Low-cost rare earth high-strength dual-phase steel, and preparation method and application thereof

Abstract

The application discloses a low-cost rare earth high-strength dual-phase steel and a preparation method and application thereof, and belongs to the technical field of rare earth dual-phase steel. The low-cost rare earth high-strength dual-phase steel has the following chemical component compositions and mass percentages: C: 0.05-0.09%; Si: 0.3-0.5%; Mn: 1.0-1.5%; Als: 0.020-0.055%; Cr: 0.25-0.55%; Ti: 0.05-0.09%; Ce: 0.0030-0.0070%; P: <=0.010%; S: <=0.004%; N: <=0.004%, and the rest is Fe and inevitable impurity elements. The application does not add molybdenum and niobium, and through the addition of Mn and Si elements in a specific proportion, Cr and Ti in a specific proportion and rare earth Ce, and in combination with a multi-stage homogenization treatment process, a high-elongation, high-hardness, low-cost rare earth high-strength dual-phase steel is obtained.

Description

Technical Field

[0001] This invention belongs to the field of rare earth dual-phase steel technology, and relates to a low-cost rare earth high-strength dual-phase steel, its preparation method and application, especially a 780MPa-level low-cost rare earth high-strength dual-phase steel, its preparation method and application. Background Technology

[0002] Molybdenum (Mo) is present in the Earth's crust at a concentration of approximately 1.5 ppm (parts per million), equivalent to 1.5 grams per ton of rock, making it a globally scarce strategic mineral. Molybdenum has a very high melting point and is widely used in industry to manufacture steel alloys. Molybdenum possesses high strength, high hardness, and excellent mechanical properties, maintaining these characteristics even at high temperatures. Molybdenum is primarily used in steelmaking; alloy steels incorporating Molybdenum exhibit high strength, high toughness, outstanding heat resistance, and corrosion resistance.

[0003] Similarly, niobium's abundance in the Earth's crust is generally estimated at 0.002% (20 ppm), classifying it as a rare element. Niobium is primarily used in high-strength alloys (such as those used in aerospace, nuclear industry, and superconducting materials). It is an important microalloying element with multiple key roles in the steel industry, including grain refinement, precipitation strengthening, improved weldability, enhanced heat and corrosion resistance, and improved performance in high-temperature alloys. Currently, the main challenge for 780-grade duplex steel is cracking during high-speed stamping. High-speed stamping is accompanied by localized temperature rises, which may activate hydrogen-induced delayed cracking. Handan Iron & Steel's customized HC420 / 780DP successfully solved the cracking problem in the inner panel of the car door through microalloying design and optimized controlled rolling and cooling + annealing processes. However, the hardness of HC420 / 780DP is below 300 HB, and its wear resistance and impact resistance need to be improved.

[0004] Therefore, there is an urgent need for a rare earth high-strength duplex steel that is free of molybdenum and niobium, and is wear-resistant, low-cost, has a long service life, excellent formability, does not crack during high-speed stamping, and has good weldability, as well as its preparation method and application. Summary of the Invention

[0005] The purpose of this invention is to provide a rare earth high-strength duplex steel that is free of molybdenum and niobium, and is wear-resistant, low-cost, has a long service life, excellent formability, does not crack during high-speed stamping, and has good weldability.

[0006] Meanwhile, this invention provides a low-cost method for preparing rare-earth high-strength dual-phase steel. In this method, Ti preferentially combines with carbon to avoid chromium forming chromium carbide, retaining the chromium content at grain boundaries, maintaining wear resistance, and improving wear life. At the same time, Mn and Si are dissolved in ferrite in large quantities and efficiently to form a substitution solid solution, which hinders dislocation movement through lattice distortion, thereby achieving solid solution strengthening. Combined with rare-earth elements, it synergistically refines the grains and improves the hardness, wear resistance, and formability of the dual-phase steel.

[0007] Meanwhile, this invention provides an application of low-cost rare-earth high-strength duplex steel in wear-resistant components.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A low-cost, high-strength rare-earth dual-phase steel has the following chemical composition and mass percentage: C: 0.05-0.09%; Si: 0.3-0.5%; Mn: 1.0-1.5%; Als: 0.020-0.055%; Cr: 0.25-0.55%; Ti: 0.05-0.09%; Ce: 0.0030-0.0070%; P: ≤0.010%; S: ≤0.004%; N: ≤0.004%, with the remainder being Fe and unavoidable impurities. The mass ratio of Si to Mn is 1:(2-5); the mass ratio of Cr to Ti is (10-11):(1-3.6).

