JP5828306B2 - Manufacturing method of hot-rolled steel sheet - Google Patents

Description

  The present invention relates to a method for manufacturing a hot-rolled steel sheet, and more particularly, to a method for manufacturing a hot-rolled steel sheet that is hot-rolled at a high reduction rate while being lubricated.

  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, the structure of the steel material is refined. It is effective. Therefore, many methods for obtaining a steel material having a fine structure have been sought. Further, according to the refinement of the structure, it is possible to produce a high-strength hot-rolled steel sheet having excellent mechanical properties even if the amount of alloy element added is reduced.

  As a method for refining the structure, particularly in the latter stage of hot finish rolling, rolling is performed at a high reduction rate to refine the austenite grains and accumulate rolling strain in the steel sheet to refine the ferrite grains obtained after rolling. It is known to plan.

  Therefore, the rolling reduction of the rear stand in the hot finish rolling mill row (the rolling mill of the stand located downstream from the half of the conveyance direction of the material to be rolled) is set as the rolling reduction of the preceding stand (the conveyance direction of the material to be rolled). Rolling with a rolling reduction higher than a predetermined value (hereinafter, sometimes referred to as “high pressure rolling”), such as finish rolling with a rolling reduction higher than the rolling reduction of a stand located on the upstream side of the half). Do. This makes it possible to manufacture a steel sheet having a fine structure.

  However, in rolling under high pressure, the rolling load becomes extremely high, and problems such as the load exceeding the equipment limit of the rolling mill are likely to occur. On the other hand, the load concerning a rolling mill can be reduced by rolling, supplying a lubricant to the work roll with which a rolling mill is equipped. However, in a work roll that is set to perform rolling under high pressure and supplied with a lubricant, the leading end portion of the material to be rolled (hereinafter sometimes simply referred to as “leading end portion”) slips. There was a risk of rolling troubles that could not enter between the work rolls, resulting in so-called biting failure and inability to start rolling.

In order to prevent such a biting failure, for example, Patent Document 1 discloses a technique for preventing slipping by spraying the work oil directly on the work roll while suppressing the amount of lubricating oil to a necessary minimum amount.
Patent Document 2 discloses a technique for preventing a slip by using a high frictional force due to a grease lubricant having a high friction.
Furthermore, Patent Document 3 discloses a technique for preventing slip by obtaining a high frictional force using a high friction solid lubricant such as mica.

JP 2003-94104 A JP 2003-193079 A Japanese Patent Application Laid-Open No. 6-234989

However, according to the technique disclosed in Patent Document 1, since the lubrication effect of the tip portion is reduced, the biting can be surely carried out. I can't get it. Therefore, the tip portion could not be rolled under high pressure.
Further, according to the techniques disclosed in Patent Document 2 and Patent Document 3, although biting is possible, a load reducing effect is obtained over the entire rolling length from the front end to the rear end because the frictional force is high. There is a problem that rolling under high pressure is difficult.

  In addition, if the equipment specifications are increased in size, it can withstand rolling with a high load, but the cost increases due to the increase in the size of the equipment.

  Therefore, in the present invention, even when performing rolling under high pressure, the load is prevented while preventing the slip at the time of biting the tip part and ensuring the biting property of the tip part so that the equipment cost does not become excessive. It is an object to provide a method for producing a hot-rolled steel sheet that can be reduced.

  The present invention will be described below.

  As a result of diligent research, the inventor of the present invention uses a work roll made of a high alloy grain, which is usually used in a rolling mill at a subsequent stage of a hot finishing rolling mill row, to produce a synthetic ester having a high rolling load reduction effect. When the lubricant containing the lubricant or the oil-soluble Ca compound is supplied and the surface roughness of the work roll is polished so as to be in a predetermined range, the tip of the material to be rolled is used when performing high-pressure rolling. The present invention was completed based on the knowledge that even if the lubricant was supplied before the part was bitten, rolling was possible without causing slippage at the time of biting. The present invention will be described below.

  The invention according to claim 1 is a rolling mill arranged in a subsequent stage of the hot finish rolling mill row, the diameter of the work roll of the rolling mill, the opening, and the end of the material to be rolled immediately before entering the rolling mill When rolling under high pressure where the contact angle calculated from the plate thickness is 9 degrees or more, high alloy grain is used as the work roll material, and the surface roughness of the work roll is set to 1.0 μm to 1.5 μm in terms of Ra. A method for producing a hot-rolled steel sheet, wherein rolling is performed by supplying a predetermined amount or more of a lubricant containing a synthetic ester or an oil-soluble Ca compound to the work roll surface from before the start of rolling to after the end of rolling. .

