High-speed rail gear steel bar produced through continuous casting and rolling technology and manufacturing method of high-speed rail gear steel bar

Abstract

The invention relates to a high-speed rail gear steel bar produced through a continuous casting and rolling process and a manufacturing method of the high-speed rail gear steel bar, and belongs to the technical field of metallurgy. The steel comprises the following chemical components in percentage by mass: 0.15 to 0.20 percent of C, less than or equal to 0.40 percent of Si, 0.50 to 0.90 percent of Mn, 1.50 to 1.80 percent of Cr, less than or equal to 0.025 percent of P, less than or equal to 0.025 percent of S, less than or equal to 0.30 percent of Cu, less than or equal to 0.005 percent of Ti, 0.02 to 0.05 percent of Al, 1.40 to 1.70 percent of Ni, 0.25 to 0.35 percent of Mo, 0.015 to 0.035 percent of Nb, less than or equal to 0.0030 percent of Ca, 0.0090 to 0.0150 percent of N, less than or equal to 0.0012 percent of [O], less than or equal to 0.0001 percent of [H] and the balance of Fe and inevitable impurity elements. A narrow hardenability bandwidth control technology is realized by establishing a hardenability prediction model, accurately controlling smelting components and uniformly controlling solidification components, and the hardenability bandwidth of the material is less than or equal to 4 HRC; the gear steel is subjected to high-temperature carburization at 980 DEG C for 4 h, and the grain size reaches the level 5 or above.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of iron-based alloys, and particularly relates to a manufacturing method of gear steel round bar. BACKGROUND

[0002] The high-iron gear box is a core component of the driving system of the EMU train, and is in a high-speed and heavy-load working state for a long time. With the increasing of the running speed of the EMU train and the development trend of the light weight of the train in recent years, the working environment of the gear box becomes more severe. Once the gear fails, the running safety of the high-speed train will be endangered, and then the safety of the life and property of the passengers will be endangered.

[0003] The gear is a key component in the driving device of the gear box of the high-speed EMU train, and the working performance of the gear directly affects the reliability and safety of the high-speed EMU train. Since the gear needs to bear a large starting torque, the load is large and the impact performance is required to be high, and the purity of the material, the grain size and the hardenability are extremely harsh. SUMMARY

[0004] The present application aims to provide a continuous casting manufacturing method of high-iron gear steel bar (round bar), which adopts a pure steel smelting process to realize high purity of molten steel and low oxygen content of the steel (≤12ppm), and to ensure the stable fatigue life requirement of the finished gear.

[0005] By adopting the Nb, Al and N compound micro-alloying technology, Nb and Al can form carbides, nitrides and carbonitrides with C and N, so as to form grain refinement and precipitation strengthening. The fine-grain strengthening can not only improve the strength of the material, but also improve the plasticity and toughness of the material. After the carbonitride is precipitated, the grain boundary is pinned, the austenite recrystallization temperature is improved, and the grain growth is inhibited. Finally, the part can realize high-temperature carburizing capacity (980℃×4h high-temperature carburizing).

[0006] By establishing a hardenability prediction model, precisely controlling the smelting composition and controlling the solidification composition uniformity, the narrow hardenability bandwidth control technology is realized, and the material hardenability (Rockwell hardness) bandwidth can reach ≤4HRC, which meets J5=42~46HRC, J10=39~43HRC, J25=34-38HRC, J40=32-36HRC, and significantly reduces the hardness fluctuation of the material.

[0007] By adopting the large reduction special rolling process technology, the center density of the material is first ensured, and the macro low-multiple organization of the material is optimized to realize the symmetry and uniformity of the low-multiple organization.

[0008] The technical scheme adopted by the present application is: a high-iron gear steel bar produced by a continuous casting and rolling process, the chemical composition is designed as follows in percentage by mass: C: 0.15-0.20%, Si: ≤0.40%, Mn: 0.50-0.90%, Cr: 1.50-1.80%, P: ≤0.025%, S: ≤0.025%, Cu: ≤0.30%, Ti: ≤0.005%, Al: 0.02-0.05%, Ni: 1.40-1.70%, Mo: 0.25-0.35%, Nb: 0.015-0.035%, Ca ≤0.0030%, N: 0.0090-0.0150%, [O] ≤0.0012%, [H] ≤0.0001%, and the balance is Fe and inevitable impurity elements.

