Steel bar for subcritical steam guide pipe and production method of steel bar

Abstract

The invention belongs to the technical field of metallurgical manufacturing, and particularly relates to a steel bar for a subcritical steam conduit and a production method thereof, and the steel comprises the following chemical components in percentage by weight: 0.09%-0.13% of C, 0.22%-0.35% of Si, 0.45%-0.60% of Mn, less than or equal to 0.016% of P, less than or equal to 0.007% of S, 0.95%-1.10% of Cr, less than or equal to 0.25% of Ni, 0.26%-0.33% of Mo, 0.16%-0.25% of V, less than or equal to 0.15% of Cu and the balance of Fe and inevitable impurities. The steel bar for the subcritical steam guide pipe is produced through the ecological electric furnace, LF, RH and continuous casting smelting process and the rolling process, the mechanical property requirement is met, and the steel purity is guaranteed.

Description

Technical Field

[0001] The present invention belongs to the technical field of metallurgical manufacturing, and particularly relates to a steel bar for a subcritical steam conduit and a production method thereof. Background Art

[0002] A steam conduit is a device for transporting high-pressure superheated steam. During operation, the steam pipeline is subjected to the temperature and pressure of the superheated steam inside the pipe, as well as additional loads caused by the weight of the steel pipe, the weight of the medium, the weight of the thermal insulation material, etc. The wall temperature of the pipe is close to the temperature of the superheated steam, and it also has to withstand cyclic fatigue loads. Therefore, very high requirements are imposed on the high-temperature resistance, wear resistance, mechanical properties, fatigue life, and steel purity of the steel used for the steam conduit to ensure the normal and safe operation during the operation of the steam conduit.

[0003] In order to meet the usage requirements of steam conduit operations, a steel bar for a subcritical steam conduit with excellent mechanical properties and high steel purity has been designed and developed to meet the requirements of high-end products.

[0004] The steel bar for a subcritical steam conduit is produced by using an ecological electric furnace + LF + RH + continuous casting smelting process and a rolling process, meeting the high-end usage requirements and achieving a breakthrough in the batch production of steel bars for subcritical steam conduits in the ecological electric furnace continuous casting process. Summary of the Invention

[0005] The purpose of the present invention is to provide a steel bar for a subcritical steam conduit and a production method thereof, providing corresponding composition design and process design to produce and manufacture the steel bar for a subcritical steam conduit, which not only ensures the mechanical properties and high steel purity and other indicators of the finished steel of the steel bar for a subcritical steam conduit, but also ensures the surface quality level of the steel bar for a subcritical steam conduit, meeting the quality requirements of the steel bar for a subcritical steam conduit.

[0006] To achieve the above purpose, the present invention is implemented by adopting the following technical solutions: For a steel bar for a subcritical steam conduit, the chemical components in the steel are as follows by weight percentage: C: 0.09% - 0.13%, Si: 0.22% - 0.35%, Mn: 0.45% - 0.60%, P: ≤0.016%, S: ≤0.007%, Cr: 0.95% - 1.10%, Ni: ≤0.25%, Mo: 0.26% - 0.33%, V: 0.16% - 0.25%, Cu: ≤0.15%, and the rest is Fe and unavoidable impurities.

[0007] The macrostructure of the steel bar: general looseness ≤1.5, central looseness ≤1.5, ingot type segregation ≤1.5, general spotted segregation ≤1.0, edge spotted segregation ≤1.0.

[0008] The mechanical properties of the steel bar are: Rm ≥490 MPa, R el ≥245 MPa, A ≥ 22%, z ≥ 50%. At -46 °C, the KU2 impact energy ≥ 71 J.

[0009] For the non-metallic inclusions of the steel bar: Class A is not more than 2.0, Class B is not more than 1.5, Class C is not more than 1.5, Class D is not more than 1.5, and DS is not more than 2.0.

[0010] A production method of a steel bar for a subcritical steam conduit, including an ecological electric furnace, LF furnace refining, RH furnace refining, continuous casting, heating furnace heating, rolling, heat preservation and heat treatment; specifically including the following method steps: 1) Smelting in an ecological electric furnace: Adopt a smelting process with an iron water ratio of 65% - 70% and a scrap steel ratio of 30% - 35% by weight percentage; the iron water inlet temperature is 1290 - 1310 °C, the tapping temperature is 1615 - 1620 °C, the C content at tapping is 0.06% - 0.08%, P ≤ 0.010%. When 1 / 4 - 1 / 3 of the steel is tapped, slag materials, pre-deoxidizers, and alloys are added. The smelting cycle is 40 - 50 min, and the furnace oxygen consumption is 28 - 29 m 3 / t; The alloy addition amount per ton of steel: 4.2 - 4.3 kg of silico-manganese alloy, 12.0 - 12.5 kg of low-carbon ferrochrome, 2 - 2.1 kg of aluminum wire segments (φ10 - 16 mm); The auxiliary material addition amount per ton of steel: 13 - 13.2 kg of coke particles, 5.8 - 6.2 kg of ladle ash, 35 - 36 kg of active lime (φ10 - 70 mm), 13.0 - 13.2 kg of magnesite (φ10 - 60 mm).

[0011] 2) LF furnace refining: The temperature when entering the LF furnace is 1540 - 1550 °C. High current of 35000 - 36000 A is used for heating up and slag melting. When the slag surface fluctuates and the molten steel and arc are not exposed, reactive lime is added. After 5 - 6 minutes, the first sample is taken for chemical composition analysis. Alloys are added according to the median value of the chemical composition range, and carbon is increased to promote the rapid melting and homogenization of the alloys and carbon powder. When the temperature of the molten steel reaches 1610 - 1620 °C, 1.4 - 1.5 kg / t of alumina balls as diffusion deoxidizer are added for diffusion deoxidation. The furnace door is closed for 10 - 13 minutes. When the temperature of the molten steel reaches 1650 - 1660 °C, the second sample is taken for chemical composition analysis to confirm the deviation value of the content of each chemical element from the requirement of the median value of the composition range. After the second sample is taken away, when the temperature of the molten steel reaches 1680 - 1690 °C, it leaves the station. The LF smelting cycle is 90 - 100 minutes, and the free space is 420 - 430 mm. Alloy addition: 2.0 - 2.1 kg / t of high-carbon ferromanganese, 3.7 - 3.8 kg / t of low-carbon ferrochrome, 4.7 - 4.8 kg / t of ferromolybdenum, 4.5 - 4.6 kg / t of ferrovanadium (FeV50 - B). Auxiliary material addition: 1.5 - 1.6 kg / t of silicon carbide, 4 - 4.2 kg / t of reactive lime (φ10 - 70 mm).

[0012] 3) RH furnace refining: The temperature when entering the furnace is 1685 - 1695 °C, and the operation time is 35 - 40 minutes. Before starting the vacuum pump, the argon pressure is controlled at 0.1 - 0.3 MPa, with the slag surface slightly moving and the molten steel not exposed. When the vacuum degree reaches 100 - 110 Pa, timing starts and the holding time is 10 - 15 minutes. At the same time, the argon pressure is adjusted to 0.3 - 0.5 MPa. After the static argon blowing ends, 0.8 - 0.9 kg / t of covering agent is added. The free space is 340 - 360 mm. The temperature for refining and recompression is 1655 - 1665 °C, and the temperature when leaving the station is 1640 - 1650 °C; After breaking the vacuum, 0.84 - 0.86 kg / t of calcium-silicon alloy cored wire (φ14 - 15 mm) is added.

