Method for producing φ650mm large round billet by using high alloy steel continuous casting

Abstract

The present application relates to a kind of high alloy steel using continuous casting production φ650mm big round billet method, belong to metallurgical casting technical field.To solve the problem that alloy component precision control is difficult, easy to produce casting billet defect and the continuity of production is insufficient in existing continuous casting process, the present application provides a kind of high alloy steel using continuous casting production φ650mm big round billet method, including using converter or electric furnace smelting, tapping and joining aluminium ingot and first batch low chromium alloy control in place chromium≤1.5%;Using multiple batches to join low-carbon chromium iron to refine, to the vacuum treatment and feeding silicon calcium line calcium treatment of refined molten steel;When continuous casting, using crystallizer electromagnetic stirring and terminal electromagnetic stirring, according to superheat and draft speed dynamic matching control draft speed, using specific pull straightener pressure curve.The present application optimizes multiple processes, accurately controls component, improves the quality inside and outside casting billet, guarantees production continuity, improves efficiency, reduces cost, realizes large-scale efficient production.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical casting technology, and particularly relates to a method for producing φ650mm large round billets of high alloy steel using continuous casting. Background Technology

[0002] High-alloy steel is widely used in high-end fields such as petrochemicals and nuclear power, and the quality of its large-section cast billets directly determines the reliability of downstream products. Traditionally, the production of large-section high-alloy steel billets mostly employs ingot casting. While this process involves simple equipment investment, it suffers from inherent defects such as low yield and poor production efficiency, making it difficult to meet the demands of large-scale, high-quality production. Therefore, continuous casting has become the mainstream development direction for the production of large-section high-alloy steel billets. However, when using continuous casting to produce large-section round billets (φ650mm), numerous intractable technical defects exist, becoming the core bottleneck restricting production.

[0003] In terms of composition control, there are significant defects in the continuous casting production process. It is extremely difficult to accurately control key alloying elements such as carbon, phosphorus, and chromium in high alloy steel. Furthermore, harmful elements such as arsenic tend to accumulate inside the billet, directly damaging the mechanical properties and corrosion resistance of the billet and posing a serious hidden danger to the safe operation of downstream products.

[0004] In terms of billet forming, various forming defects are prone to occur during continuous casting. Among them, central cracks are mainly caused by the superposition of solidification shrinkage stress and thermal stress during billet solidification, while surface slag grooves are closely related to the selection of protective slag performance and improper setting of crystallizer vibration parameters. Such forming defects will significantly reduce the billet qualification rate and significantly increase production energy consumption and production costs.

[0005] In subsequent processing, the large cross-sectional dimensions of continuously cast round billets present challenges in cutting, and the hot delivery temperature of the billets after cutting is difficult to guarantee effectively, which can easily lead to secondary oxidation on the billet surface, thereby affecting the processing quality of subsequent rolling processes and further reducing the product yield.

[0006] In terms of production continuity, billet warping defects are prone to occur during continuous casting straightening. These defects are mainly caused by factors such as mismatch between casting speed and cooling speed and improper control of straightening pressure. Once warping occurs, it will directly lead to production interruption, seriously affecting production continuity and efficiency. Summary of the Invention

[0007] To address the challenges of precise alloy composition control, billet defects, and insufficient production continuity in existing continuous casting processes, this invention provides a method for producing φ650mm large round billets of high alloy steel using continuous casting.

[0008] The technical solution of this invention:

[0009] A method for producing φ650mm large round billets of high alloy steel using continuous casting is disclosed. The steel is smelted in a converter or electric furnace, with the carbon content controlled at 0.05~0.07%, phosphorus content ≤0.007%, and tapping temperature not lower than 1620℃. Aluminum ingots are added during tapping, and the initial batch of low-chromium alloy is controlled to achieve a chromium content ≤1.5%. Refining is achieved by adding low-carbon ferrochrome in multiple batches, with a refining time controlled at no less than 140 minutes and a white slag retention time of no less than 20 minutes. The final carbon content is 0.16~0.19%, and the chromium content is 12.35~12.55%. The refined steel is subjected to a deep vacuum of ≤67Pa and vacuum maintenance. Vacuum treatment and calcium treatment of the silicon-calcium wire feed for no less than 15 minutes, soft blowing time for no less than 15 minutes; during continuous casting, control the tundish baking temperature to be no less than 1050℃, the crystallizer water flow rate to be 4500L / min, the secondary cooling water flow rate to be 0.15L / kg, and the nozzle depth to be 110±10mm; use crystallizer electromagnetic stirring and end electromagnetic stirring, control the casting speed according to the dynamic matching of superheat and casting speed, and use a specific tension leveling machine pressure curve, with the pressure of tension leveling machines 1-7 being 40bar, 45bar, 45bar, 55bar, 55bar, 55bar, and 60bar respectively.

