Copper-niobium composite reinforced high-temperature carburizing gear steel and production method thereof

Abstract

The invention belongs to the technical field of metallurgy, and relates to copper-niobium composite reinforced high-temperature carburizing gear steel and a production method thereof. The alloy comprises the following components in percentage by weight: 0.15 to 0.19 percent of C, less than or equal to 0.20 percent of Si, 0.70 to 0.95 percent of Mn, 1.50 to 1.90 percent of Cr, 0.045 to 0.055 percent of Nb, less than or equal to 0.10 percent of Mo, 0.04 to 0.060 percent of Al, 0.10 to 0.20 percent of Cu, 0.016 to 0.020 percent of N, less than or equal to 0.015 percent of P, less than or equal to 0.020 percent of S and less than or equal to 8ppm of O. And the balance of Fe and inevitable impurities. Performance breakthrough is achieved through the following technical paths that Cu is subjected to solid solution in austenite, the matrix strength is improved, and the uniformity of a carburized layer is promoted; nb and N form a nanoscale Nb (C, N) precipitated phase, Al accurately controls the precipitation time of AlN, internal cracks of a continuous casting blank are avoided, and original austenite grains are refined.

Description

Technical Field

[0001] The present invention belongs to the technical field of iron and steel metallurgy, and relates to a copper-niobium composite strengthened high-temperature carburized gear steel and a production method thereof. Background Art

[0002] With the development of new energy vehicles, wind power equipment and heavy machinery towards high speed, heavy load and high reliability, gear components need to serve for a long time under high temperature (200 - 300 °C), high stress and complex lubrication conditions. As the core material, high-temperature carburized gear steel needs to have the following characteristics: high surface hardness (≥58 HRC) and deep carburizing ability (case depth 1.5 - 2.5 mm) to resist contact fatigue and wear; excellent core toughness (impact energy ≥50 J) and hardenability to prevent gear root fracture; fine and uniform grain structure (grain size ≥8 grades) to inhibit distortion and grain boundary embrittlement during the carburizing process; high purity (inclusions ≤1.5 grades, O / N / S ≤20 ppm) to improve fatigue life. However, the traditional process has significant bottlenecks in terms of cost, performance and process stability.

[0003] Existing Technical Bottlenecks

[0004] (1) Limitations of the smelting process

[0005] Dependence on electric furnaces and high costs: Traditional gear steels are mostly smelted in electric arc furnaces (EAF→LF→VD), with high energy consumption and difficulty in matching the needs of large-scale industrial production, increasing the cost per ton of steel by 15 - 20%. Insufficient cleanliness of the converter process: Although the converter process has low costs, the end-point oxygen activity is relatively high ([O]≥300 ppm), resulting in difficult-to-precisely-control addition amounts of deoxidizers (such as Si, Al), easily generating Al2O3 and SiO2 inclusions and deteriorating fatigue performance. Difficulties in controlling sulfur and nitrogen: Sulfides (MnS) and nitrides (AlN) are prone to segregate at grain boundaries. The traditional process has difficulty in synergistically controlling S≤0.020% and N≤0.020%, leading to the risk of hot processing brittleness.

[0006] (2) Defects in alloy design

[0007] Dependence on high molybdenum and cost pressure: Traditional solutions rely on Mo (0.20 - 0.40%) to improve high-temperature strength, but molybdenum is expensive (about 300,000 yuan / ton), and excessive Mo exacerbates the center segregation of continuous casting billets (segregation index ≥1.2), increasing the distortion rate after carburization. Lack of coordinated control of copper and nitrogen: Although copper (Cu≥0.15%) can achieve solid solution strengthening, it is prone to cause hot brittleness; the interaction between nitrogen (N) and Al, Nb has not been fully utilized, and the existing technology is difficult to achieve the precise matching of Cu (0.10 - 0.20%) and N (0.014 - 0.020%).

[0008] (3) Defects in the continuous casting process

[0009] Composition segregation and crack sensitivity: Molten steel with high Cr (1.50 - 1.90%) has high viscosity, and columnar crystals are likely to form during continuous casting (equiaxed crystal ratio ≤ 30%), resulting in central segregation (class C ≥ 1.5 grade) and surface cracks; Insufficient dynamic control: Traditional continuous casting lacks the coordinated regulation of electromagnetic stirring and soft reduction, and the distribution of elements such as Nb and Cu inside the billet is uneven, deteriorating the carburizing uniformity. Summary of the Invention

[0010] To solve the above technical problems, the present invention provides a copper-niobium composite strengthened high-temperature carburizing gear steel and its production method, solving the problems existing in the prior art.

