Extrusion production method of 13cr type boron-containing seamless steel tube for shielding neutrons of nuclear fuel

Abstract

The application discloses an extrusion production method of boron-containing seamless steel pipes for shielding neutrons of nuclear power fuel, which comprises the following steps: blank outer diameter selection and surface treatment, saw cutting, deep hole, horn mouth and circular arc machining and other extrusion blank preparation process machining treatments; ring furnace heating: the heating temperature and heating time of the preheating section, heating section and soaking section of the ring furnace heating are set; induction furnace heating: the heating temperature, heating power and heating time of the primary and secondary induction furnaces are set; deformation process: the deformation process comprises hole expanding and extrusion, and the hole expanding deformation is a pre-hole expanding process of the extrusion deformation. The newly designed work dies participating in the deformation comprise a hole expanding cone design, and the key dimensions of the hole expanding cone, such as the diameter and conical angle, are defined; the shearing ring design defines the diameter of the shearing ring working belt and the shearing ring outer diameter tolerance matching and other design contents. Through the above steps and the work die design, the material is successfully produced into the seamless steel pipe with the quality meeting the standard requirements on the extruder.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of seamless steel pipe preparation, in particular to an extrusion production method of 13Cr type boron-containing seamless steel pipe for shielding nuclear fuel neutrons. BACKGROUND

[0002] The boron-containing steel has a high content of boron element, the content of boron is between 1.5% and 1.7%, the boron element is dispersedly distributed in the form of boride at the grain boundary, which prevents the emission of alpha, gamma rays and neutrons and other micro-particles of nuclear fuel and the like, effectively reduces the nuclear radiation transmission rate, and is a good nuclear fuel storage container.

[0003] However, since the content of boron in the stainless steel is very high, most of the boron elements form boride on the grain boundary, and the boride is a hard and brittle compound, so that the plasticity and toughness of the material are very poor, and the process processing difficulty is very large.

[0004] To solve the above-mentioned problems in the prior art, the present application provides an extrusion production method of 13Cr type boron-containing seamless steel pipe. SUMMARY

[0005] The purpose of the present application is to solve the above-mentioned problems, and provide an extrusion production method of 13Cr type boron-containing seamless steel pipe for shielding nuclear fuel neutrons.

[0006] The purpose of the present application is achieved in that the extrusion production method of shielding nuclear fuel neutrons with 13Cr type boron-containing seamless steel pipe, comprising the following steps: step one: selection of blank outer diameter and surface treatment: selecting series size, turning the surface of the steel blank, and ensuring the smoothness of the outside after turning; step two: sawing: determining the length of the blank, and sawing to the required size, both ends are sawn to flat head, and finally the burrs are polished clean using an angular grinding wheel; step three: deep hole: the blank is drilled with a deep hole in the center to ensure the quality requirements of the deep hole surface roughness and the concentricity of the deep hole and the outer surface; step four: horn mouth and arc machining: machining the horn mouth and arc surface on the same end surface of the blank according to the process requirements; step five: ring furnace heating: the processed blank is heated in a ring furnace, and is divided into three sections according to different temperature intervals of the furnace, namely preheating section, heating section and soaking section; step six: first induction furnace heating: after ring furnace heating, the blank is heated once in the induction furnace, and the heating temperature, heating power and selection of electric capacity are set according to the material properties; step seven: design of hole expanding cone: the design of hole expanding cone includes hole expanding cone diameter, shear circle working plane width, two-line angle of conical surface axis section, smooth transition connection radius of shear circle working plane and conical surface, nose diameter, nose angle, smooth transition connection radius of nose conical surface and working conical surface, two-section connection angle of reverse conical angle of hole expanding cone, axis direction length, and surface machining smoothness; step eight: design of shear ring: the design of shear ring includes shear ring working belt diameter, working surface length, guide section diameter, shear ring thickness, shear ring outer diameter, shear ring outer diameter and shear ring support cooperation, concentricity of shear ring working circle and outer diameter circle; step nine: hole expanding: hole expanding process uses glass powder lubrication, determines the type and lubrication method of glass powder, determines the preheating temperature of hole expanding cylinder, and sets the hole expanding force level; step ten: second induction furnace heating: after hole expanding, the blank is heated twice in the induction furnace, and the heating temperature, heating power and selection of electric capacity are set according to the material properties; step eleven: extrusion: setting the preheating temperature of the extrusion cylinder, selecting the appropriate temperature interval of the glass powder, selecting the pressure level of the extruder, and determining the cooling method of the extruded pipe after extrusion.

[0007] In step one, the machining outer diameter tolerance is -2mm-0mm, and the outer circle finish turning surface roughness Ra≤1.6um; in step two, the blank sawing length is 800mm-850mm, both ends are flush, the sawing length tolerance is ±2mm, and the sawing slope is <2mm; in step three, the deep hole diameter is φ100mm-φ110mm, the deep hole eccentricity is ≤1mm, and the deep hole surface roughness is ≤3.2um.

[0008] In step four, the horn mouth is turned, the diameter of the conical bottom on one side of the blank end face is φ290mm-φ310mm, the conical surface and the end face are connected by R10mm-R15mm smooth transition, the angle between the conical surface and the center axis of the blank is 30°-35°, the conical top end and the deep hole are connected by R15mm-R25mm smooth transition, and the arc at the connection between the blank end face and the outer cylindrical surface is R25mm-R35mm.

