EP0230780A1 - Steel strip cooling method - Google Patents

Steel strip cooling method Download PDF

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Publication number
EP0230780A1
EP0230780A1 EP86310098A EP86310098A EP0230780A1 EP 0230780 A1 EP0230780 A1 EP 0230780A1 EP 86310098 A EP86310098 A EP 86310098A EP 86310098 A EP86310098 A EP 86310098A EP 0230780 A1 EP0230780 A1 EP 0230780A1
Authority
EP
European Patent Office
Prior art keywords
cooling
steel strip
steel
rolls
strips
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP86310098A
Other languages
German (de)
English (en)
French (fr)
Inventor
Setsuo Mizushima Works Mega
Sachihiro Mizushima Works Iida
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
JFE Steel Corp
Original Assignee
Kawasaki Steel Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Kawasaki Steel Corp filed Critical Kawasaki Steel Corp
Publication of EP0230780A1 publication Critical patent/EP0230780A1/en
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • C21D9/54—Furnaces for treating strips or wire
    • C21D9/56—Continuous furnaces for strip or wire
    • C21D9/573—Continuous furnaces for strip or wire with cooling

Definitions

  • This invention relates to a method of cooling steel strips after continuous annealing of the steel strips, and more particularly to a method of cooling steel strips capable of enabling cooling capacity of roll cooling process to increase to a maximum possible extent without detrimentally affecting quality of steel products.
  • a roll cooling method among them in which a steel strip is wound about cooling rolls so as to be in contact therewith is advantageous in that its cooling speed is sufficiently high with a relatively low cost of operation without any risk of oxidation on a surface of the strip.
  • Such a phenomenon detrimentally affects figure of a steel strip to cause serpentine movements of the steel strip, which obstruct stable passing of the steel strip through the heat-treatment passage and make difficult the contact between the cooling rolls and the steel strip wound thereabout so as to lower the cooling capacity of the cooling rolls.
  • the unevenness in temperature in the width directions of the steel strip causes compressive stresses in the width directions on a surface of the steel strip in contact with the cooling rolls with a risk of buckling of the steel strip. If the buckling exceeds a certain value, the steel strip may undergo violent serpentine movements resulting in breaking down of the steel strip in a furnace.
  • Japanese Laid-open Patent Application No. 59-129737 discloses a feature of providing gas jetting means in opposition to cooling rolls, capable of controlling cooling intensity in width directions of a steel strip subjected to the roll cooling, thereby reducing the unevenness in temperature in the width directions of the steel strip to prevent defects in figure of the steel strip.
  • it does not solve the problem of the uneven cooling sufficiently because of low contact pressure between the steel strip and the cooling rolls resulting from a slight tensile force in the steel strip of the order of less than 0.8 kgf/mm2 in order to prevent the buckling of the steel strip in high temperature zones in a usual continuous annealing installation.
  • Japanese Laid-open Patent Application No. 59-20428 discloses a feature of cooling a steel strip under tension of 2-5 kgf/mm2 with more than two rolls. If even a slight fault of contact in width directions of the steel strip occurs, a large tensile force concentration locally occurs to give rise to a plastic deformation of the steel strip and an exceeding defect in figure of the steel strip causing large serpentine movements of the steel strip to decrease the production capacity. Moreover, motor power for bridle rolls located upstream and downstream of the cooling rolls increases and a large number of bridle rolls are required because of a usual restriction of coefficient of friction between the steel strip and bridle rolls to increase a space for the bridle rolls resulting in an increased initial cost.
