Steel bar for connecting rod of automobile engine and preparation method of steel bar

Abstract

The invention discloses a steel bar for an automobile engine connecting rod and a preparation method of the steel bar. The steel bar for the automobile engine connecting rod comprises, by mass, 0.48%-0.53% of C, 0.20%-0.35% of Si, 0.55%-0.75% of Mn, smaller than or equal to 0.015% of P, smaller than or equal to 0.012% of S, 0.85%-1.05% of Cr, smaller than or equal to 0.25% of Ni, smaller than or equal to 0.05% of Mo, 0.11%-0.19% of V, smaller than or equal to 0.15% of Cu and the balance iron and inevitable impurities. The steel bar for the connecting rod of the automobile engine, which is produced by adopting the ecological electric furnace, LF, RH, continuous casting and rolling processes, meets the high-end use requirements, not only ensures the indexes such as mechanical properties and high steel purity of a finished steel product of the steel bar for the connecting rod of the automobile engine, but also ensures the surface quality level of the steel bar for the connecting rod of the automobile engine.

Description

Technical Field

[0001] The invention relates to the technical field of materials and metallurgy, and more specifically, to a steel bar for connecting rods of automobile engines and a preparation method thereof. Background Art

[0002] The connecting rod of an automobile engine is subjected to the gas force transmitted from the piston pin, its own swing, and the periodic action of the reciprocating inertia force of the piston group. Therefore, the connecting rod is subjected to alternating loads such as compression and tension, which requires that the connecting rod must have sufficient fatigue strength and structural rigidity. If the fatigue strength is insufficient, it will often cause the connecting rod body or connecting rod bolt to break, and then cause a major accident of complete machine damage. If the rigidity is insufficient, it will cause the rod body to bend and deform, and the big end of the connecting rod to lose roundness, resulting in eccentric wear of the piston, cylinder, bearing, crank pin, etc. The quality of the steel used for the automobile engine connecting rod directly affects the service life and wear resistance of the automobile engine, and even affects the safety of the entire automobile operation process.

[0003] Currently, the steel used for automobile engine connecting rods has many impurities, poor wear resistance, low fatigue life, and mechanical properties that are difficult to meet application requirements. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects of the prior art, and to provide a steel bar for automobile engine connecting rod and a preparation method thereof. The steel bar for automobile engine connecting rod produced by the smelting and rolling process of the ecological electric furnace + LF + RH + continuous casting smelting process meets the high-end use requirements, and realizes a breakthrough in the batch production of steel bars for automobile engine connecting rods by the ecological electric furnace continuous casting process. It not only ensures the mechanical properties of the finished steel and high steel purity of the steel bar for automobile engine connecting rod, but also ensures the surface quality level of the steel bar for automobile engine connecting rod, and meets the quality requirements of the steel bar for automobile engine connecting rod.

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

[0006] A steel bar for automobile engine connecting rods, comprising the following components in percentage by mass:

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

[0008] The present invention also discloses a method for preparing a steel bar for automobile engine connecting rod as described above, comprising the following steps: ecological electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating process, rolling process and heat preservation process; wherein, in the ecological electric furnace smelting, scrap steel is used as a furnace charge, and the scrap steel accounts for 100% by mass; the scrap steel includes alloy structural steel cutting heads, heavy scrap steel and lump-type scrap steel; wherein, the mass percentage of alloy structural steel cutting heads in the furnace charge is 15% to 30%, the mass percentage of heavy scrap steel is 60% to 80%, and the mass percentage of lump-type scrap steel is 7% to 15%; the tapping temperature is 1570°C to 1580°C, the electric furnace endpoint composition: C: 0.10% to 0.15%, P≤0.010%; slag is added when 1 / 4 to 1 / 3 of the steel is tapped , pre-deoxidizer, alloy, smelting cycle 40min ~ 45min; alloy addition amount per ton of steel: 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, 0.6Kg / t ~ 0.7Kg / t of aluminum segments, wherein the size of the aluminum segments is Φ10mm ~ Φ16mm; auxiliary materials added per ton of steel: 40Kg / t ~ 41Kg / t of active lime, 25Kg / t ~ 26Kg / t of magnesite, 6Kg / t ~ 6.2Kg / t of ladle ash, 20Kg / t ~ 21Kg / t of small pieces of coke; wherein the particle size of the active lime is 10mm ~ 70mm; the particle size of the magnesite is 10mm ~ 60mm.

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

[0010] (1) The ecological electric furnace + LF + RH + 390mm * 480mm smelting process and rolling process are used to produce steel bars for automobile engine connecting rods, which meets the mechanical performance requirements and ensures the purity of the steel.

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

[0012] (3) The macrostructure and non-metallic inclusions of the finished steel meet the requirements of high-end products. DETAILED DESCRIPTION

[0013] The present invention is further described below in conjunction with specific embodiments, but the present invention is not limited in any way.

[0014] 1. Chemical composition

[0015] The invention discloses a steel bar for connecting rods of automobile engines, comprising the following components in 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 is iron and inevitable impurities.

[0016] 2. Production technology

[0017] The method for preparing a steel bar for a connecting rod of an automobile engine of the present invention comprises the following steps: ecological electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating process, rolling process and heat preservation process.

