Rare earth high-strength dual-phase steel and forming method and application thereof

Abstract

The application discloses a rare earth high-strength dual-phase steel and a forming method and application thereof, and belongs to the technical field of dual-phase steel. The forming method of the rare earth high-strength dual-phase steel comprises the following steps: converter smelting, LF refining, RH refining, adding cerium iron and yttrium iron at the end of the RH refining or before continuous casting, continuous casting, three-stage hot rolling, cold rolling and three-stage annealing. The rare earth high-strength dual-phase steel has good cold stamping formability, high weldability, no rare earth element segregation, no cracking of steel forming, high yield, and can be directly used to prepare automobile bodies after cold stamping forming at normal temperature. There is no rare earth inclusion or coarse carbon nitride brittle bulk agglomerate on the surface layer of the weld, the rare earth element is in a dispersed distribution state, has excellent dispersion strengthening effect, the weld is not prone to cracking, and the mechanical properties of the weld are superior to those of the base material.

Description

Technical Field

[0001] This invention belongs to the field of dual-phase steel technology, and relates to a rare earth high-strength dual-phase steel, its forming method and application, and particularly to a 980MPa grade rare earth high-strength dual-phase steel, its forming method and application. Background Technology

[0002] The core advantage of duplex steel is its strength-ductility balance. Strength comes from the high-density, fine martensite islands that significantly enhance tensile strength through second-phase reinforcement. Ductility comes from the continuous, flat ferrite matrix, which provides ample space for plastic deformation. Work hardening capability: the interface between the martensite islands and ferrite hinders dislocation movement, giving the material a high work hardening index.

[0003] Rare earth dual-phase steel can solve the problems of corrosion and wear in harsh environments. It is mainly used to replace traditional dual-phase steel in high-corrosion and high-stress extreme conditions. However, when the amount of microalloyed rare earth added to dual-phase steel is insufficient, the improvement effect is limited. Excessive addition will form large rare earth inclusions, which will become crack sources, leading to a sharp decrease in toughness and corrosion resistance, making it difficult to stamp and form.

[0004] The core challenge in forming rare-earth high-strength duplex steel lies in the conflict between high strength and formability. While rare earth elements can improve toughness and mitigate corrosion and wear, they cannot alter the inherent physical properties of duplex steel, making it far more difficult to form than ordinary stainless steel.

[0005] Therefore, there is an urgent need for a rare earth high-strength duplex steel that is easy to form, highly weldable, does not easily segregate rare earth elements, is not easily cracked, and its forming method and application. Summary of the Invention

[0006] The purpose of this invention is to provide a rare earth high-strength dual-phase steel. This rare earth high-strength dual-phase steel has good formability (cold stamping), high weldability, no segregation of rare earth elements, no cracking during steel forming, high yield, and can be directly used to manufacture automobile bodies after room temperature stamping.

[0007] Meanwhile, the present invention provides a method for forming rare earth high-strength dual-phase steel.

[0008] Meanwhile, this invention provides an application of rare earth high-strength dual-phase steel.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A rare-earth high-strength dual-phase steel has the following chemical composition and mass percentage: C: 0.08-0.10%; Si: 0.3-0.5%; Mn: 1.3-2.5%; Als: 0.025-0.050%; Nb: 0.02-0.03%; Ti: 0.02-0.03%; Cr: 0.1-0.2%; Ce: 40-100ppm; Y: 10-30ppm; P: ≤0.015%; S: ≤0.003%; N: ≤0.005%, with the remainder being Fe and unavoidable impurities. The mass ratio of Ce to Y is (4-3):1.

[0010] A method for forming rare-earth high-strength dual-phase steel includes the following steps: Converter smelting: Add raw materials other than rare earth elements for alloying treatment. The converter temperature is 1500-1550℃ and the time is 0.5-1h.

[0011] LF refining: The temperature of molten steel entering the station is 1500-1550℃, and the refining time is 15-30 minutes. Argon gas is used for strong stirring at the bottom of the ladle to quickly remove sulfur from the molten steel.

[0012] RH refining: Molten steel exits the LF refining furnace and undergoes RH refining with a vacuum degree ≤100Pa, a refining time of 30-40 minutes, and a molten steel exit temperature of 1550-1600℃.

[0013] Ferrocerium (CeFe90) and yttrium (FeY30) are added at the end of RH refining or before continuous casting.

