Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
  • B21B3/003—Rolling non-ferrous metals immediately subsequent to continuous casting, i.e. in-line rolling
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
  • B21B45/04—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing
  • B21B45/08—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for de-scaling, e.g. by brushing hydraulically
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
  • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
  • B21B1/24—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process
  • B21B1/26—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process by hot-rolling, e.g. Steckel hot mill
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
  • B21B3/02—Rolling special iron alloys, e.g. stainless steel
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23C—MILLING
  • B23C3/00—Milling particular work; Special milling operations; Machines therefor
  • B23C3/14—Scrubbing or peeling ingots or similar workpieces
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K7/00—Cutting, scarfing, or desurfacing by applying flames
  • B23K7/06—Machines, apparatus or equipment specially designed for scarfing or desurfacing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23P—METAL-WORKING NOT OTHERWISE PROVIDED FOR; COMBINED OPERATIONS; UNIVERSAL MACHINE TOOLS
  • B23P17/00—Metal-working operations, not covered by a single other subclass or another group in this subclass
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23P—METAL-WORKING NOT OTHERWISE PROVIDED FOR; COMBINED OPERATIONS; UNIVERSAL MACHINE TOOLS
  • B23P23/00—Machines or arrangements of machines for performing specified combinations of different metal-working operations not covered by a single other subclass
  • B23P23/04—Machines or arrangements of machines for performing specified combinations of different metal-working operations not covered by a single other subclass for both machining and other metal-working operations
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
  • B21B1/46—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting
  • B21B1/466—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling metal immediately subsequent to continuous casting in a non-continuous process, i.e. the cast being cut before rolling
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
  • B21B45/004—Heating the product

Definitions

• This disclosure relates to hot rolling equipment and hot rolling methods.
• WO 2008/146891 describes a method for preparing the surface of a hot slab, in which part or all of the surface of a steel material (e.g., a slab) after continuous casting is cut off from the surface of the steel material by 1 mm or more using a milling-type surface cutting device made up of an electric rotary cutting tool with multiple cutting blades.
• a steel material e.g., a slab
• Japanese Patent Application Laid-Open No. 6-198304 describes a hot rolling method in which the surface layer of a steel material (e.g., a slab) after continuous casting is removed using a cutting device or a grinding device, and then the steel material is hot rolled.
• a steel material e.g., a slab
• iron sources other than iron ore have come to be used in order to reduce carbon dioxide emissions in the steel manufacturing process.
• scrap iron when scrap iron is used as an iron source, surface defects due to the copper (Cu) contained in the scrap iron can occur during the steel manufacturing stage. For example, during the hot rolling process, red-hot embrittlement cracking can occur due to Cu concentrating on the surface of the steel, reducing the surface quality of the steel. For this reason, it is difficult to increase the proportion of scrap iron containing Cu used as an iron source, making it difficult to realize an environmentally friendly steel manufacturing process.
• Cu copper
• JP 6-198304 A does not take into consideration the effect that removing the surface layer of the steel material using a cutting device or the like has on the subsequent rolling of the steel material, and there is room for improvement in terms of the rolling quality of the steel material.
• the purpose of this disclosure is to provide a hot rolling method and hot rolling equipment that can suppress red embrittlement cracking of steel while suppressing deterioration of the rolling quality of the steel.
• the hot rolling equipment is a hot rolling equipment for hot rolling a steel material containing Cu, and includes a heating furnace for heating the steel material after casting to a predetermined temperature, a rolling device for rolling the steel material heated in the heating furnace, a removal device provided downstream of the heating furnace and upstream of the rolling device in the conveying direction of the steel material, for removing a target area from the steel material heated in the heating furnace, the target area including a Cu-enriched layer that is present on the surface side of the steel material and has a higher concentration of Cu components than in the base material of the steel material, and a post-removal descaling device provided downstream of the removal device and upstream of the rolling device in the conveying direction of the steel material, for removing scales from the steel material using cooling water.
• the hot rolling equipment of the second aspect is the hot rolling equipment of the first aspect, in which the post-removal descaling device cools the steel material so that the surface temperature of the steel material is less than 1100°C.
• the hot rolling equipment according to the third aspect is the hot rolling equipment according to the first or second aspect, and includes a width reduction device that is provided downstream of the heating furnace and upstream of the removal device in the conveying direction of the steel material, and reduces the steel material in the width direction of the steel material.
• the hot rolling equipment according to the fourth aspect is the hot rolling equipment according to any one of the first to third aspects, and includes a pre-removal descaling device that is provided downstream of the heating furnace and upstream of the removal device in the conveying direction of the steel material and that removes scale from the steel material using cooling water.
• the hot rolling equipment according to the fifth aspect is the hot rolling equipment according to any one of the first to fourth aspects, in which the rolling device is a rough rolling device that performs rough rolling on the steel material, or a finish rolling device that performs finish rolling on the steel material.
• the hot rolling equipment according to the sixth aspect is the hot rolling equipment according to any one of the first to fifth aspects, in which the target area is an area 2 mm or less from the surface of the steel material in the thickness direction of the steel material.
• the hot rolling equipment according to the seventh aspect is the hot rolling equipment according to any one of the second to sixth aspects, in which the removal device removes the target area from the steel material by machining, or removes the target area from the steel material by mechanical removal.
