Steel cooling method and steel manufacturing method

Abstract

To provide a cooling method of a steel material and a manufacturing method of the steel material which can improve cooling capability of a cooling bed without increasing generation rate of red rust.SOLUTION: A cooling method of a steel material is a cooling method of a steel material where a hot-rolled steel material is cooled by a cooling bed. Cooling devices arranged outside of an end of a steel material in a longer direction on the cooling bed simultaneously inject air and refrigerant liquid of mist / dropwise in the longer direction to a surface of the steel material extending in the longer direction to cool the steel material.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for cooling a steel material and a method for manufacturing a steel material. [Background technology]

[0002] The manufacturing process will be described using steel sections, particularly H-section steel, as an example of steel material. After the hot rolling process, the steel material is cut to a predetermined length using a hot sawing machine and then transported to a cooling bed while still hot. The steel material is transported through the cooling bed at a predetermined speed and cooled to approximately room temperature. After cooling on the cooling bed, the steel material then undergoes a cold straightening process using a straightening machine and an inspection process to become a finished product. In the case of H-beams, which are shaped steel, the H-beams are often cooled in an I-position on the cooling bed. To accelerate the cooling of the H-beams, spray nozzles are sometimes used to spray cooling water onto the flanges from above and below the H-beams in the I-position. The flanges are spray-cooled because they are thicker than the webs and therefore cool slower than the webs with air cooling.

[0003] Patent Document 1 discloses a technique for cooling an H-shaped steel beam in an I position by spraying cooling water onto the outer surfaces of the upper and lower flanges and the web surface. The technique disclosed in Patent Document 1 aims to reduce variations in strength quality by cooling the H-shaped steel beam in the I position, thereby preventing water from accumulating on the web and suppressing uneven cooling of the web. Patent Document 2 discloses a technique for arranging bundled steel bars in a grid pattern and cooling them with cooling mist sprayed from below by a mist fan. Patent Document 3 discloses a technique for cooling stacked hot-rolled coils with cooling mist sprayed from a mist fan. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 07-185638 [Patent Document 2] Japanese Patent Application Publication No. 2020-164984 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-188753 Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of H-section steel, the size of steel sheets is increasing, and accordingly, the number of thicker products is increasing. In particular, there is a strong tendency for flange thickness to be relatively thicker compared to web thickness. As flange thickness increases, the cooling time in the cooling bed after hot rolling increases, resulting in reduced productivity of H-section steel sheets. For this reason, improving the cooling capacity of the cooling bed is desirable. While spray cooling is one method of cooling in the cooling bed, increasing the amount of water used for spray cooling requires an increased drainage capacity for the cooling water, which requires significant capital investment. Furthermore, increasing the amount of water used for spray cooling tends to leave the cooling water on the surface of the steel sheet after cooling, which is undesirable because it can cause red rust to form on the steel sheet surface. Therefore, a simpler method is desirable for improving the cooling capacity of the cooling bed without major equipment modifications and without increasing the incidence of red rust, which is prone to form on the steel sheet surface. Patent Documents 2 and 3 disclose techniques for cooling steel bars and hot-rolled coils by spraying cooling mist from a mist fan, but the cooling is performed in a place other than a cooling bed that sequentially cools steel sheets that have undergone a hot rolling process online. Therefore, the techniques disclosed in Patent Documents 2 and 3 cannot be used as they are for cooling steel materials in a cooling bed.

[0006] The present invention has been made in consideration of the above-mentioned problems, and its object is to provide a steel cooling method and a steel manufacturing method that can increase the cooling capacity of a cooling bed without increasing the rate of red rust generation. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, the method for cooling steel according to the present invention is a method for cooling hot-rolled steel in a cooling bed, characterized in that the steel is cooled by simultaneously spraying air and atomized refrigerant liquid in a direction along the longitudinal direction of a surface extending in the longitudinal direction of the steel from a cooling device arranged outside the longitudinal end of the steel in the cooling bed.

[0008] Furthermore, the steel cooling method according to the present invention is characterized in that, in the above invention, the amount of air sprayed from the cooling device is 200 [Nm3 / min] or more per unit length in the horizontal direction perpendicular to the spraying direction, the flow rate of the refrigerant liquid sprayed from the cooling device is 0.2 to 4.0 [L / min] per unit length in the horizontal direction perpendicular to the spraying direction, and the particle diameter (average droplet diameter) of the droplets of the refrigerant liquid sprayed from the cooling device is 10 to 200 [μm].

