WO2010123152A1 - 冷延鋼板の製造方法及びその製造設備 - Google Patents
冷延鋼板の製造方法及びその製造設備 Download PDFInfo
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- WO2010123152A1 WO2010123152A1 PCT/JP2010/057641 JP2010057641W WO2010123152A1 WO 2010123152 A1 WO2010123152 A1 WO 2010123152A1 JP 2010057641 W JP2010057641 W JP 2010057641W WO 2010123152 A1 WO2010123152 A1 WO 2010123152A1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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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
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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
- C21D9/52—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
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
Definitions
- the present invention relates to a method for manufacturing a cold-rolled steel sheet and a manufacturing facility therefor, which manufacture a cold-rolled steel sheet by hot rolling, acid cleaning, cold rolling, and continuous annealing of a slab manufactured by a thin slab continuous casting method.
- Patent Document 1 proposes a method of manufacturing a thin steel sheet that can manufacture a cold-rolled steel sheet having excellent material stability by balancing the heat treatment and hot working of the slab to control the material.
- JP 9-316533 A JP-A 61-279341 JP-A-11-77102
- annealing of cold-rolled steel sheets using a batch annealing furnace requires a long time, so there is a problem that running costs are increased.
- the coiled cold-rolled steel sheet is charged into the batch annealing furnace, so that the entire coiled cold-rolled steel sheet can be uniformly annealed. It is difficult and the problem that the workability of a cold-rolled steel plate changes in a longitudinal direction arises.
- material control is aimed at balancing the heat processing and hot processing of a slab.
- the slab is held for 3 to 30 minutes in the range of Ar3 point (temperature at which transformation starts from ⁇ iron to ⁇ iron and austenite to ferrite during cooling) to 1120 ° C, or the continuously cast slab is cooled once.
- Ar3 point temperature at which transformation starts from ⁇ iron to ⁇ iron and austenite to ferrite during cooling
- the load on the hot rolling process is increased by maintaining the temperature in the range of Ar 3 point to 1120 ° C. for 3 to 30 minutes.
- the manufacturing method of the thin steel plate of patent document 1 is applicable to any annealing process of batch annealing and continuous annealing, each condition of annealing process is not disclosed.
- the present invention has been made in view of such circumstances, and continuously anneals a steel plate formed from a slab produced by a thin slab continuous casting method to produce a cold-rolled steel plate having a uniform quality at a low cost and a high yield.
- An object of the present invention is to provide a manufacturing method of a possible cold-rolled steel sheet and a manufacturing facility with a simple configuration at low cost.
- the present inventors have grown crystal grains in the steel plate in the soaking process of continuous annealing, and subsequently applied tensile stress and bending stress to the steel plate in the cooling process. It has been found that residual stress is generated in the steel sheet, and further, precipitation of carbides can be promoted by the residual stress generated in the overaging process, and the present invention has been achieved. As a result, the amount of carbon dissolved in the crystal grains in the steel sheet can be reduced, and even a steel sheet formed from a slab produced by a thin slab continuous casting method can be uniformly softened. A steel plate can be obtained.
- the gist of the present invention is as follows.
- the manufacturing method of the cold-rolled steel sheet according to the first invention is a method of hot rolling, acid cleaning, cold rolling, and continuous annealing of a slab manufactured by a thin slab continuous casting method, so that carbon is reduced to 0.0.
- the continuous annealing is performed by the cold A soaking step for holding the rolled steel plate at a temperature of 800 ° C. or more and 850 ° C. or less for 40 seconds or more and 60 seconds or less, and the steel plate that has passed through the soaking step is 350 ° C.
- the cooling step the tensile stress applied to the steel sheet is 0.5 kg / mm 2 or more and at 1.5 kg / mm 2 or less, the bending stress is 10 kg / mm 2 or more and 35 kg / mm 2 It is as follows.
- the bending stress is oriented in an axial direction in a direction (plate width direction) perpendicular to the sheet passing direction of the steel sheet passing through the pass line of the cooling step.
- the path line is shifted in the direction (plate thickness direction) perpendicular to the pass line by moving both or any one of the pair of small diameter rolls disposed on both sides in the thickness direction of the steel plate with the center position shifted in the plate passing direction. It is preferable to generate by pushing in excess of.
- the outer diameter of the paired small-diameter rolls is 200 mm or more and 500 mm or less
- the distance between the axial centers is 500 mm or more and 1000 mm or less
- the pushing distance of the small-diameter roll that is pushed beyond the pass line is 10 mm or more and It is preferable that it is 100 mm or less.
- the value of the bending stress is changed according to the amount of carbon contained in the steel sheet.
- the cold rolled steel sheet manufacturing facility is a cold rolled steel sheet obtained by hot rolling, acid cleaning, cold rolling, and continuous annealing of a slab manufactured by a thin slab continuous casting method.
