Hot rolling equipment and method

Description

41 Hot Rolling Equipment and Method - Technical Field

[001] The present description refers to a hot rolling machine and a hot rolling method. FUNDAMENTALS OF THE TECHNIQUE

[002] Document JP-A No. H7-242938 describes a method for manufacturing a hot-rolled steel sheet with excellent workability, distinguished by coiling at 500°C or lower after hot rolling, from steel containing, in % by weight, C: 0.01 to 0.20%, Si: 2.0% or less, Mn: 0.05 to 2.0%, and Ni: 0 to 0.50% and also containing, as residual elements, Cu: 0.01 to 0.50%, Sn: 0.001 to 0.050%, Pb: 0.001 to 0.010%, and As: 0.001 to 0.050%.

[003] In addition, JP-A document no. H6-297026 describes a method for preventing hot cracking in Cu and Sn-containing steel, distinguished by adding Si as an alloying component to the Cu and Sn-containing steel, then heating the steel until fouling is obtained and then rolling the steel.

[004] In addition, JP-A document no. 2005-29886 describes a Cu-containing steel material, distinguished in that a Cu-containing steel material at 0.06% by mass or more contains any one or more of the following solute concentrations: Ti, Nb, and V at 0.01% by mass to 0.15% by mass, P at 0.01% by mass to 0.1% by mass, REM at 0.002% by mass to 0.15% by mass, and S at 0.01% by mass to 0.05% by mass. SUMMARY Technical Problem

[005] In recent years, sources of iron other than iron ores have been used to reduce carbon dioxide emissions in the steelmaking process. For example, increasing the rate of use of scrap iron as a source of iron is being considered. Petition 870250086917, dated 09 / 25 / 2025, p. 12 / 69 / 41

[006] However, when scrap iron is used as a source of iron, surface defects caused by the copper (Cu) included in the scrap iron can occur during the steelmaking process. For example, in the hot rolling process, hot brittleness cracks can occur due to the concentration of Cu on the surface of the steel material, reducing the surface quality of the steel material. For this reason, it is difficult to increase the utilization rate of scrap iron by including Cu as a source of iron, hindering the achievement of an environmentally friendly steelmaking process.

[007] The techniques described in JP-A document no. H7-242938, JP-A no. H6-297026 and JP-A no. 2005-29886 inhibit hot brittleness cracking by adding alloys to the steel material. In JP-A document no. H7-242938, Ni caro is added to the steel material, which increases costs.

[008] Furthermore, in the technique described in JP-A document No. H6297026, Si is added to the steel material, which leads to a decrease in the workability of the steel material. For this reason, in the technique described in JP-A document No. H6-297026, the range of use of the steel material is limited, making it particularly difficult to use the steel material as an external panel. In addition, in the technique described in JP-A document No. H6297026, the steel material is processed in a temperature range equal to or greater than the normal hot rolling temperature, which reduces the productivity of the steel material.

[009] Furthermore, in the technique described in JP-A document no. 200529886, elements that affect the material properties, such as Ti, V, and Nb, are added to the steel material. Additionally, in the technique described in JP-A document no. 2005-29886, expensive REM is added to the steel material, which increases costs. Therefore, the techniques described in JP-A documents no. H7-242938, H6-297026, and 2005-29886 have room for improvement. Petition 870250086917, dated 09 / 25 / 2025, p. 13 / 69 / 41

[0010] Thus, an objective of the present description is to provide hot rolling equipment and a hot rolling method that can inhibit hot brittleness cracking. Solution to the Problem

[0011] Hot rolling equipment pertaining to a first aspect is hot rolling equipment for hot rolling a Cu-containing steel material, the hot rolling equipment including: a heating furnace that heats the steel material to a predetermined temperature after melting; a rough rolling apparatus including a plurality of rolling mills that rough roll the steel material that has been heated in the heating furnace; a finishing rolling apparatus that finish rolls the steel material that has been rough rolled by the rough rolling apparatus;and a stripping apparatus that removes a target region including cracks caused by a Cu-rich layer that is present on one side of the surface of the steel material being roughly rolled or has been roughly rolled and in which a concentration of Cu components is greater than a concentration of Cu components in a base material of the steel material, wherein the stripping apparatus is provided downstream of a rolling mill located further upstream among the plurality of rolling mills in the rough rolling mill in a direction of conveying the steel material and upstream of the finishing rolling mill.

[0012] Hot rolling equipment pertaining to a second aspect is hot rolling equipment pertaining to the first aspect, wherein the hot rolling equipment includes a post-stripping descaling apparatus which is provided downstream of the stripping apparatus and upstream of the finishing rolling apparatus in the direction of conveying the steel material and which descales the steel material using cooling water. Petition 870250086917, dated 09 / 25 / 2025, p. 14 / 69 / 41

[0013] Hot rolling equipment pertaining to a third aspect is hot rolling equipment pertaining to the first or second aspect, wherein the hot rolling equipment includes a pre-stripping descaling apparatus which is provided between the stripping apparatus and a rolling mill located upstream of, and adjacent to, the stripping apparatus in the direction of conveying the steel material between the plurality of rolling mills in the rough rolling mill and which descales the steel material using cooling water.

[0014] Hot rolling equipment belonging to a fourth aspect is hot rolling equipment belonging to any of the first to third aspects, wherein the stripping apparatus is provided between one rolling mill and another rolling mill adjacent to the single rolling mill among the plurality of rolling mills in the rough rolling mill apparatus.

[0015] The hot rolling equipment belonging to a fifth aspect is the hot rolling equipment belonging to the fourth aspect, in which the stripping apparatus is provided after the rolling mill located most upstream among the plurality of rolling mills in the raw rolling mill apparatus in the direction of transport of the steel material.

[0016] Hot rolling equipment belonging to a sixth aspect is hot rolling equipment belonging to any of the first to third aspects, wherein the stripping apparatus is provided downstream of the rough rolling apparatus and upstream of the finishing rolling apparatus in the direction of conveying the steel material.

[0017] Hot rolling equipment belonging to a seventh aspect is hot rolling equipment belonging to any of the first to sixth aspects, wherein the stripping apparatus removes the target region of the steel material by means of scarification or removes the target region of the steel material by means of mechanical stripping.

[0018] Hot rolling equipment belonging to one eighth Petition 870250086917, dated 09 / 25 / 2025, p. 15 / 69 / 41 aspect is the hot rolling equipment belonging to any of the first to seventh aspects, in which the heating furnace is supplied separately with a production line of a casting machine that melts the steel material.

[0019] Hot rolling equipment belonging to a ninth aspect is hot rolling equipment belonging to any of the first to seventh aspects, wherein the heating furnace is provided in a production line of a casting machine that melts the steel material.

[0020] The hot rolling method pertaining to a tenth aspect is a hot rolling method for hot rolling a Cu-containing steel material, the hot rolling method including: a heating process that heats the steel material to a predetermined temperature after casting; a rough rolling process that performs a plurality of rough rolling passes on the steel material that was heated in the heating process; a finishing rolling process that performs finishing rolling on the steel material that was rough rolled in the rough rolling process;It is a stripping process that removes a target region, including cracks caused by a Cu-rich layer present on one side of the surface of the steel material being roughly rolled or having been roughly rolled, and in which the concentration of Cu components is greater than the concentration of Cu components in the base material of the steel material, wherein the stripping process is carried out after a first rough rolling pass between multiple rough rolling passes and before the finish rolling process.

[0021] A hot rolling method belonging to an eleventh aspect is the hot rolling method belonging to the tenth aspect, further comprising a post-removal descaling process. Petition 870250086917, dated 09 / 25 / 2025, page 16 / 69 / 41, which removes scale from steel material using cooling water after the removal process and before the finishing rolling process.

[0022] A hot rolling method belonging to a twelfth aspect is a hot rolling method belonging to the tenth or eleventh aspect, further comprising a pre-stripping descaling process that descales the steel material using cooling water after a rolling pass that occurs immediately before the stripping process between the plurality of rough rolling passes and before the stripping process.

[0023] A hot rolling method belonging to a thirteenth aspect is a hot rolling method belonging to any of the tenth to twelfth aspects, in which the stripping process is carried out with a surface temperature of the steel material being rolled crude or having been rolled crude being 1000°C or lower.

[0024] A hot rolling method belonging to a fourteenth aspect is a hot rolling method belonging to any of the tenth to thirteenth aspects, in which, when the removal of the target region is carried out by scarifying in the removal process, a conveying speed of the steel material being rolled rough or has been rolled rough is 20 m / min or higher.