[0018] Further, the method specifically includes the following steps:

[0019] S1. In the ecological electric furnace smelting, scrap steel is used as the furnace charge, and scrap steel accounts for 100% by mass; scrap steel includes alloy structural steel cuttings, heavy scrap steel and lump-type scrap steel; among them, the mass percentage of alloy structural steel cuttings in the furnace charge is 15% to 30%, the mass percentage of heavy scrap steel is 60% to 80%, and the mass percentage of lump-type scrap steel is 7% to 15%; the steel tapping temperature is 1570℃ to 1580℃, and the end point composition of the electric furnace is: C: 0.10% to 0.15%, P ≤ 0.010%; slag, pre-deoxidizer, and alloy are added when 1 / 4 to 1 / 3 of the steel is tapped, and the steel tapping amount is 1 08t~112t, smelting cycle 40min~45min; alloy addition per ton of steel: 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, 0.6Kg / t~0.7Kg / t of aluminum wire segment; auxiliary material addition per ton of steel: 40Kg / t~41Kg / t of active lime, 25Kg / t~26Kg / t of magnesite, 6Kg / t~6.2Kg / t of ladle ash, 20Kg / t~21Kg / t of small coke.

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

[0021] In a specific embodiment, the loading amount of scrap steel is 102t~104t, the alloy structural steel cutting head is 20t~21t, the heavy scrap steel is 72t~73t, and the lump scrap steel is 10t~11t.

[0022] During S2 and LF refining, the LF inlet temperature is 1490℃~1500℃. After heating and melting the slag with a high current of 35000A~36000A, when the slag surface fluctuates and the molten steel and arc are not exposed, 35Kg / t steel~45Kg / t steel of active lime is added. After 5min~6min, the chemical composition is analyzed for the first time. The alloy is added according to the target composition requirements, and carbon is added to promote the rapid melting and homogenization of the alloy 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℃, the second sampling analysis is carried out to confirm the deviation value of the content of each chemical element from the target value requirement. After the secondary sample is taken away, when the molten steel temperature reaches 1600℃~1610℃, leave the station, LF smelting cycle 35min~45min, additional alloy addition per ton of steel: 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, 0.4kg / t~0.42m / t of aluminum wire, the size of the aluminum wire is Φ10mm~Φ12mm; additional auxiliary materials added per ton of steel: 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, 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 to be 0.1MPa~0.3MPa, so that the molten steel is not exposed when the slag surface moves slightly. When the vacuum degree reaches 100Pa~110Pa, the time is maintained for 10min~15min. At the same time, the argon pressure is adjusted to 0.3MPa~0.5MPa. After the static argon blowing is completed, 0.6kg / t steel~0.7kg / t steel covering agent and 2m / t steel~2.1m / t steel silicon-calcium alloy cored wire are added, and the size specification of the silicon-calcium alloy cored wire is Φ14mm~Φ14.2mm; the outlet temperature is 1560℃~1570℃.

[0024] S4. During continuous casting, the arrival temperature of the ladle is 1507℃~1515℃, the amount of molten steel is 100t~105t, the H in the tundish is controlled to be ≤2ppm, the casting time is 40min~45min, the whole process is protected casting, and the mold protection slag uses medium carbon steel protection slag.

[0025] S5. In the heating process, the billets produced in the continuous casting process are fed into the heating furnace, and the temperature of the heating furnace is 470℃~560℃; the temperature of the preheating section is 680℃~700℃, and the time is 1.3h~1.5h; the heating section includes heating section 1 with a temperature of 1190℃~1220℃, and the time is 1.3h~1.5h; heating section 2 with a temperature of 850℃~860℃, and the time is 1.3h~1.5h; the temperature of the soaking section is 1190℃~1210℃, and the time is 1.3h~1.5h; and the steel tapping temperature is 1180℃~1190℃.

[0026] S6, in the rolling process, the heated continuous casting billet is initially rolled and opened, and the initial rolling adopts 9 rolling passes, four steel turnings, passing through 3 850mm rolling mills and 1 735mm rolling mill, and then entering the 8-frame continuous rolling mill group for rolling; the steel is turned once before rolling 1 pass, the steel is turned for the second time after rolling 2 passes, the steel is turned for the third time after rolling 2 passes, and the steel is turned for the fourth time after rolling 4 passes; the width of the first pass is 408mm~408.05mm, Height 421mm~421.05mm, reduction 65mm~65.05mm; 2nd pass width 426mm~426.05mm, height 351mm~351.05mm, reduction 70mm~70.05mm; 3rd pass width 370mm~370.05mm, height 362mm~362.05mm, reduction 64mm~64.05mm; 4th pass width 397mm~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 07mm~307.05mm, height 280mm~280.05mm, reduction 35mm~35.05mm; the 8th pass width 317mm~317.05mm, height 246mm~246.05mm, reduction 34mm~34.05mm; the 9th pass width 271mm~271.05mm, height 235mm~235.05mm, reduction 82mm~82.05mm.

[0027] The continuous rolling product is rolled in 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 170mm~180.05mm wide. 8.2mm~178.25mm; the 6th pass is 142mm~142.05mm high and 190mm~190.05mm wide; the 7th pass is 158mm~158.05mm high and 154.8mm~154.85mm wide; the 8th pass is 121mm~121.05mm high and 162.8mm~162.85mm wide; the 9th pass is 131.76mm~131.80mm high and 131.76mm~131.80mm wide; the finished product is produced after the 9th pass.

