Low-density steel based on short process and preparation method thereof

Abstract

The invention relates to low-density steel based on a short process and a preparation method of the low-density steel. The steel comprises the following chemical components in percentage by mass: 0.051%-0.14% of C, 0.42%-0.92% of Si, 0.63%-1.3% of Mn, less than or equal to 0.03% of P, less than or equal to 0.02% of S, 3.0%-6.0% of Al, 0.011%-0.051% of Ti, 0.0011%-0.0041% of N and the balance of Fe and inevitable impurities. The production process has the advantages that the production process of converter or electric furnace smelting, medium and thin slab continuous casting and rolling, acid pickling, cold rolling, continuous annealing, acid pickling and nickel electroplating is adopted, the cold-rolled high-strength light steel with the tensile strength larger than 590 MPa and the elongation higher than 26% is produced, and the cold-rolled high-strength light steel has the advantages of being low in density, high in formability and high in phosphorization performance.

Description

Technical Field

[0001] The invention belongs to the field of alloy steel manufacturing, and in particular relates to a short-process low-density steel and a preparation method thereof. Background Art

[0002] At present, with the rapid development of new energy vehicles, lightweighting has become the mainstream trend of the automotive industry. The development and application of high-strength and ultra-high-strength automotive steels have greatly promoted the development of lightweighting of automobiles. Among them, low-density steel has the characteristics of high strength and low density, which reduces the thickness and weight of plate components and has attracted widespread attention from automobile manufacturers.

[0003] At present, most low-density steels are designed with high manganese and high aluminum alloy components and produced by traditional production lines, which are costly, complex in process, and difficult to produce. For example, patent publication number CN115216704 A discloses a short-process production method for low-density steel based on thin strip continuous casting, which adopts a high manganese and high aluminum component design, with a manganese content of 16% to 25% and an aluminum content of 6% to 12%. Due to the high content of alloy elements, the cost of the product is high, and the production is difficult, and the application is limited. Patent publication number CN112877606A discloses an ultra-high-strength fully austenitic low-density steel and preparation method, which adopts a high alloy component design, with a manganese content of 25% to 30%. Due to the high alloy content, the price of the product is high and the production is difficult. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a short-process low-density steel and a preparation method thereof, which reduces the production difficulty by cleverly matching the composition design with the process design, and produces cold-rolled high-strength low-density steel with a yield strength of 340 to 510 MPa, a tensile strength of 590 to 680 MPa, and an elongation of 26% to 36%.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions:

[0006] A short-process low-density steel, the chemical composition of the steel is as follows by mass percentage:

[0007] C: 0.051%~0.14%, Si: 0.42%~0.92%, Mn: 0.63%~1.3%, P≤0.03%, S≤0.02%, Al: 3.0%~6.0%, Ti: 0.011%~0.051%, N: 0.0011%~0.0041%, and the balance is Fe and unavoidable impurities.

[0008] The microstructure of the low-density steel consists of ferrite, martensite, bainite and a small amount of austenite, the volume percentage of ferrite is 70% to 85%, the total volume percentage of martensite and bainite is 8% to 20%, and the volume percentage of austenite is 5% to 10%.

[0009] The yield strength of the low-density steel is 340-510 MPa, the tensile strength is 590-680 MPa, and the elongation is 26%-36%.

[0010] The main functions of the components in the short process low-density steel in the present invention are:

[0011] C: C element plays a major role in solid solution strengthening in steel, improving the strength of steel plates. It is also an austenite stabilizing element, stabilizing austenite. If the C element content is too low, the strength of the steel will be reduced; if the C element content is too high, cementite will easily precipitate at the grain boundary, reducing the plasticity of the steel. Therefore, the C element content ranges from 0.051% to 0.14%.

[0012] Mn: Mn plays a role in solid solution strengthening and stabilizing austenite in steel. If the Mn content is too low, the strength of the steel plate will be reduced; if the Mn content is too high, the strength of the steel plate will be too high and the elongation will decrease. Therefore, the Mn content ranges from 0.63% to 1.3%.

[0013] Si: Si can inhibit the precipitation of cementite and also play a role in solid solution strengthening. If the Si content is too low, it will not inhibit the precipitation of cementite; if the Si content is too high, the surface quality of the steel plate will be reduced.

[0014] Al: Al in steel plays a role in reducing the density of steel plates, increasing the strength of ferrite and inhibiting the precipitation of cementite. If the Al content is too low, the density reduction effect will not be obvious; if the Al content is too high, it will cause production difficulties.

[0015] P: The P element plays a role in strengthening steel on the one hand, and inhibits the precipitation of cementite on the other hand.

[0016] S: S is a harmful element in steel, and the lower its content, the better.

