100 KG-GRADE ULTRAHIGH-STRENGTH GALVANIZED STEEL SHEET AND MANUFACTURING METHOD THEREFOR

Abstract

The present invention provides a 100 kg-grade ultra-high-strength galvanized steel sheet having excellent resistance spot welding properties and excellent resistance to liquid metal embrittlement (LME) cracking. The steel sheet contains the following components in percentage by weight: C: 0.17-0.25%, Mn: 1.7-2.7%, Si: 0.35-1.5%, Al: 0.01-1.0%, 0.7%Si+Al1.7%, and at least one of Nb, Ti and B, with the balance being Fe and unavoidable impurities. When the thickness of the steel sheet is t, the resistivity thereof is 0<R.sub.150 .Math.cm; and, in the direction from the coating layer/steel sheet substrate interface to the steel sheet substrate, when the thickness of the steel sheet is in the range of greater than or equal to 0.010t to less than or equal to 0.035t the resistivity thereof is 0<R.sub.215 .Math.cm, and when the thickness of the steel sheet is in the range of greater than 0.035t to less than or equal to 0.065t the resistivity thereof is 0<R.sub.330 .Math.cm, wherein (R.sub.2/2+R.sub.3/3)(3.1R.sub.1.sup.1/21.5) is satisfied.

Claims

1. A 100 Kg grade ultra-high strength galvanized steel plate, which comprises the following chemical elements by weight percentage: C: 0.17-0.25%, Mn: 1.7-2.7%, Si: 0.35-1.5%, Al: 0.01-1.0%, 0.7%Si+Al1.7%, at least one of Nb, Ti and B, and a balance of Fe and unavoidable impurities, wherein the thickness of the steel plate is set to t, the resistivity R.sub.1 of the steel plate is 0<R.sub.150.Math.cm; in the direction from the interface between the plating layer and the steel plate matrix to the steel plate matrix, the resistivity R.sub.2 of the steel plate in the range of 0.010 t to 0.035 t is 0<R.sub.215.Math.cm, and the resistivity R.sub.3 of the steel plate in the range of greater than 0.035 t to less than or equal to 0.065 t is 0<R.sub.330.Math.cm, and they satisfy (R.sub.2/2+R.sub.3/3)(3.1R.sub.1.sup.1/21.5).

2. The 100 Kg grade ultra-high strength galvanized steel plate according to claim 1, wherein the mass percentages of Nb, Ti, B are as follows: $0<\mathrm{Nb}0.1\%;$ $0<\mathrm{Ti}0.1\%;$ $0<B0.003\%.$

3. The 100 Kg grade ultra-high strength galvanized steel plate according to claim 1, wherein it comprises, by mass percentage, among other unavoidable impurities: $P0.015\%$ $S0.01\%;$ $N0.008\%;$ $\mathrm{REM}0.01\%.$

4. The 100 Kg grade ultra-high strength galvanized steel plate according to claim 1, wherein it comprises at least one of the following components by mass percentage: Nb: 0.03%-0.05%; Ti: 0.001%-0.02%; B: 0.0002%-0.0025%.

5. The 100 Kg grade ultra-high strength galvanized steel plate according to claim 1, wherein the thickness of the steel plate is set to t, the resistivity R.sub.1 of the steel plate is 37.Math.cmR.sub.150.Math.cm, in the direction from the interface between the plating layer and the steel plate matrix to the steel plate matrix, the resistivity R.sub.2 of the steel plate in the range of 0.010t to 0.035t is 9.Math.cmR.sub.215.Math.cm, and the resistivity R.sub.3 of the steel plate in the range of greater than 0.035t to less than or equal to 0.065t is 24.Math.cmR.sub.330.Math.cm, and satisfies (R.sub.2/2+R.sub.3/3)(3.1R.sub.1.sup.1/21.5).

6. The 100 Kg grade ultra-high strength galvanized steel plate according to claim 1, wherein the steel plate is configured as a GA plate or a GI plate.

