JPH0713243B2 - Method for producing highly corrosion resistant Ni-based alloy tube - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a tube from a high Mo Ni-based alloy that has excellent corrosion resistance but is difficult to process, and in particular, sulfur (S) as a single substance is used. The present invention relates to a technique for producing a seamless pipe suitable for oil wells by a powder metallurgy method, which shows excellent stress corrosion cracking resistance and hydrogen cracking resistance even in a mixed sour gas environment.

(Prior art) The recent energy situation is such that deep wells in oil wells and wells in sour gas environments are inevitable.
A high-strength, high-corrosion-resistant Ni-base alloy for oil country tubular goods has been developed and put into practical use, although it is expensive but can sufficiently withstand harsh environments. Such a Ni-based alloy is disclosed, for example, in JP-A-54
-107828 and Japanese Patent Laid-Open No. 54-127831.

However, according to recent oil well information, in addition to the sour gas environment, which is said to be severe in corrosiveness, an environment in which S as a simple substance is further mixed in this sour gas environment is found. It has become clear that even with the Ni-based alloys for sour gas that have been proposed so far, they are not sufficiently satisfactory in terms of corrosion resistance.

As a method of imparting excellent corrosion resistance under the environment containing the simple substance S as described above, a method of heavily cutting the Mo content of the Ni-based alloy and increasing it can be considered. However, since a high Mo Ni-based alloy is extremely difficult to work, even if a billet is produced from a molten material, it cannot be hot extruded to form a seamless pipe.

By the way, recently, hot-extrusion pipe making is performed by a powder metallurgy method which is advantageous for hot-forming of difficult-to-process materials. For example, C is 0.1 to 075%, Ni is 20 to 40%, and Cr is 20 to 30% by weight.
In this specification, Japanese Patent Laid-Open No. 1-108301 proposes a method for producing a heat-resistant steel pipe containing the alloy components by weight by the powder metallurgy method.
However, the Ni-based alloys targeted there have a Mo content of at most about 3%, and the corrosion resistance of the alloy itself is insufficient for the above-mentioned applications.

(Problems to be Solved by the Invention) A high Mo high Cr Ni-based alloy having a Mo content higher than a certain level is expected to exhibit excellent corrosion resistance and high mechanical properties even in a sour gas environment containing elemental S. , Seems promising as a material for oil country tubular goods in harsh environments. However, this alloy has a very poor hot workability due to the segregation of Mo and the precipitation of intermetallic compounds in ordinary ingots, and it is difficult to hot extrude pipes. Further, the ingot is not always good in corrosion resistance.
Under these circumstances, the high-Mo, high-Cr Ni-based alloy has not yet been used as a material for oil country tubular goods.

In view of the present situation, the present invention has a high corrosion resistance.
It is intended to propose a method for easily manufacturing a Mo-high Cr-based Ni-based alloy tube.

(Means for Solving the Problems) A powder metallurgy method is known as a method for molding difficult-to-process materials. As described above, a method for manufacturing a heat-resistant tube made of a Ni-based alloy is also proposed in, for example, Japanese Patent Laid-Open No. 1-108301. However, in order to manufacture a high Mo high Cr system Ni-based alloy tube that is more difficult to machine than the Ni-based alloys described therein, it is necessary to reexamine in detail from the selection of the component system to the processing conditions. .

The present inventors have determined an alloy composition having sufficient high corrosion resistance in a severe corrosive environment of a sour gas atmosphere containing the above-mentioned elemental S and also having high strength as an oil country tubular good, and together with this, The present invention has been completed by determining the conditions for producing pipes by the powder metallurgy method.

The gist of the present invention is as follows.

(1)% by weight, C: 0.05% or less, Si: 0.20% or less, Mn: 1.0% or less, Ni: 50-60%, Cr: 10-20%, Mo: more than 18% and 30% or less, Al : Ni-based alloy powder containing 0.3% or less, the balance being Fe and unavoidable impurities is filled in a metal hollow cylindrical container with good workability and sealed to form a hollow billet. Is heated to a temperature of 1000 to 1300 ° C and hot extruded, and after further solution heat treatment at 1100 to 1300 ° C, 5
A method for producing a highly corrosion-resistant Ni-based alloy pipe, characterized by cold working at a cross-sectional reduction rate of -60%.

