WO2023246799A1 - Seamless steel tube used for electric motor shaft and having high strength and toughness and good processing performance, and manufacturing method therefor - Google Patents

Abstract

Disclosed in the present invention are a seamless steel tube used for an electric motor shaft and having high strength and toughness and good processing performance, and a manufacturing method therefor. The seamless steel tube comprises Fe and inevitable impurity elements, and further comprises the following chemical elements in percentages by mass: C: 0.40-0.60%, 0<Si≤0.25%, Mn: 0.5-1.2%, Ti≤0.045%, B≤0.0045%, N: 0.0040-0.009%, Al: 0.015-0.045%, and Ca+Mg: 0.001-0.006%. The seamless steel tube has very good mechanical performance before and after quenching and high-temperature tempering; and after quenching and high-temperature tempering, the seamless steel tube has a hardness of up to 58 HRC or more, and a product of strength and elongation of greater than 15000 MPa%, and can resist a torque of 300 kN or more.

Description

A high-strength seamless steel pipe for motor shafts with good processing performance and its manufacturing method Technical field

The present invention relates to a steel pipe and a manufacturing method thereof, in particular to a seamless steel pipe and a manufacturing method thereof.

Background technique

In recent years, under the background of carbon reduction and pollution reduction, the production and sales of electric vehicles have begun to increase by leaps and bounds, and the market and application requirements for the lightweight of electric vehicles have become more and more demanding. In order to achieve maximum weight reduction, in addition to the use of high-strength steel and lightweight materials for the main body, parts such as motor shafts and other vehicle structural parts that account for a relatively small proportion of the vehicle's weight have also begun to be gradually included in the weight reduction process. The industry uses It is a general trend to replace solid rods and forged materials with hollow pipes.

In the existing technology, components such as electric vehicle motor shafts are responsible for transmitting motor torque to the driving wheels and are very important safety components. Due to the high-speed operation of the motor shaft, the motor shaft not only bears a huge torsional moment during actual use, but also bears traction and braking forces from the wheels, such as longitudinal force, lateral force, vertical force and vibration impact force. Therefore, in the face of such harsh usage requirements, when actually preparing motor shafts, the industry usually requires materials with high strength and plasticity to ensure sufficient anti-torsion and anti-fatigue properties.

In addition, due to the differences between various types of vehicle models, different motor shafts need to undergo integral cold extrusion, cutting and other processing processes to obtain the required torsion resistance and fatigue resistance performance under high-speed rotation conditions. Therefore, when designing the steel for this type of motor shaft, while considering high strength, toughness, and fatigue performance, it must also have good cold workability.

For example: the publication number is CN104962838A, the publication date is October 7, 2015, and the Chinese patent document titled "A high-strength steel, high-strength plastic seamless steel pipe for automobile transmission half shaft and its manufacturing method" discloses a high-strength plastic seamless steel pipe Strength steel, high-strength plastic seamless steel pipe for automobile transmission half shaft and manufacturing method thereof, its chemical composition is: C: 0.07~0.15%, Si: 0.1~1.0%, Mn: 2.0~2.6%, Ni: 0.05~0.6% , Cr: 0.2~1.0%, Mo: 0.1~0.6%, B: 0.001-0.006%, Cu: 0.05~0.50%; Al: 0.015~0.060%; Nb: 0.02-0.1%; V: 0.02-0.15%. In this technical solution, the steel pipe adopts a low-C design. The strength of the prepared finished product is low, but it is conducive to welding and is more suitable for automobile axle shafts produced by friction stir welding.

Another example: the publication number is CN1388834A, the publication number is January 1, 2003, the Chinese patent document titled "A high carbon steel pipe with excellent cold working performance and high frequency hardening performance and its manufacturing method" discloses a High carbon steel pipe with excellent cold working performance and high frequency hardening performance and its manufacturing method, its public chemical composition mass percentage is: C 0.30 ~ 0.80%, Si ≤ 2%, Mn ≤ 3%. In this technical solution, special rolling technology is used to obtain a structure with cementite less than 1 μm, thereby improving the cold working performance and high-frequency hardening performance of the steel.

Different from the above-mentioned existing technical solutions, in order to solve the problems existing in the existing technology, the present invention hopes to develop and obtain a new high-strength seamless steel pipe and its manufacturing method for preparing motor shafts.