7. The 100 Kg grade ultra-high strength galvanized steel plate according to claim 1, wherein when Type III specimens according to ISO 6892-1 standard are stretched at room temperature perpendicularly to the rolling direction, the steel plate has a tensile strength of 980 MPa, an elongation at break of 20%, and a hole expansion ratio of 20%.

8. The 100 Kg grade ultra-high strength galvanized steel plate according to claim 1, wherein when the steel plate is welded with 1 to 1.25 times of the I.sub.splash current, no Type B or Type C cracks will occur, and the depth of Type D cracks is not greater than 10% of the thickness of the base metal plate if Type D cracks are generated; when the steel plate is welded with 1 time or less of the I.sub.splash current, no Type B or Type C cracks will occur, and the depth of Type A cracks is not greater than 10% of the thickness of the base metal plate if Type A cracks are generated, wherein I.sub.splash is the minimum current at which splashing occurs.

9. A manufacturing method for the 100 Kg grade ultra-high strength galvanized steel plate according to claim 1, which comprises the following steps: (1) Smelting and continuous casting to obtain a cast billet that satisfies the above composition of the steel plate according to claim 1; (2) Hot rolling: the cast billet obtained in step (1) is heated, subjected to final rolling, laminar flow cooling and coiling to obtain a hot-rolled coil; (3) Pickling and cold rolling: the hot-rolled coil obtained in step (2) is pickled, cold-rolled to obtain a cold rolled coil without annealing; (4) Continuous annealing: the cold rolled coil without annealing obtained in step (3) is subjected to a multi-stage heat treatment; (5) Galvanizing: the strip steel obtained in step (4) enters the zinc pot at a temperature of (zinc pot temperature T.sub.ZP15 C.) for galvanizing, to obtain a galvanized steel plate.

10. The manufacturing method for the 100 Kg grade ultra-high strength galvanized steel plate according to claim 9, wherein the multi-stage heat treatment comprises the following (a)-(d): (a) First stage annealing: the cold rolled coil without annealing is heated to a first stage temperature in the range of not less than 600 C.(A.sub.c1+40 C.) to obtain a steel coil, (b) Second stage annealing: the steel coil obtained in (a) is further heated to a second stage temperature in the range of (A.sub.c1+50 C.)(A.sub.c3+80 C.) or (A.sub.c1+50 C.)900 C., and held for 30300 s to obtain a strip steel, wherein the smaller value from (A.sub.c3+80 C.) and 900 C. is taken as the upper limit of the second stage temperature range, (c) Third stage annealing: the strip steel obtained in (b) is cooled to a third stage temperature in the range of M.sub.sM.sub.f at a cooling rate that is not less than a certain cooling rate V.sub.2-3 and held for 10200 s, (d) Fourth stage annealing, the strip steel obtained in (c) is heated again to a fourth stage temperature in the range of (350 C.zinc pot temperature) and held for 1590 s, wherein A.sub.c1 is the temperature at which the pearlite transforms into austenite when heated, A.sub.c3 is the final temperature of transforming into austenite when heated, M.sub.s is the temperature at which martensite appears, and M.sub.f is the temperature of full martensitization, V.sub.2-3 represents the cooling rate, which is not less than 50 C./s.

11. The manufacturing method for the 100 Kg grade ultra-high strength galvanized steel plate according to claim 10, wherein in (b), the second stage annealing temperature is controlled to be (A.sub.c1+70 C.)(A.sub.c3+80 C.) or (A.sub.c1+70 C.)900 C., the holding time is controlled to be 35120 s, and the smaller value from (A.sub.c3+80 C.) and 900 C. is taken as the upper limit of the second stage temperature range; and/or in (d), the fourth stage temperature is in the range of 350 C.(T.sub.ZP35 C.), and the holding time is 3060 s.

