High-strength seamless steel pipe for automobile transmission half shaft and manufacturing method of high-strength seamless steel pipe

Abstract

The invention discloses a high-strength seamless steel pipe for an automobile transmission half shaft, which contains Fe and inevitable impurities, and also contains the following chemical elements in percentage by mass: 0.18-0.31% of C; 0.1 to 1.0 percent of Si; 0.8% to 1.2% of Mn; 0.05 to 0.6 percent of Ni; 0.2 to 1.0 percent of Cr; 0.1% to 0.6% of Mo; 0.015 to 0.060% of Al; 0.02 to 0.2 percent of Nb; 0.02 to 0.25 percent of V; 0.02 to 0.1 percent of N; and Ca, Mg and rare earth elements are not contained. The invention further discloses a manufacturing method of the seamless steel tube. The manufacturing method comprises the following steps: heating a tube blank and then uniformly heating; after hot piercing, continuous rolling and tension reducing are conducted, natural cooling is conducted, and the steel pipe is subjected to annealing treatment; pickling, phosphating and saponifying; performing cold machining to a finished product size; and carrying out sectional tempering heat treatment in a protective atmosphere furnace.

Description

Technical Field

[0001] The present invention relates to a steel pipe and a manufacturing method thereof, and in particular to a high-strength seamless steel pipe and a manufacturing method thereof. Background Art

[0002] The half shaft for automobile transmission is an important force transmission component of the automobile, especially the non-full floating half shaft. To transmit the torque from the engine, it must first have good static torsion performance and anti-torsion fatigue performance. The processing technology of the one-piece transmission shaft is to heat treat the steel tube after rotary forging to ensure the strength. In the actual processing and production process, small cracks are easily generated on the inner surface of the steel tube during rotary forging in a cold state, which is easy to form a fatigue crack source in the subsequent rotary fatigue process, affecting the fatigue performance. Therefore, it is an important factor to ensure the rotary fatigue performance that the inner wall of the steel tube does not crack during the rotary forging process.

[0003] The Chinese patent with publication number CN 113846262 A and publication date December 28, 2021, entitled "A seamless steel pipe for an integral hollow transmission half-shaft for automobiles and its manufacturing method" involves a method for manufacturing a seamless steel pipe for a hollow transmission half-shaft. The invention patent adopts a higher carbon content and a higher finished product heat treatment temperature, and its rotational fatigue performance is lower.

[0004] The Chinese patent document with publication number CN100384553C and publication date April 30, 2008, entitled "Seamless steel pipe for drive shaft and manufacturing method thereof" relates to a steel material for a hollow drive shaft and a manufacturing method thereof. The invention improves the torsional fatigue performance of the steel pipe by controlling the surface roughness and hardness of the steel pipe, and has no special requirements on the strength of the steel pipe. Summary of the invention

[0005] One of the purposes of the present invention is to provide a high-strength seamless steel pipe for automobile transmission half shaft, which has good processing performance in cold state, no cracks on the inner surface after high-speed rotary forging in cold state, high strength and strength-plasticity product, and good torsional fatigue performance.

[0006] In order to achieve the above object, the present invention provides a high-strength seamless steel pipe for automobile transmission half shaft, which contains Fe and inevitable impurities, and further contains the following chemical elements in the following mass percentages:

[0007] C: 0.18-0.31%; Si: 0.1-1.0%; Mn: 0.8-1.2%; Ni: 0.05-0.6%; Cr: 0.2-1.0%; Mo : 0.1-0.6%; Al: 0.015-0.060%; Nb: 0.02-0.2%; V: 0.02-0.25%; N: 0.02-0.1%;

[0008] It does not contain Ca, Mg and rare earth elements;

[0009] It also satisfies: 2.5≤(V+Nb) / N≤4, where each chemical element is substituted into the value before the percentage sign of its mass percentage content.

