WO2013137068A1 - Method for producing hot-rolled steel sheet - Google Patents

Description

Manufacturing method of hot rolled steel sheet

In the present invention, a steel plate is manufactured on a hot rolling line and wound in a coil shape by a winder, and the steel plate is held in a coil place or conveyed in a down-end state with the winding shaft hole oriented horizontally. The present invention relates to a method for producing a hot rolled (hot rolled) steel sheet for preventing the coiled steel sheet from being crushed by its own weight.

As shown in FIG. 1, in order to manufacture a hot-rolled steel sheet, a slab is heated to a predetermined temperature in a heating furnace 1, and the heated slab is rolled with a roughing mill 2 to form a rough bar. In a continuous hot finish rolling mill 3 composed of a plurality of rolling stands, a hot rolled (hot rolled) steel plate 4 having a predetermined thickness is obtained. And after cooling this hot-rolled steel plate 4 by supplying a cooling water from the upper direction and the downward direction with the cooling device 5 installed in the run-out table, it winds with the winder 6 and makes it the coiled hot-rolled steel plate 7.

The tension applied to the steel plate 4 in the longitudinal direction when the hot-rolled steel plate 4 is wound by the winder 6 is within the coiled hot-rolled steel plate (hereinafter also simply referred to as “coil”) 7 after winding. It acts as a radial surface pressure and generates a frictional force between steel sheet layers. Thereby, the slip of a steel plate is suppressed and the rigidity of the coil 7 is improved.

By the way, if the phase transformation of the steel sheet is not completed at the time of winding, the steel sheet undergoes volume expansion due to the phase transformation after winding. When this volume expansion is large at the outer periphery of the coil, the surface pressure in the radial direction is reduced, and the frictional force between the steel sheet layers is also reduced. Thereby, a steel plate becomes easy to slide and the rigidity of the coil 7 falls. When the rigidity of the coil 7 is significantly reduced, a phenomenon called “coil collapse” occurs in which the coil 7 is crushed by its own weight in the down-end state. In some cases, the winding shaft hole is excessively deformed. However, in some cases, a process for rewinding the coil is added and the production efficiency is lowered. In particular, this coil crush includes, in mass%, C: 0.05% to 0.3%, Mn: 1.0% to 2.7%, Si: 0.2% to 1.5%, and other inevitable impurities. In the case of the added hot-rolled steel sheet, it tends to occur.

Therefore, conventionally, as a method for controlling the phase transformation of the steel sheet after winding and suppressing coil collapse in the down-end state, for example, as described in Patent Document 1, the coil is gradually cooled using a heat insulating cover. How to do is known.

JP 2010-89107 A JP 2011-240354 A

The method described in Patent Document 1 controls the behavior of the phase transformation by temperature control after winding, but the phase transformation is greatly affected by the temperature history on the run-out table. There is a case where the behavior control of the transformation cannot be sufficiently performed. For this reason, the method described in Patent Document 1 has a problem that it cannot be said that coil collapse can be sufficiently suppressed.
The method described in Patent Document 2 controls the behavior of the phase transformation of the inner and outer circumferences of the coil by controlling the winding temperature in the longitudinal direction. By changing the winding temperature, which is a quality control index, in the longitudinal direction. In some cases, the coiling temperature deviates from the target temperature, and a material defect may occur or the material may fluctuate in the longitudinal direction. For this reason, the method described in Patent Document 2 has a problem that even if coil collapse can be suppressed, it may not be shipped as a product due to poor quality.

Therefore, the present invention provides a method for producing a hot-rolled steel sheet that sufficiently suppresses coil collapse and improves productivity by controlling the temperature of the steel sheet on the run-out from the finishing mill to the winder. The purpose is to do.

