High-strength galvanized steel sheet and method for manufacturing the same

Abstract

Provided are a high-strength galvanized steel sheet which can preferably be used as a material for automobile parts and a method for manufacturing the steel sheet. The steel sheet has a C content of 0.15% or less, in which an area ratio of ferrite is 10% or less, an area ratio of bainitic ferrite is 2% or more and 30% or less, an area ratio of martensite is 60% or more and 98% or less, an area ratio of retained austenite is less than 2%, an average grain diameter of martensite adjacent to bainite is 15 m or less, a proportion of massive martensite adjacent only to bainite to the whole metallographic structure is 10% or less, and a value (Hv) calculated by subtracting the Vickers hardness at a position located at 20 m from the surface of the steel sheet from the Vickers hardness at a position located at 100 m from the surface of the steel sheet is 30 or more.

Claims

1. A high-strength galvanized steel sheet having a chemical composition containing, by mass %, C: 0.05% or more and 0.15% or less, Si: 0.01% or more and 1.00% or less, Mn: 1.5% or more and 4.0% or less, P: 0.100% or less, S: 0.02% or less, Al: 0.01% or more and 0.50% or less, Cr: 0.010% or more and 2.000% or less, Nb: 0.005% or more and 0.100% or less, Ti: 0.005% or more and 0.100% or less, B: 0.0005% or more and 0.0050% or less, and the balance being Fe and inevitable impurities, in which K, which is expressed by equation (1) below, is 3.0 or more and a metallographic structure including, in terms of area ratio determined by performing structure observation at a position located at of the thickness in a cross section at a right angle to the surface of the steel sheet, ferrite: 10% or less, bainitic ferrite: 2% or more and 30% or less, and martensite: 60% or more and 98% or less, wherein the proportion of retained austenite determined by using an X-ray diffraction method is less than 2%, an average grain diameter of martensite adjacent to bainite is 15 m or less, the proportion of massive martensite adjacent only to bainite to the whole metallographic structure is 10% or less, and a value (Hv) calculated by subtracting the Vickers hardness at a position located at 20 m from the surface of the steel sheet from the Vickers hardness at a position located at 100 m from the surface of the steel sheet is 30 or more:
K=0.4[Si]+1.0[Mn]+1.3[Cr]+200[B](1), where, in equation (1) above, [Si] denotes the content [mass %] of Si, [Mn] denotes the content [mass %] of Mn, [Cr] denotes the content [mass %] of Cr, and [B] denotes the content [mass %] of B.

2. The high-strength galvanized steel sheet according to claim 1, wherein the steel sheet has the chemical composition further containing, by mass %, at least one chemical element selected from among Mo: 0.005% or more and 2.000% or less, V: 0.005% or more and 2.000% or less, Ni: 0.005% or more and 2.000% or less, and Cu: 0.005% or more and 2.000% or less.

3. The high-strength galvanized steel sheet according to claim 1, wherein the steel sheet has the chemical composition further containing, by mass %, at least one chemical element selected from among Ca: 0.001% or more and 0.005% or less and REM: 0.001% or more and 0.005% or less.

4. The high-strength galvanized steel sheet according to claim 1, wherein the galvanized steel sheet is a galvannealed steel sheet.

5. A method for manufacturing a high-strength galvanized steel sheet, the method comprising hot-rolling a slab having the chemical composition according to claim 1 by performing finish rolling in which a final finish rolling pass is performed with a rolling reduction of 10% or more at a temperature of 850 C. or higher and 950 C. or lower, then performing cooling so that the total retention time in a temperature range of 600 C. or higher and 700 C. or lower is 10 seconds or less, and coiling the cooled steel sheet at a temperature of 450 C. or higher and lower than 600 C., following the hot rolling process, cold-rolling the hot-rolled steel sheet with a rolling reduction of more than 20%, following the cold rolling process, heating the cold-rolled steel sheet to an annealing temperature in an atmosphere having a dew point of 45 C. or higher and +20 C. or lower and an air ratio of 0.80 or more at an average heating rate of 0.5 C./s or more in a temperature range of 300 C. or higher and equal to or lower than the annealing temperature, which is a temperature in a temperature range of (Ac3-20 C.) or higher and 950 C. or lower, and holding the heated steel sheet at the annealing temperature for 10 seconds or more and 1000 seconds or less, cooling the annealed cold-rolled steel sheet at an average cooling rate of 5 C./s or more to a cooling stop temperature, which is a temperature in a temperature range of 450 C. or higher and 550 C. or lower, and holding the cooled steel sheet at the cooling stop temperature for 30 seconds or more and 1000 seconds or less, and galvanizing the cooled cold-rolled steel sheet.

