KR20210130219A - Electric resistance welded steel pipe, manufacturing method thereof, and steel pipe pile - Google Patents

Abstract

An electric resistance resistance steel pipe having a welded portion in the axial direction with a base metal part, the component composition of the base metal part has a specific component composition, and when the plate thickness of the base metal part is t, a depth of 1/4 t of the plate thickness t from the outer surface of the electric resistance resistance steel pipe In the steel structure in the position, bainite is 70% or more in area ratio, the average effective particle size of bainite is 10.0 µm or less in average equivalent circle diameter, and the average aspect ratio of bainite is 0.1 to 0.8, and the tube axis direction has a tensile strength of 590 MPa or more, a 0.2% yield strength of 450 MPa or more, a yield ratio of 85 to 95%, and a Charpy absorbed energy of 70 J or more at -30°C with the tube axial direction in the base metal part as the longitudinal direction of the specimen. , wherein the residual stress in the pipe axial direction of the outer surface of the steel pipe in the base metal part is 250 MPa or less, a method for manufacturing the same, and a steel pipe pile.

Description

Electric resistance welded steel pipe, manufacturing method thereof, and steel pipe pile

The present invention relates to an electric resistance resistance steel pipe suitable for a steel pipe pile used as a basis for a structure, a method for manufacturing the same, and a steel pipe pile. In particular, the present invention uses a hot rolled steel sheet (hot rolled steel strip) as a material, and increases the strength, toughness, optimization of yield ratio and buckling resistance ( buckling resistance) to improve performance.

In recent years, as a response to a large-scale earthquake, it has been strongly desired to increase the strength and improve the strain energy absorbing capacity also for a steel pipe pile used as a foundation for a structure. In general, in order to improve the strain energy absorption capacity of a steel pipe, it is effective to use a steel pipe having a high tensile strength and a low yield ratio. However, in the steel pipe pile, it is difficult to make the yield ratio in the pipe axis direction excessively low from the viewpoint of suppressing the deformation of the steel pipe during pile driving. Moreover, high low-temperature toughness is also required for the steel pipe pile used especially in cold districts. In addition, high buckling resistance is also required to withstand deformation due to earthquakes or the like.

Patent Document 1 describes a method for manufacturing an earthquake-resistant welded steel pipe excellent in local buckling properties. In Patent Document 1, by weight%, C: 0.03 to 0.15%, Mn: 1.0 to 2.0%, Cu: 0.05 to 0.50%, Ni: 0.05 to 0.50%, Cr: 0.05 to 0.50%, Mo: 0.05 -0.50%, Nb: 0.005-0.10%, V: 0.005-0.10%, Ti: 0.005-0.080% of Ti: 0.005-0.080% of a composition containing at least one, Pcm of 0.10-0.25 steel is hot-rolled, and after completion of rolling A steel sheet obtained by cooling to 600°C or less at a cooling rate of 5°C/s or more is cold-formed to obtain a steel pipe. Accordingly, it is possible to obtain a steel pipe having excellent deformation performance in which the work hardening index in the tensile test in the tube axial direction is 0.10 or more. It is said that the occurrence of brittle cracking or fracture can be prevented.

Patent Document 2 contains, in wt%, C: 0.02 to 0.20%, Si: 0.02 to 0.50%, Mn: 0.50 to 2.00%, and further Cu: 0.10 to 1.5%, Ni: 0.10 to 0.50%, Nb : 0.005-0.10% and V: 0.005-0.10% In a steel piece containing one or more selected from the group consisting of 0.005-0.10%, and Ceq: 0.38-0.45, the reduction ratio per pass in a temperature range of 900 ° C. or higher is Hot rolling is performed so as to be 4% or less to obtain a hot-rolled steel sheet, and the hot-rolled steel sheet is reheated in a dual-phase temperature region of Ac1 point or more and Ac3 point or less, and quenched from the two-phase temperature region. A method for manufacturing a steel pipe in which a steel pipe is further subjected to tempering and then pipe-making is described. The steel pipe thus obtained is a high tensile strength steel pipe with a resistive yield ratio of 0.2% yield strength: 440 MPa or more, tensile strength: 590 to 700 MPa, and yield ratio: 80% or less, and is said to be suitable for use in steel structures such as buildings, bridges, and tanks. .

In Patent Document 3, in the production of a steel pipe having a composition containing C: 0.10 to 0.18%, Si: 0.1 to 0.5%, and Mn: 1 to 2% by mass%, heating to an Ac3 point or higher, followed by rapid cooling And, after heating to the two-phase temperature range of Ac1 point to Ac3 point, the process of air cooling, the process of forming into a tube shape in cold, and the process of reheating to 500 to 600 ° C. A manufacturing method using a steel pipe is described. Accordingly, it is said that a steel pipe for building structures having a tensile strength of 590 MPa or more can be manufactured without using an expensive alloying element.

Patent Document 4 includes, in mass%, C: 0.11 to 0.20%, Si: 0.05 to 0.50%, Mn: 1.00 to 2.00%, P: 0.030% or less, S: 0.010% or less, and Al: 0.01 to 0.08%. In addition, the ferrite phase is the main phase, the second phase other than the main phase is pearlite and/or pseudo-pearlite having an area ratio of 8 to 30%, and the average particle size including the main phase and the second phase is 4.0 to 10 µm A high-resistance electric resistance welded steel pipe with a resistive yield ratio for steel pipe piles having a phosphorous structure and having a 0.2% yield strength YS: 450 MPa or more, a tensile strength TS: 590 MPa or more, and a yield ratio: 90% or less in the pipe circumferential direction and the pipe axial direction is described. .

Japanese Laid-Open Patent Publication No. 11-6032 Japanese Patent Publication No. 2687841 Japanese Laid-Open Patent Publication No. 2004-300461 Japanese Patent No. 6123734 publication

However, in the steel pipe manufactured by the technique described in Patent Document 1, the yield ratio in the pipe axial direction is excessively decreased. For this reason, when applied as a steel pipe pile, there exists a possibility that problems, such as buckling, may arise by driving in the case of pile driving.

The technique described in Patent Document 2 requires a heat treatment step for tempering. Moreover, in the technique described in patent document 3, a large sized conventional heat processing apparatus is required, and also a heat processing process is required after can-making. Techniques requiring these heat treatments have a problem that the yield ratio becomes too low. In addition, there is also a problem that the process becomes complicated and productivity decreases. Moreover, production cost increases and it becomes difficult to provide cheaply.