[0014] Continuous casting: Molten steel with added cerium iron and yttrium iron is poured into the tundish. During the pouring process, protective slag (commercially available product, Shinagawa 43A special protective slag) is added. The temperature of the molten steel in the tundish is 1500-1550℃, and the casting speed is 1.0-1.5m / min to obtain the cast billet.

[0015] Hot rolling: The rolling process is carried out in three stages. First stage (rough rolling first stage): Rolling entry temperature 1150-1180℃; total rolling reduction 50-60%, single-pass rolling reduction ≥10%, final rolling temperature 1050-1100℃; this stage ensures the dissolution of rare earth element inclusions and uniform distribution of composition, eliminates segregation, reduces the resistance of subsequent forming (such as room temperature stamping), and, in conjunction with large reduction rolling, eliminates ferrite / martensite banded structures that are prone to occur in hot rolling, preventing cracking along the banded lines during subsequent forming.

[0016] The second stage (rough rolling stage 2): rolling inlet temperature 1030-1080℃; total rolling reduction 60-65%, single-pass rolling reduction 13-18%, and final rolling temperature 1000-1030℃; this stage refines ferrite grains, improves toughness, lays the foundation for obtaining a fine ferrite / martensite dual-phase structure in the finished product, and improves strength.

[0017] The third stage (finish rolling): the rolling inlet temperature is 980-1020℃; the total rolling reduction rate is 65-75%; the single-pass rolling reduction is 5-12%; and the final rolling temperature is 700-750℃. This stage further refines the ferrite grains and controls a large number of fine ferrite nuclei to prepare for obtaining fine grains in the finished product.

[0018] After hot rolling, the material is cooled at a rate of 6-10℃ / s, with a coiling temperature of 500-530℃ and a hot-rolled thickness of 2-3mm, to provide a uniform microstructure for subsequent annealing.

[0019] Cold rolling: with a reduction rate of 50%-65%, sufficient deformation energy is accumulated, and the finished product thickness is 0.7-1.5mm. Steel of this thickness is used for automobile bodies, achieving lightweighting of automobile bodies while ensuring quality and safety.

[0020] Three-stage annealing (organic regulation): Soaking zone: 780-830℃ for 250-370s: This keeps the steel coil in the ferrite + austenite two-phase region, allowing carbon to diffuse into the austenite.

[0021] Rapid cooling section: Cool to 280-350℃ at ≥30℃ / s and hold for 120-250s to force austenite to transform into martensite.

[0022] Over-aging stage: 200-250℃ for 230-360s: eliminate internal stress, moderately temper the martensite, balance strength and toughness, and obtain rare earth high-strength dual-phase steel.

[0023] The rare-earth high-strength dual-phase steel of this invention achieves a part dimensional accuracy of ±0.05mm after cold stamping. When the limit bending angle is tested, the limit bending angle is 90-135 degrees when the inner corner radius of the bend is 0.2mm, demonstrating excellent forming performance.

[0024] High-quality welds can be formed by irradiating the butt joint of two rare-earth high-strength dual-phase steels with a fiber laser. The welds are fully martensitic, and the fracture zone in tensile tests is not located in the weld area. Preferably, the fiber laser has an average power of 2000-4000W, a scanning speed of 100-150mm / s, and a wavelength of 1000-1500nm.

[0025] The application of rare earth high-strength duplex steel in lightweight automobile bodies according to the present invention.

[0026] A lightweight car body is prepared from the rare-earth high-strength dual-phase steel of the present invention.

[0027] Rare earth high-strength duplex steel components obtained by the welding method of the present invention.

[0028] The application of rare earth high-strength dual-phase steel components of the present invention in lightweight automobile bodies.

[0029] A lightweight automobile body is obtained by preparing rare earth high-strength dual-phase steel components according to the present invention.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows: The rare earth high-strength dual-phase steel of this invention has good formability (room temperature stamping), high weldability, no rare earth element segregation, no cracking during steel forming, and high yield. After room temperature stamping, it can be directly used to manufacture automobile bodies. The surface of the weld of the rare earth high-strength dual-phase steel component does not contain rare earth inclusions or large brittle agglomerates such as coarse carbonitrides. The rare earth elements are in a dispersed distribution state, which has excellent dispersion strengthening effect. The weld is not easy to crack, and the mechanical properties of the weld are better than those of the base material.

