Low-alloy high hardenability ultra-high strength steel and method for manufacturing the same

Abstract

The application discloses a kind of low alloy high hardenability ultra-high strength steel and its preparation method, with mass percent, its chemical composition is C:0.29~0.33%, Mn:1.30~1.60%, Si:1.30~1.60%, Cr:1.10~1.40%, Ni:0.40~0.50%, Mo:0.30~0.50%, V:0.08~0.15%, Cu:≤0.20%, Ti:0.02~0.06%, B:0.001~0.005%, Al:0.01~0.06%, S:≤0.0060%, P:≤0.013%, the balance is Fe.The application is based on 30CrMnSiA, by trace addition alloying element Ni, Mo, V, Ti, B, Al, and cooperate production process to obtain the high-strength steel of strength 1600MPa grade;Strength is also obtained excellent hardenability while promoting, not only can be used as civil structural material, also can be applied to military industry.

Description

Technical Field

[0001] This invention belongs to the field of high-strength steel technology, and relates to a low-alloy high-hardenability ultra-high-strength steel and its preparation method. Background Technology

[0002] 30CrMnSi alloy structural steel (GB / T3077) belongs to hypoeutectoid steel, with a tensile strength ≥1080MPa and a yield strength ≥835MPa. This material typically requires tempering before use: quenching + high-temperature tempering, chemical heat treatment, flame quenching, or high-frequency quenching, etc., to obtain a uniform sorbite, bainite, or very fine pearlite microstructure with good comprehensive mechanical properties. Due to the strengthening effect of fine grains, these microstructures achieve high strength and appropriate toughness and plasticity. Therefore, 30CrMnSi material is suitable for civilian applications and defense / military applications where high strength requirements are not critical.

[0003] However, with the advancement and development of technology, not only is the demand for ultra-high strength steel increasing, but the performance requirements are also becoming more stringent, while production costs must also be reduced. Summary of the Invention

[0004] The problem solved by this invention is to provide a low-alloy high-hardenability ultra-high strength steel and its preparation method, with a strength of not less than 1600MPa, hardenability of not less than J46-50, and low-cost production capability.

[0005] To achieve the objectives of this invention, the following technical solution is provided:

[0006] A low-alloy, high-hardenability, ultra-high-strength steel, with the following chemical composition by mass percentage:

[0007] C: 0.29–0.33%, Mn: 1.30–1.60%, Si: 1.30–1.60%, Cr: 1.10–1.40%, Ni: 0.40–0.50%, Mo: 0.30–0.50%, V: 0.08–0.15%, Cu: ≤0.20%, Ti: 0.02–0.06%, B: 0.001–0.005%, Al: 0.01–0.06%, S: ≤0.0060%, P: ≤0.013%, balance Fe.

[0008] Furthermore, its chemical composition, expressed as a percentage by mass, is as follows:

[0009] C: 0.29–0.30%, Mn: 1.30–1.60%, Si: 1.36–1.60%, Cr: 1.24–1.40%, Ni: 0.45–0.50%, Mo: 0.30–0.46%, V: 0.08–0.15%, Cu: ≤0.20%, Ti: 0.02–0.041%, B: 0.001–0.0027%, Al: 0.02–0.06%, S: ≤0.0060%, P: ≤0.013%, balance Fe.

[0010] Furthermore, its chemical composition, expressed as a percentage by mass, is as follows:

[0011] C: 0.29–0.33%, Mn: 1.30–1.42%, Si: 1.30–1.54%, Cr: 1.10–1.33%, Ni: 0.40–0.47%, Mo: 0.43–0.50%, V: 0.08–0.10%, Cu: ≤0.20%, Ti: 0.023–0.06%, B: 0.003–0.005%, Al: 0.01–0.06%, S: ≤0.0060%, P: ≤0.013%, balance Fe.

[0012] Furthermore, its chemical composition, expressed as a percentage by mass, is as follows:

[0013] C: 0.31–0.33%, Mn: 1.44–1.60%, C: 0.29–0.33%, Mn: 1.30–1.42%, Si: 1.40–1.52%, Cr: 1.20–1.31%, Ni: 0.40–0.46%, Mo: 0.43–0.50%, V: 0.08–0.12%, Cu: ≤0.20%, Ti: 0.042–0.052%, B: 0.001–0.003%, Al: 0.01–0.06%, S: ≤0.0060%, P: ≤0.013%, balance Fe.

[0014] This invention also proposes a method for preparing the aforementioned low-alloy high-hardenability ultra-high-strength steel, comprising the following operations:

[0015] S1 electric arc furnace melting

[0016] Before charging the furnace, lime is laid at the bottom of the electric arc furnace, and then the furnace charge is loaded; the furnace charge includes carbon steel, ferrochrome, ferronickel, and ferromolybdenum, with a carbon content of ≥0.6%;

[0017] After being loaded into the furnace, the furnace is powered on for melting. Fluorite is added during the melting process to form slag. The entire process involves foam slag submerged arc operation and slag flow operation to ensure that the slag content in the furnace is 3-5%. After complete melting, the furnace enters the oxidation period and oxygen is blown to remove phosphorus.

[0018] The melting process temperature is controlled between 1550 and 1670℃, the current is ≤60000A, and the melting time is 2 to 4 hours.

