High-reaming-performance low-density steel plate for automobile rear anti-collision beam and preparation method of high-reaming-performance low-density steel plate
The development of high-porosity low-density steel plates with specific chemical composition and processing addresses the challenge of reducing vehicle weight while maintaining safety and performance, achieving effective lightweighting and mechanical properties for automotive rear crash components.
Patent Information
- Application Number
- CN202411860584.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-17
- Publication Date
- 2025-03-28
AI Technical Summary
The automotive industry faces challenges in reducing vehicle weight while maintaining safety and performance, as existing methods for lightweighting vehicles are either ineffective or require high material demands, and there is a lack of detailed research and industrialization of low-density high-strength steel in China.
A high-porosity low-density steel plate for automotive rear crash beams is developed, with a specific chemical composition and processing method involving vacuum melting, hot rolling, acid washing, cold rolling, and heat treatment, resulting in a steel plate with a density ≤7.48 g/cm3, expansion rate ≥50%, yield strength >368 MPa, tensile strength >668 MPa, and elongation >26%, achieving both lightweighting and enhanced mechanical properties.
The solution effectively reduces vehicle weight without significantly increasing costs, meeting the mechanical performance requirements for automotive rear crash components while achieving high porosity and strength, as demonstrated by the best performance in example 5 of the experimental steel.
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Figure CN119710493A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of low-density steel and relates to a low-density steel plate for a rear anti-collision beam of an automobile with high hole expansion and a preparation method thereof. Background Art
[0002] In recent years, my country's automobile industry has developed rapidly. From the 1970s to the present, my country's automobile enterprises have grown from nothing to something, and the number has increased from a small number to a large number. Now the scale is unprecedentedly large, and the environmental problems that come with it are becoming increasingly prominent. By 2023, my country's car ownership will exceed 400 million, and the huge number of cars has brought tremendous pressure on energy, resources and the environment.
[0003] Literature shows that for every 10% reduction in vehicle weight, fuel efficiency can be improved by 6-8%; for every 100kg reduction in vehicle mass, fuel consumption per 100km can be reduced by 0.3-0.6L; for every 1% reduction in vehicle weight, fuel consumption can be reduced by 0.7%, and carbon emissions can be reduced by 8-11g. At the same time, vehicle safety will also be greatly improved.
[0004] Generally, there are three ways to reduce the weight of a vehicle: First, by redesigning the structure of the workpiece, minimizing the use of materials as much as possible while ensuring its performance, so as to achieve the purpose of reducing the weight of the vehicle, such as changing the workpiece from a solid structure to a hollow structure, and strengthening the workpiece by adding ribs and tendons to ensure its working strength. For example, automobile wheels adopt this design, but the weight reduction effect of this method is extremely limited; second, using materials with low density, from the perspective of lightweight, such as magnesium alloys, aluminum alloys, zirconium alloys, engineering polymer materials and carbon fiber composite materials with very low density compared to traditional steel materials; third, using high-strength steel to replace traditional steel, reducing the use of materials by increasing the strength of the material, but this method has a very limited weight reduction effect and has extremely high requirements for materials.
[0005] Due to the excellent performance of high-strength steel plates, they will be used in automobiles in the future, and countries around the world are also actively conducting relevant research. Studies have shown that by adding a certain amount of aluminum to high-strength steel, under reasonable process control, a steel plate for automobiles that combines low density and high strength can be obtained. my country's research on low-density high-strength steel started relatively late, lacking detailed reports on smelting and production processes, and there is still a long way to go before industrialization. Summary of the invention
[0006] The object of the present invention is to provide a low-density steel plate for a rear anti-collision beam of an automobile with high hole expansion and a preparation method thereof. The present invention adopts the following technical scheme: A low-density steel plate for a rear anti-collision beam of an automobile with high hole expansion performance, the chemical composition and mass percentage of which are C: 0.08-0.20%, Mn: 4.2-5.7%, Al: 3.2-4.34%, Ni: 0.02-0.04%, Cr: 0.60-0.70%, Si: 0.53-0.89%, S<0.005%, P<0.007%, and the balance is Fe and unavoidable impurities.
[0007] Furthermore, the mass percentage of the chemical components of the steel plate satisfies: [C%]-3×[Ni%]<0.1%, [Al%]<0.8×[Mn%].
[0008] Furthermore, the thickness of the steel plate is 1.12-1.2 mm, and the metallographic structure at room temperature is a ferrite matrix and carbides distributed thereon.
