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

Abstract

Disclosed in the present invention are a steel bar for an automobile engine connecting rod and a preparation method for the steel bar. The steel bar for an automobile engine connecting rod comprises the following components in percentage by mass: 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 remainder being iron and inevitable impurities. The steel bar for an automobile engine connecting rod in the present invention produced by the ecological electric furnace, LF, RH, continuous casting, and rolling processes meets the advanced use requirements, ensures indexes such as mechanical properties and high steel cleanliness of a finished steel product for a steel bar for an automobile engine connecting rod, and ensures the surface quality level of the steel bar for an automobile engine connecting rod.

Description

Steel bar for automobile engine connecting rod and preparation method thereof TECHNICAL FIELD

[0001] The present application relates to the field of materials and metallurgy, and more particularly to a steel bar for automobile engine connecting rod and a preparation method thereof. BACKGROUND

[0002] The automobile engine connecting rod bears the gas force 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 the connecting rod to have sufficient fatigue strength and structural rigidity. If the fatigue strength is insufficient, the connecting rod body or connecting rod bolt may be broken, and a major accident of the whole machine may occur. If the rigidity is insufficient, the rod body may be bent and deformed, and the big end of the connecting rod may be out-of-round deformed, which may cause the piston, cylinder, bearing and crank pin to be unevenly worn. The quality of the steel for automobile engine connecting rod directly affects the service life and wear resistance of the automobile engine, and even the safety of the whole automobile during operation.

[0003] Currently, the steel for automobile engine connecting rod has the problems of many impurities, poor wear resistance, low fatigue life and difficult to meet the application requirements in terms of mechanical properties.

[0004] SUMMARY

[0005] The present application aims to overcome the above-mentioned defects in the prior art, and provides a steel bar for automobile engine connecting rod and a preparation method thereof. The steel bar for automobile engine connecting rod produced by the ecological electric furnace + LF + RH + continuous casting smelting process and rolling process meets the high-end use requirements, realizes the breakthrough of batch production of the steel bar for automobile engine connecting rod in the ecological electric furnace continuous casting process, ensures the mechanical properties and high steel purity of the finished steel bar for automobile engine connecting rod, and ensures the surface quality level of the steel bar for automobile engine connecting rod, thereby meeting the quality requirements of the steel bar for automobile engine connecting rod.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0007] A steel bar for automobile engine connecting rod, comprising the following components in mass percentage:

[0008] 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 being iron and unavoidable impurities.

[0009] The application further discloses a preparation method of the automobile engine connecting rod steel bar, which comprises 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 the furnace charge, and the scrap steel accounts for 100% in mass fraction; the scrap steel comprises alloy structural steel cut head, heavy scrap steel and bale-type scrap steel; wherein, the mass percentage of the alloy structural steel cut in the furnace charge is 15%-30%, the mass percentage of the heavy scrap steel is 60%-80%, and the mass percentage of the bale-type scrap steel is 7%-15%; the tapping temperature is 1570-1580 DEG C, the electric furnace endpoint composition is C: 0.10%-0.15%, and P<=0.010%; the slag material, pre-deoxidizer and alloy are added when 1 / 4-1 / 3 of the tapping is completed, and the smelting cycle is 40-45 min; the alloy addition amount per ton of steel is 5.1-5.2 Kg / t of silicon manganese, 2.1-2.2 Kg / t of high-carbon ferromanganese, 14.5-15 Kg / t of high-carbon ferrochrome and 0.6-0.7 Kg / t of aluminum wire segment, wherein the size specification of the aluminum wire segment is Phi 10-Phi 16 mm; the auxiliary material addition amount per ton of steel is 40-41 Kg / t of active lime, 25-26 Kg / t of magnesite, 6-6.2 Kg / t of ladle slag and 20-21 Kg / t of small block coke; wherein, the particle size of the active lime is 10-70 mm; and the particle size of the magnesite is 10-60 mm.

[0010] The embodiment of the application has the following beneficial effects:

[0011] (1) The automobile engine connecting rod steel bar is produced by using the ecological electric furnace+LF+RH+390mm*480mm smelting process and rolling process, the mechanical property requirements are met, and the steel purity is ensured.

[0012] (2) The reasonable component design and production process ensure the surface quality and mechanical property.

[0013] (3) The macrostructure and non-metallic inclusions of the finished steel material meet the requirements of high-end products. DETAILED DESCRIPTION

[0014] The application will be further described below in combination with specific embodiments, but the application is not limited by the embodiments in any way.

[0015] I. Chemical composition

[0016] The application discloses a kind of steel bar for automobile engine connecting rod, including the following mass percentage components: 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 unavoidable impurities.

[0017] II. Production process technology

[0018] The preparation method of the steel bar for automobile engine connecting rod of the application comprises the following steps: ecological electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating process, rolling process and heat preservation process.

[0019] Further, it specifically comprises the following steps:

[0020] S1, in ecological electric furnace smelting, scrap steel is used as furnace charge, and 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 material, pre-deoxidizer and alloy are added when 1 / 4~1 / 3 of the tapping amount is reached, the tapping amount is 108t~112t, and the smelting period 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; 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.

