Steel bar for automobile heat-resistant fastener and production process therefor

Abstract

Disclosed in the present invention are a steel bar for an automobile heat-resistant fastener and a production process therefor. The bar of the present invention comprises the following chemical components in percentage by mass: C: 0.23-0.27%, Si: 0.20-0.35%, Mn: 0.42-0.60%, P: ≤0.015％, S: ≤0.012％, Cr: 1.52-1.70%, Ni: ≤0.25％, Mo: 0.26-0.33%, V: 0.16-0.25%, Cu: ≤0.15％, and the balance being Fe and inevitable impurities. The production process route comprises: eco-friendly electric arc furnace smelting, LF refining, RH refining, continuous casting, annealing, heating furnace-based heating, rolling, heat preservation, and heat treatment. The present invention ensures that indicators such as mechanical properties and high steel purity for the steel bar for an automobile heat-resistant fastener meet standards, and also ensures the surface quality of the steel bar for an automobile heat-resistant fastener, thereby meeting the use requirements for high-end automobile heat-resistant fasteners.

Description

A steel bar for automotive heat-resistant fasteners and its manufacturing process Technical Field

[0001] This invention belongs to the field of special steel preparation technology, specifically relating to a steel bar for automotive heat-resistant fasteners and its production process. Background Technology

[0002] Automotive fasteners, as fundamental components of automobiles, are numerous and play a crucial connecting role, even a safety guarantee, in most locations. In recent years, my country's automotive manufacturing industry has experienced rapid development and accelerated industrial upgrading, placing increasingly higher demands on the product quality and technological level of my country's automotive fastener industry. With the increasing requirements for heat resistance, mechanical properties, fatigue life, and steel purity in automotive fasteners, the quality of steel used in heat-resistant automotive fasteners directly affects the service life and wear resistance of automobiles, and even the safety of the entire vehicle operation. Therefore, researching and developing heat-resistant steel for automotive fasteners with excellent heat resistance, mechanical properties, and high steel purity has become an important and urgent research topic.

[0003] Summary of the Invention

[0004] Therefore, the purpose of this invention is to provide a steel bar for automotive heat-resistant fasteners and its manufacturing process. This invention employs an ECOARC eco-friendly electric furnace smelting + LF furnace refining + RH refining + continuous casting + annealing + rolling + heat treatment process to produce steel bars for automotive heat-resistant fasteners. This process ensures both the mechanical properties and high purity of the finished steel bars, as well as the surface quality. Furthermore, it represents a breakthrough in the mass production of automotive heat-resistant fastener steel bars using the eco-friendly electric furnace continuous casting process, meeting the requirements of high-end automotive heat-resistant fasteners.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention provides a steel bar for automotive heat-resistant fasteners. The chemical composition and mass percentage of the steel bar for automotive heat-resistant fasteners are as follows: C: 0.23%~0.27%, Si: 0.20%~0.35%, Mn: 0.42%~0.60%, P: ≤0.015%, S: ≤0.012%, Cr: 1.52%~1.70%, Ni: ≤0.25%, Mo: 0.26%~0.33%, V: 0.16%~0.25%, Cu: ≤0.15%, with the balance being Fe and unavoidable impurities.

[0007] The present invention also provides the above-mentioned production process of steel bars for automotive heat-resistant fasteners, the production process route is as follows: ECOARC ecological electric furnace smelting → LF furnace refining → RH refining → continuous casting → annealing → heating furnace heating → rolling → heat preservation → heat treatment.

[0008] The ECOARC eco-friendly electric furnace smelting process has a tapping temperature of 1600–1610℃, a carbon content of 0.08–0.10%, a phosphorus content of ≤0.010%, a tapping volume of 106–113t, and a smelting cycle of 35–45min.

[0009] In the LF furnace refining process, the LF furnace inlet temperature is 1540-1550℃, and the molten steel leaves the furnace when the temperature reaches 1640-1650℃. The LF smelting cycle is 60-70 minutes.

[0010] For the RH refining process, the inlet temperature is 1580-1590℃. Before starting the vacuum pump, the argon pressure is controlled so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum reaches 100-110Pa, the timing starts and is maintained for 10-15 minutes. Argon is blown statically, and the outlet temperature is 1580-1590℃. The operation time is 40-50 minutes.

[0011] In the continuous casting process, the ladle temperature upon arrival is 1565-1575℃, the molten steel volume is 95-105t, the H in the tundish is controlled to be ≤2ppm, the entire process is protected during casting, and medium carbon steel protective slag is used in the crystallizer.

[0012] The annealing process involves an annealing temperature of 640–650℃, an annealing time of 30–35 hours, and a furnace exit temperature of ≤200℃.

[0013] The heating process in the heating furnace involves an initial temperature of 450℃~560℃, a soaking zone temperature controlled at 1190℃~1210℃, and a duration of 1.3~1.5 hours; the tapping temperature is 1185℃~1195℃.

[0014] The rolling process has an initial rolling temperature of 1000–1050℃ and a final rolling temperature of 800–900℃.

[0015] For the insulation process, the temperature in the insulation pit is 550-590℃, the insulation time is 50-55 hours, and the temperature after exiting the pit is ≤180℃.

[0016] Based on the above technical solution, furthermore, in the ECOARC ecological electric furnace smelting process, slag, pre-deoxidizer, and ferroalloys are added when the steel is 1 / 4 to 1 / 3 tapped. The alloy addition amounts per ton of steel are: silicon manganese 5.0–5.2 kg / t, high-carbon ferrochrome 10–10.5 kg / t, low-carbon ferrochrome 16–16.5 kg / t, and aluminum wire segments (10-16 mm) 1.0–1.2 kg / t. The auxiliary material addition amounts per ton of steel are: active lime (10-70 mm) 40–41 kg / t, magnesite (10-60 mm) 25–26 kg / t, ladle ash 6–6.2 kg / t, small coke lumps 20–21 kg / t, and coking CDQ powder 18–19 kg / t.

