Production and preparation method of converter process carburizing gear shaft bar

Abstract

A production and preparation method of a steel bar for a converter process carburized gear shaft, the chemical composition of the bar is C: 0.18% to 0.22%, Si: 0.20% to 0.30%, Mn: 0.50% to 0.60%, P: ≤0.015%, S: ≤0.008%, Cr: 1.35% to 1.45%, Ni: 3.30% to 3.40%, Cu: ≤0.05%, Mo: ≤0.05%, Alt: 0.025% to 0.035%, and the remainder is iron and unavoidable impurities. A process of converter smelting → LF refining → RH vacuum degassing → continuous casting → heating process → rolling process is adopted to ensure the mechanical properties, high hardness, and high steel purity of the finished steel for carburized gear shaft, and also ensure the surface quality level of the steel for carburized gear shaft.

Description

A method for producing carburized gear shaft bars in a converter process Technical Field

[0001] The present invention relates to the field of special steel, and in particular to a method for producing and preparing carburized gear shaft bars in a converter process. Background Art

[0002] Gear shafts are mechanical components that support rotating parts and rotate with them to transmit motion, torque, or bending moment. The harsh operating environment places stringent demands on the comprehensive performance of the steel used for gear shafts, including wear resistance and fatigue life. As a crucial component of transmission systems, gear shafts are subject to stringent quality requirements.

[0003] The quality of gear shaft steel directly affects the service life and wear resistance of the transmission device, and even affects the safety of the entire transmission device working process.

[0004] Therefore, it is necessary to develop carburized gear shaft steel with excellent mechanical properties, high hardness and high steel purity to meet the requirements of high-end products.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to provide a production process and preparation method for carburized gear shaft steel 20Cr2Ni4A bars. The method adopts a converter + LF + RH + continuous casting smelting process to produce carburized gear shaft steel 20Cr2Ni4A bars, which meets high-end use requirements and achieves a breakthrough in the batch production of carburized gear shaft steel 20Cr2Ni4A bars in the converter continuous casting process. It not only ensures the mechanical properties, macrostructure and high steel purity of the finished steel of carburized gear shaft steel 20Cr2Ni4A, but also ensures the surface quality level of carburized gear shaft steel 20Cr2Ni4A.

[0007] To achieve the aforementioned objectives, the present invention provides a 20Cr2Ni4A steel bar for carburized gear shafts and a production method thereof. The method includes composition and process design, specifically the following steps: converter smelting → LF refining → RH vacuum degassing → continuous casting → heating → rolling. This method meets the quality requirements for carburized gear shaft 20Cr2Ni4A steel bar, while also meeting standard specifications for mechanical properties, high hardness, and high steel purity.

[0008] A 20Cr2Ni4A steel bar for carburizing gear shafts has the following internal controlled chemical composition, calculated by mass percentage: C: 0.18%-0.22%, Si: 0.20%-0.30%, Mn: 0.50%-0.60%, P: ≤0.015%, S: ≤0.008%, Cr: 1.35%-1.45%, Ni: 3.30%-3.40%, Cu: ≤0.05%, Mo: ≤0.05%, Alt: 0.025%-0.035%, and the balance being iron and unavoidable impurities.

[0009] The production and preparation method of the carburized gear shaft steel 20Cr2Ni4A bar comprises the following process routes: converter smelting → refining outside the furnace (LF+RH) → continuous casting → heating in a heating furnace → rolling → insulation;

[0010] The converter smelting process utilizes scrap steel and molten iron, with scrap steel accounting for 27-30% by mass and molten iron accounting for 70-73% by mass. Oxygen oxidation and vigorous boiling are employed, with a tapping temperature of 1695-1700°C, a C content of 0.10-0.12% at tapping, and P ≤ 0.010%. Auxiliary materials and alloys are added when 1 / 4-1 / 3 of the steel has been tapped. The alloy addition per ton of steel includes: 6.4-6.5 kg / t of silicon manganese, 0.7-0.8 kg / t of aluminum granules, 36-36.5 kg / t of nickel plate, and 0.2-0.22 kg / t of ferrosilicon. Auxiliary material addition per ton of steel includes: 29-30 kg / t of dolomite, 34-35 kg / t of lime, 18.2-19 kg / t of limestone, and 6-6.2 kg / t of sintered ore.

[0011] The LF refining process comprises the following steps: using a high current of 20,000 to 25,000 A to heat and melt the slag; adding active lime when the slag surface fluctuates and the molten steel and arc are not exposed; taking a first sample of the molten steel for chemical composition analysis after 5 minutes; and adding alloy and fluorite according to target chemical composition values; and adding the alloy and fluorite to the argon flow to promote rapid melting and homogenization of the alloy and fluorite. When the temperature of the molten steel reaches 1570-1580℃, 1-3kg / t of diffusion deoxidizer is added for diffusion deoxidation, and the furnace door is closed for 10-12 minutes. When the temperature of the molten steel reaches 1620-1630℃, the chemical composition of the molten steel 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, 1-3kg / t of diffusion deoxidizer is added to continue slag adjustment. The additional alloy addition amount per ton of steel is: 7.5-7.7kg / t of high carbon ferrochrome, 18.7-19kg / t of low carbon ferrochrome, 1.6-1.7kg / t of aluminum particles, 1.35-1.42kg / t of ferrosilicon, and 1.9-2.0kg / t of nickel plate. Maintain the slag basicity pH at 2.5-3.5 and the slag viscosity at 0.80-1.20 Pa·s. Continue white slag smelting for 20-30 minutes. When the molten steel temperature reaches 1630-1640°C, perform final deoxidation by feeding 0.9-1.0 m / t of Al wire. After the wire feeding is complete, initiate static argon purge for 10-20 minutes. Supplementary materials are added per ton of steel: 8.7-9 kg / t of active lime and 0.75-0.80 kg / t of fluorite.

