JP6760027B2 - Manufacturing method of seamless metal tube - Google Patents

Description

The present invention relates to a method for producing a seamless metal tube. More specifically, the present invention has a high Cr content of mass%, Cr: 14 to 30%, Ni: 29 to 65%, Mo: 2 to 17%. The present invention relates to a method for manufacturing a seamless metal tube made of a high Ni / high Mo alloy.

A hot extrusion pipe manufacturing method is known as a method for manufacturing a seamless metal pipe. Japanese Patent Application Laid-Open No. 1-241318 describes a method for hot extrusion of a 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 additive 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 form a pilot hole in the billet in advance for inserting the mandrel. When the inner diameter of the seamless metal pipe to be manufactured is large, the productivity and the yield are lowered if the prepared hole is formed only by machining. Therefore, the billet may be expanded (perforated) hot using a perforation press.

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

Japanese Unexamined Patent Publication No. 1-241318 Special Publication No. 59-6724 Japanese Patent No. 5998614

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

Therefore, in order to manufacture a high alloy metal tube having a large inner diameter, it is necessary to perform drilling by dividing into a plurality of paths or to increase the pilot hole diameter of the billet. Multi-pass perforation reduces production efficiency, such as requiring reheating of billets, and increasing the pilot hole diameter reduces yield.

Further, in the hot extrusion tube manufacturing method, it is necessary to separate the extruded material with a hot saw. Since a high alloy metal tube has high hot strength and a large cutting load, the blade of the hot saw is easily worn, the blade of the hot saw needs to be replaced frequently, and the production efficiency is low.

An object of the present invention is to provide a method for producing a seamless metal tube having improved production efficiency by suppressing an increase in drilling force at the end of a drilling process and reducing a cutting load after extrusion.

The method for producing a seamless metal tube according to an embodiment of the present invention includes a step of preparing a billet with an additive piece having an additive piece attached to one end of a hollow billet, and a step of heating the billet with the additive piece to a temperature T1. , The step of perforating the heated billet with an additive piece from the end opposite to the end to which the additive piece is attached, the step of reheating the perforated billet with an additive piece, and the step of reheating the reheated billet with an additive piece. The present invention includes a step of extruding the raw pipe so that the end opposite to the end to which the additive piece is attached faces forward, and a step of cutting the raw pipe at the position of the additive piece. The hollow billet has a chemical composition of mass%, Cr: 14 to 30%, Ni: 29 to 65%, Mo: 2 to 17%, and has a hot strength Ka at a temperature T1 of the additive piece and the above. The hot intensity Kb at the temperature T1 of the hollow billet satisfies the following equation.
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.

According to the present invention, a method for producing a seamless metal tube having improved production efficiency can be obtained by suppressing an increase in drilling force at the end of the drilling process and reducing the cutting load after extrusion.

FIG. 1 is a flow chart showing a method for manufacturing a seamless metal tube according to an embodiment of the present invention. FIG. 2 is a perspective view of a billet with an additive piece. FIG. 3 is a schematic cross-sectional view showing a state in which a billet with an additive piece is drilled by a drilling press device. FIG. 4 is a schematic cross-sectional view showing a state in which a billet with an additive piece is extruded by an extrusion press device. FIG. 5 is a schematic cross-sectional view showing a state in which a billet with an additive piece is extruded by an extrusion press device. FIG. 6 is a schematic cross-sectional view showing a state in which the raw pipe is cut by a hot saw. FIG. 7 is a heat pattern of a compression test for measuring hot intensity. FIG. 8 is a graph showing the relationship between the material temperature and the hot strength of the Ni-based alloy (Alloy625) and the 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 the additive piece. FIG. 14 is a graph showing the time change of the drilling force in the drilling process. FIG. 15 is a diagram showing a deformation state of the additive piece during drilling obtained by numerical analysis. FIG. 16 is a diagram showing a deformation state of the additive piece at the end of drilling obtained by numerical analysis. FIG. 17 is a stress-strain curve of Hastelloy C276.

