A continuous casting round billet for producing an electroslag roller and a production process thereof

Abstract

The application discloses a continuous casting round billet for producing an electroslag roller and a production process thereof, and belongs to the technical field of steel production, and the technical scheme is as follows: the continuous casting round billet for producing the electroslag roller comprises the following chemical components in percentage by weight: C: 0.89-0.95%, Si: 0.35-0.45%, Mn: 0.25-0.35%, Cr: 2.90-3.10%, Ni: 0.10-0.20%, Mo: 0.23-0.28%, Al: 0.020-0.030%, Ti: ≤0.0025%, P: ≤0.012%, S: ≤0.005%, and the balance is Fe and inevitable impurities, so that the titanium content in the steel and the level of inclusions are reduced, and the service life of the cold rolling roller is improved.

Description

Technical Field

[0001] This invention relates to the field of steel production technology, and in particular to a continuous casting round billet for producing electroslag remelting rolls and its production process. Background Technology

[0002] Electroslag remelting is a secondary refining technology that combines steel refining with directional solidification in a comprehensive metallurgical casting process. Its principle is that the resistance heat generated by the current passing through the liquid slag pool continuously melts the metal electrodes. The molten metal gathers into droplets, which fall through the slag layer and enter the molten metal pool, where they then crystallize and solidify into steel ingots in a water-cooled crystallizer.

[0003] Commonly used steels for cold rolling rolls include 9Cr, 9Cr2, 9CrV, 9Cr2W, and 9Cr2Mo steels. These steels are low-alloy tool steels made by adding elements such as molybdenum, tungsten, and vanadium to high-carbon chromium steel. The steel grade is selected appropriately according to the size of the roll and the hardenability of various steel grades. For example, 9Cr2W or 9Cr2Mo steel is used when the roll diameter exceeds 500mm. Cold rolling rolls with a roll diameter exceeding 400mm and a large load should be made of 9Cr2MoV steel. Cold rolling rolls with a roll diameter of 300-500mm can be made of 9Cr2 steel. When the roll diameter is less than 300mm, 9Cr or 9CrV steel can be used.

[0004] Because cold rolling rolls need to withstand significant stress during use, the presence of large non-metallic inclusions and coarse-grained structures, such as type A, B, C, D, and DS inclusions exceeding grade 1.5, can cause cracking during intense water quenching. Large inclusions on the roll surface also shorten the roll's service life. For cold rolling rolls, when inclusion sizes are the same, nitrides are more harmful than oxide inclusions. Currently, existing cold rolling rolls contain more than 50 ppm titanium and 80 ppm nitrogen, so the nitrides in cold rolling rolls are mainly TiN or TiCN, which are high-hardness, non-deformable inclusions, significantly reducing the fatigue life of the cold rolling rolls.

[0005] The existing difficulties in reducing the titanium content in cold rolling rolls are: firstly, the alloy and refining slag contain a certain amount of titanium; secondly, in the later stage of refining, some of the titanium in the slag will return to the molten steel, increasing the titanium content in the molten steel by 5-8 ppm, which is not conducive to the production of steel with low titanium content. Summary of the Invention

[0006] In order to reduce the titanium content and inclusion level in steel and improve the service life of cold rolling rolls, this invention provides a continuous casting round billet for producing electroslag rolling rolls and its production process.

[0007] A first aspect of the present invention provides a continuously cast round billet for producing electroslag remelting rolls, comprising the following technical solution: a continuously cast round billet for producing electroslag remelting rolls, wherein the chemical composition of the continuously cast round billet, by weight percentage, comprises C: 0.89-0.95%, Si: 0.35-0.45%, Mn: 0.25-0.35%, Cr: 2.90-3.10%, Ni: 0.10-0.20%, Mo: 0.23-0.28%, Al: 0.020-0.030%, Ti: ≤0.0025%, P: ≤0.012%, S: ≤0.005%, with the balance being Fe and unavoidable impurities.

