JP2567151B2 - Manufacturing method of oil well steel pipe with excellent SSC resistance - Google Patents

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 oil country tubular goods having good sulfide stress corrosion cracking resistance even in a sulfide stress corrosion environment.

[0002]

2. Description of the Related Art Conventionally, in order to obtain good sulfide stress corrosion cracking resistance (hereinafter referred to as SSC resistance) even in a sulfide stress corrosion environment, for example, CAMP-ISIJ Vol.
No. 1 (1988) -1932, it was necessary to perform reheating quenching-tempering treatment after rolling the steel to which the hardenability improving element was added.

[0003]

However, in addition to the problem of thermal efficiency, the above-mentioned process complicates the manufacturing process, and addition of a large amount of the hardenability-improving element causes quench cracking. However, there was a problem in increasing the strength. The present invention solves such a conventional problem, and by controlling the components added to steel and hot rolling conditions, it is possible to obtain good S resistance even in a sulfide stress corrosion environment.
An object of the present invention is to provide a method for manufacturing a steel pipe for oil wells having excellent SC property.

[0004]

In order to achieve the above object, the present invention has the following structures. That is, wt%
As C: 0.05 to 0.35%, Si: 0.01 to 0.5
%, Mn: 0.15-1.0%, S: 0.01% or less, P: 0.02% or less, Al: 0.005-0.1%, Ti; 0.005-0.2% , B; 0.0003-0.
003, N; contains 70 ppm or less, further Cr: 0.1 to 1.5%, Mo: 0.05 to 0.4
%, Ni: 0.1 to 2.0%, V: 0.01 to 0.1%, one or more kinds, and a rare earth element: 0.001 to 0.05%, Ca : 0.00
1 to 0.02%, Co: 0.05 to 0.5%, Cu: 0.1 to 0.5% to a steel slab containing one or more and the balance substantially Fe. A hollow shell that is hot-pierced and continuously rolled, and in the final process, processed at a temperature of 900 ° C to 700 ° C with a reduction rate of ₃ to 15% and lowered to a temperature of Ar ₃ -100 ° C to Ar ₃ + 50 ° C. Is reheated to 900 ° C. to 1000 ° C., hot finish rolling is performed at a finishing temperature of Ar ₃ points + 50 ° C. or higher, and the obtained steel pipe is subjected to a quenching treatment to be rapidly cooled from the temperature of Ar ₃ points or higher. And a tempering process of heating to a temperature of Ac ₁ or lower and air cooling is performed to produce a steel pipe for oil wells having excellent SSC resistance.

[0005]

The operation of the present invention will be described in detail below.
First, the reason why the present invention is limited to the above steel components will be described. C enhances strength and yield point 60-80
It is important for stably obtaining high-strength steel of kgf / mm ² .
If it is too small, the effect is not obtained, and if it is too large, it causes quench cracking in the present invention in which quenching is performed from relatively coarse austenite grains. Therefore, 0.05-0.
The range was 35%. Mn is important because it enhances the quenching effect to increase strength and yield a yield point of 60 to 80 kgf / mm ² high strength steel. If the amount is too small, the effect is not obtained, and if the amount is too large, the SSC resistance is deteriorated, and in the present invention in which quenching is performed from relatively coarse austenite particles, it causes deterioration of the low temperature toughness. It was set to 15 to 1.0%. Si is a residual deoxidizer, and is an effective component for increasing strength. If it is too small, the effect will not be obtained, and if it is too large, inclusions will increase and the properties of the steel will become brittle.
It was set to 1 to 0.5%. P is a harmful component that causes grain boundary segregation and easily causes cracks during processing, and its content is 0.
It was set to 02% or less. S is a component harmful to the low temperature toughness formed by forming MnS inclusions and stretching by hot rolling, and the content thereof is 0.01 % or less.