6. A method for manufacturing a high-strength galvanized steel sheet according to claim 5, the method further comprising performing an alloying treatment on the high-strength galvanized steel sheet.

7. The high-strength galvanized steel sheet according to claim 2, wherein the steel sheet has the chemical composition further containing, by mass %, at least one chemical element selected from among Ca: 0.001% or more and 0.005% or less and REM: 0.001% or more and 0.005% or less.

8. The high-strength galvanized steel sheet according to claim 2, wherein the galvanized steel sheet is a galvannealed steel sheet.

9. The high-strength galvanized steel sheet according to claim 3, wherein the galvanized steel sheet is a galvannealed steel sheet.

10. The high-strength galvanized steel sheet according to claim 7, wherein the galvanized steel sheet is a galvannealed steel sheet.

11. The high-strength galvanized steel sheet according to claim 1, wherein the steel sheet has a tensile strength of 1180 MPa or more, as determined by JIS Z 2201.

12. The high-strength galvanized steel sheet according to claim 1, wherein the steel sheet has an anti-crash property indicated by AE/TS of 0.050 or more.

13. A method for manufacturing a high-strength galvanized steel sheet, the method comprising hot-rolling a slab having the chemical composition according to claim 2 by performing finish rolling in which a final finish rolling pass is performed with a rolling reduction of 10% or more at a temperature of 850 C. or higher and 950 C. or lower, then performing cooling so that the total retention time in a temperature range of 600 C. or higher and 700 C. or lower is 10 seconds or less, and coiling the cooled steel sheet at a temperature of 450 C. or higher and lower than 600 C., following the hot rolling process, cold-rolling the hot-rolled steel sheet with a rolling reduction of more than 20%, following the cold rolling process, heating the cold-rolled steel sheet to an annealing temperature in an atmosphere having a dew point of 45 C. or higher and +20 C. or lower and an air ratio of 0.80 or more at an average heating rate of 0.5 C./s or more in a temperature range of 300 C. or higher and equal to or lower than the annealing temperature, which is a temperature in a temperature range of (Ac3-20 C.) or higher and 950 C. or lower, and holding the heated steel sheet at the annealing temperature for 10 seconds or more and 1000 seconds or less, cooling the annealed cold-rolled steel sheet at an average cooling rate of 5 C./s or more to a cooling stop temperature, which is a temperature in a temperature range of 450 C. or higher and 550 C. or lower, and holding the cooled steel sheet at the cooling stop temperature for 30 seconds or more and 1000 seconds or less, and galvanizing the cooled cold-rolled steel sheet.

14. A method for manufacturing a high-strength galvanized steel sheet, the method comprising hot-rolling a slab having the chemical composition according to claim 3 by performing finish rolling in which a final finish rolling pass is performed with a rolling reduction of 10% or more at a temperature of 850 C. or higher and 950 C. or lower, then performing cooling so that the total retention time in a temperature range of 600 C. or higher and 700 C. or lower is 10 seconds or less, and coiling the cooled steel sheet at a temperature of 450 C. or higher and lower than 600 C., following the hot rolling process, cold-rolling the hot-rolled steel sheet with a rolling reduction of more than 20%, following the cold rolling process, heating the cold-rolled steel sheet to an annealing temperature in an atmosphere having a dew point of 45 C. or higher and +20 C. or lower and an air ratio of 0.80 or more at an average heating rate of 0.5 C./s or more in a temperature range of 300 C. or higher and equal to or lower than the annealing temperature, which is a temperature in a temperature range of (Ac3-20 C.) or higher and 950 C. or lower, and holding the heated steel sheet at the annealing temperature for 10 seconds or more and 1000 seconds or less, cooling the annealed cold-rolled steel sheet at an average cooling rate of 5 C./s or more to a cooling stop temperature, which is a temperature in a temperature range of 450 C. or higher and 550 C. or lower, and holding the cooled steel sheet at the cooling stop temperature for 30 seconds or more and 1000 seconds or less, and galvanizing the cooled cold-rolled steel sheet.

