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
  • C21D9/46—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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
• • 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
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum

Definitions

• the present invention relates to a hot-rolled steel sheet that is particularly suitable as a base material for can steel sheets with high strength, high ductility, and a high r-value, and to a method for manufacturing the same.
• DR Double Reduce
• DR material is known as a high-strength steel sheet for cans.
• DR material is a steel sheet for cans that has been strengthened by cold rolling, annealing, and then cold rolling again.
• DR material has a problem of low formability due to its small elongation.
• it is effective to reduce the reduction ratio during secondary cold rolling after annealing, but there is a concern that reducing the reduction ratio will reduce the strength of the steel sheet.
• it is necessary to increase the strength of the base material by utilizing strengthening mechanisms such as solid solution strengthening and grain refinement strengthening.
• Patent Document 1 proposes a hot-rolled steel sheet for use as a base material for cans, which contains, by mass, 0.02-0.12% C, 0.005-0.5% Si, 0.3-1.5% Mn, 0.005-0.2% P, 0.10% or less Al, 0.012% or less N, 0.005-0.10% Nb, with the balance being iron and unavoidable impurities, has a substantially ferrite single-phase structure, has an average ferrite grain size of 6 ⁇ m or more, and after paint baking treatment has a yield strength of 500 MPa or more, a yield ratio of 0.9 or more, a total elongation of 10% or more, and a ⁇ r of -0.50 to 0.
• Patent Document 1 makes it possible to manufacture hot-rolled steel sheets for use as high-strength, high-ductility base steel sheets for cans, but does not specify the r-value of the steel sheets for cans.
• When drawing steel sheets for cans it is necessary to prevent breakage during the drawing process, and one way to achieve this is to increase the r-value of the steel sheets for cans.
• Controlling the structure of the hot-rolled steel sheets is important for increasing the r-value of steel sheets for cans, but this is not considered in the technology described in Patent Document 1.
• the present invention has been made to solve the above-mentioned problems, and aims to provide a hot-rolled steel sheet that can be used as a raw material for can steel sheets with high strength, high ductility, and a high r-value, as well as a manufacturing method for the same.
• the steel sheets for cans manufactured using such hot-rolled steel sheets can achieve high strength, high ductility, and a high r-value.
• controlling the temperature of the steel sheets during hot rolling is important for refining the ferrite grains in hot-rolled steel sheets.
• the present invention has been made to solve the above problems, and the gist of the present invention is as follows.
• C 0.010% or more and 0.150% or less
• Si 0.10% or less
• Mn 0.10% or more and 1.20% or less
• P 0.025% or less
• S 0.040% or less
• Al 0.100% or less
• N 0.0050% or more and 0.0200% or less
• Cr 0.010% or more and 0.150% or less
• the hot-rolled steel sheet has an average ferrite grain size of 15 ⁇ m or less in equivalent circle diameter, and the amount of N present as nitrides and the total amount of N satisfy the following formula (1): (Amount of N present as nitride)/(Total amount of N) ⁇ 0.40 (1)
• the total N content is the total amount of N contained in the hot-rolled steel sheet
• the component composition further includes, in mass%, Nb: 0.003% or more and 0.030% or less; The hot-rolled steel sheet according to [1], wherein the amount of Nb present as Nb precipitates and the total amount of Nb satisfy the following formula (2): 0.10 ⁇ (amount of Nb present as Nb precipitates)/(total amount of Nb) ⁇ 0.80 (2)
• the total Nb content is the total amount of Nb contained in the hot-rolled steel sheet.
• the component composition further includes, in mass%, Cu: 0.40% or less, Sn: 0.04% or less, Ni: 0.15% or less, Mo: Contains one or more selected from 0.10% or less, The hot-rolled steel sheet according to [1] or [2].
• [4] A method for producing a hot-rolled steel sheet according to any one of [1] to [3], a heating step of heating a steel material having the above-mentioned composition at 1150°C or higher; a hot rolling process in which, after the heating process, the steel material is hot rolled at a finishing temperature of 800°C or more and 950°C or less, cooled from 800°C to a coiling temperature of 450°C or more and 700°C or less at an average cooling rate of 20°C/s or more, and coiled at the coiling temperature, A manufacturing method for hot-rolled steel sheets.