[0028] S7. In the insulation process, the bars prepared by the rolling process are insulated, the temperature of the lower insulation pit is ≥570°C, the insulation is 50h~55h, and the exit temperature is ≤160°C.

[0029] S8, in the heat treatment, the steel material after heat preservation is heat treated, and the heat treatment includes the following steps:

[0030] (1) The steel is quenched after being kept warm, with the heating temperature at 840°C to 860°C, the heat preservation time at 0.9h to 1.2h, and oil cooling.

[0031] (2) After quenching and cooling, the steel is tempered at a temperature of 490°C to 510°C, kept at this temperature for 1.9h to 2.2h, and water-cooled.

[0032] The following are specific embodiments

[0033] Embodiment 1:

[0034] 1Chemical composition

[0035] The internal controlled 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%, and the balance is iron and inevitable impurities.

[0036] 2. Electric furnace continuous casting production processes of steel bars for automobile engine connecting rods

[0037] Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery.

[0038] (2) Ecological electric furnace smelting

[0039] 100% scrap steel smelting, scrap steel loading: 103t, alloy structural steel cutting head 20t, heavy scrap steel 72t, lump scrap steel 10t; tapping temperature 1575℃, C: 0.12%, P: 0.008% when tapping, slag, pre-deoxidizer, alloy added when 1 / 4 of the steel is tapped, tapping amount 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 segment (12mm) 0.6Kg / t. Auxiliary materials added per ton of steel: active lime (35mm) 40Kg / t, magnesite (40mm) 25Kg / t, ladle ash 6Kg / t, small coke 20Kg / t.

[0040] (2) LF furnace refining

[0041] The LF station temperature is 1495℃, and the 35500A high current is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, active lime is added. After 5 minutes, the chemical composition is analyzed for the first time. The alloy is added according to the target value of the chemical composition, and carbon is added to promote the rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1606℃, 1.5kg / t steel of alumina balls as a diffusion deoxidizer is added for diffusion deoxidation. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1590℃, the chemical composition is analyzed for the second time to confirm the deviation value of the content of each chemical element from the target value. After the second sample is taken away, the station is left when the molten steel temperature reaches 1605℃. The LF smelting cycle is 40 minutes. The amount of alloy added to each ton of steel is: 1.0kg / t of ferrosilicon, 1.8kg / t of high carbon ferromanganese, 3.0kg / t of high carbon ferrochrome, 1.9kg / t of ferrovanadium, and 0.4m / t of aluminum wire (Φ12mm). Supplementary materials added per ton of steel: Active lime (35mm) 4Kg / t, Silicon carbide (3mm) 2.1kg / t, Coke particles 0.6kg / t.

[0042] (3) RH refining

[0043] The inlet temperature is 1615℃, the operation time is 37min, and 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 103Pa, the timing starts and the maintenance 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 steel of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t steel of covering agent are added. The outlet temperature is 1567℃.

[0044] (5) Continuous casting

[0045] The temperature of the ladle at the station is 1510℃, the amount of molten steel is 102t, the H content of the tundish is controlled at 1.5ppm, the casting time is 42min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag.

[0046] (5) Heating process: The temperature entering the heating furnace is 520℃, the temperature of the preheating section is required to be 690℃, and the time is 1.4h; the temperature of the heating section 2 is required to be 855℃, and the time is 1.4h; the temperature of the heating section 1 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 steel tapping temperature is 1185℃.

[0047] (6) Rolling process

[0048] Primary rolling process: 9 passes, steel turning → 1st pass width 408mm, height 421mm, reduction 65mm → 2nd pass width 426mm, height 351mm, reduction 70mm → steel turning → 3rd pass width 370mm, height 362mm, reduction 64mm → 4th pass width 397mm, height 272mm, reduction 90mm → steel turning → 5th pass width 285mm, height 355mm, reduction 42mm→The 6th pass is 297mm wide, 315mm high, and 40mm reduction→The 7th pass is 307mm wide, 280mm high, and 35mm reduction→The 8th pass is 317mm wide, 246mm high, and 34mm reduction→Steel turning→The 9th pass is 271mm wide, 235mm high, and 82mm reduction, passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters the continuous rolling mill for rolling.

[0049] Continuous rolling product rolling process: 9 passes, the 1st pass is 229mm high and 245mm wide; the 2nd pass is 192mm high and 235mm wide; the 3rd pass is 200mm high and 195mm wide; the 4th pass is 173mm high and 210mm wide; the 5th pass is 180mm high and 178.2mm wide; the 6th pass is 142mm high and 190mm wide; the 7th pass is 158mm high and 154.8mm wide; the 8th pass is 121mm high and 162.8mm wide; the 9th pass is 131.76mm high and 131.76mm wide; the finished product is produced after 9 passes.

[0050] (7) Insulation process

[0051] Insulation process: Steel insulation, lower insulation pit temperature 580℃, insulation 54h, exit pit temperature 150℃.

[0052] (8) Heat treatment process

[0053] The steel after heat preservation is heat treated, and the heat treatment includes the following steps:

[0054] 1) Quenching: 850℃, holding time 1.0h, oil cooling;

[0055] 2) Tempering: 500℃, keep warm for 2.0h, water cooling.

[0056] Embodiment 2:

[0057] 1Chemical composition

[0058] The internal controlled 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%, and the balance is iron and unavoidable impurities.

[0059] 2. Electric furnace continuous casting production processes of steel bars for automobile engine connecting rods

[0060] Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery.

