JPH04254520A - Manufacture of resistance welded oil well pipe high in young's modulus in the circumferential direction of steel pipe and excellent in crushing property - Google Patents

Abstract

PURPOSE:To offer a method for manufacturing a resistance welded oil well pipe high in the Young's modulus in the circumferential direction of the steel pipe and excellent in crushing properties. CONSTITUTION:This is a method for manufacturing a resistance welded oil well pipe high in the Young's modulus in the circumferential direction of a steel pipe and excellent in crushing properties having features that, at the time of subjecting a slab to hot rolling, the cumulative draft of the steel in the temp. range of [the Ar3 point +50 deg.C] or below to the Ar1 point to 3 to 10% to the thickness of the initial slab and the sizing reduction of area at the time of manufacturing a resistance welded steel pipe is regulated to 2 to 30%.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides an electric resistance welded steel pipe having a circumferential Young's modulus of 2.10×104 (
The present invention relates to a method for producing an ERW oil country tubular product having a higher crushing property (kgf/mm2) and excellent crushing properties.

0002

BACKGROUND OF THE INVENTION In recent years, the drilling depth of oil wells has tended to become deeper and deeper, and as a result, there has been an increasing demand for steel pipes for oil wells with excellent crushing properties. In addition, by increasing the collapse resistance, it becomes possible to reduce the thickness of oil country tubular goods, which makes it possible to reduce the weight of oil wells and reduce the amount of steel used. Requirements for steel pipes for industrial use are becoming extremely strict.

[0003] As a prior art related to electric resistance welded oil country tubular goods having excellent crushability, there is one described in Japanese Patent Application Laid-Open No. 59-260442 [High crush type oil country tubular goods with high yield strength on inner and outer surfaces of pipe]. With this technology, after manufacturing ERW steel pipes, heat treatment is performed at low temperatures and by effectively utilizing strain aging strengthening, the yield strength of the pipe's inner and outer surfaces is increased, thereby producing ERW oil country tubular goods with excellent crushing properties. That is.

0004

[Problem to be Solved by the Invention] Generally, the factors governing the crushing characteristics of steel pipes for oil wells are yield strength, residual stress,
Examples include the roundness of the steel pipe and the unevenness of wall thickness. In addition, the Poisson's ratio and Young's modulus of steel are also considered to be factors that control the crushing properties, but these values were generally considered to be unchangeable values.

[0005] The present invention improves the Young's modulus, which has conventionally been assumed to be a constant value (the Young's modulus in the circumferential direction of the steel pipe that affects the crushing characteristics is 2.10×104 (kgf/mm2)). The object of the present invention is to provide a manufacturing technology for ERW oil country tubular goods that improves the crushing characteristics by actively increasing the crushing characteristics.

[0006]

[Means for Solving the Problems] The gist of the present invention is as described above. (1) C: 0.05-0.50%, Si: 0.05
~0.30%, Mn: 0.5~2.0% as a basic component, and the balance is Fe and unavoidable impurity elements.
°C] or less in the temperature range up to Ar1 point, the cumulative rolling rate is 3% or more and 10% or less of the initial slab thickness, and the sizing reduction rate during the production of ERW steel pipe is 2% or more and 30% or less. A method for producing ERW oil country tubular goods that have a high Young's modulus in the circumferential direction and excellent crushing properties.

(2) C: 0.05-0.50%, S
i; 0.05 to 0.30%, Mn; 0.5 to 2.0 as basic components, Nb; 0.005 to 0.060%, V;
0.005-0.060%, Mo; 0.10-1.00
%, Ti; 0.005 to 0.030%, and the balance is Fe and unavoidable impurity elements.
The cumulative rolling rate in the temperature range up to the Ar1 point (+50°C) and below shall be 3% to 10% of the initial slab thickness, and the sizing reduction rate during the manufacture of ERW steel pipes shall be 2% to 30%. A method for producing ERW oil country tubular goods that feature a high Young's modulus in the circumferential direction of steel pipes and excellent crushing properties.

Generally, the Young's modulus of steel is 2.10×104
(kgf/mm2). On the other hand, it is known that when steel is subjected to strong warm or cold working, a texture is formed and the Young's modulus changes accordingly. Metallurgically, it is known that the Young's modulus of an α-iron single crystal in the [111] direction is at most 2.90×10 4 (kgf/mm 2 ). Also, the Young's modulus in the [110] direction is 2.1
It is said to be 6×104 (kgf/mm2). That is, it is possible to increase the Young's modulus by aligning the crystal orientation in the [111] direction. By aligning the crystal orientation in the direction perpendicular to the rolling of the coil, that is, in the circumferential direction of the steel pipe, to the [111] direction, the Young's modulus in this direction is 2.
10×10 4 (kgf/mm 2 ), thereby making it possible to improve the crushing characteristics of the ERW steel pipe.

