JP7342831B2 - Hot rolling mill and hot rolled steel sheet manufacturing method - Google Patents

Description

The present invention relates to a hot rolling mill that hot-rolls a material to be rolled, and a method for manufacturing hot rolled steel sheets, and particularly to a hot rolling mill and a hot rolling method that can suppress the occurrence of roll marks transferred to the surface of hot rolled steel sheets. This invention relates to a method for manufacturing steel plates.

Generally, in a hot rolling facility that manufactures hot rolled steel sheets, a hot rolling mill is used to roll a material to be rolled to manufacture hot rolled steel sheets. As this hot rolling mill, a 4Hi hot rolling mill, a 6Hi hot rolling mill, or the like is used. The 4Hi hot rolling mill includes a pair of upper and lower work rolls that roll a material to be rolled, and a pair of upper and lower backup rolls that support each work roll. In addition, the 6Hi hot rolling mill has a pair of upper and lower work rolls that roll the material to be rolled, a pair of upper and lower backup rolls that support each work roll, and a pair of upper and lower backup rolls that are arranged between each work roll and each backup roll. It is configured to include a pair of upper and lower intermediate rolls.

By the way, high quality is required of hot rolled steel sheets manufactured using this hot rolling mill, and in recent years, particularly high demands have been made on the surface quality of hot rolled steel sheets. For example, it is required to prevent the occurrence of minute convex defects called roll marks that are formed on the surface of hot rolled steel sheets.

These roll marks are caused by minute depressions occurring on the surface of the work roll, and when the material to be rolled is rolled with the work roll that has the depressions, minute protrusions are transferred to the surface of the hot rolled steel sheet. This is often caused by. The cause of minute dents on the surface of the work roll is thought to be that foreign matter gets in between the work roll and the backup roll or intermediate roll that comes into contact with the work roll, and that foreign matter creates minute dents on the surface of the work roll. It will be done.
When roll marks are transferred to the surface of a hot-rolled steel sheet, the rolls must be suddenly replaced and flaws must be removed, leading to problems such as a decrease in line operation rate and a decrease in roll consumption.

Conventionally, a six-high rolling mill shown in Patent Document 1, for example, has been proposed as a device for suppressing the occurrence of roll marks.
The 6-high rolling mill shown in Patent Document 1 is a rolling mill in which an intermediate roll configured to be movable in the axial direction is arranged between a work roll and a reinforcing roll, and the reinforcing roll has a surface hardness of the roll. HS60-80, intermediate roll HS82-90, and work roll HS90-97.

Further, as a rolling mill that suppresses the occurrence of roll marks and can obtain rolled materials of copper and copper alloys having excellent surface quality, a rolling mill disclosed in Patent Document 2, for example, is conventionally known.
The rolling mill shown in Patent Document 2 has a pair of upper and lower work rolls for rolling a material to be rolled made of copper or a copper alloy, and is equipped with at least one pair of rolls that support these work rolls. The work roll is a forged steel roll with a surface hardness of 95HS or more, and the intermediate roll or backup roll in contact with the work roll has a surface hardness lower than that of the work roll in the range of 25HS to 40HS. It is hardness.

Furthermore, as a method for preventing foreign matter from entering between a work roll and an intermediate roll or between a work roll and a backup roll during cold rolling, for example, a method for controlling the pressure of a cold rolling coolant disclosed in Patent Document 3 has been known. ing.
The pressure control method for cold rolling coolant shown in Patent Document 3 is such that during cold rolling by a continuous cold rolling mill, when a part with many defects passes through, a normal roll cooling and lubrication coolant or roll cooling coolant is used. This is a pressure control method for cold rolling coolant such as high-pressure coolant for both lubrication and foreign matter removal. In this pressure control method, the ejection pressure from the exit side of the work roll of the continuous cold rolling mill is increased to prevent foreign matter from entering between the work roll and the intermediate roll or between the work roll and the backup roll. There is.

