Cold rolling machining process of steel coil for gearbox planetary gear carrier

Abstract

The invention relates to a cold rolling machining process of a steel coil for a gearbox planetary gear carrier. The cold rolling machining process comprises the following steps that a hot rolled steel coil is selected for primary longitudinal shearing and splitting; pickling; performing primary rolling; performing isothermal spheroidizing annealing; rough rolling; recrystallizing and annealing; finish rolling; secondary longitudinal shearing and splitting; and packaging and warehousing. The method has the beneficial effects that the hot rolled steel coil is firstly subjected to stripping, acid pickling and rolling and then is subjected to spheroidizing annealing, so that grains in the steel coil are extruded to have certain grain boundary energy, through subsequent isothermal spheroidizing annealing, the internal structure of the steel coil is well spheroidized, equiaxed grains are generated, and through secondary rolling, the unconventional 170-200 HB hardness requirement of 16MnCr5 is met; and after recrystallization annealing, small rolling reduction finish rolling is carried out subsequently, so that the excellent mechanical property, high-precision tolerance size and smooth surface state are guaranteed, and the quality of produced products is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of strip steel production and processing technology, and in particular to a cold rolling process for steel coils used in planetary gear carriers of gearboxes. Background Technology

[0002] The current mainstream 9AT transmissions (such as ZF 9HP and Mercedes-Benz 9G-TRONIC) have achieved multi-gear transmission ratio optimization, but the gear carrier material still faces the challenge of balancing strength and lightweight. Its hardness cannot be designed according to conventional cold rolling. Otherwise, during fine blanking, the gear tooth tip part will suffer from abnormal wear or even tooth breakage due to the excessively large blanking corner surface and the small tooth tip contact surface, resulting in insufficient load-bearing capacity. The subsequent heat treatment process will also cause a series of problems such as large changes in hole position accuracy, affecting assembly. Summary of the Invention

[0003] The purpose of this invention is to provide a cold rolling process for steel coils used in planetary gear carriers of gearboxes, thereby solving the aforementioned problems in the prior art.

[0004] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A cold rolling process for a steel coil used in a gearbox planetary gear carrier includes the following steps: Step 1: Prepare raw materials: Select hot-rolled steel coils of appropriate grade; Step 2, Initial slitting: The hot-rolled steel coil is slitting to obtain slitting narrow strip steel coils of the required width; Step 3, pickling: Pickling the slit narrow strip steel coils to obtain pickled steel coils; Step 4, Preliminary rolling: The pickled steel coil is repeatedly rolled to obtain a preliminary rolled steel coil; Step 5, Isothermal spheroidizing annealing: The initial rolled steel coil is subjected to isothermal spheroidizing annealing to obtain isothermal spheroidized annealed steel coil; Step 6, Rough rolling: The isothermal spheroidizing annealed steel coil is repeatedly rolled to obtain a rough rolled steel coil; Step 7, recrystallization annealing: The double-rolled steel coil is recrystallized and annealed to obtain recrystallized annealed steel coil; Step 8, Finish rolling: Roll the recrystallized annealed steel coil to obtain a finish rolled steel coil; Step 9, Secondary slitting: The tertiary rolled steel coil is slitting to obtain the finished steel coil; Step 10, Packaging and Warehousing: Pack the finished steel coils.

[0005] The beneficial effects of this invention are as follows: Hot-rolled steel coils are first slitted, pickled, rolled, and then spheroidized annealed. This process compresses the internal grains of the coil, giving them a certain grain boundary energy. Subsequent isothermal spheroidizing annealing further spheroidizes the internal structure of the coil, generating equiaxed grains. After a second rolling process, the unconventional hardness requirement of 170-200 HB for 16MnCr5 is met (the typical hardness requirement for cold-rolled 16MnCr5 is ≤160 HB). Subsequent recrystallization annealing followed by low-reduction precision rolling ensures excellent mechanical properties, high-precision dimensional tolerances, and a smooth surface finish, resulting in a significant improvement in the quality of the produced products.

[0006] Based on the above technical solution, the present invention can be further improved as follows.

[0007] Furthermore, the primary rolling and roughing rolling are repeatedly performed on the AGC reversible rolling mill production line; the finishing rolling is performed on the finishing mill.

