JP6160587B2 - Manufacturing method of high-strength ERW steel pipe with excellent creep characteristics in the middle temperature range of ERW welds - Google Patents

Description

  The present invention relates to a method for producing a high-strength ERW steel pipe that is suitable as a steel pipe for steam piping. In particular, there is little decrease in strength (yield strength) even during long-term use in an intermediate temperature range, and excellent long-term softening resistance. The present invention relates to a method for producing a high-strength ERW steel pipe excellent in creep characteristics of an ERW weld. Here, “high strength” refers to the case where the yield strength is YS: 450 MPa or more. The “medium temperature range” refers to a temperature range of 300 to 400 ° C.

  In recent years, with the development of oil mining technology, super heavy crude oil called oil sand has attracted attention. Crude oil with high viscosity such as heavy oil called “bitumen” contained in the oil sand cannot be recovered from the oil well in the usual way. Therefore, a high-temperature steam exceeding 300 ° C is injected into the oil sand containing layer, the viscosity of the crude oil is lowered, and a heavy oil called “bitumen” is pumped up and recovered. Has been. As a method for injecting high-temperature steam into the oil sand-containing layer, for example, there is a steam injection method. In this method, steam heated to a high temperature is conveyed by piping and injected through an injection steel pipe.

  From the viewpoint of pipe reliability, seamless steel pipes or UOE steel pipes welded with weld metal have been used for steam pipes for transporting steam over a long distance to a steam injection well. In ERW steel pipes, the reliability of ERW welds is insufficient, so it has not been used in applications where high temperature strength characteristics are required. ERW steel pipes have been limited to locations that are used near room temperature where high temperature strength characteristics are not required.

  For example, Patent Document 1 describes a method for manufacturing a steel pipe for high-strength steam piping that is excellent in weld heat-affected zone toughness. The technique described in Patent Document 1 is mass%, C: 0.05 to 0.09%, Si: 0.05 to 0.20%, Mn: 1.5 to 2.0%, P: 0. 0.020% or less, S: 0.002% or less, Mo: 0.05 to 0.3%, Nb: 0.005 to 0.05%, Ti: 0.005 to 0.02%, Al: 0. The steel slab having a composition containing 01 to 0.04%, N: 0.004 to 0.006% and satisfying Ti / N: 2.0 to 4.0 is heated to 1000 to 1200 ° C and then 900 ° C or less. After hot rolling with a cumulative rolling reduction at 50% or more and a rolling end temperature of 850 ° C. or less, it was accelerated and cooled to 400 to 550 ° C. at a cooling rate of 5 ° C./s or more. This is a technology in which a steel plate is cold formed into a tubular shape and the butt portion is welded to form a welded steel pipe. According to the technique described in Patent Document 1, a high-strength welded steel pipe for steam piping having a high yield strength at 350 ° C. and a high weld heat affected zone toughness is obtained.

  Patent Document 2 describes a method for producing a steel pipe for steam transport piping having excellent high temperature characteristics. The technique described in Patent Document 2 is mass%, C: 0.02 to 0.10%, Si: 0.01 to 0.50%, Mn: 0.5 to 2.0%, Nb: 0. 0.005 to 0.050%, Ti: 0.005 to 0.050%, N: 0.001 to 0.010%, B: 0.0001 to 0.0050%, or Mo, Cr, Containing V, Ca, REM, etc., P: 0.020% or less, S: 0.005% or less, Al: 0.04% or less, satisfying Ti / N: 2.0 to 4.0 A steel slab having a composition to be heated to 1000 to 1250 ° C., hot rolled at 900 ° C. or less with a cumulative reduction ratio of 50% or more and an end temperature of 850 ° C. or less, and then 5 ° C. to a range of 400 to 550 ° C. / S Accelerated cooling at a cooling rate of more than / s, high strength steel sheet is formed into a tubular shape, and the butt is welded It is an excellent method of producing a high strength steel pipe for steam transportation pipeline in high temperature properties. According to the technique described in Patent Document 2, a high-strength steel pipe for a large-diameter steam transport pipe excellent in high-temperature characteristics and long-time creep characteristics can be manufactured.

JP 2006-183133 A Japanese Patent No. 4741528

  However, in the techniques described in Patent Documents 1 and 2, the heat-affected zone having a large particle size that is heated to just below the melting point and the oxide and residual oxide generated during ERW welding is inevitable in the ERW weld of the steel pipe. Exists. Due to the presence of the oxide and the weld heat-affected zone, the high-temperature strength of the ERW weld zone is lowered, and there is a concern that the strength may be lowered and creep rupture may occur during long-term use in the intermediate temperature range (300 to 400 ° C.). Therefore, when used as a steel pipe for steam piping, there is a problem that it is necessary to expect a large strength safety factor, and it is necessary to limit the steam temperature and internal pressure.

  The present invention solves the problems of the prior art, injects high-temperature steam into the oil sand-containing layer, and dissolves heavy oil called “bitumen” more efficiently without limiting the steam temperature and internal pressure. YS: Yield strength suitable for steam transport piping that can be mined economically, high strength of 450 MPa or more, and high strength excellent in creep characteristics in the middle temperature range (300-400 ° C) of ERW welds It aims at providing the manufacturing method of an electric resistance steel pipe.

Here, “excellent creep characteristics in the middle temperature region of the electric resistance welded portion” means that a creep test at 400 ° C. × 2340 h was performed, and the creep rupture stress σ _creep was 80% of the yield strength YS _RT at room temperature. This is the case. The 400 ° C. × 2340 h creep rupture stress is a Larson-Miller parameter (FR Larson, and J. Miller; Trans. ASME, vol. 74 (1952)) used in organizing creep rupture data at different temperatures. , 99.765-775), and corresponds to the creep rupture stress when stress is applied at 350 ° C. for 20 years. The Larson-Miller parameter is the following equation: Larson-Miller parameter = (T + 273) × (C + logt)
(Where T: temperature (° C.), t: time (h), C: constant = 20)
Defined by

  In order to achieve the above-mentioned object, the present inventors diligently studied various factors affecting the creep characteristics in the middle temperature region of the ERW weld. As a result, in order to improve the high-temperature strength and creep characteristics in the medium temperature range, the microstructure of the base metal part and the ERW welded part is made into a fine structure with the quasi-polygonal ferrite phase as the main phase. It has been found that it is important to eliminate the steel pipe having the ERW weld part in which the oxide having a size that has an adverse effect on the creep characteristics remains, while stabilizing the structure via the steel.

