embodiment of the present invention is shown in FIG.

  FIG. 3 is a diagram for explaining another embodiment of the present invention. In FIG. 3, the finish rolling mill 15 and the finish rolling mill 16 and the spray headers 22 x ′ and 22 y ′ arranged immediately before the finish rolling mill 16 are shown in an enlarged manner. The spray header 22x'22y 'shown in FIG. 3 differs from the spray headers 22x, 22y only in a specific position arranged immediately before the finish rolling mill 16, and is sprayed from the spray headers 22x', 22y '. The pressure and jet direction of water can be made equal to the pressure and jet direction of water jetted from the spray headers 22x and 22y. As shown in FIG. 3, at least a part of the medium-high pressure water 2 sprayed from the spray headers 22x ′ and 22y ′ is in the immediate vicinity of the work roll 16a, more specifically, a roll bite of the finish rolling mill 16; It collides with the surface of the material 1 to be rolled at a position between the roll tool and the upstream position in the moving direction of the material 1 by the radius of the work roll 16a. By causing the medium-high pressure water 2 to collide with the surface of the material 1 to be rolled at such a site, the material to be rolled using the work roll 16a within 0.2 seconds at the latest after the surface of the material 1 is cooled. 1 can be rolled. By adopting such a form, only the surface of the material 1 to be rolled can be cooled immediately before rolling, and as a result, the temperature of the material 1 to be rolled on the exit side of the hot finish rolling mill 10 is controlled to a target value. It becomes easy to do. Therefore, for example, the spray header arranged immediately before the finish rolling mill 15 and the spray header arranged just before the finishing mill 17 are also in the immediate vicinity of the work roll 15a and the work roll 17a, respectively. By performing hot rolling while jetting medium-high pressure water so as to collide with the surface of the material 1 to be rolled, it becomes easy to produce high-strength steel having target properties.

  Although the form with which one spray header is provided immediately before the work roll of a finishing rolling mill was shown in FIGS. 1-3, this invention is not limited to the said form. Therefore, another embodiment of the present invention is shown in FIG.

  FIG. 4 is a diagram for explaining another embodiment of the present invention. In FIG. 4, the finish rolling mill 15 and the finish rolling mill 16, and the spray headers 24x, 24y, 22x ', and 22y' arranged immediately before the finish rolling mill 16 are shown in an enlarged manner. The spray headers 24x and 24y shown in FIG. 4 are spray headers that incline toward the work roll 16a from the vertical direction, and spray the medium-high pressure water 2 toward the material 1 to be rolled. It is a spray header that injects medium-high pressure water 2 for the purpose of peeling off the scale formed on the surface of the material 1. By adopting such a configuration, scale peeling by the medium and high pressure water sprayed from the play headers 24x and 24y and cooling of the material 1 to be rolled by the medium and high pressure water sprayed from the spray headers 22x 'and 22y' are performed. Since it becomes possible to control separately, it becomes easy to expand the manufacturing conditions of the hot-rolled steel sheet which can respond.

  As described above, in the present invention, the material to be rolled is sprayed from the spray header disposed immediately before the finishing mill toward the material to be rolled by water that is sprayed at an angle toward the finishing mill from the vertical direction. The scale formed on the surface of the substrate is peeled off and removed, and the material to be cooled is cooled. On the other hand, in the conventional hot rolling process, the high-pressure water jet for peeling the scale is performed in a place where the plate is thick and the steel plate is not excessively cooled. Specifically, before performing finish rolling by a hot finish rolling mill, high-pressure water is injected toward the upstream side in the moving direction of the steel sheet. Here, the high-pressure water that has been used so far for peeling off the scale has a water pressure of about 10 to 30 MPa, and an amount of water of about 300 to 500 L / min is injected per stand.

