JP5601295B2 - Spiral steel pipe with internal protrusion with low yield ratio and its manufacturing method - Google Patents

Description

  The present invention relates to a spiral steel pipe with an internally projecting projection having a yield strength of 450 MPa or more and 650 MPa or less and a yield ratio of less than 0.85, which is used for a concrete-filled steel pipe used for a foundation structure such as a building, a bridge, or a steel tower. It is about the law.

  In general, a building such as a building or a basic structure such as a bridge or a steel tower has a structure in which a footing is supported on a pile head of a steel pipe pile. The pile heads of steel pipe piles are subject to axial forces, shearing forces and bending moments due to the weight of buildings, etc., and horizontal forces generated during earthquakes. Against the backdrop of rationalization of the foundation structure due to composting etc., the proof stress required for the pile head is increasing. Large diameter and thick steel pipe piles are also used to meet such demands, but spiral steel pipes used for large diameter steel pipe piles are limited in strength and thickness for processing reasons. . Therefore, conventionally, a pile head where a particularly large bending moment is generated in a steel pipe pile is separately reinforced.

  For example, Patent Document 1 discloses a structure in which reinforcing bars and concrete are filled inside a pile head. Patent Document 2 discloses a method for constructing a double-pipe pile head structure. Patent Document 3 discloses a method of increasing horizontal proof stress by filling a material in a space formed between a steel pipe pile and an outer pipe below the footing. Patent Document 4 discloses a structure for increasing the adhesion between concrete and steel pipe by attaching a stopper or a reinforcing bar.

  On the other hand, against the backdrop of the increase in the number of piles accompanying the increase in the size of building structures and the increase in bearing capacity of steel pipe piles, a greater bearing capacity has been required for the pile heads. In order to increase the strength of the pile head, it is effective to increase the strength, diameter, thickness, and concrete-filled steel pipe of the steel pipe. There are many methods for increasing the strength of a steel pipe. For example, Patent Document 5 discloses a method for manufacturing a thick-walled high-strength bent pipe by heating and cooling a steel pipe. Patent Document 6 discloses a method for manufacturing a synthetic steel pipe filled with concrete.

  Furthermore, Patent Document 7 and Patent Document 8 disclose a method for manufacturing a high-strength spiral steel pipe having an inner surface protrusion.

JP 2005-163421 A JP 2009-30372 A JP 2009-46879 A JP 2009-46881 A JP-A-5-279743 JP-A-53-53021 JP 2011-63878 A JP 2011-63879 A

  However, in order to reinforce from the inside of the pile head as in Patent Document 1, the inside of the pile head is washed after the steel pipe pile is placed on the ground or during the placement. Etc., and there is a problem that the workability is lowered. Moreover, in the method of the said patent documents 2-4, the operation | work which reinforces a pile head at a construction site must be performed in any case, and there also exists a subject that construction becomes complicated and construction cost becomes high.

  In order to increase the strength of the pile head of the steel pipe pile, it is effective to increase the strength, increase the diameter, increase the thickness of the steel pipe, and fill the concrete-filled steel pipe. Patent Document 5 includes the API standard X65 to X70 class. Although a manufacturing method of high strength thick-walled curved pipe is disclosed, it is not a steel pipe intended for a composite structure with concrete, so when the steel pipe pile is only a bare pipe (a steel pipe that is not a composite structure with concrete) Does not provide sufficient strength of the pile head. As a method for improving the adhesion strength between the steel pipe and the concrete, a method in which a weld bead or a stud bolt is applied to the steel pipe is also conceivable. However, it is difficult to control the construction of the high strength material and to make a composite structure. In addition, when the steel pipe pile is a raw pipe, in order to obtain a sufficient yield strength of the pile head, for example, a steel pipe having a yield strength of 700 MPa or more is required, and the amount of alloying elements is inevitably increased. There has been a problem that the low-temperature toughness of the weld metal after tempering (welding cold cracking resistance) and tempering treatment is reduced.

  Patent Document 6 discloses a method of manufacturing a spiral steel pipe with an inner protrusion used for a composite structure with concrete. High strength hot rolled coils are required to produce high strength spiral steel pipes with internal protrusions, but high strength and thick hot rolled coils are economically manufactured from the viewpoint of the winding ability of hot rolled coils. It is difficult to do. In addition, when a high-strength hot-rolled coil is spirally formed, a large forming load is required, which causes a manufacturing problem.

