Production and preparation method of steel for ecological electric furnace process automobile engine connecting rod

Abstract

The invention discloses a production and preparation method of steel for an ecological electric furnace process automobile engine connecting rod, which comprises the following chemical components in percentage by mass: 0.38 to 0.42 percent of C, 0.22 to 0.35 percent of Si, 0.55 to 0.70 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.008 percent of S, 0.65 to 0.80 percent of Cr, 1.30 to 1.55 percent of Ni, less than or equal to 0.15 percent of Cu, 0.16 to 0.23 percent of Mo and the balance of iron and inevitable impurities. The process route comprises the steps of ECOARC ecological electric furnace + LF refining + RH refining + billet continuous casting-heating furnace heating-rolling process-heat preservation, the produced steel bar for the automobile engine connecting rod meets the mechanical property requirement, and the steel purity is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of special steel technology, specifically to an eco-friendly electric furnace process for producing steel for automotive engine connecting rods. Background Technology

[0002] The connecting rod of an automotive engine consists of the connecting rod body, connecting rod big end cap, connecting rod small end bushing, connecting rod big end bearing, and connecting rod bolts (or screws). The connecting rod assembly bears the force of the gas transmitted from the piston pin, as well as its own oscillation and the reciprocating inertial force of the piston assembly; the magnitude and direction of these forces change periodically. The engine connecting rod operates in a harsh environment, placing extremely stringent requirements on the wear resistance, fatigue life, and other comprehensive performance characteristics of the steel used in the connecting rod. As a crucial component of the transmission system, the geared engine connecting rod has stringent quality requirements.

[0003] The quality of the steel used in engine connecting rods directly affects the service life and wear resistance of the transmission system, and even the safety of the entire transmission system during operation.

[0004] Therefore, it is essential to develop steel bars for automotive engine connecting rods with excellent mechanical properties, high hardness, and high steel purity to meet the requirements of high-end products. Summary of the Invention

[0005] The purpose of this invention is to provide a manufacturing process for steel bars used in automotive engine connecting rods. This method employs an ECOARC eco-friendly electric furnace + LF + RH + continuous casting smelting process to produce steel bars for automotive engine connecting rods, meeting high-end application requirements. It represents a breakthrough in the mass production of automotive engine connecting rod steel bars using the eco-friendly electric furnace continuous casting process. This method ensures the mechanical properties, high hardness, and high purity of the finished steel bars for automotive engine connecting rods, while also guaranteeing the surface quality of the steel bars.

[0006] To achieve the aforementioned objectives, this invention provides a manufacturing process for steel bars used in automotive engine connecting rods, including composition and process design. The specific steps are: ECOARC eco-friendly electric furnace + LF + RH + continuous casting billet → heating furnace → rolling process. This method meets the quality requirements for steel bars used in automotive engine connecting rods, and also achieves the required standards for mechanical properties, high hardness, and high steel purity.

[0007] A steel bar for connecting rods in automobile engines has the following chemical composition by mass percentage: C: 0.38%–0.42%, Si: 0.22%–0.35%, Mn: 0.55%–0.70%, P: ≤0.015%, S: ≤0.008%, Cr: 0.65%–0.80%, Ni: 1.30%–1.55%, Cu: ≤0.15%, Mo: 0.16%–0.23%, with the balance being iron and unavoidable impurities.

[0008] A manufacturing process for steel bars used in automotive engine connecting rods, the process route including: ECOARC eco-friendly electric furnace + LF refining + RH refining + continuous casting billet → heating furnace heating → rolling process → heat preservation.

[0009] The eco-friendly electric furnace smelting process involves: using scrap steel, with scrap steel accounting for 100% by mass fraction; the scrap steel loading is 113-118t, the tapping temperature is 1645-1650℃, the smelting cycle is 55-65min, the tapping time is 1.8-2.2min, the carbon content at tapping is 0.15-0.20%, and the phosphorus content is ≤0.010%. Auxiliary materials and alloys are added when 1 / 4 to 1 / 3 of the steel has been tapped, and the tapping amount is 108-115t. Alloy steel addition per ton: 4.5-4.6 kg / t silicon manganese, 4.5-4.6 kg / t high-carbon ferromanganese, 15-15.5 kg / t high-carbon ferrochrome, 14.5-14.8 kg / t low-carbon ferrochrome, 2.2-2.3 kg / t aluminum ferro (Φ40-70mm), 1.8-1.9 m / t aluminum wire segments (Φ10-12mm, length 20-30mm), 90-91 kg / t alloy structural steel cut-off pieces, heavy-duty... Scrap steel (≥800mm*600mm) 940~943Kg / t; Auxiliary materials added per ton of steel: steel ladle ash 5.4~5.5Kg / t, dolomite (Φ20~70mm) 16~16.5Kg / t, active lime (Φ10~70mm) 41~42Kg / t, coke granules (Φ20~60mm) 33~34Kg / t, graphite briquettes (Φ20~60mm) 7.2~7.3Kg / t.

