Cooling device, cooling method and manufacturing method for round billets

Abstract

To provide a cooling device, a cooling method, and a manufacturing method of a round billet, which can uniformly cool the circumferential direction of the billet and can cope with variations in cooling conditions.SOLUTION: A cooling device 1 for a round billet 2, which water-cools the cooled round billet 2 on a cooling floor after finish-rolling, includes nozzles 11 and 12 which are provided above and below the round billet 2 and inject cooling water, and a cooling control device 16 which determines the ratio of upper and lower volumes of the cooling water injected from the nozzles 11 and 12 on the basis of past manufacturing records and warpage amounts of the round billets 2, which are the round billets 2 manufactured in the past, and adjusts the injection flow rate of the cooling water so as to achieve the determined ratio of the upper and lower volumes. The cooling control device 16 uses at least the ratio of the upper and lower volumes of the past round billets 2 as the past manufacturing records of round billets, and determines the ratio of the upper and lower volumes so that the warpage amount of the subsequent round billet 2 to be water-cooled next falls within a target range.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a cooling device, a cooling method and a manufacturing method for a round billet.

[0002] A round billet, which is a raw material for rolling, is generally manufactured by subjecting a slab cast by a continuous casting method to multi-stage caliber rolling, and then shaping and lengthening the slab. After rolling, the φ170 to φ310 round billet has a temperature of about 700°C to 900°C, and is cooled to a predetermined temperature by air or water cooling in a cooling bed provided on the exit side of the finishing rolling mill. As such a cooling bed, for example, there are those that transport the round billet, such as those using a roll conveyor (or chain conveyor) or a walking beam.

[0003] In any of the above cooling bed types, the round billet that has reached the cooling bed after rolling is transported in sequence to the outlet side of the cooling bed, and then transported from the cooling bed to a storage area (hereinafter also referred to as a "yard"). When transporting the round billet, it is difficult to grip the round billet, which has a relatively small cross section, using tongs with gripping claws, so a lifting magnet (hereinafter also referred to as a "lifting magnet") that utilizes magnetic force is often used for transportation.

[0004] When transporting using a lift mag, if the temperature of the round billet is high, the steel structure is a non-magnetic austenitic structure, so the round billet is not magnetized by the lift mag and cannot be discharged from the cooling bed. Therefore, it is necessary to quickly cool the round billet on the cooling bed at least to a temperature where it can be magnetized by the lift mag. In particular, if the round billet is made of high alloy steel, it has high hardenability and martensitic transformation will occur even if it is left to cool. Since the martensitic structure is a ferromagnetic material, it can be magnetized by the lift mag, but the martensitic transformation end temperature M f (Hereinafter, simply "M f Since the temperature of the container (also called "cooking") is low at around 60°C, it takes more than 12 hours to cool it down if it is left to cool naturally.

[0005] In order to shorten the cooling time of the steel material on such a cooling bed, Patent Documents 1 and 2 propose a method of spraying a coolant, such as water or a mixture of water and air, onto the steel material. However, depending on the cooling method and conditions, a temperature difference may occur in the circumferential direction of the round billet, and plastic strain may occur due to local thermal contraction or transformation expansion, which may result in warping after cooling. If warping remains after cooling, additional processes such as pressing are required, which increases manufacturing costs and reduces productivity.

[0006] Therefore, methods that have been used up until now have been used to suppress warping, such as mechanical methods or methods of suppressing warping by uniform cooling in the circumferential direction of the billet.

[0007] The following describes the techniques that have been disclosed so far to prevent warping after cooling. Patent Document 3 describes a technique for preventing warping after cooling by measuring the temperature at which the cooling starts and the martensitic transformation starts, M s (Hereinafter, simply "M s The material is then quenched while mechanically restraining it with a press until it reaches just above the M s A method is disclosed in which the steel material is slowly cooled by repeatedly compressing and releasing the press straightening load by reciprocating the steel material in the longitudinal direction from directly above.

[0008] Patent Document 4 discloses that cooling water is sprayed from nozzles arranged asymmetrically above and below the steel material, and the ratio of the amount of water sprayed from the upper and lower nozzles is adjusted based on the amount of warping during and after cooling. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2006-55865 A [Patent Document 2] JP 2008-221316 A [Patent Document 3] JP 2004-332089 A [Patent Document 4] JP2009-256707 Public Relations Summary of the Invention [Problem to be solved by the invention]

[0010] However, the technology disclosed in Patent Document 3 is a method of cooling a steel material by repeatedly reducing and releasing the press straightening load by reciprocating the steel material in the longitudinal direction, which requires a reciprocating function and a press straightening machine, resulting in a problem of high equipment costs.