Furthermore, as a method for preventing roll flaws in a rolling stand due to foreign objects flying in, a method for preventing defects caused by foreign objects flying into a rolling mill is known, for example, as disclosed in Patent Document 4.
In the method for preventing defects caused by foreign matter in a rolling mill disclosed in Patent Document 4, there is a contact area between a rolling roll and a backup roll of a rolling mill stand, a contact area between a rolling roll and an intermediate roll, a contact area between an intermediate roll and an intermediate roll, and an intermediate roll. A nozzle header is placed near the contact area between the roll and the backup roll, and the roll contact area is covered in the lengthwise direction of the body with a fluid film formed by spraying fluid. As a result, flying foreign matter is blocked by this fluid film, and thus is prevented from being caught between the rolls.

Japanese Unexamined Patent Publication No. 55-22421 Japanese Patent Application Publication No. 2009-113088 Patent No. 3266729 Japanese Patent Application Publication No. 2007-21544

However, the conventional six-high rolling mill shown in Patent Document 1, the rolling mill shown in Patent Document 2, the cold rolling coolant pressure control method shown in Patent Document 3, and the prevention of defects caused by foreign matter in the rolling mill shown in Patent Document 4 The method had the following problems.

That is, in the case of the six-high rolling mill shown in Patent Document 1, it is applied to cold rolling, and is not applied to hot rolling for manufacturing the hot-rolled steel sheet described above. Providing a hardness difference between the two rolls by making the hardness of the intermediate roll lower than that of the work roll, as in the six-high rolling mill shown in Patent Document 1, is effective in preventing flaws from occurring in the work roll. The principles of rolling cannot be directly applied to hot rolling. In other words, a hot rolling mill has a larger rolling load than a cold rolling mill. In addition, in hot rolling mills, the hardness of work rolls is determined by accident resistance (in hot rolling of thin sheets, there are many troubles such as drawing and sagging due to batch rolling of leading and trailing ends, and when problems occur, deep cracks in work rolls occur. (The hardness of work rolls in cold rolling mills is generally 90HS or higher, and the hardness of work rolls in hot rolling mills is generally 81HS to 84HS). For this reason, the technology of setting the surface hardness of the intermediate roll in a six-high rolling mill to HS82 to 90 and the surface hardness of the work roll to HS90 to 97, as shown in Patent Document 1, has been applied to the surface hardness of the intermediate roll in the hot rolling mill and the surface hardness of the work roll It cannot be directly applied to surface hardness. In a hot rolling mill, the rolling load is greater than in cold rolling, so if the surface hardness of the intermediate roll is set lower than the surface hardness of the work roll, there is a risk that the intermediate roll will be deformed.

Further, in the case of the rolling mill shown in Patent Document 2, the material to be rolled is a coil obtained by hot rolling, annealing, and cold rolling a lead frame material made of copper or a copper alloy. In the above-mentioned hot rolling, the rolling load is still larger than in the case of rolling a coil that has gone through this cold rolling, so the Shore hardness of the surface of the intermediate roll or backup roll in contact with the work roll is set to 25HS higher than that of the work roll. The technique disclosed in Patent Document 2, which aims to achieve a low hardness in the range of 40 HS or less, cannot be directly applied to a hot rolling mill.

Furthermore, in the case of the cold rolling coolant pressure control method disclosed in Patent Document 3, not only is it not applicable to the above-mentioned hot rolling, but also it is necessary to inject high-pressure coolant for removing foreign matter from the exit side of the work roll, and the foreign matter The equipment configuration for removal becomes complicated.
In addition, in the case of the method for preventing defects caused by foreign matter in a rolling mill disclosed in Patent Document 4, it is necessary to arrange a nozzle header that covers the roll contact area in the lengthwise direction of the roll with a fluid film formed by spraying fluid. The equipment configuration to prevent this becomes complicated.

Therefore, the present invention has been made to solve these conventional problems, and its purpose is to provide a hot rolling mill that can suppress the occurrence of roll marks transferred to the surface of hot rolled steel sheets with a simple equipment configuration. and to provide a method for manufacturing a hot rolled steel sheet.

