B3 grinding ball steel with bloom with section of 390mm*510mm and preparation method of B3 grinding ball steel

Abstract

The invention relates to 390mm * 510mm section bloom B3 grinding ball steel and a preparation method thereof, and the preparation method comprises the following steps: loading a certain amount of molten iron and scrap steel for primary smelting in a converter, and sequentially adding an aluminum ingot, an alloy, pre-melting type calcium aluminate and refined lime when 1 / 4 of the steel is tapped; carrying out LF refining on the tapping molten steel subjected to primary smelting in the converter to obtain refined molten steel; the refined molten steel is subjected to RH vacuum refining, and RH vacuum refined molten steel is obtained through superheat degree control, RH working vacuum degree control, retention time control and soft blowing time control; and continuous casting is conducted, specifically, the RH vacuum refined molten steel is subjected to set pulling speed, crystallizer and tail end electromagnetic stirring and soft reduction treatment according to the pouring section, and the bloom B3 grinding ball steel with the section being 390 mm * 510 mm is obtained. According to the method, the converter primary smelting, the LF refining, the RH vacuum refining and the molten steel whole-process protection pouring smelting process are controlled, the cleanliness of the molten steel is guaranteed, and generation of large-particle inclusions is avoided; and process parameters are reasonably set in the continuous casting process, so that the internal quality of the bloom is obviously improved, and the production efficiency is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of steelmaking and continuous casting, and particularly relates to a 390mm×510mm cross-section bloom B3 grinding ball steel and a preparation method thereof. Background Art

[0002] Grinding ball steel is widely used in industries such as mining, metallurgy, and cement. In recent years, with the rapid development of the mining industry, stringent requirements have been placed on the quality of grinding ball steel, requiring it to have good internal quality, wear resistance, overall hardness and uniformity, and good impact toughness to reduce the consumption of wear-resistant balls during the ore crushing process. Macrosegregation and central shrinkage are two major defects that affect the internal quality of continuous casting billets. This is especially true for large square billets of high-carbon, high-alloy steel. Due to the high carbon and alloy content, the solid-liquid phase zone is long and wide, and the solidification time is long, which makes it more likely to form severe macrosegregation and central shrinkage, affecting the quality of subsequent rolled products. With the improvement of intelligent metallurgical equipment, various methods have been developed to improve the internal defects of casting billets, such as reducing harmful elements in steel, low superheat casting technology, reasonable control of casting speed, reasonable control of secondary cooling water ratio, electromagnetic stirring technology, and end-of-slab solidification reduction technology. The above measures have achieved some results when used alone or in combination, but there is still little research on the coordinated control of the entire steelmaking process to improve the internal quality of grinding ball steel blooms. In particular, there are problems in the smelting process of large square billet B3 grinding ball steel, such as large particle inclusions that are difficult to control, large central shrinkage and central segregation of the large square billet, and low flaw detection pass rate of rolled round steel. Summary of the Invention

[0003] In order to overcome the problems existing in the prior art, the present invention provides a 390mm×510mm cross-section bloom B3 grinding ball steel and a preparation method thereof.

[0004] A method for preparing a 390mm×510mm cross-section bloom B3 grinding ball steel comprises the following steps: converter primary refining→LF refining→RH vacuum refining→continuous casting.

[0005] Among them, the converter primary refining: a certain amount of molten iron and scrap steel are charged for primary refining, so that the carbon content of the tapped steel is ≥0.020%, the P content of the tapped steel is ≤0.015%, and the tapping temperature is ≥1620℃. When 1 / 4 of the steel is tapped, aluminum ingots, alloys, pre-melted calcium aluminate and refined lime are added in sequence;

[0006] LF refining: When the molten steel from the primary converter enters the LF refining station, the temperature of the molten steel is ≥1500℃. The power is turned on for a period of time, during which white slag is formed in the molten steel and the molten steel temperature is controlled at 1530-1540℃. The white slag is maintained for ≥30 minutes. The refining cycle is 60-80 minutes to obtain refined molten steel.

[0007] RH vacuum refining: When the refined steel liquid is subjected to RH vacuum refining, the superheat is controlled to be ≤30℃, the liquidus temperature is 1471℃, the RH working vacuum is ≤67Pa, the holding time is ≥15min, and the soft blowing time is ≥17min to obtain RH vacuum refined steel liquid;

[0008] Continuous casting: The RH vacuum refined molten steel is subjected to a set casting speed, crystallizer and end electromagnetic stirring, and soft reduction treatment according to the casting section to obtain a large square bloom B3 grinding ball steel with a cross-section of 390mm×510mm.

[0009] According to the aspects and any possible implementations described above, an implementation is further provided, wherein the certain amount of molten iron and scrap steel includes 110±2t molten iron and 22±2t scrap steel, and the steel output is 120 tons of molten steel.

[0010] According to the aspects and any one of the above-mentioned aspects, an implementation method is further provided, wherein the alloy is an alloy added to the molten steel when the steel is tapped after the initial smelting in the converter, and the alloy element content is controlled in the range of C: 0.45~0.51%, Mn: 0.63~0.69%, Si: 1.50~1.60%, Cr: 0.67~0.73%, and Alt: 0.018~0.030%.

[0011] According to the above aspects and any possible implementation, an implementation is further provided, wherein the period of time is 12 minutes.

[0012] According to the aspects and any possible implementation methods described above, an implementation method is further provided. In the LF refining process, 50 kg of calcium carbide, 160 kg of lime, 300 kg of pre-melted calcium aluminate and 10 kg of aluminum particles are added to the molten steel after the power is turned on for the first time; 50 kg of calcium carbide, 100 kg of lime and 260 kg of pre-melted calcium aluminate are added after the power is turned on for the second time. After the power is turned on for the third time, white slag is formed, and the molten steel temperature is 1530-1540°C. When sampling determines that Alt≤0.020%, Alt is adjusted to 0.025%, and 20 kg of calcium carbide is used to continue slag surface diffusion deoxidation. The white slag effect is maintained until the end of refining. The second time is greater than the third time, and the third time is greater than the first time.

[0013] According to the aspects described above and any possible implementation method, an implementation method is further provided, wherein the composition of the refined molten steel is C: 0.59~0.61%, Mn: 0.68~0.74%, Si: 1.67~1.74%, Cr: 0.73~0.77%, S≤0.005%, P≤0.015%, Alt: 0.022~0.030%.

