A steel bar for automotive engine connecting rods and its preparation method

Abstract

This invention discloses a steel bar for automotive engine connecting rods and its preparation method. The steel bar comprises the following components by mass percentage: C: 0.48%–0.53%, Si: 0.20%–0.35%, Mn: 0.55%–0.75%, P≤0.015%, S≤0.012%, Cr: 0.85%–1.05%, Ni≤0.25%, Mo≤0.05%, V: 0.11%–0.19%, Cu≤0.15%, with the balance being iron and unavoidable impurities. This invention utilizes an eco-friendly electric furnace + LF + RH + continuous casting and rolling process to produce the steel bar for automotive engine connecting rods, meeting high-end application requirements. It ensures both the mechanical properties and high purity of the finished steel bar, as well as the surface quality.

Description

Technical Field

[0001] This invention relates to the fields of materials and metallurgy, and more specifically, to a steel bar for automobile engine connecting rods and its preparation method. Background Technology

[0002] The connecting rod of an automotive engine bears the periodic forces of the gas transmitted from the piston pin, its own oscillation, and the reciprocating inertial forces of the piston assembly. Therefore, the connecting rod is subjected to alternating loads such as compression and tension, requiring sufficient fatigue strength and structural rigidity. Insufficient fatigue strength often leads to breakage of the connecting rod body or connecting rod bolts, resulting in a major accident causing complete engine failure. Insufficient rigidity causes bending deformation of the rod body and out-of-roundness deformation of the connecting rod big end, leading to uneven wear of the piston, cylinder, bearings, and crankpin. The quality of the steel used in automotive engine connecting rods directly affects the service life and wear resistance of the engine, and even the safety of the entire vehicle operation.

[0003] Currently, the steel used for connecting rods in automotive engines suffers from problems such as high impurity content, poor wear resistance, low fatigue life, and mechanical properties that fail to meet application requirements. Summary of the Invention

[0004] The purpose of this invention is to overcome the aforementioned defects in the existing technology and provide a steel bar for automotive engine connecting rods and its preparation method. The steel bar for automotive engine connecting rods produced by the eco-friendly electric furnace + LF + RH + continuous casting smelting process and rolling process meets the requirements of high-end applications. It achieves a breakthrough in the mass production of steel bars for automotive engine connecting rods through the eco-friendly electric furnace continuous casting process. It not only ensures the mechanical properties and high purity of the finished steel bars for automotive engine connecting rods, but also ensures the surface quality level of the steel bars for automotive engine connecting rods, thus meeting the quality requirements for steel bars for automotive engine connecting rods.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A steel bar for automotive engine connecting rods comprises the following components by weight percentage:

[0007] C: 0.48%–0.53%, Si: 0.20%–0.35%, Mn: 0.55%–0.75%, P≤0.015%, S≤0.012%, Cr: 0.85%–1.05%, Ni≤0.25%, Mo≤0.05%, V: 0.11%–0.19%, Cu≤0.15%, and the balance being iron and unavoidable impurities.

[0008] This invention also discloses a method for preparing steel bars for automotive engine connecting rods as described above, comprising the following steps: eco-friendly electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating process, rolling process, and heat preservation process; wherein, in the eco-friendly electric furnace smelting, scrap steel is used as the furnace charge, accounting for 100% by mass fraction; the scrap steel includes alloy structural steel cuts, heavy scrap steel, and bale-shaped scrap steel; wherein, the mass percentage of alloy structural steel cuts in the furnace charge is 15%–30%, the mass percentage of heavy scrap steel is 60%–80%, and the mass percentage of bale-shaped scrap steel is 7%–15%; the tapping temperature is 1570℃–1580℃, and the final composition of the electric furnace is: C: 0.10%–0.15%, P ≤ 0.010%; slag is added when 1 / 4–1 / 3 of the steel is tapped. Pre-deoxidizer, alloy; smelting cycle 40-45 minutes; alloy addition per ton of steel: 5.1-5.2 kg / t silicon manganese, 2.1-2.2 kg / t high-carbon ferromanganese, 14.5-15 kg / t high-carbon ferrochrome, 0.6-0.7 kg / t aluminum wire segments, wherein the aluminum wire segments have a size specification of Φ10-Φ16 mm; auxiliary material addition per ton of steel: 40-41 kg / t active lime, 25-26 kg / t magnesite, 6-6.2 kg / t ladle ash, 20-21 kg / t small coke pieces; wherein the particle size of the active lime is 10-70 mm; the particle size of the magnesite is 10-60 mm.

[0009] Implementing the embodiments of the present invention will have the following beneficial effects:

[0010] (1) Steel bars for connecting rods of automobile engines are produced by using an ecological electric furnace + LF + RH + 390mm*480mm smelting process and rolling process to meet mechanical performance requirements and ensure steel purity.

[0011] (2) Reasonable composition design and production process ensure surface quality and mechanical properties.

[0012] (3) The low magnification structure and non-metallic inclusions of the finished steel meet the requirements of high-end products. Detailed Implementation

[0013] The present invention will be further described below with reference to specific embodiments, but this does not limit the present invention in any way.

[0014] 1. Chemical composition

[0015] This invention discloses a steel bar for automotive engine connecting rods, comprising the following components by mass percentage: C: 0.48%–0.53%, Si: 0.20%–0.35%, Mn: 0.55%–0.75%, P≤0.015%, S≤0.012%, Cr: 0.85%–1.05%, Ni≤0.25%, Mo≤0.05%, V: 0.11%–0.19%, Cu≤0.15%, and the balance being iron and unavoidable impurities.

[0016] II. Production Process Technology

[0017] The method for preparing steel bars for connecting rods of automobile engines according to the present invention includes the following steps: ecological electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating process, rolling process and heat preservation process.