[0009] In step five, the heating is divided into three stages according to different temperature intervals of the furnace, namely preheating stage, heating stage and soaking stage, the preheating stage temperature is ≤750℃, the first heating stage is 900±15℃, the second heating stage is 930±15℃, the third heating stage is 950±15℃, the soaking stage is 930±15℃, the discharge temperature is 910±20℃, the heating time is 6h-6.5h, and the soaking time is 0.5h-0.6h.

[0010] In step six, the induction furnace temperature is set to 1030℃-1060℃, the capacitor is selected as No.3 and No.4 capacitor, the power is set to 250kw-280kw, and the heating and soaking time is 30min-40min.

[0011] In step seven, the reaming cone diameter is 290±0.1mm, the shear circle working plane width is 30mm-35mm, the angle between the two lines of the conical surface axial section is 42°-45°, the shear circle working plane and the conical surface are connected by R3mm-R6mm smooth transition, the nose diameter is 50mm-60mm, the nose angle is 8°-12°, the nose conical surface and the working conical surface are connected by R4mm-R6mm smooth transition, the angle between the two sections of the reaming cone reverse conical angle is 18°-23° and 27°-32°, the axial direction lengths are 5mm-8mm and 12mm-15mm respectively, and the surface roughness is ≤0.8um.

[0012] In step eight, the shear ring working band diameter is 290.5mm-290.8mm, the working face length is ≤10mm, the guide section diameter is 295.5mm-295.7mm, the shear ring thickness is 49.9mm-50mm, the shear ring outer diameter is 330mm-340mm, the shear ring outer diameter is matched with p6 interference tolerance, and the concentricity of the shear ring working circle and the outer diameter circle is ≤0.03mm.

[0013] In step nine, the outer surface lubrication adopts platform rolling dyeing mode, the outer coating powder uses GW7 type, the inner hole uses glass wool plug, glass powder is poured into the horn mouth, the glass powder uses 844-7 (80-120) type, the reaming cylinder is preheated to a temperature of 200℃-400℃ before production, the reaming force level is set to 25MN-28MN, the actual maximum reaming force is ≤15MN, and the average reaming force is ≤12MN.

[0014] In step ten, the induction furnace temperature is set to 1080-1110 DEG C, the capacitor is selected as No. 2 and No. 4 capacitor, the power is set to 500-550 kw, and the heating and holding time is less than or equal to 20 min.

[0015] In step eleven, the extrusion cylinder preheating temperature is 300-350 DEG C, the inner surface is free of sticky steel and pits, the glass pad melting point temperature interval is 1050-1080 DEG C, the extruder pressure grade is selected as 55-60 MN, and the extrusion forming is selected as air cooling mode to cool to less than or equal to 40 DEG C.

[0016] The 13Cr type boron-containing steel is applied to the container for storing nuclear fuel in the third generation nuclear power technology, the material effectively shields the neutrons emitted during nuclear radiation, the successful production of the material has the first creativity in China, and the significance is great.

[0017] The production of the boron-containing steel makes the storage of nuclear fuel safer, the radiation dose to people is less, the thickness of the anti-radiation material is greatly reduced, and the weight of the related equipment is reduced. In addition to the above outstanding performance, the 13Cr type boron-containing steel also has the characteristics of corrosion resistance and rust prevention in the atmospheric environment, and the martensitic type organization makes the material have very high hardness and strength, and the load capacity is more excellent. BRIEF DESCRIPTION OF DRAWINGS

[0018] The drawings described herein are used to provide further understanding of the embodiments of the present application, and constitute a part of the present application. The schematic embodiments of the present application and the description thereof are used to explain the present application, and do not constitute an improper limitation on the present application. In the drawings: Figure 1 It is a reaming cone schematic diagram of the extrusion production method of the 13Cr type boron-containing seamless steel pipe for shielding neutrons of nuclear fuel. Figure 2 It is a top view of a shear ring in the extrusion production method of the 13Cr type boron-containing seamless steel pipe for shielding neutrons of nuclear fuel. Figure 3 It is a left view of a shear ring in the extrusion production method of the 13Cr type boron-containing seamless steel pipe for shielding neutrons of nuclear fuel. DETAILED DESCRIPTION

[0019] Boron is the key element of absorbing radiation, so the concentration of boron in the material must reach the required value, which can play an effective role in preventing radiation. Due to the high boron content of 1.7% in the steel, the increase of non-metallic element content will make the plasticity and impact toughness at room temperature very poor, and the control of supercooling degree is crucial. In addition, high boron content will significantly reduce the melting point of the metal material, at which time the minimum temperature of the metal material under the basis of the expansion hole and the extrusion bearing force needs to be tested. The heating temperature, heating power and heating time need to ensure that the boride in the metal material is fully dissolved in the crystal lattice from the grain boundary, and the high temperature plasticity of the material is ensured. The lubrication needs to fully consider the low temperature of the steel, and since the average suitable temperature of the glass powder is above 1100 DEG C, the particle size, composition and type of the glass powder are very important to ensure its good lubrication state.

[0020] In order to meet the final outer diameter and wall thickness requirements, the expansion cone diameter reaches 290mm, and the expansion coefficient reaches 1.55 or more, which exceeds the current maximum expansion diameter of 280mm. Based on the above situation, the expansion cone and the matching shear ring tool need to be redesigned, and the corresponding expansion, induction heating and other process parameters are formulated.

