A method for producing a carburized gear steel

Abstract

The application discloses a production method of car carburizing gear steel, and chemical component mass percentage includes: C 0.12%-0.18%, Si 0.17%-0.37%, Mn 0.55%-0.90%, P≤0.025%, S≤0.025%, Cr 0.85-1.25%, the rest is Fe and inevitable impurities, and the total mass percentage is 100%; the production method includes: converter smelting, LF refining, continuous casting, casting blank heating furnace heating and round steel rolling.The purpose of the application is to provide a production method of 15CrH car carburizing gear steel, to significantly improve the mechanical properties of hot-rolled round steel under the premise of reducing production cost, so as to produce 15CrH car carburizing gear steel, and further significantly improve the overall service life and safety of sucker rods.

Description

Technical Field

[0001] This invention belongs to the field of smelting and rolling technology, and particularly relates to a method for producing carburized gear steel for automobiles. Background Technology

[0002] Automotive carburized gear steel needs to possess excellent wear resistance and strength to withstand the wear and impact caused by long-term high-speed operation. Steel developed by steel mills ensures that gears maintain stable performance during extended use, extending their service life. The automotive working environment is complex, affected by various chemicals and humid conditions. Therefore, carburized gear steel needs good corrosion resistance and stability to resist damage from oxidation, corrosion, and environmental changes, ensuring long-term stable gear operation. Using high-quality carburized gear steel can reduce automotive manufacturing and maintenance costs, improving overall vehicle performance and economy. Simultaneously, extending gear life reduces the frequency of replacement and repair, saving costs for both automakers and users. With the rapid development of the automotive industry and consumers' increasing pursuit of vehicle performance, the demand for high-performance, high-quality gears is constantly increasing. Therefore, high-quality automotive carburized gear steel developed by steel mills will gain widespread application and market recognition in the automotive manufacturing industry. Thus, the promotion and application of automotive carburized gear steel by steel mills has clear feasibility and broad prospects. By meeting the automotive manufacturing industry's requirements for performance, quality, and cost, steel mills can achieve a significant position in this field, gaining considerable market share and economic benefits. Summary of the Invention

[0003] The purpose of this invention is to provide a production method for carburized gear steel (grade 15CrH) for automobiles. By utilizing the principle of Cr alloying, the mechanical properties of hot-rolled round steel are significantly improved while reducing production costs, thereby producing 15CrH carburized gear steel for automobiles, which in turn significantly improves the overall lifespan and safety of sucker rods.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a method for producing carburized gear steel for automobiles. The chemical composition, by mass percentage, comprises: C 0.12%–0.18%, Si 0.17%–0.37%, Mn 0.55%–0.90%, P ≤ 0.025%, S ≤ 0.025%, Cr 0.85%–1.25%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass. The production method includes: converter smelting, LF refining, continuous casting, billet heating furnace heating, and round steel rolling.

[0006] The re-blown converter smelting process ensures the dryness of the smelting materials to prevent moisture from entering the steel and causing white spots; [P] < 0.012%, [S] < 0.030%; the converter bottom blowing uses nitrogen and argon switching to ensure carbon removal in one go and avoid post-blowing; the final carbon control is > 0.10% to reduce the oxidizability of the molten steel and reduce decarburization; the final [P] ≤ 0.020%; slag blocking is used during tapping, and argon is blown throughout the tapping process;

[0007] During the refining of white slag, the molten steel must not be exposed at any point. The calcium wire feed is used to deform inclusions to prevent nozzle clogging. No slag is added after the calcium wire feed to purify the molten steel. The soft blowing time is ≥10 minutes to ensure that inclusions float to the surface.

[0008] Strictly implement the tundish baking system to ensure the baking time and temperature; the molten steel outside the long nozzle must not be exposed to prevent secondary oxidation; ensure the crystallizer is centered, use weak cooling for the secondary cooling, and maintain a constant casting speed; use electromagnetic stirring to improve the surface quality of the billet.

[0009] The billet heating temperature is 1080~1120℃, with an allowable temperature difference of ≤50℃. The total heating time is controlled at 2 hours, and the initial rolling temperature is 1030~1050℃. Overheating, burning, and decarburization should be prevented. The temperature should be increased slowly to ensure uniform billet heating temperature and reduce temperature difference.

[0010] Furthermore, the rolled product specification is φ120mm.

[0011] Furthermore, the heat treatment process is normalizing at 915–935℃.