[0010] Based on the above technical solution, further, the LF refining process involves: using a high current of 20000-22000A to heat and slag; when the slag surface fluctuates and the molten steel and electric arc are not exposed, adding active lime; and taking a sample for the first time to analyze the chemical composition after 5 minutes. Alloy and silicon carbide are then added according to the target chemical composition values. The alloy and silicon carbide should be added to the argon gas flow to promote rapid melting and homogenization of the alloy and silicon carbide. When the molten steel temperature reaches 1565-1575℃, add 2-3 kg / t of diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10-15 minutes. When the molten steel temperature reaches 1575-1585℃, take a second sample to analyze the chemical composition to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, the smelting cycle is 70-80 minutes. The amount of alloy added per ton of steel is as follows: ferrosilicon 2.0-2.1 kg / t, high carbon ferromanganese 3.5-3.6 kg / t, high carbon ferrochrome 5.8-5.9 kg / t, alumina balls (Φ10-15mm) 1.5-1.6 kg / t, ferromolybdenum (FeMo60-B) 3.0-3.1 kg / t, and aluminum wire (Φ10-12mm) 1.1-1.2 m / t. Additional auxiliary materials per ton of steel: 9-9.2 kg / t of active lime (Φ10-70mm) and 0.8-0.9 kg / t of silicon carbide (Φ2-5mm).

[0011] Based on the above technical solution, the RH refining process is further defined as follows: inlet temperature 1640–1650℃, operation time 30–34 minutes, argon pressure controlled at 0.1–0.3 MPa before vacuum pump startup to prevent molten steel exposure due to slight slag movement, timing begins when vacuum reaches 100–110 Pa and maintained for 10–15 minutes, while simultaneously adjusting argon pressure to 0.3–0.5 MPa. After static argon blowing, 2–2.1 meters of silicon-calcium alloy cored wire (Φ12–14 mm) per t of steel and 0.6–0.7 kg / t of covering agent (by mass percentage, main components: SiO2: ≥50%; CaO: ≤10%; FC free carbon: 15–30%, balance being impurities) are added, with an outlet temperature of 1580–1590℃.

[0012] Based on the above technical solution, the continuous casting is further defined as follows: the ladle temperature is 1590-1595℃, the molten steel volume is 100-105t, the H in the tundish is controlled to ≤2ppm, the casting is protected throughout the process, and medium carbon steel protective slag is used for the crystallizer.

[0013] Based on the above technical solution, further, the heating process is as follows: the furnace inlet temperature is 350℃~540℃, the preheating section temperature is required to be 600℃~650℃, and the time is 1.0~1.5h; the second heating section temperature is required to be 850℃~870℃, and the time is 1.0~1.5h; the first heating section temperature is required to be 1210℃~1240℃, and the time is 1.0~1.5h; the soaking section temperature is required to be 1210℃~1230℃, and the time is 1.0~1.5h; the tapping temperature is 1170℃~1190℃.

[0014] Based on the above technical solution, the rolling process is further as follows:

[0015] Billeting process: The billet is started using a BD primary rolling mill, with 9 rolling passes. The rolling reduction is as follows: Turning steel → 1st pass reduction 65-65.2mm → 2nd pass reduction 70-70.2mm → Turning steel → 3rd pass reduction 64-64.2mm → 4th pass reduction 90-90.2mm → Turning steel → 5th pass reduction 42-42.2mm → 6th pass reduction 40-40.2mm → 7th pass reduction 35-35.2mm → 8th pass reduction 34-34.2mm → Turning steel → 9th pass reduction 82-82.2mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters an 8-stand continuous rolling mill group for rolling.

[0016] Finished product rolling process: The intermediate billet is rolled to a height of 232-232.2 mm and a width of 268-268.2 mm; the first pass is rolled to a height of 229-229.2 mm and a width of 245-245.2 mm; the second pass is rolled to a height of 192-192.2 mm and a width of 235-235.2 mm; the third pass is rolled to a height of 200-200.2 mm and a width of 195-195.2 mm; the fourth pass is rolled to a height of 173-173.2 mm and a width of 205-205.2 mm; the fifth pass is rolled to a height of 182.4-182.5 mm and a width of 182.4-182.5 mm; the sixth pass is rolled to a height of 182.4-182.5 mm and a width of 182.4-182.5 mm; the finished product is produced after the sixth pass.

[0017] Based on the above technical solution, the insulation process is further as follows: the temperature of the lower insulation pit is ≥580℃, the insulation time is 50~55h, and the temperature of the pit exits is ≤130℃.

[0018] Based on the above technical solution, the dimensions of the continuously cast billet are further defined as 390mm*480mm.

[0019] Based on the above technical solution, the process route further includes heat preservation followed by finishing, inspection, packaging and warehousing, and then shipment.

[0020] Based on the above technical solution, the insulated steel section is further subjected to heat treatment, which includes the following steps:

[0021] 1) Quenching: 840~860℃, hold for 0.6~0.8h, oil cooling;

[0022] 2) Tempering: 195~205℃, hold for 1.8~2.2h, then water-cooled.

[0023] The beneficial effects of this invention are:

[0024] (1) Steel bars for connecting rods of automobile engines are produced using the ECOARC eco-friendly electric furnace + LF + RH + 390mm*480mm smelting and rolling processes. The production specification is Φ180mm, which meets the mechanical performance requirements and ensures the purity of the steel.

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

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

[0027] 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.

