A method for producing a continuous-casting and rolling pre-hardened round steel

Abstract

The application belongs to the field of metallurgy and pressure processing, and discloses a production method of continuous-casting and continuous-rolling pre-hardened round steel, which comprises the following steps: smelting furnace materials in sequence by using an electric furnace, an AOD furnace, an LF furnace and a VD furnace to obtain billets; treating the billets by adopting a three-flow drawing process to obtain continuous-casting square billets; performing continuous-rolling treatment on the continuous-casting square billets to obtain steel materials; performing air cooling, sawing and air cooling on the steel materials to obtain round steels; and performing tempering on the round steels to obtain pre-hardened round steels. The application solves the problems of segregation and porosity of the pre-hardened round steel by improving the production process parameters of the pre-hardened round steel. The production process of the pre-hardened round steel is optimized, the blooming process is omitted, the production cycle is shortened, and the production cost is saved.

Description

Technical Field

[0001] This invention belongs to the field of metallurgy and pressure processing, and particularly relates to a method for producing pre-hardened round steel through continuous casting and rolling. Background Technology

[0002] Pre-hardened steel refers to steel that has undergone pre-heat treatment to achieve the hardness required for mold use. This type of steel is characterized by its ability to be directly machined, drilled, milled, engraved, and finely filed at a hardness of 30–40 HRC. After finishing, it can be directly delivered for use, completely avoiding the effects of heat treatment deformation and thus ensuring the manufacturing precision of the mold.

[0003] Most existing pre-hardened plastic mold steels are based on medium carbon steel, with appropriate amounts of alloying elements such as chromium, manganese, nickel, molybdenum, and vanadium added. To address the difficulty of machining at higher hardness levels, elements such as sulfur, calcium, lead, and selenium are added to the steel to improve its machinability, thus producing free-machining pre-hardened steels. Some pre-hardened steels can undergo nitriding treatment after mold forming, significantly improving the surface hardness and wear resistance of the mold without reducing the hardness of the base material.

[0004] The existing production process for pre-hardened plastic mold steel includes smelting steel ingots → billet preparation → rolling round steel in a continuous rolling mill → air cooling → tempering → flaw detection → inspection. The production process requires billet preparation, and the continuous casting and rolling process has poor results. Therefore, it is necessary to provide a continuous casting and rolling method for producing pre-hardened round steel that eliminates the billet preparation step, shortens the production cycle, saves costs, and solves the problems of steel segregation and porosity, thereby improving product quality. Summary of the Invention

[0005] The purpose of this invention is to provide a method for producing pre-hardened round steel through continuous casting and rolling, which omits the billet preparation step, shortens the production cycle, saves costs, and solves the problems of steel segregation and porosity, thereby improving product quality.

[0006] To achieve the above objectives, the present invention provides a method for producing pre-hardened round steel through continuous casting and rolling, comprising:

[0007] The billet is obtained by sequentially smelting the furnace charge using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace.

[0008] The billet is processed using a three-strand steel drawing process to obtain a continuously cast square billet;

[0009] Steel is obtained by continuously rolling continuously cast square billets.

[0010] Steel is air-cooled, sawed, and air-cooled to obtain round steel.

[0011] Pre-hardened round steel is obtained by tempering round steel.

[0012] The furnace charge includes low-phosphorus scrap steel, low-sulfur scrap steel, recycled steel of the same grade, contract billets, alloy materials and alloy material substitutes.

[0013] Furthermore, the billet is obtained by sequentially smelting the furnace charge using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace, including:

[0014] When smelting the furnace charge using an electric furnace, the furnace temperature is controlled at ≥1620℃. 300kg of silicon carbide is added to every 40 tons of furnace charge and stirred with nitrogen. The pre-reduction time is ≥10 minutes. At the end of the pre-reduction, the furnace temperature is ≥1630℃ to obtain molten steel.

[0015] Furthermore, the process of sequentially smelting the furnace charge using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace to obtain the billet also includes:

[0016] The molten steel is mixed and blown using an AOD furnace, and lime and alloys are added to the molten steel.

