CN112845658A

CN112845658A - Preparation method of UNS N08825 small-caliber precise seamless tube

Info

Publication number: CN112845658A
Application number: CN202110008158.3A
Authority: CN
Inventors: 楚志兵; 拓雷锋; 沈卫强; 高虹; 康喜唐; 程逸明; 帅美荣; 黎毅
Original assignee: Taiyuan University of Science and Technology
Current assignee: Taiyuan University of Science and Technology
Priority date: 2021-01-05
Filing date: 2021-01-05
Publication date: 2021-05-28
Anticipated expiration: 2041-01-05
Also published as: CN112845658B

Abstract

The invention discloses a preparation method of a UNS N08825 small-caliber precise seamless tube, and belongs to the technical field of metal tube processing. The method comprises the following steps: circular forging stock UNS N08825 → blank processing → blank preheating → blank primary induction heating → blank hot reaming → blank secondary induction heating → pierced billet hot extrusion → solution annealing → finishing → 2-5 passes of cold rolling/cold drawing → small-caliber precision seamless pipe finished product physical and chemical inspection, and each index meets the 6-grade or finer grain size of the technical standard and special requirement of ASTM SB423 and GB/T30059-2013. The invention adopts a cold-drawing forming process, solves the problem of wall increasing by empty drawing according to the finished specification of the small-caliber precise seamless tube, the elongation of UNS N08825 material and the principle that the volume of the tube is not changed before and after deformation, and ensures that the wall thickness of the finished tube meets the design wall thickness.

Description

Preparation method of UNS N08825 small-caliber precise seamless tube

Technical Field

The invention belongs to the technical field of metal pipe processing, and particularly relates to a preparation method of a UNS N08825 small-caliber precise seamless pipe.

Background

UNS N08825 is a nickel-iron-chromium solid solution strengthening type corrosion-resistant alloy containing molybdenum, copper and titanium, has good pitting corrosion resistance, crevice corrosion resistance and chloride ion stress corrosion cracking resistance, can be used in oxidative environments (such as nitric acid, nitrate and the like) and reductive environments (such as sulfuric acid, phosphoric acid and the like), and is mainly applied to industrial equipment as a pipe.

At present, researches on manufacturing technologies of UNS N08825 seamless pipes are more related to two units of Long Steel company of Steel group and Wujin stainless Steel Limited company of Jiangsu, and specifically, the research on thermal piercing process of UNS N08825 alloy pipes is published in the journal of Special Steel technology of Deng Xingji, a piercing temperature interval and defect control are researched, and researches on small-size precise seamless pipes are not carried out. Wu Yougong has published a paper entitled "research and development of domestic NS1402(UNS N08825) alloy pipe" in journal of iron and steel research bulletin, and hot extrusion and multi-pass cold rolling process are adopted to manufacture seamless pipe with phi 19 x 2mm specification, and the outer diameter is larger than phi 15 mm. Chenjie published in the journal of Special Steel technology entitled "investigation on intergranular corrosion of UNS N08825 pipe finished products", carried out corrosion performance research on UNS N08825 alloy, and related to a minimum specification of phi 19 multiplied by 2mm, did not introduce a forming process of seamless pipes and an outer diameter of more than phi 15 mm. The research and development of the alloy pipe for the large-caliber thick-wall UNS N08825 petrochemical hydrogenation device is published in the journal of modern metallurgy by the highly-rainbow, and the large-caliber thick-wall pipe is developed by adopting a forming method combining oblique rolling perforation and cold rolling/cold drawing, and the specification with the outer diameter of less than phi 15mm is not involved. Generally, the smaller the outer diameter, the more difficult the deformation process, dimensional tolerance and physical and chemical property control.

Regarding the manufacture of UNS N08825, chemical compositions (Table 1), heat treatment temperature range (rapid water cooling after annealing at 960-1070 ℃), stretching performance range value, size and surface technical requirements of UNS N08825 seamless tubes are proposed in American standard ASTM SB423 and national standard GB/T30059-.