  And by increasing the sensitivity of flaw detection using a phased array ultrasonic flaw detection (hereinafter also referred to as array UT) device, the distribution of oxides inherent in the ERW seam can be measured, and the high temperature creep characteristics of the ERW weld can be measured. We found that it can be evaluated by nondestructive inspection.

The present invention has been completed based on such findings and further studies. That is, this invention consists of the following summaries.
(1) After continuously forming a hot-rolled steel strip into an open pipe having a substantially circular cross section, the vicinity of the butt portion of the open pipe is heated to the melting point or more and subjected to electro-welding welding that is pressed with a squeeze roll. In the manufacture of an ERW steel pipe having an ERW welded portion and then subjecting the ERW steel pipe to on-line heat treatment, after the heat treatment, the reference echo height of the through hole of φ1.6 mm is 80% The ERW weld was continuously detected with a phased array ultrasonic flaw detector with a sensitivity 20 dB higher than the sensitivity, and a steel pipe with a detected echo height of 80% or less was placed at 350 ° C. of the ERW weld. A high-strength electric wire with excellent creep characteristics in the middle temperature range of the ERW weld, characterized in that the creep rupture stress for 20 years satisfies the API5L standard yield strength specification lower limit x 2/3 or more. Manufacturing method of sewn steel pipe .
(2) The electric resistance welded steel pipe is mass%, C: 0.025 to 0.084%, Si: 0.10 to 0.30%, Mn: 0.70 to 1.90%, P: 0.00. 018% or less, S: 0.0029% or less, Al: 0.01 to 0.10%, Nb: 0.001 to 0.070%, V: 0.001 to 0.065%, Ti: 0.001 -0.033%, Ca: 0.0001-0.0035%, N: 0.0050% or less, O: 0.0030% or less, and Pcm defined by the following formula (1) is 0.20 Containing so as to satisfy the following, the composition consisting of the balance Fe and inevitable impurities, and the pseudopolygonal ferrite phase with a volume ratio of 90% or more as the main phase and the balance consisting of a hard phase other than the pseudopolygonal ferrite phase The base material structure in which the average particle size of the pseudo-polygonal ferrite phase is 10 μm or less Electrosewing welding in which the pseudopolygonal ferrite phase with a volume ratio of 90% or more is the main phase, the remainder is a hard phase other than the pseudopolygonal ferrite phase, and the average particle size of the pseudopolygonal ferrite phase is 10 μm or less The manufacturing method of the high intensity | strength ERW steel pipe as described in (1) characterized by having a structure | tissue consisting of a part structure.
Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20
+ Mo / 15 + V / 10 + 5B (1)
Here, C, Si, Mn, Cu, Ni, Cr, Mo, V, B: Content of each element (mass%)

(3) In addition to the above composition, Cu: 0.001 to 0.350%, Ni: 0.001 to 0.350%, Mo: 0.001 to 0.350%, Cr: 0 by mass% The method for producing a high-strength ERW steel pipe according to (2), comprising one or more selected from 0.001 to 0.350%.
(4) After heating the on-line heat treatment to a temperature in the range of 800 ° C. to 1150 ° C. in the vicinity of the thickness of the ERW weld, the temperature in the center of the thickness is 780 ° C. to 620 ° C. So that the average cooling rate in the range of 7 to 299 ° C./s is applied to a cooling stop temperature of 620 ° C. or less, and the accumulated residence time in the temperature range of 500 to 360 ° C. is 2 to 200 s. The method for producing a high-strength ERW steel pipe according to any one of (1) to (3), wherein the adjusted heat history is applied.
(5) In the fin-pass forming of the roll forming, the distance in the thickness direction of the hot-rolled steel strip between the taper start position and the surface serving as the outer surface of the tube or the surface serving as the inner surface of the tube is formed on both end surfaces in the width direction of the hot-rolled steel strip. method of producing a high strength electric resistance welded steel pipe of the mounting serial to any one of (1), characterized in applying a tapered groove which becomes 2 to 80% of the hot rolled strip thickness (4).
(6) The high-strength electric sewing according to any one of (1) to (5), wherein the electric resistance welding is performed in an atmosphere in which an oxygen partial pressure is reduced compared to an oxygen partial pressure in the atmosphere. Steel pipe manufacturing method.
(7) The total content of Si, Mn, Al, and Ca contained in inclusions having an equivalent circle diameter of 5 μm or more present in the ERW weld is 49 mass ppm or less (1) Thru | or the manufacturing method of the high intensity | strength ERW steel pipe in any one of (6).

According to the present invention, the yield strength YS: high strength of 450 MPa or more, and excellent creep properties in the middle temperature range (300 to 400 ° C.) of the electric resistance welded portion, it can be applied as a steel pipe for steam piping. High-strength ERW steel pipe can be manufactured stably, and it has a remarkable industrial effect.

It is a figure which shows the relationship between the echo rupture stress at the time of applying stress for 20 years at 350 degreeC, and the echo height detected by the array UT of an electric-welding part. It is a figure which shows the relationship between the magnitude | size of the oxide which exists in an electric-welding seam part, and the echo height detected by the array UT.

  First, hot-rolled steel strip is continuously roll-formed to form an open tube with a substantially circular cross section, and then the ordinary electric resistance welding, in which the butt portion of the open tube is heated to the melting point or higher and pressed with a squeeze roll. Then, an electric resistance welded pipe having an electric resistance welded portion is formed, and then the electric resistance welded steel pipe is subjected to on-line heat treatment.

Next, after the heat treatment, in order to efficiently detect an oxide larger than φ100 μm with an equivalent circle diameter that affects the mechanical properties of the ERW weld, a reference echo height of a through hole of φ1.6 mm is set. The ERW weld is continuously detected with a phased array ultrasonic flaw detector with a sensitivity 20 dB higher than the sensitivity of 80%, and the oxides present in the ERW weld seam are detected. The relationship between the echo height detected by the array UT having the above sensitivity and the size of the oxide (equivalent circle diameter) existing in the seam welded seam portion was obtained by experiments. The result is shown in FIG. When an ultrasonic wave is applied to the oxide existing in the seam welded seam portion, the intensity of the ultrasonic echo reflected is increased according to the size (density) of the oxide.

  Therefore, the relationship between the echo height of the ERW weld detected by the array UT having the above sensitivity and the creep rupture stress of the ERW weld when stress was applied at 350 ° C. for 20 years was determined. As an example, FIG. 1 shows the results when an API5L standard X80M ERW steel pipe (outer diameter 508 mm × tube thickness 20.6 mm) is used as a test material. From FIG. 1, if the echo height detected by the array UT is 80% or less, the creep characteristics required for a steel pipe for steam transport piping of X80 standard (creep rupture stress at 350 ° C. × 20 years ≧ YS standard lower limit × 2 / 3 = 370 MPa). Similar results were obtained for other strength standards (X65, X70, etc.).

