High-hardness impact-resistant ultrahigh-strength low alloy steel and production method thereof

Abstract

The invention discloses high-hardness impact-resistant ultrahigh-strength low alloy steel and a production method thereof, and belongs to the technical field of metal materials. The low alloy steel comprises the following chemical components in percentage by mass: 0.40 to 0.48 percent of C, 1.60 to 2.40 percent of Si, 1.0 to 1.50 percent of Mn, 4.50 to 6.50 percent of Ni, 0.20 to 0.80 percent of Cr, 0.01 to 0.25 percent of W, 0.01 to 0.25 percent of Nb and the balance of Fe and inevitable impurities. Through component regulation and process improvement, the hardness of the obtained low alloy steel is larger than or equal to 56 HRC, the impact energy is larger than or equal to 500 J, the tensile strength is larger than or equal to 2200 MPa, the yield strength is larger than or equal to 1600 MPa, and the low alloy steel has the advantages of being high in hardness, high in strength, resistant to impact, resistant to abrasion and the like and is suitable for national defense military industry, engineering machinery and other key equipment serving under the extreme environments of high loads, abrasion resistance, impact resistance and the like.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology, specifically relating to a high-hardness, impact-resistant, ultra-high-strength low-alloy steel and its production method. Background Technology

[0002] Ultra-high strength steel is the preferred material for manufacturing major national defense equipment and large-scale engineering machinery. However, with the rapid development of industrial technology and the continuous upgrading of equipment, the requirements for material selection have become increasingly stringent. Currently, existing ultra-high strength steels can no longer meet the needs of design and application. This is because traditional low-alloy steels such as AISI430, D6AC, and D406A have reached their strength limits, leading to a decrease in the safety factor of key structural components. High-alloy steels such as AF1410, AerMet100, and the 18Ni-9Co series of ultra-high strength steels mainly achieve steel reinforcement and toughening by adding large amounts of precious elements Ni and Co, which undoubtedly significantly increases production costs.

[0003] Patent CN104328359B discloses a high-toughness, easily spin-formed, and easily weldable ultra-high-strength D506A steel and its preparation method. This steel slightly increases the carbon content compared to D406A, achieving high strength and toughness primarily through the addition of 2.0%–3.0% metallic Ni and ≤0.2% metallic Nb. However, its published data shows that the steel's highest strength is only 2008 MPa, which no longer meets the latest requirements. Patent CN118639139B discloses a low-alloy ultra-high-strength and toughness steel HF1800 and its preparation method. This patent also achieves high strength and toughness by adding 3.5%–4.2% metallic Ni and 0.05%–0.3% metallic Nb, but its maximum tensile strength does not exceed 1972 MPa, also failing to meet the latest requirements. Patent CN112981275B discloses an ultra-high strength steel with a strength exceeding 2200 MPa and its manufacturing method. This steel primarily achieves composite strengthening through the secondary strengthening phase M2C and NiAl aging precipitates, enabling the steel's tensile strength to reach the 2200 MPa level. However, the addition of 11%–16% metallic Ni and 11%–15% metallic Co to its composition significantly increases production costs.

[0004] Therefore, in the face of the urgent need for model iteration in major equipment fields such as national defense and military industry and engineering machinery, it is particularly necessary to develop a low alloy steel that can guarantee excellent strength and hardness, as well as good impact toughness and low cost, in order to solve the problem of material selection for ultra-high strength steel for key structural components. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a high-hardness, impact-resistant, ultra-high-strength low-alloy steel and its production method through reasonable component design and process control.

[0006] To achieve the above-mentioned objectives, the technical solution adopted by this invention is as follows:

[0007] A high-hardness, impact-resistant, ultra-high-strength low-alloy steel has the following chemical composition and mass percentage: C: 0.40–0.48%, Si: 1.60–2.40%, Mn: 1.0–1.50%, Ni: 4.50–6.50%, Cr: 0.20–0.80%, W: 0.01–0.25%, Nb: 0.01–0.25%, with the remainder being Fe and unavoidable impurities.

[0008] The selection of chemical components and the determination of their content range in this invention are based on the following criteria:

[0009] C: The carbon (C) content in steel directly determines its strength. It is mainly improved through two mechanisms: solid solution strengthening and phase transformation strengthening. However, the C content needs to be properly controlled; otherwise, excessively high levels will affect the steel's toughness. In this invention, the mass percentage of C is controlled between 0.40% and 48%, which is higher than that of traditional ultra-high-strength steels such as HF1800 and D506A. Therefore, this ensures the strength and hardness of the high-hardness, impact-resistant ultra-high-strength steel described in this invention. However, to maintain good toughness, Ni (Ni) needs to be added.

[0010] Si: Among all alloying elements, Si has one of the strongest solid solution strengthening effects. Unlike interstitial atoms such as carbon and nitrogen, Si's solid solution strengthening has a relatively small negative impact on plasticity and toughness, making it a cost-effective strengthening method. Furthermore, increasing the Si content allows steel to maintain high strength and hardness even after tempering at higher temperatures, thus endowing the steel with excellent thermal stability. In this invention, the mass percentage of Si is strictly controlled between 1.6% and 2.4%.

[0011] Mn is one of the most effective and cost-efficient elements for improving hardenability. During quenching, even with slower cooling rates (such as oil quenching), it is easier to obtain a high-strength martensitic structure. Simultaneously, Mn effectively eliminates the hot brittleness problem caused by sulfur during hot working. In this invention, the mass percentage content of Mn is controlled between 1.0% and 1.5%, ensuring hardenability while avoiding the risk of increased temper brittleness due to excessive content.

[0012] Ni not only significantly enhances the strength of steel but also effectively improves its ductility and toughness. Appropriately increasing the Ni content helps form Fe-Ni solid solution, which causes lattice distortion, generates a stress field, and thus hinders dislocation movement, further increasing the steel's strength. Simultaneously, Ni lowers the initiation temperature of martensitic transformation, resulting in a higher and more stable content of retained austenite after quenching. These stable retained austenite islands can absorb a large amount of energy and passivate the crack tip during crack propagation through a transformation-induced plastic effect, thereby significantly enhancing the fracture toughness of the steel. In this invention, the mass percentage of Ni is controlled between 4.5% and 6.5%, ensuring the stability of austenite while compensating for the toughness loss caused by increasing the C content.

