HIGH FORMABILITY SUPER STRENGTH COLD-ROLL STEEL SHEET OR STEEL STRIP, AND MANUFACTURING METHOD THEREFOR

Abstract

A high formability super strength cold-roll steel sheet or steel strip, and a method for manufacturing same. The steel sheet or steel strip comprises the following ingredients by weight percent: C 0.15% to 0.35%, Si 1.0% to 2.0%, Mn 1.6% to 2.6%, Mo 0.1% to 0.4%, P≦0.02%, S≦0.004%, N≦0.005%, Nb 0.015% to 0.04%, Ti 0.02% to 0.06%, Al 0.015% to 0.045%, B 0.0003% to 0.001% and B≧P %/30, and the balance being Fe and inevitable impurities. The steel sheet or steel strip has a tensile strength greater than or equal to 980 MPa, an elongation rate greater than or equal to 15% and a hole expansion rate greater than or equal to 40%, and has balanced performance.

Claims

1. A high formability super strength cold-roll steel sheet or steel strip, comprising the following ingredients by weight percent: C 0.15% to 0.35%, Si 1.0% to 2.0%, Mn 1.6% to 2.6%, Mo 0.1% to 0.4%, P≦0.02%, S≦0.004%, N≦0.005%, Nb 0.015% to 0.04%, Ti 0.02% to 0.06%, Al 0.015% to 0.045%, B 0.0003% to 0.001% and B≧P %/30, and the balance being Fe and inevitable impurities.

2. The high formability super strength cold-roll steel sheet or steel strip of claim 1, characterized by comprising the following ingredients by weight percent: C 0.17% to 0.32%, Si 1.2% to 1.8%, Mn 1.8% to 2.5%, Mo 0.15% to 0.4%, P≦0.012%, S≦0.002%, N≦0.005%, Nb 0.015% to 0.04%, Ti 0.02% to 0.06%, Al 0.015% to 0.045%, B 0.0003% to 0.001% and B≧P %/30, and the balance being Fe and inevitable impurities.

3. The high formability super strength cold-roll steel sheet or steel strip of claim 1 further comprising by weight percent: Zr 0.005% to 0.015%.

4. The high formability super strength cold-roll steel sheet or steel strip of claim 1, characterized in that said super strength cold-roll steel sheet or steel strip has a tensile strength greater than or equal to 980 MPa, a product of strength and elongation, i.e., tensile strength×elongation rate, greater than or equal to 17000 and a hole expansion rate greater than or equal to 45%.

5. The high formability super strength cold-roll steel sheet or steel strip of claim 1, characterized in that said super strength cold-roll steel sheet or steel strip has the structure characteristics: a ferrite grain diameter of less than or equal to 10 microns, and a main structures of ferrite, bainite, martensite and 10% or less by volume percent of residual austenite.

6. A method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 1, comprising the following steps: 1) Smelting and casting smelting and casting according to the composition in claim 1, and rapid cooling the continuous casting slab, wherein the water spray amount per kilogram of steel is ≧0.65 litres of water, and the water spray ending temperature is ≦800° C.; 2) Hot rolling heating at 1100° C. to 1250° C., holding the temperature for a time of 0.6 hours or more, hot-rolling at a temperature of Ar3 or higher, after the rolling, firstly air cooling, maintaining a slow cooling state at a temperature between 700° C. and 800° C. for 5 s or more, and then rapidly cooling, the coiling temperature being 500° C. to 600° C.; 3) Cold-rolling at a reduction rate of 40% to 65%; and 4) Annealing holding a temperature at 820° C. to 880° C., cooling to a starting temperature of rapid cooling at v1=5-20° C./s with the starting temperature of rapid cooling being ≧820-10×v1, rapidly cooling to 200° C. to 450° C. at a rate of 40-120° C./s, tempering at 250° C. to 450° C. for 100 s to 400 s, and then further performing 0% to 0.3% temper rolling.

7. The method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 6, characterized in that rapid cooling is used for the continuous casting slab, the water spray amount per kilogram of steel is ≧0.7 litres of water, and the water spray ending temperature is ≦800° C.

8. The method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 6, characterized in that in the hot rolling procedure of step 2), heating at 1100° C. to 1250° C., holding the temperature for a time of 0.8 hours to 1.2 hours, hot-rolling at a temperature of Ar3 or higher, after the rolling, firstly air cooling, maintaining at a slow cooling state at a temperature between 700° C. and 800° C. for 10 s or more, and then rapidly cooling, the coiling temperature being 500° C. to 600° C.

9. The method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 6, characterized in that in the annealing procedure of step 4), holding a temperature at 830° C. to 860° C., cooling to a starting temperature of rapid cooling at v1=5-20° C./s with the starting temperature of rapid cooling being ≧820-10×cooling rate v1, cooling to 240° C. to 400° C. at a rate of 40-120° C./s, tempering at 270° C. to 400° C. for 100 s to 400 s, and then further performing 0% to 0.3% temper rolling.

10. The method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 6, characterized in that the composition of said super strength cold-roll steel sheet or steel strip further comprises by weight percent: Zr 0.005% to 0.015%.

11. The method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 6, characterized in that the thickness of said super strength cold-roll steel sheet or steel strip is 0.8 mm to 2.3 mm.