15. A method for manufacturing a high-strength galvanized steel sheet, the method comprising hot rolling a slab having the chemical composition according to claim 7 by performing finish rolling in which a final finish rolling pass is performed with a rolling reduction of 10% or more at a temperature of 850 C. or higher and 950 C. or lower, then performing cooling so that the total retention time in a temperature range of 600 C. or higher and 700 C. or lower is 10 seconds or less, and coiling the cooled steel sheet at a temperature of 450 C. or higher and lower than 600 C., following the hot rolling process, cold-rolling the hot-rolled steel sheet with a rolling reduction of more than 20%, following the cold rolling process, heating the cold-rolled steel sheet to an annealing temperature in an atmosphere having a dew point of 45 C. or higher and +20 C. or lower and an air ratio of 0.80 or more at an average heating rate of 0.5 C./s or more in a temperature range of 300 C. or higher and equal to or lower than the annealing temperature, which is a temperature in a temperature range of (Ac3-20 C.) or higher and 950 C. or lower, and holding the heated steel sheet at the annealing temperature for 10 seconds or more and 1000 seconds or less, cooling the annealed cold-rolled steel sheet at an average cooling rate of 5 C./s or more to a cooling stop temperature, which is a temperature in a temperature range of 450 C. or higher and 550 C. or lower, and holding the cooled steel sheet at the cooling stop temperature for 30 seconds or more and 1000 seconds or less, and galvanizing the cooled cold-rolled steel sheet.

16. A method for manufacturing a high-strength galvanized steel sheet according to claim 13, further comprising performing an alloying treatment on the high-strength galvanized steel sheet.

17. A method for manufacturing a high-strength galvanized steel sheet according to claim 14, further comprising performing an alloying treatment on the high-strength galvanized steel sheet.

18. A method for manufacturing a high-strength galvanized steel sheet according to claim 15, further comprising performing an alloying treatment on the high-strength galvanized steel sheet.

Description

EXAMPLES OF EMBODIMENTS OF THE PRESENT INVENTION

(1) Non-limiting, exemplary molten steels having the chemical compositions given in Table 1 were manufactured by using a vacuum melting furnace, and by casting the molten steels, and then performing slabbing, steel slabs were obtained (in Table 1, N is an inevitable impurity). By heating these steel slabs to a temperature of 1200 C., and then by performing rough rolling, finish rolling, and coiling, hot-rolled steel sheets were obtained (hot rolling conditions are given in Tables 2 and 3). Subsequently, by performing cold rolling to a thickness of 1.4 mm, cold-rolled steel sheets were obtained (rolling reductions are given in Tables 2 and 3). Subsequently, the cold-rolled steel sheets were subjected to annealing. By performing annealing in a laboratory under the conditions given in Tables 2 and 3 in order to simulate annealing in a continuous galvanizing line, galvanized steel sheets and galvannealed steel sheets 1 through 42 were obtained. The galvanized steel sheets were manufactured by dipping the steel sheets in a galvanizing bath having a temperature of 460 C. in order to form coating layers having a coating weight of 35 g/m.sup.2 to 45 g/m.sup.2 on the surface of the steel sheets, and by then cooling the coated steel sheets at a cooling rate of 10 C./s. In addition, the galvannealed steel sheets were manufactured by performing an alloying treatment on the galvanized steel sheets at a temperature of 530 C., and by then cooling the treated steel sheets at a cooling rate of 10 C./s. The obtained steel sheets were subjects to skin pass rolling with a rolling reduction of 0.3%.

(2) Subsequently, the microstructure of the base steel sheets of the galvanized steel sheets and the galvannealed steel sheets were observed by using the methods described above. The results are given in Tables 4 and 5.

