2100mpa grade low-alloy high-strength and high-toughness steel and preparation method thereof

Abstract

The present application relates to a kind of 2100MPa grade low alloy high-strength high toughness steel and its preparation method, belong to the technical field of super high-strength alloy steel.Solve the problem of mismatching of strength and toughness performance when alloy content is low in existing alloy steel.The alloying composition of the low alloy high-strength high toughness steel of the present application is as follows: C: 0.37-0.42%, Mn: 0.4-1.2%, Si: 1.40-1.80%, Cr: 3.0-4.0%, Ni: 0.4-1.5%, Mo: 0.4-1.0%, W: 0.4-0.8%, Nb≤0.02%, V≤0.02%, the balance is Fe and unavoidable impurities, its microstructure is composed of martensite and thin film austenite;The preparation process includes forging-normalizing-quenching-tempering, quenching adopts oil quenching slow cooling conditioning, and the prepared low alloy steel has high strength and high toughness.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ultra-high strength alloy steel, and particularly relates to a 2100MPa-grade low-alloy high-strength high-toughness steel and a preparation method thereof. BACKGROUND

[0002] In the field of aerospace, the demand for performance improvement, large-scale equipment and low cost is increasingly prominent. However, the existing ultra-high strength steel (strength > 2000MPa) cannot meet the requirements of low cost and high strength and toughness. At present, 2100MPa-grade ultra-high strength steel mainly relies on high carbon content and high alloy content, such as using nano-bainite structure, secondary hardening mechanism or ultra-high Ni series of maraging steel. The high carbon content steel limits the process performance such as hot deformation and welding due to the ultra-high carbon content, and the matching of strength and fracture toughness still faces challenges; although the high alloy content steel can reach the target strength, the manufacturing cost is high, which limits its wide application in practical application. Therefore, it is of great significance to develop a low-alloy high-strength high-toughness steel.

[0003] In the existing ultra-high strength steel preparation process, it is usually desired that the material can be rapidly cooled to obtain high dislocation density, but too fast cooling speed is not the best way to obtain high-density substructure, and may cause internal stress accumulation to form cracks, so that the material is difficult to have strength, toughness and overall stability. Therefore, under the challenge of low alloy limit, a preparation method of ultra-high strength alloy steel capable of balancing the strength, toughness and stability of the material needs to be developed. SUMMARY

[0004] In view of the above analysis, the present application aims to provide a 2100MPa-grade low-alloy high-strength high-toughness steel and a preparation method thereof, to solve the problem of mismatching of strength and toughness performance when the alloy content in the existing alloy steel is low.

[0005] In one aspect, the present application provides a 2100MPa-grade low-alloy high-strength high-toughness steel, and the alloy composition of the low-alloy high-strength high-toughness steel is as follows in terms of weight percentage: C: 0.37-0.42%, Mn: 0.4-1.2%, Si: 1.40-1.80%, Cr: 3.0-4.0%, Ni: 0.4-1.5%, Mo: 0.4-1.0%, W: 0.4-0.8%, Nb≤0.02%, V≤0.02%, and the balance is Fe and unavoidable impurities.

[0006] Further, the microstructure of the high-strength high-toughness steel is composed of martensite and thin film austenite.

[0007] Further, the volume fraction of the thin film austenite is 5-8%.

[0008] Further, the low-alloy high-strength and high-toughness steel has the following alloying components: C: 0.38-0.41%, Mn: 0.5-0.8%, Si: 1.50-1.70%, Cr: 3.2-3.6%, Ni: 0.9-1.2%, Mo: 0.5-0.7%, W: 0.5-0.7%, Nb≤0.02%, and V≤0.015%.

[0009] In another aspect, the application also provides a method for preparing a 2100MPa-grade low-alloy high-strength and high-toughness steel, which is used for preparing the above-mentioned 2100MPa-grade low-alloy high-strength and high-toughness steel, and comprises the following steps:

[0010] S1: forging, the steel billet with the required alloying components is heated in a soaking furnace and then forged to obtain a first forged material;

[0011] S2: annealing, the first forged material is annealed and then air-cooled to obtain a second forged material;

[0012] S3: normalizing, the second forged material is normalized and then cooled to room temperature to obtain a third forged material;

[0013] S4: oil quenching, the third forged material is subjected to first-stage and second-stage heat preservation and then oil-cooled to room temperature to obtain a fourth forged material;

[0014] S5: tempering, the fourth forged material is subjected to first-time and second-time tempering, and the second-time tempering temperature is not higher than the first-time tempering temperature, to obtain the low-alloy high-strength and high-toughness steel.

[0015] Further, in the step S1, the initial forging temperature is 1000-1130℃, the final forging temperature is 870-930℃, and the forging ratio is≥5.

[0016] Further, in the step S2, the annealing temperature is 600-660℃, and the annealing time is 1-10h.

[0017] Further, in the step S3, the normalizing temperature is 940-980℃, and the normalizing time is 1-3h.

[0018] Further, in the step S4, the first-stage heat preservation temperature is 650-670℃, and the heat preservation time is 1-2h;

[0019] the second-stage heat preservation temperature is 930-960℃, and the heat preservation time is 1-2h.

