SF1900 high-strength and high-toughness steel and a preparation method thereof

Abstract

This application relates to the technical field of high-strength and high-toughness steel, specifically to an SF1900 high-strength and high-toughness steel and its preparation method. The preparation method specifically includes the following steps: smelting and casting, homogenization treatment, forging, normalizing treatment, annealing treatment, quenching treatment, cryogenic treatment, low-temperature heat treatment, and tempering treatment; wherein, the tempering treatment includes heating the bar to 400-510℃, holding at that temperature for 4-14 hours, and air cooling to room temperature. The SF1900 high-strength and high-toughness steel prepared using the method of this application has a tensile strength ≥2000MPa, a yield strength ≥1730MPa, an elongation after fracture ≥12%, a reduction of area ≥43%, and an impact toughness ≥12J / cm². 2 .

Description

Technical Field

[0001] This application relates to the technical field of high-strength and high-toughness steel, and more particularly to an SF1900 high-strength and high-toughness steel and its preparation method. Background Technology

[0002] In key fields such as aerospace, high-end equipment manufacturing, and energy engineering, the comprehensive performance requirements for core structural components such as drive shafts are becoming increasingly stringent. SF1900 high-strength, high-toughness steel, as an alloy material with high strength and high toughness potential, has become an important candidate material for key structural components in these fields that withstand high power, high speed, large deformation, and heavy maneuvering overload conditions due to its excellent mechanical properties and machinability. SF1900 high-strength, high-toughness steel achieves strengthening through a dual nano-precipitation mechanism of intermetallic compounds and alloy carbides, belonging to a composite secondary hardening type of ultra-high-strength steel. Compared with traditional maraging steels for aerospace shafts such as C250 steel, SF1900 steel does not contain titanium, eliminating the formation factors of non-metallic inclusions such as titanium carbonitride and titanium nitride from the root, resulting in superior fatigue performance. It can be used as a material for the preparation of core components such as low-pressure turbine shafts and drive shafts of aero-engines, providing key material technology support for achieving high thrust output and green emission reduction goals in internationally advanced turbofan engines.

[0003] However, SF1900 high-strength and high-toughness steel prepared by existing technology has a technical defect in the poor matching of strength and toughness in practical engineering applications. The core reason is that the precipitation behavior of intermetallic compounds and alloy carbides during the preparation process is difficult to achieve the best synergistic matching state in terms of morphology, size and distribution. This leads to the limitation of the material's comprehensive mechanical properties, which cannot meet the service reliability requirements of key components such as aero-engine drive shafts under extreme working conditions.

[0004] Therefore, improving the balance between strength and toughness of SF1900 high-strength and high-toughness steel has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This application provides an SF1900 high-strength, high-toughness steel and its preparation method. The SF1900 high-strength, high-toughness steel prepared using the method of this application has a tensile strength ≥2000MPa, a yield strength ≥1730MPa, an elongation after fracture ≥12%, a reduction of area ≥43%, and an impact toughness ≥12J / cm². 2 .

[0006] This application achieves precise control over the microstructure of SF1900 high-strength and high-toughness steel by accurately adjusting the preparation process parameters, thereby significantly improving the balance between its strength and toughness. Therefore, the technical solution of this application not only effectively expands the application range of SF1900 high-strength and high-toughness steel, but also has significant practical and industrial value for ensuring the performance leap of aerospace equipment and promoting the technological upgrading of the high-end equipment manufacturing industry.

[0007] In a first aspect, this application provides a method for preparing SF1900 high-strength and high-toughness steel, employing the following technical solution:

[0008] A method for preparing SF1900 high-strength and high-toughness steel, the method specifically includes the following steps: smelting and casting, homogenization treatment, forging, normalizing treatment, annealing treatment, quenching treatment, cryogenic treatment, low-temperature heat treatment, and tempering treatment;

[0009] The normalizing treatment includes heating the bar to 930-960℃, holding it at that temperature for 1-3 hours, and then air-cooling it to room temperature.

[0010] The annealing process includes heating the bar to 630-680℃, holding it at that temperature for 6-15 hours, and then air-cooling it to room temperature.