[0018] Furthermore, the specific steps include:

[0019] S1. In the ecological electric arc furnace smelting, scrap steel is used as the furnace charge, accounting for 100% by mass fraction. The scrap steel includes alloy structural steel cuts, heavy scrap steel, and bale-shaped scrap steel. Among them, the mass percentage of alloy structural steel cuts in the furnace charge is 15%–30%, the mass percentage of heavy scrap steel is 60%–80%, and the mass percentage of bale-shaped scrap steel is 7%–15%. The tapping temperature is 1570℃–1580℃, and the final composition of the electric arc furnace is: C: 0.10%–0.15%, P≤0.010%. Slag, pre-deoxidizer, and alloy are added when 1 / 4–1 / 3 of the steel is tapped. The tapping volume is 1. 0.8t~112t, smelting cycle 40min~45min; alloy addition per ton of steel: 5.1Kg / t~5.2Kg / t silicon manganese, 2.1Kg / t~2.2Kg / t high carbon ferromanganese, 14.5Kg / t~15Kg / t high carbon ferrochrome, 0.6Kg / t~0.7Kg / t aluminum wire segments; auxiliary material addition per ton of steel: 40Kg / t~41Kg / t active lime, 25Kg / t~26Kg / t magnesite, 6Kg / t~6.2Kg / t ladle ash, 20Kg / t~21Kg / t small coke pieces.

[0020] In one specific embodiment, the aluminum wire segment has a size specification of Φ10mm~Φ16mm; the active lime has a particle size of 10mm~70mm; and the magnesite has a particle size of 10mm~60mm.

[0021] In one specific embodiment, the amount of scrap steel loaded is 102t to 104t, alloy structural steel cut-off is 20t to 21t, heavy scrap steel is 72t to 73t, and bale-shaped scrap steel is 10t to 11t.

[0022] In the S2 and LF refining processes, the LF inlet temperature is 1490℃~1500℃. After slag formation using a high current of 35000A~36000A, when the slag surface fluctuates and the molten steel and electric arc are not exposed, 35Kg / t steel~45Kg / t steel of active lime is added. After 5min~6min, the first sample is taken for chemical composition analysis. Alloys are added according to the target composition requirements, and carbon is increased to promote rapid melting and homogenization of alloys and carbon powder. When the molten steel temperature reaches 1600℃~1610℃, 1.5kg / t steel~1.6kg / t steel of diffusion deoxidizer alumina balls are added for diffusion deoxidation, and the furnace door is closed for 10min~13min. When the molten steel temperature reaches 1580℃~1600℃, a second sample is taken for analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken away, the molten steel is removed from the station when the temperature reaches 1600℃~1610℃. The LF smelting cycle is 35min~45min. The amount of alloy added per ton of steel is as follows: 1.0kg / t~1.2kg / t of ferrosilicon, 1.7kg / t~1.9kg / t of high carbon ferromanganese, 3.0kg / t~3.2kg / t of high carbon ferrochrome, 1.8kg / t~2.0kg / t of ferrovanadium, and 0.4kg / t~0.42m / t of aluminum wire, of which the size of aluminum wire is Φ10mm~Φ12mm. The amount of auxiliary materials added per ton of steel is as follows: 4kg / t~4.2Kg / t of active lime with a particle size of 10mm~70mm, 2.1kg / t~2.2kg / t of silicon carbide with a particle size of 2mm~5mm, and 0.6~0.65kg / t of coke particles.

[0023] In S3 and RH vacuum refining, the inlet temperature is 1610℃~1620℃, the operation time is 30min~40min, and the vacuum pump is started when the argon pressure is controlled at 0.1MPa~0.3MPa. The molten steel is kept from being exposed by slight movement of the slag surface. When the vacuum degree reaches 100Pa~110Pa, it is held for 10min~15min. At the same time, the argon pressure is adjusted to 0.3MPa~0.5MPa. After the static argon blowing is completed, a covering agent of 0.6kg / t steel~0.7kg / t steel and a silicon-calcium alloy cored wire of 2m / t steel~2.1m / t steel are added. The size of the silicon-calcium alloy cored wire is Φ14mm~Φ14.2mm. The outlet temperature is 1560℃~1570℃.

[0024] S4. In continuous casting, the ladle temperature is 1507℃~1515℃, the molten steel volume is 100t~105t, the H in the tundish is controlled to be ≤2ppm, the casting time is 40min~45min, the entire process is protected during casting, and medium carbon steel protective slag is used for the mold mold.

[0025] S5. In the heating process, the billet from the continuous casting process is fed into the heating furnace at a temperature of 470℃~560℃; the preheating section is at a temperature of 680℃~700℃ for 1.3h~1.5h; the heating section includes heating section 1 at a temperature of 1190℃~1220℃ for 1.3h~1.5h; heating section 2 at a temperature of 850℃~860℃ for 1.3h~1.5h; the soaking section is at a temperature of 1190℃~1210℃ for 1.3h~1.5h; and the tapping temperature is 1180℃~1190℃.

[0026] S6. In the rolling process, the heated continuously cast billet is initially rolled into a billet using a 9-pass rolling process, with four turns of steel. It passes through three 850mm rolling mills and one 735mm rolling mill, then enters an 8-stand continuous rolling mill group for further rolling. The billet is turned once before the first pass, a second time after the second pass, a third time after the second pass, and a fourth time after the fourth pass. The width of the first pass is 408mm to 408.05mm. The first pass has a width of 421mm to 421.05mm, a reduction of 65mm to 65.05mm; the second pass has a width of 426mm to 426.05mm, a height of 351mm to 351.05mm, and a reduction of 70mm to 70.05mm; the third pass has a width of 370mm to 370.05mm, a height of 362mm to 362.05mm, and a reduction of 64mm to 64.05mm; the fourth pass has a width of 397mm to 39... 7.05mm, height 272mm~272.05mm, reduction 90mm~90.05mm; 5th pass width 285mm~285.05mm, height 355mm~355.05mm, reduction 42mm~42.05mm; 6th pass width 297mm~297.05mm, height 315mm~315.05mm, reduction 40mm~40.05mm; 7th pass width 3... 0.07mm~307.05mm, height 280mm~280.05mm, reduction 35mm~35.05mm; 8th pass width 317mm~317.05mm, height 246mm~246.05mm, reduction 34mm~34.05mm; 9th pass width 271mm~271.05mm, height 235mm~235.05mm, reduction 82mm~82.05mm.