12. The manufacturing method for the 100 Kg grade ultra-high strength galvanized steel plate according to claim 9, wherein, in step (4), the atmosphere in (a) contains 0.010.5% by volume of O.sub.2, with a balance of N.sub.2 and unavoidable impurities; the atmosphere in (b) contains at least 0.5% by volume of H.sub.2, with a balance of N.sub.2 and unavoidable impurities, and a dew point of 2015 C.

13. The manufacturing method for the 100 Kg grade ultra-high strength galvanized steel plate according to claim 9, wherein in step (2), the heating temperature is in the range of 11001300 C., the temperature of the final rolling is in the range of A.sub.c31000 C., the holding temperature of laminar flow cooling is in the range of (A.sub.c145 C.), and the laminar flow cooling residence time is 530 s, and then the steel is cooled to 450550 C. and coiled, and the coiled steel coil is thermally insulated in the range of (a coiling temperature of T.sub.C30 C.) for 30300 min.

14. The manufacturing method for the 100 Kg grade ultra-high strength galvanized steel plate according to claim 9, wherein in step (5), when the galvanized steel plate is a hot-dip galvanized steel plate with a zinc plating layer, the steel plate with a zinc plating layer is cooled to room temperature after it is discharged from the zinc pot; when the galvanized steel plate is a hot-dip galvanized steel plate with a zinc iron alloy plating layer, the hot-dip galvanized steel plate with a zinc iron alloy plating layer is thermally insulated in the range of (zinc pot temperature T.sub.ZP20 C.)(zinc pot temperature T.sub.ZP+35 C.) for 560 s for alloying after it is discharged from the zinc pot, and then cooled to room temperature.

15. The manufacturing method for the 100 Kg grade ultra-high strength galvanized steel plate according to claim 9, wherein, in step (5), the strip steel enters the zinc pot at a temperature of (T.sub.ZP10 C.), and is alloyed at a temperature in the range of (T.sub.ZP10 C.)(T.sub.ZP+25 C.), and the holding time is 1020 s.

16. The 100 Kg grade ultra-high strength galvanized steel plate according to claim 1, wherein the thickness of the steel plate is 1-2 mm.

17. The manufacturing method for the 100 Kg grade ultra-high strength galvanized steel plate according to claim 12, wherein the atmosphere in the second stage temperature range contains 0.520% by volume of H.sub.2, with a balance of N.sub.2 and unavoidable impurities, and a dew point of 1010 C.

18. The manufacturing method for the 100 Kg grade ultra-high strength galvanized steel plate according to claim 13, wherein: the temperature of the final rolling is (A.sub.c3+20 C.)950 C.; in the laminar flow cooling process of the strip steel, the temperature is controlled in the range of (A.sub.c120 C.)(A.sub.c1+30 C.), and the laminar flow cooling residence time is 815 s; and/or in the process of holding the strip steel after coiling, the holding time is controlled to be 60210 min.

19. The manufacturing method for the 100 Kg grade ultra-high strength galvanized steel plate according to claim 9, wherein the mass percentages of Nb, Ti and B of the steel plate are as follows: 0<Nb0.1%, 0<Ti0.1%, and 0<B0.003%; or the steel plate comprises at least one of the following components by mass percentage: Nb: 0.03%-0.05%, Ti: 0.001%-0.02%, and B: 0.0002%-0.0025%.

20. The manufacturing method for the 100 Kg grade ultra-high strength galvanized steel plate according to claim 9, wherein: the thickness of the steel plate is set to t, the resistivity R.sub.1 of the steel plate is 37.Math.cmR.sub.150.Math.cm, in the direction from the interface between the plating layer and the steel plate matrix to the steel plate matrix, the resistivity R.sub.2 of the steel plate in the range of 0.010t to 0.035t is 9.Math.cmR.sub.215.Math.cm, and the resistivity R.sub.3 of the steel plate in the range of greater than 0.035t to less than or equal to 0.065t is 24.Math.cmR.sub.330.Math.cm, and satisfies (R.sub.2/2+R.sub.3/3)(3.1R.sub.1.sup.1/21.5); and/or when Type III specimens according to ISO 6892-1 standard are stretched at room temperature perpendicularly to the rolling direction, the steel plate has a tensile strength of 980 MPa, an elongation at break of 20%, and a hole expansion ratio of 20%; and/or when the steel plate is welded with 1 to 1.25 times of the I.sub.splash current, no Type B or Type C cracks will occur, and the depth of Type D cracks is not greater than 10% of the thickness of the base metal plate if Type D cracks are generated; when the steel plate is welded with 1 time or less of the I.sub.splash current, no Type B or Type C cracks will occur, and the depth of Type A cracks is not greater than 10% of the thickness of the base metal plate if Type A cracks are generated, wherein I.sub.splash is the minimum current at which splashing occurs.