[0011] The quenching process includes heating the bar to 870-930℃, holding it at that temperature for 1-5 hours, and then oil cooling it to room temperature.

[0012] The cryogenic treatment includes cryogenically treating the bar at -80~-65℃, holding it at that temperature for 1-2 hours, and then air-cooling it to room temperature.

[0013] The low-temperature heat treatment includes holding the bar at 180-220℃ for 4-8 hours, followed by air cooling to room temperature.

[0014] The tempering process includes heating the bar to 400-510℃, holding it at that temperature for 4-14 hours, and then air-cooling it to room temperature.

[0015] The chemical composition of the SF1900 high-strength and high-toughness steel, by mass percentage, includes: Ni 13.55-14.05 wt.%; Co 9.75-10.25 wt.%; Cr 2.35-2.65 wt.%; Mo 1.30-1.50 wt.%; Al 0.85-0.95 wt.%; C 0.195-0.225 wt.%; with the balance being Fe and unavoidable impurities.

[0016] Optionally, in the smelting and casting step, a dual vacuum smelting process of VIM+VAR is used to prepare steel ingots with chemical composition that meet the requirements.

[0017] Optionally, in the homogenization process, the steel ingot is loaded into a furnace and heated to 1200-1220°C at a heating rate of 80-150°C / h, and held at this temperature for 8-12 hours.

[0018] Optionally, in the forging process, the steel ingot obtained by homogenization treatment is subjected to three upsetting and three drawing forging, with an initial forging temperature of 1050-1200℃ and a final forging temperature of not less than 850℃, thereby obtaining bar stock or billet.

[0019] The ultra-high strength steel of this application comprises 0.195-0.225 wt.% C by mass percentage. In this application, C is the most important strengthening element. C atoms can exist in the interstitial positions of the matrix lattice as interstitial solid solution atoms. The interstitial solid solution strengthening effect caused by lattice distortion is far greater than that of substitutional solid solution strengthening. The C content directly determines the strength of the martensite. As a composite secondary hardening ultra-high strength steel, the M2C type carbides formed during aging provide a significant strengthening effect. However, excessively high C content will significantly deteriorate the toughness and plasticity of the material. Therefore, the C content in this application is controlled at 0.195-0.225 wt.%.

[0020] The ultra-high strength steel of this application comprises Ni at a mass percentage of 13.55-14.05 wt.%. In this application, Ni is a crucial element ensuring the excellent strength and toughness balance of the composite secondary hardening ultra-high strength steel. Ni is an austenite stabilizing element that can expand the austenite phase region, not only lowering the Ms point of the steel but also promoting the formation of reverse-transformed austenite and improving the steel's toughness, although it also reduces the steel's strength. Simultaneously, Ni can combine with Al during tempering to form the intermetallic compound β-NiAl. A high Ni content can lower the precipitation temperature of β-NiAl, thus maintaining it within the same tempering temperature range as the precipitation temperature of M2C type carbides, further enhancing the steel's strength. Therefore, the Ni content is controlled at 13.55-14.05 wt.%.

[0021] The ultra-high strength steel of this application comprises 1.30-1.50 wt.% Mo by mass. Mo is the main forming element of M2C carbides. Through the interaction of Mo, Cr, and C, fine and dispersed nano-precipitates can be obtained, thereby improving strength. Simultaneously, appropriate Mo addition can increase the precipitation temperature of M2C carbides, thus maintaining it within the same tempering temperature range as β-NiAl, enhancing the effect of composite secondary hardening. Excessive Mo content can easily lead to an excessive volume fraction of precipitates, impairing the material's toughness and plasticity. Therefore, this application controls the Mo content to 1.30-1.50 wt.%.

[0022] The ultra-high strength steel of this application comprises 9.75-10.25 wt.% Co by mass percentage. Co does not form precipitates in the steel and enhances its strength through solid solution strengthening. Co can delay dislocation recovery in the martensitic matrix during tempering and strongly promotes secondary hardening. However, excessive Co content can impair toughness and plasticity; therefore, this application controls the Co content to 9.75-10.25 wt.%.