[0013] Cr: Its primary function is to improve the hardenability of steel. However, Cr has a strong affinity for C, easily forming compounds including (Fe,Cr). 23 Various carbide particles, including C6, tend to coarsen or form a continuous network at grain boundaries or within grains, severely impairing the toughness and plasticity of steel. Therefore, to avoid excessively large (Fe,Cr) particles... 23 C6 particles are formed. In this invention, the mass percentage content of Cr element is controlled between 0.2% and 0.8%. In addition, the increased Ni content will further promote the solid solution of Cr element and reduce the precipitation of Cr-rich carbides. Therefore, a small amount of Cr-containing carbides will be dispersed in the matrix, which can effectively hinder dislocation movement and improve the hardness, strength and wear resistance of the material.

[0014] W (metal) significantly enhances the strength and hardness of steel, especially its red hardness, primarily through carbide strengthening and secondary hardening. W-rich carbides possess extremely high hardness, thermal stability, and wear resistance. These fine carbide particles are uniformly dispersed in the steel matrix, exerting a dual effect of dispersion strengthening and grain refinement strengthening, thereby greatly improving the steel's room temperature strength, hardness, and wear resistance. Furthermore, during tempering, extremely fine, dispersed, and stable MC-type carbides precipitate, producing a strong precipitation strengthening effect, further enhancing the steel's strength and hardness. In this invention, the W content is controlled between 0.01% and 0.25% by mass. Excessive content will lead to an increase in carbides, thereby reducing the steel's plasticity.

[0015] Nitrogen (Nb): Both Nitrogen and W are strong carbon alloying elements, primarily achieving their strengthening effect through carbides. On one hand, Nb-rich carbide particles significantly hinder the movement of austenite grain boundaries, effectively suppressing austenite recrystallization and grain growth, thus achieving fine-grain strengthening. On the other hand, during cooling, nanoscale carbide particles disperse and precipitate from austenite or ferrite. These particles effectively pin dislocations, hindering their movement, thereby producing a significant precipitation strengthening effect and greatly improving the yield strength and tensile strength of the steel. In this invention, the mass percentage content of Nb is controlled between 0.01% and 0.25%; excessive content can also impair plasticity.

[0016] The high-hardness, impact-resistant, ultra-high-strength low-alloy steel of this invention has the following mass percentage content of carbide-forming elements Cr, W, and Nb: 0.12% ≤ Cr + W + Nb ≤ 1%.

[0017] Furthermore, the carbides precipitate uniformly during the heat treatment processes of solution annealing and quenching and tempering. Ideal carbide types and sizes can be obtained by controlling the heating temperature and cooling rate. Specifically, the average particle size of Cr-rich carbides is 100 nm to 200 nm, while the average particle size of W-rich and Nb-rich carbides is 10 nm to 50 nm.

[0018] Furthermore, the Ni and Mn austenitizing elements are uniformly dissolved in the matrix, and after multiple tempering treatments, stable retained austenite is formed, with a retained austenite content of 5% to 10%.

[0019] The present invention also provides a method for producing the above-mentioned high-hardness, impact-resistant, ultra-high-strength low-alloy steel, which includes the following steps;

[0020] S1. The above alloy raw materials are smelted and then cast into electrode ingots;

[0021] S2. Anneal the electrode ingots obtained in S1.

[0022] S3. Electroslag remelting of the electrode round ingots obtained in S2 under a protective atmosphere to obtain electroslag steel ingots.

[0023] S4. The electroslag steel ingot obtained in S3 is subjected to high-temperature diffusion treatment before forging, and then forged. Through multiple forging processes, including upsetting, drawing, and shaping, a forged bar is finally obtained.

[0024] S5. The forged bar obtained in S4 is subjected to solution treatment and annealing treatment. The solution treatment temperature is 950℃~1000℃ and the annealing temperature is 620℃~720℃.

[0025] S6. The annealed forged bar obtained in S5 is subjected to quenching and tempering treatment to finally obtain high-hardness, impact-resistant, ultra-high-strength low-alloy steel.

[0026] Quenching treatment: Heat the forged bar to 850℃~900℃ at a heating rate of 60℃ / h~100℃ / h, hold for 1h~2h, cool with oil or air to ≤100℃, and then temper.

[0027] Tempering treatment: Place the forged bar in a heating furnace at 200℃~300℃, hold it at that temperature for 3h~5h, and then air cool it after removing it from the furnace.

[0028] In step S1, electrode ingots are prepared by using an electric arc furnace combined with ladle refining. The casting temperature is 1520℃~1540℃, the casting time is 220s~720s, and the diameter of the electrode ingots is 420mm~720mm.

[0029] In step S2, the annealing temperature is 650℃~750℃, and the holding time is 10h~18h.

[0030] In step S3, the diameter of the electroslag steel ingot is 500mm to 900mm, and the electroslag melting rate is 8.0kg / min to 12.0kg / min.

[0031] In step S4, the heating temperature of the high-temperature diffusion treatment is 1200℃~1250℃, and after holding at that temperature for 24h~36h, it is lowered to 1150℃~1180℃ before being taken out of the furnace for forging. The diameter of the forging bar is 120mm~280mm.

[0032] In step S5, during solution treatment, the forged bar is heated to 950℃~1000℃ at a heating rate of 60℃ / h~100℃ / h, held for 3h~5h, water-cooled to ≤100℃, and then removed from the water for annealing. The forged bar is then heated to 620℃~720℃ at a heating rate of 60℃ / h~100℃ / h, held for 6h~12h, and then cooled in the furnace to 500℃ before being removed from the furnace and air-cooled.

[0033] In step S6, the tempering process involves multiple tempering processes. The first tempering temperature is 240℃~300℃, and the second tempering temperature is 20℃~40℃ lower than the first tempering temperature. The holding time for both tempering processes is the same.

[0034] The beneficial effects of adopting the above technical solution are as follows: By rationally controlling the types and contents of elements in steel and improving the production process, the present invention makes full use of the synergistic strengthening characteristics of alloying elements such as Ni, Cr, Si, Mn, Nb, and W, and significantly improves the strength, hardness and impact resistance of steel.

