Steel bar for ecological electric furnace automobile speed reducer and preparation method of steel bar

Abstract

The invention discloses a steel bar for an ecological electric furnace automobile speed reducer and a preparation method of the steel bar. The steel bar comprises, by mass, 0.18%-0.22% of C, 0.17%-0.37% of Si, 0.90%-1.20% of Mn, smaller than or equal to 0.015% of P, smaller than or equal to 0.007% of S, 1.10%-1.40% of Cr, smaller than or equal to 0.30% of Ni, 0.20%-0.30% of Mo, 0.15%-0.20% of V, smaller than or equal to 0.20% of Cu and the balance iron and inevitable impurities. The steel bar for the automobile speed reducer is produced by combining ecological electric furnace smelting, LF, RH, continuous casting and rolling processes with reasonable component design, the high-end use requirement is met, and the breakthrough of batch production of the steel bar for the automobile speed reducer in the ecological electric furnace continuous casting process is achieved.

Description

Technical Field

[0001] The present invention relates to the fields of materials and metallurgy, and more particularly to a steel bar for an ecological electric furnace automobile reducer and a preparation method thereof. Background Art

[0002] An automotive reducer is an independent, closed transmission device that reduces speed and increases torque through gear engagement. It is typically used in transmissions to reduce engine speed during gear shifts, enabling smoother shifts. The quality of the steel used in automotive reducers directly impacts the safety of the reducer's operation. Therefore, extremely high requirements are placed on the high-temperature resistance, wear resistance, mechanical properties, fatigue life, and steel purity of the steel bars used in these reducers to ensure safe and normal operation. However, the mechanical properties and high steel purity of current automotive reducer steel bars do not meet the requirements of high-end products. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and provide a steel bar for an ecological electric furnace automobile reducer and a preparation method thereof. The steel bar for an automobile reducer produced by combining "ecological electric furnace smelting + LF + RH + continuous casting and rolling process" with reasonable composition design meets high-end usage requirements and achieves a breakthrough in the mass production of steel bars for automobile reducers through the ecological electric furnace continuous casting process.

[0004] To achieve the above object, the technical solution of the present invention is as follows:

[0005] A steel bar for an ecological electric furnace automobile reducer comprises the following components in percentage by mass: C: 0.18% to 0.22%, Si: 0.17% to 0.37%, Mn: 0.90% to 1.20%, P≤0.015%, S≤0.007%, Cr: 1.10% to 1.40%, Ni≤0.30%, Mo: 0.20% to 0.30%, V: 0.15% to 0.20%, Cu≤0.20%, and the balance being iron and unavoidable impurities.

[0006] The present invention also discloses a method for preparing the steel bar for the above-mentioned ecological electric furnace automobile reducer, comprising the following steps: ecological electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating, rolling, heat preservation and heat treatment;

[0007] In the ecological electric furnace smelting, scrap steel and molten iron are used as furnace charge, wherein the mass of the scrap steel accounts for 60% to 70% of the total mass of the furnace charge;

[0008] In the LF refining, the molten steel discharged from the ecological electric furnace is put into the LF furnace for refining treatment;

[0009] During the RH vacuum refining, the molten steel treated by the LF refining is hoisted into the RH vacuum furnace for refining;

[0010] During the continuous casting, the molten steel after the RH vacuum refining treatment is continuously cast, and the obtained continuous casting billet is heated, rolled and kept warm;

[0011] During the heat treatment, the steel after insulation is quenched at a heating temperature of 840°C to 860°C, a insulation time of 0.8h to 1.2h, and oil cooling; the quenched and cooled steel is then tempered at a tempering temperature of 190°C to 210°C, a insulation time of 1.8h to 2.2h, and air cooling to obtain the steel bar for the ecological electric furnace automobile reducer.

[0012] The implementation of the present invention will have the following beneficial effects:

[0013] The present invention provides a steel bar for an ecological electric furnace automobile reducer and a preparation method thereof. The steel bar for an automobile reducer is produced by "ecological electric furnace smelting + LF + RH + continuous casting and rolling process" combined with reasonable component design and production, with a tensile strength ≥1280MPa, a yield strength ≥965MPa, A ≥11%, z ≥46%, and KU2 ≥57J. This ensures that the finished steel material macrostructure, non-metallic inclusions, mechanical properties and other indicators of the steel bar for an automobile reducer meet the steel purity requirements and the surface quality level of the steel bar for an automobile reducer, both of which meet the requirements of high-end products. DETAILED DESCRIPTION

[0014] The present invention will be further described below with reference to specific examples, but the present invention is not limited thereto in any way.

[0015] 1. Chemical composition

[0016] A steel bar for an ecological electric furnace automobile reducer comprises the following components in percentage by mass: C: 0.18% to 0.22%, Si: 0.17% to 0.37%, Mn: 0.90% to 1.20%, P≤0.015%, S≤0.007%, Cr: 1.10% to 1.40%, Ni≤0.30%, Mo: 0.20% to 0.30%, V: 0.15% to 0.20%, Cu≤0.20%, and the balance being iron and unavoidable impurities.

[0017] In a specific embodiment, the tensile strength of the steel bar for the ecological electric furnace automobile reducer is ≥1280MPa, the yield strength is ≥965MPa, A ≥11%, z ≥46%, and KU2 ≥57J.

[0018] 2. Production Technology

[0019] The present invention also discloses a method for preparing a steel bar for an eco-electric furnace automobile reducer according to any embodiment of the present invention, comprising the following steps: eco-electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating, rolling, insulation, and heat treatment; specifically, the method comprises the following steps:

[0020] S1. In ecological electric furnace smelting, scrap steel and molten iron are used as furnace charges, among which the mass of scrap steel accounts for 60% to 70% of the total mass of the furnace charge, and the mass of molten iron accounts for 30% to 40% of the total mass of the furnace charge.

