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
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • 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
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron

Definitions

• the present invention relates to a steel sheet with high strength, high ductility, and low yield elongation, which is particularly suitable for use as steel sheet for cans, and a method for manufacturing the same.
• DR (double reduce) 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 again after cold rolling and annealing.
• it has issues with low workability due to its small elongation, and high manufacturing costs due to the need to perform cold rolling again after annealing.
• SR single reduce
• Patent Document 1 proposes a steel plate containing, by mass%, C: 0.03% to 0.13%, Si: 0.05% or less, Mn: 0.01% to 0.6%, P: 0.025% or less, S: 0.020% or less, Al: 0.01% to 0.20%, N: 0.0001% to 0.02%, Ti: 0.005% to 0.02%, and B: 0.0005% to 0.02%, with the remainder being iron and unavoidable impurities, and containing, by area percentage, 84.0% or more ferrite, 0.5% to 10.0% martensite, and 0.1% to 10.0% bainite.
• Patent document 2 states, in mass%, C: 0.085% to 0.130%, Si: 0.04% or less, Mn: 0.10% to 0.60%, P: 0.02% or less, S: over 0.010% to 0.020%, Al: 0.02% to 0.10%, N: 0.0005% to 0.0040%, Nb: 0.007% to 0.030%, B: 0.0010% to 0.0050%.
• the proposed steel sheet for cans contains the following, has a B/N ratio (mass%) of 0.80 or more, with the balance being Fe and unavoidable impurities, has a ferrite structure containing pearlite at an area fraction of 1.0% or more, has a yield stress of 500 MPa or more, a tensile strength of 550 MPa or more, a uniform elongation of 10% or more, and a yield elongation of 5.0% or less.
• Patent Document 1 allows a yield elongation of up to 10%, which means that wrinkles due to stretcher strain may occur when the can body is subjected to complex processing.
• the lower limit of the upper yield stress is 400 MPa and the lower limit of the tensile strength is 500 MPa, there is an issue that the can body strength is insufficient when the steel plate is gauged down.
• Patent Document 2 produces high-strength steel sheets with a yield stress of 500 MPa or more and a tensile strength of 550 MPa or more, but because a yield elongation of up to 5.0% is permitted, there is an issue of wrinkles occurring due to stretcher strain. Furthermore, to ensure the strength when the steel sheet is used for the body of a can, a certain level of Rockwell superficial hardness is required, but neither Patent Document 1 nor Patent Document 2 makes any mention of hardness.
• the present invention aims to provide a steel plate with high strength, high ductility and low yield elongation that solves the above problems, and a manufacturing method thereof.
• the present invention has been made to solve the above problems, and the gist of the invention is as follows:
• [4] The steel plate according to any one of [1] to [3], having a yield stress of 450 MPa or more, a tensile strength of 550 MPa or more, an HR30T of 68 or more, a fracture elongation of 10% or more, and a yield elongation of 4.5% or less.
• a method for producing a steel sheet comprising: a cold rolling step in which the hot-rolled sheet after the hot rolling step is cold-rolled at a rolling ratio of 80% or more; and an annealing step in which the cold-rolled sheet after the cold rolling step is held at an annealing temperature of 700° C. or more and 900° C. or less for 5 s to 90 s and then cooled at an average cooling rate of 50° C./s or more to a cooling stop temperature range of 600° C. or less.
• the present invention has made it possible to manufacture steel sheets with high strength, high ductility and low yield point elongation.
• the present invention enables further gauge down of steel sheets for cans, which can reduce the weight of can bodies and reduce CO2 emissions during can body transportation. Furthermore, the occurrence of wrinkles due to stretcher strain is suppressed, which allows more complex processing to be performed on the can bodies.
• % means mass %.
• high strength when the tensile strength, yield stress and HR30T are excellent, it is called high strength.
• C 0.03% or more and 0.15% or less C is an element that contributes to improving the yield stress, tensile strength, and HR30T. It also plays a role in reducing the yield elongation by forming pearlite, bainite, martensite, and granular cementite. If the C content is less than 0.03%, the fraction of pearlite, bainite, martensite, and granular cementite decreases, and the yield stress, tensile strength, and HR30T decrease, so the C content needs to be 0.03% or more.
• the C content is preferably 0.06% or more, and more preferably 0.09% or more. It is even more preferable that the C content is 0.10% or more.
• the C content needs to be 0.15% or less.
• the C content is preferably 0.14% or less.
