A production method of high homogenization cold upsetting steel SWRCH35K casting blank

Abstract

This invention discloses a method for producing high-homogeneity cold heading steel SWRCH35K billets in the field of iron and steel metallurgy. The method employs an electric arc furnace (EAF) for smelting, during which carbon powder, porous rare-earth-doped titanium-silicon oxide composite microspheres, aluminum ingots, and alloys are sequentially added for deoxidation and alloying. Subsequently, LF refining is performed, and after slag formation and heating, silicon carbide and the composite microspheres are added for further treatment. Finally, a Si-Ca wire treatment is conducted to obtain a steel-to-billet mixture. This molten steel is then continuously cast into billets, with argon blowing and electromagnetic stirring performed before casting, and a four-stage light pressure applied at the end of solidification. After exiting the straightening machine, the billet is held at a low temperature for slow cooling. The composite microspheres are produced through steps such as sol-gel, spray molding, stepped calcination, secondary loading, and surface silanization. This method, by optimizing the smelting and continuous casting processes and introducing specific functional microspheres, significantly improves the purity of the molten steel and the uniformity of the billet structure, effectively enhancing the processing performance and quality stability of cold heading steel.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel metallurgy technology, specifically relating to a production method of high homogeneous cold heading steel SWRCH35K billet. Background Technology

[0002] Cold heading steel is a fundamental material for manufacturing various fasteners such as bolts, nuts, and rivets. Its product quality directly affects the connection reliability and service safety of mechanical equipment. With the rapid development of high-end equipment manufacturing, unprecedentedly stringent requirements have been placed on the purity, microstructure uniformity, and cold working performance of cold heading steel. Traditional cold heading steel production processes typically involve key steps such as primary refining in electric arc furnaces or converters, ladle refining, and continuous casting, aiming to improve steel quality through deoxidation, desulfurization, alloying, and inclusion control. However, in actual large-scale production, how to consistently and stably obtain highly homogeneous cast billets with low segregation and minimal microscopic defects remains a common technical challenge in the industry, especially in improving the consistency of the material's transverse and longitudinal properties, where there is still considerable room for improvement.

[0003] In existing technologies, metallurgists have adopted various process optimization measures to improve the quality of cold-heading steel. For example, strengthening deoxidation and slag-forming operations in the refining process to reduce oxide inclusion content, or altering the morphology and distribution of inclusions through calcium treatment to prevent them from becoming crack sources during rolling and cold heading. Furthermore, the application of electromagnetic stirring technology in continuous casting to expand the equiaxed grain zone in the billet center and reduce center segregation, as well as the use of light reduction technology to compensate for shrinkage at the end of billet solidification and suppress center porosity, are also common homogenization control methods. Despite these efforts, even with the combined application of these technologies, it is still difficult to completely eliminate small, harmful inclusions in molten steel, and their effect on improving the microscopic segregation of elements during solidification is limited. Especially for steel grades with specific requirements for silicon and manganese content, the compositional fluctuations and microstructure inhomogeneity in the central region of the billet often lead to cracking in subsequent products during cold heading, making it difficult to further improve the yield.

[0004] Therefore, the industry urgently needs an innovative production method that synergistically improves both molten steel purification and solidification control to overcome the bottlenecks of existing technologies. The purpose of this invention is precisely to solve the above problems and provide a novel production process that can significantly improve the homogenization level of cold heading steel billets. The core innovation of this method lies in the creative preparation and introduction of a functional additive with a specific structure, combined with a carefully designed set of process parameters that run throughout the entire process of tapping, refining, and continuous casting. This additive can function at multiple metallurgical stages, deeply purifying the molten steel and refining the solidification structure, thereby fundamentally improving the chemical composition uniformity and internal density of the billet, ultimately obtaining high-performance, highly consistent cold heading steel products to meet the demands of the high-end market. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for producing highly homogeneous cold heading steel SWRCH35K billets.

[0006] A first aspect of the present invention provides a method for producing a highly homogeneous cold heading steel SWRCH35K billet, comprising the following steps: S1. SWRCH35K steel is smelted in an electric arc furnace; the tapping temperature is 1610-1630℃; during the tapping process, carbon powder and porous rare earth-doped titanium silicon oxide composite microspheres are first added to the bottom of the ladle; then aluminum ingots are added for strong deoxidation; finally, pre-baked Fe-Mn and Fe-Si alloys are added to complete the alloying. S2. Hoist the SWRCH35K molten steel into the LF station, add lime and fluorite to form slag; heat the steel to 1595-1605℃, add silicon carbide and porous rare earth doped titanium silicon oxide composite microspheres; before the refining is finished, add Si-Ca wire to obtain a mixture. S3. Cast the mixture into billets using a billet continuous casting machine. Before casting, argon is blown to remove oxygen and electromagnetic stirring is performed. S4. At the end of solidification, implement four-stage light pressing to ensure dynamic matching between the pressing position and the end of the liquid core; after the billet exits the straightening machine, it enters the heat preservation cover for slow cooling.

[0007] In this invention, during the preparation of highly homogeneous cold heading steel billets, the aforementioned porous rare-earth-doped titanium-silicon oxide composite microspheres serve as a multifunctional additive, exerting a triple metallurgical effect. Firstly, they disperse in the molten steel during the initial deoxidation stage, providing numerous heterogeneous interfaces for newly formed alumina inclusions, prompting them to be rapidly encapsulated and transformed into low-melting-point, easily deformable composite inclusions, significantly improving the cleanliness of the molten steel. Secondly, the microspheres themselves act as highly stable heterogeneous nucleation cores, effectively promoting equiaxed crystal nucleation at the solidification front, expanding the proportion of equiaxed crystal regions, and inhibiting the transgranular growth of columnar crystals, thereby reducing macroscopic segregation. Thirdly, their porous structure and surface active sites can adsorb segregating components such as carbon and sulfur in the solute element enrichment layer, weakening the supercooling of the solidification interface front and further inhibiting the formation of central segregation. By combining precise temperature control throughout the entire process of electric furnace-LF-continuous casting, a two-stage microsphere addition strategy, and the synergistic effect of electromagnetic stirring and dynamic light pressure, a high-quality billet with dense center, uniform composition, and fine and dispersed inclusions is finally obtained, providing an ideal microstructure basis for subsequent cold heading.

[0008] According to a preferred embodiment of the present invention, in step S1, the SWRCH35K molten steel comprises C: 0.33-0.35%, Si: 0.15-0.25%, Mn: 0.6-0.7%, P≤0.015%, S≤0.010%, Cr≤0.10%, Ni≤0.10%, Cu≤0.15%, and Al: 0.020-0.040%.

[0009] According to a preferred embodiment of the present invention, in step S2, the Si-Ca wire comprises Si: 55-65% and Ca: 28-32%.