(2) In addition to the above component (1), it further contains at least one component selected from one or both of the following Group 1 and Group 2 elements, with the balance being Fe and inevitable impurities.
A method for producing a highly corrosion-resistant Ni-based alloy tube, which comprises hot-extruding and then cold-working using a Ni-based alloy powder as in (1).

Group 1 elements: Cu: 3.0% or less, Nb: 2.0% or less, W: 4.0% or less and Co: 2.
0% or less Group 2 element; Ti: 1.0% or less and Zr: 0.5% or less The alloy powder used in the method of the present invention is preferably one produced by a gas atomizing method.

The metal container having good workability is a metal container having good ductility at room temperature and hot extrusion temperature, such as low alloy steel and low carbon steel.

(Function) Hereinafter, the reason for selecting the composition of the alloy powder used in the method of the present invention and the reason for selecting the molding processing conditions will be described together with desirable conditions.

Reason for selection of alloy powder composition: C: 0.05% or less When the C content in the alloy exceeds 0.05%, M ₆ C type carbides (however, M is Mo, Ni, Cr, W, etc.) increase, Not only the ductility and toughness of the alloy deteriorate, but also the stress corrosion resistance deteriorates significantly. Therefore, the C content must be 0.05% or less.

Si: 0.20% or less Si is added as a deoxidizing agent, but if added in a large amount, it is an intermetallic compound (hereinafter referred to as “TCP phase”) which is not preferable for ductility and toughness such as σ, P and Laves phase. (Abbreviated)
Is easy to generate. Therefore, the Si content is set to 0.20% or less. It is more desirable that Si is less than 0.05%.

Mn: 1.0% or less Mn is usually added as a desulfurizing agent, but its content is 1.
If it exceeds 0%, the generation of TCP phase may be promoted, so it should be kept to 1.0% or less.

Ni: 50-60% The alloy used as the material of the method of the present invention is basically strengthened by adding Mo, Cr, or W, Nb, etc., which have the effects of solid solution strengthening and work hardening, to the Ni matrix. But,
Even if a large amount of the above elements is added, Ni must be contained enough to stabilize the austenite matrix. That Ni
The minimum required content of is 50%.

On the other hand, Ni is an element which itself improves the work hardening ability, and if the content exceeds 60%, the hydrogen cracking resistance deteriorates, so the upper limit of the Ni content was set to 60%.

Cr: 10 to 20% Cr is a component that improves the corrosion resistance and strength of the alloy together with Mo, but this effect becomes remarkable when the content is 10% or more. On the other hand, if the Cr content exceeds 20%, the hot workability of the alloy decreases. Therefore, the proper range of Cr content is 10 to 20%.

Mo: 12-30% Mo coexists with Cr and has the effect of significantly improving the strength and corrosion resistance of the alloy, especially the pitting corrosion resistance. Since the tube produced by the method of the present invention is intended to be used in a harsh environment such as a sour gas atmosphere containing a simple substance of S, Mo is added to the material alloy in a particularly high amount. That is, in order to ensure the above effects, Mo is contained in an amount of 12% or more. But,
If the Mo content exceeds 30%, the austenite matrix becomes unstable.

Al: 0.3% or less Although Al is added as a deoxidizer, if the content of Al exceeds 0.3%, it becomes difficult to produce powder by atomization, so the content is set to 0.3% or less.

One of the alloy powders used in the method of the present invention contains each of the above components, and the balance is Fe and inevitable impurities. Of the impurities, P and S are particularly unfavorable, so P should be 0.01% or less and S should be 0.005% or less. If they are present in a large amount in the alloy, they degrade the hot workability due to grain boundary segregation and also deteriorate the corrosion resistance.

Further, if the N content of the alloy powder exceeds 0.1%, coarse nitrides are formed and the ductility and toughness of the product deteriorate, so it is desirable to keep the N content to 0.1% or less.