[0009] In addition, the method for manufacturing steel material according to the present invention is characterized by comprising a hot rolling process for hot rolling steel material, and a cooling process for cooling the steel material hot rolled in the hot rolling process on a cooling bed using the cooling method for steel material of the present invention described above. [Effects of the Invention]

[0010] The steel cooling method and steel manufacturing method according to the present invention have the effect of increasing the cooling capacity of the cooling bed without increasing the rate of red rust generation. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing the cross-sectional shape of an H-beam manufactured by a method for manufacturing a steel material according to an embodiment. [Figure 2] FIG. 2 is a diagram showing the cross-sectional shape of a steel sheet pile. [Figure 3] FIG. 3 is a diagram showing an example of each step of the method for producing a steel material according to the embodiment. [Figure 4]FIG. 4 is a diagram showing another example of each step of the method for producing a steel material according to the embodiment. [Figure 5] FIG. 5 is a plan view schematically showing each step performed in the cooling bed cooling step. [Figure 6] FIG. 6 is a front view schematically showing each step performed in the cooling bed cooling step. [Figure 7] Figure 7(a) is a front view showing an example of a mist cooling device used in the mist cooling step, and Figure 7(b) is a side view showing an example of a mist cooling device used in the mist cooling step. [Figure 8] Figure 8(a) is a front view showing another example of the mist cooling device used in the mist cooling step, and Figure 8(b) is a side view showing another example of the mist cooling device used in the mist cooling step. [Figure 9] FIG. 9 is a diagram showing an example of the installation position of the mist cooling device on the cooling bed. [Figure 10] FIG. 10 is a diagram showing an example of a spray cooling device used in the spray cooling process. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the steel cooling method and steel manufacturing method according to the present invention will be described, but the present invention is not limited to these embodiments.

[0013] FIG. 1 is a diagram showing the cross-sectional shape of an H-beam steel 1 manufactured by a method for manufacturing a steel material according to an embodiment.

[0014] The method for manufacturing a steel material according to the embodiment is used, for example, to manufacture an H-shaped steel beam 1 as shown in FIG. 1 , which is a structural steel beam. The H-shaped steel beam 1 has a cross-sectional shape perpendicular to the longitudinal direction, a web 10 extending in one direction, and a pair of flanges 11 connected to both ends of the web 10 in the extending direction and extending in a width direction perpendicular to the extending direction. In this embodiment, the position of the H-shaped steel beam 1 in which the extending direction of the web 10 is horizontal and the width direction of the flanges 11 is vertical is referred to as an H position. In this embodiment, the position of the H-shaped steel beam 1 in which the extending direction of the web 10 is vertical and the width direction of the flanges 11 is horizontal is referred to as an I position.

[0015] It should be noted that the steel material manufactured by the steel material manufacturing method according to the embodiment is not limited to the H-shaped steel 1. That is, the manufacturing method according to the embodiment can also be applied to the manufacturing of steel shapes other than the H-shaped steel 1, such as a steel sheet pile 101 having a web 111, a flange 112, and a joint portion 113 as shown in Fig. 2, a channel steel, and an angle steel. Furthermore, the manufacturing method according to the embodiment can also be applied to the manufacturing of round bars, steel pipes, thick steel plates, and the like.

[0016] FIG. 3 is a diagram showing an example of each step of the method for producing a steel material according to the embodiment.

[0017] The method for manufacturing a steel material according to the embodiment shown in FIG. 3 includes a heating step S1, a hot rolling step S2, a hot sawing step S3, a cooling bed cooling step S4, a cold straightening step S5, and an inspection step S6. The heating step S1 is a step of heating a steel material such as an H-beam 1 in a heating furnace. The hot rolling step S2 is a step of hot rolling the heated steel material in a rolling mill. The hot sawing step S3 is a step of hot sawing the rolled steel material to a predetermined length. The cooling bed cooling step S4 is a step of cooling the hot sawed steel material to room temperature. The cold straightening step S5 is a step of cold straightening the steel material cooled on the cooling bed for distortions and the like using a straightening machine. The inspection step S6 is a step of measuring the dimensions and inspecting the appearance of the cold straightened steel material. The steel material that has undergone the inspection step S6 is transported to a shipping step as a finished product.

[0018] FIG. 4 is a diagram showing another example of each step of the method for producing a steel material according to the embodiment.

