20MnCr5 alloy steel as well as preparation method and application thereof

Abstract

The invention relates to 20MnCr5 alloy steel and a preparation method and application thereof, and the 20MnCr5 alloy steel comprises the following components in percentage by mass: 0.15%-0.20% of C, less than or equal to 0.12% of Si, 1.10%-1.30% of Mn, less than or equal to 0.015% of P, less than or equal to 0.005% of S, 1.00%-1.10% of Cr, less than or equal to 0.10% of Mo, 0.02%-0.05% of Al, 0.007%-0.013% of N and the balance of iron. According to the 20MnCr5 alloy steel provided by the invention, the chemical components of the 20MnCr5 alloy steel are optimally designed, so that the problems of cracking, fish scale-shaped cracks and the like in a cold spinning process can be avoided, and the strength, toughness and wear resistance of a motor shaft are ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of alloy materials, and in particular to a 20MnCr5 alloy steel and a preparation method and application thereof. Background Art

[0002] With the rapid development of the new energy vehicle industry, demand for motor shafts, core components of drive motors, continues to increase. As a key component of motors, hollow motor shafts must meet multiple performance requirements. First, during operation, the motor shaft must withstand multiple loads, including electromagnetic torque, rotor gravity, and vibration. Therefore, it must possess sufficient strength and rigidity to prevent deformation or fracture during operation and ensure proper functioning of the motor. Second, the motor shaft must exhibit good toughness, capable of withstanding a certain degree of impact loads to avoid brittle fracture under sudden external forces, thereby improving its reliability and service life. Furthermore, due to the relative motion between the motor shaft and components such as bearings, it also requires excellent wear resistance to reduce wear, ensure the motor's precision and performance stability, and reduce maintenance costs. Therefore, the performance of the motor shaft is directly related to the motor's efficient and stable operation, placing higher demands on its materials and manufacturing processes.

[0003] 20MnCr5 steel is a high-strength alloy steel with high strength, high toughness, good hardenability and fatigue resistance. It is widely used in the field of heat-treated gears and shaft steel.

[0004] The cold spinning process has the advantages of high production efficiency, high precision, and good surface quality, and is widely used in the production of motor shafts. However, when using the existing cold spinning process to produce motor shafts made of high-strength alloy steel, especially 20MnCr5 steel, there are problems such as: (1) 20MnCr5 steel is prone to cracking during the cold spinning process; (2) fish-scale cracks often appear on the surface of 20MnCr5 steel after spinning, which not only affects the appearance of the motor shaft but also reduces the service life and reliability of the motor shaft.

[0005] Therefore, providing a 20MnCr5 alloy steel for cold spinning process and avoiding cracking, fish-scale cracks and the like during the preparation of motor shafts is a technical problem that needs to be solved in the current field. Summary of the Invention

[0006] In response to the above problems, the purpose of the present invention is to provide a 20MnCr5 alloy steel, a preparation method and use thereof. Compared with the prior art, the 20MnCr5 alloy steel provided by the present invention can avoid problems such as cracking and fish-scale cracks in the cold spinning process by optimizing its chemical composition, and ensure the strength, toughness and wear resistance of the motor shaft.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a 20MnCr5 alloy steel, which comprises the following components in terms of mass percentage: C: 0.15-0.20%, Si: ≤0.12%, Mn: 1.10-1.30%, P: ≤0.015%, S: ≤0.005%, Cr: 1.00-1.10%, Mo: ≤0.10%, Al: 0.02-0.05%, N: 0.007-0.013% and the balance iron.

[0009] The 20MnCr5 alloy steel provided by the present invention optimizes its chemical composition, especially controls the contents of P and S within specific ranges, and adds a specific content of N element, so as to refine the grain structure in the steel, improve the strength, toughness and wear resistance of the 20MnCr5 alloy steel, and avoid problems such as cracking and fish-scale cracks generated during the cold spinning process.

