Method for producing and manufacturing steel for automobile engine connecting rod by means of eco-friendly electric arc furnace process

Abstract

A method for producing and manufacturing steel for automobile engine connecting rods by means of an eco-friendly electric arc furnace process, comprising the following chemical components in percentage by mass: 0.38% -0.42% of C, 0.22% -0.35% of Si, 0.55% -0.70% of Mn, ≤0.015% of P, ≤0.008% of S, 0.65%-0.80% of Cr, 1.30%-1.55% of Ni, ≤0.15% of Cu, 0.16%-0.23% of Mo, and the balance iron and inevitable impurities. The process route comprises: ECOARC eco-friendly electric arc furnace+LF refining+RH refining+continuous casting billet+heating by heating furnace+rolling process+heat preservation, and produced steel bars for automobile engine connecting rods meet the mechanical property requirements and ensure the purity of steel.

Description

A method for producing steel for automobile engine connecting rods using an ecological electric furnace process Technical Field

[0001] The present invention relates to the technical field of special steel, and in particular to a method for producing steel for automobile engine connecting rods using an ecological electric furnace process. Background Art

[0002] An automotive engine connecting rod consists of a connecting rod body, a connecting rod cap, a connecting rod bushing, a connecting rod bearing, and connecting rod bolts (or screws). The connecting rod assembly withstands the gas forces transmitted from the piston pin, its own oscillation, and the reciprocating inertia of the piston assembly. The magnitude and direction of these forces vary periodically. The engine connecting rod operates in a harsh environment, placing stringent demands on the comprehensive performance of the connecting rod steel, including wear resistance and fatigue life. As a crucial component of the transmission system, the engine connecting rod is subject to stringent quality requirements.

[0003] The quality of engine connecting rod steel directly affects the service life and wear resistance of the transmission device, and even affects the safety of the entire transmission device working process.

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

[0005] Summary of the Invention

[0006] The purpose of the present invention is to provide a production process and preparation method for steel bars for automobile engine connecting rods. The method adopts the ECOARC ecological electric furnace + LF + RH + continuous casting smelting process to produce steel bars for automobile engine connecting rods, which meets high-end usage requirements and achieves a breakthrough in the batch production of steel bars for automobile engine connecting rods using the ecological electric furnace continuous casting process. It not only ensures the mechanical properties, high hardness and high steel purity of the finished steel bars for automobile engine connecting rods, but also ensures the surface quality level of the steel bars for automobile engine connecting rods.

[0007] To achieve the aforementioned objectives, the present invention provides a production process for steel bars for automotive engine connecting rods, including component and process design. Specifically, the process involves an ECOARC electric furnace, LF furnace, RH furnace, continuous casting, heating in a heating furnace, and rolling. This method meets the quality requirements for automotive engine connecting rod steel bars, while also meeting standard specifications for mechanical properties, high hardness, and high steel purity.

[0008] A steel bar for connecting rods of automobile engines has the following chemical compositions, 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%, and the balance being iron and unavoidable impurities.

[0009] A production process and preparation method for steel bars for automobile engine connecting rods, wherein the process route includes: ECOARC ecological electric furnace + LF refining + RH refining + continuous casting → heating in a heating furnace → rolling process → insulation.

[0010] Among them, the ecological electric furnace smelting is: using scrap steel smelting, scrap steel accounts for 100% by mass fraction; the scrap steel loading amount is 113~118t, the steel tapping temperature is 1645~1650℃, the smelting cycle is 55~65min, the steel tapping time is 1.8~2.2min, C at steel tapping is 0.15~0.20%, P≤0.010%, auxiliary materials and alloys are added when 1 / 4~1 / 3 of the steel is tapped, and the steel tapping amount is 108~115t. Alloy steel addition amount: silicon manganese 4.5 ~ 4.6 kg / t, high carbon ferromanganese 4.5 ~ 4.6 kg / t, high carbon ferrochrome 15 ~ 15.5 kg / t, low carbon ferrochrome 14.5 ~ 14.8 kg / t, aluminum iron (Φ40 ~ 70 mm) 2.2 ~ 2.3 kg / t, aluminum wire segment (Φ10 ~ 12 mm, length 20-30 mm) 1.8 ~ 1.9 m / t, alloy structural steel cutting head 90 ~ 91 kg / t, heavy Scrap steel (≥800mm*600mm) 940~943Kg / t; auxiliary materials added per ton of steel: ladle dust 5.4~5.5Kg / t, dolomite (Φ20~70mm) 16~16.5Kg / t, active lime (Φ10~70mm) 41~42Kg / t, coke particles (Φ20~60mm) 33~34Kg / t, graphite balls (Φ20~60mm) 7.2~7.3Kg / t.