• the present invention makes it possible to manufacture hot-rolled steel sheets that are suitable as base materials for can steel sheets, which have high strength, high ductility, and a high r-value.
• the present invention also makes it possible to reduce the gauge of can steel sheets, thereby enabling the weight of can bodies to be reduced.
• the improved workability of can steel sheets makes it possible to apply more complex processing to can bodies and can ends.
• the chemical composition, structure and manufacturing conditions of the hot-rolled steel sheet of the present invention will be explained below. As will be described later, the hot-rolled steel sheet is subjected to cold rolling, annealing, and temper rolling to produce a steel sheet for cans. First, the chemical composition of the hot-rolled steel sheet will be described. In the description of the chemical composition, % means mass %.
• C 0.010% or more and 0.150% or less C is an element that contributes to improving strength. If the C content is less than 0.010%, the strength of the hot-rolled steel sheet (base material) will decrease due to coarsening of ferrite grain size and a decrease in the amount of solute C. Therefore, the C content must be 0.010% or more.
• the C content is preferably 0.012% or more.
• the C content is more preferably 0.014% or more, even more preferably 0.016% or more, and most preferably 0.018% or more.
• the C content exceeds 0.150%, the ductility and r-value of the base material and the steel sheet for cans will decrease. Therefore, the C content must be 0.150% or less.
• the C content is preferably 0.135% or less, more preferably 0.100% or less, further preferably 0.080% or less, and most preferably 0.070% or less.
• Si 0.10% or less While Si is an element that contributes to improving strength, excessive Si content reduces the corrosion resistance of hot-rolled steel sheets and steel sheets for cans. Therefore, the Si content needs to be 0.10% or less.
• the Si content is preferably 0.08% or less, more preferably 0.06% or less, even more preferably 0.05% or less, and most preferably 0.03% or less. There is no particular need to set the lower limit, but in order to improve the strength of the base metal, the Si content is preferably 0.01% or more, more preferably 0.02% or more.
• Mn 0.10% or more and 1.20% or less Mn is an element that improves hardenability and promotes the solid solution of C in ferrite. Furthermore, it is known that Mn itself contributes to improving strength through solid solution strengthening, and that increasing the Mn content refines the ferrite grain size. Since a base metal with sufficient strength cannot be obtained when the Mn content is less than 0.10%, the Mn content is set to 0.10% or more. The Mn content is preferably set to 0.20% or more. The Mn content is more preferably set to 0.30% or more, even more preferably set to 0.40% or more, and most preferably set to 0.50% or more.
• the Mn content is set to 1.20% or less.
• the Mn content is preferably set to 1.00% or less, and more preferably set to 0.80% or less.
• the Mn content is more preferably 0.70% or less, and most preferably 0.65% or less.
• the P content is set to 0.025% or less.
• the P content is preferably set to 0.023% or less.
• the P content is more preferably set to 0.020% or less, even more preferably set to 0.018% or less, and most preferably set to 0.016% or less.
• P contributes to improving the strength of hot-rolled steel sheets, it is preferable to include 0.001% or more.
• the lower limit is not particularly limited, but in order to increase the strength of hot-rolled steel sheets, it is preferably set to 0.005% or more, and more preferably set to 0.007% or more.
• S 0.040% or less S forms MnS in steel and reduces the amount of Mn, which contributes to improving the strength of the hot-rolled steel sheet, so the S content is set to 0.040% or less.
• the S content is preferably set to 0.030% or less.
• the S content is more preferably set to 0.025% or less, even more preferably set to 0.023% or less, and most preferably set to 0.020% or less.
• Al 0.100% or less
• Al is an element contained to remove oxygen from steel.
• the formation of AlN in steel increases the amount of precipitated N and decreases the amount of dissolved N, thereby reducing the strength of the hot-rolled steel sheet. Therefore, the Al content is set to 0.100% or less. It is preferably set to 0.080% or less.