[0008] The further beneficial effects of adopting the above are: increasing the rolling reduction during the initial rolling process causes the steel coil to be subjected to greater compression, resulting in partial grain breakage and higher grain boundary dislocation energy. This reduces the required AC1 eutectoid transformation temperature, and subsequently allows for a reduction in the isothermal spheroidizing annealing temperature, thereby reducing annealing production costs while ensuring that the finished product performance is not affected. Attached Figure Description

[0009] Figure 1 This is a line graph showing the spheroidizing annealing process of a cold rolling process for a steel coil used in a planetary gear carrier of a gearbox according to the present invention. Figure 2 This is a line graph showing the recrystallization annealing process of a cold-rolling process for a planetary gear carrier steel coil of a gearbox according to the present invention. Detailed Implementation

[0010] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0011] Example 1 like Figure 1 and Figure 2 As shown, a cold rolling process for a steel coil used in a gearbox planetary gear carrier includes the following steps: Step 1: Prepare raw materials: Select hot-rolled steel coils of appropriate grade; Step 2, Initial slitting: The hot-rolled steel coil is slitting to obtain slitting narrow strip steel coils of the required width; Step 3, pickling: Pickling the slit narrow strip steel coils to obtain pickled steel coils; Step 4, Preliminary rolling: The pickled steel coil is repeatedly rolled to obtain a preliminary rolled steel coil; Step 5, Isothermal spheroidizing annealing: The initial rolled steel coil is subjected to isothermal spheroidizing annealing to obtain isothermal spheroidized annealed steel coil; Step 6, Rough rolling: The isothermal spheroidizing annealed steel coil is repeatedly rolled to obtain a rough rolled steel coil; Step 7, recrystallization annealing: The double-rolled steel coil is recrystallized and annealed to obtain recrystallized annealed steel coil; Step 8, Finish rolling: Roll the recrystallized annealed steel coil to obtain a finish rolled steel coil; Step 9, Secondary slitting: The tertiary rolled steel coil is slitting to obtain the finished steel coil; Step 10, Packaging and Warehousing: Pack the finished steel coils.

[0012] In specific implementation, hot-rolled steel coils with grade 16MnCr5 are selected in step 1.

[0013] The process involves first slitting, pickling, and rolling hot-rolled steel coils, followed by spheroidizing annealing. This process compresses the grains within the coil, giving them sufficient grain boundary energy. Subsequent isothermal spheroidizing annealing further spheroidizes the internal microstructure, generating equiaxed grains. A second rolling process then meets the unconventional hardness requirement of 170-200 HB for 16MnCr5 (the typical hardness requirement for cold-rolled 16MnCr5 is ≤160 HB). Subsequent recrystallization annealing and low-reduction precision rolling ensure excellent mechanical properties, high-precision dimensional tolerances, and a smooth surface finish, significantly improving the quality of the produced product.

[0014] Based on the process characteristics of cold-rolled steel strip for the planetary gear carrier of the 9AT transmission, after pickling, the steel is first rolled to induce extrusion deformation energy within the steel, causing grain distortion. Sub-temperature isothermal spheroidizing annealing then yields excellent equiaxed grains and a spheroidized microstructure, providing excellent adaptability for subsequent complex processing techniques such as fine blanking, carbonitriding, and localized high-frequency quenching heat treatment at the gear tips. Unlike the traditional 16MnCr5 cold-rolling production process, this special cold-rolling process, involving three rolling passes and two annealing processes, ensures stable quality control and meets customers' specific requirements for hardness, quenching deformation, and other aspects.

[0015] Example 2 This embodiment is a further improvement on embodiment 1, as detailed below: The isothermal spheroidizing annealing process specifically includes: transferring the slit narrow strip steel coil to an annealing furnace for annealing; firstly, heating the annealing furnace to 200℃ at full speed; then, after 4 hours, heating the annealing furnace to 420℃; after 6 hours, heating the annealing furnace to 715℃ and holding for 2 hours; after 1 hour, heating the annealing furnace to 735℃ and holding for 10 hours; rapidly cooling in the furnace to 685℃ and holding for 12 hours; after the holding period, cooling in the furnace to 650℃; air cooling the annealing furnace to reduce the temperature to 320℃; after the annealing furnace temperature drops to 320℃, water cooling the annealing furnace to reduce the temperature to 80℃ before removing the coil from the furnace, thus obtaining the isothermal spheroidized annealed steel coil.

