JP2018094565A - Manufacturing method of seamless metallic pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method which improves production efficiency of a high-strength low-alloy seamless metallic pipe for oil well excellent in hydrogen embrittlement resistance.SOLUTION: A manufacturing method of a seamless metallic pipe comprises: a step of preparing a billet 10 with an addition piece in which the addition piece 12 is added to one end of a hollow billet 11; a step of heating the billet with an addition piece to the temperature T1; a step of drilling the billet with an addition piece; a step of reheating the billet with an addition piece; a step of extruding the billet with an addition piece to be an element tube; and a step of cutting the billet with an addition piece. The hollow billet 11 has the chemical composition comprising, by mass%, Cr: 14-30%, Ni: 29-65%, and Mo: 2-17%. When Ka is hot strength of the addition piece 12 at the temperature T1, and Kb is hot strength of the hollow billet 11 at the temperature T1, the following formula is satisfied: 0.3≤Ka/Kb≤0.75.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a method for producing a seamless metal pipe, and more particularly, a high Cr · chemical composition having a mass% of Cr: 14-30%, Ni: 29-65%, Mo: 2-17%. The present invention relates to a method for producing a seamless metal pipe of a high Ni / high Mo alloy.

  As a method for producing a seamless metal pipe, a hot extrusion pipe making method is known. Japanese Patent Application Laid-Open No. 1-224118 describes a hot extrusion method of metal by an extrusion press. The publication describes that when an expensive billet is extruded by hot extrusion, an additive piece made of an inexpensive metal is integrally attached to the rear portion of the billet in advance. Further, it is described that the occurrence of the crossing portion can be reduced by heating the added piece portion so that the heating temperature is lower than that of the billet.

  In the hot extrusion pipe manufacturing method, it is necessary to previously form a pilot hole for inserting a mandrel in a billet. When the inner diameter of the seamless metal pipe to be manufactured is large, if the prepared hole is formed only by machining, productivity and yield decrease. Therefore, there is a case where the billet is expanded (drilled) hot using a drilling press.

  Japanese Patent Publication No. 59-6724 discloses a horo billet expansion tool. Japanese Patent No. 5998614 describes a billet lubricant for hot spreading and a hot spreading method using the same.

JP-A-1-241318 Japanese Patent Publication No.59-6724 Japanese Patent No. 5998614

  When drilling a high-alloy metal tube such as a Ni-based alloy, an increase in the drilling force at the end of the drilling process becomes significant. Therefore, in order to realize pipe making within the equipment specifications, it is necessary to reduce the billet inner diameter expansion amount per pass of the drilling process or increase the billet inner diameter.

  Therefore, in order to manufacture a high-alloy metal tube having a large inner diameter, it is necessary to divide into a plurality of passes or to increase the diameter of the billet. Multi-pass drilling necessitates reheating of the billet and lowers the production efficiency, and enlargement of the pilot hole diameter reduces the yield.

  Furthermore, in the hot extrusion tube manufacturing method, it is necessary to cut the extruded material with a hot saw. A high alloy metal tube has high hot strength and a high cutting load, so the hot saw blade (blade) is likely to be worn, the hot saw blade needs to be frequently replaced, and the production efficiency is low.

  The objective of this invention is providing the manufacturing method of the seamless metal pipe which improved the production efficiency by suppressing the increase in the piercing | punching force at the end of a piercing process, and reducing the cutting load after extrusion.