- a continuous annealing line for performing the continuous annealing includes a heat-equalizing device for soaking the cold-rolled steel plate, and a cooling device for cooling the so-heated steel plate.
- An overaging device for overaging the cooled steel plate, and the cooling device is provided on a cooling means for cooling the steel plate and / or on one or both of the inlet side and the outlet side of the cooling means.
- the cooling is performed while directing the axial direction in a direction orthogonal to the plate passing direction of the steel plate and shifting the axial center position to the plate passing direction so as to be arranged on both sides in the thickness direction of the steel plate to support the movement of the steel plate.
- the path line is perpendicular to the device pass line.
- the pushed beyond and a bending stress applying means comprises a small-diameter rolls to be paired to impart bending stresses in the steel sheet.
- the soaking temperature in the soaking step of continuous annealing is set to 800 to 850 ° C., which is higher than 700 to 800 ° C. set in the conventional continuous annealing furnace. Therefore, the crystal grains in the steel plate can be grown. And, by applying tensile stress and bending stress to the steel sheet in the cooling process, dislocations can be generated in the crystal grains in the steel sheet, and precipitation of carbides can be promoted by the dislocations generated in the overaging process. . As a result, the amount of carbon dissolved in the crystal grains in the steel sheet can be reduced, and the steel sheet formed from the slab manufactured by the thin slab continuous casting method is softened by applying continuous annealing.
- the bending stress is oriented in the axial direction in a direction orthogonal to the sheet passing direction of the steel sheet passing through the pass line in the cooling step and the axial position is shifted in the sheet passing direction.
- the outer diameter of the paired small-diameter rolls is 200 mm or more and 500 mm or less, the distance between the axes is 500 mm or more and 1000 mm or less, and the small diameter is pushed beyond the pass line.
- the indentation distance of the roll is 10 mm or more and 100 mm or less, the bending curvature can be adjusted to 10 kg / mm 2 or more and 35 kg / mm 2 or less by adjusting the processing curvature radius.
- tensile stress and bending stress can be applied to the steel sheet in the cooling process by a cheap and simple mechanism in the continuous annealing line, and the crystal grains of the steel sheet It is possible to reduce the amount of solid solution carbon of the crystal grains by promoting the precipitation of carbides during the overaging process by using the dislocations generated therein. As a result, it is possible to manufacture a cold-rolled steel sheet having a uniform quality within the steel sheet at low cost and in large quantities at a low temperature by continuously annealing the steel sheet formed from the slab manufactured by the thin slab continuous casting method.
- FIG. 1 is an explanatory diagram of a continuous annealing line provided in a cold rolled steel sheet manufacturing facility according to an embodiment of the present invention.
- FIG. 2 is an explanatory view of the cooling device of the continuous annealing line.
- FIG. 3 is an explanatory diagram showing the relationship between the annealing temperature and softening of the steel sheet (tensile strength, yield stress, elongation).
- FIG. 4 is an explanatory diagram showing the relationship between soaking time and softening of the steel sheet (tensile strength, yield stress, elongation).
- FIG. 5 is an explanatory diagram showing the relationship between the cooling rate and the softening (elongation) of the steel sheet.
- FIG. 6 is an explanatory diagram showing the relationship between bending stress and steel sheet softening (elongation).
- a continuous annealing line 10 provided in a cold rolled steel sheet manufacturing facility according to an embodiment of the present invention includes, for example, an entry side facility 11, an annealing facility 12, and an exit side facility 13.
- the entry-side equipment 11 is a payoff reel that rewinds a coil 15 that has wound a steel plate 14 obtained by hot rolling, acid cleaning, and cold rolling a slab manufactured by a thin slab continuous casting method.
- the exit side equipment 13 includes an exit side looper 20 that gradually sends out the steel sheet 14 delivered from the annealing equipment 12, and elimination of yield point elongation and surface roughness of the steel sheet 14 delivered from the exit side looper 20.
- the temper rolling mill 36 for adjusting the winding the winder 22 for winding the steel plate 14 that has passed through the temper rolling mill 36 to form the coil 21, and the steel plate 14 is cut in accordance with the end of winding of the coil 21.
- a shearing machine 23 a shearing machine 23.
- the annealing equipment 12 includes a heating device 24 that heats the cold-rolled steel sheet 14 to an annealing temperature (for example, 800 to 850 ° C.), and the steel sheet 14 that has been heated to the annealing temperature at the annealing temperature for a certain time (for example, 40 ⁇ 60 seconds)
- the soaking device 25 that keeps the steel plate 14 soaked, and the soaking steel plate 14 at an aging temperature (eg, 10 ° C./second or more) at a preset cooling rate (eg, 10 ° C./second or more).