• the C content is more preferably 0.13% or less, and further preferably 0.12% or less.
• Si 0.05% or less Si is an element that contributes to improving yield stress and tensile strength, but if the content exceeds 0.05%, corrosion resistance decreases. Therefore, the Si content must be 0.05% or less, and is preferably 0.04% or less, more preferably 0.03% or less, and even more preferably 0.02% or less. There is no need to particularly limit the lower limit, but in order to increase the strength of the steel sheet, it is preferable that the Si content be 0.01% or more.
• Mn 0.10% or more and 0.60% or less Mn is an element that improves hardenability and promotes the formation of pearlite, bainite, and martensite. It is also known that Mn contributes to the improvement of yield stress, tensile strength, and HR30T by solid solution strengthening. If the Mn content is less than 0.10%, pearlite, bainite, and martensite are not sufficiently formed, and the yield stress, tensile strength, and HR30T decrease, so the Mn content is set to 0.10% or more. The Mn content is preferably set to 0.12% or more, and more preferably set to 0.15% or more. In addition, in order to ensure sufficient strength, the Mn content is more preferably set to 0.30% or more.
• the Mn content exceeds 0.60%, the fracture elongation decreases, so the Mn content is set to 0.60% or less. It is preferable to set the Mn content to 0.58% or less.
• the Mn content is more preferably 0.57% or less, further preferably 0.56% or less, and most preferably 0.55% or less.
• the P content is set to 0.025% or less.
• the P content is preferably set to 0.022% or less.
• the P content is more preferably set to 0.021% or less, further preferably set to 0.020% or less, and most preferably set to 0.019% or less.
• P contributes to improving the yield stress and tensile strength of the steel sheet, it is preferable to contain 0.001% or more.
• the P content is more preferably set to 0.003% or more.
• S 0.020% or less S forms sulfides such as MnS and TiS in steel and reduces ductility, so the S content is set to 0.020% or less.
• the S content is preferably set to 0.018% or less.
• the S content is more preferably set to 0.017% or less, even more preferably set to 0.016% or less, and most preferably set to 0.015% or less.
• the lower limit is not particularly limited, but in order to reduce the manufacturing load, it is preferably set to 0.005% or more.
• the S content is more preferably set to 0.006% or more.
• Al 0.20% or less
• Al is an element contained to remove oxygen in steel.
• it reduces the amount of solute N and reduces the yield elongation. Therefore, although there is no lower limit, it is preferable to contain 0.02% or more. It is more preferable that the Al content is 0.03% or more.
• the Al content is 0.15% or less, and more preferable that it is 0.12% or less. In order to achieve both high strength and high ductility, it is even more preferable that the Al content is 0.09% or less. It is most preferable that the Al content is 0.08% or less. Note that Al here refers to the total Al content.
• N is an element that contributes to the improvement of yield stress and tensile strength by solid solution strengthening. Therefore, the N content is set to 0.0001% or more.
• the N content is preferably set to 0.0003% or more, more preferably set to 0.0005% or more, and even more preferably set to 0.0008% or more.
• the N content is most preferably set to 0.0010% or more.
• the N content is preferably set to 0.0150% or less, and more preferably set to 0.0100% or less. In order to achieve both high strength and low yield elongation, the N content is more preferably set to 0.0040% or less.
• the N content is most preferably set to 0.0035% or less.
• Nb 0.005% 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, the Nb content is set to 0.005% or more.
• the Nb content is preferably set to 0.006% or more, and more preferably set to 0.007% or more. In order to achieve both high strength and high ductility, the Nb content is more preferably set to 0.010% or more. On the other hand, if the Nb content exceeds 0.030%, it becomes difficult to ensure sufficient ductility due to the increase in recrystallization temperature. Therefore, the Nb content is set to 0.030% or less. In order to achieve both high strength and high ductility, the Nb content is preferably set to 0.028% or less. The Nb content is more preferably set to 0.026% or less, more preferably set to 0.024% or less, and most preferably set to 0.022% or less.
• the steel sheet of the present invention preferably contains one or more elements selected from the following (Ni: 0.15% or less, Mo: 0.050% or less, Cr: 0.10% or less, Ti: 0.02% or less, B: 0.02% or less, V: 0.02% or less).
• Ni, Mo, and Cr are elements that promote the formation of pearlite, bainite, and martensite by improving hardenability. On the other hand, excessive addition of these elements reduces ductility.