[0061] (3) Ecological electric furnace smelting

[0062] 100% scrap steel smelting, scrap steel loading: 102t, alloy structural steel cutting head 20t, heavy scrap steel 72t, lump scrap steel 11t; tapping temperature 1575℃, C: 0.12%, P: 0.008% when tapping, slag, pre-deoxidizer, alloy added when 1 / 4 of the steel is tapped, tapping amount 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 segment (12mm) 0.6Kg / t. Auxiliary materials added per ton of steel: active lime (35mm) 40Kg / t, magnesite (40mm) 25Kg / t, ladle ash 6Kg / t, small coke 20Kg / t.

[0063] (2) LF furnace refining

[0064] The LF station temperature is 1497℃, and the 35600A high current is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, active lime is added. After 5 minutes, the chemical composition is analyzed for the first time. The alloy is added according to the target value of the chemical composition, and carbon is added to promote the rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1605℃, 1.5kg / t steel of alumina balls as a diffusion deoxidizer is added for diffusion deoxidation. The furnace door is closed for 10 minutes. When the molten steel temperature reaches 1590℃, the chemical composition is analyzed for the second time to confirm the deviation value of the content of each chemical element from the target value. After the second sample is taken away, the station is left when the molten steel temperature reaches 1605℃. The LF smelting cycle is 39 minutes. The amount of alloy added to each ton of steel is: 1.0kg / t of ferrosilicon, 1.8kg / t of high carbon ferromanganese, 3.0kg / t of high carbon ferrochrome, 1.9kg / t of ferrovanadium, and 0.4m / t of aluminum wire (Φ12mm). Supplementary materials added per ton of steel: Active lime (35mm) 4Kg / t, Silicon carbide (3mm) 2.1kg / t, Coke particles 0.6kg / t.

[0065] (3) RH refining

[0066] The inlet temperature is 1615℃, the operation time is 37min, and 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 105Pa, the timing starts and the maintenance 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 are added. The outlet temperature is 1567℃.

[0067] (6) Continuous casting

[0068] The temperature of the ladle at the station is 1510℃, the amount of molten steel is 102t, the H content of the tundish is controlled at 1.5ppm, the casting time is 42min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag.

[0069] (5) Heating process: The temperature entering the heating furnace is 500℃, the temperature of the preheating section is required to be 690℃, and the time is 1.4h; the temperature of the heating section 2 is required to be 856℃, and the time is 1.4h; the temperature of the heating section 1 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 steel tapping temperature is 1187℃.

[0070] (6) Rolling process

[0071] Primary rolling process: 9 passes, steel turning → 1st pass width 408mm, height 421mm, reduction 65mm → 2nd pass width 426mm, height 351mm, reduction 70mm → steel turning → 3rd pass width 370mm, height 362mm, reduction 64mm → 4th pass width 397mm, height 272mm, reduction 90mm → steel turning → 5th pass width 285mm, height 355mm, reduction 42mm→The 6th pass is 297mm wide, 315mm high, and 40mm reduction→The 7th pass is 307mm wide, 280mm high, and 35mm reduction→The 8th pass is 317mm wide, 246mm high, and 34mm reduction→Steel turning→The 9th pass is 271mm wide, 235mm high, and 82mm reduction, passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters the continuous rolling mill for rolling.

[0072] Continuous rolling product rolling process: 9 passes, the 1st pass is 229mm high and 245mm wide; the 2nd pass is 192mm high and 235mm wide; the 3rd pass is 200mm high and 195mm wide; the 4th pass is 173mm high and 210mm wide; the 5th pass is 180mm high and 178.2mm wide; the 6th pass is 142mm high and 190mm wide; the 7th pass is 158mm high and 154.8mm wide; the 8th pass is 121mm high and 162.8mm wide; the 9th pass is 131.76mm high and 131.76mm wide; the finished product is produced after 9 passes.

[0073] (7) Insulation process

[0074] Insulation process: Steel insulation, lower insulation pit temperature 590℃, insulation 54h, exit pit temperature 120℃.

[0075] (8) Heat treatment process

[0076] The steel after heat preservation is heat treated, and the heat treatment includes the following steps:

[0077] 1) Quenching: 850℃, holding time 1.0h, oil cooling;

[0078] 2) Tempering: 500℃, keep warm for 2.0h, water cooling.

[0079] Embodiment 3:

[0080] 1Chemical composition

[0081] The internal controlled 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%, and the balance is iron and unavoidable impurities.

[0082] 2. Electric furnace continuous casting production processes of steel bars for automobile engine connecting rods

[0083] Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery.

[0084] (4) Ecological electric furnace smelting

[0085] 100% scrap steel smelting, scrap steel loading: 103t, alloy structural steel cutting head 20t, heavy scrap steel 72t, lump scrap steel 10t; tapping temperature 1578℃, C: 0.12%, P: 0.009% when tapping, slag, pre-deoxidizer, alloy added when 1 / 4 of the steel is tapped, tapping amount 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 segment (12mm) 0.6Kg / t. Auxiliary materials added per ton of steel: active lime (35mm) 40Kg / t, magnesite (40mm) 25Kg / t, ladle ash 6Kg / t, small coke 20Kg / t.

