Method for producing and preparing high-temperature-resistant steel bar for automobile axle

Abstract

Disclosed in the present invention is a method for producing and preparing a high-temperature-resistant steel bar for an automobile axle. The steel bar comprises the following chemical components in percentages by mass: 0.39-0.42% of C, 0.22-0.30% of Si, 1.45-1.70% of Mn, less than or equal to 0.015% of P, less than or equal to 0.006% of S, less than or equal to 0.20% of Cr, less than or equal to 0.20% of Ni, less than or equal to 0.05% of Mo, less than or equal to 0.10% of Cu, and the balance of Fe and inevitable impurities. The method comprises: ecological electric furnace smelting → LF refining → RH refining → continuous casting → an annealing process → a heating process → a rolling process → a holding process. The present invention meets the quality requirements for the steel bar for the automobile axle. Moreover, indexes such as mechanical properties and high steel purity can also meet standard requirements.

Description

A method for producing high-temperature resistant steel bars for automotive axles Technical Field

[0001] This invention relates to the field of special steel, specifically to a method for producing high-temperature resistant steel bars for automotive axles. Background Technology

[0002] As a drive shaft, the automobile axle is a crucial component of a vehicle, transmitting power from one part to another and realizing different forms of energy conversion. The quality of the steel used in automobile axles is related to the safety of power transmission. Therefore, the requirements for the high temperature resistance, wear resistance, mechanical properties, fatigue life, and steel purity of the steel used in automobile axles are extremely high to ensure the normal and safe operation of the axle during force transmission.

[0003] Therefore, it is essential to develop steel bars for automotive axles with excellent mechanical properties and high steel purity to meet the requirements of high-end products. Summary of the Invention

[0004] The purpose of this invention is to provide a manufacturing process for high-temperature resistant steel bars for automotive axles. This method employs an eco-friendly electric furnace smelting process combined with LF refining, RH refining, and continuous casting, along with a rolling process, to produce steel bars for automotive axles. This process ensures both the mechanical properties and high purity of the finished steel bars, as well as the surface quality, meeting the requirements for high-end applications. It represents a breakthrough in the mass production of automotive axle steel bars using an eco-friendly electric furnace continuous casting process.

[0005] To achieve the aforementioned objectives, this invention provides a method for manufacturing high-temperature resistant steel bars for automotive axles, including composition and process design. The specific steps are: ecological electric furnace + LF refining + RH refining + continuous casting → annealing → heating → rolling. This method meets the quality requirements for automotive axle steel bars, and its mechanical properties and high steel purity also meet standard requirements.

[0006] A high-temperature resistant steel bar for automotive axles has the following chemical composition by mass percentage: C: 0.39%–0.42%, Si: 0.22%–0.30%, Mn: 1.45%–1.70%, P: ≤0.015%, S: ≤0.006%, Cr: ≤0.20%, Ni: ≤0.20%, Mo: ≤0.05%, Cu: ≤0.10%, with the balance being iron and unavoidable impurities.

[0007] The specification of the high-temperature resistant steel bar for automotive axles of this invention is Φ100mm.

[0008] The above-mentioned manufacturing process for steel bars used in automotive axle sleeves includes the following process route: ecological electric furnace smelting → LF refining → RH refining → continuous casting → annealing → heating furnace heating → rolling → heat preservation.

[0009] The eco-friendly electric furnace smelting process involves: using 100% scrap steel by mass fraction, including 80%–90% heavy scrap and 10%–20% alloy structural steel cut-offs; tapping temperature of 1640–1650℃; carbon content of 0.10–0.15% and phosphorus content of ≤0.010% at tapping; addition of auxiliary materials and alloys when 1 / 4–1 / 3 of the steel has been tapped; smelting cycle of 55–65 minutes; and furnace oxygen consumption of 21–22 m³ / min. 3 / t steel. Alloy addition per ton of steel: High-carbon ferromanganese 16.5~17.5Kg / t, ferroaluminum (Φ40-70mm) 1.9~2.1Kg / t. Auxiliary material addition per ton of steel: Graphite briquettes 7.8~8.2Kg / t, coke granules 35~36Kg / t, steel ladle ash 5.8~6.3Kg / t, active lime (Φ10-70mm) 40~41Kg / t, dolomite (Φ20-70mm) 29~31Kg / t.

[0010] The LF furnace refining process is as follows: the LF inlet temperature is 1540-1550℃, and the slag is heated by a high current of 35000-36000A. When the slag surface fluctuates and the molten steel and electric arc are not exposed, active lime is added. After 5-6 minutes, the first sample is taken to analyze the chemical composition. Alloy and silicon carbide are added according to the target chemical composition value, and coke particles are added to increase carbon content. Alloy, silicon carbide and coke particles should be added to the argon flow to promote the rapid melting and homogenization of alloy, silicon carbide and coke. When the molten steel temperature reaches 1600-1610℃, add 1.4-1.5 kg / t of diffusion deoxidizer (aluminum granules) for diffusion deoxidation. Close the furnace door for 10-13 minutes. When the molten steel temperature reaches 1630-1640℃, take a second sample to analyze the chemical composition to confirm the deviation of each chemical element content from the target value. After the second sample is taken, leave the furnace when the molten steel temperature reaches 1650-1660℃. The LF smelting cycle is 100-110 minutes. The amount of alloy added per ton of steel is: 2.3-2.4 kg / t ferrosilicon, 3.5-3.6 kg / t high-carbon ferromanganese, 1.4-1.5 kg / t alumina balls, and 0.4-0.6 kg / t aluminum wire (Φ10-14mm). Additional auxiliary materials per ton of steel: 4-4.2 kg / t of active lime (Φ10-70mm), 1.1-1.2 kg / t of silicon carbide (Φ2-5mm), and 0.5-0.6 kg / t of coke granules.