[0019] The method for manufacturing a steel material according to the embodiment shown in FIG. 4 includes a heating step S11, a hot rolling step S12, a cooling bed cooling step S13, a cold straightening step S14, a cold sawing step S15, and an inspection step S16. The heating step S11 is a step of heating a steel material such as an H-beam 1 in a heating furnace. The hot rolling step S12 is a step of hot-rolling the heated steel material in a rolling mill. The cooling bed cooling step S13 is a step of cooling the hot-rolled steel material to room temperature. The cold straightening step S14 is a step of cold-straightening the steel material cooled on the cooling bed using a straightening machine to remove distortions, etc. The cold sawing step S15 is a step of cold-straightening the cold-straightened steel material to a predetermined length. The inspection step S16 is a step of measuring the dimensions and inspecting the appearance, etc., of the cold-sawed steel material. The steel material that has undergone the inspection step S16 is transported to a shipping step as a product.

[0020] Next, in the method for manufacturing a steel material according to the embodiment, a cooling bed cooling step will be described in which an H-shaped steel 1 as a steel material is cooled on a cooling bed 3. Fig. 5 is a plan view schematically showing each step performed in the cooling bed cooling step. Fig. 6 is a front view schematically showing each step performed in the cooling bed cooling step. Note that, here, an example will be described in which an H-shaped steel 1 that has been hot sawn to various lengths (10 to 30 m) in the longitudinal direction after hot rolling is cooled on a cooling bed 3.

[0021] The cooling bed cooling process according to the embodiment includes (1) an intake process, (2) a first air-cooling process, (3) a mist cooling process, (4) a second air-cooling process, (5) a spray cooling process, and (6) a discharge process. In the cooling bed cooling process according to the embodiment, the H-shaped steel 1 is cooled to room temperature (for example, about 50°C) during transport within the cooling bed 3. The residence time (cooling time) of the H-shaped steel 1 within the cooling bed 3 is, for example, about 1 to 3 hours.

[0022] As shown in Figures 5 and 6, the H-shaped steel 1 that has been hot-sawed after hot rolling is transported in an H position on table rollers 2 in the Y direction, which is the same direction as the longitudinal direction of the H-shaped steel 1, up to the entrance side of the cooling bed 3. Then, in the removal process of removing the H-shaped steel from the table rollers 2 to the cooling bed 3, the H-shaped steel 1 is turned 90° in a direction perpendicular to the longitudinal direction of the H-shaped steel 1 to place it in an I position, and the H-shaped steel 1 is placed on a plurality of skid rails 31 provided on the cooling bed 3. The H-shaped steel 1 placed on the skid rails 31 is transported in the X direction, which is the direction perpendicular to the longitudinal direction of the H-shaped steel 1 (the Y direction in Figure 5), for example, by moving the skid rails 31 using a moving mechanism or by pressing with dogs (generally triangular pushing claws) attached to a moving chain or wire.

[0023] The H-shaped steel 1 removed from the cooling bed 3 is air-cooled in a first air-cooling process while being transported continuously or intermittently on skid rails 31. After being air-cooled in the first air-cooling process, the H-shaped steel 1 is mist-cooled by a plurality of mist cooling devices 4 while being transported continuously or intermittently on the skid rails 31. In the mist cooling process, the mist cooling devices 4, which are arranged outside the longitudinal ends of the H-shaped steel 1 to be cooled, simultaneously spray air and atomized refrigerant liquid (cooling mist) along the longitudinal direction of the H-shaped steel 1 (in this example, the inner and outer surfaces of the flanges 11), thereby cooling the H-shaped steel 1. Note that an air-cooling process before the mist cooling process is not essential, but it is preferable to provide the air-cooling process before the mist cooling process because it allows the H-shaped steel 1 to be checked for warpage and the presence or absence of defects during air-cooling.

[0024] The H-shaped steel 1 that has been mist-cooled in the mist cooling process is transported continuously or intermittently on a skid rail 31 and air-cooled in the second air-cooling process. The H-shaped steel 1 that has been air-cooled in the second air-cooling process is spray-cooled by a plurality of spray cooling devices 5 in the spray cooling process. Note that although the mist cooling process is performed before the spray cooling process here, there are no particular restrictions on the order of the mist cooling process and the spray cooling process, and the mist cooling process may be performed after the spray cooling process. Furthermore, the mist cooling process and the spray cooling process may be performed consecutively without providing an air-cooling period (second air-cooling process) between them. Furthermore, it is not essential to perform the spray cooling process.

