JPS61207550A - Martensitic stainless steel for acidic oil well - Google Patents

Abstract

PURPOSE:To obtain a martensitic stainless steel for an oil well having superior resistance to sulfide stress corrosion cracking by adding a specified amount of B to a 13Cr martensitic stainless steel. CONSTITUTION:The composition of a martensitic stainless steel for an oil well is composed of, by weight, 0.1-0.25% C, <1% Si, <1% Mn, 12-14% Cr, 0.001-0.006% B and the balance Fe with inevitable impurities. The composition may further contain 0.5-4% Mo and/or 0.5-6% Ni as required.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to steel for oil country tubular goods used in oil wells and gas wells for crude oil and natural gas.
), carbon dioxide (C(h)), hydrogen sulfide (HffiS)
The present invention relates to a martensitic stainless steel with excellent sulfide stress corrosion cracking resistance and suitable for acid oil wells including the like.

Conventional technology In recent years, due to the soaring price of crude oil and the depletion of petroleum resources, the development of deep oil and gas wells, which were previously undeveloped, and acid oil and gas wells, whose development had once been abandoned, have become increasingly important. Development is now underway. Such oil and gas wells often contain large amounts of chloride, CCh, and HtS, and therefore it is necessary to use steel that has sufficient corrosion resistance for such environments.

Conventionally, general oil country tubular goods are made of carbon steel or, for example, Japanese Patent Application Laid-Open No. 58
-147545 and JP-A No. 58-199850, it has been common to use low-alloy steels, but these generally have extremely poor CO2 corrosion resistance.
It is inherently unsuitable for use in the above-mentioned environment, and the reality is that it cannot withstand use unless it is combined with the incomplete and costly anti-corrosion method of injection of an inhibitor. Therefore, as steel used in oil wells and gas wells in the above-mentioned environments, there is a strong desire for high-alloy steel materials that exhibit excellent corrosion resistance without using means such as injection of inhibitors.

By the way, known high alloy steels with excellent corrosion resistance include 13cr martensitic stainless steel, duplex stainless steel, high Ni austenitic stainless steel, and Ni-based alloys. However, 13cr martensitic stainless steel is especially resistant to C.
It is currently the most resistant to O3 corrosion, and its yield point can be varied over a wide range of 50 to 70 kll/fnl by combining heat treatment and carbon content, and it is also inexpensive. Widely used.

Problems to be Solved by the Invention As mentioned above, martensitic stainless steel has various advantages, but the biggest problem when using it in oil wells in the environment described above is that cz"-(chloride ), C0., and H, S, sulfide stress corrosion cracking (SS
C). That is, if conventional martensitic stainless steel is used as it is in oil wells in the above-mentioned environment, there is a risk that SSC will occur, so there is a strong desire to develop martensitic stainless steel with excellent SSC resistance.

This invention was made against the background of the above circumstances, and as mentioned above, martensitic stainless steel exhibits excellent SSC resistance even in an environment containing a large amount of chloride, C(h:l Has). The purpose is to provide the following.

Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors conducted various experiments and studies on additive elements for 13C'r martensitic stainless steel, and found that a trace amount of B (boron)
It has been found that SSC resistance can be improved by adding .

That is, the inventors have determined that CQ, lO ~ 0.20%, C
r13%, NiO~2.5%, MoO~1.0
%, B For steel whose alloy composition was changed in the range of 0.0005 to 0.0060%, the specimen size was 2.5 am thick.
A U-bent specimen with a width of 151 mm and a length of 75% g and a bending radius of 4R was heated to 5% NaC1-0.7aim CO2 at room temperature.
-0.03 atm When the relationship between the yield strength and the occurrence of cracking was investigated when immersed in a Has-Nt aqueous solution for two weeks, as shown in Fig. 1, it was found that the B content was 0.03 atm. ootos
In the above case, even with a proof stress of 60 to 70 kgfAd, no cracking occurs, and the ssc resistance and property are 0. It has been found that the improvement can be achieved by adding more than ootos.

SSC is a type of hydrogen cracking in which hydrogen generated by a corrosion reaction penetrates into the steel and cracks under stress.
Material-side factors that improve SSC resistance are mainly (1) generation of a surface film that suppresses hydrogen intrusion, and (2) formation of a large number of trap sites that reduce the amount of intruded hydrogen below the cracking limit. (3) Since the SSC of martensitic stainless steel mainly has many intergranular cracks, the above three points can be considered, but as mentioned above, the addition of a small amount of B can strengthen the synmartin. The reasons why the SSC resistance of site-based stainless steel improves are the above (2),
This seems to be due to (3).

Specifically, the martensitic stainless steel of the first invention of the present application has a C0. lo-0,25chi1. Contains less than 1.0% Si, less than 1.0% Mn, 12.0 to 14.0% Cr, 0.0010 to 0.0060% B, and the remainder is F.
It is characterized by consisting of e and unavoidable impurities.

, and the full version of the second invention of the present application. Ten, site stainless steel is C0.03~0.20 inch, Si is less than 1.0 inch,
Mn less than 1.0%, Cr 12.0-14.0%,
B0. Contains ooto~0.0060chi, and further MO
It is characterized by containing 1 m or 2 of 0.5 to 4.0 mm and 0.5 to 6.0 mm of Ni, with the remainder consisting of Fe and unavoidable impurities □.

