CN115305409B - High-strength high-toughness easily-welded nano steel with thickness of 5-60 mm and thickness of 850MPa and preparation method thereof - Google Patents
High-strength high-toughness easily-welded nano steel with thickness of 5-60 mm and thickness of 850MPa and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a high-strength high-toughness easily-welded nano steel with the thickness of 5-60 mm and 850MPa and a preparation method thereof, wherein the nano steel comprises the following components: and C:0.02 to 0.08, si:0.1 to 0.4, mn:0.5 to 1.1, P is less than or equal to 0.01, S is less than or equal to 0.0015, cu:1.0 to 1.5, ni:2.5 to 4.0, cr:0.2 to 0.8, mo:0.3 to 0.6, nb:0.02-0.1, ti:0.01 to 0.05, al: 0.005-0.05, and the balance of Fe and unavoidable impurities. The preparation method of the high-strength high-toughness easy-to-weld steel comprises the following steps: smelting and refining-continuous casting or die casting-rolling-heat treatment. The high-strength high-toughness easy-to-weld steel provided by the invention can achieve the characteristics of yield strength of more than or equal to 850MPa, charpy V notch impact energy of more than or equal to 200J at-80 ℃ and elongation of more than or equal to 15%, magnetic conductivity equivalent to that of 20# steel, and high strength, high toughness, high plasticity, easy welding, high cleanliness and excellent magnetic conductivity by controlling inversion austenite form, distribution and volume fraction to optimize plasticity and low-temperature toughness while precipitating a large amount of nano-precipitate phases to improve strength by adjusting the content of nano-precipitate phase forming elements and a thermo-mechanical treatment process under the condition of ultralow carbon content. The high-strength high-toughness easy-to-weld steel can be widely applied to key structures such as ships, ocean engineering, engineering machinery, bridges, oil pipelines, aerospace engineering, magnetic shielding equipment and the like.
Description
Technical Field
The invention belongs to the field of alloy steel, and particularly relates to high-strength high-toughness easily-welded steel with the thickness of 5-60 mm and the thickness of 850MPa, which can be used in the fields of ships, ocean engineering equipment, pipelines, heavy machinery equipment, magnetic shielding equipment and the like.
Background
With the rapid development of manufacturing industry, there is an increasing demand for properties of steel materials. The strengthening mechanism of traditional high strength steel comes from its martensite or lower bainite microstructure with higher carbon content. In order to ensure that the steel plate with thicker specification has enough hardenability, the steel needs to be added with higher content of C, ni, cr, mo and other alloy elements. The higher the strength grade requirement of the steel, the higher the content of added alloying elements, which necessarily results in the loss of other properties of the steel, such as ductility, fracture toughness, weldability, workability, etc. In addition, as the strength is increased, the carbon equivalent of the steel is also increased greatly, which can increase the welding difficulty of the materials and increase the welding processing cost.
In the early 80 s of the 20 th century, people began to explore high-strength low-alloy steel, elements are formed by adding precipitation phases such as Cu and Ni on the basis of the original materials, the hardenability and the number of the precipitation phases of the materials are further improved, the obtained precipitation-strengthened high-strength low-alloy steel is provided, precipitation of the precipitation phases can be promoted by reducing grain boundaries by adding Ni, the strength of the materials is improved, meanwhile, the plasticity and toughness of the materials are improved, and the hot brittleness of the materials is reduced. In later studies, the strength level was further improved by optimizing the thermo-mechanical treatment and thermo-working process.
At present, low alloy steel strengthened by Cu-containing precipitation phases published at home and abroad has the strength grade of more than 800MPa, and better low-temperature toughness is difficult to ensure. In the patent document with publication number of CN108004475B, a 900 MPa-grade hot rolled precipitation strengthening type high-strength high-toughness steel and a manufacturing method thereof are disclosed, wherein the yield strength is more than 800MPa, but the carbon content is higher than 0.1 percent, the steel is not easy to weld, and the impact energy at minus 40 ℃ is less than 100J.
In the patent document with publication number of CN110229999A, a 900MPa grade precipitation strengthening high-toughness steel plate and a preparation method thereof are disclosed, and the yield strength of martensitic steel obtained through copper-rich precipitation phase strengthening is more than 900MPa. Because the nickel element content is not high, vanadium, boron and more chromium are required to be added to improve the hardenability, but the low-temperature toughness is still lower than 80J at-80 ℃, and the high-strength high-toughness easily-welded nano steel with the thickness of 5-60 mm and the thickness of 850MPa can be used under more severe conditions.