[0025] The H-shaped steel 1 that has been spray-cooled in the spray cooling process is discharged from the skid rails 31 of the cooling bed 3 onto the table rollers 6 in the discharge process. In this discharge process, the H-shaped steel 1 is rotated 90° in a direction perpendicular to the longitudinal direction of the H-shaped steel 1 to take an H position, and the H-shaped steel 1 is placed on the table rollers 6. The H-shaped steel 1 discharged onto the table rollers 6 in the discharge process is transported by the table rollers 6 from the outlet side of the cooling bed 3 in the longitudinal direction of the H-shaped steel 1, and sent to the next process (for example, a cold straightening process).

[0026] Fig. 7(a) is a front view showing an example of the mist cooling device 4 used in the mist cooling step, and Fig. 7(b) is a side view showing an example of the mist cooling device 4 used in the mist cooling step.

[0027] The mist cooling device 4 shown in FIGS. 7(a) and 7(b) includes a cylindrical barrel 42 containing a fan 41 that rotates around a rotation axis 40. The cylindrical barrel 42 is supported on a base 46 via a shaft 45 so as to be rotatable in the vertical direction. An annular piping 44 is arranged around the air outlet of the cylindrical barrel 42. A plurality of mist nozzles 43 are connected to the piping 44 at predetermined intervals in the circumferential direction, surrounding the air outlet of the cylindrical barrel 42. The mist nozzles 43 are arranged forward of the fan 41, as shown in FIGS. 7(a) and 7(b). A refrigerant liquid flows through the piping 44, and a cooling mist M, which is a mist-like refrigerant liquid, is sprayed from the mist nozzles 43 connected to the piping 44. The cooling liquid may be, for example, water (cooling water). The cooling mist M sprayed from the multiple mist nozzles 43 is carried to the H-shaped steel 1 by the air current generated by the fan 41, thereby cooling the H-shaped steel 1. In addition, in the mist cooling device 4 shown in Figures 7(a) and 7(b), the air current (air flow) generated by the fan 41 itself has the effect of promoting convection cooling of the H-shaped steel 1, thereby improving the cooling capacity.

[0028] The mist cooling device 4 may have a configuration in which multiple mist nozzles 43 are arranged behind the fan 41, as shown in Figures 8(a) and 8(b). In the mist cooling device 4 shown in Figures 8(a) and 8(b), the cooling mist M sprayed from the multiple mist nozzles 43 behind the fan 41 is sucked into the cylindrical body 42 by the airflow generated by the fan 41, and is sprayed together with air from the air outlet of the cylindrical body 42.

[0029] Here, the mist cooling device 4 is generally required to be able to spray cooling mist M at least 10 meters in the longitudinal direction of the H-beam 1, cooling an H-beam 1 with a length of 10 meters or more, although this depends on the length of the H-beam 1 to be cooled in the cooling bed 3. For this reason, the amount of air sprayed from the mist cooling device 4 is preferably 200 Nm³ / min or more per meter in the conveying direction of the H-beam 1 (per unit length in the horizontal direction perpendicular to the spraying direction) in the cooling bed 3. If the amount of air sprayed from the mist cooling device 4 is less than 200 Nm³ / min, the cooling mist M cannot be carried far by the airflow, and the cooling capacity may be insufficient for a portion of the H-beam 1 in the longitudinal direction. Note that there is no particular upper limit to the amount of air sprayed from the mist cooling device 4, but if the amount of air sprayed is too large, there is a concern that the mist cooling device 4 will become large-scale and increase equipment costs.

[0030] The amount of air sprayed from the mist cooler 4 here is a value measured at the position closest to the mist cooler 4 on the cooled surface at one end of the longitudinal direction of the H-shaped steel 1 to be cooled. Usually, the distance from the mist cooler 4 to the position closest to the mist cooler 4 on the cooled surface of the H-shaped steel 1 in the longitudinal direction of the H-shaped steel 1 is set to about 1 to 3 m.

[0031] The size of the droplets of the cooling mist M is preferably 10 to 200 μm in terms of Sauter mean particle diameter (hereinafter referred to as mean diameter). If the mean diameter of the droplets is smaller than 10 μm, the cooling capacity for the H-shaped steel 1 may be insufficient. On the other hand, if the mean diameter of the droplets is larger than 200 μm, it may be difficult to carry the cooling mist M on the air current and carry it far, and the cooling capacity may be insufficient for a portion of the H-shaped steel 1 in the longitudinal direction.