Fig. 2 shows an example of a TTT diagram of medium carbon steel and medium carbon / high Mn steel, and Fig. 3 shows an example of cooling equipment after finish rolling. In FIG. 2, curve A is the relationship between ferrite transformation start temperature and time of medium carbon steel, curve B is the relationship between ferrite transformation start temperature and time of medium carbon / high Mn steel, and curve C is the bainite transformation of medium carbon steel. The relationship between the start temperature and time, curve D shows the relationship between the bainite transformation start temperature and time of medium carbon / high Mn steel. In this specification, medium carbon steel is carbon steel containing C: 0.3% to 0.7% by mass%, and high Mn steel is mass% containing Mn: 1.0% or more. Carbon steel. In general, the phase transformation includes ferrite transformation, bainite transformation, pearlite transformation, and martensitic transformation, but in the steel types targeted by the present invention, the time from finish rolling to winding is 10 to 20 s (seconds), Since the coiling temperature is 500 ° C. to 650 ° C. and the phase transformation that occurs under these conditions is mainly the ferrite transformation (γ → α transformation), the present invention focuses on the ferrite transformation.

In FIG. 2, for the medium carbon steel, since the start of the ferrite transformation is within 1 s, it is sufficiently short with respect to the winding time, and the phase transformation is almost completed from finish rolling to winding. On the other hand, in the case of medium carbon / high Mn steel, the start of the ferrite transformation is around 10 s (seconds), and if the phase transformation is not the earliest temperature (ferrite nose temperature), the phase transformation further proceeds. The phase transformation is slow, and the phase transformation does not progress so much from finish rolling to winding.

In order to sufficiently suppress the coil collapse, it is necessary to suppress the volume expansion of the outer periphery of the coil due to the phase transformation after winding. Also, if the phase transformation of the coil outer periphery before winding is advanced more than the coil inner periphery, the volume expansion after winding is greater on the coil inner side than on the coil outer side. Since the coil becomes larger and the coil is tightened, coil collapse can be effectively suppressed. Therefore, in order to sufficiently suppress coil crushing, it is important to increase the phase transformation rate on the coil outer peripheral side than on the coil inner peripheral side.

In view of the knowledge of the present inventors, the method for producing a hot-rolled steel sheet of the present invention that solves the above problems is as follows.
When the hot-rolled steel sheet is cooled on the run-out table after hot rolling, and then wound into a coil shape by a winder,
In order to increase monotonically as the phase transformation rate of the hot rolled steel sheet reaches the tail end from the tip of the hot rolled steel sheet at the time when the hot rolling steel sheet reaches the winder, respectively. It is characterized by controlling the phase transformation rate of the hot-rolled steel sheet by controlling the temperature.
Here, the “intermediate temperature” is the temperature of the hot-rolled steel sheet at a position 1/5 to 1/2 on the rolling mill side of the distance from the rolling mill to the winder on the runout table.

According to the method for producing a hot-rolled steel sheet of the present invention, the phase transformation rate on the outer periphery side of the coil, which is the tail end side of the hot-rolled steel sheet, is greater than that on the inner periphery side of the coil, which is the front end side of the hot-rolled steel sheet. Therefore, it is possible to sufficiently suppress the coil crushing, and it is possible to improve the productivity and manufacture the steel plate.

In the method for producing a hot-rolled steel sheet according to the present invention, the tip of the hot-rolled steel sheet is moved from the ferrite nose temperature at a position 1/5 to 1/2 of the distance from the rolling mill to the winder. The temperature of the hot rolled steel sheet is within ± 20 ° C from the ferrite nose temperature, and the temperature between the tip and tail ends is changed from the tip to the tail end. It is preferable to control the temperature so as to decrease monotonously as it goes to, and to make the winding temperature constant.

In the method for producing a hot-rolled steel sheet of the present invention, the tip of the hot-rolled steel sheet is moved from the ferrite nose temperature at a position 1/5 to 1/2 of the rolling mill side of the distance from the rolling mill to the winder. Also, the temperature is lowered from 30 ° C. to the lower limit (for example, 60 ° C.) at which the bainite transformation does not occur, and the tail end of the hot-rolled steel sheet is within ± 20 ° C. from the ferrite nose temperature. It is preferable to make the coiling temperature constant by performing temperature control that monotonously increases the temperature between the tip end portion and the tail end portion.

