CN114086080B - Dual-phase-isomerism light high-strength steel and preparation method thereof - Google Patents

Abstract

The invention discloses dual-phase-isomerism light high-strength steel and a preparation method thereof, and belongs to the technical field of light high-strength automobile steel. The chemical components are as follows: 0.1-0.3wt.% of C, 10-14wt.% of Mn, 6-8wt.% of Al, 0.5-0.7wt.% of Si, less than or equal to 0.01wt.% of P, less than or equal to 0.005wt.% of S, and the balance of Fe and inevitable impurities. The cast structure of the dual-phase isomerism lightweight high-strength steel is a complex phase structure containing coarse fishbone delta ferrite and coarse granular austenite, and the structure of the prepared finished product dual-phase isomerism lightweight high-strength steel plate is strip delta ferrite and fine equiaxed austenite. The finished product of the dual-phase heterogeneous light high-strength steel plate has the yield strength of 388-807MPa, the tensile strength of 656-945MPa, the elongation of 33-55 percent, the product of strength and elongation of 31-38GPa percent, and the density of 6.9-7.1g/cm ³ 。

Description

A dual-phase heterogeneous light-weight high-strength steel and its preparation method

technical field

The invention belongs to the technical field of light-weight high-strength automobile steel, and relates to a dual-phase heterogeneous light-weight high-strength steel and a preparation method thereof.

Background technique

In recent decades, the automobile industry has developed rapidly, and the number of automobiles is on the rise. However, the following problems such as fuel shortage and automobile environmental pollution are becoming more and more serious, and energy conservation and environmental protection have become a new direction for the development of the automobile industry.

The lightweight design of the car can not only reduce the weight of the car body on the premise of ensuring the safety of the car, but also improve the fuel economy of the car and reduce carbon emissions, which is an effective way to deal with the aforementioned problems.

At present, there are two main ways to achieve lightweight: one is to further increase the strength of automobile steel, and reduce the amount of steel while ensuring the mechanical performance requirements of parts; the other way is to use lightweight materials, such as aluminum with low density, Magnesium alloys, engineering plastics or carbon fiber composite materials, etc. However, the aforementioned materials often have disadvantages such as low strength, high preparation cost, and poor thermal stability, which limit the application and development of these lightweight materials in the automotive industry.

The research found that by adding a certain amount of light Al elements to the steel, the developed Fe-Mn-Al-C low-density steel has high strength, toughness, and good fatigue and oxidation resistance. It is a very Potential new automotive steel. However, the currently developed Fe-Mn-Al-C low-density steel often has problems such as low strength and plasticity, high cost, and complicated processing and preparation processes, which cannot meet the application requirements of lightweight high-strength steel for automobiles.

For example: Chinese patent CN113278896A discloses a Fe-Mn-Al-C series high-strength low-density steel and a preparation method thereof. The key point of this patent is that the chemical composition of the steel is: C 1.0-2.0%, Mn 20-40%, Al 10-14%, 2%≤Ni+Cr≤15%, the balance is Fe, obtained by forging and hot rolling with a large amount of Although the austenite structure of the DO3 precipitated phase can obtain relatively superior mechanical properties under the strengthening effect of the second phase, the disadvantage is that a large amount of Cr and Ni elements are added, resulting in high production costs, and the C content exceeds 1.0 % lead to poor weldability of steel. Moreover, it can be seen from Table 2 that the strength-plasticity product of the prepared high-strength low-density steel is up to 19.5GPa%, which is far less than the requirement of lightweight high-strength steel for automobiles.

Chinese patent CN111235484A discloses a high-strength high-hardness low-density steel and its preparation method and application. The focus of this patent is to increase the strength and hardness of steel materials through smelting, hot forging, water toughening, hot rolling, solid solution, cold rolling, aging, nitriding, and annealing in sequence, but it does not increase the strength and plasticity and reduce the C content, and too high manganese content makes the steel brittle and hard, and reduces the rust resistance and weldability of the steel. In addition, the disadvantage of the prepared high-strength, high-hardness and low-density steel is that the overall process is relatively complicated, and the nitriding and denitrification processes require high production equipment, which is not conducive to production.

In summary, although many technical achievements have been made in the technical field of high-strength light-weight steel, the high-strength light-weight steel currently developed still has a large number of alloys added, which leads to high cost, high C equivalent leads to poor weldability of steel, and manganese A high content will cause the steel to become brittle and hard, reduce rust resistance and weldability, and the complex preparation process is not conducive to large-scale industrial production and promotion.