Contents of the invention

One of the purposes of the present invention is to provide a high-strength seamless steel pipe for motor shafts with good processing performance. The high-strength seamless steel pipe for motor shafts can obtain excellent mechanical properties through reasonable component matching and process design. It has very excellent mechanical properties before and after quenching and tempering heat treatment, and the hardness after quenching and tempering heat treatment can reach more than 58HRC, the strong plastic product (the product of tensile strength and elongation) is more than 15000MPa%, and it can withstand torque of more than 300KN. It is particularly suitable for It is suitable for preparing motor shaft parts that carry high torsional loads, and has good promotion prospects and application value.

In order to achieve the above object, the present invention provides a high-strength seamless steel pipe for motor shafts with good processing performance, which contains Fe and inevitable impurity elements, and also contains the following chemical elements in the following mass percentages:

C: 0.40～0.60%, 0<Si≤0.25%, Mn: 0.5～1.2%, Ti≤0.045%, B≤0.0045%, N: 0.0040～0.009%, Al: 0.015～0.045%, Ca+Mg: 0.001 ~0.006%.

Further, in the high-strength seamless steel pipe for motor shafts of the present invention, the mass percentage of each chemical element is:

C: 0.40～0.60%, 0<Si≤0.25%, Mn: 0.5～1.2%, Ti≤0.045%, B≤0.0045%, N: 0.0040～0.009%, Al: 0.015～0.045%, Ca+Mg: 0.001 ~0.006%; the balance is Fe and inevitable impurities.

Preferably, the mass percentage of each chemical element is:

C: 0.4～0.57%, Si: 0.01～0.23%, Mn: 0.5～1.2%, Ti: 0～0.043%, B: 0～0.0042%, N: 0.004～0.009%, Al: 0.016～0.045%, Ca +Mg: 0.001～0.006%.

In the high-strength seamless steel pipe for motor shafts of the present invention, the design principles of each chemical element are as follows:

C: In the high-strength seamless steel pipe for motor shafts of the present invention, the increase in the C element content is beneficial to improving the strength and fatigue resistance of the material, but the C element content in the steel pipe should not be too high. When the C element content When it is too high, the toughness and plasticity of the material will decrease, which is not conducive to cold processing, and it is prone to quality problems such as processing cracks and serious decarburization. Therefore, in the high-strength seamless steel pipe for motor shafts of the present invention, in order to ensure the quenching hardness and hardenability of the material, the mass percentage content of the C element is controlled between 0.40 and 0.60%, thereby ensuring both the quenching hardness and hardenability of the material. It has good hardenability and reduces the sensitivity of quenching cracking, which can ensure the cold working performance of steel.

Of course, in some preferred embodiments, in order to obtain better implementation effects, the mass percentage of the C element can be further preferably controlled between 0.45% and 0.55%.

Si: In the high-strength seamless steel pipe for motor shafts of the present invention, the Si element has a greater influence on the cold working performance. The lower the Si element content in the steel pipe, the better the cold working performance of the steel pipe. Generally speaking, Si is the residual element after deoxidation of steel during smelting. If the steel is required to have a lower content of Si, the deO2 method during the smelting process of molten steel needs to be changed. Therefore, it is necessary to comprehensively control the Al and Ca contents to ensure deoxidation. level, and ensure that the corresponding non-metallic inclusions have no adverse impact on the fatigue resistance of the steel. Based on this, in the high-strength seamless steel pipe for motor shafts of the present invention, the mass percentage content of Si element is controlled to 0<Si≤0.25%.

Of course, in some preferred embodiments, in order to obtain better implementation effects, the mass percentage content of the Si element can be further preferably controlled to 0<Si≤0.20%. In some preferred embodiments, the mass percentage content of Si element is controlled to be 0.01%≤Si≤0.20%. In some preferred embodiments, the mass percentage content of Si element is controlled to be 0.01%≤Si≤0.23%.

Mn: In the high-strength seamless steel pipe for motor shafts of the present invention, increasing the content of Mn element can improve the strength of the material, and Mn can stabilize the P and S elements, avoid the formation of low-melting point sulfide, and improve the material's strength. Thermal processing properties. In order to achieve the above effects, the Mn element content in the steel should not be too low. When the Mn element content in the steel is too low, the P and S elements cannot be well stabilized and the required effects cannot be achieved. At the same time, the Mn element content in the steel must not be too low. It should not be too high. When the Mn element content in steel is too high, it will lead to serious cold working deformation hardening and increase mold wear. Therefore, considering the influence of Mn element content on steel properties, in the high-strength seamless steel pipe for motor shafts of the present invention, the mass percentage content of Mn element is controlled between 0.5% and 1.2%.