[0009] In the component design, appropriate Nb and Al micro-alloying elements are added to the steel, the Nb and Al composite micro-alloying technology is adopted, the growth of austenite grains in the high-temperature carburizing process of the gear steel is controlled, and the gear satisfies the grain size of more than 5 levels under the high-temperature carburizing condition of 980 DEG C. C is the most basic element in the steel and is also the most economical strengthening element. In all elements, the ability of carbon to improve the strength of the steel is the largest, the strengthening of carbon to the quenched and tempered steel is about 9 times that of chromium and 18 times that of manganese, so the steel needs to have appropriate carbon content to ensure that the heart of the gear has good strength and toughness after carburizing heat treatment, and the carbon content range in the present application is determined to be 0.15-0.20%.

[0010] Si can be used as a deoxidizing element and is also a basic solid solution strengthening element and improves the hardenability; Si is an easily oxidized element, and is easy to cause intergranular oxidation of the gear steel during carburizing, and the silicon content range in the present application is determined to be ≤0.40%.

[0011] Mn is an element acting as a deoxidizing agent, improves the strength of the steel through solid solution strengthening, in addition, Mn fixes S in the steel in the form of MnS, which can eliminate or reduce the hot brittleness caused by sulfur, thereby improving the hot working performance of the steel. Mn is a carbide-forming element, replaces a part of iron atoms in the cementite, and Mn reduces the critical transformation temperature in the steel, plays a role in refining the pearlite, and indirectly plays a role in improving the strength of the pearlite. The ability of Mn to stabilize the austenite structure is only next to Ni, and also strongly increases the hardenability of the steel, and the manganese content range in the present application is determined to be 0.50-0.90%.

[0012] Cr can increase the hardenability of the steel and has the effect of secondary hardening, can have solid solution strengthening effect on the steel, and improve the hardenability of the steel. In addition, Cr reduces the activity of C, can reduce the overheating tendency of the steel and the surface decarburization speed, and the chromium content range in the present application is determined to be 1.50-1.80%.

[0013] P is an inevitable impurity, easy to form segregation, inclusions and other defects, especially P will reduce the cold deformation performance of the material, resulting in brittle fracture of the steel during cold working, that is, the so-called "cold brittle" phenomenon, the range of phosphorus content is determined as ≤0.025% in the application.

[0014] S will make the steel produce hot brittleness, reduce the plasticity and toughness of the steel, the range of sulfur content is determined as ≤0.025% in the application.

[0015] Ti element is very strong in combination with N, easy to form large particle TiN inclusions, such inclusions belong to brittle inclusions, and present rhombus morphology, which will significantly reduce the fatigue life of the material, therefore, the Ti content is required to be controlled to ≤0.005% in the application.

[0016] Al is an effective deoxidizing element, mainly used for deoxidization and grain refinement, the range of aluminum content is determined as Al: 0.02-0.05% in the application.

[0017] Nb: Nb element in steel combines with C and N to form NbCN precipitates, which can significantly improve the high temperature austenite stability of the steel, preventing high temperature austenite grain growth, therefore, the Nb content is required to be controlled to 0.015-0.035% in the application.

[0018] N element combines with Nb, Al and other elements in the form of nitride, which can significantly improve the high temperature austenite grain stability of the gear steel, preventing high temperature austenite grain growth, the range of nitrogen content is determined as N: 0.0090-0.0150% in the application.

[0019] O mainly exists in the form of oxide inclusions such as Al2O3, MnO, CaO and SiO2 in steel, after a large amount of research, a large amount of oxide inclusions in steel significantly deteriorate the fatigue life of the steel, the range of oxygen content is determined as O: ≤0.0012% in the application.

[0020] H element is a harmful element in steel, especially for the high iron gear steel of the application, which has large size (φ140-φ250) and high strength, hydrogen in the steel will cause hydrogen embrittlement, white spot and other defects, therefore, the range of hydrogen content is determined as [H] ≤0.0001% in the application.

[0021] Ni strengthens ferrite and refines pearlite in steel, which can strongly improve the strength, while keeping the toughness of the steel at a very high level. In addition, Ni also has a certain effect on improving the hardenability of the steel. The Ni content is 1.40-1.70% in the application.

[0022] Mo can improve the hardenability and thermal strength of the steel, prevent temper brittleness, and reduce the tendency of carbides to form a continuous network on the grain boundary in the carburized layer, reduce the residual austenite in the carburized layer, and relatively increase the wear resistance of the surface layer. The range of molybdenum content in the present application is determined as Mo: 0.25-0.35%.

