Production and preparation method for steel bar for steam turbine impeller

Abstract

Disclosed in the present invention is a production and preparation method for a steel bar for a steam turbine impeller. The steel bar comprises the following chemical components in percentages by mass: C: 0.31-0.36%, Si: 0.22-0.35%, Mn: 0.45-0.60%, P: ≤0.013%, S: ≤0.008%, Cr: 1.05-1.20%, Ni: ≤0.20%, Cu: ≤0.10%, Mo: 0.21-0.28%, and V: 0.11-0.18%. The method comprises: converter smelting → LF refining → RH refining → continuous casting → a heating furnace heating process → a rolling process → a heat preservation process. The present invention satisfies the quality requirements of a steel bar for a steam turbine impeller, and indexes, such as mechanical properties, a high hardness and a high steel purity, can also satisfy high-standard requirements.

Description

A method for producing steel bars for steam turbine impellers Technical Field

[0001] The present invention relates to the technical field of steel materials, and in particular to a method for producing a steel bar for a steam turbine impeller. Background Art

[0002] The steam turbine impeller is one of the most critical components in a steam turbine, converting the kinetic energy of high-speed fluid into mechanical energy. It performs a crucial role within the steam turbine. As the only component in the steam turbine that comes into direct contact with the fluid, the impeller operates under extremely harsh conditions, needing to withstand complex operating conditions such as high pressure, high temperature, high speed, and strong vibration. As a crucial component of the steam turbine, the impeller is subject to stringent quality requirements.

[0003] The quality of turbine impeller steel directly affects the service life and wear resistance of the turbine, and even affects the safety of the entire turbine operation process.

[0004] Therefore, it is necessary to develop steel for turbine impellers 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 method for producing and preparing steel bars for turbine impellers. The method adopts a converter + LF + RH + continuous casting smelting process smelting and rolling process to produce a steel bar for turbine impellers that meets high-end usage requirements and achieves a breakthrough in the batch production of steel bars for turbine impellers using a converter continuous casting process. It not only ensures the mechanical properties, high hardness and high steel purity of the finished steel bar for turbine impellers, but also ensures the surface quality level of the steel bar for turbine impellers.

[0007] To achieve the aforementioned objectives, the present invention provides a method for producing steel bars for steam turbine impellers, including composition and process design, specifically the following steps: converter smelting → LF refining → RH vacuum degassing → continuous casting → heating → blooming mill rolling → continuous rolling mill. This method meets the quality requirements for steam turbine impeller steel bars, while also achieving high standards for mechanical properties, high hardness, and high steel purity.

[0008] A steel bar for a steam turbine impeller has the following chemical compositions, by mass percentage: C: 0.31%-0.36%, Si: 0.22%-0.35%, Mn: 0.45%-0.60%, P: ≤0.013%, S: ≤0.008%, Cr: 1.05%-1.20%, Ni: ≤0.20%, Cu: ≤0.10%, Mo: 0.21%-0.28%, and V: 0.11%-0.18%.

[0009] A method for producing steel bars for steam turbine impellers, wherein the process route comprises: converter smelting → refining outside the furnace (LF+RH) → continuous casting → heating process in a heating furnace → rolling process → insulation process.

[0010] Based on the above technical solution, the converter smelting method further comprises: using scrap steel and molten iron, with scrap steel accounting for 26-30% by mass and molten iron accounting for 70-74% by mass; oxygen oxidation and vigorous boiling; a tapping temperature of 1685-1695°C, an oxygen supply time of 15-20 minutes, an operating time of 45-55 minutes, an end-point oxygen content of 620-640 ppm, a carbon content of 0.13-0.15% at tapping, and a phosphorus content of ≤0.007%. Auxiliary materials and alloys are added when 1 / 4-1 / 3 of the steel has been tapped. The alloy addition per ton of steel is: 6.2-6.3 kg / t silicon manganese, 0.9-0.95 kg / t ferrosilicon, 1.6-1.7 kg / t ferroaluminum, 2.8-2.9 kg / t ferrovanadium, and 3.8-4.0 kg / t ferromolybdenum. Auxiliary materials added per ton of steel: limestone 11-11.5 kg / t, activated limestone 34-35 kg / t, dolomite 19-20 kg / t, sintered ore 11-11.5 kg / t.

[0011] Based on the above technical solution, the LF refining is further as follows: a high current of 20,000 to 25,000 A 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 to 7 minutes, the chemical composition is analyzed for the first time; alloy is added according to the target chemical composition value, and butane carburizer is added for carburization; the alloy and butane carburizer should be added to the argon flow to promote rapid melting and homogenization of the alloy and butane carburizer. When the temperature of the molten steel reaches 1580-1600℃, 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 1610-1620℃, a second sample is taken for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, 0.5-1kg / t of diffusion deoxidizer is added to continue slag adjustment; the additional alloy addition per ton of steel is: 3.2-3.3kg / t of high carbon ferrochrome, 0.35-0.37kg / t of ferrosilicon, 0.38-0.40kg / t of aluminum particles, and 1.1-1.15kg / t of carbon cored wire. Maintain the slag basicity pH at 2.5-3.5 and the slag viscosity at 0.80-1.20 Pa.s. Continue smelting the white slag for 20-30 minutes. When the molten steel temperature reaches 1630-1640°C, begin static argon blowing for 10-20 minutes. The ladle clearance is 400-420 mm, and the slag thickness is 80-85 mm. Supplementary materials are added per ton of steel: 6.2-6.3 kg / t of active lime and 0.8-1.0 kg / t of coke butane recarburizer.

[0012] Based on the above technical solution, further, the diameter of the carbon cored wire is 10-10.5 mm.