[0009] A method for preparing low-cost rare-earth high-strength dual-phase steel includes the following steps: Converter smelting: Alloying treatment is carried out by adding raw materials other than rare earth element Ce. The final temperature is 1600-1650℃, and the converter smelting time is 60-100min. Oxygen is then blown and quicklime is added for slag formation. The steel is tapped using a sliding plate to block the slag and obtain molten steel.

[0010] LF refining: Heat to 1650-1680℃, use argon gas to strongly stir the ladle, slag formation and desulfurization, LF refining time is 30-40min.

[0011] RH refining: Molten steel exits the LF refining furnace and undergoes RH refining with a vacuum degree ≤100Pa, a refining time of 10-20 minutes, and a steel exit temperature of 1550-1600℃. Rare earth element Ce is added 1-3 minutes before the RH refining is completed.

[0012] Continuous casting: Molten steel with added Ce enters 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 1600-1700℃, and the casting speed is 1.0-1.5m / min. After the molten steel solidifies and is cooled to room temperature, it is taken out to obtain the billet.

[0013] Multi-stage homogenization treatment: The billet is heated to 950-1050℃ at 10-20℃ / min and held for 1-2 hours, then heated to 1050-1200℃ at 20-30℃ / min and held for 1-2 hours, then cooled to 850-950℃ at 80-100℃ / min and held for 5-8 hours, and finally cooled to room temperature at 5-10℃ / min.

[0014] Multi-stage homogenization treatment can release residual stress and allow Mn and Si to dissolve into ferrite in large quantities, distributing them more evenly in the matrix. This further eliminates casting defects and creates a uniform microstructure, preparing the material for subsequent rolling. Simultaneously, the multi-stage homogenization treatment of this invention enables Ti to preferentially combine with carbon, preventing chromium from forming chromium carbide, retaining grain boundary chromium content, maintaining wear resistance, and improving wear life.

[0015] Simultaneously, multi-stage homogenization treatment allows a large amount of Mn and Si to dissolve into ferrite, forming a substitutional solid solution. This solid solution strengthens the steel by hindering dislocation movement through lattice distortion. Combined with the addition of specific proportions of Cr, Ti, and rare earth element Ce, the grains are synergistically refined (ferrite grain size ≥ 10), improving the plasticity and toughness of the rare earth dual-phase steel, and enhancing its hardness and wear resistance. This process yields a high-elongation, high-hardness, and low-cost rare earth high-strength dual-phase steel.

[0016] Hot rolling process: hot rolling inlet temperature 1100-1150℃, final rolling temperature 920-950℃, coiling temperature 500-600℃, hot rolling thickness 1-2.5mm.

[0017] Cold rolling process: reduction rate 60-65%, rolling force 30-40MN, finished product thickness 0.4-1mm, resulting in a finished product with good shape, good edge plasticity, and no edge cracks or thickness fluctuation defects.

[0018] Continuous annealing process: In the annealing furnace, the process speed is 100-120m / min, the temperature of the slow cooling section is 650-680℃, the temperature of the soaking section is 700-800℃, the temperature of the rapid cooling section is 250-300℃, and the flattening elongation is 49-51%. The continuous annealing process improves the product strength and forming performance through high temperature soaking and low temperature rapid cooling.

[0019] The low-cost rare-earth high-strength dual-phase steel obtained by this invention has a yield strength of 425-470 MPa, a tensile strength of 800-880 MPa, a hardness of 310-330 HB, an elongation of 31-38%, a grain size of 10.0-12.0, and an abrasion wear of 5.0-10.2 mm. 3 / m, achieving a synergistic improvement in strength, toughness, and wear resistance.

[0020] In the prior art, high elongation (31-38%) dual-phase steel indicates that the material has good plasticity and its hardness is generally less than 300 HB. In this invention, through multi-stage homogenization treatment combined with the addition of rare earth elements, specific Mn and Si elements, a high elongation, high hardness, and low cost rare earth high-strength dual-phase steel is obtained.

[0021] The low-cost rare-earth high-strength dual-phase steel of the present invention is composed of two phases, ferrite and martensite, and has a low yield strength ratio, high elongation, and high processing hardness. It is suitable for deep drawing and bulging of complex shapes and can be efficiently formed at room temperature and stamping speed of 50-800 mm / s without cracking.

[0022] 1. Forming conditions 1. When the low-cost rare earth high-strength dual-phase steel of this invention is transversely formed, the radius of the extreme sharp corner rounded corner R≥0.2mm can stably achieve defect-free forming of stamping inner angle number ≤165°; the radius of the extreme sharp corner rounded corner R≥0.4mm can achieve stable forming of any stamping inner angle in the full range of 0°-180°.