[0021] In a specific embodiment, in the ecological electric furnace smelting, the scrap steel includes heavy scrap steel and light scrap steel; the mass percentage of heavy scrap steel in the scrap steel is 50% to 60%, and the rest is light scrap steel; the tapping temperature is 1610°C to 1620°C; the tapping end composition is: C: 0.08% to 0.12%, P ≤ 0.010%; deoxidation and alloying are performed during the tapping process; slag, pre-deoxidizer and alloy are added when 1 / 4 to 1 / 3 of the steel is tapped, the smelting cycle is 45 minutes to 50 minutes, and the furnace oxygen consumption is 25m 3 / t steel~26m 3 / t steel; alloy addition per ton of steel: 9.0Kg / t~9.1Kg / t silicon manganese alloy, 4.0Kg / t~4.1Kg / t high carbon ferromanganese, 4.0Kg / t~4.1Kg / t high carbon ferrochrome, 12.0Kg / t~12.5Kg / t low carbon ferrochrome, 1.0Kg / t~1.1Kg / t aluminum wire segment; auxiliary material addition per ton of steel: 26Kg / t~2 7kg / t of active lime, 12kg / t~12.5kg / t of coking CDQ powder, 6.0kg / t~6.1kg / t of ladle dust, 20.0kg / t~20.5kg / t of dolomite; among which, the size specification of aluminum wire segment is Φ10mm~Φ16mm, the particle size of active lime is 10mm~70mm, and the particle size of dolomite is 20mm~70mm.

[0022] In S2 and LF refining, the molten steel discharged from the ecological electric furnace is put into the LF furnace for refining.

[0023] In a specific embodiment, during LF refining, the LF inlet temperature is 1495°C to 1505°C, and after heating and melting the slag with a high current of 35000A to 36000A, when the slag surface fluctuates and the molten steel and the arc are not exposed, 3.9kg / t to 4.0kg / t of active lime is added. After 5min to 6min, the first sampling and analysis is performed, and the composition content of the molten steel is adjusted according to the target composition requirements to promote rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1620°C to 1630°C, 1.4kg / t to 1.5kg / t of alumina balls are added as a slag regulator to adjust the slag basicity to ≥ 2.5. The furnace door is closed for 10min to 13min. When the molten steel temperature reaches 1640°C to 1650°C, a second sampling and analysis is performed to confirm the slag basicity. Identify the deviation value of the content of each chemical element from the target value; after the secondary sample is taken, leave the station when the molten steel temperature is 1670℃~1680℃, the LF smelting cycle is 45min~50min, the clearance is 440mm~450mm, and the slag thickness is 140mm~150mm; the additional alloy addition per ton of steel: 0.65kg / t~0.7kg / t of ferrosilicon, 1.9kg / t~2.0kg / t of high carbon ferromanganese, 3.5kg / t~3.6kg / t of ferromolybdenum, 3.5kg / t~3.6kg / t of ferrovanadium; the additional auxiliary material addition per ton of steel: 3.9kg / t~4.0kg / t of active lime with a particle size of 10mm~70mm, 1.4Kg / t~1.5Kg / t of silicon carbide.

[0024] In S3 and RH vacuum refining, the molten steel treated by LF refining is hoisted into the RH vacuum furnace for refining.

[0025] In a specific embodiment, during RH vacuum refining, the inlet temperature is 1680°C to 1690°C, the operation time is 55min to 65min, and the vacuum pump is started when the argon pressure is controlled to be 0.1MPa to 0.3MPa, so that the slag surface is slightly moved and the molten steel is not exposed. When the vacuum degree reaches 100Pa to 105Pa, the time is maintained for 20min to 25min, and the argon pressure is adjusted to 0.3MPa to 0.5MPa. After re-pressing, the temperature is 16 35℃~1645℃, after the static argon blowing is completed, add 0.5kg / t steel to 0.6kg / t steel covering agent, the clearance is 480mm~520mm, the leaving station temperature is 1615℃~1625℃, after breaking the vacuum, add 0.55kg / t steel to 0.60kg / t steel covering agent and 0.80kg / t steel to 0.82kg / t steel silicon-calcium alloy cored wire. The size of the silicon-calcium alloy cored wire is Φ14mm~Φ15mm.

[0026] S4. In continuous casting, the molten steel after RH vacuum refining is continuously cast.

[0027] In a specific embodiment, during continuous casting, the ladle arrival temperature is 1605°C to 1615°C, the casting time is 45min to 55min, the superheat is 20°C to 25°C, the H content in the tundish is ≤2ppm, the casting speed is 0.44m / min to 0.45m / min, the casting is protected throughout the entire process, and the crystallizer protection slag uses 3.6kg / t steel to 3.7kg / t steel of medium carbon steel protection slag.

[0028] S5. In the heating process, the billets produced in the continuous casting process are fed into a heating furnace with a temperature of 500°C to 600°C; the temperature of the preheating section is 850°C to 870°C, and the time is 1.6h to 1.8h; the heating section includes heating section 1 with a temperature of 1210°C to 1230°C, and the time is 1.6h to 1.8h; heating section 2 with a temperature of 860°C to 890°C, and the time is 1.6h to 1.8h; the temperature of the soaking section is 1210°C to 1220°C, and the time is 1.6h to 1.8h; and the tapping temperature is 1180°C to 1200°C.

[0029] S6. In the rolling process, the heated continuous casting billet is rolled into a billet in 9 passes, passes through 3 850mm rolling mills, and then enters a 9-stand continuous rolling mill group for rolling; the rolling speed of each pass is 0.31m / s to 1.219m / s.

[0030] In a specific embodiment, 9 passes are rolled, the first pass is 229-229.01 mm high, 245-245.01 mm wide, and the rolling speed is 0.27-0.272 m / s; the second pass is 192-192.01 mm high, 235-235.01 mm wide, and the rolling speed is 0.31-0.312 m / s; the third pass is 200-200.01 mm high, 195-195.01 mm wide, and the rolling speed is 0.35-0.352 m / s; the fourth pass is 160-160.01 mm high, 214.7-214.71 mm wide, and the rolling speed is 0.474-0.476 m / s; the fifth pass is 168-168.01 mm high, 174.6-174.71 mm wide, and the rolling speed is 0.474-0.476 m / s; The 6th pass is 120~120.01mm high, 187.6~187.61mm wide, and the rolling speed is 0.743~0.745m / s; the 7th pass is 142~142.01mm high, 138.5~138.51mm wide, and the rolling speed is 0.934~0.936m / s; the 8th pass is 111~111.01mm high, 151.5~151.51mm wide, and the rolling speed is 1.102~1.104m / s; the 9th pass is 122.04~122.05mm high, 122.04~122.05mm wide, and the rolling speed is 1.217~1.219m / s; the finished product is produced after 9 passes.

[0031] S7. During insulation, the temperature of the lower insulation pit is ≥560℃, the insulation time is 50h~55h, and the temperature out of the pit is ≤120℃.