  Patent Document 7 discloses a method of increasing the strength by heating a spiral steel pipe with an inner surface protrusion and then cooling it with water from the outer surface side. In this manufacturing method, since the yield ratio exceeds 0.85, there is a problem that the reliability of the structure at the time of the occurrence of a huge earthquake is lowered.

  Patent Document 8 discloses a method of increasing strength by heating a spiral steel pipe with an inner protrusion in a state where the longitudinal direction of the steel pipe is in the vertical direction and then cooling with water from the outer surface side. Similar to the above-mentioned Patent Document 7, this manufacturing method has a problem that the yield ratio exceeds 0.85, and thus the reliability of the structure at the time of the occurrence of a huge earthquake is lowered.

  An object of the present invention is to provide a spiral steel pipe with an internal protrusion that can be used for a concrete-filled steel pipe that can omit reinforcement work on site and has sufficient strength and low yield ratio against axial force and bending moment received from a building or the like. And providing a manufacturing method thereof.

According to the present invention, by mass%, C: 0.05-0.20, Si: 0.01-0.6, Mn: 0.8-2.2, P: 0.02 or less, S: 0 0.005 or less, Nb: 0.005 to 0.080, Ti: 0.005 to 0.030, Al: 0.001 to 0.05, N: 0.001 to 0.006, O: 0.006 or less The balance is made of iron and inevitable impurities, and the CE value defined by the following formula (1) is in the range of 0.40 to 0.55, the ferrite fraction is 16 to 50%, and the balance There is provided a spiral steel pipe with an inner surface protrusion having a yield strength of 450 MPa or more and 650 MPa or less and a yield ratio of less than 0.85, characterized in that the structure of bainite and martensite.
CE = C + Si / 24 + Mn / 6 (1)

In this spiral steel pipe, the steel component is in mass%, and Cr: 0.1 to 0.5 , Mo: 0.1 to 0.5 , V: 0.01 to 0.10, B: 0.0003 to Even if it contains one or two or more of 0.002 and the CE value defined by the following formula (2) is in the range of 0.40 to 0.55 instead of the formula (1), good.
CE = C + Si / 24 + Mn / 6 + Cr / 5 + Mo / 4 + V / 14 (2)

Moreover, according to the present invention, by mass, C: 0.05 to 0.20, Si: 0.01 to 0.6, Mn: 0.8 to 2.2, P: 0.02 or less, S : 0.005 or less, Nb: 0.005 to 0.080, Ti: 0.005 to 0.030, Al: 0.001 to 0.05, N: 0.001 to 0.006, O: 0.00. 006 or less, the balance is made of iron and inevitable impurities, and the spiral steel pipe with an inner surface protrusion is made of a base material whose CE value defined by the following formula (1) is in the range of 0.40 to 0.55 After heating to 860-960 ° C., the steel pipe outer surface is immersed in a water tank from a temperature of 650-850 ° C., and water-cooled to 200 ° C. or less so as to have a cooling rate of 10 ° C./second or more, Thereafter, tempering is performed at 650 ° C. or lower, and 450 MPa or more and 650 MPa Yield strength of the lower and inner surface projections with the preparation of the spiral pipe is provided having a yield ratio of less than 0.85.
CE = C + Si / 24 + Mn / 6 (1)

In this production method, the base material is in mass%, and Cr: 0.1 to 0.5, Mo: 0.1 to 0.5, V: 0.01 to 0.10, B: 0.0. One or more of 0003 to 0.002 are contained, and the CE value defined by the following formula (2) is in the range of 0.40 to 0.55 instead of the formula (1). May be.
CE = C + Si / 24 + Mn / 6 + Cr / 5 + Mo / 4 + V / 14 (2)

  ADVANTAGE OF THE INVENTION According to this invention, the spiral steel pipe with an inner surface protrusion which has the yield strength of 450 Mpa or more excellent in weldability, and the yield ratio of less than 0.85 can be manufactured stably. As a result, the safety of buildings such as buildings and foundation structures such as bridges and steel towers is improved.

  Below, the spiral steel pipe with an internal protrusion of the low yield ratio of this invention and its manufacturing method are demonstrated in detail.