Furthermore, in the method for producing a hot-rolled steel sheet according to the present invention, the tip of the hot-rolled steel sheet is moved from the ferrite nose temperature at a position 1/5 to 1/2 of the rolling mill side of the distance from the rolling mill to the winder. In addition, when the temperature of the hot rolled steel sheet is set within ± 20 ° C. from the ferrite nose temperature, the tip of the hot rolled steel sheet is adjusted to 660 ° C. to 710 ° C. The tail end of the hot-rolled steel sheet is preferably 610 ° C to 650 ° C.

In the method for producing a hot-rolled steel sheet of the present invention, the tip of the hot-rolled steel sheet is moved from the ferrite nose temperature at a position 1/5 to 1/2 of the rolling mill side of the distance from the rolling mill to the winder. However, when the temperature of the hot rolled steel sheet is lowered from 30 ° C. to the lower limit where bainite transformation does not occur and the tail end of the hot rolled steel sheet is within ± 20 ° C. from the ferrite nose temperature, the tip of the hot rolled steel sheet is Preferably, the temperature is 600 ° C. and the tail end of the hot-rolled steel sheet is 610 ° C. to 650 ° C.

According to these temperature controls, the phase transformation rate of those hot rolling steel sheets in the longitudinal direction at the time when each of the hot rolling steel sheets reaches the winder is directed from the front end portion to the tail end portion of the hot rolled steel plate. Accordingly, the phase transformation rate of the hot-rolled steel sheet can be controlled so as to increase monotonously.

It is a block diagram which shows the outline of a normal hot rolling line. It is a relationship diagram which shows the example of the phase transformation of medium carbon steel and medium carbon and high Mn steel. It is a block diagram which shows the run-out cooling equipment of the hot rolling line shown in FIG. 1 to which the Example of the manufacturing method of the hot rolled steel plate of this invention is applied. It is a relationship diagram which shows the change of the steel plate longitudinal direction of the intermediate temperature in one Example of the manufacturing method of the hot rolled steel plate of this invention. It is a relationship diagram which shows the change of the steel plate longitudinal direction of the intermediate temperature in other one Example of the manufacturing method of the hot rolled steel plate of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, FIG. 1 is a configuration diagram showing an outline of a normal hot rolling line to which an embodiment of the method for producing a hot rolled steel sheet according to the present invention is applied. The slab heated to a predetermined temperature is rolled with a roughing mill 2 to form a rough bar, and then this rough bar is hot-rolled (heated) with a predetermined thickness in a continuous hot finishing mill 3 composed of a plurality of rolling stands. And steel plate 4. And after cooling this hot-rolled steel plate 4 by supplying a cooling water from the upper direction and the downward direction with the cooling device 5 installed in the run-out table, it winds with the winder 6 and makes it the coiled hot-rolled steel plate 7.

By the way, the additive elements of steel in which the occurrence of coil crushing has been confirmed are C: 0.05% to 0.3%, Mn: 1.0% to 2.7%, Si: 0.2 in mass%. % To 1.5% and other inevitable impurities, especially Mn is added in a large amount of 1.0% by mass or more. These are the conditions in which the progress of phase transformation is slow compared to other steel types and coil collapse is likely to occur.

In order to sufficiently suppress the coil collapse, it is important to advance the phase transformation of the outer peripheral portion of the coil 7 more than the inner peripheral portion by the phase transformation control before winding as described above, and the phase transformation rate is, for example, The applicant of the present application previously disclosed in Japanese Patent Application Laid-Open No. 08-062181 and Japanese Patent Application Laid-Open No. 09-049017 can be measured on-line by using a transformation rate meter such as a transformation rate meter using a change in magnetic permeability of a hot-rolled steel sheet. Is possible.

