Classifications

• • 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
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/74—Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material
  • C21D1/76—Adjusting the composition of the atmosphere
• • 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
  • C21D8/0421—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 working steps
  • C21D8/0426—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
  • C21D8/0421—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 working steps
  • C21D8/0436—Cold 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
  • C21D8/0468—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 between cold rolling steps
• • 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
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • 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
• • 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
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/005—Ferrite
• • 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
  • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets

Definitions

• Patent Literature 1 discloses a method for manufacturing a steel sheet having a high r value and excellent flange formability by producing a DR material from low-carbon steel with a primary cold reduction ratio of 85% or less.
• Patent Literature 2 it is necessary to apply the nitriding treatment after recrystallization is completed. Therefore, even in the case where the nitriding treatment is applied in the continuous annealing step, cost increases, e.g., a reduction in line speed and an increase in furnace length, are not avoided.
• a second invention is the high-strength high-formability steel sheet for a can, according to the first invention, characterized in that regarding the above-described grain size, the difference in average grain size determined by subtracting an average grain size between a depth of three-eighths of the sheet thickness and a depth of four-eighths of the sheet thickness from an average grain size between the surface and a depth of one-eighth of the sheet thickness is 1 ⁇ m or more.
• the steel sheet for a can according to the present invention is a high-strength high-formability steel sheet for a can having a tensile strength of 500 MPa or more and an elongation after fracture of 10% or more. Then, such a steel sheet can be produced by using a steel containing 0.070% or more and less than 0.080% of C and specifying the coiling temperature after hot rolling and the secondary cold reduction ratio to be appropriate conditions.
• Si 0.003% or more and 0.10% or less If the amount of Si exceeds 0.10%, problems, e.g., reduction in surface-treatability and degradation of corrosion resistance, are brought about. Therefore, the upper limit is specified to be 0.10%. Meanwhile, a smelting cost becomes too high to achieve less than 0.003%. Therefore, the lower limit is specified to be 0.003%.
• Mn 0.51% or more and 0.60% or less
• Manganese has functions of preventing hot shortness due to S during hot rolling and making crystal grains finer and is an element necessary for ensuring desirable material properties. Furthermore, in order to satisfy the can strength with a material having a reduced thickness, it is necessary to increase the strength of the material. In order to respond to this increase in strength, a required amount of addition of Mn is 0.51% or more. On the other hand, if Mn is added too much, the corrosion resistance is degraded and the steel sheet becomes hard excessively. Therefore, the upper limit is specified to be 0.60%.
• Phosphorus is a harmful element which makes the steel hard, which degrades the formability and, at the same time, which degrades even the corrosion resistance. Therefore, the upper limit is specified to be 0.100%. Meanwhile, if P is specified to be less than 0.001%, a dephosphorization cost is too large. Therefore, the lower limit is specified to be 0.001%.
• N 0.010% or less If large amounts of N is added, hot elongation is degraded and cracking of slab occurs in continuous casting. Therefore, the upper limit is specified to be 0.010%. Meanwhile, if the amount of N is specified to be less than 0.001%, a smelting cost is too large. Therefore, it is preferable that the amount of N is specified to be 0.001% or more. In this regard, the remainder is specified to be Fe and incidental impurities.
• the tensile strength is specified to be 500 MPa or more. If the tensile strength is less than 500 MPa, the thickness of the steel sheet cannot be reduced to the extent that a significant economic effect is obtained because the strength of the steel sheet serving as a raw material for can production is ensured. Therefore, the tensile strength is specified to be 500 MPa or more.
• the Vickers hardness can be measured by the test method for hardness shown in "JIS Z 2244".
• the Vickers hardness test with a load of 10 gf is performed in such a way that the hardness distribution in a steel sheet cross-section in the sheet thickness direction can be evaluated appropriately.
• the measurement is performed at 10 places each, and an average value of the measured values is specified to be the average hardness of each cross-section.
• a maximum of the Vickers hardness measurement is specified to be a cross-section Vickers maximum hardness.
• a difference in cross-section average hardness is less than 10 points and/or the cross-section maximum hardness is less than 20 points, the whole sheet has a uniform hardness and, therefore, there is no difference from a current material and a high-strength high-formability steel sheet cannot be obtained.
• the tensile strength of 500 MPa or more and the elongation after fracture of 10% can be achieved by specifying the difference in cross-section average hardness to be 10 points or more and/or the cross-section maximum hardness to be 20% or more.
• Difference in average grain size 1 ⁇ m or more
• a difference in average grain size determined by subtracting an average grain size between a depth of three-eighths of the sheet thickness and a depth of four-eighths of the sheet thickness from an average grain size between the surface and a depth of one-eighth of the sheet thickness is 1 ⁇ m or more. This is because in the case where the difference in average grain size is 1 ⁇ m or more, a steel sheet having excellent characteristics ensuring the compatibility between the strength and the elongation can be obtained.
• the amount of N of a sample which had been subjected to electrolytic polishing up to the depth of three-eighths of the sheet thickness was measured by using a combustion method.
• the average amount of N between the surface and a depth of one-eighth of the sheet thickness after one surface of a sample was sealed with a tape, chemical polishing was performed from the surface up to the depth of one-eighth of the sheet thickness with oxalic acid, and the amount of N of the remaining sample was measured by using a combustion method.