• the Al content is more preferably set to 0.070% or less, even more preferably set to 0.055% or less, and most preferably set to 0.040% or less.
• N 0.0050% or more and 0.0200% or less
• N is an element that contributes to improving the strength of hot-rolled steel sheets through solid solution strengthening. Therefore, the N content is set to 0.0050% or more.
• the N content is preferably set to 0.0060% or more.
• the N content is more preferably set to 0.0065% or more, even more preferably set to 0.0068% or more, and most preferably set to 0.0070% or more.
• the N content exceeds 0.0200%, the amount of N present as nitrides increases, and the r-value decreases. Therefore, the N content is set to 0.0200% or less.
• the N content is preferably set to 0.0180% or less.
• the N content is more preferably set to 0.0160% or less, even more preferably set to 0.0140% or less, and most preferably set to 0.0120% or less.
• the Cr content is set to 0.010% or more.
• Cr is preferably contained in an amount of 0.020% or more.
• the Cr content is more preferably 0.025% or more, even more preferably 0.028% or more, and most preferably 0.030% or more.
• the Cr content is set to 0.150% or less.
• the Cr content is preferably set to 0.100% or less.
• the Cr content is more preferably 0.080% or less, even more preferably 0.070% or less, and most preferably 0.060% or less.
• the above components are essential, and it is more preferable to contain the following elements in addition to the above component composition.
• Nb 0.003% or more and 0.030% or less
• Nb is an element that contributes to precipitation strengthening and grain refinement strengthening by forming fine NbC in steel. Therefore, when Nb is contained, the Nb content is set to 0.003% or more.
• the Nb content is preferably set to 0.005% or more.
• the Nb content is more preferably set to 0.010% or more.
• the Nb content is further preferably set to 0.012% or more, and most preferably set to 0.014% or more.
• the ductility of the steel sheet for cans decreases due to an increase in the recrystallization temperature after cold rolling.
• the Nb content when Nb is contained, the Nb content is set to 0.030% or less. In order to achieve both high strength and high ductility in the steel sheet for cans, the Nb content is preferably set to 0.025% or less. The Nb content is more preferably 0.022% or less, further preferably 0.021% or less, and most preferably 0.020% or less.
• the present invention may contain one or more elements selected from the following:
• Cu 0.40% or less
• Sn 0.04% or less
• Ni 0.15% or less
• Mo 0.10% or less
• Cu, Sn, Ni, and Mo improve the strength of the base material through solid solution strengthening.
• excessive content of these elements reduces the ductility of the hot-rolled steel sheet and the steel sheet for cans. Therefore, when Cu, Sn, Ni, and Mo are contained, the Cu content is set to 0.40% or less, the Sn content is set to 0.04% or less, the Ni content is set to 0.15% or less, and the Mo content is set to 0.10% or less.
• the Cu content is preferably set to 0.30% or less, the Sn content is preferably set to 0.03% or less, the Ni content is preferably set to 0.12% or less, and the Mo content is preferably set to 0.08% or less.
• the Cu content is more preferably 0.25% or less, the Sn content is more preferably 0.02% or less, the Ni content is more preferably 0.10% or less, and the Mo content is more preferably 0.06% or less.
• the Cu content is preferably 0.01% or more, and more preferably 0.03% or more.
• the Sn content is preferably 0.01% or more.
• the Ni content is preferably 0.01% or more, and more preferably 0.02% or more.
• the Mo content is preferably 0.01% or more, and more preferably 0.02% or more.
• Hot-rolled steel sheet according to one embodiment of the present invention has a chemical composition containing the above-mentioned components, with the remainder being Fe and unavoidable impurities.
• unavoidable impurities include H, Ca, O, Co, W, Zn, Pb, As, Sb, and Bi, which are mixed in with the raw materials or during the manufacturing process.
• the hot-rolled steel sheet of the present invention has a ferrite-based structure.
• a ferrite-based structure is defined as one in which the area ratio (area fraction) of ferrite is 70% or more. Therefore, the area fraction of ferrite is 70% or more.
