US20100101690A1 - Method for continously annealing steel strip having a curie point and continous annealing facility of the same - Google Patents

Method for continously annealing steel strip having a curie point and continous annealing facility of the same Download PDF

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Publication number
US20100101690A1
US20100101690A1 US12/450,650 US45065008A US2010101690A1 US 20100101690 A1 US20100101690 A1 US 20100101690A1 US 45065008 A US45065008 A US 45065008A US 2010101690 A1 US2010101690 A1 US 2010101690A1
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United States
Prior art keywords
heating
steel strip
zone
curie point
induction heating
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US12/450,650
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English (en)
Inventor
Shigenobu Koga
Takaharu Kataoka
Tsuyoshi Hamaya
Hiroaki Mochinaga
Makoto Atake
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Nippon Steel Corp
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Individual
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Priority claimed from JP2007099238A external-priority patent/JP5135534B2/ja
Priority claimed from JP2008070241A external-priority patent/JP5217542B2/ja
Application filed by Individual filed Critical Individual
Assigned to NIPPON STEEL CORPORATION reassignment NIPPON STEEL CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: ATAKE, MAKOTO, HAMAYA, TSUYOSHI, KATAOKA, TAKAHARU, KOGA, SHIGENOBU, MOCHINAGA, HIROAKI
Publication of US20100101690A1 publication Critical patent/US20100101690A1/en
Assigned to NIPPON STEEL & SUMITOMO METAL CORPORATION reassignment NIPPON STEEL & SUMITOMO METAL CORPORATION MERGER (SEE DOCUMENT FOR DETAILS). Assignors: NIPPON STEEL CORPORATION
Abandoned legal-status Critical Current

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/28—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity for treating continuous lengths of work
    • 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
    • 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
    • C21D8/12—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of articles with special electromagnetic properties
    • 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
    • C21D9/60—Continuous furnaces for strip or wire with induction heating
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F27—FURNACES; KILNS; OVENS; RETORTS
    • F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
    • F27B9/00—Furnaces through which the charge is moved mechanically, e.g. of tunnel type; Similar furnaces in which the charge moves by gravity
    • F27B9/30—Details, accessories, or equipment peculiar to furnaces of these types
    • F27B9/36—Arrangements of heating devices
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Definitions

  • the present invention relates to a method for continuous annealing of a steel strip having a Curie point (also expressed as a “Curie temperature Tc”) and a continuous annealing facility of the same.
  • a Curie point also expressed as a “Curie temperature Tc”
  • Tc Curie point
  • a continuous annealing facility of the same enabling uniform annealing along a longitudinal direction of a steel strip.
  • a grain-oriented electrical steel sheet containing Si ⁇ 4.5 mass % or a ferrite type stainless steel sheet, martensite type stainless steel sheet, and the like containing Cr ⁇ 18 mass % may be mentioned.
  • the heating temperature, heating time, and the like are strictly controlled.
  • strict temperature control is demanded such as in the decarburization annealing step of the process of production of low core-loss grain-oriented electrical steel sheet preferable for applications as the cores of transformers and other electrical devices.
  • Japanese Patent Publication No. (A) 10-324922 discloses an invention relating to a method and apparatus for decarburization annealing of a grain-oriented electrical steel sheet heating a steel sheet up to a temperature of 550 to 650° C. by a gas heating system using radiant tubes having a high heating ability, then heating from the above temperature until reaching the soaking temperature using tube-shaped heaters having a large heat generating density comprised of densely arranged heat generating resistance members.
  • this invention regardless of the furnace being large in processing ability, flexible response to a wide range of changes in steel sheet size is possible, overshooting and undershooting in heating are eliminated, and thereby stable decarburization annealing becomes possible.
  • Japanese Patent Publication (A) No. 2003-328039 discloses an invention relating to a method of continuous annealing of steel sheet and applying an induction heating device for changing the sheet temperature of a condition changer so as to enable smooth change of annealing conditions from a preceding material to a following material having different annealing conditions.
