Control method for carburizing and quenching deformation of gear steel and gear steel

Abstract

The invention provides a control method for carburizing and quenching deformation of gear steel, which comprises the following steps: S1, proportioning according to the component proportion of the gear steel, and smelting and casting the proportioned raw materials to obtain a cast ingot; s2, the cast ingot is subjected to first-stage heating, second-stage heating and soaking, and then rolling is conducted; and S3, the rolled blank is subjected to carburizing heat treatment, the carburizing heat treatment temperature is smaller than or equal to 890 DEG C, and the quenching temperature is smaller than or equal to 830 DEG C. The invention further provides the gear steel prepared through the control method. The components of the gear steel and the carburizing heat treatment process are controlled, effective control over carburizing and quenching deformation of the gear steel is achieved through the synergistic effect of the components and the carburizing heat treatment process, and heat treatment distortion of the gear steel is remarkably reduced; the result shows that according to the control method provided by the invention, the average diameter deformation is smaller than or equal to 0.10 mm and the average radius deformation is smaller than or equal to 0.05 mm after the gear steel with the diameter smaller than or equal to 50 mm is carburized and quenched.

Description

Technical Field

[0001] The present invention relates to the technical field of gear steel, and in particular to a method for controlling carburizing and quenching deformation of gear steel and gear steel. Background Art

[0002] Gears, as key components of automotive transmission systems, are crucial for ensuring gearbox precision, speed reduction, speed increase, and direction change. Therefore, the base steel used to produce gears must possess high toughness, fatigue strength, and wear resistance. Carburizing and quenching are the primary processes used to produce high-quality gears. Gears treated with carburizing heat treatment possess excellent wear resistance and toughness, capable of withstanding alternating loads, impact loads, and abrasion. However, deformation during carburizing heat treatment can reduce gear meshing accuracy, leading to uneven gear operation, excessive noise generation, and uneven wear on the tooth surfaces, reducing gear service life.

[0003] At present, there are many studies on gear heat treatment deformation at home and abroad, mainly focusing on the influence of pretreatment parameters, carburizing parameters and quenching parameters on their deformation characteristics. In fact, although gear distortion is formed in the heat treatment process, the metallurgical material has a great influence on deformation. Under the existing continuous casting and rolling conditions, the gear steel materials produced with different process parameters meet the general metallurgical requirements, but under the same heat treatment parameters, irregular gear deformation or fluctuation range will still occur. In particular, the 20CrMnTi series is one of the most widely used gear steel varieties. During the carburizing and quenching process, the gear distortion is uncontrolled, which seriously restricts the gear processing and production. Therefore, the control of gear carburizing and quenching deformation has become a common technical problem in the gear production process. Summary of the Invention

[0004] The technical problem solved by the present invention is to provide a method for controlling the carburizing and quenching deformation of gear steel. The control method provided in this application can significantly reduce the heat treatment distortion of gear steel.

[0005] In view of this, the present application provides a method for controlling gear steel carburizing and quenching deformation, comprising the following steps:

[0006] S1. Mixing the gear steel according to its composition ratio, smelting and casting the mixed raw materials to obtain an ingot;

[0007] The composition of the ingot is calculated by mass percentage and includes: C 0.19-0.20%, Si 0.24-0.27%, Mn 0.9-1.0wt%, P 0.008-0.012%, S 0.019-0.024%, Cr 1.1-1.2%, Ti 0.06-0.07%, N 0.006-0.007%, Al 0.02-0.04%; the balance is Fe and unavoidable impurities;

[0008] S2, performing a first-stage heating, a second-stage heating and soaking step on the ingot, and then rolling;

[0009] S3. Carburizing the rolled blank. The carburizing heat treatment temperature is ≤890°C, and the quenching temperature is ≤830°C.

