US20250230519A1 - Method for annealing hot-rolled steel strip - Google Patents

Method for annealing hot-rolled steel strip

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Publication number
US20250230519A1
US20250230519A1 US18/848,992 US202318848992A US2025230519A1 US 20250230519 A1 US20250230519 A1 US 20250230519A1 US 202318848992 A US202318848992 A US 202318848992A US 2025230519 A1 US2025230519 A1 US 2025230519A1
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US
United States
Prior art keywords
steel strip
temperature
annealing
heating
hot
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
US18/848,992
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English (en)
Inventor
Hirokazu Kobayashi
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
JFE Steel Corp
Original Assignee
JFE Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by JFE Steel Corp filed Critical JFE Steel Corp
Assigned to JFE STEEL CORPORATION reassignment JFE STEEL CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: KOBAYASHI, HIROKAZU
Publication of US20250230519A1 publication Critical patent/US20250230519A1/en
Pending legal-status Critical Current

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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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/34—Methods of heating
    • C21D1/42—Induction heating
    • 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
    • C21D11/00—Process control or regulation for heat treatments
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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 of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1216—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties characterised by the working steps
    • C21D8/1222—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
    • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
    • C21D8/12—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • C21D8/1244—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties characterised by the heat treatment
    • C21D8/1261—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties characterised by the heat treatment following 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
    • 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
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/573—Continuous furnaces for strip or wire with cooling
    • 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
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/60—Continuous furnaces for strip or wire with induction heating
    • 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/34—Methods of heating
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/34—Methods of heating
    • C21D1/40—Direct resistance heating
    • 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
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/62—Continuous furnaces for strip or wire with direct resistance heating