[0013] 4) Continuous casting: The temperature of the ladle when arriving at the station is 1630 - 1640 °C, the H in the tundish is controlled ≤2 ppm, the casting time is 38 - 42 minutes, the superheat is 25 - 30 °C, the drawing speed is 0.42 - 0.43 m / min, and the whole process is protected by casting. The mold powder used is medium-carbon steel mold powder at 3.6 - 3.7 kg / t.

[0014] 5) Heating in the heating furnace: The temperature when entering the heating furnace is 450 - 550 °C. The temperature requirement for the preheating section is 600 - 650 °C, and the time is 1.4 - 1.5 h; The temperature requirement for the heating section 2 is 850 - 870 °C, and the time is 1.3 - 1.5 h; The temperature requirement for the heating section 1 is 1210 - 1240 °C, and the time is 1.3 - 1.5 h; The temperature requirement for the soaking section is 1200 - 1230 °C, and the time is 1.3 - 1.5 h; The tapping temperature is 1180 - 1210 °C.

[0015] 6) Rolling process Primary rolling process: 11 rolling passes, steel turning → Pass 1, width 405.2 - 405.21 mm, height 435 - 435.01 mm, reduction 51 - 51.01 mm, rolling speed 2.3 - 2.31 m / s → Pass 2, width 416.45 - 416.46 mm, height 390 - 390.01 mm, reduction 45 - 45.01 mm, rolling speed 2.5 - 2.51 m / s → steel turning → Pass 3, width 400.94 - 400.95 mm, height 380 - 380.01 mm, reduction 36.45 - 36.46 mm, rolling speed 2.5 - 2.51 m / s → Pass 4, width 408.44 - 408.45 mm, height 355 - 355.01 mm, reduction 25 - 25.01 mm, rolling speed 2.5 - 2.51 m / s → steel turning → Pass 5, width 372.53 - 372.54 mm, height 350 - 350.01 mm, reduction 58.44 - 58.45 mm, rolling speed 2.5 - 2.51 m / s → Pass 6, width 387.53 - 387.54 mm, height 300 - 300.01 mm, reduction 50 - 50.01 mm, rolling speed 2.5 - 2.51 m / s → steel turning → Pass 7, width 317.26 - 317.27 mm, height 330 - 330.01 mm, reduction 57.53 - 57.54 mm, rolling speed 2.5 - 2.51 m / s → Pass 8, width 332.86 - 332.87 mm, height 278 - 278.01 mm, reduction 52 - 52.01 mm, rolling speed 2.5 - 2.51 m / s → steel turning → Pass 9, width 290.86 - 290.87 mm, height 290 - 290.01 mm, reduction 42.86 - 42.87 mm, rolling speed 2.5 - 2.51 m / s → Pass 10, width 304.06 - 304.07 mm, height 246 - 246.01 mm, reduction 44 - 44.01 mm, rolling speed 2.5 - 2.51 m / s → steel turning → Pass 11, width 267.62 - 267.63 mm, height 232 - 232.01 mm, reduction 72.06 - 72.07 mm, rolling speed 2.5 - 2.51 m / s; Pass through 3 sets of 850 mm rolling mills and 1 set of 735 mm rolling mill, and then enter the continuous rolling mill for rolling.

[0016] Continuous rolling process for producing steel products: Rolling is carried out in 8 passes. In the first pass, the height is 229 - 229.01 mm, the width is 245 - 245.01 mm, and the rolling speed is 0.27 - 0.272 m / s; in the second pass, the height is 192 - 192.01 mm, the width is 235 - 235.01 mm, and the rolling speed is 0.31 - 0.312 m / s; in the third pass, the height is 200 - 200.01 mm, the width is 195 - 195.01 mm, and the rolling speed is 0.35 - 0.352 m / s; in the fourth pass, the height is 163 - 163.01 mm, the width is 200 - 200.01 mm, and the rolling speed is 0.393 - 0.395 m / s; in the fifth pass, the height is 169 - 169.01 mm, the width is 212.8 - 212.81 mm, and the rolling speed is 0.356 - 0.357 m / s; in the sixth pass, the height is 177 - 177.01 mm, the width is 180 - 180.01 mm, and the rolling speed is 0.445 - 0.446 m / s; in the seventh pass, the height is 152 - 152.01 mm, the width is 152 - 152.01 mm, and the rolling speed is 0.614 - 0.615 m / s; in the eighth pass, the height is 152 - 152.01 mm, the width is 152 - 152.01 mm, and the rolling speed is 0.614 - 0.615 m / s; The finished product is obtained after 8 passes.

[0017] 7) Heat preservation: The steel after rolling is heat-preserved. The temperature in the lower heat-preservation pit is ≥580 °C, the heat-preservation time is 48 - 55 h, and the temperature when leaving the pit is ≤150 °C.

[0018] 8) Heat treatment: Samples are taken from the heat-preserved steel for heat treatment. The heat treatment includes the following steps: Quenching temperature: 960 - 980 °C, heat preservation for 0.8 - 1.2 h, air cooling; Tempering temperature: 740 - 760 °C, heat preservation for 1.8 - 2.2 h, air cooling.

[0019] Compared with the prior art, the beneficial effects of the present invention are: The present invention uses an ecological electric furnace + LF + RH + continuous casting smelting process and a rolling process to produce steel bars for subcritical steam pipelines, meeting the mechanical property requirements and ensuring the steel purity. The reasonable composition design and production process ensure the surface quality and mechanical properties. The macrostructure and non-metallic inclusions of the finished steel meet the requirements of high-end products. A breakthrough has been achieved in the batch production of steel bars for subcritical steam pipelines in the ecological electric furnace continuous casting process.

[0020] The macrostructure of the steel bars of the present invention: General looseness ≤1.5, central looseness ≤1.5, ingot type segregation ≤1.5, general spotty segregation ≤1.0, edge spotty segregation ≤1.0; The mechanical properties are: R m ≥490 MPa, R el≥245 MPa, A ≥ 22%, z ≥ 50%, at -46 °C, the KU2 impact energy ≥ 71 J; non-metallic inclusions: class A not more than 2.0, class B not more than 1.5, class C not more than 1.5, class D not more than 1.5, DS not more than 2.0. Detailed implementation manners

[0021] The following further explains the detailed implementation manners of the present invention in conjunction with embodiments.

[0022] Embodiment 1: 1. Chemical composition: It is determined that the chemical composition by weight percentage is: C: 0.11%, Si: 0.25%, Mn: 0.48%, P: 0.012%, S: 0.005%, Cr: 0.98%, Ni: 0.05%, Mo: 0.29%, V: 0.20%, Cu: 0.05%, and the rest are Fe and inevitable impurities.

[0023] 2. Each production process of the electric furnace continuous casting of the steel bar for the subcritical steam conduit: Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → heat preservation → heat treatment.