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

FIG. 1 is a flow chart showing a method for manufacturing a seamless metal tube according to an embodiment of the present invention. The method for manufacturing a seamless metal tube according to the present embodiment includes a step of preparing a billet with an additive piece (step S1), a step of heating the billet with an additive piece to a temperature T1 (step S2), and a step of drilling the heated billet with an additive piece (step S2). Step S3), a step of reheating the perforated billet with an additive piece (step S4), a step of extruding the reheated billet with an additive piece into a raw tube (step S5), and cutting the raw tube at the position of the additive piece. It includes a step (step S6). Hereinafter, each step will be described in detail.

[Billet preparation step with additive piece (step S1)]
A billet with an additive 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 additive piece includes a hollow billet 11 and an additive piece 12.

The hollow billet 11 is a round billet having a through hole 11a formed in the center. The additive piece 12 is attached to one end of the hollow billet 11. The addition piece 12 is formed with a through hole 12a coaxial with the through hole 11a of the hollow billet 11. It is preferable that the hollow billet 11 and the addition piece 12 have substantially the same diameter. Further, 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 additive piece may have a through hole 11a and a through hole 12a formed in the hollow billet 11 and the addition piece 12, respectively, and then the hollow billet 11 and the addition piece 12 are attached to each other. Alternatively, the billet 10 with an additive piece may have a through hole 11a and a through hole 12a formed after the hollow billet 11 and the addition piece 12 are adhered to each other. The through hole 11a and the through hole 12a can be formed by, for example, machining.

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 Cr: 14 to 30%, Ni: 29 to 65%, and Mo: 2 to 17% in mass%. To manufacture. Therefore, the chemical composition of the hollow billet 11 also contains 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 Alloy625 (alloy containing Cr: 20 to 23%, Ni: 58% or more, Mo: 8 to 10%), SM2535 (Cr: 24-27%, Ni: 29-37%, Mo: 2-4% alloy), SM2550 (Cr: 23-26%, Ni: 47-54%, Mo: 6-9% alloy) and the like.

The additive piece 12 is made of a material having a lower hot strength than the hollow billet 11. The additive piece 12 is formed of, for example, SUS304. The 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 additive piece is heated to the temperature T1 (step S2). The preferable value of the temperature T1 depends on the material of the hollow billet 11, but is, for example, 1000 to 1200 ° C. If the temperature T1 is too low, the load in the drilling step (step S3) becomes large. On the other hand, if the temperature T1 is too high, the hot workability is lowered depending on the material of the hollow billet 11, and flaws and the like are likely to occur.

The heating step (step S2) may include a step of preheating (equalizing heat) the billet 10 with an additive piece from room temperature to about 950 ° C. The heating method is not particularly limited, but 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 the additive piece is perforated from the end opposite to the end to which the additive piece 12 is attached (step S3). In the present application, "perforation" means expanding the hole of a hollow billet having a hole (guide hole) in the center by machining or the like in advance (increasing the inner diameter of the hollow billet). FIG. 3 is a schematic cross-sectional view showing a state in which the billet 10 with an additive piece is drilled by the drilling press device 20. The drilling press device 20 includes a container 21, a mandrel 22, a plug 23, and a shirring 24.

As shown in FIG. 3, the billet 10 with the additive piece is charged into the container 21 so that the additive piece 12 is in contact with 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. As a result, the through holes of the hollow billet 11 and the through holes of the addition piece 12 are enlarged in diameter.

[Reheating step (step S4)]
The perforated billet 10 with additive 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 step (step S5) becomes large. On the other hand, if the reheating temperature is too high, the hot workability is lowered depending on the material of the hollow billet 11, and flaws and the like are likely to occur.

[Extrusion step (step S5)]
The reheated billet 10 with an additive piece is extruded so that the end opposite to the end to which the additive piece 12 is attached faces forward (step S5). 4 and 5 are schematic cross-sectional views showing a state in which the billet 10 with an additive piece is extruded by the extrusion press device 30. The extrusion press device 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.

While inserting the mandrel 34 into the reheated billet 10 with the additive piece and the dummy block 38, the stem 32 simultaneously pushes the mandrel 34 into the container 31. At this time, the billet 10 with the additive piece is arranged so that the end opposite to the end to which the additive piece 12 is attached faces forward. That is, the billet 10 with the additive piece is arranged so that the additive piece 12 is in contact with the dummy block 38. The billet 10 with an additive piece pressurized in the container 31 is filled and upset in the container 31. By further pressurizing and advancing the stem 32, 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 tube P (FIG. 4). reference). By further pressurizing and advancing the stem 32, a part of the additive piece 12 is processed in the same manner (see FIG. 5).

