High-broaching-performance high-strength steel plate and preparation method thereof

Abstract

The invention discloses a high-strength steel plate with high reaming performance and a preparation method thereof. The high-strength steel plate comprises the following chemical components in percentage by mass: 0.03%-0.09% of C, 0.07%-0.60% of Si, 1.45%-1.90% of Mn, 0.12%-0.25% of Ti, 0.010%-0.050% of Nb, 0.27%-0.50% of Al, less than or equal to 0.007% of N, less than or equal to 0.020% of P, less than or equal to 0.008% of S, 0.02%-1.0% of Cr and / or 0.10%-0.50% of Mo, and the balance of Fe and inevitable impurities. The steel plate obtained through the method has high ductility, atmospheric corrosion resistance and high reaming performance, the tensile strength is 800-1080 MPa, the yield strength is larger than or equal to 680 MPa, the percentage elongation after fracture A80 is larger than or equal to 10.0%, the uniform elongation Ag is larger than or equal to 5%, the reaming rate is larger than or equal to 40.0%, the weather resistance index is larger than or equal to 1.0, the product structure is mainly composed of ferrite, bainite, carbide and the like, the production process is simple, and the cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular to a high-strength steel plate with high hole expansion performance and a preparation method thereof. Background Art

[0002] With the continuous development of the automobile industry, the requirements for automobile safety, environmental protection, comfort, etc. are constantly increasing. In order to meet the needs of high strength, toughness and lightweight of automobile parts, high-strength steel is increasingly used to replace the original ordinary structural steel in the design of parts. The successful development of high-strength steel plates with high ductility, atmospheric corrosion resistance and high hole expansion performance and their preparation methods have provided new options for automobile parts design.

[0003] Patent application CN202410306178.2 discloses a low-cost, high-expansion performance 500MPa grade hot-dip galvanized dual-phase steel plate, whose chemical composition by mass percentage is: C: 0.05%-0.08%, Si: 0.20-0.40%, Mn: 1.20%-1.60%, Cr: 0.2%-0.4%, P≤0.020%, S≤0.007%, Alt: 0.035%-0.065%, N≤0.0050%, and the remaining elements are Fe and unavoidable impurities; the microstructure by volume percentage is: ferrite 85-90%, martensite 7-12%, bainite 3-5%. The material strength of the steel plate is low, which is not conducive to the user's weight reduction design.

[0004] Patent application CN202310063301.8 discloses a 780MPa grade ultra-high hole expansion performance cold-rolled complex phase steel for automobiles, which is composed of the following chemical components by weight percentage: C: 0.08% to 0.13%; Si: 0.1% to 0.5%; Mn: 1.8% to 2.5%; Cr: 0.25% to 0.6%; Mo: 0.1% to 0.5%; Ti: 0.01% to 0.04%; Nb: 0.01% to 0.04%; B: 0 to 0.0004%; P≤0.02%; S≤0.01%, and the balance is Fe and unavoidable impurities. The alloy is relatively expensive, and is produced by cold rolling, so the production process is relatively complex and the cost is relatively high.

[0005] Patent application CN202010966385.2 discloses a hot-rolled medium manganese steel plate with high hole expansion rate, high strength and high elongation. The components and mass percentages of the components in the hot-rolled medium manganese steel plate with high hole expansion rate, high strength and high elongation are as follows: C: 0.18-0.22%, Mn: 6.0-9.0%, 0<A1≤4%, and the balance is Fe and unavoidable impurities; the hot-rolled medium manganese steel plate with high hole expansion rate, high strength and high elongation has a tensile strength of 900-1307MPa, a total elongation of 32-40%, a hole expansion rate of 35-73%, a yield strength of 553-597MPa, and an austenite phase stability k value of 1.2-7.6. The steel plate has a high carbon content and manganese content, and is a composition design of medium manganese steel.