[0017] Based on the above technical solution, the ECOARC eco-friendly electric furnace smelting process further includes 38-45t of molten iron, 20-21t of alloy structural steel cuts, 43-45t of heavy scrap steel, and 10-11t of bale-shaped scrap steel as raw materials.

[0018] Based on the above technical solution, further, in the LF furnace refining process, after the LF furnace enters the station, it is heated to slag with 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 is added according to the target chemical composition value, and carbon is added to promote the rapid melting and homogenization of alloy and carbon powder. When the molten steel temperature reaches 1600-1610℃, 1.5-1.6 kg / t of diffusion deoxidizer alumina balls is added for diffusion deoxidation. The furnace door is closed for 10-13 minutes. When the molten steel temperature reaches 1620-1630℃, the second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value.

[0019] Based on the above technical solution, further, in the LF furnace refining process, the added alloys include: ferrosilicon 1.1~1.2kg / t, high-carbon ferromanganese 2.1~2.2kg / t, high-carbon ferrochrome 3.9~4.0kg / t, ferromolybdenum 0.4~0.5kg / t, ferrovanadium (FeV50-B) 3.5~3.6kg / t, and aluminum wire (Φ10~Φ12mm) 1~1.1m / t; the added auxiliary materials are: active lime (10-70mm) 4~4.2kg / t, silicon carbide (1-5mm) 2.1~2.2kg / t, and coke particles 0.75~0.80kg / t.

[0020] Based on the above technical solution, further, in the RH refining process, the argon pressure is controlled at 0.1-0.3 MPa before the vacuum pump is started, and the argon pressure is adjusted to 0.3-0.5 MPa during the static argon blowing process. After the static argon blowing is completed, 2-2.1 meters / t of silicon-calcium alloy cored wire (Φ14-Φ14.2mm) and 0.6-0.7 kg / t of covering agent are added.

[0021] Based on the above technical solution, further, in the heating process of the heating furnace, the temperature of the preheating section is controlled at 660℃~700℃ for 1.3~1.5h; the temperature of the second heating section is controlled at 850℃~860℃ for 1.3~1.5h; and the temperature of the first heating section is controlled at 1190℃~1220℃ for 1.3~1.5h.

[0022] Based on the above technical solution, further, the rolling process of the continuous casting billet initial rolling is as follows: 9 rolling passes, rolling reduction: Turning steel → 1st pass reduction 64.9~65.1mm → 2nd pass reduction 69.9~70.1mm → Turning steel → 3rd pass reduction 63.9~64.1mm → 4th pass reduction 89.9~90.1mm → Turning steel → 5th pass reduction 41.9~42.1mm → 6th pass reduction 39.9~40.1mm → 7th pass reduction 34.9~35.1mm → 8th pass reduction 33.9~34.1mm → Turning steel → 9th pass reduction 81.9~82.1mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters an 8-stand continuous rolling mill group for rolling.

[0023] Rolling process: 8 passes. Pass 1: Height 228.9–229.1 mm, width 244.9–245.1 mm; Pass 2: Height 191.9–192.1 mm, width 234.9–235.1 mm; Pass 3: Height 199.9–200.1 mm, width 194.9–195.1 mm; Pass 4: Height 168.9–169.1 mm, width 212.7–212.9 mm. mm; the 5th pass has a height of 176.9–177.1 mm and a width of 179.9–180.1 mm; the 6th pass has a height of 140.9–141.1 mm and a width of 191.9–192.1 mm; the 7th pass has a height of 151.9–152.1 mm and a width of 151.9–152.1 mm; the 8th pass has a height of 151.9–152.1 mm and a width of 151.9–152.1 mm; the finished product is produced after the 8th pass.

[0024] Based on the above technical solution, the heat treatment process further includes the following steps:

[0025] 1) Quenching: 890~910℃, hold for 0.9~1.2h, oil cooling;

[0026] 2) Tempering: 630~650℃, hold for 1.9~2.2h, then air cool.

[0027] The advantages of this invention over the prior art are as follows:

[0028] (1) This invention uses a 100t ECOARC ecological electric furnace + LF + RH + 390mm*480mm continuous casting, rolling and heat treatment process to produce steel bars for automotive heat-resistant fasteners with a production specification of Φ150mm, which meets the mechanical performance requirements and ensures the purity of the steel.

[0029] (2) The reasonable composition design and production process of this invention ensure the surface quality and mechanical properties of steel bars for automotive heat-resistant fasteners.

[0030] (3) The finished steel bar for automotive heat-resistant fasteners prepared by this invention has low magnification structure and non-metallic inclusions that meet the requirements of high-end products. Detailed Implementation

[0031] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0032] Example 1:

[0033] This embodiment provides a manufacturing process for steel bars used in automotive heat-resistant fasteners. The specific process is as follows:

[0034] The chemical composition and mass percentage of the steel bars for automotive heat-resistant fasteners are as follows: C: 0.25%, Si: 0.26%, Mn: 0.48%, P: 0.011%, S: 0.006%, Cr: 1.59%, Ni: 0.05%, Mo: 0.28%, V: 0.19%, Cu: 0.05%, with the balance being Fe and unavoidable impurities.

