CN117327991A - A high-strength, tough, low-density steel with multi-level nanostructure strengthening effect and its preparation method - Google Patents

Abstract

The invention discloses a high-strength, tough, low-density steel with multi-level nanostructure strengthening effect and a preparation method thereof, and belongs to the technical field of metal materials. Including the following components in terms of atomic percentage: Mn 25~32%, Al 12~18%, C 3.0~7.0%, 0≤Nb≤0.2%, 0≤V≤0.8%, the balance is Fe and unavoidable Impurities. The invention forms a multi-level coherent structure inside the steel material including sub-nanometer κ' phase, several nanometer-level κ phase, and tens of nanometer-level MC carbides. Strengthening through this multi-level nanostructure can make the alloy have extremely high strength. , while maintaining good toughness, and the density and cost of this steel material are low, which can meet the needs of high specific strength steel materials.

Description

A high-strength, tough, low-density steel with multi-level nanostructure strengthening effect and its preparation method

Technical field

The invention belongs to the technical field of metal materials, and specifically relates to a high-strength, tough, low-density steel with a multi-level nanostructure strengthening effect and a preparation method thereof.

Background technique

Improving the specific strength of structural materials is crucial to improving energy efficiency, reducing environmental pollution, saving resources, and protecting the environment. Especially in the field of automobile manufacturing, lightweighting has become an inevitable trend. Currently, the main methods to achieve lightweight equipment include two approaches. The first method is to use lower-density structural materials, such as aluminum alloys, magnesium alloys, and titanium alloys. However, due to poor strength and toughness and high cost, their wide application in the field of structural materials is limited. The second method is to use high-strength structural materials to reduce the overall weight by reducing the size of structural components, such as CP steel, DP steel, TRIP steel, TWIP steel, martensitic steel and Q&P steel, etc. However, as the strength increases, the plasticity of these materials will be significantly reduced, and the density will be higher, which cannot meet the needs of high-strength and low-density materials. Therefore, the use of low-density and high-strength structural materials can effectively solve the limitations of the above two approaches.

FeMnAlC series low-density steel is a new type of lightweight high-strength material. According to its microstructure, it can be divided into three categories: austenitic low-density steel, dual-phase low-density steel and ferritic low-density steel. Among them, austenitic low-density steel has excellent comprehensive mechanical properties and is a very promising next-generation high-strength, low-density steel material. However, austenitic low-density steel easily forms large-sized κ phase, DO3 phase, βMn phase, etc. at the grain boundaries, which seriously affects the mechanical properties of the alloy. Therefore, it is difficult for existing low-density steel to have extremely high specific strength.

In the existing technology, the Chinese invention patent with publication number CN115216703A proposes a low-density steel with high strength. The mass percentage of its components is: Mn 25~30%, Al 11~12%, C 1.0~1.2%, The rest is Fe and inevitable impurities. Although this invention makes full use of work hardening and dispersion strengthening of κ-carbide to improve the strength of low-density steel (1900MPa), its plasticity is low (~5%) and it is difficult to meet the requirements of high specific strength and high toughness structural materials.

The Chinese invention patent with publication number CN114752864A discloses an ultra-high-strength plastic low-density steel with mass percentages of Mn 30 to 34%, Al 11 to 11.9%, C 1.2 to 1.29%, Cr 4 to 7%, Cu 0.5～1.2%, Nb 0.01～0.3%, V 0.01～0.3%, Ti 0.01～0.3%, La 0.05～0.1%, B 0.0001～0.005%, N 0.05～0.1%, P≤0.012%, S≤0.003% With the remaining iron and inevitable impurities, the low-density, ultra-high-strength and high-plasticity steel has good plasticity, but its specific strength is low, with the yield strength below 1.0GPa and the tensile strength below 1.1GPa.

