A high-strength and high-toughness alloy steel, a manufacturing method and application thereof

Abstract

The application discloses high-strength and high-toughness alloy steel and a manufacturing method and application thereof. The high-strength and high-toughness alloy steel comprises the following components in percentage by mass: C 0.24-0.41%, Si≤0.10%, Mn 1.80-3.20%, Ni 4.00-7.00%, Cr 2.50-4.8%, Cu 0.50-0.80%, Nb 0.04-0.08%, Ti 0.06-0.09%, V 0.08-0.18%, B 0.0010-0.0050%, P≤0.0050%, S≤0.0050%, O≤0.0015%, N≤0.0040%, and the balance of Fe and inevitable impurity elements. The application significantly improves the impact toughness and crack resistance while maintaining high yield strength and hardness, and solves the problems of imbalance between strength and toughness of armor steel and unstable performance of thick plates.

Description

Technical Field

[0001] This invention belongs to the field of special alloy steel and its heat treatment technology, specifically relating to a high-strength and high-toughness alloy steel, its manufacturing method and application. Background Technology

[0002] As modern armored vehicles, shipborne protective facilities, and key engineering equipment develop towards lightweight, high mobility, and multi-functionality, armor steel needs to reduce thickness and weight while maintaining high areal density. This places extremely high demands on the matching of strength and toughness in materials. Traditional homogeneous armor steel (RHA) simply relies on increasing thickness to improve protection levels, resulting in a significant increase in equipment weight. Furthermore, when the thickness exceeds 40mm, conventional quenching-tempering processes are prone to problems such as insufficient hardenability, uneven microstructure in the thickness direction, residual stress concentration, and temper brittleness.

[0003] In the prior art, patent CN119571017A discloses a multi-element alloy steel process using homogenization annealing + high-temperature quenching + two-phase zone quenching + tempering. However, its composition design has a Ce content as high as 0.57~0.60%, leading to a sharp increase in smelting costs and deterioration in weldability. Another patent, US20210123456A1, proposes Cu age-hardened armor steel, but it does not solve the technical bottleneck of large hardness gradient (typically >45HB) in thick plate sections. More importantly, the existing technologies have not established a quantitative relationship between the proportion of microalloying elements (such as Cu / Nb) and segmented isothermal time, resulting in uncontrolled process windows and poor batch-to-batch stability of product performance during industrial production.

[0004] Therefore, there is an urgent need in this field for an alloy armor steel that combines high yield strength (≥1150MPa), high and low temperature toughness (-40℃ Akv≥30J) and high thickness direction hardness uniformity (section hardness difference ≤25HB), and is equipped with a manufacturing method that can be precisely controlled and repeated, in order to meet the stringent service requirements of modern protective equipment. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the primary objective of this invention is to provide a high-strength and high-toughness alloy steel.

[0006] Another object of the present invention is to provide a method for manufacturing the above-mentioned high-strength and high-toughness alloy steel.

[0007] Another object of the present invention is to provide an application of the above-mentioned high-strength and high-toughness alloy steel.

[0008] This invention, through the rational design of chemical composition and the introduction of a composite heat treatment process combining segmented isothermal quenching and medium-temperature aging, significantly improves impact toughness and crack resistance while achieving high yield strength and high hardness, thereby overcoming the technical defects of existing armor steels that are difficult to balance strength and toughness and have unstable performance of thick plates.

[0009] The objective of this invention is achieved through the following technical solution: A high-strength, high-toughness alloy steel comprises the following components by mass percentage: C 0.24~0.41%, Si≤0.10%, Mn 1.80~3.20%, Ni 4.00~7.00%, Cr 2.50~4.8%, Cu 0.50~0.80%, Nb 0.04~0.08%, Ti 0.06~0.09%, V 0.08~0.18%, B 0.0010~0.0050%, P≤0.0050%, S≤0.0050%, O≤0.0015%, N≤0.0040%, with the balance being Fe and unavoidable inclusions.

[0010] Preferably, the high-strength and high-toughness alloy steel comprises the following components by mass percentage: C 0.26~0.35%, Si 0.02~0.08%, Mn 2.00~2.80%, Ni 4.50~6.00%, Cr 2.80~3.80%, Cu 0.55~0.72%, Nb 0.05~0.07%, Ti 0.065~0.085%, V 0.10~0.16%, B 0.0015~0.0030%, P≤0.0050%, S≤0.0050%, O≤0.0015%, N≤0.0040%, with the balance being Fe and unavoidable inclusions; The content of each component satisfies the following conditions: (1) 8.5≤Cu / Nb≤12; (2) 1.7≤(Mn+Ni) / Cr≤2.8; (3) 0.5%≤C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+V / 10+5B≤0.84%. Among them, (3) can be regarded as a comprehensive index for controlling the welding carbon equivalent and hardening tendency, which is used to reduce the risk of quenching cracks and welding cold cracks.