- the entrance side equipment 11, the exit side equipment 13, the heating device 24 of the annealing equipment 12, the soaking device 25, the overaging device 27, and the secondary cooling device 28 are cast pieces manufactured by a normal continuous casting method.
- the same equipment and equipment used in the continuous annealing line when producing a cold-rolled steel sheet by hot rolling, acid cleaning, cold rolling, and continuous annealing can be used.
- the cooling device 26 of the annealing equipment 12 is provided on each of the entry side and the exit side, and applies tensile stress (for example, 0.5 kg / mm 2 or more and 1.5 kg / mm 2 or less) to the steel plate 14.
- tensile stress for example, 0.5 kg / mm 2 or more and 1.5 kg / mm 2 or less
- the first and second window boxes 31 and 32 for blowing cold air onto both surfaces of the passing steel sheet 14, the entrance side of the first window box 31, and the first window are examples of cooling means for cooling the steel sheet 14.
- the axial direction is perpendicular to the plate passing direction of the steel plate 14.
- the axial center position is shifted in the plate direction and arranged on both sides in the thickness direction of the steel plate 14 to support the movement of the steel plate 14, while exceeding the pass line PL in a direction perpendicular to the pass line PL of the cooling device 26.
- Bending stress applying means 35 provided with a pair of small diameter rolls 33 and 34 for applying bending stress (for example, 10 kg / mm 2 or more and 35 kg / mm 2 or less) to the steel sheet 14 by being pushed by ⁇ . .
- the small-diameter rolls 33 and 34 are respectively supported by bearings (not shown) on both sides, and the bearings are fixed to the mounting base so that the axial direction of the small-diameter rolls 33 and 34 is oriented in a direction perpendicular to the sheet passing direction of the steel plate 14.
- the mounting base is provided with a driving mechanism (for example, a fluid pressure cylinder) (not shown) that moves the mounting base so that the small-diameter rolls 33 and 34 advance and retreat in a direction perpendicular to the pass line PL of the cooling device 26. .
- a driving mechanism for example, a fluid pressure cylinder
- the outer diameters of the first and second hot bridle rolls 29 and 30 are, for example, not less than 800 mm and not more than 1200 mm.
- the outer diameters of the small-diameter rolls 33 and 34 are 200 mm or more and 500 mm or less.
- a bending stress larger than the bending stress caused by bending applied to the steel plate 14 when passing through the first and second hot bridle rolls 29 and 30 can be applied by pushing the small-diameter rolls 33 and 34. If the outer diameter of the small-diameter rolls 33, 34 is less than 200 mm, the small-diameter rolls 33, 34 themselves have insufficient strength.
- the outer diameter of the small-diameter rolls 33, 34 exceeds 500 mm, bending stress is effectively applied to the steel plate 14.
- the installation space for the small-diameter rolls 33 and 34 increases, and the cooling efficiency decreases.
- the pair of small diameter rolls are provided at three locations on the entry side and the exit side of the first window box 31 (in the middle of the first and second window boxes) and the exit side of the second window box 32. Therefore, it is more effective if the bending stress applied to the steel sheet by the pair of small diameter rolls is applied more by the small diameter roll provided in a place where the temperature of the steel sheet is low.
- the distance between the shaft centers of the small diameter rolls 33 and 34 is 500 mm or more and 1000 mm or less.
- the processing curvature radius due to the indentation of the small-diameter rolls 33 and 34 increases, so that the bending stress can be adjusted by controlling the indentation amount ⁇ of the small-diameter rolls 33 and 34. It becomes difficult and the length of the pass line PL in the cooling device 26 becomes long, and the cooling efficiency is lowered.
- the distance between the shaft centers of the small diameter rolls 33 and 34 is less than 500 mm, when the small diameter rolls 33 and 34 are pushed in, the distance between the shaft centers of the small diameter rolls 33 and 34 is the diameter of the small diameter rolls 33 and 34. There is a risk that the steel sheet 14 may be rolled down by the two small-diameter rolls 33 and 34.
- the pushing distance ⁇ of the small diameter roll 34 pushed beyond the pass line PL is preferably 10 mm or more and 100 mm or less. When the pushing distance is less than 10 mm, when the small-diameter rolls 33 and 34 come into contact with the steel plate 14, a slip occurs in the steel plate 14, causing a problem of generating wrinkles in the steel plate 14.
- the wall thickness of the small diameter rolls 33 and 34 is 10 to 20 mm. Since this requires strength because the steel sheet is pushed in with a small-diameter roll, it is preferable that the wall thickness be slightly thicker than the wall thickness (about 15 mm) generally used in the furnace.
