CN101481779A - High plasticity, high tenacity and ultra-high tensile steel, and manufacturing method thereof - Google Patents

Abstract

The invention discloses a high-plasticity, high-toughness ultra-high-strength steel and a manufacturing method thereof. The chemical composition of the steel is (wt%): C 0.15～0.30, Mn 0.20～1.40, Si 0.10～0.50, P≤0.015, S≤0.012, Ni≤0.20, Cr 0.40～1.50, Mo 0.25～1.35, V 0～0.10, Cu≤0.2, Al 0.01～0.05, B 0.0005～0.0020, [O+N]≤0.010, the balance is Fe and impurities. Its manufacturing method includes smelting according to the formula, continuous casting into billets, hot rolling into plates or pipes, quenching and tempering at 875-930°C for 25-40 minutes, tempering at 625-675°C for 30-90 minutes, and air cooling for heat treatment . The yield strength of the steel is ≥1000MPa, the tensile strength is ≥1100MPa, the Charpy impact energy at 0°C is ≥100J, and the elongation is 20-30%. It is suitable for the manufacture of important structures such as construction machinery, high-rise buildings, and oil well pipes.

Description

High plasticity high toughness ultra high strength steel and its manufacturing method

technical field

The invention relates to a method for manufacturing ultra-high strength steel, in particular to a composite phase characterized by the formation of clean ultra-fine tempered lath martensite in the steel and dispersed nano-scale precipitates Microstructure, and thus obtain a high-performance, low-cost steel material manufacturing method with various mechanical properties such as ultra-high-strength steel, high plasticity and high toughness.

Background technique

At present, steel materials are still the main body of structural materials. The development of high-performance steel materials and their key manufacturing technologies with multiple characteristics such as ultra-high strength, high plasticity and excellent low-temperature impact toughness is the key to meet the needs of large-scale construction machinery and high-rise buildings. It is an important way for modern important structures such as oil well pipes and harsh geological service environments to develop in the direction of long-term safety, weight reduction, energy saving and consumption reduction. It is generally believed internationally that structural steel with a yield strength ≥ 840MPa (120ksi) can be called ultra-high-strength structural steel. In actual engineering, the yield strength of structural steel is sometimes required to reach more than 1000MPa. How to make this kind of steel have high plasticity and excellent low-temperature impact toughness while reaching the ultra-high strength level, so as to meet the requirements of the structure for heavy load, impact resistance and adaptability to large displacement deformation, has been a challenge in the past ten years. research and development hotspots.

Generally speaking, the strength, plasticity, and toughness of steel usually exhibit a trade-off relationship. Steel with high strength often has low plasticity and toughness. On the contrary, in order to pursue high plasticity and toughness, the strength of steel must be sacrificed. Therefore, the development of high-plasticity, high-toughness, and ultra-high-strength steel is extremely difficult, and new explorations are needed in the metallurgical means of strengthening toughness and plasticizing ultra-high-strength steel.

At present, in the development of ultra-high-strength steel, in order to increase the strength, bainite or martensite is usually used as the main structure, and various refinement methods are used to obtain higher strength and toughness. This has been extensively explored at home and abroad, and a number of achievements or patents have been formed. Analyzing the ultra-high-strength steels disclosed in such achievements or patents and related manufacturing methods, it can be found that they all have one, or two, or more than two of the following deficiencies:

1) When the disclosed ultra-high-strength steel is strengthened with a refined martensite/bainite structure, although it also achieves high low-temperature impact toughness, the elongation is generally not high, usually only reaching 10%-20% %, the plastic index of the proposed ultra-high-strength steel is generally not high, or even does not mention any requirements. For example, the ultra-high-strength steel pipe disclosed in the international patent "Ultra-high-strength low-carbon alloy steel pipe with excellent low-temperature toughness and its manufacturing method" (publication No. The transformation temperature is below -60°C, but the elongation is only ≧9%; such as a kind of ultra-high-strength steel disclosed in the domestic patent "Non-quenched and tempered easy-weldable ultra-high-strength steel and its production method" (publication number CN101086015), although the The yield strength of the steel has reached above 980MPa, and the low-temperature impact energy at -60°C has reached above 100J, but the plasticity of the steel is low, and the elongation cannot reach above 20% stably. Another example is a kind of ultra-high-strength thick steel plate or hot-rolled steel plate disclosed in the domestic patent "Ultra-high-strength steel with excellent corrosion resistance and fatigue resistance and its manufacturing method" (publication number CN1888120A). The tensile strength can reach more than 880MPa and 980MPa respectively, and the impact energy at -20°C can reach more than 100J, but the plasticity of the steel is obviously insufficient, and the elongation is always below 20%. For example, the ultra-high-strength steel plate disclosed in the international patent "Weldable High-Strength Steel with Excellent Low-Temperature Toughness" (publication number CN1146784A), through the use of micro-alloying combined with controlled rolling, although the tensile strength of the material has reached more than 950 MPa, it is tough and brittle. The transition temperature is below -85°C, but the relevant claims and examples do not mention the elongation data of the material, which shows that the patent does not put forward plasticity index requirements for the disclosed ultra-high-strength steel; another example is the domestic patent "Petroleum Although the yield strength and tensile strength of the material can reach above 966-1103MPa and 1034MPa respectively, the ultra-high-strength casing disclosed in "Petroleum Casing and Production Method for Mid-Deep Well and Ultra-Deep Well in Natural Gas Exploitation" (publication number CN1619005A) The dimensional impact energy is more than 40J, but the relevant claims and examples do not mention the elongation data of the material, which shows that the ultra-high-strength steel disclosed in this patent does not set requirements for the plasticity index.

2) Although the disclosed ultra-high-strength steel has achieved high plasticity, its low-temperature impact toughness is obviously insufficient. For example, a low-alloy ultra-high-strength steel disclosed in the domestic patent "Low-alloy ultra-high-strength steel" (publication number CN1390972), the yield strength and tensile strength of the material can reach 860-1200Mpa and 1000-1300MPa respectively. The rate is 15-25%, but the full-scale low-temperature impact energy at 0°C is only ≧33J.

3) The plasticity and low-temperature impact toughness of the disclosed ultra-high-strength steels are insufficient. For example, a kind of ultra-high-strength steel disclosed in the domestic patent "Ultra-high-strength anti-collapse oil casing with special connection structure and its production method", although its yield strength and tensile strength can reach 896-1150Mpa and ≧970MPa respectively, but the extension The efficiency is only ≧9%, and the full-scale low-temperature impact energy at 0°C is only ≧33J.

4) Although the disclosed ultra-high-strength steels also achieve high low-temperature toughness, and may also achieve high plasticity, the cost of the alloy is relatively high. For example, an ultra-high-strength low-temperature steel disclosed in the international patent "Ultra-high-strength steel with excellent low-temperature toughness" (publication number CN1282381A), although the tensile strength of the material can reach more than 830MPa, after the chemical composition is optimized, the material's resistance The tensile strength can even reach more than 1000MPa. Since the main means to improve the plasticity and low-temperature toughness of the material is to include more than 1.0% nickel, the optimized nickel addition is even more than 1.5%. Deformability, but thus increases the cost of alloy raw materials.

It can be seen that the above-mentioned existing ultra-high-strength steels either have insufficient plasticity or low-temperature toughness of the material, or both the plasticity and low-temperature toughness of the material are insufficient, or the cost of the alloy raw material is relatively high, neither of which belongs to the category of ultra-high-strength, high-strength steel. A high-performance economical steel material with multiple properties such as plasticity and excellent low-temperature toughness.

