Core rod for seamless alloy steel pipe rolling mill and method of manufacturing the same

Abstract

The present application relates to a kind of alloy seamless steel tube rolling mill mandrel and its manufacturing method.It solves the defects such as unreasonable design of prior art.The alloy seamless steel tube rolling mill mandrel includes bite section and unthreaded section, the bite section and unthreaded section are solid structure section, the rear end of the bite section and the front end of the unthreaded section are connected by seamless steel tube, the bite section, the unthreaded section and the seamless steel tube form closed chamber inside.The application has the advantages that closed chamber makes alloy seamless steel tube rolling mill mandrel after pipe threading, when cooling in cooling pool, cooling water cannot enter to the inside of seamless steel tube, and because the inside of seamless steel tube has larger inner hole diameter, in the process of pipe rolling, the air inside due to low heat exchange rate, alloy seamless steel tube rolling mill mandrel at this time will not form rapid heat exchange to pipe rolling, to improve pipe rolling quality.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of metal pipe manufacturing, and particularly relates to an alloy seamless steel pipe rolling mill mandrel and a manufacturing method thereof. BACKGROUND

[0002] The Asel rolling mill mandrel is a main deformation tool in the Asel rolling mill unit, which mainly plays a role in wall reduction and extension in the rolling process. An ideal and uniform wall thickness steel pipe can be rolled by selecting a suitable mandrel. In the rolling process, the mandrel is used under the working conditions of high temperature above 1000 DEG C, high pressure and friction. If the rigidity and strength of the mandrel are insufficient, torsional deformation and longitudinal crack failure are prone to occur. Therefore, the length of the working section of the mandrel cannot be too short. The demand for the mandrel increases in proportion to the output of the seamless steel pipe. The diameter of the rolling mill mandrel is 107-277 mm, and the working length thereof is generally 15-18 m, belonging to an ultralong rod. Currently, the material used for the mandrel is American hot work die steel H13 (4Cr5MoSiV1), which has a high cost.

[0003] For example, a seamless steel pipe rolling mill mandrel is disclosed in Chinese Patent No. CN201920368432.6, which comprises a rod body, a first threaded groove is formed in one side of the rod body, a rod head is threadedly connected to the inner wall of the first threaded groove, a second threaded groove is formed in the end of the rod body away from the first threaded groove, a rod tail is threadedly connected to the inner wall of the second threaded groove, a through hole is formed in the inner center of the rod body, the rod head and the rod tail, an annular groove is arranged on the side of the rod head and the rod tail close to the rod body, and a rotating ring is arranged on the middle surface of the annular groove. The seamless steel pipe rolling mill mandrel solves the problems of the traditional mandrel, such as long length, heavy weight, inconvenience in moving, solid rod, long heating cycle, not conducive to recycling, deformation of the rod body caused by cold and hot alternation, easy damage of the top head and increase of economic loss.

[0004] Although the above scheme has the advantages as above, the hole in the scheme is open at one end. When the pipe is cooled in the cooling pool after the pipe is processed, the open end is pre-entered into the pool and axially pushed. At this time, the inside of the mandrel will enter the cooling water. The open side is the front end, which not only affects the pushing speed of the mandrel, but also causes the internal cooling water to be not completely discharged in time due to repeated use after cooling, resulting in heat exchange with the heating temperature of the rolling mill in the process of secondary pipe rolling, and the water flowing out of the internal hole falls on the inner wall of the rolling pipe, which seriously affects the rolling quality.

[0005] Secondly, due to the open hole at the rear end in the above scheme, the internal and external of the rod body are unevenly heated due to repeated rolling and cooling, the rod body is prone to deformation, and the rolling quality is affected.

[0006] In addition, when the rod head is rolled into a pipe, the rod head circumferential surface contacts the pipe at the single largest diameter of the rod head curved surface and the inner wall of the pipe, and the rod head has poor uniformity in processing the wall thickness of the pipe due to the small contact surface with the pipe and the high temperature. SUMMARY

[0007] The present application aims to solve the above problems and provides an alloy seamless steel pipe rolling mill mandrel and a manufacturing method thereof.

