High-strength cold-rolled steel sheet

Abstract

A high-strength cold-rolled steel sheet which is a steel sheet having a tensile strength of 980 MPa or more has a predetermined chemical component composition, a metallographic microstructure of the steel sheet contains, by area ratio, ferrite and granular bainite: 10% or more and 50% or less in total, one or both of upper bainite and lower bainite: 10% or more and 50% or less in total, tempered martensite: more than 0% and 30% or less, retained austenite: 5% or more, and one or more of pearlite, cementite, and martensite: 0% to 10% in total, and an area ratio of the ferrite with respect to a total area ratio of the ferrite and the granular bainite is 25% or less.

Claims

1. A high-strength cold-rolled steel sheet comprising, as a chemical composition, by mass %: C: 0.15% or more and 0.30% or less; P: 0.040% or less; S: 0.0100% or less; N: 0.0100% or less; O: 0.0060% or less; one or both of Si and Al: 0.70% or more and 2.50% or less in total; one or both of Mn and Cr: 1.50% or more and 3.50% or less in total; Mo: 0% or more and 1.00% or less; Ni: 0% or more and 1.00% or less; Cu: 0% or more and 1.00% or less; Nb: 0% or more and 0.30% or less; Ti: 0% or more and 0.30% or less; V: 0% or more and 0.30% or less; B: 0% or more and 0.0050% or less; Ca: 0% or more and 0.0400% or less; Mg: 0% or more and 0.0400% or less; REM: 0% or more and 0.0400% or less; and a remainder of Fe and impurities wherein a metallographic microstructure of the steel sheet contains, by area ratio, one or both of ferrite and granular bainite: 10% or more and 50% or less in total, one or both of upper bainite and lower bainite: 10% or more and 50% or less in total, tempered martensite: more than 0% and 30% or less, retained austenite: 5% or more, and one or more of pearlite, cementite, and martensite: 0% to 10% in total, an area ratio of the ferrite with respect to a total area ratio of the ferrite and the granular bainite is 25% or less, if the area ratio is determined from a cross-section of the steel sheet in a rolling direction or a cross-section in a direction perpendicular to the rolling direction at a magnification of 1,000 to 50,000 times and the structure is observed by electron back scattering diffraction (EBSD), X-ray diffraction, and a scanning electron microscope after corrosion using a nital reagent or a lepera liquid, and the steel sheet has a tensile strength of 980 MPa or more, when the tensile strength is measured by collecting a test piece in a direction perpendicular to the rolling direction of the steel sheet and by performing a tensile test according to Japanese Industrial Standards JISZ2242.

2. The high-strength cold-rolled steel sheet according to claim 1, wherein the martensite is contained in an amount of 3% or less by area ratio in the metallographic microstructure.

3. The high-strength cold-rolled steel sheet according to claim 1, wherein the chemical composition contains, by mass %, one or more selected from Mo: 0.01% or more and 1.00% or less, Ni: 0.05% or more and 1.00% or less, Cu: 0.05% or more and 1.00% or less, Nb: 0.005% or more and 0.30% or less, Ti: 0.005% or more and 0.30% or less, V: 0.005% or more and 0.30% or less, B: 0.0001% or more and 0.0050% or less, Ca: 0.0005% or more and 0.0400% or less, Mg: 0.0005% or more and 0.0400% or less, and REM: 0.0005% or more and 0.0400% or less.

4. The high-strength cold-rolled steel sheet according to claim 1, wherein a hot-dip galvanized layer is formed on a surface of the steel sheet.

5. The high-strength cold-rolled steel sheet according to claim 1, wherein an alloyed hot-dip galvannealed layer is formed on a surface of the steel sheet.

6. The high-strength cold-rolled steel sheet according to claim 2, wherein the chemical composition contains, by mass %, one or more selected from Mo: 0.01% or more and 1.00% or less, Ni: 0.05% or more and 1.00% or less, Cu: 0.05% or more and 1.00% or less, Nb: 0.005% or more and 0.30% or less, Ti: 0.005% or more and 0.30% or less, V: 0.005% or more and 0.30% or less, B: 0.0001% or more and 0.0050% or less, Ca: 0.0005% or more and 0.0400% or less, Mg: 0.0005% or more and 0.0400% or less, and REM: 0.0005% or more and 0.0400% or less.

7. The high-strength cold-rolled steel sheet according to claim 2, wherein a hot-dip galvanized layer is formed on a surface of the steel sheet.

