WO2004000476A1 - Procede de laminage a chaud et appareil destine a une tole d'acier laminee a chaud - Google Patents

Procede de laminage a chaud et appareil destine a une tole d'acier laminee a chaud Download PDF

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Publication number
WO2004000476A1
WO2004000476A1 PCT/JP2003/007229 JP0307229W WO2004000476A1 WO 2004000476 A1 WO2004000476 A1 WO 2004000476A1 JP 0307229 W JP0307229 W JP 0307229W WO 2004000476 A1 WO2004000476 A1 WO 2004000476A1
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WO
WIPO (PCT)
Prior art keywords
width direction
temperature
steel sheet
heating
bar
Prior art date
Application number
PCT/JP2003/007229
Other languages
English (en)
Inventor
Mitsuru Yoshida
Hiroshi Kimura
Koji Noguchi
Takehiro Nakamoto
Hiroki Sakaue
Koya Takahashi
Tomoaki Yoshiyama
Tetsuya Yamada
Yusuke Iwao
Original Assignee
Nippon Steel Corporation
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
Priority claimed from JP2002193300A external-priority patent/JP4133042B2/ja
Priority claimed from JP2002206831A external-priority patent/JP2004050183A/ja
Priority claimed from JP2002365867A external-priority patent/JP3793503B2/ja
Priority claimed from JP2003034808A external-priority patent/JP3793512B2/ja
Priority claimed from JP2003070030A external-priority patent/JP3793515B2/ja
Application filed by Nippon Steel Corporation filed Critical Nippon Steel Corporation
Priority to AU2003238695A priority Critical patent/AU2003238695A1/en
Priority to KR1020047019940A priority patent/KR100698502B1/ko
Priority to CNB038187701A priority patent/CN100333846C/zh
Publication of WO2004000476A1 publication Critical patent/WO2004000476A1/fr

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B37/00—Control devices or methods specially adapted for metal-rolling mills or the work produced thereby
    • B21B37/74—Temperature control, e.g. by cooling or heating the rolls or the product
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
    • B21B45/004—Heating the product
    • 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
    • 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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • 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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0478—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing involving a particular surface treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B1/24—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process
    • B21B1/26—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process by hot-rolling, e.g. Steckel hot mill
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B2261/00—Product parameters
    • B21B2261/20—Temperature
    • B21B2261/21—Temperature profile
    • 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
    • C21D2221/00—Treating localised areas of an article
    • C21D2221/02—Edge parts

Definitions

  • the present invention relates to hot rolling of steel sheet, more particularly relates to a hot rolling method and apparatus for producing hot rolled steel sheet with a high yield by making a temperature in a width direction of a rough bar at a finishing mill entry side a predetermined temperature profile.
  • Hot rolling of steel sheet is performed by loading into a heating furnace 1 a low temperature slab 2 to reheat it to a predetermined temperature, rolling the reheated slab 2 to a predetermined thickness by a roughing mill 3 to obtain a rough bar 4, using a crop shear 5 to crop off the front and tail ends of the rough bar, restoring the temperatu're drop at the two edges in the width direction of the rough bar 4 by heating the two edges by an edge heater 6, using a continuous finishing mill 7 comprised of a plurality of stands to finishing roll the bar to a predetermined hot rolled steel sheet, then cooling this by a cooling stand 8 on a runout table and coiling this by a coiler 9.
  • a heater and edge heater between the roughing mill and finishing mill to heat the rough bar rough rolled by the roughing mill.
  • a solenoid type induction heater for heating a rough bar over its entire width direction and an edge heater for heating the two edges of the rough bar and using the solenoid type induction heater and edge heater to heat the rough bar at the entry side of the finishing mill to a temperature uniform in the width direction (for example, Japanese Unexamined Patent Publication (Kokai) No. 3-314216).
  • the solenoid type induction heater used here is characterized by its magnetic field property, i.e., coiling so as to surround the sheet and generating a magnetic field parallel to the sheet. It concentratedly heats the entire sheet surface and uses heat conduction so that the temperature becomes averaged out, so the temperature rises by exactly a uniform amount in the state of a substantially constant temperature profile in the width direction. That is, the technology proposed above attempts to reduce the rolling load by uniformly heating a rough bar as a whole in the width direction by a solenoid type induction heater and by heating the two edges by an edge heater to give a temperature profile uniform in the width direction.
  • the inventors however researched the material properties in the width direction of hot rolled steel sheet and as a result discovered that even if heating the edges with their large temperature drop by an edge heater to make the temperature profile in the width direction uniform, there would be variation in the mechanical properties in the width direction of the steel sheet obtained by the finishing rolling. That is, with the heating method of uniformly heating the entire rough bar in the width direction and heating the two edges with their large temperature drop by an edge heater between the roughing mill and finishing mill, it was difficult to obtain uniform mechanical properties in the width direction of the hot rolled steel sheet.
  • the inventors conducted various experiments to elucidate the causes for this and discovered that the cause is when heating the slab in the heating furnace.
  • a heating furnace heats the slab in a high temperature atmosphere, so inevitably the temperature is low at the center of the thickness of the slab.
  • This temperature profile is maintained even if the thickness is reduced by rolling, so the temperature becomes lower at the center than the average temperature in the width direction and becomes higher toward the edges.
  • the inventors discovered that this trend in this temperature profile remains unchanged even if the thickness is reduced by rolling, so the cause lies in the temperature profile, that is, the temperature profile of the rough bar becoming asymmetric to the left and right in the width direction, the temperature becoming lower at the center than the average temperature in the width direction and higher toward the edges, and the edges becoming the lowest in temperature.
  • the present invention has as its object to provide a hot rolling method and apparatus for stably producing hot rolled steel sheet having predetermined material properties in the width direction by changing the temperature rise in the width direction of the rough bar (preferably increasing the temperature rise at the center low temperature part in the width direction) to obtain a predetermined temperature profile in the width direction of the rough bar at the finishing mill entry side or exit side. Further, the present invention, in consideration of the above situation, has as its object to provide a method of heating steel sheet capable of heating any region in the width direction of steel sheet (steel strip) and capable of controlling the temperature profile in the width direction of the steel sheet.
  • the present invention has as its object to provide a hot rolling method and apparatus producing hot rolled steel sheet free from variation of mechanical properties in the width direction with a high yield by finishing rolling by heating the center low temperature part and two end low temperature parts of a rough bar to raise their temperature to achieve a uniform temperature profile over the entire width direction of the rough bar at the finishing mill entry side or exit side and by raising the temperature of the rough bar as a whole to lighten the load at the time of finishing rolling to secure the temperature for obtaining the required material properties.
  • the present invention has as its object to provide a hot rolling method and apparatus for producing hot rolled steel sheet free from variation in material properties in the width direction with a high yield by finishing rolling by heating the center low temperature part and two end low temperature parts of a rough bar and by eliminating the left-right asymmetric temperature profile in the width direction to achieve a uniform temperature profile over the entire width direction of the rough bar at the finishing mill entry side to secure the temperature for obtaining the required material properties.
  • the inventors discovered that to obtain hot rolled steel sheet free from variation in material properties in the width direction, it is necessary to make the temperature profile in the width direction of a rough bar at the finishing mill entry side uniform and that for this purpose, it is possible to heat and raise the temperature of the center low temperature part of the rough bar arising due to the low temperature of the center of the slab during slab heating and heat and raise the temperature of the temperature drop parts of the two edges of the rough bar arising at the time of rough rolling so as to achieve a uniform temperature profile in the width direction of the rough bar and that heating the entire width direction to secure the finishing rolling temperature and using a transverse type induction heater superior in heating properties as the heater are advantageous and thereby completed the present invention.
  • tailored blanks differing in strength in the width direction are being produced. These tailored blanks have to give different mechanical properties at predetermined portions of the body parts when pressed to such body parts.
  • the general practice had been to weld together a plurality of steel strips to obtain tailored blanks, but in recent years various methods have been proposed for producing tailored blanks without welding by changing the cooling temperature in the width direction of steel strip when water cooling hot rolled steel strip by a runout table (ROT) so as to give different mechanical properties in the width direction of the steel strip (for example, Japanese Unexamined Patent Publication (Kokai) No. 11-192501 and Japanese ' Unexamined Patent Publication (Kokai) No. 2000-11541).
  • ROT runout table
  • a slab is heated to a predetermined temperature, then rolled by a roughing mill to form a rough bar.
  • a finishing mill Before finishing rolling this rough bar by a finishing mill, the front and tail ends of the rough bar in the longitudinal direction are cropped off by a shear.
  • One of the objects of cropping off the front and tail ends of a rough bar is to remove the shape defects at the front and tail ends of the rough bar so as to prevent misrolling in the finishing rolling, while another object is to remove the low temperature portions at the front and tail ends. If finishing rolling a rough bar while leaving the low temperature portions at the front and tail ends, the steel strip will crack at the low temperature portions during finishing rolling and flaws will be caused at the surface of the work roll. If leaving these flaws at the roll surface and rolling the succeeding rough bars, the flaws of the roll will be transferred to the products at constant intervals matching with the period of rotation of the roll and lead to surface defects in the products. Therefore, in cropping off the front and tail ends of a rough bar, normally, as shown in FIG.
  • Japanese Unexamined Patent Publication (Kokai) No. 2-6002 describes a rolling method comprising cropping off the front and tail ends of a rough bar by a crop shear, then using an apparatus for heating the ends in the width direction of the rough bar (also called “edge heater”) to heat the ends in the longitudinal direction.
  • an edge heater having the ability to locally heat just the ends in the width direction is moved for use, so it is necessary to make the rough bar stop on the conveyance tables when heating the front and tail ends of the rough bar. Accordingly, when heating the front end, the temperature difference between the portions contacting the conveyance rolls and the portions not becomes conspicuously larger. Further, when heating the tail end, the rough bar is being taken in by the finishing mill, therefore it is not possible t ⁇ stop the conveyance of the rough bar to sufficiently heat it.
  • Japanese Unexamined Patent Publication (Kokai) No. 10-291016 discloses an invention installing a solenoid type induction heater for heating the entire width direction of a rough bar around the crop shear between the roughing mill and finishing mill.