[0035] Process route: ECOARC eco-friendly electric furnace smelting → LF furnace refining → RH refining → continuous casting → annealing → heating furnace heating → rolling → heat holding → heat treatment → finishing → inspection → packaging and warehousing → shipment;

[0036] (1) Ecological electric furnace smelting

[0037] The molten iron loading was 42t; the scrap steel loading was: 20t of alloy structural steel cuts, 44t of heavy scrap steel, and 10t of bale-shaped scrap steel; the tapping temperature was 1605℃, with C at 0.09% and P at 0.008% at tapping; slag, pre-deoxidizer, and ferroalloys were added when 1 / 4 of the steel was tapped, resulting in a tapping volume of 109t and a smelting cycle of 40min. Alloy additives per ton of steel included: 5.1kg / t silicon manganese, 10.2kg / t high-carbon ferrochrome, 16kg / t low-carbon ferrochrome, and 1.1kg / t aluminum wire (10mm). Auxiliary materials per ton of steel included: 40kg / t quicklime (35mm), 25kg / t magnesite (40mm), 6kg / t ladle ash, 20kg / t small coke lumps, and 18kg / t coking CDQ powder.

[0038] (2) LF furnace refining

[0039] The LF inlet temperature is 1545℃, and the slag is heated by 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 to analyze the chemical composition. Alloy is added according to the target value of chemical composition, and carbon is added to promote the rapid melting and homogenization of alloy and carbon powder. When the molten steel temperature reaches 1605℃, 1.5 kg / t of diffusion deoxidizer alumina balls is added for diffusion deoxidation. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1626℃, 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 temperature reaches 1645℃ and leaves the furnace. The LF smelting cycle is 65 minutes. The following alloys are added: ferrosilicon 1.1 kg / t, high-carbon ferromanganese 2.1 kg / t, high-carbon ferrochrome 3.9 kg / t, ferromolybdenum 0.45 kg / t, ferrovanadium (FeV50-B) 3.5 kg / t, and aluminum wire (Φ10mm) 1.0 m / t. The following auxiliary materials are added: active lime (35mm) 4 kg / t, silicon carbide (3mm) 2.1 kg / t, and coke particles 0.77 kg / t.

[0040] (3) RH refining

[0041] The inlet temperature is 1586℃, the operation time is 46min, the argon pressure is controlled at 0.1MPa before the vacuum pump is started, so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum degree reaches 100Pa, 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, 2.0m / t of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t of covering agent are added. The outlet temperature is 1587℃.

[0042] (4) Continuous casting

[0043] The ladle temperature upon arrival is 1570℃, the molten steel volume is 98t, the tundish H is controlled at 1.5ppm, the entire casting process is protected, and medium carbon steel protective slag is used in the crystallizer.

[0044] (5) Annealing

[0045] The continuously cast billet was annealed at a temperature of 646℃ for 33 hours and a tapping temperature of 160℃.

[0046] (6) Heating process

[0047] Heating process: Inlet temperature to the heating furnace is 490℃; preheating zone temperature is required to be 680℃ for 1.3 hours; heating zone 2 temperature is required to be 854℃ for 1.3 hours; heating zone 1 temperature is required to be 1205℃ for 1.5 hours; soaking zone temperature is required to be 1200℃ for 1.3 hours; tapping temperature is 1190℃.

[0048] (7) Rolling process

[0049] The initial rolling temperature is 1050℃, and the final rolling temperature is 880℃.

[0050] The initial rolling process of continuously cast billets is as follows: 9 rolling passes, with the following rolling reduction: Turning steel → 1st pass reduction 65mm → 2nd pass reduction 70mm → Turning steel → 3rd pass reduction 64mm → 4th pass reduction 90mm → Turning steel → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → Turning steel → 9th pass reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters an 8-stand continuous rolling mill group for rolling.

[0051] Rolling process of raw material: 8 rolling passes. The first pass is 229mm high and 245mm wide; the second pass is 192mm high and 235mm wide; the third pass is 200mm high and 195mm wide; the fourth pass is 169mm high and 212.8mm wide; the fifth pass is 177mm high and 180mm wide; the sixth pass is 141mm high and 192mm wide; the seventh pass is 152mm high and 152mm wide; the eighth pass is 152mm high and 152mm wide; the finished product is produced after 8 passes.

[0052] (8) Thermal Insulation Process

[0053] Insulation process: steel insulation, temperature in the lower insulation pit is 590℃, insulation time is 53 hours, and the temperature after exiting the pit is 150℃.

[0054] (9) Heat treatment process

[0055] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0056] 1) Quenching: 900℃, hold for 1.0h, oil cooling;

[0057] 2) Tempering: 640℃, hold for 2.0h, then air cool.

[0058] Example 2:

[0059] This embodiment provides a manufacturing process for steel bars used in automotive heat-resistant fasteners. The specific process is as follows:

[0060] The chemical composition and mass percentage of the steel bars for automotive heat-resistant fasteners are as follows: C: 0.24%, Si: 0.26%, Mn: 0.49%, P: 0.012%, S: 0.006%, Cr: 1.59%, Ni: 0.05%, Mo: 0.28%, V: 0.20%, Cu: 0.05%, with the balance being Fe and unavoidable impurities.