[0011] In addition, the technology disclosed in Patent Document 4 is a method of adjusting the ratio of the water amounts sprayed from the upper and lower nozzles based on the amount of warping during and after cooling, so appropriate cooling conditions must be set each time. However, the setting method is not specifically described. Furthermore, if there has been recent deterioration of the equipment or if there has been a change in the water temperature or air temperature, the cooling conditions for setting the warping to the target value will change, making it difficult to prevent intermittent warping.

[0012] Therefore, the present invention has been made with attention to the above-mentioned problems, and aims to provide a cooling device, cooling method, and manufacturing method for a round billet that can uniformly cool the circumferential direction of the round billet and can also accommodate fluctuations in cooling conditions. [Means for solving the problem]

[0013] According to one aspect of the present invention, there is provided a round billet cooling device that water-cools a round billet that has been left to cool on a cooling bed after finish rolling, the cooling device comprising: nozzles provided above and below the round billet for spraying cooling water; and a cooling control device that determines a water / steam volume ratio of the cooling water sprayed from the nozzles based on the production record and warpage of past round billets, which are round billets produced in the past, and adjusts the spray flow rate of the cooling water so as to achieve the determined water / steam volume ratio, wherein the cooling control device uses at least the water / steam volume ratio of the past round billet as the production record of the past round billet, and determines the water / steam volume ratio so that the warpage of the next round billet to be water-cooled, which is the round billet to be water-cooled next, is within a target range.

[0014] According to one aspect of the present invention, there is provided a method for cooling a round billet, which involves water-cooling a round billet that has been left to cool on a cooling bed after finish rolling, the method comprising: a determination step of determining a water / upstream / downstream amount ratio of cooling water to be sprayed from the nozzles provided above and below the round billet based on a manufacturing record and a warpage of a round billet that has been previously manufactured; a water volume adjustment step of adjusting a spray flow rate of the cooling water so as to achieve the water / upstream / downstream amount ratio determined in the determination step; and a water-cooling step of spraying the cooling water from the nozzles onto the round billet at the amount of water adjusted in the water volume adjustment step, wherein in the determination step, at least the water / upstream / downstream amount ratio of the past round billet is used as the manufacturing record of the past round billet, and the method determines the water / upstream / downstream amount ratio so that the warpage of the next round billet to be water-cooled, which is the round billet to be water-cooled next, is within a target range.

[0015] According to one aspect of the present invention, there is provided a method for manufacturing a round billet, in which a round billet that has been finish-rolled is allowed to cool on a cooling bed and then the round billet is water-cooled, and the above-mentioned cooling method is used when water-cooling the round billet. Effect of the Invention

[0016] According to one aspect of the present invention, a cooling device, a cooling method, and a manufacturing method for a round billet are provided that can uniformly cool the round billet in the circumferential direction and can also accommodate variations in cooling conditions. [Brief description of the drawings]

[0017] [Figure 1] FIG. 2 is a plan view showing a cooling device and a cooling bed according to an embodiment of the present invention. [Diagram 2] 1 is a configuration diagram showing a cooling device according to an embodiment of the present invention; [Diagram 3] 1A and 1B are plan views showing the cooling water injection area, in which (A) shows the case where a full cone nozzle is used, and (B) shows the case where a square nozzle is used. [Figure 4] 1 is a schematic diagram showing the definition of the amount of warpage of a round billet and a method for measuring the amount of warpage using a laser displacement meter. FIG. [Diagram 5] 1 is a graph showing the relationship between the amount of warping and the ratio of water and sewage flow rates. [Figure 6] 1 is a graph showing the relationship between the number of round billets produced and the amount of warpage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In the following detailed description, an embodiment of the present invention will be described with reference to the drawings. In the description of the drawings, identical or similar parts are given identical or similar symbols, and duplicated explanations are omitted. Each drawing is schematic and may differ from the actual one. In addition, the embodiments shown below are examples of devices and methods for embodying the technical idea of ​​the present invention, and the technical idea of ​​the present invention does not specify the materials, structures, arrangements, etc. of the components as described below. The technical idea of ​​the present invention can be modified in various ways within the technical scope defined by the claims described in the claims.

[0019] <Round billet cooling device> Hereinafter, a cooling device for round billets according to one embodiment of the present invention will be described. As shown in Fig. 1, the cooling device 1 is provided at the outlet side of a cooling bed 3 on which a round billet 2 is cooled, and is a device for cooling (water-cooling) the round billet 2 transported on the cooling bed 3 with cooling water. Fig. 2 is a configuration diagram showing the cooling device 1 for round billets 2 according to this embodiment. The cooling device 1 includes nozzles 11 and 12, a shape meter 13, a calculator 14, a thermometer 15, and a cooling control device 16.