• the hot rolling equipment according to the eighth aspect is a hot rolling equipment according to any one of the first to seventh aspects, in which the heating furnace is provided separately from the production line of the casting machine that casts the steel material.
• the hot rolling equipment according to the ninth aspect is the hot rolling equipment according to any one of the first to seventh aspects, in which the heating furnace is provided on the production line of a casting machine that casts the steel material.
• the hot rolling method is a hot rolling method for hot rolling a steel material containing Cu, and includes a heating step for heating the steel material after casting to a predetermined temperature, a removal step for treating the steel material heated in the heating step, which is a step for removing a target area that is present on the surface side of the steel material and includes a Cu-enriched layer having a higher concentration of Cu than in the base material of the steel material, a post-removal descaling step for removing scale from the steel material using cooling water after the removal step, and a rolling step for rolling the steel material after the post-removal descaling step.
• the hot rolling method according to the eleventh aspect is the hot rolling method according to the tenth aspect, in which in the post-removal descaling process, the steel is cooled so that the surface temperature of the steel is less than 1100°C.
• the hot rolling method according to the twelfth aspect is the hot rolling method according to the tenth or eleventh aspect, further including a width reduction step of reducing the steel material in the width direction of the steel material after the heating step and before the removing step.
• the hot rolling method according to the thirteenth aspect is a hot rolling method according to any one of the tenth to twelfth aspects, further including a pre-removal descaling step in which scale is removed from the steel material using cooling water after the heating step and before the removing step.
• the hot rolling method according to the 14th aspect is a hot rolling method according to any one of the 10th to 13th aspects, in which the rolling step includes performing rough rolling on the steel material.
• the hot rolling method according to the fifteenth aspect is a hot rolling method according to any one of the tenth to fourteenth aspects, in which the target region is a region that is 2 mm or less from the surface of the steel material in the thickness direction of the steel material.
• the hot rolling method according to the 16th aspect is a hot rolling method according to any one of the 10th to 15th aspects, in which in the removing step, the target area is removed from the steel material by laser cutting, or the target area is removed from the steel material by mechanical removal.
• the hot rolling method according to the seventeenth aspect is a hot rolling method according to any one of the tenth to sixteenth aspects, in which the steel material contains 0.15 mass% or more of the Cu.
• the present disclosure provides a hot rolling method and hot rolling equipment that can suppress red embrittlement cracking of steel while suppressing deterioration in the rolling quality of the steel.
• FIG. 1 is a schematic diagram showing an example of a schematic configuration of a hot rolling facility according to a first embodiment of the present disclosure.
• FIG. 2 is a schematic diagram showing an example of a thermal history of a steel material in hot rolling equipment according to the first embodiment of the present disclosure.
• 1 is a cross-sectional view showing a steel material to be laser-cut by a laser-cutting device according to a first embodiment of the present disclosure.
• 1 is a schematic diagram showing an example of a schematic configuration of a cutting device according to a first embodiment of the present disclosure.
• FIG. 2 is a schematic diagram showing an example of a schematic configuration of a target region according to the first embodiment of the present disclosure.
• FIG. 1 is a schematic diagram showing an example of a schematic configuration of a hot rolling facility according to a first embodiment of the present disclosure.
• FIG. 2 is a schematic diagram showing an example of a thermal history of a steel material in hot rolling equipment according to the first embodiment of the present disclosure.
• 1 is a cross
• FIG. 2 is a flowchart illustrating an example of a hot rolling process according to the first embodiment of the present disclosure.
• FIG. 2 is a schematic diagram showing an example of a schematic configuration of a hot rolling apparatus according to a first modified example.
• FIG. 13 is a schematic diagram showing an example of a schematic configuration of a hot rolling apparatus according to a second modified example.
• FIG. 11 is a schematic diagram showing an example of a thermal history of a steel material in a hot rolling facility according to a second modified example.
• FIG. 4 is a schematic diagram showing an example of a schematic configuration of a hot rolling facility according to a second embodiment of the present disclosure.
• FIG. 11 is a schematic diagram showing an example of a schematic configuration of a cutting device according to a second embodiment of the present disclosure.
• FIG. 13 is a schematic diagram showing an example of a schematic configuration of a hot rolling facility according to a third embodiment of the present disclosure.
• FIG. 11 is a schematic diagram showing an example of a thermal history of a steel material in hot rolling equipment according to a third embodiment of the present disclosure.
• FIG. 13 is a schematic diagram showing an example of a schematic configuration of a hot rolling apparatus according to a second modified example.
• FIG. 11 is a schematic diagram showing an example of a thermal history of a steel material in a hot rolling facility according to a second modified example.
• 1 is a graph showing the relationship between the number ratio of Cu-enriched portions and the depth of thermal cutting according to an embodiment of the present disclosure.
• Fig. 1 is a diagram showing a schematic configuration of the hot rolling facility 10.
• hot rolling equipment 10 is equipment for hot rolling steel material 1.
• this hot rolling equipment 10 is provided separately from a production line of a continuous casting machine 11 that continuously casts steel material 1.
