High-purity high-strength steel and manufacturing method thereof

Abstract

According to the high-purity high-strength steel and the manufacturing method thereof, by optimizing chemical components and adopting a vacuum induction, electroslag remelting and vacuum consumable triple smelting process, the purity and mechanical property of steel are remarkably improved. The steel comprises the following chemical components: C, Mn, Si, Ni, Cr, Mo, V and the like, the contents of impurities such as P, S, Al, Ti and the like are strictly controlled, and the contents of gas elements such as H, O, N and the like are greatly reduced, so that the steel has excellent toughness and plasticity under the condition of ultrahigh strength. According to the manufacturing method, multiple smelting and refining are combined with quenching, tempering and heat treatment processes, so that the internal structure of the steel is uniform, defects such as white spots are eliminated, the impact resistance of the steel is remarkably improved, and the fatigue life of the steel is remarkably prolonged. Finally, the high-purity and high-strength steel has wide application prospects in the fields with high requirements such as aerospace, military industry and pressure-bearing components, and is particularly suitable for key components needing high strength and high toughness.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy preparation, and in particular to a high-purity and high-strength steel and a method for manufacturing the same. Background Art

[0002] High-strength steel refers to steel with a room temperature tensile strength exceeding 1500MPa and a yield strength greater than 1300MPa. In addition to requiring a tensile strength of more than 1500MPa, this type of steel must also have good plasticity and toughness, minimize notch sensitivity, have high fatigue strength, and exhibit good processability. Therefore, a variety of medium-high alloy ultra-high strength steels have been developed and are now widely used in a number of high-strength and high-demand fields, including but not limited to aircraft landing parts, bulletproof steel plates, missile and artillery shells, aerospace gear shafts, pressure-bearing components, rocket launcher shells, high-end molds, fasteners, etc. These steels exhibit good comprehensive performance under high stress and complex environments, and their application areas are still expanding, showing broad development prospects.

[0003] The development of medium alloy ultra-high strength steel is based on the rational addition of elements such as C, Ni, Cr, Si, V, and Mo to the steel. By optimizing the ratio of these elements, a large amount of martensite structure is formed after quenching and tempering. The pinning effect of carbides in the martensite dislocation structure significantly improves the strength and hardness of the material while maintaining a certain degree of plasticity and toughness. Generally speaking, the total alloying element content of medium alloy ultra-high strength steel is greater than 5%, of which C, Ni, Cr, Mo, V, and Si are the main strengthening elements. Through the scientific design and organizational control of these chemical components, the mechanical properties of medium alloy ultra-high strength steel have been significantly improved.

[0004] For example, there is a medium alloy ultra-high strength steel 45CrNiMoV used for shells in the aviation field, and its chemical composition is shown in Table 1:

[0005] Table 1 Chemical composition (wt%) of alloy ultra-high strength steel 45CrNiMoV

[0006]

[0007] This steel grade is produced by the following process: First, the raw material is melted into a diameter using a vacuum induction furnace. The electrode rod is then remelted into a diameter of The ingot is forged into a product by a fast forging machine, and finally the steel is processed by annealing and polishing. However, this production process has the following significant problems:

[0008] Poor toughness and plasticity: Although 45CrNiMoV steel has high tensile strength, its toughness and plasticity are relatively poor. In practical applications, especially under dynamic loads and impacts, the material is prone to fracture or other damage, which limits its further application in high-load, high-stress environments.

[0009] Gas pollution during the smelting process: The smelting process uses a vacuum induction furnace plus electroslag remelting. During the electroslag remelting process, the content of gas elements such as oxygen, nitrogen and hydrogen increases, which makes it easy for more oxide inclusions to exist in the finished forgings. In particular, the increase in hydrogen content will greatly increase the risk of white spot formation. White spots are microscopic cracks induced by hydrogen, which can easily lead to brittle fracture of steel in subsequent processing or use, greatly reducing the strength and toughness of the material, and may even cause the product to be completely scrapped.

[0010] Uncertainty in the smelting process: Even with high-purity raw materials, the uncertainty in the electroslag remelting process will still lead to a high gas content, which will affect the final mechanical properties of the material. In particular, the content of gases such as hydrogen, oxygen, and nitrogen is difficult to control accurately, which may eventually lead to fluctuations in the strength and toughness of the material. This uncertainty increases the risk in the production process and affects the reliability of the material.

[0011] Therefore, although the existing ultra-high strength steel has been widely used in many fields, its insufficient toughness and plasticity, gas pollution problems in the smelting process, and uncertainty in the smelting process still plague the development of this field. These technical difficulties limit the promotion and use of ultra-high strength steel in higher-demand application scenarios. In order to solve these problems and improve the comprehensive performance of steel, especially to further improve toughness and plasticity while ensuring ultra-high strength, reduce gas content, and eliminate the tendency of white spot defects, it is necessary to improve the smelting process and optimize the material composition. Summary of the invention

[0012] The technical problem to be solved by the present invention is to provide a method for manufacturing high-purity and high-strength steel to solve the problems of poor strength and toughness, poor reliability and gas pollution in the smelting process of steel manufactured by conventional manufacturing methods in the prior art.

[0013] The present invention provides a method for manufacturing high-purity and high-strength steel, comprising the following steps:

[0014] S1: Vacuum induction furnace smelting

[0015] High-purity raw materials are used, smelted in a vacuum induction furnace, and the raw materials are melted and then degassed to obtain electrode rods, and the gas content and the mass percentage of chemical elements are controlled to be: C: 0.44-0.46%, Mn: 0.60-1.00%, Si: 1.65-1.85%, S≤0.002%, P≤0.005%, Ni: 1.20-1.40%, Cr: 1.30-1.50%, Mo: 1.20-1.40%, V: 0.05-0.10%, Al: ≤0.015%, Ti: ≤0.015%, H: ≤0.00005%, O: ≤0.0008%, N: ≤0.0010%, and the balance is Fe and other inevitable impurities;

[0016] S2: Electroslag Remelting

[0017] Electroslag ingots are obtained by electroslag remelting the electrode rods obtained by S1, using a slag system with a slag ratio of fluorite and Al2O3 of 70:30, and adjusting the melting speed to improve the segregation of chemical elements and the purity of steel;

[0018] S3: Electroslag ingot forging vacuum consumable electrode:

[0019] The electroslag ingot obtained in step S2 is subjected to heat treatment and then forged to obtain a vacuum consumable electrode;

[0020] S4: Vacuum consumable remelting

[0021] The vacuum consumable electrode in step S3 is subjected to vacuum consumable remelting to further degas and improve the purity of the steel, and the vacuum degree is controlled to be ≤0.5Pa during the melting process;

[0022] S5: Forging treatment

[0023] The electroslag ingot after the step S4 is forged, and before forging, the temperature is gradually raised to 800° C. and kept at this temperature for ≥1 hour, and then further raised to 1140° C. to 1210° C. and kept at this temperature for ≥2 hours, and then forged in the temperature range of 1000° C. to 850° C., and slowly cooled after forging;

[0024] S6: Heat treatment after calcination

[0025] The forged steel is subjected to post-forging heat treatment, which includes normalizing, tempering, quenching and re-tempering, so as to optimize the mechanical properties and structural uniformity of the steel.