  • Japanese Patent Publication (B2) No. 06-051887 discloses an invention for decarburization annealing of grain-oriented electrical steel sheet during which rapidly heating a cold rolled steel strip at a heating rate of 230° C./se or more to a 705° C. or more temperature so as to enable reduction of the core loss.
  • Examples 2 and 3 disclose a heating operation performed using a special electromagnetic induction heating coil with a basic frequency of 450 kHz which provides a heating rate of 1100 or 1200° C./sec to the Curie point of 746° C.
  • Japanese Patent Publication (A) No. 2006-206927 discloses an invention that solves problems, such as the variation in mechanical properties and shape defects of steel sheet caused by the uneven temperature that occurs easily because of the high cooling characteristics when employing accelerated cooling in a process of production of thick-gauge steel sheet and the slit camber resulting from residual stress, by carrying out heat treatment using an induction heating apparatus setting a heating target temperature of the steel sheet after accelerated cooling at a magnetic transformation temperature (Curie point) of the steel material or 700 to 760° C. to thereby raise the temperature uniformity in the steel sheet and then hot straightening the sheet.
  • problems such as the variation in mechanical properties and shape defects of steel sheet caused by the uneven temperature that occurs easily because of the high cooling characteristics when employing accelerated cooling in a process of production of thick-gauge steel sheet and the slit camber resulting from residual stress
  • Document 1 does not describe changes of the heating characteristics of the steel strip itself in the longitudinal direction of the steel strip.
  • the invention as set forth in Document 1, there was the problem that it was impossible to avoid the problem of lack of uniformity of the heating characteristics in the longitudinal direction originating from fluctuations in the temperature history in the longitudinal direction when actually hot rolling a steel strip and the resultant problem of the variation in the characteristics of the steel strip along the longitudinal direction arising as a result.
  • the invention set forth in Document 2 has as its object the smooth changing of annealing conditions from a preceding material to a following material having different annealing conditions and in no way describes uniform heating of a steel strip along the longitudinal direction.
  • Document 3 discloses the application of rapid heating by electromagnetic induction heating for heating of an electrical steel sheet up to the Curie point of decarburization annealing to improve the core loss of electrical steel sheet, however in no way discloses temperature uniformity along the longitudinal direction of steel strip.
  • the invention set forth in the above Document 4 discloses that if applying heat treatment making the heating target temperature of the induction heating apparatus the electromagnetic transformation temperature (Curie point) of the steel material or 700 to 760° C., it is possible to improve the temperature uniformity in the steel sheet, however in no way discloses or suggests whether it is possible to apply this to the continuous annealing of a steel strip where the annealing temperature exceeds the Curie point so as to increase the temperature uniformity in the steel sheet.
  • the present invention has as its object to provide a method of continuously annealing a steel strip having a Curie point and a continuous annealing facility of the same capable of heating a steel strip having a Curie point extremely uniformly in the longitudinal direction until an annealing temperature which exceeds the Curie point.
  • the gist of the present invention is as follows:
  • a method of continuously annealing a steel strip having a Curie point by an annealing temperature exceeding the Curie point at a continuous annealing facility comprising a heating zone, soaking zone, and cooling zone, or a heating zone, soaking zone, nitriding zone, and cooling zone, which method of continuously annealing a steel strip having a Curie point characterized by dividing heat treatment at the heating zone into a first to third, that is, three regions,
  • a continuous annealing facility for continuously annealing a steel strip having a Curie point by an annealing temperature exceeding the Curie point comprising a heating zone, soaking zone, and cooling zone, or a heating zone, soaking zone, nitriding zone, and cooling zone, said continuous annealing facility for a steel strip having a Curie point characterized by dividing the heating zone into a first to third, that is, three regions,
  • FIG. 1 is a view schematically showing a typical continuous heat treatment facility for decarburization annealing (including coating an annealing separating agent) of a cold rolled sheet of grain-oriented silicon steel by an isometric projection.