TABLE 1 main chemical composition

TABLE 2 tensile Properties

Disclosure of Invention

In order to overcome the problems in the prior art, the invention aims to provide a preparation method of UNS N08825 small-caliber precise seamless tube. By adopting the method, the UNS N08825 small-caliber precise seamless pipe with the diameter of 10-15 mm can be prepared.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

the technical route of the invention is as follows: circular forging stock UNS N08825 → blank processing → blank preheating → blank primary induction heating → blank hot reaming → blank secondary induction heating → pierced billet hot extrusion → solution annealing → finishing (straightening, flat end and acid pickling) → 3-5 cold rolling/cold drawing (degreasing and deoiling after each cold rolling/cold drawing) → 6-grade or finer grain size of the small-diameter precision seamless pipe finished product, all indexes of which meet the technical standards and special requirements of ASTM SB423 and GB/T30059-2013.

A preparation method of UNS N08825 small-caliber precise seamless tube comprises the following steps:

step 1, blank processing: cutting a round forging stock UNS N08825 into short sections according to a specified fixed length, and processing into a designed blank shape;

step 2, blank preheating: preheating the processed blank;

step 3, primary induction heating of the blank: heating the preheated blank in an induction heating mode;

step 4, hot reaming of the blank: reaming the inner hole of the blank after the primary induction heating from the size of the deep hole to the size of the inner hole required by the hot extrusion;

step 5, secondary induction heating of the blank: carrying out secondary heating on the blank subjected to hot reaming in an induction heating mode;

step 6, hot extrusion of the pierced billet: carrying out seamless tube hot forming on the blank subjected to secondary induction heating in an extrusion mode;

step 7, solution annealing and finishing: carrying out solution treatment again on the extruded seamless pipe and finishing;

step 8, cold rolling treatment: performing diameter reduction and wall reduction treatment on the finished seamless pipe in a cold rolling mode;

step 9, cold drawing forming: the seamless pipe after reducing the diameter and reducing the wall is manufactured into a small-caliber precise seamless pipe by a cold-drawing forming method;

step 10, physical and chemical inspection: and performing physical and chemical inspection on the manufactured small-caliber precise seamless pipe. Ensuring that the technical indexes meet the 6-grade or finer grain size of the technical standards and special requirements of ASTM SB423, GB/T30059-2013.

Further, a round billet UNS N08825 was cut into short pieces to a predetermined length and processed into a designed billet shape. The UNS N08825 round billet can be forged from a square billet by using a universal radial forging machine, and the forging ratio is not less than 4; cutting short sections from the forged blank according to a specified fixed length by using a band saw machine, and then processing a designed blank shape by adopting a deep hole drill and a lathe, wherein the outer diameter of the tube blank is phi 219-phi 277mm, and the deep hole is phi 40-60 mm.

Still further, the blank preheating of step 2 is to preheat the processed blank to 1000 ℃ ± 10 ℃ by using an annular gas furnace.

Further, the blank in the step 3 is subjected to primary induction heating, specifically, the preheated blank is heated to 1180 ℃ +/-10 ℃ in a vertical induction heating mode.

Further, the blank hot reaming in the step 4 is to ream the blank inner hole after the primary induction heating from the deep hole size to the inner hole size required by the hot extrusion by using a vertical reaming model, wherein the reaming cone used for reaming is phi 80-120 mm.

Further, the blank in the step 5 is subjected to secondary induction heating, specifically, the blank after hot hole expansion is quickly subjected to heat compensation to 1210 +/-10 ℃ by adopting an induction heating mode.

Further, the pierced billet hot extrusion in the step 6 is to adopt a horizontal extrusion model to hot extrude the tube blank after the secondary induction heating into a seamless tube with phi 57 mm-phi 168 mm; the outside diameter and inside diameter of the extruded tube during extrusion have shrinkage coefficients of 1.025 and 1.02, respectively, and the extrusion ratio is not more than 40.