  • the low temperature portions at the front and tail ends in the longitudinal direction are heated without stopping when passing through the solenoid type induction heater to give a temperature whereby the finishing rolling temperature becomes more than the ferrite transformation start temperature, then the bar is finishing rolled to obtain the hot rolled steel strip. Since just the shape defects are removed without also cropping off the low temperature portions in the past, a drop in the yield is incurred.
  • the temperature drop at the front and tail ends of the rough bar becomes larger the closer to the frontmost end or tailmost end.
  • a temperature drop of over 200 °C is seen compared with the steady state locations.
  • a solenoid type induction heater features the ability to uniformly heat any location in the width direction and longitudinal direction.
  • the size of the heater is determined in accordance with the maximum temperature rise of the rough bar. If trying to compensate for a temperature drop of more than 200 °C at the frontmost end or tailmost end, a massive heater would become required and the capital investment would become huge. On the other hand, if an ordinary size solenoid type induction heater is used, it is not possible to compensate for the over 200 °C temperature drop of the front and tail ends of the rough bar and therefore portions where the temperature has not sufficiently risen remain at the front end or tail end other than the shape defects, so the remaining low temperature portions have to be cropped off.
  • the present invention was completed with the object of providing an array of hot rolling facilities and hot rolling method not requiring a rough bar to be stopped at the time of heating, not requiring massive capital investment, enabling the temperature of a temperature drop part at a frontmost end and tailmost end of a rough bar to be sufficiently raised, and enabling just shape defects to be cropped off. Its gist is as follows:
  • a hot rolling method for steel sheet said hot rolling method for steel sheet characterized by heating a rolling material while changing a temperature rise in a width direction of the rolling material so that a width direction temperature of the rolling material at a finishing mill entry side or exit side becomes a predetermined temperature profile.
  • a method of heating steel sheet characterized by shifting a plurality of bar heaters arranged in a steel sheet longitudinal direction in a steel sheet width direction, operating the bar heaters for heating, and controlling a temperature profile in a steel sheet width direction.
  • a method of heating steel sheet characterized by shifting a plurality of bar heaters arranged in a steel sheet longitudinal direction in a steel sheet width direction so that there are overlapping portions in the steel sheet longitudinal direction and controlling the amount of the overlapping portions so as to control a temperature profile in a steel sheet width direction.
  • (2) or (3) characterized by concentratedly heating a center in the steel sheet width direction by operating the plurality of bar heaters for heating after moving them to the center in the steel sheet width direction.
  • a method of heating steel sheet as set forth in (2) or (3) characterized by heating an overall part in the steel sheet width direction by operating the plurality of bar heaters for heating after moving them to be positioned at constant intervals.
  • a hot rolling apparatus for steel sheet said hot rolling apparatus for steel sheet characterized by arranging a heater for heating while changing a temperature rise in a width direction of a rolling material at a roughing mill entry side in a rolling line, between roughing mills, between a roughing mill and finishing mill, or between finishing mills.
  • said heater is a transverse type induction heater able to heat while changing a temperature rise in the width direction of the rolling material.
  • said transverse type induction heater is at least two transverse type induction heaters differing in lengths of core widths in the width direction.
  • a hot rolling apparatus for steel sheet free from variation in material properties in the width direction provided with a slab heating furnace, a roughing mill, and a finishing mill, said hot rolling apparatus for steel sheet characterized by being provided with transverse type induction heaters able to heat just a center of steel sheet and transverse type induction heaters able to heat the overall width of the steel sheet and able to heat by larger temperature rises at the edges than the center.
  • An array of hot rolling facilities characterized by consecutively arranging a transverse type induction heater for induction heating an entire width direction of a rough bar and a shear able to crop off front and tail ends of the rough bar in the longitudinal direction between a roughing mill and finishing mill.
  • An arrangement of hot rolling facilities characterized by consecutively arranging a shear able to crop off front and tail ends of a rough bar in the longitudinal direction and a transverse type induction heater for induction heating of the entire width direction of the rough bar between a roughing mill and finishing mill.
  • a hot rolling method characterized by using a hot rolling facility having an array of hot rolling facilities as set forth in (18) or (19) and heating at least a portion of not more than 1 m from the end of one or both of the front and tail ends of the rough bar by said transverse type induction heaters.
  • a hot rolling apparatus for steel sheet provided with a heating furnace for heating a slab, a roughing mill for rough rolling of the slab, and a finishing mill for finishing rolling of the roughly rolled bar, said hot rolling apparatus for steel sheet characterized by arranging transverse type induction heaters able to heat by a larger temperature rise at the center of the steel sheet facing each other vertically between the roughing mill and finishing mill and providing a tilter for making the upper or lower or both of said transverse type induction heaters tilt in the width direction of the rolling line.
  • a hot rolling apparatus for steel sheet provided with a heating furnace for heating a slab, a roughing mill for rough rolling of the slab, and a finishing mill for finishing rolling of the roughly rolled rough bar, said hot rolling apparatus for steel sheet characterized by arranging a plurality of transverse type induction heaters facing each other, vertically between the roughing mill and finishing mill along the width direction of the rolling line and providing an output adjuster able to adjust the outputs of the transverse type induction heaters.
  • a hot rolling apparatus for steel sheet provided with a heating furnace for heating a slab, a roughing mill for rough rolling of the slab, and a finishing mill for finishing rolling of the roughly rolled bar, said hot rolling apparatus for steel sheet characterized by arranging transverse type induction heaters facing each other vertically between the roughing mill and finishing mill and providing a retractable shield for changing the magnetic flux of said transverse type induction heaters with respect to the width direction of the rolling line.
  • FIG. 1 is a view showing an outline of a conventional continuous hot rolling apparatus.
  • FIG. 2 is a view showing an outline of a conventional endless rolling apparatus.
  • FIG. 3 are views for explaining a temperature profile in a width direction of a slab reheated in a heating furnace, wherein (a) is a view of the state where there is a low temperature part at a center in the slab thickness and (b) is a view of the state where there is a low temperature part at a center in the width direction of the slab.
  • FIG. 1 is a view showing an outline of a conventional continuous hot rolling apparatus.
  • FIG. 2 is a view showing an outline of a conventional endless rolling apparatus.
  • FIG. 3 are views for explaining a temperature profile in a width direction of a slab reheated in a heating furnace, wherein (a) is a view of the state where there is a low temperature part at a center in the slab thickness and (b) is a view of the state where there is a low temperature part at a center
  • FIG. 4 are views for explaining a temperature profile in a width direction of steel sheet after rough rolling and finishing rolling, wherein (a) is a view of a rough bar, (b) is a view of the temperature profile in the width direction after rough rolling, and (c) is a view of the temperature profile in the width direction after finishing rolling.
  • FIG. 5 are views of the temperature profile in the width direction of steel sheet after finishing rolling, where (a) is a view of the temperature profile in the width direction of a slab, (b) that of a rough bar, and (c) that of the steel sheet after finishing rolling.
  • FIG. 6 are views of the temperature profile in the width direction in the case of hot rolling after heating two edges of a rough bar by an edge heater, wherein (a) is a view of the temperature profile in the width direction of a slab, (b) that of a rough bar heated by an edge heater, and (c) that of the steel sheet after finishing rolling.
  • FIG. 7 are views of the temperature profile in the width direction when hot rolling after heating a rough bar by a solenoid type induction heater, wherein (a) is a view of the temperature profile in the width direction of a slab, (b) that of a rough bar heated by an edge heater, and (c) that of the steel sheet after finishing rolling.
  • FIG. 8 is a view for explaining transverse type induction heaters.
  • FIG. 9 is a view of an example of arranging transverse type induction heaters, wherein (a) is a view of an example of arranging three transverse type induction heaters having equivalent core widths and (b) is a view of an example of arranging two transverse type induction heaters having different core widths.
  • FIG. 10 is a view for explaining the temperature profile in the width direction when raising the temperature by three transverse type induction heaters having equivalent core widths.
  • FIG. 11(a) is a view of the relationship between a hot rolling temperature (°C) and hole enlargement rate of 600 MPa high tensile steel
  • FIG. 11(b) is a view of the relationship between the hot rolling temperature (°C) and elongation EL (%) of 600 MPa class high tensile steel.
  • FIG. 12 is a schematic view of the temperature rise in the width direction when heating steel sheet while shifting a plurality of bar heaters in a width direction of steel sheet.
  • FIG. 13 is a view of the temperature rise profile in the width direction due to bar heaters and the improvement in temperature difference in the width direction.
  • FIG. 14 is a view for explaining a shift in the width direction of bar heaters in examples.
  • FIG. 15 is a view for explaining definitions of temperature rise and temperature rise difference by bar heaters in the examples .
  • FIG. 16 is a view of improvement of the temperature difference in the width direction of steel sheet in the examples .
  • FIG. 17 is a view of the state of shift in width direction corresponding to heating tests of (a) to (e) in the examples.
  • FIG. 18 is a view of an example of arrangement of two transverse type induction heaters differing in core widths.
  • FIG. 19 are views of the temperature rise profiles of transverse type induction heaters and an edge heater, wherein (a) is a view of the temperature rise profile of a narrow width transverse type induction heater, (b) is a view of the temperature rise profile of a broad width transverse type induction heater, (c) is a view of the total temperature rise profile of two transverse type induction heaters, and (d) is a view of the temperature rise profile of an edge heater.
  • FIG. 20 is a view for explaining a temperature profile of a front of a rough bar before rolling.
  • FIG. 21 is a view for explaining a temperature profile of a middle of a rough bar before rolling.
  • FIG. 22(a) is a view for explaining a temperature profile of a tail of a rough bar before rolling.
  • FIG. 22(b) is a view of the relationship between a temperature difference of a finishing mill entry side and an elongation rate difference of a finished steel sheet.
  • FIG. 23 is a perspective view of transverse type induction heaters of the present invention.
  • FIG. 24 is a schematic view of an array of hot rolling facilities of the present invention.
  • FIG. 25 are perspective views of the state of induction current generated in a rough bar when using a transverse type induction heater, wherein (a) shows the state near the frontmost end of the rough bar and (b) shows the state of a steady state part.