Therefore, after online heat treatment, the ERW weld is continuously detected by a phased array ultrasonic flaw detector with a sensitivity that is 20 dB higher than the sensitivity with a reference echo height of φ1.6 mm through-hole being 80%. If the echo height is 80% or less, it can be determined that the ERW weld is an ERW steel pipe that satisfies the creep characteristics at 350 ° C., which is a required characteristic of a steel pipe for steam transport piping.

  Next, the reasons for limiting the composition of the high-strength ERW steel pipe of the present invention will be described. Hereinafter, the mass% in the composition is simply expressed as%.

C: 0.025 to 0.084%
C contributes to the formation of hard phases such as pearlite, pseudo pearlite, cementite, paynite, martensite, and has an action of increasing the steel pipe strength. In order to obtain such an effect and ensure a desired yield strength: YS 450 MPa or more, it is desirable to contain 0.025% or more. On the other hand, when it contains more than 0.084%, the amount of hard phases in the base metal part and the ERW welded part may increase and the creep characteristics may deteriorate. Therefore, C is preferably limited to a range of 0.025 to 0.084%. In addition, More preferably, it is 0.030 to 0.060%. In addition to the above-described effects, C affects the oxide formation of the ERW weld through the freezing point depression, the CO formation reaction with O _{2 in} the gas phase, and the like during ERW welding.

Si: 0.10 to 0.30%
Si contributes to an increase in strength of the steel pipe by solid solution strengthening. Si has a stronger affinity with O than Fe, and forms a eutectic oxide having a high viscosity together with Mn oxide at the time of ERW welding. If Si is less than 0.10%, the Mn concentration in the eutectic oxide increases, and the melting point of the oxide exceeds the molten steel temperature, so that it easily remains in the ERW weld as an oxide during ERW welding. For this reason, the amount of Mn contained in the inclusion having an equivalent circle diameter of 5 μm or more existing in the ERW welded portion increases, and the total amount of Si, Mn, Al, Ca, Cr exceeds 49 mass ppm. As a result, the creep characteristics of the ERW weld may be degraded. On the other hand, if the Si content exceeds 0.30%, the Si concentration in the eutectic oxide rises during ERW welding, the melting point of the oxide exceeds the molten steel temperature, and the absolute amount as an oxide increases. At the same time, it tends to remain in the ERW weld as an oxide. Therefore, the amount of Si and Mn contained in the inclusion having an equivalent circle diameter of 5 μm or more existing in the ERW welded portion increases, and the total amount of Si, Mn, Al, Ca, and Cr exceeds 49 mass ppm. As a result, the creep characteristics of the ERW weld may be degraded. For this reason, Si is preferably limited to a range of 0.10 to 0.30%. In addition, More preferably, it is 0.15-0.25%.

Mn: 0.70 to 1.90%
Mn contributes to increasing the strength of the steel pipe by solid solution strengthening and transformation structure strengthening. Further, Mn has a stronger affinity with O than Fe, and forms a highly viscous eutectic oxide together with Si oxide during electro-welding welding. If Mn is less than 0.70%, the Si concentration in the eutectic oxide is increased during electro-welding, the melting point of the oxide exceeds the molten steel temperature, and the oxide easily remains in the electro-welded weld. Therefore, the total amount of Si, Mn, Al, Ca, Cr contained in inclusions having an equivalent circle diameter of 5 μm or more present in the ERW weld exceeds 49 mass ppm. As a result, the creep characteristics of the ERW weld may be degraded. On the other hand, if Mn is contained excessively exceeding 1.90%, the Mn concentration in the eutectic oxide is increased during ERW welding, the melting point of the oxide exceeds the molten steel temperature, and the absolute amount as an oxide increases. , It tends to remain in the ERW weld as an oxide. Therefore, the total amount of Si, Mn, Al, Ca, Cr contained in inclusions having an equivalent circle diameter of 5 μm or more present in the ERW weld exceeds 49 mass ppm. As a result, the creep characteristics of the ERW weld may be degraded. Moreover, when Mn is contained excessively exceeding 1.90%, a hard phase will increase in the structure | tissue of a base material part and an ERW weld part, and a creep characteristic may fall.

  Therefore, Mn is preferably limited to a range of 0.70 to 1.90%. In addition, More preferably, it is 0.85-1.85%.

P: 0.018% or less P is preferably segregated as much as possible because it co-segregates with Mn and lowers the creep characteristics of the base metal part and the ERW weld, but is acceptable if it is 0.018% or less. . For this reason, it is preferable to limit P to 0.018% or less. Excessive reduction leads to an increase in refining costs. It is preferable to set it as 0.001% or more from a viewpoint of economical efficiency in a steelmaking process.

S: 0.0029% or less S is bonded to Mn to form MnS, which is present as an inclusion in the steel and reduces ductility and toughness. Therefore, it is desirable to reduce S as much as possible. In particular, a content exceeding 0.0029% may deteriorate the creep characteristics. For this reason, it is preferable to limit S to 0.0029% or less. Excessive reduction leads to an increase in refining costs. From the viewpoint of economic efficiency in the steel making process, it is preferably 0.0001% or more.

Al: 0.01-0.10%
Al acts as a deoxidizer in the steelmaking stage. Moreover, Al combines with N and precipitates as AIN, suppresses γ grain growth during heating, and contributes to improvement of low temperature toughness of steel. In order to acquire such an effect, it is desirable to contain 0.01% or more. If the Al content is less than 0.01%, the deoxidizing ability cannot be ensured in the steelmaking stage, the cleanliness of the steel decreases, the amount of oxide present in the ERW welds increases, and the equivalent circle diameter is 5 μm or more. The total amount of Si, Mn, Al, Ca and Cr contained in the product exceeds 49 ppm. As a result, the creep characteristics may deteriorate. In addition, Al has a stronger affinity for O than Si and Mn, and forms an oxide in a form of being dissolved in a Mn—Si eutectic oxide such as 2MnO · SiO ₂ (Tephrite). On the other hand, if the Al content exceeds 0.35% and excessively contained, the Al concentration in the eutectic oxide increases during ERW welding, and the melting point of the oxide exceeds the molten steel temperature. Easily remain. For this reason, the amount of Si, Mn, and Al contained in inclusions present in the ERW weld is increased, and the total amount of Si, Mn, Al, Ca, and Cr contained in inclusions having an equivalent circle diameter of 5 μm or more. Exceeds 49 mass ppm. As a result, the creep characteristics may deteriorate. For this reason, Al is preferably limited to a range of 0.01 to 0.10%. Preferably, it is 0.02 to 0.08%.