[0014] According to the above aspects and any possible implementation, an implementation is further provided, wherein in the RH refining process, [H] in the molten steel is ≤1.0ppm, and after the RH vacuum refining is completed, the molten steel is calcium treated, and the amount of pure calcium wire fed is 50 to 70m / furnace.

[0015] In the above aspects and any possible implementation, an implementation is further provided, wherein a 5-machine 5-strand bloom continuous casting machine is used in the continuous casting to produce a 390mm×510mm cross-section, the tundish adopts an integral tundish with an internal nozzle, the superheat of the molten steel is controlled to be 18-28°C, full-process protection casting is adopted, the ladle adopts a long nozzle for protection casting, the long nozzle of the ladle is equipped with a sealing gasket and argon sealing protection, and the argon sealing gas flow rate is 10-13Nm 3 / h, argon pressure is 0.10~0.15MPa.

[0016] The present invention also provides a 390mm×510mm cross-section bloom B3 grinding ball steel, which is obtained by adopting the preparation method.

[0017] According to the above aspects and any possible implementation, an implementation is further provided, wherein the chemical composition of the B3 grinding ball steel includes, by weight percentage, the following: C: 0.59-0.61%, Mn: 0.67-0.73%, Si: 1.64-1.74%, Cr: 0.71-0.77%, S≤0.010%, P≤0.015%, Alt: 0.015-0.025%, Ti≤0.015%, O≤15ppm, N≤40ppm, H≤1.0ppm, and the rest is Fe and unavoidable impurities.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The preparation method of the present invention strengthens the control of the entire process of protective pouring and smelting in the converter, LF refining, RH vacuum refining, and continuous casting, ensuring the required cleanliness of the molten steel and avoiding non-compliant rolled product inspections due to large particle inclusions. By rationally setting the process parameters for the continuous casting process, the internal quality of the ingot is significantly improved, production efficiency is significantly increased, and non-compliant rolled product inspections due to central shrinkage and segregation defects in the large square billet are avoided. The 390mm×510mm cross-section B3 grinding ball steel continuous casting ingots produced using the present invention have central looseness and central shrinkage within 0.5, and central segregation within 0.95-1.05. The slow cooling time of the ingot is shortened to 48 hours. The round steel products obtained after rolling the continuous casting billet are tested and the total oxygen content is controlled to be less than 15ppm. The non-metallic inclusions are tested according to method A in GB / T10561 standard: Class A fine series ≤0.5 level, Class A coarse series ≤0 level, Class B fine series ≤0.5 level, Class B coarse series ≤0 level, Class D fine series ≤0.5 level, Class D coarse series ≤0 level. The ultrasonic flaw detection result according to GB / T4162 is Class A. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a transverse low-magnification photograph of a 390 mm × 510 mm cross-section bloom B3 grinding ball steel sample prepared in Example 6;

[0021] Figure 2 This is a low-magnification longitudinal sample of a 390 mm × 510 mm cross-section bloom B3 grinding ball steel prepared in Example 6;

[0022] Figure 3 Schematic diagram of the full-point segregation sampling positions of the transverse macro-magnification specimen of B3 grinding ball steel with a cross-section of 390 mm × 510 mm prepared in Example 6;

[0023] Figure 4 Schematic diagram of the full-point segregation sampling positions of a longitudinal macro-magnification specimen of B3 grinding ball steel with a cross-section of 390 mm × 510 mm prepared in Example 6;

[0024] Figure 5 This is a schematic diagram of the full-point segregation results of a transverse macro-magnification specimen of a 390 mm × 510 mm cross-section bloom B3 grinding ball steel prepared in Example 6;

[0025] Figure 6 This is a schematic diagram of the central segregation results of a longitudinal macro-magnification specimen of a 390 mm × 510 mm cross-section bloom B3 grinding ball steel prepared in Example 6;

[0026] Figure 7 Flow chart of the method of the present invention. DETAILED DESCRIPTION

[0027] To better understand the technical solutions of the present invention, the present invention includes but is not limited to the specific embodiments described below. Similar technologies and methods should be considered within the scope of protection of the present invention. To further clarify the technical problems, technical solutions, and advantages to be solved by the present invention, the following detailed description is provided in conjunction with the accompanying drawings and specific embodiments.

[0028] It should be understood that the embodiments described herein are only a portion of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "an", "the" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0030] like Figure 7 As shown, the present invention provides a method for preparing 390mm×510mm cross-section bloom B3 grinding ball steel, comprising the following steps: converter primary refining→LF refining→RH vacuum refining→continuous casting.

[0031] The converter primary refining specifically includes: loading a certain amount of molten iron and scrap steel for primary refining, so that the C content of the tapped steel is ≥0.020%, the tapping P is ≤0.015%, and the tapping temperature is ≥1620°C, and aluminum ingots, alloys, pre-melted calcium aluminate and refined lime are added in sequence when 1 / 4 of the steel is tapped. During the converter primary refining and tapping process, the aluminum ingots are first strongly deoxidized to reduce the oxygen content of the molten steel, improve the hit rate of the alloy components, reduce the large particles of aluminum oxide caused by insufficient deoxidation, and promote the rapid floating and removal of clustered Al2O3 deoxidation products. Adding pre-melted calcium aluminate and refined lime during the converter primary refining and tapping process is beneficial to promote rapid slag formation in LF refining, facilitate the rapid removal of inclusions, and reduce the damage of large particle inclusions to rolled material flaw detection. In the present invention, the certain amount is preferably 110±2t of molten iron and 22±2t of scrap steel, and the tapping amount is 120 tons of molten steel at this time.

[0032] LF refining specifically includes: when the molten steel from the primary converter enters the LF refining station, the incoming molten steel temperature is ≥1500°C, and power is applied for a period of time, during which white slag forms in the molten steel and the molten steel temperature is controlled at 1530-1540°C. The white slag is maintained for ≥30 minutes, and the refining cycle is 60-80 minutes to obtain refined molten steel. By controlling the molten steel temperature and white slag effect during LF refining, LF refining is conducive to early removal of non-metallic inclusions through rapid slagging, ensuring sufficient time for inclusion removal;

[0033] RH vacuum refining specifically includes: when refining molten steel through RH vacuum refining, the superheat is controlled to be ≤30°C, the liquidus temperature is 1471°C, the RH working vacuum is ≤67Pa, the holding time is ≥15min, and the soft blowing time is ≥17min. Through strict control of superheat, continuous casting is facilitated to achieve constant casting speed, obtain good internal quality of continuous casting billets, reduce the level of central shrinkage and segregation, and through the control of RH vacuum degree and holding time, ensure the number of circulations of molten steel under vacuum conditions, reduce the content of harmful gases such as hydrogen and nitrogen in the steel, reduce the formation of large TiN inclusions, and promote the floating removal of inclusions during RH vacuum refining, thereby improving the cleanliness of molten steel and reducing the harm of large inclusions, thereby obtaining RH vacuum refined molten steel.