[0010] In some specific embodiments, in step S1, the smelting includes converter smelting, LF refining and RH vacuum degassing performed in sequence. In the LF refining of the smelting, the refining time is ≥35 min, the binary basicity of the slag is 4-6, the Al2O3 content in the slag is 25-35wt%, the CaF2 content in the slag is 8-15wt%, and 2-5m / t silicon-calcium wire is fed before the LF leaves the station.

[0011] In some specific embodiments, in step S1, during the RH vacuum degassing of the smelting, the vacuum degree is ≤5 mbar, the time is ≥10 min, the sulfur content is 0.015-0.024 wt%, and 2-5 m / t calcium silicon wire is fed after the vacuum is ended. The soft argon blowing time after the wire feeding is ≥10 min.

[0012] In some specific embodiments, the calcium silicon wire contains Ca≥25wt%, Si is 55-65wt%, and the balance is Fe and unavoidable impurities.

[0013] In some specific embodiments, the electromagnetic stirring frequency of the casting crystallizer is 2.0-3.0 Hz, and the current intensity is 100-200 A; the end electromagnetic stirring frequency is 6.5-7.5 Hz, and the current intensity is 200-300 A; the superheat of the casting molten steel is 25-35°C, and the continuous casting casting speed is 0.55-0.65 m / min.

[0014] In some specific embodiments, the temperature of the first stage heating is 930-960° C., the temperature of the second stage heating is 1130-1160° C., the temperature of the soaking is 1230-1260° C., and the soaking time is 80-90 min.

[0015] In some specific embodiments, the starting rolling temperature is 1000-1100°C, and the finishing rolling temperature is 800-900°C.

[0016] In some specific embodiments, the carburizing heat treatment temperature is 860-880°C, and the quenching temperature is 810-820°C.

[0017] The present application also provides gear steel prepared by the control method, which comprises, in mass percentage, C 0.19-0.20%, Si 0.24-0.27%, Mn 0.9-1.0wt%, P 0.008-0.012%, S 0.019-0.024%, Cr 1.1-1.2%, Ti 0.06-0.07%, N 0.006-0.007%, Al 0.02-0.04%; the balance is Fe and unavoidable impurities.

[0018] In some specific embodiments, the gear steel has an average diameter deformation of ≤0.10 mm and an average radius deformation of ≤0.05 mm.

[0019] The present application provides a method for controlling the deformation of gear steel during carburizing and quenching, which firstly prepares the gear steel according to its composition ratio, smelts and casts the steel after preparation to obtain an ingot, then performs one-stage heating, two-stage heating and uniform heating on the ingot, and then performs rolling, and finally performs carburizing heat treatment on the rolled billet; in the method for controlling the deformation of gear steel during carburizing and quenching, the present application controls the composition of the gear steel and the carburizing heat treatment process, and the synergistic effect of the two achieves effective control of the deformation of gear steel during carburizing and quenching, and significantly reduces the heat treatment distortion of the gear steel. The results show that the control method provided by the present application achieves an average diameter deformation of ≤0.10mm and an average radius deformation of ≤0.05mm for gear steel with a diameter of ≤50mm after carburizing and quenching. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a low-magnification microstructure photograph of the gear steel prepared in Example 1 of the present invention;

[0021] Figure 2 These are photos of dendrite morphology at different positions from the inner arc side surface to the outer arc side surface of the gear steel prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0022] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0023] In view of the problem of uncontrolled dimensional distortion during carburizing and quenching of gear steel in the prior art, the present application provides a method for controlling deformation of gear steel during carburizing and quenching. The method achieves effective control of deformation of gear steel during carburizing and quenching through dual-phase coordinated control of metallurgical materials and heat treatment processes. Specifically, an embodiment of the present invention discloses a method for controlling deformation of gear steel during carburizing and quenching, comprising the following steps:

[0024] S1. Smelting and casting the gear steel according to the composition ratio to obtain an ingot;

[0025] The composition of the ingot is calculated by mass percentage and includes: C 0.19-0.20%, Si 0.24-0.27%, Mn 0.9-1.0wt%, P 0.008-0.012%, S 0.019-0.024%, Cr 1.1-1.2%, Ti 0.06-0.07%, N 0.006-0.007%, Al 0.02-0.04%; the balance is Fe and unavoidable impurities;

[0026] S2, performing a first-stage heating, a second-stage heating and soaking step on the ingot, and then rolling;

[0027] S3. Carburizing the rolled blank. The carburizing treatment temperature is ≤890°C, and the quenching temperature is ≤830°C.

