High energy absorption characteristic light q&p steel and preparation method thereof

Abstract

The application provides a high-energy-absorbing lightweight Q&P steel and a preparation method thereof, and belongs to the technical field of advanced ultra-high-strength steel. The chemical composition and the weight percentage of the steel are as follows: C: 0.20-0.25%, Si: 1.50-2.00%, Mn: 1.80-2.10%, Al: 4.0-6.2%, Cr: 0.015-0.020%, S+P≤0.015%, Dy: 0.003-0.015%, and the rest is Fe and inevitable impurities. The high-uniformity slab is obtained by using a spray forming process, the thin plate is obtained after hot deformation, and the Q&P treatment process is finally carried out. The microstructure obtained at room temperature is a mixed microstructure of primary martensite, stable residual austenite and newly generated martensite, the tensile strength is between 1500-1750 MPa, and the elongation is greater than 25%. The new Q&P steel has the characteristics of low density and high energy absorption, and can further realize lightweight while improving the safety of automobile collision.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of advanced ultra-high strength steel, and particularly relates to a high-energy-absorption lightweight Q&P steel and a preparation method thereof. BACKGROUND

[0002] In recent years, with the development of society, automobiles have brought great convenience to people's life and work, but also have brought a series of practical problems, such as energy consumption, environmental pollution, driving safety, etc. Automobile lightweight is one of the effective methods to reduce energy consumption. At present, major automobile companies and colleges and universities are carrying out research on automobile lightweight, using lightweight high-strength steel, new technology, etc., to reduce the weight of the vehicle, achieve the goal of energy saving and emission reduction, driving safety, etc.

[0003] The high-energy-absorption lightweight Q&P steel is prepared through component system design, spray forming technology and corresponding Q&P heat treatment process. In the melting process, by controlling the content of Al element, the density is reduced, and the formation and precipitation of carbides are effectively hindered in the microstructure transformation process, and the residual austenite is stabilized; by adding rare earth element Dy, the modification effect is achieved, the grain is refined, the grain boundary is purified, the surface quality is improved, and the comprehensive mechanical properties are improved. In the preparation process, spray forming technology is used, taking droplets as units to achieve the effect of rapid solidification, effectively reducing alloy element segregation and inhibiting the generation of crystalline phase, and obtaining a lightweight Q&P steel plate blank with uniform and fine microstructure. In summary, the finally obtained Q&P steel has low density, uniform and fine matrix microstructure, small component segregation, and high energy absorption characteristics in the collision process. SUMMARY

[0004] One of the purposes of the application is to provide a high-energy-absorption lightweight Q&P steel, which is prepared by reasonable component design, spray forming process and heat deformation treatment, and obtains a lightweight Q&P steel sheet with uniform and fine microstructure. The chemical composition of the Q&P steel according to the application is C: 0.20-0.25%, Si: 1.50-2.00%, Mn: 1.80-2.10%, Al: 4.0-6.2%, Cr: 0.015-0.020%, S+P≤0.015%, Dy: 0.003-0.015%, and the rest is Fe and inevitable impurities.

[0005] The second purpose of the application is to provide a high-energy-absorption lightweight Q&P steel and a preparation method thereof. Through the heat treatment process, the temperature is raised at a rate of 5-20℃ / min to 900-1000℃ for 5-30min, then rapidly cooled to 200-300℃, and then immediately heated to 300-400℃ at a rate of 10-20℃ / min for 5-60min, and air-cooled to room temperature. By controlling the quenching and partitioning temperature and time, the matrix microstructure is adjusted, and a high-energy-absorption Q&P steel with high tensile strength and good plasticity is obtained.

[0006] In order to achieve the above-mentioned object of the present application, the following technical solutions are adopted:

[0007] A high-energy-absorbing lightweight Q&P steel and a preparation method thereof, comprising the following steps:

[0008] In the melting process, the content of Al is 4.0-6.2%, and the content of rare earth Dy is 0.003-0.015%.

[0009] Preferably, on the basis of the technical solutions provided by the present application, the content of Al is 4.5-5.5%, and the content of rare earth Dy is 0.006-0.013%.

[0010] Further, in the spray forming process, the superheat degree of the molten steel is controlled to be 50-100 DEG C, the molten steel flow is fully broken by the impact of high-pressure inert gas, and a slab with fine structure is obtained.

