1800MPa-grade thick-specification hot stamping plate with excellent corrosion resistance and manufacturing method of 1800MPa-grade thick-specification hot stamping plate

Abstract

The invention discloses a 1800MPa-grade thick-specification hot stamping plate with excellent corrosion resistance and a manufacturing method of the 1800MPa-grade thick-specification hot stamping plate. The stamping plate comprises, by mass, 0.28%-0.33% of C, 0.10%-0.30% of Si, 1.20%-1.70% of Mn, smaller than or equal to 0.015% of P, smaller than or equal to 0.004% of S, 0.02%-0.06% of Als, 0.03%-0.06% of Nb, 1.5%-2.5% of Cr, 0-0.40% of Cu, 0-0.40% of Ni, 0.020%-0.040% of rare earth elements La + Ce, smaller than or equal to 0.005% of N and the balance Fe and inevitable impurities, the tensile strength is larger than or equal to 1800 MPa, the yield strength is larger than or equal to 1300 MPa, the ductility is 9%-15%, the impact energy at the temperature of 20 DEG C below zero is larger than or equal to 90 J, the corrosion rate is smaller than or

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of hot-formed steel, and particularly relates to an 1800 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 technologies that have developed the fastest 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, and at the same time performs pressure maintaining and quenching to 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 significantly 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 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, and the strength of the steel plate is mainly 1500 MPa. However, with the expansion of the application fields, 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 CN105568145 A proposes a cold-rolled ultra-high strength dual-phase steel plate for automobiles with corrosion resistance. The chemical composition of the steel plate is as follows in mass percentage: 0.13% - 0.16% C, 1.8% - 2.0% Si, 2.3% - 2.5% Mn, 1.8% - 2.2% Cr, 0.010% - 0.025% Al, 0.001% - 0.008% S, 0.002% - 0.012% P, 0.001% - 0.004% N, and the rest is Fe and inevitable impurity elements; the microstructure of the steel is mainly martensite and a small amount of diffusely distributed ferrite; the mechanical properties of the steel plate are: Rp 0.2 = 1020 - 1100 MPa, R m = 1600 MPa - 1850 MPa, A 50= 4.55% - 9.50%; According to "Artificial Atmosphere Corrosion Test - Salt Spray Test GB / T 10125 - 2012", the marine atmospheric environment is simulated through the neutral salt spray test. An NaCl solution with a concentration of 50 g / L ± 5 g / L is used. During the 96 - h and 144 - h test cycles, the corrosion rates are 1.26 g / (m 2 ·h) and 1.11 g / (m 2 ·h) respectively. This steel type is cold - rolled dual - phase steel. The steel plate has high strength and good corrosion resistance, but it has relatively high alloying elements such as Si, Mn, and Cr in its composition, resulting in high costs, difficult production, and the steel plate thickness is less than 2.5 mm, which is not suitable for manufacturing thick - specification commercial vehicle parts.

[0005] In summary, researching and developing a 1800 - MPa - 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 1800 - MPa - grade thick - specification 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 - specification, good corrosion resistance, and significant lightweight effect for commercial vehicles.

[0007] The purpose of the present invention is achieved in the following ways: In the first aspect, the present invention provides a thick - specification hot - rolled steel plate with excellent corrosion resistance. Its chemical composition by mass percentage is: C: 0.28% - 0.33%, Si: 0.10% - 0.30%, Mn: 1.20% - 1.70%, P ≤ 0.015%, S ≤ 0.004%, Als: 0.02% - 0.06%, Nb: 0.03% - 0.06%, Cr: 1.5% - 2.5%, Cu: 0 - 0.40%, Ni: 0 - 0.40%, rare earth elements La + Ce: 0.020% - 0.040%, N ≤ 0.005%, and the balance is Fe and inevitable impurities, where 0.60 ≥ Ni + Cu ≥ 0.30.

[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 600 - 750 MPa, the yield strength is 450 - 600 MPa, the elongation is 23 - 33%, the grain size is ≥ 10 grades, and the banded structure is ≤ 1.5 grades.

[0009] The main action mechanisms of each component in the steel plate of the present invention are as follows: C: Carbon ensures 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 is high after hot rolling and coiling, 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. In the present invention, the optimal range of C is 0.28% - 0.33%.

[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. In the present invention, the optimal range of Si 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. In the present invention, the Mn content is 1.2% - 1.7%.

[0012] P, S: In the present invention, phosphorus and sulfur are harmful elements. P is easy to cause segregation defects in the continuous casting billet, and S 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 deoxidizing and fixing nitrogen during the smelting process, but too much aluminum will lead to a large number of aluminum-based inclusions. In the present invention, the range of Al is 0.020% - 0.060%.