Wang Z, Lu W, Zhao H and others reported a low-density steel material Fe-26Mn- in a paper published in Science Advances: Ultrastronglightweight compositionally complex steels via dual-nanoprecipitation[J]. 16Al-5Ni-5C, this material has two coherent precipitates. After heat treatment at 900°C for 3 minutes, it obtained excellent mechanical properties, including a tensile strength of 1.4GPa and an elongation at break of 38%. However, this alloy contains nickel, which is a relatively expensive element, which is not conducive to reducing alloy costs.

Contents of the invention

The purpose of this section is to outline some aspects of embodiments of the invention and to briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section, the abstract and the title of the invention to avoid obscuring the purpose of this section, the abstract and the title of the invention, and such simplifications or omissions cannot be used to limit the scope of the invention.

In view of the above and/or problems existing in the prior art, the present invention is proposed.

One of the objects of the present invention is to provide a high-strength, low-density steel with a multi-level nanostructure strengthening effect.

In order to solve the above technical problems, the present invention provides the following technical solution: a high-strength, low-density steel with multi-level nanostructure strengthening effect, including the following components in terms of atomic percentage: Mn 25~32%, Al 12~18 %, C 3.0～7.0%, 0≤Nb≤0.2%, 0≤V≤0.8%, the balance is Fe and inevitable impurities;

Among them, in terms of atomic percentage, Mn/Al≥1.0, (Mn+Al)/C≥30, (Nb+V)≤1.0% and V/Nb≥4.

As a preferred solution of the present invention for high-strength, toughness and low-density steel with multi-level nanostructure strengthening effect, the high-strength, toughness and low-density steel is formed internally including sub-nanometer κ' phase, several nanometer-level κ phase, tens of nanometers Multilevel coherent structure of MC carbide.

As a preferred solution of the present invention for high-strength, toughness and low-density steel with multi-level nanostructure strengthening effect, the alloy has the following characteristics:

(i) Yield strength 800~2000MPa;

(ii) Tensile strength 1000~2248MPa;

(iii) Elongation after fracture is 3 to 70%;

(iv) The specific strength is 150 to 330MPa·cm ³ g ^-1 .

Another object of the present invention is to provide a method for preparing high-strength, low-density steel with multi-level nanostructure strengthening effects as described above, including:

Each component is prepared according to the atomic ratio, smelted under vacuum or inert gas protection conditions, and cast into a slab. After the slab is hot rolled, homogenized, cold rolled, and annealed, a multi-level nanostructure strengthening effect is obtained. High strength, low density steel.

As a preferred solution for the preparation method of the high-strength, tough, low-density steel with multi-level nanostructure strengthening effect of the present invention, the raw materials of each component of the alloy are pure elements or master alloys, and the purity is ≥99.0%. Eliminate the disadvantages of introducing inclusions due to low purity of raw materials and damaging the overall performance of the alloy.

As a preferred embodiment of the method for preparing high-strength, tough, low-density steel with multi-level nanostructure strengthening effects of the present invention, the smelting includes smelting using an induction furnace, an electric arc furnace or a suspension furnace, and the smelting temperature is 1450-2200°C. , the holding time is greater than 0.1 hours; for the above-mentioned smelting, the vacuum degree in the furnace is maintained below 1 Pa or the inert gas pressure in the furnace is maintained below 100 MPa. The alloy must be repeatedly smelted no less than once to ensure uniform smelting of the alloy components.

As a preferred solution of the present invention for the preparation method of high-strength, toughness and low-density steel with multi-level nanostructure strengthening effect, the hot rolling adopts multi-pass hot rolling, the hot rolling temperature is 800-1250°C, and the single-pass The secondary rolling reduction is ≤25%, and the total rolling reduction is 30-90%.

As a preferred solution for the preparation method of high-strength, tough, low-density steel with multi-level nanostructure strengthening effect of the present invention, wherein: the homogenization, the homogenization treatment temperature is 1100-1250°C, and the homogenization time is greater than 30 minutes; The homogenization treatment is carried out under vacuum or a protective atmosphere, and the protective atmosphere is selected from one of argon, nitrogen or helium.