In the technique described in Patent Document 4, after hot rolling, it is cooled from the finish rolling end temperature to a temperature range of 550 to 700° C. in 10 to 100 s to obtain a structure mainly composed of ferrite and pearlite, and a desired structure cannot be obtained. have. In addition, a facility having a very long cooling zone is required, and it becomes difficult to provide an inexpensive, high-strength, high-toughness electric resistance welded steel pipe for steel pipe piles.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an electric resistance resistance steel pipe having an optimum yield ratio and high buckling resistance, and also having high strength and high toughness, a method for manufacturing the same, and a steel pipe pile .

In addition, the present invention also provides an electric resistance resistance steel pipe, a manufacturing method thereof, and a steel pipe pile that can achieve the above object when a hot-rolled steel sheet having a sheet thickness of 16 mm or less is mainly used as a raw material.

As used herein, "high strength" means 0.2% yield strength (YS): 450 MPa or more, tensile strength (TS): 590 MPa in the tube axial direction in the base metal zone of the electric resistance resistance steel pipe. In case of more than "High toughness" as used herein refers to a case where the Charpy absorbed energy at -30°C is 70 J or more, with the tube axis direction in the base metal part of the electric resistance welded steel pipe being the length direction of the test piece. In other words, it is assumed that the above-described high toughness is satisfied in both the pipe circumferential direction and the pipe axial direction of the electric resistance resistance steel pipe. The "optimum yield ratio" here means 85-95 % of ratio (YR) of 0.2% yield strength with respect to said tensile strength. "High buckling resistance" as used herein refers to a case in which the residual stress in the tube axial direction of the outer surface of the steel pipe in the base metal portion of the electric resistance resistance steel pipe is 250 MPa or less, and the yield ratio is 95% or less.

MEANS TO SOLVE THE PROBLEM In order to achieve said objective, the present inventors earnestly examined the influence of various alloying elements and manufacturing conditions on a yield ratio, 0.2% yield strength, tensile strength, and a Charpy impact characteristic. Moreover, the buckling resistance performance of the obtained steel pipe (electric resistance resistance steel pipe) was also earnestly examined. As a result, it was recognized that high strength and high toughness can be achieved while keeping the yield ratio relatively low, and that there is an appropriate component composition, steel structure, and manufacturing conditions having high buckling resistance.

That is, a hot-rolled steel sheet manufactured by limiting to a specific component composition and hot rolling conditions is reduced diameter rolling under specific conditions after welding in the cold roll forming process by cold roll forming. Accordingly, in the steel structure at a depth of 1/4 t of the plate thickness t from the outer surface of the steel pipe of the base metal part of the electric resistance resistance steel pipe, bainite is 70% or more by area ratio, and the average effective particle size of bainite is equivalent to the average circle 10.0 µm or less in diameter, and the average aspect ratio of bainite can be 0.1 to 0.8, 0.2% yield strength is 450 MPa or more, tensile strength is 590 MPa or more, and the yield ratio is 85 to 95%, -30 Charpy absorbed energy at ° C is 70J or more, and the residual stress in the tube axial direction of the outer surface of the steel pipe in the base material part is 250 MPa or less. found to be obtained.

The present invention has been completed by further examination based on such recognition, and the gist of the present invention is as follows.

[1] An electric resistance welded steel pipe having a base metal part and a welding part in the pipe axis direction,

The component composition of the base material part is in mass%,

C: 0.020 to 0.11%;

Si: 0.60% or less;

Mn: 0.50 to 1.70%;

P: 0.030% or less;

S: 0.015% or less;

Al: 0.010 to 0.060%,

Nb: 0.010 to 0.080%;

V: 0.001 to 0.060%;

Ti: 0.010 to 0.050%,

N: 0.006% or less

contains, and the balance consists of Fe and unavoidable impurities,

When the plate thickness of the base metal part is t, the steel structure at a depth of 1/4 t of the plate thickness t from the outer surface of the electric resistance resistance steel pipe is,

Bainite is 70% or more in area ratio,

The average effective particle diameter of the bainite is 10.0 μm or less in terms of the average equivalent circle diameter, and the average aspect ratio of the bainite is 0.1 to 0.8,

The tensile strength in the tube axial direction is 590 MPa or more, the 0.2% yield strength is 450 MPa or more, and the yield ratio is 85 to 95%,

The Charpy absorbed energy at -30°C with the tube axial direction in the base material as the longitudinal direction of the test piece is 70 J or more,

The electric resistance resistance steel pipe whose residual stress in the pipe axial direction of the outer surface of the steel pipe in the base metal part is 250 MPa or less.

[2] The electric resistance resistance steel pipe according to [1], further comprising, in mass%, B: 0.008% or less in addition to the above component composition.

[3] In addition to the above component composition, in mass%,

Cr: 0.01 to 1.0%,

Mo: 0.01 to 1.0%,

Cu: 0.01 to 0.50%,

Ni: 0.01 to 1.0%,

Ca: 0.0005 to 0.010%

The electric resistance resistance steel pipe according to [1] or [2], containing one or two or more selected from the group consisting of:

[4] A method of manufacturing an electric resistance resistance steel pipe in which a steel material is subjected to a hot rolling process and a cooling process in this order to obtain a hot-rolled steel sheet, and further subjected to a cold roll forming process to the hot-rolled steel sheet to obtain an electric resistance resistance steel pipe,

The steel material has the component composition according to any one of [1] to [3],

In the hot rolling process, after heating the steel material to a heating temperature: 1100 to 1280 ° C, rough rolling end temperature: 850 to 1150 ° C, finish rolling end temperature: 750 to 850 ° C, In addition, rough rolling and finish rolling The total rolling reduction at 930°C or less in: a step of performing rough rolling and finish rolling of 65% or more to obtain a hot-rolled sheet,

The cooling step is a step of cooling the hot-rolled sheet at an average cooling rate from cooling start to cooling stop: 15 to 35° C./s, and cooling stop temperature: 450 to 650° C. at the plate thickness center temperature,

In the cold roll forming step, a steel pipe material subjected to roll forming processing is welded to the hot rolled steel sheet, and diameter reduction is performed with respect to the circumference of the outer surface of the steel pipe after welding with a diameter reduction ratio of 0.2 to 0.5%.

