1300MPa-grade thick-specification hot stamping plate with excellent corrosion resistance and manufacturing method of 1300MPa-grade thick-specification hot stamping plate

Abstract

The invention discloses a 1300MPa-grade thick-specification hot stamping plate with excellent corrosion resistance and a manufacturing method of the 1300MPa-grade thick-specification hot stamping plate. The hot stamping plate comprises the following chemical components in percentage by mass: 0.12%-0.16% of C, 0.10%-0.30% of Si, 1.00%-1.50% 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%-0.05% of Nb, 1.0%-2.50% of Cr, 0-0.30% of Cu, 0-0.30% of Ni, less than or equal to 0.005% of N and the balance of Fe and inevitable impurities. The tensile strength is larger than or equal to 1300 MPa, the yield strength is larger than or equal to 900 MPa, the ductility is 12%-20%, the impact energy at the temperature of-20 DEG C is larger than or equal to 70 J, the corrosion rate is smaller than or equal to 0.62 g / (m < 2 >. H), the requirements for the thick specification, good corrosion resistance and the remarkable lightweight effect needed by commercial vehicles are met, and very good application prospects are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot-formed steel preparation, and particularly relates to a 1300 MPa 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 fastest-developing technologies in the past 20 years. It mainly heats the hot-formed steel plate to the austenite region and holds it, 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 1100 MPa 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 part design, but also greatly reduces the vehicle weight. Therefore, hot-formed steel is widely used in the field of automotive part manufacturing and has achieved good lightweighting effects.

[0003] In recent years, the application of thick uncoated hot-formed steel in the field of automotive manufacturing has gradually increased. For example, in the field of commercial vehicle manufacturing, the lightweighting effect achieved 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. Generally, it is required that the steel has high strength and toughness while having good corrosion resistance. However, the current hot-formed steel products in the industry still cannot meet the use requirements of such components.

[0004] Chinese invention patent CN109023092A proposes a 1300MPa grade hot-formed steel for wheel rims and its manufacturing method. The chemical composition of the steel plate is as follows in mass percentage: C: 0.19 - 0.24%, Si: 0.1 - 0.3%, Mn: 1.0 - 1.4%, S: ≤0.004%, P: ≤0.01%, Ti: 0.02 - 0.04%, B: 0.003 - 0.004%, and the rest is iron and inevitable impurities. By adopting the hot rolling + batch annealing process, the strength and elongation of the hot-rolled substrate are reduced, which is beneficial to improving the cold forming performance of the steel plate. After conventional hot forming, the steel plate has a tensile strength of over 1300MPa, a yield strength greater than 1000MPa, an elongation greater than 10%, and the thickness of the steel plate is 3.0 - 6.0mm. The steel plate proposed in this patent has good strength-plasticity matching, but does not involve corrosion resistance, and the thickness specification of the steel plate is less than 6.0mm. Chinese invention patent CN115612921A proposes a 600MPa grade automotive wheel steel with good corrosion resistance and its manufacturing method. In the chemical composition of the steel plate, C: 0.12 - 0.2%, Si ≤1.0%, Mn: 0.55 - 0.9%, S: ≤0.005%, P: ≤0.025%, Ti: 0.065 - 0.085%, Cu: 0.2 - 0.3%, Cr: 0.4 - 1.0%, and the balance is iron and inevitable impurities. After smelting, hot rolling, cooling, and coiling, a high-strength wheel steel with a tensile strength greater than 600MPa is obtained. The thickness of the steel plate can reach more than 8mm, and its cyclic corrosion rate is lower than 1.8g / (m 2 ·h). The steel plate proposed in this patent has good corrosion resistance, but its tensile strength is low and does not meet the lightweight requirements of commercial vehicles.

[0005] In summary, researching and developing a 1300MPa grade thick-specification hot-formed steel with excellent corrosion resistance has become an important topic that urgently needs to be studied currently. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a 1300MPa grade thick-specification hot stamping plate with excellent corrosion resistance and its manufacturing method, aiming to improve the comprehensive performance of hot-formed steel plates and meet the requirements of thick specifications, good corrosion resistance, and significant lightweight effect for commercial vehicles.