[0021] In a specific embodiment, the size specification 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.

[0022] In a specific embodiment, the scrap steel loading amount is 102t~104t, the alloy structural steel cut head is 20t~21t, the heavy scrap steel is 72t~73t, and the bale type scrap steel is 10t~11t.

[0023] S2, in LF refining, the LF inlet temperature is 1490-1500℃, after using 35000A-36000A large current to heat and slag, 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, the alloy is added according to the target component requirement, and the carbon is increased to promote the rapid melting and homogenization of the alloy and carbon powder; when the molten steel temperature reaches 1600-1610℃, 1.5-1.6 Kg / t of diffusion deoxidizer alumina ball 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 to confirm the deviation of the chemical element content from the target value, after the second sampling, when the molten steel temperature reaches 1600-1610℃, the LF refining cycle is 35-45 minutes, the alloy addition amount per ton of steel is 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 Kg / t of aluminum wire, wherein the size specification of the aluminum wire is Φ10-Φ12 mm; the auxiliary material addition amount per ton of steel is 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.

[0024] S3, in 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 slag surface is slightly moved without exposing the molten steel, when the vacuum degree reaches 100-110 Pa, the holding time is 10-15 minutes, at the same time, the argon pressure is adjusted to 0.3-0.5 MPa, after the static argon blowing is finished, 0.6-0.7 Kg / t of covering agent and 2-2.1 Kg / 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℃.

[0025] S4, in continuous casting, the ladle arrives at the station 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.

[0026] S5, in the heating process, the billet is sent into the heating furnace after being discharged from the continuous casting process, the temperature of the heating furnace is 470-560℃; the temperature of the preheating section is 680-700℃, and the time is 1.3-1.5h; the heating section includes heating section 1 with a temperature of 1190-1220℃ and a time of 1.3-1.5h; heating section 2 with a temperature of 850-860℃ and a time of 1.3-1.5h; the soaking section with a temperature of 1190-1210℃ and a time of 1.3-1.5h; the temperature of the billet when being discharged is 1180-1190℃.

[0027] S6, in the rolling process, the heated continuous casting billet is rolled and broken down, the initial rolling adopts 9 passes of rolling and breaking down, four times of turning, and passes through 3 sets of 850mm rolling mills, 1 set of 735mm rolling mill, and then enters 8 sets of continuous rolling mill groups; the first turning is performed before 1 pass of rolling, the second turning is performed after 2 passes of rolling, the third turning is performed after 2 more passes of rolling, and the fourth turning is performed after 4 more passes of rolling; the width of the first pass is 408-408.05mm, the height is 421-421.05mm, and the reduction is 65-65.05mm; the width of the second pass is 426-426.05mm, the height is 351-351.05mm, and the reduction is 70-70.05mm; the width of the third pass is 370-370.05mm, the height is 362-362.05mm, and the reduction is 64-64.05mm; the width of the fourth pass is 397-397.05mm, the height is 272-272.05mm, and the reduction is 90-90.05mm; the width of the fifth pass is 285-285.05mm, the height is 355-355.05mm, and the reduction is 42-42.05mm; the width of the sixth pass is 297-297.05mm, the height is 315-315.05mm, and the reduction is 40-40.05mm; the width of the seventh pass is 307-307.05mm, the height is 280-280.05mm, and the reduction is 35-35.05mm; the width of the eighth pass is 317-317.05mm, the height is 246-246.05mm, and the reduction is 34-34.05mm; the width of the ninth pass is 271-271.05mm, the height is 235-235.05mm, and the reduction is 82-82.05mm.

[0028] The 9-passes of the continuous rolling production material rolling are as follows: the first-pass high 229mm~229.05mm, width 245mm~245.05mm; the second-pass high 192mm~192.05mm, width 235mm~235.05mm; the third-pass high 200mm~200.05mm, width 195mm~195.05mm; the fourth-pass high 173mm~173.05mm, width 210mm~210.05mm; the fifth-pass high 180mm~180.05mm, width 178.2mm~178.25mm; the sixth-pass high 142mm~142.05mm, width 190mm~190.05mm; the seventh-pass high 158mm~158.05mm, width 154.8mm~154.85mm; the eighth-pass high 121mm~121.05mm, width 162.8mm~162.85mm; the ninth-pass high 131.76mm~131.80mm, width 131.76mm~131.80mm; and the finished product is discharged after the ninth-pass.

[0029] S7, in the heat preservation process, the bar 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 pit discharge temperature is ≤160℃.

[0030] S8, in the heat treatment, the heat preserved steel is heat treated, and the heat treatment comprises the following steps:

[0031] (1) the heat treated steel is quenched, the heating temperature is 840℃~860℃, the heat preservation time is 0.9h~1.2h, and the oil cooling is performed.

[0032] (2) the quenched and cooled steel is tempered, the tempering temperature is 490℃~510℃, the heat preservation time is 1.9h~2.2h, and the water cooling is performed.

[0033] The following is a specific embodiment

[0034] Embodiment 1:

[0035] 1 Chemical composition

[0036] 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%, and the balance is iron and inevitable impurities.