In order to solve the above problems, a hot rolling mill according to one aspect of the present invention is a hot rolling mill that hot-rolls a material to be rolled, and includes a pair of upper and lower work rolls that roll the material to be rolled. and a rolling stand equipped with a pair of upper and lower backup rolls supporting each work roll, and a pair of upper and lower intermediate rolls disposed between each work roll and each backup roll, In a hot rolling mill configured to be able to shift each intermediate roll in the axial direction, the body length of each intermediate roll is made longer than the body length of each work roll, and the surface hardness of each intermediate roll is set relative to the surface hardness of each work roll. The gist is to have a low hardness of 10HS or more.

Further, a hot rolling mill according to another aspect of the present invention is a hot rolling mill that hot-rolls a material to be rolled, and includes a pair of upper and lower work rolls for rolling the material to be rolled, and each work roll. In a hot rolling mill, the hot rolling mill is equipped with a rolling stand equipped with a pair of upper and lower backup rolls that support the work rolls, and each of the pair of upper and lower work rolls can be shifted in the axial direction. The gist is to have a hardness that is 10HS or more lower than the hardness of the surface.

Moreover, the gist of a method for manufacturing a hot-rolled steel sheet according to another aspect of the present invention is to manufacture a hot-rolled steel sheet by rolling a material to be rolled using the above-mentioned hot rolling mill.

According to the hot rolling mill and the method for producing a hot rolled steel plate according to the present invention, the hot rolling mill and the production of the hot rolled steel plate can suppress the occurrence of roll marks transferred to the surface of the hot rolled steel plate with a simple equipment configuration. I can provide a method.

1 is a schematic configuration diagram of a hot rolling facility including a hot rolling mill according to a first embodiment of the present invention. The shift operation of the intermediate rolls in each rolling stand of the hot rolling mill shown in FIG. It is a schematic block diagram in a certain case. It is a schematic block diagram of the hot rolling equipment provided with the hot rolling mill based on 2nd Embodiment of this invention. The shift operation of the work rolls in each rolling stand of the hot rolling mill shown in Figure 3 is shown. (a) is a schematic configuration diagram when the work rolls are in the first state, and (b) is a schematic diagram when the work rolls are in the second state. It is a schematic block diagram in a certain case. It is a graph which compares and shows the ratio of the degree of a flaw in an example and a comparative example.

Embodiments of the present invention will be described below with reference to the drawings. The embodiments shown below illustrate devices and methods for embodying the technical idea of the present invention. It is not limited to the embodiments described below. Furthermore, the drawings are schematic. Therefore, it should be noted that the relationships, ratios, etc. between thickness and planar dimensions are different from those in reality, and the drawings also include portions where the relationships and ratios of dimensions are different.

(First embodiment)
FIG. 1 shows a schematic configuration of a hot rolling facility including a hot rolling mill according to a first embodiment of the present invention.
The hot rolling equipment 1 shown in FIG. 1 hot-rolls a steel plate (thin plate) S as a material to be rolled, and heats the steel plate S in a heating furnace (not shown), and then finish-rolls the rough-rolled steel plate S. The hot rolling mill (finishing rolling mill) 2 is equipped with a hot rolling mill (finishing mill) 2. The steel plate S rolled by the hot rolling mill 2 is cooled by a cooling facility (not shown) to produce a hot rolled steel plate.

The hot rolling mill 2 includes a plurality of (n units in this embodiment) rolling stands 2 ₁ to 2 _n extending from the upstream side to the downstream side in the conveyance direction of the steel plate S. Each of the rolling stands 2 ₁ to 2 _n is a 6Hi rolling mill, and includes a pair of upper and lower work rolls 3a for rolling the steel plate S, a pair of upper and lower backup rolls 3b that support each work roll 3a, and each work roll 3a. A pair of upper and lower intermediate rolls 3c are provided between each backup roll 3b.