8. The high-strength cold-rolled steel sheet according to claim 3, wherein a hot-dip galvanized layer is formed on a surface of the steel sheet.

9. The high-strength cold-rolled steel sheet according to claim 6, wherein a hot-dip galvanized layer is formed on a surface of the steel sheet.

10. The high-strength cold-rolled steel sheet according to claim 2, wherein an alloyed hot-dip galvannealed layer is formed on a surface of the steel sheet.

11. The high-strength cold-rolled steel sheet according to claim 3, wherein an alloyed hot-dip galvannealed layer is formed on a surface of the steel sheet.

12. The high-strength cold-rolled steel sheet according to claim 6, wherein an alloyed hot-dip galvannealed layer is formed on a surface of the steel sheet.

Description

EXAMPLES

(1) Next, examples of the present invention will be described. The conditions in the examples are merely a condition example employed to confirm the feasibility and effects of the present invention, although the present invention is not limited to the one condition example. The present invention can employ various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

(2) A cast slab having a component composition (chemical composition) shown in Table 1 was directly hot-rolled after casting, or hot-rolled after being cooled and then heated under conditions shown in Tables 2 and 3. Then, coiling was performed. The hot-rolled steel sheet was pickled, and then cold-rolled, annealed, and cooled under conditions shown in Tables 2 and 3. After the cooling, the steel sheet was reheated in an overaging zone under conditions shown in Tables 4 and 5. Some examples were further subjected to tempering, hot-dip galvanizing, and/or an alloying treatment under conditions shown in Tables 4 and 5. In Table 1, a blank indicates that the element was not intentionally added, and the symbol “-” in Tables 4 and 5 indicates that the corresponding process was not performed. The symbol “-” in the column of cooling stop temperature in the reheating process indicates that the cooling was performed to room temperature without being stopped on the way. An underlined value in the tables indicates that the value is out of the range of the present invention.

(3) The metallographic microstructure and the mechanical properties of the steel sheet after annealing, tempering, or hot-dip galvanizing and/or an alloying treatment were examined.

(4) (Metallographic Microstructure)

(5) As a metallographic microstructure, area ratios of ferrite, granular bainite, upper bainite or lower bainite, tempered martensite, retained austenite, and a retained structure (pearlite, martensite, cementite) were observed. Identification and calculation of area ratios of ferrite, granular bainite, tempered martensite, upper bainite, lower bainite, retained austenite, pearlite, cementite, and martensite were performed by performing observation and measurement of a cross-section of the steel sheet in a rolling direction or a cross-section in a direction perpendicular to the rolling direction at a magnification of 1,000 to 50,000 times through structure observation in a range from ⅛ to ⅜ in thickness centered at ¼ position of the sheet thickness from the surface by electron back scattering diffraction (EBSD), X-ray measurement, corrosion using a nital reagent or a lepera liquid, and a scanning electron microscope as described above. The results are shown in Tables 6 and 7.

(6) (Mechanical Properties)

(7) Tensile strength, total elongation, and hole expansibility were evaluated as mechanical properties. Tensile strength (TS) and total elongation (EL) were measured by collecting a JIS No. 5 test piece in a direction perpendicular to the rolling direction of the steel sheet and by performing a tensile test according to JISZ2242. Hole expansibility (λ) was evaluated according to the hole expansion test method described in Japanese Industrial Standards JISZ2256. The results are shown in Tables 6 and 7.