[0020] The nozzles 11 and 12 are spray nozzles that spray cooling water onto the round billet 2, and are provided above and below the round billet 2 being transported. The nozzle 11 is provided above the round billet 2 being transported, and is also called an upper nozzle. The nozzle 12 is provided below the round billet 2 being transported, and is also called a lower nozzle. The nozzles 11 and 12 are provided in a row at a predetermined interval in the longitudinal direction of the round billet 2, forming a nozzle row. In addition, the cooling device 1 is provided with a plurality of nozzle rows arranged in the transport direction of the round billet 2, above and below the round billet 2. Note that, if one nozzle 11 and 12 can cool the entire length of the round billet 2 in the longitudinal direction, one nozzle 11 and 12 may be provided in the longitudinal direction. Usually, the round billet 2 has a long length of several meters or more, so it is preferable to provide a plurality of nozzles 11 and 12 in the longitudinal direction. Furthermore, in consideration of the improvement in productivity due to the shortened cooling time and the installation costs and maintainability due to the reduced number of nozzles, it is preferable to cool 4 to 8 round billets 2 with a pair of nozzles arranged above and below the round billet 2. Furthermore, although a single nozzle row may be provided in the conveying direction, providing multiple rows expands the area of ​​the cooling device 1, thereby shortening the cooling time and improving productivity.

[0021] Moreover, it is preferable that the nozzles 11 and 12 are spray nozzles having a rectangular spray pattern. Fig. 3 shows a schematic diagram of the round billet 2 being cooled by the cooling device 1, viewed from above. Fig. 3(A) shows a case where a full cone nozzle with a circular cooling water spray pattern is used as the nozzle 11, and Fig. 3(B) shows a case where a square spray nozzle with a rectangular cooling water spray pattern is used as the nozzle 11. In Fig. 3, the hatched area is the cooling water spray area.

[0022] As shown in FIG. 3(A), when a full cone nozzle is used for the nozzle 11, there may be a non-cooled area where the cooling water does not hit the round billet 2 locally in the injection area, which is the area where the cooling water sprayed from the nozzle 11 hits directly on the round billet 2, and temperature unevenness may occur in the longitudinal direction. If temperature unevenness occurs, that is, if there is unevenness in magnetism, it becomes difficult to magnetize the round billet 2 with the lift magnet. On the other hand, as shown in FIG. 3(B), when a square nozzle is used for the nozzle 11, it is possible to eliminate the non-cooled area where the cooling water sprayed from the nozzle 11 does not hit the round billet 2 directly, so that the round billet 2 can be cooled uniformly. In addition, when using a full cone nozzle or an oval nozzle with an oval injection pattern, in order to reduce temperature unevenness, it is sufficient to arrange the spray nozzles closely or use a nozzle with a sufficiently large injection area, but it is preferable to use a square nozzle in consideration of installation costs and maintainability.

[0023] In addition, the water density from the nozzles 11 and 12 is 2000 L / m 2 min, the cooling capacity hardly changes, so from an economical point of view, the water flow density is 2000L / m 2 min or less. In addition, the water flow rate from the nozzles 11 and 12 is preferably 20 L / m 2 If the cooling rate is less than 20 L / m, the cooling rate will be almost the same as air cooling, and no improvement in productivity can be expected. 2 min or more. In addition, since the cooling water sprayed from below contacts the lower surface of the round billet 2 and then falls from the surface of the round billet 2 due to gravity, spray cooling from below tends to have a lower cooling capacity than cooling from above, even with the same water volume density. Therefore, when nozzles 11 and 12 are installed above and below the round billet 2, if uniform cooling is possible under normal operating conditions, it is preferable that the water volume density of the nozzle 12 installed below is 1.0 to 1.5 times that of the nozzle 11 installed above. However, this does not apply when the upper and lower parts of the round billet 2 cannot always be uniformly cooled with the same water volume ratio due to fluctuations in water temperature or air temperature, or equipment deterioration such as nozzle clogging.

[0024] The shape meter 13 is a device for measuring the warpage of the round billet 2 after water cooling, and the measuring means is not particularly limited. For example, a one-dimensional laser displacement meter capable of measuring the distance of one point can be used as the measuring means of the shape meter 13. Usually, the round billet 2 during cooling is warped in an arc shape as shown in FIG. 4. Therefore, for example, as the measuring means of the shape meter 13, a plurality of laser displacement meter 131 may be arranged in the longitudinal direction, and the measured distance may be used to perform a quadratic equation or an approximation to an arc in the calculator 14 to calculate the warpage after cooling. In the case of such a measuring means, it is preferable to install at least three or more laser displacement meter 131. Also, a two-dimensional laser displacement meter capable of measuring the entire length of the round billet 2 may be used. The amount of warpage of the round billet 2 is the maximum height of the end face based on the vicinity of the longitudinal center of the round billet 2, as shown in FIG. 4. Also, since it is difficult to stably measure the amount of warpage of the round billet 2 for a long period of time due to the influence of scale falling off and the like when the laser displacement meter 131 is installed below the round billet 2, it is preferable to install it above the round billet 2.