[0028] In the method for controlling carburizing and quenching deformation of gear steel provided in the present application, that is, the method for preparing gear steel, the ingredients are first prepared according to the composition ratio of the gear steel, and then the obtained raw materials are smelted and cast to obtain an ingot; in the present application, the gear steel is a 20CrMnTi series gear steel, and its composition is adjusted on the basis of conventional 20CrMnTi gear steel, specifically: C 0.19-0.20%, Si 0.24-0.27%, Mn 0.9-1.0wt%, P 0.008-0.012%, S0.019-0.024%, Cr 1.1-1.2%, Ti 0.06-0.07%, N 0.006-0.007%, Al0.02-0.04%; the balance is Fe and unavoidable impurities.

[0029] With the solid solution strengthening and carbide precipitation of C, the matrix hardness increases with the increase of C content. However, if the matrix hardness increases and deformation occurs during heat treatment, it will increase the difficulty of straightening or grinding, which is not conducive to dimensional accuracy control. In the present invention, the C content is controlled to 0.19-0.20wt%.

[0030] Mn can significantly improve the hardenability and hardness of the matrix, but the increase in matrix hardness is not conducive to controlling deformation, and the increase in hardenability will increase the heat treatment deformation of the gear; in view of this, the Mn content is controlled to 0.9~1.0wt% in this application, specifically, the Mn content is 0.91wt%, 0.92wt%, 0.93wt%, 0.94wt%, 0.95wt%, 0.96wt%, 0.97wt%, 0.98wt%, and 0.99wt%.

[0031] Cr can improve the hardenability and impact toughness of the matrix. Similar to C and Mn, increased matrix hardness is not conducive to deformation control. In the present invention, the Cr content is controlled to 1.1-1.2wt%. Specifically, the Cr content is 1.11wt%, 1.12wt%, 1.13wt%, 1.14wt%, 1.15wt%, 1.16wt%, 1.17wt%, 1.18wt%, and 1.19wt%.

[0032] In gear steel, Ti primarily inhibits austenite grain growth by forming second-phase particles, which helps control heat treatment deformation. However, when the Ti content is too high, large TiN particles are formed during solidification, which is detrimental to matrix performance. In the present invention, the Ti content is controlled to 0.06-0.07 wt%.

[0033] N has the functions of solid solution strengthening, grain size control and austenitization, and is mainly used to control grain size in the gear steel of the present application; as the N content increases, the total amount of TiN within the carburizing temperature and high-temperature diffusion annealing temperature range increases, which is beneficial to grain refinement; however, if the N content is too high, large-sized TiN inclusions will be generated, and such inclusions are difficult to deform during rolling, increasing the risk of gear fatigue cracks, and too high a N content will also affect the hot working performance; therefore, in the present invention, the N content is controlled to 0.006-0.007wt%, specifically, the N content is 0.0061wt%, 0.0062wt%, 0.0063wt%, 0.0064wt%, 0.0065wt%, 0.0066wt%, 0.0067wt%, 0.0068wt%, and 0.0069wt%.