In order to control the plate crown of the steel plate S as the material to be rolled, each intermediate roll 3c is shifted by a movement amount δ1 in the axial direction of each intermediate roll 3c, as shown in FIGS. 2(a) and 2(b). configured to be possible. In other words, each intermediate roll 3c is shifted in the axial direction by the amount of movement δ1 from the first state shown in FIG. 2(a) to the second state shown in FIG. 2(b), and It is possible to shift by an amount of movement δ1 in the axial direction from the second state to the first state shown in FIG. 2(a).
Here, the surface hardness of each work roll 3a for rolling the steel sheet S is preferably set to 75HS to 90HS, taking into account rolling conditions such as rolling load and roll tonnage, and accident resistance.

The surface hardness of each intermediate roll 3c will be explained next.
The surface hardness of the intermediate roll 3c that rotates in contact with each work roll 3a is set from the maximum contact stress between the work roll 3a and the intermediate roll 3c depending on rolling conditions such as rolling load and roll tonnage, and is determined to be the best roll unit consumption. It is desirable that the hardness is such that yield loss can be achieved.
On the other hand, the hot rolling mill 2 differs from the cold rolling mill shown in Patent Document 1 in that it rolls down the steel plate S under a high load, and may cause operational troubles due to excessive contact surface pressure between the work roll 3a and the intermediate roll 3c. In order to prevent this, the surface hardness of the intermediate roll 3c is generally set to be equal to or higher than the work roll 3a in many cases.

However, if the surface hardness of the intermediate roll 3c is equal to or higher than the surface hardness of the work roll 3a, when foreign matter enters between the work roll 3a and the intermediate roll 3c that contacts the work roll 3a, the foreign matter may Minute depressions may be formed on the surface of the work roll 3a. When a minute depression is formed on the surface of the work roll 3a, rolling the steel plate S with the work roll 3a with the depression causes minute convex portions to be transferred to the surface of the hot rolled steel plate, resulting in damage to the hot rolled steel plate. Roll marks will be formed on the surface.
Therefore, in the hot rolling mill 2 according to the present embodiment, the surface hardness of each intermediate roll 3c is set to be 10HS or more lower than the surface hardness of each work roll 3a.

On the other hand, if the surface hardness of each intermediate roll 3c is lower than the surface hardness of each work roll 3a, there is a risk that each intermediate roll 3c will be deformed because the rolling load is high.
Therefore, in the hot rolling mill 2 according to the present embodiment, by making the body length L3c of each intermediate roll 3c configured to be shiftable in the axial direction longer than the body length L3a of each work roll 3a, each intermediate roll 3c is made longer than the body length L3a of each work roll 3a. The contact length between the roll 3c and each work roll 3a is secured to be the same length as the body length L3a of the work roll 3a, and the contact surface pressure between the work roll 3a and the intermediate roll 3c is reduced, and the surface hardness of each intermediate roll 3c is can be lowered relative to the surface hardness of each work roll 3a.

As a result, it is possible to suppress the occurrence of roll marks that are transferred to the surface of the hot rolled steel sheet due to foreign matter being caught between the work roll 3a and the intermediate roll 3c, and it is possible to improve the yield rate of the hot rolled steel sheet. By reducing the number of abnormal recombinations of the rolls 3a, it is possible to reduce operational losses.
In addition, there is no need to inject high-pressure coolant for removing foreign objects from the exit side of the work roll as in Patent Document 3, and there is no need to arrange a nozzle header to prevent foreign objects from getting caught as in Patent Document 4. Therefore, the occurrence of roll marks transferred to the surface of hot rolled steel sheets can be suppressed with a simple equipment configuration.

Here, if the surface hardness of each intermediate roll 3c is set to be 10HS or more lower than the surface hardness of each work roll 3a, the roll flaw occurrence rate in the hot rolled steel sheet will be 0.6%, compared to the case where this is not the case. Roll flaw occurrence rate decreases by 0.4%.
Further, the surface hardness of each intermediate roll 3c is more preferably 15HS or more lower than the surface hardness of each work roll 3a. As a result, the roll flaw occurrence rate in the hot rolled steel sheet is further reduced to 0.4%.