[0016] Recrystallization annealing includes the following steps: the rough-rolled steel coil is transferred to an annealing furnace for recrystallization annealing; first, the annealing furnace is heated to 200℃ at full speed; then, after 4 hours, the annealing furnace is heated to 420℃ and held for 2 hours; after 1 hour, the annealing furnace is heated to 450℃ and held for 12 hours; after the holding period, the annealing furnace is air-cooled to reduce the furnace temperature to 320℃; after the furnace temperature drops to 320℃, the furnace is water-cooled to reduce the furnace temperature to 80℃ before the coil is removed from the furnace, thus obtaining the recrystallized annealed steel coil.

[0017] The annealing furnace is a bell-type annealing furnace.

[0018] Hot-rolled steel coils, slit narrow strip steel coils, pickled steel coils, primary rolled steel coils, isothermal spheroidizing annealed steel coils, rough rolled steel coils, recrystallized annealed steel coils, finish rolled steel coils, and finished steel coils are all transported by overhead cranes.

[0019] Example 3 This embodiment is a further improvement on embodiment 1, as detailed below: Its characteristic is that the initial rolling and rough rolling are repeatedly performed on the AGC reversible rolling mill production line; the finishing rolling is performed on the finishing mill.

[0020] Increasing the rolling reduction during the initial rolling process causes the steel coil to be subjected to greater compression, resulting in the breakage of some grains and higher grain boundary dislocation energy. This reduces the required AC1 eutectoid transformation temperature, which in turn allows for a reduction in the isothermal spheroidizing annealing temperature. This ensures that the finished product performance is not affected while reducing annealing production costs.

[0021] During rough rolling, the increased extrusion deformation reduces the isothermal spheroidizing annealing time, resulting in a slight increase in hardness.

[0022] The initial rolling process reduces the thickness of the pickled steel coil from 7.5mm to 6.0mm, resulting in an initial rolled steel coil. The rough rolling process reduces the thickness of the isothermal spheroidizing annealed steel coil from 6.0mm to 4.86±0.03mm, resulting in a rough rolled steel coil. The finish rolling process reduces the thickness of the recrystallized annealed steel coil from 4.86±0.03mm to 4.8±0.03mm, resulting in a finish rolled steel coil. In practice, the initial rolling process can be modified by increasing the rolling amount from the original design of rolling from 7.5mm to 6.0mm, changing it to rolling from 7.5mm to 5.3mm. Similarly, the rough rolling process can be modified by decreasing the rolling amount from the original design of rolling from 6.0mm to 4.86mm, changing it to rolling from 5.3mm to 4.86mm. This process can meet the non-standard requirements for hardness, microstructure, and mechanical properties of 170-200HB. Example 4 This embodiment is a further improvement on any one of embodiments 1 to 3, as detailed below: Pickling of slit narrow strip steel coils is carried out on a pickling production line, which is equipped with two pickling tanks, one passivation tank, and one neutralization tank in sequence. The pickling concentration in the two pickling tanks is set to 18% to 22%, the acid level in the pickling tank is 380mm to 420mm, and the acid temperature is 45℃ to 60℃. The pH value of the neutralization tank is 11 to 13. The pH value of the passivation tank is 7 to 8, and the temperature of the passivation tank is 40℃ to 50℃. The cleaning speed of the pickling production line is 10m / min to 15m / min. Specific Implementation Example 1 The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A cold rolling process for steel coils used in planetary gear carriers of gearboxes, characterized in that, Includes the following steps: Step 1: Prepare raw materials: Select hot-rolled steel coils of appropriate grade; Step 2, Initial slitting: The hot-rolled steel coil is slitting to obtain slitting narrow strip steel coils of the required width; Step 3, pickling: Pickling the slit narrow strip steel coils to obtain pickled steel coils; Step 4, Preliminary rolling: The pickled steel coil is repeatedly rolled to obtain a preliminary rolled steel coil; Step 5, Isothermal spheroidizing annealing: The initial rolled steel coil is subjected to isothermal spheroidizing annealing to obtain isothermal spheroidized annealed steel coil; Step 6, Rough rolling: The isothermal spheroidizing annealed steel coil is repeatedly rolled to obtain a rough rolled steel coil; Step 7, recrystallization annealing: The double-rolled steel coil is recrystallized and annealed to obtain recrystallized annealed steel coil; Step 8, Finish rolling: Roll the recrystallized annealed steel coil to obtain a finish rolled steel coil; Step 9, Secondary slitting: The tertiary rolled steel coil is slitting to obtain the finished steel coil; Step 10, Packaging and Warehousing: Pack the finished steel coils.