[0008] Preferably, the unavoidable impurities, by weight percentage, include Cu: ≤0.20%, Pb: ≤0.010%, Sn: ≤0.010%, As: ≤0.010%, Sb: ≤0.010%, Bi: ≤0.010%, H: ≤0.00015%, O: ≤0.0015%, and N: ≤0.0060%.

[0009] By adopting the above technical solution, the control of the content of each element in this application can effectively reduce the level of inclusions in the rolls and improve the service life of the rolls.

[0010] Carbon, as one of the main elements of rolling mill rolls, can improve the hardness and strength of the rolls and increase their wear resistance. Generally speaking, rolling mill rolls with higher carbon content have higher hardness and wear resistance. However, excessive carbon content will increase the brittleness of the rolls. Therefore, when the carbon content of the rolling mill rolls is controlled within the range of 0.89-0.95%, not only can the hardness and wear resistance of the rolls be guaranteed, but also the service life of the rolls can be guaranteed.

[0011] The addition of manganese improves the toughness and wear resistance of the rolls, as well as their heat treatment properties. Increased silicon content enhances the rolls' hardness and fatigue resistance, while also improving thermal conductivity and service life. Chromium addition enhances the rolls' hardness and wear resistance, and also increases their fatigue resistance. The addition of molybdenum and nickel further improves the rolls' fatigue resistance and toughness, while controlled impurity elements effectively reduce their impact on the rolls' strength, hardness, and wear resistance.

[0012] In addition, the titanium content in the rolls of this application is ≤0.0025% and the nitrogen content is ≤0.0060%, which effectively reduces the titanium and nitrogen content in the rolls.

[0013] The second aspect of the present invention is to provide a production process for a continuously cast round billet for producing electroslag remelting rolls, comprising the following steps: converter smelting, LF furnace refining, VD vacuum treatment, and continuous casting;

[0014] During the converter smelting process, the following components are added sequentially: 2.9-3.2 kg / t of low-titanium refining slag, 3.5-4.5 kg / t of lime blocks, 1.4-2.1 kg / t of aluminum ingots, 50-51 kg / t of low-titanium high-carbon ferrochrome, 3.8-4.2 kg / t of silicon-manganese alloy, 2.0-2.1 kg / t of low-titanium ferrosilicon, 4.1-4.3 kg / t of ferromolybdenum, and a low-nitrogen carbon raiser. This ensures that the steel composition reaches the following levels: C 0.72-0.82%, Si 0.25-0.32%, Mn 0.26-0.31%, Cr 2.80-2.90%, Mo 0.240-0.260%, Al 0.025-0.035%, P≤0.010%, and S≤0.030%.

[0015] The basicity of the refining slag used in the early stage of LF furnace refining is 4-5, and the basicity of the refining slag is reduced to 2-3 in the last 5 minutes after the end of LF furnace refining; the vacuum degree during VD vacuum treatment is ≤67Pa, the vacuum holding time is ≥15min, and the soft blowing time is ≥20min.

[0016] By adopting the above technical solution, since titanium in steel mainly comes from alloy materials, this application can effectively reduce the titanium content in steel by adding low-titanium refining slag, low-titanium high-carbon ferrochrome, and low-titanium ferrosilicon in converter steelmaking. Furthermore, by strictly controlling the basicity of the refining slag in the early and late stages of refining, it can effectively prevent the titanium content in the slag from being partially reduced into the molten steel during the VD vacuum treatment process, thus preventing the titanium content in the steel from rising again.

[0017] Preferably, the low-titanium refining slag, lime blocks, aluminum ingots, low-titanium high-carbon ferrochrome, silicon-manganese alloy, low-titanium ferrosilicon, ferromolybdenum, and low-nitrogen carbon raiser are added when the steel is tapped from the converter, between one-quarter and one-half of the way through the tapping process.

[0018] Preferably, the particle size of the lime blocks, aluminum ingots, silicon-manganese alloy, and ferromolybdenum is 10-50 mm.

[0019] Preferably, the chemical composition of the low-titanium refining slag, by weight percentage, is: CaO 45-55%, SiO2 4.0-6.0%, Al2O3 40-50%, TiO≤0.03%, and moisture≤0.5%, and the particle size of the low-titanium refining slag is 5-30mm.