[0035] Firstly, by increasing the content of Ni and Mn austenite elements, on the one hand, it promotes the full solid solution of Cr, reduces the precipitation of large carbide particles, and improves the strength and toughness of the matrix; on the other hand, solution quenching is conducive to the stable formation of residual austenite, further improving the toughness of the steel. In particular, the addition of appropriate amounts of strong carbon alloying elements Nb and W is conducive to the formation of a large number of fine, dispersed, and stable MC-type carbides, exerting a strong dual effect of fine grain strengthening and dispersion strengthening, and achieving a multi-scale synergistic strengthening effect. Especially during the quenching process, Nb-rich carbides significantly inhibit austenite grain growth, and during the tempering process, the precipitation of extremely fine W-rich carbide particles produces a strong precipitation strengthening effect, both of which will further improve the strength and hardness of the steel.

[0036] Compared with existing product technologies, the low-alloy steel of this invention has a room temperature hardness ≥56HRC, impact energy ≥500J, tensile strength ≥2200MPa, and yield strength ≥1600MPa, exhibiting advantages such as high hardness, high strength, impact resistance, and wear resistance. It can be mass-produced using a non-vacuum electric furnace system at low cost, making it suitable for large-scale critical equipment in defense, military, and engineering machinery operating under extreme environments requiring wear resistance, impact resistance, and high loads. Attached Figure Description

[0037] Figure 1 This is a metallographic diagram of the low-alloy steel obtained in Example 4 of the present invention in the solution-annealed state;

[0038] Figure 2 This is a scanning electron microscope image of the low alloy steel obtained in Example 4 of the present invention in the solution-annealed state;

[0039] Figure 3 This is a bright-field transmission image of the low-alloy steel obtained in the solution-annealed state in Example 4 of the present invention.

[0040] Figure 4 This is a metallographic diagram of the low-alloy steel obtained in Example 4 of the present invention in its quenched and tempered state.

[0041] Figure 5 This is a scanning electron microscope image of the low alloy steel obtained in Example 4 of the present invention in the quenched and tempered state;

[0042] Figure 6 This is a high-resolution transmission atomic image of Nb-rich carbides in the quenched and tempered state of low-alloy steel obtained in Example 4 of the present invention.

[0043] Figure 7 This is a high-resolution atomic transmission image of W-rich carbides in the quenched and tempered state of the low-alloy steel obtained in Example 4 of the present invention.

[0044] Figure 8 The image shows the XRD pattern of the low alloy steel obtained in Example 4 of this invention in the quenched and tempered state. Detailed Implementation

[0045] Example 1

[0046] The production method of high-hardness, impact-resistant, ultra-high-strength low-alloy steel in this embodiment includes the following steps:

[0047] S1. The raw materials are proportioned according to the element mass percentage shown in Table 1. The raw materials are melted into molten steel using a 10t non-vacuum electric furnace. Then, the steel is desulfurized and impurities are removed in an LF furnace and degassed in a VD furnace. Finally, it is cast into electrode round ingots with a diameter of 420mm. The casting temperature is 1520℃ and the casting time is 220s.

[0048] S2. In order to avoid electrode cracking, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing. The annealing temperature is 650℃ and the holding time is 18h. After the furnace is cooled to 300℃, the electrode is taken out of the furnace and air-cooled. The surface of the electrode ingot is then ground smooth and welded to the dummy electrode to prepare for electroslag.

[0049] S3. Electrode round ingots with a diameter of 420mm are remelted in a 3t protective atmosphere electroslag remelting furnace. The steady-state melting rate is set to 8.0kg / min. After cutting off the bottom plate and riser, an electroslag steel ingot with a diameter of 530mm, a height of about 1500mm, and a weight of 2.5t is obtained.

[0050] S4. The electroslag steel ingot is heated in the furnace to 1250℃ at a rate of 100℃ / h and held at that temperature for 24 hours. Then it is cooled to 1180℃ and held for 3 hours before being taken out of the furnace for forging. The forging process adopts the "three-up and three-draw" method, with each upsetting and pressing down to 1 / 3 of the height. Each furnace reheating time is 1.5 hours. Finally, the forged bar is shaped to obtain a forged bar with an average cross-sectional diameter of 120mm.

[0051] S5. After the forged bar is air-cooled to 200℃, it is loaded into the furnace for solution treatment and annealing. Solution treatment: The forged bar is heated to 950℃ at a heating rate of 60℃ / h, held for 5h, water-cooled to 100℃ and then removed from the water. Annealing treatment: The forged bar is heated to 620℃ at a heating rate of 60℃ / h, held for 8h, and then cooled in the furnace to 500℃ before being removed from the furnace and air-cooled.

[0052] S6. Perform quenching and tempering treatment. Quenching treatment: Heat the forging bar to 850℃ at a heating rate of 100℃ / h, hold for 1h, cool to 100℃ with oil or air, and then perform two tempering treatments.

[0053] First tempering: Place the forged bar directly into a 300℃ heating furnace, hold it at that temperature for 3 hours, and then air cool it after removing it from the furnace;

[0054] Second tempering: The forged bar is placed directly into a 260℃ heating furnace, held for 3 hours, and then air-cooled to obtain high-hardness, impact-resistant, ultra-high-strength low-alloy steel.

[0055] Example 2

[0056] The production method of high-hardness, impact-resistant, ultra-high-strength low-alloy steel in this embodiment includes the following steps:

[0057] S1. The raw materials are proportioned according to the element mass percentage shown in Table 1. The raw materials are melted into molten steel using a 10t non-vacuum electric furnace. Then, the steel is desulfurized and impurities are removed in an LF furnace and degassed in a VD furnace. Finally, it is cast into electrode round ingots with a diameter of 520mm. The casting temperature is 1530℃ and the casting time is 480s.

[0058] S2. In order to avoid electrode cracking, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing treatment. The annealing temperature is 700℃ and the holding time is 15h. After the furnace is cooled to 300℃, the electrode is taken out of the furnace and air-cooled. The surface of the electrode ingot is ground smooth and then welded to the dummy electrode to prepare for electroslag.

