Production and preparation process of steel bar for converter process automobile transmission shaft

Abstract

The invention discloses a production and preparation process of a steel bar for a converter process automobile transmission shaft, which comprises the following chemical components in percentage by mass: 0.33 to 0.38 percent of C, 0.22 to 0.35 percent of Si, 0.40 to 0.70 percent of Mn, less than or equal to 0.012 percent of P, less than or equal to 0.004 percent of S, 0.85 to 1.00 percent of Cr, 0.16 to 0.23 percent of Mo, 0.10 to 0.20 percent of V, less than or equal to 0.15 percent of Cu, less than or equal to 0.25 percent of Ni and the balance of iron and inevitable impurities. The process route comprises converter smelting, LF refining, RH refining, continuous casting, a heating furnace heating process, a rolling process and a heat preservation process. The invention realizes the breakthrough of batch production of the steel bar for the automobile transmission shaft in the converter continuous casting process.

Description

Technical Field

[0001] The present invention relates to the field of special steel, and specifically relates to a production preparation process for steel bars used for automotive drive shafts in a converter process. Background Art

[0002] The automotive drive shaft is an important component for transmitting power in the automotive transmission system. Its function is to transmit the power of the engine to the wheels together with the gearbox and the drive axle, enabling the vehicle to generate driving force. The steel used for automotive drive shafts needs to have comprehensive properties such as high strength and high corrosion resistance, and the requirements are very strict. As an important part of automotive transmission, the steel for automotive drive shafts bears high-pressure loads during high-speed operation.

[0003] The quality of the steel for automotive drive shafts directly affects the service life and stability of the automotive transmission device, and even relates to the safety of the entire vehicle during driving.

[0004] Therefore, it is necessary to develop a steel bar for automotive drive shafts with excellent impact performance, high hardness and high steel purity to meet the requirements of high-end products. Summary of the Invention

[0005] The purpose of the present invention is to provide a production preparation process for steel bars used for automotive drive shafts. This method uses a converter + LF + RH + continuous casting smelting process and a rolling process to produce steel bars for automotive drive shafts, which not only ensures the impact performance, high hardness, high steel purity and other indicators of the finished steel of the steel bars for automotive drive shafts, but also ensures the surface quality level of the steel bars for automotive drive shafts, meets the high-end use requirements, and realizes a breakthrough in batch production of steel bars for automotive drive shafts in the converter continuous casting process.

[0006] To achieve the above invention purpose, the present invention provides a production preparation process for steel bars used for automotive drive shafts, including composition design and process design. The specific steps are: converter smelting → LF refining → RH vacuum degassing → continuous casting → heating → rolling process → heat preservation process, which meets the quality requirements of the steel bars for automotive drive shafts, and the indicators such as impact performance, high hardness and high steel purity can also meet the standard requirements.

[0007] For a steel bar for automotive drive shafts in a converter process, its chemical composition, by mass percentage, is C: 0.33% - 0.38%, Si: 0.22% - 0.35%, Mn: 0.40% - 0.70%, P: ≤0.012%, S: ≤0.004%, Cr: 0.85% - 1.00%, Mo: 0.16% - 0.23%, V: 0.10% - 0.20%, Cu: ≤0.15%, Ni: ≤0.25%, and the balance is iron and unavoidable impurities.

[0008] The specification of the steel bar for the automobile drive shaft in the converter process of the present invention is Φ150mm.

[0009] The production preparation process of the above-mentioned steel bar for the automobile drive shaft in the converter process, the process route: converter smelting → secondary refining (LF+RH) → continuous casting → heating furnace heating process → rolling process → heat preservation process;

[0010] Among them, the converter smelting is: by mass fraction, scrap steel accounts for 20-25%, hot metal accounts for 75-80%; oxidized by oxygen, with intense boiling, tapping temperature of 1675-1685°C, oxygen supply time of 13-14min, end point oxygen of 460-470ppm, operation time of 45-55min, C is 0.13-0.15% when tapping, P≤0.010%, and auxiliary materials and alloys are added when 1 / 4-1 / 3 of the steel is tapped. The addition amount of alloy per ton of steel: silicomanganese 8.1-8.2Kg / t, high-carbon ferrochrome 13.5-14.0Kg / t, ferromolybdenum 2.6-2.8Kg / t, aluminum pellets 0.8-0.85Kg / t. The addition amount of auxiliary materials per ton of steel: dolomite 11-11.5Kg / t, active lime 28-29Kg / t, pulverized coal 2.2-2.3Kg / t.

[0011] The refining of the LF furnace is: using a large current of 20000-25000A to raise the temperature and melt the slag. When the slag surface fluctuates and the molten steel and electric arc are not exposed, add active lime. Take the first sample for chemical composition analysis after 5-10min, and add alloys according to the chemical composition target value. The alloys should be added onto the argon flow to promote the rapid melting and homogenization of the alloys. The net space of the furnace body is 440-450mm, the slag thickness is 70-80mm, the argon blowing time is 55-65min, the operation time is 85-90min. When the molten steel temperature reaches 1550-1560°C, add 1-3kg / t of steel of diffusion deoxidizer (aluminum pellets) for diffusion deoxidation, close the furnace door for 10-12min. When the molten steel temperature reaches 1580-1590°C, take the second sample for chemical composition analysis to confirm the deviation value of the content of each chemical element component from the target value requirement. After the second sample is taken away, add 0.58-0.59kg / t of steel of diffusion deoxidizer (aluminum pellets) to continue adjusting the slag. The addition amount of alloy per ton of steel for supplementary addition: high-carbon ferrochrome 2.0-2.1kg / t, ferrosilicon 1.0-1.1kg / t, ferrovanadium (FeV50-B) 3.5-3.6kg / t. Keep the basicity pH value of the molten slag at 2.2-3.2, and the viscosity of the molten slag at 0.95-1.10Pa.s, and at the same time continue to maintain white slag melting for 20-30min. The addition amount of auxiliary materials per ton of steel for supplementary addition: active lime 6.5-7kg / t.

[0012] The RH refining process is as follows: the temperature before treatment is 1600 - 1610°C, the argon pressure is controlled at 0.1 - 0.3 MPa before starting the vacuum pump, with the slag surface slightly moving and the molten steel not exposed. When the vacuum degree reaches 90 - 100 Pa, timing starts, the holding time is 10 - 15 min, the minimum vacuum degree is 55 - 65 Pa, the free space is 570 - 590 mm, the slag thickness is 85 - 95 mm, the operation time is 28 - 32 min, the circulation time is 12 - 17 min. At the same time, the argon pressure is adjusted to 0.3 - 0.5 MPa. After the static argon blowing ends, 1.0 - 1.2 m / t of silicon-calcium wire (with a diameter of 10 - 12 mm) is added.