[0020] Further, in the step S5, the first-time tempering temperature is 230-240℃, and the tempering time is 2-5h; the second-time tempering temperature is 220-230℃, and the tempering time is 2-5h.

[0021] Compared with the prior art, the application can realize at least one of the following beneficial effects:

[0022] 1. The low-alloy high-strength and high-toughness steel provided by the application forms a microstructure composed of martensite and thin-film austenite under the restriction of low alloy components; the microstructure has the characteristics of small size and uniform distribution of thin-film austenite, and effectively improves the strength and toughness of the material. Therefore, under the restriction of alloy cost, the application enables the high-strength steel to not only have excellent strength but also exhibit excellent toughness performance.

[0023] 2. Generally, too much or too little austenite volume fraction will adversely affect the toughness of the high-strength steel. The austenite volume fraction in the conventional nano-bainite steel of the same strength grade is generally more than 15%, and the austenite volume fraction in the secondary hardening steel of the same grade and high-alloy content is generally less than 5%. The low-alloy high-strength and high-toughness steel provided by the application has a suitable thin-film austenite volume fraction (5-8%) under the restriction of low alloy components, and has the characteristics of low alloy content and limited austenite volume, thereby realizing the maintenance of high strength, the reduction of material cost and the improvement of the toughness of the high-strength steel.

[0024] 3. The preparation method provided by the application effectively reduces impurity elements near the grain boundary of the steel by reasonably designing the addition amount of Mo and W elements, thereby improving the purity of the austenite grain boundary; helps to inhibit the formation of softening structures such as ferrite and upper bainite in the forging material during the cooling process, and ensures the change of the structure and performance of the material during quenching.

[0025] 4. The preparation method provided by the application realizes that the microstructure of the steel has high-density high-angle grain boundaries, and the orientation change between the crystals is large, which helps to prevent the propagation of cracks, thereby improving the strength and toughness of the steel, by reasonably designing the temperature and time of oil cooling and slow cooling, including oil quenching in quenching, two-stage heating, heating to 650-670 DEG C for 1-2 hours in the first stage, heating to 945-955 DEG C for 1-2 hours in the second stage, and then oil cooling and slow cooling to room temperature.

[0026] 5. The preparation method provided by the application precisely controls the tempering temperature and uses low-temperature tempering to inhibit the desorption of carbon elements; eliminates the residual stress of the material while ensuring the change of specific structures during tempering, and the change of the structures includes the synergistic effect of the pure matrix and high-density high-angle interface and thin-film residual austenite, thereby ensuring that the prepared steel has excellent high-strength and high-toughness performance.

[0027] 6、The low-alloy high-strength high-toughness steel of the present application has the following properties: tensile strength > 2100 MPa, elongation after fracture > 10%, room temperature impact toughness ≥ 50 J / cm, and fracture toughness > 85 MPa·m, which realizes the good strength and toughness performance of the steel under the restriction of alloy cost. 2 1 / 2

[0028] The above technical solutions can be combined with each other in the present application to realize more preferred combination solutions. BRIEF DESCRIPTION OF DRAWINGS

[0029] The accompanying drawings are included to provide a further understanding of the present application, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the present application and, together with the description, serve to explain the principles of the present application.

[0030] Figure 1 SEM image of the microstructure of the low-alloy high-strength high-toughness steel of the present application;

[0031] Figure 2 TEM image of the microstructure of the low-alloy high-strength high-toughness steel of the present application;

[0032] Figure 3 Schematic diagram of the two-stage heating quenching and twice tempering process in the preparation method of the 2100 MPa low-alloy high-strength high-toughness steel of the present application.

[0033] Reference signs:

[0034] 1 - thin film austenite. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings, which form a part of this application. The accompanying drawings illustrate the principles of the present application and, together with the description, serve to explain the principles of the present application and do not limit the scope of the present application.

[0036] ​​The embodiment of the present application discloses a 2100MPa grade low alloy high strength and high toughness steel, alloy components of the low alloy high strength and high toughness steel are as follows in percentage by weight: C: 0.37-0.42%, Mn: 0.4-1.2%, Si: 1.40-1.80%, Cr: 3.0-4.0%, Ni: 0.4-1.5%, Mo: 0.4-1.0%, W: 0.4-0.8%, Nb≤0.02%, V≤0.02%, and the balance is Fe and inevitable impurities; the microstructure of the low alloy high strength and high toughness steel is composed of martensite and thin film austenite.

[0037] The reason for limiting the composition of the casting blank of the 2100MPa grade low alloy high strength and high toughness steel and the preparation method thereof in the present application is described as follows, only % is used to represent the percentage by weight in the composition.

[0038] C: the content of carbon has a significant influence on the hardness, strength and toughness of the steel. Reasonable carbon content can improve the hardness of the material, but too high content may increase brittleness. In the present application, the method of using precipitated transition carbide to produce strengthening effect in the traditional method is not used; the content of carbon is between 0.37% and 0.42%, so as to ensure sufficient toughness while maintaining the strength of the steel.

[0039] Mn: the addition of manganese can improve the strength and wear resistance of the steel, reduce the martensite transformation temperature and the phase transformation speed of the steel, increase the content of residual austenite, and increase the tendency of temper brittleness of the steel. Moderate manganese content helps to maintain the stability of the alloy and ensure consistent performance during the manufacturing process. In the present application, the manganese content is between 0.4% and 1.2% to balance between strength and stability.

