Ecological electric furnace-based steel bar for automobile transmission shaft and production method of ecological electric furnace-based steel bar

Abstract

The invention relates to a steel bar for an automobile transmission shaft based on an ecological electric furnace and a production method. The steel bar for the automobile transmission shaft comprises the following chemical components: 0.18-0.22% of C, 0.22-0.33% of Si, 0.85-1.00% of Mn, less than or equal to 0.015% of P, less than or equal to 0.005% of S, 1.05-1.20% of Cr, less than or equal to 0.25% of Ni, less than or equal to 0.10% of Mo, 0.05-0.09% of Ti and less than or equal to 0.15% of Cu. And the balance of Fe and impurities. The production process comprises the steps of ecological electric furnace smelting, LF refining, RH refining, continuous casting, casting blank heating, rolling, heat preservation and heat treatment. According to the invention, a smelting continuous casting process of'ecological electric furnace + LF + RH + continuous casting 'is adopted, and is matched with a proper rolling process, so that the steel bar for the automobile transmission shaft, which is high in steel purity and excellent in mechanical property and surface quality, is produced, and the requirements of high-end products can be met.

Description

Technical Field

[0001] The invention relates to the technical field of bar production, and in particular to a steel bar for automobile transmission shaft based on an ecological electric furnace and a production method thereof. Background Art

[0002] The automobile transmission shaft is a vital component in the automobile transmission system, which is mainly responsible for transmitting the power generated by the engine to the driving wheels of the vehicle. The quality of the steel used in the automobile transmission shaft is related to the safety of power transmission during the driving process of the vehicle. Therefore, the requirements for the steel used in the automobile transmission shaft in terms of high temperature resistance, wear resistance, mechanical properties, fatigue life, steel purity, etc. are very high to ensure the safety of the vehicle driving process.

[0003] The ecological electric furnace (also known as the eco-friendly electric furnace) is a high-efficiency electric arc furnace that uses advanced energy recovery and environmental protection technologies. It has a high degree of airtightness and the characteristics of preventing air from penetrating into the scrap steel preheating chamber and the furnace body. The ecological electric furnace includes a melting furnace and a preheating chamber. It uses high-temperature exhaust gas to preheat the scrap steel and loads the scrap steel into the vertical preheating chamber connected to the furnace shell. By using the CO gas contained in the exhaust gas, the ecological electric furnace only needs to add a small amount of fuel to achieve molten steel smelting, which can avoid the production of harmful chemicals. In addition, the ecological electric furnace can also realize different process production of full scrap steel or 0-60% molten iron. The raw materials are not limited by material type and size. It can not only select economical light scrap steel to organize full scrap steel smelting, but also increase the proportion of molten iron to develop high-cleanliness molten steel.

[0004] The Chinese patent application with application publication number CN 116837291 A discloses a "method for producing and preparing steel bars for automobile axle sleeves in an ecological electric furnace". The chemical composition of the bars is C: 0.18% to 0.23%, Si: 0.20% to 0.35%, Mn: 0.42% to 0.60%, P: ≤0.015%, S: ≤0.010%, Cr: 0.82% to 1.00%, Ni: ≤0.25%, Mo: 0.41% to 0.53%, Cu: ≤0.15%, and the remainder is iron and unavoidable impurities. It adopts ecological electric furnace smelting → LF refining → RH refining → continuous casting → heating process → rolling process, achieving a breakthrough in the batch production of steel bars for automobile axle sleeves in the ecological electric furnace continuous casting process.

[0005] This application develops a steel bar for automobile transmission shafts with excellent mechanical properties and high steel purity, with the aim of meeting high-end product requirements. Summary of the invention

[0006] The present invention provides a steel bar for automobile transmission shaft based on an ecological electric furnace and a production method. The smelting and continuous casting process of "ecological electric furnace + LF + RH + continuous casting" is adopted in combination with an appropriate rolling process to produce a steel bar for automobile transmission shaft with high steel purity, excellent mechanical properties and surface quality. The steel bar can meet the requirements of high-end products and achieve a breakthrough in the mass production of steel bars for automobile transmission shafts by the ecological electric furnace continuous casting process.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The invention discloses a steel bar material for automobile transmission shaft based on an ecological electric furnace. The chemical composition of the steel bar material for automobile transmission shaft is C: 0.18%-0.22%, Si: 0.22%-0.33%, Mn: 0.85%-1.00%, P≤0.015%, S≤0.005%, Cr: 1.05%-1.20%, Ni≤0.25%, Mo≤0.10%, Ti: 0.05%-0.09%, Cu≤0.15% by mass percentage; the rest is Fe and unavoidable impurities.

[0009] Furthermore, the finished product performance of the steel bar for automobile transmission shaft is as follows: tensile strength Rm≥1080MPa, yield strength Rel≥850MPa, elongation A≥10%, cross-sectional shrinkage z≥45%, 5mm notch room temperature longitudinal impact absorption energy KU2≥55J; macrostructure index: general looseness ≤1.5 level, central looseness ≤1.5 level, ingot-shaped segregation ≤1.5 level, general spot-like segregation ≤1.0 level, edge spot-like segregation ≤1.0 level; non-metallic inclusion index: Class A ≤2.0 level, Class B ≤1.5 level, Class C ≤1.5 level, Class D ≤1.5 level, Class DS ≤2.0 level.

[0010] A production method for steel bars for automobile transmission shafts based on an ecological electric furnace, the production process comprising ecological electric furnace smelting, LF refining, RH refining, continuous casting, billet heating, rolling, insulation and heat treatment;

[0011] The ecological electric furnace smelting process is as follows: by weight percentage, the proportion of molten iron is 35% to 40%, and the proportion of scrap steel is 60% to 65%; the temperature of molten iron entering the furnace is 1280 to 1290°C, and the tapping temperature is 1615 to 1625°C; the C content of molten steel during tapping is 0.08% to 0.12%, and P is ≤ 0.010%; when the tapping volume reaches 1 / 4 to 1 / 3 of the total molten steel volume, slag, pre-deoxidizer and alloy are added; the smelting cycle is 55 to 65 minutes, and the furnace oxygen consumption is 21 to 22 m3 / t steel; the alloy and addition amount are : Silicon manganese alloy 4.0~4.2kg / t steel, medium carbon ferromanganese 6.0~6.2kg / t steel, low carbon ferrochrome 14.0~14.2kg / t steel; the slag is bearing steel synthetic slag, and the addition amount is 5.0~5.2kg / t steel; the pre-deoxidizer is aluminum wire segment, and the addition amount is 0.8~0.9kg / t steel; the auxiliary materials and the addition amount are: coke particles 6.5~6.7kg / t steel, ladle ash 5.8~6.2kg / t steel, active lime 35~36kg / t steel, magnesite 13.0~13.5kg / t steel.

[0012] Furthermore, the LF refining process is as follows: the LF inlet temperature is 1515-1525°C, a large current of 35000-36000A is used to heat and melt the slag, and active lime is added when the slag surface fluctuates and the molten steel and the arc are not exposed; the chemical composition is first sampled and analyzed after 5-6 minutes of refining, and alloy is added and carbon is increased according to the chemical composition; when the molten steel temperature reaches 1610-1620°C, 1.4-1.5kg / t steel of alumina balls as a diffusion deoxidizer are added for diffusion deoxidation; the furnace door is closed for 10-13 minutes, and when the molten steel temperature reaches 1625-1 The second sampling is carried out at 635℃ to analyze the chemical composition; after the second sampling, the molten steel temperature reaches 1645-1655℃ and the station is left; the LF smelting cycle is 45-50min, and the clearance is 420-430mm; the additional alloys and the added amounts are: ferrosilicon 0.3-0.32kg / t steel, high carbon ferromanganese 3.5-3.6kg / t steel, high carbon ferrochrome 5.8-6.0kg / t steel, ferrotitanium 1.4-1.5kg / t steel, cutting aluminum 0.4-0.45kg / t steel; in addition, the auxiliary material active lime is added at 5-5.2kg / t steel.

[0013] Furthermore, the RH refining process is as follows: the temperature of the molten steel entering the station is 1635-1645°C, and the refining time is 45min-55min; the argon pressure is controlled at 0.1-0.3MPa before the vacuum pump is started, and the timing starts when the vacuum degree reaches 100-110Pa and is maintained for 10-15min, and the argon pressure is adjusted to 0.3-0.5MPa at the same time; after the static argon blowing is completed, 0.5-0.6kg / t of covering agent is added, and the clearance is maintained at 480-520mm; the temperature of the molten steel leaving the station is 1585-1595°C; after breaking the vacuum, 0.6-0.62kg / t of ladle covering agent, 0.84-0.86kg / t of silicon-calcium alloy cored wire, and 0.56-0.58kg / t of sulfur concentrate powder cored wire are added.