At present, in the development of low-alloy high-strength steel, in order to improve the plasticity of steel, it is usually adopted to form ferrite/pearlite, ferrite/martensite, ferrite/bainite, retained austenite/ Bainite, bainite/M-A island and other multi-phase structure of different soft and hard phases, and through heat treatment or controlled cooling to control the proportion of each constituent phase to improve the plasticity of the steel. For example, a ferrite/martensitic dual-phase steel disclosed in the domestic patent "A heat treatment method for producing fine-grained dual-phase steel" (publication number CN1039621A) is obtained by controlling hot rolling or heat treatment in the two-phase region. The biphase proportions are 80% and 20%, respectively, the yield strength and tensile strength reach about 500MPa and 750MPa, respectively, and the elongation is slightly higher than 20%. For example, a ferrite/pearlite dual-phase steel disclosed in the domestic patent "Manufacturing Method of Ultrafine Grain Strip Steel with Low Yield Strength Ratio" (publication number CN1928130A) uses controlled cooling to refine the ferrite and reach a ratio of 85. %, the yield strength and tensile strength reach about 295-415MPa and 460-510MPa respectively, and the elongation reaches 26-40%. In the ultrafine bainite/ferrite dual-phase steel proposed in literature (Shang Chengjia et al., Journal of University of Science and Technology Beijing, 2003, Vol.25(3): 288-290), ferrite accounts for about 20%, and after 680 After tempering at ℃ for 1 hour, the elongation can reach more than 25% stably, but the yield strength and tensile strength only reach 720MPa and 780MPa. The ultra-fine bainite/martensite dual-phase steel proposed in the literature (Wang Xuemin et al., 2001 China Iron and Steel Annual Conference Proceedings, 859-872), after tempering at 675°C for 3 hours, the yield strength and tensile strength respectively reach 747MPa and 772MPa, the elongation is only about 16%. The acicular ferrite/martensitic dual-phase steel proposed in literature (Zhang Yujun et al., Journal of Northeastern University (Natural Science Edition), 2006, Vol.27(4): 414-417) obtained 10-30 % acicular ferrite, the elongation can reach 23-29%, but the yield strength and tensile strength only reach 550-610MPa and 740-840MPa respectively. The retained austenite/bainite dual-phase steel proposed in the literature (Dong Yun et al., Journal of Hebei University of Technology, 2000, Vol.29(1): 67-70) has a content of 11 after isothermal treatment at 350-400°C. -15% retained austenite, the yield strength and tensile strength reach 800-1000MPa and 1300-1600MPa respectively, and the elongation can reach 20-30%. The document does not mention the low-temperature impact toughness of the steel, but due to the carbon The content is as high as 0.60-0.75%, it is expected that its low temperature impact toughness may be insufficient. According to the literature (I.Nobuyuki et al., JFE Technical Report 2006, No.7: 20-26), the anti-large deformation ferrite/bainite and bainite/M-A island dual-phase steel developed by Japan JFE, although The uniform deformation elongation can reach more than 16% and 12% respectively, but the yield strength can only reach more than 460MPa and 530MPa respectively.

It can be seen that although the above-mentioned existing dual-phase steels can all achieve high plasticity. But there is a problem: either the strength is insufficient, or the low-temperature impact toughness is insufficient. Similarly, they are not high-performance economical steel materials that combine ultra-high strength, high plasticity, and excellent low-temperature toughness.

Contents of the invention

In order to solve the above-mentioned deficiencies in the prior art, the present invention provides a high-plasticity, high-toughness, ultra-high-strength steel and its manufacturing method, so as to meet the load-bearing requirements of modern important structures such as large-scale engineering machinery, high-rise buildings, and oil well pipes in severe geological service environments. Load, impact resistance and adaptation to large displacement and deformation requirements, and the method must also have the advantages of less consumption of precious metal nickel, shorter heat treatment time, and lower production costs.

In order to achieve the above object, the manufacturing method involved in the present invention includes the following steps: using pure steel smelting technology, according to the pre-designed alloy composition, making billets of various cross-sectional shapes such as slabs or round billets; After deformation such as manufacturing or piercing and rolling, the shape and size of a plate or tube are obtained; the formed workpiece is kept at 875°C-930°C for 25-40 minutes, then quenched, and then tempered at 625°C-675°C for 30- After 90 minutes, the process of air cooling is carried out for quenching and tempering heat treatment. By precisely controlling the above-mentioned relevant process parameters, a complex phase structure characterized by clean ultra-fine tempered lath martensite as the matrix and a certain number of nano-scale precipitates dispersed in the steel is formed, and the above-mentioned various mechanical properties are obtained. properties of sheets or pipes.

In order to achieve the above object, at first the chemical composition of the steel involved in the present invention needs to be carefully designed and controlled, wherein the mechanism of action of each alloy composition is:

(1) Carbon (C) Carbon is an alloying element that can effectively improve strength and is low in cost. When the carbon content is less than 0.15%, the hardenability is low for the above-mentioned plate or pipe, and it is difficult to obtain a uniform tempered martensite structure on the entire cross-section of the rolled piece through heat treatment, resulting in low strength. When the carbon content is higher than 0.30%, the toughness of the steel is insufficient, and it is difficult to match the strength and toughness under ultra-high strength. Therefore, the carbon content should be controlled at 0.15-0.30%, and the appropriate carbon content range should be 0.18-0.28%.