[5] Having the component composition according to any one of [1] to [3], and when the plate thickness is t, the steel structure at a depth of 1/4 t of the plate thickness t from the outer surface has an area of bainite 70% or more, the average effective particle diameter of the bainite is 10.0 μm or less in terms of the average equivalent circle diameter, and the average aspect ratio of the bainite is 0.1 to 0.8. A method for manufacturing an electric resistance welded steel pipe, comprising:

In the cold roll forming step, a steel pipe material subjected to roll forming processing is welded to the hot rolled steel sheet, and diameter reduction is performed with respect to the circumference of the outer surface of the steel pipe after welding with a diameter reduction ratio of 0.2 to 0.5%.

[6] A steel pipe pile using the electric resistance resistance steel pipe according to any one of [1] to [3].

ADVANTAGE OF THE INVENTION According to this invention, it has an optimal yield ratio and high buckling-resistance performance, and is further equipped with high strength and high toughness, a manufacturing method thereof, and a steel pipe pile, which are suitably used as a steel pipe pile. The electric resistance resistance steel pipe of the present invention can be easily manufactured, resulting in remarkable industrial effects.

(Form for implementing the invention)

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

First, the reason for limiting the component composition of the electric resistance resistance steel pipe of this invention is demonstrated. Hereinafter, unless otherwise indicated, "mass %" in a component composition is simply described as "%".

The electric resistance resistance steel pipe of the present invention has a base metal part and a welded part, and the base metal part has C: 0.020 to 0.11%, Si: 0.60% or less, Mn: 0.50 to 1.70%, P: 0.030% or less, S: 0.015% or less, Al: 0.010 to 0.060%, Nb: 0.010 to 0.080%, V: 0.001 to 0.060%, Ti: 0.010 to 0.050%, N: 0.006% or less, and the balance has a component composition consisting of Fe and unavoidable impurities.

Moreover, the electric resistance resistance steel pipe of this invention has a weld part in the pipe|tube axial direction. A "hot-rolled steel sheet" mentioned later shall include a hot-rolled steel sheet and a hot-rolled steel strip.

C: 0.020 to 0.11%

C is an element that increases the strength of a steel pipe (electric resistance welded pipe) by solid solution strengthening and is involved in the production of steel structures such as bainite. Moreover, C is an element effective for reduction of a yield ratio by formation of a hard structure. A steel pipe having a relatively small plate thickness (eg, a steel pipe having a plate thickness of 16 mm or less) has a small difference between the outer diameter and the inner diameter. For this reason, even if the C content is 0.020%, the yield ratio can be made into 95% or less. On the other hand, a steel pipe with a relatively small plate thickness tends to have a large cooling rate when manufacturing a hot-rolled steel plate, which is a raw material for the steel pipe. For this reason, when C content exceeds 0.11 %, it becomes easy to produce|generate martensite, and toughness falls easily.

Therefore, in order to obtain the above-mentioned effect, it is required to contain 0.020% or more of C. On the other hand, if the content of C exceeds 0.11%, martensite tends to be formed, and the target steel structure in the present invention cannot be obtained. As a result, the high toughness targeted in the present invention cannot be secured. Therefore, C is set to 0.020 to 0.11%. C is preferably 0.040% or more, and more preferably 0.050% or more. C is preferably 0.10% or less.

Si: 0.60% or less

Si is an element that can increase the strength of the steel pipe while acting as a deoxidizer. However, when Si is contained excessively, toughness will fall. From this point of view, Si is made 0.60% or less. Si is preferably 0.50% or less, and more preferably 0.45% or less. In addition, although the lower limit in particular of Si is not prescribed|regulated, it is preferable to set it as 0.01 % or more from a viewpoint of electric resistance welding property. More preferably, it is made into 0.02 % or more.

Mn: 0.50 to 1.70%

Mn is an element that increases the strength of the steel pipe through solid solution strengthening. In order to acquire such an effect and to ensure the high strength targeted by this invention, it is required to contain 0.50% or more of Mn. On the other hand, when Mn is contained exceeding 1.70 %, a steel structure will refine|miniaturize and yield strength will become high, and it will become impossible to ensure the target yield ratio in this invention. For this reason, Mn is set to 0.50 to 1.70%. Mn is preferably 0.55% or more, and more preferably 0.60% or more. Mn is preferably 1.65% or less, and more preferably 1.60% or less.

P: 0.030% or less

P is an element that segregates at grain boundaries to reduce toughness, and is preferably reduced as an impurity as much as possible, but in the present invention, up to 0.030% is acceptable. From this point of view, P is made 0.030% or less. P is preferably 0.025% or less, and more preferably 0.020% or less. However, since excessive reduction of P causes an increase in refining cost, it is preferable that P be 0.002% or more. More preferably, it is made into 0.003 % or more.

S: 0.015% or less

S exists as MnS in steel when manufacturing a hot-rolled steel sheet which is a raw material of a steel pipe, and has a bad influence on the ductility and toughness of a steel pipe by extending thinly in a hot-rolling process. For this reason, in the present invention, it is preferable to reduce S as an impurity as much as possible, but the S content is permissible up to 0.015%. For this reason, S is made into 0.015 % or less. S is preferably 0.010% or less, and more preferably 0.008% or less. However, since excessive reduction of S causes an increase in refining cost, S is preferably set to 0.0002% or more. More preferably, it is made into 0.001 % or more.

Al: 0.010 to 0.060%

Al acts as a deoxidizer, combines with N to form AlN, and contributes to refinement of crystal grains. In order to obtain such an effect, it is necessary to contain 0.010% or more of Al. On the other hand, the content of a large amount of Al exceeding 0.060% lowers the cleanliness of the steel (hot rolled steel sheet, which is a raw material for the steel pipe), and lowers the ductility and toughness of the steel pipe. For this reason, Al is set to 0.010 to 0.060%. Al is preferably 0.015% or more, and more preferably 0.020% or more. Al is preferably 0.055% or less, and more preferably 0.050% or less.

Nb: 0.010 to 0.080%

Nb combines with carbon or nitrogen to form fine precipitates, and increases the strength of the steel pipe by precipitation strengthening. In order to acquire such an effect, it is necessary to contain 0.010% or more of Nb. On the other hand, when Nb is contained exceeding 0.080 %, when manufacturing the hot rolled steel sheet which is a raw material of a steel pipe, it will become difficult to make it into solid solution by heating in a hot rolling process. As a result, it remains as a coarse precipitate, and toughness falls. For this reason, Nb is set to 0.010 to 0.080%. Nb is preferably 0.015% or more, and more preferably 0.020% or more. Nb is preferably 0.075% or less, and more preferably 0.070% or less.