[0014] Furthermore, the continuous casting process is as follows: the arrival temperature of the ladle is 1580-1590°C, the H content of the molten steel in the middle ladle is controlled to be ≤2ppm, the casting time is 38-42min, the superheat is controlled at 25-30°C, and the pulling speed is 0.45-0.47m / min; the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag, and the addition amount is 3.6-3.7kg / t steel.

[0015] Furthermore, the ingot heating process is as follows: the ingot entering the heating furnace has a temperature of 500°C to 550°C, the preheating section temperature is 660°C to 680°C, and the preheating section heating time is 1.4 to 1.5 hours; the heating section 2 temperature is 850°C to 870°C, and the heating time is 1.3 to 1.5 hours; the heating section 1 temperature is 1210°C to 1240°C, and the heating time is 1.3 to 1.5 hours; the soaking section temperature is 1210°C to 1230°C, and the soaking section heating time is 1.3 to 1.5 hours; and the tapping temperature is 1180°C to 1210°C.

[0016] Furthermore, the rolling process includes an initial rolling process and a continuous rolling process, wherein:

[0017] The primary rolling process is rolled 9 times; the rolling reduction is: steel turning → 1st pass reduction 65~65.01mm → 2nd pass reduction 70~70.01mm → steel turning → 3rd pass reduction 64~64.01mm → 4th pass reduction 90~90.01mm → steel turning → 5th pass reduction 42~42.01mm → 6th pass reduction 40~40.01mm → 7th pass reduction 35~35.01mm → 8th pass reduction 34~34.01mm → steel turning → 9th pass reduction 82~82.01mm; after rolling by 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling unit for rolling;

[0018] The continuous rolling process is rolled for 7 times; the rolling speed is: the rolling speed of the first pass is 0.27-0.272 m / s; the rolling speed of the second pass is 0.31-0.312 m / s; the rolling speed of the third pass is 0.31-0.312 m / s; the rolling speed of the fourth pass is 0.393-0.395 m / s; the rolling speed of the fifth pass is 0.499-0.500 m / s; the rolling speed of the sixth pass is 0.607-0.608 m / s; the finished product is produced after 7 rolling passes;

[0019] The size of the billet changes during the initial rolling process: the first pass is rolled to a width of 408-408.01mm and a height of 421-421.01mm; the second pass is rolled to a width of 426-426.01mm and a height of 351-351.01mm; the third pass is rolled to a width of 370-370.01mm and a height of 362-362.01mm; the fourth pass is rolled to a width of 397-397.01mm and a height of 272-272.01mm; the fifth pass is rolled to a width of 285 ~285.01mm, height 355~355.01mm; the 6th pass is rolled to a width of 297~297.01mm, a height of 315~315.01mm; the 7th pass is rolled to a width of 307~307.01mm, a height of 280~280.01mm; the 8th pass is rolled to a width of 317~317.01mm, a height of 246~246.01mm; the 9th pass is rolled to a width of 271~271.01mm, a height of 235~235.01mm;

[0020] The size changes of the steel billet during the continuous rolling process are as follows: the first pass is rolled to a height of 229-229.01mm and a width of 245-245.01mm; the second pass is rolled to a height of 192-192.01mm and a width of 235-235.01mm; the third pass is rolled to a height of 200-200.01mm and a width of 195-195.01mm; the fourth pass is rolled to a height of 163-163.01mm and a width of 200-200.01mm; the fifth pass is rolled to a height of 169-169.01mm and a width of 176-176.01mm; the sixth pass is rolled to a height of 128-128.01mm and a width of 172-172.01mm; the seventh pass is rolled to a height of 142-142.01mm and a width of 142-142.01mm.

[0021] Furthermore, during the insulation process, the temperature of the insulation pit under the steel is ≥570°C, the insulation time is 48 to 55 hours, and the temperature out of the insulation pit is ≤150°C.

[0022] Furthermore, the heat treatment process comprises the following steps:

[0023] (1) First quenching: quenching temperature 870-890°C, holding time 0.8-1.2h, oil cooling to room temperature;

[0024] (2) Second quenching: quenching temperature 860-880°C, holding time 0.8-1.2h, oil cooling to room temperature;

[0025] (3) Tempering: Tempering temperature 190 ~ 210 ℃, holding time 1.8 ~ 2.2h, water cooling to room temperature.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The production process of "ecological electric furnace + LF + RH + continuous casting → heating → primary rolling mill → continuous rolling unit" is adopted to ensure the purity of steel and the product has excellent mechanical properties;

[0028] (2) The surface quality and mechanical properties of steel bars are guaranteed through reasonable component design and supporting production processes;

[0029] (3) The macrostructure and non-metallic inclusion indicators of the finished steel bars meet the requirements of high-end products. DETAILED DESCRIPTION

[0030] The invention discloses a steel bar for automobile transmission shaft based on an ecological electric furnace. The chemical composition of the steel bar for automobile transmission shaft is, by mass percentage, C: 0.18%-0.22%, Si: 0.22%-0.33%, Mn: 0.85%-1.00%, P≤0.015%, S≤0.005%, Cr: 1.05%-1.20%, Ni≤0.25%, Mo≤0.10%, Ti: 0.05%-0.09%, Cu≤0.15%; the rest is Fe and unavoidable impurities.

[0031] Furthermore, the finished product performance of the steel bar for automobile transmission shaft is as follows: tensile strength Rm≥1080MPa, yield strength Rel≥850MPa, elongation A≥10%, cross-sectional shrinkage z≥45%, 5mm notch room temperature longitudinal impact absorption energy KU2≥55J; macrostructure index: general looseness ≤1.5 level, central looseness ≤1.5 level, ingot-shaped segregation ≤1.5 level, general spot-like segregation ≤1.0 level, edge spot-like segregation ≤1.0 level; non-metallic inclusion index: Class A ≤2.0 level, Class B ≤1.5 level, Class C ≤1.5 level, Class D ≤1.5 level, Class DS ≤2.0 level.

[0032] The present invention discloses a method for producing steel bars for automobile transmission shafts based on an ecological electric furnace, wherein the production process includes ecological electric furnace smelting, LF refining, RH refining, continuous casting, heating of ingots, rolling, heat preservation and heat treatment;

[0033] The ecological electric furnace smelting process is as follows: by weight percentage, the proportion of molten iron is 35% to 40%, and the proportion of scrap steel is 60% to 65%; the temperature of molten iron entering the furnace is 1280 to 1290°C, and the tapping temperature is 1615 to 1625°C; the C content of molten steel during tapping is 0.08% to 0.12%, and P is ≤ 0.010%; when the tapping volume reaches 1 / 4 to 1 / 3 of the total molten steel volume, slag, pre-deoxidizer and alloy are added; the smelting cycle is 55 to 65 minutes, and the furnace oxygen consumption is 21 to 22 m3 / t steel; the alloy and addition amount are : Silicon manganese alloy 4.0~4.2kg / t steel, medium carbon ferromanganese 6.0~6.2kg / t steel, low carbon ferrochrome 14.0~14.2kg / t steel; the slag is bearing steel synthetic slag, and the addition amount is 5.0~5.2kg / t steel; the pre-deoxidizer is aluminum wire segment, and the addition amount is 0.8~0.9kg / t steel; the auxiliary materials and the addition amount are: coke particles 6.5~6.7kg / t steel, ladle ash 5.8~6.2kg / t steel, active lime 35~36kg / t steel, magnesite 13.0~13.5kg / t steel.

[0034] Furthermore, the LF refining process is as follows: the LF inlet temperature is 1515-1525°C, a large current of 35000-36000A is used to heat and melt the slag, and active lime is added when the slag surface fluctuates and the molten steel and the arc are not exposed; the chemical composition is first sampled and analyzed after 5-6 minutes of refining, and alloy is added and carbon is increased according to the chemical composition; when the molten steel temperature reaches 1610-1620°C, 1.4-1.5kg / t steel of alumina balls as a diffusion deoxidizer are added for diffusion deoxidation; the furnace door is closed for 10-13 minutes, and when the molten steel temperature reaches 1625-1 The second sampling is carried out at 635℃ to analyze the chemical composition; after the second sampling, the molten steel temperature reaches 1645-1655℃ and the station is left; the LF smelting cycle is 45-50min, and the clearance is 420-430mm; the additional alloys and the added amounts are: ferrosilicon 0.3-0.32kg / t steel, high carbon ferromanganese 3.5-3.6kg / t steel, high carbon ferrochrome 5.8-6.0kg / t steel, ferrotitanium 1.4-1.5kg / t steel, cutting aluminum 0.4-0.45kg / t steel; in addition, the auxiliary material active lime is added at 5-5.2kg / t steel.