(3) In addition, surface hardness, tensile properties, bending formability, spot weldability, and impact energy absorption capability were determined by using the testing methods below.

(4) <Hardness Test>

(5) By using a test piece having a width of 10 mm and a length of 15 mm taken from a vertical cross section parallel to the rolling direction, a Vickers hardness test was performed at positions located at 20 m and 100 m from the surface layer of the steel sheet. After determining hardness at five points at each of the positions in the thickness direction with a test load of 50 g, the Vickers hardness Hv at the position was defined as the average value of the Vickers hardness Hv of the three points other than the points where the maximum value and the minimum value were determined.

(6) <Tensile Test>

(7) YS and TS were determined by performing a tensile test on a JIS No. 5 tensile test piece (JIS Z 2201) taken in a direction at a right angle to the rolling direction of the steel sheet with a strain rate of 10.sup.3/s in accordance with the prescription in JIS Z 2241. YS was defined as 0.20-proof stress.

(8) <Bending Test>

(9) A bending test was performed on a strip-type test piece having a width of 35 mm and a length of 100 mm taken from the steel sheet so that the direction of the bending axis in the test was parallel to the rolling direction. By performing a 90-V-bend test with a stroke speed of 10 mm/s, a pressing load of 10 tons, a press holding time of 5 seconds, and a bending radius R of 1.5 mm, and by observing the ridge line at the bending position by using a loupe at a magnification of 10 times, a case where a crack of 1 mm or more was recognized was judged as poor, and a case where only a crack of less than 1 mm was recognized was judged as excellent.

(10) <Spot Weldability Test>

(11) The test was performed by using electrode DR6mm-40R with a pressing load of 4802 N (490 kgf), an initial pressing time of 30 cycles/60 Hz, an energizing time of 17 cycles/60 Hz, and a holding time of 1 cycle/60 Hz. The test current was varied at intervals of 0.2 kA in a current range from 4.6 kA to 10.0 kA and at intervals of 0.5 kA in a current range from 10.0 kA to a welding point for each steel sheet number. Each test piece was subjected to a cross tensile test and the nugget diameter of the welded part of each test piece was determined. The cross tensile test of a resistance spot welded joint was performed in accordance with the prescription in JIS Z 3137. The nugget diameter was determined in accordance with the prescription in JIS Z 3139 as described hereafter. A symmetrical circular plug formed by performing resistance spot welding was halved along the cross section extending in a direction at a right angle to the surface of the steel sheet and almost including the center of the weld by using an appropriate cutting method. By polishing and etching the cut surface, and by performing cross-section microstructure observation by using an optical microscope, the nugget diameter was determined. Here, the nugget diameter was defined as the maximum diameter of the weld zone excluding a corona bond. By performing a cross tensile test on the welded sample having a nugget diameter of 4 t.sup.1/2 (mm) or more (t: the thickness of the steel sheet), a case where fracturing occurred in the base metal was judged as excellent, and a case where fracturing occurred in the nugget was judged as poor.

(12) <Impact Tensile Test>

(13) Impact energy absorption capability (anti-crash property) was evaluated by taking a tensile test piece having a parallel portion with a width of 5 mm and a length of 7 mm so that the tensile direction in the test was a direction at a right angle to the rolling direction, by performing a tensile test with a strain rate of 2000/s using an impact tensile tester utilizing a Hopkinson bar method, and by determining the absorbed energy (AE) until the strain was 5% (refer to The Iron and Steel Institute of Japan: Tetsu-to-Hagane, vol. 83 (1997), No. 11, pp. 748-753). Here, the absorbed energy (AE) described above was derived by integrating the stress with respect to the strain from 0% to 5% along the stress-true strain curve. The results obtained as described above are given in Tables 4 and 5.