[0061] Process route: ECOARC eco-friendly electric furnace smelting → LF furnace refining → RH refining → continuous casting → annealing → heating furnace heating → rolling → heat holding → heat treatment → finishing → inspection → packaging and warehousing → shipment;

[0062] (1) Ecological electric furnace smelting

[0063] The molten iron loading was 42t; the scrap steel loading was: 20t of alloy structural steel cuts, 44t of heavy scrap steel, and 10t of bale-shaped scrap steel; the tapping temperature was 1606℃, with C at 0.08% and P at 0.008% at tapping; slag, pre-deoxidizer, and ferroalloys were added when 1 / 4 of the steel was tapped, resulting in a tapping volume of 109t and a smelting cycle of 40min. Alloy additives per ton of steel included: 5.1kg / t silicon manganese, 10kg / t high-carbon ferrochrome, 16.2kg / t low-carbon ferrochrome, and 1.1kg / t aluminum wire (10mm). Auxiliary materials per ton of steel included: 40kg / t quicklime (35mm), 25kg / t magnesite (40mm), 6.0kg / t ladle ash, 20kg / t small coke lumps, and 18kg / t coking CDQ powder.

[0064] (2) LF furnace refining

[0065] The LF inlet temperature is 1545℃, and the slag is heated by a high current of 35500A. 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 to analyze the chemical composition. Alloy is added according to the target value of chemical composition, and carbon is added to promote the rapid melting and homogenization of alloy and carbon powder. When the molten steel temperature reaches 1603℃, 1.5 kg / t of diffusion deoxidizer alumina balls is added for diffusion deoxidation. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1625℃, 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 temperature reaches 1646℃ and leaves the furnace. The LF smelting cycle is 64 minutes. The following alloys are added: ferrosilicon 1.1 kg / t, high-carbon ferromanganese 2.1 kg / t, high-carbon ferrochrome 3.9 kg / t, ferromolybdenum 0.45 kg / t, ferrovanadium (FeV50-B) 3.5 kg / t, and aluminum wire (Φ10mm) 1.0 m / t. The following auxiliary materials are added: active lime (35mm) 4.0 kg / t, silicon carbide (5mm) 2.1 kg / t, and coke particles 0.77 kg / t.

[0066] (3) RH refining

[0067] The inlet temperature is 1585℃, the operation time is 46min, the argon pressure is controlled at 0.1MPa before the vacuum pump is started, so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum degree reaches 105Pa, 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, 2.0m / t of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t of covering agent are added. The outlet temperature is 1586℃.

[0068] (4) Continuous casting

[0069] The ladle temperature upon arrival is 1570℃, the molten steel volume is 98t, the tundish H is controlled at 1.4ppm, the entire casting process is protected, and medium carbon steel protective slag is used in the crystallizer.

[0070] (5) Annealing

[0071] The continuously cast billet was annealed at a temperature of 647℃ for 32 hours and a tapping temperature of 160℃.

[0072] (6) Heating process

[0073] Heating process: Inlet temperature of 520℃, preheating zone temperature requirement of 680℃, time 1.4h; heating zone 2 temperature requirement of 854℃, time 1.4h; heating zone 1 temperature requirement of 1198℃, time 1.5h; soaking zone temperature requirement of 1200℃, time 1.3h; tapping temperature of 1190℃.

[0074] (7) Rolling process

[0075] The initial rolling temperature was 1020℃, and the final rolling temperature was 855℃.

[0076] The initial rolling process for continuously cast billets is as follows: 9 rolling passes with the following reduction amounts: Turning steel → 1st pass reduction 65mm → 2nd pass reduction 70mm → Turning steel → 3rd pass reduction 64mm → 4th pass reduction 90mm → Turning steel → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → Turning steel → 9th pass reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters an 8-stand continuous rolling mill group for further rolling.

[0077] Rolling process of raw material: 8 rolling passes. The first pass is 229mm high and 245mm wide; the second pass is 192mm high and 235mm wide; the third pass is 200mm high and 195mm wide; the fourth pass is 169mm high and 212.8mm wide; the fifth pass is 177mm high and 180mm wide; the sixth pass is 141mm high and 192mm wide; the seventh pass is 152mm high and 152mm wide; the eighth pass is 152mm high and 152mm wide; the finished product is produced after 8 passes.

[0078] (8) Thermal Insulation Process

[0079] Insulation process: steel insulation, temperature in the lower insulation pit is 570℃, insulation time is 53 hours, and the temperature after exiting the pit is 150℃.

[0080] (9) Heat treatment process

[0081] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0082] 1) Quenching: 900℃, hold for 1.0h, oil cooling;

[0083] 2) Tempering: 640℃, hold for 2.0h, then air cool.

[0084] Example 3:

[0085] This embodiment provides a manufacturing process for steel bars used in automotive heat-resistant fasteners. The specific process is as follows:

[0086] The chemical composition and mass percentage of the steel bars for automotive heat-resistant fasteners are as follows: C: 0.25%, Si: 0.26%, Mn: 0.50%, P: 0.010%, S: 0.005%, Cr: 1.60%, Ni: 0.05%, Mo: 0.28%, V: 0.20%, Cu: 0.05%, with the balance being Fe and unavoidable impurities.

[0087] Process route: ECOARC eco-friendly electric furnace smelting → LF furnace refining → RH refining → continuous casting → annealing → heating furnace heating → rolling → heat holding → heat treatment → finishing → inspection → packaging and warehousing → shipment;

[0088] (1) Ecological electric furnace smelting

[0089] The molten iron loading was 41t; the scrap steel loading was: 20t of alloy structural steel cuts, 44t of heavy scrap steel, and 10t of bale-shaped scrap steel; the tapping temperature was 1607℃, with C at 0.08% and P at 0.009% at tapping; slag, pre-deoxidizer, and ferroalloys were added when 1 / 4 of the steel was tapped, resulting in a tapping volume of 110t and a smelting cycle of 39min. Alloy additives per ton of steel included: 5.1kg / t silicon manganese, 10kg / t high-carbon ferrochrome, 16kg / t low-carbon ferrochrome, and 1.1kg / t aluminum wire (10mm). Auxiliary materials per ton of steel included: 40kg / t quicklime (35mm), 25kg / t magnesite (40mm), 6.1kg / t ladle ash, 20kg / t small coke lumps, and 18kg / t coking CDQ powder.