[0025] The calculator 14 is a device that calculates the amount of warpage of the round billet 2 from the measurement results of the shape meter 13. The calculation results by the calculator 14 are transmitted to the cooling control device 16.

[0026] The thermometer 15 is a device for measuring the surface temperature of the round billet 2 after water cooling, and the measuring means is not particularly limited. For example, a spot radiation thermometer capable of measuring the temperature at one point can be used as the thermometer 15. In this case, since the cooling rate at the longitudinal ends of the round billet 2 tends to be faster than that at the center due to heat radiation from the end faces, the longitudinal position of the round billet 2 for measuring the temperature is preferably the center. Also, a two-dimensional radiation thermometer may be used as the thermometer 15 instead of the spot thermometer to measure the temperature of the entire longitudinal length of the round billet 2.

[0027] The cooling control device 16 is a device that determines the amount of cooling water to be sprayed from the nozzles 11, 12 and the ratio of the amount of water to be discharged and the amount of water to be discharged based on the manufacturing record of the round billet 2 (also referred to as the "past round billet 2") manufactured in the past and the amount of warping of the past round billet 2 after water cooling, and adjusts the injection flow rate of the cooling water, and is composed of a calculator such as a computer. The cooling control device 16 includes a recording unit 161, a water amount ratio determination unit 162, and a water amount adjustment unit 163. The recording unit 161 records various data transmitted from the upper computer 17, the amount of warping transmitted from the calculator 14, and data such as the temperature transmitted from the thermometer 15. The water amount ratio determination unit 162 includes a collecting unit 164, a calculating unit 165, and a setting unit 166, and determines the amount of water to be discharged and the amount of water to be described later based on the data recorded in the recording unit 161. The water volume adjustment unit 163 is a valve controller that adjusts the volume of cooling water sprayed from the nozzles 11 and 12, and adjusts the volume of water so as to achieve the upper and lower volume ratio determined by the water volume ratio determination unit 162.

[0028] <Manufacturing method and cooling method for round billet> A method for manufacturing and cooling the round billet 2 according to this embodiment will be described. In this embodiment, a slab cast by a continuous casting method is rolled to manufacture a round billet 2 of a predetermined length and cross-sectional shape. The round billet 2 that has been subjected to finish rolling is then cooled (water-cooled) by a cooling method using a cooling bed 3 and a cooling device 1. The round billet 2 that has been subjected to finish rolling has a size of φ170 to φ310, and a surface temperature of approximately 700°C to 900°C.

[0029] After the finish rolling, the round billet 2 is transported to the cooling bed 3 and allowed to cool on the cooling bed 3. The round billet 2 transported to the cooling bed 3 and water-cooled is also referred to as the "round billet 2 to be water-cooled next time." When the round billet 2 to be water-cooled next time is carried into the cooling bed 3, the cooling control device 16 acquires manufacturing results (composition of the round billet 2, size of the round billet 2, air temperature, water temperature, and ratio of upper and lower water volumes) from the host computer 17 and records them in the recording unit 161. In addition, the recording unit 161 records the operating conditions of round billets 2 manufactured in the past and data on warpage after water-cooling as manufacturing results.

[0030] After acquiring the data of the manufacturing results, the cooling control device 16 performs a process for determining the ratio of the amount of cooling water to be sprayed from the nozzles 11 and 12 (a determination process). The determination process is performed before the water-cooling of the round billet 2 to be water-cooled next time is started.

[0031] In the determination process, first, the cooling control device 16 reads out the relationship between the upper and lower water volume ratio and the warpage amount after water cooling for the past round billet 2 having parameters, such as components and size, similar to those of the round billet 2 to be water-cooled next time, from the recording unit 161 to the collecting unit 164 based on the acquired operating conditions of the round billet 2 to be water-cooled next time. Here, whether the past round billet 2 is similar to the parameters of the round billet 2 to be water-cooled next time can be determined based on the distance between the vectors of information representing the operating conditions. The upper and lower water volume ratio is the ratio between the amount of cooling water sprayed from the upper nozzle (also referred to as the "upper water volume") and the amount of cooling water sprayed from the lower nozzle (also referred to as the "lower water volume"), and in this embodiment, it is expressed as the ratio of the lower water volume to the upper water volume.

