JPS58133351A - Steel for oil well excellent in sulfide stress corrosion crack resistance - Google Patents

Abstract

PURPOSE:To provide steel for an oil well having high yield strength and excellent sulfide stress corrosion crack resistance, containing C, Si, Mn, Cr, Co and at least one kind or more of Ca, Mg, Y and a lanthanide element respectively in a predetemined ratio and having an annealed martensite structure mainly. CONSTITUTION:The titled steel for an oil well contains, on the basis of wt%, 0.15-0.50% C, 0.1-1.0% Si, 0.3-1.5% Mn, 0.6-2.0% C, 0.3-5.0% Co, 0.001- 0.10% sol. Al and one kind or more Ca, Mg, and Y and lanthanide element and comprises the remainder Fe and inevitable impurities. In this case, in the contents of each components as the aforementioned inevitable impurities, it is necessary to adjust P to 0.025% or less, Si to 0.010% or less, Mo to 0.05% or less and W to 0.05% or less. This steel for oil well is has high yield strength of at least 70kg/mm.<2> and sulfide stress corrosion crack resistance and is especially suitable for a steel pipe used in an oil well or a gas well and a material used for preparing various valves.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention provides high strength with a yield strength of near 0 kg/- or more;
It has excellent sulfide stress corrosion cracking resistance (hereinafter referred to as 5SCC resistance), and is particularly suitable for steel pipes used in oil and gas wells, such as drill nodules for drilling, tubing and casing for production, and also for oil and gas wells. This relates to steel for oil wells, which is suitable for use in manufacturing sucker rods and various valves used in wells.

In recent years, oil and gas fields have been actively developed in order to cope with the deteriorating energy situation. There is a strong need to develop oil and gas fields in the region. However, as the depth of the well increases, the pressure from the crude oil and gas produced, the soil pressure from the strata, and the tensile load due to the weight of the steel used also increase, so it is difficult to operate under these sour environments. The development of deep oil and gas fields requires steel that has both high strength to withstand these forces and excellent 5SCC resistance.
It is said that it is necessary to use steel that has a yield strength of kg/mJ or more and a "cracking limit ratio" of 70 to 75% or more in terms of 5SCC resistance.

Furthermore, the "cracking limit ratio" referred to here is defined as sulfide stress corrosion cracking (hereinafter referred to as 5SCC) occurring when stress exceeding a certain value acts on steel materials used in a humid sour environment containing hydrogen sulfide, etc. This is a type of environmental embrittlement phenomenon that occurs when Since it depends on the strength, the ratio of the yield strength to the critical stress for 5SCC generation, i.e. (critical stress for SSCC generation)/(
Yield strength) x 100 (%).
The 5SCC resistance is evaluated based on the "cracking limit ratio". Therefore, the higher the cracking limit ratio, the higher the steel's resistance to 5SCC.
For example, if the cracking limit ratio is 100,
%, that is, when the critical stress for 5SCC occurrence is close to the yield strength of the steel material, there is no need to consider 5SCC when using the steel material. However, if the critical cracking ratio is small, the steel material is Therefore, even if the steel material has high strength, it can only be used at a stress below the 5scc critical stress. What value is required as the cracking limit ratio that indicates satisfactory 5SCC resistance is determined by the safety factor in steel material design and cannot be definitively stated, but generally speaking, the cracking limit ratio is 70 to 75% or more. It is said that a ratio is necessary.

On the other hand, various types of steel for oil wells have been proposed that have a yield strength of near 0 kg/- or more, but when the strength of the steel increases, 5scc tends to occur more easily. Currently, all of these conventional high-strength oil well steels have a cracking limit ratio of less than 70 inches.

From the above-mentioned viewpoint, the present inventors conducted research to obtain oil well steel that has high strength and excellent 5SCC resistance required for the development of deep oil and gas fields in sour environments. As a result, in terms of weight, C: 0.15-0.50%
, Si: O, l~1.0%, Mn: 0,3~1.
5%, Cr 20,6 ~ 2.0
%, Co: 0.3-5.0%,
sot, Al: 0.001~O, l 0%, and Ca.