  • FIG. 2 is a view schematically showing a typical configuration according to the prior art of a furnace 12 in FIG. 1 by a cross-sectional view vertical to the longitudinal direction.
  • FIG. 3 is a view showing an example of the longitudinal direction transition of the sheet temperature of a steel strip measured at three representative locations inside of the heating region 31 of FIG. 2 according to the prior art.
  • FIG. 4 is a view schematically showing a configuration according to an embodiment of the present invention of a furnace 12 in FIG. 1 by a cross-sectional view vertical to the longitudinal direction.
  • FIG. 5 is a view showing an example of the longitudinal direction transition of a sheet temperature of a steel strip measured at exit sides of heating regions 31 A, 35 , and 31 B of FIG. 4 according to the present invention.
  • FIG. 6 is a view schematically showing a typical continuous heat treatment facility for bright annealing of a cold rolled sheet of ferrite type stainless steel by an isometric projection.
  • FIG. 7 is a view schematically showing a typical configuration according to the prior art of a furnace 12 in FIG. 6 by a cross-sectional view vertical to the longitudinal direction.
  • FIG. 8 is a view schematically showing a configuration according to an embodiment of the present invention of a furnace 12 in FIG. 6 by a cross-sectional view vertical to the longitudinal direction.
  • FIG. 9 is a view schematically showing a configuration according to a different embodiment of the present invention of a furnace 12 in FIG. 4 by a cross-sectional view vertical to the longitudinal direction.
  • FIG. 10 is a view explaining an example of a control system of a plurality of induction heating means in the embodiment of FIG. 9 .
  • FIG. 11 is a view showing examples of longitudinal direction transitions of the sheet temperatures of steel strips measured at exit sides of the heating regions 31 A and 35 B and the actual output power values of the induction heating means when operating by the control system of FIG. 10 .
  • FIG. 12 is a view explaining a different control system of a plurality of induction heating means in the embodiment of FIG. 9 .
  • FIG. 13 is a view showing examples of longitudinal direction transitions of the sheet temperatures of steel strips measured at exit sides of the heating regions 31 A and 35 B and the actual output power values of the induction heating means when operating by the control system of FIG. 12 .
  • FIG. 1 is a schematic isometric projection of a typical continuous heat treatment facility for decarburization annealing (including coating an annealing separating agent) of a final cold rolled sheet of grain-oriented silicon steel.
  • the main elements of the production facility line include a payoff reel 1 for carrying a coil-shaped steel strip 60 of a final cold rolled grain-oriented silicon steel and paying it off from there, an entry side shear 2 for shearing off a front and tail end of the steel strip to prepare it for welding, a welder 3 for continuously joining the ends of steel strips to each other, an entry side storage looper 4 for storing the steel strip while preparing the steel strip for welding and during the welding so as to enable the steel strip to be run through an entry side cleaner 11 and furnace 12 without slowing or halting, an entry side cleaner 11 for cleaning the surface of the steel strip and removing rolling oil, iron, and other dirt, a furnace 12 comprising a heating, soaking, and cooling regions and decarburization annealing the steel strip, an exit side storage looper 5 for storing the steel strip when recoiling of a coil is finished and an exit side shear 6 is in operation so as to enable the steel strip to be run through the entry side cleaner 11 and furnace 12 without slowing or halt
  • the annealing separating agent dryer 15 is configured as a fast response furnace comprised of a furnace material with low thermal inertia and an open flame burner. It is structured to be capable of rapidly responding to unavoidable halts and delay of steel strip in the annealing separating agent dryer 15 when the exit side shear 6 is in operation.
  • the tension of the steel strip 60 before and after the furnace 12 is measured with tension meters 41 and 42
  • the tension of the steel strip 60 at the annealing separating agent dryer 15 is measured with a tension meter 43 .
  • the measurement results are fed back to bridle rolls 23 to 26 through which the strip passes so as to secure the steel strip tension before and after the bridle rolls.
  • an exit side cleaner 13 is not necessarily required when the dirt on the steel strip at the furnace 12 is small.