[0023] In order to realize narrow hardenability bandwidth and reduce hardness fluctuation range, the present application establishes a hardenability prediction model to realize precise control of smelting composition and solidification composition uniformity control technology. Based on the actual production of hundreds of furnaces of the same kind of steel, a high-precision hardenability prediction model is established by nonlinear equation method, and the prediction accuracy is ≤±2HRC. The hardenability prediction model is mainly based on chemical composition and is used for composition design, composition adjustment and control. The hardenability calculation equation is:

[0024] In the formula, H is the hardenability value at different distances, i.e. Rockwell hardness, a is an empirical constant, b x,i is the chemical element coefficient, w x,i is the percentage content of the chemical element, and the empirical constant a and the chemical element coefficient b x,i are obtained based on the actual production of hundreds of furnaces of the same kind of steel, such as the parameter table of the hardenability calculation equation.

[0025] .

[0026] In terms of precise control of smelting composition, precise control of chemical composition is realized through precise weighing, raw material control, rapid analysis and other means in the production process. The control precision of main element composition such as C, Mn and Cr is: the control precision of C element composition is ≤±0.01%, the control precision of Mn element composition is ≤±0.02%, and the control precision of Cr element composition is ≤±0.02%.

[0027] The influence of superheat of molten steel on composition uniformity in continuous casting process is studied, as shown in Figure 1 The influence of superheat of molten steel on center segregation in continuous casting stage, Figure 2 The influence of superheat of molten steel on equiaxed crystal rate. As can be seen from the figure, when the superheat of molten steel is ΔT>25℃, the columnar crystal is developed and the center segregation is serious; when ΔT<25℃, the center equiaxed crystal zone is expanded and the center segregation is obviously reduced; when ΔT<10℃, the center segregation is not significant, but too low superheat is easy to cause nozzle blockage and serious skull of ladle and tundish. Considering the production quality, the superheat of molten steel is controlled in the range of 15-20℃ to obtain good internal quality of the casting blank and ensure the smooth continuous casting production.

[0028] The electromagnetic stirring process in the continuous casting process is studied, the solidification front is forced to flow, the dendrite of the solidification front is broken, the fragments of the dendrite are re-melted, the temperature of the molten steel is reduced, the equiaxed crystal core is increased, the development of the columnar crystal front is blocked, the wide equiaxed crystal zone is formed, the temperature gradient of the liquid core from outside to inside is reduced by the agitation of the molten steel, the surrounding crystallization develops uniformly, thereby the equiaxed crystal rate on the cross section of the casting blank is improved, the segregation elements are uniformly distributed, the aggregation of the solute elements is avoided, and finally the segregation of the casting blank is improved. Figure 3 The segregation state of the casting blank before the electromagnetic stirring parameter is improved, Figure 4 The segregation state of the casting blank after the electromagnetic stirring parameter is improved.

[0029] The end light press-down technology of the casting blank can effectively break the dendrite bridge at the liquid core of the casting blank, prevent the residual molten steel rich in segregation elements from flowing to the center of the casting blank caused by solidification shrinkage, avoid the macro-segregation on the center line of the casting blank, can very effectively reduce and improve the center segregation of the casting blank, and finally improve the composition uniformity of the casting blank. Combined with the solidification characteristics of the material of the application, the light press-down device is used after the electromagnetic stirring at the solidification end of the continuous casting, a total of 8 light press-down rollers, the total light press-down amount is 10mm, and the light press-down parameters of the 8 light press-down rollers are 0-1-2-3-2-1-1-0 (mm).

[0030] The application provides a continuous casting and rolling process for producing high-iron gear steel bars and a manufacturing method thereof. The chemical composition of each element of the steel is accurately controlled during smelting, the whole process is protected casting, a continuous casting bloom (the cross-sectional specification is 390 mm*510 mm or more) is used, a high-performance precise combined slag is selected for steelmaking, the inclusions have good deformability. The ladle maintains a long-time inclusion removal process, the non-metallic inclusions are fully floated, the special precise combined slag and the tundish protection slag are selected to better adsorb the inclusions, nitrogen gas is used as the lifting gas for vacuum degassing, the vacuum degassing is not allowed to be treated again after breaking the vacuum, the pure molten steel is prevented from being polluted again, the continuous casting process adopts full protection casting, advanced equipments such as a mold electromagnetic stirring and end electromagnetic stirring and tundish induction heating are used, and the segregation of the material is maximally reduced.