[0008] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0009] The alloy seamless steel pipe rolling mill mandrel comprises a biting section and a mandrel removing section, both of which are solid structure sections, the biting section has a Rockwell hardness of 42-50HRC, the mandrel removing section has a Rockwell hardness of 42-50HRC, the rear end of the biting section and the front end of the mandrel removing section are connected by a seamless steel pipe, the surface hardness of the seamless steel pipe is 300-360HBW, the biting section, the mandrel removing section and the seamless steel pipe form a closed chamber inside, the front end of the biting section has a first cylindrical surface, the rear end of the biting section has a second cylindrical surface, the axial length of the first cylindrical surface is longer than that of the second cylindrical surface, the axial center line of the first cylindrical surface coincides with that of the second cylindrical surface and both have equal diameters, the diameter of the first cylindrical surface is equal to the outer diameter of the seamless steel pipe, and the outer diameter of the mandrel removing section is equal to the outer diameter of the seamless steel pipe.

[0010] In the above-mentioned alloy seamless steel pipe rolling mill mandrel, an annular groove is arranged on the biting section and connected to the first cylindrical surface and the second cylindrical surface.

[0011] In the above-mentioned alloy seamless steel pipe rolling mill mandrel, the rear end of the biting section has a first insertion part inserted into the front end of the seamless steel pipe, the seamless steel pipe and the first insertion part are clearance fit, and the seamless steel pipe and the rear end of the biting section are welded; the front end of the mandrel removing section has a second insertion part inserted into the rear end of the seamless steel pipe, the seamless steel pipe and the second insertion part are clearance fit, and the seamless steel pipe and the front end of the mandrel removing section are welded.

[0012] In the above-mentioned alloy seamless steel pipe rolling mill mandrel, the rear end surface of the biting section and / or the front end surface of the seamless steel pipe is provided with a first annular inclined surface, and the rear end surface of the biting section and the front end surface of the seamless steel pipe form a first V-shaped surfacing space.

[0013] In the alloy seamless steel tube rolling mill mandrel described above, the front end face of the knock-out section and / or the rear end face of the seamless steel tube is provided with a second annular inclined face, and the front end face of the knock-out section and the rear end face of the seamless steel tube form a second V-shaped build-up space.

[0014] In the alloy seamless steel tube rolling mill mandrel described above, the front end of the bite-in section has a first tapered portion.

[0015] In the alloy seamless steel tube rolling mill mandrel described above, the rear end of the knock-out section has a second tapered portion.

[0016] The application also provides a manufacturing method of the alloy seamless steel tube rolling mill mandrel, which comprises the following steps:

[0017] S1, blank preforming, selecting a H13 steel preformed bite-in section blank, selecting a H13 steel preformed knock-out section blank, and selecting a 4145MOD steel seamless pipe blank to be cut to obtain a seamless steel tube blank;

[0018] S2, machining, machining the bite-in section blank, the knock-out section blank and the seamless steel tube blank of S1 to obtain a machined bite-in section, a machined knock-out section and a machined seamless steel tube, wherein the machining comprises turning an outer circle, turning an end face and turning an inner hole;

[0019] S3, heat treatment, air quenching the machined bite-in section, air quenching the machined knock-out section and water quenching the machined seamless steel tube, wherein the machined bite-in section is subjected to multiple tempering treatments after air quenching, and the tempering temperature gradually decreases from the first time to the Nth time; the machined knock-out section is subjected to multiple tempering treatments after air quenching, and the tempering temperature gradually decreases from the first time to the Nth time;

[0020] S4, assembling, assembling the heat-treated bite-in section to the front end of the heat-treated seamless steel tube, assembling the heat-treated knock-out section to the rear end of the heat-treated seamless steel tube, and then welding and fixing the heat-treated bite-in section and the heat-treated seamless steel tube by welding, and welding and fixing the heat-treated knock-out section and the heat-treated seamless steel tube by welding, and finally polishing the welding scar to obtain the alloy seamless steel tube rolling mill mandrel.