Contents of the invention

The technical problem solved by the present invention is that the cost of adding alloy elements in the light-weight high-strength steel for automobiles in the prior art is high, the preparation process is complicated, and the operation is difficult, and the added alloy elements will deteriorate the strength and toughness of the light-weight high-strength steel for automobiles , weldability, density and rust resistance, which is not conducive to industrial production.

In order to solve the above technical problems, the present invention provides the following technical solutions:

A dual-phase heterogeneous lightweight high-strength steel, the chemical composition of the dual-phase heterogeneous lightweight high-strength steel is calculated by mass percentage: C 0.1-0.3wt.%, Mn 10-14wt.%, Al 6-8wt. %, Si 0.5-0.7wt.%, P≤0.01wt.%, S≤0.005wt.%, and the rest are Fe and unavoidable impurities.

Preferably, the as-cast structure of the dual-phase heterogeneous light-weight high-strength steel is a multi-phase structure comprising coarse herringbone δ-ferrite and coarse granular austenite, and the prepared finished dual-phase heterogeneous lightweight high-strength steel plate is The organization is banded delta ferrite and fine equiaxed austenite.

Preferably, the yield strength of the finished dual-phase heterogeneous lightweight high-strength steel plate is 388-807MPa, the tensile strength is 656-945MPa, the elongation is 33-55%, the strength-plastic product is 31-38GPa%, and the density is 6.9 -7.1 g/cm ³ .

The preparation method of the dual-phase heterogeneous light-weight high-strength steel, the preparation method includes the following steps:

S1. Raw material selection: Weigh Fe, Mn, C, Al, Si powders with purity ≥ 99.9% according to the chemical composition ratio of the dual-phase heterogeneous light-weight high-strength steel as alloy raw materials, and put the alloy raw materials into the electric In the magnetic induction furnace, vacuum melting is carried out under the protection of argon, and then the molten steel is cast into ingots;

S2. Hot forging after homogenization treatment: homogenize the ingot described in step S1, and then hot forge the homogenized ingot into a square billet;

S3, hot rolling: reheating the square steel billet described in step S2 to the hot rolling temperature, using a rolling mill to perform multi-pass rolling to obtain a hot rolled steel plate with a thickness of 5-7mm, and air cooling to room temperature after hot rolling;

S4, cold rolling after pickling: pickling the hot-rolled steel sheet described in step S3, and then using a cold rolling mill to perform multi-pass rolling and 1-pass skin-pass rolling to obtain a cold-rolled steel sheet with a thickness of 3-4mm ;

S5. Annealing treatment: the cold-rolled steel sheet described in step S4 is annealed. After the cold-rolled steel sheet is annealed, it is quickly quenched into water and cooled to room temperature to obtain a finished dual-phase heterogeneous lightweight high-strength steel sheet.

Preferably, the temperature of the homogenization treatment in the step S2 is 1200±30°C, the holding time is 3-5h, and the forging temperature is 900-1150°C.

Preferably, the hot rolling temperature in the step S3 is 1200±30°C, the holding time is 0.3-0.7h; the starting rolling temperature is 1150±20°C, and the finishing rolling temperature is higher than 900°C.

Preferably, the multi-pass rolling in the step S3 is 4-6 passes, and the rolling reduction is 55-65%.

Preferably, the multi-pass rolling in the step S4 is 8-10 passes, and the rolling reduction is 45-55%.

Preferably, the annealing temperature in the step S5 is 660-1000° C., and the holding time is 25-35 minutes.

Preferably, the cold rolling mill in the step S4 is a four-roll cold rolling mill.

The above technical solutions provided by the embodiments of the present invention have at least the following beneficial effects:

In the above scheme, compared with the high-strength light steel in the prior art: in terms of composition, the content of C element is greatly reduced, which improves the weldability of the material; the addition of an appropriate amount of Si element plays the role of solid solution strengthening and inhibition of carbide precipitation Effect; the addition of a large amount of Al elements not only reduces the density of the steel, but also improves the corrosion resistance, and at the same time promotes the preservation of high-temperature δ ferrite into the room temperature structure.

In the composition design of the double-phase heterogeneous light-weight high-strength steel ingot of the present invention, less Mn elements and more Al elements are added to promote the formation of high-temperature δ ferrite and keep it at room temperature. The as-cast structure contains coarse fishbone The multiphase structure of δ ferrite and coarse granular austenite, followed by homogenization treatment, hot forging, hot rolling, cold rolling and annealing treatment, to obtain striped δ ferrite and fine equiaxed austenite structure The finished steel of the structure can effectively reduce the density of the steel, improve the strength and plasticity, and realize light weight.