Another alloy powder used in the method of the present invention is an alloy containing, in addition to the above components, one or more components selected from the elements of the first group and the second group described above. These components have the effects of improving the ductility and toughness of the alloy as well as improving the corrosion resistance, so it is preferable to contain one or more of them, if necessary. Hereinafter, the reason why the content of each element is limited will be described together with its characteristic action.

Cu: 3.0% or less In the sour gas environment in which S is contained alone, Cu is
It is a component that is extremely effective in improving corrosion resistance together with Mo.
Even if it is contained in excess of%, the effect will be saturated.

Nb: 2.0% or less Nb is a component that improves the corrosion resistance performance of the alloy in the sour gas environment containing S alone, but if it exceeds 2.0%, the TCP phase is likely to be formed, so If it is added, its content should be 2.0% or less.

W: 4.0% or less W, like Mo, has the effect of improving the strength and corrosion resistance of the alloy in the coexistence of Cr, but if the W content exceeds 4.0%, the austenite matrix becomes unstable. . Therefore, the W content is 4.0% or less.

Co: 2.0% or less Co is effective for improving the hydrogen cracking resistance of the alloy,
If the content exceeds 2.0%, the TCP phase is likely to form.

Ti: 1.0% or less, Zr: 0.5% or less Ti and Zr are effective in stabilizing a trace amount of C in the alloy, but when their contents exceed 1.0% and 0.5%, respectively.
TCP phase is easily generated.

The alloy powder having the composition described above is preferably produced by a rapid solidification method such as a gas atomizing method. According to this method, a spherical alloy powder having almost no segregation or intermetallic compound can be obtained.

Pipe manufacturing process The alloy powder is first filled in a metal container having good workability. The container has a hollow cylindrical shape, as shown in its longitudinal sectional view in FIG. As described above, the container 1 is made of a metal such as low carbon steel having good malleability at room temperature and hot extrusion temperature, and preferably has a wall thickness of 1 to 4 mm. When performing cold isostatic pressing prior to heating before hot extrusion,
Since the entire metal container is compressed and deformed by strain, it must be malleable at room temperature. Also, during hot extrusion pipe making,
The contact with the die and the mandrel occurs through the metal container, and the hot spreadability of the metal container has a great influence on the formability of the extruded pipe material.

The metal container is sealed after filling with powder, but in order to improve the corrosion resistance, it is 1 × 10 ^-1 mmHg at room temperature to 600 ℃.
It is desirable to perform vacuum deaeration for 10 minutes or more at the above vacuum degree to remove water, hydroxide and air adsorbed on the powder surface, and then seal under a vacuum (reduced pressure). The hollow cylindrical powder-filled body thus obtained is hereinafter referred to as "powder billet".

The powder billet before hot extrusion may be subjected to soaking heating in an electric furnace or a gas furnace, but it is preferable to perform high frequency induction heating capable of increasing the heating rate and heating to the holding temperature in a short time. At this time, in order to smoothly perform high-frequency induction heating, the powder billet is preheated to 800 ℃ -1000 ℃.
It is recommended that the powder billet be subjected to cold isostatic pressing to bring the relative filling density of the alloy powder to 75% or more before performing pre-sintering or by high frequency heating. By doing so, it is possible to reduce the non-uniformity of the temperature distribution of the powder billet during high frequency induction heating.

The heating temperature of the powder billet is 1000 to 1300 ° C. 1000 ° C
This is because the deformation resistance of the alloy powder is large at a temperature of less than 1, the plastic deformation of the alloy powder does not occur, and the alloy powder is clogged during extrusion or cannot retain a predetermined shape even if extrusion is possible. On the other hand, 1300
When heated at a temperature higher than 0 ° C, the solidus temperature of the alloy powder becomes higher than the solidus temperature of the alloy powder, and a part of the alloy melts to cause segregation.