[0009] Furthermore, the steel plate density is ≤7.48g / cm 3 , hole expansion rate ≥50%, yield strength>368MPa, tensile strength>668MPa, elongation after break>26%.
[0010] The present invention also provides a method for preparing the above-mentioned low-density steel plate for automobile rear anti-collision beam with high hole expandability, which includes vacuum melting casting, hot rolling, pickling, cold rolling and heat treatment processes; in the heat treatment process, the cold-rolled steel plate is kept at 800-950°C for 5-20 minutes, then cooled to 650-750°C with the furnace, then taken out and air-cooled to room temperature, and then kept at 400-550°C for 8-60 minutes, then taken out and air-cooled to room temperature.
[0011] Furthermore, in the vacuum melting and casting process, smelting is carried out according to the component ratio, and the obtained molten steel is cast into a steel ingot with a thickness of 138 to 143 mm.
[0012] Furthermore, in the hot rolling process, the steel ingot is heated to 1150-1200° C. in the furnace, kept warm for 100-120 minutes for homogenization, and then rough rolled, and then returned to the furnace to heat to 1150-1200° C., kept warm for 30-40 minutes, and then finished rolled.
[0013] Furthermore, in the hot rolling process, the starting temperature of the rough rolling is 1076-1108°C, and the total reduction rate is 77-80%; the starting temperature of the finishing rolling is 1053-1120°C, the final rolling temperature is not less than 840°C, and the total reduction rate is 89-90%. After air cooling to 550-600°C, the steel is placed in a heat treatment furnace and cooled to room temperature along with the furnace.
[0014] Furthermore, in the pickling process, the hot-rolled plate is immersed in a concentrated hydrochloric acid pool for 40 to 60 minutes, and then washed with water to remove the surface acid.
[0015] Furthermore, in the cold rolling process, the total reduction rate is 60-65%.
[0016] The beneficial effect of adopting the above technical scheme is that: in the heat treatment process of the present invention, the solid solution adopts a cooling method of first furnace cooling and then air cooling, which controls the ratio of different crystal index α phases in the organization to be close to 1:1, and reduces the amount of banded structure in the steel plate organization through appropriate solid solution aging temperature and time treatment, so that the plate steel has excellent comprehensive mechanical properties and high hole expansion performance.
[0017] The density of the steel plate obtained by the present invention is ≤7.48g / cm 3 , hole expansion rate ≥ 50%, yield strength > 368MPa, tensile strength > 668MPa, elongation after fracture > 26%. The present invention achieves lightweight effect without significantly increasing the cost, while the mechanical properties can meet the requirements of automobile rear anti-collision beam parts and have high hole expansion performance. BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Figure 1 The room temperature metallographic structure diagram of the low-density steel plate prepared in the comparative example; Figure 2 The room temperature metallographic structure diagram of the low-density steel plate prepared in Example 5; Figure 3 This is the XRD phase detection result diagram of the low-density steel plate prepared in Example 5. DETAILED DESCRIPTION Example 1
[0019] This embodiment uses a 50kg vacuum induction furnace, a Φ450×1100mm rolling mill, a resistance furnace and other equipment to produce low-density steel, and its production steps include: (1) Vacuum melting and casting The ingredients were prepared according to the chemical composition shown in Table 1, added into a furnace for melting, and cast into an ingot to obtain an ingot with a thickness of 142 mm.
[0020] (2) Hot rolling The ingot was kept at 1170℃ for 115min to homogenize its internal composition, then taken out of the furnace for rough rolling, the starting rolling temperature was 1076℃, and it was rolled to 30mm thick through 6 passes, with a total reduction rate of 78.9%, and the process was 142mm→110mm→85mm→65mm→50mm→40mm→30mm. It was then cut into three pieces along the length direction and returned to the furnace for heating to 1200℃. After keeping warm for 30min, it was finished rolled, the starting rolling temperature was 1120℃, and it was rolled to 3mm thick through 6 passes, with a total reduction rate of 90%, and the process was 30mm→17mm→10mm→7mm→5mm→3.5mm→3mm. The final rolling temperature was 863℃. After rolling, the steel plate was air-cooled to 570℃ and placed in a heat treatment furnace to cool to room temperature with the furnace.
[0021] (3) Pickling Immerse the hot-rolled plate in a concentrated hydrochloric acid pool for 55 minutes, then immerse it in a water pool to wash off the surface acid and then fish it out.
