JPS63137133A - Highly corrosion-resistant precipitation hardening-type ni-base alloy - Google Patents

Abstract

PURPOSE:To obtain the titled alloy having superior stress corrosion cracking resistance, etc., even in an environment in which S as a simple substance is further mixed into the conventional sour-gas environment, by providing a composition consisting of respectively prescribed percentages of Cr, Mo, Nb, Fe, Ni, C, Si, Mn, P, S, and N. CONSTITUTION:A highly corrosion resistant precipitation hardening-type Ni-base alloy of this invention has a composition consisting of, by weight, 12-22% Cr, 9.0-15% Mo, 4.0-6.0% Nb, 5.0-20% Fe, 50-60% Ni, <=0.050% C, <=0.50% Si, <=1.0% Mn, <=0.025% P, <=0.0050% S, and <=0.050% N. This Ni-base alloy has such a high strength as to be outstandingly excellent in corrosion resistance, that is, stress corrosion cracking resistance and hydrogen cracking resistance even under the above-mentioned severe environment and, as a result, it is useful for pit-mouth and bottom-hole members for oil well.

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
For oil wells, it has good stress cracking resistance and hydrogen cracking resistance in an environment where sulfur (S) is mixed as a single substance rather than in the form of sulfides such as FeS and NiS. This invention relates to a highly corrosion-resistant precipitation hardening Ni-based alloy used for members (particularly mineheads and pile bottom 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 performance of i-based alloys is particularly improved by increasing the Cr, Mo, and W contents, so an alloy component system suitable for the target corrosive environment is selected while taking these into account.

Furthermore, the strength is 77 kgf at 0.2% yield strength.
A high strength of 91 kgf/arm" or higher is required. Therefore, for these alloy component systems, tubular members such as tubing, casings, and liners are made to have high strength by cold working. In order to increase the strength of pile bottom members, etc., precipitation hardening of intermetallic compounds such as To or γ'' is used.

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 Ni-based alloys no longer have sufficient corrosion resistance.

(Problem to be solved by the invention) As mentioned above, sour gas environment (H2S-Co□-Cf2
-) and sulfur (S), N1-based alloy members exhibit a unique form of corrosion, but the applicant has developed an alloy that maintains good corrosion resistance even in such environments. For tubular members such as chaping, casings, and liners, alloys whose strength can be increased by cold working are disclosed in Japanese Patent Application Nos. 61-1199 and 1982-120.
This has already been proposed in issue 4.

However, even with the above alloys, if the strength cannot be increased by cold working for oil wellheads, pile bottom members, etc.
It is necessary to increase the strength by precipitation hardening of intermetallic compounds such as γ° or T1.

However, these existing precipitation hardening alloys suffer from localized corrosion or stress corrosion cracking (hereinafter referred to as rscc) in a sour gas environment containing the above-mentioned sulfur (S) as a single element.
It has been confirmed that the product generates That is,
The simple substance S depends on temperature and pressure (particularly H2S partial pressure) (S
□+ +HtS:! According to the reaction of HtS*), 3B (
SX-1, u, s, 1ids, ) oxidizes, but sulfur (S) or H2 liberated as Slm-1
If S is present, it will locally adhere to the oil well entrance and pile bottom members, causing pitting corrosion or SCC in those areas.
It was found that this leads to. This is 4S+4H,S;l! 3
This is thought to be because the ozsA degree locally increases due to the reaction of H2S+H,504, and at the same time, ntsa is generated to lower the pH. In order to exhibit sufficient corrosion resistance in an environment with such a unique form of corrosion,
In the case of tubular members (see Japanese Patent Application No. 1199/1986 and others)
Similarly, it is essential to form a corrosion-resistant skin H with even higher strength and better repairability than before in precipitation hardening alloys for wellhead and pile bottom members. However, existing precipitation hardening type Ni-based alloys have poor precipitation hardenability and structural stability (γ
The second phase that causes embrittlement other than °, γ''; sigma phase, La
There are restrictions on alloying elements from the viewpoint of prevention of precipitation of ves 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 (
A high-strength precipitation hardening type for oil well entrances and pile bottom members that has good stress corrosion cracking resistance and hydrogen cracking resistance even in environments where sulfur (S) is further mixed into His-Co□-C2-). An object of the present invention is to provide a Ni-based alloy.

(Means for solving the problem) Therefore, the present inventors solved the problem without impairing the precipitation hardening ability.
In order to obtain an alloy component system that provides a hard film with good repairability, the strength and repairability of the film in a sour gas environment are approximately Cr, Mo, We conducted a study focusing on the fact that Cu and Nb improve in proportion to the content of W, and that Cu and Nb are effective when they contain elemental S, and the following findings were obtained.