[0010] Accordingly, the present invention provides a high-strength seamless steel pipe for automobile transmission half shaft, wherein the mass percentage of each chemical element is:

[0011] C: 0.18-0.31%; Si: 0.1-1.0%; Mn: 0.8-1.2%; Ni: 0.05-0.6%; Cr: 0.2-1.0%; Mo: 0.1-0.6%; Al: 0.015-0.060%; Nb: 0.02-0.2%; V: 0.02-0.25%; N: 0.02-0.1%; the balance is Fe and unavoidable impurities.

[0012] Furthermore, in the high-strength seamless steel tube for automobile transmission half-axle of the present invention, the mass percentage of Ni is: Ni: 0.2-0.6%.

[0013] The high-strength plastic seamless steel pipe for automobile transmission half-axle described in the present invention does not contain high-cost additive elements such as Ca, Mg or rare earth metals. Through the optimization design of chemical composition and combined with a reasonable manufacturing process, the high-strength plastic seamless steel pipe for automobile transmission half-axle described in the present invention has high strength after tempering, high cold forging performance in the cold state before tempering, and the finished product has good torsional fatigue resistance.

[0014] Specifically, the design principles of the chemical elements in the high-strength seamless steel tube for automobile transmission half shaft of the present invention are:

[0015] C: In the high-strength seamless steel pipe described in the present invention, the C element is one of the main elements for improving the strength of steel. It can effectively improve the strength of steel through the formation of carbides, and the cost of addition is low. When the C content is lower than 0.18%, the seamless steel pipe cannot reach a tensile strength of more than 1100MPa after quenching and tempering. However, when the C content is higher than 0.31%, the plasticity of the seamless steel pipe is reduced, and cracking is likely to occur during the rotary forging process. Therefore, in the high-strength seamless steel pipe described in the present invention, the mass percentage of the C element can be controlled between 0.18-0.31%.

[0016] Si: In the high-strength seamless steel pipe described in the present invention, Si element is added as a reducing agent and deoxidizer during the steelmaking process. It does not form carbides in steel, and its solid solubility in steel is relatively large, which can strengthen the ferrite in the steel to improve the strength of the steel. Therefore, this steel grade appropriately increases the Si content to improve the strength of the air-cooled steel. However, if the silicon content exceeds 1.0%, the plasticity of the steel pipe will be greatly reduced, and the welding performance of the steel pipe will also be reduced. Therefore, in the high-strength seamless steel pipe described in the present invention, the mass percentage of Si element can be controlled between 0.10-1.0%.

[0017] Mn: In the high-strength seamless steel pipe described in the present invention, the Mn element is an important alloying element and a weak carbide forming element. The Mn element mainly improves the strength of steel through solid solution strengthening. Increasing the Mn element content can lower the phase transition temperature of steel and reduce the critical cooling rate of quenching. When the Mn element content increases by more than 1.2%, the plasticity and impact toughness of the steel decrease significantly, especially the cold state rotary forging plasticity increases, which increases the risk of rotary forging cracking. Therefore, in the high-strength seamless steel pipe described in the present invention, the mass percentage of the Mn element can be controlled between 0.8-1.2%.

[0018] Ni: In the high-strength seamless steel pipe of the present invention, the Ni element is an element that can improve the strength and hardenability of steel, and also an element that can improve the toughness of steel. Considering the cost factor of steel, in order to achieve the ideal strengthening effect and improve the toughness of steel in combination with other elements, in the high-strength seamless steel pipe of the present invention, the mass percentage of the Ni element can be controlled between 0.05-0.6%. Further, the mass percentage of the Ni element can be controlled between 0.2-0.6%.