[0022] (4) Cold rolling The pickled plate was cold rolled using a four-roll cold rolling mill with a total reduction of 60.7% and a final plate thickness of 1.18 mm.
[0023] (5) Heat treatment First, the furnace is heated at 950°C and kept at this temperature for 20 minutes, then cooled to 750°C with the furnace, and then air-cooled to room temperature. Then, the furnace is heated at 550°C and kept at this temperature for 55 minutes, then air-cooled to room temperature.
[0024] After the above process, the composition and performance of the steel plate were tested. The chemical composition and actual content are shown in Table 1, and the performance test results are shown in Table 2. Example 2
[0025] This embodiment uses a 50kg vacuum induction furnace, a Φ450×1100mm rolling mill, a resistance furnace and other equipment to produce low-density steel, and its production steps include: (1) Vacuum melting and casting The ingredients were prepared according to the chemical composition shown in Table 2, added into a furnace for melting, and cast into an ingot to obtain an ingot with a thickness of 138 mm.
[0026] (2) Hot rolling The ingot was kept at 1200℃ for 120min to homogenize its internal composition, then taken out of the furnace for rough rolling, the starting rolling temperature was 1087℃, and it was rolled to 31.74mm thick through 6 passes, with a total reduction rate of 77%, and the process was 138mm→110mm→85mm→65mm→50mm→40mm→31.74mm. Then it was cut into three pieces along the length direction and returned to the furnace for heating to 1150℃. After keeping warm for 40min, it was finished rolled, the starting rolling temperature was 1078℃, and it was rolled to 3.3mm thick through 6 passes, with a total reduction rate of 89.6%, and the process was 30mm→17mm→10mm→7mm→5mm→3.5mm→3.3mm. The final rolling temperature was 878℃. After rolling, the steel plate was air-cooled to 576℃ and then placed in a heat treatment furnace and cooled to room temperature with the furnace.
[0027] (3) Pickling Immerse the hot-rolled plate in a concentrated hydrochloric acid pool for 60 minutes, then immerse it in a water pool to wash off the surface acid and then fish it out.
[0028] (4) Cold rolling The pickled plate was cold rolled using a four-roll cold rolling mill with a total reduction of 65% and a final plate thickness of 1.15 mm.
[0029] (5) Heat treatment First, place it in a warm furnace at 820°C and keep it for 5 minutes, then cool it to 670°C with the furnace, then take it out and air cool it to room temperature, then place it in a warm furnace at 450°C and keep it for 10 minutes, then air cool it to room temperature.
[0030] After the above process, the composition and performance of the steel plate were tested. The chemical composition and actual content are shown in Table 1, and the performance test results are shown in Table 2. Example 3
[0031] This embodiment uses a 50kg vacuum induction furnace, a Φ450×1100mm rolling mill, a resistance furnace and other equipment to produce low-density steel, and its production steps include: (1) Vacuum melting and casting The ingredients were prepared according to the chemical composition shown in Table 3, added into a furnace for melting, and cast into an ingot to obtain an ingot with a thickness of 140 mm.
[0032] (2) Hot rolling The ingot was kept at 1150℃ for 100min to homogenize its internal composition, then taken out of the furnace for rough rolling, the starting rolling temperature was 1097℃, and it was rolled to 28mm thick through 6 passes, with a total reduction rate of 80%. The process was 140mm→110mm→85mm→65mm→50mm→40mm→28mm, then cut into three pieces along the length direction and returned to the furnace for heating to 1160℃, kept for 33min and then finished rolling was carried out, the starting rolling temperature was 1108℃, and it was rolled to 2.8mm thick through 6 passes, with a total reduction rate of 90%, with the process being 30mm→17mm→10mm→7mm→5mm→3.5mm→2.8mm, and the final rolling temperature was 840℃. After rolling, the steel plate was air-cooled to 596℃ and then placed in a heat treatment furnace and cooled to room temperature with the furnace.
[0033] (3) Pickling Immerse the hot-rolled plate in a concentrated hydrochloric acid pool for 50 minutes, then immerse it in a water pool to wash off the surface acid and then fish it out.
[0034] (4) Cold rolling The pickled plate was cold rolled using a four-roll cold rolling mill with a total reduction of 60% and a final plate thickness of 1.12 mm.