Nb: 0.001 to 0.070%
Nb precipitates mainly as carbides and has the effect of increasing the steel pipe strength by precipitation strengthening. In order to acquire such an effect, it is desirable to contain 0.001% or more. On the other hand, if the content exceeds 0.065%, undissolved large-sized Nb carbonitrides remain, and as a result, creep characteristics may be deteriorated. For this reason, it is preferable to limit Nb to 0.001 to 0.070% of range. In addition, More preferably, it is 0.051 to 0.065%.

V: 0.001 to 0.065%
V, like Nb, precipitates mainly as carbides and has the effect of increasing the steel pipe strength by precipitation strengthening. In order to acquire such an effect, it is desirable to contain 0.001% or more. On the other hand, if the content exceeds 0.065%, undissolved large-sized V carbonitrides remain, and as a result, creep characteristics may deteriorate. For this reason, it is preferable to limit V to 0.001 to 0.065% of range. In addition, More preferably, it is 0.005 to 0.050%.

Ti: 0.001 to 0.033%
Ti, like Nb and V, precipitates mainly as carbides and has the effect of increasing the steel pipe strength by precipitation strengthening. In order to acquire such an effect, it is desirable to contain 0.001% or more. On the other hand, when the content exceeds 0.033%, undissolved large Ti carbonitrides remain, and as a result, the creep characteristics may deteriorate. For this reason, Ti is preferably limited to a range of 0.001 to 0.033%. In addition, More preferably, it is 0.005-0.020%.

Ca: 0.0001 to 0.0035%
Ca has an effect of controlling the shape of sulfide in steel into a spherical shape, and has an effect of improving the toughness and HIC resistance in the vicinity of the ERW weld portion of the steel pipe. In order to acquire such an effect, it is desirable to contain 0.0001% or more. On the other hand, if the content exceeds 0.0035%, the Ca concentration in the oxide increases, the melting point of the oxide exceeds the molten steel temperature, and the amount of oxide increases. It tends to remain in the weld. Therefore, the amount of Ca in the inclusions present in the electric resistance welded portion increases, and the total amount of Si, Mn, Al, Ca, Cr contained in the inclusion having an equivalent circle diameter of 5 μm or more present in the electric resistance welded portion is 49. Exceeds ppm by mass. As a result, the creep characteristics may deteriorate. For this reason, Ca is preferably limited to a range of 0.0001 to 0.0035%. In addition, More preferably, it is 0.0002 to 0.0028%.

N: 0.0050% or less N is combined with Ti, which is a carbonitride-forming element, and precipitates as Ti (N, C) or remains as solid solution N. If the N content exceeds 0.0050%, Ti (N, C) and solid solution N increase, and thus the creep characteristics may be deteriorated. For this reason, it is preferable to limit N to 0.0050% or less. In addition, More preferably, it is 0.0040% or less.

O: 0.0030% or less O exists mainly as oxide inclusions in steel, and lowers ductility and toughness. If the O content exceeds 0.0030%, the amount of inclusions is excessively increased, and the creep characteristics may be particularly deteriorated. For this reason, it is preferable to limit O to 0.0030% or less.

  The above components are basic components. In addition to the above basic composition, Cu: 0.001 to 0.350%, Ni: 0.001 to 0.350%, Mo: 0.001 to 0 .350%, Cr: One or more selected from 0.001 to 0.350% may be contained.

  Cu, Ni, Mo, and Cr are all elements that contribute to improving the hardenability, and can be selected as necessary to contain one or more kinds in order to ensure a desired high strength.

Cu: 0.001 to 0.350%
Cu is an element that improves the hardenability, and it is desirable to contain it particularly for increasing the strength of thick-walled materials. In order to acquire such an effect, it is desirable to contain 0.001% or more. On the other hand, even if it contains exceeding 0.350%, an effect is saturated and the effect corresponding to content cannot be expected. For this reason, when it is contained, it is preferably limited to a range of 0.001 to 0.350%. In addition, Preferably it is 0.05 to 0.290%.

Ni: 0.001 to 0.350%
Ni, like Cu, is an element that improves hardenability, and it is desirable to contain Ni for increasing the strength of thick materials. In order to acquire such an effect, it is desirable to contain 0.001% or more. On the other hand, even if it contains exceeding 0.350%, an effect is saturated and the effect corresponding to content cannot be expected. For this reason, when it is contained, it is preferably limited to a range of 0.001 to 0.350%. In addition, Preferably it is 0.05 to 0.290%.

Mo: 0.001 to 0.350%
Mo, like Ni and Cu, is an element that improves hardenability, and it is desirable to contain it to increase the strength of thick materials. In order to acquire such an effect, it is desirable to contain 0.001% or more. On the other hand, even if it contains exceeding 0.350%, an effect is saturated and the effect corresponding to content cannot be expected. For this reason, when it is contained, it is preferably limited to a range of 0.001 to 0.350%. In addition, Preferably it is 0.05 to 0.290%.

Cr: 0.001 to 0.700%
Cr is an element that improves hardenability, and it is desirable to contain Cr for increasing the strength of thick materials. Moreover, Cr can make the intensity | strength and structure | tissue of a steel pipe the desired high intensity | strength and structure | tissue through transformation strengthening like Mn. In order to acquire such an effect, it is desirable to contain 0.001% or more. In addition, Cr has a stronger affinity with O than Fe, and if it is contained in excess of 0.700%, the Cr concentration in the oxide increases during electro-welding, the melting point of the oxide exceeds the molten steel temperature, and oxidation occurs. The quantity increases, and it tends to remain in the ERW weld as an oxide. For this reason, the amount of inclusions present in the ERW weld is increased, and the total amount of Si, Mn, Al, Ca, Cr contained in the inclusion having an equivalent circle diameter of 5 μm or more in the ERW weld exceeds 49 ppm by mass. . As a result, the creep characteristics may deteriorate. For this reason, when contained, Cr is preferably 0.001 to 0.700%. Still more preferably, it is 0.02 to 0.290%.

