Ultra-high strength steel with a high product of strength and ductility and method of making

Abstract

The application relates to the field of high-strength steel, and provides an ultrahigh-strength steel with a product of strength and ductility greater than 30 GPa% and a preparation method, the preparation method comprising the following steps: S1, smelting raw materials according to a set ratio to form a casting blank or a steel ingot; S2, performing open forging on the casting blank or the steel ingot and then air cooling to room temperature; S3, re-heating the open-forged rod material to an austenitizing temperature, keeping warm, performing multi-pass hot rolling to form a plate or performing multi-pass secondary forging in a rotating state to form a rod, and cooling to room temperature; S4, performing not less than one austenitizing short-time keeping warm quenching treatment; and S5, performing tempering treatment. The ultrahigh-strength steel provided by the application is prepared through low-cost alloy design, the total alloy element content is less than 10%, and hot forging / hot rolling preparation which can be completely industrialized is adopted, so that the requirement for equipment is low compared with warm rolling, cold rolling and the like. Meanwhile, the ultrahigh-strength steel has excellent comprehensive mechanical properties, the tensile strength is greater than 2400 MPa, and the product of strength and ductility is greater than 30 GPa%.

Description

Technical Field

[0001] This invention relates to the field of high-strength steel technology, and in particular to an ultra-high-strength steel with a strength-ductility product greater than 30 GPa·% and its preparation method. Background Technology

[0002] High-strength steel is of paramount value in breakthrough material applications and has broad prospects for future use in civil infrastructure, machinery, transportation, aerospace, and marine engineering. While maintaining the same load-bearing capacity, using ultra-high-strength steel with a strength greater than 2000 MPa can significantly reduce material usage, achieving lightweight requirements. However, when the strength exceeds 2400 MPa, the inverse relationship between strength and ductility becomes particularly pronounced, with most alloys exhibiting elongation below 2%. Therefore, maintaining good ductility while increasing steel strength is extremely challenging in the field of ultra-high-strength steel. The strength-ductility product is one of the most important indicators for determining the comprehensive mechanical properties of high-strength steel. Currently, the strength-ductility product of ultra-high-strength steel is difficult to exceed 30 GPa·%, making it difficult for ultra-high-strength steel to meet requirements for ductility and toughness, severely limiting its application.

[0003] Chinese patent CN 113604753A discloses a 2700MPa grade high-ductility, high-toughness, and high-corrosion-resistant martensitic aging stainless steel and its preparation method. This steel is the highest strength steel reported in current patent literature, possessing excellent elongation (>10%). With optimized composition and processing, the highest strength can reach 2737MPa, with an elongation of 10.3%. Even so, the strength-ductility product of this steel is 27.8 GPa·%, still below 30 GPa·%. Furthermore, the alloy content of the optimized composition of this high-ductility, high-toughness, and high-corrosion-resistant martensitic aging stainless steel exceeds 30%, making it extremely expensive. The steel is also prepared using a cold-rolling process, which results in high resistance to cold-rolling deformation and places extremely high demands on rolling equipment. Therefore, this 2700MPa grade high-ductility, high-toughness, and high-corrosion-resistant martensitic aging stainless steel is difficult to produce and widely apply.

[0004] The literature “Li Junkui, Yang Zhinan, Ma Hua, et al. A medium-C martensite steel with 2.6GPa Tensile strength and large ductility[J].Scripta Materialia,2023,228,115327” describes the preparation of 2590MPa grade ultra-high strength steel using a hot rolling + warm rolling + low temperature tempering process combined with optimized composition. The total elongation is 14.5%, and the strength-ductility product is 37.6GPa·%. Although the strength-ductility product of this steel is higher than 30GPa·%, the warm rolling process at 400-600℃ still places high demands on the rolling equipment and is difficult to achieve in actual production.

[0005] Chinese patent CN110055465A discloses a medium-manganese ultra-high strength steel and its preparation method. The patent has a maximum strength-ductility product of 40 GPa·%, which is excellent in terms of comprehensive mechanical properties. However, the maximum tensile strength is only 1950 MPa, which cannot reach 2000 MPa or more to meet the requirements of higher strength. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide an ultra-high strength steel with a strength-ductility product greater than 30 GPa·% and a preparation method thereof. The alloy content is low (<10%), the preparation cost is low, and the comprehensive mechanical properties of the high strength steel of this invention are extremely excellent. Under the preferred composition and process, the ultra-high strength steel of this invention has a tensile strength greater than 2400 MPa while the strength-ductility product can reach more than 30 GPa·%.