As a preferred solution for the preparation method of high-strength, toughness and low-density steel with multi-level nanostructure strengthening effect of the present invention, wherein: the cold rolling adopts multi-pass cold rolling, the pass rolling reduction is ≤ 25%, and the total rolling The reduction amount is 40 to 90%.

As a preferred embodiment of the preparation method of the high-strength, tough, low-density steel with multi-level nanostructure strengthening effect of the present invention, wherein: the annealing is one of the first annealing and/or the second annealing;

Wherein, the first annealing temperature is 900-1100°C, and the holding time is 5-300 minutes; the second annealing temperature is 550-650°C, and the holding time is not less than 5 minutes.

As a preferred embodiment of the method for preparing high-strength, low-density steel with multi-level nanostructure strengthening effects of the present invention, the annealing is performed in vacuum or in a protective atmosphere, and the protective atmosphere is selected from argon, nitrogen or helium. kind of.

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

The present invention designs reasonable contents of Mn, Al, and C, and strictly controls the ratios of Mn/Al, (Mn+Al)/C and V/Nb, and simultaneously controls the total amounts of Nb and V, so that the content of Mn, Al, and C can be formed inside the steel material. The multi-level coherent structure of sub-nanometer level (κ' phase), several nanometer level (κ phase), and tens of nanometer level (MC carbide) can make the alloy have extremely high strength through strengthening of this multi-level nanostructure. It maintains good toughness, and the density and cost of this steel material are low. Its specific strength can reach 150~330MPa·cm ³ g ^-1 , which can meet the needs of high specific strength steel materials.

Description of drawings

In order to explain the technical solutions of the embodiments of the present invention more clearly, the drawings needed 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. Those of ordinary skill in the art can also obtain other drawings based on these drawings without exerting any creative effort. in:

Figure 1 is a scanning electron backscattered morphology diagram of the high-strength, low-density steel material provided in Embodiment 1 of the present invention;

Figure 2 is a selected area electron diffraction pattern of the high-strength, low-density steel material provided in Embodiment 1 of the present invention;

Figure 3 is an atomic resolution high-angle annular dark field image of the high-strength, low-density steel material provided in Embodiment 1 of the present invention;

Figure 4 is a transmission dark field image of the (010) kappa diffraction spot of the high-strength, low-density steel material provided in Embodiment 1 of the present invention;

Figure 5 is a tensile property diagram of the high-strength, low-density steel material provided in Embodiment 1 of the present invention;

Figure 6 is a scanning electron backscattering morphology of the high-strength, low-density steel material provided in Embodiment 2 of the present invention;

Figure 7 is a high-angle annular dark field image of the high-strength, low-density steel material provided in Embodiment 2 of the present invention and the energy spectrum element surface distribution diagram of the corresponding area;

Figure 8 is an atomic resolution high-angle annular dark field image of the high-strength, low-density steel material provided in Embodiment 2 of the present invention;

Figure 9 is a selected area electron diffraction pattern of the high-strength, low-density steel material provided in Embodiment 2 of the present invention;

Figure 10 is a transmission dark field image of the (010) kappa diffraction spot of the high-strength, low-density steel material provided in Embodiment 2 of the present invention;

Figure 11 is a tensile performance diagram of the high-strength, low-density steel material provided in Embodiment 2 of the present invention;

Figure 12 is a scanning electron backscattered morphology diagram of the high-strength, low-density steel material provided in Embodiment 3 of the present invention;

Figure 13 is a selected area electron diffraction pattern of the high-strength, low-density steel material provided in Embodiment 3 of the present invention;

Figure 14 is a transmission dark field image of the (010) kappa diffraction spot of the high-strength, low-density steel material provided in Embodiment 3 of the present invention;

Figure 15 is a graph of tensile properties of the high-strength, low-density steel material provided in Embodiment 3 of the present invention;

Figure 16 is a graph of the tensile properties of the high-strength, low-density steel material provided in Embodiment 4 of the present invention;

Figure 17 is a graph of tensile properties of the high-strength, low-density steel material provided in Comparative Example 1 of the present invention.