[0011] Based on the above technical solution, further, the LF refining: adopts 20000 ~ 22000A high current to heat and slag, when the slag surface fluctuates and the molten steel and the arc are not exposed, active lime is added, and the chemical composition is analyzed for the first time after 5 minutes, and the alloy and silicon carbide are added according to the target chemical composition value. The alloy and silicon carbide should be added to the argon flow to promote rapid melting and homogenization of the alloy and silicon carbide. When the temperature of the molten steel reaches 1565-1575°C, 2-3 kg / t of diffusion deoxidizer is added for diffusion deoxidation, and the furnace door is closed for 10-15 minutes. When the temperature of the molten steel reaches 1575-1585°C, a second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, the smelting cycle is 70-80 minutes. The additional alloy addition per ton of steel is as follows: 2.0-2.1 kg / t of ferrosilicon, 3.5-3.6 kg / t of high carbon ferromanganese, 5.8-5.9 kg / t of high carbon ferrochromium, 1.5-1.6 kg / t of alumina balls (Φ10-15 mm), 3.0-3.1 kg / t of ferromolybdenum (FeMo60-B), and 1.1-1.2 m / t of aluminum wire (Φ10-12 mm). The amount of supplementary materials added per ton of steel: active lime (Φ10-70mm) 9~9.2Kg / t, silicon carbide (Φ2-5mm) 0.8~0.9Kg / t.

[0012] Based on the above technical solution, further, the RH refining is as follows: the station entry temperature is 1640-1650°C, the operation time is 30min-34min, the argon pressure is controlled at 0.1-0.3MPa before the vacuum pump is started, so that the slag surface moves slightly and the molten steel is not exposed, the timing starts when the vacuum degree reaches 100-110Pa, and the holding time is 10-15min. At the same time, the argon pressure is adjusted to 0.3-0.5MPa. After the static argon blowing is completed, 2-2.1 meters / t of silicon-calcium alloy cored wire (Φ12-14mm) is added, and a covering agent (by mass percentage, the main components SiO2: ≥50%; CaO: ≤10%; FC free carbon: 15-30%, and the balance is impurities) is added. 0.6-0.7kg / t of steel, and the station exit temperature is 1580-1590°C.

[0013] Based on the above technical solution, further, the continuous casting is as follows: the ladle arrival temperature is 1590-1595°C, the molten steel volume is 100-105t, the H in the tundish is controlled to be ≤2ppm, the whole process is protected casting, and the crystallizer protective slag uses medium carbon steel protective slag.

[0014] Based on the above technical solution, further, the heating process: the temperature entering the heating furnace is 350℃~540℃, the temperature of the preheating section is required to be 600℃~650℃, and the time is 1.0~1.5h; the temperature of the heating section 2 is required to be 850℃~870℃, and the time is 1.0~1.5h; the temperature of the heating section 1 is required to be 1210℃~1240℃, and the time is 1.0~1.5h; the temperature of the soaking section is required to be 1210℃~1230℃, and the time is 1.0~1.5h; the steel tapping temperature is 1170℃~1190℃.

[0015] Based on the above technical solution, further, the rolling process is:

[0016] Coiling process: Coiling is done by BD blooming mill, with 9 rolling passes. The rolling reduction is as follows: steel turning → 1st pass reduction 65-65.2mm → 2nd pass reduction 70-70.2mm → steel turning → 3rd pass reduction 64-64.2mm → 4th pass reduction 90-90.2mm → steel turning → 5th pass reduction 42-42.2mm → 6th pass reduction 40-40.2mm → 7th pass reduction 35-35.2mm → 8th pass reduction 34-34.2mm → steel turning → 9th pass reduction 82-82.2mm. The steel passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters 8-stand continuous rolling mill group for rolling.

[0017] Finished product rolling process: the intermediate billet is rolled to a height of 232~232.2mm and a width of 268~268.2mm; the first pass is 229~229.2mm high and 245~245.2mm wide; the second pass is 192~192.2mm high and 235~235.2mm wide; the third pass is 200~200.2mm high and 195~195.2mm wide; the fourth pass is 173~173.2mm high and 205~205.2mm wide; the fifth pass is 182.4~182.5mm high and 182.4~182.5mm wide; the sixth pass is 182.4~182.5mm high and 182.4~182.5mm wide; the finished product is produced after the 6th pass.

[0018] Based on the above technical solution, further, the insulation process is: the temperature of the lower insulation pit is ≥580°C, insulation is 50-55h, and the exit temperature is ≤130°C.

[0019] Based on the above technical solution, further, the size of the continuous casting billet is 390mm*480mm.

[0020] Based on the above technical solution, further, the process route includes the following steps: after insulation, finishing → inspection → packaging and storage → shipment.