[0025] A hot rolling method belonging to a fifteenth aspect is a hot rolling method belonging to any of the tenth to fourteenth aspects, wherein the target region is a region of 1 mm or less in a thickness direction of a surface of the steel material being roughly rolled or has been roughly rolled. Advantageous Effects of the Invention

[0026] As described above, according to this description, hot rolling equipment and a rolling method are provided. Petition 870250086917, dated 09 / 25 / 2025, p. 17 / 69 / 41 hot that can inhibit hot brittleness cracking. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram showing an example of the schematic configuration of hot rolling equipment belonging to a first embodiment of the description.

[0028] Figure 2 is a schematic diagram showing an example of the thermal history of the hot rolling equipment belonging to the first embodiment of the description.

[0029] FIG. 3 is a cross-sectional diagram showing a steel material being scarified by a scarifying device belonging to the first embodiment of the description.

[0030] Figure 4 is a schematic diagram showing an example of the schematic configuration of the scarifying device belonging to the first embodiment of the description.

[0031] Figure 5 is a schematic diagram showing an example of the schematic configuration of a target region belonging to the first embodiment of the description.

[0032] Figure 6 is a flowchart showing an example of a hot rolling process belonging to the first embodiment of the description.

[0033] Figure 7 is a schematic diagram showing an example of the schematic configuration of a hot rolling mill and a scarifying machine belonging to a first example modification.

[0034] Figure 8 is a schematic diagram showing an example of the schematic configuration of a hot rolling mill and a scarifying machine belonging to a second example modification.

[0035] Figure 9 is a schematic diagram showing a Petition 870250086917, dated 09 / 25 / 2025, page 18 / 69 / 41 example of the schematic configuration of a hot rolling mill and a scarifying machine belonging to a second example modification.

[0036] Figure 10 is a schematic diagram showing an example of the schematic configuration of a hot rolling mill and a scarifying machine belonging to a third example modification.

[0037] Figure 11 is a schematic diagram showing an example of the schematic configuration of a hot rolling mill and a scarifying machine belonging to a fourth example modification.

[0038] Figure 12 is a schematic diagram showing an example of the schematic configuration of hot rolling equipment belonging to a second embodiment of the description.

[0039] Figure 13 is a schematic diagram showing an example of the schematic configuration of a cutting apparatus belonging to the second embodiment of the description.

[0040] Figure 14 is a schematic diagram showing an example of the schematic configuration of hot rolling equipment belonging to a third embodiment of the description.

[0041] Figure 15 is a schematic diagram showing an example of the thermal history of the hot rolling equipment belonging to the third embodiment of the description.

[0042] Figure 16 is a graph showing, in relation to steel plates belonging to an Example and a Comparative Example, the relationship between the concentration of Cu in the steel plates and the depth of surface cracks in the steel plates. DETAILED DESCRIPTION

[0043] The preferred modes of description will be described in Petition 870250086917, dated 09 / 25 / 2025, p. 19 / 69 / 41 details below with reference to the attached drawings. It should be noted that redundant description will be omitted when assigning identical reference signs to constituent elements that have substantially identical functional configurations in the descriptive report and drawings. Furthermore, unless otherwise specified, each constituent element is not limited to one and may be plural. <Primeira Modalidade>

[0044] First, the schematic configuration of the hot rolling equipment 10 belonging to a first embodiment of the description will be described with reference to figure 1. Figure 1 is a diagram showing the schematic configuration of the hot rolling equipment 10.

[0045] As shown in Figure 1 as an example, the hot rolling equipment 10 is equipment for hot rolling a steel material 1. The hot rolling equipment 10 is, for example, provided separately from a production line of a continuous casting machine 11 that continuously melts the steel material 1. The hot rolling equipment 10 includes a heating furnace 20, a scarifying apparatus 30, a descaling apparatus 40, a rough rolling apparatus 50 and a finishing rolling apparatus 60. It should be noted that the steel material 1 is not limited to being melted continuously and can also be melted individually.

[0046] Heating furnace 20 heats steel material 1 (e.g., a plate 1A) to a predetermined temperature. This material is obtained by cutting steel material 1 discharged from the continuous casting machine 11 to a predetermined length. The “predetermined temperature” here is, for example, 1100°C or higher. Plate 1A is heated by heating furnace 20 while being transported by conveyor rollers 22. It should be noted that although plate 1A is mentioned as an example of steel material 1 here, it is only an example, and the Petition 870250086917, dated 09 / 25 / 2025, page 20 / 69 / 41 steel material 1 can also be a billet.

[0047] Steel material 1 is a steel material containing Cu and is, for example, a steel material containing Cu at 0.15% by weight (% by mass) or more and particularly containing Cu at 0.25% by weight or more. It should be noted that the Cu content here means the average Cu content in the base material of steel material 1 described below or the average Cu content in the cast steel that becomes steel material 1. Furthermore, the Cu content in steel material 1 is, for example, 5.6% by weight or less.

[0048] The descaling apparatus 40 removes the scale (i.e., an oxide film) formed on the surfaces of plate 1A on both sides in the thickness direction and on the surfaces (lateral end faces) of plate 1A on both sides in the width direction before rough rolling by the rough rolling apparatus 50. The descaling apparatus 40 removes the scale by spraying a fluid (e.g., cooling water) from a nozzle 42 onto plate 1A. That is, the descaling apparatus 40 sprays cooling water W, which is supplied, for example, from a cooling water tank (not shown in the drawings) and pressurized to a predetermined hydraulic pressure using a pump (not shown in the drawings), from the nozzle 42 onto the surfaces of plate 1A.The fouling on the surfaces of plate 1A is removed by the descaling apparatus 40, and the temperature of the surfaces of plate 1A is cooled to less than 1100°C by heat removal using cooling water W. Here, the temperature of the surfaces of plate 1A (e.g., the surfaces in the width direction of plate 1A) after fouling removal by the descaling apparatus 40 is measured by an infrared thermometer.

[0049] The rough rolling mill 50 rolls (hot rough rolling) plate 1A to thin plate 1A to a predetermined thickness. Specifically, the rough rolling mill 50 reduces plate 1A, which has been reduced in the width direction by vertical rolls 24, from Petition 870250086917, dated 09 / 25 / 2025, p. 21 / 69 / 41 upper and lower directions to form a rough bar 1B. In the example shown in Figure 1, the rough rolling mill 50 includes four rolling mills 51, 52, 53, 54. Each of the rolling mills 51 to 54 has a plurality of rolls that interleave the plate 1A on both sides in the thickness direction. The rough rolling mill 50 uses the rolling mills 51 to 54 to continuously roll the plate 1A. In the rough rolling mill 50, the plate 1A is thinned to a thickness of about 25 to 50 mm, for example, and formed into the rough bar 1B.

[0050] The scarifying apparatus 30 removes the surface layer of the steel material 1 by scarifying the steel material 1 from the rough rolling process (i.e., during roughing or after roughing). Details about the scarifying apparatus 30 will be described later. In the example shown in Figure 1, the scarifying apparatus 30 is provided downstream of the rolling mill 51 located further upstream in the direction of transport of the steel material 1 between the plurality of rolling mills 51 to 54 with which the rough rolling apparatus 50 is equipped. Furthermore, the scarifying apparatus 30 is provided upstream of the rough rolling mill 60 in the direction of transport of the steel material 1. The surface temperature of the steel material 1 is 1000°C or less at the stage when the steel material 1 is scarified by the scarifying apparatus 30.It should be noted that, in this descriptive report, "removal" is a concept that is not limited to complete removal and also includes cases where there is insufficient removal within a generally acceptable range in the technical field to which the description pertains and to an extent that does not contradict the spirit of the description. It should be noted that the 30 scarifying device is an example of a removal device.

[0051] The scarifying apparatus 30 is provided between the upstream rolling mill 51 and the second-stage rolling mill 52 in the rough rolling mill 50 in the material transport direction. Petition 870250086917, dated 09 / 25 / 2025, p. 22 / 69 / 41 steel 1 (i.e., after the rolling mill 51 provided further upstream). In other words, the scarifying apparatus 30 is provided between rolling mill 51 and rolling mill 52 adjacent to rolling mill 51.