[0012] The RH refining is as follows: before the vacuum pump is started, the argon pressure is controlled at 0.1-0.3 MPa, so that the slag surface moves slightly and the molten steel is not exposed. When the vacuum degree reaches 100 Pa-110 Pa, the timing is started and the time is maintained for 10-15 minutes. Aluminum particles and high manganese are added according to the target composition of the molten steel. At the same time, the argon pressure is adjusted to 0.3-0.5 MPa. After the static argon blowing is completed, 1.1-1.2 meters / t of silicon calcium wire is added.

[0013] The continuous casting is as follows: continuous pouring at 1545-1555°C, tundish temperature at 1530-1540°C, casting speed at 0.43-0.44 m / min, H in the tundish molten steel controlled ≤2ppm, crystallizer electromagnetic stirring current at 400-420A, terminal electromagnetic stirring current at 330-350A, and frequency at 8-9Hz; full-process protective casting, crystallizer protective slag using medium-carbon steel protective slag; lightly pressing down to put in the second, third, and fourth rollers, with the reduction amounts being 3-3.2mm, 4-4.2mm, and 4-4.2mm, respectively; the ingot cutting adopts a combination of automatic and manual methods, with the continuous casting ingot having a red steel bottom and upper pressure on the ingots from two furnaces to ensure flatness, and the holding time being 30-40h.

[0014] Based on the above technical solution, further, the size of the continuous casting billet is 350mm*470mm.

[0015] Based on the above technical solution, further, the heating process is as follows: the temperature of the heating furnace is 300℃~540℃, and a three-stage heating system is adopted. The preheating section is heated for 0.6~0.8h, and the temperature is required to reach 650℃~700℃, and the holding time is 0.3~0.5h; the temperature of the heating section 2 is required to be heated for 0.6~0.8h, and the temperature is required to reach 850℃~870℃, and the holding time is 0.5~0.8h; the temperature of the heating section 1 is required to be heated for 0.6~0.8h, and the temperature is required to reach 1210℃~1240℃, and the holding time is 1.0~1.2h; the temperature of the soaking section is required to be cooled for 0.3~0.5h, and the temperature is required to reach 1200℃~1230℃, and the holding time is 0.8~1.0h; the steel tapping temperature is 1180℃~1210℃.

[0016] Based on the above technical solution, further, the specification of the rod is Φ35~Φ250mm, preferably Φ200mm.

[0017] Based on the above technical solution, further, the rolling process includes blooming mill rolling and tandem mill rolling, specifically:

[0018] Hot rolled products (specifications ≥Φ83mm): starting rolling temperature 1100℃~1200℃, finishing rolling temperature ≥850℃.

[0019] Hot rolled products (specifications ≤Φ82mm): starting rolling temperature 980℃~1050℃, finishing rolling temperature 800℃~950℃.

[0020] 1) Blooming: Blooming is done using a 1150mm BD blooming mill, with 7 passes of rolling, with reductions of: 60-61mm for the 1st pass, 70-71mm for the 2nd pass, 65-66mm for the 3rd pass, 56-57mm for the 4th pass, 65-66mm for the 5th pass, 71-72mm for the 6th pass, and 71-72mm for the 7th pass. The steel then passes through three 850mm rolling mills and one 735mm rolling mill, and then enters an 8-stand continuous rolling mill group for rolling.

[0021] 2) Rolling process of product specification Φ200mm:

[0022] Rolling process for large bars Φ200mm: the initial rolling produces an intermediate billet with a height of 268~268.5mm and a width of 232~232.5mm; the first pass has a height of 229~229.5mm and a width of 240~240.5mm; the second pass has a height of 203~203.5mm and a width of 238~238.5mm; the third pass has a height of 225~225.5mm and a width of 206~206.5mm; the fourth pass has a height of 196~196.5mm and a width of 230~230.5mm; the fifth pass has a height of 202.5~202.7mm and a width of 202.5~202.7mm, and the finished product is produced after the fifth pass.

[0023] Based on the above technical solution, further, the insulation process is: steel insulation, pit entry temperature ≥ 550°C, pit exit temperature ≤ 200°C, insulation time ≥ 48h.

[0024] Based on the above technical solution, further, the process route includes insulation, followed by finishing → inspection → packaging and storage → delivery.

[0025] Based on the above technical solution, further, a sample of the steel after insulation is taken for heat treatment, and the heat treatment includes the following steps:

[0026] 1) First quenching: 870-890℃, holding time 0.8-1.0h, oil cooling;

[0027] 2) Second quenching: 770-790℃, holding time 0.8-1.0h, oil cooling;

[0028] 3) Tempering: 195-205℃, keep warm for 1.8-2.2h, water cooling.

[0029] Beneficial effects of the present invention:

[0030] (1) The converter + LF + RH + continuous casting smelting process and rolling process are used to produce carburized gear shaft steel 20Cr2Ni4A bars with a production specification of Φ200mm, which meets the mechanical performance requirements and ensures the purity of the steel.

[0031] (2) Reasonable component design and production process ensure surface quality and impact performance.

[0032] (3) The macrostructure, non-metallic inclusions and mechanical properties of the finished steel meet the requirements of high-end products. DETAILED DESCRIPTION

[0033] The following non-limiting examples may enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention in any way.

[0034] Example 1

[0035] 1. Component optimization design

[0036] The chemical composition, by mass percentage, is C: 0.20%, Si: 0.25%, Mn: 0.53%, P: 0.010%, S: 0.005%, Cr: 1.38%, Ni: 3.35%, Cu: 0.01%, Mo: 0.02%, Alt: 0.028%, and the balance is iron and inevitable impurities.