Further, the solution annealing and finishing of step 7, wherein the finishing comprises straightening, flatting and pickling processes.

Further, the cold rolling treatment in the step 8 is specifically a pilger cold rolling mode, the diameter and the wall of the finished seamless pipe are reduced to phi 14-phi 22mm through 3-5 times of cold rolling, and degreasing are performed after each time of cold rolling, and then bright annealing is performed; the deformation ratio of the last pass of rolling, namely the ratio of the sectional areas before and after rolling is not less than 2, and the specification of the seamless tube formed by the last pass of cold rolling is calculated according to the specification of the finished seamless tube and the principle that the volume of the tube is not changed before and after deformation; the annealing target temperature of the seamless tube semi-finished product in the bright annealing is 1040 +/-10 ℃, and the annealing target temperature of the seamless tube finished product is 980 +/-10 ℃.

Further, the cold-drawing forming in the step 9 is to adopt a cold-drawing model, to make a small-caliber precise seamless pipe with phi 10mm to phi 15mm by cold-drawing for one time, and to perform degreasing and bright annealing after cold-drawing; the target temperature for annealing the seamless tube finished product in the bright annealing is 980 +/-10 ℃.

Compared with the prior art, the invention has the following beneficial effects:

1. the invention adopts a manufacturing method combining hot extrusion, annealing, acid pickling and cold rolling to manufacture UNS N08825 round solid blank into a small-caliber precise seamless tube, meets the technical standards of ASTM SB423 and GB/T30059-.

2. The invention adopts a method of combining hot extrusion and cold pilger rolling to manufacture a seamless tube which is made of UNS N08825 and has the diameter of phi 19 mm-phi 25 mm; and then the cold-drawing forming process is adopted to realize the manufacture of the small-caliber precise seamless pipe with the diameter of phi 10mm to phi 15 mm.

3. The invention adopts a cold-drawing forming process, solves the problem of wall increasing by empty drawing according to the finished specification of the small-caliber precise seamless tube, the elongation of UNS N08825 material and the principle that the volume of the tube is not changed before and after deformation, and ensures that the wall thickness of the finished tube meets the design wall thickness.

Drawings

FIG. 1 is a schematic structural diagram of a blank after the blank is processed in step 1 of the present invention;

FIG. 2 is a schematic view of a vertical induction heating structure in the primary induction heating of the blank in step 3 of the present invention;

FIG. 3 is a schematic structural view of a vertical reaming model in step 4 blank hot reaming according to the invention;

FIG. 4 is a schematic structural diagram of a horizontal type extrusion model in the hot extrusion of the pierced billet in step 6 of the invention;

FIG. 5 is a schematic view showing the structure of a cold rolling model in the step 8 cold rolling process of the present invention.

FIG. 6 is a schematic structural diagram of a cold-drawn mold in the step 9 cold-drawing molding of the present invention.

Wherein, 1-blank, 2-coil, 3-reaming cone, 4-reaming cylinder, 5-glass powder, 6-shearing ring, 7-shearing ring seat, 8-extruding cylinder, 9-extruding rod, 10-extruding pad, 11-extruding die system, 12-seamless tube, 13-extruding needle, 14-glass pad, 15-roller, 16-conical core rod, 17-external die, 18-clamping plate and 19-welding drawing head.

Detailed Description

The technical scheme of the invention is further explained by combining the drawings and the specific embodiments. It should be understood by those skilled in the art that the specific embodiments described are merely to assist in understanding the invention and should not be construed as specifically limiting the invention.

Example 1

As shown in fig. 1 to 6, UNS N08825 small-caliber precision seamless tube (Φ 13.7 × 1.2mm) was prepared by the method of the present invention, comprising the steps of:

step 1, blank processing: cutting a round forging stock UNS N08825 into short sections according to a fixed length, and processing into a designed stock shape as shown in figure 1; the method specifically comprises the following steps:

step 1.1 stock inspection

(1) The outer diameter phi 219 (-2-0) mm;

(2) the surface is not allowed to have obvious defects which can be seen by naked eyes, such as pits, grooves, cracks, scabs, black skin, steps, loose centers and the like.