- the method for producing a cold-rolled steel sheet according to the present embodiment includes hot-rolling, acid cleaning, cold-rolling, and continuous annealing of a slab produced by a thin slab continuous casting method, so that carbon is 0.5% by mass.
- it is a method for producing a cold-rolled steel sheet made of a low carbon steel containing 0.02 mass% or more of silicon, 0.15 mass% or more of manganese, and 0.001 mass% or more of calcium.
- the thickness of the steel sheet to which the present invention can be applied is to produce a cold-rolled steel sheet by hot-rolling, pickling, and cold-rolling a slab produced by a conventionally known thin slab continuous casting method.
- a steel sheet of 0.15 mm or more and 3.2 mm or less is suitable.
- the continuous annealing first, the cold-rolled steel sheet 14 is heated by a heating device 24 to an annealing temperature of 800 ° C. or more and 850 ° C. or less (heating process), and the steel plate 14 heated to the annealing temperature is heated by a soaking device 25. And the steel sheet 14 is held for 40 seconds to 60 seconds at the annealing temperature (soaking step).
- the cold-rolled steel sheet 14 was annealed in a temperature range of 730 to 850 ° C. for 40 seconds, then cooled to 400 ° C. at a cooling rate of 10 ° C./second and held at 400 ° C. for 180 seconds. Then, after cooling to 20 ° C., 1.0% temper rolling was performed, and then a tensile test was performed to determine the tensile strength, yield stress, and elongation to break of the steel sheet 14. The result is shown in FIG. As shown in FIG. 3, it was confirmed that the tensile strength and the yield stress were lowered and the elongation was increased as the annealing temperature was raised.
- the steel plate 14 becomes softer as the annealing temperature is higher.
- the temperature is too high, the steel plate 14 becomes too soft, and the plateability of the steel plate 14 in the heating device 24 and the heat equalizing device 25 is likely to be affected (for example, a heat buckle is generated).
- the upper limit of the annealing temperature (soaking temperature) was set to 850 ° C.
- the lower limit of the annealing temperature (soaking temperature) was set to 800 ° C. at which the increase in elongation starts.
- the cold-rolled steel sheet 14 was annealed (soaking) at an annealing temperature of 850 ° C. for 20 to 60 seconds and then cooled to 400 ° C. at a cooling rate of 10 ° C./second to 400 ° C. For 180 seconds. Thereafter, it was cooled to 20 ° C., subjected to temper rolling at 1.0%, and then a tensile test was conducted to determine the tensile strength, yield stress, and elongation to break of the steel sheet 14. The result is shown in FIG. As shown in FIG. 4, it can be seen that the steel plate 14 becomes softer because the tensile strength and the yield stress decrease as the soaking time becomes longer.
- the elongation shows a maximum value when the soaking time is 40 seconds, and shows a tendency to decrease when it exceeds 40 seconds. For this reason, taking into account that the tensile strength and yield stress decrease with increasing soaking time and that the elongation shows a maximum value when the soaking time is 40 seconds, the holding time (soaking time) is It was 40 seconds or more and 60 seconds or less.
- the cooling process After performing the annealing process which hold
- the cooling rate is increased (the steel plate 14 is softened). It is understood that there is no effect on Therefore, the lower limit of the cooling rate is set at 10 ° C./second and there is no problem.
- the upper limit of the cooling rate is 40 ° C./second. It is preferable to set.
- stress may be applied to the steel sheet 14 in the cooling process.
- the tension applied to the steel plate 14 in the cooling process may be made larger than the tension applied to the steel sheet 14 in the soaking process and the overaging process.
- the tensile stress due to the tension applied to the steel sheet 14 in the cooling process is within a practical range, for example, 0.5 kg / mm. 2 or more (preferably 1 kg / mm 2 or more) and 1.5 kg / mm 2 or less.
- the stress that is insufficient for the occurrence of dislocation is applied to the steel sheet 14 by pushing one of the small-diameter rolls 33 and 34, for example, the small-diameter roll 34 beyond the pass line PL in a direction orthogonal to the pass line PL.
- a tensile stress generated by a bending stress that can be applied is applied to the steel sheet 14.
- the small-diameter rolls 33 and 34 have their roll axis directions oriented in a direction orthogonal to the sheet passing direction of the steel sheet 14 passing through the pass line PL in the cooling process, and their roll axis positions.
- the steel plates 14 are arranged so as to oppose both sides of the steel plate 14 while being shifted in the through plate direction.
- the outer diameters of the paired small-diameter rolls 33 and 34 are 200 mm or more and 500 mm or less and smaller than the outer diameters of the first and second hot bridle rolls 29 and 30 (for example, 800 mm or more and 1200 mm or less).
- a bending stress larger than the bending stress applied to the steel sheet 14 when passing through the second hot bridle rolls 29 and 30 can be applied by pushing the small diameter roll 34.