[0090] (2) LF furnace refining

[0091] The LF inlet temperature is 1545℃, and the slag is heated by a high current of 35700A. 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 to analyze the chemical composition. Alloy is added according to the target value of chemical composition, and carbon is added to promote the rapid melting and homogenization of alloy and carbon powder. When the molten steel temperature reaches 1603℃, 1.5 kg / t of diffusion deoxidizer alumina balls is added for diffusion deoxidation. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1625℃, 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 temperature reaches 1644℃ and leaves the station. The LF smelting cycle is 67 minutes. The following alloys are added: ferrosilicon 1.1 kg / t, high-carbon ferromanganese 2.1 kg / t, high-carbon ferrochrome 3.9 kg / t, ferromolybdenum 0.44 kg / t, ferrovanadium (FeV50-B) 3.5 kg / t, and aluminum wire (Φ10mm) 1.1 m / t. The following auxiliary materials are added: active lime (35mm) 4.0 kg / t, silicon carbide (5mm) 2.1 kg / t, and coke particles 0.78 kg / t.

[0092] (3) RH refining

[0093] The inlet temperature is 1584℃, the operation time is 48min, the argon pressure is controlled at 0.1MPa before the vacuum pump is started, so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum degree reaches 103Pa, 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, 2.0m / t of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t of covering agent are added. The outlet temperature is 1586℃.

[0094] (4) Continuous casting

[0095] The ladle temperature upon arrival is 1570℃, the molten steel volume is 101t, the tundish H is controlled at 1.4ppm, the entire process is protected during casting, and medium carbon steel protective slag is used in the crystallizer.

[0096] (5) Annealing

[0097] The continuously cast billet was annealed at a temperature of 645℃ for 32 hours and a tapping temperature of 140℃.

[0098] (6) Heating process

[0099] Heating process: Inlet temperature of 500℃, preheating zone temperature requirement of 680℃, time 1.3h; heating zone 2 temperature requirement of 854℃, time 1.4h; heating zone 1 temperature requirement of 1195℃, time 1.5h; soaking zone temperature requirement of 1198℃, time 1.3h; tapping temperature of 1190℃.

[0100] (7) Rolling process

[0101] The initial rolling temperature was 1010℃, and the final rolling temperature was 835℃.

[0102] The initial rolling process for continuously cast billets is as follows: 9 rolling passes with the following reduction amounts: Turning steel → 1st pass reduction 65mm → 2nd pass reduction 70mm → Turning steel → 3rd pass reduction 64mm → 4th pass reduction 90mm → Turning steel → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → Turning steel → 9th pass reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters an 8-stand continuous rolling mill group for further rolling.

[0103] Rolling process of raw material: 8 rolling passes. The first pass is 229mm high and 245mm wide; the second pass is 192mm high and 235mm wide; the third pass is 200mm high and 195mm wide; the fourth pass is 169mm high and 212.8mm wide; the fifth pass is 177mm high and 180mm wide; the sixth pass is 141mm high and 192mm wide; the seventh pass is 152mm high and 152mm wide; the eighth pass is 152mm high and 152mm wide; the finished product is produced after 8 passes.

[0104] (8) Thermal Insulation Process

[0105] Insulation process: steel insulation, temperature in the insulation pit is 570℃, insulation time is 52 hours, and the temperature after exiting the pit is 160℃.

[0106] (9) Heat treatment process

[0107] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0108] 1) Quenching: 900℃, hold for 1.0h, oil cooling;

[0109] 2) Tempering: 640℃, hold for 2.0h, then air cool.

[0110] Example 4:

[0111] This embodiment provides a manufacturing process for steel bars used in automotive heat-resistant fasteners. The specific process is as follows:

[0112] The chemical composition and mass percentage of the steel bars for automotive heat-resistant fasteners are as follows: C: 0.24%, Si: 0.26%, Mn: 0.49%, P: 0.011%, S: 0.006%, Cr: 1.59%, Ni: 0.05%, Mo: 0.30%, V: 0.19%, Cu: 0.05%, with the balance being Fe and unavoidable impurities.

[0113] Process route: ECOARC eco-friendly electric furnace smelting → LF furnace refining → RH refining → continuous casting → annealing → heating furnace heating → rolling → heat holding → heat treatment → finishing → inspection → packaging and warehousing → shipment;

[0114] (1) Ecological electric furnace smelting

[0115] The molten iron loading was 43t; the scrap steel loading was: 20t of alloy structural steel cuts, 44t of heavy scrap steel, and 10t of bale-shaped scrap steel; the tapping temperature was 1606℃, with C at 0.09% and P at 0.008% at tapping; slag, pre-deoxidizer, and ferroalloys were added when 1 / 4 of the steel was tapped, resulting in a tapping volume of 109t and a smelting cycle of 40min. Alloy additives per ton of steel included: 5.1kg / t silicon manganese, 10.2kg / t high-carbon ferrochrome, 16kg / t low-carbon ferrochrome, and 1.1kg / t aluminum wire segments (10-16mm). Auxiliary materials per ton of steel included: 40kg / t active lime (35mm), 25kg / t magnesite (40mm), 6.0kg / t ladle ash, 20kg / t small coke lumps, and 18kg / t coking CDQ powder.