[0006] Patent application CN202210714704.X discloses an ultra-high hole expansion steel and a manufacturing method thereof, wherein the weight percentage of the components is: C 0.03-0.09%, Si≤0.2%, Mn 0.5-2.0%, P≤0.02%, S≤0.003%, Al 0.2-1.2%, N≤0.004%, Ti 0.05-0.20%, Mo 0.05~0.5%, Mg≤0.005%, O≤0.003%, the balance includes Fe and other inevitable impurities, and must simultaneously meet the following requirements: 0.25≤2×C+Mn / 3+Mo+150×B≤1.5; the yield strength of the ultra-high hole expansion steel is ≥700MPa, the tensile strength is ≥780MPa, the elongation (transverse A50) is ≥17%, and the hole expansion rate is ≥80%, showing excellent strength, plasticity and hole expansion performance matching, and can be used in passenger car chassis parts such as control arms and subframes that require high-strength thinning. The steel does not have atmospheric corrosion resistance, which affects the service life of the parts. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a high-strength steel plate with high ductility and atmospheric corrosion resistance and high hole expansion performance; the present invention also provides a preparation method of the high-strength steel plate with high hole expansion performance.

[0008] To solve the above technical problems, the technical solution adopted by the present invention includes the following chemical components in mass percentage: C 0.03%-0.09%, Si 0.07%-0.60%, Mn 1.45%-1.90%, Ti 0.12%-0.25%, Nb 0.010%-0.050%, Al 0.27%-0.50%, N≤0.007%, P≤0.020%, S≤0.008%, Cr 0.02%-1.0% and / or Mo0.10%-0.50%, and the balance is Fe and unavoidable impurities.

[0009] Furthermore, it also includes the following chemical components in percentage by mass: Ni 0.015% to 0.20% and / or Cu 0.015% to 0.50%.

[0010] Furthermore, the steel plate has a tensile strength of 800-1080 MPa, a yield strength of ≥680 MPa, an elongation after fracture A80 ≥10.0%, a uniform elongation Ag ≥5%, a hole expansion rate ≥40.0%, and a weather resistance index ≥1.0.

[0011] In order to solve the above technical problems, the technical solution adopted by the method of the present invention includes slab heating, controlled rolling and coiling processes; The controlled rolling process: adopts rough rolling + finishing rolling process; the rolling temperature of the rough rolling is 1000-1140°C, and the final rolling temperature of the finishing rolling is 800-930°C; The coiling process adopts a two-stage cooling process; the cooling rate of the first stage cooling is ≥40°C / S, and air cooling is performed for 2 to 4 seconds when cooling to 660±20°C; the cooling rate of the second stage cooling is ≥40°C / S, and the coiling temperature is 420 to 550°C.

[0012] Furthermore, the slab heating process has a heating temperature of 1150 to 1300° C. and a heating time of 150 to 240 minutes.

[0013] The beneficial effects of the above technical scheme are as follows: the composition design of the present invention adopts a low-carbon composition design. Under the rolling process of controlled rolling and controlled cooling, the higher titanium forms a carbon-titanium compound to fix the carbon element, reduce the solid solution carbon atoms, and inhibit the generation of pearlite; an appropriate amount of manganese can expand the austenite region, expand the process window of controlled rolling of microalloyed steel, increase solid solution strengthening, and improve the strength of the material; an appropriate amount of niobium can prevent the growth of austenite grains during the controlled rolling process, form small and flat austenite grains, and achieve grain refinement during the controlled cooling process; molybdenum inhibits the generation of pearlite, increases the hardenability of steel, and eliminates temper brittleness. It can promote bainite transformation through controlled cooling and increase hole expansion performance; aluminum promotes the generation of proeutectoid ferrite, and under the process conditions of controlled cooling, promotes bainite transformation and increases the hole expansion performance of the material; chromium has the effect of reducing the austenite region, increasing the hardenability of the material, inhibiting the generation of pearlite, and increasing temper brittleness; at the same time, nickel, copper, and chromium have atmospheric corrosion resistance and improve the strength of the material.

[0014] The steel plate obtained by the present invention and method has high ductility, atmospheric corrosion resistance and high hole expansion performance, tensile strength of 800-1080MPa, yield strength (Rp0.2) ≥680MPa, elongation after fracture A80 ≥10.0%, uniform elongation Ag ≥5%, hole expansion ratio (HER) ≥40.0%, weathering index (I) ≥1.0, the product structure is mainly composed of ferrite, bainite and carbide, and the production process is simple and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0016] Figure 1 is the metallographic structure diagram of the steel plate obtained in Example 1 of the present invention; Figure 2 is the metallographic structure diagram of the steel plate obtained in Example 2 of the present invention; Figure 3 is the metallographic structure diagram of the steel plate obtained in Example 3 of the present invention; Figure 4 is the metallographic structure diagram of the steel plate obtained in Example 4 of the present invention; Figure 5 3 is the metallographic structure diagram of the steel plate obtained in Example 5 of the present invention. DETAILED DESCRIPTION