[0011] In this invention, the content and uses of each element are statistically summarized as follows: C element: The C content is controlled in the medium to high carbon range of 0.24~0.41%, which can significantly improve the strength and hardness of the martensitic and bainitic matrix and provide sufficient carbon source for subsequent precipitation strengthening; the upper limit is controlled at 0.41% to avoid excessive carbon causing increased quenching crack sensitivity and significant reduction in low-temperature impact toughness.

[0012] Mn, Ni, and Cr elements: Mn, Ni, and Cr are the main hardenability elements. Among them, Mn and Ni have significant effects on improving hardenability and low-temperature toughness. The Ni content can be controlled at 4~7% to balance toughness and cost. Cr and B work together to improve hardenability and inhibit pearlite formation, but too high Cr may increase the risk of temper brittleness. Therefore, it is controlled in the range of 2.50~4.8%.

[0013] Cu element: The Cu content is 0.50~0.80%. During the medium-temperature aging process, fine ε-Cu precipitates are formed, which achieves significant aging strengthening. If the content is too low, the strengthening will be insufficient, and if it is too high, hot brittleness and segregation problems will easily occur.

[0014] Nb, Ti, and V elements: As typical microalloying elements, Nb, Ti, and V can form carbonitrides such as NbC, TiN, and VC, achieving grain refinement and precipitation strengthening. By controlling the Cu / Nb and V+Ti / N ratios, the size and distribution of the precipitated phases can be made more reasonable. Ti mainly combines with N to form TiN, inhibiting austenite grain growth, while Nb and V precipitate fine carbides during subsequent heat treatment, improving yield strength.

[0015] Bo (B): The amount of B added is 0.0010~0.0050%. Its segregation at grain boundaries can significantly improve hardenability and inhibit the formation of grain boundary ferrite, making the hardening of thick plate sections more complete. If the B content is insufficient, the improvement in hardenability is limited, and if the content is too high, it can easily lead to grain boundary embrittlement. Therefore, it is controlled within the above-mentioned narrow range.

[0016] Si and impurity elements: Si mainly acts as a deoxidizing element, and an appropriate amount can also improve tempering stability. However, excessive amounts will reduce impact toughness and deteriorate weldability. Therefore, it should be controlled at ≤0.10%, preferably 0.02~0.08%. Strict control of impurities such as P, S, O, and N can reduce segregation and brittle phases, and improve toughness and thickness-direction performance stability.

[0017] The manufacturing method of the above-mentioned high-strength and high-toughness alloy steel includes the following steps: (1) The raw materials of each element are proportioned according to the corresponding mass percentage, and molten steel is obtained after smelting. After casting, steel billet is obtained. The steel billet is heated to 1160~1180℃ and kept warm for diffusion. It is formed by rolling or forging to obtain steel plate of target thickness. It is then air-cooled to room temperature for later use. (2) Austenitizing treatment: According to the thickness of the steel plate, the steel plate described in step (1) is heated to 820~930℃ and held for 3~7h to obtain an austenitized steel plate; (3) Single isothermal quenching and double isothermal quenching The austenitized steel plate described in step (2) is transferred to a nitrate bath at a temperature of 300~470℃ for a first isothermal quenching of 6~10h; then the sample is taken out and transferred to another nitrate bath at a temperature of 175~230℃ for a second isothermal quenching of 3.5~6h. Isothermal quenching is carried out in the range of 300~470℃. Within this temperature range, some austenite is transformed into granular bainite, which can form a matrix structure with good toughness and avoid directly obtaining large lath martensite.

[0018] The secondary isothermal quenching is carried out in the range of 170~230℃. Within this temperature range, the remaining austenite in the steel is rapidly transformed into fine lath martensite. The low temperature environment effectively inhibits the self-tempering of martensite in the range of 250~300℃, thereby avoiding the precipitation of coarse carbides and providing a high degree of supersaturation for the precipitation of nano-sized carbides and ε-Cu in the subsequent medium-temperature aging.

[0019] (4) Medium-temperature aging treatment The sample after secondary isothermal quenching is heated to 450-570℃ at a heating rate of 6-12℃ / min and held for 4-8 hours. Then it is cooled in the furnace to below 180℃ and air-cooled to obtain the high-strength and high-toughness alloy steel.

[0020] The intermediate temperature aging treatment is carried out in the range of 450~570℃. In this temperature range, Cu undergoes dispersed precipitation to form nano-sized ε-Cu particles. At the same time, NbC, VC and other carbides undergo secondary precipitation or growth regulation, thereby significantly improving the yield strength and yield ratio while maintaining high hardness, and also taking into account a certain impact toughness.

[0021] Preferably, the specific steps for obtaining molten steel after smelting by batching each element raw material according to the corresponding mass percentage in step (1) are as follows: The metallurgical process combines electric arc furnace (EAF) primary refining, ladle refining furnace (LF) refining, and vacuum degassing furnace (VD). High-quality low-carbon scrap steel and industrial pure iron are used as base materials, supplemented with ferrochrome, ferroniobium, ferrovanadium, electrolytic nickel, and electrolytic copper for primary and refining. In the later stage of refining, titanium, boron, and final deoxidized aluminum wire are added sequentially by wire feeding. During the refining process, samples are periodically extracted from the furnace front, and the content of multiple alloying elements is tracked in real time using a spark direct-reading spectrometer and dynamically replenished to ensure that the composition is accurately up to standard and to obtain molten steel.