• Hot rolling equipment 10 includes a heating furnace 20, a laser cutting device 30, a width reduction device 23, a descaling device 40, a rough rolling device 50, and a finish rolling device 60.
• steel material 1 may be cast individually, not limited to continuous casting.
• the heating furnace 20 heats the steel material 1 (e.g., slab 1A) obtained by cutting the steel material 1 discharged from the continuous casting machine 11 to a predetermined length, to a predetermined temperature.
• the "predetermined temperature” here is, for example, 1100°C or higher.
• the slab 1A is heated by the heating furnace 20 while being transported by the transport rolls 22.
• the slab 1A is given as an example of the steel material 1, but this is merely one example, and the steel material 1 may also be a billet.
• Steel material 1 is a steel material containing Cu, for example, a steel material containing 0.15 wt% (mass%) or more of Cu, and in particular, a steel material containing 0.25 wt% or more of Cu.
• the Cu content here means the average Cu content in the base material of steel material 1, which will be described later, or the average Cu content in the molten steel that becomes steel material 1.
• the Cu content of steel material 1 is, for example, 5.6 wt% or less.
• the cutting device 30 performs cutting on the slab 1A discharged from the heating furnace 20 to remove the surface portion (surface layer) of the slab 1A. Details of the cutting device 30 will be described later.
• the cutting device 30 is located downstream of the heating furnace 20 in the conveying direction of the slab 1A.
• the cutting device 30 is also located upstream of the width reduction device 23 and the descaling device 40 in the conveying direction of the slab 1A. More specifically, the cutting device 30 is located downstream of the heating furnace 20 and upstream of the width reduction device 23 in the conveying direction of the slab 1A.
• the width reduction device 23 is a device that adjusts the width of the slab 1A by reducing (pressing) the slab 1A heated in the heating furnace 20 in the width direction of the slab 1A.
• the descaling device 40 removes scale (i.e., oxide film) formed on both surfaces in the thickness direction of the slab 1A and both surfaces (side end faces) in the width direction of the slab 1A before rough rolling by the rough rolling device 50.
• the descaling device 40 removes scale from the surface of the slab 1A by spraying a fluid (e.g., cooling water) from a nozzle 42 onto the surface of the slab 1A.
• the descaling device 40 also cools the slab 1A by spraying a fluid from the nozzle 42 onto the slab 1A. This suppresses the generation of scale.
• the rough rolling device 50 performs rough rolling (hot rough rolling) on the slab 1A to thin the slab 1A to a predetermined thickness. Specifically, the rough rolling device 50 rolls the slab 1A, which has been rolled down in the width direction by the width reduction device 23 (vertical rolls 24), from above and below to form a rough bar 1B.
• the rough rolling device 50 is equipped with four rolling mills 51, 52, 53, and 54. Each of the rolling mills 51 to 54 has multiple rolls that sandwich the slab 1A from both sides in the thickness direction. The rough rolling device 50 continuously rolls the slab 1A using the rolling mills 51 to 54.
• the slab 1A is thinned to a plate thickness of, for example, about 25 to 50 mm and formed into a rough bar 1B.
• the rough rolling device 50 may be equipped with two rolling mills. In this case, in the rough rolling device 50, reciprocating rolling is performed between the two rolling mills.
• the rough rolling device 50 is an example of a rolling device.
• finishing rolling device 60 having 6 to 7 stands of finishing rolls 64 is shown here, this is merely one example, and the finishing rolling device 60 may have, for example, a 5-stand group of finishing rolls 64. Note that the finishing rolling device 60 is an example of a rolling device.
• the cooling device 70 cools the steel strip 1C after finish rolling with cooling water W.
• the cooling device 70 is, for example, a pipe laminar nozzle type cooling device.
• the 1C cooled by the cooling device 70 is wound into a coil by the winding device 80 and transported from the hot rolling equipment 10 to the next process as a hot rolled coil 1D.
• FIG. 2 shows an example of the thermal history of the steel material 1 in a series of processes of continuous casting, hot rolling, and cold rolling.
• the iron oxide formed on the surface of the steel material 1 also contains Cu. Since Cu in the iron oxide exists in a liquid phase state without being oxidized, it infiltrates from the iron oxide into the surface layer of the base metal part of the steel material 1. Cu that has infiltrated from the iron oxide into the surface layer of the bare metal part of the steel material 1 mainly precipitates and concentrates at the grain boundaries of the surface layer.
• the Cu-enriched layer refers to the region in the unoxidized bare metal part of the steel material where the concentration of Cu is higher than the average concentration of Cu in the base material of the steel material when a scale formed on the surface of the steel material due to oxidation occurs.
• the Cu-enriched layer refers to the region from the interface between the scale formed on the surface of the steel material and the bare metal part of the steel material, i.e., the surface of the bare metal part of the unoxidized steel material, toward the center of the thickness direction of the steel material, where concentrated Cu at the grain boundaries is no longer observed.
• the "region where concentrated Cu at the grain boundaries is not observed" here refers to the region where the concentration of Cu at the grain boundaries is the average concentration of the steel material + 1% or less.
• the base material of the steel material refers to the part of the steel material excluding the Cu-enriched layer.
• surface defects such as iron oxide formed on the surface of slab 1A, inclusions and casting powder that have become embedded in the surface layer of slab 1A during casting, or air bubble marks on the surface layer of slab 1A are removed by a grinder or the like.