During the tensile test process of the finished steel product of the present invention, due to the existence of two heterogeneous structures with different forms and properties, the transfer of strain in the two phases is promoted, a mutation-induced strain hardening effect is formed, and the appearance of plastic instability is delayed, so that The yield strength of the new high-strength light steel is 388-807MPa, the tensile strength is 656-945MPa, the elongation is 33-55%, the strength-plastic product is 31-38GPa%, and the density is 6.9-7.1g/cm ³ . The performance requirements of the third-generation automotive steel have greater practical application value than ordinary third-generation automotive steel.

The preparation process of the finished steel product of the invention is simple and economical, and large-scale industrial production can be realized relying on the existing production line. The development and application of the finished steel has important economic value and social significance for promoting the lightweight design of automobiles, reducing energy consumption, and reducing greenhouse gas emissions.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings that need to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained based on these drawings without creative effort.

Fig. 1 is the metallographic diagram of the dual-phase heterogeneous lightweight high-strength steel of Example 1 of the present invention;

Fig. 2 is the metallographic diagram of the dual-phase heterogeneous lightweight high-strength steel of Example 2 of the present invention;

Fig. 3 is the EBSD figure of the dual-phase heterogeneous lightweight high-strength steel of Example 2 of the present invention;

Fig. 4 is the metallographic diagram of the dual-phase heterogeneous lightweight high-strength steel of Example 3 of the present invention;

Fig. 5 is the engineering stress-strain curve diagram of uniaxial tension at room temperature for the dual-phase heterogeneous lightweight high-strength steel of Examples 1-6 of the present invention, wherein: Mark 1 is the finished dual-phase heterogeneous lightweight high-strength steel of Example 1 The tensile curve of the high-strength steel plate, mark 2 is the tensile curve of the finished dual-phase heterogeneous light-weight high-strength steel plate of embodiment 2, and mark 3 is the tensile curve of the finished dual-phase heterogeneous light-weight high-strength steel plate of embodiment 3, marked 4 is the tensile curve of the finished dual-phase heterogeneous light-weight high-strength steel plate of Example 4, and 5 is the tensile curve of the finished dual-phase heterogeneous lightweight high-strength steel plate of Example 5, and 6 is the finished double-phase heterogeneous light-weight high-strength steel plate of Example 6. Tensile curves of phase-heterogeneous lightweight high-strength steel plates.

Detailed ways

In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will describe in detail with reference to the drawings and specific embodiments.

Example 1

A dual-phase heterogeneous lightweight high-strength steel, the chemical composition of which is calculated by mass percentage: C 0.14wt.%, Mn13.9wt.%, Al 6.1wt.%, Si 0.68wt.%, P≤0.01wt.% , S≤0.005wt.%, the rest is Fe and unavoidable impurities.

The preparation method of the dual-phase heterogeneous light-weight high-strength steel, the preparation method includes the following steps:

S1. Raw material selection: Weigh Fe, Mn, C, Al, Si powders with purity ≥ 99.9% according to the chemical composition ratio of the dual-phase heterogeneous light-weight high-strength steel as alloy raw materials, and put the alloy raw materials into the electric In the magnetic induction furnace, vacuum melting is carried out under the protection of argon, and then the molten steel is cast into ingots;

S2. Hot forging after homogenization treatment: homogenize the ingot described in step S1, the temperature of the homogenization treatment is 1200±30°C, and the holding time is 3-5h; after that, hot forge the ingot after the homogenization treatment Formed into a square billet, the forging temperature is 900-1150°C;

S3, hot rolling: reheat the square billet described in step S2 to the hot rolling temperature, the hot rolling temperature is 1200±30°C, and the holding time is 0.3-0.7h; The amount is 55-65%, to obtain a hot-rolled steel plate with a thickness of 5-7mm, air-cooled to room temperature after hot-rolling, the starting rolling temperature is 1150±20°C, and the final rolling temperature is higher than 900°C;

S4. Cold rolling after pickling: Pickling the hot-rolled steel sheet described in step S3, and then using a cold rolling mill to perform 8-10 passes of rolling and 1 pass of temper rolling, with a rolling reduction of 45-55% , obtaining a cold-rolled steel plate with a thickness of 3-4mm;

S5. Annealing treatment: Anneal the cold-rolled steel sheet described in step S4. The annealing temperature is 660° C., and the holding time is 25 minutes. High-strength steel plate.

