CN116065105B

CN116065105B - Ultrahigh-strength self-tempering steel plate and preparation method thereof

Info

Publication number: CN116065105B
Application number: CN202211090986.7A
Authority: CN
Inventors: 何燕霖; 张宇; 丁敏龙; 王静静; 郑伟森; 周天鹏; 刘仁东; 李麟
Original assignee: SHANGHAI UNIVERSITY; Ansteel Beijing Research Institute Co Ltd
Current assignee: SHANGHAI UNIVERSITY; Ansteel Beijing Research Institute Co Ltd
Priority date: 2022-09-06
Filing date: 2022-09-07
Publication date: 2025-02-18
Anticipated expiration: 2042-09-07
Also published as: CN116065105A

Abstract

The invention discloses an ultra-high strength self-tempering automobile steel plate and a preparation method thereof, wherein the steel plate comprises, by mass, 0.15-0.23% of C, 1.8-2.5% of Mn, 0.8-1.5% of Si, 1.0-1.5% of Cr, 0.2-0.8% of Al, less than or equal to 0.03% of Ti+Nb, 0.02% of P, 0.01% of S and the balance of Fe. And heating the hot rolled plate with the thickness of 1.8-2.0 mm to 900 ℃, preserving heat for at least 3 minutes, and then cooling in air to obtain the test steel. The invention solves the problem of how to obtain test steel with proper components under the hot rolling process condition, so that the tensile strength is not lower than 1400MPa and the elongation is not lower than 10% due to the self-tempering phenomenon of martensite during quenching and air cooling. The method is favorable for realizing the short-process preparation of the ultra-high strength steel plate, and has remarkable application value for the lightweight development of automobiles.

Description

Ultrahigh-strength self-tempering steel plate and preparation method thereof

Technical Field

The invention relates to an ultra-high strength self-tempering automobile steel plate and a preparation method thereof, belonging to the special steel preparation technology.

Background

In the face of energy crisis, environmental pollution and increase of automobile demand, how to realize energy conservation and emission reduction is a real problem which puzzles the development of automobile industry in China. It is reported that 75% of oil consumption of an automobile is related to the mass of the whole automobile, and compared with other light materials such as magnesium alloy, aluminum alloy and other composite materials, steel materials, particularly steel plates, are still main materials of the automobile in China, can account for more than 70% of the dead weight of the automobile body due to obvious advantages in cost and service performance, and theoretically, when the thickness of the steel plates is reduced by 0.05mm,0.10mm and 0.15mm, the weight of the automobile body can be reduced by about 6%, 12% and 18%. Therefore, the development of the automobile steel plate to ultrahigh reinforcement can realize light weight and ensure the safety during collision.

Currently, based on the industry trend of global development of greenization, high efficiency and intelligence of steel, the near-net-shape short-process production of high-performance steel grade gradually becomes the main stream of the steel industry. The self-tempering steel production process is relatively simple, and is an ideal steel grade for near-net-type production. However, the matching of the ultrahigh-strength automobile steel alloy components and the self-tempering process needs to be fully researched, and the strong plasticity of the alloy needs to be further improved so as to meet the requirements of industrial application.

Disclosure of Invention

In order to solve the problems in the prior art, the invention aims to overcome the defects in the prior art, and provides the ultrahigh-strength self-tempering steel plate and the preparation method thereof, wherein low-carbon low-alloy is used as a basic component, and a hot rolling and quenching air cooling process is adopted to realize self-tempering transformation of martensite in the steel through special component regulation and control, so that the plasticity of the martensite can be effectively improved, the preparation method has the preparation characteristic of a short process, and the ultrahigh-strength self-tempering steel plate has remarkable application value in the field of ultrahigh-strength automobile steel research and development.

In order to achieve the aim of the invention, the invention adopts the following technical scheme:

The ultra-high strength self-tempering steel plate comprises the following main components in percentage by mass:

0.15-0.23% of C, 1.8-2.5% of Mn, 0.8-1.5% of Si, 1.0-1.5% of Cr, 0.2-0.8% of Al, less than or equal to 0.03% of Ti+Nb, less than 0.02% of P, less than 0.01% of S and the balance of Fe;

the ultra-high strength self-tempering steel plate is prepared by the following method:

(1) And (3) a casting process:

smelting and solidifying in a vacuum induction furnace to prepare a steel billet with the components, charging argon for protection in the smelting process, die casting, and cutting into ingot casting blocks with the thickness of not more than 35mm after demoulding;

(2) Rolling a steel plate:

And (3) hot rolling the ingot block, controlling the initial rolling temperature of the hot rolling to be not lower than 1200 ℃ and the final rolling temperature to be not lower than 950 ℃, carrying out multi-pass hot rolling until the thickness is 1.8-2.0 mm to obtain a hot rolled steel plate, heating the hot rolled steel plate to 900 ℃ and preserving heat for at least 3 minutes for heat treatment, and then carrying out air cooling to obtain the ultrahigh-strength self-tempering steel plate.