• the removal of these surface defects is performed before the heating step in the hot rolling process (i.e., heating by the heating furnace 20).
• the surface defects are removed from slab 1A before the hot rolling process.
• slab 1A is heated again to 1100°C or higher (e.g., about 1400°C), so scale is formed again on the surface of slab 1A.
• the Cu concentration phenomenon reoccurs in slab 1A, and red embrittlement cracking also reoccurs.
• the inventors therefore, after extensive research, came up with the idea of removing the Cu-enriched layer on the surface of slab 1A after heating slab 1A in heating furnace 20 in the hot rolling process. That is, in the thermal history of steel material 1 shown in FIG. 2, after steel material 1 leaves heating furnace 20 and drops to 1000°C or below in the rough rolling process, it is not heated to 1100°C or above again. In other words, no scale is generated on steel material 1 in processes subsequent to the heating process of steel material 1 in heating furnace 20. Therefore, no Cu-enriched phenomenon occurs in steel material 1, and no red-hot embrittlement cracking occurs in steel material 1 in processes subsequent to the heating process of steel material 1 in heating furnace 20.
• the surface layer of the slab 1A is removed by a scarifying device 30 located downstream of the heating furnace 20 in the transport direction of the slab 1A.
• the scarifying device 30 has two scarfer units 31 that face both sides (top and bottom) of the surface of the steel material 1 in the thickness direction, and two scarfer units 31 that face both sides (left and right) of the surface (side end faces) in the width direction of the steel material 1.
• the four scarfer units 31 have the same configuration. Therefore, the following will describe the scarfer unit 31 that faces one (upper) surface of the steel material 1 in the thickness direction.
• the scarfer unit 30 has a scarfer unit 31 arranged to face the surface of the steel material 1.
• This scarfer unit 31 is equipped with a preheating gas jetting section 34 and a scarfer oxygen jetting section 36.
• the preheating gas jetting section 34 jets preheating oxygen 32 and combustible gas 33.
• the scarfer oxygen jetting section 36 jets oxygen for scarfer cutting 37.
• a shielding gas 38 consisting of combustible gas is jetted together with the oxygen for scarfer cutting 37.
• the steel material 1 is configured to be transported in the direction of arrow Y in FIG. 4.
• the flow of oxygen 37 for cutting ejected from the oxygen ejection section 36 for cutting is ejected further forward in the conveying direction Y of the steel material 1 than the flow of preheating oxygen 32 and combustible gas 33 ejected from the preheating gas ejection section 34.
• a preheating process is carried out.
• preheating oxygen 32 and combustible gas 33 are ejected from the preheating gas ejection portion 34 of the scarfer unit 31 toward the surface of the steel material 1, and the combustible gas 33 is burned.
• a part of the surface of the steel material 1 is melted by the heat of the burning combustible gas 33, forming a basin portion 1E.
• the length of the pool portion 1E formed on the surface of the steel material 1 along the conveying direction Y is, for example, in the range of approximately 20 mm to 30 mm.
• the cutting process is carried out.
• oxygen 37 for cutting is ejected from the oxygen ejection section 36 of the scarfer unit 31 toward the surface of the steel material 1, and the steel material 1 on which the basin section 1E has been formed is transported in the transport direction Y.
• shielding gas 38 is ejected from the oxygen ejection section 36 for cutting together with the oxygen 37 for cutting, and the oxygen 37 for cutting is protected by the shielding gas 38.
• the cutting process is an example of a removal process.
• the jet of cutting oxygen 37 ejected from the cutting oxygen ejection section 36 passes through the pool 1E of the steel material 1 being transported, and an oxidation reaction between the cutting oxygen 37 and iron occurs with the pool 1E as a heat source.
• the heat of this oxidation reaction melts the surface of the steel material 1, and the surface of the steel material 1 is laser-cut.
• the surface of the steel material 1 is laser-cut by the heat of the oxidation reaction on the rear side of the pool 1E in the transport direction Y.
• the laser-cutting device 30 laser-cuts the surface of the slab 1A after it has been heated in the heating furnace 20.
• the cutting device 30 removes a target area T, which is an area including a Cu-enriched layer R.
• the target area T is a range of a predetermined distance from the surface of the slab 1A (i.e., the surface of the scale S) in the thickness direction t of the slab 1A.
• the predetermined distance is, for example, greater than 0 mm and less than or equal to 3 mm (0 ⁇ distance ⁇ 3 mm), preferably greater than 0 mm and less than or equal to 1 mm (0 ⁇ distance ⁇ 1 mm), more preferably greater than 0 mm and less than or equal to 2 mm (0 ⁇ distance ⁇ 2 mm), and even more preferably greater than 1 mm and less than or equal to 2 mm (1 ⁇ distance ⁇ 2 mm).
• the thickness of slab 1A is, for example, about 250 mm. Therefore, by removing an area 1 mm or less from the surface of slab 1A as the target area T in the thickness direction t of slab 1A, the reduction in the thickness of slab 1A is reduced, and the yield of slab 1A can be improved. Furthermore, by removing an area 2 mm or less from the surface of slab 1A as the target area T in the thickness direction t of slab 1A, the yield of slab 1A can be improved while the Cu-enriched layer R can be removed more reliably.