In the patent document with publication number of CN106636961A, a Cu precipitation phase reinforced easy-to-weld steel and a preparation method are disclosed, wherein the preparation of steel with the thickness of less than 15mm is only carried out, and the steel plate with the thickness of more than 15mm is not explained.
Materials that are generally capable of shielding magnetic fields such as external magnetic fields, geomagnetic fields, etc. are called magnetic shielding materials, and the most important properties of such materials are magnetic shielding properties in addition to strength and toughness. This property is mainly determined by permeability (μ) and coercivity (Hc). If the magnetic shielding performance is to be ensured, it is required that the impurity elements of steel be low while the amount of nonmetallic inclusions is low. The common high magnetic conductive materials mainly comprise pure iron, silicon steel sheets, permalloy sheets, amorphous alloy sheets and the like, but the strength of the materials is low, the yield strength is generally not more than 400MP, and the low-temperature toughness is poor. Although the strength of the amorphous material is high, the plasticity and toughness are very poor, and the amorphous material is difficult to be made into a thickness of more than 1 mm. Compared with the traditional magnetic shielding material and high-strength steel, the nano phase precipitation strengthening replaces carbon strengthening and alloy strengthening, so that the carbon content is greatly reduced, and compared with the steel with the same strength grade, the alloy element content is also greatly reduced, and the novel steel material with high strength and toughness and excellent magnetic conductivity is obtained.
In the patent documents with publication numbers CN113416901A and CN113403547ADisclosed is a weather-proof soft magnetic steel with excellent low temperature toughness and high magnetic induction performance and its production method, wherein the magnetic induction characteristics under the conditions of magnetic field intensity of 300A/m, 4000A/m and 5000A/m are respectively 1.00T, 1.65T and 1.70T, but the yield strength is less than 400MPa, the impact toughness is only characterized by KV at-30 DEG C 2 。
In the publication No. CN113403547A, a high-clean soft magnetic steel with excellent welding performance and its production process are disclosed, wherein the magnetic induction characteristics under the conditions of magnetic field strength of 300A/m, 4000A/m and 5000A/m are respectively above 0.89T, 1.60T and 1.69T, but the yield strength is less than 380MPa, and the impact toughness is only characterized by-25 ℃ KV 2 。
In view of the above, there is no steel material capable of satisfying high strength, high toughness, good welding performance and high magnetic permeability at the same time, which is a great challenge for the conventional organization design thought and heat treatment process.
Disclosure of Invention
The invention aims to: the invention aims to provide high-strength high-toughness easily-welded nano steel with the thickness of 5-60 mm and 850MPa and a preparation method thereof, which can meet the requirements on high strength, high toughness and good welding performance of a steel plate, and the yield strength of the steel plate is more than or equal to 850MPa, the Charpy V notch impact energy at minus 84 ℃ is more than or equal to 200J, and the elongation is more than or equal to 15 percent through a solution treatment and aging treatment two-step heat treatment process. The magnetic permeability is equivalent to that of No. 20 steel.
The technical scheme of the invention is as follows:
a preparation method of 850 MPa-level high-strength high-toughness easily-welded nano steel with the thickness of 5-60 mm comprises the following steps:
(1) Smelting and refining: adopting blast furnace molten iron or molten iron smelted by an electric furnace, blowing oxygen, dephosphorizing and decarbonizing, deoxidizing aluminum, transferring into a ladle furnace for refining, and simultaneously adding alloy materials, wherein the alloy materials comprise the following components in percentage by mass: 0.02 to 0.08, si:0.1 to 0.4, mn:0.5 to 1.1, P is less than or equal to 0.01, S is less than or equal to 0.0015, cu:1.0 to 1.5, ni:2.5 to 4.0, cr:0.2 to 0.8, mo:0.3 to 0.6, nb:0.02-0.1, ti:0.01 to 0.05, al: 0.005-0.05, and balancing Fe and unavoidable impurities, adjusting the components to target components, and then performing dehydrogenation and deoxidation in a VD vacuum furnace;
(2) Continuous casting or die casting: continuous casting is adopted in converter smelting, die casting is adopted in electric furnace smelting, and casting blanks are stacked and slowly cooled for more than 24 hours;
(3) Rolling: heating a casting blank to 1160-1200 ℃, preserving heat for 2-6 hours, removing iron scales by using high-pressure water before rolling, removing phosphorus by using high-pressure water in the rolling process, and performing continuous rolling comprising rough rolling and finish rolling, wherein the rough rolling temperature is controlled to be 1000-1150 ℃; the initial rolling temperature of the finish rolling is 950-1050 ℃, the final rolling temperature is higher than 900 ℃, and the finish rolling is carried out to obtain a steel plate with the thickness of 5-60 mm;
(4) And (3) heat treatment: after the steel plate is subjected to heat preservation for 30-90 minutes at 800-950 ℃, cooling and quenching to room temperature; and tempering at 550-700 deg.c for 50-120 min and air cooling to room temperature.