[0017] Furthermore, the process of sequentially smelting the furnace charge using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace to obtain the billet also includes:

[0018] When smelting molten steel using an LF furnace, aluminum wire is fed into the molten steel at a rate of 0.06 wt% at a feeding speed of ≥2.5 m / s. After feeding the aluminum wire, the temperature of the molten steel is measured, and the LF furnace is powered on. 150 kg of steel slag and 60 kg of carbon powder are added to every 40 tons of molten steel. The steel slag and carbon powder are added in batches. The first batch consists of 80 kg of steel slag and 30 kg of carbon powder, and subsequent batches consist of 15-40 kg of steel slag and 15-40 kg of carbon powder. When the slag turns white and the temperature of the molten steel reaches ≥1560℃, the molten steel is sampled and analyzed. Based on the analysis results, steel slag or carbon powder is added to maintain a reducing atmosphere.

[0019] Furthermore, the process of sequentially smelting the furnace charge using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace to obtain the billet also includes:

[0020] Before smelting molten steel in a VD furnace, feed Ca-Si wire into the molten steel at a rate of 250m / 40 tons, with a feeding speed of ≥2.5m / s;

[0021] When smelting molten steel using a VD furnace, adjust the argon flow rate, evacuate the VD furnace, control the ultimate vacuum degree of the VD furnace to ≤67Pa and maintain it for more than 15 minutes, adjust the argon flow rate to ≤20L / min 1 minute before rupturing the vacuum, and measure the temperature and take samples of the molten steel after rupturing the vacuum.

[0022] Furthermore, the billet is processed using a three-strand steel drawing process to obtain a continuously cast square billet, including:

[0023] The throwing speed is controlled according to the degree of superheat.

[0024] When the superheat is below 20℃, the casting speed should be controlled at 0.95-0.85 m / min.

[0025] When the superheat is 20-25℃, the casting speed should be controlled at 0.85-0.80 m / min.

[0026] When the superheat is 26-35℃, the casting speed should be controlled at 0.80-0.75 m / min.

[0027] When the superheat is 36-40℃, the casting speed should be controlled at 0.75-0.70 m / min.

[0028] With a superheat of 40℃ or higher, the casting speed should be controlled at 0.70 m / min.

[0029] After slow cooling for 8-11 hours, the continuously cast square billet is annealed.

[0030] Furthermore, the composition of the continuously cast square billet includes: 0.36-0.45 wt% C, 0.45-0.60 wt% Si, 12.8-13.8 wt% Cr, 0.02-0.05 wt% Al, 0.3-0.6 wt% Ni, 0.40-0.80 wt% Mn, ≤0.02 wt% P, ≤0.005 wt% S, ≤0.02 wt% As, ≤0.01 wt% Sn, ≤0.01 wt% Pb, ≤0.01 wt% Sb, ≤0.01 wt% Bi, ≤0.0002 wt% H, ≤0.0025 wt% O, with the balance being Fe;

[0031] Wherein, As+Sn+Pb+Sb+Bi≤0.04wt%.

[0032] Furthermore, the continuously cast billet is continuously rolled to obtain steel, including:

[0033] The continuously cast billet is heated, with the preheating temperature controlled at 660-710℃, the first heating temperature at 870-910℃, the second heating temperature at 1100-1120℃, and the soaking temperature at 1150-1170℃. The total heating time is 180-210 min, and the soaking time is 48-55 min.

[0034] Furthermore, the steel is subjected to air cooling, sawing, and air cooling to obtain round steel, including:

[0035] The steel is air-cooled to ≤400℃ before sawing.

[0036] After sawing, the steel is air-cooled to a surface temperature of 100-115℃ and then bundled and collected.

[0037] Further, the round steel is tempered to obtain pre-hardened round steel, including:

[0038] The round steel is heated to T℃ within 6-8 hours and held at that temperature for t hours, then air-cooled to room temperature. The temperature T and time t are adjusted according to the amount of material loaded.

[0039] When the loading amount of round steel does not exceed 30 tons, 540≤T≤550, 25≤t≤27;

[0040] When the loading amount of round steel is 30-45 tons, 535≤T≤545, 35≤t≤37;

[0041] When the loading amount of round steel is 45-60 tons, 530≤T≤540, 45≤t≤47;

[0042] Among them, the difference between the maximum and minimum diameters of the round steel is ≤20mm.

[0043] The technical effects and advantages of this invention are as follows:

[0044] 1. This invention optimizes the production process of pre-hardened round steel, omits the billet-making step, shortens the production cycle, and saves production costs.