[0037] 2 Steel bar for automobile engine connecting rod produced by electric furnace continuous casting and each production process

[0038] The process route is as follows: ecological electric furnace + LF + RH + continuous casting billet→heating furnace heating→rolling→heat preservation→finishing→inspection→packaging and delivery to the warehouse→shipment.

[0039] (1) EAF smelting

[0040] 100% scrap smelting, scrap charging: 103 t, alloy structural steel scrap 20 t, heavy scrap 72 t, bale scrap 10 t; tapping temperature 1575 °C, C: 0.12%, P: 0.008% at tapping, slag, pre-deoxidizer, alloy added at 1 / 4 tapping, tapping amount 110 t, smelting cycle 43 min. Alloy addition per ton of steel: silicon manganese 5.1 Kg / t, high-carbon ferromanganese 2.1 Kg / t, high-carbon ferrochrome 14.7 Kg / t, aluminum wire segment (12 mm) 0.6 Kg / t. Auxiliary material addition per ton of steel: active lime (35 mm) 40 Kg / t, magnesite (40 mm) 25 Kg / t, ladle lime 6 Kg / t, small block coke 20 Kg / t.

[0041] (2) LF refining

[0042] LF inlet temperature 1495 °C, 35500 A large current to heat and slag, when the slag surface fluctuates, the molten steel and the electric arc are not exposed, active lime is added, the first sampling analysis of chemical composition is taken after 5 min, 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 1606 °C, 1.5 kg / t of steel of diffusion deoxidizer alumina balls is added for diffusion deoxidation, the furnace door is closed for 11 min, and when the temperature of the molten steel reaches 1590 °C, the second sampling analysis of chemical composition is taken to confirm the deviation of the content of each chemical element from the target value. After the second sampling, when the temperature of the molten steel reaches 1605 °C, the LF refining cycle is 40 min, and the alloy addition per ton of steel is: ferrosilicon 1.0 kg / t, high-carbon ferromanganese 1.8 kg / t, high-carbon ferrochrome 3.0 kg / t, ferrovanadium 1.9 kg / t, and aluminum wire (Φ12 mm) 0.4 m / t. Auxiliary material addition per ton of steel: active lime (35 mm) 4 Kg / t, silicon carbide (3 mm) 2.1 kg / t, and coke particles 0.6 kg / t.

[0043] (3) RH refining

[0044] Inlet temperature 1615 °C, operation time 37 min, argon pressure controlled at 0.1 MPa before the vacuum pump is started, the molten steel is slightly moved without being exposed, the timing starts when the vacuum degree reaches 103 Pa, the holding time is 12 min, and the argon pressure is adjusted to 0.3 MPa at the same time. After the end of the argon blowing, 2 meters / t of steel of silicon-calcium alloy cored wire (Φ14 mm) is added, and 0.6 kg / t of steel of covering agent is added. Outlet temperature 1567 °C.

[0045] (4) Continuous casting

[0046] The ladle station temperature is 1510℃, the molten steel amount is 102t, the tundish H control is 1.5ppm, the casting time is 42min, the whole process is protected casting, and the crystallizer protection slag uses a medium carbon steel protection slag.

[0047] (5) Heating process: the inlet heating furnace temperature is 520℃, the preheating section temperature requirement is 690℃, the time is 1.4h; the heating 2 section temperature requirement is 855℃, the time is 1.4h; the heating 1 section temperature requirement is 1210℃, the time is 1.4h; the soaking section temperature requirement is 1200℃, the time is 1.5h; the tapping temperature is 1185℃.

[0048] (6) Rolling process

[0049] Primary rolling process: rolling 9 passes, turning over the steel→the 1st pass width 408mm, height 421mm, reduction 65mm→the 2nd pass width 426mm, height 351mm, reduction 70mm→turning over the steel→the 3rd pass width 370mm, height 362mm, reduction 64mm→the 4th pass width 397mm, height 272mm, reduction 90mm→turning over the steel→the 5th pass width 285mm, height 355mm, reduction 42mm→the 6th pass width 297mm, height 315mm, reduction 40mm→the 7th pass width 307mm, height 280mm, reduction 35mm→the 8th pass width 317mm, height 246mm, reduction 34mm→turning over the steel→the 9th pass width 271mm, height 235mm, reduction 82mm, passing through 3 850mm rolling mills, 1 735mm rolling mill, and then entering a continuous rolling mill group to roll.

[0050] Continuous rolling product rolling process: rolling 9 passes, the 1st pass height 229mm, width 245mm; the 2nd pass height 192mm, width 235mm; the 3rd pass height 200mm, width 195mm; the 4th pass height 173mm, width 210mm; the 5th pass height 180mm, width 178.2mm; the 6th pass height 142mm, width 190mm; the 7th pass height 158mm, width 154.8mm; the 8th pass height 121mm, width 162.8mm; the 9th pass height 131.76mm, width 131.76mm; after 9 passes, the finished product is discharged.

[0051] (7) Holding process

[0052] Holding process: the steel is held, the temperature of the holding pit is 580℃, the holding time is 54h, and the pit discharge temperature is 150℃.