[0019] After smelting, the steel is tapped at a temperature of 1650–1670℃; the steel composition requirements by mass fraction are: C≤0.1%, P≤0.002%, Cu≤0.10%.

[0020] S2 refining furnace smelting

[0021] When the steel is tapped from the electric arc furnace to the refining furnace, Al material, ferrosilicon, ferromanganese, and pre-melted slag are added along with the flow, followed by slag-forming materials; Ar protection is applied during the steel receiving process in the refining furnace, with a flow rate ≥80NL / min;

[0022] Then add deoxidizing C powder and aluminum granules all at once, and close the furnace door; then quickly raise the temperature to above 1620℃, and after the slag turns white, enter the refining stage;

[0023] The refining temperature is 1620-1650℃ and the refining time is not less than 40 minutes. During the refining process, samples are taken to analyze the composition. Based on the analysis results, ferromolybdenum, ferrovanadium, ferroboron, and other materials required to supplement the composition are added, and Ar gas is stirred at 30-50 NL / min.

[0024] After sufficient refining time and qualified composition, refining is completed. After heating to 1670-1700℃, the ladle is hoisted into the vacuum degassing furnace.

[0025] S3 Vacuum Degassing

[0026] Vacuum degassing vacuum degree ≤67Pa, pressure holding time not less than 20min, Ar gas flow rate controlled 10~40NL / min, sufficient pressure holding time to break the vacuum;

[0027] When the temperature is controlled to 1560-1580℃, the steel ladle is used to pour the electrodes.

[0028] After the electrode is cast, the mold is cooled. After the mold has cooled for 12 hours, the electrode is demolded to obtain the electrode.

[0029] S4 Electroslag Remelting

[0030] After removing the oxide scale from the electrode surface, electroslag remelting is performed. The amount of pre-melted slag is 3-5% by mass. Ar gas protection is used throughout the electroslag remelting process, and the remelting rate is 5-7 kg / min. After remelting and exiting the furnace, annealing treatment is performed.

[0031] S5 Forged

[0032] The steel ingots obtained by electroslag remelting are heated and held at 1190-1230℃ for 2-4 hours, and then forged after being taken out of the furnace.

[0033] The forging ratio must be no less than 7, the initial forging temperature must be ≥1120℃, and the final forging temperature must be ≥850℃.

[0034] S6 Heat Treatment

[0035] After forging, the heat treatment process is carried out in sequence: normalizing, quenching and tempering. During normalizing, the temperature is 920±10℃, and the temperature is held for 3 to 5 hours before air cooling. During quenching, the temperature is 930±10℃, and the temperature is held for 3 to 5 hours before oil cooling. During tempering, the temperature is 260±10℃, and the temperature is held for 2 to 10 hours before air cooling.

[0036] Furthermore, the furnace charge includes carbon scrap steel and CrNiMo recycled steel, ferrochrome, ferronickel, and ferromolybdenum, with a carbon content of 0.70% of the furnace charge mass; the lime lining at the furnace bottom accounts for 0.020 to 0.030% of the furnace charge.

[0037] Furthermore, during the refining furnace smelting, the slag-forming materials include pre-melted slag, lime, and fluorite; by mass ratio, the amount of pre-melted slag is 1.0 to 1.60% of the molten steel, the amount of lime is 1.0 to 1.50% of the molten steel, and the lime:fluorite ratio is 4 to 5:1.

[0038] Compared with the prior art, the present invention has the following beneficial technical effects:

[0039] The low-alloy, high-hardenability ultra-high-strength steel provided by this invention has a high-strength tensile strength Rm≥1600MPa, yield strength Rp0.2≥1300MPa, elongation A≥10%, impact energy Aku≥50J, fracture toughness K1c≥110MPa*m0.5, and hardenability ≥J46-50. It is a low-alloy, low-cost, high-hardenability ultra-high-strength steel. This ultra-high-strength steel can be used not only as a civilian structural material but also in military applications.

[0040] The low-alloy, high-hardenability, ultra-high-strength steel provided by this invention is based on 30CrMnSiA. Strength is enhanced by increasing trace amounts of Si, Mn, Cr, and Ni elements, utilizing the principle of substitutional solid solution strengthening. By adding trace amounts of Al, Ti, and V elements, these elements preferentially combine with dissolved N and C atoms in the alloy melt during solidification to form fine, dispersed strengthening phases AlN, TiN, and V4C3. These phases, present in the matrix, hinder grain boundary movement and grain growth, refining the grain size and increasing strength and toughness. Furthermore, the inclusion content is reduced, ultimately achieving a tensile strength of not less than 1600 MPa. Compared to the tensile strength of 1080 MPa for 30CrMnSiA, the tensile strength of this invention is significantly improved.

[0041] The low-alloy high-hardenability ultra-high-strength steel provided by this invention further improves hardenability by adding trace amounts of Mo and B elements to hinder the diffusion of C atoms and the formation of pearlite during quenching, thereby creating favorable conditions for the formation of martensite.