[0037] 2 Design of production process parameters for 20Cr2Ni4A converter continuous casting steel for carburized gear shaft

[0038] Process route: 180t converter smelting → refining outside the furnace (LF+RH) → 350mm*470mm continuous casting → heating in a heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery; including:

[0039] (1) Converter smelting: Scrap steel and molten iron are used for smelting, with scrap steel accounting for 28% by mass and molten iron accounting for 72% by mass. Oxygen oxidation and intense boiling are used, with a tapping temperature of 1698°C, a C content of 0.11% and a P content of 0.008% at tapping time, and auxiliary materials and alloys are added when 1 / 4 of the steel is tapped. Alloy addition per ton of steel: 6.4 kg / t silicon manganese, 0.7 kg / t aluminum pellets, 36 kg / t nickel plate, and 0.2 kg / t ferrosilicon. Auxiliary material addition per ton of steel: 29 kg / t dolomite, 34 kg / t lime, 18.5 kg / t limestone, and 6 kg / t sintered ore.

[0040] (2) LF furnace: Use 22000A high current to heat and melt slag. When the slag surface fluctuates and the molten steel and arc are not exposed, add active lime. After 5 minutes, take the first sample to analyze the chemical composition of the molten steel. Add alloy and fluorite according to the target chemical composition. The alloy and fluorite should be added to the argon flow to promote rapid melting and homogenization of the alloy and fluorite. When the molten steel temperature reaches 1575℃, add 2kg / t of diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1625℃, take the second sample to analyze the chemical composition of the molten steel to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, add 2kg / t of diffusion deoxidizer to continue slag adjustment. Add alloy: high carbon ferrochrome 7.6kg / t, low carbon ferrochrome 18.7kg / t, aluminum particles 1.6kg / t, ferrosilicon 1.38kg / t, nickel plate 2.0kg / t. Maintaining the slag alkalinity pH at 2.8 and the slag viscosity at 1.10 Pa·s, white slag smelting was continued for 25 minutes. When the molten steel temperature reached 1634°C, final deoxidation was initiated by feeding 0.9 m / t of Al wire. After the wire feeding was completed, static argon purging was initiated for 14 minutes. Additional auxiliary materials included 8.8 kg / t of active lime and 0.77 kg / t of fluorite.

[0041] (3) RH refining: Before starting the vacuum pump, the argon pressure is controlled at 0.1 MPa, so that the slag surface moves slightly and the molten steel is not exposed. When the vacuum degree reaches 100 Pa, the timing starts and the time is maintained for 12 minutes. Aluminum particles and high manganese are added according to the composition of the molten steel. At the same time, the argon pressure is adjusted to 0.35 MPa. After the static argon blowing is completed, 1.1 meters / t of silicon calcium wire is added.

[0042] (4) Continuous casting: continuous casting temperature 1548℃, tundish temperature 1533℃, casting speed 0.43m / min, H control in tundish molten steel 1.6ppm, crystallizer electromagnetic stirring current 400A, end electromagnetic stirring current 330A, frequency 8Hz; full process protection casting, crystallizer protective slag uses medium carbon steel protective slag; light pressure is applied to put in the second, third and fourth rollers, the pressure reduction is 3mm, 4mm and 4mm respectively; the billet cutting adopts a combination of automatic and manual methods, the continuous casting billet is made of red steel as the bottom, and the billet from two furnaces is pressed to ensure the straightness, and the holding time is 35h.

[0043] (5) Heating process: The temperature of the heating furnace is 510℃, and a three-stage heating system is adopted. The preheating stage is heated for 0.6h, and the temperature is required to reach 670℃, and the holding time is 0.4h; the temperature of the heating stage 2 is required to be heated for 0.6h, and the temperature is required to reach 850℃, and the holding time is 0.7h; the temperature of the heating stage 1 is required to be heated for 0.6h, and the temperature is required to reach 1220℃, and the holding time is 1.0h; the temperature of the soaking stage is required to be cooled for 0.4h, and the temperature is required to reach 1210℃, and the holding time is 1.0h; the steel tapping temperature is 1190℃.

[0044] (6) Rolling process

[0045] The starting rolling temperature is 1130℃ and the finishing rolling temperature is 880℃.

[0046] 1) Blooming:

[0047] The steel bar is produced by using an 1150mm BD primary rolling mill and rolled in 7 passes with a reduction of 60mm in the first pass, 70mm in the second pass, 65mm in the third pass, 56mm in the fourth pass, 65mm in the fifth pass, 71mm in the sixth pass and 71mm in the seventh pass. It passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters an 8-pass continuous rolling mill group for rolling.

[0048] 2) Rolling process of product specification Φ200mm:

[0049] Rolling process for large bars Φ200mm: the initial rolling produces an intermediate billet with a height of 268mm and a width of 232mm; the first pass has a height of 229mm and a width of 240mm; the second pass has a height of 203mm and a width of 238mm; the third pass has a height of 225mm and a width of 206mm; the fourth pass has a height of 196mm and a width of 230mm; the fifth pass has a height of 202.5mm and a width of 202.5mm, and the finished product is produced after the fifth pass.

[0050] (7) Insulation process: Steel insulation, pit entry temperature 580℃, pit exit temperature 150℃, insulation time 54h.

[0051] Example 2

[0052] 1. Component optimization design

[0053] The chemical composition, by mass percentage, is C: 0.19%, Si: 0.26%, Mn: 0.55%, P: 0.007%, S: 0.004%, Cr: 1.39%, Ni: 3.37%, Cu: 0.01%, Mo: 0.01%, Alt: 0.028%, and the balance is iron and inevitable impurities.

[0054] 2 Design of production process parameters for 20Cr2Ni4A converter continuous casting steel for carburized gear shaft

[0055] Process route: 180t converter smelting → refining outside the furnace (LF+RH) → 350mm*470mm continuous casting → heating in a heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery; including:

[0056] (1) Converter smelting: Scrap steel and molten iron are used for smelting, with scrap steel accounting for 28% by mass and molten iron accounting for 72% by mass. Oxygen oxidation and intense boiling are used, with a tapping temperature of 1698°C, a C content of 0.10% and a P content of 0.008% at tapping time, and auxiliary materials and alloys are added when 1 / 4 of the steel is tapped. Alloy addition per ton of steel: 6.4 kg / t silicon manganese, 0.7 kg / t aluminum pellets, 36 kg / t nickel plate, and 0.22 kg / t ferrosilicon. Auxiliary material addition per ton of steel: 29 kg / t dolomite, 34 kg / t lime, 18.5 kg / t limestone, and 6 kg / t sintered ore.