• the area fraction of ferrite is preferably 80% or more, more preferably 85% or more, even more preferably 90% or more, and most preferably 92% or more.
• the upper limit is not particularly limited, but may be 100%. 99% or less is more preferable.
• the remainder other than ferrite may include cementite, pearlite, bainite, martensite, retained austenite, etc. If the area fraction of the remainder is 30% or less, the requirements of the present invention are met, and the area fraction of the remainder may be 0%.
• Average ferrite grain size of hot-rolled steel sheet is 15 ⁇ m or less in equivalent circle diameter.
• the most important technology is as follows: by refining the ferrite grains in the hot-rolled steel sheet, the ferrite texture of the steel sheet for cans obtained using the hot-rolled steel sheet can be controlled, enabling the steel sheet for cans to have a high r-value.
• the reason is presumably that, in order to improve the r-value of a steel sheet for cans, it is necessary to develop the ⁇ 111 ⁇ texture of the steel sheet for cans, and refinement of ferrite grains in the hot-rolled steel sheet promotes the development of the ⁇ 111 ⁇ texture of the steel sheet for cans. Therefore, the average ferrite grain size of the hot-rolled steel sheet is set to 15 ⁇ m or less in equivalent circle diameter. Preferably, it is set to 12 ⁇ m or less.
• the average ferrite grain size is preferably set to 3 ⁇ m or more in equivalent circle diameter. More preferably, it is set to 4 ⁇ m or more, and even more preferably, it is set to 5 ⁇ m or more. As will be described later, in order to obtain a predetermined average ferrite grain size, it is important to control the finishing temperature in hot rolling, the average cooling rate from 800°C to the coiling temperature, and the coiling temperature.
• the amount of N present as nitrides and the total amount of N satisfy the following formula (1): (amount of N present as nitrides)/(total amount of N) ⁇ 0.40 (1)
• the total N content is the total amount of N contained in the hot-rolled steel sheet.
• Nitride the ratio of the amount of N present as nitrides in the hot-rolled steel sheet (Nas Nitride) to the total amount of N in the hot-rolled steel sheet. If formula (1) is not satisfied, the amount of dissolved N becomes insufficient, resulting in a decrease in the strength of the hot-rolled steel sheet.
• the ratio (amount of N present as nitrides)/(total amount of N) is set to 0.40 or less. Furthermore, if the amount of N present as nitrides in the hot-rolled steel sheet becomes excessive, there is a concern that the r-value of the steel sheet for cans manufactured using the hot-rolled steel sheet will decrease. Therefore, in order to increase the r-value of the steel sheet for cans, the ratio (amount of N present as nitrides)/(total amount of N) in the hot-rolled steel sheet is preferably set to 0.30 or less. It is more preferably set to 0.28 or less, even more preferably set to 0.25 or less, most preferably set to 0.23 or less, and even more preferably set to 0.20 or less.
• the lower limit is not particularly limited, but is preferably set to 0.01 or more, and more preferably set to 0.03 or more. Note that, since the formula (1) is significantly affected by the coiling temperature and the cooling rate from 800°C to the coiling temperature, in order to obtain the formula (1), it is important to control the coiling temperature and the average cooling rate from 800°C to the coiling temperature within predetermined ranges.
• the amount of Nb present as Nb precipitates and the total amount of Nb satisfy the following formula (2): 0.10 ⁇ (amount of Nb present as Nb precipitates)/(total amount of Nb) ⁇ 0.80 (2)
• the total Nb content is the total amount of Nb contained in the hot-rolled steel sheet. When Nb is contained, it is important to increase the strength of the hot-rolled steel sheet by increasing the ratio of the amount of Nb present as Nb precipitates in the hot-rolled steel sheet to the total amount of Nb in the hot-rolled steel sheet. If the value of (amount of Nb present as Nb precipitates)/(total amount of Nb) is less than 0.10, the amount of Nb contributing to precipitation strengthening is small, and further strengthening of the hot-rolled steel sheet cannot be expected.
