JP2018145490A - Oil well tube excellent in tube expansion property and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oil well tube excellent in tube expansion property and a manufacturing method therefor.SOLUTION: There is provided a low C steel tube containing, by mass%, C:0.010 to 0.100%, Si:0.50% or less, Mn:0.30 to 2.00%, P:0.030% or less, S:0.010% or less, Al:0.01 to 0.10% and the balance Fe with inevitable impurities, having parameter β value represented by the following formulae (1) and (2) satisfying 1.8 or more, having a metal structure consisting of tempered martensite of 95 area% or more as area fraction and the balance inevitable impurities, and having circumferential direction compression yield strength after tube expansion of 350 MPa to 700 MPa. Mn/Si>2 (1). β=2.7C+0.4Si+Mn+0.45 Ni+0.45Cu+0.8Cr+2Mo (2). Element symbols are contents of each element [mass%].SELECTED DRAWING: Figure 2

Description

  The present invention relates to an oil well pipe excellent in pressure crushing characteristics and having high pipe expansion characteristics with high circumferential compressive strength after pipe expansion, and a method for producing the same.

  Steel pipes with excellent pipe expansion characteristics are currently used for oil well repair. However, if the steel pipe can be applied to oil well slimming and monodialysis, etc., it has the potential to dramatically reduce oil well drilling costs. There is an increasing demand for characteristics that do not crush (hereinafter referred to as pressure crush characteristics).

  The crushing characteristics are related to the circumferential compressive strength of the steel pipe. In a normal oil well pipe (an oil well pipe that is not expanded), improving the yield strength of the steel pipe is one measure for improving the crushing characteristics.

  On the other hand, when expanding pipes underground, it is becoming clear that the compressive yield strength after pipe expansion is not determined only by the strength of the steel pipe. Specifically, a laboratory test showed that the new component system is based on DP steel, which has a high strength of raw pipe and newly developed burring steel, and has almost the same crushing characteristics. Furthermore, it was found that the collapse crushing strength was almost the same as Q70 (our product, high-C tempered martensite steel), which has a higher pipe strength than DP steel. It has become necessary to elucidate these phenomena and to develop a steel pipe having a high compressive yield strength after pipe expansion, that is, a high pressure crushing characteristic.

  Patent Document 1 discloses a technique in which the microstructure is DP (Dual Phase) in order to improve tube expansion characteristics. However, as described in detail in the present disclosure, having the microstructure as DP has the effect of significantly reducing the compression yield strength after pipe expansion, and there is a problem that the collapse performance after pipe expansion is reduced. .

  In patent document 2, the manufacturing method of the expanded steel pipe of tempered martensitic steel is disclosed. However, the component system disclosed in Patent Document 2 contains a relatively large amount of C, and these component systems have the effect of significantly reducing the compression yield strength after pipe expansion, and the collapse performance after pipe expansion is reduced. There is a problem.

  Patent Document 3 discloses a method for producing a steel pipe having high collapse characteristics after pipe expansion by suppressing the Bauschinger effect by using a dual phase steel. However, recently, higher collapse performance has been required, and there is a problem that Patent Document 3 cannot cope with it.

Japanese Patent No. 5014831 Japanese Patent No. 4943325 Japanese Patent No. 4833835

  The present invention is an investigation for solving the above-mentioned problem, characterized in that the circumferential compression yield strength after pipe expansion is in the range of 350 MPa to 700 MPa, and an oil well pipe having excellent pipe expansion characteristics And it aims at providing the manufacturing method.

  As a result of intensive studies to solve the above-described problems, the present inventors have been able to obtain the following knowledge. The compressive yield strength after tube expansion is governed by the strength of the tube and the Bausinger effect, and it has been found that suppression of the Bausinger effect is the most effective in the previous studies. The bausinger effect is promoted when a large amount of hard second phase (island martensite, pearlite, cementite, etc.) is contained, and the bausinger effect is small in uniform structure steel (ferrite single phase, martensite steel). From the above knowledge, it is considered that ferrite single-phase steel or tempered martensite steel is a candidate for a microstructure for increasing the compressive yield strength after pipe expansion.