As shown in Figure 1, the microstructure of the finished dual-phase heterogeneous lightweight high-strength steel plate is striped δ ferrite and fine equiaxed austenite.

Tensile performance tests were performed on the dual-phase heterogeneous lightweight high-strength steel prepared in this example. According to GBT228-2002, "Metallic Materials Tensile Test Method at Room Temperature", the finished dual-phase heterogeneous light-weight high-strength steel plate is processed into a standard tensile sample, and the tensile rate is 0.05mm/s. The tensile properties thus measured are shown in Table 1, and the engineering stress-strain curves are shown in Figure 5. The yield strength of the high-strength light steel prepared in Example 1 is 807MPa, the tensile strength is 945MPa, the total elongation is 32.5%, the strength-plastic product is 30.6GPa%, and the density is 7.08g/cm ³ , reaching the current advanced high-strength The level of strength and plasticity of automotive steel.

Example 2

A dual-phase heterogeneous lightweight high-strength steel, the chemical composition of which is calculated by mass percentage: C 0.22wt.%, Mn12.1wt.%, Al 7.2wt.%, Si 0.63wt.%, P≤0.01wt.% , S≤0.005wt.%, the rest is Fe and unavoidable impurities.

The preparation method of the dual-phase heterogeneous light-weight high-strength steel, the preparation method includes the following steps:

S1. Raw material selection: Weigh Fe, Mn, C, Al, Si powders with purity ≥ 99.9% according to the chemical composition ratio of the dual-phase heterogeneous light-weight high-strength steel as alloy raw materials, and put the alloy raw materials into the electric In the magnetic induction furnace, vacuum melting is carried out under the protection of argon, and then the molten steel is cast into ingots;

S2. Hot forging after homogenization treatment: homogenize the ingot described in step S1, the temperature of the homogenization treatment is 1200±30°C, and the holding time is 3-5h; after that, hot forge the ingot after the homogenization treatment Formed into a square billet, the forging temperature is 900-1150°C;

S3, hot rolling: reheat the square billet described in step S2 to the hot rolling temperature, the hot rolling temperature is 1200±30°C, and the holding time is 0.3-0.7h; The amount is 55-65%, to obtain a hot-rolled steel plate with a thickness of 5-7mm, air-cooled to room temperature after hot-rolling, the starting rolling temperature is 1150±20°C, and the final rolling temperature is higher than 900°C;

S4. Cold rolling after pickling: Pickling the hot-rolled steel sheet described in step S3, and then using a cold rolling mill to perform 8-10 passes of rolling and 1 pass of temper rolling, with a rolling reduction of 45-55% , obtaining a cold-rolled steel plate with a thickness of 3-4mm;

S5. Annealing treatment: Anneal the cold-rolled steel sheet described in step S4. The annealing temperature is 800° C., and the holding time is 30 minutes. High-strength steel plate.

As shown in Figures 2 and 3, the microstructure of the finished duplex heterogeneous lightweight high-strength steel plate is striped δ ferrite and fine equiaxed austenite, and striped δ ferrite and fine equiaxed austenite Austenite differs greatly in phase morphology and size.

Tensile performance tests were performed on the dual-phase heterogeneous lightweight high-strength steel prepared in this example. According to GBT228-2002, "Metallic Materials Tensile Test Method at Room Temperature", the finished dual-phase heterogeneous light-weight high-strength steel plate is processed into a standard tensile sample, and the tensile rate is 0.05mm/s. The tensile properties thus measured are shown in Table 1, and the engineering stress-strain curves are shown in Figure 5. The yield strength of the high-strength light steel prepared in Example 1 is 449MPa, the tensile strength is 720MPa, the total elongation is 52.3%, the strength-plastic product is 37.6GPa%, and the density is 6.97g/cm ³ , reaching the current advanced high-strength The level of strength and plasticity of automotive steel.

Example 3

A dual-phase heterogeneous lightweight high-strength steel, the chemical composition of which is calculated by mass percentage: C 0.28wt.%, Mn10.1wt.%, Al 8.1wt.%, Si 0.55wt.%, P≤0.01wt.% , S≤0.005wt.%, the rest is Fe and unavoidable impurities.