[0010] Furthermore, the smelting process uses blast furnace iron with the following chemical composition as raw material: C 3.97~4.11%, Si 0.33%, Mn 0.28~0.30%, P 0.131~0.150%, S 0.037~0.039%, As 0.0160%, Sn 0.0001%, Pb 0.0010%, Sb 0.0001%, Bi 0.0009~0.0010%, with the remainder being Fe and unavoidable impurities.

[0011] Furthermore, the steel output of the smelting is 80-85 tons, and 600 kg of lime, 300 kg of deoxidation and desulfurization refining slag and 100 kg of aluminum ingots are added during the steel tapping process; the initial amount of low-chromium alloy added during steel tapping is 2 tons.

[0012] Furthermore, the refined low-carbon ferrochrome is added in 4 to 5 batches, with each batch containing ≤6 tons, and the temperature of the molten steel is not lower than 1620℃ when it is added; after adding the low-carbon ferrochrome in batches, medium-chromium or high-chromium ferrochrome is used to fine-tune the composition.

[0013] Furthermore, the feed rate of the silicon-calcium wire is 80-100 meters per furnace.

[0014] Furthermore, the initial pouring level of the continuous casting is not less than 12 tons.

[0015] Furthermore, the special protective slag used in continuous casting contains the following components by mass percentage: SiO2 20~25%, Al2O3 10~15%, Fe2O3 1.30~1.50%, CaO 20~25%, MgO 4~6%, alkali metal oxide R2O (Na2O+K2O) 4.00~4.50%, F 2.40~2.60%, and fixed carbon C 6~10%; the binary basicity R=CaO / SiO2 of the protective slag is 1.00~1.05, the melting point is 1215~1225℃, and the viscosity at 1300℃ is [missing information]. The bulk density is 0.70~0.90 g / cm³. 3 The covering agent contains the following components by mass percentage: SiO2 40~45%, CaO 3~8%, MgO 11.00~11.50%, Fe2O3 3.20~3.60%, Al2O3 3~8%, C 20~25%, H2O 0.20~0.40%, and the melting point of the covering agent is 1345~1355℃.

[0016] Furthermore, the secondary cooling water distribution ratio in the continuous casting is 40% / 38% / 22%; the electromagnetic stirring parameters of the crystallizer are 300A / 2Hz, and the terminal electromagnetic stirring parameters are 450A / 4Hz.

[0017] Furthermore, the casting speed is 0.24 m / min when the superheat is <20℃, 0.23 m / min when the superheat is 20~40℃, and 0.22 m / min when the superheat is >40℃.

[0018] Furthermore, during the continuous casting fire cutting, the cut-off head of the billet is no less than 2000mm and the cut-off tail is no less than 3000mm. Iron powder is sprayed as an auxiliary during fire cutting, and the cutting time for each cut is 8.5~9min.

[0019] The beneficial effects of this invention are:

[0020] This invention achieves precise and stable control of key components (especially C, Cr, P, S, and As) in high-alloy steel by employing alloying processes involving chromium addition during steel tapping and fine-tuning in multiple batches of refining, combined with vacuum treatment and calcium treatment processes. This solves the problems of unstable component control and excessive levels of harmful elements in existing continuous casting processes, ensuring that the composition of the finished billet strictly meets stringent protocol requirements, and providing a qualified raw material base for downstream high-end equipment manufacturing.

[0021] This invention significantly improves the internal quality of the billet by optimizing the secondary cooling water distribution parameters, rationally setting the electromagnetic stirring parameters, and establishing a dynamic matching model of "superheat-casting speed". It effectively reduces the tendency of central segregation and cracking in the billet, improves the internal density and uniformity of the φ650mm large round billet, reduces the incidence of internal defects, and enhances the mechanical properties and corrosion resistance of the billet.