[0116] (2) LF furnace refining

[0117] The LF inlet temperature is 1547℃, and the slag is heated by a high current of 35700A. 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 to analyze the chemical composition. Alloy is added according to the target value of chemical composition, and carbon is added to promote the rapid melting and homogenization of alloy and carbon powder. When the molten steel temperature reaches 1605℃, 1.5 kg / t of diffusion deoxidizer alumina balls is added for diffusion deoxidation. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1625℃, 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 temperature reaches 1648℃ and leaves the furnace. The LF smelting cycle is 63 minutes. The following alloys are added: ferrosilicon 1.1 kg / t, high-carbon ferromanganese 2.1 kg / t, high-carbon ferrochrome 3.9 kg / t, ferromolybdenum 0.43 kg / t, ferrovanadium (FeV50-B) 3.5 kg / t, and aluminum wire (Φ10mm) 1.0 m / t. The following auxiliary materials are added: active lime (35mm) 4.1 kg / t, silicon carbide (5mm) 2.1 kg / t, and coke particles 0.77 kg / t.

[0118] (3) RH refining

[0119] The inlet temperature is 1586℃, the operation time is 48min, the argon pressure is controlled at 0.1MPa before the vacuum pump is started, so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum degree reaches 103Pa, 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, 2.0m / t of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t of covering agent are added. The outlet temperature is 1585℃.

[0120] (4) Continuous casting

[0121] The ladle temperature upon arrival was 1571℃, the molten steel volume was 98t, the tundish H was controlled at 1.5ppm, the entire casting process was protected, and medium carbon steel protective slag was used in the crystallizer.

[0122] (5) Annealing

[0123] The continuously cast billet was annealed at a temperature of 645℃ for 33 hours and a tapping temperature of 160℃.

[0124] (6) Heating process

[0125] Heating process: Inlet temperature of 520℃, preheating zone temperature requirement of 680℃, time 1.3h; heating zone 2 temperature requirement of 854℃, time 1.3h; heating zone 1 temperature requirement of 1198℃, time 1.3h; soaking zone temperature requirement of 1200℃, time 1.3h; tapping temperature of 1190℃.

[0126] (7) Rolling process

[0127] The initial rolling temperature was 1030℃, and the final rolling temperature was 860℃.

[0128] The initial rolling process for continuously cast billets is as follows: 9 rolling passes with the following reduction amounts: Turning steel → 1st pass reduction 65mm → 2nd pass reduction 70mm → Turning steel → 3rd pass reduction 64mm → 4th pass reduction 90mm → Turning steel → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → Turning steel → 9th pass reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters an 8-stand continuous rolling mill group for further rolling.

[0129] Rolling process of raw material: 8 rolling passes. The first pass is 229mm high and 245mm wide; the second pass is 192mm high and 235mm wide; the third pass is 200mm high and 195mm wide; the fourth pass is 169mm high and 212.8mm wide; the fifth pass is 177mm high and 180mm wide; the sixth pass is 141mm high and 192mm wide; the seventh pass is 152mm high and 152mm wide; the eighth pass is 152mm high and 152mm wide; the finished product is produced after 8 passes.

[0130] (8) Thermal Insulation Process

[0131] 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 150℃.

[0132] (9) Heat treatment process

[0133] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0134] 1) Quenching: 900℃, hold for 1.0h, oil cooling;

[0135] 2) Tempering: 640℃, hold for 2.0h, then air cool.

[0136] Example 5:

[0137] This embodiment provides a manufacturing process for steel bars used in automotive heat-resistant fasteners. The specific process is as follows:

[0138] The chemical composition and mass percentage of the steel bars for automotive heat-resistant fasteners are as follows: C: 0.25%, Si: 0.27%, Mn: 0.48%, P: 0.012%, S: 0.005%, Cr: 1.60%, Ni: 0.05%, Mo: 0.30%, V: 0.20%, Cu: 0.05%, with the balance being Fe and unavoidable impurities.

[0139] Process route: ECOARC eco-friendly electric furnace smelting → LF furnace refining → RH refining → continuous casting → annealing → heating furnace heating → rolling → heat holding → heat treatment → finishing → inspection → packaging and warehousing → shipment;

[0140] (1) Ecological electric furnace smelting

[0141] The molten iron loading is 42t; the scrap steel loading is: 20t of alloy structural steel cuts, 44t of heavy scrap steel, and 10t of bale-shaped scrap steel; the tapping temperature is 1605℃, the carbon content at tapping is 0.08%, and the phosphorus content is 0.009%; slag, pre-deoxidizer, and ferroalloys are added when 1 / 4 of the steel has been tapped, the tapping volume is 110t, and the smelting cycle is 40min. Alloy additions per ton of steel: 5.1Kg / t silicon manganese, 10.0Kg / t high-carbon ferrochrome, 16Kg / t low-carbon ferrochrome, and 1.1Kg / t aluminum wire (10mm). Auxiliary materials additions per ton of steel: 40Kg / t active lime (35mm), 25Kg / t magnesite (40mm), 6.0Kg / t ladle ash, 20Kg / t small coke lumps, and 18Kg / t coking CDQ powder.