[0013] Based on the above technical solution, the RH refining further comprises the following steps: before starting the vacuum pump, the argon pressure is controlled at 0.1-0.3 MPa, so that the slag surface is slightly moved to prevent the molten steel from being exposed. The ladle clearance is 400-420 mm, and the slag thickness is 95-105 mm. When the vacuum reaches 90-100 Pa, the timing is started and maintained for 15-25 minutes. The argon pressure is then adjusted to 0.3-0.5 MPa. After the static argon blowing is completed, 1.1-1.2 meters of calcium silicon wire per ton of steel is added, and the post-treatment temperature is 1570-1580°C.

[0014] Based on the above technical solution, further, the diameter of the carbon cored wire is 10-10.5 mm.

[0015] Based on the above technical scheme, further, the continuous casting is: continuous casting 1530~1535℃, platform temperature 1560~1570℃, pulling speed 0.42~0.43m / min, tundish H control ≤2ppm, crystallizer electromagnetic stirring current 400~410A, end electromagnetic stirring current 330~340A, frequency 7~8Hz; full process protection casting, crystallizer protective slag uses medium carbon steel protective slag; light pressure is applied to put in the 2nd, 3rd and 4th rollers, and the reduction amount is 3~3.1mm, 4~4.1mm and 4~4.1mm respectively; the billet cutting adopts a combination of automatic and manual methods, the continuous casting billet is padded with red steel, and the billets from two furnaces are pressed up to ensure flatness, and the holding time is 30~40h.

[0016] Based on the above technical solution, further, the heating process is as follows: the temperature entering the heating furnace is 350℃~520℃, the temperature of the preheating section is required to be 650℃~700℃, and the time is 1.2~1.5h; the temperature of the heating section 2 is required to be 850℃~870℃, and the time is 1.2~1.5h; the temperature of the heating section 1 is required to be 1210℃~1240℃, and the time is 1.2~1.5h; the temperature of the soaking section is required to be 1200℃~1230℃, and the time is 1.2~1.5h; the steel tapping temperature is 1180℃~1210℃.

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

[0018] Initial rolling: BD initial rolling mill is used for initial rolling, and 7 passes are rolled with the following reduction amounts: steel turning → 1st pass 70~70.1mm, 2nd pass 75~75.1mm, steel turning → 3rd pass 58~58.1mm, 4th pass 58~58.1mm, steel turning → 5th pass 60~60.1mm, 6th pass 59~59.1mm, steel turning → 7th pass 76~76.1mm, and then enters the continuous rolling mill for rolling.

[0019] Continuous rolling process: the initial rolling process produces an intermediate billet with a height of 268-268.1mm and a width of 232-232.1mm; the first pass has a height of 229-229.1mm and a width of 245-245.1mm; the second pass has a height of 192-192.1mm and a width of 235-235.1mm; the third pass has a height of 200-200.1mm and a width of 195-195.1mm; the fourth pass has a height of 160-160.1mm and a width of 214.7-214.8mm; the fifth pass has a height of 229-229.1mm and a width of 245-245.1mm; the fifth pass has a height of 192-192.1mm and a width of 235-235.1mm; the fifth pass has a height of 200-200.1mm and a width of 195-195.1mm; the fifth pass has a height of 160-160.1mm and a width of 214.7-214.8mm; The second high is 168~168.1mm, and the width is 174.6~174.7mm; the sixth high is 120~120.1mm, and the width is 187.6~187.7mm; the seventh high is 142~142.1mm, and the width is 138.5~138.6mm; the eighth high is 111~111.1mm, and the width is 151.5~151.6mm; the ninth high is 122~122.05mm, and the width is 122~122.05mm. The finished product is produced after the 9th pass.

[0020] Based on the above technical solution, further, the insulation process is: steel insulation, pit entry temperature ≥ 560°C, pit exit temperature ≤ 200°C, insulation time ≥ 48h.

[0021] Based on the above technical solution, further, the steel after insulation is subjected to heat treatment, and the heat treatment process includes the following steps:

[0022] 1) Quenching: 880-920℃, holding time 0.8-1.0h, oil cooling;

[0023] 2) Tempering: 620-640℃, keep warm for 1.8-2.2h, air cool.

[0024] Beneficial effects of the present invention:

[0025] (1) The converter + LF + RH + continuous casting smelting process and rolling process are used to produce steel bars for steam turbine impellers. The production specification is Φ120mm, which meets the mechanical performance requirements and ensures the purity of the steel.

[0026] (2) Reasonable component design and production process ensure surface quality and impact performance.

[0027] (3) The macrostructure, non-metallic inclusions and mechanical properties of the finished steel meet the requirements of high-end products. DETAILED DESCRIPTION

[0028] 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.

[0029] Example 1

[0030] 1Chemical composition

[0031] The chemical composition, by mass percentage, is C: 0.34%, Si: 0.25%, Mn: 0.50%, P: 0.010%, S: 0.005%, Cr: 1.10%, Ni: 0.05%, Cu: 0.02%, Mo: 0.25%, V: 0.15%, and the balance is iron and inevitable impurities.

[0032] 2 Design of production process parameters for converter continuous casting of steel for turbine impeller

[0033] Process route: converter smelting → refining outside the furnace (LF+RH) → continuous casting → heating in a heating furnace → rolling → insulation.

