STEEL SHEET, METHOD FOR MANUFACTURING SAME AND PLATED STEEL SHEET

Abstract

This steel sheet has a predetermined chemical composition and the steel sheet in which, at a ¼ depth position of a sheet thickness from a surface, an average grain size is 15.0 μm or less, a total grain boundary number density of solute C and solute B is 1.0 solute/nm.sup.2 or more and 12.0 solutes/nm.sup.2 or less, a total of pole densities of {211}<011> and {332}<113> in a thickness middle portion is 12.0 or less, and a tensile strength is 780 MPa or more is adopted.

Claims

1. A steel sheet having a chemical composition containing, by mass %: C: 0.02% to 0.15%, Si: 0.005% to 2.000%, Mn: 1.00% to 3.00%, Ti: 0.010% to 0.200%, sol. Al: 0.001% to 1.000%, N: 0.0010% to 0.0100%, P: 0.100% or less, S: 0.0100% or less, Nb: 0% to 0.100%, V: 0% to 0.500%, Mo: 0% to 0.500%, Cu: 0% to 1.00%, Ni: 0% to 1.00%, Cr: 0% to 2.00%, B: 0% to 0.0020%, Ca: 0% to 0.0100%, Mg: 0% to 0.0100%, REM: 0% to 0.0100%, and Bi: 0% to 0.0200% with a remainder consisting of Fe and an impurity, wherein, at a ¼ depth position of a sheet thickness from a surface, a total area fraction of tempered martensite and tempered bainite is 10% or more and 100% or less, an area fraction of ferrite is 0% or more and 90% or less, an area fraction of residual austenite is 0% or more and less than 4%, a total area fraction of the residual austenite, fresh martensite, cementite, and pearlite is 0% or more and 10% or less, an average grain size is 15.0 μm or less, a total grain boundary number density of solute C and solute B is 1.0 solute/nm.sup.2 or more and 12.0 solutes/nm.sup.2 or less, a total of pole densities of {211}<011> and {332}<113> in a thickness middle portion is 12.0 or less, and a tensile strength is 780 MPa or more.

2. The steel sheet according to claim 1, wherein the chemical composition contains, by mass %, one or more of Nb: 0.001% to 0.100%, V: 0.005% to 0.500%, Mo: 0.001% to 0.500%, Cu: 0.02% to 1.00%, Ni: 0.02% to 1.00%, Cr: 0.02% to 2.00%, B: 0.0001% to 0.0020%, Ca: 0.0002% to 0.0100%, Mg: 0.0002% to 0.0100%, REM: 0.0002% to 0.0100%, and Bi: 0.0001% to 0.0200%.

3. A method for manufacturing the steel sheet according to claim 1 or 2, the method comprising: a step of performing multi-pass hot rolling on a slab or steel piece having the chemical composition according to claim 1 or 2 using a plurality of rolling stands; and a step of performing a heat treatment, wherein, in the step of performing multi-pass hot rolling, a heating temperature is set to 1200° C. to 1350° C., when a finish temperature is expressed as FT in a unit of ° C., a total rolling reduction in a temperature range of higher than the FT+50° C. and the FT+150° C. or lower is set to 50% or more, a total rolling reduction within a temperature range of from the FT to the FT+50° C. is set to 40% to 80%, a time necessary for rolling within the temperature range of from the FT to the FT+50° C. is set to 0.5 to 10.0 seconds, two or more passes of rolling are performed in each of the temperature range of higher than the FT+50° C. and the FT+150° C. or lower and the temperature range of from the FT to the FT+50° C., an average cooling rate within a temperature range of from the FT to the FT+100° C. is set to 6.0° C./sec or faster, finish rolling is completed with the FT set to equal to or higher than Ar.sub.3 that is obtained from Expression (1) and set to equal to or higher than TR that is obtained from Expression (2) and 1100° C. or lower, then, water cooling is initiated within 3.0 seconds, cooling is performed by setting an average cooling rate within a temperature range of from the FT to 750° C. to 30° C./sec or faster, retaining the slab or steel piece within a temperature range of from 750° C. to 600° C. for 20 seconds or shorter, and then setting an average cooling rate within a temperature range of from a cooling stop temperature of 600° C. to lower than Ms−200° C. to 30° C./sec or faster, in the step of performing the heat treatment, a maximum attainment temperature Tmax during the heat treatment is set to 300° C. to 720° C., and a tempering parameter Ps is set to 14.6×Tmax+5891 or more and 17.1×Tmax+6223 or less,
Ar.sub.3(° C.)=901−325×[C]+33×[Si]−92×[Mn]+287×[P]+40×[sol. Al]  (1)
TR(° C.)=800+700×[Ti]+1000×[Nb]  (2) here, each element symbol in Expression (1) and Expression (2) indicates an amount of each element by mass %, and zero is assigned in a case where the element is not contained.