Figure 18 is a graph showing the tensile properties of the high-strength, low-density steel material provided in Comparative Example 2 of the present invention.

Detailed ways

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific implementation modes of the present invention will be described in detail below in conjunction with the examples in the description.

Many specific details are set forth in the following description to fully understand the present invention. However, the present invention can also be implemented in other ways different from those described here. Those skilled in the art can do so without departing from the connotation of the present invention. Similar generalizations are made, and therefore the present invention is not limited to the specific embodiments disclosed below.

Second, reference herein to "one embodiment" or "an embodiment" refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. "In one embodiment" appearing in different places in this specification does not all refer to the same embodiment, nor is it a separate or selective embodiment that is mutually exclusive with other embodiments.

Unless otherwise stated, the raw materials used in the examples were commercially purchased.

Example 1

(1) Make ingredients according to the chemical formula Fe ₅₀ Mn ₃₀ Al ₁₅ C ₅ (atomic percentage). The raw materials use blocks corresponding to pure elements, and the purity is greater than 99.9%;

(2) Use induction smelting of the prepared raw materials. First, pass high-purity argon gas into the furnace for gas cleaning, then pump low vacuum to below 5 Pa, then pump high vacuum to below 5×10 ^-3 Pa, and finally pass Add 5 MPa of high-purity argon as a protective gas, the melting temperature is 1600°C, and the ingot is poured after holding for 30 minutes;

(3) The alloy ingot is subjected to multi-pass hot rolling, the hot rolling temperature is 900°C, the single rolling reduction is 10%, and the total rolling reduction is 50%;

(4) The hot-rolled alloy block is subjected to high-temperature homogenization treatment under vacuum (vacuum degree is 10 ^-2 Pa), the temperature is 1200°C, the homogenization treatment time is 2 hours, and then water quenched;

(5) The high-temperature homogenized alloy block is subjected to multi-pass room temperature rolling, with a single-pass rolling reduction of 10% and a total rolling reduction of 70%;

(6) Anneal the cold-rolled alloy sheet under vacuum (vacuum degree is 10 ^-2 Pa). The first annealing temperature is 900°C and the annealing time is 30 minutes. The second annealing temperature is 600°C. The time is 40 minutes, and high strength, toughness and low density steel are obtained.

The morphology of the high-strength, toughness and low-density steel obtained above was observed, as shown in Figures 1 to 5. Figure 1 is an electron backscattered scanning picture of high-strength, tough, and low-density steel. The grain size of this high-strength, tough, and low-density steel material is uniform and there is no obvious grain boundary precipitation phase. Figure 2 is a transmission selected area diffraction photo of high-strength and low-density steel. From the picture, it can be found that the high-strength and toughness steel material has a single-phase austenite structure and has a coherent κ-carbide precipitation phase. Figure 3 is an atomic resolution high-angle annular dark field image of high-strength, tough, low-density steel, showing the coherent κ-carbide precipitation phase. Figure 4 shows the transmission dark field image of high-strength, tough, low-density steel. It can be found that there are a large number of nanoscale coherent κ-carbide in this alloy.

The mechanical properties of the obtained high-strength, toughness and low-density steel were tested. The steel stress strain curve obtained in Example 1 is shown in Figure 5. It can be seen from Figure 5 that the yield strength of the high-strength, tough, low-density steel with multi-level nanostructure strengthening effect obtained in this example is about 1063MPa, the tensile strength is about 1241MPa, the elongation after fracture is about 20%, and the density is 6.7g/cm ³ , the specific strength is 185MPa·cm ³ g ^-1 .

