JP2009241113A - Method of manufacturing hot-rolled steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method in which the rapid cooling of a steel plate is performed from just after finish rolling, light draft rolling is not performed after the rapid cooling and which has not adverse effect on a measuring instrument group on the downstream side of a finishing mill, in a method of manufacturing the hot-rolled steel plate by which a rough-rolled steel material is finish-rolled with the finishing mill composed of a plurality of stands. <P>SOLUTION: In this method of manufacturing a hot-rolled steel plate, a steel material 1 to be rolled is water-cooled in one or more spaces 3 between the stands on the late stage of the finishing mill, the rolling rolls 4 of a stand 2 on the downstream side of a position where the water-cooling is performed are released, the roll gap between those rolling rolls is taken as not more than the value which is obtained by adding 7 mm to the target thickness and the water on the plate which leaks out from the downmost-stream stand 2e is removed, on the outlet side of the downmost-stream stand 2e of the finishing mill. Since the light reduction after performing the rapid cooling just after rolling is not performed, the mechanical properties of the steel plate is improved by the rapid cooling of the steel plate just after the finish rolling. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method of manufacturing a hot-rolled steel sheet that is finish-rolled with a finish rolling mill composed of a plurality of stands, and particularly relates to a method for water-cooling a steel material to be rolled between the stands at the latter stage of the finishing mill. It is.

  In the method for producing a hot-rolled steel sheet, a slab produced by a continuous casting machine or the like is heated in a heating furnace to be a rough-rolled steel material by a roughing mill, and then finish-rolled by a finishing mill, The steel sheet is cooled by a predetermined cooling pattern to obtain a hot-rolled steel sheet. In the finishing mill, a plurality of finishing rolling stands are arranged in series, and the rough rolled steel material is finish-rolled by sequentially passing through the plurality of stands.

It is known that by rapidly cooling the steel sheet immediately after finishing rolling, the grain size of the steel sheet crystal grains can be reduced and a hot rolled steel sheet having excellent mechanical properties can be produced. For example, in Patent Document 1, Ti or Nb is added to ultra-low carbon steel, C or N in the steel is fixed in the form of precipitates, and IF steel (Interstitial atom free steel without solid solution interstitial elements) is present. ) To finish the cold rolling at the Ar ₃ transformation point or higher, and immediately after the rolling, the average cold speed from the Ar ₃ transformation point to −50 ° C. at an average cooling rate of 50 ° C./second or more is abrupt. A method of cooling is described. Thereby, crystal refinement | miniaturization of a hot-rolled steel plate can fully be achieved, and the deep drawability of a final product can be achieved. The rapid cooling immediately after rolling can be performed by water cooling in which water is sprayed onto both surfaces of the steel sheet that has been finish-rolled.

  A steel plate thickness gauge, width meter and thermometer are installed on the downstream side near the finishing mill exit, and the thickness and width of the steel sheet rolled by these measuring instruments and the steel plate temperature are measured. Control and perform quality control. These measuring instruments use X-rays for thickness meters, optical types for width meters, and infrared rays for thermometers.

  If rapid cooling of the steel sheet is performed immediately after the finish rolling, it is necessary to perform water cooling in which water is sprayed onto both surfaces of the steel sheet immediately after the exit of the finish rolling mill. However, as described above, a steel plate thickness gauge, width meter, and thermometer are installed on the downstream side of the exit of the finishing mill. It becomes possible. Therefore, it is difficult to perform water cooling of the steel sheet on the downstream side of the exit of the finishing mill.

  Patent Document 2 describes a method of quenching a steel sheet by installing a quenching device between the most downstream stand of the finishing mill and one of the upstream stands. Since a large amount of cooling water accompanying rapid cooling is blocked by the most downstream stand and does not flow into the point where the measuring instrument is installed, the size and temperature of the steel sheet can be accurately measured as in the past. On the other hand, when normal rolling is performed at the most downstream stand after quenching the steel plate, problems such as coarsening of the grain size of the steel plate occur again. Therefore, in the method described in Patent Document 2, the reduction at the most downstream stand is made extremely light, the reduction rate is set to, for example, 5% or less, and the finish rolling is substantially completed up to the one upstream side stand. is doing. The most downstream stand is used as a draining stand that does not perform substantial rolling.

