JPS63140055A - Highly corrosion resistant precipitation hardening-type ni-base alloy - Google Patents

Abstract

PURPOSE:To obtain a highly corrosion resistant precipitation hardening-type Ni-base alloy showing superior SCC resistance under a severe sour-gas environment containing S as a simple substance, by specifying a composition consisting of Cr, Mo, Nb, Fe, Ni, C, Si, Mn, P, S, and N. CONSTITUTION:The highly corrosion resistant precipitation hardening-type Ni-base alloy has a composition consisting of, by weight, 12-25% Cr, 5.5-<9.0% Mo, 4.0-6.0% Nb, 5.0-25% Fe, 45-60% Ni, <=0.050% C, <=0.50% Si, <=1.0% Mn, <=0.025% P, <=0.0050% S, and <=0.050% N and further containing, if necessary, 0.01-1.0% Ti and/or 0.01-2.0% Al and shows excellent SCC resistance under the severe sour-gas environment further containing S as a simple substance. By using the above alloy, pit-mouth and bottom-hole members for oil well having superior stress corrosion cracking resistance and hydrogen cracking resistance can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention is suitable for use in corrosive environments, particularly in conventional sour gas environments (l
An oil well component that has good stress cracking resistance and hydrogen cracking resistance in an environment where sulfur (S) is mixed in as a single substance rather than in the form of sulfides such as FeS and NiS under The present invention relates to a highly corrosion-resistant precipitation-hardening Ni-based alloy used for (particularly sun-resistant and bottom-resistant members).

(Conventional technology) In recent years, there has been a demand for deeper oil wells and for drilling wells in sour gas environments.
Base alloys and the like have been applied to such applications. These N
The corrosion resistance of i-base alloys is particularly high for Cr.

This is improved by increasing the Mo and W contents, so an alloy component system suitable for the target corrosive environment is selected while taking these into consideration. Furthermore, regarding strength, 0.2%
Proof strength of 77 kgf/mm2 or more, or 91 k
Therefore, for these alloy component systems, tubular members such as tubing, casings, and liners are required to have high strength through cold working. Precipitation hardening of intermetallic compounds such as T' or T' is used to increase the strength of thick-walled or irregularly shaped sun-resistant and bottom-resistant members that cannot be subjected to machining.

By the way, according to recent oil well information, in addition to the above-mentioned sour gas environment, there are environments in which sulfur (S) is mixed as a single substance, that is, not in the form of sulfides, etc., and in such environments, conventional sour gas resistant Ni1 alloys no longer have sufficient corrosion resistance.

(Problem to be solved by the invention) As mentioned above, in a sour gas environment (lIzs COz
In an environment where sulfur (S) is further mixed into Cf, -), Ni-based alloy members exhibit a unique form of corrosion, but the applicant has maintained good corrosion resistance even in such an environment. For tubing, casings, liners, and other tubular members, alloys whose strength can be increased by cold working are disclosed in Japanese Patent Application No. 1199/1983.
It has already been proposed in No.-1204.

However, even with the above alloys, if the strength cannot be increased by cold working for oil wellheads, bottom shaft members, etc.,
It is necessary to increase the strength by precipitation hardening of intermetallic compounds such as T'' or T''.

However, these existing precipitation hardening alloys suffer from localized corrosion or stress corrosion cracking (rSCC) in sour gas environments containing the above-mentioned sulfur (S) as a single element.
It has been confirmed that the product (referred to as J) is generated. That is,
The simple substance S depends on temperature and pressure (especially Has partial pressure).
)l-1+I1. s =)1.5. ) According to the reaction of 3a
(S, -+, lhs, Ih5x), but
Sulfur (S) or ozs liberated as Sm-1
It was found that when x exists, it locally adheres to the oil well head and bottom shaft member, leading to pitting corrosion or SCC in those areas. This is 4S+411□S! 311
Due to the reaction of □S+11□SO4, 11□Sn is produced locally and at the same time 11□S04 is generated, resulting in low p.
This is thought to be due to H conversion. In order to exhibit sufficient corrosion resistance in an environment exhibiting such a unique form of corrosion, it is necessary to use precipitation hardening type anti-Japanese and anti-bottom members, as in the case of tubular members (see Japanese Patent Application No. 61-1199 and others). It is also essential to form a corrosion-resistant film on alloys that has higher strength and better repairability than before. However, in existing precipitation hardening type Ni-based alloys, etc., precipitation hardenability and structural stability (second phase that causes embrittlement other than T", γ"; sigma phase,
There are restrictions on alloying elements from the viewpoint of preventing the precipitation of aves phase, etc., and a good corrosion-resistant film having sufficient corrosion resistance in this environment could not be obtained.

