Steel bar for ecological electric furnace petroleum drill bit and preparation method of steel bar

Abstract

The invention discloses a steel bar for an ecological electric furnace petroleum drill bit and a preparation method of the steel bar. The steel bar comprises, by mass, 0.18%-0.22% of C, 0.22%-0.35% of Si, 0.60%-0.90% of Mn, smaller than or equal to 0.012% of P, smaller than or equal to 0.005% of S, 0.85%-1.00% of Cr, smaller than or equal to 0.25% of Ni, 0.17%-0.23% of Mo, 0.10%-0.20% of V, smaller than or equal to 0.15% of Cu and the balance iron and inevitable impurities. According to the produced steel bar for the petroleum drill bit, the breakthrough of batch production of the steel bar for the petroleum drill bit in the ecological electric furnace continuous casting process is achieved, indexes such as finished steel macrostructures, non-metallic inclusions and mechanical properties of the steel bar for the petroleum drill bit are guaranteed, and the surface quality level of the steel bar for the petroleum drill bit is also guaranteed; and the quality requirement of the steel bar for mining machinery is met.

Description

Technical Field

[0001] The present invention relates to the technical field of materials and metallurgy, and more particularly to a steel bar for an ecological electric furnace oil drill bit and a preparation method thereof. Background Art

[0002] The oil drill bit is a vital tool in oil drilling, a key device used to extract oil and break rock formations during oil extraction. The quality of the steel used in oil drill bits directly impacts drilling quality, efficiency, and costs, as well as the safety of the drilling process. Therefore, extremely high requirements are placed on the steel's high-temperature resistance, wear resistance, mechanical properties, fatigue life, and purity to ensure the normal and safe operation of drilling operations. However, existing oil drill bits often suffer from defects such as unstable mechanical properties, low fatigue life, and poor wear resistance. Summary of the Invention

[0003] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and provide a steel bar for ecological electric furnace oil drill bits with excellent mechanical properties and high steel purity and a preparation method thereof.

[0004] To achieve the above object, the technical solution of the present invention is as follows:

[0005] A steel bar for an ecological electric furnace oil drill bit comprises the following components in percentage by mass: C: 0.18% to 0.22%, Si: 0.22% to 0.35%, Mn: 0.60% to 0.90%, P≤0.012%, S≤0.005%, Cr: 0.85% to 1.00%, Ni≤0.25%, Mo: 0.17% to 0.23%, V: 0.10% to 0.20%, Cu≤0.15%, and the balance being iron and unavoidable impurities.

[0006] The present invention also discloses a method for preparing the above-mentioned steel bar for ecological electric furnace oil drill bit, comprising the following steps: ecological electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating, rolling, heat preservation and heat treatment;

[0007] In the ecological electric furnace smelting, scrap steel is used as the furnace charge, and the scrap steel accounts for 100% by mass; the end composition of the electric furnace is: C: 0.08% to 0.12%, P≤0.010%; deoxidation and alloying are carried out during the steel tapping process;

[0008] In the LF refining, the molten steel discharged from the ecological electric furnace is put into the LF furnace for refining treatment;

[0009] During the RH vacuum refining, the molten steel treated by the LF refining is hoisted into the RH vacuum furnace for refining;

[0010] During the continuous casting, the molten steel after the RH vacuum refining treatment is continuously cast, the ladle arrival temperature is 1570℃~1580℃, the casting time is 40min~45min, the superheat is 20℃~25℃, the H content in the ladle is ≤2ppm, the pulling speed is 0.47m / min~0.48m / min, the whole process is protected casting, the crystallizer protective slag uses 3.6kg / t steel~3.7kg / t steel medium carbon steel protective slag, and the obtained continuous casting billet is heated, rolled and kept warm, the lower holding pit temperature is ≥580℃, the holding time is 48h~55h, the pit exit temperature is ≤150℃, and finally the steel bar for the ecological electric furnace oil drill bit is obtained through heat treatment.

[0011] The implementation of the present invention will have the following beneficial effects:

[0012] The present invention adopts "ecological electric furnace smelting + LF + RH + continuous casting and rolling process" combined with reasonable composition design to produce steel bars for oil drill bits, which meet high-end usage requirements and achieve a breakthrough in the mass production of steel bars for oil drill bits using the ecological electric furnace continuous casting process. It not only ensures the indicators such as the macrostructure, non-metallic inclusions, and mechanical properties of the finished steel bars for oil drill bits, but also ensures the surface quality level of the steel bars for oil drill bits, meeting the quality requirements of steel bars for mining machinery. DETAILED DESCRIPTION

[0013] The present invention will be further described below with reference to specific examples, but the present invention is not limited thereto in any way.

[0014] 1. Chemical composition

[0015] The invention discloses a steel bar for an ecological electric furnace oil drill bit, comprising the following components in percentage by mass: C: 0.18% to 0.22%, Si: 0.22% to 0.35%, Mn: 0.60% to 0.90%, P≤0.012%, S≤0.005%, Cr: 0.85% to 1.00%, Ni≤0.25%, Mo: 0.17% to 0.23%, V: 0.10% to 0.20%, Cu≤0.15%, and the balance being iron and unavoidable impurities.

[0016] In a specific embodiment, the tensile strength of the steel bar for the ecological electric furnace oil drill bit is ≥920 MPa, the yield strength is ≥865 MPa, A ≥10%, z ≥45%, and KU2 ≥55J.

[0017] 2. Production Technology

[0018] The present invention also discloses a method for preparing a steel bar for an ecological electric furnace oil drill bit according to any embodiment of the present invention, comprising the following steps: ecological electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating, rolling, insulation and heat treatment. The specific steps are as follows:

[0019] S1. In the ecological electric furnace smelting, scrap steel is used as the furnace charge, and the scrap steel accounts for 100% by mass; the final composition of the electric furnace is: C: 0.08%~0.12%, P≤0.010%; deoxidation and alloying are carried out during the steel tapping process.

[0020] In a specific embodiment, in the ecological electric furnace smelting, the scrap steel includes heavy scrap steel and light scrap steel; the mass percentage of heavy scrap steel in the furnace charge is 50% to 60%; the tapping temperature is 1620°C to 1630°C; slag, pre-deoxidizer and alloy are added when 1 / 4 to 1 / 3 of the steel is tapped; the smelting cycle is 40 minutes to 50 minutes, and the furnace oxygen consumption is 25m 3 / t steel~26m 3 / t steel; alloy addition per ton of steel: 6.2Kg / t~6.5Kg / t of silicon-manganese alloy, 4.5Kg / t~4.8Kg / t of high carbon ferromanganese, 9.0Kg / t~9.5Kg / t of low carbon ferrochrome, 1.7Kg / t~1.8Kg / t of aluminum ingots; auxiliary material addition per ton of steel: 18Kg / t~18.5Kg / t of coke particles, 5.5Kg / t~5.8Kg / t of ladle dust, 26Kg / t~27Kg / t of active lime, 8.0Kg / t~8.5Kg / t of magnesite; among which, the particle size of active lime is 10mm~70mm; the particle size of magnesite is 10mm~60mm.