JP-A-6-17140 JP 2003-305502 A

  In the method for producing a hot-rolled steel sheet described in Patent Document 2, after the finish-rolled steel sheet is rapidly cooled, light reduction is further applied at a most downstream stand with a reduction rate of 5% or less. However, when the rolling reduction is about 5% or less, the crystal structure of the outermost layer of the steel sheet becomes coarse, leading to a decrease in the elongation characteristics of the steel sheet. In order to reduce the reduction ratio to 5% or less, it is necessary to reduce the reduction force to 130 tons or less. However, this does not stabilize rolling, and the steel plate flutters on the most downstream stand exit side, and the shape is also reduced. The problem that it becomes a middle stretch shape will arise. In order to perform light reduction stably, the reduction force needs to be 500 tons or more, and the reduction ratio becomes about 20%.

  In addition, because the steel sheet is rapidly cooled in front of the most downstream stand, the deformation resistance in the longitudinal direction of the steel sheet changes suddenly, and if this is rolled at the most downstream stand, the reverse speed during rolling changes greatly even under light pressure. Therefore, the mass flow of the steel plate changes greatly, and the plate passing property is not stabilized. In Patent Document 2, this problem is solved by making the rolling roll drive motor of the upstream stand between the stands that perform rapid cooling have high-speed response performance with a speed control cut-off frequency of 35 rad / s or more. This is a solution, but it involves a great investment in motor remodeling.

  Furthermore, if the upper and lower roll gaps are opened to the open limit and the reduction rate is zero, water leakage between the steel sheet and the rolls cannot be prevented, and measurement is performed with a measuring instrument placed downstream of the most downstream stand. Becomes impossible.

  The present invention provides a method for producing a hot-rolled steel sheet in which a rolled steel material is finish-rolled by a finish rolling mill composed of a plurality of stands. It is an object of the present invention to provide a method that does not adversely affect a group of instruments on the downstream side of the machine.

That is, the gist of the present invention is as follows.
(1) In a method for producing a hot-rolled steel sheet, in which rough rolled steel is finish-rolled by a finish rolling mill comprising a plurality of stands, the steel to be rolled is water-cooled between one or two or more stands at the latter stage of the finish rolling mill, and the water cooling is performed. The rolling roll of the stand on the downstream side of the position where the rolling is performed is opened, the roll gap of the rolling roll is aimed at a value equal to or less than the value obtained by adding 7 mm to the plate thickness, and on the exit side of the most downstream stand of the finishing mill, A method for producing a hot-rolled steel sheet, comprising removing water on a plate leaked from a downstream stand.
(2) On the exit side of the most downstream stand of the finishing mill, water is injected onto the plate from a plurality of water injection nozzles, and the injection direction of the injection water is the direction opposite to the component Vz and the rolling direction from the upper side to the lower side. The method for producing a hot-rolled steel sheet according to (1) above, wherein the on-plate water having a component Vx toward the surface and leaked from the most downstream stand by the water jet is removed.

  The present invention relates to a method for producing a hot-rolled steel sheet in which a rolled steel material is finish-rolled by a finish rolling mill comprising a plurality of stands, and the steel material to be rolled is water-cooled between one or more stands at the latter stage of the finish rolling mill. The rolling roll of the stand on the downstream side of the implementation position is opened. For this reason, since there is no light reduction after performing rapid cooling immediately after rolling, the mechanical properties of the steel sheet can be improved by rapid cooling immediately after finish rolling without causing adverse effects of light reduction. In addition, aiming at the roll gap of the rolling roll, limiting the amount of on-board water leaking to a value less than the value obtained by adding 7 mm to the plate thickness, leaking from the most downstream stand on the outlet side of the most downstream stand of the finishing mill Since the on-board water is removed, the measuring instrument group on the downstream side of the finishing mill is not adversely affected even though light reduction is not performed.