[0034] (1) Converter smelting: The raw materials are 28% scrap steel and 72% molten iron by mass. The raw materials are oxidized by oxygen and subjected to intense boiling. The tapping temperature is 1688°C, the oxygen supply time is 18 minutes, the operation time is 50 minutes, the final oxygen content is 625ppm, the carbon content is 0.14% and the phosphorus content is 0.005% at the time of tapping. Auxiliary materials and alloys are added when 1 / 4 of the steel is tapped. The amount of alloy added per ton of steel is: 6.2 kg / t silicon manganese, 0.92 kg / t ferrosilicon, 1.6 kg / t ferroaluminum, 2.8 kg / t ferrovanadium, and 3.9 kg / t ferromolybdenum. The amount of auxiliary materials added per ton of steel is: 11.2 kg / t limestone, 34 kg / t activated limestone, 19 kg / t dolomite, and 11.2 kg / t sintered ore.

[0035] (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 for chemical composition analysis. Add alloy according to the target chemical composition value and add carbon nitrate carburizer for carbonization. The alloy and carbon nitrate carburizer should be added to the argon flow to promote rapid melting and homogenization of the alloy and carbon nitrate carburizer. When the molten steel temperature reaches 1590℃, add 2kg / t diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1615℃, take the second sample for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, add 0.8kg / t diffusion deoxidizer to continue slag adjustment. Add alloy: 3.2kg / t high carbon ferrochromium, 0.36kg / t ferrosilicon, 0.38kg / t aluminum particles, and 1.1kg / t carbon cored wire (diameter 10mm). Maintain the slag basicity at a pH of 2.8 and a viscosity of 0.95 Pa.s. Continue smelting the white slag for 25 minutes. When the molten steel temperature reaches 1635°C, begin static argon blowing for 15 minutes. The ladle clearance is 410 mm, and the slag thickness is 80 mm. Supplementary materials include 6.2 kg / t of active lime and 0.9 kg / t of coke recarburizer.

[0036] (3) RH refining: Before starting the vacuum pump, the argon pressure is controlled at 0.15 MPa. The molten steel is not exposed to the slight movement of the slag surface. The ladle clearance is 410 mm and the slag thickness is 98 mm. When the vacuum reaches 95 Pa, the timing is started and maintained for 20 minutes. The argon pressure is adjusted to 0.4 MPa. After the static argon blowing is completed, 1.1 meters / t of calcium silicon wire (diameter 10 mm) is added. The temperature after treatment is 1575°C.

[0037] (4) Continuous casting: continuous casting at 1533℃, platform temperature at 1565℃, casting speed at 0.42m / min, tundish H control at 1.4ppm, crystallizer electromagnetic stirring current at 405A, terminal electromagnetic stirring current at 335A, frequency at 7Hz; 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 37h.

[0038] (5) Heating process

[0039] Heating process: The temperature entering the heating furnace is 450℃, the preheating section temperature is required to be 680℃, and the time is 1.4h; the temperature of the heating section 2 is required to be 860℃, and the time is 1.4h; the temperature of the heating section 1 is required to be 1230℃, and the time is 1.3h; the temperature of the soaking section is required to be 1220℃, and the time is 1.3h; the steel tapping temperature is 1195℃.

[0040] (6) Initial rolling: The steel is rolled using the BD initial rolling mill and rolled for 7 passes with the following reductions: steel turning → 70 mm for the first pass, 75 mm for the second pass, steel turning → 58 mm for the third pass, 58 mm for the fourth pass, steel turning → 60 mm for the fifth pass, 59 mm for the sixth pass, and 76 mm for the seventh pass. The steel is then rolled in the continuous rolling mill.

[0041] (7) Continuous rolling process:

[0042] Rolling process: The intermediate billet produced by initial rolling is 268mm high and 232mm wide; the first pass is 229mm high and 245mm wide, the second pass is 192mm high and 235mm wide; the third pass is 200mm high and 195mm wide; the fourth pass is 160mm high and 214.7mm wide; the fifth pass is 168mm high and 174.6mm wide; the sixth pass is 120mm high and 187.6mm wide; the seventh pass is 142mm high and 138.5mm wide; the eighth pass is 111mm high and 151.5mm wide; the ninth pass is 122.04mm high and 122.04mm wide, and the finished product is produced after the 9th pass.

[0043] (8) Insulation process

[0044] Insulation process: Steel insulation, pit entry temperature 580℃, pit exit temperature 175℃, insulation time 55h.

[0045] (9) Heat treatment process

[0046] The steel material after heat preservation is subjected to heat treatment, and the heat treatment comprises the following steps:

[0047] 1) Quenching: 900℃, hold for 1h, oil cooling;

[0048] 2) Tempering: 630℃, keep warm for 2.0h, air cool.

[0049] Example 2

[0050] 1. Component optimization design

[0051] The chemical composition, by mass percentage, is C: 0.33%, Si: 0.25%, Mn: 0.50%, P: 0.011%, S: 0.004%, Cr: 1.08%, Ni: 0.05%, Cu: 0.02%, Mo: 0.25%, V: 0.15%, and the balance is iron and inevitable impurities.

[0052] 2 Design of production process parameters for converter continuous casting of steel for turbine impeller

[0053] Process route: converter smelting → refining outside the furnace (LF+RH) → continuous casting → heating in a heating furnace → rolling → insulation.

[0054] (1) Converter smelting: The raw materials are 27% scrap steel and 73% molten iron by mass. The raw materials are oxidized by oxygen and subjected to intense boiling. The tapping temperature is 1688°C, the oxygen supply time is 18 minutes, the operation time is 50 minutes, the final oxygen content is 625ppm, the carbon content is 0.14% and the phosphorus content is 0.006% at the time of tapping. Auxiliary materials and alloys are added when 1 / 4 of the steel is tapped. The amount of alloy added per ton of steel is: 6.2 kg / t silicon manganese, 0.92 kg / t ferrosilicon, 1.6 kg / t ferroaluminum, 2.8 kg / t ferrovanadium, and 3.9 kg / t ferromolybdenum. The amount of auxiliary materials added per ton of steel is: 11.3 kg / t limestone, 35 kg / t activated limestone, 19 kg / t dolomite, and 11.2 kg / t sintered ore.

