JPH03104818A - Oxide dispersion strengthened alloy tube and production thereof - Google Patents

Abstract

PURPOSE:To produce the above alloy tube having an excellent internal pressure creep rapture strength by making the tube of an Fe-based oxide dispersion strengthened alloy and subjecting this tubular body to twisting below the recrystallization temp. to impart the texture of a spiral structure thereto. CONSTITUTION:The oxide dispersion strengthened alloy tube 4 of a prescribed size is produced by the conventional method using the Fe-based or Ni-based oxide dispersion strengthened alloy. One end of this alloy tube 4 is chucked by a head stock 2 and the other head is chucked by a tail stock 3. While tensile force is acted axially on the tube, the tube is twisted circumferentially below the recrystallization temp. (about 400 to 1100 deg.C). The tube is so twisted that the torsional angle theta of this time is about 20 deg.<=theta<=45 deg.. The texture of the spiral structure is generated in the alloy tube 4 in this way and the excellent internal pressure creep rupture strength is imparted to the tube. The alloy tube 4 useful for a boiler tube, etc., is thus obtd..

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an oxide dispersion strengthened alloy tube having excellent internal pressure strength, particularly internal pressure creep rupture strength, and a method for manufacturing the same.

The alloy tube according to the present invention is promising as a tube material used under high temperature and pressure, such as boiler tubes, internal combustion engine piping, chemical industry piping, and nuclear reactor fuel cladding tubes.

(Prior Art) In recent years, there has been an increasing demand for materials that can withstand high temperatures and high pressures and have corrosion resistance. Dispersion-strengthened alloys are considered to be one of the promising materials to meet these demands. Dispersion strengthened alloys, particularly oxide dispersion strengthened alloys, are materials in which fine inert particles are uniformly dispersed in a matrix, and can exhibit useful strength up to temperatures close to the melting point of the matrix alloy.

The most common manufacturing method for such dispersion-strengthened alloys is
This is a mechanical alloying method in which metal powder and hard particles (oxides, carbides, nitrides, etc.) are strongly ground and mixed in a high-energy ball mill. Such a process was developed in the 1970s.
It is disclosed in Publication No. 37631. (Problems to be Solved by the Invention) For example, the dispersion-strengthened alloy powder produced by the mechanical alloying method as described above is vacuum-sealed in a steel capsule and sintered to form a final product with a desired shape. Or simply use it as a material such as a board or a shank. By the way, when manufacturing pipes from such alloy materials, extrusion, rolling, or drawing processes for such raw materials are indispensable.

However, the structure of oxide dispersion strengthened alloys generally becomes elongated grains that are elongated in the processing direction (extrusion, rolling, drawing direction) through these steps.

Note that there is also a method of directly producing a pipe from alloy powder through sintering, but even in such a case, the raw pipe must be finished by extrusion, rolling, or drawing, and the structure becomes an elongated grain.

For materials with such a structure, for example, CAMP-ISIJ Vol. 1. I (198B)-
As shown in No. 856, the strength in the processing direction is excellent, but
There is a tendency for the strength to be inferior in the vertical direction. For this reason, in the case of pipes that are subjected to internal pressure stress at high temperatures, there is a problem in that the internal pressure strength, especially the internal pressure creep rupture strength, of materials with this type of structure is significantly inferior to the strength expected from the longitudinal direction. Therefore, for members that are mainly subjected to stress only in the longitudinal direction, such as gas turbine blades, Japanese Patent Application Laid-Open No. 63-3109
As shown in Japanese Patent No. 44, heat treatment that promotes the anisotropy of the structure has been carried out. This disclosed example is characterized by inducing unidirectional recrystallization in the axial direction of the extruded billet by twisting at a temperature higher than the recrystallization temperature, and attempts to promote recrystallization by introducing strain through twisting. It is something. However, in this method, the amount of strain is as high as 30%, and uniform heating to the recrystallization temperature is required, and when applied to pipe materials, the unidirectional recrystallization is promoted in the pipe axis direction. , which has the disadvantage of lowering the internal pressure strength.

Further, it is generally known that it is very difficult to make the elongated grains of oxide dispersion strengthened alloys into isotropic grains by normal heat treatment.