• the target area T including the Cu-enriched layer R is removed from the steel material 1 by melt cutting (removal), thereby removing the Cu-enriched area R1 present at the grain boundary GB. As a result, red embrittlement cracking on the surface of the slab 1A is suppressed.
• FIG. 6 is a flow chart for explaining a part of the manufacturing process of the hot rolled steel sheet according to this embodiment.
• the heating furnace 20 heats the slab 1A after continuous casting to a predetermined temperature (e.g., about 1300°C).
• a predetermined temperature e.g., about 1300°C.
• step ST12 the surface layer of slab 1A heated in step ST10 is cut by the cutting device 30, thereby removing the target area T including the Cu-enriched layer from slab 1A.
• the manufacturing process proceeds to step ST14.
• the average concentration of the Cu component in the base material of steel material 1 is less than 0.15 wt%, it is difficult for a Cu-enriched layer to form in steel material 1 (slab 1A), so it is not necessary to perform the cutting process (removal process) of step ST12 using the cutting device 30. In other words, if the average concentration of the Cu component in the base material of steel material 1 is less than 0.15 wt%, it is not necessary to perform the cutting process (removal process) of step ST12.
• step ST14 the descaling device 40 performs descaling using cooling water W on the slab 1A from which the target area T has been removed in step ST12. As a result of the descaling, the surface temperature of the slab 1A drops to, for example, less than 1100°C. After the descaling process of step ST14 is performed, the manufacturing process proceeds to step ST16.
• a width reduction process is performed after step ST12 (scaling process) and before step ST14 (descaling process).
• the slab 1A that was scalded in step ST12 is width-reduced by the width reduction device 23, thereby adjusting the width of the slab 1A.
• step ST16 the slab 1A descaled in step ST14 is rough rolled by the rough rolling device 50. As a result, the slab 1A is formed into a rough bar 1B having a predetermined thickness. After the rough rolling process of step ST16 is performed, the manufacturing process proceeds to step ST18.
• step ST18 the rough bar 1B obtained in step ST16 is finish-rolled by the finishing rolling device 60. As a result, the rough bar 1B is formed into a steel strip 1C having a predetermined thickness. After the finishing rolling process of step ST18 is performed, the manufacturing process proceeds to step ST20.
• step ST20 the steel strip 1C that was finish-rolled in step ST18 is wound by the winding device 80 and formed into a hot-rolled coil 1D. After the winding process of step ST20 is performed, part of the manufacturing process of the hot-rolled steel sheet according to this embodiment is completed.
• the target area T including the Cu-enriched layer formed in the steel material 1 is removed after heating in the heating furnace 20.
• a predetermined temperature e.g., 1300°C
• liquid-phase Cu is concentrated at the grain boundaries GB near the surface (surface layer) of the steel material 1.
• the portion (surface layer) of the steel material 1 where Cu is concentrated is less ductile than the base metal portion of the steel material 1.
• the occurrence of the Cu-enriched layer is one of the causes of red embrittlement cracking.
• the target area T including the Cu-enriched layer is removed from the steel material 1 after heating in the heating furnace 20. Therefore, according to this embodiment, the occurrence of red embrittlement cracking in the steel material 1 is suppressed.
• the steel material 1 is heated to a predetermined temperature in the heating furnace 20, and the Cu-enriched layer is formed again in the steel material 1. For this reason, it is difficult to suppress red embrittlement cracking of the steel material 1.
• the target area T including the Cu-enriched layer is removed from the steel material 1.
• the steel material 1 is not heated to a temperature above the temperature at which the Cu-enriched layer is formed (e.g., 1100°C), so the re-generation of the Cu-enriched layer is suppressed. As a result, the occurrence of red embrittlement cracking in the steel material 1 is suppressed.
• the steel material 1 is descaled by the descaling device 40.
• cooling water W is sprayed onto the surface of the steel material 1 to remove the scale S formed on the surface.
• This descaling removes the scale S from the surface of the steel material 1 and also reduces the temperature of the surface of the steel material 1.
• the reduction in the temperature of the surface of the steel material 1 further suppresses the re-occurrence of the Cu-enriched layer. Therefore, according to this embodiment, the occurrence of red embrittlement cracking in the steel material 1 is suppressed.
• the surface temperature of the steel material 1 is cooled to less than 1100°C by the descaling device 40.
• the reduction in the surface temperature of the steel material 1 further suppresses the re-occurrence of the Cu-enriched layer. Therefore, according to this embodiment, the occurrence of red embrittlement cracking in the steel material 1 is suppressed.
• the steel material 1 is rough rolled by the rough rolling device 50.
• the rough rolling reduces the surface temperature of the steel material 1, which further suppresses the re-occurrence of the Cu-enriched layer. Therefore, according to this embodiment, the occurrence of red embrittlement cracking in the steel material 1 is suppressed.
• an area of 2 mm or less from the surface of the steel material 1 in the thickness direction t of the steel material 1 is removed by the cutting device 30.