[0021] In the manufacturing method of the alloy seamless steel tube rolling mill mandrel described above, in the S3 step described above,

[0022] The air quenching temperature of the machined bite-in section is 1000-1060℃, and multiple tempering treatments are performed after air quenching, the first tempering temperature is 600-640℃, the second tempering temperature is 580-620℃, the Rockwell hardness of the heat-treated bite-in section after tempering is 42-50HRC, and the impact absorption energy is ≥20J;

[0023] The air quenching temperature of the machined rod-removing section is 1000°C-1060°C, and multiple tempering treatments are performed after air quenching, with the first tempering temperature being 600°C-640°C and the second tempering temperature being 580°C-620°C. The Rockwell hardness of the heat-treated rod-removing section after tempering is 42-50HRC, and the impact absorption energy is ≥20J;

[0024] The water quenching temperature of the machined seamless steel pipe is 840°C-920°C, and after water quenching, it is tempered at a temperature of 600°C-640°C. The heat-treated seamless steel pipe after tempering has a tensile strength of ≥965MPa, a yield strength of ≥758MPa, an impact absorption energy of ≥70J, and a surface hardness of 300-360HBW.

[0025] In the above-mentioned method for manufacturing the alloy seamless steel pipe rolling mill core rod, in the above-mentioned step S1, the seamless steel pipe material is straightened at least once and spot-corrected at least once; between the above-mentioned S3 and S4, the seamless steel pipe after heat treatment is straightened at least once and spot-corrected at least once.

[0026] Compared with the existing technology, the advantages of this application are:

[0027] The closed chamber prevents cooling water from entering the seamless steel pipe when the alloy seamless steel pipe rolling mill core rod is cooled in the cooling water pool after passing through the pipe. In addition, since the seamless steel pipe has a large inner hole diameter, during the pipe rolling process, the internal air has a low heat exchange rate. At this time, the alloy seamless steel pipe rolling mill core rod will not form a rapid heat exchange with the rolled pipe, thereby improving the rolled pipe quality.

[0028] When cooling in the cooling water pool, the closed chamber can provide better buoyancy so that the mandrel of the alloy seamless steel pipe rolling mill will not be hindered in advancing in the cooling water pool; at the same time, since it is a closed chamber, during the pipe rolling process, the closed chamber retains heat at a certain temperature, and the heat retained at a certain temperature inside can greatly reduce the heat exchange with the pipe rolling temperature, thereby improving the pipe rolling quality.

[0029] Since there is heat of a certain temperature in the closed chamber, it can reduce the temperature difference between the inner and outer walls of the mandrel during the pipe rolling process, so as to prevent deformation and ensure the straightness of the mandrel, thereby improving the quality of pipe rolling. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The present invention provides a schematic diagram of the structure of a core rod of a seamless alloy steel pipe rolling mill.

[0031] Figure 2 It is a schematic diagram of the assembled structure of the alloy seamless steel pipe and the biting section provided by the present invention.

[0032] Figure 3It is a schematic diagram of the assembled structure of the alloy seamless steel pipe and the rod stripping section provided by the present invention.

[0033] Figure 4 It is a schematic diagram of the optimized structure of the biting section provided by the present invention.

[0034] In the figure, the biting section 1, the first cylindrical surface 10, the second cylindrical surface 11, the annular groove 12, the first insertion portion 13, the first conical portion 14, the rod-removing section 2, the second insertion portion 20, the second conical portion 21, the seamless steel pipe 3, the closed chamber A, the first annular inclined surface a1, and the second annular inclined surface a2. DETAILED DESCRIPTION

[0035] The following are specific embodiments of the invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0036] Example 1

[0037] like Figure 1 As shown, the core rod of the alloy seamless steel pipe rolling mill includes a biting section 1 and a stripping section 2, and a seamless steel pipe 3. The seamless steel pipe 3 is made by cutting seamless steel pipe material, has a stable structure, is easy to obtain materials, and has high efficiency.