One or two of Mg, Y, and lanthanide elements
More than species: Contains O, OOO 3 to 0.10%, and if necessary, Cu:O, 1 to 1.0%, Ni20,
1-1, 0%, Nb: 0.01-0.15%, V:
O, 01-050%, Zr: 0.01 NO, 5
0%, Ti:O,OOl~0.10%, and B:
O,0O03~0. One or two of OO50%
Contains more than seeds, the remainder consists of Fe and unavoidable impurities,
And the contents of P, S, Mo, and W as unavoidable impurities are respectively P: 0025% or less, S: 0
．． 010% or less, Mo20, 05% or less, W: 0.05
% or less, and has a structure mainly composed of tempered martensite, it has a yield strength of 70 kg/- or more and a cracking limit ratio of 75 inches or more, and therefore, this steel can be used for oil well applications. As a result, they discovered that it exhibited extremely superior performance.

This invention was made based on the above knowledge, and the reason why the component composition range was limited as described above will be explained below.

(a) C The C component has the effect of increasing the strength of steel and improving hardenability and tempering resistance, but if its content is 0.15
If the amount is less than 0%, the desired effect cannot be obtained;
If the content exceeds 50%, quench cracking will increase and toughness will deteriorate, so the content should be reduced to 0.1%.
It was set at 5 to 0.50%.

(b) The 5i Si component has a deoxidizing effect and also has an effect of improving the strength and hardenability of steel, but if its content is less than 0.1%, the desired effect cannot be obtained; 1.0%
If the content exceeds 0.1 to 1.0, the crystal grains will become coarse and the toughness will deteriorate. ′
It turned out to be 0%.

(c) Mn The Mn component has a deoxidizing effect like Sl, and also has the effect of improving the strength and toughness of steel, but if its content is less than 0.3%, the desired effect will not be achieved. Not obtained,
On the other hand, if the content exceeds 1.5%, the 5SCC resistance, that is, the cracking limit ratio, and toughness will deteriorate, so the content was determined to be 0.3 to 1.5%.

(d) Cr The Cr acid component has the effect of improving the strength and tempering resistance of steel, but if its content is less than 0.6%, the desired effect cannot be obtained; If the content exceeds 0.06 to 20%, the toughness will deteriorate, so the content was set at 0.6 to 20%.

(e) C.

5SCC is a type of hydrogen embrittlement that occurs when hydrogen generated by a corrosion reaction on the steel surface penetrates into the steel, and therefore 5SC
Suppression of hydrogen intrusion is considered to be an effective means of preventing C. Since the COC component has the effect of suppressing hydrogen intrusion in a sour environment, the inclusion of co is essential to ensure excellent 5SCC resistance (cracking limit ratio). But C.

If the content is less than 0.3%, the desired 5SCC resistance cannot be obtained, so it is necessary to contain 0.3% or more.
Even if the content exceeds 5.0%, no further improvement effect will be obtained, and in consideration of economic efficiency, the content should be reduced to 0.3 to 50%.
'

(fl sot-M The sot-M component has a deoxidizing action and a grain refining action, but if its content is less than 0.001%, the desired effect 4. on the above action lO- cannot be obtained; If the content exceeds 0.10%, the amount of nonmetallic inclusions will increase and the steel will become brittle.
It was set as 0chi.

(g) C”+ Mgy Yt and lanthanide elements These components have 5SCC resistance in coexistence with CO.
However, if the content is less than 3% O, OOO, the desired excellent 5scc resistance cannot be ensured, so it is necessary to contain 3% or more of O, OOO. However, if the content exceeds 0.10%, the 5SCC resistance tends to be laborious, so the content was set at 3 to 0.10%.

(h) Cu The Cu component has 5SC resistance provided by the CO acid component.
Since it has the effect of increasing the effect of improving C properties (cracking limit ratio), it is included as necessary when even higher 5SCC resistance is required, but if the content is less than 0.1%, the desired The effect of improving S8C'C resistance cannot be obtained, and on the other hand, even if the content exceeds 1.0 inch, no further improvement effect will be obtained, but rather it will cause deterioration of workability, so the content should be It was set as 01 to 1.0ch.