[0040] Si: the content of silicon can affect the formation of the oxide layer and the grain size of the steel, and inhibit the formation of carbide during tempering. It is usually replaced in solid solution in steel, which can significantly improve the elastic limit, yield point and tensile strength of the steel. In the present application, the silicon content is between 1.40% and 1.80% to achieve the grain boundary strengthening effect.

[0041] Cr: chromium can increase the hardenability of the steel and has a secondary hardening effect, so that the steel has good comprehensive mechanical properties after quenching and tempering, and improves the corrosion resistance and oxidation resistance of the steel. However, its cost is high. In the present application, the chromium content is between 3.0% and 4.0% to reduce the cost while ensuring the mechanical properties.

[0042] Ni: The addition of nickel can improve the fatigue resistance of the steel and reduce the sensitivity of the steel to notches. Nickel reduces the low-temperature brittleness transition temperature of the steel, improves the strength and toughness of the steel, is an indispensable alloying element for obtaining high impact toughness, and is used to improve the mechanical stability of residual austenite. After the addition of nickel, the bainite transformation can be effectively delayed, the critical cooling rate of bainite is greatly reduced, the martensite transformation is promoted, and the Ms (Martensite start; martensite transformation start temperature) point is lowered. Fine ε-carbides are precipitated during the martensite tempering process, promoting the decomposition and stabilization of residual austenite in the martensite of the steel. In the present invention, an appropriate amount of nickel content can enhance the strength of the grain boundary, thereby improving the overall performance of the material. The nickel content is between 0.4% and 1.5% to balance the toughness and strength.

[0043] Mo: The addition of molybdenum can improve the hardenability and thermal strength of the steel and prevent temper brittleness. In quenched and tempered steel, when coexisting with chromium, manganese, etc., molybdenum reduces or inhibits temper brittleness caused by other elements, deepens and hardens the quenched steel of larger sections, improves the temper resistance or temper stability of the steel, and allows the parts to be tempered at a higher temperature, thereby more effectively eliminating (or reducing) residual stress and improving plasticity. It has an effect on lowering the Ms (Martensite start; martensite transformation start temperature) point and improving the hardenability, which is only second to Mn element. Mo has a beneficial effect on improving the ductility and toughness of the steel and wear resistance. In the present invention, the molybdenum content is between 0.4% and 1.0% to improve the performance of the material.

[0044] W: The addition of tungsten can improve the hardness, strength, and wear resistance of the material. The use of tungsten also helps to improve the high-temperature stability of the material. Reasonable addition of molybdenum and tungsten elements can effectively purify the austenite grain boundary and prevent the formation of softening structures such as ferrite and upper bainite during cooling, thereby ensuring the hardenability of the material. In the present invention, the tungsten content is between 0.4% and 0.8% to optimize the heat treatment process and material performance.

[0045] Nb: Moderate addition of niobium helps to form carbide precipitates, thereby strengthening the grain boundary and improving the hardness and strength of the material. In the present invention, the content of niobium is ≤0.02% to obtain the required strength and toughness.

[0046] V: Moderate addition of vanadium can also form carbide precipitates, strengthen the grain boundary, and improve the hardness and strength of the material, but a lower N content will not cause V to precipitate in the high-temperature austenite. In the present invention, the content of vanadium is controlled below 0.02%.

[0047] Impurity elements in the billet will affect the performance and organization of the material in the subsequent heat treatment process, and the content of impurity elements is limited to: P≤0.005%, S≤0.0025%, O≤0.0025%, N≤0.005%, H≤0.0005%.

[0048] The specific description is as follows:

[0049] P: the presence of phosphorus will cause the brittleness of the material to increase, and too high phosphorus content will adversely affect the cold working performance and toughness of the material; therefore, maintaining low phosphorus content helps to improve the toughness and plasticity of the material, and the content of P≤0.005%.

[0050] S: the presence of sulfur is easy to cause thermal and cold brittleness of the material, and too high sulfur content will cause the toughness of the material to decrease; therefore, limiting the sulfur content helps to improve the plasticity and toughness of the material; the content of S≤0.0025%.

[0051] O: the presence of oxygen will affect the heat treatment performance of the material, especially in high temperature environment. The presence of excessive oxide will greatly affect the toughness of the material, and the content of O≤0.0025%.

[0052] N: the presence of nitrogen will affect the gas absorption and precipitation behavior of the material, thereby affecting the heat treatment result; too high nitrogen content may cause the formation of bubbles and inclusions, affecting the strength and toughness of the material; at the same time, it may increase the size and density of nitride inclusions, affecting the toughness of the material, therefore, controlling appropriate nitrogen content helps to maintain the uniformity and performance of the material, and the content of N≤0.005%.

[0053] H: the presence of hydrogen may adversely affect the ductility and toughness of the material, especially during cold working process; high hydrogen content may cause hydrogen embrittlement, making the material more prone to crack and brittle fracture; therefore, limiting the hydrogen content helps to improve the toughness and plasticity of the material, and the content of H≤0.0005%.

[0054] By controlling the content of the above impurity elements, especially limiting them at a low level, it helps to ensure that the material can achieve the expected performance and organizational structure during heat treatment process, while improving the toughness, plasticity and stability of the material.