[0059] S3. Electrode round ingots with a diameter of 520mm are remelted in a 6t protective atmosphere electroslag remelting furnace. The steady-state melting rate is set to 10.0kg / min. After cutting off the bottom plate and riser, an electroslag steel ingot with a diameter of 640mm, a height of about 1800mm, and a weight of 4.5t is obtained.

[0060] S4. The electroslag steel ingot is heated in the furnace to 1250℃ at a rate of 100℃ / h and held at that temperature for 32 hours. Then it is cooled to 1160℃ and held for 3 hours before being taken out of the furnace for forging. The forging process adopts a "three-up and three-draw" method, with each upsetting and pressing down to 1 / 3 of the height. Each furnace reheating time is 1.5 hours. Finally, the forged bar is shaped to obtain an average cross-sectional diameter of 200mm.

[0061] S5. After the forged bar is air-cooled to 200℃, it is loaded into the furnace for solution treatment and annealing. Solution treatment: The forged bar is heated to 980℃ at a heating rate of 100℃ / h, held for 4h, water-cooled to 100℃ and then removed from the water. Annealing treatment: The forged bar is heated to 660℃ at a heating rate of 100℃ / h, held for 10h, and then cooled to 500℃ in the furnace before being removed from the furnace and air-cooled.

[0062] S6. Perform quenching and tempering treatment. Quenching treatment: Heat the forging bar to 860℃ at a heating rate of 60℃ / h, hold for 1.5h, cool to 100℃ with oil or air, and then perform two tempering treatments.

[0063] First tempering: The forged bar is placed directly into a 280℃ heating furnace, held at that temperature for 5 hours, and then air-cooled after being taken out of the furnace;

[0064] Second tempering: The forged bar is placed directly into a 220℃ heating furnace, held for 5 hours, and then air-cooled to obtain high-hardness, impact-resistant, ultra-high-strength low-alloy steel.

[0065] Example 3

[0066] The production method of high-hardness, impact-resistant, ultra-high-strength low-alloy steel in this embodiment includes the following steps:

[0067] S1. The raw materials are proportioned according to the element mass percentage shown in Table 1. The raw materials are melted into molten steel using a 10t non-vacuum electric furnace. Then, the steel is desulfurized and impurities are removed in an LF furnace and degassed in a VD furnace. Finally, it is cast into electrode round ingots with a diameter of 720mm. The casting temperature is 1540℃ and the casting time is 720s.

[0068] S2. In order to avoid electrode cracking, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing treatment. The annealing temperature is 750℃ and the holding time is 18h. After the furnace is cooled to 300℃, the electrode is taken out of the furnace and air-cooled. The surface of the electrode ingot is then ground smooth and welded to the dummy electrode to prepare for electroslag.

[0069] S3. Electrode round ingots with a diameter of 720mm are remelted in a 10t protective atmosphere electroslag remelting furnace. The steady-state melting rate is set to 12.0kg / min. After cutting off the bottom plate and riser, an electroslag steel ingot with a diameter of 860mm, a height of about 2000mm, and a weight of 9t is obtained.

[0070] S4. The electroslag steel ingot is heated in the furnace to 1250℃ at a rate of 100℃ / h and held at that temperature for 36 hours. Then it is cooled to 1180℃ and held for 3 hours before being taken out of the furnace for forging. The forging process adopts the "three-up and three-draw" method. Each upsetting is 1 / 3 of the height, and the reheating time for each heat is 1.5 hours. Finally, the forged bar with an average cross-sectional diameter of 280mm is obtained.

[0071] S5. After the forged bar is air-cooled to 200℃, it is loaded into the furnace for solution treatment and annealing. Solution treatment: The forged bar is heated to 1000℃ at a heating rate of 80℃ / h, held for 5h, water-cooled to 100℃ and then removed from the water. Annealing treatment: The forged bar is heated to 720℃ at a heating rate of 80℃ / h, held for 6h, and then cooled in the furnace to 500℃ before being removed from the furnace and air-cooled.

[0072] S6. Perform quenching and tempering treatment. Quenching treatment: Heat the forging bar to 900℃ at a heating rate of 80℃ / h, hold for 2h, cool to 100℃ with oil or air, and then perform two tempering treatments.

[0073] First tempering: The forged bar is placed directly into a 290℃ heating furnace, held at that temperature for 4 hours, and then air-cooled after being taken out of the furnace;

[0074] Second tempering: The forged bar is placed directly into a 250℃ heating furnace, held for 4 hours, and then air-cooled to obtain high-hardness, impact-resistant, ultra-high-strength low-alloy steel.

[0075] Example 4

[0076] The production method of high-hardness, impact-resistant, ultra-high-strength low-alloy steel in this embodiment includes the following steps:

[0077] S1. The raw materials are proportioned according to the element mass percentage shown in Table 1. The raw materials are melted into molten steel using a 10t non-vacuum electric furnace. Then, the steel is desulfurized and impurities are removed in an LF furnace and degassed in a VD furnace. Finally, it is cast into electrode round ingots with a diameter of 420mm. The casting temperature is 1540℃ and the casting time is 300s.

[0078] S2. To avoid electrode cracking, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing. The annealing temperature is 650℃ and the holding time is 10h. After the furnace is cooled to 300℃, the electrode is taken out and air-cooled. The surface of the electrode ingot is then ground smooth and welded to the dummy electrode to prepare for electroslag remelting.

[0079] S3. Electrode round ingots with a diameter of 420mm are remelted in a 3t protective atmosphere electroslag remelting furnace. The steady-state melting rate is set to 9.0kg / min. After cutting off the bottom plate and riser, an electroslag steel ingot with a diameter of 530mm, a height of about 1500mm, and a weight of 2.5t is obtained.

[0080] S4. The electroslag steel ingot is heated in the furnace to 1240℃ at a rate of 100℃ / h and held at that temperature for 30 hours. Then it is cooled to 1180℃ and held for 3 hours before being taken out of the furnace for forging. The forging process adopts a "three-up and three-draw" method, with each upsetting and pressing down to 1 / 3 of the height. Each furnace reheating time is 1.5 hours. Finally, the forged bar is shaped to obtain a forged bar with an average cross-sectional diameter of 180mm.

