High-formability low-density steel and preparation method thereof

Abstract

The invention discloses high-formability low-density steel and a preparation method thereof. The high-formability low-density steel comprises the following chemical components in percentage by mass: 0.02%-0.08% of C, 0.2%-0.6% of Si, 0.2%-1.2% of Mn, 0.05%-0.12% of P, less than or equal to 0.03% of S, 3.0%-5.0% of Al, 0.8%-1.5% of Cr and the balance of Fe and inevitable impurities, and the Al / Cr is 3-5%. The tensile strength Rmgt of the high-formability low-density steel; the tensile strength is 400 MPa, the yield strength Rel is 180-300 MPa, the percentage elongation after fracture A is larger than or equal to 25%, and the density is 7.3-7.5 Kg / m < 3 >; a metallographic structure of the high-formability low-density steel is composed of ferrite, martensite, bainite and retained austenite, the ferrite accounts for 70%-86%, the martensite and the bainite account for 10%-26%, and the retained austenite accounts for 4%-7%. The production process of converter or electric furnace smelting, medium and thin slab continuous casting and rolling, acid pickling, cold rolling and hot galvanizing is adopted, the high-formability low-density steel is produced, and the high-formability low-density steel has the advantages of being low in density, high in formability, high in corrosion resistance, low in emission and high in surface quality.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy, and particularly relates to a high-formability low-density steel and a preparation method thereof. BACKGROUND

[0002] In order to achieve the goal of carbon emission reduction, lightweight has become the mainstream trend of the development of the automobile industry. Low-density steel has the characteristics of high strength and low density, and the density is less than 7.4*103 kg / m 3 , which has attracted widespread attention from automobile manufacturers and steel enterprises. At present, most of the low-density steels are designed by high-manganese and high-aluminum alloy components and produced by traditional production lines, which are high in cost, complex in process and difficult to produce, and are difficult to meet the requirements.

[0003] Patent CN 108950392 B discloses an ultra-high ductility low-density steel and a preparation method thereof, the ultra-high ductility low-density steel includes the following chemical components by weight percentage: C: 0.3%-0.5%, Si: 0.2%-0.5%, Mn: 8%-10%, Alt: 3%-5%, Ce: 0.02%-0.04%, P≤0.01%, S≤0.01%, N≤0.005%, and the balance is Fe and trace elements; it adopts a medium-manganese high-carbon component design, the manganese content reaches 8%-10%, the processing process is complex, and the production is difficult.

[0004] Patent CN 114480988 A discloses a multi-phase composite high-strength high-toughness low-density steel and a preparation method thereof, the chemical components of the multi-phase composite high-strength high-toughness low-density steel are as follows in terms of mass percentage: 1.05 1.10wt.%C, 27.0 28.0wt.%Mn, 10.3 11.0wt.%Al, 3.0 3.5wt.%Cr, 0 3.6wt.%Ni, 0.02 0.04wt.%Nb, S≤0.01%, P≤0.005%, and the balance is Fe and inevitable impurities; it adopts a high-manganese high-carbon component design, the manganese content reaches 27%-28%, which leads to high alloy cost and limited application.

[0005] Patent CN 114892084 A discloses a high-strength austenitic lightweight steel with high impact toughness and a manufacturing method thereof. The chemical composition of the high-strength austenitic lightweight steel includes, by mass percentage: Mn 23-26%, Al 6.90-8.20%, C 0.83-0.92%, Si 0.10-0.35%, Cr 0.05-0.14%, Cu 0.10-0.30%, Nb 0.01-0.04%, N≤0.10%, P≤0.008%, S≤0.002%, and the balance being iron and unavoidable impurities. In this scheme, the manganese content reaches 23%-26%, resulting in high cost and great difficulty in production. SUMMARY

[0006] The present application aims to overcome the defects of the above-mentioned technology and provide a high-formability low-density steel and a preparation method thereof.

[0007] According to an aspect of the present application, a high-formability low-density steel is provided, and the chemical composition of the steel is as follows in terms of mass percentage: C: 0.02%-0.08%, Si: 0.2%-0.6%, Mn: 0.2%-1.2%, P: 0.05-0.12%, S≤0.03%, Al: 3.0%-5.0%, Cr: 0.8%-1.5%, and the balance being Fe and unavoidable impurities, wherein Al / Cr: 3-5.