[0057] (2) LF furnace: Use 23000A high current to heat and melt slag. When the slag surface fluctuates and the molten steel and arc are not exposed, add active lime. After 5 minutes, take the first sample to analyze the chemical composition of the molten steel. Add alloy and fluorite according to the target chemical composition. The alloy and fluorite should be added to the argon flow to promote rapid melting and homogenization of the alloy and fluorite. When the molten steel temperature reaches 1576℃, add 1.5kg / t of diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1624℃, take the second sample to analyze the chemical composition of the molten steel to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, add 1.5kg / t of diffusion deoxidizer to continue slag adjustment. Add alloy: 7.6kg / t of high carbon ferrochrome, 18.8kg / t of low carbon ferrochrome, 1.65kg / t of aluminum particles, 1.38kg / t of ferrosilicon, and 1.95kg / t of nickel plate. The slag basicity pH was maintained at 2.8, and the slag viscosity was maintained at 0.95 Pa·s. White slag smelting was continued for 27 minutes. When the molten steel temperature reached 1635°C, final deoxidation was carried out by feeding 0.9 m / t of Al wire. After the wire feeding was completed, static argon blowing was started and maintained for 16 minutes. Auxiliary materials were added: 8.8 kg / t of active lime and 0.77 kg / t of fluorite.

[0058] (3) RH refining: Before starting the vacuum pump, the argon pressure is controlled at 0.15 MPa, so that the slag surface moves slightly and the molten steel is not exposed. When the vacuum degree reaches 100 Pa, the timing starts and the time is maintained for 12 minutes. Aluminum particles and high manganese are added according to the composition of the molten steel. At the same time, the argon pressure is adjusted to 0.4 MPa. After the static argon blowing is completed, 1.1 meters / t of silicon calcium wire is added.

[0059] (4) Continuous casting: continuous casting at 1548℃, tundish temperature at 1535℃, casting speed at 0.43m / min, H in tundish steel controlled at 1.6ppm, crystallizer electromagnetic stirring current at 400A, end electromagnetic stirring current at 330A, frequency at 8Hz; full-process protective casting, crystallizer protective slag using medium carbon steel protective slag; lightly press down the second, third, and fourth rollers, with a reduction of 3mm, 4mm, and 4mm respectively; ingot cutting is carried out by a combination of automatic and manual methods, with red steel as the bottom of the continuous casting ingot and upper pressure on the two furnaces to ensure straightness, and the holding time is 35h.

[0060] (5) Heating process

[0061] Heating process: The temperature entering the heating furnace is 390℃, and a three-stage heating system is adopted. The preheating stage is required to heat up for 0.6h, and the temperature is required to reach 680℃, and the holding time is 0.4h; the temperature of the heating stage 2 is required to heat up for 0.6h, and the temperature is required to reach 870℃, and the holding time is 0.6h; the temperature of the heating stage 1 is required to heat up for 0.6h, and the temperature is required to reach 1220℃, and the holding time is 1.0h; the temperature of the soaking stage is required to cool down for 0.3h, and the temperature is required to reach 1210℃, and the holding time is 0.8h; the steel tapping temperature is 1190℃.

[0062] (6) Rolling process

[0063] The starting rolling temperature is 1120℃ and the finishing rolling temperature is 890℃.

[0064] 1) Blooming:

[0065] The steel bar is produced by using an 1150mm BD primary rolling mill and rolled in 7 passes with a reduction of 60mm in the first pass, 70mm in the second pass, 65mm in the third pass, 56mm in the fourth pass, 65mm in the fifth pass, 71mm in the sixth pass and 71mm in the seventh pass. It passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters an 8-pass continuous rolling mill group for rolling.

[0066] 2) Rolling process of product specification Φ200mm:

[0067] Rolling process for large bars Φ200mm: the initial rolling produces an intermediate billet with a height of 268mm and a width of 232mm; the first pass has a height of 229mm and a width of 240mm; the second pass has a height of 203mm and a width of 238mm; the third pass has a height of 225mm and a width of 206mm; the fourth pass has a height of 196mm and a width of 230mm; the fifth pass has a height of 202.5mm and a width of 202.5mm, and the finished product is produced after the fourth pass.

[0068] (7) Insulation process

[0069] Insulation process: Steel insulation, pit entry temperature 570℃, pit exit temperature 140℃, insulation time 52h.

[0070] Example 3

[0071] 1. Component optimization design

[0072] The chemical composition, by mass percentage, is C: 0.20%, Si: 0.25%, Mn: 0.54%, P: 0.008%, S: 0.004%, Cr: 1.39%, Ni: 3.38%, Cu: 0.02%, Mo: 0.01%, Alt: 0.028%, and the balance is iron and inevitable impurities.

[0073] 2 Design of production process parameters for 20Cr2Ni4A converter continuous casting steel for carburized gear shaft

[0074] Process route: 180t converter smelting → refining outside the furnace (LF+RH) → 350mm*470mm continuous casting → heating in a heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery; including:

[0075] (1) Converter smelting: Scrap steel and molten iron are used for smelting, with scrap steel accounting for 28% by mass and molten iron accounting for 72% by mass. Oxygen oxidation and intense boiling are used, with a tapping temperature of 1700°C, a C content of 0.10% and a P content of 0.007% at tapping time, and auxiliary materials and alloys are added when 1 / 4 of the steel is tapped. Alloy addition per ton of steel: 6.4 kg / t silicon manganese, 0.7 kg / t aluminum pellets, 36 kg / t nickel plate, and 0.2 kg / t ferrosilicon. Auxiliary material addition per ton of steel: 30 kg / t dolomite, 34 kg / t lime, 18.6 kg / t limestone, and 6 kg / t sintered ore.