[0032] S8. During the heat treatment, the steel after insulation is quenched at a heating temperature of 840°C to 860°C, a insulation time of 0.8h to 1.2h, and oil cooling; the steel after quenching and cooling is then tempered at a tempering temperature of 190°C to 210°C, a insulation time of 1.8h to 2.2h, and air cooling to obtain steel bars for ecological electric furnace automobile reducers.

[0033] The following are specific embodiments

[0034] Example 1

[0035] 1. Chemical composition

[0036] Steel bars for ecological electric furnace automobile reducers include the following components in percentage by mass: C: 0.20%, Si: 0.25%, Mn: 0.97%, P: 0.013%, S: 0.006%, Cr: 1.18%, Ni: 0.06%, Mo: 0.25%, V: 0.17%, Cu: 0.05%, and the balance is iron and unavoidable impurities.

[0037] 2. Electric furnace continuous casting production processes for steel bars for automobile reducers

[0038] Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → insulation → heat treatment.

[0039] (1) Ecological electric furnace smelting

[0040] Scrap steel and molten iron are used as furnace charges, of which the mass of scrap steel accounts for 65% of the total mass of the furnace charge, and the mass of molten iron accounts for 35% of the total mass of the furnace charge; scrap steel includes heavy scrap steel and light scrap steel; among the scrap steel, the mass percentage of heavy scrap steel accounts for 53%, and the rest is light scrap steel; the tapping temperature is 1616℃, the C content is 0.09% and the P content is 0.008% when tapping, slag, pre-deoxidizer and alloy are added when 1 / 4 of the steel is tapped, the smelting cycle is 47min, and the furnace oxygen consumption is 25m 3 / t steel. Alloy addition per ton of steel: 9.0 kg / t silicon manganese alloy, 4.0 kg / t high carbon ferromanganese, 4.0 kg / t high carbon ferrochrome, 12.2 kg / t low carbon ferrochrome, 1.0 kg / t aluminum wire (Φ10 mm). Auxiliary material addition per ton of steel: 26.5 kg / t active lime (Φ35 mm), 12.2 kg / t coking coal CDQ powder, 6.0 kg / t ladle dust, and 20.3 kg / t dolomite (Φ40 mm).

[0041] (2) LF furnace refining

[0042] The LF station temperature is 1501°C, and a high current of 35500A is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, 3.9kg / t of active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloy is added according to the median chemical composition, and carbon is increased to promote rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1625°C, 1.4kg / t of alumina balls are added as a slag regulator to adjust the slag basicity to 2.7. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1644°C, a second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, the station is left when the molten steel temperature reaches 1675°C. The LF smelting cycle is 47 minutes, the clearance is 446mm, and the slag thickness is 145mm. The amount of additional alloy added per ton of steel is: 0.66kg / t of ferrosilicon, 1.9kg / t of high carbon ferromanganese, 3.5kg / t of ferromolybdenum, and 3.6kg / t of ferrovanadium (FeV50-B). The amount of additional auxiliary materials added per ton of steel is: 3.9kg / t of active lime (Φ35mm), and 1.5kg / t of silicon carbide.

[0043] (3)RH refining

[0044] The station entry temperature is 1685℃, the operation time is 58 minutes, and the argon pressure is controlled at 0.1MPa before the vacuum pump is started. The molten steel is not exposed when the slag surface moves slightly. When the vacuum reaches 100Pa, the timing starts and the holding time is 22 minutes. At the same time, the argon pressure is adjusted to 0.3MPa, and the re-pressurization temperature is 1640℃. After the static argon blowing is completed, 0.5kg / t of covering agent is added, the clearance is 490mm, and the station exit temperature is 1618℃. After breaking the vacuum, 0.57kg / t of ladle covering agent and 0.80kg / t of silicon-calcium alloy cored wire (Φ14mm) are added.

[0045] (4) Continuous casting

[0046] The arrival temperature of the ladle is 1610℃, the H of the tundish is controlled at 1.6ppm, the casting time is 48min, the superheat is 22℃, the casting speed is 0.44m / min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag 3.6kg / t steel.

[0047] (5) Heating process

[0048] Heating process: the temperature entering the heating furnace is 540℃, the temperature of the preheating section is 858℃, and the time is 1.7h; the temperature of the heating section 2 is 870℃, and the time is 1.6h; the temperature of the heating section 1 is 1219℃, and the time is 1.8h; the temperature of the soaking section is 1215℃, and the time is 1.8h; the tapping temperature is 1193℃.

[0049] (6) Rolling process

[0050] The product is rolled in 9 passes, passes through 3 850mm rolling mills, and then enters 9 continuous rolling mills for rolling. The continuous rolling process is as follows: 9 passes, the first pass is 229mm high, 245.01mm wide, and the rolling speed is 0.272m / s; the second pass is 192.01mm high, 235mm wide, and the rolling speed is 0.312m / s; the third pass is 200mm high, 195.01mm wide, and the rolling speed is 0.35m / s; the fourth pass is 160.01mm high, 214.71mm wide, and the rolling speed is 0.476m / s; the The 5th pass is 168.01mm high, 174.6mm wide, and the rolling speed is 0.600m / s; the 6th pass is 120.01mm high, 187.61mm wide, and the rolling speed is 0.745m / s; the 7th pass is 142.01mm high, 138.5mm wide, and the rolling speed is 0.936m / s; the 8th pass is 111.01mm high, 151.51mm wide, and the rolling speed is 1.104m / s; the 9th pass is 122.04mm high, 122.05mm wide, and the rolling speed is 1.219m / s; the finished product is produced after 9 passes.

[0051] (7) Insulation process

[0052] Insulation process: Steel insulation, the temperature of the lower insulation pit is 580℃, insulation for 53h, and the temperature out of the pit is 110℃.

[0053] (8) Heat treatment process

[0054] After the insulation, the steel sample is taken for heat treatment, which includes the following steps:

[0055] 1) Quenching: 850℃, holding time 1.0h, oil cooling;

[0056] 2) Tempering: 200℃, keep warm for 2.0h, air cool.

[0057] Example 2:

[0058] 1. Chemical composition

[0059] The steel bar for the ecological electric furnace automobile reducer of this embodiment includes the following components in mass percentage: C: 0.19%, Si: 0.26%, Mn: 0.97%, P: 0.011%, S: 0.005%, Cr: 1.18%, Ni: 0.05%, Mo: 0.26%, V: 0.17%, Cu: 0.06%, and the balance is iron and unavoidable impurities.