[0017] The chemical composition of the high-strength steel plate with high hole expansion performance is as follows: C 0.03%-0.09%, Si 0.07%-0.60%, Mn 1.45%-1.90%, Ti 0.12%-0.25%, Nb 0.010%-0.050%, Al 0.27%-0.50%, N≤0.007%, P≤0.020%, S≤0.008%, Cr 0.02%-1.0% and / or Mo 0.10%-0.50%, the balance is Fe and unavoidable impurities; preferably, Ni 0.015%-0.20% and / or Cu 0.015%-0.50% may also be contained. The thickness of the steel plate is 1.5-6.0 mm.

[0018] The preparation method of the high-strength steel plate with high hole expansion performance includes smelting, continuous casting, slab heating, controlled rolling and coiling processes; the processes of each process are as follows: 1) Smelting process: According to the requirements of the chemical composition of the steel plate, the molten iron is subjected to pre-treatment desulfurization, converter smelting, LF refining and composition fine-tuning, and RH furnace degassing process in sequence to obtain molten steel with qualified composition.

[0019] 2) Continuous casting process: A continuous casting machine is used for continuous casting of steel. During the continuous casting process, the superheat of the molten steel is controlled at 15-35°C, and the casting speed of the continuous casting machine is controlled at 1.0-1.5m / min to obtain a slab with qualified composition.

[0020] 3) Slab heating process: heating temperature is 1150~1300℃, and heating time is 150~240min.

[0021] 4) Controlling the rolling process: the heated slab is first descaled, and after the slab is taken out of the furnace, the oxidized iron scale on the surface of the slab is removed by descaling water with a pressure of ≥18MPa, and the slab is rolled by a rough rolling + finishing rolling process; the rolling temperature of the rough rolling is 1000-1140°C, and the thickness of the intermediate slab is ≥30mm; the finishing rolling adopts a finishing rolling 7 stand to roll the intermediate slab, and the final rolling temperature is 800-930°C.

[0022] 5) Coiling process: The steel plate is coiled after cooling. When cooling online, a two-stage cooling process is adopted; the cooling rate of the first stage cooling is ≥40℃ / S, and air cooling is performed for 2 to 4 seconds when cooling to 660±20℃; after air cooling, the second stage cooling is entered, and the cooling rate of the second stage cooling is ≥40℃ / S, and the coiling temperature is 420 to 550℃; the high hole expansion performance and high strength steel plate can be obtained.

[0023] Example 1: The preparation method of the high-strength steel plate with high hole expansion performance is specifically described as follows.

[0024] 1) Smelting process: According to the requirements of the chemical composition of the steel plate, the molten iron is pre-treated for desulfurization, converter smelting, LF refining fine-tuning composition, and RH furnace degassing process; 2) Continuous casting process: A slab continuous casting machine is used for continuous casting of steel. During the continuous casting process, the superheat of the molten steel is controlled at 15-20°C, and the casting speed of the continuous casting machine is controlled at 1.2-1.3m / min to obtain a slab with qualified composition.

[0025] 3) Slab heating process: The slab is transported to a heating furnace for heating at a temperature of 1300°C for 240 minutes.

[0026] 4) Control the rolling process: After the steel billet is taken out of the furnace, the scale on the surface of the slab is removed by descaling water with a pressure of ≥18MPa; the rolling temperature of the rough rolling is 1140℃, and the thickness of the intermediate billet is 30mm; the finishing rolling adopts the finishing rolling 7 stand to roll the intermediate billet, and the final rolling temperature is 800℃.

[0027] 5) Coiling process: When cooling online, a two-stage cooling process is adopted. The first cooling process: after leaving the finishing rolling F7 stand, the cooling rate is 41℃ / S, and air cooling is performed for 2 seconds when cooling to 640℃; the second cooling process: after the steel plate leaves the air cooling section, the cooling rate is 42℃ / S, and the coiling temperature is 510℃.

[0028] Figure 1This is a metallographic structure diagram of a steel plate with high ductility and high hole expansion performance according to Example 1 of the present invention. The figures of other embodiments are similar and thus omitted.

[0029] Example 2: The preparation method of the high-strength steel plate with high hole expansion performance is specifically described as follows.