[0011] Preferably, the superheat degree of the molten steel is controlled to be 50-70 DEG C.

[0012] Further, in the hot rolling process, the slab is heated to 1200-1250 DEG C, and after holding for 1-2 h, multi-pass hot deformation with large reduction is carried out in the austenite recrystallization zone, the deformation amount of each pass is ensured to be greater than 50%, the initial rolling temperature is 1050-1100 DEG C, and the final rolling temperature is 950 DEG C.

[0013] Preferably, in the hot rolling process, the slab is heated to 1250 DEG C, and after holding for 1.5 h, hot rolling is carried out, multi-pass hot deformation with large reduction is carried out in the austenite recrystallization zone, the deformation amount of each pass is ensured to be greater than 60%, the initial temperature is 1100 DEG C, and the final rolling temperature is 950 DEG C.

[0014] Further, in the heat treatment process, the temperature is raised to 950-1000 DEG C at a heating rate of 10-15 DEG C / min, and held for 10-20 min, then rapidly cooled to 200-250 DEG C, immediately heated to 300-350 DEG C at a heating rate of 15-20 DEG C / min, and held for 10-30 min, and air-cooled to room temperature.

[0015] Compared with the prior art, the present application has the following beneficial effects:

[0016] A high-energy-absorbing lightweight Q&P steel and a preparation method thereof, by adding a high proportion of Al and a certain amount of Dy, combined with spray forming technology, the prepared steel has the advantages of fine structure, uniform composition, high density and good comprehensive mechanical properties. The high-energy-absorbing lightweight Q&P steel prepared by the preparation method has a density of 7.40-7.46 g·cm -3Furthermore, by optimizing the heat treatment process, a mixed structure of carbon-rich stable residual austenite, primary martensite and newly formed martensite is obtained. The preparation method obtains a high energy absorption characteristic lightweight Q&P steel with a yield strength of 800-850 MPa, an ultimate tensile strength of 1550-1700 MPa, and an elongation of more than 25%. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a schematic diagram of a preparation method of a high energy absorption characteristic lightweight Q&P steel according to the present application.

[0018] Figure 2 is a stress-strain curve diagram of the comparative examples and the examples.

[0019] Figure 3 is a tensile strength and energy absorption index comparison diagram of the comparative examples and the examples.

[0020] Figure 4 is a microstructure diagram of Comparative Example 1.

[0021] Figure 5 is a microstructure diagram of Example 4.

[0022] DETAILED DESCRIPTION

[0023] In order to facilitate the understanding of the present application, the embodiments of the present application will be described in detail below in combination with the examples and the accompanying drawings, as shown in the accompanying drawings. Figures 1 to 5

[0024] Example 1

[0025] The present application relates to a preparation method of a high energy absorption characteristic lightweight Q&P steel, which has a chemical composition of C: 0.21%, Si: 1.8%, Mn: 1.9%, Al: 4.5%, Cr: 0.017%, S+P≤0.015%, Dy: 0.013%, and the rest is Fe and inevitable impurities, and the process includes the following steps:

[0026] (1) Smelting process: according to the mixed alloy powder ingredients of the chemical composition, smelting is carried out in an electric resistance furnace, and the smelting temperature is 1550-1600℃.

[0027] (2) Forming process: the superheat is controlled at 50-70℃, the spray forming process is used, the atomizing gas is nitrogen, the spray pressure is 0.3MPa, the melt casting temperature is 1530-1550℃, the spray distance is 400mm, and the droplet cooling rate is 1000℃ / s, to obtain a 10-25mm slab;

[0028] ​(3) Hot rolling process: the slab is heated to 1250℃, and after holding for 1.5h, multi-pass hot rolling is carried out, the deformation of each pass is ensured to be greater than 60%, the initial rolling temperature is 1100℃, and the final rolling temperature is 950℃, to obtain a thin plate with a thickness of 1.2-1.5mm, which is quenched to room temperature.

[0029] (4) Heat treatment process: the thin plate is heated to 980℃ at 15℃ / min and held for 20min, so that carbon and manganese are comprehensively partitioned in the austenite region. After rapid cooling to 210℃, it is immediately heated to 300℃ at 20℃ / min and held for 10min, and then air-cooled to room temperature. Through carbon partitioning treatment, carbon is diffused from the supersaturated martensite to the residual austenite, and finally a mixed structure of primary martensite, carbon-rich stable residual austenite and newly formed martensite is obtained.