Furthermore, in the high strength electric resistance welded steel pipe of the present invention, the above-described components are contained within the above-mentioned range, and the following formula (1): Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20 + Mo / 15 + V / 10 + 5B (1)
(Here, C, Si, Mn, Cu, Ni, Cr, Mo, V, B: content of each element (mass%))
It is preferable to adjust so that Pcm defined by the above satisfies 0.20 or less. If each element is not included, 0 (zero) is set.

  Pcm is an index that affects the formation of the structure during rapid cooling of the ERW weld, and is preferably limited to 0.20 or less in the present invention.

  If Pcm exceeds 0.20, the ERW weld cannot be made into a structure having a pseudo-polygonal ferrite phase as a main phase. And the creep characteristic of an electric-welding welding part may fall. The lower limit of Pcm is not particularly limited, but it is desirable to adjust it to 0.07 or more in order to stably secure YS: 450 MPa or more.

  Next, the reason for limiting the structure of the high strength ERW steel pipe of the present invention will be described.

  Both the base material part and the ERW welded part of the high strength electric resistance steel pipe of the present invention have a pseudopolygonal ferrite phase of 90% or more by volume ratio as the main phase, and the balance is made of a hard phase other than the pseudopolygonal ferrite phase, It is desirable to have a structure in which the average particle size of the main phase such as the pseudopolygonal ferrite phase is 10 μm or less. The second phase other than the main phase has a volume ratio of 10% or less, and is a hard phase such as pearlite, pseudo-pearlite, cementite, bainite, martensite. When the hard phase, which is the second phase, increases by more than 10%, the strength increases excessively and the creep characteristics may deteriorate.

  Incidentally, the “pseudopolygonal ferrite phase” referred to here is in an irregular shape, formed at a temperature lower than about 600 ° C. and higher than 400 ° C. and lower than the polygonal ferrite and beyond the austenite boundary before transformation, This refers to an organization that has recovered most of its transformation strain. This structure is described in “Steel Bainite Photobook-1” (edited by the Japan Iron and Steel Institute Basic Research Group, Bainite Research Group, published by the Japan Iron and Steel Institute (1992.6.29), page 4). It is the same tissue as Quasi-po1ygon Ferrite αq.

  By using a fine pseudo-polygonal ferrite phase with an average particle size of 10 μm or less as the main phase and a structure occupying 90% or more in volume ratio, the yield strength YS: high strength of 450 MPa or more and creep in the middle temperature range ERW steel pipe with excellent characteristics can be obtained. If the structure fraction of the pseudo-polygonal ferrite phase decreases and, for example, a bainite phase other than the pseudo-polygonal ferrite phase becomes the main phase, the strength may increase excessively and the creep characteristics may deteriorate. Further, when the main phase is a polygonal ferrite phase, the strength is lowered, and a desired high strength cannot be obtained, and the creep characteristics may be lowered. Further, when the average particle size exceeds 10 μm and becomes coarse, the strength in the intermediate temperature range may be lowered.

  Next, the preferable manufacturing method of this invention electric resistance welded steel pipe is demonstrated.

  After the hot-rolled steel strip is continuously roll-formed into an open pipe with a substantially circular cross section, the vicinity of the butt portion of the open pipe is heated to the melting point or higher and pressure welded with a squeeze roll, and then the conventional electric resistance welding is performed. The ERW steel pipe having the ERW welded part is used.

  The hot-rolled steel strip used as the steel pipe material is preferably a steel material having the above composition as a starting material. The method for producing the steel material is not particularly limited, but it is preferable that the steel material is melted in a conventional converter or the like and is made into a slab or the like by a conventional continuous casting method.

  The steel material having the above composition is heated and soaked, hot-rolled, wound into a coil shape, made into a hot-rolled steel strip, and a steel pipe material.

Heating temperature: more than 1200 ° C. and 1280 ° C. or less, holding time: 90 min or more The heating temperature affects the strength of the base material and long-term softening resistance. When the heating temperature is 1200 ° C. or lower, precipitation strengthening elements such as Nb, V, and Ti remain coarse without being re-dissolved, so that a desired high strength of YS: 450 MPa or more may not be ensured. Further, if coarse precipitates remain without being dissolved, the creep characteristics of the base material portion may be deteriorated. On the other hand, if the heating temperature exceeds 1280 ° C., the structure becomes coarse and the toughness may be reduced.

  In addition, when the heating and holding time is less than 90 minutes, precipitation strengthening elements such as Nb, V, and Ti are not re-dissolved in the center of the thickness, and remain coarse. Coarse precipitates may reduce creep properties. For this reason, it is preferable to limit the heating temperature to more than 1200 ° C. and 1280 ° C. and holding time: 90 min or more.

  The heated and soaked steel material is then subjected to hot rolling consisting of rough rolling and finish rolling to form a hot rolled steel strip.

  The conditions for the rough rolling need not be particularly limited as long as the sheet bar can have a predetermined size and shape. After rough rolling, finish rolling is performed. In the finish rolling, it is preferable to adjust the hot rolling rate in the non-recrystallization temperature range: 20% or more and the finish rolling finish temperature: 750 ° C. or more.

Hot rolling rate in the non-recrystallization temperature range: 20% or more If the hot rolling rate in the non-recrystallization temperature range is less than 20%, the resulting hot rolled steel strip structure becomes coarser than the average grain size of 10 μm. In some cases, the creep characteristics of the base material portion may deteriorate. The upper limit of the hot rolling rate is not particularly limited, but is preferably 95% or less from the viewpoint of the load on the rolling mill.

Finish rolling end temperature: 750 ° C. or higher If the finish rolling end temperature is less than 750 ° C., the rolling strain remains, and the creep characteristics may deteriorate even after cooling. For this reason, it is preferable to limit the finish rolling end temperature to 750 ° C. or higher.

  The hot-rolled steel strip that has finished finish rolling is then cooled on a hot-rolled runout table. The cooling after rolling is preferably performed to a cooling stop temperature of 620 ° C. or lower, in which the average cooling rate in the temperature range of 780 to 620 ° C. is in the range of 7 to 299 ° C./s at the plate thickness center temperature.

Average cooling rate in the temperature range of 780 to 620 ° C. at the plate thickness center temperature: 7 to 299 ° C./s
When the average cooling rate in the temperature range of 780 ° C. to 620 ° C. is less than 7 ° C./s, a coarse polygonal ferrite phase having an average particle size of more than 10 μm is formed, and a desired base material structure may not be obtained. is there. For this reason, the desired high strength of YS: 450 MPa or more cannot be ensured, and the creep characteristics may deteriorate. On the other hand, when the average cooling rate exceeds 299 ° C./s, the fraction of the pseudopolygonal ferrite phase is less than 90%, the strength is increased, and the creep characteristics may be lowered. For this reason, the cooling after rolling is preferably cooling having a cooling rate in the range of 7 to 299 ° C./s at an average cooling rate in the temperature range of 780 to 620 ° C. at the plate thickness center temperature.