• the Ni content is set to 0.15% or less.
• the Ni content is preferably set to 0.14% or less, and more preferably set to 0.13% or less.
• Mo is contained, the Mo content is set to 0.050% or less.
• the Mo content is preferably set to 0.048% or less, more preferably set to 0.047% or less, and even more preferably set to 0.046% or less.
• the Cr content is set to 0.10% or less.
• the Cr content is preferably set to 0.09% or less, and more preferably set to 0.08% or less.
• the Ni content is preferably 0.02% or more, more preferably 0.07% or more, and even more preferably 0.12% or more.
• the Mo content is preferably 0.010% or more, more preferably 0.020% or more, and even more preferably 0.030% or more.
• the Cr content is preferably 0.04% or more, more preferably 0.05% or more, and even more preferably 0.06% or more.
• Ti 0.02% or less
• B 0.02% or less
• Ti contributes to reducing the yield elongation by forming TiN in the steel and reducing the amount of solute N.
• TiN is generated preferentially over BN, by containing both Ti and B, sufficient solute B is ensured and hardenability is improved.
• the Ti content exceeds 0.02% and the B content exceeds 0.02%, it becomes difficult to ensure sufficient ductility.
• the Ti content is 0.02% or less. It is more preferable that the Ti content is 0.018% or less, and it is even more preferable that the Ti content is 0.016% or less.
• the B content When B is contained, the B content is 0.02% or less. It is preferable that the B content is 0.018% or less, and it is more preferable that the B content is 0.016% or less.
• the Ti content is preferably 0.005% or more, and more preferably 0.008% or more.
• the B content is preferably 0.0005% or more, and more preferably 0.002% or more.
• V 0.02% or less V contributes to improving yield stress, tensile strength and HR30T by promoting the formation of pearlite, bainite and martensite through solid solution strengthening, precipitation strengthening and improved hardenability.
• the V content is set to 0.02% or less.
• the V content is preferably set to 0.018% or less.
• the V content is more preferably set to 0.017% or less, even more preferably set to 0.016% or less, and most preferably set to 0.015% or less.
• the lower limit is not particularly limited, the V content is preferably set to 0.004% or more.
• the V content is more preferably set to 0.006% or more, and even more preferably set to 0.008% or more.
• the present invention preferably contains the following elements (Sn: 0.020% or less).
• Sn 0.020% or less
• Sn is an element that contributes to increasing the strength of the steel sheet by solid solution strengthening.
• the Sn content is 0.020% or less.
• the Sn content is preferably 0.018% or less, more preferably 0.015% or less, and preferably 0.012% or less.
• the Sn content is preferably 0.001% or more.
• the Sn content is more preferably 0.002% or more, and even more preferably 0.003% or more.
• the steel sheet according to one embodiment of the present invention has a composition containing the above-mentioned components, with the remainder being Fe and unavoidable impurities.
• unavoidable impurities include Cu, Ca, O, H, Co, W, Zn, Pb, As, Sb, Bi, etc.
• Area fraction of martensite 0.5% or more and 10.0% or less
• the area fraction of martensite is set to 0.5% or more.
• the area fraction of martensite is preferably set to 1.0% or more.
• the area fraction of martensite is more preferably set to 1.1% or more, and even more preferably set to 1.2% or more.
• the area fraction of martensite exceeds 10.0%, the ductility decreases, so the area fraction of martensite is set to 10.0% or less.
• the area fraction of martensite is preferably set to 8.0% or less.
• the area fraction of martensite is more preferably set to 7.9% or less, even more preferably set to 7.7% or less, and most preferably set to 7.5% or less.
• Sum of area fractions of pearlite, bainite, and granular cementite 5% to 30% Pearlite, bainite, and granular cementite contribute to improving yield stress, tensile strength, and HR30T, and also reduce yield elongation.
• the sum of the area fractions of pearlite, bainite, and granular cementite is set to 5% or more.
• the sum of the area fractions of pearlite, bainite, and granular cementite is preferably set to 10% or more.
• the sum of the area fractions of pearlite, bainite, and granular cementite is more preferably set to 11% or more, and even more preferably set to 12% or more.
• the sum of the area fractions of pearlite, bainite, and granular cementite exceeds 30%, ductility decreases, so the sum of the area fractions of pearlite, bainite, and granular cementite is set to 30% or less.
• the sum of the area fractions of pearlite, bainite, and granular cementite is preferably set to 25% or less.