A high-strength high-toughness easily-welded nano steel with the thickness of 5-60 mm and the thickness of 850MPa is composed of an ultralow-carbon lath martensitic structure and flaky contravariant austenite.
Furthermore, the yield strength of the nano steel is more than or equal to 850MPa, the Charpy V notch impact energy at-84 ℃ is more than or equal to 200J, and the elongation is more than or equal to 15%.
Compared with the prior art, the invention has the following beneficial effects:
1. the copper-rich nano precipitation phase strengthening with a hierarchical structure is used for replacing the traditional precipitation strengthening and carbon strengthening, so that the high-strength high-toughness easy-to-weld steel with the thickness of 5-60 mm and the thickness of 850MPa is low, and the welding performance is good; meanwhile, the content of alloy elements is low, and the cost is low.
2. The preparation method of the 850 MPa-level high-strength high-toughness easy-to-weld steel with the thickness of 5-60 mm is simple, has strong process controllability, and is easy to realize industrial production.
3. The yield strength of the high-strength high-toughness easily-welded steel with the thickness of 5-60 mm and the strength of 850MPa is more than or equal to 850MPa, the Charpy V notch impact energy at-84 ℃ is more than or equal to 200J, and the elongation is more than or equal to 15%. Has the characteristics of excellent toughness matching, high plasticity, easy welding and the like.
4. The magnetic induction characteristics of the high-strength high-toughness easy-to-weld steel with the thickness of 5-60 mm and the thickness of 850MPa are respectively above 0.32T, 1.65T and 1.61T under the conditions that the magnetic field intensity is 300A/m, 4000A/m and 5000A/m, and the coercive force is lower than 0.33kA/m.
Drawings
FIG. 1 is an organizational chart of a 20mm thick steel plate according to example 1;
FIG. 2 is an organizational chart of a 25mm thick steel plate of example 2;
FIG. 3 is an organizational chart of a 30mm thick steel plate of example 3;
FIG. 4 engineering stress strain curve for example 1.
FIG. 5 is a graph showing the comparison of the B-H curves of the magnetic properties of the steels of examples 1 and 20.
Detailed Description
The invention will now be further described with reference to the accompanying drawings and examples:
the invention relates to a high-strength high-toughness easy-to-weld steel with the thickness of 5-60 mm and the thickness of 850MPa, which comprises the following components: and C:0.02 to 0.05, si:0.1 to 0.3, mn:0.5 to 1.0, P is less than or equal to 0.01, S is less than or equal to 0.0015, cu:1.0 to 1.5, ni:2.5 to 3.2, cr:0.2 to 0.5, mo:0.3 to 0.5, nb:0.02-0.1, ti:0.01 to 0.05, al: 0.005-0.05, and the balance of Fe and unavoidable impurities.
The invention principle and component design basis of the 850 MPa-level high-strength high-toughness easy-to-weld steel are as follows:
the principle of the invention: the microstructure of the high-strength high-toughness easily-welded steel with the thickness of 5-60 mm and the height of 850MPa is lath martensite, copper-rich nickel-aluminum composite nano precipitated phase and inverted austenite. The high strength of steel comes mainly from four aspects: the method comprises the steps of precipitation strengthening of a copper-rich nano phase, fine grain strengthening of lath martensite, dislocation strengthening and solid solution strengthening of alloy elements. The precipitation strengthening mainly comes from the precipitation of copper, nickel and manganese elements added in the alloy in the aging process, and the copper, nickel and manganese elements are uniformly distributed in a matrix phase to form a composite nano phase with the size of less than 10 nanometers, so that dislocation movement is prevented to play a role in strengthening. The fine grain strengthening firstly is to pin grain boundaries in a recrystallization rough rolling stage and then further refine austenite grain sizes in a non-crystallization region finish rolling stage due to the fact that the effective grain sizes of lath martensite are lath bundles, and the lath bundles are only a fraction of the original austenite sizes, so that the fine grain strengthening brings great strength contribution. Dislocation enhancement results mainly from high density dislocations in the lath martensite. Solid solution strengthening results from strengthening by the addition of various alloying elements. According to the invention, carbon reinforcement and alloy reinforcement are replaced by nano-phase precipitation reinforcement, so that the carbon content is greatly reduced, and compared with steel with the same strength grade, the alloy element content is also greatly reduced, and good welding performance is ensured. The excellent magnetic conductivity is obtained mainly by reducing the carbon content and the alloy element content through nano-phase strengthening, and simultaneously, reducing and refining the nonmetallic impurity content through a refining process and a thermo-mechanical treatment process. Therefore, the invention replaces carbon strengthening and alloying by nano-phase strengthening, combines the refining process and the thermo-mechanical treatment process, and realizes that the high strength, the excellent low-temperature toughness and the excellent welding performance and the good magnetic conductivity are obtained.