(8) TABLE-US-00001 TABLE 1 Steel Chemical Composition/mass % (remainder: Fe and impurities) No. C P S N O Si Al Mn Cr Si + Al Mn + Cr Mo Ni A 0.12 0.012 0.0042 0.0032 0.0009 1.35 0.01 2.35 0.01 1.36 2.36 B 0.19 0.013 0.0033 0.0035 0.0013 1.44 0.02 2.11 0.01 1.46 2.12 C 0.22 0.009 0.0041 0.0029 0.0008 1.71 0.02 2.34 0.01 1.73 2.35 D 0.32 0.011 0.0034 0.0028 0.0008 1.31 0.01 2.45 0.01 1.32 2.46 E 0.17 0.008 0.0028 0.0034 0.0007 1.08 0.03 2.55 0.31 1.11 2.86 F 0.20 0.010 0.0037 0.0022 0.0011 1.64 0.02 2.66 0.02 1.66 2.68 0.05 G 0.25 0.050 0.0031 0.0025 0.0014 0.85 0.33 2.35 0.01 1.18 2.36 0.13 H 0.16 0.008 0.0044 0.0038 0.0010 1.44 0.03 2.44 0.21 1.47 2.65 I 0.18 0.009 0.0130 0.0035 0.0010 1.22 0.03 2.33 0.01 1.25 2.34 J 0.19 0.011 0.0028 0.0115 0.0010 1.46 0.02 2.22 0.01 1.48 2.23 K 0.23 0.009 0.0032 0.0041 0.0077 1.41 0.02 2.35 0.01 1.43 2.36 L 0.19 0.012 0.0036 0.0035 0.0010 2.30 0.22 2.66 0.02 2.52 2.68 M 0.21 0.011 0.0041 0.0031 0.0010 1.23 1.35 2.44 0.02 2.58 2.46 N 0.19 0.009 0.0044 0.0031 0.0008 1.44 0.03 3.78 0.01 1.47 3.79 O 0.18 0.008 0.0039 0.0035 0.0015 1.22 0.05 2.15 1.50 1.27 3.65 0.04 P 0.27 0.007 0.0041 0.0032 0.0011 1.44 0.03 2.44 0.01 1.47 2.45 Q 0.19 0.008 0.0032 0.0034 0.0009 1.65 0.32 2.11 0.02 1.97 2.13 0.03 R 0.16 0.006 0.0033 0.0052 0.0012 1.06 0.03 2.77 0.03 1.09 2.80 0.05 S 0.21 0.008 0.0011 0.0032 0.0008 0.99 0.44 2.55 0.22 1.43 2.77 0.03 T 0.25 0.007 0.0022 0.0034 0.0009 1.34 0.03 1.85 0.03 1.37 1.88 0.25 0.03 U 0.22 0.009 0.0034 0.0031 0.0011 1.55 0.04 2.11 0.31 1.59 2.42 0.05 V 0.19 0.011 0.0035 0.0051 0.0019 0.65 0.03 2.35 0.01 0.68 2.36 W 0.21 0.013 0.0041 0.0031 0.0015 0.04 0.61 2.20 0.03 0.65 2.23 0.065 X 0.19 0.009 0.0034 0.0030 0.0011 1.34 0.03 1.34 0.02 1.37 1.36 Y 0.24 0.012 0.0034 0.0036 0.0009 1.35 0.11 1.06 0.35 1.46 1.41 Z 0.19 0.010 0.0041 0.0056 0.0008 1.35 0.04 1.55 0.15 1.39 1.70 0.150 Ar3 Steel Chemical Composition/mass % (remainder: Fe and impurities) Transformation No. Cu Nb Ti V B Ca Mg REM Point Remarks A 690 Comparative Steel B 692 Invention Steel C 0.0011 670 Invention Steel D 0.0023 614 Comparative Steel E 0.03 0.0015 633 Invention Steel F 0.02 0.0011 642 Invention Steel G 625 Comparative Example H 0.02 0.01 0.03 0.0022 661 Invention Steel I 668 Comparative Steel J 0.02 683 Comparative Steel K 0.03 0.0023 656 Comparative Steel L 0.03 0.0024 670 Comparative Steel M 648 Comparative Steel N 0.01 0.03 0.0021 539 Comparative Steel O 0.0025 614 Comparative Steel P 0.0021 636 Invention Steel Q 0.02 697 Invention Steel R 0.02 0.0016 625 Invention Steel S 0.02 0.0016 619 Invention Steel T 0.02 0.0025 680 Invention Steel U 0.03 0.0022 670 Invention Steel V 0.03 0.0019 644 Comparative Steel W 0.01 0.02 0.0018 627 Comparative Steel X 0.01 0.0019 759 Comparative Steel Y 0.02 0.0017 754 Comparative Steel Z 0.02 0.03 0.0021 727 Invention Steel