• the ratio (amount of Nb present as Nb precipitates)/(total amount of Nb) is preferably 0.10 or more, more preferably 0.15 or more, even more preferably 0.17 or more, and most preferably 0.20 or more.
• the value of (amount of Nb present as Nb precipitates)/(total amount of Nb) exceeds 0.80, the ductility of the steel sheet for cans decreases due to an increase in the recrystallization temperature after cold rolling.
• (amount of Nb present as Nb precipitates)/(total amount of Nb) is preferably 0.80 or less, more preferably 0.70 or less, even more preferably 0.69 or less, most preferably 0.68 or less, and most preferably 0.60 or less.
• Nb precipitates include all of Nb carbides, Nb nitrides, and Nb-containing carbonitrides.
• the method for manufacturing hot-rolled steel sheet according to the present invention is characterized by comprising a heating step in which a steel material having the above-described chemical composition is heated to 1150°C or higher, and a hot rolling step in which the steel material after the heating step is hot-rolled to a finishing temperature of 800°C or higher and 950°C or lower, cooled from 800°C to a coiling temperature of 450°C or higher and 700°C or lower at an average cooling rate of 20°C/s or higher, and coiled at a temperature of 450°C or higher and 700°C or lower.
• the steel sheet temperature described in the present invention refers to the temperature of the steel sheet surface, and this temperature is measured with a radiation thermometer.
• Heating temperature 1150°C or higher If the heating temperature in the heating step is low, coarse nitrides such as AlN are formed, and the ratio of the amount of N present as nitrides to the total amount of N in the hot-rolled steel sheet increases, resulting in a decrease in the strength of the base material and the r-value of the steel sheet for cans. Therefore, the heating temperature is set to 1150°C or higher.
• the heating temperature is preferably set to 1170°C or higher, more preferably 1180°C or higher, even more preferably 1200°C or higher, and most preferably 1220°C or higher. There is no upper limit to the heating temperature, but from the viewpoint of production costs, it is preferably set to 1300°C or lower, more preferably 1280°C or lower.
• Finishing temperature 800°C or higher and 950°C or lower If the finishing temperature in the hot rolling process exceeds 950°C, ferrite grains become coarse, not only reducing the strength of the hot-rolled steel sheet but also reducing the r-value of the steel sheet for cans manufactured using the hot-rolled steel sheet, so the finishing temperature is set to 950°C or lower.
• the finishing temperature is preferably set to 930°C or lower.
• the finishing temperature is more preferably set to 920°C or lower, and most preferably set to 900°C or lower.
• the finishing temperature is set to 800°C or higher.
• coarse Nb(C,N) precipitates during hot rolling if the finishing temperature is less than 800°C.
• the coarse Nb(C,N) does not contribute to improving the strength of the hot-rolled steel sheet and also reduces the amount of solute C and N, thereby reducing the strength of the hot-rolled steel sheet. Therefore, the finishing temperature in the hot-rolling process is set to 800°C or higher.
• the finishing temperature is preferably set to 820°C or higher, more preferably 830°C or higher, even more preferably 840°C or higher, and most preferably 850°C or higher.
• Average cooling rate from 800°C to the coiling temperature 20°C/s or more If the average cooling rate from 800°C to the coiling temperature is less than 20°C/s, ferrite grains after the hot rolling process will become coarse, and the strength of the hot-rolled steel sheet will decrease. Therefore, the average cooling rate from 800°C to the coiling temperature is set to 20°C/s or more. In order to increase the strength of the hot-rolled steel sheet, the average cooling rate is preferably 25°C/s or more, more preferably 30°C/s or more. It is further preferably 35°C/s or more, and most preferably 40°C/s or more.
• the average cooling rate to the coiling temperature is preferably 80°C/s or less, more preferably 75°C/s or less, and even more preferably 70°C/s or less.
• the average cooling rate can be calculated by dividing the temperature difference between the cooling start temperature (here, 800°C) and the cooling stop temperature (here, the coiling temperature) by the cooling time required for cooling.
• Coiling temperature 450°C or higher and 700°C or lower
• the coiling temperature exceeds 700°C
• ferrite grains become coarse, and the strength of the hot-rolled steel sheet decreases.
