WO2022234760A1 - Method for producing steel sheet for cold rolling and method for producing cold-rolled steel sheet - Google Patents

Method for producing steel sheet for cold rolling and method for producing cold-rolled steel sheet Download PDF

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Publication number
WO2022234760A1
WO2022234760A1 PCT/JP2022/017334 JP2022017334W WO2022234760A1 WO 2022234760 A1 WO2022234760 A1 WO 2022234760A1 JP 2022017334 W JP2022017334 W JP 2022017334W WO 2022234760 A1 WO2022234760 A1 WO 2022234760A1
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Prior art keywords
steel sheet
mass
rolling
less
cold
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PCT/JP2022/017334
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French (fr)
Japanese (ja)
Inventor
冬馬 北川
俊夫 村上
貴志 寺岡
拓馬 米田
駿 原田
啓太 中山
克馬 石飛
正宜 小林
浩樹 福島
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株式会社神戸製鋼所
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Priority to CN202280033546.XA priority Critical patent/CN117295831A/en
Priority to KR1020237040251A priority patent/KR20240000569A/en
Publication of WO2022234760A1 publication Critical patent/WO2022234760A1/en

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • 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
    • 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
    • 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
    • B21B45/02—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 lubricating, cooling, or cleaning
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
    • C21D8/0215—Rapid solidification; Thin strip casting
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

  • the present invention relates to a method for manufacturing a steel plate for cold rolling in the intermediate process of manufacturing a high-strength cold-rolled steel plate having a tensile strength of 980 MPa or more, and a method for manufacturing a cold-rolled steel plate using the steel plate manufactured by the method. .
  • edges in the width direction (hereinafter also referred to as “width direction edges” or “width direction edges”) and the edges in the direction parallel to the rolling direction (hereinafter referred to as “width direction edges”) , also called “longitudinal tips” or “longitudinal tails”).
  • edges in the width direction also called “width direction edges” or “width direction edges”
  • width direction edges also called “longitudinal tips” or “longitudinal tails”.
  • the cooling rate of the width direction end portions of the coiled steel sheet is the same as the width direction center portion of the steel plate (hereinafter also referred to as “width direction center portion”). comparatively faster. Therefore, in a hot-rolled steel sheet in which a steel containing a large amount of elements such as Mn that improve hardenability is used, the ferrite-pearlite transformation at both ends in the width direction of the steel sheet does not sufficiently progress, and both ends in the width direction of the steel sheet The part becomes a hard structure containing a relatively large amount of martensite. The same applies to the longitudinal tip and longitudinal tail of the steel plate. For this reason, it is believed that edge cracks are likely to occur in steel sheets during cold rolling or the like in the manufacture of high-strength cold-rolled steel sheets.
  • Patent Document 1 discloses a method for cold rolling a strip-shaped hot-rolled steel sheet that has been wound into a coil and cooled.
  • a cold rolling method is described that includes a pickling step of washing a hot-rolled steel sheet with an acid and a cold-rolling step of cold-rolling the hot-rolled steel sheet after the pickling step.
  • the present invention is a method for manufacturing a steel plate in the intermediate process of manufacturing a high-strength cold-rolled steel plate, and is a method for manufacturing a steel plate for cold rolling that can suppress edge cracks of the steel plate during cold rolling later.
  • the purpose is to provide a method.
  • the present inventors arrived at the present invention as a result of diligent studies aimed at solving the above problems.
  • the chemical composition is: C: 0.15% by mass or more and 0.25% by mass or less, Si: 0.8% by mass or more and 3.0% by mass or less, Mn: 1.8% by mass or more and 3.0% by mass or less, Ni, Cu, Cr, Mo: 1.0% by mass or less (including 0% by mass), Ti, Nb, V: 1.0 mass% or less (including 0 mass%), and B: 0.01% or less (including 0 mass%)
  • the method for manufacturing a cold-rolled steel sheet according to the second aspect of the present invention further comprises cold-rolling the steel sheet manufactured by the method according to the first aspect described above at a rolling reduction of 30% to 80%. include.
  • FIG. 1 is a schematic diagram showing an example of a method for manufacturing a steel sheet for cold rolling according to the present embodiment.
  • FIG. 2 is a schematic diagram showing the positions of test pieces of steel plates for hardness measurement in this example.
  • the present inventors conducted various studies on a new method of manufacturing a steel sheet for cold rolling that can suppress edge cracking of the steel sheet during cold rolling.
  • the present invention has been completed by paying attention to the temperature at the delivery side of the finishing mill in hot rolling and the water cooling control process after passing through the final stand of the finishing mill.
  • hot rolling is performed using a slab that satisfies a predetermined chemical composition so that the delivery side temperature of the finishing mill is within a predetermined temperature range. followed by water cooling the steel sheet under predetermined conditions after passing through the final stand of the finishing mill, and then coiling the steel sheet at or above a predetermined temperature.
  • the ferrite-pearlite transformation can be promoted at both ends in the width direction of the hot-rolled steel sheet, the leading end, or the trailing end, and these ends can be moderately softened.
  • the manufactured steel sheet can suppress edge cracks during subsequent cold rolling.
  • the manufactured steel sheet is subsequently subjected to cold rolling and optional heat treatment to obtain a high-tensile cold-rolled steel sheet, especially a high-tensile cold-rolled steel sheet with a tensile strength (TS) of 980 MPa or more. be done.
  • TS tensile strength
  • a method for manufacturing a steel sheet in an intermediate process of manufacturing a high-strength cold-rolled steel sheet which can suppress edge cracking of the steel sheet during subsequent cold rolling. It is possible to provide a method for manufacturing a steel plate.
  • FIG. 1 shows a schematic diagram of an example of a method for manufacturing a steel plate for cold rolling according to the present embodiment.
  • each reference numeral denotes a rolling facility 1, a heating furnace 2, a hot rolling mill 3, a runout table 4, a cooling facility 5, a roughing mill 31, a final stand 311 of the rolling mill, a lifting mill 32, and a finishing mill.
  • the slab extracted from the heating furnace 2 is hot-rolled while being controlled by the hot rolling mill 3 so that the delivery side temperature of the finishing mill 32 is within a specific temperature range.
  • the hot-rolled steel sheet sent out onto the runout table 4 is water-cooled by the cooling equipment 5 under specific conditions. After that, the steel sheet is wound while adjusting the winding temperature to a specific temperature or higher.
  • slab preparation First, a slab that satisfies a given chemical composition is prepared.
  • the slab can be prepared by any known method.
  • a method for producing a slab there is a method for producing a slab by melting steel having the chemical composition described below and then continuously casting the steel. If necessary, a slab may be obtained by blooming a cast material obtained by ingot casting or continuous casting.
  • the slab used in the method for manufacturing a steel sheet for cold rolling in the present embodiment has a chemical composition of C: 0.15% by mass or more and 0.25% by mass or less, Si: 0.8% by mass or more, 3 .0% by mass or less, Mn: 2.0% by mass or more and 3.0% by mass or less, Ni, Cu, Cr, Mo: 1.0% by mass or less (including 0% by mass), Ti, Nb, V: 1.0% by mass or less (including 0% by mass), and B: 0.01% or less (including 0% by mass).
  • the slab has P: 0.1% by mass or less (including 0% by mass), S: 0.01% by mass or less (including 0% by mass), Al: 0.10% by mass or less (0% by mass including), and N: 0.01% by mass or less (including 0% by mass).
  • C 0.15% by mass or more and 0.25% by mass or less
  • C is an important element for improving the strength of the steel sheet.
  • the C content is preferably 0.16% by mass or more, more preferably 0.17% by mass or more, and still more preferably 0.18% by mass or more.
  • the C content is preferably 0.23% by mass or less, more preferably 0.21% by mass or less, and even more preferably 0.19% by mass or less.
  • Si 0.8% by mass or more and 3.0% by mass or less
  • Si is an element that contributes to increasing the strength of a steel sheet as a solid-solution strengthening element.
  • the Si content is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and still more preferably 1.8% by mass or more.
  • the Si content is preferably 2.5% by mass or less, more preferably 2.1% by mass or less, and even more preferably 1.9% by mass or less.
  • Mn is an element that contributes to an increase in the strength of a steel sheet as a solid-solution strengthening element, and is also an element that is effective in improving hardenability and strength of the steel sheet.
  • Mn content 1.8% by mass or more
  • the effect of improving the strength can be exhibited, and finally, a high-strength cold-rolled steel sheet of 980 MPa or more can be obtained.
  • the Mn content 3.0% by mass or less
  • the hardenability is improved, and it is possible to prevent insufficient promotion of ferrite-pearlite transformation.
  • the Mn content is preferably 2.0% by mass or more, more preferably 2.3% by mass or more, and still more preferably 2.5% by mass or more. Also, the Mn content is preferably 2.9% by mass or less, more preferably 2.8% by mass or less, and even more preferably 2.7% by mass or less.
  • Ni, Cu, Cr, Mo 1.0% by mass or less (including 0% by mass)
  • Ni, Cu, Cr, or Mo is an element that contributes to increasing the strength of the steel sheet as a solid-solution strengthening element. These elements are also effective elements for enhancing the hardenability and strength of the steel sheet. Therefore, one or more elements selected from these elements may be included in the chemical composition of the slab. In order to effectively exhibit the strength improving action, the content of each of the one or more elements selected from Ni, Cu, Cr and Mo is preferably 0.05% by mass or more. In addition, the content of each of one or more elements selected from Ni, Cu, Cr, and Mo is 1. It is 0% by mass or less (including 0% by mass). The content of each of the one or more elements selected from Ni, Cu, Cr and Mo is more preferably 0.1% by mass or more. Also, the content of each of the one or more elements selected from Ni, Cu, Cr and Mo is preferably 0.5% by mass or less.
  • Ti, Nb, V 1.0% by mass or less (including 0% by mass)
  • Ti, Nb, or V is an element that contributes to an increase in the strength of a steel sheet as a precipitation strengthening element. Therefore, one or more elements selected from these elements may be included in the chemical composition of the slab.
  • the content of each of the one or more elements selected from Ti, Nb and V is preferably 0.01% by mass or more.
  • the content of each of one or more elements selected from Ti, Nb and V is 1.0% by mass or less in order to avoid the effect of increasing the strength described above being saturated and the cost being wasted. is.
  • the content of each of the one or more elements selected from Ti, Nb and V is preferably 0.02% by mass or more.
  • the content of each of the one or more elements selected from Ti, Nb and V is more preferably 0.5% by mass or less.
  • B 0.01% by mass or less (0% by mass or more)
  • B is an effective element for enhancing hardenability and strength of the steel sheet. Therefore, B may be included in the chemical composition of the slab.
  • the B content is preferably 0.0001% by mass or more.
  • the B content is 0.01% by mass or less, preferably 0.005% by mass or less, in order to improve hardenability and prevent insufficient promotion of ferrite-pearlite transformation.
  • P preferably 0.1% by mass or less (including 0% by mass)
  • P is an element that inevitably exists as an impurity element. P contributes to an increase in strength through solid-solution strengthening, but segregates at prior austenite grain boundaries and embrittles the grain boundaries, thereby causing edge cracks. Therefore, the P content is preferably suppressed to 0.1% by mass or less, and more preferably suppressed to 0.05% by mass or less.
  • S preferably 0.01% by mass or less (including 0% by mass)
  • S is an element that inevitably exists as an impurity element.
  • S forms MnS inclusions. These MnS inclusions cause edge cracks by becoming starting points for cracks. Therefore, the S content is preferably suppressed to 0.01% by mass or less, and more preferably suppressed to 0.005% by mass or less.
  • Al (S-Al) preferably 0.10% by mass or less (including 0% by mass)] Al is added as a deoxidizer.
  • the Al (S—Al) content is preferably 0.001% by mass or more in order to effectively exhibit the action as a deoxidizer. Also, Al may deteriorate the cleanliness of steel. Therefore, the Al (S—Al) content is preferably 0.10% by mass or less, more preferably 0.05% by mass or less.
  • N is an element that inevitably exists as an impurity element. N forms coarse nitrides. This coarse nitride becomes a starting point of cracks and causes edge cracks. Therefore, the N content is preferably suppressed to 0.01% by mass or less, and more preferably suppressed to 0.005% by mass or less.
  • the chemical composition of the slab in the present embodiment further contains other well-known arbitrary components within a range that does not hinder the promotion of ferrite/pearlite transformation, the required strength, sufficient workability, etc.
  • Other well-known optional components include, for example, Zr, Hf, Ca, Mg, REM (rare earth elements), and the like.
  • the balance is Fe and unavoidable impurities.
  • unavoidable impurities include trace elements (eg, As, Sb, Sn, etc.) brought in depending on the conditions of raw materials, materials, manufacturing equipment, etc., and inclusion of such trace elements is permitted.
  • trace elements eg, As, Sb, Sn, etc.
  • the content of these elements is restricted to a specific range so that the effect of the present invention can be exhibited more satisfactorily.
  • "inevitable impurities" constituting the balance is a concept excluding elements whose composition ranges are defined.
  • the slab extraction temperature in the heating furnace is set to 1180°C or higher and 1280°C or lower.
  • the heating furnace extraction temperature of the slab is the temperature calculated by the method described later in Examples.
  • the slab extracted from the heating furnace is hot-rolled to obtain a hot-rolled steel sheet.
  • Other conditions are not particularly limited as long as the hot rolling is performed so that the delivery side temperature of the finishing mill is 800° C. or higher and 940° C. or lower, and can be appropriately set within a range that does not impair the effects of the present embodiment. can.
  • hot rolling includes rough rolling and finish rolling. Each rolling will be described below.
  • Rough rolling can be performed using, for example, the rough rolling mill 31 shown in FIG. Rough rolling is preferably carried out so that the temperature on the delivery side of the roughing mill 31 shown in FIG. 1, specifically the temperature of the steel sheet on the delivery side of the final stand 311 of the roughing mill, is 1000° C. or more and 1200° C. or less. .
  • the delivery-side temperature of the roughing mill By setting the delivery-side temperature of the roughing mill to 1200°C or less, coarsening of the microstructure of the steel sheet can be suppressed. As a result, it is possible to prevent suppression of ferrite/pearlite transformation and cause edge hardening.
  • the delivery-side temperature of the roughing mill By setting the delivery-side temperature of the roughing mill to 1000° C. or more, it is possible to prevent the rolling load from becoming excessively large and making hot rolling difficult.
  • the temperature at the delivery side of the roughing mill can be measured by the method described later in Examples.
  • the radiation thermometer may be placed at a position 0.1 m to 20 m from the final stand of the roughing mill.
  • the time from heating furnace extraction to completion of rough rolling is preferably 240 seconds or less.
  • time from heating furnace extraction to completion of rough rolling is preferably 240 seconds or less.
  • Finish rolling can be performed, for example, using the finish rolling mill 32 shown in FIG. Finish rolling is performed so that the delivery side temperature of the finishing rolling mill 32 shown in FIG. 1, specifically, the temperature of the steel sheet measured at the delivery side of the final stand 321 of the finishing rolling mill is 800° C. or more and 940° C. or less. .
  • the worked structure formed by hot rolling recovers, recrystallizes, and/or grains grow.