  The slab heated in the heating furnace is rolled with a rough rolling mill to become a rough rolled steel material, and then rolled with a finish rolling mill. In the finishing mill, finishing rolling stands by a quadruple rolling mill are usually arranged in series in 5 to 7 stands, and the coarsely rolled steel material is finish-rolled by sequentially passing through these stands. In the example shown in FIG. 1, seven stands 2 from F1 to F7 are arranged, and F7 is the most downstream stand 2e. The steel plate that has been finish-rolled is wound by a coiler through a hot run table. A steel sheet thickness meter, width meter, and thermometer are installed on the downstream side of the exit of the finishing mill, and the dimensions such as the thickness and width of the steel sheet rolled by these measuring instruments and the steel sheet temperature are controlled. And perform quality control. These measuring instruments use X-rays for thickness meters, optical types for width meters, and infrared rays for thermometers. The hot run table is provided with a hot run cooling device for cooling the steel plate.

  In the present invention, immediately after finishing rolling, the steel sheet is rapidly cooled to reduce the grain size of the steel sheet crystal grains, thereby producing a hot-rolled steel sheet having excellent mechanical properties. The steel sheet rapid cooling immediately after finishing rolling is not performed after the exit of the finishing mill, but is performed by water-cooling the rolled steel material 1 between the stands 3 at the latter stage of the finishing mill. In the example shown in FIG. 1A, water cooling is performed between three stands 3, and between the most downstream stand and the most downstream stand 2 e (hereinafter “the most downstream stand 3 e”). Water cooling. In the example shown in FIG. 1 (b), water cooling is performed between two stands. In addition to the most downstream stand 3e, a stand having a second front stand and a first stand from the most downstream side. Perform additional water cooling at 3a.

  Water cooling between the finishing mill stands is performed by applying water to one or both of the upper surface and the lower surface of the steel material to be rolled between the stands 3. As for water cooling to the upper surface of the steel material to be rolled, either a spray method in which pressure water is ejected from a nozzle or a lamina method in which laminar flow rod-like water is produced may be used. A spray method is used for water cooling to the lower surface. In the example shown in FIG. 1, spray water is sprayed on the upper surface of the steel material 1 to be rolled by the upper cooling device 11, and spray water is sprayed on the lower surface of the steel material 1 to be rolled by the lower cooling device 12.

  In the present invention, the rolling roll is opened without light reduction at the stand downstream of the water cooling execution position. Thereby, the coarsening of the crystal structure of the outermost layer of the steel sheet due to light pressure can be prevented. In addition, instability of the sheet passing property due to a sudden change in the deformation resistance of the steel plate can be prevented.

  On the other hand, the water supplied to the upper surface of the steel plate by water cooling stays on the upper surface of the steel plate between the stands as water on the plate. In the present invention, the rolling roll is opened at the stand downstream of the water cooling execution position, so that the on-board water staying between the stands leaks more downstream than between the water-cooled stands.

  In the present invention, the amount of on-plate water leaking downstream from the stand by setting the roll gap of the rolling roll of the stand on the downstream side of the water cooling execution position to a value equal to or less than the plate thickness plus 7 mm. In addition, on the outlet side of the most downstream stand 2e of the finishing mill, the on-board water leaked from the most downstream stand 2e is removed. In the example shown in FIG. 1, the on-board water removal is performed using the on-board water removing device 13 arranged on the exit side of the most downstream stand 2 e and on the upper surface side of the steel material 1 to be rolled. The on-board water removing device 13 is arranged on the upstream side of measuring instruments (not shown). Water is sprayed from the on-plate water removing device 13 toward the upper surface of the steel material 1 to be rolled to remove the on-board water. Since the amount of plate water leaking from the most downstream stand outlet side of the finishing mill is sufficiently limited, it is possible to sufficiently remove the leaked plate water on the outlet side of the most downstream stand. Become. As a result, the measurement by the measuring instrument provided on the exit side of the finish rolling mill is not hindered even though light reduction is not performed at the stand downstream of the water cooling execution position. It is more preferable if the roll gap of the rolling roll of the stand on the downstream side of the water cooling execution position is aimed at a value equal to or less than the value obtained by adding 5 mm to the plate thickness.

