HIGH-STRENGTH HIGH-TENACITY STEEL PLATE WITH TENSILE STRENGTH OF 800 MPA AND PRODUCTION METHOD THEREFOR

Abstract

Disclosed are a high-strength and high-toughness steel plate with an 800 MPa grade tensile strength and a method for manufacturing the same, the chemical composition of the steel plate in weight percentage being: C: 0.15-0.25%, Si: 1.0-2.0%, Mn: 1.2-2.0%, P≦0.015%, S≦0.005%, Al: 0.5-1.0%, N: ≦0.006%, Nb: 0.02-0.06%, O≦0.003%, and the balance being Fe and other inevitable impurities, and 1.5%≦Si+Al≦2.5%. By adopting an isothermal heat treatment a high-strength and high-toughness steel plate with an 800 MPa grade tensile strength, which has a microstructure mainly including bainite ferrite and residual austenite, is obtained impact energy.

Claims

1. A high-strength and high-toughness steel plate with an 800 MPa grade tensile strength, the chemical composition of the steel plate in weight percentage being: C: 0.15-0.25%, Si: 1.0-2.0%, Mn: 1.2-2.0%, P≦0.015%, S≦0.005%, Al: 0.5-1.0%, N≦0.006%, Nb: 0.02-0.06%, O≦0.003%, and the balance being Fe and other inevitable impurities, and 1.5%≦Si+Al≦2.5%.

2. The high-strength and high-toughness steel plate with an 800 MPa grade tensile strength according to claim 1, characterized in that in said chemical composition, the content of Si, in weight percentage, is in a range of 1.3-1.7%.

3. The high-strength and high-toughness steel plate with an 800 MPa grade tensile strength according to claim 1, characterized in that in said chemical composition, the content of Mn, in weight percentage, is in a range of 1.4-1.8%.

4. The high-strength and high-toughness steel plate with an 800 MPa grade tensile strength according to claim 1, characterized in that in said chemical composition, the content of N, in weight percentage, is ≦0.004%.

5. The high-strength and high-toughness steel plate with an 800 MPa grade tensile strength according to claim 1, characterized in that in said chemical composition, the content of Nb, in weight percentage, is in a range of 0.03-0.05%.

6. The high-strength and high-toughness steel plate with an 800 MPa grade tensile strength according to claim 1, characterized by having a microstructure mainly including bainite ferrite and residual austenite.

7. The high-strength and high-toughness steel plate with an 800 MPa grade tensile strength according to claim 1, characterized by having a yield strength of ≧390 MPa, a tensile strength of ≧800 MPa, an elongation of >20%, and an impact energy at −20° C. of >100 J.

8. A method for manufacturing the high-strength and high-toughness steel plate with an 800 MPa grade tensile strength of claim 1 characterized by comprising the following steps: 1) smelting, secondary refining, and casting smelting by using a converter furnace or an electric furnace, secondary refining by using a vacuum furnace, and casting to form a cast slab or cast ingot, with the following chemical components and amounts thereof in weight percentage: C: 0.15-0.25%, Si: 1.0-2.0%, Mn: 1.2-2.0%, P: ≦0.015%, S: ≦0.005%, Al: 0.5-1.0%, N: ≦0.006%, Nb: 0.02-0.06%, O: ≦0.03%, and the balance of Fe and other inevitable impurities, and 1.5%≦Si+Al≦2.5%; 2) heating, hot rolling, coiling, and re-uncoiling the cast slab or cast ingot obtained in step 1) and cutting to plates to obtain a substrate; and 3) heat treatment heating the substrate obtained in step 2) to Ac.sub.3+(30-50)° C., Ac.sub.3=955−350C−25Mn+51Si+106Nb+68Al, with the various element symbols all referring to the contents in weight percentage in the formula; holding for 10-30 min after the temperature of the core of the substrate arrives at a temperature of Ac.sub.3+(30-50)° C., then rapidly cooling to 350-500° C. at a cooling rate >50° C./s, and then subjecting to isothermal transformation for 200-500 s, quenching at a cooling rate of greater than 30° C./s to room temperature to obtain a high-strength and high-toughness steel plate with an 800 MPa grade tensile strength.

9. The method for manufacturing the high-strength and high-toughness steel plate with an 800 MPa grade tensile strength according to claim 8, characterized in that the microstructure of the steel plate obtained by the manufacturing method mainly includes bainite ferrite and residual austenite.