[0028] Example 1

[0029] 1Chemical composition

[0030] The chemical composition, by mass percentage, is C: 0.39%, Si: 0.27%, Mn: 0.59%, P: 0.011%, S: 0.005%, Cr: 0.72%, Ni: 1.39%, Cu: 0.08%, Mo: 0.19%, with the balance being iron and unavoidable impurities.

[0031] 2. Production process parameters for electric furnace continuous casting of steel bars for automotive engine connecting rods

[0032] Process route: 100t ECOARC eco-friendly electric furnace + LF + RH + 390mm*480mm continuous casting billet → heating in the heating furnace → rolling → heat preservation → finishing → inspection → packaging and warehousing → shipment. Among them:

[0033] (1) Ecological electric furnace smelting: 100% scrap steel; scrap steel loading amount 115t, tapping temperature 1647℃, smelting cycle 59min, tapping time 1.9min, C at tapping is 0.18%, P is 0.008%, auxiliary materials and alloys are added when 1 / 4 of the steel is tapped, and the steel output is 110t. Alloy addition per ton of steel: silicon manganese 4.5Kg / t, high carbon ferromanganese 4.5Kg / t, high carbon ferrochrome 15Kg / t, low carbon ferrochrome 14.6Kg / t, aluminum ferro (Φ50mm) 2.2Kg / t, aluminum wire segment (Φ10mm) 1.8m / t. Alloy structural steel cut-off head 90Kg / t, heavy scrap steel (1000mm*600mm) 942Kg / t; auxiliary materials added per ton of steel: steel ladle ash 5.4Kg / t, dolomite (Φ40mm) 16.2Kg / t, active lime (Φ40mm) 41Kg / t, coke granules (Φ40mm) 33Kg / t, graphite briquettes (Φ50mm) 7.2Kg / t.

[0034] (2) LF furnace: Use a 20000A high current to heat up and slag. When the slag surface fluctuates and the molten steel and electric arc are not exposed, add active lime. After 5 minutes, take the first sample to analyze the chemical composition. Add alloy and silicon carbide according to the target value of chemical composition. The alloy and silicon carbide should be added to the argon gas flow to promote the rapid melting and homogenization of the alloy and silicon carbide. When the molten steel temperature reaches 1568℃, add 2.5 kg / t of diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 12 minutes. When the molten steel temperature reaches 1578℃, 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, the smelting cycle is 75 minutes. Add the following alloys: 2.0 kg / t ferrosilicon, 3.5 kg / t high-carbon ferromanganese, 5.8 kg / t high-carbon ferrochrome, 1.5 kg / t alumina balls (Φ10mm), 3.0 kg / t ferromolybdenum (FeMo60-B), and 1.1 m / t aluminum wire (Φ10mm). Add auxiliary materials: 9 kg / t quicklime (Φ40mm) and 0.8 kg / t silicon carbide (Φ3mm).

[0035] (3) RH refining: The inlet temperature is 1645℃, the operation time is 32min, the argon pressure is controlled at 0.15MPa 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 10min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 2m / t of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t of covering agent (main components SiO2: 55%; CaO: 8%; FC free carbon: 18%; the balance is impurities) are added. The outlet temperature is 1585℃.

[0036] (4) Continuous casting: The ladle temperature is 1590℃, the steel volume is 100t, the H in the tundish is controlled at 1.2ppm, the whole process is protected during casting, and medium carbon steel protective slag is used for the crystallizer.

[0037] (5) Heating process

[0038] Heating process: Inlet temperature to the heating furnace is 480℃; preheating zone temperature is required to be 620℃ for 1.2 hours; heating zone 2 temperature is required to be 850℃ for 1.3 hours; heating zone 1 temperature is required to be 1220℃ for 1.2 hours; soaking zone temperature is required to be 1220℃ for 1.2 hours; tapping temperature is 1180℃.

[0039] (6) Rolling process:

[0040] Billeting process: The billet is started using a BD primary rolling mill, with 9 rolling passes. The rolling reduction is as follows: turn the steel over → 1st pass reduction 65mm → 2nd pass reduction 70mm → turn the steel over → 3rd pass reduction 64mm → 4th pass reduction 90mm → turn the steel over → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → turn the steel over → 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.

[0041] Finished product rolling process: The intermediate billet is rolled to a height of 232mm and a width of 268mm; 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 173mm high and 205mm wide; the fifth pass is 182.4mm high and 182.4mm wide; the sixth pass is 182.4mm high and 182.4mm wide; the finished product is produced after the sixth pass.

[0042] (7) Thermal Insulation Process

[0043] Insulation process: The temperature in the lower insulation pit is 600℃, the insulation time is 52 hours, and the temperature after exiting the pit is 100℃.

[0044] Example 2

[0045] 1Chemical composition

[0046] The chemical composition, by mass percentage, is: C: 0.40%, Si: 0.30%, Mn: 0.61%, P: 0.012%, S: 0.005%, Cr: 0.72%, Ni: 1.38%, Cu: 0.06%, Mo: 0.20%, with the balance being iron and unavoidable impurities. Among these:

[0047] 2. Production process parameters for electric furnace continuous casting of steel bars for automotive engine connecting rods

[0048] Process route: 100t ECOARC ecological electric furnace + LF + RH + 390mm*480mm continuous casting billet → heating furnace heating → rolling → heat preservation → finishing → inspection → packaging and warehousing → delivery.