[0053] (8) Heat treatment process

[0054] The steel after holding is subjected to heat treatment, and the heat treatment comprises the following steps:

[0055] 1) Quenching: 850℃, holding for 1.0h, oil cooling;

[0056] 2) tempering: 500°C, holding for 2.0h, water cooling.

[0057] Example 2:

[0058] 1 Chemical composition

[0059] The internal control chemical composition was 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 being iron and inevitable impurities.

[0060] 2 Steel bar for automobile engine connecting rod by EAF continuous casting

[0061] Process route: ecological EAF + LF + RH + continuous casting billet → heating furnace heating → rolling → holding → finishing → inspection → packaging and delivery to warehouse → shipment.

[0062] (1) Ecological EAF smelting

[0063] 100% total scrap smelting, scrap charging amount: 102t, alloy structural steel head 20t, heavy scrap 72t, bag block type scrap 11t; tapping temperature 1575℃, C: 0.12% at tapping, P: 0.008% at tapping, slag, pre-deoxidizer, alloy were added at 1 / 4 tapping, 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 material addition per ton of steel: active lime (35mm) 40Kg / t, magnesite (40mm) 25Kg / t, ladle lime 6Kg / t, small block coke 20Kg / t.

[0064] (2) LF furnace refining

[0065] LF entry temperature 1497℃, 35600A large current temperature slag, when the slag surface fluctuation, molten steel and arc not exposed, add active lime, 5 min after the first sampling analysis of chemical composition, according to the chemical composition target value of alloy and carbon, to promote alloy and carbon powder rapid melting and homogenization. When the molten steel temperature reaches 1605℃, add diffusion deoxidizer alumina ball 1.5kg / t steel for diffusion deoxidation, closed furnace door 10 min, when the molten steel temperature reaches 1590℃, second sampling analysis of chemical composition, to confirm the deviation of each chemical element composition content from the target value, after the second sample, when the molten steel temperature reaches 1605℃, off station, LF smelting cycle 39 min, the amount of alloy added per ton of steel: silicon iron 1.0kg / t, high carbon ferromanganese 1.8kg / t, high carbon chromium iron 3.0kg / t, ferrovanadium 1.9kg / t, aluminum wire (Φ12mm) 0.4m / t. The amount of auxiliary material added per ton of steel: active lime (35mm) 4Kg / t, silicon carbide (3mm) 2.1kg / t, coke particles 0.6kg / t.

[0066] (3) RH refining

[0067] Entry temperature 1615℃, operation time 37min, before the vacuum pump starts, argon pressure control 0.1MPa, with slag surface micro motion molten steel not exposed, when the vacuum degree reaches 105Pa, start timing, keep time 12min, at the same time, adjust the argon pressure to 0.3MPa, after static argon blowing, add silicon calcium alloy cored wire (Φ14mm) 2m / t, covering agent 0.6kg / t, exit temperature 1567℃.

[0068] (4) Continuous casting

[0069] Ladle to station temperature 1510℃, molten steel 102t, tundish H control 1.5ppm, casting time 42min, whole process protection casting, mold protection slag using medium carbon steel protection slag.

[0070] (5) Heating process: entry heating furnace temperature 500℃, preheating temperature requirement 690℃, time 1.4h; heating 2 temperature requirement 856℃, time 1.4h; heating 1 temperature requirement 1210℃, time 1.4h; soaking temperature requirement 1200℃, time 1.4h; exit steel temperature 1187℃.

[0071] (6) Rolling process

[0072] Initial rolling process: 9 passes, turn over the steel → 1st pass, width 408 mm, height 421 mm, reduction 65 mm → 2nd pass, width 426 mm, height 351 mm, reduction 70 mm → turn over the steel → 3rd pass, width 370 mm, height 362 mm, reduction 64 mm → 4th pass, width 397 mm, height 272 mm, reduction 90 mm → turn over the steel → 5th pass, width 285 mm, height 355 mm, reduction 42 mm → 6th pass, width 297 mm, height 315 mm, reduction 40 mm → 7th pass, width 307 mm, height 280 mm, reduction 35 mm → 8th pass, width 317 mm, height 246 mm, reduction 34 mm → turn over the steel → 9th pass, width 271 mm, height 235 mm, reduction 82 mm, through 3 850 mm rolling mills, 1 735 mm rolling mill, and then into a continuous rolling mill group to roll.

[0073] Continuous rolling process: 9 passes, 1st pass, height 229 mm, width 245 mm; 2nd pass, height 192 mm, width 235 mm; 3rd pass, height 200 mm, width 195 mm; 4th pass, height 173 mm, width 210 mm; 5th pass, height 180 mm, width 178.2 mm; 6th pass, height 142 mm, width 190 mm; 7th pass, height 158 mm, width 154.8 mm; 8th pass, height 121 mm, width 162.8 mm; 9th pass, height 131.76 mm, width 131.76 mm; after 9 passes, the finished product is out.

[0074] (7) Holding process

[0075] Holding process: the steel is held, the temperature in the holding pit is 590℃, holding for 54 h, and the temperature out of the pit is 120℃.

[0076] (8) Heat treatment process

[0077] The steel after holding is subjected to heat treatment, and the heat treatment comprises the following steps:

[0078] 1) Quenching: 850℃, holding for 1.0 h, oil cooling;

[0079] 2) Tempering: 500℃, holding for 2.0 h, water cooling.