[0007] To achieve the above purpose, the present invention provides the following technical solutions: In a first aspect, the present invention provides a thick - gauge hot - rolled steel plate with excellent corrosion resistance. Its chemical composition by mass percentage is as follows: C: 0.12% - 0.16%, Si: 0.10% - 0.30%, Mn: 1.00% - 1.50%, P ≤ 0.015%, S ≤ 0.004%, Als: 0.02% - 0.06%, Nb: 0.02% - 0.05%, Cr: 1.0% - 2.50%, Cu: 0 - 0.30%, Ni: 0 - 0.30%, N ≤ 0.005%, and the balance is Fe and unavoidable impurities, where 0.50 ≥ Ni + Cu ≥ 0.20.

[0008] Based on the above - mentioned technical solution, further, the thickness of the hot - rolled steel plate is 4 - 12 mm, the tensile strength is 500 - 650 MPa, the yield strength is 380 - 500 MPa, the elongation is 28 - 35%, the grain size is ≥ 9.0 grades, and the banded structure is ≤ 1.5 grades.

[0009] The main action mechanisms of each element in 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 0.12% - 0.16%.

[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, color difference and other 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 processes, and it is easy to have serious banded structure defects in the tissue. The selected Mn content in the present invention is 1.0% - 1.50%.

[0012] P, S: In the present invention, phosphorus and sulfur are harmful elements. P is easy to cause segregation defects in the casting billet, and S will form MnS inclusions, deteriorating the microstructure, mechanical properties and impact properties of the steel plate. In the present invention, P ≤ 0.015% and S ≤ 0.004%.

[0013] Als: Aluminum plays a role in deoxidizing and fixing nitrogen during the smelting process, but too much aluminum will lead to a large amount of aluminum - based inclusions. The range of Al in the present invention is 0.020% - 0.060%.

[0014] Cr: Adding chromium in the present invention can effectively improve the hardenability of 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 structure 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, the Cr content range in the present invention is 1.0% - 2.5%.

[0015] Nb: Niobium mainly plays the roles of fine grain strengthening and precipitation strengthening in steel. At high temperatures, niobium exists in the austenite in a solid solution state, which can inhibit the growth of austenite grains. At the same time, the precipitation of niobium carbides and nitrides can also delay recrystallization and prevent the growth of austenite grains, having obvious fine grain strengthening and precipitation strengthening effects, which can effectively reduce the banded structure grade of the hot-rolled substrate, improve the grain size, and finally refine the phases of the steel plate after hot forming, improving the impact performance. The optimal range of niobium content in the present invention is 0.02% - 0.05%.

[0016] Ni: Nickel can improve the corrosion resistance of steel, and improve heat resistance, cold brittleness, and hardenability. However, too high Ni will lead to an increase in manufacturing cost. The optimal range of Ni content in the present invention is 0 - 0.30%.

[0017] Cu: Copper plays a role in solid solution strengthening and precipitation strengthening in the hot-formed steel of the present invention. 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. The optimal range of Ni content in the present invention is 0 - 0.30%.

[0018] N: The lower the content of N, the better, but too low will lead to production difficulties and increase costs. Therefore, the N content in the present invention is ≤0.005%.

[0019] In the second aspect, the present invention provides a manufacturing method for the above-mentioned thick-specification 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 1180 - 1220 °C, hold for 1 - 3 hours, and the finish rolling temperature is 800 - 840 °C; Cooling process: After finish rolling, adopt a rapid cooling mode, with a cooling rate ≥50 °C / s. Cool the steel plate to 600 - 630 °C and then coil it, and air-cool it to room temperature to obtain the hot-rolled steel plate. Based on the above technical solution, further, the cooling rate in the cooling process is controlled at 50 - 70 °C / s.

[0020] Based on the above technical solutions, further, the smelting process adopts the RH+LF double process, strictly controlling the contents of H and O, with H≤0.00018% and O≤0.001%; calcium treatment is carried out in the LF refining process, and the feeding amount of silicon-calcium wire is ≥1 kg / t.

[0021] Based on the above technical solutions, further, electromagnetic stirring and soft reduction technologies are adopted during continuous casting to obtain a slab with a thickness of 150 - 230 mm.

