JP5577655B2 - Hot-rolled steel sheet cooling equipment and cooling method - Google Patents

Description

  The present invention relates to a cooling facility and a cooling method for a steel plate (hot rolled steel plate) produced by hot rolling. Here, the hot-rolled steel sheet is a general term for a thin steel sheet (steel strip) and a thick steel sheet (thick sheet) manufactured by hot rolling.

  In a hot-rolled steel sheet production line for producing steel sheets by hot rolling, for example, as shown in FIG. 1, a thin unit provided with a heating furnace 11, a rough rolling machine 12, a finishing mill 13, a cooling facility 14, and a winder 15. In the steel sheet hot rolling facility, the slab extracted from the heating furnace 11 is subjected to rough rolling with a roughing mill 12 and finish rolling with a finishing mill 13, followed by water cooling or air cooling with a cooling facility 14. The structure of the steel sheet is controlled.

  When the steel sheet is cooled to a relatively low temperature by water cooling, for example, about 500 ° C., a fine ferrite and bainite structure can be obtained, and the strength of the steel sheet can be secured. Therefore, the technology for cooling the steel sheet with spray cooling water, laminar cooling water, etc. It is common. In recent years, the development of techniques for obtaining a high cooling rate, making the structure finer, and increasing the strength of the steel sheet has been active.

  For example, there are technologies of Patent Document 1 and Patent Document 2 as a technique for cooling a steel sheet by supplying a large amount of rod-shaped laminar cooling water. As shown in FIG. 7, for example, these cooling facilities 14 </ b> Z are directed obliquely downward in the width direction of the steel plate 10 from the upper header 41 (upper nozzle 42) installed above the steel plate 10 conveyed by the table roller 20. A large amount of cooling water (rod-shaped cooling water) 43 is sprayed onto the upper surface of the steel plate 10, and it is said that uniform cooling can be performed at a high cooling rate.

JP 2007-090428 A JP 2008-207200 A

  However, since the techniques of Patent Documents 1 and 2 originally inject the rod-shaped cooling water 43 obliquely downward in the width direction of the steel plate 10 in order to perform strong cooling, when trying to give a relatively low cooling rate. Since the water amount density, that is, the injection speed has to be lowered, the injection line of the cooling water 43 is curved as shown in FIG. Occurs, resulting in uneven cooling in the width direction. Therefore, a wide range of cooling rates could not be set.

For example, when a steel sheet having a tensile strength of 450 MPa or less is manufactured, it is only necessary to have a cooling rate of about several tens of degrees Celsius / s, so there is no need to supply a large amount of cooling water, and the water density is 1.5 m ³ / m ²・ It should be within min. Since such products occupy a large proportion of the production amount of the factory, it is not possible to install the cooling equipment as shown in Patent Documents 1 and 2, and ordinary cooling equipment is also required.

  However, it was not possible to install a header for strong cooling and a normal cooling header at the same time due to a problem of installation space.

  For example, when a cooling facility having a header 21 and a nozzle 22 for strong cooling as shown in FIG. 2 is installed above the steel plate 10 and the cooling water 23 is jetted diagonally forward and downward, the header 21 and the header 21 Since the space is narrowed, it is difficult to install a cooling facility including a normal cooling header 25 and a nozzle 26 as shown in FIG. It is not preferable to open the normal cooling header 25 between the strong cooling headers 21 a little more, because the strong cooling becomes intermittent and the cooling rate decreases.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a hot-rolled steel sheet cooling facility and a cooling method capable of providing various cooling rates when cooling a hot-rolled steel sheet. It is said.

  In order to solve the above problems, the present invention has the following features.

[1] In a hot-rolled steel sheet cooling facility installed in a hot-rolled steel sheet production line and supplying cooling water to the upper and lower surfaces of the steel sheet after finish rolling,
A header for supplying cooling water to the upper surface of the steel plate after the finish rolling is directly above the steel plate, and a normal cooling header for supplying cooling water at a flow density of 0.5 to 2.0 m ³ / m ² · min; And a strong cooling header that is above the outer side in the width direction of the steel plate and supplies bar-like cooling water at a flow density of 2.0 to 10.0 m ³ / m ² · min toward the inner side in the width direction. Hot-rolled steel sheet cooling equipment.