(1) In the case of precipitation hardening N+ base alloys for wellheads and pile bottom members, the content of Cr, MO% W, CLI, etc. is increased (and embrittlement phases such as sigma phase and Laves phase are They also remained in the coating, preventing precipitation hardening of γ'' and γ'', and at the same time, did not effectively improve the strength or repair ability of the coating itself.

(2) As a result of further studying the mechanism, the present inventors found that Mo: 9.0 to 15%, Nb: 4. O~6.0
By combining specific component systems including A corrosion-resistant film with good repair ability is obtained, and exhibits 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: 12-22%, Mo:
9.0-15%, Nb: 4.0-6.0%, F
e: 5.0-20%, Nt: 50-60%,
C: 0.050% or less, St: 0.50% or less,
Mn: 1.0% or less, P: 0.025% or less, S: 0.0050% or less, N: 0.0
50% or less, further optionally Ti: 0.01 to 1.0% and/or
It is a highly corrosion-resistant precipitation-hardening Ntli alloy that exhibits excellent SCC resistance in a harsh environment where elemental S is mixed in a sour gas environment having a composition consisting of 0.01 to 2.0% of 8Q.

Furthermore, if the above-mentioned component system is limited to the range of formula 11 below, the m-weave will be stabilized, a homogeneous alloy with extremely excellent hot workability will be obtained, and the SCC resistance will also be good, thus achieving the object of the present invention. This is achieved even more effectively.

Ni-2(Mo+15(Cr-12)l-4(Nb+
1.57i+ 0.5 (Al -0,5) l ≧0
(1) Thus, according to the present invention, 200
Excellent SC resistance even under high temperatures of 'C or higher, even in harsh environments where sML bodies are mixed with sour gas environments.
A precipitation-hardening Ni-based alloy is obtained that exhibits C properties and hydrogen cracking resistance.

(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.
'Construct austenitic matrix links for precipitation hardening. In the conventional sour gas environment, it was 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 A0, Ni, etc. For this purpose, Cr21
2% is necessary, but from the viewpoint of tissue stability, Cr522
%.

Mo: Mo is an essential element for forming a corrosion-resistant film in the relevant environment, and when the temperature is 250° C. or lower, Mo≧9.0% is required. However, the addition of large amounts of sigma phase, Lev
In order to facilitate precipitation of the es phase and to reduce hot workability, the Mo content is set at 515%.

Note that W is generally considered to have the same effect as Mo, and considering the atomic weight of W, 2% W to 1% Mo is usually used.
However, it is virtually impossible to add a high amount of W due to the composition of the component system. However, it is possible to partially replace Mo with W.

Ni: Ni is an essential element for To and γ" precipitation hardening, but it also plays an important role in strengthening the corrosion-resistant film in the relevant environment. For this purpose, Ni ≥ 50% is required, but it is necessary to balance it with other components. and Ni560 from the viewpoint of hydrogen cracking resistance.
%.

Fe: Fe is an essential element for improving To and γ″ precipitation hardenability.For this purpose, Fe≧5.0% is required, but
Considering the balance with other components, Fe≦20%.

Nb: In this alloy system, Nb is mainly To-Ni3Nb (D
Otz-type regular structure) precipitation hardening provides high strength and high corrosion resistance. This is because the stress concentration is small due to the deformation mechanism unique to T'', and it has excellent pitting corrosion resistance.For this purpose, Nb≧4.0% is required, but adding a large amount of La
N to precipitate undesirable second phases such as the formation of ves phase.
b≦6.0%.

Ti: When added in a large amount, Ti forms a γ' phase, but in the present alloy system, a trace amount of Ti 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 serves as an effective deoxidizer when M≦0.5% and further contributes to stabilizing the tissue. M≧0.01% is required to obtain these effects. Since it also contributes to the precipitation of γ'' or γ'' phase, M≧0.5% may be acceptable, but Al>2% is rather unfavorable for improving strength.

C:C becomes coarse MC type (M:N
b.

(Ti, etc.) forms carbides, significantly reducing ductility and toughness. Therefore, it is preferable to set C50°020%.

Sis Mn: Sis Mrl is usually added as a deoxidizing agent and desulfurizing agent, but adding a large amount leads to a decrease in ductility and toughness.
It is preferable to set the S content to 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%.

N: N is set at N≦o, oso% because addition of a large amount of N hinders To, T' precipitation hardening due to the formation of MN type (M: Nb5Ti, etc.) nitrides and reduces ductility and toughness.
It is preferable that

In the preferred embodiment M of the present invention, the alloy composition may be further restricted by the following formula, but in that case, the hot workability will be even better, and the structure will be more homogeneous. Therefore, corrosion resistance such as SCC resistance is also synergistically improved.