[0019] Cr: In the high-strength seamless steel pipe described in the present invention, the Cr element is a forming element of medium-strong carbides. A part of the Cr element in the steel is replaced by iron to form alloy cementite to improve its stability. The other part is dissolved in the ferrite to play a solid solution strengthening role, improving the strength and hardness of the ferrite. The Cr element is also the main element for improving the hardenability of steel. However, once the Cr element content exceeds 1.0%, it will affect the toughness of the welding part, and considering the cost of addition, in the high-strength seamless steel pipe described in the present invention, the mass percentage of the Cr element can be controlled between 0.2-1.0%.

[0020] Mo: In the high-strength seamless steel pipe described in the present invention, the Mo element has the effect of solid solution strengthening and improving the hardenability of the steel, and can also improve the tempering stability of the steel. When the Mo element content reaches 0.05%, it will have a significant effect of solid solution strengthening and improving hardenability. Since this type of steel needs to be air-cooled to obtain higher strength, the Mo element content can be appropriately increased to more than 0.1%, and combined with other elements to fully increase the hardenability of the steel. When the Mo element content exceeds a certain range, it will affect the toughness of the welding part of the steel pipe. At the same time, cost factors must also be considered. In the high-strength seamless steel pipe described in the present invention, the mass percentage of the Mo element can be controlled between 0.1-0.6%.

[0021] Al: In the high-strength seamless steel pipe described in the present invention, the Al element has a deoxidizing effect in the steel and helps to improve the toughness and processability of the steel. When the Al element content reaches 0.015% or more, the effect of improving the toughness and processability of the steel is more significant. However, when the Al content exceeds 0.060%, the tendency of cracks to appear in the steel increases. Therefore, in the high-strength seamless steel pipe described in the present invention, the mass percentage of the Al element can be controlled between 0.015-0.060%.

[0022] Nb: In the high-strength seamless steel pipe of the present invention, the role of Nb element is to improve the toughness of steel. When the Nb element content is greater than or equal to 0.02%, the addition effect is more obvious. When the Nb element content is greater than 0.2wt.%, the toughness of the steel will be reduced. Therefore, in the high-strength seamless steel pipe of the present invention, the mass percentage of N element can be controlled between 0.02-0.2%.

[0023] V: In the high-strength seamless steel pipe described in the present invention, the V element is a strong carbide-forming element, and its ability to combine with carbon is very strong. The fine dispersed VC particles formed can play a role in dispersion strengthening, which significantly increases the strength of the steel. When the V content is less than 0.02%, the dispersion strengthening effect is not obvious. When the V content is greater than 0.25%, it will also affect the processing properties of the steel. Therefore, in the high-strength seamless steel pipe described in the present invention, the mass percentage of the V element can be controlled between 0.02-0.25%.

[0024] N: In the high-strength seamless steel pipe described in the present invention, the N element mainly acts together with Nb and V in the steel to form fine dispersed nitrides to improve the strength and pin dislocations, thereby improving the cold forging ability of the steel. Excessive N content will form lamellar nitrides that affect the cold working performance of the steel. Therefore, in the high-strength seamless steel pipe described in the present invention, the mass percentage of the N element can be controlled between 0.02-0.1%.

[0025] Furthermore, among the inevitable impurities in the high-strength seamless steel pipe for automobile transmission half-shafts of the present invention, S≤0.015% and P≤0.025%.

[0026] The inevitable impurities in the present invention are mainly S and P elements. If conditions permit, it is hoped that their content is as low as possible. In some embodiments, the S mass percentage can be controlled to be below 0.015%, and the P mass percentage can be controlled to be below 0.025%.

[0027] Furthermore, in the high-strength seamless steel tube for automobile transmission half-axle described in the present invention, its microstructure includes spheroidized ferrite pearlite structure and precipitates dispersedly precipitated on the matrix.

[0028] Furthermore, in the high-strength seamless steel pipe for automobile transmission half-axle described in the present invention, the grain size of the spheroidized ferrite pearlite structure is greater than grade 8.

[0029] Furthermore, in the high-strength seamless steel pipe for automobile transmission half shaft of the present invention, the precipitates include fine-grained VC, NbC, VN and NbN, and C 6 Cr 23 .