[0022] Preferably, the time for heating the steel billet to 1160~1180℃ and holding it for diffusion in step (1) is 5~6h.

[0023] Preferably, during the rolling or forging process described in step (1), the final forging / rolling temperature is ≥850℃.

[0024] Preferably, in step (2), the steel plate described in step (1) is heated to 820-930°C at a heating rate of 5-15°C / min and held at that temperature for 3-7 hours.

[0025] Preferably, in step (2), for steel plates with a thickness not greater than 40 mm (20 mm ≤ thickness ≤ 40 mm), the temperature is heated to 850~900℃ and held for 3~5 hours; for steel plates with a thickness greater than 40 mm and not greater than 60 mm (40 mm < thickness ≤ 60 mm), the temperature is heated to 870~930℃ and held for 5~7 hours.

[0026] Preferably, in step (3), the first isothermal quenching is performed in a nitrate bath at 350~450℃, and the second isothermal quenching is performed in a nitrate bath at 180~220℃.

[0027] Preferably, the holding time for the secondary isothermal quenching is 4 to 5.5 hours.

[0028] Preferably, in step (4), the sample is heated to 460-550°C at a heating rate of 8-12°C / min and held at that temperature for 5-7 hours.

[0029] The application of the above-mentioned high-strength and high-toughness alloy steel in the preparation of armor steel.

[0030] Compared with the prior art, the beneficial effects of the present invention include: Compared with traditional RHA steel and publicly disclosed multi-alloy armor steel technologies, the present invention has the following substantial beneficial effects: (1) Relationship between multi-component microalloying system and compositional constraint By introducing microalloying elements such as Cu, Nb, Ti, V, and B, and establishing Cu / Nb, (Mn+Ni) / Cr, and comprehensive carbon equivalent relationships, the quantification and controllability of alloy design are achieved. This effectively balances strength, toughness, and weldability while ensuring the hardenability of thick plates and fine-grained microstructure.

[0031] (2) Segmented isothermal quenching process The combination of "austenitization - primary isothermal quenching - secondary isothermal quenching" is adopted: A single isothermal quenching at 300~470℃ (preferably 350~450℃) forms a tough matrix mainly composed of granular bainite; Secondary isothermal quenching at 175~230℃ (preferably 180~220℃) generates fine lath martensite and inhibits self-tempering.

[0032] This process effectively avoids the precipitation of bulk martensite and coarse carbides caused by traditional single-stage quenching, achieving a refined and uniform microstructure, improving impact toughness and reducing quenching crack sensitivity.

[0033] (3) Synergistic enhancement of intermediate temperature aging During the intermediate-temperature aging process at 450–570℃, synergistic strengthening is achieved through Cu nanoprecipitation and secondary precipitation of Nb, Ti, and V carbonitrides. This not only improves the yield strength and yield strength ratio but also enhances the ductility-toughness balance by pinning dislocations and refining the microstructure through fine precipitated phases. Compared to existing technologies that only use Cu for aging, this invention achieves higher yield strength and superior impact toughness while maintaining a similar hardness level.

[0034] (4) Thickness direction hardness uniformity and batch stability Because the process of this invention employs isothermal temperature control via a nitrate bath, it enhances the uniformity of temperature and phase transformation processes within the thick plate cross-section, significantly improving the hardness gradient along the thickness direction. The hardness difference in a typical cross-section is controlled within approximately 25 HB. Combined with a clearly defined formula for controlling component proportions, this provides a clear process window, facilitating improved batch performance stability in industrial production. Attached Figure Description

[0035] Figure 1 The OM diagram shows the microstructure of the high-strength and high-toughness alloy steel prepared in Example 1 of this invention.

[0036] Figure 2 This is a SEM image of the high-strength, high-toughness alloy steel prepared in Example 1 of the present invention.

[0037] Figure 3 This is a SEM image of the high-strength, high-toughness alloy steel prepared in Comparative Example 1 of this invention. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0039] Example 1 A high-strength and high-toughness alloy steel, the corresponding constituent elements and mass percentages are shown in Table 1.

[0040] The manufacturing method of the high-strength and high-toughness alloy steel includes the following specific steps: (1) A metallurgical process combining electric arc furnace (EAF) primary refining, ladle refining furnace (LF) refining and vacuum degassing furnace (VD) is adopted. High-quality low-carbon scrap steel and industrial pure iron are used as base materials, supplemented by ferrochrome, ferroniobium, ferrovanadium, electrolytic nickel and electrolytic copper for primary refining and refining. In the later stage of refining, titanium, boron and final deoxidized aluminum wire are added sequentially by wire feeding method. During the refining process, samples are periodically extracted from the furnace front, and the content of multi-element alloying elements is tracked in real time and dynamically replenished using a spark direct reading spectrometer to ensure that the composition meets the standard and obtain molten steel.