[0011] The RH refining process is as follows: the inlet temperature is 1630-1640℃, the operation time is 35-45 minutes, and before the vacuum pump is started, argon is statically blown to control the argon pressure at 0.1-0.3 MPa, so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum degree reaches 100-110 Pa, the timing starts and is maintained for 10-15 minutes. At the same time, the argon pressure is adjusted to 0.3-0.5 MPa. After the static argon blowing is completed, 0.5-0.6 kg / t of steel is added as a covering agent (carbonized rice husk). The outlet temperature is 1585-1595℃.

[0012] The continuous casting process is as follows: ladle arrival temperature 1580~1590℃, tundish H control ≤2ppm, casting time 35min~45min, superheat 25~30℃, casting speed 0.4~0.42m / min, full-process protective casting, and medium carbon steel protective slag used in the crystallizer.

[0013] The annealing process is as follows: annealing is carried out in an annealing furnace at a temperature of 580-620℃ for a time of more than 32 hours.

[0014] Furthermore, the heating process is as follows: the furnace inlet temperature is 500℃~540℃; the preheating section temperature is required to be 650℃~680℃ for 1.3~1.5h; the second heating section temperature is required to be 860℃~880℃ for 1.3~1.5h; the first heating section temperature is required to be 1210℃~1220℃ for 1.3~1.5h; the soaking section temperature is required to be 1200℃~1210℃ for 1.3~1.5h; and the tapping temperature is 1190℃~1198℃.

[0015] Furthermore, the rolling process includes a primary rolling process and a continuous rolling process for finished products, specifically:

[0016] Preliminary rolling process: 9 rolling passes; specifically: Turning steel → Pass 1: Width 408-408.01mm, Height 421-421.01mm, Reduction 65-65.01mm → Pass 2: Width 426-426.01mm, Height 351-351.01mm, Reduction 70-70.01mm → Turning steel → Pass 3: Width 370-370.01mm, Height 362-362.01mm, Reduction 64-64.01mm → Pass 4: Width 397-397.01mm, Height 272-272.01mm, Reduction 90-90.01mm → Turning steel → Pass 5: Width 285-285.01mm, Height 355-355.01mm mm, reduction 42~42.01mm → 6th pass width 297~297.01mm, height 315~315.01mm, reduction 40~40.01mm → 7th pass width 307~307.01mm, height 280~280.01mm, reduction 35~35.01mm → 8th pass width 317~317.01mm, height 246~246.01mm, reduction 34~34.01mm → turn over → 9th pass width 271~271.01mm, height 235~235.01mm, reduction 82~82.01mm, passing through 3 850mm rolling mills and 1 735mm rolling mill, then entering the continuous rolling mill group for rolling.

[0017] Continuous rolling process: 11 passes; specifically: Pass 1: Height 229–229.01 mm, width 245–245.01 mm; Pass 2: Height 192–192.01 mm, width 235–235.01 mm; Pass 3: Height 200–200.01 mm, width 195–195.01 mm; Pass 4: Height 160–160.01 mm, width 214.7–214.71 mm; Pass 5: Height 164–164.01 mm, width 174.6–174.61 mm; Pass 6: Height 121–121.0 mm. 1 mm high, 187.6–187.61 mm wide; 7th pass: 139–139.01 mm high, 138.5–138.51 mm wide; 8th pass: 106–106.01 mm high, 152–152.01 mm wide; 9th pass: 118–118.01 mm high, 121–121.01 mm wide; 10th pass: 91–91.01 mm high, 130.2–130.21 mm wide; 11th pass: 101.4–101.41 mm high, 101.4–101.41 mm wide; finished steel is produced after the 11th pass.

[0018] Furthermore, the insulation process is as follows: steel insulation, the temperature of the lower insulation pit is ≥560℃, the insulation time is 48~55h, and the temperature of the material leaving the pit is ≤120℃.

[0019] Furthermore, the process route includes heat preservation followed by finishing, inspection, packaging and warehousing, and then shipment.

[0020] Furthermore, the insulated steel undergoes heat treatment, which includes the following steps:

[0021] 1) Quenching: 830~850℃, hold for 0.8~1.2h, oil cooling;

[0022] 2) Tempering: 530~550℃, hold for 1.8~2.2h, then water-cooled.

[0023] The beneficial effects of this invention are:

[0024] (1) Steel bars for automobile axles are produced by ecological electric furnace smelting + LF refining + RH refining + continuous casting and rolling process to meet mechanical performance requirements and ensure steel purity.

[0025] (2) Reasonable composition design and production process ensure surface quality and mechanical properties.

[0026] (3) The low magnification structure and non-metallic inclusions of the finished steel meet the requirements of high-end products.

[0027] (4) The finished steel has good high temperature resistance (400-600℃). Detailed Implementation

[0028] The following non-limiting embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0029] Example 1

[0030] 1Chemical composition

[0031] The chemical composition by mass percentage is: C: 0.40%, Si: 0.26%, Mn: 1.55%, P: 0.010%, S: 0.005%, Cr: 0.08%, Ni: 0.05%, Mo: 0.02%, Cu: 0.01%, with the balance being iron and unavoidable impurities.