[0030] Furthermore, in the high-strength seamless steel pipe for automobile transmission half-axle described in the present invention, the wall thickness is 1.5 to 8 mm.

[0031] Furthermore, the high-strength seamless steel pipe for automobile transmission half-axle described in the present invention has an outer diameter of 30 to 60 mm.

[0032] Furthermore, the high-strength seamless steel pipe for automobile transmission half-axle described in the present invention has the following properties: tensile strength ≥ 800MPa; yield strength ≥ 600MPa; elongation ≥ 30%; no cracking after cold rotary forging with a cold rotary forging thickening rate greater than 70%; and the number of torsional fatigue tests at room temperature greater than 600,000 times.

[0033] Correspondingly, another object of the present invention is to provide a method for manufacturing a high-strength seamless steel pipe for an automobile transmission half-axle, which forms a spheroidized ferrite pearlite structure through a finished product segmented tempering heat treatment to ensure the cold rotary forging performance of the steel pipe. After the rotary forging process, there is no cracking on the inner surface, thereby ensuring the rotational fatigue performance of the steel pipe.

[0034] In order to achieve the above object, the present invention proposes a method for manufacturing the above-mentioned high-strength seamless steel pipe for automobile transmission half shaft, which comprises the steps of:

[0035] (1) Heating the tube and then heating it evenly;

[0036] (2) After hot piercing, continuous rolling, and tension reducing, the steel pipe is naturally cooled and annealed;

[0037] (3) Pickling, phosphating and saponifying;

[0038] (4) Cold working to finished size;

[0039] (5) Performing a staged tempering heat treatment in a protective atmosphere furnace, wherein the first stage tempering temperature is 700-830°C, and the holding time is 15-40 minutes; the second stage tempering temperature is 450-600°C, and the holding time is 15-40 minutes.

[0040] The manufacturing method of the high-strength seamless steel pipe for automobile transmission half shaft described in the present invention finally adopts the segmented tempering method for heat treatment, which can make full use of the production capacity of the continuous roller hearth furnace. Different furnace sections use different temperatures, thereby improving the heat treatment efficiency of the steel pipe. This heat treatment method reduces the process energy consumption of the seamless steel pipe, avoids the quality problems of bending and cracking that are easy to occur in the quenching process, and ensures the dimensional accuracy requirements of the steel pipe. The process and the element ratio of the steel pipe ensure that the steel pipe can obtain spheroidized ferrite pearlite structure and fine granular precipitates after segmented tempering, so that the finished steel pipe has high strength and strength-plasticity product, and ensures the excellent torsional fatigue resistance of the steel pipe.

[0041] Furthermore, in step (1) of the method for manufacturing a high-strength seamless steel tube for an automobile transmission half shaft of the present invention, the tube blank is heated to 1180° C.-1250° C., and the soaking time is 20-30 minutes.

[0042] Furthermore, in step (2) of the method for manufacturing a high-strength seamless steel tube for an automobile transmission half shaft according to the present invention, the hot perforation temperature is 1170-1220°C.

[0043] Furthermore, in step (2) of the method for manufacturing a high-strength seamless steel tube for an automobile transmission half shaft of the present invention, the annealing treatment temperature is 600-850° C. and the heat preservation time is 30-60 min.

[0044] Furthermore, in step (4) of the method for manufacturing a high-strength seamless steel tube for an automobile transmission half shaft of the present invention, a stress relief annealing process is performed between adjacent cold working passes at a temperature of 450-600° C. for 30-60 minutes.

[0045] Furthermore, in step (4) of the method for manufacturing a high-strength seamless steel tube for an automobile transmission half shaft according to the present invention, the elongation coefficient of each cold working pass is 1.5-2.0.