An extrusion method that eliminates mm anisotropy was published in JP-A-62-8340.
Although it is shown in Publication No. 6, it is rare that products are produced as they are extruded due to dimensional accuracy, surface texture, etc., and the IJlm anisotropy develops again in subsequent steps such as rolling, and the internal pressure creep rupture strength increases. It is quite conceivable that this could lead to a decrease in Furthermore, in carrying out the above invention,
In some cases, it may be necessary to perform mechanical alloying at low temperatures, as disclosed in Japanese Patent No. 2-83402, which poses the problem of complicating the manufacturing process.

An object of the present invention is to solve all of the above-mentioned problems in the prior art and to provide an oxide dispersion strengthened alloy tube having internal pressure strength, particularly excellent internal pressure creep rupture strength, and a method for manufacturing the same.

(Means for Solving the Problems) In order to achieve the above object, the present inventors have made extensive efforts to study the anisotropy of the structure and high-temperature strength of dispersion-strengthened alloys, particularly oxide dispersion-strengthened alloys, and pipe manufacturing methods. As a result of repeated research, we have discovered an oxide dispersion-strengthened alloy tube with excellent internal pressure creep rupture strength and a method for manufacturing the same, and have brought the present invention to fruition. That is, one aspect of the present invention is to provide an oxide dispersion strengthened alloy which is made of an Fe-based or Ni-based oxide dispersion strengthened alloy and has a helical structure, and which has excellent internal pressure strength. It's a tube.

In addition, from another aspect of the present invention, Fel or Ni
An oxide dispersion-strengthened alloy tube with excellent internal pressure strength, which is characterized by manufacturing a tube from a base oxide decomposition-strengthened alloy and then subjecting the obtained tube to twisting at a temperature below the recrystallization temperature. It is a manufacturing method.

Here, the spiral structure &II weave &! ! ! li refers to a crystal structure in which the long sleeves of the expanded grains are preferably inclined at 20 to 45 degrees with respect to the tube axis direction.

(effect) The present invention will be specifically described with reference to the drawings.

The pipe material according to the present invention is typically manufactured through the steps of mechanical alloying → vacuum encapsulation → extrusion, but is not limited to a specific pipe manufacturing method, and is formed from a forged plate material using a forge welding method. In any case, the oxide dispersion strengthened alloy tube produced by the conventional method is then finished into a tube of a predetermined size by rolling or the like.

In any case, the method of manufacturing pipes from dispersion-strengthened alloys is well known to those skilled in the art, and in order to simplify the explanation, further explanation will be omitted8. Examples of alloys include IN
Is it commercially available from CO? There are IA956 and PA957 (both trade names), and examples of Ni groups include INCO as above.
There are commercially available MA754 and MA6000 (both trade names), both of which are well known to those skilled in the art, and the present invention is not limited to any particular one.

According to the present invention, after the pipe is manufactured to the final product size in this manner, it is subjected to bending in the circumferential direction at a temperature below the recrystallization temperature using an apparatus such as that shown in FIGS. 1(a) and (b). Processed,
Gives a spiral structure to the tissue.

The device shown in FIG. 1(a) utilizes a stretcher device, which is originally used to straighten a tube by twisting it in order to improve the straightness of the tube after tube manufacturing. The illustrated stretcher device includes a hydraulic cylinder 1, a hydraulic cylinder 2 connected to the hydraulic cylinder 1, and a cylinder 2 that applies a tensile force in the axial direction to the material.
As shown by arrows in the figure, the tube 4 is provided with a tail stylus 3 that applies a torsion torque in the circumferential direction to the tube 4.

When carrying out the present invention using the apparatus shown in FIG. The tube is chucked with the tail striker 3, and the twisting process is performed in the tube circumferential direction without applying tensile force in the tube axis direction.

The twisting temperature needs to be below the recrystallization temperature to ensure a helical structure within the tissue.

The recrystallization temperature referred to here refers to a temperature range accompanied by a certain length of grains, and does not include a temperature range only for recovery. If twisting is performed above the recrystallization temperature, recrystallization will develop in the tube axis direction, making it difficult to obtain a sufficient twist angle. The recrystallization temperature of oxide dispersion strengthened alloys is very high, sometimes exceeding 1100°C, but oxide dispersion strengthened alloys have high strength, low ductility, and poor workability at room temperature, and almost Since the ductility peaks in the hot working temperature range of 400 to 1000'C [G. ll. Gessinger"Powder M
etallogy of Superalloys (1
984) BuLterworth & Co. P.
264), twisting at 400 to 1100°C is preferable. 1) shows a stretcher device in which a heating device 5 is provided between a headstock 2 and a tailstock 3. When twisting a thin-walled pipe, a drop in temperature is expected during the twisting process, and the
Since the temperature may drop beyond the range of °C, a heating device 5 is installed as shown in Fig. 1(b), and while running the heating device from the tail stock 3 side to the henodo stock 2 side, It is good to add batter.