[0008] The reasons for the alloy design of the present application are as follows: C: C element plays a role in solid solution strengthening and stabilizing austenite in steel, improving the strength and elongation of the steel plate. If the content of C element is too low, the strength and elongation of the steel will be reduced; if the content of C element is too high, the welding performance of the steel plate will be reduced. Therefore, the content of C element ranges from 0.02% to 0.08%.

[0009] Mn: Mn element plays a role in solid solution strengthening and stabilizing austenite in steel. If the content of Mn element is too low, the strength and elongation of the steel plate will be reduced; if the content of Mn element is too high, the strength of the steel plate will be too high and the elongation will decrease. Therefore, the content of Mn element ranges from 0.2% to 1.2%.

[0010] Si: Si element can play a role in solid solution strengthening and reducing the density of the steel plate. If the content of Si element is too low, it will not have a strengthening effect; if the content of Si element is too high, the surface quality of the steel plate will be reduced.

[0011] Al: Al element in the steel plays a role in reducing the density of the steel plate, improving the strength of ferrite, elongation and corrosion resistance, Al element can form a passivation film on the surface of the steel, which plays a role in corrosion resistance. Al element also plays a role in inhibiting the precipitation of C element in austenite, stabilizing austenite, improving the strength and forming property of the steel plate. If the content of Al element is too low, the density reduction effect will not be obvious, and a good passivation film cannot be formed; if the content of Al element is too high, it will lead to production difficulty, and at the same time, it will lead to grain coarsening and reduce the forming property of the steel plate.

[0012] P: P element in the steel plays a role in strengthening, and also plays a role in improving corrosion resistance and inhibiting the precipitation of cementite.

[0013] S: S element is a harmful element in steel, and the lower the content is, the better.

[0014] Cr: Cr element mainly plays a role in improving corrosion resistance and improving the stability of austenite. Cr element plays a role in stabilizing austenite, thereby increasing the strength and forming property of the steel plate. In addition, the present application significantly improves the strength, forming property and corrosion resistance of the steel plate through the synergistic effect of Al and Cr. Cr plays a role in improving the corrosion resistance of the steel plate by increasing the electrode potential of the steel plate, and cooperates with Al element to form a composite passivation film, thereby enhancing the density and penetration resistance of the film and improving the corrosion resistance of the steel plate. Therefore, the ratio between Al and Cr is limited as follows: Al / Cr: 3~5.

[0015] The metallographic structure of the high-forming-property low-density steel is composed of ferrite, martensite, bainite and residual austenite, wherein the ferrite accounts for 70%~86%, the martensite and bainite account for 10%~26%, and the residual austenite accounts for 4%~7%, based on the total content of 100%.

[0016] Based on the above technical scheme, the high-forming-property low-density steel has a tensile strength Rm>400MPa, a yield strength Rel of 180~300MPa, an elongation A after breaking of >25%, and a density of 7.3~7.5Kg / m 3 .

[0017] According to another aspect of the present application, a preparation method of high-forming-property low-density steel is provided, comprising the following steps: converter or electric furnace smelting, medium-thin slab continuous casting and rolling, pickling, cold rolling, continuous annealing; converter or electric furnace smelting; medium-thin slab continuous casting and rolling: the continuous casting process adopts medium-thin slab continuous casting to obtain a continuous casting billet; hot charging and hot feeding are performed, hot rolling is carried out, the opening rolling temperature is 1000~1150℃, the final rolling temperature is 860~950℃, the laminar cooling rate is 10~50℃ / s, and the coiling temperature is 520~730℃; pickling; Cold rolling: reduction rate of 30-70%; Continuous annealing: heating and soaking temperature of the strip is 760-850℃, soaking time is 60-90s, slow cooling exit temperature is 680-700℃, slow cooling rate is 2-10℃ / s, fast cooling exit temperature is 350-420℃, fast cooling rate is >20℃ / s, then aging holding is carried out, holding time is 300-500s, holding temperature is 300-420℃.

[0018] Based on the above technical solution, when a converter is used for smelting, the smelting conditions are as follows: the smelting temperature is 1650-1710℃; the smelting time is 25-35min.

[0019] Based on the above technical solution, when an electric furnace is used for smelting, the smelting conditions are as follows: the smelting temperature is 1610-1680℃; the smelting time is 40-70min. Based on the above technical solution, the chemical composition of the molten steel obtained by the converter or electric furnace smelting is as follows in terms of mass percentage: C: 0.02%-0.08%, Si: 0.2%-0.6%, Mn: 0.2%-1.2%, P: 0.05-0.12%, S≤0.03%, Al: 3.0%-5.0%, Cr: 0.3%-1.5%, the balance being Fe and unavoidable impurities, wherein Al / Cr: 3-5.