  However, as described above, the compressive yield strength after tube expansion is also affected by the strength of the raw tube, and as shown in FIG. 1, it was found that tempered martensite with a higher strength of the base material has a higher compressive yield strength. As for the influence of cementite, it can be seen from FIG. 1 that the compressive yield strength of the low C tempered martensite is higher than that of the high C and high strength martensite. In general, the Bausinger effect is thought to originate from internal stress between phases, but it was difficult to generate the internal stress in low C materials, so it is thought that the Bausinger effect amount was reduced. Note that this result is calculated not from the actual compression yield strength after tube expansion, but from the Bausinger effect amount calculated by experiment, and the compression yield strength does not make sense in terms of absolute values.

The present disclosure has been made based on these findings, and the gist is as follows.
(1) By mass%, C: 0.010 to 0.100%, Si: 0.50% or less, Mn: 0.30 to 2.00%, P: 0.030% or less, S: 0.010 % Or less, Al: 0.01 to 0.10% or less, the balance is made of Fe and inevitable impurities, and the parameter β value represented by the following formulas (1) and (2) is 1.8 or more. Satisfied, the metal structure is excellent in tube expansion characteristics characterized in that the area fraction of tempered martensite is 95 area% or more and the remainder is an inevitable structure, and the circumferential compressive yield strength after tube expansion is 350 MPa to 700 MPa. Oil well pipe.
Mn / Si> 2 (1)
β = 2.7C + 0.4Si + Mn + 0.45Ni + 0.45Cu + 0.8Cr + 2Mo (2)
Here, the element symbol is the content [% by mass] of each element.

  (2) Further, by mass%, B: 0.001 to 0.010%, Ti: 0.005 to 0.050% or less Nb: 0.01 to 0.10%, Ni: 0.05 to 0.50 %: Cu: 0.05 to 0.50% or less, Mo: 0.01% to 0.30% or less, Cr: 0.05 to 0.50% or less, V: 0.01% to 0.10 The oil well pipe having excellent tube expansion characteristics according to claim 1, wherein the oil well pipe contains one or more of Ca: 0.0010% to 0.0060%.

(3) By mass%, C: 0.010 to 0.100%, Si: 0.50% or less, Mn: 0.30 to 2.00%, P: 0.030% or less, S: 0.010 % Or less, Al: 0.01 to 0.10% or less, the balance is made of Fe and inevitable impurities, and the parameter β value represented by the following formulas (1) and (2) is 1.8 or more. A satisfactory ERW steel pipe is heated to a range of A3 point or higher and A3 point + 100 ° C or lower after pipe forming, and cooled from a temperature of 750 ° C or higher to 100 ° C or lower at a cooling rate of 50 ° C / s or higher The manufacturing method of the oil well pipe excellent in the pipe expansion characteristic of Claim 1.
Mn / Si> 2 (1)
β = 2.7C + 0.4Si + Mn + 0.45Ni + 0.45Cu + 0.8Cr + 2Mo (2)
Here, the element symbol is the content [% by mass] of each element.

  (4) After the said cooling, it reheats to the temperature of 300 degreeC or more and A1 point or less, and cools, The manufacturing method of the oil well pipe excellent in the pipe expansion characteristic of Claim 3 characterized by the above-mentioned.

  (5) The electric resistance welded steel pipe is further mass%, B: 0.001 to 0.010%, Ti: 0.005 to 0.050% or less, Nb: 0.01 to 0.10%, Ni: 0.05 to 0.50% or less, Cu: 0.05 to 0.50% or less, Mo: 0.01% to 0.30% or less, Cr: 0.05 to 0.50% or less, V: 0 It is excellent in the pipe expansion characteristic of Claim 3 and 4 characterized by containing 1 type (s) or 2 or more types of 0.01%-0.10% or less, Ca: 0.0010%-0.0060% or less Manufacturing method of oil well pipe.