[0086] (2) LF furnace refining

[0087] The LF station temperature is 1497℃, and the 35600A high current is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, active lime is added. After 5 minutes, the chemical composition is analyzed for the first time. The alloy is added according to the target value of the chemical composition, and carbon is added to promote the rapid melting and homogenization of the alloy and carbon powder. When the temperature of the molten steel reaches 1605℃, 1.5kg / t steel of alumina balls as a diffusion deoxidizer is added for diffusion deoxidation. The furnace door is closed for 10 minutes. When the temperature of the molten steel reaches 1592℃, the chemical composition is analyzed for the second time to confirm the deviation value of the content of each chemical element from the target value. After the second sample is taken away, the station is left when the temperature of the molten steel reaches 1604℃. The LF smelting cycle is 40 minutes. The amount of alloy added to each ton of steel is: 1.0kg / t of ferrosilicon, 1.8kg / t of high carbon ferromanganese, 3.0kg / t of high carbon ferrochrome, 1.9kg / t of ferrovanadium, and 0.4m / t of aluminum wire (Φ12mm). Supplementary materials added per ton of steel: Active lime (35mm) 4Kg / t, Silicon carbide (3mm) 2.1kg / t, Coke particles 0.6kg / t.

[0088] (3) RH refining

[0089] The inlet temperature is 1614℃, the operation time is 38min, and 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 the maintenance 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 steel of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t steel of covering agent are added. The outlet temperature is 1565℃.

[0090] (7) Continuous casting

[0091] The temperature of the ladle at the station is 1510℃, the amount of molten steel is 102t, the H content of the tundish is controlled at 1.5ppm, the casting time is 42min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag.

[0092] (5) Heating process: The temperature entering the heating furnace is 520℃, the temperature of the preheating section is required to be 690℃, and the time is 1.4h; the temperature of the heating section 2 is required to be 853℃, and the time is 1.4h; the temperature of the heating section 1 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 steel tapping temperature is 1185℃.

[0093] (6) Rolling process

[0094] Primary rolling process: 9 passes, steel turning → 1st pass width 408mm, height 421mm, reduction 65mm → 2nd pass width 426mm, height 351mm, reduction 70mm → steel turning → 3rd pass width 370mm, height 362mm, reduction 64mm → 4th pass width 397mm, height 272mm, reduction 90mm → steel turning → 5th pass width 285mm, height 355mm, reduction 42mm→The 6th pass is 297mm wide, 315mm high, and 40mm reduction→The 7th pass is 307mm wide, 280mm high, and 35mm reduction→The 8th pass is 317mm wide, 246mm high, and 34mm reduction→Steel turning→The 9th pass is 271mm wide, 235mm high, and 82mm reduction, passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters the continuous rolling mill for rolling.

[0095] Continuous rolling product rolling process: 9 passes, the 1st pass is 229mm high and 245mm wide; the 2nd pass is 192mm high and 235mm wide; the 3rd pass is 200mm high and 195mm wide; the 4th pass is 173mm high and 210mm wide; the 5th pass is 180mm high and 178.2mm wide; the 6th pass is 142mm high and 190mm wide; the 7th pass is 158mm high and 154.8mm wide; the 8th pass is 121mm high and 162.8mm wide; the 9th pass is 131.76mm high and 131.76mm wide; the finished product is produced after 9 passes.

[0096] (7) Insulation process

[0097] Insulation process: Steel insulation, lower insulation pit temperature 600℃, insulation 54h, exit pit temperature 130℃.

[0098] (8) Heat treatment process

[0099] The steel after heat preservation is heat treated, and the heat treatment includes the following steps:

[0100] 1) Quenching: 850℃, holding time 1.0h, oil cooling;

[0101] 2) Tempering: 500℃, keep warm for 2.0h, water cooling.

[0102] Embodiment 4:

[0103] 1Chemical composition

[0104] The internal controlled 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%, and the balance is iron and unavoidable impurities.

[0105] 2. Electric furnace continuous casting production processes of steel bars for automobile engine connecting rods

[0106] Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery.

[0107] (5) Ecological electric furnace smelting

[0108] 100% scrap steel smelting, scrap steel loading: 102t, alloy structural steel cutting head 20t, heavy scrap steel 72t, lump scrap steel 10t; tapping temperature 1575℃, C: 0.12%, P: 0.008% when tapping, slag, pre-deoxidizer, alloy added when 1 / 4 of the steel is tapped, tapping amount 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 segment (12mm) 0.6Kg / t. Auxiliary materials added per ton of steel: active lime (35mm) 40Kg / t, magnesite (40mm) 25Kg / t, ladle ash 6Kg / t, small coke 20Kg / t.

[0109] (2) LF furnace refining

[0110] The LF station temperature is 1497℃, and the 35700A high current is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, active lime is added. After 5 minutes, the chemical composition is analyzed for the first time. According to the target value of the chemical composition, alloy is added and carbon is added to promote the rapid melting and homogenization of the alloy and carbon powder. When the temperature of the molten steel reaches 1605℃, 1.5kg / t steel of alumina balls as a diffusion deoxidizer is added for diffusion deoxidation. The furnace door is closed for 10 minutes. When the temperature of the molten steel reaches 1590℃, the chemical composition is analyzed for the second time to confirm the deviation value of the content of each chemical element from the target value. After the second sample is taken away, the station is left when the temperature of the molten steel reaches 1604℃. The LF smelting cycle is 40 minutes. The amount of alloy added to each ton of steel is: 1.0kg / t of ferrosilicon, 1.8kg / t of high carbon ferromanganese, 3.0kg / t of high carbon ferrochrome, 1.9kg / t of ferrovanadium, and 0.4m / t of aluminum wire (Φ12mm). Supplementary materials added per ton of steel: Active lime (35mm) 4Kg / t, Silicon carbide (3mm) 2.1kg / t, Coke particles 0.62kg / t.

