JP5381901B2 - ERW steel pipe for brace having excellent buckling resistance and manufacturing method thereof - Google Patents

Description

  The present invention relates to an electric-welded steel pipe for braces having excellent buckling resistance constituting a brace used as a seismic reinforcement for buildings and a method for manufacturing the same.

  A steel pipe brace (Patent Document 1) using a steel pipe is known as a brace used as a seismic reinforcement for buildings. Braces are intended to prevent the building from collapsing in the event of an earthquake and require buckling resistance. Since earthquake vibration is repeated, it is advantageous to have a small load drop during repeated loading. The steel pipe brace of Patent Document 1 has a double steel pipe structure to improve the buckling resistance. However, since the structure becomes complicated, the cost becomes high. Therefore, there is a demand for braces using a single steel pipe.

  On page 104 of the Architectural Institute of Japan Proceedings No. 260, which is Non-Patent Document 1, it is described that an ERW steel pipe that can be manufactured at a lower cost than a seamless steel pipe is used as a brace. However, general electric resistance welded steel pipes have a large load drop during repeated loading, and their buckling resistance is insufficient for use as braces with a single steel pipe.

JP 2008-223415 A

The Architectural Institute of Japan Proceedings No. 260, published in October 1977, pp. 99-108 “Resilience characteristics of skeletal skeletal structures”

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide an electric-welded steel pipe for braces having sufficient buckling resistance for use as a brace with a single steel pipe, and a method for manufacturing the same.

The electric resistance welded steel pipe for braces having excellent buckling resistance according to the present invention, which has been made to solve the above-mentioned problems, is in mass%, C: 0.03-0.25, Si: 0.05-1.0, Mn: 0.3-1.6, P : 0.03 or less, S: 0.015 or less, Sol.Al: 0.005 to 0.1, N: 0.0005 to 0.006, balance Fe and inevitable impurities, the average value of the dislocation density of the steel pipe base material part is 2 × 10 ¹⁵ / m ² The difference td (μm) between the maximum plate thickness and the minimum plate thickness and the 10-point average roughness Rz (μm) of the outer surface is 0 ≦ td ² × √Rz ≦ 40000 The condition of the expression 1 is satisfied.

  Moreover, the manufacturing method of the electric-resistance-welded steel pipe for braces excellent in buckling resistance property of the present invention made to solve the above-mentioned problems is in mass%, C: 0.03-0.25, Si: 0.05-1.0, Mn: 0.3 ~ 1.6, P: 0.03 or less, S: 0.015 or less, Sol.Al: 0.005 to 0.1, N: 0.0005 to 0.006, balance Fe and unavoidable impurities after heating the steel slab to 1070 ° C or higher and 1300 ° C or lower, Hot-rolled to a finish rolling end temperature of 800 ° C or higher and 1070 ° C or lower, made into a hot-rolled steel sheet at a coiling temperature of 500 ° C or higher and 700 ° C or lower, then rolled into a steel pipe and reduced by 4-roll sizing. Shaping is performed so that the total radial strain is 0.2% or more and 0.6% or less. After that, the heating temperature T (K) and the heating time t (h) are expressed by Formula 2 where 12800 ≦ T (logt + 20) ≦ 19000 and T ≦ 1000 It is characterized by performing annealing that satisfies the conditions.

  In any of the inventions, the steel constituting the braided electric resistance welded steel pipe is further used as a hardenability improving element group, Cu: 0.005-1.0, Ni: 0.005-1.0, Cr: 0.03-1.0, Mo: 0.1-0.5, B: 0.0001-0.01, crystal refinement element group, Ti: 0.005-0.1, Nb: 0.003-0.2, V: 0.001-0.2, W: 0.001-0.1, inclusion form control element, Ca: 0.0001-0.02, It is preferable to contain one or more elements selected from Mg: 0.0001 to 0.02, Zr: 0.0001 to 0.02, and REM: 0.0001 to 0.02.

The electric braided steel pipe for braces with excellent buckling resistance according to the present invention has an average dislocation density of the steel pipe base material as low as 2 × 10 ¹⁵ / m ² or less, and has a maximum thickness and a minimum thickness. By making the difference td (μm) and the 10-point average roughness Rz (μm) of the outer surface satisfy the condition of Equation 1 where 0 ≦ td ² × √Rz ≦ 40000, the uniform elongation during load application The stress concentration is high and the load reduction coefficient kd is large and the absolute value is small. For this reason, the buckling resistance characteristic when a repeated load is applied by the repeated vibration of the earthquake can be enhanced, and the buckling resistance characteristic of the electric braided steel pipe for braces can be improved.