- the value of the bending stress applied to the steel plate 14 is increased as the amount of carbon contained in the steel plate 14 is increased, and as the amount of carbon contained in the steel plate 14 is increased, more dislocations are generated in the crystal grains. Good.
- the steel plate 14 passing through the cooling device 26 is conveyed by a hearth roll, a bending stress of about 10 kg / mm 2 is applied. For this reason, it is not effective to apply a bending stress of less than 10 kg / mm 2 to the steel sheet 14, but as shown in FIG. 6, it is confirmed that the elongation increases when the bending stress exceeds 10 kg / mm 2. It was. Therefore, the lower limit value of the bending stress applied to the steel plate 14 by pushing the small diameter roll 34 is set to 10 kg / mm 2 . On the other hand, after performing an annealing treatment (soaking) for 40 seconds at 850 ° C., the cold-rolled steel sheet 14 was cooled to 400 ° C.
- the elongation shows a maximum value when the bending stress is 23 kg / mm 2 , and shows a tendency to slightly decrease when the bending stress exceeds 23 kg / mm 2 .
- the elongation is greatly reduced when the bending stress exceeds 35 kg / mm 2 .
- the upper limit of the bending stress is set to 35 kg / mm 2 .
- the value of the bending stress is desirably 23 kg / mm 2 or more and 35 kg / mm 2 or less.
- the steel plate 14 that has passed through the cooling step and has dislocations introduced into the crystal grains is introduced into the overaging device 27 and held at a temperature of 350 ° C. or higher and 400 ° C. or lower for a period of 60 seconds or longer and 180 seconds or shorter (overaging step). ).
- carbon that is dissolved in the crystal grains is precipitated while generating carbide around the dislocation.
- the amount of carbon dissolved in the crystal grains is reduced, and the steel plate 14 is softened.
- the amount of carbon contained in the steel plate 14 is large, the value of the bending stress applied to the steel plate 14 is increased to introduce a large amount of dislocations into the crystal grains.
- the amount of carbon dissolved in the crystal grains is reduced. It can reduce efficiently and the softening of the steel plate 14 is attained.
- the amount of carbon contained in the steel sheet 14 is small, the amount of carbon dissolved in the crystal grains is small, so that the dislocation introduced into the crystal grains by reducing the value of the bending stress applied to the steel sheet 14. Therefore, the steel plate 14 can be softened while suppressing an increase in residual stress due to the occurrence of dislocations.
- the steel plate 14 that has been over-aged is delivered to the exit looper 20. After the overaging treatment is completed, it may be conveyed to the secondary cooling device 28 and further cooled (for example, cooled to 40 to 60 ° C.). (Secondary cooling step).
- both of the paired small-diameter rolls may be pushed over the pass line in a direction orthogonal to the pass line to apply bending stress to the steel sheet.
- three small-diameter rolls are provided in one place in the vertical direction, and the small-diameter roll provided at the center is passed.
- the cooling apparatus of the annealing equipment of the continuous annealing line used when manufacturing a normal steel plate may be provided with a support roll that abuts on both sides of the steel plate and supports the through plate, this support roll Can also be used as the small diameter roll of the present invention. By doing so, the cooling device which can be used for the manufacturing method of the cold-rolled steel plate of this invention can be manufactured cheaply.
- the present invention can be used in the manufacture of steel sheets.
- the present invention can be applied to a cooling device for a continuous annealing line that can be used when a cold-rolled steel sheet is manufactured from a slab manufactured by a slab continuous casting method.
