JPH01259125A - Manufacture of high-strength oil well tube excellent in corrosion resistance - Google Patents

Abstract

PURPOSE:To manufacture a high-strength oil well tube excellent in corrosion resistance by successively applying respective treatments of hardening, tempering, plastic working, hardening, and tempering to a tube of low alloy steel with a specific composition under respectively specified conditions. CONSTITUTION:Hardening is applied at 880-980 deg.C to a tube of a low alloy steel having a composition consisting of, by weight, 0.15-0.45% C, 0.1-1% Si, 0.3-1.8% Mn, <=0.01% SolAl, <=0.002% N, <=0.005% AlN, and the balance essentially Fe. Subsequently tempering is applied to the above tube at 600-730 deg.C, and also, plastic working is applied in the above temp. region once or plural times so that the total amount of strain reaches 1-20%. Further, the above tube is subjected to hardening at 800-950 deg.C and tempering at 600-730 deg.C. By this method, the high-strength oil well tube excellent in corrosion resistance, particularly in sulfide stress corrosion cracking resistance, can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing high-strength oil country tubular goods having excellent corrosion resistance, particularly resistance to sulfide stress corrosion cracking. In other words, sulfide stress corrosion cracking is called 5scc.

[Conventional technology]

Conventionally, in order to achieve both strength, 5SCC resistance, and toughness, oil country tubular goods have been basically manufactured by quenching and tempering low-alloy steel as a heath.

On the other hand, due to the recent tightening of the oil and natural gas situation, there is a marked trend toward deeper oil and gas wells, and the number of oil and gas wells that contain wet hydrogen sulfide in their output is also increasing. There is. Therefore, oil country tubular goods are now required to have high strength and excellent 5SCC resistance, more than ever before.

However, as steel materials generally increase in strength, their corrosion resistance tends to decrease, and in oil country tubular goods, where corrosion resistance, especially 5scc resistance, is particularly important, there are strong restrictions on strength from the perspective of ensuring 5scc resistance. It has become.

By the way, three types of evaluation methods for 5scc resistance are well known: shell test, NA CIE test (constant load method), and SSINT test (low strain rate tensile test).

All of these show the same tendency, but the shell test below is the most severe.

In other words, in the shell test, two holes with a diameter of 0.7 mm are provided in the longitudinal center of a test piece with a thickness of 1.7 mm and a width of 4.5 mm, and stress is applied to this portion by bending it at three points. Under a specific environment (room temperature, 0.5% CH, C00I), 1 atm.
2S saturation) at 200-50 (l hr) and evaluate the cracking limit stress by S c, the value (1l114 eating index).

When looking at the relationship between the strength of oil country tubular goods and the required 5scc resistance in terms of the Sc value, as shown in Figure 1, in order to prevent cracking, the higher the material strength, the higher the SCC value.
c4fi is required, and if the strength is 80 ksi (56 kgf /+n2) class with 02% proof stress, the Sc value is required to be 10.7 or more, and 90 ksi
(63kif 7mm”) class, 100ksi (
70kf? f/n+2) class,] l Ok s i
(71 kqf /u+2) class requires Sc values of 120 or higher, 13.3 or higher, and 147 or higher, respectively.

This requirement is extremely strict considering the contradictory relationship between strength and CC property, and as long as an industrially possible manufacturing method is adopted, 1I
iJ S S Strength is 90k due to restrictions due to CC property.
The limit is S l ([i 3 kgf /am') class.

This point will be explained in more detail with reference to the relationship with crystal grain size.

It has been well known that even if the crystal II is refined with a deviation of G:1 and high strength is ensured, side surface 4sscc properties can be obtained.

Figure 2 shows the low alloy steel (111%) normally used for oil country tubular goods.
0.27%C-0,2/I%5i-1,2%Mn
-0, [124%5off, Aj! -11,0032%
N), Y and S were tempered to 75 kgr/
This figure shows the relationship between the Sc value and the grain size number of prior austenite grains, assuming that the value is 'Higashishiki'. As is clear from the figure, even if Y and S are 75 kgr/w+2, if the grain size number is 10 or more, the Sc value is 13.3.
exceeds the requirements of 1QQksi class.