[0010] According to a preferred embodiment of the present invention, in step S3, the time for argon blowing before casting the billet is 10-12 minutes.

[0011] According to a preferred embodiment of the present invention, in step S4, the solidification coefficient at the solidification end is 0.3-0.9.

[0012] According to a preferred embodiment of the present invention, the preparation steps of the porous rare-earth-doped titanium-silicon oxide composite microspheres include: A1. By weight, tetraethyl orthosilicate and tetrabutyl titanate are added to anhydrous ethanol and stirred to obtain solution A; lanthanum nitrate hexahydrate and cerium nitrate hexahydrate are dissolved in deionized water to obtain mixed rare earth salt solution B; under stirring, mixed rare earth salt solution B is added dropwise to solution A, and ammonia is added to adjust the pH to 9.3-9.7, and stirring is continued to obtain sol; then polyvinylpyrrolidone is added, and the mixture is aged in a water bath at 58-62℃ to obtain precursor sol; A2. Spray the precursor sol into a continuous liquid paraffin phase containing sorbitan monooleate to obtain microdroplets; place the microdroplets at 78-82℃ to obtain gel microspheres; transfer the gel microspheres to a muffle furnace, heat to 295-305℃ and hold, then heat to 595-605℃ and hold, and finally heat to 945-955℃ and hold, then cool naturally to obtain an intermediate; A3. The intermediate was impregnated in anhydrous toluene solution of tetraisopropyl titanate and refluxed at 110-111℃; after filtration and washing, it was calcined in air at 495-505℃; then placed in a tube furnace and calcined at 695-705℃ under a hydrogen / argon atmosphere to obtain the product; the product was ultrasonically cleaned and vacuum dried to obtain the dried product. A4. The dried product is sieved; then, in a fluidized bed, trimethylchlorosilane vapor is introduced at 100-150℃ for surface silanization treatment.

[0013] In this invention, the formation mechanism of the porous rare-earth-doped titanium-silicon oxide composite microspheres is based on the synergistic effect of sol-gel chemistry and controllable thermal treatment. First, under alkaline conditions, the silicon and titanium sources undergo co-hydrolysis and condensation reactions to construct a three-dimensional TiO2-SiO2 inorganic network framework; simultaneously, La... 3+ and Ce 3+Due to its strong hydrolytic tendency, the microspheres rapidly transform into La(OH)3 / Ce(OH)3 colloidal nanoclusters, which are then encapsulated by an in-situ formed silicon-titanium oxide network. During this process, the polymeric pore-forming agent not only regulates the microsphere morphology but also induces the formation of a hierarchical pore structure. Subsequently, through multi-stage gradient calcination, organic components are gradually removed, promoting densification and partial crystallization of the titanium and silicon oxides. The encapsulated rare earth hydroxides dehydrate and transform into La2O3 / CeO2 nanocrystals, which are uniformly dispersed in the pores and surface of the framework, forming high-density active centers. This ultimately generates an amorphous / nanocrystalline TiO2-SiO2-based composite oxide framework with a high melting point and high thermal stability. The surface of this framework is rich in oxygen vacancies and highly dispersed rare earth oxide active sites, exhibiting excellent inclusion adsorption capacity. Further surface modification constructs a tunable amorphous titanium oxide layer on the outer layer of the microspheres, and reduction treatment introduces low-valence titanium species, significantly enhancing its interfacial wettability and chemical affinity with alumina inclusions in the molten steel, thereby achieving efficient capture and spheroidization of harmful inclusions.

[0014] According to a preferred embodiment of the present invention, in step A1, the aging time in a water bath at 58-62°C is 12-14 hours.

[0015] According to a preferred embodiment of the present invention, in step A2, the time for holding the temperature at 945-955°C is 4-6 hours.

[0016] According to a preferred embodiment of the present invention, in step A3, the reflux reaction at 110-111°C is carried out for 4-6 hours.

[0017] According to a preferred embodiment of the present invention, in step A4, the surface silanization treatment time is 30-60 min.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) This method innovatively introduces porous rare earth-doped titanium-silicon oxide composite microspheres with specific structures in stages during the tapping and refining processes, and coordinates them with silicon carbide deoxidation and calcium treatment processes to achieve a significant improvement in the purity of molten steel. The composite microspheres have a rich porous structure and highly active rare earth and titanium elements. In molten steel, they can efficiently adsorb small oxide and sulfide inclusions, and the active elements they release can combine with residual oxygen and sulfur in the steel, transforming harmful inclusions into smaller, more dispersed, and more thermoplastic composite inclusions. This dual effect of "adsorption" and "modification" significantly reduces the number and size of inclusions in the steel, avoids the formation of large hard inclusions, and thus greatly purifies the molten steel, laying a solid foundation for obtaining high-purity billets and directly reducing the risk of cracking caused by inclusions during subsequent cold heading.

[0019] (2) During the solidification and forming stage of the billet, this method effectively improves the uniformity of the internal macro- and micro-structure of the billet through a combination of precisely controlled electromagnetic stirring, four-stage light reduction based on the dynamic matching of the liquid core position at the end of solidification, and heat preservation and slow cooling after billet removal. Electromagnetic stirring promotes the freeing and proliferation of grains at the solidification front and expands the central equiaxed crystal zone; while the precisely implemented light reduction technology effectively compensates for the shrinkage of the billet core at the end of solidification and significantly inhibits the formation of central porosity and segregation. The subsequent heat preservation and slow cooling process smooths the temperature gradient of the billet, reduces internal stress, and prevents crack formation. This series of solidification control measures makes the structure of the billet from the surface to the core more dense and uniform, and the degree of compositional segregation is greatly reduced, thereby obtaining a highly homogeneous billet product, and the performance consistency of its cross-section and longitudinal direction is reliably guaranteed.