[0032] It is preferable that the past data of the round billet 2 read out to the collection unit 164 is data of a plurality of past round billets 2. Furthermore, the number of pieces of data of the past round billets 2 read out is preferably three or more, and more preferably about 20 pieces. It is also preferable that the past data of the round billet 2 used is the most recent one. As described above, the optimal water and sewage flow ratio fluctuates due to fluctuations in water temperature and air temperature, or equipment deterioration such as nozzle clogging, so by using the most recent data, it is possible to calculate the optimal water and sewage flow ratio that follows these changes in the equipment environment.

[0033] In the determination step, the calculation unit 165 then calculates the upper and lower water volume ratio that will be the target warpage of the round billet 2 to be water-cooled next time from the relationship between the upper and lower water volume ratio of the past round billet 2 read out by the collection unit 164 and the warpage after water-cooling. FIG. 5 shows data on the upper and lower water volume ratio and the warpage when cooling the past round billet 2 having similar parameters to the round billet 2 to be water-cooled next time, which is stored in the recording unit 161 as an example. As shown in FIG. 5, there is a linear correlation between the upper and lower water volume ratio and the warpage, so the calculation unit 165 can calculate an approximation line as shown in FIG. 5 and determine the upper and lower water volume ratio (plotted with ☆ in the figure) that will make the warpage after cooling fall within the range of the target value.

[0034] The target warpage does not necessarily have to be 0 mm. In the normal manufacture of the round billet 2, if the warpage exceeds 15 mm in total length, a press is required for correction, so the target warpage is preferably 15 mm or less.

[0035] In the determination step, the setting unit 166 further sets the amounts of cooling water sprayed from the nozzles 11, 12 so as to achieve the upper and lower water volume ratio calculated by the calculation unit 165. The determined upper and lower water volume ratio is recorded in the recording unit 161. From the viewpoint of shortening the cooling time, it is preferable that the water volume value is as large as possible within the equipment constraints. Therefore, for example, specific water volume values ​​for the upper and lower nozzles may be determined so as to satisfy the following formulas (1) and (2). Here, α is the upper and lower water volume ratio determined in the determination step, W u is the water volume of the upper nozzle (L / min), W b is the water volume of the lower nozzle (L / min), and X is the upper limit of the water volume that can be sprayed due to equipment restrictions (L / min). W u ≦X / (1+α) (1) W b = α × W u (2)

[0036] After the determination step, the water volume adjustment unit 163 adjusts the water volume so that the amount of cooling water for the nozzles 11, 12 is the determined amount (water volume adjustment step). That is, in the water volume adjustment step, the amount of cooling water is adjusted so that the determined ratio of upper and lower water volumes is achieved. The determination step and the water volume adjustment step are performed between the time the round billet 2 is transported to the cooling bed 3 and the time it arrives at the cooling device 1.

[0037] After the water amount adjustment process, the round billet 2 is transported to the cooling device 1, where cooling water is sprayed from the nozzles 11, 12 onto the round billet 2 at the amount of water adjusted in the water amount adjustment process, thereby water-cooling the round billet 2 (water-cooling process). In the cooling device 1, the round billet 2 is water-cooled while being transported in the transport direction, so that the round billet 2 is cooled to a predetermined temperature.

[0038] When the water-cooling by the cooling device 1 is completed, the shape meter 13 and the calculator 14 measure the amount of warpage of the round billet 2 after water-cooling. The measured amount of warpage is recorded in the recording unit 161. In addition to measuring the amount of warpage, the thermometer 15 measures the temperature of the round billet 2 after water-cooling, and the measurement result is recorded in the recording unit 161. Then, when the measurement result of the thermometer 15 indicates that the round billet 2 after water-cooling has reached a temperature at which it can be magnetized by the lift magnet, it is transported to the next process by the lift magnet. Note that, when the amount of warpage of the round billet 2 after water-cooling falls outside the target range, for example, the number of most recent data used to calculate the ratio of the amount of water and the amount of water is increased, and the same operation as described above is repeated to further reduce the amount of warpage after water-cooling.

[0039] According to the cooling device and cooling method for the round billet 2 of this embodiment, the nozzles 11, 12 are used to spray cooling water from above and below the round billet 2, thereby uniformly cooling the round billet 2 in the circumferential direction. At this time, the relationship between the ratio of the amount of water and the amount of upstream and downstream flow and the amount of warpage is obtained from the most recent production results, and the ratio of the amount of water and the amount of upstream and downstream flow is determined using this relationship. As a result, even if there is a change in the cooling conditions, such as when there has been recent deterioration of the equipment or when there has been a change in the water temperature or air temperature, it is possible to reduce unevenness in cooling in the circumferential direction by adjusting the ratio of the amount of water and the amount of downstream and upstream flow in response to this change, and to intermittently keep the amount of warpage within the target range.