[0013] The continuous casting process is as follows: the tundish temperature is 1535 - 1540°C, the casting speed is 0.48 - 0.50 m / min, the H content in the tundish is controlled ≤ 1.8 ppm, the current of the mold electromagnetic stirrer is 400 - 450 A, the current of the final electromagnetic stirrer is 330 - 340 A, and the frequency is 8 - 8.2 Hz; the whole process is protected by casting. The mold powder used is medium-carbon steel mold powder, and the consumption of medium-carbon steel mold powder is 3.6 - 3.7 kg / t of steel; soft reduction is applied to the 2nd, 3rd, and 4th rolls, and the reduction amounts are 3 - 3.1 mm, 4 - 4.1 mm, and 4 - 4.1 mm respectively; the slab cutting adopts a combination of automatic and manual methods. The hot billet of the continuous casting slab is used as the bottom layer, and the upper two furnace billets are pressed to ensure flatness, and the heat preservation time is 30 - 40 h.

[0014] The heating process is as follows: the temperature entering the heating furnace is 360°C - 420°C, the temperature requirement for the preheating section is 450°C - 610°C, and the time is 1.3 - 1.4 h; the temperature requirement for the second heating section is 850°C - 880°C, and the time is 2.3 - 2.4 h; the temperature requirement for the first heating section is 1190°C - 1220°C, and the time is 2.3 - 2.4 h; the temperature requirement for the soaking section is 1190°C - 1210°C, and the time is 1.3 - 1.4 h; the tapping temperature is 1180°C - 1210°C.

[0015] Furthermore, the rolling process includes the cogging process and the continuous rolling process, specifically:

[0016] Cogging: The 1150 mm BD cogging mill is used for cogging, with 7 rolling passes. The rolling reduction amounts are: turning the steel → the reduction amount of the first pass is 70 - 70.1 mm → the reduction amount of the second pass is 80 - 80.1 mm → turning the steel → the third pass is 74 - 74.1 mm → the fourth pass is 81 - 81.1 mm → turning the steel → the fifth pass is 92 - 92.1 mm → the sixth pass is 30 - 30.1 mm → turning the steel → the seventh pass is 38 - 38.1 mm. After passing through 3 sets of 850 mm rolling mills, it then enters the 9-stand continuous rolling mill for rolling.

[0017] Continuous rolling process: In the first pass, the height is 229 - 229.01 mm, the width is 245 - 245.01 mm, and the rolling speed is 0.27 - 0.272 m / s; in the second pass, the height is 192 - 192.01 mm, the width is 235 - 235.01 mm, and the rolling speed is 0.31 - 0.312 m / s; in the third pass, the height is 200 - 200.01 mm, the width is 195 - 195.01 mm, and the rolling speed is 0.31 - 0.312 m / s; in the fourth pass, the height is 169 - 169.01 mm, the width is 212.8 - 212.81 mm, and the rolling speed is 0.356 - 0.358 m / s; in the fifth pass, the height is 177 - 177.01 mm, the width is 180 - 180.01 mm, and the rolling speed is 0.445 - 0.447 m / s; in the sixth pass, the height is 141 - 141.01 mm, the width is 192 - 192.01 mm, and the rolling speed is 0.526 - 0.528 m / s; in the seventh pass, the height is 152 - 152.01 mm, the width is 152 - 152.01 mm, and the rolling speed is 0.614 - 0.616 m / s; in the eighth pass, the height is 152 - 152.01 mm, the width is 152 - 152.01 mm, and the rolling speed is 0.614 - 0.616 m / s; the finished product is obtained after 8 passes.

[0018] Furthermore, the heat preservation process is as follows: for the steel to be heat-preserved, the temperature when entering the pit is ≥560 °C, the temperature when leaving the pit is ≤200 °C, and the heat preservation time is ≥52 h.

[0019] Furthermore, the heat-preserved steel is subjected to heat treatment, and the heat treatment includes the following steps:

[0020] 1) Quenching: at 840 - 860 °C, heat preservation for 1.0 - 1.2 h, oil cooling;

[0021] 2) Tempering: at 550 - 570 °C, heat preservation for 2.0 - 2.2 h, water cooling.

[0022] Advantages of the present invention:

[0023] (1) Using the converter + LF refining + RH refining + continuous casting smelting process and rolling process to produce steel bars for automotive drive shafts, meeting the mechanical property requirements and ensuring the steel purity.

[0024] (2) Reasonable composition design and production process ensure the surface quality and impact performance.

[0025] (3) The macrostructure, non-metallic inclusions, and hardness of the finished steel all meet the requirements of high-end products. Detailed implementation manners

[0026] The following non-limiting examples can enable those of ordinary skill in the art to understand the present invention more comprehensively, but do not limit the present invention in any way.

[0027] Example 1

[0028] 1 Chemical composition of steel bars for automotive drive shafts

[0029] By mass percentage: C: 0.35%, Si: 0.28%, Mn: 0.52%, P: 0.010%, S: 0.003%, Cr: 0.92%, Mo: 0.18%, V: 0.16%, Cu: 0.05%, Ni: 0.05%, and the balance is iron and inevitable impurities.

[0030] 2 Design of production process parameters for converter continuous casting of steel bars for automotive drive shafts

[0031] Process route: Converter smelting → Secondary refining (LF+RH) → Continuous casting → Heating in heating furnace → Rolling → Heat preservation → Heat treatment. Among them:

[0032] (1) Converter smelting: The mass fraction of scrap steel is 22% and that of hot metal is 78%; Oxygen oxidation, intense boiling, tapping temperature 1680°C, oxygen supply time 13 min, end point oxygen 465 ppm, operation time 49 min, C is 0.14% and P is 0.008% at tapping, and auxiliary materials and alloys are added when 1 / 4 of the steel is tapped. Alloy addition per ton of steel: 8.1 Kg / t of silicomanganese, 13.70 Kg / t of high-carbon ferrochrome, 2.7 Kg / t of ferromolybdenum, 0.82 Kg / t of aluminum pellets. Auxiliary material addition per ton of steel: 11.3 Kg / t of dolomite, 28.5 Kg / t of active lime, 2.2 Kg / t of steam coal.

