High-strength steel prepared by scrap steel billet and production process thereof

Abstract

The application discloses a kind of high-strength steel prepared by scrap billet and production process thereof, and relates to the technical field of scrap billet resource recycling, comprising the following steps: S1.LF refining: adding scrap billet melting to molten steel, then carrying out slagging desulfurization and composition adjustment, ladle out station;S2.RH refining, then continuous casting;S3.hot rolling: after heating, then rough rolling and finish rolling, after cooling, coiling;S4. Quenching and tempering heat treatment: first quenching treatment, then tempering treatment, after treatment, obtain high-strength steel prepared by scrap billet.The application can reduce the use of alloy by resource utilization of scrap billet, and the production process is safe, the product production qualified rate is high, and the quality of high-strength steel is excellent.

Description

Technical Field

[0001] This invention belongs to the field of waste steel billet resource recycling technology, specifically a high-strength steel prepared from waste steel billets and its production process. Background Technology

[0002] In the fields of engineering machinery and heavy equipment manufacturing, the demand for high-strength steel is increasing. Traditionally, high-strength steel mainly relies on molten steel as the primary raw material and alloy blocks as a means of supplementing trace elements. However, with the popularization of scrap steel recycling, metallurgical equipment such as converters and LF furnaces are incorporating scrap steel smelting, reducing the use of iron ore and thus reducing carbon emissions.

[0003] However, scrap steel has several limitations, such as significant fluctuations in composition, the risk of impurity accumulation, and large size making it difficult to melt. Traditional scrap smelting methods can also lead to uncontrolled smelting endpoints due to uneven composition. Because high-strength steel has low phosphorus content and strict requirements for impurities and inclusions, existing technologies typically involve adding alloy blocks to the ladle, without exploring direct addition of slabs. This results in the loss of alloy elements from the slabs, without reducing the amount of alloy used, and the alloy preparation process still generates significant carbon emissions. This invention, in exploring the addition of scrap steel billets to the ladle, has discovered several potential problems, such as frozen ladles causing continuous casting dead flow, ladle penetration, or damage to the ladle lining. Summary of the Invention

[0004] To overcome the aforementioned technical problems, this invention provides a method for preparing high-strength steel using scrap steel billets and its production process. This invention utilizes scrap steel billets in a resource-efficient manner, reducing the use of alloys, ensuring a safe production process, achieving a high product qualification rate, and producing high-quality high-strength steel.

[0005] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0006] This invention discloses a production process for preparing high-strength steel using scrap steel billets, comprising the following steps: S1.LF Refining: Scrap steel billets are added to molten steel and melted, followed by slag formation, desulfurization, and composition adjustment, before the steel ladle leaves the station; After refining with S2.RH, continuous casting is carried out; S3. Hot rolling: After heating, rough rolling and finish rolling are performed, and the coil is then cooled and coiled. S4. Quenching and tempering heat treatment: First, quenching treatment is performed, followed by tempering treatment, and high-strength steel prepared from scrap steel billets is obtained after post-treatment. The quenching process involves first holding the temperature at 900~950℃ for 15~40 minutes, and then cooling it to below 80℃ at a cooling rate of ≥50℃ / s. The tempering process involves holding at 280-350℃ for 20-50 minutes, then holding at 550-610℃ for 50-100 minutes, followed by air cooling.

[0007] In S1, the molten steel contains 0.02~0.05% C by mass fraction, preferably 0.03~0.04% C.

[0008] In S1, the scrap steel billet comprises the following chemical composition by mass percentage: 0.04~1.0%C, 0.05~3.30%Si, 0.1~12.5%Mn, 0.005~1.30%Mo, 0.002~0.6%Nb, and 0~0.20%V; Preferably, the scrap steel billet comprises the following chemical composition by mass percentage: 0.15~0.20%C, 0.20~0.30%Si, 1.1~1.5%Mn, 0.3~0.6%Mo, 0.20~0.50%Nb, and 0.01~0.08%V.

[0009] In S1, for every 180-210t of molten steel, the mass of the scrap steel billet added is 5-50t. Preferably, for every 180-205t of molten steel, the mass of the scrap steel billet added is 5-25t.

[0010] In S1, the scrap steel billets are added in two or more batches; each batch of scrap steel billets added is ≤15t, preferably 5~15t.

[0011] In S1, the length of the scrap steel billet is 900~2100mm, the width is 150~300mm, and the thickness is 220~300mm; preferably, the length of the scrap steel billet is 1500~2100mm, the width is 150~200mm, and the thickness is 220~250mm.

[0012] In S1, the temperature at which the scrap steel billet is added is ≥1600℃, preferably 1601~1615℃.

[0013] In S1, after adding the scrap steel billet, the process of adjusting the argon flow rate and powering the melting process is also carried out.

[0014] Furthermore, the argon flow rate is adjusted to ≥400L / min, preferably 400~800L / min. In traditional methods, the addition of scrap steel billets can lead to problems such as frozen ladle, sudden temperature drop, and component segregation. This invention adds the scrap steel billets in stages and controls the argon blowing to ensure small temperature fluctuations in the molten pool and avoid the risk of frozen ladle.

[0015] Furthermore, after adjusting the argon flow rate, argon is blown for 3-10 minutes, preferably 4-8 minutes; adjusting the argon flow rate before blowing argon again prevents temperature stratification.

[0016] Furthermore, the heating rate of the electric melting process is controlled at 2~10℃ / min, preferably 5~10℃ / min.

[0017] Furthermore, the temperature inside the ladle drops to 1530~1580℃ after the slab is added, preferably 1540~1570℃; Subsequently, the electric melting is brought to a temperature >1600°C, preferably 1601~1612°C.

[0018] In S1, the composition adjustment is achieved by adding an alloy according to the target composition, and the alloy includes ferromolybdenum, metallic manganese, ferrosilicon, and ferroniobium.

[0019] In S2, the RH refining process involves vacuum degassing to achieve [H] ≤ 2ppm and [O] ≤ 20ppm; preferably, the RH refining process involves vacuum degassing to achieve [H] ≤ 2ppm and [O] ≤ 15ppm. In S2, the superheat of the continuous casting is 20~30℃.

[0020] In S2, the thickness of the billet obtained after continuous casting is 200~250mm.

[0021] In S3, the heating is performed at 1200~1250℃ for ≥2 hours; preferably, the heating is performed at 1200~1250℃ for 2~5 hours.

[0022] In S3, the initial rolling temperature of the rough rolling is 1100~1180℃, and the final rolling temperature is ≥1000℃; Preferably, the initial rolling temperature of the roughing roll is 1100~1150℃ and the final rolling temperature is 1000~1080℃.

[0023] In S3, the reduction rate of each pass of the rough rolling is 10~15%, and the total deformation is ≥60%; the temperature control of the finishing rolling and final rolling can induce the precipitation of nano-sized NbC.

[0024] In S3, the final rolling temperature of the finishing mill is 850~900℃.

[0025] In S3, the cooling process adopts laminar flow cooling technology, and the cooling rate is 15~20℃ / s.

[0026] In S3, the winding temperature is 550~600℃.

[0027] In S4, the quenching is first held at 900~920℃ for 20~30min, and then cooled to below 80℃ at a cooling rate of 50~65℃ / s. In S4, the tempering is performed by holding at 280~320℃ for 30~40 min, then holding at 580~600℃ for 60~90 min, followed by air cooling; the two-stage tempering achieves dislocation strengthening and precipitation of nano-carbide.

[0028] The present invention also discloses a high-strength steel prepared from scrap steel billets, wherein the high-strength steel prepared from scrap steel billets comprises the following chemical composition by mass percentage: 0.05~0.09%C, 0.15~0.30%Si, 1.5~2.0%Mn, P≤0.02%, S≤0.03%, 0.10~0.20%Mo, and 0.03~0.06%Nb; Preferably, the high-strength steel prepared from scrap steel billets comprises the following chemical composition by mass percentage: 0.06~0.08% C, 0.18~0.25% Si, 1.6~1.8% Mn, P≤0.015%, S≤0.03%, 0.10~0.20% Mo, and 0.03~0.06% Nb; In the high-strength steel of this invention, an appropriate amount of Cr can improve hardenability, Mo can suppress temper brittleness, and Nb can refine grains.

[0029] In this invention, the yield strength of the high-strength steel prepared from scrap steel billets is 770~795MPa, preferably 770~790MPa; In this invention, the high-strength steel prepared from scrap steel billets has a tensile strength of 800~850MPa, preferably 820~850MPa; In this invention, the elongation of the high-strength steel prepared from scrap steel billets is 16-19%, preferably 17-19%.

[0030] The present invention relates to the application of high-strength steel prepared from scrap steel billets in the fields of construction, bridge and machinery manufacturing; The aforementioned mechanical manufacturing field includes the manufacturing of heavy machinery booms, turntables, container main beams, etc.

[0031] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0032] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses large-sized scrap steel billets as raw materials, which reduces the reliance on alloy blocks and is well-suited to the fast-paced smelting process, thus effectively improving smelting efficiency while ensuring production stability and safety. High-strength steel produced using this method is of excellent quality and has a high yield rate.

[0033] 2. During the production process, scrap steel is added in batches for melting, and the argon blowing process is adjusted to control the uniformity of the steel composition. In the LF and RH refining stages, the impurity content is strictly controlled to improve the purity of the finished steel and meet higher composition requirements. By precisely controlling the rolling process, a uniform martensitic structure can be obtained, thereby effectively improving the yield strength and elongation of high-strength steel.

[0034] 3. In addition, the quenching and tempering heat treatment process of the present invention adopts a rapid quenching-gradient tempering method, wherein rapid quenching can promote the transformation of the full martensitic structure; the first stage of tempering is low-temperature tempering, which can eliminate quenching stress through dislocation reorganization and avoid grain boundary weakening during subsequent high-temperature tempering; the second stage is high-temperature tempering, which can promote the precipitation of nano carbides and achieve precipitation strengthening.

[0035] 4. The high-strength steel obtained by the production process of the present invention has the characteristics of high strength and high yield. According to some embodiments of the present invention, the yield can reach ≥90%; in some preferred embodiments, the yield can reach ≥95%. Detailed Implementation

[0036] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0037] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0038] The "range" disclosed in this invention is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is understood that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this invention, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed herein; "0-5" is merely a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer greater than or equal to 2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0040] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0041] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0042] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0043] Unless otherwise specified, the term "or" is inclusive in this invention. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0044] The scrap steel billets used in the following examples, by mass fraction, consist of 0.17% C, 0.25% Si, 1.3% Mn, 0.4% Mo, 0.33% Nb, 0.04% V, and the balance being Fe and unavoidable impurities; The dimensions of the scrap steel billet are 1820mm (length) × 170mm (width) × 223mm (thickness). The dimensions of the scrap steel billet can be adjusted appropriately based on these dimensions to meet the requirements of the total weight of the scrap steel billet.

[0045] Example 1 The production process steps for high-strength steel prepared from scrap steel billets in this embodiment are as follows: S1.LF Refining: 20 tons of scrap steel billets are added to 200 tons of molten steel, and the 20 tons of scrap steel billets are added in two batches. The first addition of scrap steel billets was at a temperature of 1605℃. After adding 10t of scrap steel billets, the argon flow rate was adjusted to 400L / min and argon was purged for 5 minutes. At this time, the temperature inside the ladle dropped to 1545℃. Then, electric melting was performed, and the temperature was raised to 1602℃ at a heating rate of 7℃ / min. The second addition of 10t of scrap steel billets was performed, and the argon flow rate was adjusted to 500L / min and argon was purged for 5 minutes. At this time, the temperature inside the ladle dropped to 1560℃. Then, electric melting was performed, and the temperature was raised to 1610℃ at a heating rate of 7℃ / min. After melting, slag formation and desulfurization were carried out. Add ferromolybdenum, metallic manganese, ferrosilicon, and ferroniobium alloys to adjust the composition to match the target composition; ladle then exits the station; S2.RH refining involves vacuum degassing to achieve [H]: 1.3ppm and [O]: 8ppm; followed by continuous casting with a superheat of 25℃, resulting in a billet thickness of 220mm. S3. Hot-rolled: After heating at 1200℃ for 3 hours, rough rolling and finish rolling are carried out. The initial rolling temperature of rough rolling is 1130℃ and the final rolling temperature is 1020℃. The reduction rate of each pass of rough rolling is 12~14%, and the total deformation is 76%. The final rolling temperature of finish rolling is 860℃. The cooling adopts a laminar flow cooling process with a cooling rate of 20℃ / s, and the coil is wound at 600℃. S4. Tempering heat treatment: Hold at 900℃ for 30 minutes, then cool to below 80℃ at a cooling rate of 60℃ / s for quenching treatment; The steel is tempered by holding it at 300℃ for 35 minutes and then at 600℃ for 65 minutes; after straightening, high-strength steel prepared from scrap steel billets is obtained.

[0046] No problems such as frozen ladles causing continuous casting dead flow, ladle penetration, or lining damage occurred during the above production process.

[0047] The high-strength steel (LG700T) prepared from scrap steel billets in this embodiment has the following composition: 0.075%C, 0.21%Si, 1.7%Mn, 0.012%P, 0.0015%S, 0.16%Mo, 0.043%Nb, with the balance being Fe and unavoidable impurities; The high-strength steel prepared from scrap steel billets has a yield strength of 785 MPa, a tensile strength of 833 MPa, and an elongation of 18.1%.

[0048] Example 2 The production process steps for high-strength steel prepared from scrap steel billets in this embodiment are as follows: S1.LF Refining: 25 tons of scrap steel billets were added in three separate additions to 183 tons of molten steel. The temperature of the first addition of scrap steel billet is 1605℃. After 5t of scrap steel billet is added, the argon flow rate is adjusted to 400L / min and argon is blown for 5min. At this time, the temperature inside the ladle drops to 1562℃. Then, electric melting is sent to raise the temperature to 1608℃ at a heating rate of 7℃ / min. The second 10t of scrap steel billet was added, and then the argon flow rate was adjusted to 500L / min and argon was blown for 5min. At this time, the temperature inside the ladle dropped to 1562℃, and then electric melting was performed to raise the temperature to 1610℃ at a heating rate of 5℃ / min. The third time, 10 tons of scrap steel billets were added, and the argon flow rate was adjusted to 500 L / min and argon was blown for 5 minutes. At this time, the temperature inside the ladle dropped to 1567℃. Then, electric melting was performed, and the temperature was raised to 1610℃ at a heating rate of 7℃ / min. After melting, slag formation and desulfurization were carried out. Add ferromolybdenum, metallic manganese, ferrosilicon, and ferroniobium alloys to adjust the composition to match the target composition; ladle then exits the station; S2.RH refining involves vacuum degassing to achieve [H]: 0.9ppm and [O]: 12.3ppm; followed by continuous casting with a superheat of 25℃, resulting in a billet thickness of 220mm. S3. Hot-rolled: After heating at 1200℃ for 3 hours, rough rolling and finish rolling are carried out. The initial rolling temperature of rough rolling is 1130℃ and the final rolling temperature is 1020℃. The reduction rate of each pass of rough rolling is 12~14%, and the total deformation is 76%. The final rolling temperature of finish rolling is 860℃. The cooling adopts a laminar flow cooling process with a cooling rate of 20℃ / s, and the coil is wound at 600℃. S4. Tempering heat treatment: Hold at 900℃ for 30 minutes, then cool to below 80℃ at a cooling rate of 60℃ / s for quenching treatment; The steel is tempered by holding it at 300℃ for 35 minutes and then at 600℃ for 65 minutes; after straightening, high-strength steel prepared from scrap steel billets is obtained.

[0049] No problems such as frozen ladles causing continuous casting dead flow, ladle penetration, or lining damage occurred during the above production process.

[0050] The high-strength steel (LG700T) prepared from scrap steel billets in this embodiment has the following composition: 0.067%C, 0.21%Si, 1.73%Mn, 0.011%P, 0.015%S, 0.164%Mo, 0.048%Nb, with the balance being Fe and unavoidable impurities; The high-strength steel prepared from scrap steel billets has a yield strength of 781 MPa, a tensile strength of 835 MPa, and an elongation of 17.3%.

[0051] Example 3 The production process steps for high-strength steel prepared from scrap steel billets in this embodiment are as follows: S1.LF Refining: 20 tons of scrap steel billets are added to 200 tons of molten steel, and the 20 tons of scrap steel billets are added in two batches. The first addition of scrap steel billets was at a temperature of 1605℃. After adding 10t of scrap steel billets, the argon flow rate was adjusted to 400L / min and argon was purged for 5 minutes. At this time, the temperature inside the ladle dropped to 1545℃. Then, electric melting was performed, and the temperature was raised to 1602℃ at a heating rate of 7℃ / min. The second addition of 10t of scrap steel billets was performed, and the argon flow rate was adjusted to 500L / min and argon was purged for 5 minutes. At this time, the temperature inside the ladle dropped to 1560℃. Then, electric melting was performed, and the temperature was raised to 1610℃ at a heating rate of 7℃ / min. After melting, slag formation and desulfurization were carried out. Add ferromolybdenum, metallic manganese, ferrosilicon, and ferroniobium alloys to adjust the composition to match the target composition; ladle then exits the station; S2.RH refining involves vacuum degassing to achieve [H]: 1.0ppm and [O]: 13ppm; followed by continuous casting with a superheat of 25℃, resulting in a billet thickness of 220mm. S3. Hot-rolled: After heating at 1200℃ for 3 hours, rough rolling and finish rolling are carried out. The initial rolling temperature of rough rolling is 1130℃ and the final rolling temperature is 1020℃. The reduction rate of each pass of rough rolling is 12~14%, and the total deformation is 76%. The final rolling temperature of finish rolling is 860℃. The cooling adopts a laminar flow cooling process with a cooling rate of 20℃ / s, and the coil is wound at 600℃. S4. Tempering heat treatment: Hold at 920℃ for 20 minutes, then cool to below 80℃ at a cooling rate of 55℃ / s for quenching treatment; The steel is tempered by holding it at 320℃ for 30 minutes and then at 580℃ for 80 minutes; after straightening, high-strength steel prepared from scrap steel billets is obtained.

[0052] The high-strength steel (LG700T) prepared from scrap steel billets in this embodiment has the following composition: 0.075%C, 0.21%Si, 1.7%Mn, 0.012%P, 0.0015%S, 0.16%Mo, 0.043%Nb, with the balance being Fe and unavoidable impurities; The high-strength steel prepared from scrap steel billets has a yield strength of 788 MPa, a tensile strength of 829 MPa, and an elongation of 18.6%.

[0053] Example 4 The production process steps for high-strength steel prepared from scrap steel billets in this embodiment are as follows: S1.LF Refining: 20 tons of scrap steel billets are added to 200 tons of molten steel, and the 20 tons of scrap steel billets are added in two batches. The first addition of scrap steel billets was at a temperature of 1605℃. After adding 10t of scrap steel billets, the argon flow rate was adjusted to 400L / min and argon was purged for 5 minutes. At this time, the temperature inside the ladle dropped to 1545℃. Then, electric melting was performed, and the temperature was raised to 1602℃ at a heating rate of 7℃ / min. The second addition of 10t of scrap steel billets was performed, and the argon flow rate was adjusted to 500L / min and argon was purged for 5 minutes. At this time, the temperature inside the ladle dropped to 1560℃. Then, electric melting was performed, and the temperature was raised to 1610℃ at a heating rate of 7℃ / min. After melting, slag formation and desulfurization were carried out. Add ferromolybdenum, metallic manganese, ferrosilicon, and ferroniobium alloys to adjust the composition to match the target composition; ladle then exits the station; S2.RH refining involves vacuum degassing to achieve [H]: 1.8ppm and [O]: 9.6ppm; followed by continuous casting with a superheat of 25℃, resulting in a billet thickness of 220mm. S3. Hot-rolled: After heating at 1200℃ for 3 hours, rough rolling and finish rolling are carried out. The initial rolling temperature of rough rolling is 1050℃ and the final rolling temperature is 970℃. The reduction rate of each pass of rough rolling is 11~13%, and the total deformation is 72%. The final rolling temperature of finish rolling is 860℃. The cooling adopts a laminar flow cooling process with a cooling rate of 22℃ / s, and the coil is wound at 500℃. S4. Tempering heat treatment: Hold at 900℃ for 30 minutes, then cool to below 80℃ at a cooling rate of 60℃ / s for quenching treatment; The steel is tempered by holding it at 300℃ for 35 minutes and then at 600℃ for 65 minutes; after straightening, high-strength steel prepared from scrap steel billets is obtained.

[0054] No problems such as frozen ladles causing continuous casting dead flow, ladle penetration, or lining damage occurred during the above production process.

[0055] The high-strength steel (LG700T) prepared from scrap steel billets in this embodiment has the following composition: 0.075%C, 0.21%Si, 1.7%Mn, 0.012%P, 0.0015%S, 0.16%Mo, 0.043%Nb, with the balance being Fe and unavoidable impurities; In this embodiment, the low final rolling temperature and excessively high interlayer cooling efficiency resulted in large NbC carbide grains, leading to a decrease in the strength of the high-strength steel product. The high-strength steel prepared using scrap steel billets had a yield strength of 772 MPa, a tensile strength of 817 MPa, and an elongation of 14.8%.

[0056] Comparative Example 1 The production process steps for preparing high-strength steel using scrap steel billets in this comparative example are as follows: S1.LF Refining: Scrap steel billets were added to 205 tons of molten steel, with 17 tons added at a time. The temperature of the added scrap steel billets was 1605℃. After adding the scrap steel billets, the argon flow rate was adjusted to 500 L / min and argon was blown for 8 minutes. At this point, the temperature inside the ladle dropped to 1501℃. Then, electric melting was applied, and the temperature was raised to 1600℃ at a rate of 20℃ / min. The heating rate of the molten steel was abnormally fast. The reason for this was that the temperature of the molten steel dropped significantly after the addition of the scrap steel billets, leading to the formation of cold steel at the bottom of the ladle. Under these circumstances, the electric melting operation could only melt the molten steel too quickly in a localized area. Even with argon blowing to improve the circulation of the molten steel, the cold steel at the bottom of the ladle and the poor argon blowing effect of the bottom permeable bricks made it difficult to achieve the desired stirring effect. Therefore, the molten steel had to be turned over. After turning over, the molten steel continued to be processed according to the conventional refining and smelting process, and no more scrap steel billets were added at this stage.

[0057] Comparative Example 2 The production process steps for preparing high-strength steel using scrap steel billets in this comparative example are as follows: S1.LF Refining: 20 tons of scrap steel billets are added to 200 tons of molten steel, and the 20 tons of scrap steel billets are added in two batches. The first addition of scrap steel billets was at a temperature of 1605℃. After adding 10t of scrap steel billets, the argon flow rate was adjusted to 400L / min and argon was purged for 5 minutes. At this time, the temperature inside the ladle dropped to 1545℃. Then, electric melting was performed, and the temperature was raised to 1602℃ at a heating rate of 7℃ / min. The second addition of 10t of scrap steel billets was performed, and the argon flow rate was adjusted to 500L / min and argon was purged for 5 minutes. At this time, the temperature inside the ladle dropped to 1560℃. Then, electric melting was performed, and the temperature was raised to 1610℃ at a heating rate of 7℃ / min. After melting, slag formation and desulfurization were carried out. Add ferromolybdenum, metallic manganese, ferrosilicon, and ferroniobium alloys to adjust the composition to match the target composition; ladle then exits the station; S2.RH refining involves vacuum degassing to achieve [H]: 1.1ppm and [O]: 15ppm; followed by continuous casting with a superheat of 25℃, resulting in a billet thickness of 220mm. S3. Hot-rolled: After heating at 1200℃ for 3 hours, rough rolling and finish rolling are carried out. The initial rolling temperature of rough rolling is 1130℃ and the final rolling temperature is 1020℃. The reduction rate of each pass of rough rolling is 13~15%, and the total deformation is 76%. The final rolling temperature of finish rolling is 860℃. The cooling adopts a laminar flow cooling process with a cooling rate of 20℃ / s, and the coil is wound at 600℃. S4. Tempering heat treatment: Hold at 900~920℃ for 20~30 minutes, then cool to below 80℃ at a cooling rate of 50~65℃ / s for quenching treatment; The steel was held at 560℃ for 50 minutes and then tempered; after straightening, high-strength steel was obtained using scrap steel billets.

[0058] No problems such as frozen ladles causing continuous casting dead flow, ladle penetration, or lining damage occurred during the above production process.

[0059] The high-strength steel (LG700T) prepared from scrap steel billets in this comparative example has the following composition: 0.075%C, 0.21%Si, 1.7%Mn, 0.012%P, 0.0015%S, 0.16%Mo, 0.043%Nb, with the balance being Fe and unavoidable impurities. The high-strength steel prepared from scrap steel billets has a yield strength of 759 MPa, a tensile strength of 803 MPa, and an elongation of 13.4%.

[0060] The comparative tempering process only uses single-stage tempering, resulting in low dislocation density and difficulty in refining the microstructure to obtain nanoscale carbides. Therefore, the mechanical properties of the high-strength steel produced are reduced.

[0061] Comparative Example 3 The production process steps for the high-strength steel prepared in this comparative example are as follows: S1.LF Refining: Add ferromolybdenum, metallic manganese, ferrosilicon, and ferroniobium alloy to 200t of molten steel to adjust the composition to match the target composition; the ladle is then discharged from the station. S2.RH refining involves vacuum degassing to achieve [H]: 1.3ppm and [O]: 8ppm; followed by continuous casting with a superheat of 25℃, resulting in a billet thickness of 220mm. S3. Hot-rolled: After heating at 1200℃ for 3 hours, rough rolling and finish rolling are carried out. The initial rolling temperature of rough rolling is 1130℃ and the final rolling temperature is 1020℃. The reduction rate of each pass of rough rolling is 12~14%, and the total deformation is 76%. The final rolling temperature of finish rolling is 860℃. The cooling adopts a laminar flow cooling process with a cooling rate of 20℃ / s, and the coil is wound at 600℃. S4. Tempering heat treatment: Hold at 900℃ for 30 minutes, then cool to below 80℃ at a cooling rate of 60℃ / s for quenching treatment; The steel is tempered by holding it at 300℃ for 35 minutes and then at 600℃ for 65 minutes; after straightening, high-strength steel prepared from scrap steel billets is obtained.

[0062] The high-strength steel (LG700T) prepared from scrap steel billets in this embodiment has the following composition: 0.073%C, 0.23%Si, 1.68%Mn, 0.010%P, 0.0018%S, 0.14%Mo, 0.047%Nb, with the balance being Fe and unavoidable impurities.

[0063] The high-strength steel has a yield strength of 784 MPa, a tensile strength of 828 MPa, and an elongation of 18.7%.

[0064] Test case The high-strength steel surfaces of the above embodiments and comparative examples were inspected for cracks, scale, or residual iron oxide scale; crack marks ≥2mm, scale or residual iron oxide scale area >5mm. 2 When the high-strength steel plate is deemed unqualified, the finished product qualification rates of the above embodiments and comparative examples are shown in Table 1.

[0065] Table 1

[0066] Application examples The costs of the alloys added in Example 1 and Comparative Example 3 are shown in Table 2; Table 2

[0067] The following alloy raw materials contain iron and unavoidable impurities as the balance: The Mo content in ferromolybdenum is 61.38 wt%. The Mn content in metallic manganese is 97.18 wt%; The Nb content in ferroniobium is 65.83 wt%; The Si content in ferrosilicon is 73.30 wt%.

[0068] Unless otherwise specified, all raw materials, reagents, instruments, and equipment used in this invention can be purchased commercially or prepared using existing methods. The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this invention. It should be understood that the above descriptions are merely specific embodiments of this invention and are not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A production process for preparing high-strength steel using scrap steel billets, characterized in that, Includes the following steps: S1.LF Refining: Scrap steel billets are added to the molten steel in two or more batches, with each batch containing ≤15t of scrap steel billets. Then, slag formation, desulfurization, and composition adjustment are carried out, and the ladle is discharged from the station. After refining with S2.RH, continuous casting is carried out; S3. Hot rolling: After heating, rough rolling and finish rolling are performed, and the coil is then cooled and coiled. S4. Quenching and tempering heat treatment: First, quenching treatment is performed, followed by tempering treatment, and high-strength steel prepared from scrap steel billets is obtained after post-treatment. The quenching process involves first holding the temperature at 900~950℃ for 15~40 minutes, and then cooling it to below 80℃ at a cooling rate of ≥50℃ / s. The tempering process involves holding at 280-350℃ for 20-50 minutes, then holding at 550-610℃ for 50-100 minutes, followed by air cooling.

2. The production process for preparing high-strength steel using scrap steel billets as described in claim 1, characterized in that, At least one of the following conditions ① to ② must be met: ① The scrap steel billet comprises the following chemical composition by mass percentage: 0.04~1.0% C, 0.05~3.30% Si, 0.1~12.5% ​​Mn, 0.005~1.30% Mo, 0.002~0.6% Nb, and 0~0.20% V; ②The length of the scrap steel billet is 900~2100mm, the width is 150~300mm, and the thickness is 220~300mm.

3. The production process for preparing high-strength steel using scrap steel billets as described in claim 1, characterized in that, At least one of the following conditions ① to ② must be met: ① The scrap steel billet comprises the following chemical composition by mass percentage: 0.15~0.20% C, 0.20~0.30% Si, 1.1~1.5% Mn, 0.3~0.6% Mo, 0.20~0.50% Nb, and 0.01~0.08% V; ②The length of the scrap steel billet is 1500~2100mm, the width is 150~200mm, and the thickness is 220~250mm.

4. The production process for preparing high-strength steel using scrap steel billets as described in claim 2, characterized in that, At least one of the following conditions ① to ⑥ must be met: ①The molten steel contains 0.02~0.05% C by mass fraction; ② For every 180~210t of molten steel, the mass of the scrap steel billet added is 5~50t; ③ The scrap steel billets are added in two or more batches; each batch of scrap steel billets is 5 to 15 tons. ④ The temperature at which the scrap steel billet is added is ≥1600℃; ⑤ After the addition of scrap steel billets, the temperature inside the ladle drops to 1530~1580℃; ⑥ The process of adding scrap steel billets involves adjusting the argon flow rate and electrifying the melt.

5. The production process for preparing high-strength steel using scrap steel billets as described in claim 4, characterized in that, At least one of the following conditions ① to ④ must be met: ① The argon flow rate is adjusted to ≥400 L / min; ② After adjusting the argon flow rate, blow argon for 3-10 minutes; ③ The heating rate of the electric melting process is controlled at 2~10℃ / min; ④ The electric melting is carried out to a temperature >1600℃.

6. The production process for preparing high-strength steel using scrap steel billets as described in claim 1, characterized in that, At least one of the following conditions ① to ③ must be met: ①The RH refining process involves vacuum degassing to ensure that [H] ≤ 2ppm and [O] ≤ 20ppm; ②The superheat of the continuous casting is 20~30℃; ③ The thickness of the billet obtained after continuous casting is 200~250mm.

7. The production process for preparing high-strength steel using scrap steel billets as described in claim 1, characterized in that, At least one of the following conditions ① to ⑥ must be met: ① The heating process involves maintaining the temperature at 1200~1250℃ for ≥2 hours; ②The initial rolling temperature of the rough rolling is 1100~1180℃, and the final rolling temperature is ≥1000℃; ③ The reduction rate per pass of the rough rolling is 10~15%, and the total deformation is ≥60%; ④ The finishing rolling temperature is 850~900℃; ⑤ The cooling in S3 adopts a laminar flow cooling process with a cooling rate of 15~20℃ / s; ⑥ The winding temperature is 550~600℃.

8. The production process for preparing high-strength steel using scrap steel billets as described in claim 1, characterized in that, At least one of the following conditions ① to ② must be met: ①The quenching process involves first holding the temperature at 900~920℃ for 20~30 minutes, and then cooling it to below 80℃ at a cooling rate of 50~65℃ / s; ②The tempering process involves holding at 280~320℃ for 30~40 minutes, then holding at 580~600℃ for 60~90 minutes, followed by air cooling.

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