Seamless steel tube for pin shaft and manufacturing method of seamless steel tube

Abstract

The invention belongs to the technical field of metal pressure processing, and particularly relates to a seamless steel tube for a pin shaft and a manufacturing method thereof, and the manufacturing method comprises the following steps: taking a continuous casting round billet as a raw material, and sequentially carrying out a heating process, a perforating process, a skew rolling process and a diameter reducing process on the continuous casting round billet to obtain the seamless steel tube after hot rolling. The seamless steel pipe with the medium-thickness wall is prepared by adjusting the specific technological parameters in the perforating and skew rolling procedures, so that the seamless steel pipe can be used for manufacturing the pin shaft, the total cost of manufacturing the pin shaft is reduced, and the yield is high.

Description

Technical Field

[0001] The invention belongs to the technical field of metal pressure processing, and in particular relates to a seamless steel pipe for a pin shaft and a manufacturing method thereof. Background Art

[0002] The connection between the booms and between the booms and the hydraulic cylinders of the pump truck is realized by pin articulation. During the operation of the pump truck, the pin is subjected to alternating loads and strong alternating stresses of impact, shearing and bending. Therefore, the pin needs to have high yield strength, impact performance, shear resistance, wear resistance and other comprehensive mechanical properties to meet the use requirements.

[0003] At present, the engineering industry uses solid round steel to make pins by boring holes. The main production process is: solid round steel → boring → cutting → rough processing → quenching and tempering → fine processing to make the pin. The existing process has the following defects and shortcomings: (1) long production cycle and low efficiency; (2) high cost of boring process; (3) low yield rate of solid round steel → pin, generally around 70%. The above results in high overall cost of manufacturing pins from solid round steel.

[0004] Therefore, it is of great significance to provide a method for manufacturing a seamless steel pipe for a pin shaft to solve the problems of low production efficiency, low yield rate and high cost in the prior art of manufacturing pin shafts. Summary of the invention

[0005] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a seamless steel pipe for a pin shaft and a method for manufacturing the same. The present invention prepares a seamless steel pipe with a relatively small diameter-to-thickness ratio (medium-thick wall) by adjusting specific process parameters in the perforation and tube rolling (oblique rolling) procedures, so that the seamless steel pipe can be used to manufacture pin shafts, thereby improving the production efficiency of manufacturing pin shafts, reducing the cost of manufacturing pin shafts and achieving a high yield rate.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for manufacturing a seamless steel pipe for a pin shaft, the manufacturing method comprising: using a continuously cast round billet as a raw material, subjecting the continuously cast round billet to a heating process, a perforating process, a skew rolling process, and a diameter reducing process in sequence to obtain a hot-rolled seamless steel pipe.

[0008] The present invention prepares a seamless steel pipe with a relatively small diameter-to-thickness ratio (medium-thick wall) by adjusting specific process parameters in the perforation and tube rolling (oblique rolling) procedures, so that the seamless steel pipe can be used to manufacture pins, thereby improving the production efficiency of manufacturing pins, reducing the cost of manufacturing pins and increasing the yield rate.

[0009] Furthermore, the diameter of the continuous casting round billet is 150 to 500 mm;

[0010] And / or, by weight percentage, the chemical composition of each element in the continuous casting round billet is: C: 0.38 wt% - 0.45 wt%, Si: 0.17 wt% - 0.37 wt%, Mn: 0.50 wt% - 0.80 wt%, Cr: 0.90 wt% - 1.20 wt%, Mo: 0.15 wt% - 0.25 wt%, and the balance is Fe and inevitable impurities;

[0011] And / or, the continuous casting round billet is obtained by subjecting production raw materials to ironmaking treatment, desulfurization treatment, steelmaking treatment, refining treatment, vacuum degassing treatment, and continuous casting treatment.

[0012] Further, in the heating process, an annular furnace is used to uniformly heat the continuous casting round billet to obtain a heated tube billet; the temperature for uniform heating is 1220 - 1280 °C, and the holding time is 1.5 h to 10 h.