  In foundation structures such as buildings, bridges, and steel towers, increasing the strength, diameter, thickness, and concrete-filled steel pipes of steel pipes is effective for increasing the strength of pile heads of steel pipe piles. However, as a result of studying the increase in yield strength of steel pipe piles from the viewpoint of weldability, the present invention has been achieved. That is, while limiting the range of chemical composition and yield strength of steel pipes with internal protrusions used for concrete-filled steel pipes, and after heating spiral steel pipes to 860-960 ° C., the outer surface of the steel pipe is adjusted from the temperature of 650-850 ° C. By immersing the steel pipe in it, cooling it with water, and then tempering it, a spiral steel pipe with internal protrusions having high strength and a low yield ratio can be obtained.

  When the steel pipe pile has a composite structure with concrete, the pile head has a bending strength (proof strength against bending moment) of 15,000 kN · m or more in the NM curve (relation curve between axial force N and bending moment M). It has been demanded. In order to achieve this, it is necessary that the yield strength of the steel pipe with an internal protrusion is 450 MPa or more and 650 MPa or less and the thickness of the steel pipe is 14 mm or more and 25 mm or less. The thickness of the steel pipe at this time indicates the thickness of the portion having no inner surface protrusion. For example, when the outer diameter is 1400 mm and the steel pipe thickness is 25 mm, the yield strength is 450 MPa and the bending strength is 19,000 kN · m. Further, when the outer diameter is 1400 mm and the steel pipe thickness is 14 mm, the yield strength is 650 MPa and the bending strength is 16,500 kN · m. In addition, it is preferable that the steel pipe thickness is set to a maximum thickness of 25 mm from the viewpoint of the hot rolling winding ability. Moreover, since the weldability of a steel pipe falls when the yield strength exceeds 650 MPa, the upper limit of the yield strength is limited to 650 MPa from the viewpoint of weldability. In addition, it was found that a low yield ratio of less than 0.85 is necessary as a foundation pile for construction from the viewpoint of the safety of the structure when a huge earthquake occurs. As a metal structure that achieves such a high strength and a low yield ratio, in the present invention, the ferrite fraction must be 16 to 50%, the remaining structure must be bainite or martensite, and the ferrite fraction is 15% or less. Then, a low yield ratio cannot be achieved, and if it is 50% or more, the yield strength cannot satisfy 450 MPa. The ferrite fraction is the sum of the fractions of polygonal ferrite generated before the start of water cooling and acicular ferrite generated during water cooling.

  Next, the reasons for limiting chemical components will be described. In addition, the description of% about a component means the mass% unless there is particular notice.

  The lower limit of 0.05% of C is the minimum amount for ensuring the strength, precipitation hardening by adding Nb and V, and the effect of refining crystal grains. However, if the amount of C is too large, the weldability and low temperature toughness are significantly reduced, so the upper limit was made 0.20%.

  Si is an element added for deoxidation and strength improvement, and its lower limit is 0.01%. However, if added in a large amount, the weldability and low temperature toughness are lowered, so the upper limit was made 0.6%.

  Mn is an indispensable element for securing strength and low temperature toughness, and its lower limit is 0.8%. However, if Mn is too much, not only the hardenability of the steel is increased and the weldability and the low temperature toughness are lowered, but also the center segregation of the continuously cast steel piece is promoted and the low temperature toughness is also lowered. %.

  In the present invention, the amount of P which is an inevitable impurity is set to 0.02% or less. The main reason for this is to further improve the low temperature toughness of the base material. Reduction of the amount of P reduces the center segregation of a continuous casting slab, prevents a grain boundary fracture, and improves low temperature toughness. In the present invention, P is an impurity and may not be contained.

  Further, the S amount is set to 0.005% or less. The reduction of the amount of S has the effect of improving the ductility by reducing the stretched MnS. In the present invention, S is an impurity and may not be contained.

  Nb contributes to crystal grain refinement and precipitation hardening in controlled rolling, and has the effect of strengthening steel. As a minimum amount for exhibiting this effect, the lower limit was made 0.005%. However, if Nb is added in an amount of 0.080% or more, the amount of Nb in the weld metal increases, which lowers the low temperature toughness of the weld metal and adversely affects weldability and low temperature toughness, so the upper limit was made 0.080%.

  Ti addition forms fine TiN, suppresses coarsening of austenite grains during slab reheating and welded HAZ, refines the microstructure, and improves low-temperature toughness. In order to exhibit such an effect of TiN, it is necessary to add at least 0.005% Ti. However, when the amount of Ti is too large, TiN coarsening and precipitation hardening due to TiC occur, and the low-temperature toughness decreases, so the upper limit was limited to 0.030%.