  Invention of Claim 2 is a rolling mill arrange | positioned in the back | latter stage of a hot finishing rolling mill row | line | column, the diameter of a work roll of this rolling mill, an opening degree, and the edge part of the to-be-rolled material just before entering a rolling mill When performing high-pressure rolling under which the contact angle calculated from the plate thickness is 8.5 degrees or more and less than 9 degrees, high alloy grain is used as the work roll material, and the surface roughness of the work roll is 0.5 μm or more in terms of Ra. A hot-rolled steel sheet that is 1.5 μm or less and performs rolling by supplying a predetermined amount or more of a lubricant containing a synthetic ester or a lubricant containing an oil-soluble Ca compound to the work roll surface from before the start of rolling to after the end of rolling. It is a manufacturing method.

  Invention of Claim 3 is the manufacturing method of the hot-rolled steel sheet of Claim 1, When the surface roughness of a work roll is measured before rolling start and Ra is smaller than 1.0 micrometer, The surface roughness is adjusted to 1.0 μm or more.

  Invention of Claim 4 is the manufacturing method of the hot-rolled steel sheet of Claim 2, When the surface roughness of a work roll is measured before rolling start and Ra is smaller than 0.5 micrometer, The surface roughness is adjusted to 0.5 μm or more.

The invention according to claim 5 is the method for producing a hot-rolled steel sheet according to claim 3 or 4, in which the surface roughness of the work roll is adjusted before high-pressure rolling of a plurality of materials to be rolled. The normal rolling is performed under conditions where the contact angle is smaller than under rolling.

  According to the present invention, high-pressure rolling can be performed by a rolling mill subsequent to the finish rolling mill while securing biting performance and maintaining operational stability. Therefore, it is not always necessary to increase the size of the equipment, and existing equipment can be used.

It is the figure which showed typically a part of manufacturing apparatus of the hot-rolled steel plate used for the manufacturing method of the hot-rolled steel plate concerning one embodiment. It is the figure expanded paying attention to the rolling mill of the last stand among FIG. It is a figure explaining calculation of a contact angle.

  The above-mentioned operation and gain of the present invention will be clarified from the following embodiments for carrying out the invention. However, the present invention is not limited to these embodiments.

Before describing the method for producing a hot-rolled steel sheet according to one embodiment, an example of a hot-rolled steel sheet production apparatus used in the method for producing a hot-rolled steel sheet will be described. FIG. 1 is a diagram schematically showing a part of a hot-rolled steel sheet manufacturing apparatus 10 used in a method for manufacturing a hot-rolled steel sheet. In FIG. 1, a steel sheet 1 as a material to be rolled is conveyed from the left side (upstream side, upper process side) to the right side (downstream side, lower process side) of the paper surface, and the vertical direction is the vertical direction of the paper surface. The direction from the upstream side (upper process side) to the downstream side (lower process side) may be referred to as the passing plate direction, and the direction of the width of the steel plate to be passed in the direction perpendicular to this is the plate width direction. May be described.
FIG. 2 is a view of FIG. 1 focusing on the rolling mill 11g of the final stand.

  As shown in FIG. 1, a hot rolled steel sheet manufacturing apparatus 10 includes a hot finish rolling mill row 11, a cooling device 12, and a winding device 13. Although illustration and explanation are omitted, a heating furnace, a rough rolling mill row, and the like are arranged upstream from the hot finish rolling mill row 11 to adjust the conditions of the steel sheet for entering the hot finish rolling mill row 11. ing.

  In the hot finish rolling mill row 11 in this embodiment, as can be seen from FIG. 1, seven rolling mills 11a,... 11f, 11g are arranged in parallel along the sheet passing direction. Each of the rolling mills 11a, ... 11f, 11g is a rolling mill included in so-called stands.

  The rolling mills 11a,..., 11f, 11g of each stand are in contact with a pair of work rolls 11aw, 11aw,. Have a pair of backup rolls 11ab, 11ab,..., 11fb, 11fb, 11gb, 11gb. Further, the rolling mill includes a housing (not shown) that includes a work roll and a backup roll inside, forms an outer shell of the rolling mill, and supports the work roll and the backup roll.