(14) TABLE-US-00001 TABLE 1 Chemical Composition (mass %) Steel C Si Mn P S Al N Cr Ti Nb B Other Ac3 K Note A 0.09 0.5 2.5 0.020 0.002 0.032 0.004 0.590 0.021 0.040 0.0028 790 3.6 within Preferred Scope of Invention B 0.06 0.7 2.9 0.015 0.003 0.033 0.003 0.630 0.020 0.045 0.0036 798 4.2 within Preferred Scope of Invention C 0.12 0.3 2.2 0.020 0.002 0.015 0.003 0.850 0.019 0.037 0.0022 778 3.6 within Preferred Scope of Invention D 0.09 0.3 2.4 0.027 0.001 0.040 0.003 0.660 0.051 0.026 0.0039 783 3.9 within Preferred Scope of Invention E 0.12 0.3 2.5 0.012 0.005 0.028 0.002 0.600 0.079 0.011 0.0031 771 3.8 within Preferred Scope of Invention F 0.10 0.4 2.5 0.005 0.003 0.033 0.003 0.450 0.020 0.041 0.0028 Mo:0.1 784 3.5 within Preferred Scope of Invention G 0.12 0.5 2.2 0.003 0.002 0.039 0.004 0.560 0.015 0.040 0.0029 V:0.05 790 3.3 within Preferred Scope of Invention H 0.10 0.1 2.3 0.021 0.002 0.044 0.003 0.550 0.054 0.044 0.0035 Ni:0.5 775 3.7 within Preferred Scope of Invention I 0.08 0.1 3.0 0.013 0.003 0.025 0.003 0.610 0.021 0.034 0.0026 Cu:0.2 760 4.3 within Preferred Scope of Invention J 0.09 0.2 2.7 0.016 0.003 0.036 0.005 0.600 0.020 0.041 0.0030 Ca:0.001 770 4.0 within Preferred Scope of Invention K 0.09 0.4 2.3 0.012 0.002 0.024 0.001 0.730 0.008 0.043 0.0023 REM:0.002 790 3.5 within Preferred Scope of Invention L 0.03 0.4 2.6 0.006 0.004 0.025 0.003 0.550 0.021 0.038 0.0030 809 3.8 out of Preferred Scope of Invention M 0.18 0.5 2.6 0.010 0.003 0.032 0.004 0.600 0.020 0.039 0.0028 762 3.7 out of Preferred Scope of Invention N 0.11 0.3 1.4 0.011 0.002 0.035 0.002 0.810 0.015 0.042 0.0035 805 3.0 out of Preferred Scope of Invention O 0.07 0.1 2.8 0.014 0.002 0.035 0.003 0.005 0.018 0.041 0.0034 777 3.4 out of Preferred Scope of Invention P 0.08 0.5 2.4 0.013 0.002 0.029 0.003 0.580 0.001 0.035 0.0033 797 3.6 out of Preferred Scope of Invention Q 0.09 0.3 2.7 0.018 0.003 0.041 0.002 0.510 0.016 0.003 0.0027 776 3.8 out of Preferred Scope of Invention R 0.09 0.2 2.1 0.015 0.002 0.041 0.002 0.750 0.019 0.040 0.0002 787 3.0 out of Preferred Scope of Invention S 0.12 0.8 2.3 0.022 0.003 0.041 0.002 0.350 0.019 0.040 0.0020 803 2.8 out of Preferred Scope of Invention T 0.08 0.3 1.9 0.018 0.003 0.035 0.003 0.430 0.023 0.033 0.0025 804 2.8 out of Preferred Scope of Invention