[0034] The continuous casting process includes: subjecting RH vacuum refined molten steel to a set drawing speed, crystallizer and end electromagnetic stirring, and soft reduction treatment according to the casting section to obtain a 390mm×510mm cross-section large square bloom B3 grinding ball steel.

[0035] Furthermore, during continuous casting, the ladle containing RH vacuum refined molten steel is hoisted to the turret of the 5-machine 5-strand bloom continuous casting machine, and the molten steel is poured into the tundish to form a ladle. A long nozzle is used between the ladle and the tundish for protection casting. The long nozzle of the ladle is equipped with a sealing gasket, and the long nozzle sealing gasket is sealed with argon gas with a flow rate of 10 to 13 Nm 3 / h, the argon pressure is 0.10-0.15MPa, the present invention adopts an integral tundish with an internal nozzle, which ensures the protection of the continuous casting process, prevents the secondary oxidation of the molten steel, and avoids the damage of large particle inclusions caused by the secondary oxidation to the rolling flaw detection. The molten steel in the tundish is injected into the crystallizer for primary cooling. The cross section of the casting is 390mm×510mm, and the water volume of the crystallizer is 150±3m 3 / h, the crystallizer adopts the crystallizer electromagnetic stirring technology, and the crystallizer electromagnetic stirring operating parameters are set to: 450A, 1.5HZ, to ensure that the ingot obtains a reasonable equiaxed crystal ratio, which is beneficial to reduce the shrinkage cavity and segregation in the center of the ingot. The continuous casting speed is set to 0.43m / min by numerical simulation, to ensure that the solid phase ratio at the center of the light pressure position is 0.30-0.90, the superheat of the molten steel is controlled at 18-28℃, and the continuous casting is cast at a constant pulling speed throughout the whole process. In order to ensure the uniformity of cooling, the secondary cooling water volume is 0.12L / Kg, and the water distribution ratio of the four cooling zones of the secondary cooling water is 25%, 40%, 25% and 10% In order to reduce the dendrite bridging at the end of solidification of the ingot and reduce the level of central shrinkage, the operating parameters of the end electromagnetic stirring are 600A and 8.0HZ. Soft reduction is used to compensate for the shrinkage of the molten steel at the end of solidification and reduce the level of central shrinkage and segregation. The 1#-6# light reduction rollers at the end of solidification are 1.5mm, 2.5mm, 3.5mm, 4.5mm, 4mm, and 4mm respectively, with a total reduction of 20mm. The prepared 390mm×510mm cross-section large square billet B3 grinding ball steel continuous casting billet is centrally loose, the central shrinkage is controlled within 0.5 level, and the central segregation is controlled within 0.95~1.05.

[0036] Furthermore, in the continuous casting process, the produced 390mm×510mm cross-section B3 grinding ball steel large square billets are put into the pit for slow cooling or hot delivery. The slow-cooled billets are placed in a line in the slow cooling pit in the same direction. The slow-cooled billets entering the pit are ≥550°C. The pit cover is tightly closed after entering the pit. The pit cover is opened after 15 hours. The slow cooling time is 48 hours and the billet temperature is ≤300°C before the billet is removed from the pit. The billet has a small stress concentration and is subsequently rolled to obtain a round steel product. At this time, the 390mm×510mm cross-section large square billet B3 grinding ball steel continuous casting billet is obtained, whose central looseness and central shrinkage cavity are controlled within 0.5 levels, the central segregation is controlled within 0.95-1.05, and the billet slow cooling time is shortened to 48 hours. The round steel products obtained after rolling the continuous casting billet are tested and the total oxygen content is controlled to be less than 15ppm. The non-metallic inclusions tested according to method A in GB / T10561 standard are: Class A fine series ≤0.5 level, Class A coarse series ≤0 level, Class B fine series ≤0.5 level, Class B coarse series ≤0 level, Class D fine series ≤0.5 level, Class D coarse series ≤0 level. The ultrasonic flaw detection result according to GB / T4162 is Class A, which fully meets the requirements.

[0037] Furthermore, in the converter primary refining process, the alloy is an alloy added to the molten steel when the converter primary refining is completed and the steel is tapped. The content of the converter alloying components is controlled within the following ranges: C: 0.45-0.51%, Mn: 0.63-0.69%, Si: 1.50-1.60%, Cr: 0.67-0.73%, Alt: 0.018-0.030%. This setting makes the composition of the molten steel close to the lower limit of the target composition, thereby reducing the amount of LF refining component fine-tuning and subsequently reducing the large particle inclusions generated when the refined alloy is added.

[0038] Furthermore, in the LF refining process, refined lime and pre-melted calcium aluminate are added in batches, with the weight of each batch not exceeding 100 kg. A deoxidizer is added to the slag surface to perform diffusion deoxidation of the molten steel, so that FeO+MnO in the slag is less than 1%, thereby preventing secondary oxidation of the molten steel, promoting the floating of inclusions, and preventing the generation of large-particle inclusions. The slag should be added frequently and in small amounts during the entire process to ensure the above-mentioned effects. Calcium carbide and aluminum particles are mixed in bulk and then added in batches to ensure uniform composition and properties of the refined slag, and to prevent concentrated addition from generating large-particle inclusions. For the first time after power is applied, such as within 5 minutes, 50 kg of calcium carbide, 160 kg of lime, 300 kg of pre-melted calcium aluminate, and 10 kg of aluminum particles are added. For the second time after power is applied, such as within 8 minutes, 50 kg of calcium carbide, 100 kg of lime, and 260 kg of pre-melted calcium aluminate are added to form a low-melting-point refined slag to ensure that the steel slag has a suitable The above addition amounts are related to the amount of molten steel. After the third time of power-on, such as 12 minutes, the slag melts and has good fluidity, white slag is formed, and the molten steel temperature is 1530℃~1540℃. When the first sample Alt≤0.020%, the Alt is adjusted to 0.025% by feeding aluminum wire. In the later stage of refining, aluminum is not adjusted, and 20Kg of calcium carbide is used to continue slag surface diffusion deoxidation. The white slag effect is maintained until the end of refining. The composition is fine-tuned to the set internal control target requirements. The internal control target range is C: 0.59~0.61%, Mn: 0.68~0.74%, Si: 1.67~1.74%, Cr: 0.73~0.77%, S≤0.005%, P≤0.015%, Alt: 0.022~0.030%.