[0055] (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 for chemical composition analysis. Add alloy according to the target chemical composition value and add carbon nitrate carburizer for carbonization. The alloy and carbon nitrate carburizer should be added to the argon flow to promote rapid melting and homogenization of the alloy and carbon nitrate carburizer. When the molten steel temperature reaches 1592℃, add 1.5kg / t diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1615℃, take the second sample for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, add 0.8kg / t diffusion deoxidizer and continue slag adjustment. Add alloy: 3.2kg / t high carbon ferrochromium, 0.36kg / t ferrosilicon, 0.38kg / t aluminum particles, 1.1kg / t carbon cored wire (diameter 10mm). Maintain the slag basicity at a pH of 2.8 and a viscosity of 0.95 Pa.s. Continue smelting the white slag for 26 minutes. When the molten steel temperature reaches 1636°C, begin static argon blowing for 15 minutes. The ladle clearance is 405 mm, and the slag thickness is 82 mm. Supplementary materials include 6.2 kg / t of active lime and 0.9 kg / t of coke recarburizer.

[0056] (3) RH refining: Before starting the vacuum pump, the argon pressure was controlled at 0.15 MPa. The molten steel was not exposed to the slight movement of the slag surface. The ladle clearance was 408 mm and the slag thickness was 99 mm. When the vacuum reached 95 Pa, the timing was started and maintained for 18 minutes. The argon pressure was adjusted to 0.3 MPa. After the static argon blowing was completed, 1.1 meters / t of calcium silicon wire (10 mm diameter) was added. The temperature after treatment was 1576°C.

[0057] (4) Continuous casting: continuous casting at 1532℃, platform temperature at 1565℃, casting speed at 0.42m / min, tundish H control at 1.2ppm, crystallizer electromagnetic stirring current at 405A, terminal electromagnetic stirring current at 336A, 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.

[0058] (5) Heating process

[0059] Heating process: The temperature entering the heating furnace is 460℃, the temperature of the preheating section is required to be 675℃, and the time is 1.4h; the temperature of the heating section 2 is required to be 860℃, and the time is 1.4h; the temperature of the heating section 1 is required to be 1232℃, and the time is 1.3h; the temperature of the soaking section is required to be 1220℃, and the time is 1.3h; the steel tapping temperature is 1200℃.

[0060] (6) Initial rolling: The steel is rolled using the BD initial rolling mill and rolled for 7 passes with the following reductions: steel turning → 70 mm for the first pass, 75 mm for the second pass, steel turning → 58 mm for the third pass, 58 mm for the fourth pass, steel turning → 60 mm for the fifth pass, 59 mm for the sixth pass, and 76 mm for the seventh pass. The steel is then rolled in the continuous rolling mill.

[0061] (7) Continuous rolling process:

[0062] Rolling process: The intermediate billet produced by initial rolling is 268mm high and 232mm wide; the first pass is 229mm high and 245mm wide, the second pass is 192mm high and 235mm wide; the third pass is 200mm high and 195mm wide; the fourth pass is 160mm high and 214.7mm wide; the fifth pass is 168mm high and 174.6mm wide; the sixth pass is 120mm high and 187.6mm wide; the seventh pass is 142mm high and 138.5mm wide; the eighth pass is 111mm high and 151.5mm wide; the ninth pass is 122.04mm high and 122.04mm wide, and the finished product is produced after the 9th pass.

[0063] (8) Insulation process

[0064] Insulation process: Steel insulation, pit entry temperature 580℃, pit exit temperature 150℃, insulation time 50h.

[0065] (9) Heat treatment process

[0066] The steel material after heat preservation is subjected to heat treatment, and the heat treatment comprises the following steps:

[0067] 1) Quenching: 900℃, holding time 1.0h, oil cooling;

[0068] 2) Tempering: 630℃, keep warm for 2h, air cool.

[0069] Example 3

[0070] 1. Component optimization design

[0071] The chemical composition, by mass percentage, is C: 0.34%, Si: 0.26%, Mn: 0.49%, P: 0.010%, S: 0.005%, Cr: 1.10%, Ni: 0.05%, Cu: 0.03%, Mo: 0.25%, V: 0.15%, and the balance is iron and inevitable impurities.

[0072] 2 Design of production process parameters for converter continuous casting of steel for turbine impeller

[0073] Process route: converter smelting → refining outside the furnace (LF+RH) → continuous casting → heating in a heating furnace → rolling → insulation.

[0074] (1) Converter smelting: The raw materials are 28% scrap steel and 72% molten iron by mass. The raw materials are oxidized by oxygen and subjected to intense boiling. The tapping temperature is 1690°C, the oxygen supply time is 17 minutes, the operation time is 49 minutes, the final oxygen content is 630ppm, the carbon content is 0.14% and the phosphorus content is 0.006% at the time of tapping. Auxiliary materials and alloys are added when 1 / 4 of the steel is tapped. The amount of alloy added per ton of steel is: 6.2 kg / t silicon manganese, 0.92 kg / t ferrosilicon, 1.6 kg / t ferroaluminum, 2.8 kg / t ferrovanadium, and 3.9 kg / t ferromolybdenum. The amount of auxiliary materials added per ton of steel is: 11.5 kg / t limestone, 35 kg / t activated limestone, 19 kg / t dolomite, and 11.3 kg / t sintered ore.

