A material and processing method suitable for cold stamping of flexible wheels

Abstract

This invention discloses a material and processing method suitable for cold-stamped flexible wheels, belonging to the field of metal materials and forming technology. The material of this invention has a tensile strength of 500-550 MPa, a yield strength of 320-380 MPa, an elongation after fracture of 35-38%, an r-value of 2.0-2.3, a {111}-faceted ferrite content of ≥70%, and a ferrite grain size of ≥9 grade. Based on traditional high-quality medium-carbon alloy steel, this invention reduces the C element content and increases the AlN content. Combined with strict continuous casting control processes and online spheroidizing annealing after hot rolling, cold rolling with large cumulative deformation, and recrystallization annealing at lower temperatures, it fully refines the ferrite grains and spheroidizes the cementite. It controls the ferrite to be mainly distributed with a {111}-faceted texture, maximizing the plasticity of the steel plate while improving the r-value and deep-drawing performance, thus enabling the material of this invention to meet the basic requirements for cold-stamping of flexible wheels.

Description

Technical Field

[0001] This invention relates to a material and processing method suitable for cold stamping of flexible wheels, belonging to the field of metal materials and forming technology. Background Technology

[0002] The flexible gear is a core component of harmonic gear transmission. It takes the form of a thin-walled cup or thin-walled cylinder, with a wall thickness typically less than 1 mm. It requires excellent wear resistance and fatigue performance, placing high demands on material purity and uniformity. Traditional flexible gear manufacturing commonly uses medium-carbon alloy steel such as 40CrNiMoA, forging round bars into flexible gear blanks, followed by repeated heat treatment and extensive cutting to achieve the final shape. The yield rate is far below 50%, resulting in significant material waste. Furthermore, it suffers from uneven microstructure and damaged metal flow lines, affecting service life. Newer flexible gears can use age-hardening stainless steel or high-entropy alloy steel plates, with properties controlled by heat treatment after cold stamping. This method offers high yield, intact flow lines, and a long service life, but the material cost is at least 2-3 times higher than that of medium-carbon alloy steel.

[0003] Cold stamping of flexible wheels offers significant advantages, but reducing material costs is a crucial issue. Medium-carbon alloy steel, due to its high carbon content, has poor formability, and even after thorough spheroidizing annealing, its cold stamping performance remains low. Among various cold plastic forming methods, cold stamping is used for thin sheets, where the local deformation during bending is very large. Compared to cold forging and cold extrusion, cold stamping requires not only high sheet plasticity but also high deep-drawing performance, i.e., a high r-value (plastic strain ratio, the ratio of strain in the width direction to strain in the thickness direction during a tensile test). It is generally believed that a steel sheet with an r-value greater than 1.0 possesses good stamping performance, and cold stamping flexible wheels require an r-value greater than 2.0. The r-value of medium-carbon alloy steel sheets after spheroidizing annealing generally barely reaches 1.0, which is still some distance from suitable for cold stamping. Therefore, a method is needed to increase the r-value of medium-carbon alloy steel sheets without significantly reducing their post-heat-treatment strength to meet the requirements of cold stamping.

[0004] Medium carbon alloy steel plates have high carbon content and poor plasticity, making it difficult to cold roll with large cumulative deformation, which in turn makes it difficult to control the texture of the steel plate. Therefore, there is an urgent need for a material and processing method that can reduce material costs, use medium carbon alloy steel as raw material, and is suitable for cold stamping forming of flexible wheels. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to obtain a medium carbon alloy steel material suitable for cold stamping of flexible wheels without significantly reducing strength.

[0006] Meanwhile, this invention provides a processing method for medium carbon alloy steel materials suitable for cold stamping forming flexible wheels.

[0007] Meanwhile, this invention provides an application of medium carbon alloy steel material suitable for cold stamping of flexible wheels.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for processing materials suitable for cold-stamped flexible wheels mainly includes the following steps: S01: Preparation of high-quality medium-carbon alloy steel; S02: The high-quality medium carbon alloy steel obtained in step S01 is hot rolled into thin plates and then coiled into steel coils. The final rolling temperature is 800~900℃, the coiling temperature is 670~680℃, and the coil is held at 660~670℃ for 2 hours. It is then cooled to 550℃ at a cooling rate of 5~10℃ / min and then air-cooled to room temperature. S03: After pickling, cold rolling is performed, with a cumulative total deformation of 60%~90%; S04: After cold rolling, the steel coil is opened and continuously heated to a temperature of 670~685℃, held for 5~10 minutes, cooled to 550℃ at a rate of 5~10℃ / min, and then air-cooled to room temperature.