  • ferrite-pearlite transformation after coiling is suppressed, which causes edge hardening of the steel sheet. Therefore, by setting the delivery side temperature of the finishing mill to 940° C. or less, austenite recovery, recrystallization and/or grain growth can be suppressed, and edge hardening of the steel sheet can be suppressed.
  • the delivery side temperature of the finishing mill By setting the delivery side temperature of the finishing mill to 800° C. or higher, it is possible to prevent the rolling load from increasing and making hot rolling difficult.
  • the exit temperature of the finishing mill is preferably 930°C or lower, more preferably 920°C or lower.
  • the delivery side temperature of the finishing mill is preferably 850° C. or higher, more preferably 870° C. or higher.
  • the delivery side temperature of the finishing mill can be measured by the method described in the examples below.
  • the radiation thermometer may be placed at a position 0.1 m to 10 m from the final stand of the finishing mill.
  • the time from passing the final stand of the rough rolling mill to reaching the first stand of the finishing mill is preferably 50 seconds or less.
  • the time from passing the final stand of the roughing mill to reaching the first stand of the finishing mill is preferably 50 seconds or less.
  • the hot-rolled steel sheet that has left the final stand of the finishing mill is fed onto the runout table 4, for example, as shown in FIG.
  • the speed of the hot-rolled steel sheet on the runout table 4 varies depending on the position of the steel sheet in the longitudinal direction, but is about 300 m/min to 1000 m/min.
  • the worked structure formed by hot rolling will recover, recrystallize and/or grain grow.
  • the ferrite-pearlite transformation after coiling is suppressed, causing edge hardening of the steel sheet. Therefore, by performing such cooling control on the runout table, austenite recovery, recrystallization and/or grain growth can be suppressed, and edge hardening of the steel sheet can be suppressed.
  • the thickness of the hot-rolled steel sheet to be cooled is not particularly limited, and may be about 1.0 mm to 5.0 mm, which is the thickness of hot-rolled steel sheets commonly used in this technical field.
  • the steel sheet means a portion of the hot-rolled steel sheet to be water-cooled.
  • “at least a portion of the steel sheet” may be any of the entire surface of the steel sheet, a specific region of the steel sheet, or a specific portion of the steel sheet. From the viewpoint of ease of cooling control, the "at least part of the steel sheet” is preferably the entire steel sheet.
  • the "at least a portion of the steel sheet” includes the areas near both ends in the width direction of the steel sheet, the areas near the ends in the longitudinal direction, and the areas near the tail ends in the longitudinal direction. It preferably includes one or more regions selected from regions. In other words, the method of manufacturing a steel plate for cold rolling according to the present embodiment can be applied more effectively by making these regions the portions to be water-cooled in the steel plate.
  • cooling at least a portion of the steel sheet within 3.0 seconds after at least a portion of the steel sheet passes the final stand of the finishing mill and is delivered onto the runout table is strictly means: Cooling within 3.0 seconds after the part to be cooled of the steel plate is sent out on the runout table as it is, based on the time when the part to be cooled passes the final stand of the finishing mill for hot rolling (that is, as the 0 second point) be done. Specifically, for example, in FIG. 1, it means that the part to be cooled in the steel plate reaches the cooling equipment 5 and is cooled within 3.0 seconds after passing the final stand 321 of the finishing mill. do.
  • the time until such cooling is started is also referred to as "water cooling start time". Note that the plate speed of the steel plate fluctuates according to its position in the longitudinal direction. Therefore, in this specification, the water cooling start time is defined as the time obtained by the method described later, that is, the time calculated from the minimum value of the plate speed.
  • the water cooling start time is preferably within 2.5 seconds, more preferably within 2.0 seconds, and even more preferably within 1.5 seconds.
  • Insufficient cooling of the steel sheet on the runout table can be avoided by setting the water volume density at the time of cooling to 100 L/min/m 2 or more. Insufficient cooling of the steel sheet causes recovery, recrystallization and/or grain growth of the worked structure formed by hot rolling. As a result, the ferrite-pearlite transformation after coiling is suppressed, and the edge hardening of the steel sheet is caused.
  • the water density during cooling is preferably 200 L/min/m 2 or more, more preferably 250 L/min/m 2 or more.
  • the upper limit of the water density is not particularly limited, it is preferably, for example, 3000 L/min/m 2 or less from the viewpoint of ensuring the threadability of the steel sheet.
  • the water density is the water flow rate (L / min) used for cooling in the part to be cooled of the steel plate, as in the method described in the later examples, and the length of the section such as the cooling equipment ( m) and the width (m).
  • the water volume density is calculated when the part of the steel sheet to be cooled is located at the position of 4/5 of the total length of the steel sheet from the tip in the longitudinal direction of the steel sheet.
  • the flow rate of water used for cooling can be controlled by adjusting valves or the like provided in the cooling equipment.
  • the cooling time specifically, the total water cooling time within 3 seconds after passing the final stand of the finishing mill (hereinafter also referred to as "total water cooling time within 3 seconds") is 0.1 seconds or more. Insufficient cooling can be avoided. Insufficient cooling of the steel sheet causes recovery, recrystallization and/or grain growth of the worked structure formed by hot rolling. As a result, the ferrite-pearlite transformation after coiling is suppressed, and the edge hardening of the steel sheet is caused.
  • the total water cooling time within 3 seconds is preferably 0.2 seconds or longer, more preferably 0.4 seconds or longer.
  • the upper limit of the total water cooling time within 3 seconds is not particularly limited, and is less than 3 seconds.
  • the total water cooling time within 3 seconds can also vary according to the position in the longitudinal direction of the steel sheet, similar to the water cooling start time described above. Therefore, in this specification, the total water cooling time of 3 seconds or less is defined as the time obtained by the method described later in Examples, that is, the time calculated from the maximum value of the plate speed.
  • the temperature measured at a position 1/4 to 3/4 from the final stand of the finishing mill is preferably 650 ° C. or higher, It is more preferably 700° C. or higher, still more preferably 750° C. or higher.
  • intermediate temperature is temperatures measured in the same manner as shown in the examples below. Specifically, when the total length of the runout table is 1, the intermediate temperature is measured by a radiation thermometer installed at a position 1/4 to 3/4 from the final stand of the finishing mill. is the temperature of
  • any known method may be applied for such cooling, and is not particularly limited.
  • water cooling can be applied by top laminar equipment, bottom spray equipment, or the like.
  • the cooled hot-rolled steel sheet is coiled at a coiling temperature of 550° C. or higher.
  • the coiling temperature By setting the coiling temperature to 550°C or higher, it is possible to secure a sufficient time for holding the steel sheet in the temperature range where ferrite/pearlite transformation proceeds after coiling. As a result, edge hardening of the steel sheet can be suppressed.
  • the winding temperature is preferably 600°C or higher, more preferably 630°C or higher. Also, the winding temperature is preferably 750° C. or lower, more preferably 700° C. or lower.
  • the coiling temperature can be measured by the method described in Examples below. When the total length of the runout table is 1, the radiation thermometer is arranged at a position 1/5 from the winder side.
  • the coiled hot-rolled steel sheet after winding may be naturally cooled to room temperature.
  • the coil-shaped steel sheet for cold rolling according to the present embodiment can be obtained through the steps described above and optionally included steps.
  • the steel sheet for cold rolling according to the present embodiment thus obtained can suppress edge cracking of the steel sheet during subsequent cold rolling. In that case, no additional equipment and running costs for high temperature heating are required.
  • the method of manufacturing a steel sheet for cold rolling according to the present embodiment it is possible to solve the problem of a decrease in yield due to the removal of portions that are likely to cause edge cracks during subsequent cold rolling.
  • the method for manufacturing a cold-rolled steel plate in this embodiment further includes cold-rolling the steel plate manufactured by the method in the above-described embodiment.
  • An example of the method for manufacturing the cold-rolled steel sheet according to the present embodiment will be described below.
  • the steel sheet for cold rolling manufactured by the method in the above embodiment may be pickled.
  • the pickling method is not particularly limited, and any known method may be applied.
  • the scale may be removed by immersion in hydrochloric acid or the like.
  • the cold rolling method is not particularly limited, and any known method may be applied.
  • cold rolling can be carried out at a rolling reduction of 30% to 80% to obtain a desired plate thickness.
  • the plate thickness of the cold-rolled steel plate is not particularly limited.
  • a cold-rolled steel sheet used for manufacturing a high-strength cold-rolled steel sheet having a tensile strength (TS) of 980 MPa or more by going through the above-described steps and optionally included steps in the method for manufacturing a cold-rolled steel plate. can be obtained.
  • a high-strength cold-rolled steel sheet having a tensile strength (TS) of 980 MPa or more can be suitably produced by annealing the cold-rolled steel sheet by any method.
  • the chemical composition is: C: 0.15% by mass or more and 0.25% by mass or less, Si: 0.8% by mass or more and 3.0% by mass or less, Mn: 1.8% by mass or more and 3.0% by mass or less, Ni, Cu, Cr, Mo: 1.0% by mass or less (including 0% by mass), Ti, Nb, V: 1.0 mass% or less (including 0 mass%), and B: 0.01% or less (including 0 mass%)
  • the slab is P: 0.1% by mass or less (including 0% by mass), S: 0.01% by mass or less (including 0% by mass), Al: 0.10% by mass or less (including 0% by mass), and N: 0.01% by mass or less (including 0% by mass) is preferably further contained.
  • the method for manufacturing a cold-rolled steel sheet according to the second aspect of the present invention further comprises cold-rolling the steel sheet manufactured by the method according to the first aspect described above at a rolling reduction of 30% to 80%. include.
  • a steel having a chemical composition (target chemical composition) shown in Table 1 below was melted in a converter, and then a slab was produced by continuous casting.
  • a slab produced by continuous casting was directly charged into a heating furnace with a surface temperature of 200° C. or higher and 900° C. or lower, and heated to a high temperature. After that, the slab was extracted from the heating furnace and hot rolled by rough rolling and finish rolling. The plate thickness was finally set to 2.3 mm.
  • the hot-rolled steel sheet was directly sent onto the runout table, and the steel sheet on the runout table was cooled by an upper surface laminating facility and/or a lower surface spraying facility installed ahead of it. Thereafter, the cooled hot-rolled steel sheet was coiled and cooled to produce a steel sheet for cold rolling.
  • the total length of the runout table extending from the final stand of the finishing mill to the steel sheet winder was 188.3 m.
  • steel sheets for cold rolling were manufactured under various conditions by changing the hot rolling, cooling and coiling conditions.
  • Reheating furnace extraction temperature during hot rolling, roughing mill delivery temperature, time from heating furnace extraction to completion of rough rolling (time between extraction and rough rolling) when manufacturing various steel sheets the time from passing the final stand of the roughing mill to reaching the first stand of the finishing mill (time between roughing and finishing rolling), the delivery side temperature of the finishing mill, the runout table from the passage of the final stand of the finishing mill Time until the start of water cooling (water cooling start time), total water cooling time within 3 seconds after passing the final stand of the finishing mill (total water cooling time within 3 seconds), water density at the time of cooling, near the middle of the runout table
  • the temperature of the steel sheet (intermediate temperature), the time from passing through the finish rolling mill to the temperature measurement near the middle of the runout table (time between finish rolling and intermediate temperature measurement), and the coiling temperature are shown in Table 2 below. shown in Table 2 below, "-" indicates that the total water cooling time and water volume density within
  • Heating furnace extraction temperature The heating furnace extraction temperature was calculated by heat transfer calculation from the slab temperature at the time of charging into the heating furnace, the atmospheric temperature in the heating furnace, and the residence time in the heating furnace.
  • Temperature at the delivery side of the roughing mill The temperature at the central portion in the width direction of the coil was measured with a radiation thermometer installed at the delivery side of the roughing mill. A thermometer was placed 16.6 m from the final stand of the roughing mill.
  • Time between extraction and rough rolling The time between extraction and rough rolling was defined as the time from heating furnace extraction to completion of rough rolling at the tail end of the steel sheet in the longitudinal direction.
  • ⁇ Time between rough rolling and finish rolling The time from the end of rough rolling of the tail end in the longitudinal direction of the steel plate to the start of finish rolling of the front end of the steel plate in the longitudinal direction is defined as rough rolling time - finish rolling. It was the time in between.
  • - Temperature at the delivery side of the finishing rolling mill The temperature at the central portion in the width direction of the coil was measured with a radiation thermometer installed at the delivery side of the finishing rolling mill. A thermometer was installed 5.9 m from the last stand of the finishing mill.
  • ⁇ Water cooling start time The strip speed on the delivery side of the finishing mill fluctuates according to the position of the strip in the longitudinal direction.
  • the water cooling start time was defined based on the plate speed at the tip position in the longitudinal direction where the plate speed is slowest in the longitudinal direction of the steel plate and where grain growth is likely to occur. Specifically, the water cooling start time was obtained by dividing the distance from the final stand of the finishing mill to the position on the runout table where water cooling is performed by the minimum strip speed in the longitudinal direction of the strip. ⁇ Total water cooling time within 3 seconds: The total water cooling time within 3 seconds is the position of 4/5 of the total length of the steel plate from the tip of the steel plate in the longitudinal direction (in other words, 1/5 of the total length of the steel plate from the tail end of the longitudinal direction). position).
  • Water volume density The water volume density was obtained at a position 4/5 of the total length of the steel plate from the tip of the steel plate in the longitudinal direction (in other words, a position of 1/5 of the total length of the steel plate from the tail end of the steel plate in the longitudinal direction).
  • the water flow density at this position asked for - Intermediate temperature: The temperature at the center in the width direction of the coil was measured with a radiation thermometer installed near the middle of the runout table. A thermometer was installed at a position 56.1 m from the final stand of the finishing mill. ⁇ Time between finishing rolling and intermediate temperature measurement: After the longitudinal tip of the steel plate reaches the radiation thermometer installed on the delivery side of the finishing mill, the radiation thermometer is installed near the middle of the runout table. was taken as the time between finish rolling and intermediate temperature measurement. - Winding temperature: The temperature at the center in the width direction of the coil was measured with a radiation thermometer installed near the end of the runout table. A thermometer was placed 180.1 m from the last stand of the finishing mill.
  • the present invention example is a test piece in which the finish rolling delivery side temperature is 800°C or higher and 940°C or lower and the water cooling start time is 3.0 seconds or less.
  • Comparative Example 1 is a test piece in which the finish rolling delivery side temperature is higher than 940° C. and the water cooling start time is 3.0 seconds or less.
  • Comparative Example 2 is a test piece in the case where the finish rolling delivery side temperature is 940° C. or less and the water cooling start time is longer than 3.0 seconds.
  • Comparative Example 3 is a test piece in which the finish rolling delivery side temperature is higher than 940° C. and the water cooling start time is longer than 3.0 seconds.
  • FIG. 2 is a schematic diagram showing the position of a steel plate test piece for hardness measurement.
  • the position of the longitudinal tail end is indicated by the arrow X. Specifically, as shown in FIG.