(15) TABLE-US-00002 TABLE 2 Hot Rolling Condition Cold Retention Rolling Finish Rolling Time in Condition Annealing Condition Final Pass Range from Cold Average Annealing Average Cooling Steel Rolling Finish Rolling 600 C. to Coiling Rolling Heating Annealing Holding Cooling Stop Holding Sheet Reduction Temperature 700 C. Temperature Reduction Dew Point Air Rate Temperature Time Rate Temperature Time Coating No. Steel (%) ( C.) (s) ( C.) (%) ( C.) Ratio ( C./s) ( C.) (s) ( C./s) ( C.) (s) Condition* Note 1 A 15 900 2 560 50 30 1.09 3.1 860 200 5 500 60 GA Example 2 20 870 2 580 50 33 1.00 6.5 830 150 8 480 100 GI Example 3 8 870 2 550 50 42 1.00 3.2 850 150 8 500 80 GA Comparative Example 4 15 800 2 550 50 39 1.01 3.2 850 150 8 500 80 GA Comparative Example 5 15 870 12 550 50 35 1.02 3.2 850 150 8 500 80 GA Comparative Example 6 15 870 2 620 50 31 1.00 3.2 820 150 8 500 80 GA Comparative Example 7 15 870 1 500 10 32 1.05 3.2 850 150 8 500 80 GA Comparative Example 8 15 870 1 500 50 48 1.00 3.3 850 150 8 500 80 GA Comparative Example 9 15 870 1 550 50 33 0.79 3.2 850 150 8 500 80 GA Comparative Example 10 15 870 1 550 50 35 1.02 0.1 850 150 8 500 80 GA Comparative Example 11 15 870 2 550 50 37 1.01 3.5 765 150 8 500 80 GA Comparative Example 12 15 870 2 550 50 32 1.04 3.5 960 150 8 500 50 GA Comparative Example 13 15 870 2 550 50 31 1.00 3.5 810 5 8 500 50 GA Comparative Example 14 15 870 2 550 50 34 1.06 3.5 850 1200 8 500 50 GA Comparative Example 15 B 15 890 1 550 65 28 1.00 2.5 870 100 15 500 100 GA Example 16 15 890 1 550 65 34 1.00 2.5 870 100 15 390 100 GA Comparative Example 17 15 890 1 550 65 36 1.01 2.5 870 100 15 500 1200 GA Comparative Example 18 15 890 1 550 65 34 1.00 2.5 870 100 15 500 5 GA Comparative Example 19 C 15 930 5 500 60 37 1.10 12 820 90 12 500 80 GI Example 20 15 930 5 500 60 34 1.02 12 820 90 12 620 80 GI Comparative Example 21 15 930 5 500 60 39 1.05 12 820 90 4 500 80 GI Comparative Example *GI: galvanized steel sheet, GA: galvannealed steel sheet

(16) TABLE-US-00003 TABLE 3 Hot Rolling Condition Cold Retention Rolling Finish Rolling Time in Condition Annealing Condition Final Pass Range from Cold Average Annealing Average Cooling Steel Rolling Finish Rolling 600 C. to Coiling Rolling Heating Annealing Holding Cooling Stop Holding Sheet Reduction Temperature 700 C. Temperature Reduction Dew Point Air Rate Temperature Time Rate Temperature Time Coating No. Steel (%) ( C.) (s) ( C.) (%) ( C.) Ratio ( C./s) ( C.) (s) ( C./s) ( C.) (s) Condition* Note 22 D 25 900 1 470 55 33 1.02 2.2 850 200 10 470 80 GA Example 23 25 960 1 470 55 31 1.03 2.2 850 200 10 500 80 GA Comparative Example 24 25 900 1 470 55 48 1.02 2.2 850 200 10 500 80 GA Comparative Example 25 E 25 880 2 540 60 33 1.01 1.5 830 200 30 460 30 GI Example 26 25 880 2 540 60 46 0.78 1.5 830 200 30 460 30 GI Comparative Example 27 25 880 2 540 60 40 0.75 1.5 830 200 30 460 30 GI Comparative Example 28 F 18 880 2 500 50 38 1.00 3.9 850 200 10 500 150 GA Example 29 G 18 880 2 520 50 34 1.02 4.0 850 200 10 500 80 GA Example 30 H 18 880 2 500 40 35 1.00 4.0 900 200 10 500 100 GI Example 31 I 18 880 2 560 40 33 1.03 4.0 800 300 10 480 100 GA Example 32 J 18 880 2 500 50 31 1.00 4.0 820 300 10 530 100 GI Example 33 K 18 880 2 500 55 38 1.08 4.0 840 100 10 530 100 GI Example 34 L 18 880 2 500 55 35 1.01 4.0 850 150 25 540 30 GI Comparative Example 35 M 18 880 2 500 55 29 1.10 4.0 850 150 10 460 150 GA Comparative Example 36 N 18 880 2 500 55 35 1.01 4.0 830 150 10 500 100 GA Comparative Example 37 O 18 880 2 500 55 33 1.00 4.0 800 150 10 500 100 GA Comparative Example 38 P 18 880 2 500 55 33 1.00 4.0 850 150 10 500 100 GI Comparative Example 39 Q 18 880 2 500 55 35 1.01 4.0 830 150 15 500 100 GI Comparative Example 40 R 18 880 2 500 55 36 1.04 4.0 830 150 15 500 100 GA Comparative Example 41 S 18 880 2 500 55 35 1.00 4.0 860 150 15 500 30 GA Comparative Example 42 T 18 880 2 500 55 35 1.01 4.0 810 150 15 500 30 GA Comparative Example *GI: galvanized steel sheet, GA: galvannealed steel sheet