[0009] Preferably, the high-quality medium-carbon alloy steel in step S01 has the following chemical composition by mass percentage: C: 0.32%~0.39%, Si: 0.17%~0.37%, Mn: 0.50%~0.80%, P: ≤0.015%, S: ≤0.015%, Cr: 0.60%~0.90%, Ni: 1.00~1.50%, Mo: 0.15%~0.25%, Al: 0.040%~0.060%, N: 0.020%~0.030%, with the balance being Fe and unavoidable impurities.

[0010] Preferably, the preparation method of high-quality medium-carbon alloy steel adopts the smelting process and billet quality control in the existing technology (Tian Zhiguo, Xu Ruijun. Research and development of alloy structural steel 40CrNiMo [C] Chinese Society for Metals. Proceedings of the 11th China Iron and Steel Annual Conference-S07. Automotive Steel. Technical and Quality Department of Hunan Valin Xiangtan Iron and Steel Co., Ltd.; 2017:163-165), and finally obtains high-quality medium-carbon alloy steel with appropriately reduced C element content through AlN strengthening.

[0011] Preferably, in step S01, the high-quality medium-carbon alloy steel is designed with the superheat controlled at ≤20℃ during continuous casting; the electromagnetic stirring current in the crystallizer is 200~300A, and the electromagnetic stirring current at the solidification end is 400~500A; combined with non-sinusoidal vibration and light pressing, the partial pressing amount between the crystallizer and the solidification end is 1.0~1.5mm / m, so as to minimize macroscopic segregation, ensure direct air cooling after final rolling, and the banded structure of the sample is ≤1.0 grade. After continuous casting, a slab is obtained with a rectangular cross section and a thickness of about 200-250mm.

[0012] Preferably, in step S02, the slab obtained after continuous casting (i.e., the high-quality medium carbon alloy steel obtained in step S01) is heated to 1150~1200℃, and the final rolling temperature is 800~900℃.

[0013] Preferably, in step S02, the thickness of the hot-rolled sheet is 3-5 mm, and after final rolling, it is cooled to the coiling temperature by spraying water. The coiled steel coil is kept at a controlled temperature in a heating furnace to room temperature to complete online spheroidizing annealing, which fully improves plasticity and facilitates obtaining a larger amount of cold rolling deformation.

[0014] Preferably, in step S03, the pickling process is as follows: the hot-rolled steel plate is passed through a hydrochloric acid aqueous solution with a concentration of 15%-20% and a temperature of 70-85℃ for a corrosion time of about 1-3 minutes.

[0015] Preferably, in step S03, the cold rolling process requires the use of a high-performance rolling lubricant with the following composition: 86.5%~93.4% base oil (preferably one or two of hydrocracked mineral oil and polyα-olefin) + 5%~10% oiliness agent (preferably one or two of methyl palmitate and oleic acid) + 1%~2% extreme pressure agent (preferably one or two of tricresyl phosphate and thiophosphate) + 0.5%~1% antioxidant (preferably one or two of 2,6-di-tert-butyl-p-cresol and alkylated diphenylamine) + 0.1%~0.5% rust inhibitor (preferably one or two of dodecenylsuccinic acid and petroleum sulfonic acid). The lubricant must ensure 100% coverage of the plate surface during rolling to prevent surface defects, achieve greater cold rolling deformation, and promote the development of a favorable texture. An intermediate annealing process with a protective atmosphere can be added during cold rolling, but the total cold rolling deformation after the final intermediate annealing pass should still not be less than 60%.

[0016] Preferably, in step S04, the process of continuous heating and controlled cooling to room temperature must be protected with ammonia decomposition gas (75% hydrogen + 25% nitrogen, which is a commonly used industrial gas with a pressure of 100~200 Pa) to avoid surface decarburization and promote the growth of {111} textured grains.