[0026] Compared with the conventional steel smelting process in the prior art, the present invention adopts the triple smelting process of "vacuum induction furnace smelting + electroslag remelting + vacuum consumable remelting", which greatly reduces the gas content in the steel, especially gas impurities such as hydrogen, oxygen and nitrogen, and significantly improves the purity of the steel. At the same time, by optimizing the chemical composition and smelting process parameters, the steel of the present invention has good plasticity and toughness while maintaining high strength. The technical principle of the preparation method in the present invention is to use a vacuum induction furnace to degas the raw materials, effectively reduce the gas impurities in the steel, and further remove residual inclusions and segregation by electroslag remelting. Vacuum consumable remelting further improves the purity of the steel, reduces the number and volume of inclusions, optimizes the microstructure of the steel, and thus improves the mechanical properties of the material. The final technical effect achieved is that through this set of smelting processes, the steel produced has high strength (tensile strength exceeds 1500MPa), high plasticity and high toughness, and its fatigue performance and fracture resistance are significantly improved, which is particularly suitable for high-end fields such as aerospace and military industry.

[0027] In a possible implementation, in step S1, the smelting temperature of the vacuum induction furnace is 1520-1600°C, the vacuum degree during refining is ≤5Pa, the refining temperature is 1530-1570°C, and the refining time is ≥30 minutes.

[0028] Compared with the existing technology, the above technical solution can significantly reduce the content of gas impurities (such as oxygen, nitrogen, hydrogen, etc.) in the molten steel by finely controlling the temperature and vacuum degree of the vacuum induction furnace, thereby reducing the generation of inclusions. Maintaining the refining stage for a sufficiently long time is conducive to further degassing and homogenizing the molten steel, ensuring that the steel has high purity and good mechanical properties in the end.

[0029] In a possible implementation, in step S1, when O≤15ppm, N≤15ppm, and H≤1ppm in the molten steel, Ar≥3000Pa is added, and metallic Mn or electrolytic Mn is started to be added, and the casting temperature of the electrode is 1540-1580°C.

[0030] Compared with the prior art, the above technical solution can further reduce the gas content by adding high-purity inert gas (such as argon) to the molten steel during the smelting process. At the same time, by controlling the casting temperature, it is prevented that the molten steel is not completely cast due to too low a temperature, or that the electrode is cracked due to too high a temperature, thereby ensuring the quality of the electrode.

[0031] In a possible implementation manner, in step S2, the electroslag remelting current is 3KA-19KA, the power is 60kw-800kw, the melting rate is 3.5-10.5kg / min, and slow cooling is performed for ≥24 hours after the electroslag remelting is completed.

[0032] Compared with the existing technology, the above technical scheme can improve the segregation in the steel by accurately controlling the current and melting rate of the electroslag remelting. At the same time, through slow cooling (slow cooling), the accumulation of internal stress in the steel can be effectively reduced to prevent the material from cracking in subsequent processing.

[0033] In a possible implementation, in step S3, the heat treatment includes the following steps:

[0034] Initial heating stage: The initial temperature is controlled below 600°C, and then the temperature is raised to 800°C at a steady rate. The entire heating process lasts for more than 2 hours.

[0035] 800℃ insulation stage: When the temperature reaches 800℃, keep it at this temperature for at least 1 hour;

[0036] Further heating stage: After keeping at 800℃, continue to heat up until the temperature reaches between 1140℃ and 1210℃. The heating time should be no less than 2 hours to ensure gradual heating to avoid thermal stress or uneven structure of the material.

[0037] High temperature insulation stage: maintain the temperature within the temperature range of 1140℃ to 1210℃ for at least 2 hours.

[0038] Compared with the existing technology, the above technical solution can ensure that all parts of the material are heated evenly during the heating process by controlling the temperature rise and fall and the insulation time in stages, avoiding the problems of thermal stress concentration and uneven structure, and ensuring that the forged steel has good toughness and grain size control.

[0039] In a possible implementation manner, in step S3, the forging includes the following steps:

[0040] Re-burning stage: the electroslag ingot is heated to 1120-1160°C to ensure the thermoplasticity of the material during the forging process;

[0041] This temperature range enables the material to maintain good plasticity during forging and reduces the risk of cracks and other defects during processing. At the same time, during the re-burning process, the chemical composition of the material is homogenized, further improving the machinability of the steel.

[0042] Forging stage: Forging is carried out within the temperature range of starting forging temperature ≥ 1000℃ and final forging temperature ≥ 850℃ to ensure the best formability and grain size control of the material;

[0043] This temperature range ensures that the material is formed within the optimal thermoplastic range and ensures that the material has the best grain size control to avoid grain growth. By gradually reducing the forging temperature, the toughness of the steel can be effectively improved while maintaining its high strength.

[0044] Slow cooling stage: After forging is completed, slow cooling treatment is carried out. The slow cooling method is hood cooling, sand cooling, pit cooling or furnace cooling. The slow cooling time is not less than 24 hours.

[0045] By slow cooling, the internal stress in the steel is released, avoiding cracks or uneven structure caused by rapid cooling. This step has a significant effect on improving the material's fracture resistance and fatigue strength.

[0046] Polishing treatment: After slow cooling, the forgings are polished to ensure that they meet the electrode size requirements matched by the vacuum consumable crystallizer. Polishing treatment can remove the oxide layer and other impurities on the surface of the forgings, ensure that the electrode has good surface quality, and provide an ideal electrode shape for subsequent vacuum consumable remelting.

[0047] Compared with the prior art, the above technical scheme can significantly improve the plasticity and microstructure of steel during the forging process. The re-burning stage reduces the generation of thermal stress in the material by uniformly heating and controlling the temperature of the material, and controls the temperature gradient in the forging stage to ensure the grain refinement of the steel. Slow cooling (slow cooling) after forging further reduces the accumulation of internal stress, reduces the risk of thermal cracking during the cooling process, and maintains the good structural uniformity of the steel. The technical principle is to ensure that the thermoplasticity of the material is fully utilized by accurately controlling the temperature during the forging process, especially operating in the high-temperature plastic region. At the same time, the slow cooling treatment effectively releases the residual stress in the material, making the microstructure of the steel more stable, and the grains are fine and uniform, thereby improving the mechanical properties and service life of the material. The final technical effect obtained is: the present invention not only ensures the formability and toughness of the steel during the forging process through this forging process step, but also the grain size of the steel is significantly refined after forging, and the material exhibits high strength, high toughness and good fatigue resistance, which is suitable for aerospace and military fields with demanding mechanical properties.

[0048] In a possible implementation, in step S4, the melting rate during the vacuum consumable remelting process is 2.5-6.5 kg / min, and helium cooling is used to prevent segregation of chemical composition and ingot shape.

[0049] Compared with the existing technology, the above technical scheme can improve the segregation in the steel by accurately controlling the current and melting rate of the electroslag remelting. At the same time, through slow cooling (slow cooling), the accumulation of internal stress in the steel can be effectively reduced to prevent the material from cracking in subsequent processing.

[0050] In a possible implementation manner, in step S5, the slow cooling after forging is performed by hood cooling, sand cooling, pit cooling or furnace cooling, and the slow cooling time is not less than 24 hours.

[0051] Compared with the existing technology, the above technical solution can reduce the stress generated by the material during the rapid cooling process through a slow cooling method, ensure that the internal structure of the material is more stable, avoid cracks or other defects in subsequent processing, and improve the final mechanical properties of the material.