[0022] This invention solves the problems of slag groove defects on the surface of the billet and head lifting during the straightening process by using special protective slag, optimizing the nozzle depth to 110±10mm, optimizing the pressure parameters of the straightening machine, and formulating operating procedures such as manual intervention and pressure raising. It ensures the surface quality of the billet and the continuity and stability of continuous casting production, and avoids losses caused by production interruption.

[0023] This invention applies continuous casting technology to the production of φ650mm high alloy steel large round billets, thereby improving production efficiency and optimizing production costs. Compared with the traditional die casting process, it significantly improves the billet yield and production efficiency, reduces the risk of production anomalies, material waste and energy consumption, and realizes the large-scale and high-efficiency production of high alloy steel large cross-section round billets, which has significant industrial application value. Attached Figure Description

[0024] Figure 1 A low-magnification microstructure photograph of a φ650mm continuous casting billet of high alloy steel prepared in Example 2;

[0025] Figure 2 A photograph of the surface of a φ650mm high-alloy steel continuous casting billet prepared for Example 2. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention. In the following embodiments, the process equipment or apparatus not specifically specified are all conventional equipment or apparatus in the art. Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available; unless otherwise specified, the technical means used in the embodiments of the present invention are all conventional means well known to those skilled in the art.

[0027] Example 1

[0028] This embodiment provides a method for producing φ650mm large round billets of high alloy steel using continuous casting. The specific implementation steps include smelting, refining, vacuum treatment, continuous casting, and billet treatment. The specific method is as follows:

[0029] Step 1: Smelting Process

[0030] High-alloy steel is smelted using a converter or electric furnace, with strict control over tapping parameters. Specifically, the carbon content is controlled at 0.05-0.07%, the phosphorus content at ≤0.007%, and the tapping temperature at ≥1620℃. A double-sliding slag-blocking process is employed during tapping to effectively prevent slag from entering the molten steel and affecting its purity. Aluminum ingots and an initial batch of low-chromium alloy are added during tapping, with 100 kg of aluminum ingots and approximately 2 tons of the initial low-chromium alloy. The chromium content is strictly controlled to be below 1.5%, laying the compositional foundation for subsequent refining processes.

[0031] Step 2, Refining Process:

[0032] The refining process employs a multi-batch addition of low-carbon ferrochrome, with a total of 4-5 batches added, each batch ≤6 tons, preferably 4 tons. The steel temperature must be ≥1620℃ during addition to ensure complete dissolution and uniform distribution of the ferrochrome. The entire refining process lasts ≥150 minutes, including a white slag retention time of ≥20 minutes. White slag refining removes harmful impurities from the molten steel, improving its purity. After refining, the composition at the point of departure is precisely controlled, with carbon content controlled at 0.16-0.19% and chromium content at 12.35-12.55%. Simultaneously, phosphorus, sulfur, and aluminum contents are strictly controlled to ensure the steel composition meets the requirements for continuous casting production.

[0033] Step 3: Vacuum treatment process:

[0034] The refined molten steel is fed into a vacuum treatment device for further processing. The deep vacuum level is controlled to be ≤67Pa, and the vacuum holding time is ≥15 minutes. For the first furnace of molten steel, the vacuum holding time is extended by 5 minutes to further remove gases and inclusions from the molten steel. Calcium treatment is performed during the vacuum treatment process by feeding in a calcium silicate wire at a rate of 80-100 meters per furnace to improve the fluidity of the molten steel and the cleanliness of the billet. After calcium treatment, soft blowing is performed for >15 minutes to homogenize the composition and temperature of the molten steel and reduce defects in subsequent continuous casting processes.

[0035] Step 4: Continuous casting process:

[0036] The continuous casting process includes four stages: tundish and protection, cooling and stirring, matching of casting speed and superheat, and straightening and cutting.

[0037] Packaging and Protection:

[0038] Before continuous casting, the tundish is baked to ensure a baking temperature ≥1050℃ to avoid the molten steel temperature stability being affected by excessively low tundish temperature. During continuous casting, a special protective slag and covering agent are used. The special protective slag used in continuous casting contains the following components by mass percentage: SiO2 22.83%, Al2O3 13.48%, Fe2O3 1.41%, CaO 23.58%, MgO 5.59%, alkali metal oxide R2O (Na2O+K2O) 4.25%, F 2.53%, and fixed carbon C 8.63%. The binary basicity R=CaO / SiO2 of the protective slag is 1.03, the melting point is 1221℃, and the viscosity at 1300℃ is [missing information]. The bulk density is 0.79 g / cm³. 3 The covering agent contains the following components by mass percentage: SiO2 44.37%, CaO 3.64%, MgO 11.24%, Fe2O3 3.39%, Al2O3 4.22%, C 22.38%, H2O 0.30%, and the melting point of the covering agent is 1350℃.