[0027] The continuous rolling mill produces a product in 9 passes; the first pass has a height of 229mm–229.05mm and a width of 245mm–245.05mm; the second pass has a height of 192mm–192.05mm and a width of 235mm–235.05mm; the third pass has a height of 200mm–200.05mm and a width of 195mm–195.05mm; the fourth pass has a height of 173mm–173.05mm and a width of 210mm–210.05mm; the fifth pass has a height of 180mm–180.05mm and a width of 17... 8.2mm~178.25mm; 6th pass: height 142mm~142.05mm, width 190mm~190.05mm; 7th pass: height 158mm~158.05mm, width 154.8mm~154.85mm; 8th pass: height 121mm~121.05mm, width 162.8mm~162.85mm; 9th pass: height 131.76mm~131.80mm, width 131.76mm~131.80mm; finished product after 9th pass.

[0028] S7. In the heat preservation process, the bar material prepared by the rolling process is heat-preserved. The temperature of the lower heat preservation pit is ≥570℃, the heat preservation time is 50h~55h, and the temperature of the bar material leaving the pit is ≤160℃.

[0029] S8. In heat treatment, the steel after heat preservation is subjected to heat treatment, which includes the following steps:

[0030] (1) The steel after heat preservation is quenched at a temperature of 840℃~860℃, held for 0.9h~1.2h, and then oil cooled.

[0031] (2) Temper the quenched and cooled steel at a temperature of 490℃~510℃, hold for 1.9h~2.2h, and then water cool.

[0032] The following are specific embodiments.

[0033] Example 1:

[0034] 1Chemical composition

[0035] The internal control chemical composition is determined as follows: C: 0.50%, Si: 0.25%, Mn: 0.59%, P: 0.010%, S: 0.005%, Cr: 0.95%, Ni: 0.08%, Mo: 0.02%, V: 0.15%, Cu: 0.05%, with the balance being iron and unavoidable impurities.

[0036] 2. Production processes of electric furnace continuous casting for steel bars used in automotive engine connecting rods

[0037] Process route: Ecological electric furnace + LF + RH + continuous casting billet → heating furnace heating → rolling → heat preservation → finishing → inspection → packaging and warehousing → delivery.

[0038] (2) Ecological electric furnace smelting

[0039] 100% scrap steel smelting; scrap steel input: 103t, alloy structural steel cuts: 20t, heavy scrap steel: 72t, bale-shaped scrap steel: 10t; tapping temperature: 1575℃; C: 0.12%, P: 0.008% at tapping; slag, pre-deoxidizer, and alloys added when 1 / 4 of the steel has been tapped; tapping yield: 110t; smelting cycle: 43min. Alloy addition per ton of steel: silicon manganese 5.1Kg / t, high-carbon ferromanganese 2.1Kg / t, high-carbon ferrochrome 14.7Kg / t, aluminum wire segments (12mm) 0.6Kg / t. Auxiliary material addition per ton of steel: active lime (35mm) 40Kg / t, magnesite (40mm) 25Kg / t, ladle ash 6Kg / t, small pieces of coke 20Kg / t.

[0040] (2) LF furnace refining

[0041] The LF furnace enters at a temperature of 1495℃, and is heated and slag-forming with a high current of 35500A. When the slag surface fluctuates and the molten steel and electric arc are not exposed, active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloys are added according to the target chemical composition values, and carbon is increased to promote rapid melting and homogenization of the alloys and carbon powder. When the molten steel temperature reaches 1606℃, 1.5 kg / t of diffusion deoxidizer alumina balls is added for diffusion deoxidation. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1590℃, 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 furnace leaves the station when the molten steel temperature reaches 1605℃. The LF smelting cycle is 40 minutes. The amount of alloys added per ton of steel is: 1.0 kg / t ferrosilicon, 1.8 kg / t high-carbon ferromanganese, 3.0 kg / t high-carbon ferrochrome, 1.9 kg / t ferrovanadium, and 0.4 m / t aluminum wire (Φ12mm). Additional auxiliary materials per ton of steel: 4 kg / t of active lime (35 mm), 2.1 kg / t of silicon carbide (3 mm), and 0.6 kg / t of coke granules.

[0042] (3) RH refining

[0043] The inlet temperature is 1615℃, the operation time is 37min, the argon pressure is controlled at 0.1MPa before the vacuum pump is started, so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum degree reaches 103Pa, the timing starts and is maintained for 12min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 2 meters of silicon-calcium alloy cored wire (Φ14mm) per t of steel and 0.6kg of covering agent per t of steel are added. The outlet temperature is 1567℃.

[0044] (5) Continuous casting

[0045] The ladle temperature upon arrival was 1510℃, the molten steel volume was 102t, the tundish H was controlled at 1.5ppm, the casting time was 42min, the entire casting process was protected, and medium carbon steel protective slag was used for the crystallizer.

[0046] (5) Heating process: The temperature of the furnace is 520℃, the temperature of the preheating section is 690℃, and the time is 1.4h; the temperature of the second heating section is 855℃, and the time is 1.4h; the temperature of the first heating section is 1210℃, and the time is 1.4h; the temperature of the soaking section is 1200℃, and the time is 1.5h; the tapping temperature is 1185℃.

[0047] (6) Rolling process

[0048] Initial rolling process: 9 rolling passes, turning over → Pass 1: Width 408mm, Height 421mm, Reduction 65mm → Pass 2: Width 426mm, Height 351mm, Reduction 70mm → Turning over → Pass 3: Width 370mm, Height 362mm, Reduction 64mm → Pass 4: Width 397mm, Height 272mm, Reduction 90mm → Turning over → Pass 5: Width 285mm, Height 355mm, Reduction 42mm → 6th pass, width 297mm, height 315mm, reduction 40mm → 7th pass, width 307mm, height 280mm, reduction 35mm → 8th pass, width 317mm, height 246mm, reduction 34mm → Turning steel → 9th pass, width 271mm, height 235mm, reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling mill unit for rolling.

[0049] Continuous rolling process: 9 passes. Pass 1: height 229mm, width 245mm; Pass 2: height 192mm, width 235mm; Pass 3: height 200mm, width 195mm; Pass 4: height 173mm, width 210mm; Pass 5: height 180mm, width 178.2mm; Pass 6: height 142mm, width 190mm; Pass 7: height 158mm, width 154.8mm; Pass 8: height 121mm, width 162.8mm; Pass 9: height 131.76mm, width 131.76mm; Finished product after 9 passes.