[0020] (3) The synergistic improvement in purity and homogeneity achieved by this invention directly translates into superior comprehensive mechanical properties and process adaptability of cold-heading steel products. The billets produced by this method have high internal cleanliness and uniform, dense structure, making the subsequent rolling process smoother and fully utilizing the plasticity and toughness of the steel. The cold-heading steel wires or bars processed from these billets exhibit excellent deformation capacity during cold heading, are less prone to surface or core cracking, and significantly improve the product forming qualification rate. At the same time, the strength and toughness of the steel are better matched, and the fatigue life is extended, fully meeting the stringent requirements of high-end fasteners for high strength, high precision, and high reliability, and possessing significant market competitive advantages and economic benefits. Detailed Implementation

[0021] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention. Example

[0022] This embodiment provides a method for producing high-homogeneity cold heading steel SWRCH35K billets, including the following steps: Preparation of porous rare-earth-doped titanium-silicon oxide composite microspheres: A1. First, accurately weigh 80.00 g of tetraethyl orthosilicate and 20.00 g of tetrabutyl titanate, and add them to a dry 1000 mL three-necked flask. Add 500 mL of anhydrous ethanol to the flask, place the flask on a magnetic stirrer, and stir continuously at 300 rpm for 30 min at room temperature (25±2℃) until the mixture is homogeneous and transparent, and label it solution A. Separately, take a 250 mL beaker, accurately weigh 8.00 g of lanthanum nitrate hexahydrate and 2.00 g of cerium nitrate hexahydrate, add 50 mL of deionized water, and place it on another magnetic stirrer to stir until the solids are completely dissolved, obtaining a clear mixed rare earth salt solution B. Using a constant flow pump, while continuously stirring solution A, slowly and evenly add solution B dropwise to the three-necked flask at a rate of approximately 1.67 mL / min over 30 min. During the dropwise addition, a 25% ammonia solution was simultaneously added dropwise to the system using another dropping funnel. The pH of the reaction system was monitored in real-time using a precision pH meter and precisely adjusted and stabilized at 9.5. After solution B was completely added, the stirring speed was maintained at 300 rpm for 60 minutes, during which time the system gradually transformed into a light yellow, translucent sol. Subsequently, 10.00 g of polyvinylpyrrolidone was added to this sol, and stirring continued until it was completely dissolved. The three-necked flask was transferred to a 60°C constant temperature water bath and aged for 13 hours with gentle stirring to obtain a stable and homogeneous precursor sol.

[0023] A2. Transfer the above precursor sol to a storage tank equipped with a 0.5 mm diameter stainless steel nozzle for a spray device. Use high-purity nitrogen as the atomizing gas and adjust the pressure to 0.2 MPa. Add 1000 mL of liquid paraffin containing 5.00 g of sorbitan monooleate to a 2000 mL glass reactor and preheat to 80°C. Turn on the spray device to atomize the precursor sol and spray it into the continuous phase of liquid paraffin, forming uniformly dispersed microdroplets. Maintain the oil phase temperature in the reactor at 80°C and gently stir mechanically at 200 rpm for 4 hours. During this period, the solvent in the microdroplets gradually evaporates, a gelation reaction occurs, and finally, well-formed solid gel microspheres are formed. After the reaction, use a Buchner funnel for vacuum filtration to separate and collect the gel microspheres. Wash the gel microspheres three times (approximately 167 mL each time) with 500 mL of anhydrous ethanol to thoroughly remove the paraffin and residual dispersant adhering to the surface. The cleaned gel microspheres were placed in a clean alumina crucible and then placed in a box-type muffle furnace. A stepped calcination program was set: in the first stage, the temperature was increased from room temperature to 300°C at a rate of 5°C / min and held at 300°C for 120 min; in the second stage, the temperature was increased to 600°C at a rate of 5°C / min and held for 180 min; in the third stage, the temperature was increased again to 950°C at a rate of 5°C / min and calcined at this temperature for 300 min. After the calcination program was completed, the power to the muffle furnace was turned off, and the material was allowed to cool naturally to room temperature (approximately 25°C) to obtain a white, hard, porous intermediate.

[0024] A3. Accurately weigh 20.00 g of the above porous intermediate and immerse it in a 500 mL round-bottom flask containing 200 mL of anhydrous toluene, in which 30.00 g of tetraisopropyl titanate has been pre-dissolved. Assemble the flask with a spherical condenser and place it in a heated, magnetically stirred oil bath. Turn on the stirrer and heat, maintaining the mixture under gentle reflux at 110 °C for 300 min. After the reaction is complete, stop heating and allow the system to cool. Filter the mixture using a sintered glass funnel to separate the solid and liquid phases. Wash the filtered solid thoroughly with 300 mL of anhydrous ethanol three times (100 mL each time) to remove unreacted titanate esters and byproducts. Transfer the washed solid to a new alumina crucible and place it in a muffle furnace. Heat the crucible to 500 °C at a rate of 5 °C / min under static air atmosphere and calcine at this temperature for 180 min. Then, transfer the material to a quartz boat in a tube furnace. A mixed reducing gas consisting of 5% hydrogen and 95% argon (by volume) was introduced into a tube furnace at a total flow rate of 100 mL / min. The furnace temperature was raised to 700 °C at a heating rate of 10 °C / min and calcined at this temperature for 120 min. After calcination, the mixture was allowed to cool naturally to room temperature under a protective atmosphere. The resulting product was transferred to a 250 mL beaker, and 200 mL of anhydrous ethanol was added. The beaker was then placed in an ultrasonic cleaner with a power of 100 W and a frequency of 40 kHz and ultrasonically cleaned for 20 min. After cleaning, the mixture was filtered again, and the solid was placed in a vacuum drying oven and dried at 80 °C and -0.1 MPa for 360 min to obtain a dried composite powder.

[0025] A4. The dried composite powder was sieved using a standard metal sieve, and the sieved product with a particle size between 150 μm and 200 μm was collected. Approximately 50 g of the sieved product was loaded into a 50 mm diameter glass fluidized bed reactor. The heating system was turned on, and the bed temperature was stabilized at 120 °C. Dry nitrogen was introduced as a carrier gas, and trimethylchlorosilane liquid was vaporized at a rate of 0.05 mL / min and carried into the fluidized bed. The vapor contacted the microspheres and carried out a surface modification reaction for 45 min. After the reaction was completed, the silane supply was stopped, and the mixture was cooled to room temperature under nitrogen protection. The product was then removed, yielding the final porous rare earth-doped titanium silicon oxide composite microspheres, which were then sealed and stored in a desiccator.

[0026] Production of high homogeneous cold heading steel SWRCH35K billets: S1. Smelting is carried out using an AC electric arc furnace with a nominal capacity of 50t. Through decarburization during the oxidation period, the final carbon content of the molten steel is controlled at 0.08%. When the molten steel temperature reaches 1620℃, tapping begins. When approximately 1 / 3 of the total steel has been tapped, the operator first adds 3000g of carbon powder (0.5-1.0mm particle size) and 1500g of the aforementioned prepared porous rare-earth-doped titanium-silicon oxide composite microspheres to the bottom of an empty ladle pre-placed on the ladle car. When approximately 1 / 2 of the steel has been tapped, 40000g of aluminum ingots (99.7% purity) are added to the impact zone of the steel flow for precipitation and strong deoxidation. When approximately 3 / 4 of the steel has been tapped, 200000g of medium-manganese ferroalloy (Fe-Mn, Mn content 78%) and 50000g of ferrosilicon alloy (Fe-Si, Si content 75%), preheated to 400℃, are added to complete the alloying of the main alloying elements. The entire process of tapping the steel takes about 5 minutes.

