COLD-ROLLED ANNEALED DUAL-PHASE STEEL, STEEL PLATE, AND MANUFACTURING METHOD THEREFOR

Abstract

A cold-rolled annealed dual-phase steel is provided, having a microstructure of ferrite and martensite, and comprising the following chemical elements in mass percentage: 0.08% to 0.1% of C, 1.95% to 2.2% of Mn, 0.1% to 0.6% of Si, 0.020% to 0.050% of Nb, 0.020% to 0.050% of Ti, 0.015% to 0.045% of Als, 0.40% to 0.60% of Cr, 0.2% to 0.4% of Mo, 0.001% to 0.005% of Ca, and the balance being Fe and other inevitable impurities. A method for manufacturing the cold-rolled annealed dual-phase steel is also provided, comprising the steps of: (1) smelting and casting; (2) hot rolling; (3) cold rolling; (4) annealing; and (5) temper rolling.

Claims

1. 1. A cold-rolled annealed dual-phase steel, wherein the steel has a microstructure of ferrite and martensite, and comprises the following chemical elements in mass percentage: 0.08% to 0.1% of C, 1.95% to 2.2% of Mn, 0.1% to 0.6% of Si, 0.020% to 0.050% of Nb, 0.020% to 0.050% of Ti, 0.015% to 0.045% of Als, 0.40% to 0.60% of Cr, 0.2% to 0.4% of Mo, 0.001% to 0.005% of Ca, and the balance being Fe and other inevitable impurities.

2. The cold-rolled annealed dual-phase steel as claimed in claim 1, wherein the ratio of martensite phase is 50% or more, and the ratio of martensite phase to ferrite phase is more than 1 and less than 4.

3. The cold-rolled annealed dual-phase steel as claimed in claim 1, wherein the martensite has an average grain size of 3 to 6 μm.

4. The cold-rolled annealed dual-phase steel as claimed in claim 1, wherein the cold-rolled annealed dual-phase steel has a tensile strength of 1000 MPa or more and an elongation at break of 12% or more.

5. A cold-rolled annealed dual-phase steel plate made of the cold-rolled annealed dual-phase steel as claimed in claim 1.

6. The cold-rolled annealed dual-phase steel plate as claimed in claim 5, wherein the steel plate has a thickness of 0.5 to 0.7 mm.

7. A method for manufacturing the cold-rolled annealed dual-phase steel plate as claimed in claim 5, comprising the steps of: (1) smelting and casting; (2) hot rolling; (3) cold rolling; (4) annealing; (5) temper rolling.

8. The method as claimed in claim 7, wherein in the step (2), a slab is soaked at a temperature of 1200 to 1260° C., then rolled wherein finish rolling temperature is controlled to 840˜930° C.; after rolling, resultant steel plate is cooled at a rate of 20 to 70° C./s; and then coiled at a temperature of 500˜620° C.

9. The method as claimed in claim 7, wherein in the step (3), a cold rolling reduction ratio is controlled to 65 to 78%.

10. The method as claimed in claim 7, wherein in the step (4), soaking temperature during annealing is 780 to 820° C., and annealing time is 40 to 200 s; after annealing, rapidly cooling is performed at a rate of 45 to 100° C./s, and start temperature of rapidly cooling is 650 to 730° C., aging temperature is 200 to 260° C., and overaging time is 100 to 400 s.

11. The method as claimed in claim 7, wherein in the step (5), temper rolling is performed at a reduction ratio of 0.3% or less.

12. The method as claimed in claim 7, wherein the steel plate has a thickness of 0.5 to 0.7 mm.

13. The cold-rolled annealed dual-phase steel plate made of the cold-rolled annealed dual-phase steel as claimed in claim 2.

14. The cold-rolled annealed dual-phase steel plate made of the cold-rolled annealed dual-phase steel as claimed in claim 3.

15. The cold-rolled annealed dual-phase steel plate made of the cold-rolled annealed dual-phase steel as claimed in claim 4.

Description

DETAILED DESCRIPTION

[0041] The cold-rolled annealed dual-phase steel and the manufacturing method thereof according to the present invention will be further explained and illustrated below with reference to the specific Examples. However, the explanations and illustrations do not unduly limit the technical solutions of the present invention.