[0052] In a possible implementation, in step S6, the post-calcination heat treatment includes the following steps:

[0053] Normalizing: temperature is 920±10℃, insulation is 2.5mm / min+60min, cooling method is air cooling;

[0054] Tempering: temperature is 680±10℃, holding time is 120~240 minutes, cooling method is air cooling;

[0055] Quenching: temperature is 890±10℃, holding time is 60 minutes, cooling method is oil cooling;

[0056] Re-tempering: temperature is 510-550℃, holding time is 120 minutes, cooling method is air cooling.

[0057] Compared with the existing technology, the above technical solution can ensure that all parts of the material are heated evenly during the heating process by controlling the temperature rise and fall and the insulation time in stages, avoiding the problems of thermal stress concentration and uneven structure, and ensuring that the forged steel has good toughness and grain size control.

[0058] Another technical problem to be solved by the present invention is to provide a high-purity and high-strength steel to solve the contradiction between high strength and high toughness of conventional steels in the prior art.

[0059] In order to solve the above technical problems, the present invention also provides a high-purity and high-strength steel, which is prepared by the manufacturing method, and the composition of the high-purity and high-strength steel includes: C: 0.44-0.46%; Mn: 0.60-1.00%; Si: 1.65-1.85%; S≤0.002%; P≤0.005%; Ni: 1.20-1.40%; Cr: 1.30-1.50%; Mo: 1.20-1.40%; V: 0.05-0.10%; Al: ≤0.015%; Ti: ≤0.015%; H: ≤0.00005%; O: ≤0.0008%; N: ≤0.0010%; the balance is Fe and other inevitable impurities.

[0060] The technical effect of the above-mentioned high-purity and high-strength steel is that, through the composition ratio of the above-mentioned high-purity and high-strength steel of the present invention, the obtained steel has excellent mechanical properties, low impurity element content and high purity, and can be widely used in aerospace, military and high-end equipment and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is the effect of Si content on cementite formation temperature during tempering;

[0062] Figure 2 This is the effect of Si content on tempering hardness;

[0063] Figure 3 This is the heating curve of the electrode forging for electroslag ingot;

[0064] Figure 4 This is a low-magnification structure diagram of the steel finished material prepared in Example 1, and the left and right diagrams correspond to the head and tail of the steel finished material, respectively;

[0065] Figure 5 This is a grain size diagram of the steel finished material prepared in Example 1. The left and right figures correspond to the head and tail of the steel finished material, respectively. DETAILED DESCRIPTION

[0066] First, those skilled in the art should understand that these implementations are only used to explain the technical principles of the embodiments of the present application, and are not intended to limit the protection scope of the embodiments of the present application. Those skilled in the art can make adjustments to them as needed to adapt to specific application scenarios.

[0067] The present invention provides a method for manufacturing high-purity and high-strength steel, comprising the following steps:

[0068] S1: Vacuum induction furnace smelting

[0069] High-purity raw materials are used, smelted in a vacuum induction furnace, and the raw materials are melted and then degassed to obtain electrode rods, and the gas content and the mass percentage of chemical elements are controlled to be: C: 0.44-0.46%, Mn: 0.60-1.00%, Si: 1.65-1.85%, S≤0.002%, P≤0.005%, Ni: 1.20-1.40%, Cr: 1.30-1.50%, Mo: 1.20-1.40%, V: 0.05-0.10%, Al: ≤0.015%, Ti: ≤0.015%, H: ≤0.00005%, O: ≤0.0008%, N: ≤0.0010%, and the balance is Fe and other inevitable impurities;

[0070] S2: Electroslag Remelting

[0071] Electroslag ingots are obtained by electroslag remelting the electrode rods obtained by S1, using a slag system with a slag ratio of fluorite and Al2O3 of 70:30, and adjusting the melting speed to improve the segregation of chemical elements and the purity of steel;

[0072] S3: Electroslag ingot forging vacuum consumable electrode:

[0073] The electroslag ingot obtained in step S2 is subjected to heat treatment and then forged to obtain a vacuum consumable electrode;

[0074] S4: Vacuum consumable remelting

[0075] The vacuum consumable electrode in step S3 is subjected to vacuum consumable remelting to further degas and improve the purity of the steel, and the vacuum degree is controlled to be ≤0.5Pa during the melting process;

[0076] S5: Forging treatment

[0077] The electroslag ingot after the step S4 is forged, and before forging, the temperature is gradually raised to 800° C. and kept at this temperature for ≥1 hour, and then further raised to 1140° C. to 1210° C. and kept at this temperature for ≥2 hours, and then forged in the temperature range of 1000° C. to 850° C., and slowly cooled after forging;

[0078] S6: Heat treatment after calcination

[0079] The forged steel is subjected to post-forging heat treatment, which includes normalizing, tempering, quenching and re-tempering, so as to optimize the mechanical properties and structural uniformity of the steel.

[0080] As a preferred solution, in step S1, the smelting temperature of the vacuum induction furnace is 1520-1600°C, the vacuum degree during refining is ≤5Pa, the refining temperature is 1530-1570°C, and the refining time is ≥30 minutes.

[0081] As a preferred solution, in step S1, when O≤15ppm, N≤15ppm, and H≤1ppm in the molten steel, Ar≥3000Pa is added, and metallic Mn or electrolytic Mn is started to be added, and the casting temperature of the electrode is 1540-1580°C.

[0082] As a preferred solution, in step S2, the electroslag remelting current is 3KA-19KA, the power is 60kw-800kw; the melting rate is 3.5-10.5kg / min, and slow cooling is performed for ≥24 hours after the electroslag remelting is completed.

[0083] As a preferred solution, in step S3, the heat treatment includes the following steps:

[0084] Initial heating stage: The initial temperature is controlled below 600°C, and then the temperature is raised to 800°C at a steady rate. The entire heating process lasts for more than 2 hours.

[0085] 800℃ insulation stage: When the temperature reaches 800℃, keep it at this temperature for at least 1 hour;

[0086] Further heating stage: After keeping at 800℃, continue to heat up until the temperature reaches between 1140℃ and 1210℃. The heating time should be no less than 2 hours to ensure gradual heating to avoid thermal stress or uneven structure of the material.

[0087] High temperature insulation stage: maintain the temperature within the temperature range of 1140℃ to 1210℃ for at least 2 hours.

[0088] As a preferred solution, in step S3, the forging includes the following steps:

[0089] Re-burning stage: the electroslag ingot is heated to 1120-1160°C to ensure the thermoplasticity of the material during the forging process;

[0090] Forging stage: Forging is carried out within the temperature range of starting forging temperature ≥ 1000℃ and final forging temperature ≥ 850℃ to ensure the best formability and grain size control of the material;

[0091] Slow cooling stage: After forging is completed, slow cooling treatment is carried out. The slow cooling method is hood cooling, sand cooling, pit cooling or furnace cooling. The slow cooling time is not less than 24 hours.

[0092] Polishing treatment: After slow cooling, the forgings are polished to ensure that they meet the electrode size requirements matched by the vacuum consumable crystallizer.

[0093] As a preferred solution, in the step S4, the melting rate during the vacuum consumable remelting process is 2.5-6.5 kg / min, and helium cooling is used to prevent segregation of chemical composition and ingot shape.

[0094] As a preferred solution, in step S5, the slow cooling after forging adopts hood cooling, sand cooling, pit cooling or furnace cooling, and the slow cooling time is not less than 24 hours.

[0095] As a preferred solution, in step S6, the post-calcination heat treatment includes the following steps:

[0096] Normalizing: temperature is 920±10℃, insulation is 2.5mm / min+60min, cooling method is air cooling;

[0097] Tempering: temperature is 680±10℃, holding time is 120~240 minutes, cooling method is air cooling;

[0098] Quenching: temperature is 890±10℃, holding time is 60 minutes, cooling method is oil cooling;

[0099] Re-tempering: temperature is 510-550℃, holding time is 120 minutes, cooling method is air cooling.