[0035] (5) Heat treatment First, heat it to 800℃ and keep it in a warm furnace for 10 minutes, then cool it to 650℃ with the furnace, then take it out and air cool it to room temperature, then heat it to 470℃ and keep it in a warm furnace for 8 minutes, then air cool it to room temperature.
[0036] After the above process, the composition and performance of the steel plate were tested. The chemical composition and actual content are shown in Table 1, and the performance test results are shown in Table 2. Example 4
[0037] This embodiment uses a 50kg vacuum induction furnace, a Φ450×1100mm rolling mill, a continuous annealing simulation test machine and other equipment to produce low-density steel, and its production steps include: (1) Vacuum melting and casting The ingredients were prepared according to the chemical composition shown in Table 4, added into a furnace for melting, and cast into an ingot to obtain an ingot with a thickness of 143 mm.
[0038] (2) Hot rolling The ingot was kept at 1180℃ for 110min to homogenize its internal composition, then taken out of the furnace for rough rolling, the starting rolling temperature was 1108℃, and it was rolled to 29mm thick through 6 passes, with a total reduction rate of 79.7%, and the process was 143mm→110mm→85mm→65mm→50mm→40mm→29mm. It was then cut into three pieces along the length direction and returned to the furnace for heating to 1190℃. After keeping it for 36min, it was finished rolled, the starting rolling temperature was 1082℃, and it was rolled to 3.19mm thick through 6 passes, with a total reduction rate of 89%, and the process was 30mm→17mm→10mm→7mm→5mm→3.5mm→3.19mm. The final rolling temperature was 868℃. After rolling, the steel plate was air-cooled to 550℃ and then placed in a heat treatment furnace and cooled to room temperature with the furnace.
[0039] (3) Pickling Immerse the hot-rolled plate in a concentrated hydrochloric acid pool for 40 minutes, then immerse it in a water pool to wash off the surface acid and then fish it out.
[0040] (4) Cold rolling The pickled plate was cold rolled using a four-roll cold rolling mill with a total reduction of 62.3% and a final plate thickness of 1.2 mm.
[0041] (5) Heat treatment First, place the furnace in a warm-loading furnace at 850°C and keep it for 5 minutes, then cool it to 720°C with the furnace, take it out and air-cool it to room temperature, then place it in a warm-loading furnace at 500°C and keep it for 50 minutes, then air-cool it to room temperature.
[0042] After the above process, the composition and performance of the steel plate were tested. The chemical composition and actual content are shown in Table 1, and the performance test results are shown in Table 2. Example 5
[0043] This embodiment uses a 50kg vacuum induction furnace, a Φ450×1100mm rolling mill, a continuous annealing simulation test machine and other equipment to produce low-density steel, and its production steps include: (1) Vacuum melting and casting The ingredients were prepared according to the chemical composition shown in Table 5, added into a furnace for melting, and cast into an ingot to obtain an ingot with a thickness of 142 mm.
[0044] (2) Hot rolling The ingot was kept at 1165℃ for 118min to homogenize its internal composition, then taken out of the furnace for rough rolling, the starting rolling temperature was 1088℃, and it was rolled to 29.11mm thick through 6 passes, with a total reduction rate of 79.5%, and the process was 142mm→110mm→85mm→65mm→50mm→40mm→29.11mm. It was then cut into three pieces along the length direction and returned to the furnace for heating to 1195℃. After keeping warm for 35min, it was finished rolled, the starting rolling temperature was 1077℃, and it was rolled to 3.11mm thick through 6 passes, with a total reduction rate of 89.3%, and the process was 30mm→17mm→10mm→7mm→5mm→3.5mm→3.11mm. The final rolling temperature was 864℃. After rolling, the steel plate was air-cooled to 600℃ and then placed in a heat treatment furnace to cool to room temperature with the furnace.
[0045] (3) Pickling Immerse the hot-rolled plate in a concentrated hydrochloric acid pool for 45 minutes, then immerse it in a water pool to wash off the surface acid and then fish it out.
[0046] (4) Cold rolling The pickled plate was cold rolled using a four-roll cold rolling mill with a total reduction of 61.7% and a final plate thickness of 1.19 mm.
[0047] (5) Heat treatment First, heat it to 900℃ and keep it in a warm furnace for 19 minutes, then cool it to 740℃ with the furnace, then take it out and air cool it to room temperature, then heat it to 550℃ and keep it in a warm furnace for 60 minutes, then air cool it to room temperature.