[0032] The spray rate (flow rate) of the cooling mist M (cooling water) is preferably 0.2 to 4.0 L / min per meter in the direction of transport of the H-beam 1 within the cooling bed 3 (per unit length in the horizontal direction perpendicular to the spray direction). If the spray rate is less than 0.2 L / min, the cooling capacity for the H-beam 1 may be insufficient. On the other hand, if the spray rate is greater than 4.0 L / min, it becomes difficult to transport the cooling mist M far away on the airflow, and the cooling capacity may be insufficient for a portion of the longitudinal direction of the H-beam 1. Furthermore, if the spray rate is within the appropriate range, the cooling mist M evaporates after landing on the H-beam 1, so there is no need to consider wastewater treatment. On the other hand, if the spray rate is too high, a large amount of cooling water remains on the H-beam 1 without evaporating after the cooling mist M lands on it, which may require wastewater treatment. Furthermore, if too much water is sprayed, some of the cooling water adhering to the H-shaped steel 1 will not evaporate immediately and will remain on the H-shaped steel 1, which may cause red rust in the areas where the cooling water remains, damaging the appearance of the H-shaped steel 1.

[0033] The amount of sprayed cooling mist M (cooling water) and the size of the droplets of the cooling mist M referred to here are values measured at the outlet side of the mist cooler 4 installed at one longitudinal end of the H-section steel 1. The original pressure of the cooling mist M (cooling water) sprayed from the mist nozzles 43 is preferably 0.2 MPa or more, although this depends on the specifications of the mist nozzles 43. The number of mist nozzles 43 also depends on the specifications of the mist nozzles 43 and the amount of sprayed water, but preferably 10 to 30 per mist cooler 4.

[0034] FIG. 9 is a diagram showing an example of the installation position of the mist cooling device 4 on the cooling bed 3.

[0035] The mist cooling device 4 is disposed on the cooling bed 3 at a position outside the longitudinal end of the H-shaped steel 1. In FIG. 9, the mist cooling device 4AU and the mist cooling device 4AL are disposed above and below the leading H-shaped steel 1A, further forward of the longitudinal tip of the leading H-shaped steel 1A, in the extension direction of the web 10A of the H-shaped steel 1A. The mist cooling device 4AU sprays cooling mist M toward the top flange 11AU of the leading H-shaped steel 1A in a direction along the longitudinal direction of the inner and outer surfaces of the top flange 11AU. The mist cooling device 4AL sprays cooling mist M toward the bottom flange 11AL of the leading H-shaped steel 1A in a direction along the longitudinal direction of the inner and outer surfaces of the bottom flange 11AL. 9, the mist coolers 4BU and 4BL are arranged above and below the trailing H-shaped steel 1B in the extending direction of the web 10B of the H-shaped steel 1B, further rearward of the longitudinal rear end of the trailing H-shaped steel 1B. The mist coolers 4BU spray cooling mist M toward the top flange 11BU of the trailing H-shaped steel 1B in a direction along the longitudinal direction of the inner and outer surfaces of the top flange 11BU. The mist coolers 4BL spray cooling mist M toward the bottom flange 11BL of the trailing H-shaped steel 1B in a direction along the longitudinal direction of the inner and outer surfaces of the bottom flange 11BL.

[0036] Furthermore, a plurality of mist cooling devices 4 used in the mist cooling process can be installed along the direction in which the H-shaped steel 1 is transported within the cooling bed 3. The number of mist cooling devices 4 to be installed may be determined according to the required cooling capacity.

[0037] FIG. 10 is a diagram showing an example of a spray cooling device 5 used in the spray cooling step.

[0038] The spray cooling device 5 includes an upper header 52U having a plurality of upper spray nozzles 51U and a lower header 52L having a plurality of lower spray nozzles 51L. The upper header 52U is disposed above the H-shaped steel 1 being transported within the cooling bed 3. The lower header 52L is disposed below the H-shaped steel 1 being transported within the cooling bed 3. The upper header 52U sprays cooling water W from the plurality of upper spray nozzles 51U toward the upper surface (outer surface) of the upper flange 11AU of the leading H-shaped steel 1A and the upper surface (outer surface) of the upper flange 11BU of the trailing H-shaped steel 1B. The lower header 52L sprays cooling water W from the plurality of lower spray nozzles 51L toward the lower surface (outer surface) of the bottom flange 11AL of the leading H-shaped steel 1A and the lower surface (outer surface) of the bottom flange 11BL of the trailing H-shaped steel 1B. In this manner, the spray cooling device 5 cools the leading H-shaped steel 1A and the trailing H-shaped steel 1B. The cooling capacity of the spray cooling device 5 is determined by, for example, the amount of cooling water W and the transport speed of the H-beam steel 1.