  According to the present invention, pipe expansion is possible, the circumferential compressive strength after pipe expansion is high, that is, the collapse characteristic is high, and a method for manufacturing an electric resistance welded steel pipe suitable for an oil well pipe can be provided, which contributes to industrial contributions. Extremely prominent.

It is a figure which shows the relationship between a microstructure and the compressive yield strength at the time of inversion load. It is a figure which shows the relationship between the tempered martensite area fraction and the compression yield strength after pipe expansion. It is a figure which shows the relationship between parameter (beta) and tempered martensite area fraction. It is a figure which shows the relationship between a no-pipe expansion rate and Mn / Si.

  Hereinafter, the present invention will be described in detail. First, the reason for limiting the component composition of the steel material will be described. Hereinafter, the notation of% means mass% unless otherwise specified.

  C is an element that improves the strength of steel. If the amount of C is less than 0.010%, the effect is not sufficient. On the other hand, when C exceeds 0.100%, the compressive yield strength after tube expansion decreases. Therefore, C is set to 0.010 to 0.100%. A low C system is effective for compressive yield strength after tube expansion, preferably 0.080% or less, more preferably 0.060% or less.

  Si is an element used as a deoxidizer for steel, but if it exceeds 0.50%, inclusions may be generated in the ERW weld and expansion may not be possible. .

  Mn is an element that can enhance the hardenability when added. In addition to the effect of increasing hardenability, it is essential for detoxifying S, and 0.30% or more is added. On the other hand, if Mn is contained excessively, segregation of P and the like are promoted to cause expansion cracking, so the upper limit was made 2.00%.

  P is an element present as an inevitable impurity in the steel, and if it exceeds 0.0300%, it segregates at the grain boundary to impair the tube expandability, so the upper limit is made 0.0300%.

  S is an element present as an unavoidable impurity in the steel, and when added in excess, the expandability is degraded.

  Al is added as a deoxidizer in the same manner as Si. In order to obtain the effect, 0.010% or more is added. On the other hand, if it exceeds 0.100%, in ordinary ERW welding equipment, the adhesion of the welded portion may be reduced with the generation of the Al-based oxide, so the content is made 0.100% or less.

Furthermore, you may add B, Ti, Nb, Ni, Cu, Mo, Cr, V, and Ca which influence a hardenability and a strength through a precipitate as needed.
B is an element that greatly improves the hardenability by adding a small amount and affects the strength. To obtain the effect, B is added in an amount of 0.0010% or more. On the other hand, if it exceeds 0.0100%, the pipe expandability deteriorates due to precipitates such as BN, so the upper limit is made 0.0100%.

  Ti is an element that forms carbonitrides, contributes to refinement of crystal grain size, and affects strength. In order to exhibit the effect, 0.005% or more of addition is necessary, so the lower limit was made 0.005%. However, if Ti exceeds 0.050%, coarse TiN is generated and the pipe expandability is lowered, so Ti is made 0.050%.

  Nb is an element that contributes to strength and toughness. In order to obtain the effect, 0.010% or more is added. However, if the addition amount is too large, the tube expandability deteriorates due to Nb precipitates, so the upper limit is made 0.100%.

  Ni is an element that contributes to improving hardenability and affects strength. In order to obtain the effect, 0.05% or more is added. However, when Ni is added in a large amount, the strength becomes too high and the tube expandability is inhibited. Therefore, the upper limit is 0.50%.

  Cu is an element effective for improving the hardenability and affecting the strength. To obtain the effect, 0.05% or more is added. However, if added in a large amount, fine Cu particles are generated, and the compression yield strength after tube expansion may be significantly deteriorated. Therefore, it is preferable that the upper limit of the Cu amount is 0.50%.

  The reason for adding Mo is to improve the hardenability of the steel material and to obtain high strength. In order to obtain the effect, 0.01% or more is added. If added in a large amount, there is a possibility that the compression yield strength after pipe expansion is reduced due to the formation of Mo carbonitride, so the upper limit was made 0.30%.

  Cr is an element that improves the hardenability, and in order to obtain the effect, 0.05% or more is added. On the other hand, it is also an element that degrades weldability. When it is added in a large amount, the pipe expandability is lowered by the Cr-based inclusions generated in the ERW weld. Therefore, it is preferable to set the upper limit of the Cr amount to 0.50%.