Therefore, it is an object of the present invention to overcome the conventional sour gas environment (
HzS-COz -CQ-) and sulfur (S) mixed with a single element of sulfur (S) The objective is to provide a base alloy.

(Means for Solving the Problems) Therefore, the present inventors have developed an alloy component system that can be used in a sour gas environment to obtain an alloy composition system that can provide a tough film with good repairability without decreasing precipitation hardening ability. In the case of a cold-worked Ni-based alloy for tubular members, the strength and repair ability of the film improve in proportion to the content of CrsM2SW, and in the case of containing elemental S, , conducted a study focusing on the effectiveness of Nb.

In the case of precipitation hardening Ni-based alloys for wellheads and pile bottom members,
When the content of CrSMaSWs Cu is increased, brittle phases such as sigma phase and Laνes phase remain in the product, which impedes precipitation hardening of γ゛ and γ'' and at the same time improves the strength and repair of the film itself. Even his abilities did not improve effectively.

As a result of further studying the mechanism, the present inventors found that
Mo: 5.5% or more, less than 9.0%, and Nb: 4
The combination of a specific component system containing ~6.0% ゜O allows for sufficient hardening in an environment of 200°C or lower, including elemental S, without reducing the precipitation hardenability, that is, the precipitation of intermetallic compounds of γ'' and T''. It was found that a corrosion-resistant film having high strength and good repair ability was obtained, and exhibited good SCC resistance and hydrogen cracking resistance in the relevant environment.

That is, the present invention was completed based on such knowledge, and its gist is as follows: Cr: 12 to 25%, Mo: 5.5% or more, 9.
Less than 0%, Nb: 4.0-6.0%, Fe: 5
．． 0-25%, Ni: 45-60%, C:
0.050% or less, Si: 0.50% or less, M
n: 1.0% or less, P: 0.025% or less,
S: 0.0050% or less, N: 0.050% or less, and optionally Ti: O, O 1 to 1.0% and/or Al: 0.01 to 2.0%, preferably Q: 0.
This is a highly corrosion-resistant precipitation-hardening Ni-based alloy that exhibits excellent SCC resistance in a harsh environment where elemental S is mixed in a sour gas environment having a composition of 5 to 2.0%.

Furthermore, if the above-mentioned component system is limited to the range expressed by the following formula (1), the structure will be stabilized, a homogeneous alloy with extremely excellent hot workability will be obtained, and the SCC resistance will also be good. This is achieved even more effectively.

Ni-2(Mo+1.5(Cr-12)] 3 (N
b+1.5Ti+0.5(Al-0,5) l ≧O・
(11) Thus, according to the present invention, even at high temperatures of up to 200°C, it exhibits excellent SCC resistance and hydrogen cracking resistance in a harsh environment in which simple S is mixed in a sour gas environment. A precipitation hardening Niy!E alloy is obtained.

(Function) Next, the reason why the component composition is limited as described above in the present invention will be explained.

Cr: Cr is γ゛,7 along with Mo, Ni, Fe, etc.
"Constitutes an austenite matrix for precipitation hardening. In the conventional sour gas environment, it is said to be effective for corrosion resistance, especially at high temperatures, but in this environment, it contributes to a corrosion-resistant film in balance with M2S Ni etc. For this purpose, Cr11
2% is necessary, but from the viewpoint of tissue stability, Cr525
%.