Step 1.2 blank processing

(1) Cutting slope: the end face cutting slope is less than or equal to 2 mm;

(2) deep hole: phi is 40mm, no step is allowed, and the concentricity of the drilled holes is less than or equal to 0.3 mm;

(3) a bell mouth: the diameter phi is 90mm, and the cone angle is 33.5 degrees;

(4) arc angle: r35 mm;

(5) machining surface roughness: r is less than or equal to 1.6 mu m;

(6) cleanliness: the inner surface and the outer surface are not allowed to have obvious visible impurities such as oil stains and the like.

Step 2, blank preheating: preheating the processed blank 1 to 1000 +/-10 ℃ by adopting an annular gas furnace; the target temperature and charging/discharging residence time were carried out according to the ring furnace preheating process shown in Table 3, and the temperatures of the center and outer surface of the blank were confirmed by using a temperature measuring gun after discharge.

TABLE 3 preheating process of annular furnace

Step 3, primary induction heating of the blank: heating the preheated blank 1 by adopting a vertical induction heating mode; the heating target temperature is 1180 +/-10 ℃, so that the whole blank is uniformly heated, and dark black cannot appear in the center. The vertical induction heating structure is schematically shown in fig. 2, in which a billet 1 is fed from the bottom up into a heating coil 2 in a closed vertical induction furnace, and the billet 1 is heated after the coil is energized.

Glass lubrication: the outer surface of the blank is lubricated by adopting W8 model glass powder, the inner surface of the blank is lubricated by adopting N26 model glass powder, and a D19 model glass pad is arranged between the extrusion die and the extrusion blank.

Step 4, hot reaming of the blank: the vertical reaming model shown in figure 3 is adopted, the vertical reaming model mainly comprises a reaming cylinder 8, a shearing ring seat 7, a shearing ring 6, a reaming cone 3 and other tools and dies and a blank 1, the inner hole of the blank 1 after primary induction heating is enlarged to the size of the inner hole required by hot extrusion through the acting force applied on the reaming cone 3, the excess material generated by reaming is transversely sheared and broken by utilizing the gap of 0.25mm at the single side between the reaming cone 3 and the shearing ring 6, a certain amount of glass powder 5 can be scattered at the outlet of the reaming cone 3 and the horn mouth of the blank, and the lubricating effect in the reaming deformation process is achieved; the specific parameters are as follows: the diameter of the reaming cone is 80mm, the diameter of the shearing ring is 80.5mm, the reaming extension coefficient is 1.04, and the preheating temperature of the reaming cylinder is above 300 ℃.

Step 5, secondary induction heating of the blank: carrying out secondary heating on the blank 1 subjected to hot reaming in an induction heating mode; the heating target temperature is 1210 +/-10 ℃, the integral heating of the blank is ensured to be uniform, the dark black cannot appear in the center, and the temperature difference between the inside and the outside is measured to be not higher than 20 ℃ after the blank is taken out of the furnace.

Step 6, hot extrusion of the pierced billet: a horizontal extrusion model as shown in fig. 4 is adopted, and the horizontal extrusion model mainly comprises an extrusion rod 9, an extrusion needle 13, an extrusion pad 10, an extrusion cylinder 8, an extrusion die system 11 and other tools and dies, a blank 1 and a glass pad 14. The billet after the secondary induction heating is hot-extruded by the extrusion force applied to the tail end of the extrusion stem 9 to form a seamless tube 12. The specific parameters are as follows: extruding a die: phi 91.2 (considering the shrinkage coefficient of the outer diameter of the pipe is 1.025)

And (3) extruding a needle: phi 76.5 (considering the shrinkage factor of the inner diameter of the tube is 1.02)

Extruding a rod: outside diameter phi 225/inside diameter phi 100 (load class 38MN)

Extrusion ratio: 19

Extrusion speed: 100 to 150mm/s

Extrusion force: burst force 35MN

And (3) cooling: and cooling the extruded product with water.