[0027] S2. After tapping, the ladle is hoisted to the LF (Ladle Refining Furnace) station using an overhead crane. The ladle is positioned in the electric arc heating position, and the graphite electrode is lowered. First, 60,000g of lime (CaO≥92%) and 8,000g of fluorite (CaF2≥95%) are added to the surface of the molten steel to form slag. The power is turned on, and the submerged arc heating mode is used to uniformly raise the temperature of the molten steel from approximately 1580℃ after tapping to 1600℃ within about 25 minutes. Subsequently, the ladle is hoisted from the heating position to a dedicated alloy addition station, where 5,000g of silicon carbide powder (SiC≥98%, particle size 0.2-0.5mm) and 800g of the aforementioned composite microspheres are fed into the depth of the molten steel through a wire feeder. Afterward, the ladle is returned to the heating position, and the electric arc is maintained at a temperature of 1600±5℃ for 15 minutes of refining, during which the slag condition is observed and fine-tuned. Three minutes before the end of refining, 120 meters of 13mm diameter silicon-calcium cored wire (Si-Ca wire) was fed into the molten steel at a constant speed of 120m / min using another wire feeder. The core powder composition of the Si-Ca wire was: 60% Si, 30% Ca, with the remainder being iron and unavoidable trace elements.

[0028] S3. After refining and settling for 5 minutes, the processed molten steel is transported to the continuous casting platform. A full-arc R9m square billet continuous casting machine is used for casting, with a crystallizer cross-section of 150mm × 150mm. A submerged entry nozzle is used for protective casting. When the temperature of the molten steel in the tundish stabilizes at 1520℃, the stopper is opened, and casting begins. High-purity argon gas (Ar ≥ 99.999%) is blown into the molten steel in the crystallizer at a constant flow rate of 10L / min through a porous vent plug installed at the bottom of the submerged entry nozzle for 11 minutes. Simultaneously, the electromagnetic stirring device of the crystallizer is activated, with the stirring current set to 300A and the frequency to 3.0Hz.

[0029] S4. In the secondary cooling zone of the continuous casting machine, based on temperature data measured by multiple thermocouples installed on the billet support guide section, and combined with the established solidification heat transfer mathematical model, the position of the end of the liquid core of the billet is dynamically calculated and determined in real time. When the billet reaches the solidification end area, the four-stage light reduction function of the straightening machine is activated. According to the model calculation results, the position of the reduction rollers is dynamically adjusted to ensure that the four reduction intervals (reduction positions) are always precisely matched with the moving end of the liquid core. In this embodiment, the total reduction is set to 8mm, with each of the four reduction rollers bearing 2mm. Under these process conditions, the solidification coefficient of the billet is 0.6. After the billet is completely solidified, it is straightened by the straightening machine, and the surface temperature when exiting the straightening machine is approximately 900℃. Subsequently, the billet is immediately sent into a 24m long heat insulation hood for slow cooling. The billet is slowly cooled in the heat insulation hood at a cooling rate of less than 50℃ / h until its surface temperature drops below 300℃, and then removed to obtain a highly homogenized SWRCH35K cold heading steel billet. Example

[0030] This embodiment provides a method for producing high-homogeneity cold heading steel SWRCH35K billets, including the following steps: Preparation of porous rare-earth-doped titanium-silicon oxide composite microspheres: A1. First, accurately weigh 75.00 g of tetraethyl orthosilicate and 25.00 g of tetrabutyl titanate, and add them to a dry 1000 mL three-necked flask. Add 480 mL of anhydrous ethanol to the flask, place the flask on a magnetic stirrer, and stir continuously at 280 rpm for 35 min at room temperature (25±2℃) until the mixture is homogeneous and transparent, and label it solution A. Separately, take a 250 mL beaker, accurately weigh 10.00 g of lanthanum nitrate hexahydrate and 1.00 g of cerium nitrate hexahydrate, add 50 mL of deionized water, and place it on another magnetic stirrer to stir until the solids are completely dissolved, obtaining a clear mixed rare earth salt solution B. Using a constant flow pump, while continuously stirring solution A, slowly and evenly add solution B dropwise to the three-necked flask at a rate of approximately 1.43 mL / min over 35 min. During the dropwise addition, a 25% (w / w) ammonia solution was simultaneously added dropwise to the system using another dropping funnel. The pH of the reaction system was monitored in real-time using a precision pH meter and precisely adjusted and stabilized at 9.3. After solution B was completely added, the stirring speed was maintained at 280 rpm for 50 minutes, during which time the system gradually transformed into a light yellow, translucent sol. Subsequently, 12.00 g of polyvinylpyrrolidone was added to this sol, and stirring continued until it was completely dissolved. The three-necked flask was transferred to a 58°C constant temperature water bath and aged for 14 hours with gentle stirring to obtain a stable and homogeneous precursor sol.

[0031] A2. Transfer the above precursor sol to a storage tank equipped with a 0.5 mm diameter stainless steel nozzle for a spray device. Use high-purity nitrogen as the atomizing gas and adjust the pressure to 0.18 MPa. Add 950 mL of liquid paraffin containing 4.00 g of sorbitan monooleate to a 2000 mL glass reactor and preheat to 78 °C. Turn on the spray device to atomize the precursor sol and spray it into the continuous phase of liquid paraffin, forming uniformly dispersed microdroplets. Maintain the oil phase temperature in the reactor at 78 °C and gently stir mechanically at 180 rpm for 4.5 h. During this period, the solvent in the microdroplets gradually evaporates, a gelation reaction occurs, and finally, well-formed solid gel microspheres are formed. After the reaction, use a Buchner funnel for vacuum filtration to separate and collect the gel microspheres. Wash the gel microspheres three times (approximately 150 mL each time) with 450 mL of anhydrous ethanol to thoroughly remove the paraffin and residual dispersant adhering to the surface. The cleaned gel microspheres were placed in a clean alumina crucible and then placed in a box-type muffle furnace. A stepped calcination program was set: in the first stage, the temperature was increased from room temperature to 300°C at a rate of 5°C / min and held at 300°C for 120 min; in the second stage, the temperature was increased to 600°C at a rate of 5°C / min and held for 180 min; in the third stage, the temperature was increased again to 950°C at a rate of 5°C / min and calcined at this temperature for 240 min. After the calcination program was completed, the power to the muffle furnace was turned off, and the material was allowed to cool naturally to room temperature (approximately 25°C) to obtain a white, hard, porous intermediate.