Therefore, in this embodiment, a transformation rate meter is installed before the winder on the run-out table of the hot rolling line, and the phase transformation rate of the hot rolled steel sheet tail end corresponding to the outer periphery of the coil is set in the inner periphery of the coil. It is made higher than the corresponding hot-rolled steel sheet tip so that the phase transformation rate monotonously increases linearly or curvedly from the tip to the tail edge of the hot-rolled steel sheet. . Thus, coil collapse can be effectively suppressed by controlling the phase transformation rate of the hot-rolled steel sheet.

In addition, the front-end | tip part of a hot-rolled steel plate here means the site | part of the length range equivalent to 10% of full length from the most advanced part of a hot-rolled steel plate, and the tail end part of a hot-rolled steel plate is the last part of a hot-rolled steel plate. It means a portion having a length range corresponding to 10% of the entire length from the end. Further, the position in the width direction for measuring the phase transformation rate is not particularly limited because the temperature deviation in the plate width direction can be ignored.

In order to increase the phase transformation rate during coil winding, it is important to maintain the steel plate temperature at the ferrite nose temperature for a long time. To this end, the hot-rolled steel plate is cooled to the ferrite nose temperature in a short time after finish rolling. Thereafter, the temperature of the hot-rolled steel sheet is maintained, and the hot-rolled steel sheet may be rapidly cooled to a predetermined winding temperature constant in the longitudinal direction immediately before winding. Here, it is desirable to hold the temperature until just before winding as much as possible. However, since a general hot rolling line performs accelerated rolling, the time required for the run-out to pass is longer at the front end in the longitudinal direction of the hot-rolled steel sheet than at the tail end. Therefore, when each part in the longitudinal direction of the steel sheet is held at the same holding temperature, particularly the ferrite nose temperature, the phase transformation rate decreases from the tip part to the tail part, and the coil is easily crushed.

In order to make the phase transformation rate of the coil outer peripheral part higher than that of the inner peripheral part, it is good to change the intermediate temperature along the longitudinal direction of the hot-rolled steel sheet. The ferrite nose temperature is set at the tail end that is the outer periphery of the coil, and the temperature at the tip that is the inner periphery of the coil is higher than the ferrite nose temperature, so that the phase transformation rate on the outer periphery of the coil is higher than that on the inner periphery. It can be increased. Further, the same effect can be obtained even when the ferrite nose temperature is set at the tail end portion serving as the coil outer peripheral portion and the temperature is lower than the ferrite nose temperature at the tip portion serving as the coil inner peripheral portion. However, since the bainite transformation is faster than the ferrite transformation, the transformation progresses faster if the bainite transformation occurs at the tip. Therefore, it is desirable not to lower the temperature below the lower limit of the temperature at which bainite transformation does not occur.

Therefore, in the present embodiment, specifically, in order to sufficiently suppress coil crushing, the intermediate temperature at the tip of the hot-rolled steel sheet is made 30 ° C. to 80 ° C. higher than the ferrite nose temperature after finish rolling, The intermediate temperature of the tail end portion of the rolled steel sheet is set within a ferrite nose temperature ± 20 ° C., and the temperature between the tip end portion and the tail end portion is monotonously decreased from the tip end portion toward the tail end portion. The “intermediate temperature” is a temperature at a position 1/5 to 1/2 of the rolling mill side of the distance from the rolling mill to the winding machine on the runout table. It is the temperature during intermediate holding. Here, the reason for setting the intermediate temperature of the tail end within ± 20 ° C. from the ferrite nose temperature is that temperature control is difficult with high-tensile steel, and control within 20 ° C. is difficult. On the other hand, the reason why the intermediate temperature of the tip end is 30 ° C. to 80 ° C. higher than the ferrite nose temperature is 30 ° C. or higher so that a difference is produced even when the tail end is ferrite nose temperature + 20 ° C. This is because if it is increased, it becomes difficult to obtain the target winding temperature.