[0021] The application provides an extrusion production method of a 13Cr type boron-containing seamless steel pipe for shielding nuclear power fuel neutrons, and the technical scheme of the application is as follows: 1. The outer diameter of the incoming material is selected as extrusion 450 series, which is the largest series in extrusion, so as to meet the process requirement that the outer diameter of the blank pipe is above 300, thereby providing sufficient extrusion ratio to ensure the quality requirement of the inner and outer surfaces of the blank pipe. The outer diameter after turning is 432mm, and the tolerance is-2mm-0mm. The selection of the turning outer diameter and the tolerance range thereof are finally determined according to the expansion amount of the material production process temperature and the expansion amount under the working temperature of the expansion cylinder. The blank surface is free of cracks, scabs and other defects, and the surface roughness Ra of the outer circle after finish turning is less than or equal to 1.6um. The quality requirement of the outer surface fully ensures the uniform adhesion of the outer surface glass lubricant on the blank surface in the extrusion process. In order to prevent cracking during the expansion process, the blank center is required to be free of porosity, shrinkage and other defects.

[0022] 2. The length of the blank sawing is 830mm, the sawing length tolerance is ±1mm, the design of the length of the blank shall ensure the final required length of the pipe and the length after reaming is ≤1300mm. The two ends are flush, the outer diameter must be measured before marking, the sawing is carried out according to the standard of the process card, the material information is clearly marked on the blank after sawing, the sawing slope is ≤1mm, the tolerance of the cutting slope ensures the perpendicularity of the first induction furnace, so as to ensure that the blank entering and leaving the first induction furnace maintains a distance from the lining of the induction furnace and does not scratch the blank and the lining of the induction furnace. The edge formed after sawing is polished clean with an angular grinding wheel or other tools, the unevenness of the sawing end face will cause the quality of the outer surface of the pipe end to have waves after the final extrusion breakthrough, and the adhered sawdust will form extrusion pressure marks on the inner and outer surfaces of the pipe.

[0023] 3. A deep hole is drilled through the center of the blank, the deep hole drilling process is φ100mm, the deep hole diameter tolerance is 0mm-2mm, the size of the deep hole diameter is closely related to the size of the final reaming and the diameter of the blank, and both determine the reaming coefficient of the reamer. For materials with poor plasticity, the appropriate reaming coefficient is selected to ensure the size of the pipe while ensuring that the inner hole surface does not crack after reaming. The eccentricity of the deep hole is ≤1mm, the requirement of the eccentricity makes the inner hole and the outer circle as concentric as possible after reaming, and finally ensures that the extruded pipe does not produce a wall. The surface roughness of the deep hole is ≤3.2um, the inner surface of the deep hole is checked after drilling, and the oil stains and iron filings in the inner hole are removed clean, and the smoothness standard of the inner surface of the deep hole makes the uniform attachment of the glass powder in the molten state on the inner hole, which is directly related to the quality of the inner surface after reaming.

[0024] 4. The horn mouth is turned, the diameter of the conical bottom on one side of the blank end face is φ300mm, the reaming cone diameter is 290mm, the horn mouth diameter shall ensure that the reaming cone smoothly enters the horn mouth, and a gap must be left to ensure the accommodation of glass powder to ensure the full lubrication of the inner hole. The R10mm round is used to transition between the conical surface and the end face, which ensures the uniformity of the edge during the extension of the reaming blank, prepares for the extrusion of the pipe, and reduces the occurrence of wall deviation as much as possible. The angle between the conical surface and the center axis of the blank is 33.5°, which is greater than the corresponding half-angle of the reaming cone, and the reaming cone and the horn mouth of the blank form a certain angle, which not only meets the stress characteristics of reaming, but also reduces the stress and ensures the uniform lubrication of the glass powder. R20mm round is used to transition between the conical top and the deep hole, the stress of the arc transition is more uniform, and the possibility of tearing the inner hole is reduced as much as possible. The arc at the junction of the blank end face and the outer surface is R35mm, which is more consistent with the arc of the extrusion die set, reduces the extrusion breakthrough force, and reduces the probability of wall deviation and tearing of the extruded pipe end.

[0025] 5. Heating is divided into three sections according to different temperature intervals of the furnace, which are preheating section, heating section and soaking section. The heating section is divided into one section, two sections and three sections. The preheating section temperature is ≥750℃, the one section is 900±15℃, the two section is 930±15℃, the three section is 950±15℃, the soaking section is 930±15℃, the out of furnace temperature is 910±20℃. The setting of each section temperature needs to consider the microstructure of the material at high temperature. First, it is necessary to ensure that the transformation of martensite structure to austenite structure is completed in the temperature interval. Second, the titanium boride compound in the material needs to be melted into the face-centered cubic structure of austenite from the grain boundary. Finally, the heating time is 6h-6.5h, the soaking time is 0.5h-0.6h. The heating time and soaking time are determined according to the size of the blank diameter and its thermal conductivity. It not only ensures that the blank surface to the core is evenly and thoroughly burned, but also meets the time of fully melting titanium boride compound into the lattice, finally ensuring the uniformity of the blank from the ring furnace to the first induction furnace.

[0026] 6. The induction furnace temperature is set to 1050℃. This temperature is a temperature parameter developed according to the material properties and high temperature mechanical properties. On the one hand, the temperature must reach the sufficient dissolution of titanium boride compound, and on the other hand, it must not cause the intercrystalline melting of the substance to produce overburning phenomenon. The capacitor is selected to be No. 3 and No. 4 capacitor, so that the frequency is maintained in the interval of 40HZ-50HZ. This interval ensures the depth of the skin effect of the induction furnace, avoids the temperature stratification of the blank, and finally reduces the possibility of causing the layered defects of the extruded hollow pipe. The power is set to 260kw, the heating and soaking time is 30min-40min. Considering the temperature conduction speed of the material, the power setting value should be in the appropriate interval, which not only ensures the realization of the blank heating temperature, but also avoids the heating level difference of the blank.