  In the present invention, a plurality of water jet nozzles 14 are preferably used as the on-board water removing device 13. As shown in FIG. 2, on the exit side of the most downstream stand of the finishing mill, water is injected onto the plate from a plurality of water injection nozzles 14, and the injection direction of the injection water is a component Vz from the upper side to the lower side. It has a component Vx that goes in the direction opposite to the rolling direction, and the jet water collides with the rolled steel material 1 in the jet region 21. The on-plate water leaked from the most downstream stand 2e is removed by the water jet. By performing the water injection in this way, the injection direction of the injection water has a component Vz that goes from the upper side to the lower side, so that the injection water can collide with the steel plate surface, and the component Vx that goes in the direction opposite to the rolling direction. Therefore, the water on the plate leaked from the most downstream side stand 2e of the finishing mill can be damped and can be prevented from flowing downstream from the collision position of the jet water. The dammed plate water flows down from both sides of the steel plate. Since the steel plate is heated to a high temperature, a few droplets on the plate that are not blocked by the jet water evaporate before reaching the measuring instrument and do not adversely affect the measurement.

  A direction (rolling roll axis direction) perpendicular to the rolling direction of the water injection nozzle 14 for removing the water on the plate is a position where the region in which the steel material 1 to be rolled travels deviates to the side. Thereby, even if the front-and-rear end part of the rolled steel material 1 that travels floats, the nozzle is not damaged by colliding with the water jet nozzle 14. In order to inject the spray water onto the steel material to be rolled from the above position in the roll axis direction of the rolling roll, the injection direction of the spray water also has a component Vy that goes in the roll axis direction. Therefore, the water on the plate is dammed by the component Vx that goes in the direction opposite to the rolling direction of the jet water, and is washed away laterally on the steel plate by the component Vy that goes in the rolling roll axis direction of the jet water, It will flow out of the steel plate from the side opposite to where it is installed.

  The spray water from the water spray nozzle needs to collide with the steel sheet surface in the full width of the steel sheet. Therefore, it is preferable that the jet water has a jet shape that spreads in the width direction of the steel sheet, and that two or more water jet nozzles are installed and the nozzles share the jet region in the width direction of the steel sheet. In the example shown in FIG. 2, the water injection nozzles (14 a, 14 b) select the injection shape so that the wide range is the injection region 21, and the width direction of the steel material to be rolled by the injection region 21 a and the injection region 21 b Covers the entire width.

About the amount of water required to be sprayed from the water spray nozzle 14, after the water spray nozzle 14 is provided on the exit side of the finish rolling mill, the water on the plate is actually removed by performing the operation of removing the plate water by water jet. It is possible to easily determine the amount of jet water required for sufficient removal. The width of the rolled steel is about 550～1750Mm, when attempting to remove the plate clean water using two water injection nozzle, the injection water amount of the water injection nozzle is 0.4m ³ /min~0.7m ³ In the range of / min, it is possible to find a suitable amount of jet water that can remove the water on the plate.

  As described above, since the rolling roll of the stand on the downstream side of the water cooling execution position is opened, finish rolling is not performed on the stand on the downstream side of the water cooling execution position. Therefore, the most downstream stand upstream of the water cooling execution position is the final rolling stand 2p. In the example shown in FIG. 1A, since water cooling is performed between one stand, the stand (F6) immediately before the most downstream stand 2e becomes the final rolling stand 2p. In the example shown in FIG. 1 (b), water cooling is performed between the two stands, so the stand (F5) that is two steps before the most downstream stand 2e becomes the final rolling stand 2p.

Using the present invention, the steel plate temperature passing through the final rolling stand, that is, the rolling end temperature is set to Ar ₃ transformation point temperature or higher, and the steel plate temperature is cooled to Ar ₃ transformation temperature −30 ° C. or lower between the stands performing water cooling of the present invention. can do. The reason why the rolling end temperature is set to be equal to or higher than the Ar ₃ transformation point temperature is that if the temperature is lower than this, processed grains or recrystallized grains of ferrite are generated, and sufficient refinement cannot be achieved. Since the water cooling of the present invention is performed between the stands, the steel plate can be rapidly cooled immediately after rolling, and the steel plate can be sufficiently refined. If the steel sheet temperature is cooled to Ar ₃ transformation temperature −30 ° C. or lower by water cooling between the stands, the steel sheet can be sufficiently refined by continuing the rapid cooling to this temperature.