[0034] Al has the functions of deoxidation, precision control, and alloying. In the gear steel of this application, it is mainly used for deoxidation and improving the cleanliness of the gear steel. If the Al content is too high, a large amount of Al2O3 inclusions will be generated, affecting the castability of the continuous casting steel and the performance of the gear steel. In the present invention, the Al content is controlled to 0.02-0.04wt%. Specifically, the Al content is 0.021wt%, 0.022wt%, 0.023wt%, 0.024wt%, 0.025wt%, 0.026wt%, 0.027wt%, 0.028wt%, 0.029wt%, 0.030wt%, 0.031wt%, 0.032wt%, 0.033wt%, 0.034wt%, 0.035wt%, 0.036wt%, 0.037wt%, 0.039wt%, and 0.038wt%.

[0035] Specifically, the Si content is 0.25 wt%, 0.26 wt%, and 0.27 wt%.

[0036] The specific P content is 0.009 wt%, 0.010 wt%, and 0.011 wt%.

[0037] The specific S content is 0.020 wt%, 0.021 wt%, 0.022 wt%, and 0.023 wt%.

[0038] During the batching process, the raw materials for the above components are selected in accordance with what is well known to those skilled in the art, and this application does not impose any special restrictions on this. After the raw materials are batched, they are smelted and cast to obtain ingots, wherein the smelting includes converter smelting, LF refining and RH vacuum degassing in sequence; this application has no special restrictions on the operating procedures of the above three smelting stages; specifically, in the LF refining, the refining time is ≥35min, the binary basicity of the slag is 4-6, the content of Al2O3 in the slag is 25-35wt%, the content of CaF2 in the slag is 8-15wt%, and 2-5m / t silicon calcium wire is fed before the LF leaves the station; specifically, The refining time is 36 to 39 minutes, more specifically, the refining time is 37 to 38 minutes; specifically, the binary basicity of the slag is 4, 5, or 6; specifically, the Al2O3 content in the slag is 28 to 33wt%, and the CaF2 content is 9 to 13wt%, more specifically, the Al2O3 content in the slag is 29 to 30wt%, and the CaF2 content is 11 to 12wt%; specifically, the LF is fed into a 3 to 3.5m / t silicon-calcium line before leaving the station. In RH vacuum degassing, the vacuum degree is ≤5mbar and the time is ≥10min. Specifically, the vacuum degree is <3mbar and the time is 12-13min. The sulfur content is 0.015-0.024wt%, specifically, the sulfur content is 0.020-0.022wt%. After the vacuum is completed, 2-5m / t of calcium silicon wire is fed, and the time for soft argon blowing after feeding the wire is ≥10min. Specifically, 3-3.5m / t of calcium silicon wire is fed, and the time for soft argon blowing after feeding the wire is 10-12min. In the present application, the calcium silicon wire contains Ca ≥25wt%, Si 55-65wt%, and the balance is Fe and unavoidable impurities. Specifically, the Ca content is 26-28wt%, the Si content is 58-60wt%, and the balance is Fe.

[0039] The casting adopts a continuous casting method. In order to ensure the uniformity of the ingot composition and structure, the electromagnetic stirring frequency of the casting crystallizer is 2.0-3.0 Hz, and the current intensity is 100-200 A; specifically, the electromagnetic stirring frequency of the crystallizer is 2.2-2.4 Hz, and the current intensity is 150-180 A; the end electromagnetic stirring frequency is 6.5-7.5 Hz, and the current intensity is 200-300 A, specifically, the end electromagnetic stirring frequency is 6.8-7.0 Hz, and the current intensity is 230-250 A; the superheat of the casting steel liquid is 25-35°C, and the continuous casting billet drawing speed is 0.55-0.65 m / min, specifically, the superheat of the casting steel liquid is 28-33°C, and the continuous casting billet drawing speed is 0.60-0.61 m / min.