The preparation method of the dual-phase heterogeneous light-weight high-strength steel, the preparation method includes the following steps:

S1. Raw material selection: Weigh Fe, Mn, C, Al, Si powders with purity ≥ 99.9% according to the chemical composition ratio of the dual-phase heterogeneous light-weight high-strength steel as alloy raw materials, and put the alloy raw materials into the electric In the magnetic induction furnace, vacuum melting is carried out under the protection of argon, and then the molten steel is cast into ingots;

S2. Hot forging after homogenization treatment: homogenize the ingot described in step S1, the temperature of the homogenization treatment is 1200±30°C, and the holding time is 3-5h; after that, hot forge the ingot after the homogenization treatment Formed into a square billet, the forging temperature is 900-1150°C;

S3, hot rolling: reheat the square billet described in step S2 to the hot rolling temperature, the hot rolling temperature is 1200±30°C, and the holding time is 0.3-0.7h; The amount is 55-65%, to obtain a hot-rolled steel plate with a thickness of 5-7mm, air-cooled to room temperature after hot-rolling, the starting rolling temperature is 1150±20°C, and the final rolling temperature is higher than 900°C;

S4. Cold rolling after pickling: Pickling the hot-rolled steel sheet described in step S3, and then using a cold rolling mill to perform 8-10 passes of rolling and 1 pass of temper rolling, with a rolling reduction of 45-55% , obtaining a cold-rolled steel plate with a thickness of 3-4mm;

S5. Annealing treatment: Anneal the cold-rolled steel sheet described in step S4. The annealing temperature is 1000° C., and the holding time is 35 minutes. High-strength steel plate.

As shown in Figure 4, the microstructure of the finished dual-phase heterogeneous light-weight high-strength steel plate is striped δ ferrite and fine equiaxed austenite; High, although the sizes of ferrite and austenite gradually increase, they still maintain a dual-phase heterogeneous structure.

Tensile performance tests were performed on the dual-phase heterogeneous lightweight high-strength steel prepared in this example. According to GBT228-2002, "Metallic Materials Tensile Test Method at Room Temperature", the finished dual-phase heterogeneous light-weight high-strength steel plate is processed into a standard tensile sample, and the tensile rate is 0.05mm/s. The tensile properties thus measured are shown in Table 1, and the engineering stress-strain curves are shown in Figure 5. The yield strength of the high-strength light steel prepared in Example 1 is 388MPa, the tensile strength is 656MPa, the total elongation is 54.6%, the strength-plastic product is 35.6GPa%, and the density is 6.9g/cm ³ , reaching the current advanced high-strength The level of strength and plasticity of automotive steel.

Example 4

A dual-phase heterogeneous lightweight high-strength steel, the chemical composition of which is calculated by mass percentage: C 0.12wt.%, Mn13.5wt.%, Al 6.1wt.%, Si 0.69wt.%, P≤0.01wt.% , S≤0.005wt.%, the rest is Fe and unavoidable impurities.

The preparation method of the dual-phase heterogeneous light-weight high-strength steel, the preparation method includes the following steps:

S1. Raw material selection: Weigh Fe, Mn, C, Al, Si powders with purity ≥ 99.9% according to the chemical composition ratio of the dual-phase heterogeneous light-weight high-strength steel as alloy raw materials, and put the alloy raw materials into the electric In the magnetic induction furnace, vacuum melting is carried out under the protection of argon, and then the molten steel is cast into ingots;

S2. Hot forging after homogenization treatment: homogenize the ingot described in step S1, the temperature of the homogenization treatment is 1200±30°C, and the holding time is 3-5h; after that, hot forge the ingot after the homogenization treatment Formed into a square billet, the forging temperature is 900-1150°C;

S3, hot rolling: reheat the square billet described in step S2 to the hot rolling temperature, the hot rolling temperature is 1200±30°C, and the holding time is 0.3-0.7h; The amount is 55-65%, to obtain a hot-rolled steel plate with a thickness of 5-7mm, air-cooled to room temperature after hot-rolling, the starting rolling temperature is 1150±20°C, and the final rolling temperature is higher than 900°C;

S4. Cold rolling after pickling: Pickling the hot-rolled steel sheet described in step S3, and then using a cold rolling mill to perform 8-10 passes of rolling and 1 pass of temper rolling, with a rolling reduction of 45-55% , obtaining a cold-rolled steel plate with a thickness of 3-4mm;

S5. Annealing treatment: Anneal the cold-rolled steel sheet described in step S4. The annealing temperature is 700° C., and the holding time is 25 minutes. High-strength steel plate.