Each rolling mill 11a,... 11f, 11g is set with rolling conditions such as rolling reduction so as to satisfy conditions such as the thickness, mechanical properties, and surface properties of the steel sheet required in the final product. .
In the manufacturing apparatus 10, from the viewpoint of refining the austenite grains by performing high-pressure rolling and accumulating rolling strain in the steel sheet and refining the ferrite grains obtained after rolling, In the embodiment, it is set to perform rolling under high pressure with at least one rolling mill of rolling mills 11e, 11f, 11g).
Here, high-pressure rolling means that the contact angle θ is 8.5 degrees or more. The contact angle θ can be obtained as follows. FIG. 3 shows an explanatory diagram. The contact angle θ is the lower side of the upper work roll facing the lower dead center A and the lower dead center A of the rotation direction angles of the work roll around the rotation axes 0, 0 ′ of the work roll. Means the angle between the top dead center A ′ of the work roll and the points T and T ′ where the material to be rolled first contacts the work roll. Here, assuming that the upper and lower work rolls are symmetrical with respect to the thickness direction center line of the material to be rolled as indicated by the alternate long and short dash line, and considering only the upper work roll, the contact angle θ is as shown in FIG. Using the symbols r and a in the middle
θ = cos ⁻¹ (a / r) (1)
Is required.

  Here, r is the radius of the upper work roll. On the other hand, a can be calculated as follows.

If the distance between the point A and the point A ′ is the opening degree s and the tip end plate thickness of the material to be rolled is H, the size represented by b in FIG.
b = (H−s) / 2 (2)
It is. Also, r is the radius of the work roll between OA. Therefore a is
a = r−b = r− (H−s) / 2 (3)
Is required.

Substituting equation (3) into equation (1) and organizing it,
θ = cos ⁻¹ (1− (H−s) / (2 · r)) (4)
Get. If the diameter of the work roll is D,
θ = cos ⁻¹ (1- (H−s) / D) (5)
It is.

That is, the contact angle θ can be calculated from the radius r (or diameter D) of the work roll, the opening s between the upper and lower work rolls, and the tip end plate thickness H of the material to be rolled. As described above, in the present invention, at least one of the subsequent rolling mills in the finish rolling mill row is set to perform high-pressure rolling with a contact angle θ of 8.5 degrees or more. Here, if θ is large, the rolling reduction becomes large. And it is preferable that the last rolling mill 11g is contained in the rolling mill used as such high pressure rolling.
This is because, when cooling is performed by the cooling device 12 or another quenching device on the downstream side of the final rolling mill 11g, the ferrite transformation during cooling is induced as the rolling reduction of the rolling mill 11g of the final stand increases. It is.

  In this embodiment, the work rolls 11gw and 11gw of the final rolling mill 11g, which are work rolls of a rolling mill in which high-pressure rolling is performed, are formed of high alloy grain. Known high alloy grains can be used. Moreover, it is possible to apply a work roll having a normal diameter. It is not always necessary to prepare a special work roll whose diameter is changed for rolling under high pressure.

The surface of the work roll 11gw that performs rolling under high pressure, that is, the surface of the high alloy grain has a predetermined roughness. Specifically, it is as follows.
When the contact angle θ is 8.5 degrees or more and less than 9.0 degrees, the surface of the high alloy grain has a roughness Ra in the range of 0.5 μm to 1.5 μm. Here, Ra of the surface roughness means arithmetic average roughness, and is as per JIS B 0601-2001.
On the other hand, when the contact angle θ is 9.0 degrees or more, the surface of the high alloy grain has a roughness Ra in the range of 1.0 μm to 1.5 μm.

Usually, a high-alloy glen roll is often used for the work roll of the subsequent stage of the hot finish rolling mill row in order to ensure the surface properties of the rolled material. In order to ensure the surface properties, the surface is often polished with Ra to about 0.3 μm.
On the other hand, in this invention, it grind | polishes so that the surface roughness after grinding | polishing of a work roll may be 0.5 micrometer or more or 1.0 micrometer or more by Ra by the conditions of contact angle (theta). This is because when Ra is smaller than the above value, there is a high possibility that a problem of biting will occur when rolling under high pressure.
The upper limit of Ra was 1.5 μm. When Ra becomes larger than this and Ra becomes about 2.0 micrometers, there exists a possibility of impairing the surface property of a to-be-rolled material, such as a grinding roll of a work roll being transcribe | transferred on the surface of a to-be-rolled material. Therefore, if it is this range, the surface property of the steel plate as a product will be ensured.