[0050] (7) Thermal Insulation Process

[0051] Insulation process: steel insulation, temperature in the insulation pit is 580℃, insulation time is 54 hours, and the temperature after exiting the pit is 150℃.

[0052] (8) Heat treatment process

[0053] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0054] 1) Quenching: 850℃, hold for 1.0h, oil cooling;

[0055] 2) Tempering: 500℃, hold for 2.0h, then water-cooled.

[0056] Example 2:

[0057] 1Chemical composition

[0058] The internal control chemical composition is determined as follows: C: 0.50%, Si: 0.25%, Mn: 0.65%, P: 0.010%, S: 0.005%, Cr: 0.95%, Ni: 0.06%, Mo: 0.02%, V: 0.14%, Cu: 0.05%, with the balance being iron and unavoidable impurities.

[0059] 2. Production processes of electric furnace continuous casting for steel bars used in automotive engine connecting rods

[0060] Process route: Ecological electric furnace + LF + RH + continuous casting billet → heating furnace heating → rolling → heat preservation → finishing → inspection → packaging and warehousing → delivery.

[0061] (3) Ecological electric furnace smelting

[0062] 100% scrap steel smelting; scrap steel input: 102t, alloy structural steel cuts: 20t, heavy scrap steel: 72t, bale-shaped scrap steel: 11t; tapping temperature: 1575℃; C: 0.12%, P: 0.008% at tapping; slag, pre-deoxidizer, and alloys are added when 1 / 4 of the steel has been tapped; tapping yield: 110t; smelting cycle: 44min. Alloy addition per ton of steel: silicon manganese 5.1Kg / t, high-carbon ferromanganese 2.1Kg / t, high-carbon ferrochrome 14.7Kg / t, aluminum wire segments (12mm) 0.6Kg / t. Auxiliary material addition per ton of steel: active lime (35mm) 40Kg / t, magnesite (40mm) 25Kg / t, ladle ash 6Kg / t, small pieces of coke 20Kg / t.

[0063] (2) LF furnace refining

[0064] The LF furnace enters at a temperature of 1497℃, and is heated and slag-forming with a high current of 35600A. When the slag surface fluctuates and the molten steel and electric arc are not exposed, active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloys are added according to the target chemical composition values, and carbon is increased to promote rapid melting and homogenization of the alloys and carbon powder. When the molten steel temperature reaches 1605℃, 1.5 kg / t of diffusion deoxidizer alumina balls are added for diffusion deoxidation. The furnace door is closed for 10 minutes. When the molten steel temperature reaches 1590℃, 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 furnace leaves the station when the molten steel temperature reaches 1605℃. The LF smelting cycle is 39 minutes. The amount of alloys added per ton of steel is: 1.0 kg / t ferrosilicon, 1.8 kg / t high-carbon ferromanganese, 3.0 kg / t high-carbon ferrochrome, 1.9 kg / t ferrovanadium, and 0.4 m / t aluminum wire (Φ12mm). Additional auxiliary materials per ton of steel: 4 kg / t of active lime (35 mm), 2.1 kg / t of silicon carbide (3 mm), and 0.6 kg / t of coke granules.

[0065] (3) RH refining

[0066] The inlet temperature is 1615℃, the operation time is 37min, the argon pressure is controlled at 0.1MPa before the vacuum pump is started, so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum degree reaches 105Pa, the timing starts and is maintained for 12min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 2m / t of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t of covering agent are added. The outlet temperature is 1567℃.

[0067] (6) Continuous casting

[0068] The ladle temperature upon arrival was 1510℃, the molten steel volume was 102t, the tundish H was controlled at 1.5ppm, the casting time was 42min, the entire casting process was protected, and medium carbon steel protective slag was used for the crystallizer.

[0069] (5) Heating process: The temperature of the furnace is 500℃, the temperature of the preheating section is required to be 690℃, and the time is 1.4h; the temperature of the second heating section is required to be 856℃, and the time is 1.4h; the temperature of the first heating section is required to be 1210℃, and the time is 1.4h; the temperature of the soaking section is required to be 1200℃, and the time is 1.4h; the tapping temperature is 1187℃.

[0070] (6) Rolling process

[0071] Initial rolling process: 9 rolling passes, turning over → Pass 1: Width 408mm, Height 421mm, Reduction 65mm → Pass 2: Width 426mm, Height 351mm, Reduction 70mm → Turning over → Pass 3: Width 370mm, Height 362mm, Reduction 64mm → Pass 4: Width 397mm, Height 272mm, Reduction 90mm → Turning over → Pass 5: Width 285mm, Height 355mm, Reduction 42mm → 6th pass, width 297mm, height 315mm, reduction 40mm → 7th pass, width 307mm, height 280mm, reduction 35mm → 8th pass, width 317mm, height 246mm, reduction 34mm → Turning steel → 9th pass, width 271mm, height 235mm, reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling mill unit for rolling.

[0072] Continuous rolling process: 9 passes. Pass 1: height 229mm, width 245mm; Pass 2: height 192mm, width 235mm; Pass 3: height 200mm, width 195mm; Pass 4: height 173mm, width 210mm; Pass 5: height 180mm, width 178.2mm; Pass 6: height 142mm, width 190mm; Pass 7: height 158mm, width 154.8mm; Pass 8: height 121mm, width 162.8mm; Pass 9: height 131.76mm, width 131.76mm; Finished product after 9 passes.

[0073] (7) Thermal Insulation Process

[0074] Insulation process: steel insulation, temperature in the insulation pit is 590℃, insulation time is 54 hours, and the temperature after exiting the pit is 120℃.

[0075] (8) Heat treatment process

[0076] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0077] 1) Quenching: 850℃, hold for 1.0h, oil cooling;

[0078] 2) Tempering: 500℃, hold for 2.0h, then water-cooled.

[0079] Example 3:

[0080] 1Chemical composition

[0081] The internal control chemical composition is determined as follows: C: 0.51%, Si: 0.26%, Mn: 0.62%, P: 0.010%, S: ≤0.006%, Cr: 0.92%, Ni: 0.06%, Mo: 0.02%, V: 0.15%, Cu: 0.04%, with the balance being iron and unavoidable impurities.