[0020] Advantages (1) The present application develops a high-formability low-density steel with high aluminum, chromium, low carbon and low manganese, which has low cost and can be produced on traditional production lines. In the component design, in addition to meeting the content of main alloying elements such as C, Al, Cr, Mn and Si, the Al / Cr ratio is also limited to 3-5, which ensures that the low-density steel not only has the characteristics of good strength, formability and low density, but also has the advantage of high corrosion resistance.

[0021] (2) In the manufacturing process of the steel plate, through process control and the mutual cooperation of C, Al and Cr elements, a low-density steel with a certain content of residual austenite is obtained, so as to ensure that phase transformation strengthening occurs during the deformation of the steel plate, thereby improving the strength and formability of the steel plate. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 Metallographic structure of the high-formability low-density steel prepared in Example 4 of the present application. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions of the present application more clear, the following embodiments, the present application is further illustrated, but the protection scope of the present application is not limited to these embodiments, the embodiments are only used to explain the present application. Those skilled in the art should understand that any change or equivalent replacement without departing from the concept of the present application is included in the protection scope of the present application.

[0024] Unless otherwise specified, the reagents, raw materials used in the present application are obtained by purchase.

[0025] The present application provides a high formability low density steel in the specific embodiment part, and the chemical composition is as follows: C: 0.02%~0.08%, Si: 0.2%~0.6%, Mn: 0.2%~1.2%, P: 0.05~0.12%, S≤0.03%, Al: 3.0%~5.0%, Cr: 0.8%~1.5%, the balance is Fe and inevitable impurities, wherein Al / Cr: 3~5.

[0026] Based on the above technical solutions, the tensile strength Rm of the high formability low density steel is greater than 400 MPa, the yield strength Rel is 180~300 MPa, the elongation A after breaking is greater than 25%, and the density is 7.3~7.5 Kg / m 3 .

[0027] The present application further provides a preparation method of the high formability low density steel in the specific embodiment part, which comprises the following steps: converter or electric furnace smelting, medium thin slab continuous casting and rolling, pickling, cold rolling, continuous annealing; The method of converter or electric furnace smelting is used for smelting, and the chemical composition of the molten steel is as follows: C: 0.02%~0.08%, Si: 0.2%~0.6%, Mn: 0.2%~1.2%, P: 0.05~0.12%, S≤0.03%, Al: 3.0%~5.0%, Cr: 0.3%~1.5%, the balance is Fe and inevitable impurities.

[0028] Based on the above technical solutions, when the converter is used for smelting, the smelting conditions are as follows: the smelting temperature is 1650~1710 ℃; the smelting time is 25~35 min.

[0029] Based on the above technical solutions, when the electric furnace smelting is used, the smelting conditions are as follows: the smelting temperature is 1610~1680 ℃; the smelting time is 40~70 min.

[0030] Medium-thin slab continuous casting and rolling: the continuous casting process adopts medium-thin slab continuous casting to obtain continuous casting billets; hot charging and hot feeding are performed, and hot rolling is performed, and the rolling process is as follows: the opening rolling temperature is 1000-1150℃, the final rolling temperature is 860-950℃, the cooling mode adopts laminar cooling mode, the rate of the laminar cooling is 10-50℃ / s, and the coiling temperature is 520-730℃.

[0031] Pickling: a conventional pickling method is adopted, and the main purpose is to remove the oxides on the surface of the hot-rolled steel plate.

[0032] Cold rolling: the cold rolling reduction rate is 30-70%.

[0033] Continuous annealing: the heating and soaking temperature during the heating process of the strip steel is 760-850℃, the soaking time is 60-90s, the slow cooling outlet temperature is 680-700℃, the slow cooling rate is 2-10℃ / s, the fast cooling outlet temperature is 350-420℃, the fast cooling rate is >20℃ / s, and then aging soaking is performed, the soaking time is 300-500s, and the soaking temperature is 300-420℃.