Description

DESCRIPTION OF THE DRAWINGS

[0074] FIG. 1 schematically shows the relative positions of the four kinds of resistance spot welding LME cracks of the present disclosure.

[0075] FIG. 2 illustratively shows the change of microstructure of the steel plate of the present disclosure in the thickness direction.

DETAILED DESCRIPTION

[0076] Specific embodiments will be further explained and illustrated below with reference to the specific Examples. However, such explanation and illustration do not constitute any improper limitation on the technical solution of the present disclosure.

[0077] In the present disclosure, galvanizing refers to hot-dip zinc galvanizing or hot-dip zinc iron alloy galvanizing.

[0078] In the present disclosure, A.sub.c1 refers to the temperature at which the pearlite transforms into austenite when heated, and the unit is C.

[0079] In the present disclosure, A.sub.c3 refers to the final temperature of transforming into austenite when heated, and the unit is C.

[0080] In the present disclosure, T.sub.C refers to the coiling temperature in step (2), and the unit is C.

[0081] In the present disclosure, M.sub.s is the temperature at which martensite appears, and M.sub.f is the temperature of full martensitization, and the unit is C.

[0082] In the present disclosure, T.sub.ZP represents the zinc pot temperature, and the unit is C.

[0083] In the present disclosure, V.sub.2-3 represents the cooling rate.

Examples 1-14 and Comparative Examples 1-2

[0084] Table 1 lists the mass percentages of the various chemical elements of the ultra-high-strength galvanized steel plates of Examples 1-14 and the galvanized steel plates of Comparative Examples 1-2.

TABLE-US-00001 TABLE 1 (wt %, the balance is Fe and other unavoidable impurities except P, S and N) Steel Chemical elements grade C Si Mn P S Al Nb Ti B N REM Cr Mo Sb Ac1 Ac3 A 0.170 1.15 2.25 0.008 0.0005 0.45 0.03 0.018 0.0025 0.007 0.0091 707 881 B 0.183 0.82 2.50 0.012 0.0003 0.71 0.020 0.004 704 883 C 0.198 0.98 1.98 0.015 0.0011 0.63 0.05 0.004 0.0035 717 896 D 0.215 1.5 1.72 0.009 0.0007 0.01 0.001 0.0005 0.005 721 838 E 0.229 0.77 2.35 0.010 0.0009 0.93 0.0002 0.003 715 894 F 0.242 0.48 2.66 0.012 0.0012 1.00 0.006 0.0018 0.006 707 878 G 0.250 0.35 2.44 0.010 0.0005 0.88 0.04 0.001 0.005 708 866 CEx. 1 0.17 1.45 2.66 0.0100 0.0029 0.031 0 0.020 713 814 CEx. 2 1.0 0.0064 0.0055 612 839