[0017] The applicable thickness of the finished steel plate obtained by the present invention is 0.5mm-2.0mm, preferably 0.5mm-1.0mm, and more preferably 0.5mm-0.8mm.

[0018] The steel plate finally obtained by this invention has a tensile strength of 500-550MPa, a yield strength of 320-380MPa, an elongation after fracture of 35-38%, an r-value of 2.0-2.3, a {111} textured ferrite content of ≥70%, and a ferrite grain size of ≥9.

[0019] The application of the material obtained by this invention in cold stamping forming flexible wheels.

[0020] A cold-stamped flexible wheel is prepared from the material of this invention.

[0021] Application of a cold-stamped flexible wheel in harmonic gears.

[0022] The present invention has the following beneficial effects: This invention, based on the composition of traditional medium-carbon alloy steel 40CrNiMoA, reduces the carbon content and increases the al and nitrogen content. Combined with controlled rolling and cooling processes, it reduces pearlite content and increases the amount of AlN precipitates, significantly improving the material's plasticity while maintaining minimal changes in strength. The hot-rolled AlN precipitates are fine and dispersed, with a large amount having a solution temperature exceeding 900℃. They remain undissolved during subsequent heat treatment, continuously ensuring grain refinement. Ultimately, the ferrite grains of the raw material are refined to grade 9 or higher, while also ensuring a similarly fine microstructure during the final quenching and tempering after flexible wheel forming.

[0023] The medium-carbon alloy steel of this invention achieves a strong {111} texture. The abundant AlN precipitation refines the grains, resulting in numerous ferrite grain boundaries. A rigorous heat treatment process following hot rolling enables online spheroidizing annealing of the steel sheet, improving formability and ensuring a large cumulative deformation during cold rolling. The lower-temperature recrystallization annealing after cold rolling causes a large number of {111} texture grains to nucleate and grow, suppressing the formation of other oriented grains, thus achieving excellent deep-drawing performance. Furthermore, the cold rolling deformation and recrystallization annealing produce a curing effect, further coarsening and spheroidizing the cementite, reducing strength while improving plasticity and cold formability.

[0024] Traditional medium-carbon alloy steels improve formability by controlling ferrite grain size and cementite morphology, but cannot achieve deep-drawing performance. This invention, while fully controlling these factors, also controls the texture of the ferrite matrix. Compared to traditional processes, by using ultra-fine hot-rolled grains + large-deformation cold rolling + low-temperature recrystallization annealing, the {111} surface texture ratio of the sheet is significantly increased, thereby significantly improving the r-value and cold-stamping performance of the steel sheet. This makes it possible to produce flexible wheels from low-cost medium-carbon alloy steel via cold stamping.

[0025] This invention achieves online spheroidizing annealing of medium carbon alloy steel after hot rolling by extending the holding time after coiling and controlling the cooling rate during the hot rolling process. The increase in process cost is minimal, but it makes large deformation cold rolling possible. Appropriately lowering the recrystallization annealing temperature after cold rolling ensures the growth of the {111} texture while also guaranteeing ferrite grain refinement and improved strength and toughness; simultaneously, it also appropriately reduces annealing costs.

[0026] The roles and proportions of the elements in this invention are based on the following: Carbon (C): A fundamental strengthening element in steel, providing the basic strength after quenching and tempering. It forms pearlite in steel sheets, increasing strength but reducing plasticity. This causes cracking in medium-carbon steel sheets with low cold rolling / cold stamping deformation, preventing the accumulation of large deformations. Therefore, to ensure large cold rolling deformation and high cold stamping performance, the C content needs to be appropriately reduced. Thus, the C content in this invention is 0.32%~0.39%.

[0027] Si: A fundamental element for strengthening ferrite. Increased silicon content leads to increased strength but decreased plasticity in steel components. The Si content in this invention is 0.17%~0.37%.

[0028] Mn: In solid solution form, it strengthens the matrix, slightly refines the room temperature microstructure, and improves strength and toughness. The Mn content in this invention is 0.50%~0.80%.

[0029] Cr: A common element in steel that improves strength and hardenability. It can refine cementite size, accelerate the spheroidizing annealing process, and improve the final wear resistance of flexible wheels. Therefore, the Cr content in this invention is 0.60%~0.90%.