[0023] The ultra-high strength steel of this application comprises Cr: 2.35-2.65 wt.% by mass. Cr can effectively improve hardenability and, as a strong carbide-forming element, replaces Mo in M2C, promoting secondary hardening reaction and improving the strength of the material. However, excessive Cr content will lead to an excessively high volume fraction of precipitated phases, and high Cr can easily lead to a change in carbide type. Therefore, the Cr content of this application is controlled at 2.35-2.65 wt.%.

[0024] The ultra-high strength steel of this application comprises Al: 0.85-0.95 wt.% by mass. Al is a strong deoxidizer, and adding a certain amount of Al can significantly reduce the O content in molten steel. In this application, Al is also a strengthening element, forming β-NiAl intermetallic compounds by combining with Ni, and together with M2C, forming composite precipitation strengthening. However, excessive Al content will drastically deteriorate the toughness and plasticity of the material. Therefore, the Al content in this application is controlled at 0.85-0.95 wt.%.

[0025] The ultra-high strength steel of this application also includes unavoidable impurity elements. By mass percentage, Ti ≤ 0.10 wt.%; Si ≤ 0.10 wt.%; Mn ≤ 0.10 wt.%; Cu ≤ 0.050 wt.%; P ≤ 0.006 wt.%; Zr ≤ 0.005 wt.%; B ≤ 0.005 wt.%; Mg ≤ 0.005 wt.%; Sn ≤ 0.005 wt.%; Ca ≤ 0.0025 wt.%; N ≤ 0.0025 wt.%; As ≤ 0.0025 wt.%; La ≤ The impurity elements are controlled within the above ranges to ensure the strength, toughness, and fatigue performance of the material. (Note: The original text contains some inconsistencies and likely refers to specific impurity elements. A more accurate translation would require the full context.)

[0026] SF1900 high-strength and high-toughness steel, as a composite secondary hardening ultra-high-strength steel, primarily consists of nano-sized M2C carbides and β-NiAl intermetallic compounds as its reinforcing phases. By controlling the tempering time and temperature, high-density, fine M2C and β-NiAl phases are uniformly dispersed on the martensitic laths. Simultaneously, the content of reverse-transformed austenite (RA) is controlled, resulting in a steel that combines high strength and high toughness.

[0027] Secondly, this application provides an SF1900 high-strength and high-toughness steel prepared using the above-described preparation method.

[0028] In summary, this application includes at least one of the following beneficial technical effects:

[0029] The SF1900 high-strength and high-toughness steel prepared using the method of this application has a tensile strength ≥2000MPa, with a maximum of 2267MPa; a yield strength ≥1730MPa, with a maximum of 1889MPa; an elongation after fracture ≥12%; a reduction of area ≥43%, with a maximum of 57%; and an impact toughness ≥12J / cm. 2 The highest it can reach is 24 J / cm 2 . Attached Figure Description

[0030] Figure 1 TEM morphology of carbide precipitation, β-NiAl precipitation, and reverse-transformed austenite in Example 4 (tempering temperature 500℃) ((a) and (b) are bright field phase and dark field phase, respectively).

[0031] Figure 2 The TEM morphology of carbide precipitation, β-NiAl precipitation, and reverse-transformed austenite in Comparative Example 2 (tempering temperature 550℃) is shown in ((a) and (b) for bright field phase and dark field phase, respectively).

[0032] Figure 3 TEM morphology of carbide precipitation in Comparative Example 3 (tempering time 1 h) ((a) and (b) are bright field phase and dark field phase, respectively). Detailed Implementation

[0033] Before describing the embodiments of this application in detail, it should be understood that the terminology used herein is for the purpose of describing a particular embodiment only. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the term pertains.

[0034] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more.

[0035] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0036] In this application, the terms "comprising" or "including" are open-ended expressions, meaning they include the content specified in this application but do not exclude other aspects.

[0037] This application provides a method for preparing SF1900 high-strength and high-toughness steel, specifically including the following steps:

[0038] (1) Smelting and casting: Steel ingots with chemical composition within the required range are prepared by using a dual vacuum smelting process of VIM+VAR (vacuum induction smelting + vacuum arc remelting).