Inspecting an extruded tube:

(1) the tolerance of the outer diameter is +/-0.8 mm, and the tolerance of the wall thickness is +/-0.7 mm;

(2) the surface should have no defects such as cracks, scars, scratches, etc.

Step 7, solution annealing and finishing: re-solution treating and finishing the extruded seamless pipe 12;

in order to improve the plasticity of the extruded tube, the extruded seamless tube 12 is subjected to solution annealing at the annealing temperature of 1120 ℃ in a rapid water cooling mode. Wherein the finishing comprises straightening, flatting and pickling processes.

Step 8, cold rolling treatment: reducing the diameter and the wall of the finished seamless tube 12 in a cold rolling way; specifically, a pilger cold rolling mode is adopted, namely a rotary cold rolling mill group of a double-roller gradual-change type groove bottom hole pattern and a conical core rod is adopted to roll the seamless pipe 12 to enable the seamless pipe to generate radial shrinkage, wall thickness reduction and longitudinal extension plastic deformation, a cold rolling model is shown as figure 5, the conical core rod 16 is placed in a seamless pipe 17, two rollers 15 roll along the seamless pipe 12, the diameter reduction and the wall reduction of the finished seamless pipe are carried out to phi 19-phi 25mm through 4 times of cold rolling, and degreasing and bright annealing are carried out after each time of cold rolling. The cold deformation process route comprises the following steps: the blank pipe Φ 89 × 7mm → the cold rolled Φ 57 × 3.5mm → the cold rolled Φ 38 × 2.5mm → the cold rolled Φ 25 × 2mm → the cold rolled Φ 19 × 1.18 mm.

Step 9, cold drawing forming: the seamless pipe 12 after reducing the diameter and reducing the wall is manufactured into a small-caliber precise seamless pipe by adopting a cold-drawing forming method, namely, the longitudinal tension applied on a welding drawing head 19 at the front end of the seamless pipe by a clamping plate 18 causes the seamless pipe 12 to generate radial shrinkage and longitudinal extension plastic deformation after passing through an outer die, and the cold-drawing die is composed of an outer die 17, the clamping plate 18 and the welding drawing head 19 as shown in figure 6. The small-caliber precise seamless pipe with the diameter of 10 mm-15 mm is manufactured by one-time cold drawing, and degreasing and bright annealing are carried out after each-time cold drawing.

The cold rolled phi 19 multiplied by 1.18mm is manufactured into phi 13.7 multiplied by 1.2mm by adopting a one-pass empty-drawing forming method. The wall thickness of the thin-wall seamless pipe with small caliber (less than or equal to phi 25mm) after drawing forming when the ratio of the diameter to the wall thickness exceeds 10 is considered to be increased, and the specification of the final cold rolling pass is inverted to be phi 19 x 1.18mm according to the principle that the specification of the finished product is phi 13.7 x 1.2mm, the elongation of the plastic property of the material is 40 percent (the elongation of UNS N08825 after bright annealing is in the range of 30-50 percent) and the volume of the pipe before and after deformation is unchanged.

And (3) annealing the subsequent cold-rolled or cold-drawn semi-finished products in the

steps

8 and 9 by adopting a bright annealing process, wherein the furnace is heated in two sections to reach the target temperature in order to ensure that the temperature of the furnace is uniformly increased and the thermal inertia is reduced. The heating temperatures and soaking times of the finished and semi-finished products are shown in tables 4 and 5.