[0041] During the refining process, samples are extracted from the furnace every 10 minutes. A spark direct-reading spectrometer tracks the content of elements such as C, Si, Mn, Ni, Cr, Cu, Nb, Ti, V, and B in real time, with dynamic feeding. The tolerances for key elements are controlled as follows: C ≤ ±0.015%, Ni ≤ ±0.08%, Cr ≤ ±0.08%, Mn ≤ ±0.08%. Vacuum degassing (≤67 Pa, held for ≥15 minutes) removes hydrogen, oxygen, and inclusions.

[0042] After VD breaking the void, the billet is formed by ingot casting or protective casting. After the steel ingot / billet is slowly cooled, the surface defects are repaired. The chemical composition is verified by wet analysis before it can be transferred. The billet is heated to 1170℃ and held for diffusion for 5 hours. It is then formed by rolling or forging to obtain the target thickness steel plate (40mm). It is then air-cooled to room temperature for later use. (2) Based on the thickness of the steel plate, heat the steel plate described in step (1) to 870°C at a heating rate of 10°C / min and hold for 3 hours to obtain an austenitized steel plate. (3) The austenitized steel plate described in step (2) is transferred to a nitrate bath at 400°C within 30s for a first isothermal quenching of 6h; then the sample is taken out and transferred to another nitrate bath at 180°C within 30s for a second isothermal quenching of 3.5h. (4) The sample after secondary isothermal quenching is heated to 490°C at a heating rate of 10°C / min and held for 4 hours. Then it is cooled in the furnace to below 180°C and air-cooled to obtain the high-strength and high-toughness alloy steel.

[0043] Figure 1 The image shows the microstructure of the high-strength, high-toughness alloy steel prepared in Example 1 of this invention. (From...) Figure 1 We can see that the microstructure is composed of uniform granular bainite and fine lath martensite, without coarse dendrites or obvious segregation bands, and the grain size is uniform. This indicates that the segmented isothermal quenching process effectively achieves microstructure refinement and cross-sectional homogenization, providing a microstructure basis for the material's good strength and toughness matching.

[0044] Figure 2 This is a SEM image of the high-strength, high-toughness alloy steel prepared in Example 1 of the present invention. From... Figure 2 We can observe that a large number of nano-sized ε-Cu particles and NbC, VC and other carbide precipitates are dispersed on the bainitic-martensite matrix. The precipitates are small in size and uniformly distributed, which can effectively pin dislocations and hinder slip. This is the core microscopic mechanism for the material to achieve a synergistic improvement in high strength and high toughness.

[0045] Example 2 A high-strength and high-toughness alloy steel, the corresponding constituent elements and mass percentages are shown in Table 1.

[0046] The manufacturing method of the high-strength and high-toughness alloy steel includes the following specific steps: (1) A metallurgical process combining electric arc furnace (EAF) primary refining, ladle refining furnace (LF) refining and vacuum degassing furnace (VD) is adopted. High-quality low-carbon scrap steel and industrial pure iron are used as base materials, supplemented by ferrochrome, ferroniobium, ferrovanadium, electrolytic nickel and electrolytic copper for primary refining and refining. In the later stage of refining, titanium, boron and final deoxidized aluminum wire are added sequentially by wire feeding method. During the refining process, samples are periodically extracted from the furnace front, and the content of multi-element alloying elements is tracked in real time and dynamically replenished using a spark direct reading spectrometer to ensure that the composition meets the standard and obtain molten steel.

[0047] During the refining process, samples are extracted from the furnace every 10 minutes. A spark direct-reading spectrometer tracks the content of elements such as C, Si, Mn, Ni, Cr, Cu, Nb, Ti, V, and B in real time, with dynamic feeding. The tolerances for key elements are controlled as follows: C ≤ ±0.015%, Ni ≤ ±0.08%, Cr ≤ ±0.08%, Mn ≤ ±0.08%. Vacuum degassing (≤67 Pa, held for ≥15 minutes) removes hydrogen, oxygen, and inclusions.

[0048] After VD breaking the void, the billet is formed by ingot casting or protective casting. After the steel ingot / billet is slowly cooled, the surface defects are repaired. The chemical composition is verified by wet analysis before it can be transferred. The billet is heated to 1165℃ and held for diffusion for 5.5 hours. It is then formed by rolling or forging to obtain the target thickness steel plate (40mm). It is then air-cooled to room temperature for later use. (2) Based on the thickness of the steel plate, heat the steel plate described in step (1) to 850°C at a heating rate of 8°C / min and hold for 5 hours to obtain an austenitized steel plate. (3) The austenitized steel plate described in step (2) is transferred to a nitrate bath at 380°C within 30s for a first isothermal quenching of 7h; then the sample is taken out and transferred to another nitrate bath at 190°C within 30s for a second isothermal quenching of 5.5h. (4) The sample after secondary isothermal quenching is heated to 535°C at a heating rate of 9°C / min and held for 6 hours. Then it is cooled in the furnace to below 180°C and air-cooled to obtain the high-strength and high-toughness alloy steel.