4. The method for manufacturing a steel sheet according to claim 3, wherein, in the step of performing multi-pass hot rolling, an average cooling rate within a temperature range of from the cooling stop temperature of Ms that is obtained from Expression (3) to lower than Ms−200° C. is set to 80° C./sec or faster,
Ms(° C.)=561−474×[C]−33×[Mn]−17×[Ni]−21×[Mo]  (3) here, each element symbol in Expression (3) indicates an amount of each element by mass %, and zero is assigned in a case where the element is not contained.

5. The method for manufacturing a steel sheet according to claim 3, wherein, in the step of performing multi-pass hot rolling, the water cooling is initiated within 0.3 seconds after completion of the finish rolling, and cooling in which an average cooling rate within a temperature range of from the FT to the FT−40° C. is 100° C./sec or faster is performed.

6. The method for manufacturing a steel sheet according to claim 5, wherein, in the step of performing multi-pass hot rolling, a step of performing cooling in which an average cooling rate within a temperature range from the FT to the FT−40° C. is 100° C./sec or faster is performed between the rolling stands.

7. A plated steel sheet comprising: the steel sheet according to claim 1 or 2; and a plating layer formed on a surface of the steel sheet.

8. The plated steel sheet according to claim 7, wherein the plated layer is a hot-dip galvanized layer.

9. The plated steel sheet according to claim 7, wherein the plated layer is a hot-dip galvannealed layer.

10. The method for manufacturing a steel sheet according to claim 4, wherein, in the step of performing multi-pass hot rolling, the water cooling is initiated within 0.3 seconds after completion of the finish rolling, and cooling in which an average cooling rate within a temperature range of from the FT to the FT−40° C. is 100° C./sec or faster is performed.

11. A steel sheet having a chemical composition containing, by mass %: C: 0.02% to 0.15%, Si: 0.005% to 2.000%, Mn: 1.00% to 3.00%, Ti: 0.010% to 0.200%, sol. Al: 0.001% to 1.000%, N: 0.0010% to 0.0100%, P: 0.100% or less, S: 0.0100% or less, Nb: 0% to 0.100%, V: 0% to 0.500%, Mo: 0% to 0.500%, Cu: 0% to 1.00%, Ni: 0% to 1.00%, Cr: 0% to 2.00%, B: 0% to 0.0020%, Ca: 0% to 0.0100%, Mg: 0% to 0.0100%, REM: 0% to 0.0100%, and Bi: 0% to 0.0200% with a remainder comprising Fe and an impurity, wherein, at a ¼ depth position of a sheet thickness from a surface, a total area fraction of tempered martensite and tempered bainite is 10% or more and 100% or less, an area fraction of ferrite is 0% or more and 90% or less, an area fraction of residual austenite is 0% or more and less than 4%, a total area fraction of the residual austenite, fresh martensite, cementite, and pearlite is 0% or more and 10% or less, an average grain size is 15.0 μm or less, a total grain boundary number density of solute C and solute B is 1.0 solute/nm.sup.2 or more and 12.0 solutes/nm.sup.2 or less, a total of pole densities of {211}<011> and {332}<113> in a thickness middle portion is 12.0 or less, and a tensile strength is 780 MPa or more.

Description

EXAMPLES

[0222] Next, the effect of one aspect of the present invention will be more specifically described using examples, but conditions in the examples are simply examples of the conditions adopted to confirm the feasibility and effect of the present invention, and the present invention is not limited to these examples of the conditions. The present invention is capable of adopting a variety of conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

[0223] Steels having a chemical composition shown in Table 1 were melted, cast and then made into steel pieces having a thickness of 30 to 40 mm by hot forging. The obtained steel pieces were heated, hot rolled by performing rolling a plurality of times (two to four passes) in a small tandem mill for testing within both of a temperature range of higher than FT+50° C. and FT+150° C. or lower and a temperature range of from FT to FT+50° C. to obtain sheet thicknesses of 2.5 to 3.5 mm, and subjected to a heat treatment, thereby obtaining steel sheets. The manufacturing conditions are shown in Table 2A and Table 2B. It should be noted that the time interval at the time of calculating the tempering parameter Ps was set to 1 second. In addition, plating was performed on a part of the steel sheets.

