JPWO2013171935A1 - Seamless steel pipe manufacturing method - Google Patents

Abstract

Inserting a mandrel into a hollow billet and processing it into a rough tube with a predetermined diameter and thickness by forging, drawing one end of the rough tube, and placing a metal core on the rough tube with one end drawn A method of manufacturing a seamless steel pipe including a step of inserting and punching using a push bench. According to this method, a seamless steel pipe having a wide manufacturable range (large diameter, thick wall) can be manufactured with high dimensional accuracy, particularly with high wall thickness dimensional accuracy.

Description

  The present invention relates to a method for manufacturing a seamless steel pipe capable of manufacturing a seamless steel pipe having a high dimensional accuracy in a wide range of dimensions. Specifically, it is related with the manufacturing method of the seamless steel pipe which applies the push bench pipe manufacturing method to the rough raw pipe manufactured with the mandrel forge pipe manufacturing method.

Unless otherwise stated, the definitions of terms in this specification are as follows.
“Hollow billet”: refers to a billet to be used in Step 1 (mandrel forge pipe making process) described herein. This is a billet in which an ingot is perforated in advance and processed into a hollow shape.
"Rough tube": A tube used in Step 2 (drawing step) described in this specification. It is a tube manufactured from a hollow billet in Step 1.
“Union tube”: A tube used for the push bench thinning process described in the present specification. This is a pipe whose inner and outer surfaces are leveled in the push bench leveling process.
“Large diameter” means that the outer diameter of the tube is 1000 mm or more.
“Dimensional accuracy”: The absolute value of the difference between the target dimensions of the outer diameter and thickness of the pipe and the actual dimensions after processing.

  Generally, a spiral steel pipe is applied to a large diameter pipe, for example, a large diameter reheat steam pipe used in a thermal power plant. In recent years, the performance required for large-diameter pipes has increased, for example, the steam pressure setting for large-diameter reheat steam pipes used in thermal power plants has increased, and high-quality, large-diameter seamless steel pipes are required. It is becoming.

  Conventionally, there is an example in which a mandrel forge pipe manufacturing method is applied as a hot manufacturing method of a large diameter seamless steel pipe.

  As described in Patent Document 1, the mandrel forge pipe manufacturing method is a method in which a mandrel is inserted into a hollow billet and the thickness of the hollow billet is successively reduced by free forging in the hot state.

  The advantage of the mandrel forging pipe manufacturing method is that the degree of freedom of pipe manufacturing size is large by repeating forging and reheating. That is, it is possible to produce a thick steel large diameter seamless steel pipe.

  On the other hand, the disadvantage of the mandrel forge pipe manufacturing method is that the dimensional accuracy is low because it is formed by forging. For this reason, in the finishing process after the hot pipe making process, the machining allowance on the surface of the steel pipe is large and the yield is poor.

Japanese Examined Patent Publication No. 7-22802 JP-A-56-128611

  An object of the present invention is to provide a method of manufacturing a seamless steel pipe that can achieve both high dimensional accuracy, particularly excellent wall thickness dimensional accuracy, and a wide manufacturable range (large diameter, thick wall).

  The present inventor has focused on a push bench pipe manufacturing method capable of manufacturing a seamless steel pipe with high wall thickness accuracy. As disclosed in Patent Document 2, the push bench pipe manufacturing method is a method of reducing the wall thickness by inserting a cored bar into a hollow steel material having a bottom and punching with a die. . The advantage of the push bench pipe manufacturing method is that the outer diameter and inner diameter regulating tools such as a die and a core metal are used, and therefore the dimensional accuracy is high. For this reason, in a finishing process, the pipe surface cutting allowance is small and the yield is high.

  If the advantages of both the mandrel forge pipe manufacturing method and the push bench pipe manufacturing method can be utilized, there is a possibility that a seamless steel pipe with a wide dimensional range can be manufactured with high dimensional accuracy. However, in the push bench pipe manufacturing method, a hollow steel blank having a bottom is used. Therefore, the seamless steel pipe manufactured by the mandrel forge pipe manufacturing method cannot be applied to the push bench pipe manufacturing method as a raw steel piece as it is. This is because it is not a hollow steel piece with a bottom and cannot be punched out with a cored bar.