[0021] In S2 and LF refining, the molten steel discharged from the ecological electric furnace is put into the LF furnace for refining.

[0022] In a specific embodiment, the LF inlet temperature is 1540°C to 1550°C, and after heating and slagging with a high current of 35000A to 36000A, when the slag surface fluctuates and the molten steel and the arc are not exposed, 6.5Kg / t steel to 6.8Kg / t steel of active lime is added, and the first sampling and analysis is taken after 5min to 6min, and the composition content of the molten steel is adjusted according to the target composition requirements; when the molten steel temperature reaches 1610°C to 1620°C, 1.4kg / t steel to 1.5kg / t steel of alumina balls as a slag regulator are added to adjust the slag alkalinity to ≥2.5, the furnace door is closed for 10min to 13min, and when the molten steel temperature reaches 1625°C to 1630°C, the slag is heated to 1000°C. When the temperature of the molten steel reaches 1630℃~1640℃, the station is left, the LF smelting cycle is 45min~50min, the clearance is 420mm~430mm, and the following alloys are added per ton of steel: 0.3kg / t~0.35kg / t of ferrosilicon, 2.5kg / t~2.6kg / t of ferromolybdenum, 3.5kg / t~3.6kg / t of ferrovanadium, 1.1kg / t~1.2kg / t of aluminum wire segments, where the size of the aluminum wire segments is Φ10mm~Φ60mm; additional auxiliary materials are added per ton of steel: 6.5kg / t~6.8kg / t of active lime with a particle size of 10mm~70mm.

[0023] In S3 and RH vacuum refining, the molten steel treated by LF refining is hoisted into the RH vacuum furnace for refining.

[0024] In a specific embodiment, the inlet temperature is 1625℃~1635℃, the operation time is 50min~60min, the vacuum pump is started when the argon pressure is controlled to 0.1MPa~0.3MPa, and when the vacuum degree reaches 100Pa~110Pa, the time is maintained for 20min~25min, and the argon pressure is adjusted to 0.3MPa~0.5MPa at the same time. The temperature after re-pressurization is 1585℃~1595℃. After the static argon blowing is completed, 0.5kg / t steel~0.6kg / t steel is added. The covering agent for t steel has a clearance of 480mm~520mm, and the leaving station temperature is 1570℃~1580℃. After breaking the vacuum, 0.6kg / t steel~0.62kg / t steel covering agent, 0.75kg / t steel~0.80kg / t steel silicon-calcium alloy cored wire and 0.56kg / t steel~0.58kg / t steel sulfur concentrate powder cored wire are added. The size of the silicon-calcium alloy cored wire is Φ14mm~Φ15mm, and the size of the sulfur concentrate powder cored wire is Φ13mm~Φ14mm.

[0025] In S4, continuous casting, the molten steel after RH vacuum refining is continuously cast, the ladle arrival temperature is 1570℃~1580℃, the casting time is 40min~45min, the superheat is 20℃~25℃, the H content in the tundish is ≤2ppm, the casting speed is 0.47m / min~0.48m / min, the whole process is protected casting, and the mold protection slag uses 3.6kg / t steel~3.7kg / t steel of medium carbon steel protection slag.

[0026] S5. During heating, the billets produced in the continuous casting process are fed into a heating furnace with a temperature of 500°C to 600°C; the temperature of the preheating section is 850°C to 870°C, and the time is 1.7h to 2.0h; the heating section includes heating section 1 with a temperature of 1210°C to 1240°C, and the time is 1.7h to 2.0h; heating section 2 with a temperature of 850°C to 870°C, and the time is 1.7h to 2.0h; the temperature of the soaking section is 1210°C to 1230°C, and the time is 1.7h to 2.0h; and the tapping temperature is 1180°C to 1210°C.

[0027] S6, during rolling, the heated continuous casting slab is initially rolled and opened. The initial rolling adopts 9-pass rolling and four-time steel turning. It passes through 3 850mm rolling mills and then enters 9-stand continuous rolling mill group for rolling. Steel turning is performed once before rolling 1 pass, the second time after rolling 2 passes, the third time after rolling 2 passes, and the fourth time after rolling 4 passes. The width of the first pass is 408mm~408.01mm, and the height is 421mm~421.01 mm, reduction 65mm~65.01mm; the second pass width 426mm~426.01mm, height 351mm~351.01mm, reduction 70mm~70.01mm; the third pass width 370mm~370.01mm, height 362mm~362.01mm, reduction 64mm~64.01mm; the fourth pass width 397mm~397.01mm, height 2 72mm~272.01mm, reduction 90mm~90.01mm; 5th pass width 285mm~285.01mm, height 355mm~355.01mm, reduction 42mm~42.01mm; 6th pass width 297mm~297.01mm, height 315mm~315.01mm, reduction 40mm~40.01mm; 7th pass width 307mm~ 307.01mm, height 280mm~280.01mm, reduction 35mm~35.01mm; the 8th pass width 317mm~317.01mm, height 246mm~246.01mm, reduction 34mm~34.01mm; the 9th pass width 271mm~271.01mm, height 235mm~235.01mm, reduction 82mm~82.01mm.

[0028] In a specific embodiment, the continuous rolling product is rolled 7 times; the first pass is 229mm-229.01mm high, 245mm-245.01mm wide, and the rolling speed is 0.27m / s-0.272m / s; the second pass is 192mm-192.01mm high, 235mm-235.01mm wide, and the rolling speed is 0.31m / s-0.312m / s; the third pass is 200mm-200.01mm high, 195mm-195.01mm wide, and the rolling speed is 0.35m / s-0.352m / s; the fourth pass is 177mm-177.01mm high, 210mm wide ~210.01mm, rolling speed 0.362m / s~0.364m / s; the 5th pass is 189mm~189.01mm high, 178.2mm~178.21mm wide, rolling speed 0.456m / s~0.458m / s; the 6th pass is 152mm~152.01mm high, 199mm~199.01mm wide, rolling speed 0.519m / s~0.521m / s; the 7th pass is 162mm~162.01mm high, 162mm~162.01mm wide, rolling speed 0.585m / s~0.587m / s; the finished product is produced after the 7th pass.