[0042] The low-alloy, high-hardenability, ultra-high-strength steel provided by this invention uses as little expensive and scarce resources as possible, such as nickel, cobalt, tungsten, and molybdenum. The total content of the precious metals Ni, Mo, and V used is less than 1%, and the smelting process is an inexpensive electric arc furnace + refining furnace + electroslag remelting. Therefore, the production cost of ultra-high-strength steel is reduced while ensuring quality. Attached Figure Description

[0043] Figure 1 This is the hardenability test curve of the ultra-high strength steel of the present invention.

[0044] Figure 2 The grain size test results of the ultra-high strength steel of this invention are shown.

[0045] Figure 3 The results of the detection of inclusions in ultra-high strength steel according to the present invention. Detailed Implementation

[0046] The present invention will be further described in detail below with reference to embodiments. These descriptions are for illustrative purposes only and are not intended to limit the scope of the invention.

[0047] The low-alloy, high-hardenability, ultra-high-strength steel provided by this invention is based on 30CrMnSiA. By increasing the amount of trace Si, Mn, Cr, and Ni elements, the strength is improved by utilizing the principle of substitution solid solution strengthening. By adding trace Al, Ti, and V elements, they preferentially combine with N and C atoms dissolved in the alloy liquid during solidification to form fine and dispersed strengthening phases AlN, TiN, and V4C3. These phases exist in the matrix and hinder the movement of grain boundaries and grain growth in the steel, thus refining the grain size.

[0048] Example 1

[0049] A low-alloy, high-hardenability, ultra-high-strength steel, with the following chemical composition by mass percentage:

[0050] C: 0.30%, Mn: 1.30%, Si: 1.36%, Cr: 1.24%, Ni: 0.45%, Mo: 0.46%, V: 0.08%, Cu: ≤0.010%, Ti: 0.041%, B: 0.0027%, Al: 0.02%, S: 0.002%, P: 0.004%, balance Fe.

[0051] The preparation method of the low-alloy high-hardenability ultra-high-strength steel includes the following steps:

[0052] S1 electric arc furnace melting

[0053] A. Select furnace charge according to composition requirements. The furnace charge is mainly composed of carbon scrap steel (50% to 70%), CrNiMo recycled steel (30% to 50%), ferrochrome, ferronickel, and ferromolybdenum, with a carbon content of 0.70%.

[0054] Before charging the furnace, 750 kg of lime is laid at the bottom of the furnace, and then scrap steel is charged and smelted by electricity. The charging amount is 30 tons. The lime laid at the bottom makes the molten steel slag alkaline, which has a dephosphorization effect.

[0055] B. During the material processing, 375 kg of fluorite is added, and the slag production is 3.75%. The entire process involves foam slag submerged arc operation (oxygen and carbon powder are injected at the arc generation point to increase the viscosity of the liquid slag and transform it into foam slag), and slag flow operation is used. After full melting, the process enters the oxidation period and oxygen blowing is used for dephosphorization.

[0056] The current control is ≤60000A, the melting time is 2-4h, and the melting process temperature is controlled between 1550-1670℃.

[0057] C. Steel composition control: C: 0.070%, P ≤ 0.001%, Cu ≤ 0.10%. The tapping temperature is 1668℃.

[0058] S2 refining furnace smelting

[0059] A. During the tapping of steel from the electric arc furnace, 30 kg of Al cake, 150 kg of silicon-manganese alloy, and 150 kg of pre-melted slag are added in the flow; the Ar flow rate during the steel receiving process in the refining furnace is 87 NL / min.

[0060] B. Add slag-forming materials to the refining furnace, including 600 kg of lime (lime:fluorite = 5:1), and add it after tapping the steel. Then add 60 kg of C powder, 60 kg of calcium carbide, and 30 kg of aluminum granules at once, and close the furnace door for diffusion deoxidation.

[0061] C. After adding the slag-forming materials and deoxidizer, rapidly raise the temperature to 1633℃. Once the slag turns white, proceed to the refining stage. Refining temperature: 1633℃; Refining time: 45 minutes.

[0062] During the refining process, samples were taken for analysis of the components. Based on the analysis results and wiring calculations, 10 kg of carbon powder, 65 kg of ferromanganese, 25 kg of ferrosilicon, 60 kg of ferrochrome, 29 kg of ferronickel, 2 kg of ferromolybdenum, 20 kg of ferrovanadium, 3.1 kg of sponge titanium, and 1.5 kg of ferroboron were added.

[0063] D. After sufficient refining time and qualified composition, the refining process is completed. The temperature is raised to 1688℃, and the ladle is placed into the vacuum degassing furnace.

[0064] S3 Vacuum Degassing

[0065] Vacuum degassing was performed at a vacuum level of 33 Pa, with a holding time of 20 min and an Ar gas flow rate of 30 NL / min. The vacuum was broken after the holding time was sufficient.

[0066] Temperature measurement: 1563℃. Electrode for steel ladle casting: dimensions are φ530*L, where L is the length in mm.

[0067] After the electrode casting is completed and the mold is cooled for 12 hours, the electrode is obtained after demolding.

[0068] S4 Electroslag Remelting

[0069] After removing the oxide scale from the electrode surface, electroslag remelting is performed.

[0070] The amount of pre-melted slag used is 180 kg. The composition of the pre-melted slag by mass percentage is: CaF2: 37.5%, CaO: 21.7%, MgO: 3.3%, Al2O3: 31.5%, SiO2: 6.0%, C: ≤0.05%, P: ≤0.01%, S: ≤0.03%.