[0039] To cool the upper flanges 11AU, 11BU of the H-shaped steel beams 1A, 1B, an upper header 52U must be provided, for example, that is longer than the longitudinal length of the H-shaped steel beams 1A, 1B, and multiple upper spray nozzles 51U must be provided on the upper header 52U. Furthermore, piping must also be installed to supply cooling water W to the multiple upper spray nozzles 51U. Therefore, once the upper header 52U has been designed and installed, it is difficult to easily expand the upper header 52U. The location of the lower header 52L must also be designed, taking into account interference with the movement mechanism and movement chain of the skid rail 31, making it difficult to easily expand the lower header 52L. Furthermore, spray cooling requires a relatively large amount of cooling water W, so wastewater treatment must also be considered.

[0040] In the steel manufacturing method according to the embodiment, the amount of cooling water used in the mist cooling process using the mist cooling device 4 in the cooling bed cooling process is small, and most of the cooling water evaporates as the H-shaped steel 1 cools. Therefore, in many cases, it is not necessary to provide a separate cooling water discharge facility for the mist cooling process. Therefore, in the steel manufacturing method according to the embodiment, by providing a mist cooling process using the mist cooling device 4 in the cooling bed cooling process in which the H-shaped steel 1 is cooled on the cooling bed 3, it is possible to easily enhance the facilities for cooling the H-shaped steel 1 online. [Example]

[0041] In this example, an H-shaped steel 1, which is a steel material, was cooled in a cooling bed 3 used in a steel manufacturing method according to an embodiment, by setting the cooling conditions as in Examples 1 and 2 described below. The size of the H-shaped steel 1 used in this example was a web height of 1000 mm, a flange width of 400 mm, a web thickness of 19 mm, and a flange thickness of 40 mm, and the length in the longitudinal direction on the cooling bed 3 was 15 m.

[0042] The size of the cooling bed 3 in this embodiment is 34 m in the longitudinal direction of the H-shaped steel 1 (Y direction in FIG. 5), and 45 m in the transport direction of the H-shaped steel 1 within the cooling bed 3 (X direction in FIG. 5). In this embodiment, the mist cooling devices 4 shown in FIG. 7 are installed at five locations at predetermined intervals in a section 7.5 m to 15 m from the entrance of the cooling bed 3 in the transport direction. At each location in the transport direction, two mist cooling devices 4 are installed, one above the other, on both sides of the H-shaped steel 1 in the longitudinal direction, as shown in FIG. 9. That is, in this embodiment, 20 mist cooling devices 4 are installed on the cooling bed 3.

[0043] In this example, two H-shaped steel beams 1 each having a longitudinal length of 15 m were taken from one raw material. As shown in Figure 5, the two H-shaped steel beams 1 were placed in the cooling bed 3 with the leading H-shaped steel beam 1 placed in the front and the trailing H-shaped steel beam 1 placed in the rear.

[0044] Example 1 In Example 1, the mist cooling process and the spray cooling process were performed on the H-shaped steel 1 of Suitable Examples 1 to 3, while the H-shaped steel 1 of Comparative Examples 1 to 3 was subjected to only the spray cooling process without the mist cooling process. Specifically, in Suitable Examples 1 to 3, the respective steps in the cooling bed cooling process were an intake process, a first air-cooling process, a mist cooling process, a second air-cooling process, a spray cooling process, and a discharge process. In addition, in Comparative Examples 1 to 3, the respective steps in the cooling bed cooling process were an intake process, an air-cooling process, a spray cooling process, and a discharge process.

[0045] In Example 1, the feed rate of the H-shaped steel 1 in the cooling bed 3 was 0.5 m / min. The length of the cooling bed 3 in the conveying direction (the X direction) was 45 m, so the total time required for the H-shaped steel 1 to pass through the cooling bed 3 was 90 minutes. In Compliant Examples 1 to 3, the mist cooling process was performed within 15 to 30 minutes after the H-shaped steel 1 was taken (charged) into the cooling bed 3, and mist cooling using the mist cooling device 4 was performed from both longitudinal ends of the H-shaped steel 1. The spray cooling process was performed within 70 to 85 minutes after the H-shaped steel 1 was taken (charged) into the cooling bed 3. The installation length of the spray cooling device 5 in the conveying direction (the X direction) was 7.5 m, the same as that of the mist cooling device 4.