Note that it is desirable to quench the pipe after extrusion to suppress precipitation of intermetallic compounds. Further, cold working is performed in order to improve the dimensional accuracy of the alloy pipe and to increase the strength, but prior to that, it is necessary to perform solution heat treatment at 1100 ° C to 1300 ° C. This is to sufficiently suppress the intermetallic compound. When performing cold working, it is necessary to reduce the sectional area by at least 5% or more. However, in cold working where the reduction in cross-sectional area exceeds 60%, work hardening is large and good formability cannot be maintained. If solution treatment is carried out after cold working, the alloy tube is softened by recrystallization, so by repeating this, it is possible to work with a large reduction in cross-sectional area.

[Example 1] The alloy powder of sample No. 1 shown in Table 1 (particle size: 250 µm or less) was produced by Ar gas atomization method and filled in the low carbon steel container (1) shown in Fig. 1. Vacuum degassing of 1 × 10 ^-2 mmHg was performed at the temperature of 400 ° C for 1 hour through the degassing port (3), and after cooling, the hollow powder billet (height h:
600 mm, inner diameter d: 80 mm, outer diameter D: 210 mm) were manufactured.

The above hollow powder billet was placed in a gas heating furnace, heated to 1200 ° C., and subjected to a Eugen type hot extrusion tube at an extrusion ratio of 8 and water cooled.

This pipe material is pickled to remove the low carbon steel container, and 1250 ℃
After solution heat treatment for 10 minutes, a cross-section reduction work of 20% was performed by a cold drawing machine. The properties of the obtained alloy tube are shown in Table 2 as Test No. 1.

The corrosion resistance test in Table 2 was performed under the following conditions.

(A) the stress corrosion cracking test corrosion solution: 20% NaCl-1g / lS -10atmH 2 S -20atmCO 2 test temperature: 300 ° C. Immersion time: 500 hr additional stress: 1 [sigma _y specimen: 10 mm width × 2 mm thickness × 75 mm length in, with R0.25U notch (b) resistance to hydrogen cracking tests NACE conditions: 5% NaCl-0.5% CH 3 COOH-1atmH 2 S test temperature: 25 ° C. immersion time: 720Hr additional stress: 1 [sigma _y specimen: 10 mm width × 2 mm thick x 75 mm long, with R0.25U notch As is clear from the results in Table 2, the pipe material obtained in this example has very good mechanical properties and corrosion resistance.

[Example 2] By the N ₂ gas atomizing method, alloy powders (particle size: 500 μm or less) of the chemical components of Sample Nos. _{2 to} 3 in Table 1 were produced, and the low carbon steel container shown in FIG. The hollow powder billet having the same size as that of Example 1 was prepared by filling the inside of (1) with vacuum degassing of 1 × 10 ^-2 mmHg through the degassing port (3) at room temperature for 1 hr. did.

4000kg by cold isostatic pressing on this hollow powder billet
A pressure of / cm ² was applied to raise the relative density of powder filling to 80%. Subsequently, this hollow powder billet was preheated to 800 ° C in a rotary gas furnace, and subsequently heated to 1000 to 1360 ° C in a high-frequency induction heating furnace, and extruded by a Eugene hot extruder to form a pipe and water-cooled. did.

This pipe material is pickled to remove the low carbon steel container, and 1250 ℃
After the solid solution treatment for 10 minutes, the cross-sectional area reduction work of 5 to 60% was performed by a cold drawing machine. The characteristics of the obtained alloy pipe are
Shown in the table as Test Nos. 2-9.

No. 2 and No. 8 in Table 2 are an example in which the heating temperature before hot extrusion is too low and an example in which it is too high. These had poor hot workability and could not be extruded.

Nos. 3 to 7 and No. 9 were produced according to the method of the present invention, and tubes having satisfactory mechanical properties and corrosion resistance were obtained.

[Reference example]

Manufactured ingots with chemical composition of sample No.4 and No.5 in Table 1, hollow ingot billet (h: 600mm, D: 210)
mm, d: 80 mm) was manufactured.

This molten billet is preheated to 800 ° C in a rotary gas furnace, and subsequently 1200 ° C in a high frequency induction heating furnace.
After heating up to 6 with an extrusion ratio of 6 using a Ugene hot extruder
The tube was extruded at 1150 ° C.