[0023] 2. When forming low-cost rare-earth high-strength dual-phase steel longitudinally, the radius of the extreme sharp corner radius R is ≥ 0.2mm, which can achieve one-time defect-free forming of any stamping inner corner in the full range of 0°-180°.

[0024] II. Supporting Molding Process Conditions In the low-cost rare-earth high-strength dual-phase steel forming process of this invention, the matching process parameters are adapted to its excellent forming performance, which can further ensure forming quality and improve production efficiency, as detailed below: Molding temperature: The above molding requirements can be stably achieved by using room temperature molding, without the need for additional heating or cooling, thus reducing production costs.

[0025] Stamping speed: It is suitable for high-speed continuous stamping and conventional stamping processes. The stamping speed can be controlled between 50mm / s and 800mm / s. When stamping at high speed (150mm / s-800mm / s), it can still ensure that the forming is defect-free and the dimensional consistency is good, which can meet the needs of mass production.

[0026] Blank clamping force: The blank clamping force is controlled between 80kN and 300kN, which can effectively suppress wrinkling and warping of the sheet during the forming process, and ensure that the forming surface is smooth and the contour is regular. For every 0.5mm increase in sheet thickness, the blank clamping force can be increased by 30kN to 50kN, which is highly adaptable.

[0027] III. Performance Advantages Compared with conventional high-strength dual-phase steel, the low-cost rare-earth high-strength dual-phase steel of this invention has better formability and a wider process window. Under the above-mentioned forming conditions and supporting processes, it can realize complex processing such as precision sharp corners, full-angle bending, and high-speed continuous stamping, and the forming efficiency is improved by more than 20%. It balances low cost and high performance and is suitable for the component manufacturing needs of multiple fields such as automobiles and home appliances.

[0028] The low-cost rare-earth high-strength duplex steel of this invention is subjected to narrow lap welding, resulting in a wide welding process window. Even at high-speed welding speeds of 10-12 m / min, a stable welding process is maintained without significant spatter, incomplete fusion, or porosity defects. A combination of parameters—lap length of 1.1-1.2 mm, welding pressure of 17-18 KN, and welding temperature of 1110-1120℃—achieves rapid and efficient welding, increasing production efficiency by over 30% compared to conventional lap welding. During welding, rare-earth Ce purifies the molten pool and pins grain boundaries, effectively suppressing grain coarsening under welding thermal cycling. No complex preheating or post-heat treatment is required; only simple low-temperature stress relief treatment is needed to meet performance requirements. The process is simple, cost-controllable, suitable for automated mass production, and exhibits good welding consistency.

[0029] After narrow lap welding of the low-cost rare-earth high-strength duplex steel of this invention, the tensile strength of the welded joint is ≥95% of that of the base material, and the yield strength is ≥90% of that of the base material. All fractures occur in the base material region, with no joint fracture, thus meeting the stress requirements of the structural components. The welded joint deformation is small: narrow lap welding combined with precise parameter control results in welding deformation ≤0.03mm / mm. This leads to high dimensional accuracy after welding thin plates, good joint flatness, and no warping or deformation at the lap edges.

[0030] This invention provides an application of low-cost rare-earth high-strength duplex steel in wear-resistant parts, including wear-resistant parts for automobiles or wear-resistant parts for household appliances.

[0031] This invention provides an application of low-cost rare-earth high-strength duplex steel in automotive wear-resistant parts, including engine underbody protection plates, chassis protection plates, etc.

[0032] This invention provides an application of low-cost rare-earth high-strength duplex steel in wear-resistant parts for home appliances, including slicer blades, washing machine drums, etc.

[0033] A wear-resistant component is prepared from a low-cost rare-earth high-strength duplex steel according to the present invention.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows: In this invention, a low-cost rare-earth high-strength dual-phase steel is produced without the addition of molybdenum or niobium. Through the addition of specific proportions of Mn and Si elements, specific proportions of Cr and Ti elements, and rare-earth Ce, combined with multi-stage homogenization processes, a high-elongation, high-hardness, and low-cost rare-earth high-strength dual-phase steel is obtained. This solves the problem of the inverse relationship between high elongation and high hardness / wear resistance, resulting in a low-cost rare-earth high-strength dual-phase steel with low production costs, wear resistance, and long service life. It is particularly suitable for applications in abrasive environments, exhibiting excellent overall economic performance.