[0111] (3) RH refining

[0112] The inlet temperature is 1615℃, the operation time is 38min, and 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 104Pa, the timing starts and the maintenance 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 steel of silicon-calcium alloy cored wire (Φ14mm) and 0.6kg / t steel of covering agent are added. The outlet temperature is 1565℃.

[0113] (8) Continuous casting

[0114] The temperature of the ladle at the station is 1510℃, the amount of molten steel is 102t, the H content of the tundish is controlled at 1.5ppm, the casting time is 42min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag.

[0115] (5) Heating process: The temperature entering the heating furnace is 520℃, the temperature of the preheating section is required to be 692℃, and the time is 1.5h; the temperature of the heating section 2 is required to be 854℃, and the time is 1.3h; the temperature of the heating section 1 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 steel tapping temperature is 1187℃.

[0116] (6) Rolling process

[0117] Primary rolling process: 9 passes, steel turning → 1st pass width 408mm, height 421mm, reduction 65mm → 2nd pass width 426mm, height 351mm, reduction 70mm → steel turning → 3rd pass width 370mm, height 362mm, reduction 64mm → 4th pass width 397mm, height 272mm, reduction 90mm → steel turning → 5th pass width 285mm, height 355mm, reduction 42mm→The 6th pass is 297mm wide, 315mm high, and 40mm reduction→The 7th pass is 307mm wide, 280mm high, and 35mm reduction→The 8th pass is 317mm wide, 246mm high, and 34mm reduction→Steel turning→The 9th pass is 271mm wide, 235mm high, and 82mm reduction, passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters the continuous rolling mill for rolling.

[0118] Continuous rolling product rolling process: 9 passes, the 1st pass is 229mm high and 245mm wide; the 2nd pass is 192mm high and 235mm wide; the 3rd pass is 200mm high and 195mm wide; the 4th pass is 173mm high and 210mm wide; the 5th pass is 180mm high and 178.2mm wide; the 6th pass is 142mm high and 190mm wide; the 7th pass is 158mm high and 154.8mm wide; the 8th pass is 121mm high and 162.8mm wide; the 9th pass is 131.76mm high and 131.76mm wide; the finished product is produced after 9 passes.

[0119] (7) Insulation process

[0120] Insulation process: Steel insulation, lower insulation pit temperature 580℃, insulation 54h, exit pit temperature 140℃.

[0121] (8) Heat treatment process

[0122] The steel after heat preservation is heat treated, and the heat treatment includes the following steps:

[0123] 1) Quenching: 850℃, holding time 1.0h, oil cooling;

[0124] 2) Tempering: 500℃, keep warm for 2.0h, water cooling.

[0125] Embodiment 5:

[0126] 1Chemical composition

[0127] The internal control chemical composition was determined; 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%, and the balance was iron and inevitable impurities.

[0128] 2. Electric furnace continuous casting production processes of steel bars for automobile engine connecting rods

[0129] Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery.

[0130] (6) Ecological electric furnace smelting

[0131] 100% scrap steel smelting, scrap steel loading: 103t, alloy structural steel cutting head 20t, heavy scrap steel 72t, lump scrap steel 10t; tapping temperature 1576℃, C: 0.12%, P: 0.008% when tapping, slag, pre-deoxidizer, alloy added when 1 / 4 of the steel is tapped, tapping amount 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 segment (12mm) 0.6Kg / t. Auxiliary materials added per ton of steel: active lime (35mm) 40Kg / t, magnesite (40mm) 25Kg / t, ladle ash 6Kg / t, small coke 20Kg / t.

[0132] (2) LF furnace refining

[0133] The LF station temperature is 1497℃, and the 35700A high current is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, active lime is added. After 5 minutes, the chemical composition is analyzed for the first time. According to the target value of the chemical composition, alloy is added and carbon is added to promote the rapid melting and homogenization of the alloy and carbon powder. When the temperature of the molten steel reaches 1605℃, 1.5kg / t steel of alumina balls as a diffusion deoxidizer is added for diffusion deoxidation. The furnace door is closed for 10in. When the temperature of the molten steel reaches 1590℃, the chemical composition is analyzed for the second time to confirm the deviation value of the content of each chemical element from the target value. After the second sample is taken away, the station is left when the temperature of the molten steel reaches 1606℃. The LF smelting cycle is 41min. The amount of alloy added to each ton of steel is: 1.0kg / t of ferrosilicon, 1.8kg / t of high carbon ferromanganese, 3.0kg / t of high carbon ferrochrome, 1.9kg / t of ferrovanadium, and 0.4m / t of aluminum wire (Φ12mm). Supplementary materials added per ton of steel: Active lime (35mm) 4Kg / t, Silicon carbide (3mm) 2.1kg / t, Coke particles 0.62kg / t.

[0134] (3) RH refining

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

[0136] (9) Continuous casting

[0137] The temperature of the ladle at the station is 1512℃, the amount of molten steel is 102t, the H content of the tundish is controlled at 1.4ppm, the casting time is 42min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag.