  V has substantially the same effect as Nb, and 0.010% or more is added to obtain the effect. V also has the effect of suppressing softening of the weld. However, when a large amount of V is added, the compression yield strength after the pipe expansion is lowered by the V carbonitride. Therefore, the V addition amount is preferably 0.100%.

  Ca is an element that controls the form of sulfide inclusions and improves strength and low-temperature toughness. In order to obtain the effect, 0.0010% or more is added. If the Ca content exceeds 0.0060%, CaO—CaS becomes a large cluster or inclusion, which may adversely affect the tube expandability. Therefore, it is preferable that the upper limit of the Ca addition amount be 0.0060%.

  The balance other than the above elements consists of Fe and inevitable impurities. In addition to the above elements, an element that does not impair the effects of the present invention may be added in a trace amount.

The required microstructure and its ratio are as follows.
As described above, in the present disclosure, it has been found that the low C and tempered martensite structure improves the compressive yield strength after tube expansion. As shown in FIG. 2, the compressive yield strength after tube expansion decreased with a decrease in the tempered martensite area fraction. In order to exceed 350 MPa, it is important that the tempered martensite area fraction is 95 area% or more.

The parameter β shown in the formula (1) is an index related to the hardenability of the steel material, and each element is the mass%. Higher numerical values indicate higher hardenability. In order to increase the compressive yield strength after pipe expansion, in addition to the low C system, a tempered martensite structure is required, and steel with high hardenability is required. As shown in FIG. 3, if this value is 1.8 or more, 95% by area or more can be tempered martensite structure in the process described later, and a steel pipe having high compressive yield strength after pipe expansion can be produced. is there.
β = 2.7C + 0.4Si + Mn + 0.45Ni + 0.45Cu + 0.8Cr + 2Mo (1)

TEM (Transmission Electron Microscopy) is used for the measurement of the microstructure fraction. In TEM observation, a sample prepared by a thin film method is used to observe a visual field corresponding to a total area of 100 um ² , preferably a square or rectangular visual field of about 10 μm in length and width, and the area fraction of bainite, ferrite, and tempered martensite. taking measurement. Bainite is characterized in that the preferred growth orientation of cementite precipitated in Lath is oriented in one direction.

On the other hand, that of tempered martensite can be distinguished from the characteristic that it is random. Also, the distinction between tempered martensite and as-marsted martensite can be made by the presence or absence of the formation of cementite. A feature of ferrite is that it has undergone diffusion transformation, and ferrite does not contain dislocations in the grains. In addition, bainite, perlite, and retained austenite may be included. Regarding the measurement of the circumferential compressive yield strength after tube expansion, the round bar compression test piece is taken from the seam portion at 90 °, 180 ° and 270 ° so that the cylindrical axis is in the circumferential direction. . A compression test is performed on the collected compression test pieces. The test conditions are a strain rate of 10 ⁻⁴ / s and the strain is measured using a strain gauge. The yield strength of compression is read from the obtained load-displacement curve. The compression yield strength in the present disclosure was defined as the stress value at 0.05% strain.

  As shown in FIG. 4, when the Mn / Si parameter is smaller than 2.0, MnSi inclusions are generated in the welded portion, and cracks are generated during pipe expansion. If Mn / Si is 2.0 or more, cracking during tube expansion can be suppressed, so Mn / Si was set to 2.0 or more.

Next, the manufacturing method of the ERW steel pipe in this invention is demonstrated.
In order to increase the compressive yield strength after expansion, it is effective to homogenize the microstructure, and tempered martensitic steel is effective to increase the strength in a uniform structure. In order to obtain tempered martensitic steel, it is important that the steel material has sufficient hardenability with respect to the quenching process, and the β value is an index of hardenability. In the steel pipe in which the β value is appropriately controlled, a tempered martensite structure can be formed by performing the following process, and the compression yield strength after the pipe expansion can be improved.