[0033] (2) LF furnace refining: Use a large current of 23000 A to raise the temperature and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, add active lime. Take the first sample for chemical composition analysis after 5 min, and add alloys according to the target values of chemical composition. The alloys should be added onto the argon flow to promote rapid melting and homogenization of the alloys. The furnace body clearance is 445 mm, the slag thickness is 75 mm, argon blowing is 60 min, the operation time is 87 min. When the molten steel temperature reaches 1556°C, add 1 kg / t of diffusion deoxidizer (aluminum pellets) for diffusion deoxidation, close the furnace door for 10 min. When the molten steel temperature reaches 1585°C, take the second sample for chemical composition analysis to confirm the deviation value of the content of each chemical element from the target value. After the second sample is taken away, add 0.59 kg / t of diffusion deoxidizer (aluminum pellets) to continue adjusting the slag. Alloy addition per ton of steel for supplementary addition: 2.0 kg / t of high-carbon ferrochrome, 1.1 kg / t of ferrosilicon, 3.5 kg / t of ferrovanadium (FeV50-B). Keep the basicity pH value of the molten slag at 2.6 and the viscosity of the molten slag at 0.98 Pa·s, and at the same time continue to maintain white slag smelting for 24 min. Auxiliary material addition per ton of steel for supplementary addition: 6.7 kg / t of active lime.

[0034] (3) RH refining: The temperature before treatment is 1605°C. Before starting the vacuum pump, the argon pressure is controlled at 0.1 MPa, with the slag surface slightly moving and the molten steel not exposed. When the vacuum degree reaches 97 Pa, timing starts, the holding time is 12 min, the minimum vacuum degree is 60 Pa, the freeboard is 580 mm, the slag thickness is 92 mm, the operation time is 29 min, the cycle time is 15 min. At the same time, the argon pressure is adjusted to 0.4 MPa. After the static argon blowing is completed, 1.1 m / t of silicon-calcium wire (10 mm) is added.

[0035] (4) Continuous casting: The tundish temperature is 1537°C, the casting speed is 0.49 m / min, the H content in the tundish is controlled at 1.3 ppm, the current of the mold electromagnetic stirrer is 435 A, the current of the final electromagnetic stirrer is 336 A, and the frequency is 8 Hz; the whole process is protected by casting. The mold powder used is medium-carbon steel mold powder at 3.7 kg / t; soft reduction is applied to the 2nd, 3rd, and 4th rolls, and the reduction amounts are 3 mm, 4.1 mm, and 4.1 mm respectively; the slab cutting adopts a combination of automatic and manual methods. The hot billet of the continuous casting billet is used as the bottom layer, and the upper layer presses two furnace billets to ensure flatness, and the heat preservation time is 35 h.

[0036] (5) Heating process

[0037] Heating process: The temperature entering the heating furnace is 395°C, the temperature requirement for the preheating section is 550°C, and the time is 1.3 h; the temperature requirement for the 2nd heating section is 860°C, and the time is 2.3 h; the temperature requirement for the 1st heating section is 1210°C, and the time is 2.3 h; the temperature requirement for the soaking section is 1205°C, and the time is 1.3 h; the tapping temperature is 1195°C.

[0038] (6) Rolling process

[0039] Primary rolling and blooming: The 1150 mm BD primary rolling mill is used for blooming, with 7 rolling passes. The rolling reduction: turning over the steel → the reduction amount of the 1st pass is 70 mm → the reduction amount of the 2nd pass is 80.1 mm → turning over the steel → the 3rd pass is 74.1 mm → the 4th pass is 81.1 mm → turning over the steel → the 5th pass is 92.1 mm → the 6th pass is 30 mm → turning over the steel → the 7th pass is 38.1 mm. After passing through 3 sets of 850 mm rolling mills, it then enters the 9-stand continuous rolling mill for rolling.

[0040] Continuous rolling process: The first pass has a height of 229.01 mm, a width of 245 mm, and a rolling speed of 0.272 m / s; the second pass has a height of 192 mm, a width of 235 mm, and a rolling speed of 0.312 m / s; the third pass has a height of 200 mm, a width of 195.01 mm, and a rolling speed of 0.312 m / s; the fourth pass has a height of 169 mm, a width of 212.8 mm, and a rolling speed of 0.358 m / s; the fifth pass has a height of 177.01 mm, a width of 180 mm, and a rolling speed of 0.447 m / s; the sixth pass has a height of 141.01 mm, a width of 192 mm, and a rolling speed of 0.528 m / s; the seventh pass has a height of 152 mm, a width of 152.01 mm, and a rolling speed of 0.616 m / s; the eighth pass has a height of 152 mm, a width of 152.01 mm, and a rolling speed of 0.616 m / s. The finished product is obtained after 8 passes.

[0041] (7) Heat preservation process

[0042] Heat preservation process: The steel is heat-preserved, with the entry pit temperature of 590 °C, the exit pit temperature of 150 °C, and the heat preservation time of 55 h.

[0043] (8) Heat treatment process

[0044] The heat-preserved steel is heat-treated, and the heat treatment includes the following steps:

[0045] 1) Quenching: 850 °C, heat preservation for 1.0 h, oil cooling;

[0046] 2) Tempering: 560 °C, heat preservation for 2.0 h, water cooling.

[0047] Example 2

[0048] 1 Chemical composition of steel bars for automotive drive shafts

[0049] By mass percentage: C: 0.36%, Si: 0.28%, Mn: 0.55%, P: 0.010%, S: 0.003%, Cr: 0.92%, Mo: 0.19%, V: 0.15%, Cu: 0.05%, Ni: 0.06%, and the balance is iron and unavoidable impurities.

[0050] 2 Design of production process parameters for converter continuous casting of steel bars for automotive drive shafts

[0051] Process route: Converter smelting → Secondary refining (LF + RH) → Continuous casting → Heating in heating furnace → Rolling → Heat preservation → Heat treatment. Among them:

[0052] (1) Converter steelmaking: The mass fraction of scrap steel is 22% and that of hot metal is 78%; oxidized by oxygen, with intense boiling, tapping temperature of 1681°C, oxygen supply time of 14 min, final oxygen content of 465 ppm, operation time of 52 min, C content of 0.14% and P content of 0.008% at tapping, and additives and alloys are added at 1 / 4 of tapping. Alloy addition per ton of steel: 8.2 Kg / t of silicomanganese, 13.7 Kg / t of high-carbon ferrochrome, 2.7 Kg / t of ferromolybdenum, and 0.82 Kg / t of aluminum pellets. Additive addition per ton of steel: 11.2 Kg / t of dolomite, 28 Kg / t of active lime, and 2.3 Kg / t of steam coal.