[0027] 7. The hole expansion cone diameter is 290±0.1mm, the size of the hole expansion cone should meet the limit requirements of the hole expansion expansion coefficient, and the inner hole diameter of the blank after the hole expansion by the hole expansion cone should match the extrusion needle, which not only ensures the smooth entry of the extrusion needle into the inner hole, but also makes the gap between the extrusion needle and the hole expansion inner diameter within the process requirement range, the tolerance range of the hole expansion cone should meet the cooperation requirements of the shear ring working belt, so that the excess and the original blank can be smoothly sheared and separated. The working circle plane width is 32mm, which ensures the shearing length of the hole expansion cone and the shear ring working belt, so that the shearing is fully clean, the excess length is reduced, and the yield is improved. Through the stress analysis of the hole expansion enlargement process, the angle between the two lines of the conical surface axis section is designed to be 44°, and the working circle plane and the conical surface are connected by R5mm round smooth transition. The design of such stress is uniform, and the length of the hole expansion cone will not be too long. The nose diameter is 56mm, the nose angle is 10°, the nose conical surface and the working circle conical surface are connected by R5 round smooth transition, the design of the nose diameter and the nose angle should match the diameter of the deep hole, and can play the role of hole expansion guide design. The angle of the two sections of the reverse cone of the hole expansion cone is 20° and 30°, and the length in the axis direction is 7mm and 13mm respectively. The design of the reverse cone makes the hole expansion cone and the excess separate smoothly. The surface roughness of the whole contact with the inner hole of the blank is ≤0.8um, which can reduce the friction between the hole expansion cone and the inner hole of the blank.

[0028] 8. The shear ring working belt diameter is 290.3mm-290.5mm, the working surface length is ≤10mm, the diameter of the shear ring should match the working belt of the hole expansion cone, so that the shear ring and the hole expansion cone form shearing, and finally the excess and the shear ring are separated smoothly, which is very important to effectively reduce the size of the excess. In order to ensure that the excess can be smoothly guided out after shearing, the guide section diameter is set to 295.5mm-295.7mm, and the shear ring thickness is 49.9mm-50mm. The outer diameter of the shear ring should be in interference fit with the shear ring support, and the outer diameter of the shear ring is designed to be 328-333mm, and the outer diameter of the shear ring is in p6 tolerance fit. The concentricity of the shear ring working circle and the outer diameter circle is ≤0.03mm, which ensures the concentricity in the shearing process, so that the shearing force is more uniform.

[0029] 9. The outer surface lubrication adopts a platform rolling dyeing method, the outer coating powder uses GW7 type, the selection of the outer coating method and the outer coating glass powder, one is to ensure the uniform coating of the glass powder, and the other is to ensure the formation of a uniform molten lubrication mold on the outer surface, to reduce the extension friction between the billet and the hole expanding cylinder during the hole expanding process, and to ensure the quality of the outer surface of the pre-extrusion billet after hole expansion. The inner hole is blocked with glass wool plug, and glass powder is poured into the horn mouth. The glass powder uses 844-7 (80-120) type. The selection of the inner hole lubrication method and the inner hole lubrication glass powder ensures the formation of uniform lubrication during the expansion of the hole expansion cone in the inner hole of the billet, so as to ensure the uniform coverage of the glass powder on the inner surface of the hole expansion, and ensure the quality of the inner surface of the hole expansion. In order to reduce the temperature difference between the billet and the hole expansion cylinder, the hole expansion cylinder is preheated to a temperature of 200-400°C before production. Considering the bearing capacity of the tooling, the protection of the tooling and related equipment, and the hole expansion force, the hole expansion force is set to 28MN, the actual maximum hole expansion force is not more than 15MN, and the average hole expansion force is not more than 12MN.

[0030] 10. The setting of the temperature, frequency and heating time of the secondary induction furnace should consider the inherent characteristics of boron-containing steel, ensure that the boron compound enters the crystal cell in the form of boron element from the grain boundary, and ensure its sufficiency without making the grain grow and the plasticity deteriorate. The temperature of the secondary induction furnace is set to 1050°C, the power is set to 550kw, and the heating and holding time is ≤20min. The capacitors selected are No. 2 and No. 4 capacitors. The selection of the capacitor determines the heating frequency, thereby determining the depth of the skin effect, and ensuring the uniformity of the heating temperature of the outer surface and the inner surface.

[0031] 11. In order to reduce the temperature difference between the billet and the extrusion cylinder after hole expansion, the extrusion cylinder is preheated to a temperature of 300-350°C. Preheating the extrusion cylinder can increase the service life of the tooling, prevent brittle cracking caused by thermal expansion and cold contraction. Before production, check that the inner surface of the extrusion cylinder is free of sticky steel and pits to ensure the surface quality of the billet. Since the hot working temperature of the billet is lower than that of conventional austenitic stainless steel, the melting point temperature range of the glass pad is 1050-1090°C to ensure the quality of the inner and outer surfaces of the extruded raw pipe. The extruded raw pipe of this specification is the 450 series, which is the largest series in the 7 series of extrusion machines. The pressure rating of the extrusion machine is selected to be 60MN. Since the material is 13Cr type, its normal temperature is martensitic structure, and the required supercooling degree for quenching is low. After extrusion forming, the air cooling method is selected for cooling.