Of course, in some preferred embodiments, in order to obtain better implementation effects, the mass percentage of the Mn element can be further preferably controlled between 0.6 and 1.0%.

Ti: In the high-strength seamless steel pipe for motor shafts of the present invention, an appropriate amount of Ti element can improve the hardenability of the steel. The Ti element can play a role in refining the grains together with C and N elements, but the steel The content of the Ti element should not be too high. Too high a content of Ti may cause difficulties in smelting and continuous casting. Therefore, in the high-strength seamless steel pipe for motor shafts of the present invention, when added, the mass percentage content of the Ti element is controlled to Ti ≤ 0.045%.

Of course, in some preferred embodiments, in order to obtain better implementation effects, the mass percentage of the Ti element can be further preferably controlled between 0.02% and 0.04%.

B: In the high-strength seamless steel pipe for motor shafts of the present invention, an appropriate amount of B content can improve the hardenability and plasticity of the steel, but an excessively high content of B element may cause high-temperature brittleness of the steel. Therefore, in the high-strength seamless steel pipe for motor shafts of the present invention, when added, the mass percentage content of the B element is controlled to be B≤0.0045%.

Of course, in some preferred embodiments, in order to obtain better implementation effects, the mass percentage of element B can be further preferably controlled between 0.002% and 0.004%.

N: In the high-strength seamless steel pipe for motor shafts of the present invention, N is controlled within an appropriate range so that it can refine the grains together with Ti and B elements, thereby improving the performance of the material. Therefore, in the high-strength seamless steel pipe for motor shafts of the present invention, the mass percentage content of the N element is controlled between 0.0040% and 0.009%.

Of course, in some preferred embodiments, in order to obtain better implementation effects, the mass percentage of the N element can be further preferably controlled between 0.0045% and 0.0085%.

Al: In the high-strength seamless steel pipe for motor shafts of the present invention, Al is a deoxidizer during the smelting process. It can ensure the deoxidation effect of the steel together with Si and other elements, ensure the purity of the steel, and thus ensure the quality of the material. Anti-fatigue properties. However, it should be noted that the content of Al element in steel should not be too high. When the content of Al element in steel is too high, it may lead to the production of abnormal alumina inclusions. Therefore, in order to exert the beneficial effects of the Al element, in the high-strength seamless steel pipe for motor shafts of the present invention, the mass percentage content of the Al element is controlled between 0.015% and 0.045%.

Of course, in some preferred embodiments, in order to obtain better implementation effects, the mass percentage of the N element can be further preferably controlled between 0.015% and 0.035%.

Ca, Mg: In the high-strength seamless steel pipe for motor shafts of the present invention, an appropriate amount of Ca and Mg can To improve the shape and performance of non-metallic inclusions, thereby improving the fatigue properties of materials, etc. Therefore, in order to exert the beneficial effects of Ca and Mg elements in the high-strength and easy-to-cut seamless steel pipe for motor shafts of the present invention, the inventor can consider adding Ca and/or Mg elements to the steel, which requires Ca, The sum of the mass percentages of the Mg element "Ca+Mg" is controlled between 0.001 and 0.006%.

Of course, in some preferred embodiments, in order to obtain better implementation effects, the sum of the mass percentages of Ca and Mg elements "Ca+Mg" can be further preferably controlled between 0.001 and 0.004%.

Furthermore, in the high-strength seamless steel pipe for motor shafts according to the present invention, among the inevitable impurities, P≤0.020%, S≤0.008%, and O≤0.0030%.

Furthermore, in the high-strength seamless steel pipe for motor shafts according to the present invention, among the inevitable impurities, P≤0.015%, S≤0.005%, and O≤0.0025%.

In the high-strength seamless steel pipe for motor shafts of the present invention, the P element and the S element are both impurity elements in the steel pipe. When technical conditions permit, in order to obtain a pipe with better performance and better quality, all efforts should be made to obtain a pipe with better performance and better quality. It is possible to reduce the content of impurity elements in high-strength seamless steel pipes for motor shafts.