[0138] (5) Heating process: The temperature entering the heating furnace is 530℃, the temperature of the preheating section is required to be 690℃, and the time is 1.4h; the temperature of the heating section 2 is required to be 856℃, and the time is 1.5h; the temperature of the heating section 1 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 steel tapping temperature is 1187℃.

[0139] (6) Rolling process

[0140] Primary rolling process: 9 passes, steel turning → 1st pass width 408mm, height 421mm, reduction 65mm → 2nd pass width 426mm, height 351mm, reduction 70mm → steel turning → 3rd pass width 370mm, height 362mm, reduction 64mm → 4th pass width 397mm, height 272mm, reduction 90mm → steel turning → 5th pass width 285mm, height 355mm, reduction 42mm→The 6th pass is 297mm wide, 315mm high, and 40mm reduction→The 7th pass is 307mm wide, 280mm high, and 35mm reduction→The 8th pass is 317mm wide, 246mm high, and 34mm reduction→Steel turning→The 9th pass is 271mm wide, 235mm high, and 82mm reduction, passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters the continuous rolling mill for rolling.

[0141] Continuous rolling product rolling process: 9 passes, the 1st pass is 229mm high and 245mm wide; the 2nd pass is 192mm high and 235mm wide; the 3rd pass is 200mm high and 195mm wide; the 4th pass is 173mm high and 210mm wide; the 5th pass is 180mm high and 178.2mm wide; the 6th pass is 142mm high and 190mm wide; the 7th pass is 158mm high and 154.8mm wide; the 8th pass is 121mm high and 162.8mm wide; the 9th pass is 131.76mm high and 131.76mm wide; the finished product is produced after 9 passes.

[0142] (7) Insulation process

[0143] Insulation process: Steel insulation, lower insulation pit temperature 590℃, insulation 52h, exit pit temperature 140℃.

[0144] (8) Heat treatment process

[0145] The steel after heat preservation is heat treated, and the heat treatment includes the following steps:

[0146] 1) Quenching: 850℃, holding time 1.0h, oil cooling;

[0147] 2) Tempering: 500℃, keep warm for 2.0h, water cooling.

[0148] 2. Finished product inspection results

[0149] (1) Φ130mm specification macrostructure

[0150] Serial number Generally loose Loose center Ingot segregation General spot segregation Edge spot 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) Φ130mm non-metallic inclusions

[0152]

[0153] (3) Mechanical properties of Φ130mm specification

[0154]

[0155]

[0156] According to the above table, Examples 1-5 use an ecological electric furnace + LF + RH + continuous casting → heating → primary rolling mill → continuous rolling unit to produce steel bars for automobile engine connecting rods, which meets the quality requirements for steel bars for automobile engine connecting rods, and indicators such as mechanical properties and high steel purity can also meet standard requirements.

[0157] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the patent application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A steel bar for automobile engine connecting rod, characterized in that: The following components are included in mass percentage: C: 0.48% to 0.53%, Si: 0.20% to 0.35%, Mn: 0.55% to 0.75%, P≤0.015%, S≤0.012%, Cr: 0.85% to 1.05%, Ni≤0.25%, Mo≤0.05%, V: 0.11% to 0.19%, Cu≤0.15%, and the balance is iron and unavoidable impurities.

2. A method for preparing a steel bar for automobile engine connecting rod according to claim 1, characterized in that: The following steps are involved: Ecological electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating process, rolling process and insulation process; Among them, in the ecological electric furnace smelting, scrap steel is used as the furnace charge, and the scrap steel accounts for 100% by mass; the scrap steel includes alloy structural steel cutting heads, heavy scrap steel and lump-type scrap steel; wherein the mass percentage of alloy structural steel cutting heads in the furnace charge is 15% to 30%, the mass percentage of heavy scrap steel is 60% to 80%, and the mass percentage of lump-type scrap steel is 7% to 15%; the steel tapping temperature is 1570°C to 1580°C, and the end point composition of the electric furnace is: C: 0.10% to 0.15%, P≤0.010%; slag, pre-deoxidizer, and alloy are added when 1 / 4 to 1 / 3 of the steel is tapped, and the smelting cycle is 40min to 45min; the amount of alloy added to a ton of steel: 5.1K g / 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, 0.6Kg / t~0.7Kg / t of aluminum segments, wherein the size of the aluminum segments is Φ10mm~Φ16mm; the amount of auxiliary materials added per ton of steel: 40Kg / t~41Kg / t of active lime, 25Kg / t~26Kg / t of magnesite, 6Kg / t~6.2Kg / t of ladle ash, 20Kg / t~21Kg / t of small pieces of coke; wherein the particle size of the active lime is 10mm~70mm; the particle size of the magnesite is 10mm~60mm.