[0055] In the present application, the content of alloying elements is carefully balanced to meet the performance requirements of the material, while taking into account the manufacturing feasibility and cost effectiveness, reducing the addition amount of high-cost alloys such as Cr and Ni. The content of each element is selected within a specific range to obtain the best overall performance.

[0056] Preferably, the alloying components of the low-alloy high-strength and high-toughness steel are as follows in terms of weight percentage: C: 0.38-0.41%, Mn: 0.5-0.8%, Si: 1.50-1.70%, Cr: 3.2-3.6%, Ni: 0.9-1.2%, Mo: 0.5-0.7%, W: 0.5-0.7%, Nb≤0.02%, V≤0.015%.

[0057] The application also provides a preparation method of the low-alloy high-strength and high-toughness steel of 2100 MPa grade, for preparing the low-alloy high-strength and high-toughness steel, comprising the following steps:

[0058] S1: forging, the steel billet meeting the alloying component requirements is heated in a soaking furnace and then forged to obtain a first forged material;

[0059] S2: annealing, the first forged material is annealed and then air-cooled to obtain a second forged material;

[0060] S3: normalizing, the second forged material is normalized and then cooled to room temperature to obtain a third forged material;

[0061] S4: oil quenching, the third forged material is subjected to first-stage and second-stage heat preservation and then oil-cooled to room temperature to obtain a fourth forged material;

[0062] S5: tempering, the fourth forged material is subjected to first-time and second-time tempering, the second-time tempering temperature is not higher than the first-time tempering temperature, and a low-alloy high-strength and high-toughness steel is obtained.

[0063] Specifically, in step S1, the steel billet is obtained by vacuum induction combined with vacuum consumable or vacuum induction combined with electroslag remelting; the initial forging temperature is 1000-1130℃, the final forging temperature is 870-930℃, and the soaking temperature is 1150-1250℃; the forging is performed within the initial forging and final forging temperature ranges, which can effectively avoid the inhibition of recrystallization caused by the pinning of austenite interface by niobium (Nb) and vanadium (V) elements, and ensure the stability of the grain boundary of the material. Preferably, the final forging temperature is 900-920℃.

[0064] Specifically, in step S1, the forging ratio of the forging process is ≥5. Satisfying the forging ratio can promote the material to deform and compact more fully during the forging process, which helps to improve the uniformity and stability of the material.

[0065] Specifically, in step S2, the first forged material is sent into an annealing furnace for annealing, the annealing temperature is 600-660℃, the annealing time is 1-10 hours, and the material is air-cooled to room temperature after annealing. During the annealing process, the material will undergo temperature rising and falling, which helps to eliminate the residual stress generated during the forging process, improve the overall stability of the material, and reduce the risk of cracks and deformation.

[0066] Specifically, in step S3, the normalizing temperature is 940-980℃, the normalizing time is 1-3 hours, and the material is cooled to room temperature; the normalizing temperature and time can make the material fully undergo solid solution treatment, obtain a more uniform structure, and be beneficial to improving the strength and stability of the material. The cooling mode is sand cooling or furnace cooling, which can relieve the stress of the material in the cooling process, reduce the risk of cracking, and ensure the integrity of the material. Preferably, the normalizing temperature is 950-970℃, and the normalizing time is 2-3 hours.

[0067] Specifically, in step S4, the quenching heating process of the third forging material is two stages. The first stage is to heat the third forging material to 650-670℃ and keep it for 1-2 hours; the second stage is to heat the forging material after the first stage quenching to 930-960℃ and keep it for 1-2 hours, and then oil quenching to room temperature. This segmented heating process helps to refine and homogenize the material structure, form the required structure during quenching, and further improve the hardness and strength of the material. Properly controlling the quenching temperature and holding time can help the material quickly form martensite structure, thereby improving the hardness and strength of the material; the higher quenching temperature is mainly used to effectively dissolve carbides during oil quenching, and to control the thermal stability of austenite grains while controlling the grain size. Preferably, the second stage holding temperature is 945-955℃, and the holding time is 1-2 hours.

[0068] In the process of oil quenching, the forging material is slowly cooled to below 80℃ in 15-90 minutes, and then cooled to room temperature. Finally, a high-density large-angle grain boundary structure is obtained.

[0069] Specifically, in step S5, the fourth forging material is subjected to first tempering and second tempering, the second tempering temperature is not higher than the first tempering temperature, the first tempering temperature is 230-240℃, the tempering time is 2-5 hours, and the material is air cooled to room temperature before second tempering; the second tempering temperature is 220-230℃, and the tempering time is 2-5 hours. Two tempering processes can ensure that the material undergoes appropriate structural changes during tempering, thereby obtaining superior high strength and toughness.

[0070] The precise control of the process parameters in the above preparation method helps to ensure that the final product has the required mechanical properties and microstructure, and further improves the comprehensive performance of the material.

[0071] The low-alloy high-strength high-toughness steel prepared by the method has a microstructure of martensite and thin film austenite; the volume fraction of the thin film austenite is 5-8%, and the thickness is 15-50nm.