Al, like Si, has a deoxidizing agent remaining, and is combined with N contained as an impurity component in the steel to suppress the growth of crystal grains and lower the transition temperature of the steel to improve the low temperature toughness. To do. If it is too small, the effect will not be obtained, and if it is too large, inclusions will increase and the properties of the steel will become brittle.
It was set to 0.1%. Ti combines with N, which is contained as an impurity component in the steel, to suppress the growth of crystal grains and increase the strength, and to exert the hardenability of B due to the effects of deoxidation and denitrification. If it is too small, the effect is not obtained, and if it is too large, TiC is precipitated to embrittle the steel, and inclusions increase to embrittle the properties of the steel, so the content was made 0.005 to 0.2 %. B remarkably improves the hardenability and enhances the strength. If it is too small, the effect will not be obtained, and if it is too large, the effect will not change and the toughness and hot workability will be deteriorated, so 0.0003 to 0.003%
And N is a harmful component that reduces the effect of B, and its content is 70 ppm or less.

When the strength of the steel is further increased in the steel having the above component composition, components such as Cr, Mo, Ni and V are selectively added as required. These elements are added in order to enhance the hardenability of steel and the strength. If too little without the effect, in the present invention for performing quenching from the too many relatively coarse austenite grains, cause inducing quenching cracks, since moreover is very expensive, content of each component amount of 0.1 to 1.5 percent, 0.05
It was set to 0.4%, 0.1 to 2.0%, and 0.01 to 0.1%.

Further, in view of the recent environment of use of steel pipes, the present invention selects rare earth elements and components such as Ca, Co and Cu as necessary in order to improve the SSC of the steel having the above composition. To be added. The rare earth element, Ca, is an effective component that makes the inclusions spherical and harmless.
If it is too small, the effect is not obtained, and if it is too large, inclusions increase and SSC resistance is reduced.
.About.0.05% and 0.001 to 0.02%. Co,
Cu has an effect of suppressing hydrogen invasion into the steel and effectively acts on SSC resistance. If it is too small, the effect will not be obtained, and if it is too large, the effect will be saturated.
% And 0.1 to 0.5%.

Next, the reason for limiting the rolling conditions in the final step of hot indenting continuous rolling as described above will be explained. The steel having the above composition is melted in a melting furnace such as a converter or an electric furnace or further subjected to a vacuum degassing process, and a steel slab is manufactured by a continuous casting method or an ingot lump method. Immediately or once cooled and then heated to a high temperature, the steel slab is conveyed to a hot piercing continuous rolling mill, rolled to a target outer diameter and wall thickness, and roughly formed into a hollow shell.

This rolling has a great influence on the material of the manufactured steel pipe. That is, in FIG. 1 and FIG. 2, the austenite (hereinafter referred to as γ) grain size of the steel that has been directly quenched after rolling and the rolling reduction conditions in the final step of hot-rolling continuous rolling,
The relationship between the reheating start temperature and the reheating furnace temperature is shown. The γ grain size after direct quenching treatment is ASTM No.
It changes greatly from 0 to 8.

According to the study by the present inventors, the SSC resistance of high strength steel deteriorates when the γ grain size becomes coarse, and conversely, if the grain size becomes too fine, the martensite ratio after quenching decreases. It was found that the suitable γ grain size that can ensure deterioration and further stable SSC resistance is ASTM Nos. 3 to 6. Further, in order to obtain γ grain size of ASTM No. 3 to 6, use of γ coarse grain enlargement phenomenon caused by secondary recrystallization after strain-induced grain growth that occurs in the final process of hot piercing continuous rolling to reheating process. It was found that is essential. The γ grain size control utilizing the strain-induced grain growth can be performed by defining the rolling conditions, the reheating start temperature, and the reheating furnace temperature in the final process of hot piercing continuous rolling as follows. That is, the reduction temperature in the final step of hot-rolling continuous rolling is 900
Above ℃, the strain energy introduced by processing recovers and decreases due to recrystallization, so the driving force for strain-induced grain growth decreases, and at 700 ° C or less, the accumulated strain energy becomes too large and after or after rolling. During the reheating process, γ grains without strain are generated and the driving force for strain-induced grain growth disappears. Therefore, the rolling reduction temperature in the final step of the hot piercing continuous rolling is limited to 900 ° C to 700 ° C. Under these rolling temperature conditions, if the rolling amount is 0 to 2%, the strain energy that serves as the driving force for strain-induced grain growth is insufficient, and if it is 15% or more, the strain energy accumulated becomes too large and the strain energy is reduced after the rolling or after the rolling. In the heating process, γ grains without strain are generated and the driving force for strain-induced grain growth disappears. Therefore, the amount of reduction in the final process of hot piercing continuous rolling was limited to 3 to 15%.