On the other hand, the lower limit of the surface hardness of each intermediate roll 3c is preferably 25HS lower hardness than the surface hardness of each work roll 3a, and is preferably 60HS in absolute value. If the surface hardness of each intermediate roll 3c is lower than this, it may cause seizure, excessive wear, and spalling due to excessive contact surface pressure between the intermediate roll 3c and the work roll 3a, and increase roll cost. invite
The surface hardness of each intermediate roll 3c is adjusted by appropriately setting quenching conditions and annealing conditions during roll manufacture. In addition, when designing the hardness of each intermediate roll 3c, the most effect can be obtained by taking into account the reduction in hardness from the effective diameter of the roll in use, and setting the discarded diameter within a range that does not fall below the lower limit of hardness for use.

Further, the trunk length L3c of each intermediate roll 3c is determined when each intermediate roll 3c shifts by a movement amount δ1 in the axial direction from the first state to the second state and from the second state to the first state. In either state, the length of contact between each intermediate roll 3c and each work roll 3a is set to be the same length as the trunk length L3a of the work roll 3a.

(Second embodiment)
Next, hot rolling according to a second embodiment of the present invention will be described with reference to FIGS. 3 and 4. FIG. 3 shows a schematic configuration of a hot rolling facility equipped with a hot rolling mill according to a second embodiment of the present invention. FIG. 4 shows a shift operation of work rolls in each rolling stand of the hot rolling mill shown in FIG. 3.
Similar to the hot rolling mill 2 shown in FIG. 1, the hot rolling equipment 11 shown in FIG. 3 hot-rolls a steel plate (thin plate) S as a material to be rolled. The hot rolling mill (finishing mill) 12 is provided to finish-roll the steel sheet S that has been heated and roughly rolled. The steel plate S rolled by the hot rolling mill 12 is cooled by a cooling facility (not shown) to produce a hot rolled steel plate.

The hot rolling mill 12 includes a plurality of (n units in this embodiment) rolling stands 12 ₁ to 12 _n extending from the upstream side to the downstream side in the conveyance direction of the steel plate S. Each of the rolling stands 12 ₁ to 12 _n is different from the rolling stands 2 ₁ to 2 _n of the hot rolling mill 2 shown in FIG. It is composed of a pair of upper and lower backup rolls 13b that support each work roll 13a.

In order to control the plate crown of the steel plate S as the material to be rolled, each work roll 13a is shifted by a movement amount δ2 in the axial direction of each work roll 13a, as shown in FIGS. 4(a) and 4(b). configured to be possible. In other words, each work roll 13a shifts in the axial direction by a movement amount δ2 from the first state shown in FIG. 4(a) to the second state shown in FIG. 4(b), and also shifts from the first state shown in FIG. It is possible to shift by a movement amount δ2 in the axial direction from the second state to the first state shown in FIG. 4(a).
Here, the surface hardness of each work roll 3a for rolling the steel plate S is preferably set to 75HS to 85HS, taking into account rolling conditions such as rolling load and roll tonnage, and accident resistance.

The surface hardness of each backup roll 13b will be described next.
The surface hardness of the backup roll 13bb that rotates in contact with each work roll 13a is set from the maximum contact stress between the work roll 13a and the backup roll 13b depending on rolling conditions such as rolling load and roll tonnage, and is determined to be the best roll unit consumption. It is desirable that the hardness is such that yield loss can be achieved.
On the other hand, as mentioned above, unlike the cold rolling mill, the hot rolling mill 12 rolls down the steel plate S under a high load, and prevents operational troubles due to excessive contact surface pressure between the work roll 13a and the backup roll 13b. Therefore, the surface hardness of the backup roll 13b is generally set to be equal to or higher than the work roll 13a in many cases.

However, if the surface hardness of the backup roll 13b is equal to or higher than the surface hardness of the work roll 13a, when foreign matter gets between the work roll 13a and the backup roll 13b that contacts the work roll 13a, the foreign matter Minute depressions may be formed on the surface of the work roll 13a. When a minute depression is formed on the surface of the work roll 13a, by rolling the steel plate S with the work roll 13a where the depression has occurred, minute convex portions are transferred to the surface of the hot-rolled steel plate, and the hot-rolled steel plate is Roll marks will be formed on the surface.
Therefore, in the hot rolling mill 2 according to the present embodiment, the surface hardness of each backup roll 13b is set to be 10HS or more lower than the surface hardness of each work roll 13a.