  Al is an element usually contained in steel as a deoxidizer, and is effective in refining the structure, and its lower limit is 0.001%. However, if the Al content exceeds 0.05%, Al-based non-metallic inclusions increase to impair the cleanliness of the steel, so the upper limit was made 0.05%.

  N forms TiN and suppresses the coarsening of austenite grains in the slab reheating and welding heat affected zone (HAZ) to improve the low temperature toughness of the base material and HAZ. The minimum amount required for this is 0.001%. However, if the amount is too large, the HAZ toughness is reduced due to slab surface flaws or solute N, so the upper limit must be limited to 0.006%.

  The reduction of the amount of O reduces the oxide in the steel and is effective in improving the low temperature toughness, so the upper limit was made 0.006% or less. In the present invention, O is an impurity and may not be contained.

Further, the spiral steel pipe of the present invention has a CE value defined by the following formula (1) in the range of 0.40 to 0.55.
CE = C + Si / 24 + Mn / 6 (1)
In this formula (1), “C”, “Si”, and “Mn” mean mass% of each chemical component contained in the spiral steel pipe.

  If the CE value is less than 0.40, sufficient strength cannot be obtained. On the other hand, when the CE value exceeds 0.55, the weldability and toughness are lowered.

  Further, the spiral steel pipe of the present invention has a steel component in mass%, and Cr: 0.1 to 1.0, Mo: 0.1 to 1.0, V: 0.01 to 0.10, B: You may contain 1 type, or 2 or more types among 0.0003-0.002.

  Further, the reason for adding Cr, Mo, V, B will be described. The main purpose of adding these elements to the basic component is to improve the properties such as strength and low temperature toughness without impairing the characteristics of the steel of the present invention. Therefore, the amount of addition is a property that should be restricted by itself.

  Cr has an effect of increasing the strength of the base material, and in order to exert this effect, addition of 0.1% or more is necessary. However, if too much, weldability and HAZ toughness are reduced. For this reason, the upper limit of the Cr amount is 0.5%.

  Mo is an element that increases the strength of the base metal and the welded portion. However, when it exceeds 0.5%, the base metal, the HAZ toughness and the weldability are reduced in the same manner as Cr. In addition, the effect is small when 0.1% or less is added.

  V has substantially the same effect as Nb, but the effect is much weaker than Nb. In order to exhibit the effect, addition of 0.01% or more is necessary. Further, the upper limit is allowable up to 0.1% from the viewpoint of on-site weldability and HAZ toughness.

  B is a very small amount, which dramatically enhances the hardenability of the steel and provides good strength and toughness. In order to exert this effect, 0.0003% or more must be added. Moreover, since it will reduce HAZ toughness when there is too much, the upper limit value was limited to 0.002%.

Moreover, when the spiral steel pipe of this invention contains 1 type, or 2 or more types among Cr, Mo, V, and B in this way, it replaces with said Formula (1) and is defined by following formula (2). The CE value is in the range of 0.40 to 0.55.
CE = C + Si / 24 + Mn / 6 + Cr / 5 + Mo / 4 + V / 14 (2)
In this formula (2), “C”, “Si”, “Mn”, “Cr”, “Mo”, and “V” mean mass% of each chemical component contained in the spiral steel pipe.

  The CE value defined by the formula (2) is limited to the range of 0.40 to 0.55. If the CE value is less than 0.40, sufficient strength cannot be obtained. On the other hand, when the CE value exceeds 0.55, the weldability and toughness are lowered.

  In addition, in the spiral steel pipe of this invention, these Cr, Mo, V, and B are chemical components contained selectively. Therefore, when Cr, Mo, V, and B are not contained, they are calculated as 0 in the above (Equation 2).

Next, the reasons for limiting the manufacturing conditions will be described.
In this invention, after heating the spiral steel pipe with an internal protrusion which has said component to 860-960 degreeC, the steel pipe outer surface is a temperature of 650-850 degreeC, and a steel pipe is put in a water tank in the state from which a steel pipe longitudinal direction becomes a horizontal direction. Is immersed in water and cooled to 200 ° C. or lower so that the cooling rate is 10 ° C./second or higher, and then tempered at 650 ° C. or lower.