[0035] Furthermore, the RH refining process is as follows: the temperature of the molten steel entering the station is 1635-1645°C, and the refining time is 45min-55min; the argon pressure is controlled at 0.1-0.3MPa before the vacuum pump is started, and the timing starts when the vacuum degree reaches 100-110Pa and is maintained for 10-15min, and the argon pressure is adjusted to 0.3-0.5MPa at the same time; after the static argon blowing is completed, 0.5-0.6kg / t of covering agent is added, and the clearance is maintained at 480-520mm; the temperature of the molten steel leaving the station is 1585-1595°C; after breaking the vacuum, 0.6-0.62kg / t of ladle covering agent, 0.84-0.86kg / t of silicon-calcium alloy cored wire, and 0.56-0.58kg / t of sulfur concentrate powder cored wire are added.

[0036] Furthermore, the continuous casting process is as follows: the arrival temperature of the ladle is 1580-1590°C, the H content of the molten steel in the middle ladle is controlled to be ≤2ppm, the casting time is 38-42min, the superheat is controlled at 25-30°C, and the pulling speed is 0.45-0.47m / min; the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag, and the addition amount is 3.6-3.7kg / t steel.

[0037] Furthermore, the ingot heating process is as follows: the ingot entering the heating furnace has a temperature of 500°C to 550°C, the preheating section temperature is 660°C to 680°C, and the preheating section heating time is 1.4 to 1.5 hours; the heating section 2 temperature is 850°C to 870°C, and the heating time is 1.3 to 1.5 hours; the heating section 1 temperature is 1210°C to 1240°C, and the heating time is 1.3 to 1.5 hours; the soaking section temperature is 1210°C to 1230°C, and the soaking section heating time is 1.3 to 1.5 hours; and the tapping temperature is 1180°C to 1210°C.

[0038] Furthermore, the rolling process includes an initial rolling process and a continuous rolling process, wherein:

[0039] The primary rolling process is rolled 9 times; the rolling reduction is: steel turning → 1st pass reduction 65~65.01mm → 2nd pass reduction 70~70.01mm → steel turning → 3rd pass reduction 64~64.01mm → 4th pass reduction 90~90.01mm → steel turning → 5th pass reduction 42~42.01mm → 6th pass reduction 40~40.01mm → 7th pass reduction 35~35.01mm → 8th pass reduction 34~34.01mm → steel turning → 9th pass reduction 82~82.01mm; after rolling by 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling unit for rolling;

[0040] The continuous rolling process is rolled for 7 times; the rolling speed is: the rolling speed of the first pass is 0.27-0.272 m / s; the rolling speed of the second pass is 0.31-0.312 m / s; the rolling speed of the third pass is 0.31-0.312 m / s; the rolling speed of the fourth pass is 0.393-0.395 m / s; the rolling speed of the fifth pass is 0.499-0.500 m / s; the rolling speed of the sixth pass is 0.607-0.608 m / s; the finished product is produced after 7 rolling passes;

[0041] The size of the billet changes during the initial rolling process: the first pass is rolled to a width of 408-408.01mm and a height of 421-421.01mm; the second pass is rolled to a width of 426-426.01mm and a height of 351-351.01mm; the third pass is rolled to a width of 370-370.01mm and a height of 362-362.01mm; the fourth pass is rolled to a width of 397-397.01mm and a height of 272-272.01mm; the fifth pass is rolled to a width of 285 ~285.01mm, height 355~355.01mm; the 6th pass is rolled to a width of 297~297.01mm, a height of 315~315.01mm; the 7th pass is rolled to a width of 307~307.01mm, a height of 280~280.01mm; the 8th pass is rolled to a width of 317~317.01mm, a height of 246~246.01mm; the 9th pass is rolled to a width of 271~271.01mm, a height of 235~235.01mm;

[0042] The size changes of the steel billet during the continuous rolling process are as follows: the first pass is rolled to a height of 229-229.01mm and a width of 245-245.01mm; the second pass is rolled to a height of 192-192.01mm and a width of 235-235.01mm; the third pass is rolled to a height of 200-200.01mm and a width of 195-195.01mm; the fourth pass is rolled to a height of 163-163.01mm and a width of 200-200.01mm; the fifth pass is rolled to a height of 169-169.01mm and a width of 176-176.01mm; the sixth pass is rolled to a height of 128-128.01mm and a width of 172-172.01mm; the seventh pass is rolled to a height of 142-142.01mm and a width of 142-142.01mm.

[0043] Furthermore, during the insulation process, the temperature of the insulation pit under the steel is ≥570°C, the insulation time is 48 to 55 hours, and the temperature out of the insulation pit is ≤150°C.

[0044] Furthermore, the heat treatment process comprises the following steps:

[0045] (1) First quenching: quenching temperature 870-890°C, holding time 0.8-1.2h, oil cooling to room temperature;

[0046] (2) Second quenching: quenching temperature 860-880°C, holding time 0.8-1.2h, oil cooling to room temperature;

[0047] (3) Tempering: Tempering temperature 190 ~ 210 ℃, holding time 1.8 ~ 2.2h, water cooling to room temperature.

[0048] All percentages not specified in the present invention are by weight.

[0049] The following embodiments are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following embodiments.

[0050] [Example 1]

[0051] In this embodiment, the chemical composition of the steel bar for automobile transmission shaft is C: 0.19%, Si: 0.26%, Mn: 0.88%, P: 0.012%, S: 0.004%, Cr: 1.08%, Ni: 0.08%, Mo: 0.02%, Ti: 0.07%, Cu: 0.02%, and the rest is Fe and unavoidable impurities.

[0052] In this embodiment, the steel bars for automobile transmission shafts are smelted in an ecological electric furnace. The specific process route is: ecological electric furnace smelting + LF refining + RH refining + continuous casting → heating furnace heating → rolling → insulation → heat treatment. The specific process is as follows:

[0053] (1) Ecological electric furnace smelting

[0054] The proportion of molten iron is 37%, and the proportion of scrap steel is 63%. The temperature of molten iron entering the furnace is 1285℃, the temperature of steel tapping is 1620℃, the C content is 0.09% and the P content is 0.008% when steel tapping. When the total amount of molten steel is 1 / 4, slag, pre-deoxidizer and alloy are added. The smelting cycle is 60min, and the oxygen consumption of the furnace is 21m 3 / t steel. Alloy and addition amount are: silicon manganese alloy 4.0kg / t steel, medium carbon ferromanganese 6.0kg / t steel, low carbon ferrochrome 14.0kg / t steel. Slag is bearing steel synthetic slag, addition amount is 5.0kg / t steel. Pre-deoxidizer is aluminum wire segment (diameter 12mm), addition amount is 0.8kg / t steel. Auxiliary materials and addition amount are: coke particles 6.6kg / t steel, ladle ash 6.0kg / t steel, active lime (particle size 30mm) 35kg / t steel, magnesite (particle size 40mm) 13.0kg / t steel.

[0055] (2) LF furnace refining

[0056] The LF station temperature is 1521℃, and a large current of 35300A is used to heat and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, active lime is added. After 5 minutes of refining, the chemical composition is analyzed for the first time, and alloys are added according to the chemical composition, and carbon is added to promote the rapid melting and homogenization of alloys and carbon powder. When the molten steel temperature reaches 1615℃, 1.4kg / t of diffusion deoxidizer (alumina balls) is added for diffusion deoxidation, and the furnace door is closed for 12 minutes. When the molten steel temperature reaches 1628℃, the chemical composition is analyzed for the second time to confirm the deviation value of the content of each chemical element from the target value requirement; after the second sample is taken, the station is left when the molten steel temperature reaches 1648℃. The LF smelting cycle is 47min, and the clearance is 425mm. The additional alloys include: 0.3kg / t steel of ferrosilicon, 3.5kg / t steel of high carbon ferromanganese, 5.9kg / t steel of high carbon ferrochrome, 1.4kg / t steel of ferrotitanium (FeTi70-A), 0.42kg / t steel of cutting aluminum (size 10mm×3mm×1mm). Additional auxiliary materials: 5kg / t steel of active lime (particle size 30mm).