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Abstract
Description
一方、特許文献1の薄鋼板の製造方法では、スラブの熱処理と熱間加工とをバランスさせて材質制御を図るものである。そのために、鋳片をAr3点(冷却時、γ鉄からα鉄、オーステナイトからフェライトへ変態開始する温度)~1120℃の範囲で3~30分保持したり、連続鋳造した鋳片を一度冷却してからAr3点~1120℃の範囲で3~30分保持したりして熱間圧延工程への負担が高くなるという問題を有している。また、特許文献1の薄鋼板の製造方法は、バッチ焼鈍及び連続焼鈍のいずれの焼鈍プロセスにも適用可能としているが、焼鈍プロセスの各条件については開示されていない。
ここで、前記対となる小径ロールの外径は200mm以上かつ500mm以下、軸心間距離は500mm以上かつ1000mm以下であって、前記パスラインを超えて押し込む該小径ロールの押し込み距離は10mm以上かつ100mm以下であることが好ましい。
また、鋼板の焼鈍方法を、従来のコイル状とした冷延鋼板のバッチ焼鈍でなく、連続焼鈍炉にて実施するため焼鈍に要する時間が、従来の約2日間から数十分に短縮され、冷延鋼板の生産性が大幅に向上すると共に焼鈍後の鋼板の長手方向での品質が均一となる。
図2は、同連続焼鈍ラインの冷却装置の説明図である。
図3は、焼鈍温度と鋼板軟質化(引張り強度、降伏応力、伸び)の関係を示す説明図である。
図4は、均熱時間と鋼板軟質化(引張り強度、降伏応力、伸び)の関係を示す説明図である。
図5は、冷却速度と鋼板軟質化(伸び)の関係を示す説明図である。
図6は、曲げ応力と鋼板軟質化(伸び)の関係を示す説明図である。
本発明の一実施の形態に係る冷延鋼板の製造設備について説明する。図1に示すように、本発明の一実施の形態に係る冷延鋼板の製造設備に設けられた連続焼鈍ライン10は、例えば入側設備11、焼鈍設備12、及び出側設備13を有している。ここで、入側設備11は、薄スラブ連続鋳造法で製造された鋳片を熱間圧延、酸洗浄、及び冷間圧延して得られた鋼板14を巻き取ったコイル15を巻き戻すペイオフリール16と、先に巻き戻された鋼板14の尾端と後に巻き戻される鋼板14の先端とを接続する溶接機17と、巻き戻された鋼板14を清浄化する電解清浄装置18と、清浄化された鋼板14を蓄えながら徐々に送出す入側ルーパー19とを有している。また、出側設備13は、焼鈍設備12から送出された鋼板14を蓄えながら徐々に送出す出側ルーパー20と、出側ルーパー20から送出された鋼板14の降伏点伸びの消去と表面粗度を調整する調質圧延機36と、調質圧延機36を通過した鋼板14を巻き取ってコイル21を形成する巻き取り機22と、コイル21の巻き取りの終了に合わせて鋼板14を切断する剪断機23とを有している。
前記一対の小径ロールは第1のウィンドボックス31の入側と出側(第1と第2ウィンドボックスの中間)、第2のウィンドボックス32の出側の3箇所に設けている。よって、前記一対の小径ロールにより前記鋼板へ付与する曲げ応力は鋼板の温度が低い場所に設けた小径ロールでより多く付与すればより効果的である。
なお、一対の小径ロールにおける直径の最適組合せについて、品質的には前記外径が200mm~500mmの範囲内であれば、同径、異径をともに差異がない。前記一対の小径ロールの外径を同径としておくことにより、当該ロールの破損・損耗時の交換用(予備品)ロールの在庫を少なくでき、保守が容易となる。
一方、小径ロール33、34の軸心間の距離が500mm未満では、小径ロール33、34を押し込んでいったときに、小径ロール33、34の軸心間の距離が小径ロール33、34の直径に近くなり、鋼板14を2本の小径ロール33、34で圧下するおそれがある。また、パスラインPLを超えて押し込む小径ロール34の押し込み距離δは10mm以上かつ100mm以下がよい。押し込み距離が10mm未満では、小径ロール33、34が鋼板14に当接した際に鋼板14にスリップが発生して、鋼板14に疵を発生させる問題が出てくる。一方、押し込み距離が100mmを超えると、鋼板14が第1、第2のウィンドボックス31、32と干渉するおそれが出てくる。
また、前記小径ロール33、34の表面粗度をRa=2~3とした。これは該小径ロールで鋼板を10mm~100mm押し込むため、鋼板は小径ロールの周囲の一部に巻きつけられ、該小径ロールでの鋼板のスリップが無くなる。よって、小径ロールの表面粗度を前記のとおり下げることが可能となる。これにより、小径ロール製作時のコストダウンが可能になる。尚、一般的に炉内に使用されるロールの表面粗度Raは4~5である。
前記小径ロール33、34の肉厚は、10~20mmとする。これは小径ロールで鋼板を押し込むため強度が必要となるため、一般的に炉内に使用されるロールの肉厚(15mm程度)に比し、若干肉厚は厚くした方が好ましい。