[0007] The present invention adopts the following technical solution:

[0008] On one hand, the present invention provides a method for preparing ultra-high strength steel with a strength-ductility product greater than 30 GPa·%, comprising:

[0009] S1. Smelt the alloy raw materials with a set ratio and cast them into billets or steel ingots.

[0010] S2. The billet or steel ingot is forged at a set temperature to obtain a forged bar, and then air-cooled to room temperature;

[0011] S3. The forged bar stock treated in step S2 is reheated to the austenitizing temperature and held at that temperature. The forged bar stock is then hot-rolled into a sheet in multiple passes or forged into a bar in multiple passes while rotating, and then cooled to room temperature.

[0012] S4. Perform austenitizing short-time holding quenching treatment on the plate obtained by hot rolling or the bar obtained by forging in step S3 for no less than one time.

[0013] S5. Temper the plate or bar after step S4 to obtain ultra-high strength steel with a strength-ductility product greater than 30 GPa·%.

[0014] In addition to any of the possible implementations described above, another implementation is provided in which, in step S1, the alloy raw materials are in the following mass percentages: C: 0.4-0.7%, Si: 0.2-2.0%, Mn: 0.2-2.5%, Cr: 0.2-2%, Ni: 0.5-3%, Mo: 0.3-2%, V: 0.1-0.7%, Nb: ≤0.3%, with the balance being Fe and unavoidable impurities.

[0015] In addition to any of the possible implementations described above, another implementation is provided in which, in step S2, the set temperature is 1150℃~1250℃, and the temperature is maintained for 1~3 hours.

[0016] In addition to any of the possible implementations described above, another implementation is provided in which, in step S3, the austenitizing temperature is 850–1200°C and the holding time is 0.5 h or more.

[0017] In addition to any of the possible implementations described above, another implementation is provided in which, in step S3, the total deformation of the multi-pass hot rolling or multi-pass forging is greater than 60%, and the final rolling temperature of the multi-pass hot rolling or the final forging temperature of the multi-pass forging is greater than 700°C.

[0018] In addition to any of the possible implementations described above, another implementation is provided in which, in step S4, the austenitizing temperature of the at least one austenitizing short-time holding quenching treatment is 800-950°C, and the holding quenching time for each treatment is 1-10 minutes.

[0019] In addition to any of the possible implementations described above, another implementation is provided in which the cooling method for the at least one austenitizing quenching in step S4 includes air cooling, wind cooling, water mist cooling, oil cooling, water cooling, or liquid nitrogen cooling.

[0020] In addition to any of the possible implementations described above, another implementation is provided in which the tempering process in step S5 includes: holding the rolled plate or the forged bar at 100-320°C for 0.1-48 hours.

[0021] On the other hand, the present invention also provides an ultra-high strength steel with a strength-ductility product greater than 30 GPa·%, the composition percentages being: C: 0.4-0.7%, Si: 0.2-2.0%, Mn: 0.2-2.5%, Cr: 0.2-2%, Ni: 0.5-3%, Mo: 0.1-2%, V: 0.1-0.7%, Nb: ≤0.3%, with the balance being Fe and unavoidable impurities;

[0022] The ultra-high strength steel is obtained by the above preparation method. The microstructure of the ultra-high strength steel includes equiaxed fine martensite and highly stable retained austenite, with the retained austenite content accounting for 5-15%. The tensile strength of the ultra-high strength steel is greater than 2400 MPa.

[0023] The design principle of the chemical composition of this invention is as follows:

[0024] C element: C is the most important alloying element in steel. A certain C content in high-strength martensitic steel can ensure sufficient strength through interstitial solid solution strengthening and dislocation strengthening effect provided by the interaction between carbon and dislocations. However, excessive carbon content will increase the stability of austenite, resulting in an excessively high content of residual austenite in the microstructure obtained after quenching, thereby reducing the strength of high-strength steel. Therefore, this invention limits the weight percentage of C to between 0.4% and 0.7%.

[0025] Si (Si): Si can improve the tempering stability of martensitic steel and increase the tempering brittleness temperature range of steel, thus increasing the tempering temperature of steel and obtaining excellent plasticity and toughness. Simultaneously, Si also provides good solid solution strengthening. Therefore, the weight percentage of Si in this invention is limited to 0.2% to 2.0%.