[0021] Based on the above technical solution, further, the steel material segment after insulation is heat treated, and the heat treatment includes the following steps:

[0022] 1) Quenching: 840-860°C, holding time 0.6-0.8h, oil cooling;

[0023] 2) Tempering: 195-205℃, keep warm for 1.8-2.2h, water cooling.

[0024] Beneficial effects of the present invention:

[0025] (1) The ECOARC ecological electric furnace + LF + RH + 390mm*480mm smelting process and rolling process are used to produce steel bars for automobile engine connecting rods. The production specification is Φ180mm, which meets the mechanical performance requirements and ensures the purity of the steel.

[0026] (2) Reasonable component design and production process ensure surface quality and impact performance.

[0027] (3) The macrostructure, non-metallic inclusions and mechanical properties of the finished steel meet the requirements of high-end products. DETAILED DESCRIPTION

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

[0029] Example 1

[0030] 1Chemical composition

[0031] 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%, and the balance is iron and inevitable impurities.

[0032] 2. Production process parameters of electric furnace continuous casting steel bars for automobile engine connecting rods

[0033] Process route: 100t ECOARC ecological electric furnace + LF + RH + 390mm*480mm continuous casting billet → heating in heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery.

[0034] (1) Ecological electric furnace smelting: 100% scrap steel; scrap steel charge 115t, tapping temperature 1647°C, smelting cycle 59min, tapping time 1.9min, C 0.18%, P 0.008% at tapping, auxiliary materials and alloys added when 1 / 4 of the steel is tapped, tapping capacity 110t. Alloy addition per ton of steel: 4.5kg / t silicon manganese, 4.5kg / t high carbon ferromanganese, 15kg / t high carbon ferrochrome, 14.6kg / t low carbon ferrochrome, 2.2kg / t aluminum iron (Φ50mm), 1.8m / t aluminum wire segment (Φ10mm). Alloy structural steel cutting head 90Kg / t, heavy scrap steel (1000mm*600mm) 942Kg / t; auxiliary materials added per ton of steel: ladle dust 5.4Kg / t, dolomite (Φ40mm) 16.2Kg / t, active lime (Φ40mm) 41Kg / t, coke particles (Φ40mm) 33Kg / t, graphite balls (Φ50mm) 7.2Kg / t.

[0035] (2) LF refining: Use a high current of 20,000A to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, add active lime. Take the first sample to analyze the chemical composition after 5 minutes. Add alloy and silicon carbide according to the target chemical composition value. Alloy and silicon carbide should be added to the argon flow to promote rapid melting and homogenization of alloy and silicon carbide. When the molten steel temperature reaches 1568°C, 2.5 kg / t of diffusion deoxidizer is added for diffusion deoxidation. The furnace door is closed for 12 minutes. When the molten steel temperature reaches 1578°C, a second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, the smelting cycle is 75 minutes. The following alloys are added: 2.0 kg / t of ferrosilicon, 3.5 kg / t of high-carbon ferromanganese, 5.8 kg / t of high-carbon ferrochromium, 1.5 kg / t of alumina balls (Φ10 mm), 3.0 kg / t of ferromolybdenum (FeMo60-B), and 1.1 m / t of aluminum wire (Φ10 mm). Additional auxiliary materials include 9 kg / t of active lime (Φ40 mm) and 0.8 kg / t of silicon carbide (Φ3 mm).

[0036] (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 slag surface moves slightly and the molten steel is not exposed. When the vacuum degree reaches 100Pa, the timing starts and the holding time is 10min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 2 meters / 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℃.

[0037] (4) Continuous casting: The temperature of the ladle at the station is 1590℃, the amount of molten steel is 100t, the H in the tundish is controlled at 1.2ppm, the whole process is protected casting, and the mold protection slag uses medium carbon steel protection slag.

[0038] (5) Heating process: The temperature of the heating furnace is 480℃, the temperature of the preheating section is required to be 620℃, and the time is 1.2h; the temperature of the heating section 2 is required to be 850℃, and the time is 1.3h; the temperature of the heating section 1 is required to be 1220℃, and the time is 1.2h; the temperature of the soaking section is required to be 1220℃, and the time is 1.2h; the steel tapping temperature is 1180℃.

[0039] (6) Rolling process:

[0040] Coiling process: Coiling is done with the BD blooming mill, with 9 rolling passes. The rolling reduction is as follows: steel turning → 1st pass reduction 65mm → 2nd pass reduction 70mm → steel turning → 3rd pass reduction 64mm → 4th pass reduction 90mm → steel turning → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → steel turning → 9th pass reduction 82mm. The steel passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters the 8-stand tandem 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 6th pass.