Preferably, the ultra-high strength self-tempering steel plate comprises the following chemical components in percentage by mass:

0.16-0.22% of C, 1.8-2.4% of Mn, 0.8-1.4% of Si, 1.1-1.5% of Cr, 0.3-0.6% of Al, less than or equal to 0.01% of Ti, less than or equal to 0.02% of Nb, less than or equal to 0.01% of P, less than or equal to 0.008% of S, and the balance of Fe.

Preferably, according to the mass percentage, the ultra-high strength self-tempering steel plate has the yield strength of not lower than 767MPa, the tensile strength of not lower than 1357MPa and the elongation of not lower than 9.1 percent under the quenching condition of 880-920 ℃.

Further preferably, the ultra-high strength self-tempering steel plate according to the present invention has a yield strength of not less than 857MPa, a tensile strength of not less than 1410MPa, and an elongation of not less than 10.2% in terms of mass percent under a quenching condition of 900 ℃.

The preparation method of the ultra-high strength self-tempering steel plate comprises the following steps:

(1) And (3) a casting process:

(2) Rolling a steel plate:

The principle of the invention is as follows:

It is known that the martensitic structure formed after quenching of Fe-Mn-Si-Cr-C system low-carbon low-alloy steel has the performance characteristics of high strength and high hardness, and therefore, in order to achieve the aim of weight reduction, martensite is an important structural factor for the development of the automobile steel to ultra-high strength. However, while ultra-high strength is being pursued, the loss of plasticity is unavoidable, and how to balance strength and plasticity indexes to obtain ideal mechanical properties has been a bottleneck problem in developing ultra-high strength steel grades. At present, the prior researches mostly adopt processes such as continuous annealing treatment or quenching distribution treatment, and the like, and residual austenite is introduced into a tissue, so that the residual austenite exerts a transformation induced plasticity effect to obtain strength increase and plasticity increase. However, to realize the development of ultra-high strengthening, the components of the steel types are complex, the content of alloy elements is high, the corresponding technological parameter requirements are strict, and the preparation of a short process is difficult to realize.

Researches show that for steel with a lower matrix carbon content, the martensite transformation starting temperature (Ms) is higher, martensite is formed at a higher temperature in the quenching and cooling process, and supersaturated carbon atoms still have strong diffusion capacity, so that the supersaturated carbon atoms can escape from the interstitial positions of a martensite phase crystal lattice to form metastable carbide, and the martensite spontaneously generates tempering transformation, namely self-tempering phenomenon, so that the solid solution strengthening effect of the martensite is weakened, and the plasticity is correspondingly improved.

However, the different cooling rates during quenching have a significant effect on the self-tempering phenomenon. According to the invention, a calculation formula of accumulated diffusion distance of carbon atoms in martensite in a literature is adopted, namely equations (1) and (2) are compared with diffusion conditions of carbon atoms in experimental steel under different cooling conditions, so that the diffusion distance of carbon atoms in air cooling is 4 times that in water cooling, obviously, the self-tempering possibility of martensite in air cooling is higher, and the experimental steel can obtain ultra-high strength and ideal plasticity without additional tempering treatment.

D=2×10⁶ exp(-1.092×10⁵/8.314T) (2)

Wherein T is time, D is the diffusion coefficient of carbon, and T is temperature (K).

In addition, in terms of alloying design, the invention combines computational analysis to find that the increase of the alloying elements of carbon, manganese, chromium and silicon can reduce the martensite start temperature, wherein the influence of carbon is most remarkable. At the same time, the carbon content is a fundamental factor affecting the strength of martensite. As the carbon content increases, the martensite start temperature decreases and the strength of the formed martensite structure increases. That is, the carbon content is high, and the martensite strength is increased, but the self-tempering transformation of the martensite is suppressed, so that the purpose of the balance strength and the plasticity index is difficult to achieve. Therefore, the invention introduces alloy element aluminum, and thermodynamic calculation shows that the addition of proper amount of aluminum can obviously improve the martensite transformation starting temperature without affecting other phase transformation behaviors basically, thereby being beneficial to generating self-tempering effect. In addition, scientific researches show that, unlike the traditional automobile steel plate preparation process, the cold rolling process after hot rolling is not needed, the test steel with the niobium-vanadium composite addition has a good structure state after being treated by the multi-pass hot rolling process, and the fine crystal strengthening and precipitation strengthening effects of the microalloy elements further improve the strong plasticity of the test steel.