In the present embodiment, specifically, in order to sufficiently suppress the coil crushing, the intermediate temperature at the tip of the hot-rolled steel sheet is 30 ° C. to 60 ° C. higher than the ferrite nose temperature after finish rolling, instead of the above conditions. The temperature at the tail end of the hot-rolled steel sheet is set within the ferrite nose temperature ± 20 ° C, and the temperature between the tip and tail ends is monotonously increased from the tip to the tail end. May be. Here, the reason for setting the intermediate temperature of the tail end within ± 20 ° C. from the ferrite nose temperature is that temperature control is difficult with high-tensile steel, and control within 20 ° C. is difficult. On the other hand, the reason why the intermediate temperature at the tip is 30 ° C. to 60 ° C. lower than the ferrite nose temperature is 30 ° C. or less so that the difference in phase transformation rate is obtained even when the tail end is at the ferrite nose temperature −20 ° C. Further, when the temperature is lower than 60 ° C., it is easy to transition to the bainite transformation and it is difficult to obtain a target structure. That is, a temperature lower by 60 ° C. than the ferrite nose temperature is the lower limit of the temperature at which bainite transformation does not occur.

The ferrite nose temperature varies depending on the steel components, but is 560 ° C. to 650 ° C. for the above-described steel types that tend to cause coil collapse. Further, in order to make the phase transformation rate of the coil outer peripheral portion higher than that of the inner peripheral portion, after finish rolling, the intermediate temperature is 660 ° C. to 710 ° C. at the tip portion serving as the coil inner peripheral portion, and the tail end portion serving as the coil outer peripheral portion. 560 ° C. to 650 ° C., and the distance between them may be monotonously decreased from the tip to the tail, and in this way, the phase transformation rate gradually increases from the coil inner periphery to the outer periphery. It is possible to make it higher. In addition, after finish rolling, the intermediate temperature is set to 500 ° C. to 550 ° C. at the tip end that is the inner periphery of the coil, and 560 ° C. to 650 ° C. at the tail end that is the outer periphery of the coil. Also by increasing monotonously toward the direction, it is possible to gradually increase the phase transformation rate from the coil inner periphery toward the outer periphery.

Next, the example based on this embodiment demonstrates the case where the hot-rolled steel plate 4 is cooled in the run-out cooling equipment shown in FIG. 3 of the production line of the hot-rolled steel plate shown in FIG. In this run-out cooling facility, the finishing thermometer 8 is in the vicinity of the exit of the finishing mill 3, and the intermediate thermometer 9 is 1/5 to 1/2 of the rolling mill side of the distance from the finishing mill 3 to the winder 6. Among the positions, the table length of the run-out table provided with the cooling device 5 is installed at a position 1/3 of the finishing mill 3 side, and the winding thermometer 10 is installed in the vicinity of the winding machine 6, and further transformation The rate meter 11 is installed at the same place as the winding thermometer 10. As described above, the transformation rate meter 11 can use, for example, a change in magnetic permeability of the hot-rolled steel plate 4.

By using this run-out cooling equipment and controlling the operating conditions of the cooling device 5 (temperature and amount of cooling water supplied to the hot-rolled steel sheet 4), the following Comparative Examples 1 to 3 and Examples 1 to 3 A hot rolled steel sheet having a finished sheet thickness of 3.0 mm, a lateral width of 1000 mm, and a total length of 800 m was produced by each of the production methods. The results are shown in Table 1. However, the additive elements of the steel sheet to be produced are C: 0.15% by mass, Mn: 2% by mass, Si: 0.3% by mass, and other elements are in minute amounts that do not affect the phase transformation behavior. is there. The coil inner diameter is 750 mm, and the phase transformation rate is a value measured by the transformation rate meter 11.