[0046] In addition, the manufacturing method of the high-strength seamless steel pipe for automobile transmission half shaft described in the present invention not only ensures the production efficiency of the steel pipe manufacturing, but also effectively avoids the cracking of the steel pipe by controlling the elongation coefficient of each cold working.

[0047] The high-strength seamless steel pipe for automobile transmission half shaft and the manufacturing method thereof of the present invention have the following advantages and beneficial effects:

[0048] The high-strength seamless steel pipe for automobile transmission half-axle described in the present invention mainly forms fine-grained precipitates through the ratio of V, Nb and N elements to ensure the strength and toughness of the steel, forms a spheroidized ferrite pearlite structure through the finished product segmented tempering heat treatment, ensures the cold rotary forging performance of the steel pipe, and has no cracks on the inner surface after rotary forging, thereby ensuring the rotational fatigue performance of the steel pipe.

[0049] The high-strength seamless steel pipe for automobile transmission half-axle described in the present invention has high strength before tempering treatment through optimized design of chemical composition and combined with reasonable manufacturing process, and has high cold forging performance in the cold state before tempering and good torsional fatigue resistance.

[0050] The high-strength seamless steel pipe for automobile transmission half shaft of the present invention adopts the above technical scheme, so that it has high strength and strength-plasticity product, good cold forging processing performance, and good torsional fatigue resistance. In some embodiments, its tensile strength is ≥800MPa, yield strength is ≥600MPa, elongation is ≥30%, cold forging thickening rate is >70%, no cracking after cold forging, and the number of torsional fatigue resistance at room temperature exceeds 600,000 times.

[0051] In addition, the high-strength seamless steel tube for the automobile transmission half shaft described in the present invention has a thin wall, light weight and good dimensional accuracy, and can meet the use requirements of lightweight vehicle series. DETAILED DESCRIPTION

[0052] The high-strength seamless steel pipe for automobile transmission half shaft and the manufacturing method thereof described in the present invention will be further explained and illustrated in conjunction with specific embodiments below. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0053] Examples A1-A10 and Comparative Examples B1-B5

[0054] The high-strength seamless steel tubes for automobile transmission half shafts of Examples A1-A10 and the comparative tubes of Comparative Examples B1-B5 are prepared by the following steps:

[0055] (1) Smelting and forming a tube blank, the mass percentage of chemical elements of the tube blank is shown in Table 1.

[0056] (2) Heating the tube billet and then evenly heating it: Use a ring heating furnace to heat the tube billet to 1180℃-1250℃, and the even heating time is 20-30min.

[0057] (3) After hot piercing, continuous rolling and tension reducing, the steel pipe is naturally cooled and annealed: a vertical conical hot piercing machine is used for hot piercing, and the piercing temperature is 1170-1220°C. The tube blank is reduced in diameter and wall thickness by a three-roll tension reducing mill. The cooling bed is cooled naturally without air cooling, and the steel pipe is annealed in time. The annealing temperature is controlled at 600-850°C and kept warm for 30-60 minutes to prevent cracking during the placement of the steel pipe.

[0058] (4) After pickling, phosphating and saponifying are carried out.

[0059] (5) Cold drawing or cold rolling is used to cold process the steel pipe to the finished product size. The elongation coefficient of each cold process can be 1.5-2.0, so as to ensure the production efficiency of the steel pipe while avoiding the defect of cracking of the steel pipe after cold processing.

[0060] In addition, preferably, an annealing process of 450-600°C for 30-60 minutes can be used between each cold working to eliminate the processing stress and soften the steel pipe. The finished steel pipe after cold working has a wall thickness of 1.5-8 mm and an outer diameter of 30-60 mm.

[0061] (6) Performing a staged tempering heat treatment in a protective atmosphere furnace, wherein the first stage tempering temperature is 700-830°C, the holding time is 15-40 min, and the second stage tempering temperature is 450-600°C, the holding time is 15-40 min.