[0053] (2) LF furnace refining: Use a large current of 23000 A to heat up and melt the slag. When the slag surface fluctuates and the molten steel and electric arc are not exposed, add active lime. Take the first sample for chemical composition analysis after 5 min, and add alloys according to the target values of chemical composition. The alloys should be added onto the argon flow to promote rapid melting and homogenization of the alloys. The clear height of the furnace body is 445 mm, the slag thickness is 75 mm, argon blowing time is 60 min, operation time is 88 min. When the molten steel temperature reaches 1557°C, add 1 kg / t of diffusion deoxidizer (aluminum pellets) for diffusion deoxidation, close the furnace door for 10 min. When the molten steel temperature reaches 1585°C, take the second sample 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 away, add 0.59 kg / t of diffusion deoxidizer (aluminum pellets) to continue adjusting the slag. Alloy addition per ton of steel for supplementary addition: 2.1 kg / t of high-carbon ferrochrome, 1.1 kg / t of ferrosilicon, and 3.6 kg / t of ferrovanadium (FeV50-B). Keep the basicity pH value of the molten slag at 2.6 and the viscosity of the molten slag at 0.97 Pa·s, and continue to maintain white slag melting for 25 min. Additive addition per ton of steel for supplementary addition: 6.7 kg / t of active lime.

[0054] (3) RH refining: Temperature before treatment is 1604°C. Control the argon pressure at 0.1 MPa before starting the vacuum pump, with the slag surface slightly moving and the molten steel not exposed. Start timing when the vacuum degree reaches 94 Pa, keep the time for 12 min, the lowest vacuum degree is 58 Pa, the clear height is 578 mm, the slag thickness is 90 mm, operation time is 30 min, circulation time is 15 min. At the same time, adjust the argon pressure to 0.4 MPa. After the static argon blowing ends, add 1.0 m / t of calcium silicate wire (10 mm).

[0055] (4)Continuous casting: The tundish temperature is 1538 °C, the casting speed is 0.49 m / min, the H content in the tundish is controlled at 1.5 ppm, the mold electromagnetic stirring current is 430 A, the final electromagnetic stirring current is 335 A, and the frequency is 8.1 Hz; the whole process is protected by casting, and the mold powder used is medium carbon steel mold powder at 3.6 kg / t; soft reduction is applied to the 2nd, 3rd, and 4th rolls, and the reduction amounts are 3 mm, 4 mm, and 4.1 mm respectively; the billet cutting adopts a combination of automatic and manual methods, the red-hot continuous casting billet is used as the bottom layer, and the billets of the upper two furnaces are pressed to ensure flatness, and the heat preservation time is 35 h.

[0056] (5)Heating process

[0057] Heating process: The temperature entering the heating furnace is 390 °C, the temperature requirement for the preheating section is 480 °C, and the time is 1.4 h; the temperature requirement for the second heating section is 865 °C, and the time is 2.4 h; the temperature requirement for the first heating section is 1198 °C, and the time is 2.3 h; the temperature requirement for the soaking section is 1198 °C, and the time is 1.3 h; the tapping temperature is 1190 °C.

[0058] (6)Rolling process

[0059] Blooming: The 1150 mm BD blooming mill is used for blooming, with 7 rolling passes. The rolling reduction: turning over the steel → the reduction amount of the first pass is 70 mm → the reduction amount of the second pass is 80.1 mm → turning over the steel → the third pass is 74 mm → the fourth pass is 81 mm → turning over the steel → the fifth pass is 92.1 mm → the sixth pass is 30 mm → turning over the steel → the seventh pass is 38.1 mm. After passing through 3 sets of 850 mm rolling mills, it then enters the 9-stand continuous rolling mill for rolling.

[0060] Continuous rolling process: The height of the first pass is 229 mm, the width is 245.01 mm, and the rolling speed is 0.272 m / s; the height of the second pass is 192 mm, the width is 235.01 mm, and the rolling speed is 0.312 m / s; the height of the third pass is 200 mm, the width is 195 mm, and the rolling speed is 0.312 m / s; the height of the fourth pass is 169.01 mm, the width is 212.81 mm, and the rolling speed is 0.358 m / s; the height of the fifth pass is 177.01 mm, the width is 180 mm, and the rolling speed is 0.447 m / s; the height of the sixth pass is 141.01 mm, the width is 192.01 mm, and the rolling speed is 0.528 m / s; the height of the seventh pass is 152 mm, the width is 152.01 mm, and the rolling speed is 0.616 m / s; the height of the eighth pass is 152 mm, the width is 152.01 mm, and the rolling speed is 0.614 m / s; finished products are obtained after 8 passes.

[0061] (7)Heat preservation process

[0062] Heat preservation process: The steel is heat-preserved, the temperature entering the pit is 580 °C, the temperature leaving the pit is 150 °C, and the heat preservation time is 55 h.

[0063] (8) Heat treatment process

[0064] The steel after heat preservation is subjected to heat treatment, and the heat treatment includes the following steps:

[0065] 1) Quenching: at 850 °C, heat preservation for 1.0 h, oil cooling;

[0066] 2) Tempering: at 550 °C, heat preservation for 2.0 h, water cooling.

[0067] Example 3

[0068] 1 Chemical composition of steel bars for automotive drive shafts

[0069] By mass percentage: C: 0.35%, Si: 0.26%, Mn: 0.54%, P: 0.010%, S: 0.003%, Cr: 0.92%, Mo: 0.19%, V: 0.14%, Cu: 0.06%, Ni: 0.06%, and the balance is iron and inevitable impurities.

[0070] 2 Design of production process parameters for converter continuous casting of steel bars for automotive drive shafts

[0071] Process route: converter smelting → secondary refining (LF + RH) → continuous casting → heating in heating furnace → rolling → heat preservation → heat treatment. Among them:

[0072] (1) Converter smelting: the mass fraction of scrap steel is 22%, and that of hot metal is 78%; oxygen oxidation, intense boiling, tapping temperature 1680 °C, oxygen supply time 13 min, end point oxygen 465 ppm, operation time 49 min, C is 0.14% and P is 0.009% at tapping, and auxiliary materials and alloys are added when 1 / 4 of the steel is tapped. Alloy addition per ton of steel: silicomanganese 8.2 Kg / t, high-carbon ferrochrome 13.8 Kg / t, ferromolybdenum 2.7 Kg / t, aluminum pellets 0.81 Kg / t. Auxiliary material addition per ton of steel: dolomite 11.3 Kg / t, active lime 29 Kg / t, pulverized coal 2.3 Kg / t.