[0029] S7. During the insulation process, the bars prepared by the rolling process are kept warm, the temperature of the lower insulation pit is ≥580°C, the insulation time is 48h~55h, and the temperature out of the pit is ≤150°C.

[0030] S8, heat-treating the steel after insulation, the heat treatment comprising the following steps:

[0031] (1) The steel is quenched after being kept warm, with the heating temperature at 870°C to 890°C, the temperature being kept warm for 0.8h to 1.2h, and then oil-cooled;

[0032] (2) The steel after quenching and cooling is tempered at a temperature of 490°C to 510°C, kept warm for 1.8h to 2.2h, and oil-cooled.

[0033] The following are specific embodiments

[0034] Example 1

[0035] The steel bar for the ecological electric furnace oil drill bit of this embodiment includes the following components in mass percentage: C: 0.19%, Si: 0.26%, Mn: 0.72%, P: 0.010%, S: 0.004%, Cr: 0.92%, Ni: 0.05%, Mo: 0.19%, V: 0.14%, Cu: 0.05%, and the remainder is iron and unavoidable impurities.

[0036] The method for preparing steel bars for oil drill bits in an ecological electric furnace of this embodiment has a process route of: ecological electric furnace + LF + RH + continuous casting → heating in a heating furnace → rolling → insulation → heat treatment, which specifically includes the following steps:

[0037] (1) Ecological electric furnace smelting

[0038] The 100% scrap steel smelting process is adopted, of which 54% is heavy scrap steel and the rest is light scrap steel; the tapping temperature is 1625℃, the C content is 0.09% and the P content is 0.008% when tapping, slag, pre-deoxidizer and alloy are added when 1 / 4 of the steel is tapped, the smelting cycle is 45 minutes, and the furnace oxygen consumption is 25m 3 / t steel. Alloy addition per ton of steel: 6.3 kg / t silicon-manganese alloy, 4.6 kg / t high-carbon ferrochrome, 9.2 kg / t low-carbon ferrochrome, 1.7 kg / t aluminum ingot. Auxiliary material addition per ton of steel: 18.2 kg / t coke pellets, 5.6 kg / t ladle dust, 26 kg / t active lime (Φ30 mm), and 8.2 kg / t magnesite (Φ40 mm).

[0039] (2) LF furnace refining

[0040] The LF station temperature is 1546℃, and a high current of 35500A is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, 6.6kg / t of active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloy is added according to the median chemical composition, and carbon is increased to promote rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1614℃, 1.4kg / t of alumina balls as a slag regulator are added to adjust the slag basicity to 2.7. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1626℃, the second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, the station is left when the molten steel temperature reaches 1635℃. The LF smelting cycle is 46 minutes, and the clearance is 424mm. The amount of additional alloy added per ton of steel is: 0.32kg / t of ferrosilicon, 2.5kg / t of ferromolybdenum, 3.5kg / t of ferrovanadium (FeV50-B), 1.1kg / t of aluminum wire (Φ10mm). The amount of additional auxiliary materials added per ton of steel is: 6.6kg / t of active lime (Φ30mm).

[0041] (3)RH refining

[0042] The entry temperature was 1628°C, the operation time was 55 minutes, and the argon pressure was controlled at 0.1 MPa before the vacuum pump was started, so that the molten steel would not be exposed due to slight movement of the slag surface. When the vacuum reached 103 Pa, the timing was started and maintained for 22 minutes. At the same time, the argon pressure was adjusted to 0.3 MPa, and the re-pressurization temperature was 1591°C. After the static argon blowing was completed, 0.5 kg / t of covering agent was added, the clearance was 500 mm, and the exit temperature was 1575°C. After breaking the vacuum, 0.6 kg / t of ladle covering agent, 0.77 kg / t of silicon-calcium alloy cored wire (Φ14 mm) and 0.57 kg / t of sulfur concentrate cored wire (Φ13 mm) were added.

[0043] (4) Continuous casting

[0044] The arrival temperature of the ladle is 1576℃, the H of the tundish is controlled at 1.5ppm, the casting time is 42min, the superheat is 22℃, the casting speed is 0.47m / min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag 3.6kg / t steel.

[0045] (5) Heating process

[0046] The temperature entering the heating furnace is 550℃, the temperature of the preheating section is required to be 860℃, and the time is 1.8h; the temperature of the heating section 2 is required to be 860℃, and the time is 1.8h; the temperature of the heating section 1 is required to be 1220℃, and the time is 1.9h; the temperature of the soaking section is required to be 1215℃, and the time is 1.8h; the steel tapping temperature is 1195℃.

[0047] (6) Rolling process

[0048] Initial rolling process: 9 passes, steel turning → 1st pass width 408mm, height 421mm, reduction 65.01mm → 2nd pass width 426.01mm, height 351mm, reduction 70mm → steel turning → 3rd pass width 370.01mm, height 362.01mm, reduction 64mm → 4th pass width 397.01mm, height 272.01mm, reduction 90mm → steel turning → 5th pass width 285.01mm, height 35 5mm, reduction 42mm → 6th pass width 297.01mm, height 315mm, reduction 40.01mm → 7th pass width 307mm, height 280mm, reduction 35.01mm → 8th pass width 317.01mm, height 246mm, reduction 34mm → steel turning → 9th pass width 271mm, height 235.01mm, reduction 82mm, passes through 3 850mm rolling mills, and then enters 9 continuous rolling mills for rolling.

[0049] Continuous rolling product rolling process: 7 passes, the first pass is 229mm high, 245.01mm wide, and the rolling speed is 0.272m / s; the second pass is 192mm high, 235mm wide, and the rolling speed is 0.312m / s; the third pass is 200.01mm high, 195mm wide, and the rolling speed is 0.352m / s; the fourth pass is 177.01mm high, 210mm wide, and the rolling speed is 0.362m / s; the fifth pass is 189.01mm high, 178.21mm wide, and the rolling speed is 0.456m / s; the sixth pass is 152.01mm high, 199.01mm wide, and the rolling speed is 0.519m / s; the seventh pass is 162mm high, 162.01mm wide, and the rolling speed is 0.587m / s; the finished product is produced after 7 passes.

[0050] (7) Insulation process

[0051] The temperature of the lower insulation pit is 590℃, the insulation is 50h, and the temperature out of the pit is 130℃.

[0052] (8) Heat treatment process

[0053] After the insulation, the steel sample is taken for heat treatment, and the heat treatment includes the following steps:

[0054] 1) Quenching: 880℃, holding time 1.0h, oil cooling;

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

[0056] Example 2

[0057] The steel bar for the ecological electric furnace oil drill bit of this embodiment includes the following components in mass percentage: C: 0.20%, Si: 0.26%, Mn: 0.74%, P: 0.011%, S: 0.003%, Cr: 0.92%, Ni: 0.04%, Mo: 0.20%, V: 0.15%, Cu: 0.05%, and the remainder is iron and unavoidable impurities.