[0071] The electroslag remelting process is protected by Ar gas, and the remelting rate is 7 kg / min.

[0072] After remelting, the dimensions are φ640*L. After remelting and exiting the furnace, the product undergoes annealing.

[0073] S5 Forged

[0074] The steel ingot obtained from electroslag remelting was heated to 1210±20℃ and held at that temperature for 4 hours before forging. The initial forging temperature was 1187℃, and the final forging temperature was 883℃. The forging ratio was 1:3, and the forged dimensions were φ250*L.

[0075] Heat treatment of S6 bars

[0076] The heat treatment process is normalizing + quenching + tempering.

[0077] Normalizing: Hold at 920±10℃ for 4.5h, then air cool; Normalizing can refine and homogenize the matrix grains, making it easier to obtain equiaxed grains;

[0078] Quenching: Hold at 930±10℃ for 4.5h, then oil cool; Quenching allows the austenitic structure to bypass the pearlite and form a C-curve, maximizing the acquisition of martensite structure;

[0079] Tempering: Hold at 260±10℃ for 12 hours, then air cool after removal from the furnace; tempering can reduce the internal stress of the martensitic structure and improve the toughness of the material.

[0080] The low-alloy, high-hardenability, ultra-high-strength steel prepared in this embodiment, after corresponding testing, has a tensile strength of 1637 MPa, a yield strength of 1356 MPa, an elongation of 13.5%, an impact energy of 77 J, a fracture toughness K1c of 115.3 MPa*m0.5, and a hardenability of J46-50.

[0081] Figure 1 To test the hardenability, the test method is in accordance with GB / T 225-2006: the end-quenching test method for hardenability of steel is the Jominy test.

[0082] Example 2

[0083] A low-alloy, high-hardenability, ultra-high-strength steel, with the following chemical composition by weight percentage:

[0084] C: 0.29%, Mn: 1.42%, Si: 1.54%, S: 0.001%, P: 0.0025%, Cr: 1.33%, Ni: 0.47%, Mo: 0.43%, V: 0.08%, Cu: 0.01%, Ti: 0.023%, B: 0.0022%, Al: 0.017%, balance Fe.

[0085] The preparation method of the low-alloy high-hardenability ultra-high-strength steel includes the following steps:

[0086] S1 electric arc furnace melting

[0087] A. The furnace charge consists of carbon scrap steel, CrNiMo recycled steel, ferrochrome, ferronickel, and ferromolybdenum, with a carbon content of 0.70%.

[0088] Before loading the furnace, 825 kg of lime was laid at the bottom of the furnace, and then scrap steel was loaded and smelted by electricity. The loading amount was 33 tons.

[0089] B. During the chemical processing, 413 kg of fluorite was added, and the slag production rate was 3.75%. The entire process involved foamed slag submerged arc operation and slag flow operation. After complete melting, the process entered the oxidation period, followed by oxygen blowing for dephosphorization.

[0090] C. Steel composition control: C: 0.080%, P: 0.001%, Cu ≤ 0.10%. The tapping temperature is 1663℃.

[0091] S2 refining furnace smelting

[0092] A. 33 kg of Al cake, 165 kg of silicon-manganese alloy, and 165 kg of pre-melted slag are added along with the tapping of the electric arc furnace.

[0093] Ar flow rate during steel receiving process in refining furnace is 85 NL / min.

[0094] B. Lime and fluorite are also added to the refining furnace to form slag. 660 kg of lime is added, with a lime:fluorite ratio of 5:1. The lime is added after the steel is tapped.

[0095] Then add 66 kg of C powder and 33 kg of aluminum granules at once, close the furnace door, and perform diffusion deoxidation.

[0096] C. After adding the slag-forming materials (pre-melted slag, lime, fluorite) and deoxidizers (carbon powder, aluminum granules), rapidly raise the temperature to 1637℃. Once the slag turns white, the refining process begins. The refining temperature is 1637℃, and the refining time is 45 minutes. During the refining process, samples are taken for composition analysis. Based on the analysis results and the calculations, the following components are added: 8 kg of carbon powder, 55 kg of ferromanganese, 11 kg of ferrosilicon, 31 kg of ferrochrome, 5 kg of ferronickel, 17 kg of ferromolybdenum, 22 kg of ferrovanadium, 3.5 kg of sponge titanium, 1.7 kg of ferroboron, and 1 kg of aluminum granules.

[0097] D. With sufficient refining time and qualified composition, refining is completed. The temperature is raised to 1686℃, and the ladle is placed into the vacuum degassing furnace.

[0098] S3 Vacuum Degassing

[0099] Vacuum degassing was performed at a vacuum level of 34 Pa, with a holding time of 20 min and an Ar gas flow rate of 37 NL / min. The vacuum was broken after sufficient holding time. The temperature was measured at 1562℃. Electrodes with dimensions of φ530*L were cast using a steel ladle. After casting, the mold was cooled for 12 hours before demolding to obtain the electrode.

[0100] S4 Electroslag Remelting

[0101] After removing the oxide scale from the electrode surface, electroslag remelting is performed. The amount of pre-melted slag used is 180 kg, and the composition of the pre-melted slag is: CaF2: 37.5%, CaO: 21.7%, MgO: 3.3%, Al2O3: 31.5%, SiO2: 6.0%, C: ≤0.05%, P: ≤0.01%, S: ≤0.03%.