[0030] Ni: A commonly added element in steel to improve hardenability and toughness. It can significantly improve the cold formability of steel, especially its low-temperature toughness, and is an important alloying element for high strength, high toughness, and high fatigue resistance in flexible steel. Therefore, the Ni content in this invention is 1.00%~1.50%.

[0031] Mo: A common element in steel that improves strength and hardenability. It can also refine cementite size, accelerate the spheroidizing annealing process, and has a certain effect on refining ferrite and austenite grains. Therefore, the Mo content in this invention is 0.15%~0.25%.

[0032] Al and N are microalloying elements commonly used in steel to refine grain size during hot rolling. Due to the high fatigue life required for flexible rolling, large-sized inclusions or precipitates with sharp angles are unacceptable; therefore, elements such as Ti and Nb cannot be added. V has a low precipitation temperature and cannot continuously refine grains. Therefore, this invention selects AlN as the main precipitate for refining grains, improving strength and toughness, and obtaining the {111} texture, while compensating for the strength reduction caused by decreasing C. To avoid excessive Al or N content and the formation of other inclusions, the Al content in this invention is 0.040%~0.060%, and the N content is 0.020%~0.030%.

[0033] P and S: Common impurity elements in steel, reducing the plasticity and toughness of steel materials, easily forming agglomerated regions, and subsequently forming banded structures and strip-shaped inclusions, thus reducing the deep-drawing performance of steel plates. Their content should be reduced as much as possible, provided that smelting costs allow. Therefore, in this invention, the P content is ≤0.015% and the S content is ≤0.015%.

[0034] In addition, this invention controls the continuous casting process. The superheat of the continuous casting process should be controlled to be ≤20℃; the electromagnetic stirring current of the crystallizer is 200~300A, and the electromagnetic stirring current at the end of solidification is 400~500A; combined with non-sinusoidal vibration and light pressing, the partial pressing amount between the crystallizer and the end of solidification is 1.0~1.5mm / m, which ensures that no serious dendritic segregation occurs when the molten steel solidifies, and thus no obvious banded structure is generated during rolling, resulting in anisotropy, ensuring high isotropy and deep drawing performance.

[0035] This invention, without significantly increasing the cost of alloying elements, reduces the C content and increases the AlN content. Combined with strict continuous casting control, online spheroidizing annealing after hot rolling, cold rolling with large cumulative deformation, and recrystallization annealing at lower temperatures, it fully refines ferrite grains and spheroidizes cementite. Furthermore, it controls the orientation distribution of ferrite primarily with a {111} facet texture, maximizing the plasticity of the steel sheet while simultaneously improving the r-value and deep-drawing performance. This allows the material to meet the basic requirements for flexible wheel cold stamping. The final steel sheet exhibits a tensile strength of 500-550 MPa, a yield strength of 320-380 MPa, an elongation after fracture of 35-38%, an r-value of 2.0-2.3, a {111} facet texture ferrite content ≥70%, and a ferrite grain size ≥9.

[0036] This invention discloses a material and processing method suitable for cold-stamped flexible wheels. Based on traditional high-quality medium-carbon alloy steel, it reduces the C element content and increases the AlN content. Combined with strict continuous casting control process, online spheroidizing annealing after hot rolling, cold rolling with large cumulative deformation, and recrystallization annealing at a lower temperature, it fully refines the ferrite grains and spheroidizes the cementite. It controls the orientation distribution of ferrite mainly with {111} face texture, thereby improving the plasticity of the steel plate to the highest level, while improving the r value and deep drawing performance. This invention enables the material to meet the basic requirements for cold-stamping of flexible wheels. Attached Figure Description