  • FIG. 26 is a view of the state of temperature rise near the front and tail ends of a rough bar when using a transverse type induction heater.
  • FIG. 27(a) is a view of the cropping position at the front end of a rough bar, while (b) is a view of that near the tail end.
  • FIG. 28 are views of the temperature of a rough bar near the front and tail ends of a rough bar in the presence/absence of transverse type induction heating, where (a) is a view of the temperature of the front end of the rough bar and (b) is a view of the temperature of the tail end of the rough bar.
  • FIG. 29 is a perspective view of a conventional solenoid type induction heater.
  • FIG. 30 is a view for explaining the fact that when heating a slab by a heating furnace, the temperatures in the width direction of the slab are asymmetric.
  • FIG. 31 are views for explaining the temperature profile in the width direction of a slab reheated in a heating furnace, wherein (a) is a view showing there is a low temperature part at the center of the slab and (b) is a view showing that the temperature profile in the width direction of the slab is asymmetric and there is a low temperature part at the center of the width direction.
  • FIG. 32 are views of the temperature profile in the width direction of steel sheet after rough rolling and finishing rolling, wherein (a) is a view of a rough bar, (b) is a view of the left-right asymmetric temperature profile in the width direction after rough rolling, and (c) is a view of the left-right asymmetric temperature profile in the width direction after finishing rolling.
  • FIG. 33 are views of the temperature profile in the width direction when heating and hot rolling a rough bar by an induction heater moving in the width direction, wherein (a) is a view of the temperature profile in the width direction of a slab, (b) that of a rough bar heated by movement of an induction heater in the width direction, and (c) that of a view of the temperature profile.
  • FIG. 34 is a view of the relationship between a gap and temperature rise when changing a gap distance by tilting a transverse type induction heater.
  • FIG. 35 is a view of an example of arrangement of two tiltable transverse type induction heaters differing in core width on a rolling line.
  • FIG. 36 are views of temperature rise profiles of transverse type induction heaters, wherein (a) is a view of the temperature rise profile of a narrow width transverse type induction heater, (b) is a view of the temperature rise profile of a broad width transverse type induction heater, and (c) is a view of the total temperature rise profile of two transverse type induction heaters .
  • FIG. 37 is a view for explaining a tilter of a transverse type induction heater.
  • FIG. 38 are views for explaining control of the temperature rise in the width direction of transverse type induction heaters
  • (a) is a view of an example of making a plurality of transverse type induction heaters arranged in the width direction raise the temperature
  • (b) is a view of an example of dividing the core of a transverse type induction heater into a plurality of sections in the width direction and making these cores raise the temperature
  • (c) is a view of an example of controlling the heating and temperature rise of a plurality of transverse type induction heaters arranged in the width direction
  • (d) is a view of an example of providing a shield sheet for changing the magnetic flux between the transverse type induction heaters and a rough bar .
  • the inventors conducted various experiments to throw light on the causes and as a result found out that the cause was at the time of heating the slab in the heating furnace.
  • the heated slab 2 becomes the highest temperature part 14 at its periphery, but a low temperature part 13 unavoidably occurs at the center in the width direction including 1/2 width. Further, if measuring the temperature profile at the surface of the roughing mill entry side of the slab, as shown in FIG. 3(b), the temperature becomes lower
  • the temperature profile of the rough bar becomes a lower temperature (1033°C) at the center of 1/2 width of the center line compared with the average temperature in the width direction, a higher temperature (1056°C) between the center and the edges, and a lower temperature (1002°C) toward the edges up to 100 mm from the two edges, thereby resulting in an M-shaped temperature profile.
  • the M-shaped temperature profile is maintained even if the sheet becomes thinner due to the finishing rolling and the center ends up at 842 °C, the intermediate parts at the highest temperatures (865°C), and the edges at 800°C.
  • FIG. 5(a), (b), and (c) The temperature profiles in the width direction of a slab after heating by a heating furnace, a rough bar after rough rolling, and steel sheet at the finishing mill exit side explained above are shown in FIG. 5(a), (b), and (c). In each case, the result was an M-shaped temperature profile in the width direction.
  • the temperature profile at the surface in the width direction of a slab before rough rolling becomes a temperature profile where the temperature of the center of the center line (CL) is 1200 °C and the temperature rises to 1230 °C toward the edges.
  • CL center of the center line
  • FIG. 6(b) If using an edge heater to heat the two edges of the rough bar to compensate for the temperature drop of the two edges of the rough rolled rough bar, as shown in FIG. 6(b), a temperature rise is given at the hatched portions and therefore the temperature at the two edges rises to 1056 °C.
  • the temperature at the center low temperature part (1033°C) does not rise and therefore the temperature profile in the width direction does not become uniform. This state was judged as a uniform temperature profile in the width direction of a rough bar in the past.
  • the temperature profile in the width direction of the hot rolled steel sheet at the finishing mill exit side has a lower temperature at the center (842°C) than the average temperature in the width direction.
  • the temperature profile in the width direction of the slab is shown in FIG. 7(a).
  • the temperature profile in the width direction of a rough bar obtaining by rough rolling a slab of this temperature profile, as shown in FIG. 7(b), has a center low temperature part of 1033°C, a highest temperature of the intermediate parts of 1056 °C, and a temperature of the edges of 1002 °C. If heating this rough bar uniformly in the width direction by a solenoid type induction heater, the center ends up at 1046°C, the intermediate parts at 1069°C, and the edges at 1015°C. In this case as well, however, the temperature profile in the width direction becomes an M-shaped temperature profile.
  • a hot rolled steel sheet having an M-shaped temperature profile in the width direction is obtained.
  • the inventors obtained the new discovery that when hot rolling a slab heated by a heating furnace, with the conventional method of heating the two edges of a rough bar by an edge heater in the middle of rolling or method of heating a rough bar by a solenoid type induction heater to raise its temperature generally uniformly in the width direction, contrary to the conventional thinking, the temperature profile in the width direction of the steel sheet at the finishing mill entry side did not necessarily become uniform and as a result variation occurred in the material properties in the width direction of the hot rolled steel sheet.
  • the temperature rise was changed in the width direction to make the temperature profile in the width direction of the rough bar uniform.
  • the rough bar is heated so that the temperature rise of the center low temperature part of sheet width including 1/2 width becomes at least larger than the temperature rise of the intermediate parts (including 1/4 width and 3/4 width) between the center and the two edges in the width direction and more preferably the low temperature parts of the two edges in the width direction (at least from two ends in width toward the center of the width by 100 mm) are raised in temperature from the intermediate parts of the sheet width so as to make the temperature profile in the width direction of the rough bar uniform.
  • the "center” or “center low temperature part” in the width direction of a rough bar or other rolling material in the present invention means a region at the center of the sheet width including the position of 1/2 width of the low temperature from the highest temperature in the temperature profile in the width direction as explained above.
  • the "intermediate part” in the sheet width means the region, excluding the “center” in the width direction as explained above, including the highest temperature part in the temperature profile in the width direction, and including the position of 1/4 width and 3/4 width.
  • the heater it is possible to use any heater which gives a temperature rise profile in the width direction where the temperature becomes particularly large at the center and becomes smaller toward the ends. It is possible to use gas heaters arranged concentratedly at the center in the width direction or an electric heater which can heat just the center, but the most preferable heating is heating by a transverse type induction heater. That is, a gas heater is inexpensive in capital cost, but scale easily forms on the surface of the rough bar. Further, an electric heater may cause flaws in the rough bar if sparks occur between the rough bar and the electrodes.
  • a transverse induction heater differs from a solenoid type induction heater in that it has the characteristic of being able to heat a rough bar uniformly at a specific portion in the width direction in accordance with the core width, so if arranging a plurality of transverse type induction heaters of narrower widths than the rough bar width along the rolling line and using two or more transverse type induction heaters of narrower widths than the rough bar width together, it is possible to heat a desired specific portion in the width direction.
  • the transverse type induction heater 20 is comprised of a coil 19 wound around a core 18. It is possible to arrange such heaters at positions above and below the steel sheet 18, so they are easy to handle. Since no flaws are caused on the surface of the rough bar and the surface is not overheated, there are no restrictions on the relative arrangement with the roughing mill, descaler, and other facilities.
  • induction heaters and an edge heater are arranged between the roughing mill and finishing mill as shown schematically in FIG. 9(a) so as to form a hot rolling apparatus.
  • An entry side width direction thermometer 22 is placed as a width direction temperature monitor at the entry side of the three transverse induction heaters 23, 24, and 25 narrower in core width than the rough bar width and of substantially the same core widths, while an exit side width direction thermometer 26 is placed at the exit side.
  • a rough bar 4 rolled at the roughing mill is conveyed in the arrow direction by conveyer rolls.
  • the temperature profile in the width direction of the rough bar 4 is measured by the entry side width direction thermometer 22 and the temperature rises of the rough bar due to the heating by the transverse type induction heaters 23, 24, and 25 are determined by the temperature rise controller based on the temperature profile in the width direction.
  • the rough bar is heated by the transverse type induction heater 23 near the center low temperature part, then is heated at the intermediate part near 1/4 width, including the center, by the transverse type induction heater 24, then is heated at the intermediate part near 3/4 width, including the center, by the transverse type induction heater 25.
  • the two edge low temperature parts of the rough bar are heated and raised in temperature by an edge heater 6 (to become larger than the temperature rise of the intermediate parts in the width direction).
  • the amounts of heating and temperature rise are controlled by the temperature rise controller.
  • the temperature profile in the width direction of the rough bar after heating is measured by the exit side width direction thermometer 26.
  • the measurement data is fed back to the temperature rise controller of the transverse type induction heater 23 and edge heater 6. The controller then controls the heaters to change the outputs of the temperature rises to make the temperature profile in the width direction of the rough bar uniform.
  • the temperature difference in the temperature profile in the width direction is not more than 10°C, preferably not more than 5°C.