[0042] (7) Insulation process: the temperature of the lower insulation pit is 600℃, the insulation is 52h, and the temperature out of the pit is 100℃.

[0043] Example 2

[0044] 1Chemical composition

[0045] 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%, and the balance is iron and unavoidable impurities. Among them:

[0046] 2. Production process parameters of electric furnace continuous casting steel bars for automobile engine connecting rods

[0047] Process route: 100t ECOARC ecological electric furnace + LF + RH + 390mm*480mm continuous casting billet → heating in heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery.

[0048] (1) Ecological electric furnace smelting: Scrap steel accounts for 100%; scrap steel charge is 116 tons, tapping temperature is 1649°C, smelting cycle is 58 minutes, tapping time is 1.9 minutes, carbon content is 0.18%, phosphorus content is 0.007% at tapping, auxiliary materials and alloys are added when 1 / 4 of the steel is tapped, and the tapping volume is 111 tons. Alloy addition per ton of steel: 4.5 kg / t silicon manganese, 4.5 kg / t high carbon ferromanganese, 15 kg / t high carbon ferrochrome, 14.6 kg / t low carbon ferrochrome, 2.2 kg / t aluminum iron (Φ50 mm), and 1.8 m / t aluminum wire segment (Φ10 mm). Alloy structural steel cutting head 90Kg / t, heavy scrap steel (1000mm*600mm) 941Kg / t; auxiliary materials added per ton of steel: ladle dust 5.4Kg / t, dolomite (Φ40mm) 16Kg / t, active lime (Φ50mm) 41Kg / t, coke particles (Φ50mm) 33Kg / t, graphite balls (Φ50mm) 7.2Kg / t.

[0049] (2) LF refining: Use a high current of 20,000A to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, add active lime. Take the first sample to analyze the chemical composition after 5 minutes. Add alloy and silicon carbide according to the target chemical composition value. Alloy and silicon carbide should be added to the argon flow to promote rapid melting and homogenization of alloy and silicon carbide. When the molten steel temperature reaches 1569°C, 2kg / t of diffusion deoxidizer is added for diffusion deoxidation. The furnace door is closed for 10 minutes. When the molten steel temperature reaches 1580°C, a second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, the smelting cycle is 74 minutes. The following alloys are added: 2.0kg / t of ferrosilicon, 3.5kg / t of high-carbon ferromanganese, 5.8kg / t of high-carbon ferrochromium, 1.5kg / t of alumina balls (Φ10mm), 3.0kg / t of ferromolybdenum (FeMo60-B), and 1.1m / t of aluminum wire (Φ10mm). Additional auxiliary materials include 9kg / t of active lime (10-70mm) and 0.8kg / t of silicon carbide (Φ3mm).

[0050] (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 slag surface moves slightly and the molten steel is not exposed. When the vacuum degree reaches 100Pa, the timing starts and the holding time is 10min. At the same time, the argon pressure is adjusted to 0.4MPa. After the static argon blowing is completed, 2 meters / 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℃.

[0051] (4) Continuous casting: The temperature of the ladle at the station is 1590℃, the amount of molten steel is 100t, the H in the tundish is controlled at 1.2ppm, the whole process is protected casting, and the mold protection slag uses medium carbon steel protection slag.

[0052] (5) Heating process: The temperature of the heating furnace is 450℃, the temperature of the preheating section is required to be 620℃, and the time is 1.2h; the temperature of the heating section 2 is required to be 860℃, and the time is 1.2h; the temperature of the heating section 1 is required to be 1220℃, and the time is 1.2h; the temperature of the soaking section is required to be 1220℃, and the time is 1.2h; the steel tapping temperature is 1180℃.

[0053] (6) Rolling process:

[0054] Coiling process: Coiling is done with the BD blooming mill, with 9 rolling passes. The rolling reduction is as follows: steel turning → 1st pass reduction 65mm → 2nd pass reduction 70mm → steel turning → 3rd pass reduction 64mm → 4th pass reduction 90mm → steel turning → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → steel turning → 9th pass reduction 82mm. The steel passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters the 8-stand tandem rolling mill group for rolling.

[0055] 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 6th pass.

[0056] (7) Insulation process: the temperature of the lower insulation pit is 600℃, the insulation time is 52h, and the exit temperature is 110℃.

[0057] Example 3

[0058] 1Chemical composition

[0059] 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%, and the balance is iron and unavoidable impurities. Among them:

[0060] 2. Production process parameters of electric furnace continuous casting steel bars for automobile engine connecting rods

[0061] Process route: 100t ECOARC ecological electric furnace + LF + RH + 390mm*480mm continuous casting billet → heating in heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery.