[0076] (2) LF furnace: Use 22000A high current to heat and melt slag. When the slag surface fluctuates and the molten steel and arc are not exposed, add active lime. After 5 minutes, take the first sample to analyze the chemical composition of the molten steel. Add alloy and fluorite according to the target chemical composition. The alloy and fluorite should be added to the argon flow to promote rapid melting and homogenization of the alloy and fluorite. When the molten steel temperature reaches 1575℃, add 2kg / t of diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1626℃, take the second sample to analyze the chemical composition of the molten steel to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, add diffusion deoxidizer and continue to adjust the slag. Add alloy: high carbon ferrochrome 7.6kg / t, low carbon ferrochrome 18.8kg / t, aluminum particles 1.6kg / t, ferrosilicon 1.37kg / t, nickel plate 1.9kg / t. Maintaining the slag alkalinity pH at 2.5 and the slag viscosity at 0.9 Pa·s, continue white slag smelting for 25 minutes. When the molten steel temperature reaches 1635°C, final deoxidation is initiated by feeding 0.9 m / t of Al wire. After the wire feeding is completed, static argon purging is initiated for 15 minutes. Additional auxiliary materials include 8.8 kg / t of active lime and 0.78 kg / t of fluorite.

[0077] (3) RH refining: Before starting the vacuum pump, the argon pressure is controlled at 0.2 MPa, so that the slag surface moves slightly and the molten steel is not exposed. When the vacuum degree reaches 100 Pa, the timing starts and the time is maintained for 13 minutes. Aluminum particles and high manganese are added according to the composition of the molten steel. At the same time, the argon pressure is adjusted to 0.4 MPa. After the static argon blowing is completed, 1.1 meters / t of silicon calcium wire is added.

[0078] (4) Continuous casting: continuous casting at 1548℃, tundish temperature at 1535℃, casting speed at 0.43m / min, H in tundish steel at 1.4ppm, crystallizer electromagnetic stirring current at 400A, end electromagnetic stirring current at 330A, frequency at 8Hz; full-process protective casting, crystallizer protective slag using medium carbon steel protective slag; lightly press down the second, third, and fourth rollers, with a reduction of 3mm, 4mm, and 4mm respectively; ingot cutting is carried out by a combination of automatic and manual methods, with red steel as the bottom of the continuous casting ingot and upper pressure on the two furnaces to ensure straightness, and the holding time is 35h.

[0079] (5) Heating process

[0080] Heating process: The temperature entering the heating furnace is 480℃, and a three-stage heating system is adopted. The preheating stage is required to heat up for 0.6h, and the temperature is required to reach 670℃, and the holding time is 0.3h; the temperature of the heating stage 2 is required to heat up for 0.6h, and the temperature is required to reach 860℃, and the holding time is 0.6h; the temperature of the heating stage 1 is required to heat up for 0.6h, and the temperature is required to reach 1220℃, and the holding time is 1.0h; the temperature of the soaking stage is required to cool down for 0.3h, and the temperature is required to reach 1210℃, and the holding time is 0.8h; the steel tapping temperature is 1190℃.

[0081] (6) Rolling process

[0082] The starting rolling temperature is 1120℃ and the final rolling temperature is 885℃.

[0083] 1) Blooming:

[0084] The steel bar is produced by using an 1150mm BD primary rolling mill and rolled in 7 passes with a reduction of 60mm in the first pass, 70mm in the second pass, 65mm in the third pass, 56mm in the fourth pass, 65mm in the fifth pass, 71mm in the sixth pass and 71mm in the seventh pass. It passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters an 8-pass continuous rolling mill group for rolling.

[0085] 2) Rolling process of product specification Φ200mm:

[0086] Rolling process for large bars Φ200mm: the initial rolling produces an intermediate billet with a height of 268mm and a width of 232mm; the first pass has a height of 229mm and a width of 240mm; the second pass has a height of 203mm and a width of 238mm; the third pass has a height of 225mm and a width of 206mm; the fourth pass has a height of 196mm and a width of 230mm; the fifth pass has a height of 202.5mm and a width of 202.5mm, and the finished product is produced after the fourth pass.

[0087] (7) Insulation process

[0088] Insulation process: Steel insulation, pit entry temperature 570℃, pit exit temperature 160℃, insulation time 55h.

[0089] Example 4

[0090] 1. Component optimization design

[0091] The chemical composition, by mass percentage, is C: 0.20%, Si: 0.26%, Mn: 0.54%, P: 0.009%, S: 0.005%, Cr: 1.40%, Ni: 3.36%, Cu: 0.01%, Mo: 0.02%, Alt: 0.029%, and the balance is iron and inevitable impurities.

[0092] 2 Design of production process parameters for 20Cr2Ni4A converter continuous casting steel for carburized gear shaft

[0093] Process route: 180t converter smelting → refining outside the furnace (LF+RH) → 350mm*470mm continuous casting → heating in a heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery; including:

[0094] (1) Converter smelting: Scrap steel and molten iron are used for smelting, with scrap steel accounting for 29% by mass and molten iron accounting for 71% by mass. Oxygen oxidation and intense boiling are used, with a tapping temperature of 1698°C, a C content of 0.10% and a P content of 0.008% at tapping time, and auxiliary materials and alloys are added when 1 / 4 of the steel is tapped. Alloy addition per ton of steel: 6.4 kg / t silicon manganese, 0.7 kg / t aluminum pellets, 36 kg / t nickel plate, and 0.2 kg / t ferrosilicon. Auxiliary material addition per ton of steel: 29 kg / t dolomite, 34 kg / t lime, 18.5 kg / t limestone, and 6 kg / t sintered ore.