[0039] Furthermore, in the LF refining process, double-permeable brick ladle bottom blowing of argon is used throughout the refining process. When power is supplied, the argon flow rate of the ladle bottom blowing is 300-400NL / min to uniformly distribute the molten steel temperature. When adjusting the composition, the electrode is lifted, and the argon flow rate of the ladle bottom blowing is 500-600NL / min to uniformly distribute the molten steel composition and adjust the composition. The argon blowing intensity of the ladle bottom blowing is reduced to prevent secondary oxidation and avoid the generation of large-particle inclusions.

[0040] Furthermore, in the LF refining process, the composition of the molten steel at the time of LF refining is controlled to be C: 0.59-0.61%, Mn: 0.68-0.74%, Si: 1.67-1.74%, Cr: 0.73-0.77%, S≤0.005%, P≤0.015%, Alt: 0.022-0.030%, providing qualified molten steel composition for RH vacuum refining.

[0041] Furthermore, in the RH refining process, the working vacuum degree is ≤67Pa and the holding time is ≥15min, and the [H] in the molten steel is ≤1.0ppm to prevent the generation of white spot hydrogen cracks. After the RH vacuum refining is completed, calcium treatment is performed to plasticize and modify the inclusions. The pure calcium wire is fed at a rate of 50 to 70m / furnace, the soft blowing time is ≥17min, and the calming time after the soft blowing is ≥15min to promote the further floating and removal of fine inclusions, making the molten steel cleaner.

[0042] As a public embodiment of the present invention, the present invention also provides a 390mm×510mm cross-section large square bloom B3 grinding ball steel, which is obtained by the preparation method of the present invention, wherein the chemical composition of the B3 grinding ball steel includes, by weight percentage: C: 0.59~0.61%, Mn: 0.67~0.73%, Si: 1.64~1.74%, Cr: 0.71~0.77%, S≤0.010%, P≤0.015%, Alt: 0.015~0.025%, Ti≤0.015%, O≤15ppm, N≤40ppm, H≤1.0ppm, and the rest are Fe and unavoidable impurities. The obtained continuous casting billet has a loose center, a central shrinkage cavity controlled within 0.5 level, a central segregation controlled within 0.95~1.05, and the billet slow cooling time is shortened to 48h.

[0043] The following uses specific embodiments to illustrate:

[0044] Example 1

[0045] This embodiment provides a method for improving the internal quality of 390mm×510mm cross-section bloom B3 grinding ball steel. The process steps specifically include: converter primary refining → LF refining → RH vacuum refining → continuous casting, specifically:

[0046] Converter primary refining:

[0047] The tapping volume is 120 tons of molten steel, and the loading volume is 110±2t of molten iron and 22±2t of scrap steel; the tapping C content is ≥0.020%, the tapping P content is ≤0.015%, and the tapping temperature is ≥1620℃; aluminum ingots are added when 1 / 4 of the steel is tapped according to the tapping C content, and aluminum ingots, alloy, pre-melted calcium aluminate and refined lime are added in sequence according to the initial alloying composition control requirements. During the primary tapping process of the converter, the aluminum ingots are first strongly deoxidized to reduce the oxygen content of the molten steel, improve the alloy composition hit rate, reduce large alumina particle inclusions caused by insufficient deoxidation, and promote the rapid floating removal of clustered Al2O3 deoxidation products. The addition of pre-melted calcium aluminate and refined lime during the primary tapping process of the converter is beneficial to promote rapid slag formation in LF refining, facilitate the rapid removal of inclusions, and reduce the damage of large particle inclusions to rolled material flaw detection;

[0048] LF Refining:

[0049] The temperature of the molten steel entering the LF refining station is ≥1500℃, white slag is formed after 12 minutes of power-on, and the molten steel temperature is controlled at 1530-1540℃. The white slag holding time is ≥30 minutes, and the refining cycle is 60-80 minutes. By controlling the molten steel temperature and white slag effect during LF refining, it is beneficial for LF refining to remove non-metallic inclusions early through rapid slag formation, ensuring sufficient time for inclusion removal.

[0050] RH vacuum refining:

[0051] The superheat is controlled at ≤30℃, the liquidus temperature is 1471℃, the working vacuum is ≤67Pa, the holding time is ≥15min, and the soft blowing time is ≥17min. Through strict control of superheat, it is beneficial to achieve constant casting speed during continuous casting, obtain good internal quality of continuous casting billets, reduce the level of central shrinkage and segregation, and through the control of RH vacuum and holding time, ensure the number of circulations of molten steel under vacuum conditions, reduce the content of harmful gases such as hydrogen and nitrogen in the steel, reduce the formation of large TiN inclusions, and promote the floating removal of inclusions in RH vacuum refining, improve the cleanliness of molten steel, and reduce the harm of large inclusions.

[0052] Continuous Casting:

[0053] During continuous casting, the ladle containing RH vacuum refined molten steel is hoisted to the turret of the 5-machine 5-strand bloom continuous casting machine, and the molten steel is poured into the tundish. A long nozzle is used between the ladle and the tundish for protection pouring. The ladle long nozzle is equipped with a sealing gasket, and the long nozzle sealing gasket is sealed with argon gas with a sealing gas flow rate of 10-13Nm 3 / h, argon pressure is 0.10~0.15MPa, and an integral tundish with built-in nozzle is used to ensure the protection of continuous casting throughout the casting process, prevent the secondary oxidation of molten steel, and avoid the damage of large particle inclusions caused by secondary oxidation to rolling flaw detection. The molten steel in the tundish is injected into the crystallizer for primary cooling. The cross section of the ingot is 390mm×510mm, and the water volume of the crystallizer is 150±3m 3 / h, the crystallizer adopts the crystallizer electromagnetic stirring technology, and the crystallizer electromagnetic stirring operating parameters are set to: 450A, 1.5HZ, to ensure that the ingot obtains a reasonable equiaxed crystal ratio, which is beneficial to reduce the shrinkage cavity and segregation in the center of the ingot. The continuous casting pulling speed is set to 0.43m / min by numerical simulation, to ensure that the solid phase ratio in the center of the light pressure position is 0.30-0.90, the superheat of the molten steel is controlled at 18-28℃, and the continuous casting is cast at a constant pulling speed throughout the whole process. In order to ensure the uniformity of cooling, the water volume of the secondary cooling water is 0.12L / Kg, and the water volume distribution ratio of the four cooling zones of the secondary cooling water is 25%, 40%, 25% and 10%. In order to reduce the dendrite bridging in the late solidification stage of the ingot and reduce the level of the central shrinkage cavity, the end electromagnetic stirring The operating parameters are 600A and 8.0HZ. Light reduction is used to compensate for the shrinkage of molten steel at the end of solidification and reduce the level of central shrinkage and segregation. The 1#-6# reduction rollers for light reduction at the end of solidification are 1.5mm, 2.5mm, 3.5mm, 4.5mm, 4mm and 4mm respectively, with a total reduction of 20mm. The produced 390mm×510mm cross-section B3 grinding ball steel large square billets are put into the pit for slow cooling or hot delivery. The slow-cooled billets are placed in a line in the same direction in the slow-cooling pit. The temperature of the slow-cooled billets entering the pit is ≥550℃. After entering the pit, the pit cover is tightly fastened and opened after 15h. The slow cooling time is 48 hours and the billet temperature is ≤300℃ before the billet is taken out of the pit to obtain billets with smaller stress concentration. Subsequently, steel rolling is carried out to obtain round steel products. At this time, a 390mm×510mm cross-section large square bloom B3 grinding ball steel continuous casting billet is obtained, the central porosity and central shrinkage cavity of which are controlled within level 0.5, the central segregation is controlled within 0.95~1.05, and the billet slow cooling time is shortened to 48h.