[0013] Further, in the piercing process, a conical piercing mill is used to expand the diameter and pierce the heated tube billet to obtain a pierced mandrel tube; the reduction ratio for diameter expansion and piercing is 10% - 13%, the feeding angle is 8° - 15°, and the rolling speed is 20 rpm - 50 rpm.

[0014] Further, in the skew rolling process, an ASEEL tube rolling mill is used to roll the pierced mandrel tube to obtain a rolled steel tube; during rolling, the feeding angle of the ASEEL tube rolling mill is 6° - 8°, the rolling angle is 2° - 4°, the rolling time ≤ 25 seconds, the roll speed is 20 rpm - 300 rpm, the wall thickness reduction is 4 - 7 mm, and the core rod specification used by the ASEEL tube rolling mill is 35 - 450 mm.

[0015] Further, in the reducing process, a two-roll micro-tension reducing mill is used to reduce the diameter of the rolled steel tube, the temperature of the reducing mill is 800 - 900 °C, and the dimensional accuracy of the reduced steel tube can reach: outer diameter ± 0.75% D, where D represents the outer diameter.

[0016] Further, in the manufacturing method, the sum of the process times for piercing, skew rolling, and reducing of the continuous casting round billet is 2 - 4 minutes.

[0017] Further, after the reducing process, the manufacturing method further includes: physical and chemical inspection process, straightening process, non-destructive inspection process, finishing process, and warehousing process, and finally a finished seamless steel tube is obtained.

[0018] In a second aspect, the present invention provides a seamless steel tube for a pin shaft, and the seamless steel tube for a pin shaft is manufactured by the manufacturing method described in the first aspect.

[0019] Furthermore, the outer diameter of the seamless steel pipe for the pin shaft is 50-535 mm, and the wall thickness is 5-130 mm.

[0020] Compared with the prior art, the beneficial effects of the present invention include at least one of the following:

[0021] The present invention prepares a seamless steel pipe with a relatively small diameter-to-thickness ratio (medium-thick wall) by adjusting specific process parameters in the perforation and tube rolling (oblique rolling) procedures, so that the seamless steel pipe can be used to manufacture pins, thereby reducing the overall cost of manufacturing the pins and increasing the yield rate. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following embodiments are usually in accordance with conventional conditions. Unless otherwise specified, all raw materials can be purchased from the market or are commonly used materials in the industry.

[0023] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0024] In a first aspect, the present invention provides a method for manufacturing a seamless steel pipe for a pin shaft, the manufacturing method comprising: using a continuously cast round billet as a raw material, subjecting the continuously cast round billet to a heating process, a perforating process, a skew rolling process, and a diameter reducing process in sequence to obtain a hot-rolled seamless steel pipe.

[0025] The seamless steel pipe manufactured by the manufacturing method provided by the present invention can be used to manufacture pins, thereby improving the production efficiency of manufacturing the pins, reducing the cost of manufacturing the pins and achieving a high yield rate.

[0026] The prior art process for manufacturing a pin includes: continuous casting billet → rolling solid round steel → boring → blanking → rough machining → quenching and tempering → finishing to obtain a pin. The manufacturing method provided by the present invention includes: continuous casting round billet → heating → perforation → oblique rolling → diameter reduction → blanking → rough machining → quenching and tempering → finishing to obtain a pin. The present invention adopts a continuous casting round billet → seamless steel pipe process, which is similar to the cost of continuous casting billet → rolling solid round steel, but the pin is manufactured by a seamless steel pipe, and the production process includes: seamless steel pipe → blanking → rough machining → quenching and tempering → finishing, which reduces the boring process. The boring process takes about 300 to 500 minutes, shortens the production cycle by 40%, has high production efficiency, and reduces the overall manufacturing cost by 20%.

[0027] The invention realizes the transformation from seamless steel pipe to pin shaft, the turning loss of the seamless steel pipe is small, the yield rate is high, and the yield rate is about 82%, which is 10% to 13% higher than that of the existing process.

