JPH07179941A - Production of high collapse strength steel pipe - Google Patents

Abstract

PURPOSE:To produce a seamless steel pipe having high collapse strength without consuming a large quantity of heat energy by subjecting a steel billet having a specified compsn. to rolling, hardening and tempering under specified temp. conditions and thereafter executing straightening. CONSTITUTION:The compsn. of a steel is constituted of a one contg., by weight, 0.08 to 0.35% C, 0.05 to 0.50% Si, 0.3 to 2.0% Mn, 0.005 to 0.05% Al, 0.005 to 0.O3% N, and the balance Fe. This steel billet is rolled at >=20% draft in the range from 950 to 850 deg.C, and the rolling is finished at 850 to 900 deg.C. Immediately after the rolling, the steel pipe is subjected to online hardening and is tempered at 550 to 700 deg.C. After the tempering, it is straightened at 450 to 550 deg.C. If required, this steel is furthermore incorporated with one or >= two kinds selected from 0.05 to 1.5% Cr, 0.05 to 1.0% Mo, 0.01 to O.O3% Ti, 0.0005 to 0.003% B, 0.05 to 1% Cu, 0.05 to 1% Ni, 0.01 to 0.1% Nb, 0.01 to 0.1% V and 0.0003 to 0.01% Ca.

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-collapse strength steel pipe used in an environment where there is a risk of being crushed by pressure from the outside, such as a seamless steel pipe used as a casing for oil wells. It is a thing.

[0002]

2. Description of the Related Art A high-collapse-strength steel pipe capable of withstanding crushing is used for a steel pipe to which an external pressure acts, such as a seamless steel pipe used as a casing for oil wells. The conditions for a high-collapse strength steel pipe are:
The crystal structure of the material is a fine grain structure and the yield strength is high,
The strength of the steel pipe is uniform, there is no uneven thickness, the cross-sectional shape of the steel pipe is uniform, and there is no bending in the longitudinal direction.

A conventional high-collapse strength steel pipe is manufactured through the steps shown in FIG. That is, the billet, which is a rolling material, is heated in a heating furnace in the heating step 21, and then rolled into a seamless steel pipe in the rolling step 22. The rolled steel pipe undergoes an air-cooling process 23, a heating process 24 for quenching, and a quenching process 25. The quenched steel pipe is tempered in a tempering step 26 and then straightened in a final straightening step 27.

In the manufacturing process of the above-mentioned conventional high-collapse strength steel pipe, the rolling process 22 prioritizes various rolling requirements such as deformation resistance.
It was carried out in the temperature range of 1050 ° C., and therefore the rolling end temperature was also set high. A steel pipe that has been rolled in such a high temperature range recovers during rolling or after rolling, and recrystallization actively occurs, and the crystal grains become coarse. ~ 95
It is reheated to 0 ° C. to be recrystallized so that the crystal grains are made finer, and after the quenching step 25 and the tempering step 26, straightening is performed. The straightening temperature was set as high as possible over 450 ° C. (600 ° C. as an example) so that straightening can be easily performed in the straightening step 27.

[0005]

However, the above-mentioned conventional method for producing a high-collapse strength steel pipe has the following problems. That is, deformation occurs during reheating of a steel pipe for quenching, and during subsequent quenching, the deformation is enlarged or new deformation occurs. As a result, the amount of straightening required becomes large, and the straightening temperature is inevitably higher than the workability, and the straightening lowers the yield strength in the vicinity of the inner and outer surfaces of the steel pipe, leading to a drop in the collapse strength. Also, the high heating temperature means that
There is also a problem that the manufacturing cost becomes high because the cost of installing the heating furnace and the energy cost required for heating are high.