  • a final cold rolled sheet of grain-oriented silicon steel is decarburization annealed (including coating of an annealing separating agent) on the above line, then is annealed at a high temperature and, further, smooth annealed to become a final product.
  • FIG. 2 is a view schematically showing a configuration of a furnace 12 according to the prior art by a cross-sectional view vertical to the longitudinal direction.
  • the furnace 12 generally comprises a heating region 31 using a radiant tube heating system, a soaking region 32 heating with electric heaters, a nitriding region 33 heating with electric heaters, and a cooling region 34 .
  • the heating region 31 is provided with sheet thermometers 36 , 37 , and 38 for monitoring the sheet temperature during heating.
  • the steel strip 60 cleaned at its surface by the entry side cleaner 11 is heated at the heating region 31 by the radiant tube system, heated until a decarburization temperature of approximately 820° C., and decarburization annealed at the soaking zone 32 by heating by electric heaters.
  • the steel strip is heated so as not to be an obstruction to decarburization.
  • the temperature of the furnace is controlled while monitoring the sheet thermometers 36 and 37 arranged in the heating region and the sheet thermometer 38 at the exit side of the heating region.
  • FIGS. 3( a ) to (c) show an example of the temperature distribution along the longitudinal direction of one steel strip coil at the positions of the sheet thermometers 36 , 37 , and 38 when decarburization annealing grain-oriented electrical steel sheet with the facility of FIGS. 1 and 2 according to the prior art.
  • the sheet temperature of the steel strip measured with the sheet thermometer 38 at the heating regional exit side fluctuates along the longitudinal direction.
  • the inventors analyzed the sheet temperature in the process of the temperature elevation of the steel strip in the longitudinal direction and discovered that the rate of temperature elevation fluctuates quite a bit even in the longitudinal direction of the steel strip in a steel sheet coil.
  • the inventors further analyzed the cause of this fluctuation, whereupon they found that in a radiant tube furnace used in a continuous heating facility of steel strip, the steel sheet is heated by the radiant heat transmission between the radiant tubes and the steel strip, the amount of heat transmission determining the amount of temperature elevation of the steel sheet is determined by the emissivities and geometrical positional relationship of the radiant tubes and the steel sheet, and that, since the emissivities and geometrical positional relationship of the radiant tubes do not change in the short term, the temperature of the steel strip changes due to fluctuations of the emissivity of the steel strip.
  • the emissivity of the steel sheet is used for temperature measurement of the steel sheet, the accuracy of the measurement values of the sheet temperature will worsen if the emissivity changes. While a sheet thermometer using a plurality of wavelengths has slightly improved accuracy, it cannot prevent this problem.
  • the inventors further, engaged in intensive research and as a result took note of the fact that with solenoid coil type high frequency induction heating, near the Curie point, the magnetic permeability of the steel strip rapidly drops and along with this the depth of penetration also becomes larger and the heating ability of steel strip rapidly decreases, so it is possible to bring the temperature of steel strip close to a constant value without being affected by the emissivity of the steel strip in the longitudinal direction and thereby arrived at the present invention making it possible to increase the uniformity of the heating rate of steel strip in the longitudinal direction. Further, they discovered that the emissivity of the steel sheet becomes large in absolute value if over 700° C. and is not easily influenced by the conditions of the surface of the comparative sheet and thereby arrived at the present invention.
  • FIG. 4 is a view schematically showing a configuration of a furnace 12 of a continuous heat treatment facility ( FIG. 1 ) for annealing a cold rolled grain-oriented silicon steel of one example of the present invention by a cross-sectional view vertical to the longitudinal direction.
  • a solenoid coil type high frequency induction heating device 35 is arranged at the center of the heating zone. Further, sheet thermometers 36 and 37 are arranged before and after the solenoid coil type high frequency induction device 35 .