[0039] The use of carbonized rice husks is strictly prohibited to prevent harmful substances from mixing into the molten steel. At the same time, the initial pouring level should be controlled at ≥12 tons to ensure a stable pouring process and reduce molten steel splashing and secondary oxidation.

[0040] Cooling and stirring process:

[0041] The crystallizer water flow rate is set to 4500 L / min, the secondary cooling water flow rate is set to 0.15 L / kg, and the secondary cooling water distribution ratio is 40% / 38% / 22%. By controlling the solidification rate of the billet through reasonable cooling parameters, the solidification stress is reduced. At the same time, a dual stirring method is adopted, with the crystallizer electromagnetic stirring parameter being 300 A / 2 Hz and the terminal electromagnetic stirring parameter being 450 A / 4 Hz. This improves the internal structure of the billet and reduces center segregation and center cracks.

[0042] Matching of pulling speed and superheat:

[0043] A dynamic control model for superheat and casting speed was established. The casting speed was adjusted in real time according to the superheat of the molten steel. Specifically, when the superheat was <20℃, the casting speed was controlled at 0.24 m / min; when the superheat was between 20-40℃, the casting speed was controlled at 0.23 m / min; and when the superheat was >40℃, the casting speed was controlled at 0.22 m / min. The goal was to stably control the superheat of the molten steel between 28-38℃, achieve precise matching between casting speed and superheat, and reduce defects in the cast billet.

[0044] Straightening and cutting process:

[0045] A specific pressure curve for the straightening machine is adopted, with the pressures of straightening machines 1-7 set at 40 bar, 45 bar, 45 bar, 55 bar, 55 bar, 55 bar, and 60 bar respectively, to avoid billet warping caused by improper straightening pressure. When cutting the billet, the cutting head length is ≥2000 mm and the cutting tail length is ≥3000 mm to remove the poor quality parts at both ends of the billet. The fire cutting process is optimized, and auxiliary iron powder is used during the cutting process. The cutting time for each cut is controlled at 8.5~9 minutes to ensure a 100% online successful cutting rate and avoid production interruption caused by cutting failure.

[0046] Step 5: Billet processing procedure:

[0047] After continuous casting, the billet is rapidly hot-fed with a target hot-fed temperature of ≥550℃ to reduce billet temperature loss and secondary oxidation. At the same time, asbestos insulation is applied to both ends of the billet to prevent the end temperature from dropping too quickly and causing cracks. Shrinkage cavities at the ends of the billet are repaired by welding to further improve the quality of the billet and ensure that the billet meets the requirements of subsequent processing.

[0048] By precisely controlling each of the above processes, various technical defects in the existing continuous casting process can be effectively solved, the internal and surface quality of high alloy steel large cross-section round billets can be stably guaranteed, production efficiency and yield can be improved, and it is suitable for the large-scale production of high alloy steel large cross-section round billets.

[0049] Example 2

[0050] This embodiment provides a method for producing φ650mm large round billets of high-alloy steel using continuous casting. Using blast furnace hot metal as the initial smelting raw material, the steel undergoes converter steelmaking, refining, vacuum treatment, continuous casting, and billet treatment sequentially to prepare 13Cr high-alloy steel. The specific method is as follows:

[0051] Step 1: Smelting Process

[0052] The raw material is molten iron with the following chemical composition: C 3.97%, Si 0.33%, Mn 0.28%, P 0.131%, S 0.037%, As 0.0160%, Sn 0.0001%, Pb 0.0010%, Sb 0.0001%, Bi 0.0009%, with the remainder being Fe and unavoidable impurities.

[0053] Molten iron is added to the converter, and decarburization and dephosphorization are carried out through top and bottom blowing. The final steel composition and temperature are controlled: the carbon content of the steel is 0.06%, the phosphorus content is 0.006%, the steel output is 80.6t, and the steel output temperature is 1634℃; the Al content is 0.026%; during the steel tapping process, 600kg of lime, 300kg of deoxidation and desulfurization refining slag and 100kg of aluminum ingot are added for slag washing and preliminary deoxidation; 2 tons of low-chromium alloy are added at the time of tapping to control the chromium content to 1.4%.