[0045] 2. This invention solves the problems of segregation and porosity in pre-hardened round steel by improving the production process parameters of pre-hardened round steel. The pre-hardened round steel produced has a hardness difference of ≤3HRC in the same cross section, A, C and D type inclusions ≤1.5 grade, B type inclusions ≤2.0 grade, and a yield of 96.5%, which greatly improves the production quality of pre-hardened round steel.

[0046] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0047] Figure 1 This is a flowchart of the continuous casting and rolling pre-hardened round steel production method of the present invention. Detailed Implementation

[0048] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0049] like Figure 1 As shown, the present invention provides a method for producing pre-hardened round steel through continuous casting and rolling, comprising:

[0050] The billet is obtained by sequentially smelting the furnace charge using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace.

[0051] The billet is processed using a three-strand steel drawing process to obtain a continuously cast square billet;

[0052] Steel is obtained by continuously rolling continuously cast square billets.

[0053] Steel is air-cooled, sawed, and air-cooled to obtain round steel.

[0054] Pre-hardened round steel is obtained by tempering round steel.

[0055] The furnace charge includes low-phosphorus scrap steel, low-sulfur scrap steel, return material of the same steel grade (or similar steel grade), contract billet, alloy material and alloy material substitutes.

[0056] In some optional embodiments of the present invention, when obtaining billets by sequentially smelting the furnace charge using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace, the process includes...

[0057] When smelting the furnace charge using an electric furnace, the furnace temperature is controlled at ≥1620℃. 300kg of silicon carbide is added to every 40 tons of furnace charge and stirred with nitrogen. The pre-reduction time is ≥10 minutes. At the end of the pre-reduction, the furnace temperature is ≥1630℃ to obtain molten steel.

[0058] In some optional embodiments of the present invention, when the charge is smelted sequentially using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace to obtain the billet, the method further includes:

[0059] The molten steel is mixed and blown using an AOD furnace, and lime and alloys are added to the molten steel.

[0060] In some optional embodiments of the present invention, when the charge is smelted sequentially using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace to obtain the billet, the method further includes:

[0061] When smelting molten steel using an LF furnace, aluminum wire is fed into the molten steel at a rate of 0.06 wt% at a feeding speed of ≥2.5 m / s. The temperature of the molten steel is measured after the aluminum wire is fed.

[0062] Power is supplied to the LF furnace, and 150 kg of steel slag and 60 kg of carbon powder are added to every 40 tons of molten steel. The steel slag and carbon powder are added in batches. The first batch is 80 kg of steel slag and 30 kg of carbon powder. Subsequent batches are 15-40 kg each of steel slag and carbon powder. When the slag turns white and the temperature of the molten steel reaches ≥1560℃, the molten steel is sampled and analyzed. Based on the analysis results, steel slag or carbon powder is added to maintain the reducing atmosphere.

[0063] In some optional embodiments of the present invention, the billet is obtained by sequentially smelting the furnace charge using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace, and the method further includes:

[0064] Before smelting molten steel using a VD furnace, feed Ca-Si wire into the molten steel at a rate of 250m / 40 tons, with a feeding speed ≥2.5m / s;

[0065] When smelting molten steel using a VD furnace, adjust the argon flow rate, evacuate the VD furnace, control the ultimate vacuum degree of the VD furnace to ≤67Pa and maintain it for more than 15 minutes, adjust the argon flow rate to ≤20L / min 1 minute before rupturing the vacuum, and measure the temperature and take samples of the molten steel after rupturing the vacuum.

[0066] In some optional embodiments of the present invention, a three-strand steel drawing process is used to process the billet to obtain a continuously cast square billet, including:

[0067] The throwing speed is controlled according to the degree of superheat.

[0068] When the superheat is below 20℃, the casting speed should be controlled at 0.95-0.85 m / min.

[0069] When the superheat is 20-25℃, the casting speed should be controlled at 0.85-0.80 m / min.

[0070] When the superheat is 26-35℃, the casting speed should be controlled at 0.80-0.75 m / min.

[0071] When the superheat is 36-40℃, the casting speed should be controlled at 0.75-0.70 m / min.

[0072] With a superheat of 40℃ or higher, the casting speed should be controlled at 0.70 m / min.