(9) TABLE-US-00002 TABLE 2 Hot Rolling Finish Cold Rolling Rolling Cold Annealing Heating Completion Coiling Sheet Rolling Sheet Annealing Manufacturing Steel Temperature Temperature Temperature Thickness Ratio Thickness Temperature No. No. (° C.) (° C.) (° C.) (mm) (%) (mm) (° C.) 1 A 1230 900 550 3.2 56 1.4 815 2 B 1230 900 550 3.2 56 1.4 809 3 C 1230 900 550 3.2 56 1.4 810 4 D 1230 900 550 3.2 56 1.4 806 5 E 1230 900 550 3.2 56 1.4 805 6 F 1230 900 550 3.2 56 1.4 807 7 G 1230 900 550 3.2 56 1.4 810 8 H 1230 900 550 3.2 56 1.4 806 9 I 1230 900 550 3.2 56 1.4 820 10 J 1230 900 550 3.2 56 1.4 810 11 K 1230 900 550 3.2 56 1.4 815 12 L 1230 900 550 3.2 56 1.4 804 13 M 1230 900 550 3.2 56 1.4 803 14 N 1230 900 550 3.2 56 1.4 809 15 O 1230 900 550 3.2 56 1.4 811 16 P 1230 900 550 3.2 56 1.4 831 17 Q 1230 900 550 3.2 56 1.4 809 18 R 1230 900 550 3.2 56 1.4 810 19 S 1230 900 550 3.2 56 1.4 798 20 T 1230 900 550 3.2 56 1.4 801 21 U 1230 900 550 3.2 56 1.4 795 22 V 1230 900 550 3.2 56 1.4 815 23 W 1230 900 550 3.2 56 1.4 816 24 X 1230 900 550 3.2 56 1.4 814 25 Y 1230 900 550 3.2 56 1.4 813 26 Z 1230 900 550 3.2 56 1.4 809 38 B 1230 900 550 3.2 56 1.4 808 39 B 1230 900 550 3.2 56 1.4 802 Cooling Cooling Rate Ms Point to Temperarure Retention Immediately Annealing Range of Time at Cooling Before Cooling Annealing 500° C. to 500° C. to Rate After Stopping of Stop Manufacturing Time 650° C. 650° C. Retention Cooling Temperature No. (s) (° C./s) (s) (° C./s) (° C.) (° C.) 1 93 87 43 27 275 255 2 165 82 15 68 356 264 3 144 73 31 53 333 253 4 155 82 10 77 323 221 5 82 59 38 81 348 281 6 67 77 580 79 350 265 7 72 62 6 25 334 235 8 115 82 5 74 357 266 9 166 86 34 27 368 235 10 175 60 32 51 367 269 11 88 80 11 29 322 233 12 56 95 41 17 273 242 13 55 85 31 62 291 235 14 64 90 38 88 328 281 15 68 92 10 41 379 261 16 82 61 46 57 332 219 17 76 60 23 50 368 266 18 228 69 92 70 352 277 19 315 64 41 51 349 261 20 305 67 29 48 361 234 21 166 80 242 67 357 266 22 199 73 4 57 341 254 23 288 82 18 81 348 266 24 177 87 22 58 370 266 25 155 94 7 45 365 275 26 165 88 19 42 375 253 38 124 79 8 79 350 289 39 99 73 21 81 344 325

(10) TABLE-US-00003 TABLE 3 Hot Rolling Finish Cold Rolling Rolling Cold Annealing Heating Completion Coiling Sheet Rolling Sheet Annealing Manufacturing Steel Temperature Temperature Temperature Thickness Ratio Thickness Temperature No. No. (° C.) (° C.) (° C.) (mm) (%) (mm) (° C.) 27 B 1230 900 720 3.2 56 1.4 815 28 B 1230 900 550 3.2 56 1.4 905 29 B 1230 900 550 3.2 56 1.4 809 30 B 1230 900 550 3.2 56 1.4 816 31 B 1230 900 550 3.2 56 1.4 816 32 B 1230 900 550 3.2 56 1.4 733 33 B 1230 900 550 3.2 56 1.4 795 34 B 1230 900 550 3.2 56 1.4 799 35 B 1230 900 550 3.2 56 1.4 811 36 B 1230 900 550 3.2 56 1.4 813 37 B 1230 900 550 3.2 56 1.4 809 40 B 1230 900 550 3.2 56 1.4 813 41 B 1230 900 550 3.2 56 1.4 821 42 B 1230 900 550 3.2 56 1.4 882 43 B 1230 900 550 3.2 56 1.4 815 Cooling Cooling Rate Ms Point to Temperature Retention Immediately Annealing Range of Time at Cooling Before Cooling Annealing 500° C. to 500° C. to Rate After Stopping of Stop Manufacturing Time 650° C. 650° C. Retention Cooling Temperature No. (S) (° C./s) (s) (° C./s) (° C.) (° C.) 27 211 97 29 75 358 266 28 166 85 37 23 384 247 29 155 83 44 61 357 156 30 157 83 42 62 362 219 31 134 70 41 29 360 225 32 144 59 17 59 290 255 33 146 73 19 53 354 277 34 366 59 16 61 356 275 35 377 97 38 64 360 211 36 9 65 18 91 359 254 37 92 80 40 46 353 416 40 306 90 2 19 351 245 41 423 46 3 33 361 226 42 262 52 17 28 377 322 43 373 82 24 8 352 247