[Cut 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 in which the raw pipe P is cut by the hot saw 39. After the extrusion is completed, the container 31 is retracted by about 100 mm, a hot saw 39 is charged 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 pipe P and the push residue (discard) remaining in the container 31 are separated.

A part of the additive piece 12 still adheres to the rear end of the raw pipe P, but this may be cut again in a later step.

[Relationship between the hot strength of the hollow billet 11 and the hot strength of the additive piece 12]
In the present embodiment, the hot intensity Ka at the temperature T1 of the addition piece 12 and the hot intensity Kb at the temperature T1 of the hollow billet 11 satisfy the following equations.
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 when the strain rate is 1.0 / sec and the strain is 0.5 is used in accordance with the deformation rate and the amount of deformation of the material to be pressed (hollow billet) at the time of drilling press.

More specifically, the hot intensity 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 is performed at a high temperature. FIG. 7 is a heat pattern of the same test. First, the test piece is heated from room temperature to 1250 ° C. at a heating rate of 5 ° C./sec. After holding at 1250 ° C. for 60 seconds, the temperature is lowered to temperature T1 at 2 ° C./sec, and the temperature is held at T1 for 5 seconds. However, when the temperature T1 is 1250 ° C., this temperature lowering and holding is not performed. Then, compressive stress is applied to the test piece at a strain rate of 1.0 / sec, and the 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 reaches 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 effects of the present embodiment.

FIG. 8 is a graph showing the relationship between the material temperature and the hot strength of the Ni-based alloy (Alloy625) and the stainless steel (SUS304). As shown in FIG. 8, high alloys such as Ni-based alloys have a larger rate of increase in hot strength with temperature decrease than stainless steel. This is considered to be the cause of the increase in the drilling force at the final stage of the drilling step (step S3 in FIG. 1).

In the present embodiment, a billet 10 with an additive piece is prepared by attaching an additive piece 12 having a lower hot strength than the hollow billet 11 to one end of the hollow billet 11 which is a material of a seamless metal tube (FIG. 2). See). Then, the billet 10 with the additive piece is charged into the container 21 so that the additive piece 12 is in contact with the shirring 24, and is drilled from the end opposite to the end to which the additive piece 12 is attached (see FIG. 3).

During the drilling process, the temperature of the billet 10 with additive pieces gradually decreases. In particular, the temperature of the additive piece 12 is significantly lowered due to heat removal due to contact with the shirring 24. According to the present embodiment, at the end of the drilling process where the temperature is the lowest, the additive piece 12 having a lower hot strength than the hollow billet 11 is drilled. Therefore, it is possible to suppress an increase in the drilling force at the end of the drilling process.

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

If the ratio Ka / Kb of the hot strength of the addition piece 12 to the hot strength of the hollow billet 11 is too low, the addition piece is deformed in the drilling step (step S3 of FIG. 1) and the extrusion step (step S5 of FIG. 1). Machining may become impossible due to the 12 entering the gap between the tools. Therefore, Ka / Kb needs to be 0.3 or more. The Ka / Kb is preferably small from the viewpoint of the effect of suppressing an increase in the drilling force at the end of the drilling process and reducing the cutting load after extrusion. However, as described above, if it is too low, processing becomes impossible. The lower limit of Ka / Kb is preferably 0.35 from the viewpoint of operational stability, that is, reduction of trouble that it becomes impossible to enclose during operation.

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

The method for manufacturing a seamless metal tube according to an embodiment of the present invention has been described above. According to the present embodiment, a method for manufacturing a seamless metal tube having improved production efficiency can be obtained by suppressing an increase in the drilling force at the end of the drilling process and reducing the cutting load after extrusion. Further, by suppressing the increase in the drilling force at the end of the drilling process, it is possible to suppress the breakage of the mandrel 22 (FIG. 3) and the seizure of the plug 23 (FIG. 3).

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

The hot intensities of each material having the chemical composition shown in Table 1 were measured by the method described in the embodiment. In addition, "-" in Table 1 means that the content of the corresponding element is an impurity level.