[0046] In Compliant Examples 1 to 3, the H-shaped steel 1 was cooled in the mist cooling process under the following conditions. Note that the following conditions are values per 1 m in the direction in which the H-shaped steel 1 is transported within the cooling bed 3, and are values at one end of the H-shaped steel 1 in the longitudinal direction. ·Air volume: 320 [Nm3 / min] ·Droplet diameter: 20[μm] ·Droplet water volume: 1.0 [L / min]

[0047] In addition, in the compatible examples 1 to 3, the H-beam 1 was cooled under the following conditions in the spray cooling process. Note that the following conditions are the water flow density per unit area when the cooling bed 3 is viewed from above. ·Water density: 1.0[L / (m 2 ·min)]

[0048] In contrast to this, in Comparative Examples 1 to 3, the mist cooling step was not performed, and only the spray cooling step was performed. The conditions for the spray cooling step in Comparative Examples 1 to 3 were the same as those in Suitable Examples 1 to 3.

[0049] The H-shaped steel 1 was cooled under each of these conditions, and the temperatures of the web 10 and flange 11 of the H-shaped steel 1 when it was taken into (loaded into) the cooling bed 3, and the temperatures of the web 10 and flange 11 of the H-shaped steel 1 when it was removed from the cooling bed 3 were measured using a two-dimensional radiation thermometer. Note that if the next process performed after the cooling bed cooling process is a cold straightening process, there is a restriction that straightening is possible when the temperature of the flange 11 is 50°C or less. Therefore, if the temperature of the flange 11 of the H-shaped steel 1 when it is removed from the cooling bed 3 exceeds 50°C, the H-shaped steel 1 was made to wait on the table rollers 6 after removal until the temperature of the flange 11 became 50°C or less, and the waiting time was recorded.

[0050] The cooling results of the H-shaped steel 1 of each of the Compliant Examples 1 to 3 and the Comparative Examples 1 to 3 are shown in Table 1. The temperatures shown in Table 1 are the temperatures of the longitudinal center portion of the H-shaped steel 1 on the leading side.

[0051] [Table 1]

[0052] As can be seen from Table 1, in all of the Compliant Examples 1 to 3, the temperature of the flange 11 was 50°C or less as the temperature on the outlet side of the cooling bed when the material was discharged from the cooling bed 3, and there was no particular need to wait for cooling on the table roller 6 after discharge. In contrast, in all of the Comparative Examples 1 to 3, the temperature of the flange 11 was over 50°C as the temperature on the outlet side of the cooling bed when the material was discharged from the cooling bed 3, and it was necessary to wait 5 to 15 minutes for cooling on the table roller 6 after discharge.

[0053] Example 2 In Example 2, only the mist cooling process was performed on the H-shaped steel 1 of Compliant Examples 4 to 6, without the spray cooling process, and neither the mist cooling process nor the spray cooling process was performed on the H-shaped steel 1 of Comparative Examples 4 to 6. Specifically, in Compliant Examples 4 to 6, the cooling bed cooling process consisted of an intake process, a first air-cooling process, a mist cooling process, a second air-cooling process, and a discharge process. In Comparative Examples 4 to 6, the intake process, the air-cooling process, and a discharge process were performed. That is, by not performing the spray cooling process in Example 2, the occurrence of red rust on the surface of the H-shaped steel 1 due to wetting with water due to spray cooling is suppressed, and an H-shaped steel 1 with a beautiful appearance is obtained.

[0054] In Example 2, the feed rate of the H-shaped steel 1 in the cooling bed 3 was 0.375 m / min. The length of the cooling bed 3 in the conveying direction (the X direction) was 45 m, so the total time required for the H-shaped steel 1 to pass through the cooling bed 3 was 120 minutes. In Compliant Examples 4 to 6, the mist cooling process was carried out within 20 to 40 minutes after the H-shaped steel 1 was taken in (charged) onto the cooling bed 3, and mist cooling using the mist cooling device 4 was carried out from both ends of the H-shaped steel 1 in the longitudinal direction.