[0095] (2) LF furnace: Use 23000A high current to heat and melt slag. When the slag surface fluctuates and the molten steel and arc are not exposed, add active lime and fluorite. After 5 minutes, take the first sample to analyze the chemical composition of the molten steel. Add alloy and fluorite according to the target chemical composition. The alloy and fluorite powder should be added to the argon flow to promote rapid melting and homogenization of the alloy and fluorite. When the molten steel temperature reaches 1576℃, add 2kg / t of diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1626℃, take the second sample to analyze the chemical composition of the molten steel to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, add 2kg / t of diffusion deoxidizer to continue slag adjustment. Add alloy: high carbon ferrochrome 7.6kg / t, low carbon ferrochrome 18.8kg / t, aluminum particles 1.6kg / t, ferrosilicon 1.37kg / t, nickel plate 1.9kg / t. Maintaining the slag alkalinity pH at 2.5 and the slag viscosity at 0.9 Pa·s, continue white slag smelting for 25 minutes. When the molten steel temperature reaches 1634°C, final deoxidation is initiated by feeding 0.9 m / t of Al wire. After the wire feeding is completed, static argon purging is initiated for 15 minutes. Additional auxiliary materials include 8.8 kg / t of active lime and 0.77 kg / t of fluorite.

[0096] (3) RH refining: Before starting the vacuum pump, the argon pressure is controlled at 0.15 MPa, so that the slag surface moves slightly and the molten steel is not exposed. When the vacuum degree reaches 100 Pa, the timing starts and the time is maintained for 12 minutes. Aluminum particles and high manganese are added according to the composition of the molten steel. At the same time, the argon pressure is adjusted to 0.4 MPa. After the static argon blowing is completed, 1.1 meters / t of silicon calcium wire is added.

[0097] (4) Continuous casting: continuous casting temperature 1548℃, tundish temperature 1533℃, casting speed 0.43m / min, H control in tundish molten steel 1.6ppm, crystallizer electromagnetic stirring current 400A, end electromagnetic stirring current 330A, frequency 8Hz; full process protection casting, crystallizer protective slag uses medium carbon steel protective slag; light pressure is applied to put in the second, third and fourth rollers, the pressure reduction is 3mm, 4mm and 4mm respectively; the billet cutting adopts a combination of automatic and manual methods, the continuous casting billet is made of red steel as the bottom, and the billet from two furnaces is pressed to ensure the straightness, and the holding time is 35h.

[0098] (5) Heating process

[0099] Heating process: The temperature entering the heating furnace is 450℃, and a three-stage heating system is adopted. The preheating stage is required to heat up for 0.6h, and the temperature is required to reach 670℃, and the holding time is 0.3h; the temperature of the heating stage 2 is required to heat up for 0.6h, and the temperature is required to reach 850℃, and the holding time is 0.7h; the temperature of the heating stage 1 is required to heat up for 0.6h, and the temperature is required to reach 1220℃, and the holding time is 1.0h; the temperature of the soaking stage is required to cool down for 0.3h, and the temperature is required to reach 1210℃, and the holding time is 0.8h; the steel tapping temperature is 1190℃.

[0100] (6) Rolling process

[0101] The starting rolling temperature is 1130℃ and the finishing rolling temperature is 885℃.

[0102] 1) Blooming:

[0103] The steel bar is produced by using an 1150mm BD primary rolling mill and rolled in 7 passes with a reduction of 60mm in the first pass, 70mm in the second pass, 65mm in the third pass, 56mm in the fourth pass, 65mm in the fifth pass, 71mm in the sixth pass and 71mm in the seventh pass. It passes through 3 850mm rolling mills and 1 735mm rolling mill, and then enters an 8-pass continuous rolling mill group for rolling.

[0104] 2) Rolling process of product specification Φ200mm:

[0105] Rolling process for large bars Φ200mm: the initial rolling produces an intermediate billet with a height of 268mm and a width of 232mm; the first pass has a height of 229mm and a width of 240mm; the second pass has a height of 203mm and a width of 238mm; the third pass has a height of 225mm and a width of 206mm; the fourth pass has a height of 196mm and a width of 230mm; the fifth pass has a height of 202.5mm and a width of 202.5mm, and the finished product is produced after the fourth pass.

[0106] (7) Insulation process

[0107] Insulation process: Steel insulation, pit entry temperature 580℃, pit exit temperature 160℃, insulation time 54h.

[0108] Example 5

[0109] 1. Component optimization design

[0110] The chemical composition, by mass percentage, is C: 0.21%, Si: 0.26%, Mn: 0.53%, P: 0.009%, S: 0.005%, Cr: 1.38%, Ni: 3.36%, Cu: 0.01%, Mo: 0.02%, Alt: 0.029%, and the balance is iron and inevitable impurities.

[0111] 2 Design of production process parameters for 20Cr2Ni4A converter continuous casting steel for carburized gear shaft

[0112] Process route: 180t converter smelting → refining outside the furnace (LF+RH) → 350mm*470mm continuous casting → heating in a heating furnace → rolling → insulation → finishing → inspection → packaging and storage → delivery; including:

[0113] (1) Converter smelting: Scrap steel and molten iron are used for smelting, with scrap steel accounting for 28% by mass and molten iron accounting for 72% by mass. Oxygen oxidation and intense boiling are used, with a tapping temperature of 1690°C, a C content of 0.10% and a P content of 0.007% at tapping time, and auxiliary materials and alloys are added when 1 / 4 of the steel is tapped. Alloy addition per ton of steel: 6.4 kg / t silicon manganese, 0.7 kg / t aluminum pellets, 36 kg / t nickel plate, and 0.22 kg / t ferrosilicon. Auxiliary material addition per ton of steel: 29 kg / t dolomite, 34 kg / t lime, 18.6 kg / t limestone, and 6 kg / t sintered ore.