[0073] The continuously cast billet was covered and slowly cooled for 8-11 hours before annealing.

[0074] In some optional embodiments of the present invention, the composition of the continuously cast billet includes: 0.36-0.45 wt% C, 0.45-0.60 wt% Si, 12.8-13.8 wt% Cr, 0.02-0.05 wt% Al, 0.3-0.6 wt% Ni, 0.40-0.80 wt% Mn, ≤0.02 wt% P, ≤0.005 wt% S, ≤0.02 wt% As, ≤0.01 wt% Sn, ≤0.01 wt% Pb, ≤0.01 wt% Sb, ≤0.01 wt% Bi, ≤0.0002 wt% H, ≤0.0025 wt% O, with the balance being Fe;

[0075] Wherein, As+Sn+Pb+Sb+Bi≤0.04wt%.

[0076] In some optional embodiments of the present invention, steel is obtained by continuous rolling of continuously cast billets, including:

[0077] The continuously cast billet is heated, with the preheating temperature controlled at 660-710℃, the first heating temperature at 870-910℃, the second heating temperature at 1100-1120℃, and the soaking temperature at 1150-1170℃. The total heating time is 180-210 min, and the soaking time is 48-55 min.

[0078] In some optional embodiments of the present invention, steel is subjected to air cooling, sawing, and air cooling to obtain round steel, including:

[0079] The steel is air-cooled to ≤400℃ before sawing.

[0080] After sawing, the steel is air-cooled to a surface temperature of 100-115℃ and then bundled and collected.

[0081] In some optional embodiments of the present invention, tempering the round steel to obtain pre-hardened round steel includes:

[0082] The round steel is heated to T℃ within 6-8 hours and held at that temperature for t hours, then air-cooled to room temperature. The temperature T and time t are adjusted according to the amount of material loaded.

[0083] When the loading amount of round steel does not exceed 30 tons, 540≤T≤550, 25≤t≤27;

[0084] When the loading amount of round steel is 30-45 tons, 535≤T≤545, 35≤t≤37;

[0085] When the loading amount of round steel is 45-60 tons, 530≤T≤540, 45≤t≤47;

[0086] Among them, the difference between the maximum and minimum diameters of the round steel is ≤20mm.

[0087] To better explain this solution, embodiments are also provided.

[0088] Example

[0089] S1. Load the furnace charge into the electric furnace and melt it. When the charge is completely melted and the temperature reaches 1635℃, add 300kg of silicon carbide, purge with nitrogen and stir thoroughly. The pre-reduction time is 14 minutes. Depending on the slag condition, slag can be removed as needed. At the end of the pre-reduction, the temperature is 1637℃. Remove the slag and tap the steel.

[0090] The molten steel is then hoisted to the AOD furnace station for steel mixing, blowing, adding lime and alloys, and then tapping.

[0091] The molten steel is hoisted to the LF furnace station. The argon flow rate is adjusted, and aluminum wire is immediately fed into the molten steel at a rate of 0.06% wt%, with a feeding speed ≥2.5 m / s. After feeding the aluminum wire, the temperature of the molten steel is measured. Power is supplied to the LF furnace. For every 40 tons of molten steel, 150 kg of steel slag and 60 kg of carbon powder are added in batches. The first batch consists of 80 kg of steel slag and 30 kg of carbon powder, with subsequent batches adding 30 kg of steel slag and 15 kg of carbon powder. Once the slag turns white and the temperature reaches 1567℃, a sample of the molten steel is taken for full analysis. Based on the analysis results, the composition is adjusted, and steel slag or carbon powder is continued to be added to maintain the reducing atmosphere.

[0092] Then, the molten steel is smelted in a VD furnace. Before the VD vacuum treatment, Ca-Si wire is fed into the molten steel at a rate of 250m / 40 tons, with a feeding speed of ≥2.5m / s. After the molten steel enters the VD furnace, the argon flow rate is adjusted, and the VD furnace is evacuated. The ultimate vacuum degree of the VD furnace is controlled to be ≤67Pa and maintained for 23min. One minute before the vacuum is broken, the argon flow rate is adjusted to ≤20L / min. After the vacuum is broken, the temperature of the molten steel is measured and samples are taken.