[0060] 2. Electric furnace continuous casting production processes for steel bars for automobile reducers

[0061] Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → insulation → heat treatment.

[0062] (1) Ecological electric furnace smelting

[0063] Scrap steel and molten iron are used as furnace charges, of which the mass of scrap steel accounts for 67% of the total mass of the furnace charge, and the mass of molten iron accounts for 33% of the total mass of the furnace charge; scrap steel includes heavy scrap steel and light scrap steel; among the scrap steel, the mass percentage of heavy scrap steel accounts for 55%, and the rest is light scrap steel; the tapping temperature is 1614℃, C is 0.09% and P is 0.009% when tapping, slag, pre-deoxidizer and alloy are added when 1 / 4 of the steel is tapped, the smelting cycle is 47min, and the furnace oxygen consumption is 25m 3 / t steel. Alloy addition per ton of steel: 9.1 kg / t silicon manganese alloy, 4.1 kg / t high carbon ferromanganese, 4.0 kg / t high carbon ferrochrome, 12.2 kg / t low carbon ferrochrome, 1.1 kg / t aluminum wire (Φ10 mm). Auxiliary material addition per ton of steel: 27 kg / t active lime (Φ35 mm), 12.2 kg / t coking coal CDQ powder, 6.0 kg / t ladle dust, and 20.2 kg / t dolomite (Φ40 mm).

[0064] (2) LF furnace refining

[0065] The LF station temperature is 1499°C, and a high current of 35450A is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, 4.0 kg / t of active lime is added. After 6 minutes, the first sample is taken for chemical composition analysis. Alloy is added according to the median chemical composition, and carbon is increased to promote rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1626°C, 1.5 kg / t of alumina balls are added as a slag regulator to adjust the slag basicity to 2.8. The furnace door is closed for 12 minutes. When the molten steel temperature reaches 1645°C, a second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, the station is left when the molten steel temperature reaches 1674°C. The LF smelting cycle is 47 minutes, the clearance is 447 mm, and the slag thickness is 143 mm. The amount of additional alloy added per ton of steel is: 0.68kg / t of ferrosilicon, 1.9kg / t of high carbon ferromanganese, 3.6kg / t of ferromolybdenum, and 3.6kg / t of ferrovanadium (FeV50-B). The amount of additional auxiliary materials added per ton of steel is: 4.0kg / t of active lime (Φ35mm), and 1.5kg / t of silicon carbide.

[0066] (3)RH refining

[0067] The station entry temperature is 1685℃, the operation time is 62 minutes, and the argon pressure is controlled at 0.1MPa before the vacuum pump is started, so that the slag surface does not move slightly and the molten steel is not exposed. When the vacuum reaches 103Pa, the timing starts and the holding time is 22 minutes. At the same time, the argon pressure is adjusted to 0.3MPa, and the re-pressurization temperature is 1638℃. After the static argon blowing is completed, 0.5kg / t of covering agent is added, the clearance is 495mm, and the station exit temperature is 1618℃. After breaking the vacuum, 0.57kg / t of ladle covering agent and 0.80kg / t of silicon-calcium alloy cored wire (Φ14mm) are added.

[0068] (4) Continuous casting

[0069] The arrival temperature of the ladle is 1611℃, the H of the tundish is controlled at 1.4ppm, the casting time is 48min, the superheat is 21℃, the casting speed is 0.44m / min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag 3.7kg / t steel.

[0070] (5) Heating process

[0071] Heating process: the temperature entering the heating furnace is 550℃, the temperature of the preheating section is 865℃, and the time is 1.7h; the temperature of the heating section 2 is 875℃, and the time is 1.7h; the temperature of the heating section 1 is 1220℃, and the time is 1.6h; the temperature of the soaking section is 1215℃, and the time is 1.7h; the steel tapping temperature is 1192℃.

[0072] (6) Rolling process

[0073] The product is rolled in 9 passes, passes through 3 850mm rolling mills, and then enters the 9-stand continuous rolling mill group for rolling. The continuous rolling process is as follows: 9 passes, the first pass is 229mm high, 245.01mm wide, and the rolling speed is 0.272m / s; the second pass is 192.01mm high, 235mm wide, and the rolling speed is 0.312m / s; the third pass is 200.01mm high, 195.01mm wide, and the rolling speed is 0.35m / s; the fourth pass is 160.01mm high, 214.7mm wide, and the rolling speed is 0.476m / s. The 5th pass is 168.01mm high, 174.6mm wide, and the rolling speed is 0.600m / s; the 6th pass is 120.01mm high, 187.6mm wide, and the rolling speed is 0.745m / s; the 7th pass is 142.01mm high, 138.51mm wide, and the rolling speed is 0.936m / s; the 8th pass is 111.01mm high, 151.51mm wide, and the rolling speed is 1.104m / s; the 9th pass is 122.05mm high, 122.05mm wide, and the rolling speed is 1.219m / s; the finished product is produced after 9 passes.

[0074] (7) Insulation process

[0075] Insulation process: Steel insulation, the temperature of the lower insulation pit is 580℃, insulation for 53h, and the temperature out of the pit is 110℃.

[0076] (8) Heat treatment process

[0077] After the insulation, the steel sample is taken for heat treatment, which includes the following steps:

[0078] 1) Quenching: 850℃, holding for 1h, oil cooling;

[0079] 2) Tempering: 200℃, keep warm for 2.0h, air cool.

[0080] Example 3:

[0081] 1. Composition optimization design

[0082] The steel bar for the ecological electric furnace automobile reducer of this embodiment includes the following components in mass percentage: C: 0.19%, Si: 0.24%, Mn: 0.98%, P: 0.013%, S: 0.005%, Cr: 1.17%, Ni: 0.06%, Mo: 0.25%, V: 0.17%, Cu: 0.05%, and the balance is iron and unavoidable impurities.

[0083] 2. Electric furnace continuous casting production processes for steel bars for automobile reducers

[0084] Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → insulation → heat treatment.