  Therefore, the present inventor examined a method of applying a seamless steel pipe manufactured by the mandrel forging pipe manufacturing method to the push bench pipe manufacturing method. As a result of rigorous trial and error, both pipe making methods can be achieved by drawing the bottom end of the seamless steel pipe produced by the mandrel forge pipe making method so that the outer diameter and inner diameter of the end are reduced and an alternative part is provided at the bottom. Found that can be combined.

The present invention has been made based on the results of this study, and the gist of the present invention is as follows.
(1) Inserting a mandrel into a hollow billet and processing it into a rough tube with a predetermined diameter and thickness by forging;
(2) A step of drawing one end of the rough tube and reducing the outer diameter and the inner diameter;
(3) a step of inserting a metal core into the rough tube whose one end has been drawn and performing a punching process using a push bench;
It is a manufacturing method of the seamless steel pipe characterized by including.

  The effect of the method of manufacturing a seamless steel pipe according to the present invention is that, after applying the mandrel forge pipe manufacturing method, the push bench pipe manufacturing method is applied, so that a seamless steel pipe having a wide dimensional range (large diameter, thick wall) has a high dimension. It is to be able to manufacture with high accuracy, particularly high wall thickness accuracy.

FIG. 1 is a longitudinal sectional view of a rough tube after drawing. FIG. 2 is a side view of the tip portion of the core bar used in the push bench pipe manufacturing process. FIG. 3 is a configuration diagram of a rough tube, a cored bar, and a die in a push bench pipe manufacturing process. FIG. 4 is a diagram comparing the manufacturable range of seamless steel pipes by the conventional push bench pipe manufacturing method and the manufacturing method of the present invention.

  The manufacturing method includes step 1 (mandrel forge pipe making process), step 2 (squeezing process), and step 3 (push bench pipe making process). Each step will be described.

[Step 1 (Mandrel Forge Pipe Making Process)]
In step 1, a crude tube is manufactured. The procedure is as follows:
(1) In a state where the tool with a sharp tip is rotated, the tool is pressed against the upper surface of the ingot arranged with the longitudinal direction vertical, and the ingot is perforated hot to form a hollow billet.
(2) The hollow billet is arranged with the longitudinal direction horizontal, and the mandrel is hot pressed against the inner surface of the hollow billet in a state where the hollow billet is rotated, and the thickness is reduced.
(3) The step (2) is repeated once or a plurality of times to finish a rough tube with a predetermined outer diameter and thickness.

  The hot forging of the hollow billet in the mandrel forge pipe making process is desirably performed in a temperature range of 900 ° C to 1250 ° C.

[Step 2 (drawing process)]
FIG. 1 is a longitudinal sectional view of a rough tube after drawing. In Step 2, while rotating the rough tube 1 manufactured in Step 1, one end thereof is drawn to reduce its outer diameter and inner diameter.

  The drawn portion includes a tip portion 1a on the tip side of the rough tube 1 and a reduced diameter portion 1b. The reduced diameter portion 1b is located between the distal end portion 1a and the body portion that has not been drawn. The distal end portion 1a has a constant outer diameter and thickness. As the diameter-reduced portion 1b is closer to the tip, the outer diameter and the inner diameter become smaller.

  This drawing process may be performed again as appropriate when the drawn part after step 3 is deformed. The drawing process can be applied not only by pressing, but also by a method in which one end of the rough tube 1 is crushed with a hammer or a rotary forging method using a swager or the like.

[Shaped part shape]
FIG. 2 is a side view of the tip portion of the core bar used in the push bench pipe manufacturing process. The cored bar 2 includes a columnar main body 2a and a truncated cone-shaped reduced diameter portion 2b provided at the tip of the main body 2a. The diameter of the reduced diameter portion 2b becomes smaller as it is closer to the tip of the core metal 2. Usually, the reduced diameter portion 2b is formed in a tapered shape.