[0037] Figure 1 The changes in austenite content with temperature in the phase diagram obtained by computer simulation of the raw material composition in Example 1 were used to obtain key parameters such as A1 and A3 temperatures. Figure 2 The equilibrium solid solution precipitation law of the main precipitated phase obtained by computer simulation of the raw material composition in Example 1; Figure 3 The supercooled austenite transformation curves obtained using computer simulation of the raw material composition in Example 1; Figure 4 The microstructure of the longitudinal section after recrystallization annealing in Example 1; Figure 5The ODF plot obtained by XRD after recrystallization annealing in Example 1 is a section with φ2=45° (the position of the dashed box corresponding to Φ=55º is the intensity distribution of the {111} surface texture). Figure 6 The microstructure of the longitudinal section after recrystallization annealing in Comparative Example 1 is shown. Figure 7 The section with φ2=45° is the ODF plot obtained by XRD after recrystallization annealing in Comparative Example 1 (the position of the dashed box corresponding to Φ=55º is the intensity distribution of the {111} surface texture). Figure 8 The microstructure of the longitudinal section after recrystallization annealing in Comparative Example 3 is shown. Detailed Implementation

[0038] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Example 1

[0039] A material suitable for cold stamping forming flexible wheels, the chemical composition of which is shown in Table 1.

[0040] Table 1 Chemical composition (wt%) (the remainder is Fe and impurity elements)

[0041] Continuous casting billets were produced according to the compositions of the above embodiments and comparative examples. Embodiments 1, 1 (comparative example), 2, and 3 all employed the following process: hot rolling into thin plates, followed by coiling into steel coils. The final rolling temperature was 850°C, and the coiling temperature was 675°C. After coiling, the steel coils were held at 664°C for 2 hours, then cooled to 550°C at a rate of 8°C / min, and finally air-cooled to room temperature. The steel coils were pickled and then cold-rolled, with a cumulative total deformation of 80%. After cold rolling, the steel coils were opened and continuously heated to 680°C, held for 7 minutes, and then cooled to 550°C at a rate of 8°C / min before air-cooling to room temperature. The superheat in the continuous casting process was 15°C, the electromagnetic stirring current in the crystallizer was 250A, and the electromagnetic stirring current at the solidification end was 450A. Combined with non-sinusoidal vibration and light pressing, the partial reduction between the crystallizer and the solidification end was 1.2 mm / m. Cold rolling uses a high-performance rolling lubricant with a ratio of 90% polyalphaolefin, 8% methyl palmitate, 1.2% tricresyl phosphate, 0.6% 2,6-di-tert-butyl-p-cresol, and 0.2% dodecenyl succinic acid; recrystallization annealing uses ammonia decomposition gas protection.

[0042] Application of the material obtained in Example 1 in cold stamping forming flexible wheels.

[0043] A cold-stamped flexible wheel was prepared from the material of Example 1.

[0044] The production process of Comparative Example 2 is as follows: hot rolling into thin sheets and then coiling into steel coils, with a final rolling temperature of 850°C and a coiling temperature of 675°C, followed by air cooling to room temperature. The steel coils are pickled and then cold rolled, with a cumulative total deformation of 30% after the final intermediate annealing pass. After cold rolling, the steel coils are opened and continuously heated to 680°C, held for 10 minutes, and then cooled to 550°C at a rate of 8°C / min before air cooling to room temperature. The continuous casting process, cold rolling process, and recrystallization annealing process are the same as in Example 1.

[0045] That is, in this comparative example, the online spheroidizing annealing after hot rolling is omitted, and the total cumulative deformation of cold rolling is 30%, which is not the large cumulative deformation of the present invention.

[0046] Comparative Example 3: The only difference from Example 1 is that the superheat during continuous casting was 35°C, the light reduction process was not used, and the reduction between the crystallizer and the solidification end was 1.8 mm / m. All other production processes were the same as in Example 1. The banded microstructure of the air-cooled sample after hot rolling was grade 2.0.

[0047] Comparative Example 4: The only difference from Example 1 is that the cold rolling uses ordinary lubricating oil (90% polyalphaolefin + 9.4% methyl palmitate + 0.6% 2,6-di-tert-butyl-p-cresol) without extreme pressure agents and rust inhibitors, and the recrystallization annealing uses N2 protection (the ammonia decomposition gas of the present invention is not used).

[0048] Comparative Example 5: The only difference from Example 1 is that the cumulative total cold rolling deformation is 55%, which is not the large cumulative deformation of Example 1.

[0049] Comparative Example 6: The only difference from Example 1 is that the lubricating oil used in cold rolling is: 88.1% polyalphaolefin + 8% methyl palmitate + 2.5% tricresyl phosphate + 0.6% 2,6-di-tert-butyl-p-cresol + 0.8% dodecenyl succinic acid.