The present invention relates to a manufacturing technique for an electric resistance welded steel pipe that improves crushing characteristics by actively increasing the Young's modulus in the circumferential direction of the electric resistance welded steel pipe. In order to control the crystal orientation of steel, it is generally considered that a method of generating texture by changing hot rolling conditions is considered. In contrast, in addition to hot rolling, the present inventors controlled the forming conditions of the ERW steel pipe to increase the Young's modulus in the circumferential direction of the steel pipe to the conventional value (2.10×
104 (kgf/mm2)) by about 10%, thereby providing an ERW oil country pipe with superior crushing properties compared to conventional ones.

The means for increasing Young's modulus will be specifically explained below. First, regarding hot rolling, hot rolling is performed after heating the continuous cast slab to a temperature higher than the Ac3 temperature of the steel, but there are no particular restrictions on the initial rolling, and the Ar1 point is below [Ar3 point + 50℃] of the steel. It is necessary to carry out finish rolling in between and make the cumulative rolling amount 3% or more of the initial slab thickness. Although there is no particular restriction on the upper limit of the cumulative rolling amount, 10% or less is appropriate in view of the capacity of the rolling mill.

[0011] Finish rolling is carried out in a low temperature range below [Ar3 point + 50°C], and the formation of the texture of the steel is promoted by applying strong reduction such that the reduction amount is 3% or more of the initial slab thickness. be done. This creates anisotropy between the Young's modulus in the rolling direction and the Young's modulus in the direction perpendicular to the rolling direction. This is because at temperatures below [Ar3 point +50°C], the steel remains in its processed structure. That is, recrystallization of austenite is difficult to occur in such a low temperature range, and therefore a texture is formed.

Furthermore, when the final rolling is carried out in a so-called two-phase region between the Ar3 temperature at which ferrite transformation begins and the Ar1 temperature, the formation of texture is further promoted. In this way, the final rolling of hot rolling is carried out [Ar3 point +50℃]
By performing the following process between Ar1 points, a texture is formed, thereby making it possible to generate L and C anisotropy in the Young's modulus of the coil. In this case, the Young's modulus in the rolling direction of the coil is approximately 2.10×104 (kgf/mm2), while the Young's modulus in the rolling direction is approximately 7 to 8 due to the formation of texture.
% (Young's modulus anisotropy).

Next, an electric resistance welded steel pipe is manufactured using the coil having Young's modulus anisotropy, and the Young's modulus anisotropy can be further promoted by changing the forming conditions. The method for manufacturing ERW steel pipes will be described below. ERW steel pipes are manufactured by cold forming from hot rolled coils. In the present invention, by controlling the processing amount with the sizing roll, it has been realized that the Young's modulus anisotropy obtained at the coil stage can be further promoted. As mentioned earlier, the texture formed during the hot rolling stage is affected by the processing amount (
In this case, by controlling the sizing amount), it is further stabilized, and the Young's modulus anisotropy tends to expand accordingly.

[0014] The present inventors have reduced the amount of processing in sizing to 2.
% or more, it was found that the Young's modulus anisotropy obtained in the hot rolling stage could be further expanded. Incidentally, at the hot rolling stage, Young's modulus in the rolling direction (2.10×
104 kgf/mm2), the Young's modulus in the direction perpendicular to rolling is approximately 7 to 8% higher (2.27 x 104 kgf/mm2).
/mm2), but by controlling the processing amount during the forming of the ERW steel pipe, the Young's modulus anisotropy was further expanded to approximately 10% (2.30 x 104) compared to the rolling direction (tube axis direction).
kgf/mm2) is a high value.

The amount of sizing processing at this time is a value obtained from (outer circumference length before sizing - outer circumference length after sizing)/outer circumference length before sizing x 100. Further, when the processing amount in sizing is less than 2%, the effect of expanding Young's modulus anisotropy is small. Furthermore, a high processing amount of over 30% is difficult due to the capacity of the rolling mill. Therefore, the processing amount for sizing is 2
% to 30% is appropriate.

By controlling the hot rolling conditions and the amount of processing in the steel pipe as described above, the Young's modulus (2.10×104 kgf/mm2) that is generally used can be The Young's modulus of can be improved by about 10% at most. In such a high-pressure collapse type ERW oil country pipe, there are no particular restrictions on its components, and the component system may be selected as necessary, but it is preferable to manufacture the product using a component system that is as inexpensive as possible.

[0017] The ingredients recommended by the present inventors will be briefly introduced below. C is important in order to obtain the necessary strength, but if it is less than 0.05%, it is very difficult to secure the yield strength of 35 kgf/mm2 or more, which is the aim of the present invention, so C is contained in an amount of 0.05% or more. It is preferable to do so. Also, if it exceeds 0.50%, the strength will become too high,
Since low-temperature toughness and corrosion characteristics are significantly deteriorated, an appropriate upper limit is 0.50%.

[0018] Although Si is also important in order to obtain the necessary strength, it is preferably 0.05% to 0.30% from the viewpoint of electric resistance weldability. Mn is also important to obtain the necessary strength, but if it is less than 0.5%, the yield strength targeted by the present invention is 35%.
Since it is very difficult to ensure a content of kgf/mm2 or more, it is preferable to contain 0.5% or more. Also, 2
．． The upper limit is 2.0%, considering that if it exceeds 0%, the low temperature toughness will significantly deteriorate and the alloy cost will increase.
% is desirable.