In the present invention, P and S are both raw materials and auxiliary materials of steel or impurity elements introduced during the production process. The P element can embrittle the grain boundaries and deteriorate the toughness and processing performance of the material; while the S element can be combined to form low melting point sulfides, resulting in a decrease in the processing performance and mechanical properties of the steel.

Therefore, in the present invention, the contents of P, S, and O elements in the steel must be strictly controlled, and controlled to be P≤0.020%, S≤0.008%, and O≤0.0030%. Of course, in some preferred embodiments, in order to obtain better implementation effects, the contents of P, S, and O elements can be further controlled to satisfy: P ≤ 0.015%, S ≤ 0.005%, and O ≤ 0.0025%.

Furthermore, in the high-strength seamless steel pipe for motor shafts of the present invention, the mass percentage content of each chemical element further satisfies at least one of the following items:

C: 0.45～0.55%,

0＜Si≤0.20%,

Mn: 0.6～1.0%,

Ti: 0.02～0.04%,

B: 0.002～0.004%,

N: 0.0045～0.0085%,

Al: 0.015～0.035%,

Ca+Mg: 0.001～0.004%.

Further, in the high-strength seamless steel pipe for motor shafts of the present invention, the microstructure is ferrite + pearlite; preferably, the seamless steel pipe has been normalized.

Furthermore, in the high-strength seamless steel pipe for motor shafts according to the present invention, the microstructure after quenching and tempering heat treatment is martensite + retained austenite with a volume phase ratio of 1-25%. Preferably, the retained austenite proportion is 3-24%

Further, in the high-strength seamless steel pipe for motor shafts of the present invention, its yield strength Rp _0.2 ≥ 400MPa, tensile strength R _m ≥ 550MPa, and elongation A ₅₀ ≥ 22%; preferably, the seamless The steel pipe is normalized.

Further, in the high-strength seamless steel pipe for motor shafts of the present invention, its yield strength Rp _0.2 ≥ 420MPa, tensile strength R _m ≥ 570MPa, and elongation A ₅₀ ≥ 25%; preferably, the seamless The steel pipe is normalized.

Further, in the high-strength seamless steel pipe for motor shafts of the present invention, its yield strength Rp _0.2 ≥ 430MPa, tensile strength R _m ≥ 590MPa, and elongation A ₅₀ ≥ 25%; preferably, the seamless The steel pipe is normalized.

Furthermore, in the high-strength seamless steel pipe for motor shafts of the present invention, its performance after quenching and tempering heat treatment satisfies: yield strength R _p0.2 ≥ 1000MPa, tensile strength R _m ≥ 1400MPa, and elongation A ₅₀ ≥ 5%, its hardness is ≥58HRC, its strong plastic area is greater than 15000MPa%, and its torsion resistance is ≥300KN.

Furthermore, in the high-strength seamless steel pipe for motor shafts of the present invention, its performance after quenching and tempering heat treatment satisfies: yield strength R _p0.2 ≥ 1050MPa, tensile strength R _m ≥ 1500MPa, and elongation A ₅₀ ≥ 7%, its hardness is ≥58HRC, its strong plastic area is greater than 16000MPa%, and its torsion resistance is ≥350KN.

Furthermore, in the high-strength seamless steel pipe for motor shafts of the present invention, its performance after quenching and tempering heat treatment satisfies: yield strength R _p0.2 ≥ 1100MPa, tensile strength R _m ≥ 1600MPa, and elongation A ₅₀ ≥ 7%, its hardness is ≥60HRC, its strong plastic area is greater than 18000MPa%, and its torsion resistance is ≥400KN.

Accordingly, another object of the present invention is to provide a method for manufacturing the above-mentioned high-strength seamless steel pipe for motor shafts. This manufacturing method optimizes the design of the process. The manufacturing process is simple and easy to implement, and can effectively prepare the above-mentioned high-strength seamless steel pipe of the present invention. High-strength seamless steel pipes are used for motor shafts, which have very good application prospects.

In order to achieve the above object, the present invention proposes the above-mentioned manufacturing method of high-strength seamless steel pipe for motor shaft, which includes the steps:

(1) Prepare tube blank;

(2) Heating, piercing, hot rolling and tensioning;

(3) Intermediate heat treatment: anneal the hot-rolled pipe material in the temperature range of 650 to 800°C, and the holding time is 20 to 80 minutes;

(4) Cold drawing;

(5) Heat treatment of cold drawn tube: Normalize in the temperature range of 750~820℃, and the holding time is 20~60min to obtain the ferrite + pearlite structure.