[0032] A3. Accurately weigh 20.00 g of the above porous intermediate and immerse it in a 500 mL round-bottom flask containing 180 mL of anhydrous toluene, in which 25.00 g of tetraisopropyl titanate has been pre-dissolved. Assemble the flask with a spherical condenser and place it in a heated, magnetically stirred oil bath. Turn on the stirrer and heat, maintaining the mixture under gentle reflux at 111 °C for 240 min. After the reaction is complete, stop heating and allow the system to cool. Filter the mixture using a sintered glass funnel to separate the solid and liquid phases. Wash the filtered solid thoroughly with 270 mL of anhydrous ethanol three times (90 mL each time) to remove unreacted titanate esters and byproducts. Transfer the washed solid to a new alumina crucible and place it in a muffle furnace. Calcine the solid at 500 °C at a rate of 5 °C / min under static air atmosphere for 120 min. Then, transfer the material to a quartz boat in a tube furnace. A mixed reducing gas consisting of 5% hydrogen and 95% argon (by volume) was introduced into a tube furnace, with the total gas flow rate controlled at 100 mL / min. The furnace temperature was raised to 700 °C at a heating rate of 10 °C / min and calcined at this temperature for 180 min. After calcination, the mixture was allowed to cool naturally to room temperature under a protective atmosphere. The resulting product was transferred to a 250 mL beaker, and 200 mL of anhydrous ethanol was added. The beaker was then placed in an ultrasonic cleaner with a power of 100 W and a frequency of 40 kHz and ultrasonically cleaned for 20 min. After cleaning, the mixture was filtered again, and the solid was placed in a vacuum drying oven and dried at 80 °C and -0.1 MPa for 300 min to obtain a dried composite powder.

[0033] A4. The dried composite powder was sieved using a standard metal sieve, collecting the sieved product with a particle size between 150 μm and 200 μm. Approximately 50 g of the sieved product was loaded into a 50 mm diameter glass fluidized bed reactor. The heating system was turned on, and the bed temperature was stabilized at 100 °C. Dry nitrogen was introduced as a carrier gas, and trimethylchlorosilane liquid was vaporized at a rate of 0.05 mL / min and carried into the fluidized bed. The vapor contacted the microspheres and carried out a surface modification reaction for 60 min. After the reaction was completed, the silane supply was stopped, and the mixture was cooled to room temperature under nitrogen protection. The product was then removed, yielding the final porous rare earth-doped titanium silicon oxide composite microspheres, which were then sealed and stored in a desiccator.

[0034] Production of high homogeneous cold heading steel SWRCH35K billets: S1. Smelting is carried out using an AC electric arc furnace with a nominal capacity of 50t. Through decarburization during the oxidation period, the final carbon content of the molten steel is controlled at 0.08%. When the molten steel temperature reaches 1610℃, tapping begins. When approximately one-third of the total steel has been tapped, the operator first adds 2800g of carbon powder (0.5-1.0mm particle size) and 1200g of the aforementioned prepared porous rare-earth-doped titanium-silicon oxide composite microspheres to the bottom of an empty ladle pre-placed on the ladle car. When approximately half of the steel has been tapped, 38000g of aluminum ingots (99.7% purity) are added to the impact zone of the steel flow for precipitation and strong deoxidation. When approximately three-quarters of the steel has been tapped, 190000g of medium-manganese ferroalloy (Fe-Mn, Mn content 78%) and 45000g of ferrosilicon alloy (Fe-Si, Si content 75%), preheated to 400℃, are added to complete the alloying of the main alloying elements. The entire process of tapping the steel takes about 5 minutes.

[0035] S2. After tapping, the ladle is hoisted to the LF (Ladle Refining Furnace) station using an overhead crane. The ladle is positioned in the electric arc heating position, and the graphite electrode is lowered. First, 58,000g of lime (CaO≥92%) and 7,500g of fluorite (CaF2≥95%) are added to the surface of the molten steel to form slag. The power is turned on, and the submerged arc heating mode is used to uniformly raise the temperature of the molten steel from approximately 1575℃ after tapping to 1595℃ within about 28 minutes. Subsequently, the ladle is hoisted from the heating position to a dedicated alloy addition station, where 4,500g of silicon carbide powder (SiC≥98%, particle size 0.2-0.5mm) and 600g of the aforementioned composite microspheres are fed into the depth of the molten steel through a wire feeder. Afterward, the ladle is returned to the heating position, and the electric arc is maintained at a temperature of 1595±5℃ for refining for another 12 minutes, during which the slag condition is observed and fine-tuned. Three minutes before the end of refining, 100 meters of 13mm diameter silicon-calcium cored wire (Si-Ca wire) was fed into the molten steel at a constant speed of 100m / min using another wire feeder. The core powder composition of the Si-Ca wire was: 60% Si, 30% Ca, with the remainder being iron and unavoidable trace elements.

[0036] S3. After refining and settling for 5 minutes, the processed molten steel is transported to the continuous casting platform. A full-arc R9m square billet continuous casting machine is used for casting, with a crystallizer cross-section of 150mm × 150mm. A submerged entry nozzle is used for protective casting. When the temperature of the molten steel in the tundish stabilizes at 1515℃, the stopper is opened, and casting begins. High-purity argon gas (Ar ≥ 99.999%) is blown into the molten steel in the crystallizer at a constant flow rate of 10L / min through a porous vent plug installed at the bottom of the submerged entry nozzle for 10 minutes. Simultaneously, the electromagnetic stirring device of the crystallizer is started, with the stirring current set to 280A and the frequency to 2.5Hz.

[0037] S4. In the secondary cooling zone of the continuous casting machine, based on temperature data measured by multiple thermocouples installed on the billet support guide section, and combined with the established solidification heat transfer mathematical model, the position of the end of the liquid core of the billet is dynamically calculated and determined in real time. When the billet reaches the solidification end area, the four-stage light reduction function of the straightening machine is activated. According to the model calculation results, the position of the reduction rollers is dynamically adjusted to ensure that the four reduction intervals (reduction positions) are always precisely matched with the moving end of the liquid core. In this embodiment, the total reduction is set to 7mm, and the reductions of each segment are 1.5mm, 2.0mm, 1.5mm, and 2.0mm, respectively. Under these process conditions, the solidification coefficient of the billet is 0.3. After the billet is completely solidified, it is straightened by the straightening machine, and the surface temperature when exiting the straightening machine is approximately 900℃. Subsequently, the billet is immediately sent into a 24m long insulation hood for slow cooling. The billet is slowly cooled in the heat insulation hood at a cooling rate of less than 50℃ / h until its surface temperature drops below 300℃, and then removed to obtain a highly homogenized SWRCH35K cold heading steel billet. Example