Example 2

(1) Make ingredients according to the chemical formula Fe ₄₉ Mn ₃₀ Al ₁₅ C ₅ V _0.8 Nb _0.2 (atomic percentage). The raw materials use blocks corresponding to pure elements, and the purity is greater than 99.9%;

(2) Use induction smelting of the prepared raw materials. First, pass high-purity argon gas into the furnace for gas cleaning, then pump low vacuum to below 5 Pa, then pump high vacuum to below 5×10 ^-3 Pa, and finally pass Add 5 MPa of high-purity argon as a protective gas, the melting temperature is 1700°C, hold for 15 minutes, and cast under vacuum conditions to obtain an alloy ingot;

(3) The smelted alloy ingot is subjected to multi-pass hot rolling. The hot rolling temperature is 1000°C, the single rolling reduction is 15%, and the total rolling reduction is 60%;

(4) The hot-rolled alloy block is subjected to high-temperature homogenization treatment under vacuum (vacuum degree is 10 ^-2 Pa), the temperature is 1200°C, the homogenization treatment time is 4 hours, and then water quenched;

(5) The high-temperature homogenized alloy block is subjected to multi-pass room temperature rolling, with a single-pass rolling reduction of 15% and a total rolling reduction of 60%;

(6) Anneal the cold-rolled alloy sheet under vacuum (vacuum degree is 10 ^-2 Pa). The first annealing temperature is 900°C and the annealing time is 5 minutes. The second annealing temperature is 600°C. The time is 20 minutes, and high strength, toughness and low density steel are obtained.

The morphology of the high-strength, toughness and low-density steel obtained above was observed, as shown in Figures 6 to 11. Figure 6 is an electron backscattered scanning picture of high-strength, tough, low-density steel. From the picture, it can be found that the material contains some unrecrystallized areas, and the grains are fine in the completely recrystallized areas. Figure 7 is a transmission high-angle annular dark field image of high-strength, tough, low-density steel. From the image, MC-carbide precipitates with a size less than 20nm can be clearly found. Figure 8 shows the atomic resolution high-angle annular dark field image of high-strength, tough and low-density steel. From the image, it can be clearly seen that MC-carbide is coherent with the austenite matrix. Figure 9 is a transmission selected area diffraction photo of high-strength and low-density steel. From the picture, it can be found that the high-strength and toughness steel material has a single-phase austenite structure and has a coherent κ-carbide precipitation phase. Figure 10 shows the transmission dark field image of high strength, toughness and low density steel. It can be found that this alloy also contains a large number of nanoscale coherent κ-carbides.

The mechanical properties of the obtained high-strength, toughness and low-density steel were tested. The steel stress strain curve obtained in Example 2 is shown in Figure 11. It can be seen from Figure 11 that the yield strength of the high-strength, tough, low-density steel with multi-level nanostructure strengthening effect obtained in this example is about 1423MPa, the tensile strength is about 1580MPa, the elongation after fracture is about 33%, and the density is 6.8g/cm ³ , the specific strength is 232MPa·cm ³ g ^-1 .

Example 3

(1) Make ingredients according to the chemical formula Fe ₅₀ Mn ₃₀ Al ₁₅ C ₅ (atomic percentage). The raw materials use blocks corresponding to pure elements, and the purity is greater than 99.9%;

(2) Use induction smelting of the prepared raw materials. First, pass high-purity argon gas into the furnace for gas cleaning, then pump low vacuum to below 5 Pa, then pump high vacuum to below 5×10 ^-3 Pa, and finally pass Add 5 MPa of high-purity argon as a protective gas, the melting temperature is 1600°C, and the alloy ingot is cast after 10 minutes of heat preservation;

(3) The smelted alloy ingot is subjected to multi-pass hot rolling. The hot rolling temperature is 950°C, the single rolling reduction is 10%, and the total rolling reduction is 50%;

(4) The hot-rolled alloy block is subjected to high-temperature homogenization treatment under vacuum (vacuum degree is 10 ^-2 Pa), the temperature is 1200°C, the homogenization treatment time is 3 hours, and then water quenched;

(5) The cold-rolled alloy sheet is annealed under vacuum (vacuum degree is 10 ^-2 Pa). The high-temperature homogenized alloy block is subjected to multi-pass room temperature cold rolling and single-pass rolling. The amount is 20%, and the total rolling reduction is 70%;

(6) Anneal the cold-rolled alloy sheet under vacuum (vacuum degree is 10 ^-2 Pa). The first annealing temperature is 900°C and the annealing time is 3 minutes. The second annealing temperature is 600°C. The time is 40 minutes, and high strength, toughness and low density steel are obtained.