[0032] 2. Production processes of electric furnace continuous casting for steel bars used in automobile axles

[0033] Process route: Eco-friendly electric furnace + LF refining + RH refining + continuous casting billet → annealing → heating furnace → rolling → holding → finishing → inspection → packaging and warehousing → shipment. Among them:

[0034] (1) Ecological electric furnace smelting

[0035] The steel is smelted using scrap steel and molten iron, with 100% scrap steel by mass fraction, including 85% heavy scrap steel and 15% alloy structural steel cut-offs. The tapping temperature is 1646℃, with carbon content at 0.12% and phosphorus content at 0.008% at tapping. Auxiliary materials and alloys are added when 1 / 4 of the steel has been tapped. The smelting cycle is 60 minutes, and the furnace oxygen consumption is 21 m³ / s. 3 / t steel. Alloy addition per ton of steel: High-carbon ferromanganese 16.8Kg / t, ferroaluminum (Φ50mm) 2Kg / t. Auxiliary material addition per ton of steel: Graphite briquettes 8Kg / t, coke granules 35Kg / t, steel ladle ash 5.9Kg / t, active lime (Φ35mm) 40Kg / t, dolomite (Φ40mm) 30Kg / t.

[0036] (2) LF furnace refining

[0037] The LF furnace enters at a temperature of 1547℃, and is heated and slag-forming with a high current of 35600A. When the slag surface fluctuates and the molten steel and electric arc are not exposed, active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloy and silicon carbide are added according to the target chemical composition values, and coke particles are added for carbonization. The alloy, silicon carbide, and coke particles melt and homogenize rapidly. When the molten steel temperature reaches 1604℃, 1.4 kg / t of diffusion deoxidizer (aluminum particles) is added for diffusion deoxidation. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1635℃, a second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the required target value. After the second sample is taken, the molten steel leaves the station when the temperature reaches 1657℃. The LF smelting cycle is 104 minutes. The amount of alloy added per ton of steel is: 2.3 kg / t ferrosilicon, 3.5 kg / t high-carbon ferromanganese, 1.4 kg / t alumina balls, and 0.5 kg / t aluminum wire (Φ10mm). Additional auxiliary materials per ton of steel: 4 kg / t of active lime (Φ35mm), 1.1 kg / t of silicon carbide (Φ3mm), and 0.5 kg / t of coke granules.

[0038] (3) RH refining

[0039] The inlet temperature is 1636℃, the operation time is 42min. Before the vacuum pump is started, static argon is blown to control the argon pressure at 0.1MPa, so that the molten steel is not exposed when the slag surface is slightly moved. When the vacuum degree reaches 102Pa, the timing starts and is maintained for 11min. At the same time, the argon pressure is adjusted to 0.4MPa. After the static argon blowing is completed, 0.5kg / t of covering agent (carbonized rice husk) is added. The outlet temperature is 1588℃.

[0040] (4) Continuous casting

[0041] The ladle temperature upon arrival was 1586℃, the tundish H was controlled at 1.5ppm, the casting time was 41min, the superheat was 27℃, the casting speed was 0.4m / min, and the entire casting process was protected. Medium carbon steel protective slag was used in the crystallizer.

[0042] (5) Annealing process

[0043] Annealing was carried out in an annealing furnace at a temperature of 600℃ for 35 hours.

[0044] (6) Heating process

[0045] Heating process: Inlet temperature of 520℃, preheating zone temperature requirement of 660℃, time 1.4h; heating zone 2 temperature requirement of 870℃, time 1.3h; heating zone 1 temperature requirement of 1216℃, time 1.3h; soaking zone temperature requirement of 1205℃, time 1.5h; tapping temperature of 1195℃.

[0046] (7) Rolling process

[0047] Initial rolling process: 9 rolling passes, turning over → Pass 1: Width 408mm, Height 421mm, Reduction 65mm → Pass 2: Width 426mm, Height 351mm, Reduction 70mm → Turning over → Pass 3: Width 370mm, Height 362mm, Reduction 64mm → Pass 4: Width 397mm, Height 272mm, Reduction 90mm → Turning over → Pass 5: Width 285mm, Height 355mm, Reduction 42mm → 6th pass, width 297mm, height 315mm, reduction 40mm → 7th pass, width 307mm, height 280mm, reduction 35mm → 8th pass, width 317mm, height 246mm, reduction 34mm → Turning steel → 9th pass, width 271mm, height 235mm, reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling mill unit for rolling.

[0048] Continuous rolling process: 11 passes. Pass 1: 229mm high, 245mm wide; Pass 2: 192mm high, 235mm wide; Pass 3: 200mm high, 195mm wide; Pass 4: 160mm high, 214.7mm wide; Pass 5: 164mm high, 174.6mm wide; Pass 6: 121mm high, 187.6mm wide; Pass 7: 139mm high, 138.5mm wide; Pass 8: 106mm high, 152mm wide; Pass 9: 118mm high, 121mm wide; Pass 10: 91mm high, 130.2mm wide; Pass 11: 101.4mm high, 101.4mm wide; Finished steel is produced after 11 passes.

[0049] (8) Thermal Insulation Process

[0050] Insulation process: steel insulation, temperature of the lower insulation pit is 580℃, insulation time is 52 hours, and the temperature of the lower insulation pit is 100℃.

[0051] (9) Heat treatment process

[0052] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0053] 1) Quenching: 840℃, hold for 1.0h, oil cooling;

[0054] 2) Tempering: 540℃, hold for 2.0h, then water-cooled.

[0055] Example 2

[0056] 1Chemical composition

[0057] The chemical composition by mass percentage is: C: 0.39%, Si: 0.26%, Mn: 1.52%, P: 0.010%, S: 0.004%, Cr: 0.06%, Ni: 0.02%, Mo: 0.01%, Cu: 0.01%, with the balance being iron and unavoidable impurities.