  Adhesion between concrete and steel pipe can be improved by using a steel pipe formed by welding a hot-rolled coil with an inner protrusion in a spiral shape and welding it to a composite structure with concrete. In addition, the protrusion height and protrusion space | interval of the steel pipe with an inner surface protrusion are prescribed | regulated by JISA5525 (2009).

  The reason why the heating temperature of the steel pipe is set to 860 to 960 ° C. is to make the alloy elements in solution in the austenite region and improve strength and low temperature toughness. However, when the heating temperature exceeds 960 ° C., austenite grains during heating grow and the crystal grains become large, leading to a decrease in low temperature toughness, and the steel pipe is greatly deformed by its own weight during heating. For this reason, the upper limit of heating temperature was 960 degreeC.

  After heating, the outer surface of the steel tube is immersed in a water bath from a temperature of 650 to 850 ° C., and cooled to 200 ° C. or less at a cooling rate of 10 ° C./second or more, thereby allowing the microstructure to become ferrite and bainite or martensite. A two-phase mixed structure is achieved, and a predetermined strength and a low yield ratio of less than 0.85 are achieved. The reason for water cooling from 650 ° C. or more is to suppress the formation of excessive ferrite and to obtain sufficient strength by transformation strengthening of untransformed austenite. The reason for water cooling from 850 ° C. or lower is to achieve a low yield ratio by using a microstructure after water cooling as a two-phase mixed structure of ferrite and bainite or martensite. Further, the reason for cooling at a cooling rate of 10 ° C./second or more is to obtain bainite and martensite by transformation strengthening of untransformed austenite to obtain sufficient strength. Further, the reason for cooling to 200 ° C. or lower is to obtain sufficient strength by generating bainite and martensite by transformation strengthening by water cooling. When cooling a steel pipe, it is necessary to immerse it in a water tank. This is because the method of cooling from the outer surface side of the steel pipe without immersing it in the water tank requires time for cooling, increases the material variation in the steel pipe and increases the manufacturing cost. When the steel pipe is cooled by being immersed in the water tank, the material variation in the steel pipe can be reduced. When tempering at a temperature exceeding 650 ° C., a predetermined strength cannot be obtained, so the upper limit temperature was set to 650 ° C.

  Examples of the present invention will be described. Spiral forming and welding were performed from hot-rolled coils having various components, and a spiral steel pipe with an inner surface protrusion having an outer diameter of 1400 mm was manufactured. Thereafter, the steel pipe was heated, cooled with water, and tempered to investigate various properties. The low temperature toughness was evaluated by the absorbed energy at 0 ° C. after a Charpy impact test. The weldability of the steel pipe was evaluated by the presence or absence of cold cracking when the accessories were welded to the steel pipe.

  Steel No. of the present invention whose component range and production conditions are within the scope of the present invention. Table 1 shows the composition, structure, yield strength, and yield ratio of 1-16. Moreover, comparative steel No. which has the conditions in which the component range or manufacturing conditions deviated from the scope of the present invention. Table 2 shows the composition, structure, yield strength, and yield ratio of 17-35. Table 3 shows the heating, cooling, tempering conditions and various properties of the spiral steel pipes made of the respective base materials shown in Table 1. Table 4 shows the heating, cooling, tempering conditions and various properties of the spiral steel pipes made of the respective base materials shown in Table 2. In Tables 2 and 4, the columns indicating conditions or properties that are out of the scope of the present invention are underlined.

  As shown in Tables 1 and 3, No. The steel pipes having 1-16 inner surface protrusions had excellent characteristics in strength, low temperature toughness, and weldability. On the other hand, as shown in Tables 2 and 4, comparative steel No. In Nos. 17 to 35, the chemical components or the manufacturing conditions of the spiral steel pipe were not appropriate, and any of the characteristics was inferior. No. Since No. 17 has too much C content of a base material, low temperature toughness is low. No. Since No. 18 has too much Mn content of the base material, low temperature toughness is low. No. Since No. 19 has too much Nb content of the base material, low temperature toughness is low. No. No. 20 has low Cr toughness due to too much Cr. No. Since No. 21 has too much Mo amount, low temperature toughness is low. No. Since 22 has too much V amount, low temperature toughness is low. No. Since No. 23 has too much B content, low temperature toughness is low. No. Since the CE value of No. 24 was too large, the strength was remarkably increased, the low temperature toughness was low, and low temperature cracks occurred during welding. No. No. 25 has a low CE value and a low yield strength YS, so a sufficient bending strength cannot be obtained. No. No. 26 has a high ferrite fraction and a low yield strength, so a sufficient bending strength cannot be obtained. No. No. 27 had a high CE value and too high strength, so the low temperature toughness was low and cold cracking occurred during welding. No. In No. 28, since the heating temperature of the steel pipe is too low, the yield strength is low and sufficient bending strength cannot be obtained.