  • a rapid cooling of a steel strip by winding it about a plurality of cooling rolls in succession to bring it into contact therewith is started at a temperature of a range of 550-720°C and simultaneously a tensile force a (kgf/mm2) of the steel strip is adjusted within a range determined by an inequality of (1900-Ts)/1670 ⁇ (1980-Ts)/720 according to the starting temperature Ts(°C) of said rapid cooling.
  • a rapid cooling of a steel strip by winding it about a plurality of cooling rolls in succession to bring it into contact therewith and at the same time by jetting a gas against a back surface of the steel strip is started at a temperature of a range of 550-720°C and simultaneously a tensile force a' (kgf/mm 2 ) of the steel strip is adjusted within a range determined by an inequality of (1570-Ts)/1670 ⁇ a' ⁇ (2410-TS)/630 according to the starting temperature Ts(°C) of said rapid cooling.
  • Fig. 1 schematically illustrates a continuous heat-treatment furnace for steel strips 1 suitable for carrying out the cooling process including the rapid cooling above described.
  • the furnace comprises in a cooling zone 2 deflector rolls 3, 7, 10, 21 and 25, upstream bridle rolls 4, 5 and 6, downstream bridle rolls 22, 23 and 24, gas jetting means 8 and 9, a plurality of cooling rolls 11, 12, 13, 14 and 15 for the roll cooling process and gas jetting means 16, 17, 18, 19 and 20 for assisting the roll cooling with the cooling rolls 11 -15.
  • Fig. 2 illustrates a typical heat cycle in the roll cooling process.
  • a steel strip is maintained soaked at 700-800°C in a soaking zone not shown in Fig. 1 and then gradually cooled to a temperature between approximately 640°C and an A l transformation point (723°C) of the strip in a cooling zone upstream of the rapid cooling zone 2 shown in Fig. 1.
  • the steel strip 1 is then cooled by jetting a gas from the gas jetting means 8 and 9 shown in Fig. 1.
  • the steel strip 1 is extended around the plurality of cooling rolls 11-15 so as to be in contact therewith and is simultaneously subjected to the jetting cooling gas from the gas jetting means 16-20, so that the steel strip is rapidly cooled to about 400°C.
  • the steel strip 1 is then maintained at this temperature for overaging the strip, it is fed out of the heat-treatment system.
  • the temperature Ts at which the rapid cooling by the roll cooling is started has been slightly explained referring to Fig. 2 in connection with the gas jetting means 8 and 9 located upstream of the cooling rolls.
  • the starting temperature Ts of the rapid cooling is lower than 640°C, defects in figure of strips would often occur depending upon materials and sizes of the strips.
  • a starting temperature Ts of the rapid cooling lower than 600-550°C can be acceptable without a risk of the defects in figure of strips.
  • an excessively low starting temperature such as lower than 550°C would cause a requirement of an unduly widened heating zone of the gas jetting means 8 and 9 as the previous cooling resulting in increased electric power cost. Accordingly, the temperature range of 550-720°C is applicable for the starting temperature Ts of rapid cooling with the roll cooling.
  • Fig. 3 illustrates observed results of strip figures at the termination of cooling with the starting temperature Ts of 650°C wherein results of only the roll cooling (case A) are shown in solid lines, and results of addition of gas jetting onto back surfaces of the strips (case B) in broken lines.
  • the low tension of the steel strips in the proximity of 0.5 kgf/mm 2 causes uneven cooling which detrimentally affects the figure of strips because of lower contact pressure of the rolls with the strips.
  • the uneven cooling is greatly prevented with the tension within 0.8-2 kgf/mm 2 of the case A and within 0.6-3 kgf/mm2 of the case B, so that unevenness of the steel strips is less than 1% in both cases.
  • the tension further increases, it again adversely affects the figure of strips.
  • the decrease in contact area at the respective cooling rolls 11-15 causes tensile stress concentration at the excessively cooled portions of the strip, so that when average tension is more than 2 kgf/mm2 in the case A and 3 kgf/mm 2 in the case B, it becomes in excess of yield stress of the steels trip (5-6 kgf/mm2) at a temperature of the order of 650°C shown in Fig. 6. Accordingly, such a tensile force causes plastic deformation of the strip which will be further enhanced by the subsequent roll cooling.
