JPH05287381A - Manufacture of high strength corrosion resistant steel pipe - Google Patents

Abstract

PURPOSE:To easily obtain an oil well pipe satisfying both high strength and high corrosion resistance and furthermore small in bending by executing prescribed bend removing after hardening and tempering repeated for two times for a steel pipe contg. specified C, Si, Mn, P, S, Cr, Mo, Al, Nb or the like. CONSTITUTION:Steel contg. <=0.3% C, 0.05 to 1% Si, 0.3 to 1% Mn, <=0.03% P, <=0.03% S, 0.3 to 1.5% Cr, 0.1 to 2% Mo, 0.01 to 0.05% Al and <=0.015% N, contg. one or more kinds among 0.01 to 0.04% Nb, 0.03 to 0.1% V, 0.01 to 0.05% Ti, 0.001 to 0.005% B and 0.001 to 0.005% Ca, and the balance Fe is melted. The steel pipe constituted of the steel is subjected to primary hardening and tempering and is thereafter subjected to perfect cold or warm bend removing. Next, it is subjected to secondary hardening and tempering and is thereafter subjected to slight warm bend removing or the like, by which the objective steel pipe small in bending and having a uniform distribution of the hardness in the direction of the thickness can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-strength corrosion-resistant steel pipe suitable for use as an oil country tubular good or the like having high strength and excellent corrosion resistance.

[0002]

2. Description of the Related Art Since the oil shock, demand for oil and natural gas has increased, and oil and gas fields have been developed all over the world. However, the number of ore deposits that can be easily mined has decreased. The ratio of oil wells and gas wells in deep corrosive atmospheres, which are difficult to mine, and contain moist hydrogen sulfide and carbon dioxide in their products, is increasing. In deep oil wells and gas wells, long oil well pipes and gas well pipes (hereinafter referred to as oil well pipes) of several thousand meters are hung, and high strength is required because large load is applied to the oil well pipes near the ground. In addition, in a corrosive environment such as hydrogen sulfide or carbon dioxide, an oil country tubular good having excellent corrosion resistance, particularly sulfide stress corrosion cracking resistance (hereinafter referred to as SSCC resistance), is required. Because of this, the oil well,
BACKGROUND ART Steel pipes used as oil well pipes for gas well drilling, oil collection, and gas collection have become more demanding than ever with high strength and corrosion resistance.

Conventionally, strength design of oil country tubular goods has generally been performed by yield stress (YS), and the hardness that affects corrosion resistance is equivalent to tensile strength (TS). As for the point of pipe manufacturing,
High yield stress (YS), low tensile strength (TS), that is, high yield ratio (YR = YS / TS). In order to achieve a high yield ratio, conventionally, a method of adding Mo to C-Si-Mn-Cr steel and using a material having good hardenability,
The method of refining the structure by repeating quenching and tempering and the method of refining the structure by performing cold working such as drawing have been adopted individually or in combination.

There are three known methods for evaluating the SSCC resistance, namely, the shell test method, the NACE test method (constant load method), and the SSRT method (low strain rate tensile test method). All of them show the same tendency, but the strictness is highest in the shell test method. The shell test method is a test piece having a thickness of 1.7 mm and a width of 4.5 mm, and a diameter of 0.7 mm at the center in the length direction.
2 holes were drilled, and stress was applied to this part by three-point bending, and kept in an environment of 20 ° C., 0.5% CH ₃ COOH, 1 atm, and H ₂ S saturation for 200 to 720 hours. Then, the crack limit stress is evaluated by the Sc value (corrosion resistance index). In order to increase this Sc value, it is necessary to reduce the Rockwell hardness HRC, and the strength is reduced.

Mo is added to the conventional C-Si-Mn-Cr steel described above.
If the method of adding fine particles and the method of refining the structure by repeating quenching and tempering are combined, the strength will be 0.2%.
Proof strength 100 ksi (70 kgf / mm ² ) grade, 110
It is possible to mass-produce ksi (77 kgf / mm ² ) grade seamless steel pipe, but in order to obtain more stable corrosion resistance or to obtain higher corrosion resistance, addition of Mo to C-Si-Mn-Cr steel It is necessary to combine a method of making the structure fine by performing cold working such as drawing, and the cost increases correspondingly and becomes expensive, which cannot be realized as an industrial product.

As a measure against this, C: 0.15 in weight%
~ 0.45%, Si: 0.1-1.0%, Mn: 0.3
~ 1.8%, Sol. Al: 0.01% or less, Ti:
0.005-0.1% and Zr: 0.01-0.2% of 1
Or two, N: {0.002+ [Ti (%) + Zr
(%)] / 8}% or less, AlN: 0.005% or less, and the balance is 8 for a low alloy steel pipe consisting essentially of Fe.
After quenching from 80 to 980 ° C, 600 to 730
While tempering at 600C, plastic working is performed once or plural times in the temperature range of 600 to 730C so that the total strain amount becomes 1 to 20%, and then quenching from 800 to 950C and 600 to 730C. A method of performing tempering (Japanese Patent Laid-Open No. 1-283322) has been proposed.