  Here, in the conventional hot rolling process, the high-pressure water was jetted toward the upstream side because the water that flowed upstream in the moving direction of the steel plate after colliding with the steel plate was transferred from the side surface side of the steel plate. It is considered that there was an aim to avoid excessive cooling of the steel sheet by draining. Therefore, it is considered that there is no precedent for the configuration of the present invention in which the medium-high pressure water is injected immediately downstream of the finish rolling mill in the moving direction of the material to be rolled.

On the other hand, the water pressure and water amount of high-pressure water jet for scale peeling, which has been performed in the conventional hot rolling process, are directly applied to the subsequent stage stand of the hot finishing mill in the present invention, When water is sprayed while being inclined toward the downstream side in the moving direction, the material to be rolled is excessively cooled. Hot finish rolling step of the manufacturing process of the hot rolled steel sheet is usually, A ₃ steel beyond the transformation point is completed rolled state is austenitic structure, then, by transformation by cooling the steel sheet, ferrite And has gained organization such as bainite. If the steel material is excessively cooled before rolling by the finish rolling mill, ferrite transformation or the like occurs in the steel material before rolling. Since the ferrite generated in this manner is stretched by rolling with a finish rolling mill, it is difficult to obtain the targeted equiaxed structure. As a result, the rolling texture develops or becomes a layered structure, and it becomes difficult to obtain a rolled steel material having predetermined processing characteristics.

  Thus, in order to prevent excessive cooling, it is necessary to moderately quench only the surface of the steel sheet just before the finishing mill. Here, the local temperature rise due to frictional heat generation that causes rough skin is about 30 to 60 ° C. Therefore, it is effective to balance the temperature drop of the steel sheet due to cooling performed immediately before the finish rolling mill within this range, and it is necessary to ensure the scale peeling ability.

  From such a viewpoint, in the present invention, the water pressure of water sprayed from the spray header arranged immediately before the finishing mill is 1.5 MPa or more and 10 MPa or less, and the spray header arranged just before the finishing mill. It is preferable that the amount of water per one finishing rolling mill (stand) is 100 L / min to 200 L / min. By jetting such water pressure and water amount onto the material to be rolled immediately before the finish rolling mill, the surface properties of the material to be rolled and the rolling roll can be easily maintained.

  In the above description, spray headers are provided immediately before the plurality of subsequent stands constituting the hot finish rolling mill, and each of these spray headers is inclined from the vertical direction to the downstream side in the moving direction of the material to be rolled. Although the form in which the medium-high pressure water is sprayed toward the material to be rolled is illustrated, the present invention is not limited to this form. The present invention sprays medium-high pressure water, which is inclined from the vertical direction toward the downstream side in the moving direction of the material to be rolled, toward the material to be rolled, immediately before at least one subsequent stand constituting the hot finish rolling mill. It is sufficient if a spray header is provided. That is, in the present invention, medium-high pressure water inclined from the vertical direction toward the downstream side in the moving direction of the material to be rolled is directed to the material to be rolled only immediately before one subsequent stand constituting the hot finish rolling mill. A spray header for spraying may be provided. Even if it is a hot finish rolling mill of such a form, and even if high-load and high-speed rolling is performed using the hot finish rolling mill of the form, the surface properties of the material to be rolled and the rolling roll are excellent. It is possible to keep.

  The present invention will be further described with reference to examples.

  A spray header is installed just before the sixth stand from the upstream (stand corresponding to the finishing mill 16 in the hot finishing mill 10) of the hot finishing mill equipped with seven finishing mills (stands). From the spray header to the stand arranged immediately after that, the rolling test applying the form of the present invention was performed by rolling while spraying the medium-high pressure water at an appropriate inclination from the vertical direction. The work roll diameter of the stand used in the rolling test was 720 mm, and the plate thickness reduction conditions of the stand were 4.5 mm on the entry side and 3.0 mm on the exit side. The temperature of the material to be rolled by the stand is 880 ° C., and the plate width of the material to be rolled is 800 mm. For the rolling test, all the same components as the material to be rolled are high strength carbon steel plates (high strength steel). Was used. Table 1 shows the rolling test conditions and results.