[0100] The present invention also provides a high-purity and high-strength steel, which is prepared by the manufacturing method, and the components of the high-purity and high-strength steel include: C: 0.44-0.46%; Mn: 0.60-1.00%; Si: 1.65-1.85%; S≤0.002%; P≤0.005%; Ni: 1.20-1.40%; Cr: 1.30-1.50%; Mo: 1.20-1.40%; V: 0.05-0.10%; Al: ≤0.015%; Ti: ≤0.015%; H: ≤0.00005%; O: ≤0.0008%; N: ≤0.0010%; the remainder is Fe and other inevitable impurities.

[0101] The following is an explanation of the analysis of the elements in the high-purity and high-strength steel of the present invention, and further explains the composition configuration and reasons for the configuration of the high-purity and high-strength steel of the present invention:

[0102] As an ultra-high purity and ultra-high strength steel, extremely low residual elements and the interaction between alloy elements and the matching of addition amounts are very important.

[0103] The role of carbon in this steel is reflected in the following aspects: ① During austenitization, it dissolves in the martensite matrix and plays a role in solid solution strengthening, ensuring that the steel has ultra-high strength. Studies have shown that after low-temperature tempering of low-carbon steel and medium-carbon steel, when the solid solution C content in the martensite is in the range of 0.2%-0.5%, the tensile strength and the mass fraction of carbon atoms maintain a linear relationship: tensile strength (MPa) = 2940*C+820. While the interstitial solid solution strengthening of C atoms significantly improves the strength, it also harms the toughness and plasticity of the material. Tempering treatment must be performed to precipitate a part of carbon atoms in the supersaturated martensite, which significantly improves the toughness and plasticity of the material while appropriately reducing the solid solution strengthening effect. ② Fine ε-carbides are formed during tempering, producing a precipitation strengthening effect.

[0104] The role of silicon in Ben Steel is reflected in the following aspects: Si is an element that reduces the austenite phase area, but it increases the stability of supercooled austenite. At higher temperatures, the activity of carbon atoms in austenite is increased, promoting the diffusion of carbon in the austenite phase area, while at lower temperatures, Si increases the binding force between carbon atoms and iron atoms, increasing the diffusion activation energy of carbon in austenite, thereby inhibiting the diffusion of carbon in the austenite phase area. At the same time, Si has a strong inhibitory effect on the precipitation of cementite. There are currently two views: one is that Si diffuses into ε-carbide, improving its stability, making it difficult to form cementite; the other view is that Si is insoluble in cementite, and the growing cementite sheets will push silicon atoms outward, while the diffusion of silicon at low temperatures is quite difficult, thus forming a kinetic barrier that hinders the further growth of cementite. Regardless of the mechanism, the result is that Si pushes the first type of temper brittleness to the high temperature direction, thereby improving its plasticity, toughness and notch sensitivity. The effect of Si content on the cementite formation temperature during tempering can be found in. Figure 1 , Figure 2 As shown, when the Si content is below 3% (atomic percentage), the cementite formation temperature increases significantly with the increase of the Si content.

[0105] The role of nickel in Benxi steel is reflected in the following aspects: Ni is an element that expands the austenite phase region. During the cooling process after austenitization, it strongly inhibits the transformation of austenite to pearlite and bainite, and improves the hardenability of martensite; Ni reduces the temperature of the transformation of supercooled austenite to martensite, increases the content of residual austenite, and is beneficial to toughness; Ni can increase the stacking fault energy of the steel matrix, making it easier for screw dislocations to produce cross slip, thereby improving toughness.

[0106] The role of manganese in Benxi steel is reflected in the following aspects: Mn, like Ni, is an element that expands the austenite phase region. Mn reduces the temperature at which supercooled austenite transforms to martensite, increases the content of retained austenite, and is beneficial to toughness.

[0107] The role of vanadium in this steel is reflected in the following aspects: V is a strong carbide-forming element, forming a stable VC phase, organizing the growth of austenite grains during quenching and heating, thereby refining the martensite structure, improving the toughness of tempered martensite while increasing the strength, and increasing the cleavage fracture stress.

[0108] The role of chromium and molybdenum in this steel is reflected in the following aspects: Cr and Mo delay the transformation of supercooled austenite to pearlite during quenching and cooling, thus improving the hardenability of steel; during tempering, they enter carbides to form alloy carbides, thus increasing the stability of carbides and improving the tempering resistance of steel. At the same time, Cr can also improve the corrosion resistance of steel.

[0109] The role of aluminum and titanium in this steel is reflected in the following aspects: Al and Ti are easy to combine with N in the steel to form AlN and TiN, which increases the number of E-type non-metallic inclusions and leads to a decrease in the strength and toughness of the steel. In order to achieve the theoretical matrix strength of this steel and improve the purity of the steel, the content of Al and Ti must be strictly controlled as low as possible.

[0110] The role of phosphorus and sulfur in Ben Steel is reflected in the following aspects: phosphorus will reduce the cold bending performance of steel and deteriorate weldability. At the same time, phosphorus will improve the strength, hardness, wear resistance and corrosion resistance of steel, but these positive effects are usually offset by the cold brittleness caused by it. Phosphorus dissolves in ferrite. Due to its large atomic diameter, it will cause ferrite lattice distortion, thereby significantly reducing the plasticity and toughness of steel, especially in low temperature environment. This reduction is particularly obvious. In addition, phosphorus is easy to segregate during the crystallization process of steel and is difficult to eliminate by heat treatment, which increases the risk of cold brittleness of steel. Hazards of sulfur: Sulfur is easy to cause brittle cracking during the hot working of steel, a phenomenon called hot brittleness. The presence of sulfur will also reduce the impact toughness, fatigue strength, weldability and corrosion resistance of steel. Even if sulfur exists in trace amounts, it is harmful to steel, so the sulfur content needs to be strictly controlled. Sulfur will form brittle compounds in the weld, resulting in brittle welded joints and even cracking during welding. Sulfur also reduces the cold forming properties of steel and affects its plastic deformation capacity, making it easy for cracks and fractures to occur during bending, stamping and other processing processes. The presence of phosphorus and sulfur in steel will have a negative impact on its physical properties and processing properties, so its content in steel needs to be strictly controlled.

[0111] To summarize, harmful elements P, S, Al, Ti and gases H, O, N, etc. are regarded as impurity elements and are kept as low as possible. The raw materials are selected from intermediate alloys and metal materials of Bensteel or similar steels. After vacuum induction, electroslag remelting and vacuum consumable remelting, high-purity medium-alloy ultra-high-strength steel is achieved.

[0112] More specifically, the above steps S1-S6 also include the following detailed steps:

[0113] In step S1: (1) Requirements for raw materials of vacuum induction furnace:

[0114] ① Add high-purity pure iron, the pure iron requires S ≤ 0.002%, P ≤ 0.005% or refined steel smelted by electric furnace + LF + VOD + VD, the refined steel requires the residual elements S, P, Al are ≤ 0.001%.

[0115] ② Add high-purity metal molybdenum, metal nickel, metal chromium, metal vanadium, metal manganese or electrolytic manganese; check the surface of the raw materials before loading the furnace, and no rust, oil stains or oxidation are allowed. If there is any rust, oil stains or oxidation, it must be cleaned.