[0072] It should be noted that when the material is subjected to rapid cooling during heat treatment, the orientation selection of the large-angle grain boundary between martensite variants will be weakened, and the overall large-angle grain boundary density of the material will be reduced; and slow cooling process can cause premature formation of ferrite, upper bainite and carbide in the material, which will adversely affect the strength and toughness of the material. The preparation method provided by the application effectively purifies the austenite grain boundary by reasonably adding Mo and W elements, prevents the formation of softening structures such as upper bainite during cooling, and thus ensures the hardenability of the material. At the same time, the oil quenching process cooperates to slow down the actual martensitic phase transition process of the material and improve the large-angle grain boundary density in the martensite.

[0073] The generation and content of thin film austenite are affected by the types and contents of alloying elements and heat treatment. The application ensures the generation of high-density thin film austenite by precisely designing the alloy composition and controlling the temperature, holding time and cooling rate in processes such as forging, annealing and tempering. Too little or too much austenite volume fraction will adversely affect the toughness of high-strength steel. The austenite volume fraction in traditional nanometer bainite steel of the same strength grade is generally more than 15%, while the austenite volume fraction in secondary hardening steel of the same grade with high alloy content is generally less than 5%. The low-alloy high-strength high-toughness steel provided by the application has a lower austenite volume under the restriction of lower alloy content, combining the characteristics of low-alloy content and limited austenite volume, thereby realizing the maintenance of high strength of the steel while reducing the material cost and improving the toughness.

[0074] The application realizes the synergistic improvement of hardenability, strength and toughness of the material by adding appropriate amounts of carbon, manganese, silicon, nickel, molybdenum and tungsten elements; and obtains a high-strength and high-toughness microstructure by precisely controlling the process parameters in the preparation process, such as final forging temperature, forging ratio, normalizing temperature, quenching temperature and segmented heating. In particular, the segmented heating and oil cooling slow cooling means effectively promote the generation of large-angle grain boundaries, further improving the toughness of the material. The application realizes that the high-strength low-alloy steel has excellent tensile strength, elongation after fracture, room temperature impact toughness and fracture toughness and other excellent performances under the condition of lower alloy content. The tensile strength is > 2100 MPa, the elongation after fracture is > 10%, the room temperature impact toughness is ≥ 50 J / cm 2 , and the fracture toughness is > 85 MPa·m 1 / 2 , realizing that the high-strength steel has good strength and toughness performance under the restriction of alloy cost.

[0075] Example 1

[0076] The alloying components and impurity components of the raw steel blank of the embodiment are as follows in terms of percentage by weight: C: 0.39%, Mn: 0.58%, Si: 1.65%, Cr: 3.44%, Ni: 1.1%, Mo: 0.5%, W: 0.6%, Nb: 0.01%, V: 0.01%;

[0077] P: 0.0024%, S: 0.0021%, O: 0.014%, N: 0.0015%, H: <0.0005%.

[0078] The preparation steps are as follows:

[0079] S1: forging, the steel blank meeting the alloying component requirements is heated in a soaking furnace and then forged to obtain a first forged material;

[0080] The initial forging temperature is 1100°C, the final forging temperature is 920°C, the soaking temperature is 1180°C, and the forging ratio is 6.

[0081] S2: annealing, the first forged material is annealed and then air-cooled to obtain a second forged material;

[0082] The annealing temperature is 640°C, the annealing time is 8 hours, and the post-air cooling is to room temperature.

[0083] S3: normalizing, the second forged material is normalized and then cooled to room temperature to obtain a third forged material;

[0084] The normalizing temperature is 970°C, the normalizing time is 2 hours, and the sand-embedded cooling is to room temperature.

[0085] S4: oil quenching, the third forged material is subjected to first-stage and second-stage heat preservation and then oil-cooled to room temperature to obtain a fourth forged material;

[0086] The first-stage heat preservation temperature is 650°C, and the heat preservation time is 2 hours; the forged material after the first-stage heat preservation is heated to 950°C, heat preserved for 1.5 hours, and then oil-cooled to room temperature.

[0087] S5: tempering, the fourth forged material is subjected to first-time and second-time tempering, the second-time tempering temperature is not higher than the first-time tempering temperature, and a low-alloy high-strength high-toughness steel is obtained;

[0088] The first-time tempering temperature is 230°C, the heat preservation time is 4 hours, and the post-air cooling is to room temperature; the second-time tempering temperature is 225°C, and the tempering time is 2 hours.

[0089] The diameter of the forged rod is 60 mm.

[0090] Embodiment 2

[0091] The alloying components and impurity compositions of the raw steel billet of the embodiment are as follows in terms of percentage by weight: C: 0.41%, Mn: 0.7%, Si: 1.51%, Cr: 3.37%, Ni: 1.0%, Mo: 0.65%, W: 0.52%, Nb: 0.016%, V: 0.002%;

[0092] P: 0.0025%, S: 0.0020%, O: 0.0009%, N: 0.0016%, H: <0.0005%.

[0093] The preparation method of the embodiment is similar to that of Example 1, except that the process parameters in the preparation process are different; the process parameters in the preparation process all meet the requirements of the application, as shown in Table 3.

[0094] The diameter of the forged bar is 100 mm.