[0038] This embodiment provides a method for producing high-homogeneity cold heading steel SWRCH35K billets, including the following steps: Preparation of porous rare-earth-doped titanium-silicon oxide composite microspheres: A1. First, accurately weigh 85.00 g of tetraethyl orthosilicate and 15.00 g of tetrabutyl titanate, and add them to a dry 1000 mL three-necked flask. Add 520 mL of anhydrous ethanol to the flask, place the flask on a magnetic stirrer, and stir continuously at 320 rpm for 25 min at room temperature (25±2℃) until the mixture is homogeneous and transparent, and label it solution A. Separately, take a 250 mL beaker, accurately weigh 6.00 g of lanthanum nitrate hexahydrate and 4.00 g of cerium nitrate hexahydrate, add 50 mL of deionized water, and place it on another magnetic stirrer to stir until the solids are completely dissolved, obtaining a clear mixed rare earth salt solution B. Using a constant flow pump, while continuously stirring solution A, slowly and evenly add solution B dropwise to the three-necked flask at a rate of approximately 2.00 mL / min over 25 min. During the dropwise addition, a 25% ammonia solution was simultaneously added dropwise to the system using another dropping funnel. The pH of the reaction system was monitored in real time using a precision pH meter and precisely adjusted and stabilized at 9.7. After solution B was completely added, the stirring speed was maintained at 320 rpm for 70 minutes, during which time the system gradually transformed into a light yellow, translucent sol. Subsequently, 8.00 g of polyvinylpyrrolidone was added to this sol, and stirring continued until it was completely dissolved. The three-necked flask was transferred to a constant temperature water bath at 62°C and aged for 12 hours with gentle stirring to obtain a stable and homogeneous precursor sol.

[0039] A2. Transfer the above precursor sol to a storage tank equipped with a 0.5 mm diameter stainless steel nozzle for a spray device. Use high-purity nitrogen as the atomizing gas and adjust the pressure to 0.22 MPa. Add 1050 mL of liquid paraffin containing 6.00 g of sorbitan monooleate to a 2000 mL glass reactor and preheat to 82°C. Turn on the spray device to atomize the precursor sol and spray it into the continuous phase of liquid paraffin, forming uniformly dispersed microdroplets. Maintain the oil phase temperature in the reactor at 82°C and gently stir mechanically at 220 rpm for 3.5 h. During this period, the solvent in the microdroplets gradually evaporates, a gelation reaction occurs, and finally, well-formed solid gel microspheres are formed. After the reaction, use a Buchner funnel for vacuum filtration to separate and collect the gel microspheres. Wash the gel microspheres three times (approximately 183 mL each time) with 550 mL of anhydrous ethanol to thoroughly remove the paraffin and residual dispersant adhering to the surface. The cleaned gel microspheres were placed in a clean alumina crucible and then placed in a box-type muffle furnace. A stepped calcination program was set: in the first stage, the temperature was increased from room temperature to 300°C at a rate of 5°C / min and held at 300°C for 120 min; in the second stage, the temperature was increased to 600°C at a rate of 5°C / min and held for 180 min; in the third stage, the temperature was increased again to 950°C at a rate of 5°C / min and calcined at this temperature for 360 min. After the calcination program was completed, the power to the muffle furnace was turned off, and the material was allowed to cool naturally to room temperature (approximately 25°C) to obtain a white, hard, porous intermediate.

[0040] A3. Accurately weigh 20.00 g of the above porous intermediate and immerse it in a 500 mL round-bottom flask containing 220 mL of anhydrous toluene, in which 35.00 g of tetraisopropyl titanate has been pre-dissolved. Assemble the flask with a spherical condenser and place it in a heated, magnetically stirred oil bath. Turn on the stirrer and heat, maintaining the mixture under gentle reflux at 110 °C for 360 min. After the reaction is complete, stop heating and allow the system to cool. Filter the mixture using a sintered glass funnel to separate the solid and liquid phases. Wash the filtered solid thoroughly with 330 mL of anhydrous ethanol three times (110 mL each time) to remove unreacted titanate esters and byproducts. Transfer the washed solid to a new alumina crucible and place it in a muffle furnace. Calcine the solid at 500 °C at a rate of 5 °C / min under static air atmosphere for 240 min. Then, transfer the material to a quartz boat in a tube furnace. A mixed reducing gas consisting of 5% hydrogen and 95% argon (by volume) was introduced into a tube furnace, with the total gas flow rate controlled at 100 mL / min. The furnace temperature was raised to 700 °C at a heating rate of 10 °C / min and calcined at this temperature for 90 min. After calcination, the mixture was allowed to cool naturally to room temperature under a protective atmosphere. The resulting product was transferred to a 250 mL beaker, and 200 mL of anhydrous ethanol was added. The beaker was then placed in an ultrasonic cleaner with a power of 100 W and a frequency of 40 kHz and ultrasonically cleaned for 20 min. After cleaning, the mixture was filtered again, and the solid was placed in a vacuum drying oven and dried at 80 °C and -0.1 MPa for 420 min to obtain a dried composite powder.

[0041] A4. The dried composite powder was sieved using a standard metal sieve, and the sieved product with a particle size between 150 μm and 200 μm was collected. Approximately 50 g of the sieved product was loaded into a 50 mm diameter glass fluidized bed reactor. The heating system was turned on, and the bed temperature was stabilized at 150 °C. Dry nitrogen was introduced as a carrier gas, and trimethylchlorosilane liquid was vaporized at a rate of 0.05 mL / min and carried into the fluidized bed. The vapor contacted the microspheres and carried out a surface modification reaction for 30 min. After the reaction was completed, the silane supply was stopped, and the mixture was cooled to room temperature under nitrogen protection. The product was then removed, yielding the final porous rare earth-doped titanium silicon oxide composite microspheres, which were then sealed and stored in a desiccator.

[0042] Production of high homogeneous cold heading steel SWRCH35K billets: S1. Smelting is carried out using an AC electric arc furnace with a nominal capacity of 50t. Through decarburization during the oxidation period, the final carbon content of the molten steel is controlled at 0.08%. When the molten steel temperature reaches 1630℃, tapping begins. When approximately one-third of the total steel has been tapped, the operator first adds 3200g of carbon powder (0.5-1.0mm particle size) and 1800g of the aforementioned prepared porous rare-earth-doped titanium-silicon oxide composite microspheres to the bottom of an empty ladle pre-placed on the ladle car. When approximately half of the steel has been tapped, 42000g of aluminum ingots (99.7% purity) are added to the impact zone of the steel flow for precipitation and strong deoxidation. When approximately three-quarters of the steel has been tapped, 210000g of medium-manganese ferroalloy (Fe-Mn, Mn content 78%) and 55000g of ferrosilicon alloy (Fe-Si, Si content 75%), preheated to 400℃, are added to complete the alloying of the main alloying elements. The entire process of tapping the steel takes about 5 minutes.