[0048] After the above process, the composition and performance of the steel plate were tested. The chemical composition and actual content are shown in Table 1, and the performance test results are shown in Table 2. Example 6
[0049] This embodiment uses a 50kg vacuum induction furnace, a Φ450×1100mm rolling mill, a continuous annealing simulation test machine and other equipment to produce low-density steel, and its production steps include: (1) Vacuum melting and casting The ingredients were prepared according to the chemical composition shown in Table 6, added into a furnace for melting, and cast into an ingot to obtain an ingot with a thickness of 140 mm.
[0050] (2) Hot rolling The ingot was kept at 1185℃ for 110min to homogenize its internal composition, then taken out of the furnace for rough rolling, the starting rolling temperature was 1093℃, and it was rolled to 30.5mm thick through 6 passes, with a total reduction rate of 78.2%. The process was 140mm→110mm→85mm→65mm→50mm→40mm→30.5mm, and then cut into three pieces along the length direction and returned to the furnace for heating to 1180℃. After keeping warm for 37min, it was finished rolled, the starting rolling temperature was 1053℃, and it was rolled to 3.17mm thick through 6 passes, with a total reduction rate of 89.6%. The process was 30mm→17mm→10mm→7mm→5mm→3.5mm→3.17mm, and the final rolling temperature was 857℃. After rolling, the steel plate was air-cooled to 573℃ and then placed in a heat treatment furnace and cooled to room temperature with the furnace.
[0051] (3) Pickling The hot-rolled plate was immersed in a concentrated hydrochloric acid pool for 53 minutes, then immersed in a water pool to wash off the surface acid and then fished out.
[0052] (4) Cold rolling The pickled plate was cold rolled using a four-roll cold rolling mill with a total reduction of 63.4% and a final plate thickness of 1.16 mm.
[0053] (5) Heat treatment First, place it in a warm furnace at 850°C and keep it for 7 minutes, then cool it to 700°C with the furnace, then take it out and air cool it to room temperature, then place it in a warm furnace at 400°C and keep it for 8 minutes, then air cool it to room temperature.
[0054] After the above process, the composition and performance of the steel plate were tested. The chemical composition and actual content are shown in Table 1, and the performance test results are shown in Table 2.
[0055] Comparative Example This comparative example uses a 50kg vacuum induction furnace, a Φ450×1100mm rolling mill, a continuous annealing simulation test machine and other equipment to produce low-density steel, and its production steps include: (1) Vacuum melting and casting The ingredients were prepared according to the chemical composition shown in Table 7, added into a furnace for melting, and cast into an ingot to obtain an ingot with a thickness of 142 mm.
[0056] (2) Hot rolling The ingot was kept at 1165℃ for 118min to homogenize its internal composition, then taken out of the furnace for rough rolling, the starting rolling temperature was 1088℃, and it was rolled to 29.11mm thick through 6 passes, with a total reduction rate of 79.5%, and the process was 142mm→110mm→85mm→65mm→50mm→40mm→29.11mm. It was then cut into three pieces along the length direction and returned to the furnace for heating to 1195℃. After keeping warm for 35min, it was finished rolled, the starting rolling temperature was 1077℃, and it was rolled to 3.11mm thick through 6 passes, with a total reduction rate of 89.3%, and the process was 30mm→17mm→10mm→7mm→5mm→3.5mm→3.11mm. The final rolling temperature was 864℃. After rolling, the steel plate was air-cooled to 600℃ and then placed in a heat treatment furnace to cool to room temperature with the furnace.
[0057] (3) Pickling Immerse the hot-rolled plate in a concentrated hydrochloric acid pool for 45 minutes, then immerse it in a water pool to wash off the surface acid and then fish it out.
[0058] (4) Cold rolling The pickled plate was cold rolled using a four-roll cold rolling mill with a total reduction of 61.7% and a final plate thickness of 1.19 mm.
[0059] (5) Annealing First, heat the furnace at 900°C and keep it for 20 minutes, then take it out and air cool it to room temperature. Then heat the furnace at 550°C and keep it for 60 minutes, then air cool it to room temperature.
[0060] After the above process, the composition and performance of the steel plate were tested. The chemical composition and actual content are shown in Table 1, and the performance test results are shown in Table 2.
[0061] Table 1: Chemical composition and content of low-density steel in various embodiments and comparative examples (wt%)
[0062] Note: In Table 1, the balance is Fe and unavoidable impurity elements.