It is preferable to use an ultra-low carbon steel to which Ti or Nb has been added as a variety that uses the present invention. For this type, the rolling end temperature is set to the Ar ₃ transformation point temperature or higher, and the steel plate temperature is cooled to Ar ₃ transformation temperature −30 ° C. or less between the water-cooling stands, thereby sufficiently achieving crystal refinement of the hot-rolled steel plate. This is because the deep drawability of the final product can be achieved. As a component of steel, the component described in Patent Document 1 can be used.

In the present invention, when the steel material to be rolled is water-cooled between the stands, the cooling water density is W (m ³ / m ² · min) (water quantity per minute per square meter of steel plate) in total of the upper surface and the lower surface, as shown in FIG. In addition, when the length in the rolling direction of the region where the cooling water is sprayed onto the steel plate surface is L (m), the plate passing speed is U (m / second), and the plate passing plate thickness is t (mm), the plate thickness t = In the case of 4.2 mm, if W ≧ 8.2 m ³ / m ² · min, the cooling rate of the steel sheet can be set to 150 ° C./second or more. If W = 11.8 m ³ / m ² · min, the cooling rate of the steel sheet can be 200 ° C./sec. If the plate thickness t is in the range of 2.8 to 4.9 mm, a cooling rate of 200 ° C./second can be sufficiently secured by adjusting the water density W as the plate thickness increases.

  If the length L of the cooling water region is 1.75 m and the sheet passing speed U is 10 m / sec, the temperature drop allowance of the steel sheet is 35 ° C. when the steel sheet cooling speed is 200 ° C./sec.

  Since the distance between the rolling stands is short, there is a limit to lengthening the length L of the water-coolable region between the stands, and L is at most about 1.8 m. Therefore, there is a limit to the temperature drop allowance of the steel sheet between one stand. When the required amount of the rapid cooling temperature drop allowance after finishing rolling is large, as shown in FIG. It is necessary to perform the water cooling of the present invention using a gap.

  In a normal finishing mill in which finishing rolling stands by a quadruple rolling mill are arranged in series, the diameter of the rolling roll is about 650 mm. In the present invention, when the steel material to be rolled is water-cooled between the stands, water cooling can be started from a position about 500 mm away from the rolling point of the final rolling stand. In this case, if the sheet passing speed U = 10 m / second, water cooling can be started within 0.05 seconds from the end of finish rolling, and before the grain starts to coarsen after finish rolling. Rapid cooling can be performed.

  The present invention was applied during hot rolling of Ti-added ultra-low carbon steel. Using a finishing mill having 7 stands of F1 to F7, as shown in FIGS. 1 (b) and 3 (b), F5 is the final rolling stand 2p, and between the stands of F5 and F6 3a and between F6 and F7 The steel material to be rolled was water-cooled between the stands 3e. An upper cooling device 11 and a lower cooling device 12 were provided between the stands. On the outlet side of the most downstream stand 2e, a plate water removing device 13 having two water injection nozzles 14 as shown in FIG. 2 was provided. The plate width of the steel material to be rolled has various sizes from a minimum of 550 mm to a maximum of 1750 mm.

For the F6 and F7 stands, the rolling roll was opened and the roll gap of the rolling roll was aimed at and the value obtained by adding 5 mm to the plate thickness. The plate passing speed U between F5 and F7 is U = 600 mpm, the plate thickness t is 4.2 mm, and the cooling water is applied to the steel plate surface for both the upper cooling device 11 and the lower cooling device 12 between the stands 3a and the stands 3e. The length L in the rolling direction of the region to be sprayed is 1.75 m, and the cooling water density W is 11.8 m ³ / m ² · min.

As for the water spray nozzle 14, two spray nozzles 14a and 14b are provided as shown in FIG. The spray region of the water spray nozzle is narrow in the rolling direction and has a wide spray region in the direction perpendicular to the rolling direction. A vector indicating the direction from the water injection nozzle 14 to the center of the injection region 21 is referred to as an injection direction vector V. One of the water injection nozzles 14a has an injection water amount of 0.4 m ³ / min, and when the injection direction vector V is normalized to 1, the component Vx in the direction opposite to the rolling direction of the injection direction is 0.54. The injection direction is determined so that the component Vy going in the direction of the rolling roll axis in the direction is 0.82, and the component Vz going from the upper side to the lower side in the injection direction is 0.22, and the injection region 21a is the maximum width of the rolled steel material 1 ( 1750 mm) half. The other water injection nozzle 14b has an injection water amount of 0.3 m ³ / min, and the injection direction vector V is normalized to 1. When Vx is 0.54, Vy is 0.82 and Vz is 0.22. The injection direction is determined so that the injection region 21b covers the remaining half of the maximum width (1750 mm) of the steel material 1 to be rolled.

When the rolling end temperature in the final rolling stand 2p (F5) is 945 ° C., the steel material temperature to be rolled decreases to 900 ° C. by water cooling between the stands 3a, and the steel material temperature to be rolled becomes 860 ° C. by water cooling between the stands 3e. It dropped to. During the water cooling between the stands 3e, the steel to be rolled passed through the Ar ₃ temperature (890 ° C.) at a cooling rate of 200 ° C./sec.

  The on-plate water leaked from between the rolls of the most downstream stand 2e (F7) is blocked by the two water injection nozzles (14a, 14b), flows down from the side of the steel material to be rolled, and is downstream of the water injection nozzle installation position. Never flowed to the side. Even when the rolling was carried out by changing the thickness of the rolling roll to a value obtained by adding 7 mm to the plate thickness, the water on the plate did not flow downstream from the water injection nozzle installation position.

  Since there was no light reduction after rapid cooling immediately after rolling, the mechanical properties of the steel sheet could be improved by rapid cooling immediately after finish rolling without causing adverse effects of light reduction.

  Moreover, by not performing light reduction, the microstructure after cooling was able to have a grain size of about 30 μm without generating coarse grains in the outermost surface layer of the steel sheet.

It is a side view which shows an example of the finishing mill to which this invention is applied, (a) is a case where water cooling is performed between 1 stands, (b) is a case where water cooling is performed between 2 stands. It is a figure which shows the board top water removal apparatus of this invention, (a) is a top view, (b) is a BB arrow line view, (c) is a CC arrow line view. It is a partial side view which shows an example of the finishing mill to which this invention is applied, (a) is a case where water cooling is performed between 1 stands, (b) is a case where water cooling is performed between 2 stands.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel rolled material 2 Stand 2e The most downstream stand 2p Final rolling stand 3 Between stands 4 Rolling roll 11 Upper cooling device 12 Lower cooling device 13 On-board water removal device 14 Water injection nozzle 20 Rolling steel material traveling direction 21 Injection region F1- F7 Finish rolling stand Vx Component Vy in the direction opposite to the rolling direction of the injection direction Component Vy In the direction of the rolling roll axis in the injection direction Vz Component in the downward direction from the upper side of the injection direction

Claims (2)

  In a method for producing a hot-rolled steel sheet, in which a rough rolled steel is finish-rolled by a finish rolling mill comprising a plurality of stands, the steel to be rolled is water-cooled between one or more stands at the latter stage of the finish rolling mill, and the water cooling is performed. The rolling roll of the stand on the downstream side of the position is opened, the roll gap of the rolling roll is aimed at a value equal to or less than the value obtained by adding 7 mm to the plate thickness, and on the exit side of the most downstream stand of the finishing mill, A method for producing a hot-rolled steel sheet, characterized in that water on the plate leaked from the steel sheet is removed.   On the exit side of the most downstream stand of the finish rolling mill, water is jetted onto the plate from a plurality of water jet nozzles, and the jet direction of the jet water includes a component going from the top to the bottom and a component going in the direction opposite to the rolling direction. 2. The method for producing a hot-rolled steel sheet according to claim 1, wherein the on-plate water leaked from the most downstream stand by the water jet is removed.

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