2000MPa-grade thick-specification hot stamping plate with excellent corrosion resistance and manufacturing method of 2000MPa-grade thick-specification hot stamping plate

Abstract

The invention discloses a 2000MPa-grade thick-specification hot stamping plate with excellent corrosion resistance and a manufacturing method of the 2000MPa-grade thick-specification hot stamping plate. The hot stamping plate comprises the following chemical components in percentage by mass: 0.34%-0.38% of C, 0.10%-0.30% of Si, 1.10%-1.70% of Mn, less than or equal to 0.015% of P, less than or equal to 0.004% of S, 0.02%-0.06% of Als, 0.02%-0.06% of Nb, 0.5%-2.5% of Cr, 0-0.3% of Mo, 0-0.40% of Cu, 0-0.40% of Ni, 0.020%-0.050% of rare earth elements La + Ce, less than or equal to 0.005% of N and the balance of Fe and inevitable impurities. The thick-specification hot stamping plate with good comprehensive performance is obtained by adopting a hot rolling and hot forming process which is reasonably matched with component design, the requirements of the commercial vehicle for thick specification, good corrosion resistance and remarkable lightweight effect are met, and the application prospect is very good.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of hot-formed steel, and particularly relates to a 2000MPa-grade thick hot stamping plate with excellent corrosion resistance and a manufacturing method thereof. Background Art

[0002] With the continuous development of automotive lightweighting, high-strength steel materials for automobiles have been continuously developed and applied. Among them, hot-formed steel and hot-forming technology are one of the technologies that have developed the fastest in the past 20 years. It mainly heats the hot-formed steel plate to the austenite region and keeps it warm, and then quickly transfers the steel plate to the mold for hot forming. At the same time, pressure maintaining and quenching can obtain ultra-high-strength components of 1100MPa level and above. Using hot-formed steel and hot-forming technology can produce complex parts with excellent dimensional accuracy, which not only effectively simplifies the body structure and parts design, but also significantly reduces the vehicle weight. Therefore, hot-formed steel is widely used in the field of automotive parts manufacturing and has achieved good lightweighting effects.

[0003] In recent years, the application of thick uncoated hot-formed products in the field of automotive manufacturing has gradually increased. For example, in the field of commercial vehicle manufacturing, the lightweighting effect obtained is more significant than that of passenger vehicles. At present, thick uncoated hot-formed products are mainly applied to components such as the compartments, beams, and wheels of commercial vehicles. The strength of the steel plate after hot forming is mainly 1500MPa. However, with the expansion of the application field, for related application components such as mining trucks and railway transportation vehicles, due to their harsh service conditions, it is generally required that the steel has good corrosion resistance while having high strength and toughness. However, the current hot-formed steel products in the industry still cannot meet the use requirements of such components in terms of corrosion resistance.

[0004] Chinese invention patent CN106811689B proposes a preparation method of hot-formed steel with a tensile strength ≥2000MPa. In the chemical composition of the steel plate, C: 0.3 - 0.5%, Si: 1.2 - 1.7%, Mn: 1.4 - 2.0%, Al: 0.01 - 0.07%, S: ≤0.005%, P: ≤0.008%, Nb: 0.01 - 0.08%, Ti: 0.05 - 0.10%, B: 0.001 - 0.01%, Cr ≤ 1.5%. The hot-formed steel is obtained by smelting, hot rolling, cold rolling, and batch annealing. The tensile strength of the steel plate reaches more than 2000MPa, and the elongation A 50 : 8 - 9%. The steel plate proposed by this patent has good strength-ductility matching, but does not involve corrosion resistance, and the thickness specification of the steel plate is less than 2.5mm.

[0005] In summary, developing 2000MPa-grade thick hot-formed steel with excellent corrosion resistance has good application prospects. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a 2000 MPa grade thick hot stamping plate with excellent corrosion resistance and its manufacturing method, aiming to improve the comprehensive performance of the steel plate after hot forming, and meet the requirements of thick specifications, good corrosion resistance and significant lightweight effect for commercial vehicles.