  • the steel strip 60 is heated by the heating region (first half) 31 A by a radiant tube system. After the sheet temperature reaches from 500° C. to a predetermined temperature lower than the Curie point Tc (° C.) by over 50° C. (temperature of less than Tc ⁇ 50° C.), the strip is heated by a solenoid coil type high frequency induction heating device 35 to a temperature of Tc ⁇ 30° C. to Tc ⁇ 5° C., then is heated to about 825° C. at the heating region (second half) 31 B by a radiant tube system and is decarburization annealed at the soaking zone 32 by heating by electric heaters.
  • the sheet temperature of the steel strip 60 of the entry side of the solenoid coil type high frequency induction heating device has to be made 500° C. or more. If the sheet temperature is less than 500° C., the required temperature elevation by the induction heating device becomes larger. Therefore, the ability of the induction heating device would have to be made excessive which is not realistic. Further, when the heat treatment furnace atmosphere contains hydrogen, an ambient temperature of 750° C. or more enabling the danger of hydrogen explosion to be avoided becomes unable to be secured.
  • the sheet temperature is Tc ⁇ 50° C. or more, the heating fluctuation by radiant type heating cannot be absorbed at the peak sheet temperature at the induction heating device, so the temperature must be made less than Tc ⁇ 50° C.
  • the sheet temperature of the steel strip 60 at the exit side of the solenoid coil type high frequency induction heating device 35 is over Tc ⁇ 5° C.
  • the magnetic permeability of the steel strip at the exit side will become too small and therefore the magnetic field required for the high frequency induction heating device will become larger and the required facility will end up becoming enormous and impractical.
  • the sheet temperature is less than Tc ⁇ 30° C., the magnetic permeability of the steel strip at the exit side will not be small and heating fluctuations by radiant type heating will not be able to be suppressed by high frequency induction heating.
  • the sheet temperature of the steel strip 60 at the exit side of the solenoid coil type high frequency induction heating device 35 has to be made a temperature region of Tc ⁇ 30° C. to Tc ⁇ 5° C.
  • FIGS. 5( a ) to (c) show an example of the temperature distribution in the longitudinal direction of one steel strip coil measured at the positions of the sheet thermometers 36 , 37 , and 38 at the exit sides of the heating regions 31 A, 35 , and 31 B in the furnace 2 of the present invention.
  • the sheet thermometer 36 of FIG. 5( a ) As shown by the measurement data of the sheet thermometer 36 of FIG. 5( a ), at the exit side of the heating region 31 A using the radiant tube system, there is temperature unevenness of the steel strip. Despite this, by heating in accordance with the present invention, at the exit side of the solenoid coil type high frequency induction heating device 35 , the temperature becomes substantially uniform like with the measurement data of the sheet thermometer 37 of FIG. 5( b ). Further, at the exit side of the heating region 31 B using a radiant tube system, the sheet temperature in the longitudinal direction of the steel strip is extremely stable without fluctuating much at all like with the measurement data of the sheet thermometer 38 of FIG. 5( c ).
  • the steel strip in the decarburization annealing of a grain-oriented silicon steel sheet, the steel strip can be annealed extremely uniformly in the longitudinal direction, so the quality of the obtained grain-oriented silicon steel sheet also becomes uniform.
  • the decarburization becomes uniform and coating defects are almost all eliminated.
  • FIG. 4 shows an example having a nitriding region 33 , but the present invention is not limited to a decarburization annealing facility of a cold rolled grain-oriented electrical steel sheet having a nitriding region and is also valid for a decarburization annealing facility not having a nitriding region.
  • FIG. 6 is a schematic isometric projection of a typical continuous heat treatment facility for bright annealing a cold rolled sheet of ferrite type stainless steel.
  • the main elements of the production line are similar to FIG. 1 except for the point of not having an annealing separating agent coater and dryer at the furnace exit side.
  • FIG. 7 is a view schematically showing a configuration according to the prior art of a furnace 12 by a cross-sectional view vertical to the longitudinal direction.
  • the furnace 12 is generally configured by a heating region 51 using a muffle furnace system (indirect heating), a soaking region 52 , and a cooling region 54 .