[0052] The finishing rolling mill 60 also hot finish rolls the raw bar 1B to a predetermined thickness. Specifically, the finishing rolling mill 60 finish rolls raw bar 1B, which has been reheated by a raw bar heating apparatus 62, to a thickness of about a few mm (e.g., 1 to 2 mm). The finishing rolling mill 60 has a plurality of finishing rolling mill groups 64 through 6 to 7 rolling mill stands. Each finishing rolling mill group 64 has a plurality of rolling mill rolls arranged in a vertically straight line. The finishing rolling mill 60 gradually reduces the raw bar 1B by passing the raw bar 1B through openings in the various finishing rolling mill groups 64.A steel strip 1C, obtained as a result of the finishing rolling of the raw bar 1B to a thickness predetermined by the finishing rolling mill 60, is fed to a cooling mill 70. It should be noted that, although an example in which the finishing rolling mill 60 has 6 to 7 rolling stands is described here, this is only an example, and the finishing rolling mill 60 may, for example, have five rolling stands of finishing roll groups 64.

[0053] Cooling apparatus 70 cools finished steel strip 1C with cooling water W. Cooling apparatus 70 is, for example, a tube laminar nozzle type cooling apparatus. 1C cooled by cooling apparatus 70 is wound into a coil by a coiling apparatus 80 and transported as a hot-rolled coil 1D from the hot rolling equipment 10 to the next process.

[0054] Figure 2 shows an example of the thermal history of Petition 870250086917, dated 09 / 25 / 2025, page 23 / 69 / 41 steel material 1 in a series of continuous casting, hot rolling and cold rolling processes. As shown in Figure 2, at the beginning of continuous casting, the temperature of steel material 1 is about 1500°C, for this reason, scale forms on the surface of steel material 1. This occurs because when steel material 1 reaches 1100°C or more, a 2Fe+O2 = 2FeO reaction proceeds mainly on the surface of steel material 1, so that iron oxide (i.e., FeO) is formed on the surface of steel material 1 and becomes scale.At this point, Cu remains in steel material 1 without oxidizing, but in this temperature range, if the base material of steel material 1 includes a relatively large amount of Cu (for example, if the average concentration of Cu components in the base material is 0.15% by weight (% by mass) or more), Cu is locally removed from the iron oxide and infiltrates the boundary between the iron oxide and the base metal piece of steel material 1. The Cu removed from the iron oxide infiltrates mainly and concentrates at the grain boundaries in the surface layer of the base metal piece of steel material 1. In this way, a region (hereinafter referred to as the "Cu-rich layer") in which the concentration of Cu components is greater than the average concentration of Cu components in the base material of steel material 1 is formed in the surface layer (surface side) of the base metal piece of steel material 1 (i.e., a Cu concentration phenomenon occurs).

[0055] It should be noted that the “Cu-rich layer” means a region where the concentration of Cu components is greater than the average concentration of Cu components in the base material of the steel material in the base metal part of the steel material that is not oxidized when the fouling associated with oxidation is formed on the surface of the steel material. In other words, “Cu-rich layer” means a region at the boundary between the fouling formed on the surface of the steel material and the base metal part of the steel material, that is, the surface of the base metal of the steel material. Petition 870250086917, dated 09 / 25 / 2025, page 24 / 69 / 41, which is not oxidized, towards the center of the thickness direction of the steel material until the Cu components concentrated at the grain boundaries are no longer observed. The “region where the Cu components concentrated at the grain boundaries are not observed” here means a region where the concentration of Cu components present at the grain boundaries is equal to or less than the average concentration of the steel material + 1%. Furthermore, “base material of the steel material” means the piece of steel material excluding the Cu-rich layer.

[0056] When Cu is present in a liquid phase state (e.g., at 1100°C or more) at the grain boundaries, the ductility of the grain boundaries decreases. For this reason, when a Cu-rich layer is formed on steel material 1, steel material 1 exhibits hot brittleness, and hot brittle cracks occur caused by the Cu-rich layer on the surface of steel material 1. Hot brittle cracks that occur on the surface of steel material 1 need to be removed because they become a quality defect. Particularly in high-quality steel materials and automotive steel sheets, where importance is given to surface quality, surface cracks in steel material 1 need to be removed.

[0057] In conventionally known surface cutting methods, surface layer defects, such as iron oxide that has formed on the surface of plate 1A, inclusions and casting dust that have become incorporated into the surface layer of plate 1A during casting, or air bubble marks in the surface layer of plate 1A, are removed by a scarifying machine or similar. This removal of surface layer defects is carried out before the heating process (i.e., heating by heating furnace 20) in the hot rolling process. That is, the surface layer defects are removed from plate 1A before the hot rolling process. However, in the heating process in the process Petition 870250086917, dated 09 / 25 / 2025, page 25 / 69 / 41 of hot rolling, plate 1A is reheated to 1100°C or more (for example, about 1300°C), so that fouling forms again on the surface of plate 1A. As a result, the phenomenon of Cu concentration occurs again in plate 1A, and hot brittleness cracks also occur again.

[0058] Thus, as a result of extensive research, the present inventors arrived at the idea of ​​removing, in the rough rolling process in the hot rolling process, hot brittleness cracks caused by the Cu-rich layer on the surface of plate 1A. That is, in the thermal history of steel material 1 shown in figure 2, steel material 1 cools to 1000°C or lower during the rough rolling process after exiting the heating furnace 20 and, from then on, its temperature does not rise to 1100°C or higher. For this reason, in processes from the rough rolling process, both the phenomenon of Cu concentration and hot brittleness cracks are inhibited.Consequently, when hot brittleness cracks are removed from steel material 1 during or after the rough rolling process, it becomes unnecessary to remove hot brittleness cracks from steel material 1 again in subsequent processes.

[0059] It should be noted that even if steel material 1 is heated to 1100°C or more in the rough rolling process or in the finishing rolling process, the fouling that causes a Cu-rich layer will not form on the surface of steel material 1 because the heating of steel material 1 associated with rolling is of short duration.

[0060] Furthermore, hot brittleness caused by the phenomenon of Cu concentration occurs mainly between 1100°C and 1250°C. Additionally, the upper limit value of the temperature at which hot brittleness occurs becomes higher the greater the concentration of Cu in the steel material 1. Furthermore, in terms of the relationship between the heating temperature Petition 870250086917, dated 09 / 25 / 2025, p. 26 / 69 / 41 of steel material 1 and the depth of hot brittleness cracks in steel material 1, the higher the heating temperature of steel material 1, the coarser the γ (austenite) grain boundaries become, so the depth of hot brittleness cracks caused by Cu concentration at the grain boundaries also increases. On the other hand, in terms of the relationship between the heating temperature of steel material 1 and the number of hot brittleness cracks in steel material 1, the higher the heating temperature of steel material 1, the smaller the number of grain boundaries, therefore, the smaller the number of hot brittleness cracks in steel material 1.

[0061] Here, the depth to which Cu infiltrates the base metal piece of steel material 1 from the iron oxide is relatively shallow and is at most about 50 μm. The reason for this is believed to be as follows. That is, when cracks occurring on the surface of steel material 1 progress, in the initial stage of crack progression, liquid-phase Cu infiltrates the leading edges of the cracks. For this reason, the ductility of the grain boundaries decreases, facilitating the advancement of the cracks. On the other hand, as crack progression continues, the residual amount of Cu remaining at the grain boundaries increases. As a result, the amount of Cu present at the leading edges of the cracks gradually decreases and eventually the crack progression stops. At this point, the depth of the surface cracks is approximately the size of an austenite grain.

[0062] Furthermore, when the amount of displacement caused by tensile stress increases near the surface of the steel material 1, the depth of the surface cracks increases in the initial stage of displacement, but as the displacement progresses, the depth of the surface cracks does not increase, but the width of the surface cracks increases. Consequently, in hot brittleness cracks caused Petition 870250086917, dated 09 / 25 / 2025, page 27 / 69 / 41 due to the phenomenon of Cu concentration, the depth to which surface cracks progress is at most a few mm (e.g., 1 mm). For this reason, if a few mm (e.g., 1 mm) of the surface layer of steel material 1 are removed from steel material 1 after its rolling, quality defects on the surface of steel material 1 can be inhibited.

[0063] Thus, in the hot rolling equipment 10 belonging to the present embodiment, the surface layer of the plate 1A is removed by the scarifying apparatus 30. As shown in Figure 3 as an example, the scarifying apparatus 30 has two scarifying units 31 that oppose the surfaces of the steel material 1 on both sides (upper and lower sides) in the thickness direction and two scarifying units 31 that oppose the surfaces (lateral end faces) of the steel material 1 on both sides (left and right sides) in the width direction. It should be noted that the four scarifying units 31 have the same configuration. For this reason, the scarifying unit 31 that opposes the surface of the steel material 1 on one side (the upper side) in the thickness direction will be described below.