The reheating start temperature after reduction is Ar ₃ -100.
Between ℃ and Ar ₃ -150 ℃, abrupt coarsening of γ grains occurs and the SSC resistance is significantly deteriorated. Also, Ar ₃ +5
At 0 ° C. or higher, the driving force for strain-induced grain growth is released.
Therefore, the reheating start temperature after rolling is, Ar ₃ -100 ° C.
˜Ar ₃ + 50 ° C.

If the reheating temperature is 900 ° C. or lower, the γ grain size is insufficient to grow, and if the reheating temperature is 1000 ° C. or higher, the γ grains are suddenly coarsened and the SSC resistance is significantly deteriorated.
The temperature was limited to 000 ° C. Also, if the hot final finishing temperature is too low, the state of perfect γ at the time of quenching, which is necessary for obtaining high strength, cannot be secured, so Ar ₃ +5
It was set to 0 ° C. or higher.

The quenching temperature is important for stabilizing the SSC resistance. If Ar ₃ or less, a uniform structure cannot be obtained, and the SSC resistance becomes unstable. Therefore, the quenching temperature is
It was set to Ar ₃ or more . The cooling temperature at the time of quenching is not particularly limited, but it is faster than air cooling. The tempering temperature was set to Ac ₁ or less because it is necessary to ensure the stability of strength and toughness.
The heating method is not particularly limited.

The steel obtained under the above manufacturing conditions is effective for manufacturing oil country tubular goods which exhibits good SSC resistance even in a sulfide stress corrosion environment.

[0016]

EXAMPLES Next, examples of the present invention will be described. Steel pieces having the chemical composition shown in Table 2 produced by melting in a converter and through continuous casting were hot-pressed continuously and then reheated under the rolling conditions shown in Table 2 and then hot final finish rolling was performed. Quenching-tempering steel pipes are manufactured, and the strength, γ
The particle size and SSC resistance are shown. SSC resistance is NAC
Σth by constant load method according to ETM01-77
(Threshold Stress) was obtained and evaluated.

[0017]

[Table 1]

[0018]

[Table 2]

The steel pipe manufactured according to the present invention has high strength and has an SSC resistance of 0.2 at σth as compared with the conventional method.
It can be seen that it is improved by σy or more.

[0020]

The steel pipe produced by the method of the present invention as described above has high strength and excellent SSC resistance, and is used in a sulfide stress corrosion environment.

[Brief description of drawings]

FIG. 1 shows a relationship between a rolling condition, a reheating start temperature, and an austenite grain size in a final process of hot-piercing continuous rolling.

FIG. 2 shows a relationship between a rolling condition, a reheating start temperature and an austenite grain size in a final process of hot-piercing continuous rolling.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP 63-213620 (JP, A) JP 4-52226 (JP, A) JP 5-98350 (JP, A) JP 4- 221018 (JP, A)

Claims (4)