[0062] Table 1 lists the mass percentages of chemical elements of the high-strength seamless steel tubes for automobile transmission half shafts of Examples A1-A10 and the comparative tubes of Comparative Examples B1-B5.

[0063] Table 1. (wt.%, the balance is Fe and other inevitable impurities except P and S)

[0064]

[0065]

[0066] Table 2 lists the process parameters of the high-strength seamless steel tubes for automobile transmission half shafts of Examples A1-A10 and the control tubes of Comparative Examples B1-B5.

[0067] Table 2.

[0068]

[0069] The high-strength seamless steel pipes for automobile transmission half shafts of Examples A1-A10 finally obtained were sampled respectively, and the microstructure was observed by the method specified in GB / T13299 standard, and the grain size was graded by the method of GB / T6394. The test results are listed in Table 3.

[0070] Table 3.

[0071]

[0072] It can be seen from Table 3 that the microstructure of the high-strength seamless steel tube for automobile transmission half shaft of Examples A1-A10 includes spheroidized ferrite pearlite structure and precipitates dispersed on the matrix, wherein the grain size of the spheroidized ferrite pearlite structure is greater than 8 levels, and the precipitates include fine-grained VC, NbC, VN and NbN, and C with a size of less than 300 μm. 6 Cr 23 , which makes the finished steel pipe have high strength and strength-plasticity product, ensuring the excellent torsional fatigue resistance of the steel pipe.

[0073] In addition, the finally obtained high-strength seamless steel pipes for automobile transmission half shafts of Examples A1-A10 and the comparative steel pipes of Comparative Examples B1-B5 were sampled and their various properties were tested, and the results and the wall thickness and outer diameter of the seamless steel pipes are listed in Table 4. Among them:

[0074] (1) Use the test methods for tensile strength, yield strength and elongation as required by GB / T228;

[0075] (2) Cold rotary forging performance: The rotary forging force is greater than 120N, the rotary forging frequency is 800HZ, the rotary forging deformation rate is greater than 2, and the rotary forging is performed. If there is no crack on the inner surface after rotary forging, it is considered qualified.

[0076] (3) Torsional fatigue life test: The load alternating torque is 3000Nm, and a torsional fatigue test is performed. If the number of torsional fatigue tests is greater than 600,000 times, it is considered qualified.

[0077] Table 4.

[0078]

[0079] It can be seen from Table 4 above that since the seamless steel pipes in Examples A1-A10 have the mass percentage ratio of the chemical elements specified in the technical solution of the present invention, and they are all processed and produced according to the manufacturing method provided by the present invention, the high-strength plastic seamless steel pipes for automobile transmission half shafts in Examples A1-A10 all meet the requirements of tensile strength greater than 800 MPa, yield strength greater than 600 MPa, elongation greater than 30%, no cracks after cold rotary forging with a cold rotary forging thickening rate greater than 70%, and the number of torsional fatigue tests under a load alternating torque of 3000 Nm is greater than 600,000 times.

[0080] However, since the mass percentage of certain chemical elements in each seamless steel pipe in comparative examples B1-B5 has exceeded the range specified by the technical solution of the present invention, or the processing technology has not been processed and produced according to the manufacturing method provided by the present invention, at least one of the comprehensive mechanical properties of these seamless steel pipes does not meet the standards of high-strength plastic seamless steel pipes for automobile transmission axles.

[0081] In addition, the combination of the various technical features 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 technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0082] It should also be noted that the above examples are only specific embodiments of the present invention, and the present invention is obviously not limited to the above examples, and there are many similar variations. All variations directly derived or associated from the contents disclosed by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A high-strength seamless steel tube for automobile transmission half shaft, containing Fe and inevitable impurities, It is characterized in that It also contains the following chemical elements in the following mass percentages: C: 0.18-0.31%; Si: 0.1-1.0%; Mn: 0.8-1.2%; Ni: 0.05-0.6%; Cr: 0.2-1.0%; Mo: 0.1-0.6%; Al: 0.015-0.060%; Nb: 0.02-0.2%; V：0.02-0.25％； N：0.02-0.1％； It does not contain Ca, Mg and rare earth elements; It also satisfies: 2.5≤(V+Nb) / N≤4, where each chemical element is substituted into the value before the percentage sign of its mass percentage content.