[0049] Example 3 A high-strength and high-toughness alloy steel, the corresponding constituent elements and mass percentages are shown in Table 1.

[0050] The manufacturing method of the high-strength and high-toughness alloy steel includes the following specific steps: (1) A metallurgical process combining electric arc furnace (EAF) primary refining, ladle refining furnace (LF) refining and vacuum degassing furnace (VD) is adopted. High-quality low-carbon scrap steel and industrial pure iron are used as base materials, supplemented by ferrochrome, ferroniobium, ferrovanadium, electrolytic nickel and electrolytic copper for primary refining and refining. In the later stage of refining, titanium, boron and final deoxidized aluminum wire are added sequentially by wire feeding method. During the refining process, samples are periodically extracted from the furnace front, and the content of multi-element alloying elements is tracked in real time and dynamically replenished using a spark direct reading spectrometer to ensure that the composition meets the standard and obtain molten steel.

[0051] During the refining process, samples are extracted from the furnace every 10 minutes. A spark direct-reading spectrometer tracks the content of elements such as C, Si, Mn, Ni, Cr, Cu, Nb, Ti, V, and B in real time, with dynamic feeding. The tolerances for key elements are controlled as follows: C ≤ ±0.015%, Ni ≤ ±0.08%, Cr ≤ ±0.08%, Mn ≤ ±0.08%. Vacuum degassing (≤67 Pa, held for ≥15 minutes) removes hydrogen, oxygen, and inclusions.

[0052] After VD breaking the void, the steel billet is formed by ingot casting or protective casting continuous casting. After the steel ingot / billet is slowly cooled, the surface defects are repaired. The chemical composition is verified by wet analysis before it can be transferred. The steel billet is heated to 1175℃ and held for diffusion for 5.2 hours. It is then formed by rolling or forging to obtain the target thickness steel plate (40mm). It is then air-cooled to room temperature for later use. (2) Based on the thickness of the steel plate, heat the steel plate described in step (1) to 880°C at a heating rate of 12°C / min and hold for 4 hours to obtain an austenitized steel plate. (3) The austenitized steel plate described in step (2) is transferred to a nitrate bath at 460°C within 30s for a first isothermal quenching of 8h; then the sample is taken out and transferred to another nitrate bath at 220°C within 30s for a second isothermal quenching of 6h. (4) The sample after secondary isothermal quenching is heated to 550°C at a heating rate of 11°C / min and held for 5.5h. Then it is cooled in the furnace to below 180°C and air-cooled to obtain the high-strength and high-toughness alloy steel.

[0053] Example 4 A high-strength and high-toughness alloy steel, the corresponding constituent elements and mass percentages are shown in Table 1.

[0054] The manufacturing method of the high-strength and high-toughness alloy steel includes the following specific steps: (1) A metallurgical process combining electric arc furnace (EAF) primary refining, ladle refining furnace (LF) refining and vacuum degassing furnace (VD) is adopted. High-quality low-carbon scrap steel and industrial pure iron are used as base materials, supplemented by ferrochrome, ferroniobium, ferrovanadium, electrolytic nickel and electrolytic copper for primary refining and refining. In the later stage of refining, titanium, boron and final deoxidized aluminum wire are added sequentially by wire feeding method. During the refining process, samples are periodically extracted from the furnace front, and the content of multi-element alloying elements is tracked in real time and dynamically replenished using a spark direct reading spectrometer to ensure that the composition meets the standard and obtain molten steel.

[0055] During the refining process, samples are extracted from the furnace every 10 minutes. A spark direct-reading spectrometer tracks the content of elements such as C, Si, Mn, Ni, Cr, Cu, Nb, Ti, V, and B in real time, with dynamic feeding. The tolerances for key elements are controlled as follows: C ≤ ±0.015%, Ni ≤ ±0.08%, Cr ≤ ±0.08%, Mn ≤ ±0.08%. Vacuum degassing (≤67 Pa, held for ≥15 minutes) removes hydrogen, oxygen, and inclusions.

[0056] After VD breaking the void, the billet is formed by ingot casting or protective casting. After the steel ingot / billet is slowly cooled, the surface defects are repaired. The chemical composition is verified by wet analysis before it can be transferred. The billet is heated to 1160℃ and held for diffusion for 5 hours. It is then formed by rolling or forging to obtain the target thickness steel plate (40mm). It is then air-cooled to room temperature for later use. (2) Based on the thickness of the steel plate, heat the steel plate described in step (1) to 860°C at a heating rate of 7°C / min and hold for 3 hours to obtain an austenitized steel plate. (3) The austenitized steel plate described in step (2) is transferred to a nitrate bath at 350°C within 30s for a first isothermal quenching of 6h; then the sample is taken out and transferred to another nitrate bath at 230°C within 30s for a second isothermal quenching of 5h. (4) The sample after secondary isothermal quenching is heated to 460°C at a heating rate of 8°C / min and held for 6.5h. Then it is cooled in the furnace to below 180°C and air-cooled to obtain the high-strength and high-toughness alloy steel.