[0028] Hot rolling forming and flexible specification change, the manufacturing method provided by the invention is suitable for batch production of seamless steel pipes with multiple specifications.

[0029] In the above-mentioned method for manufacturing seamless steel pipe for pin shaft, as an optional embodiment, the diameter of the continuously cast round billet is 150-500 mm, for example, it can be 150 mm, 195 mm, 330 mm, 500 mm.

[0030] In the above-mentioned method for manufacturing seamless steel pipe for pin shaft, as an optional embodiment, the chemical composition of each element in the continuous casting round billet is, in weight percentage: C: 0.38wt%-0.45wt%, Si: 0.17wt%-0.37wt%, Mn: 0.50wt%-0.80wt%, Cr: 0.90wt%-1.20wt%, Mo: 0.15wt%-0.25wt%, and the remainder is Fe and unavoidable impurities.

[0031] In the above-mentioned method for manufacturing seamless steel pipe for pin shaft, as an optional embodiment, the continuous casting round billet is obtained by subjecting the production raw materials to ironmaking treatment, desulfurization treatment, steelmaking treatment, refining treatment, vacuum degassing treatment, and continuous casting treatment.

[0032] In the above-mentioned method for manufacturing seamless steel pipe for pin shaft, as an optional implementation mode, the ironmaking process is carried out in a blast furnace to obtain molten iron.

[0033] In the above-mentioned manufacturing method of seamless steel pipe for pin shaft, as an optional implementation mode, in the desulfurization treatment step, the molten iron obtained by iron-making treatment is desulfurized by molten iron KR desulfurization method to obtain desulfurized iron, and S in the desulfurized iron is ≤0.005wt%.

[0034] In the manufacturing method of the seamless steel pipe for the above-mentioned pin shaft, as an alternative embodiment, the steelmaking treatment is carried out in an electric furnace or a converter, and alloys are added during the tapping process to obtain molten steel. In the molten steel, S ≤ 0.002w%. By controlling the content of S in the molten steel, sulfide inclusions in the steel can be effectively reduced, the crack sources in the steel can be reduced, and the toughness and service life of the pin shaft can be improved.

[0035] In the manufacturing method of the seamless steel pipe for the above-mentioned pin shaft, as an alternative embodiment, the refining treatment is carried out in an LF refining furnace, and the refining time ≥ 45 min.

[0036] In the manufacturing method of the seamless steel pipe for the above-mentioned pin shaft, as an alternative embodiment, the vacuum degassing treatment is carried out in a VD vacuum degassing furnace or an RH vacuum degassing furnace, and the vacuum degassing time ≥ 20 min to reduce the gas content and make the composition uniform.

[0037] In the manufacturing method of the seamless steel pipe for the above-mentioned pin shaft, as an alternative embodiment, in the heating process, a ring furnace is used to uniformly heat the continuous casting round billet to obtain a heated tube blank; the uniform heating temperature is 1220 - 1280 °C (for example, it can be 1220 °C, 1240 °C, 1260 °C or 1280 °C), and the holding time is 1.5 h to 10 h (for example, it can be 1.5 h, 3 h, 6 h, 9 h or 10 h).

[0038] In the manufacturing method of the seamless steel pipe for the above-mentioned pin shaft, as an alternative embodiment, in the piercing process, a conical piercing mill is used to expand the diameter and pierce the heated tube blank to obtain a pierced semi-finished tube; the reduction ratio of diameter expansion and piercing is 10% - 13%, the feeding angle is 8° - 15°, and the rolling speed (roll speed) is 20 rpm - 50 rpm (for example, it can be 20 rpm, 30 rpm, 40 rpm or 50 rpm).