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The method disclosed in Japanese Unexamined Patent Publication No. 322 recrystallizes ferrite by introducing mild warm plastic working into the double quenching of an oil country tubular good and adding mild plastic working to the martensite obtained by quenching. Is promoted to prevent coarsening of recrystallized grains in the second quenching, and to obtain fine-grained crystals that cannot be obtained only by the second quenching and tempering, and to obtain a strength of 110 ksi (77 kgf / mm ² ) or higher. The SSCC resistance required for this can be secured. However, in the case where the straightener is used to bend the pipe, if the bend is taken cold, the plastic strain deteriorates the corrosion resistance. In addition, in bending in the warm state, hardness distribution occurs in the pipe wall thickness direction due to the work softening phenomenon. In order to reduce the hardness distribution, if the bending condition is made mild, the bending cannot be sufficiently removed, and the target performance of the pipe with the thread cut at the pipe end as a high-strength corrosion-resistant steel pipe for oil wells (bending of the pipe ≤ 1 mm / m , Intensity YS = 90 to 125 ksi, TS = 100 to 125 k
si, hardness HRC = 30 or less, hardness variation, 1 cross section △
It has a drawback that HRC ≦ 2) cannot be satisfied.

An object of the present invention is to provide a method for producing a high-strength corrosion-resistant steel pipe capable of satisfying the target performance of the pipe having a threaded end as the high-strength corrosion-resistant steel pipe for oil wells.

[0009]

[Means for Solving the Problems] The present inventors have conducted various test studies in order to achieve the above object. As a result, in the production of a steel pipe excellent in high-strength corrosion resistance in which quenching and tempering is performed twice, the steel pipe subjected to the first quenching and tempering is
Complete bending is performed cold or warm, and after the second quenching and tempering, extremely slight bending is performed in the warm, or not, so that the bending of the pipe is small and the hardness in the wall thickness direction is small. It was clarified that a high-strength corrosion-resistant steel pipe having a uniform thickness distribution was obtained, and the present invention was reached.

That is, according to the present invention, C ≦ 0.30%, S
i: 0.05 to 1.00%, Mn: 0.30 to 1.00
%, P ≦ 0.03%, S ≦ 0.03%, Cr: 0.30
~ 1.50%, Mo: 0.10 to 2.00%, Al:
0.01 to 0.05%, including N ≦ 0.015%, N
b: 0.01 to 0.04%, V: 0.03 to 0.10.
%, Ti: 0.01 to 0.05%, B: 0.0010
0.0050%, Ca: 0.0010 to 0.0050%
In a method for producing a high-strength corrosion-resistant steel pipe, which comprises one or more of the above, the balance of which is Fe and unavoidable impurities, and which is subjected to quenching and tempering twice, cold or after the first quenching and tempering. Complete bending is performed at a warm temperature, and after the second quenching and tempering, a slight bending is performed at a warm temperature or no bending is performed.

[0011]