[0085] (1) Ecological electric furnace smelting

[0086] Scrap steel and molten iron are used as furnace charges, of which the mass of scrap steel accounts for 66% of the total mass of the furnace charge, and the mass of molten iron accounts for 34% of the total mass of the furnace charge; scrap steel includes heavy scrap steel and light scrap steel; among the scrap steel, the mass percentage of heavy scrap steel accounts for 55%, and the rest is light scrap steel; the tapping temperature is 1615℃, C is 0.09% and P is 0.009% when tapping, slag, pre-deoxidizer and alloy are added when 1 / 4 of the steel is tapped, the smelting cycle is 48min, and the furnace oxygen consumption is 25m 3 / t steel. Alloy addition per ton of steel: 9.1 kg / t silicon manganese alloy, 4.1 kg / t high carbon ferromanganese, 4.1 kg / t high carbon ferrochrome, 12.3 kg / t low carbon ferrochrome, 1.1 kg / t aluminum wire (Φ10 mm). Auxiliary material addition per ton of steel: 26 kg / t active lime (Φ35 mm), 12.2 kg / t coking coal CDQ powder, 6.1 kg / t ladle dust, and 20.2 kg / t dolomite (Φ40 mm).

[0087] (2) LF furnace refining

[0088] The LF station temperature is 1502°C, and a high current of 35600A is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, 3.9kg / t of active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloy is added according to the median chemical composition, and carbon is increased to promote rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1625°C, 1.5kg / t of alumina balls are added as a slag regulator to adjust the slag basicity to 2.6. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1645°C, a second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, the station is left when the molten steel temperature reaches 1674°C. The LF smelting cycle is 48 minutes, the clearance is 446mm, and the slag thickness is 143mm. The amount of additional alloy added per ton of steel is: 0.68kg / t of ferrosilicon, 2.0kg / t of high carbon ferromanganese, 3.6kg / t of ferromolybdenum, and 3.6kg / t of ferrovanadium (FeV50-B). The amount of additional auxiliary materials added per ton of steel is: 4.0kg / t of active lime (Φ35mm), and 1.5kg / t of silicon carbide.

[0089] (3)RH refining

[0090] The station entry temperature is 1685℃, the operation time is 60min, and the argon pressure is controlled at 0.3MPa before the vacuum pump is started. The slag surface is slightly moved to prevent the molten steel from being exposed. When the vacuum reaches 102Pa, the timing starts and the holding time is 22min. At the same time, the argon pressure is adjusted to 0.4MPa, and the re-pressurization temperature is 1639℃. After the static argon blowing is completed, 0.6kg / t of covering agent is added, the clearance is 495mm, and the station exit temperature is 1620℃. After breaking the vacuum, 0.57kg / t of ladle covering agent and 0.80kg / t of silicon-calcium alloy cored wire (Φ14mm) are added.

[0091] (4) Continuous casting

[0092] The arrival temperature of the ladle is 1609℃, the H of the tundish is controlled at 1.3ppm, the casting time is 48min, the superheat is 22℃, the casting speed is 0.44m / min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag 3.7kg / t steel.

[0093] (5) Heating process

[0094] Heating process: the temperature entering the heating furnace is 560℃, the temperature of the preheating section is 860℃, the time is 1.8h; the temperature of the heating section 2 is 875℃, the time is 1.8h; the temperature of the heating section 1 is 1222℃, the time is 1.7h; the temperature of the soaking section is 1216℃, the time is 1.7h; the tapping temperature is 1190℃.

[0095] (6) Rolling process

[0096] The product is rolled in 9 passes, passes through 3 850mm rolling mills, and then enters 9 continuous rolling mills for rolling. The continuous rolling process is as follows: 9 passes, the first pass is 229.01mm high, 245mm wide, and the rolling speed is 0.272m / s; the second pass is 192.01mm high, 235mm wide, and the rolling speed is 0.312m / s; the third pass is 200mm high, 195.01mm wide, and the rolling speed is 0.35m / s; the fourth pass is 160mm high, 214.71mm wide, and the rolling speed is 0.476m / s; the The 5th pass is 168.01mm high, 174.6mm wide, and the rolling speed is 0.600m / s; the 6th pass is 120.01mm high, 187.6mm wide, and the rolling speed is 0.745m / s; the 7th pass is 142.01mm high, 138.51mm wide, and the rolling speed is 0.936m / s; the 8th pass is 111mm high, 151.51mm wide, and the rolling speed is 1.102m / s; the 9th pass is 122.05mm high, 122.04mm wide, and the rolling speed is 1.219m / s; the finished product is produced after 9 passes.

[0097] (7) Insulation process

[0098] Insulation process: Steel insulation, the temperature of the lower insulation pit is 590℃, insulation for 54h, and the temperature out of the pit is 110℃.

[0099] (8) Heat treatment process

[0100] After the insulation, the steel sample is taken for heat treatment, which includes the following steps:

[0101] 1) Quenching: 850℃, holding time 1.0h, oil cooling;

[0102] 2) Tempering: 200℃, keep warm for 2.0h, air cool.

[0103] Example 4:

[0104] 1. Composition optimization design

[0105] The steel bar for the ecological electric furnace automobile reducer of this embodiment includes the following components in mass percentage: C: 0.21%, Si: 0.25%, Mn: 0.97%, P: 0.012%, S: 0.005%, Cr: 1.17%, Ni: 0.07%, Mo: 0.25%, V: 0.16%, Cu: 0.06%, and the balance is iron and unavoidable impurities.

[0106] 2. Electric furnace continuous casting production processes for steel bars for automobile reducers

[0107] Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → insulation → heat treatment.

[0108] (1) Ecological electric furnace smelting

[0109] Scrap steel and molten iron are used as furnace charges, of which the mass of scrap steel accounts for 64% of the total mass of the furnace charge, and the mass of molten iron accounts for 36% of the total mass of the furnace charge; scrap steel includes heavy scrap steel and light scrap steel; among the scrap steel, the mass percentage of heavy scrap steel accounts for 54%, and the rest is light scrap steel; the tapping temperature is 1615℃, the C content is 0.09% and the P content is 0.008% when tapping, slag, pre-deoxidizer and alloy are added when 1 / 4 of the steel is tapped, the smelting cycle is 47min, and the furnace oxygen consumption is 25m 3 / t steel. Alloy addition per ton of steel: 9.0 kg / t silicon manganese alloy, 4.0 kg / t high carbon ferromanganese, 4.1 kg / t high carbon ferrochrome, 12.3 kg / t low carbon ferrochrome, 1.1 kg / t aluminum wire (Φ10 mm). Auxiliary material addition per ton of steel: 26 kg / t active lime (Φ35 mm), 12.3 kg / t coking coal CDQ powder, 6.1 kg / t ladle dust, and 20.3 kg / t dolomite (Φ40 mm).