[0011] The technical solution adopted by the present invention is a copper-niobium composite strengthened high-temperature carburizing gear steel, and its composition components are calculated by mass percentage as follows: C: 0.15 - 0.19%, Si ≤ 0.20%, Mn: 0.70 - 0.95%, Cr: 1.50 - 1.90%, Nb: 0.045 - 0.055%, Mo ≤ 0.10%, Al: 0.04 - 0.060%, Cu: 0.10 - 0.20%, N: 0.016 - 0.020%, P ≤ 0.015%, S ≤ 0.020%, O ≤ 8 ppm; the balance is Fe and unavoidable impurities.

[0012] Furthermore, the mass ratio of Nb to N satisfies Nb / N = 2.25 - 3.5, and the mass ratio of Al to N satisfies Al / N = 2.0 - 4.0.

[0013] Furthermore, for the high-temperature carburizing gear steel, the hardness gradient fluctuation of the carburized layer ≤ 3%, the distortion amount < 0.05 mm / m, the gear bending fatigue life ≥ 1.5 × 10^7 times, the contact fatigue strength at 200°C ≥ 1300 MPa, the central segregation of the billet ≤ 0.5 grade, the Cu segregation index ≤ 1.05, the steel purity: class D inclusions ≤ 1.0 grade, O ≤ 6 ppm.

[0014] The present invention also provides a production method of a copper-niobium composite strengthened high-temperature carburizing gear steel, which includes the steps:

[0015] Step 1: Converter smelting, pre-desulfurizing molten iron to S ≤ 0.002% and titanium content ≤ 0.005%; the end-point carbon content of the top-bottom combined blown converter is 0.05 - 0.08%, and the tapping temperature is 1620 - 1640°C; during tapping, add aluminum ingots, electrolytic copper plates and ferroniobium for composite deoxidation alloying, control the Al content at 0.05%, the Cu content at 0.15%, the Nb content error ≤ ±0.002%, and prohibit the addition of ferrosilicon;

[0016] Step 2: LF refining, adopting a high-alkalinity and low-oxidation slag system with CaO / Al2O3 = 2.0 - 2.5 and CaF2 5 - 8%, and a slag thickness of 60 - 80 mm; adding manganese nitride in batches to control the N content to 0.016 - 0.018%, maintaining Al / N = 2.0 - 3.0; feeding Ca-Si wire with Ca / Si = 1:1 for desulfurization until S ≤ 0.015%.

[0017] Step 3: RH vacuum treatment, maintaining the pressure ≥ 30 min under a vacuum degree ≤ 20 Pa, and blowing argon softly at a flow rate of 20 - 30 L / min for ≥ 30 min; precisely controlling the final refining [N] = 0.016 - 0.020%, [H] ≤ 0.8 ppm, and [O] ≤ 6 ppm.

[0018] Step 4: Continuous casting process, fully protected casting, with a superheat of 12 - 23°C, and the electromagnetic stirring parameters of the mold being a frequency of 3 - 5 Hz and a current of 250 - 350 A; applying electromagnetic braking of 0.4 - 0.6 T in the secondary cooling zone, with an equiaxed crystal ratio ≥ 50%; dynamic soft reduction at the solidification end, with a casting speed of 0.65 - 0.75 m / min; after the cast slab is stack-cooled for 72 h, it is subjected to hydrogen diffusion annealing at 250 - 300°C for 10 - 12 h.

[0019] Furthermore, in the above Step 2, the addition timing of manganese nitride is to add it in 3 - 5 batches starting from 15 - 25 min after the start of refining, with an interval of 5 - 8 min between each batch.

[0020] Furthermore, the amount of dynamic soft reduction in the above Step 4 is 8 - 12 mm.