[0058] 2. Production processes of electric furnace continuous casting for steel bars used in automobile axles

[0059] Process route: Eco-friendly electric furnace + LF refining + RH refining + continuous casting billet → annealing → heating furnace → rolling → holding → finishing → inspection → packaging and warehousing → shipment. Among them:

[0060] (2) Ecological electric furnace smelting

[0061] The steel is smelted using scrap steel and molten iron, with 100% scrap steel by mass fraction, including 84% heavy scrap steel and 16% alloy structural steel cuts. The tapping temperature is 1646℃, with carbon at 0.12% and phosphorus at 0.007% at tapping. Auxiliary materials and alloys are added when 1 / 4 of the steel has been tapped. The smelting cycle is 60 minutes, and the furnace oxygen consumption is 21 m³ / s. 3 / t steel. Alloy addition per ton of steel: High-carbon ferromanganese 16.9Kg / t, ferroaluminum (Φ50mm) 1.9Kg / t. Auxiliary material addition per ton of steel: Graphite briquettes 7.9Kg / t, coke granules 35Kg / t, steel ladle ash 6.0Kg / t, active lime (Φ35mm) 40Kg / t, dolomite (Φ40mm) 30Kg / t.

[0062] (2) LF furnace refining

[0063] The LF furnace is fed into the station at a temperature of 1547℃. A high current of 35400A is used for heating and slag formation. When the slag surface fluctuates and the molten steel and electric arc are not exposed, active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloy and silicon carbide are added according to the target chemical composition values, and coke particles are added for carbonization. The alloy, silicon carbide, and coke particles melt and homogenize rapidly. When the molten steel temperature reaches 1606℃, 1.4 kg / t of diffusion deoxidizer (aluminum particles) is added for diffusion deoxidation. The furnace door is closed for 12 minutes. When the molten steel temperature reaches 1635℃, a second sample is taken for chemical composition analysis to confirm the deviation of each chemical element content from the target value. After the second sample is taken, the molten steel leaves the station when the temperature reaches 1655℃. The LF smelting cycle is 105 minutes. The amount of alloy added per ton of steel is: 2.3 kg / t ferrosilicon, 3.5 kg / t high-carbon ferromanganese, 1.4 kg / t alumina balls, and 0.5 kg / t aluminum wire (Φ10mm). Additional auxiliary materials per ton of steel: 4 kg / t of active lime (Φ35mm), 1.1 kg / t of silicon carbide (Φ3mm), and 0.5 kg / t of coke granules.

[0064] (3) RH refining

[0065] The inlet temperature is 1637℃, the operation time is 42min. Before the vacuum pump is started, static argon is blown to control the argon pressure at 0.1MPa, so that the molten steel is not exposed when the slag surface is slightly moved. When the vacuum degree reaches 104Pa, the timing starts and is maintained for 12min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 0.5kg / t of covering agent (carbonized rice husk) is added. The outlet temperature is 1592℃.

[0066] (4) Continuous casting

[0067] The ladle temperature upon arrival is 1585℃, the H concentration in the tundish is controlled at 1.5ppm, the casting time is 40min, the superheat is 27℃, the casting speed is 0.4m / min, the entire casting process is protected, and medium carbon steel protective slag is used in the crystallizer.

[0068] (5) Annealing process

[0069] Annealing was carried out in an annealing furnace at a temperature of 600℃ for 34 hours.

[0070] (6) Heating process

[0071] Heating process: Inlet temperature of 520℃, preheating zone temperature requirement of 660℃, time 1.3h; heating zone 2 temperature requirement of 870℃, time 1.4h; heating zone 1 temperature requirement of 1214℃, time 1.3h; soaking zone temperature requirement of 1204℃, time 1.3h; tapping temperature of 1195℃.

[0072] (7) Rolling process

[0073] Initial rolling process: 9 rolling passes, turning over → Pass 1: Width 408mm, Height 421mm, Reduction 65mm → Pass 2: Width 426mm, Height 351mm, Reduction 70mm → Turning over → Pass 3: Width 370mm, Height 362mm, Reduction 64mm → Pass 4: Width 397mm, Height 272mm, Reduction 90mm → Turning over → Pass 5: Width 285mm, Height 355mm, Reduction 42mm → 6th pass, width 297mm, height 315mm, reduction 40mm → 7th pass, width 307mm, height 280mm, reduction 35mm → 8th pass, width 317mm, height 246mm, reduction 34mm → Turning steel → 9th pass, width 271mm, height 235mm, reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling mill unit for rolling.

[0074] Continuous rolling process: 11 passes. Pass 1: 229mm high, 245mm wide; Pass 2: 192mm high, 235mm wide; Pass 3: 200mm high, 195mm wide; Pass 4: 160mm high, 214.7mm wide; Pass 5: 164mm high, 174.6mm wide; Pass 6: 121mm high, 187.6mm wide; Pass 7: 139mm high, 138.5mm wide; Pass 8: 106mm high, 152mm wide; Pass 9: 118mm high, 121mm wide; Pass 10: 91mm high, 130.2mm wide; Pass 11: 101.4mm high, 101.4mm wide; Finished steel is produced after 11 passes.

[0075] (8) Thermal Insulation Process

[0076] Insulation process: steel insulation, temperature of the lower insulation pit is 600℃, insulation time is 49 hours, and the temperature of the lower insulation pit is 100℃.

[0077] (9) Heat treatment process

[0078] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0079] 1) Quenching: 840℃, hold for 1.0h, oil cooling;

[0080] 2) Tempering: 540℃, hold for 2.0h, then water-cooled.

[0081] Example 3

[0082] 1Chemical composition

[0083] The chemical composition by mass percentage is: C: 0.41%, Si: 0.26%, Mn: 1.55%, P: 0.010%, S: 0.005%, Cr: 0.05%, Ni: 0.03%, Mo: 0.01%, Cu: 0.01%, with the balance being iron and unavoidable impurities.