• the formation of coarse alloy carbides and nitrides is promoted, which reduces the amount of solute C and solute N, causing a decrease in the strength of the hot-rolled steel sheet. Therefore, the coiling temperature is set to 700°C or lower.
• the coiling temperature is preferably set to 650°C or lower.
• the coiling temperature is more preferably set to 640°C or lower, even more preferably set to 630°C or lower, and most preferably set to 620°C or lower.
• the coiling temperature is set to 450°C or higher.
• the coiling temperature is preferably set to 500°C or higher.
• the coiling temperature is more preferably 520° C. or higher, even more preferably 530° C. or higher, most preferably 540° C. or higher, and most preferably 550° C. or higher.
• the steel sheet may be pickled with an aqueous solution of H 2 SO 4 , HCl, H 3 PO 4 or the like to remove scale.
• the cooling rate after coiling is not particularly limited, but particularly when the coiling temperature is high (650°C or higher but 700°C or lower), this affects the average ferrite grain size and the size of nitrides and Nb precipitates, so the average cooling rate after coiling is preferably 1°C/s or higher, more preferably 2°C/s or higher, and even more preferably 3°C/s or higher. Furthermore, the average cooling rate after coiling is preferably 100°C/s or lower, more preferably 95°C/s or lower, and even more preferably 90°C/s or lower.
• the average cooling rate after coiling refers to the average cooling rate from the coiling temperature to 300°C, and is calculated by dividing the temperature difference between the coiling temperature and 300°C by the cooling time (the time required for cooling during this period).
• the hot-rolled steel sheet obtained above can be subjected to cold rolling, annealing, and temper rolling, which are the usual manufacturing conditions for steel sheets for cans, to obtain steel sheets for cans having high strength, high ductility, and a high r-value.
• the cold rolling, annealing, and temper rolling are not particularly limited.
• cold rolling is preferably performed at a rolling reduction of 70% or more, more preferably 75% or more.
• it is preferably performed at a rolling reduction of 95% or less, more preferably 93% or less.
• annealing is preferably performed at 680°C or more, more preferably 700°C or more.
• annealing is preferably performed at 850°C or less, more preferably 800°C or less.
• the annealing is preferably held at the above temperature for 5 seconds or more, more preferably 10 seconds or more. Furthermore, it is preferably held at the above temperature for 90 seconds or less, more preferably 85 seconds or less. After holding for the above time, it is preferably cooled to a cooling stop temperature of 600°C or less at an average cooling rate of 10°C/s or more, more preferably 30°C/s or more. Furthermore, it is preferably cooled at 150°C/s or less, more preferably 130°C/s or less. Temper rolling is preferably carried out at a reduction rate of 0.1% or more, more preferably 0.3% or more. Temper rolling is preferably carried out at a reduction rate of 5.0% or less, more preferably 3.0% or less. The average cooling rate to the cooling stop temperature of 600°C or less is calculated by dividing the temperature difference between the annealing temperature and the cooling stop temperature by the cooling time required for cooling during this period.
• the chemical composition of steel sheets for cans is preferably the same as that of the hot-rolled steel sheets described above, for the reasons explained for the hot-rolled steel sheets.
• the microstructure of steel sheets for cans is preferably a structure mainly composed of ferrite.
• a steel sheet for cans having an upper yield stress of 380 MPa or more, a total elongation of 20% or more, and an r-value of 0.9 or more was obtained.
• the upper yield stress is 700 MPa or less
• the total elongation is 50% or less
• the r-value is 2.5 or less.
• the upper yield stress, total elongation, and r-value mentioned above were determined using the test methods explained in the examples, and are the properties after the obtained steel sheet was subjected to aging heat treatment at 210°C for 10 minutes.
• the hot-rolled steel sheet structure was observed using the following procedure.
• a test piece was taken from the hot-rolled steel sheet so that the observation surface was the centre of the sheet width, and then a cross section parallel to the rolling direction and sheet thickness direction (L cross section) at a position halfway in the sheet thickness direction was polished and etched with nital to reveal the structure, which was used as a sample for structure observation.