[0080] Example 3:

[0081] 1 Chemical composition

[0082] 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%, and the balance is iron and inevitable impurities.

[0083] 2 Steel bar for automobile engine connecting rod by EAF-LF-RH-CC process

[0084] Process route: EAF + LF + RH + CC billet → heating furnace heating → rolling → holding → finishing → inspection → packing and delivery to warehouse → delivery.

[0085] (1) EAF smelting

[0086] 100% full scrap smelting, scrap loading amount: 103 t, alloy structural steel head 20 t, heavy scrap 72 t, package type scrap 10 t; tapping temperature 1578℃, C: 0.12%, P: 0.009% at tapping, slag, pre-deoxidizer, alloy are added at 1 / 4 tapping, tapping amount 109 t, smelting cycle 41 min. Alloy addition per ton of steel: silicon manganese 5.1 Kg / t, high carbon ferromanganese 2.1 Kg / t, high carbon ferrochrome 14.8 Kg / t, aluminum wire segment (12 mm) 0.6 Kg / t. Auxiliary material addition per ton of steel: active lime (35 mm) 40 Kg / t, magnesite (40 mm) 25 Kg / t, ladle lime 6 Kg / t, small block coke 20 Kg / t.

[0087] (2) LF refining

[0088] LF inlet temperature 1497℃, 35600A large current temperature rising slag, when the slag surface fluctuates, the molten steel and the arc are not exposed, active lime is supplemented, the first sampling analysis of chemical composition is taken after 5 min, alloy is added according to the target value of chemical composition, and carbon is added to promote the rapid melting and homogenization of alloy and carbon powder. When the temperature of the molten steel reaches 1605℃, 1.5 kg / t of steel of diffusion deoxidizer alumina ball is added for diffusion deoxidization, the furnace door is closed for 10 min, and when the temperature of the molten steel reaches 1592℃, the second sampling analysis of chemical composition is taken to confirm the deviation of each chemical element content from the target value. After the second sampling, when the temperature of the molten steel reaches 1604℃, the LF smelting cycle is 40 min, and the alloy addition per ton of steel is: ferrosilicon 1.0 kg / t, high carbon ferromanganese 1.8 kg / t, high carbon ferrochrome 3.0 kg / t, ferrovanadium 1.9 kg / t, aluminum wire (Φ12 mm) 0.4 m / t. Auxiliary material addition per ton of steel: active lime (35 mm) 4 Kg / t, silicon carbide (3 mm) 2.1 kg / t, coke particles 0.6 kg / t.

[0089] (3) RH refining

[0090] Inlet temperature 1614℃, operation time 38min, argon pressure control 0.1MPa before vacuum pump starting, slag surface slightly moving molten steel not exposed, when vacuum degree reaches 105Pa, start timing, holding time 12min, at the same time, adjust argon pressure to 0.3MPa, after static argon blowing, add silicon-calcium alloy cored wire (Φ14mm) 2m / t steel, covering agent 0.6kg / t steel, outlet temperature 1565℃.

[0091] (4) Continuous casting

[0092] Ladle inlet temperature 1510℃, molten steel amount 102t, tundish H control 1.5ppm, casting time 42min, whole process protective casting, mold powder using medium carbon steel powder.

[0093] (5) Heating process: inlet temperature 520℃, preheating section temperature requirement 690℃, time 1.4h; heating 2 section temperature requirement 853℃, time 1.4h; heating 1 section temperature requirement 1210℃, time 1.4h; soaking section temperature requirement 1200℃, time 1.4h; outlet temperature 1185℃.

[0094] (6) Rolling process

[0095] Initial rolling process: rolling 9 passes, turning over→1st pass width 408mm, height 421mm, reduction 65mm→2nd pass width 426mm, height 351mm, reduction 70mm→turning over→3rd pass width 370mm, height 362mm, reduction 64mm→4th pass width 397mm, height 272mm, reduction 90mm→turning over→5th pass 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 over→9th pass width 271mm, height 235mm, reduction 82mm, passing through 3 850mm rolling mills, 1 735mm rolling mill, then entering continuous rolling mill group.

[0096] Continuous rolling product rolling process: rolling 9 passes, 1st pass height 229mm, width 245mm; 2nd pass height 192mm, width 235mm; 3rd pass height 200mm, width 195mm; 4th pass height 173mm, width 210mm; 5th pass height 180mm, width 178.2mm; 6th pass height 142mm, width 190mm; 7th pass height 158mm, width 154.8mm; 8th pass height 121mm, width 162.8mm; 9th pass height 131.76mm, width 131.76mm; after 9 passes, outlet finished product.

[0097] (7) Holding process

[0098] Holding process: holding of steel material, temperature of lower holding pit 600°C, holding for 54h, temperature of pit exit 130°C.

[0099] (8) Heat treatment process

[0100] The steel material after holding is subjected to heat treatment, and the heat treatment includes the following steps:

[0101] 1) Quenching: 850°C, holding for 1.0h, oil cooling;

[0102] 2) Tempering: 500°C, holding for 2.0h, water cooling.