[0039] In the manufacturing method of the seamless steel pipe for the above-mentioned pin shaft, as an alternative embodiment, in the skew rolling process, an ASEEL pipe mill is used to roll the pierced semi-finished tube to obtain a rolled steel pipe; during rolling, the feeding angle of the ASEEL pipe mill is 6° - 8°, the rolling angle is 2° - 4°, the rolling time ≤ 25 seconds, the roll speed is 20 rpm - 300 rpm (for example, it can be 20 rpm, 100 rpm, 150 rpm, 200 rpm, 250 rpm or 300 rpm), the wall thickness reduction is 4 - 7 mm, and the mandrel specifications used by the ASEEL pipe mill are 35 - 450 mm. The rolling deformation is large, the deviation correction ability is strong, and the dimensional accuracy can reach: outer diameter ± 0.75% D (D represents the outer diameter), wall thickness ± 7.5% S (S represents the wall thickness), which is more suitable for turning processing and has a high utilization rate of the steel pipe.

[0040] In the manufacturing method of the seamless steel pipe for the pin shaft, as an alternative embodiment, in the said reducing process, a two-roll micro-tension reducing mill is used to reduce the diameter of the rolled steel pipe, and the temperature of the reducing mill is 800 - 900 °C. For example, it can be 800 °C, 820 °C, 840 °C, 860 °C, 880 °C or 900 °C. The dimensional accuracy of the steel pipe after reducing can reach: outer diameter ±0.75%D, where D represents the outer diameter.

[0041] In the manufacturing method of the seamless steel pipe for the pin shaft, as an alternative embodiment, in the said manufacturing method, the sum of the working times of the processes of piercing, skew rolling, and reducing for the continuous casting round billet is 2 - 4 minutes.

[0042] In the manufacturing method of the seamless steel pipe for the pin shaft, as an alternative embodiment, after the said reducing process, the manufacturing method further includes: physical and chemical inspection process, straightening process, non-destructive inspection process, finishing process, and warehousing process, and finally a finished seamless steel pipe, that is, the seamless steel pipe for the pin shaft is obtained. The seamless steel pipe for the pin shaft can be processed through blanking → rough machining → quenching and tempering → finish machining to obtain pins of different specifications.

[0043] In the manufacturing method of the seamless steel pipe for the pin shaft, as an alternative embodiment, a six-roll straightening machine is used for straightening in the said straightening process, and the pipe camber ≤ 1 mm / m.

[0044] In the manufacturing method of the seamless steel pipe for the pin shaft, as an alternative embodiment, an ultrasonic flaw detector is used for flaw detection in the said non-destructive inspection process, and the detection standard is carried out in accordance with GB / T 5777, and the acceptance level is U2.

[0045] In the second aspect, the present invention provides a seamless steel pipe for a pin shaft, and the seamless steel pipe for the pin shaft is manufactured by the manufacturing method described in the first aspect.

[0046] In the above-mentioned seamless steel pipe for the pin shaft, as an alternative embodiment, the outer diameter of the seamless steel pipe for the pin shaft is 50 - 535 mm (for example, it can be 50 mm, 100 mm, 150 mm, 200 mm, 250 mm, 300 mm, 400 mm or 535 mm), and the wall thickness is 5 - 130 mm (for example, it can be 5 mm, 10 mm, 50 mm, 100 mm or 130 mm). The present invention can produce steel pipes with an outer diameter of ∮50 mm - ∮535 mm, realizing full coverage of pin shaft specifications.

[0047] The present invention will be further described in detail below with specific embodiments.

[0048] Example 1

[0049] This embodiment provides a manufacturing method for 42CrMoA seamless steel pipes used for pin shafts with an outer diameter of ∮140 (outer diameter) × 40 (wall thickness) mm, including continuous casting round billet smelting, steel pipe rolling, physical and chemical inspection, straightening, non-destructive inspection, finishing, and packaging and warehousing. The specific processes are as follows:

[0050] (1) Continuous casting round billet smelting: It successively includes blast furnace ironmaking, hot metal desulfurization treatment, electric furnace steelmaking, LF ladle furnace refining, RH vacuum degassing, and continuous casting processes. Among them,