2. The high-strength seamless steel pipe for automobile transmission half shaft according to claim 1, It is characterized in that The mass percentage of each chemical element is: C: 0.18-0.31%; Si: 0.1-1.0%; Mn: 0.8-1.2%; Ni: 0.05-0.6%; Cr: 0.2-1.0%; Mo: 0.1-0.6%; Al: 0.015-0.060%; Nb: 0.02-0.2%; V：0.02-0.25％； N: 0.02-0.1%; the balance is Fe and inevitable impurities.

3. The high-strength seamless steel pipe for automobile transmission half shaft according to claim 1 or 2, It is characterized in that The mass percentage of Ni is: Ni: 0.2-0.6%.

4. The high-strength seamless steel pipe for automobile transmission half shaft according to claim 1 or 2, It is characterized in that Among the inevitable impurities, S≤0.015%, P≤0.025%.

5. The high-strength seamless steel pipe for automobile transmission half shaft according to claim 1 or 2, It is characterized in that Its microstructure includes spheroidized ferrite pearlite structure and precipitates dispersed in the matrix.

6. The high-strength seamless steel pipe for automobile transmission half shaft according to claim 5, It is characterized in that The grain size of the spheroidized ferrite pearlite structure is greater than grade 8.

7. The high-strength seamless steel pipe for automobile transmission half shaft according to claim 5, It is characterized in that The precipitates include fine-grained VC, NbC, VN and NbN, and C 6 Cr 23 .

8. The high-strength seamless steel pipe for automobile transmission half shaft according to claim 1 or 2, It is characterized in that Its wall thickness is 1.5 to 8 mm.

9. The high-strength seamless steel pipe for automobile transmission half shaft according to claim 1 or 2, It is characterized in that Its outer diameter is 30 to 60 mm.

10. The high-strength seamless steel pipe for automobile transmission half shaft according to claim 1 or 2, It is characterized in that Its performance meets the following requirements: tensile strength ≥ 800MPa, yield strength ≥ 600MPa, elongation ≥ 30%; cold rotary forging thickening rate is greater than 70% and there is no cracking after cold rotary forging; the number of torsional fatigue times at room temperature is greater than 600,000 times.

11. A method for manufacturing a high-strength seamless steel pipe for automobile transmission half shaft according to any one of claims 1 to 10, It is characterized in that Includes steps: (1) Heating the tube and then heating it evenly; (2) After hot piercing, continuous rolling, and tension reducing, the steel pipe is naturally cooled and annealed; (3) Pickling, phosphating and saponifying; (4) Cold working to finished size; (5) Performing a staged tempering heat treatment in a protective atmosphere furnace, wherein the first stage tempering temperature is 700-830°C, and the holding time is 15-40 minutes; the second stage tempering temperature is 450-600°C, and the holding time is 15-40 minutes.

12. The manufacturing method according to claim 11, It is characterized in that In step (1), the tube blank is heated to 1180°C-1250°C, and the soaking time is 20-30 minutes.

13. The manufacturing method according to claim 11, It is characterized in that In step (2), the thermal perforation temperature is 1170-1220°C.

14. The manufacturing method according to claim 11, It is characterized in that In step (2), the annealing temperature is 600-850°C and the temperature is maintained for 30-60 minutes.

15. The manufacturing method according to claim 11, It is characterized in that In step (4), a stress relief annealing process is performed between adjacent cold working passes at a temperature of 450-600° C. for 30-60 minutes.

16. The manufacturing method according to claim 11, It is characterized in that In step (4), the elongation coefficient of each cold working pass is 1.5-2.0.

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