  Moreover, according to the manufacturing method of the electric braided steel pipe for braces excellent in buckling resistance according to the present invention, the electric brazed electric pipe for braces having the above-described characteristics and a low dislocation density can be efficiently produced.

5 is a graph showing the relationship between dislocation density and load reduction coefficient kd. It is a graph which shows the relationship between e and n. It is a graph which shows the relationship between e and n which extracted only the compression cycle. It is a graph showing the relationship between the value and the load reduction factor kd of td ² × √Rz.

The present invention is described in further detail below.
The basic steel composition of the ERW steel pipe for braces excellent in buckling resistance of the present invention is mass%, C: 0.03 to 0.25, Si: 0.05 to 1.0, Mn: 0.3 to 1.6, P: 0.03 or less, S: 0.015 or less, Sol.Al: 0.005 to 0.1, N: 0.0005 to 0.006, balance Fe and inevitable impurities. By subjecting the ERW steel pipe made of steel having such a composition to the processing and heat treatment described later, the average value of the dislocation density is lowered to 2 × 10 ¹⁵ / m ² or less, and the condition of Formula 1 is further satisfied. An electric resistance welded steel pipe for braces can be obtained efficiently. First, the reason for limiting the numerical values of each element will be described.

C is an element that affects the strength of steel, and 0.03% or more is necessary to obtain a strength that can withstand repeated loading of compression and tension during an earthquake. However, if it exceeds 0.25%, the dislocation density of the ERW steel pipe base metal part becomes excessively high and the strength becomes excessive. Therefore, in order to ensure the buckling resistance, the content is made 0.25% or less. Si needs to be added at least 0.05% as a deoxidizing element, but if added in excess, the electric resistance weldability is lowered, so the maximum is 1.0%. Mn is an effective element to improve the hardenability and reduce the dislocation density of the ERW steel pipe base material in combination with heat treatment of the ERW steel pipe. The average value of the dislocation density is 2 × 10. It can be controlled to ¹⁵ / m ² or less. For this purpose, it is necessary to add at least 0.3%, but if added excessively, the electric resistance weldability is lowered and the buckling resistance is remarkably lowered due to microcracking or the like, so 1.6% or less.

  P and S are elements that reduce the cleanliness of steel, so they are 0.03% or less and 0.015% or less, respectively. Al needs to be added as a deoxidizing element, and AlN is produced to suppress the crystal grain refinement and coarsening, thereby preventing the hardenability from being excessively increased and keeping the dislocation density low. For this purpose, it is necessary to add 0.005% or more. However, if it exceeds 0.1%, the cleanliness of the steel will be remarkably lowered, and there is a concern that cracks due to coarse AlN will occur in the ERW steel pipe for braces when cyclic compression-tensile repeated loads are applied. ~ 0.1%. N, like Al, generates AlN and promotes crystal grain refinement and suppression of coarsening, thereby preventing the hardenability from being excessively improved and keeping the dislocation density low. For this purpose, it is necessary to add 0.0005% or more. However, if it exceeds 0.006%, the cleanliness of the steel will be remarkably reduced, and cracks due to coarse AlN may occur in the braided ERW steel pipe when repeated compression-tensile loads are loaded in an earthquake. 0.0005 to 0.006%.

In addition to the basic elements described above, the hardenability improving element group is Cu: 0.005-1.0, Ni: 0.005-1.0, Cr: 0.03-1.0, Mo: 0.1-0.5, B: 0.0001-0.01, crystal refinement As element group, Ti: 0.005-0.1, Nb: 0.003-0.2, V: 0.001-0.2, W: 0.001-0.1, Inclusion form control element group, Ca: 0.0001-0.02, Mg: 0.0001-0.02, Zr: One or more elements selected from 0.0001 to 0.02 and REM: 0.0001 to 0.02 can be contained. All of the hardenability-enhancing elements (Cu, Ni, Cr, Mo, B) improve the hardenability and efficiently dislocation when subjected to the above-mentioned processing and annealing in an ERW steel pipe after welding. It is an effective element for controlling the average density to 2 × 10 ¹⁵ / m ² or less. However, if added excessively, it becomes difficult to lower the average value of dislocation density to 2 × 10 ¹⁵ / m ² or less. In addition, the above range is preferable because it also causes an increase in cost. Crystal refinement elements (Ti, Nb, V, W) reduce the dislocation density of the base metal part of the braided ERW steel pipe by reducing the crystal size or suppressing the coarsening, thereby suppressing the hardenability. Is an effective element. However, if excessively added, coarse carbides and carbonitrides are likely to be formed, and even if the condition of Formula 1 is satisfied, the buckling resistance may be reduced, and the cost may be increased. It is preferable to do.