The temperature history of Comparative Example 1 is 870 ° C. for the finishing thermometer 8, 660 ° C. for the intermediate thermometer 9, and 590 ° C. for the winding thermometer 10. The temperature history of Comparative Example 2 is 870 ° C. for the finishing thermometer 8, 600 ° C. for the intermediate thermometer 9, and 590 ° C. for the winding thermometer 10. The temperature history of Comparative Example 3 is 870 ° C. for the finishing thermometer 8, 630 ° C. for the intermediate thermometer 9, and 590 ° C. for the winding thermometer 10. The temperature history of Comparative Example 4 is 870 ° C. for the finishing thermometer 8, 660 ° C. for the intermediate thermometer 9, 660 ° C. for the winding thermometer 10 at the tip of the hot rolled steel sheet 4, and finish at the tail end. The thermometer 8 is 870 ° C., the intermediate thermometer 9 is 660 ° C., and the winding thermometer 10 is 630 ° C.

In Example 1, the indicated value of the transformation rate meter 11 is 50% at the front end portion of the hot-rolled steel sheet 4, 60% at the central portion in the longitudinal direction, and 70% at the tail end portion. The temperature history of Example 2 is 870 ° C. for the finishing thermometer 8, 660 ° C. for the intermediate thermometer 9, and 550 ° C. for the winding thermometer 10 at the front end of the hot-rolled steel sheet 4. The thermometer 8 is 870 ° C., the intermediate thermometer 9 is 630 ° C., and the winding thermometer 10 is 550 ° C. However, the longitudinal temperature change of the hot-rolled steel sheet 4 measured by the intermediate thermometer 9 is as shown in FIG. 4, and the left side in the figure is the tip end side and the right side is the tail end side. The temperature history of Example 3 is 870 ° C. at the finishing thermometer 8 at the front end of the hot-rolled steel sheet 4, 600 ° C. at the intermediate thermometer 9, and 550 ° C. at the winding thermometer 10. The thermometer 8 is 870 ° C., the intermediate thermometer 9 is 630 ° C., and the winding thermometer 10 is 550 ° C. However, the longitudinal temperature change of the hot-rolled steel sheet 4 measured by the intermediate thermometer 9 is as shown in FIG. 5, and the left side in the figure is the tip end side and the right side is the tail end side.

As shown in Table 1, in Comparative Example 1, the phase transformation rate at the tip portion was 36%, the phase transformation rate at the tail end portion was 14%, the coil 7 was largely crushed, and the inner diameter was changed from 750 mm to 720 mm. Since this coil 7 cannot be used as it is in the next process, a coil rewinding process is added, and productivity is lowered. In Comparative Example 2, the phase transformation rate at the tip portion was 47%, the phase transformation rate at the tail end portion was 20%, the coil 7 was largely crushed, and the inner diameter was changed from 750 mm to 715 mm. Since this coil 7 cannot be used as it is in the next process, a coil rewinding process is added, and productivity is lowered. In Comparative Example 3, the phase transformation rate at the tip end was 96%, the phase transformation rate at the tail end was 72%, the coil 7 was largely crushed, and the inner diameter was changed from 750 mm to 715 mm. Since this coil 7 cannot be used as it is in the next process, a coil rewinding process is added, and productivity is lowered. In Comparative Example 4, the coil 7 was not crushed, but the winding temperature on the tip side 2/3 was deviated from the winding target temperature of 590 ° C. ± 50 ° C., resulting in poor quality. became.

On the other hand, in Example 1, the phase transformation rate at the tip end was 60%, the phase transformation rate at the tail end was 80%, and the coil 7 was not crushed. This coil 7 could be used as it is in the next process. Further, in Example 2, the phase transformation rate at the tip end portion was 36% and the phase transformation rate at the tail end portion was 72%, and the coil 7 was not crushed. This coil 7 could be used as it is in the next process. In Example 3, the phase transformation rate at the tip end portion was 47%, the phase transformation rate at the tail end portion was 72%, and the coil 7 was not crushed. This coil 7 could be used as it is in the next process. In all of Examples 1 to 3, the coiling temperature was within the target range, and no cutting due to poor quality occurred.