[0031] The continuous casting blank is heated to 1220-1260 DEG C before rolling, and is kept for 5 hours or more before being discharged, by sufficiently increasing the heating temperature, the elements such as Nb and Al can be fully and uniformly dissolved in the austenite phase, and the preferred heating temperature is 1220 DEG C or more, in addition, if the heating temperature is too high, the austenite phase has a tendency to be coarsened and overheated, therefore, the heating temperature is preferably 1260 DEG C or less. The starting rolling temperature is 1100-1150 DEG C, the final rolling temperature is 960-1000 DEG C, after rolling, the steel is cooled to 500-700 DEG C on the cooling bed, and then is annealed, and is cooled in the furnace after being kept at 690 DEG C for 4-8 hours.

[0032] The rough rolling process of the rolled steel adopts a rough rolling mill with a nominal diameter of φ1350mm or more, and adopts a large reduction schedule for rough rolling, and the single pass maximum reduction is 100mm, so that the blank can obtain a large penetration rolling force, and the blank core can obtain effective deformation, and the segregation and center porosity can be obviously improved, and the blank core quality can be stably improved. At the same time, a specific rolling schedule is adopted, and the blank is face rolling (since the blank adopts a rectangular continuous casting blank, the low-magnification square ratio of the finished product is completely different in different directions, the face rolling requires that the blank is specified to roll a certain face of the continuous casting blank when entering the first mill, and the original rectangular low-magnification organization of the continuous casting blank is adjusted to a square low-magnification organization or a circular low-magnification organization, the low-magnification square ratio is controlled, and the gear material can obtain a symmetrical and uniform macroscopic organization, so that the uniformity of the deformation of the subsequent gear parts can be effectively ensured. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Influence of the overheat degree of the continuous casting of the steel of the present application on the center segregation; Figure 2 Influence of the overheat degree of the continuous casting of the steel of the present application on the equiaxed crystal ratio; Figure 3 Segregation state of the blank before the electromagnetic stirring parameter is improved; Figure 4 Segregation state of the blank corresponding to the improved electromagnetic stirring parameter of the present application; Figure 5 Comparison diagram of the rough rolling reduction process of the present application and the reduction of the conventional rough rolling process; Figure 6 Low-magnification quality of the organization under the conventional rough rolling process; Figure 7 Low-magnification quality of the organization under the rough rolling process of the present application; Figure 8 Schematic diagram of the face rolling process of the rectangular blank; Figure 9 Square low-magnification obtained after face rolling; Figure 10 Grain diagram of the gear steel of example 1 of the present application under the austenitizing temperature test of 930 DEG C x 5h; Figure 11 Grain structure of the gear steel of the present application example 2 under austenitizing temperature test at 930℃x5h; Figure 12 Grain structure of the gear steel of the present application example 3 under austenitizing temperature test at 930℃x5h; Figure 13 Grain structure of the gear steel of the comparative example under austenitizing temperature test at 930℃x5h; Figure 14 Grain structure of the gear steel of the present application example 1 under austenitizing temperature test at 980℃x5h; Figure 15 Grain structure of the gear steel of the present application example 2 under austenitizing temperature test at 980℃x5h; Figure 16 Grain structure of the gear steel of the present application example 3 under austenitizing temperature test at 980℃x5h; Figure 17 Grain structure of the gear steel of the comparative example under austenitizing temperature test at 980℃x5h; Figure 18 Macrostructure of the gear steel of the present application example 1; Figure 19 Macrostructure of the gear steel of the present application example 2; Figure 20 Macrostructure of the gear steel of the present application example 3; Figure 21 Macrostructure of the gear steel of the comparative example. DETAILED DESCRIPTION

[0034] The present application is further described in detail below with reference to the examples, which are illustrative and intended to explain the present application, and cannot be understood as limiting the present application.

[0035] The present application adopts gear steel with specific components, and three furnaces of the present application steel are produced, and converter smelting-LF refining-RH vacuum treatment-continuous casting-rolling-finishing are adopted, the continuous casting billet is discharged after being kept at 1220-1260℃ for 5 hours or more, φ220mm round steel rolling is carried out, the opening rolling temperature is 1100-1150℃, the final rolling temperature is 960-1000℃, the round steel is cooled to 500-700℃ after rolling through the cooling bed, offline slow cooling is carried out, and the cooled steel is annealed, and the steel is cooled after being kept at 690℃ for 5 hours. Take round steel samples, respectively, carry out hardenability test (three for each furnace) and grain size test, and macrostructure detection.