[0020] Preferably, the chemical composition of the low-titanium high-carbon ferrochrome, by weight percentage, is: Cr 60-80%, C≤10%, Si≤1%, P≤0.015%, S≤0.025%, Ti≤0.02%, W≤0.1%, with the balance being iron, and the particle size of the low-titanium high-carbon ferrochrome is 10-70 mm.

[0021] Preferably, the chemical composition of the low-titanium ferrosilicon, by weight percentage, is: Si 72-80%, P≤0.04%, S≤0.02%, C≤0.2%, Ti≤0.05%, W≤0.1%, Mn≤0.5%, Cr≤0.5%, Al≤2%, with the balance being iron, and the particle size of the low-titanium ferrosilicon is 10-70 mm.

[0022] Preferably, the continuous casting adopts a crystallizer, end electromagnetic stirring, secondary cooling with weak cooling, and low superheat casting. The superheat is controlled at 15-25℃, the casting speed is 0.23m / min, the crystallizer water flow rate is 4600L / min, and the secondary cooling water flow rate is 0.08L / kg.

[0023] Preferably, the continuous casting slow cooling requirements are: the temperature upon entering the pit is ≥500℃, the slow cooling time is ≥48h, the cover is opened for cooling when the billet temperature is ≤200℃, and the billet exiting the pit temperature is ≤150℃.

[0024] By adopting the above technical solution, the setting of slow cooling requirements for continuous casting can avoid the transformation temperature of martensite formation, and prevent the formation of martensite in the rolls and the generation of structural stress cracks.

[0025] In summary, the present invention has the following beneficial effects:

[0026] This application incorporates low-titanium alloy materials during the converter tapping process while controlling the basicity of the refining slag in the early and late stages of LF furnace refining. This effectively prevents the partial reduction of titanium content in the slag into the molten steel during VD vacuum treatment, thus preventing a rebound in the titanium content in the steel. Consequently, it effectively ensures that the titanium content in the rolls is stably controlled within ≤0.0025%. Furthermore, this application uses low-nitrogen materials to control the nitrogen content within 0.0060%, and controlling the slow cooling temperature and time upon entering the pit can prevent the formation of martensite and stress cracks in the microstructure. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the embodiments.

[0028] Example 1

[0029] A production process for continuously cast round billets used in the production of electroslag remelting rolls includes the following steps:

[0030] (1) Converter smelting: The composition of the molten iron entering the furnace is P 0.10%, S 0.045%, Pb 0.012%, Sn 0.013%, As 0.015%, Sb 0.013%, and Bi 0.010%. The final C content in the converter is ≥0.10%, and P ≤0.010%. The tapping temperature of the converter is 1630℃. When the steel is tapped from 1 / 4 to 1 / 2 of the way through the converter, 2.9 kg / t of low-titanium refining slag, 3.5 kg / t of lime blocks, 1.4 kg / t of aluminum ingots, 50 kg / t of low-titanium high-carbon ferrochrome, 3.8 kg / t of silicon-manganese alloy, 2.0 kg / t of low-titanium ferrosilicon, 4.1 kg / t of ferromolybdenum, and an appropriate amount of low-nitrogen carbon raiser are added sequentially to make the steel composition reach C 0.72%, Si 0.25%, Mn 0.26%, Cr 2.80%, and Mo 0.25%. 0.24%, Al0.025%, P 0.010%, S 0.030%;

[0031] The chemical composition of the low-titanium refining slag, by weight percentage, is: CaO 45.4%, SiO2 4.07%, Al2O3 50.0%, TiO 0.03%, and moisture 0.5%, and the particle size of the low-titanium refining slag is 5-30mm.

[0032] The chemical composition of low-titanium high-carbon ferrochrome by weight percentage is: Cr 60%, C 10%, Si 0.8%, P 0.013%, S 0.025%, Ti 0.01%, W 0.1%, with the balance being iron. The particle size of low-titanium high-carbon ferrochrome is 10-70 mm.