TABLE 4 target temperature for bright annealing of semi-finished products and finished products

TABLE 5 soaking time

Step 10, physical and chemical inspection of finished products: and performing physical and chemical inspection on the manufactured small-caliber precise seamless pipe. Ensure that the technical indexes thereof meet the 6-grade or finer grain size of the ASTM SB423, GB/T30059-2013 technical standard and special requirements. Specific mechanical and grain size results are shown in table 6.

TABLE 6 mechanical and grain size results

As is apparent from Table 6, the mechanics of the UNS N08825 small-caliber precision seamless pipe prepared by the method is far better than the technical standards of ASTM SB423 and GB/T30059-2013, and the grain size reaches more than grade 6.

Example 2

This example uses the method of the invention to prepare UNS N08825 small-caliber precision seamless tubes (Φ 10 × 1.2mm), differing from example 1 only in that:

and step 8, in the cold rolling treatment, reducing the diameter and the wall of the finished seamless pipe to phi 19-phi 25mm through 4 times of cold rolling, wherein the cold deformation process route is as follows: extruded mother pipe Φ 89 × 7mm → cold rolled Φ 57 × 4mm → cold rolled Φ 38 × 2.5mm → cold rolled Φ 21.7 × 1.8mm → cold rolled Φ 14 × 1.15 mm.

And 9, cold-drawing forming, namely manufacturing the cold-rolled phi 14 multiplied by 1.15mm into phi 10 multiplied by 1.2mm by adopting a one-pass empty-drawing forming method.

In the cold rolling treatment in step 8 of this embodiment, the finished seamless pipe may also be subjected to diameter reduction and wall reduction to Φ 14 × 1.15mm by 5-pass cold rolling, and the prepared pipe may have a higher grain size by 5-pass cold rolling treatment. In the embodiment, 4-pass cold rolling treatment is adopted, so that the method is economical, and the prepared pipe meets the technical index requirement.

Example 3

This example uses the method of the invention to produce UNS N08825 small-caliber precision seamless tubes (Φ 15 × 2mm), differing from example 1 only in that:

the outer diameter of the tube blank in the tube blank processing in the step 1 is phi 219 (-2-0) mm; deep hole: phi 40 mm;

and step 4, the concrete parameters in the blank hot reaming are as follows: 75mm phi of a reaming cone, 75.5mm of a shearing ring, 1.02 of reaming extension coefficient and over 300 ℃ of preheating temperature of a reaming cylinder.

Step 6, the concrete parameters in the hot extrusion of the pierced billet are as follows: extruding a die: phi 91.2 (considering the shrinkage coefficient of the outer diameter of the pipe is 1.025)

And (3) extruding a needle: phi 70.38 (considering the shrinkage factor of the tube inner diameter is 1.02)

Extruding a rod: outside diameter phi 225/inside diameter phi 75 (load class 38MN)

Extrusion ratio: 14.2

Extrusion speed: 100 to 150mm/s

Extrusion force: burst force 32MN

And (3) cooling: and cooling the extruded product with water.

And step 8, in the cold rolling treatment, reducing the diameter and the wall of the finished seamless pipe to phi 19-phi 25mm through 3 times of cold rolling, wherein the cold deformation process route is as follows: extruded mother pipe Φ 89 × 10mm → cold rolled Φ 57 × 6mm → cold rolled Φ 38 × 3.5mm → cold rolled Φ 21.7 × 1.83 mm.

And 9, cold-drawing forming, namely manufacturing the cold-rolled phi 21.7 multiplied by 1.83mm into phi 15 multiplied by 2mm by adopting a one-pass empty-drawing forming method.