[0095] Example 3

[0096] The alloying components and impurity compositions of the raw steel billet of the embodiment are as follows in terms of percentage by weight: C: 0.40%, Mn: 0.75%, Si: 1.68%, Cr: 3.56%, Ni: 1.18%, Mo: 0.68%, W: 0.67%, Nb: 0.007%, V: 0.013%;

[0097] P: 0.0018%, S: 0.0013%, O: 0.0011%, N: 0.0021%, H: <0.0003%.

[0098] The preparation method of the embodiment is similar to that of Example 1, except that the process parameters in the preparation process are different; the process parameters in the preparation process all meet the requirements of the application, as shown in Table 3.

[0099] The diameter of the forged bar is 60 mm.

[0100] Example 4

[0101] The alloying components and impurity compositions of the raw steel billet of the embodiment are the same as those of Example 3, as shown in Tables 1 and 2.

[0102] The preparation method of the embodiment is similar to that of Example 1, except that the process parameters in the preparation process are different; the process parameters in the preparation process all meet the requirements of the application, as shown in Table 3.

[0103] The diameter of the forged bar is 60 mm.

[0104] Example 5

[0105] The alloying components and impurity compositions of the raw steel billet of the embodiment are the same as those of Example 2, as shown in Tables 1 and 2.

[0106] The preparation method of the embodiment is similar to that of Example 1, except that the process parameters in the preparation process are different; the process parameters in the preparation process all meet the requirements of the application, as shown in Table 3.

[0107] The diameter of the forged bar is 60 mm.

[0108] Comparative Example 1

[0109] The alloy composition and impurity composition of the raw steel billet of the present comparative example are the same as those of Example 1, as shown in Table 1 and Table 2.

[0110] The preparation method of the present comparative example is similar to that of Example 1, except that the preparation process is water quenching, as shown in Table 3.

[0111] The diameter of the forged bar is 60 mm.

[0112] Comparative Example 2

[0113] The alloy composition and impurity composition of the raw steel billet of the present comparative example are the same as those of Example 2, as shown in Table 1 and Table 2.

[0114] The preparation process of the present comparative example is water quenching, without tempering, as shown in Table 3.

[0115] The diameter of the forged bar is 100 mm.

[0116] Comparative Example 3

[0117] The alloy composition and impurity composition of the raw steel billet of the present comparative example are the same as those of Example 1, as shown in Table 1 and Table 2.

[0118] The preparation method of the present comparative example is similar to that of Example 1, except that the process parameters in the preparation process are different; part of the process parameters in the preparation process do not meet the requirements of the application, as shown in Table 3.

[0119] The diameter of the forged bar is 60 mm.

[0120] Comparative Example 4

[0121] The alloy composition and impurity composition of the raw steel billet of the present comparative example are the same as those of Example 1, as shown in Table 1 and Table 2.

[0122] The preparation method of the present comparative example is similar to that of Example 1, except that the process parameters in the preparation process are different; part of the process parameters in the preparation process do not meet the requirements of the application, as shown in Table 3.

[0123] The diameter of the forged bar is 60 mm.

[0124] Comparative Example 5

[0125] The alloy composition and impurity composition of the raw steel billet of the present comparative example are the same as those of Example 1, as shown in Table 1 and Table 2.

[0126] The preparation method of the present comparative example is similar to that of Example 1, except that the process parameters in the preparation process are different; some of the process parameters in the preparation process do not meet the requirements of the present application, as shown in Table 3.

[0127] The diameter of the forged bar is 60 mm.

[0128] Comparative Example 6

[0129] The alloy composition and impurity composition of the raw steel billet of the present comparative example are the same as those of Example 3, as shown in Tables 1 and 2.

[0130] The preparation method of the present comparative example is similar to that of Example 1, except that the process parameters in the preparation process are different; some of the process parameters in the preparation process do not meet the requirements of the present application, as shown in Table 3.

[0131] The diameter of the forged bar is 60 mm.

[0132] Comparative Example 7

[0133] The alloy composition and impurity composition of the raw steel billet of the present comparative example, in terms of weight percentage, are as follows: C: 0.39%, Mn: 0.52%, Si: 1.65%, Cr: 3.40%, Ni: 1.0%, Mo: 0.1%, W: 0.1%, Nb: 0.008%, V: 0.012%; which do not meet the requirements of the present application.

[0134] P: 0.0015%, S: 0.0020%, O: 0.0016%, N: 0.0022%, H: <0.0005%.

[0135] The preparation method of the present comparative example is similar to that of Example 1, except that the preparation process is water quenching; as shown in Table 3.

[0136] The diameter of the forged bar is 60 mm.

[0137] Comparative Example 8

[0138] The alloy composition and impurity composition of the raw steel billet of the present comparative example, in terms of weight percentage, are as follows: C: 0.51%, Mn: 0.32%, Si: 1.8%, Cr: 3.32%, Ni: 0.8%, Mo: 0.15%, W: 0.25%, Nb: 0.002%; which do not meet the requirements of the present application.

[0139] P: 0.0012%, S: 0.0023%, O: 0.0010%, N: 0.0030%, H: <0.0003%.

[0140] The preparation method of the present comparative example is similar to that of Example 1, except that the preparation process is one-time quenching, as shown in Table 3.

[0141] Forged bar diameter 80 mm.