[0010] In the present invention, C is 0.15-0.20%, for example, it can be 0.15%, 0.16%, 0.17%, 0.18%, 0.19% or 0.20%, but is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0011] In the present invention, Si≤0.12%, for example, it can be 0.12%, 0.11%, 0.10%, 0.09%, 0.08% or 0.07%, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0012] In the present invention, Mn is 1.10-1.30%, for example, it can be 1.10%, 1.12%, 1.14%, 1.16%, 1.18%, 1.20%, 1.22%, 1.24%, 1.26%, 1.28% or 1.30%, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0013] In the present invention, P≤0.015%, for example, it can be 0.015%, 0.014%, 0.013%, 0.012%, 0.011%, 0.010%, 0.009% or 0.008%, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0014] In the present invention, S≤0.005%, for example, it can be 0.005%, 0.004%, 0.003% or 0.002%, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0015] In the present invention, Cr is 1.00-1.10%, for example, it can be 1.00%, 1.01%, 1.02%, 1.03%, 1.04%, 1.05%, 1.06%, 1.07%, 1.08%, 1.09% or 1.10%, but is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0016] In the present invention, Mo≤0.10%, for example, it can be 0.10%, 0.09%, 0.08%, 0.07% or 0%, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0017] In the present invention, Al is 0.02-0.05%, for example, it can be 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045% or 0.05%, but is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0018] In the present invention, N is 0.007-0.013%, for example, it can be 0.007%, 0.008%, 0.009%, 0.010%, 0.011%, 0.012% or 0.013%, but is not limited to the listed values. Other values not listed within the numerical range are also applicable.

[0019] Preferably, the mass percentage of C in the 20MnCr5 alloy steel is 0.16-0.18%.

[0020] Preferably, the mass percentage of Si in the 20MnCr5 alloy steel is ≤0.10%.

[0021] Preferably, the mass percentage of Mn in the 20MnCr5 alloy steel is 1.20-1.26%.

[0022] Preferably, the mass percentage of S in the 20MnCr5 alloy steel is ≤0.003%.

[0023] Preferably, the mass percentage of Cr in the 20MnCr5 alloy steel is 1.04-1.10%.

[0024] Preferably, the mass percentage of Al in the 20MnCr5 alloy steel is 0.03-0.04%.

[0025] Preferably, the mass percentage of N in the 20MnCr5 alloy steel is 0.009-0.012%.

[0026] In the present invention, by further preferably controlling the chemical composition of the 20MnCr5 alloy steel within a specific range, the grains can be further refined and the mechanical strength can be improved.

[0027] In a second aspect, the present invention provides a method for preparing the 20MnCr5 alloy steel as described in the first aspect of the present invention, the preparation method comprising the following steps:

[0028] The molten steel is continuously cast, heated, rolled and cooled in sequence to obtain 20MnCr5 alloy steel.

[0029] In the preparation method provided by the present invention, the chemical composition of 20MnCr5 alloy steel is optimized and the continuous casting, heating, rolling and cooling processes are adopted to improve the strength and toughness of the steel, thereby ensuring the yield of the motor shaft prepared by the cold spinning process.

[0030] In the present invention, the method for preparing molten steel comprises: selecting raw materials according to the composition of the 20MnCr5 alloy steel described in the first aspect, and sequentially subjecting the raw materials to KR pretreatment, converter smelting, LF refining and VD vacuum to obtain molten steel.

[0031] In the present invention, the cooling method includes slow cooling, which is a conventional operation in this field, for example: slow cooling is adopted when the material enters the pit, slowly cools to ≤180℃ and then removes the cover, slowly cools to ≤150℃ and then exits the pit, and prepares the lower layer and upper cover.

[0032] Preferably, the superheat of the continuous casting is 15-35°C, for example, it can be 15°C, 16°C, 17°C, 18°C, 19°C, 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 32°C, 34°C or 35°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0033] Preferably, the continuous casting speed is 0.46-0.48 m / min, for example, 0.46 m / min, 0.47 m / min or 0.48 m / min, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0034] Preferably, the continuous casting includes sequentially performing electromagnetic stirring at the head end and electromagnetic stirring at the tail end.