3. The preparation method according to claim 2, characterized in that: In the LF refining, the LF inlet temperature is 1490°C to 1500°C, and after heating and melting the slag with a large current of 35000A to 36000A, when the slag surface fluctuates and the molten steel and the arc are not exposed, 35Kg / t steel to 45Kg / t steel of active lime is added, and the first sampling and analysis is performed after 5min to 6min, and the molten steel component content is adjusted according to the target component requirements; when the molten steel temperature reaches 1600°C to 1610°C, 1.5kg / t steel to 1.6kg / t steel of diffusion deoxidizer alumina balls are added for diffusion deoxidation, and the furnace door is closed for 10min to 13min; when the molten steel temperature reaches 1580°C to 1600°C, the second sampling and analysis is performed; when the molten steel temperature reaches 1600°C to 1610°C, the molten steel is heated to 1500°C and the furnace door is closed for 10min to 13min. Leaving the station, the LF smelting cycle is 35min to 45min, and the amount of additional alloy added per ton of steel: 1.0kg / t to 1.2kg / t of ferrosilicon, 1.7kg / t to 1.9kg / t of high carbon ferromanganese, 3.0kg / t to 3.2kg / t of high carbon ferrochrome, 1.8kg / t to 2.0kg / t of ferrovanadium, 0.4kg / t to 0.42m / t of aluminum wire, wherein the size of the aluminum wire is Φ10mm to Φ12mm; the amount of additional auxiliary materials added per ton of steel: 4kg / t to 4.2Kg / t of active lime with a particle size of 10mm to 70mm, 2.1kg / t to 2.2kg / t of silicon carbide with a particle size of 2mm to 5mm, and 0.6 to 0.65kg / t of coke particles.

4. The preparation method according to claim 2, characterized in that: In the RH vacuum refining, the inlet temperature is 1610°C to 1620°C, the operation time is 30min to 40min, the vacuum pump is started when the argon pressure is controlled to be 0.1MPa to 0.3MPa, and when the vacuum degree reaches 100Pa to 110Pa, the time is maintained for 10min to 15min, and the argon pressure is adjusted to 0.3MPa to 0.5MPa. After the static argon blowing is completed, 0.6kg / t steel to 0.7kg / t steel covering agent and 2m / t steel to 2.1m / t steel silicon-calcium alloy cored wire are added, wherein the size specification of the silicon-calcium alloy cored wire is Φ14mm to Φ14.2mm; the outlet temperature is 1560°C to 1570°C.

5. The preparation method according to claim 2, characterized in that: In the continuous casting, the arrival temperature of the ladle is 1507°C to 1515°C, the amount of molten steel is 100t to 105t, the H content of the tundish is controlled to be ≤2ppm, the casting time is 40min to 45min, the casting is protected throughout the whole process, and the mold protection slag uses medium carbon steel protection slag.

6. The preparation method according to claim 2, characterized in that: In the heating process, the square billets produced in the continuous casting process are fed into a heating furnace, the temperature of the heating furnace is 470°C to 560°C; the temperature of the preheating section is 680°C to 700°C, and the time is 1.3h to 1.5h; the heating section includes a heating section 1 with a temperature of 1190°C to 1220°C, and a time of 1.3h to 1.5h; a heating section 2 with a temperature of 850°C to 860°C, and a time of 1.3h to 1.5h; a soaking section with a temperature of 1190°C to 1210°C, and a time of 1.3h to 1.5h; and a tapping temperature of 1180°C to 1190°C.

7. The preparation method according to claim 2, characterized in that: In the rolling process, the heated continuous casting billet is initially rolled to form a billet, and the initial rolling adopts 9 rolling passes to form a billet, and the steel is turned four times, and then passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters the 8-frame continuous rolling mill group for rolling; the steel is turned once before rolling 1 pass, the steel is turned for the second time after rolling 2 passes, the steel is turned for the third time after rolling 2 passes, and the steel is turned for the fourth time after rolling 4 passes; the width of the first pass is 408mm-408.05mm, and the height is 421m m~421.05mm, reduction 65mm~65.05mm; 2nd pass width 426mm~426.05mm, height 351mm~351.05mm, reduction 70mm~70.05mm; 3rd pass width 370mm~370.05mm, height 362mm~362.05mm, reduction 64mm~64.05mm; 4th pass width 397mm~397.05 mm, height 272mm~272.05mm, reduction 90mm~90.05mm; the 5th pass width 285mm~285.05mm, height 355mm~355.05mm, reduction 42mm~42.05mm; the 6th pass width 297mm~297.05mm, height 315mm~315.05mm, reduction 40mm~40.05mm; the 7th pass width 307 mm~307.05mm, height 280mm~280.05mm, reduction 35mm~35.05mm; the 8th pass width 317mm~317.05mm, height 246mm~246.05mm, reduction 34mm~34.05mm; the 9th pass width 271mm~271.05mm, height 235mm~235.05mm, reduction 82mm~82.05mm.

8. The preparation method according to claim 2, characterized in that: In the rolling process, the continuous rolling product rolling process is rolled 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 mm, width 178.2mm~178.25mm; the 6th pass is 142mm~142.05mm high, 190mm~190.05mm wide; the 7th pass is 158mm~158.05mm high, 154.8mm~154.85mm wide; the 8th pass is 121mm~121.05mm high, 162.8mm~162.85mm wide; the 9th pass is 131.76mm~131.80mm high, 131.76mm~131.80mm wide; the finished product is produced after the 9th pass.

9. The preparation method according to claim 2, characterized in that: In the insulation process, the rods prepared by the rolling process are insulated, the temperature of the lower insulation pit is ≥570°C, the insulation is 50h-55h, and the exit temperature is ≤160°C.

10. The preparation method according to claim 2, characterized in that: The steel material after heat preservation is heat treated, and the heat treatment comprises the following steps: (1) The steel after heat preservation is quenched at a heating temperature of 840°C to 860°C, kept at a temperature of 0.9h to 1.2h, and oil cooled; (2) After quenching and cooling, the steel is tempered at a temperature of 490°C to 510°C, kept at this temperature for 1.9h to 2.2h, and water-cooled.

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