On the other hand, if the surface hardness of each backup roll 13b is lower than that of each work roll 13a, there is a risk that each backup roll 13b may be deformed because the rolling load is high.
Here, the amount of movement (shift amount) δ2 of each work roll 13a shown in FIGS. 4(a) and (b) is the amount of movement of each work roll 3a of the 6Hi rolling mill shown in FIGS. 2(a) and (b). (Shift amount) It is set smaller than δ1. Therefore, even if the trunk length L13a of each work roll 13a configured to be shiftable in the axial direction is made almost the same as the trunk length L13b of each backup roll 13b, the contact length between each backup roll 13b and each work roll 13a From the first state shown in FIG. 4(a) to the second state shown in FIG. 4(b), approximately the same length as the trunk length L13b of the backup roll 13b can be secured. This makes it possible to reduce the contact surface pressure between the work roll 13a and the backup roll 13b, and to lower the surface hardness of each backup roll 13b relative to the surface hardness of each work roll 13a.

As a result, it is possible to suppress the occurrence of roll marks that are transferred to the surface of the hot rolled steel sheet due to foreign matter being caught between the work roll 13a and the backup roll 13b, and it is possible to improve the yield rate of the hot rolled steel sheet. By reducing the number of abnormal recombinations of the rolls 13a, it is possible to reduce operational losses.
On the other hand, the lower limit of the surface hardness of each backup roll 13b is preferably 25HS lower than the surface hardness of each work roll 13a, and is preferably 60HS in absolute value. If the surface hardness of each backup roll 13b is lower than this, it may cause seizure or excessive wear due to excessive contact surface pressure between the backup roll 13b and the work roll 13a, leading to an increase in roll cost.

Although the embodiments of the present invention have been described above, the present invention is not limited thereto, and various changes and improvements can be made.
For example, the hot rolling mill 2 according to the first embodiment includes a plurality of rolling stands 2 ₁ to 2 _n , and the hot rolling mill 12 according to the second embodiment includes a plurality of rolling stands 12 ₁ to 12 _n . , the number of stands may be one each.

In the hot rolling mill 2 having a 6Hi rolling stand (7 rolling stands) shown in FIG. 1, in the embodiment, the work roll 3a has a surface hardness of 82HS, and the intermediate roll 3c rotates in contact with the work roll 3a. Rolling was performed by setting the surface hardness of 72HS and the difference in surface hardness between the work roll 3a and the intermediate roll 3c to 10HS. The surface hardness of each of the work roll 3a and the intermediate roll 3c is measured by Shore hardness at five points equally spaced along the length of the body on each surface of the work roll 3a and the intermediate roll 3c, and the average value is measured. value. As a result, the incidence of convex roll marks on the surface of the hot rolled steel sheet was reduced by 40% compared to a comparative example in which there was no difference in surface hardness between the work roll 3a and the intermediate roll 3c. In addition, as a result of rolling under various conditions in which the surface hardness of the work roll 3a and the surface hardness of the intermediate roll 3c are respectively changed, the surface hardness of the intermediate roll 3c is lower than the surface hardness of the work roll 3a by 10HS or more. When the roll flaw occurrence rate is 0.6% or less and the surface hardness of the intermediate roll 3c is 15HS or more lower than the surface hardness of the work roll 3a, the roll flaw occurrence rate is confirmed to be 0.4% or less. did.

Furthermore, in the example, even when roll marks were generated, the degree of convex flaws transferred to the surface of the steel plate was reduced (see FIG. 5). That is, when comparing the case of a comparative example in which there is no difference in surface hardness between the work roll 3a and the intermediate roll 3c and the case of an example in which the surface hardness difference is 10HS, it is found that by setting the surface hardness difference to 10HS, the steel plate surface There were no A grade flaws with a convex flaw height higher than 50 μm and 80 μm or less, and the C grade flaws with a convex flaw height of 30 μm or less became dominant (see FIG. 5).