[0039] (2) Homogenization treatment: The steel ingot is loaded into the furnace and heated to 1200-1220℃ at a heating rate of 80-150℃ / h, and held at this temperature for 8-12h;

[0040] (3) Forging: The steel ingots obtained by homogenization treatment are subjected to three upsetting and three drawing forging. The initial forging temperature is 1050-1200℃ and the final forging temperature is not lower than 850℃, thereby obtaining bar stock (or billet).

[0041] (4) Normalizing treatment: Heat the bar to 930-960℃, keep it at that temperature for 1-3 hours, and then air cool it to room temperature.

[0042] (5) Annealing treatment: Heat the bar to 630-680℃, keep it at that temperature for 6-15 hours, and then air cool it to room temperature.

[0043] (6) Quenching treatment: Heat the bar to 870-930℃, keep it at that temperature for 1-5 hours, and then cool it to room temperature with oil; perform deep cryogenic treatment within 24 hours.

[0044] (7) Cryogenic treatment: The bar is cryogenically treated at -80~-65℃, kept at the temperature for 1-2 hours, air-cooled to room temperature, and then subjected to low-temperature heat treatment within 6-10 hours.

[0045] (8) Low temperature heat treatment: keep the bar at 180-220℃ for 4-8 hours and air cool to room temperature.

[0046] (9) Tempering treatment: Heat the bar to 400-510℃, hold for 4-14 hours, and air cool to room temperature;

[0047] The chemical composition of the SF1900 high-strength and high-toughness steel of this application, by mass percentage, includes: Ni 13.55-14.05wt.%; Co 9.75-10.25wt.%; Cr 2.35-2.65wt.%; Mo 1.30-1.50wt.%; Al 0.85-0.95wt.%; C 0.195-0.225wt.%; with the balance being Fe and unavoidable impurities.

[0048] Impurities, by mass percentage, include: Ti ≤ 0.10 wt.%; Si ≤ 0.10 wt.%; Mn ≤ 0.10 wt.%; Cu ≤ 0.050 wt.%; P ≤ 0.006 wt.%; Zr ≤ 0.005 wt.%; B ≤ 0.005 wt.%; Mg ≤ 0.005 wt.%; Sn ≤ 0.005 wt.%; Ca ≤ 0.0025 wt.%; N ≤ 0.0025 wt.%; As ≤ 0.0025 wt.%; La ≤ 0.002 wt.%; Ce ≤ 0.002 wt.%; O ≤ 0.0015 wt.%; Sb ≤ 0.0015 wt.%; H ≤ 0.0010 wt.%; S ≤ 0.0007 wt.%; Pb ≤ 0.0005 wt.%; Ag ≤ 0.0005 wt.%; Se ≤ 0.0003 wt.%; Bi ≤ 0.00003 wt.%.

[0049] This application also provides SF1900 high-strength and high-toughness steel prepared using the above-described method. This SF1900 high-strength and high-toughness steel has a tensile strength ≥2000 MPa, a yield strength ≥1730 MPa, an elongation after fracture ≥12%, a reduction of area ≥43%, and an impact toughness ≥12 J / cm². 2 .

[0050] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0051] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0052] The present application will be further described in detail below with reference to the embodiments, accompanying drawings and test results.

[0053] Example 1

[0054] This embodiment provides a method for preparing SF1900 high-strength and high-toughness steel.

[0055] The chemical composition of the above-mentioned high-strength and high-toughness steel is as follows, by mass percentage: Ni 13.8 wt.%; Co 10.0 wt.%; Cr 2.5 wt.%; Mo 1.40 wt.%; Al 0.90 wt.%; C 0.21 wt.%; balance being Fe and unavoidable impurities.

[0056] The preparation method of the above-mentioned high-strength and high-toughness steel specifically includes the following steps:

[0057] (1) Smelting and casting: Steel ingots with chemical composition within the required range are prepared by using a dual vacuum smelting process of VIM+VAR (vacuum induction smelting + vacuum arc remelting).

[0058] (2) Homogenization treatment: The steel ingot is loaded into the furnace and heated to 1210℃ at a heating rate of 100℃ / h, and held at this temperature for 10h;

[0059] (3) Forging: The steel ingot obtained by homogenization treatment is subjected to three upsetting and three drawing forging. The initial forging temperature is 1100℃ and the final forging temperature is 900℃, thereby obtaining the bar stock.