TABLE-US-00001 TABLE 1 Chemical composition (mass %) Remainder: Fe and impurity Ar.sub.3 Ms TR Steel C Si Mn Ti sol. Al N P S Others (° C.) (° C.) (° C.) Note A 0.07 1.050 1.89 0.109 0.310 0.0035 0.010 0.0030 754 465 876 Invention Steel B 0.09 1.180 3.58 0.100 0.200 0.0032 0.015 0.0025 594 400 870 Comparative Steel C 0.07 1.100 1.85 0.095 0.300 0.0031 0.016 0.0025 B: 0.0012 761 467 867 Invention Steel D 0.26 0.980 2.10 0.060 0.340 0.0028 0.012 0.0030 673 368 842 Comparative Steel E 0.06 0.950 1.75 0.107 0.380 0.0022 0.010 0.0018 Nb: 0.008 770 475 875 Invention Steel F 0.06 1.050 1.72 0.117 0.290 0.0029 0.014 0.0030 Mo: 0.150, Cr: 0.36 774 473 882 Invention Steel G 0.06 1.050 1.70 0.134 0.410 0.0022 0.017 0.0031 781 476 894 Invention Steel H 0.07 0.990 1.77 0.234 0.380 0.0024 0.014 0.0039 767 469 964 Comparative Steel I 0.06 1.010 1.85 0.119 0.410 0.0028 0.016 0.0033 Nb: 0.048 766 472 931 Invention Steel J 0.07 1.080 1.63 0.130 0.280 0.0036 0.013 0.0039 Ca: 0.0018 779 474 891 Invention Steel K 0.06 1.060 1.73 0.129 0.390 0.0034 0.017 0.0031 Bi: 0.0012 778 475 890 Invention Steel L 0.07 1.180 1.78 0.120 0.040 0.0036 0.019 0.0040 760 469 884 Invention Steel M 0.06 1.100 1.73 0.123 0.320 0.0030 0.019 0.0044 V: 0.090 777 475 886 Invention Steel N 0.15 1.150 1.60 0.099 0.320 0.0025 0.012 0.0035 759 437 869 Invention Steel O 0.11 0.550 2.20 0.120 0.510 0.0041 0.012 0.0032 705 436 884 Invention Steel P 0.07 1.100 0.85 0.100 0.410 0.0035 0.010 0.0022 856 500 870 Comparative Steel Q 0.07 1.070 1.71 0.128 0.400 0.0040 0.019 0.0049 Mg: 0.0012 778 471 890 Invention Steel R 0.07 1.040 1.84 0.119 0.370 0.0032 0.021 0.0031 764 467 883 Invention Steel S 0.07 1.080 2.06 0.135 0.400 0.0032 0.017 0.0036 REM: 0.0016 745 460 895 Invention Steel T 0.07 1.340 1.74 0.110 0.070 0.0029 0.012 0.0025 769 470 877 Invention Steel U 0.05 0.980 1.66 0.134 0.360 0.0037 0.019 0.0038 Cu: 0.15, Ni: 0.30 784 477 894 Invention Steel V 0.04 0.010 1.52 0.112 0.350 0.0025 0.015 0.0021 Nb: 0.021 767 492 899 Invention Steel Underlines indicate that values are outside the scope of the present invention.