(11) TABLE-US-00004 TABLE 4 Reheating Ms Point at Time of Completion Overaging of Holding Cooling Tempering Plating Zone Holding in Overaging Stop Tempering Tempering Plating Heating Alloying Manufacturing Temperature Time Zone Temperature Temperature Time Presence/ Temperature Temperature Temperature No. (° C.) (s) (° C.) (° C.) (° C.) (s) Absence (° C.) (° C.) (° C.) 1 355 412 — — — — Absence — — — 2 389 244 — — — — Absence — — — 3 395 132 — — — — Absence — — — 4 367 67 — — — — Absence — — — 5 367 108 — — — — Absence — — — 6 395 110 — — — — Absence — — — 7 377 241 — — — — Absence — — — 8 371 254 — — — — Absence — — — 9 365 344 — — — — Absence — — — 10 346 108 — — — — Absence — — — 11 368 191 — — — — Absence — — — 12 399 79 — — — — Absence — — — 13 366 201 — — — — Absence — — — 14 371 119 — — — — Absence — — — 15 355 131 — — — — Absence — — — 16 344 175 — — — — Absence — — — 17 377 121 — — — — Absence — — — 18 381 233 — — — — Absence — — — 19 395 143 — — — — Absence — — — 20 406 119 — — — — Absence — — — 21 400 76 — — — — Absence — — — 22 382 88 — — — — Absence — — — 23 375 223 — — — — Absence — — — 24 401 220 — — — — Absence — — — 25 388 195 — — — — Absence — — — 26 385 205 — — — — Absence — — — 38 433 278 — — — — Presence 462 458 — 39 301 103 — — — — Presence 454 469 478

(12) TABLE-US-00005 TABLE 5 Reheating Ms Point at Time of Completion Overaging of Holding Cooling Tempering Plating Zone Holding in Overaging Stop Tempering Tempering Plating Heating Alloying Manufacturing Temperature Time Zone Temperature Temperature Time Presence/ Temperature Temperature Temperature No. (° C.) (s) (° C.) (° C.) (° C.) (s) Absence (° C.) (° C.) (° C.) 27 377 68 — — — — Absence — — — 28 366 223 — — — — Absence — — — 29 346 306 — — — — Absence — — — 30 264 309 — — — — Absence — — — 31 493 68 — — — — Absence — — — 32 376 91 — — — — Absence — — — 33 366 10 — — — — Absence — — — 34 355 194 — — — — Absence — — — 35 366 235 193 43 419 30 Presence 466 460 488 36 345 255 — — — — Absence — — — 37 377 124 — — — — Absence — — — 40 429 115 — — — — Absence — — — 41 329 92 — — — — Absence — — — 42 433 342 — — — — Absence — — — 45 333 31 — — — — Absence — — —

(13) TABLE-US-00006 TABLE 6 Metallographic microstructure Ratio of Ratio of Granular Ferrite in Bainite in Sum of Sum of Total Area Total Area Area Ratios Area Ratios Fraction of Fraction of of Upper of Ferrite Ferrite and Ferrite and Bainite Area Ratio and Granular Granular Granular and Lower of Tempered Manufacturing Steel Bainite Bainite Bainite Bainite Martensite No. No. (%) (%) (%) (%) (%) 1 A 65 65 35 15 5 2 B 35 18 82 39 12 3 C 35 13 87 38 9 4 D  9 60 40 36 21 5 E 31 23 77 41 13 6 F 19 21 79 32 28 7 G 25 19 81 33 19 8 H 31 21 79 31 23 9 I 22 21 79 41 22 10 J 23 24 76 35 23 11 K 39  9 91 38 11 12 L 55 38 62 29 6 13 M 52 44 56 21 5 14 N  9  9 91 22 9 15 O  8  7 93 21 21 16 P 19  9 91 35 26 17 Q 25 13 87 36 24 18 R 25 12 88 33 26 19 S 19 21 79 45 21 20 T 18 22 78 43 23 21 U 23  9 91 40 27 22 V 37 35 65 32 25 23 W 32 33 67 36 22 24 X 52 65 35 21 13 25 Y 53 69 31 19 9 26 Z 38 16 84 35 13 38 B 33 20 80 41 11 39 B 37 11 89 35 13 Metallographic microstructure Area Ratio of Retained Area Ratio Mechanical Properties Manufacturing Austenite of Remainder TS TS × EL TS × λ No. (%) (%) (MPa) (MPa .Math. %) (MPa .Math. %) Remarks 1  2 13  1011 11121 17187 Comparative Example 2 11 3 1015 21315 23345 Example 3 12 6 1032 24768 26832 Example 4 16 18  1410 26790 2820 Comparative Example 5  7 8 1020 13260 23460 Example 6 12 9 1195 19120 38240 Example 7 13 10  1051 23122 13663 Comparative Example 8  9 6  991 20811 22793 Example 9  9 6  985 18715 12805 Comparative Example 10 11 8  998 18962 15968 Comparative Example 11  8 4 1035 18630 13455 Comparative Example 12  9 1  981 15696 15696 Comparative Example 13  8 14   971 17478 11652 Comparative Example 14  5 55  1235 11115 13585 Comparative Example 15  6 44  1246 9968 16198 Comparative Example 16 19 1 1316 17108 32900 Example 17  9 6  985 22655 28565 Example 18 13 3 1191 17865 38112 Example 19 13 2 1193 19088 46527 Example 20 13 3 1183 16562 18928 Example 21 10 0 1199 14388 35970 Example 22  4 2 1033 9297 13429 Comparative Example 23  3 7 1025 10250 16400 Comparative Example 24  3 11   996 13944 12948 Comparative Example 25  3 16  1186 11860 35580 Comparative Example 26 12 2 1011 29319 31341 Example 38 11 4 1009 21953 31572 Example 39 14 1 1017 22781 26243 Example