The amount of torsion is defined as the angle between the long sleeve direction of unrecrystallized expanded grains and the tube axis direction, that is, the torsion angle is θ.If θ is less than 20°, sufficient strength improvement effect cannot be obtained, and if θ is more than 45°, Because there is a risk of buckling during the bending process, 20゛
It is desirable that ≦θ≦45''.

In addition, in order to make the twist uniform in the pipe axis direction, the twisting process is performed with tensile force applied, but care must be taken to ensure that this tensile stress does not exceed the proof stress of the material in the processing temperature range of the pipe. No.

Incidentally, even in the past, twisting was sometimes applied to the pipe for the purpose of straightening, but in that case, the amount of bending was less than 20 degrees at the heel angle θ, and the twisting and twisting according to the present invention The helical structure &tlwh provided thereby is clearly distinguishable from those obtained by those conventional methods.

In this way, a spiral structure is imparted to the structure of the tube material, and the long sleeve direction of the elongated grains is inclined with respect to the tube axis direction. The anisotropy of the material is improved accordingly. In the case of the present invention, such improvement is evaluated by internal pressure creep rupture strength, and an improvement of approximately 50 to 70% of the rupture strength in the tube axis direction is observed.

Next, the present invention will be explained in more detail with reference to Examples.

(Example) In this example, oxide dispersion-strengthened ferrite NMA956 (trade name) extruded material and oxide dispersion-strengthened old-base heat-resistant alloy MA754 (trade name) commercially available from INCO were used.
It was revealed that the anisotropy of forged materials can be improved by forming tubes by groove roll rolling and then twisting them.

The chemical composition of the oxide dispersion strengthened alloy used is shown in Table 1.

(Example 1) First, a 956 extruded bar with a diameter of 50 mm and a length of 500 pieces was cut into 50 mm in diameter and 3 mm in thickness.
After processing into a tube material with a length of 500+s+e, the diameter is 20.
It was rolled into a tube of 0*m x thickness 2.0 open x length 2000+u+. The recrystallization temperature at this time was 1150°C.

This was heated at 1000°C for 30 minutes to remove strain, and immediately after that it was twisted 15 times using the stretcher device shown in FIG. 1(a). The temperature during the rolling process is 800 to 60
The twist angle θ at this time was approximately 25°. This twisted pipe was heated at 1000°C x 10 minutes AC.
The resulting tube was subjected to strain relief annealing and subjected to internal pressure and uniaxial (tube axial direction) creep tests at 650°C.

For comparison, a tube obtained by subjecting an as-rolled tube to AC heat treatment at 1000°C for 10 minutes was subjected to internal pressure and uniaxial creep tests at <650'C.

Strenochar used in carrying out the present invention! The J position has the structure shown in Fig. 1(a), and has the structure shown in Fig. 1(a).
The maximum tensile capacity was 50 tons, the stroke was 1000 mm, and the maximum torsion torque of Tailstonok 3 was 300 kg-m.

To roughly estimate the amount of torsion in terms of the torsion angle, as shown in Figure 2, for a pipe of diameter D and length, the torsion angle is λ.
(in radians) and ignoring the deformation in the tube axis direction, there is a relationship of 2L. Adding the condition 20゜≦θ≦45゜ to this, 0.728L/D ≦λ (radian) ≦ 21/D
is obtained, and when expressed as the helix rotation speed R per tube length, πD
πD, which is the twisting range.

In addition, in the internal pressure creep rupture test of the prototype pipe material, as shown in Fig. 3, an end plug 6 was made at one end of the pipe 4, and an end plug 7 having a guide hole 8 at the other end was made of the same material. They were bonded by phase diffusion bonding to form test pieces.