[0116] (2) Vacuum induction furnace smelting process:

[0117] ① Slow and low-temperature melting of materials during the melting period, the temperature after full melting is 1520-1600℃; vacuum induction furnace smelting can improve the degassing effect by increasing the molten steel level, so the use of slow and low-power melting of materials can achieve a good degassing effect.

[0118] ② The vacuum degree during the refining period is required to be ≤5Pa, the holding time during the refining period is ≥30min, and the temperature during the refining period is 1530~1570℃; if the temperature is too low, the refining effect will not be achieved, and if the temperature is too high, the Al and Ti in the crucible will be reduced to the molten steel.

[0119] ③ After the refining period, when the gas meets the requirements, that is, O≤15ppm, N≤15ppm, H≤1ppm, fill Ar≥3000Pa and start adding metallic Mn or electrolytic Mn.

[0120] ④ Pouring temperature 1540~1580℃. If the pouring temperature is too low, the molten steel solidification pouring cannot be completed; if the pouring temperature is too high, the electrode is easy to crack.

[0121] ⑤ The electrode requires slow cooling (including sand cooling, hood cooling, pit cooling, furnace slow cooling and other cooling methods) and then polishing and flattening before electroslag remelting. Effectively reduce the content of chemical element S in steel, and improve non-metallic inclusions to ensure the purity of steel, in preparation for improving the strength and toughness of steel.

[0122] In step S2: (3) Preparation for electroslag remelting:

[0123] ① Each electrode corresponds to a steel ingot, the shrinkage hole is required to face downwards and the shrinkage hole end should be cut flat.

[0124] ② Slag ratio: fluorite: Al2O3 = 70:30; slag weight 36-230kg (select the appropriate slag weight depending on the type of electroslag ingot).

[0125] ③ Slag baking temperature: 600-1000℃; single hopper baking time: 3-10h. When there are other slags in the heating furnace, the baking time is required to be ≥5h.

[0126] ④Arc starter: steel bell or carbon steel conductive block.

[0127] (4) Electroslag remelting smelting process parameters (argon gas protection electroslag furnace)

[0128] ① Arc starting stage: current and power control, different parameters are used for different ingot types. The parameter range given below is used for 1 ton steel ingot to 6 ton steel ingot. The parameters are as follows:

[0129] Current: 3KA-19KA; Power 60kw-800kw; Arc starting time ≥30min.

[0130] ② Melting stage: The melting process is controlled by the melting rate. Different melting rates are specified according to different ingot types. The melting period is based on the melting rate. Keeping the melting rate as low as possible can improve the segregation of chemical elements. Melting rate: 3.5-10.5kg / min.

[0131] ③Hot sealing stage: Hot sealing is controlled by melting rate. The starting weight of hot sealing is different according to different ingot types. In order to achieve shrinkage compensation effect, hot sealing requires sufficient weight support. The starting weight of hot sealing is 100kg-550kg; the melting rate gradually decreases to 10.5-2.0kg / min.

[0132] ④ After the steel ingot is demoulded, it is slowly cooled (including hood cooling, sand cooling, pit cooling, and furnace cooling) for ≥ 24h; or it can be sent for forging in hot metal.

[0133] In step S3: (5) Electroslag ingot forging vacuum consumable electrode process

[0134] ① Reference for the heating curve of electroslag ingot forging Figure 3 As shown:

[0135] ② The re-firing temperature is 1120~1160℃, the forging temperature is ≥1000℃, and the final temperature is ≥850℃. Within this temperature range, the steel can be formed in the best thermoplastic zone and the grain size can be effectively controlled.

[0136] ③ Allows forging the required electrode size directly in one fire.

[0137] ④ Slow cooling after forging (including hood cooling, sand cooling, pit cooling, and furnace cooling) ≥ 24h.

[0138] ⑤ After slow cooling, polishing is carried out according to the electrode size matched by the vacuum consumable crystallizer.

[0139] In step S4: (6) Vacuum consumable furnace smelting process:

[0140] ① The vacuum degree of the vacuum consumable furnace is required to be ≤0.5Pa to achieve remelting and degassing.

[0141] ② Vacuum consumable furnace smelting specifies different melting rates according to different ingot types. The melting period is based on the melting rate. Keeping the melting rate as low as possible can improve the segregation of chemical elements.

[0142] Parameters: The current in the initial stage is 4.0~11.5 (KA), the melting speed in the melting stage is 2.5~6.5 kg / min, and the shrinkage stage is controlled at 2.5~6.5 (KA), which can effectively prevent the occurrence of segregation.

[0143] ③ Vacuum consumable furnace smelting requires turning on helium cooling to accelerate cooling, melting and condensing at the same time, and the use of droplet pulse technology is beneficial to improving chemical composition segregation and ingot shape segregation, and improving the purity of the steel ingot.

[0144] ④ After the ingot is remelted in a vacuum consumable furnace, it needs to be slowly cooled (including hood cooling, sand cooling, pit cooling, and furnace cooling) for ≥24h and the surface of the ingot is polished or turned.

[0145] In step S5: (6) Forging: The vacuum consumable steel ingot is heated to 1220°C and kept at this temperature for more than 25 hours to diffuse the carbides. After diffusion, the ingot is taken out of the furnace for forging, with the starting forging temperature of 1180-1200°C and the final forging temperature of 850-900°C. Within this temperature range, the steel can be formed in the best thermoplastic zone, thereby avoiding forging cracking.

[0146] In step S6: (7) normalizing at 920±10°C, keeping warm at 2.5mm / min+60min, and air cooling.

[0147] (8) Tempering is carried out at 680±10℃, at 2.5mm / min+120min~240min

[0148] Keep warm, air cool. This tempering is to remove the structural stress in the steel.

[0149] (9) Quenching should be carried out at 890±10℃, keeping warm at 2.5mm / min+60min, and oil cooling.

[0150] (10) Tempering again at 510-550℃, 2.5mm / min+120min holding, air cooling. This tempering is a heat treatment step set to achieve the best mechanical properties.

[0151] The following provides specific embodiments in combination with the above data ranges to further explain the present invention:

[0152] Embodiment 1:

[0153] Embodiment 1 provides a high-purity and high-strength steel and a method for manufacturing the same, wherein the high-purity and high-strength steel comprises the following components: C: 0.45%; Mn: 0.80%; Si: 1.75%; S≤0.002%; P≤0.005%; Ni: 1.30%; Cr: 1.40%; Mo: 1.30%; V: 0.075%; Al: ≤0.015%; Ti: ≤0.015%; H: ≤0.00005%; O: ≤0.0008%; N: ≤0.0010%; the remainder is Fe and other unavoidable impurities.

[0154] The manufacturing method comprises the following steps:

[0155] S1: Vacuum induction furnace smelting

[0156] High-purity raw materials are used for smelting in a vacuum induction furnace. The raw materials are melted and then degassed to obtain electrode rods. The gas content and the mass percentage of chemical elements are controlled as follows: C: 0.45%; Mn: 0.80%; Si: 1.75%; S≤0.002%; P≤0.005%; Ni: 1.30%; Cr: 1.40%; Mo: 1.30%; V: 0.075%; Al: ≤0.015%; Ti: ≤0.015%; H: ≤0.00 005%; O: ≤0.0008%; N: ≤0.0010%; the balance is Fe and other inevitable impurities; the smelting temperature of the vacuum induction furnace is 1560℃, when O≤15ppm, N≤15ppm, H≤1ppm in the molten steel, fill with Ar≥3000Pa, and start adding metal Mn or electrolytic Mn, and the casting temperature of the electrode is 1560℃, the vacuum degree during refining is ≤5Pa, the refining period temperature is 1550℃, and the refining time is ≥30 minutes.