Measures to improve S S CC resistance developed from this perspective include Nb addition from the component perspective and two-dimensional improvement from the heat treatment perspective.
Double quenching treatment, cold working for strength from the machined surface (Note 1.2
) or warm processing (Note 3).

Master ] ) Recrystallization
n and Formation of Hachihe st
EniLe in Deformed I+it
l+ martensiticStructure
of low carbon' 5teels.

M, TOKTZANIE, N, M to 'rsUMUIN, to, 1'5UZAKl, T, MAKI.

and l, TAMURA: Metalur8
ical Tr+ins+1ctions 8, vol.
138 (1982) pp, ] 3794388 Note 2) Refinement of austenite grains by cold rolling of steel: High pressure, Ameyama 5 Tokiji: Tetsu to Hagane, vol. 73. No,
5 (1987) S 4fifi Note 3) Austenite grain refinement by tempering warm working of low alloy steel, Matsuoka,
Ameyama 3 Tokimi: Tetsu to Hagane, vol 73. Nb, 5(1
987) S 467 In addition to the measures taken by grain refinement, the present inventors have also attempted to reduce AffN by limiting the amount of N in low alloy steel.
We have developed and proposed measures to suppress the generation of and improve the 5scc resistance (Japanese Patent Application No. 62-067023).

[Problem to be solved by the invention]

However, it is not possible to achieve sufficient grain refinement using conventional grain refinement methods such as addition of Nb or double quenching treatment, and it is impossible to achieve a prior austenite grain size number of 10 or more. Therefore, the strength is limited to 90k due to the 5scc resistance.
The limit is s I class.

On the other hand, grain refinement by cold working or warm working achieves a prior austenite grain size number of 10 or more. However, the effect is not necessarily stable, and above all, 730'C
Plastic working of 50% or more, at least 30%, is required at the following temperatures: Therefore, it is extremely difficult to implement this method on an industrial scale due to constraints in terms of production equipment and production costs.

In addition, the measures to improve the 5scc resistance developed by the present inventors are as follows:
Normal double quenching treatment and 3;
However, depending on the product size, grain refinement was not stable, and it was not necessarily a method that could be mass-produced. However, if it is combined with an effective grain refining treatment, it can be expected to stably secure a grade of IO(l k s i or higher).

The present invention utilizes this newly developed low-alloy steel pipe.
An object of the present invention is to provide a method for manufacturing oil country tubular goods that can ensure strength of 100 kis or higher and the 5 SCC resistance required for this, and that can be easily implemented on an industrial scale.

[Failure to solve the problem]

As mentioned above, it is well known that strong cold pressing or warm working is effective in refining crystal grains (Note 1.2.3).
.

In other words, if the martensite obtained by quenching is subjected to strong processing (either cold or warm after quenching), the ferrite recrystallization temperature will decrease during tempering, and depending on the tempering conditions, fine recrystallization particles may appear. generate. Based on this, it is presumed that if fine recrystallized ferrite is hardened again and turned into martensite through austenitization, martensite can be obtained in which fine prior austenite grains are transformed.

However, according to the investigation by the present inventors, when cold working is adopted, the fine prior austenite grains generated in the first quenching cause grain growth in the second quenching, and the stable fine grains are I couldn't get it. In addition, when warm pressurization is adopted, as mentioned above, 50% or more or at least 3
If processing with a strength of 0% or more is added, it is possible to sufficiently refine the grains. However, there was a problem with the apparatus for applying 41 force to the steel pipe at low temperatures.

Therefore, the present inventors continued their research. As a result, 6 (10 to 730
If a rather small plastic deformation of 20% or less, for example about 10%, is applied at warm temperatures at ℃, recrystallization of J, Lie 1~ will easily occur, and some of the carbides will precipitate due to plastic deformation. It has been found that the coarsening of crystal grains during the second quenching can be prevented. It was also revealed that the remaining alloying elements were dissolved in the matrix and this also prevented grain growth during the second quenching.

In other words, if mild warm plastic working is introduced during double quenching of oil country tubular goods, it will be possible to effectively promote ferrite recrystallization and prevent coarsening of recrystallized grains, which cannot be achieved by double quenching alone. Fine crystal grains can be obtained, and when the above-mentioned low alloy steel for oil country tubular goods developed by the present inventors is used, the
i (70kxf /**2) The strength on the edge plate and the surface 4SSCC properties required for this can be stably ensured.