  • the test piece was positioned 30 m from the tail end in the longitudinal direction of the steel plate (indicated by broken line Y) and 1 mm from both ends in the width direction of the steel plate (indicated by arrow Z). cut to include Using the test piece cut in this way, the position of 1 mm from both ends in the width direction of the steel plate at the position of 30 m from the tail end in the longitudinal direction of the steel plate for cold rolling, and the position at 1/4 of the plate thickness The Vickers hardness was measured at The Vickers hardness test was measured with a load of 9.807 N, and the maximum value among the measured values at both ends in the width direction was evaluated. When the Vickers hardness obtained in this way is greater than 290 HV, the manufactured steel sheet for cold rolling is hardened at the edges, and it was evaluated that there is a risk of edge cracking of the steel sheet during cold rolling.
  • the position 30 m from the tail end of the steel plate in the longitudinal direction is closer to the tail end than the position 4/5 of the total length of the steel plate from the tip of the steel plate in the longitudinal direction, which is the position where the water density was obtained in the manufacturing process described above. .
  • the plate speed of the steel plate becomes higher as it approaches the tail end, and generally end hardening is more likely to occur. Therefore, if edge hardening is not observed at a position 30 m from the tail end in the longitudinal direction of the steel plate, edge hardening is naturally not observed at a position 4/5 of the total length of the steel plate from the tip in the longitudinal direction of the steel plate. Conceivable.
  • edge hardening can be suppressed over the entire longitudinal direction of the steel plate from the tip to the tail end by appropriately adjusting the portion to be cooled in the steel plate as necessary.
  • Table 3 below shows the Vickers hardness (HV) measured in the test piece of each steel plate and the evaluation results thereof.
  • the edge crack risk rate was calculated from the number of test pieces in each category in Table 3 above and the results of hardness evaluation based on Vickers hardness. The calculation results are shown in Table 4 below.
  • test pieces of the present invention example had a Vickers hardness of 290 HV or less, so the risk of edge cracking was zero.
  • test pieces of Comparative Examples 1 to 3 had edge cracking risk factors of 0.33, 0.5 or 1.0. From these results, by setting the delivery side temperature of the finishing mill to 940 ° C. or less and the water cooling start time to 3.0 seconds or less, austenite recovery, recrystallization and / or grain growth are suppressed, and the edge of the steel plate It turned out that hardening can be suppressed.
  • the present invention it is possible to provide a method for manufacturing a steel sheet for cold rolling that can suppress edge cracking of the steel sheet during cold rolling.
  • the produced steel sheet for cold rolling can be suitably used for producing high-strength cold-rolled steel sheet having a tensile strength of 980 MPa or more without causing a problem of yield reduction.

Abstract

The present invention can provide a method for producing a steel sheet for cold rolling in an intermediate process of production of a high-tensile cold-rolled steel sheet, said method making it possible to prevent an end portion of the steel sheet from cracking during the subsequent cold rolling. The method for producing a steel sheet for cold rolling comprises: hot-rolling a slab having a specific chemical composition so that the outlet temperature of a finishing rolling mill is 800-940°C; cooling at least a part of a steel sheet, obtained by the hot rolling, at a water volume density of not less than 100 L/minute/m2 for not shorter than 0.1 seconds, within 3.0 seconds after at least said part of the steel sheet has passed through the last stand of the finishing rolling mill and has been sent out on a run-out table; and winding up, at a wind-up temperature of not lower than 550°C, the hot-rolled steel sheet that has been cooled.

Description

冷間圧延用の鋼板の製造方法および冷間圧延鋼板の製造方法Method for manufacturing steel plate for cold rolling and method for manufacturing cold-rolled steel plate
　本発明は、引張強度９８０ＭＰａ以上の高張力冷間圧延鋼板の製造の中間過程における、冷間圧延用の鋼板の製造方法、およびその方法により製造された鋼板を用いる冷間圧延鋼板の製造方法に関する。 The present invention relates to a method for manufacturing a steel plate for cold rolling in the intermediate process of manufacturing a high-strength cold-rolled steel plate having a tensile strength of 980 MPa or more, and a method for manufacturing a cold-rolled steel plate using the steel plate manufactured by the method. .
　熱間圧延した鋼板を冷間圧延すると、板幅方向の端部（以下、「幅方向端部」または「幅方向両端部」とも言う）および圧延方向に対して平行な方向の端部（以下、「長手方向の先端」または「長手方向の尾端」とも言う）に割れが発生することがある。これらの端部割れは、Ｍｎ等の焼入れ性を向上させる元素を多く含む鋼が用いられる高張力冷間圧延鋼板の製造の際に生じやすい。このように生じた端部割れは、当該冷間圧延時、さらには、焼鈍工程、めっき工程等のその後の工程の際において、この端部割れを起点とした鋼板の破断の原因となり得る。そこで、このような端部割れを原因とするリスクを低減するために、熱間圧延した鋼板における端部割れが生じやすい部分が除去される。しかしながら、その結果、歩留が低下することが問題となっている。 When a hot-rolled steel plate is cold-rolled, the edges in the width direction (hereinafter also referred to as “width direction edges” or “width direction edges”) and the edges in the direction parallel to the rolling direction (hereinafter referred to as “width direction edges”) , also called “longitudinal tips” or “longitudinal tails”). These edge cracks are likely to occur during the production of high-strength cold-rolled steel sheets using steel containing a large amount of elements such as Mn that improve hardenability. The edge cracks that occur in this way can cause breakage of the steel sheet starting from the edge cracks during the cold rolling, and further during subsequent processes such as the annealing process and the plating process. Therefore, in order to reduce the risk caused by such edge cracks, portions of hot-rolled steel sheets that are prone to edge cracks are removed. However, as a result, there is a problem that the yield is lowered.
　一方、巻取り後の熱間圧延鋼板の冷却過程では、コイル状の鋼板の幅方向端部の冷却速度が、鋼板の板幅方向の中央部（以下、「幅方向中央部」とも言う）と比較して、速くなっている。そのため、Ｍｎ等の焼入れ性を向上させる元素を多く含む鋼が用いられている熱間圧延鋼板では、鋼板の幅方向両端部のフェライト・パーライト変態が十分に進行せず、当該鋼板の幅方向両端部はマルテンサイトを比較的多く含む硬質組織となる。鋼板の長手方向の先端および長手方向の尾端についても同様である。このような理由のため、高張力冷間圧延鋼板の製造の際における冷間圧延時等において、鋼板の端部割れが発生し易くなっていると考えられる。 On the other hand, in the cooling process of the hot-rolled steel sheet after coiling, the cooling rate of the width direction end portions of the coiled steel sheet is the same as the width direction center portion of the steel plate (hereinafter also referred to as “width direction center portion”). comparatively faster. Therefore, in a hot-rolled steel sheet in which a steel containing a large amount of elements such as Mn that improve hardenability is used, the ferrite-pearlite transformation at both ends in the width direction of the steel sheet does not sufficiently progress, and both ends in the width direction of the steel sheet The part becomes a hard structure containing a relatively large amount of martensite. The same applies to the longitudinal tip and longitudinal tail of the steel plate. For this reason, it is believed that edge cracks are likely to occur in steel sheets during cold rolling or the like in the manufacture of high-strength cold-rolled steel sheets.
　上述した鋼板の端部割れを抑制する方法として、例えば、特許文献１には、コイル状に巻き取られて冷却された帯状の熱間圧延鋼板を冷間圧延する方法であって、上記熱間圧延鋼板をコイルから繰り出す繰出工程と、上記繰り出された熱間圧延鋼板の幅方向両端部を熱間圧延鋼板材料のＡ１点以下４００℃以上の温度に加熱する加熱工程と、上記加熱工程後の熱間圧延鋼板を酸によって洗浄する酸洗工程と、上記酸洗工程後の熱間圧延鋼板を冷間圧延する冷間圧延工程とを備える冷間圧延方法が記載されている。 As a method for suppressing edge cracks in the steel sheet described above, for example, Patent Document 1 discloses a method for cold rolling a strip-shaped hot-rolled steel sheet that has been wound into a coil and cooled. A feeding step of feeding a rolled steel plate from a coil, a heating step of heating both ends in the width direction of the fed hot-rolled steel plate to a temperature of 400 ° C. or higher below the A1 point of the hot-rolled steel plate material, and after the heating step. A cold rolling method is described that includes a pickling step of washing a hot-rolled steel sheet with an acid and a cold-rolling step of cold-rolling the hot-rolled steel sheet after the pickling step.
特開２０１９－１４１８８８号公報JP 2019-141888 A
　本発明は、高張力冷間圧延鋼板の製造の中間過程における鋼板の製造方法であって、後の冷間圧延時における鋼板の端部割れを抑制することができる冷間圧延用の鋼板の製造方法を提供することを目的とする。 The present invention is a method for manufacturing a steel plate in the intermediate process of manufacturing a high-strength cold-rolled steel plate, and is a method for manufacturing a steel plate for cold rolling that can suppress edge cracks of the steel plate during cold rolling later. The purpose is to provide a method.
　本発明者らは、上記課題を解決すべく鋭意検討を行った結果、本発明に到達した。 The present inventors arrived at the present invention as a result of diligent studies aimed at solving the above problems.
　すなわち、本発明の第一の局面に係る冷間圧延用の鋼板の製造方法は、化学組成において、
　Ｃ：０．１５質量％以上、０．２５質量％以下、
　Ｓｉ：０．８質量％以上、３．０質量％以下、
　Ｍｎ：１．８質量％以上、３．０質量％以下、
　Ｎｉ、Ｃｕ、Ｃｒ、Ｍｏ：１．０質量％以下（０質量％を含む）、
　Ｔｉ、Ｎｂ、Ｖ：１．０質量％以下（０質量％を含む）、および
　Ｂ：０．０１％以下（０質量％を含む）
を含有するスラブを、仕上げ圧延機の出側温度が８００℃以上９４０℃以下となるように熱間圧延することと、
　前記熱間圧延後の鋼板の少なくとも一部分が前記仕上げ圧延機の最終スタンドを通過してランナウトテーブル上に送り出されてから３．０秒以内に、前記鋼板の少なくとも一部分を１００Ｌ／分／ｍ２以上の水量密度で０．１秒間以上冷却することと、
　５５０℃以上の巻取り温度において前記冷却後の熱延鋼板を巻取ることと、を含む。 That is, in the method for manufacturing a steel sheet for cold rolling according to the first aspect of the present invention, the chemical composition is:
C: 0.15% by mass or more and 0.25% by mass or less,
Si: 0.8% by mass or more and 3.0% by mass or less,
Mn: 1.8% by mass or more and 3.0% by mass or less,
Ni, Cu, Cr, Mo: 1.0% by mass or less (including 0% by mass),
Ti, Nb, V: 1.0 mass% or less (including 0 mass%), and B: 0.01% or less (including 0 mass%)
Hot rolling the slab containing
Within 3.0 seconds after at least part of the steel sheet after hot rolling passes the final stand of the finishing mill and is sent out onto the runout table, at least part of the steel sheet is reduced to 100 L / min / m 2 or more cooling for 0.1 seconds or more at a water density of
and coiling the cooled hot-rolled steel sheet at a coiling temperature of 550° C. or higher.
　本発明の第二の局面に係る冷間圧延鋼板の製造方法は、前述の第一の局面に係る方法で製造された鋼板を、３０％～８０％の圧下率で冷間圧延することをさらに含む。 The method for manufacturing a cold-rolled steel sheet according to the second aspect of the present invention further comprises cold-rolling the steel sheet manufactured by the method according to the first aspect described above at a rolling reduction of 30% to 80%. include.
図１は、本実施形態における冷間圧延用の鋼板の製造方法の一例を示す概略図である。FIG. 1 is a schematic diagram showing an example of a method for manufacturing a steel sheet for cold rolling according to the present embodiment. 図２は、本実施例における硬度測定のための鋼板の試験片の位置を示す概略図である。FIG. 2 is a schematic diagram showing the positions of test pieces of steel plates for hardness measurement in this example.
　上述したように、特許文献１に記載の方法では、加熱することによって、鋼板の幅方向両端部のミクロ組織におけるマルテンサイトが焼戻しマルテンサイトに変性する。その結果、鋼板の幅方向両端部が適度に軟質化することによって、鋼板の端部割れが抑制される。 As described above, in the method described in Patent Document 1, the martensite in the microstructure at both ends in the width direction of the steel sheet is transformed into tempered martensite by heating. As a result, both ends of the steel sheet in the width direction are moderately softened, thereby suppressing edge cracks of the steel sheet.
　しかしながら、鋼板をＡ１点以下４００℃以上の温度に加熱するためには、高温での加熱を可能にする装置および当該装置の設置にかかるコストが必要となる。さらに、冷間圧延鋼板の生産ラインに必要となる電力も大きくなるため、それによるコストもかかる。従って、そのような追加の高温加熱工程による設備コストおよびランニングコストを必要としない、冷間圧延時の端部割れを抑制することができる新規な手法が求められる。 However, in order to heat the steel plate to a temperature of 400°C or higher, which is below the A1 point, a device that enables heating at a high temperature and the installation cost of the device are required. In addition, the production line for cold-rolled steel sheets requires a large amount of electric power, resulting in high costs. Therefore, there is a demand for a novel technique capable of suppressing edge cracks during cold rolling without the need for additional equipment and running costs due to the high-temperature heating step.
　そこで、本発明者らは、冷間圧延時における鋼板の端部割れを抑制することができる新たな冷間圧延用の鋼板の製造方法について、様々な研究を重ねた。そして、特に、熱間圧延における仕上げ圧延機の出側温度および仕上げ圧延機の最終スタンドを通過した後における水冷制御工程に着目し、本発明を完成した。 Therefore, the present inventors conducted various studies on a new method of manufacturing a steel sheet for cold rolling that can suppress edge cracking of the steel sheet during cold rolling. In particular, the present invention has been completed by paying attention to the temperature at the delivery side of the finishing mill in hot rolling and the water cooling control process after passing through the final stand of the finishing mill.
　具体的には、本実施形態に係る冷間圧延用の鋼板の製造方法は、所定の化学組成を満たすスラブを用いて仕上げ圧延機の出側温度が所定の温度範囲となるように熱間圧延を行うこと、次いで、仕上げ圧延機の最終スタンドを通過した後に鋼板を所定の条件下で水冷すること、その後、鋼板を所定の温度以上で巻取ることを含む。このような方法によると、熱間圧延鋼板の幅方向両端部、先端または尾端におけるフェライト・パーライト変態を促進することができ、これらの端部を適度に軟質化することができる。その結果、製造された鋼板は、後の冷間圧延時における端部割れを抑制することができる。製造された鋼板に、続けて冷間圧延、任意での熱処理等を施すことによって、高張力冷間圧延鋼板、特に９８０ＭＰａ以上の引張強度（ＴＳ：Ｔｅｎｓｉｌｅ　Ｓｔｒｅｎｇｔｈ）の高張力冷間圧延鋼板が得られる。 Specifically, in the method for manufacturing a steel sheet for cold rolling according to the present embodiment, hot rolling is performed using a slab that satisfies a predetermined chemical composition so that the delivery side temperature of the finishing mill is within a predetermined temperature range. followed by water cooling the steel sheet under predetermined conditions after passing through the final stand of the finishing mill, and then coiling the steel sheet at or above a predetermined temperature. According to such a method, the ferrite-pearlite transformation can be promoted at both ends in the width direction of the hot-rolled steel sheet, the leading end, or the trailing end, and these ends can be moderately softened. As a result, the manufactured steel sheet can suppress edge cracks during subsequent cold rolling. The manufactured steel sheet is subsequently subjected to cold rolling and optional heat treatment to obtain a high-tensile cold-rolled steel sheet, especially a high-tensile cold-rolled steel sheet with a tensile strength (TS) of 980 MPa or more. be done.