• the sum of the area fractions of pearlite, bainite, and granular cementite is more preferably 23% or less, and further preferably 20% or less.
• the granular cementite having a maximum grain size of 3 ⁇ m or less is 1.0% or more in area fraction relative to the entire structure.
• the granular cementite having a maximum grain size of 3 ⁇ m or less suppresses an increase in yield elongation due to excessive solute C.
• the granular cementite is set to be 1.0% or more in area fraction relative to the entire structure.
• the granular cementite is preferably set to be 1.1% or more in area fraction relative to the entire structure, more preferably 1.2% or more, and even more preferably 1.3% or more in area fraction.
• the presence of coarse granular cementite reduces the yield stress and tensile strength, so the area fraction of fine granular cementite is important, and it is necessary to limit the area fraction of granular cementite having a maximum grain size of 3 ⁇ m or less.
• the granular cementite having a maximum grain size of 3 ⁇ m or less is preferably set to be 5.0% or less in area fraction.
• the area fraction of granular cementite having a maximum grain size of 3 ⁇ m or less is more preferably 5.0% or less, even more preferably 4.5% or less, and most preferably 4.0% or less.
• the area fraction of granular cementite having a maximum grain size of 2 ⁇ m or less it is more preferable to limit the area fraction of granular cementite having a maximum grain size of 2 ⁇ m or less, and it is preferable that the area fraction of granular cementite having a maximum grain size of 2 ⁇ m or less is 0.80% or more. It is even more preferable that the area fraction of granular cementite having a maximum grain size of 2 ⁇ m or less is 0.82% or more. Furthermore, it is preferable that the area fraction of granular cementite having a maximum grain size of 2 ⁇ m or less is 0.85% or less, and it is even more preferable that the area fraction of granular cementite having a maximum grain size of 2 ⁇ m or less is 0.83% or less.
• Yield stress 450 MPa or more, tensile strength: 550 MPa or more, HR30T: 68 or more, breaking elongation: 10% or more, yield elongation: 4.5% or less
• the yield stress (yield strength) of the steel sheet needs to be 450 MPa or more.
• the tensile strength needs to be 550 MPa or more.
• the HR30T needs to be 68 or more.
• the yield stress is preferably 480 MPa or more, more preferably 490 MPa or more, and even more preferably 500 MPa or more.
• the tensile strength is preferably 570 MPa or more, more preferably 580 MPa or more, and even more preferably 590 MPa or more.
• the HR30T is preferably 70 or more, more preferably 70.5 or more, and even more preferably 71 or more.
• the breaking elongation needs to be 10% or more, and is more preferably 12% or more.
• the breaking elongation is more preferably 12.5% or more, and most preferably 13% or more.
• the yield stress is preferably 700 MPa or less, more preferably 690 MPa or less, and even more preferably 680 MPa or less.
• the tensile strength is preferably 800 MPa or less, more preferably 790 MPa or less, and even more preferably 780 MPa or less.
• HR30T is preferably 80 or less, more preferably 79.5 or less, and even more preferably HR30T is 79 or less.
• the breaking elongation is preferably 25% or less.
• the breaking elongation is more preferably 24% or less, and even more preferably 23% or less.
• the yield elongation needs to be 4.5% or less.
• the yield elongation is preferably 4.0% or less.
• the yield elongation is more preferably 3.5% or less.
• the yield elongation is even more preferably 3.0% or less.
• the yield elongation is preferably 1.0% or more.
• the yield elongation is more preferably 1.1% or more.
• the method for manufacturing steel sheet in the present invention is characterized by including a heating step in which a steel material having the above-mentioned composition is heated to 1150°C or higher, a hot rolling step in which the steel after the heating step is hot rolled under conditions of a finishing temperature of 800°C to 950°C and a coiling temperature of 450°C to 700°C and then pickled, a cold rolling step in which the hot rolled sheet after the hot rolling step is cold rolled under conditions of a rolling ratio of 80% or higher, and an annealing step in which the cold rolled sheet after the cold rolling step is held at an annealing temperature of 700°C to 900°C for 5s to 90s and then cooled to a temperature range of 600°C or lower.
• Heating temperature 1150°C or higher If the heating temperature in the heating step is low, coarse nitrides such as AlN may be formed, which may reduce the strength and ductility of the steel sheet, so the heating temperature is set to 1150°C or higher.
• the heating temperature is preferably set to 1170°C or higher.