  [2] A circular pipe nozzle having an inner diameter of 3 to 8 mm is attached to the strong cooling header. From the circular pipe nozzle, a rod-shaped cooling water having a flow velocity of 8 to 15 m / s is directed inward and downward in the width direction. The cooling facility for hot-rolled steel sheets according to [1], wherein the landing points are sprayed so as to be arranged at equal intervals in the width direction.

[3] A method for cooling a hot-rolled steel sheet that cools a steel sheet using the cooling facility according to [1] or [2], wherein the cooling is performed from the normal cooling header according to characteristics required by the product. a case of supplying to the upper surface of the steel sheet of water at a flow rate density 0.5~2.0m ³ / ^m 2 · min, the strong flow density 2.0~10.0m ³ / ^{m 2} · bar-shaped cooling water from the cooling headers A method for cooling a hot-rolled steel sheet, characterized in that the case of supplying to the upper surface of the steel sheet in min is properly used.

  In the present invention, various cooling rates can be given when the hot-rolled steel sheet is cooled. As a result, a high cooling rate can be given to the steel sheet, the structure can be refined, and a high-tensile steel sheet can be produced. A general steel sheet having a tensile strength of 450 MPa or less can also be produced with a high yield.

The figure which shows the hot rolling equipment of a thin steel plate. The side view (steel plate width direction outside) showing the cooling equipment concerning one embodiment of the present invention. The side view (the steel plate width direction center) which shows the cooling equipment concerning one embodiment of the present invention. The top view which shows the cooling equipment which concerns on one Embodiment of this invention. The injection state when performing strong cooling with the cooling facility which concerns on one Embodiment of this invention (front view). The injection state when performing normal cooling with the cooling facility which concerns on one Embodiment of this invention (front view). Injection state when performing strong cooling with conventional strong cooling equipment (front view). Injection state (front view) when normal cooling is performed with conventional strong cooling equipment. The temperature distribution when normal cooling is performed with the cooling equipment which concerns on one Embodiment of this invention, and the temperature distribution when normal cooling is performed with the conventional strong cooling equipment.

  An embodiment of the present invention will be described with reference to the drawings. Here, a thin steel plate (steel strip) will be described as a hot-rolled steel plate.

  As shown in FIG. 1, the hot rolling equipment for thin steel sheets used in this embodiment includes a heating furnace 11, a rough rolling mill 12, a finish rolling mill 13, a cooling equipment (runout cooling equipment) 14, and a winder 15. The rolling material (slab) extracted from the heating furnace 11 is subjected to rough rolling with a roughing mill 12 and finish rolling with a finishing mill 13, and then the rolled material (slab) with a run-out cooling facility 14 ( After the cooling water is supplied to the upper and lower surfaces of the steel sheet and cooled to a predetermined temperature, the structure of the steel sheet is controlled and then wound by the winder 15.

  The products manufactured by this hot rolling equipment include various types such as steel types and dimensions. For example, a high-tensile and high-toughness steel plate with a plate thickness of 20.0 mm and a tensile strength target of 780 MPa, or a plate thickness of 2.0 mm And a high workability steel plate having a tensile strength target of 340 MPa. Note that the finish rolling finish temperature of the high-tensile and high-toughness steel sheet is 800 ° C., and the winding temperature target is 480 ° C. On the other hand, the finish rolling finish temperature of the high workability steel sheet is 850 ° C., and the winding temperature target is 600 ° C.

And the cooling equipment 14A which concerns on this embodiment is an upper surface of the steel plate 10, as shown in a side view (outside of the steel plate width direction) in FIG. 2, a side view (center in the steel plate width direction) in FIG. 3, and a top view in FIG. The upper header for supplying the cooling water to the head is composed of the strong cooling header 21 and the normal cooling header 25, and the strong cooling header 21 is located above the outer side in the steel plate width direction and is bar-shaped cooling water toward the lower side in the width direction. 23 is supplied at a flow density of 2.0 to 10.0 m ³ / m ² · min. The normal cooling header 25 is directly above the steel plate 10 and the cooling water 27 is supplied at a flow density of 0.5 to 2.0 m ^3. / M ² · min.