As is apparent from the results described above, according to the method for manufacturing a hot-rolled steel sheet of the present embodiment, three portions (the front end part, the intermediate part, and the tail end part) in the longitudinal direction of the hot-rolled steel sheet 4 are respectively wound up by the winder 6. Since the phase transformation rate at those points at the time of reaching the point monotonically increases from the tip of the hot-rolled steel plate 4 toward the tail end, the coil outer peripheral portion formed of the tail end of the hot-rolled steel plate 4 The phase transformation rate can be made higher than that of the inner peripheral portion of the coil formed of the tip portion of the hot rolled steel sheet 4, thereby making it possible to sufficiently suppress coil crushing and to improve productivity.

Although the present invention has been described based on the illustrated examples, the present invention is not limited to the above-described examples, and can be appropriately changed within the scope of the claims. Although it is changing linearly along the longitudinal direction of the hot-rolled steel sheet (FIGS. 4 and 5), it may be changed in a curved line as long as it is not linear but monotonously decreases or monotonously increases.

Thus, according to the method for producing a hot-rolled steel sheet of the present invention, the phase transformation rate on the coil outer peripheral side that is the tail end side of the hot-rolled steel sheet is changed from the coil inner peripheral side that is the tip end side of the hot-rolled steel sheet. Therefore, the coil collapse can be sufficiently suppressed, and the productivity can be improved and the steel sheet can be manufactured.

DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Coarse rolling mill 3 Finishing rolling mill 4 Hot-rolled steel plate 5 Cooling device 6 Winding machine 7 Coiled hot-rolled steel plate (coil)
8 Finishing thermometer 9 Intermediate thermometer 10 Winding thermometer 11 Transformation rate meter

Claims (6)

When the hot rolled steel sheet is cooled on a runout table after hot rolling in a rolling mill, and then wound into a coil shape by a winder,
In order to increase monotonically as the phase transformation rate of the hot rolled steel sheet reaches the tail end from the tip of the hot rolled steel sheet at the time when the hot rolling steel sheet reaches the winder, respectively. A method for producing a hot-rolled steel sheet, characterized by controlling the phase transformation rate of the hot-rolled steel sheet by controlling the temperature. At the 1/5 to 1/2 position on the rolling mill side of the distance from the rolling mill to the winder, the tip of the hot rolled steel sheet is set to a temperature 30 to 80 ° C. higher than the ferrite nose temperature. The temperature at which the tail end of the rolled steel sheet is within ± 20 ° C. from the ferrite nose temperature, and the temperature between the tip and tail ends decreases monotonically from the tip toward the tail end, and the coiling temperature The method for producing a hot-rolled steel sheet according to claim 1, wherein At the 1/5 to 1/2 position on the rolling mill side of the distance from the rolling mill to the winder, the tip of the hot rolled steel sheet is set to a temperature 30 to 60 ° C. lower than the ferrite nose temperature. The temperature at which the tail end of the rolled steel sheet is within ± 20 ° C. from the ferrite nose temperature, and the temperature between the tip and tail ends is monotonously increased from the tip toward the tail end, and the coiling temperature The method for producing a hot-rolled steel sheet according to claim 1, wherein At the 1/5 to 1/2 position on the rolling mill side of the distance from the rolling mill to the winder, the hot rolled steel plate has its tip at 660 ° C to 710 ° C and the tail of the hot rolled steel plate. The method for producing a hot-rolled steel sheet according to claim 2, wherein the temperature is 610 ° C to 650 ° C and the coiling temperature is constant. At the 1/5 to 1/2 position on the rolling mill side of the distance from the rolling mill to the winder, the tip of the hot rolled steel sheet is set to 550 ° C. to 600 ° C., and the tail end of the hot rolled steel sheet The method for producing a hot-rolled steel sheet according to claim 3, wherein the temperature is set to 610 ° C to 650 ° C and the coiling temperature is made constant. The hot-rolled steel sheet is C: 0.05% to 0.3%, Mn: 1.0% to 2.7%, Si: 0.2% to 1.5% and other inevitable impurities in mass%. The method for producing a hot-rolled steel sheet according to any one of claims 1 to 5, characterized in that is added.

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