CrMo series gear steel production method

Abstract

The invention discloses a production method of CrMo gear steel, which comprises the following steps of: controlling the superheat degree of tundish molten steel in a continuous casting process, a crystallizer electromagnetic stirring process, a tail end electromagnetic stirring process, the pulling speed and the specific water flow of secondary cooling water, controlling the heating temperature of a heating section and optimizing a rolling process; c element segregation of round steel and the size and the length-width ratio of an ingot segregation frame are reduced, and the deformation stability of the gear after heating is improved. According to the method, center segregation of the gear steel casting blank can be effectively controlled, the component uniformity on the cross section of the gear steel rectangular blank is improved, and the internal quality of the casting blank is improved.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, and in particular to a method for producing CrMo series gear steel. Background Art

[0002] With the rapid development of the automobile industry, the market demand for vehicle gears is increasing, and gear transmission is gradually transforming and upgrading to a simpler and lighter structure with high speed, low noise, high efficiency, high precision and long life. CrMo gear steel has stable hardenability, and the processed gears can withstand huge alternating loads and impact loads. It has good strength and toughness, wear resistance, small deformation, high precision and low noise. Therefore, CrMo gear steel has been widely used in the field of heavy-duty gears due to its excellent comprehensive performance. However, in recent years, automobiles have gradually tightened their requirements for operating noise, vibration, fatigue strength, etc., and the performance indicators of gear steel are also getting higher and higher.

[0003] The heat treatment deformation of carburized gears will affect the accuracy, noise and service life of the gears. Even if the gears are deformed after carburizing heat treatment and then grinding, the accuracy level of the gears will still be affected. There are many factors affecting the deformation of carburizing heat treatment. Relevant experiments have shown that the raw material of the gear is one of the main factors affecting the deformation of the gear during heat treatment. In particular, the composition of the raw material of the gear must be strictly controlled to ensure the uniformity and consistency of the composition, otherwise the gears are very likely to deform during the heat treatment process.

[0004] However, the currently produced CrMo gear round steel cannot fully meet the requirements for detecting C element deviation along 1 / 2R circumference, C element deviation of the entire cross section, and round steel ingot segregation frame. Summary of the invention

[0005] The purpose of the present invention is to provide a method for producing CrMo gear steel in order to overcome the defects of the prior art.

[0006] The present invention solves the technical problem by adopting the following technical solutions.

[0007] The embodiment of the present invention provides a CrMo series gear steel production method, which includes: controlling the superheat of molten steel in the tundish during the continuous casting process, the electromagnetic stirring process of the crystallizer and the end electromagnetic stirring process, the drawing speed and the water volume ratio of the secondary cooling water, and controlling the heating temperature of the heating section and optimizing the rolling process, thereby reducing the segregation of the C element in the round steel and the size and aspect ratio of the ingot segregation frame, and improving the post-thermal deformation stability of the gear.

[0008] In some embodiments of the present invention, the chemical composition of the CrMo gear steel is, by mass percentage, C 0.12%-0.25%, Si 0.15%-0.37%, Mn 0.40%-0.90%, Cr 0.40%-1.25%, Mo 0.15%-0.55%, and the remainder is iron and unavoidable impurities.

[0009] In some embodiments of the present invention, the superheat of the molten steel in the tundish during the continuous casting process is controlled at 15-35°C.

[0010] In some embodiments of the present invention, the electromagnetic stirring process of the crystallizer is to close the electromagnetic stirring, and the end electromagnetic stirring process is 200±20A / 3.5Hz.

[0011] In some embodiments of the present invention, the pulling speed is controlled at 0.65±0.05 m / min.

[0012] In some embodiments of the present invention, the secondary cooling water volume is controlled at 0.36±0.02 L / kg.

[0013] In some embodiments of the present invention, the ratio of water volume on the narrow side to water volume on the wide side is controlled to be ≥1.5:1.

[0014] In some embodiments of the present invention, the temperature of the heating and soaking section is controlled above 1150°C.

[0015] In some embodiments of the present invention, the ingot used is a 320*425 mm rectangular ingot, and the ingot is rolled using a segregation frame to improve the process.

[0016] In some embodiments of the present invention, the C element segregation at 1 / 2R of the produced round steel is within 0.01%, the C element segregation of the entire cross-section is within 0.015%, the ingot segregation frame size is within 1 / 2R, the ingot segregation frame aspect ratio is within 1.10, and the aspect ratio of the segregation frame of the equiaxed crystal zone of the ingot is reduced to 1.45-1.55.

