JPH10310821A - Manufacture of high tensile strength steel tube for construction use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacture of a high tensile strength steel tube for construction use, capable of stably and inexpensively mass-producing a 60kg-class low-yield-ratio steel tube of <=50 mm tube thickness, used for a concrete-filling-type composite steel tube pillar, etc., while obviating the necessity of plate heat treatment after rolling and heat treatment after cold forming. SOLUTION: A steel, having a composition consisting of, by weight. 0.06-0.17% C, 0.06-0.5% Si, 0.5-1.6% Mn, <=0.05% P, <=0.01% S, <=0.07% Al, <=0.006% N, further one or <=2 kinds among 0.05-0.5% Mo, 0.01-0.1% V, and 0.005-0.015% Ti, and the balance Fe with inevitable impurities, is heated to >=1000 deg.C and hot rolled in the temp. region not lower than the Ar3 point. The resultant steel plate is subjected to accelerated cooling down to the temp. region of Ar3 -50 deg.C±30 deg.C at a rate of (1 to 40) deg.C/sec. Subsequently, the acceleratedly cooled steel plate is held in the temp. region of Ar3 -50 deg.C±30 deg.C for 1-150 sec and subjected to accelerated cooling down to 400-600 deg.C at a rate of (1 to 40 deg.C)/sec. The resultant steel plate is cold-formed into steel tube, and further, the tube expanding rate in the final stage of tube manufacture is regulated to >=0.8%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel structure, such as a building, having a pipe thickness of 50 mm or less and an outer diameter of 400 mm or less.
The present invention relates to a method of manufacturing a relatively thin high-strength steel pipe for construction of about 2000 mm.

[0002]

2. Description of the Related Art In today's high-rise buildings, when a huge earthquake is hit, the ground energy is absorbed by plastic deformation of columns and beams to avoid large collapses. The design method is applied. Therefore, it is desired that the column / beam member used in the limit state design method has a yield ratio (YR) of 80% or less as a measure of high plastic deformability. When impact is applied to the structure at the column / beam joint,
Since the stress is mainly applied in the pipe axis direction of the steel pipe column, YR in the pipe axis direction is a measure of the plastic deformability of the structure. Also,
Due to the tendency of design emphasis in today's buildings and the high degree of freedom of structures such as beam mounting, the demand for steel pipes having a circular cross section has increased more than conventional box columns having a square cross section.
There are two methods for manufacturing circular steel pipes: centrifugal casting and cold forming of thick steel plates.The latter is superior in toughness, which is important in terms of seismic resistance, as well as productivity, dimensional accuracy, and weldability. This is also advantageous.

[0003] In this case, the strain amount of the steel sheet due to the cold forming during the production of the steel pipe is represented by t / D where t is the thickness of the steel pipe and D is the outer diameter of the steel pipe. Due to the work hardening, the YR in the tube axis direction of the round column increases, and the required value of YR ≦ 80% cannot be satisfied. Therefore, it cannot be said that the pillar used in the limit state design method is sufficient. In addition, the toughness is deteriorated by work hardening, and there is a concern about earthquake-resistant safety.

As a method of avoiding this, a sheet thickness of 100 m
Various techniques described below have been disclosed with respect to a method for producing a thick steel pipe up to about m. Japanese Patent Application Laid-Open No. 3-173719 discloses a method in which a steel pipe is subjected to tempering after cold forming. Japanese Patent Application Laid-Open Nos. 5-65535, 5-117746, and 5-117747 disclose tempering steel sheets. After two-phase heating and quenching, and after forming, SR
(Stress relief annealing) is disclosed in JP-A-6-49540.
JP, JP-A-6-49541, JP-A-6-1212
JP-A-8641 discloses a method of subjecting a steel sheet to a heat treatment and then normalizing the steel pipe.
JP-A-6-3264 and JP-A-6-264144 disclose a method in which the yield ratio before forming is strictly controlled by tempering a steel sheet or performing a two-phase heating quenching-tempering treatment.
Japanese Patent No. 40922 discloses a technique that strictly defines the amount of reduction per pass when rolling a steel sheet.