[0036] The smelting process adopts chemical component accurate control technology process: (1) In the raw material selection and charging: through the raw material procurement control, the stability of the raw material composition content is ensured, and the alloy adding time, adding order, adding amount are accurately grasped, and the precision and appropriateness of the raw material adding are ensured by means of precise weighing and other means, an alloying charging computer control model is established, and the stability and accuracy of the composition control are improved.

[0037] (2) Perfect the molten steel and alloy weighing system, and improve the measurement accuracy.

[0038] (3) In the smelting process, after adding alloy material, the molten steel circulation condition is adjusted to ensure that the added alloy is fully melted and uniformly distributed.

[0039] (4) At the end of the converter tapping, the oxygen content of the slag and molten steel is reduced, and good tapping slag stopping technology is adopted to prevent the converter from slagging and stabilize the element yield.

[0040] (5) In the aspect of analysis and detection, a high-precision spectral analyzer is used to quickly and accurately reflect the sample composition, so as to achieve accurate control of charging.

[0041] High uniformity control technology is adopted in the continuous casting process: (1) Low superheat process: the intermediate ladle induction heating technology is adopted in the continuous casting of the present application, and the superheat of the molten steel can be controlled in a lower range, which can be stably controlled within 15-20℃, so as to obtain good internal quality of the casting blank and ensure the smooth operation of the continuous casting production.

[0042] (2) Reasonable electromagnetic stirring process: reasonable mold electromagnetic stirring and flow stirring process are adopted in the continuous casting process to improve the flowability, temperature and uniformity of the cross-section molten steel of the casting blank.

[0043] (3) Light press-down technology process: the light press-down technology is adopted in the continuous casting of the present application, which effectively breaks the dendritic crystal bridge at the liquid core of the casting blank, prevents the residual molten steel rich in segregation elements from flowing to the center of the casting blank caused by solidification shrinkage, avoids the macro-segregation on the center line of the casting blank, and can effectively reduce and improve the center segregation of the casting blank, and finally improve the composition uniformity of the casting blank. Combined with the solidification characteristics of the material of the present application, the light press-down device is adopted after the electromagnetic stirring at the solidification end of the continuous casting, a total of 8 light press-down rollers, the total light press-down amount is 10mm, and the light press-down parameters of the 8 light press-down rollers are 0-1-2-3-2-1-1-0 (mm).

[0044] Large press-down special rolling process technology is adopted in the rolling process: (1) Large press-down rough rolling process: the traditional rolling method cannot make the rolling force penetrate into the whole casting blank, mainly concentrated on the surface, so the center porosity and segregation of the rolled material are more serious. The large press-down rolling technology is adopted in the rough rolling process, which can make the rolling force penetrate into the center of the casting blank, and significantly improve the segregation and center porosity.

[0045] (2) Recognized rolling process: using a specific rolling schedule, the blank is subjected to large reduction recognized rolling, and the original rectangular frame low magnification structure of the continuous casting blank is adjusted to a square frame low magnification structure.

[0046] The chemical compositions of the three groups of example steels and one group of comparative example steels are as shown in Table 1.

[0047] Table 1 Chemical compositions of examples and comparative examples

[0048] The heat treatment system of the end quenching sample is executed according to Table 2.

[0049] Table 2 Heat treatment system of end quenching sample

[0050] The end quenching results of the three groups of example steels and the comparative example steel are compared as shown in Table 3.

[0051] Table 3 Test results of end quenching sample

[0052] According to the results in Table 3, compared with the comparative example steel, the hardenability fluctuation range of the example gear steel is small, and the bandwidth is significantly narrowed.

[0053] The samples are subjected to simulated carburizing and quenching, and the process is: the carburizing temperature is 930℃ and 980℃ respectively, and the quenching is performed after 4h of holding.

[0054] The three groups of example steels and one group of comparative example steels are respectively subjected to quenching after austenitizing at 930℃ and 980℃ for 4h, and the grain size of the samples is observed under a microscope after supersaturated picric acid etching, and the detection results are shown in the following Table 4. Figures 7-14 It can be seen from the detection results that the austenite grains of the ordinary steel are fine under the condition of 930℃ x 5h, and the austenite grains appear mixed grains under the condition of 980℃ x 5h. However, the austenite grains of the three groups of example steels remain above grade 5 under the high temperature simulated carburizing condition of 930℃-980℃ x 4h, and the grains are not found to grow.

[0055] Therefore, after the example steel is subjected to the simulated carburizing process at 980℃, the austenite grain size of the whole cross section can still be maintained above grade 5, and no mixed grains and coarse grain structure are found, which can meet the technical requirements of the grain growth resistance required by high temperature carburizing, can effectively shorten the carburizing time, save energy consumption, reduce carbon emissions, and reduce production cost.