[0084] 2. Production processes of electric furnace continuous casting for steel bars used in automobile axles

[0085] Process route: Eco-friendly electric furnace + LF refining + RH refining + continuous casting billet → annealing → heating furnace → rolling → holding → finishing → inspection → packaging and warehousing → shipment. Among them:

[0086] (1) Ecological electric furnace smelting

[0087] The steel is smelted using scrap steel and molten iron, with 100% scrap steel by mass fraction, including 86% heavy scrap steel and 14% alloy structural steel cut-offs. The tapping temperature is 1646℃, with carbon content at 0.12% and phosphorus content at 0.008% at tapping. Auxiliary materials and alloys are added when 1 / 4 of the steel has been tapped. The smelting cycle is 65 minutes, and the furnace oxygen consumption is 21 m³ / s. 3 / t steel. Alloy addition per ton of steel: High-carbon ferromanganese 16.8Kg / t, ferroaluminum (Φ50mm) 2.0Kg / t. Auxiliary material addition per ton of steel: Graphite briquettes 8.0Kg / t, coke granules 35Kg / t, steel ladle ash 6.0Kg / t, active lime (Φ35mm) 40Kg / t, dolomite (Φ40mm) 30Kg / t.

[0088] (2) LF furnace refining

[0089] The LF furnace is fed into the station at a temperature of 1546℃. A high current of 35400A is used for heating and slag formation. When the slag surface fluctuates and the molten steel and electric arc are not exposed, active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloy and silicon carbide are added according to the target chemical composition values, and coke particles are added for carbonization. The alloy, silicon carbide, and coke particles melt and homogenize rapidly. When the molten steel temperature reaches 1604℃, 1.4 kg / t of diffusion deoxidizer (aluminum particles) is added for diffusion deoxidation. The furnace door is closed for 10 minutes. When the molten steel temperature reaches 1635℃, a second sample is taken for chemical composition analysis to confirm the deviation of each chemical element content from the target value. After the second sample is taken, the molten steel is removed from the station when the temperature reaches 1656℃. The LF smelting cycle is 104 minutes. The amount of alloy added per ton of steel is: 2.3 kg / t ferrosilicon, 3.5 kg / t high-carbon ferromanganese, 1.4 kg / t alumina balls, and 0.4 kg / t aluminum wire (Φ10mm). Additional auxiliary materials per ton of steel: 4 kg / t of active lime (Φ35mm), 1.1 kg / t of silicon carbide (Φ3mm), and 0.5 kg / t of coke granules.

[0090] (3) RH refining

[0091] The inlet temperature is 1635℃, the operation time is 40min. Before the vacuum pump is started, static argon is blown to control the argon pressure at 0.1MPa, so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum degree reaches 104Pa, the timing starts and is maintained for 12min. At the same time, the argon pressure is adjusted to 0.4MPa. After the static argon blowing is completed, 0.5kg / t of covering agent (carbonized rice husk) is added. The outlet temperature is 1590℃.

[0092] (4) Continuous casting

[0093] The ladle temperature upon arrival is 1585℃, the H concentration in the tundish is controlled at 1.5ppm, the casting time is 40min, the superheat is 27℃, the casting speed is 0.4m / min, the entire casting process is protected, and medium carbon steel protective slag is used in the crystallizer.

[0094] (5) Annealing process

[0095] Annealing was carried out in an annealing furnace at a temperature of 600℃ for 36 hours.

[0096] (6) Heating process

[0097] Heating process: Inlet temperature of 520℃, preheating zone temperature requirement of 660℃, time 1.5h; heating zone 2 temperature requirement of 870℃, time 1.3h; heating zone 1 temperature requirement of 1214℃, time 1.3h; soaking zone temperature requirement of 1204℃, time 1.3h; tapping temperature of 1195℃.

[0098] (7) Rolling process

[0099] Initial rolling process: 9 rolling passes, turning over → Pass 1: Width 408mm, Height 421mm, Reduction 65mm → Pass 2: Width 426mm, Height 351mm, Reduction 70mm → Turning over → Pass 3: Width 370mm, Height 362mm, Reduction 64mm → Pass 4: Width 397mm, Height 272mm, Reduction 90mm → Turning over → Pass 5: Width 285mm, Height 355mm, Reduction 42mm → 6th pass, width 297mm, height 315mm, reduction 40mm → 7th pass, width 307mm, height 280mm, reduction 35mm → 8th pass, width 317mm, height 246mm, reduction 34mm → Turning steel → 9th pass, width 271mm, height 235mm, reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling mill unit for rolling.

[0100] Continuous rolling process: 11 passes. Pass 1: 229mm high, 245mm wide; Pass 2: 192mm high, 235mm wide; Pass 3: 200mm high, 195mm wide; Pass 4: 160mm high, 214.7mm wide; Pass 5: 164mm high, 174.6mm wide; Pass 6: 121mm high, 187.6mm wide; Pass 7: 139mm high, 138.5mm wide; Pass 8: 106mm high, 152mm wide; Pass 9: 118mm high, 121mm wide; Pass 10: 91mm high, 130.2mm wide; Pass 11: 101.4mm high, 101.4mm wide; Finished steel is produced after 11 passes.

[0101] (8) Thermal Insulation Process

[0102] Insulation process: steel insulation, temperature in the insulation pit is 580℃, insulation time is 52 hours, and the temperature after exiting the pit is 110℃.

[0103] (9) Heat treatment process

[0104] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0105] 1) Quenching: 840℃, hold for 1.0h, oil cooling;

[0106] 2) Tempering: 540℃, hold for 2.0h, then water-cooled.

[0107] Example 4

[0108] 1Chemical composition

[0109] The chemical composition by mass percentage is: C: 0.40%, Si: 0.26%, Mn: 1.53%, P: 0.010%, S: 0.005%, Cr: 0.06%, Ni: 0.02%, Mo: 0.01%, Cu: 0.01%, with the balance being iron and unavoidable impurities.