[0022] In the third aspect, the present invention provides a 1300 MPa grade thick hot stamping plate with excellent corrosion resistance, which is made by hot stamping the above-mentioned thick hot-rolled steel plate.

[0023] Based on the above technical solutions, further, the structure of the hot stamping plate consists of all martensite, the thickness of the hot stamping plate is 4 - 12 mm, the tensile strength is ≥1300 MPa, the yield strength is ≥900 MPa, the elongation is 12 - 20%, the impact energy at -20°C is ≥70 J. According to GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test", the neutral salt spray test is used to simulate the marine atmospheric environment. Using a NaCl solution with a concentration of 50 g / L ± 5 g / L, within a 168-hour test cycle, the corrosion rate is ≤0.62 g / (m 2 ·h).

[0024] In the fourth aspect, the present invention provides a manufacturing method of the above-mentioned 1300 MPa grade thick hot stamping plate, including the following steps: heating the above-mentioned hot-rolled steel plate to the austenitizing temperature for austenitization, and then quickly transferring it to a hot stamping device for hot stamping forming. The hot stamping deformation temperature is ≥750°C. After hot stamping, through the rapid cooling function of the hot forming die, the steel plate is quickly cooled to below 250°C, the rapid cooling rate is ≥25°C / s, the pressure is maintained for more than 15 s, and then air-cooled to room temperature.

[0025] Based on the above technical solutions, further, in the hot stamping process, the austenitizing temperature is 880 - 930°C, and the holding time is 7 - 15 min.

[0026] Based on the above technical solutions, further, in the hot stamping process, the hot stamping deformation temperature is controlled at 750 - 790°C.

[0027] Based on the above technical solutions, further, in the hot stamping process, the rapid cooling rate is controlled at 25 - 50°C / s.

[0028] 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-formed steel, adopts a B-free component design, and ensures the strength and hardenability of the steel plate by adding appropriate C, Mn, Cr and other alloys, so that the steel plate can obtain a full martensitic structure under a certain cooling rate condition. By adding Cr, Cu and Ni elements, the corrosion resistance of the steel plate is greatly improved, making it suitable for the high-corrosion service environment of commercial vehicles; the addition of Nb element in the composition of the steel plate can greatly refine the microstructure of the hot-rolled base plate and the hot-formed steel plate, which is beneficial to improving the comprehensive performance of the steel plate.

[0029] (2) The present invention adopts a new composition design with reasonable hot rolling and hot forming processes to obtain thick-gauge hot-formed steel with good comprehensive performance, with a thickness of 4-12 mm, a tensile strength of ≥1300 MPa, a yield strength of ≥900 MPa, an elongation of ≥12%, and an impact energy of ≥70 J at -20°C; (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", a neutral salt spray test is performed to simulate the marine atmosphere environment. A NaCl solution with a concentration of 50g / L±5g / L is used. Within a test period of 168h, the corrosion rate is ≤0.62g / (m 2 h), suitable for use in highly corrosive service environments of commercial vehicles; (4) The production process of the steel plate of the present invention is simple and can be implemented on existing equipment without the need for equipment modification. DETAILED DESCRIPTION

[0030] The present invention is described in detail below with reference to the embodiments, but the embodiments 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, other similar embodiments obtained without creative labor all fall within the protection scope of the present invention.

[0031] Examples 1-6 This example provides a 1300MPa grade thick 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 hot stamping plates of Examples 1-6

[0032] The steps include: Smelting → continuous casting → hot rolling → cooling → hot stamping; Smelting: The smelting process adopts RH+LF double process, strictly controlling the H and O contents, H≤0.00018%, O≤0.001%; ​​calcium treatment is carried out in the refining process, and the amount of silicon calcium wire fed is ≥1kg / t; Continuous casting: Electromagnetic stirring and soft reduction technologies are adopted during continuous casting to obtain a slab with a thickness of 150 - 230 mm; Hot rolling: The slab is heated to 1180 - 1200 °C and held for 2 hours, and the finish rolling temperature is 800 - 840 °C; Cooling: After finish rolling, a fast cooling mode in the front section is adopted, with a cooling rate of 53 - 67 °C / s. The steel plate is cooled to 600 - 630 °C and then coiled, and air-cooled to room temperature; The thickness of the finished hot-rolled steel plate is 4 - 12 mm; The microstructures and mechanical property parameters of the hot-rolled steel plate are shown in Table 3.