(17) TABLE-US-00004 TABLE 4 Anti-crash property Absorbed Energy Tensile for Strain Steel *Microstructure *Hard- Property up to 5% Spot Sheet V (F) V (B) V (M) V () Other d (Mb) V (LM) ness YS TS AE AE/TS Weld- Bend- No. (%) (%) (%) (%) (%) (m) (%) Hv (MPa) (MPa) (MJ/m3) (J/m3 .Math. Pa) ability ability Note 1 0 8 92 0 0 6.5 0 53 918 1210 74 0.061 Excellent Excellent Example 2 0 23 77 0 0 5.1 2 33 891 1188 69 0.058 Excellent Excellent Example 3 0 7 93 0 0 6.1 0 23 930 1222 75 0.061 Excellent Poor Comparative example 4 0 9 91 0 0 6.4 0 25 915 1219 73 0.060 Excellent Poor Comparative example 5 2 43 55 0 0 7.0 18 36 785 1126 54 0.048 Excellent Poor Comparative example 6 14 44 42 0 0 6.6 26 48 739 1114 46 0.041 Excellent Excellent Comparative example 7 0 10 90 0 0 17 0 44 909 1218 58 0.048 Excellent Excellent Comparative example 8 0 9 91 0 0 6.7 0 11 911 1220 72 0.059 Excellent Poor Comparative example 9 0 9 91 0 0 6.8 0 15 908 1221 72 0.059 Excellent Poor Comparative example 10 0 8 92 0 0 17 0 37 854 1206 57 0.047 Excellent Poor Comparative example 11 12 29 59 0 0 3.8 21 35 796 1135 56 0.049 Excellent Poor Comparative example 12 0 7 93 0 0 26 0 43 843 1202 50 0.042 Excellent Poor Comparative example 13 15 51 34 0 0 2.5 11 40 795 1108 59 0.053 Excellent Excellent Comparative example 14 0 9 91 0 0 16 0 43 860 1208 59 0.049 Excellent Poor Comparative example 15 0 6 94 0 0 6.2 0 45 993 1195 86 0.072 Excellent Excellent Example 16 0 50 47 3 0 5.9 23 37 822 1098 54 0.049 Excellent Excellent Comparative example 17 0 46 53 1 0 6.0 18 38 769 1092 51 0.047 Excellent Excellent Comparative example 18 0 1 99 0 0 6.0 0 34 1018 1012 90 0.074 Excellent Poor Comparative example 19 0 26 74 0 0 5.7 5 46 913 1240 69 0.056 Excellent Excellent Example 20 33 1 66 0 0 5.6 0 39 753 1160 43 0.037 Excellent Poor Comparative example 21 15 25 60 0 0 5.1 12 38 776 1139 49 0.043 Excellent Poor Comparative example *V(F): area ratio of ferrite, V(B): area ratio of bainitic ferrite V(M): area ratio of martensite, V(): area ratio of retained austenite, Other: area ratio of phases othe than those described above, d(Mb): average grain diameter of martensite adjacent to bainite, V(LM): area ratio of martensite adjacent only to bainite Hv: a value calculated by subtracting the Vickers hardness at a position located at 20 m from the surface of the steel sheet from the Vickers hardness at a position located at 100 m from the surface of the steel sheet