[0024] (1) Smelting in the ecological electric furnace; The smelting process with 65% hot metal ratio and 35% scrap ratio by weight percentage is adopted; the hot metal tapping temperature is 1296 °C, the tapping temperature is 1617 °C, the C is 0.07% and the P is 0.008% at tapping. Slag materials, pre-deoxidizers, and alloys are added at 1 / 4 of tapping. The smelting cycle is 45 min, and the oxygen consumption of the furnace is 28 m 3 / t steel. The addition amount of alloys per ton of steel: 4.2 kg of silicomanganese alloy, 12.2 kg of low-carbon ferrochrome, and 2 kg of aluminum wire rod (φ12 mm). The addition amount of auxiliary materials per ton of steel: 13 kg of coke particles, 6.0 kg of ladle ash, 35 kg of active lime (φ30 mm), and 13.0 kg of magnesite (φ40 mm).

[0025] (2) Refining in the LF furnace; The LF tapping temperature is 1545°C. With a large current of 35500A for heating and slag melting, when the slag surface fluctuates and the molten steel and arc are not exposed, reactive lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloys are added according to the median value of the chemical composition range, and carbon is increased to promote the rapid melting and homogenization of the alloys and carbon powder. When the molten steel temperature reaches 1615°C, 1.4 kg / t of alumina balls for diffusion deoxidation are added for diffusion deoxidation. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1655°C, the second sample is taken for chemical composition analysis to confirm the deviation value of the content of each chemical element from the median value requirement of the composition range. After the second sample is taken away, when the molten steel temperature reaches 1686°C, it leaves the station. The LF smelting cycle is 96 minutes, and the free space is 425 mm. Alloys added: 2.0 kg / t of high-carbon ferromanganese, 3.7 kg / t of low-carbon ferrochromium, 4.7 kg / t of ferromolybdenum, 4.5 kg / t of ferrovanadium (FeV50-B). Auxiliary materials added: 1.5 kg / t of silicon carbide, 4 kg / t of reactive lime (φ30 mm).

[0026] (3)RH refining; The tapping temperature is 1688°C, and the operation time is 37 minutes. Before the vacuum pump is started, the argon pressure is controlled at 0.1 MPa, with the slag surface slightly moving and the molten steel not exposed. When the vacuum degree reaches 105 Pa, timing starts and the holding time is 12 minutes. At the same time, the argon pressure is adjusted to 0.3 MPa. After the static argon blowing ends, 0.8 kg / t of covering agent is added, the free space is 350 mm, the refining recompression temperature is 1660°C, and the tapping temperature is 1646°C. After breaking the vacuum, 0.85 kg / t of calcium-silicon alloy cored wire (φ14 mm) is added.

[0027] (4)Continuous casting; The ladle arrival temperature is 1634°C, the middle package H is controlled at 1.4 ppm, the casting time is 40 minutes, the superheat is 27°C, the casting speed is 0.42 m / min, and the whole process is protected by casting. The mold powder used is 3.6 kg / t of medium-carbon steel mold powder.

[0028] (5)Heating process; Heating process: The temperature entering the heating furnace is 480°C, the temperature requirement for the preheating section is 620°C, and the time is 1.4 h; the temperature requirement for the second heating section is 860°C, and the time is 1.4 h; the temperature requirement for the first heating section is 1230°C, and the time is 1.3 h; the temperature requirement for the soaking section is 1215°C, and the time is 1.4 h; the tapping temperature is 1195°C.

[0029] (6)Rolling process; Primary rolling process: 11 rolling passes, steel turning → The first pass: width 405.2 mm, height 435 mm, reduction 51 mm, rolling speed 2.3 m / s → The second pass: width 416.46 mm, height 390 mm, reduction 45 mm, rolling speed 2.5 m / s → Steel turning → The third pass: width 400.95 mm, height 380 mm, reduction 36.46 mm, rolling speed 2.5 m / s → The fourth pass: width 408.44 mm, height 355.01 mm, reduction 25 mm, rolling speed 2.5 m / s → Steel turning → The fifth pass: width 372.54 mm, height 350 mm, reduction 58.44 mm, rolling speed 2.5 m / s → The sixth pass: width 387.54 mm, height 300 mm, reduction 50 mm, rolling speed 2.5 m / s → Steel turning → The seventh pass: width 317.27 mm, height 330 mm, reduction 57.54 mm, rolling speed 2.5 m / s → The eighth pass: width 332.87 mm, height 278 mm, reduction 52 mm, rolling speed 2.5 m / s → Steel turning → The ninth pass: width 290.86 mm, height 290 mm, reduction 42.86 mm, rolling speed 2.5 m / s → The tenth pass: width 304.06 mm, height 246 mm, reduction 44 mm, rolling speed 2.5 m / s → Steel turning → The eleventh pass: width 267.63 mm, height 232 mm, reduction 72.06 mm, rolling speed 2.5 m / s; Passing through 3 850-mm rolling mills and 1 735-mm rolling mill, and then entering the continuous rolling mill for rolling.

[0030] Continuous rolling process for finished products: 8 rolling passes, The first pass: height 229 mm, width 245 mm, rolling speed 0.272 m / s; The second pass: height 192 mm, width 235 mm, rolling speed 0.31 m / s; The third pass: height 200 mm, width 195 mm, rolling speed 0.35 m / s; The fourth pass: height 163 mm, width 200 mm, rolling speed 0.393 m / s; The fifth pass: height 169 mm, width 212.8 mm, rolling speed 0.356 m / s; The sixth pass: height 177 mm, width 180 mm, rolling speed 0.445 m / s; The seventh pass: height 152 mm, width 152 mm, rolling speed 0.614 m / s; The eighth pass: height 152 mm, width 152 mm, rolling speed 0.614 m / s; Finished products are obtained after 8 passes.

[0031] (7)Heat preservation process; Heat preservation process: Heat preservation of steel, temperature in the lower heat preservation pit 590 °C, heat preservation for 52 h, temperature out of the pit 120 °C.

[0032] (8)Heat treatment process; Samples are taken from the heat-preserved steel for heat treatment, and the heat treatment includes the following steps: 1) Quenching: 970 °C, holding for 1.0 h, air cooling; 2) Tempering: 750 °C, holding for 2.0 h, air cooling.

[0033] Example 2: 1. Chemical composition: The determined chemical composition is by weight percentage: C: 0.12%, Si: 0.25%, Mn: 0.50%, P: 0.011%, S: 0.005%, Cr: 1.02%, Ni: 0.05%, Mo: 0.29%, V: 0.21%, Cu: 0.06%, and the rest is Fe and unavoidable impurities.

[0034] 2. Each production process of the electric furnace continuous casting of steel bars for subcritical steam pipelines: Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → heat preservation → heat treatment.

[0035] (1) Smelting in ecological electric furnace; Adopt a smelting process with a hot metal ratio of 67% and a scrap ratio of 33% by weight percentage; the hot metal inlet temperature is 1297 °C, the tapping temperature is 1618 °C, the C content at tapping is 0.07%, the P content is 0.008%, slag materials, pre-deoxidizer, and alloy are added at 1 / 4 tapping, the smelting cycle is 46 min, and the furnace oxygen consumption is 28 m 3 / t. Alloy addition per ton of steel: 4.2 kg of silicomanganese alloy, 12.1 kg of low-carbon ferrochrome, and 2 kg of aluminum wire segment (φ12 mm). Auxiliary material addition per ton of steel: 13 kg of coke granules, 5.9 kg of ladle ash, 35 kg of active lime (φ30 mm), and 13.0 kg of magnesite (φ40 mm).