[0026] Mn, Cr, and Ni elements: Mn, Cr, and Ni are all elements that increase hardenability and provide some solid solution strengthening. However, excessive Mn and Ni content can lead to overly stable retained austenite, which is detrimental to maintaining high strength. Excessive Cr content can lead to the formation of coarse carbides. Furthermore, excessive addition of Mn, Cr, and Ni content can significantly increase the cost of the alloy. Therefore, this invention limits the weight percentage of Mn to 0.2–2.5%; the weight percentage of Cr to 0.2–2%; and the weight percentage of Ni to 0.5–3%.

[0027] Mo, V, and Nb elements: Mo, V, and Nb can form carbides with C, significantly improving the strength of steel through precipitation strengthening, while also refining the microstructure. However, excessive addition of Mo, V, and Nb can lead to an increase in the size of the precipitated phases, reducing the precipitation strengthening effect and significantly increasing the alloy cost. Therefore, this invention limits the weight percentage of Mo to 0.1–2%, the weight percentage of V to 0.1–0.7%, and the weight percentage of Nb to 0–0.3%.

[0028] The process design concept of this invention is as follows: This invention uses hot forging / hot rolling combined with subsequent re-austenitizing quenching and tempering to prepare ultra-high strength steel, which is suitable for existing ultra-high strength steel production lines such as 300M steel and can be fully industrialized. This invention utilizes forging or rolling above the austenitizing temperature to effectively reduce deformation resistance. Refining the original austenite grains can lower the Ms temperature of the martensitic transformation, which is beneficial for obtaining more stable and relatively abundant retained austenite (5-15%). The more stable retained austenite avoids the explosive phase transformation from retained austenite to martensite during deformation, thus preventing a decrease in toughness. Instead, it provides a good toughening effect through the continuous transformation of retained austenite to martensite, i.e., the TRIP effect. Simultaneously, refining the original austenite grains also refines the martensitic substructure. The refinement of the original austenite grains and the martensitic plate substructure can deflect cracks during propagation, effectively hindering crack propagation and ultimately improving the fracture toughness of the martensitic steel. Furthermore, refining the original austenite grains can suppress the formation of brittle twinned martensite. Therefore, the core of the process design in this invention lies in microstructure refinement. The method employed is to obtain a non-recrystallized or fine dynamically recrystallized microstructure through thermomechanical deformation above the austenitizing temperature, preparing for the subsequent austenitizing process to obtain a fine martensite microstructure. Simultaneously, at least one austenitizing treatment is used to further refine the original austenite microstructure based on the existing fine microstructure. The austenitizing holding time is limited to 1–10 min to suppress grain growth after austenitization, ultimately achieving a good balance between strength and ductility. The tempering temperature range (100–300℃) provided by this invention is lower than the lower limit of the general martensite tempering temperature range (150–300℃), which is beneficial for suppressing dislocation recovery and the precipitation of solid solution carbides, thereby retaining higher strength after tempering.

[0029] The beneficial effects of this invention are as follows:

[0030] (1) The present invention adopts a low-cost alloy design scheme with low alloy content (<10%) and low preparation cost. The high-strength steel of the present invention has excellent comprehensive mechanical properties. Under the preferred composition and process, the tensile strength of the ultra-high strength steel of the present invention is greater than 2400MPa while the strength-ductility product can reach more than 30GPa·%.

[0031] (2) The preparation process of this invention includes hot forging / hot rolling, at least one short-time austenitizing quenching, and low-temperature tempering. The process is simple and fully industrializable. Hot forging or hot rolling requires less equipment than warm rolling or cold rolling. The repeated short-time austenitizing quenching after hot rolling or forging described in this invention can obtain a fine martensitic structure and 5-15% relatively stable retained austenite, providing excellent strength-plasticity balance.

[0032] (3) The steel of the present invention has excellent hardenability. After hot rolling / hot forging, controlled cooling can be achieved by air cooling, wind cooling, water mist cooling, oil cooling, water cooling and liquid nitrogen cooling to obtain a large amount of martensite (>85%). The cooling method is flexible and the cooling process is highly selective for production enterprises.

[0033] (4) Unlike general martensitic steels that require tempering at temperatures above 150-300°C to obtain a certain degree of plasticity, this invention broadens the tempering temperature range of martensitic steel to 100-320°C. That is, the high-strength steel of this invention can still obtain good plasticity when tempered at 150°C. At the same time, since the recovery of dislocations is significantly suppressed when the tempering temperature is below 150°C, this invention can obtain a tensile strength of up to 2800MPa while maintaining a strength-ductility product of 30GPa·% and far exceeds the highest strength-ductility product (19.9GPa·%) of the currently reported 2800MPa grade ultra-high strength steel. Attached Figure Description

[0034] Figure 1 The diagram shown is a flow chart of an ultra-high strength steel with a strength-ductility product greater than 30 GPa·% according to an embodiment of the present invention.