• the Cu-enriched layer is mainly formed in an area of 2 mm or less from the surface of the steel material 1 in the thickness direction t of the steel material 1. Therefore, removing an area of 2 mm or less from the surface of the steel material 1 in the thickness direction t of the steel material 1 contributes to removing the Cu-enriched layer. Therefore, according to this embodiment, the occurrence of red embrittlement cracking in the steel material 1 is suppressed.
• the steel material 1 is subjected to laser cutting by the laser cutting device 30, thereby removing the target area T including the Cu-enriched layer from the steel material 1. Removal of the target area T by laser cutting is more productive than removal of the target area T by cutting. Therefore, according to this embodiment, the productivity of the steel material 1 can be improved.
• the hot rolling equipment 10 is provided separately from the production line of the continuous casting machine 11. As a result, for example, depending on the production capacity of the continuous casting machine 11 and the hot rolling equipment 10, it becomes possible to hot roll the steel material 1 continuously cast by each of the two continuous casting machines 11 by one (one line) of hot rolling equipment 10. Also, for example, even if the hot rolling equipment 10 is stopped, the continuous casting of the steel material 1 can be continued without stopping the continuous casting machine 11. Furthermore, since the thickness (slab thickness) of the steel material 1 becomes thicker, the removal ratio of the Cu-enriched layer relative to the steel material 1 can be made relatively thin.
• a pre-removal descaling device 40A is provided downstream of the heating furnace 20 and upstream of the cutting device 30 in the conveying direction of the steel material 1.
• the basic configuration of this pre-removal descaling device 40A is the same as that of the descaling device 40.
• the combustion reaction between the shave-off oxygen 37 (see FIG. 4) sprayed from the shave-off device 30 and the steel material 1 is inhibited, and shave-off of the steel material 1 may be interrupted.
• the shave-off thickness of the steel material 1 by the shave-off device 30 is kept at around 1 mm to 2 mm, shave-off of the steel material 1 by the shave-off device 30 is likely to be interrupted.
• the pre-removal descaling device 40A removes scale adhering to the surface of the steel material 1. This makes it easier to stabilize the combustion reaction between the melt-cutting oxygen 37 (see Figure 4) sprayed from the melt-cutting device 30 and the steel material 1. Therefore, interruptions in the melt-cutting of the steel material 1 by the melt-cutting device 30 can be suppressed.
• the pre-removal descaling device 40A also removes scale adhering to the surface of the steel material 1 by spraying cooling water W onto the surface of the steel material 1. At this time, the surface of the steel material 1 is cooled by the cooling water W, which further suppresses the re-occurrence of a Cu-enriched layer on the steel material 1. Furthermore, in the fourth modified example, the pre-removal descaling device 40A cools the surface of the steel material 1 to less than 1100°C. Therefore, the re-occurrence of a Cu-enriched layer on the steel material 1 is further suppressed.
• a post-removal descaling device 40B is provided downstream of the cutting device 30 and upstream of the width reduction device 23 in the conveying direction of the steel material 1.
• the basic configuration of this post-removal descaling device 40B is the same as that of the descaling device 40.
• the post-removal descaling device 40B removes scale and the like formed on the surface of the steel material 1 after the steel material 1 has been scalded by the scalding device 30.
• the post-removal descaling process is performed after the scalding process and before the width reduction process.
• the post-removal descaling device 40B to remove scale and the like formed on the surface of the steel material 1, the quality of the width adjustment of the steel material 1 by the width reduction device 23 can be improved.
• the post-removal descaling device 40B removes scale adhering to the surface of the steel material 1 by spraying cooling water W onto the surface of the steel material 1. At this time, the surface of the steel material 1 is cooled by the cooling water W, which further suppresses the re-generation of a Cu-enriched layer on the steel material 1. Furthermore, in the first modified example, the surface of the steel material 1 is cooled to less than 1100°C by the post-removal descaling device 40B. Therefore, the re-generation of a Cu-enriched layer on the steel material 1 is further suppressed. Therefore, the occurrence of red-hot embrittlement cracking in the steel material 1 is suppressed.
• Figure 8 shows an example of the thermal history of the steel material 1 in a series of processes of continuous casting, hot rolling, and cold rolling in the first modified example.
• the temperature of the steel material 1 is about 1500°C.
• scale forms on the surface of the steel material 1.
• the steel material 1 becomes 1000°C or lower during the rough rolling process, and is not heated to 1100°C or higher thereafter. Therefore, in the first modified example, the same effect as in the first embodiment can be obtained.
• a pre-removal descaling process is performed before the cutting process (removal process), and a post-removal descaling process is performed after the cutting process (removal process).
• a pre-removal descaling process is performed before the cutting process (removal process)
• a post-removal descaling process is performed after the cutting process (removal process).
• at least one of the pre-removal descaling process and the post-removal descaling process can be omitted.
• a laser cutting process (removal process) is performed before the width reduction process
• the present disclosure is not limited to this example.
• a laser cutting process (removal process) is performed after the width reduction process and before the rough rolling process.
• a pre-removal descaling process is performed after the width reduction process and before the laser cutting process
• a post-removal descaling process is performed after the laser cutting process and before the rough rolling process.
• the laser cutting device 30 is provided downstream of the width reduction device 23 and upstream of the rough rolling device 50 in the conveying direction of the steel material 1.