As shown in Table 2 as No.10 and No.11, the ingots of sample No.4 (with 32.0% Mo) in Table 1 have poor hot workability and cannot be extruded. there were. On the other hand, the ingot made from sample No. 5 in Table 1 (having a low Mo content of 11.4%) produced an extruded pipe but had poor corrosion resistance.

(Effects of the Invention) The present invention provides a new method for producing a tube made of a high Mo, high Cr system Ni alloy having extremely excellent corrosion resistance but poor hot workability.

According to this method, there is no segregation or precipitation of intermetallic compounds,
It is possible to manufacture a tube that can withstand a harsh environment such as a sour gas atmosphere containing a simple substance S. The method of the present invention is particularly suitable for producing seamless pipes for oil wells.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a hollow cylindrical powder-filled body (powder billet) produced in an example of the present invention. FIG. 2 is a vertical cross-sectional view of a hollow billet made of a conventional ingot material.

Claims (4)

[Claims] 1. By weight%, C: 0.05% or less, Si: 0.20% or less, Mn: 1.0% or less, Ni: 50-60%, Cr: 10-20%, Mo: more than 18% and 30% or less. , Al: containing 0.3% or less, the balance is Ni-based alloy powder consisting of Fe and unavoidable impurities, filled in a metal hollow cylindrical container with good workability, and sealed to form a hollow billet, After heating the hollow billet to a temperature of 1000 to 1300 ℃ and hot extruding it, after further solution heat treatment at 1100 to 1300 ℃, 5
A method for producing a highly corrosion-resistant Ni-based alloy pipe, characterized by cold working at a cross-sectional reduction rate of -60%. 2. Ni-based alloy powder, in% by weight, C: 0.05% or less, Si: 0.20% or less, Mn: 1.0% or less, Ni: 50-60%, Cr: 10-20%, Mo: 18 %, 30% or less, Al: 0.3% or less, Cu: 3.0% or less, Nb: 2.0% or less, W: 4.0% or less, and Co: 2.0% or less The balance is Ni-based alloy powder consisting of Fe and unavoidable impurities, filled in a hollow cylindrical metal container with good workability and sealed to form a hollow billet. The hollow billet is heated to a temperature of 1000 to 1300 ° C. A method for producing a highly corrosion-resistant Ni-based alloy pipe, which comprises heating and hot extruding, and further performing solution treatment at 1100-1300 ° C., followed by cold working at a cross-sectional reduction rate of 5-60%. 3. Ni-based alloy powder, in% by weight, C: 0.05% or less, Si: 0.20% or less, Mn: 1.0% or less, Ni: 50-60%, Cr: 10-20%, Mo: 18 %, 30% or less, Al: 0.3% or less, further, Ti: 1.0% or less and Zr: 0.5% or less, or both, and the balance is a Ni-based alloy powder consisting of Fe and unavoidable impurities. , Filled in a metal hollow cylindrical container with good workability, closed to form a hollow billet, heated this hollow billet to a temperature of 1000 to 1300 ° C and hot extruded, and further 1100 to 1300 ° C The method for producing a highly corrosion-resistant Ni-based alloy pipe, which comprises cold-working at a cross-section reduction rate of 5 to 60% after the solution heat treatment of. 4. Ni-based alloy powder, in% by weight, C: 0.05% or less, Si: 0.20% or less, Mn: 1.0% or less, Ni: 50-60%, Cr: 10-20%, Mo: 18 %, 30% or less, Al: 0.3% or less, Cu: 3.0% or less, Nb: 2.0% or less, W: 4.0% or less, and Co: 2.0% or less, and Ti: 1.0%
One or both of the following and Zr: 0.5% or less, with the balance being Fe
And Ni-based alloy powder consisting of unavoidable impurities is filled in a hollow cylindrical container made of metal with good workability and sealed to form a hollow billet, and this hollow billet is heated to a temperature of 1000 to 1300 ° C. After hot extrusion, 1100-1300 ℃
The method for producing a highly corrosion-resistant Ni-based alloy pipe, which comprises cold-working at a cross-section reduction rate of 5 to 60% after the solution heat treatment of.