(2) Manganese (Mn) Manganese is an element that can effectively improve the hardenability of steel, and can improve both strength and toughness. However, when the manganese content is too high, segregation should be formed in the billet, thereby forming a banded structure in the rolled piece and reducing the toughness. Therefore, the manganese content should be controlled at 0.20% to 1.40%. The appropriate range of manganese content should be 0.40% to 1.00%.

(3) Silicon (Si) Silicon is an effective deoxidizing element in steelmaking and can increase the strength of steel. When the silicon content is less than 0.10%, the steel is easily oxidized, but when the silicon content exceeds 0.50%, the toughness of the steel is damaged. Therefore, the silicon content should be controlled at 0.10% to 0.50%. The suitable range of silicon content should be 0.10%-0.40%.

(4) Chromium (Cr) Chromium is an element that can simultaneously improve the strength, toughness and corrosion resistance of steel in an appropriate range of addition. When the chromium content is lower than 0.40%, the hardenability is relatively low for the plate or pipe required above, so that the strength is relatively low. When the chromium content is higher than 1.50%, the toughness of the sleeve is insufficient, and it is difficult to match the strength and toughness under ultra-high strength. Therefore, the chromium content should be controlled at 0.40-1.50%. The appropriate range of chromium content should be 0.40-1.10%.

(5) Molybdenum (Mo) Molybdenum is an element that can effectively resist temper softening and improve the strength of steel. Especially when it is added in combination with chromium in quenched and tempered steel, the strengthening effect is more obvious. When the molybdenum content is lower than 0.25%, the strength is low. When the molybdenum content is higher than 1.35%, the cost of the expensive alloy material increases significantly, and the toughness of the steel decreases obviously, making it difficult to match the strength and toughness under ultra-high strength. Therefore, the content of molybdenum should be controlled at 0.25% to 1.35%, and the suitable range of molybdenum content should be 0.25% to 0.95%.

(6) Vanadium (V) Vanadium is an element that can improve the strength of steel. Even if 0.01% vanadium is added, it can resist temper softening. The amount of vanadium added is generally about 0.10%. However, due to the high price of vanadium-iron alloy, the maximum amount of vanadium added is limited. Therefore, the suitable range of vanadium content is 0-0.10%.

(7) Nickel (Ni) Nickel is an element that can improve the strength and toughness of steel at the same time, especially to improve low temperature toughness. However, due to the high price of nickel, it is not advisable to add more or even not add as much as possible. Therefore, the suitable nickel content range is ≦0.20%.

(8) Copper (Cu) Copper is a corrosion-resistant element. At the same time, it can also play a role in solid solution strengthening (≦0.20%) or precipitation strengthening (precipitation of ε-Cu particles during tempering) in steel. Excessive copper content can easily cause hot embrittlement, which needs to be suppressed by adding nickel at the same time. It is advisable to limit the maximum amount or not add it. Therefore, the copper content should be controlled at ≦0.20%.

(9) Aluminum (Al) Aluminum is a deoxidizing element that needs to be added in steelmaking. It has a denaturing effect on inclusions. In addition, it forms stable fine AlN precipitated particles in steel, which has the effect of refining grains. Therefore, the suitable aluminum content range is 0.01-0.05%.

(10) Boron (B) Adding 5 to 20 ppm of trace boron in steel can significantly increase the hardenability of low-carbon and low-alloy steel, which is beneficial to obtain martensite or bainite hard phase during quenching, and can save Chromium, molybdenum, vanadium and other precious iron alloy resources, and B can combine with N to fix free N, so as to reduce the aging embrittlement effect caused by N. Therefore, the boron content range in steel can be controlled at 5-20ppm, and the suitable boron content range is 8-20ppm.

Therefore, according to the above-mentioned production method, the chemical composition of the high-plasticity, high-toughness, ultra-high-strength steel involved in the present invention is (wt%): C: 0.15-0.30, Mn: 0.20-1.40, Si: 0.10-0.50, P: ≦ 0.015, S: ≦0.012, Ni: ≦0.20, Cr: 0.40～1.50, Mo: 0.25～1.35, V: 0～0.10, Cu: ≦0.2, Al: 0.01～0.05, B: 0.0005～0.0020, the balance is Fe and incidental impurity elements.