Mo: Mo is an essential element for forming a corrosion-resistant film in the relevant environment, and when temperatures up to 200° C. are targeted, Mo≧5.5% is required. However, it is unnecessary to add a large amount from the viewpoint of economic efficiency, etc., and Mo is set to <9.0%.

In addition, W is generally considered to have the same effect as Mo, and considering the atomic weight of W, it is usually said that 2% W can be substituted for 1%Mo, but in this component system, the component It is virtually impossible to add W as a component. However, Mo
It is possible to replace a part of with W.

Ni: Ni is an essential element for precipitation hardening of To and T″, but it also plays an important role in strengthening the corrosion-resistant film in the relevant environment.For this purpose, N + 945% is required, but the balance with other components and the resistance N4560 from the perspective of hydrogen cracking
%.

Fe: Fe is an essential element for improving To and γ1 precipitation hardenability. For that purpose, Fe≧5.0% is required,
Considering the balance with other components, Fc≦25%.

Nb: In this alloy system, Nb is mainly T”-NiJb (Do
□Precipitation hardening of type 2 regular structure) provides high strength and high corrosion resistance. This is because stress concentration is small due to the deformation mechanism unique to γ'', and it has excellent pitting corrosion resistance.For this purpose, Nb≧4.0% is required, but adding a large amount
Nb is used to precipitate undesirable second phases such as the formation of es phase.
S shall be 2.0%.

Ti: When Ti is added in a large amount, it forms a γ'' phase, but in this alloy system, if it is added in a small amount, it has the effect of promoting T'' precipitation. Therefore, it is not necessary to add a large amount of TiS.
It shall be 2.0%. To obtain this effect, the lower limit of Ti addition is set to 0.01%.

Al: Al is an effective deoxidizing agent when 8Q≦0.5%.
Furthermore, it contributes to tissue stabilization. Al≧0.01% is required to obtain these effects. Also γ” or γ
Although Al≧0.5% may be acceptable since it also contributes to the precipitation of the ' phase, Al>2% is rather unfavorable for improving strength.

C:C becomes coarse MC type (M:Nb
, Ti, etc.) to form carbides, resulting in a significant decrease in ductility and toughness. Therefore, it is preferable to set C50°020%.

Sis Mn: Sis Mn is usually added as a deoxidizing agent and desulfurizing agent, but adding a large amount leads to a decrease in ductility and toughness.
The content is preferably 2.0%.

P, S: P and S are impurities that are inevitably mixed,
If present in a large amount, it will adversely affect hot workability and corrosion resistance, so it is preferable that P≦0.025% and S≦0°0050%.

NUN is MN type (M: Nb, Ti
etc.) N≦0.050 because the formation of nitrides impedes precipitation hardening and reduces ductility and toughness.
% is preferable.

In preferred embodiment B of the present invention, the alloy composition may be further limited by the following formula (1), but in that case, the hot workability will be even better, and the microstructure will be further improved. Since it becomes homogeneous, corrosion resistance such as SCC resistance is also synergistically improved.

Ni-2(Mo+1.5(Cr12)) 3
(Nb+1.5Ti+0.5(Al-0,5)) ≧
0...(11) Even in the alloy system of the present invention, Cus C0% R[!M
, Mg, Cas Y, etc. may be added as appropriate, but when they are added, the following restrictions apply.

Cu contributes to the formation of a corrosion-resistant film in this environment, but adding a large amount hinders the precipitation hardening of γ' and γ'', so Cu
3P is preferably 0%.

Although Co is effective in improving hydrogen cracking resistance, adding a large amount leads to a decrease in ductility and toughness, so it is preferable to set the Cas content to 5.0%.

The addition of at least one of REM, Mg, Ca, and Y improves thermal processability, but the addition of 0.1θ% each
, 0.10%, 0.10%, or 0.20%, conversely, low melting point compounds tend to be produced and processability decreases.
0.10%, 0.10%, 0.10%, 0.2 respectively
It is preferably 0% or less.

In addition, V, Zr, Ta, Hf, etc. are said to contribute to the stabilization of C, and may be added up to a total of 2.0% even in the present alloy system according to the present invention.