The morphology of the high-strength, toughness and low-density steel obtained above was observed, as shown in Figures 12 to 15. Figure 12 is an electron backscattered scanning picture of high-strength, tough, low-density steel. From the picture, it can be found that the grain size of this material is uniform and there is no obvious grain boundary precipitation phase. Figure 13 is a transmission selected area diffraction photo of high-strength and low-density steel. From the picture, it can be found that the high-strength and toughness steel material has a single-phase austenite structure and has a coherent κ-carbide precipitation phase. Figure 14 shows the transmission dark field image of high-strength, tough, low-density steel. It can be found that this alloy also contains a large number of nanoscale coherent κ-carbides.

The mechanical properties of the obtained high-strength, toughness and low-density steel were tested. The steel stress-strain curve obtained in Example 2 is shown in Figure 15. It can be seen from Figure 15 that the yield strength of the high-strength, tough, low-density steel with multi-level nanostructure strengthening effect obtained in this example is about 1094MPa, the tensile strength is about 1324MPa, the elongation after fracture is about 53%, and the density is 6.7g/cm ³ , the specific strength is 198MPa·cm ³ g ^-1 .

Example 4

(1) Make ingredients according to the chemical formula Fe ₄₉ Mn ₃₀ Al ₁₅ C ₅ V _0.8 Nb _0.2 (atomic percentage). The raw materials use blocks corresponding to each pure element, with a purity greater than 99.9%. The carbon uses graphite, with a purity greater than 99.9%;

(2) Place the prepared raw materials in a copper crucible and use an electric arc furnace for smelting. First, introduce high-purity argon gas into the crucible for gas cleaning, then pump low vacuum to below 5 Pa, and then pump high vacuum to 5×10 ^- Below ³ Pa, high-purity argon gas of 5 MPa is finally introduced as the protective gas, the melting temperature is 1700°C, the temperature is maintained for 15 minutes, and the melted alloy ingot is obtained by repeating the melting 5 times;

(3) The alloy is subjected to multi-pass hot rolling, the hot rolling temperature is 900°C, the single rolling reduction is 10%, and the total rolling reduction is 50%;

(4) The hot-rolled alloy block is subjected to high-temperature homogenization treatment under vacuum (vacuum degree is 10 ^-2 Pa), the temperature is 1200°C, the homogenization treatment time is 2 hours, and then water quenched;

(5) The high-temperature homogenized alloy block is subjected to multi-pass room temperature rolling, with a single-pass rolling reduction of 15% and a total rolling reduction of 75%;

(6) Anneal the cold-rolled alloy sheet under vacuum (vacuum degree is 10 ^-2 Pa), the annealing temperature is 600°C, and the annealing time is 40 minutes to obtain a high-strength, tough, metastable polyethylene with precipitation strengthening effect. Component alloy materials.

The mechanical properties of the obtained high-strength, tough, metastable multi-component alloy material were tested. The stress-strain curve of the high-strength and tough metastable multi-component alloy material obtained in Example 4 is shown in Figure 16. It can be seen from Figure 16 that the yield strength of the high-strength, tough, low-density steel with multi-level nanostructure strengthening effect obtained in this example is about 2165MPa, the tensile strength is about 2248MPa, the elongation after fracture is about 3.7%, and the density is 6.8g/cm ³ , the specific strength is 330MPa·cm ³ g ^-1 .