[0073] (2) LF furnace refining: Use a large current of 23,500 A to heat up and melt the slag. When the slag surface fluctuates and the molten steel and electric arc are not exposed, add reactive lime. Take the first sample for chemical composition analysis after 5 minutes, and add alloys according to the target values of chemical composition. The alloys should be added onto the argon flow to promote rapid melting and homogenization of the alloys. The furnace free space is 445 mm, the slag thickness is 75 mm, the argon blowing time is 59 minutes, and the operation time is 87 minutes. When the molten steel temperature reaches 1557 °C, add 1.2 kg / t of diffusion deoxidizer (aluminum pellets) for diffusion deoxidation, close the furnace door for 10 minutes. When the molten steel temperature reaches 1586 °C, take the second sample for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value requirements. After taking the second sample, add 0.59 kg / t of diffusion deoxidizer (aluminum pellets) to continue adjusting the slag. The addition amount of alloys per ton of steel: high-carbon ferrochrome 2.0 kg / t, ferrosilicon 1.1 kg / t, ferrovanadium (FeV50-B) 3.6 kg / t. Keep the basicity pH value of the molten slag at 2.7 and the viscosity of the molten slag at 1.02 Pa·s, and at the same time continue to maintain white slag smelting for 25 minutes. The addition amount of auxiliary materials per ton of steel: reactive lime 6.7 kg / t.

[0074] (3) RH refining: The temperature before treatment is 1606 °C. Control the argon pressure at 0.1 MPa before starting the vacuum pump, with the slag surface slightly moving and the molten steel not exposed. Start timing when the vacuum degree reaches 95 Pa, keep the time for 13 minutes, the lowest vacuum degree is 59 Pa, the free space is 580 mm, the slag thickness is 88 mm, the operation time is 30 minutes, the circulation time is 15 minutes. At the same time, adjust the argon pressure to 0.4 MPa. After the static argon blowing ends, add 1.0 m / t of calcium silicate wire (10 mm).

[0075] (4) Continuous casting: The tundish temperature is 1537 °C, the casting speed is 0.49 m / min, the H control in the tundish is 1.5 ppm, the electromagnetic stirring current in the mold is 425 A, the electromagnetic stirring current at the end is 334 A, and the frequency is 8 Hz; Protect the casting throughout the process. Use 3.7 kg / t of medium-carbon steel mold powder for the mold powder; Light reduction is applied to the 2nd, 3rd, and 4th rolls, and the reduction amounts are 3 mm, 4 mm, and 4 mm respectively; The billet cutting adopts a combination of automatic and manual methods. The hot billet of the continuous casting billet is used as the bottom layer, and the billets of the upper two furnaces are pressed to ensure flatness, and the heat preservation time is 35 h.

[0076] (5) Heating process

[0077] Heating process: The temperature entering the heating furnace is 385 °C, the temperature requirement in the preheating section is 496 °C, and the time is 1.4 h; The temperature requirement in the second heating section is 874 °C, and the time is 2.4 h; The temperature requirement in the first heating section is 1210 °C, and the time is 2.4 h; The temperature requirement in the soaking section is 1202 °C, and the time is 1.3 h; The tapping temperature is 1195 °C.

[0078] (6) Rolling process

[0079] Blooming: The billets are produced by a 1150mm BD blooming mill, with 7 passes of rolling. The reduction per pass is as follows: steel turning → 70mm reduction in the first pass → 80.1mm reduction in the second pass → steel turning → 74.1mm in the third pass → 81.1mm in the fourth pass → steel turning → 92mm in the fifth pass → 30.1mm in the sixth pass → steel turning → 38mm in the seventh pass. Then it passes through 3 850mm rolling mills and enters a 9-stand continuous rolling mill for rolling.

[0080] Continuous rolling process: In the first pass, the height is 229mm, the width is 245.01mm, and the rolling speed is 0.27m / s; in the second pass, the height is 192.01mm, the width is 235mm, and the rolling speed is 0.312m / s; in the third pass, the height is 200mm, the width is 195mm, and the rolling speed is 0.312m / s; in the fourth pass, the height is 169mm, the width is 212.81mm, and the rolling speed is 0.356m / s; in the fifth pass, the height is 177.01mm, the width is 180mm, and the rolling speed is 0.447m / s; in the sixth pass, the height is 141.01mm, the width is 192mm, and the rolling speed is 0.528m / s; in the seventh pass, the height is 152mm, the width is 152.01mm, and the rolling speed is 0.616m / s; in the eighth pass, the height is 152mm, the width is 152.01mm, and the rolling speed is 0.616m / s. The finished product is obtained after 8 passes.

[0081] (7) Heat preservation process

[0082] Heat preservation process: The steel is heat-preserved. The temperature when entering the pit is 580°C, the temperature when leaving the pit is 150°C, and the heat preservation time is 54h.

[0083] (8) Heat treatment process

[0084] The heat-preserved steel is subjected to heat treatment, and the heat treatment includes the following steps:

[0085] 1) Quenching: At 850°C, heat preservation for 1.0h, oil cooling;

[0086] 2) Tempering: At 560°C, heat preservation for 2.0h, water cooling.

[0087] Example 4

[0088] 1 Chemical composition of steel bars for automotive drive shafts

[0089] By mass percentage: C: 0.36%, Si: 0.29%, Mn: 0.54%, P: 0.010%, S: 0.003%, Cr: 0.92%, Mo: 0.18%, V: 0.16%, Cu: 0.06%, Ni: 0.05%, and the balance is iron and unavoidable impurities.

[0090] 2 Design of production process parameters for converter continuous casting of steel bars for automotive drive shafts

[0091] Process route: Converter smelting → Secondary refining (LF + RH) → Continuous casting → Heating in heating furnace → Rolling → Heat preservation → Heat treatment. Among them:

[0092] (1) Converter smelting: The mass fraction of scrap steel is 24%, and that of hot metal is 76%; Oxidized by oxygen, with intense boiling, tapping temperature of 1678 °C, oxygen supply time of 14 min, end-point oxygen of 464 ppm, operation time of 51 min, C of 0.14% and P of 0.008% at tapping, and additives and alloys are added at 1 / 4 of tapping. Alloy addition per ton of steel: 8.2 Kg / t of silicomanganese, 13.8 Kg / t of high-carbon ferrochrome, 2.7 Kg / t of ferromolybdenum, and 0.82 Kg / t of aluminum pellets. Additive addition per ton of steel: 11.3 Kg / t of dolomite, 28 Kg / t of active lime, and 2.3 Kg / t of steam coal.

[0093] (2) LF furnace refining: Use a large current of 23600 A to raise the temperature and melt the slag. When the slag surface fluctuates and the molten steel and electric arc are not exposed, add active lime. Take the first sample for chemical composition analysis after 5 min, and add alloys according to the target values of chemical composition. The alloys should be added onto the argon flow to promote the rapid melting and homogenization of the alloys. The clear height of the furnace body is 447 mm, the slag thickness is 74 mm, argon blowing time is 61 min, operation time is 87 min. When the molten steel temperature reaches 1557 °C, add 1 kg / t of diffusion deoxidizer (aluminum pellets) for diffusion deoxidation, close the furnace door for 10 min. When the molten steel temperature reaches 1587 °C, take the second sample for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value requirements. After the second sample is taken away, add 0.59 kg / t of diffusion deoxidizer (aluminum pellets) to continue adjusting the slag. Alloy addition per ton of steel for supplementary addition: 2.1 kg / t of high-carbon ferrochrome, 1.1 kg / t of ferrosilicon, and 3.6 kg / t of ferrovanadium (FeV50 - B). Keep the basicity pH value of the molten slag at 2.8 and the viscosity of the molten slag at 0.99 Pa·s, and at the same time continue to maintain white slag smelting for 25 min. Additive addition per ton of steel for supplementary addition: 6.7 kg / t of active lime.