[0082] 2. Production processes of electric furnace continuous casting for steel bars used in automotive engine connecting rods

[0083] Process route: Ecological electric furnace + LF + RH + continuous casting billet → heating furnace heating → rolling → heat preservation → finishing → inspection → packaging and warehousing → delivery.

[0084] (4) Ecological electric furnace smelting

[0085] 100% scrap steel smelting; scrap steel input: 103t, alloy structural steel cuts: 20t, heavy scrap steel: 72t, bale-shaped scrap steel: 10t; tapping temperature: 1578℃; carbon content at tapping: 0.12%, phosphorus content: 0.009%; slag, pre-deoxidizer, and alloys are added when 1 / 4 of the steel has been tapped; tapping yield: 109t; smelting cycle: 41min. Alloy addition per ton of steel: silicon manganese 5.1kg / t, high-carbon ferromanganese 2.1kg / t, high-carbon ferrochrome 14.8kg / t, aluminum wire segments (12mm) 0.6kg / t. Auxiliary materials addition per ton of steel: active lime (35mm) 40kg / t, magnesite (40mm) 25kg / t, ladle ash 6kg / t, small pieces of coke 20kg / t.

[0086] (2) LF furnace refining

[0087] The LF furnace enters at a temperature of 1497℃, and is heated and slag-forming with a high current of 35600A. When the slag surface fluctuates and the molten steel and electric arc are not exposed, active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloys are added according to the target chemical composition values, and carbon is increased to promote rapid melting and homogenization of the alloys and carbon powder. When the molten steel temperature reaches 1605℃, 1.5 kg / t of diffusion deoxidizer alumina balls are added for diffusion deoxidation. The furnace door is closed for 10 minutes. When the molten steel temperature reaches 1592℃, 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 furnace leaves the station when the molten steel temperature reaches 1604℃. The LF smelting cycle is 40 minutes. The amount of alloys added per ton of steel is: 1.0 kg / t ferrosilicon, 1.8 kg / t high-carbon ferromanganese, 3.0 kg / t high-carbon ferrochrome, 1.9 kg / t ferrovanadium, and 0.4 m / t aluminum wire (Φ12mm). Additional auxiliary materials per ton of steel: 4 kg / t of active lime (35 mm), 2.1 kg / t of silicon carbide (3 mm), and 0.6 kg / t of coke granules.

[0088] (3) RH refining

[0089] The inlet temperature is 1614℃, the operation time is 38min, the argon pressure is controlled at 0.1MPa before the vacuum pump is started, so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum degree reaches 105Pa, the timing starts and is maintained for 12min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 2 meters of silicon-calcium alloy cored wire (Φ14mm) per t of steel and 0.6kg of covering agent per t of steel are added. The outlet temperature is 1565℃.

[0090] (7) Continuous casting

[0091] The ladle temperature upon arrival was 1510℃, the molten steel volume was 102t, the tundish H was controlled at 1.5ppm, the casting time was 42min, the entire casting process was protected, and medium carbon steel protective slag was used for the crystallizer.

[0092] (5) Heating process: The temperature of the furnace is 520℃, the temperature of the preheating section is required to be 690℃, and the time is 1.4h; the temperature of the second heating section is required to be 853℃, and the time is 1.4h; the temperature of the first heating section is required to be 1210℃, and the time is 1.4h; the temperature of the soaking section is required to be 1200℃, and the time is 1.4h; the tapping temperature is 1185℃.

[0093] (6) Rolling process

[0094] Initial rolling process: 9 rolling passes, turning over → Pass 1: Width 408mm, Height 421mm, Reduction 65mm → Pass 2: Width 426mm, Height 351mm, Reduction 70mm → Turning over → Pass 3: Width 370mm, Height 362mm, Reduction 64mm → Pass 4: Width 397mm, Height 272mm, Reduction 90mm → Turning over → Pass 5: Width 285mm, Height 355mm, Reduction 42mm → 6th pass, width 297mm, height 315mm, reduction 40mm → 7th pass, width 307mm, height 280mm, reduction 35mm → 8th pass, width 317mm, height 246mm, reduction 34mm → Turning steel → 9th pass, width 271mm, height 235mm, reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling mill unit for rolling.

[0095] Continuous rolling process: 9 passes. Pass 1: height 229mm, width 245mm; Pass 2: height 192mm, width 235mm; Pass 3: height 200mm, width 195mm; Pass 4: height 173mm, width 210mm; Pass 5: height 180mm, width 178.2mm; Pass 6: height 142mm, width 190mm; Pass 7: height 158mm, width 154.8mm; Pass 8: height 121mm, width 162.8mm; Pass 9: height 131.76mm, width 131.76mm; Finished product after 9 passes.

[0096] (7) Thermal Insulation Process

[0097] Insulation process: steel insulation, temperature of the lower insulation pit is 600℃, insulation time is 54 hours, and the temperature of the lower insulation pit is 130℃.

[0098] (8) Heat treatment process

[0099] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0100] 1) Quenching: 850℃, hold for 1.0h, oil cooling;

[0101] 2) Tempering: 500℃, hold for 2.0h, then water-cooled.

[0102] Example 4:

[0103] 1Chemical composition

[0104] The internal control chemical composition is determined as follows: C: 0.50%, Si: 0.25%, Mn: 0.59%, P: 0.010%, S: 0.005%, Cr: 0.95%, Ni: 0.07%, Mo: 0.01%, V: 0.15%, Cu: 0.03%, with the balance being iron and unavoidable impurities.

[0105] 2. Production processes of electric furnace continuous casting for steel bars used in automotive engine connecting rods

[0106] Process route: Ecological electric furnace + LF + RH + continuous casting billet → heating furnace heating → rolling → heat preservation → finishing → inspection → packaging and warehousing → delivery.

[0107] (5) Ecological electric furnace smelting

[0108] 100% scrap steel smelting; scrap steel input: 102t, alloy structural steel cuts: 20t, heavy scrap steel: 72t, bale-shaped scrap steel: 10t; tapping temperature: 1575℃; C: 0.12%, P: 0.008% at tapping; slag, pre-deoxidizer, and alloys added when 1 / 4 of the steel has been tapped; tapping yield: 109t; smelting cycle: 43min. Alloy addition per ton of steel: silicon manganese 5.1Kg / t, high-carbon ferromanganese 2.1Kg / t, high-carbon ferrochrome 14.7Kg / t, aluminum wire segments (12mm) 0.6Kg / t. Auxiliary materials addition per ton of steel: active lime (35mm) 40Kg / t, magnesite (40mm) 25Kg / t, ladle ash 6Kg / t, small pieces of coke 20Kg / t.