The microstructure of the finished duplex heterogeneous light-weight high-strength steel plate is banded δ ferrite and fine equiaxed austenite.

Tensile performance tests were performed on the dual-phase heterogeneous lightweight high-strength steel prepared in this example. According to GBT228-2002, "Metallic Materials Tensile Test Method at Room Temperature", the finished dual-phase heterogeneous light-weight high-strength steel plate is processed into a standard tensile sample, and the tensile rate is 0.05mm/s. The tensile properties thus measured are shown in Table 1, and the engineering stress-strain curves are shown in Figure 5. The high-strength light-weight steel prepared in Example 4 has a strength of 717MPa, a tensile strength of 857MPa, an elongation of 35.7%, a strength-plastic product of 30.6GPa%, and a density of 7.08g/cm ³ , reaching the strength of current advanced high-strength automotive steel. plasticity level.

Example 5

A dual-phase heterogeneous lightweight high-strength steel, the chemical composition of which is calculated by mass percentage: C 0.24wt.%, Mn12.7wt.%, Al 6.8wt.%, Si 0.61wt.%, P≤0.01wt.% , S≤0.005wt.%, the rest is Fe and unavoidable impurities.

The preparation method of the dual-phase heterogeneous light-weight high-strength steel, the preparation method includes the following steps:

S1. Raw material selection: Weigh Fe, Mn, C, Al, Si powders with purity ≥ 99.9% according to the chemical composition ratio of the dual-phase heterogeneous light-weight high-strength steel as alloy raw materials, and put the alloy raw materials into the electric In the magnetic induction furnace, vacuum melting is carried out under the protection of argon, and then the molten steel is cast into ingots;

S2. Hot forging after homogenization treatment: homogenize the ingot described in step S1, the temperature of the homogenization treatment is 1200±30°C, and the holding time is 3-5h; after that, hot forge the ingot after the homogenization treatment Formed into a square billet, the forging temperature is 900-1150°C;

S3, hot rolling: reheat the square billet described in step S2 to the hot rolling temperature, the hot rolling temperature is 1200±30°C, and the holding time is 0.3-0.7h; The amount is 55-65%, to obtain a hot-rolled steel plate with a thickness of 5-7mm, air-cooled to room temperature after hot-rolling, the starting rolling temperature is 1150±20°C, and the final rolling temperature is higher than 900°C;

S4. Cold rolling after pickling: Pickling the hot-rolled steel sheet described in step S3, and then using a cold rolling mill to perform 8-10 passes of rolling and 1 pass of temper rolling, with a rolling reduction of 45-55% , obtaining a cold-rolled steel plate with a thickness of 3-4mm;

S5. Annealing treatment: Anneal the cold-rolled steel sheet described in step S4. The annealing temperature is 750° C., and the holding time is 30 minutes. High-strength steel plate.

The microstructure of the finished duplex heterogeneous light-weight high-strength steel plate is banded δ ferrite and fine equiaxed austenite.

Tensile performance tests were performed on the dual-phase heterogeneous lightweight high-strength steel prepared in this example. According to GBT228-2002, "Metallic Materials Tensile Test Method at Room Temperature", the finished dual-phase heterogeneous light-weight high-strength steel plate is processed into a standard tensile sample, and the tensile rate is 0.05mm/s. The tensile properties thus measured are shown in Table 1, and the engineering stress-strain curves are shown in Figure 5. The high-strength light-weight steel prepared in Example 5 has a strength of 479MPa, a tensile strength of 771MPa, an elongation of 45.6%, a strong-plastic product of 35.1GPa%, and a density of 7g/cm ³ , reaching the strength and plasticity of current advanced high-strength automotive steel. accumulation level.

Example 6

A dual-phase heterogeneous lightweight high-strength steel, the chemical composition of which is calculated by mass percentage: C 0.26wt.%, Mn11.1wt.%, Al 7.8wt.%, Si 0.51wt.%, P≤0.01wt.% , S≤0.005wt.%, the rest is Fe and unavoidable impurities.