[0110] 2. Production processes of electric furnace continuous casting for steel bars used in automobile axles

[0111] Process route: Eco-friendly electric furnace + LF refining + RH refining + continuous casting billet → annealing → heating furnace → rolling → holding → finishing → inspection → packaging and warehousing → shipment. Among them:

[0112] (3) Ecological electric furnace smelting

[0113] The steel is smelted using scrap steel and molten iron, with 100% scrap steel by mass fraction, including 85% heavy scrap steel and 15% alloy structural steel cut-offs. The tapping temperature is 1645℃, with carbon content at 0.11% and phosphorus content at 0.007% at tapping. Auxiliary materials and alloys are added when 1 / 4 of the steel has been tapped. The smelting cycle is 65 minutes, and the furnace oxygen consumption is 21 m³ / s.3 / t steel. Alloy addition per ton of steel: High-carbon ferromanganese 16.8Kg / t, ferroaluminum (Φ50mm) 2.0Kg / t. Auxiliary material addition per ton of steel: Graphite briquettes 7.9Kg / t, coke granules 35Kg / t, steel ladle ash 6.0Kg / t, active lime (Φ35mm) 40Kg / t, dolomite (Φ40mm) 30Kg / t.

[0114] (2) LF furnace refining

[0115] The LF furnace is fed into the plant at a temperature of 1545℃. A high-current (35500A) is used for slag formation. When the slag surface fluctuates and the molten steel and electric arc are not exposed, active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloy and silicon carbide are added according to the target chemical composition values, and coke particles are added for carbonization. The alloy, silicon carbide, and coke particles melt and homogenize rapidly. When the molten steel temperature reaches 1604℃, 1.4 kg / t of diffusion deoxidizer (aluminum particles) is added for diffusion deoxidation. The furnace door is closed for 10 minutes. When the molten steel temperature reaches 1635℃, a second sample is taken for chemical composition analysis to confirm the deviation of each chemical element content from the target value. After the second sample is taken, the molten steel is removed from the plant when the temperature reaches 1657℃. The LF smelting cycle is 102 minutes. The amount of alloy added per ton of steel is: 2.3 kg / t ferrosilicon, 3.5 kg / t high-carbon ferromanganese, 1.4 kg / t alumina balls, and 0.5 kg / t aluminum wire (Φ10mm). Additional auxiliary materials per ton of steel: 4 kg / t of active lime (Φ35mm), 1.1 kg / t of silicon carbide (Φ3mm), and 0.5 kg / t of coke granules.

[0116] (3) RH refining

[0117] The inlet temperature is 1635℃, the operation time is 41min. Before the vacuum pump is started, static argon is blown to control the argon pressure at 0.1MPa, so that the molten steel is not exposed when the slag surface is slightly moved. When the vacuum degree reaches 103Pa, the timing starts and is maintained for 10min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 0.5kg / t of covering agent (carbonized rice husk) is added. The outlet temperature is 1588℃.

[0118] (4) Continuous casting

[0119] The ladle temperature upon arrival is 1586℃, the H concentration in the tundish is controlled at 1.5ppm, the casting time is 40min, the superheat is 26℃, the casting speed is 0.4m / min, the entire casting process is protected, and medium carbon steel protective slag is used in the crystallizer.

[0120] (5) Annealing process

[0121] Annealing was carried out in an annealing furnace at a temperature of 600℃ for 35 hours.

[0122] (6) Heating process

[0123] Heating process: Inlet temperature of 520℃, preheating zone temperature requirement of 670℃, time 1.4h; heating zone 2 temperature requirement of 870℃, time 1.5h; heating zone 1 temperature requirement of 1215℃, time 1.3h; soaking zone temperature requirement of 1204℃, time 1.4h; tapping temperature of 1194℃.

[0124] (7) Rolling process

[0125] Initial rolling process: 9 rolling passes, turning over → Pass 1: Width 408mm, Height 421mm, Reduction 65mm → Pass 2: Width 426mm, Height 351mm, Reduction 70mm → Turning over → Pass 3: Width 370mm, Height 362mm, Reduction 64mm → Pass 4: Width 397mm, Height 272mm, Reduction 90mm → Turning over → Pass 5: Width 285mm, Height 355mm, Reduction 42mm → 6th pass, width 297mm, height 315mm, reduction 40mm → 7th pass, width 307mm, height 280mm, reduction 35mm → 8th pass, width 317mm, height 246mm, reduction 34mm → Turning steel → 9th pass, width 271mm, height 235mm, reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling mill unit for rolling.

[0126] Continuous rolling process: 11 passes. Pass 1: 229mm high, 245mm wide; Pass 2: 192mm high, 235mm wide; Pass 3: 200mm high, 195mm wide; Pass 4: 160mm high, 214.7mm wide; Pass 5: 164mm high, 174.6mm wide; Pass 6: 121mm high, 187.6mm wide; Pass 7: 139mm high, 138.5mm wide; Pass 8: 106mm high, 152mm wide; Pass 9: 118mm high, 121mm wide; Pass 10: 91mm high, 130.2mm wide; Pass 11: 101.4mm high, 101.4mm wide; Finished steel is produced after 11 passes.

[0127] (8) Thermal Insulation Process

[0128] Insulation process: steel insulation, temperature of the lower insulation pit is 580℃, insulation time is 52 hours, and the temperature of the lower insulation pit is 100℃.

[0129] (9) Heat treatment process

[0130] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0131] 1) Quenching: 840℃, hold for 1.0h, oil cooling;

[0132] 2) Tempering: 540℃, hold for 2.0h, then water-cooled.