The above-mentioned high-plasticity, high-toughness and ultra-high-strength steel involved in the present invention can make full use of the ultra-fine tempered lath martensite/nano-scale precipitated phase composite structure due to the tempering process of precisely controlling the quenched martensite. Therefore, it can reduce the amount of precious alloy elements added, reduce the carbon content, and improve the comprehensive mechanical properties of steel. The optimized chemical composition is (wt%): C: 0.18 ~ 0.28, Mn: 0.40～1.00, Si: 0.10～0.40, P: ≦0.012, S: ≦0.010, Ni: ≦0.20, Cr: 0.40～1.10, Mo: 0.25～0.95, V: 0～0.10, Cu: ≦0.2, Al: 0.01-0.05, B: 0.0008-0.0020, and the balance is Fe and impurity elements.

The above-mentioned high-plasticity, high-toughness ultra-high-strength steel and its manufacturing method involved in the present invention must adopt a pure steel smelting process when producing blanks, which is one of the key measures to improve the low-temperature toughness of ultra-high-strength steel. After comprehensively adopting measures such as raw material control, molten iron pretreatment, converter top and bottom double blowing, ladle blowing argon refining, vacuum treatment, Ca/Si wire inclusion denaturation treatment, etc., the metallurgical quality of the billet should meet the following requirements:

(1) The total oxygen content in the steel is limited to ≦30ppm, the total nitrogen content is limited to ≦70ppm, or the total oxygen and nitrogen content is limited to ≦100ppm.

(2) Harmful elements in steel S+P≦0.025%, Pb+Sn+As+Sb+Bi≦0.15%;

(3) The content of inclusions in steel is determined according to ASTM E45 standard "Worst Field Method (Method A)". The maximum content of inclusions is: level of thin inclusions≦2; level of thick inclusions≦1.

The above-mentioned high-plasticity, high-toughness, ultra-high-strength steel and its manufacturing method involved in the present invention include high-performance structural parts with different cross-sectional shapes such as hot-rolled plates and pipes. After the blank is subjected to thermal deformation to obtain the required shape and In terms of dimensions, controlled rolling should be adopted as much as possible within the range allowed by metallurgical technical equipment conditions, that is, to properly control the heating temperature of the billet, distribute the deformation temperature and deformation amount according to the rolling table (or forging table), and spray water after rolling. cool down. Its main purpose is to refine the deformed austenite grains as much as possible and obtain a uniform as-rolled structure. The hot deformation process can adopt the following typical parameters: when producing plates, the heating temperature of the slab is 1200 ℃ ~ 1250 ℃, the rough rolling temperature is 1200 ℃ ~ 1250 ℃, the total reduction rate is 60 ~ 70%; the finishing rolling temperature is 950 ℃ ～850℃, the deformation is 30～40%; air cooling after rolling. When producing pipes, the round billet is heated at a temperature of 1200°C to 1250°C. After heat centering, it is hot-rolled and pierced above 1200°C, and the deformation is 60-70%; The amount of deformation is 20-30%; after sizing at 850°C-950°C, the deformation amount is 10-20%. The deformed austenite undergoes sufficient recrystallization to avoid the formation or residual shear bands.

In order to obtain ultra-fine tempered lath martensite/nano-scale precipitated phase multi-phase structure of the above-mentioned high-plasticity, high-toughness, ultra-high-strength steel and its manufacturing method involved in the present invention, the tempering process of quenched martensite must be for precise control. Specifically, it is necessary to control the tempering temperature and tempering time to control the width of the tempered lath martensite between 0.20 and 0.40 μm, the volume percentage of the precipitated phase between 8 and 12%, and the equivalent scale between Between 30-50nm, the shape is acicular or rod-like and other suitable tissue parameters, which is convenient to play the synergistic effect of the precipitated phase as the hard phase and the tempered lath martensite as the soft phase during deformation, thereby meeting the steel requirements of the present invention at the same time It has the requirements of comprehensive mechanical properties such as ultra-high strength, high plasticity and excellent low temperature impact toughness. For the steel of the present invention, when quenching and tempering heat treatment is carried out, the suitable process parameters are: quenching after heat preservation at 875°C-930°C for 25-40 minutes, then tempering at 625°C-675°C for 30-90 minutes, then air cooling.

Description of drawings

Figure 1 is the metallographic structure of high ductility and high toughness ultra-high strength steel.