The method of manufacturing a seamless metal pipe according to an embodiment of the present invention includes a step of preparing a billet with an added piece having an added piece attached to one end of a hollow billet, and a step of heating the billet with an added piece to a temperature T1. A step of perforating the heated billet with an added piece from an end opposite to an end to which the added piece is attached; a step of reheating the perforated billet with an added piece; and the reheated billet with an added piece of the billet Extruding so that the end opposite to the end to which the added piece is attached becomes the front, and forming a raw pipe; and cutting the raw pipe at the position of the added piece. The hollow billet has a chemical composition of mass%, Cr: 14-30%, Ni: 29-65%, Mo: 2-17%, the hot strength Ka at the temperature T1 of the added piece, and the The hot strength Kb at the temperature T1 of the hollow billet satisfies the following formula.
0.3 ≦ Ka / Kb ≦ 0.75
Here, the hot strength is the deformation resistance when the strain becomes 0.5 when the stress-strain curve is measured at a strain rate of 1.0 / sec.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the seamless metal pipe which improved the production efficiency is obtained by suppressing the increase in the piercing | punching force at the end of a piercing process, and reducing the cutting load after extrusion.

FIG. 1 is a flowchart showing a method of manufacturing a seamless metal pipe according to an embodiment of the present invention. FIG. 2 is a perspective view of a billet with additive pieces. FIG. 3 is a schematic cross-sectional view showing a state in which a billet with an added piece is punched by a punch press apparatus. FIG. 4 is a schematic cross-sectional view showing a state in which the billet with additive pieces is being extruded by an extrusion press apparatus. FIG. 5 is a schematic cross-sectional view showing a state in which the billet with additive pieces is being extruded by an extrusion press apparatus. FIG. 6 is a schematic cross-sectional view showing a state where the raw tube is cut by a hot saw. FIG. 7 is a heat pattern of a compression test for hot strength measurement. FIG. 8 is a graph showing the relationship between the material temperature and hot strength of the Ni-based alloy (Alloy 625) and stainless steel (SUS304). FIG. 9 is a stress-strain curve of Alloy 625. FIG. 10 is a stress-strain curve of SUS304. FIG. 11 is a stress-strain curve of SM2535. FIG. 12 is a stress-strain curve of SM2550. FIG. 13 is a schematic cross-sectional view of the vicinity of the welded portion of the billet with an added piece. FIG. 14 is a graph showing the change over time of the piercing force in the piercing step. FIG. 15 is a diagram showing a deformation state of the added piece in the middle of drilling, obtained by numerical analysis. FIG. 16 is a diagram showing the deformation state of the added piece at the end of drilling, obtained by numerical analysis. FIG. 17 is a stress-strain curve of Hastelloy C276.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated. The dimensional ratio between the constituent members shown in each drawing does not necessarily indicate the actual dimensional ratio.

  FIG. 1 is a flowchart showing a method of manufacturing a seamless metal pipe according to an embodiment of the present invention. The method of manufacturing a seamless metal pipe according to the present embodiment includes a step of preparing a billet with an added piece (step S1), a step of heating the billet with an added piece to a temperature T1 (step S2), and a step of punching the heated billet with an added piece ( Step S3), the step of reheating the pierced billet with an added piece (Step S4), the step of extruding the reheated billet with an added piece into a blank (Step S5), and cutting the blank at the position of the added piece. A process (step S6) is provided. Hereinafter, each process will be described in detail.

[Additional billet preparation step (step S1)]
A billet with an added piece having an added piece attached to one end of the hollow billet is prepared (step S1). FIG. 2 is a perspective view of the billet 10 with an additive piece used in the present embodiment. The billet 10 with an added piece includes a hollow billet 11 and an added piece 12.

  The hollow billet 11 is a round billet in which a through hole 11a is formed at the center. The additive piece 12 is attached to one end of the hollow billet 11. A through hole 12 a coaxial with the through hole 11 a of the hollow billet 11 is formed in the additive piece 12. It is preferable that the hollow billet 11 and the additive piece 12 have substantially the same diameter. Moreover, it is preferable that the through hole 11a and the through hole 12a have substantially the same diameter.

  The hollow billet 11 and the additive piece 12 are fixed by welding, for example. The billet 10 with an added piece may be formed by forming the through-hole 11a and the through-hole 12a in the hollow billet 11 and the added piece 12, respectively, and then attaching the hollow billet 11 and the added piece 12 to each other. Or the billet 10 with an addition piece may form the through-hole 11a and the through-hole 12a after making the hollow billet 11 and the addition piece 12 adhere. The through hole 11a and the through hole 12a can be formed by machining, for example.