  In cooling after rolling, the cooling rate at each position in the plate thickness direction excluding the outermost layer of 0.2 mm is a deviation from the center of the thickness, within 5 ° C / s on the slow side and within 20 ° C / s on the fast side. It is desirable that

Cooling stop temperature for cooling after rolling: 620 ° C. or lower It is desirable that cooling after rolling is stopped at a temperature of 620 ° C. or lower at the cooling rate described above. When the cooling stop temperature is higher than 620 ° C., the stop temperature is too high, and a structure having a desired pseudopolygonal ferrite as a main phase may not be obtained. For this reason, it is preferable to set the cooling stop temperature for cooling after rolling to 620 ° C. or less. In addition, More preferably, it is 595-475 degreeC.

  After stopping the cooling after rolling, the hot-rolled steel strip is wound into a coil at a winding temperature of 595 to 475 ° C.

Winding temperature: 595-475 ° C
When the coiling temperature is less than 475 ° C., the coiling temperature becomes too low and the structure becomes a structure mainly composed of a bainite phase, and the creep characteristics may be deteriorated. For this reason, the coiling temperature is desirably 475 ° C. or higher. Note that if the coiling temperature exceeds 595 ° C. and becomes high, the coiling temperature is too high and a desired structure may not be secured. For this reason, it is preferable that winding temperature shall be 595-475 degreeC.

  The wound hot-rolled steel strip is then subjected to a thermal history adjusted so that the residence time in the temperature range of 480 to 350 ° C. is 2 to 20 hours.

Cumulative residence time in the temperature range of 480-350 ° C .: 2-20 h
Adjustment of the thermal history in the temperature range of 480 to 350 ° C. is an important requirement for ensuring desired characteristics, particularly excellent creep characteristics in the intermediate temperature range of the base material. Even when a precipitate, dislocation structure, microstructure, etc. are stabilized for a predetermined time in the temperature range of 480 to 350 ° C. at the plate thickness center temperature, and stress is applied for a long time in the intermediate temperature range thereafter, Less change. When the accumulated residence time in the temperature range of 480 to 350 ° C. is less than 2 h, the structure is not sufficiently stabilized, and when stress is applied for a long time in the intermediate temperature range, the precipitate, dislocation structure, microstructure, etc. change. In some cases, the creep characteristics may deteriorate. On the other hand, when the accumulated residence time in the temperature range of 480 to 350 ° C. exceeds 20 h and becomes a long time, the high temperature strength of the base material part may be lowered. Therefore, it is preferable to limit the accumulated residence time in the temperature range of 480 to 350 ° C. to 2 to 20 hours. In addition, More preferably, it is 3-12h. The adjustment of the accumulated residence time in the temperature range of 480 to 350 ° C. is preferably based on the adjustment of the coiling temperature and the coil cooling conditions. In addition, after adjusting the heat history in a 480-350 degreeC temperature range, it cools.

  Next, using the obtained hot-rolled steel strip as a steel pipe material, the hot-rolled steel strip is continuously roll-formed into an open tube having a substantially circular cross section, and then the vicinity of the butt portion of the open tube is heated to the melting point or higher. ERW welding is performed with pressure squeeze rolls to form ERW steel pipes.

  In the fin pass forming of the continuous roll forming, it is preferable to give a taper groove to the width end face of the hot-rolled steel strip (end face of the butt portion of the open pipe). The taper groove to be applied is preferably a groove in which the distance in the thickness direction of the steel strip between the taper start position and the surface serving as the pipe outer surface or the surface serving as the pipe inner surface is 2 to 80% of the steel strip thickness. As a result, discharge of inclusions in the ERW welded portion is promoted, inclusions are reduced, and Si, Mn, Al, Ca, Cr contained in inclusions having an equivalent circle diameter of 5 μm or more present in the ERW welded portion. The total amount of can be reduced by about 10 ppm, and the creep characteristics can be further improved. The tapered shape is not limited to a straight line, and may be an arbitrary curved shape.

  In addition, any of the commonly known electric resistance welding methods can be applied to electric resistance welding. Electro-sewing welding is usually performed in an air atmosphere, but electro-sealing welding may be performed by performing atmospheric control with reduced atmospheric oxygen partial pressure.

  As a method for controlling the atmosphere, for example, a method of sealing a region to be electro-welded with a box structure and supplying a non-oxidizing gas can be mentioned. When the non-oxidizing gas is blown, the surrounding atmosphere (atmosphere) may be involved, and the oxygen partial pressure may rather increase. Therefore, it is preferable to blow the non-oxidizing gas using the gas injection port as a nozzle having a multilayer structure such as three layers.

  The electric resistance welded portion of the obtained electric resistance welded steel pipe is subjected to heat treatment for heating and cooling online.

  For this heat treatment, it is preferable to use a high-frequency induction heating apparatus that is installed online and can heat only the vicinity of the ERW weld. In addition, it is preferable to provide a cooling device in which a plurality of cooling headers connected to a plurality of nozzles are provided above the ERW weld portion, which is a material to be cooled, so that the cooling rate can be adjusted. In this heat treatment, the total thickness in the vicinity of the ERW weld is heated to a temperature in the range of 800 ° C. to 1150 ° C., and the average cooling rate in the temperature range of 780 ° C. to 620 ° C. is 7 in the thickness central portion temperature. Cooling in a range of ˜299 ° C./s is performed to a cooling stop temperature of 620 ° C. or less, and further, the accumulated residence time in the temperature range of 500 to 360 ° C. is adjusted to 2 to 200 s at the thickness center temperature. It is preferable that the heat history be applied. In order to set the accumulated residence time in the temperature range of 500 to 360 ° C. within the above-described range, the temperature range is gradually cooled or heated to a range of 500 to 360 ° C. (tempering treatment). Preferably it is done.

  By performing such heat treatment, a fine pseudo-polygonal ferrite phase with an average particle size of 10 μm or less becomes a volume ratio of 90% or more, and the remainder becomes an electro-welded welded structure composed of a hard phase such as pearlite. The welded portion has a high yield strength YS: 450 MPa or more and excellent creep characteristics. In particular, the creep characteristics of ERW welds are strongly influenced by oxides and structures of ERW welds.