Detailed ways

The present invention will be described in further detail below in conjunction with specific examples.

The chemical composition (wt%) of the high-plasticity, high-toughness, ultra-high-strength steel involved in the present invention is listed in Table 1.

Table 1: Chemical composition (wt%) of the steel of the present invention

Note: The unit of chemical composition of B, O, N and other elements in the table is ppm. The total amount of residual elements Pb+Sn+As+Sb+Bi:≦0.15.

Example 1

Embodiment 1 of the present invention selects raw materials with low sulfur and phosphorus content, and adopts 50Kg vacuum furnace to smelt, so that the chemical composition in the steel meets the requirements of Table 1, and the balance is Fe and unavoidable impurity elements. Then use inert gas protection to cast, pour two ingots in each furnace, and the average diameter of the ingot is? 120mm. After the riser of the ingot was cut off, it was made into a hot-rolled plate with a plate thickness of 12 mm and a width of 200 mm on a 250 mm rolling mill. Among them, the main hot rolling process is: the slab heating temperature is 1200-1250°C, the initial rolling start temperature is 1150-1180°C, the rough rolling total reduction rate is 60-70%, and the rough rolling end temperature is 1020-1070°C . The start temperature of finish rolling is 930-980°C, the total reduction ratio of finish rolling is 30-40%, and the end temperature of finish rolling is 850-870°C. Cool in air after rolling. Subsequently, samples were taken on the hot-rolled plate and processed into a test piece with a size of 12mm×12mm×80mm. Two box-type resistance furnaces were used to perform quenching and tempering according to the processes shown in Table 2, and the quenching medium was saturated salt water. After quenching and tempering treatment, the longitudinal tensile properties of the test steel at room temperature and the transverse low-temperature impact energy of the whole sample at 0°C were tested. The results are shown in Table 2.

Table 2: Quenched and tempered heat treatment process and mechanical property test results of the steel of the present invention

It can be seen from Table 2 that the steel plates prepared according to the method of the present invention, such as process steel 6-12, all have comprehensive mechanical properties of ultra-high strength, high plasticity and excellent low-temperature toughness. As for process steel 1-5, although the composition and hot forming process are the same, due to the different tempering process, the matching of strength and toughness of steel is not as good as that of process steel 6-12.

Example 2

Example 2 of the present invention selects high-quality steel scrap with pretreated molten iron + P and low S content as raw material, and uses a 150-ton electric furnace for smelting, and adopts out-of-furnace refining, vacuum degassing (VD), inclusion denaturation, and argon blowing and stirring, etc. Pure steel smelting process, so that the chemical composition in the steel meets the requirements in Table 1, and the level of inclusions meets the above requirements. Then the inventive steel was continuously cast into a round billet with an outer diameter of 310mm. During piercing and continuous rolling of tube blanks, the temperature of each process is strictly controlled. The billet is heated to 1250°C, and after heat centering, it is cross-rolled and pierced at 1200-1250°C, with a deformation of 60-70%; the rolling temperature range is controlled at 1100-1150°C, and the deformation is 20-30%; The diameter temperature is controlled above Ar3, and the deformation is 10-20%, then air-cooled, sawed, and once hot straightened, and the straightening temperature is 500-600 °C. The as-rolled tube is heated at 880-900°C and held for 35 minutes, then quenched in a water-based quenching solution, and then tempered at 645-675°C for 45-75 minutes and then air-cooled. After quenching and tempering heat treatment, carry out secondary heat straightening, and the straightening temperature is 500-600°C. The size of the formed tube body is Φ244.48mm×15.11mm. Sampling on the finished pipe to test the comprehensive mechanical properties of the steel pipe. The longitudinal tensile properties of the steel pipe are: the yield strength is 1030-1170MPa, the tensile strength is 1120-1260MPa, the elongation is 20-30%, and the transverse full-scale Charpy impact energy of the steel pipe at 0°C is 105-130J.