The preparation method of the dual-phase heterogeneous light-weight high-strength steel, the preparation method includes the following steps:

S1. Raw material selection: Weigh Fe, Mn, C, Al, Si powders with purity ≥ 99.9% according to the chemical composition ratio of the dual-phase heterogeneous light-weight high-strength steel as alloy raw materials, and put the alloy raw materials into the electric In the magnetic induction furnace, vacuum melting is carried out under the protection of argon, and then the molten steel is cast into ingots;

S2. Hot forging after homogenization treatment: homogenize the ingot described in step S1, the temperature of the homogenization treatment is 1200±30°C, and the holding time is 3-5h; after that, hot forge the ingot after the homogenization treatment Formed into a square billet, the forging temperature is 900-1150°C;

S3, hot rolling: reheat the square billet described in step S2 to the hot rolling temperature, the hot rolling temperature is 1200±30°C, and the holding time is 0.3-0.7h; The amount is 55-65%, to obtain a hot-rolled steel plate with a thickness of 5-7mm, air-cooled to room temperature after hot-rolling, the starting rolling temperature is 1150±20°C, and the final rolling temperature is higher than 900°C;

S4. Cold rolling after pickling: Pickling the hot-rolled steel sheet described in step S3, and then using a cold rolling mill to perform 8-10 passes of rolling and 1 pass of temper rolling, with a rolling reduction of 45-55% , obtaining a cold-rolled steel plate with a thickness of 3-4mm;

S5. Annealing treatment: Anneal the cold-rolled steel sheet described in step S4. The annealing temperature is 900° C., and the holding time is 35 minutes. High-strength steel plate.

The microstructure of the finished duplex heterogeneous light-weight high-strength steel plate is banded δ ferrite and fine equiaxed austenite.

Tensile performance tests were performed on the dual-phase heterogeneous lightweight high-strength steel prepared in this example. According to GBT228-2002, "Metallic Materials Tensile Test Method at Room Temperature", the finished dual-phase heterogeneous light-weight high-strength steel plate is processed into a standard tensile sample, and the tensile rate is 0.05mm/s. The tensile properties thus measured are shown in Table 1, and the engineering stress-strain curves are shown in Figure 5. The high-strength light-weight steel prepared in Example 6 has a strength of 403MPa, a tensile strength of 682MPa, an elongation of 51.9%, a strength-plastic product of 35.4GPa%, and a density of 6.9g/cm ³ , reaching the strength of current advanced high-strength automotive steel. plasticity level.

Each embodiment of table 1 obtains the mechanical property data of finished steel plate

In the above scheme, compared with the high-strength light steel in the prior art: in terms of composition, the content of C element is greatly reduced, which improves the weldability of the material; the addition of an appropriate amount of Si element plays the role of solid solution strengthening and inhibition of carbide precipitation Effect; the addition of a large amount of Al elements not only reduces the density of the steel, but also improves the corrosion resistance, and at the same time promotes the preservation of high-temperature δ ferrite into the room temperature structure.

In the composition design of the double-phase heterogeneous light-weight high-strength steel ingot of the present invention, less Mn elements and more Al elements are added to promote the formation of high-temperature δ ferrite and keep it at room temperature. The as-cast structure contains coarse fishbone The multiphase structure of δ ferrite and coarse granular austenite, followed by homogenization treatment, hot forging, hot rolling, cold rolling and annealing treatment, to obtain striped δ ferrite and fine equiaxed austenite structure The finished steel of the structure can effectively reduce the density of the steel, improve the strength and plasticity, and realize light weight.

During the tensile test process of the finished steel product of the present invention, due to the existence of two heterogeneous structures with different forms and properties, the transfer of strain in the two phases is promoted, a mutation-induced strain hardening effect is formed, and the appearance of plastic instability is delayed, so that The yield strength of the new high-strength light steel is 388-807MPa, the tensile strength is 656-945MPa, the elongation is 33-55%, the strength-plastic product is 31-38GPa%, and the density is 6.9-7.2g/cm ³ . The performance requirements of the third-generation automotive steel have greater practical application value than ordinary third-generation automotive steel.

The preparation process of the finished steel product of the invention is simple and economical, and large-scale industrial production can be realized relying on the existing production line. The development and application of the finished steel has important economic value and social significance for promoting the lightweight design of automobiles, reducing energy consumption, and reducing greenhouse gas emissions.

The above description is a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, these improvements and modifications It should also be regarded as the protection scope of the present invention.