  In Table 1, “None” indicating whether or not spraying was performed without spraying medium-high pressure water from a spray header (hereinafter simply referred to as “spray header”) installed immediately before the sixth stand. “Yes” means that rolling was performed while spraying medium-high pressure water from the spray header. Further, the pressure is the pressure of water sprayed from the spray header (water pressure, header pressure: (MPa)), and the amount of water is the amount of water sprayed from the spray header toward the material to be rolled per stand ( L / min). In addition, the “upstream side” in the tilt direction means that the water is sprayed from the spray header by tilting to the upstream side in the moving direction (rolling direction) of the material to be rolled rather than the vertical direction, as in the past. “Downstream side” means that water is sprayed from the spray header while being inclined to the downstream side in the moving direction (rolling direction) of the material to be rolled rather than the vertical direction. “Distance A” is a distance (m) between a portion where water sprayed from the spray header collides with the material to be rolled and a roll bit of a stand arranged immediately after the spray header. "" Is the time (seconds) from the time when water sprayed from the spray header collides with the material to be rolled until it is rolled by a rolling roll of a stand arranged immediately after the spray header. In addition, the surface property of the material to be rolled is “large roughness” when the surface property is poor and the product cannot be shipped even if the material to be rolled (hot rolled material, the same applies hereinafter) is pickled. When it was a level that could be shipped after pickling, it was evaluated as “small roughness”, and when it did not correspond to the above, it was evaluated as “good”. In addition, the surface properties of the rolling rolls are “rough” when they are rough enough to require roll replacement, such as when partial seizure occurs. By performing skin recovery rolling or the like, when the level was such that the operation could be continued without replacing the roll, it was evaluated as “small roughness”, and when it was not equivalent to the above, it was evaluated as “good”. In addition, the finish temperature is “low” when there is a decrease of 10 ° C. or more with respect to the target value, “slightly low” when the decrease stays below 10 ° C., and “good” when the finish temperature is higher than the target temperature It was evaluated. When the surface properties of the material to be rolled, the surface properties of the rolling roll, and the finishing temperature were all “good”, the overall evaluation was ◎, and the surface properties of the material to be rolled were “large roughness”. In the case where the surface texture of the material corresponds to any one of “large roughness” and the finishing temperature is “low”, the product evaluation and the continuation of production are impossible, and the overall evaluation is x. In addition, if the surface texture of the material to be rolled corresponds to any one of “low roughness”, the surface texture of the rolling roll is “low roughness”, and the finishing temperature is “slightly low”, the product is subject to constraints. Since the production can be continued, the overall evaluation is rated as “good”, and when it falls under two or more, the overall evaluation is marked as “poor” because the impact on the continuous production of products that can be shipped increases. In addition, “first form” means a case where the rolling test is performed in the form shown in FIG. 2, and “second form” means a case where the rolling test is carried out in the form shown in FIG. The “third form” means a case where a rolling test is performed in the form shown in FIG. Here, when the rolling test is carried out in the “second form”, the roll tool of the finishing mill and the work roll radius (0.36 m) of the finish mill than the roll tool of the material to be rolled Medium-high pressure water was sprayed toward the upstream position in the moving direction of the material to be rolled by 0.3 m from the roll bite, which is a portion between the upstream position in the moving direction. Also, when carrying out a rolling test in the “third form”, two spray headers are installed immediately before the sixth stand, and medium-high pressure water is supplied from these two spray headers in the vertical direction. Rolling was performed while inclining and injecting to the side of the stand (the downstream side in the moving direction of the material to be rolled) arranged immediately after. In this case, the pressure shown in Table 1 is the pressure of water sprayed from the spray header installed at the position of the spray header 22 'in FIG. 4, and sprayed from the spray header installed at the position of the spray header 24 in FIG. The water pressure was 15 MPa. The amount of water shown in Table 1 is the total amount of water sprayed from two spray headers installed immediately before the stand. Further, the distance A is defined by the portion where water sprayed from the spray header installed at the position of the spray header 22 ′ in FIG. 4 collides with the material to be rolled, and the roll bit of the stand disposed immediately after the spray header. It is a distance (m), and “time B” is arranged immediately after the water sprayed from the spray header installed at the position of the spray header 22 ′ in FIG. 4 collides with the material to be rolled. It is the time (seconds) until rolling with a rolling roll of a stand.