[0049] (1) Ecological electric furnace smelting: 100% scrap steel; scrap steel loading amount 116t, tapping temperature 1649℃, smelting cycle 58min, tapping time 1.9min, C at tapping is 0.18%, P is 0.007%, auxiliary materials and alloys are added when 1 / 4 of the steel is tapped, and the steel output is 111t. Alloy addition per ton of steel: silicon manganese 4.5Kg / t, high carbon ferromanganese 4.5Kg / t, high carbon ferrochrome 15Kg / t, low carbon ferrochrome 14.6Kg / t, aluminum ferro (Φ50mm) 2.2Kg / t, aluminum wire segment (Φ10mm) 1.8m / t. Alloy structural steel cut-off head 90Kg / t, heavy scrap steel (1000mm*600mm) 941Kg / t; auxiliary materials added per ton of steel: steel ladle ash 5.4Kg / t, dolomite (Φ40mm) 16Kg / t, active lime (Φ50mm) 41Kg / t, coke granules (Φ50mm) 33Kg / t, graphite briquettes (Φ50mm) 7.2Kg / t.

[0050] (2) LF furnace: Use a 20000A high current to heat up and slag. When the slag surface fluctuates and the molten steel and electric arc are not exposed, add active lime. After 5 minutes, take the first sample to analyze the chemical composition. Add alloy and silicon carbide according to the target value of chemical composition. The alloy and silicon carbide should be added to the argon gas flow to promote the rapid melting and homogenization of the alloy and silicon carbide. When the molten steel temperature reaches 1569℃, add 2kg / t of diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1580℃, 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, the smelting cycle is 74 minutes. Add the following alloys: ferrosilicon 2.0kg / t, high-carbon ferromanganese 3.5kg / t, high-carbon ferrochrome 5.8kg / t, alumina balls (Φ10mm) 1.5kg / t, ferromolybdenum (FeMo60-B) 3.0kg / t, and aluminum wire (Φ10mm) 1.1m / t. Add auxiliary materials: active lime (10-70mm) 9kg / t and silicon carbide (Φ3mm) 0.8kg / t.

[0051] (3) RH refining: The inlet temperature is 1645℃, the operation time is 32min, 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 10min. At the same time, the argon pressure is adjusted to 0.4MPa. After the static argon blowing is completed, 2m / t of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t of covering agent (main components SiO2: 56%; CaO: 8%; FC free carbon: 20%; the balance is impurities) are added. The outlet temperature is 1586℃.

[0052] (4) Continuous casting: The ladle temperature is 1590℃, the steel volume is 100t, the H in the tundish is controlled at 1.2ppm, the whole process is protected during casting, and medium carbon steel protective slag is used for the crystallizer.

[0053] (5) Heating process

[0054] Heating process: Inlet temperature to the heating furnace is 450℃; preheating zone temperature is required to be 620℃ for 1.2 hours; heating zone 2 temperature is required to be 860℃ for 1.2 hours; heating zone 1 temperature is required to be 1220℃ for 1.2 hours; soaking zone temperature is required to be 1220℃ for 1.2 hours; tapping temperature is 1180℃.

[0055] (6) Rolling process:

[0056] Billeting process: The billet is started using a BD primary rolling mill, with 9 rolling passes. The rolling reduction is as follows: turn the steel over → 1st pass reduction 65mm → 2nd pass reduction 70mm → turn the steel over → 3rd pass reduction 64mm → 4th pass reduction 90mm → turn the steel over → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → turn the steel over → 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.

[0057] Finished product rolling process: The intermediate billet is rolled to a height of 232mm and a width of 268mm; 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 173mm high and 205mm wide; the fifth pass is 182.4mm high and 182.4mm wide; the sixth pass is 182.4mm high and 182.4mm wide; the finished product is produced after the sixth pass.

[0058] (7) Thermal Insulation Process

[0059] Insulation process: The temperature in the lower insulation pit is 600℃, the insulation time is 52 hours, and the temperature after exiting the pit is 110℃.

[0060] Example 3

[0061] 1Chemical composition

[0062] The chemical composition, by mass percentage, is: C: 0.39%, Si: 0.28%, Mn: 0.60%, P: 0.010%, S: 0.005%, Cr: 0.70%, Ni: 1.38%, Cu: 0.07%, Mo: 0.21%, with the balance being iron and unavoidable impurities. Among these:

[0063] 2. Production process parameters for electric furnace continuous casting of steel bars for automotive engine connecting rods

[0064] Process route: 100t ECOARC ecological electric furnace + LF + RH + 390mm*480mm continuous casting billet → heating furnace heating → rolling → heat preservation → finishing → inspection → packaging and warehousing → delivery.