[0021] For the copper-niobium composite strengthened high-temperature carburized gear steel of the present invention, the core functions of each chemical component are as follows: C is used to balance the hardness gradient of the carburized layer and the toughness of the core; Si is used to reduce grain boundary brittleness and inhibit the formation of oxide inclusions; Mn is used to improve hardenability and stabilize retained austenite; Cr is used to enhance high-temperature oxidation resistance and contact fatigue strength; Nb is used to form Nb(C,N) to refine grains and inhibit carburization distortion; Mo ≤ 0.10% is used to reduce costs and avoid banded structures caused by molybdenum segregation; Al is used as a deoxidizer to regulate the precipitation behavior of AlN; Cu is used for solid solution strengthening to improve the matrix strength and corrosion resistance; N and Nb cooperate to form nano-precipitation phases to optimize the grain boundary structure; P ≤ 0.015% reduces the risk of grain boundary embrittlement; S ≤ 0.020% controls the grade of sulfide inclusions; O ≤ 8 ppm ensures the purity of the steel.

[0022] The technical principle of the present invention:

[0023] Based on the theories of "copper-niobium composite strengthening" and "dynamic nitrogen alloying", performance breakthroughs are achieved through the following technical paths:

[0024] 1. Solution strengthening of copper: Cu (0.10 - 0.20%) is dissolved in austenite, enhancing the matrix strength and promoting the uniformity of the carburized layer.

[0025] 2. Synergistic precipitation of niobium and nitrogen: Nb (0.045 - 0.055%) and N (0.016 - 0.020%) form nano-scale Nb(C,N) precipitation phases, pinning grain boundaries and inhibiting the growth of carburized grains.

[0026] 3. Dynamic balance of aluminum and nitrogen: Al (0.04 - 0.060%) precisely controls the precipitation timing of AlN, avoiding internal cracks in continuous casting billets and refining the original austenite grains.

[0027] Technical innovation points of the present invention:

[0028] (1) Synergistic deoxidation of aluminum and nitrogen: By controlling the Al / N ratio, the precipitation morphology of AlN is optimized, combining the functions of deoxidation and grain refinement.

[0029] (2) Composite strengthening of copper and niobium: The synergistic effect of solution strengthening of Cu and precipitation strengthening of Nb(C,N) replaces the traditional high-molybdenum solution.

[0030] (3) Dynamic nitrogen alloying: LF-VD two-stage nitrogen regulation technology realizes an accuracy of [N] of ±0.002%.

[0031] The beneficial effects of the present invention are:

[0032] 1. Cost advantage: The molybdenum content is reduced to ≤0.10%, and the cost per ton of steel is reduced by 18 - 22%.

[0033] 2. Performance improvement: The hardness gradient fluctuation of the carburized layer is ≤3%, and the distortion amount is <0.05 mm / m; the gear bending fatigue life is ≥1.5×10 7 times (load 1200 MPa), which is 30% higher than the traditional process; the high-temperature (200°C) contact fatigue strength is ≥1300 MPa.

[0034] 3. Process stability: The central segregation of the casting billet is ≤0.5 grade, and the Cu segregation index is ≤1.05; the steel purity: Class D inclusions are ≤1.0 grade, and O ≤ 6 ppm. Description of the drawings

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is the macrostructure diagram of the product in Example 1;

[0037] Figure 2 It is the macrostructure diagram of the billet in Example 2. Specific implementation manners

[0038] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0039] The following co - control has not been achieved in the prior art:

[0040] Balance between low cost and high performance: Co - achievement of low Si (≤0.20%), low Mo (≤0.10%) and high purity (O≤8 ppm) under the converter process;

[0041] Optimization of multi - element interaction: Dynamic matching of Cu solid - solution strengthening, Nb(C, N) precipitation strengthening and AlN grain - boundary control; Homogenization of continuous - casting structure: Inhibition of segregation and cracks in high - Cr steel by the combined technology of electromagnetic field - soft reduction.

[0042] The upgrading of high - temperature carburizing gear steel urgently needs to break through the three major technical chains of "low - cost smelting - multi - element coordination - billet homogenization", and achieve precise composition control, efficient inclusion removal and refinement of continuous - casting structure in the converter process to meet the stringent requirements of high - end equipment for long service life, low deformation and high reliability of gears.