[0031] The rare earth high-strength dual-phase steel obtained by this invention is suitable for cold stamping and direct welding. The rare earth high-strength dual-phase steel of this invention has a yield strength of 720-745MPa, a tensile strength of 1000-1050MPa, and an elongation of 19-22%, achieving a synergistic improvement in strength and toughness. Attached Figure Description

[0032] Figure 1 This is a microstructure diagram of the present invention; Figure 2 This is a bending diagram of the rare-earth high-strength dual-phase steel of the present invention; Figure 3 This is a drawing of a cold-stamped part according to the present invention. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Example 1

[0034] A rare-earth high-strength dual-phase steel has the following chemical composition and mass percentage: C: 0.09%; Si: 0.4%; Mn: 2.0%; Als: 0.035%; Nb: 0.025%; Ti: 0.025%; Cr: 0.15%; Ce: 80ppm; Y: 20ppm; P: 0.015%; S: 0.003%; N: 0.005%, with the remainder being Fe and unavoidable impurities. The mass ratio of Ce to Y is 4:1.

[0035] A method for forming rare-earth high-strength dual-phase steel includes the following steps: Converter smelting: Add raw materials other than rare earth elements for alloying treatment. The converter temperature is 1520℃ and the time is 45min.

[0036] LF refining: The molten steel inlet temperature is 1520℃, and the refining time is 20 minutes. Argon gas is used for strong stirring at the bottom of the ladle to quickly remove sulfur from the molten steel.

[0037] RH refining: Molten steel exits the LF refining furnace and undergoes RH refining with a vacuum of 100Pa and a refining time of 35 minutes. The molten steel exit temperature is 1580℃.

[0038] Ferrocerium (CeFe90) and yttrium (FeY30) are added at the end of RH refining or before continuous casting.

[0039] Continuous casting: Molten steel with added cerium iron and yttrium iron is poured into the tundish. During the pouring process, protective slag (commercially available product, Shinagawa 43A special protective slag) is added. The molten steel temperature in the tundish is 1520℃, and the casting speed is 1.3m / min to obtain the billet.

[0040] Hot rolling: The rolling process is carried out in three stages. First stage (rough rolling first stage): Rolling entry temperature 1170℃; total rolling reduction rate 55%, single-pass rolling reduction 10%, final rolling temperature 1080℃; this stage ensures the dissolution of rare earth element inclusions and uniform distribution of composition, eliminates segregation, reduces the resistance of subsequent forming (such as room temperature stamping), and, in conjunction with large reduction rolling, eliminates the ferrite / martensite banded structure that is prone to occur in hot rolling, preventing cracking along the banded line during subsequent forming.

[0041] Second stage (rough rolling stage 2): Rolling entry temperature 1050℃; total rolling reduction 62%, single-pass rolling reduction 15%, final rolling temperature 1015℃; this stage refines ferrite grains, improves toughness, lays the foundation for obtaining a fine ferrite / martensite dual-phase structure in the finished product, and improves strength.

[0042] The third stage (finish rolling): the rolling inlet temperature is 1000℃; the total rolling reduction rate is 70%, the single-pass rolling reduction is 6%, and the final rolling temperature is 720℃; this stage further refines the ferrite grains and controls a large number of fine ferrite nuclei to prepare for the finished product to obtain fine grains.

[0043] After hot rolling, the material is cooled at a rate of 8℃ / s, with a coiling temperature of 520℃ and a hot-rolled thickness of 2.5mm, to provide a uniform microstructure for subsequent annealing.

[0044] Cold rolling: with a reduction rate of 60%, sufficient deformation energy is accumulated, and the finished product thickness is 1.0 mm. Steel of this thickness is used for automobile bodies, achieving lightweighting of automobile bodies while ensuring quality and safety.

[0045] Three-stage annealing (organic regulation): Soaking zone: 800℃ for 300s: This keeps the steel coil in the ferrite + austenite two-phase region, allowing carbon to diffuse into the austenite.

[0046] Rapid cooling section: Cool to 300℃ at 30℃ / s and hold for 200s to force austenite to transform into martensite.

[0047] Over-aging stage: 220℃ for 300s: eliminate internal stress, moderately temper the martensite, balance strength and toughness, and obtain rare earth high-strength dual-phase steel.