[0035] Figure 2 The figures shown are the engineering stress-strain curves for Examples 1 and 2.

[0036] Figure 3 The image shown is a reconstruction diagram of the original austenite grains in Example 2 using EBSD. Detailed Implementation

[0037] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered in isolation, but can be combined with each other to achieve better technical effects.

[0038] like Figure 1 As shown, an embodiment of the present invention provides a method for preparing ultra-high strength steel with a strength-ductility product greater than 30 GPa·% including:

[0039] S1. Smelt the alloy raw materials with a set ratio and cast them into billets or steel ingots.

[0040] S2. The billet or steel ingot is forged at a set temperature to obtain a forged bar, and then air-cooled to room temperature;

[0041] S3. The forged bar stock treated in step S2 is reheated to the austenitizing temperature and held at that temperature. The forged bar stock is then hot-rolled into a sheet in multiple passes or forged into a bar in multiple passes while rotating, and then cooled to room temperature.

[0042] S4. Perform multiple austenitizing short-time heat treatment on the plate or bar obtained by hot rolling in step S3.

[0043] S5. Temper the plate or bar after step S4 to obtain ultra-high strength steel with a strength-ductility product greater than 30 GPa·%.

[0044] In one specific embodiment, in step S1, the alloy raw materials are as follows by mass percentage: C: 0.4-0.7%, Si: 0.2-2.0%, Mn: 0.2-2.5%, Cr: 0.2-2%, Ni: 0.5-3%, Mo: 0.1-2%, V: 0.1-0.7%, Nb: ≤0.3%, with the balance being Fe and unavoidable impurities.

[0045] In one specific embodiment, in step S2, the set temperature is 1150℃~1250℃, and the temperature is maintained for 1~3 hours.

[0046] In one specific embodiment, in step S3, the austenitizing temperature is 850–1200°C, and the holding time is 0.5 h or more.

[0047] In one specific embodiment, in step S3, the total deformation of the multi-pass hot rolling or multi-pass forging is greater than 80%, and the final rolling temperature of the multi-pass hot rolling or the final forging temperature of the multi-pass forging is greater than 700°C.

[0048] In one specific embodiment, in step S4, the austenitizing temperature of the at least one austenitizing short-time holding and quenching treatment is 800-950°C, and the holding and quenching time for each treatment is 1-10 minutes.

[0049] In one specific embodiment, in step S4, the cooling method for the multiple short-time austenitizing quenching includes air cooling, wind cooling, water mist cooling, oil cooling, water cooling, or liquid nitrogen cooling.

[0050] In one specific embodiment, step S5, the tempering treatment includes: holding the rolled plate or the forged bar at 100-320°C for 0.1-48 hours.

[0051] This invention discloses an ultra-high strength steel with a strength-ductility product greater than 30 GPa·%, comprising the following percentages: C: 0.4–0.7%, Si: 0.2–2.0%, Mn: 0.2–2.5%, Cr: 0.2–2%, Ni: 0.5–3%, Mo: 0.1–2%, V: 0.1–0.7%, Nb: ≤0.3%, with the balance being Fe and unavoidable impurities.

[0052] The ultra-high strength steel is obtained by the above preparation method. The microstructure of the ultra-high strength steel includes equiaxed fine martensite and retained austenite, with a retained austenite content of 5-15%. The tensile strength of the ultra-high strength steel is greater than 2400 MPa.

[0053] The present invention will be further described below with reference to specific embodiments.

[0054] In this embodiment, the mechanical properties were tested according to GB / T228-2021 "Metallic materials, tensile testing - Part 1: Test at room temperature"; the gauge length of the specimen was 10 mm.

[0055] Example 1

[0056] The chemical composition of ultra-high strength steel with a strength-ductility product greater than 30 GPa·% includes, by weight percentage: C: 0.43, Si: 0.4, Mn: 0.4, Cr: 0.8, Ni: 3, Mo: 0.5, V: 0.3, Nb: 0, with the balance being Fe and unavoidable impurity elements, and the total alloying element content is 5.83%.

[0057] Its preparation process is as follows: smelting → casting → billet forging → secondary forging → primary austenitizing quenching → tempering.