(i) Ni, Nb, V, Zr, Ti, and B
Since these components have a uniform effect of improving the strength of steel, they are included as necessary when even higher strength is required.
When the content is less than 1%, Nb: less than 0.01%, V: less than 0.01%, Zr: less than 0.01%, Ti: less than 0.001%, and B: less than O, 0003%, the desired strength improvement is achieved. No effect was obtained, while Ni:1. O%, Nb: 0.1
5%, V: 0.50%, Zr: 0.50%, T
If the content exceeds N1:0.10 and B:0.0050, the toughness will deteriorate, so the content should be adjusted to N1:01 to 1.0%, respectively.

Nb: 0°01~O, 15%, V: 0.01~050%
.

Zr: 0.01-0.50%, 'I'i: 0.0
01-0.10%.

B: O,0O03 to O,OO50%. Hereinafter, these components will be collectively referred to as reinforcing components.

(j) Unavoidable impurities P, S, Mo, and W as unavoidable impurities are P: 0.025%, 3: 0.010%, Mo:
If the content exceeds 0.05% and W: 0.05%, the steel's mechanical properties will deteriorate significantly, so the content should be reduced to P: 0.025% or less and S: 0. ．．
010% or less, Mo: 0.05 or less, W: 0.05%
Must be as follows. In particular, P not only segregates at grain boundaries and promotes grain boundary cracking (but also segregates in the coexistence of Mn, etc., and has the effect of degrading the 5SCC resistance of this segregated portion, so it is possible to improve the In order to ensure 5SCC properties, it is desirable to contain 5% or less of O and OO. Also, since S also has the effect of increasing sulfide inclusions and deteriorating 5SCC resistance, it is better to ensure excellent 5SCC resistance. Therefore, it is desirable that the content of S is 0.002% or less.

Next, the steel for oil wells of the present invention will be explained using examples and comparing with comparative examples.

Examples Steels 1 to 55 of the present invention and Comparative Steels 1 to 11, each having the composition shown in Table 1, were melted by a conventional melting method, cast under normal conditions, and then After hot rolling to make a hot-rolled plate with a thickness of 12 mm, the temperature: 9
After holding at 20℃ for 30 minutes, quenching with water cooling and 400~70℃
A tempering treatment was performed at a predetermined temperature within the temperature range of 0°C.

In addition, Comparative Steels 1 to 11 all have compositions in which the content of any one of the constituent components (including unavoidable impurities) (those marked with * in Table 1) is outside the scope of the present invention. It is something that we have.

Next, the yield strengths and cracking limit ratios of the resulting invention steels 1 to 55 and comparative steels 1 to 11 were measured.

The cracking limit ratio for evaluating the 5scc resistance was determined by using a constant strain type tester schematically shown in Fig. 1, using a round bar tensile test piece 1 with an outer diameter of 6.4 m at the parallel part. 05% CH3CO0H-5%) JaC1 aqueous solution saturated with hydrogen sulfide (PH
: 2.8 to 3.6), a constant tensile load was applied to the test piece by tightening the nut 3 and bending the blue ring 4.
The stress value that does not cause cracking within =14-time is determined as the 5SCC generation limit stress, and this 5S
The ratio of the critical stress for CC occurrence and the previously measured yield strength, i.e. (critical stress for SSCC occurrence)/(yield strength) x 10
It was determined by calculating 0 (%). These results are shown in Table 1.

From the results shown in Table 1, the present invention steels 1 to 55 all exhibit a yield strength of 70 kg/- or more and a cracking limit ratio of 75 inches or more, and have high strength and excellent 5 SCC resistance. is clear. In contrast, comparative steels 1 to 11
As can be seen, it is clear that if the content of any one of the constituent components falls outside the range of the present invention, at least one of the properties of strength and cracking limit ratio becomes inferior.