10. The method for manufacturing the high-strength and high-toughness steel plate with an 800 MPa grade tensile strength according to claim 8, characterized in that the steel plate obtained by the manufacturing method has a yield strength of ≧390 MPa, a tensile strength of ≧800 MPa, an elongation of >20%, and an impact energy at −20° C. of >100 J.

Description

DESCRIPTION OF THE DRAWINGS

[0045] FIG. 1 is a flow diagram of a heat treatment process of examples of the present invention.

PARTICULAR EMBODIMENTS

[0046] The present invention is further illustrated below in conjunction with the examples and the drawing.

[0047] The method for manufacturing the high-strength and high-toughness steel plate with an 800 MPa grade tensile strength of the present invention specifically comprises the following steps:

[0048] 1) smelting, secondary refining, and casting:

[0049] according to the composition of each steel in table 1, smelting is performed using a rotary furnace or electric furnace, secondary refining is performed using a vacuum furnace, and casting is performed to form a cast slab or cast ingot;

[0050] 2) the cast slab or cast ingot obtained in step 1) is subjected to heating, hot rolling, coiling, re-uncoiling and plate cutting to obtain a substrate; and

[0051] 3) heat treatment

[0052] the substrate obtained in step 3) is heated to Ac.sub.3+(30-50°) C., for a full austenite homogenization; after the core part of the steel plate is heated to the temperature, the steel plate is continued to be maintained at the temperature for 10-30 min, is further rapidly cooled to a certain temperature between 350-500° C., i.e., a first cooling stopping temperature, at a cooling rate of >50° C./s, is subjected to isothermal transformation for 200-500 s, and is quenched at a cooling rate of greater than 30° C./s to room temperature to obtain a high-strength and high-toughness steel plate with an 800 MPa grade tensile strength. Reference is made to FIG. 1.

[0053] The specific composition and process parameters of the examples are as shown in tables 1 and 2. The corresponding properties of the steel plate in each example are as shown in table 3.

[0054] By a rational alloy composition and process design in the present invention, the steel plate having a high strength, a high plasticity and a high toughness produced using the novel heat treatment process, wherein the steel plate has a tensile strength which can reach not less than 800 MPa, and further has a good elongation (>20%) and a low-temperature impact toughness (an impact energy −20° C. of >100 J), and shows an excellent match of strength, plasticity and toughness.

TABLE-US-00001 TABLE 1 Unit: weight percentage Exam- Ms Ac.sub.3 ple C Si Mn P S Al N Nb O ° C. ° C. 1 0.19 1.8 1.25 0.007 0.003 0.53 0.0055 0.050 0.0028 401 990 2 0.22 1.7 1.55 0.007 0.004 0.65 0.0052 0.040 0.0027 380 974 3 0.25 1.2 1.97 0.008 0.005 0.94 0.0046 0.020 0.0022 360 945 4 0.23 1.4 1.90 0.010 0.004 0.87 0.0038 0.035 0.0029 369 961 5 0.15 1.9 1.45 0.009 0.005 0.55 0.0039 0.060 0.0026 409 1012 6 0.20 1.5 1.63 0.008 0.004 0.82 0.0041 0.045 0.0027 388 981 7 0.17 1.0 1.38 0.009 0.003 0.75 0.0043 0.030 0.0023 414 966

TABLE-US-00002 TABLE 2 Heat treatment process Cooling Thickness of Heating Homogenization stopping Isothermal steel plate, temperature, time, temperature, transformation Example mm ° C. min ° C. time, s 1 10 1020 25 400 250 2 3 1005 13 475 200 3 6 945 18 350 300 4 12 995 30 450 500 5 5 1050 15 375 450 6 9 1115 10 500 400 7 7 1000 20 425 375

TABLE-US-00003 TABLE 3 Mechanical property Residual Tensile yield Tensile Elonga- Impact austenite Exam- strength, strength, Yield tion, energy, Content, ple MPa MPa ratio % J % 1 420 880 0.48 23 150 18.0 2 400 870 0.46 29 155 14.5 3 420 900 0.47 22 120 15.0 4 415 875 0.47 28 148 14.0 5 412 895 0.46 21 144 17.5 6 390 850 0.46 28 145 13.0 7 425 875 0.49 32 158 17.5