[0040] Here, the cooling method using the cooling device 1 shown in Figures 1 and 2 will be specifically described together with the procedure, taking as an example the results of an actual implementation. In this example, spray nozzles of the same model number are installed as the nozzles 11 and 12 in each nozzle row in the vertical direction of the round billet 2, and the cooling device 1 having five nozzle rows was used. Moreover, each nozzle row can simultaneously cool four round billets 2, and the injection distances of the nozzles 11 and 12 were set to be equal. Furthermore, the temperature of the cooling water was 15°C, and the air temperature was 20°C.

[0041] In this example, a round billet with a diameter of 207 mm and a length of 12.5 m, mainly containing Fe with 7.0 wt% Cr and 0.8 wt% Mo, was cooled so that the water cooling start temperature was 300°C and the water cooling end temperature was 50°C.

[0042] In this example, the upper and lower water volume ratio was determined by the same method as in this embodiment. At this time, three past manufacturing results similar to each other were read from the recording unit 161 to the collecting unit 164. From the read data, the calculating unit 165 obtained a graph showing the relationship between the past upper and lower water volume ratios and the warpage after the completion of water cooling, as shown in FIG. 5. From this graph, the upper and lower water volume ratio at which the warpage after the completion of water cooling becomes 0 mm was determined to be 1.2. Note that the upper and lower water volume ratio at the most recent water cooling in the past was 1.1, the water cooling start temperature was 310°C, and the warpage after the completion of water cooling was 8 mm.

[0043] Based on the manufacturing results, the ratio of the amount of water flowing through the top and bottom of the round billet 2 to be water-cooled next time (next water flow ratio) was determined according to formula (3) to realize the calculated target water flow ratio of 1.2 as follows: In formula (3), r is the next water flow ratio (-), r0 is the calculated ratio of the amount of water flowing through the top and bottom of the billet when the warpage becomes 0 mm (target water flow ratio) (-), r A is the ratio of water and sewage volume in the previous cooling record (previous water and sewage volume ratio) (-), K p indicates the proportional gain (-). Note that the proportional gain K p Proportional control was performed with =0.6. r = (r0 - r A )×K p +r A (3)

[0044] Next, the values ​​were substituted into equation (2) to calculate the next water / sewage volume ratio as (1.2-1.1) x 0.6 + 1.1 = 1.16. Furthermore, the setting unit 166 set the upper and lower water volume ratio to 1.16, and the water volume adjustment unit 163 adjusted the upper and lower water volume ratio according to the setting to water-cool the round billet 2. After water-cooling was completed, the warpage measured by the shape meter 13 was 4 mm, and it was confirmed that the warpage approached 0 mm compared to the previous warpage.

[0045] The production results of the round billet 2 thus produced (components of the round billet 2, size of the round billet 2, air temperature, water temperature, upper and lower water volume ratio of 1.16, and warpage after water cooling of 4 mm) were recorded in the recording unit 161, and the above procedure was repeated to adjust the upper and lower water volume ratio. The relationship between the number of round billets 2 produced and the warpage is shown in FIG. 6. As is clear from FIG. 6, by adjusting the upper and lower water volume ratio of the round billet to be water-cooled next time using the production results, the upper and lower water volume ratio approaches the target value, and warpage can be gradually and further improved. In particular, when the number of produced billets was 5 or more, the warpage was almost 0 mm, and it was found that the warpage after water cooling could be suppressed to an extremely high degree.

[0046] <Modification> Although the present invention has been described above with reference to specific embodiments, it is not intended that the invention be limited by these descriptions. By referring to the description of the present invention, other embodiments of the present invention including various modifications in addition to the disclosed embodiments will be apparent to those skilled in the art. Therefore, it should be understood that the embodiments of the invention described in the claims also include embodiments including these modifications described herein, either alone or in combination.

[0047] For example, in addition to the above-mentioned items, a thermometer may be further provided on the inlet side of the cooling device 1, and the temperature of the round billet 2 before the start of water cooling may be recorded in the recording unit 161, and this measurement result may be used to determine whether the parameters of the past round billet 2 are similar to those of the round billet 2 to be water-cooled next time. Here, it is known that warping due to plastic strain caused by transformation expansion can be reduced by water cooling from a temperature below the transformation start temperature, and the water cooling start temperature is an influencing factor of warping (for example, JP 2020-69490 A). Since it is estimated that the influence of transformation plasticity is also large during phase transformation, the amount of warping can be further reduced by considering this temperature.