[0043] Based on this, the present invention provides a copper - niobium composite - strengthened high - temperature carburizing gear steel and its production method. The composition of the steel is as follows by mass percentage: C: 0.15 - 0.19%, Si≤0.20%, Mn: 0.70 - 0.95%, Cr: 1.50 - 1.90%, Nb: 0.045 - 0.055%, Mo≤0.10%, Al: 0.04 - 0.060%, Cu: 0.10 - 0.20%, N: 0.016 - 0.020%, P≤0.015%, S≤0.020%, O≤8 ppm; the balance is Fe and inevitable impurities.

[0044] The production method includes the following steps:

[0045] Step 1: Converter smelting

[0046] Raw material pretreatment: Pre - desulfurize hot metal to S≤0.002% and the titanium content≤0.005% (to prevent TiN from consuming nitrogen).

[0047] Low-carbon end-point control: The carbon content at the end-point of the top-bottom combined blowing converter is 0.05 - 0.08%, and the tapping temperature is 1620 - 1640 °C (to reduce the oxidation of Al by FeO in the slag).

[0048] Compound deoxidation and alloying: Add aluminum ingots (target Al 0.05%), electrolytic copper plates (target Cu 0.15%), and ferroniobium (Nb accurate to ±0.002%) during tapping, and prohibit the addition of ferrosilicon.

[0049] Step 2: LF refining

[0050] Slag system optimization: Adopt a high-alkalinity and low-oxidation slag (CaO / Al2O3 = 2.0 - 2.5, CaF2 5 - 8%), with a slag thickness of 60 - 80 mm, to adsorb Al2O3 inclusions.

[0051] Nitrogen alloying: Increase nitrogen to 0.016 - 0.018% in batches through manganese nitride (MnN), and dynamically regulate the ratio of [N] to [Al] (Al / N = 2.0 - 3.0).

[0052] Sulfur control: Feed Ca-Si wire (Ca / Si = 1:1) for deep desulfurization to S ≤ 0.015%.

[0053] Step 3: RH vacuum treatment

[0054] The vacuum degree ≤ 20 Pa, the pressure holding time ≥ 30 min, and the soft blowing argon gas flow rate is 20 - 30 L / min (time ≥ 30 min).

[0055] Precise nitrogen control: After vacuum treatment, [N] = 0.014 - 0.020%, [H] ≤ 0.8 ppm, [O] ≤ 6 ppm.

[0056] Step 4: Continuous casting process

[0057] Full protection casting: Submerged nozzle + argon sealing, with a superheat of 12 - 23 °C (narrow superheat inhibits the growth of columnar crystals).

[0058] Electromagnetic composite regulation:

[0059] Electromagnetic stirring in the mold (frequency 3 - 5 Hz, current 250 - 350 A) to break dendrites;

[0060] Electromagnetic braking in the secondary cooling zone (magnetic field strength 0.4 - 0.6 T) to increase the equiaxed crystal ratio to ≥ 50%.

[0061] Dynamic soft reduction: The reduction amount at the solidification end is 8 - 12 mm, and the casting speed is 0.65 - 0.75 m / min to eliminate the Cu segregation band.

[0062] Post-treatment of the casting blank: Stack cooling for 72 h, and the hydrogen diffusion annealing temperature is 250 - 300 °C (holding for 10 - 12 h).

[0063] The present invention will be further described below in conjunction with embodiments:

[0064] Embodiment 1:

[0065] Chemical composition (mass percentage): C: 0.17%, Si: 0.18%, Mn: 0.82%, Cr: 1.70%, Nb: 0.050%, Mo: 0.08%, Al: 0.050%, Cu: 0.15%, N: 0.017%, P: 0.012%, S: 0.018%, O: 5 ppm, the balance is Fe. (Meet Nb / N = 2.94, Al / N = 2.94)

[0066] Smelting process:

[0067] 1. The carbon content at the end of the converter is 0.06%, the tapping temperature is 1630 °C, and aluminum ingots (Al 0.05%), electrolytic copper plates (Cu 0.15%), and ferroniobium (Nb 0.050% ± 0.002%) are added;

[0068] 2. The LF refining uses a slag system of CaO / Al2O3 = 2.2 and CaF2 6%, and manganese nitride is added in 4 batches until N = 0.016%;

[0069] 3. The RH vacuum treatment maintains pressure for 35 min, soft blows argon at 25 L / min for 30 min, and the final refining [N] = 0.017%, [H] = 0.6 ppm, [O] = 5 ppm;

[0070] 4. The continuous casting superheat is 16 °C, the mold electromagnetic stirring (frequency 4 Hz, current 300 A), the electromagnetic braking in the secondary cooling zone is 0.5 T, and the dynamic soft reduction amount is 8 mm (casting speed 0.70 m / min).