  Inclusion morphology control elements (Ca, Mg, Zr, REM) suppress the formation of coarse inclusions in the braided ERW steel pipe and finely disperse the inclusions. Even when a compression-tensile load is repeatedly applied in the long direction, it is an effective element for reducing the concern that cracks will occur in the base material part or welded part of the ERW steel pipe. However, if added excessively, complex compounds such as coarse sulfides and clustered oxides of Ca, Mg, Zr, and REM will form on the base and welded parts of the ERW steel pipe, and the cleanliness of the base will be improved. Since there is a possibility that the buckling resistance characteristics at the time of repeated load loading at the ERW welded portion may be lowered, the above range is preferable.

The electric resistance steel pipe for braces of the present invention has an average dislocation density of 2 × 10 ¹⁵ / m ² or less. As shown in FIG. 1, when the dislocation density is 2 × 10 ¹⁵ / m ² or less, there is no decrease in the load reduction characteristic, but when the dislocation density increases, the load reduction characteristic decreases rapidly. Here, the load reduction coefficient kd shown in FIG. 1 will be described. FIG. 2 shows the deformation history of the steel pipe obtained by alternately applying a compressive load and a tensile load to the steel pipe. The vertical axis is the dimension n obtained by dividing the load by the yield load (yield stress x tube wall thickness cross section before loading), and the horizontal axis is the yield displacement (yield strain x steel pipe length before loading). It is a value e which is divided by the above and made dimensionless. For the yield stress and the yield strain on the compression load side and the tensile load side, values obtained by a steel pipe tensile test may be used. FIG. 3 is a graph in which only the compression cycle is extracted from the graph of FIG. 2 and the horizontal axis is the integrated value of e. The slope of the straight line connecting the vertices in the graph of FIG. 3 is the load reduction coefficient kd. The smaller the kd value and the larger the absolute value, the greater the strength reduction against repeated loads. Further details will be described in the example section. In addition, when the average value of dislocation density is 2 × 10 ¹⁵ / m ² or less, as in another invention of the present inventors, the base material structure of the ERW steel pipe is 3% in area fraction of the hard phase. If there are more, it is difficult.

In addition, the electric resistance welded steel pipe for braces of the present invention has a difference td (μm) between the maximum thickness and the minimum thickness excluding the welded portion, and the 10-point average roughness Rz (μm) of the outer surface is 0 ≦ td ² X√Rz ≦ 40000 The condition of the expression 1 is satisfied. FIG. 4 is a graph showing the relationship between the value of td ² × √Rz in Equation 1 and the load reduction coefficient kd. As is apparent from this graph, the load reduction coefficient kd is constant in the range of 0 ≦ td ² × √Rz ≦ 40000, but rapidly decreases when it exceeds 40000. Here, a large value of td ² × √Rz means that at least one of td and Rz is large, and when td is large, the load is concentrated at a thin plate thickness, and Rz is When it becomes larger, the load concentrates on the concaves and convexes on the outer surface of the steel pipe, so the load reduction coefficient kd is considered to be significantly reduced.

  Next, the manufacturing method of the electric resistance steel pipe for braces of this invention is demonstrated. The electric braided steel pipe for braces of the present invention is a steel slab made of steel having the above composition, heated to 1070 ° C. or higher and 1300 ° C. or lower, and then subjected to hot rolling with a finish rolling end temperature of 800 ° C. or higher and 1070 ° C. or lower, After forming a hot-rolled steel sheet at a coiling temperature of 500 ° C. or more and 700 ° C. or less, it is rolled to form a steel pipe, and shaped so that the total diameter reduction strain in a 4-roll sizing is 0.2% to 0.6%, The heating temperature T (K) and the heating time t (h) are manufactured in a process characterized by performing annealing satisfying Expression 2 where 12800 ≦ T (logt + 20) ≦ 19000 and T ≦ 1000. In order to wind a steel pipe by roll forming, both ends of the steel plate width are brought close to each other by roll forming, and electric resistance welding is performed on both ends of the steel plate width.