• the heating temperature is more preferably set to 1200°C or higher.
• the heating temperature is further preferably set to 1230°C or higher, and most preferably set to 1250°C or higher. There is no upper limit to the heating temperature, but from the viewpoint of manufacturing costs, it is preferably set to 1300°C or lower.
• the heating temperature is more preferably set to 1280°C or lower.
• finishing temperature 800°C or more and 950°C or less If the finishing temperature in the hot rolling process exceeds 950°C, the ferrite grain size of the hot rolled sheet becomes coarse, and the ferrite grain size also becomes coarse in the steel sheet that has undergone the subsequent process, making it difficult to ensure sufficient strength. Therefore, the finishing temperature is set to 950°C or less.
• the finishing temperature is preferably set to 930°C or less, and more preferably set to 900°C or less.
• the finishing temperature is more preferably set to 895°C or less, and most preferably set to 890°C or less.
• the finishing temperature in the hot rolling process is set to 800°C or more.
• the finishing temperature is preferably set to 820°C or more, and more preferably set to 850°C or more.
• Winding temperature 450°C or more and 700°C or less
• the winding temperature exceeds 700°C
• the ferrite grain size becomes coarse, and the strength of the steel sheet decreases.
• the formation of coarse alloy carbides is promoted, so that cementite does not dissolve sufficiently in the annealing process and coarse granular cementite remains, thereby reducing the area fraction of granular cementite with a maximum grain size of 3 ⁇ m or less.
• the area fraction of martensite, pearlite, and bainite decreases, which causes a decrease in strength and an increase in yield elongation. Therefore, the winding temperature is set to 700°C or less.
• the winding temperature is preferably set to 670°C or less, and more preferably set to 650°C or less.
• the winding temperature is more preferably set to 640°C or less, and most preferably set to 630°C or less.
• the coiling temperature is set to 450° C. or higher.
• the coiling temperature is preferably set to 480° C. or higher, and more preferably set to 500° C. or higher.
• the coiling temperature is further preferably set to 510° C. or higher, and most preferably set to 520° C. or higher.
• pickling is performed with an aqueous solution of H 2 SO 4 , HCl, H 3 PO 4, or the like in order to remove scale.
• Reduction ratio in cold rolling 80% or more After the hot rolling process, cold rolling is performed. The ferrite grain size is refined by this cold rolling process, and the yield stress and tensile strength are increased. In order to ensure sufficient yield stress and tensile strength, the rolling ratio is set to 80% or more.
• the rolling ratio is preferably set to 82% or more, and more preferably set to 85% or more.
• the rolling ratio is further preferably set to 86% or more, and most preferably set to 88% or more. There is no upper limit to the rolling ratio, but it is preferably set to 95% or less in order to ensure sufficient ductility. In addition, the rolling ratio is more preferably set to 93% or less.
• Annealing temperature 700°C or more and 900°C or less, holding time: 5s or more and 90s or less, cooling stop temperature: 600°C or less, average cooling rate to 600°C or less (cooling stop temperature range): 50°C/s or more Annealing is performed after the cold rolling process.
• the annealing temperature is set to 700°C or more in order to achieve high strength, high ductility, and low yield elongation by promoting the formation of pearlite, bainite, and martensite.
• the annealing temperature is preferably 720°C or more.
• the annealing temperature is more preferably 730°C or more, even more preferably 735°C or more, and most preferably 740°C or more.
• the annealing temperature is set to 900°C or less.
• the annealing temperature is preferably set to 850°C or less, more preferably 830°C or less, and even more preferably 800°C or less.
• the holding time at the annealing temperature is set to 5 seconds or more.
• the holding time is preferably set to 6 seconds or more, more preferably set to 7 seconds or more, even more preferably set to 8 seconds or more, and most preferably set to 10 seconds or more.
• the holding time at the annealing temperature is set to 90 seconds or less.
• the holding time is preferably set to 85 seconds or less, more preferably set to 80 seconds or less, even more preferably set to 75 seconds or less, and most preferably set to 70 seconds or less.
• the cooling stop temperature after annealing exceeds 600°C, the formation of martensite becomes insufficient and the tensile strength decreases, so the cooling stop temperature is set to 600°C or less.
• the cooling stop temperature is preferably set to 595°C or less, more preferably 590°C or less, even more preferably 585°C or less, and most preferably 580°C or less.
• the cooling stop temperature is preferably set to 300°C or more.