[0040] This application then rolls the ingot, and the rolling process includes one-stage heating, two-stage heating and soaking, the temperature of the one-stage heating is 930-960°C, the temperature of the two-stage heating is 1130-1160°C, the temperature of the soaking is 1230-1260°C, and the soaking time is 80-90min; specifically, the temperature of the one-stage heating is 940-950°C, the temperature of the two-stage heating is 1140-1150°C, the temperature of the soaking is 1240-1250°C, and the soaking time is 84-85min. The above-mentioned one-stage heating shortens the heating time by rapid heating (the furnace temperature remains basically unchanged), and the one-stage heating is equivalent to the preheating stage; after low-temperature preheating, the temperature is quickly raised to the rolling temperature, i.e., the second-stage heating, to improve the plasticity of the ingot and reduce deformation resistance; the soaking is to eliminate the black mark of the water-cooled slide, reduce the cross-section temperature difference to ≤20°C, and ensure rolling stability.

[0041] If only one stage of heating is performed, uneven temperature will occur, resulting in a large temperature difference between the inside and outside of the ingot, which will easily cause dimensional fluctuations or rolling mill accidents during rolling, and rapid heating may cause thermal stress cracks in the bearing steel; at the same time, the high temperature residence time is long, the iron oxide scale thickens (burning rate ≥ 2%), and the decarburization of the gear steel surface is aggravated.

[0042] If only two-stage heating is performed, that is, direct high-temperature heating is performed without one stage of heating, which will increase fuel consumption, and the lack of a low-temperature stage is not conducive to eliminating residual stress, which can easily lead to cracking of the alloy steel. Or if there is a lack of a soaking stage, the temperature difference of the ingot section will remain (such as ≥50°C), and the steel will be prone to surface cracks or internal grain coarsening (such as grain size exceeding level 6) after rolling.

[0043] Therefore, this application performs three-stage heating before rolling, and realizes the improvement of ingot plasticity, energy consumption optimization and defect control through gradient temperature control; heating with only one or two stages is prone to cause oxidation, decarburization, grain coarsening and other problems due to the lack of temperature uniformity guarantee, especially for high-precision materials such as gear steel, a three-stage process must be strictly adopted. After heating, the ingot is rolled. The specific operation means of the rolling are well known to those skilled in the art, and this application does not impose any special restrictions on this; the starting rolling temperature of the rolling is 1000-1100°C, and the final rolling temperature is 800-900°C. Specifically, the starting rolling temperature of the rolling is 1060-1090°C, and the final rolling temperature is 830-860°C. More specifically, the starting rolling temperature of the rolling is 1070-1080°C, and the final rolling temperature is 840-850°C.

[0044] According to the present invention, the initial steel billet after rolling is finally subjected to carburizing heat treatment, the temperature of the carburizing heat treatment is ≤890°C, and the quenching temperature is ≤830°C. Specifically, the temperature of the carburizing heat treatment is 860-880°C, and the quenching temperature is 810-820°C. More specifically, the temperature of the carburizing heat treatment is 870-875°C, and the quenching temperature is 812-818°C.

[0045] The present application also provides a gear steel prepared by the above method, which comprises, in mass percentage, C 0.19-0.20%, Si 0.24-0.27%, Mn 0.9-1.0wt%, P 0.008-0.012%, S0.019-0.024%, Cr1.1-1.2%, Ti 0.06-0.07%, N 0.006-0.007%, Al0.02-0.04%; the balance is Fe and unavoidable impurities.

[0046] The composition of the gear steel has been described in detail above and will not be repeated here.

[0047] The method for controlling gear steel carburizing and quenching deformation provided by the present invention can significantly reduce gear steel heat treatment distortion through chemical composition design and production process, while utilizing existing carburizing furnace equipment and setting heat treatment conditions, and achieves an average diameter deformation of ≤0.10mm and an average radius deformation of ≤0.05mm after carburizing and quenching of gear steel samples with a diameter of ≤50mm.