[0094] (3) RH refining: Temperature before treatment is 1604 °C. Before starting the vacuum pump, control the argon pressure at 0.1 MPa, with the slag surface slightly moving and the molten steel not exposed. Start timing when the vacuum degree reaches 95 Pa, keep the time for 12 min, the lowest vacuum degree is 61 Pa, the clear height is 580 mm, the slag thickness is 90 mm, operation time is 30 min, circulation time is 14 min. At the same time, adjust the argon pressure to 0.4 MPa. After the static argon blowing ends, add 1.0 m / t of calcium silicate wire (10 mm).

[0095] (4)Continuous casting: The tundish temperature is 1537°C, the casting speed is 0.49 m / min, the H control in the tundish is 1.5 ppm, the mold electromagnetic stirring current is 425 A, the final electromagnetic stirring current is 334 A, and the frequency is 8 Hz; the whole process is protected by casting, and the mold powder used is medium carbon steel mold powder at 3.7 kg / t; soft reduction is applied to the 2nd, 3rd, and 4th rolls, and the reduction amounts are 3 mm, 4 mm, and 4 mm respectively; the billet cutting adopts a combination of automatic and manual methods, the continuous casting billet with red hot steel is used as the bottom layer, and the billets of the upper two furnaces are pressed to ensure flatness, and the heat preservation time is 35 h.

[0096] (5)Heating process

[0097] Heating process: The temperature entering the heating furnace is 395°C, the temperature requirement for the preheating section is 485°C, and the time is 1.4 h; the temperature requirement for the 2nd heating section is 860°C, and the time is 2.3 h; the temperature requirement for the 1st heating section is 1212°C, and the time is 2.4 h; the temperature requirement for the soaking section is 1205°C, and the time is 1.3 h; the tapping temperature is 1194°C.

[0098] (6)Rolling process

[0099] Blooming: The 1150 mm BD blooming mill is used for blooming, with 7 rolling passes. The rolling reduction amounts are: turning over → the reduction amount of the 1st pass is 70 mm → the reduction amount of the 2nd pass is 80.1 mm → turning over → the 3rd pass is 74 mm → the 4th pass is 81.1 mm → turning over → the 5th pass is 92 mm → the 6th pass is 30.1 mm → turning over → the 7th pass is 38 mm. After passing through 3 sets of 850 mm rolling mills, it then enters the 9-stand continuous rolling mill for rolling.

[0100] Continuous rolling process: The height of the 1st pass is 229 mm, the width is 245.01 mm, and the rolling speed is 0.272 m / s; the height of the 2nd pass is 192 mm, the width is 235 mm, and the rolling speed is 0.312 m / s; the height of the 3rd pass is 200.01 mm, the width is 195 mm, and the rolling speed is 0.312 m / s; the height of the 4th pass is 169.01 mm, the width is 212.81 mm, and the rolling speed is 0.358 m / s; the height of the 5th pass is 177.01 mm, the width is 180 mm, and the rolling speed is 0.447 m / s; the height of the 6th pass is 141 mm, the width is 192.01 mm, and the rolling speed is 0.528 m / s; the height of the 7th pass is 152 mm, the width is 152.01 mm, and the rolling speed is 0.616 m / s; the height of the 8th pass is 152 mm, the width is 152.01 mm, and the rolling speed is 0.614 m / s; finished products are obtained after 8 passes.

[0101] (7)Heat preservation process

[0102] Heat preservation process: The steel is heat-preserved, the temperature when entering the pit is 580°C, the temperature when leaving the pit is 160°C, and the heat preservation time is 55 h.

[0103] (8)Heat treatment process

[0104] The heat-treated steel after heat preservation, and the heat treatment includes the following steps:

[0105] 1) Quenching: at 850 °C, hold for 1.0 h, and cool in oil;

[0106] 2) Tempering: at 560 °C, hold for 2.0 h, and cool in water.

[0107] Example 5

[0108] 1 Chemical composition of steel bars for automotive drive shafts

[0109] By mass percentage: C: 0.35%, Si: 0.27%, Mn: 0.53%, P: 0.011%, S: 0.003%, Cr: 0.89%, Mo: 0.19%, V: 0.15%, Cu: 0.05%, Ni: 0.05%, and the balance is iron and inevitable impurities.

[0110] 2 Design of production process parameters for converter continuous casting of steel bars for automotive drive shafts

[0111] Process route: converter smelting → secondary refining (LF + RH) → continuous casting → heating in heating furnace → rolling → heat preservation → heat treatment. Among them:

[0112] (1) Converter smelting: the mass fraction of scrap steel is 23%, and that of hot metal is 77%; oxidized by oxygen, with intense boiling, tapping temperature of 1682 °C, oxygen supply time of 13 min, final oxygen content of 465 ppm, operation time of 50 min, C content of 0.14% and P content of 0.008% at tapping, and slag materials and alloys are added when 1 / 4 of the steel is tapped. Alloy addition amount per ton of steel: silicomanganese 8.2 Kg / t, high-carbon ferrochrome 13.7 Kg / t, ferromolybdenum 2.7 Kg / t, aluminum pellets 0.82 Kg / t. Auxiliary material addition amount per ton of steel: dolomite 11.2 Kg / t, active lime 28 Kg / t, and steam coal 2.2 Kg / t.

[0113] (2) LF furnace refining: Use a large current of 23,000 A to heat up and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, add reactive lime. Take the first sample for chemical composition analysis after 5 minutes, and add alloys according to the target values of chemical composition. The alloys should be added onto the argon flow to promote rapid melting and homogenization of the alloys. The furnace body clearance is 446 mm, the slag thickness is 75 mm, the argon blowing time is 58 minutes, and the operation time is 88 minutes. When the molten steel temperature reaches 1556 °C, add 1 kg / t of diffusion deoxidizer (aluminum pellets) for diffusion deoxidation, close the furnace door for 10 minutes. When the molten steel temperature reaches 1585 °C, take the second sample for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value requirements. After taking the second sample, add 0.59 kg / t of diffusion deoxidizer (aluminum pellets) to continue adjusting the slag. The addition amount of alloys per ton of steel: 2.1 kg / t of high-carbon ferrochrome, 1.0 kg / t of ferrosilicon, 3.6 kg / t of ferrovanadium (FeV50-B). Keep the basicity pH value of the molten slag at 2.8 and the viscosity of the molten slag at 1.02 Pa·s, and at the same time continue to maintain white slag smelting for 27 minutes. The addition amount of auxiliary materials per ton of steel: 6.8 kg / t of reactive lime.