[0081] S5. After the forged bar is air-cooled to 200℃, it is loaded into the furnace for solution treatment and annealing. Solution treatment: The forged bar is heated to 980℃ at a heating rate of 60℃ / h, held for 3h, water-cooled to 100℃ and then removed from the water. Annealing treatment: The forged bar is heated to 650℃ at a heating rate of 60℃ / h, held for 8h, and then cooled in the furnace to 500℃ before being removed from the furnace and air-cooled.

[0082] S6. Perform quenching and tempering treatment. Quenching treatment: Heat the forging bar to 900℃ at a heating rate of 100℃ / h, hold for 1h, cool to 100℃ with oil or air, and then perform two tempering treatments.

[0083] First tempering: The forged bar is placed directly into a 270℃ heating furnace, held at that temperature for 3 hours, and then air-cooled after being taken out of the furnace;

[0084] Second tempering: The forged bar is placed directly into a 250℃ heating furnace, held for 3 hours, and then air-cooled to obtain high-hardness, impact-resistant, ultra-high-strength low-alloy steel.

[0085] Example 5

[0086] The production method of high-hardness, impact-resistant, ultra-high-strength low-alloy steel in this embodiment includes the following steps:

[0087] S1. The raw materials are proportioned according to the element mass percentage shown in Table 1. The raw materials are melted into molten steel using a 10t non-vacuum electric furnace. Then, the steel is desulfurized and deimpurified in an LF furnace and degassed in a VD furnace. Finally, it is cast into electrode round ingots with a diameter of 520mm. The casting temperature is 1540℃ and the casting time is 600s.

[0088] S2. To avoid electrode cracking, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing. The annealing temperature is 680℃ and the holding time is 14h. After the furnace is cooled to 300℃, the electrode is taken out of the furnace and air-cooled. The surface of the electrode ingot is then ground smooth and welded to the dummy electrode to prepare for electroslag remelting.

[0089] S3. Electrode round ingots with a diameter of 520mm are remelted in a 6t protective atmosphere electroslag remelting furnace. The steady-state melting rate is set to 9.0kg / min. After cutting off the bottom plate and riser, an electroslag steel ingot with a diameter of 640mm, a height of about 1800mm, and a weight of 4.5t is obtained.

[0090] S4. The electroslag steel ingot is heated in the furnace to 1240℃ at a rate of 100℃ / h and held at that temperature for 24 hours. Then it is cooled to 1180℃ and held for 3 hours before being taken out of the furnace for forging. The forging process adopts the "three-up and three-draw" method, with each upsetting and pressing down to 1 / 3 of the height. Each furnace reheating time is 1.5 hours. Finally, the forged bar is shaped to obtain a forged bar with an average cross-sectional diameter of 240mm.

[0091] S5. After the forged bar is air-cooled to 200℃, it is loaded into the furnace for solution treatment and annealing. Solution treatment: The forged bar is heated to 960℃ at a heating rate of 60℃ / h, held for 3h, water-cooled to 100℃ and then removed from the water. Annealing treatment: The forged bar is heated to 680℃ at a heating rate of 80℃ / h, held for 9h, and then cooled in the furnace to 500℃ before being removed from the furnace and air-cooled.

[0092] S6. Perform quenching and tempering treatment. Quenching treatment: Heat the forged bar to 880℃ at a heating rate of 100℃ / h, hold for 2 hours, then oil cool or air cool to 100℃, and then perform two tempering treatments.

[0093] First tempering: The forged bar is placed directly into a 270℃ heating furnace, held at that temperature for 3 hours, and then air-cooled after being taken out of the furnace;

[0094] Second tempering: The forged bar is placed directly into a 240℃ heating furnace, held for 3 hours, and then air-cooled to obtain high-hardness, impact-resistant, ultra-high-strength low-alloy steel.

[0095] Example 6

[0096] The production method of high-hardness, impact-resistant, ultra-high-strength low-alloy steel in this embodiment includes the following steps:

[0097] S1. The raw materials are proportioned according to the element mass percentage shown in Table 1. The raw materials are melted into molten steel using a 10t non-vacuum electric furnace. Then, the steel is desulfurized and impurities are removed in an LF furnace and degassed in a VD furnace. Finally, it is cast into electrode round ingots with a diameter of 420mm. The casting temperature is 1530℃ and the casting time is 250s.

[0098] S2. To avoid electrode cracking, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing. The annealing temperature is 720℃ and the holding time is 14h. After the furnace is cooled to 300℃, the electrode is taken out of the furnace and air-cooled. The surface of the electrode ingot is then ground smooth and welded to the dummy electrode to prepare for electroslag remelting.

[0099] S3. Electrode round ingots with a diameter of 420mm are remelted in a 3t protective atmosphere electroslag remelting furnace. The steady-state melting rate is set to 8.0kg / min. After cutting off the bottom plate and riser, an electroslag steel ingot with a diameter of 530mm, a height of about 1500mm, and a weight of 2.5t is obtained.

[0100] S4. The electroslag steel ingot is heated in the furnace to 1220℃ at a rate of 100℃ / h and held at that temperature for 32 hours. Then it is cooled to 1170℃ and held for 3 hours before being taken out of the furnace for forging. The forging process adopts a "three-up and three-draw" method, with each upsetting and pressing down to 1 / 3 of the height. Each furnace reheating time is 1.5 hours. Finally, the forged bar is shaped to obtain a forged bar with an average cross-sectional diameter of 240mm.

[0101] S5. After the forged bar is air-cooled to 200℃, it is loaded into the furnace for solution treatment and annealing. Solution treatment: The forged bar is heated to 970℃ at a heating rate of 70℃ / h, held for 4h, water-cooled to 100℃ and then removed from the water. Annealing treatment: The forged bar is heated to 630℃ at a heating rate of 100℃ / h, held for 8h, and then cooled in the furnace to 500℃ before being removed from the furnace and air-cooled.

[0102] S6. Finally, the solution-annealed forging bar is quenched and tempered. Quenching treatment: The forging bar is heated to 870°C at a heating rate of 90°C / h, held for 2 hours, oil-cooled or air-cooled to 100°C, and then tempered twice.