  As the backup roll 11gb, a normal roll, that is, a roll having a diameter of about 1200 mm to 1650 mm can be applied. However, when the elastic modulus in the vicinity of the surface of the work roll 11gw is increased, the Hertz pressure acting on the portion where the work roll and the backup roll come into contact with each other increases. From the viewpoint of reducing the Hertz pressure, it is advantageous that the diameter of the backup roll is large, and the diameter of the backup roll is preferably 1350 mm or more.

Further, as shown in FIG. 2, a lubricant supply device for supplying a lubricant to the work roll 11gw and the backup roll 11gb in a stand having at least a high-pressure rolling mill in the hot finish rolling mill row 11 21 (in this embodiment, the lubricant is directly supplied to the work roll 11gw). A known device can be used as the lubricant supply device 21.
On the other hand, the supplied lubricant is a lubricant having a high effect of reducing the rolling load in the hot finish rolling mill, and specifically includes a lubricant containing a synthetic ester and a lubricant containing an oil-soluble Ca compound. (For example, Ca sulfonate, Ca phenate, Ca salicylate).

  A well-known thing can be used for the cooling device 12 and the winding device 13.

  Next, the manufacturing method of the hot-rolled steel sheet concerning one embodiment is demonstrated. In this embodiment, a hot-rolled steel sheet is manufactured as follows, for example. Here, although the case where the said manufacturing apparatus 10 is used is demonstrated as an example, it does not necessarily need to be based on the manufacturing apparatus 10, and may be based on another apparatus.

The rough bar extracted from the heating furnace and rolled to a predetermined thickness by the rough rolling mill is continuously rolled to the predetermined thickness by the hot finish rolling mill row 11 while the temperature is controlled.
Here, in the rolling mill 11g of the final stand that performs high pressure rolling in the hot finish rolling mill row 11, as described above, the contact angle θ is 8.5 degrees or more with the work roll 11gw formed of high alloy grain. It may be rolled to become. At this time, when the contact angle θ is 8.5 degrees or more and less than 9.0 degrees, the surface roughness of the work roll is set within a range of 0.5 μm or more and 1.5 μm or less in terms of Ra.
On the other hand, when the contact angle θ is 9.0 degrees or more, the surface roughness of the work roll is set within a range of 1.0 μm or more and 1.5 μm or less in terms of Ra.

Furthermore, at the time of rolling, the lubricant is supplied so that the lubricant adheres to the surface of the work roll 11gw until the tip of the steel plate 1 as the material to be rolled comes into contact with the work roll 11gw. The lubricant may be supplied directly to the work roll 11gw, or the lubricant supplied to the backup roll 11gb may be transmitted to the work roll 11gw.
The supplied lubricant is a lubricant having a high effect of reducing the rolling load in the hot finish rolling mill and improving the surface properties. Specifically, the lubricant includes a synthetic ester, and an oil-soluble Ca. A lubricant containing a compound (for example, Ca sulfonate, Ca phenate, Ca salicylate).
The amount of lubricant supplied is sufficient to reduce the load to a load that the rolling mill can tolerate in high-pressure rolling. Specifically, a lubricant stock solution of about 50 cc / min to 500 cc / min is mixed with 20 to 200 times carrier water and sprayed onto a work roll or a backup roll for each target rolling stand. It is common.
The lubricant is supplied until the rolling of the rear end of the steel plate is completed.

In the present invention, in a rolling mill that performs high-pressure rolling, high alloy grain is used for the work roll, the surface roughness is set within the predetermined range as described above, and the load is lowered to a load that the rolling mill can tolerate. Supply an amount of lubricant that can.
Thereby, sufficient lubricant is supplied from the front end to the rear end of the steel sheet, and high-pressure rolling can be performed over the entire length. Further, since the work roll surface has an appropriate roughness, it is possible to prevent biting defects and to ensure proper steel sheet surface properties.
That is, high-pressure rolling can be performed from the front end to the rear end of the steel sheet without increasing the size of the rolling mill, and the problem of biting can be solved at the same time. In spite of such high-pressure rolling, since the biting property is excellent, it is possible to operate without impairing the production stability.