[0006]

The method for producing a high-collapse strength steel pipe according to the present invention is C: 0.08% by weight, in% by weight.
0.35, Si: 0.05 to 0.50, Mn: 0.3 to
2.0, Al: 0.005-0.05, N: 0.00
Billet composed of 5 to 0.03 is 9
Roll at a rolling reduction of 20% or more between 50 and 850 ° C.,
Immediately after completion of rolling in the temperature range of 50 to 900 ° C, quenching is performed, tempering is performed at 550 to 700 ° C, and after tempering 450 to
A method for producing a seamless steel pipe having high collapse strength, characterized by straightening at 550 ° C.
C: 0.08 to 0.35, Si: 0.05 to 0.50,
Mn: 0.3-2.0, Al: 0.005-0.0
5, N: 0.005-0.03, and further Cr:
0.05-1.5, Mo: 0.05-1.0, Ti:
0.01 to 0.03, B: 0.0005 to 0.00
3, billet consisting of a component composition containing one or more of Cu: 0.05 to 1 and Ni: 0.05 to 9
Rolling with a reduction rate of 20% or more between 50 and 850 ° C.
Immediately after completion of rolling in the temperature range of 50 to 900 ° C, quenching is performed, tempering is performed at 550 to 700 ° C, and after tempering 450 to
A method for producing a seamless steel pipe having high collapse strength, which is characterized by straightening at 550 ° C.

[0007]

The present invention relates to a method for producing a seamless steel pipe having high collapse strength. The conditions for having high collapse strength are that the yield strength of the material is high and that the reduction in strength due to straightening is small. Therefore, it is required to manufacture a steel pipe that does not bend in the longitudinal direction after rolling and heat treatment. In order to meet these requirements, the manufacturing process as described above is adopted in the present invention, and the reason is given below.

(A) Reasons for limiting the composition of steel C: 0.08 to 0.35% C acts as an essential element for improving the hardenability and the tempering resistance as well as the function of ensuring the strength of the steel. The amount was 0.08% or more. Further, the reason for setting it to 0.35% or less is that if it exceeds 0.35%, cracking occurs during quenching or deterioration of toughness is caused.

Si: 0.05 to 0.50% Si acts as a deoxidizing agent for steel. It also has the effect of improving the strength of the steel. These effects are not clear at additions below 0.05%. Further, if the content exceeds 0.5%, the toughness deteriorates and the grain boundary strength also decreases, so that
It was set to 5% or less.

Mn: 0.3-2.0% Mn is a strong strengthening element. It is also a deoxidizing agent similar to Si, and has an effect of preventing hot brittleness due to sulfide.
In order to effectively obtain those effects, the addition amount is set to 0.3% or more. Further, even if added in excess of 2%, the effect is saturated and deterioration of toughness is caused, so 2% was made the upper limit.

Al: 0.005-0.05% Al is an element useful as a deoxidizer for steel. Also with Ti
In addition, it forms a nitride by combining with N in steel and the action of B
Since it is an element that manifests
It was set to 5% or more. Also, if added over 0.05%
Al in steel₂O ₃Increases and the cleanliness decreases, so the upper limit is
It was set to 0.05%.

N: 0.005 to 0.03% N is a strengthening element together with C. Further, it forms a nitride with Ti and Al, and particularly TiN has an action of suppressing grain growth of steel and refining crystal grains. Those effects are 0.005%
The following is not sufficient, and if it exceeds 0.03%, the toughness deteriorates, so the content was made 0.005 to 0.03%.

Cr: 0.05 to 1.5% Cr is an element that has a remarkable effect on the improvement of hardenability.
It has the effect of increasing the strength of steel, but its content is 0.0
If it is less than 5%, the above effect cannot be expected, and if it is added in a large amount, the hardenability becomes excessive, so the upper limit is 1.5%.
And

Mo: 0.05-1% Mo has the function of increasing the tempering resistance of steel, but 0.05
%, The effect is small. On the other hand, if the content exceeds 1%, the steel becomes brittle and the toughness deteriorates, so the upper limit was made 1%.

Ti: 0.01 to 0.03% Ti fixes N as TiN like Al, improves the hardenability of B, and finely disperses and precipitates, so that the crystal grains become coarse during billet heating. It has the effect of suppressing deterioration. However, if the content is less than 0.01%, the desired effects as described above cannot be obtained, while if the content exceeds 0.03%, TiN agglomerates and coarsens to suppress grain growth. In addition to having no effect, it causes deterioration of toughness, so the content range was made 0.01 to 0.03%.