V: 0.001 to 0.060%

V combines with carbon or nitrogen to form fine precipitates, and increases the strength of the steel pipe by precipitation strengthening. In order to obtain such an effect, it is necessary to contain 0.001% or more of V. On the other hand, when V is contained in excess of 0.060%, the precipitates are coarsened and toughness is lowered. For this reason, V is set to 0.001 to 0.060%. V is preferably 0.002% or more, and more preferably 0.003% or more. V is preferably 0.055% or less, and more preferably 0.050% or less.

Ti: 0.010 to 0.050%

Ti combines with carbon or nitrogen to form fine precipitates, and increases the strength of the steel pipe by precipitation strengthening. In order to acquire such an effect, it is necessary to contain 0.010% or more of Ti. On the other hand, when Ti is contained exceeding 0.050 %, a precipitate will coarsen and toughness will fall. For this reason, Ti is made into 0.010 to 0.050%. Ti is preferably 0.012% or more, and more preferably 0.015% or more. Ti is preferably 0.045% or less, and more preferably 0.040% or less.

N: 0.006% or less

When N is small, it has the effect of increasing the strength of the steel pipe, but when it is contained in a large amount, it forms coarse precipitates at high temperatures and reduces toughness. For this reason, N is made into 0.006 % or less. Since excessive reduction of N causes a raise of refining cost, Preferably it is 0.001 % or more, More preferably, it is set as 0.002 % or more. N is preferably 0.005% or less, and more preferably 0.004% or less.

The remainder is Fe and unavoidable impurities. Moreover, in the range which does not impair the effect of this invention, O: 0.0050% or less of containing as an unavoidable impurity is permissible.

The above components are the basic component compositions of the electric resistance resistance steel pipe in the present invention. Although the characteristics aimed at in the present invention are obtained from the above essential elements, in addition to this basic component composition, the following elements may be further contained as necessary.

B: 0.008% or less

B is an element contributing to refinement|miniaturization of a steel structure by reducing a ferrite transformation start temperature, and can contain it as needed. However, when the content of B exceeds 0.008%, it tends to segregate at grain boundaries, and there is a fear that toughness may decrease. Therefore, when B is contained, it is preferable to make B into 0.008% or less. More preferably, it is made into 0.006 % or less. Further, B is preferably 0.0003% or more, and more preferably 0.0005% or more.

Cr: 0.01 to 1.0%, Mo: 0.01 to 1.0%, Cu: 0.01 to 0.50%, Ni: 0.01 to 1.0%, Ca: 0.0005 to 0.010% one or more selected from the group consisting of

Cr: 0.01 to 1.0%

Cr is an element that increases the strength of the steel pipe by improving the hardenability, and may be contained as necessary. In order to acquire such an effect, it is preferable to contain 0.01% or more of Cr. On the other hand, since there exists a possibility of reducing toughness and weldability when Cr is contained exceeding 1.0 %, it is preferable to set it as 1.0 % or less. Therefore, when it contains Cr, it is preferable to make Cr into 0.01 to 1.0%. Cr is more preferably 0.02% or more, and still more preferably 0.03% or more. Cr is more preferably 0.8% or less, and still more preferably 0.6% or less.

Mo: 0.01 to 1.0%

Mo is an element which raises the intensity|strength of a steel pipe by improving hardenability, and can contain it as needed. In order to acquire such an effect, it is preferable to contain 0.01% or more of Mo. On the other hand, since there exists a possibility of reducing toughness when Mo is contained exceeding 1.0 %, it is preferable to set it as 1.0 % or less. Therefore, when it contains Mo, it is preferable to make Mo into 0.01 to 1.0%. Mo is more preferably 0.02% or more, and still more preferably 0.03% or more. Mo is more preferably 0.8% or less, still more preferably 0.6% or less.

Cu: 0.01 to 0.50%

Cu is an element that increases the strength of the steel pipe by solid solution strengthening, and may be contained as necessary. In order to acquire such an effect, it is preferable to contain 0.01% or more of Cu. On the other hand, since there exists a possibility of reducing toughness when Cu is contained exceeding 0.50 %, it is preferable to set it as 0.50 % or less. Therefore, when Cu is contained, it is preferable to make Cu into 0.01 to 0.50%. Cu is more preferably 0.02% or more, and still more preferably 0.03% or more. Cu is more preferably 0.45% or less, and still more preferably 0.40% or less.

Ni: 0.01 to 1.0%

Ni is an element that increases the strength of the steel pipe by solid solution strengthening, and may be contained as necessary. In order to acquire such an effect, it is preferable to contain 0.01% or more of Ni. On the other hand, since there exists a possibility of reducing toughness when Ni is contained exceeding 1.0 %, it is preferable to set it as 1.0 % or less. Therefore, when Ni is contained, it is preferable to make Ni into 0.01 to 1.0%. Ni is more preferably 0.02% or more, and still more preferably 0.03% or more. Ni is more preferably 0.8% or less, and still more preferably 0.6% or less.

Ca: 0.0005 to 0.010%

Ca is an element that contributes to the improvement of toughness of steel by forming sphericity of sulfides such as MnS that are thinly stretched in the hot rolling process when manufacturing a hot-rolled steel sheet, which is a material of a steel pipe, and may be contained as necessary. In order to obtain such an effect, when Ca is contained, it is preferable to contain 0.0005% or more. However, when the content of Ca exceeds 0.010%, Ca oxide clusters are formed in the steel, and there is a fear that the toughness deteriorates. Therefore, when Ca is contained, it is preferable to make Ca into 0.0005 to 0.010%. Ca is more preferably 0.0010% or more, still more preferably 0.0015% or more. Ca is more preferably 0.005% or less, and still more preferably 0.004% or less.

Next, the reason for limiting the steel structure of the electric resistance resistance steel pipe of this invention is demonstrated.

In the electric resistance resistance steel pipe of the present invention, when the plate thickness of the base metal part is t, the steel structure of the base metal part at a depth of 1/4 t of the plate thickness t from the outer surface of the electric resistance resistance steel pipe is 70 in area ratio of bainite. % or more, and has a steel structure in which the average effective particle diameter of bainite is 10.0 µm or less in terms of the average equivalent circle diameter, and the average aspect ratio of bainite is 0.1 to 0.8.