• the cooling stop temperature is more preferably set to 310°C or more, even more preferably 320°C or more, and most preferably 330°C or more.
• the temperature may be held in a temperature range of 150°C or more after cooling is stopped.
• the holding temperature range is preferably 170°C or more, and more preferably 200°C or more. It may also be held in a temperature range of 600°C or less.
• the holding temperature range is preferably 590°C or less, and more preferably 580°C or less.
• the holding time in the temperature range of 150°C to 600°C (if the temperature range is the preferred temperature range) after cooling is stopped is preferably 300 seconds or less.
• the holding time is more preferably 280 seconds or less, even more preferably 260 seconds or less, and most preferably 240 seconds or less.
• the holding time is preferably 200 seconds or more, and more preferably 220 seconds or more.
• the average cooling rate after annealing is set to 50°C/s or more.
• the average cooling rate after annealing is preferably set to 55°C/s or more, and more preferably set to 60°C/s or more.
• the average cooling rate after annealing is set to 80°C/s or more. It is most preferable that the average cooling rate after annealing is set to 85°C/s or more. There is no particular upper limit, but it is preferable that the average cooling rate is set to 200°C/s or less in order to reduce the manufacturing load. It is more preferable that the average cooling rate after annealing is set to 195°C/s or less, and even more preferable that it is set to 190°C/s or less.
• Temper rolling may be performed after the annealing step. Since temper rolling can increase the yield stress and reduce the yield elongation, it is preferable to perform temper rolling with a reduction of 0.5% or more. A reduction of 0.6% or more is more preferable, a reduction of 0.8% or more is even more preferable, and a reduction of 0.9% or more is most preferable. On the other hand, since a large reduction in temper rolling reduces ductility, a reduction of 10% or less is preferable. A reduction of 8% or less is more preferable, a reduction of 6% or less is even more preferable, and a reduction of 5% or less is most preferable.
• Steel slabs were obtained by melting and casting steel containing the components of steel types No. 1 to 29 shown in Table 1, with the remainder being Fe and unavoidable impurities.
• the steel slabs obtained here were heated, hot rolled, cold rolled and annealed under the conditions shown in Table 2, and then temper rolled with a reduction ratio of 1% to obtain steel plates No. 1 to 39.
• JIS No. 5 tensile test pieces with the tensile direction along the rolling direction and 30 mm square test pieces for measuring Rockwell superficial hardness were taken from the above steel plate and aged in an incubator at 210°C for 10 minutes.
• Tensile tests were conducted on the tensile test pieces in accordance with JIS Z 2241 to evaluate the yield stress, tensile strength, fracture elongation and yield elongation.
• HR30T was also calculated by measuring the Rockwell superficial hardness of the plate surface at HR15T and converting it using the conversion table in JIS G 3303 (2017).
• Table 3 shows the evaluation results for yield stress, tensile strength, breaking elongation, yield elongation and HR30T.
• the steel plate structure was observed as follows. After taking a test piece from the steel plate, the cross section parallel to the rolling direction was polished and etched with nital to reveal the structure, and a sample for structure observation was taken. A scanning electron microscope (SEM) was used to observe the position at 1/2 the plate thickness direction at a magnification of 3000 times, and the structure of three randomly selected fields was photographed. Table 3 shows the area fraction of granular cementite, the area fraction of martensite, and the sum of the area fractions of pearlite, bainite, and granular cementite in the SEM images measured using image processing software.
• martensite was defined as the second phase that exists at the ferrite grain boundary or grain boundary triple junction and has a relatively smooth surface.
• the combined fraction of pearlite, bainite, and granular cementite was calculated by subtracting the martensite fraction from the fraction of the entire second phase.
• the area fractions shown in Table 3 were the average values of the three fields.
• Granular cementite was identified using the image processing software Image-J, and size measurements were made using the scale bar used when photographing the SEM image.
• All of the examples of the invention in Table 3 have a yield stress of 450 MPa or more, a tensile strength of 550 MPa or more, an HR30T of 68 or more, a breaking elongation of 10% or more, and a yield elongation of 4.5% or less. Therefore, it can be said that the examples of the invention are steel sheets with high strength, high ductility, and low yield elongation, suitable as a material for cans.
• the comparative examples in which one or more of the component composition, the area fraction of the steel sheet structure, and the manufacturing conditions are outside the range of the invention, have any of the yield stress, tensile strength, HR30T, breaking elongation, and yield elongation that are outside the range of the invention.

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