The method for manufacturing oil country tubular goods of the present invention was developed based on such knowledge, and in terms of weight percentages, C: 0.15 to 0.45%, Si:
0°1~I%, Mn: 0.3~1.8%, So 7! ,
Aj! :0.01% or more, N:O, [102% or less,
AIN: Contains 0.005% or less, and further contains Cr as necessary.
:0.05~2%, Mo:0.02~0.8%, Nb
:o, o 05~0.2%, V:o,o (15~
0.2%, B: O, O, 0,0] to 0.003%, and the remainder substantially consists of Fe, from 880 to 980°C. After quenching, tempering is performed at 600 to 730°C, and plastic working is performed once or multiple times in that temperature range so that the total strain is 1 to 20%, and then to 800 to 950°C.
Hardening is performed at a temperature of 600 to 730°C.

Figure 3 shows vehicle volume as %: 0.25-0.29%C-0.3%S
i -0,5%Mn11.5%Cr -0,2%Mo
-0°03~0.08%Zr-0,005~0.06
%5off.

Aβ-0,0008~0.0 In low alloy steel with a composition consisting of O84%N, the 02% yield strength is increased to 75k by tempering.
3 c when gf/**2, I-nao and board 1-chu/IN
This shows the relationship with quantity. As is clear from the same M, by reducing the amount of AβN in the steel, the Sc value can be improved while maintaining high strength.

Due to the limitation of NV in steel, the low alloy steel pipe targeted by the present invention is A7! It suppresses the generation of N and improves S S CC resistance, and when conventional double quenching is used, it is 100 k s
i (70 kgf /* (77kg f/1
n2) or higher and the SC value required for this (14,'
7 or higher).

[For production]

Below, the reasons for limitations in the manufacturing method of the present invention will be explained in detail in the order of the chemical composition of the steel pipe, the heat treatment applied to the steel pipe, and the plastic working.

■, Chemical composition C: ]0Oks i (70kgf/+am”)
0.15% or more is required in order to obtain the 0.2% proof stress described above and to ensure strength and toughness in high temperature tempering for the purpose of improving S S CC resistance. However, 0.
If it exceeds 45%, quench cracking is likely to occur during quenching of the steel pipe. Therefore, it is set at 0.15 to 0.45%.

Si: itself does not change the 5scc resistance.

However, when the amount of Al added is reduced, it has the effect of suppressing Aj7N and improving the 5scc resistance, and is also an essential component as a deoxidizing element. If it is less than 0.1%, deoxidation will not be sufficient, and if it exceeds 1%, the prior austenite grains will become coarse after quenching, reducing toughness. Therefore 0.1
~1%.

Mn: Improves hardenability and evenly distributes cementite after tempering to improve toughness. The effect of Mn becomes saturated when it exceeds 1.8%, and furthermore, it increases micro-segregation and deteriorates the 5scc resistance.

If sufficient hardenability is ensured by other elements, the resistance to 5
From the point of view of ensuring scc property, it is better not to include Mn. On the other hand, if it is less than 0.3%, it is caused by insufficient hardenability.
s s c Cl') and lower the knife 14. Therefore, it is set at 0.3 to 1.8%. However, if quenching M can be ensured with thin-walled materials or other elements, 0. (1
5% or more.

Sob, A7! , N, AlN: Conventional 5 SCC resistant steel pipes improve S S CC resistance by ensuring sufficient quenching and by uniformly dispersing carbides (mainly cementite) in tempering after quenching. The grain size was 2~l, and the grain refinement also contributed to 1s s c c (41i+l-1-).

However, the research conducted by the present inventors has revealed that the 5scc resistance is dominated by precipitates (A ff N) that are much finer than cementite. That is, as shown in FIG. 3, by limiting the amount of AlN, the SC value, which is an index of 5scc resistance, improves, and A7
! Noticeable i-t when N≦0.005% (50ppm) or less
The effect of improving S S c c properties can be obtained. Based on the above, the amount of AlN is set to 0.005% or less, and therefore A7
! Construct N/l! , the amount of N is SOβ, Ap≦
0.01%, N22.002%.