Through the process and the component design, the ultra-high strength self-tempering steel plate with tensile strength not lower than 1357MPa and elongation not lower than 9.1 percent and capable of being prepared in a short process is obtained.

Compared with the prior art, the invention has the following obvious prominent substantive features and obvious advantages:

1. The Fe-Mn-Si-Cr-Al-C hot rolled steel plate designed by the invention can generate good martensite self-tempering effect under the condition of air cooling quenching, thereby having ultrahigh strength and ideal plasticity and meeting the development requirement of automobile weight reduction;

2. according to the invention, the steel plate with uniform structure can be obtained by the niobium-vanadium composite addition and the combination of the multi-pass hot rolling process, so that the short-process preparation of the ultra-high strength steel is realized;

3. the invention adopts niobium-titanium composite refined crystal grains and combines multi-pass hot rolling to lead the hot rolling structure of the test steel to be uniform, and the air cooling process after the austenite single-phase region is insulated ensures that martensite generates self tempering, and compared with the water cooling process, the air cooling ensures that carbon atoms can be fully diffused to increase the tempering degree of martensite, thereby obtaining tempered martensite structure, effectively improving the strong plasticity and obtaining the ultra-high strength self-tempering steel with the tensile strength not lower than 1357MPa and the elongation not lower than 9.1 percent;

4. The method is simple and feasible, has low cost and is suitable for popularization and application.

Detailed Description

The foregoing aspects are further described in conjunction with specific embodiments, and the following detailed description of preferred embodiments of the present invention is provided:

Example 1

In the embodiment, the ultra-high strength self-tempering steel plate comprises the following main components in percentage by mass:

0.16% of C, 2.4% of Mn, 1.4% of Si, 1.5% of Cr, 0.5% of Al, 0.01% of Ti, 0.01% of Nb, 0.01% of P, 0.008% of S and the balance of Fe;

(1) And (3) a casting process:

Smelting and solidifying in a vacuum induction furnace to prepare a steel billet with the components, filling argon for protection in the smelting process, die casting, and cutting into ingot casting blocks with the thickness of 35mm after demoulding;

(2) Rolling a steel plate:

And (3) hot rolling the ingot block, controlling the initial rolling temperature of the hot rolling to be 1200 ℃ and the final rolling temperature to be 950 ℃, carrying out multi-pass hot rolling to a thickness of 1.8-2.0 mm to obtain a hot rolled steel plate, heating the hot rolled steel plate to 900 ℃ and preserving heat for 3 minutes for heat treatment, and then carrying out air cooling to room temperature to obtain the ultrahigh-strength self-tempering steel plate.

Test analysis:

After microstructure analysis and room temperature tensile property test, the steel mainly comprises tempered martensite and martensitic structure after quenching treatment at different temperatures, and various mechanical property values of the test steel plate are shown in table 1:

TABLE 1 comparison of room temperature tensile Properties of the Steel grades after quenching at different temperatures

As is clear from Table 1, the present example gave an ultra-high strength self-tempered steel having a tensile strength of 1461MPa and an elongation of 11% under a quenching condition at 900 ℃.

Example two

This embodiment is substantially the same as the first embodiment, and is characterized in that:

0.18% of C, 2.0% of Mn, 1.1% of Si, 1.1% of Cr, 0.3% of Al, 0.01% of Ti, 0.01% of Nb, 0.01% of P, 0.008% of S and the balance of Fe;

(1) And (3) a casting process:

(2) Rolling a steel plate:

Test analysis:

After microstructure analysis and room temperature tensile property test, the steel mainly comprises tempered martensite and martensitic structure after quenching treatment at different temperatures, and various mechanical property values of the test steel plate are shown in table 2:

TABLE 2 comparison of room temperature tensile Properties of the Steel grades after quenching at different temperatures of example two

As is clear from Table 2, the present example gave an ultra-high strength self-tempered steel having a tensile strength of 1410MPa and an elongation of 12.0% under a quenching condition of 900 ℃.