  • Fig. 7 illustrates threshold values for causing defects in figure of steel strips (more than 1% of the unevenness) with the rapid cooling starting temperatures Ts of 400-750°C in relation to tensile forces of the strips, wherein solid lines are for the case A and broken lines are for the case B.
  • Ts the starting temperature
  • the strips are prone to defects in figure.
  • Ts the range of the tensile force not causing defects of figure becomes wider.
  • the tensile force not causing defects in figure with the starting temperature of 550-720°C is approximately obtained as follows.
  • the starting temperature for the rapid cooling is within 550-600°C.
  • the zone causing the defects in figure is substantially the same as that shown in Fig. 7.
  • Fig. 8 illustrates the relation between the tensile forces of steel strips and cost of bridle rolls to be arranged upstream and downstream of cooling rolls in order to apply the tensile forces to the steels trips.
  • This graph shows the increase of the cost of bridle rolls with increase of the tensile forces in comparison with the cost of bridle rolls (indicated by an index 100) required to cause the tensile force of 1.0 kgf/mm2 acting upon the steel strips.
  • the cost of the bridle rolls is rapidly increased in order to increase the tensile force of the steel strips to more than 3 kgf/mm 2 , because of not only an increase of power for bridle rolls but also considerably bulky bridle rolls requiring a great space for settling such bulky bridle rolls.
  • the starting temperature of the rapid cooling of a strip winding around and in contact with a plurality of rolls is limited to 550-720°C.
  • the lower limitation of the starting temperature is defined in order to avoid the disadvantage of increase power cost due to undue increase of the gas jetting cooling zone for unduly lowering the temperature to 550°C.
  • the upper limitation of the starting temperature is defined in order to avoid the risk of defects of figure of steel strip at a temperature higher than 720°C.
  • the tensile force a (kgf/mm2) of the steel strip to be cooled only by roll cooling without jetting the gas against the back surface of the strip is defined within the following range.
  • the tensile force a' (kgf/mm 2 ) of the steel strip to be cooled by roll cooling and by jetting the gas against the back surface of the strip is defined within the following range.
  • the strips were fed in the heating and soaking zones under tensile force of the order of 0.7 kgf/mm 2.
  • the tensile force was then increased from 0.7 kgf/mm 2 to 2.7 kgf/mm 2 according to thicknesses and widths of the strips by means of the front and rear bridle rolls 4-6 and 22-24.
  • the steel strips were then subjected to the first cooling by the previous gas jetting means 8 and 9 and thereafter the strips were extended around the cooling rolls 11-15 to be cooled and simultaneously cooled on their back sides by means of the gas jetting chambers 16-20 arranged in opposition to the cooling rolls 11-15.
  • the tensile force was lowered to value of the order of 0.7 kgf/mm2 by the rear bridle rolls 22-24.
  • Fig. 10 illustrates the effects of the present invention in the two cases, one of which uses only the roll cooling and the other of which uses both the roll cooling and the gas jetting.
  • a ⁇ kgf/mm2
  • a rate of steel strips of inferior quality due to defect of figure was lowered to less than 0.5% and the capacity decline of the operation resulting from serpentine movements of steel strips due to defects of figure was significantly prevented.
  • the cooling capacity in roll cooling of steel strips can be exhibited to the maximum possible limitation without causing any defect of figure of strips in their cooling after continuous annealing by roll cooling.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Strip Materials And Filament Materials (AREA)
EP86310098A 1985-12-24 1986-12-23 Steel strip cooling method Withdrawn EP0230780A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP289320/85 1985-12-24
JP60289320A JPS62149820A (ja) 1985-12-24 1985-12-24 鋼帯の冷却方法