  • the plurality of induction heaters do not necessarily have to be the same in core widths. They may be suitably changed in accordance with the temperature profile in the width direction. For example, as shown in FIG. 9(b), instead of the induction heaters 24 and 25 of FIG. 9(a), it is also possible to provide an inductor heater 27 and induction heater 23 having two times the core widths of the induction heaters 24 and 25.
  • the plurality of transverse type induction heaters and edge heater are not necessarily limited to the order of arrangement shown in FIG. 9(a) and (b), but if considering the overall temperature controllability, close positions are preferable.
  • thermometer it is preferable to provide a width direction thermometer as explained above near the transverse type induction heaters as a temperature monitor, but it is also possible to provide a device for monitoring the temperature profile in the width direction at the entry side of the transverse type induction heaters by numerical computation based on the internal temperature of the heating furnace, the slab temperature at the exit side of the heating furnace, and other measured temperatures and the rough bar conveyance conditions up to near the induction heaters (rough rolling conditions, conveyance speed, time from heating furnace to induction heaters, etc.) Alternatively, it is possible to provide a width direction thermometer at the finishing mill exit side to monitor the temperature profile in the width direction of the entry side of the transverse type induction heaters.
  • FIG. 10(a) to (c) show the temperature profile of a rough bar 4 due to heating in the case of using three heaters 23, 24, and 25 of similar core widths.
  • FIG. 10 is an example of the case of raising the temperature of the rough bar uniformly by a maximum 40 °C corresponding to the core widths of the heaters . Note that away from the core width, the temperature rise gradually fell.
  • the temperature profile resulting from the three transverse type induction heaters becomes a total of the three temperature rises, so as shown in FIG. 10(d), the temperature rises 28, 29, and 30 of the heaters 23, 24 and 25 are overlaid resulting in a smooth peak-shaped temperature rise profile changed in temperature rise in the width direction.
  • a rough bar having an M-shaped temperature profile where the lowest temperature at the center is 1060 °C and the highest temperature at the intermediate parts is 1100 °C can be given a uniform temperature profile with a temperature at the center in the width direction of 1100°C due to the total temperature rise (40°C) shown in FIG. 10(e) of the three transverse type induction heaters. Further, the two edges are heated by the edge heater, so are raised in temperature by the temperature rise 16 of the edge heater. As a result, the temperature difference in the width direction of the rough bar is made uniform down to not more than 5°C. Due to this, it is possible to keep down the difference in material properties obtained (for example, the tensile strength TS) to not more than 5%.
  • the tensile strength TS for example, the tensile strength
  • the core width of the transverse type induction heater with the narrowest width used in the present invention is preferably within the range of 400 to 700 mm.
  • the typical sheet width of a hot rolled steel sheet is 550 to 800 mm, so to keep down the edge heating and heat the center, a transverse type induction heater of a width narrower by this by 100 to 150 mm becomes necessary.
  • Second Embodiment Further, the inventors discovered that if finishing rolling to give a temperature difference in the width direction of the steel sheet before finishing rolling to produce a tailored steel sheet having properties different in the width direction of steel strip, in particular different properties of the hole expanding property and elongation property, by hot rolling, the hole expanding property of the steel sheet is effectively improved by the hot finishing temperature.
  • the part when applying 590 MPa class high tensile steel strip comprised of 0.09 to 0.11% of C, 1.30 to 1.50% of Si, 1.25 to 1.45% of Mn, not more than 0.010% of P, and not more than 0.002% of S to a cross member or other automobile part, the part is taken in the width direction of the steel strip. From the shape of the part, the main processing is hole expanding forming near the center of the coil width and punch stretch forming at the 1/4 width to full width edge of the steel strip.
  • FIG. 11(a) is a view of the relationship between the hot finishing temperature (°C) and hole expansion rate (%) of 590 MPa class high tensile steel strip
  • FIG. 11(b) is a view of the relationship between the hot finishing temperature (°C) and elongation EL (%) of 590 Mpa class high tensile steel strip.
  • the hole expansion rate of the steel strip is improved along with the rise in the hot finishing temperature, but as shown in FIG. 11(b), the elongation of the steel strip is lowered along with the rise in the hot finishing temperature. That is, the hole expanding property and the elongation property exhibit opposite trends with respect to the hot finishing temperature.
  • the present invention by designating as hot finishing conditions ones for heating the center of the width of the steel strip by at least 20 °C so as to make the hot finishing temperature in the width direction of the steel strip different, obtain a hot finishing temperature of at least 870 °C near the center of the width of the steel strip, and obtain a hot finishing temperature of not more than 860 °C at the 1/4 width to full width edge of the steel strip, it was learned that it is possible to easily produce a "tailored steel strip" differing in mechanical properties in the width direction so as to have an over 70% hole enlargement rate near the center of the width of the steel strip and have an over 31% elongation rate at the 1/4 width to full width edge of the steel strip.
  • the inventors engaged in intensive research on a method and apparatus for heating steel sheet able to freely control the temperature profile in the width direction of the steel sheet and discovered that by arranging a plurality of bar heaters comprised of transverse type induction heaters in the longitudinal direction of the steel sheet (rolling line), shifting the bar heaters in the width direction to control the overlapping portions of the bar heaters in the longitudinal direction of the steel sheet, and operating the bar heaters to heat the sheet, it is possible to freely control the temperature profile in the width direction.
  • FIG. 12(a) is a view of the arrangement of one bar heater in the width direction of the steel sheet and its temperature rise
  • FIGS. 12(c) to (e) are views of the temperature rises in the width direction of the steel sheet when arranging three bar heaters in the longitudinal direction of the steel sheet and shifting the bar heaters by predetermined amounts in the width direction.
  • the temperature rise profile 23 in the width direction of the steel sheet becomes a peak-shaped temperature rise profile corresponding to the width of the bar heater (core width) . If arranging three bar heaters having such a temperature rise property in the longitudinal direction of the steel sheet and shifting the bar heaters in the width direction of the steel sheet by predetermined amounts (using the center in the width direction as the reference point for the amount of shift and including also the case of zero shift), for example, FIG.
  • FIG. 12(b) shows the example of the case where the amount of shift is zero, the three bar heaters completely overlap, and therefore the temperature rises of the three bar heaters are added and the temperature rise profile at the center in the width direction of the steel sheet is high as shown by the bottom part of the figure
  • FIG. 12(c) shows the example of the case of not shifting the bar heater at the center, shifting the two upstream side and downstream side bar heaters in the opposite directions, and thereby somewhat reducing the overlapping portions of the bar heaters and therefore the temperature rises of the three heaters are added in states shifted in accordance with the amount of shift and the temperature rise profile becomes a peak-shaped one broad in the width direction of the steel sheet as shown by the bottom part of the figure
  • FIG. 12(d) shows the example of the case of making the amounts of shift of the two upstream side and downstream side bar heaters greater than in FIG. 12(c) and thereby further reducing the overlapping portions of the bar heaters and therefore the temperature rise profile of the three bar heaters becoming a peak- shaped one broader than FIG. 12(c).
  • FIG. 12(e) shows an example of the case of moving the bar heaters to certain intervals in the width direction as a whole to eliminate the overlapping parts of the bar heaters and heat the entire width and thereby the temperature rise profile becoming a peak-shaped one broader than FIG. 12(c) .
  • the bar heater shifted is not limited to the downstream side one. It is possible to shift any bar heaters to achieve similar temperature rise profiles.
  • the example of three bar heaters was shown, but if further increasing the number of bar heaters, it is possible to raise the total temperature rise and possible to precisely control the temperature rise profile in the width direction of the steel sheet. That is, since it is possible to shift a plurality of (two or more) bar heaters in the width direction of the steel sheet and by shifting change the profile of the load of the temperature rise of the steel sheet in the width direction, it is possible to raise the temperature of any region in the width direction of the steel sheet and possible to control the temperature profile in the width direction. Further, the bar heaters can be shifted during hot rolling. Further, the bar heaters can be used combining bar heaters of the same width and/or different widths.
  • the plurality of bar heaters can be changed independently in amounts of heating of the bar heaters or core distances in coil and thereby further improve the controllability of the temperature. For example, an example of reducing the temperature difference in the width direction using three bar heaters of equal width when the temperature at the center of the steel sheet (rough bar) is low will be explained.
  • the temperature profile in the width direction of a 1500 mm width rough bar becomes an M-shape 40 °C lower at the center (shown by dotted line) . Therefore, to raise the temperature of the center of the steel sheet by 40 °C in an upside down M-shape and make the temperature profile in the width direction uniform, three bar heaters are used to heat and raise its temperature (hatched region is temperature rise).
  • the total temperature rise of the three bar heaters (shown by solid line) has to be a gentle peak-shaped temperature rise profile (upside down M-shape) with a center 40 °C higher.
  • the three bar heaters are made ones the same in core distances and temperature rises.
  • the position 600 mm to 900 mm in distance in the width direction is the portion where the cores of all of the No. 1 to 3 bar heaters overlap
  • the position 450 mm to 600 mm in distance in the width direction is the portion where the cores of the two No.
  • the position 750 mm to 900 mm in distance in the width direction (+150 mm to +300 mm about center in width direction) is the portion where the cores of the two No. 2 and 3 bar heaters overlap.
  • the temperature rise profiles of the bar heaters (No. 1 to No. 3) form a gentle peak shape.
  • the total temperature rise of the three becomes a peak-shaped temperature rise profile higher by 40 °C at the center.
  • the method of determining the temperature rises of the steel sheet is to store heating profiles in the width direction of the bar heaters in a computer by widths of the steel sheet (rough bar), by shifts of the bar heaters, and by temperature rises of the bar heaters, monitor the temperature profile in the width direction of the steel sheet by a width direction thermometer arranged at the upstream side of the bar heaters, select the closest shifts and temperature rises so as to heat the differences in profiles of the temperature profile in the width direction desired, and instruct this to an electric sequencer to set the bar heater shifts (overlapping portions of bar heaters) and heating. Due to this, it becomes possible to raise the temperature of any region in the width direction of the steel sheet by a predetermined amount.
  • two transverse type induction heaters 2 of different core widths that is, a transverse type induction heater 23 having a core width greater than the width of the rough bar 4 and a transverse type induction heater 24 having a core width narrower than the width of the rough bar, and an edge heater 6 were arranged to make a hot rolling apparatus .