[0071] The macrostructure of the product produced according to the above process is as Figure 1 shown, the grain size is ASTM 10, the carburized layer hardness gradient is gentle (transition from the surface 59 HRC to the core 32 HRC); high-temperature oxidation resistance (oxidation weight gain ≤ 1.2 mg / cm 2 / h); the equiaxed crystal ratio of the macrostructure is 52%, and there is no Cu segregation band (segregation index ≤ 1.05).

[0072] Embodiment 2:

[0073] Chemical composition (mass percentage): C: 0.18%, Si: 0.10%, Mn: 0.95%, Cr: 1.90%, Nb: 0.055%, Mo: 0.05%, Al: 0.060%, Cu: 0.20%, N: 0.018%, P: 0.010%, S: 0.015%, O: 7 ppm, the balance is Fe. (Meet Nb / N = 3.06, Al / N = 3.33)

[0074] Smelting process:

[0075] 1. The carbon content at the end of the converter is 0.08%, the tapping temperature is 1640 °C, aluminum ingots (Al 0.06%), electrolytic copper plates (Cu 0.20%), ferroniobium (Nb 0.055% ± 0.002%);

[0076] 2. In the LF refining, a slag system with CaO / Al2O3 = 2.5 and CaF2 8% is adopted, and manganese nitride is added in 5 batches until N = 0.017%;

[0077] 3. The RH vacuum treatment maintains pressure for 40 min, soft blows argon at 30 L / min for 35 min, and the final refining [N] = 0.018%, [H] = 0.7 ppm, [O] = 6 ppm;

[0078] 4. The continuous casting superheat is 17 °C, the mold electromagnetic stirring (frequency 5 Hz, current 350 A), the electromagnetic braking in the secondary cooling zone is 0.6 T, and the dynamic soft reduction amount is 9 mm (casting speed 0.70 m / min).

[0079] The macrostructure of the product produced according to the above process is as Figure 2 shown, the density of nano Nb(C,N) precipitation phases ≥ 3×10 3 pieces / μm 2 , the contact fatigue life L 10 ≥ 1.5×10 7 times; the retained austenite content is stably at 12 - 15%; the center segregation of the casting blank is class C 1.0, and there is no Mo banded structure.

[0080] Example 3:

[0081] Chemical composition (mass percentage): C: 0.16%, Si: 0.20%, Mn: 0.70%, Cr: 1.50%, Nb: 0.045%, Mo: 0.10%, Al: 0.040%, Cu: 0.10%, N: 0.017%, P: 0.015%, S: 0.010%, O: 4 ppm, the balance is Fe. (Meet Nb / N = 2.65, Al / N = 2.35)

[0082] Smelting process:

[0083] 1. The carbon content at the end of the converter is 0.05%, the tapping temperature is 1620°C, aluminum ingots (Al 0.04%), electrolytic copper plates (Cu 0.10%), ferroniobium (Nb 0.045% ± 0.002%);

[0084] 2. In LF refining, a slag system with CaO / Al2O3 = 2.0 and CaF2 5% is adopted, and manganese nitride is added in 3 batches until N = 0.016%;

[0085] 3. In RH vacuum treatment, the pressure is maintained for 30 min, soft blowing of argon is carried out at 20 L / min for 30 min, and the final refining results in [N] = 0.017%, [H] = 0.5 ppm, and [O] = 4 ppm;

[0086] 4. The superheat in continuous casting is 16°C, electromagnetic stirring in the mold (frequency 3 Hz, current 250 A), electromagnetic braking in the secondary cooling zone is 0.4 T, and the dynamic soft reduction amount is 7 mm (casting speed 0.65 m / min).

[0087] The product effects of the products produced according to the above process are shown in Table 1:

[0088] The carburizing distortion amount ≤ 0.05 mm (40% lower than that of traditional steel);

[0089] The impact energy at room temperature ≥ 120 J (-40°C ≥ 60 J);

[0090] The critical stress ratio of hydrogen-induced delayed cracking ≥ 0.85.