[0110] (2) LF furnace refining

[0111] The LF station temperature is 1498°C, and a high current of 35600A is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, 4.0 kg / t of active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloy is added according to the median chemical composition, and carbon is increased to promote rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1624°C, 1.4 kg / t of alumina balls are added as a slag regulator to adjust the slag basicity to 2.8. The furnace door is closed for 12 minutes. When the molten steel temperature reaches 1645°C, a second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, the station is left when the molten steel temperature reaches 1675°C. The LF smelting cycle is 47 minutes, the clearance is 446 mm, and the slag thickness is 143 mm. The amount of additional alloy added per ton of steel is: 0.67kg / t of ferrosilicon, 1.9kg / t of high carbon ferromanganese, 3.6kg / t of ferromolybdenum, and 3.6kg / t of ferrovanadium (FeV50-B). The amount of additional auxiliary materials added per ton of steel is: 4.0kg / t of active lime (Φ35mm), and 1.5kg / t of silicon carbide.

[0112] (3)RH refining

[0113] The entry temperature is 1685℃, the operation time is 58 minutes, and the argon pressure is controlled at 0.2MPa before the vacuum pump is started. The slag surface is slightly moved so that the molten steel is not exposed. When the vacuum reaches 102Pa, the timing starts and the holding time is 23 minutes. At the same time, the argon pressure is adjusted to 0.4MPa, and the re-pressurization temperature is 1639℃. After the static argon blowing is completed, 0.6kg / t of covering agent is added, the clearance is 505mm, and the exit temperature is 1619℃. After breaking the vacuum, 0.58kg / t of ladle covering agent and 0.82kg / t of silicon-calcium alloy cored wire (Φ14mm) are added.

[0114] (4) Continuous casting

[0115] The arrival temperature of the ladle is 1608℃, the H of the tundish is controlled at 1.3ppm, the casting time is 52min, the superheat is 22℃, the casting speed is 0.44m / min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag 3.7kg / t steel.

[0116] (5) Heating process

[0117] Heating process: the temperature entering the heating furnace is 550℃, the temperature of the preheating section is 860℃, the time is 1.8h; the temperature of the heating section 2 is 870℃, the time is 1.7h; the temperature of the heating section 1 is 1225℃, the time is 1.8h; the temperature of the soaking section is 1216℃, the time is 1.6h; the steel tapping temperature is 1192℃.

[0118] (6) Rolling process

[0119] The slab is rolled in 9 passes, passes through 3 850mm rolling mills, and then enters 9 continuous rolling mills for rolling. The continuous rolling process is as follows: 9 passes, the first pass is 229mm high, 245mm wide, and the rolling speed is 0.27m / s; the second pass is 192.01mm high, 235mm wide, and the rolling speed is 0.312m / s; the third pass is 200.01mm high, 195mm wide, and the rolling speed is 0.352m / s; the fourth pass is 160.01mm high, 214.7mm wide, and the rolling speed is 0.476m / s; the fifth pass is 200.01mm high, 195mm wide, and the rolling speed is 0.352m / s; the fifth pass is 200.01mm high, 214.7mm wide, and the rolling speed is 0.476m / s. The second high is 168.01mm, the width is 174.61mm, and the rolling speed is 0.600m / s; the 6th pass has a high of 120.01mm, a width of 187.61mm, and a rolling speed of 0.745m / s; the 7th pass has a high of 142mm, a width of 138.51mm, and a rolling speed of 0.936m / s; the 8th pass has a high of 111.01mm, a width of 151.51mm, and a rolling speed of 1.104m / s; the 9th pass has a high of 122.04mm, a width of 122.05mm, and a rolling speed of 1.219m / s; the finished product is produced after 9 passes.

[0120] (7) Insulation process

[0121] Insulation process: Steel insulation, the temperature of the lower insulation pit is 585℃, insulation for 52h, and the temperature out of the pit is 115℃.

[0122] (8) Heat treatment process

[0123] After the insulation, the steel sample is taken for heat treatment, which includes the following steps:

[0124] 1) Quenching: 850℃, holding time 1.0h, oil cooling;

[0125] 2) Tempering: 200℃, keep warm for 2.0h, air cool.

[0126] Example 5:

[0127] 1. Composition optimization design

[0128] The steel bar for the ecological electric furnace automobile reducer of this embodiment includes the following components in mass percentage: C: 0.20%, Si: 0.25%, Mn: 1.05%, P: 0.012%, S: 0.005%, Cr: 1.17%, Ni: 0.06%, Mo: 0.24%, V: 0.16%, Cu: 0.05%, and the balance is iron and unavoidable impurities.

[0129] 2. Electric furnace continuous casting production processes for steel bars for automobile reducers

[0130] Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → insulation → heat treatment.

[0131] (1) Ecological electric furnace smelting

[0132] Scrap steel and molten iron are used as furnace charges, of which the mass of scrap steel accounts for 65% of the total mass of the furnace charge, and the mass of molten iron accounts for 35% of the total mass of the furnace charge; scrap steel includes heavy scrap steel and light scrap steel; among the scrap steel, the mass percentage of heavy scrap steel accounts for 54%, and the rest is light scrap steel; the tapping temperature is 1615℃, C is 0.09% and P is 0.009% when tapping, slag, pre-deoxidizer and alloy are added when 1 / 4 of the steel is tapped, the smelting cycle is 47min, and the furnace oxygen consumption is 26m 3 / t steel. Alloy addition per ton of steel: 9.1 kg / t silicon manganese alloy, 4.1 kg / t high carbon ferromanganese, 4.1 kg / t high carbon ferrochrome, 12.2 kg / t low carbon ferrochrome, 1.1 kg / t aluminum wire (Φ10 mm). Auxiliary material addition per ton of steel: 27 kg / t active lime (Φ35 mm), 12.3 kg / t coking coal CDQ powder, 6.1 kg / t ladle dust, and 20.4 kg / t dolomite (Φ40 mm).