[0030] The high-energy-absorbing lightweight Q&P steel obtained in this embodiment has a mixed structure of primary martensite, carbon-rich stable residual austenite and newly formed martensite, a tensile strength of 1540MPa, an elongation of 27.8%, and a fracture energy absorption characteristic of 389.85×10 -3 J·mm -3 , and a density of 7.46g·cm -3 .

[0031] Example 2

[0032] This embodiment provides a method for preparing a high-energy-absorbing lightweight Q&P steel. The specific method is the same as that of Example 1, and the difference from Example 1 is that the content of Al is changed to 5.0%.

[0033] The high-energy-absorbing lightweight Q&P steel obtained in this embodiment has a mixed structure of primary martensite, carbon-rich stable residual austenite and newly formed martensite, a tensile strength of 1611MPa, an elongation of 26.7%, and a fracture energy absorption characteristic of 398.11×10 -3 J·mm -3 , and a density of 7.46g·cm -3 .

[0034] Example 3

[0035] This embodiment provides a method for preparing a high-energy-absorbing lightweight Q&P steel. The specific method is the same as that of Example 1, and the difference from Example 1 is that the partitioning temperature is changed to 330℃.

[0036] The high-energy-absorbing lightweight Q&P steel obtained in this embodiment has a mixed structure of primary martensite, carbon-rich stable residual austenite and newly formed martensite, a tensile strength of 1615MPa, an elongation of 29.8%, and a fracture energy absorption characteristic of 439.62×10 -3 J·mm -3 , and a density of 7.43g·cm-3 .

[0037] Example 4

[0038] The embodiment provides a preparation method of a high-energy-absorbing lightweight Q&P steel, and the specific mode is the same as that in Example 1, and the difference from Example 1 is that the content of Al is changed to 5.5%, and the partitioning temperature is changed to 330 DEG C.

[0039] The high-energy-absorbing lightweight Q&P steel obtained through the embodiment has a mixed structure of primary martensite, carbon-rich stable residual austenite and newly generated martensite, a tensile strength of 1680 MPa, an elongation of 32.0%, and a fracture energy absorption characteristic of 487.53 x 10 -3 J·mm -3 , and a density of 7.41 g·cm -3 .

[0040] Example 5

[0041] The embodiment provides a preparation method of a high-energy-absorbing lightweight Q&P steel, and the specific mode is the same as that in Example 1, and the difference from Example 1 is that the content of Al is changed to 5.5%.

[0042] The high-energy-absorbing lightweight Q&P steel obtained through the embodiment has a mixed structure of primary martensite, carbon-rich stable residual austenite and newly generated martensite, a tensile strength of 1711 MPa, an elongation of 28.1%, and a fracture energy absorption characteristic of 447.34 x 10 -3 J·mm -3 , and a density of 7.40 g·cm -3 .

[0043] Comparative Example 1

[0044] The comparative example provides a common Q&P steel and a preparation method thereof, and the difference from Example 1 in element composition is that the content of Al is 2.2%, and no rare earth Dy is added; and the difference from Example 1 in the preparation method is that a casting forming process is used to obtain a casting blank; the thin plate is heated to 980 DEG C at a heating rate of 15 DEG C / min, and then held for 20 min, quenched to 210 DEG C and held for 3 min, and then heated to 330 DEG C and held for 10 min, and then air-cooled to room temperature.

[0045] The Q&P steel after the heat treatment in the comparative example has a mixed structure of residual austenite and martensite, a tensile strength of 990 MPa, an elongation of 21.5%, a fracture energy absorption characteristic of 192.60 x 10 -3 J·mm -3 , and a density of 7.78 g·cm -3 .

[0046] Comparative Example 2

[0047] The comparative example provides a common Q&P steel and a preparation method thereof, which is different from example 1 in element composition in that the Al content is 2.2%, and is different from example 1 in the preparation method in that a casting forming process is used to obtain a casting blank; the thin plate is heated to 980℃ at a heating rate of 15℃ / min and kept for 20min, quenched to 210℃ and kept for 3min, then heated to 330℃ and kept for 10min, and finally air-cooled to room temperature.

[0048] The Q&P steel after the heat treatment of the comparative example has a structure of residual austenite and martensite, a tensile strength of 1055MPa, an elongation of 24.0%, and a fracture energy absorption characteristic of 233.06×10 -3 J·mm -3 , and a density of 7.78g·cm -3 .