[0062] (1) Ecological electric furnace smelting: 100% scrap steel; scrap steel charge: 115t; tapping temperature: 1647°C; smelting cycle: 57min; tapping time: 1.9min; carbon content: 0.17%; phosphorus content: 0.009%; auxiliary materials and alloys are added when 1 / 4 of the steel is tapped; tapping volume: 110t. Alloy additions per ton of steel: 4.5kg / t silicon manganese, 4.5kg / t high carbon ferromanganese, 15.2kg / t high carbon ferrochrome, 14.6kg / t low carbon ferrochrome, 2.2kg / t ferroaluminum (Φ50mm), 1.8m / t aluminum wire (Φ10mm). Alloy structural steel cutting head 90Kg / t, heavy scrap steel (1000mm*600mm) 940Kg / t; auxiliary materials added per ton of steel: ladle dust 5.4Kg / t, dolomite (Φ45mm) 16Kg / t, active lime (Φ40mm) 41Kg / t, coke particles (Φ40mm) 33Kg / t, graphite pellets (Φ50mm) 7.2Kg / t.

[0063] (2) LF refining: Use a high current of 20,000A to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, add active lime. Take the first sample to analyze the chemical composition after 5 minutes. Add alloy and silicon carbide according to the target chemical composition value. Alloy and silicon carbide should be added to the argon flow to promote rapid melting and homogenization of alloy and silicon carbide. When the molten steel temperature reaches 1569°C, 2kg / t of diffusion deoxidizer is added for diffusion deoxidation. The furnace door is closed for 10 minutes. When the molten steel temperature reaches 1578°C, a second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, the smelting cycle is 75 minutes. The following alloys are added: 2.0kg / t of ferrosilicon, 3.5kg / t of high-carbon ferromanganese, 5.8kg / t of high-carbon ferrochromium, 1.5kg / t of alumina balls (Φ10mm), 3.0kg / t of ferromolybdenum (FeMo60-B), and 1.1m / t of aluminum wire (Φ10mm). Additional auxiliary materials include 9kg / t of active lime (Φ40mm) and 0.8kg / t of silicon carbide (Φ3mm).

[0064] (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 slag surface moves slightly and the molten steel is not exposed. When the vacuum degree reaches 100Pa, the timing starts and the holding time is 12min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 2 meters / 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℃.

[0065] (4) Continuous casting: The temperature of the ladle at the station is 1592℃, the amount of molten steel is 102t, the H in the tundish is controlled at 1.0ppm, the whole process is protected casting, and the mold protection slag uses medium carbon steel protection slag.

[0066] (5) Heating process: The temperature of the heating furnace is 520℃, the temperature of the preheating section is required to be 620℃, and the time is 1.2h; the temperature of the heating section 2 is required to be 850℃, and the time is 1.2h; the temperature of the heating section 1 is required to be 1220℃, and the time is 1.2h; the temperature of the soaking section is required to be 1220℃, and the time is 1.2h; the steel tapping temperature is 1185℃.

[0067] (6) Rolling process:

[0068] Coiling process: Coiling is done with the BD blooming mill, with 9 rolling passes. The rolling reduction is as follows: steel turning → 1st pass reduction 65mm → 2nd pass reduction 70mm → steel turning → 3rd pass reduction 64mm → 4th pass reduction 90mm → steel turning → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → steel turning → 9th pass reduction 82mm. The steel passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters the 8-stand tandem rolling mill group for rolling.

[0069] 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 6th pass.

[0070] (7) Insulation process: the temperature of the lower insulation pit is 600℃, the insulation time is 53h, and the exit temperature is 110℃.

[0071] Example 4

[0072] 1Chemical composition

[0073] 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%, and the balance is iron and inevitable impurities.

[0074] 2. Production process parameters of electric furnace continuous casting steel bars for automobile engine connecting rods

[0075] Process route: 100t ECOARC ecological electric furnace + LF + RH + 390mm*480mm continuous casting billet → heating in heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery.

[0076] (1) Ecological electric furnace smelting: 100% scrap steel; scrap steel charge 115t, tapping temperature 1648°C, smelting cycle 58min, tapping time 2.0min, carbon content 0.17%, phosphorus content 0.007% at tapping, auxiliary materials and alloys added when 1 / 4 of the steel is tapped, tapping volume 111t. Alloy addition per ton of steel: 4.5kg / t silicon manganese, 4.5kg / t high carbon ferromanganese, 15.2kg / t high carbon ferrochrome, 14.6kg / t low carbon ferrochrome, 2.2kg / t ferroaluminum (Φ50mm), 1.8m / t aluminum wire (Φ10mm). Alloy structural steel cutting head 90Kg / t, heavy scrap steel (1000mm*600mm) 940Kg / t; auxiliary materials added per ton of steel: ladle dust 5.4Kg / t, dolomite (Φ40mm) 16.2Kg / t, active lime (Φ40mm) 41Kg / t, coke particles (Φ50mm) 33Kg / t, graphite balls (Φ50mm) 7.2Kg / t.