[0035] Preferably, the current of the electromagnetic stirring at the head end is 190-200A, for example, it can be 190A, 191A, 192A, 193A, 194A, 195A, 196A, 197A, 198A, 199A or 200A, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0036] Preferably, the frequency of the electromagnetic stirring at the head end is 2-3 Hz, for example, it can be 2 Hz, 2.1 Hz, 2.2 Hz, 2.3 Hz, 2.4 Hz, 2.5 Hz, 2.6 Hz, 2.7 Hz, 2.8 Hz, 2.9 Hz or 3 Hz, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0037] Preferably, the current of the end electromagnetic stirring is 300-450A, for example, it can be 300A, 310A, 320A, 330A, 340A, 350A, 360A, 370A, 380A, 390A, 400A, 410A, 420A, 430A, 440A or 450A, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0038] Preferably, the frequency of the end electromagnetic stirring is 5-7 Hz, for example, it can be 5 Hz, 5.2 Hz, 5.4 Hz, 5.6 Hz, 5.8 Hz, 6 Hz, 6.2 Hz, 6.4 Hz, 6.6 Hz, 6.8 Hz or 7 Hz, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0039] In the present invention, by controlling the superheat, casting speed, current and frequency of the continuous casting process, the uniformity of the steel can be improved, thereby further improving the strength and toughness.

[0040] Preferably, the heating includes a preheating section, a heating section and a uniform heating section which are performed in sequence.

[0041] Preferably, the temperature of the preheating section is ≤900°C, for example, it can be 900°C, 890°C, 880°C, 870°C, 860°C or 850°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0042] Preferably, the temperature of the heating section is 1190-1260°C, for example, it can be 1190°C, 1200°C, 1210°C, 1220°C, 1230°C, 1240°C, 1250°C or 1260°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0043] Preferably, the temperature of the uniform heating section is 1180-1250°C, for example, it can be 1180°C, 1190°C, 1200°C, 1210°C, 1220°C, 1230°C, 1240°C or 1250°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0044] Preferably, the starting temperature of the rolling is 1100-1150°C, for example, it can be 1100°C, 1110°C, 1120°C, 1130°C, 1140°C or 1150°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0045] Preferably, the rolling reduction ratio is ≥7, for example, it can be 7, 8 or 9, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0046] In the present invention, the compression ratio refers to the ratio of the surface area of the billet before rolling to the surface area of the billet after rolling.

[0047] In the present invention, the strength and toughness of the steel can be further improved by heating and rolling, making it more suitable for preparing motor shafts by cold spinning process.

[0048] As a preferred technical solution of the second aspect of the present invention, the preparation method comprises the following steps:

[0049] The molten steel is continuously cast under the conditions of superheat of 15-35°C and pulling speed of 0.46-0.48m / min, and the continuous casting includes: firstly performing electromagnetic stirring at the head end under the conditions of current of 190-200A and frequency of 2-3Hz, and then performing electromagnetic stirring at the end end under the conditions of current of 300-450A and frequency of 5-7Hz, and then heating is performed, and the heating includes a preheating section, a heating section and a uniform heating section performed in sequence, the temperature of the preheating section is ≤900°C, the temperature of the heating section is 1190-1260°C, and the temperature of the uniform heating section is 1180-1250°C, and then rolling is performed, the starting rolling temperature of the rolling is 1100-1150°C, and the compression ratio of the rolling is ≥7, and then cooling is performed to obtain 20MnCr5 alloy steel.

[0050] In a third aspect, the present invention provides a use of the 20MnCr5 alloy steel as described in the first aspect of the present invention, wherein the 20MnCr5 alloy steel is used for preparing a motor shaft by a cold spinning method.

[0051] The 20MnCr5 alloy steel provided by the present invention has good strength, toughness, plasticity and ductility, and has a small grain size. It can be used to prepare motor shafts by a cold spinning method to effectively avoid problems such as cracking and fish-scale cracks.