　すなわち、本発明によれば、高張力冷間圧延鋼板の製造の中間過程における鋼板の製造方法であって、後の冷間圧延時における鋼板の端部割れを抑制することができる冷間圧延用の鋼板の製造方法を提供することができる。 That is, according to the present invention, there is provided a method for manufacturing a steel sheet in an intermediate process of manufacturing a high-strength cold-rolled steel sheet, which can suppress edge cracking of the steel sheet during subsequent cold rolling. It is possible to provide a method for manufacturing a steel plate.
　以下、本発明の実施形態について、詳細に説明する。なお、本発明の範囲はここで説明する実施形態に限定されるものではなく、本発明の趣旨を損なわない範囲で種々の変更をすることができる。 Hereinafter, embodiments of the present invention will be described in detail. Note that the scope of the present invention is not limited to the embodiments described here, and various modifications can be made without departing from the gist of the present invention.
　１．冷間圧延用の鋼板の製造方法
　図１に、本実施形態における冷間圧延用の鋼板の製造方法の一例の概略図を示す。図１において各符号は、圧延設備１、加熱炉２、熱間圧延機３、ランナウトテーブル４、冷却設備５、粗圧延機３１、圧延機の最終スタンド３１１、上げ圧延機３２、および仕上げ圧延機の最終スタンド３２１を表している。本実施形態における冷間圧延用の鋼板の製造方法では、例えば、図１に示すように、圧延設備１において、まず、特定の化学組成を含有するスラブが加熱炉２に装入される。その後、加熱炉２から抽出されたスラブは、熱間圧延機３によって仕上げ圧延機３２の出側温度が特定の温度範囲内になるように制御されながら熱延される。次いで、ランナウトテーブル４上に送り出された熱延後の鋼板は、特定の条件下で冷却設備５により水冷される。その後、巻取り温度を特定の温度以上となるように調整しながら、鋼板を巻取る。 1. Method for Manufacturing Steel Plate for Cold Rolling FIG. 1 shows a schematic diagram of an example of a method for manufacturing a steel plate for cold rolling according to the present embodiment. In FIG. 1, each reference numeral denotes a rolling facility 1, a heating furnace 2, a hot rolling mill 3, a runout table 4, a cooling facility 5, a roughing mill 31, a final stand 311 of the rolling mill, a lifting mill 32, and a finishing mill. The final stand 321 of the . In the method of manufacturing a steel sheet for cold rolling according to the present embodiment, for example, as shown in FIG. After that, the slab extracted from the heating furnace 2 is hot-rolled while being controlled by the hot rolling mill 3 so that the delivery side temperature of the finishing mill 32 is within a specific temperature range. Then, the hot-rolled steel sheet sent out onto the runout table 4 is water-cooled by the cooling equipment 5 under specific conditions. After that, the steel sheet is wound while adjusting the winding temperature to a specific temperature or higher.
　以下、これらの工程および任意にて含まれる工程について詳細に説明する。 These steps and optionally included steps are described in detail below.
　（スラブの準備）
　まず、所定の化学組成を満たすスラブを準備する。スラブは既知の任意の方法により準備することができる。スラブの作製方法としては、以下に述べる化学組成を有する鋼を溶製し、その後連続鋳造することによって、スラブを作製する方法が挙げられる。必要に応じて、造塊または連続鋳造により得た鋳造材を分塊圧延することによって、スラブを得てもよい。 (Slab preparation)
First, a slab that satisfies a given chemical composition is prepared. The slab can be prepared by any known method. As a method for producing a slab, there is a method for producing a slab by melting steel having the chemical composition described below and then continuously casting the steel. If necessary, a slab may be obtained by blooming a cast material obtained by ingot casting or continuous casting.
　本実施形態における冷間圧延用の鋼板の製造方法で用いられるスラブは、その化学組成において、Ｃ：０．１５質量％以上、０．２５質量％以下、Ｓｉ：０．８質量％以上、３．０質量％以下、Ｍｎ：２．０質量％以上、３．０質量％以下、Ｎｉ、Ｃｕ、Ｃｒ、Ｍｏ：１．０質量％以下（０質量％を含む）、Ｔｉ、Ｎｂ、Ｖ：１．０質量％以下（０質量％を含む）、およびＢ：０．０１％以下（０質量％を含む）を含有する。また、スラブは、Ｐ：０．１質量％以下（０質量％を含む）、Ｓ：０．０１質量％以下（０質量％を含む）、Ａｌ：０．１０質量％以下（０質量％を含む）、およびＮ：０．０１質量％以下（０質量％を含む）をさらに含有することが好ましい。 The slab used in the method for manufacturing a steel sheet for cold rolling in the present embodiment has a chemical composition of C: 0.15% by mass or more and 0.25% by mass or less, Si: 0.8% by mass or more, 3 .0% by mass or less, Mn: 2.0% by mass or more and 3.0% by mass or less, Ni, Cu, Cr, Mo: 1.0% by mass or less (including 0% by mass), Ti, Nb, V: 1.0% by mass or less (including 0% by mass), and B: 0.01% or less (including 0% by mass). In addition, the slab has P: 0.1% by mass or less (including 0% by mass), S: 0.01% by mass or less (including 0% by mass), Al: 0.10% by mass or less (0% by mass including), and N: 0.01% by mass or less (including 0% by mass).
　以下、スラブの化学組成をより詳細に説明する。 Below, the chemical composition of the slab will be explained in more detail.
　［Ｃ：０．１５質量％以上０．２５質量％以下］
　Ｃは、鋼板の強度を向上させるために重要な元素である。Ｃ含有量を０．１５質量％以上にすることによって、強度向上作用を発揮させることができ、最終的に、９８０ＭＰａ以上の高張力冷間圧延鋼板を得ることができる。Ｃ含有量を０．２５質量％以下とすることによって、焼入れ性が向上して、フェライト・パーライト変態の促進が不十分となることを防ぐことができる。さらに、Ｃ含有量が過剰になることによる鋼板の溶接性の低下を抑制することができる。Ｃ含有量は、好ましくは０．１６質量％以上、より好ましくは０．１７質量％以上、さらに好ましくは０．１８質量％以上である。また、Ｃ含有量は、好ましくは０．２３質量％以下、より好ましくは０．２１質量％以下、さらに好ましくは０．１９質量％以下である。 [C: 0.15% by mass or more and 0.25% by mass or less]
C is an important element for improving the strength of the steel sheet. By setting the C content to 0.15% by mass or more, the effect of improving the strength can be exhibited, and finally a high-strength cold-rolled steel sheet of 980 MPa or more can be obtained. By setting the C content to 0.25% by mass or less, the hardenability is improved, and insufficient promotion of ferrite-pearlite transformation can be prevented. Furthermore, deterioration of the weldability of the steel sheet due to an excessive C content can be suppressed. The C content is preferably 0.16% by mass or more, more preferably 0.17% by mass or more, and still more preferably 0.18% by mass or more. Also, the C content is preferably 0.23% by mass or less, more preferably 0.21% by mass or less, and even more preferably 0.19% by mass or less.
　［Ｓｉ：０．８質量％以上３．０質量％以下］
　Ｓｉは、固溶強化元素として鋼板の強度上昇に寄与する元素である。Ｓｉ含有量を０．８質量％以上にすることによって、強度向上作用を発揮させることができ、最終的に、９８０ＭＰａ以上の高張力冷間圧延鋼板を得ることができる。Ｓｉ含有量を３．０質量％以下にすることによって、Ｓｉ量が過剰になることによる鋼板の溶接性の著しい低下を抑制することができる。Ｓｉ含有量は、好ましくは１．０質量％以上、より好ましくは１．５質量％以上、さらに好ましくは１．８質量％以上である。また、Ｓｉ含有量は、好ましくは２．５質量％以下、より好ましくは２．１質量％以下、さらに好ましくは１．９質量％以下である。 [Si: 0.8% by mass or more and 3.0% by mass or less]
Si is an element that contributes to increasing the strength of a steel sheet as a solid-solution strengthening element. By setting the Si content to 0.8% by mass or more, the effect of improving the strength can be exhibited, and finally, a high-strength cold-rolled steel sheet of 980 MPa or more can be obtained. By setting the Si content to 3.0% by mass or less, it is possible to suppress a significant decrease in the weldability of the steel sheet due to an excessive Si content. The Si content is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and still more preferably 1.8% by mass or more. Also, the Si content is preferably 2.5% by mass or less, more preferably 2.1% by mass or less, and even more preferably 1.9% by mass or less.
　［Ｍｎ：１．８質量％以上３．０質量％以下］
　Ｍｎは、固溶強化元素として鋼板の強度上昇に寄与する元素であり、かつ、焼入れ性を高めて鋼板の強度を向上させるために有効な元素でもある。Ｍｎ含有量を１．８質量％以上にすることによって、強度向上作用を発揮させることができ、最終的に、９８０ＭＰａ以上の高張力冷間圧延鋼板を得ることができる。Ｍｎ含有量を３．０質量％以下にすることによって、焼入れ性が向上して、フェライト・パーライト変態の促進が不十分となることを防ぐことができる。Ｍｎ含有量は、好ましくは２．０質量％以上、より好ましくは２．３質量％以上、さらに好ましくは２．５質量％以上である。また、Ｍｎ含有量は、好ましくは２．９質量％以下、より好ましくは２．８質量％以下、さらに好ましくは２．７質量％以下である。 [Mn: 1.8% by mass or more and 3.0% by mass or less]
Mn is an element that contributes to an increase in the strength of a steel sheet as a solid-solution strengthening element, and is also an element that is effective in improving hardenability and strength of the steel sheet. By setting the Mn content to 1.8% by mass or more, the effect of improving the strength can be exhibited, and finally, a high-strength cold-rolled steel sheet of 980 MPa or more can be obtained. By setting the Mn content to 3.0% by mass or less, the hardenability is improved, and it is possible to prevent insufficient promotion of ferrite-pearlite transformation. The Mn content is preferably 2.0% by mass or more, more preferably 2.3% by mass or more, and still more preferably 2.5% by mass or more. Also, the Mn content is preferably 2.9% by mass or less, more preferably 2.8% by mass or less, and even more preferably 2.7% by mass or less.
　［Ｎｉ、Ｃｕ、Ｃｒ、Ｍｏ：１．０質量％以下（０質量％を含む）］
　Ｎｉ、Ｃｕ、ＣｒまたはＭｏは、固溶強化元素として鋼板の強度上昇に寄与する元素である。また、これらの元素は、焼入れ性を高めて鋼板の強度を向上させるために有効な元素でもある。そのため、これらの元素から選択される１つ以上の元素が、スラブの化学組成に含まれていてもよい。強度向上作用を有効に発揮させるためには、Ｎｉ、Ｃｕ、ＣｒおよびＭｏから選択される１つ以上の各々の元素の含有量は、０．０５質量％以上であることが好ましい。また、Ｎｉ、Ｃｕ、ＣｒおよびＭｏから選択される１つ以上の各々の元素の含有量は、焼入れ性が向上して、フェライト・パーライト変態の促進が不十分となることを防ぐために、１．０質量％以下（０質量％を含む）である。Ｎｉ、Ｃｕ、ＣｒおよびＭｏから選択される１つ以上の各々の元素の含有量は、より好ましくは０．１質量％以上である。また、Ｎｉ、Ｃｕ、ＣｒおよびＭｏから選択される１つ以上の各々の元素の含有量は、好ましくは０．５質量％以下である。 [Ni, Cu, Cr, Mo: 1.0% by mass or less (including 0% by mass)]
Ni, Cu, Cr, or Mo is an element that contributes to increasing the strength of the steel sheet as a solid-solution strengthening element. These elements are also effective elements for enhancing the hardenability and strength of the steel sheet. Therefore, one or more elements selected from these elements may be included in the chemical composition of the slab. In order to effectively exhibit the strength improving action, the content of each of the one or more elements selected from Ni, Cu, Cr and Mo is preferably 0.05% by mass or more. In addition, the content of each of one or more elements selected from Ni, Cu, Cr, and Mo is 1. It is 0% by mass or less (including 0% by mass). The content of each of the one or more elements selected from Ni, Cu, Cr and Mo is more preferably 0.1% by mass or more. Also, the content of each of the one or more elements selected from Ni, Cu, Cr and Mo is preferably 0.5% by mass or less.
　［Ｔｉ、Ｎｂ、Ｖ：１．０質量％以下（０質量％を含む）］
　Ｔｉ、ＮｂまたはＶは、析出強化元素として鋼板の強度上昇に寄与する元素である。そのため、これらの元素から選択される１つ以上の元素が、スラブの化学組成に含まれていてもよい。析出強化作用を有効に発揮させるためには、Ｔｉ、ＮｂおよびＶから選択される１つ以上の各々の元素の含有量は、０．０１質量％以上であることが好ましい。また、Ｔｉ、ＮｂおよびＶから選択される１つ以上の各々の元素の含有量は、前述の強度上昇の効果が飽和し、費用が無駄になることを避けるために、１．０質量％以下である。Ｔｉ、ＮｂおよびＶから選択される１つ以上の各々の元素の含有量は、好ましくは０．０２質量％以上である。また、Ｔｉ、ＮｂおよびＶから選択される１つ以上の各々の元素の含有量は、より好ましくは０．５質量％以下である。 [Ti, Nb, V: 1.0% by mass or less (including 0% by mass)]
Ti, Nb, or V is an element that contributes to an increase in the strength of a steel sheet as a precipitation strengthening element. Therefore, one or more elements selected from these elements may be included in the chemical composition of the slab. In order to effectively exhibit the precipitation strengthening action, the content of each of the one or more elements selected from Ti, Nb and V is preferably 0.01% by mass or more. In addition, the content of each of one or more elements selected from Ti, Nb and V is 1.0% by mass or less in order to avoid the effect of increasing the strength described above being saturated and the cost being wasted. is. The content of each of the one or more elements selected from Ti, Nb and V is preferably 0.02% by mass or more. Also, the content of each of the one or more elements selected from Ti, Nb and V is more preferably 0.5% by mass or less.
　［Ｂ：０．０１質量％以下（０質量％以上）］
　Ｂは、焼入れ性を高めて鋼板の強度を向上させるために有効な元素である。そのため、Ｂは、スラブの化学組成に含まれていてもよい。焼入れ性を有効に発揮させるためには、Ｂ含有量は、０．０００１質量％以上であることが好ましい。また、Ｂ含有量は、焼入れ性が向上して、フェライト・パーライト変態の促進が不十分となることを防ぐために、０．０１質量％以下であり、好ましくは０．００５質量％以下である。 [B: 0.01% by mass or less (0% by mass or more)]
B is an effective element for enhancing hardenability and strength of the steel sheet. Therefore, B may be included in the chemical composition of the slab. In order to effectively exhibit hardenability, the B content is preferably 0.0001% by mass or more. The B content is 0.01% by mass or less, preferably 0.005% by mass or less, in order to improve hardenability and prevent insufficient promotion of ferrite-pearlite transformation.