[0057] Example 5 A high-strength and high-toughness alloy steel, the corresponding constituent elements and mass percentages are shown in Table 1.

[0058] The manufacturing method of the high-strength and high-toughness alloy steel includes the following specific steps: (1) A metallurgical process combining electric arc furnace (EAF) primary refining, ladle refining furnace (LF) refining and vacuum degassing furnace (VD) is adopted. High-quality low-carbon scrap steel and industrial pure iron are used as base materials, supplemented by ferrochrome, ferroniobium, ferrovanadium, electrolytic nickel and electrolytic copper for primary refining and refining. In the later stage of refining, titanium, boron and final deoxidized aluminum wire are added sequentially by wire feeding method. During the refining process, samples are periodically extracted from the furnace front, and the content of multi-element alloying elements is tracked in real time and dynamically replenished using a spark direct reading spectrometer to ensure that the composition meets the standard and obtain molten steel.

[0059] During the refining process, samples are extracted from the furnace every 10 minutes. A spark direct-reading spectrometer tracks the content of elements such as C, Si, Mn, Ni, Cr, Cu, Nb, Ti, V, and B in real time, with dynamic feeding. The tolerances for key elements are controlled as follows: C ≤ ±0.015%, Ni ≤ ±0.08%, Cr ≤ ±0.08%, Mn ≤ ±0.08%. Vacuum degassing (≤67 Pa, held for ≥15 minutes) removes hydrogen, oxygen, and inclusions.

[0060] After VD breaking the void, the billet is formed by ingot casting or protective casting. After the steel ingot / billet is slowly cooled, the surface defects are repaired. The chemical composition is verified by wet analysis before it can be transferred. The billet is heated to 1180℃ and held for diffusion for 5.3h. It is then formed by rolling or forging to obtain the target thickness steel plate (40mm). It is then air-cooled to room temperature for later use. (2) Based on the thickness of the steel plate, heat the steel plate described in step (1) to 860°C at a heating rate of 10°C / min and hold for 5 hours to obtain an austenitized steel plate. (3) The austenitized steel plate described in step (2) is transferred to a nitrate bath at 440°C within 30s for a first isothermal quenching for 10h; then the sample is taken out and transferred to another nitrate bath at 210°C within 30s for a second isothermal quenching for 4h. (4) The sample after secondary isothermal quenching is heated to 470°C at a heating rate of 9°C / min and held for 6.5h. Then it is cooled in the furnace to below 180°C and air-cooled to obtain the high-strength and high-toughness alloy steel.

[0061] Comparative Example 1 A high-strength and high-toughness alloy steel, the corresponding constituent elements and mass percentages are shown in Table 1.

[0062] The manufacturing method of the high-strength and high-toughness alloy steel includes the following specific steps: (1) A metallurgical process combining electric arc furnace (EAF) primary refining, ladle refining furnace (LF) refining and vacuum degassing furnace (VD) is adopted. High-quality low-carbon scrap steel and industrial pure iron are used as base materials, supplemented by ferrochrome, ferroniobium, ferrovanadium, electrolytic nickel and electrolytic copper for primary refining and refining. In the later stage of refining, titanium, boron and final deoxidized aluminum wire are added sequentially by wire feeding method. During the refining process, samples are periodically extracted from the furnace front, and the content of multi-element alloying elements is tracked in real time and dynamically replenished using a spark direct reading spectrometer to ensure that the composition meets the standard and obtain molten steel.

[0063] During the refining process, samples are extracted from the furnace every 10 minutes. A spark direct-reading spectrometer tracks the content of elements such as C, Si, Mn, Ni, Cr, Cu, Nb, Ti, V, and B in real time, with dynamic feeding. The tolerances for key elements are controlled as follows: C ≤ ±0.015%, Ni ≤ ±0.08%, Cr ≤ ±0.08%, Mn ≤ ±0.08%. Vacuum degassing (≤67 Pa, held for ≥15 minutes) removes hydrogen, oxygen, and inclusions.

[0064] After VD breaking the void, the billet is formed by ingot casting or protective casting. After the steel ingot / billet is slowly cooled, the surface defects are repaired. The chemical composition is verified by wet analysis before it can be transferred. The billet is heated to 1170℃ and held for diffusion for 5 hours. It is then formed by rolling or forging to obtain the target thickness steel plate (40mm). It is then air-cooled to room temperature for later use. (2) Based on the thickness of the steel plate, heat the steel plate described in step (1) to 880°C at a heating rate of 10°C / min and hold for 4 hours to obtain an austenitized steel plate. (3) The austenitized steel plate described in step (2) is transferred to a nitrate bath at 500°C within 30s for a first isothermal quenching of 3h; then the sample is taken out and transferred to another nitrate bath at 260°C within 30s for a second isothermal quenching of 5h. (4) The sample after secondary isothermal quenching is heated to 600℃ at a heating rate of 10℃ / min and held for 10h. Then it is cooled in the furnace to below 180℃ and then air-cooled to obtain the high-strength and high-toughness alloy steel.