  • the heating region 51 is provided with sheet thermometers 56 , 57 , and 58 for monitoring the sheet temperature in the middle of the heating.
  • FIG. 8 is a view schematically showing the configuration of a furnace 12 of a continuous heat treatment facility ( FIG. 6 ) for bright annealing of cold rolled ferrite type stainless steel of one example of the present invention by a cross-sectional view vertical to the longitudinal direction.
  • the structure is the same as a conventional continuous annealing facility.
  • the center of the heating zone is provided with a solenoid coil type high frequency induction heating device 55 .
  • a solenoid coil type high frequency induction heating means was used to heat the steel strip to a temperature region of Tc ⁇ 30° C. to Tc ⁇ 5° C.
  • FIG. 9 shows an example of dividing the second heating zone 35 of FIG. 4 into a former stage and latter stage respectively provided with solenoid coil type high frequency induction heating devices 35 A and 35 B.
  • FIG. 10 shows an example of a control system of such a high frequency induction device.
  • This control system monitors a sheet thermometer 36 at the entry side of the upstream solenoid coil type high frequency induction heating device 35 A to monitor the state of the radiant tube system heating region (former stage) 31 A. Further, it computes the amount of heat of the heating required so that the sheet temperature of the steel sheet at the entry side of the downstream most high frequency induction heating device 35 B will become the target value and finds the set output power value WA of the upstream high frequency induction heating device 35 A from that amount of heat. Further, it controls the upstream high frequency induction heating device 35 A so that the actual output power value becomes the set power value WA and runs the steel strip through the downstream most solenoid coil type high frequency induction heating device 35 B while controlling the value of the current run through the coil so as to give the target current value IB.
  • the system monitors the exit side sheet thermometer 37 , confirms that the sheet temperature of the exit side of the downstream most high frequency induction heating device 35 B has become constant, and then runs the steel strip.
  • FIGS. 11( a ) to (d) show examples of the temperature distribution in the longitudinal direction of one coil of steel strip measured at the positions of the sheet thermometers 36 and 37 at the exit sides of the heating regions 31 A and 35 B in the furnace 2 at that time and the actual output power values of the solenoid type high frequency induction heating devices 35 A and 35 B.
  • the steel strip has uneven temperature, but at the exit side of the solenoid coil type high, frequency induction heating device 35 B, the temperature becomes substantially even as shown in FIG. 11( b ).
  • the actual output power value of the downstream high frequency induction heating device 35 B fluctuates as shown in FIG. 11( d ).
  • the temperature elevation rate of the steel strip fluctuates.
  • the system runs the steel strip through the downstream most high frequency induction heating device 35 B while controlling the current run through the coil so as to give the target current value IB. It detects the actual output power value W B of the downstream most high frequency induction heating device 35 B at that time, computes the difference ⁇ W B between this actual output power value and the target output power value, corrects the set output power value W A0 of the high frequency heating device 35 A upstream of the downstream most high frequency induction heating device 35 B so that the actual output power value becomes a constant value, and controls the current value of the high frequency heating device 35 A so that the actual output power value of the high frequency heating device 35 A becomes the corrected set output power value ⁇ W B +W A0 .
  • the system monitors the entry side sheet thermometer 36 to monitor the state of the radiant tube system heating region (former stage) 31 A and monitors the exit side sheet thermometer 37 to confirm that the sheet temperature at the exit side of the downstream most solenoid coil type high frequency induction heating device 35 B becomes constant and then runs the steel strip.
  • FIGS. 13( a ) to (d) show examples of the temperature distribution in the longitudinal direction of one coil of steel strip measured at the positions of the sheet thermometers 36 and 37 at the exit sides of the heating regions 31 A and 35 B in the furnace 2 at that time and the actual output power values of the solenoid type high frequency induction heating devices 35 A and 35 B.
  • the target sheet temperature of the steel strip 60 at the boundary of the solenoid type high frequency induction heating devices 35 A and 35 B at that time was 680° C.