Comparative example 1

According to Materials letters [Quoting Materials letters: GFZhang.,HYShi.,STWang.,YHTang.,XYZhang.,Q.Jing.,RPLiu., Ultrahigh strength and highductility lightweight steel achieved by dual nanoprecipitate strengthening and dynamic slip refinement.Materials Letters, 2023.330:133366], after Fe-25Mn-10Al-1.2C-0.4V (mass ratio) casting, hot forging (1120℃-1145℃) and hot rolling (1050℃, 85%) and cold rolling (60%) After annealing, annealing includes 2h at 1050°C and 2h at 600°C. The mechanical properties of the prepared low-density steel are tested, as shown in Figure 18. The yield strength is 1216MPa, the tensile strength is 1356MPa, and the elongation is 28%. . The density is about 6.5g/cm ³ and the specific strength is 208MPa·cm ³ g ^-1 .

Comparative example 2

The highest strength low-density steels recorded in Science Advances [Citation Science Advances: ZW, LW, ZH, CH, Liebscher., J.He., D.Ponge., D.Raabe., and LZ, Ultrastrong lightweight compositionally complex steels via dual-nanoprecipitation.ScienceAdvances, 2020.6:9543], Fe ₄₈ Mn ₂₆ Al ₁₆ C ₅ Ni ₅ (atomic ratio) has been homogenized (1200℃, 1h), hot rolled (1100℃), and cold rolled (total rolling reduction 60 %), the tensile strength after annealing (800℃, 3min) is 1700MPa respectively, the elongation is 13%, the density is 6.5g/cm ³ , and its specific strength is 260MPa·cm ³ g ^-1 . The stress of the alloy material The strain curve is shown in Figure 17.

Comparing Examples 1, 2, 3 and 4 with Comparative Example 1, it can be seen that the performance of low-density steel outside the composition range of the present invention is far lower than that of the low-density steel material of the present invention based on the same or similar processing technology. . By comparing Examples 1, 2, 3 and 4 with Comparative Example 2, it can be seen that the optimal performance of the alloy of the present invention is 548MPa higher than the tensile strength of the current alloy. The density of the alloy of the present invention is 6.7-6.8g/cm ³ , which is higher than the tensile strength of the current alloy. The maximum strength can reach 330MPa·cm ³ g ^-1 . The invention does not contain precious elements Cr, Ni, etc., and its comprehensive cost is low. The improved performance of the high-strength, tough, low-density steel of the present invention is due to the multi-level nanostructure from sub-nanometer to nanometer in the alloy. This multi-scale nanostructure greatly improves the strength and toughness of the material.

In addition, hot rolling of the alloy cast billet can effectively eliminate defects (such as micropores, microcracks, etc.) produced in the alloy during melting and casting, and improve the overall performance of the alloy; subsequent homogenization treatment can further promote the improvement of each component in the alloy. The elements are uniformly distributed, and through subsequent cold rolling and annealing, multi-level nanostructures can be formed. By adjusting the annealing process parameters, the present invention can control the multi-scale nanostructure, grain size, etc. of the alloy, thereby adjusting the mechanical properties and ensuring On the premise of good plasticity of the alloy, the strength of the alloy is improved.

The present invention designs reasonable contents of Mn, Al, and C, and strictly controls the ratios of Mn/Al, (Mn+Al)/C and V/Nb, and simultaneously controls the total amounts of Nb and V, so that the content of Mn, Al, and C can be formed inside the steel material. The multi-level coherent structure of sub-nanometer level (κ' phase), several nanometer level (κ phase), and tens of nanometer level (MC carbide) can achieve extremely high strength of the alloy through strengthening of this multi-level nanostructure. It maintains good toughness, and the density and cost of this steel material are low, which can meet the needs of high specific strength steel materials.

It should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solution of the present invention can be carried out. Modifications or equivalent substitutions without departing from the spirit and scope of the technical solution of the present invention shall be included in the scope of the claims of the present invention.

