JP5609366B2 - Winding method for hot-rolled steel sheet - Google Patents

Description

The present invention, hot-rolled steel sheet, in which relates to a particularly high strength pipe material become high-strength hot rolled thick steel plate winding takes Way Method for producing stably a.

  In recent years, demand for large-diameter, thick-walled, high-strength pipe materials such as X70 to X100 as API standards has been increasing mainly for the purpose of improving the transportation efficiency of resources such as crude oil and natural gas in continental pipelines. In order to efficiently transport these resources, high internal pressure is applied to the inside of the pipe, and characteristics such as high toughness and high strength are also considered for pipe materials in consideration of crustal deformation due to use in cold regions and earthquakes. It has become very important. The pipes used in these pipelines have a large diameter of about 15 to 25 mm and an outer diameter of about 20 inches or more. Conventionally, as a high-strength pipe, it is a short steel plate that is vertically long in the longitudinal direction. UOE steel pipes are often used in which the side is formed into a circular shape and then the butt portion is subjected to submerged arc welding in the longitudinal direction to form a pipe. Usually, a thick steel plate is manufactured in a substantially rectangular shape by multi-pass rolling in a thick plate mill having one or two hot slabs, and the product length is about 30 m at the maximum. is there.

  On the other hand, in recent years, after rolling a thick steel plate in a hot rolling line for thin plate rolling and winding it into a coil shape to form a hot rolled steel strip coil, unwinding the coil and forming it into an electric resistance welded tube, There is an increasing demand for spiral steel pipes that are formed into a pipe while forming a hot-rolled steel sheet in a spiral shape in the longitudinal direction and simultaneously welding the butted portion at the end of the sheet width. The hot-rolled steel sheet coil can be manufactured up to about 45 tons. For example, if the thickness is 20 mm and the width is about 1900 mm, the length of the hot-rolled steel sheet is about 151 m. Is about 151 m and the pipe length when formed into a spiral steel pipe having a diameter of 28 inches is about 128 m. Thus, by using a hot-rolled steel sheet coil as the base material before forming the pipe, it is possible to manufacture a long pipe continuously as compared with the case of manufacturing from a thick steel sheet, and thus an improvement in productivity can be expected.

  Now, when winding a high-strength thick steel sheet in a coil shape, the rigidity of the material is high, so the pinch roll or wrapper roll of the winding device is insufficient, the torque of the mandrel is insufficient, other winding defects at the tip, etc. Various issues arise. For example, it is difficult to bend the leading edge of a thick steel plate with a pinch roll or a wrapper roll, etc. In order to improve the winding failure of the leading edge, the mandrel outer diameter is increased up to about three laps after winding. A method has been proposed in which the adhesion between the steel sheet and the steel sheet is improved to prevent slipping and to facilitate winding (for example, Patent Document 1).

JP 2003-80313 A

  When winding a high-strength thick-walled hot-rolled steel sheet in a coil shape, the tip portion can be handled by, for example, the technique disclosed in Patent Document 1, but the strip tail end portion on the outer periphery side of the coil is spring-backed. When the winding looseness is likely to occur and the winding looseness is severe, the coil is lifted and falls off the cart when it is pulled out of the coiler while mounted on the coil cart. Normally, in winding a strip with a hot-rolling coiler, as shown in FIG. 3, the mandrel is controlled so that the rearmost end 1b stops at a position below the coil. This suppresses springback deformation at the tail end. However, recent needs for increasing the strength and thickness of line pipe materials are remarkable, and when winding these materials, the springback deformation of the tail end cannot be suppressed only by the weight of the coil. For this reason, even in a hot rolling line equipped with a strong rolling mill capable of rolling a high-strength material, whether or not winding with a coiler determines whether or not a high-strength thick hot-rolled steel sheet can be produced is determined. It is no exaggeration. In the present invention, the definition of high strength is X65 or more according to the API standard, and the thick hot-rolled steel sheet is intended to have a product thickness of 19 mm or more.

FIG. 4 shows a conventional general hot-rolled steel sheet winding device.
Generally, when winding the front-end | tip part of the hot-rolled steel plate 1 with a coiler, the peripheral speed of each roll, such as the pinch roll 3, the mandrel 7, and the wrapper rolls 5a-5d, is the thickness and hardness (strength of the hot-rolled steel plate 1). ) And the like, the value is adjusted to a value having a lead rate of 10 to 30% with respect to the conveyance speed of the hot-rolled steel sheet 1, that is, a speed that is 10 to 30% faster. At this time, the lead rate of the mandrel 7 and the wrapper rolls 5 a to 5 d is set to be equal to or higher than the lead rate of the pinch roll 3. And the lead rate is cleared at the time when the winding of the front end portion of the hot-rolled steel sheet 1 is completed, and thereafter, the conveyance speed of the hot-rolled steel sheet 1 and substantially (except for the effects of heat shrinkage due to cooling and width shrinkage due to tension, etc. Meaning) In FIG. 4, the number of wrapper rolls is four, but in general, many hot-rolled steel sheet winding apparatuses have three wrapper rolls.

  In the coiler, when the leading end of the hot-rolled steel sheet 1 is loosened and is wound in a wavy manner, the subsequent winding cannot be continued or even if it is fortunately wound, When the winding wound up and overlaps outside, the winding becomes thicker, and it becomes a size that protrudes from the housing of the coiler.As a result, it becomes clogged and cannot be pulled out. The damage to each part is great, and it takes many hours to recover.

  In any case, in order to prevent such a situation from occurring, when winding the tip of the hot rolled steel sheet 1 with a coiler, the hot rolled steel sheet 1 is used for the purpose of minimizing the looseness of the hot rolled steel sheet 1. From the start of winding the mandrel 7 to the completion of winding, the peripheral speed of each of the pinch roll 3, the mandrel 7, and the wrapper rolls 5 a to 5 d is given a lead rate to the hot rolled steel sheet 1. By winding up the wire, it is possible to prevent the hot-rolled steel sheet 1 from being loosened and undulated and wound up. And after completion of winding of the front-end | tip part of the hot-rolled steel plate 1, the mandrel 7 is substantially equal to the conveyance speed of the hot-rolled steel plate 1, that is, the conveyance speed of the hot-rolled steel plate 1 on the exit side of the final rolling mill of the finish rolling mill. The winding up to the tail end is performed while controlling the tension close to the desired tension with the pinch roll 3 while synchronizing with the pinch roll 3. At this time, when the winding of the tip end is about 5 or more, the wrapper rolls 5a to 5d are retracted from the coil, and the winding is performed without loosening only by the tension between the pinch roll 3 and the mandrel 7. In addition, since the tension | tensile_strength does not act on the hot-rolled steel plate 1 after the rearmost end part of the hot-rolled steel plate 1 passes through the pinch roll 3, it is made to evacuate in the general winding operation of a hot-rolled steel plate. At least one wrapper roll among the existing wrapper rolls 5a to 5d is pressed against the outer peripheral portion of the coil to suppress loosening of the coil tail end portion 1b.

  However, high-strength thick materials represented by the line pipe material particularly targeted in the present invention have a large cross-sectional area of the steel plate and very high strength, so that tension for winding up tightly is applied. Becomes very difficult. In general, a high-strength material has a very large spring back after bending, and after winding of the coil is completed, the cradle roll 8 is raised from below the coil and pressed against the coil, and then the wrapper roll 5a for extracting the coil. -5d is retracted and the mandrel which has been the center of coil rotation is reduced in diameter, the elastic strain component fixed by the mandrel 7 and the wrapper rolls 5a-5d is released, that is, springback occurs, and the coil outer periphery Part loosening becomes remarkable. Fig. 5 shows an example of the winding shape when the coil is pulled out after winding the high-strength thick material. If the coil is loose enough, it cannot be pulled out from the coiler. Has become prominent and the posture becomes unstable, and after banding, the band is cut off during transportation.

The present invention has been made in view of the above circumstances, it is an object to provide a winding take Way Method of high-strength hot rolled thick steel plate in hot rolling lines.

  As described above, normally, in winding a hot-rolled coil, after the mandrel is stopped so that the rearmost end of the hot-rolled steel sheet is located on the lower side of the coil, the coil is waiting under the coil during winding. The coil carriage is lifted and brought into contact with the tail end of the coil, and the mandrel and wrapper roll are released after the coil's own weight has suppressed the loosening of the tail end, and the coil carriage is mounted on the coil carriage as it is. I'm pulling out. The hot-rolled coil extracted from the coiler has one or more strip steel strips at the outermost periphery in a banding device installed adjacent to the coiler in order to prevent winding looseness during conveyance. The part is fixed in an annular shape. However, when winding a high-strength thick-walled hot-rolled steel sheet, due to the loosening of the outer periphery, it tends to become unstable before it is extracted from the coiler and transferred to the banding device, and some countermeasure technology needs to be established. there were.

The present invention has been made in view of the above situation, and is as follows.
(1) A method of winding a high-strength hot-rolled steel sheet in a coil shape with a hot-rolled steel sheet winder, after winding the hot-rolled steel sheet from the front end portion to the tail end portion in a coil shape, On the other hand, cooling water is sprayed onto the coil in a state where a plurality of wrapper rolls arranged in a planetary shape are pressed against the coil, and the coil outer periphery is cooled for a predetermined cooling time. A method for winding a hot-rolled steel sheet, wherein the wrapper roll is released after being held in the winding device for a predetermined staying time and extracted from the winding machine.
(2) The method for winding a hot-rolled steel sheet according to (1), wherein the predetermined cooling time of the outer periphery of the coil is 5 seconds or more.
(3) The method for winding a hot-rolled steel sheet according to (1) or (2) above, wherein the predetermined residence time of the coil after cooling is stopped is 20 seconds or longer .

  According to the present invention, it is possible to stably wind up a high-strength thick-walled hot-rolled steel sheet coil, which has conventionally been a problem of loose winding due to springback.

The schematic side view which shows the example of the winding apparatus of the hot rolled sheet steel by this invention A sketch showing an example of a strip guide according to the invention Schematic side view showing an example of a state without coil lifting Schematic side view showing an example of a conventional hot-rolled steel sheet winding device Schematic side view showing an example of coil lifting and winding looseness Cooling curve diagram showing an example of the temperature transition of the outer peripheral surface and inner peripheral surface during coil outer periphery cooling Cooling curve diagram showing an example of the transition of the temperature difference between the outer peripheral surface and the inner peripheral surface during coil outer periphery cooling

Hereinafter, embodiments of the present invention will be described.
As a result of intensive studies on the technology for suppressing coil loosening due to springback of the above-described high-strength hot-rolled steel sheet coil, the present inventors have rapidly cooled the outer periphery of the hot-rolled steel sheet immediately after winding. The idea was to reduce the springback by heat shrinking and generating circumferential strain in the outer periphery of the coil. Generally, in bending, tensile stress is applied outside the bend, and compressive stress is applied inside the bend to remove the processing force, that is, elastically up to a position where the bending moment in the plate thickness section becomes zero in the unloading process. Springback deformation with a changing curvature occurs. When cooling from the outer periphery of the coil, the temperature decrease is larger toward the outer periphery of the coil, and the hot-rolled steel sheet whose temperature has decreased causes thermal contraction according to the amount of temperature decrease, but the amount of thermal contraction inside the coil with little temperature decrease is small. Therefore, since the winding shape is maintained at the outer peripheral portion of the coil that is largely thermally contracted, it cannot be contracted, and elongation strain occurs. For example, in the case of a high-strength hot-rolled steel sheet coil having a thickness of 25.4 mm and a coil outer diameter of φ1600 mm made of a material having a winding temperature of 500 ° C., a yield stress σy of 450 MPa, a Young's modulus E of 160 GPa, bending at the outermost periphery The strain ε ₁ is about ± 0.016 according to the following equation (1).

In equation (1), h is the thickness of the hot-rolled steel sheet, and ρ is the radius of curvature at the outer periphery of the coil. Further, the outer surface side of the outermost hot-rolled steel sheet is tensile strain and the inner surface side is compressive strain, and the elastic-plastic boundary strain ε ₀ calculated by the following equation (2) is about 0.0028. It is in a plastic state except for the vicinity of the thickness center portion.

In general, since the thermal expansion coefficient of steel is about 1.2 × 10 ⁻⁵ (/ ° C.), for example, by reducing the steel plate temperature by 100 ° C. by cooling, a thermal shrinkage strain of 0.0012 or 200 ° C. If it is lowered, 0.0024 heat shrinkage strain is generated. This is almost the same as the elastoplastic boundary strain ε ₀ calculated by the equation (2). In fact, the shrinkage deformation is constrained by the internal resistance with a small thermal shrinkage. A large elongation strain occurs in the steel sheet. At this time, the wrapper rolls 5a to 5d are pressed against the coil with a predetermined pressure to constrain the movement of the coil due to cooling contraction, and the coil outer periphery side is uniformly cooled in the circumferential direction so that the mandrel is rotated at a constant speed. It is desirable to keep it. In such a state, that is, in a state where a plurality of wrapper rolls are pressed against the coil, while cooling the outer periphery of the coil, the cooling water is sprayed onto the coil to cool the outer periphery of the coil for a predetermined cooling time. If the coil is retained in the winder after cooling is stopped after a large temperature distribution is generated in the thickness direction of the outermost coil of the coil, The temperature of the surface layer rises rapidly, and after several tens of seconds, the cooling phenomenon due to air cooling / radiation from the outer peripheral side and the recuperation phenomenon from the inside are in an equilibrium state, and then the temperature gradually decreases. In this process, the outer peripheral side thermally expands due to a temperature rise, so that deformation occurs in the direction in which the bending curvature increases, that is, in the direction in which the elongation on the outer peripheral side is relaxed. That is, with respect to the distribution of the tensile stress on the outer peripheral side-the compressive stress on the inner peripheral side that was originally caused by the bending deformation by winding, the compressive stress is superimposed on the outer peripheral side and the tensile stress is superimposed on the inner peripheral side, The stress distribution in the plate thickness direction caused by bending by winding is greatly relaxed. When unloading from this state, that is, when the cradle roll 8 is lifted and pressed against the coil to remove the coil from the winder, the diameter of the mandrel 7 is reduced, and the wrapper rolls 5a to 5d are separated from the coil. It was confirmed that the fluctuations of up, down, left and right can be greatly reduced.

According to the study by the present inventors, the effect of reducing the springback is exhibited when the cooling time of the coil outer peripheral plate is substantially equal to the time when the temperature difference between the outer peripheral surface and the inner peripheral surface of the coil outermost peripheral plate is maximum. I found out. This is because the effect of reducing the spring back according to the present invention is derived from the outer peripheral strain generated by the outer periphery cooling of the coil, and it is not necessary to excessively increase the cooling time. For example, in FIG. 6 and FIG. 7, with API standard X80, product thickness 25.4 mm, the target winding temperature (coil outer periphery water cooling start temperature) is 470 ° C., the cooling heat transfer coefficient is 20 kW / m ² K, An example of transition of the temperature difference between the outer peripheral surface and the inner peripheral surface of the outermost surface of the coil and the temperature difference between the outermost surface and the inner peripheral surface when performing coil outer periphery cooling according to the present invention is shown. It has been found that a cooling time of about 5 seconds is sufficient to reach the maximum. Also, according to the stress calculation (numerical analysis) performed at this time, even if the cooling time is extended excessively, the effect on reducing the springback is almost constant, so the basic unit and productivity of utilities such as cooling water and electric power are reduced. It becomes a factor.

Such coil winding experiment, temperature calculation, stress calculation, hot rolled steel sheet strength: API standard X65 or more (X80 or less), plate thickness: 19 mm or more (25.4 mm or less), target winding temperature: 450-600 Cooling heat transfer coefficient: 3 to 60 kW / m ² K, various conditions are changed and executed to determine the optimal cooling time for reducing the springback, and the results are the subject of the present invention. For materials with an API standard of X65 or more and a product thickness of 19 mm or more, the predetermined cooling time of the coil outer peripheral portion is defined as 5 seconds or more in (2) of the present invention. However, in order to reduce utility loss, it is desirable to make it within 15 seconds.

  In addition, according to the results of the above-mentioned experiment, temperature calculation, and stress calculation, the bending stress distribution is greatly relaxed during recuperation after the coil outer periphery cooling is stopped. After the elapse of time, that is, the time calculated in advance until the temperature change of each part in the outermost peripheral plate reaches a steady state), the effect of reducing the springback becomes almost constant. It is desirable that the time (predetermined residence time) in which the slag is retained in the winding device is continued for a time longer than the recuperation time. Further, according to the recuperation behavior obtained from the results of the above-mentioned experiment, temperature calculation, and stress calculation, the recuperation time is 20 seconds or more in the material of API standard X65 or more and product thickness of 19 mm or more which is the object of the present invention. Therefore, in (3) of the present invention, a predetermined residence time (also referred to as a residence time in the winding device) is defined as 20 seconds or more. According to the recuperation behavior, the recuperation time does not exceed 30 seconds, and it is desirable from the viewpoint of productivity to open the wrapper roll immediately after the recuperation time has elapsed. Within 30 seconds is desirable.

Further, in order to efficiently cool the outer periphery of the coil in the winding device, it is necessary to spray a large amount of cooling water on the outer periphery of the coil by spraying or the like. In general, a hot-rolled steel sheet take-up apparatus handles a coil in a high temperature state, and thus is equipped with a minimum necessary cooling facility for protecting the equipment from a high temperature state. Therefore, ordinary cooling equipment is not sufficient. In the hot-rolled steel sheet winding device, in order to improve the winding property of the tip of the hot-rolled steel sheet, bending is actively performed using the strip guide between the wrapper rolls, and the coil outer periphery is rapidly cooled. This guide is a physical obstacle. Therefore, the present inventors have conceived that this strip guide is provided with a cooling water injection nozzle for actively quenching the coil. FIG. 1 and FIG. 2 show an example of a winding device having the strip guide and a strip guide shape. In the strip guide of FIG. 2, a plurality of holes 10 for injecting cooling water are provided on the entire guide surface, and as shown in FIG. 1, a large amount of cooling water is injected into the coil through the holes. Note that the strip guide is generally used to be separated from the coil after winding of the coil tip is completed. However, in the present invention, at least immediately before the coil tail end is wound, the strip guide is positioned near the outer periphery of the coil. And a large flow rate of cooling water is jetted from the hole 10 on the entire surface. From this, it is possible to cool the coil appropriately by installing the nozzle 9 for injecting the cooling water directly on the strip guide.

At this time, in consideration of the production pitch of the hot rolling line, the cooling rate of the coil outer peripheral temperature may be adjusted by controlling the amount of coil cooling water, but the inventors' investigation (the above-described experiment, temperature calculation, According to the result of stress calculation), in order to greatly reduce the spring back of the material of API standard X65 or more and the product thickness of 19 mm or more, which is the object of the present invention, the heat transfer coefficient during coil outer periphery cooling (water cooling) is 6 to needs to be about 25 kW / m ^{2 K,} the cooling water injection nozzle 9 to be used, it is not to desirable and as it can realize the heat transfer coefficient. The heat transfer coefficient of water cooling generally does not depend on the steel type and thickness of the material, but generally depends on the water density, and the heat transfer coefficient increases as the water density increases. The amount of water that can be obtained from heat transfer calculation, or can be obtained from literature (for example, “Forced Cooling of Steel”, S53 / 11, Japan Iron and Steel Institute), from which the cooling heat transfer coefficient can be realized. Since the density is obtained, the cooling water injection nozzle 9 capable of injecting the water amount corresponding to the water amount density may be appropriately selected (refer to catalogs of various nozzle manufacturers) and used as the nozzle used in the present invention. The lower limit of the heat transfer coefficient is an indispensable value for preventing a decrease in coil lift due to springback, and the upper limit is defined by realizing a heat transfer coefficient higher than this when cooling thick materials. This is to prevent utility loss due to an excessive increase in the amount of water since the springback reduction effect is almost saturated.

  In addition to the effect of reducing the spring back at the outer periphery of the coil as described above, the effect of the present invention has a great effect on the reduction of winding looseness by tightening the inside of the coil. A preventive effect is obtained.

  Examples of the present invention will be described below. The target material is an API standard X80 grade, and a slab (weight: 33 tons) having a thickness of 250 mm, a width of 1850 mm, and a length of 9090 mm is subjected to a rough rolling process and a finishing rolling process of a hot rolling line to a thickness of 19 to 25. After finishing to 4 mm and cooling to 450 to 600 ° C. on a cooling table, it was wound up by a winding device. The winding device is as shown in FIG. 1 and FIG. 2, the diameter of the wrapper rolls 5a to 5d is 440 mm, the outer diameter of the mandrel 7 is 750 mm, and the coil outer diameter in a state where it is wound loosely as shown in FIG. Is a coil of φ1858 mm. The hot-rolled steel plate speed on the exit side of the final finishing mill, that is, on the cooling table is 150 mpm, and the hot-rolled steel plate leading end 1a enters the coiler (meaning the winding device, the same applies hereinafter) at a speed of 150 mpm and is wound. Be started. At this time, the mandrel 7 and the wrapper rolls 5a to 5d are wound at the tip of the hot-rolled steel sheet so that winding is started at a predetermined lead rate with respect to the speed of the hot-rolled steel sheet 1. Acceleration has begun around the missing timing. And the read rate of the mandrel 7 at the start of winding was set to 15%, and the read rate of the wrapper rolls 5a to 5d was set to 25%. And after winding start, the deceleration of the mandrel 7 and the wrapper rolls 5a-5d is started, and the speed of the mandrel 7 and the wrapper rolls 5a-5d becomes the sheet passing speed of the hot-rolled steel sheet 1 when the winding is set to 5 laps. Decelerated to 150 mpm to synchronize. The tail end 1b of the hot-rolled steel sheet 1 started decelerating from a position about 20 m before the coiler, and the rotation was stopped at a position where the tail end 1b of the hot-rolled steel sheet 1 was on the coil lower side. Then, the cradle roll 8 that has been waiting under the coil is raised and pressed to the lower surface of the coil to fix the vertical position, and then the cooling is stopped by cooling the outermost coil with water cooling for 0 to 15 seconds. In that state, the residence time in the winding device was changed in the range of 0 to 30 sec. Thereafter, the wrapper rolls 5a to 5d were retracted from the coil, and the diameter of the mandrel 7 was reduced to extract the coil. At this time, depending on the winding condition, the coil may loosen due to the springback and vibrate up and down and left and right. Therefore, a video camera is used to shoot the movement of the coil, and detailed analysis of the vertical and horizontal movement is performed. Went. Since the inner circumference of the coil cannot be expanded by the spring back, the shape hardly changes.Therefore, the coil movement is evaluated by defining the maximum amount of vertical movement of the center point of the inner circumference as the coil lift. went. In addition, when the measurement result of the outer surface temperature in the cooling test with an actual machine was compared with the FEM analysis result, the heat transfer coefficient of water cooling in this example was as shown in Table 1.

  The results are shown in Table 1. In the case of determination, “◯” indicates the case where the coil lifting amount is 3 mm or less, “Δ” is 3 to 5 mm, and “x” is 5 mm or more. According to the present invention, the coil lift by the spring back after unwinding and unloading was as good as 3 mm or less at any plate thickness. On the other hand, in the comparative example in which the heat transfer coefficient and cooling time of the coil outer periphery water cooling after winding or the subsequent residence time in the winding device (recovery time) was insufficient, 22 mm, 25.4 mm, etc. The effect of the present invention was confirmed because the coil lifting with the thick material was insufficiently reduced.

1 Hot-rolled steel sheet (coil)
1b tail end 2 apron 3a, 3b pinch rolls 4 throat guide 5a No.1 wrapper roll 5b No.2 Rapparo Lumpur 5c No.3 wrapper roll 5d No.4 wrapper roll 6 strips guide 7 the mandrel 8 cradle roll
9 Cooling water injection nozzle
10 holes

Claims (3)

  A method of winding a high-strength hot-rolled steel sheet in a coil shape with a hot-rolled steel sheet winding device, winding the coil from the front end to the tail end of the hot-rolled steel sheet in a coil shape, and then planeting the coil In a state where a plurality of wrapper rolls arranged in a shape are pressed against the coil, the cooling water is sprayed on the coil, the outer periphery of the coil is cooled for a predetermined cooling time, and then the cooling is stopped to keep the coil at a predetermined retention time. A method for winding a hot-rolled steel sheet, wherein the wrapper roll is released after being retained in the winding device for a period of time, and then extracted from the winding machine.   The method for winding a hot-rolled steel sheet according to claim 1, wherein the predetermined cooling time for the outer periphery of the coil is 5 seconds or longer. The method for winding a hot-rolled steel sheet according to claim 1 or 2, wherein the predetermined residence time of the coil after stopping the cooling is 20 seconds or more .

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