The component design is based on:
c: carbon is a solid solution strengthening element and plays an important role in improving strength. The strength of the traditional steel material is improved mainly through solid solution strengthening of carbon, but excessive carbon can form massive brittle cementite in the tempering process to seriously influence toughness, the increase of high carbon content can influence weldability, and meanwhile, the carbon can also obviously reduce magnetic permeability, increase coercivity and be unfavorable for magnetic shielding performance. The invention replaces the traditional carbon reinforcement by using nano phase reinforcement, so the carbon content is controlled between 0.02 and 0.05 percent.
Cu: copper is the most important forming element of the precipitated phase, the strength can be improved under the condition of not losing the toughness by forming the nano-scale precipitated phase, and meanwhile, copper has the effect of refining grains. Too low copper content can affect the strengthening effect, and too high copper content can easily produce thermal embrittlement, affecting welding and thermal processing. Therefore, the copper content of the invention is controlled to be 1.0-1.5%.
Ni: nickel is one of main elements formed by nano precipitated phases, a B2 ordered structure is formed and wrapped on the surface of a precipitated phase formed by copper elements, so that the thermal stability of the precipitated phase can be increased, meanwhile, the nickel can strengthen a matrix, the low-temperature toughness is obviously improved, and the nickel content of the invention is controlled to be 2.5-3.2%.
Mn: manganese is one of main constituent elements of nano precipitated phase, and can refine crystal grains, improve strength and low-temperature toughness of steel, but the content is too high, so that casting blank segregation, large structural stress, welding performance reduction and the like are easily caused, and the manganese content is controlled to be 0.5-1.0%.
Al: aluminum is a strong deoxidizing element in the steelmaking process, and can play a role in refining grains, but when the content is too high, the graphitization tendency of carbon in steel is promoted, the effect of refining grains is reduced, and the aluminum content is controlled to be 0.005-0.05%.
Cr: chromium can increase corrosion resistance of steel while improving hardenability and tempering stability of steel. The chromium content of the invention is controlled between 0.2 and 0.5 percent.
Si: silicon can improve the magnetic permeability of steel and reduce the coercive force, but can reduce the welding performance, silicate inclusions are easy to form, and meanwhile, the plasticity and toughness of steel can be obviously reduced by excessive silicon. The silicon content of the invention is controlled to be 0.1-0.3%.
Mo: molybdenum can increase the hardenability of steel, refine grains, form carbide to improve strength, and promote nucleation of nano-precipitated phase. The molybdenum content of the invention is controlled between 0.3 and 0.5 percent.
Nb: niobium can form a carbonitride pinning austenite grain boundary to prevent the growth of grains, and can play a role in precipitation strengthening to improve the strength. The niobium content of the invention is controlled between 0.02 and 0.1 percent.
Ti: titanium may form carbonitride pinning grain boundaries, refining the grains. The niobium content of the invention is controlled to be 0.01 to 0.05 percent
The invention relates to 850 MPa-level high-strength high-toughness easy-to-weld steel and a preparation method thereof, comprising the following steps:
smelting molten iron in a converter or an electric furnace, oxygen blowing dephosphorization decarburization, LF ladle refining, VD vacuum furnace treatment, continuous casting or die casting, casting blank heating, rolling, quenching, tempering, flaw detection and performance inspection;
the specific operation of the main procedures is as follows:
1) Smelting and refining: adopting blast furnace molten iron or molten iron smelted by an electric furnace, blowing oxygen, dephosphorizing, decarbonizing, deoxidizing aluminum, transferring into a ladle furnace for refining, adding alloy materials at the same time, adjusting the components to target components, and then performing dehydrogenation and deoxidization in a VD vacuum furnace;
2) Continuous casting or die casting: continuous casting is adopted in converter smelting, die casting is adopted in electric furnace smelting, and casting blanks are stacked and slowly cooled for more than 24 hours;
3) Rolling: heating the casting blank to 1160-1200 ℃, preserving heat for 2-6 hours, removing iron oxide scales by using high-pressure water before rolling, and removing phosphorus by using the high-pressure water in the rolling process.