[0014] Cr: Adding chromium can effectively improve the hardenability of the steel, make up for the reduction of hardenability caused by the absence of B in the composition, and enable a large amount of martensite to be obtained in the tissue 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 Cr content range is 1.5% - 2.5%.

[0015] Nb: Niobium mainly plays roles such as fine grain strengthening and precipitation strengthening 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, which can effectively reduce the banded structure grade of the hot-rolled base plate, improve the grain size, and ultimately refine the phases of the steel plate after hot forming and improve the impact performance. In the present invention, the optimal range of niobium content is 0.03% - 0.06%.

[0016] Ni: Nickel can improve the corrosion resistance of steel, and also enhance heat resistance, cold brittleness, and hardenability. However, excessive Ni will lead to an increase in manufacturing costs. In this invention, the optimal range of Ni content is 0 - 0.40%.

[0017] Cu: Copper plays a role in solution strengthening and precipitation strengthening in the hot-formed steel of this patent. At the same time, it can 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 this invention, the optimal range of Ni content is 0 - 0.40%.

[0018] 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 that 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 invention, the content of rare earth (La + Ce) is 0.02% - 0.04%.

[0019] N: The lower the content of N, the better. However, too low a content will cause production difficulties and increase costs. Therefore, in this patent, the N content ≤ 0.005%.

[0020] In the second aspect, the present invention provides a method for manufacturing 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 finishing rolling temperature is 820 - 860 °C; Cooling process: After finishing rolling, adopt the rapid cooling mode, with a cooling rate ≥ 60 °C / s. Cool the steel plate to 640 - 670 °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 60 - 80 °C / s.

[0021] Based on the above technical solution, further, the smelting process adopts the RH + LF double 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 silicon-calcium wire ≥ 1 kg / t.

[0022] Based on the above technical solution, further, electromagnetic stirring and soft reduction technologies are adopted during continuous casting to obtain a slab with a thickness of 150 - 230 mm.

[0023] In the third aspect, the present invention provides an 1800 MPa grade thick-specification hot stamping plate with excellent corrosion resistance, which is made by hot stamping the above-mentioned thick-specification hot-rolled steel plate.

[0024] Based on the above technical solution, further, the structure of the hot stamping plate consists of martensite or ferrite + martensite, with the martensite content being 90 - 100%. The thickness of the hot stamping plate is 4 - 12 mm, the tensile strength ≥ 1800 MPa, the yield strength ≥ 1300 MPa, the elongation 9 - 15%, the impact energy at -20 °C ≥ 90 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 ≤ 0.50 g / (m 2 ·h).

[0025] Fourthly, the present invention provides a manufacturing method for the above-mentioned 1800 MPa grade thick specification hot stamping plate, including the following steps: heating the above-mentioned 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 ≥ 660 °C, and 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 ≥ 20 °C / s, maintaining pressure for more than 15 s, and air cooling to room temperature.

[0026] 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 - 15 min.

[0027] Based on the above technical solution, further, in the hot stamping process, the hot stamping deformation temperature is controlled at 660 - 750 °C.

[0028] Based on the above technical solution, further, in the hot stamping process, the rapid cooling rate is controlled at 20 - 50 °C / s.

[0029] 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 composition design, and ensures the strength and hardenability of the steel plate by adding appropriate alloying elements such as C, Mn, Cr, etc., so that the steel plate can obtain a steel plate structure composed of a small amount of ferrite + a large amount of martensite 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; adding rare earth elements to the composition of the steel plate can increase the plasticity of the steel plate and improve the fatigue performance and welding performance of the steel plate; adding Nb element to the steel plate 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.

[0030] (2) The present invention adopts a novel composition design in combination with a reasonable hot rolling and hot forming process to obtain a thick - gauge hot - formed steel with good comprehensive properties. The tensile strength of the steel plate is ≥1800 MPa, the yield strength is ≥1300 MPa, the elongation is ≥9%, and the impact energy at - 20 °C is ≥90 J. (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", the neutral salt spray test is used to simulate the marine atmospheric environment. An NaCl solution with a concentration of 50 g / L ± 5 g / L is adopted. During the 168 - h test cycle, the corrosion rate is ≤0.50 g / (m 2 ·h), and it is 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. Specific Embodiments

[0031] 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.