[0058] Process parameters: The final forging temperature for the secondary forging is 750℃, the forging deformation is 95%, and the cooling method after forging is water cooling; the austenitizing treatment process involves a single austenitizing quenching, i.e., holding at 800℃ for 8 minutes followed by air cooling to room temperature; the tempering temperature is 90℃, and the tempering time is 48 hours. The resulting high-strength steel has a strength of 2433 MPa, an elongation of 15.5%, and a strength-ductility product of 37.7 GPa·%, as shown in the engineering stress-strain curve. Figure 2 As shown.

[0059] Example 2

[0060] The chemical composition of the steel, by weight percentage, includes: C: 0.58, Si: 1.4, Mn: 0.8, Cr: 1, Ni: 1.8, Mo: 0.5, V: 0.3, Nb: 0, with the balance being Fe and unavoidable impurity elements, and the total alloying element content is 6.38%.

[0061] Its preparation process is as follows: smelting → casting → billet forging → secondary forging → primary austenitizing quenching → tempering.

[0062] Process parameters: The final forging temperature for the secondary forging is 850℃, the forging deformation is 85%, and the cooling method after forging is water cooling; the austenitizing treatment process involves a single austenitizing quenching, i.e., holding at 900℃ for 2 minutes followed by water cooling to room temperature; the tempering temperature is 100℃, and the tempering time is 24 hours. The resulting high-strength steel has a strength of 2920 MPa, a total elongation of 12.0%, and a strength-ductility product of 35.0 GPa·%, as shown in the engineering stress-strain curve. Figure 1 As shown, the obtained martensite structure is fine, and the original austenite grain size reconstructed by EBSD is 1.89 μm, demonstrating a significant microstructure refinement effect. Figure 3 As shown.

[0063] Example 3

[0064] The chemical composition of the steel, by weight percentage, includes: C: 0.58, Si: 1.4, Mn: 0.8, Cr: 1, Ni: 1.8, Mo: 0.5, V: 0.3, Nb: 0, with the balance being Fe and unavoidable impurity elements, and the total alloying element content is 6.38%.

[0065] Its preparation process is as follows: smelting → casting → billet forging → secondary forging → tertiary austenitizing quenching → tempering.

[0066] Process parameters: The final forging temperature of the secondary forging was 850℃, the forging deformation was 85%, and the cooling method after forging was water cooling; the austenitizing treatment process was to perform three austenitizing quenchings, that is, to cycle the sample three times, hold it at 900℃ for 2 minutes, and then water cool it to room temperature; the tempering temperature was 200℃, and the tempering time was 1 hour. The resulting high-strength steel had a strength of 2621 MPa, an elongation of 12.5%, and a strength-ductility product of 32.8 GPa·%. The original austenite grain size reconstructed by EBSD was only 1.7 μm, and the microstructure refinement effect was more significant than that of a single austenitizing treatment.

[0067] Example 4

[0068] The chemical composition of the steel, by weight percentage, includes: C: 0.67, Si: 1.8, Mn: 2.3, Cr: 2.0, Ni: 0.5, Mo: 1.8, V: 0.3, Nb: 0.1, with the balance being Fe and unavoidable impurity elements, and the total alloying element content is 9.47%.

[0069] Its preparation process is as follows: smelting → casting → billet forging → rolling → tempering.

[0070] Process parameters: final rolling temperature 950℃, total rolling reduction 85%, post-rolling cooling method is air cooling; austenitizing treatment process is holding at 950℃ for 1 min followed by water cooling to room temperature, tempering temperature 320℃, tempering time 0.2 h, resulting in a high-strength steel with a strength of 2488 MPa, elongation of 13.8%, and strength-ductility product of 34.3 GPa·%.

[0071] Example 5

[0072] The chemical composition of the steel, by weight percentage, includes: C: 0.52, Si: 1.0, Mn: 0.6, Cr: 0.8, Ni: 2.2, Mo: 0.8, V: 0.5, Nb: 0, with the balance being Fe and unavoidable impurity elements, and the total alloying element content is 6.42%.

[0073] Its preparation process is as follows: smelting → casting → billet forging → rolling → first austenitizing quenching → tempering.

[0074] Process parameters: final rolling temperature 900℃, rolling deformation 60%, post-forging cooling method is oil cooling; austenitizing treatment process is two austenitizing quenching processes, that is, the sample is cyclically held at 900℃ for 2 min twice and then water cooled to room temperature, tempering temperature is 120℃, tempering time is 1 h, and the strength of the above high-strength steel is 2518 MPa, the total elongation is 12.1%, and the strength-ductility product is 30.4 GPa·%.