[0075] (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 for chemical composition analysis. Add alloy according to the target chemical composition value and add carbon nitrate carburizer for carbonization. The alloy and carbon nitrate carburizer should be added to the argon flow to promote rapid melting and homogenization of the alloy and carbon nitrate carburizer. When the molten steel temperature reaches 1592℃, add 1.6kg / t diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1614℃, take the second sample for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, add 0.8kg / t diffusion deoxidizer to continue slag adjustment. Add alloy: 3.2kg / t high carbon ferrochromium, 0.36kg / t ferrosilicon, 0.39kg / t aluminum particles, and 1.1kg / t carbon cored wire (diameter 10mm). Maintain the slag basicity at a pH of 2.9 and a viscosity of 1.10 Pa.s. Continue smelting the white slag for 26 minutes. When the molten steel temperature reaches 1635°C, begin static argon blowing for 15 minutes. The ladle clearance is 410 mm, and the slag thickness is 82 mm. Additional auxiliary materials include 6.2 kg / t of active lime and 0.9 kg / t of coke recarburizer.

[0076] (3) RH refining: Before starting the vacuum pump, the argon pressure is controlled at 0.2 MPa. The molten steel is not exposed to the slight movement of the slag surface. The ladle clearance is 410 mm and the slag thickness is 98 mm. When the vacuum reaches 98 Pa, the timing is started and maintained for 20 minutes. The argon pressure is adjusted to 0.4 MPa. After the static argon blowing is completed, 1.1 meters / t of calcium silicon wire (diameter 10 mm) is added. The temperature after treatment is 1575°C.

[0077] (4) Continuous casting: continuous casting at 1532℃, platform temperature at 1565℃, casting speed at 0.42m / min, tundish H control at 1.5ppm, crystallizer electromagnetic stirring current at 404A, terminal electromagnetic stirring current at 335A, frequency at 7Hz; 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 34h.

[0078] (5) Heating process

[0079] Heating process: The temperature entering the heating furnace is 460℃, the temperature of the preheating section is required to be 675℃, and the time is 1.3h; the temperature of the heating section 2 is required to be 860℃, and the time is 1.3h; the temperature of the heating section 1 is required to be 1230℃, and the time is 1.3h; the temperature of the soaking section is required to be 1225℃, and the time is 1.3h; the steel tapping temperature is 1196℃.

[0080] (6) Initial rolling: The steel is rolled using the BD initial rolling mill and rolled for 7 passes with the following reductions: steel turning → 70 mm for the first pass, 75 mm for the second pass, steel turning → 58 mm for the third pass, 58 mm for the fourth pass, steel turning → 60 mm for the fifth pass, 59 mm for the sixth pass, and 76 mm for the seventh pass. The steel is then rolled in the continuous rolling mill.

[0081] (7) Continuous rolling process:

[0082] Rolling process: The intermediate billet produced by initial rolling is 268mm high and 232mm wide; the first pass is 229mm high and 245mm wide, the second pass is 192mm high and 235mm wide; the third pass is 200mm high and 195mm wide; the fourth pass is 160mm high and 214.7mm wide; the fifth pass is 168mm high and 174.6mm wide; the sixth pass is 120mm high and 187.6mm wide; the seventh pass is 142mm high and 138.5mm wide; the eighth pass is 111mm high and 151.5mm wide; the ninth pass is 122.04mm high and 122.04mm wide, and the finished product is produced after the 9th pass.

[0083] (8) Insulation process

[0084] Insulation process: Steel insulation, pit entry temperature 585℃, pit exit temperature 145℃, insulation time 52h.

[0085] (9) Heat treatment process

[0086] The steel material after heat preservation is subjected to heat treatment, and the heat treatment comprises the following steps:

[0087] 1) Quenching: 900℃, hold for 1h, oil cooling;

[0088] 2) Tempering: 630℃, keep warm for 2h, air cool.

[0089] Example 4

[0090] 1. Component optimization design

[0091] The chemical composition, by mass percentage, is C: 0.35%, Si: 0.25%, Mn: 0.52%, P: 0.010%, S: 0.004%, Cr: 1.10%, Ni: 0.06%, Cu: 0.04%, Mo: 0.24%, V: 0.14%, and the balance is iron and inevitable impurities.

[0092] 2 Design of production process parameters for converter continuous casting of steel for turbine impeller

[0093] Process route: converter smelting → refining outside the furnace (LF+RH) → continuous casting → heating in a heating furnace → rolling → insulation.

[0094] (1) Converter smelting: The raw materials are 27% scrap steel and 73% molten iron by mass. The raw materials are oxidized by oxygen and subjected to intense boiling. The tapping temperature is 1690°C, the oxygen supply time is 17 minutes, the operation time is 50 minutes, the final oxygen content is 630ppm, the carbon content is 0.14% and the phosphorus content is 0.006% at the time of tapping. Auxiliary materials and alloys are added when 1 / 4 of the steel is tapped. The amount of alloy added per ton of steel is: 6.2 kg / t silicon manganese, 0.93 kg / t ferrosilicon, 1.6 kg / t ferroaluminum, 2.8 kg / t ferrovanadium, and 3.9 kg / t ferromolybdenum. The amount of auxiliary materials added per ton of steel is: 11.4 kg / t limestone, 35 kg / t activated limestone, 19 kg / t dolomite, and 11.3 kg / t sintered ore.