B: 0.0001 to 0.005% B has the effect of improving the hardenability of steel, and is 0.000
The effect appears when the content is 1% or more. But,
Even if added in excess of 0.005%, the effect is not only saturated, but also causes cracking during hot working, so the upper limit was made 0.005%.

Cu: 0.05 to 1% Ni: 0.05 to 1% Cu and Ni are both effective in improving strength, but 0.05%
Since the effect is not clear below, 0.05% is made the lower limit. If it exceeds 1%, the hardenability becomes excessive,
Further, the upper limit is set to 1% or less because the manufacturing cost increases.

Nb: 0.01 to 0.1% Nb has a function of refining austenite grains. 0.
If it is less than 01%, its effect is not clear, and if it is added over 0.1%, the toughness is lowered.
And

V: 0.01 to 0.1% V has the same effect as Nb. Similarly, excessive addition of more than 0.1% causes deterioration of toughness, so 0.01
˜0.1%. Ca: 0.0003 to 0.01% In addition to the above alloying elements, the impurities usually contained in steel materials are limited as follows.

P: 0.020% or less Since P causes grain boundary segregation and lowers workability, the content of P is 0.
It was set to 020% or less. S: 0.020% or less S is an unavoidable impurity in steel, and if contained in a large amount, Mn.
In order to form S and reduce toughness, it is made 0.020% or less.

(B) Reason for rolling at a rolling reduction of at least 20% in the range of 850 to 950 ° C. Rolling should be performed at a temperature as low as possible and the workability should be increased to form an expanded structure in which crystal grains extend in the rolling direction. Will lead to higher strength. Since the strain applied to the steel by rolling is recovered at high temperature and released by recrystallization, an expanded structure cannot be obtained when the rolling temperature and the rolling end temperature are high and the workability is low. Since the recovery and recrystallization become remarkable when the temperature exceeds 950 ° C, the specified temperature range is set to 950 ° C or less. On the other hand, if the working temperature becomes lower than 850 ° C, the working resistance of steel increases and it becomes difficult to work, so the lower limit is 850 ° C.
And However, by finishing the rolling at 850 ° C. or higher, the structure of the steel after quenching can be made a martensite structure of 90% or higher.

The higher the degree of processing, the more pronounced the expanded structure,
The martensite structure becomes finer. (Expanded structure refers to the case where the grain size in the rolling direction of austenite crystal grains is more than twice the grain size in the direction perpendicular to rolling, and 50% means that the proportion of such crystal grains is 50%. If the workability between 850 and 950 ° C is less than 20%, the desired microstructure cannot be obtained. Also, the processing temperature range is 8
Even in the case of 50 to 950 ° C, it is necessary to roll a certain amount in the temperature range of 900 ° C or lower. By setting the workability between 850 and 900 ° C. to 7% or more, the expanded structure becomes remarkable, the martensite structure after quenching becomes finer, and the yield strength can be further increased.

FIG. 2 is a graph showing the relationship between the rolling end temperature (° C.) and the spread structure generation ratio (%). Using Steel 1 shown in Table 1, rolling was started at a temperature about 50 ° C. higher than the finishing temperature and rolling was performed at a rolling reduction of 20%. By setting the rolling end temperature to 900 ° C. or less, the expansion structure generation ratio is 1
It will be close to 00%. As a result, the crystal structure after quenching can be made fine.

(C) Online Direct Quenching By adopting online direct quenching, a steel pipe that has been expanded and has high strength is quenched, and a steel pipe with little bending can be obtained. The temperature of the steel pipe immediately after rolling is more uniform than when it is reheated, which is also effective in reducing the bending of the steel pipe. Since there is no reheating step, there is no deformation during heating, but in the conventional method, the deformation during reheating and quenching was large and it was necessary to raise the straightening temperature.

(D) Reduction of straightening temperature By setting the straightening temperature to 550 ° C. or less, the recovery phenomenon of the material during straightening is prevented, the lowering of the yield strength near the inner and outer surfaces of the steel pipe is prevented, and the straightening temperature By setting the lower limit to 450 ° C. or higher, it is possible to prevent a decrease in collapse strength due to the Bausinger effect.