[0133] Example 5

[0134] 1Chemical composition

[0135] The chemical composition by mass percentage is: C: 0.41%, Si: 0.25%, Mn: 1.52%, P: 0.011%, S: 0.005%, Cr: 0.06%, Ni: 0.02%, Mo: 0.01%, Cu: 0.01%, with the balance being iron and unavoidable impurities.

[0136] 2. Production processes of electric furnace continuous casting for steel bars used in automobile axles

[0137] Process route: Eco-friendly electric furnace + LF refining + RH refining + continuous casting billet → annealing → heating furnace → rolling → holding → finishing → inspection → packaging and warehousing → shipment. Among them:

[0138] (1) Ecological electric furnace smelting

[0139] The steel is smelted using scrap steel and molten iron, with 100% scrap steel by mass fraction, including 86% heavy scrap steel and 14% alloy structural steel cut-offs. The tapping temperature is 1645℃, with carbon at 0.10% and phosphorus at 0.007% at tapping. Auxiliary materials and alloys are added when 1 / 4 of the steel has been tapped. The smelting cycle is 65 minutes, and the furnace oxygen consumption is 21 m³ / s. 3 / t steel. Alloy addition per ton of steel: High-carbon ferromanganese 16.8Kg / t, ferroaluminum (Φ50mm) 2.0Kg / t. Auxiliary material addition per ton of steel: Graphite briquettes 8.0Kg / t, coke granules 35Kg / t, steel ladle ash 6.0Kg / t, active lime (Φ35mm) 40Kg / t, dolomite (Φ40mm) 30Kg / t.

[0140] (2) LF furnace refining

[0141] The LF furnace enters at a temperature of 1546℃, and is heated and slag-forming with a high current of 35400A. When the slag surface fluctuates and the molten steel and electric arc are not exposed, active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloy and silicon carbide are added according to the target chemical composition values, and coke particles are added for carbonization. The alloy, silicon carbide, and coke particles melt and homogenize rapidly. When the molten steel temperature reaches 1605℃, 1.4kg / t of diffusion deoxidizer (aluminum particles) is added for diffusion deoxidation. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1635℃, a second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the required target value. After the second sample is taken, the molten steel leaves the station when the temperature reaches 1655℃. The LF smelting cycle is 104 minutes. The amount of alloy added per ton of steel is: 2.3kg / t ferrosilicon, 3.5kg / t high-carbon ferromanganese, 1.4kg / t alumina balls, and 0.5kg / t aluminum wire (Φ10mm). Additional auxiliary materials per ton of steel: 4 kg / t of active lime (Φ35mm), 1.1 kg / t of silicon carbide (Φ3mm), and 0.5 kg / t of coke granules.

[0142] (3) RH refining

[0143] The inlet temperature is 1636℃, the operation time is 40min. Before starting the vacuum pump, static argon is blown to control the argon pressure at 0.1MPa, so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum degree reaches 102Pa, the timing starts and is maintained for 13min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 0.5kg / t of covering agent (carbonized rice husk) is added. The outlet temperature is 1589℃.

[0144] (4) Continuous casting

[0145] The ladle temperature upon arrival is 1585℃, the tundish H is controlled at 1.5ppm, the casting time is 40min, the superheat is 26℃, the casting speed is 0.4m / min, the entire casting process is protected, and medium carbon steel protective slag is used in the crystallizer.

[0146] (5) Annealing process

[0147] Annealing was carried out in an annealing furnace at a temperature of 600℃ for 35 hours.

[0148] (6) Heating process

[0149] Heating process: Inlet temperature of 520℃, preheating zone temperature requirement of 660℃, time 1.4h; heating zone 2 temperature requirement of 870℃, time 1.3h; heating zone 1 temperature requirement of 1215℃, time 1.4h; soaking zone temperature requirement of 1203℃, time 1.3h; tapping temperature of 1194℃.

[0150] (7) Rolling process

[0151] Initial rolling process: 9 rolling passes, turning over → Pass 1: Width 408mm, Height 421mm, Reduction 65mm → Pass 2: Width 426mm, Height 351mm, Reduction 70mm → Turning over → Pass 3: Width 370mm, Height 362mm, Reduction 64mm → Pass 4: Width 397mm, Height 272mm, Reduction 90mm → Turning over → Pass 5: Width 285mm, Height 355mm, Reduction 42mm → 6th pass, width 297mm, height 315mm, reduction 40mm → 7th pass, width 307mm, height 280mm, reduction 35mm → 8th pass, width 317mm, height 246mm, reduction 34mm → Turning steel → 9th pass, width 271mm, height 235mm, reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling mill unit for rolling.

[0152] Continuous rolling process: 11 passes. Pass 1: 229mm high, 245mm wide; Pass 2: 192mm high, 235mm wide; Pass 3: 200mm high, 195mm wide; Pass 4: 160mm high, 214.7mm wide; Pass 5: 164mm high, 174.6mm wide; Pass 6: 121mm high, 187.6mm wide; Pass 7: 139mm high, 138.5mm wide; Pass 8: 106mm high, 152mm wide; Pass 9: 118mm high, 121mm wide; Pass 10: 91mm high, 130.2mm wide; Pass 11: 101.4mm high, 101.4mm wide; Finished steel is produced after 11 passes.

[0153] (8) Thermal Insulation Process

[0154] Insulation process: steel insulation, temperature in the insulation pit is 590℃, insulation time is 52 hours, and the temperature after exiting the pit is 100℃.

[0155] (9) Heat treatment process

[0156] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0157] 1) Quenching: 840℃, hold for 1.0h, oil cooling;

[0158] 2) Tempering: 540℃, hold for 2.0h, then water-cooled.