[0034] Examples and comparative examples The chemical components of the high-formability low-density steel of the examples and comparative examples are shown in Table 1, the process parameters related to the medium-thin slab continuous casting and rolling of the examples and comparative examples are shown in Table 2, the examples and comparative examples are subjected to pickling, cold rolling and continuous annealing after hot rolling, the process parameters related to cold rolling and continuous annealing are shown in Table 3, and the mechanical properties, density and metallographic structure of the steel plates of the examples and comparative examples are shown in Table 4, and the corrosion resistance is shown in Table 5. The metallographic structure of the high-formability low-density steel prepared in Example 4 is shown in Figure 1 .

[0035] Table 1 Chemical components of high-formability low-density steel, wt%

[0036] Table 2 Process parameters related to smelting and medium-thin slab continuous casting and rolling

[0037] Table 3 Process parameters related to cold rolling and continuous annealing

[0038] Table 4 Mechanical properties, density and metallographic structure of steel plates

[0039] Test example In order to determine the corrosion resistance of the material, the steel plates obtained from the comparative example and the examples are respectively placed in a mixed solution of 0.1 mol / L NaCl and 0.01 mol / L NaHSO3 for electrochemical measurement, the corrosion current and corrosion potential of the material are analyzed to evaluate the corrosion resistance of the material. The results are shown in Table 5, which shows that the corrosion resistance of the examples is significantly better than that of the comparative example, and the steel material obtained from the examples has good corrosion resistance.

[0040] Table 5 Corrosion resistance of steel plate

[0041] The above is only a few embodiments of the present application, and does not limit the present application in any form. Although the present application is disclosed with the preferred embodiments, it is not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical content without departing from the scope of the technical solution of the present application, which is equivalent to the equivalent implementation examples, and belongs to the scope of the technical solution.

Claims

1. A high formability low density steel, characterized in that, The chemical composition in mass percentage is: C: 0.02%~0.08%, Si: 0.2%~0.6%, Mn: 0.2%~1.2%, P: 0.05~0.12%, S≤0.03%, Al: 3.0%~5.0%, Cr: 0.8%~1.5%, and the balance is Fe and inevitable impurities, wherein Al / Cr is 3~5.

2. The high formability low density steel according to claim 1, characterized in that, The high-formability low-density steel has a tensile strength Rm > 400 MPa, a yield strength Rel of 180-300 MPa, an elongation after break A ≥ 25%, and a density of 7.3-7.5 Kg / m 3 ; The metallographic structure of the high-formability low-density steel is composed of ferrite, martensite, bainite and residual austenite, wherein the ferrite accounts for 70%~86%, the martensite and bainite account for 10%~26%, and the residual austenite accounts for 4%~7%, based on the total content of 100%.

3. The method of producing a high-formability low-density steel according to any one of claims 1 to 2, characterized by, The method comprises the following steps: converter or electric furnace smelting, medium-thin slab continuous casting and rolling, pickling, cold rolling, continuous annealing; The converter or electric furnace smelting; The medium-thin slab continuous casting and rolling: the continuous casting process adopts medium-thin slab continuous casting to obtain a continuous casting billet; the continuous casting billet is hot charged and hot sent to perform hot rolling, the opening rolling temperature is 1000~1150℃, the final rolling temperature is 860~950℃, the laminar cooling rate is 10~50℃ / s, and the coiling temperature is 520~730℃; The pickling; The cold rolling: the reduction rate is 30~70%; The continuous annealing: the heating and soaking temperature of the strip steel is 760~850℃, the soaking time is 60~90s, the slow cooling outlet temperature is 680~700℃, the slow cooling rate is 2~10℃ / s, the fast cooling outlet temperature is 350~420℃, the fast cooling rate is >20℃ / s, and then aging heat preservation is performed, the heat preservation time is 300~500s, and the heat preservation temperature is 300~420℃.

4. The preparation method according to claim 3, characterized in that, When the converter is used for smelting, the smelting conditions are as follows: the smelting temperature is 1650~1710℃; and the smelting time is 25~35min.

5. The preparation method according to claim 3, characterized in that, When the electric furnace is used for smelting, the smelting conditions are as follows: the smelting temperature is 1610~1680℃; and the smelting time is 40~70min.

6. The preparation method according to claim 3, characterized in that, The chemical composition of the molten steel obtained by the converter or electric furnace smelting in mass percentage is: C: 0.02%~0.08%, Si: 0.2%~0.6%, Mn: 0.2%~1.2%, P: 0.05~0.12%, S≤0.03%, Al: 3.0%~5.0%, Cr: 0.3%~1.5%, and the balance is Fe and inevitable impurities.

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