[0103] Example 4:

[0104] 1 Chemical composition

[0105] 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%, and the balance being iron and inevitable impurities.

[0106] 2 Steel bar for automobile engine connecting rod by electric furnace continuous casting

[0107] Process route: ecological electric furnace + LF + RH + continuous casting billet → heating furnace heating → rolling → holding → finishing → inspection → packaging and delivery to warehouse → shipment.

[0108] (1) Ecological electric furnace smelting

[0109] 100% total scrap smelting, scrap charging amount: 102t, alloy structural steel head 20t, heavy scrap 72t, package type scrap 10t; tapping temperature 1575°C, C at tapping: 0.12%, P: 0.008%, slag, pre-deoxidizer, alloy are added at 1 / 4 tapping, 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 material addition per ton of steel: active lime (35mm) 40Kg / t, magnesite (40mm) 25Kg / t, ladle lime 6Kg / t, small block coke 20Kg / t.

[0110] (2) LF furnace refining

[0111] LF inlet temperature 1497℃, 35700A large current temperature slag, when the slag surface fluctuation, molten steel and arc not exposed, add active lime, 5 min after the first sampling analysis of chemical composition, according to the chemical composition of the target value of alloying, and carbon, to promote alloy and carbon powder rapid melting and homogenization. When the molten steel temperature reaches 1605℃, add diffusion deoxidizer alumina ball 1.5kg / t steel for diffusion deoxidation, closed furnace door 10 min, when the molten steel temperature reaches 1590℃, second sampling analysis of chemical composition, to confirm the deviation of each chemical element composition from the target value, after the second sample, when the molten steel temperature reaches 1604℃, off station, LF smelting cycle 40 min, the amount of alloying per ton of steel: silicon iron 1.0kg / t, high carbon ferromanganese 1.8kg / t, high carbon chromium iron 3.0kg / t, vanadium iron 1.9kg / t, aluminum wire (Φ12mm) 0.4m / t. The amount of auxiliary material per ton of steel: active lime (35mm) 4Kg / t, silicon carbide (3mm) 2.1kg / t, coke particles 0.62kg / t.

[0112] (3) RH refining

[0113] Inlet temperature 1615℃, operation time 38min, before the vacuum pump starts, argon pressure control 0.1MPa, with slag surface micro motion molten steel not exposed, when the vacuum degree reaches 104Pa, start timing, keep time 12min, at the same time, adjust the argon pressure to 0.3MPa, after static argon blowing, add silicon calcium alloy cored wire (Φ14mm) 2m / t steel, covering agent 0.6kg / t steel, outlet temperature 1565℃.

[0114] (4) Continuous casting

[0115] Ladle to station temperature 1510℃, molten steel 102t, tundish H control 1.5ppm, casting time 42min, whole process protection casting, mold protection slag using medium carbon steel protection slag.

[0116] (5) Heating process: inlet heating furnace temperature 520℃, preheating section temperature requirement 692℃, time 1.5h; heating 2 section temperature requirement 854℃, time 1.3h; heating 1 section temperature requirement 1210℃, time 1.3h; soaking section temperature requirement 1200℃, time 1.3h; steel temperature 1187℃.

[0117] (6) Rolling process

[0118] Initial rolling process: 9 passes, turn over the steel → 1st pass, width 408 mm, height 421 mm, reduction 65 mm → 2nd pass, width 426 mm, height 351 mm, reduction 70 mm → turn over the steel → 3rd pass, width 370 mm, height 362 mm, reduction 64 mm → 4th pass, width 397 mm, height 272 mm, reduction 90 mm → turn over the steel → 5th pass, width 285 mm, height 355 mm, reduction 42 mm → 6th pass, width 297 mm, height 315 mm, reduction 40 mm → 7th pass, width 307 mm, height 280 mm, reduction 35 mm → 8th pass, width 317 mm, height 246 mm, reduction 34 mm → turn over the steel → 9th pass, width 271 mm, height 235 mm, reduction 82 mm, through 3 850 mm rolling mills, 1 735 mm rolling mill, and then into a continuous rolling mill group.

[0119] Continuous rolling product rolling process: 9 passes, 1st pass, height 229 mm, width 245 mm; 2nd pass, height 192 mm, width 235 mm; 3rd pass, height 200 mm, width 195 mm; 4th pass, height 173 mm, width 210 mm; 5th pass, height 180 mm, width 178.2 mm; 6th pass, height 142 mm, width 190 mm; 7th pass, height 158 mm, width 154.8 mm; 8th pass, height 121 mm, width 162.8 mm; 9th pass, height 131.76 mm, width 131.76 mm; after 9 passes, the finished product is out.

[0120] (7) Holding process

[0121] Holding process: the steel is held, the temperature in the holding pit is 580℃, the holding time is 54 h, and the temperature out of the pit is 140℃.

[0122] (8) Heat treatment process

[0123] The steel after holding is subjected to heat treatment, and the heat treatment comprises the following steps:

[0124] 1) Quenching: 850℃, holding for 1.0 h, oil cooling;

[0125] 2) Tempering: 500℃, holding for 2.0 h, water cooling.