[0036] (2) Refining in LF furnace; The LF inlet temperature is 1546 °C, and the large current of 35600 A is used to raise the temperature and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, add active lime. After 6 min, take the first sample for chemical composition analysis, add alloy according to the median value of the chemical composition range, and increase carbon to promote the rapid melting and homogenization of the alloy and carbon powder. When the molten steel temperature reaches 1616 °C, add 1.4 kg / t of diffusion deoxidizer alumina balls for diffusion deoxidation, close the furnace door for 10 min. When the molten steel temperature reaches 1656 °C, take the second sample for chemical composition analysis to confirm the deviation value of the content of each chemical element from the median value requirement of the composition range. After the second sample is taken away, when the molten steel temperature reaches 1685 °C, leave the station. The LF smelting cycle is 96 min, and the net space is 420 mm. Alloy addition: 2.0 kg / t of high-carbon ferromanganese, 3.7 kg / t of low-carbon ferrochrome, 4.7 kg / t of ferromolybdenum, and 4.5 kg / t of ferrovanadium (FeV50-B). Auxiliary material addition: 1.5 kg / t of silicon carbide and 4 kg / t of active lime (φ30 mm).

[0037] (3)RH refining; The incoming station temperature is 1690°C, the operation time is 36 min. Before starting the vacuum pump, the argon pressure is controlled at 0.1 MPa, with the slag surface slightly moving and the molten steel not exposed. When the vacuum degree reaches 106 Pa, timing starts, and the holding time is 11 min. At the same time, the argon pressure is adjusted to 0.3 MPa. After the static argon blowing ends, 0.8 kg / t of covering agent is added, the free space is 352 mm, the refined recompression temperature is 1659°C, and the outgoing station temperature is 1647°C. After breaking the vacuum, 0.85 kg / t of calcium-silicon alloy cored wire (φ14 mm) is added as a supplement.

[0038] (4)Continuous casting; The ladle arrival temperature is 1635°C, the medium package H is controlled at 1.5 ppm, the casting time is 39 min, the superheat is 27°C, the drawing speed is 0.43 m / min, and the whole process is protected by casting. The mold powder used for the continuous casting mold is 3.6 kg / t of medium carbon steel mold powder.

[0039] (5)Heating process; Heating process: The temperature entering the heating furnace is 480°C, the temperature requirement for the preheating section is 620°C, and the time is 1.4 h; the temperature requirement for the second heating section is 855°C, and the time is 1.4 h; the temperature requirement for the first heating section is 1230°C, and the time is 1.3 h; the temperature requirement for the soaking section is 1220°C, and the time is 1.3 h; the tapping temperature is 1198°C.

[0040] (6)Rolling process; Primary rolling process: 11 rolling passes, steel turning → The 1st pass: width 405.2 mm, height 435 mm, reduction 51 mm, rolling speed 2.3 m / s → The 2nd pass: width 416.45 mm, height 390 mm, reduction 45 mm, rolling speed 2.5 m / s → Steel turning → The 3rd pass: width 400.94 mm, height 380 mm, reduction 36.45 mm, rolling speed 2.5 m / s → The 4th pass: width 408.44 mm, height 355 mm, reduction 25 mm, rolling speed 2.5 m / s → Steel turning → The 5th pass: width 372.54 mm, height 350 mm, reduction 58.44 mm, rolling speed 2.5 m / s → The 6th pass: width 387.53 mm, height 300 mm, reduction 50 mm, rolling speed 2.5 m / s → Steel turning → The 7th pass: width 317.26 mm, height 330 mm, reduction 57.53 mm, rolling speed 2.5 m / s → The 8th pass: width 332.86 mm, height 278 mm, reduction 52 mm, rolling speed 2.5 m / s → Steel turning → The 9th pass: width 290.86 mm, height 290 mm, reduction 42.86 mm, rolling speed 2.5 m / s → The 10th pass: width 304.07 mm, height 246 mm, reduction 44 mm, rolling speed 2.5 m / s → Steel turning → The 11th pass: width 267.62 mm, height 232 mm, reduction 72.06 mm, rolling speed 2.5 m / s; Passing through 3 sets of 850 mm rolling mills and 1 set of 735 mm rolling mill, then entering the continuous rolling mill for rolling.

[0041] Continuous rolling product rolling process: 8 rolling passes, The 1st pass: height 229 mm, width 245 mm, rolling speed 0.27 m / s; The 2nd pass: height 192 mm, width 235 mm, rolling speed 0.31 m / s; The 3rd pass: height 200 mm, width 195 mm, rolling speed 0.35 m / s; The 4th pass: height 163 - 163.01 mm, width 200 mm, rolling speed 0.393 - 0.395 m / s; The 5th pass: height 169 mm, width 212.8 mm, rolling speed 0.356 m / s; The 6th pass: height 177 mm, width 180 mm, rolling speed 0.445 m / s; The 7th pass: height 152 mm, width 152 mm, rolling speed 0.614 m / s; The 8th pass: height 152 mm, width 152.01 mm, rolling speed 0.614 m / s; Finished products are obtained after 8 passes.

[0042] (7)Insulation process; Insulation process: Insulating the steel, the temperature of the lower insulation pit is 590 °C, insulating for 53 h, and the temperature when taking out of the pit is 120 °C.

[0043] (8)Heat treatment process; Taking samples of the steel after insulation for heat treatment, the heat treatment includes the following steps: 1) Quenching: 970 °C, holding for 1.0 h, air cooling; 2) Tempering: 750 °C, holding for 2.0 h, air cooling.

[0044] Example 3: 1. Chemical composition: The determined chemical composition by weight percentage is: C: 0.11%, Si: 0.25%, Mn: 0.51%, P: 0.010%, S: 0.005%, Cr: 1.02%, Ni: 0.05%, Mo: 0.29%, V: 0.21%, Cu: 0.04%, and the rest is Fe and inevitable impurities.

[0045] 2. Each production process of the electric furnace continuous casting of the steel bar for the subcritical steam conduit: Process route: ecological electric furnace + LF + RH + continuous casting billet → heating furnace heating → rolling → heat preservation → heat treatment.

[0046] (1) Smelting in the ecological electric furnace; Adopt a smelting process with an iron water ratio of 68% and a scrap steel ratio of 32% by weight percentage; the iron water inlet temperature is 1302 °C, the tapping temperature is 1618 °C, C is 0.07% and P is 0.007% when tapping. Add slag materials, pre-deoxidizers, and alloys when 1 / 4 of the steel is tapped. The smelting cycle is 46 min, and the furnace oxygen consumption is 29 m 3 / t steel. Alloy addition per ton of steel: 4.2 kg of silicomanganese alloy, 12.3 kg of low-carbon ferrochrome, and 2.0 kg of aluminum wire segment (φ12 mm). Auxiliary material addition per ton of steel: 13 kg of coke particles, 5.9 kg of ladle ash, 35 kg of active lime (φ30 mm), and 13.0 kg of magnesite (φ40 mm).