[0048] A high-quality weld can be formed by irradiating the butt joint of two rare-earth high-strength dual-phase steels with a fiber laser. The weld is fully martensitic, and the fracture zone in the tensile test is not located in the weld area. Preferably, the fiber laser has an average power of 3000W, a scanning speed of 120mm / s, and a wavelength of 1200nm.

[0049] The rare earth high-strength dual-phase steel obtained in this embodiment has a yield strength of 735 MPa, a tensile strength of 1020 MPa, and an elongation of 20%.

[0050] This embodiment describes the application of rare-earth high-strength duplex steel in lightweight automotive bodies.

[0051] A lightweight automobile body is prepared from rare-earth high-strength dual-phase steel according to this embodiment.

[0052] Rare earth high-strength duplex steel components obtained using the welding method of this embodiment.

[0053] This embodiment describes the application of rare-earth high-strength duplex steel components in lightweight automotive bodies.

[0054] A lightweight automobile body is prepared from rare-earth high-strength dual-phase steel components according to this embodiment.

[0055] like Figure 1 As shown, the rare-earth high-strength dual-phase steel obtained in this embodiment has a dark-colored substrate of ferrite and island-like structures consisting of martensite—black or dark gray islands dispersed in the ferrite matrix. The figure shows no large non-metallic inclusions (such as elongated MnS), rare-earth inclusions, or large carbonitride precipitates, ensuring the purity and uniformity of the ferrite matrix.

[0056] like Figures 2-3As shown, the rare earth high-strength dual-phase steel obtained in this embodiment has a part dimensional accuracy of ±0.05mm after cold stamping. When the radius of the inner corner of the material at the bend is 0.2mm, the limit bending angle is 90 degrees, which shows excellent forming performance. Example 2

[0057] A rare-earth high-strength dual-phase steel has the following chemical composition and mass percentage: C: 0.08%; Si: 0.3%; Mn: 1.3%; Als: 0.025%; Nb: 0.02%; Ti: 0.02%; Cr: 0.1%; Ce: 60ppm; Y: 20ppm; P: 0.010%; S: 0.001%; ​​N: 0.003%, with the remainder being Fe and unavoidable impurities. The mass ratio of Ce to Y is 3:1.

[0058] A method for forming rare-earth high-strength dual-phase steel includes the following steps: Converter smelting: Add raw materials other than rare earth elements for alloying treatment. The converter temperature is 1500℃ and the time is 0.5h.

[0059] LF refining: The molten steel inlet temperature is 1500℃, and the refining time is 15 minutes. Argon gas is used for strong stirring at the bottom of the ladle to quickly remove sulfur from the molten steel.

[0060] RH refining: Molten steel exits the LF refining furnace and undergoes RH refining with a vacuum of 80 Pa for 30 minutes. The temperature of the molten steel exiting the furnace is 1550℃.

[0061] Ferrocerium (CeFe90) and yttrium (FeY30) are added at the end of RH refining or before continuous casting.

[0062] Continuous casting: Molten steel with added cerium iron and yttrium iron is poured into the tundish. During the pouring process, protective slag (commercially available product, Shinagawa 43A special protective slag) is added. The molten steel temperature in the tundish is 1500℃, and the casting speed is 1.0m / min to obtain the cast billet.

[0063] Hot rolling: The rolling process is carried out in three stages. First stage: Rolling entry temperature 1150℃; total rolling reduction rate 50%, single-pass rolling reduction 12%, final rolling temperature 1050℃; this stage ensures the dissolution of rare earth element inclusions and uniform distribution of composition, eliminates segregation, reduces the resistance of subsequent forming (such as room temperature stamping), and, in conjunction with large reduction rolling, eliminates the ferrite / martensite banded structure that is prone to occur in hot rolling, preventing cracking along the banded line during subsequent forming.

[0064] Second stage: Rolling entry temperature 1030℃; total rolling reduction rate 60%, single-pass rolling reduction 13%, final rolling temperature 1000℃; this stage refines ferrite grains, improves toughness, lays the foundation for obtaining a fine ferrite / martensite dual-phase structure in the finished product, and improves strength.

[0065] The third stage: the rolling inlet temperature is 980℃; the total rolling reduction rate is 65%, the single-pass rolling reduction is 5%, and the final rolling temperature is 700℃; this stage further refines the ferrite grains and controls a large number of fine ferrite nuclei to prepare for obtaining fine grains in the finished product.