[0017] The present invention has the following beneficial effects:

[0018] The present invention provides a method for producing CrMo series gear steel. By controlling the superheat of molten steel in the tundish during continuous casting, the electromagnetic stirring process of the crystallizer and the electromagnetic stirring process at the end, the drawing speed and the water volume ratio of the secondary cooling water, and controlling the heating temperature of the heating section and optimizing the rolling process, the C element segregation of the round steel and the size and aspect ratio of the ingot segregation frame are reduced, and the post-heat deformation stability of the gear is improved. The present invention effectively controls the central segregation of the gear steel ingot, reduces the ratio of equiaxed crystals, reduces element segregation, and effectively guarantees the internal quality of the ingot. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 A round steel ingot-type segregation frame (φ100mm20CrMoH) prepared in Comparative Example 1;

[0021] Figure 2 The round steel ingot type segregation frame (φ100mm20CrMoH) prepared in Example 1;

[0022] Figure 3 The equiaxed crystal region morphology of the ingot prepared in Comparative Example 1 (320*325mm ingot);

[0023] Figure 4 This is the equiaxed crystal zone morphology of the ingot prepared in Example 1 (320*325mm ingot). DETAILED DESCRIPTION

[0024] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0025] The following is a detailed description of a method for producing CrMo gear steel provided in an embodiment of the present invention.

[0026] The uniformity of C element in round steel is affected by the entire smelting and rolling process. It is necessary to conduct tests based on the characteristics of the steel grade and select a more appropriate production process. The ingot segregation frame of round steel is mainly inherited from the morphology of the equiaxed crystal zone segregation frame of the original ingot. When rolling with 320*425mm continuous casting ingot, the ingot size aspect ratio is about 1.33. Affected by electromagnetic stirring, pulling speed, cooling speed and other factors during the continuous casting process, the aspect ratio of the ingot equiaxed crystal zone segregation frame is about 1.55-1.70, and the length of the equiaxed crystal zone is often above 212.5mm (more than half of the ingot length). Under conventional rolling technology, the aspect ratio of the ingot segregation frame is improved after rolling into round steel, but the result is still poor, usually in the range of 1.15-1.40, and the ingot segregation frame also exceeds 1 / 2R.

[0027] The embodiment of the present invention provides a method for producing CrMo gear steel, wherein the chemical composition of the CrMo gear steel is as follows by mass percentage: C 0.12%-0.25%, Si 0.15%-0.37%, Mn 0.40%-0.90%, Cr 0.40%-1.25%, Mo 0.15%-0.55%, and the remainder is iron and unavoidable impurities. The ingot used is a 320*425mm rectangular ingot. By optimizing the continuous casting and rolling process, the uniformity of the C element of the round steel and the size and aspect ratio of the ingot segregation frame are reduced, thereby improving the post-thermal deformation stability of the gear. The specific process is as follows:

[0028] Continuous casting: The superheat of molten steel in the tundish is controlled at 15-35℃, the electromagnetic stirring process of the crystallizer is to close the electromagnetic stirring, the end electromagnetic stirring process is 200±20A / 3.5Hz, the casting speed is controlled at 0.65±0.05m / min, the secondary cooling water ratio is controlled at 0.36±0.02L / kg, and the water volume on the narrow side: the water volume on the wide side is controlled to be ≥1.5:1.

[0029] The continuous casting process can reduce the equiaxed crystal nucleation points by eliminating the electromagnetic stirring of the crystallizer, thereby significantly reducing the range of the equiaxed crystal zone, and reducing the equiaxed crystal zone to less than 1 / 2 of the billet size. The end electromagnetic stirring process adopts 200±20A / 3.5Hz, which can reduce the positive segregation of C element in the core of the billet, and will not cause serious negative segregation of C element in the core due to excessive stirring current, thereby improving the uniformity of C element. The continuous casting process uses a pulling speed of 0.65±0.05m / min, which reduces the equiaxed crystal zone while ensuring the quality of the billet. Since increasing the water ratio of the secondary cooling water can reduce the equiaxed crystal zone, the secondary cooling water process uses a water ratio of 0.36±0.02L / kg. This higher water ratio is beneficial to further reduce the equiaxed crystal zone on the one hand, and also refines the secondary dendrite spacing of the columnar crystal, improving the composition segregation of the billet. In addition, the water volume on the narrow side and the water volume on the wide side of the secondary cooling water are controlled at a ratio of ≥1.5:1, so that the equiaxed crystals on the narrow side are reduced more than those on the wide side, thereby improving the length-to-width ratio of the segregation frame of the equiaxed crystal zone of the ingot. By this method, the length-to-width ratio of the segregation frame of the equiaxed crystal zone of the ingot can be reduced to 1.45-1.55.