[0047] (2) Refining in the LF furnace; The LF inlet temperature is 1546 °C. Raise the temperature and melt the slag with a large current of 35600 A. When the slag surface fluctuates and the molten steel and arc are not exposed, add active lime. Take the first sample for chemical composition analysis after 6 min. Add alloys according to the median value of the chemical composition range and increase carbon to promote the rapid melting and homogenization of the alloys and carbon powder. When the molten steel temperature reaches 1616 °C, add 1.5 kg / t of diffusion deoxidizer alumina balls for diffusion deoxidation, close the furnace door for 11 min. When the molten steel temperature reaches 1655 °C, take the second sample for chemical composition analysis to confirm the deviation value of the content of each chemical element from the median value requirement of the composition range. After the second sample is taken away, leave the station when the molten steel temperature reaches 1684 °C. The LF smelting cycle is 96 min, and the clear height is 425 mm. Alloy addition: 2.0 kg / t of high-carbon ferro manganese, 3.7 kg / t of low-carbon ferrochrome, 4.8 kg / t of ferromolybdenum, and 4.5 kg / t of ferrovanadium (FeV50 - B). Auxiliary material addition: 1.5 kg / t of silicon carbide and 4.1 kg / t of active lime (φ30 mm).

[0048] (3)RH refining; The temperature at the time of entering the station is 1692 °C, the operation time is 36 min, the argon pressure is controlled at 0.1 MPa before the vacuum pump is started, so that the molten steel is not exposed with the slight movement of the slag surface. When the vacuum degree reaches 100 Pa, the timing starts, and the holding time is 12 min. At the same time, the argon pressure is adjusted to 0.4 MPa. After the static argon blowing is completed, 0.9 kg / t of covering agent is added, the free space is 355 mm, the temperature after refining and recompression is 1662 °C, and the temperature at the time of leaving the station is 1646 °C. After breaking the vacuum, 0.85 kg / t of calcium-silicon alloy cored wire (φ14 mm) is added as a supplement.

[0049] (4)Continuous casting; The temperature of the ladle when it arrives at the station is 1635 °C, the H content in the tundish is controlled at 1.5 ppm, the casting time is 39 min, the superheat is 28 °C, the casting speed is 0.43 m / min, and the whole process is protected by casting. The mold powder used is medium-carbon steel mold powder at 3.6 kg / t.

[0050] (5)Heating process; Heating process: The temperature when entering the heating furnace is 500 °C, the temperature requirement for the preheating section is 630 °C, and the time is 1.5 h; the temperature requirement for the second heating section is 860 °C, and the time is 1.4 h; the temperature requirement for the first heating section is 1225 °C, and the time is 1.4 h; the temperature requirement for the soaking section is 1220 °C, and the time is 1.3 h; the tapping temperature is 1196 °C.

[0051] (6)Rolling process; Primary rolling process: 11 rolling passes, steel turning → Pass 1: width 405.2 mm, height 435 mm, reduction 51 mm, rolling speed 2.3 m / s → Pass 2: width 416.45 mm, height 390 mm, reduction 45 mm, rolling speed 2.5 m / s → steel turning → Pass 3: width 400.94 mm, height 380 mm, reduction 36.45 mm, rolling speed 2.5 m / s → Pass 4: width 408.44 mm, height 355 mm, reduction 25 mm, rolling speed 2.5 m / s → steel turning → Pass 5: width 372.54 mm, height 350 mm, reduction 58.44 mm, rolling speed 2.5 m / s → Pass 6: width 387.53 mm, height 300 mm, reduction 50 mm, rolling speed 2.51 m / s → steel turning → Pass 7: width 317.27 mm, height 330 mm, reduction 57.53 mm, rolling speed 2.5 m / s → Pass 8: width 332.86 mm, height 278 mm, reduction 52 mm, rolling speed 2.5 m / s → steel turning → Pass 9: width 290.86 mm, height 290 mm, reduction 42.87 mm, rolling speed 2.5 m / s → Pass 10: width 304.07 mm, height 246 mm, reduction 44 mm, rolling speed 2.5 m / s → steel turning → Pass 11: width 267.62 mm, height 232.01 mm, reduction 72.06 mm, rolling speed 2.5 m / s; Pass through 3 850-mm rolling mills and 1 735-mm rolling mill, and then enter the continuous rolling mill for rolling.

[0052] Continuous rolling process for finished products: 8 rolling passes, Pass 1: height 229 mm, width 245 mm, rolling speed 0.27 m / s; Pass 2: height 192 mm, width 235 mm, rolling speed 0.31 m / s; Pass 3: height 200 mm, width 195 mm, rolling speed 0.35 m / s; Pass 4: height 163 mm, width 200 mm, rolling speed 0.393 m / s; Pass 5: height 169 mm, width 212.81 mm, rolling speed 0.357 m / s; Pass 6: height 177 mm, width 180 mm, rolling speed 0.445 m / s; Pass 7: height 152 mm, width 152 mm, rolling speed 0.614 m / s; Pass 8: height 152 mm, width 152 mm, rolling speed 0.614 m / s; Finished products are obtained after 8 passes.

[0053] (7)Heat preservation process; Heat preservation process: Heat preservation of steel, temperature in the lower heat preservation pit 600 °C, heat preservation for 54 h, temperature out of the pit 100 °C.

[0054] (8)Heat treatment process; Take samples of the steel after heat preservation for heat treatment, and the heat treatment includes the following steps: 1) Quenching: 970 °C, holding for 1.0 h, air cooling; 2) Tempering: 750 °C, holding for 2.0 h, air cooling.

[0055] Example 4:

[0056] 1. Chemical composition: The determined chemical composition by weight percentage is: C: 0.12%, Si: 0.26%, Mn: 0.48%, P: 0.012%, S: 0.005%, Cr: 1.01%, Ni: 0.05%, Mo: 0.30%, V: 0.20%, Cu: 0.05%, and the rest is Fe and unavoidable impurities.

[0057] 2. Each production process of the electric furnace continuous casting of the steel bar for the subcritical steam conduit: Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → heat preservation → heat treatment.

[0058] (1) Smelting in ecological electric furnace; Adopt a smelting process with 66% hot metal ratio and 34% scrap ratio by weight percentage; the hot metal tapping temperature is 1302 °C, the tapping temperature is 1617 °C, C is 0.07% and P is 0.007% at tapping. Slag materials, pre-deoxidizers, and alloys are added when 1 / 4 of the steel is tapped. The smelting cycle is 46 min, and the oxygen consumption of the furnace is 29 m 3 / t. Alloy addition per ton of steel: 4.3 kg of silicomanganese alloy, 12.2 kg of low-carbon ferrochrome, and 2.1 kg of aluminum wire segment (φ12 mm). Auxiliary material addition per ton of steel: 13 kg of coke granules, 6.0 kg of ladle ash, 36 kg of active lime (φ30 mm), and 13.1 kg of magnesite (φ40 mm).