[0066] After hot rolling, the material is cooled at a rate of 6℃ / s, with a coiling temperature of 500℃ and a hot-rolled thickness of 3mm, to provide a uniform microstructure for subsequent annealing.

[0067] Cold rolling: with a reduction rate of 50%, sufficient deformation energy is accumulated, and the finished product thickness is 1.5mm. Steel of this thickness is used for automobile bodies, achieving lightweighting of automobile bodies while ensuring quality and safety.

[0068] Three-stage annealing (organic regulation): Soaking zone: 780℃ for 250s: This keeps the steel coil in the ferrite + austenite two-phase region, allowing carbon to diffuse into the austenite.

[0069] Rapid cooling section: Cool to 280℃ at 40℃ / s and hold for 120s to force austenite to transform into martensite.

[0070] Over-aging stage: Hold at 200℃ for 230s: Eliminate internal stress, moderately temper the martensite, balance strength and toughness, and obtain rare earth high-strength dual-phase steel.

[0071] A high-quality weld can be formed by irradiating the butt joint of two rare-earth high-strength dual-phase steels with a fiber laser. The weld is fully martensitic, and the fracture zone in the tensile test is not located in the weld area. Preferably, the fiber laser has an average power of 2000W, a scanning speed of 100mm / s, and a wavelength of 1000nm.

[0072] This embodiment describes the application of rare-earth high-strength duplex steel in lightweight automotive bodies.

[0073] A lightweight automobile body is prepared from rare-earth high-strength dual-phase steel according to this embodiment.

[0074] Rare earth high-strength duplex steel components obtained using the welding method of this embodiment.

[0075] This embodiment describes the application of rare-earth high-strength duplex steel components in lightweight automotive bodies.

[0076] A lightweight automobile body is prepared from rare-earth high-strength dual-phase steel components according to this embodiment.

[0077] The rare-earth high-strength dual-phase steel in this embodiment has a yield strength of 720 MPa, a tensile strength of 1000 MPa, and an elongation of 22%, achieving a synergistic improvement in strength and toughness. Furthermore, in this embodiment, when the inner corner radius at the bend is 0.2 mm, the ultimate bending angle is 117 degrees. Example 3

[0078] A rare-earth high-strength dual-phase steel has the following chemical composition and mass percentage: C: 0.10%; Si: 0.5%; Mn: 2.5%; Als: 0.050%; Nb: 0.03%; Ti: 0.03%; Cr: 0.2%; Ce: 50ppm; Y: 12.5ppm; P: 0.012%; S: 0.002%; N: 0.004%, with the remainder being Fe and unavoidable impurities. The mass ratio of Ce to Y is 4:1.

[0079] A method for forming rare-earth high-strength dual-phase steel includes the following steps: Converter smelting: Add raw materials other than rare earth elements for alloying treatment. The converter temperature is 1550℃ and the time is 1 hour.

[0080] LF refining: The molten steel inlet temperature is 1550℃, and the refining time is 30 minutes. Argon gas is used for strong stirring at the bottom of the ladle to quickly remove sulfur from the molten steel.

[0081] RH refining: Molten steel exits the LF refining furnace and undergoes RH refining with a vacuum of 90 Pa for 40 minutes. The temperature of the molten steel exiting the furnace is 1600℃.

[0082] Ferrocerium (CeFe90) and yttrium (FeY30) are added at the end of RH refining or before continuous casting.

[0083] Continuous casting: Molten steel with added cerium iron and yttrium iron is poured into the tundish. During the pouring process, protective slag (commercially available product, Shinagawa 43A special protective slag) is added. The molten steel temperature in the tundish is 1550℃, and the casting speed is 1.5m / min to obtain the cast billet.

[0084] Hot rolling: The rolling process is carried out in three stages. First stage: Rolling entry temperature 1180℃; total rolling reduction rate 60%, single-pass rolling reduction 15%, final rolling temperature 1100℃; this stage ensures the dissolution of rare earth element inclusions and uniform distribution of composition, eliminates segregation, reduces the resistance of subsequent forming (such as room temperature stamping), and, in conjunction with large reduction rolling, eliminates the ferrite / martensite banded structure that is prone to occur in hot rolling, preventing cracking along the banded line during subsequent forming.