[0054] Example 2

[0055] The only difference between this embodiment and embodiment 1 is that the specific operation method of the BOF converter process in this embodiment is as follows:

[0056] BOF converter

[0057] In order to prevent the ladle residue from contaminating the molten steel and producing large Al2O3 and TiN inclusions, and to stably control the superheat of the molten steel, it is required that non-aluminum-containing ladles and ladles for producing titanium-containing steels must not be used during pre-production preparation. The ladle residue and ladle edge must be cleaned, and online turnover ladles used in normal production must be used.

[0058] In order to ensure the primary smelting production cycle of the converter and provide the appropriate temperature for LF refined molten steel, the steel output is controlled at 120 tons, the loading amount is 110±2t molten iron and 22±2t scrap steel, the converter smelting cycle is controlled at 35~38min, and the steel tapping temperature is ≥1620℃.

[0059] In order to reduce the temperature drop of steel tapping from the converter and reduce the hydrogen content in the molten steel, the alloy used must be baked before use, with the baking temperature ≥650℃ and the time ≥15min.

[0060] In order to reduce the total amount of inclusions in steel and achieve low phosphorus and low oxygen control, the P of the converter tapping is ≤ 0.015%. The converter tapping adopts double slag stops in front and behind the slide. When the tapping C is ≥ 0.020%, 13 kg of aluminum ingots are added when the tapping volume is 1 / 4. The alloy adding order is reasonably selected. After 1 / 4 of the steel is tapped, aluminum ingots are added in the order of electrochemical coke → silicon-manganese alloy → high carbon ferrochrome → ferrosilicon → pre-melted calcium aluminate → refined lime. It is not allowed to add alloys and slag at the bottom of the ladle before tapping. The addition is completed when 3 / 4 of the steel is tapped. During the primary steelmaking and tapping process of the converter, the aluminum ingots are first strongly deoxidized to reduce the oxygen content of the molten steel, improve the alloy composition hit rate, reduce large alumina inclusions caused by insufficient deoxidation, and promote the rapid floating removal of clustered Al2O3 deoxidation products. Adding pre-melted calcium aluminate and refined lime during the primary steelmaking and tapping process of the converter is beneficial to promote rapid slagging in LF refining, facilitate the rapid removal of inclusions, and reduce the harm of large particle inclusions to rolled product flaw detection.

[0061] In order to reduce the amount of alloy added in the LF refining process and ensure sufficient time for inclusions to float up and be removed, the converter primary refining process adopts a narrow range control of the initial alloying composition. The initial alloying composition is controlled as follows: C: 0.45-0.51%, Mn: 0.63-0.69%, Si: 1.50-1.60%, Cr: 0.67-0.73%, Alt: 0.018-0.030%.

[0062] Example 3

[0063] The only difference between this embodiment and embodiment 1 and embodiment 2 is that the specific operation method of the LF refining process in this embodiment is as follows:

[0064] In order to ensure the ventilation effect of the LF refining ladle air bricks and prevent the LF refining slag from crusting, the LF refining molten steel inlet temperature is ≥1500℃, and the argon gas strong blowing is first turned on from the ladle seat to the LF refining station with an argon flow rate of 600~700NL / min. The normal ventilation argon is adjusted to weak blowing with an argon flow rate of 200~300NL / min.

[0065] To ensure the adsorption effect of the refined slag on inclusions, after the slag is melted by electricity in the ladle, refined lime and pre-melted calcium aluminate are added in batches, with the weight of each batch not exceeding 100kg. Deoxidizer is added to the slag surface frequently and in small amounts. Calcium carbide and aluminum particles are mixed in bulk and added in batches; 50kg of calcium carbide, 160kg of lime, 300kg of pre-melted calcium aluminate and 10kg of aluminum particles are added 5min after electricity is applied; 50kg of calcium carbide, 100kg of lime and 260kg of pre-melted calcium aluminate are added 8min after electricity is applied; 12min after electricity is applied, the slag melts and has good fluidity, white slag is formed, and the temperature of the molten steel is 1530℃~1540℃. When the Alt of the first sample is ≤0.020, the Alt is adjusted to 0.025% to avoid aluminum adjustment in the later stage of refining. The white slag effect is maintained until the end of refining. 20kg of calcium carbide is used to continue diffusion deoxidation on the slag surface, and the composition is fine-tuned to the internal control target requirements.

[0066] In order to ensure that inclusions can fully float and prevent secondary oxidation of molten steel, argon is blown from the bottom of the ladle through double-permeable bricks throughout the LF refining process. When power is supplied, the argon flow rate at the bottom of the ladle is 300-400NL / min to uniformly control the temperature of the molten steel. When adjusting the composition, the electrode is lifted and the argon flow rate at the bottom of the ladle is 500-600NL / min to uniformly control the composition of the molten steel and adjust the composition. The argon blowing intensity at the bottom of the ladle is reduced to prevent secondary oxidation and avoid the generation of large-particle inclusions.