本実施の形態に係る冷延鋼板の製造方法は、薄スラブ連続鋳造法で製造された鋳片を熱間圧延、酸洗浄、冷間圧延、及び連続焼鈍して、炭素を0.5質量%以下、珪素を0.02質量%以上、マンガンを0.15質量%以上、カルシウムを0.001質量%以上含有する低炭素鋼からなる冷延鋼板を製造する方法である。また、本発明が適用可能な鋼板の板厚は、従来から知られている薄スラブ連続鋳造法で製造された鋳片を熱間圧延、酸洗浄、及び冷間圧延して冷延鋼板を製造する場合の鋼板であり、0.15mm以上、3.2mm以下のものが適している。そして、連続焼鈍では、先ず、冷間圧延された鋼板14を800℃以上850℃以下の焼鈍温度まで加熱装置24で加熱し(加熱工程)、焼鈍温度まで加熱された鋼板14を均熱装置25に導入して、焼鈍温度で40秒以上かつ60秒以下の時間に亘って鋼板14を保持する(均熱工程)。これによって、冷間圧延されて硬化した鋼板14の結晶粒内では転位が消滅し、焼鈍温度及び保持時間に対応した大きさの結晶粒が生成すると共に、結晶粒内の析出物は分解し結晶粒内に固溶する。
図3に示すように、焼鈍温度が上昇するのに伴って引張り強度及び降伏応力が低下し、伸びが増加することが確認された。つまり、焼鈍温度が高い程鋼板14が軟質化することが判る。しかし、温度が高過ぎると鋼板14が軟らかくなり過ぎ、加熱装置24、均熱装置25における鋼板14の通板性に影響が出易くなる(例えば、ヒートバックルが発生する)。このため焼鈍温度(均熱温度)の上限を850℃とし、焼鈍温度(均熱温度)の下限を伸びの増加が開始する800℃とした。
図4に示すように、均熱時間が長くなる程、引張り強度及び降伏応力が低下するため、鋼板14が軟質化することが判る。一方、伸びは、均熱時間が40秒のときに極大値を示し、40秒を超えると減少する傾向を示す。このため、均熱時間の増加に伴って引張り強度及び降伏応力が低下すること、伸びが均熱時間40秒のときに極大値を示すことを考慮して、保持する時間(均熱時間)を40秒以上60秒以下とした。
図5に示すように、冷却速度の範囲が通常の連続焼鈍における一般的な冷却速度である10℃/秒以上かつ40℃/秒以下であれば、冷却速度が伸び(鋼板14が軟質化)に及ぼす影響はないと解される。従って、冷却速度の下限は10℃/秒に設定して問題ない。一方、冷却速度が50℃/秒では伸びの値が若干低下していること、冷却速度を大きくすることによって設備費の増大を招くこと等を考慮すると、冷却速度の上限は40℃/秒に設定することが好ましい。
そして、転位の発生に不足する分の応力は、小径ロール33、34のいずれか一方、例えば小径ロール34を、パスラインPLと直交する方向にパスラインPLを超えて押し込むことにより鋼板14に付与することができる曲げ応力により発生する引張応力を加えて鋼板14に付与する。ここで、前述したように、小径ロール33、34は、それらのロール軸方向を冷却工程のパスラインPLを通過する鋼板14の通板方向と直交する方向に向けると共に、それらのロール軸心位置を通板方向にずらせて鋼板14の両側にそれぞれ対向するように配置する。
また、加工曲率半径RはパスラインPLを超えて押し込む小径ロール34の押し込み距離δと関係するので、小径ロール34の押し込み距離δを調節することで、鋼板14に付与する曲げ応力の値を決めることができる。なお、対となる小径ロール33、34の外径は200mm以上かつ500mm以下と、第1、第2のホットブライドルロール29、30の外径(例えば800mm以上かつ1200mm以下)より小さいので、第1、第2のホットブライドルロール29、30を通過する際に鋼板14に加えられる曲げ応力より大きな曲げ応力を、小径ロール34の押し込みで与えることができる。ここで、鋼板14に付与する曲げ応力の値は、鋼板14に含まれる炭素量が多い程大きくし、鋼板14に含まれる炭素量が多い程多くの転位を結晶粒中に発生させるようにするとよい。
図6に示すように、伸びは、曲げ応力が23kg/mm2のときに極大値を示し、23kg/mm2を超えると僅かに減少する傾向を示す。そして、伸びは曲げ応力が35kg/mm2を超えると大きく減少する。なお、曲げ応力を大きく設定すると、加工曲率半径Rを小さくするために小径ロール34の押し込み距離δが大きくなり過ぎるので、曲げ応力の上限を35kg/mm2とした。以上により、曲げ応力の値として望ましくは、23kg/mm2以上、35kg/mm2以下にするとよい。
一方、鋼板14に含まれる炭素量が少ない場合は、結晶粒中に固溶している炭素量が少ないので、鋼板14に付与する曲げ応力の値を小さくして結晶粒中に導入される転位の個数を少なく、転位の発生による残留応力の増加を抑制しながら鋼板14を軟質化することが可能になる。
過時効処理が終了した鋼板14は、出側ルーパー20に送出される。過時効処理終了後、二次冷却装置28に搬送されて、更に冷却され(例えば、40~60℃まで冷却して)もよい。(二次冷却工程)。