[0033] The chemical composition of low-titanium ferrosilicon, by weight percentage, is: Si 72%, P 0.04%, S 0.02%, C 0.1%, Ti 0.03%, W 0.1%, Mn 0.3%, Cr 0.2%, Al 1.5%, with the balance being iron. The particle size of low-titanium ferrosilicon is 10-70 mm.

[0034] The particle size of lime blocks, aluminum ingots, silicon-manganese alloy, and ferromolybdenum is 10-50 mm. The silicon-manganese alloy contains 17 wt% silicon and 68 wt% manganese, with the balance being iron. The ferromolybdenum alloy contains 60 wt% molybdenum.

[0035] (2) LF furnace refining: In the early stage of refining, the basicity of the refining slag is 4-5 (CaO:SiO2 is 4-5). In the last 5 minutes before the end of LF furnace refining, the basicity of the refining slag is adjusted to 2-3.

[0036] (3) VD vacuum degassing treatment: vacuum degree 67Pa, vacuum time 20min, soft blowing time 20min, thereby improving the purity of steel;

[0037] (4) Continuous casting process: The continuous casting process adopts a crystallizer electromagnetic stirring current of 200A and a frequency of 2.0Hz, an end electromagnetic stirring current of 410A and a frequency of 9Hz, a crystallizer water flow of 4600L / min, a secondary cooling water flow of 0.08L / kg, a superheat of 15-25℃, and a casting speed of 0.23m / min.

[0038] The billet was transported to the heat preservation pit, with an initial temperature of 500℃ and a slow cooling time of 48 hours. When the billet temperature reached 200℃, the lid was removed for cooling. The billet exited the pit at a temperature of 150℃. The chemical composition of the final billet is shown in Table 1.

[0039] Example 2

[0040] A production process for continuously cast round billets used in the production of electroslag remelting rolls includes the following steps:

[0041] (1) Converter smelting: The composition of the molten iron entering the furnace is P 0.10%, S 0.050%, Pb 0.013%, Sn 0.013%, As 0.015%, Sb 0.011%, Bi 0.010%, and the final C content at the converter is 0.15%, P 0.010%. The converter tapping temperature is 1640℃. When the steel is tapped from 1 / 4 to 1 / 2 of the way through the converter, 3.0 kg / t of low-titanium refining slag, 4.0 kg / t of lime blocks, 1.8 kg / t of aluminum ingots, 50 kg / t of low-titanium high-carbon ferrochrome, 4.0 kg / t of silicon-manganese alloy, 2.0 kg / t of low-titanium ferrosilicon, 4.2 kg / t of ferromolybdenum, and an appropriate amount of low-nitrogen carbon raiser are added sequentially to make the steel composition reach C 0.78%, Si 0.27%, Mn 0.29%, Cr 2.80%, Mo The chemical composition of the low-titanium refining slag, by weight percentage, is: CaO 50.8%, SiO2 6.0%, Al2O3 43.09%, TiO 0.01%, and moisture 0.1%, and the particle size of the low-titanium refining slag is 5-30 mm.

[0042] The chemical composition of low-titanium high-carbon ferrochrome by weight percentage is: Cr 70%, C 9%, Si 0.9%, P 0.014%, S 0.023%, Ti 0.02%, W 0.1%, with the balance being iron. The particle size of low-titanium high-carbon ferrochrome is 10-70 mm.

[0043] The chemical composition of low-titanium ferrosilicon, by weight percentage, is: Si 76%, P 0.04%, S 0.02%, C 0.15%, Ti 0.05%, W 0.1%, Mn 0.3%, Cr 0.5%, Al 2%, with the balance being iron. The particle size of low-titanium ferrosilicon is 10-70 mm.

[0044] The particle size of lime blocks, aluminum ingots, silicon-manganese alloy, and ferromolybdenum is 10-50 mm; the silicon-manganese alloy contains 20 wt% silicon and 65 wt% manganese, with the balance being iron; the ferromolybdenum alloy contains 65 wt% molybdenum.