  After hot-rolling steel sheets are continuously roll-formed to form an open pipe, the vicinity of the butt portion is heated to the melting point or higher and electro-welding welding is performed by pressure welding with a squeeze roll. Although seam heat treatment may be performed online after ERW welding, the process is not particularly limited.

As the heat treatment after pipe forming, heating is performed within a range of A3 point or higher and A3 point + 100 ° C. or lower to completely remove strain introduced by pipe forming. The A3 temperature can be calculated using equation (2).
A3 = 937.2-436.5C + 56Si-19.7Mn-16.3Cu-26.6Ni-4.9Cr + 38.1Mo + 124.8V + 136.3Ti-19.1Nb + 198.4Al + 3315B (2)

  The heated steel pipe is cooled immediately after several seconds to several tens of seconds after leaving the heating furnace. At this time, if the cooling start temperature is 750 ° C. or higher and the cooling rate is 50 ° C./s or higher and 100 ° C. or lower on a steel pipe whose parameter β is appropriately controlled, the temperature is low C. It is also possible to generate martensite by quenching. The end temperature of cooling does not affect the properties as long as the austenite produced during heating is completely transformed into martensite. Although it is difficult to estimate the transformation end temperature, at least within the component range of the present invention, if the temperature is 100 ° C. or lower, the martensitic transformation is completely completed. Preferably, it is cooled to room temperature.

Preferably, as the second heat treatment, heating is performed to a temperature range of A1 temperature or lower and 300 ° C or higher. The A1 temperature can be calculated using equation (3). Since the holding time does not affect the characteristics, it is not particularly specified, but it is preferably 5 minutes or more. There is no restriction | limiting in particular about the cooling process of tempering, and slow cooling or rapid cooling may be sufficient.
A1 = 750.8-26.6C + 17.6Si-11.6Mn-22.9Cu-23Ni + 24.1Cr + 22.5Mo-39.7V-5.7Ti + 232.4Nb-169.4Al-894.7B (3)

Hereinafter, the effects of the present invention will be described with reference to examples, but the present invention is not limited to the conditions used in the following examples. In the test, the size of the steel pipe was φ279.4 mm × t15.9 mm. The compressive yield strength in the table is the value after 15% tube expansion by the water tube expansion test.
As shown in Table 1, no. 1 to No. No. 25 is within the range of components and microstructures defined in the claims, and the compression yield strength after pipe expansion is within the specified range.

Comparative Example No. In No. 1, since the C addition amount exceeded the upper limit, the Bauschinger effect became prominent and the compression yield strength after tube expansion became low.
Comparative Example No. In No. 2, since the amount of addition of C was below the lower limit, the strength of the tube was lowered and the compression yield strength after the tube expansion was lowered.
Comparative Example No. In No. 3, since the amount of Si added exceeded the upper limit, cracks due to welding defects occurred at the time of pipe expansion, and the pipe could not be expanded.
Comparative Example No. No. 4 could not be expanded due to cracks due to center segregation because the Mn addition amount exceeded the upper limit.
Comparative Example No. In No. 5, since the amount of Mn added was lower than the lower limit, solid solution S remained, which caused cracks during tube expansion.
Comparative Example No. In No. 6, since the P addition amount exceeded the upper limit, embrittlement caused by grain boundary segregation occurred and the pipe expanded.
Comparative Example No. In No. 7, since the addition amount of S exceeded the upper limit, the center segregation part became brittle and cracks occurred during pipe expansion.
Comparative Example No. In No. 8, since the Al addition amount exceeded the upper limit, cracks due to welding defects occurred at the time of pipe expansion, and the pipe could not be expanded.
Comparative Example No. In No. 9, since the amount of Al added was below the lower limit, deoxidation was insufficient and voids were generated inside the slab, and cracks occurred during pipe expansion. Comparative Example No. In No. 10, since the β value was below the lower limit, the hardenability was insufficient, and the martensite area fraction was below 95 area%. Along with this, the compression yield strength after pipe expansion did not reach the specified value.
Comparative Example No. In No. 11, since the ratio of Mn / Si was below the lower limit, cracks due to welding defects occurred and the tube could not be expanded.
Comparative Example No. In No. 12, since the heating temperature exceeded the upper limit, the toughness of the steel material deteriorated and cracks occurred during pipe expansion.
Comparative Example No. In No. 13, since the heating temperature was lower than the lower limit, the martensite area fraction was low, and the compression yield strength after tube expansion was reduced.
Comparative Example No. No. 14, since the cooling rate start temperature was below the lower limit, the martensite area fraction was low, and the compression yield strength after tube expansion was reduced.
Comparative Example No. In No. 15, since the cooling rate was lower than the lower limit, the martensite area fraction was low, and the compression yield strength after tube expansion was reduced.
Comparative Example No. In No. 16, since the cooling end temperature exceeded the upper limit, the martensite area fraction was lowered, and the compression yield strength after tube expansion was lowered.
Comparative Example No. In No. 17, since the second heating temperature exceeded the upper limit, the martensite area fraction was low, and the compression yield strength after tube expansion was reduced.