[0057] (3) RH refining

[0058] The inlet temperature is 1640℃, and the refining time is 49min. Before the vacuum pump is started, the argon pressure is controlled at 0.1MPa, the slag surface moves slightly and the molten steel is not exposed. When the vacuum reaches 100Pa, the timing starts and is maintained for 12min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 0.5kg / t of covering agent is added, the clearance is 500mm, and the temperature leaving the station is 1589℃. After breaking the vacuum, 0.6kg / t of ladle covering agent, 0.85kg / t of silicon-calcium alloy cored wire (diameter 14mm), and 0.56kg / t of sulfur concentrate powder cored wire (diameter 13mm) are added.

[0059] (5) Continuous casting

[0060] The arrival temperature of the ladle is 1586℃, the H content of the molten steel in the middle ladle is controlled at 1.5ppm, the casting time is 40min, the superheat is 27℃, the pulling speed is 0.46m / min, the whole process is protected casting, the crystallizer protection slag uses medium carbon steel protection slag, and the addition amount is 3.6kg / t steel.

[0061] (5) Heating

[0062] The temperature of the ingot entering the heating furnace is 520℃, the temperature of the preheating section is 660℃, and the heating time is 1.4h; the temperature of the heating section 2 is 870℃, and the heating time is 1.3h; the temperature of the heating section 1 is 1216℃, and the heating time is 1.3h; the temperature of the equalizing section is 1205℃, and the heating time is 1.5h; the steel tapping temperature is 1195℃.

[0063] (6) Rolling

[0064] The initial rolling process is rolled in 9 passes, specifically: steel turning → the first pass is rolled to a width of 408mm, a height of 421mm, and a reduction of 65mm → the second pass is rolled to a width of 426mm, a height of 351mm, and a reduction of 70mm → steel turning → the third pass is rolled to a width of 370mm, a height of 362mm, and a reduction of 64mm → the fourth pass is rolled to a width of 397mm, a height of 272mm, and a reduction of 90mm → steel turning → the fifth pass is rolled to a width of 285mm, a height of 355mm, and a reduction of 10mm. The steel is rolled at a width of 42mm, a height of 315mm and a reduction of 40mm in the 6th pass. The steel is rolled at a width of 307mm, a height of 280mm and a reduction of 35mm in the 7th pass. The steel is rolled at a width of 317mm, a height of 246mm and a reduction of 34mm in the 8th pass. The steel is turned over. The steel is rolled at a width of 271mm, a height of 235mm and a reduction of 82mm in the 9th pass. After being rolled by three 850mm rolling mills and one 735mm rolling mill, the steel enters the continuous rolling unit for rolling.

[0065] The continuous rolling process is rolled for 7 passes, specifically: the first pass is rolled to a height of 229mm, a width of 245mm, and a rolling speed of 0.27m / s; the second pass is rolled to a height of 192mm, a width of 235mm, and a rolling speed of 0.31m / s; the third pass is rolled to a height of 200mm, a width of 195mm, and a rolling speed of 0.31m / s; the fourth pass is rolled to a height of 163mm, a width of 200mm, and a rolling speed of 0.393m / s; the fifth pass is rolled to a height of 169mm, a width of 176mm, and a rolling speed of 0.499m / s; the sixth pass is rolled to a height of 128mm, a width of 172mm, and a rolling speed of 0.607m / s; the seventh pass is rolled to a height of 142mm and a width of 142mm; the finished product is produced after 7 rolling passes.

[0066] (7) Insulation

[0067] The temperature of the insulation pit under the steel is 580℃, the insulation time is 52h, and the temperature out of the pit is 120℃.

[0068] (8) Heat treatment

[0069] After the insulation, the steel samples are taken for heat treatment, and the heat treatment includes the following steps:

[0070] 1) First quenching: 880℃ for 1.0h, oil cooling;

[0071] 2) Second quenching: 870℃ for 1.0h, oil cooling;

[0072] 3) Tempering: 200℃ for 2.0h, water cooling.

[0073] [Example 2]

[0074] In this embodiment, the chemical composition of the steel bar for automobile transmission shaft is C: 0.21%, Si: 0.27%, Mn: 0.90%, P: 0.011%, S: 0.005%, Cr: 1.10%, Ni: 0.07%, Mo: 0.02%, Ti: 0.07%, Cu: 0.02%, and the rest is Fe and unavoidable impurities.

[0075] In this embodiment, the steel bars for automobile transmission shafts are smelted in an ecological electric furnace. The specific process route is: ecological electric furnace smelting + LF refining + RH refining + continuous casting → heating furnace heating → rolling → insulation → heat treatment. The specific process is as follows:

[0076] (1) Ecological electric furnace smelting

[0077] The proportion of molten iron is 38%, and the proportion of scrap steel is 62%. The temperature of molten iron entering the furnace is 1285℃, the temperature of steel tapping is 1619℃, the C content is 0.09% and the P content is 0.008% when tapping. When the total amount of molten steel is 1 / 4, slag, pre-deoxidizer and alloy are added. The smelting cycle is 62 minutes, and the furnace oxygen consumption is 21m 3 / t steel. Alloy and addition amount: silicon manganese alloy 4.0kg / t steel, medium carbon ferromanganese 6.0kg / t steel, low carbon ferrochrome 14.0kg / t steel. Slag is bearing steel synthetic slag, and the addition amount is 5.0kg / t. Pre-deoxidizer is aluminum wire segment (diameter 12mm), and the addition amount is 0.8kg / t steel. Auxiliary materials and addition amount are: coke particles 6.5kg / t steel, ladle ash 5.9kg / t steel, active lime (particle size 30mm) 35kg / t steel, magnesite (particle size 40mm) 13.2kg / t steel.

[0078] (2) LF refining

[0079] The LF station temperature is 1520℃, and a large 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, active lime is added. After 5 minutes of refining, the chemical composition is analyzed for the first time, and alloys are added according to the chemical composition, and carbon is added to promote the rapid melting and homogenization of alloys and carbon powder. When the molten steel temperature reaches 1615℃, 1.4kg / t of diffusion deoxidizer (alumina balls) is added for diffusion deoxidation, and the furnace door is closed for 10 minutes. When the molten steel temperature reaches 1629℃, the chemical composition is analyzed for the second time to confirm the deviation value of the content of each chemical element from the target value requirement; after the second sample is taken, the station is left when the molten steel temperature reaches 1650℃. The LF smelting cycle is 48min, and the clearance is 425mm. The additional alloys include: 0.3kg / t of ferrosilicon, 3.5kg / t of high carbon ferromanganese, 5.8kg / t of high carbon ferrochrome, 1.4kg / t of ferrotitanium (FeTi70-A), 0.42kg / t of cutting aluminum (size 10mm×3mm×1mm). Additional auxiliary materials: 5kg / t of active lime (particle size 30mm).

[0080] (3) RH refining

[0081] The inlet temperature is 1640℃, and the refining time is 48min. Before the vacuum pump is started, the argon pressure is controlled at 0.1MPa, the slag surface moves slightly and the molten steel is not exposed. When the vacuum reaches 100Pa, the timing starts and is maintained for 11min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 0.52kg / t of covering agent is added, the clearance is 495mm, and the temperature leaving the station is 1590℃. After breaking the vacuum, 0.6kg / t of ladle covering agent, 0.85kg / t of silicon-calcium alloy cored wire (diameter 14mm), and 0.57kg / t of sulfur concentrate powder cored wire (diameter 13mm) are added.

[0082] (6) Continuous casting

[0083] The arrival temperature of the ladle is 1586℃, the H content of the molten steel in the middle ladle is controlled at 1.3ppm, the casting time is 39min, the superheat is 28℃, the pulling speed is 0.46m / min, the whole process is protected casting, the crystallizer protection slag uses medium carbon steel protection slag, and the addition amount is 3.6kg / t steel.

[0084] (5) Heating

[0085] The temperature of the ingot entering the heating furnace is 520℃, the temperature of the preheating section is 660℃, and the heating time is 1.3h; the temperature of the heating section 2 is 870℃, and the heating time is 1.4h; the heating section 1 requires 1214℃, and the heating time is 1.3h; the temperature of the soaking section is 1204℃, and the heating time is 1.3h; the steel tapping temperature is 1195℃.