[0035] This invention discloses a low-cost, high-strength rare-earth dual-phase steel preparation method. In this method, Mn and Si are dissolved in ferrite in large quantities and efficiently to form a substitution solid solution. This solid solution strengthens the steel by hindering dislocation movement through lattice distortion. At the same time, Ti preferentially combines with carbon to prevent chromium from forming chromium carbide, thus maintaining the chromium content at grain boundaries, preserving wear resistance, and improving wear life. Furthermore, the combination of rare-earth elements synergistically refines the grain size (to 10-12 grade), improves the hardness, wear resistance, and formability of the dual-phase steel. Attached Figure Description

[0036] Figure 1 This is a microstructure diagram of the present invention. Detailed Implementation

[0037] 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

[0038] A low-cost, high-strength rare-earth dual-phase steel has the following chemical composition and mass percentage: C: 0.07%; Si: 0.4%; Mn: 1.2%; Al: 0.035%; Cr: 0.40%; Ti: 0.08%; Ce: 0.0050%; P: 0.005%; S: 0.003%; N: 0.002%, with the remainder being Fe and unavoidable impurities. The mass ratio of Si to Mn is 1:3; the mass ratio of Cr to Ti is 10:2.

[0039] A method for preparing low-cost rare-earth high-strength dual-phase steel includes the following steps: Converter smelting: Alloying treatment is carried out by adding raw materials other than rare earth element Ce. The final temperature is 1625℃ and the converter smelting time is 80min. Oxygen is then blown and quicklime is added to form slag. The steel is tapped using a sliding plate to block the slag and obtain molten steel.

[0040] LF refining: Heat to 1665℃, use argon gas to stir strongly at the bottom of the ladle, slag formation and desulfurization, LF refining time is 35min.

[0041] RH refining: Molten steel exits the LF refining furnace and undergoes RH refining at a vacuum of 100 Pa for 15 minutes. The steel exit temperature is 1570℃. Rare earth element Ce is added 2 minutes before the RH refining is completed.

[0042] Continuous casting: Molten steel with added Ce enters 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 1650℃, and the casting speed is 1.2m / min. After the molten steel solidifies and is cooled to room temperature, it is taken out to obtain the billet.

[0043] Multi-stage homogenization treatment: The billet is heated to 1000℃ at 15℃ / min and held for 1.5h, then heated to 1120℃ at 25℃ / min and held for 1.5h, then cooled to 900℃ at 90℃ / min and held for 6.5h, and finally cooled to room temperature at 8℃ / min.

[0044] Hot rolling process: hot rolling inlet temperature 1125℃, final rolling temperature 930℃, coiling temperature 550℃, hot rolling thickness 2mm.

[0045] Cold rolling process: 60% reduction rate, 35MN rolling force, 0.8mm finished product thickness. The resulting finished product has good shape, good edge plasticity, and no edge cracks or thickness fluctuation defects.

[0046] Continuous annealing process: In the annealing furnace, the process speed is 110m / min, the temperature of the slow cooling section is 660℃, the temperature of the soaking section is 750℃, the temperature of the rapid cooling section is 280℃, and the flattening elongation is 50%. The continuous annealing process improves the product strength and forming performance through high temperature soaking and low temperature rapid cooling.

[0047] The low-cost rare-earth high-strength dual-phase steel obtained in this embodiment has a yield strength of 468 MPa, a tensile strength of 875 MPa, a hardness of 324 HB, an elongation of 31.5%, a grain size of 12.0 grade, and a wear rate of 5.0 mm. 3 / m, achieving a synergistic improvement in strength, toughness, and wear resistance.

[0048] In this embodiment, when the low-cost rare-earth high-strength dual-phase steel is transversely formed, the radius of the extreme sharp corner rounded corner R is greater than or equal to 0.2 mm, which can stably achieve defect-free forming of stamping inner angles ≤ 165°; the radius of the extreme sharp corner rounded corner R is greater than or equal to 0.4 mm, which can stably form any stamping inner angle in the full range of 0°-180°.

[0049] In this embodiment, when the low-cost rare-earth high-strength dual-phase steel is longitudinally formed, the radius of the extreme sharp corner rounded corner R is ≥ 0.2mm, which can achieve one-time defect-free forming of any stamping inner corner in the full range of 0°-180°.

[0050] In the low-cost rare-earth high-strength dual-phase steel forming process of this embodiment, the forming temperature can be stably achieved by using room temperature forming, without the need for additional heating or cooling, thus reducing production costs.

[0051] Stamping speed: It is suitable for high-speed continuous stamping and conventional stamping processes. The stamping speed can be controlled between 50mm / s and 800mm / s. When stamping at high speed (150mm / s-800mm / s), it can still ensure that the forming is defect-free and the dimensional consistency is good, which can meet the needs of mass production.

[0052] Blank clamping force: The blank clamping force is controlled between 80kN and 300kN, which can effectively suppress wrinkling and warping of the sheet during the forming process, and ensure that the forming surface is smooth and the contour is regular. For every 0.5mm increase in sheet thickness, the blank clamping force can be increased by 30kN to 50kN, which is highly adaptable.