[0032] An extrusion production method of 13Cr type boron-containing seamless steel pipe for shielding nuclear power fuel neutrons, comprising the following steps: S1, selection of billet outer diameter and surface treatment: selecting the series size, and turning the surface of the steel billet. After turning, the smoothness of the outer surface is ensured.

[0033] S2, sawing: determine the length of the blank, and sawing to the required size, both ends of the sawing flat head, and finally using the angular grinding wheel to polish the burr clean.

[0034] S3, deep hole: the blank is drilled through the deep hole in its heart by deep hole drilling, ensuring the quality requirements such as deep hole surface roughness and deep hole and outer surface concentricity.

[0035] S4, horn mouth and arc processing: machining horn mouth and arc surface on the same end surface of the blank according to process requirements.

[0036] S5, ring furnace heating: the processed blank is heated in a ring furnace, and is divided into three sections according to different temperature intervals of the furnace, namely preheating section, heating section and soaking section.

[0037] S6, first induction furnace heating: after ring furnace heating, the blank is subjected to first induction heating between the hole expansion, and the heating temperature, heating power and selection of capacitance are set according to the material properties.

[0038] S7, hole expansion cone design: the design content of the hole expansion cone includes hole expansion cone diameter, shear circle working plane width, two line angle of conical surface axis section, shear circle working plane and conical surface smooth transition connection radius, nose diameter, nose angle, nose conical surface and working conical surface smooth transition connection radius, two section connection angle of hole expansion cone reverse angle, axis direction length, and surface machining finish.

[0039] S8, shear ring design: the design content of the shear ring includes shear ring working belt diameter, working surface length, guide section diameter, shear ring thickness, shear ring outer diameter, shear ring outer diameter and shear ring support cooperation, shear ring working circle and outer diameter circle concentricity.

[0040] S9, hole expansion: hole expansion process uses glass powder lubrication first, determines the type and lubrication method of glass powder, determines the preheating temperature of the hole expansion cylinder, and sets the hole expansion force level.

[0041] S10, second induction furnace heating: after hole expansion, the blank is subjected to second induction heating, and the heating temperature, heating power and selection of capacitance are set according to the material properties.

[0042] S11, extrusion: set the preheating temperature of the extrusion cylinder, select the appropriate temperature interval of the glass powder, select the pressure level of the extruder, and determine the cooling method of the extruded raw pipe after extrusion.

[0043] In step S1, the machining outer diameter tolerance is-2mm-0mm, and the outer circle finish machining surface roughness Ra≤1.6um.

[0044] In step S2, the blank is sawed to a length of 800mm-850mm, with both ends flush, and the sawing length tolerance is ±2mm, and the sawing slope is <2mm.

[0045] In step S3, the deep hole has a diameter of φ100mm-φ110mm, a deep hole eccentricity of ≤1mm, and a deep hole surface roughness of ≤3.2um.

[0046] In step S4, the horn mouth is turned, the diameter of the conical bottom on one side of the blank end face is φ290mm-φ310mm, the conical surface and the end face are smoothly connected by an R10mm-R15mm arc, the included angle between the conical surface and the center axis of the blank is 30°-35°, and the conical top end and the deep hole are smoothly connected by an R15mm-R25mm arc. The connecting part between the blank end face and the outer circular face is processed to have an arc of R25mm-R35mm.

[0047] In step S5, the heating is divided into three sections according to different temperature ranges of the furnace, namely a preheating section, a heating section, and a soaking section. The preheating section temperature is ≤750℃, the first heating section is 900±15℃, the second heating section is 930±15℃, the third heating section is 950±15℃, the soaking section is 930±15℃, the furnace outlet temperature is 910±20℃, the heating time is 6h-6.5h, and the soaking time is 0.5h-0.6h.

[0048] In step S6, the induction furnace temperature is set to 1030℃-1060℃, the capacitor is selected to be No. 3 and No. 4, the power is set to be 250kw-280kw, and the heating and soaking time is 30min-40min.

[0049] In step S7, the reaming cone diameter is 290±0.1mm, the shear circle working plane width is 30mm-35mm, the included angle of the two lines in the axial section of the conical surface is 42°-45°, the shear circle working plane and the conical surface are smoothly connected by an R3mm-R6mm arc, the nose diameter is 50mm-60mm, the nose angle is 8°-12°, the nose conical surface and the working conical surface are smoothly connected by an R4mm-R6mm arc, the two connecting angles of the reaming cone reverse conical angle are 18°-23° and 27°-32°, the axial direction lengths are 5mm-8mm and 12mm-15mm, respectively, and the surface roughness is ≤0.8um.

[0050] In step S8, the shear ring working band diameter is 290.5mm-290.8mm, the working face length is ≤10mm, the guide section diameter is 295.5mm-295.7mm, the shear ring thickness is 49.9mm-50mm, the shear ring outer diameter is 330mm-340mm, the shear ring outer diameter is fitted with a p6 interference tolerance, and the concentricity of the shear ring working circle and the outer diameter circle is ≤0.03mm.

[0051] In step S9, the outer surface lubrication adopts a platform rolling dyeing mode, the outer coating powder uses GW7 type, the inner hole uses a glass cotton plug, glass powder is poured into the horn, and the glass powder uses 844-7 (80-120) type. The preheating temperature of the hole expanding cylinder before production is 200-400 DEG C, the hole expanding force level is set to 25-28 MN, the actual maximum hole expanding force is less than or equal to 15 MN, and the average hole expanding force is less than or equal to 12 MN.