[0005]

However, the above-mentioned techniques relating to the conventional method for manufacturing a thick steel pipe having a thickness of up to about 100 mm achieve a high strength and a low yield ratio of 60 kg class with an extremely thick steel pipe. For this reason, the production method requires labor and costly heat treatment, or requires a sacrifice such as a reduction in rolling efficiency, and leaves much room for improvement from an industrial viewpoint. On the other hand, JP-A-5-156357 discloses a steel pipe having a low YR even as it is rolled or cold formed, but its strength level is limited to a 50 kg class.

[0006] As a kind of steel pipe column, practical use of a new type of column which is filled with concrete inside a steel pipe and has rigidity and strength as a composite structure has been studied. In this case, since the composite material is a steel pipe and concrete, the thickness of the steel pipe for obtaining the same load-bearing performance can be reduced to about の of the thickness of the steel pipe alone. Therefore, for example, 5
Although a relatively thin 60 kg class low yield ratio steel pipe having a thickness of 0 mm or less is required, the disclosed thick wall steel pipe manufacturing technology has problems in economy and productivity, and the thin wall 60 kg class low yield ratio steel pipe has problems. There is a need for a technology that can produce a specific steel pipe at low cost and in large quantities.

An object of the present invention is to provide a low-yield-ratio 60-kilometer steel pipe having a pipe thickness of 50 mm or less used for a concrete-filled composite steel pipe column or the like without requiring sheet heat treatment after rolling and heat treatment after cold forming. An object of the present invention is to provide a method for manufacturing a high-strength steel pipe for building, which can be stably manufactured at a low cost and in large quantities.

[0008]

The present invention uses the following means to solve the above-mentioned problems and achieve the object.

(1) The method for producing a steel pipe according to the present invention is characterized in that
And C: 0.06 to 0.17% and Si: 0.06 to
0.5%, Mn: 0.5 to 1.6%, and P ≦ 0.05
%, S ≦ 0.01%, Al ≦ 0.07%, and N ≦
0.006%, and further, Mo: 0.05 to 0.5%,
V: 0.01-0.1%, and Ti: 0.005-0.
In a method for producing a steel pipe having a steel composition composed of one or more selected from the group of 015% and a balance of Fe and unavoidable impurities, the steel is heated to 1000 ° C. or more and then heated to a temperature of Ar ₃ or more. Hot rolling in the zone,
A step of accelerated cooling the hot rolled steel sheet by Ar ₃ -50 ℃ ± 30 ℃ temperature range up to 1 to 40 ° C. / sec, the accelerated cooled steel sheet at a temperature range of Ar ₃ -50 ℃ ± 30 ℃ 1 to 1
After waiting for 50 seconds, until the temperature range of 400-600 ° C
A step of accelerating cooling at ４０40 ° C./sec, and a step of cold-forming the obtained steel sheet into a steel pipe, and setting a pipe expansion ratio to 0.8% or more in a final pipe-forming step. This is a method for producing a high-strength steel pipe for construction.

(2) The method for producing a steel pipe according to the present invention comprises:
And C: 0.06 to 0.17% and Si: 0.06 to
0.5%, Mn: 0.5 to 1.6%, and P ≦ 0.05
%, S ≦ 0.01%, Al ≦ 0.07%, and N ≦
0.006%, and further, Cu: 0.05 to 0.5%,
Ni: 0.05 to 0.8%, Cr: 0.05 to 0.5
%, And Nb: in a method for producing a steel pipe having a steel composition comprising one or more selected from the group of 0.005 to 0.05% and a balance of Fe and inevitable impurities, A step of hot rolling in a temperature range of Ar ₃ or more after heating to 1000 ° C. or more;
r ₃ -50 ° C. a step of accelerated cooling to a temperature range of ± 30 ℃ 1~40 ℃ / sec, the accelerated cooled steel plate Ar ₃ -50
After waiting for 1 to 150 seconds in the temperature range of
A step of accelerated cooling at a temperature of 1 to 40 ° C./sec to a temperature range of 0 to 600 ° C., and a step of cold-forming the obtained steel sheet to form a steel pipe, and a pipe expansion ratio of 0.8% or more in a final pipe forming step. When,
A method for producing a high-strength steel pipe for buildings, characterized by comprising:

(3) In the method for producing a steel pipe according to the present invention,
% By weight, Cu: 0.05 to 0.5%, Ni:
Contains one or more selected from the group consisting of 0.05 to 0.8%, Cr: 0.05 to 0.5%, and Nb: 0.005 to 0.05%. A method for producing a high-strength steel pipe for construction according to the above (1), which is characterized by the following.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor has proposed a method for producing a low yield ratio 60 kg class steel pipe having a pipe thickness of 50 mm or less without heat treatment of a steel sheet or a steel pipe after rolling or pipe forming without heat treatment. Next, the rolling and accelerated cooling conditions were examined.