[0048] In order to further understand the present invention, the method for controlling carburizing and quenching deformation of gear steel provided by the present invention is described in detail below in conjunction with embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0049] Example

[0050] A method for controlling deformation during carburizing and quenching of 20CrMnTi series gear steel comprises the following steps:

[0051] 1) Smelting and continuous casting

[0052] Prepare raw materials according to the gear steel component ratio, mix the raw materials, smelt them, and then cast them to obtain ingots;

[0053] In the smelting process, converter smelting is used, followed by LF refining and RH vacuum degassing:

[0054] During the LF refining process, the refining time is ≥35min, the binary basicity of the slag is 5, the Al2O3 content in the slag is 28wt%~30wt%, the CaF2 content in the slag is 9wt%~11wt%, and the LF is fed into a 3~3.5m / t silicon-calcium line before leaving the station;

[0055] During the RH refining process, the vacuum degree is ≤3 mbar, the refining time is ≥10 minutes, the sulfur content is 0.020-0.022 wt%, and 3-3.5 m / t of calcium silicon wire is fed after the vacuum is completed. The soft argon blowing time after the wire feeding is 10-12 minutes. The chemical composition of the calcium silicon wire is as follows: Ca: 26-28%, Si: 58%-60%, and the balance is Fe and unavoidable impurities.

[0056] During the casting process, continuous casting is selected, the crystallizer electromagnetic stirring frequency is 2.0~3.0Hz, the current intensity is 100~200A; the end electromagnetic stirring frequency is 6.5~7.5Hz, the current intensity is 200~300A; the superheat of the casting steel liquid is 25~35℃; the continuous casting billet drawing speed is 0.55~0.65m / min.

[0057] 2) Rolling and heat treatment

[0058] The obtained ingot is heated and then rolled, and finally subjected to carburizing heat treatment to obtain gear steel;

[0059] The heating includes a first stage heating, a second stage heating and a soaking heat, wherein the first stage heating temperature is 930°C to 960°C, the second stage heating temperature is 1130°C to 1160°C, the soaking heat temperature is 1230°C to 1260°C, and the soaking heat time is 80 to 90 minutes;

[0060] The starting rolling temperature is 1050-1100°C, and the finishing rolling temperature is 800-900°C.

[0061] The carburizing temperature of the carburizing heat treatment is ≤890°C, and the quenching temperature is ≤830°C.

[0062] The following examples and comparative examples were prepared according to the above steps to prepare gear steel, wherein the composition of the gear steel is shown in Table 1, with the balance being Fe and unavoidable impurities;

[0063] Some parameters involved in the preparation steps are shown in Tables 2 and 3, and the remaining parameters are as described in the above embodiment (the parameters are range values, indicating that there are fluctuations in actual production and it cannot be confirmed whether they are customized); GB / T3077-1999 is used to process the gear C-type specimen, and the gear radial deformation is tested. The data are shown in Table 4.

[0064] Table 1 Main chemical composition data of gear steel of embodiment and comparative example (wt%)

[0065]

[0066]

[0067] Table 2 Smelting process data of the embodiment and comparative example

[0068]

[0069] Table 3 Data table of heating and rolling process of embodiment and comparative example

[0070]

[0071]

[0072] Table 4 Deformation data of C-type specimens (gear steel) prepared in the examples and comparative examples

[0073] serial number C-type specimen diameter / mm Diameter deformation / mm Radius deformation / mm Example 1 50 0.08 0.04 Example 2 50 0.08 0.04 Example 3 50 0.09 0.045 Example 4 50 0.10 0.05 Comparative Example 1 50 0.16 0.08 Comparative Example 2 50 0.18 0.09

[0074] As shown in Table 4, the method provided by the present invention regulates the gear steel composition and the parameters in the steps to achieve an average diameter deformation of the obtained gear steel of ≤0.10 mm and an average radius deformation of ≤0.05 mm, significantly reducing the heat treatment distortion of the gear steel. While reducing the loss in the gear processing process, it also meets the requirements of green and environmentally friendly sustainable development.