  The hollow billet 11 has the same chemical composition as the seamless metal tube to be manufactured. In the present embodiment, a seamless metal tube of a high Cr / high Ni / high Mo alloy containing, by mass%, Cr: 14 to 30%, Ni: 29 to 65%, and Mo: 2 to 17%. To manufacture. Therefore, the chemical composition of the hollow billet 11 also includes Cr: 14 to 30%, Ni: 29 to 65%, and Mo: 2 to 17% in mass%. Examples of the high Cr / high Ni / high Mo alloy include Alloy 625 (Cr: 20 to 23%, Ni: an alloy containing 58% or more, Mo: 8 to 10%), SM2535 (Cr: 24 to 27%, Ni: 29-37%, Mo: alloy containing 2-4%), SM2550 (Cr: 23-26%, Ni: 47-54%, Mo: alloy containing 6-9%) and the like.

  The additive piece 12 is formed of a material having a lower hot strength than the hollow billet 11. The additive piece 12 is made of, for example, SUS304. Details of the relationship between the hot strength of the hollow billet 11 and the hot strength of the additive piece 12 will be described later.

[Heating Step (Step S2)]
The billet 10 with the added piece is heated to the temperature T1 (step S2). Although the suitable value of temperature T1 depends on the material of the hollow billet 11, it is 1000-1200 degreeC, for example. If the temperature T1 is too low, the load in the drilling step (step S3) increases. On the other hand, if the temperature T1 is too high, depending on the material of the hollow billet 11, hot workability is reduced, and wrinkles and the like are likely to occur.

  The heating step (Step S2) may include a step of preheating (soaking) the billet 10 with an added piece from room temperature to about 950 ° C. The heating method is not particularly limited. For example, a rotary hearth furnace can be used for preheating, and an induction heating furnace can be used for heating from the preheating temperature to the temperature T1.

[Punching Step (Step S3)]
The heated billet 10 with an added piece is punched from the end opposite to the end to which the added piece 12 is attached (step S3). In the present application, “perforation” refers to expanding a hole of a hollow billet provided with a hole (guide hole) in the center in advance by machining or the like (expanding the inner diameter of the hollow billet). FIG. 3 is a schematic cross-sectional view showing a state where the billet 10 with an added piece is punched by the punch press apparatus 20. The perforating press apparatus 20 includes a container 21, a mandrel 22, a plug 23, and a shearing 24.

  As shown in FIG. 3, the billet 10 with the added piece is loaded into the container 21 so that the added piece 12 contacts the shirring 24. The tip of the plug 23 is brought into contact with the opening of the through hole of the hollow billet 11. In this state, the plug 23 is lowered. Thereby, the through-hole of the hollow billet 11 and the through-hole of the addition piece 12 are expanded.

[Reheating process (step S4)]
The perforated billet 10 with added pieces is reheated (step S4). A suitable reheating temperature depends on the material of the hollow billet 11, but is, for example, 1000 to 1200 ° C. The reheating temperature may be the same as or different from the temperature T1 in the heating step (step S3). If the reheating temperature is too low, the load in the extrusion process (step S5) increases. On the other hand, if the reheating temperature is too high, depending on the material of the hollow billet 11, hot workability is lowered, and wrinkles and the like are likely to occur.

[Extrusion process (step S5)]
The reheated billet 10 with an added piece is extruded so that the end opposite to the end where the added piece 12 is attached is forward, thereby forming a blank (step S5). 4 and 5 are schematic cross-sectional views showing a state in which the billet 10 with additive pieces is being extruded by the extrusion press device 30. FIG. The extrusion press apparatus 30 includes a container 31, a stem 32, a mandrel holder 33, a mandrel 34, a die holder 35, a die 36, and a holster 37.