[0052] In step S10, the temperature of the induction furnace is set to 1080-1110 DEG C, the capacitor is selected to be No. 2 and No. 4 capacitor, the power is set to be 500-550 kw, and the heating and holding time is less than or equal to 20 min.

[0053] In step S11, the preheating temperature of the extrusion cylinder is 300-350 DEG C, the inner surface is free of sticky steel and pits, the melting point temperature range of the glass pad is 1050-1080 DEG C, the extrusion pressure level is selected to be 55-60 MN, and the extrusion is cooled to less than or equal to 40 DEG C after being selected to be air cooling.

[0054] In order to make the purpose, technical scheme and advantages of the present application clearer, the technical scheme of the present application will be clearly and completely described below in combination with specific embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0055] The technical scheme provided by the embodiments of the present application will be described in detail below in combination with the drawings.

[0056] Embodiment 1

[0057] (1) Selection of blank outer diameter and quality parameters: the incoming material outer diameter is selected to be extruded 450 series, the outer diameter after turning is 430 mm, the blank surface is free of cracks, scabs and other defects, the surface roughness Ra of the outer circle after turning is 1.2 um, and the blank center is free of porosity, shrinkage and other defects.

[0058] (2) Sawing: the blank sawing length is 830 mm, the two ends are flush, the outer diameter must be measured before marking, the sawing is performed according to the standard of the process card, the material information is clearly marked on the blank after sawing, and the sawing slope is 1.5 mm. The edge chain formed after sawing or the adhered sawdust is polished clean with an angular grinding wheel or other tools.

[0059] (3) Deep hole: a through deep hole is punched in the center of the blank, the deep hole drilling processes a deep hole diameter of φ102 mm, the deep hole eccentricity is 0.6 mm, the deep hole surface roughness is 2.8 um, and the inner surface of the deep hole is checked after drilling to remove the oil stains and iron filings in the inner hole.

[0060] (4) Horn mouth, arc: the horn mouth is processed by turning, the diameter of the conical bottom on one side of the blank end face is φ305mm, the conical surface and the end face are smoothly connected by R12mm, the included angle between the conical surface and the center axis of the blank is 33.5°, the conical top end and the deep hole are smoothly connected by R20mm. The arc at the connecting position of the blank end face and the outer cylindrical surface is R35mm.

[0061] (5) Ring furnace heating: the heating is divided into three sections according to different temperature zones of the hearth, which are preheating section, heating section and soaking section respectively. The heating temperature and heating time of each section are as follows.

[0062]

[0063] (6) Primary induction heating: the induction furnace temperature is set to 1050℃, the capacitors are selected as No. 3 and No. 4 capacitors, the power is set to 260kw, and the heating and soaking time is 30min.

[0064] (7) Design and selection of hole expanding die: 7.1 Hole expanding cone design: the diameter of the hole expanding cone is 290.1mm, the shear circle working plane width is 32mm, the included angle of the two lines of the conical surface axis section is 44°, the shear circle working plane and the conical surface are smoothly connected by R5mm, the nose diameter is 56mm, the nose angle is 10°, the nose conical surface and the working conical surface are smoothly connected by R5, the reverse conical angle of the hole expanding cone is 20° and 30°, and the axis direction lengths are 7mm and 13mm respectively. The surface roughness is 0.8um.

[0065] 7.2 Shear ring design: the shear ring working belt diameter is 290.3mm, the working face length is 10mm, the guide section diameter is 295.7mm, the shear ring thickness is 49.9mm, the shear ring outer diameter is 330mm, the shear ring outer diameter is p6 interference fit, and the concentricity of the shear ring working circle and the outer diameter circle is 0.02mm.

[0066] (8) Hole expanding process control: the outer surface lubrication adopts platform rolling dyeing method, GW7 type powder is used for outer coating, glass wool plug is used for inner hole, glass powder is poured into the horn mouth, and the glass powder is 844-7 (80-120) type. The preheating temperature before the production of the hole expanding cylinder is 270℃, the hole expanding force level is set to 28MN, the actual maximum hole expanding force does not exceed 15MN, and the average hole expanding force does not exceed 12MN.

[0067] (9) Secondary induction heating: the induction furnace temperature is set to 1090℃, the capacitors are selected as No. 2 and No. 4 capacitors, the power is set to 550kw, and the heating and soaking time is 20min.

[0068] (10) Extrusion process control: the preheating temperature of the extrusion cylinder is 320℃, the inner surface is free of adhered steel and pits, the melting point temperature range of the glass pad is 1060℃, the pressure rating of the extrusion machine is selected to be 60 MN, and the extruded product is cooled by air cooling. Example 2

[0069] (1) Selection of blank outer diameter and quality parameters: the incoming outer diameter is selected to be extruded 450 series, the outer diameter after turning is 431 mm, the blank surface is free of cracks, scabs and other defects, the surface roughness Ra of the outer circle after finishing turning is 1.0 um, and the blank center is free of porosity, shrinkage and other defects.

[0070] (2) Sawing: the blank sawing length is 815 mm, the two ends are flush, the outer diameter must be measured before marking, sawing is carried out according to the standard of the process card, the material information is clearly marked on the blank after sawing, and the sawing slope is 1.7 mm. The edge chain formed after sawing or the adhered sawdust is polished clean with an angular grinding wheel and other tools.

[0071] (3) Deep hole: a through deep hole is drilled in the center of the blank, the deep hole diameter is φ100 mm, the deep hole eccentricity is 0.9 mm, and the deep hole surface roughness is 3.0 um. After drilling, the inner surface of the deep hole is checked, and the oil stains and iron filings in the hole are removed clean.