  Cases 1 to 4 are conditions in which medium-high pressure water is not jetted immediately before the finish rolling mill. In Cases 1 to 3, roughening occurred in one or both of the material to be rolled and the rolling roll. Although Case 4 with extremely reduced rolling speed was able to suppress rough skin, the finishing temperature could not be ensured. On the other hand, Cases 5 to 7 are conditions in which high-pressure water or medium-high pressure water is jetted inclining to the upstream side in the moving direction of the material to be rolled immediately before the finish rolling mill. In Case 5 in which water (high-pressure water) was sprayed at the same pressure as that used in the preceding stage of a hot finish rolling mill, the material to be rolled was excessively cooled and the finishing temperature could not be secured. In Cases 6 to 7, which are conditions where the water pressure and the amount of water are lower than in Case 5, mild skin roughness occurred. This is presumably because the cooling of the material to be rolled immediately before rolling was insufficient because the water was injected while being inclined toward the upstream side in the moving direction of the material to be rolled.

  Cases 8 to 13 and 15 to 24 are conditions in which high-pressure water or medium-high pressure water is jetted inclining to the downstream side in the moving direction of the material to be rolled immediately before the finish rolling mill. On the other hand, Case 14 is a condition in which water having a water pressure of 0.5 MPa is injected immediately before the finish rolling mill and inclined to the downstream side in the moving direction of the material to be rolled. Cases 8 to 10 are the first form, Cases 11, 15, and 20 are the second form, and Cases 12 to 13, 16 to 19, and 21 to 24 are the third form. Cases 9, 12 to 13, 16 to 19, and 21 to 24 have an overall evaluation of “◎”, and Cases 8, 10 to 11, 15, and 20 have an overall evaluation of “good”.

  Of Cases 8 to 24, Cases 8, 11, and 15 had slightly lower finishing temperatures. The reason why the finishing temperature was slightly low in Cases 8 and 11 was considered that the water pressure was 15 MPa, and the reason that the finishing temperature was slightly low in Case 15 was because the amount of water was as high as 300 L / min per finishing mill. It is thought that.

In Cases 10 and 20, mild roughening occurred on the material to be rolled. This is because, in Case 10, the portion where the water sprayed from the spray header collides with the material to be rolled is equal to the radius of the work roll of the finishing mill rather than the roll bite of the finishing mill arranged immediately after the spray header. It is considered that cooling of the material to be rolled was slightly insufficient because the pressure of the water sprayed from the spray header was 1.5 MPa further than the upstream portion. On the other hand, rough skin was suppressed in Case 13 made into the 2nd form by changing the installation place of a spray header, making the pressure of the water sprayed from the spray header the same as Case10. From this result, it was found that the effect of the present invention is more easily obtained in the second form than in the first form.
In addition, in Case 20, the mild roughening occurred on the material to be rolled because the amount of water sprayed from the spray header was as small as 50 L / min per finishing mill, and the surface of the material to be rolled was slightly insufficiently cooled. Conceivable.

  Further, in Case 14, mild roughening occurred on the material to be rolled, and mild roughening occurred on the rolling roll. This is presumably because, in Case 14, the pressure of water sprayed from the spray header was as low as 0.5 MPa, and scale peeling was insufficient. While the conditions other than the pressure of water sprayed from the spray header were the same as those of Case 14, Case 12 in which the pressure was set to 10 MPa and Case 13 in which the pressure was set to 1.5 MPa were evaluated as ◎.