Here, the 1/4t depth position of the plate thickness t means the outermost layer in which the cooling rate in the hot rolling process when manufacturing a hot-rolled steel sheet, which is a material for a steel pipe, which is important in controlling the steel structure, is greatest; It is a position in the middle of the 1/2t depth position, which is the smallest. In addition, in this invention, the cross section parallel to the rolling direction at the position of 1/4W of the board width W in hot rolling is made into the evaluation surface of a steel structure. In the present invention, since no heat treatment or the like is performed after hot rolling, the structure of the hot-rolled steel sheet and the structure of the steel pipe (base material portion) are the same.

Area ratio of bainite: 70% or more

In order to make high strength and high toughness compatible in this invention, it is important to contain 70% or more of bainite by area ratio. When the bainite content is less than 70%, it becomes difficult to obtain the target strength in the present invention. Accordingly, the steel structure of the base metal portion at a depth of 1/4 t of the plate thickness t from the outer surface of the steel pipe is 70% or more of bainite in terms of area ratio. Preferably it is 72 % or more. In addition, since the yield ratio becomes too high when the area ratio of bainite is excessive, it is preferable to make bainite into 98% or less by area ratio. More preferably, it is made into 95 % or less.

As the structure (residual structure) other than bainite, ferrite, pearlite, martensite, austenite, or the like can be considered. When the total area ratio of these structures becomes 30% or more with respect to the entire steel structure, insufficient strength or toughness and excessive reduction in yield ratio are caused. Therefore, it is preferable to set the remaining structure to less than 30% in total of the area ratio. More preferably, it is made into less than 28 %. In consideration of obtaining the target yield ratio in the present invention, the lower limit of the total area ratio of the residual tissue is preferably more than 2%, and more preferably more than 5%.

In addition, in the present invention, the measurement of the area ratio of each tissue described above can be performed by the method described in Examples to be described later.

Average effective particle diameter of bainite: 10.0㎛ or less in terms of average equivalent circle diameter

In the present invention, in order to achieve both high strength and high toughness, it is important that the average equivalent circle diameter of the average effective particle diameter of bainite be 10.0 µm or less. When the average effective particle diameter of bainite exceeds 10.0 µm in terms of the average equivalent circle diameter, the toughness targeted in the present invention cannot be obtained. In addition, the strength aimed at in the present invention cannot be obtained. Preferably it is 8.0 micrometers or less. In addition, when the bainite becomes too fine, the yield ratio becomes too high. Therefore, the average equivalent circle diameter of the average effective particle size of bainite is preferably set to 1.0 µm or more, and more preferably set to 2.0 µm or more.

Here, the orientation difference of adjacent crystals is obtained, and when a region surrounded by a boundary where the orientation difference (crystal orientation difference) of adjacent crystals is 15° or more as a crystal grain, the diameter of a circle equal to that of the crystal grain is bainite was taken as the effective particle size of The arithmetic mean of the particle diameters was calculated|required from the obtained effective particle diameter, and it was set as the average equivalent circle diameter (average effective particle diameter). In addition, in this invention, a crystal orientation difference, an effective particle diameter, and an average equivalent circle diameter can be measured by the method described in the Example mentioned later.

Average aspect ratio of bainite: 0.1 to 0.8

In the present invention, in order to control the yield ratio in the tube axial direction to 85 to 95%, it is necessary to set the average aspect ratio of bainite to 0.1 to 0.8. Here, (average of the lengths in the plate thickness direction)/(average of the lengths in the tube axis direction) of the above-mentioned crystal grains of bainite was calculated and set as the average aspect ratio of bainite. When the average aspect ratio of bainite exceeds 0.8, the plastic deformation capacity in the tube axial direction decreases, and the yield ratio tends to exceed 95%. On the other hand, if the average aspect ratio of bainite is less than 0.1, the strength in the tube axial direction decreases, and the desired strength in the present invention cannot be obtained.

Incidentally, in the present invention, the average of the lengths in the plate thickness direction and the average of the lengths in the rolling direction in the crystal grains of bainite can be measured by the method described in Examples to be described later.

Next, the manufacturing method of the electric resistance resistance steel pipe in one Embodiment of this invention is demonstrated.

In the electric resistance resistance steel pipe of the present invention, for example, a hot rolling process, a cooling process, and a winding process are performed in this order on a steel material having the above-described component composition to obtain a hot rolled steel sheet, and further, cold roll forming on the hot rolled steel sheet The process is carried out to make an electric resistance welded steel pipe.

In addition, in the following description of the manufacturing method, the "degreeC" indication regarding temperature is made into the surface temperature of a steel raw material or a steel plate (hot-rolled steel plate) unless otherwise stated. These surface temperatures can be measured with a radiation thermometer or the like. In addition, the temperature of the center of a steel plate plate thickness can be calculated|required by calculating the temperature distribution in a steel plate cross section by electrothermal analysis, and correct|amending the result with the surface temperature of a steel plate. In addition, a "hot-rolled steel sheet" shall include a hot-rolled steel sheet and a hot-rolled steel strip.

In the present invention, the method for melting a steel raw material (steel slab) is not particularly limited. Molten steel having the above component composition is melted by a commercial melting method such as a converter, an electric furnace, and a vacuum melting furnace, and is melted by a commercial casting method such as a continuous casting method. It is preferable to use cast steel, such as a slab, from a viewpoint of quality, productivity, etc. In addition, there is no problem at all even if an ingot casting-slabbing process is applied instead of the continuous casting method. You may further perform secondary refining, such as ladle refining, to molten steel.

Next, a hot rolling process is performed on the obtained steel raw material (steel slab). In the hot rolling step, after heating the steel material to a heating temperature of 1100 to 1280 ° C., rough rolling is performed to a rough rolling end temperature: 850 to 1150 ° C., and finish rolling is performed to a finish rolling end temperature: 750 to 850 ° C. is a step of performing hot rolling to obtain a hot-rolled sheet by performing hot rolling and further performing hot rolling with a total rolling reduction at 930° C. or lower at 930° C. or lower in rough rolling and finish rolling: 65% or more.