[0085] Second stage: Rolling entry temperature 1080℃; total rolling reduction 65%, single-pass rolling reduction 18%, final rolling temperature 1030℃; this stage refines ferrite grains, improves toughness, lays the foundation for obtaining a fine ferrite / martensite dual-phase structure in the finished product, and improves strength.

[0086] The third stage: the rolling inlet temperature is 1020℃; the total rolling reduction rate is 75%, the single-pass rolling reduction is 12%, and the final rolling temperature is 750℃; this stage further refines the ferrite grains and controls a large number of fine ferrite nuclei to prepare for obtaining fine grains in the finished product.

[0087] After hot rolling, the material is cooled at a rate of 10℃ / s, with a coiling temperature of 530℃ and a hot-rolled thickness of 2mm, to provide a uniform microstructure for subsequent annealing.

[0088] Cold rolling: with a reduction rate of 65%, sufficient deformation energy is accumulated, and the finished product thickness is 0.7mm. Steel of this thickness is used for automobile bodies, achieving lightweighting of automobile bodies while ensuring quality and safety.

[0089] Three-stage annealing (organic regulation): Soaking zone: 830℃ for 370s: This keeps the steel coil in the ferrite + austenite two-phase region, allowing carbon to diffuse into the austenite.

[0090] Rapid cooling section: Cool to 350℃ at 50℃ / s and hold for 250s to force austenite to transform into martensite.

[0091] Over-aging stage: Hold at 250℃ for 360s: Eliminate internal stress, moderately temper the martensite, balance strength and toughness, and obtain rare earth high-strength dual-phase steel.

[0092] A high-quality weld can be formed by irradiating the butt joint of two rare-earth high-strength duplex steels with a fiber laser. The weld is fully martensitic, and the fracture zone in the tensile test is not located in the weld area. Preferably, the fiber laser has an average power of 4000W, a scanning speed of 150mm / s, and a wavelength of 1500nm.

[0093] This embodiment describes the application of rare-earth high-strength duplex steel in lightweight automotive bodies.

[0094] A lightweight automobile body is prepared from rare-earth high-strength dual-phase steel according to this embodiment.

[0095] Rare earth high-strength duplex steel components obtained using the welding method of this embodiment.

[0096] This embodiment describes the application of rare-earth high-strength duplex steel components in lightweight automotive bodies.

[0097] A lightweight automobile body is prepared from rare-earth high-strength dual-phase steel components according to this embodiment.

[0098] The rare-earth high-strength dual-phase steel in this embodiment has a yield strength of 745 MPa, a tensile strength of 1050 MPa, and an elongation of 19%, achieving a synergistic improvement in strength and toughness. Furthermore, in this embodiment, when the inner corner radius at the bend is 0.2 mm, the limiting bending angle is 135 degrees. Example 4

[0099] The only difference between this embodiment and Embodiment 1 is that Ce: 100ppm; Y: 25ppm. Example 5

[0100] The only difference between this embodiment and Embodiment 1 is that: Ce: 90ppm; Y: 30ppm, with a mass ratio of Ce to Y of 3:1. Example 6

[0101] The only difference between this embodiment and Embodiment 1 is that Ce: 40ppm; Y: 10ppm.

[0102] Comparative Example 1

[0103] The only difference between this comparative example and Example 1 is that: Ce: 80ppm; Y: 16ppm, with a mass ratio of Ce to Y of 5:1.

[0104] The rare earth high-strength dual-phase steel in this comparative example has a yield strength of 701 MPa, a tensile strength of 905 MPa, and an elongation of 13%.

[0105] The rare earth high-strength dual-phase steel obtained in this comparative example was cold-stamped and then tested for its ultimate bending angle. When the radius of the fillet on the inner side of the material at the bend was 0.2 mm, the ultimate bending angle was 83 degrees.

[0106] Comparative Example 2

[0107] The only difference between this comparative example and Example 1 is that: Ce: 80ppm; Y: 40ppm, with a mass ratio of Ce to Y of 2:1.

[0108] The yield strength of the rare earth high-strength dual-phase steel in this comparative example is 709 MPa, the tensile strength is 890 MPa, and the elongation is 15%.

[0109] The rare earth high-strength dual-phase steel obtained in this comparative example was cold-stamped and then tested for its ultimate bending angle. When the radius of the fillet on the inner side of the material at the bend was 0.2 mm, the ultimate bending angle was 85 degrees.