[0067] The composition of LF refining outlet is controlled to be C: 0.59~0.61%, Mn: 0.68~0.74%, Si: 1.67~1.74%, Cr: 0.73~0.77%, S≤0.005%, P≤0.015%, Alt: 0.022~0.030%, Ti≤0.010%, O≤12ppm. The temperature of LF refining outlet molten steel is controlled to be 1580±10℃, and the refining cycle is 60~80min.

[0068] Example 4

[0069] The only difference between this embodiment and embodiments 1 to 3 is that the specific operation method of the RH vacuum refining process in this embodiment is as follows:

[0070] To ensure the degassing and inclusion removal effect of RH vacuum refining, the working vacuum degree is ≤67Pa and the holding time is ≥15min, [H] in the molten steel is ≤1.0ppm, and calcium treatment is carried out after the RH vacuum refining is completed. The pure calcium wire is fed at a rate of 50-70m / furnace, the soft blowing time is ≥17min, and the soft blowing argon flow rate is controlled at 10-30NL / min to make the molten steel surface creep slightly without exposing the molten steel. After the soft blowing is completed, the molten steel is kept calm for ≥15min to promote the further floating and removal of fine inclusions, making the molten steel cleaner.

[0071] In order to accurately control the superheat of molten steel to meet the requirement of 18-28℃ and realize continuous casting with constant casting speed, the RH vacuum refining temperature is dropped by 50-60℃, and the RH outlet temperature is controlled at 1525±5℃.

[0072] Example 5

[0073] The only difference between this embodiment and embodiments 1 to 4 is that the specific operation method of the continuous casting process in this embodiment is as follows:

[0074] The ladle containing RH vacuum refined molten steel is hoisted to the turret of the 5-machine 5-strand bloom continuous casting machine, and the molten steel is poured into the tundish. A long nozzle is used between the ladle and the tundish for protection pouring. The long nozzle of the ladle is equipped with a sealing gasket, and the long nozzle sealing gasket is sealed with argon gas with a flow rate of 10-13Nm 3 / h, argon pressure is 0.10~0.15MPa, and an integral tundish with built-in nozzle is used to ensure the protection of continuous casting throughout the casting process, prevent the secondary oxidation of molten steel, and avoid the damage of large particle inclusions caused by secondary oxidation to rolling flaw detection. The molten steel in the tundish is injected into the crystallizer for primary cooling. The cross section of the ingot is 390mm×510mm, and the water volume of the crystallizer is 150±3m 3 / h, the crystallizer adopts the crystallizer electromagnetic stirring technology, and the crystallizer electromagnetic stirring operating parameters are set to: 450A, 1.5HZ, to ensure that the ingot obtains a reasonable equiaxed crystal ratio, which is beneficial to reducing the shrinkage cavity and segregation in the center of the ingot. According to the numerical simulation calculation, the electromagnetic stirring at the end of solidification and the solid phase ratio at the center of the light pressure roller position are obtained. The design pulling speed is 0.43m / min, ensuring that the solid phase ratio at the center of the light pressure position is 0.30-0.90, and the superheat of the molten steel is controlled at 18-28℃. The continuous casting process is cast at a constant casting speed. To ensure cooling uniformity, the secondary cooling water ratio is 0.12L / Kg, and the water distribution ratio of the four cooling zones of the secondary cooling water is 25% / 40% / 25% / 10%. In order to reduce dendrite bridging at the end of solidification of the ingot and reduce the level of central shrinkage, the terminal electromagnetic stirring operation parameters are 600A and 8.0HZ. Soft pressure is used to compensate for the shrinkage of the molten steel at the end of solidification and reduce the level of central shrinkage and segregation. The 1#-6# pressure rollers for soft pressure at the end of solidification are 1#, 1#, 2#, 3#, 4#, 5#, 6#, 7#, 8#, 9#, 10#, 11#, 12#, 13#, 14#, 15#, 16#, 17#, 18#, 19#, 20#, 21#, 22#, 23#, 24#, 25#, 26#, 27#, 28#, 29#, 30#, 31#, 32#, 33#, 34#, 35#, 36#, 37#, 38#, 39#, 40#, 41#, 42#, 43#, 44#, 45#, 46#, 47#, 48#, 49#, 50#, 51#, 52#, 53#, 54#, 55#, 56#, 57#, 58#, 59#, 60#, 61#, 61#, 62#, 63#, 64#, 65#, 66#, 67#, 68#, The total reduction of .5mm, 2.5mm, 3.5mm, 4.5mm, 4mm and 4mm is 20mm. The 390mm×510mm cross-section B3 grinding ball steel large square billets are put into the pit for slow cooling or hot delivery. The slow cooling billets are placed in a line in the same direction in the slow cooling pit. The temperature of the slow cooling billets entering the pit is ≥550℃. After entering the pit, the pit cover is tightly fastened and opened after 15h. The slow cooling time is 48 hours and the billet temperature is ≤300℃. The billets are taken out of the pit to obtain billets with smaller stress concentration, and then rolled. , round steel products were obtained, and the light reduction process parameters were formulated according to the central shrinkage prediction model. The crystallizer and electromagnetic stirring parameters at the end of solidification were designed according to the solidification structure and segregation conditions. Combined with the slow cooling temperature field and stress field simulation of the billet, the billet slow cooling process was formulated. At this time, a 390mm×510mm cross-section large square billet B3 grinding ball steel continuous casting billet was obtained, of which the central porosity and central shrinkage were controlled within level 0.5, the central segregation was controlled within 0.95~1.05, and the billet slow cooling time was shortened to 48h.

[0075] Example 6

[0076] This example provides a method for improving the internal quality of 390mm×510mm cross-section bloom B3 grinding ball steel. The process steps include BOF converter primary refining → LF refining → RH vacuum refining → continuous casting. The specific process method is as follows:

[0077] BOF converter

[0078] In order to prevent the ladle residue from contaminating the molten steel and producing large Al2O3 and TiN inclusions, and to stably control the superheat of the molten steel, it is required that non-aluminum-containing ladles and ladles for producing titanium-containing steels must not be used during pre-production preparation. The ladle residue and ladle edge must be cleaned, and online turnover ladles used in normal production must be used.

[0079] In order to ensure the primary smelting production cycle of the converter and provide the appropriate temperature for LF refined molten steel, the tapping volume is controlled at 120 tons, the loading volume is 110±2t molten iron and 22±2t scrap steel, the converter smelting cycle is controlled at 35~38min, and the tapping temperature is ≥1620℃.

[0080] In order to reduce the temperature drop of steel tapping from the converter and reduce the hydrogen content in the molten steel, the alloy used must be baked before use, with the baking temperature ≥650℃ and the time ≥15min.