Heating temperature: 1100~1280℃

When the heating temperature is less than 1100°C, the coarse carbide present in the steel material produced at the time of casting cannot be dissolved in a solid solution. As a result, the effect of the contained carbide-forming element cannot be sufficiently obtained. On the other hand, when the heating temperature exceeds 1280° C. and becomes high, the crystal grains are remarkably coarsened, and the structure of the hot-rolled steel sheet, which is the material of the steel pipe, is coarsened, making it difficult to secure the desired properties in the present invention. For this reason, it is necessary to make the heating temperature of a steel raw material into 1100-1280 degreeC. Preferably, it is set as 1120-1230 degreeC. In addition, let this temperature be set temperature in the furnace of a heating furnace.

Rough rolling end temperature: 850∼1150℃

When the rough rolling completion temperature is less than 850°C, the recovery of the structure during hot rolling does not occur and crystal grains excessively elongated in the rolling direction are likely to be formed. As a result, the average aspect ratio of bainite tends to be less than 0.1. On the other hand, when the rough rolling end temperature exceeds 1150°C, the reduction amount in the austenite non-recrystallization temperature region is insufficient, and fine austenite grains are not obtained. becomes difficult to obtain. For this reason, the rough rolling completion|finish temperature shall be 850-1150 degreeC. Preferably it is set as 860-1000 degreeC.

Finish rolling end temperature: 750 to 850°C

When the finish rolling completion temperature is less than 750°C, the recovery of the structure during hot rolling does not occur, and crystal grains excessively elongated in the rolling direction are likely to be formed. As a result, the average aspect ratio of bainite tends to be less than 0.1. On the other hand, when the finish rolling end temperature exceeds 850°C, the reduction in the austenite non-recrystallization temperature region is insufficient, and fine austenite grains are not obtained. becomes difficult to obtain. For this reason, the finish rolling end temperature is set to 750 to 850°C. Preferably it is set as 770-830 degreeC.

Total rolling reduction at 930°C or lower in rough rolling and finish rolling: 65% or more

In the present invention, by refining austenite in the hot rolling process, bainite and residual structure generated in the subsequent cooling process and winding process are refined, and thus suitable as a material for electric resistance resistance steel pipe having the strength and toughness targeted in the present invention. A hot-rolled steel sheet can be obtained. In order to refine the austenite in the hot rolling process, it is necessary to increase the reduction ratio in the austenite non-recrystallization temperature range to introduce sufficient working strain. In order to obtain this effect, in the present invention, the total rolling reduction in the temperature range up to the finish rolling end temperature of 930° C. or less is set to 65% or more. Here, the total reduction ratio refers to the sum of the reduction ratios of each rolling pass in the temperature range up to the finish rolling end temperature of 930° C. or less.

When the total reduction ratio in the temperature range up to the finish rolling end temperature of 930° C. or less is less than 65%, since sufficient working strain cannot be introduced in the hot rolling process, the average effective particle size of bainite targeted in the present invention A steel structure with The total rolling reduction in the temperature range up to the finish rolling end temperature of 930°C or less is more preferably 70% or more. Although the upper limit in particular is not prescribed|regulated, when it exceeds 80 %, the effect of the toughness improvement with respect to the raise of the rolling-reduction|draft ratio becomes small, and equipment load only increases. For this reason, 80% or less of the total rolling reduction in the temperature range up to 930 degreeC or less finish rolling completion|finish temperature is preferable. More preferably, it is 75 % or less.

The reason that the temperature is set to 930°C or lower in the present invention is that, if the temperature exceeds 930°C, austenite recrystallizes in the hot rolling step, dislocations introduced by rolling are lost, and refined austenite cannot be obtained.

Further, in the present invention, when hot rolling a steel material, in both the rough rolling and finish rolling described above, hot rolling may be performed in which the total reduction ratio up to the finish rolling end temperature of 930 ° C. or less is 65% or more, It is good also as hot rolling which makes the total reduction ratio up to 930 degreeC or less finish rolling completion|finish temperature 65 % or more only by finish rolling. In the latter case, if the total reduction ratio up to the finish rolling finish temperature of 930° C. or less cannot be made 65% or more by finish rolling alone, the slab is cooled in the middle of rough rolling to bring the temperature to 930° C. or less, and then rough rolling is performed. It is good also considering the total rolling-reduction|draft ratio up to 930 degreeC or less finish-rolling completion temperature in both and finish-rolling 65 % or more.

Next, a cooling process is performed on the hot-rolled sheet after a hot-rolling process. In a cooling process, it is a process of cooling a hot-rolled sheet to average cooling rate from a cooling start to cooling stop: 15-35 degreeC/s, and cooling stop temperature:450-650 degreeC at plate thickness center temperature.

Average cooling rate from cooling start to cooling stop: 15 to 35°C/s

If the average cooling rate in the temperature range from the start of cooling to the cooling stop temperature to be described later is less than 15° C./s at the plate thickness center temperature of the hot-rolled sheet, the area ratio of bainite decreases due to the generation of ferrite, In the present invention, the desired strength cannot be obtained. On the other hand, when the average cooling rate exceeds 35° C./s, the average aspect ratio of bainite exceeds 0.8. As a result, the yield ratio tends to exceed 95%. The average cooling rate is preferably 20°C/s or more, and preferably 30°C/s or less.

In addition, in the present invention, the average cooling rate is a value (cooling time) obtained from ((plate thickness center temperature of the hot-rolled sheet before cooling-plate thickness center temperature of the hot-rolled sheet after cooling)/cooling time), unless otherwise specified. speed) as the average. As the cooling method, for example, water cooling by spraying water from a nozzle, cooling by injection of a cooling gas, or the like. In the present invention, it is preferable to perform cooling operation (process) on both surfaces of the hot-rolled sheet so that both surfaces of the hot-rolled sheet are cooled under the same conditions.

Cooling stop temperature: 450-650℃

At the plate thickness center temperature of the hot-rolled sheet, if the cooling stop temperature is less than 450°C, the average aspect ratio of bainite exceeds 0.8, and as a result, the yield ratio tends to exceed 95%. On the other hand, when the cooling stop temperature exceeds 650°C, the area ratio of bainite cannot be 70% or more because it exceeds the bainite transformation start temperature. The cooling stop temperature is preferably 480°C or higher, and preferably 620°C or lower.

Next, the winding process of winding up the hot-rolled steel sheet after a cooling process, and standing to cool after that is implemented.

In the winding step, from the viewpoint of the steel sheet structure of the hot-rolled steel sheet, which is the raw material of the steel pipe, winding is preferably performed at a winding temperature: 450 to 650°C. When the coiling temperature is less than 450°C, the average aspect ratio of bainite exceeds 0.8, and as a result, the yield ratio may exceed 95%. On the other hand, if the coiling temperature is higher than 650°C, the area ratio of bainite may not be 70% or more because it exceeds the bainite transformation start temperature. The coiling temperature is more preferably 480 to 620°C.