  As described above, by applying the present invention, the surface property of the material to be rolled and the surface property of the rolling roll can be maintained well even under conditions of high load and high speed rolling, especially in the subsequent stage of a hot finishing mill. In addition, a predetermined rolling structure can be obtained while ensuring the finishing temperature.

  In recent years, the output of rolling mill motors has improved due to technological innovations in rolling mill drive motors and drive devices, and motors and other equipment have been updated to increase productivity even in the production of high-load materials. In particular, in the latter stage stand of a hot finish rolling mill, high load and high speed of rolling are directed. By applying the present invention, surface property defects such as rough skin can be suppressed even when the rolling speed is increased. As a result, it is possible to increase the rolling speed under the production conditions that could not be increased due to the occurrence of rough skin, and thus the productivity can be increased.

1 ... Rolled material 2 ... Water (medium / high pressure water)
DESCRIPTION OF SYMBOLS 10 ... Hot finish rolling mill 11, 12, 13, 14, 15, 16, 17 ... Finish rolling mill 11a, 12a, 13a, 14a, 15a, 16a, 17a ... Work roll 11b, 12b, 13b, 14b, 15b, 16b, 17b ... backup roll 21x, 21y, 22x, 22y, 23x, 23y ... spray header 22x'22y ', 24x, 24y ... spray header

Claims (8)

A hot finish rolling method for hot rolling a material to be rolled using a hot finish rolling mill having a plurality of finish rolling mills arranged continuously in the moving direction of the material to be rolled,
Among the plurality of finish rolling mills, a spray header that sprays medium-high pressure water immediately before at least one of the finish rolling mills arranged on the downstream side in the moving direction,
The material to be rolled is tilted from the spray header to the entry side of the finishing mill disposed immediately after the spray header from the vertical direction, and water is injected at an injection pressure of 1.5 MPa or more and 15 MPa or less. A hot finish rolling method, characterized by rolling The part where the water sprayed from the spray header collides with the material to be rolled is a roll bite of the finish rolling mill arranged immediately after the spray header, and a work roll of the finish rolling mill than the roll bite. 2. The hot finish rolling method according to claim 1, wherein rolling is performed while spraying water from the spray header so as to be between the upstream position in the moving direction by a radius. The hot finish rolling method according to claim 1, wherein a plurality of the spray headers are provided immediately before the finish rolling mill. The finish rolling mill has an injection pressure of 1.5 MPa or more and 10 MPa or less when spraying the water from the spray header, and the amount of water sprayed from the spray header to the material to be rolled is one. It is 100 L / min or more and 200 L / min or less per hit, The hot rolling finish rolling method of any one of Claims 1-3 characterized by the above-mentioned. A method for producing a hot-rolled steel sheet, comprising a step of finish-rolling a steel sheet using the hot-rolled finish rolling method according to any one of claims 1 to 4. A hot finish rolling mill having a plurality of finish rolling mills arranged continuously in the moving direction of the material to be rolled,
Among the plurality of finish rolling mills, a spray header that sprays medium-high pressure water immediately before at least one of the finish rolling mills arranged on the downstream side in the moving direction,
The spray header is arranged so that water is injected at an injection pressure of 1.5 MPa or more and 15 MPa or less by tilting toward the entry side of the finishing mill arranged immediately after the spray header from the vertical direction. A hot finish rolling mill characterized by comprising: The part where the water sprayed from the spray header collides with the material to be rolled is a roll bite of the finish rolling mill arranged immediately after the spray header, and a work roll of the finish rolling mill than the roll bite. The hot finish rolling mill according to claim 6, wherein the hot finish rolling mill is between the upstream side position in the moving direction by a radius. The hot finish rolling mill according to claim 6 or 7, comprising a plurality of the spray headers immediately before the finish rolling mill.

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