[0050] Comparative Example 7: The only difference from Example 1 is that the lubricant used in cold rolling is: 90.85% polyalphaolefin + 8% methyl palmitate + 0.5% tricresyl phosphate + 0.6% 2,6-di-tert-butyl-p-cresol + 0.05% dodecenyl succinic acid.

[0051] Comparative Example 8: The only difference from Example 1 is that the recrystallization annealing was protected with N2, and the ammonia decomposition gas of Example 1 was not used.

[0052] To characterize the properties of the finished steel plates, tensile specimens were taken from the steel plates according to national standards GB / T 228.1-2021 and GB / T 5027-2016 for tensile testing. Tensile strength, yield strength, elongation after fracture, and r-value (plastic strain ratio, the ratio of strain in the width direction to strain in the thickness direction during the tensile test) were measured. XRD was used to determine the surface texture of the steel plates, and a cross-sectional view at φ2=45° was plotted to calculate the approximate proportion of the {111} surface texture. The test results are shown in Table 2.

[0053] like Figure 1 As shown, the austenite presence temperature range and A3 and A1 temperature values ​​calculated according to the composition of Example 1 are shown. Figure 2 The AlN equilibrium solid solution precipitation pattern calculated according to the composition of Example 1 shows that at 850℃, the final rolling temperature is in the non-recrystallization region of austenite, and AlN has been almost completely precipitated, which can pin the austenite grain boundaries and prevent austenite grain growth. When cooled to the coiling temperature of 675℃, the proeutectoid ferrite has been completely precipitated, but according to... Figure 3 The C-type supercooled austenite transformation curve shows that pearlite has not yet formed. Online spheroidizing annealing was achieved by holding at 664℃ for 2 hours and then cooling to 550℃ at a rate of 8℃ / min, forming granular pearlite to significantly reduce strength and improve plasticity and cold formability. The steel coil was cold-rolled after pickling without intermediate annealing for softening. The cumulative total deformation during cold rolling reached 80%, achieving a large deformation that provided the driving force for subsequent recrystallization. The recrystallization annealing temperature was 680℃, held for 7 minutes, ensuring that no austenite was formed in the microstructure, only recrystallization of deformed ferrite grains and maturation of cementite occurred (small cementite dissolved, large cementite continued to grow, and irregular cementite edges dissolved). Due to the higher proportion of cold-deformed ferrite grain boundaries and the lower recrystallization annealing temperature, only {111}-faceted textured ferrite grains, which are more prone to nucleation, nucleated and grew, while the recrystallization of other oriented grains was suppressed. The final microstructure consists mainly of {111}-textured ferrite with spherical cementite. It is then cooled to 550°C at a rate of 8°C / min and subsequently air-cooled to room temperature to avoid the possible formation of lamellar cementite. Figure 4 As shown, the cementite in the steel plate is well spheroidized. (As indicated...) Figure 5 As shown, the {111} surface texture strength is high when Φ=55º. Therefore, the steel plate of Example 1 not only has good plasticity, but also an r value of 2.2, which meets the conditions for cold stamping production of flexible wheels.

[0054] Comparative Example 1, due to its higher C content, exhibited a significantly reduced elongation after fracture. Although it underwent the same processing procedure as Example 1, the spheroidizing annealing effect ( Figure 6 The results are similar to those in Example 1, but due to the lack of AlN refinement of the microstructure before cold rolling, the grains are coarse and the number of grain boundaries before cold rolling is insufficient, resulting in a lower proportion of {111} texture after cold rolling and annealing. Figure 7This results in a significantly lower r-value, which cannot meet the requirements of cold stamping flexible wheels.

[0055] In Comparative Example 2, due to the lack of spheroidizing annealing after hot rolling and insufficient cumulative deformation after the last intermediate annealing, the proportion of the {111} surface texture was also low, resulting in a significantly lower r value, which could not meet the requirements of cold stamping flexible wheels.

[0056] Comparative Example 3, due to its high overheating during continuous casting and the lack of a uniform continuously cast billet composition under light pressure, exhibited severe dendritic segregation, resulting in a distinct banded structure in the final microstructure. Figure 8 Significant macroscopic anisotropy was observed, resulting in a severely low r-value, which could not meet the requirements of cold stamping flexible wheels.