[0114] (2) LF furnace: Use 22000A high current to heat and melt slag. When the slag surface fluctuates and the molten steel and arc are not exposed, add active lime. After 5 minutes, take the first sample to analyze the chemical composition of the molten steel. Add alloy and fluorite according to the target chemical composition. The alloy and fluorite should be added to the argon flow to promote rapid melting and homogenization of the alloy and fluorite. When the molten steel temperature reaches 1575℃, add 2kg / t of diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1625℃, take the second sample to analyze the chemical composition of the molten steel to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, add 2kg / t of diffusion deoxidizer to continue slag adjustment. Add alloy: high carbon ferrochrome 7.6kg / t, low carbon ferrochrome 18.7kg / t, aluminum particles 1.6kg / t, ferrosilicon 1.38kg / t, nickel plate 2.0kg / t. The slag alkalinity pH was maintained at 2.6, and the slag viscosity was maintained at 0.92 Pa·s. White slag smelting was continued for 27 minutes. When the molten steel temperature reached 1635°C, final deoxidation was carried out by feeding 0.9 m / t of Al wire. After the wire feeding was completed, static argon blowing was started and maintained for 15 minutes. Auxiliary materials were added: 8.8 kg / t of active lime and 0.78 kg / t of fluorite.

[0115] (3) RH refining: Before starting the vacuum pump, the argon pressure is controlled at 0.1 MPa, so that the slag surface moves slightly and the molten steel is not exposed. When the vacuum degree reaches 100 Pa, the timing starts and the time is maintained for 13 minutes. Aluminum particles and high manganese are added according to the composition of the molten steel. At the same time, the argon pressure is adjusted to 0.35 MPa. After the static argon blowing is completed, 1.1 meters / t of silicon calcium wire is added.

[0116] (4) Continuous casting: continuous casting at 1548℃, tundish temperature at 1533℃, casting speed at 0.43m / min, H in tundish steel at 1.4ppm, crystallizer electromagnetic stirring current at 400A, end electromagnetic stirring current at 330A, frequency at 8Hz; full-process protective casting, crystallizer protective slag using medium carbon steel protective slag; lightly press down the second, third, and fourth rollers, with a reduction of 3mm, 4mm, and 4mm respectively; ingot cutting is carried out by a combination of automatic and manual methods, with red steel as the bottom of the continuous casting ingot and upper pressure on the two furnaces to ensure straightness, and the holding time is 35h.

[0117] (5) Heating process

[0118] Heating process: The temperature entering the heating furnace is 480℃, and a three-stage heating system is adopted. The preheating stage is required to heat up for 0.6h, and the temperature is required to reach 680℃, and the holding time is 0.4h; the temperature of the heating stage 2 is required to heat up for 0.6h, and the temperature is required to reach 860℃, and the holding time is 0.6h; the temperature of the heating stage 1 is required to heat up for 0.6h, and the temperature is required to reach 1220℃, and the holding time is 1.0h; the temperature of the soaking stage is required to cool down for 0.4h, and the temperature is required to reach 1210℃, and the holding time is 1.0h; the steel tapping temperature is 1190℃.

[0119] (6) Rolling process

[0120] The starting rolling temperature is 1125℃ and the final rolling temperature is 880℃.

[0121] 1) Blooming:

[0122] The steel bar is produced by using an 1150mm BD blooming mill and rolled in 7 passes with a reduction of 60mm in the first pass, 70mm in the second pass, 65mm in the third pass, 56mm in the fourth pass, 65mm in the fifth pass, 71mm in the sixth pass and 71mm in the seventh pass. It then passes through three 850mm rolling mills and one 735mm rolling mill, and then enters an 8-pass continuous rolling mill group for rolling.

[0123] 2) Rolling process of product specification Φ200mm:

[0124] Rolling process for large bars Φ200mm: the initial rolling produces an intermediate billet with a height of 268mm and a width of 232mm; the first pass has a height of 229mm and a width of 240mm; the second pass has a height of 203mm and a width of 238mm; the third pass has a height of 225mm and a width of 206mm; the fourth pass has a height of 196mm and a width of 230mm; the fifth pass has a height of 202.5mm and a width of 202.5mm, and the finished product is produced after the fourth pass.

[0125] (7) Insulation process

[0126] Insulation process: Steel insulation, pit entry temperature 570℃, pit exit temperature 150℃, insulation time 55h.

[0127] Test results of finished products of Examples 1 to 5

[0128] (1) Macrostructure of Φ200mm steel

[0129] (2) Non-metallic inclusions in Φ200mm steel

[0130] (3) Impact performance of Φ200mm steel

[0131] Anyone skilled in the art will be able to utilize the above-disclosed technical content to make many possible changes and modifications to the technical solution of the present invention, or to modify it into equivalent embodiments with equivalent changes, without departing from the scope of the technical solution of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention that do not depart from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A carburized gear shaft bar, characterized in that: The chemical composition of the rod is calculated by mass percentage as follows: C: 0.18%-0.22%, Si: 0.20%-0.30%, Mn: 0.50%-0.60%, P: ≤0.015%, S: ≤0.008%, Cr: 1.35%-1.45%, Ni: 3.30%-3.40%, Cu: ≤0.05%, Mo: ≤0.05%, Alt: 0.025%-0.035%, and the balance is iron and unavoidable impurities.