[0077] (2) LF refining: Use a high current of 20,000A to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, add active lime. Take the first sample to analyze the chemical composition after 5 minutes. Add alloy and silicon carbide according to the target chemical composition value. Alloy and silicon carbide should be added to the argon flow to promote rapid melting and homogenization of alloy and silicon carbide. When the molten steel temperature reaches 1569°C, 2kg / t of diffusion deoxidizer is added for diffusion deoxidation. The furnace door is closed for 10 minutes. When the molten steel temperature reaches 1578°C, a second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, the smelting cycle is 75 minutes. The following alloys are added: 2.0kg / t of ferrosilicon, 3.5kg / t of high-carbon ferromanganese, 5.8kg / t of high-carbon ferrochromium, 1.5kg / t of alumina balls (Φ10mm), 3.0kg / t of ferromolybdenum (FeMo60-B), and 1.1m / t of aluminum wire (Φ10mm). Additional auxiliary materials include 9kg / t of active lime (Φ40mm) and 0.8kg / t of silicon carbide (Φ3mm).

[0078] (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 slag surface moves slightly and the molten steel is not exposed. When the vacuum degree reaches 100Pa, the timing starts and the holding time is 10min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 2 meters / 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℃.

[0079] (4) Continuous casting: The temperature of the ladle at the station is 1592℃, the amount of molten steel is 102t, the H content of the tundish is controlled at 1.2ppm, the whole process is protected casting, and the mold protection slag uses medium carbon steel protection slag.

[0080] (5) Heating process: The temperature of the heating furnace is 510℃, the temperature of the preheating section is required to be 610℃, and the time is 1.2h; the temperature of the heating section 2 is required to be 850℃, and the time is 1.2h; the temperature of the heating section 1 is required to be 1220℃, and the time is 1.2h; the temperature of the soaking section is required to be 1220℃, and the time is 1.2h; the steel tapping temperature is 1180℃.

[0081] (6) Rolling process:

[0082] Coiling process: Coiling is done with the BD blooming mill, with 9 rolling passes. The rolling reduction is as follows: steel turning → 1st pass reduction 65mm → 2nd pass reduction 70mm → steel turning → 3rd pass reduction 64mm → 4th pass reduction 90mm → steel turning → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → steel turning → 9th pass reduction 82mm. The steel passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters the 8-stand tandem rolling mill group for rolling.

[0083] 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 6th pass.

[0084] (7) Insulation process: The temperature of the lower insulation pit is 590℃, the insulation time is 53h, and the exit temperature is 115℃.

[0085] Example 5

[0086] 1Chemical composition

[0087] 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%, and the balance is iron and inevitable impurities.

[0088] 2. Production process parameters of electric furnace continuous casting steel bars for automobile engine connecting rods

[0089] Process route: 100t ECOARC ecological electric furnace + LF + RH + 390mm*480mm continuous casting billet → heating in heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery.

[0090] (1) Ecological electric furnace smelting: 100% scrap steel; scrap steel charge: 114t; tapping temperature: 1647°C; smelting cycle: 59min; tapping time: 2.0min; carbon content: 0.18%; phosphorus content: 0.008%; auxiliary materials and alloys are added when 1 / 4 of the steel is tapped; tapping volume: 112t. Alloy additions per ton of steel: 4.5kg / t silicon manganese, 4.5kg / t high carbon ferromanganese, 15.3kg / t high carbon ferrochrome, 14.6kg / t low carbon ferrochrome, 2.2kg / t aluminum iron (Φ50mm), 1.8m / t aluminum wire (Φ10mm). Alloy structural steel cutting head 90Kg / t, heavy scrap steel (1000mm*600mm) 940Kg / t; auxiliary materials added per ton of steel: ladle dust 5.4Kg / t, dolomite (Φ50mm) 16.2Kg / t, active lime (Φ40mm) 41Kg / t, coke particles (Φ50mm) 33Kg / t, graphite balls (Φ50mm) 7.2Kg / t.