[0126] Example 5:

[0127] 1 Chemical composition

[0128] The internal control chemical composition is determined to be 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 is iron and inevitable impurities.

[0129] 2 Steel bar for automobile engine connecting rod

[0130] Process route: ecological electric furnace + LF + RH + continuous casting billet → heating furnace heating → rolling → heat preservation → finishing → inspection → packaging and delivery to the warehouse → delivery.

[0131] (1) Ecological electric furnace smelting

[0132] 100% full scrap smelting, scrap loading amount: 103 t, alloy structural steel head 20 t, heavy scrap 72 t, package type scrap 10 t; tapping temperature 1576℃, C: 0.12% at tapping, P: 0.008%, slag, pre-deoxidizer, alloy are added at 1 / 4 tapping, tapping amount 110 t, smelting cycle 42 min. Alloy addition per ton of steel: silicon manganese 5.1 Kg / t, high carbon ferromanganese 2.1 Kg / t, high carbon ferrochrome 14.7 Kg / t, aluminum wire segment (12 mm) 0.6 Kg / t. Auxiliary material addition per ton of steel: active lime (35 mm) 40 Kg / t, magnesite (40 mm) 25 Kg / t, ladle ash 6 Kg / t, small block coke 20 Kg / t.

[0133] (2) LF furnace refining

[0134] LF inlet temperature 1497℃, 35700A large current temperature rise slag, when the slag surface fluctuates, the molten steel and the arc are not exposed, the active lime is supplemented, the chemical composition is analyzed after 5 min, the alloy is supplemented according to the chemical composition target value, and the carbon is increased to promote the rapid melting and homogenization of the alloy and carbon powder. When the temperature of the molten steel reaches 1605℃, 1.5 kg / t of steel of diffusion deoxidizer alumina ball is added for diffusion deoxidization, and the furnace door is closed for 10 in. When the temperature of the molten steel reaches 1590℃, the chemical composition is analyzed for the second time to confirm the deviation of the chemical element content from the target value. After the second sampling is taken away, when the temperature of the molten steel reaches 1606℃, the LF smelting cycle is 41 min, the alloy addition per ton of steel: ferrosilicon 1.0 kg / t, high carbon ferromanganese 1.8 kg / t, high carbon ferrochrome 3.0 kg / t, ferrovanadium 1.9 kg / t, aluminum wire (Φ12 mm) 0.4 m / t. Auxiliary material addition per ton of steel: active lime (35 mm) 4 Kg / t, silicon carbide (3 mm) 2.1 kg / t, coke particles 0.62 kg / t.

[0135] (3) RH refining

[0136] Inlet temperature 1614℃, operation time 35min, argon pressure control 0.1MPa before vacuum pump starting, with slag surface slightly moving molten steel not exposed, when vacuum degree reaches 100Pa, start timing, holding time 10min, at the same time, adjust argon pressure to 0.3MPa, after static argon blowing, add silicon-calcium alloy cored wire (Φ14mm) 2m / t steel, covering agent 0.6kg / t steel, outlet temperature 1565℃.

[0137] (4) Continuous casting

[0138] Ladle inlet temperature 1512℃, molten steel amount 102t, tundish H control 1.4ppm, casting time 42min, whole process protective casting, mold powder using medium carbon steel mold powder.

[0139] (5) Heating process: inlet temperature 530℃, preheating section temperature requirement 690℃, time 1.4h; heating 2 section temperature requirement 856℃, time 1.5h; heating 1 section temperature requirement 1210℃, time 1.4h; soaking section temperature requirement 1200℃, time 1.5h; outlet temperature 1187℃.

[0140] (6) Rolling process

[0141] Initial rolling process: rolling 9 passes, turning over→1st pass width 408mm, height 421mm, reduction 65mm→2nd pass width 426mm, height 351mm, reduction 70mm→turning over→3rd pass width 370mm, height 362mm, reduction 64mm→4th pass width 397mm, height 272mm, reduction 90mm→turning over→5th pass 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 over→9th pass width 271mm, height 235mm, reduction 82mm, through 3 sets of 850mm rolling mill, 1 set of 735mm rolling mill, then enter continuous rolling mill group for rolling.

[0142] Continuous rolling product rolling process: rolling 9 passes, 1st pass height 229mm, width 245mm; 2nd pass height 192mm, width 235mm; 3rd pass height 200mm, width 195mm; 4th pass height 173mm, width 210mm; 5th pass height 180mm, width 178.2mm; 6th pass height 142mm, width 190mm; 7th pass height 158mm, width 154.8mm; 8th pass height 121mm, width 162.8mm; 9th pass height 131.76mm, width 131.76mm; after 9 passes, outlet finished product.

[0143] (7) holding process

[0144] Holding process: steel holding, holding pit temperature 590℃, holding 52h, out of pit temperature 140℃.

[0145] (8) heat treatment process

[0146] The steel after holding is subjected to heat treatment, and the heat treatment comprises the following steps:

[0147] 1) quenching: 850℃, holding 1.0h, oil cooling;

[0148] 2) tempering: 500℃, holding 2.0h, water cooling.