Claims (10)

1. A high-strength and high-toughness low-density steel with a multi-stage nanostructure strengthening effect is characterized in that: comprises the following components in atom percent: 25 to 32 percent of Mn, 12 to 18 percent of Al, 3.0 to 7.0 percent of C, 0 to or less than or equal to Nb and 0.2 percent, 0 to or less than or equal to V and 0.8 percent, and the balance of Fe and unavoidable impurities;

wherein, according to the atomic percentage, mn/Al is more than or equal to 1.0, (Mn+Al)/C is more than or equal to 30, (Nb+V) is less than or equal to 1.0 percent and V/Nb is more than or equal to 4.

2. The high strength and toughness low density steel having multi-stage nanostructured reinforcing effect according to claim 1, wherein: the high-strength and high-toughness low-density steel internally forms a multi-stage coherent structure containing sub-nano-scale kappa phase, nano-scale kappa phase and tens of nano-scale MC carbide.

3. The high strength and toughness low density steel having multi-stage nanostructure strengthening effect according to claim 1 or 2, characterized in that: the alloy has the following characteristics:

(i) Yield strength is 800-2000 MPa;

(ii) Tensile strength is 1000-2248 MPa;

(iii) The elongation after fracture is 3-70%;

(iv) The specific strength is 150-330 MPa cm ³ g ^-1 。

4. A method for producing a high strength and toughness low density steel having a multi-stage nanostructure strengthening effect as set forth in any one of claims 1 to 3, characterized in that: comprising the steps of (a) a step of,

the components are prepared according to the atomic ratio, and are smelted under the protection of vacuum or inert gas, cast into a casting blank, and the casting blank is subjected to hot rolling, homogenization, cold rolling and annealing treatment to obtain the high-strength and high-toughness low-density steel with the multi-stage nanostructure strengthening effect.

5. The method for preparing high-strength and high-toughness low-density steel with multi-stage nanostructure strengthening effect according to claim 4, wherein the method comprises the following steps: the smelting is carried out at 1450-2200 ℃ for more than 0.1 hour; the smelting is carried out by maintaining the vacuum degree in the furnace below 1 Pa or maintaining the inert gas pressure in the furnace below 100 MPa.

6. The method for preparing high-strength and high-toughness low-density steel with multi-stage nanostructure strengthening effect according to claim 4, wherein the method comprises the following steps: the hot rolling adopts multi-pass hot rolling, the hot rolling temperature is 800-1250 ℃, the single-pass rolling reduction is less than or equal to 25%, and the total rolling reduction is 30-90%.

7. The method for preparing high-strength and high-toughness low-density steel with multi-stage nanostructure strengthening effect according to claim 4, wherein the method comprises the following steps: homogenizing, wherein the homogenizing treatment temperature is 1100-1250 ℃, and the homogenizing time is more than 30min; the homogenization treatment is performed under vacuum or a protective atmosphere, wherein the protective atmosphere is selected from one of argon, nitrogen or helium.

8. The method for preparing high-strength and high-toughness low-density steel with multi-stage nanostructure strengthening effect according to claim 4, wherein the method comprises the following steps: the cold rolling adopts multi-pass cold rolling, the pass rolling reduction is less than or equal to 25 percent, and the total rolling reduction is 40 to 90 percent.

9. The method for preparing high-strength and high-toughness low-density steel with multi-stage nanostructure strengthening effect according to any one of claims 4 to 8, characterized in that: the annealing is one of the first annealing and/or the second annealing;

wherein the first annealing temperature is 900-1100 ℃, and the heat preservation time is 5-300 min; the second annealing temperature is 550-650 ℃, and the heat preservation time is not less than 5min.

10. The method for preparing high-strength and high-toughness low-density steel with multi-stage nanostructure strengthening effect according to claim 9, wherein the method comprises the following steps: the annealing is performed under vacuum or a protective atmosphere, wherein the protective atmosphere is selected from one of argon, nitrogen or helium.