[0048] Also, the temperature of the round billet 2 may be measured by a thermometer provided on the inlet side of the cooling device 1, and water cooling may be started after the target temperature is reached. In general steel, the transformed structure and transformation start temperature change depending on the cooling rate, but high alloy steel has high hardenability and martensitic transformation occurs at a constant transformation start temperature regardless of the cooling rate. Therefore, for example, in the case of high alloy steel, s The occurrence of plastic strain may be suppressed by water cooling from less than M, thereby further reducing warpage. s It is preferable to perform water cooling from a temperature below which the phase transformation rate has progressed by about 30%. The high alloy steel referred to here is a material that is mainly composed of Fe and contains 7.0 wt% Cr and 0.8 wt% or more Mo.

[0049] Furthermore, M s Since is a value that depends on the chemical composition of the steel, it can be estimated in advance. For example, it can be estimated with little error from the following formula (4). Substitute the component amount (wt%) of the element for the element symbol in formula (4). Also, substitute zero for elements that are not included in the chemical composition.

[0050]

number

[0051] Furthermore, M smay be estimated in advance from the relationship between temperature and strain for the target steel type. The relationship between temperature and strain can be measured in advance by controlling the temperature via a thermocouple welded to the test piece using a Fuji Electric Industrial Co., Ltd. THERMEC MASTER (hot processing simulation test device) and measuring the expansion and contraction of the test piece in advance using a displacement meter during the process. From the relationship between temperature and strain obtained in this way, M can be calculated for each steel type. s It is sufficient to estimate

[0052] Also, a known transformation rate sensor (for example, a transformation rate measuring device described in Japanese Patent Application Laid-Open No. 8-62181) may be installed on the inlet side of the cooling device 1 instead of a thermometer, and water cooling may be started after the target phase transformation rate is reached. In this case, as in the above-mentioned modified example, M s It is preferable to perform water cooling after the phase transformation rate has progressed by about 30% at or below this temperature. EXAMPLES

[0053] Examples carried out by the present inventors will be described below. Note that the examples do not limit the present invention in any way. Table 1 shows the experimental results when steel type A (mainly Fe, Cr: 7wt%, Mo: 0.8wt%) and steel type B (mainly Fe, Cr: 17wt%, Mo: 1.0wt%) were cooled in the equipment shown in Figures 1 and 2. The cooling times when left to cool were 12 hours and 20 hours, respectively. The temperature at which both steel types A and B could be magnetized by a lifting magnet was 60°C. The configuration of the equipment was the same as in the above embodiment, and the cooling water temperature was 15°C and the air temperature was 20°C.

[0054] [Table 1]

[0055] The water cooling start temperature in Table 1 is the temperature measured with a thermoviewer before the start of water cooling, and the transformation rate at the start of water cooling is a value calculated from the relationship between the temperature and transformation rate that was determined in advance. Here, the water flow density column lists the water flow densities of the upper and lower nozzles, with the water flow density of the upper nozzle listed on the first line and the water flow density of the lower nozzle listed on the second line. Note that the upper and lower nozzles are the same model number and have the same spray distance. The upper and lower water flow ratio column lists (water flow rate of the lower nozzle / water flow rate of the upper nozzle) as the upper and lower water flow ratio.

[0056] In addition, in Table 1, the column for cooling time indicates the time required from when the round billet 2 reaches the inlet side of the cooling bed 3 until it is discharged from the cooling bed 3, that is, the time required for it to be cooled to a temperature at which it can be magnetized by the lift magnet by natural cooling on the cooling bed 3 and water cooling by the cooling device 1.

[0057] Furthermore, in Table 1, the column for warpage indicates the amount of warpage measured by the shape meter 6 after water cooling. For examples in which the cooling method according to the above embodiment was applied, the value of the amount of warpage when the number of manufactured pieces was increased and gradually decreased at the end was indicated as shown in Fig. 6. Note that a positive value of warpage indicates an upward warpage (a downward convex shape) and a negative value indicates a downward warpage (an upward convex shape).

[0058] Comparative Example 1 is the result of water cooling of a round billet 2 without applying the present invention, with a water cooling start temperature of 400°C, a transformation rate of 0% at the start of water cooling, and an upper and lower water volume ratio of 0.8. The cooling time was 7 hours, and the amount of warpage after the end of water cooling was 35 mm. The upper and lower water volume ratio of 0.8 was out of the preferred range (1.0 to 1.3), and the amount of warpage did not fall within the target range of 15 mm.

[0059] Example 1 is the result of applying the present invention to round billets 2 having the same water-cooling start temperature and transformation rate at the start of water-cooling as Comparative Example 1, and water-cooling while increasing the number of productions. As the number of productions increased, the value of warpage gradually decreased, and finally the value of warpage was about 10 mm. At this time, the ratio of the amount of water flowing into and out of the water was 1.23, and the cooling time was 6 hours. In Example 1, by applying the present invention, as the number of productions increased, the ratio of the amount of water flowing into and out of the water fell within a suitable range (1.0 to 1.3), and the amount of warpage was 10 mm, an improvement over Comparative Example 1 and falling within the target range of 15 mm.