EXAMPLES 1-6 AND COMPARATIVE EXAMPLES 1-9

[0042] Table 1 lists the mass percentages of chemical elements in the cold-rolled annealed dual-phase steels of Examples 1-6 and the conventional steels of Comparative Examples 1-9.

TABLE-US-00001 TABLE 1 (wt %, the balance is Fe and other inevitable impurity elements other than P, S, N) No. C Si Mn P S Cr Mo Nb Ti Al N Ca Example 1 0.095 0.24 2.08 0.012 0.004 0.52 0.25 0.028 0.024 0.035 38 ppm 0.004 Example 2 0.09 0.18 2.02 0.01 0.002 0.48 0.28 0.025 0.034 0.028 42 ppm 0.003 Example 3 0.088 0.35 1.99 0.01 0.003 0.55 0.32 0.033 0.029 0.040 27 ppm 0.003 Example 4 0.1 0.10 2.12 0.014 0.003 0.40 0.20 0.020 0.042 0.022 12 ppm 0.001 Example 5 0.083 0.60 1.95 0.013 0.002 0.60 0.40 0.050 0.020 0.045 50 ppm 0.002 Example 6 0.08 0.47 2.20 0.015 0.005 0.43 0.38 0.043 0.050 0.015  9 ppm 0.005 Comparative Example 1 0.098 0.33 2.2 0.011 0.005 0.58 0.36 0.027 0.025 0.026 42 ppm 0.002 Comparative Example 2 0.087 0.45 2.03 0.013 0.001 0.48 0.22 0.023 0.024 0.032 39 ppm 0.002 Comparative Example 3 0.086 0.37 2.11 0.009 0.003 0.51 0.26 0.024 0.026 0.04 33 ppm 0.005 Comparative Example 4 0.081 0.12 1.96 0.006 0.004 0.43 0.21 0.025 0.02 0.028 35 ppm 0.002 Comparative Example 5 0.091 0.36 2.08 0.007 0.006 0.47 0.28 0.022 0.025 0.028 40 ppm 0.004 Comparative Example 6 0.42 2.04 0.01 0.004 0.44 0.3 0.029 0.029 0.019 30 ppm 0.002 Comparative Example 7 0.089 0.28 1.97 0.014 0.005 0.21 0.024 0.022 0.025 28 ppm 0.002 Comparative Example 8 0.083 0.29 2.16 0.014 0.002 0.52 0.23 0.026 0.028 0.033 35 ppm 0.001 Comparative Example 9 0.25 2.09 0.008 0.007 0.49 0.25 0.025 0.026 0.024 38 ppm 0.004

[0043] The cold-rolled annealed dual-phase steels of Examples 1-6 and the conventional steels of Comparative Examples 1-9 are made into steel plates by a manufacturing method including the following steps:

[0044] (1) smelting and casting according to the mass percentages of chemical elements listed in Table 1;

[0045] (2) hot rolling: the slab was soaked at a temperature of 1200 to 1260° C. and then rolled; the finish rolling temperature was 840 to 930° C.; after rolling, it was cooled at a rate of 20 to 70° C./s, and then coiled; the coiling temperature was 500 to 620° C.;

[0046] (3) cold rolling: the cold rolling reduction ratio was 65 to 78%;

[0047] (4) annealing: the soaking temperature during annealing was 780 to 820° C., and the annealing time was 40 to 200 s; after annealing, rapidly cooling was performed at a rate of 45 to 100° C./s; the start temperature of rapidly cooling was 650 to 730° C., the aging temperature was 200 to 260° C., and the overaging time was 100 to 400 s;

[0048] (5) temper rolling at a reduction ratio of 0.3% or less.

[0049] Table 2 lists the specific process parameters of the manufacturing methods of the cold-rolled annealed dual-phase steels of Examples 1-6 and the conventional steels of Comparative Examples 1-9.

