Manufacturing method for high-temperature carburizing gear steel for new energy vehicles

Abstract

The present invention discloses a manufacturing method for a high-temperature carburizing gear steel for new energy vehicles, which method belongs to the technical field of special steels, and the manufacturing steps are as follows: performing converter smelting, LF refining, vacuum treatment, continuous casting and rolling. By optimizing the production process of the gear steel, a high-temperature resistant carburizing gear steel meeting the requirements of steels for new energy vehicles is obtained without increasing production costs. The high-temperature carburizing gear steel for new energy vehicles of the present invention has an austenite grain size of 7-8 after being kept at 950-960℃ for 4 h and after water quenching, without abnormal grains or mixed crystals, which meets the high-temperature carburizing requirements of users of new energy vehicles. The gear steel produced by the manufacturing method of the present invention has good purity, and good stability with regard to high-temperature carburizing resistance, thereby meeting the usage requirements of high-temperature carburizing gear steel for new energy vehicles.

Description

A method for manufacturing high-temperature carburized gear steel for new energy vehicles Technical Field

[0001] The present invention belongs to the technical field of special steels and relates to a method for manufacturing high-temperature carburized gear steel for new energy vehicles. Background Art

[0002] The rapid development and widespread adoption of new energy vehicles has, on the one hand, increased the comparative advantage of steel over aluminum alloys and modified plastics, and on the other hand, raised the bar for manufacturers in serving new energy vehicle manufacturing. Compared to traditional vehicles, new energy vehicle gears and motor shafts rotate at higher speeds, requiring the gear steel used to be highly hardenable and low-noise, while also placing higher demands on contact fatigue and rotational fatigue.

[0003] Faced with increasingly severe cost pressures and energy conservation and emission reduction requirements, high-temperature carburizing has become a key development direction for gear steel. High-temperature carburizing can effectively improve production efficiency, reduce production costs, and reduce carbon emissions. Research shows that when the carburizing temperature is increased from the conventional 920°C to 930°C to 950°C, the carburizing cycle can be reduced by approximately 30%. When the carburizing temperature is increased to 1000°C, the carburizing cycle can be reduced by approximately 55%. However, when the carburizing temperature of general gear steel reaches 950°C, coarse austenite grains are easily formed, resulting in increased gear heat treatment deformation, affecting gear accuracy and stability.

[0004] To achieve high-temperature carburization requirements for gears, microalloying elements are often added. Chinese Patent No. CN103361559A discloses "A Nb-Ti Composite Microalloyed High-Temperature Carburizing Gear Steel." By adding Nb to conventional 20CrMnTiH, and employing a Nb-Ti microalloying process, Nb forms precipitates at austenite grain boundaries, refining the austenite grains. However, the addition of Nb increases the production cost of gear steel.

[0005] Chinese patent CN109402498A discloses a high-temperature carburized gear steel and its manufacturing method. A small amount of V microalloying element is added to the steel, the addition of Nb is eliminated, and the Ti content is reduced to ensure the formation of sufficient V (C, N) and Ti (C, N) precipitates to pin the grain boundaries and inhibit grain growth. However, the effect of V element in controlling the high-temperature austenite grain size is not obvious.

[0006] Currently, gear steel in my country is often microalloyed with Al, Nb, V, and Ti to refine grains and increase the gear carburizing temperature. The addition of these microalloying elements inevitably increases costs. Furthermore, the addition of large amounts of Al can easily lead to nozzle blockage, hindering steel pouring. Therefore, a low-cost method for manufacturing high-temperature-resistant carburized gear steel is needed.

[0007] Summary of the Invention

[0008] In response to the above problems, the purpose of the present invention is to solve the defects existing in the prior art and propose a manufacturing method for high-temperature carburized gear steel for new energy vehicles. By optimizing the gear steel production process, high-temperature resistant carburized gear steel that meets the requirements of steel for new energy vehicles is obtained without increasing production costs.