[0142] Comparative Example 9

[0143] The alloying and impurity compositions of the raw steel billet of this comparative example, in weight percent, were: C: 0.35%, Mn: 1.0%, Si: 1.25%, Cr: 3.38%, Ni: 1.2%, Mo: 0.34%, W: 0.38%, Nb: 0.006%, V: 0.01%.

[0144] P: 0.0009%, S: 0.0015%, O: 0.0012%, N: 0.0024%, H: <0.0003%.

[0145] The preparation method of this comparative example was similar to Example 1, except that the preparation process was one quenching, as shown in Table 3.

[0146] Forged bar diameter 60 mm.

[0147] Table 1 Alloying chemical compositions of raw steel billets in Examples and Comparative Examples (wt.%)

[0148] Item C Cr Ni Mn Mo Si W Nb V Example 1 0.39 3.44 1.1 0.58 0.5 1.65 0.6 0.01 0.01 Example 2 0.41 3.37 1.0 0.7 0.65 1.51 0.52 0.016 0.002 Example 3 0.40 3.56 1.18 0.75 0.68 1.68 0.67 0.007 0.013 Example 4 0.40 3.56 1.18 0.75 0.68 1.68 0.67 0.007 0.013 Example 5 0.41 3.37 1.0 0.7 0.65 1.51 0.52 0.016 0.002 Comparative Example 1 0.39 3.44 1.1 0.58 0.5 1.65 0.6 0.01 0.01 Comparative Example 2 0.41 3.37 1.0 0.7 0.65 1.51 0.52 0.016 0.002 Comparative Example 3 0.39 3.44 1.1 0.58 0.5 1.65 0.6 0.01 0.01 Comparative Example 4 0.39 3.44 1.1 0.58 0.5 1.65 0.6 0.01 0.01 Comparative Example 5 0.39 3.44 1.1 0.58 0.5 1.65 0.6 0.01 0.01 Comparative Example 6 0.40 3.56 1.18 0.75 0.68 1.68 0.67 0.007 0.013 Comparative Example 7 0.39 3.40 1.0 0.52 0.1 1.65 0.1 0.008 0.012 Comparative Example 8 0.51 3.32 0.8 0.32 0.15 1.8 0.25 0.002 -- Comparative Example 9 0.35 3.38 1.2 1.0 0.34 1.25 0.38 0.006 0.01

[0149] Table 2 Impurity compositions of raw steel billets in Examples and Comparative Examples (wt.%)

[0150]

[0151]

[0152] Table 3 Process parameters during preparation of Examples and Comparative Examples

[0153]

[0154]

[0155]

[0156] Table 4 Mechanical properties of steels in Examples and Comparative Examples

[0157]

[0158]

[0159] From Table 4, it can be seen that the steels prepared in Examples 1-5 all have good strength and toughness indexes. Example 1 adopts a higher normalizing temperature and a two-stage heating strategy during quenching, has a lower volume fraction of residual austenite and a more superior toughness performance; compared with Example 1, Examples 3 and 4 slightly increase the overall alloying element content and the volume fraction of thin film austenite, and the strength and fracture toughness are comparable to those of Example 1; Example 5 adopts a lower quenching temperature, although the strength also reaches the 2100 MPa level, but the toughness is poorer than other examples.

[0160] The alloying element contents of Comparative Example 1 and Example 1 are the same, and the alloying element contents of Comparative Example 2 and Example 2 are the same. Examples 1 and 2 control the transformation of internal unstable austenite by slow cooling oil quenching, avoiding stress concentration easily produced during deformation. While Comparative Example 1 adopts a water tank water quenching method for rapid cooling, which cools to room temperature within 3 minutes. This rapid cooling strategy results in a steel strength that is about 50 MPa lower than that of the steel obtained by using the oil quenching method in Example 1, and the fracture toughness is less than 85 MPa·m 1 / 2 In Comparative Example 2, the water quenching process results in quenching cracks in the forged bar.

[0161] Comparative Examples 3-5 use the same alloying elements as Example 1, but the two tempering temperatures during tempering are not within the range required by the present application, and the volume fraction of thin film austenite of the finally prepared steel is too high or too low, not within the range of 5-8%. The steel of Comparative Example 3 has a strength reaching the 2100 MPa level, but the fracture toughness is less than 85 MPa·m 1 / 2 ; the toughness of Comparative Example 4 is higher, but the strength is lower than 2100 MPa; the strength of Comparative Example 5 is lower than 2100 MPa, and the fracture toughness is less than 85 MPa·m 1 / 2 ; that is, the strength and toughness of the steels of Comparative Examples 3-5 are not compatible.

[0162] Comparative Example 6 uses the same alloying elements as Example 3, but the two tempering temperatures during tempering are not within the range required by the present application, both are lower than the range required by the present application, and the volume fraction of thin film austenite of the finally prepared steel is too high. The steel has a strength reaching the 2100 MPa level, but the fracture toughness is less than 85 MPa·m 1 / 2 , and the fracture toughness is reduced.

[0163] In Comparative Example 7, the alloying element content of the steel is low, which does not meet the requirements of the present application. The strength and toughness of the finally prepared steel are significantly reduced.