[0059] (2) Refining in LF furnace; The LF tapping temperature is 1547°C. With a large current of 35700A for heating and slag melting, when the slag surface fluctuates and the molten steel and arc are not exposed, reactive lime is added. After 6 minutes, the first sample is taken for chemical composition analysis. Alloys are added according to the median value of the chemical composition range, and carbon is increased to promote the rapid melting and homogenization of the alloys and carbon powder. When the molten steel temperature reaches 1616°C, 1.5 kg / t of alumina balls for diffusion deoxidation are added for diffusion deoxidation. The furnace door is closed for 12 minutes. When the molten steel temperature reaches 1655°C, the second sample is taken for chemical composition analysis to confirm the deviation value of the content of each chemical element from the median value requirement of the composition range. After the second sample is taken away, when the molten steel temperature reaches 1685°C, it leaves the station. The LF smelting cycle is 97 minutes, and the free space is 425 mm. Alloys added: 2.0 kg / t of high-carbon ferromanganese, 3.7 kg / t of low-carbon ferrochromium, 4.7 kg / t of ferromolybdenum, 4.5 kg / t of ferrovanadium (FeV50-B). Auxiliary materials added: 1.5 kg / t of silicon carbide, 4.1 kg / t of reactive lime (φ30 mm).

[0060] (3)RH refining; The tapping temperature is 1692°C, and the operation time is 36 minutes. Before starting the vacuum pump, the argon pressure is controlled at 0.1 MPa, with the slag surface slightly moving and the molten steel not exposed. When the vacuum degree reaches 104 Pa, timing starts, and the holding time is 13 minutes. At the same time, the argon pressure is adjusted to 0.4 MPa. After the static argon blowing ends, 0.8 kg / t of covering agent is added. The free space is 348 mm, the refining recompression temperature is 1659°C, and the tapping temperature is 1647°C. After breaking the vacuum, 0.85 kg / t of calcium-silicon alloy cored wire (φ14 mm) is added.

[0061] (4)Continuous casting; The ladle arrival temperature is 1635°C, the middle package H is controlled at 1.2 ppm, the casting time is 39 minutes, the superheat is 27°C, the drawing speed is 0.42 m / min, and the whole process is protected by casting. The mold powder used is 3.6 kg / t of medium-carbon steel mold powder.

[0062] (5)Heating process; Heating process: The temperature entering the heating furnace is 510°C, the temperature requirement for the preheating section is 620°C, and the time is 1.5 h; the temperature requirement for heating section 2 is 860°C, and the time is 1.4 h; the temperature requirement for heating section 1 is 1228°C, and the time is 1.4 h; the temperature requirement for the soaking section is 1220°C, and the time is 1.3 h; the tapping temperature is 1195°C.

[0063] (6)Rolling process; Primary rolling process: 11 rolling passes, steel turning → The first pass: width 405.2 mm, height 435 mm, reduction 51 mm, rolling speed 2.3 m / s → The second pass: width 416.46 mm, height 390 mm, reduction 45 mm, rolling speed 2.5 m / s → Steel turning → The third pass: width 400.95 mm, height 380 mm, reduction 36.46 mm, rolling speed 2.51 m / s → The fourth pass: width 408.45 mm, height 355 mm, reduction 25 mm, rolling speed 2.51 m / s → Steel turning → The fifth pass: width 372.54 mm, height 350 mm, reduction 58.45 mm, rolling speed 2.5 m / s → The sixth pass: width 387.54 mm, height 300 mm, reduction 50 mm, rolling speed 2.51 m / s → Steel turning → The seventh pass: width 317.27 mm, height 330 mm, reduction 57.54 mm, rolling speed 2.5 m / s → The eighth pass: width 332.87 mm, height 278 mm, reduction 52 mm, rolling speed 2.51 m / s → Steel turning → The ninth pass: width 290.86 mm, height 290 mm, reduction 42.87 mm, rolling speed 2.51 m / s → The tenth pass: width 304.06 mm, height 246 mm, reduction 44 mm, rolling speed 2.51 m / s → Steel turning → The eleventh pass: width 267.63 mm, height 232 mm, reduction 72.07 mm, rolling speed 2.5 m / s; Pass through 3 sets of 850 mm rolling mills and 1 set of 735 mm rolling mill, and then enter the continuous rolling mill for rolling.

[0064] Continuous rolling process for finished products: 8 rolling passes, The first pass: height 229 mm, width 245 mm, rolling speed 0.27 m / s; The second pass: height 192 mm, width 235 mm, rolling speed 0.31 m / s; The third pass: height 200 mm, width 195 mm, rolling speed 0.35 m / s; The fourth pass: height 163 mm, width 200 mm, rolling speed 0.395 m / s; The fifth pass: height 169 mm, width 212.8 mm, rolling speed 0.357 m / s; The sixth pass: height 177 mm, width 180 mm, rolling speed 0.445 m / s; The seventh pass: height 152 mm, width 152 mm, rolling speed 0.614 m / s; The eighth pass: height 152 mm, width 152 mm, rolling speed 0.614 m / s; Finished products are obtained after 8 passes.

[0065] (7)Heat preservation process; Heat preservation process: Heat preservation of steel, temperature in the lower heat preservation pit 590 °C, heat preservation for 52 h, temperature out of the pit 120 °C.

[0066] (8)Heat treatment process; Take samples of the steel after heat preservation for heat treatment, and the heat treatment includes the following steps: 1) Quenching: 970 °C, holding for 1.0 h, air cooling; 2) Tempering: 750 °C, holding for 2.0 h, air cooling.

[0067] Example 5:

[0068] 1. Chemical composition: The determined chemical composition is by weight percentage: C: 0.12%, Si: 0.25%, Mn: 0.52%, P: 0.010%, S: 0.005%, Cr: 1.02%, Ni: 0.05%, Mo: 0.29%, V: 0.19%, Cu: 0.05%, and the rest is Fe and inevitable impurities.

[0069] 2. Each production process of the electric furnace continuous casting of the steel bar for the subcritical steam conduit: Process route: ecological electric furnace + LF + RH + continuous casting billet → heating in heating furnace → rolling → heat preservation → heat treatment.

[0070] (1) Smelting in ecological electric furnace; Adopt a smelting process with a hot metal ratio of 66% and a scrap ratio of 34% by weight percentage; the hot metal tapping temperature is 1302 °C, the tapping temperature is 1618 °C, C is 0.07% and P is 0.007% at tapping. Add slag materials, pre-deoxidizers, and alloys when 1 / 4 of the steel is tapped. The smelting cycle is 45 min, and the furnace oxygen consumption is 28 m 3 / t. The addition amount of alloy per ton of steel: 4.2 kg of silicomanganese alloy, 12.3 kg of low-carbon ferrochrome, and 2.0 kg of aluminum wire rod (φ12 mm). The addition amount of auxiliary materials per ton of steel: 13 kg of coke granules, 6.1 kg of ladle ash, 35 kg of active lime (φ30 mm), and 13.1 kg of magnesite (φ40 mm).