[0081] In order to reduce the total amount of inclusions generated in steel and achieve low-phosphorus and low-oxygen control, the converter tapping P is ≤ 0.015%, and the converter tapping adopts double slag blocks in front and behind the slide. When the tapping C is ≥ 0.020%, 13 kg of aluminum ingots are added when the tapping amount is 1 / 4, and the order of adding alloys is reasonably selected. After 1 / 4 of the steel is tapped, aluminum ingots → electrochemical coke → silicon-manganese alloy → high-carbon ferrochrome → ferrosilicon → pre-melted calcium aluminate → refined lime are added in sequence. It is not allowed to add alloys and slag at the bottom of the ladle before tapping, and all additions are completed when 3 / 4 of the steel is tapped.

[0082] In order to reduce the amount of alloy added in the LF refining process and ensure sufficient time for inclusions to float up and be removed, the converter primary refining process adopts a narrow range control of the initial alloying composition. The initial alloying composition is controlled as follows: C: 0.45-0.51%, Mn: 0.63-0.69%, Si: 1.50-1.60%, Cr: 0.67-0.73%, Alt: 0.018-0.030%.

[0083] LF Refining

[0084] In order to ensure the ventilation effect of the LF refining ladle air bricks and prevent the LF refining slag from crusting, the LF refining molten steel inlet temperature is ≥1490℃, and the argon gas strong blowing is first turned on from the ladle seat to the LF refining station with an argon flow rate of 600~700NL / min. The normal ventilation argon is adjusted to weak blowing with an argon flow rate of 200~300NL / min.

[0085] To ensure the adsorption effect of refined slag inclusions, after the slag is melted by power on the ladle, refined lime and pre-melted calcium aluminate are added in batches, with the weight of each batch not exceeding 100kg. Deoxidizer is added to the slag surface, and it should be added frequently and in small amounts. Calcium carbide and aluminum particles are mixed in bulk and added in batches; 50kg of calcium carbide, 160kg of lime, 300kg of pre-melted calcium aluminate, and 10kg of aluminum particles are added 5min after power on; 50kg of calcium carbide, 100kg of lime, and 260kg of pre-melted calcium aluminate are added 8min after power on; 12min after power on, the slag melts and has good fluidity, white slag is formed, and the temperature of the molten steel is 1530℃~1540℃. When the Alt of the first sample is ≤0.020, the Alt is adjusted to 0.025% to avoid aluminum adjustment in the later stage of refining. The white slag effect is maintained until the end of refining. 20kg of calcium carbide is used to continue diffusion deoxidation on the slag surface, and the composition is fine-tuned to the internal control target requirements.

[0086] In order to ensure that inclusions fully float and prevent secondary oxidation of molten steel, LF refining adopts argon blowing from the bottom of the double-permeable brick ladle throughout the process. The argon flow rate is 300-400NL / min when power is supplied, and the argon flow rate is 500-600NL / min when the electrode is raised to adjust the composition. After the composition is adjusted, the argon blowing intensity is reduced.

[0087] The composition of LF refining outlet is controlled to be C: 0.59~0.61%, Mn: 0.68~0.74%, Si: 1.67~1.74%, Cr: 0.73~0.77%, S≤0.005%, P≤0.015%, Alt: 0.022~0.030%, Ti≤0.010%, O≤12ppm. The temperature of LF refining outlet molten steel is controlled to be 1580±10℃, and the refining cycle is 60~80min.

[0088] RH vacuum refining

[0089] To ensure the degassing and inclusion removal effect of RH vacuum refining, the working vacuum degree is ≤67Pa and the holding time is ≥15min, [H] in the molten steel is ≤1.0ppm, and calcium treatment is carried out after the RH vacuum refining is completed. The pure calcium wire is fed at a rate of 50-70m / furnace, the soft blowing time is ≥17min, and the soft blowing argon flow rate is controlled at 10-30NL / min to make the molten steel surface creep slightly without exposing the molten steel. The molten steel is calmed for ≥15min after the soft blowing is completed.

[0090] In order to accurately control the superheat of molten steel to meet the requirement of 18-28℃, the RH vacuum refining temperature drop is 50-60℃, and the RH outlet temperature is controlled at 1525±5℃.

[0091] Five-machine five-stream continuous casting

[0092] In order to ensure the full protection of continuous casting and prevent secondary oxidation, a 5-machine 5-strand bloom continuous casting machine is used to produce 390mm×510mm cross-sections. The tundish adopts an integral tundish with an internal nozzle. The superheat of the molten steel is controlled at 18-28℃. Full protection casting is adopted. The ladle adopts a long nozzle for protection casting. The long nozzle of the ladle is equipped with a sealing gasket and argon sealing protection. The argon sealing gas flow rate is 10-13Nm 3 / h, the argon pressure is 0.10~0.15MPa, so that the surface of the impact zone of the tundish creeps slightly and the molten steel is not exposed.

[0093] The casting speed is 0.43m / min, the secondary cooling water volume is 0.12L / Kg, the secondary cooling water distribution ratio is 25 / 40 / 25 / 10, and the crystallizer water volume is 150±3m 3 / h; the crystallizer electromagnetic stirring operating parameters are: 450A, 1.5HZ; the end electromagnetic stirring operating parameters are 600A, 8.0HZ; the soft reduction at the end of solidification uses 1.5mm, 2.5mm, 3.5mm, 4.5mm, 4mm and 4mm, and the total reduction is 20mm.

[0094] In order to reduce the thermal stress of the billet, the continuous casting process adopts the 390mm×510mm cross-section large square billet B3 grinding ball steel entering the pit for slow cooling. The billet temperature entering the pit for slow cooling is ≥550℃. The billets are placed in a straight line in the same direction in the slow cooling pit. After entering the pit, the pit cover is tightly fastened and the pit cover is completely opened after 15 hours. The slow cooling time is 48 hours and the billet temperature is ≤300℃ before the billet is out of the pit.

[0095] The continuous casting slab obtained in this embodiment was inspected:

[0096] (1) The chemical composition of B3 grinding ball steel includes the following by weight percentage: C: 0.60%, Mn: 0.70%, Si: 1.68%, Cr: 0.70%, S: 0.003%, P≤0.012%, Alt: 0.020%, Ti: 0.010%, O: 8ppm, N: 30ppm, H: 0.3ppm, and the rest is Fe and unavoidable impurities. The chemical composition meets the requirements, the Ti and N contents are controlled low, avoiding the generation of large particles of TiN, the O content is low, the molten steel is clean, avoiding the non-conformity of the rolled material due to large particles of inclusions and other reasons of molten steel cleanliness.