[0093] S2. A three-flow drawing process is adopted. The drawing speed is controlled according to the superheat. When the superheat is below 20℃, the drawing speed is controlled at 0.95-0.85m / min; when the superheat is 20-25℃, the drawing speed is controlled at 0.85-0.80m / min; when the superheat is 26-35℃, the drawing speed is controlled at 0.80-0.75m / min; when the superheat is 36-40℃, the drawing speed is controlled at 0.75-0.70m / min; when the superheat is above 40℃, the drawing speed is controlled at 0.70m / min. The target drawing speed is 0.80-0.75m / min.

[0094] After the steel pulling is completed, the resulting continuously cast square billet is covered and slowly cooled for 10 hours before annealing.

[0095] The mass percentage composition of the obtained continuously cast square billet is shown in the table below:

[0096]

[0097] The content of As+Sn+Pb+Sb+Bi in continuously cast square billets is ≤0.04wt%.

[0098] S3. The continuously cast square billet is subjected to continuous rolling treatment. The continuously cast square billet is heated, and the temperature of the preheating section is controlled at 700℃, the temperature of the first heating section is 899℃, the temperature of the second heating section is 1117℃, and the temperature of the soaking section is 1166℃. The total heating time is 207min, and the soaking time is 54min, to obtain steel.

[0099] S4. After air-cooling the surface temperature of the steel obtained in S3 to 270℃, it is sawn.

[0100] After the sawn steel is air-cooled to a surface temperature of 103°C, it is bundled and collected to obtain round steel.

[0101] S5. Set the tempering process parameters according to the furnace charge of the steel, and temper the round steel obtained in S4 to obtain pre-hardened round steel with a diameter of φ16mm-φ60mm. The tempering process parameters are shown in the table below:

[0102] ≤30 tons 540-550℃ 25-27h 30 tons < Q ≤ 45 tons 535-545℃ 35-37h 45 tons < Q ≤ 60 tons 530-540℃ 45-47h

[0103] The difference between the maximum and minimum diameters of the round steel bars loaded into the furnace is 18 mm.

[0104] The product hardness of this embodiment is shown in the table below:

[0105]

[0106] As shown in the table, the hardness difference of the pre-hardened round steel at the same cross section obtained in this embodiment is ≤3HRC, and the pass rate is 100%.

[0107] The inclusion data of the product in this embodiment are shown in the table below:

[0108]

[0109] As shown in the table, the product in this embodiment has a grade of ≤1.5 for inclusions of types A, C, and D, and a grade of ≤2.0 for inclusions of type B, with a pass rate of 100%.

[0110] In summary, the method of this invention optimizes the production process of pre-hardened round steel, omits the billet opening step, shortens the production cycle, and saves costs. At the same time, by optimizing process parameters, it effectively solves the problems of segregation and porosity in pre-hardened round steel. The hardness difference of the same cross section of the pre-hardened round steel is ≤3HRC, and the non-metallic inclusions in the product are ≤1.5 grade for A, C, and D type inclusions and ≤2.0 grade for B type inclusions. The yield rate reaches 96.5%, which greatly improves the production quality of pre-hardened round steel.

[0111] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing pre-hardened round steel through continuous casting and rolling, characterized in that, Includes the following steps: The billet is obtained by sequentially smelting the furnace charge using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace, including: Before smelting the molten steel using a VD furnace, Ca-Si wire is fed into the molten steel at a rate of 250m / 40 tons, with a feeding speed ≥2.5m / s; When smelting molten steel using a VD furnace, adjust the argon flow rate, evacuate the VD furnace, control the ultimate vacuum degree of the VD furnace to ≤67Pa and maintain it for more than 15 minutes, adjust the argon flow rate to ≤20L / min 1 minute before rupturing the vacuum, and measure the temperature and take samples of the molten steel after rupturing the vacuum. The billet is processed using a three-strand drawing process to obtain a continuously cast square billet, including: controlling the drawing speed according to the superheat: 0.95-0.85 m / min when the superheat is less than 20℃, 0.85-0.80 m / min when the superheat is 20-25℃, 0.80-0.75 m / min when the superheat is 26-35℃, 0.75-0.70 m / min when the superheat is 36-40℃, and 0.70 m / min when the superheat is greater than 40℃; annealing the continuously cast square billet after slow cooling under a cover for 8-11 hours; the composition of the continuously cast square billet includes: 0.36... -0.45wt% C, 0.45-0.60wt% Si, 12.8-13.8wt% Cr, 0.02-0.05wt% Al, 0.3-0.6wt% Ni, 0.40-0.80wt% Mn, ≤0.02wt% P, ≤0.005wt% S, ≤0.02wt% As, ≤0.01wt% Sn, ≤0.01wt% Pb, ≤0.01wt% Sb, ≤0.01wt% Bi, ≤0.0002wt% H, ≤0.0025wt% O, balance Fe; wherein, As+Sn+Pb+Sb+Bi≤0.04wt%; The continuously cast billet is subjected to continuous rolling to obtain steel. The steel is subjected to air cooling, sawing, and air cooling to obtain round steel. The round steel is tempered to obtain pre-hardened round steel; The furnace charge includes low-phosphorus scrap steel, low-sulfur scrap steel, recycled steel of the same grade, contract billets, alloy materials, and alloy material substitutes.