[0109] (2) LF furnace refining

[0110] The LF furnace enters at a temperature of 1497℃, and is heated and slag-forming with a high current of 35700A. When the slag surface fluctuates and the molten steel and electric arc are not exposed, active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloys are added according to the target chemical composition values, and carbon is increased to promote rapid melting and homogenization of the alloys and carbon powder. When the molten steel temperature reaches 1605℃, 1.5 kg / t of diffusion deoxidizer alumina balls is added for diffusion deoxidation. The furnace door is closed for 10 minutes. When the molten steel temperature reaches 1590℃, 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 furnace leaves the station when the molten steel temperature reaches 1604℃. The LF smelting cycle is 40 minutes. The amount of alloys added per ton of steel is: 1.0 kg / t ferrosilicon, 1.8 kg / t high-carbon ferromanganese, 3.0 kg / t high-carbon ferrochrome, 1.9 kg / t ferrovanadium, and 0.4 m / t aluminum wire (Φ12mm). Additional auxiliary materials per ton of steel: 4 kg / t of active lime (35 mm), 2.1 kg / t of silicon carbide (3 mm), and 0.62 kg / t of coke granules.

[0111] (3) RH refining

[0112] The inlet temperature is 1615℃, the operation time is 38 minutes, the argon pressure is controlled at 0.1MPa before the vacuum pump is started, so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum degree reaches 104Pa, the timing starts and is maintained for 12 minutes. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 2 meters of silicon-calcium alloy cored wire (Φ14mm) per t of steel and 0.6kg of covering agent per t of steel are added. The outlet temperature is 1565℃.

[0113] (8) Continuous casting

[0114] The ladle temperature upon arrival was 1510℃, the molten steel volume was 102t, the tundish H was controlled at 1.5ppm, the casting time was 42min, the entire casting process was protected, and medium carbon steel protective slag was used for the crystallizer.

[0115] (5) Heating process: The temperature of the furnace is 520℃, the temperature of the preheating section is required to be 692℃, and the time is 1.5h; the temperature of the second heating section is required to be 854℃, and the time is 1.3h; the temperature of the first heating section is required to be 1210℃, and the time is 1.3h; the temperature of the soaking section is required to be 1200℃, and the time is 1.3h; the tapping temperature is 1187℃.

[0116] (6) Rolling process

[0117] Initial rolling process: 9 rolling passes, turning over → Pass 1: Width 408mm, Height 421mm, Reduction 65mm → Pass 2: Width 426mm, Height 351mm, Reduction 70mm → Turning over → Pass 3: Width 370mm, Height 362mm, Reduction 64mm → Pass 4: Width 397mm, Height 272mm, Reduction 90mm → Turning over → Pass 5: Width 285mm, Height 355mm, Reduction 42mm → 6th pass, width 297mm, height 315mm, reduction 40mm → 7th pass, width 307mm, height 280mm, reduction 35mm → 8th pass, width 317mm, height 246mm, reduction 34mm → Turning steel → 9th pass, width 271mm, height 235mm, reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling mill unit for rolling.

[0118] Continuous rolling process: 9 passes. Pass 1: height 229mm, width 245mm; Pass 2: height 192mm, width 235mm; Pass 3: height 200mm, width 195mm; Pass 4: height 173mm, width 210mm; Pass 5: height 180mm, width 178.2mm; Pass 6: height 142mm, width 190mm; Pass 7: height 158mm, width 154.8mm; Pass 8: height 121mm, width 162.8mm; Pass 9: height 131.76mm, width 131.76mm; Finished product after 9 passes.

[0119] (7) Thermal Insulation Process

[0120] Insulation process: steel insulation, temperature in the insulation pit is 580℃, insulation time is 54 hours, and the temperature after exiting the pit is 140℃.

[0121] (8) Heat treatment process

[0122] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0123] 1) Quenching: 850℃, hold for 1.0h, oil cooling;

[0124] 2) Tempering: 500℃, hold for 2.0h, then water-cooled.

[0125] Example 5:

[0126] 1Chemical composition

[0127] The internal control chemical composition was determined as follows: C: 0.51%, Si: 0.25%, Mn: 0.65%, P: 0.010%, S: 0.006%, Cr: 0.93%, Ni: 0.06%, Mo: 0.02%, V: 0.15%, Cu: 0.04%, with the balance being iron and unavoidable impurities.

[0128] 2. Production processes of electric furnace continuous casting for steel bars used in automotive engine connecting rods

[0129] Process route: Ecological electric furnace + LF + RH + continuous casting billet → heating furnace heating → rolling → heat preservation → finishing → inspection → packaging and warehousing → delivery.

[0130] (6) Ecological electric furnace smelting

[0131] 100% scrap steel smelting; scrap steel input: 103t, alloy structural steel cuts: 20t, heavy scrap steel: 72t, bale-shaped scrap steel: 10t; tapping temperature: 1576℃; C: 0.12%, P: 0.008% at tapping; slag, pre-deoxidizer, and alloys are added when 1 / 4 of the steel has been tapped; tapping yield: 110t; smelting cycle: 42min. Alloy addition per ton of steel: silicon manganese 5.1Kg / t, high-carbon ferromanganese 2.1Kg / t, high-carbon ferrochrome 14.7Kg / t, aluminum wire segments (12mm) 0.6Kg / t. Auxiliary material addition per ton of steel: active lime (35mm) 40Kg / t, magnesite (40mm) 25Kg / t, ladle ash 6Kg / t, small pieces of coke 20Kg / t.