[0051] Hot metal desulfurization treatment: The hot metal KR desulfurization method is used to desulfurize the molten hot metal obtained from blast furnace ironmaking, and the S content of the hot metal entering the electric furnace is controlled to be 0.005 wt%;

[0052] Electric furnace steelmaking: The desulfurized hot metal is transferred to the electric furnace for steelmaking, and the element S in the molten steel is controlled to be ≤0.002 wt%. Alloys are added during the tapping process to obtain molten steel;

[0053] LF ladle furnace refining: The molten steel obtained from electric furnace steelmaking is subjected to LF ladle furnace refining. The refining adopts the whole-process argon blowing process, and the refining time is 60 minutes;

[0054] RH vacuum degassing: The vacuum degassing time is 20 minutes, reducing the inclusion and gas content in the molten steel and making the molten steel composition uniform;

[0055] Continuous casting process: The molten steel after RH vacuum degassing is continuously cast to obtain a continuous casting round billet with a specification of ∮195 mm. The chemical composition of each element in the continuous casting round billet is: C: 0.41 wt%, Si: 0.19 wt%, Mn: 0.70 wt%, Cr: 0.98 wt%, Mo: 0.20 wt%, and the balance is Fe and inevitable impurities.

[0056] (2) Steel pipe rolling: The continuous casting round billet obtained from smelting is heated, pierced, skew-rolled, and reduced in diameter to obtain a steel pipe with a specification of ∮140 (outer diameter) × 40 (wall thickness) mm. Among them,

[0057] Tube blank heating: The continuous casting round billet obtained from smelting is heated by a rotary hearth furnace, and the soaking section temperature is controlled at 1250 °C, and the soaking time is 2 hours;

[0058] Piercing: A conical piercing mill is used to expand and pierce the heated continuous casting round billet to obtain a seamless tube blank with a size of ∮197×44 mm. The reduction ratio is 11.28%. The piercing mill uses a 195 mm guide plate, a roll pitch of 173 mm, a plug of 95 mm, a feeding angle of 11°, and a rolling speed of 35 rpm;

[0059] Oblique rolling: The rough tube obtained after perforation is finely rolled using the ASEEL tube rolling mill to obtain a rough tube with a size of ∮161mm (outer diameter) × 40mm (wall thickness), wherein the rolling time is 17 seconds, the roller speed is 165rpm, the wall reduction is 4mm, the mandrel specification used by the ASEEL tube rolling mill is 76mm, the throat diameter is 156mm, the feed angle is 6.5°, the rolling angle is 3°, and the wall thickness accuracy of the steel tube is ±7.5%S, where S represents the wall thickness;

[0060] Reducing: A 2-roller micro-tension reducing mill is used to reduce the seamless steel pipe obtained by oblique rolling to obtain a steel pipe with a specification of ∮140mm (outer diameter) × 40mm (wall thickness). The reducing mill has 12 frames, the reducing temperature is 875℃, and the outer diameter accuracy of the steel pipe is ±0.75%D, where D represents the outer diameter.

[0061] (3) Physical and chemical testing: Take 140mm specimens from both ends of the steel pipe to check whether the mechanical properties meet user requirements.

[0062] (4) Straightening: Use six rollers to straighten and calibrate, the curvature per meter is ≤1mm / m.

[0063] (5) Nondestructive testing: Ultrasonic testing of steel pipes is carried out in accordance with GB / T5777 standard, with acceptance level U2.

[0064] (6) Finishing quality inspection: The surface quality and dimensional accuracy of the steel pipe are inspected to meet the outer diameter tolerance of ±0.75%D and the wall thickness tolerance of ±7.5%S. The surface quality is qualified.

[0065] (7) Packaging and warehousing: After being weighed and marked, the steel pipes are packaged and put into storage.

[0066] In this embodiment, the total time of the continuous casting round billet in the piercing, oblique rolling and diameter reducing processes is 3 minutes, and the yield rate of the pin prepared from the seamless steel pipe is 82%.