  The reason why the heating temperature is set to 1070 ° C. or higher is to re-dissolve carbides, nitrogen compounds, and carbonitride compounds precipitated during the melting and solidification process of the steel slab to uniformly disperse the elements. However, when the heating temperature exceeds 1300 ° C, AlN precipitates coarsely in the hot rolling process, reducing the cleanliness of the steel, and cracks due to coarse AlN are used for braces due to repeated loading of compression-tensile loads during earthquakes. The heating temperature was set to 1070 ° C or higher and 1300 ° C or lower because there was a concern that it would occur in ERW steel pipes.

The rolling end temperature is set to 800 ° C or higher if the temperature is lower than this temperature, the dislocation density of the steel sheet increases during finish rolling, and the average value of the dislocation density at the steel pipe base is 2 × 10 ¹⁵ / m ² . It is because it is easy to exceed. However, when the temperature exceeds 1070 ° C., the grain growth becomes remarkable and the crystal grains become coarse. Therefore, the rolling end temperature in the hot rolling is set to 800 ° C. or more and 1070 ° C. or less.

The coiling temperature is set to 500 ° C or higher. If the temperature is lower than this temperature, the average value of the dislocation density in the base material of the ERW steel pipe may exceed 2 × 10 ¹⁵ / m ^2. This is because there is a concern that the bending characteristics may deteriorate. However, if the temperature exceeds 700 ° C., there is a concern that the nucleation of ferrite is insufficient and coarse grains may be formed, so the coiling temperature is set to 500 ° C. or more and 700 ° C. or less.

  The hot-rolled steel sheet thus obtained is wound by roll forming, and the two ends of the steel sheet are electro-welded to form an electric-welded steel pipe, and the total shrinkage distortion is 0.2% or more and 0.6% by 4-roll sizing. Perform the following formatting. The electric resistance welding of the electric resistance welded steel pipe of the present invention includes electric resistance welding (including high frequency welding, low and medium frequency welding, high frequency induction welding), laser welding, laser / arc hybrid welding, and the like. The 4-roll sizing is used to ensure the uniformity in the circumferential direction of the steel pipe. With 2 rolls, strain is concentrated at the 0 ° position and 180 ° position of the steel pipe. Since strain concentrates at the 120 ° position and the 240 ° position, it is difficult to reduce the values of td and Rz so as to satisfy the above formula 1.

  The reason why the total reduction strain is set to 0.2% or more in the 4-roll sizing is to make the thickness difference and the outer surface roughness of the ERW steel pipe uniform while reducing the diameter. However, if the reduced diameter strain exceeds 0.6%, the steel pipe is excessively distorted and the wall thickness difference td and the outer surface roughness Rz become too large, so that it is difficult to stably satisfy the condition of Equation 1 and will be described later. Even if the annealing heat treatment of Formula 2 is applied to the ERW steel pipe, it is difficult to reduce the dislocation density of the steel pipe base material portion because of too many work dislocations. For this reason, the total diameter reduction strain is set to 0.2% to 0.6%.

Thereafter, annealing is performed such that the heating temperature T (K) and the heating time t (h) satisfy Expression 2 where 12800 ≦ T (logt + 20) ≦ 19000 and T ≦ 1000. The reason why the value of T (logt + 20) in Equation 2 is 12800 or more is that it is effective for making the average value of the dislocation density of the steel pipe base material 2 × 10 ¹⁵ / m ² or less. The reason for this is to ensure the strength to withstand repeated loads. When the heating temperature T (K) exceeds 1000 (K), the hard phase may exist in the steel pipe base material part by 3% or more from the austenite produced during the heat treatment. It is difficult to reduce the density.

The measuring method of each value in the present invention is as follows.
The dislocation density was measured by the Williamson-Hall method (CAMP-ISIJ Vol.17 (2004) -396) with X-rays. Five square test pieces of 10 mm each in the circumferential direction and the longitudinal direction of the pipe are taken from the base material of the ERW steel pipe, the scale on the pipe surface is pickled and removed, and then the test piece for measuring the dislocation density. It was. The dislocation density was measured by X-rays on the surface of the test piece by the method described above. The average value of the measured five dislocation densities was taken as the average value of the dislocation density of the steel pipe base material part.

  td was measured by cutting the cross section of the steel pipe and measuring the plate thickness in the circumferential direction, and the difference between the maximum plate thickness and the minimum plate thickness excluding the weld was taken as td. Rz was calculated as the difference between the average value of the top of the fifth peak in the height direction and the average value of the bottom of the valley from the deepest to the fifth in the reference length (longitudinal direction) of 2.5 mm.