[0114] (3) RH refining: The temperature before treatment is 1605 °C. Control the argon pressure at 0.1 MPa before starting the vacuum pump, with the slag surface slightly moving and the molten steel not exposed. Start timing when the vacuum degree reaches 96 Pa, keep the time for 11 minutes, the minimum vacuum degree is 58 Pa, the clearance is 582 mm, the slag thickness is 89 mm, the operation time is 29 minutes, and the cycle time is 13 minutes. At the same time, adjust the argon pressure to 0.4 MPa. After the static argon blowing ends, add 1.0 m / t of calcium silicate wire (10 mm).

[0115] (4) Continuous casting: The tundish temperature is 1538 °C, the casting speed is 0.49 m / min, the H control in the tundish is 1.4 ppm, the electromagnetic stirring current in the mold is 435 A, the electromagnetic stirring current at the end is 336 A, and the frequency is 8 Hz; carry out protective casting throughout the process, and use 3.6 kg / t of medium-carbon steel mold powder for the mold powder; light reduction is applied to the 2nd, 3rd, and 4th rolls, and the reduction amounts are 3 mm, 4 mm, and 4 mm respectively; the billet cutting adopts a combination of automatic and manual methods, the hot billet of the continuous casting billet is used as the bottom layer, and the billets of the upper two furnaces are pressed to ensure flatness, and the heat preservation time is 34 h.

[0116] (5) Heating process

[0117] Heating process: The temperature entering the heating furnace is 400 °C, the temperature requirement for the preheating section is 485 °C, and the time is 1.4 h; the temperature requirement for the second heating section is 860 °C, and the time is 2.3 h; the temperature requirement for the first heating section is 1212 °C, and the time is 2.3 h; the temperature requirement for the soaking section is 1205 °C, and the time is 1.4 h; the tapping temperature is 1197 °C.

[0118] (6) Rolling process

[0119] Blooming: The 1150mm BD blooming mill is used for blooming, with 7 rolling passes. The rolling reduction: steel turning → reduction in the 1st pass: 70mm → reduction in the 2nd pass: 80mm → steel turning → reduction in the 3rd pass: 74.1mm → reduction in the 4th pass: 81.1mm → steel turning → reduction in the 5th pass: 92.1mm → reduction in the 6th pass: 30.1mm → steel turning → reduction in the 7th pass: 38mm. After passing through 3 sets of 850mm rolling mills, it then enters the 9-stand continuous rolling mill for rolling.

[0120] Continuous rolling process: In the 1st pass, the height is 229mm, the width is 245mm, and the rolling speed is 0.272m / s; in the 2nd pass, the height is 192mm, the width is 235.01mm, and the rolling speed is 0.312m / s; in the 3rd pass, the height is 200mm, the width is 195mm, and the rolling speed is 0.312m / s; in the 4th pass, the height is 169mm, the width is 212.81mm, and the rolling speed is 0.358m / s; in the 5th pass, the height is 177.01mm, the width is 180.01mm, and the rolling speed is 0.445m / s; in the 6th pass, the height is 141.01mm, the width is 192.01mm, and the rolling speed is 0.526m / s; in the 7th pass, the height is 152mm, the width is 152.01mm, and the rolling speed is 0.614m / s; in the 8th pass, the height is 152.01mm, the width is 152mm, and the rolling speed is 0.616m / s. The finished product is obtained after 8 passes.

[0121] (7) Heat preservation process

[0122] Heat preservation process: The steel is heat-preserved. The temperature when entering the pit is 580°C, the temperature when leaving the pit is 145°C, and the heat preservation time is 56h.

[0123] (8) Heat treatment process

[0124] The heat-preserved steel is subjected to heat treatment, and the heat treatment includes the following steps:

[0125] 1) Quenching: 850°C, heat preservation for 1.0h, oil cooling;

[0126] 2) Tempering: 560°C, heat preservation for 2.0h, water cooling.

[0127] Inspection results of the finished products in Examples 1 - 5

[0128] (1) Macrostructure of Φ150mm steel bars (finished steel bars obtained by the heat preservation process)

[0129] Serial number General porosity Center porosity Ingot shape segregation General mottled segregation Edge mottled segregation Standard ≤2.0 ≤2.0 ≤2.0 ≤1.0 ≤1.0 Example 1 0.5 0.5 0.5 0 0 Example 1 0.5 0.5 0.5 0 0 Example 2 0.5 0.5 0.5 0 0 Example 2 0.5 0.5 0.5 0 0 Example 3 0.5 0.5 0.5 0 0 Example 3 0.5 0.5 0.5 0 0 Example 4 0.5 0.5 0.5 0 0 Example 4 0.5 0.5 0.5 0 0 Example 5 0.5 0.5 0.5 0 0 Example 5 0.5 0.5 0.5 0 0

[0130] (2) Non-metallic inclusions in Φ150mm steel bars (finished steel bars obtained by the heat preservation process)

[0131]

[0132] (3) Mechanical properties of steel bars with a specification of Φ150mm (finished steel bars obtained after heat treatment)

[0133] Serial number Quenching / °C Soaking time Tempering / °C Soaking time Rm / MPa Rel / MPa A / ％ z / ％ KU2 / J Standard 850, oil cooling 0.8～1.2h 560, water cooling 1.8～2.2h ≥1080 ≥930 ≥12 ≥45 ≥63 Example 1 850, oil cooling 1h 560, water cooling 2h 1125 1050 17 65 82 Example 1 850, oil cooling 1h 560, water cooling 2h 1130 1048 18 64 80 Example 2 850, oil cooling 1h 560, water cooling 2h 1108 1045 16 62 79 Example 2 850, oil cooling 1h 560, water cooling 2h 1123 1030 18 66 80 Example 3 850, oil cooling 1h 560, water cooling 2h 1138 1036 16 60 81 Example 3 850, oil cooling 1h 560, water cooling 2h 1142 1025 16 64 78 Example 4 850, oil cooling 1h 560, water cooling 2h 1136 1030 17 62 79 Example 4 850, oil cooling 1h 560, water cooling 2h 1129 1020 18 63 81 Example 5 850, oil cooling 1h 560, water cooling 2h 1130 1015 19 65 76 Example 5 850, oil cooling 1h 560, water cooling 2h 1131 1035 17 63 80

[0134] For any person skilled in the art, without departing from the scope of the technical solution of the present invention, many possible changes and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or it can be modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A steel bar for automobile transmission shaft, characterized in that: Its chemical composition, by mass percentage, is C: 0.33% ~ 0.38%, Si: 0.22% ~ 0.35%, Mn: 0.40% ~ 0.70%, P: ≤ 0.012%, S: ≤ 0.004%, Cr: 0.85% ~ 1.00%, Mo: 0.16% ~ 0.23%, V: 0.10% ~ 0.20%, Cu: ≤ 0.15%, Ni: ≤ 0.25%, and the balance is iron and unavoidable impurities.