[0091] Table 1: Carburizing distortion amount

[0092]

[0093] Table 2: Comparative advantages with traditional carburized steel

[0094] Parameter Conventional 20CrMnTi steel Steel of this patent Surface hardness (HRC) 58-60 58-60 Core hardness (HRC) 28-30 32-34 Transition zone slope (HRC / mm) 18-22 10-14 <![CDATA[Contact fatigue life (L 10 )]]> <![CDATA[8×10 6 times]]> <![CDATA[≥1.5×10 7 times]]>

[0095] As can be seen from Table 2, the surface hardness (HRC), core hardness (HRC), transition zone slope (HRC / mm), and contact fatigue life (L10) of the steel produced by the technical solution of the present invention are all superior to those of the 20CrMnTi steel produced by the traditional process.

[0096] The above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are all included in the protection scope of the present invention.

Claims

1. A copper-niobium composite strengthened high temperature carburized gear steel, characterized in that: Its components are calculated by mass percentage: C: 0.15-0.19%, Si≤0.20%, Mn: 0.70-0.95%, Cr: 1.50-1.90%, Nb: 0.045-0.055%, Mo≤0.10%, Al: 0.04-0.060%, Cu: 0.10-0.20%, N: 0.016-0.020%, P≤0.015%, S≤0.020%, O≤8ppm; the balance is Fe and unavoidable impurities.

2. The copper-niobium composite strengthened high temperature carburized gear steel according to claim 1, characterized in that: The mass ratio of Nb to N satisfies Nb / N=2.25-3.5, and the mass ratio of Al to N satisfies Al / N=2.0-4.

0.

3. The copper-niobium composite strengthened high temperature carburized gear steel according to claim 1, characterized in that: The carburized layer hardness gradient fluctuation of the high temperature carburized gear steel is ≤3%, the distortion is <0.05mm / m, and the gear bending fatigue life is ≥1.5×10 7 times, contact fatigue strength at 200℃ ≥1300MPa, ingot center segregation ≤0.5 level, Cu segregation index ≤1.05, steel purity: D-type inclusions ≤1.0 level, O ≤6ppm.

4. A method for producing a copper-niobium composite reinforced high temperature carburized gear steel as claimed in any one of claims 1 to 3, characterized in that: It includes the steps of: Step 1: Converter smelting, pre-desulfurization of molten iron to S≤0.002%, titanium content≤0.005%; top and bottom combined blowing converter end point carbon content 0.05-0.08%, tapping temperature 1620-1640℃; adding aluminum ingots, electrolytic copper plates and ferroniobium for composite deoxidation alloying during tapping, controlling Al content 0.05%, Cu content 0.15%, Nb content error ≤±0.002%, prohibiting the addition of ferrosilicon; Step 2: LF refining, using a high basicity and low oxidation slag system with CaO / Al2O3=2.0-2.5 and CaF25-8%, with a slag thickness of 60-80mm; adding manganese nitride in batches to adjust the N content to 0.016-0.018%, maintaining Al / N=2.0-3.0; feeding Ca-Si line with Ca / Si=1:1 to desulfurize until S≤0.015%; Step 3: RH vacuum treatment, vacuum degree ≤20Pa, pressure maintenance ≥30min, soft blowing argon flow rate 20-30L / min for ≥30min; accurately control the final refining [N] = 0.016-0.020%, [H] ≤0.8ppm, [O] ≤6ppm; Step 4: Continuous casting process, full protection pouring, superheat 12-23℃, crystallizer electromagnetic stirring parameters are frequency 3-5Hz, current 250-350A; 0.4-0.6T electromagnetic braking is applied in the second cooling zone, and the equiaxed crystal rate is ≥50%; dynamic light pressure is applied at the end of solidification, and the pulling speed is 0.65-0.75m / min; after the billet is cooled for 72h, hydrogen diffusion annealing at 250-300℃ is carried out, and it is kept warm for 10-12h.

5. The method for producing a copper-niobium composite reinforced high temperature carburized gear steel as claimed in claim 4, characterized in that: In step 2, manganese nitride is added in 3-5 batches 15-25 minutes after the start of refining, with an interval of 5-8 minutes between each batch.

6. The method for producing a copper-niobium composite strengthened high temperature carburized gear steel according to claim 4, characterized in that: The dynamic soft pressing amount in step 4 is 8-12 mm.

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