[0067] Example 2

[0068] This embodiment provides a method for manufacturing a 42CrMoA seamless steel pipe for a pin shaft of ∮285 (outer diameter) × 80 (wall thickness) mm, including continuous casting of round billets, steel pipe rolling, physical and chemical testing, straightening, non-destructive testing, finishing, packaging and warehousing. The specific steps are as follows:

[0069] (1) Continuous casting round billet smelting: It includes blast furnace ironmaking, hot metal desulfurization, electric furnace steelmaking, LF refining, RH vacuum degassing and continuous casting.

[0070] Hot metal desulfurization treatment: The hot metal KR desulfurization method is used to desulfurize the hot metal obtained from blast furnace ironmaking, and the sulfur content of the hot metal entering the electric furnace is controlled to 0.005wt%;

[0071] Electric arc furnace steelmaking: The hot metal after desulfurization treatment is transferred to the electric arc furnace for steelmaking, and the element S in the molten steel is controlled to be ≤0.002wt%.

[0072] LF secondary refining: The molten steel obtained from electric arc furnace steelmaking is subjected to LF secondary refining. The whole process uses argon blowing technology, and the refining time is 60 minutes.

[0073] RH vacuum degassing: The vacuum degassing time is 20 minutes, which reduces the inclusion and gas content in the molten steel and makes the composition of the molten steel uniform.

[0074] Continuous casting process: The molten steel after RH vacuum degassing is continuously cast to obtain a continuous casting round billet with a specification of ∮330mm. The chemical composition of each element in the continuous casting round billet is as follows: C: 0.40wt%, Si: 0.21wt%, Mn: 0.72wt%, Cr: 1.01wt%, Mo: 0.22wt%, and the balance is Fe and unavoidable impurities.

[0075] (2) Steel pipe rolling: The continuous casting round billet obtained from smelting is heated, pierced, skew-rolled, and reduced in diameter to obtain a steel pipe with a specification of ∮285 (outer diameter) × 80 (wall thickness) mm. Among them,

[0076] Tube blank heating: The continuous casting round billet obtained from smelting is heated by a rotary hearth furnace, and the soaking section temperature is controlled at 1270°C, and the soaking time is 2 hours.

[0077] Piercing: A conical piercing mill is used to expand and pierce the heated continuous casting round billet to obtain a pilger pipe with a size of ∮362 (outer diameter) × 85 (wall thickness) mm. The reduction ratio is 9.7%. The piercing mill uses a 330mm guide plate, a roll pitch of 298mm, a plug of 177mm, a feeding angle of 10.8°, and a rolling speed of 27rpm.

[0078] Skew rolling: An ASEEL tube mill is used to finish rolling the pilger pipe obtained after piercing to obtain a rough tube with a size of ∮318mm × 80mm. Among them, the roll speed is 50rpm, the wall thickness reduction is 5mm, the mandrel specification used by the ASEEL tube mill is 147mm, the throat diameter is 313mm, the feeding angle is 6.5°, the rolling angle is 3°, and the wall thickness accuracy of the steel pipe is ±7.5%S, where S represents the wall thickness.

[0079] Sizing: A 2-roll mini-mill is used to reduce the diameter of the seamless steel pipe obtained by skew rolling to obtain a steel pipe with a specification of ∮285mm (outer diameter) × 80mm (wall thickness). The sizing mill has 10 stands, the sizing temperature is 850°C, and the outer diameter accuracy of the steel pipe is ±0.75%D, where D represents the outer diameter.

[0080] (3) Physical and chemical testing: 140mm specimens are taken from both ends of the steel pipe to test that the mechanical properties meet the user's requirements.

[0081] (4) Straightening: Use six rollers to straighten and calibrate, the curvature per meter is ≤1mm / m.

[0082] (5) Nondestructive testing: Ultrasonic testing of steel pipes is carried out in accordance with GB / T5777 standard, with acceptance level U2.