  When the heating temperature is lower than 800 ° C., a hard structure as it is electroweld remains, and the desired toughness may not be ensured. On the other hand, when the heating temperature exceeds 1150 ° C., the crystal grains become coarse and desired toughness may not be ensured.

  In the cooling after heating, if the average cooling rate in the temperature range of 780 ° C. to 620 ° C. is less than 7 ° C./s, the structure of the ERW weld is coarsened and coarse polygonal ferrite is used as the main phase. Therefore, the yield strength YS: a high strength of 450 MPa or more cannot be secured, and the creep characteristics may be deteriorated. On the other hand, if it exceeds 229 ° C./s, the fraction of pseudopolygonal ferrite is less than 90%, the strength is increased, and the creep characteristics are decreased.

  In addition, the cooling stop temperature of the above cooling is set to a temperature of 620 ° C. or lower. When the cooling stop temperature exceeds 620 ° C., the structure may become polygonal ferrite.

  In addition, creep characteristics in the middle temperature region of ERW welds are controlled by controlling the heat history in the temperature range of 500 to 360 ° C. in the on-line heat treatment after ERW welding. Etc. can be stabilized and excellent characteristics can be expressed. When the accumulated residence time in the temperature range of 500 to 360 ° C. is less than 2 s, the precipitate, dislocation structure, microstructure, etc. change and the high temperature strength decreases when kept in the middle temperature range for a long time, and the creep characteristics May decrease. On the other hand, when it becomes longer than 200 s, the high temperature strength of the ERW weld may decrease. Therefore, it is preferable to limit the accumulated residence time in the temperature range of 500 to 360 ° C. to 2 to 200 s. More preferably, it is 3 to 120 s.

  Hereinafter, the present invention will be further described based on examples.

  A steel material (slab: thickness 250 mm) having the composition shown in Table 1 is heated for 110 minutes at a heating temperature of 1230 ° C. shown in Table 2, and then the hot rolling rate at 55% or less of the rough rolling and the non-recrystallization temperature or less. As a hot rolled steel strip having a plate thickness of 20.6 mm, a hot rolling consisting of finish rolling with a finish rolling finish temperature of 810 ° C. was applied. In addition, the steel raw material used what melted the molten steel of the composition shown in Table 1 with the converter, and made it the slab of thickness 250mm by the continuous casting method.

  Immediately after finishing rolling, the hot-rolled steel strip is cooled on the hot-rolled run-out table at a cooling rate with an average cooling rate of 28 ° C./s in the temperature range of 780 to 620 ° C. at the plate thickness center temperature. The coil was wound in a coil shape at a winding temperature of 500 ° C. The wound hot-rolled steel strip was further subjected to a heat history for adjusting the residence time in the temperature range of 350 to 480 ° C. to 4 h.

  The obtained hot-rolled steel strip is used as a steel pipe material, slitted to a predetermined width, continuously rolled to form an open pipe having a substantially circular cross section, and the vicinity of the butt portion of the open pipe is heated to the melting point or higher. ERW welding, which is pressure-welded with a squeeze roll, was performed to obtain an ERW steel pipe (outer diameter 508 mmφ).

  In some cases, tapered grooves were provided to both end surfaces in the width direction of the hot-rolled steel strip by fin pass forming in roll forming. The applied taper groove has, on the end surface in the width direction of the hot rolling retreat, the distance between the surface serving as the pipe outer surface and the taper starting position is 20% of the thickness of the hot-rolled steel strip, and the surface serving as the pipe inner surface and the taper starting position. The distance is 20% of the thickness of the hot-rolled steel strip, 20% on the outer surface side-20% on the inner surface side.

Further, the electric resistance welding was mainly performed in an air atmosphere (oxygen partial pressure: 210,000 ppm). In some cases, electro-welding was performed in an atmosphere in which an inert gas (N ₂ gas) was injected and the oxygen partial pressure was reduced to 45 ppm by using a nozzle having injection layers arranged in three layers.

Subsequently, the ERW welded portion of the obtained ERW steel pipe was heated online under the conditions shown in Table 2 and then cooled. For the heating, a high frequency induction heating apparatus having a structure capable of heating only the vicinity of the ERW weld was used. For cooling, a cooling header in which a nozzle capable of injecting rod-shaped cooling water having a water amount density of 0.9 m ³ / m ² min is provided above the ERW weld, which is a material to be cooled, is set to 0. The cooling was performed with a cooling device that enabled injection of rod-shaped cooling water at a speed of 9 m / s. Further, the cooling header has a structure in which cooling water injection can be individually controlled on and off.

  In addition, the temperature of the ERW welded part is measured on the downstream side in the steel pipe conveying direction, and the cooling rate of the ERW welded part is displayed by controlling the water injection from each cooling header based on the measured steel pipe temperature. It adjusted so that it might become the cooling rate shown in 2, and it cooled to 300 degreeC. Subsequently, the ERW welded portion of the ERW steel pipe was tempered by heating to 450 ° C. online, and the accumulated residence time in the temperature range of 360 to 500 ° C. was adjusted to the conditions shown in Table 2.

Further, after the heat treatment, the electro-welded welded portion was continuously subjected to flaw detection with a phased array ultrasonic flaw detector having a sensitivity that is 20 dB higher than the sensitivity with a reference echo height of a φ1.6 mm through hole being 80%, and detected echoes. A steel pipe having a height of 80% or less and a steel pipe having a height of 80% or more were selected.

Test pieces were collected from the steel pipes obtained by sorting and subjected to structure observation, inclusion analysis of the ERW weld, tensile test, and creep test. The test method was as follows.
(1) Microstructure observation From the base material part of the obtained ERW steel pipe, a specimen for microstructural observation was collected, the circumferential cross section (C cross section) was polished and corroded, and a scanning electron microscope (magnification: 1000). The tissue was observed and imaged, the tissue was identified, and the tissue fraction and the average particle diameter were determined by image analysis. The average particle size was calculated by measuring the area of each particle by image analysis, obtaining the equivalent circle diameter, and arithmetically averaging. Here, in the case of the bainite phase, the region size (packet size) in the same direction was measured as the particle size.
(2) Inclusion analysis of the ERW welded part From the ERW welded part of the obtained ERW steel pipe, the width: 2mm plate test piece <width: 2mm x thickness: total thickness centered on the center of the ERW welded part X length: total thickness> was collected. This plate sample is subjected to electrolytic extraction in an electrolytic solution (10% AA solution), and the obtained extraction residue is collected by a filter mesh (hole diameter: 5 μm), and SiP contained in the residue is obtained by ICP emission analysis. , Mn, Al, and Ca amounts (mass ppm) were respectively calculated, and the total amount thereof was calculated, and the total amount (mass ppm) of Si, Mn, Al, and Ca contained in inclusions having an equivalent circle diameter of 5 μm or more It was.
(3) Tensile test ASTM E8 round bar test piece (parallel part: 6.35 mmφ, GL: so that the pipe circumferential direction is the tensile direction from the base metal part and the ERW welded part of the obtained ERW steel pipe, respectively. 25.4 mm) was collected. The base material portion was positioned 180 ° from the ERW weld. Moreover, the round bar test piece of the electric resistance welding part was extract | collected so that a seam might be located in the center of a parallel part. Note that the flattening of the steel pipe was not performed when collecting the test piece.