The portion of the rough tube 1 that has been drawn in step 2 is the drawing tube inner diameter B (mm) of the rough tube, and the tip diameter D (mm) of the metal core used in the push bench pipe manufacturing process. It is desirable to satisfy the following formula (1). This is to reduce the possibility that the cored bar 2 will break through the distal end portion 1a and the reduced diameter portion 1b of the rough tube 1 at the time of punching in step 3 (push bench pipe manufacturing process). When the expression (1) is satisfied, the case where the drawn part is completely closed is also included.
B <D / 4 (1)

[Step 3 (push bench pipe making process)]
FIG. 3 is a configuration diagram of a rough tube, a cored bar, and a die in a push bench pipe manufacturing process. A plurality of dies 3 may be connected or one. Usually, a taper die is used as the die 3, and a die half angle α is 10 to 20 ° and a die width W is 150 to 200 mm.

  In step 3, the cored bar 2 is inserted into the rough tube 1 whose one end has been drawn, and is punched using a push bench. Step 3 is desirably divided into a leveling process and a thinning process (hereinafter also referred to as “push bench leveling process” and “push bench thinning process”, respectively).

[Leveling process]
In the leveling step, the cored bar 2 is inserted into the rough tube 1 whose one end has been drawn, and the inside of the die 3 is pushed out hot to level the shape of the inner and outer surfaces. In order to equalize the shape of the inner and outer surfaces of the rough tube 1 with the taper die described above, the blank tube 1 is subjected to a punching process under a light pressure to obtain the tube 1 to be subjected to a thinning process.

  In the leveling step, fluctuations in the outer diameter and thickness of the rough tube 1 in the longitudinal direction are reduced by the die 3. For example, when the rough tube 1 is pushed out with a taper die, if there are large irregularities on the outer surface, the irregularities may interfere with the taper die, making it difficult or impossible to push out.

  The degree of processing in the leveling process is preferably about 3 to 7%.

  It is desirable that the temperature of the punched portion (portion other than the drawn portion) of the rough tube 1 in the leveling process be 900 ° C. to 1250 ° C. This is because deformation resistance can be reduced and processing is facilitated.

  Since the drawn portion is a portion to which the core metal 2 is pressed, it is desirable that the temperature be lowered by water jet in order to suppress deformation at the time of punching. In order to surely push out the rough tube 1 with the cored bar 2, the drawn portion is desirably 500 ° C. or less. The lower limit temperature is preferably 400 ° C. This is because, for example, some steel types such as 9% Cr steel may be cracked by thermal stress during martensitic transformation when cooled to a low temperature.

[Thinning process]
In the thinning process, the blank 1 obtained by the punching process by light reduction in the leveling process is provided. Also in the thinning process, the core metal 2 and the die 3 having the same configuration as in FIG. 2 are used. Selection of the die 3 to be used can add a predetermined degree of processing to the raw tube 1.

The thinning process consists of the following steps:
(1) Using a die 3 having a smaller inner diameter, the raw tube whose inner and outer surfaces have been smoothed in the leveling step is hot-extruded while thinning to reduce the thickness.
(2) By performing the step (1) once or a plurality of times, a seamless steel pipe having excellent thickness dimensional accuracy can be manufactured. Specifically, the difference from the target thickness dimension can be 10 mm or less regardless of the thickness dimension obtained by punching.

  Also in the thinning process, in order to reduce deformation resistance and facilitate processing, it is desirable that the body portion to be punched is set to 900 to 1250 ° C. On the other hand, it is desirable that the drawn portion is subjected to water injection or the like to be 500 ° C. or lower in order to surely push out the raw tube 1 with the core 2. The lower limit temperature is preferably 400 ° C.

You may provide a finishing process after the process of said step 1-3. The finishing process consists of the following steps:
(1) Cut the drawn portion of the seamless steel pipe manufactured in Step 3;
(2) If necessary, heat-treat the seamless steel pipe cut from the drawn part.
(3) As a finishing process of the obtained seamless steel pipe, the inner surface and the outer surface of the steel pipe are cut or polished, and finished to predetermined surface properties and dimensions.