[0049] The components and heat treatment processes of the examples and comparative examples are compared, and the data results are shown in Table 1.

[0050] Table 1

[0051] Al Dy Quenching temperature Partitioning temperature Partitioning time Example 1 4.5％ 0.013％ 210℃ 300℃ 10 min Example 2 5.0％ 0.013％ 210℃ 300℃ 10 min Example 3 5.0％ 0.013％ 210℃ 330℃ 10 min Example 4 5.5％ 0.013％ 210℃ 330℃ 10 min Example 5 5.5％ 0.013％ 210℃ 300℃ 10 min Comparative Example 1 2.2％ - 210°C (3 min) 330℃ 10 min Comparative Example 2 2.2％ 0.013％ 210°C (3 min) 330℃ 10 min

[0052] The present application realizes the preparation of high-energy-absorption lightweight Q&P steel by preparing lightweight Q&P steel and applying it to the field of advanced automobile steel, which has guiding significance in automobile lightweighting and safety.

[0053] The high-energy-absorption lightweight Q&P steel prepared in example 4 has a structure of primary martensite, carbon-rich stable residual austenite and newly formed martensite mixed structure, a tensile strength of 1680MPa, which is increased by 69.69% compared with comparative example 1; an elongation of 32.0%, which is increased by 48.83% compared with comparative example 1; a fracture energy absorption characteristic of 487.53×10 -3 J·mm -3 , which is increased by 153.13% compared with comparative example 1; and a density of 7.40g·cm -3 , which is decreased by 4.78% compared with comparative example 1.

[0054] The data of the examples and comparative examples are compared, and the data results are shown in Table 2.

[0055] Table 2

[0056]

[0057] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A high-energy-absorbing lightweight Q&P steel with the following chemical composition: C: 0.20-0.25%, Si: 1.50-2.00%, Mn: 1.80-2.10%, Al: 4.0-6.2%, Cr: 0.015-0.020%, S+P≤0.015%, Dy: 0.003-0.015%, and the balance of Fe and inevitable impurities. The specific steps of the preparation method of the high-energy-absorbing lightweight Q&P steel are as follows: (1) Smelting process: The mixed alloy powder according to the chemical composition is dosed and smelted in an electric resistance furnace, and the smelting temperature is 1550-1600°C. (2) Forming process: The superheat is controlled at 50-100°C, the spray forming process is adopted, the atomizing gas is nitrogen, the spray pressure is 0.2-0.4 MPa, the melt casting temperature is 1530-1550°C, the spray distance is 350-450 mm, the cooling rate of the liquid droplets is 900-1000°C / s, and a 10-25 mm slab is prepared. (3) Hot rolling process: The slab is heated to 1200-1250°C, and after holding for 1-2 h, multi-pass hot rolling is performed, the deformation of each pass is ensured to be greater than 50%, the rough rolling temperature is 1050-1100°C, the finish rolling temperature is 950°C, a 1.2-1.5 mm thin plate is obtained, and the thin plate is quenched to room temperature. (4) Heat treatment process: The thin plate is heated to 950-1000°C at a rate of 10-15°C / min, held for 10-20 min, rapidly cooled to 200-250°C, immediately heated to 300-350°C at a rate of 15-20°C / min, held for 10-30 min, and air-cooled to room temperature.

2. The high energy absorbing lightweight Q&P steel according to claim 1, characterized in that: The content of Al is 4.5-5.5%, and the content of rare earth Dy is 0.006-0.013%.

3. The high energy absorbing lightweight Q&P steel according to claim 1, characterized in that: The superheat is controlled at 50-70°C, the spray forming process is adopted to achieve the effect of instantaneous solidification, and the prepared slab is uniform and grain refined.

4. The high energy absorbing lightweight Q&P steel according to claim 1, characterized in that: Large reduction hot deformation is realized in the austenite recrystallization zone, and the deformation of each pass is ensured to be greater than 60%.

5. The high energy absorbing lightweight Q&P steel according to claim 1, characterized in that: The fracture energy absorption property of the high energy absorption property lightweight Q&P steel is ≥ 389.85 × 10 -3 J·mm -3 .

6. The high energy absorbing lightweight Q&P steel according to claim 1, characterized in that: The high energy-absorbing property lightweight Q&P steel has a density of 7.40-7.46 g·cm -3 .

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