  The mandrel 34 is inserted into the reheated billet 10 with added pieces and the dummy block 38 and simultaneously pushed into the container 31 by the stem 32. At this time, the billet 10 with an addition piece is arrange | positioned so that the edge part on the opposite side to the edge part to which the addition piece 12 adhered may become the front. That is, the billet 10 with the added piece is arranged so that the added piece 12 contacts the dummy block 38. The billet 10 with an added piece pressurized in the container 31 is filled in the container 31 and is upset. By further advancing the stem 32 under pressure, the hollow billet 11 continuously undergoes plastic deformation from the concentric opening formed by the mandrel 34 and the die 36 and flows out to become a raw pipe P (see FIG. 4). reference). By further advancing the stem 32 under pressure, a part of the addition piece 12 is processed in the same manner (see FIG. 5).

[Cutting step (step S6)]
The raw tube P is cut at the position of the addition piece 12 (step S6). FIG. 6 is a schematic cross-sectional view showing a state where the raw tube P is cut by the hot saw 39. After the extrusion, the container 31 is retracted by about 100 mm, the hot saw 39 is inserted between the container 31 and the die 36, and the raw pipe P is cut at the position of the addition piece 12. As a result, the raw tube P and the push-in (discard) remaining in the container 31 are separated.

  In addition, although the part of the addition piece 12 remains adhering to the rear end of the raw tube P, this may be cut again in a later step.

[Relationship between hot strength of hollow billet 11 and hot strength of additive piece 12]
In the present embodiment, the hot strength Ka at the temperature T1 of the additive piece 12 and the hot strength Kb at the temperature T1 of the hollow billet 11 satisfy the following formula.
0.3 ≦ Ka / Kb ≦ 0.75
Here, the hot strength is the deformation resistance when the strain becomes 0.5 when the stress-strain curve is measured at a strain rate of 1.0 / sec. The deformation resistance in the case of a strain rate of 1.0 / second and a strain of 0.5 is used in accordance with the deformation speed and deformation amount of the pressed material (hollow billet) at the time of punching press.

  More specifically, the hot strength is measured as follows. A cylindrical test piece having an outer diameter of 8 mm and a length of 12 mm is prepared, and a compression test at a high temperature is performed. FIG. 7 is a heat pattern of the test. First, the test piece is heated from room temperature to 1250 ° C. at a heating rate of 5 ° C./second. After holding at 1250 ° C. for 60 seconds, the temperature is lowered to temperature T 1 at 2 ° C./second, and held at temperature T 1 for 5 seconds. However, when the temperature T1 is 1250 ° C., the temperature lowering and holding are not performed. Thereafter, a compressive stress is applied to the test piece at a strain rate of 1.0 / second, and a stress-strain curve is measured. The processing amount is 9.5 mm. That is, compressive stress is applied until the length of the test piece becomes 2.5 mm. The deformation resistance when the strain becomes 0.5 is defined as the hot strength at the temperature T1.

  Hereinafter, the reason for limiting the relationship between the hot strength of the hollow billet 11 and the hot strength of the additive piece 12 as described above will be described together with the effect of the present embodiment.

  FIG. 8 is a graph showing the relationship between the material temperature and hot strength of the Ni-based alloy (Alloy 625) and stainless steel (SUS304). As shown in FIG. 8, a high alloy such as a Ni-based alloy has a higher rate of increase in hot strength due to a temperature drop than stainless steel. This is considered to be the cause of the increase in the drilling force at the end of the drilling process (step S3 in FIG. 1).

  In the present embodiment, a billet 10 with an added piece is prepared in which an added piece 12 having a lower hot strength than the hollow billet 11 is attached to one end of a hollow billet 11 that is a material of a seamless metal pipe (FIG. 2). See). And the billet 10 with an addition piece is inserted in the container 21 so that the addition piece 12 may contact | connect the shearing 24, and it drills from the edge part on the opposite side to the edge part to which the addition piece 12 adhered (refer FIG. 3).