(18) TABLE-US-00005 TABLE 5 Anti-crash property Absorbed Energy Tensile for Strain Steel *Microstructure *Hard- Property up to 5% Spot Sheet V (F) V (B) V (M) V () Other d (Mb) V (LM) ness YS TS AE AE/TS Weld- Bend- No. (%) (%) (%) (%) (%) (m) (%) Hv (MPa) (MPa) (MJ/m3) (J/m3 .Math. Pa) ability ability Note 22 0 18 82 0 0 5.3 2 38 912 1204 72 0.060 Excellent Excellent Example 23 0 10 90 0 0 16 0 43 846 1193 56 0.047 Excellent Poor Comparative example 24 0 17 83 0 0 5.5 2 22 919 1211 73 0.060 Excellent Poor Comparative example 25 0 28 72 0 0 3.3 6 35 928 1229 75 0.061 Excellent Excellent Example 26 0 26 74 0 0 3.5 5 9 926 1230 74 0.060 Excellent Poor Comparative example 27 0 29 71 0 0 3.3 5 18 919 1225 74 0.060 Excellent Poor Comparative example 28 0 6 94 0 0 3.0 0 34 971 1243 82 0.066 Excellent Excellent Example 29 0 10 90 0 0 4.8 0 39 960 1264 78 0.062 Excellent Excellent Example 30 0 13 87 0 0 4.1 1 36 959 1217 79 0.065 Excellent Excellent Example 31 0 21 79 0 0 3.6 3 42 910 1205 72 0.060 Excellent Excellent Example 32 0 7 93 0 0 4.0 0 40 962 1222 81 0.066 Excellent Excellent Example 33 0 5 95 0 0 5.5 0 42 938 1220 76 0.062 Excellent Excellent Example 34 0 11 89 0 0 6.0 0 39 850 1077 69 0.064 Excellent Excellent Comparative example 35 0 25 71 4 0 5.3 3 52 881 1382 51 0.037 Poor Poor Comparative example 36 13 53 31 3 0 2.3 21 38 701 996 42 0.042 Excellent Excellent Comparative example 37 13 52 35 0 0 2.2 23 38 688 1010 43 0.043 Excellent Excellent Comparative example 38 7 48 43 2 0 6.5 23 39 764 1119 46 0.041 Excellent Excellent Comparative example 39 0 52 48 0 0 16 26 36 749 1130 41 0.036 Excellent Poor Comparative example 40 7 50 43 0 0 6.3 22 40 763 1121 48 0.043 Excellent Excellent Comparative example 41 3 28 66 3 0 6.5 12 38 823 1205 51 0.042 Excellent Poor Comparative example 42 5 30 65 0 0 5.6 11 35 833 1183 54 0.046 Excellent Poor Comparative example *V(F): area ratio of ferrite, V(B): area ratio of bainitic ferrite V(M): area ratio of martensite, V(): area ratio of retained austenite, Other: area ratio of phases othe than those described above, d(Mb): average grain diameter of martensite adjacent to bainite, V(LM): area ratio of martensite adjacent only to bainite Hv: a value calculated by subtracting the Vickers hardness at a position located at 20 m from the surface of the steel sheet from the Vickers hardness at a position located at 100 m from the surface of the steel sheet

(19) It is clarified that the galvanized steel sheets and the galvannealed steel sheets according to aspects of the present invention had a TS of 1180 MPa or more, excellent anti-crash property indicated by an AE/TS of 0.050 or more, and excellent bending formability and spot weldability.

(20) Therefore, according to the present invention, it is possible to obtain a galvanized steel sheet and a galvannealed steel sheet excellent in terms of spot weldability, anti-crash property, bending formability, and so forth, which has an excellent effect of contributing to weight reduction of an automobile and thereby significantly contributing to an increase in the quality of an automobile body.

(21) According to the present invention, it is possible to obtain a high-strength galvanized steel sheet having a TS of 1180 MPa or more excellent in terms of spot weldability, anti-crash property, and bending formability. By using the high-strength galvanized steel sheet according to an embodiment of the present invention for automobile parts, it is possible to significantly contribute to weight reduction of an automobile, thereby contributing to an increase in the quality of an automobile body by contributing.