[0157] S2: Electroslag Remelting

[0158] Electroslag ingots are obtained by electroslag remelting the electrode rods obtained by S1, using a slag system with a slag ratio of fluorite and Al2O3 of 70:30, and adjusting the melting speed to improve the segregation of chemical elements and the purity of steel;

[0159] The electroslag remelting current is 3KA-19KA, the power is 60kw-800kw; the melting speed is 7kg / min, and slow cooling is performed for ≥24 hours after the electroslag remelting is completed.

[0160] S3: Electroslag ingot forging vacuum consumable electrode:

[0161] The electroslag ingot obtained in step S2 is subjected to heat treatment and then forged to obtain a vacuum consumable electrode;

[0162] In step S3, the heat treatment comprises the following steps:

[0163] Initial heating stage: The initial temperature is controlled below 600°C, and then the temperature is raised to 800°C at a steady rate. The entire heating process lasts for more than 2 hours.

[0164] 800℃ insulation stage: When the temperature reaches 800℃, keep it at this temperature for at least 1 hour;

[0165] Further heating stage: After keeping at 800℃, continue to heat up until the temperature reaches 1175℃. The heating time should be no less than 2 hours to ensure gradual heating to avoid thermal stress or uneven structure of the material.

[0166] High temperature insulation stage: maintain the temperature at 1175℃ for at least 2 hours.

[0167] The forging comprises the following steps:

[0168] Re-burning stage: the electroslag ingot is heated to 1140°C to ensure the thermoplasticity of the material during the forging process;

[0169] Forging stage: Forging is carried out within the temperature range of starting forging temperature ≥ 1000℃ and final forging temperature ≥ 850℃ to ensure the best formability and grain size control of the material;

[0170] Slow cooling stage: After forging is completed, slow cooling treatment is carried out. The slow cooling method is hood cooling, sand cooling, pit cooling or furnace cooling. The slow cooling time is not less than 24 hours.

[0171] Polishing treatment: After slow cooling, the forgings are polished to ensure that they meet the electrode size requirements matched by the vacuum consumable crystallizer.

[0172] S4: Vacuum consumable remelting

[0173] The vacuum consumable electrode in step S3 is subjected to vacuum consumable remelting to further degas and improve the purity of the steel, and the vacuum degree is controlled to be ≤0.5Pa during the melting process;

[0174] The melting rate during the vacuum consumable remelting process is 4.5 kg / min, and helium cooling is used to prevent segregation of chemical composition and ingot shape.

[0175] S5: Forging treatment

[0176] The electroslag ingot treated in step S4 is forged, and before forging, the temperature is gradually increased to 800°C and kept for ≥1 hour, and then further increased to 11750°C and kept for ≥2 hours, and then forged at 925°C, and slowly cooled after forging; the slow cooling after forging adopts hood cooling, sand cooling, pit cooling or furnace cooling, and the slow cooling time is not less than 24 hours.

[0177] S6: Heat treatment after calcination

[0178] The forged steel is subjected to post-forging heat treatment, which includes normalizing, tempering, quenching and re-tempering, so as to optimize the mechanical properties and structural uniformity of the steel.

[0179] The post-calcination heat treatment comprises the following steps:

[0180] Normalizing: temperature is 920℃, insulation is 2.5mm / min+60min, cooling method is air cooling;

[0181] Tempering: temperature is 680℃, holding time is 180 minutes, cooling method is air cooling;

[0182] Quenching: temperature is 890℃, holding time is 60 minutes, cooling method is oil cooling;

[0183] Re-tempering: temperature is 530℃, holding time is 120 minutes, cooling method is air cooling.

[0184] Embodiment 2:

[0185] Embodiment 2 provides a high-purity and high-strength steel and a method for manufacturing the same, wherein the high-purity and high-strength steel comprises the following components: C: 0.44%; Mn: 0.60%; Si: 1.65%; S≤0.002%; P≤0.005%; Ni: 1.20%; Cr: 1.30%; Mo: 1.20%; V: 0.05%; Al: ≤0.015%; Ti: ≤0.015%; H: ≤0.00005%; O: ≤0.0008%; N: ≤0.0010%; the remainder is Fe and other unavoidable impurities.

[0186] The manufacturing method comprises the following steps:

[0187] S1: Vacuum induction furnace smelting

[0188] High-purity raw materials are used, smelted in a vacuum induction furnace, and the raw materials are melted and degassed to obtain electrode rods. The gas content and the mass percentage of chemical elements are controlled as follows: C: 0.44%; Mn: 0.60%; Si: 1.65%; S≤0.002%; P≤0.005%; Ni: 1.20%; Cr: 1.30%; Mo: 1.20%; V: 0.05%; Al: ≤0.015%; Ti: ≤0.015%; H: ≤0.000 05%; O: ≤0.0008%; N: ≤0.0010%; the balance is Fe and other inevitable impurities; the smelting temperature of the vacuum induction furnace is 1520℃, when O≤15ppm, N≤15ppm, H≤1ppm in the molten steel, fill with Ar≥3000Pa, and start adding metal Mn or electrolytic Mn, and the casting temperature of the electrode is 1540℃, the vacuum degree during refining is ≤5Pa, the refining period temperature is 1530℃, and the refining time is ≥30 minutes.

[0189] S2: Electroslag Remelting

[0190] Electroslag ingots are obtained by electroslag remelting the electrode rods obtained by S1, using a slag system with a slag ratio of fluorite and Al2O3 of 70:30, and adjusting the melting speed to improve the segregation of chemical elements and the purity of steel;

[0191] The electroslag remelting current is 3KA-19KA, the power is 60kw-800kw; the melting speed is 3.5kg / min, and slow cooling is performed for ≥24 hours after the electroslag remelting is completed.

[0192] S3: Electroslag ingot forging vacuum consumable electrode:

[0193] The electroslag ingot obtained in step S2 is subjected to heat treatment and then forged to obtain a vacuum consumable electrode;

[0194] In step S3, the heat treatment comprises the following steps:

[0195] Initial heating stage: The initial temperature is controlled below 600°C, and then the temperature is raised to 800°C at a steady rate. The entire heating process lasts for more than 2 hours.

[0196] 800℃ insulation stage: When the temperature reaches 800℃, keep it at this temperature for at least 1 hour;

[0197] Further heating stage: After keeping at 800℃, continue to heat up until the temperature reaches 1140℃. The heating time should be no less than 2 hours to ensure gradual heating to avoid thermal stress or uneven structure of the material.

[0198] High temperature insulation stage: maintain the temperature at 1140℃ for at least 2 hours.

[0199] The forging comprises the following steps:

[0200] Re-burning stage: the electroslag ingot is heated to 1120°C to ensure the thermoplasticity of the material during the forging process;

[0201] Forging stage: Forging is carried out within the temperature range of starting forging temperature ≥ 1000℃ and final forging temperature ≥ 850℃ to ensure the best formability and grain size control of the material;

[0202] Slow cooling stage: After forging is completed, slow cooling treatment is carried out. The slow cooling method is hood cooling, sand cooling, pit cooling or furnace cooling. The slow cooling time is not less than 24 hours.

[0203] Polishing treatment: After slow cooling, the forgings are polished to ensure that they meet the electrode size requirements matched by the vacuum consumable crystallizer.