[0063] Table 2: Mechanical properties and density of steel plates in various embodiments and comparative examples
[0064] The low-density steel for the rear anti-collision beam of the automobile in the present invention is lightweight by adding Al elements. After heat treatment, the hole expansion rate is ≥50%, the yield strength is >368MPa, the tensile strength is >668MPa, the elongation after fracture is >26%, and the density is ≤7.48g / cm 3 Among them, the experimental steel in Example 5 has the best comprehensive performance.
[0065] Figure 1 , 2They are room temperature metallographic structure diagrams of the low-density steel plates prepared in the comparative example and Example 5, respectively. The microstructures of both are a ferrite matrix and carbides distributed thereon. It can be seen from the figure that the amount of carbides in the metallographic structure of the low-density steel in Example 5 is significantly less than that in the comparative example.
[0066] Figure 3 This is the XRD phase detection result diagram of the low-density steel plate prepared in Example 5. There are two α phases with different crystal plane indices, (110) and (101), in its structure, accounting for 51% and 49% respectively.
Claims
1. A low-density steel plate with high hole expansion for automobile rear anti-collision beam, characterized in that: The chemical composition and mass percentage of the steel plate are C: 0.08-0.20%, Mn: 4.2-5.7%, Al: 3.2-4.34%, Ni: 0.02-0.04%, Cr: 0.60-0.70%, Si: 0.53-0.89%, S<0.005%, P<0.007%, and the balance is Fe and unavoidable impurities.
2. The low-density steel plate with high hole expandability for automobile rear anti-collision beam according to claim 1, characterized in that: The mass percentage of the chemical components of the steel plate satisfies: [C%]-3×[Ni%]<0.1%, [Al%]<0.8×[Mn%].
3. The low-density steel plate with high hole expandability for automobile rear anti-collision beam according to claim 2, characterized in that: The steel plate has a thickness of 1.12-1.2 mm, and a metallographic structure at room temperature of a ferrite matrix and carbides distributed thereon.
4. The low-density steel plate with high hole expandability for automobile rear anti-collision beam according to claim 3, characterized in that: The steel plate density is ≤7.48g / cm 3 , hole expansion rate ≥50%, yield strength>368MPa, tensile strength>668MPa, elongation after break>26%.
5. The method for preparing a low-density steel plate for a rear anti-collision beam of an automobile with high hole expansion according to any one of claims 1 to 4, characterized in that: The method comprises vacuum melting casting, hot rolling, pickling, cold rolling and heat treatment steps; in the heat treatment step, the cold rolled steel plate is kept at 800-950°C for 5-20 minutes, then cooled to 650-750°C with the furnace, then taken out and air-cooled to room temperature, and then kept at 400-550°C for 8-60 minutes, then taken out and air-cooled to room temperature.
6. The method for preparing a low-density steel plate with high hole expandability for a rear anti-collision beam of an automobile according to claim 5, characterized in that: The vacuum melting and casting process is to perform smelting according to the component ratio, and cast the obtained molten steel into a steel ingot with a thickness of 138 to 143 mm.
7. The method for preparing a low-density steel plate with high hole expandability for a rear anti-collision beam of an automobile according to claim 6, characterized in that: In the hot rolling process, the steel ingot is heated to 1150-1200° C. in a furnace, kept warm for 100-120 minutes for homogenization, and then rough rolled, and then returned to the furnace to heat to 1150-1200° C., kept warm for 30-40 minutes, and then finished rolled.
8. The method for preparing a low-density steel plate with high hole expandability for a rear anti-collision beam of an automobile according to claim 7, characterized in that: In the hot rolling process, the starting temperature of the rough rolling is 1076-1108°C, and the total reduction rate is 75-80%; the starting temperature of the finishing rolling is 1053-1120°C, the final rolling temperature is not less than 840°C, and the total reduction rate is 85-90%. After air cooling to 550-600°C, the steel is placed in a heat treatment furnace and cooled to room temperature along with the furnace.
9. The method for preparing a low-density steel plate for a rear anti-collision beam of an automobile with high hole expandability according to any one of claims 1 to 8, characterized in that: In the pickling process, the hot rolled plate is immersed in a concentrated hydrochloric acid tank for 40 to 60 minutes, and then washed with water to remove the surface acid.
10. The method for preparing a low-density steel plate with high hole expandability for a rear anti-collision beam of an automobile according to claim 9, characterized in that: In the cold rolling process, the total reduction rate is 60-65%.