[0052] Preferably, the rotation speed of the cold spinning method is 450-550r / min, for example, it can be 450r / min, 460r / min, 470r / min, 480r / min, 490r / min, 500r / min, 510r / min, 520r / min, 530r / min, 540r / min or 550r / min, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0053] Preferably, the feed speed of the cold spinning method is 15-17 mm / s, for example, it can be 15 mm / s, 15.2 mm / s, 15.4 mm / s, 15.6 mm / s, 15.8 mm / s, 16 mm / s, 16.2 mm / s, 16.4 mm / s, 16.8 mm / s or 17 mm / s, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0054] Preferably, the cold spinning method is followed by heat treatment.

[0055] Preferably, the temperature of the heat treatment is 910-930°C, for example, it can be 910°C, 912°C, 914°C, 916°C, 918°C, 920°C, 922°C, 924°C, 926°C, 928°C or 930°C, but is not limited to the listed values, and other unlisted values within the numerical range are also applicable.

[0056] Preferably, the heat treatment time is 4-7 hours, for example, 4 hours, 5 hours, 6 hours or 7 hours, but is not limited to the listed values, and other values not listed within the numerical range are also applicable.

[0057] Compared with the prior art, the present invention has the following beneficial effects:

[0058] (1) The 20MnCr5 alloy steel provided by the present invention can refine the grain structure in the steel by optimizing its chemical composition, especially controlling the contents of P and S within a specific range, and adding a specific content of N element, thereby improving the strength, toughness and wear resistance of the 20MnCr5 alloy steel and avoiding problems such as cracking and fish-scale cracks generated during the cold spinning process.

[0059] (2) Under optimal conditions, the 20MnCr5 alloy steel provided by the present invention can achieve a tensile strength of more than 1092 MPa, a yield strength of more than 925 MPa, a grain size of less than 20.9 μm, and no cracking or fish-scale cracking after cold spinning. DETAILED DESCRIPTION

[0060] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0061] Example 1

[0062] This embodiment provides a 20MnCr5 alloy steel. In the 20MnCr5 alloy steel, the proportions of C, Si, Mn, P, S, Cr, Mo, Al, and N, calculated by mass percentage, are as shown in Table 1, and the balance is iron.

[0063] This embodiment also provides a method for preparing the above-mentioned 20MnCr5 alloy steel, which comprises the following steps:

[0064] The molten steel is continuously cast under the conditions of superheat of 20°C and pulling speed of 0.47m / min, and the continuous casting includes: firstly performing electromagnetic stirring at the head end under the conditions of current of 195A and frequency of 2.5Hz, and then performing electromagnetic stirring at the end end under the conditions of current of 400A and frequency of 6Hz, and then heating, and the heating includes a preheating section, a heating section and a uniform heating section in sequence, the temperature of the preheating section is 800°C, the temperature of the heating section is 1200°C, and the temperature of the uniform heating section is 1220°C, and then rolling is carried out, the starting rolling temperature of the rolling is 1130°C, the compression ratio of the rolling is 7, and then the steel is put into a pit for slow cooling to obtain 20MnCr5 alloy steel.

[0065] Example 2

[0066] This embodiment provides a 20MnCr5 alloy steel. In the 20MnCr5 alloy steel, the proportions of C, Si, Mn, P, S, Cr, Mo, Al, and N, calculated by mass percentage, are as shown in Table 1, and the balance is iron.

[0067] This embodiment also provides a method for preparing the above-mentioned 20MnCr5 alloy steel, which comprises the following steps:

[0068] The molten steel is continuously cast under the conditions of superheat of 15°C and pulling speed of 0.48m / min, and the continuous casting includes: firstly performing electromagnetic stirring at the head end under the conditions of current of 190A and frequency of 3Hz, and then performing electromagnetic stirring at the end end under the conditions of current of 300A and frequency of 7Hz, and then heating, and the heating includes a preheating section, a heating section and a uniform heating section carried out in sequence, the temperature of the preheating section is 900°C, the temperature of the heating section is 1250°C, and the temperature of the uniform heating section is 1250°C, and then rolling is carried out, the starting rolling temperature of the rolling is 1150°C, the compression ratio of the rolling is 7, and then the steel is put into a pit for slow cooling to obtain 20MnCr5 alloy steel.