[Suitable steel grade]
The following three types are exemplified as the steel types suitable for the above manufacturing method.
(1) Chemical composition comprising, by mass%, C: 0.3% or less, Si: 1% or less, Mn: 0.1 to 2% and N: 0.02% or less, with the balance being Fe and impurities Carbon steel having 2% by mass, C: 0.15% or less, Si: 1% or less, Mn: 0.1 to 2%, Cr: 0.5 to 3.0%, Ni: 0.5 %: Mo: 0.1 to 3.0%, W: 0 to 2%, Cu: 0.1% or less and N: 0.002 to 0.030%, with the balance being Fe and impurities Low alloy steel (3) having a chemical composition, C: 0.15% or less, Si: 1% or less, Mn: 0.1 to 2%, Cr: 8.0 to 12.5%, Ni: 1.0% or less, Mo: 0.1 to 3.0%, W: 0 to 4%, Cu: 0 to 1.5% and N: 0.01 to 0.10%, the balance being Fe And from impurities High Cr ferritic heat-resistant steel having a chemical composition

  Hereinafter, it will be described that a seamless steel pipe excellent in thickness dimensional accuracy can be manufactured based on the examples, and that the manufacturable range of the seamless steel pipe can be expanded.

(Example 1)
In Example 1, an example in which the manufacturable range of the outer diameter can be expanded will be described.

1. Pipe making schedule in each process (mandrel forge pipe making process): The mandrel is inserted into the hollow billet (weight 13850 kg) melted from the above-mentioned high Cr ferritic heat resistant steel, and the outer diameter is 1250 mm by the mandrel forge pipe making method. A crude tube having an inner diameter of 1090 mm, a wall thickness of 80 mm and a length of 6000 mm was produced.

(Drawing step) One end of the obtained rough tube was drawn to reduce the outer diameter and the inner diameter. At this time, the inner diameter B on the drawing end side of the rough tube was 200 mm.

(Push bench leveling process) Inserting a core metal with an outer diameter of 1060 mm into a rough pipe with one end drawn, and using a push bench with a die with an inner diameter of 1240 mm to lightly reduce the inner and outer surfaces Manufactured. Since the tip diameter D of the metal core at this time was 950 mm, the above formula (1) was satisfied.

(Push Bench Thinning Step) The obtained raw pipe was punched using a core metal having an outer diameter of 1060 mm and dies having an inner diameter of 1210 mm and 1190 mm with a push bench to produce a seamless steel pipe.

(Finishing process) The dimensions of the manufactured seamless steel pipe were an outer diameter of 1190 mm, an inner diameter of 1060 mm, a wall thickness of 65 mm, and a length of 7600 mm. The drawn end of this seamless steel pipe was cut to a length of 300 mm, heat treated, and then the inner and outer surfaces were cut.

2. Comparison of wall thickness dimensional accuracy Although the dimensions of the seamless steel pipe manufactured in Example 1 were as large as an outer diameter of 1190 mm, an inner diameter of 1060 mm and a wall thickness of 65 mm, the dimensional accuracy of the wall thickness was less than 10 mm. Met. Then, the inner and outer surfaces were cut to finish to an outer diameter of 1170 mm, an inner diameter of 1080 mm, and a wall thickness of 45 mm.

  That is, in Example 1, the amount of cutting required for finishing was 10 mm for both the outer surface and the inner surface.

  As a comparative example of Example 1, the thickness dimensional accuracy of a rough tube having an outer diameter of 1250 mm, an inner diameter of 1090 mm, and a wall thickness of 80 mm manufactured by the mandrel forge tube manufacturing method exceeded 20 mm.

  From the above, while the cutting amount in Example 1 remains at 10 mm for both the outer surface and the inner surface, the finishing cutting amount required in the comparative example is assumed to exceed 25 mm for both the outer surface and the inner surface. It can be seen that Example 1 has a remarkable effect.

(Example 2)
In Example 2, a case where the manufacturable range of the wall thickness can be expanded will be described.

1. Pipe making schedule in each process (mandrel forge pipe making process): The mandrel is inserted into the hollow billet (weight 25600 kg) melted from the above-mentioned high Cr ferritic heat resistant steel, and the outer diameter is 1050 mm by the mandrel forge pipe making method. A crude tube having an inner diameter of 640 mm, a wall thickness of 205 mm and a length of 6000 mm was produced.