2. The method for producing pre-hardened round steel by continuous casting and rolling according to claim 1, characterized in that, The method of sequentially smelting furnace charge using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace to obtain billets includes: When smelting the furnace charge using an electric furnace, the furnace temperature is controlled at ≥1620℃. 300kg of silicon carbide is added to every 40 tons of the furnace charge and stirred with nitrogen. The pre-reduction time is ≥10 minutes. At the end of the pre-reduction, the furnace temperature is ≥1630℃ to obtain molten steel.

3. The method for producing pre-hardened round steel by continuous casting and rolling according to claim 2, characterized in that, The method of sequentially smelting furnace charge using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace to obtain billets also includes: The molten steel is mixed and blown using an AOD furnace, and lime and alloys are added to the molten steel.

4. The method for producing pre-hardened round steel by continuous casting and rolling according to claim 3, characterized in that, The method of sequentially smelting furnace charge using an electric furnace, an AOD furnace, an LF furnace, and a VD furnace to obtain billets also includes: When smelting the molten steel using an LF furnace, aluminum wire is fed into the molten steel at a rate of 0.06 wt% at a feeding speed of ≥2.5 m / s. After feeding the aluminum wire, the temperature of the molten steel is measured, and power is supplied to the LF furnace. 150 kg of steel slag and 60 kg of carbon powder are added to every 40 tons of molten steel. The steel slag and carbon powder are added in batches. The first batch consists of 80 kg of steel slag and 30 kg of carbon powder, and subsequent batches consist of 15-40 kg of steel slag and 15-40 kg of carbon powder. When the slag turns white and the temperature of the molten steel reaches ≥1560℃, the molten steel is sampled and analyzed. Based on the analysis results, steel slag or carbon powder is added to maintain a reducing atmosphere.

5. The method for producing pre-hardened round steel by continuous casting and rolling according to claim 1, characterized in that, The process of continuously rolling the continuously cast billet to obtain steel includes: The continuously cast billet is heated, with the preheating temperature controlled at 660-710℃, the first heating temperature at 870-910℃, the second heating temperature at 1100-1120℃, and the soaking temperature at 1150-1170℃. The total heating time is 180-210 min, and the soaking time is 48-55 min.

6. The method for producing pre-hardened round steel by continuous casting and rolling according to claim 1, characterized in that, The process of air-cooling, sawing, and air-cooling the steel to obtain round steel includes: The steel is air-cooled to ≤400℃ before being sawn. After sawing, the steel is air-cooled to a surface temperature of 100-115℃ and then bundled and collected.

7. A method for producing pre-hardened round steel by continuous casting and rolling according to any one of claims 1-6, characterized in that, The process of tempering the round steel to obtain pre-hardened round steel includes: The round steel is heated to T℃ within 6-8 hours and held at that temperature for t hours, then air-cooled to room temperature. The temperature T and time t are adjusted according to the amount of material loaded. The amount of round steel charged is Q. When Q≤30 tons, 540≤T≤550, 25≤t≤27; When 30 tons < Q ≤ 45 tons, 535 ≤ T ≤ 545, 35 ≤ t ≤ 37; When 45 tons < Q ≤ 60 tons, 530 ≤ T ≤ 540, 45 ≤ t ≤ 47; Wherein, the difference between the maximum and minimum diameters of the round steel is ≤20mm.

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