• average nitride number density ratio 1.5 or less If the average nitride number density ratio is 1.5 or more, the nitride number density of the surface layer increases and precipitation strengthening due to nitrides occurs, so that significant enhancement of mildness is not expected. However, the tensile strength of 500 MPa or more and the elongation after fracture of 10% or more can be achieved easily by specifying the average nitride number density ratio to be less than 1.5. Consequently, a high-strength high-formability steel sheet is obtained easily.
• the amount of solid solution C was calculated from a peak of internal friction.
• the internal friction was measured with a torsional vibration type internal friction measuring apparatus produced by Vibran, where the shape of a test piece was 1 mm ⁇ 1 mm ⁇ 80 mm, the measurement frequency was 0.001 to 10 Hz, and the temperature was 0°C, background of the measured data was removed and, thereafter, Q-1 of the peak value was read. Calculation was performed from Q-1 and a calibration curve. If the amount of solid solution C in the steel is large, the strength increases on the basis of strengthening due to solid solution C, and the ductility increases because the amount of carbide serving as a start point of fracture is reduced.
• the high-strength high-formability steel sheet for a can is produced by using a steel slab which is produced through continuous casting and which has the above-described composition, performing hot rolling so as to coil at a temperature lower than 620°C, performing rolling with a primary cold reduction ratio of 86% or more and a cold reduction ratio of a final stand in primary cold rolling of 30% or more, performing annealing in an atmosphere containing less than 0.020 percent by volume of ammonia gas, and performing secondary cold rolling with a reduction ratio of 20% or less.
• Coiling temperature after hot rolling lower than 620°C If the coiling temperature after the hot rolling is 620°C or higher, formed pearlite microstructures become coarse, and these serve as start points of brittle fracture. Therefore, local ductility is reduced and the elongation after fracture of 10% or more is not obtained. Therefore, the coiling temperature after the hot rolling is specified to be lower than 620°C. More preferably, the coiling temperature is 560°C to 620°C.
• Primary cold reduction ratio 86% or more
• the primary cold reduction ratio is specified to be less than 86%, production is difficult. Therefore, the primary cold reduction ratio is specified to be 86% or more. More preferably, 90% to 92% is employed.
• Reduction ratio of final stand in primary cold rolling 30% or more
• the reduction ratio of a final stand In order to make the surface layer of the steel sheet coarse grains so as to enhance mildness, it is necessary to increase the reduction ratio of a final stand to introduce a strain into the steel sheet surface layer and, thereby, facilitate growth of ferrite grains during annealing.
• the reduction ratio of a final stand in primary cold rolling is specified to be 30% or more.
• the resulting steel slab was reheated at 1,250°C and, thereafter, hot rolling and primary cold rolling were applied under the condition shown in Table 2.
• the finish rolling temperature of the hot rolling was specified to be 890°C, and pickling was applied after the rolling.
• continuous annealing at a soaking temperature of 630°C and a soaking time of 25 seconds and secondary cold rolling under the condition shown in Table 2 were applied.
• the grain size, the amount of N, and the nitride number density refers to the average grain size, the average amount of N, and the average nitride number density, respectively.
• the coated steel sheet (tin plate) obtained as described above was subjected to a heat treatment corresponding to painting and baking at 210°C for 10 minutes and, thereafter, a tensile test was performed.
• a tensile test piece of JIS No. 5 size was used and the tensile strength (strength after fracture) and the elongation after fracture was measured at a cross head speed of 10 mm/min.
• a sample of the coated steel sheet was taken, and the average grain size and the grain elongation rate in a cross-section in the rolling direction were measured.
• the average grain size and the grain elongation rate in a cross-section in the rolling direction were measured by a cutting method with a straight test line described in "JIS G 0551" after the vertical cross-section of the steel sheet was polished and grain boundaries were revealed through nital etching.
• a sample having a sheet thickness of 0.21 mm was formed into a lid of 63 mm ⁇ and was attached to a welded can body of 63 mm ⁇ through seaming. Compressed air was introduced into the can, and a pressure at which the can lid was deformed was measured.
• the case where the can lid was not deformed even when the pressure of the inside was 0.20 MPa was indicated by a symbol ⁇
• the case where the can lid was not deformed when the pressure of the inside was increased up to 0.19 MPa and the can lid was deformed when the pressure of the inside was 0.20 MPa was indicated by a symbol O
• the case where the can lid was deformed at 0.19 MPa or less was indicated by a symbol x.
• the tester specified in JIS B 7729 was used, and a test was performed by a method specified in JIS Z 2247.
• No. 6 to No. 12 and No. 18, which are invention examples, have excellent strength and achieve the tensile strength of 500 MPa or more required of a very thin steel sheet for a can. Furthermore, excellent formability is exhibited and the ductility of 10% or more required for forming a lid and a three-piece can body is provided.
• a steel sheet for a can having high strength and high formability in combination that is, a tensile strength of 500 MPa or more and an elongation after fracture of 10% or more, can be obtained.
• the formability of the steel sheet is improved and, thereby, cracking does not occur even during rivet forming of the EOE and during flange forming of the three-piece can. Consequently, can production from the DR material having a small sheet thickness becomes possible, so that it is possible to contribute to development of the industry to a great extent, for example, significant thickness reduction of the steel sheet for a can is achieved.

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• 2011
  • 2011-11-22 CA CA2818682A patent/CA2818682C/en not_active Expired - Fee Related
  • 2011-11-22 EP EP11845152.5A patent/EP2634282A1/de not_active Withdrawn
  • 2011-11-22 CN CN2011800575709A patent/CN103270183A/zh active Pending
  • 2011-11-22 KR KR1020137016568A patent/KR101570755B1/ko not_active IP Right Cessation
  • 2011-11-22 WO PCT/JP2011/077446 patent/WO2012073914A1/ja active Application Filing

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