Furthermore, since B, Sn, Zn, Pb, etc. do not have any particular adverse effects in trace amounts, their presence as impurities is allowed up to a total of 0.10%.

Next, the present invention will be explained in more detail based on examples.

Examples Each alloy having the chemical composition shown in Table 1 was tm m 1&
The material was made into a plate material by hot working, and after the specified solution treatment shown in Table 2, it was subjected to various aging treatments to achieve the specified strength of 77 kgf/mm" or more at 0.2% proof stress (room temperature). The following test specimens were taken from this plate material,
Each test was conducted under the following test conditions.

The results are summarized in Table 2.

Strain test Temperature: Room temperature test piece: 4. Ons+φX GL = 20mm
Strain rate: I Mixed liquid: 20%
NaCQ -1,0g/pS40atm, llI25
-20at Temperature: 200°C Immersion time: 500h Test piece: 2tX10w x75j! (ms),
R0,2511 Non-chip added reaction crab 1.0 σy ■i Serum meter NACE conditions: 5XNaCQ-0,5χclhCO
OIl-1atm 1lts, 25℃ Test piece: Carbon steel coupling, 2t X Low X 75 j! (am), R0,
Added stress with 250 notches = 1.0σy Immersion time: 1000h In the above corrosion tests (■) and (■), those in which cracking, pitting corrosion, or local corrosion did not occur are ``O'', and those in which they occur are ``×''.
”.

(Effects of the Invention) Coz As described above, according to the present invention, a high-strength oil well entrance and bottom member with excellent corrosion resistance, that is, stress cracking resistance and hydrogen cracking resistance can be obtained.

Therefore, the present invention is of great benefit to the industry.

Claims (4)

[Claims] (1) In weight%, Cr: 12-25%, Mo: 5.5% or more, less than 9.0%, Nb: 4.0-6.0%, Fe: 5.0-25%,
Ni: 45-60%, C: 0.050% or less, Si: 0
．． 50% or less, Mn: 1.0% or less, P: 0.025%
The following is a highly corrosion-resistant precipitation hardening type Ni having a composition consisting of S: 0.0050% or less and N: 0.050% or less, which exhibits excellent SCC resistance in a harsh environment where S alone is mixed in a sour gas environment. Base alloy. (2) In weight%, Cr: 12 to 25%, Mo: 5.5% or more but less than 9.0%, Nb: 4.0 to 6.0%, Fe: 5.0 to 25%,
Ni: 45-60%, C: 0.050% or less, Si: 0
．． 50% or less, Mn: 1.0% or less, P: 0.025%
The following composition has a composition consisting of S: 0.0050% or less, N: 0.050% or less, and Ti: 0.01 to 1.0%, and is excellent in a harsh environment where S alone is mixed in a sour gas environment. A highly corrosion-resistant precipitation-hardening Ni-based alloy that exhibits SCC resistance. (3) In weight%, Cr: 12-25%, Mn: 5.5% or more but less than 9.0%, Nb: 4.0-6.0%, Fe: 5.0-25%,
Ni: 45-60%, C: 0.050% or less, Si: 0
．． 50% or less, Mn: 1.0% or less, P: 0.025%
Below, it has a composition consisting of S: 0.0050% or less, N: 0.050% or less, and Al: 0.01 to 2.0%, and is excellent in a harsh environment where S alone is mixed in a sour gas environment. A highly corrosion-resistant precipitation-hardening Ni-based alloy that exhibits SCC resistance. (4) In weight%, Cr: 12 to 25%, Mo: 5.5% or more but less than 9.0%, Nb: 4.0 to 6.0%, Fe: 5.0 to 25%,
Ni: 45-60%, C: 0.050% or less, Si: 0
．． 50% or less, Mn: 1.0% or less, P: 0.025%
Below, S: 0.0050% or less, N: 0.050% or less, Ti: 0.01-1.0%, Al: 0.01-2.0
%, a highly corrosion-resistant precipitation hardening Ni-based alloy that exhibits excellent SCC resistance in a harsh environment where elemental S is mixed in a sour gas environment.