[0038] Preferably, the biting section 1 and the rod stripping section 2 of this embodiment are both solid structural sections, for example, made by forging, with high structural strength and good consistency of forged products.

[0039] Preferred options, such as Figure 1 and Figure 2 As shown, the front end of the biting section 1 has a first tapered portion 14, the rear end of the biting section 1 and the front end of the rod-removing section 2 are connected by a seamless steel pipe 3, and the rear end of the rod-removing section 2 has a second tapered portion 21. For example, the welding connection is performed in a sleeve-type manner. After the welding is completed, a closed chamber A is formed inside the biting section 1, the rod-removing section 2 and the seamless steel pipe 3. The closed chamber A prevents the cooling water from entering the seamless steel pipe 3 when the core rod of the alloy seamless steel pipe rolling mill is cooled in the cooling water pool after passing through the pipe. Moreover, since the interior of the seamless steel pipe 3 has a larger inner hole diameter, during the pipe rolling process, the internal air has a low heat exchange rate, and the core rod of the alloy seamless steel pipe rolling mill at this time will not form a rapid heat exchange with the rolled pipe, so as to improve the quality of the rolled pipe.

[0040] Secondly, when cooling in the cooling water pool, since it is a closed chamber, it can provide better buoyancy so that the advancement of the alloy seamless steel pipe rolling mill mandrel in the cooling water pool will not be hindered; at the same time, since it is a closed chamber, during the pipe rolling process, the closed chamber retains a certain temperature of heat, and the heat retained at a certain temperature inside can greatly reduce the heat exchange with the pipe rolling temperature, thereby improving the pipe rolling quality.

[0041] In addition, since there is heat at a certain temperature in the closed chamber, it can reduce the temperature difference between the inside and the outer wall of the mandrel during the pipe rolling process to prevent deformation and ensure the straightness of the mandrel, thereby improving the quality of pipe rolling.

[0042] Preferred options, such as Figure 2 As shown, a first cylindrical surface 10 is provided at the front end of the biting section 1, and a second cylindrical surface 11 is provided at the rear end of the biting section 1. The axial length of the first cylindrical surface 10 is longer than the axial length of the second cylindrical surface 11. The axis center line of the first cylindrical surface 10 and the axis center line of the second cylindrical surface 11 coincide with each other and their diameters are equal. The diameter of the first cylindrical surface 10 is equal to the outer diameter of the seamless steel pipe 3, and the outer diameter of the rod stripping section 2 is equal to the outer diameter of the seamless steel pipe 3.

[0043] The design of the first cylindrical surface 10 and the second cylindrical surface 11 ensures that the biting section 1 forms surface-to-surface contact with the tube during the advancement of the mandrel. Furthermore, the second cylindrical surface 11 provides a secondary uniform reinforcement of the tube wall thickness after treatment by the first cylindrical surface 10, resulting in a more uniform tube wall thickness. Furthermore, the front-to-back arrangement of the first and second cylindrical surfaces 10, 11, enhances the biting section 1's resistance to deformation, significantly extending its service life.

[0044] In a preferred embodiment, an annular groove 12 is provided on the engaging section 1, connecting the first cylindrical surface 10 and the second cylindrical surface 11. This groove 12 saves material and reduces friction, allowing for smoother advancement of the engaging section 1. Furthermore, the two walls of the groove 12 are inclined, facilitating manufacturing.