The electric resistance welded steel pipe for braces of the present invention thus produced has sufficient buckling resistance characteristics for use as a brace. In addition, as a steel pipe for braces, steel pipes having a tensile strength of 400 MPa class, 490 MPa class, and 590 MPa class are generally used. The electric braided steel pipe for braces of the present invention can sufficiently satisfy this strength level. With an ERW steel pipe having a significantly lower strength level (for example, a yield strength of 100 MPa class in which the C content is less than the lower limit of the present invention), it is difficult to sufficiently withstand repeated loading of a compression-tensile load during an earthquake. For extremely high strength steel pipes with extremely high strength (for example, tensile strengths with C content exceeding the upper limit of the present invention are 1050 MPa class and 1150 MPa class), both the dislocation density condition of the present invention and Equation 1 must be satisfied at the same time. Therefore, as for the steel pipe for braces, the load drop becomes large and the buckling resistance characteristic may be lowered with respect to repeated loading of compression-tensile load at the time of earthquake. In addition, if the electric braided steel pipe for braces of the present invention satisfies all the steel composition conditions, dislocation density conditions, and the condition of Formula 1, the hot rolled steel sheet is further subjected to cold rolling or annealing as the base steel sheet of the steel pipe. Steel plates obtained by adding surface treatment (rust prevention treatment, lubrication treatment, etc.) to these steel plates may be used. Even an ERW steel pipe that has undergone surface treatment (such as rust prevention treatment) after ERW welding does not depart from the scope of the present invention. If the conditions of Formula 1 are satisfied, the pipe dimensions of the ERW steel pipe of the present invention can be determined according to the design conditions for using the ERW steel pipe for braces. For example, the outer diameter of the electric resistance steel pipe may be 100 mm to 400 mm, and the plate thickness (pipe thickness excluding the welded portion) may be 3 to 25 mm.
Examples of the present invention are shown below together with comparative examples.

Table 2 shows the results of producing braided ERW steel pipes from the steel compositions shown in Table 1 under the production conditions shown in Table 2 and measuring the buckling resistance of each steel pipe. The dimensions of the ERW steel pipe used for the test are φ244.5mm × t8.0mm × L2600mm. The method for measuring the buckling resistance is as follows. Similar to the method used in Non-Patent Document 1, a tensile-compressive load was repeatedly applied to the steel pipe by displacement control. When the yield displacement of the steel pipe is δ _y and the ratio δ / δ _y to the applied displacement δ is e, the displacement applied in each cycle is added so that the value of e is equal to the number of cycles. Then the load applied to the steel pipe is P, the value P / P _y obtained by dividing the P at yield axial force P _y is n, was determined a relationship between the e-n obtained in each cycle as illustrated in Figure 2. The upper side is compression and the lower side is tension. Next, as shown in FIG. 3, an approximate straight line connecting the maximum load points was drawn, and the gradient was used as the load reduction coefficient kd. The value of e when local buckling occurred in the center of the steel pipe was also recorded.

Further, the calculated value of kd predicted for the conventional electric resistance welded steel pipe obtained from the equation of kd = −0.1 (√ε _y × λ−0.75) described in Non-Patent Document 1 is also shown in Table 2 for reference. Indicated. The buckling resistance was evaluated based on the value of e when local buckling actually occurred.

In all of Examples 1 to 24 of the invention, the average value of the dislocation density of the steel pipe base material part is sufficiently small as 2 × 10 ¹⁵ / m ² or less, and dislocations are generated in the ERW pipe during repeated loading of compression-tensile load during earthquakes. Even if it is introduced, local buckling is unlikely to occur, and since td ² × √Rz satisfies Equation 1 and is small, the concentration of the load is small. For this reason, the measured value of kd is larger than the calculated value of kd estimated from the conventional ERW steel pipe, and as a result, the value of e causing buckling is more than 10, which is about several times that of the comparative example and excellent resistance. Shows buckling characteristics. As shown in Table 2, in the examples, td falls within the range of 40 to 70 μm, and Rz falls within the range of 10 to 30 μm.