[0043] S2. After tapping, the ladle is hoisted to the LF (Ladle Refining Furnace) station using an overhead crane. The ladle is positioned in the electric arc heating position, and the graphite electrode is lowered. First, 62,000g of lime (CaO≥92%) and 8,500g of fluorite (CaF2≥95%) are added to the surface of the molten steel to form slag. The power is turned on, and the submerged arc heating mode is used to uniformly raise the temperature of the molten steel from approximately 1585℃ after tapping to 1605℃ within about 22 minutes. Subsequently, the ladle is hoisted from the heating position to a dedicated alloy addition station, where 5,500g of silicon carbide powder (SiC≥98%, particle size 0.2-0.5mm) and 1,000g of the aforementioned composite microspheres are fed into the depth of the molten steel using a wire feeder. Afterward, the ladle is returned to the heating position, and the electric arc is maintained at a temperature of 1605±5℃ for 18 minutes of refining, during which the slag condition is observed and fine-tuned. Three minutes before the end of refining, 140 meters of 13mm diameter silicon-calcium cored wire (Si-Ca wire) was fed into the molten steel at a constant speed of 140m / min using another wire feeder. The core powder composition of the Si-Ca wire was: 60% Si, 30% Ca, with the remainder being iron and unavoidable trace elements.

[0044] S3. After refining and settling for 5 minutes, the processed molten steel is transported to the continuous casting platform. A full-arc R9m square billet continuous casting machine is used for casting, with a crystallizer cross-section of 150mm × 150mm. A submerged entry nozzle is used for protective casting. When the temperature of the molten steel in the tundish stabilizes at 1525℃, the stopper is opened, and casting begins. High-purity argon gas (Ar ≥ 99.999%) is blown into the molten steel in the crystallizer at a constant flow rate of 10L / min through a porous vent plug installed at the bottom of the submerged entry nozzle for 12 minutes. Simultaneously, the electromagnetic stirring device of the crystallizer is activated, with the stirring current set to 320A and the frequency to 3.5Hz.

[0045] S4. In the secondary cooling zone of the continuous casting machine, based on temperature data measured by multiple thermocouples installed on the billet support guide section, and combined with the established solidification heat transfer mathematical model, the position of the end of the liquid core of the billet is dynamically calculated and determined in real time. When the billet reaches the solidification end area, the four-stage light reduction function of the straightening machine is activated. According to the model calculation results, the position of the reduction rollers is dynamically adjusted to ensure that the four reduction intervals (reduction positions) are always precisely matched with the moving end of the liquid core. In this embodiment, the total reduction is set to 9mm, and the reductions of each segment are 2.5mm, 2.0mm, 2.5mm, and 2.0mm, respectively. Under these process conditions, the solidification coefficient of the billet is 0.9. After the billet is completely solidified, it is straightened by the straightening machine, and the surface temperature when exiting the straightening machine is approximately 900℃. Subsequently, the billet is immediately sent into a 24m long insulation hood for slow cooling. The billet is slowly cooled in the heat insulation hood at a cooling rate of less than 50℃ / h until its surface temperature drops below 300℃, and then removed to obtain a highly homogenized SWRCH35K cold heading steel billet.

[0046] Comparative Example 1 The difference between this comparative example and Example 1 is that no porous rare-earth-doped titanium-silicon oxide composite microspheres are added in this comparative example. S1: During the steel tapping process, only 3000g of carbon powder is added to the bottom of the ladle; the composite microspheres are not added. S2: After heating at the LF station, only 5000g of silicon carbide is added; the composite microspheres are not added. All other steps, process parameters, and material addition amounts are exactly the same as in Example 1.

[0047] Comparative Example 2 The difference between this comparative example and Example 1 is that this comparative example uses conventional commercially available bulk rare-earth ferrosilicon alloy instead of the porous rare-earth doped titanium silicon oxide composite microspheres. The production method differs from Example 1 only in the following ways: S1, during the tapping process, 3000g of carbon powder and 1500g of conventional rare-earth ferrosilicon alloy (RE 30%, Si 40%, Fe balance) are added to the bottom of the ladle. S2, after heating at the LF station, 5000g of silicon carbide and 800g of the same conventional rare-earth ferrosilicon alloy are added. All other steps, process parameters, and material addition amounts are exactly the same as in Example 1.

[0048] Comparative Example 3 The difference between this comparative example and Example 1 is that this comparative example uses composite microspheres without surface silanization treatment, i.e., the surface treatment in step A4 is omitted. The preparation and production methods differ from Example 1 only in the following aspects: Preparation of porous rare-earth-doped titanium silicon oxide composite microspheres: A1, same as step A1 in Example 1. A2, same as step A2 in Example 1. A3, same as step A3 in Example 1. A4, the dried product is sieved, and the portion with a particle size of 150-200 μm is selected for direct use without surface silanization treatment with trimethylchlorosilane vapor. Production of high-homogeneity cold heading steel SWRCH35K billet: S1, during the tapping process, the composite microspheres added are the aforementioned un-silanized microspheres. S2, the composite microspheres added at the LF station are the aforementioned un-silanized microspheres. All other steps, process parameters, and material addition amounts are exactly the same as in Example 1.

[0049] In accordance with national and industry standard testing specifications, a series of standardized tests were conducted on the production methods of high homogeneous cold heading steel SWRCH35K billets described in Examples 1-3 and Comparative Examples 1-3.

[0050] Eighteen full-section samples, each 300 mm long, were taken from the head, middle, and tail sections of the cold-heading steel billets obtained in each embodiment and comparative example. First, chemical composition analysis was performed: steel chips were drilled from the center and half radius of the cross-section of each sample, mixed thoroughly, and then the mass percentage content of C, Si, Mn, P, S, Cr, Ni, Cu, and acid-soluble aluminum (Als) was determined using spark discharge atomic emission spectrometry. Next, non-metallic inclusion rating was performed: each sample was longitudinally sectioned, and the cross-section was selected, ground and polished to a mirror finish, and then observed under a metallographic microscope at 100x magnification in an uncorroded state. Based on standard spectra, the largest inclusions within the observation field were rated, and the most severe levels of Class A sulfides, Class B alumina, Class C silicates, and Class D spherical oxide inclusions were recorded.

[0051] Subsequently, the solidification structure and defects of the cast billet were analyzed: the same polished sample was etched with a 4% nitric acid alcohol solution, and a complete microstructure photograph from the surface to the core of the cast billet was taken under a metallographic microscope. The proportion of the equiaxed crystal region to the total area on the cross section was calculated using image analysis software. At the same time, the degree of carbon segregation in the central region of the cast billet and the severity of central porosity defects were qualitatively rated according to the standard rating chart.