[0045] Preferred options, such as Figure 2 As shown, the rear end of the biting section 1 has a first insertion portion 13 inserted into the front end of the seamless steel pipe 3. The wall thickness of the seamless steel pipe 3 is smaller than the inner diameter radius of the seamless steel pipe 3. To improve the fit accuracy, reaming holes are provided at both ends of the seamless steel pipe 3. The reaming holes have a diameter larger than the original inner diameter of the seamless steel pipe 3. At the same time, the bottom surface of the reaming holes forms a stop for assembly. For example, a stop is formed for the first insertion portion 13 to be installed in place. The seamless steel pipe 3 and the first insertion portion 13 are loosely fitted, and the seamless steel pipe 3 and the rear end of the biting section 1 are welded together. Specifically, a first annular inclined surface a1 is provided on the rear end face of the biting section 1 and / or the front end face of the seamless steel pipe 3. The rear end face of the biting section 1 and the front end face of the seamless steel pipe 3 form a first V-shaped surfacing space. A weld scar is formed in the first V-shaped surfacing space to connect the seamless steel pipe 3 to the rear end of the biting section 1.

[0046] The first way: Figure 4As shown, a first annular inclined surface a1 is provided on the rear end face of the biting section 1. Furthermore, a plurality of first spiral grooves are provided in the axial direction of the first inserting portion 13. The length of the first spiral grooves is shorter than the axial length of the first inserting portion 13. The ends of the first spiral grooves adjacent to the first annular inclined surface a1 are connected to the through grooves provided on the first annular inclined surface a1. During welding, the solder flows into the through grooves and into the first spiral grooves, thereby improving the weld strength between the biting section 1 and the seamless steel pipe 3.

[0047] The second way: Figure 2 As shown, a first annular inclined surface a1 is provided on the front end surface of the seamless steel pipe 3 .

[0048] The third method: a first annular inclined surface a1 is provided on the rear end surface of the biting section 1 and the front end surface of the seamless steel pipe 3 .

[0049] The first annular inclined surface mentioned above can be understood as a chamfer.

[0050] Preferred options, such as Figure 3 As shown, the front end of the rod-removing section 2 has a second insertion portion 20 inserted into the rear end of the seamless steel pipe 3. The seamless steel pipe 3 and the second insertion portion 20 are clearance-fitted, and the front end of the seamless steel pipe 3 and the rod-removing section 2 are welded together. Specifically, a second annular inclined surface a2 is provided on the front end face of the rod-removing section 2 and / or the rear end face of the seamless steel pipe 3, and the front end face of the rod-removing section 2 and the rear end face of the seamless steel pipe 3 form a second V-shaped surfacing space.

[0051] The configuration of the second annular inclined surface can refer to the three configurations of the first annular inclined surface a1.

[0052] The biting section core rod head of this embodiment is made of H13 steel with the following properties: Rockwell hardness 42-50 HRC, impact absorption energy ≥ 20 J. H13 steel has excellent comprehensive properties.

[0053] The seamless steel pipe 3 is made of 4145MOD steel with the following properties: tensile strength ≥965MPa, yield strength ≥758MPa, impact absorption energy ≥70J, and surface hardness 300-360HBW.

[0054] The seamless steel pipe is the stage with stable stress during the rolling process. The rolled products are mainly carbon steel and medium and low alloy seamless steel pipes, so the improved 4145MOD steel is selected.

[0055] The rod stripping section 2 is made of H13 steel, with a Rockwell hardness of 42-50 HRC and an impact strength of ≥20J. The rod stripping section's primary function is to pull the mandrel from the pipe after the pipe is rolled, clamping the rod stripping section with the rod stripping machine. This section bears enormous clamping forces and multi-directional impacts, so H13 hot-working die steel was selected for its exceptionally high overall performance.

[0056] Example 2

[0057] The embodiment provides a manufacturing method of an alloy seamless steel pipe rolling mill mandrel.

[0058] Specifically, as shown in the drawings, the manufacturing method of the alloy seamless steel pipe rolling mill mandrel comprises the following steps: Figure 1-Figure 3

[0059] S1, blank preforming, selecting H13 steel to preform a biting section blank, selecting H13 steel to preform a rod ejection section blank, preforming by forging, and cutting a seamless pipe steel pipe material of 4145MOD steel to obtain a seamless steel pipe blank pipe;

[0060] S2, machining, machining the biting section blank, the rod ejection section blank and the seamless steel pipe blank pipe of the step S1, the machining comprising turning an outer circle, turning an end face and turning an inner hole;

[0061] The biting section blank is turned at multiple outer circles, for example, a first cylindrical surface 10, a second cylindrical surface 11 and a first insertion part 13 are obtained by turning, and meanwhile, an end face connecting the first insertion part 13 and the second cylindrical surface 11 is also machined.