[0030] 1) Smelting process: According to the requirements of the chemical composition of the steel plate, the molten iron is pre-treated for desulfurization, converter smelting, LF refining fine-tuning composition, and RH furnace degassing process; 2) Continuous casting process: A slab continuous casting machine is used for continuous casting of steel. During the continuous casting process, the superheat of the molten steel is controlled at 20-25°C, and the casting speed of the continuous casting machine is controlled at 1.4-1.5m / min to obtain a slab with qualified composition.

[0031] 3) Slab heating process: The slab is transported to a heating furnace for heating at a temperature of 1150°C for 150 minutes.

[0032] 4) Control the rolling process: After the steel billet is taken out of the furnace, the scale on the surface of the slab is removed by descaling water with a pressure of ≥18MPa; the rolling temperature of the rough rolling is 1000℃, and the thickness of the intermediate billet is 34mm; the finishing rolling adopts the finishing rolling 7 stand to roll the intermediate billet, and the final rolling temperature is 850℃.

[0033] 5) Coiling process: When cooling online, a two-stage cooling process is adopted. The first cooling process: out of the finishing rolling F7 stand, the cooling rate is 41℃ / S, and air cooling is performed for 3 seconds when cooling to 663℃; the second cooling process: after the steel plate exits the air cooling section, the cooling rate is ≥40℃ / S, and the coiling temperature is 420℃.

[0034] Example 3: The preparation method of the high-strength steel plate with high hole expansion performance is specifically described as follows.

[0035] 1) Smelting process: According to the requirements of the chemical composition of the steel plate, the molten iron is pre-treated for desulfurization, converter smelting, LF refining fine-tuning composition, and RH furnace degassing process; 2) Continuous casting process: A slab continuous casting machine is used for continuous casting of steel. During the continuous casting process, the superheat of the molten steel is controlled at 25-30°C, and the casting speed of the continuous casting machine is controlled at 1.3-1.4m / min to obtain a slab with qualified composition.

[0036] 3) Slab heating process: The slab is transported to a heating furnace for heating at a temperature of 1290°C for 210 minutes.

[0037] 4) Control the rolling process: After the steel billet is taken out of the furnace, the scale on the surface of the slab is removed by descaling water with a pressure of ≥18MPa; the rolling temperature of the rough rolling is 1100℃, and the thickness of the intermediate billet is 36mm; the finishing rolling adopts the finishing rolling 7 stand to roll the intermediate billet, and the final rolling temperature is 930℃.

[0038] 5) Coiling process: When cooling online, a two-stage cooling process is adopted. The first cooling process: after the steel plate leaves the finishing rolling F7 stand, the cooling rate is 43℃ / S, and air cooling is performed for 4 seconds when the steel plate cools to 657℃; the second cooling process: after the steel plate leaves the air cooling section, the cooling rate is 40℃ / S, and the coiling temperature is 550℃.

[0039] Example 4: The preparation method of the high-strength steel plate with high hole expansion performance is specifically described as follows.

[0040] 1) Smelting process: According to the requirements of the chemical composition of the steel plate, the molten iron is pre-treated for desulfurization, converter smelting, LF refining fine-tuning composition, and RH furnace degassing process; 2) Continuous casting process: A slab continuous casting machine is used for continuous casting of steel. During the continuous casting process, the superheat of the molten steel is controlled at 30-35°C, and the casting speed of the continuous casting machine is controlled at 1.0-1.2 m / min to obtain a slab with qualified composition.

[0041] 3) Slab heating process: The slab is transported to a heating furnace for heating at a temperature of 1260°C for 240 minutes.

[0042] 4) Control the rolling process: After the billet is out of the furnace, the scale on the surface of the slab is removed by descaling water with a pressure of ≥18MPa; the rolling temperature of the rough rolling is 1090℃, and the thickness of the intermediate billet is 38mm; the finishing rolling adopts the finishing rolling 7 stand to roll the intermediate billet, and the final rolling temperature is 860℃.

[0043] 5) Coiling process: When cooling online, a two-stage cooling process is adopted. The first cooling process: after leaving the finishing rolling F7 stand, the cooling rate is 40℃ / S, and air cooling is performed for 3 seconds when cooling to 680℃; the second cooling process: after the steel plate leaves the air cooling section, the cooling rate is 43℃ / S, and the coiling temperature is 490℃.

[0044] Example 5: The preparation method of the high-strength steel plate with high hole expansion performance is specifically described as follows.