[0097] (2) Low-magnification inspection

[0098] Take 400mm long ingot sample and conduct cross section + longitudinal section low magnification pickling test. The cross section low magnification sample photo is shown in Figure 1 , the low-magnification photograph of the longitudinal section is shown in Figure 2 The low-magnification inspection results of the transverse sample showed that the center was loose and the center shrinkage cavity was controlled below level 0.5. The low-magnification inspection results of the longitudinal sample showed that there was no V-shaped segregation and center shrinkage cavity. By reasonably setting the process parameters of the continuous casting process, the internal quality of the ingot was greatly improved, avoiding the non-conformity of the flaw detection caused by the internal quality of the continuous casting ingot.

[0099] (3) Continuous casting macrosegregation

[0100] Uniformity of composition of cross section and longitudinal section of continuous casting billet: Use φ4 drill bit to drill and take chips from cross section and longitudinal section. The drilling and taking chips positions are as follows: Figure 3 、 Figure 4 The actual carbon content is detected using an infrared carbon-sulfur analyzer, and the calculation formula is: segregation index = C content at each point / C content in the tundish.

[0101] The segregation index of the horizontal macroscopic specimen can be controlled between 0.95 and 1.05, achieving an ideal segregation control effect. Figure 5The segregation test results of the transverse low-magnification specimen of the B3 grinding ball steel continuous casting slab prepared in Example 6 are shown. It can be seen that the segregation index of the longitudinal low-magnification specimen can be controlled between 0.95 and 1.06, achieving an ideal segregation control effect. Figure 6 This is the longitudinal macro-sample segregation result of the B3 grinding ball steel continuous casting billet prepared in Example 6.

[0102] The foregoing description shows and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the form disclosed herein and should not be construed as excluding other embodiments. Rather, the present invention can be used in various other combinations, modifications, and environments and can be modified within the scope of the application concept described herein by the teachings above or by techniques or knowledge in the relevant field. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention are intended to be protected by the appended claims.

Claims

1. A method for preparing 390mm×510mm cross-section bloom B3 grinding ball steel, characterized in that: It includes the following steps: converter primary refining → LF refining → RH vacuum refining → continuous casting. Among them, the converter is pre-smelted: a certain amount of molten iron and scrap steel are charged for pre-smelting, so that the C in the molten steel is ≥0.020%, the P of the steel is ≤0.015%, the tapping temperature is ≥1620℃, and aluminum ingots, alloys, pre-melted calcium aluminate and refined lime are added in sequence when 1 / 4 of the steel is tapped; LF refining: When the molten steel from the converter enters the LF refining, the temperature of the molten steel entering the station is ≥1500℃, and the power is turned on for a period of time, during which white slag is formed in the molten steel and the molten steel temperature is controlled at 1530-1540℃, the white slag retention time is ≥30min, and the refining cycle is 60-80min to obtain refined molten steel; RH vacuum refining: When the refined steel liquid is subjected to RH vacuum refining, the superheat is controlled to be ≤30℃, the RH working vacuum is ≤67Pa, the holding time is ≥15min, and the soft blowing time is ≥17min to obtain RH vacuum refined steel liquid; Continuous casting: The RH vacuum refined molten steel is subjected to set drawing speed, crystallizer and end electromagnetic stirring and soft reduction treatment according to the casting section to obtain 390mm×510mm cross-section large square bloom B3 grinding ball steel.

2. The method according to claim 1, characterized in that The certain amount of molten iron and scrap steel includes 110±2t molten iron and 22±2t scrap steel, and the output of steel is 120t molten steel.

3. The method according to claim 1, characterized in that The element contents of the alloy are C: 0.45-0.51%, Mn: 0.63-0.69%, Si: 1.50-1.60%, Cr: 0.67-0.73%, and Alt: 0.018-0.030%.

4. The method according to claim 2, characterized in that: The period of time is 12 minutes.

5. The method according to claim 2, characterized in that: In the LF refining process, 50Kg of calcium carbide, 160Kg of lime, 300Kg of pre-melted calcium aluminate and 10Kg of aluminum particles are added to the molten steel after the power is turned on for the first time; 50Kg of calcium carbide, 100Kg of lime and 260Kg of pre-melted calcium aluminate are added after the power is turned on for the second time. After the power is turned on for the third time, white slag is formed, and the temperature of the molten steel is 1530-1540°C. When sampling determines that Alt≤0.020%, Alt is adjusted to 0.025%, and 20Kg of calcium carbide is used to continue slag surface diffusion deoxidation. The white slag effect is maintained until the end of refining. The second time is greater than the third time, and the third time is greater than the first time.

6. The method according to claim 1, characterized in that The components of the refined molten steel are C: 0.59-0.61%, Mn: 0.68-0.74%, Si: 1.67-1.74%, Cr: 0.73-0.77%, S≤0.005%, P≤0.015%, and Alt: 0.022-0.030%.

7. The method according to claim 4, characterized in that In the RH refining process, [H] in the molten steel is ≤1.0ppm. After the RH vacuum refining is completed, the molten steel is calcium treated, and the amount of pure calcium wire fed is 50-70m / furnace.

8. The method according to claim 1, characterized in that The continuous casting adopts a 5-machine 5-stream large square billet continuous casting machine to produce a cross section of 390mm×510mm, the tundish adopts an integral tundish with an internal nozzle, the superheat of the molten steel is controlled at 18-28°C, the whole process protection casting is adopted, the ladle adopts a long nozzle for protection casting, the long nozzle of the ladle is equipped with a sealing pad and argon sealing protection, and the argon sealing gas flow rate is 10-13Nm 3 / h, argon pressure is 0.10~0.15MPa.

9. A 390mm×510mm cross-section bloom B3 grinding ball steel, characterized in that: The B3 grinding ball steel is obtained by the preparation method described in any one of claims 1-8.

10. The B3 grinding ball steel according to claim 9, characterized in that: The chemical composition of the B3 grinding ball steel includes, by weight percentage, C: 0.59-0.61%, Mn: 0.67-0.73%, Si: 1.64-1.74%, Cr: 0.71-0.77%, S≤0.010%, P≤0.015%, Alt: 0.015-0.025%, Ti≤0.015%, O≤15ppm, N≤40ppm, H≤1.0ppm, and the rest is Fe and unavoidable impurities.

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