[0085] The ultra-high-strength galvanized steel plates of Examples 1-14 were prepared by the following steps: [0086] (1) Smelting and continuous casting to obtain a cast billet that satisfies the above composition of the present disclosure; [0087] (2) Hot rolling: the cast billet obtained in step (1) was heated in the range of 11001300 C., subjected to final rolling in the range of A.sub.c31000 C.; the strip steel after final rolling was cooled to the range of (A.sub.c145 C.), and the laminar flow cooling residence time was 530 s, then cooled to 450550 C. and coiled with a coiling temperature of T.sub.C, and the coiled steel coil is kept in the range of (T.sub.C30 C.) for 30300 min to obtain the hot-rolled coil; [0088] (3) Pickling and cold rolling: the hot-rolled coil obtained in step (1) was pickled, cold-rolled to obtain a cold rolled coil without annealing, [0089] (4) Continuous annealing: the cold rolled coil without annealing obtained in step (3) was subjected to a multi-stage heat treatment, [0090] (a) First stage annealing: the cold rolled coil without annealing was heated to a first stage temperature in the range of not less than 600 C.(A.sub.c1+40 C.) to obtain a steel coil, [0091] (b) Second stage annealing: the steel coil obtained in (a) is further heated to a second stage temperature in the range of (A.sub.c1+50 C.)(A.sub.c3+80 C.) or (A.sub.c1+50 C.)900 C., and held for 30300 s to obtain a strip steel, [0092] (c) Third stage annealing: the strip steel obtained in (b) was cooled to a third stage temperature in the range of M.sub.sM.sub.f at a cooling rate that is no less than a certain cooling rate V.sub.2-3 and held for 10200 s; [0093] (d) Fourth stage annealing: the strip steel obtained in (c) was heated again to a fourth stage temperature in the range of (350 C.T.sub.ZP) and held for 1590 s, [0094] wherein, in step (4), the atmosphere in (a) contained 0.010.5% by volume of O.sub.2, with a balance of N.sub.2 and unavoidable impurities; the atmosphere in (b) contained at least 0.5% by volume of H.sub.2, with a balance of N.sub.2 and unavoidable impurities, and a dew point of 20-15 C.; the smaller value from (A.sub.c3+80 C.) and 900 C. was taken as the upper limit of the second stage temperature range; in (c), V.sub.2-3 represented the cooling rate, which was not less than 50 C./s; in (d), T.sub.ZP was the temperature of the zinc pot; [0095] (5) Galvanizing: the strip steel obtained after the fourth stage annealing (d) in step (4) entered the zinc pot at a temperature of (T.sub.ZP15 C.) for galvanizing, to obtain a galvanized steel plate, wherein, when the galvanized steel plate was a hot-dip galvanized steel plate with a zinc plating layer, the steel plate with a zinc plating layer was cooled to room temperature after it was discharged from the zinc pot, and when the galvanized steel plate was a hot-dip galvanized steel plate with a zinc iron alloy plating layer, the hot-dip galvanized steel plate with a zinc iron alloy plating layer was thermally insulated in the range of (T.sub.ZP20 C.)(T.sub.ZP+35 C.) for 560 s for alloying, and then cooled to room temperature.

[0096] Tables 2-1 and 2-2 list the specific process parameters for the ultra-high-strength galvanized steel plates of Examples 1-14 and the galvanized steel plates of Comparative Examples 1-2.

TABLE-US-00002 TABLE 2-1 Laminar flow Laminar cooling cooling Holding Heating Final rolling insulation residence Coiling time after No. Ingredient temperature/ C. temperature/ C. temperature/ C. time/s temperature/ C. coiling/min Ex. 1 A 1240 920 730 5 550 30 Ex. 2 A 1230 920 720 8 520 90 Ex. 3 B 1250 940 720 10 520 120 Ex. 4 B 1230 910 710 9 510 150 Ex. 5 C 1220 900 710 12 490 210 Ex. 6 C 1200 900 710 9 470 240 Ex. 7 D 1270 950 710 11 510 180 Ex. 8 D 1260 940 690 15 530 60 Ex. 9 E 1230 910 680 13 450 300 Ex. 10 E 1210 900 690 16 470 270 Ex. 11 F 1200 900 670 21 510 120 Ex. 12 F 1150 880 665 28 490 210 Ex. 13 G 1230 910 680 15 510 180 Ex. 14 G 1190 890 670 25 520 120