[0054] Step 2, Refining Process:

[0055] Molten steel from the converter is sent to the LF refining station, where 750 kg of lime, 100 kg of refining slag, 40 kg of aluminum granules, and 80 kg of ferrosilicon powder are added to create white slag. Then, low-carbon ferrochrome is added in four batches, with 5 tons added in each batch. The temperature of the molten steel is controlled at 1625℃ during the addition. After the low-carbon ferrochrome is added in batches, medium chromium is used to fine-tune the composition. The amount of medium chromium added is 1450 kg, and 35 kg of ferrovanadium is added at the same time.

[0056] The refining temperature reaches 1525℃, rises to 1583℃ after 15-20 minutes of energization, and ends at 1689℃; the total refining time is 142 minutes, including a 22-minute white slag holding time. The final composition at the refining station is controlled as follows: C: 0.17%, Cr: 12.40%, with strict control over phosphorus, sulfur, and aluminum content to meet standards: P ≤ 0.015%, S ≤ 0.005%, Al: 0.010-0.030%.

[0057] Step 3: Vacuum treatment process:

[0058] The deep vacuum degree is 60Pa, and the vacuum holding time is 15 minutes; the calcium treatment feed silicon-calcium wire is 90 meters / furnace, and the soft blowing time is 16 minutes.

[0059] Step 4: Continuous casting process:

[0060] Continuous casting process control: Tundish baking temperature 1060℃, initial pouring level 12.5 tons. A special protective slag and covering agent are used during continuous casting. The special protective slag contains the following components by mass percentage: SiO2 22.83%, Al2O3 13.48%, Fe2O3 1.41%, CaO 23.58%, MgO 5.59%, alkali metal oxides R2O (Na2O+K2O) 4.25%, F 2.53%, and fixed carbon C 8.63%. The binary basicity R=CaO / SiO2 of the protective slag is 1.03, the melting point is 1221℃, and the viscosity at 1300℃ is... The bulk density is 0.79 g / cm³. 3 The covering agent contains the following components by mass percentage: SiO2 44.37%, CaO 3.64%, MgO 11.24%, Fe2O3 3.39%, Al2O3 4.22%, C 22.38%, H2O 0.30%, and the melting point of the covering agent is 1350℃.

[0061] The nozzle depth is 110mm; the crystallizer water flow rate is 4500L / min, the secondary cooling water flow rate is 0.15L / kg, and the secondary cooling water distribution ratio is 40% / 38% / 22%; the crystallizer electromagnetic stirring is 300A / 2Hz, and the end electromagnetic stirring is 450A / 4Hz; the molten steel superheat is 32℃, and the drawing speed is 0.23m / min; the pressures of the 1st to 7th stand straighteners are 40bar, 45bar, 45bar, 55bar, 55bar, 55bar, and 60bar, respectively; the billet head is cut 2000mm, the tail is cut 3000mm, the fire cutting time is 8.6min, and the online successful cutting rate is 100%.

[0062] Step 5: Billet processing procedure:

[0063] The billet is rapidly heated to a temperature of 560℃. Both ends of the billet are insulated with asbestos, and the shrinkage cavities at the ends are repaired by welding.

[0064] Figure 1 A low-magnification microstructure photograph of a φ650mm continuous casting billet of high-alloy steel prepared in Example 2; from Figure 1 As can be seen, the cast billet has no macroscopic cracks, the central equiaxed crystal zone is well developed, the central porosity is grade 1.5, there are no other defects, and the overall internal quality is stable.

[0065] Figure 2 A surface photograph of a φ650mm high-alloy steel continuous casting billet prepared in Example 2, from... Figure 2 As can be seen, the surface of the continuously cast billet is free of defects such as slag pits and cracks.

[0066] The carbon segregation index of the continuous casting billet at nine points was tested, and the results are shown in Table 1.

[0067] Table 1

[0068]

[0069] Example 3

[0070] This embodiment provides a method for producing φ650mm large round billets of high alloy steel using continuous casting. The specific implementation steps include smelting, refining, vacuum treatment, continuous casting, and billet treatment. The specific method is as follows:

[0071] Step 1: Smelting Process

[0072] The chemical composition of the molten iron, by weight percentage, includes: C 4.11%, Si 0.33%, Mn 0.30%, P 0.150%, S 0.039%, As 0.0160%, Sn 0.0001%, Pb 0.0011%, Sb 0.0001%, and Bi 0.0010%.