[0045] 1) Smelting process: According to the requirements of the chemical composition of the steel plate, the molten iron is pre-treated for desulfurization, converter smelting, LF refining fine-tuning composition, and RH furnace degassing process; 2) Continuous casting process: A slab continuous casting machine is used for continuous casting of steel. During the continuous casting process, the superheat of the molten steel is controlled at 20-33°C, and the casting speed of the continuous casting machine is controlled at 1.2-1.2 m / min to obtain a slab with qualified composition.

[0046] 3) Slab heating process: The slab is transported to a heating furnace for heating at a temperature of 1280°C for 220 minutes.

[0047] 4) Control the rolling process: After the steel billet is taken out of the furnace, the scale on the surface of the slab is removed by descaling water with a pressure of ≥18MPa; the rolling temperature of the rough rolling is 1100℃, and the thickness of the intermediate billet is 34.5mm; the finishing rolling adopts the finishing rolling 7 stand to roll the intermediate billet, and the final rolling temperature is 910℃.

[0048] 5) Coiling process: When cooling online, a two-stage cooling process is adopted. The first cooling process: after the steel plate leaves the finishing rolling F7 stand, the cooling rate is 41℃ / S, and air cooling is performed for 3.5 seconds when the steel plate cools to 649℃; the second cooling process: after the steel plate leaves the air cooling section, the cooling rate is 43℃ / S, and the coiling temperature is 530℃.

[0049] Figure 1-5 These are the metallographic organization diagrams of Examples 1-5, respectively. It can be seen from the diagrams that the internal organization of the obtained steel plates is mainly composed of ferrite, bainite and carbide.

[0050] The chemical composition of the steel plates obtained in Examples 1-5 is shown in Table 1. The mechanical properties, cold bending properties and corrosion resistance of the steel plates obtained were tested and calculated, and the results are shown in Table 2.

[0051] Table 1: Steel plate thickness and chemical composition (wt%) of Examples 1-4

[0052] In Table 1, the balance is Fe and unavoidable impurities.

[0053] Table 2: Mechanical properties of high-strength steel plates prepared in Examples 1-4

[0054] In Table 2, the weathering index formula is I = 26.01 (%Cu) + 3.88 (%Ni) + 1.20 (%Cr) + 1.49 (%Si) + 17.28 (%P) - 7.29 (%Cu × %Ni) - 9.10 (%Ni × %P) - 33.39 (%Cu) 2 , where %Cu, %Ni, %Cr, %Si, and %P are the mass percentages of Cu, Ni, Cr, and Si in the steel plate, respectively.

Claims

1. A high-strength steel plate with high hole expansion performance, characterized in that: Including the following chemical compositions in mass percentage: C 0.03%~0.09%, Si 0.07%~0.60%, Mn 1.45%~1.90%, Ti 0.12%~0.25%, Nb 0.010%~0.050%, Al 0.27%~0.50%, N≤0.007%, P≤0.020%, S≤0.008%, Cr 0.02%~1.0% and / or Mo0.10%~0.50%, and the balance is Fe and unavoidable impurities.

2. The high-strength steel plate with high hole expansion performance according to claim 1, characterized in that: It also includes the following chemical compositions in percentage by mass: Ni 0.015% to 0.20% and / or Cu 0.015% to 0.50%.

3. A high-strength steel plate with high hole expansion performance according to claim 1 or 2, characterized in that: The steel plate has a tensile strength of 800-1080 MPa, a yield strength of ≥680 MPa, an elongation after fracture A80 ≥10.0%, a uniform elongation Ag ≥5%, a hole expansion rate ≥40.0%, and a weather resistance index ≥1.

0.

4. The method for preparing the high-strength steel plate with high hole expansion performance according to claim 1, 2 or 3, characterized in that: Including slab heating, controlled rolling and coiling processes; The controlled rolling process: adopts rough rolling + finishing rolling process; the rolling temperature of the rough rolling is 1000-1140°C, and the final rolling temperature of the finishing rolling is 800-930°C; The coiling process adopts a two-stage cooling process; the cooling rate of the first stage cooling is ≥40°C / S, and air cooling is performed for 2 to 4 seconds when cooling to 660±20°C; the cooling rate of the second stage cooling is ≥40°C / S, and the coiling temperature is 420 to 550°C.

5. The method for preparing a high-strength steel plate with high hole expansion performance according to claim 4, characterized in that: The slab heating process: the heating temperature is 1150-1300° C., and the heating time is 150-240 minutes.

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