[0045] (2) LF furnace refining: In the early stage of refining, the basicity of the refining slag is 4-5 (CaO:SiO2 is 4-5). In the last 5 minutes before the end of LF furnace refining, the basicity of the refining slag is adjusted to 2-3.

[0046] (3) VD vacuum degassing treatment: vacuum degree 65Pa, vacuum time 15min, soft blowing time 24min, thereby improving the purity of steel;

[0047] (4) Continuous casting process: The continuous casting process adopts a crystallizer electromagnetic stirring current of 200A and a frequency of 2.0Hz, an end electromagnetic stirring current of 410A and a frequency of 9Hz, a crystallizer water flow of 4600L / min, a secondary cooling water flow of 0.08L / kg, a superheat of 15-25℃, and a casting speed of 0.23m / min.

[0048] The billet was transported to the heat preservation pit, with an initial temperature of 550℃ and a slow cooling time of 50 hours. When the billet temperature reached 200℃, the lid was removed for cooling. The billet exited the pit at a temperature of 140℃. The chemical composition of the final billet is shown in Table 1.

[0049] Example 3

[0050] A production process for continuously cast round billets used in the production of electroslag remelting rolls includes the following steps:

[0051] (1) Converter smelting: The composition of the molten iron entering the furnace is P 0.10%, S 0.050%, Pb 0.015%, Sn 0.015%, As 0.015%, Sb 0.015%, Bi 0.010%, and the final C content at the converter is 0.11%, P 0.010%. The converter tapping temperature is 1650℃. When the steel is tapped from 1 / 4 to 1 / 2 of the way through the converter, 3.2 kg / t of low-titanium refining slag, 4.5 kg / t of lime blocks, 2.1 kg / t of aluminum ingots, 51 kg / t of low-titanium high-carbon ferrochrome, 4.2 kg / t of silicon-manganese alloy, 2.1 kg / t of low-titanium ferrosilicon, 4.3 kg / t of ferromolybdenum, and an appropriate amount of low-nitrogen carbon raiser are added sequentially to make the steel composition reach C 0.82%, Si 0.32%, Mn 0.31%, Cr 2.90%, Mo 0.260%, Al 0.035%, P0.010%, S0.030%;

[0052] The chemical composition of the low-titanium refining slag, by weight percentage, is: CaO 55.0%, SiO2 5.7%, Al2O3 40.09%, TiO 0.01%, and moisture 0.2%, and the particle size of the low-titanium refining slag is 5-30mm.

[0053] The chemical composition of low-titanium high-carbon ferrochrome by weight percentage is: Cr 80%, C 10%, Si 1%, P 0.015%, S 0.025%, Ti 0.02%, W 0.1%, with the balance being iron. The particle size of low-titanium high-carbon ferrochrome is 10-70 mm.

[0054] The chemical composition of low-titanium ferrosilicon, by weight percentage, is: Si 80%, P 0.04%, S 0.02%, C 0.2%, Ti 0.05%, W 0.1%, Mn 0.5%, Cr 0.5%, Al 2%, with the balance being iron. The particle size of low-titanium ferrosilicon is 10-70 mm.

[0055] The particle size of lime blocks, aluminum ingots, silicon-manganese alloy, and ferromolybdenum is 10-50 mm; the silicon-manganese alloy contains 17 wt% silicon and 72 wt% manganese, with the balance being iron; the ferromolybdenum alloy contains 60 wt% molybdenum.

[0056] (2) LF furnace refining: In the early stage of refining, the basicity of the refining slag is 4-5 (CaO:SiO2 is 4-5). In the last 5 minutes before the end of LF furnace refining, the basicity of the refining slag is adjusted to 2-3.

[0057] (3) VD vacuum degassing treatment: vacuum degree 65Pa, vacuum time 20min, soft blowing time 25min, thereby improving the purity of steel;

[0058] (4) Continuous casting process: The continuous casting process adopts a crystallizer electromagnetic stirring current of 200A and a frequency of 2.0Hz, an end electromagnetic stirring current of 410A and a frequency of 9Hz, a crystallizer water flow of 4600L / min, a secondary cooling water flow of 0.08L / kg, a superheat of 15-25℃, and a casting speed of 0.23m / min.