TABLE-US-00002 TABLE 2A Total rolling reduction in Total rolling Average Time after temperature range reduction in Rolling time in cooling rate in finish rolling of higher than FT + temperature range temperature range temperature range to initiation Steel Heating 50° C. to FT + of FT ° C. to FT + of FT ° C. to FT + of FT to FT + Finish of water sheet temperature 150° C. or lower 50° C. 50° C. 100° C. temperature cooling No. Steel (° C.) (%) (%) (s) (° C./sec) (° C.) (s) 1 A 1267 60 79 3.2 15.1 917 0.2 2 A 1271 62 44 2.2 17.8 939 0.6 3 A 1265 58 48 2.3 16.4 951 0.4 4 A 1263 63 70 2.2 15.7 989 2.0 5 A 1266 61 73 2.0 15.8 946 0.3 6 A 1267 61 71 2.1 16.2 958 0.1 7 A 1267 65 65 3.6 15.1 951 0.1 8 A 1266 24 65 1.9 17.2 926 0.5 9 A 1272 78 85 3.2 15.1 903 0.4 10 A 1266 63 72 0.4 16.5 902 0.5 11 A 1266 65 67 3.5  2.4 921 1.0 12 B 1260 81 66 1.9 16.9 947 0.6 13 C 1262 82 66 2.2 15.0 953 0.5 14 D 1272 67 64 2.2 17.0 941 0.5 15 E 1260 69 66 2.2 15.1 966 0.1 16 E 1267 66 67 2.2 15.7 934 0.1 17 F 1273 65 66 2.1 16.8 940 0.1 18 G 1263 78 66 1.9 17.1 960 0.1 19 H 1264 67 66 1.5 16.8 940 0.1 20 I 1274 69 66 1.8 17.8 952 0.1 21 J 1271 66 65 1.7 16.7 956 0.1 Average Average Average Average Dwell cooling cooling cooling rate in cooling rate in time rate from rate from Maximum temperature range temperature range between 600° C. to Ms to Cooling attainment Steel of FT to FT − of FT to 600° C. to cooling cooling stop temperature Tempering 14.6 × 17.1 × sheet 40° C. 750° C. 750° C. stop stop temperature Tmax parameter Tmax + Tmax + No. (° C./sec) (° C./sec) (s) (° C./sec) (° C./sec) (° C.) (° C.) Ps 5891 6223 1 85 56 6 62 129 51 545 14073 13848 15543 2 85 56 7 61 129 52 553 14215 13965 15679 3 69 32 8 66 85 41 560 14404 14067 15799 4 12 42 11 67 125 24 554 14295 13979 15696 5 106 96 6 62 75 45 554 14249 13979 15696 6 178 83 6 70 131 49 652 15926 15410 17372 7 143 70 8 66 130 41 495 13193 13118 14688 8 61 52 5 75 124 40 542 14043 13804 15491 9 69 41 2 69 123 42 556 14265 14009 15731 10 59 48 6 61 135 38 554 14209 13979 15696 11 37 40 8 62 130 40 556 14257 14009 15731 12 65 55 5 60 105 45 505 14056 13264 14859 13 77 53 7 74 108 53 625 15422 15016 16911 14 75 32 6 64 115 65 550 15452 13921 15628 15 195 57 7 70 131 51 652 15896 15410 17372 16 201 18 6 69 125 36 645 15840 15308 17253 17 189 51 14 66 118 27 652 15891 15410 17372 18 178 61 15 66 128 21 600 15003 14651 16483 19 187 48 7 78 124 39 600 15984 14651 16483 20 179 47 7 75 115 60 625 15495 15016 16911 21 195 61 2 60 122 31 648 15896 15352 17304 Underlines indicate that values are outside the scope of the present invention.