  The steel plate 1 exiting the hot finish rolling mill row 11 is cooled by the cooling device 12 and taken up by the winding device 13.

  Although the manufacturing method of the hot-rolled steel sheet described above is an example in which high-pressure rolling is applied only to the final rolling mill 11g of the hot finish rolling mill row 11, it is not limited to this, and hot finishing is performed. The above-described high-pressure rolling may be applied to at least one rolling mill in the subsequent stage of the rolling mill row.

  Furthermore, the manufacturing method of this embodiment may comprise the following steps from the viewpoint of maintaining the surface roughness of the work roll in an appropriate range. This will be described below.

The inventors have continuously rolled a plurality of steel plates using a lubricant when the surface roughness of the work roll is about 1.5 μm in Ra (regardless of normal rolling or high pressure rolling). It has been found that the surface roughness of the work roll is reduced and Ra is smaller than 0.5 μm. If Ra is smaller than 0.5 μm, there is a possibility that a biting failure may occur during high-pressure rolling.
Therefore, the surface roughness of the work roll 11gw is measured by the work roll surface roughness measuring device 22 shown in FIG. 2 before rolling. The work roll surface roughness measuring device 22 can apply a known roughness measuring means used in such a hot rolling mill.
And when the biting defect of the front-end | tip part of the steel plate 1 is estimated, the work roll surface roughness adjusting means 23 shown in FIG. 2 is used so that the surface of the work roll 11gw is roughened to be within the above range. You may provide the process of adjusting the surface roughness of the work roll 11gw using.
As the work roll surface roughness adjusting means 23, a polishing apparatus capable of polishing the work roll 11gw in-line can be used. For example, in this case, a grinding wheel having a Ra target of 1.0 μm to 1.5 μm is used. And after adjusting the work roll 11gw to the surface roughness in the above-mentioned range, high-pressure rolling is started.

Moreover, the following matters can be mentioned as a work roll surface roughness adjusting means of another example.
When lubricated rolling is performed as described above, the surface roughness of the work roll may decrease as the number of rolling increases. On the other hand, when the inventor performs rolling without lubrication, the surface roughness of the work roll increases as the number of rolling increases, and when several coils are rolled, Ra may exceed 1.5 μm. I found out.

Therefore, when performing high-pressure rolling of a plurality of steel plates, in order to adjust the surface roughness of the work roll, a schedule for continuously performing high-pressure rolling is not used, and at least one material to be rolled is used in the meantime. A schedule for rolling (normal rolling) under rolling conditions. Here, normal rolling means rolling under conditions where the contact angle is smaller than that of the above-described high-pressure rolling.
And when performing normal rolling, the presence or absence of lubrication is determined so that it may become the surface roughness of the work roll required for the following high pressure rolling. That is, when the surface roughness of the work roll is smaller than the above-mentioned specified range, normal lubrication rolling is performed to increase the surface roughness of the work roll and adjust it to the specified range. On the other hand, when the surface roughness of the work roll is larger than the above-mentioned specified range, normal rolling for lubrication is performed to reduce the surface roughness of the work roll and adjust it to the specified range. Further, when the surface roughness of the work roll is already in the predetermined range, the surface roughness of the work roll is maintained by switching between lubrication and non-lubrication during normal rolling.

  In this way, the surface roughness of the work roll is adjusted by assembling a schedule in which normal rolling is performed during high-pressure rolling of a plurality of steel plates, and selecting lubrication or non-lubrication of the normal rolling as necessary. This is also a means for adjusting the surface roughness of the work roll.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to this.

  In Examples, the surface roughness Ra of the work roll surface, the type of lubricant, the thickness of the steel sheet on the rolling mill entrance side, the opening degree of the work roll, and the contact angle were changed to evaluate the biting and the surface properties of the steel sheet. . Each condition is shown in Table 1.

For rolling, a steel sheet was hot-rolled at a temperature of about 900 ° C. using a quadruple rolling mill equipped with a pair of work rolls (diameter: 550 mm) and a pair of backup rolls (diameter: 1300 mm).
The steel plate before rolling was 0.15% carbon steel having a width of about 500 mm and a length of about 1000 mm, and was conveyed at a speed of about 300 m / min by a roller table. The work roll peripheral speed of the rolling mill was set to 300 m / min.
The material of the work roll was high alloy glen.