[0062] The rod ejection section blank is turned at an outer circle and an end face, for example, an outer circle of the second insertion part 20 and an end face connecting the second insertion part 20 and a cylindrical surface of the rod ejection section blank are machined.

[0063] Two end faces of the seamless steel pipe blank pipe are turned, and two ends of an inner wall of the seamless steel pipe blank pipe are turned, so that the two ends of the inner wall of the seamless steel pipe blank pipe are respectively matched with the first insertion part 13 and the second insertion part 20 with high precision.

[0064] S3, heat treatment, air quenching the machined biting section, air quenching the machined rod ejection section and water quenching the machined seamless steel pipe, after the air quenching of the machined biting section, multiple tempering treatments are performed, and the tempering temperature gradually decreases from the first time to the Nth time; after the air quenching of the machined rod ejection section, multiple tempering treatments are performed, and the tempering temperature gradually decreases from the first time to the Nth time;

[0065] Specifically, the air quenching temperature of the machined biting section is 1000-1060℃, after the air quenching, multiple tempering treatments are performed, the first tempering temperature is 600-640℃, the second tempering temperature is 580-620℃, the hardness of the heat treated biting section after the tempering is 42-50HRC, and the impact absorption energy is greater than or equal to 20J.

[0066] ​The air quenching temperature of the machined rod drawing section is 1000-1060℃, and after air quenching, multiple tempering treatments are performed, the first tempering temperature is 600-640℃, and the second tempering temperature is 580-620℃, and the hardness of the heat treated rod drawing section after tempering is 42-50HRC, and the impact energy is ≥20J.

[0067] The water quenching temperature of the machined seamless steel pipe is 840-920℃, and after water quenching, a tempering treatment at a temperature of 600-640℃ is performed, and the tensile strength of the heat treated seamless steel pipe after tempering treatment is ≥965MPa, the yield strength is ≥758MPa, the impact energy is ≥70J, and the surface hardness is 300-360HBW.

[0068] S4, assembling, assembling the heat treated rod drawing section to the front end of the heat treated seamless steel pipe, assembling the heat treated rod drawing section to the rear end of the heat treated seamless steel pipe, after assembling, welding the heat treated rod drawing section and the heat treated seamless steel pipe, welding the heat treated rod drawing section and the heat treated seamless steel pipe, and finally polishing the weld scar of the welding position to obtain an alloy seamless steel pipe rolling mill mandrel.

[0069] In the above S1 step, the seamless pipe is subjected to at least one straightening and at least one point straightening treatment; between the above S3 and S4, the heat treated seamless steel pipe is subjected to at least one straightening and at least one point straightening treatment.

[0070] Example three

[0071] The principle of this embodiment is basically the same as that of example two, and the difference is that:

[0072] The air quenching temperature of the machined rod drawing section is 1000-1060℃, and after air quenching, multiple tempering treatments are performed, the first tempering temperature is 600-640℃, and the second tempering temperature is 580-620℃, and the hardness of the heat treated rod drawing section after tempering is 42-50HRC, and the impact energy is ≥20J.

[0073] The air quenching temperature of the machined rod drawing section is 1000-1060℃, and after air quenching, multiple tempering treatments are performed, the first tempering temperature is 600-640℃, and the second tempering temperature is 580-620℃, and the hardness of the heat treated rod drawing section after tempering is 42-50HRC, and the impact energy is ≥20J.

[0074] The water quenching temperature of the machined seamless steel pipe is 840-920℃, and after water quenching, a tempering treatment at a temperature of 600-640℃ is performed, and the tensile strength of the heat treated seamless steel pipe after tempering treatment is ≥965MPa, the yield strength is ≥758MPa, the impact energy is ≥70J, and the surface hardness is 300-360HBW.