[0095] (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 for chemical composition analysis. Add alloy according to the target chemical composition value and add carbon nitrate carburizer for carbonization. The alloy and carbon nitrate carburizer should be added to the argon flow to promote rapid melting and homogenization of the alloy and carbon nitrate carburizer. When the molten steel temperature reaches 1595℃, add 2kg / t diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1614℃, take the second sample for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, add 0.8kg / t diffusion deoxidizer to continue slag adjustment. Add alloy: 3.2kg / t high carbon ferrochromium, 0.36kg / t ferrosilicon, 0.38kg / t aluminum particles, and 1.1kg / t carbon cored wire (diameter 10mm). Maintain the slag basicity at a pH of 3.0 and a viscosity of 1.00 Pa.s while continuing to smelt the white slag for 25 minutes. When the molten steel temperature reaches 1635°C, begin static argon blowing for 14 minutes. The ladle clearance is 410 mm, and the slag thickness is 82 mm. Supplementary materials include 6.2 kg / t of active lime and 0.9 kg / t of coke butane recarburizer.

[0096] (3) RH refining: Before starting the vacuum pump, the argon pressure is controlled at 0.2 MPa. The molten steel is not exposed to the slight movement of the slag surface. The ladle clearance is 410 mm and the slag thickness is 98 mm. When the vacuum reaches 95 Pa, the timing is started and maintained for 20 minutes. The argon pressure is adjusted to 0.4 MPa. After the static argon blowing is completed, 1.1 meters / t of calcium silicon wire (diameter 10 mm) is added. The temperature after treatment is 1576°C.

[0097] (4) Continuous casting: continuous casting temperature 1533℃, platform temperature 1564℃, casting speed 0.42m / min, tundish H control 1.5ppm, crystallizer electromagnetic stirring current 406A, end electromagnetic stirring current 335A, frequency 7Hz; 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 460℃, the preheating section temperature is required to be 670℃, and the time is 1.4h; the temperature of the heating section 2 is required to be 860℃, and the time is 1.3h; the temperature of the heating section 1 is required to be 1230℃, and the time is 1.3h; the temperature of the soaking section is required to be 1220℃, and the time is 1.3h; the steel tapping temperature is 1197℃.

[0100] (6) Initial rolling: The steel is rolled using the BD initial rolling mill and rolled for 7 passes with the following reductions: steel turning → 70 mm for the first pass, 75 mm for the second pass, steel turning → 58 mm for the third pass, 58 mm for the fourth pass, steel turning → 60 mm for the fifth pass, 59 mm for the sixth pass, and 76 mm for the seventh pass. The steel is then rolled in the continuous rolling mill.

[0101] (7) Continuous rolling process:

[0102] Rolling process: The intermediate billet produced by initial rolling is 268mm high and 232mm wide; the first pass is 229mm high and 245mm wide, the second pass is 192mm high and 235mm wide; the third pass is 200mm high and 195mm wide; the fourth pass is 160mm high and 214.7mm wide; the fifth pass is 168mm high and 174.6mm wide; the sixth pass is 120mm high and 187.6mm wide; the seventh pass is 142mm high and 138.5mm wide; the eighth pass is 111mm high and 151.5mm wide; the ninth pass is 122.04mm high and 122.04mm wide, and the finished product is produced after the 9th pass.

[0103] (8) Insulation process

[0104] Insulation process: Steel insulation, pit entry temperature 575℃, pit exit temperature 150℃, insulation time 50h.

[0105] Example 5

[0106] 1. Component optimization design

[0107] The chemical composition, by mass percentage, is C: 0.34%, Si: 0.25%, Mn: 0.50%, P: 0.010%, S: 0.005%, Cr: 1.10%, Ni: 0.05%, Cu: 0.04%, Mo: 0.24%, V: 0.15%, and the balance is iron and inevitable impurities.

[0108] 2 Design of production process parameters for converter continuous casting of steel for turbine impeller

[0109] Process route: converter smelting → refining outside the furnace (LF+RH) → continuous casting → heating in a heating furnace → rolling → insulation.

[0110] (1) Converter smelting: The raw materials are 27% scrap steel and 73% molten iron by mass. The raw materials are oxidized with oxygen and subjected to intense boiling. The tapping temperature is 1690°C, the oxygen supply time is 17 minutes, the working time is 50 minutes, the final oxygen content is 630 ppm, the carbon content is 0.14% at tapping, and the phosphorus content is 0.005%. Auxiliary materials and alloys are added when 1 / 4 of the steel is tapped. The amount of alloy added per ton of steel is: 6.2 kg / t silicon manganese, 0.93 kg / t ferrosilicon, 1.6 kg / t ferroaluminum, 2.8 kg / t ferrovanadium, and 3.9 kg / t ferromolybdenum. The amount of auxiliary materials added per ton of steel is: 11.3 kg / t limestone, 35 kg / t activated limestone, 19 kg / t dolomite, and 11.3 kg / t sintered ore.

[0111] (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 for chemical composition analysis. Add alloy according to the target chemical composition value and add carbon nitrate carburizer for carbonization. The alloy and carbon nitrate carburizer should be added to the argon flow to promote rapid melting and homogenization of the alloy and carbon nitrate carburizer. When the molten steel temperature reaches 1597℃, add 1.8kg / t diffusion deoxidizer for diffusion deoxidation. Close the furnace door for 10 minutes. When the molten steel temperature reaches 1616℃, take the second sample for chemical composition analysis to confirm the deviation of the content of each chemical element from the target value. After the second sample is taken, add 0.8kg / t diffusion deoxidizer to continue slag adjustment. Add alloy: 3.2kg / t high carbon ferrochromium, 0.36kg / t ferrosilicon, 0.39kg / t aluminum particles, and 1.1kg / t carbon cored wire (diameter 10mm). Maintain the slag basicity at a pH of 3.2 and a viscosity of 0.96 Pa.s. Continue smelting the white slag for 26 minutes. When the molten steel temperature reaches 1636°C, begin static argon blowing for 15 minutes. The ladle clearance is 412 mm, and the slag thickness is 83 mm. Additional auxiliary materials include 6.2 kg / t of active lime and 0.9 kg / t of coke recarburizer.