[0058] The method for preparing steel bars for oil drill bits in an ecological electric furnace of this embodiment has a process route of: ecological electric furnace + LF + RH + continuous casting → heating in a heating furnace → rolling → insulation → heat treatment, and includes the following steps:

[0059] (1) Ecological electric furnace smelting

[0060] The 100% scrap steel smelting process is adopted, of which 56% is heavy scrap steel and the rest is light scrap steel; the tapping temperature is 1627℃, the C content is 0.09% and the P content is 0.009% when tapping, slag, pre-deoxidizer and alloy are added when 1 / 4 of the steel is tapped, the smelting cycle is 45 minutes, and the furnace oxygen consumption is 25m 3 / t steel. Alloy addition per ton of steel: 6.4 kg / t silicon-manganese alloy, 4.6 kg / t high-carbon ferrochrome, 9.2 kg / t low-carbon ferrochrome, 1.8 kg / t aluminum ingot. Auxiliary material addition per ton of steel: 18.2 kg / t coke pellets, 5.6 kg / t ladle dust, 26 kg / t active lime (Φ30 mm), and 8.2 kg / t magnesite (Φ40 mm).

[0061] (2) LF furnace refining

[0062] The LF station temperature is 1545℃, and a high current of 35600A is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, 6.7kg / t of active lime is added. After 6 minutes, the first sampling and chemical composition analysis are carried out. Alloy is added according to the median chemical composition, and carbon is increased to promote rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1615℃, 1.5kg / t of alumina balls as a slag regulator are added to adjust the slag basicity to 2.7. The furnace door is closed for 12 minutes. When the molten steel temperature reaches 1627℃, the second sampling and chemical composition analysis is carried out to confirm the deviation of the content of each chemical element from the target value. After the second sampling is taken, the station is left when the molten steel temperature reaches 1636℃. The LF smelting cycle is 48 minutes, and the clearance is 425mm. The amount of additional alloy added per ton of steel is: 0.33kg / t of ferrosilicon, 2.6kg / t of ferromolybdenum, 3.5kg / t of ferrovanadium (FeV50-B), 1.2kg / t of aluminum wire (Φ10mm). The amount of additional auxiliary materials added per ton of steel is: 6.6kg / t of active lime (Φ30mm).

[0063] (3)RH refining

[0064] The entry temperature was 1628°C, the operation time was 57 minutes, and the argon pressure was controlled at 0.2 MPa before the vacuum pump was started, so that the molten steel would not be exposed due to slight movement of the slag surface. When the vacuum reached 102 Pa, the timing was started and maintained for 22 minutes. At the same time, the argon pressure was adjusted to 0.4 MPa, and the re-pressurization temperature was 1590°C. After the static argon blowing was completed, 0.6 kg / t of covering agent was added, the clearance was 500 mm, and the exit temperature was 1575°C. After breaking the vacuum, 0.6 kg / t of ladle covering agent, 0.76 kg / t of silicon-calcium alloy cored wire (Φ14 mm) and 0.57 kg / t of sulfur concentrate cored wire (Φ13 mm) were added.

[0065] (4) Continuous casting

[0066] The arrival temperature of the ladle is 1575℃, the H of the tundish is controlled at 1.6ppm, the casting time is 42min, the superheat is 21℃, the casting speed is 0.47m / min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag 3.7kg / t steel.

[0067] (5) Heating process

[0068] The temperature entering the heating furnace is 570℃, the temperature of the preheating section is required to be 860℃, and the time is 1.8h; the temperature of the heating section 2 is required to be 860℃, and the time is 1.8h; the temperature of the heating section 1 is required to be 1218℃, and the time is 1.8h; the temperature of the soaking section is required to be 1215℃, and the time is 1.9h; the steel tapping temperature is 1192℃.

[0069] (6) Rolling process

[0070] Primary rolling process: 9 passes, steel turning → 1st pass width 408mm, height 421.01mm, reduction 65mm → 2nd pass width 426.01mm, height 351.01mm, reduction 70mm → steel turning → 3rd pass width 370.01mm, height 362.01mm, reduction 64mm → 4th pass width 397.01mm, height 272mm, reduction 90.01mm → steel turning → 5th pass width 285.01mm, height 355.01mm, Reduction 42.01mm → 6th pass width 297.01mm, height 315mm, reduction 40.01mm → 7th pass width 307.01mm, height 280.01mm, reduction 35.01mm → 8th pass width 317.01mm, height 246mm, reduction 34.01mm → Steel turning → 9th pass width 271.01mm, height 235mm, reduction 82.01mm, passes through 3 850mm rolling mills, and then enters 9 continuous rolling mills for rolling.

[0071] Continuous rolling process: 7 passes, the first pass is 229.01mm high, 245mm wide, and a rolling speed of 0.272m / s; the second pass is 192.01mm high, 235.01mm wide, and a rolling speed of 0.312m / s; the third pass is 200.01mm high, 195mm wide, and a rolling speed of 0.352m / s; the fourth pass is 177.01mm high, 235.01mm wide, and a rolling speed of 0.312m / s. 210.01mm, rolling speed 0.364m / s; the 5th pass is 189mm high, 178.21mm wide, rolling speed 0.458m / s; the 6th pass is 152.01mm high, 199.01mm wide, rolling speed 0.521m / s; the 7th pass is 162mm high, 162.01mm wide, rolling speed 0.587m / s; the finished product is produced after 7 passes.

[0072] (7) Insulation process

[0073] The temperature of the lower insulation pit is 590℃, the insulation time is 52h, and the temperature out of the pit is 120℃.

[0074] (8) Heat treatment process

[0075] After the insulation, the steel sample is taken for heat treatment, and the heat treatment includes the following steps:

[0076] 1) Quenching: 880℃, holding time 1.0h, oil cooling;

[0077] 2) Tempering: 500℃, keep warm for 2.0h, oil cooling.

[0078] Example 3

[0079] The steel bar for the ecological electric furnace oil drill bit of this embodiment includes the following components in mass percentage: C: 0.21%, Si: 0.23%, Mn: 0.75%, P: 0.010%, S: 0.004%, Cr: 0.90%, Ni: 0.05%, Mo: 0.20%, V: 0.14%, Cu: 0.05%, and the remainder is iron and unavoidable impurities.