[0072] (4) Horn mouth and arc: the horn mouth is turned, the diameter of the conical bottom on one side of the blank end face is φ300 mm, the conical surface and the end face are smoothly transitioned with R13 mm, the included angle between the conical surface and the center axis of the blank is 33.5°, and the conical top end and the deep hole are smoothly transitioned with R22 mm. The arc at the junction of the blank end face and the outer circle is R30 mm.

[0073] (5) Ring furnace heating: heating is divided into three sections according to different temperature ranges of the hearth, namely preheating section, heating section and soaking section. The heating temperature and time of each section are as follows.

[0074]

[0075] (6) First induction heating: the induction furnace temperature is set to 1030℃, the capacitors are selected to be No. 3 and No. 4, the power is set to 255 kw, and the heating and soaking time is 35 min.

[0076] (7) The design and selection of the reaming tool: 7.1 The design of the reaming cone: the diameter of the reaming cone is 290 mm, the width of the shearing circle working plane is 34 mm, the angle between the two lines of the axial section of the conical surface is 42.5°, the shearing circle working plane and the conical surface are connected by a R4 mm round transition, the diameter of the nose is 55 mm, the angle of the nose cone is 11°, the nose cone and the working conical surface are connected by a R5 round transition, the angle of the two sections of the reverse cone of the reaming cone is 22° and 32°, and the length of the axial direction is 6 mm and 13 mm respectively. The surface roughness is 0.6 um.

[0077] 7.2 The design of the shearing ring: the diameter of the shearing ring working belt is 290.4 mm, the length of the working surface is 8 mm, the diameter of the guide section is 295.5 mm, the thickness of the shearing ring is 50 mm, the outer diameter of the shearing ring is 335 mm, the outer diameter of the shearing ring is matched with a p6 interference fit, and the concentricity of the shearing ring working circle and the outer diameter circle is 0.03 mm.

[0078] (8) Reaming process control: the outer surface lubrication adopts a platform rolling dyeing mode, the outer coating powder uses GW7 type, the inner hole uses a glass wool plug, the glass powder is poured into the horn mouth, and the glass powder uses 844-7 (80-120) type. The preheating temperature before the production of the reaming cylinder is 290℃, the reaming force level is set to 26 MN, the actual maximum reaming force does not exceed 12 MN, and the average reaming force does not exceed 11 MN.

[0079] (9) Secondary induction heating: the temperature of the induction furnace is set to 1080℃, the capacitors are selected as No. 2 and No. 4 capacitors, the power is set to 520 kw, and the heating and holding time is 22 min.

[0080] (10) Extrusion process control: the preheating temperature of the extrusion cylinder is 300℃, the inner surface is free of sticky steel and pits, the melting point temperature range of the glass pad is 1050℃, the pressure level of the extrusion machine is selected as 60 MN, and the extrusion forming is selected as an air cooling mode.

[0081] The above only describes specific embodiments of the present application, but the structural features of the scope of protection of the present application are not limited thereto, and any changes or modifications made by those skilled in the art within the scope of the present application are covered by the patent scope of the present application.

Claims

1. A method for extruding 13Cr type boron-containing seamless steel tubes for shielding nuclear power fuel neutrons, characterized in that: Includes the following steps: Step 1: Selection of billet outer diameter and surface treatment: Select the series size, machine the surface of the steel billet, and ensure the surface finish after machining; Step 2: Sawing: Determine the length of the blank and saw it to the required size. Sawing both ends flat, and finally using an angle grinder to clean the rough edges. Step 3: Deep Hole: A through-hole is drilled through the center of the blank using a deep hole drill to ensure the surface roughness of the deep hole and the concentricity of the deep hole and the outer surface meet the quality requirements. Step 4: Flared Mouth and Arc Machining: Machin the flared mouth and arc surfaces on the same end face of the blank according to the process requirements; Step 5: Annular furnace heating: The processed billet is heated in an annular furnace and divided into three sections according to the different temperature ranges of the furnace chamber: the preheating section, the heating section, and the soaking section. Step Six: Primary Induction Furnace Heating: After heating in the ring furnace, the billet is subjected to primary induction heating between the expansion holes, and the heating temperature, heating power, and capacitor selection are set according to the material characteristics. Step 7: Hole Reaming Taper Design: The design of the hole reaming taper includes the diameter of the hole reaming taper, the width of the working plane of the shearing circle, the included angle between the two lines of the axial section of the conical surface, the radius of the smooth transition between the working plane of the shearing circle and the conical surface, the diameter of the nose, the nose taper angle, the radius of the smooth transition between the nose taper surface and the working conical surface, the connection angle between the two segments of the hole reaming taper, the length in the axial direction, and the surface finish of the machining. Step 8: Shearing Ring Design: The design of the shearing ring includes the diameter of the working belt, the length of the working surface, the diameter of the guide section, the thickness of the shearing ring, the outer diameter of the shearing ring, the fit between the outer diameter and the shearing ring support, and the concentricity of the working circle and the outer diameter circle of the shearing ring. Step 9: Hole Enlargement: The hole enlargement process begins with lubrication using glass powder. The type of glass powder and the lubrication method are determined, the preheating temperature of the enlargement cylinder is determined, and the enlargement force level is set. Step 10: Secondary induction furnace heating: After the hole is expanded, the billet is subjected to secondary induction heating, and the heating temperature, heating power and capacitor selection are set according to the material characteristics. Step 11: Extrusion: Set the preheating temperature of the extrusion cylinder, select glass powder with a suitable temperature range, select the pressure rating of the extruder, and determine the cooling method for the extruded blank after extrusion molding.

