Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
  • C21D9/54—Furnaces for treating strips or wire
  • C21D9/56—Continuous furnaces for strip or wire
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • 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
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
• • 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
  • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur

Definitions

• steel sheets for automotive exterior panels are manufactured by cold rolling followed by continuous annealing, and excellent surface appearance quality is required for these steel sheets.
• pickup can occur in response to fluctuations in the contact pressure between the steel sheet and the hearth roll (variations within or between steel sheet coils).
• Pickup is a phenomenon in which easily oxidizable elements contained in the steel sheet, such as Mn and Si, concentrate on the steel sheet surface during the annealing process, forming oxides, which then adhere to the hearth roll surface. This pickup can result in scratches on the steel sheet. These scratches are more likely to occur in wide steel sheets with widths exceeding 1600 mm, for the following reasons.
• Possible measures to reduce the contact pressure between the steel plate and hearth roll in order to reduce pickup include (i) reducing the steel plate tension, (ii) reducing the hearth roll crown amount, and (iii) reducing the roll roughness.
• the object of the present invention is to provide a steel plate manufacturing method that can simultaneously suppress scratches caused by pickup due to contact and friction between the steel plate and hearth rolls and suppress meandering of the steel plate when cold-rolled steel plate is continuously annealed to produce steel plate with a width exceeding 1600 mm.
• the present invention aims to provide a steel sheet manufacturing method that can simultaneously suppress the occurrence of scratches and meandering, even when the target steel sheet is quarter-stretched and the sheet threading speed within the line is 90 mpm or more.
• a manufacturing method of a steel plate having a plate width exceeding 1600 mm A manufacturing method of a steel sheet, wherein, when a cold-rolled steel sheet is continuously annealed, in a furnace region where the steel sheet temperature is in the range of 100 to 400°C in the heating step, the ratio [C/Wr] of the crown amount C (mm) to the roll width Wr (mm) of the hearth roll to be installed is set to 0.00025 or more and 0.00082 or less, and the unit tension applied to the steel sheet is set to 0.80 kgf/ mm2 or more and 1.35 kgf/mm2 or less .
• the steel sheet to be continuously annealed has a shape mode coefficient ⁇ 1 of -0.8 or more and 0.8 or less (excluding more than -0.05 and less than 0.05), or a shape mode coefficient ⁇ 2 of -1.2 or more and 1.2 or less (excluding more than -0.05 and less than 0.05).
• a manufacturing method of a steel sheet [3] The method for manufacturing a steel sheet according to [1] or [2], wherein the ratio [C/Wr] of the crown amount C (mm) of the hearth roll to the roll width Wr (mm) is 0.00045 or more and 0.00075 or less.
• the present invention when cold-rolled steel sheet is continuously annealed to produce steel sheet with a width exceeding 1600 mm, it is possible to both suppress scratches caused by pickup due to contact and friction between the steel sheet and hearth rolls and suppress meandering of the steel sheet. Furthermore, even with quarter-stretch steel sheet, which is particularly susceptible to scratches and meandering, it is possible to simultaneously suppress the occurrence of scratches and suppress meandering, with the effect of significantly improving meandering in particular. Therefore, according to the present invention, high-quality steel sheet can be efficiently produced without the occurrence of threading problems caused by meandering.
• the crown amount of the hearth roll by optimizing the crown amount of the hearth roll, it is possible to suppress both the occurrence of scratches and meandering, even when the sheet threading speed within the line is 90 mpm or more. As a result, high-quality steel sheet can be produced at high speed without encountering sheet threading problems due to meandering.
• the present invention is a manufacturing method in which cold-rolled steel sheet is subjected to continuous annealing, and is characterized by the heating process being carried out under specific conditions in order to suppress meandering of the steel sheet and the occurrence of scratches during continuous annealing.