  During the drilling process, the temperature of the billet 10 with added pieces gradually decreases. In particular, the temperature of the added piece 12 is greatly reduced by heat removal accompanying contact with the shearing 24. According to the present embodiment, at the end of the drilling process where the temperature decreases most, the additional piece 12 having a lower hot strength than the hollow billet 11 is drilled. Therefore, an increase in the punching force at the end of the punching process can be suppressed.

  Further, in the present embodiment, in the cutting process (step S6 in FIG. 1), the raw tube P is cut at the position of the addition piece 12 (see FIG. 6). Therefore, cutting load can be reduced compared with the case where the hollow billet 11 with high hot strength is cut. Thereby, the life of the hot saw 39 can be extended.

  If the ratio Ka / Kb of the hot strength of the added piece 12 to the hot strength of the hollow billet 11 is too low, the deformed added piece in the drilling process (step S3 in FIG. 1) or the extrusion process (step S5 in FIG. 1). In some cases, machining may become impossible, for example, when 12 enters a gap in the tool. Therefore, Ka / Kb needs to be 0.3 or more. Ka / Kb is preferably as small as possible from the standpoint of the effect of suppressing an increase in the piercing force at the end of the piercing process and reducing the cutting load after extrusion. However, as described above, if it is too low, processing becomes impossible. From the viewpoint of reducing the stability of the operation, that is, the trouble that it becomes impossible to enclose during operation, the lower limit of Ka / Kb is preferably 0.35.

  On the other hand, if Ka / Kb is too large, the merit of attaching the addition piece 12 is lost. Therefore, Ka / Kb is 0.75 or less. The upper limit of Ka / Kb is preferably 0.70.

  In the above, the manufacturing method of the seamless metal pipe by one Embodiment of this invention was demonstrated. According to this embodiment, a method for producing a seamless metal pipe with improved production efficiency can be obtained by suppressing an increase in piercing force at the end of the piercing process and reducing a cutting load after extrusion. Further, by suppressing an increase in the piercing force at the end of the piercing process, breakage of the mandrel 22 (FIG. 3) and seizure of the plug 23 (FIG. 3) can also be suppressed.

  Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited to these examples.

  The hot strength of each material having the chemical composition shown in Table 1 was measured by the method described in the embodiment. In Table 1, “-” means that the content of the corresponding element is at the impurity level.

  9 to 12 are stress-strain curves of Alloy 625, SUS304, SM2535, and SM2550, respectively, measured at the strain rate of 1.0 / sec.

  An added piece of SUS304 was welded to one end of a hollow billet of Alloy 625 to form a billet with an added piece. FIG. 13 is a schematic cross-sectional view of the vicinity of the welded portion of the billet with an added piece. As shown in FIG. 13, the inner diameter / outer diameter of the additive piece was made substantially equal to the inner diameter / outer diameter of the hollow billet.

  Using this billet with an added piece, a seamless metal tube was manufactured by a hot extrusion tube manufacturing method under the conditions shown in Table 2. The heating temperature T1 before the drilling process and the reheating temperature before the extrusion process were both 1100 ° C. The hot strength at 1100 ° C. is as shown in FIG. 9 and FIG. 10, and Alloy 625 is about 320 MPa, SUS304 is about 140 MPa, and Ka / Kb is about 0.44. In addition, as a comparative example, a seamless metal tube was manufactured under the same conditions without attaching an additional piece.

  FIG. 14 is a graph showing the change over time of the piercing force in the piercing step. As shown in FIG. 14, an increase in the piercing force at the end of the piercing process could be suppressed by attaching the additional piece.

  In addition, with regard to the life of the hot saw, when the added piece was not attached, the blade had to be replaced after cutting the six extruded tubes, but the blade was hardly worn by attaching the added piece. .

  Next, the steel type of the added piece was changed to carbon steel (SC45C, the hot strength at 1100 ° C. was about 80 MPa), and the production of a seamless metal tube was carried out under the same conditions. In this case, Ka / Kb is about 0.25. In this case, the deformation of the added piece during the extrusion process became significant, and the added piece entered the gap between the container and the dummy block. As a result, the material was clogged in the container, making pipe production impossible.