(Drawing step) One end of the obtained rough tube was drawn to reduce the outer diameter and the inner diameter. At this time, the inner diameter B on the drawing end side of the rough tube was 100 mm.

(Push bench leveling process) Insert a core metal with an outer diameter of 610 mm into a rough pipe with one end drawn, and use a push bench with a die with an inner diameter of 1040 mm to lightly reduce the inner and outer surfaces. Manufactured. Since the tip diameter D of the metal core at this time was 500 mm, the above formula (1) was satisfied.

(Push Bench Thinning Step) The obtained raw pipe was punched by a push bench using a core bar having an outer diameter of 610 mm and dies having an inner diameter of 1010 mm and 990 mm to produce a seamless steel pipe.

(Finishing process) The dimensions of the manufactured seamless steel pipe were an outer diameter of 990 mm, an inner diameter of 610 mm, a wall thickness of 190 mm, and a length of 6800 mm. The drawn end of this seamless steel pipe was cut to a length of 300 mm, heat treated, and then the inner and outer surfaces were cut.

2. Comparison of wall thickness dimensional accuracy The dimensions of the seamless steel pipe manufactured in Example 2 were as thick as an outer diameter of 990 mm, an inner diameter of 610 mm, and a wall thickness of 190 mm, but the thickness dimensional accuracy was less than 10 mm. Met. Then, the inner and outer surfaces were cut into an outer diameter of 970 mm, an inner diameter of 630 mm, and a wall thickness of 170 mm.

  That is, also in Example 2, the amount of cutting required for finishing was 10 mm for both the outer surface and the inner surface.

  As a comparative example of Example 2, when measuring the thickness dimensional accuracy of a rough tube having an outer diameter of 1050 mm, an inner diameter of 640 mm, and a thickness of 205 mm manufactured by the mandrel forge manufacturing method, as in Example 1, 20 mm It was over.

  For this reason, while the cutting amount in Example 2 remains at 10 mm for both the outer surface and the inner surface, the finishing cutting amount required in the comparative example is assumed to exceed 25 mm for both the outer surface and the inner surface. It can be seen that Example 2 has a remarkable effect.

  FIG. 4 is a diagram comparing a manufacturable range of a seamless push bench pipe manufacturing method and a seamless steel pipe according to Example 1 or 2. As a premise of the manufacturable range, it is essential that the thickness dimensional accuracy is 10 mm or less.

  As can be seen from FIG. 4, with the push bench pipe manufacturing method alone (comparative example), a seamless steel pipe having an outer diameter of 850 mm or a wall thickness of 150 mm could be manufactured with a wall thickness dimensional accuracy of 10 mm or less. . On the other hand, in Example 1 or 2, the manufacturable range could be expanded to a seamless steel pipe having an outer diameter of 1200 mm at maximum or a wall thickness of 170 mm at maximum.

  According to the method for manufacturing a seamless steel pipe of the present invention, a seamless steel pipe having a wide dimensional range (large diameter, thick wall) can be manufactured with high dimensional accuracy, particularly with high thickness dimensional accuracy.

1: rough tube, blank tube, 1a: tip portion, 1b: reduced diameter portion,
2: cored bar, 2a: body part, 2b: reduced diameter part,
3: Dice

The present invention has been made based on the results of this study, and the gist of the present invention is as follows.
(1) Insert the mandrel into the hollow billet of a bottomless, the first step of processing a predetermined diameter and thickness of the free base of Somotokan by forging between hot,
(2) a second step of drawing one end of the crude tube hot to reduce the outer diameter and the inner diameter;
(3) a third step of inserting a metal core into the rough tube whose one end has been drawn, and hot punching using a push bench;
It is a manufacturing method of the seamless steel pipe characterized by including.

Claims (1)

A method of manufacturing a seamless steel pipe,
The manufacturing method is
Inserting a mandrel into a hollow billet and processing it into a rough tube with a predetermined diameter and thickness by forging;
Drawing one end of the rough tube and reducing the outer diameter and inner diameter;
Inserting a cored bar into the rough tube whose one end has been drawn and performing a punching process using a push bench;
The manufacturing method of the seamless steel pipe characterized by including.

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