DETAILED DESCRIPTION OF THE INVENTION The reasons for limiting the components of the martensitic stainless steel of the present invention will be explained below. □C:
C is an important element related to the strength of martensitic stainless steel, and when Ni is not added (that is, in the case of the first invention), C is 0. If the IO is less than 0.25%, the strength required for deep oil wells cannot be obtained, and if the In one invention, C
was within the range of 0.010 to 0.25 inches. In addition, when adding Ni in the second invention, it is possible to compensate for the decrease in strength due to the reduction in the amount of C, and when the maximum amount of Ni added is 6, the strength is ensured if Ct is 0.03% or more. However, if Ct exceeds 0.20%, the workability deteriorates, so in the second invention, C is reduced to 0.03 to 0.20%.
was within the range of

S I + Mn: These are all elements necessary for deoxidation in normal steelmaking, but each at 1.0%
Since workability deteriorates if the content exceeds 1.0%, it was decided to limit both Si and Mn to 1.0% or less.

Cr: Cr is the main alloying element that determines the corrosion resistance of stainless steel, and at least 12.0% or more is required to provide corrosion resistance to CO2, but on the other hand, if it is excessively contained, ferrite 120-14.
It is within the range of 0%.

B: B is a characteristic element in the steel of the present invention, and when added in an amount of 0.0010% or more, the SSC resistance can be significantly improved. Even if the B level exceeds 0.0060%, the SSC resistance improvement effect is maintained, but solidification cracks may occur during continuous casting, etc., so the B level is 0.0%.
010-1), within the range of 0060chi.

Steel containing the above components is subjected to heat treatment applied to ordinary martensitic stainless steel, that is, air or water cooling from a temperature of about 900°C or higher, and then within a range of about 400 to 800°C. Temper at a temperature of
Martensitic stainless steel with excellent SSC resistance can be obtained by performing so-called quenching and further resetting treatment, but in the case of the second invention, in addition to the above-mentioned components, Mo 0.5 to 4.0 %, Ni 0.5-6
．． The effects of this invention can be further improved by adding 0% of one or two types of yuzu. The effects of adding these elements and the reasons for their limitations are as follows.

Mo: Mo is Ct- (chloride) -CO2-H2S
'7, it contributes to improving SSC resistance by improving the pitting corrosion resistance and crevice corrosion resistance of Boundary F, and in order to achieve this effect, it is necessary to add 0.5% or more.
If it exceeds 40 inches, the effect becomes saturated and becomes uneconomical, and the formation of ferrite becomes noticeable. Therefore M.O.
was within the range of 05 to 4.0 inches.

Ni: Ni is a ferrite-forming element Cr and MO
Added in a balanced amount, it stabilizes the martensitic structure, promotes the formation of retained austenite, and is effective in improving SSC resistance. Furthermore, Ni has the effect of improving strength, and the addition of Ni reduces Ct required to ensure strength, thereby indirectly improving SSC resistance. However, if the amount of Ni is less than 0.54, these effects will not be sufficient, and on the other hand, if it is added in excess of 60q6, no further significant improvement in the effect can be expected and will only lead to an increase in cost. It was set within the range of .0%.

Example rQ) Martensitic stainless steel having the components shown in &1 to A16 in Table 1 was melted, hot rolled, and heated to 980°C.
The yield strength was adjusted to a range of 60 to 70 k%yl by quenching and tempering at 670 to 750°C. A test piece with a thickness of 2 mm, a width of IO, and a length of 75 nm was cut from the obtained steel, and a stress corresponding to the yield point was applied using a 3-point bending test jig, and the test piece was heated to 8% Cot -0 at 130 °C. 5%Hz
S -2% C1-Medium K 20 days 1! it fl
! did. The crack occurrence status according to this test, that is, SSC
Table 1 also shows the results of investigating the cracking situation.

Table 1 As is clear from Table 1, none of the invention steels Al to 8 exhibited SSC cracking and exhibited good SSC resistance, whereas the comparative steel A9, which was outside the invention composition range, exhibited good SSC resistance. - No. 15, cracks occurred in all cases. In particular, cracking occurred when the B content was insufficient (comparative steel 410, 14.15) even when the amounts of C2Cr, Mo, and Ni were within appropriate ranges. It is found to be effective in improving sexual performance.

The reason why cracks occurred in the Al 2 comparison steel is considered to be because the ferrite phase appeared because the amount of Ni was not sufficient to match MO and Ct. Also A
In steel No. 16, cracks occurred during solidification due to the high B content.

Effects of the Invention As is clear from the above examples, the martensitic stainless steel of the present invention has Ct-(chloride)-c0
．． -Has excellent sulfide stress corrosion cracking resistance even under HtS
It can be suitably used as oil country tubular goods in acidic oil wells in harsh environments containing large amounts of.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a correlation diagram showing the relationship between proof stress and B amount exerted on SSC.

Claims (2)

[Claims] (1) C0.10-0.25% (weight%, same below),
Si less than 1.0%, Mn less than 1.0%, Cr12.0~
14.0%, B0.0010 to 0.0060%, and the remainder is Fe and inevitable impurities. (2) C0.03-0.20%, Si less than 1.0%, M
n less than 1.0%, Cr12.0-14.0%, B0.0
010 to 0.0060%, and Mo0.5 to 4
．． A martensitic stainless steel for acidic oil wells, characterized in that it contains one or two of 0% and 0.5 to 6.0% of Ni, with the remainder consisting of Fe and inevitable impurities.