  • An entry side width direction thermometer 22 was placed at the entry side of the two transverse type induction heaters with different core widths and an exit side width direction thermometer 25 at the exit side.
  • a rough bar 4 rolled by a roughing mill was conveyed in the arrow direction by conveyor rolls.
  • the temperature profile in the width direction of the rough bar 4 was measured by the entry side width direction thermometer 22, then the temperature rise of the rough bar by the heating by the transverse type induction heaters 23, 24 was determined by the temperature rise controller based on the temperature profile in the width direction. Further, the rough bar was heated over its entire width by the broad width transverse type induction heater 23, but in particular the two end low temperature parts were heated to raise them in temperature, then just the center low temperature part was heated by the narrow width transverse type induction heater 24.
  • the two low temperature parts of the rough bar are insufficiently raised in temperature by the broad width transverse type induction heater, they are in accordance with need additionally heated to be raised in temperature by the edge heater 6.
  • the temperature profile in the width direction of the rough bar after heating is measured by the exit side width direction thermometer 25.
  • the measurement data is fed back to the temperature rise controller of the transverse type induction heater. The controller then controls the heaters to change the outputs of the temperature rises to make the temperature profile in the width direction of the rough bar uniform.
  • the temperature difference in the temperature profile in the width direction is not more than 10 °C, preferably not more than 5°C.
  • the narrow width and broad width transverse type induction heaters and edge heater do not have to be limited to the order of arrangement, but if considering the overall temperature controllability, close positions are preferable.
  • thermometer as explained above near the transverse type induction heater as a temperature monitor
  • a device for monitoring the temperature profile in the width direction at the entry side of the transverse type induction heater by numerical computation based on the internal temperature of the heating furnace, the slab temperature at the exit side of the heating furnace, and other measured temperatures and the rough bar conveyance conditions up to near the induction heater (rough rolling conditions, conveyance speed, time from heating furnace to induction heater, etc.)
  • FIG. 19(a) and (b) schematically show the temperature profile of a rough bar due to heating by transverse type induction heaters of different widths.
  • (a) shows the temperature profile for a temperature rise 26 of a narrow width- transverse type induction heater using a transverse type induction heater 24 having a core width narrower than the width of the rough bar shown in FIG. 18, while
  • (b) shows the temperature profile for a temperature rise 26 of a broad width transverse type induction heater using a transverse type induction heater 23 having a core width broader than the width of the rough bar shown in FIG. 18.
  • the transverse type induction heater 24 with the narrow core width raises the temperature of the center of the rough bar uniformly by a maximum of 40 °C in accordance with the core width. Further, outside of the core width, since the temperature rises due to heat conduction, the temperature rise gradually falls, thereby resulting in a smooth peak- shaped temperature rise profile.
  • the transverse type induction heater 23 with the core width broader than the rough bar can raise the temperature of the entire width of the rough bar by a maximum of 40 °C and can raise the temperature of the two edges about 150 mm by a maximum of 150 °C in view of the property that the current at the two edges of the rough bar becomes greater.
  • the temperature profile of the width direction of the rough bar is made uniform. Further, by arranging a large number of transverse type induction heaters of different widths along the rolling line and using these together, it becomes possible to finely adjust the temperature rise profile of the rough bar. Further, by changing the outputs of the transverse type induction heaters, it is possible to change the amount of heating and temperature rise.
  • the temperature rise 16 of the edges of the rough bar due to the edge heater can raise the temperature at the two edges by a maximum of 150 °C if using an edge heater able to heat at least 150 mm of the edges. Therefore, if the amount of heating and temperature rise of the two edges due to the broad width transverse type induction heater is insufficient, it is preferable to additionally compensate and raise the temperature of the two edges by the above edge heater.
  • the core, width of the transverse type induction heater with the narrowest width used in the present invention is preferably made one within the range of 400 to 700 mm. The reason is that the typical sheet width of a hot rolled steel sheet is 550 to 800 mm, so to keep down the edge heating and heat the center, a transverse type induction heater of a width narrower by this by 100 to 150 mm becomes necessary.
  • the core width of the broad width transverse type induction heater is made one within the range of 800 to 2500 mm, preferably 800 to 2000 mm.
  • edge heating requires a core width of the same width to 500 mm wider width than the sheet, so to heat steel sheet of the typical smallest width of hot rolled steel sheet, that is, 550 to 800 mm, an 800 mm width or so transverse type induction heater is preferable, while to heat typical hot rolled steel sheet, that is, steel sheet of 1500 to 2000 mm width, a 2500 mm width or so transverse type induction heater is preferable.
  • a transverse system was difficult to use as the device for heating the entire width of a rough bar.
  • the coil 232 is arranged so as to circle the rough bar 201 and the core 233 is arranged above and below the rough bar 201.
  • the present invention employs a transverse type induction heater 204 having such a difficulty as a heater for inductively heating the entire width direction of a rough bar 201 so as to be able to sufficiently raise the temperature of the temperature drop part of the frontmost end and tailmost end of the rough bar 201 and enable the removal of only the shape defects as cropped pieces.
  • the induction current 222 flows across the wide range of the rough bar 201 and the longitudinal direction of the rough bar can be uniformly heated.
  • the front and tail ends in the longitudinal direction of the rough bar pass through the heater, for example, as shown in FIG.
  • the induction current 222 concentratedly flows near the frontmost end 223 and as a result the temperature rise of the frontmost end 223 (and tailmost end) of the rough bar 1 arising due to the induction current 222 greatly increases.
  • the temperature rise increase in the range of about 100 mm from the frontmost end 223 (or tailmost end) of the rough bar and it is possible to obtain a temperature rise of over 200°C at the frontmost part 223 (or tailmost part).
  • the transverse type induction heater 4 for induction heating of the entire width direction of the rough bar 201, so when heating the front and tail ends of the rough bar 201, it is not necessary to stop the rough bar 201, By passing the ends through at a constant speed similar to the steady state part of the rough bar 201, it is possible to obtain a large temperature rise at the front and tail ends as explained above.
  • a roughing mill 201 and finishing mill 2 between which are consecutively arranged a transverse type induction heater 4 for induction heating of the entire width direction of the rough bar 201 and a shear 208 able to crop the front and tail ends in the longitudinal direction of the rough bar.
  • a shear 208 normally a crop shear is used.
  • the front and tail ends of the rough bar after completion of rough rolling are first heated by the induction heater 204, then cropped by the shear 208.
  • the heating furnace 207 is arranged before the roughing mill 201, and a coiler 209 is arranged after the finishing mill 203.
  • the arrangement of the hot rolling facilities of the present invention in a second embodiment, as shown in FIG. 24(b), comprises a roughing mill 201 and finishing mill 203 between which are consecutively arranged a shear 208 able to crop the front and tail ends in the longitudinal direction of the rough bar and a transverse type induction heater 204 for induction heating of the entire width direction of the rough bar.
  • a shear 208 normally a crop shear is used.
  • the front and tail ends of the rough bar after completion of rough rolling are first cropped by the shear 208, then heated by the induction heater 204.
  • the temperature rise of the rough bar 201 passing through the transverse type induction heater 204 becomes highest at the frontmost end and tailmost end in the longitudinal direction. Therefore, if heating after cropping off the front and tail ends, it is possible to very effectively use portions with the highest temperature rises as the non- cropped steady state part.
  • the second embodiment since the bar is not cropped during the induction heating, when the temperature drop at the frontmost end or tailmost end of the rough bar is large, the temperature drop sometimes cannot be sufficiently compensated for by the induction heating.
  • the second embodiment since the bar is cropped at the optimum positions and then induction heated, it is possible to crop the bar at the optimal positions of temperature drop parts for the front and tail end heading ability of the induction heater and as a result sometimes the second embodiment can reduce the amount of cropping compared with the first embodiment.
  • the tenacity of the product can be improved by the finer structure, so when the increase in thickness of the rough bar is restricted by the allowable shearing torque of the shear, the bar is cropped in the high temperature state as the first embodiment so as to improve the allowable ability of the shearing torque of the shear relatively and improve the tenacity of the product more by reduction of the deformation resistance due to the higher temperature.
  • a hot rolling facility having an arrangement of hot rolling facilities of the first or second embodiment is used and at least a portion of not more ' than 1 m from the end is heated at one or both of the front and tail ends of the rough bar by the transverse type induction heater. If induction heating the portion of not more than 1 m from the end, the temperature drop parts of the front and tail ends can be sufficiently heated and raised in temperature and the amount of cropping can be reduced.
  • the "end" of the front and tail ends of the rough bar means the fishtail valley 216 of the shape defect 215 (fishtail) shown in FIG. 27, that is, the position of the reference point 17.
  • the hot rolling method of the present invention it is possible to heat in this way so as to raise the temperature of the temperature drop parts .at one or both of the front and tail ends of the rough bar by heating and thereby reduce the amount of cropping of the rough bar.
  • FIG. 27(a) showing the vicinity of the front end 213 of the rough bar 201, the bar was cropped at the conventional shearing position 219.
  • the cropping position at the tail end of the rough bar differs depending on the thickness of the hot rolled coil after finishing rolling.
  • a thin material with a coil thickness of not more than 3 mm is cropped at the temperature drop part in addition to the shape defect, while a thick material of a coil thickness of over 3 mm is cropped at a position inside the shape defect regardless of the state of temperature drop of the tail end. That is, in FIG. 27(b) showing the vicinity of the tail end 214 of the rough bar 201, the thin material is cropped at the conventional cropping position 219a, while the thick material is cropped at the conventional cropping position 219b.
  • the shape defect is drawn 10- to 20-fold in the rolling direction in accordance with a predetermined reduction rate and therefore the for example fishtail shaped non-steady state portion is rolled spanning a plurality of stands.
  • the coil is thin, the tailmost end not constrained by the difference in rolling pressure profile resulting from the uneven temperature profile in the width direction experiences rotational moment and snakes in the width direction to contact the side guides and be folded back, that is, so-called "tail pinching" occurs.