Further, in the embodiment, the trunk length L3c of the intermediate roll 3c is longer than the trunk length L3a of the work roll 3a, and the intermediate roll 3c changes from the first state to the second state and from the second state to the first state. In any state when the intermediate roll 3c and the work roll 3a are shifted by the amount of movement δ1 in the axial direction (see FIGS. 2(a) and (b)), the contact length between the intermediate roll 3c and the work roll 3a is equal to the body length of the work roll 3a. The length was set so that the same length as L3a can be secured. There were no defects such as minute cracks or chipping on the surface of the intermediate roll 3c after use, and sufficient performance was achieved in terms of plate crown for the amount of roll used.

Further, the results of rolling in a hot rolling mill 12 having 4Hi rolling stands 12 ₁ to 12 _n shown in FIG. If the surface hardness of the backup roll 13b is lower than the surface hardness of the work roll 13a by 10HS or more, the roll flaw occurrence rate will be reduced by 40%, and the surface hardness of the backup roll 13b will be lower than the surface hardness of the work roll 13a. It was confirmed that when the hardness was lowered to 15HS or more, the roll flaw occurrence rate was reduced by 60%.

1 hot rolling equipment 2 hot rolling mill 2 ₁ ~ 2 _n rolling stand 3a work roll 3b backup roll 3c intermediate roll 11 hot rolling equipment 12 hot rolling mill 12 ₁ ~ 12 _n rolling stand 13a work roll 13b backup roll S Steel plate (rolled material)

Claims (5)

A hot rolling mill for hot rolling a material to be rolled, comprising: a pair of upper and lower work rolls for rolling the material to be rolled; a pair of upper and lower backup rolls supporting each work roll; each work roll and each backup. A hot rolling mill comprising a rolling stand equipped with a pair of upper and lower intermediate rolls disposed between the rolls, and each of the pair of upper and lower intermediate rolls configured to be shiftable in the axial direction,
The body length of each intermediate roll is longer than the body length of each work roll, and the surface hardness of each intermediate roll is 10HS or more lower than the surface hardness of each work roll,
The body length of each intermediate roll is determined by the state in which each intermediate roll shifts in the axial direction from the shift start state to the shift end state, or when each intermediate roll shifts in the axial direction from the shift end state to the shift start state. Even if the contact length between each intermediate roll and each work roll is the same as the body length of the work roll, the contact surface pressure between the work roll and the intermediate roll can be reduced, and the contact length between each intermediate roll and each intermediate roll can be reduced. A hot rolling mill characterized in that the surface hardness can be lowered relative to the surface hardness of each work roll . 2. The hot rolling mill according to claim 1, wherein the surface hardness of each intermediate roll is 15HS or more lower than the surface hardness of each work roll. The hot rolling mill according to claim 1 or 2, wherein each work roll has a surface hardness of 75HS to 90HS. A hot rolling mill for hot rolling a material to be rolled, comprising a rolling stand having a pair of upper and lower work rolls for rolling the material to be rolled, and a pair of upper and lower backup rolls for supporting each work roll. , in a hot rolling mill in which each of the pair of upper and lower work rolls is configured to be shiftable in the axial direction,
The surface hardness of each backup roll is 10HS or more lower than the surface hardness of each work roll,
The body length of each work roll can be adjusted to any state when each work roll shifts in the axial direction from the shift start state to the shift end state, or when each work roll shifts in the axial direction from the shift end state to the shift start state. Even if the contact length between each backup roll and each work roll is the same as the body length of the backup roll , the contact pressure between the work roll and the backup roll can be reduced, and the contact length between each backup roll can be reduced. A hot rolling mill characterized in that the surface hardness can be lowered relative to the surface hardness of each work roll . A method for manufacturing a hot-rolled steel sheet, comprising rolling a material to be rolled using the hot rolling mill according to any one of claims 1 to 4 to manufacture a hot-rolled steel sheet.

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