Next, the hot-rolled steel sheet after the winding step is subjected to a cold roll forming step. In the cold roll forming process, a hot-rolled steel sheet is formed into a cylindrical open pipe by cold roll forming, and both ends of the steel pipe material (that is, the butt portion of an open pipe) are electric resistance welded, and the annular steel pipe after welding Diameter reduction rolling is performed at a reduction ratio of 0.2 to 0.5% with respect to the circumferential length of the outer surface of the steel pipe.

Diameter reduction ratio in diametral rolling: 0.2 to 0.5%

When the diameter reduction ratio in the reduction rolling is less than 0.2%, in the steel material of the steel pipe of the present invention described above, the reduction of the residual stress due to plastic deformation becomes insufficient. As a result, the residual stress in the pipe axial direction on the outer surface of the steel pipe exceeds 250 MPa. In addition, the yield ratio becomes less than 85% due to insufficient workability. On the other hand, when the reduction in diameter in diametral rolling exceeds 0.5%, the yield ratio exceeds 95% due to work hardening. As a result, the desired plastic deformation capacity, ie, buckling resistance performance, cannot be obtained. Moreover, even if said residual stress exceeds 250 MPa, buckling-resistant performance falls.

As described above, the electric resistance resistance steel pipe of the present invention is manufactured. According to the present invention, the tensile strength in the tube axial direction is 590 MPa or more, the 0.2% yield strength is 450 MPa or more, the yield ratio is 85 to 95%, the Charpy absorbed energy at -30°C is 70 J or more, and the outer surface of the steel pipe is An electric resistance welded steel pipe having a residual stress in the tube axial direction of 250 MPa or less is obtained. Accordingly, it is possible to easily manufacture an electric resistance welded steel pipe having excellent high strength, high toughness, optimum yield ratio and buckling resistance. Since this electric resistance resistance steel pipe can be used suitably especially for the steel pipe pile used as the foundation|base of a structure, it brings about the remarkable effect industrially.

Next, the steel pipe pile of this invention is demonstrated.

The steel pipe pile of the present invention is composed of an electric resistance resistance steel pipe having a plate thickness of 16 mm or less, an outer diameter of 300 mm or more and 700 mm or less, and having the above-described composition and steel structure. By specifying the component composition and steel structure of the electric resistance welded steel pipe as described above, the tensile strength in the tube axial direction is 590 MPa or more, the 0.2% yield strength is 450 MPa or more, the yield ratio is 85 to 95%, and Charpy absorption at -30°C A steel pipe pile having an energy of 70 J or more and a residual stress in the pipe axial direction of the outer surface of the steel pipe of 250 MPa or less is obtained. The steel pipe pile of the present invention is driven into the ground, and if necessary, the steel pipe piles are connected to each other during the driving by means of a connection such as welding or a screw joint to be constructed on site as a long pile. According to the steel pipe pile of this invention, since it has the said characteristic, it can reduce the possibility of causing problems, such as buckling, with respect to pile driving.

Example

Hereinafter, the present invention will be further described in detail based on Examples. In addition, the present invention is not limited to the following examples.

Molten steel having the component composition shown in Table 1 was melted in a converter, and a slab (steel material: thickness 250 mm) was obtained by a continuous casting method. The obtained slab was subjected to a hot rolling process, a cooling process, a winding process, and a cold roll forming process under the manufacturing conditions shown in Tables 2-1 and 2-2, and the outer diameter and plate shown in Tables 2-1 and 2-2. A thick electric resistance welded steel pipe was manufactured. In addition, in the cold roll forming process, the butt|matching part of an open pipe was electric resistance-welded.

A test piece was taken from the obtained electric resistance welded steel pipe, and the structure observation, the tensile test, the Charpy impact test, the measurement of residual stress, and the member compression test were performed by the method shown below.

[tissue observation]

A test piece for tissue observation was prepared by taking, grinding, and nital etching so that a cross section in the tube axial direction at a position of 90° in the circumferential direction was the observation surface when the electric resistance welded portion was set to 0°. For tissue observation, using an optical microscope (magnification: 1000 times) or a scanning electron microscope (SEM, magnification: 1000 times), the structure was observed at a depth of 1/4 t of the plate thickness t from the outer surface of the electric resistance resistance steel pipe. and photographed. From the obtained optical microscope image and SEM image, the area ratio of bainite was calculated|required. The area ratio of bainite was calculated as an average value of values obtained by observation in 5 or more fields of view.

In addition, the average effective particle diameter (average equivalent circle diameter) of bainite was measured using the SEM/EBSD method. The effective grain size was determined by obtaining the orientation difference between adjacent crystal grains, and when the area surrounded by the boundary with the orientation difference of 15° or more was defined as the effective grain size, the effective grain size was the diameter of a circle equal in area to the effective grain size as the effective grain size of bainite. The arithmetic mean of the obtained effective particle diameters was calculated|required, and it was set as the average equivalent circle diameter. The measurement area|region was 500 micrometers x 500 micrometers, and the measurement step size was 0.5 micrometer. In addition, in the crystal grain size analysis, those having an effective grain size of 2.0 µm or less were excluded from the analysis target as measurement noises.

In addition, the average aspect-ratio of bainite was calculated|required by measuring the length in the plate-thickness direction of each effective crystal grain measured by the said method, and the length in a tube-axis direction, and calculating each average. The length in the plate thickness direction and the length in the tube axial direction were the maximum lengths in each of the effective crystal grains in the plate thickness direction and in the tube axial direction.

[Tensile Test]

In the tensile test, a tensile test piece according to JIS No. 5 was taken so that the tensile direction was parallel to the tube axial direction at a position of 90° in the circumferential direction when the electric resistance welded portion of the obtained electric resistance welded pipe was set to 0°. A tensile test was performed in accordance with the regulations of JIS Z 2241. 0.2% yield strength (yield strength YS) and tensile strength TS were measured, and the yield ratio defined by (0.2% yield strength)/(tensile strength) was computed.

[Charpy Impact Test]

In the Charpy impact test, the V-notch test piece (V -notch test specimens were taken. Based on the regulations of JIS Z 2242, a Charpy impact test was performed at a test temperature: -30°C to determine the absorbed energy (J). In addition, the number of test pieces was made into three each, the average value was computed, and the absorbed energy (J) was calculated|required.