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

An additive piece of SUS304 was welded to one end of the hollow billet of Alloy625 to obtain a billet with an additive piece. FIG. 13 is a schematic cross-sectional view of the vicinity of the welded portion of the billet with the additive piece. As shown in FIG. 13, the inner and outer diameters of the additive pieces were made to be substantially equal to the inner and outer diameters of the hollow billet.

Using this billet with an additive 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 step and the reheating temperature before the extrusion step were both set to 1100 ° C. The hot intensities at 1100 ° C. are as shown in FIGS. 9 and 10, with Alloy 625 at about 320 MPa, SUS304 at about 140 MPa, and Ka / Kb at about 0.44. Further, as a comparative example, a seamless metal tube was manufactured under the same conditions without adhering additive pieces.

FIG. 14 is a graph showing the time change of the drilling force in the drilling process. As shown in FIG. 14, by adhering the additive pieces, it was possible to suppress an increase in the drilling force at the end of the drilling process.

Also, regarding the life of the hot saw, when the additive pieces were not attached, it was necessary to replace the blades after cutting 6 extrusion pipes, but by attaching the additive pieces, almost no wear of the blades was observed. ..

Next, the steel type of the additive piece was changed to carbon steel (SC45C, the hot strength at 1100 ° C. was about 80 MPa), and the seamless metal tube was manufactured under the same conditions as the others. In this case, Ka / Kb is about 0.25. In this case, the deformation of the additive piece during the extrusion process became remarkable, and the additive piece invaded the gap between the container and the dummy block. As a result, the material was clogged in the container, making it impossible to make pipes.

Subsequently, the steel grade of the hollow billet was changed to SM2535, and the steel grade of the additive piece was changed to SUS304 to manufacture a seamless metal pipe. The heating temperature T1 before the drilling step and the reheating temperature before the extrusion step were both set to 1200 ° C. The hot intensities at 1200 ° C. are as shown in FIGS. 10 and 11, with SM2535 being about 140 MPa, SUS304 being about 100 MPa, and Ka / Kb being 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, the steel grade of the hollow billet was changed to SM2550, and the steel grade of the additive piece was changed to SUS304 to manufacture a seamless metal pipe. The heating temperature T1 before the drilling step and the reheating temperature before the extrusion step were both set to 1200 ° C. The hot intensities at 1200 ° C. are as shown in FIGS. 10 and 12, with SM2550 being about 160 MPa, SUS304 being about 100 MPa, and Ka / Kb being about 0.63. In this case as well, 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.

The hot intensity required for the additive pieces was investigated by numerical analysis. The hot strength Kb of the base material (hollow billet) was set to 200 MPa, and the changing behavior of the added piece when 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.

15 and 16 are diagrams showing the deformation state of the added piece during and at the end of drilling, which was obtained by numerical analysis. When Ka / Kb is 0.25 or less, the deformation of the additive piece becomes remarkable, and the additive piece is inserted into the outer surface of the billet, and there is a concern that the billet may not be taken out properly or the inner surface of the container may be scratched. This is in good agreement with the manufacturing results described above. Further, when Ka / Kb was 0.20, the outflow of the additive piece to the inner surface side of the billet became remarkable. Therefore, it was found that the thickness of the added piece was reduced and the effect of reducing the drilling force was lost.

The embodiments of the present invention have been described above. The above-described embodiment is merely an example for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-described embodiment can be appropriately modified and implemented within a range that does not deviate from the gist thereof.

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

Claims (1)

The process of preparing a billet with an additive piece with the additive piece attached to one end of the hollow billet, and
The step of heating the billet with the additive piece to the temperature T1 and
The step of drilling the heated billet with the additive piece from the end opposite to the end to which the additive piece is attached, and
The step of reheating the perforated billet with the additive piece and
A step of extruding the reheated billet with an additive piece so that the end opposite to the end to which the additive piece is attached faces forward, and a step of forming a raw pipe.
A step of cutting the raw tube at the position of the additive piece is provided.
The hollow billet has a chemical composition of mass% and contains Cr: 14 to 30%, Ni: 29 to 65%, and Mo: 2 to 17%.
A method for producing a seamless metal tube, wherein the hot strength Ka at the temperature T1 of the additive piece and the hot strength Kb at the temperature T1 of the hollow billet satisfy the following formulas.
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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