[0032] Embodiments 1 - 6 This example provides an 1800 - MPa - grade thick - gauge hot stamping plate with excellent corrosion resistance. The chemical composition and mass percentage of the steel are shown in Table 1; Table 1 Chemical composition and mass percentage (wt, %) of the hot stamping plates in Embodiments 1 - 6

[0033] It includes the following steps: Smelting → Continuous casting → Hot rolling → Cooling → Hot stamping; Smelting: The smelting process adopts the RH + LF double - ladle 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 feeding amount of silicon - calcium wire is ≥1 kg / 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 1200 ± 20 °C and held for 2 hours, and the finishing rolling temperature is 820 - 860 °C; Cooling: After finishing rolling, the front - segment rapid cooling mode is adopted, with a cooling rate of 63 - 75 °C / s. The steel plate is cooled to 645 - 670 °C and then coiled, and air - cooled to room temperature; the thickness of the finished hot - rolled steel plate is 4 - 11 mm. The microstructure and mechanical property parameters of the hot - rolled steel plate are shown in Table 3.

[0034] Hot stamping: Austenitize the hot-rolled sheet by heating it to the range of 905 - 945°C, with the austenitizing holding time being 7 - 14 min. Then, quickly transfer it to a hot stamping device for hot stamping forming. The hot stamping deformation temperature is 665 - 740°C. After hot stamping, through the rapid cooling function of the hot forming die, quickly cool the steel sheet to below 250°C. After maintaining pressure for a certain time (>15 s), air cool it to room temperature, and the rapid cooling rate is 21 - 50°C / s.

[0035] The corrosion resistance is evaluated according to GB / T 10125 - 2021 "Artificial Atmosphere Corrosion Tests - Salt Spray Tests". Simulate the marine atmospheric environment through neutral salt spray tests, using an NaCl solution with a concentration of 50 g / L ± 5 g / L, and the test cycle is 168 h.

[0036] The mechanical properties and corrosion resistance of the hot-stamped sheet prepared in this example are shown in Table 5.

[0037] Table 2 Hot rolling temperature, coiling temperature and cooling rate of Examples 1 - 6

[0038] Table 3 Microstructure and mechanical properties of the hot-rolled sheets of Examples 1 - 6

[0039] Table 4 Hot stamping process parameters of Examples 1 - 6

[0040] Table 5 Mechanical properties and corrosion resistance of the steel sheets after hot stamping in Examples 1 - 6

[0041] Finally, it should be noted that: The above embodiments are only used to illustrate the technical solutions of the present invention, not 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: 0.28% - 0.33%, Si: 0.10% - 0.30%, Mn: 1.20% - 1.70%, P ≤ 0.015%, S ≤ 0.004%, Als: 0.02% - 0.06%, Nb: 0.03% - 0.06%, Cr: 1.5% - 2.5%, Cu: 0 - 0.40%, Ni: 0 - 0.40%, rare earth elements La + Ce: 0.020% - 0.040%, N ≤ 0.005%, and the balance is Fe and unavoidable impurities, where 0.60 ≥ Ni + Cu ≥ 0.30; 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 temperature is 820 - 860 °C; Cooling process: After finishing rolling, adopt the rapid - cooling mode, with a cooling rate ≥ 60 °C / s. Cool the steel plate to 640 - 670 °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, wherein The thickness of the hot - rolled steel plate described above is 4 - 12 mm, the tensile strength is 600 - 750 MPa, the yield strength is 450 - 600 MPa, the elongation is 23 - 33%, the grain size ≥ 10 grades, and the banded structure ≤ 1.5 grades.

3. The heavy-gauge hot-rolled steel plate according to claim 1, wherein, In the cooling process, the cooling rate is controlled at 60 - 80 °C / s.

4. The heavy-gauge hot-rolled steel plate according to claim 1, wherein The smelting process adopts the RH + LF double - combined 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 silicon - calcium wire ≥ 1 kg / t; during continuous casting, electromagnetic stirring and soft reduction technologies are adopted to obtain a slab with a thickness of 150 - 230 mm.

5. An 1800 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 1800 MPa grade thick hot stamping sheet according to claim 5, wherein The structure of the hot stamping sheet consists of martensite or ferrite + martensite, with the martensite content being 90 - 100%. The thickness of the hot stamping sheet is 4 - 12 mm, the tensile strength is ≥1800 MPa, the yield strength is ≥1300 MPa, the elongation is 9 - 15%, the impact energy at -20°C is ≥90 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 ≤0.50 g / (m 2 ·h).

7. The manufacturing method of the 1800 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 a hot - stamping device for hot - stamping forming. The hot - stamping deformation temperature ≥ 660 °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 ≥ 20 °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 - 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 660 - 750 °C; in the hot - stamping process, the rapid - cooling rate is controlled at 20 - 50 °C / s.

Images