[0053] The low-cost rare-earth high-strength duplex steel of this embodiment is subjected to narrow lap welding, which has a wide welding process window. It can maintain a stable welding process even at a high welding speed of 10-12m / min, without obvious defects such as spatter, lack of fusion, and porosity. The parameter combination of lap amount of 1.1-1.2mm, welding pressure of 17-18KN, and welding temperature of 1110-1120℃ can achieve fast and efficient welding, and the production efficiency is increased by more than 30% compared with conventional lap welding.

[0054] After narrow lap welding of the low-cost rare-earth high-strength duplex steel in this embodiment, the tensile strength of the welded joint is ≥95% of the base material, and the yield strength is ≥90% of the base material. All fractures occur in the base material region, with no joint fractures, thus meeting the structural stress requirements. The welded joint deformation is small: narrow lap welding combined with precise parameter control results in welding deformation ≤0.03mm / mm. This leads to high dimensional accuracy after welding thin plates, good joint flatness, and no warping or deformation at the lap edges.

[0055] This embodiment provides an application of low-cost rare-earth high-strength duplex steel in wear-resistant parts, including wear-resistant parts for automobiles or wear-resistant parts for household appliances.

[0056] This embodiment provides an application of low-cost rare-earth high-strength duplex steel in automotive wear-resistant parts, including engine underbody protection plates, chassis protection plates, etc.

[0057] This invention relates to the application of a low-cost rare-earth high-strength duplex steel in wear-resistant parts for home appliances, including blades for slicers and drums for washing machines.

[0058] A wear-resistant component is prepared from a low-cost rare-earth high-strength duplex steel according to this embodiment.

[0059] like Figure 1As shown in this embodiment, the ferrite grain size of the finally obtained low-cost rare earth high-strength dual-phase steel is grade 12, which is fine and thus plays a role in synergistically improving high hardness and high toughness. Example 2

[0060] The only difference between this embodiment and Embodiment 1 is that: A low-cost, high-strength rare-earth dual-phase steel has the following chemical composition and mass percentage: C: 0.06%; Si: 0.5%; Mn: 1.0%; Als: 0.040%; Cr: 0.25%; Ti: 0.09%; Ce: 0.0050%; P: 0.010%; S: 0.004%; N: 0.004%, with the remainder being Fe and unavoidable impurities. The mass ratio of Si to Mn is 1:2; the mass ratio of Cr to Ti is 10:3.6.

[0061] A method for preparing low-cost rare-earth high-strength dual-phase steel includes the following steps: Converter smelting: Alloying treatment is carried out by adding raw materials other than rare earth element Ce. The final temperature is 1640℃ and the converter smelting time is 90min. Oxygen is then blown and quicklime is added to form slag. The steel is tapped using a sliding plate to block the slag and obtain molten steel.

[0062] LF refining: Heat to 1660℃, use argon gas to stir strongly at the bottom of the ladle, slag formation and desulfurization, LF refining time is 38min.

[0063] RH refining: Molten steel exits the LF refining furnace and undergoes RH refining at a vacuum of 90 Pa for 12 minutes. The steel exit temperature is 1580℃. Rare earth element Ce is added 2 minutes before the RH refining is completed.

[0064] Continuous casting: Molten steel with added Ce enters 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 1660℃, and the casting speed is 1.3m / min. After the molten steel solidifies and is cooled to room temperature, it is taken out to obtain the billet.

[0065] Multi-stage homogenization treatment: The billet is heated to 980℃ at 18℃ / min and held for 1 hour, then heated to 1150℃ at 22℃ / min and held for 1 hour, then cooled to 880℃ at 85℃ / min and held for 6 hours, and finally cooled to room temperature at 9℃ / min.

[0066] Hot rolling process: hot rolling inlet temperature 1110℃, final rolling temperature 940℃, coiling temperature 580℃, hot rolling thickness 1.5mm.

[0067] Cold rolling process: reduction rate 65%, rolling force 33MN, finished product thickness 0.525mm, the obtained finished product has good shape, good edge plasticity, and no edge cracks or thickness fluctuation defects.

[0068] Continuous annealing process: In the annealing furnace, the process speed is 105m / min, the temperature of the slow cooling section is 670℃, the temperature of the soaking section is 770℃, the temperature of the rapid cooling section is 260℃, and the flattening elongation is 49%. The continuous annealing process improves the product strength and forming performance through high temperature soaking and low temperature rapid cooling.