[0080] The method for preparing steel bars for oil drill bits in an ecological electric furnace of this embodiment has a process route of: ecological electric furnace + LF + RH + continuous casting → heating in a heating furnace → rolling → insulation → heat treatment, and includes the following steps:

[0081] (1) Ecological electric furnace smelting

[0082] The 100% scrap steel smelting process is adopted, of which 56% is heavy scrap steel and the rest is light scrap steel; the tapping temperature is 1625℃, the C content is 0.09% and the P content is 0.009% when tapping, slag, pre-deoxidizer and alloy are added when 1 / 4 of the steel is tapped, the smelting cycle is 45 minutes, and the furnace oxygen consumption is 25m 3 / t steel. Alloy addition per ton of steel: 6.3 kg / t silicon-manganese alloy, 4.6 kg / t high-carbon ferrochrome, 9.2 kg / t low-carbon ferrochrome, 1.7 kg / t aluminum ingot. Auxiliary material addition per ton of steel: 18.2 kg / t coke pellets, 5.6 kg / t ladle dust, 27 kg / t active lime (Φ30 mm), and 8.2 kg / t magnesite (Φ40 mm).

[0083] (2) LF furnace refining

[0084] The LF station temperature is 1547℃, and a high current of 35600A is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, 6.8kg / t of active lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloy is added according to the median chemical composition, and carbon is increased to promote rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1614℃, 1.5kg / t of alumina balls as a slag regulator are added to adjust the slag basicity to 2.8. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1627℃, the second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, the station is left when the molten steel temperature reaches 1636℃. The LF smelting cycle is 47 minutes, and the clearance is 425mm. The amount of additional alloy added per ton of steel is: 0.33kg / t of ferrosilicon, 2.5kg / t of ferromolybdenum, 3.6kg / t of ferrovanadium (FeV50-B), 1.2kg / t of aluminum wire (Φ10mm). The amount of additional auxiliary materials added per ton of steel is: 6.6kg / t of active lime (Φ30mm).

[0085] (3)RH refining

[0086] The entry temperature was 1629°C, the operation time was 56 minutes, and the argon pressure was controlled at 0.1 MPa before the vacuum pump was started, so that the molten steel would not be exposed due to slight movement of the slag surface. When the vacuum reached 104 Pa, the timing began and was maintained for 22 minutes. At the same time, the argon pressure was adjusted to 0.3 MPa, and the re-pressurization temperature was 1590°C. After the static argon blowing was completed, 0.5 kg / t of covering agent was added, the clearance was 500 mm, and the exit temperature was 1577°C. After breaking the vacuum, 0.6 kg / t of ladle covering agent, 0.77 kg / t of silicon-calcium alloy cored wire (Φ14 mm) and 0.57 kg / t of sulfur concentrate cored wire (Φ13 mm) were added.

[0087] (4) Continuous casting

[0088] The arrival temperature of the ladle is 1575℃, the H of the tundish is controlled at 1.5ppm, the casting time is 42min, the superheat is 22℃, the casting speed is 0.47m / min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag 3.6kg / t steel.

[0089] (5) Heating process

[0090] The temperature entering the heating furnace is 550℃, the temperature of the preheating section is required to be 860℃, and the time is 1.8h; the temperature of the heating section 2 is required to be 860℃, and the time is 1.9h; the temperature of the heating section 1 is required to be 1220℃, and the time is 1.8h; the temperature of the soaking section is required to be 1216℃, and the time is 1.7h; the steel tapping temperature is 1192℃.

[0091] (6) Rolling process

[0092] Primary rolling process: 9 passes, steel turning → 1st pass width 408mm, height 421.01mm, reduction 65mm → 2nd pass width 426.01mm, height 351.01mm, reduction 70mm → steel turning → 3rd pass width 370.01mm, height 362.01mm, reduction 64mm → 4th pass width 397.01mm, height 272.01mm, reduction 90.01mm → steel turning → 5th pass width 285mm, height 355 mm, reduction 42mm → 6th pass width 297.01mm, height 315mm, reduction 40mm → 7th pass width 307mm, height 280.01mm, reduction 35.01mm → 8th pass width 317.01mm, height 246mm, reduction 34.01mm → steel turning → 9th pass width 271.01mm, height 235mm, reduction 82.01mm, passes through 3 850mm rolling mills, and then enters 9 continuous rolling mills for rolling.

[0093] Continuous rolling product rolling process: 7 passes, the first pass is 229mm high, 245.01mm wide, and the rolling speed is 0.272m / s; the second pass is 192.01mm high, 235mm wide, and the rolling speed is 0.31m / s; the third pass is 200.01mm high, 195mm wide, and the rolling speed is 0.352m / s; the fourth pass is 177.01mm high, 210mm wide, and the rolling speed is 0.364m / s; the fifth pass is 189mm high, 178.21mm wide, and the rolling speed is 0.458m / s; the sixth pass is 152mm high, 199.01mm wide, and the rolling speed is 0.519m / s; the seventh pass is 162.01mm high, 162mm wide, and the rolling speed is 0.587m / s; the finished product is produced after 7 passes.

[0094] (7) Insulation process

[0095] The temperature of the lower insulation pit is 600℃, the insulation time is 51h, and the temperature out of the pit is 130℃.

[0096] (8) Heat treatment process

[0097] After the insulation, the steel sample is taken for heat treatment, and the heat treatment includes the following steps:

[0098] 1) Quenching: 880℃, holding time 1.0h, oil cooling;

[0099] 2) Tempering: 500℃, keep warm for 2.0h, oil cooling.

[0100] Example 4

[0101] The steel bar for the ecological electric furnace oil drill bit of this embodiment includes the following components in mass percentage: C: 0.20%, Si: 0.25%, Mn: 0.70%, P: 0.010%, S: 0.004%, Cr: 0.93%, Ni: 0.05%, Mo: 0.20%, V: 0.14%, Cu: 0.05%, and the remainder is iron and unavoidable impurities.

[0102] The method for preparing steel bars for oil drill bits in an ecological electric furnace of this embodiment has a process route of: ecological electric furnace + LF + RH + continuous casting → heating in a heating furnace → rolling → insulation → heat treatment, and includes the following steps:

[0103] (1) Ecological electric furnace smelting

[0104] The 100% scrap steel smelting process is adopted, of which 57% is heavy scrap steel and the rest is light scrap steel; the tapping temperature is 1624℃, the C content is 0.09% and the P content is 0.008% when tapping, slag, pre-deoxidizer and alloy are added when 1 / 4 of the steel is tapped, the smelting cycle is 46 minutes, and the furnace oxygen consumption is 25m 3 / t steel. Alloy addition per ton of steel: 6.3 kg / t silicon-manganese alloy, 4.6 kg / t high-carbon ferrochrome, 9.2 kg / t low-carbon ferrochrome, 1.7 kg / t aluminum ingot. Auxiliary material addition per ton of steel: 18.2 kg / t coke pellets, 5.7 kg / t ladle dust, 26 kg / t active lime (Φ30 mm), and 8.2 kg / t magnesite (Φ40 mm).