[0007] The object of the present invention is achieved in the following ways: In the first aspect, the present invention provides a thick hot-rolled steel plate with excellent corrosion resistance. Its chemical composition by mass percentage is: C: 0.34% - 0.38%, Si: 0.10% - 0.30%, Mn: 1.10% - 1.70%, P ≤ 0.015%, S ≤ 0.004%, Als: 0.02% - 0.06%, Nb: 0.02% - 0.06%, Cr: 0.5% - 2.5%, Mo: 0 - 0.3%, Cu: 0 - 0.40%, Ni: 0 - 0.40%, rare earth elements La + Ce: 0.020% - 0.050%, N ≤ 0.005%, and the balance is Fe and unavoidable impurities, where 0.60 ≥ Ni + Cu ≥ 0.30 and 2.5 ≥ Cr + Mo ≥ 0.8.

[0008] Based on the above technical solution, further, the thickness of the hot-rolled steel plate is 4 - 10 mm, the tensile strength is 620 - 780 MPa, the yield strength is 480 - 620 MPa, the elongation is 20 - 30%, the grain size is ≥ 11 grades, and the banded structure is ≤ 1.5 grades.

[0009] The main functions of the steel plate composition of the present invention are as follows: C: Carbon is the guarantee of the strength of the steel plate. If the carbon content is too low, the strength of the steel plate after hot stamping cannot reach the expected target. If the carbon content is too high, the strength of the steel plate after hot rolling coiling is high, which is not conducive to pre-deformation. At the same time, the increase of carbon element is beneficial to increasing the hardenability of the steel. The optimal range of C in the present invention is 0.34% - 0.38%.

[0010] Si: Silicon is a solid solution strengthening element, which can improve the strength of the steel plate through solid solution strengthening. However, if the Si content is too high, a large amount of scale and color difference defects will appear on the surface of the hot-rolled steel plate, ultimately deteriorating the surface quality of the steel plate after hot forming; the optimal range of Si in the present invention is 0.10 - 0.30%.

[0011] Mn: Manganese has the effect of improving the strength of the steel plate through solid solution strengthening and can also significantly improve the hardenability of the steel; however, if the Mn content is too high, it will deteriorate the tissue uniformity of the steel plate during smelting and hot rolling, and it is easy to have serious banded structure defects in the tissue; the selected Mn content in the present invention is 1.1% - 1.7%.

[0012] P, S: Phosphorus and sulfur are harmful elements. Phosphorus tends to cause segregation defects in the continuous casting billet, and sulfur will form MnS inclusions, deteriorating the microstructure, mechanical properties, and impact properties of the steel plate. In this patent, P ≤ 0.015% and S ≤ 0.004%.

[0013] Als: Aluminum plays a role in deoxidation and nitrogen fixation during the smelting process. However, excessive aluminum will lead to a large number of aluminum-based inclusions. In the present invention, the content range of Al is 0.020% - 0.060%.

[0014] Cr: Adding chromium can effectively improve the hardenability of the steel, compensate for the reduction in hardenability caused by the absence of B in the composition, and enable a large amount of martensite to be obtained in the microstructure of the steel plate under the condition of rapid cooling after hot forming. In addition, chromium can form a relatively dense protective layer on the surface of the steel in a corrosive environment, playing a role in protecting the matrix and effectively improving the corrosion resistance of the steel. However, when the chromium content in the steel is too high, the toughness of the steel plate will deteriorate. Therefore, in the present invention, the content range of Cr is 0.5% - 2.5%.

[0015] Mo: Molybdenum is a medium-strength carbide-forming element, which can improve the strength and toughness of the steel plate. Mo can significantly improve the stability of retained austenite after coiling, so that a certain amount of retained austenite exists in the final microstructure, thereby enabling the steel plate to meet the expected mechanical property indicators. In this patent, the content of Mo is 0 - 0.30%.

[0016] Nb: Niobium mainly plays a role in fine grain strengthening, precipitation strengthening, etc. in the steel. At high temperatures, niobium exists in a solid solution state in austenite, which can inhibit the growth of austenite grains. At the same time, the precipitation of niobium carbonitrides can also delay recrystallization and prevent the growth of austenite grains, having obvious fine grain strengthening and precipitation strengthening effects. It can effectively reduce the banding structure grade of the hot-rolled base plate, improve the grain size, and finally refine the phases of the steel plate after hot forming, improving the impact performance. In the present invention, the optimal content range of niobium is 0.02% - 0.06%.