  Here, as shown in FIGS. 4 and 5, the strong cooling header 21 is installed above both outer sides in the steel plate width direction, and from each nozzle 22 attached to the strong cooling header 21, The rod-shaped cooling water 23 is sprayed so as to be parallel to each other. At this time, if the spray line of the rod-shaped cooling water 23 straddles the center line in the steel plate width direction, the rod-shaped cooling water 23 is deposited on the steel plate 10. Since the cooling water 23 after water does not stay on the steel plate 10 and is smoothly removed, uniform cooling is possible.

  In addition, the nozzle 22 attached to the strong cooling header 21 is a circular tube nozzle having an inner diameter of 3 to 8 mm, and the sticking water point of the rod-shaped cooling water 23 having a flow velocity of 8 to 15 m / s is lowered inward in the width direction. It is preferable to inject so that it may line up at equal intervals.

  4 and 5 show the case where the strong cooling headers 21 are installed on both outer sides in the steel plate width direction. However, when there is no space such as a water supply pipe to the strong cooling header 21, the steel plate width direction is shown. You may install only in the outside of one side.

  On the other hand, as shown in FIGS. 3 and 6, the normal cooling header 25 is installed immediately above the table roller 20, and the cooling water is directed from the nozzles 26 attached to the normal cooling header 25 toward the upper surface of the steel plate 10. 27 falls vertically to cool the steel plate 10. The cooling water 27 supplied from the normal cooling header 25 may be in the form of a film or in the form of a spray such as spray cooling.

  As shown in FIGS. 2 and 3, cooling water 33 is supplied to the lower surface of the steel plate 10 from a lower surface nozzle 32 attached to the lower surface header 31.

And when using the cooling equipment 14A which concerns on this embodiment, according to the characteristic which a product requires, the rod-shaped cooling water 23 is flow-rate density 2.0-10.0m < ³ > / m < ² > * from the strong cooling header 21. FIG. The case where the cooling water 27 is supplied from the normal cooling header 25 to the upper surface of the steel plate 10 at a flow rate density of 0.5 to 2.0 m ³ / m ² · min is selectively used. To do.

  Such a cooling facility 14 </ b> A according to this embodiment may be installed in both or one of the most upstream and downstream of the run-out cooling facility 14.

  For example, after the steel plate is cooled to about 650 ° C. with a run-out table, the ferrite transformation is advanced by air cooling for several seconds, and then cooled again to about 450 ° C. to achieve high workability and high tensile strength of the ferrite-bainite two-phase structure. When manufacturing steel, it is good to use this cooling equipment 14A. If both or one of the first and second water coolings are performed using the strong cooling header 21, the water cooling time can be shortened compared to the case where only the normal cooling header 25 is used, and the air cooling time can be increased accordingly. As a result, the ferrite transformation can be promoted, so that a high-quality product can be manufactured with a high yield.

  Further, it is desirable to install the cooling equipment 14A so that the whole or a part of the cooling equipment 14A is located within the range of 10% of the most upstream side or the range of 10% of the most downstream side of the entire length of the runout cooling equipment 14. .

  That is, for example, when the cooling facility 14A is installed on the most upstream side of the runout cooling facility 14 having an overall length of 100 m, the cooling facility 14A starts cooling within the range of the most upstream side 10m. Preferably, it is most preferable to start cooling by the cooling facility 14A from the uppermost stream. When it is far from the finish mill 13, the time from the end of rolling in the finish mill 13 to the start of cooling by the cooling equipment 14A becomes too long, during which recrystallization, recovery, austenite grain growth, etc. proceed, This is because even if strong cooling is performed, the effect of increasing the strength of the steel sheet 10 may not be obtained.