[0052] Finally, hot working performance and mechanical properties were tested: each billet was rolled into a round bar with a diameter of 20 mm, and a cylindrical sample with a height of 30 mm was cut from it. The sample was heated to 1050℃ in a resistance furnace and held for 30 min. Then, a hot upsetting test was immediately performed on a forging press. The sample was forged to 1 / 3 of its original height (i.e., 10 mm) in one pass. After air cooling, the sample was visually inspected and examined with a 10x magnifying glass to check for cracks on the side surface. The cracking status was recorded. Tensile test specimens and Charpy V-notch impact test specimens of standard size were machined from the same batch of round bars. The tensile strength was measured on a universal testing machine, and the impact absorption energy at room temperature was measured on a pendulum impact testing machine.

[0053] The performance test data above are shown in Table 1.

[0054] Table 1 Performance Test Results

[0055] As can be seen from the above, the production methods of Examples 1-3 effectively solve the core technical problem of poor overall performance of cold heading steel billets caused by insufficient cleanliness and uneven microstructure in traditional processes.

[0056] Specifically, compared to Comparative Example 1, which did not contain porous rare-earth-doped titanium-silicon oxide composite microspheres, Examples 1-3, by introducing porous rare-earth-doped titanium-silicon oxide composite microspheres, achieved effective improvement in deep purification of molten steel and solidification structure. This significantly reduced the levels of harmful Class A sulfides and Class B alumina inclusions to level 1.5 or below, increased the proportion of equiaxed crystals in the billet center to over 45%, and strictly controlled center segregation and porosity, thereby completely eliminating hot upsetting cracks and achieving higher tensile strength (above 630 MPa) and impact toughness (above 88 J). Compared to Comparative Example 2, which used conventional bulk rare-earth alloys, the unique porous composite microspheres in Examples 1-3, due to their larger specific surface area and controllable release of active elements, exhibited a synergistic strengthening effect in inclusion modification and grain refinement, resulting in more significant control of Class B alumina inclusions, improvement in center segregation, and enhancement of impact toughness. Furthermore, compared with Comparative Example 3, which did not undergo surface silanization treatment, the microspheres in Examples 1-3 exhibited better dispersibility and reaction stability in molten steel after silanization. This is reflected in the comparative advantage of Example 1 in terms of control of type B inclusions and the proportion of central equiaxed crystals.

[0057] In summary, this invention, through the synergy of composite microspheres with a specific structure and the entire process, systematically improves the purity of steel, the homogeneity of the cast billet, and the strength and toughness matching of the final product. It successfully solves the problems of traditional methods, which struggle to achieve both high purity and high homogeneity, leading to a high risk of cracking during cold heading and large fluctuations in product performance.

Claims

1. A method for producing high-homogeneity cold heading steel SWRCH35K billet, characterized in that, Includes the following steps: S1. SWRCH35K steel is smelted in an electric arc furnace; the tapping temperature is 1610-1630℃; during the tapping process, carbon powder and porous rare earth-doped titanium silicon oxide composite microspheres are first added to the bottom of the ladle; then aluminum ingots are added for strong deoxidation; finally, pre-baked Fe-Mn and Fe-Si alloys are added to complete the alloying. S2. Hoist the SWRCH35K molten steel into the LF station, add lime and fluorite to form slag; heat the steel to 1595-1605℃, add silicon carbide and porous rare earth doped titanium silicon oxide composite microspheres; before the refining is finished, add Si-Ca wire to obtain a mixture. S3. Cast the mixture into billets using a billet continuous casting machine. Before casting, argon is blown to remove oxygen and electromagnetic stirring is performed. S4. At the end of solidification, implement four-stage light pressing to ensure dynamic matching between the pressing position and the end of the liquid core; after the billet exits the straightening machine, it enters the heat preservation cover for slow cooling.

2. The method for producing high homogeneous cold heading steel SWRCH35K billet according to claim 1, characterized in that, In step S1, the SWRCH35K molten steel comprises C: 0.33-0.35%, Si: 0.15-0.25%, Mn: 0.6-0.7%, P≤0.015%, S≤0.010%, Cr≤0.10%, Ni≤0.10%, Cu≤0.15%, and Al: 0.020-0.040%.

3. The method for producing high homogeneous cold heading steel SWRCH35K billet according to claim 1, characterized in that, In step S2, the Si-Ca wire comprises 55-65% Si and 28-32% Ca.

4. The method for producing high homogeneous cold heading steel SWRCH35K billet according to claim 1, characterized in that, In step S3, the argon blowing time before casting the billet is 10-12 minutes.

5. The method for producing high homogeneous cold heading steel SWRCH35K billet according to claim 1, characterized in that, In step S4, the solidification coefficient at the end of solidification is 0.3-0.

9.

6. The method for producing high homogeneous cold heading steel SWRCH35K billet according to any one of claims 1-5, characterized in that, The preparation steps of the porous rare-earth-doped titanium-silicon oxide composite microspheres include: A1. Tetrabutyl titanate and tetrabutyl titanate were added to anhydrous ethanol and stirred to obtain solution A. Lanthanum nitrate hexahydrate and cerium nitrate hexahydrate were dissolved in deionized water to obtain mixed rare earth salt solution B. While stirring, mixed rare earth salt solution B was added dropwise to solution A, and ammonia was added to adjust the pH to 9.3-9.

7. Stirring was continued to obtain a sol. Polyvinylpyrrolidone was then added and aged in a water bath at 58-62℃ to obtain the precursor sol. A2. Spray the precursor sol into a continuous liquid paraffin phase containing sorbitan monooleate to obtain microdroplets; place the microdroplets at 78-82℃ to obtain gel microspheres; transfer the gel microspheres to a muffle furnace, heat to 295-305℃ and hold, then heat to 595-605℃ and hold, and finally heat to 945-955℃ and hold, then cool naturally to obtain an intermediate; A3. The intermediate was impregnated in anhydrous toluene solution of tetraisopropyl titanate and refluxed at 110-111℃; after filtration and washing, it was calcined in air at 495-505℃; then placed in a tube furnace and calcined at 695-705℃ under a hydrogen / argon atmosphere to obtain the product; the product was ultrasonically cleaned and vacuum dried to obtain the dried product. A4. The dried product is sieved; then, in a fluidized bed, trimethylchlorosilane vapor is introduced at 100-150℃ for surface silanization treatment.

7. The method for producing high homogeneous cold heading steel SWRCH35K billet according to claim 6, characterized in that, In step A1, the aging time in a water bath at 58-62℃ is 12-14 hours.

8. The method for producing high homogeneous cold heading steel SWRCH35K billet according to claim 6, characterized in that, In step A2, the temperature is raised to 945-955℃ and held for 4-6 hours.

9. The method for producing high homogeneous cold heading steel SWRCH35K billet according to claim 6, characterized in that, In step A3, the reflux reaction at 110-111℃ takes 4-6 hours.

10. The method for producing high homogeneous cold heading steel SWRCH35K billet according to claim 6, characterized in that, In step A4, the surface silanization treatment time is 30-60 min.

Images