12. The method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 6, characterized in that said super strength cold-roll steel sheet or steel strip has a tensile strength greater than or equal to 980 MPa, a product of strength and elongation, i.e., the tensile strength×the elongation rate, greater than or equal to 17000 and a hole expansion rate greater than or equal to 45%.

13. The method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 6, characterized in that said super strength cold-roll steel sheet or steel strip has the structure characteristics: a ferrite grain diameter of less than or equal to 10 microns, and a main structures of ferrite, bainite, martensite and 10% or less by volume percent of residual austenite.

14. The method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 10, characterized in that the thickness of said super strength cold-roll steel sheet or steel strip is 0.8 mm to 2.3 mm.

15. The method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 10, characterized in that said super strength cold-roll steel sheet or steel strip has a tensile strength greater than or equal to 980 MPa, a product of strength and elongation, i.e., the tensile strength×the elongation rate, greater than or equal to 17000 and a hole expansion rate greater than or equal to 45%.

16. The method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 10, characterized in that said super strength cold-roll steel sheet or steel strip has the structure characteristics: a ferrite grain diameter of less than or equal to 10 microns, and a main structures of ferrite, bainite, martensite and 10% or less by volume percent of residual austenite.

17. The method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 11, characterized in that said super strength cold-roll steel sheet or steel strip has a tensile strength greater than or equal to 980 MPa, a product of strength and elongation, i.e., the tensile strength×the elongation rate, greater than or equal to 17000 and a hole expansion rate greater than or equal to 45%.

18. The method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 11, characterized in that said super strength cold-roll steel sheet or steel strip has the structure characteristics: a ferrite grain diameter of less than or equal to 10 microns, and a main structures of ferrite, bainite, martensite and 10% or less by volume percent of residual austenite.

19. The method for manufacturing the high formability super strength cold-roll steel sheet or steel strip of claim 12, characterized in that said super strength cold-roll steel sheet or steel strip has the structure characteristics: a ferrite grain diameter of less than or equal to 10 microns, and a main structures of ferrite, bainite, martensite and 10% or less by volume percent of residual austenite.

Description

PARTICULAR EMBODIMENTS OF THE INVENTION

[0051] The present invention is further described below in conjunction with embodiments.

[0052] Table 1 is the chemical composition of an embodiment of the steel of the present invention, the process for manufacturing the embodiment of the steel of the present invention is as shown in table 2, and the strength of the steel of the present invention obtained after smelting, hot rolling, cold rolling, annealing and temper rolling is as shown in table 3.

[0053] It can be seen from table 3 that a super strength cold-roll steel sheet or steel strip having a strength of 980 MPa or higher can be manufactured according to the present invention, and has a good elongation and a good hole expansion rate. It is different from and superior to the existing inventions in terms of various aspects such as a composition design, resource saving, a degree of manufacturing difficulty, and final results.

TABLE-US-00001 TABLE 1 Chemical composition of the steel of the present invention (wt %) Embodiment C Si Mn Mo Zr P S Al N Nb Ti B A1 0.15 1.0 1.8 0.10 0.005 0.008 0.005 0.015 0.005 0.035 0.04 0.0003 A2 0.18 2.0 1.6 0.15 0.010 0.015 0.004 0.040 0.004 0.030 0.03 0.0006 A3 0.2 1.7 2.0 0.18 0.015 0.010 0.003 0.030 0.003 0.025 0.02 0.004 A4 0.24 1.6 2.2 0.35 0.020 0.012 0.001 0.025 0.0025 0.02 0.025 0.0008 A5 0.28 1.8 2.4 0.40 0.018 0.006 0.002 0.045 0.0015 0.015 0.05 0.0009 A6 0.30 1.4 2.6 0.22 0.010 0.001 0.025 0.0025 0.02 0.025 0.0005 A7 0.32 1.2 2.1 0.25 0.007 0.018 0.002 0.023 0.0045 0.04 0.035 0.001 A8 0.35 0.8 1.7 0.3 0.012 0.02 0.0015 0.027 0.0035 0.018 0.06 0.0007

TABLE-US-00002 TABLE 2 Inlet Primary temperature Outlet Rapid Holding cooling of temperature cooling Tempering Temper- temperature rate rapid of rapid Rate Temperature Tempering rolling Embodiment ° C. ° C./s cooling ° C. cooling ° C. ° C./s ° C. Times rate % A1 830 5 770 200 120 270 100 0.1 A2 840 7 750 250 80 300 150 0.2 A3 850 10 730 300 60 320 200 0.3 A4 860 15 740 350 40 350 250 0 A5 855 20 720 400 70 420 300 0.15 A6 870 25 740 450 90 450 350 0.25 A7 835 18 745 380 100 400 400 0.3 A8-1 840 13 760 320 110 370 320 0.1 A8-2 880 15 750 350 100 350 250 0.1

TABLE-US-00003 TABLE 3 Hole expansion Embodiment σ.sub.sMpa σ.sub.bMpa δ.box-tangle-solidup. % rate % A1 640 1040 18 45 A2 680 1090 21 50 A3 750 1120 18 54 A4 800 1150 18 55 A5 850 1180 16 55 A6 900 1270 14 51 A7 960 1320 13 60 A8-1 1050 1430 12 65 A8-2 1040 1410 13 60