  For example, when installing in the most downstream side of the runout cooling equipment 14 with the whole length of 100 m, it is preferable that the cooling by the cooling equipment 14A can be finished in the range of 10 m on the most downstream side. Generally, a feedback zone is provided at the most downstream side of the run-out cooling facility 14 to turn on and off water injection by feeding back a temperature measurement value of a winding thermometer. Usually, a cooling facility 14A is installed in the feedback zone. The cooling header 25 may be used for the feedback water injection. Alternatively, the cooling facility 14A may be installed immediately upstream of the feedback zone.

  As described above, in this embodiment, when the thin steel plate (steel strip) 10 is cooled, various cooling rates can be given. As a result, a high cooling rate can be applied to the thin steel plate (steel strip) 10, the structure can be refined, and a high-tensile steel plate can be produced. A general steel plate having a tensile strength of 450 MPa or less can also be produced with a high yield. be able to.

  In the above embodiment, the thin steel plate (steel strip) has been described as an object, but the present invention can be similarly applied to a thick steel plate (thick plate).

  Examples of the present invention are described below.

  In this example, a thin steel plate (steel strip) was manufactured using the hot rolling equipment shown in FIG. That is, the material to be rolled (slab) extracted from the heating furnace 11 is roughly rolled with a roughing mill 12 and finish-rolled with a finish rolling mill 13 and then rolled with a run-out cooling facility 14 (steel plate). The cooling water was supplied to the upper and lower surfaces of the steel sheet and cooled to a predetermined temperature, so that the structure of the steel sheet was controlled and wound by the winder 15.

  At that time, the manufactured products were a high-tensile and high-toughness steel plate (called steel plate A) with a plate thickness of 20.0 mm and a tensile strength of 780 MPa, and a high processing with a plate thickness of 2.0 mm and a tensile strength of 340 MPa. Steel sheet (referred to as steel sheet B). The finish rolling finish temperature of the steel sheet A is 800 ° C., and the winding temperature target is 480 ° C. On the other hand, the finish rolling finish temperature of the steel plate B is 850 ° C., and the winding temperature target is 600 ° C.

  As an example of the present invention, the cooling facility 14A according to the embodiment of the present invention shown in FIG. The length of the cooling equipment 14A was 25 m.

  In the cooling facility 14A, the landing points of the rod-shaped cooling water 23 are arranged at equal intervals in the width direction, and the injection line of the rod-shaped cooling water 23 straddles the center line in the width direction of the steel plate 10 The cooling water 23 after landing on the steel plate 10 did not stay on the steel plate 10 and was smoothly removed.

  In addition, in the example of the present invention, when manufacturing the steel sheet A, the rod-shaped cooling water 23 is sprayed from the strong cooling header 21 of the cooling facility 14A onto the upper surface of the steel sheet A to cool the steel sheet A to 480 ° C. I wound up.

  As a result, the temperature of the steel sheet A after the end of cooling (before winding) became a uniform distribution as shown in (a) in FIG. 9, and the temperature variation could be suppressed within 20 ° C.

  Further, in the present invention example, when the steel plate B is manufactured, the cooling water 27 is sprayed from the normal cooling header 25 of the cooling facility 14A onto the upper surface of the steel plate B, the steel plate B is cooled to 600 ° C., and then wound. I took it.

  As a result, the temperature of the steel plate B after completion of cooling (before winding) became a uniform distribution in the width direction of the steel plate as shown in (a) of FIG. 9, and the temperature variation could be suppressed within 20 ° C. . And since the cooling rate became 50 degrees C / s and the ferrite produced | generated stably, the elongation characteristic was good and the steel plate with high workability was able to be manufactured.

  As described above, in the example of the present invention, both the steel plates A and B could be uniformly cooled in the width direction, so that a high yield of 99% or more could be secured.

  On the other hand, the conventional cooling equipment 14Z shown in FIG. 7 was installed in the uppermost stream of the run-out cooling equipment 14 as a conventional example. The length of the cooling equipment 14Z was 25 m.

  In the conventional example, when manufacturing the steel sheet A, the rod-shaped cooling water 43 is sprayed from the strong cooling header 41 of the cooling facility 14Z onto the upper surface of the steel sheet A, and the steel sheet A is cooled to 480 ° C. and then wound. The steel plate A could be produced with a high yield as in the above-described examples of the present invention.