• the above target surface was observed at 400x magnification using an optical microscope, and the structure of three randomly selected fields was photographed.
• the ferrite grain size was determined using the cutting method specified in JIS G 0551, and the average value of the three fields was taken as the average ferrite crystal grain size.
• the amount of N present as nitrides and the amount of Nb present as Nb precipitates were measured by pickling samples taken from the hot-rolled steel sheets to remove scale and then using the following method.
• the amount of N present as nitrides was measured by bis-pyrazolone absorptiometry after Br methanol extraction, H2SO4 + K2SO4 decomposition , and alkaline steam distillation.
• the amount of Nb present as Nb precipitates was determined by ICP-AES measurement after AA electrolytic extraction, filter collection, and mixed acid decomposition.
• Table 3 shows the calculation results of the following formulas (1) and (2). (Amount of N present as nitride)/(Total amount of N) ⁇ 0.40 (1) The total N content is the total amount of N contained in the hot-rolled steel sheet. 0.10 ⁇ (amount of Nb present as Nb precipitates)/(total amount of Nb) ⁇ 0.80 (2) The total Nb content is the total amount of Nb contained in the hot-rolled steel sheet.
• JIS No. 5 tensile test pieces were taken from the hot-rolled steel sheets obtained above, with the tensile direction aligned with the rolling direction, and tensile tests were conducted in accordance with JIS Z 2241 to evaluate the tensile strength. Hot-rolled steel sheets with a tensile strength of 350 MPa or more were determined to have excellent tensile strength.
• hot-rolled steel sheets No. 1 to 17 were pickled, then cold-rolled at a reduction ratio of 85% to 90%, and then annealed at a soaking temperature of 720°C for 21 seconds to produce steel sheets for cans.
• Test specimens for tensile tests and Lankford tests were taken from the above-mentioned steel sheets for cans and subjected to aging heat treatment at 210°C for 10 minutes in an incubator. Tensile tests and Lankford tests were then conducted as described below.
• tensile test a JIS No. 5 tensile test piece was used, with the tensile direction aligned with the rolling direction. Tensile tests were conducted in accordance with JIS Z 2241, and the upper yield stress and total elongation were evaluated.
• the Lankford test was performed using the natural frequency method (JSS YR-05058).
• the resonance frequencies were measured in the rolling direction, at a 45° angle to the rolling direction, and perpendicular to the rolling direction to determine the Young's modulus in each direction, and the average plastic strain ratio r- was calculated and evaluated as the r-value of the can steel sheet.
• Table 3 shows the evaluation results for the structure and tensile strength of the hot-rolled steel sheets, and the evaluation results for the upper yield stress, total elongation, and r-value of the steel sheets for cans.
• the hot-rolled steel sheets had a ferrite area ratio of 70% or more, an average ferrite grain size of 15 ⁇ m or less, satisfied the following formula (1), and achieved a tensile strength of 350 MPa or more.
• All of the steel sheets for cans manufactured by cold rolling and annealing the hot-rolled steel sheets of the invention examples described above achieved an upper yield stress of 380 MPa or more, a total elongation of 20% or more, and an r-value of 0.9 or more.
• the examples of the invention can be said to be hot-rolled steel sheets suitable as base materials for steel sheets for cans, with high strength, high ductility, and a high r-value.
• the comparative examples whose chemical compositions or manufacturing conditions were outside the scope of the invention, had ferrite fraction, average ferrite grain size, or formula (1) outside the range of the present invention, and did not achieve the target properties for one or more of the tensile strength of the hot-rolled steel sheet, upper yield stress of the steel sheet for cans, total elongation, or r-value.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Sheet Steel (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=97490181

Family Applications (1)

Country Status (2)

Citations (4)

• 2025
  • 2025-04-18 WO PCT/JP2025/015258 patent/WO2025225531A1/ja active Pending
  • 2025-04-18 JP JP2025541653A patent/JP7779447B1/ja active Active

Patent Citations (4)

Also Published As

Similar Documents

Legal Events