[0159] Inspection results of finished products in Examples 1-5

[0160] (1) Low magnification microstructure of Φ100mm steel (finished steel obtained through thermal insulation process)

[0161] (2) Non-metallic inclusions in Φ100mm steel (finished steel obtained through insulation process)

[0162] (3) Mechanical properties of Φ100mm steel (finished steel after heat treatment)

Claims

1. A high-temperature-resistant steel bar for automotive axle, characterized in that, The composition by mass percentage is: C: 0.39%–0.42%, Si: 0.22%–0.30%, Mn: 1.45%–1.70%, P: ≤0.015%, S: ≤0.006%, Cr: ≤0.20%, Ni: ≤0.20%, Mo: ≤0.05%, Cu: ≤0.10%, with the balance being iron and unavoidable impurities.

2. Process for the production of a high temperature resistant automotive axle steel bar according to claim 1, characterized in that, The process includes the following steps: ecological electric furnace smelting → LF refining → RH refining → continuous casting → annealing process → heating process → rolling process → heat preservation process. The ecological electric furnace smelting is: adopting scrap steel smelting, tapping temperature 1640-1650 DEG C, tapping C 0.10-0.15%, P <=0.010%, adding auxiliary material and alloy when tapping 1 / 4-1 / 3, smelting period 55-65 min, oxygen consumption 21-22 m 3 / t steel The LF refining process is as follows: The LF inlet temperature is 1540–1550℃, and the slag is heated by a high current of 35000–36000A. When the slag surface fluctuates and the molten steel and electric arc are not exposed, active lime is added. After 5–6 minutes, the first sample is taken for chemical composition analysis. Alloy and silicon carbide are added according to the target chemical composition value, and coke particles are added for carbonization. When the molten steel temperature reaches 1600–1610℃, a diffusion deoxidizer of 1.4–1.5 kg / t steel is added for diffusion deoxidation. The furnace door is closed for 10–13 minutes. When the molten steel temperature reaches 1630–1640℃, a second sample is taken for chemical composition analysis. When the molten steel temperature reaches 1650–1660℃, the LF smelting cycle is 100–110 minutes. The RH refining process is as follows: the inlet temperature is 1630-1640℃, the operation time is 35-45 minutes, and before the vacuum pump is started, argon is statically blown to control the argon pressure at 0.1-0.3 MPa. When the vacuum degree reaches 100-110 Pa, the timing starts and is maintained for 10-15 minutes. At the same time, the argon pressure is adjusted to 0.3-0.5 MPa. After the static argon blowing is completed, 0.5-0.6 kg / t of covering agent is added, and the outlet temperature is 1585-1595℃. The continuous casting process is as follows: ladle arrival temperature 1580~1590℃, tundish H control ≤2ppm, casting time 35min~45min, superheat 25~30℃, casting speed 0.4~0.42m / min; The annealing process is as follows: annealing temperature 580-620℃, time 32 hours or more.

3. The preparation method according to claim 2, characterized in that, In the ecological electric furnace smelting process, the alloy additions per ton of steel are: 16.5-17.5 kg / t for high-carbon ferromanganese and 1.9-2.1 kg / t for ferroaluminum; the auxiliary materials added per ton of steel are: 7.8-8.2 kg / t for graphite briquettes, 35-36 kg / t for coke granules, 5.8-6.3 kg / t for steel ladle ash, 40-41 kg / t for quicklime, and 29-31 kg / t for dolomite. In the LF refining step, the following alloys are added per ton of steel: ferrosilicon 2.3-2.4 kg / t, high-carbon ferromanganese 3.5-3.6 kg / t, alumina balls 1.4-1.5 kg / t, and aluminum wire 0.4-0.6 kg / t; the following auxiliary materials are added per ton of steel: active lime 4-4.2 kg / t, silicon carbide 1.1-1.2 kg / t, and coke granules 0.5-0.6 kg / t. In the continuous casting process, the casting is protected throughout, and medium carbon steel protective slag is used in the mold.

4. The production method according to claim 2 or 3, characterized by, The diameter of the aluminum iron is 40-70mm, the diameter of the active lime is 10-70mm, and the diameter of the dolomite is 20-70mm; the diameter of the aluminum wire is 10-14mm, and the diameter of the silicon carbide is 2-5mm.

5. The preparation method according to claim 2, characterized in that, The scrap steel includes heavy scrap steel and steel cuts, with heavy scrap steel accounting for 80% to 90% and steel cuts accounting for 10% to 20% by mass fraction; the diffusion deoxidizer is aluminum granules; and the covering agent is carbonized rice husk.

6. The preparation method according to claim 2, characterized in that, In the LF refining step, alloys, silicon carbide, and coke particles are added to the argon gas stream.

7. The preparation method according to claim 2, characterized in that, The heating process is as follows: the furnace inlet temperature is 500℃~540℃; the preheating section temperature is required to be 650℃~680℃ for 1.3~1.5h; the second heating section temperature is required to be 860℃~880℃ for 1.3~1.5h; the first heating section temperature is required to be 1210℃~1220℃ for 1.3~1.5h; the soaking section temperature is required to be 1200℃~1210℃ for 1.3~1.5h; and the tapping temperature is 1190℃~1198℃.

8. The preparation method according to claim 2, characterized in that, The rolling process is as follows: (1) Initial rolling process: 9 rolling passes; (2) Continuous rolling process: 11 passes.

9. The preparation method according to claim 2, characterized in that, The insulation process is as follows: steel insulation, the temperature of the lower insulation pit is ≥560℃, the insulation time is 48~55h, and the temperature of the material leaving the pit is ≤120℃.

10. The method of claim 2, wherein, The heat-treated steel is then subjected to heat treatment, which includes the following steps: 1) Quenching: 830~850℃, hold for 0.8~1.2h, oil cooling; 2) Tempering: 530~550℃, hold for 1.8~2.2h, then water-cooled.

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