[0065] (1) Ecological electric furnace smelting: 100% scrap steel; scrap steel loading amount 115t, tapping temperature 1647℃, smelting cycle 57min, tapping time 1.9min, C at tapping is 0.17%, P is 0.009%, auxiliary materials and alloys are added when 1 / 4 of the steel is tapped, and the steel output is 110t. Alloy addition per ton of steel: silicon manganese 4.5Kg / t, high carbon ferromanganese 4.5Kg / t, high carbon ferrochrome 15.2Kg / t, low carbon ferrochrome 14.6Kg / t, aluminum ferro (Φ50mm) 2.2Kg / t, aluminum wire segment (Φ10mm) 1.8m / t. Alloy structural steel cut-off head 90Kg / t, heavy scrap steel (1000mm*600mm) 940Kg / t; auxiliary materials added per ton of steel: steel ladle ash 5.4Kg / t, dolomite (Φ45mm) 16Kg / t, active lime (Φ40mm) 41Kg / t, coke granules (Φ40mm) 33Kg / t, graphite briquettes (Φ50mm) 7.2Kg / t.

[0066] (2) LF furnace: Use a 20000A high current to heat up and slag. When the slag surface fluctuates and the molten steel and electric arc are not exposed, add active lime. After 5 minutes, take the first sample to analyze the chemical composition. Add alloy and silicon carbide according to the target value of chemical composition. The alloy and silicon carbide should be added to the argon gas flow to promote the rapid melting and homogenization of the alloy and silicon carbide. When the molten steel temperature reaches 1569℃, add 2 kg / t of diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1578℃, 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, the smelting cycle is 75 minutes. Add the following alloys: 2.0 kg / t ferrosilicon, 3.5 kg / t high-carbon ferromanganese, 5.8 kg / t high-carbon ferrochrome, 1.5 kg / t alumina balls (Φ10mm), 3.0 kg / t ferromolybdenum (FeMo60-B), and 1.1 m / t aluminum wire (Φ10mm). Add auxiliary materials: 9 kg / t quicklime (Φ40mm) and 0.8 kg / t silicon carbide (Φ3mm).

[0067] (3) RH refining: The inlet temperature is 1646℃, the operation time is 31min, 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, 2m / t of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t of covering agent (main components SiO2: 56%; CaO: 8%; FC free carbon: 19%) are added. The outlet temperature is 1585℃.

[0068] (4) Continuous casting: The ladle temperature is 1592℃, the steel volume is 102t, the H in the tundish is controlled at 1.0ppm, the whole process is protected during casting, and medium carbon steel protective slag is used for the crystallizer.

[0069] (5) Heating process

[0070] Heating process: Inlet temperature of 520℃, preheating zone temperature requirement of 620℃, time 1.2h; heating zone 2 temperature requirement of 850℃, time 1.2h; heating zone 1 temperature requirement of 1220℃, time 1.2h; soaking zone temperature requirement of 1220℃, time 1.2h; tapping temperature of 1185℃.

[0071] (6) Rolling process:

[0072] Billeting process: The billet is started using a BD primary rolling mill, with 9 rolling passes. The rolling reduction is as follows: turn the steel over → 1st pass reduction 65mm → 2nd pass reduction 70mm → turn the steel over → 3rd pass reduction 64mm → 4th pass reduction 90mm → turn the steel over → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → turn the steel over → 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.

[0073] Finished product rolling process: The intermediate billet is rolled to a height of 232mm and a width of 268mm; 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 173mm high and 205mm wide; the fifth pass is 182.4mm high and 182.4mm wide; the sixth pass is 182.4mm high and 182.4mm wide; the finished product is produced after the sixth pass.

[0074] (7) Thermal Insulation Process

[0075] Insulation process: The temperature in the lower insulation pit is 600℃, the insulation time is 53 hours, and the temperature after exiting the pit is 110℃.

[0076] Example 4

[0077] 1Chemical composition

[0078] The chemical composition, by mass percentage, is C: 0.40%, Si: 0.28%, Mn: 0.58%, P: 0.010%, S: 0.005%, Cr: 0.69%, Ni: 1.38%, Cu: 0.07%, Mo: 0.19%, with the balance being iron and unavoidable impurities.

[0079] 2. Production process parameters for electric furnace continuous casting of steel bars for automotive engine connecting rods

[0080] Process route: 100t ECOARC eco-friendly electric furnace + LF + RH + 390mm*480mm continuous casting billet → heating in the heating furnace → rolling → heat preservation → finishing → inspection → packaging and warehousing → shipment. Among them:

[0081] (1) Ecological electric furnace smelting: 100% scrap steel; scrap steel loading amount 115t, tapping temperature 1648℃, smelting cycle 58min, tapping time 2.0min, C at tapping is 0.17%, P is 0.007%, auxiliary materials and alloys are added when 1 / 4 of the steel is tapped, and the steel output is 111t. Alloy addition per ton of steel: silicon manganese 4.5Kg / t, high carbon ferromanganese 4.5Kg / t, high carbon ferrochrome 15.2Kg / t, low carbon ferrochrome 14.6Kg / t, aluminum ferro (Φ50mm) 2.2Kg / t, aluminum wire segment (Φ10mm) 1.8m / t. Alloy structural steel cut-off head 90Kg / t, heavy scrap steel (1000mm*600mm) 940Kg / t; auxiliary materials added per ton of steel: steel ladle ash 5.4Kg / t, dolomite (Φ40mm) 16.2Kg / t, active lime (Φ40mm) 41Kg / t, coke granules (Φ50mm) 33Kg / t, graphite briquettes (Φ50mm) 7.2Kg / t.