Preferably, the method also includes the following steps:

(6) Quenching and tempering: control the quenching temperature to 820-880°C, hold for 15-30 minutes, and water-cool; control the tempering temperature to 150-300°C, hold for 20-40 minutes, and air-cool.

In the above technical solution of the present invention, during the tube blank manufacturing process in step (1), the operator can specifically use an electric furnace or converter to smelt and refining to cast the tube blank, and specifically use continuous casting to cut the tube blank to obtain the required size. . In order to meet the requirements of the automotive motor shaft for the dimensional accuracy of the steel pipe and the cold working process for the surface condition, the hot-rolled pipe material obtained in step (1) must be further intermediate heat treated and cold drawn to the required specifications and dimensional accuracy, and then further finished (cold drawn) Pipe) heat treatment, and finally obtain finished raw materials with good cold and cold processing properties.

It should be noted that in the above step (3), during the intermediate heat treatment process, the hot-rolled pipe material is controlled to be annealed in the temperature range of 650 to 800°C and kept for 20 to 80 minutes, which can ensure the cold drawing of the subsequent step (4). The process went smoothly.

In addition, in the heat treatment of the finished product in the above-mentioned step (5) of the present invention, the cold-drawn pipe material prepared in the above-mentioned step (4) needs to be normalized in the temperature range of 750 to 820°C, kept for 20 to 60 minutes, and the atmosphere in the furnace needs to be controlled. , ensuring that there is no complete decarburization (that is, there is no full ferrite tissue area on the surface of the steel pipe), and the depth of semi-decarburization is ≤150 μm. In this technical solution, by controlling the normalizing temperature and the cooling method, it can ensure that the steel pipe obtains a ferrite + pearlite structure, thereby obtaining a normalized pipe whose strength and toughness meet the cold working requirements.

Further, in the manufacturing method of the present invention, in step (2), the tube blank is heated and kept at 1210-1280°C for 30-150 minutes.

Further, in the manufacturing method of the present invention, in step (2), the perforation temperature is controlled to be 1150-1250°C.

Further, in the manufacturing method of the present invention, in step (2), the hot continuous rolling temperature is controlled to be 1000-1200°C.

Further, in the manufacturing method of the present invention, in step (2), the tension and relaxation temperature is controlled to be 950～1000℃.

Further, in the manufacturing method of the present invention, at least one of the following steps is included:

In step (1), the tube blank is manufactured by circuit or converter smelting, refining and pouring, and is cut to the required size by continuous casting. Preferably, it also includes the steps of intermediate heat treatment and cold drawing to the required specifications and dimensional accuracy. ;

In step (5), the pipe obtained by normalizing treatment is not completely decarburized, and the depth of semi-decarburization is ≤150 μm.

Compared with the existing technology, the high-strength seamless steel pipe for motor shafts and its manufacturing method according to the present invention have the following advantages and beneficial effects:

In the present invention, the inventor can obtain a brand new high-strength seamless steel pipe for motor shafts through reasonable component matching and process design. The microstructure of the high-strength seamless steel pipe for motor shafts after heat treatment is iron. Prime body + pearlite, while the microstructure after further quenching and tempering heat treatment is martensite + retained austenite with a volume phase ratio of 1-25%.

The high-strength seamless steel pipe for motor shafts prepared by the present invention has Rp _0.2 ≥ 400MPa, tensile strength R _m ≥ 550MPa, and elongation A ₅₀ ≥ 22% in the finished product state; however, the high-strength seamless steel pipe for motor shafts is After further quenching and tempering heat treatment, the strength of the seam steel pipe can be significantly improved. Its yield strength Rp _0.2 ≥ 1000MPa, tensile strength R _m ≥ 1400MPa, elongation A ₅₀ ≥ 5%, and the hardness after modulation heat treatment can reach 58HRC Above, the strong plastic product (the product of tensile strength and elongation) is greater than 15000MPa% and can withstand a torque of more than 300KN. It is especially suitable for preparing motor shaft parts carrying high torsional loads and has good promotion prospects and application value. .

Detailed ways

The high-strength seamless steel pipe for motor shafts and its manufacturing method according to the present invention will be further explained and described below with reference to specific embodiments. However, this explanation and description do not unduly limit the technical solution of the present invention.