TABLE-US-00003 TABLE 2-2 Preheat- heating/ Rapid ing soaking cooling Reheating Temper- Alloy- temper- temper- temper- Rapid temper- Reheat- ature for Zinc pot ing Plat- ature ature Soak- dew ature cooling ature ing entering temper- temper- Alloy- Ingre- ing (first (second ing point/ (third holding (fourth holding zinc pot;/ ature/ ature/ ing No. dient layer stage)/ C. stage)/ C. time/s C. stage)/ C. time/s stage)/ C. time/s C. C. C. time/s Ex. 1 A GI 720 870 30 10 290 185 350 45 455 460 Ex. 2 A GA 700 860 50 8 275 155 420 55 455 460 490 5 Ex. 3 B GA 690 850 60 3 270 140 370 70 455 455 475 15 Ex. 4 B GI 700 860 45 0 250 120 390 65 460 458 Ex. 5 C GI 730 880 35 7 280 100 420 45 460 462 Ex. 6 C GA 710 840 95 5 230 60 390 60 460 465 480 20 Ex. 7 D GA 670 810 300 15 210 15 360 90 455 460 490 10 Ex. 8 D GI 685 835 120 12 245 35 410 35 460 461 Ex. 9 E GI 690 830 145 0 225 55 410 35 465 458 Ex. 10 E GA 680 840 100 5 230 70 390 55 465 462 465 45 Ex. 11 F GA 710 860 85 12 270 120 440 15 465 460 455 55 Ex. 12 F GI 700 850 100 18 250 60 455 75 455 464 Ex. 13 G GA 670 825 180 7 215 45 370 90 460 465 465 30 Ex. 14 G GI 720 850 90 2 220 60 400 60 460 461 GI: the plating layer is pure zinc layer, GA: the plating layer is zinc-iron alloy.

[0097] The ultra-high-strength galvanized steel plates of Examples 1-14 were tested for mechanical properties and resistance spot welding performance, and the obtained test results are listed in Table 3.

[0098] The following methods were used to determine the mechanical properties, resistivity and resistance spot welding performance:

[0099] Mechanical properties: the test sample was stretched and processed in accordance with the requirements of Type III specimen in the ISO 6892-1 standard perpendicularly to the rolling direction of the steel plate, and the tensile strength TS and elongation at break EL were determined by stretching the sample at room temperature. It should be emphasized that, due to the difference in measurement methods and the difference in the geometric dimensions of the specimens, there is a difference between the elongation at break measured according to the ISO 6892-1 standard and the elongation at break measured according to the JIS Z2241 standard, GB/T 228.1 standard, and the differences in the measured value of the elongation at break due to the difference between the reference standards all belong to the protection scope of the ultra-high-strength galvanized steel plate of the present disclosure.

[0100] Hole expansion ratio: the sample was processed according to the ISO 16630 standard, and the hole expansion ratio was detected at room temperature according to the requirements of the standard to determine the hole expansion ratio HER. It should be emphasized that, due to the difference in measurement methods and the difference in the geometric dimensions of the specimens, there is a difference between the hole expansion ratio measured according to the ISO 16630 standard and the hole expansion ratio measured according to the JFS T1001 standard, GB/T 15825.4 standard, and the differences in the measured value of the hole expansion ratio caused by the difference between the reference standards all belong to the protection range of the ultra-high strength galvanized steel plate of the present disclosure.

[0101] Resistivity: a steel plate having a certain area was taken and processed by processing methods including but not limited to grinding machine, wire-electrode cutting, milling machine, etc. The full thickness of the steel plate was taken as t, and the sample in the range of 0.010t to 0.035t and from greater than 0.035t to less than or equal to 0.065t in the direction of the steel plate matrix was taken and detected for the resistivity R.sub.1, R.sub.2, R.sub.3 of the sample with a resistivity measuring equipment.

[0102] LME cracks: the welded joints were cut and polished, corroded and the cross sections of the welded joints were observed by a microscope (usually an optical microscope) at a certain magnification to determine the length of different types of cracks on the observed welded joints.