[0142] (2) LF furnace refining

[0143] The LF inlet temperature is 1545℃, and the slag is heated by a high current of 35800A. 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 to analyze the chemical composition. Alloy is added according to the target value of chemical composition, and carbon is added to promote the rapid melting and homogenization of alloy and carbon powder. When the molten steel temperature reaches 1605℃, add 1.5 kg / t of diffusion deoxidizer alumina balls for diffusion deoxidation. Close the furnace door for 11 minutes. When the molten steel temperature reaches 1625℃, 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 station when the molten steel temperature reaches 1645℃. The LF smelting cycle is 65 minutes. Add the following alloys: ferrosilicon 1.1 kg / t, high-carbon ferromanganese 2.1 kg / t, high-carbon ferrochrome 3.9 kg / t, ferromolybdenum 0.4 kg / t, ferrovanadium (FeV50-B) 3.5 kg / t, and aluminum wire (Φ10mm) 1.0 m / t. Add auxiliary materials: active lime (35mm) 4.0 kg / t, silicon carbide (5mm) 2.1 kg / t, and coke particles 0.77 kg / t.

[0144] (3) RH refining

[0145] The inlet temperature is 1586℃, the operation time is 45min, the argon pressure is controlled at 0.1MPa before the vacuum pump is started, 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 0.3MPa. After the static argon blowing is completed, 2.0m / t of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t of covering agent are added. The outlet temperature is 1588℃.

[0146] (4) Continuous casting

[0147] The ladle temperature upon arrival was 1572℃, the molten steel volume was 102t, the tundish H was controlled at 1.4ppm, the entire casting process was protected, and medium carbon steel protective slag was used in the crystallizer.

[0148] (5) Annealing

[0149] The continuously cast billet was annealed at a temperature of 645℃ for 32 hours and a tapping temperature of 170℃.

[0150] (6) Heating process

[0151] Heating process: Inlet temperature of 520℃, preheating zone temperature requirement of 670℃, time 1.4h; heating zone 2 temperature requirement of 855℃, time 1.4h; heating zone 1 temperature requirement of 1205℃, time 1.5h; soaking zone temperature requirement of 1200℃, time 1.3h; tapping temperature of 1190℃.

[0152] (7) Rolling process

[0153] The initial rolling temperature is 1000℃, and the final rolling temperature is 820℃.

[0154] The initial rolling process for continuously cast billets is as follows: 9 rolling passes with the following reduction amounts: Turning steel → 1st pass reduction 65mm → 2nd pass reduction 70mm → Turning steel → 3rd pass reduction 64mm → 4th pass reduction 90mm → Turning steel → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → Turning steel → 9th pass reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters an 8-stand continuous rolling mill group for further rolling.

[0155] Rolling process of raw material: 8 rolling passes. The first pass is 229mm high and 245mm wide; the second pass is 192mm high and 235mm wide; the third pass is 200mm high and 195mm wide; the fourth pass is 169mm high and 212.8mm wide; the fifth pass is 177mm high and 180mm wide; the sixth pass is 141mm high and 192mm wide; the seventh pass is 152mm high and 152mm wide; the eighth pass is 152mm high and 152mm wide; the finished product is produced after 8 passes.

[0156] (8) Thermal Insulation Process

[0157] 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 150℃.

[0158] (9) Heat treatment process

[0159] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0160] 1) Quenching: 900℃, hold for 1.0h, oil cooling;

[0161] 2) Tempering: 640℃, hold for 2.0h, then air cool.

[0162] The low-magnification microstructure test results of the steel bars (Φ150mm) for automotive heat-resistant fasteners prepared in Examples 1-5 are shown in Table 1, the non-metallic inclusion test results are shown in Table 2, and the mechanical properties are shown in Table 3.

[0163] Table 1. Low-magnification microstructure test results of steel bars for automotive heat-resistant fasteners prepared in Examples 1-5.

[0164] Table 2. Non-metallic inclusion test results of steel bars for automotive heat-resistant fasteners prepared in Examples 1-5.

[0165] Table 3. Mechanical property test results of steel bars for automotive heat-resistant fasteners prepared in Examples 1-5.

[0166] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A steel bar for heat-resistant fasteners for automobiles, characterized by, The automobile heat-resistant fastener steel bar has the following chemical components and mass percentages: C: 0.23-0.27%, Si: 0.20-0.35%, Mn: 0.42-0.60%, P: ≤0.015%, S: ≤0.012%, Cr: 1.52-1.70%, Ni: ≤0.25%, Mo: 0.26-0.33%, V: 0.16-0.25%, Cu: ≤0.15%, and the balance of Fe and inevitable impurities.

2. Process for the production of a steel bar for automotive heat-resistant fasteners according to claim 1, characterized in that, The production process route is as follows: ECOARC ecological electric furnace smelting, LF furnace refining, RH refining, continuous casting, annealing, heating furnace heating, rolling, heat preservation, and heat treatment. The ECOARC ecological electric furnace smelting process has a tapping temperature of 1600-1610 DEG C, C of 0.08-0.10% at tapping, P of ≤0.010%, and a smelting period of 35-45 min. The LF furnace refining process has an LF entering station temperature of 1540-1550 DEG C, leaves the station when the molten steel temperature reaches 1640-1650 DEG C, and has a LF smelting period of 60-70 min. The RH refining process has an entering station temperature of 1580-1590 DEG C, controls the argon pressure before the vacuum pump starts to ensure that the molten steel is not exposed to the slag surface, starts timing when the vacuum degree reaches 100-110 Pa, maintains for 10-15 min, and blows argon statically, and has an exiting station temperature of 1580-1590 DEG C and an operation time of 40-50 min. The continuous casting process has a ladle entering station temperature of 1565-1575 DEG C, a tundish H control of ≤2 ppm, and full-process protective casting, and uses medium-carbon steel protective slag in the crystallizer. The annealing process has an annealing temperature of 640-650 DEG C, an annealing time of 30-35 h, and an out-of-furnace temperature of ≤200 DEG C. The heating furnace heating process has a heating furnace entering temperature of 450-560 DEG C, a soaking section temperature controlled at 1190-1210 DEG C, and a time of 1.3-1.5 h, and has a tapping temperature of 1185-1195 DEG C. The rolling process has a primary rolling temperature of 1000-1050 DEG C and a finish rolling temperature of 800-900 DEG C. The heat preservation process has a down heat preservation pit temperature of 550-590 DEG C, a heat preservation time of 50-55 h, and an out-of-pit temperature of ≤180 DEG C.