[0060] Comparative Example 2 is the result of water cooling of a round billet 2 without applying the present invention, with a water cooling start temperature of 250°C, a transformation rate of 35% at the start of water cooling, and an upper and lower water volume ratio of 0.8. The cooling time was 5 hours, and the amount of warpage after water cooling was 20 mm. Since the transformation rate at the start of water cooling was 35%, it is estimated that plastic strain due to transformation expansion was suppressed, and the amount of warpage was improved to 20 mm compared to Comparative Example 1, but since the upper and lower water volume ratio was 0.8, which deviated from the preferred range (1.0 to 1.3), it did not fall within the target range of 15 mm.

[0061] Example 2 is a result of applying the present invention to round billet 2 having the same water-cooling start temperature and transformation rate at the start of water-cooling as Comparative Example 2, and water-cooling while increasing the number of production. As the number of production increased, the warpage value gradually decreased, and the final warpage amount was about -3 mm. At this time, the ratio of the amount of water flowing up and down was 1.21, and the cooling time was 4 hours. Since the present invention was applied, as the number of production increased, the ratio of the amount of water flowing up and down was within the preferable range (1.0 to 1.3), and the warpage was -3 mm, which was an improvement over Comparative Example 1. In addition, since the transformation rate at the start of water-cooling was 35%, which was within the preferable range (30% or more), the warpage amount was improved from Example 1 and fell within the target range of 15 mm.

[0062] The results of Comparative Examples 3 and 4 and Examples 3 and 4 were obtained for steel type B, but since the results were similar to those of Comparative Examples 1 and 2 and Examples 1 and 2, details will be omitted. [Explanation of symbols]

[0063] 1 Cooling device 11,12 Nozzle 13 Shape meter 131 Laser Displacement Meter 14 Arithmetic unit 15 Thermometer 16 Cooling control device 161 Recording Department 162 Water ratio determination section 163 Water volume adjustment section 164 Collection Department 165 Calculation Section 166 Settings 17 Upper computer 2 Round billet 3 Cooling bed

Claims

1. A cooling device for a round billet, which water-cools a round billet that has been cooled on a cooling bed after finish rolling, comprising: Nozzles provided above and below the round billet for injecting cooling water; a cooling control device that determines a ratio of the amount of cooling water to be sprayed from the nozzle based on a production record and an amount of warpage of the round billet that has been previously produced, and adjusts the spray flow rate of the cooling water so as to achieve the determined ratio of the amount of cooling water to be sprayed; Equipped with The cooling control device uses at least the upper and lower water volume ratios of a plurality of past round billets having the same size as the round billet to be water-cooled next, as the past production records of the round billets, and determines the upper and lower water volume ratios so that the warpage amount of the round billet to be water-cooled next is within a target range.

2. 2. The cooling device for a round billet according to claim 1, wherein the cooling control device determines the relationship between the ratio of the amount of water and the amount of warping and the amount of warping from the production records and warping amounts of a plurality of the past round billets, and determines the ratio of the amount of water and the amount of water and the amount of warping using the determined relationship between the ratio of the amount of water and the amount of warping and the amount of warping so that the amount of warping of the round billet to be water-cooled next time falls within a target range.

3. A shape meter for measuring the amount of warpage of the cooled round billet is further provided.

3. The cooling device for a round billet according to claim 1, wherein the cooling control device uses an amount of warpage measured by the shape meter as the amount of warpage of the past round billet.

4. A method for cooling a round billet, comprising water cooling the round billet that has been allowed to cool on a cooling bed after finish rolling, the method comprising the steps of: Nozzles provided above and below the round billet for injecting cooling water; a determining step of determining a ratio of the amount of cooling water to be sprayed from nozzles provided above and below the round billet based on the manufacturing record and the amount of warpage of the round billet that has been manufactured in the past; a water amount adjusting step of adjusting the injection flow rate of the cooling water so as to achieve the water / sewage amount ratio determined in the determining step; a water cooling step of injecting the cooling water from the nozzle onto the round billet at the amount of water adjusted in the water amount adjustment step; Equipped with In the determination process, at least the upper and lower water volume ratios of a plurality of past round billets having the same size as the round billet to be water-cooled next time are used as the past production records of the round billet, and the upper and lower water volume ratios are determined so that the warpage amount of the round billet to be water-cooled next, which is the round billet to be water-cooled next, falls within a target range.

5. A method for producing a round billet, comprising the steps of: cooling a finish-rolled round billet on a cooling bed; and then cooling the round billet with water, A method for producing a round billet, comprising the steps of: water-cooling the round billet using the cooling method according to claim 4 .

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