[0103] First tempering: The forged bar is placed directly into a 260℃ heating furnace, held at that temperature for 4 hours, and then air-cooled after being taken out of the furnace;

[0104] Second tempering: The forged bar is placed directly into a 240℃ heating furnace, held for 4 hours, and then air-cooled to obtain high-hardness, impact-resistant, ultra-high-strength low-alloy steel.

[0105] Comparative Example 1

[0106] The comparative method for producing high-strength low-alloy steel includes the following steps:

[0107] S1. The raw materials are proportioned according to the element mass percentage shown in Table 1. The raw materials are melted into molten steel using a 10t non-vacuum electric furnace. Then, the steel is desulfurized and deimpurified in an LF furnace and degassed in a VD furnace. Finally, it is cast into electrode round ingots with a diameter of 420mm. The casting temperature is 1540℃ and the casting time is 300s.

[0108] S2. To avoid electrode cracking, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing. The annealing temperature is 650℃ and the holding time is 10h. After the furnace is cooled to 300℃, the electrode is taken out and air-cooled. The surface of the electrode ingot is then ground smooth and welded to the dummy electrode to prepare for electroslag remelting.

[0109] S3. Electrode round ingots with a diameter of 420mm are remelted in a 3t protective atmosphere electroslag remelting furnace. The steady-state melting rate is set to 9.0kg / min. After cutting off the bottom plate and riser, an electroslag steel ingot with a diameter of 530mm, a height of about 1500mm, and a weight of 2.5t is obtained.

[0110] S4. The electroslag steel ingot is heated in the furnace to 1240℃ at a rate of 100℃ / h and held for 12 hours. Then it is cooled to 1180℃ and held for 3 hours before being taken out of the furnace for forging. The forging process adopts the "three-up and three-draw" method. Each upsetting is 1 / 3 of the height, and the reheating time for each heat is 1.5 hours. Finally, the forged bar with an average cross-sectional diameter of 180mm is obtained.

[0111] S5. After the forged bar is air-cooled to 200℃, it is loaded into the furnace for solution treatment and annealing. Solution treatment: The forged bar is heated to 980℃ at a heating rate of 60℃ / h, held for 3h, water-cooled to 100℃ and then removed from the water. Annealing treatment: The forged bar is heated to 650℃ at a heating rate of 60℃ / h, held for 8h, and then cooled in the furnace to 500℃ before being removed from the furnace and air-cooled.

[0112] S6. Finally, the solution-annealed forging bar is quenched and tempered. Quenching treatment: The forging bar is heated to 900℃ at a heating rate of 100℃ / h, held for 1h, oil-cooled or air-cooled to 100℃, and then tempered twice.

[0113] First tempering: The forged bar is placed directly into a 270℃ heating furnace, held at that temperature for 3 hours, and then air-cooled after being taken out of the furnace;

[0114] Second tempering: The forged bar is placed directly into a 250℃ heating furnace, held for 3 hours, and then air-cooled to obtain low-alloy steel.

[0115] Comparative Example 2

[0116] The comparative method for producing high-strength low-alloy steel includes the following steps:

[0117] S1. The raw materials are proportioned according to the element mass percentage shown in Table 1. The raw materials are melted into molten steel using a 10t non-vacuum electric furnace. Then, the steel is desulfurized and deimpurified in an LF furnace and degassed in a VD furnace. Finally, it is cast into electrode round ingots with a diameter of 420mm. The casting temperature is 1540℃ and the casting time is 300s.

[0118] S2. To avoid electrode cracking, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing. The annealing temperature is 650℃ and the holding time is 10h. After the furnace is cooled to 300℃, the electrode is taken out and air-cooled. The surface of the electrode ingot is then ground smooth and welded to the dummy electrode to prepare for electroslag remelting.

[0119] S3. Electrode round ingots with a diameter of 420mm are remelted in a 3t protective atmosphere electroslag remelting furnace. The steady-state melting rate is set to 9.0kg / min. After cutting off the bottom plate and riser, an electroslag steel ingot with a diameter of 530mm, a height of about 1500mm, and a weight of 2.5t is obtained.

[0120] S4. The electroslag steel ingot is heated in the furnace to 1240℃ at a rate of 100℃ / h and held for 12 hours. Then it is cooled to 1180℃ and held for 3 hours before being taken out of the furnace for forging. The forging process adopts the "three-up and three-draw" method. Each upsetting is 1 / 3 of the height, and the reheating time for each heat is 1.5 hours. Finally, the forged bar with an average cross-sectional diameter of 180mm is obtained.

[0121] S5. After air cooling the forged bar to 200℃, it is loaded into the furnace for solution treatment and annealing. Solution treatment: The forged bar is heated to 980℃ at a heating rate of 60℃ / h, held for 3 hours, water-cooled to 100℃, and then removed from the water. Annealing treatment: The forged bar is heated to 650℃ at a heating rate of 60℃ / h, held for 8 hours, and then cooled in the furnace to 500℃ before being removed from the furnace and air-cooled.

[0122] S6. Finally, the solution-annealed forging bar is quenched and tempered. Quenching treatment: The forging bar is heated to 950°C at a heating rate of 100°C / h, held for 1 hour, oil-cooled or air-cooled to 100°C, and then tempered twice.

[0123] First tempering: The forged bar is placed directly into a 350℃ heating furnace, held at that temperature for 3 hours, and then air-cooled after being taken out of the furnace;

[0124] Second tempering: The forged bar is placed directly into a 330℃ heating furnace, held at that temperature for 3 hours, and then air-cooled to obtain low-alloy steel.

[0125] Comparative Example 3

[0126] The comparative method for producing high-strength low-alloy steel includes the following steps:

[0127] S1. The raw materials are proportioned according to the element mass percentage shown in Table 1. The raw materials are melted into molten steel using a 10t non-vacuum electric furnace. Then, the steel is desulfurized and deimpurified in an LF furnace and degassed in a VD furnace. Finally, it is cast into electrode round ingots with a diameter of 420mm. The casting temperature is 1540℃ and the casting time is 300s.

[0128] S2. To avoid electrode cracking, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing. The annealing temperature is 650℃ and the holding time is 10h. After the furnace is cooled to 300℃, the electrode is taken out and air-cooled. The surface of the electrode ingot is then ground smooth and welded to the dummy electrode to prepare for electroslag remelting.