Cr, Mo, V, Nb, F3: All are elements added as necessary.

0, r is extremely effective in improving hardenability, and M
Since it does not cause micro-segregation that occurs with the addition of n, it is effective in improving the 5scc resistance. 0.05%
If it is less than 2.0%, there will be no effect, and if it exceeds 2.0%, the hardenability will further improve, but the toughness will decrease. Therefore 0.0
5 to 2.0%.

MO also has a value of 0.0 for the same reason as Cr. (Set as 12~O, li%.

■ is effective in increasing the strength during high temperature tempering, and is 0°005
If it is less than 0.2%, the effect will not be sufficient, and if it exceeds 0.2%, the toughness will decrease. That's O, O'05~0.2%
shall be.

Nb is effective in improving toughness and 5scc resistance by making it finer. If it is less than 0.005%, this effect cannot be obtained,
If it exceeds 0.2%, the toughness decreases, the refinement effect is saturated, NbCm fine precipitates increase, and the 5SC resistance decreases.
Degrades C properties. Therefore, it is set at 0.005 to 0.2%.

B: Improves hardenability, improves toughness, SS CC
However, if it is less than 0.0001%, it has no effect, and if it exceeds 0.003%, it reduces the toughness after tempering. Therefore, it is set at 0.0001 to 0.003%.

Impurities: Elements contained as impurities other than those mentioned above are P≦0. +125%, S≦0.005%, 050
It is desirable to limit the content to 0.002%, Ni≦0.05%, and Cu≦0.05%. That is, limiting P, , S is mainly effective in preventing a decrease in toughness by 1F and 5scc due to micro segregation, and limiting to 0 is effective in preventing a decrease in toughness. Furthermore, limiting Ni and Cu is effective in preventing deterioration of corrosion resistance such as pitting corrosion.

2. Heat treatment and plastic working 01st quenching A quenching temperature of 880° C. or higher is required to completely form the austenite single phase. However, if the quenching temperature becomes too high, the crystal grains will become coarser during quenching.
Limit the quenching temperature to 980°C or less. In this case, in order to obtain fine ferrite grains in the next step, a martensite content of 80% or more is required after quenching.

01st tempering and plastic working 600℃ to obtain fine recrystallized ferrite in this process
or higher temperature is required. However, when the temperature exceeds 730° C., austenite forms at /4, and this portion eventually becomes coarse crystal grains. Therefore, tempering and plastic working are performed in a temperature range of 600 to 730°C.

The plastic working may be performed at the same time as the tempering or during the cooling process after the tempering, as long as a temperature of 600 to 730°C is secured.

Plastic processing includes diameter reduction processing, wall thickness adjustment processing, and bending processing (
(including bending back), etc., and the type is not limited.

The amount of deformation due to plastic working must be limited within the range of 1 to 20% expressed in terms of the degree of contraction of tensile or compressive deformation.

If this is less than 1%, it will not be possible to introduce enough strain to cause recrystallization, whereas if it exceeds 20%, a small strain will remain inside the ferrite, and the second quenching will actually make the austenite grains larger. . The optimum amount of deformation increases as the processing temperature increases.

The number of times of processing may be any number as long as the amount of shrinkage is limited within the range of 1 to 20%. Repetition of plastic deformation is effective in refining ferrite grains, and the refining progresses as the number of times increases. However, if it exceeds 7 times, the effect will be saturated.

02nd quenching If the quenching temperature is less than 800°C, austenitization will be insufficient. In addition, if the temperature exceeds 95°C (1'c), the crystal grains become coarse and the corrosion resistance deteriorates. Therefore, the range is set at 800'C to 950°C. To obtain fine prior austenite grains through this quenching, It is desirable to heat the temperature at a temperature higher than "C" at a low temperature and for a short time. From this point of view, it is desirable that the quenching temperature be 880 °C or less, and the heating holding time should be within 10 minutes.
Requires martensite content of 0% or more.