[0132] (2) LF furnace refining

[0133] The LF furnace is fed into the station at a temperature of 1497℃. A high current of 35700A is used for heating and slag formation. When the slag surface fluctuates and the molten steel and electric arc are not exposed, active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloys are added according to the target chemical composition values, and carbon is increased to promote rapid melting and homogenization of the alloys and carbon powder. When the molten steel temperature reaches 1605℃, 1.5 kg / t of diffusion deoxidizer alumina balls is added for diffusion deoxidation. The furnace door is closed for 10 minutes. When the molten steel temperature reaches 1590℃, a second sample is taken for chemical composition analysis to confirm the deviation of each chemical element content from the target value. After the second sample is taken, the furnace is removed when the molten steel temperature reaches 1606℃. The LF smelting cycle is 41 minutes. The amount of alloys added per ton of steel is: 1.0 kg / t ferrosilicon, 1.8 kg / t high-carbon ferromanganese, 3.0 kg / t high-carbon ferrochrome, 1.9 kg / t ferrovanadium, and 0.4 m / t aluminum wire (Φ12mm). Additional auxiliary materials per ton of steel: 4 kg / t of active lime (35 mm), 2.1 kg / t of silicon carbide (3 mm), and 0.62 kg / t of coke granules.

[0134] (3) RH refining

[0135] The inlet temperature is 1614℃, the operation time is 35min, 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, 2 meters of silicon-calcium alloy cored wire (Φ14mm) per t of steel and 0.6kg of covering agent per t of steel are added. The outlet temperature is 1565℃.

[0136] (9) Continuous casting

[0137] The ladle temperature upon arrival was 1512℃, the molten steel volume was 102t, the tundish H was controlled at 1.4ppm, the casting time was 42min, the entire casting process was protected, and medium carbon steel protective slag was used for the crystallizer.

[0138] (5) Heating process: The temperature of the furnace is 530℃, the temperature of the preheating section is required to be 690℃, and the time is 1.4h; the temperature of the second heating section is required to be 856℃, and the time is 1.5h; the temperature of the first heating section is required to be 1210℃, and the time is 1.4h; the temperature of the soaking section is required to be 1200℃, and the time is 1.5h; the tapping temperature is 1187℃.

[0139] (6) Rolling process

[0140] Initial rolling process: 9 rolling passes, turning over → Pass 1: Width 408mm, Height 421mm, Reduction 65mm → Pass 2: Width 426mm, Height 351mm, Reduction 70mm → Turning over → Pass 3: Width 370mm, Height 362mm, Reduction 64mm → Pass 4: Width 397mm, Height 272mm, Reduction 90mm → Turning over → Pass 5: Width 285mm, Height 355mm, Reduction 42mm → 6th pass, width 297mm, height 315mm, reduction 40mm → 7th pass, width 307mm, height 280mm, reduction 35mm → 8th pass, width 317mm, height 246mm, reduction 34mm → Turning steel → 9th pass, width 271mm, height 235mm, reduction 82mm. After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling mill unit for rolling.

[0141] Continuous rolling process: 9 passes. Pass 1: height 229mm, width 245mm; Pass 2: height 192mm, width 235mm; Pass 3: height 200mm, width 195mm; Pass 4: height 173mm, width 210mm; Pass 5: height 180mm, width 178.2mm; Pass 6: height 142mm, width 190mm; Pass 7: height 158mm, width 154.8mm; Pass 8: height 121mm, width 162.8mm; Pass 9: height 131.76mm, width 131.76mm; Finished product after 9 passes.

[0142] (7) Thermal Insulation Process

[0143] Insulation process: steel insulation, temperature in the lower insulation pit is 590℃, insulation time is 52 hours, and the temperature after exiting the pit is 140℃.

[0144] (8) Heat treatment process

[0145] The heat-treated steel is then subjected to heat treatment, which includes the following steps:

[0146] 1) Quenching: 850℃, hold for 1.0h, oil cooling;

[0147] 2) Tempering: 500℃, hold for 2.0h, then water-cooled.

[0148] 2. Finished product inspection results

[0149] (1) Low magnification tissue of Φ130mm specification

[0150] 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

[0151] (2) Non-metallic inclusions with a diameter of 130mm

[0152]

[0153] (3) Mechanical properties of Φ130mm specification

[0154]

[0155]

[0156] As shown in the table above, Examples 1-5 use an ecological electric furnace + LF + RH + continuous casting billet → heating → primary rolling mill rolling → continuous rolling mill to produce steel bars for automotive engine connecting rods. This meets the quality requirements for steel bars for automotive engine connecting rods, and the mechanical properties and high steel purity also meet the standard requirements.