  Subsequently, the steel type of the hollow billet was changed to SM2535, and the steel type of the added piece was changed to SUS304, thereby producing a seamless metal pipe. The heating temperature T1 before the drilling process and the reheating temperature before the extrusion process were both set to 1200 ° C. The hot strength at 1200 ° C. is as shown in FIGS. 10 and 11, SM2535 is about 140 MPa, SUS304 is about 100 MPa, and Ka / Kb is about 0.71. In this case, an increase in the drilling force at the end of the drilling process could be suppressed, and wear of the hot saw blade could be suppressed.

  Similarly, a seamless metal pipe was manufactured by changing the steel type of the hollow billet to SM2550 and the steel type of the added piece to SUS304. The heating temperature T1 before the drilling process and the reheating temperature before the extrusion process were both set to 1200 ° C. The hot strength at 1200 ° C. is as shown in FIGS. 10 and 12, and SM2550 is about 160 MPa, SUS304 is about 100 MPa, and Ka / Kb is about 0.63. Also in this case, an increase in the piercing force at the end of the piercing process could be suppressed, and wear of the hot saw blade could be suppressed.

  The hot strength required for the added piece was investigated by numerical analysis. The change behavior of the added piece when the hot strength Kb of the base material (hollow billet) was changed to 200 MPa and the hot strength Ka of the added piece was changed to 40, 50, 60, 100 MPa was investigated by the finite element method. The strength of the welding material was the same as that of the base material.

  FIGS. 15 and 16 are diagrams showing deformation states of the added pieces during and after the completion of drilling, which are obtained by numerical analysis. When Ka / Kb is 0.25 or less, the deformation of the added piece becomes remarkable, and the added piece is inserted into the outer surface of the billet, and there is a concern that the billet may be taken out poorly or the inner surface of the container may be damaged. This is in good agreement with the above manufacturing results. Moreover, when Ka / Kb was 0.20, outflow of the added pieces to the billet inner surface side became significant. Therefore, it was found that the thickness of the added piece was reduced and the effect of reducing the piercing force was lost.

  The embodiment of the present invention has been described above. The above-described embodiments are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and can be implemented by appropriately modifying the above-described embodiment without departing from the spirit thereof.

  For example, as a hollow billet (high Cr / high Ni / high Mo alloy), Hastelloy C276 (an alloy containing Cr: 14.5 to 15.5%, Ni: 51 to 63.5%, Mo: 15 to 17%) The same effect can be expected when SUS304 is used as the additive piece as in the above-described embodiment. FIG. 17 is a stress-strain curve of Hastelloy C276 measured at the strain rate of 1.0 / sec as described above. Hastelloy C276 can be perforated by heating to 1200 ° C., for example. As shown in FIG. 17, the hot strength of Hastelloy C276 at 1200 ° C. is about 260 MPa, and the hot strength of SUS304 is about 100 MPa as described above. Therefore, Ka / Kb in this case is about 0.38.

Claims (1)

A step of preparing a billet with an added piece with an added piece attached to one end of a hollow billet;
Heating the billet with added pieces to a temperature T1,
Perforating the heated billet with added pieces from the end opposite to the end to which the added pieces are attached;
Reheating the perforated billet with added pieces;
Extruding the reheated billet with an added piece so that the end opposite to the end to which the added piece is attached becomes the front,
Cutting the raw tube at the position of the added piece,
The hollow billet has a chemical composition of mass%, including Cr: 14-30%, Ni: 29-65%, Mo: 2-17%,
The method for producing a seamless metal pipe, wherein the hot strength Ka of the additive piece at temperature T1 and the hot strength Kb of the hollow billet at temperature T1 satisfy the following formula.
0.3 ≦ Ka / Kb ≦ 0.75
Here, the hot strength is the deformation resistance when the strain becomes 0.5 when the stress-strain curve is measured at a strain rate of 1.0 / sec.

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