  However, in the conventional example, when the steel plate B was cooled using the strong cooling header 41 of the cooling facility 14Z when the steel plate B was manufactured, the cooling rate was too high and a part of the surface layer structure became bainite. As a result, the strength was too high and the desired high workability could not be obtained.

  Further, in the conventional example, when the injection speed of the rod-shaped cooling water 43 is lowered so as not to increase the cooling speed, the injection line of the rod-shaped cooling water 43 becomes a curved line as shown in FIG. The cooling water 49 was concentrated and the supercooling part 49 was made. As a result, the temperature distribution in the width direction of the steel plate B was as shown in (b) in FIG. And the intensity | strength in the plate width center of the steel plate B was too high, and the yield was as low as 60%.

  Moreover, when the steel plate B is cooled by the normal cooling header installed downstream thereof without using the cooling equipment 14Z, the usable cooling zone length is too short and the steel plate B is cooled only to 650 ° C. The temperature was 50 ° C. higher than the target coiling temperature. In addition, since the time from finish rolling to the start of cooling was long, it was difficult to obtain the target strength, and the yield was only 90%. Furthermore, since the scale is thicker than that in the case of producing the steel plate B according to the present invention example, there was a lot of pickling loss when used as a cold rolled base metal.

DESCRIPTION OF SYMBOLS 10 Steel plate 11 Heating furnace 12 Rough rolling mill 13 Finish rolling mill 14 Cooling equipment (run-out cooling equipment)
14A Cooling equipment 14Z Cooling equipment 15 Winder 20 Table roller 21 Upper header (strong cooling header)
22 Upper nozzle (circular tube nozzle)
23 Cooling water (rod cooling water)
25 Upper header (normal cooling header)
26 Upper nozzle 27 Cooling water 31 Lower header 32 Lower nozzle 33 Cooling water 41 Upper header (strong cooling header)
42 Upper nozzle 43 Cooling water (bar-shaped cooling water)
49 Supercooled part

Claims (5)

In the hot-rolled steel sheet cooling line installed in the hot-rolled steel sheet production line and supplying cooling water to the upper and lower surfaces of the steel sheet after finish rolling,
A header for supplying cooling water to the upper surface of the steel plate after the finish rolling is directly above the steel plate, and a normal cooling header for supplying cooling water at a flow density of 0.5 to 2.0 m ³ / m ² · min; , in the upper part of the steel plate width direction outside, Ri Do and a strong cooling header for supplying rod-like cooling water flow density 2.0~10.0m ³ / ^m 2 · min inward in the width direction downward, the strong A plurality of circular pipe nozzles are attached to the cooling header, and rod-shaped cooling water is sprayed from the circular pipe nozzle group inward in the width direction so that the landing points are arranged at equal intervals in the width direction. A cooling facility for hot-rolled steel sheets. The said strong cooling header is installed in the both outer sides of the steel plate width direction, The cooling equipment of the hot rolled steel plate of Claim 1 characterized by the above-mentioned. The cooling equipment for hot-rolled steel sheets according to claim 2, wherein each circular pipe nozzle is attached so that a jet line of bar-shaped cooling water straddles a center line in the steel sheet width direction.   A circular nozzle having an inner diameter of 3 to 8 mm is attached to the strong cooling header, and rod-shaped cooling water having a flow velocity of 8 to 15 m / s is injected from the circular nozzle toward the inner side in the width direction. The cooling equipment for hot-rolled steel sheets according to any one of claims 1 to 3. It is a cooling method of the hot rolled steel sheet which cools a steel plate using the cooling equipment in any one of Claims 1-4, Comprising: Flow volume of cooling water from the said normal cooling header according to the characteristic which a product requires. When the density of 0.5 to 2.0 m ³ / m ² · min is supplied to the upper surface of the steel plate, the rod-shaped cooling water is supplied from the strong cooling header at a flow density of 2.0 to 10.0 m ³ / m ² · min. A method for cooling a hot-rolled steel sheet, wherein the case of supplying to the upper surface of the steel sheet is properly used.

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