[0204] S4: Vacuum consumable remelting

[0205] The vacuum consumable electrode in step S3 is subjected to vacuum consumable remelting to further degas and improve the purity of the steel, and the vacuum degree is controlled to be ≤0.5Pa during the melting process;

[0206] The melting rate during the vacuum consumable remelting process is 2.5 kg / min, and helium cooling is used to prevent segregation of chemical composition and ingot shape.

[0207] S5: Forging treatment

[0208] The electroslag ingot treated in step S4 is forged, and before forging, the temperature is gradually increased to 800°C and kept for ≥1 hour, and then further increased to 1140°C and kept for ≥2 hours, and then forged at 1000°C, and slowly cooled after forging; the slow cooling after forging adopts hood cooling, sand cooling, pit cooling or furnace cooling, and the slow cooling time is not less than 24 hours.

[0209] S6: Heat treatment after calcination

[0210] The forged steel is subjected to post-forging heat treatment, which includes normalizing, tempering, quenching and re-tempering, so as to optimize the mechanical properties and structural uniformity of the steel.

[0211] The post-calcination heat treatment comprises the following steps:

[0212] Normalizing: temperature is 910℃, insulation is 2.5mm / min+60min, cooling method is air cooling;

[0213] Tempering: temperature is 670℃, holding time is 120 minutes, cooling method is air cooling;

[0214] Quenching: temperature is 880℃, holding time is 60 minutes, cooling method is oil cooling;

[0215] Re-tempering: temperature is 510℃, holding time is 120 minutes, cooling method is air cooling.

[0216] Embodiment 3:

[0217] Embodiment 3 provides a high-purity and high-strength steel and a method for manufacturing the same, wherein the high-purity and high-strength steel comprises the following components: C: 0.46%; Mn: 1.00%; Si: 1.85%; S≤0.002%; P≤0.005%; Ni: 1.40%; Cr: 1.50%; Mo: 1.40%; V: 0.10%; Al: ≤0.015%; Ti: ≤0.015%; H: ≤0.00005%; O: ≤0.0008%; N: ≤0.0010%; the remainder is Fe and other unavoidable impurities.

[0218] The manufacturing method comprises the following steps:

[0219] S1: Vacuum induction furnace smelting

[0220] High-purity raw materials are used, smelted in a vacuum induction furnace, and the raw materials are melted and degassed to obtain electrode rods. The gas content and the mass percentage of chemical elements are controlled as follows: C: 0.46%; Mn: 1.00%; Si: 1.85%; S≤0.002%; P≤0.005%; Ni: 1.40%; Cr: 1.50%; Mo: 1.40%; V: 0.10%; Al: ≤0.015%; Ti: ≤0.015%; H: ≤0.000 05%; O: ≤0.0008%; N: ≤0.0010%; the balance is Fe and other inevitable impurities; the smelting temperature of the vacuum induction furnace is 1600℃, when O≤15ppm, N≤15ppm, H≤1ppm in the molten steel, fill with Ar≥3000Pa, and start adding metal Mn or electrolytic Mn, and the casting temperature of the electrode is 1580℃, the vacuum degree during refining is ≤5Pa, the refining period temperature is 1570℃, and the refining time is ≥30 minutes.

[0221] S2: Electroslag Remelting

[0222] Electroslag ingots are obtained by electroslag remelting the electrode rods obtained by S1, using a slag system with a slag ratio of fluorite and Al2O3 of 70:30, and adjusting the melting speed to improve the segregation of chemical elements and the purity of steel;

[0223] The electroslag remelting current is 3KA-19KA, the power is 60kw-800kw; the melting speed is 10.5kg / min, and slow cooling is performed for ≥24 hours after the electroslag remelting is completed.

[0224] S3: Electroslag ingot forging vacuum consumable electrode:

[0225] The electroslag ingot obtained in step S2 is subjected to heat treatment and then forged to obtain a vacuum consumable electrode;

[0226] In step S3, the heat treatment comprises the following steps:

[0227] Initial heating stage: The initial temperature is controlled below 600°C, and then the temperature is raised to 800°C at a steady rate. The entire heating process lasts for more than 2 hours.

[0228] 800℃ insulation stage: When the temperature reaches 800℃, keep it at this temperature for at least 1 hour;

[0229] Further heating stage: After keeping at 800℃, continue to heat up until the temperature reaches 1210℃. The heating time should be no less than 2 hours to ensure gradual heating to avoid thermal stress or uneven structure of the material.

[0230] High temperature insulation stage: maintain the temperature at 1210℃ for at least 2 hours.

[0231] The forging comprises the following steps:

[0232] Re-burning stage: The electroslag ingot is heated to 1160°C to ensure the thermoplasticity of the material during the forging process;

[0233] Forging stage: Forging is carried out within the temperature range of starting forging temperature ≥ 1000℃ and final forging temperature ≥ 850℃ to ensure the best formability and grain size control of the material;

[0234] Slow cooling stage: After forging is completed, slow cooling treatment is carried out. The slow cooling method is hood cooling, sand cooling, pit cooling or furnace cooling. The slow cooling time is not less than 24 hours.

[0235] Polishing treatment: After slow cooling, the forgings are polished to ensure that they meet the electrode size requirements matched by the vacuum consumable crystallizer.

[0236] S4: Vacuum consumable remelting

[0237] The vacuum consumable electrode in step S3 is subjected to vacuum consumable remelting to further degas and improve the purity of the steel, and the vacuum degree is controlled to be ≤0.5Pa during the melting process;

[0238] The melting rate during the vacuum consumable remelting process is 6.5 kg / min, and helium cooling is used to prevent segregation of chemical composition and ingot shape.

[0239] S5: Forging treatment

[0240] The electroslag ingot treated in step S4 is forged, and before forging, the temperature is gradually increased to 800°C and kept warm for ≥1 hour, and then further increased to 1210°C and kept warm for ≥2 hours, and then forged at 850°C, and slowly cooled after forging; the slow cooling after forging adopts hood cooling, sand cooling, pit cooling or furnace cooling, and the slow cooling time is not less than 24 hours.

[0241] S6: Heat treatment after calcination

[0242] The forged steel is subjected to post-forging heat treatment, which includes normalizing, tempering, quenching and re-tempering, so as to optimize the mechanical properties and structural uniformity of the steel.

[0243] The post-calcination heat treatment comprises the following steps:

[0244] Normalizing: temperature is 930℃, insulation is 2.5mm / min+60min, cooling method is air cooling;

[0245] Tempering: temperature is 690℃, holding time is 240 minutes, cooling method is air cooling;

[0246] Quenching: temperature is 900℃, holding time is 60 minutes, cooling method is oil cooling;

[0247] Re-tempering: temperature is 550℃, holding time is 120 minutes, cooling method is air cooling.

[0248] The mechanical properties of the 45CrNiMoV mentioned in the background technology are compared with the high-purity and high-strength steel prepared in the above-mentioned Example 1 of the present invention. The two are manufactured by the same method except for the heat treatment method (i.e., normalizing, tempering, and quenching corresponding to the post-forging heat treatment). The mechanical properties of the test are compared (GB / T 228 metal tensile test method) as shown in Table 2:

[0249] Table 2 Comparison of mechanical properties

[0250]

[0251] From the comparison in Table 2, we can see that:

[0252] (1) Compared with the 45CrNiMoV described in the background art, the steel described in the present invention optimizes the chemical composition and significantly reduces the residual element content, so that it has high strength while still having good plasticity;

[0253] (2) The steel of the present invention has more martensitic structure at room temperature by adjusting the chemical composition, thereby improving the strength;

[0254] (3) The present invention further improves the mechanical properties of the steel by a special heat treatment process combined with the adjustment of the chemical composition mentioned above.