[0082] (2) LF furnace: Use a 20000A high current to heat up and slag. When the slag surface fluctuates and the molten steel and electric arc are not exposed, add active lime. After 5 minutes, take the first sample to analyze the chemical composition. Add alloy and silicon carbide according to the target value of chemical composition. The alloy and silicon carbide should be added to the argon gas flow to promote the rapid melting and homogenization of the alloy and silicon carbide. When the molten steel temperature reaches 1569℃, add 2 kg / t of diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1578℃, 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, the smelting cycle is 75 minutes. Add the following alloys: 2.0 kg / t ferrosilicon, 3.5 kg / t high-carbon ferromanganese, 5.8 kg / t high-carbon ferrochrome, 1.5 kg / t alumina balls (Φ10mm), 3.0 kg / t ferromolybdenum (FeMo60-B), and 1.1 m / t aluminum wire (Φ10mm). Add auxiliary materials: 9 kg / t quicklime (Φ40mm) and 0.8 kg / t silicon carbide (Φ3mm).

[0083] (3) RH refining: The inlet temperature is 1645℃, the operation time is 32min, 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 10min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 2m / t of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t of covering agent (main components SiO2: 57%; CaO: 7%; FC free carbon: 20%) are added. The outlet temperature is 1586℃.

[0084] (4) Continuous casting: The ladle temperature is 1592℃, the steel volume is 102t, the H in the tundish is controlled at 1.2ppm, the whole process is protected during casting, and medium carbon steel protective slag is used for the crystallizer.

[0085] (5) Heating process

[0086] Heating process: Inlet temperature of 510℃, preheating zone temperature requirement of 610℃, time 1.2h; heating zone 2 temperature requirement of 850℃, time 1.2h; heating zone 1 temperature requirement of 1220℃, time 1.2h; soaking zone temperature requirement of 1220℃, time 1.2h; tapping temperature of 1180℃.

[0087] (6) Rolling process:

[0088] Billeting process: The billet is started using a BD primary rolling mill, with 9 rolling passes. The rolling reduction is as follows: turn the steel over → 1st pass reduction 65mm → 2nd pass reduction 70mm → turn the steel over → 3rd pass reduction 64mm → 4th pass reduction 90mm → turn the steel over → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → turn the steel over → 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.

[0089] Finished product rolling process: The intermediate billet is rolled to a height of 232mm and a width of 268mm; 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 173mm high and 205mm wide; the fifth pass is 182.4mm high and 182.4mm wide; the sixth pass is 182.4mm high and 182.4mm wide; the finished product is produced after the sixth pass.

[0090] (7) Thermal Insulation Process

[0091] Insulation process: The temperature in the lower insulation pit is 590℃, the insulation time is 53 hours, and the temperature when the pit is removed is 115℃.

[0092] Example 5

[0093] 1Chemical composition

[0094] The chemical composition, by mass percentage, is: C: 0.39%, Si: 0.28%, Mn: 0.60%, P: 0.011%, S: 0.006%, Cr: 0.73%, Ni: 1.40%, Cu: 0.07%, Mo: 0.20%, with the balance being iron and unavoidable impurities.

[0095] 2. Production process parameters for electric furnace continuous casting of steel bars for automotive engine connecting rods

[0096] Process route: 100t ECOARC eco-friendly electric furnace + LF + RH + 390mm*480mm continuous casting billet → heating in the heating furnace → rolling → heat preservation → finishing → inspection → packaging and warehousing → shipment. Among them:

[0097] (1) Ecological electric furnace smelting: 100% scrap steel; scrap steel loading amount 114t, tapping temperature 1647℃, smelting cycle 59min, tapping time 2.0min, C at tapping is 0.18%, P is 0.008%, auxiliary materials and alloys are added when 1 / 4 of the steel is tapped, and the steel output is 112t. Alloy addition per ton of steel: silicon manganese 4.5Kg / t, high carbon ferromanganese 4.5Kg / t, high carbon ferrochrome 15.3Kg / t, low carbon ferrochrome 14.6Kg / t, aluminum ferro (Φ50mm) 2.2Kg / t, aluminum wire segment (Φ10mm) 1.8m / t. Alloy structural steel cut-off head 90Kg / t, heavy scrap steel (1000mm*600mm) 940Kg / t; Auxiliary materials added per ton of steel: steel ladle ash 5.4Kg / t, dolomite (Φ50mm) 16.2Kg / t, active lime (Φ40mm) 41Kg / t, coke granules (Φ50mm) 33Kg / t, graphite briquettes (Φ50mm) 7.2Kg / t.

[0098] (2) LF furnace: Use a 20000A high current to heat up and slag. When the slag surface fluctuates and the molten steel and electric arc are not exposed, add active lime. After 5 minutes, take the first sample to analyze the chemical composition. Add alloy and silicon carbide according to the target value of chemical composition. The alloy and silicon carbide should be added to the argon gas flow to promote the rapid melting and homogenization of the alloy and silicon carbide. When the molten steel temperature reaches 1568℃, add 2.3 kg / t of diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1578℃, 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, the smelting cycle is 76 minutes. Add the following alloys: 2.0 kg / t ferrosilicon, 3.5 kg / t high-carbon ferromanganese, 5.8 kg / t high-carbon ferrochrome, 1.5 kg / t alumina balls (Φ10mm), 3.0 kg / t ferromolybdenum (FeMo60-B), and 1.1 m / t aluminum wire (Φ10mm). Add auxiliary materials: 9 kg / t quicklime (Φ40mm) and 0.8 kg / t silicon carbide (Φ3mm).