Claims (5)

% By mass
C: 0.010 to 0.100%
Si: 0.50% or less Mn: 0.30 to 2.00%
P: 0.0300% or less S: 0.0100% or less Al: 0.010 to 0.100% or less, with the balance consisting of Fe and inevitable impurities, represented by the following formulas (1) and (2) The indicated parameter β value satisfies 1.8 or more, the metal structure has an area fraction of tempered martensite of 95% by area or more and the remainder is an inevitable structure, and the circumferential compressive yield strength after pipe expansion is 350 MPa to 700 MPa. An oil well pipe with excellent pipe expansion characteristics.
Mn / Si> 2 (1)
β = 2.7C + 0.4Si + Mn + 0.45Ni + 0.45Cu + 0.8Cr + 2Mo (2)
Here, the element symbol is the content [% by mass] of each element. In addition,
B: 0.0010 to 0.0100%,
Ti: 0.005 to 0.050% or less Nb: 0.010 to 0.100%,
Ni: 0.05 to 0.50% or less,
Cu: 0.05 to 0.50% or less,
Mo: 0.01% to 0.30% or less,
Cr: 0.05 to 0.50% or less,
V: 0.010% to 0.100% or less,
2. The oil well pipe excellent in pipe expansion characteristics according to claim 1, characterized by containing one or more of Ca: 0.0010% to 0.0060% or less. % By mass
C: 0.010 to 0.100%
Si: 0.50% or less Mn: 0.30 to 2.00%
P: 0.030% or less S: 0.010% or less Al: 0.01 to 0.10% or less, with the balance consisting of Fe and inevitable impurities, represented by the following formulas (1) and (2) The electric resistance welded steel pipe satisfying the indicated parameter β value of 1.8 or more is heated to a range of A3 point or higher and A3 point + 100 ° C or lower after pipe forming, and cooled from 50 ° C or higher to 50 ° C / s or higher. It cools to 100 degrees C or less at a speed | rate, The manufacturing method of the oil well pipe excellent in the pipe expansion characteristic of Claim 1 characterized by the above-mentioned.
Mn / Si> 2 (1)
β = 2.7C + 0.4Si + Mn + 0.45Ni + 0.45Cu + 0.8Cr + 2Mo (2)
Here, the element symbol is the content [% by mass] of each element.   4. The method for producing an oil well pipe having excellent tube expansion characteristics according to claim 3, further comprising: after the cooling, reheating to a temperature of 300 [deg.] C. or higher and a temperature of A1 or lower. The ERW steel pipe is further in mass%,
B: 0.001 to 0.010%,
Ti: 0.005 to 0.050% or less Nb: 0.01 to 0.10%,
Ni: 0.05 to 0.50% or less,
Cu: 0.05 to 0.50% or less,
Mo: 0.01% to 0.30% or less,
Cr: 0.05 to 0.50% or less,
V: 0.01% to 0.10% or less,
Ca: One type or two or more types of 0.0010% to 0.0060% or less are contained, The method for producing an oil country tubular good with excellent pipe expansion characteristics according to claim 3 or 4.