FIG. 3 compares the collapse strengths of the conventional method and the low temperature rolling-direct quenching-high temperature straightening partially implementing the present invention and the low temperature rolling-direct quenching-low temperature straightening fully implementing the present invention. Is a graph shown by. Steel 1 (24
4.5φ × 11.99t) was used, and a comparison was made in the case where the average value of the collapse strength was 1 when manufactured by the conventional method. It can be seen from FIG. 3 that when the seamless steel pipe is manufactured by the manufacturing method of the present invention, the collapse strength is improved by 5% or more as compared with the conventional case.

[0027]

EXAMPLE A method for manufacturing a high-collapse strength steel pipe according to an example of the present invention will be described with reference to the process chart of FIG. In the method for producing a high-collapse strength steel pipe of the present invention, the billet having the above-described composition is heated in the heating step 1 and then rolled in the rolling step 3. In the rolling process 3, the latter half of 950
The rolling reduction is 20% or more between 850 ° C. and 850 to
Rolling was performed at a rolling reduction of 5 to 10% in the range of 900 ° C., and after the rolling, the steel pipe was directly quenched in the direct quenching step 4 in the temperature range of 850 to 900 ° C. immediately online. After that, tempering was performed in the subsequent tempering step 5, the temperature of the steel pipe was controlled to 450 to 550 ° C. in the temperature control step 6, and then the final straightening step 7 performed the straightening. Table 1 shows the components of the steel used. Steel 1 and steel 3 are carbon steel, and steel 2 is alloy steel. The size of each steel pipe is 177.8φ × 12065t.

[0028]

[Table 1]

Tables 2 to 4 show the collapse strengths of the steel pipes manufactured according to the present invention and the comparative examples.

[0030]

[Table 2]

[0031]

[Table 3]

[0032]

[Table 4]

Both the 690 ° C. tempered material in Table 2, the 620 ° C. tempered material in Table 3 and the 560 ° C. tempered material in Table 4 are 4% compared to the conventional method.
The above-mentioned increase in collapse strength is recognized.

[0034]

According to the present invention, a high-collapse strength steel pipe can be manufactured without consuming a large amount of heat energy.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram of a high-collapse strength steel pipe according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a rolling end temperature and an expanded structure generation ratio.

FIG. 3 is a graph comparing the collapse intensity ratios.

FIG. 4 is a manufacturing process diagram of a conventional high-collapse strength steel pipe.

[Explanation of symbols] 1 heating process 2 temperature control process 3 rolling process 4 direct quenching process 5 tempering process 6 temperature control process 7 straightening process

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Hidenori Yasuoka 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Katsumi Wadano 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Date Main Steel Pipe Co., Ltd.

Claims (2)

[Claims] 1. By weight%, C: 0.08 to 0.35, Si: 0.05 to 0.50,
Mn: 0.3-2.0, Al: 0.005-0.05,
A billet composed of a composition containing N: 0.005 to 0.03 is rolled at a rolling reduction of 20% or more between 950 and 850 ° C, and immediately after quenching in a temperature range of 850 to 900 ° C, quenching is performed. A method for producing a seamless steel pipe having high collapse strength, characterized by tempering at 550 to 700 ° C, and straightening at 450 to 550 ° C after tempering. 2. In (a)% by weight, C: 0.08 to 0.35, Si: 0.05 to 0.50,
Mn: 0.3-2.0, Al: 0.005-0.05,
N: 0.005 to 0.03, and further, Cr: 0.
05-1.5, Mo: 0.05-1.0, Ti: 0.0
1 to 0.03, B: 0.0005 to 0.003, C
u: 0.05 to 1, Ni: 0.05 to 1, Nb: 0.0
1 to 0.1, V: 0.01 to 0.1, Ca: 0.000
A billet composed of a component composition containing 1 to 3 kinds of 3 to 0.01 or more, and a reduction rate of 20% between 950 to 850 ° C.
A seam having a high collapse strength characterized by being subjected to the above rolling, rolling immediately in the temperature range of 850 to 900 ° C., immediately quenching, tempering at 550 to 700 ° C., and straightening at 450 to 550 ° C. after tempering. Steelless pipe manufacturing method.