[0086] (6) Rolling

[0087] The initial rolling process is rolled in 9 passes, specifically: steel turning → the first pass is rolled to a width of 408mm, a height of 421mm, and a reduction of 65mm → the second pass is rolled to a width of 426mm, a height of 351mm, and a reduction of 70mm → steel turning → the third pass is rolled to a width of 370mm, a height of 362mm, and a reduction of 64mm → the fourth pass is rolled to a width of 397mm, a height of 272mm, and a reduction of 90mm → steel turning → the fifth pass is rolled to a width of 285mm, a height of 355mm, and a reduction of 10mm. The steel is rolled at a width of 42mm, a height of 315mm and a reduction of 40mm in the 6th pass. The steel is rolled at a width of 307mm, a height of 280mm and a reduction of 35mm in the 7th pass. The steel is rolled at a width of 317mm, a height of 246mm and a reduction of 34mm in the 8th pass. The steel is turned over. The steel is rolled at a width of 271mm, a height of 235mm and a reduction of 82mm in the 9th pass. After being rolled by three 850mm rolling mills and one 735mm rolling mill, the steel enters the continuous rolling unit for rolling.

[0088] The continuous rolling process is rolled for 7 passes, specifically: the first pass is rolled to a height of 229mm, a width of 245mm, and a rolling speed of 0.27m / s; the second pass is rolled to a height of 192mm, a width of 235mm, and a rolling speed of 0.31m / s; the third pass is rolled to a height of 200mm, a width of 195mm, and a rolling speed of 0.31m / s; the fourth pass is rolled to a height of 163mm, a width of 200mm, and a rolling speed of 0.393m / s; the fifth pass is rolled to a height of 169mm, a width of 176mm, and a rolling speed of 0.499m / s; the sixth pass is rolled to a height of 128mm, a width of 172mm, and a rolling speed of 0.607m / s; the seventh pass is rolled to a height of 142mm and a width of 142mm; the finished product is produced after 7 rolling passes.

[0089] (7) Insulation

[0090] The temperature of the insulation pit under the steel is 585℃, the insulation time is 53h, and the temperature out of the pit is 120℃.

[0091] (8) Heat treatment

[0092] After the insulation, the steel samples are taken for heat treatment, and the heat treatment includes the following steps:

[0093] 1) First quenching: 880℃ for 1.0h, oil cooling;

[0094] 2) Second quenching: 870℃ for 1.0h, oil cooling;

[0095] 3) Tempering: 200℃ for 2.0h, water cooling.

[0096] [Example 3]

[0097] In this embodiment, the chemical composition of the steel bar for automobile transmission shaft is C: 0.20%, Si: 0.26%, Mn: 0.90%, P: 0.010%, S: 0.004%, Cr: 1.10%, Ni: 0.08%, Mo: 0.05%, Ti: 0.07%, Cu: 0.02%, and the rest is Fe and unavoidable impurities.

[0098] In this embodiment, the steel bars for automobile transmission shafts are smelted in an ecological electric furnace. The specific process route is: ecological electric furnace smelting + LF refining + RH refining + continuous casting → heating furnace heating → rolling → insulation → heat treatment. The specific process is as follows:

[0099] (1) Ecological electric furnace smelting

[0100] The proportion of molten iron is 38%, the proportion of scrap steel is 62%, the proportion of medium and heavy scrap steel is 45%, the proportion of carbon structural steel offcuts is 12%, and the rest is automobile plate packaged scrap steel. The temperature of molten iron entering the furnace is 1285℃, the temperature of steel tapping is 1620℃, the C content is 0.10% when tapping, and the P content is 0.008%. When the total amount of molten steel is 1 / 4, slag, pre-deoxidizer and alloy are added. The smelting cycle is 62min, and the furnace oxygen consumption is 21m 3 / t steel. Alloy and addition amount are: silicon manganese alloy 4.0kg / t steel, medium carbon ferromanganese 6.0kg / t steel, low carbon ferrochrome 14.0kg / t steel. Slag is bearing steel synthetic slag, addition amount is 5.0kg / t steel. Pre-deoxidizer is aluminum wire segment (diameter 12mm), addition amount is 0.8kg / t steel. Auxiliary materials and addition amount are: coke particles 6.5kg / t steel, ladle ash 6.0kg / t steel, active lime (particle size 30mm) 35kg / t steel, magnesite (particle size 40mm) 13.2kg / t steel.

[0101] (2) LF refining

[0102] The LF station temperature is 1521℃, and a large 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, active lime is added. After 5 minutes of refining, the chemical composition is analyzed for the first time, and alloys are added according to the chemical composition, and carbon is added to promote the rapid melting and homogenization of alloys and carbon powder. When the molten steel temperature reaches 1615℃, 1.4kg / t of diffusion deoxidizer (alumina balls) is added for diffusion deoxidation, and the furnace door is closed for 10 minutes. When the molten steel temperature reaches 1628℃, the chemical composition is analyzed for the second time to confirm the deviation value of the content of each chemical element from the target value. After the second sample is taken, the station is left when the molten steel temperature reaches 1652℃. The LF smelting cycle is 48min, and the clearance is 425mm. The additional alloys include: 0.3kg / t steel of ferrosilicon, 3.5kg / t steel of high carbon ferromanganese, 5.8kg / t steel of high carbon ferrochrome, 1.4kg / t steel of ferrotitanium (FeTi70-A), 0.42kg / t steel of cutting aluminum (size 10mm×3mm×1mm). Additional auxiliary materials: 5kg / t steel of active lime (particle size 30mm).

[0103] (3) RH refining

[0104] The inlet temperature is 1641℃, the refining time is 48min, the argon pressure is controlled at 0.1MPa before the vacuum pump is started, and the molten steel is not exposed when the slag surface moves slightly. The timing starts when the vacuum reaches 100Pa, and it is maintained for 12min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 0.5kg / t of covering agent is added, the clearance is 495mm, and the temperature leaving the station is 1588℃. After breaking the vacuum, 0.6kg / t of steel ladle covering agent, 0.85kg / t of steel silicon-calcium alloy cored wire (diameter 14mm), and 0.57kg / t of steel sulfur concentrate powder cored wire (diameter 13mm) are added.

[0105] (7) Continuous casting

[0106] The arrival temperature of the ladle is 1585℃, the H content of the molten steel in the middle ladle is controlled at 1.5ppm, the casting time is 40min, the superheat is 27℃, the pulling speed is 0.46m / min, the whole process is protected casting, the crystallizer protection slag uses medium carbon steel protection slag, and the addition amount is 3.6kg / t steel.

[0107] (5) Heating

[0108] The temperature of the ingot entering the heating furnace is 520℃, the temperature of the preheating section is 660℃, and the heating time is 1.5h; the temperature of the heating section 2 is 870℃, and the heating time is 1.3h; the temperature of the heating section 1 is 1214℃, and the heating time is 1.3h; the temperature of the soaking section is 1204℃, and the heating time is 1.3h; the steel tapping temperature is 1195℃.

[0109] (6) Rolling

[0110] The initial rolling process is rolled 9 times, specifically: steel turning → the first pass is rolled to 408mm in width, 421mm in height, and 65mm in reduction → the second pass is rolled to 426mm in width, 351mm in height, and 70mm in reduction → steel turning → the third pass is rolled to 370mm in width, 362mm in height, and 64mm in reduction → the fourth pass is rolled to 397mm in width, 272mm in height, and 90mm in reduction → steel turning → the fifth pass is rolled to 285mm in width and 355mm in height, Reduction 42mm→The 6th pass is rolled to 297mm width, 315mm height, and 40mm reduction→The 7th pass is rolled to 307mm width, 280mm height, and 35mm reduction→The 8th pass is rolled to 317mm width, 246mm height, and 34mm reduction→Steel turning→The 9th pass is rolled to 271mm width, 235mm height, and 82mm reduction; After passing through 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling unit for rolling.

[0111] The continuous rolling process is rolled for 7 passes, specifically: the first pass is rolled to a height of 229mm, a width of 245mm, and a rolling speed of 0.27m / s; the second pass is rolled to a height of 192mm, a width of 235mm, and a rolling speed of 0.31m / s; the third pass is rolled to a height of 200mm, a width of 195mm, and a rolling speed of 0.31m / s; the fourth pass is rolled to a height of 163mm, a width of 200mm, and a rolling speed of 0.393m / s; the fifth pass is rolled to a height of 169mm, a width of 176mm, and a rolling speed of 0.499m / s; the sixth pass is rolled to a height of 128mm, a width of 172mm, and a rolling speed of 0.607m / s; the seventh pass is rolled to a height of 142mm and a width of 142mm; the finished product is produced after 7 rolling passes.