[0009] The technical solution of the present invention is: a method for manufacturing high-temperature carburized gear steel for new energy vehicles according to the present invention, wherein the preparation process is as follows: scrap steel and molten iron are used in a converter smelting process, the end point P is ≤ 0.019%, a double-speed + slag cone is used for tapping, slag discharge is strictly controlled, and the tapping temperature is controlled at 1550°C-1700°C, and alloys are added after the furnace for precipitation deoxidation and alloying to adjust the chemical composition;

[0010] During LF refining, carbon powder, aluminum wire, silicon carbide, etc. are used for deoxidation, and the target value of final slag basicity is 4-6;

[0011] After refining outside the furnace, vacuum treatment is carried out, and the vacuum is maintained for more than 12 minutes. The chemical composition is fine-tuned according to the composition control requirements. After the composition is qualified, the static stirring time is ≥15 minutes to promote the floating of inclusions. When the static stirring time reaches the requirement and the temperature is appropriate, the continuous casting is carried out on the hanging ladle. After vacuum treatment, the hydrogen content in the molten steel is reduced to below 2.0ppm, and the possibility of white spot defects is basically eliminated.

[0012] The continuous casting adopts a full-protection pouring process to prevent the absorption and secondary oxidation of molten steel. Argon is poured during opening, the long nozzle is sealed with argon and a sealing gasket is used. The nozzle is strictly aligned. By adjusting the crystallizer electromagnetic stirring intensity + end light pressure + secondary cooling water parameter configuration, the center segregation and center looseness are reduced, the surface and internal quality of the casting billet are improved, and the constant casting speed is controlled.

[0013] In order to allow the second phase particles to fully pin the grain boundaries and play a role in grain refinement, high temperature heating is used during rolling. The holding temperature is higher than the equilibrium precipitation temperature of the second phase particles. The preheating section temperature is ≤850℃, the heating section is 950℃-1170℃, and the soaking temperature is above 1170℃. The high temperature time is guaranteed to fully heat the core of the steel billet and fully dissolve the second phase particles.

[0014] After leaving the furnace, high-pressure water is used to remove phosphorus, and the removal pressure is ≥18MPa to ensure that there is no primary iron oxide scale remaining on the surface;

[0015] High-temperature finishing rolling is used to control the austenite grain size and avoid the precipitation of coarse second-phase particles. The finishing temperature is 910-970°C. After rolling, the steel is cooled on a cooling bed and covered with an insulation cover to control the hardness to meet the requirements.

[0016] The beneficial effects of the present invention are as follows: the characteristics of the present invention are as follows: the high-temperature carburized gear steel for new energy vehicles described in the present invention has an austenite grain size of 7-8 after being kept at 950℃-960℃ for 4 hours and water quenched, with no abnormal grains and no mixed crystals, which meets the high-temperature carburizing requirements of new energy vehicle users without increasing existing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG1 is a diagram of austenite grains in Example 1 of the present invention;

[0018] FIG2 is an austenite grain diagram in Example 2 of the present invention;

[0019] FIG3 is a diagram of austenite grains in Example 3 of the present invention. DETAILED DESCRIPTION

[0020] The specific technical solutions of the present invention are further described in detail below with reference to specific examples.

[0021] The following process was used to prepare Examples 1-3 of the present invention:

[0022] (1) After converter smelting, LF refining and vacuum degassing treatment are carried out, and the chemical composition is controlled as shown in Table 1, and continuous casting is carried out into square billets with a cross section of 250×300.

[0023] Table 1 (wt.%, the balance is Fe and other inevitable impurity elements)

[0024] (2) When the billet is heated, the temperature of the preheating section is ≤850℃, and the temperature of the heating section is 950℃-1170℃. Through high-temperature heating and long-term heat preservation, the billet is rolled into round steel by high-temperature final rolling. The specific rolling parameters are shown in Table 2.