Two types of lubricants, including a synthetic ester-containing lubricant and an oil-soluble Ca compound, were used, and the stock solution was brushed on the surface of the work roll before each rolling in order to ensure a sufficient supply amount for reducing the load.
The contact angle was determined from the above formula (5).

  The determination of biting was defined as “X” when the tip of the steel sheet slipped and could not be rolled, and “◯” when biting was completed. Moreover, about the steel plate which could be rolled, the surface property regarding roughness was evaluated especially by observing the steel plate surface after rolling. The workpiece rolls were transferred to the material and the surface was rough and streaked was marked with “x”, and the surface with good surface properties was marked with “◯”. In addition, since it was not possible to judge the surface properties of those that could not be bitten, they were indicated by “−”. The results are also shown in Table 1.

  When the surface roughness after polishing of the work roll is 1.0 μm or more, rolling under high pressure is such that the contact angle is 9 degrees or more and 10 degrees or less without causing slippage at all conditions. Was possible. In that case, when the surface roughness of the work roll was Ra of 2.0 μm, the surface properties deteriorated.

  No. with a contact angle of 9 degrees. 9, no. 28, no. 13, no. As for No. 32, the surface roughness of the work roll is 0.5 μm in Ra. 9, no. In the case of 28, slip occurred and biting was not possible. On the other hand, the surface roughness of the work roll is 1.0 μm in Ra. 13 or No. In No. 32, no slip is generated, and it is shown that the biting property is improved by increasing the surface roughness of the work roll even if lubrication rolling is performed.

  No. 2, no. In the example of No. 8, the contact angle is in the range of 8.5 degrees or more and less than 9 degrees. 2 and No. 8 and No. 8, no. When the surface roughness Ra is 0.3 μm, slip occurs when the surface roughness is 0.3 μm. No slip occurred when the surface roughness was 8 and the Ra was 0.5 μm.

1 Steel plate (rolled material)
10 Production Equipment 11 Rolling Machine Row 11g Rolling Machine (Final)
DESCRIPTION OF SYMBOLS 12 Cooling device 13 Winding device 21 Lubricant supply device 22 Work roll surface roughness measuring device 23 Work roll surface roughness adjustment means

Claims (5)

Contact angle calculated from the diameter and opening degree of the work roll of the rolling mill and the end plate thickness of the material to be rolled immediately before entering the rolling mill in a rolling mill arranged in the subsequent stage of the hot finish rolling mill row When performing rolling under high pressure that is 9 degrees or more,
Using high alloy grain as the work roll material,
The surface roughness of the work roll is 1.0 μm to 1.5 μm in terms of Ra,
A method for producing a hot-rolled steel sheet, wherein rolling is performed by supplying a predetermined amount or more of a lubricant containing a synthetic ester or an oil-soluble Ca compound to the surface of the work roll from before the start of rolling to after the end of rolling. Contact angle calculated from the diameter and opening degree of the work roll of the rolling mill and the end plate thickness of the material to be rolled immediately before entering the rolling mill in a rolling mill arranged in the subsequent stage of the hot finish rolling mill row When performing high-pressure rolling under a temperature of 8.5 degrees or more and less than 9 degrees,
Using high alloy grain as the work roll material,
The surface roughness of the work roll is 0.5 μm to 1.5 μm in terms of Ra,
A method for producing a hot-rolled steel sheet, wherein rolling is performed by supplying a predetermined amount or more of a lubricant containing a synthetic ester or an oil-soluble Ca compound to the surface of the work roll from before the start of rolling to after the end of rolling.   The surface roughness of the work roll is measured before rolling, and when the Ra is smaller than 1.0 μm, the surface roughness of the work roll is adjusted to be 1.0 μm or more. A method for producing a hot-rolled steel sheet.   The surface roughness of the work roll is measured before starting rolling, and when the Ra is smaller than 0.5 μm, the surface roughness of the work roll is adjusted to be 0.5 μm or more. A method for producing a hot-rolled steel sheet. The adjustment of the surface roughness of the work roll is to perform a normal rolling in which a contact angle is smaller than that of the high pressure rolling before the high pressure rolling of a plurality of rolled materials. Item 5. The method for producing a hot-rolled steel sheet according to Item 3 or 4.

Images