[Measurement of residual stress]

The residual stress was measured by the X-ray diffraction cosα method using μ-X360 manufactured by Pulsetech. The residual stress was measured at the outer surface of the center of the pipe length of the obtained electric resistance welded steel pipe, and when the electric resistance welded portion was set to 0 °, three positions were set: 90 ° position, 180 ° position, and 270 ° position. The average value of the obtained measured values of three places was made into residual stress. In addition, the stress measurement direction was made into the tube axis direction.

[Member Compression Test]

In the present invention, for performance evaluation as a steel pipe pile, a member compression test was performed to obtain a buckling strength ratio σcr/σy (where σcr is the buckling stress degree and σy is the material yield strength). If the buckling strength ratio is larger than the reduction factor R=0.8+2.5×t/r (in addition, t is the plate thickness and r is the radius), it can be judged that the buckling strength, which is important as the performance of the steel pipe pile, is sufficient.

The obtained results are shown in Table 3-1 and Table 3-2, respectively.

(Table 1)

(Table 2-1)

(Table 2-2)

(Table 3-1)

(Table 3-2)

As shown in Tables 1 to 3-2, all electric resistance welded steel pipes within the scope of the present invention have a tensile strength of 590 MPa or more in the tube axial direction, a 0.2% yield strength of 450 MPa or more, and a yield ratio of 85 to 95%, - The Charpy absorbed energy at 30°C was 70 J or more, and the residual stress in the tube axial direction on the outer surface of the tube was 250 MPa or less. In addition, it was found that the electric resistance resistance steel pipe having these characteristics also has sufficient buckling strength, which is important as the performance of the steel pipe pile.

On the other hand, a steel pipe that is outside the scope of the present invention in terms of component composition, steel structure, and manufacturing conditions has a tensile strength in the tube axial direction, 0.2% yield strength, yield ratio, Charpy absorbed energy at -30°C, and a tube on the outer surface of the tube. Among the residual stresses in the axial direction, the target value in the present invention could not be obtained in any one or more.

In view of the above, by making the component composition, steel structure, and manufacturing conditions of the electric resistance resistance steel pipe within the scope of the present invention, it has an optimum yield ratio and high buckling resistance suitable for use in steel pipe piles, and further high strength and high toughness are compatible. One electric resistance welded pipe can be provided.

Claims (6)

An electric resistance welded steel pipe having a base metal part and a welding part in the pipe axis direction,
The component composition of the base material part is in mass%,
C: 0.020 to 0.11%;
Si: 0.60% or less;
Mn: 0.50 to 1.70%;
P: 0.030% or less;
S: 0.015% or less;
Al: 0.010 to 0.060%,
Nb: 0.010 to 0.080%;
V: 0.001 to 0.060%;
Ti: 0.010 to 0.050%,
N: 0.006% or less
contains, and the balance consists of Fe and unavoidable impurities,
When the plate thickness of the base metal part is t, the steel structure at a depth of 1/4 t of the plate thickness t from the outer surface of the electric resistance resistance steel pipe is,
Bainite is 70% or more in area ratio,
The average effective particle diameter of the bainite is 10.0 μm or less in terms of the average equivalent circle diameter, and the average aspect ratio of the bainite is 0.1 to 0.8,
The tensile strength in the tube axial direction is 590 MPa or more, the 0.2% yield strength is 450 MPa or more, and the yield ratio is 85 to 95%,
The Charpy absorbed energy at -30°C with the tube axial direction in the base metal part as the longitudinal direction of the test piece is 70 J or more,
The electric resistance resistance steel pipe whose residual stress in the pipe axial direction of the outer surface of the steel pipe in the said base material part is 250 MPa or less. According to claim 1,
The electric resistance resistance steel pipe which further contains B:0.008% or less by mass % in addition to the said component composition. 3. The method of claim 1 or 2,
In addition to the above component composition, in mass%,
Cr: 0.01 to 1.0%,
Mo: 0.01 to 1.0%,
Cu: 0.01 to 0.50%,
Ni: 0.01 to 1.0%,
Ca: 0.0005 to 0.010%
Electrical resistance steel pipe containing one or two or more selected from among. A method for manufacturing an electric resistance resistance steel pipe in which a steel material is subjected to a hot rolling process and a cooling process in this order to obtain a hot rolled steel sheet, and further, the hot rolled steel sheet is subjected to a cold roll forming process to obtain an electric resistance resistance steel pipe,
The steel material has the component composition according to any one of claims 1 to 3,
In the hot rolling process, after heating the steel material to a heating temperature of 1100 to 1280 ° C, rough rolling end temperature: 850 to 1150 ° C, finish rolling end temperature: 750 to 850 ° C, and further, rough rolling and finish rolling The total rolling reduction at 930°C or lower in: a step of performing rough rolling and finish rolling of 65% or more to obtain a hot-rolled sheet,
The cooling step is a step of cooling the hot-rolled sheet to an average cooling rate from cooling start to cooling stop: 15 to 35° C./s, and cooling stop temperature: 450 to 650° C. at the plate thickness center temperature,
In the cold roll forming step, a steel pipe material subjected to a roll forming process is welded to the hot rolled steel sheet, and the electric resistance resistance rolling is performed with respect to the circumference of the outer surface of the steel pipe after welding with a diameter reduction ratio of 0.2 to 0.5%. manufacturing method. It has the component composition according to any one of claims 1 to 3, and when the plate thickness is t, in the steel structure at a depth of 1/4t of the plate thickness t from the outer surface, bainite is an area ratio An electric resistance resistance steel pipe obtained by subjecting a hot-rolled steel sheet having an average effective particle size of 70% or more, the average effective particle diameter of the bainite to 10.0 μm or less in terms of the average equivalent circle diameter, and an average aspect ratio of the bainite of 0.1 to 0.8, to a cold roll forming process to obtain an electric resistance resistance steel pipe As a manufacturing method of
In the cold roll forming step, a steel pipe material subjected to roll forming processing is welded to the hot rolled steel sheet, and diameter reduction is performed with respect to the circumference of the outer surface of the steel pipe after welding with a diameter reduction ratio of 0.2 to 0.5%. A method of manufacturing an electric resistance resistance steel pipe. A steel pipe pile using the electric resistance resistance steel pipe according to any one of claims 1 to 3.