[0012] Furthermore, the carburized gear steel for automobiles meets the following requirements: its longitudinal mechanical properties can reach R... m ≥835MPa, R eL ≥540MPa, A≥10.0%, Z≥40%, impact energy KV2≥47J, austenite grain size of steel≥8 grade, and no cracks, scabs, folds or inclusions on the surface of the steel.

[0013] Furthermore, its chemical composition by mass percentage includes: C 0.15%, Si 0.26%, Mn 0.78%, P 0.015%, S 0.0045%, Cr 0.85%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

[0014] Furthermore, its chemical composition by mass percentage includes: C 0.17%, Si 0.28%, Mn 0.76%, P 0.016%, S 0.0053%, Cr 0.87%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

[0015] Furthermore, the chemical composition by mass percentage includes: C 0.16%, Si 0.25%, Mn 0.79%, P 0.013%, S 0.0058%, Cr 0.79%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0017] The steel of this invention has the advantages of high strength and high hardness;

[0018] This invention optimizes the preparation process by replacing the electric furnace with a converter, reducing preparation costs, and improving material cleanliness through degassing and inclusion removal, thereby significantly enhancing the strength, toughness, and lifespan of the steel. The preparation method is simple, energy-efficient, and suitable for current industrial equipment levels.

[0019] The carburized gear steel for automobiles produced using the chemical composition and process flow of this invention meets the following performance requirements: longitudinal mechanical properties can reach R... m ≥835MPa, R eL ≥540MPa, A≥10.0%, Z≥40%, impact energy KV2≥47J, austenite grain size of steel≥8 grade, and no cracks, scabs, folds or inclusions on the surface of the steel. Detailed Implementation

[0020] Table 1 shows the chemical composition of three embodiments of the present invention, and Tables 2, 3 and 4 further illustrate the present invention.

[0021] Table 1. Chemical composition (mass percentage) of various examples of carburized gear steel for automobiles.

[0022] Example C Si Mn P S Cr Example 1 0.15 0.26 0.78 0.015 0.0045 0.85 Example 2 0.17 0.28 0.76 0.016 0.0053 0.87 Example 3 0.16 0.25 0.79 0.013 0.0058 0.79

[0023] Table 2 Mechanical property indicators of various examples of carburized gear steel for automobiles

[0024]

[0025] Table 3. Non-metallic inclusions and austenite grain size in various examples of carburized gear steel for automobiles.

[0026]

[0027] Table 4. Hardness values ​​of various examples of carburized gear steel for automobiles.

[0028]

[0029] As can be seen from Tables 1-4, the carburized gear steel for automobiles of the present invention has excellent mechanical properties and a yield ratio of less than 0.7.

[0030] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for producing carburized gear steel for automobiles, characterized in that, Its chemical composition by mass percentage includes: C 0.15%, Si 0.26%, Mn 0.78%, P 0.015%, S 0.0045%, Cr 0.85%, with the remainder being Fe and unavoidable impurities, totaling 100% by mass. Its production methods are: converter smelting, LF refining, continuous casting, billet heating furnace heating, and round steel rolling; wherein: The converter smelting process is repeated to ensure the dryness of the smelting materials and prevent moisture from entering the steel and causing white spots; [P] < 0.012% and [S] < 0.030% are required; the converter bottom blowing is switched between nitrogen and argon to ensure that the carbon is pulled out in one go and to avoid subsequent blowing; the final carbon control is > 0.10% to reduce the oxidizability of the molten steel and reduce decarburization; the final [P] ≤ 0.020% is required; slag is blocked during tapping and argon is blown throughout the tapping process; During the refining of white slag, the molten steel must not be exposed at any point. The calcium wire feed is used to deform inclusions to prevent nozzle clogging. No slag is added after the calcium wire feed to purify the molten steel. The soft blowing time is ≥10 minutes to ensure that inclusions float to the surface. Strictly implement the tundish baking system to ensure the baking time and temperature; the molten steel outside the long nozzle must not be exposed to prevent secondary oxidation; ensure the crystallizer is centered, use weak cooling for the secondary cooling, and maintain a constant casting speed; use electromagnetic stirring to improve the surface quality of the billet. The billet heating temperature is 1080~1120℃, the allowable temperature difference is ≤50℃, the total heating time is controlled at 2h, the initial rolling temperature is 1030~1050℃, to prevent overheating, burning and decarburization, the temperature is increased slowly, to ensure uniform billet heating temperature and reduce temperature difference; The heat treatment process is normalizing at 915–935℃; The carburized gear steel for automobiles has a grain size of 9.5 and a yield ratio of less than 0.

7.

2. The method for producing carburized gear steel for automobiles according to claim 1, characterized in that, The rolled product has a diameter of φ120mm.

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