[0105] (2) LF furnace refining

[0106] The LF station temperature is 1546℃, and a high current of 35600A is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, 6.6kg / t of active lime is added. After 6 minutes, the first sampling and chemical composition analysis are carried out. Alloy is added according to the median chemical composition, and carbon is increased to promote rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1615℃, 1.4kg / t of alumina balls as a slag regulator are added to adjust the slag basicity to 2.7. The furnace door is closed for 12 minutes. When the molten steel temperature reaches 1627℃, the second sampling and chemical composition analysis is carried out to confirm the deviation of the content of each chemical element from the target value. After the second sampling is taken, the station is left when the molten steel temperature reaches 1635℃. The LF smelting cycle is 48 minutes, and the clearance is 425mm. The amount of additional alloy added per ton of steel is: 0.32kg / t of ferrosilicon, 2.5kg / t of ferromolybdenum, 3.5kg / t of ferrovanadium (FeV50-B), 1.2kg / t of aluminum wire (Φ10mm). The amount of additional auxiliary materials added per ton of steel is: 6.7kg / t of active lime (Φ30mm).

[0107] (3)RH refining

[0108] The entry temperature is 1628°C, the operation time is 55 minutes, and the argon pressure is controlled at 0.1MPa before the vacuum pump is started. The molten steel is not exposed due to slight movement of the slag surface. When the vacuum reaches 103Pa, the timing starts and the holding time is 22 minutes. At the same time, the argon pressure is adjusted to 0.4MPa, and the re-pressurization temperature is 1588°C. After the static argon blowing is completed, 0.5kg / t of covering agent is added, the clearance is 500mm, and the leaving station temperature is 1575°C. After breaking the vacuum, 0.6kg / t of ladle covering agent, 0.77kg / t of silicon-calcium alloy cored wire (Φ14mm) and 0.57kg / t of sulfur concentrate cored wire (Φ13mm) are added.

[0109] (4) Continuous casting

[0110] The arrival temperature of the ladle is 1575℃, the H of the tundish is controlled at 1.5ppm, the casting time is 42min, the superheat is 22℃, the casting speed is 0.47m / min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag 3.6kg / t steel.

[0111] (5) Heating process

[0112] The temperature entering the heating furnace is 570℃, the temperature of the preheating section is required to be 860℃, and the time is 1.8h; the temperature of the heating section 2 is required to be 870℃, and the time is 1.7h; the temperature of the heating section 1 is required to be 1220℃, and the time is 1.8h; the temperature of the soaking section is required to be 1215℃, and the time is 1.9h; the steel tapping temperature is 1190℃.

[0113] (6) Rolling process

[0114] Primary rolling process: 9 passes, steel turning → 1st pass width 408.01mm, height 421.01mm, reduction 65.01mm → 2nd pass width 426mm, height 351.01mm, reduction 70mm → steel turning → 3rd pass width 370.01mm, height 362.01mm, reduction 64mm → 4th pass width 397.01mm, height 272mm, reduction 90.01mm → steel turning → 5th pass width 285mm, height 355.0 1mm, reduction 42mm → 6th pass width 297.01mm, height 315mm, reduction 40.01mm → 7th pass width 307.01mm, height 280mm, reduction 35.01mm → 8th pass width 317mm, height 246.01mm, reduction 34mm → steel turning → 9th pass width 271mm, height 235.01mm, reduction 82.01mm, passes through 3 850mm rolling mills, and then enters 9 continuous rolling mills for rolling.

[0115] Continuous rolling product rolling process: 7 passes, the first pass is 229mm high, 245.01mm wide, and the rolling speed is 0.272m / s; the second pass is 192mm high, 235.01mm wide, and the rolling speed is 0.312m / s; the third pass is 200.01mm high, 195mm wide, and the rolling speed is 0.352m / s; the fourth pass is 177.01mm high, 210mm wide, and the rolling speed is 0.364m / s; the fifth pass is 189mm high, 178.21mm wide, and the rolling speed is 0.458m / s; the sixth pass is 152mm high, 199.01mm wide, and the rolling speed is 0.519m / s; the seventh pass is 162.01mm high, 162mm wide, and the rolling speed is 0.587m / s; the finished product is produced after 7 passes.

[0116] (7) Insulation process

[0117] The temperature of the lower insulation pit is 590℃, the insulation time is 52h, and the temperature out of the pit is 130℃.

[0118] (8) Heat treatment process

[0119] After the insulation, the steel sample is taken for heat treatment, and the heat treatment includes the following steps:

[0120] 1) Quenching: 880℃, holding time 1.0h, oil cooling;

[0121] 2) Tempering: 500℃, keep warm for 2.0h, oil cooling.

[0122] Example 5

[0123] The steel bar for the ecological electric furnace oil drill bit of this embodiment includes the following components in mass percentage: C: 0.19%, Si: 0.26%, Mn: 0.70%, P: 0.010%, S: 0.004%, Cr: 0.92%, Ni: 0.05%, Mo: 0.20%, V: 0.15%, Cu: 0.05%, and the remainder is iron and unavoidable impurities.

[0124] The method for preparing steel bars for oil drill bits in an ecological electric furnace of this embodiment has a process route of: ecological electric furnace + LF + RH + continuous casting → heating in a heating furnace → rolling → insulation → heat treatment, and includes the following steps:

[0125] (1) Ecological electric furnace smelting

[0126] The 100% scrap steel smelting process is adopted, of which 56% is heavy scrap steel and the rest is light scrap steel; the tapping temperature is 1626℃, the C content is 0.09% and the P content is 0.008% when tapping, slag, pre-deoxidizer and alloy are added when 1 / 4 of the steel is tapped, the smelting cycle is 46 minutes, and the furnace oxygen consumption is 25m 3 / t steel. Alloy addition per ton of steel: 6.4 kg / t silicon-manganese alloy, 4.6 kg / t high-carbon ferrochrome, 9.2 kg / t low-carbon ferrochrome, 1.7 kg / t aluminum ingot. Auxiliary material addition per ton of steel: 18.2 kg / t coke pellets, 5.6 kg / t ladle dust, 27 kg / t active lime (Φ30 mm), and 8.2 kg / t magnesite (Φ40 mm).