[0057] In Comparative Example 4, due to the poor quality of the cold-rolled lubricant and the use of N2 protection during recrystallization annealing, corrosion pits and uneven thickness appeared on the surface of the steel plate during recrystallization annealing, and the {111} surface texture failed to grow sufficiently, resulting in a decrease in its proportion.

[0058] The steel plate composition and rolling process of Examples 2 and 3 are both within the scope of this invention, with only slight variations in specific chemical composition and different thicknesses of the finished steel plates. The mechanical properties, grain size, and texture of the resulting steel plates are similar to those of Example 1, meeting the conditions for cold stamping production of flexible wheels. Example 4

[0059] A processing method for materials suitable for cold-stamping flexible wheels involves hot rolling into thin sheets and then coiling them into steel coils. The final rolling temperature is 800℃, and the coiling temperature is 670℃. After coiling, the steel coil is held at 660℃ for 2 hours, then cooled to 550℃ at a cooling rate of 5℃ / min, and finally air-cooled to room temperature. The steel coil is then pickled and cold-rolled, with a cumulative total deformation of 60%. After cold rolling, the steel coil is opened and continuously heated to 670℃, held for 5 minutes, and then cooled to 550℃ at a cooling rate of 5℃ / min before air-cooling to room temperature. The continuous casting process uses a superheat of 20℃, an electromagnetic stirring current of 200A in the crystallizer, and an electromagnetic stirring current of 400A at the solidification end. Combined with non-sinusoidal vibration and light pressing, the partial reduction between the crystallizer and the solidification end is 1.0 mm / m. Cold rolling uses a high-performance rolling lubricant with a formulation of 86.5% polyalphaolefin, 10% methyl palmitate, 2% tricresyl phosphate, 1% 2,6-di-tert-butyl-p-cresol, and 0.5% dodecenylsuccinic acid; recrystallization annealing uses ammonia decomposition gas protection.

[0060] The application of the material obtained in this embodiment in cold stamping forming flexible wheels.

[0061] A cold-stamped flexible wheel is obtained from the material prepared in this embodiment. Example 5

[0062] A processing method for materials suitable for cold-stamping flexible wheels involves hot rolling into thin sheets and then coiling them into steel coils. The final rolling temperature is 900℃, and the coiling temperature is 680℃. After coiling, the steel coil is held at 670℃ for 2 hours, then cooled to 550℃ at a cooling rate of 10℃ / min, and finally air-cooled to room temperature. The steel coil is then pickled and cold-rolled, with a cumulative total deformation of 90%. After cold rolling, the steel coil is opened and continuously heated to 685℃, held for 10 minutes, and then cooled to 550℃ at a cooling rate of 10℃ / min before air-cooling to room temperature. The continuous casting process uses a superheat of 17℃, an electromagnetic stirring current of 300A in the crystallizer, and an electromagnetic stirring current of 500A at the solidification end. Combined with non-sinusoidal vibration and light pressing, the partial reduction between the crystallizer and the solidification end is 1.5 mm / m. Cold rolling uses a high-performance rolling lubricant with a ratio of 93.4% hydrocracked mineral oil + 5% oleic acid + 1% thiophosphate + 0.5% alkylated diphenylamine + 0.1% petroleum sulfonic acid; recrystallization annealing uses ammonia decomposition gas protection.

[0063] The application of the material obtained in this embodiment in cold stamping forming flexible wheels.

[0064] A cold-stamped flexible wheel is obtained from the material prepared in this embodiment.

[0065] Table 2 Plate thickness, mechanical properties, deep drawing properties and grain size

[0066] *Note: The surface quality of the finished boards in Comparative Examples 6 and 7 was poor, and local damage occurred during the test, so the test was terminated.

[0067] It should be understood that, in order to simplify this disclosure and aid in understanding one or more of the various aspects of the invention, features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof in the above description of exemplary embodiments of the invention. However, this method of disclosure should not be interpreted as reflecting an intention that the claimed invention requires more features than expressly recited in each claim. Rather, as reflected in the claims, inventive aspects lie in fewer than all the features of the foregoingly disclosed embodiments. Therefore, the claims, following the detailed description, are hereby expressly incorporated into that detailed description, wherein each claim itself is a separate embodiment of the invention.