Examples 1-10 and Comparative Examples 1-2

The high-strength seamless steel pipes for motor shafts in Examples 1-10 of the present invention and the comparative steel pipes in Comparative Examples 1-2 are both made by the following steps:

(1) According to the mass percentage of chemical elements shown in Table 1, use an electric furnace or converter to smelt + refine and pour into a tube blank, and continuously cast and cut it to obtain the required size tube blank.

(2) Heating, perforation, hot rolling and tensioning: heat and keep the tube blank at 1210~1280℃ for 30~150min. Then perform high-temperature piercing between 1150 and 1250°C, and then perform high-temperature hot continuous rolling between 1000 and 1200°C. After completing the hot rolling, further conduct tension and reduction, and control the tension and reduction temperature to 950 to 1000°C to obtain Hot rolled pipe.

(3) Intermediate heat treatment: anneal the hot-rolled pipe material in the temperature range of 650 to 800°C, and the holding time is 20 to 80 minutes.

(4) Cold drawing.

(5) Cold-drawn pipe heat treatment: Control the cold-drawn pipe material to be normalized in the temperature range of 750 to 820°C, and the holding time is 20 to 60 minutes to obtain the ferrite + pearlite structure.

It should be noted that the chemical element composition and related process design of the high-strength seamless steel pipes for motor shafts in Embodiments 1 to 10 of the present invention meet the requirements of the design specifications of the present invention. Although the comparative steel pipes of Comparative Examples 1-2 were also produced using the above-mentioned process steps, their chemical element composition and/or related process parameters had parameters that were not in compliance with the design of the present invention.

Table 1 lists the mass percentage of each chemical element in the high-strength seamless steel pipe for motor shaft of Examples 1-10 and the comparative steel pipe of Comparative Examples 1-2.

Table 1. (The balance is Fe and other unavoidable impurities except P, S, and O)

Table 2 lists the specific process parameters used in the above manufacturing process steps for the high-strength seamless steel pipes for motor shafts in Examples 1-10 and the comparative steel pipes of Comparative Examples 1-2.

Table 2.

The prepared high-strength seamless steel pipes for the motor shafts of Examples 1-10 and the comparative steel pipes of Comparative Examples 1-2 were respectively sampled, and the microstructure of the steel pipes of each Example and Comparative Example before quenching and tempering heat treatment was analyzed. Observe and test various properties of each embodiment and comparative example to obtain the normal temperature mechanical properties before conditioning. The test results of relevant mechanical properties are listed in Table 3.

Relevant performance testing methods are as follows:

Tensile test: According to GB/T 228.1-2010 Metal Materials Tensile Test Part 1: Room Temperature Tensile Test Method, to test the steel pipes obtained in each example and comparative example before quenching and tempering heat treatment at room temperature. Yield strength, tensile strength and elongation values.

Table 3 lists the performance test results of the high-strength seamless steel pipes for motor shafts in Examples 1-10 that have not undergone quenching and tempering heat treatment and the comparative steel pipes in Comparative Examples 1-2.

table 3.

As can be seen from the above Table 3, before undergoing quenching and tempering heat treatment, the high-strength seamless steel pipes for motor shafts in Examples 1-10 already have very excellent mechanical properties, and their yield strength R _p0.2 is at 417 -506MPa, its tensile strength R _m is between 564-672MPa, and its elongation A ₅₀ is between 23-30%. In addition, it was observed that before undergoing quenching and tempering heat treatment, the microstructure of the high-strength seamless steel pipes for motor shafts in Examples 1 to 10 was all ferrite + pearlite.

Correspondingly, in order to further illustrate that the high-strength seamless steel pipe for motor shafts according to the present invention still has very excellent performance after quenching and tempering heat treatment, the inventor further tested the high-strength and toughness seamless steel pipes for motor shafts in the prepared finished product examples 1-10. Seamless steel pipes and comparative steel pipes of Comparative Examples 1-2 were sampled separately, and the steel pipes of each Example and Comparative Example were subjected to quenching and tempering heat treatment. The process of controlling the quenching and tempering heat treatment was as follows: the quenching temperature is 860°C, and the holding time is 20 minutes. Water cooling; tempering temperature is 250℃, holding time is 30min, air cooling.

After completing the quenching and tempering heat treatment of the steel pipes of the examples and comparative examples, the inventor further conducted a mechanical property test on the quenched and tempered heat treated steel pipes to measure the performance of the steel pipes after quenching and tempering heat treatment. The relevant mechanical property test results are listed below in Table 4.