2. The extrusion production method of 13Cr type boron-containing seamless steel tube for shielding nuclear power fuel neutrons according to claim 1, characterized in that: In step one, the machining outer diameter tolerance is -2mm to 0mm, and the surface roughness Ra after precision turning of the outer circle is ≤1.6um; in step two, the blank sawing length is 800mm-850mm, both ends are flush, the sawing length tolerance is ±2mm, and the sawing angle is <2mm; in step three, the deep hole diameter is φ100mm-φ110mm, the deep hole eccentricity is ≤1mm, and the deep hole surface roughness is ≤3.2um.

3. The extrusion production method of 13Cr type boron-containing seamless steel tube for shielding nuclear power fuel neutrons according to claim 1, characterized in that: In step four, the flared mouth is machined by turning. The diameter of the conical base on one side of the blank end face is φ290mm-φ310mm. The conical surface and the end face are smoothly transitioned by R10mm-R15mm. The angle between the conical surface and the central axis of the blank is 30°-35°. The top of the cone and the deep hole are smoothly transitioned by R15mm-R25mm. The arc at the connection between the blank end face and the outer cylindrical surface is machined to be R25mm-R35mm.

4. The extrusion production method of 13Cr type boron-containing seamless steel tube for shielding nuclear power fuel neutrons according to claim 1, characterized in that: In step five, the heating is divided into three sections according to different temperature ranges in the furnace: the preheating section, the heating section, and the soaking section. The temperature of the preheating section is ≤750℃, the first heating section is 900±15℃, the second heating section is 930±15℃, the third heating section is 950±15℃, the soaking section is 930±15℃, the furnace exit temperature is 910±20℃, the heating time is 6h-6.5h, and the soaking time is 0.5h-0.6h.

5. The extrusion production method of 13Cr type boron-containing seamless steel tube for shielding nuclear power fuel neutrons according to claim 1, characterized in that: In step six, the induction furnace temperature is set to 1030℃-1060℃, capacitors No. 3 and No. 4 are selected, the power is set to 250kw-280kw, and the heating and holding time is 30min-40min. The selection of capacitors No. 3 and No. 4 keeps the frequency in the range of 40HZ-50HZ. This range ensures the depth of the skin effect of the induction furnace and avoids the formation of temperature stratification in the billet, thereby ultimately reducing the possibility of stratification defects in the extruded rough tube.

6. The extrusion production method of 13Cr type boron-containing seamless steel tube for shielding nuclear power fuel neutrons according to claim 1, characterized in that: In step seven, the diameter of the expanding cone is 290±0.1mm, the width of the working plane of the shearing circle is 30mm-35mm, the included angle between the two lines of the axial section of the conical surface is 42°-45°, the working plane of the shearing circle and the conical surface are smoothly connected by a R3mm-R6mm transition, the nose diameter is 50mm-60mm, the nose cone angle is 8°-12°, the nose cone surface and the working cone surface are smoothly connected by a R4mm-R6mm transition, the two connecting angles of the expanding cone's reverse cone angle are 18°-23° and 27°-32°, the axial lengths are 5mm-8mm and 12mm-15mm respectively, and the surface roughness is ≤0.8um.

7. The extrusion production method of 13Cr type boron-containing seamless steel tube for shielding nuclear power fuel neutrons according to claim 1, characterized in that: In step eight, the working diameter of the shear ring is 290.5mm-290.8mm, the working surface length is ≤10mm, the guide section diameter is 295.5mm-295.7mm, the shear ring thickness is 49.9mm-50mm, the shear ring outer diameter is 330mm-340mm, the shear ring outer diameter is fitted with a p6 interference tolerance, and the concentricity of the shear ring working circle and outer diameter circle is ≤0.03mm.

8. The extrusion production method of 13Cr type boron-containing seamless steel tube for shielding nuclear power fuel neutrons according to claim 1, characterized in that: In step nine, the outer surface is lubricated by a platform rolling dyeing method, the outer coating powder is GW7 type, the inner hole is plugged with glass wool, glass powder is poured into the flared mouth, the glass powder is 844-7 (80-120 type), the preheating temperature of the expanding cylinder before production is 200℃-400℃, the expanding force level is set to 25MN-28MN, the actual maximum expanding force is ≤15MN, and the average expanding force is ≤12MN.

9. The extrusion production method of 13Cr type boron-containing seamless steel tube for shielding nuclear power fuel neutrons according to claim 1, characterized in that: In step ten, the induction furnace temperature is set to 1080℃-1110℃, capacitors No. 2 and No. 4 are selected, the power is set to 500kw-550kw, and the heating and holding time is ≤20min. The selection of capacitors No. 2 and No. 4 determines the heating frequency, thereby determining the depth of the skin effect and ensuring the uniformity of the heating temperature of the outer and inner surfaces.

10. The extrusion production method of 13Cr type boron-containing seamless steel tube for shielding nuclear power fuel neutrons according to claim 1, characterized in that: In step eleven, the extrusion cylinder is preheated to 300℃-350℃, with no steel sticking or pits on the inner surface. The melting point temperature range of the glass pad is 1050℃-1080℃. The extruder pressure rating is selected as 55MN-60MN. After extrusion molding, air cooling is selected to cool the cylinder to ≤40℃.

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