[0091] (2) LF refining: Use a high current of 20,000A to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, add active lime. Take the first sample to analyze the chemical composition after 5 minutes. Add alloy and silicon carbide according to the target chemical composition value. Alloy and silicon carbide should be added to the argon flow to promote rapid melting and homogenization of alloy and silicon carbide. When the molten steel temperature reached 1568°C, 2.3 kg / t of diffusion deoxidizer was added for diffusion deoxidation. The furnace door was closed for 10 minutes. When the molten steel temperature reached 1578°C, a second sample was taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample was taken, the smelting cycle lasted 76 minutes. The following alloys were added: 2.0 kg / t of ferrosilicon, 3.5 kg / t of high-carbon ferromanganese, 5.8 kg / t of high-carbon ferrochromium, 1.5 kg / t of alumina balls (Φ10 mm), 3.0 kg / t of ferromolybdenum (FeMo60-B), and 1.1 m / t of aluminum wire (Φ10 mm). Additional auxiliary materials included 9 kg / t of active lime (Φ40 mm) and 0.8 kg / t of silicon carbide (Φ3 mm).

[0092] (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 slag surface is slightly moved and the molten steel is not exposed. When the vacuum degree reaches 105Pa, the timing starts and the holding time is 12min. At the same time, the argon pressure is adjusted to 0.4MPa. After the static argon blowing is completed, 2 meters / 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℃.

[0093] (4) Continuous casting: The temperature of the ladle at the station is 1592℃, the amount of molten steel is 102t, the H content of the tundish is controlled at 1.2ppm, the whole process is protected casting, and the mold protection slag uses medium carbon steel protection slag.

[0094] (5) Heating process: The temperature of the heating furnace is 500℃, the temperature of the preheating section is required to be 620℃, and the time is 1.2h; the temperature of the heating section 2 is required to be 860℃, and the time is 1.3h; the temperature of the heating section 1 is required to be 1220℃, and the time is 1.3h; the temperature of the soaking section is required to be 1220℃, and the time is 1.3h; the steel tapping temperature is 1180℃.

[0095] (6) Rolling process:

[0096] Coiling process: Coiling is done with the BD blooming mill, with 9 rolling passes. The rolling reduction is as follows: steel turning → 1st pass reduction 65mm → 2nd pass reduction 70mm → steel turning → 3rd pass reduction 64mm → 4th pass reduction 90mm → steel turning → 5th pass reduction 42mm → 6th pass reduction 40mm → 7th pass reduction 35mm → 8th pass reduction 34mm → steel turning → 9th pass reduction 82mm. The steel passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters the 8-stand tandem rolling mill group for rolling.

[0097] 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 6th pass.

[0098] (7) Insulation process: the temperature of the lower insulation pit is 620℃, the insulation is 52h, and the temperature out of the pit is 100℃.

[0099] Test results of finished products of Examples 1 to 5

[0100] (1) Macrostructure of Φ180mm steel

[0101] (2) Non-metallic inclusions in Φ180mm steel

[0102] (3) Mechanical properties of Φ180mm steel

[0103] The steel material section after insulation is heat treated as follows, and the mechanical properties are as follows:

Claims

1. A steel bar for an automobile engine connecting rod, characterized in that, 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%, and the balance is iron and unavoidable impurities.

2. A preparation method of the steel bar for an automobile engine connecting rod 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; among which, The ecological electric furnace smelting is as follows: Scrap steel is used for smelting. The scrap steel charging amount is 113 - 118t, the tapping temperature is 1645 - 1650°C, the smelting cycle is 55 - 65min, the tapping time is 1.8 - 2.2min, the C content at tapping is 0.15 - 0.20%, P ≤0.010%. Auxiliary materials and alloys are added when 1 / 4 - 1 / 3 of the tapping amount is reached, and the tapping amount is 108 - 115t; Alloy addition per ton of steel: silicomanganese 4.5 - 4.6kg / t, high-carbon ferromanganese 4.5 - 4.6kg / t, high-carbon ferrochrome 15 - 15.5kg / t, low-carbon ferrochrome 14.5 - 14.8kg / t, ferrotitanium 2.2 - 2.3kg / t, aluminum wire segment 1.8 - 1.9m / t, alloy structural steel cuttings 90 - 91kg / t, heavy scrap 940 - 943kg / t; Auxiliary material addition per ton of steel: ladle ash 5.4 - 5.5kg / t, dolomite 16 - 16.5kg / t, active lime 41 - 42kg / t, coke granules 33 - 34kg / t, graphite briquette 7.2 - 7.3kg / t; The LF refining is as follows: A large current of 20000 - 22000A is used for heating up and slag melting. When the slag surface fluctuates and the molten steel and arc are not exposed, active lime is added. After 5min, the first chemical composition analysis sample is taken, and alloys and silicon carbide are added according to the chemical composition target values; When the molten steel temperature reaches 1565 - 1575°C, 2 - 3kg / t of steel of diffusion deoxidizer is added for diffusion deoxidation, and the furnace door is closed for 10 - 15min. When the molten steel temperature reaches 1575 - 1585°C, the second chemical composition analysis sample is taken to confirm the deviation value of the content of each chemical element from the target value requirement. After the second sample is taken away, the smelting cycle is 70min - 80min; Alloy addition per ton of steel for supplementary addition: ferrosilicon 2.0 - 2.1kg / t, high-carbon ferromanganese 3.5 - 3.6kg / t, high-carbon ferrochrome 5.8 - 5.9kg / t, alumina balls 1.5 - 1.6kg / t, ferromolybdenum 3.0 - 3.1kg / t, aluminum wire 1.1 - 1.2m / t; Auxiliary material addition per ton of steel for supplementary addition: active lime 9 - 9.2Kg / t, silicon carbide 0.8 - 0.9Kg / t.