(14) TABLE-US-00007 TABLE 7 Metallographic microstructure Ratio of Ratio of Granular Ferrite in Bainite in Sum of Sum of Total Area Total Area Area Ratios Area Ratios Fraction of Fraction of of Upper of Ferrite Ferrite and Ferrite and Bainite Area Ratio and Granular Granular Granular and Lower of Tempered Manufacturing Steel Bainite Bainite Bainite Bainite Martensite No. No. (%) (%) (%) (%) (%) 27 B 52 66 34 24  8 28 B  9  7 93 35 51 29 B 34 21 79 29 32 30 B 31 19 81 15 29 31 B 32 11 89 22 16 32 B 55 90 10 13  6 33 B 36 12 88  2 19 34 B 56 71 29 21  5 35 B 32 16 84 33 19 36 B 33 15 85 36 12 37 B 37 16 84 17  3 40 B 62 88 12 10 16 41 B 56 73 27 14 14 42 B 48 27 73 28 13 45 B 30 14 86 51 11 Metallographic microstructure Area Ratio of Retained Area Ratio Mechanical Properties Manufacturing Austenite of Remainder TS TS × EL TS × λ No. (%) (%) (MPa) (MPa .Math. %) (MPa .Math. %) Remarks 27 3 13  981 11772 17658 Comparative Example 28 3 2 1051  8408 45193 Comparative Example 29 3 2 1035  9315 45540 Comparative Example 30 4 21  1044  11484 19836 Comparative Example 31 0 30  1023  13299 16368 Comparative Example 32 0 26 924 17556 30492 Comparative Example 33 4 32 1044  16704 15660 Comparative Example 34 3 15  944 16048 15104 Comparative Example 35 4 12  988 11856 25688 Comparative Example 36 4 15  934 13076 31756 Comparative Example 37 4 39  1035  11385 15525 Comparative Example 40 11  1 917 19181 25100 Comparative Example 41 12  4 922 19123 22174 Comparative Example 42 4 7 994 11275 17238 Comparative Example 45 7 1 891 9815 34144 Comparative Example

(15) As can be seen from Tables 1 to 7, it was found that all the examples in which the chemical composition and the metallographic microstructure are within the range of the present invention have a high strength of 980 MPa or more, have a high value in TS×EL and TS×λ, and are excellent in elongation and hole expansibility, but the comparative examples in which the chemical composition and the metallographic microstructure are out of the range of the present invention have a low strength, have a low value in TS×EL and TS×λ, and are poor in elongation and/or hole expansibility.

INDUSTRIAL APPLICABILITY

(16) According to the present invention, it is possible to provide a high-strength cold-rolled steel sheet which is suitable as a structural member of a vehicle or the like, is excellent in elongation and hole expansibility, and has a tensile strength of 980 MPa or more. In a case where the cold-rolled steel sheet of the present invention is applied to a vehicle or the like, the cold-rolled steel sheet contributes to a reduction in weight of the vehicle body or an improvement in safety at the time of collision. Accordingly, the present invention has high industrial applicability.