Publications (1)

Publication Number Publication Date
EP0230780A1 true EP0230780A1 (en) 1987-08-05

Family

ID=17741662

Family Applications (1)

Application Number Title Priority Date Filing Date
EP86310098A Withdrawn EP0230780A1 (en) 1985-12-24 1986-12-23 Steel strip cooling method

Country Status (4)

Country Link
EP (1) EP0230780A1 (ko)
JP (1) JPS62149820A (ko)
KR (1) KR930005069B1 (ko)
CA (1) CA1281974C (ko)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0495115A1 (en) * 1990-07-31 1992-07-22 Nkk Corporation System for continuously cooling metal strip
EP0614992A1 (en) * 1992-06-23 1994-09-14 Nkk Corporation Metal band cooling apparatus and cooling method therefor

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0568363U (ja) * 1991-11-07 1993-09-17 株式会社ダイシン 折り畳み式ワゴン
JP2011184773A (ja) * 2010-03-10 2011-09-22 Kobe Steel Ltd 連続焼鈍設備およびその設備における急冷焼入時の金属板の波状変形抑制方法
KR101977466B1 (ko) * 2017-05-25 2019-05-13 주식회사 포스코 스트립 냉각장치

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0058607A1 (fr) * 1981-02-12 1982-08-25 Stein Heurtey Dispositif de refroidissement rapide et contrôlé dans un four de recuit en atmosphère neutre ou réductrice
DE3324548A1 (de) * 1982-07-08 1984-01-12 Kawasaki Steel Corp., Kobe, Hyogo Verfahren zum kuehlen von bandstahl mit hilfe von kuehlrollen
EP0117083A1 (en) * 1983-02-03 1984-08-29 Nippon Steel Corporation Method and apparatus for cooling a metal strip in a continuous annealing furnace
EP0145485A2 (en) * 1983-12-15 1985-06-19 Mitsubishi Jukogyo Kabushiki Kaisha Method of controlling the temperature of steel strip in the cooling zone of a continuous annealing furnace
EP0155753A1 (en) * 1984-02-14 1985-09-25 Mitsubishi Jukogyo Kabushiki Kaisha Cooling apparatus for strip metal

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5920428A (ja) * 1982-07-26 1984-02-02 Nippon Kokan Kk <Nkk> 連続焼鈍炉における鋼帯冷却方法
JPS60128219A (ja) * 1983-12-15 1985-07-09 Mitsubishi Heavy Ind Ltd 帯板冷却装置

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0058607A1 (fr) * 1981-02-12 1982-08-25 Stein Heurtey Dispositif de refroidissement rapide et contrôlé dans un four de recuit en atmosphère neutre ou réductrice
DE3324548A1 (de) * 1982-07-08 1984-01-12 Kawasaki Steel Corp., Kobe, Hyogo Verfahren zum kuehlen von bandstahl mit hilfe von kuehlrollen
EP0117083A1 (en) * 1983-02-03 1984-08-29 Nippon Steel Corporation Method and apparatus for cooling a metal strip in a continuous annealing furnace
EP0145485A2 (en) * 1983-12-15 1985-06-19 Mitsubishi Jukogyo Kabushiki Kaisha Method of controlling the temperature of steel strip in the cooling zone of a continuous annealing furnace
EP0155753A1 (en) * 1984-02-14 1985-09-25 Mitsubishi Jukogyo Kabushiki Kaisha Cooling apparatus for strip metal

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN, vol. 8, no. 106 (C-223)[1543], 18th May 1984; & JP-A-59 20 428 (NIPPON KOKAN K.K.) 02-02-1984 *
PATENT ABSTRACTS OF JAPAN, vol. 8, no. 251 (C-252)[1688], 16th November 1984; & JP-A-59 129 737 (KAWASAKI SEITETSU K.K.) 26-07-1984 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0495115A1 (en) * 1990-07-31 1992-07-22 Nkk Corporation System for continuously cooling metal strip
EP0495115A4 (en) * 1990-07-31 1993-03-17 Nkk Corporation System for continuously cooling metal strip
EP0614992A1 (en) * 1992-06-23 1994-09-14 Nkk Corporation Metal band cooling apparatus and cooling method therefor
EP0614992A4 (en) * 1992-06-23 1996-10-30 Nippon Kokan Kk Metal band cooling apparatus and cooling method therefor.

Also Published As

Publication number Publication date
CA1281974C (en) 1991-03-26
KR930005069B1 (ko) 1993-06-15
JPS62149820A (ja) 1987-07-03
KR870006215A (ko) 1987-07-10
JPH0414173B2 (ko) 1992-03-12

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Inventor name: MEGA, SETSUOMIZUSHIMA WORKS

Inventor name: IIDA, SACHIHIROMIZUSHIMA WORKS