As mentioned above, the steel of the present invention has a yield strength near 0 kli
It has high strength of more than 1/- and excellent 5SCC resistance of more than 5% near cracking limit ratio, so it is suitable for the development of oil fields and gas fields in deep and sour environments where these characteristics are required. It exhibits outstanding performance when used in drill pipes for excavation, steel pipes such as tubing and casing for production, sucker rods, and various valves.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a constant strain type testing machine. In the drawing,
1... Test piece, 2... Container, 3... Nut. 4... proof ring. Applicant Sumitomo Metal Industries Co., Ltd. Agent Tomi 1) Kazuo

Claims (4)

[Claims] (1) C: 0.15-0.50%, Si: 0.1
~1.0%. Mn: 0.3-1.5%, Cr: 0.6-2.
0%, Co: O83-5. O*, SOl,
AIl: 0.001-0.10 we and C
a. One or two of Mg, Y, and lanthanide elements
Species or higher: Contains 3 to 0.10% O, OOO, and the remainder is free from Fe and unavoidable impurities, and the content of P, S, Mo, and W as unavoidable impurities is set to P:0, respectively.
．． 025% or less, S: 0.010cm or less 1M○: 0.0
5% or less, W: 0.05% or less (wt%
) and further has a structure mainly composed of tempered martensite.Yield strength: 'yokg/
An oil well steel with high strength and excellent sulfide stress corrosion cracking resistance. (2) C: 0.15-0.50%, Si: 0.1
~1.0%. Mn: 0.3-1.5%, Cr: 0.6-2.0
%, Co: 0.3-5.0%, somAe 20001-0.10%, and Ca. One or two of Mg, Y, and lanthanide elements
Species or higher: Contains 0.0003 to 0.10%, and further contains C
u: Contains 0.1 to 1.0%, the remainder consists of Fe and unavoidable impurities, and P as an unavoidable impurity. The content of S, Mo, and W was set to P: 0.02, respectively.
5 inches or less, S: 0.010% or less, Mo: 0.0
5% or less. W: has a composition of 0.05% or less (weight% or more),
Furthermore, a steel for oil wells has a structure mainly composed of tempered martensite, has high strength with a yield strength of near 0 kg/- or more, and has excellent resistance to sulfide stress corrosion cracking. (3) C: 0.15-050%, Si: 0.1-1.0
%. Mn: 0.3-1.5%, Cr: 0.6-2.0
%, Co: 0.3-5.0%, sot, Al
:O, OO1-0.10%, and Ca. One or two of Mg, Y, and lanthanide elements
Species or higher: Contains 3 to 0.10% of O,0O, and further N
i: 0.1-1.0%, Nb: 0.01-0.
15%, V: 0.01-0.50%, Zr:
0.01-0.50%, Ti: 0.001-0.10
%, and B: 0.003 to 0.0050%, the remainder is Fe and unavoidable impurities, and the unavoidable impurities are P, S, Mo,
and W content, P: 0.025% or less, respectively.
S: 0.010% or less. A yield strength near 0 kg/- or more, characterized by having a composition (weight%) of Mo: 0.05% or less, W: 0.05% or less, and further having a structure mainly composed of tempered martensite. Oil well steel with high strength and excellent resistance to sulfide stress corrosion cracking. (4) C: 0.15-0.50%, Si-:
0.1-1.0%. Mn: O83~1.5%, Cr: 0.6~2.0
%, Co: 0.3-5.0%, 5oLI%1: 0.
001-0.10%, and Ca. One or two of Mg, Y, and lanthanide elements
Species or higher: Contains 3 to 0.10% of O,0O, and further contains C
u: 0.1-1.0%, Ni: 0.1-1, 0%
, Nb: 0.01~0.15%, V: 0.01~
0.50%, Zr: 0.01-0.50%, T
i:O,OOl~0.10%, and B:O,
Contains one or more of 0O03 to O, OO50%, the remainder being Fe and unavoidable impurities, and P, S, and Mo as unavoidable impurities. and W content, P: 0.025% or less, respectively. S: 0.010% or less, Mo: 0.05% or less, W: 0
Sulfide stress corrosion cracking resistance having high strength with yield strength near 0 kg/- or more, characterized by having a composition (weight %) of 0.05 cm or less, and further having a structure mainly composed of tempered martensite. Superior oil well steel.