As a result, by rolling steel having a specific amount of chemical components under appropriate rolling and accelerated cooling conditions,
As a two-phase mixed structure of ferrite and bainite, the steel structure achieves a tensile strength of 60 kg class and a low yield ratio of 80% or less as rolled, and further optimizes the expansion ratio in the final tube forming process to improve the structure. It has been found that it is possible to suppress a rise in the yield ratio due to work hardening during pipe formation and achieve a low yield ratio in the pipe axis direction as it is formed. Based on the above findings, the present inventor:
The steel composition, rolling / accelerated cooling conditions, and the expansion ratio in the final pipe forming process are controlled within certain ranges,
The present inventors have found a method of manufacturing a high-strength steel pipe for building having a low yield ratio of 60 kg and a pipe thickness of 50 mm or less as it is, and completed the present invention.

That is, according to the present invention, the steel composition and the production conditions are limited to the following ranges, so that a low yield ratio of not more than 50 mm and a pipe thickness of 50 mm or less used for a concrete-filled composite steel pipe column or the like is provided.
It is possible to obtain a method for manufacturing a high-strength steel pipe for building, which can stably manufacture a 0-kilometer steel pipe inexpensively and in large quantities without requiring sheet heat treatment after rolling and heat treatment after cold forming. Hereinafter, the reasons for adding the components, the reasons for limiting the components, and the reasons for limiting the production conditions of the present invention will be described.

(1) Component composition range: C: 0.06 to 0.17% C is added in an amount of 0.06% or more in order to secure the strength of steel, but if contained in a large amount, toughness or weldability deteriorates. Therefore, the upper limit is 0.17 of the limit without such an effect.
%.

Si: 0.06 to 0.5% Si is an element that is inevitably contained in steel for deoxidation.
From the viewpoint of ensuring a low yield ratio, the content is 0.06% or more. However, too much Si has an unfavorable effect from the viewpoint of HAZ (heat affected zone) toughness and weldability. It is 0.5% of the limit at which no significant effect appears.

Mn: 0.5 to 1.6% Mn is required to be 0.5% or more in order to improve the strength and toughness of the steel sheet and to suppress the generation of FeS. The upper limit is 1.6% of the limit that does not have such an adverse effect because a hardened layer appears at the time of welding to increase the crack sensitivity.

P ≦ 0.05%, S ≦ 0.01% P and S are inevitably present as impurities mixed in the steel, but the reduction of P is effective in preventing grain boundary destruction, and Since the reduction is effective in preventing hydrogen cracking in the heat affected zone, 0.05% or less, at which such effects are exhibited,
It is 0.01% or less.

Al ≦ 0.07% Al is an element contained in the deoxidized steel, but if contained in a large amount, the cleanliness of the steel is deteriorated and the toughness of the weld is deteriorated. 0.07% of the limit without significant influence
It is.

N ≦ 0.006% N is an unavoidable impurity element contained in steel.
If the amount increases, it promotes deterioration of HAZ toughness and generation of flaws in continuously cast slabs, so the upper limit is 0.006% of the limit without such influence.

In the present invention, the above components are used as basic components, and one or both of the following selected component groups A and B are added.

(Selective component group A) Mo: 0.05 to 0.5
%, V: 0.01 to 0.1%, and Ti: 0.005 to
One or more selected from the group of 0.015% Mo: 0.05 to 0.5% Mo enhances hardenability and increases temper softening resistance,
Although effective for increasing the strength, if the content is less than 0.05%, the effect is not sufficiently exhibited. If the content exceeds 0.5%, the weldability is deteriorated, and the yield ratio is increased due to precipitation of carbide. Therefore, when Mo is added, its amount is in the range of 0.05 to 0.5%.

V: 0.01% to 0.1% V is an element that improves hardenability and increases temper softening resistance by adding a small amount, but if its content is less than 0.01%, the effect is sufficient. When V is added, the amount is in the range of 0.01 to 0.1%.

Ti: 0.005 to 0.015% Ti is an element that contributes to improving the HAZ toughness by suppressing the coarsening of the structure of the welded HAZ of TiN. 0.005%
If less than Ti is added, the effect of improving the HAZ toughness is not exhibited. If it is added in excess of 0.015%, TiC precipitates during the cooling process of welding, leading to deterioration of HAZ toughness. Therefore, when Ti is added, 0.005 to 0.015%
Range.

(Selective component group B) Cu: 0.05 to 0.5
%, Ni: 0.05-0.8%, Cr: 0.05-0.
5% and Nb: one or more selected from the group of 0.005 to 0.05% Cu: 0.05 to 0.5% Cu is a very effective element for increasing the strength and improving the toughness. However, when the content is less than 0.05%, a sufficient effect is not exhibited, and when the content exceeds 0.5%, the precipitation effect is remarkable, and cracks are easily generated on the steel sheet surface. Amounts range from 0.05 to 0.5%.

Ni: 0.05-0.8% Ni has the effect of improving the strength and toughness of the base material, but if its content is less than 0.05%, a sufficient effect cannot be obtained. %, Leads to an increase in cost.
The range is 0.8%.

Cr: 0.05 to 0.5% Cr is an effective element for improving hardenability, but if its content is less than 0.05%, the effect is small, and if it exceeds 0.5%, the weldability is increased. When Cr is added to deteriorate the HAZ toughness, the amount is in the range of 0.05 to 0.5%.

Nb: 0.005 to 0.05% Nb is an element that effectively acts to increase strength and improve toughness due to the precipitation effect of fine carbonitrides.
If the content is less than 0.05%, the effect is not exhibited, and if the content exceeds 0.05%, an excessive precipitation effect prevents the reduction of the yield ratio.
The range is 0.05%.

By adjusting the component composition to the above range, a steel pipe having a low yield ratio of 60 kg and a pipe thickness of 50 mm or less used for a concrete-filled composite steel pipe column or the like can be subjected to sheet heat treatment after rolling and heat treatment after cold forming. , And can be stably obtained in large quantities at low cost without the need for.

A steel pipe having such characteristics can be manufactured by the following manufacturing method.

(2) Steel Pipe Manufacturing Process (Manufacturing conditions) 100% of steel adjusted to the above component composition range was used.
After heating to 0 ° C. or higher, the steel sheet hot-rolled in a temperature range of Ar ₃ or higher is heated to a temperature range of Ar ₃ −50 ° C. ± 30 ° C. in a range of 1 to 4
Accelerate cooling at 0 ° C / sec. Next, after accelerating and cooling the steel sheet after waiting for 1 to 150 seconds in a temperature range of Ar ₃ -50 ° C. ± 30 ° C., the steel sheet is accelerated and cooled to a temperature range of 400 to 600 ° C. at 1 to 40 ° C./sec. Cold-formed steel sheet into steel pipe,
The expansion ratio in the final pipe-making process is set to 0.8% or more. a. Heating temperature of steel: 1000 ° C. or higher The purpose of heating steel to 1000 ° C. or higher is to coarsen the prestructure in order to finally obtain a low YR.

B. Hot rolling termination temperature: Ar ₃ or more The reason for terminating rolling in the temperature range of Ar ₃ or more is to suppress the development of texture and eliminate acoustic anisotropy that adversely affects the measurement accuracy of ultrasonic flaw detection. is there.

C. Standby temperature: Ar ₃ -50 ± 30 ° C. After rolling, accelerated cooling to Ar ₃ -50 ± 30 ° C. is for cooling to a temperature at which ferrite precipitates without lowering productivity.

D. Standby time: 1 to 150 seconds The reason for waiting for 1 to 150 seconds in the temperature range of Ar ₃ -50 ± 30 ° C. is to precipitate a part of ferrite, and the remaining austenite is made into a bainite structure by further accelerated cooling. Finally, a low yield ratio is achieved as a two-phase mixed structure of ferrite and bainite. Standby temperature is Ar ₃ -20
If the temperature is higher than ℃, ferrite formation is slow,
With a standby time of 150 seconds, sufficient ferrite cannot be obtained,
In order to obtain sufficient ferrite, a lot of waiting time is required, which impairs productivity. On the other hand, when Ar _{3 is} lower than −80 ° C., ferrite is excessively generated, and it is difficult to obtain a 60 kg class tensile strength. Note that ± 30 ° C. takes into account variations during actual manufacturing. e. Accelerated cooling rate e-1. Accelerated cooling rate before standby: 1 to 40 ° C./sec The accelerated cooling rate before standby may be a cooling rate that does not impair productivity, and is 1 to 40 ° C./sec faster than air cooling.

E-2. Accelerated cooling rate after standby: 1 to 40
The appropriate cooling rate in accelerated cooling after standby at ° C./sec depends on the component system, but at least 1 ° C./sec is required to obtain a bainite structure within the above component range. On the other hand, when the temperature exceeds 40 ° C./sec, the hardness in the thickness direction such that the vicinity of the plate surface is abnormally hardened is generated, and the tube forming is performed as-rolled, that is, a temper-free state, which is a feature of the present invention. Therefore, the upper limit of the cooling rate is 40 ° C./sec.

F. Accelerated cooling stop temperature: 400 to 600 ° C. After the standby, the accelerated cooling stop temperature is 400 to 6 instead of normal temperature.
Although it is 00 ° C., this is also an essential condition for performing tube forming in an as-rolled (temper-free) state, which is a feature of the present invention. That is, the accelerated cooling stop temperature is set to 400 ° C.
If it is less than 1, since the island-like martensite generated during accelerated cooling remains without being decomposed, the toughness is poor and defects such as cracks are generated during pipe forming. On the other hand, the accelerated cooling stop temperature is 6
Above 00 ° C, bainite transformation is not sufficiently completed and
It is difficult to secure a strength of 0 kilo class.

G. Expansion ratio in final pipe making process: 0.8
% Or more UOE,
Any cold forming method such as press bend and roll bend may be used. However, in order to obtain a low yield ratio as it is, the pipe must be expanded in the final step of molding.
This means that the tensile deformation in the circumferential direction due to expansion causes compression in the longitudinal direction, and when external force is applied in the longitudinal direction again, the yield strength decreases due to the Bauschinger effect, and as a result, a low yield ratio is achieved. It was aimed. here,
As shown in FIG. 2, 80% when the expansion ratio is 0.8% or more.
Since the following low yield ratio (YR) is easily achieved, the lower limit of the pipe expansion ratio is 0.8%. As described above, by employing the above-mentioned components and rolling / accelerated cooling conditions, it is possible to secure a strength of 60 kg class and a low yield ratio as rolled, and to further increase the pipe expansion ratio by 0.8%.
With the above, an increase in the yield ratio due to work hardening at the time of pipe forming can be suppressed, and thus a low yield ratio can be achieved while the pipe is being formed. Hereinafter, examples of the present invention will be described to demonstrate the effects of the present invention.

[0038]

EXAMPLES Table 1 shows the steel No. of the present invention. Nos. 1 to 10 and Comparative Steel Nos. The chemical components and Ar ₃ temperature of 11 to 20, also the tensile and rolling and pipe forming conditions of each steel shown in Table 2 and shows the results of Charpy impact test (tensile test was carried out in accordance with JIS Z 2241).

As is clear from Tables 1 and 2, the steel No. of the present invention whose chemical composition and rolling and pipe forming conditions fall within the scope of the present invention. 1
10 to 60 are all 60 kg class (590 N / mm ² or more)
Tensile strength (TS) and low yield ratio (YR) of 80% or less,
Furthermore, it shows excellent ductility (El) of 27% or more and excellent toughness (vE0) of 47J or more.