TABLE-US-00003 TABLE 2B Total rolling reduction in Total rolling Average Time after temperature range reduction in Rolling time in cooling rate in finish rolling of higher than FT + temperature range temperature range temperature range to initiation Steel Heating 50° C. to FT + of FT ° C. to FT + of FT ° C. to FT + of FT to FT + Finish of water sheet temperature 150° C. or lower 50° C. 50° C. 100° C. temperature cooling No. Steel (° C.) (%) (%) (s) (° C./sec) (° C.) (s) 22 J 1268 76 56 3.2 16.9 940 0.1 23 K 1280 69 67 1.9 17.7 932 0.1 24 L 1267 79 66 2.1 15.1 945 0.5 25 L 1280 66 72 3.9 17.6 950 0.5 26 L 1275 70 73 3.4 15.4 948 0.6 27 M 1261 81 66 1.9 18.0 948 0.1 28 N 1271 67 66 2.1 16.7 935 0.4 29 N 1262 82 65 1.7 16.3 840 0.4 30 O 1264 66 68 3.1 17.4 951 0.5 31 P 1265 68 62 2.4 17.3 946 0.6 32 Q 1276 78 67 2.1 17.3 948 0.1 33 R 1275 69 69 3.3 17.4 962 0.1 34 S 1265 68 70 2.0 15.5 929 0.1 35 T 1260 71 67 2.0 15.1 929 0.1 36 T 1270 62 69 2.7 15.0 965 0.1 37 T 1270 66 69 3.5 15.9 952 0.1 38 U 1263 69 68 3.1 15.4 933 0.1 39 V 1270 65 64 3.6 15.5 902 0.1 40 A 1285 85 75 4.7 12.5 945 0.1 41 A 1280 75 67 3.6 15.6 1050  0.1 42 A 1275 68 70 2.5 18.6 945 0.1 43 A 1278 66 69 3.9 15.4 956 0.1 Average Average Average Average Dwell cooling cooling cooling rate in cooling rate in time rate from rate from Maximum temperature range temperature range between 600° C. to Ms to Cooling attainment Steel of FT to FT − of FT to 600° C. to cooling cooling stop temperature Tempering 14.6 × 17.1 × sheet 40° C. 750° C. 750° C. stop stop temperature Tmax parameter Tmax + Tmax + No. (° C./sec) (° C./sec) (s) (° C./sec) (° C./sec) (° C.) (° C.) Ps 5891 6223 22 144 79 2 40 80 39 503 13773 13235 14824 23 165 45 7 71 156 64 605 15168 14724 16569 24 66 54 6 93 122 39 605 15088 14724 16569 25 55 49 8 66 130 40 280 10984 10709 11866 26 52 55 7 62 130 39 752 17716 16870 19082 27 187 50 7 76 119 55 514 14054 13395 15012 28 85 74 2 77 145 18 554 14285 13979 15696 29 54 38 3 85 105 44 543 14056 13819 15508 30 73 50 7 76 102 69 565 14387 14140 15885 31 77 49 7 81 111 73 564 14413 14125 15867 32 179 52 7 72 111 58 600 15005 14651 16483 33 156 48 7 92 135 63 600 15034 14651 16483 34 174 46 7 84 184 64 620 15409 14943 16825 35 152 82 6 53 152 38 603 15112 14695 16534 36 150 79 7 60 130 41 525 11882 13556 15201 37 138 94 6 58 130 40 602 17474 14680 16517 38 178 56 7 68 119 66 605 15095 14724 16569 39 172 80 10 65 130 43 558 14296 14038 15765 40 165 86 8 102 152 35 635 15968 15162 17082 41 156 86 8 70 156 32 605 16005 14724 16569 42 135 102 18 85 145 40 523 14256 13527 15166 43 142 98 8 95 135 35 710 17856 16257 18364 Underlines indicate that values are outside the scope of the present invention.

[0224] For each of the obtained steel sheets, the area fractions of metallographic structures, the average grain size, and the total grain boundary number density of solute C and solute B at a ¼ depth position of the sheet thickness from the surface of the steel sheet and the pole density of each crystal orientation at the thickness middle portion were obtained by the above-described methods. It should be noted that, in the measurement of the pole density of the crystal orientation at the thickness middle portion, the grain orientation information of approximately 3000 to 8000 bcc grains was measured.

[0225] In order to evaluate the mechanical properties of the obtained steel sheets, the tensile strength TS(MPa) and the total elongation at fracture El(%) were evaluated with a No. 5 test piece according to JIS Z 2241: 2011. The stretch flangeability was evaluated with the limiting hole expansion ratio λ(%) that was measured according to JIS Z 2256:2010. The low temperature toughness was evaluated with the fracture appearance transition temperature vTrs(° C.) and evaluated by performing a Charpy impact test using a V-notch test piece obtained by working the steel sheet into a 2.5 mm sub-size test piece according to JIS Z 2242:2005. For the evaluation of the peeling resistance, three holes were punched in the steel sheet by the method described in JIS Z 2256:2010, and the presence or absence of the occurrence of peeling was visually confirmed.

[0226] Table 3A and Table 3B show the test results of the metallographic structures, the textures, and the mechanical properties. It should be noted that, in the ‘plating’ columns of Table 3 and Table 3B, GI indicates a hot-dip galvanized layer and GA indicates a hot-dip galvannealed layer.