When testing the mechanical properties of the steel pipes of Examples 1-10 and Comparative Examples 1-2 after quenching and tempering heat treatment, the tensile test process is the same as the test process in Table 3 above, which can also be measured corresponding to the quenching and tempering heat treatment. Yield strength, tensile strength and elongation of the steel pipes of Examples 1-10 and Comparative Examples 1-2.

In addition, in addition to the above properties, other properties of the steel pipes of the examples and comparative examples after quenching and tempering heat treatment were further tested. The relevant test methods are as follows:

Hardness test: Use a Rockwell hardness tester to measure the hardness (HRC) of the steel pipes of Examples 1-10 and Comparative Examples 1-2 after quenching and tempering heat treatment.

Anti-torsion performance test: Use a static torsion test device to measure the anti-torsion performance of the steel pipes of Examples 1-10 and Comparative Examples 1-2 after quenching and tempering heat treatment.

Table 4 lists the performance test results of the high-strength seamless steel pipes for motor shafts of Examples 1-10 and the comparative steel pipes of Comparative Examples 1-2 after quenching and tempering heat treatment.

Table 4.

Note: In the above Table 4, Rm×A50 is the strong plastic product, which is the product of tensile strength and elongation.

As can be seen from Table 4, after quenching and tempering heat treatment, the comprehensive performance of the high-strength seamless steel pipes for motor shafts in Examples 1-10 of the present invention is significantly better than that of the comparative steel pipes in Comparative Examples 1-2. At the same time, compared with before the quenching and tempering heat treatment, the yield strength and tensile strength of the high-strength seamless steel pipes for motor shafts in Examples 1 to 10 after the quenching and tempering heat treatment have been significantly improved, and the elongation A ₅₀ accordingly Decreased.

Referring to Table 4, it can be seen that the high-strength seamless steel pipes for motor shafts obtained in Examples 1-10 of the present invention all have excellent mechanical properties. Their yield strength R _p0.2 is between 1059-1169 MPa, and their tensile strength R _m is between 1400-1766MPa, elongation is between 9-15%, its strong plasticity R _m ×A ₅₀ is between 15499-24724MPa%, hardness is between 59-64HRC, and torsion resistance is between 346-597KN between.

Compared with Examples 1-10, in Comparative Examples 1-2, there are chemical components and/or processes that do not meet the design requirements of the present invention. This design makes at least one of the comparative steel pipes prepared in Comparative Examples 1-2 The mechanical properties failed to meet the requirements of the present invention. As shown in Table 4, the torsional properties of Comparative Examples 1 and 2 are lower than those of Examples 1-10.

In addition, after completing the above-mentioned testing of mechanical properties, the inventor also sampled the steel pipes of Examples 1-10 and Comparative Examples 1-2 after quenching and tempering heat treatment, and observed and analyzed their microstructures. Related observations The analysis results are shown in Table 5 below. In the present invention, a Zeiss optical microscope is used to observe the microstructure, and X-ray diffraction (XRD) is used to analyze the proportion of retained austenite.

Table 5 lists the microstructure observation and analysis results of the high-strength seamless steel pipes for motor shafts of Examples 1-10 and the comparative steel pipes of Comparative Examples 1-2 after quenching and tempering heat treatment.

table 5.

It can be seen from the above Table 5 that after quenching and tempering heat treatment, the high-strength seamless steel pipes for motor shafts in Examples 1-10 all obtained a microstructure of martensite + retained austenite, and the retained austenite The volume phase ratio is specifically between 3-24%.

It should be noted that the combination of each technical feature in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All the technical features recorded in this case can be freely combined in any way or combination, unless there is a conflict between them.

It should also be noted that the embodiments listed above are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and subsequent similar changes or deformations that those skilled in the art can directly derive from the disclosed content of the present invention or can easily associate them should all fall within the protection scope of the present invention. .