[0030] Heating: The temperature of the heating and soaking section is controlled at above 1150°C, and further, the temperature of the heating and soaking section is controlled at 1150-1260°C. Heating to high temperature is used to improve the deformation ability of the casting billet during rolling.

[0031] Rolling: The rolling process uses the segregation frame improvement process to roll the cast billet to improve the aspect ratio of the round steel ingot segregation frame to within 1.10. The segregation frame improvement process controls the aspect ratio of the ingot segregation frame by reasonably allocating the reduction amount and rolling speed of each pass of the two-roll reversible rolling mill on the basis of the original rolling process. For details, see CN 118635823 A "A rolling method for manufacturing gear round steel with large-section rectangular billets".

[0032] The present invention will be further described below in conjunction with the embodiments.

[0033] The embodiment of the present invention provides a method for producing CrMo series gear steel, comprising the following steps:

[0034] The chemical composition of CrMo gear steel is as follows by mass percentage: C 0.12%-0.25%, Si 0.15%-0.37%, Mn 0.40%-0.90%, Cr 0.40%-1.25%, Mo 0.15%-0.55%, and the balance is iron and unavoidable impurities. The billet used is a 320*425mm rectangular billet, and the specific process is as follows:

[0035] Continuous casting: The superheat of molten steel in the tundish is controlled at 15-35℃, the electromagnetic stirring process of the crystallizer is to close the electromagnetic stirring, the end electromagnetic stirring process is 200±20A / 3.5Hz, the casting speed is controlled at 0.65±0.05m / min, the secondary cooling water ratio is controlled at 0.36±0.02L / kg, and the water volume on the narrow side: the water volume on the wide side is controlled to be ≥1.5:1.

[0036] Heating: The temperature of the heating and soaking section is controlled at above 1150°C, and further, the temperature of the heating and soaking section is controlled at 1150-1260°C. Heating to high temperature is used to improve the deformation ability of the casting billet during rolling.

[0037] Rolling: The rolling process uses the segregation frame improvement process to roll the cast billet to improve the aspect ratio of the round steel ingot segregation frame to within 1.10. The segregation frame improvement process controls the aspect ratio of the ingot segregation frame by reasonably allocating the reduction amount and rolling speed of each pass of the two-roll reversible rolling mill on the basis of the original rolling process. For details, see CN 118635823 A "A rolling method for manufacturing gear round steel with large-section rectangular billets".

[0038] The method for detecting the deviation of the C element along the 1 / 2R circumference of the CrMo gear round steel in the following embodiments and comparative examples is: take 6 samples evenly at 1 / 2R of the round steel, detect the C element content and take the difference between the maximum and minimum values. The method for detecting the deviation of the C element in the full cross section is: take 6 samples each at the near surface and 1 / 2R of the round steel, and take 1 sample at the center, detect the C element content and take the difference between the maximum and minimum values.

[0039] Example 1 Rolling φ100mm 20CrMoH round steel

[0040] Continuous casting: control the superheat of molten steel in the tundish at 25°C, the electromagnetic stirring process of the crystallizer is to close the electromagnetic stirring, the end electromagnetic stirring process is 200±20A / 3.5Hz, the casting speed is 0.65±0.05m / min, and the secondary cooling water process is 0.36±0.02L / kg water volume (narrow surface water volume: wide surface water volume = 1.5:1).

[0041] Heating: The temperature of the heating and soaking section is controlled at 1180°C. Heating to high temperature is used to improve the deformation ability of the billet during rolling.

[0042] Rolling: The rolling process uses the segregation frame improvement process to roll the ingot to improve the length-to-width ratio of the round ingot segregation frame to within 1.10.

[0043] Example 2 Rolling φ130mm 22CrMoH round steel

[0044] Continuous casting: the superheat of molten steel in the tundish is 30°C, the electromagnetic stirring process of the crystallizer is to close the electromagnetic stirring, the end electromagnetic stirring process is 200±20A / 3.5Hz, the casting speed is 0.65±0.05m / min, and the secondary cooling water process is 0.36±0.02L / kg water volume (narrow surface water volume: wide surface water volume = 2:1).