TABLE-US-00004 TABLE 3 Plat- thick- ing ness/ Welding Type Type Type Type No. layer mm TS/MPa TEL/% HER/% R.sub.1/ .Math. cm R.sub.2/ .Math. cm R.sub.3/ .Math. cm current (kA) I.sub.splash(kA) A/m B/m C/m D/m Ex. 1 GI 1.6 1039 21.2 26 37.7 9.7 24.5 I.sub.splash 9.2 95.0 N/D N/D 96.5 Ex. 2 GA 1.6 1023 22.5 28 38 9.7 24.7 I.sub.splash + 9.6 44.9 N/D N/D 43.7 I.sub.splash*5% Ex. 3 GA 1.6 1006 23.4 35 41 10.1 25.2 I.sub.splash + 10.5 66.7 N/D N/D 33.8 I.sub.splash*20% Ex. 4 GI 1.6 1045 22.4 29 41 10.5 25.5 I.sub.splash + 10.3 80.2 N/D N/D N/D I.sub.splash*15% Ex. 5 GI 1.6 1056 22.1 21 39 9.8 24 I.sub.splash *80% 11.5 N/D N/D N/D N/D Ex. 6 GA 1.6 1005 24.7 22 39.5 9.8 25.8 I.sub.splash + 11.4 92.3 N/D N/D 79.5 I.sub.splash*25% Ex. 7 GA 1.6 989 25.1 27 38.6 9 26.7 I.sub.splash 8.8 110.5 N/D N/D 122.7 Ex. 8 GI 1.6 1012 22.2 31 39 9 26.8 I.sub.splash 8.5 56.4 N/D N/D 75.5 Ex. 9 GI 1.6 992 23.6 31 44 12.3 28 I.sub.splash + 9.5 N/D N/D N/D 82.1 I.sub.splash*25% Ex. 10 GA 1.6 1007 22.8 29 44.3 12.6 28.1 I.sub.splash + 9.5 N/D N/D N/D 20.3 I.sub.splash*25% Ex. 11 GA 1.6 1034 20.2 33 45.4 13.5 29 I.sub.splash + 10.6 67.4 N/D N/D N/D I.sub.splash*10% Ex. 12 GI 1.6 998 24.3 37 46 14 29 I.sub.splash 10.5 93.0 N/D N/D N/D Ex. 13 GA 1.6 1006 22.1 35 45 13.1 28.3 I.sub.splash 9.8 20.6 N/D N/D 15.1 Ex. 14 GI 1.6 990 22.6 29 44.3 12.7 28.1 I.sub.splash + 10.2 58.2 N/D N/D N/D I.sub.splash*15% TS: tensile strength, TEL: elongation at break, HER: hole expansion ratio, N/D: Not detected.

[0103] The resistance spot welding performance test of the galvanized steel plate of Comparative Examples 1-2 was carried out, and the test results obtained are listed in Table 4.

TABLE-US-00005 TABLE 4 Plating thickness/ Welding current Type Type Type Type No. layer mm (kA) I.sub.splash(kA) A/m B/m C/m D/m CEx. 1 GI I.sub.splash-0.5 kA 9.0 460 CEx. 2 GI 1.41 I.sub.splash-0.5 kA 8.3 N/D N/D 535

[0104] As can be seen from Table 1-3, the chemical elements of the steel grade used in Examples 1-14 of the present disclosure satisfied the requirement of the present disclosure. Therefore, the ultra-high-strength galvanized steel plate obtained by the method of the present disclosure had a tensile strength of 980 MPa, an elongation at break of 20%, a hole expansion ratio of 20%, and the resistivity satisfied the present disclosure. Therefore, when the steel plates of Examples 1-14 were subjected to resistance spot welding with a current in the range of I.sub.splashI.sub.splash+I.sub.splash*25%, no Type B or Type C LME cracks were generated, and Type D LME cracks did not appear or when Type D LME cracks appeared, the length of Type D cracks was not greater than 10% of the thickness of the base metal plate. For example, in Example 7, where the length of the Type D type LME cracks was the longest in examples, the length of the Type D type cracks was 7.6% of the thickness of the base metal.