[0164] The content of C in the alloy component of the steel of Comparative Example 8 is too high, the contents of Mn, Mo and W do not meet the requirements of the present application, the steel does not contain V element, and the toughness of the finally prepared steel significantly decreases; the content of C in the alloy component of the steel of Comparative Example 9 is too low, the contents of Mn, Si, Mo and W do not meet the requirements of the present application, and the strength of the material significantly decreases. Although the preparation method in the present application is used in Comparative Examples 8 and 9, the balance between the strength and the toughness of the product cannot be achieved because the component design in the present application is not used.

[0165] The above merely provides the preferred embodiments of the present application, but the protection scope of the present application is not limited to this. Any changes or replacements easily conceived by those skilled in the art within the technical range disclosed by the present application should be covered within the protection scope of the present application.

Claims

1. A 2100 MPa grade high strength high toughness low alloy steel, characterized in that, The alloying components of the low-alloy high-strength and high-toughness steel are as follows in percentage by weight: C: 0.37-0.42%, Mn: 0.4-1.2%, Si: 1.40-1.80%, Cr: 3.37-4.0%, Ni: 1.0-1.5%, Mo: 0.4-0.68%, W: 0.4-0.8%, Nb: 0.007-0.02%, V: 0.002-0.02%, and the balance of Fe and inevitable impurities; The microstructure of the low-alloy high-strength and high-toughness steel is composed of martensite and thin-film austenite, and the volume fraction of the thin-film austenite is 5-8%; The low-alloy high-strength and high-toughness steel is prepared by the following steps: S1: forging, the steel billet with the required alloying components is heated in a soaking furnace and then forged to obtain first forging material; S2: annealing, the first forging material is annealed and air-cooled to obtain second forging material; S3: normalizing, the second forging material is normalized and then cooled to room temperature to obtain third forging material; S4: oil quenching, the third forging material is subjected to first-stage and second-stage heat preservation and then oil-cooled to room temperature to obtain fourth forging material; S5: tempering, the fourth forging material is subjected to first-time and second-time tempering, and the second-time tempering temperature is not higher than the first-time tempering temperature to obtain the low-alloy high-strength and high-toughness steel; In step S4, the first-stage heat preservation temperature is 650-670 DEG C, and the heat preservation time is 1-2 h; the second-stage heat preservation temperature is 930-960 DEG C, and the heat preservation time is 1-2 h; In step S5, the first-time tempering temperature is 230-240 DEG C, and the tempering time is 2-5 h; the second-time tempering temperature is 220-230 DEG C, and the tempering time is 2-5 h; The low-alloy high-strength high-toughness steel has a tensile strength of > 2100 MPa, a room temperature impact toughness of ≥ 50 J / cm 2 , and a fracture toughness of > 85 MPa·m 1 / 2 .

2. The 2100 MPa grade high strength high toughness low alloy steel of claim 1, wherein, The volume fraction of the thin-film austenite is 5.65-8%.

3. The 2100 MPa grade high strength high toughness low alloy steel as claimed in claim 1, wherein, The alloying components of the low-alloy high-strength and high-toughness steel are as follows in percentage by weight: C: 0.38-0.41%, Mn: 0.5-0.8%, Si: 1.50-1.70%, Cr: 3.37-3.6%, Ni: 1.0-1.2%, Mo: 0.5-0.68%, W: 0.5-0.7%, Nb: 0.007-0.02%, and V: 0.002-0.015%.

4. A method for preparing a 2100 MPa grade low alloy high strength high toughness steel, characterized in that, The low-alloy high-strength and high-toughness steel of 2100 MPa grade is prepared by the following steps: S1: forging, the steel billet with the required alloying components is heated in a soaking furnace and then forged to obtain first forging material; S2: annealing, the first forging material is annealed and air-cooled to obtain second forging material; S3: normalizing, the second forging material is normalized and then cooled to room temperature to obtain third forging material; S4: oil quenching, the third forging material is subjected to first-stage and second-stage heat preservation and then oil-cooled to room temperature to obtain fourth forging material; S5: tempering, the fourth forging material is subjected to first-time and second-time tempering, and the second-time tempering temperature is not higher than the first-time tempering temperature to obtain the low-alloy high-strength and high-toughness steel; In step S4, the first-stage heat preservation temperature is 650-670 DEG C, and the heat preservation time is 1-2 h; The second-stage heat preservation temperature is 930-960 DEG C, and the heat preservation time is 1-2 h; In step S5, the first tempering temperature is 230-240℃, and the tempering time is 2-5h; the second tempering temperature is 220-230℃, and the tempering time is 2-5h.

5. The production method according to claim 4, characterized by, In step S1, the initial forging temperature is 1000-1130℃, the final forging temperature is 870-930℃, and the forging ratio is ≥5.

6. The production method according to claim 5, wherein In step S2, the annealing temperature is 600-660℃, and the annealing time is 1-10h.

7. The production method according to claim 6, wherein In step S3, the normalizing temperature is 940-980℃, and the normalizing time is 1-3h.

8. The preparation method according to claim 7, characterized in that, In step S4, the first stage holding temperature is 660-670℃, and the holding time is 1-2h; the second stage holding temperature is 940-960℃, and the holding time is 1-2h. In step S5, the first tempering temperature is 230-240℃, and the tempering time is 3-5h; the second tempering temperature is 225-230℃, and the tempering time is 2-5h.

9. The production method according to claim 8, characterized by, ​

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