Claims (15)

1. A high-strength seamless steel pipe for motor shafts with good processing performance contains Fe and inevitable impurity elements. It is characterized in that it also contains the following chemical elements in the following mass percentages:

   C: 0.40～0.60%, 0<Si≤0.25%, Mn: 0.5～1.2%, Ti≤0.045%, B≤0.0045%, N: 0.0040～0.009%, Al: 0.015～0.045%, Ca+Mg: 0.001 ~0.006%.
2. The high-strength seamless steel pipe for motor shafts according to claim 1, characterized in that the mass percentage of each chemical element is:

   C: 0.40～0.60%, 0<Si≤0.25%, Mn: 0.5～1.2%, Ti≤0.045%, B≤0.0045%, N: 0.0040～0.009%, Al: 0.015～0.045%, Ca+Mg: 0.001 ~0.006%; the balance is Fe and inevitable impurities;

   Preferably, the mass percentage of each chemical element is:

   C: 0.4～0.57%, Si: 0.01～0.23%, Mn: 0.5～1.2%, Ti: 0～0.043%, B: 0～0.0042%, N: 0.004～0.009%, Al: 0.016～0.045%, Ca +Mg: 0.001～0.006%.
3. The high-strength seamless steel pipe for motor shafts according to claim 1 or 2, characterized in that among the inevitable impurities, P≤0.020%, S≤0.008%, and O≤0.0030%.
4. The high-strength seamless steel pipe for motor shafts according to claim 3, characterized in that among the inevitable impurities, P≤0.015%, S≤0.005%, and O≤0.0025%.
5. The high-strength seamless steel pipe for motor shafts according to claim 1 or 2, characterized in that the mass percentage content of each chemical element further satisfies at least one of the following items:
   C: 0.45～0.55%,
   0＜Si≤0.20%,
   Mn: 0.6～1.0%,
   Ti: 0.02～0.04%,
   B: 0.002～0.004%,
   N: 0.0045～0.0085%,
   Al: 0.015～0.035%,
   Ca+Mg: 0.001～0.004%.
6. The high-strength seamless steel pipe for motor shafts according to claim 1 or 2, characterized in that its microstructure is ferrite + pearlite.
7. The high-strength seamless steel pipe for motor shafts according to claim 1 or 2, characterized in that its microstructure after quenching and tempering heat treatment is martensite + the volume phase ratio is 1-25% retained austenite; preferably , the proportion of retained austenite is 3-24%.
8. The high-strength seamless steel pipe for motor shafts according to claim 1 or 2, characterized in that its yield strength Rp _0.2 ≥ 400MPa, tensile strength R _m ≥ 550MPa, and elongation A ₅₀ ≥ 22%.
9. The high-strength seamless steel pipe for motor shafts according to claim 1 or 2, characterized in that its performance after quenching and tempering heat treatment satisfies: yield strength Rp _0.2 ≥ 1000MPa, tensile strength R _m ≥ 1400MPa, and elongation A ₅₀ ≥5%, its hardness ≥58HRC, strong plastic area greater than 15000MPa%, anti-torsion performance ≥300KN.
10. A method for manufacturing a high-strength seamless steel pipe for a motor shaft according to any one of claims 1 to 9, characterized in that it includes the steps:

    (1) Prepare tube blank;

    (2) Heating, piercing, hot rolling and tensioning;

    (3) Intermediate heat treatment: anneal the hot-rolled pipe material in the temperature range of 650 to 800°C, and the holding time is 20 to 80 minutes;

    (4) Cold drawing;

    (5) Heat treatment of cold drawn tube: Normalize in the temperature range of 750~820℃, and the holding time is 20~60min to obtain the ferrite + pearlite structure;

    Preferably, the method also includes the following steps:

    (6) Quenching and tempering: control the quenching temperature to 820-880°C, hold for 15-30 minutes, and water-cool; control the tempering temperature to 150-300°C, hold for 20-40 minutes, and air-cool.
11. The manufacturing method according to claim 10, characterized in that in step (2), the tube blank is heated and kept at 1210-1280°C for 30-150 minutes.
12. The manufacturing method according to claim 10, characterized in that in step (2), the perforation temperature is controlled to be 1150-1250°C.
13. The manufacturing method according to claim 10, characterized in that in step (2), the hot continuous rolling temperature is controlled to be 1000-1200°C.
14. The manufacturing method according to claim 10, characterized in that in step (2), the tension and relaxation temperature is controlled to be 950-1000°C.
15. The manufacturing method according to claim 10, characterized in that:

    In step (1), the tube blank is manufactured by circuit or converter smelting, refining and pouring, and is cut to the required size by continuous casting. Preferably, it also includes the steps of intermediate heat treatment and cold drawing to the required specifications and dimensional accuracy. ;and / or

    In step (5), the pipe obtained by normalizing treatment is not completely decarburized, and the depth of semi-decarburization is ≤150 μm.