  No. In No. 29, since the heating temperature of the steel pipe is too high, the yield ratio exceeds 0.85 and the low temperature toughness is low. No. No. 30 has a low strength because the water cooling start temperature after heating is too low. No. No. 31 has a yield ratio exceeding 0.85 because the water cooling start temperature after heating is too high. No. No. 32 has a low strength because the cooling rate after heating is slow. No. Since the cooling stop temperature is too high, 33 has low strength and low temperature toughness. No. Since 34 is not immersed in the water tank at the time of cooling but is cooled from the outer surface of the steel pipe, the variation in the yield strength in the circumferential direction is large. No. No. 35 has a low tempering temperature and therefore has low strength and low temperature toughness.

  As described above, a spiral steel pipe having good properties cannot be obtained if it deviates from any of the conditions of the present invention. On the other hand, according to the present invention, the yield strength of 450 MPa or more excellent in weldability and less than 0.85 A spiral steel pipe with an inner surface protrusion having a yield ratio and excellent weldability could be stably produced.

  INDUSTRIAL APPLICABILITY The present invention is useful for concrete-filled steel pipes used for foundation structures such as buildings, bridges, and steel towers.

Claims (4)

In mass%, C: 0.05 to 0.20, Si: 0.01 to 0.6, Mn: 0.8 to 2.2, P: 0.02 or less, S: 0.005 or less, Nb: 0.005-0.080, Ti: 0.005-0.030, Al: 0.001-0.05, N: 0.001-0.006, O: 0.006 or less, the balance being It consists of iron and unavoidable impurities, and the CE value defined by the following formula (1) is in the range of 0.40 to 0.55, the ferrite fraction is 16 to 50%, and the remaining structure is bainite and martense. A spiral steel pipe with an inner protrusion having a yield strength of 450 MPa or more and 650 MPa or less and a yield ratio of less than 0.85.
CE = C + Si / 24 + Mn / 6 (1) Steel component is mass%, and Cr: 0.1-0.5 , Mo: 0.1-0.5 , V: 0.01-0.10, B: 0.0003-0.002 1 or 2 types or more and it replaces with said Formula (1), and CE value defined by following formula (2) exists in the range of 0.40-0.55, It is characterized by the above-mentioned. 1. A spiral steel pipe with an inner surface protrusion having a yield strength of 450 MPa to 650 MPa and a yield ratio of less than 0.85.
CE = C + Si / 24 + Mn / 6 + Cr / 5 + Mo / 4 + V / 14 (2) In mass%, C: 0.05 to 0.20, Si: 0.01 to 0.6, Mn: 0.8 to 2.2, P: 0.02 or less, S: 0.005 or less, Nb: 0.005-0.080, Ti: 0.005-0.030, Al: 0.001-0.05, N: 0.001-0.006, O: 0.006 or less, the balance being A spiral steel pipe with an inner protrusion made of iron and unavoidable impurities and having a CE value defined by the following formula (1) in the range of 0.40 to 0.55 is heated to 860 to 960 ° C. After that, the steel pipe outer surface is immersed in a water bath from a temperature of 650 to 850 ° C., water cooled to 200 ° C. or lower so that the cooling rate is 10 ° C./second or higher, and then tempered at 650 ° C. or lower. Yield strength of 450 MPa or more and 650 MPa or less characterized by processing, and Preparation of the inner surface projections with spiral pipe having a yield ratio of less than .85.
CE = C + Si / 24 + Mn / 6 (1) The said base material is the mass%, and also Cr: 0.1-0.5, Mo: 0.1-0.5, V: 0.01-0.10, B: 0.0003-0.002 1 or 2 or more of them, and, instead of the formula (1), the CE value defined by the following formula (2) is in the range of 0.40 to 0.55. The manufacturing method of the spiral steel pipe with an inner surface protrusion which has the yield strength of 450 MPa or more and 650 MPa or less of Claim 3, and the yield ratio of less than 0.85.
CE = C + Si / 24 + Mn / 6 + Cr / 5 + Mo / 4 + V / 14 (2)