[0083] (6) Finishing quality inspection: The surface quality and dimensional accuracy of the steel pipe are inspected to meet the outer diameter tolerance of ±0.75%D and the wall thickness tolerance of ±7.5%S. The surface quality is qualified.

[0084] (7) Packaging and warehousing: After being weighed and marked, the steel pipes are packaged and put into storage.

[0085] In this embodiment, the total time of the continuous casting round billet in the piercing, oblique rolling and diameter reducing processes is 4 minutes, and the yield rate of the pin prepared from the seamless steel pipe is 81%.

[0086] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A method for manufacturing a seamless steel pipe for a pin, characterized in that: The manufacturing method comprises: taking a continuously cast round billet as a raw material, sequentially subjecting the continuously cast round billet to a heating process, a piercing process, a skew rolling process, and a diameter reducing process to obtain a hot-rolled seamless steel pipe.

2. The method for manufacturing a seamless steel pipe for a pin according to claim 1, characterized in that: The diameter of the continuous casting round billet is 150-500 mm; And / or, in terms of weight percentage, the chemical composition of each element in the continuous casting round billet is: C: 0.38wt%-0.45wt%, Si: 0.17wt%-0.37wt%, Mn: 0.50wt%-0.80wt%, Cr: 0.90wt%-1.20wt%, Mo: 0.15wt%-0.25wt%, and the balance is Fe and unavoidable impurities; And / or, the continuous casting round billet is obtained by subjecting the production raw materials to ironmaking treatment, desulfurization treatment, steelmaking treatment, refining treatment, vacuum degassing treatment, and continuous casting treatment.

3. The method for manufacturing a seamless steel pipe for a pin according to claim 1, characterized in that: In the heating process, a ring furnace is used to uniformly heat the continuous casting round billet to obtain a heated tube billet; the uniform heating temperature is 1220-1280° C., and the insulation time is 1.5 h to 10 h.

4. The method for manufacturing a seamless steel pipe for a pin according to claim 1, characterized in that: In the piercing process, a conical piercing machine is used to expand and pierce the heated tube blank to obtain a pierced rough tube; the reduction rate of the expansion and piercing is 10% to 13%, the feed angle is 8° to 15°, and the rolling speed is 20rpm to 50rpm.

5. The method for manufacturing a seamless steel pipe for a pin according to claim 1, characterized in that: In the oblique rolling process, the ASEEL tube rolling mill is used to roll the perforated rough tube to obtain a rolled steel tube; during rolling, the feed angle of the ASEEL tube rolling mill is 6° to 8°, the rolling angle is 2° to 4°, the rolling time is ≤25 seconds, the roller speed is 20rpm to 300rpm, the wall reduction is 4 to 7mm, and the mandrel specification used by the ASEEL tube rolling mill is 35 to 450mm.

6. The method for manufacturing a seamless steel pipe for a pin according to claim 1, characterized in that: In the diameter reducing process, a two-roller micro-tension reducer is used to reduce the diameter of the rolled steel pipe. The temperature of the reducer is 800-900°C. The dimensional accuracy of the steel pipe after diameter reduction can reach: outer diameter ±0.75%D, where D represents the outer diameter.

7. The method for manufacturing a seamless steel pipe for a pin according to any one of claims 1 to 6, characterized in that: In the manufacturing method, the total time of the processes of piercing, oblique rolling and diameter reduction of the continuously cast round billet is 2 to 4 minutes.

8. The method for manufacturing a seamless steel pipe for a pin according to any one of claims 1 to 6, characterized in that: After the diameter reducing process, the manufacturing method further comprises: a physical and chemical testing process, a straightening process, a non-destructive testing process, a finishing process, and a warehousing process, and finally a finished seamless steel pipe is obtained.

9. A seamless steel pipe for a pin, characterized in that: The seamless steel pipe for the pin is manufactured by the manufacturing method described in any one of claims 1-8.

10. The seamless steel pipe for pin according to claim 9, characterized in that: The outer diameter of the seamless steel pipe for the pin shaft is 50-535 mm, and the wall thickness is 5-130 mm.