[0102] The electroslag remelting process is conducted under Ar gas protection throughout, with a remelting rate of 7 kg / min. The remelted product has a diameter of φ640*L and undergoes annealing after being removed from the furnace.

[0103] S5 Forged

[0104] The steel ingot was heated to 1210±20℃ and held for 4 hours before forging began. The initial forging temperature was 1165℃, and the final forging temperature was 867℃. The forging ratio was 1:3, and the forged dimensions were φ250*L.

[0105] Heat treatment of S6 bars

[0106] The heat treatment process is normalizing + quenching + tempering.

[0107] Normalizing: Hold at 920±10℃ for 4.5 hours, then air cool.

[0108] Quenching: Hold at 930±10℃ for 4.5h, then oil cool.

[0109] Tempering: Hold at 260±10℃ for 12 hours, then air cool after removal from the furnace.

[0110] The low-alloy high-hardenability ultra-high-strength steel prepared in this embodiment, after being processed by this process, has a tensile strength of 1682 MPa, a yield strength of 1373 MPa, an elongation of 12.0%, an impact energy of 74 J, a fracture toughness K1c of 114.2 MPa*m0.5, and a hardenability of J47-50.

[0111] Example 3

[0112] A low-alloy, high-hardenability, ultra-high-strength steel, with the following chemical composition by weight percentage:

[0113] C: 0.32%, Mn: 1.44%, Si: 1.52%, S: 0.0010%, P: 0.0020%, Cr: 1.31%, Ni: 0.46%, Mo: 0.50%, V: 0.12%, Cu: 0.01%, Ti: 0.052%, B: 0.005%, Al: 0.045%, balance Fe.

[0114] The preparation method of the low-alloy high-hardenability ultra-high strength steel includes the following steps:

[0115] S1 electric arc furnace melting

[0116] A. The furnace charge consists of carbon scrap steel, CrNiMo recycled steel, ferrochrome, ferronickel, and ferromolybdenum, with a carbon content of 0.70%. Before charging, 775 kg of lime is laid at the bottom of the furnace for dephosphorization. Then, scrap steel is charged and energized for melting. The total charge is 31 tons.

[0117] B. During the material preparation process, 388 kg of fluorite is added, and the slag production rate is 3.75%. The entire process involves foamed slag submerged arc operation and slag flow operation. After full melting, the process enters the oxidation period, where oxygen is blown to remove phosphorus, aluminum, and titanium.

[0118] C. Steel composition: C 0.07%, P 0.002%, Cu≤0.10%. The tapping temperature is 1659℃.

[0119] S2 refining furnace smelting

[0120] A. During the tapping of steel from the electric arc furnace, 31 kg of Al cake, 155 kg of silicon-manganese alloy, and 155 kg of pre-melted slag are added in the flow. The Ar flow rate during the steel receiving process in the refining furnace is 91 NL / min.

[0121] B. Add slag-forming materials to the refining furnace: 630 kg of lime (lime:fluorite = 5:1), added after tapping. Then add 62 kg of carbon powder, 62 kg of calcium carbide, and 31 kg of aluminum granules all at once, and close the furnace door for diffusion deoxidation.

[0122] C. After adding the slag-forming materials and deoxidizer, rapidly raise the temperature to 1643℃. Once the slag turns white, proceed to the refining stage. The refining temperature is 1643℃, and the refining time is 45 minutes. During the refining process, samples are taken for composition analysis. Based on the analysis results and the calculation of the feed lines, add 12.4 kg of carbon powder, 24 kg of ferromanganese, 50 kg of ferrosilicon, 31 kg of ferrochrome, 9 kg of ferronickel, 23 kg of ferromolybdenum, 21 kg of ferrovanadium, 3.0 kg of sponge titanium, and 1.3 kg of ferroboron.

[0123] D. After sufficient refining time and qualified composition, the refining process is completed. The temperature is raised to 1681℃, and the ladle is placed into the vacuum degassing furnace.

[0124] S3 Vacuum Degassing

[0125] Vacuum degassing was performed at a vacuum level of 31 Pa, with a holding time of 20 min and an Ar gas flow rate of 31 NL / min. The vacuum was broken after sufficient holding time. Temperature was measured at 1566℃. Electrodes with dimensions φ530*L were cast using a steel ladle. After casting, the mold was cooled for 12 hours before demolding to obtain the electrode.

[0126] S4 Electroslag Remelting

[0127] After removing the oxide scale from the electrode surface, electroslag remelting is performed. The amount of pre-melted slag used is 180 kg, and its composition is: CaF2: 37.5%, CaO: 21.7%, MgO: 3.3%, Al2O3: 31.5%, SiO2: 6.0%, C: ≤0.05%, P: ≤0.01%, S: ≤0.03%. Ar gas protection is used throughout the electroslag remelting process, and the remelting rate is 7 kg / min. The remelted electrode has a diameter of φ640*L and undergoes annealing after being removed from the furnace.

[0128] S5 Forged

[0129] The steel ingot was heated to 1210±20℃ and held for 4 hours before forging began. The initial forging temperature was 1182℃, and the final forging temperature was 851℃. The forging ratio was 12, and the forged dimensions were φ250*L.

[0130] Heat treatment of S6 bars

[0131] The heat treatment process is normalizing + quenching + tempering.

[0132] Normalizing: Hold at 920±10℃ for 4.5 hours, then air cool.

[0133] Quenching: Hold at 930±10℃ for 4.5h, then oil cool.

[0134] Tempering: Hold at 260±10℃ for 12 hours, then air cool after removal from the furnace.

[0135] The low-alloy high-hardenability ultra-high-strength steel prepared in this embodiment, after being processed by this process, has a tensile strength of 1671 MPa, a yield strength of 1354 MPa, an elongation of 13.0%, an impact energy of 75 J, a fracture toughness K1c of 112.1 MPa*m0.5, and a hardenability of J48-50.

[0136] Example 4

[0137] A low-alloy, high-hardenability, ultra-high-strength steel, with the following chemical composition by weight percentage:

[0138] C: 0.31%, Mn%: 1.42%, Si: 1.30%, S: 0.0014%, P: 0.0023%, Cr: 1.31%, Ni: 0.44%, Mo: 0.49%, V: 0.12%, Cu: 0.01%, Ti: 0.042%, B: 0.003%, Al: 0.060%, balance Fe.

[0139] The preparation method of the low-alloy high-hardenability ultra-high-strength steel includes the following steps:

[0140] S1 electric arc furnace melting

[0141] A. The furnace charge consists of carbon scrap steel, CrNiMo recycled steel, ferrochrome, ferronickel, and ferromolybdenum, with a carbon content of 0.70%. Before charging, 750 kg of lime is laid at the bottom of the furnace for dephosphorization. Then, scrap steel is charged and energized for melting. The furnace charge is 30 tons.

[0142] B. During the chemical processing, 375 kg of fluorite is added, and the slag production rate is 3.75%. The entire process involves foamed slag submerged arc operation and slag flow operation. After full melting, the process enters the oxidation period, where oxygen is blown to remove phosphorus, aluminum, and titanium.

[0143] C. Steel composition: C 0.09%, P 0.001%, Cu≤0.10%. The tapping temperature is 1662℃.

[0144] S2 refining furnace smelting

[0145] A. During the tapping of steel from the electric arc furnace, 30 kg of Al cake, 150 kg of silicon-manganese alloy, and 150 kg of pre-melted slag are added in the flow. The Ar flow rate during the steel receiving process in the refining furnace is 92 NL / min.

[0146] B. Add slag-forming materials to the refining furnace: 600 kg of lime (lime:fluorite = 5:1), added after tapping. Then add 60 kg of C powder, 60 kg of calcium carbide, and 30 kg of aluminum granules all at once, and close the furnace door for diffusion deoxidation.

[0147] C. After adding the slag-forming materials and deoxidizer, rapidly raise the temperature to 1645℃. Once the slag turns white, proceed to the refining stage. The refining temperature is 1645℃, and the refining time is 45 minutes. During the refining process, samples are taken for composition analysis. Based on the analysis results and the calculation of the wiring, add 5 kg of carbon powder, 47 kg of ferromanganese, 25 kg of ferrosilicon, 8 kg of ferrochrome, 19 kg of ferronickel, 14 kg of ferromolybdenum, 27 kg of ferrovanadium, 2.9 kg of sponge titanium, 1.5 kg of ferroboron, and 1.2 kg of aluminum granules.

[0148] D. After sufficient refining time and qualified composition, the refining process is completed. The temperature is raised to 1687℃, and the ladle is placed into the vacuum degassing furnace.

[0149] S3 Vacuum Degassing

[0150] Vacuum degassing was performed at a vacuum level of 35 Pa, with a holding time of 20 min and an Ar gas flow rate of 38 NL / min. The vacuum was broken after sufficient holding time. The temperature was measured at 1568℃. Electrodes with dimensions of φ530*L were cast using a steel ladle. After casting, the mold was cooled for 12 hours before demolding to obtain the electrode.

[0151] S4 Electroslag Remelting

[0152] After removing the oxide scale from the electrode surface, electroslag remelting is performed. The amount of pre-melted slag used is 180 kg, and its composition is: CaF2: 37.5%, CaO: 21.7%, MgO: 3.3%, Al2O3: 31.5%, SiO2: 6.0%, C: ≤0.05%, P: ≤0.01%, S: ≤0.03%. Ar gas protection is used throughout the electroslag remelting process, and the remelting rate is 7 kg / min. The remelted electrode has a diameter of φ640*L and undergoes annealing after being removed from the furnace.

[0153] S5 Forged

[0154] The steel ingot was heated to 1210±20℃ and held for 4 hours before forging began. The initial forging temperature was 1177℃, and the final forging temperature was 866℃. The forging ratio was 1:3, and the forged dimensions were φ250*L.

[0155] Heat treatment of S6 bars

[0156] The heat treatment process is normalizing + quenching + tempering.

[0157] Normalizing: Hold at 920±10℃ for 4.5 hours, then air cool.

[0158] Quenching: Hold at 930±10℃ for 4.5h, then oil cool.

[0159] Tempering: Hold at 260±10℃ for 12 hours, then air cool after removal from the furnace.

[0160] The low-alloy, high-hardenability, ultra-high-strength steel prepared in this embodiment has a tensile strength of 1623 MPa, a yield strength of 1334 MPa, an elongation of 13.5%, an impact energy of 68 J, a fracture toughness K1c of 120.9 MPa*m0.5, and a hardenability of J48-50.

[0161] The grain size test results of the ultra-high strength steel of this invention are as follows: Figure 2 As shown, the test result is level 6.5; this invention refines the grain size, increasing strength and toughness; and through a reasonable process, the inclusion content is reduced, and the inclusion detection is as follows. Figure 3 As shown, the results indicate that Class B fine particles are grade 0.5, Class D fine particles are grade 0.5, and the rest are grade 0.

[0162] The low-alloy, high-hardenability ultra-high-strength steel provided by this invention has a high-strength tensile strength Rm≥1600MPa, yield strength Rp0.2≥1300MPa, elongation A≥10%, impact energy Aku≥50J, fracture toughness K1c≥110MPa*m0.5, and hardenability ≥J46-50. It is a low-alloy, low-cost, high-hardenability ultra-high-strength steel. This ultra-high-strength steel can be used not only as a civilian structural material but also in military applications.

[0163] The embodiments given above are preferred examples for implementing the present invention, and the present invention is not limited to the above embodiments. Any non-essential additions or substitutions made by those skilled in the art based on the technical features of the present invention are within the protection scope of the present invention.

Claims

1. A low-alloy, high-hardenability, ultra-high-strength steel, characterized in that, Its chemical composition, expressed as a percentage by mass, is as follows: C: 0.29~0.33%, Mn: 1.30~1.60%, Si: 1.30~1.60%, Cr: 1.10~1.40%, Ni: 0.40~0.50%, Mo: 0.30~0.50%, V: 0.08~0.15%, Cu: ≤0.20%, Ti: 0.02~0.06%, B: 0.001~0.005%, Al: 0.01~0.06%, S: ≤0.0060%, P: ≤0.013%, balance Fe; Its preparation method is as follows: S1 electric arc furnace melting Before charging, lime is laid at the bottom of the electric arc furnace, and then the furnace charge is loaded; the furnace charge includes carbon steel, ferrochrome, ferronickel, and ferromolybdenum, with a carbon content of ≥0.6%; After being loaded into the furnace, the furnace is powered on for melting. Fluorite is added during the melting process to form slag. The entire process involves foam slag submerged arc operation and slag flow operation to ensure that the slag content in the furnace is 3-5%. After complete melting, the furnace enters the oxidation period and oxygen is blown to remove phosphorus. The melting process temperature is controlled between 1550~1670℃, the current is ≤60000A, and the melting time is 2~4h; After smelting, the steel is tapped at a temperature of 1650~1670℃; the steel composition requirements by mass fraction are: C≤0.1%, P≤0.002%, Cu≤0.10%; S2 refining furnace smelting When the steel is tapped from the electric arc furnace to the refining furnace, Al materials, ferromanganese, ferrosilicon, and pre-melted slag are added along with the flow, followed by slag-forming materials; Ar protection is applied during the steel receiving process in the refining furnace, with a flow rate ≥80NL / min; Then add deoxidizing C powder and aluminum granules all at once, and close the furnace door; then quickly raise the temperature to above 1620℃, and after the slag turns white, enter the refining stage; The refining temperature is 1620~1650℃, and the refining time is not less than 40min. During the refining process, samples are taken to analyze the composition. Based on the analysis results, ferromolybdenum, ferrovanadium, ferroboron, and other materials required to supplement the composition are added, and Ar gas is stirred at 30~50NL / min. After sufficient refining time and qualified composition, refining is completed. After heating to 1670~1700℃, the ladle is hoisted into the vacuum degassing furnace. S3 Vacuum Degassing Vacuum degassing vacuum degree ≤67Pa, pressure holding time not less than 20min, Ar gas flow rate controlled 10~40NL / min; When the temperature is controlled to 1560~1580℃, the steel ladle is used to pour the electrodes. After the electrode is cast, the mold is cooled. After the mold has cooled for 12 hours, the electrode is demolded to obtain the electrode. S4 Electroslag Remelting After removing the oxide scale from the electrode surface, electroslag remelting is performed. The amount of pre-melted slag is 3-5% by mass. Ar gas protection is used throughout the electroslag remelting process, and the remelting rate is 5-7 kg / min. After remelting and exiting the furnace, annealing treatment is performed. S5 Forged The steel ingots obtained by electroslag remelting are heated and held at 1190~1230℃ for 2~4 hours, and then forged after being taken out of the furnace. The forging ratio is required to be no less than 7, the initial forging temperature is ≥1120℃, and the final forging temperature is ≥850℃; S6 Heat Treatment After forging, the heat treatment process is carried out in sequence: normalizing, quenching and tempering. During normalizing, the temperature is 920±10℃, and the temperature is held for 3~5 hours before air cooling. During quenching, the temperature is 930±10℃, and the temperature is held for 3~5 hours before oil cooling. During tempering, the temperature is 260±10℃, and the temperature is held for 2~10 hours before air cooling. Its tensile strength Rm≥1600MPa, yield strength Rp0.2≥1300MPa, elongation A≥10%, impact energy Aku≥50J, fracture toughness K1c≥110MPa*m0.5, and hardenability ≥J46-50.

2. The low-alloy high-hardenability ultra-high-strength steel as described in claim 1, characterized in that, Its chemical composition, expressed as a percentage by mass, is as follows: C: 0.29~0.30%, Mn: 1.30~1.60%, Si: 1.36~1.60%, Cr: 1.24~1.40%, Ni: 0.45~0.50%, Mo: 0.30~0.46%, V: 0.08~0.15%, Cu: ≤0.20%, Ti: 0.02~0.041%, B: 0.001~0.0027%, Al: 0.02~0.06%, S: ≤0.0060%, P: ≤0.013%, balance Fe.

3. The low-alloy high-hardenability ultra-high-strength steel as described in claim 1, characterized in that, Its chemical composition, expressed as a percentage by mass, is as follows: C: 0.29~0.33%, Mn: 1.30~1.42%, Si: 1.30~1.54%, Cr: 1.10~1.33%, Ni: 0.40~0.47%, Mo: 0.43~0.50%, V: 0.08~0.10%, Cu: ≤0.20%, Ti: 0.023~0.06%, B: 0.003~0.005%, Al: 0.01~0.06%, S: ≤0.0060%, P: ≤0.013%, balance Fe.

4. A method for preparing the low-alloy high-hardenability ultra-high-strength steel according to claim 1, characterized in that, Includes the following operations: S1 electric arc furnace melting Before charging, lime is laid at the bottom of the electric arc furnace, and then the furnace charge is loaded; the furnace charge includes carbon steel, ferrochrome, ferronickel, and ferromolybdenum, with a carbon content of ≥0.6%; After being loaded into the furnace, the furnace is powered on for melting. Fluorite is added during the melting process to form slag. The entire process involves foam slag submerged arc operation and slag flow operation to ensure that the slag content in the furnace is 3-5%. After complete melting, the furnace enters the oxidation period and oxygen is blown to remove phosphorus. The melting process temperature is controlled between 1550~1670℃, the current is ≤60000A, and the melting time is 2~4h; After smelting, the steel is tapped at a temperature of 1650~1670℃; the steel composition requirements by mass fraction are: C≤0.1%, P≤0.002%, Cu≤0.10%; S2 refining furnace smelting When the steel is tapped from the electric arc furnace to the refining furnace, Al materials, ferromanganese, ferrosilicon, and pre-melted slag are added along with the flow, followed by slag-forming materials; Ar protection is applied during the steel receiving process in the refining furnace, with a flow rate ≥80NL / min; Then add deoxidizing C powder and aluminum granules all at once, and close the furnace door; then quickly raise the temperature to above 1620℃, and after the slag turns white, enter the refining stage; The refining temperature is 1620~1650℃, and the refining time is not less than 40min. During the refining process, samples are taken to analyze the composition. Based on the analysis results, ferromolybdenum, ferrovanadium, ferroboron, and other materials required to supplement the composition are added, and Ar gas is stirred at 30~50NL / min. After sufficient refining time and qualified composition, refining is completed. After heating to 1670~1700℃, the ladle is hoisted into the vacuum degassing furnace. S3 Vacuum Degassing Vacuum degassing vacuum degree ≤67Pa, pressure holding time not less than 20min, Ar gas flow rate controlled 10~40NL / min; When the temperature is controlled to 1560~1580℃, the steel ladle is used to pour the electrodes. After the electrode is cast, the mold is cooled. After the mold has cooled for 12 hours, the electrode is demolded to obtain the electrode. S4 Electroslag Remelting After removing the oxide scale from the electrode surface, electroslag remelting is performed. The amount of pre-melted slag is 3-5% by mass. Ar gas protection is used throughout the electroslag remelting process, and the remelting rate is 5-7 kg / min. After remelting and exiting the furnace, annealing treatment is performed. S5 Forged The steel ingots obtained by electroslag remelting are heated and held at 1190~1230℃ for 2~4 hours, and then forged after being taken out of the furnace. The forging ratio is required to be no less than 7, the initial forging temperature is ≥1120℃, and the final forging temperature is ≥850℃; S6 Heat Treatment After forging, the material undergoes a heat treatment process of normalizing, quenching, and tempering in sequence. During normalizing, the temperature is 920±10℃, and the material is held for 3~5 hours before air cooling. During quenching, the temperature is 930±10℃, and the material is held for 3~5 hours before oil cooling. During tempering, the temperature is 260±10℃, and the material is held for 2~10 hours before air cooling.

5. The method for preparing low-alloy high-hardenability ultra-high-strength steel as described in claim 4, characterized in that, The furnace charge includes recycled carbon scrap steel (CrNiMo), ferrochrome, ferronickel, and ferromolybdenum, with a carbon content of 0.70% of the furnace charge mass; the lime lining at the furnace bottom is 0.020~0.030% of the furnace charge.

6. The method for preparing low-alloy high-hardenability ultra-high-strength steel as described in claim 4, characterized in that, During refining furnace smelting, the slag-forming materials include pre-melted slag, lime, and fluorite; by mass ratio, the amount of pre-melted slag is 1.0~1.60% of the molten steel, the amount of lime is 1.0~1.50% of the molten steel, and the lime:fluorite ratio is 4~5:1.

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