[0060] (4) Normalizing treatment: Heat the bar to 950°C, keep it at that temperature for 2 hours, and then air cool it to room temperature.

[0061] (5) Annealing treatment: Heat the bar to 650℃, keep it at that temperature for 10 hours, and then air cool it to room temperature.

[0062] (6) Quenching treatment: Heat the bar to 900℃, keep it at that temperature for 1 hour, cool it to room temperature with oil, and perform deep cryogenic treatment within 12 hours.

[0063] (7) Cryogenic treatment: The bar is cryogenically treated at -73℃, kept at that temperature for 1 hour, and then air-cooled to room temperature. After that, it is subjected to low-temperature heat treatment within 8 hours.

[0064] (8) Low temperature heat treatment: The bar is kept at 204℃ for 6 hours and then air-cooled to room temperature.

[0065] (9) Tempering treatment: Heat the bar to 400℃, keep it at that temperature for 10 hours, and then air cool it to room temperature.

[0066] Examples 2-5

[0067] Examples 2-5 provide a method for preparing SF1900 high-strength and high-toughness steel.

[0068] The preparation method of the above embodiments differs from that of Embodiment 1 in that the heating temperature for tempering treatment is as shown in Table 1. However, the other conditions remain consistent with those of Embodiment 1.

[0069] Comparative Examples 1-2

[0070] Comparative Examples 1 and 2 respectively provide a method for preparing SF1900 high-strength and high-toughness steel.

[0071] The preparation method of the above comparative example differs from that of Example 1 in that the heating temperature for tempering is as shown in Table 1. All other steps remain the same as in Example 1.

[0072] Performance Testing Experiment 1 – The Effect of Tempering Temperature on Mechanical Properties

[0073] The mechanical properties (tensile properties) of the SF1900 high-strength and high-toughness steels prepared in Examples 1-5 and Comparative Examples 1-2 were tested according to ASTM A 370, including tensile strength. R m ), yield strength ( R p0.2 ), elongation after fracture ( A ) and reduction of area ( Z Impact toughness (a) KV ).

[0074] The test results are shown in Table 1.

[0075] Table 1. Some parameters of the above preparation method and the mechanical properties of the prepared high-strength and high-toughness steel.

[0076]

[0077] As shown in Table 1, the strength of SF1900 high-strength and high-toughness steel exhibits typical secondary hardening characteristics as the tempering temperature changes. The tensile strength and yield strength of SF1900 high-strength and high-toughness steel both increase first and then decrease with the increase of tempering temperature, reaching a peak of 2267 MPa at 450℃.

[0078] The austenite volume fraction of SF1900 high-strength and high-toughness steels in Examples 1-5 and Comparative Examples 1-2 was calculated using XRD. The results are shown in Table 1. This data shows that the austenite content (reverse-transformed austenite, RA) gradually increases with increasing tempering temperature. A suitable RA content can improve the impact toughness of SF1900 high-strength and high-toughness steel while mitigating its impact on strength reduction.

[0079] TEM morphology observations were performed on the carbide precipitation, β-NiAl precipitation, and reverse-transformed austenite in Example 4 (tempering temperature 500℃) and Comparative Example 2 (tempering temperature 550℃) at different tempering temperatures.

[0080] Figure 1 The TEM morphology of carbide precipitation, β-NiAl precipitation, and reverse-transformed austenite in Example 4 (tempering temperature 500℃) is shown. Among them, (a) and (b) are the bright field phase and dark field phase, respectively.

[0081] Figure 2 The TEM morphology of carbide precipitation, β-NiAl precipitation, and reverse-transformed austenite in Comparative Example 2 (tempering temperature 550℃) is shown. Among them, (a) and (b) are the bright field phase and dark field phase, respectively.

[0082] Depend on Figure 1 (a) It can be seen that when the tempering temperature is low, taking Example 4 as an example, the matrix is ​​covered with fine, high-density carbides and β-NiAl, which can significantly hinder dislocation slip and improve the impact toughness of SF1900 high-strength and high-toughness steel. With the increase of the aging temperature, taking Comparative Example 2 as an example, as... Figure 2 As shown in (a), the carbides undergo significant coarsening and growth, while the β-NiAl precipitates do not show significant coarsening, resulting in a significant decrease in the strength of SF1900 high-strength and high-toughness steel.