[0127] (2) LF furnace refining

[0128] The LF station temperature is 1545℃, and a high current of 35500A is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, 6.7kg / t of active lime is added. After 6 minutes, the first sampling and chemical composition analysis are carried out. Alloy is added according to the median chemical composition, and carbon is increased to promote rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1616℃, 1.5kg / t of alumina balls as a slag regulator are added to adjust the slag basicity to 2.9. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1627℃, the second sampling and chemical composition analysis is carried out to confirm the deviation of the content of each chemical element from the target value. After the second sampling is taken, the station is left when the molten steel temperature reaches 1635℃. The LF smelting cycle is 47 minutes, and the clearance is 425mm. The amount of additional alloy added per ton of steel is: 0.32kg / t of ferrosilicon, 2.5kg / t of ferromolybdenum, 3.6kg / t of ferrovanadium (FeV50-B), 1.2kg / t of aluminum wire (Φ10mm). The amount of additional auxiliary materials added per ton of steel is: 6.7kg / t of active lime (Φ30mm).

[0129] (3)RH refining

[0130] The entry temperature is 1630°C, the operation time is 55 minutes, and the argon pressure is controlled at 0.1MPa before the vacuum pump is started. The slag surface is slightly moved so that the molten steel is not exposed. When the vacuum reaches 104Pa, the timing starts and the holding time is 23 minutes. At the same time, the argon pressure is adjusted to 0.4MPa, and the re-pressurization temperature is 1590°C. After the static argon blowing is completed, 0.5kg / t of covering agent is added, the clearance is 500mm, and the exit temperature is 1575°C. After breaking the vacuum, 0.61kg / t of ladle covering agent, 0.77kg / t of silicon-calcium alloy cored wire (Φ14mm) and 0.57kg / t of sulfur concentrate cored wire (Φ13mm) are added.

[0131] (4) Continuous casting

[0132] The arrival temperature of the ladle is 1575℃, the H of the tundish is controlled at 1.5ppm, the casting time is 43min, the superheat is 22℃, the casting speed is 0.47m / min, the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag 3.6kg / t steel.

[0133] (5) Heating process

[0134] The temperature entering the heating furnace is 540℃, the temperature of the preheating section is required to be 860℃, and the time is 1.8h; the temperature of the heating section 2 is required to be 870℃, and the time is 1.8h; the temperature of the heating section 1 is required to be 1222℃, and the time is 1.7h; the temperature of the soaking section is required to be 1216℃, and the time is 1.8h; the steel tapping temperature is 1190℃.

[0135] (6) Rolling process

[0136] Primary rolling process: 9 passes, steel turning → 1st pass width 408mm, height 421.01mm, reduction 65mm → 2nd pass width 426mm, height 351.01mm, reduction 70.01mm → steel turning → 3rd pass width 370mm, height 362.01mm, reduction 64mm → 4th pass width 397mm, height 272.01mm, reduction 90.01mm → steel turning → 5th pass width 285.01mm, height 355.0 1mm, reduction 42mm → 6th pass width 297.01mm, height 315mm, reduction 40.01mm → 7th pass width 307mm, height 280.01mm, reduction 35.01mm → 8th pass width 317mm, height 246.01mm, reduction 34mm → steel turning → 9th pass width 271mm, height 235.01mm, reduction 82mm, passes through 3 850mm rolling mills, and then enters 9 continuous rolling mills for rolling.

[0137] Continuous rolling product rolling process: 7 passes, the first pass is 229.01mm high, 245mm wide, and the rolling speed is 0.272m / s; the second pass is 192.01mm high, 235.01mm wide, and the rolling speed is 0.31m / s; the third pass is 200.01mm high, 195mm wide, and the rolling speed is 0.352m / s; the fourth pass is 177mm high, 210.01mm wide, and the rolling speed is 0.364m / s; the fifth pass is 189mm high, 178.21mm wide, and the rolling speed is 0.458m / s; the sixth pass is 152.01mm high, 199.01mm wide, and the rolling speed is 0.519m / s; the seventh pass is 162.01mm high, 162mm wide, and the rolling speed is 0.585m / s; the finished product is produced after 7 passes.

[0138] (7) Insulation process

[0139] The temperature of the lower insulation pit is 590℃, the insulation time is 51h, and the temperature out of the pit is 120℃.

[0140] (8) Heat treatment process

[0141] After the insulation, the steel sample is taken for heat treatment, and the heat treatment includes the following steps:

[0142] 1) Quenching: 880℃, holding time 1.0h, oil cooling;

[0143] 2) Tempering: 500℃, keep warm for 2.0h, oil cooling.

[0144] Test Case

[0145] The finished products of Examples 1-5 were subjected to performance tests, and the results are shown in Tables 1-3.

[0146] Table 1 Macrostructure of Φ160mm specification

[0147] Serial number Generally loose Loose center Ingot segregation General spotty 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

[0148] Table 2 Φ160mm specification non-metallic inclusions

[0149]

[0150]

[0151] Table 3 Mechanical properties of Φ160mm specification

[0152]

[0153] The above-described embodiments merely represent several implementation methods of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A steel bar for ecological electric furnace oil drill bit, characterized in that: The following components are included in mass percentage: C: 0.18% to 0.22%, Si: 0.22% to 0.35%, Mn: 0.60% to 0.90%, P≤0.012%, S≤0.005%, Cr: 0.85% to 1.00%, Ni≤0.25%, Mo: 0.17% to 0.23%, V: 0.10% to 0.20%, Cu≤0.15%, and the balance is iron and unavoidable impurities.

2. The steel bar for ecological electric furnace oil drill bit according to claim 1 is characterized in that: The steel bar material for the ecological electric furnace oil drill bit has a tensile strength of 920 MPa or more, a yield strength of 865 MPa or more, A of 10%, z of 45%, and KU2 of 55J or more.

3. A method for preparing steel bars for ecological electric furnace oil drill bits according to any one of claims 1-2, characterized in that: The process includes the following steps: ecological electric furnace smelting, LF refining, RH vacuum refining, continuous casting, heating, rolling, insulation and heat treatment; In the ecological electric furnace smelting, scrap steel is used as the furnace charge, and the scrap steel accounts for 100% by mass; the end composition of the electric furnace is: C: 0.08% to 0.12%, P≤0.010%; deoxidation and alloying are carried out during the steel tapping process; In the LF refining, the molten steel discharged from the ecological electric furnace is put into the LF furnace for refining treatment; During the RH vacuum refining, the molten steel that has undergone the LF refining treatment is hoisted into an RH vacuum furnace for refining treatment; During the continuous casting, the molten steel after the RH vacuum refining treatment is continuously cast, the ladle arrival temperature is 1570℃~1580℃, the casting time is 40min~45min, the superheat is 20℃~25℃, the H content in the ladle is ≤2ppm, the pulling speed is 0.47m / min~0.48m / min, the whole process is protected casting, the crystallizer protective slag uses 3.6kg / t steel~3.7kg / t steel medium carbon steel protective slag, and the obtained continuous casting billet is heated, rolled and kept warm, the lower holding pit temperature is ≥580℃, the holding time is 48h~55h, the pit exit temperature is ≤150℃, and finally the steel bar for the ecological electric furnace oil drill bit is obtained through heat treatment.