[0017] Ti: Ti element plays a role in precipitation strengthening in steel. On the other hand, Ti element combines with C and N elements at high temperature to form precipitates such as TiN, TiC, and Ti(CN), which inhibit the growth of ferrite and austenite grains during high-temperature rolling and play a role in grain refinement. Too high Ti element content will lead to increased costs and poor plasticity of steel plates; too low Ti element content will result in insufficient content of TiN, TiC, Ti(CN) and other precipitates, which cannot play a role in grain refinement.

[0018] N: The main function of N in steel is to combine with Ti and Al to form nitrides, which refines the grains, especially the high-temperature δ-ferrite.

[0019] A method for preparing low-density steel based on a short process, including converter or electric furnace smelting, medium-thin slab continuous casting and rolling, pickling, cold rolling, continuous annealing, light pickling, and nickel electroplating processes; specifically including:

[0020] 1) Continuous casting and rolling of medium-thin slabs: Continuous casting of medium-thin slabs is adopted to obtain continuous casting slabs with a thickness of 110-190 mm; hot charging and hot delivery are carried out for hot rolling; the rolling process is as follows: the starting rolling temperature is 1000-1150°C, the final rolling temperature is 850-1000°C, the cooling method adopts laminar cooling method, and the coiling temperature is 500-700°C;

[0021] 2) Cold rolling: The cold rolling reduction rate is 30% to 70%;

[0022] 3) Continuous annealing: annealing temperature is 760-880°C, annealing time is 130-420s, cooling rate is 10-60°C / s, cooling temperature is 200-350°C, aging treatment is performed, aging temperature is 200-350°C, aging time is 200-500s, and finally cooled to room temperature at a cooling rate of 10-40°C / s;

[0023] 4) Electroplating nickel: nickel is plated by electrochemical or chemical methods, and the thickness of the nickel layer is 5 to 30 μm.

[0024] The prepared cold-rolled low-density steel plate has a thickness of 0.5 to 2.3 mm and a density of less than 7.5×10 3 kg / m 3 .

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The low-density steel of the present invention can be used in the manufacture of automotive structural parts, safety parts, battery packs and other parts. The present invention adopts a production process of converter or electric furnace smelting, continuous casting and rolling of medium and thin slabs, pickling, cold rolling, continuous annealing, pickling, and nickel electroplating to produce cold-rolled high-strength lightweight steel with a tensile strength greater than 590MPa and an elongation of more than 26%, which has the advantages of low density, high formability, and high phosphating performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is based on the metallographic diagram of short process low density steel. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the specific implementation modes of the present invention are further described below in conjunction with examples. However, it should be noted that the implementation of the present invention is not limited to the following implementation modes.

[0029] A low-density steel based on a short process, see Figure 1 , the chemical composition of steel in mass percentage is:

[0030] C: 0.051% to 0.14%, Si: 0.42% to 0.92%, Mn: 0.63% to 1.3%, P≤0.03%, S≤0.02%, Al: 3.0% to 6.0%, Ti: 0.011% to 0.051%, N: 0.0011% to 0.0041%, the remainder is Fe and unavoidable impurities. The microstructure of low-density steel is composed of ferrite, martensite, bainite and a small amount of austenite. The volume percentage of ferrite is 70% to 85%, the total volume percentage of martensite and bainite is 8% to 20%, and the volume percentage of austenite is 5% to 10%. Among them, ferrite includes δ-Fe ferrite and a small amount of α-Fe ferrite. The yield strength of low-density steel is 340 to 510MPa, the tensile strength is 590 to 680MPa, and the elongation is 26% to 36%.

[0031] The preparation method of low-density steel based on a short process includes converter or electric furnace smelting, medium-thin slab continuous casting and rolling, pickling, cold rolling, continuous annealing, light pickling, and nickel electroplating processes; specifically includes:

[0032] 1) Smelting is carried out by converter or electric furnace smelting;

[0033] 2) Continuous casting and rolling of medium-thin slabs: Continuous casting of medium-thin slabs is adopted to obtain continuous casting slabs with a thickness of 110-190 mm; hot charging and hot delivery are carried out for hot rolling; the rolling process is as follows: the starting rolling temperature is 1000-1150°C, the final rolling temperature is 850-1000°C, the cooling method adopts laminar cooling method, and the coiling temperature is 500-700°C;

[0034] 3) Pickling: conventional pickling method is used, the main purpose of which is to remove oxides on the surface of hot-rolled steel plates;

[0035] 4) Cold rolling: The cold rolling reduction rate is 30-70%;

[0036] 5) Continuous annealing: annealing temperature is 760-880°C, annealing time is 130-420s, cooling rate is 10-60°C / s, cooling temperature is 200-350°C, aging treatment is performed, aging temperature is 200-350°C, aging time is 200-500s, and finally cooled to room temperature at a cooling rate of 10-40°C / s;

[0037] 6) Light pickling to remove oxides on the surface of the steel plate produced during the continuous annealing process.