[0099] (3) RH refining: The inlet temperature is 1645℃, the operation time is 31min, the argon pressure is controlled at 0.15MPa 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 0.4MPa. After the static argon blowing is completed, 2m / t of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t of covering agent (main components SiO2: 56%; CaO: 6%; FC free carbon: 18%) are added. The outlet temperature is 1585℃.

[0100] (4) Continuous casting: The ladle temperature is 1592℃, the steel volume is 102t, the H in the tundish is controlled at 1.2ppm, the whole process is protected during casting, and medium carbon steel protective slag is used for the crystallizer.

[0101] (5) Heating process

[0102] Heating process: Inlet temperature of 500℃, preheating zone temperature requirement of 620℃, time 1.2h; heating zone 2 temperature requirement of 860℃, time 1.3h; heating zone 1 temperature requirement of 1220℃, time 1.3h; soaking zone temperature requirement of 1220℃, time 1.3h; tapping temperature of 1180℃.

[0103] (6) Rolling process:

[0104] Billeting process: The billet is started using a BD primary rolling mill, with 9 rolling passes. The rolling reduction is as follows: turn the steel over → 1st pass reduction 65mm → 2nd pass reduction 70mm → turn the steel over → 3rd pass reduction 64mm → 4th pass reduction 90mm → turn the steel over → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → turn the steel over → 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.

[0105] Finished product rolling process: The intermediate billet is rolled to a height of 232mm and a width of 268mm; 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 173mm high and 205mm wide; the fifth pass is 182.4mm high and 182.4mm wide; the sixth pass is 182.4mm high and 182.4mm wide; the finished product is produced after the sixth pass.

[0106] (7) Thermal Insulation Process

[0107] Insulation process: The temperature in the lower insulation pit is 620℃, the insulation time is 52 hours, and the temperature when leaving the pit is 100℃.

[0108] Inspection results of finished products in Examples 1-5

[0109] (1) Low magnification structure of Φ180mm steel

[0110] Serial Number Generally loose Central loose Ingot segregation General speckled segregation Edge spot-like segregation standard ≤1.5 ≤1.5 ≤1.5 ≤1.0 ≤1.0 Example 1 0.5 0.5 0.5 0 0 Example 1 0.5 0.5 0.5 0 0 Example 2 0.5 0.5 0.5 0 0 Example 2 0.5 0.5 0.5 0 0 Example 3 0.5 0.5 0.5 0 0 Example 3 0.5 0.5 0.5 0 0 Example 4 0.5 0.5 0.5 0 0 Example 4 0.5 0.5 0.5 0 0 Example 5 0.5 0.5 0.5 0 0 Example 5 0.5 0.5 0.5 0 0

[0111] (2) Non-metallic inclusions in Φ180mm steel

[0112]

[0113]

[0114] (3) Mechanical properties of Φ180mm steel

[0115] The steel section after insulation undergoes the following heat treatment, resulting in the following mechanical properties:

[0116]

Claims

1. A steel bar for connecting rods in automobile engines, characterized in that, The composition by mass percentage is: C: 0.38%–0.42%, Si: 0.22%–0.35%, Mn: 0.55%–0.70%, P: ≤0.015%, S: ≤0.008%, Cr: 0.65%–0.80%, Ni: 1.30%–1.55%, Cu: ≤0.15%, Mo: 0.16%–0.23%, with the balance being iron and unavoidable impurities.

2. The method for preparing steel bars for automobile engine connecting rods according to claim 1, characterized in that, The method includes: ecological electric furnace smelting → LF refining → RH refining → continuous casting → heating furnace heating process → rolling process → heat preservation. The eco-friendly electric furnace smelting process involves: using scrap steel with a loading of 113-118 tons, a tapping temperature of 1645-1650℃, a smelting cycle of 55-65 minutes, a tapping time of 1.8-2.2 minutes, a carbon content of 0.15-0.20% and a phosphorus content of ≤0.010% at tapping, and the addition of auxiliary materials and alloys when 1 / 4 to 1 / 3 of the steel has been tapped, resulting in a tapping volume of 108-115 tons. The alloy addition per ton of steel is: 4.5-4.6 kg / t of silicon manganese, 4.5-4.6 kg / t of high-carbon ferromanganese, and high-carbon chromium... Iron 15-15.5 kg / t, low-carbon ferrochrome 14.5-14.8 kg / t, aluminum ferrochrome 2.2-2.3 kg / t, aluminum wire segments 1.8-1.9 m / t, alloy structural steel cuts 90-91 kg / t, heavy scrap steel 940-943 kg / t; Auxiliary materials added per ton of steel: steel ladle ash 5.4-5.5 kg / t, dolomite 16-16.5 kg / t, active lime 41-42 kg / t, coke granules 33-34 kg / t, graphite briquettes 7.2-7.3 kg / t; The LF refining process involves: using a high current of 20,000–22,000 A to heat and slag; when the slag surface fluctuates and the molten steel and electric arc are not exposed, adding active lime; taking a first sample after 5 minutes to analyze the chemical composition; and adding alloys and silicon carbide according to the target chemical composition values; when the molten steel temperature reaches 1565–1575℃, adding 2–3 kg / t of diffusion deoxidizer for diffusion deoxidation; closing the furnace door for 10–15 minutes; and taking a second sample to analyze the chemical composition when the molten steel temperature reaches 1575–1585℃ to confirm the chemical composition of each component. The deviation of elemental composition content from the target value is considered after a second sample is taken, and the smelting cycle is 70-80 minutes. The amount of alloy added per ton of steel is as follows: ferrosilicon 2.0-2.1 kg / t, high-carbon ferromanganese 3.5-3.6 kg / t, high-carbon ferrochrome 5.8-5.9 kg / t, alumina balls 1.5-1.6 kg / t, ferromolybdenum 3.0-3.1 kg / t, and aluminum wire 1.1-1.2 m / t. The amount of auxiliary materials added per ton of steel is as follows: active lime 9-9.2 kg / t and silicon carbide 0.8-0.9 kg / t.