[0133] (2) LF furnace refining

[0134] The LF station temperature is 1502°C, and a high current of 35600A is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, 3.95kg / t of active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloy is added according to the median chemical composition, and carbon is increased to promote rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1624°C, 1.4kg / t of alumina balls are added as a slag regulator to adjust the slag basicity to 2.7. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1645°C, a second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, the station is left when the molten steel temperature reaches 1674°C. The LF smelting cycle is 47 minutes, the clearance is 445mm, and the slag thickness is 146mm. The amount of additional alloy added per ton of steel is: 0.66kg / t of ferrosilicon, 1.9kg / t of high carbon ferromanganese, 3.6kg / t of ferromolybdenum, and 3.6kg / t of ferrovanadium (FeV50-B). The amount of additional auxiliary materials added per ton of steel is: 4.0kg / t of active lime (Φ35mm), and 1.4kg / t of silicon carbide.

[0135] (3)RH refining

[0136] The station entry temperature is 1687°C, the operation time is 60 minutes, and the argon pressure is controlled at 0.1MPa before the vacuum pump is started. The slag surface is slightly moved so that the molten steel is not exposed. When the vacuum reaches 101Pa, the timing starts and the holding time is 22 minutes. At the same time, the argon pressure is adjusted to 0.4MPa, and the re-pressurization temperature is 1640°C. After the static argon blowing is completed, 0.5kg / t of covering agent is added, the clearance is 502mm, and the station exit temperature is 1619°C. After breaking the vacuum, 0.58kg / t of ladle covering agent and 0.81kg / t of silicon-calcium alloy cored wire (Φ14mm) are added.

[0137] (4) Continuous casting

[0138] The arrival temperature of the ladle is 1608℃, the H of the tundish is controlled at 1.5ppm, the casting time is 51min, the superheat is 22℃, the casting speed is 0.44m / min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag 3.7kg / t steel.

[0139] (5) Heating process

[0140] Heating process: the temperature entering the heating furnace is 570℃, the temperature of the preheating section is 865℃, the time is 1.6h; the temperature of the heating section 2 is 870℃, the time is 1.8h; the temperature of the heating section 1 is 1225℃, the time is 1.8h; the temperature of the soaking section is 1217℃, the time is 1.8h; the steel tapping temperature is 1193℃.

[0141] (6) Rolling process

[0142] The product is rolled in 9 passes, passes through 3 850mm rolling mills, and then enters 9 continuous rolling mills for rolling. The continuous rolling process is as follows: 9 passes, the first pass is 229mm high, 245.01mm wide, and the rolling speed is 0.272m / s; the second pass is 192mm high, 235.01mm wide, and the rolling speed is 0.312m / s; the third pass is 200.01mm high, 195mm wide, and the rolling speed is 0.35m / s; the fourth pass is 160.01mm high, 214.71mm wide, and the rolling speed is 0.476m / s; the fifth pass is 200.01mm high, 195mm wide, and the rolling speed is 0.35m / s; the sixth pass is 200.01mm high, 214.71mm wide, and the rolling speed is 0.476m / s; the eighth pass is 200.01mm high, 195mm wide, and the rolling speed is 0.35 ... The 5th pass is 168.01mm high, 174.61mm wide, and the rolling speed is 0.600m / s; the 6th pass is 120.01mm high, 187.6mm wide, and the rolling speed is 0.743m / s; the 7th pass is 142.01mm high, 138.51mm wide, and the rolling speed is 0.936m / s; the 8th pass is 111.01mm high, 151.51mm wide, and the rolling speed is 1.104m / s; the 9th pass is 122.04mm high, 122.05mm wide, and the rolling speed is 1.219m / s; the finished product is produced after 9 passes.

[0143] (7) Insulation process

[0144] Insulation process: Steel insulation, the temperature of the lower insulation pit is 580℃, insulation for 53h, and the temperature out of the pit is 90℃.

[0145] (8) Heat treatment process

[0146] After the insulation, the steel sample is taken for heat treatment, which includes the following steps:

[0147] 1) Quenching: 850℃, holding time 1.0h, oil cooling;

[0148] 2) Tempering: 200℃, keep warm for 2.0h, air cool.

[0149] 2. Finished product inspection results

[0150] (1) Φ120mm specification macrostructure

[0151] Table 1 Macrostructure properties of Φ120mm specification

[0152]

[0153]

[0154] (2) Φ120mm non-metallic inclusions

[0155] Table 2 Analysis of non-metallic inclusions in Φ120mm size

[0156]

[0157] (3) Mechanical properties of Φ120mm specification

[0158] Table 3 Mechanical properties analysis of Φ120mm specifications

[0159] Serial number Quenching / ℃ Holding time Tempering / ℃ Holding time Rm / MPa Rel / MPa A / ％ z / ％ KU2 / J standard 850, oil cooling 0.8～1.2h 200, air cooling 1.8～2.2h ≥1280 ≥965 ≥11 ≥46 ≥57 Example 1 850, oil cooling 1h 200, air cooling 2h 1360 1030 15 64 65 Example 1 850, oil cooling 1h 200, air cooling 2h 1352 1025 16 67 66 Example 2 850, oil cooling 1h 200, air cooling 2h 1345 1028 14 65 65 Example 2 850, oil cooling 1h 200, air cooling 2h 1347 1029 16 67 64 Example 3 850, oil cooling 1h 200, air cooling 2h 1350 1034 15 66 63 Example 3 850, oil cooling 1h 200, air cooling 2h 1347 1028 17 63 63 Example 4 850, oil cooling 1h 200, air cooling 2h 1336 1034 13 63 66 Example 4 850, oil cooling 1h 200, air cooling 2h 1340 1029 14 67 67 Example 5 850, oil cooling 1h 200, air cooling 2h 1331 1024 17 66 68 Example 5 850, oil cooling 1h 200, air cooling 2h 1343 1027 15 64 66

[0160] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A steel bar for ecological electric furnace automobile reducer, characterized in that: The following components are included in mass percentage: C: 0.18% to 0.22%, Si: 0.17% to 0.37%, Mn: 0.90% to 1.20%, P≤0.015%, S≤0.007%, Cr: 1.10% to 1.40%, Ni≤0.30%, Mo: 0.20% to 0.30%, V: 0.15% to 0.20%, Cu≤0.20%, and the balance is iron and unavoidable impurities.

2. The steel bar for ecological electric furnace automobile reducer according to claim 1 is characterized in that: The steel bar for the ecological electric furnace automobile reducer has a tensile strength of ≥1280 MPa, a yield strength of ≥965 MPa, A ≥11%, z ≥46%, and KU2 ≥57J.