Claims (6)

1. A dual-phase heterogeneous lightweight high-strength steel, characterized in that the chemical composition of the dual-phase heterogeneous lightweight high-strength steel is calculated by mass percentage: C 0.1-0.3wt.%, Mn 12.1-14wt.% , Al 7.2-8wt.%, Si 0.5-0.7wt.%, P≤0.01wt.%, S≤0.005wt.%, the rest is Fe and unavoidable impurities; The preparation method of the dual-phase heterogeneous lightweight high-strength steel, the preparation method consists of the following steps: S1. Raw material selection: Weigh Fe, Mn, C, Al, Si powders with a purity ≥ 99.9% according to the chemical composition ratio of the dual-phase heterogeneous light-weight high-strength steel as alloy raw materials, and put the alloy raw materials into the electric In the magnetic induction furnace, vacuum melting is carried out under the protection of argon, and then the molten steel is cast into ingots; S2. Hot forging after homogenization treatment: homogenize the ingot described in step S1, and then hot forge the homogenized ingot into a square billet; S3, hot rolling: reheating the square steel billet described in step S2 to the hot rolling temperature, using a rolling mill to perform multi-pass rolling to obtain a hot rolled steel plate with a thickness of 5-7mm, and air cooling to room temperature after hot rolling; S4, cold rolling after pickling: pickling the hot-rolled steel sheet described in step S3, and then using a cold rolling mill to perform multi-pass rolling and 1-pass skin-pass rolling to obtain a cold-rolled steel sheet with a thickness of 3-4mm ; S5, annealing treatment: performing annealing treatment on the cold-rolled steel sheet described in step S4, quickly quenching the cold-rolled steel sheet into water to cool to room temperature after annealing, and obtaining a finished dual-phase heterogeneous lightweight high-strength steel sheet; The multi-pass rolling in the step S3 is 4-6 pass rolling, and the rolling reduction is 55-65%; The multi-pass rolling in the step S4 is 8-10 pass rolling, and the rolling reduction is 45-55%; The as-cast structure of the dual-phase heterogeneous light-weight high-strength steel is a multi-phase structure including coarse herringbone δ ferrite and coarse granular austenite, and the structure of the finished dual-phase heterogeneous light-weight high-strength steel plate is strip Banded delta ferrite and fine equiaxed austenite; The yield strength of the finished duplex heterogeneous light-weight high-strength steel plate is 388-807MPa, the tensile strength is 656-945MPa, the elongation is 33-55%, the strong-plastic product is 31-38 GPa%, and the density is 6.9-7.1 g/cm ³ . 2. the preparation method of dual-phase heterogeneous lightweight high-strength steel according to claim 1, is characterized in that, described preparation method is made up of following steps: S1. Raw material selection: Weigh Fe, Mn, C, Al, Si powders with a purity ≥ 99.9% according to the chemical composition ratio of the dual-phase heterogeneous light-weight high-strength steel as alloy raw materials, and put the alloy raw materials into the electric In the magnetic induction furnace, vacuum melting is carried out under the protection of argon, and then the molten steel is cast into ingots; S2. Hot forging after homogenization treatment: homogenize the ingot described in step S1, and then hot forge the homogenized ingot into a square billet; S3, hot rolling: reheating the square steel billet described in step S2 to the hot rolling temperature, using a rolling mill to perform multi-pass rolling to obtain a hot rolled steel plate with a thickness of 5-7mm, and air cooling to room temperature after hot rolling; S4, cold rolling after pickling: pickling the hot-rolled steel sheet described in step S3, and then using a cold rolling mill to perform multi-pass rolling and 1-pass skin-pass rolling to obtain a cold-rolled steel sheet with a thickness of 3-4mm ; S5. Annealing treatment: the cold-rolled steel sheet described in step S4 is annealed. After the cold-rolled steel sheet is annealed, it is quickly quenched into water and cooled to room temperature to obtain a finished dual-phase heterogeneous lightweight high-strength steel sheet. 3. The method for preparing dual-phase heterogeneous lightweight high-strength steel according to claim 2, characterized in that, the temperature of the homogenization treatment in the step S2 is 1200±30°C, the holding time is 3-5h, and the forging The temperature is 900-1150°C. 4. The method for preparing dual-phase heterogeneous lightweight high-strength steel according to claim 2, characterized in that the hot rolling temperature in the step S3 is 1200±30°C, and the holding time is 0.3-0.7h; The temperature is 1150±20°C, and the final rolling temperature is higher than 900°C. 5. The method for preparing dual-phase heterogeneous lightweight high-strength steel according to claim 2, characterized in that the annealing temperature in the step S5 is 660-1000° C., and the holding time is 25-35 minutes. 6. The method for preparing dual-phase heterogeneous lightweight high-strength steel according to claim 2, characterized in that the cold rolling mill in the step S4 is a four-roll cold rolling mill.

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