[0083] Depend on Figure 1 (b) It can be seen that when the tempering temperature is low, taking Example 4 as an example, the reverse-transformed austenite appears in the form of a thin, elongated film. This film-shaped reverse-transformed austenite is a tough phase, which can relax the stress at the interface and the stress concentration at the crack tip, passivate the crack tip, inhibit crack initiation or alleviate crack propagation, and is beneficial to improving the toughness of SF1900 high-strength and high-toughness steel. However, as the tempering temperature increases, the film-shaped reverse-transformed austenite will also gradually grow along the lath boundary. Taking Comparative Example 2 as an example, Figure 2 As shown in (b), this greatly damages the strength of SF1900 high-strength and high-toughness steel.

[0084] Examples 6-9

[0085] Examples 6-9 provide a method for preparing SF1900 high-strength and high-toughness steel.

[0086] The preparation method of the above embodiments differs from that of Embodiment 4 in that the tempering holding time is as shown in Table 2. All other steps remain the same as in Embodiment 4.

[0087] Comparative Examples 3-4

[0088] Comparative Examples 3 and 4 respectively provide a method for preparing SF1900 high-strength and high-toughness steel.

[0089] The preparation method of the above comparative example differs from that of Example 4 in that the tempering holding time is as shown in Table 2. All other steps remain the same as in Example 4.

[0090] Performance Test Experiment 2 – Effect of Tempering Time on Mechanical Properties

[0091] The mechanical properties (tensile properties) of the SF1900 high-strength and high-toughness steels prepared in Examples 6-9 and Comparative Examples 3-4 were tested according to ASTM A 370, including tensile strength. R m ), yield strength ( R p0.2 ), elongation after fracture ( A ) and reduction of area ( Z ).

[0092] The test results are shown in Table 2.

[0093] Table 2. Some parameters of the above preparation method and the mechanical properties of the prepared high-strength and high-toughness steel.

[0094]

[0095] As shown in Table 2, the tensile strength of SF1900 high-strength and high-toughness steel decreases with the extension of tempering time. The main reason is that the precipitated phase grows and coarsens. The yield strength first increases and then decreases, and the peak yield strength of 1888 MPa is obtained after 6 hours of tempering.

[0096] The morphology of the carbide precipitation in Comparative Example 3 (tempering time 1 h) was observed by TEM.

[0097] Figure 3 The TEM morphology of the carbide precipitation in Comparative Example 3 (tempering time 1 h) is shown. Among them, (a) and (b) are the bright field phase and dark field phase, respectively.

[0098] Depend on Figure 3(a) It can be seen that when the tempering time is short, some M3C carbides do not dissolve back into the matrix, and a small amount of fine M2C carbides, with a size of about 5 nm, begin to precipitate around the M3C phase. At this time, β-NiAl is still in the early stage of growth. A large amount of C elements are still dissolved in the matrix, and the strong interstitial solid solution strengthening effect gives it high strength, but low impact toughness. As the tempering time increases, the M3C carbides dissolve back, and a large amount of fine M2C carbides and β-NiAl precipitate, such as... Figure 1 As shown, the strength of SF1900 high-strength and high-toughness steel has decreased slightly.

[0099] Example 10

[0100] Example 10 provides a method for preparing SF1900 high-strength and high-toughness steel.

[0101] The preparation method of the above embodiments differs from that of Embodiment 4 in that the quenching temperature is as shown in Table 3. All other steps remain the same as in Embodiment 4.

[0102] Comparative Example 5

[0103] Comparative Example 5 provides a method for preparing SF1900 high-strength and high-toughness steel.

[0104] The preparation method of the above comparative example differs from that of Example 4 in that the quenching temperature is as shown in Table 3. All other steps remain the same as in Example 4.

[0105] Comparative Examples 6-7

[0106] Comparative Examples 6 and 7 each provide a method for preparing SF1900 high-strength and high-toughness steel.