[0065] Figure 3 This is a SEM image of the high-strength, high-toughness alloy steel prepared in Comparative Example 1 of this invention. From... Figure 3 We can see that the matrix structure is significantly coarsened, the bainite laths are large, and the martensite self-tempering characteristics are significant; the aging precipitates are significantly aggregated and coarsened, with uneven size and sparse distribution, and the coherent strengthening effect is greatly weakened. Therefore, the yield strength and low-temperature impact toughness of the material are significantly lower than those of the embodiments of the present invention.

[0066] Comparative Example 2 A high-strength and high-toughness alloy steel, the corresponding constituent elements and mass percentages are shown in Table 1.

[0067] The manufacturing method of the high-strength and high-toughness alloy steel includes the following specific steps: (1) A metallurgical process combining electric arc furnace (EAF) primary refining, ladle refining furnace (LF) refining and vacuum degassing furnace (VD) is adopted. High-quality low-carbon scrap steel and industrial pure iron are used as base materials, supplemented by ferrochrome, ferroniobium, ferrovanadium, electrolytic nickel and electrolytic copper for primary refining and refining. In the later stage of refining, titanium, boron and final deoxidized aluminum wire are added sequentially by wire feeding method. During the refining process, samples are periodically extracted from the furnace front, and the content of multi-element alloying elements is tracked in real time and dynamically replenished using a spark direct reading spectrometer to ensure that the composition meets the standard and obtain molten steel.

[0068] During the refining process, samples are extracted from the furnace every 10 minutes. A spark direct-reading spectrometer tracks the content of elements such as C, Si, Mn, Ni, Cr, Cu, Nb, Ti, V, and B in real time, with dynamic feeding. The tolerances for key elements are controlled as follows: C ≤ ±0.015%, Ni ≤ ±0.08%, Cr ≤ ±0.08%, Mn ≤ ±0.08%. Vacuum degassing (≤67 Pa, held for ≥15 minutes) removes hydrogen, oxygen, and inclusions.

[0069] After VD breaking the void, the billet is formed by ingot casting or protective casting. After the steel ingot / billet is slowly cooled, the surface defects are repaired. The chemical composition is verified by wet analysis before it can be transferred. The billet is heated to 1170℃ and held for diffusion for 5 hours. It is then formed by rolling or forging to obtain the target thickness steel plate (40mm). It is then air-cooled to room temperature for later use. (2) Based on the thickness of the steel plate, heat the steel plate described in step (1) to 885°C at a heating rate of 10°C / min and hold for 5 hours to obtain an austenitized steel plate. (3) The austenitized steel plate described in step (2) is transferred to a nitrate bath at 280°C within 30s for a first isothermal quenching of 12h; then the sample is taken out and transferred to another nitrate bath at 160°C within 30s for a second isothermal quenching of 2h. (4) The sample after secondary isothermal quenching is heated to 430°C at a heating rate of 10°C / min and held for 3 hours. Then it is cooled in the furnace to below 180°C and air-cooled to obtain the high-strength and high-toughness alloy steel.

[0070] The elemental mass percentages of the alloy steels described in Examples 1-5 and Comparative Examples 1-2 are shown in Table 1.

[0071] Table 1. Elemental composition (wt%) of the examples and comparative examples

[0072] Table 2 shows the statistics of the main process parameters for "segmented isothermal quenching" and "medium-temperature aging" in Examples 1-5 and Comparative Examples 1-2.

[0073] Table 2. Main process parameters of Examples 1-5 and Comparative Examples 1-2

[0074] The alloys prepared in Examples 1-5 and Comparative Examples 1-2 were subjected to performance tests. The reference methods or standards for the test parameters were: GB / T 228.1-2021 Metallic materials—Tensive testing—Part 1: Test at room temperature; GB / T229-2020: Metallic materials—Charpy impact test. The test results are shown in Table 3.

[0075] Table 3. Main process parameters of Examples 1-5 and Comparative Examples 1-2

[0076] Referring to Tables 2-3, we can see that the present invention can guarantee a yield strength of 1165-1235 MPa; elongation A is usually ≥11%; impact energy Akv (V-notch) at -40℃ can reach or exceed 35 J in most embodiments; and Brinell hardness HB is 440-473 HB.

[0077] For Comparative Example 1, the first isothermal temperature was too high and the time was insufficient, which led to coarsening of bainite and softening of the matrix; the second isothermal temperature entered the self-tempering zone, and the precipitation of coarse carbides depleted the solid carbon; the over-aging caused ε-Cu and carbides to aggregate and coarsen, and lose coherent strengthening.