After this was placed in an electric furnace and heated to a predetermined temperature, Ar gas was fed through the guide hole 8 to set a predetermined pressure. At this time, it is often used in internal pressure creep rupture tests of boiler tubes.
Average diameter formula 2t σ: Stress in the circumferential direction P: Internal pressure D: Outside diameter of the pipe t: Depending on the wall thickness of the pipe, convert the pressure into stress in the circumferential direction and compare with the axle creep rupture test in the pipe axial direction did.

The results of these tests are shown graphically in FIG. It can be seen that the internal pressure creep rupture strength of the twisted pipe is significantly improved compared to the as-rolled pipe, although it is not as good as that of the uniaxial pipe.

Figure 5 (a) shows the optical microscopic structure photographs before and after the twisting process.
, (b) respectively.

(Example 2) Same as Example 1, thickness 301×width 80llI11×
A 300cm long l'lA754 forged material was machined into a tube with a diameter of 25mm, 3 thicknesses, and a length of 300mm. On+mX thickness 0.8nv x
It was rolled into a tube with a length of 2000 mm. The recrystallization temperature of this tube material was 1230°C.

This was heated to 800°C using the stretcher device shown in Figure 1(b).
While heating the material, it was subjected to 35 revolutions of twisting. θ was approximately 30°. 1100°C× for this twisted pipe
The resulting tube was subjected to AC strain relief annealing for 10 minutes.
Internal pressure and uniaxial creep tests were conducted at °C.

For comparison, 1100'C
The tubes subjected to 10 minutes AC heat treatment were also subjected to internal pressure and uniaxial creep tests at 1000°C.

The results are shown graphically in FIG. It can be seen that the internal pressure creep rupture strength of the twisted pipe is significantly improved compared to the as-rolled pipe, although it is not as good as that of the uniaxial pipe.

(Comparative example) Same as Example 1, MA with diameter 50mm x length 500mm+
By cutting 956 extruded bar material, diameter 50mm
After processing it into a tube material of 8 mm thick x 500 + nn+ length, it is 20.0 mm in diameter x 2.0 mm thick x 2000 I in length.
It was rolled into a IIffl tube. This was heated to 200°C using the stretcher device shown in Figure I (b) and twisted 15 times. Next, add 1 to this twisted pipe.
000'C x 10 minutes AC strain relief annealing, 65
Internal pressure and axle creep tests were conducted at 0″C.

The results are shown in Fig. 4 as 1200"C processing. The optical microscopic structure at this time is shown in Fig. 7. During the twisting process, unidirectional recrystallization occurred and a θ of only about 5° was obtained. The internal pressure creep rupture strength was equivalent to that of the as-rolled tube.

(Effects of the Invention) Since the present invention is constructed as described above, an oxide breakdown-strengthened alloy tube having excellent internal pressure creep rupture strength can be obtained, and such an alloy tube can be used in boiler tubes and internal combustion engine piping. It is extremely useful industrially as a pipe material used under high temperature and pressure, such as chemical industry piping and nuclear reactor fuel cladding.

[Brief explanation of drawings]

Figures 1 (a) and (b) are side views showing an example of a device implementing the present invention; Figure 2 is an explanatory diagram for estimating the torsion angle of a pipe; Figure 3 is an internal pressure creep rupture An explanatory diagram of the shape of the test piece; Figure 4 shows the 650 mm diameter of the tubes obtained in Example 1 and Comparative Example.
Graph showing the results of the internal pressure creep rupture test at "C"; FIG. 5 (aJ is an optical microscopic metal photograph of the fracture-strengthened alloy tube as rolled in Example 1; and FIG. An optical microscopic metal photograph of the dispersion-strengthened alloy tube twisted in Example 1;
Graph showing internal pressure creep rupture test results at 00"C;
FIG. 7 is an optical micrograph of a dispersion-strengthened alloy tube twisted in a comparative example. ];Hydraulic cylinder 2: Headstock 3: Tailstock 4: Dispersion-strengthened alloy tube 5: Heating device 7; End plug 6: @Plug 8: Conduit true! Concave

Claims (2)

[Claims] (1) An oxide dispersion strengthened alloy tube made of a Fe-based or Ni-based oxide dispersion strengthened alloy and characterized by having a helical structure and excellent internal pressure strength. (2) Oxide dispersion with excellent internal pressure strength, characterized by making a tube from a Fe-based or Ni-based oxide dispersion-strengthened alloy, and then twisting the obtained tube at a temperature below the recrystallization temperature. Manufacturing method for reinforced alloy tubes.