Claims (5)

1. A high-plastic high-toughness ultra-high-strength steel, characterized in that: the chemical composition of the steel is (wt%): C: 0.15-0.30, Mn: 0.20-1.40, Si: 0.10-0.50, P: ≦ 0.015, S: ≦0.012, Ni: ≦0.20, Cr: 0.40～1.50, Mo: 0.25～1.35, V: 0～0.10, Cu: ≦0.2, Al: 0.01～0.05, B: 0.0005～0.0020, the balance is Fe and accompanying impurity elements, the maximum content of inclusions is: the level of fine inclusions ≦ 2, the level of thick inclusions ≦ 1, the content of inclusions in steel according to the ASTM E45 standard "the worst visual field method-A "To determine; the total content of oxygen is limited to ≦ 30ppm, the total content of nitrogen ≦ 70ppm, or the total amount of oxygen and nitrogen ≦ 100ppm; the total amount of residual elements is (wt%) Pb+Sn+As+Sb+Bi: ≦0.15 . 2. The high-plasticity, high-toughness and ultra-high-strength steel according to claim 1, characterized in that: lath martensite with a submicron width of 0.20 to 0.40 μm is formed in the steel, and the volume fraction of the dispersed distribution is 8 Multi-phase structure of nano-scale precipitated phase between -12% and equivalent scale between 30-50nm, yield strength ≧ 1000Mpa, tensile strength ≧ 1100Mpa, elongation 20-30%, 0°C transverse full-size Charpy Impact energy≧100J. 3. The high-plasticity, high-toughness and ultra-high-strength steel according to claim 1 or 2, characterized in that: the chemical composition of the steel is (wt%): C: 0.18-0.28, Mn: 0.40-1.00, Si: 0.10 ～0.40, P: ≦0.012, S: ≦0.010, Ni: ≦0.20, Cr: 0.40～1.10, Mo: 0.25～0.95, V: 0～0.10, Cu: ≦0.2, Al: 0.01～0.05, B: 0.0008 ～0.0020, [O+N]: ≦0.010; total residual elements Pb+Sn+As+Sb+Bi: ≦0.15, the balance is Fe and incidental impurity elements; yield strength≧1020Mpa, tensile strength≧1120Mpa, The elongation rate is 24-30%, and the transverse full-scale Charpy impact energy at 0°C is ≧100J. 4. A method for manufacturing the high-plasticity high-toughness ultra-high-strength steel described in claim 1 or 2, characterized in that: (1) Use a converter or an electric furnace to smelt molten steel with low sulfur and phosphorus content, and after further refining outside the furnace, vacuum degassing and inclusion denaturation, cast it into a slab or a round billet by continuous casting; (2) When producing plates, the slab heating temperature is 1200°C-1250°C, the rough rolling temperature is 1200°C-1250°C, the total reduction rate is 60-70%; the finish rolling temperature is 950°C-850°C, the deformation 30-40%; air-cooled after rolling; when producing pipes, the heating temperature of the round billet is 1200°C-1250°C. Continuous hot rolling at ℃～1150℃, the deformation is 20～30%; then sizing at 850℃～950℃, the deformation is 10～20%, then air cooling, sawing, hot straightening once, the straightening temperature is 500 ~600℃; (3) Quenching and tempering heat treatment after forming, the process is: 875 ℃ ~ 930 ℃ heat preservation for 25 ~ 35 minutes, then quenching, then tempering at 625 ℃ ~ 675 ℃ for 30 ~ 90 minutes, air cooling, secondary hot straightening, straightening The direct temperature is 500-600°C. 5. A method for manufacturing the high-plasticity high-toughness ultra-high-strength steel according to claim 3, characterized in that: (1) Use a converter or an electric furnace to smelt molten steel with low sulfur and phosphorus content, and after further refining outside the furnace, vacuum degassing and inclusion denaturation, cast it into a slab or a round billet by continuous casting; (2) When producing plates, the slab heating temperature is 1200°C-1250°C, the rough rolling temperature is 1200°C-1250°C, the total reduction rate is 60-70%; the finish rolling temperature is 950°C-850°C, the deformation 30-40%; air-cooled after rolling; when producing pipes, the heating temperature of the round billet is 1200°C-1250°C. Continuous hot rolling at ℃～1150℃, the deformation is 20～30%; then sizing at 850℃～950℃, the deformation is 10～20%, then air cooling, sawing, hot straightening once, the straightening temperature is 500 ~600℃; (3) Quenching and tempering heat treatment after forming, the process is: 875 ℃ ~ 930 ℃ heat preservation for 25 ~ 35 minutes, then quenching, then tempering at 625 ℃ ~ 675 ℃ for 30 ~ 90 minutes, air cooling, secondary hot straightening, straightening The direct temperature is 500-600°C.

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