[0064] As shown in Figure 4, the scarifying unit 31 includes a preheating gas blasting unit 34 and a scarifying oxygen blasting unit 36. The preheating gas blasting unit 34 ejects preheating oxygen 32 and a fuel gas 33. The scarifying oxygen blasting unit 36 ​​ejects scarifying oxygen 37. It should be noted that a shielding gas 38, comprising a fuel gas, is ejected along with the scarifying oxygen 37 from the lower portion of the scarifying oxygen blasting unit 36. The steel material 1 is configured to be transported in the direction of arrow Y in Figure 4.

[0065] It should be noted that, as shown in figure 4, the jet flow of the scarifying oxygen 37, ejected from the blasting unit of Petition 870250086917, dated 09 / 25 / 2025, page 28 / 69 / 41 scarifying oxygen 36, is ejected further forward in the Y transport direction of the steel material 1 than the jet streams of preheating oxygen 32 and fuel gas 33, ejected from the preheating gas blasting unit 34.

[0066] In the scarifying apparatus 30, first, as shown on the left side of figure 4, a preheating process is carried out. In the preheating process, preheating oxygen 32 and fuel gas 33 are ejected from the preheating gas blasting unit 34 of the scarifying unit 31 towards the surface of the steel material 1, causing the fuel gas 33 to burn. Then, a piece of the surface of the steel material 1 is melted by the heat of the burning fuel gas 33, forming a reservoir 1E.

[0067] It should be noted that the length, along the transport direction Y, of the reservoir 1E formed on the surface of the steel material 1 is in the range of about 20 mm to 30 mm, for example.

[0068] Next, as shown on the right side of Figure 4, a scarifying process is performed. In the scarifying process, scarifying oxygen 37 is ejected from the scarifying oxygen blasting unit 36 ​​of the scarifying unit 31 towards the surface of the steel material 1, and the steel material 1 in which the reservoir 1E was formed is transported in the transport direction Y. At this time, the shielding gas 38 is ejected along with the scarifying oxygen 37 from the scarifying oxygen blasting unit 36, and the scarifying oxygen 37 is shielded by the shielding gas 38. It should be noted that the scarifying process is an example of a removal process.

[0069] Next, the jet stream of scarfing oxygen 37, expelled from the scarfing oxygen blasting unit 36, strikes the molten iron in reservoir 1E in the transported steel material 1, and an oxidation reaction occurs between the molten iron and the scarfing oxygen 37. Petition 870250086917, dated 09 / 25 / 2025, page 29 / 69 / 41 The heat from the oxidation reaction successively melts the surface of steel material 1 and scarifies the surface of steel material 1. That is, the surface of steel material 1 is scarified by the heat from the oxidation reaction at the rear of reservoir 1E in the transport direction Y. Thus, the surface of plate 1A, after being heated in heating furnace 20, is scarified by scarifying apparatus 30.

[0070] As shown in Figure 5 as an example, the scarifying apparatus 30 removes a target region T, which is a region including cracks C caused by a Cu-rich layer R. Here, “target region T” means a region of predetermined thickness defined from the surface of the steel material 1 towards the center of the thickness direction of the steel material 1 so as to include the entire Cu-rich layer R, the cracks C caused by the Cu-rich layer R and the fouling S. The target region T is a strip extending a predetermined distance from the surface of the steel material 1 (i.e., the surface of the fouling S) in a thickness direction t of the steel material 1. The predetermined distance is, for example, greater than 0 mm and equal to or less than 3 mm (0 < distance < 3 mm), preferably greater than 0 mm and equal to or less than 2 mm (0 < distance < 2 mm) and more preferably greater than 0 mm and equal to or less than 1 mm (0 < distance < 1 mm).

[0071] When steel material 1 is the raw bar 1B, the thickness of steel material 1 is about 25 to 50 mm, for example. Thus, by removing a region of 1 mm or less from the surface of steel material 1 as the target region T in the direction of thickness t of plate 1A, the reduction in the thickness of steel material 1 is attenuated, so that the yield of plate 1A can be improved.

[0072] Here, the relationship between the maximum transport speed of plate 1A at which the surface of plate 1A can be continuously scarified without interruption and the scarification depth of plate 1A at that Petition 870250086917, dated 09 / 25 / 2025, page 30 / 69 / 41 moment is given by the following equation (1). h = 6xVs-0'6... (1) h (mm): scarification depth of plate 1A, Vs (m / min): maximum transport speed of plate 1A at which it can be continuously scarified without interruption

[0073] As shown in equation (1) above, the faster the transport speed of plate 1A during scarification, the finer the scarification depth of plate 1A. That is, the faster the transport speed of plate 1A, the finer the scarification depth of plate 1A. As described above, the depth of surface cracks in steel material 1 is considered to be about a few mm (e.g., 1 mm). For this reason, to maintain the scarification depth of plate 1A at about 1 mm to 2 mm, the transport speed of plate 1A is preferably set to 20 m / min or higher. Furthermore, by setting the transport speed of plate 1A to 20 m / min or higher, scarification is prevented from being partially interrupted, even during fine scarification, where the scarification depth of plate 1A is 1 mm.It is observed that the upper limit of the transport speed of plate 1A during scarifying is appropriately defined based on the operating conditions of the scarifying apparatus 30 and the thickness of the steel material 1 to be scarified, being, for example, defined as 80 m / min or less.

[0074] It should be noted that although figure 5 shows an example in which a surface of the steel material 1 in the thickness direction is scarified, the scarifying apparatus 30 belonging to the present embodiment also scarifies the other surface of the steel material 1 in the thickness direction and the surfaces (lateral end faces) of the steel material 1 on both sides in the width direction.

[0075] Because the target region T, including the Cu-rich R layer, is Petition 870250086917, dated 09 / 25 / 2025, p. 31 / 69 / 41 scarified (removed) from steel material 1, the C cracks present at the GB grain boundaries are removed. As a result, hot brittleness cracking on the surface of steel material 1 is inhibited.

[0076] Next, a hot rolling method belonging to the present embodiment will be described with reference to Figure 6. Figure 6 is a flowchart to describe a part of a manufacturing process for a hot-rolled steel sheet belonging to the present embodiment. As shown in Figure 6, first, in the heating process of step ST10, the plate 1A, after being continuously melted, is heated to a predetermined temperature (e.g., about 1300 °C) by the heating furnace 20. After the execution of the heating process of step ST10, the manufacturing process proceeds to step ST12.

[0077] In the descaling process of step ST12, descaling using cooling water W is performed by descaling apparatus 40 on plate 1A which was heated in step ST10. Due to the descaling performed, the surface temperature of plate 1A drops to less than 1100°C, for example. After the execution of the descaling process of step ST12, the manufacturing process moves on to step ST14.

[0078] In the rough rolling process of step ST14, plate 1A, which was descaled in step ST12, is rough rolled by rough rolling machine 50. Therefore, plate 1A is formed from raw bar 1B having a predetermined thickness. After the execution of the rough rolling process of step ST14, the manufacturing process moves on to step ST16.

[0079] In the scarifying (removal) process of step ST16, plate 1A, which was roughly rolled in step ST14, is scarified by scarifying apparatus 30, whereby the target region T, including the Cu-rich layer, is removed from plate 1A. Scarifying plate 1A by Petition 870250086917, dated 09 / 25 / 2025, page 32 / 69 / 41. The scarifying apparatus 30 is performed after the first rough rolling pass of plate 1A between the rough rolling passes of plate 1A performed several times (e.g., four times) by the rough rolling apparatus 50. At the stage where plate 1A is scarified by the scarifying apparatus 30, the surface temperature of plate 1A drops to 1000°C or lower. After the execution of the scarifying process of step ST16, the manufacturing process moves to step ST18.

[0080] In the rough rolling process of step ST18, the remaining rough rolling is carried out by rough rolling mill 50 on plate 1A which was scarified in step ST16. Because of this, plate 1A is formed into raw bar 1B, and the rough rolling process ends. After the execution of the rough rolling process of step ST18, the manufacturing process moves on to step ST20.

[0081] In the finishing rolling process of stage ST20, the raw bar 1B obtained in stage ST18 is finished by the finishing rolling machine 60. Therefore, the raw bar 1B is formed into a steel strip 1C with a predetermined thickness. After the execution of the finishing rolling process of stage ST20, the manufacturing process moves on to stage ST22.

[0082] In the coiling process of step ST22, the steel strip 1C obtained in step ST20 is coiled by the coiling apparatus 80 and thus formed into the hot-rolled coil 1D. After the execution of the coiling process of step ST22, a part of the manufacturing process of the hot-rolled steel sheet related to this embodiment is completed.