  • the shape defect will break. This leads to line stoppage for replacement of the work roll and therefore obstructs the productivity. Therefore, there is a large risk in leaving behind a shape defect.
  • the band will sometimes be loosened or broken by the remaining fishtail part during coil transport. It is preferable to attach a plurality of bands or adjust the band in the width direction of the product so that it does not cross with the remaining fishtail.
  • the reduction in the amount of cropping of the rough bar in the hot rolling method of the present invention covers one or both of the front end 213 of the rough bar and the tail end 214 in the case of a coil thickness of not more than 3 mm after finishing rolling.
  • the transverse type induction heaters 204 for induction heating of the entire width direction of the rough bar used in the present invention it is preferable to use ones of a type having as the core 205 a U-shaped core 5 having two vertical parts 211 and one horizontal part 212, directing the two vertical parts 211 to the surface of the rough bar 201, making the width of the core 5 a width covering the entire width of the rough bar 1, arranging the U-shaped core (205a, 205b) facing the upper surface or bottom surface of the rough bar 201, and arranging the coil 6 to surround the vertical parts (211a, 211b).
  • the coil 6 surrounding the vertical parts 211 generate a magnetic field.
  • This magnetic field is formed in the two facing U-shaped cores to form a loop magnetic field. Since the end faces of the vertical parts 211 of the cores face each other, a magnetic field is generated between the two end faces and the rough bar 1 is arranged between the two end faces , the magnetic field is formed vertically at the surface of the rough bar. Since the core 205 has a width to cover the substantially entire width of the bar 201, a magnetic field vertical to the rough bar 201 is formed over the substantially entire width of the cover 201. By passing an AC current to the coil 206 surrounding the core 205, the magnetic field passing through the rough bar 201 becomes an AC magnetic field and an eddy current is formed as the induction current in the rough bar.
  • the relationship between the width of the rough bar heated and the width W of the core 205 is preferably one where the width of the rough bar is broader than the core width W.
  • a transverse type induction heater With a transverse type induction heater, the edges of the rough bar being heated (ends in width direction) are liable to be overheated, but by making the core width W narrower than the width of the rough bar, the occurrence of overcurrent at the edges can be suppressed and overheating of the edges can be suppressed. Due to this, it is possible to uniformly heat the entire width of the rough bar.
  • the heating and temperature raising ability of the rough bar changes in accordance with the gap between the cores arranged facing the top surface and bottom surface of the rough bar.
  • the narrower the gap between the cores the greater the temperature rise of the rough bar due to the heating. Therefore, normally, the gap between the cores is set as narrow as possible.
  • the front end 213 of the rough bar has a warped shape. If the core gap of the induction heaters 204 is narrow, the front end of the warped rough bar cannot enter the gap of the cores and collision may occur. Therefore, when the front end 213 of the rough bar enters the induction heater 204, the core gap is enlarged. After the front end enters, the core gap is narrowed to increase the heating and temperature raising ability.
  • the core gap is large at the time of passage of the front end 213 of the rough bar, so the heating and temperature raising ability of the induction heater is low, while the core gap is narrow at the time of passage of the tail end 214 of the rough bar, so the heating and temperature raising ability of the induction heater is high.
  • the core gap at the time of- the tail end of the rough bar passes is 130 mm and the heating and temperature raising ability of the tailmost end is 500°C
  • the core gap at the time of passage of the front end of the rough bar is enlarged to 340 mm and as a result the heating and temperature raising ability at the frontmost end becomes 250 °C.
  • each induction heater may be given a medium capacity to secure the overall required capacity.
  • a large capacity induction heater was hard to fabricate, but by arranging a plurality of medium capacity heaters, it is possible to solve this problem.
  • hot rolling there are numerous widths of rough bars from broad to narrow.
  • the oscillation frequency of the transverse type induction heater is preferably made about 100 to 500 Hz.
  • a solenoid induction heater uses a frequency of about 1500 Hz, but it is preferable to increase the depth of penetration of the heat and to prevent breakdown due to the local heat buildup of its own components by making the frequency 100 to 500 Hz or so in the transverse type induction heater.
  • the inventors conducted various experiments to find the reasons for this and as a result found that the cause was at the time of slab heating in the heating furnace.
  • a slab is heated and raised in temperature in the high temperature atmosphere of the heating furnace in the preheating zone 313 and heating zone 314 in the arrow direction from the loading side and is taken out after being made a predetermined temperature at a soaking zone 315.
  • This slab heating results in small heating at the loading side end A in the width direction of the slab in the heating furnace and large heating at the unloading side end B.
  • the heated slab becomes higher in temperature at the loading side end A than the unloading side end B. Therefore, the temperatures at the left and right in the width direction of the heated slab sometimes feature a difference of about 20 °C. Further, as shown in FIG.
  • the heated slab 2 has the high temperature part 316 at its periphery, but unavoidably suffers from a low temperature part 317 at its center. Further, if measuring the temperature profile of the slab at the roughing mill entry side, as shown in FIG. 31(b), a left- right asymmetric temperature profile occurs in the width direction where the center of the center line (CL) becomes lower (1200°C) than the average temperature in the width direction and becomes higher (1240°C and 1220 °C) toward the edges.
  • the temperature profile of the rough bar becomes a lower temperature (1033°C) at the center line compared with the average temperature in the width direction, a higher temperature (1063°C and 1049 °C) between the center and the end parts, and a lower temperature toward the end parts, thereby resulting in an M-shaped temperature profile. If finishing rolling a rough bar with such a temperature profile, as shown in FIG. 32(a), since the two edges of the rough bar are the portions 18 of large natural cooling, the temperature profile of the rough bar, as shown in FIG. 32(b), becomes a lower temperature (1033°C) at the center line compared with the average temperature in the width direction, a higher temperature (1063°C and 1049 °C) between the center and the end parts, and a lower temperature toward the end parts, thereby resulting in an M-shaped temperature profile. If finishing rolling a rough bar with such a temperature profile, as shown in FIG.
  • the M-shaped temperature profile is maintained even if the sheet becomes thinner due to the finishing rolling, the center ends up at 842 °C, the intermediate part at the left side becomes the highest temperatures (872°C), and the intermediate part at the right side becomes 858°C.
  • the temperature profile in the width direction of the slab unloaded from the heating furnace is shown in FIG. 33(a).
  • the temperature profile in the width direction of a rough bar obtained by rough rolling a slab of this temperature profile features a center low temperature part of 1033 °C and a highest temperature at the intermediate part at the left side of 1063 °C. If heating this rough bar by moving the induction heater in the width direction, the overall temperature rises by exactly the temperature rise 19 shown by the hatching, the center becomes 1063°C, the left side intermediate part becomes 1083 °C, and the right side intermediate part becomes 1069 °C. However, in this case as well, the temperature profile in the width direction becomes the M-shaped temperature profile. Therefore, if moving the induction heater and rolling the rough bar heated overall in the width direction by a finishing mill, as shown in FIG. 33(c), a hot rolled steel sheet having an M-shaped temperature profile in the width direction is obtained.
  • the inventors obtained the new discovery that when hot rolling a slab heated by a heating furnace, with the method of heating the two ends of the rough bar by an edge heater in the middle of rolling as in the past or the method of heating the rough bar by tilting an induction heater in the width direction, contrary to the previous thinking, the temperature profile in the width direction of the steel sheet after finishing rolling does not become uniform. Further, they found the fact that the lack of uniformity in the temperature profile in the width direction of the rough bar due to the three factors of the center low temperature part of the slab heated by the heating furnace, the asymmetry of the temperature profile in the width direction, and the air cooling of the edges at the time of rolling is a major cause of variation in the material properties in the width direction of the steel sheet.
  • the center low temperature part and the two end low temperature parts of the rough bar are heated by the transverse type induction heater to make the temperature profile in the width direction of the rough bar at the finishing mill entry side uniform, but at this time the asymmetry of the temperature profile in the width direction is eliminated by tilting the transverse type induction heater to heat and raise the temperature and in accordance with need additionally compensating and raising the temperature of the two end low temperature parts by an edge heater so as to make the temperature profile in the width direction of the rough bar uniform.
  • a transverse type induction heater differs from a solenoid induction heater and has the property of being able to uniformly heat a specific portion in the width direction of a rough bar corresponding to the core width. That is, a transverse type induction heater with a core width narrower than the width of the steel sheet has the feature of being able to heat the center of the steel sheet corresponding to the core width. Further, a transverse type induction heater with a core width broader than the width of the steel sheet can heat the entire width of the steel sheet and has the feature of being able to heat by a larger temperature rise at the ends than at the center.
  • a transverse type induction heater features the fact that the temperature rise is theoretically substantially inversely proportional to the gap between the core and the steel sheet. That is, as shown in FIG.
  • the gap between the core of the transverse type induction heater and the steel sheet changes and the temperature rise changes.
  • FIG. 34(b) an example of the temperature rise characteristic of a transverse type induction heater in the case of an output of 20 MW of the transverse type induction heater at the position shown by the solid line in FIG. 34(a) is shown in FIG. 34(b).
  • transverse type induction heaters 20 comprised of cores 18 provided with coils 19 are used arranged at positions above and below the steel sheet (rough bar) 21 so are easy to handle. No flaws are caused on the surface of the rough bar, the surface is not overheated due to the properties, and the distance from the roughing mills, descaler, and other facilities is not limited.
  • two different width transverse type induction heaters that is, a transverse type induction heater 24 with a core width broader than the rough bar and a transverse type induction heater 324 with a core width narrower than the rough bar, are arranged tiltably in the width direction of the steel sheet and an edge heater 306 is arranged, thereby forming a hot rolling apparatus.
  • An entry side width direction thermometer 26 is placed at the entry side of the two transverse induction heaters with different core widths, while an exit side width direction thermometer 327 is placed at the exit side.
  • a rough bar 304 rolled at the roughing mill is conveyed in the arrow direction by a table roll.
  • the temperature profile in the width direction of the rough bar 4 is measured by the entry side width direction thermometer 326, while the temperature rises of the rough bar due to the heating by the transverse type induction heaters 324 and 325 are determined based on the temperature profile in the width direction. Further, the transverse type induction heaters are tilted so as to give a predetermined gap distance.