3. According to the preparation method described in claim 2, characterized in that, The RH refining process is as follows: the tapping temperature is 1640 - 1650 °C, the operation time is 30 - 34 min, the argon pressure is controlled at 0.1 - 0.3 MPa before the vacuum pump is started, with the slag surface slightly moving and the molten steel not being exposed. When the vacuum degree reaches 100 - 110 Pa, timing starts, and the holding time is 10 - 15 min. Meanwhile, the argon pressure is adjusted to 0.3 - 0.5 MPa. After the static argon blowing ends, 2 - 2.1 m / t of steel of calcium silicate cored wire and 0.6 - 0.7 kg / t of steel of covering agent are added, and the tapping temperature is 1580 - 1590 °C.

4. According to the preparation method described in claim 2, characterized in that, The continuous casting process is as follows: the ladle arrival temperature for continuous casting is 1590 - 1595 °C, the molten steel amount is 100 - 105 t, the content of H in the tundish is controlled ≤ 2 ppm, and the whole process is carried out under protected casting. The mold powder used in the mold is medium carbon steel mold powder.

5. According to the preparation method described in claim 2, characterized in that, The heating process is as follows: the temperature entering the heating furnace is 350 °C - 540 °C, the temperature requirement in the preheating section is 600 °C - 650 °C, and the time is 1.0 - 1.5 h; the temperature requirement in the heating section 2 is 850 °C - 870 °C, and the time is 1.0 - 1.5 h; the temperature requirement in the heating section 1 is 1210 °C - 1240 °C, and the time is 1.0 - 1.5 h; the temperature requirement in the soaking section is 1210 °C - 1230 °C, and the time is 1.0 - 1.5 h; the tapping temperature is 1170 °C - 1190 °C.

6. According to the preparation method described in claim 2, characterized in that, The rolling process is as follows: Blooming process: The BD blooming mill is used for blooming, with 9 rolling passes. The rolling reduction: turning the steel → the reduction in the 1st pass is 65 - 65.2 mm → the reduction in the 2nd pass is 70 - 70.2 mm → turning the steel → the reduction in the 3rd pass is 64 - 64.2 mm → the reduction in the 4th pass is 90 - 90.2 mm → turning the steel → the reduction in the 5th pass is 42 - 42.2 mm → the reduction in the 6th pass is 40 - 40.2 mm → the reduction in the 7th pass is 35 - 35.2 mm → the reduction in the 8th pass is 34 - 34.2 mm → turning the steel → the reduction in the 9th pass is 82 - 82.2 mm. It passes through 3 rolling mills of 850 mm and 1 rolling mill of 735 mm, and then enters the 8 - stand continuous rolling mill 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 height in the 1st pass is 229 - 229.2 mm and the width is 245 - 245.2 mm; the height in the 2nd pass is 192 - 192.2 mm and the width is 235 - 235.2 mm; the height in the 3rd pass is 200 - 200.2 mm and the width is 195 - 195.2 mm; the height in the 4th pass is 173 - 173.2 mm and the width is 205 - 205.2 mm; the height in the 5th pass is 182.4 - 182.5 mm and the width is 182.4 - 182.5 mm; the height in the 6th pass is 182.4 - 182.5 mm and the width is 182.4 - 182.5 mm; the finished product is produced after the 6th pass.

7. According to the preparation method described in claim 2, characterized in that, The heat preservation process is as follows: the temperature in the lower heat preservation pit is ≥ 580 °C, the heat preservation time is 50 - 55 h, and the temperature when leaving the pit is ≤ 130 °C.

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

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

10. According to the preparation method described in claim 2, characterized in that, The heat - treated steel after heat preservation is subjected to heat treatment, and the heat treatment includes the following steps: 1) Quenching: 840 - 860 °C, heat preservation for 0.6 - 0.8 h, oil cooling; 2) Tempering: 195 - 205 °C, heat preservation for 1.8 - 2.2 h, water cooling.

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