TABLE-US-00002 TABLE 2 Step (4) Step (2) Step (3) Soaking Start Step (5) Soaking Finish Coiling Cold temperature Rapid temperature Aging Temper temper- temper- Cooling temper- rolling during Annealing cooling of rapidly temper- rolling ature ature rate ature reduction annealing time rate cooling ature Overaging reduction No. (° C.) (° C.) (° C./s) (° C.) (%) (° C.) (s) (° C./s) (° C.) (° C.) time (s) (%) Example 1 1240 895 20 580 78 785 40 60 670 250 200 0.2 Example 2 1230 880 30 590 70 790 80 45 660 230 100 0.1 Example 3 1250 900 60 570 65 800 120 70 650 240 300 0.2 Example 4 1200 930 70 620 72 810 160 55 730 200 400 0.3 Example 5 1210 850 40 540 75 820 180 85 690 220 150 0.1 Example 6 1260 840 50 500 68 780 200 100 700 260 350 0.1 Comparative 1220 40 610 70 820 40 60 650 210 250 0.3 Example 1 Comparative 1210 860 50 580 75 800 50 80 700 200 350 0.1 Example 2 Comparative 920 40 540 82 795 70 75 680 260 200 0.1 Example 3 Comparative 910 30 550 66 60 690 240 150 0.1 Example 4 Comparative 1250 890 20 74 800 160 100 710 230 100 0.2 Example 5 Comparative 1200 50 600 66 805 120 95 720 220 250 0.3 Example 6 Comparative 1240 870 30 620 69 780 100 65 250 400 0.1 Example 7 Comparative 1210 40 585 68 810 80 45 670 210 350 0.2 Example 8 Comparative 1200 900 20 565 71 795 150 60 240 300 0.2 Example 9

[0050] Table 3 lists the typical microstructure, mechanical properties, and bending property of steel plates made of the cold-rolled annealed dual-phase steels of Examples 1-6 and the conventional steels of Comparative Examples 1-9.

TABLE-US-00003 TABLE 3 Microstructure Ratio of Mechanical property Ultimate Ratio of Ratio of martensite Martensite Yield Tensile Elongation Plate bending ferrite phase martensite phase to grain size strength strength at break thickness radius/plate No. (%) phase (%) ferrite phase (μm) (MPa) (MPa) (%) (mm) thickness Example 1 26 74 2.85 3.75 702 1055 13 0.53 0.6 Example 2 34 66 1.94 4.29 675 1036 15 0.66 0.5 Example 3 43 57 1.33 5.5 643 1028 14 0.72 0.57 Example 4 50 50 1.0 3.0 735 1072 12 0.70 0.55 Example 5 45 55 1.22 4.5 624 1011 15 0.56 0.62 Example 6 20 80 4.0 6.0 608 1002 16 0.68 0.59 Comparative 8 92 822 1126 7 0.58 1.72 Example 1 Comparative 17 83 5.11 696 1045 12 0.64 1.02 Example 2 Comparative 24 76 3.17 763 1087 0.67 1.24 Example 3 Comparative 65 4.74 522 21 0.62 0.54 Example 4 Comparative 22 78 3.55 726 1074 0.54 0.98 Example 5 Comparative 42 58 1.38 693 1042 0.62 1.16 Example 6 Comparative 14 86 4.65 688 1039 12 0.69 0.94 Example 7 Comparative 52 663 1032 14 0.59 1.07 Example 8 Comparative 36 64 1.78 677 1045 13 0.68 0.93 Example 9

[0051] As can be seen from table 3, each of the cold-rolled annealed dual-phase steels of Examples 1-6 has a tensile strength of 1000 MPa or more, an elongation at break of 12% or more, and a microstructure of ferrite and martensite, wherein the ratio of martensite phase is 50% or more, and the ratio of martensite phase to ferrite phase is more than 1 and less than 4, and the average grain size of martensite is 3 to 6 μm. The steel plate of each of the Examples has a thickness of 0.5 to 0.7 mm. It can be seen that the steel plate made of the cold-rolled annealed dual-phase steel of each of the Examples of the present invention has the advantages of high strength, thin thickness, and good bending property.

[0052] It should be noted that the above are merely illustrative of specific Examples of the invention. It is obvious that the present invention is not limited to above Examples, but has many similar variations. All variations that can be directly derived or conceived by those skilled in the art from this disclosure are intended to be within the scope of the present invention.