[0017] Ni: Nickel can improve the corrosion resistance of the steel, and also improve heat resistance, cold brittleness, and hardenability. However, excessive Ni will lead to an increase in manufacturing costs. In the present invention, the optimal content range of Ni is 0 - 0.40%.

[0018] Cu: Copper plays a role in solid solution strengthening and precipitation strengthening in the hot-formed steel of this patent. At the same time, it can also significantly improve the corrosion resistance of the steel plate. However, when the Cu content is too high, copper embrittlement is likely to occur on the surface of the steel plate. In the present invention, the optimal content range of Ni is 0 - 0.40%.

[0019] RE: Rare earth has a strong affinity with oxygen, sulfur, and nitrogen in molten steel. During smelting, it can form stable compounds and gas inclusions, which are discharged from the steel, improving the steel quality. Rare earth can control the morphology of sulfide inclusions in steel, playing a modification role and improving the plasticity, toughness, and fatigue performance of the steel plate. At the same time, adding rare earth can significantly improve the corrosion resistance of the steel plate. In this patent, the content of rare earth (La + Ce) is 0.02% - 0.05%.

[0020] N: The lower the content of N, the better, but too low will lead to production difficulties and increased costs. Therefore, in this patent, the content of N ≤ 0.005%.

[0021] Second, the present invention provides a method for manufacturing the above-mentioned thick - gauge hot - rolled steel plate with excellent corrosion resistance, including the following processes: smelting → continuous casting → hot rolling → cooling: Hot - rolling process: Heat the slab to 1200 - 1240 °C, hold for 1 - 3 hours, and the finish - rolling temperature is 840 - 880 °C; Cooling process: After finish - rolling, adopt the fast - cooling mode, with a cooling rate ≥ 50 °C / s. Cool the steel plate to 650 - 680 °C and then coil it, and air - cool it to room temperature to obtain the hot - rolled steel plate. Based on the above - mentioned technical solution, further, the cooling rate in the cooling process is controlled at 50 - 70 °C / s.

[0022] Based on the above - mentioned technical solution, further, the smelting process adopts the RH + LF double - stage process, strictly controlling the contents of H and O, H ≤ 0.00018%, O ≤ 0.001%; in the LF refining process, calcium treatment is carried out, and the feeding amount of silicon - calcium wire ≥ 1 kg / t.

[0023] Based on the above - mentioned technical solution, further, in the continuous casting process, electromagnetic stirring and soft reduction technologies are adopted to obtain a slab with a thickness of 150 - 230 mm.

[0024] Third, the present invention provides a 2000 - MPa - grade thick - gauge hot - stamping plate with excellent corrosion resistance, which is made by hot - stamping the above - mentioned thick - gauge hot - rolled steel plate.

[0025] Based on the above - mentioned technical solution, further, the thickness of the hot - stamping plate is 4 - 10 mm, which is composed of martensite or ferrite + martensite, the martensite content is 95 - 100%, the tensile strength ≥ 2000 MPa, the yield strength ≥ 1500 MPa, the elongation is 7 - 10%, the impact energy at - 20 °C ≥ 100 J. According to GB / T 10125 - 2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test", using a NaCl solution with a concentration of 50 g / L ± 5 g / L, within a 168 - h test cycle, the corrosion rate ≤ 0.53 g / (m 2 ·h).

[0026] Fourth aspect, the present invention provides a manufacturing method of the above-mentioned 2000MPa grade thick hot stamping plate, including the following steps: heating the hot-rolled steel plate to the austenitizing temperature for austenitization, then quickly transferring it to a hot stamping device for hot stamping forming, the hot stamping deformation temperature ≥ 650°C, after hot stamping, through the rapid cooling function of the hot forming die, quickly cooling the steel plate to below 250°C, the rapid cooling rate ≥ 18°C / s, maintaining pressure for more than 15s, and air cooling to room temperature.

[0027] Based on the above technical solution, further, in the hot stamping process, the austenitizing temperature is 900 - 950°C, and the holding time is 7 - 12min.

[0028] Based on the above technical solution, further, in the hot stamping process, the hot stamping deformation temperature is controlled at 650 - 720°C.

[0029] Based on the above technical solution, further, in the hot stamping process, the rapid cooling rate is controlled at 18 - 50°C / s.