[0110] Comparative Example 3

[0111] The only difference between this comparative example and Example 1 is that: The three-stage hot rolling in Example 1 was replaced with a one-stage hot rolling, with a hot rolling inlet temperature of 1170°C, a final rolling temperature of 1080°C, a total rolling reduction of 70%, and a single-pass rolling reduction of 10%.

[0112] The rare earth high-strength dual-phase steel in this comparative example has a yield strength of 680 MPa, a tensile strength of 850 MPa, and an elongation of 17%.

[0113] The rare earth high-strength dual-phase steel obtained in this comparative example, after cold stamping, was tested for its ultimate bending angle. When the radius of the fillet on the inner side of the material at the bend was 0.2 mm, the ultimate bending angle was 81 degrees.

[0114] Comparative Example 4

[0115] The only difference between this comparative example and Example 1 is that: Hot rolling: The rolling process is carried out in three stages. First stage: Rolling entry temperature 1130℃; total rolling reduction 55%, single-pass rolling reduction 5%, final rolling temperature 980℃; Second stage: Rolling entry temperature 1000℃; total rolling reduction 62%, single-pass rolling reduction 10%, final rolling temperature 980℃; Third stage: Rolling entry temperature 950℃; total rolling reduction rate 70%, single-pass rolling reduction 4%, final rolling temperature 680℃.

[0116] The rare earth high-strength dual-phase steel in this comparative example has a yield strength of 712 MPa, a tensile strength of 925 MPa, and an elongation of 13%.

[0117] The rare-earth high-strength dual-phase steel obtained in this comparative example was cold-stamped and then tested for its ultimate bending angle. When the radius of the fillet on the inner side of the material at the bend was 0.2 mm, the ultimate bending angle was 85 degrees.

[0118] Comparative Example 5

[0119] The only difference between this comparative example and Example 1 is that: Hot rolling: The rolling process is carried out in three stages. First stage: Rolling entry temperature 1200℃; total rolling reduction 55%, single-pass rolling reduction 8%, final rolling temperature 1150℃; Second stage: Rolling entry temperature 1100℃; total rolling reduction 62%; single-pass rolling reduction 20%; final rolling temperature 1050℃. Third stage: Rolling entry temperature 1030℃; total rolling reduction rate 70%, single-pass rolling reduction 13%, final rolling temperature 780℃.

[0120] The rare earth high-strength dual-phase steel in this comparative example has a yield strength of 702 MPa, a tensile strength of 930 MPa, and an elongation of 13%.

[0121] The rare earth high-strength dual-phase steel obtained in this comparative example was cold-stamped and then tested for its ultimate bending angle. When the radius of the fillet on the inner side of the material at the bend was 0.2 mm, the ultimate bending angle was 85 degrees.

[0122] Comparative Example 6

[0123] The only difference between this comparative example and Example 1 is that: Three-stage annealing: Heating zone: 750℃ for 200 seconds Rapid cooling section: Cool to 250℃ at a rate of 20℃ / s and hold for 100s; Over-aging stage: Hold at 150℃ for 200s to obtain rare earth high-strength dual-phase steel.

[0124] The rare earth high-strength dual-phase steel in this comparative example has a yield strength of 700 MPa, a tensile strength of 910 MPa, and an elongation of 14%.

[0125] The rare earth high-strength dual-phase steel obtained in this comparative example was cold-stamped and then tested for its ultimate bending angle. When the radius of the fillet on the inner side of the material at the bend was 0.2 mm, the ultimate bending angle was 86 degrees.

[0126] Comparative Example 7

[0127] The only difference between this comparative example and Example 1 is that: Three-stage annealing: Immersion heating zone: 850℃ for 400 seconds Rapid cooling section: Cool to 400℃ at a rate of 10℃ / s and hold for 300s; Over-aging stage: Hold at 280℃ for 380s to obtain rare earth high-strength dual-phase steel.

[0128] The rare earth high-strength dual-phase steel in this comparative example has a yield strength of 709 MPa, a tensile strength of 915 MPa, and an elongation of 13.5%.

[0129] The rare earth high-strength dual-phase steel obtained in this comparative example was cold-stamped and then tested for its ultimate bending angle. When the radius of the fillet on the inner side of the material at the bend was 0.2 mm, the ultimate bending angle was 85 degrees.