[0112] (7) Insulation

[0113] The temperature of the insulation pit under the steel is 580℃, the insulation time is 54h, and the temperature out of the pit is 120℃.

[0114] (8) Heat treatment

[0115] After the insulation, the steel samples are taken for heat treatment, and the heat treatment includes the following steps:

[0116] 1) First quenching: 880℃ for 1.0h, oil cooling;

[0117] 2) Second quenching: 870℃ for 1.0h, oil cooling;

[0118] 3) Tempering: 200℃ for 2.0h, water cooling.

[0119] [Example 4]

[0120] In this embodiment, the chemical composition of the steel bar for automobile transmission shaft is C: 0.20%, Si: 0.26%, Mn: 0.92%, P: 0.012%, S: 0.004%, Cr: 1.10%, Ni: 0.08%, Mo: 0.03%, Ti: 0.07%, Cu: 0.02%, and the rest is Fe and unavoidable impurities.

[0121] In this embodiment, the steel bars for automobile transmission shafts are smelted in an ecological electric furnace. The specific process route is: ecological electric furnace smelting + LF refining + RH refining + continuous casting → heating furnace heating → rolling → insulation → heat treatment. The specific process is as follows:

[0122] (1) Ecological electric furnace smelting

[0123] The proportion of molten iron is 37%, the proportion of scrap steel is 63%, the proportion of medium and heavy scrap steel is 45%, the proportion of carbon structural steel offcuts is 13%, and the rest is automobile plate packaged scrap steel. The temperature of molten iron entering the furnace is 1286℃, the temperature of steel tapping is 1622℃, the C content is 0.09% when tapping, and the P content is 0.007%. When the total amount of molten steel is 1 / 4, slag, pre-deoxidizer and alloy are added. The smelting cycle is 59min, and the furnace oxygen consumption is 21m 3 / t steel. Alloy and addition amount are: silicon manganese alloy 4.0kg / t steel, medium carbon ferromanganese 6.0kg / t steel, low carbon ferrochrome 14.0kg / t steel. Slag is bearing steel synthetic slag, addition amount is 5.0kg / t steel. Pre-deoxidizer is aluminum wire segment (diameter 12mm), addition amount is 0.9kg / t steel. Auxiliary materials and addition amount: coke particles 6.5kg / t steel, ladle ash 6.0kg / t steel, active lime (particle size 30mm) 35kg / t steel, magnesite (particle size 40mm) 13.2kg / t steel.

[0124] (2) LF refining

[0125] The LF station temperature is 1521℃, and a large 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, active lime is added. After 5 minutes of refining, the chemical composition is analyzed for the first time. The alloy is added according to the chemical composition, and carbon is added to promote the rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1614℃, 1.4kg / t of diffusion deoxidizer (alumina balls) is added for diffusion deoxidation. The furnace door is closed for 10 minutes. When the molten steel temperature reaches 1629℃, the chemical composition is analyzed for the second time to confirm the deviation of the content of each chemical element from the target value requirement; after the second sample is taken, the station is left when the molten steel temperature reaches 1648℃. The LF smelting cycle is 47min, and the clearance is 425mm. The additional alloys include: 0.3kg / t of ferrosilicon, 3.5kg / t of high carbon ferromanganese, 5.8kg / t of high carbon ferrochrome, 1.4kg / t of ferrotitanium (FeTi70-A), 0.41kg / t of cutting aluminum (size 10mm×3mm×1mm). Additional auxiliary materials: 5kg / t of active lime (particle size 30mm).

[0126] (3) RH refining

[0127] The inlet temperature is 1638℃, the refining time is 52min, the argon pressure is controlled at 0.1MPa before the vacuum pump is started, the slag surface is slightly moved and the molten steel is not exposed, the timing starts when the vacuum reaches 100Pa, and it is maintained for 10min, and the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 0.5kg / t of covering agent is added, the clearance is 510mm, and the temperature leaving the station is 1590℃. After breaking the vacuum, 0.6kg / t of steel ladle covering agent, 0.85kg / t of steel silicon-calcium alloy cored wire (diameter 14mm), and 0.57kg / t of steel sulfur concentrate powder cored wire (diameter 13mm) are added.

[0128] (8) Continuous casting

[0129] The arrival temperature of the ladle is 1585℃, the H content of the molten steel in the middle ladle is controlled at 1.5ppm, the casting time is 40min, the superheat is 27℃, the pulling speed is 0.46m / min, the whole process is protected casting, the crystallizer protection slag uses medium carbon steel protection slag, and the addition amount is 3.6kg / t steel.

[0130] (5) Heating

[0131] The temperature of the ingot entering the heating furnace is 520℃, the temperature of the preheating section is 670℃, and the heating time is 1.4h; the temperature of the heating section 2 is 870℃, and the heating time is 1.5h; the temperature of the heating section 1 is 1215℃, and the heating time is 1.3h; the temperature of the equalizing section is 1204℃, and the heating time is 1.4h; the steel tapping temperature is 1194℃.

[0132] (6) Rolling

[0133] The initial rolling process is rolled in 9 passes, specifically: steel turning → the first pass is rolled to a width of 408mm, a height of 421mm, and a reduction of 65mm → the second pass is rolled to a width of 426mm, a height of 351mm, and a reduction of 70mm → steel turning → the third pass is rolled to a width of 370mm, a height of 362mm, and a reduction of 64mm → the fourth pass is rolled to a width of 397mm, a height of 272mm, and a reduction of 90mm → steel turning → the fifth pass is rolled to a width of 285mm, a height of 355mm, and a reduction of 10mm. The steel is rolled at a width of 42mm, a height of 315mm and a reduction of 40mm in the 6th pass. The steel is rolled at a width of 307mm, a height of 280mm and a reduction of 35mm in the 7th pass. The steel is rolled at a width of 317mm, a height of 246mm and a reduction of 34mm in the 8th pass. The steel is turned over. The steel is rolled at a width of 271mm, a height of 235mm and a reduction of 82mm in the 9th pass. After being rolled by three 850mm rolling mills and one 735mm rolling mill, the steel enters the continuous rolling unit for rolling.

[0134] The continuous rolling process is rolled for 7 passes, specifically: the first pass is rolled to a height of 229mm, a width of 245mm, and a rolling speed of 0.27m / s; the second pass is rolled to a height of 192mm, a width of 235mm, and a rolling speed of 0.31m / s; the third pass is rolled to a height of 200mm, a width of 195mm, and a rolling speed of 0.31m / s; the fourth pass is rolled to a height of 163mm, a width of 200mm, and a rolling speed of 0.393m / s; the fifth pass is rolled to a height of 169mm, a width of 176mm, and a rolling speed of 0.499m / s; the sixth pass is rolled to a height of 128mm, a width of 172mm, and a rolling speed of 0.607m / s; the seventh pass is rolled to a height of 142mm and a width of 142mm; the finished product is produced after 7 rolling passes.

[0135] (7) Insulation

[0136] The temperature of the insulation pit under the steel is 580℃, the insulation time is 54h, and the temperature out of the pit is 120℃.

[0137] (8) Heat treatment

[0138] After the insulation, the steel samples are taken for heat treatment, and the heat treatment includes the following steps:

[0139] 1) First quenching: 880℃ for 1.0h, oil cooling;

[0140] 2) Second quenching: 870℃ for 1.0h, oil cooling;

[0141] 3) Tempering: 200℃ for 2.0h, water cooling.

[0142] [Example 5]

[0143] In this embodiment, the chemical composition of the steel bar for automobile transmission shaft is C: 0.20%, Si: 0.25%, Mn: 0.92%, P: 0.010%, S: 0.004%, Cr: 1.09%, Ni: 0.05%, Mo: 0.0.02%, Ti: 0.06%, Cu: 0.0.01%, and the rest is Fe and unavoidable impurities.