[0069] Example 3

[0070] This embodiment provides a 20MnCr5 alloy steel. In the 20MnCr5 alloy steel, the proportions of C, Si, Mn, P, S, Cr, Mo, Al, and N, calculated by mass percentage, are as shown in Table 1, and the balance is iron.

[0071] This embodiment also provides a method for preparing the above-mentioned 20MnCr5 alloy steel, which comprises the following steps:

[0072] The molten steel is continuously cast under the conditions of superheat of 35°C and pulling speed of 0.46m / min, and the continuous casting includes: firstly performing electromagnetic stirring at the head end under the conditions of current of 200A and frequency of 2Hz, and then performing electromagnetic stirring at the end end under the conditions of current of 450A and frequency of 5Hz, and then heating, and the heating includes a preheating section, a heating section and a uniform heating section carried out in sequence, the temperature of the preheating section is 850°C, the temperature of the heating section is 1190°C, and the temperature of the uniform heating section is 1200°C, and then rolling is carried out, the starting rolling temperature of the rolling is 1100°C, the compression ratio of the rolling is 7, and then the steel is slowly cooled in a pit to obtain 20MnCr5 alloy steel.

[0073] Examples 4-6

[0074] Embodiments 4-6 of the present invention respectively provide a 20MnCr5 alloy steel, in which the proportions of C, Si, Mn, P, S, Cr, Mo, Al and N, calculated by mass percentage, are as shown in Table 1, and the balance is iron.

[0075] The present Examples 4-6 respectively provide a preparation method of the above-mentioned 20MnCr5 alloy steel. Except that the chemical composition of the molten steel is the same as the composition of the 20MnCr5 alloy steel in Examples 4-6, the rest is the same as that in Example 1.

[0076] Comparative Examples 1-3

[0077] Comparative Examples 1-3 respectively provide a 20MnCr5 alloy steel, in which the proportions of C, Si, Mn, P, S, Cr, Mo, Al and N are as shown in Table 1, based on mass percentage, and the balance is iron.

[0078] Comparative Examples 1-3 respectively provide a preparation method of the above-mentioned 20MnCr5 alloy steel. Except that the chemical composition of the molten steel is the composition of the 20MnCr5 alloy steel in Comparative Examples 1-3, the rest are the same as Example 1.

[0079] Table 1

[0080]

[0081] The properties of the 20MnCr5 alloy steel provided in the above examples and comparative examples were tested, as shown in Table 2:

[0082] (1) Tensile strength: The mechanical properties sampling method refers to GB / T2975. The specimen is cylindrical and has a size of Φ25 mm. The specimen is heated to 860°C and then water quenched. After that, the specimen is heated to 190°C and tempered, and then air-cooled. The tensile test is performed using a universal material testing machine. The test method refers to GB / T228.

[0083] (2) Yield strength: The mechanical properties sampling method refers to GB / T2975. The specimen is cylindrical and has a size of Φ25 mm. The specimen is heated to 860°C and then water quenched. After that, the specimen is heated to 190°C and tempered, and then air-cooled. The yield strength test uses a universal material testing machine. The test method refers to GB / T228.

[0084] (3) Grain size: The grain size of steel was tested using the ASTM E112 standard. The specimens were heated to 930°C for 4 h, then water quenched and tested.

[0085] (4) Fish-scale cracks: The above-mentioned 20MnCr5 alloy steel was cold spun at a rotation speed of 500 r / min and a feed speed of 16 mm / s to prepare a motor shaft, and then heat treated at 920°C and kept warm for 5 h to check whether fish-scale cracks appeared.