[0130] After the rare earth high-strength dual-phase steels obtained in Comparative Examples 1-7 were welded using the process of Example 1, the weld contained ferrite and segregated rare earth inclusions. The fracture area in the tensile test was in the weld area.

[0131] In the foregoing description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof. However, this disclosure should not be construed as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, the inventive aspect lies in fewer than all features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0132] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0133] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A rare-earth high-strength dual-phase steel, characterized in that, The chemical composition and its mass percentage are as follows: C: 0.08-0.10%; Si: 0.3-0.5%; Mn: 1.3-2.5%; Als: 0.025-0.050%; Nb: 0.02-0.03%; Ti: 0.02-0.03%; Cr: 0.1-0.2%; Ce: 40-100ppm; Y: 10-30ppm, P: ≤0.015%; S: ≤0.003%; N: ≤0.005%, the remainder being Fe and unavoidable impurity elements; wherein the mass ratio of Ce to Y is (4-3):

1.

2. The forming method of rare earth high-strength dual-phase steel according to claim 1, characterized in that, Includes the following steps: Converter smelting: Add raw materials other than rare earth elements for alloying treatment. The converter temperature is 1500-1550℃ and the time is 0.5-1h. LF refining: The temperature of molten steel entering the station is 1500-1550℃, and the refining time is 15-30 minutes; argon gas is blown from the bottom of the ladle to stir and remove sulfur from the molten steel; RH refining: Molten steel exits the LF refining furnace and undergoes RH refining with a vacuum degree ≤100Pa, a refining time of 30-40min, and a molten steel exit temperature of 1550-1600℃. Ferrocerium and yttrium are added at the end of RH refining or before continuous casting; Continuous casting: Molten steel with added cerium iron and yttrium iron is poured into the tundish. During the pouring process, protective slag is added. The temperature of the molten steel in the tundish is 1500-1550℃, and the casting speed is 1.0-1.5m / min to obtain the billet. Hot rolling: The rolling process is carried out in three stages. First stage: Rolling entry temperature 1150-1180℃; total rolling reduction 50-60%, single-pass rolling reduction ≥10%, final rolling temperature 1050-1100℃; Second stage: Rolling entry temperature 1030-1080℃; total rolling reduction 60-65%; single-pass rolling reduction 13-18%; final rolling temperature 1000-1030℃. Third stage: Rolling entry temperature 980-1020℃; total rolling reduction 65-75%; single-pass rolling reduction 5-12%; final rolling temperature 700-750℃. After hot rolling, the cooling rate is 6-10℃ / s, the coiling temperature is 500-530℃, and the hot-rolled thickness is 2-3mm. Cold rolling: reduction rate 50%-65%, cold-rolled finished product thickness 0.7-1.5mm; Three-stage annealing: Immersion heating zone: 780-830℃, maintained for 250-370 seconds. Rapid cooling section: Cool to 280-350℃ at ≥30℃ / s and hold for 120-250s; Over-aging stage: Hold at 200-250℃ for 230-360s to obtain rare earth high-strength dual-phase steel.

3. The rare-earth high-strength dual-phase steel obtained by the forming method according to claim 2, characterized in that, Its yield strength is 720-745MPa, tensile strength is 1000-1050MPa, and elongation is 19-22%. After cold stamping, the dimensional accuracy of the parts is ±0.05mm. When the inner radius of the bend is 0.2mm, the limit bending angle is 90-135 degrees.

4. The welding method for rare earth high-strength duplex steel according to claim 3, characterized in that, High-quality welds can be formed by irradiating the joint of two rare-earth high-strength duplex steels with a fiber laser. The welds are fully martensitic, and the fracture zone in the tensile test is not in the weld area.

5. The welding method according to claim 4, characterized in that, The average power of the fiber laser is 2000-4000W, the scanning speed is 100-150mm / s, and the wavelength is 1000-1500nm.

6. Rare earth high-strength duplex steel components obtained by the welding method according to claim 4.

7. The application of the rare earth high-strength duplex steel according to claim 3 in lightweight automobile bodies.

8. A lightweight automobile body, made of the rare earth high-strength dual-phase steel as described in claim 3.

9. The application of the rare earth high-strength dual-phase steel component according to claim 6 in lightweight automobile bodies.

10. A lightweight automobile body, made from the rare earth high-strength dual-phase steel component as described in claim 6.

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