[0030] The beneficial effects of the present invention compared with the prior art are as follows: (1) The present invention changes the design concept of traditional hot forming steel, adopts a B-free composition design, and ensures the strength and hardenability of the steel plate by adding appropriate alloy elements such as C, Mn, Cr, Mo, etc., so that a large amount of martensite structure can be obtained under certain cooling rate conditions; in addition, by adding Cr, Cu, Ni and rare earth elements, the corrosion resistance of the steel plate is greatly improved, making it suitable for the high-corrosion service environment of commercial vehicles; rare earth elements are added to the composition of the steel plate, which can increase the plasticity of the steel plate and improve the fatigue performance and welding performance of the steel plate; Nb element is added to the steel plate, which can greatly refine the microstructure of the hot-rolled substrate and the steel plate after hot forming, which is beneficial to improving the comprehensive performance of the steel plate.

[0031] (2) The present invention adopts a new composition design, combined with a reasonable hot rolling and hot forming process, to obtain a thick hot forming steel with good comprehensive performance. The tensile strength of the steel plate ≥ 2000MPa, the yield strength ≥ 1500MPa, the elongation ≥ 7%, and the impact energy at -20°C ≥ 100J; (3) The steel plate of the present invention has good corrosion resistance. According to GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test", simulating the marine atmospheric environment through a neutral salt spray test, using a NaCl solution with a concentration of 50g / L ± 5g / L, within a 168h test cycle, the corrosion rate ≤ 0.53g / (m 2 ·h), suitable for use in the high-corrosion service environment of commercial vehicles; (4) The production process of the steel plate of the present invention is simple and can be realized on existing equipment without equipment modification. Detailed implementation mode

[0032] The present invention will be described in detail below in conjunction with embodiments. However, the implementation manners of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, without creative efforts, obtaining other similar embodiments will fall within the protection scope of the present invention.

[0033] Examples 1 - 6 This example provides a 2000MPa - grade thick - specification hot - stamping plate with excellent corrosion resistance. The chemical composition and mass percentage of the steel plate are shown in Table 1; Table 1 Chemical composition and mass percentage (wt, %) of the hot - stamping plates in Examples 1 - 6

[0034] The method includes the following steps: Smelting → Continuous casting → Hot rolling → Cooling → Hot stamping; Smelting: The smelting process adopts the RH + LF double - process, strictly controlling the H and O contents, H ≤ 0.00018%, O ≤ 0.0010%; Calcium treatment is carried out in the refining process, and the amount of silicon - calcium wire fed ≥ 1 kg / t; Continuous casting: Electromagnetic stirring and soft reduction technologies are adopted during continuous casting to obtain a slab with a thickness of 160 - 230 mm; Hot rolling: The slab is heated to 1200 - 1240 °C and held for 2 hours, and the finishing rolling end temperature is 840 - 880 °C; Cooling: After finishing rolling, the front - section fast - cooling mode is adopted, with a cooling rate of 53 - 68 °C / s. The steel plate is cooled to 655 - 680 °C and then coiled, and air - cooled to room temperature; The thickness of the finished hot - rolled steel plate is 4 - 10 mm; The microstructure and mechanical property parameters of the hot - rolled steel plate are shown in Table 3.

[0035] Hot stamping: The hot - rolled plate is heated to 905 - 945 °C for austenitization, and the austenitization holding time is 7 - 12 min. Then it is quickly transferred to a hot - stamping device for hot - stamping forming. The hot - stamping deformation temperature is 660 - 720 °C. After hot stamping, through the rapid - cooling function of the hot - forming die, the steel plate is quickly cooled to below 250 °C, held under pressure for a certain time (> 15 s) and then air - cooled to room temperature, and the fast - cooling rate is 18 - 47 °C / s.

[0036] The corrosion resistance is evaluated according to GB / T 10125 - 2021 "Artificial atmosphere corrosion test - Salt spray test". The marine atmospheric environment is simulated through a neutral salt spray test, using an NaCl solution with a concentration of 50 g / L ± 5 g / L, and the test cycle is 168 h.

[0037] The mechanical properties and corrosion resistance of the hot - stamping plate prepared in this example are shown in Table 5.