[0149] 2, finished product inspection results

[0150] (1) low magnification structure of Φ130mm specification

[0151] (2) non-metallic inclusions of Φ130mm specification

[0152] (3) mechanical properties of Φ130mm specification

[0153] According to the above table, the steel bars for automobile engine connecting rods are manufactured by adopting ecological electric furnace + LF + RH + continuous casting billet → heating → roughing mill rolling → continuous rolling mill set in Examples 1-5, which meet the quality requirements of the steel bars for automobile engine connecting rods, and the mechanical properties and high steel purity indexes can also meet the standard requirements.

[0154] The above described examples only express several embodiments of the present application, and the description is more specific and detailed, but it should not be understood as limiting the scope of the application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the scope of the present application. Therefore, the protection scope of the present application patent should be subject to 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.

2. A method of producing a steel bar for a connecting rod of an automobile engine as set forth in claim 1, characterized by, Comprise the following steps: Ecological electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating process, rolling process and heat preservation process; Among them, the ecological electric furnace smelting adopts scrap steel as the charge, and the 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; Among them, the mass percentage of alloy structural steel cut in the 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%; Add slag, pre-deoxidizer and alloy when 1 / 4~1 / 3 of the tapping, 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 ash, and 20Kg / t~21Kg / t of small block coke; Among them, the particle size of the active lime is 10mm~70mm; The particle size of the magnesite is 10mm~60mm.

3. The production method according to claim 2, characterized by, 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 addition amount per ton of steel is 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 addition amount per ton of steel is 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.

4. The preparation method according to claim 2, characterized in that, In the RH vacuum refining, the inlet temperature is 1610-1620℃, the operation time is 30-40 minutes, the argon pressure is controlled to be 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 be 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℃.

5. The preparation method according to claim 2, characterized in that, In the continuous casting, the ladle inlet temperature is 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 is medium-carbon steel protective slag.

6. The preparation method according to claim 2, characterized in that, In the heating process, the square billet offline in the continuous casting process is sent into a 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; the heating section includes heating section 1 temperature 1190-1220℃, time 1.3-1.5 hours; heating section 2 temperature 850-860℃, time 1.3-1.5 hours; soaking section temperature 1190-1210℃, time 1.3-1.5 hours; the steel temperature is 1180-1190℃.

7. The preparation method according to claim 2, characterized in that, The rolling process, the heated continuous casting billet is roughed, the roughing adopts 9 passes, four times of turning, through 3 850mm rolling mills, 1 735mm rolling mill, then enters 8 continuous rolling mill groups; once turning before rolling 1 pass, second turning after rolling 2 passes, third turning after rolling 2 passes again, fourth turning after rolling 4 passes again; the first pass is 408mm-408.05mm wide, 421mm-421.05mm high, the reduction is 65mm-65.05mm; the second pass is 426mm-426.05mm wide, 351mm-351.05mm high, the reduction is 70mm-70.05mm; the third pass is 370mm-370.05mm wide, 362mm-362.05mm high, the reduction is 64mm-64.05mm; the fourth pass is 397mm-397.05mm wide, 272mm-272.05mm high, the reduction is 90mm-90.05mm; the fifth pass is 285mm-285.05mm wide, 355mm-355.05mm high, the reduction is 42mm-42.05mm; the sixth pass is 297mm-297.05mm wide, 315mm-315.05mm high, the reduction is 40mm-40.05mm; the seventh pass is 307mm-307.05mm wide, 280mm-280.05mm high, the reduction is 35mm-35.05mm; the eighth pass is 317mm-317.05mm wide, 246mm-246.05mm high, the reduction is 34mm-34.05mm; the ninth pass is 271mm-271.05mm wide, 235mm-235.05mm high, the reduction is 82mm-82.05mm.

8. The preparation method according to claim 2, characterized in that, The rolling process, the continuous rolling product rolling process, rolling 9 passes; the first pass is 229mm-229.05mm high, 245mm-245.05mm wide; the second pass is 192mm-192.05mm high, 235mm-235.05mm wide; the third pass is 200mm-200.05mm high, 195mm-195.05mm wide; the fourth pass is 173mm-173.05mm high, 210mm-210.05mm wide; the fifth pass is 180mm-180.05mm high, 178.2mm-178.25mm wide; the sixth pass is 142mm-142.05mm high, 190mm-190.05mm wide; the seventh pass is 158mm-158.05mm high, 154.8mm-154.85mm wide; the eighth pass is 121mm-121.05mm high, 162.8mm-162.85mm wide; the ninth pass is 131.76mm-131.80mm high, 131.76mm-131.80mm wide; the finished product is discharged after the ninth pass.

9. The preparation method according to claim 2, characterized in that, In the heat preservation process, the bar prepared by the rolling process is heat preserved, 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 exit is less than or equal to 160 DEG C; 10. The method of claim 2, wherein, The heat treated steel is heat treated, and the heat treatment comprises the following steps: (1) the heat treated steel is quenched, the heating temperature is 840 DEG C-860 DEG C, the heat preservation time is 0.9h-1.2h, and the oil cooling is carried out; (2) the quenched and cooled steel is tempered, the tempering temperature is 490 DEG C-510 DEG C, the heat preservation time is 1.9h-2.2h, and the water cooling is carried out.

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