[0129] S3. Electrode round ingots with a diameter of 420mm are remelted in a 3t protective atmosphere electroslag remelting furnace. The steady-state melting rate is set to 9.0kg / min. After cutting off the bottom plate and riser, an electroslag steel ingot with a diameter of 530mm, a height of about 1500mm, and a weight of 2.5t is obtained.

[0130] S4. The electroslag steel ingot is heated in the furnace to 1240℃ at a rate of 100℃ / h and held at that temperature for 30 hours. Then it is cooled to 1180℃ and held at that temperature for 3 hours before being taken out of the furnace for forging. The forging process adopts a "three-up and three-draw" method, with each upsetting and pressing down to 1 / 3 of the height. Each furnace reheating time is 1.5 hours. Finally, the forged bar is shaped to obtain a forged bar with an average cross-sectional diameter of 180mm.

[0131] S5. After the forged bar is air-cooled to 200℃, it is loaded into the furnace for solution treatment and annealing. Solution treatment: The forged bar is heated to 980℃ at a heating rate of 60℃ / h, held for 3h, water-cooled to 100℃ and then removed from the water. Annealing treatment: The forged bar is heated to 650℃ at a heating rate of 60℃ / h, held for 8h, and then cooled in the furnace to 500℃ before being removed from the furnace and air-cooled.

[0132] S6. Finally, the solution-annealed forging bar is quenched and tempered. Quenching treatment: The forging bar is heated to 900℃ at a heating rate of 100℃ / h, held for 1h, oil-cooled or air-cooled to 100℃, and then tempered twice.

[0133] First tempering: The forged bar is placed directly into a 270℃ heating furnace, held at that temperature for 3 hours, and then air-cooled after being taken out of the furnace;

[0134] Second tempering: The forged bar is placed directly into a 250℃ heating furnace, held for 3 hours, and then air-cooled to obtain low-alloy steel.

[0135] Comparative Example 4

[0136] The comparative method for producing high-strength low-alloy steel includes the following steps:

[0137] S1. The raw materials are proportioned according to the element mass percentage shown in Table 1. The raw materials are melted into molten steel using a 10t non-vacuum electric furnace. Then, the steel is desulfurized and deimpurified in an LF furnace and degassed in a VD furnace. Finally, it is cast into electrode round ingots with a diameter of 420mm. The casting temperature is 1540℃ and the casting time is 300s.

[0138] S2. To avoid electrode cracking, the electrode is placed in a heating furnace with a furnace temperature ≤300℃ for annealing. The annealing temperature is 650℃ and the holding time is 10h. After the furnace is cooled to 300℃, the electrode is taken out and air-cooled. The surface of the electrode ingot is then ground smooth and welded to the dummy electrode to prepare for electroslag remelting.

[0139] S3. Electrode round ingots with a diameter of 420mm are remelted in a 3t protective atmosphere electroslag remelting furnace. The steady-state melting rate is set to 9.0kg / min. After cutting off the bottom plate and riser, an electroslag steel ingot with a diameter of 530mm, a height of about 1500mm, and a weight of 2.5t is obtained.

[0140] S4. The electroslag steel ingot is heated in the furnace to 1240℃ at a rate of 100℃ / h and held at that temperature for 30 hours. Then it is cooled to 1180℃ and held at that temperature for 3 hours before being taken out of the furnace for forging. The forging process adopts a "three-up and three-draw" method, with each upsetting and pressing down to 1 / 3 of the height. Each furnace reheating time is 1.5 hours. Finally, the forged bar is shaped to obtain a forged bar with an average cross-sectional diameter of 180mm.

[0141] S5. After the forged bar is air-cooled to 200℃, it is loaded into the furnace for solution treatment and annealing. Solution treatment: The forged bar is heated to 980℃ at a heating rate of 60℃ / h, held for 3h, water-cooled to 100℃ and then removed from the water. Annealing treatment: The forged bar is heated to 650℃ at a heating rate of 60℃ / h, held for 8h, and then cooled in the furnace to 500℃ before being removed from the furnace and air-cooled.

[0142] S6. Finally, the solution-annealed forging bar is quenched and tempered. Quenching treatment: The forging bar is heated to 900℃ at a heating rate of 100℃ / h, held for 1h, oil-cooled or air-cooled to 100℃, and then tempered twice.

[0143] First tempering: The forged bar is placed directly into a 270℃ heating furnace, held at that temperature for 3 hours, and then air-cooled after being taken out of the furnace;

[0144] Second tempering: The forged bar is placed directly into a 250℃ heating furnace, held for 3 hours, and then air-cooled to obtain low-alloy steel.

[0145] The room temperature mechanical properties of the low alloy steels obtained in each embodiment and comparative example in the quenched and tempered state are shown in Table 2.

[0146] Table 1. Chemical composition and mass percentage (%) of the low alloy steels in each example and comparative example.

[0147]

[0148]

[0149] Table 2. Room temperature mechanical properties of low alloy steels in the quenched and tempered state of each embodiment and comparative example.

[0150]

[0151] As shown in Table 1, the chemical compositions of Comparative Examples 1 and 2 are the same as those of the steel in Example 4. Comparing the production processes, Comparative Example 1 underwent high-temperature homogenization treatment at 1240℃ for 12 hours; Comparative Example 2 underwent quenching at 950℃ for 1 hour, followed by a first tempering at 350℃ for 3 hours and a second tempering at 330℃ for 3 hours. Compared to Example 4, the steel in Comparative Example 3 did not contain added W and Nb elements, while the Ni content in the steel of Comparative Example 4 was 2%.