3. A method for preparing steel bars for ecological electric furnace automobile reducers according to any one of claims 1-2, characterized in that: The following steps are involved: Ecological electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating, rolling, insulation and heat treatment; In the ecological electric furnace smelting, scrap steel and molten iron are used as furnace charge, wherein the mass of the scrap steel accounts for 60% to 70% of the total mass of the furnace charge; In the LF refining, the molten steel discharged from the ecological electric furnace is put into the LF furnace for refining treatment; During the RH vacuum refining, the molten steel treated by the LF refining is hoisted into the RH vacuum furnace for refining; During the continuous casting, the molten steel after the RH vacuum refining treatment is continuously cast, and the obtained continuous casting billet is heated, rolled and kept warm; During the heat treatment, the steel after insulation is quenched at a heating temperature of 840°C to 860°C, a insulation time of 0.8h to 1.2h, and oil cooling; the quenched and cooled steel is then tempered at a tempering temperature of 190°C to 210°C, a insulation time of 1.8h to 2.2h, and air cooling to obtain the steel bar for the ecological electric furnace automobile reducer.

4. The preparation method according to claim 3, characterized in that In the ecological electric furnace smelting, the scrap steel includes heavy scrap steel and light scrap steel; the mass percentage of heavy scrap steel in the scrap steel is 50% to 60%; the tapping temperature is 1610°C to 1620°C; the tapping end composition is: C: 0.08% to 0.12%, P ≤ 0.010%; deoxidation and alloying are carried out during the tapping process; slag, pre-deoxidizer and alloy are added when 1 / 4 to 1 / 3 of the steel is tapped, the smelting cycle is 45 minutes to 50 minutes, and the furnace oxygen consumption is 25m 3 / t steel~26m 3 / t steel; alloy addition per ton of steel: 9.0Kg / t~9.1Kg / t of silicon manganese alloy, 4.0Kg / t~4.1Kg / t of high carbon ferromanganese, 4.0Kg / t~4.1Kg / t of high carbon ferrochrome, 12.0Kg / t~12.5Kg / t of low carbon ferrochrome, 1.0Kg / t~1.1Kg / t of aluminum wire segment; auxiliary material addition per ton of steel: 26Kg / t~27Kg / t of active lime, 12Kg / t~12.5Kg / t of coking CDQ powder, 6.0Kg / t~6.1Kg / t of ladle dust, and 20.0Kg / t~20.5Kg / t of dolomite; wherein, the size specification of the aluminum wire segment is Φ10mm~Φ16mm, the particle size of the active lime is 10mm~70mm, and the particle size of the dolomite is 20mm~70mm.

5. The preparation method according to claim 3, characterized in that In the LF refining, the LF inlet temperature is 1495°C to 1505°C, and after heating and slag melting with a high current of 35000A to 36000A, 3.9kg / t to 4.0kg / t of active lime is added when the slag surface fluctuates and the molten steel and the arc are not exposed. After 5min to 6min, the first sampling and analysis is performed, and the molten steel composition content is adjusted according to the target composition requirements; when the molten steel temperature reaches 1620°C to 1630°C, 1.4kg / t to 1.5kg / t of alumina balls are added as a slag regulator to adjust the slag basicity to ≥ 2.5, the furnace door is closed for 10min to 13min, and when the molten steel temperature reaches 1640°C to 1650°C, the second sampling and analysis is performed. ; Leave the station when the molten steel temperature is 1670℃~1680℃, the LF smelting cycle is 45min~50min, the clearance is 440mm~450mm, and the slag thickness is 140mm~150mm; the additional alloy addition per ton of steel: 0.65kg / t~0.7kg / t of ferrosilicon, 1.9kg / t~2.0kg / t of high carbon ferromanganese, 3.5kg / t~3.6kg / t of ferromolybdenum, 3.5kg / t~3.6kg / t of ferrovanadium; the additional auxiliary materials addition per ton of steel: 3.9kg / t~4.0kg / t of active lime with a particle size of 10mm~70mm, 1.4Kg / t~1.5Kg / t of silicon carbide.

6. The preparation method according to claim 3, characterized in that During the RH vacuum refining, the station entry temperature is 1680° C. to 1690° C., the operation time is 55 min to 65 min, the vacuum pump is started when the argon pressure is controlled to be 0.1 MPa to 0.3 MPa, and when the vacuum degree reaches 100 Pa to 105 Pa, it is maintained for 20 min to 25 min. At the same time, the argon pressure is adjusted to 0.3 MPa to 0.5 MPa. The temperature after re-pressurization is 1635° C. to 1645° C. After the static argon blowing is completed, 0.5 kg / t steel to 0.6 kg / t steel of covering agent is added, the clearance is 480 mm to 520 mm, the station exit temperature is 1615° C. to 1625° C., and after breaking the vacuum, 0.55 kg / t steel to 0.60 kg / t steel of covering agent and 0.80 kg / t steel to 0.82 kg / t steel of silicon-calcium alloy cored wire are added. The size of the silicon-calcium alloy cored wire is Φ14 mm to Φ15 mm.

7. The preparation method according to claim 3, characterized in that During the continuous casting, the ladle arrival temperature is 1605°C to 1615°C, the casting time is 45min to 55min, the superheat is 20°C to 25°C, the H content in the tundish is ≤2ppm, the casting speed is 0.44m / min to 0.45m / min, the casting is protected throughout the entire process, and the mold protection slag uses medium carbon steel protection slag of 3.6kg / t steel to 3.7kg / t steel.

8. The preparation method according to claim 3, characterized in that In the heating process, the square billets produced in the continuous casting process are fed into a heating furnace, the temperature of the heating furnace is 500°C to 600°C; the temperature of the preheating section is 850°C to 870°C, and the time is 1.6h to 1.8h; the heating section includes heating section 1 with a temperature of 1210°C to 1230°C, and the time is 1.6h to 1.8h; heating section 2 with a temperature of 860°C to 890°C, and the time is 1.6h to 1.8h; the temperature of the soaking section is 1210°C to 1220°C, and the time is 1.6h to 1.8h; and the tapping temperature is 1180°C to 1200°C.

9. The preparation method according to claim 3, characterized in that In the rolling process, the heated continuous casting slab is rolled into a slab through 9 passes, passes through 3 850mm rolling mills, and then enters a 9-stand continuous rolling mill group for rolling; the rolling speed of each pass is 0.31m / s to 1.219m / s.

10. The preparation method according to claim 3, characterized in that During the insulation, the temperature of the lower insulation pit is ≥560°C, the insulation time is 50h-55h, and the exit temperature from the pit is ≤120°C.

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