Definitions

  • the present invention relates to a method for annealing a steel strip (a hot-rolled steel strip) after hot rolling which is used in the production of an electrical steel sheet.
  • hot-band annealing it is known that by subjecting a hot-rolled steel strip containing 1.6 to 5.0 mass % Si for an electrical steel sheet to annealing (hot-band annealing) before cold rolling, the magnetic properties of a product sheet can be improved, i.e., the Goss orientation can be highly developed.
  • Such hot-band annealing is typically performed using a continuous annealing line including a heating zone, a soaking zone, and a cooling zone.
  • the annealing temperature of the hot-band annealing is known to largely affect the magnetic properties of a product sheet. Therefore, it is necessary to control the temperature of the steel sheet so that it is constant and uniform across the entire length and width of the hot-rolled steel strip.
  • the furnace temperature in the soaking zone is controlled to be constant so that the heating temperature of the hot-rolled steel strip to be annealed can be controlled within a suitable range.
  • such a thick hot-rolled steel strip has a large variation in thickness with respect to the rolled thickness, particularly at the front and rear ends of the steel strip, and thus the heat capacity is largely varied within the same steel strip. Therefore, the hot-rolled steel strip has a significant effect on the temperature of an annealing furnace compared to a cold-rolled steel strip, and it is difficult to heat the hot-rolled steel strip to a target soaking temperature by maintaining the predetermined furnace temperature in each of the heating zone and the soaking zone.
  • the heating conditions of the annealing line are set to achieve the target annealing temperature in the longitudinal direction of the steel strip that is preferable for magnetic properties and that has been determined from the temperature distribution in the longitudinal direction of a slab during slab heating or from the temperature distribution in the longitudinal direction of the steel strip during hot rolling.
  • FIG. 1 is a schematic view showing the first half portion of a continuous annealing line that is used to perform annealing (hot-band annealing) on a hot-rolled steel strip for an electrical steel sheet of the present invention.
  • the continuous annealing line includes a heating zone, a soaking zone, and a cooling zone arranged in this order from the upstream side.
  • the hot-band annealing is usually performed by heating a steel strip S in a heating zone 3 to allow the temperature of the steel strip at the exit side of the heating zone to reach a target soaking temperature, and holding the steel strip S at the soaking temperature for a predetermined time in a soaking zone 4 , and then cooling the steel strip S in a cooling zone (not shown).
  • a hot-rolled steel strip is thicker and has a higher heat capacity than a cold-rolled steel strip, as described above. Therefore, it is difficult to heat the steel strip to the target temperature, not only because it is difficult to follow the changes of the furnace temperature in the heating zone but also because it affects the furnace temperature in the heating zone 3 . Therefore, it is desired to heat the steel strip in the heating zone 3 so that the steel strip always has the predetermined target temperature at the exit side of the heating zone, regardless of the variation in the thickness or the threading speed of the steel strip.
  • heating is performed such that the steel strip temperature at the exit side of the rapid heating device, that is, the heating temperature by the rapid heating device 2 is set lower than the conventional heating temperature for which LSD is not taken into account.
  • heating is performed such that when the threading speed has become faster, the steel strip temperature at the exit side of the rapid heating device, that is, the heating temperature by the rapid heating device 2 is set higher than the conventional heating temperature for which LSD is not taken into account.
  • the steel strip temperature at the exit side of the rapid heating device 2 that is, the heating temperature by the rapid heating device 2 is set lower than the conventional heating temperature for which LSD is not taken into account, and heating is performed.
  • the rapid heating device 2 may be any type capable of changing the steel strip temperature with high responsiveness.
  • any method having a good track record such as induction heating (solenoid method or transverse method), electric heating, or near-infrared heating, may be suitably used.
  • the rapid heating device 2 is placed on the upstream side of the soaking zone 4 in order to control the steel strip temperature at the exit side of the heating zone, and consequently, the steel strip temperature at the exit side of the soaking zone, with high accuracy.
  • the rapid heating device 2 may be placed on the upstream side of the heating zone, or alternatively, as shown in FIG. 2 , within the heating zone 3 (including between divided sections of the heating zone 3 ).
  • an induction heating device in particular, a solenoid-actuated device is used as the rapid heating device 2 , it is difficult to heat the steel strip to a temperature higher than the Curie point.
  • the rapid heating device 2 is preferably placed not on the rear stage, but on the front stage or the middle stage.
  • the rapid heating device 2 it is preferable to adjust the heating temperature by the rapid heating device 2 by taking into account information on the furnace temperature in the heating zone 3 on the stage following the rapid heating device. For example, if the heating capacity of the rapid heating device 2 is low, the rapid heating device 2 alone may be insufficient to respond to a large change in the heat capacity of the hot-rolled steel strip due to variation in the thickness or the threading speed of the steel strip or due to variation in the value of LSD, and thus the preset furnace temperature in the heating zone 3 may be intentionally changed. In such a case, the steel strip temperature at the exit side of the heating zone 3 can be controlled with even higher accuracy, by feeding back the constantly-changing furnace temperature information caused after the rapid heating device 2 and reflecting it in the preset heating temperature by the rapid heating device 2 .
  • the heating temperature for the steel strip by the rapid heating device 2 it is preferable to determine the heating temperature for the steel strip by the rapid heating device 2 by using information on the steel strip temperature at the exit side of the heating zone, the furnace temperature in the soaking zone, and the steel strip temperature at the exit side of the soaking zone, in addition to the value of LSD, the width of the steel strip, and the furnace temperature in the heating zone after the rapid heating device described above.
  • a hot-rolled steel strip for an electrical steel sheet targeted by the present invention preferably contains 1.6 to 5.0 mass % Si.
  • Si is an element effective in increasing the specific resistance of steel to reduce the iron loss and is therefore preferably contained by 1.6 mass % or more.
  • the Si content exceeds 5.0 mass %, the magnetic flux density will be reduced to cause the steel to become brittle, resulting in a significant deterioration in manufacturability such that cracks occur during cold rolling.
  • the Si content is in the range of 2.0 to 3.8 mass %.
  • the hot-rolled steel strip may also contain, in addition to Si, a known inhibitor-forming ingredient to allow secondary recrystallization to occur, or a known additional element to improve magnetic or mechanical properties.
  • a steel slab (with a slab weight of 20 tons) for an electrical steel sheet containing 3.5 mass % Si was produced by a continuous casting process.
  • the steel slab was then heated to a temperature of 1200° C. or higher and hot-rolled into a hot-rolled steel strip with a thickness of 2 mm.
  • the hot-rolled steel strip was subjected to hot-band annealing at a target annealing temperature (soaking temperature) of 1050° C. for a soaking time of 30 seconds using the continuous annealing line shown in FIG. 1 in which the thickness meter 5 and the rapid heating device 2 are arranged on the upstream side of the heating zone, and was pickled for descaling.
  • soaking temperature target annealing temperature
  • the target annealing temperature (target soaking temperature) in the longitudinal direction of the steel strip was changed by taking into account the temperature distribution in the longitudinal direction of the slab during slab heating, the temperature distribution in the longitudinal direction of the steel strip during rough rolling of the hot rolling, or the positional information of a skid during the heating of the slab.
  • the rapid heating device for the annealing line an induction heating device was used.
  • the heating temperature of the device was sequentially changed in the longitudinal direction of the steel strip by taking into account the value of LSD (thickness ⁇ threading speed) to obtain the target annealing temperature.
  • the steel strip subjected to pickling was cold rolled to an intermediate thickness of 1.5 mm.
  • the steel strip was then divided into two pieces in the longitudinal direction, and one of the two resulting steel strips was subjected to intermediate annealing at 1100° C. for 20 seconds, while the other was subjected to a second cold rolling step without the intermediate annealing performed so that a cold-rolled steel strip with a final thickness of 0.23 mm was obtained.
  • the steel strip was subjected to decarburization annealing, which also serves as primary recrystallization annealing, at a temperature of 840° C. for 100 seconds, and an annealing separating agent composed mainly of MgO was applied to each surface of the steel strip and dried.
  • the steel strip was then subjected to finishing annealing including secondary recrystallization annealing and purification treatment at a temperature of 1200° C. for 10 hours.
  • the atmospheric gas in the finishing annealing was set to H 2 when the steel strip was held at 1200° C. during the purification treatment and was set to N 2 during the rest of the time when the temperature was increased (including secondary recrystallization annealing) and when the temperature was decreased.
  • the steel strip resulting from the above finishing annealing was divided into 10 sections in the longitudinal direction, and then, test pieces for measuring magnetic properties were taken from each section. Then, the magnetic flux density B 8 was measured in accordance with the Japanese Industrial Standards JIS C2553, and the difference ⁇ B 8 between the maximum value and the minimum value of the magnetic flux density B 8 was determined as the variation in magnetic properties. The results are shown in Table 1.
  • the technology of the present invention is applicable to not only a hot-rolled steel strip for an electrical steel sheet, but also all metal strips that should be annealed by taking into account variation in the heating temperature for a slab in the longitudinal direction.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Electromagnetism (AREA)
  • Manufacturing & Machinery (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
  • Manufacturing Of Steel Electrode Plates (AREA)
US18/848,992 2022-03-31 2023-03-29 Method for annealing hot-rolled steel strip Pending US20250230519A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
JP2022-059371 2022-03-31
JP2022059371 2022-03-31
PCT/JP2023/012737 WO2023190645A1 (ja) 2022-03-31 2023-03-29 熱延鋼帯の焼鈍方法