The chemical composition of the carbon steel pipe according to the present invention and the reason for limiting the complete bending in the cold or warm straightening after the first quenching and tempering will be described in detail. C is an essential element for ensuring the strength and toughness, but if it is too much, quench cracking occurs at high temperature quenching, so the upper limit was made 0.30%. Si is necessary as a deoxidizing element and for securing strength, but if less than 0.05%, deoxidation is not sufficient, and if it exceeds 1.00%, toughness and surface properties are impaired, so 0.05 to 1. It was set to 00%. Mn is an element necessary for deoxidation and securing strength, but if it is less than 0.30%, deoxidation is not sufficient, and if it exceeds 1.00%, the cleanliness of the steel is impaired, so 0.30 to 1. It was set to 00%. Since P and S impair the cleanliness of steel and deteriorate the toughness and ductility,
The upper limit was 0.03%. Cr is an element necessary to secure hardenability and corrosion resistance, but 0.30%
If it is less than 1.0%, the effect is not sufficient, and if it exceeds 1.50%, the hardenability is further improved, but the toughness deteriorates, so
It was set to 30 to 1.50%. Mo is an element indispensable for improving hardenability, but if it is less than 0.10%, its effect is not sufficient, and if it exceeds 2.00%, quench cracking occurs, so
It was set to 0.10 to 2.00%. Al is an element effective for deoxidation and ensuring toughness, but if it is less than 0.01%, toughness cannot be obtained, and if it is added in excess of 0.05%, cleanliness is impaired. It was set to 05%. N is SSCC resistant
Although it is an element necessary for the formation of AlN that governs the property, if it is too much, corrosion resistance deteriorates, so the upper limit was made 0.015%. Nb is an element effective in improving toughness and SSCC resistance by refining, but if it is less than 0.01%, this effect cannot be obtained, and if it exceeds 0.04%, the effect of refining is saturated and NbC Since fine precipitates increase and deteriorate SSCC resistance, the content was made 0.01 to 0.04%. V is an element effective in improving the strength during high temperature tempering, but 0.03%
If it is less than 0.1%, the effect is not sufficient, and if it exceeds 0.10%, the toughness decreases, so the content was made 0.03 to 0.10%. T
i is an element effective for improving SSCC resistance by fixing N to reduce the solid solution N to improve the Sc value, and to finely disperse the carbide to disperse and reduce the stress concentration at the time of stress application. However, if it is less than 0.01%, the N fixing effect and the carbide dispersing effect are not sufficient, and if it exceeds 0.05%, the N fixing effect and the carbide dispersing effect are saturated, and the Sc value is rather lowered. It was set to 01 to 0.05%. B improves the hardenability, so it is an effective element for improving the toughness and SSCC resistance, but if it is less than 0.0010, it has no effect, and if it exceeds 0.0050%, it decreases the toughness after tempering. , 0.0010 to 0.0050%. Ca improves toughness by controlling the morphology of inclusions, SSC resistance
Although it is an element effective for improving the C property, if it is less than 0.0010%, this effect cannot be obtained, and if it exceeds 0.0050%, an adverse effect due to an increase in inclusions occurs, so 0.0010 to 0.0
It was set to 050%.

The temperature in the warm straightening after the first quenching and tempering is preferably in the range of 400 to 700 ° C., 400
If it is lower than 0 ° C, cold strain or residual stress becomes large, and if it exceeds 700 ° C, depending on the component, it exceeds the Ac ₁ transformation point, causing a structural change and adversely affecting the corrosion resistance. Considering that the cold strain or residual stress after the first quenching and tempering is reduced (disappeared) by the second quenching, the temperature for cold straightening after the first quenching and tempering is It is room temperature. When a slight bending is performed warm after the second quenching and tempering, the plastic strain in the vicinity of the inner and outer peripheral surfaces of the steel pipe is set to 20% or less of the wall thickness of the pipe. If it is 20% or more, the corrosion resistance deteriorates, which is not preferable.

In the production of the steel pipe according to the present invention,
As shown in FIG. 1, by repeating quenching and tempering twice, the former austenite grains become finer and martensite structure is obtained, and high yield stress YS and tensile strength TS are obtained, and hardness HRC30 or less by Rockwell hardness test method is obtained. Corrosion resistance is secured. First quench (Q
1) After tempering (T1), complete bending straightening is carried out cold or warm. The correction conditions in this case are
Tube cross-section the plastic deformation zone [delta] ₀ by the offset, tube wall thickness t, if the tube cross-section the plastic deformation zone [delta] _c by a crash, be carried out in the tube cross-section the plastic deformation zone _{δ 0 / t + δ c /} t ≧ 100%. By this straightening correction, the pipe bending is completely reduced, but when cold working is performed, the corrosion resistance deteriorates due to the added cold strain. Therefore, the second quenching (Q ₂ ) and tempering (T ₂ ) are performed in order to refine the structure and improve the corrosion resistance. The second quenching temperature is heated to a temperature slightly lower than the first quenching temperature in order to refine the grains. With this second quench,
After the first quenching and tempering, the cold strain applied when performed cold is completely eliminated. The straightening after the second quenching and tempering is carried out at a temperature of 400 to 700 ° C., if necessary, in order to avoid the adverse effect of cold strain on the corrosion resistance. Further, in order to reduce the hardness variation in the pipe wall thickness direction due to the work softening phenomenon, the straightening correction is performed under extremely slight conditions, or the straightening correction is not performed.
When performing straightening for straightening, a slight warming correction condition is as follows: pipe wall thickness t, pipe cross section plastic deformation region (δ ₀ / t + δ _c /
If t), the plastic deformation area of the pipe cross section is set to 20% or less. In order to apply an appropriate stress, which is slightly larger than the yield stress at the temperature at the time of straightening, to impart plastic strain to the vicinity of the inner and outer peripheral surfaces of the steel pipe in the present invention, as shown in FIG. 2, the central roll offset amount (O) of the straightening machine and By setting the roll opening (C) (crush amount) shown in FIG. 3, the plastic deformation amount of the inner and outer surfaces of the steel pipe is controlled. Note that FIG.
Shows the pipe section plastic deformation region δ ₀ due to the offset, FIG. 5 shows the pipe section plastic deformation region δ _{c due} to the crash, and FIG. 6 shows the relationship between the offset and the crush amount and the pipe section plastic deformation regions δ ₀ , δ _c It is a graph which shows an example.