• a pre-removal descaling device 40A is provided downstream of the width reduction device 23 and upstream of the laser cutting device 30 in the conveying direction of the steel material 1.
• a post-removal descaling device 40B is provided downstream of the laser cutting device 30 and upstream of the rough rolling device 50 in the conveying direction of the steel material 1.
• the cutting device 30 cuts the surface of the steel material 1 that has been reduced in the width direction by the width reduction device 23.
• the cutting process is performed after the width reduction process and before the rough rolling process.
• the width reduction device 23 when the steel material 1 is reduced in the width direction by the width reduction device 23, for example, there is a possibility that red embrittlement cracking due to a Cu-enriched layer may occur on both sides of the steel material 1 in the width direction (side end faces).
• the surfaces on both sides of the steel material 1 in the thickness direction and the surfaces on both sides of the steel material 1 in the width direction (side end faces) are scrubbed by the cutting device 30. This makes it possible to remove red embrittlement cracking formed on both sides of the steel material 1 in the width direction (side end faces). Therefore, quality defects on the surface of the steel material 1 can be suppressed.
• a pre-removal descaling process is performed before the cutting process, and a post-removal descaling process is performed after the cutting process. Therefore, in the second modified example, the same effect as in the first modified example can be obtained.
• the target region T including the Cu-enriched layer is removed from the steel material 1 by the laser cutting device 30, but the present disclosure is not limited to this example.
• the target region T is removed from the steel material 1 by a cutting device 90 instead of the laser cutting device 30.
• the cutting device 90 is an example of a removal device.
• the hot rolling equipment 10 is provided with a cutting device 90 instead of the slag cutting device 30.
• the cutting device 90 removes the surface portion of the slab 1A by cutting the slab 1A discharged from the heating furnace 20.
• the cutting device 90 will be described in detail later.
• the cutting device 90 is located downstream of the heating furnace 20 in the conveying direction of the slab 1A.
• the cutting device 90 is also located upstream of the width reduction device 23 and the descaling device 40 in the conveying direction of the slab 1A. More specifically, the cutting device 90 is located downstream of the heating furnace 20 and upstream of the width reduction device 23 (vertical rolls 24) in the conveying direction of the slab 1A.
• the cutting device 90 is equipped with a rotary cutting tool 92.
• the rotary cutting tool 92 has a holder 94 and a number of cutting blades 96 attached to the outer periphery of the holder 94.
• the rotary cutting tool 92 rotates by receiving power from a power source (not shown).
• the rotating cutting blades 96 come into contact with the surface of the steel material 1, cutting the surface of the steel material 1.
• the cutting device 90 cuts the surface of the steel material 1, thereby removing the target area T on the surface of the steel material 1 after it has been heated in the heating furnace 20.
• the present disclosure is not limited to this example embodiment.
• one surface of the steel material 1 may be cut by multiple rotary cutting tools 92.
• the cutting device 90 may be provided with rotary cutting tools 92 at positions facing both surfaces of the steel material 1 in the thickness direction and both surfaces (side end faces) of the steel material 1 in the width direction.
• the target area T including the Cu-enriched layer is removed from the steel material 1 by the cutting device 90.
• Mechanical removal such as cutting is less likely to cause deterioration of the surface properties of the steel material 1 (e.g., surface roughness, etc.) compared to removal by surface cutting. Therefore, according to this embodiment, deterioration of the surface properties of the steel material 1 during the hot rolling process can be suppressed.
• the removal device is not limited to the cutting device 90, and may be, for example, a mechanical removal method such as grinding using a grinding wheel device.
• the heating furnace 20 is provided separately from the production line of the continuous casting machine 11 that continuously casts the steel material 1
• the present disclosure is not limited to this example.
• the heating furnace 102 is provided on the production line of the continuous casting machine that continuously casts the steel material 1.
• the continuous casting machine 11 continuously casts a slab 1A that is thinner (for example, 50 mm to 100 mm) than the continuous casting machine 11 in the first embodiment.
• a hot rolling facility 100 is provided on the production line of this continuous casting machine 11.
• the hot rolling facility 100 includes a heating furnace 102, a pre-removal descaling device 40A, a slicing device 30, a post-removal descaling device 40B, a rough rolling device 50, a rough bar heating furnace 104, and a finish rolling device 60.
• the hot rolling facility 100 of the third embodiment does not include the width reduction device 23 (see FIG. 1) of the first embodiment.
• the rough rolling device 50 of the third embodiment has, as an example, two rolling mills 51 and 52.
• the heating furnace 102 is, for example, a table heating furnace.
• the heating furnace 102 is also provided upstream of the rough rolling device 50 in the conveying direction of the steel material 1.
• This heating furnace 102 heats the steel material 1 (for example, slab 1A) obtained by cutting the steel material 1 discharged from the continuous casting machine 11 to a predetermined temperature (1100°C or higher).
• the rough bar heating furnace 104 is, for example, a table heating furnace.
• the heating furnace 102 is provided downstream of the rough rolling device 50 and upstream of the finish rolling device 60 in the conveying direction of the steel material 1. This heating furnace 102 heats the steel material 1 that has been rough rolled by the rough rolling device 50 to a predetermined temperature (less than 1100°C).