  • the rate of temperature elevation of the steel strip 60 in the downstream solenoid type high frequency induction heating device 35 B is constant and very stable without fluctuating much at all.
  • induction heating devices In the above explanation of the control system, two induction heating devices were provided, but the number of induction heating devices is not limited to two and may be any number.
  • a high frequency induction heating device designed to give a constant output power value in accordance with the temperature region where an extremely strict rate of temperature elevation of the steel strip is demanded.
  • the invention is not limited to the downstream most position of the second heating zone.
  • the steel strip having a Curie point covered by the present invention is not limited to, as illustrated here, a cold rolled steel strip of a grain-oriented electrical steel sheet or a cold rolled steel strip of a ferrite type stainless steel sheet.
  • the invention is applicable to all steel strips having a Curie point.
  • the grain-oriented electrical steel sheet containing Si ⁇ 4.5 mass % covered by the present invention need only be, for example, one of a system of ingredients like the grain-oriented electrical steel sheet disclosed in Japanese Patent Publication (A) No. 2002-060842, Japanese Patent Publication (A) No. 2002-173715, etc.
  • the present invention does not particularly limit the system of ingredients.
  • JIS G 4305 SUS430, SUS430J1L, or other standard steel types or ingredient systems such as the ferrite type stainless steel sheet disclosed in Japanese Patent Publication (A) No. 05-293595, Japanese Patent Publication (A) No. 06-002044, Japanese Patent Publication (A) No. 07-118754, etc. may be used.
  • the present invention does not particularly limit the ingredient system.
  • JIS G 4305 SUS410, SUS420J1, or other standard steel types or ingredient systems such as the martensite type stainless steel sheet disclosed in Japanese Patent Publication (A) No. 07-268561 and Japanese Patent Publication (A) No. 08-199310 may be used.
  • the present invention does not particularly limit the ingredient system.
  • the means for heating the steel strip to less than Tc ⁇ 50° C. is not limited to a radiant tube system. All radiant heating means using indirect gas heating or direct gas heating and/or radiant heating means using electric heaters and/or heating means using induction heating devices are effective. Further, the system for heating from the temperature region near the Curie point of Tc ⁇ 30° C. to Tc ⁇ 5° C. to the treatment target temperature is also not limited to an electric heater heating system. All radiant heating means using indirect gas heating or direct gas heating and/or radiant heating means using electric heaters are effective. Further, in general, Tc ⁇ 30° C. exceeds 700° C.
  • the steel sheet emissivity becomes large in absolute value and is no longer governed by the state of the surface of the comparative sheet, so the sheet thermometer rises in measurement accuracy and the temperature of the steel sheet becomes easier to control, so with Tc ⁇ 30 or more, the heating system is not that much of an issue.
  • a steel slab containing, by mass %, C: 0.06%, Si: 3.3%, Mn: 0.1%, P: 0.03%, S: 0.008%, acid soluble Al: 0.028%, N: 0.008%, and Cr: 0.1% was heated at a temperature of 1150° C., then hot rolled to a sheet thickness of 2.3 mm to obtain a steel strip coil, then was annealed by two stages of annealing temperatures of 1120° C. and 920° C. Further, this was cold rolled to a sheet thickness of 0.22 mm by a reverse roller, then was decarburization annealed by a prior art decarburization annealing facility ( FIG. 1 and FIG.
  • the steel sheet temperature at the heating region exit side of the furnace 12 was measured by the sheet temperature thermometer 38 and the smooth annealed grain-oriented electrical steel sheet was measured for the coating defect rate.
  • Table 1 shows the test conditions and test results. Note that the start temperature of the induction heating was made Tc ⁇ A (° C.) and the end temperature was made Tc ⁇ B (° C.). In the table, these were shown by the values of A and B. Further, as the item for evaluation of the stability of quality in the coil longitudinal direction, since continuous measurement of the decarburization ability is difficult, the coating defect rate (area ratio of defects), which can be continuously measured, was measured.