[0069] The low-cost rare-earth high-strength dual-phase steel obtained by this invention has a yield strength of 460 MPa, a tensile strength of 859 MPa, a hardness of 321 HB, an elongation of 32%, a grain size of 11.0 grade, and a wear rate of 6.8 mm. 3 / m, achieving a synergistic improvement in strength, toughness, and wear resistance. Example 3

[0070] The only difference between this embodiment and Embodiment 1 is that: A low-cost, high-strength rare-earth dual-phase steel has the following chemical composition and mass percentage: C: 0.05%; Si: 0.3%; Mn: 1.5%; Als: 0.020%; Cr: 0.55%; Ti: 0.05%; Ce: 0.0030%; P: 0.010%; S: 0.004%; N: 0.004%, with the remainder being Fe and unavoidable impurities. The mass ratio of Si to Mn is 1:5; the mass ratio of Cr to Ti is 11:1.

[0071] A method for preparing low-cost rare-earth high-strength dual-phase steel includes the following steps: Converter smelting: Alloying treatment is carried out by adding raw materials other than rare earth element Ce. The final temperature is 1600℃ and the converter smelting time is 60min. Then oxygen is blown and quicklime is added to form slag. The steel is tapped by using a sliding plate to block the slag and obtain molten steel.

[0072] LF refining: Heat to 1650℃, use argon gas to stir strongly at the bottom of the ladle, slag formation and desulfurization, LF refining time is 30min.

[0073] RH refining: Molten steel exits the LF refining furnace and undergoes RH refining at a vacuum of 100 Pa for 10 minutes. The steel exit temperature is 1550℃. Rare earth element Ce is added 1 minute before the RH refining is completed.

[0074] Continuous casting: Molten steel with added Ce enters 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 1600℃, and the casting speed is 1.0m / min. After the molten steel solidifies and is cooled to room temperature, it is taken out to obtain the billet.

[0075] Multi-stage homogenization treatment: The billet is heated to 950℃ at 10℃ / min and held for 2 hours, then heated to 1050℃ at 20℃ / min and held for 2 hours, then cooled to 850℃ at 80℃ / min and held for 5 hours, and finally cooled to room temperature at 5℃ / min.

[0076] Hot rolling process: hot rolling inlet temperature 1100℃, final rolling temperature 920℃, coiling temperature 500℃, hot rolling thickness 2.5mm.

[0077] Cold rolling process: 60% reduction rate, 30MN rolling force, 1mm finished product thickness. The resulting finished product has good shape, good edge plasticity, and no edge cracks or thickness fluctuation defects.

[0078] Continuous annealing process: In the annealing furnace, the process speed is 100m / min, the temperature of the slow cooling section is 650℃, the temperature of the soaking section is 700℃, the temperature of the rapid cooling section is 250℃, and the flattening elongation is 49%. The continuous annealing process improves the product strength and forming performance through high temperature soaking and low temperature rapid cooling.

[0079] The low-cost rare-earth high-strength dual-phase steel obtained by this invention has a yield strength of 425 MPa, a tensile strength of 800 MPa, a hardness of 310 HB, an elongation of 38%, a grain size of 10.0 grade, and a wear rate of 10.2 mm. 3 / m, achieving a synergistic improvement in strength, toughness, and wear resistance. Example 4

[0080] The only difference between this embodiment and Embodiment 1 is that: A low-cost, high-strength rare-earth dual-phase steel has the following chemical composition and mass percentage: C: 0.09%; Si: 0.35%; Mn: 1.4%; Als: 0.055%; Cr: 0.40%; Ti: 0.05%; Ce: 0.0070%; P: 0.006%; S: 0.001%; ​​N: 0.002%, with the remainder being Fe and unavoidable impurities. The mass ratio of Si to Mn is 1:4; the mass ratio of Cr to Ti is 10:1.25.

[0081] A method for preparing low-cost rare-earth high-strength dual-phase steel includes the following steps: Converter smelting: Alloying treatment is carried out by adding raw materials other than rare earth element Ce. The final temperature is 1650℃ and the converter smelting time is 100min. Oxygen is then blown and quicklime is added to form slag. The steel is tapped using a sliding plate to block the slag and obtain molten steel.

[0082] LF refining: Heat to 1680℃, use argon gas to stir strongly at the bottom of the ladle, slag formation and desulfurization, LF refining time is 40min.

[0083] RH refining: Molten steel exits the LF refining furnace and undergoes RH refining at a vacuum of 80 Pa for 20 minutes. The steel exit temperature is 1600℃. Rare earth element Ce is added 3 minutes before the RH refining is completed.

[0084] Continuous casting: Molten steel with added Ce enters 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 1700℃, and the casting speed is 1.5m / min. After the molten steel solidifies and is cooled to room temperature, it is taken out to obtain the billet.