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US20250230519A1 true US20250230519A1 (en) 2025-07-17

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US (1) US20250230519A1 (https=)
EP (1) EP4488394A4 (https=)
JP (1) JP7673823B2 (https=)
WO (1) WO2023190645A1 (https=)

Family Cites Families (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP3260605B2 (ja) * 1995-10-27 2002-02-25 新日本製鐵株式会社 コイル内材質の均一性が良い冷延鋼板の製造方法
JP4187960B2 (ja) * 2001-11-05 2008-11-26 Ｊｆｅスチール株式会社 材質安定化システム
JP4894146B2 (ja) * 2005-01-31 2012-03-14 Ｊｆｅスチール株式会社 方向性電磁鋼スラブの加熱方法
RU2414513C1 (ru) * 2007-04-05 2011-03-20 Ниппон Стил Корпорейшн Способ непрерывного отжига полосовой стали, имеющей точку кюри, и устройство для непрерывного отжига такой стали
JP2011179035A (ja) * 2010-02-26 2011-09-15 Jfe Steel Corp 連続焼鈍炉の板温制御方法及び連続焼鈍炉
EP2557183A1 (de) * 2011-08-12 2013-02-13 Siemens Aktiengesellschaft Verfahren zum Betrieb einer Konti-Glühe für die Verarbeitung eines Walzguts
JP6160649B2 (ja) 2014-05-19 2017-07-12 Ｊｆｅスチール株式会社 方向性電磁鋼板の製造方法
JP6572864B2 (ja) * 2016-10-18 2019-09-11 Ｊｆｅスチール株式会社 電磁鋼板製造用の熱延鋼板およびその製造方法
JP6748375B2 (ja) 2016-10-19 2020-09-02 Ｊｆｅスチール株式会社 Ｓｉ含有熱延鋼板の脱スケール方法
JP6784182B2 (ja) * 2017-01-31 2020-11-11 Ｊｆｅスチール株式会社 鋼板の温度制御方法、及び、鋼板の温度制御装置
JP7557123B2 (ja) * 2020-02-06 2024-09-27 日本製鉄株式会社 無方向性電磁鋼板及びその製造方法

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EP4488394A4 (en) 2025-06-25
EP4488394A1 (en) 2025-01-08
JPWO2023190645A1 (https=) 2023-10-05
JP7673823B2 (ja) 2025-05-09
WO2023190645A1 (ja) 2023-10-05

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