[0107] The preparation method of the above comparative example differs from that of Example 4 in that the cryogenic treatment temperature is as shown in Table 3. All other steps remain the same as in Example 4.

[0108] Performance Test 3

[0109] (a) The mechanical properties (tensile properties) of the SF1900 high-strength and high-toughness steels prepared in Example 10 and Comparative Examples 5-7 were tested according to ASTM A 370. The results were then compared with those of Example 4.

[0110] The test results are shown in Table 3.

[0111] Table 3. Some parameters of the above preparation method and the mechanical properties of the prepared high-strength and high-toughness steel.

[0112]

[0113] As can be seen from Table 3, the quenching temperature and cryogenic temperature have little effect on the strength of SF1900 high-strength and high-toughness steel.

[0114] The austenite volume fraction of SF1900 high-strength and high-toughness steels in Examples 4 and Comparative Examples 6-7 was calculated using XRD. The results are shown in Table 3.

[0115] As shown in Table 3, the content of retained austenite in SF1900 high-strength and high-toughness steel gradually decreases with the decrease of cryogenic temperature. The lower the cryogenic temperature, the more completely the retained austenite in SF1900 high-strength and high-toughness steel transforms into martensite, and thus the yield strength of the alloy also increases.

[0116] In summary, SF1900 high-strength and high-toughness steel achieves a good balance of strength and toughness within a tempering temperature range of 400-510℃ and a holding time of 4-14 hours. Its tensile strength is ≥2000MPa, reaching a maximum of 2267MPa; its yield strength is ≥1730MPa, reaching a maximum of 1889MPa; and its impact toughness is ≥12J / cm². 2 The highest it can reach is 24 J / cm 2 .

[0117] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0118] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing SF1900 high-strength and high-toughness steel, characterized in that, The preparation method specifically includes the following steps: smelting and casting, homogenization treatment, forging, normalizing treatment, annealing treatment, quenching treatment, cryogenic treatment, low-temperature heat treatment, and tempering treatment; The normalizing treatment includes heating the bar to 930-960℃, holding it at that temperature for 1-3 hours, and then air-cooling it to room temperature. The annealing process includes heating the bar to 630-680℃, holding it at that temperature for 6-15 hours, and then air-cooling it to room temperature. The quenching process includes heating the bar to 870-930℃, holding it at that temperature for 1-5 hours, and then oil cooling it to room temperature. The cryogenic treatment includes cryogenically treating the bar at -80~-65℃, holding it at that temperature for 1-2 hours, and then air-cooling it to room temperature. The low-temperature heat treatment includes holding the bar at 180-220℃ for 4-8 hours, followed by air cooling to room temperature. The tempering process includes heating the bar to 400-510℃, holding it at that temperature for 4-14 hours, and then air-cooling it to room temperature. The chemical composition of the SF1900 high-strength and high-toughness steel, by mass percentage, includes: Ni 13.55-14.05 wt.%; Co 9.75-10.25 wt.%; Cr 2.35-2.65 wt.%; Mo 1.30-1.50 wt.%; Al 0.85-0.95 wt.%; C 0.195-0.225 wt.%; with the balance being Fe and unavoidable impurities. The SF1900 high-strength and high-toughness steel prepared by the aforementioned method has a tensile strength ≥2000MPa, a yield strength ≥1730MPa, an elongation after fracture ≥12%, a reduction of area ≥43%, and an impact toughness ≥12J / cm. 2 .

2. The preparation method according to claim 1, characterized in that, In the smelting and casting step, a dual vacuum smelting process of VIM+VAR is used to prepare steel ingots with chemical composition that meet the requirements.

3. The preparation method according to claim 1, characterized in that, In the homogenization process, the steel ingot is loaded into the furnace and heated to 1200-1220℃ at a heating rate of 80-150℃ / h, and held at this temperature for 8-12h.

4. The preparation method according to claim 1, characterized in that, In the forging process, the steel ingot obtained by homogenization is subjected to three upsetting and three drawing forging, with an initial forging temperature of 1050-1200℃ and a final forging temperature of not less than 850℃, thereby obtaining bar stock or billet.

5. An SF1900 high-strength and high-toughness steel prepared by any one of claims 1-4.

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