The tensile test was performed at room temperature at a tensile rate of 0.5% / min for YS or less, and 5 mm / min after exceeding YS, to determine tensile properties (yield strength YS, tensile strength TS).
(4) Creep test From the base metal part and the ERW welded part of the obtained ERW steel pipe, the test piece with a hook (parallel part: 6 mmφ, GL: 30 mm) so that the pipe circumferential direction becomes the test piece longitudinal direction ) Was collected. Note that the base material portion was positioned 180 ° from the ERW weld. Further, the ERW welded specimen was collected so that the seam was positioned at the center of the parallel part.

The test temperature was 400 ° C., and the creep rupture strength was determined. In terms by resulting creep rupture strength from Larson-Miller parameter, to calculate the estimated creep rupture strength _{sigma creep} of 20 years at 350 ° C., the ratio of the room temperature _{YS RT,} seeking _{σ creep / YS RT, σ creep} / YS _The case where _RT was 0.8 or more was evaluated as “excellent in creep rupture characteristics”.

  The obtained results are shown in Table 3.

In each of the examples of the present invention, both the base metal part and the electric-welded welded part have a pseudo-polygonal ferrite with an area ratio of 90% or more as a main phase, and have a fine structure with an average grain size of 10 μm or less, yield strength S: High strength of 450 MPa or more, ratio of creep rupture strength σ _creep to room temperature YS _RT , σ _creep / YS _RT is 0.80 or more, and has an excellent creep rupture property.

On the other hand, in a comparative example that is out of the scope of the present invention, the σ _creep / YS _RT of the ERW weld is less than 0.80, and the creep rupture characteristics are degraded.

Claims (7)

The hot-rolled steel strip is continuously roll-formed into an open tube with a substantially circular cross section, and then the vicinity of the butt portion of the open tube is heated to the melting point or higher and subjected to electro-welding welding with a squeeze roll. In the manufacture of an electric resistance welded pipe having a welded portion, and then performing an online heat treatment on the electric resistance welded steel pipe, after the heat treatment, the sensitivity of the reference echo height of the φ1.6 mm through hole to 80% is set. The ERW weld was continuously detected with a phased array ultrasonic flaw detector with a sensitivity increased by 20 dB, and a steel pipe with a detected echo height of 80% or less was placed at 350 ° C. for 20 years in the ERW weld. A high-strength ERW steel pipe excellent in creep characteristics in the middle temperature region of the ERW weld, characterized in that the product has a creep rupture stress of (API5L standard yield strength lower limit x 2/3) or more . Production method. The ERW steel pipe is in mass%,
C: 0.025 to 0.084%, Si: 0.10 to 0.30%,
Mn: 0.70 to 1.90%, P: 0.018% or less,
S: 0.0029% or less, Al: 0.01-0.10%,
Nb: 0.001 to 0.070%, V: 0.001 to 0.065%,
Ti: 0.001 to 0.033%, Ca: 0.0001 to 0.0035%,
N: 0.0050% or less, O: 0.0030% or less, and Pcm defined by the following formula (1) is contained so as to satisfy 0.20 or less, and consists of the balance Fe and inevitable impurities. A mother body having a composition and a pseudo-polygonal ferrite phase having a volume ratio of 90% or more as a main phase, the balance being a hard phase other than the pseudo-polygonal ferrite phase, and an average particle size of the pseudo-polygonal ferrite phase being 10 μm or less The material structure and the pseudo-polygonal ferrite phase with a volume ratio of 90% or more are the main phase, and the remainder is a hard phase other than the pseudo-polygonal ferrite phase, and the average particle size of the pseudo-polygonal ferrite phase is 10 μm or less. The manufacturing method of the high intensity | strength ERW steel pipe of Claim 1 which has a structure | tissue which consists of a certain ERW weld structure | tissue.
Pcm = C + Si / 30 + Mn / 20 + Cu / 20 + Ni / 60 + Cr / 20
+ Mo / 15 + V / 10 + 5B (1)
Here, C, Si, Mn, Cu, Ni, Cr, Mo, V, B: Content of each element (mass%)   In addition to the above composition, Cu: 0.001 to 0.350%, Ni: 0.001 to 0.350%, Mo: 0.001 to 0.350%, Cr: 0.001 to mass%. The method for producing a high-strength ERW steel pipe according to claim 2, comprising one or more selected from 0.350%.   In the online heat treatment, after heating the wall thickness in the vicinity of the ERW weld to a temperature in the range of 800 ° C. to 1150 ° C., the wall thickness in the temperature range of 780 ° C. to 620 ° C. Cooling with an average cooling rate in the range of 7 to 299 ° C./s was performed to a cooling stop temperature of 620 ° C. or less, and the accumulated residence time in the temperature range of 500 to 360 ° C. was adjusted to be 2 to 200 s. The method for producing a high-strength ERW steel pipe according to any one of claims 1 to 3, wherein the heat history is applied. In the fin-pass forming of the roll forming, the distance in the thickness direction between the taper start position and the surface serving as the outer surface of the tube or the surface serving as the inner surface of the tube is hot-rolled steel. method of producing a high strength electric resistance welded steel pipe of claims 1 to placing serial to any one of 4, wherein the applying a tapered groove which becomes 2 to 80% of ObibanAtsu.   The method for producing a high-strength ERW steel pipe according to any one of claims 1 to 5, wherein the ERW welding is performed in an atmosphere in which an oxygen partial pressure is reduced compared to an oxygen partial pressure in the atmosphere.   The total content of Si, Mn, Al, and Ca contained in inclusions having an equivalent circle diameter of 5 μm or more present in the ERW weld is 49 mass ppm or less. The manufacturing method of the high intensity | strength ERW steel pipe in any one.

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