[0227] In the case of 780 MPa or more, the tensile strength was regarded as a high strength and determined as pass, and, when the vTrs(° C.) was −40° C. or lower, the low temperature toughness was regarded as excellent and determined as pass. The workability was evaluated with the balance between the strength and the total elongation at fracture (TS×El) and the balance between the strength and the stretch flangeability (TS×λ). In a case where TS×El(MPa.Math.%) was 12000 MPa.Math.% or more, the strength was regarded as high, and the elongation was regarded as excellent and determined as pass. In a case where TS×λ(MPa.Math.%) was 50000 MPa.Math.% or more, the strength was regarded as high, and the stretch flangeability was regarded as excellent and determined as pass. In a case where peeling occurred, ‘Bad’ is indicated in the tables, and, in a case where there was no peeling, the peeling resistance was determined as pass, and ‘Good’ is indicated in the tables.

TABLE-US-00004 TABLE 3A Area fraction of tempered Area fraction bainite + Area fraction of pearlite, Steel tempered Area fraction of residual fresh martensite, Average sheet martensite of ferrite γ and cementite grain size {211} <011> + Solute C + B No. Steel (%) (%) (%) (%) (μm) {332} <113> (solutes/nm.sup.2)  1 A 76 21 0 3 5.4 8.6 6.0  2 A 73 26 1 0 6.7 3.4 6.2  3 A 65 32 0 3 10.5  4.5 6.0  4 A 74 23 0 3 8.6 4.0 6.0  5 A 69 30 0 1 5.4 6.5 6.0  6 A 65 34 0 1 5.4 6.3 3.3  7 A 70 28 1 1 6.8 6.1 7.0  8 A 84 15 0 1 15.6  10.9  6.3  9 A 94 6 0 0 5.0 12.5  5.5 10 A 34 62 1 3 5.4 12.2  5.7 11 A 60 39 0 1 6.8 7.8 0.8 12 B 96 0 4 0 6.0 4.1 4.5 13 C 73 25 0 2 5.6 4.8 3.8 14 D 58 20 0 22  6.9 5.4 3.5 15 E 61 36 0 3 5.2 4.0 3.2 16 E 11 75 2 12  4.6 5.5 1.2 17 F 77 23 0 0 4.7 5.4 3.3 18 G 70 28 0 2 4.5 4.5 4.6 19 H 59 39 0 2 5.6 2.4 4.6 20 I 64 35 0 1 5.0 4.5 4.1 21 J 98 2 0 0 4.9 4.8 3.4 Steel sheet TS El TS × El λ TS × λ vTrs No. (MPa) (%) (MPa %) (%) (MPa %) (° C.) Peeling Plating Note  1 999 13.7 13686 57 57135 −78 Good GI Invention Example  2 1010 14.3 14394 68 68208 −71 Good GI Invention Example  3 990 14.0 13860 65 64350 −45 Good None Invention Example  4 1008 14.8 14963 82 82339 −58 Good GA Invention Example  5 994 15.4 15308 72 71568 −76 Good GI Invention Example  6 960 16.2 15552 71 68205 −74 Good GA Invention Example  7 1015 14.6 14819 68 69020 −60 Good GI Invention Example  8 1018 13.2 13438 24 24242  −5 Good GA Comparative Example  9 1048 17.2 18026 25 26200 −61 Good GA Comparative Example 10 902 16.2 14612 26 23452 −22 Good GA Comparative Example 11 857 15.5 13256 47 40279 −32 Bad GA Comparative Example 12 1054 8.7  9170 45 47430 −20 Good GA Comparative Example 13 995 15.3 15250 73 72284 −68 Good GA Invention Example 14 1221 8.7 10623 22 26862  15 Good GA Comparative Example 15 1033 15.5 15982 76 78078 −87 Good GA Invention Example 16 784 17.5 13720 53 41552 −12 Good GA Comparative Example 17 1073 14.1 15178 75 80424 −82 Good GA Invention Example 18 1052 14.7 15500 81 85096 −83 Good GA Invention Example 19 969 13.7 13275 34 32946  −6 Good GA Comparative Example 20 985 16.0 15800 93 91917 −83 Good GA Invention Example 21 1015 16.0 16235 62 62903 −62 Good GA Invention Example Underlines indicate that values are outside the scope of the present invention and property values are insufficient