[0068] Although the invention has been described with reference to a limited number of embodiments, those skilled in the art will understand from the foregoing description that other embodiments are conceivable within the scope of the invention described herein. Furthermore, it should be noted that the language used in this specification has been chosen primarily for readability and instructional purposes, and not for the purpose of interpreting or limiting the subject matter of the invention. Therefore, many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the appended claims. The disclosure of the invention is illustrative and not restrictive, and the scope of the invention is defined by the appended claims.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for processing materials suitable for cold-stamped flexible wheels, characterized in that, Includes the following steps: S01: Preparation of high-quality medium-carbon alloy steel; S02: The high-quality medium carbon alloy steel obtained in step S01 is hot rolled into thin plates and then coiled into steel coils. The final rolling temperature is 800~900℃, the coiling temperature is 670~680℃, and the coil is held at 660~670℃ for 2 hours. It is then cooled to 550℃ at a cooling rate of 5~10℃ / min and then air-cooled to room temperature. S03: After pickling, cold rolling is performed, with a cumulative total deformation of 60%~90%; S04: After cold rolling, the steel coil is opened and continuously heated at a temperature of 670~685℃, held for 5~10 min, and then cooled to 550℃ at a rate of 5~10℃ / min before being air-cooled to room temperature. S01 is a high-quality medium-carbon alloy steel with the following chemical composition by mass percentage: C: 0.32%~0.39%, Si: 0.17%~0.37%, Mn: 0.50%~0.80%, P: ≤0.015%, S: ≤0.015%, Cr: 0.60%~0.90%, Ni: 1.00~1.50%, Mo: 0.15%~0.25%, Al: 0.040%~0.060%, N: 0.020%~0.030%, with the balance being Fe and unavoidable impurities. In S01, the superheat of high-quality medium carbon alloy steel is controlled to be ≤20℃ during continuous casting; the electromagnetic stirring current of the crystallizer is 200~300A, and the electromagnetic stirring current at the end of solidification is 400~500A; combined with non-sinusoidal vibration light pressing, the partial pressing amount between the crystallizer and the end of solidification is 1.0~1.5mm / m, and a slab with a thickness of 200-250mm is obtained after continuous casting. In S03, high-performance rolling lubricating oil is used in the cold rolling process, and the high-performance rolling lubricating oil is guaranteed to cover 100% of the plate surface during the cold rolling process. High-performance rolling lubricants include 86.5%~93.4% base oil, 5%~10% oiliness agent, 1%~2% extreme pressure agent, 0.5%~1% antioxidant and 0.1%~0.5% rust inhibitor; In S04, the process of continuous heating and air cooling to room temperature is protected by ammonia decomposition gas.

2. The processing method according to claim 1, characterized in that, In S02, the thickness of the hot-rolled sheet is 3~5mm. After final rolling, it is cooled to the coiling temperature by spraying water. The coiled steel coil is kept warm in a heating furnace.

3. The processing method according to claim 1, characterized in that, Base oils include one or both of hydrocracked mineral oils and polyalphaolefins; Oiling agents include one or both of methyl palmitate and oleic acid; Extreme pressure agents include one or both of tricresyl phosphate and thiophosphate; Antioxidants include one or both of 2,6-di-tert-butyl-p-cresol and alkylated diphenylamine; Rust inhibitors include one or both of dodecenyl succinic acid and petroleum sulfonic acid.

4. The processing method according to claim 1, characterized in that, The thickness of the finished steel plate obtained after S04 treatment is 0.5mm-2.0mm.

5. The material obtained by the processing method of a material suitable for cold stamping forming flexible wheels according to any one of claims 1 to 4, characterized in that, Tensile strength 500-550MPa, yield strength 320-380MPa, elongation after fracture 35-38%, r value 2.0-2.3, {111} textured ferrite content ≥70%, ferrite grain size ≥9.

6. The application of the material according to claim 5 in cold stamping forming flexible wheels.

7. A cold-stamped flexible wheel, characterized in that, It is prepared from the material described in claim 5.

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