例えば、対となる小径ロールの両方をパスラインと直交する方向にパスラインを超えて押しこんで鋼板に曲げ応力を付与させてもよい。
また、前記の実施の形態において、鋼板に曲げ応力を付与する小径ロールは一箇所で一対(2本)であるが、1箇所で上下方向に3本もうけ、中央部に設けた小径ロールをパスラインPLと直交する方向にパスラインPLを超えて押し込み、後半に曲げ応力を付与することも可能である。
なお、通常の鋼板を製造する際に使用する連続焼鈍ラインの焼鈍設備の冷却装置には、鋼板の両面に当接して通板を支持するサポートロールを設けている場合もあるので、このサポートロールを、本発明の小径ロールとすることもできる。そうすることにより、本発明の冷延鋼板の製造方法に使用できる冷却装置を安価に製造できる。
11:入側設備
12:焼鈍設備
13:出側設備
14:鋼板
15:コイル
16:ペイオフリール
17:溶接機
18:電解清浄装置
19:入側ルーパー
20:出側ルーパー
21:コイル
22:巻き取り機
23:剪断機
24:加熱装置
25:均熱装置
26:冷却装置
27:過時効装置
28:二次冷却装置
29:第1のホットブライドルロール
30:第2のホットブライドルロール
31:第1のウィンドボックス
32:第2のウィンドボックス
33、34:小径ロール
35:曲げ応力付与手段
36:調質圧延機
Claims (5)
- 薄スラブ連続鋳造法で製造された鋳片を熱間圧延、酸洗浄、冷間圧延、及び連続焼鈍し、炭素を0.5質量%以下、珪素を0.02質量%以上、マンガンを0.15質量%以上、カルシウムを0.001質量%以上含有する冷延鋼板を製造する方法において、前記連続焼鈍は、前記冷間圧延された鋼板を800℃以上850℃以下の温度で40秒以上60秒以下の時間保持する均熱工程と、前記均熱工程を通過した前記鋼板を10℃/秒以上の冷却速度で350℃以上400℃以下の温度まで下げながら、該鋼板に引張り応力及び曲げ応力を付与する冷却工程と、前記冷却工程を通過した前記鋼板を350℃以上400℃以下の温度で60秒以上180秒以下の時間保持する過時効工程とを有し、前記冷却工程で、前記鋼板に付与する前記引張り応力は0.5kg/mm2以上かつ1.5kg/mm2以下で、前記曲げ応力は10kg/mm2以上かつ35kg/mm2以下であることを特徴とする冷延鋼板の製造方法。
- 前記曲げ応力は、前記冷却工程のパスラインを通過する前記鋼板の通板方向と直交する方向に軸方向を向けると共に軸心位置を該通板方向にずらせて該鋼板の厚み方向両側にそれぞれ配置された対となる小径ロールの両方又はいずれか一方を、前記パスラインと直交する方向に該パスラインを超えて押し込むことにより発生させることを特徴とする請求項1に記載の冷延鋼板の製造方法。
- 前記対となる小径ロールの外径は200mm以上かつ500mm以下であって、それぞれの軸心間距離は500mm以上かつ1000mm以下であって、前記パスラインを超えて押し込む該小径ロールの押し込み距離は10mm以上かつ100mm以下であることを特徴とする請求項2に記載の冷延鋼板の製造方法。
- 前記曲げ応力の値を、前記鋼板に含まれる炭素量に応じて変化させることを特徴とする請求項1~3のいずれか1項に記載の冷延鋼板の製造方法。
- 薄スラブ連続鋳造法で製造された鋳片を熱間圧延、酸洗浄、冷間圧延、及び連続焼鈍して冷延鋼板を製造する冷延鋼板の製造設備において、
前記連続焼鈍を行う連続焼鈍ラインは、前記冷間圧延された鋼板を均熱化する均熱装置と、均熱化された前記鋼板を冷却する冷却装置と、冷却された前記鋼板を過時効処理する過時効装置とを備え、前記冷却装置は、前記鋼板を冷却する冷却手段と、前記冷却手段の入側及び出側の両方又はいずれか一方に設けられ、前記鋼板の通板方向と直交する方向に軸方向を向けると共に軸心位置を該通板方向にずらせて該鋼板の厚み方向両側にそれぞれ配置されて、前記冷却装置のパスラインと直交する方向に該パスラインを超えて押し込まれて該鋼板に引張り応力を0.5kg/mm2以上かつ1.5kg/mm2以下で、前記曲げ応力を10kg/mm2以上かつ35kg/mm2以下を付与する対となる小径ロールを備えた曲げ応力付与手段とを有することを特徴とする冷延鋼板の製造設備。
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JPH02267229A (ja) * | 1989-04-07 | 1990-11-01 | Nippon Steel Corp | 薄鋳片から加工性の優れた冷延鋼板の製造方法 |
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JPH02267229A (ja) * | 1989-04-07 | 1990-11-01 | Nippon Steel Corp | 薄鋳片から加工性の優れた冷延鋼板の製造方法 |
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