TABLE-US-00005 TABLE 3B Area fraction of tempered Area fraction bainite + Area fraction of pearlite, Steel tempered Area fraction of residual fresh martensite, Average sheet martensite of ferrite γ and cementite grain size {211} <011> + Solute C + B No. Steel (%) (%) (%) (%) (μm) {332} <113> (solutes/nm.sup.2) 22 J 99 0 0 1 4.6 6.0 6.9 23 K 70 30 0 0 4.5 5.5 4.5 24 L 73 26 1 0 5.6 4.9 4.3 25 L 46 49 5 0 5.4 5.2 8.5 26 L 48 51 0 1 5.1 5.0 0.4 27 M 60 36 0 4 4.2 5.1 4.6 28 N 97 1 1 1 5.8 6.4 5.7 29 N 84 14 1 1 5.5 13.4  5.9 30 O 75 21 0 4 6.1 5.0 5.5 31 P  2 85 0 13  6.4 5.1 5.5 32 Q 57 40 0 3 4.3 5.1 4.6 33 R 74 23 0 3 4.8 6.0 4.6 34 S 64 32 0 4 4.4 5.9 4.0 35 T 81 13 0 6 4.4 5.9 4.4 36 T 83 10 4 3 6.2 4.6 4.4 37 T 84 14 0 2 5.8 5.1 0.3 38 U 64 33 1 2 4.5 5.7 4.3 39 V 52 48 0 0 7.5 8.2 5.5 40 A 44 55 0 1 4.3 4.6 4.2 41 A 73 26 0 1 8.1 2.9 4.5 42 A 16 84 0 0 6.2 5.6 5.3 43 A 64 36 0 0 6.7 5.3 9.1 Steel sheet TS El TS × El λ TS × λ vTrs No. (MPa) (%) (MPa %) (%) (MPa %) (° C.) Peeling Plating Note 22 1048 13.6 14200 64 67072 −68 Good Invention Example 23  989 15.3 15132 68 67252 −83 Good GA Invention Example 24  999 15.8 15784 73 72927 −70 Good GA Invention Example 25 1036 12.5 12991 38 39368 −20 Good Comparative Example 26  859 15.2 13057 42 36078 −25 Bad GA Comparative Example 27  961 14.6 14031 78 74565 −82 Good GI Invention Example 28 1225 12.9 15803 52 63700 −43 Good GA Invention Example 29 1105 10.5 11603 18 19890 −25 Good GI Comparative Example 30 1175 13.0 15250 60 70198 −61 Good GI Invention Example 31  720 20.5 14760 73 52560 −39 Good GI Comparative Example 32 1022 15.7 16097 80 81762 −80 Good GA Invention Example 33 1061 14.0 14854 61 64721 −84 Good GA Invention Example 34 1102 14.2 15700 70 76983 −79 Good GA Invention Example 35 1127 14.1 15889 69 77393 −82 Good GI Invention Example 36 1058 11.5 12167 42 44436 −37 Good GA Comparative Example 37  964 13.2 12725 35 33740 −25 Bad GA Comparative Example 38  973 15.2 14757 75 72538 −82 Good GA Invention Example 39  824 19.2 15821 85 70040 −80 Good GA Invention Example 40  995 16.5 16418 60 59700 −75 Good GA Invention Example 41 1025 17.2 17630 59 60475 −55 Good GA Invention Example 42  811 21.2 17193 76 61636 −64 Good GA Invention Example 43  905 15.6 14118 68 61540 −64 Good Invention Example Underlines indicate that values are outside the scope of the present invention and property values are insufficient.

[0228] According to Table 3A and Table 3B, it is found that the, in the steel sheets (invention examples) according to the present embodiment, the strength was high, the low temperature toughness, the elongation, and the stretch flangeability were excellent, and peeling did not occur. On the other hand, it is found that, in the comparative examples, any one or more properties were poor.

INDUSTRIAL APPLICABILITY

[0229] According to the aspects of the present invention, it is possible to provide a steel sheet having a high strength and being excellent in terms of elongation, stretch flangeability, low temperature toughness, and peeling resistance, a method for manufacturing the same, and a plated steel sheet having a variety of characteristics described above. When the steel sheet or plated steel sheet according to the present invention is used as a material of a component for an inner plate member, a structural member, a suspension member, or the like of a car, it is easy to work the steel sheet or plated steel sheet into a component shape, and the steel sheet or plated steel sheet is capable of withstanding the use in an extremely cold climate, and thus industrial contribution is extremely significant.