[0083] As described above, in the hot rolling equipment 10 belonging to the first embodiment, the scarifying apparatus 30 is provided downstream of the rolling mill 51 located further upstream in the direction of transport of the steel material 1 between the plurality of rolling mills 51 to 54 in Petition 870250086917, dated 09 / 25 / 2025, page 33 / 69 / 41 rough rolling mill 50 and upstream of the finishing rolling mill 60. When steel material 1 is heated to a predetermined temperature (e.g., 1300°C) in heating furnace 20, liquid Cu concentrates at the grain boundaries GB near the surface of steel material 1. The areas of steel material 1 where Cu has concentrated have low ductility compared to the base metal of steel material 1. For this reason, the occurrence of a Cu-rich layer becomes one of the causes of hot brittleness cracking. In this embodiment, a scarifying apparatus 30 is provided that removes surface cracks caused by the Cu-rich layer of the steel material 1 that is roughly rolled after being heated by the heating furnace 20. Because of this, the cracks that occur on the surface of the steel material 1 are removed during rough rolling or after rough rolling.Consequently, according to the present embodiment, the occurrence of hot brittleness cracking in steel material 1 is inhibited.

[0084] Let us consider a case where, for example, the scarifying apparatus 30 is provided upstream of the rough rolling apparatus 50 (for example, upstream of the heating furnace 20) in the direction of transport of the steel material 1. In this case, if the temperature of the steel material 1 remains high (for example, 1100°C or higher), a Cu-rich layer will form again on the steel material 1 and hot brittle cracking will occur. For this reason, it is difficult to inhibit hot brittle cracking in the steel material 1. In the present embodiment, the cracks that occur on the surface of the steel material 1 are removed during rough rolling or after rough rolling, so that the occurrence of hot brittle cracking in the steel material 1 is inhibited.

[0085] On the other hand, let us consider a case where the scarifying apparatus 30 is supplied downstream of the finishing rolling apparatus 60 in the direction of transport of the steel material 1. In this case, the temperature of Petition 870250086917, dated 09 / 25 / 2025, page 34 / 69 / 41. Steel material 1 falls sufficiently so that the phenomenon of Cu concentration is less likely to occur. However, the thickness of steel material 1 (steel strip 1C) at the finishing rolling stage is reduced compared to the thickness of steel material 1 (plate 1A) up to the rough rolling stage. For this reason, when surface cracks in steel material 1 are removed at the finishing rolling stage, the thickness of steel material 1 decreases even further, leading to a reduction in the yield of steel material 1. In the present embodiment, the cracks that occur on the surface of steel material 1 are removed during rough rolling or after rough rolling, so that a reduction in the yield of steel material 1 in the hot rolling process is inhibited.

[0086] Furthermore, in the hot rolling equipment 10 belonging to the first embodiment, the scarifying apparatus 30 is provided between the rolling mill 51 and the rolling mill 52 adjacent to the rolling mill 51 among the plurality of rolling mills 51 to 54 in the rough rolling apparatus 50. In other words, the scarifying apparatus 30 is provided between the rolling mill 51 and the rolling mill 52 which are adjacent to each other among the plurality of rolling mills 51 to 54. Because of this, the cracks that occur on the surface of the steel material 1 are removed during the rough rolling process. Consequently, according to the present embodiment, the occurrence of hot brittleness cracks in the steel material 1 is inhibited.

[0087] Furthermore, in the hot rolling equipment 10 belonging to the first embodiment, the scarifying apparatus 30 is provided after the rolling mill 51 located further upstream in the direction of transport of the steel material 1 between the plurality of rolling mills 51 to 54. In other words, the scarifying apparatus 30 is provided on the exit side of the roll of the rolling mill 51 located further upstream in the direction of transport of the steel material 1. Because of this, the cracks that occur on the surface of the steel material 1 are removed during rough rolling. In addition, the cracks Petition 870250086917, dated 09 / 25 / 2025, page 35 / 69 / 41. Surface defects in steel material 1 are removed in a state where the thickness of steel material 1 is greater in the rough rolling stage. Consequently, according to the present embodiment, the occurrence of hot brittleness cracking in steel material 1 is inhibited, and a reduction in the yield of steel material 1 in the hot rolling process is inhibited.

[0088] Furthermore, in the hot rolling equipment 10 belonging to the first embodiment, the steel material 1 is scarified by the scarifying apparatus 30, whereby the target region T, including the Cu-rich layer, is removed from the steel material 1. Scarifying results in high productivity compared to removal by cutting. Consequently, according to the present embodiment, a reduction in productivity in the hot rolling equipment 10 can be inhibited.

[0089] Furthermore, in the hot rolling equipment 10 belonging to the first embodiment, the transport speed of the steel material 1 is set to 20 m / min or higher when the steel material 1 is scarred by the scarifying apparatus 30. Since the transport speed of the steel material 1 is set to 20 m / min or higher in this way, the scarifying depth of the steel material 1 becomes about 1 mm. In this way, surface cracks in the steel material 1 are removed. Consequently, according to the present embodiment, the occurrence of hot brittleness cracks in the steel material 1 is inhibited.

[0090] Furthermore, in the hot rolling equipment 10 belonging to the first embodiment, a region of 1 mm or less of the surface of the steel material 1 in the direction of the thickness t of the steel material 1 is removed. Cracks caused by the Cu-rich layer occur mainly in a region of 1 mm or less of the surface of the steel material 1 in the direction of the thickness t of the steel material 1. This is because, as described above, in hot brittleness caused by Cu, the Petition 870250086917, dated 09 / 25 / 2025, page 36 / 69 / 41. The depth to which surface cracks in steel material 1 progress is, at most, a few mm (e.g., 1 mm). For this reason, removing a region of up to 1 mm from the surface of steel material 1 in the direction of the thickness t of steel material 1 contributes to the removal of cracks. Consequently, according to the present embodiment, the occurrence of hot brittleness cracks in steel material 1 is inhibited. (First Example Modification)

[0091] In the first embodiment, an example was described in which the scarifying apparatus 30 is provided between the upstream provided rolling mill 51 and the rolling mill 52 provided in the second stage in the rough rolling mill 50 in the direction of conveying the steel material 1, but the description is not limited to this example. As shown in Figure 7 as an example, in a first example modification, the scarifying apparatus 30 is provided between the rolling mill 52 provided in the second stage (hereinafter also called “the second rolling mill 52”) and the rolling mill 53 provided in the third stage (hereinafter also called “the third rolling mill 53”) in the rough rolling mill 50 in the direction of conveying the steel material 1. In other words, the scarifying apparatus 30 is provided between the second rolling mill 52 and the third rolling mill 53 which are adjacent to each other.Thus, in the first example modification, the scarifying apparatus 30 is provided between the second rolling mill 52 and the third rolling mill 53 in the rough rolling mill 50. Because of this, the cracks that occur on the surface of the steel material 1 are removed during rough rolling. Consequently, according to the present example modification, the occurrence of hot brittleness cracks in the steel material 1 is inhibited.

[0092] It should be noted that, although an example is provided here in which the scarifying apparatus 30 is provided between the second rolling mill 52 and the third rolling mill 53, the description is not limited to this example. The Petition 870250086917, dated 09 / 25 / 2025, pp. 37 / 69 / 41. Scarfing apparatus 30 may also be provided between the third rolling mill 53 and the final stage rolling mill 54. Furthermore, although an example is given here where the rough rolling mill apparatus 50 includes four rolling mills, the description is not limited to this example. The rough rolling mill apparatus 50 may include five or more rolling mills or three or fewer rolling mills. (Second Example Modification)

[0093] In the first embodiment, an example was described in which the rough rolling mill 50 includes non-reversible rolling mills 51 to 54, but the description is not limited to this example. As shown in Figure 8 as an example, in a second example modification, a rough rolling mill 50A includes a reversible rolling mill 51A. In addition, a scarifying apparatus 30 is provided downstream of the reversible rolling mill 51A in the direction of transport of the steel material 1. In this case, after a first rolling pass of the steel material 1 is carried out in the reversible rolling mill 51A, the steel material 1 is scarified by the scarifying apparatus 30. After that, the steel material 1 is moved in the opposite direction to the transport direction and the steel material 1 is rolled several times in the reversible rolling mill 51A.