3. Process for the production of automotive heat-resistant fastener steel bar according to claim 2, characterized in that, The ECOARC ecological electric furnace smelting process adds slag, pre-deoxidizer, and ferroalloy at 1 / 4-1 / 3 of the tapping, and the alloy ton-steel addition amount is: silicon manganese 5.0-5.2 Kg / t, high-carbon chromium iron 10-10.5 Kg / t, low-carbon chromium iron 16-16.5 Kg / t, aluminum wire segment (10-16 mm) 1.0-1.2 kg / t; the auxiliary material ton-steel addition amount is: active lime (10-70 mm) 40-41 kg / t, magnesite (10-60 mm) 25-26 kg / t, ladle ash 6-6.2 kg / t, small coke block 20-21 kg / t, and coking CDQ powder 18-19 kg / t.

4. Process for the production of automotive heat-resistant fastener steel bar according to claim 2, characterized in that, The ECOARC ecological electric furnace smelting process has the following smelting raw materials: molten iron 38-45 t, alloy structural steel head 20-21 t, heavy scrap steel 43-45 t, and package block scrap steel 10-11 t.

5. The process for producing a steel bar for automotive heat-resistant fasteners according to claim 2, characterized in that, The LF furnace refining process, after entering the LF station, the slag is melted at a large current of 35000-36000A, when the slag surface fluctuates, the molten steel and the electric arc are not exposed, the active lime is supplemented, after 5-6 minutes, the alloy is supplemented according to the target value of the chemical composition, and the carbon is supplemented to promote the rapid melting and homogenization of the alloy and the carbon powder; when the temperature of the molten steel reaches 1600-1610℃, 1.5-1.6kg / t of aluminum oxide balls are added for diffusion deoxidization, and the furnace door is closed for 10-13 minutes.

6. The process for producing a steel bar for automotive heat-resistant fasteners according to claim 2, characterized by, The LF furnace refining process, the supplement of the alloy includes: 1.1-1.2kg / t of ferrosilicon, 2.1-2.2kg / t of high-carbon ferromanganese, 3.9-4.0kg / t of high-carbon ferrochrome, 0.4-0.5kg / t of ferromolybdenum, 3.5-3.6kg / t of ferrovanadium, and 1-1.1m / t of aluminum wire (Φ10-Φ12mm); the supplement of the auxiliary material: 4-4.2kg / t of active lime, 2.1-2.2kg / t of silicon carbide, and 0.75-0.80kg / t of coke particles.

7. The process for producing a steel bar for automotive heat-resistant fasteners according to claim 2, characterized by, The RH refining process, before the vacuum pump is started, the argon pressure is controlled at 0.1-0.3MPa, during the argon blowing process, the argon pressure is adjusted to 0.3-0.5MPa, after the argon blowing is finished, 2-2.1m / t of silicon-calcium alloy cored wire (Φ14-Φ14.2mm) is added, and 0.6-0.7kg / t of covering agent is added.

8. Process for the production of automotive heat-resistant fastener steel bar according to claim 2, characterized in that, The heating furnace heating process, the temperature control in the preheating section is 660-700℃, and the time is 1.3-1.5h; the temperature control in the heating 2 section is 850-860℃, and the time is 1.3-1.5h; the temperature control in the heating 1 section is 1190-1220℃, and the time is 1.3-1.5h.

9. Process for the production of automotive heat-resistant fastener steel bar according to claim 2, characterized in that, The rolling process, the continuous casting billet primary rolling and blooming process: 9 passes, rolling reduction: turning over→1st pass reduction 64.9-65.1mm→2nd pass reduction 69.9-70.1mm→turning over→3rd pass reduction 63.9-64.1mm→4th pass reduction 89.9-90.1mm→turning over→5th pass reduction 41.9-42.1mm→6th pass reduction 39.9-40.1mm→7th pass reduction 34.9-35.1mm→8th pass reduction 33.9-34.1mm→turning over→9th pass reduction 81.9-82.1mm, through 3 sets of 850mm rolling mills, 1 set of 735mm rolling mill, and then entering 8 sets of continuous rolling mill trains. The production material rolling process comprises 8 passes, the first pass is high 228.9-229.1mm, wide 244.9-245.1mm; the second pass is high 191.9-192.1mm, wide 234.9-235.1mm; the third pass is high 199.9-200.1mm, wide 194.9-195.1mm; the fourth pass is high 168.9-169.1mm, wide 212.7-212.9mm; the fifth pass is high 176.9-177.1mm, wide 179.9-180.1mm; the sixth pass is high 140.9-141.1mm, wide 191.9-192.1mm; the seventh pass is high 151.9-152.1mm, wide 151.9-152.1mm; the eighth pass is high 151.9-152.1mm, wide 151.9-152.1mm; the finished product is discharged after 8 passes.

10. Process for the production of automotive heat-resistant fastener steel bar according to claim 2, characterized in that, The heat treatment process comprises the following steps: 1) quenching: 890-910℃, holding for 0.9-1.2h, oil cooling; 2) tempering: 630-650℃, holding for 1.9-2.2h, air cooling.

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