4. The preparation method according to claim 3, characterized in that In the ecological electric furnace smelting, the scrap steel includes heavy scrap steel and light scrap steel; the mass percentage of heavy scrap steel in the furnace charge is 50% to 60%; the tapping temperature is 1620°C to 1630°C; slag, pre-deoxidizer and alloy are added when 1 / 4 to 1 / 3 of the steel is tapped, the smelting cycle is 40 minutes to 50 minutes, and the furnace oxygen consumption is 25m 3 / t steel~26m 3 / t steel; alloy addition per ton of steel: 6.2Kg / t~6.5Kg / t of silicon-manganese alloy, 4.5Kg / t~4.8Kg / t of high-carbon ferromanganese, 9.0Kg / t~9.5Kg / t of low-carbon ferrochrome, 1.7Kg / t~1.8Kg / t of aluminum ingots; auxiliary material addition per ton of steel: 18Kg / t~18.5Kg / t of coke particles, 5.5Kg / t~5.8Kg / t of ladle dust, 26Kg / t~27Kg / t of active lime, 8.0Kg / t~8.5Kg / t of magnesite; wherein, the particle size of the active lime is 10mm~70mm; the particle size of the magnesite is 10mm~60mm.

5. The preparation method according to claim 3, characterized in that In the LF refining, the LF inlet temperature is 1540°C to 1550°C, and after heating and slag melting with a high current of 35000A to 36000A, when the slag surface fluctuates and the molten steel and the arc are not exposed, 6.5kg / t steel to 6.8kg / t steel of active lime is added, and the first sampling and analysis is performed after 5min to 6min, and the composition content of the molten steel is adjusted according to the target composition requirements; when the molten steel temperature reaches 1610°C to 1620°C, 1.4kg / t steel to 1.5kg / t steel of alumina balls as a slag regulator are added to adjust the slag alkalinity to ≥2.5, the furnace door is closed for 10min to 13min, and when the molten steel temperature reaches 1625°C to 1630°C, the slag is heated to 1000°C and the slag is heated to 1000°C. When the temperature of the molten steel reaches 1630℃~1640℃, the station is left, the LF smelting cycle is 45min~50min, the clearance is 420mm~430mm, and the following alloys are added per ton of steel: 0.3kg / t~0.35kg / t of ferrosilicon, 2.5kg / t~2.6kg / t of ferromolybdenum, 3.5kg / t~3.6kg / t of ferrovanadium, 1.1kg / t~1.2kg / t of aluminum segments, wherein the size of the aluminum segments is Φ10mm~Φ60mm; the following auxiliary materials are added per ton of steel: 6.5kg / t~6.8kg / t of active lime with a particle size of 10mm~70mm.

6. The preparation method according to claim 3, characterized in that In the RH vacuum refining, the inlet temperature is 1625℃~1635℃, the operation time is 50min~60min, the vacuum pump is started when the argon pressure is controlled to 0.1MPa~0.3MPa, and when the vacuum degree reaches 100Pa~110Pa, the time is maintained for 20min~25min, and the argon pressure is adjusted to 0.3MPa~0.5MPa at the same time. The temperature after re-pressurization is 1585℃~1595℃. After the static argon blowing is completed, 0.5kg / t steel~0.6kg / t The covering agent for steel has a clearance of 480mm~520mm and a station temperature of 1570℃~1580℃. After breaking the vacuum, 0.6kg / t steel~0.62kg / t steel of covering agent, 0.75kg / t steel~0.80kg / t steel of silicon-calcium alloy cored wire and 0.56kg / t steel~0.58kg / t steel of sulfur concentrate powder cored wire are added. The size of the silicon-calcium alloy cored wire is Φ14mm~Φ15mm, and the size of the sulfur concentrate powder cored wire is Φ13mm~Φ14mm.

7. The preparation method according to claim 3, 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 500°C to 600°C; the temperature of the preheating section is 850°C to 870°C, and the time is 1.7h to 2.0h; the heating section includes heating section 1 with a temperature of 1210°C to 1240°C, and the time is 1.7h to 2.0h; heating section 2 with a temperature of 850°C to 870°C, and the time is 1.7h to 2.0h; the temperature of the soaking section is 1210°C to 1230°C, and the time is 1.7h to 2.0h; and the tapping temperature is 1180°C to 1210°C.

8. The preparation method according to claim 3, characterized in that In the rolling process, the heated continuous casting slab is initially rolled to form a slab. The initial rolling adopts 9 rolling passes to form a slab, four steel turnings, passes through 3 850mm rolling mills, and then enters a 9-stand continuous rolling mill group for rolling; the steel is turned once before rolling 1 pass, the steel is turned a second time after rolling 2 passes, the steel is turned a third time after rolling 2 passes, and the steel is turned a fourth time after rolling 4 passes.

9. The preparation method according to claim 8, characterized in that In the rolling process, the continuous rolling product is rolled in 7 passes; the first pass is 229mm-229.01mm high, 245mm-245.01mm wide, and the rolling speed is 0.27m / s-0.272m / s; the second pass is 192mm-192.01mm high, 235mm-235.01mm wide, and the rolling speed is 0.31m / s-0.312m / s; the third pass is 200mm-200.01mm high, 195mm-195.01mm wide, and the rolling speed is 0.35m / s-0.352m / s; the fourth pass is 177mm-177.01mm high, 210mm wide ~210.01mm, rolling speed 0.362m / s~0.364m / s; the 5th pass is 189mm~189.01mm high, 178.2mm~178.21mm wide, rolling speed 0.456m / s~0.458m / s; the 6th pass is 152mm~152.01mm high, 199mm~199.01mm wide, rolling speed 0.519m / s~0.521m / s; the 7th pass is 162mm~162.01mm high, 162mm~162.01mm wide, rolling speed 0.585m / s~0.587m / s; the finished product is produced after the 7th pass.

10. The preparation method according to claim 3, characterized in that The steel material after being kept warm is subjected to heat treatment, and the heat treatment comprises the following steps: (1) The steel is quenched after being kept warm, with the heating temperature at 870°C to 890°C, the temperature being kept warm for 0.8h to 1.2h, and then oil-cooled; (2) The steel after quenching and cooling is tempered at a temperature of 490°C to 510°C, kept warm for 1.8h to 2.2h, and oil-cooled.

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