[0075] Example four

[0076] The principle of this embodiment is basically the same as that of the second embodiment, except that:

[0077] The air quenching temperature of the machined bite section is 1000℃, and after air quenching, it is tempered multiple times, with the first tempering temperature at 600℃ and the second tempering temperature at 580℃. The Rockwell hardness of the heat-treated bite section after tempering is 42HRC, and the impact absorption energy is 20J.

[0078] The air quenching temperature of the machined rod-removing section is 1000℃, and after air quenching, it is subjected to multiple tempering treatments, with the first tempering temperature at 600℃ and the second tempering temperature at 580℃. The Rockwell hardness of the heat-treated rod-removing section after tempering is 42HRC, and the impact absorption energy is 20J.

[0079] The water quenching temperature of the machined seamless steel pipe is 840℃, and after water quenching, it is tempered at 600℃. The tensile strength of the heat-treated seamless steel pipe after tempering is ≥965MPa, the yield strength is ≥758MPa, the impact absorption energy is ≥70J, and the surface hardness is 300HBW.

[0080] Example 5

[0081] The principle of this embodiment is basically the same as that of the second embodiment, except that:

[0082] The air quenching temperature of the machined bite section is 1060℃, and after air quenching, it is tempered multiple times, with the first tempering temperature at 640℃ and the second tempering temperature at 620℃. The Rockwell hardness of the heat-treated bite section after tempering is 50HRC, and the impact absorption energy is 28J.

[0083] The air quenching temperature of the machined rod-removing section is 1060℃, and after air quenching, it is subjected to multiple tempering treatments, with the first tempering temperature at 640℃ and the second tempering temperature at 620℃. The Rockwell hardness of the heat-treated rod-removing section after tempering is 50HRC, and the impact absorption energy is 28J.

[0084] The water quenching temperature of the machined seamless steel pipe is 920℃, and after water quenching, it is tempered at 640℃. The tensile strength of the heat-treated seamless steel pipe after tempering is ≥975MPa, the yield strength is ≥770MPa, the impact absorption energy is ≥74J, and the surface hardness is 360HBW.

[0085] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A core rod for a seamless alloy steel pipe mill, comprising a biting section (1) and a stripping section (2), characterized in that: The biting section (1) and the rod-removing section (2) are both solid structural sections. The Rockwell hardness of the biting section (1) is 42-50HRC, and the Rockwell hardness of the rod-removing section (2) is 42-50HRC. The rear end of the biting section (1) and the front end of the rod-removing section (2) are connected by a seamless steel pipe (3). The surface hardness of the seamless steel pipe (3) is 300-360HBW. A closed chamber (A) is formed inside the biting section (1), the rod-removing section (2) and the seamless steel pipe (3). A first cylindrical surface (10) is provided at the front end of the biting section (1). The rear end of the segment (1) has a second cylindrical surface (11), the axial length of the first cylindrical surface (10) is longer than the axial length of the second cylindrical surface (11), the axis of the first cylindrical surface (10) and the axis of the second cylindrical surface (11) coincide with each other and have the same diameter, the biting segment (1) is provided with an annular groove (12) connected to the first cylindrical surface (10) and the second cylindrical surface (11), the diameter of the first cylindrical surface (10) is equal to the outer diameter of the seamless steel pipe (3), and the outer diameter of the stripping segment (2) is equal to the outer diameter of the seamless steel pipe (3); The rear end face of the biting section (1) and / or the front end face of the seamless steel pipe (3) are provided with a first annular inclined surface (a1), and the rear end face of the biting section (1) and the front end face of the seamless steel pipe (3) form a first V-shaped surfacing space.

2. The alloy seamless steel pipe mill mandrel according to claim 1, characterized in that: The rear end of the biting section (1) has a first insertion portion (13) inserted into the front end of the seamless steel pipe (3), the seamless steel pipe (3) and the first insertion portion (13) are clearance-matched, and the seamless steel pipe (3) and the rear end of the biting section (1) are welded together; the front end of the rod-removing section (2) has a second insertion portion (20) inserted into the rear end of the seamless steel pipe (3), the seamless steel pipe (3) and the second insertion portion (20) are clearance-matched, and the seamless steel pipe (3) and the front end of the rod-removing section (2) are welded together.