[0014]

EXAMPLES C: 0.27%, Si: 0.20%, Mn:
0.45%, P: 0.010%, S: 0.002%, C
r: 1.02%, Mo: 0.70%, Al: 0.025
%, N: 0.060%, Nb: 0.025%, outer diameter 244.5 mm, wall thickness 15.11 mm, length 12 m
The steel pipe was heated at 920 ° C. for 20 minutes, cooled with water, quenched for the first time, and then tempered at 680 ° C. for 30 minutes. Continuing on, as shown in Table 1, using the inclined roll type straightening machine shown in FIG. 7 which is a cold (normal temperature) or warm (600 ° C.) opposed type 6 roll type, the plastic deformation zone δ ₀ / Curvature correction of t + δ _c / t = 20 to 150% was performed. Then, heat at 900 ° C for 20 minutes, cool with water and perform the second quenching, then at 700 ° C for 3 minutes.
It was tempered for 0 minutes. Then, in the cold (normal temperature) or the warm (620 ° C.), the pipe cross-section plastic deformation region δ ₀ / t + δ _c / t = 0 to 100 by crushing and offset processing by the inclined 6 roll type straightening machine shown in FIG. % Curl correction was performed. In addition, 1 in FIG. 7 is a seamless steel pipe, 2
Indicates a straightening roll. The yield stress, tensile strength, outer peripheral surface, center of wall thickness, Rockwell hardness and Sc value of the inner peripheral surface of the manufactured steel pipe were measured. The results are shown in Table 2 for yield stress, tensile strength, Rockwell hardness and hardness variation of outer peripheral surface, center of wall thickness, inner peripheral surface, and Sc value, bending of tube, and evaluation in Table 3.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

As shown in Tables 2 and 3, the test No. 9 ~
In the conventional method of No. 14, the hardness variation in the thickness direction of the steel pipe is large, or the Sc value showing the corrosion resistance is low. On the other hand, the test No. which satisfies the conditions of the method of the present invention.
In Nos. 1, 2, 5 and 6, the strengths are the same, the hardness variation in the thickness direction of the steel pipe is 0.3 or less, and the S resistance is low.
There is no deterioration of the Sc value, which indicates the SCC property, and the bending of the pipe is 1 mm.
/ M or less. Further, the test No. which does not satisfy the conditions of the method of the present invention. In the case of Comparative Examples 3, 4, 7 and 8,
In all of the product performance targets, only the bend of the pipe is out.

[0019]

As described above, according to the method of the present invention, it is possible to mass-produce a high-strength corrosion-resistant oil country tubular good satisfying both high strength and high corrosion resistance without cold drawing or the like. It becomes possible, and it becomes remarkably advantageous in terms of production equipment, production efficiency and production cost, and a high-grade oil country tubular good can be industrially produced at low cost.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a heat treatment and bending method according to the present invention.

FIG. 2 is an explanatory diagram of an offset amount.

FIG. 3 is an explanatory diagram of a crash amount.

FIG. 4 is a conceptual diagram showing a pipe section plastic deformation region δ _{0 due} to an offset.

FIG. 5 is a conceptual diagram showing a plastic deformation area δ _c of a pipe section due to a crash.

FIG. 6 is a graph showing an example of changes in an offset, a crush amount, and a plastic deformation area of a pipe section.

FIG. 7 is a conceptual diagram of an inclined roll type straightening machine used in the examples.

[Explanation of symbols]

 1 Seamless steel pipe 2 Straightening roll

Claims (1)

[Claims] 1. C ≦ 0.30%, Si: 0.05-1.
00%, Mn: 0.30 to 1.00%, P ≦ 0.03
%, S ≦ 0.03%, Cr: 0.30 to 1.50%, M
o: 0.10 to 2.00%, Al: 0.01 to 0.05
%, Including N ≦ 0.015%, Nb: 0.01 to 0.0
4%, V: 0.03 to 0.10%, Ti: 0.01 to
0.05%, B: 0.0010 to 0.0050%, C
a: A method for producing a high-strength corrosion-resistant steel pipe containing one or more of 0.0010 to 0.0050% and the balance being Fe and unavoidable impurities, the quenching and tempering being repeated twice. High strength characterized by complete bending in cold or warm after the first quenching and tempering, and slight bending or no bending in the warming after the second quenching and tempering Manufacturing method of corrosion resistant steel pipe.