[0152] As shown in Table 2, Comparative Example 1 has a tensile strength of 1850 MPa, a yield strength of 1420 MPa, and an elongation of 5%. This is because the homogenization time in Comparative Example 1 was insufficient, resulting in incomplete dissolution of carbides and the precipitation of large carbide particles, ultimately leading to a decrease in both the strength and plasticity of the steel. In contrast, Comparative Example 4, with sufficient homogenization, has a tensile strength of 2225 MPa, a yield strength of 1605 MPa, and an elongation of 12%. In Comparative Example 2, due to excessively high quenching and tempering temperatures, the austenite grains became coarse, the tempered carbide size increased, and the strengthening effect weakened, ultimately leading to a decrease in the strength of the steel. Therefore, the tensile strength of Comparative Example 2 is 2080 MPa, and the yield strength is 1520 MPa. In Comparative Example 3, due to the absence of important carbide strengthening elements W and Nb, the grain refinement and carbide strengthening effects disappeared, resulting in a significant reduction in the strength of the steel, with a tensile strength of only 1450 MPa and a yield strength of only 1200 MPa. In Comparative Example 4, due to the reduction of Ni content to 2%, the plasticity of the steel was significantly reduced, with an elongation of only 5%.

[0153] Depend on Figure 1 It can be seen that the microstructure of the solution-annealed state in Example 4 is very uniform, with a large amount of retained austenite; Figure 2 It can be seen that the solution-annealed carbides in Example 4 are dispersed within the matrix; by Figure 3 It can be seen that the particle size of the carbides in the solution-annealed state in Example 4 is uniformly distributed between 100 nm and 200 nm; Figure 4 It can be seen that the microstructure of the quenched and tempered state in Example 4 is very uniform, with a large amount of retained austenite; Figure 5It can be seen that in Example 4, the quenched and tempered state forms a typical lath-shaped martensite phase, within which a large number of fine carbides precipitate; from Figure 6 It can be seen that the fine NbC carbides precipitated in the quenched and tempered state in Example 4 have a size of approximately 20 nm; from Figure 7 It can be seen that the fine carbides WC precipitated in the quenched and tempered state in Example 4 have a size of approximately 25 nm; from Figure 8 It can be seen that, in addition to the matrix phase, 10% of residual austenite can also be detected in the quenched and tempered state of Example 4.

Claims

1. A high-hardness, impact-resistant, ultra-high-strength low-alloy steel, characterized in that, Its chemical composition and mass percentage are as follows: C: 0.40-0.48%, Si: 1.60-2.40%, Mn: 1.0-1.50%, Ni: 4.50-6.50%, Cr: 0.20-0.80%, W: 0.01-0.25%, Nb: 0.01-0.25%, with the remainder being Fe and unavoidable impurities.

2. The high-hardness, impact-resistant, ultra-high-strength low-alloy steel according to claim 1, characterized in that, The mass percentages of Cr, W, and Nb elements in the low-alloy steel satisfy the following relationship: 0.12% ≤ Cr + W + Nb ≤ 1%.

3. The high-hardness, impact-resistant, ultra-high-strength low-alloy steel according to claim 1, characterized in that, At room temperature, the low alloy steel has a hardness ≥56HRC, impact energy ≥500J, tensile strength ≥2200MPa, and yield strength ≥1600MPa.

4. A method for producing high-hardness, impact-resistant, ultra-high-strength low-alloy steel according to any one of claims 1-3, characterized in that, It includes the following steps; S1. The above alloy raw materials are smelted and then cast into electrode ingots; S2. Anneal the electrode ingots obtained in S1. S3. Electroslag remelting of the electrode ingots obtained in S2 under a protective atmosphere to obtain electroslag steel ingots. S4. The electroslag steel ingot obtained in S3 is subjected to high-temperature diffusion treatment before forging, and then forged. Through multiple forging processes, including upsetting, drawing, and shaping, a forged bar is finally obtained. S5. The forged bar obtained in S4 is subjected to solution treatment and annealing treatment. The solution treatment temperature is 950℃~1000℃ and the annealing temperature is 620℃~720℃. S6. The annealed forged bar obtained in S5 is subjected to quenching and tempering treatment to finally obtain high-hardness, impact-resistant, ultra-high-strength low-alloy steel. Quenching treatment: Heat the forged bar to 850℃~900℃ at a heating rate of 60℃ / h~100℃ / h, hold for 1h~2h, cool with oil or air to ≤100℃, and then temper. Tempering treatment: Place the forged bar in a heating furnace at 200℃~300℃, hold it at that temperature for 3h~5h, and then air cool it after removing it from the furnace.

5. The method for producing high-hardness, impact-resistant, ultra-high-strength low-alloy steel according to claim 4, characterized in that, In step S1, electrode ingots are prepared by using an electric arc furnace combined with ladle refining. The casting temperature is 1520℃~1540℃, the casting time is 220s~720s, and the diameter of the electrode ingots is 420mm~720mm.

6. The method for producing high-hardness, impact-resistant, ultra-high-strength low-alloy steel according to claim 4, characterized in that, In step S2, the annealing temperature is 650℃~750℃, and the holding time is 10h~18h.

7. The method for producing high-hardness, impact-resistant, ultra-high-strength low-alloy steel according to claim 4, characterized in that, In step S3, the diameter of the electroslag steel ingot is 500mm to 900mm, and the electroslag melting rate is 8.0kg / min to 12.0kg / min.

8. The method for producing high-hardness, impact-resistant, ultra-high-strength low-alloy steel according to claim 4, characterized in that, In step S4, the heating temperature of the high-temperature diffusion treatment is 1200℃~1250℃, and after holding at that temperature for 24h~36h, it is lowered to 1150℃~1180℃ before being taken out of the furnace for forging. The diameter of the forging bar is 120mm~280mm.

9. The method for producing high-hardness, impact-resistant, ultra-high-strength low-alloy steel according to claim 4, characterized in that, In step S5, during solution treatment, the forged bar is heated to 950℃~1000℃ at a heating rate of 60℃ / h~100℃ / h, held for 3h~5h, water-cooled to ≤100℃, and then removed from the water for annealing. The forged bar is then heated to 620℃~720℃ at a heating rate of 60℃ / h~100℃ / h, held for 6h~12h, and then cooled in the furnace to 500℃ before being removed from the furnace and air-cooled.

10. The method for producing high-hardness, impact-resistant, ultra-high-strength low-alloy steel according to claim 4, characterized in that, In step S6, the tempering process involves multiple tempering processes. The first tempering temperature is 240℃~300℃, and the second tempering temperature is 20℃~40℃ lower than the first tempering temperature. The holding time for both tempering processes is the same.

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