[0019] Although C, Si, and Mn are used as the basic components above,
If necessary, one or more of Nb, V, Ti, and Mo may be added. First, Nb has the effect of greatly suppressing recrystallization of austenite during hot rolling, and is therefore effective in forming texture. However, 0
．． If it is less than 0.005%, the effect cannot be expected;
Even if it is added in excess of 60%, the effect will not change, so 0.
0.005% to 0.060% is appropriate.

There is also a report that V has a slight effect of retarding the recrystallization of austenite during hot rolling, similar to Nb, but this is not clear. Since V is effective in improving low-temperature toughness and strength, it is effective to add it as necessary. However, if it is less than 0.005%, the effect cannot be expected, and if it is added in excess of 0.060%, the effect will not change, so 0.005% to 0.060% is preferable.

[0021] Ti suppresses austenite grain coarsening during slab heating, and as a result, ferrite grains become finer, so it is effective in improving low-temperature toughness. However, if it is less than 0.005%, the effect cannot be expected;
．． Even if it is added in excess of 0.30%, the effect will not change, so
0.005% to 0.030% is preferred. Mo is a very effective element for improving strength. however,
If it is less than 0.10%, the effect cannot be expected;
Since the effect does not change even if added in excess of 0%, 0.1
0% to 1.00% is preferred.

[0022] Other P and S that are unavoidably obtained during refining
It is preferable that the number of cases is as small as possible. The components shown above are just examples; other components include Ni, Cu, and C.
r, Zr, etc. may be added as necessary. Next, a method for measuring Young's modulus will be briefly explained.

There are methods for measuring Young's modulus, such as a method of measuring resonance frequency using magnetic vibration, but in the present invention, Young's modulus was calculated by measuring the sound velocity of steel. The method is to take a small test piece 1 as shown in Figure 1 from a steel pipe, polish each surface, and then emit ultrasonic waves in the tube axis direction 2 and tube circumferential direction 3, and calculate Young's modulus from the velocity at that time. did. The calculation formula used for the calculation is theoretically determined from the wave equation, and the details are omitted, but only the calculation formula obtained as a result is shown below.

[0024]

[Math 1]

[0025]

[Examples] Examples of the present invention are shown in Tables 1 and 2 (continued from Table 1). Nos. 1 to 12 show examples of the present invention, and Nos. 13 to 17 show conventional comparative materials. Furthermore, Table 1
All of the examples shown in Table 2 (continued from Table 1) are electrical resistance welded oil country tubular goods having an outer diameter of 339.7 mm and a wall thickness of 9.6 mm.

[0026] In Examples 1 to 12 of the present invention, the rolling conditions for hot rolling were such that the cumulative rolling amount between [Ar3 +50°C and Ar1] was 3 to 10%, and the sizing amount of the steel pipe was 2 to 30%. %, the Young's modulus in the C direction of the steel pipe is reduced to the conventional general value of 2.10×104 (kgf/mm2
) by about 10%, thereby improving the crushing properties compared to conventional materials. Table 1
In the examples shown in Table 2 (continued from Table 1), the crushing value is improved by about 20% compared to the conventional material.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

Effects of the Invention The present invention provides an electric resistance welded steel pipe with a circumferential Young's modulus of 2.10×104, which is a commonly known value.
The object of the present invention is to provide a method for manufacturing an ERW oil country pipe that has an excellent crushing property and is about 10% higher than kgf/mm2. In the present invention, in order to improve the crushing characteristics by increasing the Young's modulus in the circumferential direction of the ERW steel pipe, we have developed It is also very effective.

[Brief explanation of the drawing]

[Figure 1] Figure 1 shows the Young's modulus (L, C
FIG.

Claims (2)

[Claims] Claim 1: C: 0.05-0.50%, Si: 0
．． 05 to 0.30%, Mn: 0.5 to 2.0% as a basic component, and the balance is Fe and unavoidable impurity elements. A steel pipe characterized in that the cumulative rolling ratio in the temperature range up to the Ar1 point is 3% or more and 10% or less of the initial slab thickness, and the sizing reduction ratio during the manufacture of the ERW steel pipe is 2% or more and 30% or less. A method for manufacturing ERW oil country tubing that has a high circumferential Young's modulus and excellent crushing properties. Claim 2: C: 0.05-0.50%, Si: 0
．． 05-0.30%, Mn; 0.5-2.0 as the basic component, Nb; 0.005-0.060%, V; 0.0
05-0.060%, Mo; 0.10-1.00%, T
When hot rolling a cast slab containing one or more of 0.005 to 0.030% and the balance consisting of Fe and unavoidable impurity elements, the [Ar3 point +5
The cumulative rolling rate in the temperature range up to Ar1 point (0℃) or below is set to 3% or more and 10% or less of the initial slab thickness, and the sizing reduction ratio during the production of ERW steel pipe is set to 2% or more and 30% or less. A method for manufacturing ERW oil country tubular goods that have a high Young's modulus in the circumferential direction and excellent crushing properties.