[0078] For Comparative Example 2, the first isothermal temperature was too low and the time was too long, which caused the bainite transformation to stop and a large amount of residual austenite to remain; the second isothermal temperature was too low and the time was insufficient, which interrupted the martensite transformation and further preserved the residual austenite; the aging temperature was too low and the time was insufficient, which failed to activate ε-Cu and carbide precipitation.

[0079] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A high-strength, high-toughness alloy steel, characterized in that, The composition includes the following components by mass percentage: C 0.24~0.41%, Si≤0.10%, Mn 1.80~3.20%, Ni 4.00~7.00%, Cr 2.50~4.8%, Cu 0.50~0.80%, Nb 0.04~0.08%, Ti 0.06~0.09%, V 0.08~0.18%, B 0.0010~0.0050%, P≤0.0050%, S≤0.0050%, O≤0.0015%, N≤0.0040%, with the balance being Fe and unavoidable inclusions.

2. The high-strength, high-toughness alloy steel according to claim 1, characterized in that, The composition includes the following components by mass percentage: C 0.26~0.35%, Si 0.02~0.08%, Mn 2.00~2.80%, Ni 4.50~6.00%, Cr 2.80~3.80%, Cu 0.55~0.72%, Nb 0.05~0.07%, Ti 0.065~0.085%, V 0.10~0.16%, B 0.0015~0.0030%, P≤0.0050%, S≤0.0050%, O≤0.0015%, N≤0.0040%, with the balance being Fe and unavoidable inclusions. Furthermore, the content of each component satisfies the following conditions: 8.5≤Cu / Nb≤12; 1.7≤(Mn+Ni) / Cr≤2.8; 0.5%≤C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+V / 10+5B≤0.84%.

3. The method for manufacturing the high-strength, high-toughness alloy steel according to any one of claims 1 to 2, characterized in that, Includes the following steps: (1) The raw materials of each element are proportioned according to the corresponding mass percentage, and molten steel is obtained after smelting. After casting, steel billet is obtained. The steel billet is heated to 1160~1180℃ and kept warm for diffusion. It is formed by rolling or forging to obtain steel plate of target thickness. It is then air-cooled to room temperature for later use. (2) Depending on the thickness of the steel plate, heat the steel plate described in step (1) to 820~930℃ and keep it at that temperature for 3~7h to obtain an austenitized steel plate; (3) Transfer the austenitized steel plate described in step (2) to a nitrate bath at a temperature of 300~470℃ for a first isothermal quenching for 6~10h; then take out the sample and transfer it to another nitrate bath at a temperature of 175~230℃ for a second isothermal quenching for 3.5~6h. (4) The sample after secondary isothermal quenching is heated to 450-570℃ at a heating rate of 6-12℃ / min and held for 4-8h. Then it is cooled in the furnace to below 180℃ and then air-cooled to obtain the high-strength and high-toughness alloy steel.

4. The method for manufacturing high-strength, high-toughness alloy steel according to claim 3, characterized in that, The specific steps for obtaining molten steel by batching each element raw material according to the corresponding mass percentage in step (1) are as follows: The metallurgical process combines electric arc furnace primary refining, ladle refining, and vacuum degassing furnace. High-quality low-carbon scrap steel and industrial pure iron are used as base materials, supplemented with ferrochrome, ferroniobium, ferrovanadium, electrolytic nickel, and electrolytic copper for primary and refining. In the later stage of refining, titanium, boron, and final deoxidized aluminum wire are added sequentially by wire feeding. During the refining process, samples are periodically extracted from the furnace front, and the content of multiple alloying elements is tracked in real time using a spark direct-reading spectrometer and dynamically replenished to ensure that the composition is accurately up to standard and to obtain molten steel.

5. The method for manufacturing high-strength, high-toughness alloy steel according to claim 3, characterized in that, In step (1), the steel billet is heated to 1160~1180℃ and kept at that temperature for diffusion for 5~6 hours.

6. The method for manufacturing high-strength, high-toughness alloy steel according to claim 3, characterized in that, When rolling or forging in step (1), the final forging / rolling temperature is ≥850℃.

7. The method for manufacturing high-strength, high-toughness alloy steel according to claim 3, characterized in that, In step (2), for steel plates with a thickness of 20~40mm, heat to 850~900℃ and hold for 3~5h; for steel plates with a thickness of 40~60mm, heat to 870~930℃ and hold for 5~7h.

8. The method for manufacturing high-strength, high-toughness alloy steel according to claim 3, characterized in that, In step (3), the first isothermal quenching is carried out in a nitrate bath at 350~450℃, and the second isothermal quenching is carried out in a nitrate bath at 180~220℃.

9. The method for manufacturing high-strength, high-toughness alloy steel according to claim 8, characterized in that, The holding time for the secondary isothermal quenching in step (3) is 4~5.5h; and / or In step (4), the sample is heated to 460-550℃ at a heating rate of 8-12℃ / min and held at that temperature for 5-7 hours.

10. The application of the high-strength and high-toughness alloy steel according to any one of claims 1 to 2 in the preparation of armor steel.

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