Ni-2 (gate o+1.5 (Cr-12)) -4 (N
b + 1.5 Ti + 0.5 (M - 0,5) l ≧
0 . .
M, Mg, Ca, Y, etc. may be added as appropriate, but
When adding them, 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 To and T''.
It is preferable to set it as ≦2.0%.

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 that Co≦5.0%.

REM, Mg, Ca, and Y improve hot workability by adding at least 1f11, but each
If the content exceeds 0%, 0.10%, 0.10%, or 0.20%, low melting point compounds tend to be produced and processability decreases, so if the content exceeds 0.10%, 0.10%, or 0.20%, respectively. 10%, 0
．． It is preferably 20% 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.

Further, B, Sn, Zns, Pb, etc. have no particular effect in trace amounts, so 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 After preparing each alloy having the chemical composition shown in Table 1, it was made into a plate material by hot working, and after the prescribed solution treatment shown in Table 2, it was subjected to various aging treatments to achieve 0.2% yield strength. A predetermined strength of 77 kgf/+sm" or more was obtained at (room temperature). Test pieces for the following tests were taken from this plate material, and each test was conducted under the following test conditions.

The results are summarized in Table 2.

Temperature 2. Room temperature test piece: 4. Oo++*φX GL = 20+
m Strain rate: 1xto-'s-' Test items: Tensile strength, elongation, reduction of area ■Aim W 仄temperature 20℃ Test piece: 10 x 10 x 55mm -2,
0m+w■Notched test item; Impact value■U Melting night: 20% NaCQ 1
．． Og/IS-10a tm, Hls-20atm
co.

Temperature: 250°C Immersion time: 500h Test piece: 2txlOw ×751' (mm),
R0, 25U notched additional stress = 1.0 σy ■ Two dishes of water wiped clean NACE conditions: 5χNaCQ-0,5χC1hCOO
H-1atm HzS, 25℃ Test piece: Carbon tear coupling, 2t x 10w x 751 (mm), R0,25
Additional force with 0 notch 1.0σy Immersion time: 1oooh In the corrosion tests of ■ and ■ above, "O" indicates that no cracking, pitting corrosion, or local corrosion occurred, and "×" indicates that cracking or pitting corrosion did not occur.
”.

(Effects of the Invention) As described above, according to the present invention, it is possible to obtain a high-strength oil well and bottom hole member that is excellent in corrosion resistance, that is, stress cracking resistance and hydrogen cracking resistance.

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

Claims (4)

[Claims] (1) In weight%, Cr: 12-22%, Mo: 9.0-15%, Nb: 4
．． 0 to 6.0%, Fe: 5.0 to 20%, Ni: 50 to
60%, C: 0.050% or less, Si: 0.50% or less, Mn: 1.0% or less, P: 0.025% or less, S: 0
．． 0.050% or less, N: 0.050% or less, and exhibits excellent SC resistance C in a harsh environment where elemental S is mixed in a sour gas environment. (2) In weight%, Cr: 12-22%, Mo: 9.0-15%, Nb: 4
．． 0 to 6.0%, Fe: 5.0 to 20%, Ni: 50 to
60%, C: 0.050% or less, Si: 0.50% or less, Mn: 1.0% or less, P: 0.025% or less, S: 0
．． 0.0050% or less, N: 0.050% or less, Ti: 0.
It has a composition consisting of 01 to 1.0%, and has excellent S resistance in harsh environments where S is mixed into a sour gas environment.
A highly corrosion-resistant precipitation-hardening Ni-based alloy that exhibits CC properties. (3) In weight%, Cr: 12-22%, Mo: 9.0-15%, Nb: 4
．． 0 to 6.0%, Fe: 5.0 to 20%, Ni: 50 to
60%, C: 0.050% or less, Si: 0.50% or less, Mn: 1.0% or less, P: 0.025% or less, S: 0
．． 0050% or less, N: 0.050% or less, M: 0.0
Has a composition of 1 to 2.0%, and has excellent SC resistance in harsh environments where single S is mixed in with sour gas environments.
A highly corrosion-resistant precipitation-hardening Ni-based alloy that exhibits C properties. (4) In weight%, Cr: 12-22%, Mo: 9.0-15%, Nb: 4
．． 0 to 6.0%, Fe: 5.0 to 20%, Ni: 50 to
60%, C: 0.050% or less, Si: 0.50% or less, Mn: 1.0% or less, P: 0.025% or less, S: 0
．． 0.0050% or less, N: 0.050% or less, Ti: 0.
A highly corrosion-resistant precipitation-hardening type Ni that has a composition of 0.01 to 1.0% and Al: 0.01 to 2.0%, and exhibits excellent SCC resistance in a harsh environment where S is mixed in a sour gas environment. Base alloy.