[0045] Heating: The temperature of the heating and soaking section is controlled at 1200℃. Heating to high temperature is used to improve the deformation ability of the billet rolling process and increase the life of the roll.

[0046] Rolling: The rolling process uses the segregation frame improvement process to roll the ingot to improve the length-to-width ratio of the round ingot segregation frame to within 1.10.

[0047] The following table shows the parameters and test results of the CrMo gear steel production method of the embodiment and comparative example.

[0048]

[0049] Combining the above table with Figure 1-4 It can be seen that the superheat of molten steel in the tundish, the electromagnetic stirring process of the crystallizer, the electromagnetic stirring process at the end, the pulling speed, the secondary cooling water process, and the rolling process have a significant impact on the C element segregation of the material and the round steel ingot segregation frame. The ingot-shaped segregation frame and the round steel ingot-shaped segregation frame produced by the process of the present invention are significantly reduced, the aspect ratio is also improved, and the C element segregation meets the requirements. However, the C element deviation detected along the 1 / 2R circumference of the CrMo series gear round steel produced by the solution provided in the comparative example, the full-section C element deviation, and the round steel ingot-shaped segregation frame cannot fully meet the requirements.

[0050] It can be seen that the embodiment of the present invention provides a CrMo series gear steel production method, which controls the superheat of the molten steel in the tundish, the electromagnetic stirring process of the crystallizer, the end electromagnetic stirring process, the pulling speed and the water ratio of the secondary cooling water in the continuous casting process, and optimizes the rolling process, so that the C element segregation at 1 / 2R of the round steel is within 0.01%, the C element segregation of the whole cross-section is within 0.015%, the ingot segregation frame size is within 1 / 2R, the ingot segregation frame aspect ratio is within 1.10, and the segregation frame aspect ratio of the equiaxed crystal zone of the ingot is reduced to 1.45-1.55. The gear prepared by the above-mentioned CrMo series gear steel has high post-thermal deformation stability and consistency, and the internal quality of the ingot is effectively guaranteed.

[0051] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for producing CrMo gear steel, characterized in that: It includes: By controlling the superheat of molten steel in the tundish, the electromagnetic stirring process of the crystallizer and the end electromagnetic stirring process, the pulling speed and the water ratio of the secondary cooling water during the continuous casting process, and controlling the heating temperature of the heating section and optimizing the rolling process, the C element segregation of the round steel and the ingot segregation frame size and aspect ratio are reduced, and the post-thermal deformation stability of the gear is improved.

2. The method for producing CrMo gear steel according to claim 1, characterized in that: The chemical composition of the CrMo gear steel is as follows by mass percentage: C 0.12%-0.25%, Si 0.15%-0.37%, Mn 0.40%-0.90%, Cr 0.40%-1.25%, Mo 0.15%-0.55%, and the balance is iron and unavoidable impurities.

3. The method for producing CrMo gear steel according to claim 1, characterized in that: The superheat of molten steel in the tundish during continuous casting is controlled at 15-35℃.

4. The method for producing CrMo gear steel according to claim 1, characterized in that: The electromagnetic stirring process of the crystallizer is to close the electromagnetic stirring, and the end electromagnetic stirring process is 200±20A / 3.5Hz.

5. The method for producing CrMo gear steel according to claim 1, characterized in that: The pulling speed is controlled at 0.65±0.05m / min.

6. The method for producing CrMo gear steel according to claim 1, characterized in that: The secondary cooling water volume ratio is controlled at 0.36±0.02L / kg.

7. The method for producing CrMo gear steel according to claim 6, characterized in that: Control the water volume on the narrow side: the water volume on the wide side ≥1.5:

1.

8. The method for producing CrMo gear steel according to claim 1, characterized in that: The temperature of the heating and soaking section is controlled above 1150°C.

9. The method for producing CrMo gear steel according to claim 1, characterized in that: The ingot used is a 320*425mm rectangular ingot, and the ingot is rolled using a segregation frame to improve the process.

10. The method for producing CrMo gear steel according to any one of claims 1 to 9, characterized in that: The C element segregation at 1 / 2R of the produced round steel is within 0.01%, the C element segregation in the whole cross section is within 0.015%, the ingot segregation frame size is within 1 / 2R, the ingot segregation frame aspect ratio is within 1.10, and the segregation frame aspect ratio of the ingot equiaxed crystal zone is reduced to 1.45-1.55.

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