[0157] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A steel bar for a connecting rod of an automobile engine, characterized by, Comprise the following components by mass percentage: C: 0.48%~0.53%, Si: 0.20%~0.35%, Mn: 0.55%~0.75%, P≤0.015%, S≤0.012%, Cr: 0.85%~1.05%, Ni≤0.25%, Mo≤0.05%, V: 0.11%~0.19%, Cu≤0.15%, and the balance of iron and inevitable impurities; The preparation method of the automobile engine connecting rod steel bar comprises the following steps: ecological electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating process, rolling process and heat preservation process. In the ecological electric furnace smelting, scrap steel accounts for 100% by mass fraction; the scrap steel includes alloy structural steel cut head, heavy scrap steel and bale type scrap steel; wherein the mass percentage of alloy structural steel cut in the furnace charge is 15%~30%, the mass percentage of heavy scrap steel is 60%~80%, and the mass percentage of bale type scrap steel is 7%~15%; the tapping temperature is 1570℃~1580℃, the electric furnace endpoint composition is: C: 0.10%~0.15%, P≤0.010%; slag, pre-deoxidizer and alloy are added when 1 / 4~1 / 3 of the tapping is completed, and the smelting cycle is 40min~45min; the alloy addition amount per ton of steel is: 5.1Kg / t~5.2Kg / t of silicon manganese, 2.1Kg / t~2.2Kg / t of high-carbon ferromanganese, 14.5Kg / t~15Kg / t of high-carbon ferrochrome, and 0.6Kg / t~0.7Kg / t of aluminum wire segment, wherein the size specification of the aluminum wire segment is Φ10mm~Φ16mm; the auxiliary material addition amount per ton of steel is: 40Kg / t~41Kg / t of active lime, 25Kg / t~26Kg / t of magnesite, 6Kg / t~6.2Kg / t of ladle slag, and 20Kg / t~21Kg / t of small block coke; wherein the particle size of the active lime is 10mm~70mm; the particle size of the magnesite is 10mm~60mm; In the LF refining, the LF inlet temperature is 1490-1500℃, after the slag is heated by 35000A-36000A large current, when the slag surface fluctuates, the molten steel and the arc are not exposed, 35-45 Kg / t of active lime is added, after 5-6 minutes, the first sampling analysis is carried out, and the molten steel composition content is adjusted according to the target composition requirement; when the molten steel temperature reaches 1600-1610℃, 1.5-1.6 Kg / t of alumina ball diffusion deoxidizer is added for diffusion deoxidation, and the furnace door is closed for 10-13 minutes; when the molten steel temperature reaches 1580-1600℃, the second sampling analysis is carried out; when the molten steel temperature reaches 1600-1610℃, the station is left, the LF smelting cycle is 35-45 minutes, the alloy is added at a rate of 1.0-1.2 Kg / t of ferrosilicon, 1.7-1.9 Kg / t of high-carbon ferromanganese, 3.0-3.2 Kg / t of high-carbon ferrochrome, 1.8-2.0 Kg / t of ferrovanadium, and 0.4-0.42 m / t of aluminum wire, wherein the size specification of the aluminum wire is Φ10-Φ12 mm; the auxiliary material is added at a rate of 4-4.2 Kg / t of active lime with a particle size of 10-70 mm, 2.1-2.2 Kg / t of silicon carbide with a particle size of 2-5 mm, and 0.6-0.65 Kg / t of coke particles; In the RH vacuum refining, the inlet temperature is 1610-1620℃, the operation time is 30-40 minutes, the argon pressure is controlled at 0.1-0.3 MPa, the vacuum pump is started, the vacuum degree reaches 100-110 Pa and is maintained for 10-15 minutes, the argon pressure is adjusted to 0.3-0.5 MPa, after the static argon blowing is completed, 0.6-0.7 Kg / t of covering agent and 2-2.1 m / t of silicon-calcium alloy cored wire are added, wherein the size specification of the silicon-calcium alloy cored wire is Φ14-Φ14.2 mm; the outlet temperature is 1560-1570℃; In the continuous casting, the ladle arrives at a temperature of 1507-1515℃, the molten steel amount is 100-105 t, the tundish H control is ≤2 ppm, the casting time is 40-45 minutes, the whole process is protected casting, and the crystallizer protective slag uses medium-carbon steel protective slag; In the heating process, the square billet offline in the continuous casting process is sent into the heating furnace, the heating furnace temperature is 470-560℃, the preheating section temperature is 680-700℃, and the time is 1.3-1.5 hours; In the rolling process, the heated continuous casting billet is primary rolled and bloomed, the primary rolling adopts 9 passes of rolling and blooming, four times of steel turning, passes through 3 sets of 850 mm rolling mills and 1 set of 735 mm rolling mill, and then enters 8 sets of continuous rolling mill groups for rolling; In the rolling process, the continuous rolling product rolling process is rolled for 9 passes; The heat-treated steel material is heat treated, and the heat treatment includes the following steps: (1) the steel material after heat preservation is quenched, the heating temperature is 840-860 DEG C, the heat preservation time is 0.9-1.2 h, and oil cooling is carried out; (2) the steel material after quenching cooling is tempered, the tempering temperature is 490-510 DEG C, the heat preservation time is 1.9-2.2 h, and water cooling is carried out.

2. The steel bar for automotive engine connecting rods according to claim 1, characterized by, In the heating process, the heating section comprises heating 1 section temperature 1190-1220 DEG C, time 1.3-1.5 h; heating 2 section temperature 850-860 DEG C, time 1.3-1.5 h; soaking section temperature is 1190-1210 DEG C, time 1.3-1.5 h; the tapping temperature is 1180-1190 DEG C.

3. The steel bar for automotive engine connecting rods according to claim 1, characterized by, In the rolling process, the heated continuous casting billet is rolled and opened, once turned over before rolling 1 pass, turned over again after rolling 2 passes, turned over once more after rolling 2 passes, and turned over again after rolling 4 passes; the first pass is 408-408.05 mm wide, 421-421.05 mm high, and the reduction is 65-65.05 mm; the second pass is 426-426.05 mm wide, 351-351.05 mm high, and the reduction is 70-70.05 mm; the third pass is 370-370.05 mm wide, 362-362.05 mm high, and the reduction is 64-64.05 mm; the fourth pass is 397-397.05 mm wide, 272-272.05 mm high, and the reduction is 90-90.05 mm; the fifth pass is 285-285.05 mm wide, 355-355.05 mm high, and the reduction is 42-42.05 mm; the sixth pass is 297-297.05 mm wide, 315-315.05 mm high, and the reduction is 40-40.05 mm; the seventh pass is 307-307.05 mm wide, 280-280.05 mm high, and the reduction is 35-35.05 mm; the eighth pass is 317-317.05 mm wide, 246-246.05 mm high, and the reduction is 34-34.05 mm; the ninth pass is 271-271.05 mm wide, 235-235.05 mm high, and the reduction is 82-82.05 mm.

4. The steel bar for automotive engine connecting rods according to claim 1, characterized by, In the rolling process, the continuous rolling process is used, and the rolling is performed for 9 passes; the first pass is 229mm-229.05mm high and 245mm-245.05mm wide; the second pass is 192mm-192.05mm high and 235mm-235.05mm wide; the third pass is 200mm-200.05mm high and 195mm-195.05mm wide; the fourth pass is 173mm-173.05mm high and 210mm-210.05mm wide; the fifth pass is 180mm-180.05mm high and 178.2mm-178.25mm wide; the sixth pass is 142mm-142.05mm high and 190mm-190.05mm wide; the seventh pass is 158mm-158.05mm high and 154.8mm-154.85mm wide; the eighth pass is 121mm-121.05mm high and 162.8mm-162.85mm wide; the ninth pass is 131.76mm-131.80mm high and 131.76mm-131.80mm wide; and the finished product is obtained after the ninth pass.

5. The steel bar for automotive engine connecting rods according to claim 1, characterized by, In the heat preservation process, the rod prepared by the rolling process is subjected to heat preservation, the temperature of the lower heat preservation pit is greater than or equal to 570 DEG C, the heat preservation time is 50h-55h, and the temperature of the pit outlet is less than or equal to 160 DEG C.

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