　［Ｐ：好ましくは０．１質量％以下（０質量％を含む）］
　Ｐは、不純物元素として不可避的に存在する元素である。Ｐは、固溶強化により強度の上昇に寄与するが、旧オーステナイト粒界に偏析し、粒界を脆化させることで端部割れの原因となる。そのため、Ｐ含有量を、０．１質量％以下に抑制することが好ましく、０．０５質量％以下に抑制することがより好ましい。 [P: preferably 0.1% by mass or less (including 0% by mass)]
P is an element that inevitably exists as an impurity element. P contributes to an increase in strength through solid-solution strengthening, but segregates at prior austenite grain boundaries and embrittles the grain boundaries, thereby causing edge cracks. Therefore, the P content is preferably suppressed to 0.1% by mass or less, and more preferably suppressed to 0.05% by mass or less.
　［Ｓ：好ましくは０．０１質量％以下（０質量％を含む）］
　Ｓは、不純物元素として不可避的に存在する元素である。Ｓは、ＭｎＳ介在物を形成する。このＭｎＳ介在物は、亀裂の起点となることで端部割れの原因となる。そのため、Ｓ含有量を、０．０１質量％以下に抑制することが好ましく、０．００５質量％以下に抑制することがより好ましい。 [S: preferably 0.01% by mass or less (including 0% by mass)]
S is an element that inevitably exists as an impurity element. S forms MnS inclusions. These MnS inclusions cause edge cracks by becoming starting points for cracks. Therefore, the S content is preferably suppressed to 0.01% by mass or less, and more preferably suppressed to 0.005% by mass or less.
　［Ａｌ（Ｓ－Ａｌ）：好ましくは０．１０質量％以下（０質量％を含む）］
　Ａｌは、脱酸材として添加される。脱酸材としての作用を有効に発揮させるためには、Ａｌ（Ｓ－Ａｌ）含有量は、０．００１質量％以上であることが好ましい。また、Ａｌは、鋼の清浄度を悪化させるおそれがある。そのため、Ａｌ（Ｓ－Ａｌ）含有量は、０．１０質量％以下であることが好ましく、０．０５質量％以下であることがより好ましい。 [Al (S-Al): preferably 0.10% by mass or less (including 0% by mass)]
Al is added as a deoxidizer. The Al (S—Al) content is preferably 0.001% by mass or more in order to effectively exhibit the action as a deoxidizer. Also, Al may deteriorate the cleanliness of steel. Therefore, the Al (S—Al) content is preferably 0.10% by mass or less, more preferably 0.05% by mass or less.
　［Ｎ：好ましくは０．０１質量％以下（０質量％を含む）］
　Ｎは、不純物元素として不可避的に存在する元素である。Ｎは、粗大窒化物を形成する。この粗大窒化物は、亀裂の起点となることで端部割れの原因となる。そのため、Ｎ含有量を、０．０１質量％以下に抑制することが好ましく、０．００５質量％以下に抑制することがより好ましい。 [N: preferably 0.01% by mass or less (including 0% by mass)]
N is an element that inevitably exists as an impurity element. N forms coarse nitrides. This coarse nitride becomes a starting point of cracks and causes edge cracks. Therefore, the N content is preferably suppressed to 0.01% by mass or less, and more preferably suppressed to 0.005% by mass or less.
　また、本実施形態におけるスラブの化学組成は、上記成分のほか、フェライト・パーライト変態の促進、必要とされる強度、十分な加工性等を阻害しない範囲で、他の周知の任意成分をさらに含有することもできる。他の周知の任意成分としては、例えば、Ｚｒ、Ｈｆ、Ｃａ、Ｍｇ、ＲＥＭ（希土類元素）等が挙げられる。 In addition to the above components, the chemical composition of the slab in the present embodiment further contains other well-known arbitrary components within a range that does not hinder the promotion of ferrite/pearlite transformation, the required strength, sufficient workability, etc. You can also Other well-known optional components include, for example, Zr, Hf, Ca, Mg, REM (rare earth elements), and the like.
　［残部］
　残部は、Ｆｅおよび不可避不純物である。不可避不純物としては、原料、資材、製造設備等の状況によって持ち込まれる微量元素（例えば、Ａｓ、Ｓｂ、Ｓｎ等）等が挙げられ、これらの微量元素等の混入は許容される。なお、前述したようなＰ、ＳおよびＮは、通常、含有量が少ないほど好ましい。そのため、これらの元素は、不可避不純物ともいえる。しかし、これらの元素は特定の範囲まで含有量を抑えることによって本発明がその効果をより良好に発揮することができるため、上記のように規定している。このため、本明細書において、残部を構成する「不可避不純物」は、その組成範囲が規定されている元素を除いた概念である。 [Remainder]
The balance is Fe and unavoidable impurities. Examples of unavoidable impurities include trace elements (eg, As, Sb, Sn, etc.) brought in depending on the conditions of raw materials, materials, manufacturing equipment, etc., and inclusion of such trace elements is permitted. In general, the smaller the content of P, S and N as described above, the better. Therefore, these elements can be said to be unavoidable impurities. However, the content of these elements is restricted to a specific range so that the effect of the present invention can be exhibited more satisfactorily. For this reason, in this specification, "inevitable impurities" constituting the balance is a concept excluding elements whose composition ranges are defined.
　（スラブの均熱処理）
　その後、一般的な圧延前の工程として、準備したスラブを加熱炉に装入する。 (Slab soaking)
After that, as a general pre-rolling step, the prepared slab is charged into a heating furnace.
　スラブを加熱する際、スラブの加熱炉抽出温度を１１８０℃以上１２８０℃以下とすることが好ましい。スラブの加熱炉抽出温度を１２８０℃以下とすることによって、鋼板のミクロ組織の粗大化を抑制することができる。その結果、フェライト・パーライト変態の抑制を防止し、端部硬化の原因となることを防ぐことができる。スラブの加熱炉抽出温度を１１８０℃以上とすることによって、圧延荷重が過度に大きくなり、熱間圧延が困難となることを防ぐことができる。本明細書において、加熱炉抽出温度は、後の実施例で記す方法により算出される温度とする。 When heating the slab, it is preferable to set the slab extraction temperature in the heating furnace to 1180°C or higher and 1280°C or lower. By setting the heating furnace extraction temperature of the slab to 1280° C. or lower, coarsening of the microstructure of the steel sheet can be suppressed. As a result, it is possible to prevent suppression of ferrite/pearlite transformation and cause edge hardening. By setting the heating furnace extraction temperature of the slab to 1180° C. or higher, it is possible to prevent the rolling load from becoming excessively large and making hot rolling difficult. In this specification, the heating furnace extraction temperature is the temperature calculated by the method described later in Examples.
　（熱間圧延）
　次いで、加熱炉から抽出したスラブを用いて熱間圧延を行い、熱延鋼板を得る。熱間圧延は、仕上げ圧延機の出側温度が８００℃以上９４０℃以下となるように行えば、その他の条件は特に限定されず、本実施形態における効果を損なわない範囲で適宜設定することができる。 (hot rolling)
Then, the slab extracted from the heating furnace is hot-rolled to obtain a hot-rolled steel sheet. Other conditions are not particularly limited as long as the hot rolling is performed so that the delivery side temperature of the finishing mill is 800° C. or higher and 940° C. or lower, and can be appropriately set within a range that does not impair the effects of the present embodiment. can.
　一般的に、熱間圧延は、粗圧延と仕上げ圧延とを含む。以下、各々の圧延について説明する。 Generally, hot rolling includes rough rolling and finish rolling. Each rolling will be described below.
　粗圧延は、例えば、図１に示す粗圧延機３１を用いて行うことができる。粗圧延は、図１に示す粗圧延機３１の出側温度、具体的には粗圧延機の最終スタンド３１１の出側における鋼板の温度が１０００℃以上１２００℃以下となるように行うことが好ましい。 Rough rolling can be performed using, for example, the rough rolling mill 31 shown in FIG. Rough rolling is preferably carried out so that the temperature on the delivery side of the roughing mill 31 shown in FIG. 1, specifically the temperature of the steel sheet on the delivery side of the final stand 311 of the roughing mill, is 1000° C. or more and 1200° C. or less. .
　粗圧延機の出側温度を１２００℃以下にすることによって、鋼板のミクロ組織の粗大化を抑制することができる。その結果、フェライト・パーライト変態の抑制を防止し、端部硬化の原因となることを防ぐことができる。粗圧延機の出側温度を１０００℃以上とすることによって、圧延荷重が過度に大きくなり、熱間圧延が困難となることを防ぐことができる。本明細書において、粗圧延機の出側温度は、後の実施例で記す方法により測定することができる。放射温度計を配置する位置は、粗圧延機の最終スタンドから０．１ｍ～２０ｍの位置であればよい。 By setting the delivery-side temperature of the roughing mill to 1200°C or less, coarsening of the microstructure of the steel sheet can be suppressed. As a result, it is possible to prevent suppression of ferrite/pearlite transformation and cause edge hardening. By setting the delivery-side temperature of the roughing mill to 1000° C. or more, it is possible to prevent the rolling load from becoming excessively large and making hot rolling difficult. In this specification, the temperature at the delivery side of the roughing mill can be measured by the method described later in Examples. The radiation thermometer may be placed at a position 0.1 m to 20 m from the final stand of the roughing mill.
　また、加熱炉抽出を行ってから粗圧延が完了するまでの時間（抽出－粗圧延間の時間）は、２４０秒以下であることが好ましい。加熱炉抽出を行ってから粗圧延が完了するまでの時間を２４０秒以下にすることによって、鋼板のミクロ組織の粗大化を抑制することができる。その結果、フェライト・パーライト変態の抑制を防止し、端部硬化の原因となることを防ぐことができる。本明細書において、抽出－粗圧延間の時間は、後の実施例で記す方法により測定することができる。 In addition, the time from heating furnace extraction to completion of rough rolling (time between extraction and rough rolling) is preferably 240 seconds or less. By setting the time from heating furnace extraction to completion of rough rolling to 240 seconds or less, coarsening of the microstructure of the steel sheet can be suppressed. As a result, it is possible to prevent suppression of ferrite/pearlite transformation and cause edge hardening. In this specification, the time between extraction and rough rolling can be measured by the method described later in Examples.
　仕上げ圧延は、例えば、図１に示す仕上げ圧延機３２を用いて行うことができる。仕上げ圧延は、図１に示す仕上げ圧延機３２の出側温度、具体的には仕上げ圧延機の最終スタンド３２１の出側で測定される鋼板の温度が８００℃以上９４０℃以下となるように行う。 Finish rolling can be performed, for example, using the finish rolling mill 32 shown in FIG. Finish rolling is performed so that the delivery side temperature of the finishing rolling mill 32 shown in FIG. 1, specifically, the temperature of the steel sheet measured at the delivery side of the final stand 321 of the finishing rolling mill is 800° C. or more and 940° C. or less. .
　仕上げ圧延を高温で行うと、熱間圧延で形成された加工組織が回復、再結晶および／または粒成長してしまう。その結果、巻取り後のフェライト・パーライト変態が抑制され、鋼板の端部硬化の原因となる。従って、仕上げ圧延機の出側温度を９４０℃以下にすることによって、オーステナイトの回復、再結晶および／または粒成長を抑制し、鋼板の端部硬化を抑制することができる。仕上げ圧延機の出側温度を８００℃以上にすることによって、圧延荷重が大きくなってしまい、熱間圧延が困難となることを防ぐことができる。 When finish rolling is performed at a high temperature, the worked structure formed by hot rolling recovers, recrystallizes, and/or grains grow. As a result, ferrite-pearlite transformation after coiling is suppressed, which causes edge hardening of the steel sheet. Therefore, by setting the delivery side temperature of the finishing mill to 940° C. or less, austenite recovery, recrystallization and/or grain growth can be suppressed, and edge hardening of the steel sheet can be suppressed. By setting the delivery side temperature of the finishing mill to 800° C. or higher, it is possible to prevent the rolling load from increasing and making hot rolling difficult.
　仕上げ圧延機の出側温度は、好ましくは９３０℃以下、より好ましくは９２０℃以下である。また、仕上げ圧延機の出側温度は、好ましくは８５０℃以上、より好ましくは８７０℃以上である。本明細書において、仕上げ圧延機の出側温度は、後の実施例で記す方法により測定することができる。放射温度計を配置する位置は、仕上げ圧延機の最終スタンドから０．１ｍ～１０ｍの位置であればよい。 The exit temperature of the finishing mill is preferably 930°C or lower, more preferably 920°C or lower. Also, the delivery side temperature of the finishing mill is preferably 850° C. or higher, more preferably 870° C. or higher. In this specification, the delivery side temperature of the finishing mill can be measured by the method described in the examples below. The radiation thermometer may be placed at a position 0.1 m to 10 m from the final stand of the finishing mill.
　また、鋼板の粗圧延機の最終スタンド通過から仕上げ圧延機の最初のスタンド到達までの時間（粗圧延－仕上げ圧延間の時間）は、５０秒以下であることが好ましい。粗圧延機の最終スタンド通過から仕上げ圧延機の最初のスタンド到達までの時間を５０秒以下にすることよって、熱間圧延で形成された加工組織が回復、再結晶および／または粒成長することを抑制することができる。その結果、巻取り後のフェライト・パーライト変態の抑制をより確実に防ぐことができる。本明細書において、粗圧延－仕上げ圧延間の時間は、後の実施例で記す方法により求めることができる。 In addition, the time from passing the final stand of the rough rolling mill to reaching the first stand of the finishing mill (time between rough rolling and finish rolling) of the steel plate is preferably 50 seconds or less. By setting the time from passing the final stand of the roughing mill to reaching the first stand of the finishing mill to 50 seconds or less, the worked structure formed by hot rolling recovers, recrystallizes, and/or grains grow. can be suppressed. As a result, suppression of ferrite/pearlite transformation after winding can be prevented more reliably. In this specification, the time between rough rolling and finish rolling can be determined by the method described in the examples below.
　仕上げ圧延機の最終スタンドを出た熱延後の鋼板は、例えば、図１に示すように、ランナウトテーブル４上に送り出される。この際、熱延後の鋼板のランナウトテーブル４上における板速度は、鋼板の長手方向における位置によって差異を有するが、３００ｍ／分～１０００ｍ／分程度となっている。 The hot-rolled steel sheet that has left the final stand of the finishing mill is fed onto the runout table 4, for example, as shown in FIG. At this time, the speed of the hot-rolled steel sheet on the runout table 4 varies depending on the position of the steel sheet in the longitudinal direction, but is about 300 m/min to 1000 m/min.
　（ランナウトテーブル上における冷却制御）
　次に、熱間圧延後の鋼板の少なくとも一部分が仕上げ圧延機の最終スタンドを通過してランナウトテーブル上に送り出されてから３．０秒以内に、当該鋼板の少なくとも一部分は１００Ｌ／分／ｍ２以上の水量密度で０．１秒間以上冷却される。 (Cooling control on the runout table)
Next, within 3.0 seconds after at least a portion of the hot-rolled steel plate passes the final stand of the finishing mill and is delivered onto the runout table, at least a portion of the steel plate is subjected to 100 L/min/m 2 It is cooled for 0.1 seconds or more with the above water density.