[0055] In Compliant Examples 4 to 6, the H-shaped steel 1 was cooled in the mist cooling process under the following conditions. Note that each of the following conditions is a value per 1 m in the direction in which the H-shaped steel 1 is transported within the cooling bed 3, and is a value at one end of the H-shaped steel 1 in the longitudinal direction. ·Air volume: 320 [Nm3 / min] ·Droplet diameter: 20[μm] ·Droplet water volume: 1.0 [L / min]

[0056] The H-shaped steel 1 was cooled under each of these conditions, and the temperatures of the web 10 and flange 11 of the H-shaped steel 1 when it was taken into (loaded into) the cooling bed 3, and the temperatures of the web 10 and flange 11 of the H-shaped steel 1 when it was discharged from the cooling bed 3 were measured using a two-dimensional radiation thermometer. If the temperature of the flange 11 of the H-shaped steel 1 when it was discharged from the cooling bed 3 exceeded 50°C, the H-shaped steel 1 was made to wait on the table rollers 6 after discharge until the temperature of the flange 11 fell to 50°C or below, and the waiting time was recorded.

[0057] The cooling results of the H-shaped steel 1 of each of the Compliant Examples 4 to 6 and the Comparative Examples 4 to 6 are shown in Table 2. The temperatures shown in Table 2 are the temperatures of the longitudinal center portion of the H-shaped steel 1 on the leading side.

[0058] [Table 2]

[0059] As can be seen from Table 2, in all of Compliant Examples 4 to 6, the temperature of the flange 11 was 50°C or less as the cooling bed outlet temperature when the material was discharged from the cooling bed 3, and there was no particular need to wait for cooling on the table roller 6 after discharge. In contrast, in all of Comparative Examples 4 to 6, the temperature of the flange 11 was over 50°C as the cooling bed outlet temperature when the material was discharged from the cooling bed 3, and it was necessary to wait 12 to 24 minutes for cooling on the table roller 6 after discharge.

[0060] Furthermore, for Compliant Examples 4 to 6, an external inspection of the H-shaped steel 1 was carried out in the inspection process after the cold straightening process, which is the process following the mist cooling process. As a result, it was confirmed that no red rust had occurred in any of the H-shaped steel 1 of Compliant Examples 4 to 6, and that the external appearance was good.

[0061] As described above, by mist cooling the H-shaped steel 1 using the mist cooling device 4 on the online cooling bed 3, it was possible to increase the cooling capacity of the cooling bed 3 in a simple manner without major equipment modifications and without increasing the incidence of red rust, which is likely to form on the surface of the H-shaped steel 1. As a result, the temperature of the flange 11 of the H-shaped steel 1 when it is removed from the cooling bed 3 can be lowered compared to when the H-shaped steel 1 is cooled without using the mist cooling device 4, eliminating the waiting time after removal from the cooling bed 3 and improving the productivity of the H-shaped steel 1.

[0062] In this embodiment, the steel material is an H-shaped steel, but other steel materials, such as steel sheet piles, channel steel, and angle steel, as well as round bars, steel pipes, and thick steel plates, can also achieve the same effects as those described using the H-shaped steel. For example, in the steel sheet pile 101 shown in Fig. 2, the cooling time in the cooling bed 3 can be shortened by simultaneously spraying air and atomized refrigerant liquid in the longitudinal direction of the web 111, flange 112, or joint 113. [Explanation of symbols]

[0063] 1 H-beam 2 table rollers 3 Cooling bed 4. Mist cooling device 5. Spray Cooling Device 6 Table Roller 10. Web 11 flange 31 Skid Rail 40 Rotational Axis 41 Fan 42 Cylindrical body 43 Mist nozzle 44 Piping 45 Shaft 46 Pedestal 51L Lower Spray Nozzle 51U Upper spray nozzle 52L lower header 52U upper header 101 Steel sheet pile 111 Web 112 flange 113 Joint

Claims

1. A steel cooling method for cooling a hot-rolled steel material on a cooling bed, comprising: A method for cooling steel material, characterized in that the steel material is cooled by simultaneously spraying air and atomized refrigerant liquid in a direction along the longitudinal direction of a surface extending in the longitudinal direction of the steel material from a cooling device arranged outside the longitudinal end of the steel material on the cooling bed.

2. The amount of air injected from the cooling device is 200 [Nm3 / min] or more per unit length in a horizontal direction perpendicular to the injection direction, a flow rate of the refrigerant liquid sprayed from the cooling device is 0.2 to 4.0 [L / min] per unit length in a horizontal direction perpendicular to the spray direction, 2. The steel cooling method according to claim 1, wherein the particle diameter (average droplet diameter) of the droplets of the refrigerant liquid sprayed from the cooling device is 10 to 200 μm.

3. a hot rolling process for hot rolling the steel material; a cooling step of cooling the steel material hot-rolled in the hot rolling step on a cooling bed using the steel material cooling method according to claim 1 or 2; A method for manufacturing a steel material, comprising:

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