02nd Tempering This tempering basically gives favorable results in terms of high temperature resistance to 5scc if the specified strength can be maintained. From this point of view, tempering 111. The temperature shall be 600°C or higher. If the tempering temperature is less than 60°C (1'C), even if strength is obtained, the strain in the full tensile strength 1 to 1 is not sufficiently released, and the 5scc resistance is poor. is generated and the 5 SCC resistance is deteriorated, so the temperature is limited to 730°C or less.

〔Example〕

In Table 1, the steels subject to the present invention are indicated by a ” p, and in the same table, q -
A hot-worked pipe (outer diameter 70 m, inner diameter 501 m) made of steel not subject to the present invention, indicated by The second quenching and tempering was performed. Also,
For comparison, ordinary quenching was also carried out twice.

The plastic working was performed by performing two diameter reductions using a stretch reducer during the cooling process after the first tempering, or by crushing or offset processing using a warm straightening machine. Diameter reduction processing produces tensile deformation, while crushing or offset processing produces tension and compression (bending) deformation.

Prior austenite grain size number of each manufactured steel pipe, 0
．． The investigation results of 2% proof stress, tensile strength, elongation, Charpy fracture transition temperature and 5c4- are shown in Table 2 along with details of manufacturing conditions.

In Table 2, examples of the present invention are examples in which a steel pipe made of the steels (a to p) subject to the present invention were subjected to heat treatment and plastic working within the conditions of the present invention, and comparative example I is an example of steel pipes made of the steels subject to the present invention (a to p). An example of applying heat treatment and plastic working outside the conditions of the present invention to a steel pipe,
Comparative Example 2 is an example in which a copper tube made of steel (Q-X) not subject to the present invention was subjected to heat treatment and plastic working within the conditions of the present invention, and the conventional example is a copper tube made of steel (Q-X) not subject to the present invention, which is a general-purpose steel for oil country tubular goods. steel(
This is an example in which a steel pipe consisting of (r, s) was quenched twice.

In the example of the present invention, it is 100~. 05ksi (70~80.
Sc value 1 in 0.2% proof stress range of 5kgf/Ryu 2)
3.3 or more, some items are ■10~125ks
i (77-87.5kgf/u+2)/T
The Sc value satisfies 14.7 or more, and there are no problems with other characteristics.

On the other hand, although Comparative Example 1 has high strength, it does not have a commensurate 5 SCC resistance, and Comparative Example 2 also has poor strength, toughness, and S S CC resistance. In addition, the conventional example has low strength and 5SCC resistance.

〔Effect of the invention〕

As is clear from the following explanation, the method for manufacturing oil country tubular goods of the present invention achieves both strength and 5scc resistance at an extremely high level, which could not be achieved with conventional component improvement and double quenching, and also allows for strength processing. Since there is no need to use both, it is extremely advantageous in terms of manufacturing equipment, manufacturing efficiency, and manufacturing costs, and as a result, it has a great industrial effect in that high-grade oil country tubular goods can be manufactured industrially at low cost. .

[Brief explanation of the drawing]

Figure 1 is a chart showing the relationship between the IJ strength and the S value required for oil country tubular goods, Figure 2 is a chart showing the relationship between the grain size number and the Sc value, and Figure 3 is a chart showing the relationship between the IJ strength and the S value in steel. A7! It is a chart showing the relationship between the amount of N and the value of Sc.

Claims (1)

[Claims] 1. C: 0.15 to 0.45% by weight, Si: 0.1
~1%, Mn: 0.3-1.8%, sol. Al: 0.
01% or less, N: 0.002% or less, AlN: 0.00
After quenching at 880 to 980°C to a low alloy steel pipe containing 5% or less and the remainder substantially consisting of Fe,
Tempering is performed at 0 to 730°C, and plastic working is performed once or multiple times in that temperature range so that the total strain is 1 to 20%, followed by quenching from 800 to 950°C and 600 to 730°C. A method for producing high-strength oil country tubular goods with excellent corrosion resistance, the method comprising tempering at 2. Low alloy steel pipe contains Cr: 0.05-2%, Mo
:0.02~0.8%, Nb:0.005~0.2%,
V: 0.005-0.2%, B: 0.0001-0.0
2. The method for manufacturing a high-strength oil country tubular goods excellent in corrosion resistance according to claim 1, wherein the method comprises one or more of the following.