• FIG. 13 shows an example of the thermal history of the steel material 1 in a series of processes of continuous casting, hot rolling, and cold rolling in the third embodiment.
• the temperature of the steel material 1 is about 1500°C.
• scale is generated on the surface of the steel material 1.
• the steel material 1 becomes 1000°C or less during the rough rolling process, and is not heated to 1100°C or more thereafter. Therefore, in the third embodiment, the same effect as in the first embodiment can be obtained.
• a hot rolling facility 100 is provided on the production line of the continuous casting machine 11. This reduces heat loss between the continuous casting machine 11 and the hot rolling facility 100, improving energy efficiency.
• the hot rolling facility 100 can be made more compact.
• the hot rolling equipment 100 is described by way of an example including the rough rolling device 50.
• the present disclosure is not limited to this example.
• the hot rolling equipment 110 does not include the rough rolling device 50.
• a hot rolling facility 110 includes a heating furnace 102, a pre-removal descaling device 40A, a laser cutting device 30, a post-removal descaling device 40B, a rough bar heating device 62, and a finishing rolling device 60, but does not include a rough rolling device 50.
• the hot rolling equipment 110 includes the rough bar heating device 62, but the hot rolling equipment 110 does not have to include the rough bar heating device 62.
• Figure 15 shows an example of the thermal history of steel material 1 in a series of processes of continuous casting, hot rolling, and cold rolling in the third modified example.
• the temperature of steel material 1 is about 1500°C.
• scale forms on the surface of steel material 1.
• the temperature of steel material 1 drops to 1000°C or lower during the rough rolling process, and thereafter is not raised to above 1100°C. Therefore, in the third embodiment, the same effect as in the first embodiment can be obtained.
• Example 1 the composition of steel material 1 was adjusted to C: 0.0027 wt%, Si: 0.039 wt%, Mn: 0.2 wt%, P: 0.02 wt%, S: 0.011 wt%, Cu: 0.45 wt%, balance Fe.
• the three steel materials 1 adjusted in this way were heated in the heating furnace 20 of the hot rolling equipment 10 for 120 minutes, and the temperature of each steel material 1 was raised to 1250°C. Then, the surfaces of the three steel materials 1 were respectively shave-cut to different shave-cutting thicknesses. Furthermore, after descaling was performed on the surface of each steel material 1, the temperature of each steel material 1 was lowered to about 1000°C, which corresponds to the rough rolling start temperature, and then quenched.
• the composition of the steel material 1 in Example 2 was the same as that of the steel material 1 in Example 1, except that the Cu content was 0.98 wt%.
• the four steel materials 1 prepared in this way were heated, scalded, descaled, and cooled in the same manner as in Example 1.
• the seven steel materials 1 in Examples 1 and 2 each had a different scalding thickness.
• Each of the steel materials 1 in Examples 1 and 2 manufactured in this manner was cut. Then, the cut surface near the surface of each steel material 1 was observed, and the number of grain boundaries reaching the surface of the steel material 1 where Cu enrichment was observed was counted within a range of 1 cm in the sheet passing direction (transport direction) or width direction of the steel material 1.
• the measurement results of the number of Cu-enriched areas for each steel material 1 in Examples 1 and 2 are shown in FIG. 16.
• the vertical axis in FIG. 16 indicates the ratio of the measurement results for each steel material 1 to the maximum value (100%) of the measurement results (number of Cu-enriched areas) for each steel material 1.
• the proportion of the number of Cu-enriched areas in each steel material 1 was greatly reduced after each steel material 1 was razed.
• Example 1 the proportion of the number of Cu-enriched areas in each steel material 1 was 70-90% before each steel material 1 was razed (before razed), but after each steel material 1 was razed to a razed thickness of about 1 mm (after razed), it was reduced to 30% or less.
• Example 2 as in Example 1, the number ratio of Cu-enriched areas decreased after each steel material 1 was shave-cut.
• the number ratio of Cu-enriched areas was about 70% before shave-cutting steel material 1, but was 0% after shave-cutting steel material 1.
• the number ratio of Cu-enriched areas in each steel material 1 was about 100% or 35% before shave-cutting steel material 1, but was 0% after shave-cutting steel material 1.
• the number ratio of Cu-enriched areas in steel material 1 was about 35% before shave-cutting, but was about 25% after shave-cutting. It was confirmed that the number of Cu-enriched areas was reduced by shave-cutting steel material 1 in this way.
• a hot rolling method for hot rolling a steel material containing Cu comprising: a heating step of heating the steel material after continuous casting to a predetermined temperature; a removing step for removing a target region including a Cu-enriched layer that is present on the surface side of the steel material and has a higher concentration of Cu than that in the base material, as a treatment for the steel material heated in the heating step;
• a hot rolling method comprising the steps of: (Appendix 2) 2.
• the hot rolling method according to claim 2 wherein in the descaling step, the temperature of the surface of the steel material is cooled to 1,100° C. or lower.
• the method further includes a rough rolling step of performing rough rolling on the steel material, The hot rolling method according to claim 2 or 3, wherein the rough rolling step is performed after the descaling step.
• (Appendix 5) 5.
• Appendix 6) 6.
• the hot rolling method according to claim 1, wherein in the removing step, the target area is removed by laser cutting.
• (Appendix 7) 6.

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