[0059] The billet was transported to the heat preservation pit, with an initial temperature of 520℃ and a slow cooling time of 51 hours. When the billet temperature reached 180℃, the lid was removed for cooling. The billet exited the pit at a temperature of 130℃. The chemical composition of the final billet is shown in Table 1.

[0060] Table 1 Chemical composition of continuously cast round billets (unit: wt%)

[0061] Element Example 1 Example 2 Example 3 C 0.89 0.92 0.95 Si 0.45 0.40 0.35 Mn 0.25 0.31 0.35 Cr 3.10 2.90 3.00 Ni 0.10 0.15 0.20 Mo 0.23 0.26 0.28 Al 0.020 0.030 0.025 Ti 0.0025 0.0020 0.0022 P 0.012 0.010 0.011 S 0.004 0.003 0.004 Cu 0.19 0.16 0.18 Pb 0.01 0.008 0.009 Sn 0.01 0.009 0.01 As 0.008 0.007 0.01 Sb 0.009 0.008 0.007 Bi 0.009 0.009 0.008 H 0.00014 0.00013 0.00015 O 0.0015 0.0012 0.0013 N 0.005 0.005 0.004 iron margin margin margin

[0062] Comparative Example 1

[0063] A production process for continuously cast round billets used to produce electroslag rolls differs from Example 1 in that the basicity of the refining slag used in the LF furnace refining is consistently 4-5 (CaO:SiO2 is 4-5), and the final billet has a titanium content of 0.0035%, while the contents of other chemical components are the same as in Example 1.

[0064] Performance testing

[0065] After the continuously cast round billets obtained in the above embodiments and comparative examples were further processed and forged into rolls, the non-metallic inclusion levels and fatigue properties were tested. The test results are shown in Table 2. The non-metallic inclusion levels were tested according to Method A in GB / T10561-2005 "Standard Rating Chart Microscopic Examination Method for Determination of Non-metallic Inclusion Content in Steel". Among them, Class A is sulfide inclusions, Class B is alumina inclusions, Class C is silicate inclusions, and Class D is spherical oxide inclusions.

[0066] Table 2. Results of Inclusion Detection in Continuously Cast Round Billets (Unit: Grade)

[0067]

[0068] As can be seen from Table 2, the coarse and fine series of inclusions (Type A, Type B, Type C, and Type D) in the rolls obtained in Examples 1-3 of this application are all far below the technical requirements. Moreover, as can be seen from Table 1 of this application, the titanium content in the billet obtained in the examples of this application is less than 0.0025% and the nitrogen content is less than 0.006%, indicating that the preparation method of this application can effectively control the titanium and nitrogen content in the rolls, thereby obtaining rolls with low titanium content.

[0069] Compared with Example 1, when the basicity of the refining slag was consistently 4-5 during refining in the LF furnace, the titanium content in the final billet was 0.0035%, which was much higher than that in Example 1. This is because during the vacuum treatment in the VD furnace, some of the titanium content in the slag returned to the molten steel, leading to an increase in the titanium content in the molten steel. It can be seen that by controlling the basicity of the refining slag in the early and late stages, this application can effectively prevent titanium in the slag from returning to the molten steel, thereby stably obtaining rolls with low titanium content and reducing the nitride content in the steel. In addition, as can be seen from Table 2 of this application, the grades of fine inclusions of type A, coarse and fine inclusions of type B, fine inclusions of type C, coarse and fine inclusions of type D, and inclusions of type DS in the rolls obtained in Comparative Example 1 are all higher than the grades of the corresponding types of inclusions in Example 1. This indicates that the setting of the basicity in the early and late stages of refining slag also affects the grade of non-metallic inclusions in the rolls.