[0085] Multi-stage homogenization treatment: The billet is heated to 1050℃ at 20℃ / min and held for 1 hour, then heated to 1200℃ at 30℃ / min and held for 2 hours, then cooled to 950℃ at 100℃ / min and held for 8 hours, and finally cooled to room temperature at 10℃ / min.

[0086] Hot rolling process: hot rolling inlet temperature 1150℃, final rolling temperature 950℃, coiling temperature 600℃, hot rolling thickness 1mm.

[0087] Cold rolling process: reduction rate 60%, rolling force 40MN, finished product thickness 0.4mm, the obtained finished product has good shape, good edge plasticity, and no edge cracks or thickness fluctuation defects.

[0088] Continuous annealing process: In the annealing furnace, the process speed is 120m / min, the temperature of the slow cooling section is 680℃, the temperature of the soaking section is 800℃, the temperature of the rapid cooling section is 300℃, and the flattening elongation is 51%. The continuous annealing process improves the product strength and forming performance through high temperature soaking and low temperature rapid cooling.

[0089] The low-cost, high-strength rare-earth dual-phase steel obtained by this invention has a yield strength of 470 MPa, a tensile strength of 880 MPa, a hardness of 330 HB, an elongation of 31%, a grain size of 11.0 grade, and a wear resistance of 8.5 mm. 3 / m, achieving a synergistic improvement in strength, toughness, and wear resistance.

[0090] Comparative Example 1

[0091] The only difference between this comparative example and Example 1 is that: A low-cost, high-strength rare-earth dual-phase steel has the following chemical composition and mass percentage: C: 0.07%; Si: 0.5%; Mn: 0.75%; Al: 0.035%; Cr: 0.40%; Ti: 0.033%; Ce: 0.0050%; P: 0.005%; S: 0.003%; N: 0.002%, with the remainder being Fe and unavoidable impurities. The mass ratio of Si to Mn is 1:1.5; the mass ratio of Cr to Ti is 12:1.

[0092] Comparative Example 2

[0093] The only difference between this comparative example and Example 1 is that: A low-cost, high-strength rare-earth dual-phase steel has the following chemical composition and mass percentage: C: 0.07%; Si: 0.3%; Mn: 1.8%; Als: 0.035%; Cr: 0.40%; Ti: 0.16%; Ce: 0.0050%; P: 0.005%; S: 0.003%; N: 0.002%, with the remainder being Fe and unavoidable impurities. The mass ratio of Si to Mn is 1:6; the mass ratio of Cr to Ti is 10:4.

[0094] Comparative Example 3

[0095] The only difference between this comparative example and Example 1 is that: The multi-stage homogenization process is replaced with a single-stage homogenization process. The single-stage homogenization process involves heating the billet to 1000℃ and holding it for 10 hours, then cooling it to room temperature.

[0096] Comparative Example 4

[0097] The only difference between this comparative example and Example 1 is that: The multi-stage homogenization process was replaced with a two-stage homogenization process. The two-stage homogenization process involved heating the billet to 1000℃ at a rate of 15℃ / min and holding it at that temperature for 4 hours, then cooling it down to 900℃ at a rate of 90℃ / min and holding it at that temperature for 6 hours, and finally cooling it down to room temperature.

[0098] Comparative Example 5

[0099] The only difference between this comparative example and Example 1 is that: Multi-stage homogenization treatment: The billet is heated to 900℃ at 8℃ / min and held for 2 hours, then heated to 1000℃ at 15℃ / min and held for 2 hours, then cooled to 800℃ at 70℃ / min and held for 8 hours, and finally cooled to room temperature at 3℃ / min.

[0100] Comparative Example 6

[0101] The only difference between this comparative example and Example 1 is that: Multi-stage homogenization treatment: The billet is heated to 1100℃ at 25℃ / min and held for 2 hours, then heated to 1250℃ at 40℃ / min and held for 2 hours, then cooled to 1000℃ at 120℃ / min and held for 8 hours, and finally cooled to room temperature at 15℃ / min.

[0102] The performance data of each embodiment and comparative example in this invention are shown in Table 1 below.

[0103] Table 1 Performance Data Sheet

[0104] GB / T 228.1-2021 Metallic materials, tensile testing - Part 1: Test method at room temperature.

[0105] GB / T 6394-2017 Method for determination of average grain size of metals.

[0106] GB / T 12444-2006 Wear test.

[0107] GB231-84 Brinell Hardness Test.

[0108] 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.

[0109] 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.

[0110] 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 low-cost, high-strength rare-earth dual-phase steel, characterized in that, The chemical composition and its mass percentage are as follows: C: 0.05-0.09%; Si: 0.3-0.5%; Mn: 1.0-1.5%; Als: 0.020-0.055%; Cr: 0.25-0.55%; Ti: 0.05-0.09%; Ce: 0.0030-0.0070%, P: ≤0.010%; S: ≤0.004%; N: ≤0.004%, the remainder being Fe and unavoidable impurity elements.