2. The method for preparing the carburized gear shaft bar according to claim 1, characterized in that: The process route includes: converter smelting → LF+RH refining → continuous casting → heating process → rolling → insulation; wherein, The converter smelting is as follows: using scrap steel and molten iron for smelting, wherein scrap steel accounts for 27-30% by mass and molten iron accounts for 70-73% by mass; oxygen oxidation, intense boiling, tapping temperature of 1695-1700°C, C of 0.10-0.12% when tapping, P≤0.010%, adding auxiliary materials and alloys when 1 / 4-1 / 3 of the steel is tapped; alloy addition per ton of steel: 6.4-6.5kg / t of silicon manganese, 0.7-0.8kg / t of aluminum particles, 36-36.5kg / t of nickel plate, 0.2-0.22kg / t of ferrosilicon; auxiliary material addition per ton of steel: 29-30kg / t of dolomite, 34-35kg / t of lime, 18.2-19kg / t of limestone, 6-6.2kg / t of sintered ore; The LF refining is as follows: a high current of 20000-25000A is used to heat and melt the slag; when the slag surface fluctuates and the molten steel and the arc are not exposed, active lime is added; after 5 minutes, the chemical composition of the molten steel is first sampled and analyzed; alloy and fluorite are added according to the target value of the chemical composition; when the temperature of the molten steel reaches 1570-1580°C, 1-3kg / t of diffusion deoxidizer is added for diffusion deoxidation; the furnace door is closed for 10 minutes; when the temperature of the molten steel reaches 1620-1630°C, the chemical composition of the molten steel is sampled and 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 away, 1-3kg / t of diffusion deoxidizer is added to continue slag adjustment; the amount of alloy added per ton of steel is: High carbon ferrochrome 7.5-7.7kg / t, low carbon ferrochrome 18.7-19kg / t, aluminum granules 1.6-1.7kg / t, ferrosilicon 1.35-1.42kg / t, nickel plate 1.9-2.0kg / t; keep the slag alkalinity pH value at 2.5-3.5, the slag viscosity at 0.80-1.20Pa·s, and continue to smelt the white slag for 20-30min. When the molten steel temperature reaches 1630-1640℃, carry out final deoxidation and feed Al wire at 0.9-1.0m / t steel. After the wire feeding, start static argon blowing and keep it for 10-20min. The amount of auxiliary materials added per ton of steel is: 8.7-9kg / t of active lime and 0.75-0.80kg / t of fluorite. The RH refining: before the vacuum pump is started, the argon pressure is controlled at 0.1-0.3MPa, so that the slag surface is slightly moved and the molten steel is not exposed. When the vacuum degree reaches 100Pa-110Pa, the timing starts, and the time is maintained for 10-15min. Aluminum particles and high manganese are added according to the target composition of the molten steel, and the argon pressure is adjusted to 0.3-0.5MPa. After the static argon blowing is completed, 1.1-1.2 meters / t of silicon calcium wire is added; The continuous casting is as follows: continuous pouring at 1545-1555°C, tundish temperature at 1530-1540°C, pulling speed at 0.43-0.44 m / min, H in tundish molten steel controlled ≤2ppm, crystallizer electromagnetic stirring current at 400-420A, terminal electromagnetic stirring current at 330-350A, and frequency at 8-9Hz; full-process protective casting, crystallizer protective slag using medium carbon steel protective slag; lightly pressing down to put in the second, third, and fourth rollers, with the pressing amounts being 3-3.2mm, 4-4.2mm, and 4-4.2mm respectively; the ingot cutting adopts a combination of automatic and manual methods, the continuous casting ingot is padded with red steel, the ingots from two furnaces are pressed up to ensure straightness, and the insulation time is 30-40h.

3. The preparation method according to claim 2, characterized in that: The heating process is as follows: the temperature entering the heating furnace is 300°C to 540°C, and a three-stage heating system is adopted. The preheating stage is heated for 0.6 to 0.8h, the temperature is required to reach 650°C to 700°C, and the insulation time is 0.3 to 0.5h; the temperature of the heating stage 2 is required to be heated for 0.6 to 0.8h, the temperature is required to reach 850°C to 870°C, and the insulation time is 0.5 to 0.8h; the temperature of the heating stage 1 is required to be heated for 0.6 to 0.8h, the temperature is required to reach 1210°C to 1240°C, and the insulation time is 1.0 to 1.2h; the temperature of the soaking stage is required to be cooled for 0.3 to 0.5h, the temperature is required to reach 1200°C to 1230°C, and the insulation time is 0.8 to 1.0h; the steel tapping temperature is 1180°C to 1210°C.

4. The preparation method according to claim 2, characterized in that: The production specifications of the rods are Φ35 to Φ250 mm.

5. The preparation method according to claim 4, characterized in that: When the hot-rolled material specification is ≥Φ83mm, the starting rolling temperature is 1100℃~1200℃, and the final rolling temperature is ≥850℃; When the hot-rolled material specification is ≤Φ82mm, the starting rolling temperature is 980℃~1050℃, and the finishing rolling temperature is 800℃~950℃.

6. The preparation method according to claim 2, characterized in that: The rolling process is: Initial rolling: BD initial rolling mill is used for initial rolling, and the steel is rolled for 7 passes with a reduction of 60-61mm for the first pass, 70-71mm for the second pass, 65-66mm for the third pass, 56-57mm for the fourth pass, 65-66mm for the fifth pass, 71-72mm for the sixth pass, and 71-72mm for the seventh pass. The steel is then rolled in 8 continuous rolling mills after passing through 3 850mm rolling mills and 1 735mm rolling mill. Bar rolling process: the initial rolling makes the intermediate billet 268-268.5mm high and 232-232.5mm wide; the first pass is 229-229.5mm high and 240-240.5mm wide, the second pass is 203-203.5mm high and 238-238.5mm wide; the third pass is 225-225.5mm high and 206-206.5mm wide; the fourth pass is 196-196.5mm high and 230-230.5mm wide; the fifth pass is 202.5-202.7mm high and 202.5-202.7mm wide, and the finished product is produced after the 4th pass.

7. The preparation method according to claim 2, characterized in that: The insulation process: steel insulation, pit entry temperature ≥ 550°C, pit exit temperature ≤ 200°C, insulation time ≥ 48h.

8. The preparation method according to claim 2, characterized in that: The steel after heat preservation is heat treated, and the heat treatment includes the following steps: 1) First quenching: 870-890℃, keep warm for 0.8-1.0h, oil cooling; 2) Second quenching: 770-790℃, keep warm for 0.8-1.0h, oil cooling; 3) Tempering: 195-205℃, keep warm for 1.8-2.2h, water cooling.

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