[0070] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A production process of a continuously cast round billet for producing an electro- slag roller, characterized by: The chemical composition of the continuous casting round billet includes, in percentage by weight, C: 0.89-0.95%, Si: 0.35-0.45%, Mn: 0.25-0.35%, Cr: 2.90-3.10%, Ni: 0.10-0.20%, Mo: 0.23-0.28%, Al: 0.020-0.030%, Ti: ≤0.0025%, P: ≤0.012%, S: ≤0.005%, and the balance of Fe and inevitable impurities; The production process of the continuous casting round billet comprises the following steps: converter smelting, LF furnace refining, VD vacuum treatment, and continuous casting; In the converter smelting process, low-titanium refining slag 2.9-3.2 kg / t, lime block 3.5-4.5 kg / t, aluminum ingot 1.4-2.1 kg / t, low-titanium high-carbon chromium iron 50-51 kg / t, silicon-manganese alloy 3.8-4.2 kg / t, low-titanium silicon iron 2.0-2.1 kg / t, ferromolybdenum 4.1-4.3 kg / t, and low-nitrogen carbon additive are sequentially added to make the composition of the molten steel reach C 0.72-0.82%, Si 0.25-0.32%, Mn 0.26-0.31%, Cr 2.80-2.90%, Mo 0.240-0.260%, Al 0.025-0.035%, P ≤0.010%, and S ≤0.030%; The basicity of the refining slag used in the early stage of the LF furnace refining is 4-5, and the basicity of the refining slag is 2-3 in the last 5 minutes of the LF furnace refining; The vacuum degree of the VD vacuum treatment is ≤67 Pa, the vacuum holding time is ≥15 min, and the soft blowing time is ≥20 min; The inevitable impurities include, in percentage by weight, Cu: ≤0.20%, Pb: ≤0.010%, Sn: ≤0.010%, As: ≤0.010%, Sb: ≤0.010%, Bi: ≤0.010%, H: ≤0.00015%, O: ≤0.0015%, and N: ≤0.0060%; the low-titanium refining slag, lime block, aluminum ingot, low-titanium high-carbon chromium iron, silicon-manganese alloy, low-titanium silicon iron, ferromolybdenum, and low-nitrogen carbon additive are added when the converter is one-quarter to one-half of the tapping; The particle size of the lime block, aluminum ingot, silicon-manganese alloy, and ferromolybdenum is 10-50 mm; The chemical composition of the low-titanium refining slag includes, in percentage by weight, CaO 45-55%, SiO2 4.0-6.0%, Al2O3 40-50%, TiO ≤0.03%, and moisture ≤0.5%, and the particle size of the low-titanium refining slag is 5-30 mm; The chemical composition of the low-titanium high-carbon chromium iron includes, in percentage by weight, Cr 60-80%, C ≤10%, Si ≤1, P ≤0.015%, S ≤0.025%, Ti ≤0.02%, W ≤0.1%, and the balance of iron, and the particle size of the low-titanium high-carbon chromium iron is 10-70 mm; The low-titanium ferrosilicon has chemical components in percentage by weight as follows: Si 72-80%, P≤0.04%, S≤0.02%, C≤0.2%, Ti≤0.05%, W≤0.1%, Mn≤0.5%, Cr≤0.5%, Al≤2%, and the balance is iron, and the particle size of the low-titanium ferrosilicon is 10-70 mm. The continuous casting adopts a crystallizer, end electromagnetic stirring, weak secondary cooling, and low superheat pouring, the superheat is controlled to be 15-25 ℃, the pulling speed is 0.23 m / min, the crystallizer water amount is 4600 L / min, and the secondary cooling specific water amount is 0.08 L / kg. The continuous casting slow cooling requirements are that the entering pit temperature is≥500 ℃, the slow cooling time is≥48 h, the cover is uncovered when the casting blank temperature is≤200 ℃, and the casting blank out-pit temperature is≤150 ℃.

2. A continuously cast round billet obtained by the production process according to claim 1, characterized in that: The continuous casting round blank has chemical components in percentage by weight as follows: C: 0.89-0.95%, Si: 0.35-0.45%, Mn: 0.25-0.35%, Cr: 2.90-3.10%, Ni: 0.10-0.20%, Mo: 0.23-0.28%, Al: 0.020-0.030%, Ti:≤0.0025%, P:≤0.012%, S:≤0.005%, and the balance is Fe and inevitable impurities.

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