[0112] (3) RH refining: Before starting the vacuum pump, the argon pressure is controlled at 0.2 MPa. The molten steel is not exposed to the slight movement of the slag surface. The ladle clearance is 410 mm and the slag thickness is 98 mm. When the vacuum reaches 96 Pa, the timing is started and maintained for 20 minutes. The argon pressure is adjusted to 0.4 MPa. After the static argon blowing is completed, 1.1 meters / t of calcium silicon wire (diameter 10 mm) is added. The temperature after treatment is 1574°C.

[0113] (4) Continuous casting: continuous casting temperature 1532℃, platform temperature 1564℃, casting speed 0.42m / min, tundish H control 1.5ppm, crystallizer electromagnetic stirring current 402A, end electromagnetic stirring current 334A, 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 34h.

[0114] (5) Heating process

[0115] Heating process: The temperature entering the heating furnace is 460℃, the temperature of the preheating section is required to be 680℃, and the time is 1.3h; the temperature of the heating section 2 is required to be 860℃, and the time is 1.3h; the temperature of the heating section 1 is required to be 1235℃, and the time is 1.3h; the temperature of the soaking section is required to be 1223℃, and the time is 1.3h; the steel tapping temperature is 1196℃.

[0116] (6) Initial rolling: The steel is rolled using a 1150mm BD initial rolling mill, and rolled for 7 passes with the following reductions: steel turning → 70mm for the first pass, 75mm for the second pass, steel turning → 58mm for the third pass, 58mm for the fourth pass, steel turning → 60mm for the fifth pass, 59mm for the sixth pass, and 76mm for the seventh pass. The steel is then rolled in the continuous rolling mill.

[0117] (7) Continuous rolling process:

[0118] Rolling process: The intermediate billet produced by initial rolling is 268mm high and 232mm wide; the first pass is 229mm high and 245mm wide, the second pass is 192mm high and 235mm wide; the third pass is 200mm high and 195mm wide; the fourth pass is 160mm high and 214.7mm wide; the fifth pass is 168mm high and 174.6mm wide; the sixth pass is 120mm high and 187.6mm wide; the seventh pass is 142mm high and 138.5mm wide; the eighth pass is 111mm high and 151.5mm wide; the ninth pass is 122.04mm high and 122.04mm wide, and the finished product is produced after the 9th pass.

[0119] (8) Insulation process

[0120] Insulation process: Steel insulation, pit entry temperature 590℃, pit exit temperature 160℃, insulation time 53h.

[0121] (9) Heat treatment process

[0122] The steel material after heat preservation is subjected to heat treatment, and the heat treatment comprises the following steps:

[0123] 1) Quenching: 900℃, holding time 1.0h, oil cooling;

[0124] 2) Tempering: 630℃, keep warm for 2h, air cool.

[0125] The inspection results of the finished products of Examples 1 to 5 are as follows: 2 samples were inspected for each heat of steel.

[0126] (1) Φ120mm specification macrostructure (finished steel obtained by heat preservation process)

[0127] (2) Φ120mm non-metallic inclusions (finished steel obtained by thermal insulation process)

[0128] (3) Mechanical properties of Φ120mm specification (finished steel obtained after heat treatment)

Claims

1. A steel bar for a steam turbine impeller, characterized in that: In percentage by mass, the components are C: 0.31% to 0.36%, Si: 0.22% to 0.35%, Mn: 0.45% to 0.60%, P: ≤0.013%, S: ≤0.008%, Cr: 1.05% to 1.20%, Ni: ≤0.20%, Cu: ≤0.10%, Mo: 0.21% to 0.28%, V: 0.11% to 0.18%, and the balance is Fe and unavoidable impurities.

2. The method for preparing a steel bar for a steam turbine impeller according to claim 1, characterized in that: The method comprises: converter smelting→LF refining→RH refining→continuous casting→heating process in a heating furnace→rolling process→insulation process.

3. The preparation method according to claim 2, characterized in that The converter smelting is as follows: scrap steel and molten iron are used for smelting, wherein scrap steel accounts for 26-30% by mass and molten iron accounts for 70-74% by mass; oxygen oxidation and intense boiling are performed, the tapping temperature is 1685-1695° C., the oxygen supply time is 15-20 minutes, the operation time is 45-55 minutes, the end oxygen is 620-640 ppm, C is 0.13-0.15% when tapping, P is ≤0.007%, and auxiliary agent is added when 1 / 4-1 / 3 of the tapping is performed. Materials and alloys; alloy addition per ton of steel: silicon manganese 6.2-6.3Kg / t, ferrosilicon 0.9-0.95Kg / t, ferroaluminum 1.6-1.7Kg / t, ferrovanadium 2.8-2.9Kg / t, ferromolybdenum 3.8-4.0Kg / t; auxiliary materials addition per ton of steel: limestone 11-11.5Kg / t, activated limestone 34-35Kg / t, dolomite 19-20Kg / t, sintered ore 11-11.5Kg / t.