The continuous rolling comprises rough rolling and finish rolling, and the rough rolling temperature is controlled to be 1000-1150 ℃; the initial rolling temperature of the finish rolling is 950-1050 ℃, the final rolling temperature is higher than 900 ℃, and the steel plate with the thickness of 5-60 mm is rolled.
4) And (3) heat treatment: after the steel plate is subjected to heat preservation for 30-90 minutes at 800-950 ℃, cooling and quenching to room temperature; and tempering at 550-700 deg.c for 50-120 min and air cooling to room temperature.
The chemical compositions of the examples of the present invention are shown in Table 1 (mass percent), and the balance is Fe and unavoidable impurities.
TABLE 1
| C | Si | Mn | P | S | Cu | Ni | Cr | Mo | Nb | Ti | Als | |
| Example 1 | 0.042 | 0.25 | 0.85 | 0.007 | 0.0012 | 1.21 | 2.7 | 0.50 | 0.50 | 0.040 | 0.014 | 0.025 |
| Example 2 | 0.048 | 0.25 | 0.88 | 0.005 | 0.0007 | 1.28 | 3.1 | 0.55 | 0.49 | 0.038 | 0.013 | 0.034 |
| Example 3 | 0.052 | 0.32 | 0.95 | 0.005 | 0.0006 | 1.36 | 3.6 | 0.79 | 0.56 | 0.048 | 0.023 | 0.044 |
All the embodiments adopt electric furnace smelting, oxygen blowing dephosphorization decarburization, aluminum deoxidation, ladle furnace refining, deep desulfurization, heating, refining treatment and component adjustment to target components, argon blowing is carried out from an air brick at the bottom of a ladle to molten steel, stirring is carried out to ensure uniform components, then refining treatments such as degassing, inclusion removal and the like are carried out in a VD vacuum furnace, gas and inclusion are fully removed, the purity of the molten steel is ensured, steel billets are finally cast, and stacking and slow cooling are carried out for 48 hours;
heating the casting blank to 1160-1200 ℃, preserving heat for 2-6 hours, removing iron oxide scales by using high-pressure water before rolling, and removing phosphorus by using the high-pressure water in the rolling process. The rough rolling temperature is controlled at 1000-1150 ℃; the initial rolling temperature of the finish rolling is 950-1050 ℃, the final rolling temperature is higher than 900 ℃, and the steel plate with the thickness of 5-60 mm is rolled.
After the steel plate is subjected to heat preservation for 30-90 minutes at 800-950 ℃, cooling and quenching to room temperature; and tempering at 550-700 deg.c for 50-120 min and air cooling to room temperature.
Table 2 shows the main rolling process parameters of each example.
TABLE 2
Table 3 shows the heat treatment process parameters.
TABLE 3 Table 3
The heat-treated steel sheet was subjected to transverse sampling processing into tensile and impact test pieces, and mechanical properties were measured, and the results are shown in Table 4.
TABLE 4 Table 4
Table 5 shows the inclusion grade test results of the examples of the present invention.
TABLE 5
The test steel plate has excellent strength, impact toughness and elongation, larger margin and excellent low-temperature toughness and plasticity. The magnetic induction characteristics of the magnetic field under the conditions that the magnetic field intensity is 300A/m, 4000A/m and 5000A/m are respectively above 1.61T and 1.67T, and the coercive force is lower than 0.77kA/m.
As shown in the inclusion grade detection results, the class A and class B inclusions in the steel plate of each embodiment of the invention are 0, the class C inclusions only have a small amount of fine inclusions with the width of less than 5 mu m, and the class D and DS inclusions are also few, so that the steel plate has no influence on the strength, the low-temperature toughness, the elongation and the magnetic induction performance.
FIG. 1 is a schematic view showing the structure of a 20mm thick steel plate in example 1, wherein the structure is lath martensite. The structure not only ensures that the steel has better toughness, but also ensures better elongation.