[0071] (2) Refining in LF furnace; The LF tapping temperature is 1546°C. With a large current of 35500A for heating and slag melting, when the slag surface fluctuates and the molten steel and arc are not exposed, reactive lime is added. After 5 minutes, the first sample is taken for chemical composition analysis. Alloys are added according to the median value of the chemical composition range, and carbon is increased to promote the rapid melting and homogenization of the alloys and carbon powder. When the molten steel temperature reaches 1615°C, 1.4 kg / t of alumina balls for diffusion deoxidation are added for diffusion deoxidation. The furnace door is closed for 11 minutes. When the molten steel temperature reaches 1655°C, the second sample is taken for chemical composition analysis to confirm the deviation value of the content of each chemical element from the median value requirement of the composition range. After the second sample is taken away, when the molten steel temperature reaches 1685°C, it leaves the station. The LF smelting cycle is 96 minutes, and the free space is 426 mm. Alloys added: 2.0 kg / t of high-carbon ferromanganese, 3.7 kg / t of low-carbon ferrochrome, 4.8 kg / t of ferromolybdenum, 4.6 kg / t of ferrovanadium (FeV50-B). Auxiliary materials added: 1.6 kg / t of silicon carbide, 4.2 kg / t of reactive lime (φ30 mm).

[0072] (3)RH refining; The tapping temperature is 1690°C, and the operation time is 38 minutes. Before starting the vacuum pump, the argon pressure is controlled at 0.15 MPa, with the slag surface slightly moving and the molten steel not exposed. When the vacuum degree reaches 103 Pa, timing starts, and the holding time is 12 minutes. At the same time, the argon pressure is adjusted to 0.4 MPa. After the static argon blowing ends, 0.8 kg / t of covering agent is added. The free space is 354 mm, the refining recompression temperature is 1658°C, and the tapping temperature is 1645°C. After breaking the vacuum, 0.85 kg / t of calcium-silicon alloy cored wire (φ14 mm) is added.

[0073] (4)Continuous casting; The ladle arrival temperature is 1635°C, the middle package H is controlled at 1.5 ppm, the casting time is 39 minutes, the superheat is 28°C, the drawing speed is 0.42 m / min, and the whole process is protected by casting. 3.6 kg / t of medium-carbon steel protective slag is used as the mold powder.

[0074] (5)Heating process; Heating process: The temperature entering the heating furnace is 480°C, the temperature requirement for the preheating section is 630°C, and the time is 1.5 h; the temperature requirement for the heating section 2 is 860°C, and the time is 1.4 h; the temperature requirement for the heating section 1 is 1228°C, and the time is 1.3 h; the temperature requirement for the soaking section is 1220°C, and the time is 1.4 h; the tapping temperature is 1196°C.

[0075] (6)Rolling process; Ingot rolling process: 11 rolling passes, steel turning → The 1st pass: width 405.2 mm, height 435 mm, reduction 51 mm, rolling speed 2.3 m / s → The 2nd pass: width 416.45 mm, height 390 mm, reduction 45 mm, rolling speed 2.5 m / s → Steel turning → The 3rd pass: width 400.94 mm, height 380 mm, reduction 36.45 mm, rolling speed 2.5 m / s → The 4th pass: width 408.44 mm, height 355 mm, reduction 25 mm, rolling speed 2.5 m / s → Steel turning → The 5th pass: width 372.53 mm, height 350 mm, reduction 58.44 mm, rolling speed 2.5 m / s → The 6th pass: width 387.53 mm, height 300 mm, reduction 50 mm, rolling speed 2.5 m / s → Steel turning → The 7th pass: width 317.26 mm, height 330 mm, reduction 57.53 mm, rolling speed 2.5 m / s → The 8th pass: width 332.86 mm, height 278 mm, reduction 52 mm, rolling speed 2.5 m / s → Steel turning → The 9th pass: width 290.86 mm, height 290 mm, reduction 42.86 mm, rolling speed 2.5 m / s → The 10th pass: width 304.07 mm, height 246 mm, reduction 44 mm, rolling speed 2.5 m / s → Steel turning → The 11th pass: width 267.62 mm, height 232 mm, reduction 72.06 mm, rolling speed 2.5 m / s; Passing through 3 sets of 850 mm rolling mills and 1 set of 735 mm rolling mill, then entering the continuous rolling mill for rolling.

[0076] Continuous rolling product rolling process: 8 rolling passes, The 1st pass: height 229 mm, width 245 mm, rolling speed 0.27 m / s; The 2nd pass: height 192 mm, width 235 mm, rolling speed 0.31 m / s; The 3rd pass: height 200 mm, width 195 mm, rolling speed 0.35 m / s; The 4th pass: height 163 mm, width 200 mm, rolling speed 0.393 m / s; The 5th pass: height 169 mm, width 212.8 mm, rolling speed 0.356 m / s; The 6th pass: height 177 mm, width 180 mm, rolling speed 0.445 m / s; The 7th pass: height 152 mm, width 152 mm, rolling speed 0.614 m / s; The 8th pass: height 152 mm, width 152 mm, rolling speed 0.614 m / s; The finished product comes out after 8 passes.

[0077] (7)Insulation process; Insulation process: Insulating the steel, the temperature of the lower insulation pit is 590 °C, insulating for 51 h, and the temperature when coming out of the pit is 135 °C.

[0078] (8)Heat treatment process; Taking samples from the insulated steel for heat treatment, the heat treatment includes the following steps: 1) Quenching: 970°C, holding for 1.0 h, air cooling; 2) Tempering: 750°C, holding for 2.0 h, air cooling.

[0079] The inspection results of the finished products in Examples 1 - 5 are shown in Tables 1 - 3.

[0080] Table 1 Macrostructure of Φ150mm products in Examples 1 - 5

[0081] Table 2 Non-metallic inclusions in Φ150mm products in Examples 1 - 5

[0082] Table 3 Mechanical properties of Φ150mm products in Examples 1 - 5 .

Claims

1. A steel bar for a subcritical steam conduit, characterized in that, The chemical components in the steel are by weight percentage: C: 0.09% - 0.13%, Si: 0.22% - 0.35%, Mn: 0.45% - 0.60%, P: ≤0.016%, S: ≤0.007%, Cr: 0.95% - 1.10%, Ni: ≤0.25%, Mo: 0.26% - 0.33%, V: 0.16% - 0.25%, Cu: ≤0.15%, and the rest are Fe and unavoidable impurities; the mechanical properties of the steel bars are: R m ≥490 MPa, R el ≥245 MPa, A ≥ 22%, z ≥ 50%, K at -46°C V2 ≥71 J.

2. A steel bar for a subcritical steam conduit according to claim 1, characterized in that, The macrostructure of the steel bars: general looseness ≤ 1.5, central looseness ≤ 1.5, ingot type segregation ≤ 1.5, general spotted segregation ≤ 1.0, edge spotted segregation ≤ 1.

0.

3. A steel bar for a subcritical steam conduit according to claim 1, characterized in that, The non-metallic inclusions of the steel bars: Class A ≤ 2.0, Class B ≤ 1.5, Class C ≤ 1.5, Class D ≤ 1.5, DS ≤ 2.

0.