3. The alloy seamless steel pipe mill mandrel according to claim 1, characterized in that: The front end face of the rod-removing section (2) and / or the rear end face of the seamless steel pipe (3) are provided with a second annular inclined surface (a2), and the front end face of the rod-removing section (2) and the rear end face of the seamless steel pipe (3) form a second V-shaped surfacing space.

4. The alloy seamless steel pipe mill mandrel according to claim 1, characterized in that: The front end portion of the biting section (1) has a first tapered portion (14).

5. The alloy seamless steel pipe mill mandrel according to claim 1, characterized in that: The rear end portion of the rod stripping section (2) has a second tapered portion (21).

6. A method for producing a mandrel bar for a seamless alloy steel pipe mill according to any one of claims 1 to 5, characterized in that: The method for manufacturing the alloy seamless steel pipe mill mandrel comprises the following steps: S1. Prefabrication of billets: H13 steel is used to prefabricate the biting section billet, H13 steel is used to prefabricate the rod stripping section billet, and 4145MOD steel seamless pipe material is used to cut and process to obtain seamless steel pipe billets; S2, machining, machining the biting segment billet, the stripping segment billet and the seamless steel tube billet in step S1, the machining including turning the outer circle, turning the end face and turning the inner hole; S3, heat treatment, air quenching the machined bite section after processing in step S2, air quenching the machined rod-removing section, and water quenching the machined seamless steel pipe, wherein the machined bite section is subjected to multiple tempering treatments after air quenching, and the tempering temperature is gradually reduced from the first time to the Nth time; the machined rod-removing section is subjected to multiple tempering treatments after air quenching, and the tempering temperature is gradually reduced from the first time to the Nth time; S4, assembling, assembling the heat-treated biting section after heat treatment to the front end of the heat-treated seamless steel pipe, assembling the heat-treated rod-removing section after heat treatment to the rear end of the heat-treated seamless steel pipe, after assembling in place, welding the heat-treated biting section and the heat-treated seamless steel pipe to fix them, welding the heat-treated rod-removing section and the heat-treated seamless steel pipe to fix them, and finally grinding and polishing the weld scars at the welding places to obtain the alloy seamless steel pipe rolling mill core rod.

7. The method for manufacturing a mandrel bar for a seamless alloy steel pipe rolling mill according to claim 6, characterized in that: In the above S3 step, The air quenching temperature of the machined bite section is 1000°C-1060°C, and multiple tempering treatments are performed after air quenching, with the first tempering temperature being 600°C-640°C and the second tempering temperature being 580°C-620°C. The Rockwell hardness of the heat-treated bite section after tempering is 42-50HRC, and the impact absorption energy is ≥20J; The air quenching temperature of the machined rod-removing section is 1000°C-1060°C, and multiple tempering treatments are performed after air quenching, with the first tempering temperature being 600°C-640°C and the second tempering temperature being 580°C-620°C. The Rockwell hardness of the heat-treated rod-removing section after tempering is 42-50HRC, and the impact absorption energy is ≥20J; The water quenching temperature of the machined seamless steel pipe is 840°C-920°C, and after water quenching, it is tempered at a temperature of 600°C-640°C. The heat-treated seamless steel pipe after tempering has a tensile strength of ≥965MPa, a yield strength of ≥758MPa, an impact absorption energy of ≥70J, and a surface hardness of 300-360HBW.

8. The method for manufacturing a mandrel bar for a seamless alloy steel pipe rolling mill according to claim 6, characterized in that: In the above step S1, the seamless steel pipe material is straightened at least once and spot-rectified at least once; between the above steps S3 and S4, the seamless steel pipe after heat treatment is straightened at least once and spot-rectified at least once.

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