[0105] In contrast, Comparative Example 1 and Comparative Example 2 are existing steel plates, which were not produced by the manufacturing method of the steel plates of the present disclosure. The chemical elements B and Cr, Mo, Sb in the steel grade of Comparative Example 1 did not satisfy the present disclosure, and the result was that four kinds of cracks of Type A, Type B, Type C and Type D appeared in the steel plate of Comparative Example 1 when the resistance spot welding was carried out, and the resistance spot welding performance was poor.

[0106] The contents of the steel elements C, Mn, Al, Ti used in Comparative Example 2 were different from those of the present disclosure. When the steel plate obtained in Comparative Example 2 was subjected to resistance spot welding, although Type C LME cracks did not appear, the length of Type D cracks was 37.9% of the thickness of the base metal plate. The length of Type D cracks generated in the steel plate of Comparative Example 2 was much greater than the length of Type D cracks generated in the base metal in examples of the present disclosure. The Type D cracks generated in the steel plate of Comparative Example 2 had a greater influence on the base metal, and the resistance spot welding performance is poor.

[0107] In the present disclosure, the LME cracks of the ultra-high-strength galvanized steel plate obtained in Examples 1-14 has been suppressed by optimizing the chemical elements and controlling the manufacturing process, and the resistance spot welding performance is excellent.

[0108] Based on the above, for the 100 kg grade ultra-high-strength galvanized steel plate, the present disclosure inhibits the occurrence of LME cracks in the resistance spot welding process by limiting the resistivity of different areas in the thickness direction of the steel plate and the average resistivity of the steel plate and obtains the ultra-high-strength galvanized steel plate with excellent resistance spot welding performance. When the welding current is lower than the minimum current I.sub.splash at which splashing occurs, no Type B or Type C cracks will be generated, and when Type A cracks are generated, the depth of Type A cracks will not be greater than 10% of the thickness of the base metal plate; when (I.sub.splash+I.sub.splash*25%)welding currentI.sub.splash, no Type B or Type C cracks will be generated, and when Type D cracks are generated, the depth of Type D cracks will not be greater than 10% of the thickness of the base metal plate. The composition of the ultra-high-strength galvanized steel plate of the present disclosure is simple. Through precise control of laminar flow cooling during hot rolling, hot-rolling, coiling and thermal insulation, and the continuous annealing process, the obtained steel plate having a tensile strength of 980 MPa, an elongation at break of 20%, and a hole expansion ratio of 20% has excellent resistance spot welding performance. The process equipment required for the production of ultra-high strength galvanized steel plate of the present disclosure is simple and can realize stable production in batch. The comprehensive properties of the material make it able to meet the manufacture of body parts with complex shapes, and the material has excellent resistance spot welding performance and corrosion resistance. The 100 kg grade ultra-high-strength galvanized steel plate in the present disclosure has excellent resistance to liquid metal embrittlement LME cracks and resistance spot welding performance, can be effectively applied to the manufacture of automobile body structure, meets the current development needs of automotive steel for automobile lightweight and safety, and has broad application prospects.

[0109] It should be noted that the prior art of the protection scope of the present disclosure is not limited to the examples given in the application documents, and all prior arts that do not conflict with the solution of the present disclosure, including but not limited to prior patent documents, prior publications, prior public use, etc., can be included in the protection scope of the present disclosure. In addition, combinations of the various technical features in this case are not limited to the combinations described in the claims of this case or the combinations described in the specific Examples. All technical features recorded in this case can be combined freely or associated in any way unless a contradiction occurs.

[0110] It should also be noted that the examples listed above are only specific embodiments of the present disclosure. Obviously, the present disclosure is not limited to the above examples, and changes or modifications made thereto can be directly derived from the present disclosure or easily conceived of by those skilled in the art, all of which fall within the protection scope of the present disclosure.