  • the rough bar is heated at just the center low temperature part by the narrow width transverse type induction heater 324, then is heated over its entire width by the broad width transverse type induction heater 325, but in particular the two end low temperature parts are heated and raised in temperature. Further, when the two end low temperature parts of the rough bar are insufficiently raised in temperature due to the broad width transverse induction heating, they are additionally heated and raised in temperature by the edge heater 306 in accordance with need.
  • the temperature profile in the width direction of the rough bar after heating is measured by the exit side width direction thermometer 327. When the temperature profile in the width direction as measured by the exit side width direction thermometer 327 is not uniform, the measurement data is fed back to the temperature rise controller of the transverse type induction heater. The controller then controls the heaters to change the outputs of the temperature rises to make the temperature profile in the width direction of the rough bar uniform.
  • the temperature rise characteristic of the transverse type induction heater is explained based on FIG. 36.
  • FIG. 36(a) and (b) show the temperature rise profile of the rough bar due to heating by different width transverse type induction heaters, (a) shows the temperature rise at the time of parallel posture (solid line) and tilted posture (broken line) due to the transverse type induction heater 324 of a core width narrower than the width of the rough bar shown in FIG. 9, while (b) shows the temperature rise at the time of parallel posture (solid line) and tilted posture (broken line) due to the transverse type induction heater 325 of a core width broader than the width of the rough bar shown in FIG. 35.
  • the transverse type induction heater 324 with a narrow core width can raise the temperature of the center of the rough bar by a maximum of 40°C corresponding to the core width when parallel at a gap of 200 mm and can raise the temperature by a maximum 53°C when tilted. Further, outside of the • core width, since the temperature is raised by heat conduction, the temperature rise gradually falls resulting in a smooth peak-shaped temperature rise profile.
  • the transverse type induction heater 325 with the core width of at least the width of the rough bar can raise the temperature of the center of the entire width of the rough bar by 40 °C, can raise the temperature of approximately 150 mm widths at the two ends by about 150°C when the gap is 200 mm in view of the property that the current at the two ends of the rough bar becomes greater, and can raise the temperature by a maximum of 200 °C at the left end and can raise the temperature by 120 °C when tilted so that the right side gap becomes 250 mm and the left side gap becomes 150 mm.
  • the temperature profile in the width direction of the rough bar is made uniform by the total temperature rise of the two different width transverse type induction heaters 324 and 325. Further, by arranging a plurality of transverse type induction heaters along the rolling line and using these together, it becomes possible to finely adjust the temperature rise profile of the rough bar.
  • the core width of the transverse type induction heater with the narrowest width used in the present invention is preferably made one within the range of 400 to 700 mm.
  • the typical sheet width of a hot rolled steel sheet is 550 to 800 mm, so to keep down the edge heating and heat the center, a transverse type induction heater of a width narrower by this by 100 to 150 mm becomes necessary.
  • the core width of the broad width transverse type induction heater is made one within the range of 1000 to 2000 mm. The reason is that edge heating requires a core width the same or greater than the 1000 to 2000 mm width of an ordinary hot rolled steel sheet.
  • the tilter for tilting the transverse type induction heater of the present invention is provided with a shaft 329 able to tilt a transverse type induction heater 320 suspended by a support 328 as shown in for example FIG. 37(a) and is provided with an elevator 330 at the end of the transverse type induction heater.
  • a shaft 329 able to tilt a transverse type induction heater 320 suspended by a support 328 as shown in for example FIG. 37(a) and is provided with an elevator 330 at the end of the transverse type induction heater.
  • it elevates or lowers the end of the transverse type induction heater by the elevator 330 it can tilt the transverse type induction heater by making it pivot around the shaft 329. Further, if fixing the shaft and making the heater pivot mechanically or electrically, it is possible to tilt the heater even by holding it by the elevator at one end.
  • transverse type induction heater 320 it is possible to support the two ends of the transverse type induction heater 320 by two elevators 330 and raise and lower the ends by the elevators 330 so as to tilt the transverse type induction heater.
  • the transverse type induction heater arranged under the sheet can also be tilted by a similar mechanism.
  • transverse type induction heaters provided with individually elevatable cores obtained by dividing their cores into pluralities of sections in the width direction and facing each other above and below the rough bar and raising and lowering those cores. That is, by using an elevator 333 to raise and lower individually elevatable cores obtained by dividing the core 322 into a plurality of sections in the width direction as shown in FIG. 38(b), it is possible to control the gaps of the cores and thereby control the amounts of heating and temperature rise in the width direction.
  • elevators 330, 331 it is possible to use generally used ones such as oil hydraulic, pneumatic, or other piston mechanism elevators, crank mechanism elevators, elevators using electric motors, etc .
  • a shield sheet 32 for changing (reducing) the magnetic flux between the transverse type induction heaters and rough bar so as to control the amount of heating and temperature rise of the transverse type induction heaters and thereby obtain a similar effect.
  • a shield sheet 332 is inserted into and retracted from between the upper and lower heaters in the longitudinal direction of the rough bar 304 (direction opposite to rolling) to block and change the magnetic flux, but it is also possible to insert and retract the shield sheet 332 in the width direction of the rough bar.
  • the remarkable effects arise that it is possible to make the temperature profile in the width direction of the rough bar, which had an uneven temperature profile in the width direction before finishing rolling, uniform and possible to obtain a hot rolled steel sheet free from variations in mechanical properties or other material properties in the width direction due to the finishing rolling.
  • the remarkable effects arise that it is possible to eliminate the left-right asymmetric temperature profile in the width direction of the rough bar before finishing rolling using a transverse type induction heater and possible to selectively heat and raise the temperature of the center low temperature part and two end low temperature parts, so it is possible to make the temperature profile in the width direction uniform.
  • the inventors roughly rolled a slab of a thickness of 250 mm and a width of 1250 mm heated in a heating furnace to 1200 °C by a roughing mill to a rough bar of a thickness of 30 mm.
  • the inventors heated the rough bar by three transverse type induction heaters shown in FIG. 9(a) having widths narrower than the rough bar so that the temperature rise at the center became the largest and concentratedly heated the edges by an edge heater.
  • the inventors finishing rolled the bar by a finishing mill to produce hot rolled steel sheet of a thickness of 2 mm and a width of 1250 mm.
  • the finishing rolling speed at this time was 1000 mpm.
  • To secure the target temperature of 860 °C at the exit side of the finishing mill it is necessary to make the temperature at the finishing mill entry side 1100 °C.
  • the temperature profile of the finishing mill entry side changes due to the temperature profile in the width direction and the temperature drop due to the thermal rundown in the coil longitudinal ' direction. This is compensated for by the three heaters and the edge heater.
  • the steel sheet has a temperature profile before heating as measured by an entry side width direction thermometer of 1080 °C at the center, 1100 °C at the highest point of the intermediate parts, and 1040 °C at the coolest points at the edges.
  • the three transverse type induction heaters are used to heat by a total maximum 20°C at up to 1/2 of the center to reduce the temperature rise at the intermediate parts from the center to the edges due to the center and eliminate the temperature difference of the center. Further, the edge heater is used to concentratedly raise the temperature of the edges by 60 °C. Due to this, the difference in the temperature profile in the width direction before rolling is reduced to 3°C and as a result steel sheet with small variation in material (strength) in the width direction and longitudinal direction is obtained.
  • the hot rolling method of the present invention the remarkable effects arise that it is possible to obtain a uniform temperature profile in the width direction of the rough bar before finishing rolling and it is possible to obtain a hot rolled steel sheet free from variations in mechanical properties and other material properties in the width direction by finishing rolling. Further, according to the hot rolling apparatus of the present invention, it is possible to selectively heat and raise in temperature the center low temperature part of a rough bar before finishing rolling, so the remarkable effect arises that it is possible to obtain a uniform temperature profile in the width direction. (Example 2)
  • the inventors conducted tests (a) to (e) of hot rolling using three transverse type bar heaters (BHl, BH2 , and BH3 ) of the same width of 600 mm to heat four types of roughly rolled steel sheet (rough bars) of 900 mm width, 1200 mm width, 1500 width, and 1800 width while shifting the bar heaters in the width direction before the finishing mill so as to obtain a uniform temperature profile in the width direction of the steel sheet.
  • the inventors changed the distance between cores (gap) of the upper and lower bar heaters among the three levels of (1) 210 mm, (2) 160 mm, and (3) 130 mm. Further, the inventors found the temperature rises and temperature rise differences at those levels.
  • Table 1 shows the test conditions and the temperature rises. As shown in Table 1, the narrower the distance between cores of the upper and lower bar heaters (gap), the larger the temperature rise and the temperature rise difference. Further, the larger the overlap of the bar heaters, the greater the temperature rise and temperature rise difference. Note that as shown in FIG. 14, the three bar heaters (BHl to 3) were shifted to the WS (work side) or DS (drive side). FIG. 17 (a) to (e) show the states of shift in the width direction of the bar heaters corresponding to the heating tests a to e.
  • the rough rolled steel sheets had the temperature profiles shown by the dotted lines having M-shaped temperature differences, but were raised in temperature by the total temperature rises of the temperature profiles shown by the thin solid lines due to the three bar heaters.
  • the temperature profiles in the width direction of the steel sheets became substantially uniform as shown by the thick solid lines.
  • the inventors rolled a slab of a thickness of 250 mm and a width of 1250 mm heated in a heating furnace to 1200 °C by a roughing mill to a rough bar of a thickness of 30 mm.
  • the inventors concentratedly heated the rough bar at the entire width direction of the rough bar and the edges by a transverse type induction heater 23 of a width broader than the rough bar 4, concentratedly heated it by the transverse type induction heater 24 of a width narrower than the rough bar 4 , and concentratedly heated the edges by the edge heater 6.
  • the inventors used the finishing mill to finishing roll this to produce hot rolled steel sheet of a thickness of 2 mm and a width of 1250 mm.
  • the finishing rolling speed at this time was 1000 mpm.
  • the temperature profile of the finishing mill entry side changes due to the temperature profile in the width direction and the temperature drop due to the thermal rundown in the coil longitudinal direction. This is compensated for by the two heaters and the edge heater.