[0038] Table 2 Hot rolling temperature, coiling temperature and cooling rate of Examples 1-6

[0039] Table 3 Microstructure and mechanical properties of hot rolled sheets of Examples 1-6

[0040] Table 4 Hot stamping process parameters of Examples 1-6

[0041] Table 5 Mechanical properties and corrosion resistance of steel sheets after hot stamping of Examples 1-6

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A thick hot-rolled steel plate with excellent corrosion resistance, characterized in that, Its chemical composition by mass percentage is as follows: C: 0.34% - 0.38%, Si: 0.10% - 0.30%, Mn: 1.10% - 1.70%, P ≤ 0.015%, S ≤ 0.004%, Als: 0.02% - 0.06%, Nb: 0.02% - 0.06%, Cr: 0.5% - 2.5%, Mo: 0 - 0.3%, Cu: 0 - 0.40%, Ni: 0 - 0.40%, rare earth elements La + Ce: 0.020% - 0.050%, N ≤ 0.005%, and the balance is Fe and unavoidable impurities, where 0.60 ≥ Ni + Cu ≥ 0.30, 2.5 ≥ Cr + Mo ≥ 0.8; The manufacturing method of the hot-rolled steel plate includes the following processes: smelting → continuous casting → hot rolling → cooling: Hot rolling process: Heat the billet to 1200 - 1240 °C, hold for 1 - 3 hours, and the finishing rolling temperature is 840 - 880 °C; Cooling process: After finishing rolling, adopt the rapid cooling mode, the cooling rate ≥ 50 °C / s, cool the steel plate to 650 - 680 °C and then coil it, and air-cool it to room temperature to obtain the hot-rolled steel plate.

2. The heavy-gauge hot-rolled steel plate according to claim 1, characterized in that, The thickness of the hot-rolled steel plate is 4 - 10 mm, the tensile strength is 620 - 780 MPa, the yield strength is 480 - 620 MPa, the elongation is 20 - 30%, the grain size ≥ 11 grades, and the banded structure ≤ 1.5 grades.

3. The heavy-gauge hot-rolled steel plate according to claim 1, characterized in that, In the cooling process, the cooling rate is controlled at 50 - 70 °C / s.

4. The heavy-gauge hot-rolled steel plate according to claim 1, wherein The smelting process adopts the RH + LF double process, strictly controls the H and O contents, H ≤ 0.00018%, O ≤ 0.001%; in the LF refining process, calcium treatment is carried out, and the feeding amount of calcium-silicon wire ≥ 1 kg / t; during the continuous casting process, electromagnetic stirring and soft reduction technologies are adopted to obtain a billet with a thickness of 150 - 230 mm.

5. A 2000MPa-grade thick hot stamping plate with excellent corrosion resistance, characterized in that, It is made by hot stamping the thick-specification hot-rolled steel plate described in Claim 1 or 2.

6. The 2000MPa grade thick hot stamping plate according to claim 5, wherein The thickness of the hot stamping sheet is 4 - 10 mm, which is composed of martensite or ferrite + martensite, with a martensite content of 95 - 100%, a tensile strength of ≥2000 MPa, a yield strength of ≥1500 MPa, an elongation of 7 - 10%, an impact energy at -20°C of ≥100 J. According to GB / T 10125-2021 "Artificial Atmosphere Corrosion Tests - Salt Spray Tests", using an NaCl solution with a concentration of 50 g / L ± 5 g / L, within a 168-hour test cycle, the corrosion rate is ≤0.53 g / (m 2 ·h).

7. The manufacturing method of the 2000MPa grade thick hot stamping plate according to claim 5 or 6, characterized in that, It includes the following steps: Heat the hot-rolled steel plate to the austenitizing temperature for austenitization, and then quickly transfer it to the hot stamping equipment for hot stamping forming. The hot stamping deformation temperature ≥ 650 °C. After hot stamping, through the rapid cooling function of the hot forming die, quickly cool the steel plate to below 250 °C, the rapid cooling rate ≥ 18 °C / s, hold the pressure for more than 15 s, and air-cool it to room temperature.

8. The manufacturing method according to claim 7, characterized in that, In the hot stamping process, the austenitizing temperature is 900 - 950 °C, and the holding time is 7 - 12 min.

9. The manufacturing method according to claim 7, characterized in that, In the hot stamping process, the hot stamping deformation temperature is controlled at 650 - 720 °C; in the hot stamping process, the rapid cooling rate is controlled at 18 - 50 °C / s.

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