　ランナウトテーブル上での冷却中に鋼板が高温で保持されていると、熱間圧延で形成された加工組織が回復、再結晶および／または粒成長してしまう。その結果、巻取り後のフェライト・パーライト変態が抑制され、鋼板の端部硬化が引き起こされる。そのため、このようなランナウトテーブル上における冷却制御を行うことによって、オーステナイトの回復、再結晶および／または粒成長を抑制し、鋼板の端部硬化を抑制することができる。 If the steel sheet is held at a high temperature during cooling on the runout table, the worked structure formed by hot rolling will recover, recrystallize and/or grain grow. As a result, the ferrite-pearlite transformation after coiling is suppressed, causing edge hardening of the steel sheet. Therefore, by performing such cooling control on the runout table, austenite recovery, recrystallization and/or grain growth can be suppressed, and edge hardening of the steel sheet can be suppressed.
　冷却される熱延後の鋼板の板厚は、特に限定されず、本技術分野で一般的な熱延鋼板の板厚である、１．０ｍｍ～５．０ｍｍ程度であればよい。 The thickness of the hot-rolled steel sheet to be cooled is not particularly limited, and may be about 1.0 mm to 5.0 mm, which is the thickness of hot-rolled steel sheets commonly used in this technical field.
　本明細書において、「鋼板の少なくとも一部分」とは、熱間圧延後の鋼板における水冷対象となる部分を意味する。具体的には、「鋼板の少なくとも一部分」は、鋼板全面、鋼板における特定の領域および鋼板における特定の箇所のいずれであってもよい。冷却制御の容易性の観点からは、「鋼板の少なくとも一部分」は、鋼板全体であることが好ましい。あるいは、鋼板の端部割れが生じ易い領域に重点を置く場合、「鋼板の少なくとも一部分」は、鋼板の幅方向両端部の近傍領域、長手方向の先端の近傍領域および長手方向の尾端の近傍領域から選択される１つ以上の領域を含むことが好ましい。言い換えると、これらの領域を鋼板における水冷対象となる部分とすることによって、本実施形態における冷間圧延用の鋼板の製造方法をより効果的に適用することができる。 In the present specification, "at least a portion of the steel sheet" means a portion of the hot-rolled steel sheet to be water-cooled. Specifically, "at least a portion of the steel sheet" may be any of the entire surface of the steel sheet, a specific region of the steel sheet, or a specific portion of the steel sheet. From the viewpoint of ease of cooling control, the "at least part of the steel sheet" is preferably the entire steel sheet. Alternatively, when emphasizing the areas of the steel sheet where edge cracks are likely to occur, the "at least a portion of the steel sheet" includes the areas near both ends in the width direction of the steel sheet, the areas near the ends in the longitudinal direction, and the areas near the tail ends in the longitudinal direction. It preferably includes one or more regions selected from regions. In other words, the method of manufacturing a steel plate for cold rolling according to the present embodiment can be applied more effectively by making these regions the portions to be water-cooled in the steel plate.
　本明細書において、「鋼板の少なくとも一部分が仕上げ圧延機の最終スタンドを通過してランナウトテーブル上に送り出されてから３．０秒以内に、当該鋼板の少なくとも一部分を冷却する」とは、厳密には、次のことを意味する。鋼板における冷却対象となる部分が、熱間圧延の仕上げ圧延機の最終スタンドを通過した時点を基準として（すなわち０秒地点として）、そのままランナウトテーブル上に送り出されてから３．０秒以内に冷却される。具体的には、例えば、図１において、鋼板における冷却対象となる部分が仕上げ圧延機の最終スタンド３２１を通過した時点から３．０秒以内に冷却設備５に到達して冷却されることを意味する。このような冷却が開始されるまでの時間を、以下、「水冷開始時間」とも言う。なお、鋼板の板速度は、その長手方向の位置に応じて変動する。従って、本明細書では、水冷開始時間は、後の実施例で記す方法により求められる時間、すなわち板速度の最小値から算出される時間として定義される。 In this specification, "cooling at least a portion of the steel sheet within 3.0 seconds after at least a portion of the steel sheet passes the final stand of the finishing mill and is delivered onto the runout table" is strictly means: Cooling within 3.0 seconds after the part to be cooled of the steel plate is sent out on the runout table as it is, based on the time when the part to be cooled passes the final stand of the finishing mill for hot rolling (that is, as the 0 second point) be done. Specifically, for example, in FIG. 1, it means that the part to be cooled in the steel plate reaches the cooling equipment 5 and is cooled within 3.0 seconds after passing the final stand 321 of the finishing mill. do. Hereinafter, the time until such cooling is started is also referred to as "water cooling start time". Note that the plate speed of the steel plate fluctuates according to its position in the longitudinal direction. Therefore, in this specification, the water cooling start time is defined as the time obtained by the method described later, that is, the time calculated from the minimum value of the plate speed.
　水冷開始時間を３．０秒以内にすることによって、ランナウトテーブル上で熱間圧延後の鋼板が高温で長く保持されることを避けることができる。熱間圧延後の鋼板が高温で長く保持されると、熱間圧延で形成された鋼板における加工組織が回復、再結晶および／または粒成長してしまう。その結果、最終的に、巻取り後のフェライト・パーライト変態が抑制され、鋼板の端部硬化が引き起こされる。水冷開始時間は、好ましくは２．５秒以内、より好ましくは２．０秒以内、さらに好ましくは１．５秒以内である。 By setting the water cooling start time within 3.0 seconds, it is possible to avoid the steel sheet after hot rolling from being held at high temperature for a long time on the runout table. If the hot-rolled steel sheet is kept at a high temperature for a long time, the worked structure of the hot-rolled steel sheet is recovered, and recrystallization and/or grain growth occur. As a result, the ferrite-pearlite transformation after coiling is finally suppressed, and edge hardening of the steel sheet is caused. The water cooling start time is preferably within 2.5 seconds, more preferably within 2.0 seconds, and even more preferably within 1.5 seconds.
　冷却の際の水量密度を１００Ｌ／分／ｍ２以上とすることによって、ランナウトテーブル上での鋼板の冷却が不十分となることを避けることができる。鋼板の冷却が不十分となると、熱間圧延で形成された加工組織が回復、再結晶および／または粒成長してしまう。その結果、巻取り後のフェライト・パーライト変態が抑制され、鋼板の端部硬化を引き起こしてしまう。 Insufficient cooling of the steel sheet on the runout table can be avoided by setting the water volume density at the time of cooling to 100 L/min/m 2 or more. Insufficient cooling of the steel sheet causes recovery, recrystallization and/or grain growth of the worked structure formed by hot rolling. As a result, the ferrite-pearlite transformation after coiling is suppressed, and the edge hardening of the steel sheet is caused.
　冷却の際の水量密度は、好ましくは２００Ｌ／分／ｍ２以上、より好ましくは２５０Ｌ／分／ｍ２以上である。なお、水量密度の上限は、特に限定されないが、鋼板の通板性を確保する観点から、例えば３０００Ｌ／分／ｍ２以下であることが好ましい。本明細書では、水量密度は、後の実施例で記す方法と同様に、鋼板の冷却対象となる部分における、冷却に用いる水流量（Ｌ／分）を、冷却設備等の区画の長さ（ｍ）と幅（ｍ）で除することにより求めることができる。なお、後述の実施例では、鋼板の冷却対象となる部分が、鋼板の長手方向の先端から鋼板全長の４／５の位置である場合の水量密度を算出している。また、冷却に用いる水流量は、冷却設備が備えるバルブ等を調整することにより、制御することができる。 The water density during cooling is preferably 200 L/min/m 2 or more, more preferably 250 L/min/m 2 or more. Although the upper limit of the water density is not particularly limited, it is preferably, for example, 3000 L/min/m 2 or less from the viewpoint of ensuring the threadability of the steel sheet. In this specification, the water density is the water flow rate (L / min) used for cooling in the part to be cooled of the steel plate, as in the method described in the later examples, and the length of the section such as the cooling equipment ( m) and the width (m). In the examples described later, the water volume density is calculated when the part of the steel sheet to be cooled is located at the position of 4/5 of the total length of the steel sheet from the tip in the longitudinal direction of the steel sheet. Also, the flow rate of water used for cooling can be controlled by adjusting valves or the like provided in the cooling equipment.
　冷却時間、具体的には仕上げ圧延機の最終スタンド通過から３秒以内における合計の水冷時間（以下、「３秒以内の総水冷時間」とも言う）を０．１秒間以上にすることによって、鋼板の冷却が不十分となることを避けることができる。鋼板の冷却が不十分となると、熱間圧延で形成された加工組織が回復、再結晶および／または粒成長してしまう。その結果、巻取り後のフェライト・パーライト変態が抑制され、鋼板の端部硬化を引き起こしてしまう。 The cooling time, specifically, the total water cooling time within 3 seconds after passing the final stand of the finishing mill (hereinafter also referred to as "total water cooling time within 3 seconds") is 0.1 seconds or more. Insufficient cooling can be avoided. Insufficient cooling of the steel sheet causes recovery, recrystallization and/or grain growth of the worked structure formed by hot rolling. As a result, the ferrite-pearlite transformation after coiling is suppressed, and the edge hardening of the steel sheet is caused.
　３秒以内の総水冷時間は、好ましくは０．２秒間以上、より好ましくは０．４秒間以上である。なお、３秒以内の総水冷時間の上限値は、特に限定されず、３秒未満である。３秒以内の総水冷時間も、前述の水冷開始時間と同様に、鋼板の長手方向の位置に応じて変動し得る。そのため、本明細書において、３秒以内の総水冷時間は、後の実施例で記す方法により求められる時間、すなわち板速度の最大値から算出される時間として定義される。 The total water cooling time within 3 seconds is preferably 0.2 seconds or longer, more preferably 0.4 seconds or longer. The upper limit of the total water cooling time within 3 seconds is not particularly limited, and is less than 3 seconds. The total water cooling time within 3 seconds can also vary according to the position in the longitudinal direction of the steel sheet, similar to the water cooling start time described above. Therefore, in this specification, the total water cooling time of 3 seconds or less is defined as the time obtained by the method described later in Examples, that is, the time calculated from the maximum value of the plate speed.
　また、ランナウトテーブル全長を１とした場合、仕上げ圧延機の最終スタンドから１／４～３／４の位置において測定される温度（以下、「中間温度」とも言う）は、好ましくは６５０℃以上、より好ましくは７００℃以上、さらに好ましくは７５０℃以上である。中間温度を６５０℃以上とすることによって、冷却速度が過度に速くなり、巻取り温度の確保が難しくなることを防ぐことができる。本明細書において、このような中間温度は、後の実施例で示す方法と同じ方法で測定される温度とする。具体的には、中間温度は、ランナウトテーブル全長を１とした場合、仕上げ圧延機の最終スタンドから１／４～３／４の位置において設置した放射温度計によって測定されるコイルの幅方向中央部の温度とする。 Further, when the total length of the runout table is 1, the temperature measured at a position 1/4 to 3/4 from the final stand of the finishing mill (hereinafter also referred to as "intermediate temperature") is preferably 650 ° C. or higher, It is more preferably 700° C. or higher, still more preferably 750° C. or higher. By setting the intermediate temperature to 650° C. or higher, it is possible to prevent the cooling rate from becoming excessively fast and the securing of the winding temperature to become difficult. In this specification, such intermediate temperatures are temperatures measured in the same manner as shown in the examples below. Specifically, when the total length of the runout table is 1, the intermediate temperature is measured by a radiation thermometer installed at a position 1/4 to 3/4 from the final stand of the finishing mill. is the temperature of
　このような冷却は、公知の任意の方法を適用すればよく、特に限定されない。例えば、水冷は、上面ラミナー設備、下面スプレー設備等を適用することができる。 Any known method may be applied for such cooling, and is not particularly limited. For example, water cooling can be applied by top laminar equipment, bottom spray equipment, or the like.
　（巻取り）
　その後、５５０℃以上の巻取り温度において冷却後の熱延鋼板を巻取る。 (Winding)
After that, the cooled hot-rolled steel sheet is coiled at a coiling temperature of 550° C. or higher.
　巻取り温度を５５０℃以上にすることによって、巻取り後にフェライト・パーライト変態が進行する温度領域で鋼板を保持する時間を十分確保することができる。その結果、鋼板の端部硬化を抑制することができる。 By setting the coiling temperature to 550°C or higher, it is possible to secure a sufficient time for holding the steel sheet in the temperature range where ferrite/pearlite transformation proceeds after coiling. As a result, edge hardening of the steel sheet can be suppressed.
　巻取り温度は、好ましくは６００℃以上、より好ましくは６３０℃以上である。また、巻取り温度は、好ましくは７５０℃以下、より好ましくは７００℃以下である。巻取り温度を７５０℃以下にすることによって、熱間圧延で形成された加工組織が回復、再結晶および／または粒成長することを抑制し、巻取り後のフェライト・パーライト変態の抑制を防ぐことができる。本明細書において、巻取り温度は、後の実施例で記す方法により測定することができる。放射温度計を配置する位置は、ランナウトテーブル全長を１とした場合、巻取り機側から１／５の位置とする。 The winding temperature is preferably 600°C or higher, more preferably 630°C or higher. Also, the winding temperature is preferably 750° C. or lower, more preferably 700° C. or lower. By setting the coiling temperature to 750° C. or less, the recovery, recrystallization and/or grain growth of the worked structure formed by hot rolling is suppressed, and the suppression of ferrite/pearlite transformation after coiling is prevented. can be done. In this specification, the coiling temperature can be measured by the method described in Examples below. When the total length of the runout table is 1, the radiation thermometer is arranged at a position 1/5 from the winder side.
　巻取り後のコイル状の熱間圧延鋼板は、常温まで自然冷却してもよい。 The coiled hot-rolled steel sheet after winding may be naturally cooled to room temperature.
　鋼板の製造方法において、上述してきたような工程および任意にて含まれる工程を経ることによって、コイル状の本実施形態における冷間圧延用の鋼板を得ることができる。このように得られた本実施形態における冷間圧延用の鋼板は、後の冷間圧延時における鋼板の端部割れを抑制することができる。その際、追加の高温加熱のための設備コストおよびランニングコストを必要としない。加えて、本実施形態における冷間圧延用の鋼板の製造方法によると、後の冷間圧延時において端部割れが生じ易い部分の除去による歩留の低下の問題を解消することができる。 In the steel sheet manufacturing method, the coil-shaped steel sheet for cold rolling according to the present embodiment can be obtained through the steps described above and optionally included steps. The steel sheet for cold rolling according to the present embodiment thus obtained can suppress edge cracking of the steel sheet during subsequent cold rolling. In that case, no additional equipment and running costs for high temperature heating are required. In addition, according to the method of manufacturing a steel sheet for cold rolling according to the present embodiment, it is possible to solve the problem of a decrease in yield due to the removal of portions that are likely to cause edge cracks during subsequent cold rolling.
　２．冷間圧延鋼板の製造方法
　本実施形態における冷間圧延鋼板の製造方法は、前述の実施形態における方法で製造された鋼板を、冷間圧延することをさらに含む。以下、本実施形態における冷間圧延鋼板の製造方法の一例について説明する。 2. Method for Manufacturing Cold-Rolled Steel Plate The method for manufacturing a cold-rolled steel plate in this embodiment further includes cold-rolling the steel plate manufactured by the method in the above-described embodiment. An example of the method for manufacturing the cold-rolled steel sheet according to the present embodiment will be described below.