On the other hand, in Comparative Example 1, since the C component value is high and the dislocation density of the steel pipe is too high and the ductility is low, the buckling resistance is insufficient. In Comparative Example 2, the Mn component value is too small and the strength to withstand repeated loads cannot be obtained, so the buckling resistance is poor. Comparative Example 3 has poor buckling resistance because the rolling end temperature is low and the dislocation density is high. In Comparative Example 4, since the two-roll sizing was performed, distortion deviation occurred in the circumferential direction of the steel pipe, and td and Rz were not sufficiently small, and the condition of td ² × √Rz in Equation 1 was not satisfied, so the buckling resistance was poor. . In Comparative Example 5, since the diameter reduction strain was insufficient at 0.18%, sufficient diameter reduction was not possible. Therefore, td and Rz were not sufficiently reduced, and the condition of td ² × √Rz in Equation 1 was not satisfied, so the buckling resistance was poor. bad. In Comparative Example 6, the heating temperature T in the annealing condition is over 1000K and is too high, and T (logt + 20) is too large. Therefore, Formula 2 is not satisfied and the dislocation density is too high, so the buckling resistance is poor. In Comparative Example 7, since the value of T (logt + 20) in Formula 2 is too small, the dislocation density is 2 × 10 ¹⁵ / m ² because annealing is not sufficient to reduce the dislocation density of the steel pipe base material. Since it exceeds, buckling resistance is poor. Since Comparative Example 8 was not annealed after sizing, dislocations still increased in the ERW steel pipe in the sizing process, and the dislocation density greatly exceeded 2 × 10 ¹⁵ / m ² , so Bad buckling characteristics.

Claims (4)

In mass%, C: 0.03-0.25, Si: 0.05-1.0, Mn: 0.3-1.6, P: 0.03 or less, S: 0.015 or less, Sol.Al: 0.005-0.1, N: 0.0005-0.006, the remainder Fe and inevitable The average value of dislocation density in the steel pipe base metal part is 2 × 10 ¹⁵ / m ² or less, and the difference between the maximum and minimum plate thickness td (μm), excluding the weld, An electric-welded steel pipe for braces with excellent buckling resistance, characterized in that the 10-point average roughness Rz (μm) of the surface satisfies the condition of Formula 1 where 0 ≦ td ² × √Rz ≦ 40000.   The steel constituting the ERW steel pipe for braces is further divided into Cu: 0.005-1.0, Ni: 0.005-1.0, Cr: 0.03-1.0, Mo: 0.1-0.5, B: 0.0001-0.01, crystal As refinement element group, Ti: 0.005-0.1, Nb: 0.003-0.2, V: 0.001-0.2, W: 0.001-0.1, Inclusion form control element, Ca: 0.0001-0.02, Mg: 0.0001-0.2, Zr The electric braided steel pipe for braces having excellent buckling resistance according to claim 1, comprising one or more elements selected from: 0.0001 to 0.02 and REM: 0.0001 to 0.02. .   In mass%, C: 0.03-0.25, Si: 0.05-1.0, Mn: 0.3-1.6, P: 0.03 or less, S: 0.015 or less, Sol.Al: 0.005-0.1, N: 0.0005-0.006, the remainder Fe and inevitable After heating steel slabs composed of mechanical impurities to 1070 ° C or higher and 1300 ° C or lower, they are hot-rolled to a finish rolling finish temperature of 800 ° C or higher and 1070 ° C or lower, and hot rolled at a coiling temperature of 500 ° C or higher and 700 ° C or lower. After forming into a steel plate, it is rolled into a steel pipe by roll forming, and shaping is performed so that the total reduced diameter strain in 4-roll sizing is 0.2% to 0.6%, and then heating temperature T (K) and heating time t (h ) Is an annealing process that satisfies the conditions of Formula 2 with 12800 ≦ T (logt + 20) ≦ 19000 and T ≦ 1000.   The steel constituting the ERW steel pipe for braces is further divided into Cu: 0.005-1.0, Ni: 0.005-1.0, Cr: 0.03-1.0, Mo: 0.1-0.5, B: 0.0001-0.01, crystal As refinement element group, Ti: 0.005-0.1, Nb: 0.003-0.2, V: 0.001-0.2, W: 0.001-0.1, Inclusion form control element, Ca: 0.0001-0.02, Mg: 0.0001-0.02, Zr The braided ERW steel pipe with excellent buckling resistance according to claim 3, comprising one or more elements selected from: 0.0001 to 0.02 and REM: 0.0001 to 0.02. Manufacturing method.

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