2. The low-cost rare-earth high-strength dual-phase steel according to claim 1, characterized in that, The mass ratio of Si to Mn is 1:(2-5); the mass ratio of Cr to Ti is (10-11):(1-3.6).

3. The low-cost rare-earth high-strength dual-phase steel according to claim 1, characterized in that, Yield strength is 425-470 MPa, tensile strength is 800-880 MPa, hardness is 310-330 HB, elongation is 31-38%, grain size is 10.0-12.0 grade, and abrasion wear is 5.0-10.2 mm. 3 / m.

4. The forming process for a low-cost rare-earth high-strength dual-phase steel according to any one of claims 1-3, characterized in that, The forming temperature is at room temperature; the stamping speed is 50-800 mm / s; and the blank holder force is 80-300 kN.

5. The forming process according to claim 4, characterized in that, During transverse forming, the radius of the extreme sharp corner rounded corner R ≥ 0.2 mm, which can stably achieve defect-free forming of stamping inner angles ≤ 165°; the radius of the extreme sharp corner rounded corner R ≥ 0.4 mm, which can stably form any stamping inner angle in the full range of 0°-180°; during longitudinal forming, the radius of the extreme sharp corner rounded corner R ≥ 0.2 mm, which can achieve defect-free forming of any stamping inner angle in the full range of 0°-180° in one pass.

6. The welding process for low-cost rare-earth high-strength duplex steel according to any one of claims 1-3, characterized in that, Narrow lap welding is adopted, with a welding speed of 10-12m / min, an lap length of 1.1-1.2mm, a welding pressure of 17-18KN, and a welding temperature of 1110-1120℃.

7. The welded part obtained by the welding process according to claim 6, characterized in that, The welded joints of the welded parts have a tensile strength ≥ 95% of the base material, a yield strength ≥ 90% of the base material, and all fractures occur in the base material area. There are no joint fractures, and the welding deformation is ≤ 0.03 mm / mm.

8. A method for preparing low-cost rare-earth high-strength dual-phase steel according to any one of claims 1-3, characterized in that, Includes the following steps: Converter smelting: Alloying treatment is carried out by adding raw materials other than rare earth element Ce. The final temperature is 1600-1650℃ and the converter smelting time is 60-100min. Oxygen is then blown and quicklime is added to form slag. The steel is tapped using a sliding plate to block the slag and obtain molten steel. LF refining: Heat to 1650-1680℃, use argon gas to blow strong stirring at the bottom of the ladle, slag formation and desulfurization, LF refining time is 30-40min; RH refining: Molten steel exits the LF refining furnace and undergoes RH refining with a vacuum degree ≤100Pa, refining time 10-20min, and molten steel exit temperature 1550-1600℃; rare earth element Ce is added 1-3min before the completion of RH refining. Continuous casting: Molten steel with added Ce enters the tundish. During the pouring process, protective slag is added. The temperature of the molten steel in the tundish is 1600-1700℃, and the casting speed is 1.0-1.5m / min. After the molten steel solidifies and is cooled to room temperature, it is taken out to obtain the billet. Multi-stage homogenization treatment: The billet is heated to 950-1050℃ at 10-20℃ / min and held for 1-2 hours, then heated to 1050-1200℃ at 20-30℃ / min and held for 1-2 hours, then cooled to 850-950℃ at 80-100℃ / min and held for 5-8 hours, and finally cooled to room temperature at 5-10℃ / min. Hot rolling process: hot rolling inlet temperature 1100-1150℃, finishing rolling temperature 920-950℃, coiling temperature 500-600℃, hot rolling thickness 1-2.5mm; Cold rolling process: reduction rate 60-65%, rolling force 30-40MN, finished product thickness 0.4-1mm; Continuous annealing process: In the annealing furnace, the process speed is 100-120m / min, the temperature of the slow cooling section is 650-680℃, the temperature of the soaking section is 700-800℃, the temperature of the rapid cooling section is 250-300℃, and the flattening elongation is 49-51%.

9. The application of a low-cost rare-earth high-strength duplex steel according to any one of claims 1-3 in wear-resistant components, characterized in that, Wear-resistant parts include wear-resistant parts for automobiles or wear-resistant parts for home appliances; wear-resistant parts for automobiles include engine underbody protection plates and chassis protection plates; wear-resistant parts for home appliances include slicer blades and washing machine drums.

10. A wear-resistant component, characterized in that, It is prepared from a low-cost rare-earth high-strength dual-phase steel as described in any one of claims 1-3.

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