[0144] In this embodiment, the steel bars for automobile transmission shafts are smelted in an ecological electric furnace. The specific process route is: ecological electric furnace smelting + LF refining + RH refining + continuous casting → heating furnace heating → rolling → insulation → heat treatment. The specific process is as follows:

[0145] (1) Ecological electric furnace smelting

[0146] The proportion of molten iron is 38%, the proportion of scrap steel is 62%, the proportion of medium and heavy scrap steel is 45%, the proportion of carbon structural steel offcuts is 12%, and the rest is automobile plate packaged scrap steel. The temperature of molten iron entering the furnace is 1285℃, the temperature of steel tapping is 1620℃, the C content is 0.10% when tapping, and the P content is 0.008%. When the total amount of molten steel is 1 / 4, slag, pre-deoxidizer and alloy are added. The smelting cycle is 58min, and the furnace oxygen consumption is 21m 3 / t steel. Alloy and addition amount are: silicon manganese alloy 4.0kg / t steel, medium carbon ferromanganese 6.0kg / t steel, low carbon ferrochrome 14.0kg / t steel. Slag is bearing steel synthetic slag, and the addition amount is 5.0kg / t steel. Pre-deoxidizer is aluminum wire segment (diameter 12mm), and the addition amount is 0.8kg / t steel. Auxiliary materials and addition amount: coke particles 6.6kg / t steel, ladle ash 6.0kg / t steel, active lime (particle size 30mm) 35kg / t steel, magnesite (particle size 40mm) 13.2kg / t steel.

[0147] (2) LF refining

[0148] The LF station temperature is 1520℃, and a large 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, active lime is added. After 5 minutes of refining, the chemical composition is analyzed for the first time. The alloy is added according to the chemical composition, and carbon is added to promote the rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1615℃, 1.4kg / t of diffusion deoxidizer (alumina balls) is added for diffusion deoxidation. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1630℃, the chemical composition is analyzed for the second time 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 1648℃. The LF smelting cycle is 47min, and the clearance is 425mm. The additional alloys include: 0.3kg / t of ferrosilicon, 3.5kg / t of high carbon ferromanganese, 5.9kg / t of high carbon ferrochrome, 1.4kg / t of ferrotitanium (FeTi70-A), 0.42kg / t of cutting aluminum (size 10mm×3mm×1mm). Additional auxiliary materials: 5.0kg / t of active lime (particle size 30mm).

[0149] (3) RH refining

[0150] The inlet temperature is 1640℃, the refining time is 52min, the argon pressure is controlled at 0.1MPa before the vacuum pump is started, the molten steel is not exposed when the slag surface moves slightly, and the timing starts when the vacuum reaches 100Pa, and it is maintained for 12min. At the same time, the argon pressure is adjusted to 0.3MPa. After the static argon blowing is completed, 0.5kg / t of covering agent is added, the clearance is 495mm, and the temperature leaving the station is 1591℃. After breaking the vacuum, 0.6kg / t of ladle covering agent, 0.85kg / t of silicon-calcium alloy cored wire (diameter 14mm) and 0.57kg / t of sulfur concentrate powder cored wire (diameter 13mm) are added.

[0151] (9) Continuous casting

[0152] The arrival temperature of the ladle is 1587℃, the H content of the molten steel in the middle ladle is controlled at 1.4ppm, the casting time is 40min, the superheat is 27℃, the pulling speed is 0.46m / min, the whole process is protected casting, the crystallizer protection slag uses medium carbon steel protection slag, and the addition amount is 3.6kg / t steel.

[0153] (5) Heating

[0154] The temperature of the ingot entering the heating furnace is 520℃, the temperature of the preheating section is 660℃, and the heating time is 1.4h; the temperature of the heating section 2 is 870℃, and the heating time is 1.3h; the temperature of the heating section 1 is 1215℃, and the heating time is 1.4h; the temperature of the equalizing section is 1203℃, and the heating time is 1.3h; the steel tapping temperature is 1194℃.

[0155] (6) Rolling

[0156] The initial rolling process is rolled in 9 passes, specifically: steel turning → the first pass is rolled to a width of 408mm, a height of 421mm, and a reduction of 65mm → the second pass is rolled to a width of 426mm, a height of 351mm, and a reduction of 70mm → steel turning → the third pass is rolled to a width of 370mm, a height of 362mm, and a reduction of 64mm → the fourth pass is rolled to a width of 397mm, a height of 272mm, and a reduction of 90mm → steel turning → the fifth pass is rolled to a width of 285mm, a height of 355mm, and a reduction of 10mm. The steel is rolled at a width of 42mm, a height of 315mm and a reduction of 40mm in the 6th pass. The steel is rolled at a width of 307mm, a height of 280mm and a reduction of 35mm in the 7th pass. The steel is rolled at a width of 317mm, a height of 246mm and a reduction of 34mm in the 8th pass. The steel is turned over. The steel is rolled at a width of 271mm, a height of 235mm and a reduction of 82mm in the 9th pass. After being rolled by three 850mm rolling mills and one 735mm rolling mill, the steel enters the continuous rolling unit for rolling.

[0157] The continuous rolling process is rolled for 7 passes, specifically: the first pass is rolled to a height of 229mm, a width of 245mm, and a rolling speed of 0.27m / s; the second pass is rolled to a height of 192mm, a width of 235mm, and a rolling speed of 0.31m / s; the third pass is rolled to a height of 200mm, a width of 195mm, and a rolling speed of 0.31m / s; the fourth pass is rolled to a height of 163mm, a width of 200mm, and a rolling speed of 0.393m / s; the fifth pass is rolled to a height of 169mm, a width of 176mm, and a rolling speed of 0.499m / s; the sixth pass is rolled to a height of 128mm, a width of 172mm, and a rolling speed of 0.607m / s; the seventh pass is rolled to a height of 142mm and a width of 142mm; the finished product is produced after 7 rolling passes.

[0158] (7) Insulation

[0159] The temperature of the insulation pit under the steel is 585℃, the insulation time is 52h, and the temperature out of the pit is 120℃.

[0160] (8) Heat treatment

[0161] After the insulation, the steel samples are taken for heat treatment, and the heat treatment includes the following steps:

[0162] 1) First quenching: 880℃ for 1.0h, oil cooling;

[0163] 2) Second quenching: 870℃ for 1.0h, oil cooling;

[0164] 3) Tempering: 200℃ for 2.0h, water cooling.

[0165] Finished product inspection results: The diameter of the product produced in Example 1-5 is Taking the steel bars of the specification as an example, the macrostructure test results are shown in Table 1, the non-metallic inclusion test results are shown in Table 2, and the mechanical properties are shown in Table 3.

[0166] Table 1 Diameter Macrostructure of standard steel bars

[0167] Serial number Generally loose Loose center Ingot segregation General spot segregation Edge spot segregation standard ≤1.5 ≤1.5 ≤1.5 ≤1.0 ≤1.0 Example 1 0.5 0.5 0.5 0 0 Example 1 0.5 0.5 0.5 0 0 Example 2 0.5 0.5 0.5 0 0 Example 2 0.5 0.5 0.5 0 0 Example 3 0.5 0.5 0.5 0 0 Example 3 0.5 0.5 0.5 0 0 Example 4 0.5 0.5 0.5 0 0 Example 4 0.5 0.5 0.5 0 0 Example 5 0.5 0.5 0.5 0 0 Example 5 0.5 0.5 0.5 0 0

[0168] Table 2 Diameter Specification steel bar non-metallic inclusions

[0169]

[0170] Table 3 Diameter Mechanical properties of standard steel bars

[0171]

[0172] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A steel bar for automobile transmission shaft based on ecological electric furnace, characterized in that: The chemical composition of the steel bar for automobile transmission shaft is C: 0.18% ~ 0.22%, Si: 0.22% ~ 0.33%, Mn: 0.85% ~ 1.00%, P ≤ 0.015%, S ≤ 0.005%, Cr: 1.05% ~ 1.20%, Ni ≤ 0.25%, Mo ≤ 0.10%, Ti: 0.05% ~ 0.09%, Cu ≤ 0.15%; The rest is Fe and inevitable impurities.

2. The steel bar for automobile transmission shaft based on ecological electric furnace according to claim 1 is characterized in that: The finished product properties of the steel bar for automobile transmission shaft are as follows: tensile strength Rm≥1080MPa, yield strength Rel≥850MPa, elongation A≥10%, cross-sectional shrinkage z≥45%, 5mm notch room temperature longitudinal impact absorption energy KU2≥55J; macrostructure index: general looseness ≤1.5 level, central looseness ≤1.5 level, ingot segregation ≤1.5 level, general spot segregation ≤1.0 level, edge spot segregation ≤1.0 level; non-metallic inclusion index: Class A ≤2.0 level, Class B ≤1.5 level, Class C ≤1.5 level, Class D ≤1.5 level, D S Class ≤2.

0.