[0033] Hot stamping: The hot-rolled plate is heated to 880 - 930 °C for austenitization, and the austenitization holding time is 7 - 14 min. Then it is quickly transferred to a hot stamping device for hot stamping forming. The hot stamping deformation temperature is 750 - 790 °C. After hot stamping, through the rapid cooling function of the hot forming die, the steel plate is quickly cooled to below 250 °C, and after holding pressure for a certain time (> 15 s), it is air-cooled to room temperature. The fast cooling rate is 27 - 50 °C / s.

[0034] 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.

[0035] The mechanical properties and corrosion resistance of the hot-stamped plate prepared in this example are shown in Table 5.

[0036] Table 2 Hot rolling temperature, coiling temperature and cooling rate of Examples 1 - 6

[0037] Table 3 Microstructures and mechanical properties of the hot-rolled plates of Examples 1 - 6

[0038] Table 4 Hot stamping process parameters of Examples 1 - 6

[0039] Table 5 Mechanical properties and corrosion resistance of the steel plates after hot stamping of Examples 1 - 6

[0040] 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 it; 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 for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various 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: C: 0.12% - 0.16%, Si: 0.10% - 0.30%, Mn: 1.00% - 1.50%, P ≤ 0.015%, S ≤ 0.004%, Als: 0.02% - 0.06%, Nb: 0.02% - 0.05%, Cr: 1.0% - 2.50%, Cu: 0 - 0.30%, Ni: 0 - 0.30%, N ≤ 0.005%, and the balance is Fe and unavoidable impurities, where 0.50 ≥ Ni + Cu ≥ 0.20; The manufacturing method of the thick - gauge hot - rolled steel plate described above includes the following processes: smelting → continuous casting → hot rolling → cooling; Hot - rolling process: Heat the slab to 1180 - 1220 °C, hold for 1 - 3 hours, and the finishing rolling end - rolling temperature is 800 - 840 °C; Cooling process: After finish rolling, adopt the rapid - cooling mode, with a cooling rate ≥ 50 °C / s. Cool the steel plate to 600 - 630 °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 - 12 mm, the tensile strength is 500 - 650 MPa, the yield strength is 380 - 500 MPa, the elongation is 28 - 35%, the grain size ≥ 9.0 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 - joint process, strictly controlling 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 continuous casting, electromagnetic stirring and soft reduction technology are adopted to obtain a slab with a thickness of 150 - 230 mm.

5. A 1300 MPa grade thick hot stamping sheet with excellent corrosion resistance, characterized in that, It is made by hot stamping the thick - gauge hot - rolled steel plate described in Claim 1 or 2.

6. The 1300 MPa grade thick hot stamping sheet according to claim 5, characterized in that, The structure of the hot stamping sheet consists of fully martensite. The thickness of the hot stamping sheet is 4 - 12 mm, the tensile strength ≥ 1300 MPa, the yield strength ≥ 900 MPa, the elongation is 12 - 20%, the impact energy at -20 °C ≥ 70 J. According to GB / T 10125-2021 "Artificial Atmosphere Corrosion Tests - Salt Spray Tests", using a NaCl solution with a concentration of 50 g / L ± 5 g / L, within a 168-hour test cycle, the corrosion rate ≤ 0.62 g / (m 2 ·h).

7. The manufacturing method of the 1300 MPa grade thick hot stamping sheet according to claim 5 or 6, characterized in that, It includes the following steps: Heat the above - mentioned 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 ≥ 750 °C. After hot - stamping, through the rapid - cooling function of the hot - forming die, quickly cool the steel plate to below 250 °C, with a rapid - cooling rate ≥ 25 °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 880 - 930 °C, and the holding time is 7 - 15 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 750 - 790 °C; in the hot - stamping process, the rapid - cooling rate is controlled at 25 - 50 °C / s.

Images