Claims

1. A continuous casting and rolling process for producing high-speed rail gear steel bars, characterized in that: The chemical composition by mass percentage is as follows: C: 0.15–0.20%, Si: ≤0.40%, Mn: 0.50–0.90%, Cr: 1.50–1.80%, P: ≤0.025%, S: ≤0.025%, Cu: ≤0.30%, Ti: ≤0.005%, Al: 0.02–0.05%, Ni: 1.40–1.70%, Mo: 0.25–0.35%, Nb: 0.015–0.035%, Ca: ≤0.0030%, N: 0.0090–0.0150%, [O] ≤0.0012%, [H] ≤0.0001%, with the balance being Fe and unavoidable impurity elements.

2. The continuous casting and rolling process for producing high-speed rail gear steel bars according to claim 1, characterized in that: The hardenability band of the steel is narrow, satisfying J5=42~46HRC, J10=39~43HRC, J25=34-38HRC, and J40=32-36HRC; the gear steel undergoes high-temperature carburizing at 980℃ for 4 hours, and the grain size reaches level 5 or above.

3. The continuous casting and rolling process for producing high-speed rail gear steel bars according to claim 1, characterized in that: The low-magnification microstructure of the radial section of the bar is a square frame or a circle.

4. The continuous casting and rolling process for producing high-speed rail gear steel bars according to claim 1, characterized in that: The elemental composition is further designed by establishing a hardenability prediction model to control the element content. The prediction accuracy of hardenability, i.e., Rockwell hardness, is ≤ ±2HRC. The calculation equation of the hardenability prediction model is as follows: ; In the formula, H represents the rockwell hardness value at different distances, and a is an empirical constant. b x,i The coefficient of a chemical element w x,i The percentage content of chemical elements, the empirical constant 'a', and the coefficients of chemical elements. b x,i The parameters for the hardenability calculation equation are obtained based on actual test results of hardenability values ​​from hundreds of heats of the same steel grade in actual production. 。 5. A method for producing high-speed rail gear steel bars using the continuous casting and rolling process described in claim 1, characterized in that: The process includes steel smelting, continuous casting, continuous rolling, slow cooling, and annealing. Smelting involves precise control of the chemical composition of each element in the steel, with protective casting throughout the process. Large continuous casting billets of 390 mm * 510 mm or larger are used. Before rolling, the continuously cast billets are heated to 1220–1260℃ and held for at least 5 hours before being removed from the furnace, allowing the elements to fully and uniformly dissolve in the austenite phase. The initial rolling temperature is set at 1100–1150℃, and the final rolling temperature at 960–1000℃. The billets are rolled using a face rolling process, adjusting the original rectangular low-magnification structure of the continuously cast billets to a square low-magnification structure. After rolling, the billets are removed from the cooling bed and cooled to 500–700℃ for slow cooling. The cooled steel is then annealed, held at 690℃ for 4–8 hours, and then cooled in the furnace.

6. The manufacturing method for producing high-speed rail gear steel bars using the continuous casting and rolling process according to claim 5, characterized in that: During the steelmaking stage, the composition of C, Mn, and Cr is controlled: the control accuracy of C element composition is ≤ ±0.01%, the control accuracy of Mn element composition is ≤ ±0.02%, and the control accuracy of Cr element composition is ≤ ±0.02%.

7. The manufacturing method for producing high-speed rail gear steel bars using the continuous casting and rolling process according to claim 5, characterized in that: The superheat of the continuously cast steel liquid is controlled within the range of 15~20℃.

8. The manufacturing method for producing high-speed rail gear steel bars using the continuous casting and rolling process according to claim 5, characterized in that: The frequency of the electromagnetic stirring process at the end of the continuous casting is 2Hz and the current is 350A. The end of the continuous casting adopts a light reduction process to break the dendritic bridging at the liquid core of the billet. A total of 8 light reduction rollers are set, with a total light reduction of 10mm. The light reduction parameters of the 8 light reduction rollers are 0-1-2-3-2-1-1-0, mm.

9. The manufacturing method for producing high-speed rail gear steel bars using the continuous casting and rolling process according to claim 5, characterized in that: During the rolling process, a roughing mill with a nominal diameter of φ1350mm is used for roughing, and a large reduction procedure is adopted for roughing, with a maximum reduction of 100mm per pass.

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