[0094] Furthermore, as shown in Figure 9 as an example, a rough rolling mill 50B includes a reversible rolling mill 51B, a non-reversible rolling mill 52B, and a tandem rolling mill 53B. In the example shown in Figure 9, the scarifying apparatus 30 is provided downstream of the reversible rolling mill 51B in the direction of transport of the steel material 1. That is, the scarifying apparatus 30 is provided between the reversible rolling mill 51B and the non-reversible rolling mill 52B. After a first rolling pass of the steel material 1 is carried out in the reversible rolling mill 51B, the steel material 1 is scarified by the scarifying apparatus 30. Then, after the steel material 1 is rolled several times Petition 870250086917, dated 09 / 25 / 2025, p. 38 / 69 / 41 times in the reversible rolling mill 51B, the steel material 1 is rolled in the non-reversible rolling mill 52B and in the tandem rolling mill 53B. It should be noted that, although an example in which the scarifying apparatus 30 is provided downstream of the reversible rolling mill 51B in the direction of transport of the steel material 1 is described here, the description is not limited to this example. The scarifying apparatus 30 may also be provided between the non-reversible rolling mill 52B and the tandem rolling mill 53B.

[0095] In the second example modification, the scarifying apparatus 30 is provided after the rolling mill (the reversible rolling mill 51B) located further upstream in the rough rolling apparatus 50 in the direction of transport of the steel material 1. Because of this, cracks that occur on the surface of the steel material 1 are removed during rough rolling. Furthermore, in the rough rolling process, surface cracks in the steel material 1 are removed in a state where the thickness of the steel material 1 is greater. Consequently, according to the present example modification, the occurrence of hot brittleness cracks in the steel material 1 is inhibited, and a reduction in the yield of the steel material 1 in the hot rolling process is inhibited. (Third Example Modification)

[0096] In the first embodiment, an example was described in which the scarifying of steel material 1 by scarifying apparatus 30 is carried out during rough rolling, but the description is not limited to this example. In a third example modification, the scarifying of steel material 1 by scarifying apparatus 30 is carried out after rough rolling and before finish rolling.

[0097] As shown in Figure 10, as an example, the scarifying apparatus 30 is provided downstream of the rough rolling apparatus 50 in the direction of transport of the steel material 1. Furthermore, the scarifying apparatus 30 is provided upstream of the rough rolling apparatus 60 in Petition 870250086917, dated 09 / 25 / 2025, pp. 39 / 69 / 41, direction of transport of steel material 1. Specifically, the scarifying apparatus 30 is provided between the exit side of the rough rolling apparatus 50 and the entry side of the finishing rolling apparatus 60. Thus, in the third example modification, the scarifying apparatus 30 is provided after the rough rolling apparatus 50 and before the finishing rolling apparatus 60 in the direction of transport of steel material 1. Because of this, the cracks that occur on the surface of the steel material 1 are removed after the rough rolling process. Since the temperature of steel material 1 after the rough rolling process drops sufficiently (e.g., 1000°C or lower), a Cu-rich layer is unlikely to form, and surface cracks in steel material 1 are inhibited from occurring again.Consequently, according to the present example modification, the occurrence of hot brittleness cracking in steel material 1 is inhibited.

[0098] Furthermore, in the third example modification, as steel material 1 is scarred before finish rolling, the yield in the hot rolling process improves compared to a case where steel material 1, whose thickness has been reduced by finish rolling, is scarred. (Fourth Example Modification)

[0099] In the first embodiment, an example was described in which a descaling process is not carried out before and after the scarfing process (removal process), but the description is not limited to this example. In a fourth example modification, a pre-removal descaling process is carried out before the scarfing process (removal process) and a post-removal descaling process is carried out after the scarfing process (removal process).

[00100] As shown in Figure 11 as an example, a scarifying apparatus 30 is provided downstream of the rough rolling apparatus 50 and Petition 870250086917, dated 09 / 25 / 2025, page. 40 / 69 / 41 upstream of the finishing rolling mill 60 in the direction of transport of steel material 1. In addition, a pre-removal descaling device 40A is provided downstream of the rough rolling mill 50 and upstream of the scarifying device 30 in the direction of transport of steel material 1. That is, the pre-removal descaling device 40A is provided between the rolling mill 54 located furthest downstream in the direction of transport of steel material 1 between the plurality of rolling mills 51 to 54 in the rough rolling mill 50 and the scarifying device 30. The basic configuration of the pre-removal descaling device 40A is the same as that of the descaling device 40.

[00101] The pre-removal descaling apparatus 40A removes scale formed on the surface of the steel material 1 before (immediately before) the steel material 1 is scarred by the scarifying apparatus 30. That is, in the fourth example modification, the pre-removal descaling process is carried out after the rough rolling process and before the scarifying process (removal process).

[00102] Here, if there are incrustations or similar adhering to the surface of the steel material 1 when the surface of the steel material 1 is scarified by the scarifying apparatus 30, the combustion reaction between the sprayed scarifying oxygen 37 from the scarifying apparatus 30 (see figure 4) and the steel material 1 can be prevented and the scarifying of the steel material 1 can be interrupted. Particularly by stopping the depth at which the steel material 1 is scarified by the scarifying apparatus 30 by about 1 mm to 2 mm, it is likely that the scarifying of the steel material 1 by the scarifying apparatus 30 will be interrupted.

[00103] In contrast, in the fourth example modification, as described above, the scale adhering to the surface of the steel material 1 is removed by the pre-removal descaling apparatus 40A before the steel material 1 is scarified by the scarifying apparatus 30. Due to Petition 870250086917, dated 09 / 25 / 2025, p. 41 / 69 / 41 Therefore, the combustion reaction between the sprayed scarifying oxygen 37 from the scarifying apparatus 30 (see figure 4) and the steel material 1 tends to become stable. Consequently, an interruption or something similar in the scarifying of the steel material 1 by the scarifying apparatus 30 can be inhibited.

[00104] Furthermore, the pre-removal descaling apparatus 40A removes the scale adhered to the surface of the steel material 1 by spraying cooling water W onto the surface of the steel material 1. At this point, the surface of the steel material 1 is cooled by the cooling water W, so that a Cu-rich layer is further inhibited from reforming on the steel material 1. Consequently, the occurrence of hot brittleness cracking in the steel material 1 is inhibited. Moreover, in the fourth example modification, the surface of the steel material 1 is cooled to less than 1100°C by the pre-removal descaling apparatus 40A. Consequently, a Cu-rich layer is further inhibited from reforming on the steel material 1.

[00105] In addition, the post-removal descaling apparatus 40B is provided downstream of the scarifying apparatus 30 and upstream of the finishing rolling apparatus 60 in the direction of transport of the steel material 1. The basic configuration of the post-removal descaling apparatus 40B is the same as that of the descaling apparatus 40.

[00106] The post-removal descaling apparatus 40B removes scale and similar substances that adhere to the surface of the steel material 1 after the surface of the steel material 1 has been scarified by the scarifying device 30. That is, in the fourth example modification, the post-removal descaling process is carried out after the scarifying process (removal process) and before the finishing rolling process.

[00107] In this way, the post-removal descaling device 40B removes scale and similar substances that adhere to the surface of the material. Petition 870250086917, dated 09 / 25 / 2025, page 42 / 69 / 41 steel 1, the quality of the hot finish rolling of steel material 1 by the finishing rolling machine 60 can be improved.

[00108] Furthermore, when the scarifying apparatus 30 scarifies the steel material 1, the surface temperature of the steel material 1 increases (e.g., about 50°C). In contrast, the post-removal descaling apparatus 40B removes the scale adhered to the surface of the steel material 1 by spraying cooling water W onto the surface of the steel material 1. At this point, the surface of the steel material 1 is cooled by the cooling water W, so that a Cu-rich layer is further inhibited from reforming on the steel material 1. Moreover, in the fourth example modification, the surface of the steel material 1 is cooled to less than 1100°C by the post-removal descaling apparatus 40B. Consequently, a Cu-rich layer is further inhibited from reforming in steel material 1. As a result, the occurrence of hot brittle cracking in steel material 1 is inhibited.

[00109] It should be noted that in the fourth example modification, the pre-removal descaling process, the scarifying process, and the post-removal descaling process are carried out after the rough rolling process. However, the pre-removal descaling process, the scarifying process, and the post-removal descaling process can also be carried out during the rough rolling process. In this case, for example, the pre-removal descaling apparatus 40A, the scarifying apparatus 30, and the post-removal descaling apparatus 40B are provided between the rolling mills 51, 52, 53, 54 which are adjacent to each other in the rough rolling apparatus 50.