[0025] Table 2 Rolling parameters of Examples 1-3

[0026] (3) The grain size of the rolled round steel was tested, and the heat treatment process was 950℃ for 4h and water quenched. The test results are shown in Table 3; Figures 1-3 show the austenite grain size of Examples 1-3. It can be seen that there are no coarse grains and no mixed crystal phenomenon.

[0027] Table 3

[0028] (4) The inclusion detection results of Examples 1-3 are shown in Table 4.

[0029] Table 4

[0030] According to the performance test results of the embodiment, the gear steel produced by the manufacturing method of the present invention has good purity and good high-temperature carburizing stability, meeting the use requirements of high-temperature carburized gear steel for new energy vehicles.

[0031] The present invention provides a method for manufacturing high-temperature resistant carburized gear steel for new energy vehicles without increasing the original cost of the materials. The produced material can be used in gears such as new energy vehicle reducers, and has certain economy and market competitiveness.

Claims

1. A method for manufacturing high temperature carburized gear steel for new energy vehicles, characterized in that: The preparation steps are as follows: (1): Use converter smelting, prepare ingredients according to process requirements, and adjust chemical composition through LF refining; (2): Vacuum degassing of molten steel; (3): Obtaining a continuous casting rectangular billet by continuous casting; (4): After the ingot is heated, it is dephosphorized by high-pressure water and rolled to obtain gear steel.

2. The method for manufacturing a high temperature carburized gear steel for new energy vehicles according to claim 1, characterized in that: In step (1), the converter smelting process is: the converter smelting uses scrap steel and molten iron, the end point P≤0.019%, and the steel tapping adopts double gear + slag cone.

3. The method for manufacturing a high temperature carburized gear steel for new energy vehicles according to claim 2, characterized in that: The tapping temperature is controlled between 1550°C and 1700°C, and alloys are added after the furnace for precipitation deoxidation and alloying to adjust the chemical composition.

4. The method for manufacturing a high temperature carburized gear steel for new energy vehicles according to claim 2, characterized in that: Carbon powder, aluminum wire and silicon carbide are used for deoxidation during LF refining, and the target value of final slag basicity is 4-6.

5. The method for manufacturing a high temperature carburized gear steel for new energy vehicles according to claim 1, characterized in that: In step (2), the process of vacuum treatment is: vacuum maintenance time is more than 12 minutes, chemical composition is fine-tuned according to component control requirements, and static stirring time is ≥15 minutes after the components are qualified.

6. The method for manufacturing a high temperature carburized gear steel for new energy vehicles according to claim 5, characterized in that: After vacuum treatment, the hydrogen content in the molten steel is reduced to below 2.0 ppm.

7. The method for manufacturing a high temperature carburized gear steel for new energy vehicles according to claim 1, characterized in that: In step (3), the continuous casting process is: the continuous casting adopts a full protection pouring process to prevent the molten steel from being inhaled and secondary oxidation, argon is poured, and the long water inlet is sealed with argon + sealing gasket.

8. The method for manufacturing a high temperature carburized gear steel for new energy vehicles according to claim 1, characterized in that: In step (4), the specific rolling process is as follows: in order to allow the second phase particles to fully pin the grain boundaries and play a role in refining the grains, high-temperature heating is used during rolling, and the insulation temperature is higher than the equilibrium precipitation temperature of the second phase particles. The preheating section temperature is ≤850°C, the heating section is 950°C-1170°C, and the soaking temperature is above 1170°C, so that the core of the billet is heated through and the second phase particles are fully dissolved.

9. The method for manufacturing a high temperature carburized gear steel for new energy vehicles according to claim 8, characterized in that: After the steel billet is taken out of the furnace, high-pressure water is used to remove phosphorus, and the dephosphorization pressure is ≥18MPa to ensure that there is no primary iron oxide scale remaining on the surface.

10. The method for manufacturing high temperature carburized gear steel for new energy vehicles according to claim 8, characterized in that: High temperature final rolling process is adopted during rolling, and the final rolling temperature is 910℃-970℃; After rolling, the steel is cooled on a cooling bed and covered with an insulation cover.

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