• the present invention targets the manufacture of steel sheets with a width exceeding 1600 mm. Furthermore, it is preferable for the width to be 1700 mm or more, and more preferably 1800 mm or more. On the other hand, there is no particular upper limit to the width, but it is preferable for it to be 2000 mm or less.
• the roll crown of the hearth roll installed there and the unit tension applied to the steel sheet are set as follows: (i) Ratio of hearth roll crown amount C (mm) to roll width Wr (mm) [C/Wr]: 0.00025 or more and 0.00082 or less; (ii) Unit tension applied to steel sheet: 0.80 kgf/ mm2 or more and 1.35 kgf/mm2 or less.
• Figure 1 shows a schematic planar shape of a hearth roll (roll barrel), which has a convex crown in which the outer diameter is larger at the center of the roll and decreases toward the roll ends. This convex crown applies a centering force to the steel sheet in contact with the hearth roll, allowing the steel sheet to be automatically centered.
• the diameter of the roll barrel is not particularly limited, but for example, D1 is preferably 800 mm or more, more preferably 900 mm or more, and even more preferably 950 mm or more.
• D1 is preferably 1200 mm or less, more preferably 1100 mm or less, and even more preferably 1050 mm or less.
• D2 is preferably 801 mm or more, more preferably 901 mm or more, and even more preferably 951 mm or more.
• D2 is preferably 1205 mm or less, more preferably 1105 mm or less, and even more preferably 1055 mm or less.
• the inventors of the present invention have discovered a different fact as a result of examining hearth rolls installed in the furnace region where the steel sheet temperature ranges from 100 to 400°C during the heating process of continuous annealing. Specifically, they found that for steel sheets with a width of more than 1600 mm, a crown amount of less than 2.0 mm has little effect on meandering, and conversely, for steel sheets with a quarter elongation shape, reducing the crown amount improves meandering. Furthermore, they found that for steel sheets with a width of more than 1600 mm, reducing the crown amount significantly suppresses the occurrence of scratches.
• the optimal crown amount C of the hearth roll is determined by its relationship with the roll width Wr. Specifically, it was found that both the occurrence of scratches and meandering can be suppressed by setting the ratio [C/Wr] of the crown amount C (mm) to the roll width Wr (mm) to between 0.00025 and 0.00082.
• the ratio [C/Wr] of hearth rolls in conventional technology exceeds 0.00082 (generally 0.0013 or less), and therefore this range of between 0.00025 and 0.00082 is smaller than the level of conventional technology.
• the ratio [C/Wr] be 0.00045 or more. Also, from the perspective of further suppressing the occurrence of scratches, it is preferable that the ratio [C/Wr] be 0.00075 or less. Furthermore, by keeping the ratio [C/Wr] within this range, it is possible to further suppress the occurrence of scratches, and therefore the steel plate threading speed can be increased, even making it possible to set the steel plate threading speed to 90 mpm or more.
• the hearth roll used in the present invention is not particularly limited in terms of conditions other than the ratio [C/Wr], but typically, the crown amount C is 0.5 mm or more and less than 2.0 mm, and the roll width Wr is 2000 mm or more and 2400 mm or less.
• the crown amount C is preferably 0.5 mm or more, more preferably 1.0 mm or more, and even more preferably 1.5 mm or more.
• the crown amount C is preferably less than 2.0 mm, more preferably 1.8 mm or less, and even more preferably 1.6 mm or less.
• the roll width Wr is preferably 2000 mm or more, more preferably 2100 mm or more, and even more preferably 2200 mm or more.
• the roll width Wr is preferably 2400 mm or less, more preferably 2300 mm or less, and even more preferably 2250 mm or less.
• the unit tension applied to the steel sheet in the heating step of continuous annealing is set to 0.80 kgf/mm 2 or more and 1.35 kgf/mm 2 or less.
• the unit tension is set to 0.80 kgf/mm 2 or more, preferably 0.90 kgf/mm 2 or more, and more preferably 1.00 kgf/mm 2 or more.
• the unit tension applied to the steel sheet is preferably 1.00 kgf/ mm2 or more and 1.20 kgf/ mm2 or less.
• the unit tension is preferably 1.00 kgf/ mm2 or more, and more preferably 1.05 kgf/ mm2 or more.
• the unit tension is preferably 1.20 kgf/mm2 or less , and more preferably 1.15 kgf/mm2 or less .
• the unit tension is calculated by dividing the value measured by the load cell by the cross-sectional area of the steel sheet that has passed through.