[00110] Specifically, the pre-removal descaling apparatus 40A, the scarifying apparatus 30 and the post-removal descaling apparatus 40B are provided between rolling mills 51, 52, between rolling mills 52, 53 or between rolling mills 53, 54. Petition 870250086917, dated 09 / 25 / 2025, page 43 / 69 / 41

[00111] Furthermore, in the fourth example modification, the pre-removal descaling process is performed before the scarifying process (removal process) and the post-removal descaling process is performed after the scarifying process (removal process). However, at least one of the pre-removal and post-removal descaling processes may be omitted. <Segunda Modalidade>

[00112] In the first embodiment, an example was described in which the target region T, including the Cu-rich layer, is removed from the steel material 1 by the scarifying apparatus 30, but the description is not limited to this example. In a second embodiment, the target region T is removed from the steel material 1 by a cutting apparatus 90 instead of the scarifying apparatus 30. It should be noted that the cutting apparatus 90 is an example of a removal apparatus.

[00113] As shown in Figure 12 as an example, the hot rolling equipment 10 includes the 90 cutting apparatus instead of the scarifying apparatus 30. The 90 cutting apparatus removes the workpiece from the surface of the steel material 1 by cutting the steel material 1 discharged from the heating furnace 20. Details about the 90 cutting apparatus will be described later. The cutting device 90 is provided downstream of the rolling mill 51 located further upstream in the direction of transport of the steel material 1 between the plurality of rolling mills 51 to 54 in the rough rolling mill 50. Furthermore, the cutting device 90 is provided upstream of the finishing rolling mill 60 in the direction of transport of the steel material 1. More specifically, the cutting device 90 is provided between the rolling mill 51 provided further upstream and the rolling mill 52 provided in the second stage in the rough rolling mill 50 in the direction of transport of the steel material 1.In other words, cutting apparatus 90 is provided between rolling mill 51 and rolling mill 52 adjacent to rolling mill 51. Petition 870250086917, dated 09 / 25 / 2025, pp. 44 / 69 / 41

[00114] As shown in Figure 13 as an example, the cutting apparatus 90 includes a rotary cutting tool 92. The rotary cutting tool 92 has a holder 94 and numerous cutting blades 96 fixed to the outer peripheral edge portion of the holder 94. The rotary cutting tool 92 receives energy from a power source (not shown in the drawings) and rotates. Furthermore, the rotary cutting blades 96 come into contact with the surface of the steel material 1, thus cutting the surface of the steel material 1. In this way, the surface of the steel material 1 is cut by the cutting apparatus 90, removing the target region T on the surface of the steel material 1 after it has been heated in the heating furnace 20.

[00115] It should be noted that although an example in which the cutting apparatus 90 has a rotary cutting tool 92 is described here, the description is not limited to this example. For example, a surface of the steel material 1 may be cut by a plurality of rotary cutting tools 92. Furthermore, the cutting apparatus 90 may include the rotary cutting tools 92 in positions opposite the surfaces of the steel material 1 on both sides in the thickness direction and the surfaces (lateral end faces) of the steel material 1 on both sides in the width direction.

[00116] As described above, in the hot rolling equipment 10 belonging to the second embodiment, the target region T including the Cu-rich layer is removed from the steel material 1 by the cutting apparatus 90. Mechanical removal, such as cutting, is less likely to cause deterioration in the surface texture of the steel material 1 (e.g., surface roughness) compared to removal by scarifying. Consequently, according to the present embodiment, deterioration in the surface texture of the steel material 1 in the hot rolling process can be inhibited.

[00117] It should be noted that, although in the second mode it has Petition 870250086917, dated 09 / 25 / 2025, page 45 / 69 / 41, described an example in which steel material 1 is cut by cutting apparatus 90; the description is not limited to this example. The removal apparatus is not limited to cutting apparatus 90 and may, for example, use a mechanical removal method, such as grinding using a grinding wheel apparatus. <Terceira Modalidade>

[00118] In the first embodiment, an example was described in which the heating furnace 20 is provided separately from the production line of the continuous casting machine 11 that continuously melts the steel material 1, but the description is not limited to this example. In a third embodiment, the heating furnace 102 is provided in a production line of a continuous casting machine that continuously melts the steel material 1.

[00119] As shown in Figure 14 as an example, the continuous casting machine 11 continuously casts a plate 1A that is thinner (e.g., 50 mm to 100 mm) than in the continuous casting machine 11 in the first embodiment. Hot rolling equipment 100 is provided in the production line of continuous casting machine 11. That is, the production line of hot rolling equipment 100 is continuous with the production line of continuous casting machine 11. Hot rolling equipment 100 includes a heating furnace 102, a descaling apparatus 40, a rough rolling apparatus 50, a pre-removal descaling apparatus 40A, a scarifying apparatus 30, a post-removal descaling apparatus 40B, a raw bar heating furnace 104 and a finishing rolling apparatus 60. It should be noted that the rough rolling apparatus 50 of the third embodiment has, as an example, two rolling mills 51, 52.

[00120] Heating furnace 102 is, for example, a tabletop heating furnace. Furthermore, heating furnace 102 is provided upstream of the raw rolling mill 50 in the direction of conveying the steel material 1. Heating furnace 102 heats to a temperature Petition 870250086917, dated 09 / 25 / 2025, page 46 / 69 / 41 predetermined (1100 °C or higher) the steel material 1 (for example, plate 1A), which is obtained by cutting the steel material 1 discharged from the continuous casting machine 11 to a predetermined length.

[00121] The raw bar heating furnace 104 is, for example, a table heating furnace. Furthermore, the raw bar heating furnace 104 is provided downstream of the rough rolling mill 50 and upstream of the finishing rolling mill 60 in the direction of conveying the steel material 1. The raw bar heating furnace 104 heats the steel material 1, which has been roughly rolled by the rough rolling mill 50, to a predetermined temperature (less than 1100°C).

[00122] Figure 15 shows an example of the thermal history of steel material 1 in a series of continuous casting, hot rolling, and cold rolling processes in the third embodiment. As shown in Figure 15, at the beginning of continuous casting, the temperature of steel material 1 is about 1500°C. For this reason, incrustations form on the surface of steel material 1. On the other hand, steel material 1 cools to 1000°C or lower during the rough rolling process after exiting the heating furnace 20, and from then on, its temperature does not rise to 1100°C or higher. Consequently, in the third embodiment, the same effects as those of the first embodiment can be obtained. EXAMPLES

[00123] To evaluate the performance of the hot rolling equipment 10 and the hot rolling method belonging to the description, an evaluation was conducted of the relationship between the depth of surface cracks in steel sheets (steel materials 1) and the concentrations of Cu in the steel sheets.

[00124] Specifically, as an example, several steel plates (steel materials 1) with different Cu contents were prepared. All the multiple steel plates had C: 0.2% by weight, Si: 0.01 to 0.25% Petition 870250086917, dated 09 / 25 / 2025, p. 47 / 69 / 41 by weight, Mn: 0.5% by weight, T-Al: 0.03% and Fr for the remainder, but Cu was defined as 0.2% by weight, 0.5% by weight, 1% by weight and 1.5% by weight, respectively. Then, each steel plate was heated and held at 1100°C or higher (1200°C) and then stretched at a strain rate of 5 / s until a cross-sectional area reduction rate of 33%, which caused cracking in each steel plate. Then, 1 mm of the surface of each steel plate was removed by scarification. Several steel plates belonging to a Comparative Example were the same as the several steel plates belonging to the Example, except that their surfaces were not scarified. Each steel plate belonging to the Example and the Comparative Example was cut, and the depth of the surface cracks in each steel plate was measured within the field of view, observing the cut surface.Next, the average value of the depths of the multiple surface cracks measured for each steel plate belonging to the Example and the Comparative Example was calculated.

[00125] As shown in Figure 16 as an example, in each steel plate belonging to the Comparative Example, cracks occurred on the surface of each steel plate. That is, hot brittleness cracks occurred in each steel plate in the temperature range close to the temperature at the beginning of rough rolling (e.g., 1100°C). Furthermore, as the concentration of Cu in the steel plates increased, the depth of the surface cracks increased and the phenomenon of Cu concentration became more pronounced. However, even when the Cu concentrations in the steel plates were high (e.g., 1% by weight or more), the depth of the surface cracks in the steel plate was 1 mm or less. In each steel plate belonging to the Example, 1 mm of the surface was scarified, removing the surface cracks so that the depth of the surface cracks became substantially zero. It was confirmed that hot brittleness cracks can be removed by Petition 870250086917, dated 09 / 25 / 2025, pp. 48 / 69 / 41 means of scarifying the surfaces of steel sheets in this manner.