[0075] This invention prepares ultra-high strength steel by using a low-cost alloy composition design (alloy element ratio less than 10%) combined with hot rolling / hot forging, at least one re-austenitization treatment, and low-temperature tempering. The prepared ultra-high strength steel has a strength exceeding 2400 MPa and a strength-ductility product exceeding 30 GPa·%, making it a low-cost ultra-high strength steel with extremely excellent comprehensive mechanical properties. Simultaneously, this invention broadens the lower limit of the martensitic tempering temperature from 150℃ to 100℃. Tempering below 150℃ significantly suppresses dislocation recovery, thus maintaining both extremely high strength and good ductility. In Example 2, tempering at 100℃ for 24 hours yielded a strength exceeding 2900 MPa while maintaining a total elongation of 12%, making it the highest-strength ultra-high strength steel reported to date with a total elongation exceeding 10%.

[0076] While several embodiments of the present invention have been provided herein, those skilled in the art should understand that modifications can be made to these embodiments without departing from the spirit of the invention. The above embodiments are merely exemplary and should not be construed as limiting the scope of the invention.

Claims

1. A method for preparing ultra-high strength steel with a strength-ductility product greater than 30 GPa·%, characterized in that, The preparation method includes: S1. The alloy raw materials with a set ratio are smelted and cast into billets or steel ingots; the alloy raw materials are as follows by mass percentage: C: 0.4~0.7%, Si: 0.2~2.0%, Mn: 0.2~2.5%, Cr: 0.2~2%, Ni: 0.5~3%, Mo: 0.3~2%, V: 0.1~0.7%, Nb: ≤0.3%, with the balance being Fe and unavoidable impurities; S2. The billet or steel ingot is forged at a set temperature to obtain a forged bar, and then air-cooled to room temperature; the set temperature is 1150℃~1250℃, and the temperature is maintained for 1~3 hours. S3. The forged bar stock processed in step S2 is reheated to the austenitizing temperature and held at that temperature. The forged bar stock is then hot-rolled into a sheet or forged into a bar stock in a rotating state through multiple passes, and then cooled to room temperature. The final rolling temperature of the multiple hot rolling or the final forging temperature of the multiple forging are both greater than 700°C. S4. Perform austenitizing short-time holding quenching treatment on the plate obtained by hot rolling or the bar obtained by forging in step S3 for no less than one time; wherein, the austenitizing temperature of the austenitizing short-time holding quenching treatment is 800~950℃, and the holding time for each time is 1~10min. S5. Temper the plate or bar after step S4, wherein the tempering temperature of the tempering treatment is 100~320℃, to obtain the ultra-high strength steel with a strength-ductility product greater than 30GPa·%.

2. The method for preparing ultra-high strength steel with a strength-ductility product greater than 30 GPa·% as described in claim 1, characterized in that, In step S3, the austenitizing temperature is 850~1200℃, and the holding time is more than 0.5h.

3. The method for preparing ultra-high strength steel with a strength-ductility product greater than 30 GPa·% as described in claim 1, characterized in that, In step S3, the total deformation of the multi-pass hot rolling or multi-pass forging is greater than 60%.

4. The method for preparing ultra-high strength steel with a strength-ductility product greater than 30 GPa·% as described in claim 1, characterized in that, In step S4, the cooling method for the austenitizing short-time heat preservation quenching treatment includes air cooling, wind cooling, water mist cooling, oil cooling, water cooling, or liquid nitrogen cooling.

5. The method for preparing ultra-high strength steel with a strength-ductility product greater than 30 GPa·% as described in claim 1, characterized in that, In step S5, the tempering treatment is maintained at a temperature of 0.1~48h.

6. A high-strength steel with a strength-ductility product greater than 30 GPa‧%, characterized in that, The ultra-high strength steel is obtained by the preparation method according to any one of claims 1-5, wherein the composition of the ultra-high strength steel by mass percentage is: C: 0.4~0.7%, Si: 0.2~2.0%, Mn: 0.2~2.5%, Cr: 0.2~2%, Ni: 0.5~3%, Mo: 0.3~2%, V: 0.1~0.7%, Nb: ≤0.3%, and the balance is Fe and unavoidable impurities; The microstructure of the ultra-high strength steel includes fine martensite and retained austenite, with the retained austenite content accounting for 5-15%.

7. The ultra-high strength steel with a strength-ductility product greater than 30 GPa·% as described in claim 6, characterized in that, The ultra-high strength steel has a tensile strength greater than 2400 MPa.

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