  • Comparative Example 11 where the induction heating end temperature was too high, the steel sheet did not reach the target temperature and could not satisfy the test conditions. Further, in Comparative Example 12 where the induction heating end temperature was too low and in Comparative Examples 13 and 14 where the induction heating start temperatures were high, the fluctuations in steel sheet temperatures continued to not be small and a result the coating defect rates of the steel sheets were high. Note that, Comparative Example 15 which did not use induction heating had a large variation in steel sheet temperature and an extremely large coating defect rate of the steel sheet.
  • a slab containing, by mass %, C: 0.005%, Si: 0.1%, Mn: 0.1%, Cr: 15%, P: 0.02%, S: 0.01%, and N: 0.01% was heated at a temperature of 1200° C., then hot rolled to a sheet thickness of 5 mm to obtain a steel strip coil, then annealed at 900° C. Further, it was cold rolled to a 2 mm thickness by a reverse roller, then was bright annealed at 950° C. by a prior art system ( FIG. 6 and FIG. 7 ) and by a system according to the present invention ( FIG. 6 and FIG. 8 ) at the annealing facility.
  • Table 2 shows the test conditions and results (target values A and B are similar to those of Table 1).
  • Comparative Example 31 where the induction heating end temperature was too high, the steel sheet did not reach the target temperature and could not satisfy the test conditions. Further, in Comparative Example 32 where the induction heating end temperature was too low and in Comparative Examples 33 and 34 where the induction heating start temperatures were high, the fluctuations in the ratios of parts of the steel sheets failing in mechanical strength (insufficient heating) were large. Note that, Comparative Example 35 which did not use induction heating had an extremely large ratio of parts of the steel sheet failing in mechanical strength (insufficient heating).

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KR20150135028A (ko) 2014-05-20 2015-12-02 경희대학교 산학협력단 스마트 케어 및 에코 통합 시스템 및 그 방법
US20170314096A1 (en) * 2014-10-29 2017-11-02 Fives Stein Method for orienting steel sheet grains, corresponding device, and facility implementing said method or device
US10072318B2 (en) 2012-09-03 2018-09-11 Jfe Steel Corporation Rapid heating apparatus of continuous annealing line
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US11352680B2 (en) * 2017-10-24 2022-06-07 Baoshan Iron & Steel Co., Ltd. Apparatus and method for rapidly heating cold-rolled strip steel
US11401577B2 (en) * 2016-12-19 2022-08-02 Arcelormittal Manufacturing process of hot press formed aluminized steel parts
CN115449609A (zh) * 2022-09-13 2022-12-09 浙江大学台州研究院 一种曲柄退火热处理自动上下料生产线
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CN102010978A (zh) * 2010-12-30 2011-04-13 中冶南方(武汉)威仕工业炉有限公司 预热炉内防带钢划伤的保护杆装置
US10072318B2 (en) 2012-09-03 2018-09-11 Jfe Steel Corporation Rapid heating apparatus of continuous annealing line
KR20150135028A (ko) 2014-05-20 2015-12-02 경희대학교 산학협력단 스마트 케어 및 에코 통합 시스템 및 그 방법
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US11788165B2 (en) 2016-10-19 2023-10-17 Jfe Steel Corporation Hot-band annealing equipment, hot-band annealing method and descaling method for Si-containing hot rolled steel sheet
US11401577B2 (en) * 2016-12-19 2022-08-02 Arcelormittal Manufacturing process of hot press formed aluminized steel parts
US11352680B2 (en) * 2017-10-24 2022-06-07 Baoshan Iron & Steel Co., Ltd. Apparatus and method for rapidly heating cold-rolled strip steel
CN111944986A (zh) * 2020-09-15 2020-11-17 应达工业（上海）有限公司 一种无废料焊缝在线退火工艺
CN115449609A (zh) * 2022-09-13 2022-12-09 浙江大学台州研究院 一种曲柄退火热处理自动上下料生产线
CN115505695A (zh) * 2022-09-27 2022-12-23 中冶南方（武汉）热工有限公司 一种极薄规格无取向硅钢退火炉

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