[00126] Although preferred embodiments of the description have been described in detail above with reference to the accompanying drawings, the present description is not limited to those examples. It will be evident that a variety of example alterations or example applications within the category of technical thinking set forth in the claims may occur to one skilled in the art to whom the description pertains, and it will be understood that these also naturally belong to the technical scope of the description.

[00127] In addition, the description of Japanese Patent Application No. 2023-054365 filed on March 29, 2023 is incorporated herein by reference in its entirety.

[00128] All documents, patent applications and technical standards mentioned in this descriptive report are incorporated herein by reference to the same extent as if each individual document, patent application or technical standard were specifically and individually indicated to be incorporated by reference.

[00129] In addition to the above modalities, the following addenda are also described. (Addendum 1)

[00130] Hot rolling equipment for hot rolling of a copper (Cu) containing steel material, the hot rolling equipment comprising: a heating furnace that heats the steel material to a predetermined temperature after continuous casting; a rough rolling apparatus including a plurality of rolling mills that rough rolls steel material that has been heated in the heating furnace; a finishing rolling mill that finishes rolling steel material that has been roughly rolled by the machine of Petition 870250086917, dated 09 / 25 / 2025, page 49 / 69 / 41 rough rolling; and a stripping apparatus that removes a target region including cracks caused by a Cu-rich layer that is present on one side of the surface of the steel material being rough rolled or has been rough rolled and in which a concentration of Cu components is greater than a concentration of Cu components in the base material, wherein the stripping apparatus is provided downstream of a rolling mill located further upstream in a transport direction between the plurality of rolling mills in the rough rolling mill and upstream of the finishing rolling mill. (Addendum 2)

[00131] The hot rolling equipment of appendix 1, wherein the stripping apparatus is provided between one rolling mill and another rolling mill adjacent to the single rolling mill among the plurality of rolling mills in the rough rolling mill. (Addendum 3)

[00132] The hot rolling equipment of appendix 2, wherein the stripping apparatus is provided after the rolling mill located furthest upstream in the transport direction between the plurality of rolling mills in the rough rolling mill. (Addendum 4)

[00133] The hot rolling equipment of appendix 1, wherein the stripping apparatus is provided downstream of the raw rolling apparatus in the transport direction and upstream of the finishing rolling apparatus in the transport direction. (Addendum 5)

[00134] Hot rolling equipment of any of the addenda 1 to addendum 4, wherein the stripping apparatus removes the target region by scarification. Petition 870250086917, dated 09 / 25 / 2025, pp. 50 / 69 / 41 (Addendum 6)

[00135] Hot rolling equipment of any of the addenda 1 to addendum 4, wherein the stripping apparatus removes the target region by mechanical stripping. (Addendum 7)

[00136] A hot rolling method for hot rolling a copper (Cu)-containing steel material, the hot rolling method comprising: A heating process that heats the steel material to a predetermined temperature after continuous casting. A rough rolling process that performs a plurality of rough rolling passes on steel material that has been heated in the heating process; A finishing rolling process that performs finishing rolling on steel material that was rough-rolled in the rough rolling process; and a stripping process that removes a target region, including cracks caused by a Cu-rich layer that is present on one side of the surface of the steel material being rough-rolled or has been rough-rolled and in which a concentration of Cu components is greater than a concentration of Cu components in a base material, wherein the stripping process is performed after the first rolling pass between the plurality of rough rolling passes and before the finishing rolling process. (Addendum 8)

[00137] The hot rolling method of appendix 7, in which the stripping process is carried out with the surface temperature of the steel material being rolled raw or that has been rolled raw being 1000°C or lower. Petition 870250086917, dated 09 / 25 / 2025, pp. 51 / 69 / 41 (Addendum 9)

[00138] The hot rolling method of appendix 7 or appendix 8, whereby, when the removal of the target region is carried out by scarifying in the removal process, the transport speed of the steel material being rolled raw or has been rolled raw is defined as 20 m / min or higher. (Addendum 10)

[00139] The hot rolling method of any of appendix 7 to appendix 9, wherein the target region is a region of 1 mm or less in the thickness direction of the surface of the steel material being roughly rolled or has been roughly rolled. Petition 870250086917, dated 09 / 25 / 2025, pp. 52 / 69

Claims

1 / 4 CLAIMS 1. Hot rolling equipment for hot rolling of a copper (Cu) containing steel material, the hot rolling equipment characterized in that it comprises: a heating furnace that heats the steel material to a predetermined temperature after melting; a rough rolling apparatus including a plurality of rolling mills that rough rolls the steel material that has been heated in the heating furnace; a finishing rolling apparatus that finish rolls the steel material that has been rough rolled by the rough rolling apparatus;and a stripping apparatus that removes a target region including cracks caused by a Cu-rich layer that is present on one side of the surface of the steel material being roughly rolled or has been roughly rolled and in which a concentration of Cu components is greater than a concentration of Cu components in a base material of the steel material, wherein the stripping apparatus is provided downstream of a rolling mill located further upstream among the plurality of rolling mills in the rough rolling mill in a direction of conveying the steel material and upstream of the finishing rolling mill.

2. Hot rolling equipment according to claim 1, characterized in that the hot rolling equipment includes a post-removal descaling apparatus that is provided downstream of the removal apparatus and upstream of the finishing rolling apparatus in the direction of conveying the steel material and that descales the steel material using cooling water.

3. Hot rolling equipment according to Petition 870250086917, dated 09 / 25 / 2025, page 53 / 69 2 / 4 claim 1 or 2, characterized in that the hot rolling equipment includes a pre-descaler apparatus that is provided between the scaler apparatus and a rolling mill located upstream of, and adjacent to, the scaler apparatus in the direction of transport of the steel material between the plurality of rolling mills in the rough rolling mill and that descales the steel material using cooling water.

4. Hot rolling equipment according to any one of claims 1 to 3, characterized in that the stripping apparatus is provided between one rolling mill and another rolling mill adjacent to the single rolling mill among the plurality of rolling mills in the raw rolling apparatus.

5. Hot rolling equipment according to claim 4, characterized in that the stripping apparatus is provided after the rolling mill located furthest upstream among the plurality of rolling mills in the raw rolling mill apparatus in the direction of transport of the steel material.

6. Hot rolling equipment according to any one of claims 1 to 3, characterized in that the stripping apparatus is provided downstream of the rough rolling apparatus and upstream of the finishing rolling apparatus in the direction of transport of the steel material.

7. Hot rolling equipment according to any one of claims 1 to 6, characterized in that the stripping apparatus removes the target region of the steel material by means of scarification or removes the target region of the steel material by means of mechanical stripping.

8. Hot rolling equipment according to any one of claims 1 to 7, characterized in that the heating furnace is provided separately from a production line of a casting machine that melts the steel material.

9. Hot rolling equipment according to any one of claims 1 to 7, characterized in that the heating furnace is provided in a production line of a casting machine that melts the steel material.

10. Hot rolling method for hot rolling of a copper (Cu) containing steel material, the hot rolling method characterized in that it comprises: a heating process that heats the steel material to a predetermined temperature after casting; a rough rolling process that performs a plurality of rough rolling passes on the steel material that was heated in the heating process; a finishing rolling process that performs finishing rolling on the steel material that was rough rolled in the rough rolling process;It is a stripping process that removes a target region, including cracks caused by a Cu-rich layer present on one side of the surface of the steel material being roughly rolled or having been roughly rolled, and in which the concentration of Cu components is greater than the concentration of Cu components in the base material of the steel material, wherein the stripping process is carried out after a first rough rolling pass between multiple rough rolling passes and before the finish rolling process.

11. Hot rolling method according to claim 10, characterized in that it further comprises a post-removal descaling process that descales the steel material using cooling water after the removal process and before the finishing rolling process.

12. Hot rolling method according to claim 10 or 11, characterized in that it further comprises a pre-removal descaling process that descales the steel material using cooling water after a rolling pass that occurs immediately before the removal process between the plurality of rough rolling passes and before the removal process.

13. Hot rolling method according to any one of claims 10 to 12, characterized in that the stripping process is carried out with a surface temperature of the steel material being rolled or that has been rolled in the rough being 1000°C or lower.

14. Hot rolling method according to any one of claims 10 to 13, characterized in that, when the removal of the target region is carried out by scarifying in the removal process, a transport speed of the steel material being rolled raw or has been rolled raw is 20 m / min or higher.

15. Hot rolling method according to any one of claims 10 to 14, characterized in that the target region is a region of 1 mm or less in a thickness direction of a surface of the steel material being roughly rolled or has been roughly rolled. Petition 870250086917, dated 09 / 25 / 2025, pp. 56 / 69

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