[0255] In summary, the present invention provides a method for manufacturing high-purity and high-strength steel, which solves the contradiction between high strength and toughness of steel in the prior art and the problem of gas pollution during the smelting process. The principle is to remove oxygen, nitrogen, hydrogen and other gas impurities in the steel by adopting a triple smelting process of vacuum induction furnace smelting, electroslag remelting and vacuum consumable remelting, combined with precise temperature control and gas control means, to further reduce the content of harmful elements and optimize the microstructure of the steel; the technical solution proposed in the present invention includes multiple key steps, such as the selection of high-purity raw materials, precise vacuum smelting process, control of electroslag remelting, and vacuum consumable remelting and subsequent forging treatment and heat treatment process. Through these optimized manufacturing methods, the gas impurities in the steel are effectively reduced, the formation of oxides and inclusions is reduced, and the purity and uniformity of the steel are greatly improved. At the same time, by optimizing and adjusting the composition, the strength, toughness and fatigue resistance of the steel are further enhanced; the technical effect of the present invention is remarkable, and the resulting steel has significantly improved toughness and plasticity while maintaining high strength (tensile strength exceeds 1500MPa), and fatigue strength and fracture resistance are also greatly improved. It overcomes the problems of gas pollution, poor material reliability and uncertainty in the smelting process in the prior art, and provides a high-purity, high-strength steel solution for high-end fields such as aerospace and military industry.

[0256] In the description of the present application, the description with reference to the terms "one embodiment", "some embodiments", "in the present embodiment", "specific example", or "some examples" etc. means that the specific features, mechanisms, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, mechanisms, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0257] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for producing high-purity and high-strength steel, characterized in that: The following steps are involved: S1: Vacuum induction furnace smelting High-purity raw materials are used, smelted in a vacuum induction furnace, and the raw materials are melted and then degassed to obtain electrode rods, and the gas content and the mass percentage of chemical elements are controlled to be: C: 0.44-0.46%, Mn: 0.60-1.00%, Si: 1.65-1.85%, S≤0.002%, P≤0.005%, Ni: 1.20-1.40%, Cr: 1.30-1.50%, Mo: 1.20-1.40%, V: 0.05-0.10%, Al: ≤0.015%, Ti: ≤0.015%, H: ≤0.00005%, O: ≤0.0008%, N: ≤0.0010%, and the balance is Fe and other inevitable impurities; S2: Electroslag Remelting Electroslag ingots are obtained by electroslag remelting the electrode rods obtained by S1, using a slag system with a slag ratio of fluorite and Al2O3 of 70:30, and adjusting the melting speed to improve the segregation of chemical elements and the purity of steel; S3: Electroslag ingot forging vacuum consumable electrode: The electroslag ingot obtained in step S2 is heat treated and then forged to obtain a vacuum consumable electrode; S4: Vacuum consumable remelting The vacuum consumable electrode in step S3 is subjected to vacuum consumable remelting to further degas and improve the purity of the steel, and the vacuum degree is controlled to be ≤0.5Pa during the melting process; S5: Forging treatment The electroslag ingot after the step S4 is forged, and before forging, the temperature is gradually raised to 800° C. and kept at this temperature for ≥1 hour, and then further raised to 1140° C. to 1210° C. and kept at this temperature for ≥2 hours, and then forged in the temperature range of 1000° C. to 850° C., and slowly cooled after forging; S6: Heat treatment after calcination The forged steel is subjected to post-forging heat treatment, which includes normalizing, tempering, quenching and re-tempering.

2. The manufacturing method according to claim 1, characterized in that: In the step S1, the smelting temperature of the vacuum induction furnace is 1520-1600° C., the vacuum degree during refining is ≤5 Pa, the refining temperature is 1530-1570° C., and the refining time is ≥30 minutes.

3. The manufacturing method according to claim 1, characterized in that: In the step S1, when O≤15ppm, N≤15ppm, and H≤1ppm in the molten steel, Ar≥3000Pa is added, and metallic Mn or electrolytic Mn is started to be added, and the casting temperature of the electrode is 1540-1580°C.

4. The manufacturing method according to claim 1, characterized in that: In the step S2, the electroslag remelting current is 3KA-19KA, the power is 60kw-800kw; the melting rate is 3.5-10.5kg / min, and slow cooling is performed for ≥24 hours after the electroslag remelting is completed.

5. The manufacturing method according to claim 1, characterized in that: In step S3, the heat treatment comprises the following steps: Initial heating stage: The initial temperature is controlled below 600°C, and then the temperature is raised to 800°C at a steady rate. The entire heating process lasts for more than 2 hours. 800℃ insulation stage: When the temperature reaches 800℃, keep it at this temperature for at least 1 hour; Further heating stage: After keeping at 800℃, continue to heat until the temperature reaches between 1140℃ and 1210℃, the heating time shall not be less than 2 hours, ensuring gradual heating; High temperature insulation stage: maintain the temperature within the temperature range of 1140℃ to 1210℃ for at least 2 hours.

6. The manufacturing method according to claim 1, characterized in that: In the step S3, the forging includes the following steps: Reburning stage: heat the electroslag ingot to 1120-1160℃; Forging stage: forging is carried out within the temperature range of starting forging temperature ≥ 1000°C and final forging temperature ≥ 850°C; Slow cooling stage: After forging is completed, slow cooling treatment is carried out. The slow cooling method is hood cooling, sand cooling, pit cooling or furnace cooling. The slow cooling time is not less than 24 hours. Polishing treatment: After slow cooling, the forgings are polished to ensure that they meet the electrode size requirements matched by the vacuum consumable crystallizer.

7. The manufacturing method according to claim 1, characterized in that: In the step S4, the melting rate during the vacuum consumable remelting process is 2.5-6.5 kg / min, and helium cooling is used.

8. The manufacturing method according to claim 1, characterized in that: In the step S5, the slow cooling after forging adopts hood cooling, sand cooling, pit cooling or furnace cooling, and the slow cooling time is not less than 24 hours.

9. The manufacturing method according to claim 1, characterized in that: In step S6, the post-calcination heat treatment The following steps are involved: Normalizing: temperature is 920±10℃, insulation is 2.5mm / min+60min, cooling method is air cooling; Tempering: temperature is 680±10℃, holding time is 120~240 minutes, cooling method is air cooling; Quenching: temperature is 890±10℃, holding time is 60 minutes, cooling method is oil cooling; Re-tempering: temperature is 510-550℃, holding time is 120 minutes, cooling method is air cooling.

10. A high-purity and high-strength steel, characterized in that: The high-purity and high-strength steel is prepared by the manufacturing method described in any one of claims 1 to 9, and the composition of the high-purity and high-strength steel includes: C: 0.44-0.46%; Mn: 0.60-1.00%; Si: 1.65-1.85%; S≤0.002%; P≤0.005%; Ni: 1.20-1.40%; Cr: 1.30-1.50%; Mo: 1.20-1.40%; V: 0.05-0.10%; Al: ≤0.015%; Ti: ≤0.015%; H: ≤0.00005%; O: ≤0.0008%; N: ≤0.0010%; the balance is Fe and other inevitable impurities.

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