  • the temperature profile before heating according to the entry side width direction thermometer is 1080 °C at the center, 1100 °C at the highest point, and 1040 °C at the coolest point at the edges.
  • the inventors used the narrow width transverse type induction heater to heat and raise the temperature 28 of the center by a maximum of 20 °C to eliminate the temperature difference of the center, while used the edge heater to concentratedly raise the temperature 29 of the edges by 60 °C. By this, the inventors made the temperature " profile in the width direction before rolling uniform.
  • the temperature drops overall due to the thermal rundown and the temperature profile before heating according to the entry side width direction thermometer is 1060 °C at the center, 1080 °C at the highest point, and 1000°C at the coolest point at the edges.
  • the inventors used the narrow width transverse type induction heater to heat and raise the temperature 28 of the center by a maximum of 20 °C to eliminate the temperature difference of the center, while used the broad width transverse type induction heater to raise the center temperature by 20 °C and raise the temperature 30 of edges by 40°C. Further, the inventors used the edge heater to concentratedly raise the temperature 31 of the edges by 40 °C. By this, the inventors made the temperature profile in the width direction before rolling uniform.
  • the temperature further drops due to the thermal rundown and the temperature profile before heating according to the entry side width direction thermometer is 1040 °C at the center, 1060 °C at the highest point, and 1000 °C at the coolest point at the edges .
  • the inventors used the narrow width transverse type induction heater to heat and raise the temperature 28 of the center by a maximum of 20 °C to eliminate the temperature difference of the center, while used the broad width transverse type induction heater to raise the center temperature by 40 °C and raise the temperature 32 of edges by 80°C. Further, the inventors used the edge heater to concentratedly raise the temperature 33 of the edges by 20 °C. Due to this, the inventors made the temperature profile in the width direction before rolling uniform.
  • the inventors made the front, middle, and tail a finishing mill entry side temperature of 1100°C and a finishing mill exit side temperature of 860 °C across the entire length and entire width and therefore obtained a steel sheet with little variation in the material (ductility difference) in the width direction and longitudinal direction.
  • the strength TS difference was 10%. Therefore, with the conventional method of heating the edges, since the temperature of the center low temperature part of the rough bar was 20 °C lower than the average temperature in the width direction, the difference in the strength TS at the center of the width of the steel sheet obtained was 10%, so the material properties in the width direction did not become uniform. As opposed to this, in the present invention, since the temperature difference in the width direction at the finishing mill exit side was about 3°C, the difference in the material properties in the width direction of the obtained steel sheet was about 1.5%, so the material became uniform.
  • the remarkable effects arise that it is possible to obtain a uniform temperature profile in the width direction of the rough bar before finishing rolling and it is possible to obtain hot rolled steel sheet free from variations in mechanical properties and other material properties in the width direction by finishing rolling. Further, according to the hot rolling apparatus of the present invention, it is possible to selectively heat and raise in temperature the center low temperature part of a rough bar before finishing rolling, so the remarkable effect arises that it is possible to obtain a uniform temperature profile in the width direction. (Example 4)
  • the inventors installed a transverse type induction heater 204 for induction heating of the entire width direction of a rough bar shown in FIG. 23 between a roughing mill 201 and a finishing mill 202 and induction heated the front and tail ends of the rough bar to raise the temperature of the temperature drop part by the heating to study how to reduce the amount of cropping of the rough bar.
  • the inventors studied both cases of arranging the transverse type induction heater 204 and crop shear 8 between the roughing mill 202 and finishing mill 203 in that order and arranging them in the reverse order.
  • the thickness of the rough bar 201 was 30 mm.
  • the core gap when the front end 213 of the rough bar 201 through the induction heater 204 was made 340 mm to enable even a warped rough bar 201 to stably be passed.
  • the amount of heating and temperature rise 24a of the front end 13 of the rough bar was as shown by the solid line of FIG. 4.
  • the core gap when the steady state part and the tail end 214 of the rough bar 201 pass through the induction heater 204 was narrowed to 130 mm. As a result, the amount of heating and temperature rise 224b of the tail end 214 of the rough bar became as shown by the broken line in FIG. 4.
  • the reference point 217 in the longitudinal direction of the rough bar was made the position of the fishtail valley 216 as shown by FIG. 27(a) and (b) and the distance in the longitudinal direction from the reference point 217 was made the "distance from reference point".
  • the abscissa shows the distance from the reference point
  • the ordinate shows the temperature of the rough bar 201.
  • (a) shows the state of the front end 213 of the rough bar
  • (b) shows the state of the tail end 214 of the rough bar.
  • the inventors determined the cutting position by the crop shear based on the average value X of the temperature of the rough bar before finishing rolling at the cropping position and the standard deviation ⁇ .
  • FIG. 28(a) is a view of the temperature of the rough bar before finishing rolling near the front end 213 of the rough bar
  • FIG. 28(b) is a view of the temperature of the rough bar before finishing rolling near the tail end 214 of the rough bar.
  • the black dots in the figure show the case of no induction heating
  • the white dots show the case of induction heating.
  • the inventors cropped the front end 213 of the rough bar at a cropping position 218-2 of 15 mm from the reference point 217.
  • the inventors then showed the temperature of the rough bar before finishing rolling in the case of induction heating by white squares in FIG. 6(a) the same as the first case.
  • the inventors already finished the cropping, so were able to obtain a sufficient temperature rise (250°C) at the cropping position 218-2 of 15 mm from the reference point 217.
  • the X-2 ⁇ of the temperature of the rough bar at the cropping position 18- 2 of 15 mm became 1010°C. Therefore, the inventors were able to crop a position close to the reference point of the shape defect.
  • the present invention installs a transverse type induction heater for induction heating of the overall width direction of a rough bar between a roughing mill and finishing mill to heat the rough bar and thereby enables the temperature of the temperature drop parts of the frontmost part and tailmost part of the rough bar to be sufficiently raised without requiring the rough bar to be stopped at the time of heating and without requiring massive capital investment and enables reduction of the amount of cropping of the rough bar.

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  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
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Abstract

L'invention concerne un procédé de laminage à chaud et un appareil de production d'une tôle d'acier laminée à chaud et exempte de variation au niveau des propriétés du matériau dans le sens de la largeur, grâce à une uniformisation d'un profil de température sur l'ensemble du sens de la largeur d'une barre de métal brut, au niveau d'un côté d'entrée ou de sortie d'un laminoir finisseur. Le procédé de laminage à chaud d'une tôle d'acier consiste à chauffer un matériau de laminage pendant le changement d'une augmentation de température dans le sens de la largeur du matériau de laminage, de manière qu'un profil de température dans le sens de la largeur du matériau de laminage au niveau du côté d'entrée ou de sortie du laminoir finisseur (7) devienne uniforme, par exemple, par un chauffage permettant d'obtenir une augmentation de la température au moins au centre du matériau de laminage dans le sens de la largeur devenant supérieure à celle au niveau des parties intermédiaires entre le centre et les deux bords dans le sens de la largeur ou par un chauffage permettant d'obtenir une augmentation de la température au niveau des deux bords de la barre de métal brut dans le sens de la largeur devenant supérieure à celle au niveau des parties intermédiaires dans le sens de la largeur du sens de la largeur.
PCT/JP2003/007229 2002-06-07 2003-06-06 Procede de laminage a chaud et appareil destine a une tole d'acier laminee a chaud WO2004000476A1 (fr)

Priority Applications (3)

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AU2003238695A AU2003238695A1 (en) 2002-06-07 2003-06-06 Hot rolling method and apparatus for hot steel sheet
KR1020047019940A KR100698502B1 (ko) 2002-06-07 2003-06-06 강판의 열연 방법 및 열연 장치
CNB038187701A CN100333846C (zh) 2002-06-07 2003-06-06 热钢板的热轧方法和装置

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JPNO.2002-167512 2002-06-07
JP2002167512 2002-06-07
JPNO.2002-193300 2002-07-02
JP2002193300A JP4133042B2 (ja) 2002-07-02 2002-07-02 鋼板の熱間圧延方法及び装置
JPNO.2002-206831 2002-07-16
JP2002206831A JP2004050183A (ja) 2002-07-16 2002-07-16 鋼板の熱間圧延方法及び装置
JPNO.2002-365867 2002-12-17
JP2002365867A JP3793503B2 (ja) 2002-12-17 2002-12-17 鋼板の加熱方法
JP2003034808A JP3793512B2 (ja) 2003-02-13 2003-02-13 熱間圧延設備配列及び熱間圧延方法
JPNO.2003-034808 2003-02-13
JP2003070030A JP3793515B2 (ja) 2002-06-07 2003-03-14 鋼板の熱間圧延方法及び装置
JPNO.2003-070030 2003-03-14

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US10730088B2 (en) 2014-05-30 2020-08-04 Jfe Steel Corporation Method for manufacturing hot-rolled steel sheet, steel sheet cutting location setting device, steel sheet cutting location setting method, and steel sheet manufacturing method
EP3345688B1 (fr) 2015-09-03 2022-12-14 Toshiba Mitsubishi-Electric Industrial Systems Corporation Système de commande d'installation d'acier laminé à chaud

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KR100935515B1 (ko) * 2007-01-30 2010-01-06 도시바 미쓰비시덴키 산교시스템 가부시키가이샤 열간 압연기의 온도 제어 장치
EP2287345A1 (fr) * 2009-07-23 2011-02-23 Siemens Aktiengesellschaft Procédé de commande et/ou de réglage d'un four à induction pour un laminoir, dispositif de commande et/ou de réglage pour un laminoir et laminoir destiné à la fabrication d'un produit de laminage
WO2013046346A1 (fr) * 2011-09-28 2013-04-04 三菱日立製鉄機械株式会社 Installation de laminage à chaud
KR101424472B1 (ko) * 2012-05-31 2014-08-01 현대제철 주식회사 강재 온도 조절장치
TWI485259B (zh) * 2012-12-28 2015-05-21 China Steel Corp 小鋼胚表面缺陷之減微化方法
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TWI261000B (en) 2006-09-01
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