• the occurrence of meandering and scratches in steel sheets is particularly pronounced in steel sheets with a width of over 1600 mm, particularly in steel sheets with a quarter-stretched shape, but the present invention is also effective for steel sheets with a quarter-stretched shape.
• the improvement effect in suppressing meandering is greater in steel sheets with a quarter-stretched shape.
• quarter-stretched steel sheet is defined as steel sheet having a shape mode coefficient ⁇ 1 of -0.8 or greater and 0.8 or less (excluding those greater than -0.05 and less than 0.05), or a shape mode coefficient ⁇ 2 of -1.2 or greater and 1.2 or less (excluding those greater than -0.05 and less than 0.05).
• the shape mode coefficient ⁇ 1 of the steel plate is -0.8 or greater and 0.8 or less (excluding greater than -0.05 and less than 0.05)
• Steel plates with this shape would normally exhibit noticeable meandering, but by applying the present invention, this can be significantly reduced.
• the shape mode coefficient ⁇ 2 of the steel plate is -1.2 or greater and 1.2 or less (excluding greater than -0.05 and less than 0.05)
• Steel plates with this shape would normally exhibit noticeable meandering, but by applying the present invention, this can be significantly reduced.
• Whether or not a steel sheet has a quarter-stretched shape can be determined by, for example, the following method (1) or (2).
• (1) The shape of the steel plate is measured using a shape detector, and the shape mode coefficient ⁇ 1, Calculate ⁇ 2.
• the geometric mode coefficients ⁇ 1 and ⁇ 2 are calculated from the manufacturing conditions of the steel plate.
• the entire length of the coil may be measured, or only a portion of the coil in the longitudinal direction (e.g., the tip end portion) may be measured.
• the shape detector used and the method for measuring the steel sheet shape using this shape detector may be any known technology.
• Steel sheets before cold rolling are produced, for example, through continuous casting, hot rolling, and pickling.
• the chemical composition of the steel sheet is not particularly limited, but may contain, for example, in mass %, C: more than 0% and 0.3% or less, Si: more than 0% and 2% or less, Mn: more than 0% and 5% or less, P: more than 0% and 0.2% or less, S: more than 0% and 0.03% or less, N: more than 0% and 0.03% or less, and sol. Al: more than 0% and 0.5% or less.
• the contents are C: 0.0001% or more, Si: 0.001% or more, Mn: 0.01% or more, P: 0.001% or more, S: 0.0001% or more, N: 0.0005% or more, and sol. Al: 0.001% or more.
• Nb more than 0% and 0.3% or less
• Ti more than 0% and 0.3% or less
• Cr more than 0% and 1% or less
• Mo more than 0% and 1% or less
• V more than 0.5% and 0.5% or less
• Cu more than 0% and 1% or less
• Ni more than 0% and 1% or less
• B more than 0.01% and 0.01% or less
• Sn more than 0% and 0.3% or less
• Sb more than 0.3% and 0.3% or less
• Co more than 0% and 1% or less
• Zr more than 0% and 0.5% or less
• W more than 0% and 0.5% or less
• Ca more than 0.01% and 0.01% or less
• Mg more than 0% and 0.01% or less
• REM more than 0.01% and 0.01% or less.
• the balance is iron and unavoidable impurities.
• the mechanical properties of the steel sheet are most effective when the TS (tensile strength) after annealing is between 200 MPa and 340 MPa. In other words, it is preferable for the TS to be 200 MPa or more. It is also preferable for the TS to be 340 MPa or less.
• the average meandering amount was calculated by calculating this every 10 m.
• the maximum meandering amount was determined for each coil, and the meandering occurrence rate was calculated by calculating "(number of coils with a maximum meandering amount of 30 mm or more) / (total number of coils) ⁇ 100" %.
• Nos. 2 and 3 are comparative examples in which the ratio [C/Wr] is too high, and are comparative examples of the level of the prior art.
• No. 11 is a comparative example in which the ratio [C/Wr] is too low.
• No. 8 is a comparative example in which the unit tension is too high, and
• No. 9 is a comparative example in which the unit tension is too low.

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• Organic Chemistry (AREA)
• Heat Treatment Of Strip Materials And Filament Materials (AREA)

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Citations (5)

• 2025
  • 2025-02-13 JP JP2025535988A patent/JP7848942B2/ja active Active
  • 2025-02-13 WO PCT/JP2025/004714 patent/WO2025204232A1/ja active Pending

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