3. A method for producing steel bars for automobile transmission shafts based on an ecological electric furnace as claimed in claim 1 or 2, characterized in that: The production process includes ecological electric furnace smelting, LF refining, RH refining, continuous casting, billet heating, rolling, insulation and heat treatment; The ecological electric furnace smelting process is as follows: by weight percentage, the proportion of molten iron is 35% to 40%, and the proportion of scrap steel is 60% to 65%; the temperature of molten iron entering the furnace is 1280 to 1290°C, and the tapping temperature is 1615 to 1625°C; the C content of molten steel during tapping is 0.08% to 0.12%, and P is ≤ 0.010%; when the tapping volume reaches 1 / 4 to 1 / 3 of the total molten steel volume, slag, pre-deoxidizer and alloy are added; the smelting cycle is 55 to 65 minutes, and the furnace oxygen consumption is 21 to 22 m 3 / t steel; alloys and addition amounts are: silicon manganese alloy 4.0~4.2kg / t steel, medium carbon ferromanganese 6.0~6.2kg / t steel, low carbon ferrochrome 14.0~14.2kg / t steel; slag is bearing steel synthetic slag, and the addition amount is 5.0~5.2kg / t steel; pre-deoxidizer is aluminum wire segment, and the addition amount is 0.8~0.9kg / t steel; auxiliary materials and addition amounts are: coke particles 6.5~6.7kg / t steel, ladle ash 5.8~6.2kg / t steel, active lime 35~36kg / t steel, magnesite 13.0~13.5kg / t steel.

4. The method for producing steel bars for automobile transmission shafts based on an ecological electric furnace according to claim 3, characterized in that: The LF refining process is as follows: the LF inlet temperature is 1515-1525°C, a large current of 35000-36000A is used to heat and melt the slag, and active lime is added when the slag surface fluctuates and the molten steel and the arc are not exposed; after refining for 5-6 minutes, the chemical composition is first sampled and analyzed, and alloy is added and carbon is increased according to the chemical composition; when the molten steel temperature reaches 1610-1620°C, 1.4-1.5kg / t steel of alumina balls as a diffusion deoxidizer are added for diffusion deoxidation; the furnace door is closed for 10-13 minutes, and when the molten steel temperature reaches 1625-1635 ℃, take a second sample to analyze the chemical composition; after the second sample is taken, leave the station when the molten steel temperature reaches 1645-1655℃; LF smelting cycle is 45-50min, and the clearance is 420-430mm; additional alloys and addition amounts are: ferrosilicon 0.3-0.32kg / t steel, high carbon ferromanganese 3.5-3.6kg / t steel, high carbon ferrochrome 5.8-6.0kg / t steel, ferrotitanium 1.4-1.5kg / t steel, cutting aluminum 0.4-0.45kg / t steel; in addition, auxiliary material active lime 5-5.2kg / t steel is added.

5. The method for producing steel bars for automobile transmission shafts based on an ecological electric furnace according to claim 3 is characterized in that: The RH refining process is as follows: the temperature of the molten steel entering the station is 1635-1645°C, and the refining time is 45min-55min; the argon pressure is controlled at 0.1-0.3MPa before the vacuum pump is started, and the timing starts when the vacuum degree reaches 100-110Pa and is maintained for 10-15min, and the argon pressure is adjusted to 0.3-0.5MPa at the same time; after the static argon blowing is completed, 0.5-0.6kg / t of covering agent is added, and the clearance is maintained at 480-520mm; the temperature of the molten steel leaving the station is 1585-1595°C; after breaking the vacuum, 0.6-0.62kg / t of ladle covering agent, 0.84-0.86kg / t of silicon-calcium alloy cored wire, and 0.56-0.58kg / t of sulfur concentrate powder cored wire are added.

6. The method for producing steel bars for automobile transmission shafts based on an ecological electric furnace according to claim 3, characterized in that: The continuous casting process is as follows: the arrival temperature of the ladle is 1580-1590°C, the H content of the molten steel in the middle ladle is controlled to be ≤2ppm, the casting time is 38-42min, the superheat is controlled at 25-30°C, and the pulling speed is 0.45-0.47m / min; the whole process is protected casting, and the crystallizer protection slag uses medium carbon steel protection slag, and the addition amount is 3.6-3.7kg / t steel.

7. The method for producing steel bars for automobile transmission shafts based on an ecological electric furnace according to claim 3, characterized in that: The ingot heating process is as follows: the ingot entering the heating furnace has a temperature of 500°C to 550°C, the preheating section temperature is 660°C to 680°C, and the preheating section heating time is 1.4 to 1.5 hours; the heating section 2 temperature is 850°C to 870°C, and the heating time is 1.3 to 1.5 hours; the heating section 1 temperature is 1210°C to 1240°C, and the heating time is 1.3 to 1.5 hours; the soaking section temperature is 1210°C to 1230°C, and the soaking section heating time is 1.3 to 1.5 hours; and the steel tapping temperature is 1180°C to 1210°C.

8. The method for producing steel bars for automobile transmission shafts based on an ecological electric furnace according to claim 3, characterized in that: The rolling process includes an initial rolling process and a continuous rolling process, wherein: The primary rolling process is rolled 9 times; the rolling reduction is: steel turning → 1st pass reduction 65~65.01mm → 2nd pass reduction 70~70.01mm → steel turning → 3rd pass reduction 64~64.01mm → 4th pass reduction 90~90.01mm → steel turning → 5th pass reduction 42~42.01mm → 6th pass reduction 40~40.01mm → 7th pass reduction 35~35.01mm → 8th pass reduction 34~34.01mm → steel turning → 9th pass reduction 82~82.01mm; after rolling by 3 850mm rolling mills and 1 735mm rolling mill, it enters the continuous rolling unit for rolling; The continuous rolling process is rolled for 7 times; the rolling speed is: the rolling speed of the first pass is 0.27-0.272 m / s; the rolling speed of the second pass is 0.31-0.312 m / s; the rolling speed of the third pass is 0.31-0.312 m / s; the rolling speed of the fourth pass is 0.393-0.395 m / s; the rolling speed of the fifth pass is 0.499-0.500 m / s; the rolling speed of the sixth pass is 0.607-0.608 m / s; the finished product is produced after 7 rolling passes; The size of the billet changes during the initial rolling process: the first pass is rolled to a width of 408-408.01mm and a height of 421-421.01mm; the second pass is rolled to a width of 426-426.01mm and a height of 351-351.01mm; the third pass is rolled to a width of 370-370.01mm and a height of 362-362.01mm; the fourth pass is rolled to a width of 397-397.01mm and a height of 272-272.01mm; the fifth pass is rolled to a width of 285 ~285.01mm, height 355~355.01mm; the 6th pass is rolled to a width of 297~297.01mm, a height of 315~315.01mm; the 7th pass is rolled to a width of 307~307.01mm, a height of 280~280.01mm; the 8th pass is rolled to a width of 317~317.01mm, a height of 246~246.01mm; the 9th pass is rolled to a width of 271~271.01mm, a height of 235~235.01mm; The size changes of the steel billet during the continuous rolling process are as follows: the first pass is rolled to a height of 229-229.01mm and a width of 245-245.01mm; the second pass is rolled to a height of 192-192.01mm and a width of 235-235.01mm; the third pass is rolled to a height of 200-200.01mm and a width of 195-195.01mm; the fourth pass is rolled to a height of 163-163.01mm and a width of 200-200.01mm; the fifth pass is rolled to a height of 169-169.01mm and a width of 176-176.01mm; the sixth pass is rolled to a height of 128-128.01mm and a width of 172-172.01mm; the seventh pass is rolled to a height of 142-142.01mm and a width of 142-142.01mm.

9. The method for producing steel bars for automobile transmission shafts based on an ecological electric furnace according to claim 3, characterized in that: During the insulation process, the temperature of the insulation pit under the steel is ≥570°C, the insulation time is 48-55h, and the temperature out of the insulation pit is ≤150°C.

10. The method for producing steel bars for automobile transmission shafts based on an ecological electric furnace according to claim 3, characterized in that: The heat treatment process comprises the following steps: (1) First quenching: quenching temperature 870-890°C, holding time 0.8-1.2h, oil cooling to room temperature; (2) Second quenching: quenching temperature 860-880°C, holding time 0.8-1.2h, oil cooling to room temperature; (3) Tempering: Tempering temperature 190 ~ 210 ℃, holding time 1.8 ~ 2.2h, water cooling to room temperature.

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