[0073] The steel tapping process yielded 84.4 tons of steel with a carbon content of 0.05% and a phosphorus content of 0.007%. The tapping temperature was 1620℃. The Al content at the tapping point was 0.014%. The tapping slag consisted of 600 kg of lime, 300 kg of deoxidizing and desulfurizing refining slag, and 100 kg of aluminum ingots. Two tons of the first batch of low-chromium alloy were added during tapping, resulting in a chromium content of 1.4% at the tapping point.

[0074] Step 2, Refining Process:

[0075] Molten steel from the converter is sent to the LF refining station, where 60m of aluminum wire, 500kg of lime, 40kg of aluminum granules, 110kg of ferrosilicon powder, and 60kg of medium manganese are added to create white slag. Then, low-carbon ferrochrome is added in four batches, with 5 tons added in each batch. The temperature of the molten steel is controlled at 1620℃ during the addition. After the low-carbon ferrochrome is added in batches, high-chromium is used to fine-tune the composition. The amount of high-chromium added is 100kg, and 60kg of ferrovanadium is added at the same time.

[0076] The refining temperature reaches 1524℃, rises to 1592℃ after 15-20 minutes of energization, and ends at 1629℃; the total refining time is 162 minutes, including a 25-minute white slag holding time. The composition at the point of refining is controlled at C: 0.17%, Cr: 12.40%, with strict control over phosphorus, sulfur, and aluminum content to meet standards.

[0077] Step 3: Vacuum treatment process:

[0078] The deep vacuum degree is 67 Pa, and the vacuum holding time is 20 minutes; the calcium treatment feed silicon-calcium wire is 100 meters per furnace, and the soft blowing time is 18 minutes.

[0079] Step 4: Continuous casting process:

[0080] Continuous casting process control: Tundish baking temperature 1050℃, initial casting volume 12 tons. A special protective slag and covering agent are used during continuous casting. The special protective slag contains the following components by mass percentage: SiO2 22.83%, Al2O3 13.48%, Fe2O3 1.41%, CaO 23.58%, MgO 5.59%, alkali metal oxides R2O (Na2O+K2O) 4.25%, F 2.53%, and fixed carbon C 8.63%. The binary basicity R=CaO / SiO2 of the protective slag is 1.03, the melting point is 1221℃, and the viscosity at 1300℃ is... The bulk density is 0.79 g / cm³. 3 The covering agent contains the following components by mass percentage: SiO2 44.37%, CaO 3.64%, MgO 11.24%, Fe2O3 3.39%, Al2O3 4.22%, C 22.38%, H2O 0.30%, and the melting point of the covering agent is 1350℃.

[0081] The nozzle depth is 110mm; the crystallizer water flow rate is 4500L / min, the secondary cooling water flow rate is 0.15L / kg, and the secondary cooling water distribution ratio is 40% / 38% / 22%; the crystallizer electromagnetic stirring is 300A / 2Hz, and the end electromagnetic stirring is 450A / 4Hz; the molten steel superheat is 28℃, and the drawing speed is 0.23m / min; the pressures of the 1st to 7th straightening stands are 40bar, 45bar, 45bar, 55bar, 55bar, 55bar, and 60bar, respectively; the billet head is cut 2200mm, the tail is cut 3200mm, the fire cutting time is 9min, and the online successful cutting rate is 100%.

[0082] Step 5: Billet processing procedure:

[0083] The billet is rapidly heated to a temperature of 550℃. Both ends of the billet are insulated with asbestos, and the shrinkage cavities at the ends are repaired by welding.