　（酸洗）
　冷間圧延の前に、前述の実施形態における方法で製造された冷間圧延用の鋼板を、酸洗してもよい。酸洗方法は特に限定されず、公知の任意の方法を適用すればよい。例えば、塩酸等を用いて浸漬させることにより、スケールを除去すればよい。 (Pickling)
Before cold rolling, the steel sheet for cold rolling manufactured by the method in the above embodiment may be pickled. The pickling method is not particularly limited, and any known method may be applied. For example, the scale may be removed by immersion in hydrochloric acid or the like.
　（冷間圧延）
　冷間圧延の方法は、特に限定されず、公知の任意の方法を適用すればよい。例えば、所望する板厚にするために、３０％～８０％の圧下率で冷間圧延をすることができる。冷間圧延鋼板の板厚は、特に限定されない。 (cold rolling)
The cold rolling method is not particularly limited, and any known method may be applied. For example, cold rolling can be carried out at a rolling reduction of 30% to 80% to obtain a desired plate thickness. The plate thickness of the cold-rolled steel plate is not particularly limited.
　冷間圧延鋼板の製造方法において、上述してきたような工程および任意にて含まれる工程を経ることによって、引張強度（ＴＳ）９８０ＭＰａ以上の高張力冷間圧延鋼板の製造に用いられる冷間圧延鋼板を得ることができる。このように得られた本実施形態における冷間圧延鋼板は、冷間圧延時における端部割れが抑制されているため、端部割れを原因とする鋼板の破断等の後のリスクが低減できる。そのため、任意の方法で冷間圧延鋼板に焼鈍を施すことによって、引張強度（ＴＳ）９８０ＭＰａ以上の高張力冷間圧延鋼板を好適に製造することができる。 A cold-rolled steel sheet used for manufacturing a high-strength cold-rolled steel sheet having a tensile strength (TS) of 980 MPa or more by going through the above-described steps and optionally included steps in the method for manufacturing a cold-rolled steel plate. can be obtained. In the cold-rolled steel sheet according to the present embodiment obtained in this way, edge cracks are suppressed during cold rolling, so the risk of subsequent breakage of the steel sheet due to edge cracks can be reduced. Therefore, a high-strength cold-rolled steel sheet having a tensile strength (TS) of 980 MPa or more can be suitably produced by annealing the cold-rolled steel sheet by any method.
　以上、本発明の概要について説明したが、本発明の実施形態における冷間圧延用の鋼板の製造方法および冷間圧延鋼板の製造方法をまとめると下記の通りである。 The outline of the present invention has been described above, and the method for manufacturing a steel plate for cold rolling and the method for manufacturing a cold-rolled steel plate according to the embodiments of the present invention are summarized below.
　本発明の第一の局面に係る冷間圧延用の鋼板の製造方法は、化学組成において、
　Ｃ：０．１５質量％以上、０．２５質量％以下、
　Ｓｉ：０．８質量％以上、３．０質量％以下、
　Ｍｎ：１．８質量％以上、３．０質量％以下、
　Ｎｉ、Ｃｕ、Ｃｒ、Ｍｏ：１．０質量％以下（０質量％を含む）、
　Ｔｉ、Ｎｂ、Ｖ：１．０質量％以下（０質量％を含む）、および
　Ｂ：０．０１％以下（０質量％を含む）
を含有するスラブを、仕上げ圧延機の出側温度が８００℃以上９４０℃以下となるように熱間圧延することと、
　前記熱間圧延後の鋼板の少なくとも一部分が前記仕上げ圧延機の最終スタンドを通過してランナウトテーブル上に送り出されてから３．０秒以内に、前記鋼板の少なくとも一部分を１００Ｌ／分／ｍ２以上の水量密度で０．１秒間以上冷却することと、
　５５０℃以上の巻取り温度において前記冷却後の熱延鋼板を巻取ることと、を含む。 In the method for manufacturing a steel sheet for cold rolling according to the first aspect of the present invention, the chemical composition is:
C: 0.15% by mass or more and 0.25% by mass or less,
Si: 0.8% by mass or more and 3.0% by mass or less,
Mn: 1.8% by mass or more and 3.0% by mass or less,
Ni, Cu, Cr, Mo: 1.0% by mass or less (including 0% by mass),
Ti, Nb, V: 1.0 mass% or less (including 0 mass%), and B: 0.01% or less (including 0 mass%)
Hot rolling the slab containing
Within 3.0 seconds after at least part of the steel sheet after hot rolling passes the final stand of the finishing mill and is sent out onto the runout table, at least part of the steel sheet is reduced to 100 L / min / m 2 or more cooling for 0.1 seconds or more at a water density of
and coiling the cooled hot-rolled steel sheet at a coiling temperature of 550° C. or higher.
　前述の冷間圧延用の鋼板の製造方法において、前記スラブは、
　Ｐ：０．１質量％以下（０質量％を含む）、
　Ｓ：０．０１質量％以下（０質量％を含む）、
　Ａｌ：０．１０質量％以下（０質量％を含む）、および
　Ｎ：０．０１質量％以下（０質量％を含む）
をさらに含有することが好ましい。 In the method for manufacturing a steel plate for cold rolling described above, the slab is
P: 0.1% by mass or less (including 0% by mass),
S: 0.01% by mass or less (including 0% by mass),
Al: 0.10% by mass or less (including 0% by mass), and N: 0.01% by mass or less (including 0% by mass)
is preferably further contained.
　本発明の第二の局面に係る冷間圧延鋼板の製造方法は、前述の第一の局面に係る方法で製造された鋼板を、３０％～８０％の圧下率で冷間圧延することをさらに含む。 The method for manufacturing a cold-rolled steel sheet according to the second aspect of the present invention further comprises cold-rolling the steel sheet manufactured by the method according to the first aspect described above at a rolling reduction of 30% to 80%. include.
　以下に、実施例により本発明をさらに具体的に説明するが、本発明は実施例により何ら限定されるものではない。 The present invention will be described in more detail below with reference to examples, but the present invention is not limited by the examples.
　本実施例では、本実施形態における方法で実際に冷間圧延用の鋼板を製造し、製造した当該鋼板の端部近傍の試験片の硬度から、後の冷間圧延時における鋼板の端部割れの危険率を算出した。 In this example, a steel plate for cold rolling was actually produced by the method in this embodiment, and from the hardness of the test piece near the end of the produced steel plate, the edge cracks of the steel plate during later cold rolling calculated the risk ratio of
　［冷間圧延用の鋼板の製造］
　後の表１に示す化学組成（狙い化学組成）の鋼を転炉にて溶製した後、連続鋳造によりスラブを製造した。連続鋳造により製造したスラブを表面温度が２００℃以上９００℃以下の状態で直接加熱炉に装入し、高温に加熱した。その後、スラブを加熱炉から抽出し、粗圧延および仕上げ圧延により熱間圧延した。板厚は、最終的に２．３ｍｍとした。熱延後の鋼板をそのままランナウトテーブル上に送り出し、その先に設置された上面ラミナー設備および／または下面スプレー設備によって、ランナウトテーブル上の鋼板を冷却した。その後、冷却した熱間圧延鋼板をコイル状に巻取って冷却し、冷間圧延用の鋼板を製造した。なお、仕上げ圧延機の最終スタンドから鋼板の巻取り機まで続くランナウトテーブルの全長は、１８８．３ｍであった。 [Manufacture of steel sheets for cold rolling]
A steel having a chemical composition (target chemical composition) shown in Table 1 below was melted in a converter, and then a slab was produced by continuous casting. A slab produced by continuous casting was directly charged into a heating furnace with a surface temperature of 200° C. or higher and 900° C. or lower, and heated to a high temperature. After that, the slab was extracted from the heating furnace and hot rolled by rough rolling and finish rolling. The plate thickness was finally set to 2.3 mm. The hot-rolled steel sheet was directly sent onto the runout table, and the steel sheet on the runout table was cooled by an upper surface laminating facility and/or a lower surface spraying facility installed ahead of it. Thereafter, the cooled hot-rolled steel sheet was coiled and cooled to produce a steel sheet for cold rolling. The total length of the runout table extending from the final stand of the finishing mill to the steel sheet winder was 188.3 m.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
　上記の製造方法において、熱間圧延、冷却および巻取りの条件を変えて、様々な条件下で冷間圧延用の鋼板を製造した。各種の鋼板の製造時における、熱間圧延時の加熱炉抽出温度、粗圧延機の出側温度、加熱炉抽出を行ってから粗圧延が完了するまでの時間（抽出－粗圧延間の時間）、粗圧延機の最終スタンド通過から仕上げ圧延機の最初のスタンド到達までの時間（粗圧延－仕上げ圧延間の時間）、仕上げ圧延機の出側温度、仕上げ圧延機の最終スタンド通過からランナウトテーブル上での水冷開始までの時間（水冷開始時間）、仕上げ圧延機の最終スタンド通過から３秒以内における合計の水冷時間（３秒以内の総水冷時間）、冷却時における水量密度、ランナウトテーブル中間付近における鋼板の温度（中間温度）、仕上げ圧延機の出側通過からランナウトテーブル中間付近での温度測定までの時間（仕上げ圧延－中間温度測定間の時間）、および、巻取り温度を、以下の表２に示す。なお、下記表２において、「－」は、水冷開始時間が３．０秒を経過しているため、３．０秒以内の総水冷時間および水量密度が０であることを示している。 In the above manufacturing method, steel sheets for cold rolling were manufactured under various conditions by changing the hot rolling, cooling and coiling conditions. Reheating furnace extraction temperature during hot rolling, roughing mill delivery temperature, time from heating furnace extraction to completion of rough rolling (time between extraction and rough rolling) when manufacturing various steel sheets , the time from passing the final stand of the roughing mill to reaching the first stand of the finishing mill (time between roughing and finishing rolling), the delivery side temperature of the finishing mill, the runout table from the passage of the final stand of the finishing mill Time until the start of water cooling (water cooling start time), total water cooling time within 3 seconds after passing the final stand of the finishing mill (total water cooling time within 3 seconds), water density at the time of cooling, near the middle of the runout table The temperature of the steel sheet (intermediate temperature), the time from passing through the finish rolling mill to the temperature measurement near the middle of the runout table (time between finish rolling and intermediate temperature measurement), and the coiling temperature are shown in Table 2 below. shown in In Table 2 below, "-" indicates that the total water cooling time and water volume density within 3.0 seconds are 0 because the water cooling start time has passed 3.0 seconds.
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　上記表２において、各項目の詳細な測定および算出方法は以下の通りである。
・加熱炉抽出温度：加熱炉抽出温度は、加熱炉装入時のスラブ温度、加熱炉内の雰囲気温度および加熱炉内の滞在時間から、熱伝達計算によって算出した。
・粗圧延機の出側温度：粗圧延機の出側に設置された放射温度計によって、コイルの幅方向中央部の温度を測定した。温度計は、粗圧延機の最終スタンドから１６．６ｍの位置において設置した。
・抽出－粗圧延間の時間：加熱炉抽出を行ってから、鋼板の長手方向の尾端の粗圧延が終了するまでの時間を、抽出－粗圧延間の時間とした。
・粗圧延－仕上げ圧延間の時間：鋼板の長手方向の尾端の粗圧延が終了してから、鋼板の長手方向の先端の仕上げ圧延が開始されるまでの時間を、粗圧延時間－仕上げ圧延間の時間とした。
・仕上げ圧延機の出側温度：仕上げ圧延機の出側に設置された放射温度計によって、コイルの幅方向中央部の温度を測定した。温度計は、仕上げ圧延機の最終スタンドから５．９ｍの位置において設置した。
・水冷開始時間：仕上げ圧延機の出側の板速度は、鋼板の長手方向の位置に応じて変動する。そのため、水冷開始時間は、鋼板の長手方向で最も板速度が遅く粒成長しやすい長手方向の先端位置の板速度に基づき、定義した。具体的には、水冷開始時間は、仕上げ圧延機の最終スタンドから水冷が行われるランナウトテーブル上の位置までの距離を、鋼板の長手方向における板速度の最小値で除することにより求めた。
・３秒以内の総水冷時間：３秒以内の総水冷時間は、鋼板の長手方向の先端から鋼板全長の４／５の位置（換言すると、長手方向の尾端から鋼板全長の１／５の位置）における値を求めた。具体的には、冷却を実際に行った冷却設備の区画の長さ（ｍ）を、鋼板の長手方向の板速度の最大値で除することによって、この位置における３秒以内の総水冷時間を求めた。
・水量密度：水量密度は、鋼板の長手方向の先端から鋼板全長の４／５の位置（換言すると、鋼板の長手方向の尾端から鋼板全長の１／５の位置）における値を求めた。具体的には、冷却に用いた水流量（Ｌ／分）を、冷却を実際に行った冷却設備の区画の長さ（ｍ）と幅（ｍ）で除することによって、この位置における水量密度を求めた。
・中間温度：ランナウトテーブルの中間付近に設置されている放射温度計によって、コイルの幅方向中央部の温度を測定した。温度計は、仕上げ圧延機の最終スタンドから５６．１ｍの位置において設置した。
・仕上げ圧延－中間温度測定間の時間：鋼板の長手方向の先端が、仕上げ圧延機の出側に設置された放射温度計に到達してから、ランナウトテーブルの中間付近に設置された放射温度計に到達するまでの時間を、仕上げ圧延－中間温度測定間の時間とした。
・巻取り温度：ランナウトテーブルの終端近傍に設置されている放射温度計によって、コイルの幅方向中央部の温度を測定した。温度計は、仕上げ圧延機の最終スタンドから１８０．１ｍの位置において配置した。 In Table 2 above, detailed measurement and calculation methods for each item are as follows.
Heating furnace extraction temperature: The heating furnace extraction temperature was calculated by heat transfer calculation from the slab temperature at the time of charging into the heating furnace, the atmospheric temperature in the heating furnace, and the residence time in the heating furnace.
- Temperature at the delivery side of the roughing mill: The temperature at the central portion in the width direction of the coil was measured with a radiation thermometer installed at the delivery side of the roughing mill. A thermometer was placed 16.6 m from the final stand of the roughing mill.
Time between extraction and rough rolling: The time between extraction and rough rolling was defined as the time from heating furnace extraction to completion of rough rolling at the tail end of the steel sheet in the longitudinal direction.
・ Time between rough rolling and finish rolling: The time from the end of rough rolling of the tail end in the longitudinal direction of the steel plate to the start of finish rolling of the front end of the steel plate in the longitudinal direction is defined as rough rolling time - finish rolling. It was the time in between.
- Temperature at the delivery side of the finishing rolling mill: The temperature at the central portion in the width direction of the coil was measured with a radiation thermometer installed at the delivery side of the finishing rolling mill. A thermometer was installed 5.9 m from the last stand of the finishing mill.