2. The method for preparing a steel bar for an automobile transmission shaft according to claim 1, characterized in that: The process includes the following steps: ecological electric furnace → LF refining → RH refining → continuous casting → heating process → rolling process → insulation process; The converter smelting is as follows: by mass fraction, scrap steel accounts for 20-25%, molten iron accounts for 75-80%; oxygen oxidation, intense boiling, tapping temperature 1675-1685°C, oxygen supply time 13-14min, end oxygen 460-470ppm, operation time 45-55min, C at tapping time 0.13-0.15%, P≤0.010%, auxiliary materials and alloys are added when 1 / 4-1 / 3 of the steel is tapped; alloy addition per ton of steel: silicon manganese 8.1-8.2kg / t, high carbon ferrochrome 13.5-14.0kg / t, ferromolybdenum 2.6-2.8kg / t, aluminum particles 0.8-0.85kg / t; auxiliary materials added per ton of steel: dolomite 11-11.5kg / t, active lime 28-29kg / t, thermal coal 2.2-2.3kg / t; The LF refining comprises: using a large current of 20000-25000A to heat and melt the slag, adding active lime when the slag surface fluctuates and the molten steel and the arc are not exposed, taking a sample for the first time to analyze the chemical composition after 5-10 minutes, and adding alloy according to the target value of the chemical composition; the furnace body clearance is 440-450mm, the slag thickness is 70-80mm, argon is blown for 55-65min, the operation time is 85-90min, when the temperature of the molten steel reaches 1550-1560℃, 1-3kg / t steel of diffusion deoxidizer is added for diffusion deoxidation, the furnace door is closed for 10-12min, and when the temperature of the molten steel reaches 1580-1590℃, the molten steel is heated to 1500-1560℃, and the molten steel is heated to 1500-1590℃. At the temperature, take a second sample to analyze the chemical composition to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, add 0.58-0.59 kg / t of diffusion deoxidizer to continue slag adjustment; add alloy to each ton of steel: high carbon ferrochrome 2.0-2.1 kg / t, ferrosilicon 1.0-1.1 kg / t, ferrovanadium 3.5-3.6 kg / t; keep the slag alkalinity pH value at 2.2-3.2, the slag viscosity at 0.95-1.10 Pa.s, and continue to smelt the white slag for 20-30 minutes; add auxiliary materials to each ton of steel: active lime 6.5-7 kg / t; The RH refining is as follows: the temperature before treatment is 1600-1610°C, the argon pressure is controlled at 0.1-0.3MPa before the vacuum pump is started, the molten steel is not exposed when the slag surface is slightly moved, the timing starts when the vacuum degree reaches 90-100Pa, the holding time is 10-15min, the minimum vacuum degree is 55-65Pa, the clearance is 570-590mm, the slag thickness is 85-95mm, the operation time is 28-32min, the cycle time is 12-17min, and the argon pressure is adjusted to 0.3-0.5MPa at the same time. After the static argon blowing is completed, 1.0-1.2m / t of calcium silicon wire is added; The continuous casting is as follows: the tundish temperature is 1535-1540°C, the pulling speed is 0.48-0.50 m / min, the H of the tundish is controlled to be ≤1.8 ppm, the electromagnetic stirring current of the crystallizer is 400-450A, the electromagnetic stirring current of the terminal is 330-340A, and the frequency is 8-8.2 Hz; the second, third and fourth rollers are put into the casting under light pressure, and the pressure reduction amounts are 3-3.1 mm, 4-4.1 mm and 4-4.1 mm respectively; the casting is cut, the continuous casting is made of red steel, the castings of the two furnaces are pressed to ensure the straightness, and the insulation time is 30-40 hours; The heating process is as follows: the temperature entering the heating furnace is 360°C~420°C, the temperature of the preheating section is required to be 450°C~610°C, and the time is 1.3~1.4h; the temperature of the heating section 2 is required to be 850°C~880°C, and the time is 2.3~2.4h; the temperature of the heating section 1 is required to be 1190°C~1220°C, and the time is 2.3~2.4h; the temperature of the soaking section is required to be 1190°C~1210°C, and the time is 1.3~1.4h; and the steel tapping temperature is 1180°C~1210°C.

3. The preparation method according to claim 2, characterized in that: In the LF refining step, the alloy is fed onto an argon flow.

4. The preparation method according to claim 2, characterized in that: In the continuous casting step, the casting is protected throughout the whole process, and the mold protection slag uses medium carbon steel protection slag, and the amount of medium carbon steel protection slag is 3.6-3.7kg / t steel; the ingot cutting adopts a combination of automatic and manual methods.

5. The preparation method according to claim 2, characterized in that: The ferrovanadium is FeV50-B, the diffusion deoxidizer is aluminum particles, and the diameter of the calcium silicon wire is 10-12 mm.

6. The preparation method according to claim 2, characterized in that: The continuous rolling process of the rolling process is as follows: 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 0.31-0.312 m / s; the fourth pass is 169-169.01 mm high, 212.8-212.81 mm wide, and the rolling speed is 0.356-0.358 m / s. / s; the 5th pass is 177~177.01mm high, 180~180.01mm wide, and the rolling speed is 0.445~0.447m / s; the 6th pass is 141~141.01mm high, 192~192.01mm wide, and the rolling speed is 0.526~0.528m / s; the 7th pass is 152~152.01mm high, 152~152.01mm wide, and the rolling speed is 0.614~0.616m / s; the 8th pass is 152~152.01mm high, 152~152.01mm wide, and the rolling speed is 0.614~0.616m / s; the finished product is produced after 8 passes.

7. The preparation method according to claim 2, characterized in that: The insulation process is: steel insulation, pit entry temperature ≥ 560°C, pit exit temperature ≤ 200°C, and insulation time ≥ 52h.

8. The preparation method according to claim 2, characterized in that: The steel after heat preservation is heat treated, and the heat treatment includes the following steps: 1) Quenching: 840-860°C, insulation 1.0-1.2h, oil cooling; 2) Tempering: 550-570℃, keep warm for 2.0-2.2h, water cooling.

Images