On the other hand, the comparative steel No. In the case where the heating temperature is less than 1000 ° C. outside the range of the present invention as in the case of Comparative Example No. 11, In the case where Mo and Nb were added in excess of the range of the present invention as in Examples 12 and 15, or when Comparative Steel No. 1
When the rolling finish temperature is lower than the lower limit of Ar _{3 of the} present invention, as in the case of Comparative Steel No. 3, as shown in FIG. When the pipe expansion ratio is less than the lower limit of 0.8% of the present invention as in 19, the yield ratio exceeds 80%. In addition, the comparative steel No. When the standby temperature is lower than the lower limit of Ar ₃ -80 ° C. of the present invention as in the case of Comparative Steel No. When the cooling rate of the accelerated cooling is less than the lower limit of 1 ° C./sec of the present invention as in 16, the tensile strength is insufficient as a 60 kg class (590 N / mm ² or more).
Comparative steel No. As shown in FIG. 17, the waiting time is one of the lower limits of the present invention.
In the case of less than seconds, the comparative steel No. When the standby temperature is higher than the upper limit of Ar ₃ -20 ° C. of the present invention as in No. 18, the comparative steel N
o. When the stop temperature of the accelerated cooling is less than the lower limit of 400 ° C. of the present invention as in 20, ductility or toughness is insufficient.

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

According to the present invention, by specifying the steel composition and the production conditions, a relatively thin, low-yield-ratio 60-kilometer steel pipe having a pipe thickness of 50 mm or less used for a concrete-filled composite steel pipe column or the like can be obtained. It can be manufactured as-rolled and as-formed.

Therefore, by using the manufacturing method of the present invention, it is not necessary to heat-treat the steel plate before pipe forming and the steel pipe after pipe forming, so that productivity and economic efficiency can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between a pipe expansion ratio and a yield ratio (YR) in a pipe axis direction according to an embodiment of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22C 38/58 C22C 38/58

Claims (3)

[Claims] C: 0.06 to 0.17% by weight
, Si: 0.06-0.5%, and Mn: 0.5-1.
6%, P ≦ 0.05%, S ≦ 0.01%, Al ≦
0.07%, N ≦ 0.006%, and Mo:
0.05-0.5%, V: 0.01-0.1%, and T
i: In a method for producing a steel pipe having a steel composition composed of one or more selected from the group of 0.005 to 0.015% and the balance of Fe and unavoidable impurities, Ar ₃ comprising the steps of hot rolling at heating after Ar ₃ or more temperature range, the hot rolled steel sheet
Accelerated cooling to a temperature range of −50 ° C. ± 30 ° C. at a rate of 1 to 40 ° C./sec, and holding the accelerated cooled steel sheet at a temperature range of Ar ₃ −50 ° C. ± 30 ° C. for 1 to 150 seconds; A step of accelerated cooling at a temperature of 1 to 40 ° C./sec to a temperature range of up to 600 ° C., and a step of cold-forming the obtained steel sheet to form a steel pipe, and a pipe expansion rate of 0.8% or more in a final pipe forming step. A method for producing a high-strength steel pipe for building, comprising: 2. C: 0.06-0.17% by weight
, Si: 0.06-0.5%, and Mn: 0.5-1.
6%, P ≦ 0.05%, S ≦ 0.01%, Al ≦
0.07%, N ≦ 0.006%, and Cu:
0.05-0.5%, Ni: 0.05-0.8%, C
r: 0.05 to 0.5%, and Nb: 0.005 to 0.5%.
And one or more selected from 0.05% group, the method of the remainder to produce a steel pipe having a steel composition consisting of Fe and unavoidable impurities, after heating than the Ar ₃ temperature of the steel above 1000 ° C. a step of hot rolling in range, the hot rolled steel sheet Ar ₃
Accelerated cooling to a temperature range of −50 ° C. ± 30 ° C. at a rate of 1 to 40 ° C./sec, and holding the accelerated cooled steel sheet at a temperature range of Ar ₃ −50 ° C. ± 30 ° C. for 1 to 150 seconds; A step of accelerated cooling at a temperature of 1 to 40 ° C./sec to a temperature range of up to 600 ° C., and a step of cold-forming the obtained steel sheet to form a steel pipe, and a pipe expansion rate of 0.8% or more in a final pipe forming step. A method for producing a high-strength steel pipe for building, comprising: 3. The steel, in weight%, further comprises: Cu: 0.05
0.5%, Ni: 0.05-0.8%, Cr: 0.0
2. The building height according to claim 1, comprising one or more selected from the group of 5 to 0.5% and Nb: 0.005 to 0.05%. Manufacturing method of tensile steel pipe.