・Water cooling start time: The strip speed on the delivery side of the finishing mill fluctuates according to the position of the strip in the longitudinal direction. Therefore, the water cooling start time was defined based on the plate speed at the tip position in the longitudinal direction where the plate speed is slowest in the longitudinal direction of the steel plate and where grain growth is likely to occur. Specifically, the water cooling start time was obtained by dividing the distance from the final stand of the finishing mill to the position on the runout table where water cooling is performed by the minimum strip speed in the longitudinal direction of the strip.
・ Total water cooling time within 3 seconds: The total water cooling time within 3 seconds is the position of 4/5 of the total length of the steel plate from the tip of the steel plate in the longitudinal direction (in other words, 1/5 of the total length of the steel plate from the tail end of the longitudinal direction). position). Specifically, by dividing the length (m) of the section of the cooling facility where cooling was actually performed by the maximum value of the plate speed in the longitudinal direction of the steel plate, the total water cooling time within 3 seconds at this position asked.
・Water volume density: The water volume density was obtained at a position 4/5 of the total length of the steel plate from the tip of the steel plate in the longitudinal direction (in other words, a position of 1/5 of the total length of the steel plate from the tail end of the steel plate in the longitudinal direction). Specifically, by dividing the water flow rate (L/min) used for cooling by the length (m) and width (m) of the section of the cooling facility where cooling was actually performed, the water flow density at this position asked for
- Intermediate temperature: The temperature at the center in the width direction of the coil was measured with a radiation thermometer installed near the middle of the runout table. A thermometer was installed at a position 56.1 m from the final stand of the finishing mill.
・Time between finishing rolling and intermediate temperature measurement: After the longitudinal tip of the steel plate reaches the radiation thermometer installed on the delivery side of the finishing mill, the radiation thermometer is installed near the middle of the runout table. was taken as the time between finish rolling and intermediate temperature measurement.
- Winding temperature: The temperature at the center in the width direction of the coil was measured with a radiation thermometer installed near the end of the runout table. A thermometer was placed 180.1 m from the last stand of the finishing mill.
　さらに、上記表２に示す区分において、本発明例は、仕上げ圧延出側温度が８００℃以上９４０℃以下かつ水冷開始時間が３．０秒以下の場合における試験片である。一方、比較例１は、仕上げ圧延出側温度が９４０℃より高くかつ水冷開始時間が３．０秒以下の場合における試験片である。比較例２は、仕上げ圧延出側温度が９４０℃以下かつ水冷開始時間が３．０秒より大きい場合における試験片である。比較例３は、仕上げ圧延出側温度が９４０℃より高くかつ水冷開始時間が３．０秒より大きい場合における試験片である。 Furthermore, in the categories shown in Table 2 above, the present invention example is a test piece in which the finish rolling delivery side temperature is 800°C or higher and 940°C or lower and the water cooling start time is 3.0 seconds or less. On the other hand, Comparative Example 1 is a test piece in which the finish rolling delivery side temperature is higher than 940° C. and the water cooling start time is 3.0 seconds or less. Comparative Example 2 is a test piece in the case where the finish rolling delivery side temperature is 940° C. or less and the water cooling start time is longer than 3.0 seconds. Comparative Example 3 is a test piece in which the finish rolling delivery side temperature is higher than 940° C. and the water cooling start time is longer than 3.0 seconds.
　［冷間圧延用の鋼板の試験片の硬度測定］
　上記の方法で得た各冷間圧延用の鋼板の試験片の硬度を測定した。鋼板の長手方向の尾端から３０ｍの位置を含むように、シャー切断によって鋼板の幅方向両端部における試験片を切り取った。試験片のサイズは、１０ｍｍ（圧延方向に対して平行な方向）×２０ｍｍ（板幅方向）×２．３ｍｍ（板厚）とした。図２は、硬度測定のための鋼板の試験片の位置を示す概略図である。長手方向の尾端の位置を、矢印Ｘで示す。図２に示すように、具体的には、試験片は、鋼板の長手方向の尾端から３０ｍの位置（破線Ｙで示す）における鋼板の幅方向両端部から１ｍｍの位置（矢印Ｚで示す）を含むように切り取った。このように切り取った試験片を用いて、冷間圧延用の鋼板の長手方向の尾端から３０ｍの位置における鋼板の幅方向両端部から１ｍｍの位置、かつ、板厚の４分の１における位置でのビッカース硬さを測定した。ビッカース硬さ試験は、９．８０７Ｎの荷重で測定し、当該幅方向両端部の測定値のうちの最大値で評価した。このように求められたビッカース硬さが２９０ＨＶより大きい場合、製造された冷間圧延用の鋼板は端部硬化しており、冷間圧延時に鋼板の端部割れの危険があると評価した。 [Measurement of hardness of test piece of steel plate for cold rolling]
The hardness of the test piece of each steel plate for cold rolling obtained by the above method was measured. A test piece was cut from both ends in the width direction of the steel plate by shear cutting so as to include a position 30 m from the tail end in the longitudinal direction of the steel plate. The size of the test piece was 10 mm (direction parallel to the rolling direction) x 20 mm (plate width direction) x 2.3 mm (plate thickness). FIG. 2 is a schematic diagram showing the position of a steel plate test piece for hardness measurement. The position of the longitudinal tail end is indicated by the arrow X. Specifically, as shown in FIG. 2, the test piece was positioned 30 m from the tail end in the longitudinal direction of the steel plate (indicated by broken line Y) and 1 mm from both ends in the width direction of the steel plate (indicated by arrow Z). cut to include Using the test piece cut in this way, the position of 1 mm from both ends in the width direction of the steel plate at the position of 30 m from the tail end in the longitudinal direction of the steel plate for cold rolling, and the position at 1/4 of the plate thickness The Vickers hardness was measured at The Vickers hardness test was measured with a load of 9.807 N, and the maximum value among the measured values at both ends in the width direction was evaluated. When the Vickers hardness obtained in this way is greater than 290 HV, the manufactured steel sheet for cold rolling is hardened at the edges, and it was evaluated that there is a risk of edge cracking of the steel sheet during cold rolling.
　鋼板の長手方向の尾端から３０ｍの位置は、上述した製造過程において水量密度を求めた位置である鋼板の長手方向の先端から鋼板全長の４／５の位置よりも尾端に近くなっている。鋼板の長手方向において、鋼板の板速度は尾端に近いほどより速くなり、かつ、一般的により端部硬化は生じ易くなることが想定される。そのため、鋼板の長手方向の尾端から３０ｍの位置において端部硬化が観察されなければ、鋼板の長手方向の先端から鋼板全長の４／５の位置においても端部硬化は当然に観察されないことが考えられる。加えて、この結果から、鋼板における冷却対象となる部分を必要に応じて適宜調節することによって、鋼板の長手方向の先端から尾端までの全体にわたっても端部硬化が抑制できることも想定される。 The position 30 m from the tail end of the steel plate in the longitudinal direction is closer to the tail end than the position 4/5 of the total length of the steel plate from the tip of the steel plate in the longitudinal direction, which is the position where the water density was obtained in the manufacturing process described above. . In the longitudinal direction of the steel plate, it is assumed that the plate speed of the steel plate becomes higher as it approaches the tail end, and generally end hardening is more likely to occur. Therefore, if edge hardening is not observed at a position 30 m from the tail end in the longitudinal direction of the steel plate, edge hardening is naturally not observed at a position 4/5 of the total length of the steel plate from the tip in the longitudinal direction of the steel plate. Conceivable. In addition, from this result, it is also assumed that edge hardening can be suppressed over the entire longitudinal direction of the steel plate from the tip to the tail end by appropriately adjusting the portion to be cooled in the steel plate as necessary.
　以下の表３に、各鋼板の試験片において測定されたビッカース硬さ（ＨＶ）およびその評価結果を示す。 Table 3 below shows the Vickers hardness (HV) measured in the test piece of each steel plate and the evaluation results thereof.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　上記表３の各区分における試験片の数とそのビッカース硬さによる硬度評価の結果から、端部割れ危険率を算出した。算出結果を以下の表４に示す。 The edge crack risk rate was calculated from the number of test pieces in each category in Table 3 above and the results of hardness evaluation based on Vickers hardness. The calculation results are shown in Table 4 below.
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　（考察）
　上記表４に示すように、本発明例の６つの全ての試験片は、ビッカース硬さが２９０ＨＶ以下であったため、端部割れ危険率は０であった。一方、比較例１～比較例３の試験片の端部割れ危険率は、０．３３、０．５または１．０であった。これらの結果から、仕上げ圧延機の出側温度を９４０℃以下かつ水冷開始時間を３．０秒以下にすることによって、オーステナイトの回復、再結晶および／または粒成長を抑制し、鋼板の端部硬化を抑制できることが分かった。 (Discussion)
As shown in Table 4 above, all the six test pieces of the present invention example had a Vickers hardness of 290 HV or less, so the risk of edge cracking was zero. On the other hand, the test pieces of Comparative Examples 1 to 3 had edge cracking risk factors of 0.33, 0.5 or 1.0. From these results, by setting the delivery side temperature of the finishing mill to 940 ° C. or less and the water cooling start time to 3.0 seconds or less, austenite recovery, recrystallization and / or grain growth are suppressed, and the edge of the steel plate It turned out that hardening can be suppressed.
　本出願は、２０２１年５月７日に出願された日本国特許出願特願２０２１－０７９２１８号を基礎とするものであり、その内容は、本願に含まれるものである。 This application is based on Japanese Patent Application No. 2021-079218 filed on May 7, 2021, the contents of which are included in this application.
　今回開示された実施形態および実施例は、全ての点で例示であって制限的なものではないと解されるべきである。本発明の範囲は、上記した説明ではなくて特許請求の範囲により示され、特許請求の範囲と均等の意味および範囲内での全ての変更が含まれることが意図される。 It should be understood that the embodiments and examples disclosed this time are illustrative in all respects and not restrictive. The scope of the present invention is indicated by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope of equivalence to the scope of claims.
　本発明によれば、冷間圧延時における鋼板の端部割れを抑制することができる冷間圧延用の鋼板の製造方法を提供することができる。製造された冷間圧延用の鋼板は、引張強度９８０ＭＰａ以上の高張力冷間圧延鋼板を製造する際、歩留の低下の問題を起こすことなく好適に用いることができる。 According to the present invention, it is possible to provide a method for manufacturing a steel sheet for cold rolling that can suppress edge cracking of the steel sheet during cold rolling. The produced steel sheet for cold rolling can be suitably used for producing high-strength cold-rolled steel sheet having a tensile strength of 980 MPa or more without causing a problem of yield reduction.

Claims (3)

  1. 　化学組成において、
    　Ｃ：０．１５質量％以上、０．２５質量％以下、
    　Ｓｉ：０．８質量％以上、３．０質量％以下、
    　Ｍｎ：１．８質量％以上、３．０質量％以下、
    　Ｎｉ、Ｃｕ、Ｃｒ、Ｍｏ：１．０質量％以下（０質量％を含む）、
    　Ｔｉ、Ｎｂ、Ｖ：１．０質量％以下（０質量％を含む）、および
    　Ｂ：０．０１％以下（０質量％を含む）
    を含有するスラブを、仕上げ圧延機の出側温度が８００℃以上９４０℃以下となるように熱間圧延することと、
    　前記熱間圧延後の鋼板の少なくとも一部分が前記仕上げ圧延機の最終スタンドを通過してランナウトテーブル上に送り出されてから３．０秒以内に、前記鋼板の少なくとも一部分を１００Ｌ／分／ｍ２以上の水量密度で０．１秒間以上冷却することと、
    　５５０℃以上の巻取り温度において前記冷却後の熱延鋼板を巻取ることと、を含む、冷間圧延用の鋼板の製造方法。     In chemical composition,
    C: 0.15% by mass or more and 0.25% by mass or less,
    Si: 0.8% by mass or more and 3.0% by mass or less,
    Mn: 1.8% by mass or more and 3.0% by mass or less,
    Ni, Cu, Cr, Mo: 1.0% by mass or less (including 0% by mass),
    Ti, Nb, V: 1.0 mass% or less (including 0 mass%), and B: 0.01% or less (including 0 mass%)
    Hot rolling the slab containing
    Within 3.0 seconds after at least part of the steel sheet after hot rolling passes the final stand of the finishing mill and is sent out onto the runout table, at least part of the steel sheet is reduced to 100 L / min / m 2 or more cooling for 0.1 seconds or more at a water density of
    A method for producing a steel sheet for cold rolling, comprising: coiling the cooled hot-rolled steel sheet at a coiling temperature of 550°C or higher.
  2. 　前記スラブは、
    　Ｐ：０．１質量％以下（０質量％を含む）、
    　Ｓ：０．０１質量％以下（０質量％を含む）、
    　Ａｌ：０．１０質量％以下（０質量％を含む）、および
    　Ｎ：０．０１質量％以下（０質量％を含む）
    をさらに含有する、請求項１に記載の冷間圧延用の鋼板の製造方法。     The slab is
    P: 0.1% by mass or less (including 0% by mass),
    S: 0.01% by mass or less (including 0% by mass),
    Al: 0.10% by mass or less (including 0% by mass), and N: 0.01% by mass or less (including 0% by mass)
    The method for producing a steel sheet for cold rolling according to claim 1, further comprising
  3. 　請求項１または２に記載の方法で製造された鋼板を、３０％～８０％の圧下率で冷間圧延することをさらに含む、冷間圧延鋼板の製造方法。 A method for producing a cold-rolled steel plate, further comprising cold-rolling the steel plate produced by the method according to claim 1 or 2 at a rolling reduction of 30% to 80%.
PCT/JP2022/017334 2021-05-07 2022-04-08 Method for producing steel sheet for cold rolling and method for producing cold-rolled steel sheet WO2022234760A1 (en)

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Publication number Priority date Publication date Assignee Title
JP2013032581A (en) * 2011-07-06 2013-02-14 Nippon Steel & Sumitomo Metal Corp Method for producing cold rolled steel sheet
JP2015063736A (en) * 2013-09-25 2015-04-09 新日鐵住金株式会社 High strength hot rolled steel sheet excellent in fatigue strength and production method thereof
JP2015147991A (en) * 2014-02-07 2015-08-20 新日鐵住金株式会社 Method for manufacturing cold rolled steel sheet
WO2018055695A1 (en) * 2016-09-21 2018-03-29 新日鐵住金株式会社 Steel sheet
WO2020004561A1 (en) * 2018-06-29 2020-01-02 東洋鋼鈑株式会社 Hot-rolled steel sheet, high-strength cold-rolled steel sheet, and manufacturing methods therefor

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Publication number Priority date Publication date Assignee Title
JP2013032581A (en) * 2011-07-06 2013-02-14 Nippon Steel & Sumitomo Metal Corp Method for producing cold rolled steel sheet
JP2015063736A (en) * 2013-09-25 2015-04-09 新日鐵住金株式会社 High strength hot rolled steel sheet excellent in fatigue strength and production method thereof
JP2015147991A (en) * 2014-02-07 2015-08-20 新日鐵住金株式会社 Method for manufacturing cold rolled steel sheet
WO2018055695A1 (en) * 2016-09-21 2018-03-29 新日鐵住金株式会社 Steel sheet
WO2020004561A1 (en) * 2018-06-29 2020-01-02 東洋鋼鈑株式会社 Hot-rolled steel sheet, high-strength cold-rolled steel sheet, and manufacturing methods therefor

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