2. The cold rolling process for the steel coil used in the planetary gear carrier of the gearbox according to claim 1, characterized in that, The isothermal spheroidizing annealing step specifically includes: transferring the slit narrow strip steel coil to an annealing furnace for annealing; firstly, heating the annealing furnace to 200°C at full speed; then, heating the annealing furnace to 420°C after 4 hours; heating the annealing furnace to 715°C after 6 hours and holding it at that temperature for 2 hours; heating the annealing furnace to 735°C after 1 hour and holding it at that temperature for 10 hours; rapidly cooling it in the furnace to 685°C and holding it at that temperature for 12 hours; after the holding period, cooling it in the furnace to 650°C; air-cooling the annealing furnace until the temperature drops to 320°C; after the annealing furnace temperature drops to 320°C, water-cooling the annealing furnace until the temperature drops to 80°C before removing it from the furnace, thus obtaining the isothermal spheroidized annealed steel coil.

3. The cold rolling process for the steel coil used in the planetary gear carrier of the gearbox according to claim 2, characterized in that, The recrystallization annealing includes the following steps: transferring the rough-rolled steel coil to an annealing furnace for recrystallization annealing; first, heating the annealing furnace to 200°C at full speed; then, after 4 hours, heating the annealing furnace to 420°C and holding it at that temperature for 2 hours; after 1 hour, heating the annealing furnace to 450°C and holding it at that temperature for 12 hours; after the holding period, air cooling is applied to the annealing furnace to reduce the furnace temperature to 320°C; after the furnace temperature drops to 320°C, water cooling is applied to the annealing furnace to reduce the furnace temperature to 80°C before removing the coil from the furnace, thus obtaining the recrystallized annealed steel coil.

4. The cold rolling process for the steel coil used in the planetary gear carrier of the gearbox according to claim 3, characterized in that, The annealing furnace is a bell-type annealing furnace.

5. The cold rolling process for the steel coil used in the planetary gear carrier of the gearbox according to claim 1, characterized in that, The initial slitting is performed on a slitting machine; the secondary slitting is performed on a small slitting machine.

6. The cold rolling process for the steel coil used in the planetary gear carrier of the gearbox according to claim 1, characterized in that, The hot-rolled steel coil, the slitting narrow strip steel coil, the pickled steel coil, the primary rolled steel coil, the isothermal spheroidizing annealed steel coil, the rough rolled steel coil, the recrystallization annealed steel coil, the finish rolled steel coil, and the finished steel coil are all transported by a gantry crane.

7. The cold rolling process for the steel coil used in the planetary gear carrier of the gearbox according to claim 1, characterized in that, The initial rolling and rough rolling are repeatedly performed on the AGC reversible rolling mill production line; the finishing rolling is performed on the finishing mill.

8. The cold rolling process for the steel coil used in the planetary gear carrier of the gearbox according to claim 7, characterized in that, The initial rolling process rolls the pickled steel coil from 7.5 mm to 6.0 mm to obtain the initial rolled steel coil; the rough rolling process rolls the isothermal spheroidizing annealed steel coil from 6.0 mm to 4.86 ± 0.03 mm to obtain the rough rolled steel coil; the finish rolling process rolls the recrystallization annealed steel coil from 4.86 ± 0.03 mm to 4.8 ± 0.03 mm to obtain the finish rolled steel coil.

9. The cold rolling process for the steel coil used in the planetary gear carrier of the gearbox according to claim 1, characterized in that, The pickling of the slit narrow strip steel coils is carried out on a pickling production line, which is equipped with two pickling tanks, one passivation tank, and one neutralization tank in sequence. The pickling concentration in the two pickling tanks is set to 18% to 22%, the acid level in the pickling tanks is 380mm to 420mm, and the acid temperature is 45℃ to 60℃. The pH value of the neutralization tank is 11 to 13. The pH value of the passivation tank is 7 to 8, and the temperature of the passivation tank is 40℃ to 50℃. The cleaning speed of the pickling production line is 10m / min to 15m / min.

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