Example III

This embodiment is substantially the same as the above embodiment, and is characterized in that:

0.20 percent of C, 1.9 percent of Mn, 1.0 percent of Si, 1.3 percent of Cr, 0.4 percent of Al, 0.01 percent of Ti, 0.02 percent of Nb, 0.01 percent of P, 0.008 percent of S and the balance of Fe;

(1) And (3) a casting process:

(2) Rolling a steel plate:

and (3) hot rolling the ingot block, controlling the initial rolling temperature of the hot rolling to be 1200 ℃ and the final rolling temperature to be 950 ℃, carrying out multi-pass hot rolling to a thickness of 1.8-2.0 mm to obtain a hot rolled steel plate, heating the hot rolled steel plate to 900 ℃ and preserving heat for 3 minutes for heat treatment, and then cooling to room temperature by air to obtain the ultrahigh-strength self-tempering steel plate.

Test analysis:

After microstructure analysis and room temperature tensile property test, the steel mainly comprises tempered martensite and martensitic structure after quenching treatment at different temperatures, and various mechanical property values of the test steel plate are shown in table 3:

TABLE 3 comparison of room temperature tensile Properties of the Steel grades after quenching at different temperatures of example three

As is clear from Table 3, this example gives an ultra-high strength self-tempered steel having a tensile strength of 1478MPa and an elongation of 10.2% at 900 ℃.

Example IV

0.22% of C, 1.8% of Mn, 0.8% of Si, 1.2% of Cr, 0.6% of Al, 0.01% of Ti, 0.02% of Nb, 0.01% of P, 0.008% of S and the balance of Fe;

(1) And (3) a casting process:

(2) Rolling a steel plate:

Test analysis:

after microstructure analysis and room temperature tensile property test, the steel mainly comprises tempered martensite and martensitic structure after quenching treatment at different temperatures, and various mechanical property values of the test steel plate are shown in table 4:

Table 4. Room temperature tensile properties of the Steel grades after quenching at different temperatures of example four

As is clear from Table 4, the present example gave an ultra-high strength self-tempered steel having a tensile strength of 1434MPa and an elongation of 11.2% under quenching conditions at 900 ℃.

In summary, the ultra-high strength self-tempering automobile steel plate comprises, by mass, 0.15-0.23% of C, 1.8-2.5% of Mn, 0.8-1.5% of Si, 1.0-1.5% of Cr, 0.2-0.8% of Al, less than or equal to 0.03% of Ti+Nb, less than 0.02% of P, less than 0.01% of S, and the balance of Fe. And heating the hot rolled plate with the thickness of 1.8-2.0 mm to 900 ℃, preserving heat for at least 3 minutes, and then cooling in air to obtain the test steel. The embodiment of the invention solves the problem of how to obtain test steel with proper components under the hot rolling process condition, so that the tensile strength is not lower than 1400MPa and the elongation is not lower than 10% due to the self-tempering phenomenon of martensite during quenching and air cooling. In particular, the tensile strength of the ultra-high strength self-tempering automobile steel plate is not lower than 1410MPa, and the elongation is not lower than 10.2%. The embodiment of the invention is beneficial to realizing the short-process preparation of the ultra-high strength steel plate, and has remarkable application value for the lightweight development of automobiles.

The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and various changes, modifications, substitutions, combinations or simplifications can be made according to the spirit and principles of the technical solution of the present invention, and the present invention is not limited to the above embodiments, but is limited to the protection scope of the present invention as long as the technical principles and the inventive concept of the present invention are not deviated.

Claims

1. The ultra-high strength self-tempering steel plate is characterized by comprising the following main components in percentage by mass:

C：0.15～0.23%,Mn：1.8～2.5%,Si：0.8～1.5%,Cr：1.0～1.5%,Al：0.2～0.8%,Ti≤0.01%,Nb≤0.02%,Ti+Nb≤0.03%,P<0.02%,S<0.01%, The balance being Fe, and the contents of Ti and Nb are not zero;

The ultra-high strength self-tempering steel plate is prepared by the following steps:

(1) And (3) a casting process:

(2) Rolling a steel plate:

2. The ultra-high strength self-tempering steel plate according to claim 1, wherein said steel plate consists of the following chemical components in mass percent:

0.16-0.22% of C, 1.8-2.4% of Mn, 0.8-1.4% of Si, 1.1-1.5% of Cr, 0.3-0.6% of Al, less than or equal to 0.01% of Ti, less than or equal to 0.02% of Nb, less than or equal to 0.01% of P, less than or equal to 0.008% of S, and the balance of Fe, wherein the contents of Ti and Nb are not zero.

3. The ultra-high strength self-tempered steel plate as claimed in claim 1, wherein the yield strength is not lower than 857MPa, the tensile strength is not lower than 1410MPa, and the elongation is not lower than 10.2% under 900 ℃.

4. A method for preparing the ultra-high strength self-tempering steel plate according to claim 1, wherein the method comprises the following steps:

(1) And (3) a casting process:

(2) Rolling a steel plate: