High-strength steel prepared from waste steel billets and production process of high-strength steel

Abstract

The invention discloses high-strength steel prepared from waste steel billets and a production process of the high-strength steel, and relates to the technical field of waste steel billet resource reutilization, the production process comprises the following steps: S1, LF refining: adding the waste steel billets into molten steel for melting, then carrying out slagging desulfurization and component adjustment, and discharging a steel ladle; s2, after RH refining, continuous casting is conducted; s3, hot rolling is conducted, specifically, rough rolling and finish rolling are conducted after heating, and coiling is conducted after cooling; and S4, quenching and tempering heat treatment is conducted, specifically, quenching treatment is conducted firstly, then tempering treatment is conducted, and the high-strength steel prepared from the waste steel billet is obtained after aftertreatment. According to the method, the waste steel billets are recycled, the use of alloys can be reduced, the production process is safe, the product production qualification rate is high, and the quality of the high-strength steel is excellent.

Description

Technical Field

[0001] The present invention belongs to the technical field of resource recycling of scrap steel billets, and specifically relates to high-strength steel prepared from scrap steel billets and a production process thereof. Background Art

[0002] Demand for high-strength steel is growing in the engineering machinery and heavy equipment manufacturing sectors. Traditionally, high-strength steel has relied primarily on molten steel as its primary raw material, supplemented by alloy blocks as a means of supplementing trace elements. However, with the increasing popularity of scrap steel recycling, metallurgical equipment such as converters and LF furnaces has been incorporated into scrap steel smelting, reducing iron ore utilization and carbon emissions.

[0003] However, scrap steel raw materials have many limitations, such as large fluctuations in their composition, the risk of accumulation of impurity elements, and large lumps that are difficult to melt. The traditional use of scrap materials for smelting may also lead to loss of control of the smelting end point due to uneven composition. Since high-strength steel has a low phosphorus content and strict requirements on impurity elements and inclusions, the existing technology uses alloy blocks to add to the ladle, and has not explored the solution of directly adding slabs, resulting in the loss of slab alloy elements. At the same time, the amount of alloy used has not been reduced, and the alloy preparation process also has a lot of carbon emissions. When exploring the addition of scrap steel billets to the ladle, the present invention found that various problems may arise, such as frozen ladle causing continuous casting dead flow, ladle penetration or lining damage, and other problems. Summary of the Invention

[0004] To overcome the above technical problems, the present invention provides a high-strength steel produced from scrap steel billets and a production process thereof. The present invention utilizes scrap steel billets as resources, reduces the use of alloys, and provides a safe production process, a high product qualification rate, and excellent high-strength steel quality.

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

[0006] The present invention discloses a production process for preparing high-strength steel using scrap steel billets, comprising the following steps: S1.LF refining: adding scrap steel into molten steel to melt, then slagging, desulfurization and composition adjustment are carried out, and the ladle is discharged; After S2.RH refining, continuous casting is carried out; S3. Hot rolling: After heating, rough rolling and finishing rolling are performed, and coiling is performed after cooling; S4. Quenching and tempering heat treatment: first quenching treatment, then tempering treatment, and then post-treatment to obtain high-strength steel prepared from scrap steel billets; The quenching is firstly to keep the temperature at 900-950°C for 15-40 minutes, and then to cool to below 80°C at a cooling rate of ≥50°C / s; The tempering is carried out by keeping the temperature at 280-350° C. for 20-50 minutes, then keeping the temperature at 550-610° C. for 50-100 minutes, and then air cooling.

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

[0008] In S1, the scrap steel billet comprises the following chemical components in 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 components in 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 180-210 tons of molten steel, 5-50 tons of scrap steel billets are added; Preferably, for every 180-205 t of the molten steel, the mass of the scrap steel billets added is 5-25 t.

[0010] In S1, the scrap steel billets are added in batches for more than 2 times; each time the scrap steel billets are added are ≤ 15t, preferably 5-15t.

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

[0012] In S1, the temperature when adding the scrap steel billet is ≥1600°C, preferably 1601-1615°C.

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

[0014] Furthermore, the argon flow rate is adjusted to ≥400L / min, preferably 400~800L / min; in the traditional method, the addition of scrap steel billets will lead to problems such as freezing of the ladle, sudden temperature drop and composition segregation. The present invention adds and blows argon in batches to ensure that the temperature fluctuation of the molten pool is small, thereby avoiding the risk of freezing of the ladle.

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

[0016] Furthermore, the heating rate of the power-transmission melting process is controlled at 2-10°C / min, preferably 5-10°C / min.

[0017] Furthermore, after the slab is added, the temperature in the ladle drops to 1530-1580°C, preferably 1540-1570°C; Then, the power transmission is melted to a temperature greater than 1600° C., preferably 1601-1612° C.

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

[0019] In S2, the RH refining is performed by vacuum degassing to make [H]≤2ppm, [O]≤20ppm; preferably, the RH refining is performed by vacuum degassing to make [H]≤2ppm, [O]≤15ppm In S2, the superheat degree of the continuous casting is 20-30°C.

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

[0021] In S3, the heating is carried out at 1200-1250° C. for ≥2 h; preferably, the heating is carried out at 1200-1250° C. for 2-5 h.

[0022] In S3, the starting rolling temperature of the rough rolling is 1100-1180°C, and the finishing rolling temperature is ≥1000°C; Preferably, the starting rolling temperature of the rough rolling is 1100-1150°C, and the finishing rolling temperature is 1000-1080°C.

[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 the final rolling can induce the precipitation of nano-scale NbC.

[0024] In S3, the final rolling temperature of the finishing rolling is 850-900°C.

[0025] In S3, the cooling adopts a laminar cooling process, and the cooling rate is 15-20°C / s.

[0026] In S3, the coiling temperature is 550-600°C.

[0027] In S4, the quenching is firstly holding at 900-920°C for 20-30 minutes, and then cooling to below 80°C at a cooling rate of 50-65°C / s; In S4, the tempering is carried out at 280-320°C for 30-40 minutes, then at 580-600°C for 60-90 minutes, and then air-cooled; the two-stage tempering achieves dislocation strengthening and nano-carbide precipitation.

[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 components in 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 the scrap steel billet comprises the following chemical components in 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, 0.03-0.06% Nb; An appropriate amount of Cr in the high-strength steel of the present invention can improve hardenability, Mo can suppress temper brittleness, and Nb can refine grains.

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

[0030] Application of the high-strength steel prepared from scrap steel billets in the fields of construction, bridges and machinery manufacturing; The mechanical manufacturing field includes the manufacture of crane arms, turntables, container main beams, etc.

[0031] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0032] Compared with the prior art, the present invention has the following beneficial effects: 1. This method uses larger scrap steel billets as raw materials, reducing reliance on alloy blocks while aligning with the fast-paced smelting process. This effectively improves smelting efficiency while ensuring production stability and safety. The high-strength steel produced using this method is of excellent quality, with a high yield rate of finished products.

[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 molten steel composition. In the LF and RH refining stages, the impurity content is strictly controlled to improve the purity of the finished steel composition 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 the rapid quenching can promote the transformation of the full martensite structure; the first stage of tempering is low-temperature tempering, which can eliminate the quenching stress through dislocation recombination and avoid the weakening of grain boundaries during subsequent high-temperature tempering; the second stage is high-temperature tempering, which can promote the precipitation of nanocarbides 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 DESCRIPTION

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

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

[0038] The "ranges" disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower and upper limits define the boundaries of the particular range. Ranges defined in this manner can be inclusive or exclusive of the end values ​​and can be combined in any manner, i.e., 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 a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values ​​listed are 1 and 2, and if the maximum range values ​​listed are 3, 4, and 5, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this disclosure, unless otherwise indicated, the numerical range "ab" is an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed herein, and "0-5" is merely an abbreviation for these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 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 the present invention can be combined with each other to form a new technical solution.

[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)" indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, "the method may further 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 may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

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

[0043] Unless otherwise specified, the term "or" is inclusive in this disclosure. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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 composition of the scrap steel used in the following examples is 0.17% C, 0.25% Si, 1.3% Mn, 0.4% Mo, 0.33% Nb, 0.04% V and the balance Fe and unavoidable impurities, calculated by mass fraction. The size of the scrap steel billet is 1820mm (length) × 170mm (width) × 223mm (thickness). The size of the scrap steel billet can also be appropriately adjusted on this basis to meet the requirements of the total mass of the scrap steel billet.

[0045] Example 1 The production process steps of high-strength steel prepared from scrap steel billets in this embodiment are as follows: S1.LF refining: Add scrap steel billets to 200t of molten steel, adding 20t of scrap steel billets in two batches; The temperature of the first scrap billet was 1605°C. After 10t of scrap billet was added, the argon flow rate was adjusted to 400L / min and argon was blown for 5 minutes. At this time, the temperature in the ladle dropped to 1545°C. Then, the ladle was heated to 1602°C at a heating rate of 7°C / min by electric melting. The second time 10t of scrap billet was added, the argon flow rate was adjusted to 500L / min and argon was blown for 5 minutes. At this time, the temperature in the ladle dropped to 1560°C. Then, the ladle was heated to 1610°C at a heating rate of 7°C / min by electric melting. After melting, slag formation and desulfurization were carried out. Add ferromolybdenum, manganese metal, ferrosilicon and ferroniobium alloy to adjust the composition to make it consistent with the target composition; the ladle leaves the station; S2.RH refining was performed by vacuum degassing to reduce [H]: 1.3ppm and [O]: 8ppm; continuous casting was then performed with a superheat of 25°C and a thickness of 220mm after continuous casting; S3. Hot rolling: After heating at 1200℃ for 3h, rough rolling and finish rolling are carried out. The starting 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 laminar cooling process with a cooling rate of 20℃ / s, and coiling is carried out at 600℃. S4.Quenching and tempering heat treatment: Keep the temperature at 900℃ for 30min, then cool to below 80℃ at a cooling rate of 60℃ / s for quenching; The steel was kept at 300°C for 35 minutes and then kept at 600°C for 65 minutes for tempering. After straightening, high-strength steel prepared from the scrap steel billet was obtained.

[0046] During the above production process, there were no problems such as frozen ladle causing continuous casting dead flow, ladle penetration or lining damage.

[0047] The high-strength steel (LG700T) prepared from scrap steel 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, and the balance is Fe and unavoidable impurities. The yield strength of the high-strength steel prepared using scrap steel billets is 785MPa, the tensile strength is 833MPa, and the elongation of the high-strength steel is 18.1%.

[0048] Example 2 The production process steps of high-strength steel prepared from scrap steel billets in this embodiment are as follows: S1.LF refining: Add scrap steel billets to 183t of molten steel, adding 25t of scrap steel billets in three batches; The temperature of the first scrap billet was 1605℃. After 5t of scrap billet was added, the argon flow rate was adjusted to 400L / min and argon was blown for 5 minutes. At this time, the temperature in the ladle dropped to 1562℃. Then, the electric melting was started and the temperature was raised to 1608℃ at a heating rate of 7℃ / min. The second time, 10t of scrap steel was added, and the argon flow rate was adjusted to 500L / min and argon was blown for 5 minutes. At this time, the temperature in the ladle dropped to 1562℃, and then the electric melting was sent to heat it up to 1610℃ at a heating rate of 5℃ / min; The third time, 10t of scrap steel was added, and the argon flow rate was adjusted to 500L / min and argon was blown for 5 minutes. At this time, the temperature in the ladle dropped to 1567℃, and then the electric melting was sent to heat it up to 1610℃ at a heating rate of 7℃ / min. The melting was then carried out for slagging and desulfurization. Add ferromolybdenum, manganese metal, ferrosilicon and ferroniobium alloy to adjust the composition to make it consistent with the target composition; the ladle leaves the station; S2.RH refining was performed by vacuum degassing to reduce [H]: 0.9ppm and [O]: 12.3ppm; continuous casting was then performed with a superheat of 25°C and a thickness of 220mm after continuous casting. S3. Hot rolling: After heating at 1200℃ for 3h, rough rolling and finish rolling are carried out. The starting 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 laminar cooling process with a cooling rate of 20℃ / s, and coiling is carried out at 600℃. S4.Quenching and tempering heat treatment: Keep the temperature at 900℃ for 30min, then cool to below 80℃ at a cooling rate of 60℃ / s for quenching; The steel was kept at 300°C for 35 minutes and then kept at 600°C for 65 minutes for tempering. After straightening, high-strength steel prepared from the scrap steel billet was obtained.

[0049] During the above production process, there were no problems such as frozen ladle causing continuous casting dead flow, ladle penetration or lining damage.

[0050] The high-strength steel (LG700T) prepared from scrap steel 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, and the balance is Fe and unavoidable impurities. The yield strength of the high-strength steel prepared using scrap steel billets is 781 MPa, the tensile strength is 835 MPa, and the elongation of the high-strength steel is 17.3%.

[0051] Example 3 The production process steps of high-strength steel prepared from scrap steel billets in this embodiment are as follows: S1.LF refining: Add scrap steel billets to 200t of molten steel, adding 20t of scrap steel billets in two batches; The temperature of the first scrap billet was 1605°C. After 10t of scrap billet was added, the argon flow rate was adjusted to 400L / min and argon was blown for 5 minutes. At this time, the temperature in the ladle dropped to 1545°C. Then, the ladle was heated to 1602°C at a heating rate of 7°C / min by electric melting. The second time 10t of scrap billet was added, the argon flow rate was adjusted to 500L / min and argon was blown for 5 minutes. At this time, the temperature in the ladle dropped to 1560°C. Then, the ladle was heated to 1610°C at a heating rate of 7°C / min by electric melting. After melting, slag formation and desulfurization were carried out. Add ferromolybdenum, manganese metal, ferrosilicon and ferroniobium alloy to adjust the composition to make it consistent with the target composition; the ladle leaves the station; S2.RH refining was performed by vacuum degassing to reduce [H]: 1.0 ppm and [O]: 13 ppm; continuous casting was then performed with a superheat of 25°C and a thickness of 220 mm after continuous casting. S3. Hot rolling: After heating at 1200℃ for 3h, rough rolling and finish rolling are carried out. The starting 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 laminar cooling process with a cooling rate of 20℃ / s, and coiling is carried out at 600℃. S4.Quenching and tempering heat treatment: Keep the temperature at 920℃ for 20min, then cool to below 80℃ at a cooling rate of 55℃ / s for quenching; The steel was kept at 320°C for 30 minutes and then kept at 580°C for 80 minutes for tempering. After straightening, high-strength steel was obtained from the scrap steel billet.

[0052] The high-strength steel (LG700T) prepared from scrap steel 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, and the balance is Fe and unavoidable impurities. The yield strength of the high-strength steel prepared using scrap steel billets is 788MPa, the tensile strength is 829MPa, and the elongation of the high-strength steel is 18.6%.

[0053] Example 4 The production process steps of high-strength steel prepared from scrap steel billets in this embodiment are as follows: S1.LF refining: Add scrap steel billets to 200t of molten steel, adding 20t of scrap steel billets in two batches; The temperature of the first scrap billet was 1605°C. After 10t of scrap billet was added, the argon flow rate was adjusted to 400L / min and argon was blown for 5 minutes. At this time, the temperature in the ladle dropped to 1545°C. Then, the ladle was heated to 1602°C at a heating rate of 7°C / min by electric melting. The second time 10t of scrap billet was added, the argon flow rate was adjusted to 500L / min and argon was blown for 5 minutes. At this time, the temperature in the ladle dropped to 1560°C. Then, the ladle was heated to 1610°C at a heating rate of 7°C / min by electric melting. After melting, slag formation and desulfurization were carried out. Add ferromolybdenum, manganese metal, ferrosilicon and ferroniobium alloy to adjust the composition to make it consistent with the target composition; the ladle leaves the station; S2.RH refining was performed by vacuum degassing to reduce [H]: 1.8ppm and [O]: 9.6ppm; continuous casting was then performed with a superheat of 25°C and a thickness of 220mm after continuous casting. S3. Hot rolling: After heating at 1200℃ for 3h, rough rolling and finish rolling are carried out. The starting 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 laminar cooling process with a cooling rate of 22℃ / s, and coiling is carried out at 500℃. S4.Quenching and tempering heat treatment: Keep the temperature at 900℃ for 30min, then cool to below 80℃ at a cooling rate of 60℃ / s for quenching; The steel was kept at 300°C for 35 minutes and then kept at 600°C for 65 minutes for tempering. After straightening, high-strength steel prepared from the scrap steel billet was obtained.

[0054] During the above production process, there were no problems such as frozen ladle causing continuous casting dead flow, ladle penetration or lining damage.

[0055] The high-strength steel (LG700T) prepared from scrap steel 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, and the balance is Fe and unavoidable impurities. In this example, the final rolling temperature was low and the layer cooling efficiency was too high. For example, the carbide grains of NbC were large, resulting in a decrease in the strength of the resulting high-strength steel. The high-strength steel produced from the scrap steel 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 of the high-strength steel prepared from scrap steel billets in this comparative example are as follows: S1.LF refining: Scrap billets were added to 205 tons of molten steel, 17 tons at a time. The temperature of the scrap billets was 1605°C. After the scrap was added, the argon flow rate was adjusted to 500 L / min and argon was blown for 8 minutes. The ladle temperature then dropped to 1501°C. The ladle was then heated at a rate of 20°C / min to 1600°C, but the temperature rose abnormally quickly. This was due to a significant drop in the molten steel temperature after the scrap addition, resulting in cold steel formation at the ladle bottom. In this situation, the electric melting operation only resulted in excessive melting of the steel in a certain area. Even with argon blowing to improve the circulation of the steel, ideal stirring was still difficult to achieve due to the cold steel formation at the ladle bottom and poor argon blowing through the ladle bottom air bricks. Therefore, the molten steel was forced to undergo ladle inversion. After the ladle inversion, the molten steel continued to undergo conventional refining and smelting processes, and no scrap was added at this stage.

[0057] Comparative Example 2 The production process steps of the high-strength steel prepared from scrap steel billets in this comparative example are as follows: S1.LF refining: Add scrap steel billets to 200t of molten steel, adding 20t of scrap steel billets in two batches; The temperature of the first scrap billet was 1605°C. After 10t of scrap billet was added, the argon flow rate was adjusted to 400L / min and argon was blown for 5 minutes. At this time, the temperature in the ladle dropped to 1545°C. Then, the ladle was heated to 1602°C at a heating rate of 7°C / min by electric melting. The second time 10t of scrap billet was added, the argon flow rate was adjusted to 500L / min and argon was blown for 5 minutes. At this time, the temperature in the ladle dropped to 1560°C. Then, the ladle was heated to 1610°C at a heating rate of 7°C / min by electric melting. After melting, slag formation and desulfurization were carried out. Add ferromolybdenum, manganese metal, ferrosilicon and ferroniobium alloy to adjust the composition to make it consistent with the target composition; the ladle leaves the station; S2.RH refining was performed by vacuum degassing to reduce [H]: 1.1ppm and [O]: 15ppm; continuous casting was then performed with a superheat of 25°C and a thickness of 220mm after continuous casting; S3. Hot rolling: After heating at 1200℃ for 3h, rough rolling and finish rolling are carried out. The starting 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 laminar cooling process with a cooling rate of 20℃ / s, and coiling is carried out at 600℃. S4.Quenching and tempering heat treatment: Keep the temperature at 900-920℃ for 20-30min, then cool to below 80℃ at a cooling rate of 50-65℃ / s for quenching; The steel was kept at 560°C for 50 minutes and tempered; after straightening, high-strength steel was obtained using the scrap steel billet.

[0058] During the above production process, there were no problems such as frozen ladle causing continuous casting dead flow, ladle penetration or lining damage.

[0059] The high-strength steel (LG700T) prepared from scrap steel 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, and the balance is Fe and unavoidable impurities. The yield strength of the high-strength steel prepared using scrap steel billets is 759 MPa, the tensile strength is 803 MPa, and the elongation of the high-strength steel is 13.4%.

[0060] The tempering treatment in this comparative example adopts only single-stage tempering, the dislocation density is low and the microstructure is difficult to be refined to obtain nano-scale carbides, so the mechanical properties of the obtained high-strength steel are reduced.

[0061] Comparative Example 3 The production process steps of the high-strength steel prepared in this comparative example are as follows: S1.LF refining: Add ferromolybdenum, manganese metal, ferrosilicon and ferroniobium alloy to 200t of molten steel to adjust the composition to the target composition; the ladle leaves the station; S2.RH refining was performed by vacuum degassing to reduce [H]: 1.3ppm and [O]: 8ppm; continuous casting was then performed with a superheat of 25°C and a thickness of 220mm after continuous casting; S3. Hot rolling: After heating at 1200℃ for 3h, rough rolling and finish rolling are carried out. The starting 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 laminar cooling process with a cooling rate of 20℃ / s, and coiling is carried out at 600℃. S4.Quenching and tempering heat treatment: Keep the temperature at 900℃ for 30min, then cool to below 80℃ at a cooling rate of 60℃ / s for quenching; The steel was kept at 300°C for 35 minutes and then kept at 600°C for 65 minutes for tempering. After straightening, high-strength steel prepared from the scrap steel billet was 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, and the remainder is Fe and unavoidable impurities.

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

[0064] Test Case Check the surface of the high-strength steel in the above examples and comparative examples for cracks, scars or iron oxide scale residues; crack marks ≥ 2mm, scars or iron oxide scale residue area > 5mm 2 When the high-strength steel plate is judged to be unqualified, the qualified rates of the finished products of the above embodiments and comparative examples are shown in Table 1.

[0065] Table 1

[0066] Application Examples The cost of the alloys added in Example 1 and Comparative Example 3 is shown in Table 2; Table 2

[0067] In the following alloy raw materials, the balance is iron and unavoidable impurities: The Mo content in ferromolybdenum is 61.38wt%; 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 the present invention can be purchased from the market or prepared by existing methods. The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A production process for preparing high-strength steel using scrap steel billets, characterized in that: The following steps are involved: S1.LF refining: adding scrap steel into molten steel to melt, then slagging, desulfurization and composition adjustment are carried out, and the ladle is discharged; After S2.RH refining, continuous casting is carried out; S3. Hot rolling: After heating, rough rolling and finishing rolling are carried out, and coiling is carried out after cooling. S4. Quenching and tempering heat treatment: first quenching treatment, then tempering treatment, and then post-treatment to obtain high-strength steel prepared from scrap steel billets; The quenching is firstly to keep the temperature at 900-950°C for 15-40 minutes, and then to cool to below 80°C at a cooling rate of ≥50°C / s; The tempering is carried out by keeping the temperature at 280-350° C. for 20-50 minutes, then keeping the temperature at 550-610° C. for 50-100 minutes, and then air cooling.

2. The production process for preparing high-strength steel using scrap steel billets according to claim 1, characterized in that: Meet at least one of the following conditions ①~②: ① The scrap steel billet comprises the following chemical compositions in 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; ② The 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 according to claim 1, characterized in that: Meet at least one of the following conditions ①~②: ① The scrap steel billet comprises the following chemical compositions in 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; ② The 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 according to claim 2, wherein: Meet at least one of the following conditions ① to ⑥: ① The molten steel contains 0.02-0.05% C by mass, preferably 0.03-0.04% C; ② For every 180-210 tons of molten steel, the mass of the scrap steel billets added is 5-50 tons; preferably, for every 180-205 tons of molten steel, the mass of the scrap steel billets added is 5-20 tons; ③ The scrap steel billets are added in batches for more than 2 times; each time the scrap steel billets are added is less than 15t, preferably 5-15t; ④ The temperature when adding the scrap steel billet is ≥1600°C, preferably 1601~1615°C; ⑤ After the slab is added, the temperature in the ladle drops to 1530-1580°C, preferably 1540-1570°C; ⑥ After adding the scrap steel billet, the process of adjusting the argon flow rate and sending electricity for melting is also carried out.

5. The production process for preparing high-strength steel using scrap steel billets according to claim 4, characterized in that: Meet at least one of the following conditions ① to ④: ① The argon flow rate is adjusted to ≥ 400 L / min, preferably 400~800 L / min; ② After adjusting the argon flow rate, blowing argon for 3 to 10 minutes, preferably 4 to 8 minutes; ③ The heating rate of the power melting process is controlled at 2-10°C / min, preferably 5-10°C / min; ④ The power transmission melting temperature is greater than 1600°C, preferably 1601~1612°C.

6. The production process for preparing high-strength steel using scrap steel billets according to claim 1, wherein: Meet at least one of the following conditions ①~③: ① The RH refining is performed by vacuum degassing to make [H]≤2ppm, [O]≤20ppm; preferably, the RH refining is performed by vacuum degassing to make [H]≤2ppm, [O]≤15ppm; ② The superheat degree of the continuous casting is 20-30°C; ③ The thickness of the ingot obtained after continuous casting is 200~250mm.

7. The production process for preparing high-strength steel using scrap steel billets according to claim 1, wherein: Meet at least one of the following conditions ① to ⑥: ① The heating is carried out at 1200-1250° C. for ≥2 hours; preferably, the heating is carried out at 1200-1250° C. for 2-5 hours; ② The starting rolling temperature of the rough rolling is 1100-1180°C, and the finishing rolling temperature is ≥1000°C; preferably, the starting rolling temperature of the rough rolling is 1100-1150°C, and the finishing rolling temperature is 1000-1080°C; ③ The reduction rate of each pass of the rough rolling is 10-15%, and the total deformation is ≥60%; ④ The final rolling temperature of the finishing rolling is 850~900℃; ⑤ The cooling adopts a laminar cooling process, and the cooling rate is 15~20℃ / s; ⑥ The coiling temperature is 550~600℃.

8. The production process for preparing high-strength steel using scrap steel billets according to claim 1, wherein: Meet at least one of the following conditions ①~②: ① The quenching is to first keep the temperature at 900-920°C for 20-30 minutes, and then cool it to below 80°C at a cooling rate of 50-65°C / s; ② The tempering is to keep the temperature at 280-320°C for 30-40 minutes, then keep the temperature at 580-600°C for 60-90 minutes, and then air cool.

9. A high-strength steel produced from scrap steel billets, characterized in that: The high-strength steel prepared from the scrap steel billet comprises the following chemical components in 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, 0.03-0.06% Nb; Preferably, the high-strength steel prepared from scrap steel billets comprises the following chemical components in 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.

10. The high-strength steel prepared from scrap steel billets according to claim 9, characterized in that: Meet at least one of the following conditions ①~③: ① The yield strength of the high-strength steel prepared using scrap steel billets is 770-795 MPa, preferably 770-790 MPa; ② The tensile strength of the high-strength steel prepared using scrap steel billets is 800-850 MPa, preferably 820-850 MPa; ③ The elongation of the high-strength steel prepared using scrap steel billets is 16-19%, preferably 17-19%.

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