[0075] Figure 1 This is a low-magnification microstructure photograph of the gear steel produced in Example 1. Its average equiaxed crystal ratio is 24.61%, the CET difference between the inner and outer arc sides is 20 mm, and the equiaxed crystal area has good symmetry. From the longitudinal low-magnification, very small shrinkage cavities can be seen, and the low-magnification quality is greatly improved.

[0076] like Figure 2 As shown, the sample prepared in Example 1 is columnar crystal from the inner arc side surface to No. 6, CET transition at No. 6-No. 7, equiaxed crystal at No. 8-No. 15, with several dark spots appearing inside, with a size of less than 0.3 mm, which are semi-macroscopic point segregation, CET transition at No. 16, and columnar crystal area from No. 17 to the outer arc side surface.

[0077] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0078] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for controlling deformation of gear steel during carburizing and quenching, comprising the following steps: S1. Mixing the gear steel according to its composition ratio, smelting and casting the mixed raw materials to obtain an ingot; The composition of the ingot is calculated by mass percentage and includes: C 0.19-0.20%, Si 0.24-0.27%, Mn 0.9-1.0wt%, P 0.008-0.012%, S 0.019-0.024%, Cr 1.1-1.2%, Ti 0.06-0.07%, N 0.006-0.007%, Al 0.02-0.04%; the balance is Fe and unavoidable impurities; S2, performing a first-stage heating, a second-stage heating and soaking step on the ingot, and then rolling; S3. Carburizing the rolled blank. The carburizing heat treatment temperature is ≤890°C, and the quenching temperature is ≤830°C.

2. The control method according to claim 1, characterized in that: In step S1, the smelting includes converter smelting, LF refining and RH vacuum degassing carried out in sequence. In the LF refining of the smelting, the refining time is ≥35 min, the binary basicity of the slag is 4-6, the Al2O3 content in the slag is 25-35wt%, the CaF2 content in the slag is 8-15wt%, and 2-5m / t silicon-calcium wire is fed before the LF leaves the station.

3. The control method according to claim 1 or 2, characterized in that: In step S1, during the RH vacuum degassing of the smelting, the vacuum degree is ≤5 mbar, the time is ≥10 min, the sulfur content is 0.015-0.024 wt%, and 2-5 m / t calcium silicon wire is fed after the vacuum is finished. The soft argon blowing time after the wire feeding is ≥10 min.

4. The control method according to claim 3, characterized in that: The calcium silicon wire contains Ca≥25wt%, Si is 55-65wt%, and the remainder is Fe and unavoidable impurities.

5. The control method according to claim 3, characterized in that: The electromagnetic stirring frequency of the casting crystallizer is 2.0-3.0 Hz, and the current intensity is 100-200 A; the terminal electromagnetic stirring frequency is 6.5-7.5 Hz, and the current intensity is 200-300 A; the superheat degree of the casting molten steel is 25-35° C., and the continuous casting casting speed is 0.55-0.65 m / min.

6. The control method according to claim 1 or 5, characterized in that: The temperature of the first stage heating is 930-960° C., the temperature of the second stage heating is 1130-1160° C., the temperature of the soaking is 1230-1260° C., and the soaking time is 80-90 min.

7. The control method according to claim 6, characterized in that: The starting rolling temperature is 1000-1100°C, and the finishing rolling temperature is 800-900°C.

8. The control method according to claim 1 or 7, characterized in that: The temperature of the carburizing heat treatment is 860-880°C, and the quenching temperature is 810-820°C.

9. The gear steel prepared by the control method according to any one of claims 1 to 8, comprising, by mass percentage: C 0.19~0.20%, Si 0.24~0.27%, Mn 0.9~1.0wt%, P 0.008~0.012%, S 0.019~0.024%, Cr 1.1~1.2%, Ti 0.06~0.07%, N 0.006~0.007%, Al 0.02~0.04%; the balance is Fe and unavoidable impurities.

10. The gear steel according to claim 9, characterized in that: The average diameter deformation of the gear steel is ≤0.10 mm, and the average radius deformation is ≤0.05 mm.

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