4. A production method of a steel bar for a subcritical steam conduit as described in any one of claims 1-3, including an ecological electric furnace, LF furnace refining, RH furnace refining, continuous casting, heating furnace heating, rolling, heat preservation, and heat treatment; characterized in that, Specifically, it includes the following method steps: 1) Electric furnace smelting in ecological environment: The tapping temperature of hot metal is 1290 - 1310 °C, the tapping temperature of molten steel is 1615 - 1620 °C, the C content at tapping is 0.06% - 0.08%, P ≤ 0.010%, the smelting cycle is 40 - 50 min, and the oxygen consumption of the furnace is 28 - 29 m 3 / t; 2) LF furnace refining: The LF tapping temperature is 1540 - 1550 °C. When the molten steel temperature reaches 1610 - 1620 °C, diffusion deoxidizer is added. When the molten steel temperature reaches 1680 - 1690 °C, it leaves the station. The LF smelting cycle is 90 - 100 min, and the free space is 420 - 430 mm. 3) RH furnace refining: The tapping temperature is 1685 - 1695 °C, the operation time is 35 - 40 min. Before the vacuum pump starts, the argon pressure is controlled at 0.1 - 0.3 MPa. When the vacuum degree reaches 100 - 110 Pa, the timing starts, and the holding time is 10 - 15 min. At the same time, the argon pressure is adjusted to 0.3 - 0.5 MPa. The refining recompression temperature is 1655 - 1665 °C, and the leaving station temperature is 1640 - 1650 °C. 4) Continuous casting: The ladle arrival temperature is 1630 - 1640 °C, the middle ladle H control ≤ 2 ppm, the casting time is 38 - 42 min, the superheat is 25 - 30 °C, and the casting speed is 0.42 - 0.43 m / min. 5) Heating furnace heating: The temperature entering the heating furnace is 450 - 550 °C, the preheating section temperature is 600 - 650 °C, and the time is 1.4 - 1.5 h; the heating section 2 temperature is 850 - 870 °C, and the time is 1.3 - 1.5 h; the heating section 1 temperature is 1210 - 1240 °C, and the time is 1.3 - 1.5 h; the soaking section temperature is 1200 - 1230 °C, and the time is 1.3 - 1.5 h; the tapping temperature is 1180 - 1210 °C. 6) Heat preservation: The steel after rolling is heat-preserved. The temperature of the lower heat-preservation pit ≥ 580 °C, the heat-preservation time is 48 - 55 h, and the temperature leaving the pit ≤ 150 °C. 7) Heat treatment: Quenching temperature: 960 - 980 °C, holding time 0.8 - 1.2 h, air cooling; tempering temperature: 740 - 760 °C, holding time 1.8 - 2.2 h, air cooling.

5. The production method of a steel bar for a subcritical steam conduit according to claim 4, characterized in that, In the said step 1), the hot metal ratio is 65% - 70% and the scrap ratio is 30% - 35% for smelting by weight percentage; slag materials, pre-deoxidizer, and alloy are added when 1 / 4 - 1 / 3 of the steel is tapped.

6. The production method of a steel bar for a subcritical steam conduit according to claim 4, characterized in that, In the said step 2), after entering the station, a large current of 35000 - 36000 A is used to heat up and melt the slag. When the slag surface fluctuates and the molten steel and arc are not exposed, active lime is added. After 5 - 6 min, the first sampling is taken to analyze the chemical composition. Alloy is added according to the median value of the chemical composition range, and carbon is increased. The diffusion deoxidizer is alumina balls at 1.4 - 1.5 kg / t. When the molten steel temperature reaches 1650 - 1660 °C, the second sampling is taken to analyze the chemical composition.

7. The production method of a steel bar for a subcritical steam conduit according to claim 4, characterized in that, In the said step 3), after the static argon blowing ends, 0.8 - 0.9 kg / t of covering agent is added, the free space is 340 - 360 mm, and 0.84 - 0.86 kg / t of silicon-calcium alloy cored wire is added after breaking the vacuum.

8. The production method of a steel bar for a subcritical steam conduit according to claim 4, characterized in that, In the said step 4), full-process protection casting is adopted, and 3.6 - 3.7 kg / t of medium-carbon steel mold powder is used for the mold powder.

9. The production method of a steel bar for a subcritical steam conduit according to claim 4, characterized in that, The said rolling includes: Primary rolling process: It is rolled for 11 passes. In the first pass, the width is 405.2 - 405.21 mm, the height is 435 - 435.01 mm, the reduction is 51 - 51.01 mm, and the rolling speed is 2.3 - 2.31 m / s; in the second pass, the width is 416.45 - 416.46 mm, the height is 390 - 390.01 mm, the reduction is 45 - 45.01 mm, and the rolling speed is 2.5 - 2.51 m / s; in the third pass, the width is 400.94 - 400.95 mm, the height is 380 - 380.01 mm, the reduction is 36.45 - 36.46 mm, and the rolling speed is 2.5 - 2.51 m / s; in the fourth pass, the width is 408.44 - 408.45 mm, the height is 355 - 355.01 mm, the reduction is 25 - 25.01 mm, and the rolling speed is 2.5 - 2.51 m / s; in the fifth pass, the width is 372.53 - 372.54 mm, the height is 350 - 350.01 mm, the reduction is 58.44 - 58.45 mm, and the rolling speed is 2.5 - 2.51 m / s; in the sixth pass, the width is 387.53 - 387.54 mm, the height is 300 - 300.01 mm, the reduction is 50 - 50.01 mm, and the rolling speed is 2.5 - 2.51 m / s; in the seventh pass, the width is 317.26 - 317.27 mm, the height is 330 - 330.01 mm, the reduction is 57.53 - 57.54 mm, and the rolling speed is 2.5 - 2.51 m / s; in the eighth pass, the width is 332.86 - 332.87 mm, the height is 278 - 278.01 mm, the reduction is 52 - 52.01 mm, and the rolling speed is 2.5 - 2.51 m / s; in the ninth pass, the width is 290.86 - 290.87 mm, the height is 290 - 290.01 mm, the reduction is 42.86 - 42.87 mm, and the rolling speed is 2.5 - 2.51 m / s; in the tenth pass, the width is 304.06 - 304.07 mm, the height is 246 - 246.01 mm, the reduction is 44 - 44.01 mm, and the rolling speed is 2.5 - 2.51 m / s; in the eleventh pass, the width is 267.62 - 267.63 mm, the height is 232 - 232.01 mm, the reduction is 72.06 - 72.07 mm, and the rolling speed is 2.5 - 2.51 m / s; Continuous rolling process for rolled products: Rolling is carried out in 8 passes. In the first pass, the height is 229 - 229.01 mm, the width is 245 - 245.01 mm, and the rolling speed is 0.27 - 0.272 m / s; in the second pass, the height is 192 - 192.01 mm, the width is 235 - 235.01 mm, and the rolling speed is 0.31 - 0.312 m / s; in the third pass, the height is 200 - 200.01 mm, the width is 195 - 195.01 mm, and the rolling speed is 0.35 - 0.352 m / s; in the fourth pass, the height is 163 - 163.01 mm, the width is 200 - 200.01 mm, and the rolling speed is 0.393 - 0.395 m / s; in the fifth pass, the height is 169 - 169.01 mm, the width is 212.8 - 212.81 mm, and the rolling speed is 0.356 - 0.357 m / s; in the sixth pass, the height is 177 - 177.01 mm, the width is 180 - 180.01 mm, and the rolling speed is 0.445 - 0.446 m / s; in the seventh pass, the height is 152 - 152.01 mm, the width is 152 - 152.01 mm, and the rolling speed is 0.614 - 0.615 m / s; in the eighth pass, the height is 152 - 152.01 mm, the width is 152 - 152.01 mm, and the rolling speed is 0.614 - 0.615 m / s.

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