4. The preparation method according to claim 2, characterized in that The LF refining comprises the following steps: using a high current of 20,000 to 25,000 A to heat and melt the slag; when the slag surface fluctuates and the molten steel and the arc are not exposed, adding active lime; taking a first sample for chemical composition analysis after 5 to 7 minutes; adding alloy according to the target chemical composition value; and adding a coke carburizer for carbonization; adding a diffusion deoxidizer of 1 to 3 kg / t steel for diffusion deoxidation when the molten steel temperature reaches 1580 to 1600° C.; closing the furnace door for 10 to 12 minutes; taking a second sample for chemical composition analysis when the molten steel temperature reaches 1610 to 1620° C. to confirm the deviation of the content of each chemical element from the target value; after the second sample is taken, adding a diffusion deoxidizer of 0.5 to 1 kg / t steel to continue slag adjustment. ;Additional alloy addition per ton of steel: 3.2-3.3 kg / t of high-carbon ferrochrome, 0.35-0.37 kg / t of ferrosilicon, 0.38-0.40 kg / t of aluminum granules, and 1.1-1.15 kg / t of carbon-coated wire; maintain the slag alkalinity pH value at 2.5-3.5 and the slag viscosity at 0.80-1.20 Pa.s, while continuing to slag smelting for 20-30 minutes. When the molten steel temperature reaches 1630-1640°C, start static argon blowing for 10-20 minutes, with a ladle clearance of 400-420 mm and a slag thickness of 80-85 mm;Additional auxiliary materials addition per ton of steel: 6.2-6.3 kg / t of active lime and 0.8-1.0 kg / t of coke butane recarburizer; The RH refining is as follows: before starting the vacuum pump, the argon pressure is controlled at 0.1-0.3 MPa, the slag surface is slightly moved so that the molten steel is not exposed, the ladle clearance is 400-420 mm, and the slag thickness is 95-105 mm; when the vacuum reaches 90-100 Pa, the timing is started and maintained for 15-25 minutes, the argon pressure is adjusted to 0.3-0.5 MPa, and after the static argon blowing is completed, 1.1-1.2 meters / t of silicon calcium wire is added, and the temperature after treatment is 1570-1580°C.

5. The preparation method according to claim 4, characterized in that The alloy and the coke butadiene recarburizer are added to the argon gas flow; the diameter of the carbon cored wire is 10-10.5 mm.

6. The preparation method according to claim 2, characterized in that The continuous casting is as follows: continuous pouring at 1530-1535°C, platform temperature at 1560-1570°C, pulling speed at 0.42-0.43 m / min, tundish H control ≤2ppm, crystallizer electromagnetic stirring current at 400-410A, terminal electromagnetic stirring current at 330-340A, and frequency at 7-8Hz; 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 3-3.1mm, 4-4.1mm, and 4-4.1mm, 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.

7. The preparation method according to claim 2, characterized in that The heating process of the heating furnace is as follows: the temperature entering the heating furnace is 350℃~520℃, the temperature of the preheating section is required to be 650℃~700℃, and the time is 1.2~1.5h; the temperature of the heating section 2 is required to be 850℃~870℃, and the time is 1.2~1.5h; the temperature of the heating section 1 is required to be 1210℃~1240℃, and the time is 1.2~1.5h; the temperature of the soaking section is required to be 1200℃~1230℃, and the time is 1.2~1.5h; the steel tapping temperature is 1180℃~1210℃.

8. The preparation method according to claim 2, characterized in that The rolling process includes blooming and continuous rolling; Blooming: BD blooming mill is used for blooming, and 7 passes are rolled with the following reductions: steel turning → 1st pass 70-70.1mm, 2nd pass 75-75.1mm, steel turning → 3rd pass 58-58.1mm, 4th pass 58-58.1mm, steel turning → 5th pass 60-60.1mm, 6th pass 59-59.1mm, steel turning → 7th pass 76-76.1mm, and then enters the continuous rolling mill for rolling; Continuous rolling: the initial rolling process produces an intermediate billet with a height of 268-268.1mm and a width of 232-232.1mm; the first pass has a height of 229-229.1mm and a width of 245-245.1mm; the second pass has a height of 192-192.1mm and a width of 235-235.1mm; the third pass has a height of 200-200.1mm and a width of 195-195.1mm; the fourth pass has a height of 160-160.1mm and a width of 214.7-214.8mm; the fifth pass has a height of 229-229.1mm and a width of 245-245.1mm; the fifth pass has a height of 192-192.1mm and a width of 235-235.1mm; the fifth pass has a height of 200-200.1mm and a width of 195-195.1mm; the fourth pass has a height of 160-160.1mm and a width of 214.7-214.8mm; the fifth pass has a height of 229-229.1mm and a width of 245-245.1mm; the first pass has a height of 229-229.1mm and a width of 245-245.1mm; the second pass has a height of 192-192.1mm and a width of 235-235.1mm; the third pass has a height of 200-200.1mm and a width of 195-195.1mm; the fourth pass has a height of 160-160.1mm and a width of 214.7-214.8mm; the fifth pass has a height of 229-229.1mm The height is 168~168.1mm and the width is 174.6~174.7mm; the 6th pass is 120~120.1mm high and 187.6~187.7mm wide; the 7th pass is 142~142.1mm high and 138.5~138.6mm wide; the 8th pass is 111~111.1mm high and 151.5~151.6mm wide; the 9th pass is 122~122.05mm high and 122~122.05mm wide. The finished product is produced after the 9th pass.

9. The preparation method according to claim 2, characterized in that The insulation process is: pit entry temperature ≥ 560°C, pit exit temperature ≤ 200°C, and insulation time ≥ 48h.

10. The preparation method according to claim 2, characterized in that The steel material after heat preservation is further subjected to heat treatment, and the heat treatment comprises the following steps: 1) Quenching: 880-920℃, holding time 0.8-1.0h, oil cooling; 2) Tempering: 620-640℃, keep warm for 1.8-2.2h, air cool.

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