(57) [Claims] 1. C: 0.05 to 0.35%, Si: 0.01 to 0.5 as weight%
%, Mn: 0.15-1.0%, S: 0.01% or less, P: 0.02% or less, Al: 0.005-0.1%, Ti; 0.005-0.2% , B; 0.0003-0.
003, N; 70 ppm or less, and the balance being substantially Fe, the hot piercing continuous rolling is performed on the steel slab, and in the final process, 9
The hollow shell that has been processed at a reduction rate of ₃ to 15% at a temperature of 00 ° C to 700 ° C and lowered to a temperature of Ar ₃ -100 ° C to Ar ₃ + 50 ° C is reheated to 900 ° C to 1000 ° C. Hot finish rolling with a finishing temperature of Ar ₃ + 50 ° C or higher,
An oil well having excellent SSC resistance, characterized in that the obtained steel pipe is subjected to quenching treatment by rapidly cooling from a temperature of Ar ₃ or higher, and subsequently, tempering treatment by heating to a temperature of Ac ₁ or lower and air cooling. Steel pipe manufacturing method. 2. C: 0.05 to 0.35%, Si: 0.01 to 0.5 as weight%
%, Mn: 0.15-1.0%, S: 0.01% or less, P: 0.02% or less, Al: 0.005-0.1%, Ti; 0.005-0.2% , B; 0.0003-0.
003, N; contains 70 ppm or less, further Cr: 0.1 to 1.5%, Mo: 0.05 to 0.4
%, Ni: 0.1 to 2.0%, V: 0.01 to 0.1%, continuous hot drilling to a steel slab containing one or two or more and the balance being substantially Fe. The hollow shell that has been rolled and then processed at a temperature of 900 ° C to 700 ° C with a reduction rate of ₃ to 15% and lowered to a temperature of Ar ₃ -100 ° C to Ar ₃ + 50 ° C is rolled at 900 ° C. Reheated to ~ 1000 ° C and subjected to hot finish rolling with a finishing temperature of Ar ₃ + 50 ° C or higher, and quenching the obtained steel pipe from the temperature of Ar ₃ or higher, followed by Ac ₁ or lower. A method for producing a steel pipe for oil well having excellent SSC resistance, which is characterized by performing a tempering treatment of heating to a temperature and air cooling. 3. C: 0.05 to 0.35%, Si: 0.01 to 0.5 as weight%
%, Mn: 0.15-1.0%, S: 0.01% or less, P: 0.02% or less, Al: 0.005-0.1%, Ti; 0.005-0.2% , B; 0.0003-0.
003, N; contains 70 ppm or less, and further, rare earth element: 0.001 to 0.05%, Ca: 0.00
1 to 0.02%, Co: 0.05 to 0.5%, Cu: 0.1 to 0.5% to a steel slab containing one or more and the balance substantially Fe. A hollow shell that is hot-pierced and continuously rolled, and in the final process, processed at a temperature of 900 ° C to 700 ° C with a reduction rate of ₃ to 15% and lowered to a temperature of Ar ₃ -100 ° C to Ar ₃ + 50 ° C. Is reheated to 900 ° C. to 1000 ° C., hot finish rolling is performed at a finishing temperature of Ar ₃ + 50 ° C. or more, and the obtained steel pipe is subjected to a quenching treatment in which it is rapidly cooled from a temperature of Ar ₃ points or more. A method for producing a steel pipe for oil well having excellent SSC resistance, which is characterized by performing a tempering treatment of heating to a temperature of Ac ₁ or less and air cooling. 4. C: 0.05 to 0.35%, Si: 0.01 to 0.5 as weight%
%, Mn: 0.15-1.0%, S: 0.01% or less, P: 0.02% or less, Al: 0.005-0.1%, Ti; 0.005-0.2% , B; 0.0003-0.
003, N; contains 70 ppm or less, and further Cr: 0.1-1.5%, Mo: 0.05-0.4%, Ni: 0.1-2.0%, V: 0.01-. 0.1%, 1 type, or 2 or more types, and further contains rare earth elements: 0.001 to 0.05%, Ca: 0.00
1 to 0.02%, Co: 0.05 to 0.5%, Cu: 0.1 to 0.5% to a steel slab containing one or more and the balance substantially Fe. A hollow shell that is hot-pierced and continuously rolled, and in the final process, processed at a temperature of 900 ° C to 700 ° C with a reduction rate of ₃ to 15% and lowered to a temperature of Ar ₃ -100 ° C to Ar ₃ + 50 ° C. Is reheated to 900 ° C. to 1000 ° C. and subjected to hot finish rolling with a finishing temperature of Ar ₃ + 50 ° C. or higher, and the obtained steel pipe is subjected to a quenching treatment of rapidly cooling from a temperature of Ar ₃ or higher, and then Ac. _A method for producing a steel pipe for oil well having excellent SSC resistance, which is characterized by performing a tempering treatment of heating to a temperature of ₁ or less and air cooling.