[0038] 7) Electroplating nickel: nickel is plated by electrochemical or chemical methods, and the thickness of the nickel layer is 5 to 30μm. If the thickness of the nickel layer is less than 5μ, the surface quality of the steel plate will be reduced; if the thickness is greater than 30μ, the cost of the steel plate will increase, the internal stress will increase, and the sensitivity to hydrogen embrittlement will increase.

[0039] The yield strength of low-density steel is 340-510 MPa, the tensile strength is 590-680 MPa, and the elongation is 26%-36%.

[0040] The following are the chemical compositions and preparation methods of the embodiments:

[0041] The chemical composition of the embodiment is shown in Table 1. After the ingot is obtained, hot rolling is performed, and the hot rolling process is shown in Table 2. After hot rolling, pickling, cold rolling and annealing are performed, and the cold rolling and annealing processes are shown in Table 3. Finally, the mechanical properties and phosphating properties of the steel plate are shown in Table 4.

[0042] Table 1 Chemical composition of the examples, wt%

[0043] Steel Grade C Si Mn P S Al Ti N A1 0.052 0.42 1.19 0.015 0.006 3.2 0.013 0.0023 A2 0.054 0.47 1.12 0.012 0.022 3.8 0.019 0.0034 A3 0.062 0.51 1.05 0.006 0.008 3.5 0.024 0.0015 A4 0.068 0.63 0.98 0.007 0.014 4.1 0.027 0.0018 A5 0.074 0.71 0.88 0.018 0.012 4.7 0.033 0.0029 A6 0.087 0.82 0.78 0.007 0.010 4.9 0.032 0.0039 A7 0.095 0.54 0.62 0.006 0.011 5.1 0.026 0.0037 A8 0.105 0.43 0.73 0.005 0.007 5.5 0.034 0.0028 A9 0.113 0.82 0.81 0.014 0.008 5.9 0.043 0.0016 A10 0.128 0.89 0.67 0.013 0.016 4.7 0.049 0.0019

[0044] Table 2 Hot rolling process of the embodiment

[0045]

[0046]

[0047] Table 3 Cold rolling and continuous annealing process of the embodiment

[0048]

[0049] Table 4 Mechanical test and phosphating performance test results of the examples

[0050]

[0051] Evaluation method of steel plate phosphating performance: phosphating the annealed steel plate after degreasing, washing, surface conditioning, washing ...

[0052] The present invention adopts the production process of converter or electric furnace smelting, continuous casting and rolling of medium and thin slabs, pickling, cold rolling, continuous annealing, pickling, and nickel electroplating to produce cold-rolled high-strength lightweight steel with a tensile strength greater than 590MPa and an elongation greater than 25%, and has the advantages of low density, high formability, low emissions, and high surface quality.

Claims

1. A short process low-density steel, characterized in that: The chemical composition of steel in mass percentage is: C: 0.051%~0.14%, Si: 0.42%~0.92%, Mn: 0.63%~1.3%, P≤0.03%, S≤0.02%, Al: 3.0%~6.0%, Ti: 0.011%~0.051%, N: 0.0011%~0.0041%, and the balance is Fe and unavoidable impurities.

2. A short process low-density steel according to claim 1, characterized in that: The microstructure of the low-density steel consists of ferrite, martensite, bainite and a small amount of austenite, the volume percentage of ferrite is 70% to 85%, the total volume percentage of martensite and bainite is 8% to 20%, and the volume percentage of austenite is 5% to 10%.

3. The short-process low-density steel according to claim 1, characterized in that: The yield strength of the low-density steel is 340-510 MPa, the tensile strength is 590-680 MPa, and the elongation is 26%-36%.

4. A method for preparing low-density steel based on a short process as claimed in any one of claims 1 to 3, characterized in that: It includes converter or electric furnace smelting, medium and thin slab continuous casting and rolling, pickling, cold rolling, continuous annealing, light pickling, and nickel electroplating processes; specifically, it includes: 1) Continuous casting and rolling of medium-thin slabs: Continuous casting of medium-thin slabs is adopted to obtain continuous casting slabs with a thickness of 110-190 mm; hot charging and hot delivery are carried out for hot rolling; the rolling process is as follows: the starting rolling temperature is 1000-1150°C, the final rolling temperature is 850-1000°C, the cooling method adopts laminar cooling method, and the coiling temperature is 500-700°C; 2) Cold rolling: The cold rolling reduction rate is 30% to 70%; 3) Continuous annealing: annealing temperature is 760-880°C, annealing time is 130-420s, cooling rate is 10-60°C / s, cooling temperature is 200-350°C, aging treatment is performed, aging temperature is 200-350°C, aging time is 200-500s, and finally cooled to room temperature at a cooling rate of 10-40°C / s; 4) Electroplating nickel: nickel is plated by electrochemical or chemical methods, and the thickness of the nickel layer is 5 to 30 μm.

5. The method for preparing low-density steel based on a short process according to claim 4, characterized in that: The prepared cold-rolled low-density steel plate has a thickness of 0.5 to 2.3 mm and a density of less than 7.5×10 3 kg / m 3 .

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