Claims

1. A preparation method of UNS N08825 small-caliber precise seamless tube is characterized by comprising the following steps:

step 1, processing a tube blank: cutting a round forging stock UNS N08825 into short sections in a fixed length mode, and processing the short sections into a designed tube blank shape;

step 2, preheating the pipe blank: preheating the processed tube blank;

step 3, primary induction heating of the tube blank: heating the preheated pipe blank in an induction heating mode;

step 4, hot hole expansion of the tube blank: reaming the inner hole of the tube blank after the primary induction heating from the deep hole size to the inner hole size required by the hot extrusion;

step 5, secondary induction heating of the tube blank: carrying out secondary heating on the tube blank subjected to hot hole expansion in an induction heating mode;

step 6, hot extrusion of the pierced billet: carrying out seamless tube hot forming on the tube blank subjected to secondary induction heating in an extrusion mode;

step 10, physical and chemical inspection: and performing physical and chemical inspection on the manufactured small-caliber precise seamless pipe.

2. The method for preparing the UNS N08825 small-caliber precise seamless tube according to claim 1, wherein the step 1 is carried out to form a designed tube blank, in particular to form the designed tube blank by adopting a deep hole drill and a lathe, the outer diameter of the tube blank is phi 219-phi 277mm, and the deep hole is phi 40-60 mm.

3. A method for manufacturing UNS N08825 small-caliber precision seamless tube according to claim 1, characterized in that the tube blank preheating of step 2 is to preheat the processed tube blank to 1000 ℃ ± 10 ℃ by using ring gas furnace.

4. The method for preparing UNS N08825 small-caliber precision seamless tube according to claim 1, wherein the tube blank in the step 3 is subjected to primary induction heating, specifically, the preheated tube blank is heated to 1180 ℃ +/-10 ℃ by adopting a vertical induction heating mode.

5. The method for preparing the UNS N08825 small-caliber precise seamless tube according to claim 1, wherein the tube blank hot reaming of the step 4 is to ream the inner hole of the tube blank after one-time induction heating from the deep hole size to the inner hole size required by hot extrusion by using a vertical reaming model, wherein the reaming cone used for reaming is phi 80-120 mm.

6. The method for preparing the UNS N08825 small-caliber precision seamless tube according to claim 1, wherein the tube blank obtained in the step 5 is subjected to secondary induction heating, in particular, the tube blank subjected to hot hole expanding is rapidly reheated to 1210 +/-10 ℃ by adopting an induction heating mode.

7. The method for preparing UNS N08825 small-caliber precise seamless tube according to claim 1, wherein the pierced billet in the step 6 is subjected to hot extrusion, in particular to hot extrusion molding of the tube blank subjected to secondary induction heating into a seamless tube with phi 57 mm-phi 168mm by adopting a horizontal extrusion model; the outside diameter and inside diameter of the extruded tube during extrusion have shrinkage coefficients of 1.025 and 1.02, respectively, and the extrusion ratio is not more than 40.

8. The method for preparing UNS N08825 small-caliber precise seamless tube according to claim 1, wherein the step 7 of solution annealing and finishing comprises straightening, flat-heading and acid-washing procedures.

9. The method for preparing the UNS N08825 small-caliber precise seamless pipe according to claim 1, wherein the cold rolling treatment of the step 8 is to reduce the diameter and the wall of the finished seamless pipe to phi 14-phi 22mm by 3-5 cold rolling in a pilger cold rolling mode, and each cold rolling is then degreased and then subjected to bright annealing; the last pass rolling deformation ratio, namely the ratio of the sectional areas before and after rolling is not less than 2, and the specification of the seamless tube formed by the last pass cold rolling is calculated according to the specification of the finished seamless tube and the principle that the volume of the tube is unchanged before and after deformation; the target temperature for annealing the seamless tube semi-finished product in the bright annealing is 1040 +/-10 ℃, and the target temperature for annealing the seamless tube finished product is 980 +/-10 ℃.

10. The method for preparing the UNS N08825 small-caliber precise seamless pipe according to claim 1, wherein the cold-drawing forming in the step 9 is to cold-draw the small-caliber precise seamless pipe with phi 10mm to phi 15mm by a cold-drawing model for one time, and to perform degreasing and bright annealing after cold-drawing; the target temperature for annealing the seamless tube finished product in the bright annealing is 980 +/-10 ℃.