3. The preparation method according to claim 2, characterized in that, The RH refining process is as follows: the inlet temperature is 1640–1650℃, the operation time is 30–34 minutes, the argon pressure is controlled at 0.1–0.3 MPa before the vacuum pump is started, so that the molten steel is not exposed when the slag surface is slightly moved. 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, 2–2.1 meters of silicon-calcium alloy cored wire per ton of steel and 0.6–0.7 kg of covering agent per ton of steel are added. The outlet temperature is 1580–1590℃.

4. The preparation method according to claim 2, characterized in that, The continuous casting process is as follows: the ladle temperature is 1590-1595℃, the molten steel volume is 100-105t, 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.

5. The preparation method according to claim 2, characterized in that, The heating process is as follows: the furnace inlet temperature is 350℃~540℃; the preheating section temperature is required to be 600℃~650℃ for 1.0~1.5h; the second heating section temperature is required to be 850℃~870℃ for 1.0~1.5h; the first heating section temperature is required to be 1210℃~1240℃ for 1.0~1.5h; the soaking section temperature is required to be 1210℃~1230℃ for 1.0~1.5h; and the tapping temperature is 1170℃~1190℃.

6. The preparation method according to claim 2, characterized in that, The rolling process is as follows: Billeting process: The billet is started using a BD primary rolling mill, with 9 rolling passes. The rolling reduction is as follows: Turning steel → 1st pass reduction 65-65.2mm → 2nd pass reduction 70-70.2mm → Turning steel → 3rd pass reduction 64-64.2mm → 4th pass reduction 90-90.2mm → Turning steel → 5th pass reduction 42-42.2mm → 6th pass reduction 40-40.2mm → 7th pass reduction 35-35.2mm → 8th pass reduction 34-34.2mm → Turning steel → 9th pass reduction 82-82.2mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters an 8-stand continuous rolling mill group for rolling. Finished product rolling process: The intermediate billet is rolled to a height of 232-232.2 mm and a width of 268-268.2 mm; the first pass is rolled to a height of 229-229.2 mm and a width of 245-245.2 mm; the second pass is rolled to a height of 192-192.2 mm and a width of 235-235.2 mm; the third pass is rolled to a height of 200-200.2 mm and a width of 195-195.2 mm; the fourth pass is rolled to a height of 173-173.2 mm and a width of 205-205.2 mm; the fifth pass is rolled to a height of 182.4-182.5 mm and a width of 182.4-182.5 mm; the sixth pass is rolled to a height of 182.4-182.5 mm and a width of 182.4-182.5 mm; the finished product is produced after the sixth pass.

7. The preparation method according to claim 2, characterized in that, The insulation process is as follows: the temperature of the lower insulation pit is ≥580℃, the insulation time is 50~55h, and the temperature of the pit exits is ≤130℃.

8. The preparation method according to claim 2, characterized in that, The aluminum-iron has a diameter of 40-70mm, the aluminum wire segment has a diameter of 10-12mm and a length of 20-30mm, the heavy scrap steel has a specification of ≥800mm*600mm, the dolomite has a diameter of 20-70mm, the active lime has a diameter of 10-70mm, the coke granules have a diameter of 20-60mm, the graphite briquette has a diameter of 20-60mm, the alumina spheres have a diameter of 10-15mm, the ferromolybdenum is FeMo60-B, the aluminum wire has a diameter of 10-12mm, and the silicon carbide has a diameter of 2-5mm. The alloy and silicon carbide are added to the argon gas stream.

9. The preparation method according to claim 3, characterized in that, The diameter of the silicon-calcium alloy cored wire is 12-14 mm. The composition of the covering agent, by mass percentage, is: SiO2: ≥50%; CaO: ≤10%; free carbon: 15-30%; the balance being impurities.

10. The preparation method according to claim 2, characterized in that, The heat-treated steel is then subjected to heat treatment, which includes the following steps: 1) Quenching: 840~860℃, hold for 0.6~0.8h, oil cooling; 2) Tempering: 195~205℃, hold for 1.8~2.2h, then water-cooled.

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