FIG. 4 shows the tensile curve of a 20mm thick steel plate in example 1.
FIG. 5 is a graph showing the magnetic properties B-H of the steels of examples 1 and 20. It can be seen that the curves of the example 1 and 20 steels almost coincide and that the magnetic properties are very close.
The invention has wide application, and can be applied to key structures such as ships, ocean engineering, aerospace engineering, magnetic shielding shells and the like.
The invention discloses a high-strength high-toughness easily-welded nano steel with the thickness of 5-60 mm and 850MPa, and a preparation method thereof, wherein the high-strength high-toughness easily-welded nano steel comprises the following components: and C:0.02 to 0.08, si:0.1 to 0.4, mn:0.5 to 1.1, P is less than or equal to 0.01, S is less than or equal to 0.0015, cu:1.0 to 1.5, ni:2.5 to 4.0, cr:0.2 to 0.8, mo:0.3 to 0.6, nb:0.02-0.1, ti:0.01 to 0.05, al: 0.005-0.05, and the balance of Fe and unavoidable impurities. The preparation method of the high-strength high-toughness easy-to-weld steel comprises the following steps: smelting and refining-continuous casting or die casting-rolling-heat treatment. The high-strength high-toughness easy-to-weld steel provided by the invention can achieve the characteristics of high strength, high toughness, high plasticity and easy welding by controlling the inverted austenite form, distribution and volume fraction to optimize the plasticity and low-temperature toughness while precipitating a large amount of nano precipitated phases to improve the strength by adjusting the content of nano precipitated phase forming elements and the thermo-mechanical treatment process under the condition of ultralow carbon content, wherein the Charpy V notch impact energy at-80 ℃ is more than or equal to 200J, and the elongation is more than or equal to 15%. The high-strength high-toughness easy-to-weld steel can be widely applied to key structures such as ships, ocean engineering, engineering machinery, bridges, oil pipelines, aerospace engineering, magnetic shielding shells and the like.
It should be noted that the above illustrates only specific embodiments of the present invention, and it is obvious that the present invention is not limited to the above embodiments, but many similar variations are possible as required. All modifications and variations therein may occur to those skilled in the art upon the direct derivation or communication from this disclosure.
Claims (3)
1. The preparation method of the 850 MPa-level high-strength high-toughness easily-welded nano steel with the thickness of 5-60 mm is characterized by comprising the following steps:
(1) Smelting and refining: adopting blast furnace molten iron or molten iron smelted by an electric furnace, blowing oxygen, dephosphorizing and decarbonizing, deoxidizing aluminum, transferring into a ladle furnace for refining, and simultaneously adding alloy materials, wherein the alloy materials comprise the following components in percentage by mass: 0.02 to 0.08, si:0.1 to 0.4, mn:0.5 to 1.1, P is less than or equal to 0.01, S is less than or equal to 0.0015, cu:1.0 to 1.5, ni:2.5 to 4.0, cr:0.2 to 0.8, mo:0.3 to 0.6, nb:0.02-0.1, ti:0.01 to 0.05, al: 0.005-0.05, and balancing Fe and unavoidable impurities, adjusting the components to target components, and then performing dehydrogenation and deoxidation in a VD vacuum furnace;
(2) Continuous casting or die casting: continuous casting is adopted in converter smelting, die casting is adopted in electric furnace smelting, and casting blanks are stacked and slowly cooled for more than 24 hours;
(3) Rolling: heating a casting blank to 1160-1200 ℃, preserving heat for 2-6 hours, removing iron scales by using high-pressure water before rolling, removing phosphorus by using high-pressure water in the rolling process, and performing continuous rolling comprising rough rolling and finish rolling, wherein the rough rolling temperature is controlled to be 1000-1150 ℃; the initial rolling temperature of the finish rolling is 950-1050 ℃, the final rolling temperature is higher than 900 ℃, and the finish rolling is carried out to obtain a steel plate with the thickness of 5-60 mm;
(4) And (3) heat treatment: after the steel plate is subjected to heat preservation for 30-90 minutes at 800-950 ℃, cooling and quenching to room temperature; and tempering at 550-700 deg.c for 50-120 min and air cooling to room temperature.
2. The nanosteel of claim 1, wherein the microstructure is comprised of ultra-low carbon lath martensitic structure and sheet-like inverted austenite.
3. The nanosteel of claim 2, wherein the yield strength is not less than 850MPa, the charpy V-notch impact energy at-84 ℃ is not less than 200J, and the elongation is not less than 15%.
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