Claims

1. A method for producing φ650mm large round billets of high alloy steel using continuous casting, characterized in that, The steel is smelted using a converter or electric furnace, with the carbon content controlled at 0.05-0.07%, phosphorus content ≤0.007%, and tapping temperature not lower than 1620℃. Aluminum ingots are added during tapping, and the initial low-chromium alloy is controlled to achieve a chromium content ≤1.5%. Refining is performed by adding low-carbon ferrochrome in multiple batches, with a refining time of not less than 140 minutes and a white slag holding time of not less than 20 minutes. The final carbon content is 0.16-0.19%, and the chromium content is 12.35-12.55%. The refined steel is then subjected to a deep vacuum of ≤67 Pa for at least 15 minutes. For the calcium treatment of the silicon-calcium wire feedstock, the soft blowing time shall not be less than 15 minutes; during continuous casting, the tundish baking temperature shall be controlled not lower than 1050℃, the crystallizer water flow rate shall be 4500L / min, the secondary cooling water flow rate shall be 0.15L / kg, and the nozzle depth shall be 110±10mm; the crystallizer electromagnetic stirring and the end electromagnetic stirring shall be adopted, and the casting speed shall be dynamically controlled according to the superheat and casting speed. A specific tension leveling machine pressure curve shall be adopted, and the pressure of tension leveling machines 1-7 shall be 40bar, 45bar, 45bar, 55bar, 55bar, 55bar, and 60bar respectively.

2. The method for producing φ650mm large round billets of high alloy steel using continuous casting according to claim 1, characterized in that, The smelting process uses blast furnace iron with the following chemical composition as raw material: C 3.97~4.11%, Si 0.33%, Mn 0.28~0.30%, P 0.131~0.150%, S 0.037~0.039%, As 0.0160%, Sn 0.0001%, Pb 0.0010%, Sb 0.0001%, Bi 0.0009~0.0010%, with the remainder being Fe and unavoidable impurities.

3. The method for producing φ650mm large round billets of high alloy steel using continuous casting according to claim 1 or 2, characterized in that, The steel output during the smelting process is 80-85 tons. During the tapping process, 600 kg of lime, 300 kg of deoxidizing and desulfurizing refining slag, and 100 kg of aluminum ingots are added. The initial amount of low-chromium alloy added during tapping is 2 tons.

4. The method for producing φ650mm large round billets of high alloy steel using continuous casting according to claim 3, characterized in that, The refined low-carbon ferrochrome is added in 4 to 5 batches, with each batch containing ≤6 tons, and the temperature of the molten steel is not lower than 1620℃ when it is added; after adding the low-carbon ferrochrome in batches, medium-chromium or high-chromium ferrochrome is used to fine-tune the composition.

5. The method for producing φ650mm large round billets of high alloy steel using continuous casting according to claim 4, characterized in that, The feed rate of the silicon-calcium wire is 80-100 meters per furnace.

6. The method for producing φ650mm large round billets of high alloy steel using continuous casting according to claim 5, characterized in that, The initial pouring level for continuous casting shall not be less than 12 tons.

7. The method for producing φ650mm large round billets of high alloy steel using continuous casting according to claim 6, characterized in that, The special protective slag used in continuous casting contains the following components by mass percentage: SiO2 20-25%, Al2O3 10-15%, Fe2O3 1.30-1.50%, CaO 20-25%, MgO 4-6%, alkali metal oxide R2O 4.00-4.50%, F 2.40-2.60%, and fixed carbon C 6-10%; the binary basicity R of the protective slag is 1.00-1.05, the melting point is 1215-1225℃, and the viscosity at 1300℃ is [missing information]. The bulk density is 0.70~0.90 g / cm³. 3 The covering agent contains the following components by mass percentage: SiO2 40~45%, CaO 3~8%, MgO 11.00~11.50%, Fe2O3 3.20~3.60%, Al2O3 3~8%, C 20~25%, H2O 0.20~0.40%, and the melting point of the covering agent is 1345~1355℃.

8. The method for producing φ650mm large round billets of high alloy steel using continuous casting according to claim 7, characterized in that, The secondary cooling water distribution ratio for the continuous casting is 40% / 38% / 22%; the electromagnetic stirring parameters for the crystallizer are 300A / 2Hz, and the final electromagnetic stirring parameters are 450A / 4Hz.

9. The method for producing φ650mm large round billets of high alloy steel using continuous casting according to claim 8, characterized in that, The casting speed is 0.24 m / min when the superheat is <20℃, 0.23 m / min when the superheat is 20~40℃, and 0.22 m / min when the superheat is >40℃.

10. The method for producing φ650mm large round billets of high alloy steel using continuous casting according to claim 9, characterized in that, During the continuous casting fire cutting, the cut head of the billet is not less than 2000mm and the cut tail is not less than 3000mm. Iron powder is sprayed as an auxiliary during fire cutting, and the cutting time for each cut is 8.5~9min.

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