[0086] Table 2

[0087]

[0088]

[0089] The following points can be seen from the data in Table 2:

[0090] (1) From the data of Examples 1-3, it can be seen that the 20MnCr5 alloy steel provided by the present invention can achieve a tensile strength of more than 1092 MPa, a yield strength of more than 925 MPa, a grain size of less than 20.9 μm, and no fish-scale cracks after cold spinning under optimal conditions.

[0091] (2) From the comparison between Example 1 and Examples 4-6, it can be seen that the present invention can reduce the grain size and avoid the occurrence of fish-scale cracks while ensuring high tensile strength and yield strength by further optimizing the mass percentage of S and N.

[0092] (3) From the comparison between Example 1 and Comparative Examples 1-3, it can be seen that the 20MnCr5 alloy provided by the present invention can refine the grains while ensuring high tensile strength and yield strength by adding the N element and controlling the mass percentage of P and N, thereby avoiding the occurrence of fish-scale cracks during the cold spinning process and achieving good comprehensive performance.

[0093] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A 20MnCr5 alloy steel, characterized in that: The 20MnCr5 alloy steel comprises the following components in terms of mass percentage: C: 0.15-0.20%, Si: ≤0.12%, Mn: 1.10-1.30%, P: ≤0.015%, S: ≤0.005%, Cr: 1.00-1.10%, Mo: ≤0.10%, Al: 0.02-0.05%, N: 0.007-0.013% and the balance iron.

2. The 20MnCr5 alloy steel according to claim 1, characterized in that The mass percentage of C in the 20MnCr5 alloy steel is 0.16-0.18%; Preferably, the mass percentage of Si in the 20MnCr5 alloy steel is ≤0.10%; Preferably, the mass percentage of Mn in the 20MnCr5 alloy steel is 1.20-1.26%.

3. The 20MnCr5 alloy steel according to claim 1 or 2, characterized in that: The mass percentage of S in the 20MnCr5 alloy steel is ≤0.003%; Preferably, the mass percentage of Cr in the 20MnCr5 alloy steel is 1.04-1.10%; Preferably, the mass percentage of Al in the 20MnCr5 alloy steel is 0.03-0.04%; Preferably, the mass percentage of N in the 20MnCr5 alloy steel is 0.009-0.012%.

4. A method for preparing the 20MnCr5 alloy steel according to any one of claims 1 to 3, characterized in that: The preparation method comprises the following steps: The molten steel is continuously cast, heated, rolled and cooled in sequence to obtain 20MnCr5 alloy steel.

5. The preparation method according to claim 4, characterized in that The superheat degree of the continuous casting is 15-35°C; Preferably, the continuous casting speed is 0.46-0.48 m / min.

6. The preparation method according to claim 4 or 5, characterized in that The continuous casting includes sequentially performing electromagnetic stirring at the head end and electromagnetic stirring at the tail end; Preferably, the current of the electromagnetic stirring at the head end is 190-200A; Preferably, the frequency of the electromagnetic stirring at the head end is 2-3 Hz; Preferably, the current of the terminal electromagnetic stirring is 300-450A; Preferably, the frequency of the terminal electromagnetic stirring is 5-7 Hz.

7. The preparation method according to any one of claims 4 to 6, characterized in that The heating includes a preheating section, a heating section and a uniform heating section which are performed in sequence; Preferably, the temperature of the preheating section is ≤ 900°C; Preferably, the temperature of the heating section is 1190-1260°C; Preferably, the temperature of the uniform heating section is 1180-1250°C; Preferably, the starting rolling temperature is 1100-1150°C; Preferably, the rolling reduction ratio is ≥7.

8. Use of the 20MnCr5 alloy steel according to any one of claims 1 to 3, characterized in that: The 20MnCr5 alloy steel is used for preparing a motor shaft by a cold spinning method.

9. The use according to claim 8, characterized in that The rotation speed of the cold spinning method is 450-550r / min; Preferably, the feed speed of the cold spinning method is 15-17 mm / s.

10. The use according to claim 8 or 9, characterized in that The cold spinning method is followed by heat treatment; Preferably, the temperature of the heat treatment is 910-930°C; Preferably, the heat treatment time is 4-7 hours.

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