JP4300049B2 - Manufacturing method of high-strength steel pipe for building structure with low yield ratio - Google Patents

Description

【００３５】
【表２】

【００３６】
表１および表２から次のように考察することができる。尚、以下のＮｏ．は表２における実験Ｎｏ．を示す。
【００３７】
Ｎｏ．１〜５は、本発明の規定要件を満たす実施例であり、得られた鋼管は、引張強度が５９０Ｎ／ｍｍ²以上でかつ降伏比が８５％以下と低降伏比を示しており、建築構造用鋼管として好適であることがわかる。
【００３８】
これに対しＮｏ．６〜１２は、得られた鋼管の降伏比が高いか、強度不足となっている。即ちＮｏ．６は、適正温度域（Ａｃ₁〜Ａｃ₃点）で加熱した後の冷却が水冷であるため降伏比が高い。Ｎｏ．７は、前記▲２▼の工程でＡｃ₃点を超える高温に加熱したため降伏比が高くなった。またＮｏ．８は、前記▲２▼の工程でＡｃ₁点を下回る低温で熱処理を行ったため強度不足となった。
【００３９】
Ｎｏ．９は、前記▲４▼で定める規定温度範囲を下回る低温で管状成形後の再加熱を行ったため、加工歪みを十分除去することができず降伏比が高くなった。Ｎｏ．１０は、管状成形後の再加熱温度が高すぎるため、鋼管が軟質化され強度不足となっている。
【００４０】
Ｎｏ．１１は、前記▲２▼で定める適正温度域（Ａｃ₁〜Ａｃ₃点）で加熱後の冷却を水冷とし、かつ管状成形後の再加熱温度が高すぎるため、降伏比が高くなる結果となった。更にＮｏ．１２からは、好ましい範囲を上回る量のＮｂを添加すると、降伏比が高まるので好ましくないことがわかる。
【００４１】
【発明の効果】
本発明の方法によれば、鋼板から鋼管への曲げ加工性等を低下させることなく経済的に低降伏比の高張力鋼管を製造することができる。そして、本発明で得られた鋼管に例えばコンクリートを充填し、コンクリートを拘束する円柱状鋼管としてＣＦＴ（Concrete−Filled−Tube）構造の中・低層建造物用や高層・超高層建造物に用いれば、卓越した耐震性や耐火性等を発揮する。
【図面の簡単な説明】
【図１】低降伏比の鋼板を得るための公知の方法を説明するヒートパタンである。
【図２】前記図１の工程に引き続いて鋼管を製造する方法を説明するヒートパタンである。
【図３】本発明で鋼管を得るための一方法を説明するヒートパタンである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a high-strength steel pipe for a building structure having a low yield ratio. For example, a CFT (Concrete-Filled-Tube) structure that exhibits excellent characteristics in terms of earthquake resistance and fire resistance. The present invention relates to a high-tensile steel pipe that can be suitably used.
[0002]
[Prior art]
Since a building structure is required to have excellent earthquake resistance and fire resistance, steel materials used for the building structure are required to have high strength and a low yield ratio. Conventionally, as a method of lowering the yield ratio of a high-tensile steel plate, as shown in FIG.
・ Ac After heating in the temperature range of ₃ points or more, rapidly cool to room temperature,
・ Next, after heating in the two-phase temperature range of Ac _{1 to} Ac ₃ , quench to room temperature,
There is a technique for achieving both a low yield ratio and a predetermined yield strength by tempering in a temperature range of Ac ₁ point or less (for example, Patent Document 1).
[0003]
However, even if a steel sheet with a low yield ratio is obtained by such a method, a steel pipe with a low yield ratio can be obtained because the yield ratio increases due to work hardening when the steel sheet is formed into a tubular shape as shown in FIG. Therefore, even if the steel pipe is adopted in a building, it is not possible to obtain an excellent earthquake resistance as intended.
[0004]
As a solution to such a problem, Patent Document 2 discloses that a low yield ratio is maintained after bending or pressing a steel sheet.
(A-1) Heat treatment is performed after heating to a two-phase region temperature between each of the Ac _{1 to} Ac ₃ transformation points, followed by rapid cooling,
(A-2) Next, processing is performed in a temperature range of 300 ° C. or lower,
(A-3) Thereafter, a method of reheating within a temperature range of 600 to 700 ° C. to cause partial recrystallization has been proposed. However, in this method, since the steel pipe is processed after the rapid cooling, it is difficult to say that the workability at the time of forming the steel pipe is ensured.
[0005]
Moreover, in patent document 3, after controlling a hot rolling condition and obtaining a steel plate,
(B-1) Reheating to a two-phase temperature range of Ac ₁ point or more and Ac ₃ point or less,
(B-2) Start bending in a cylindrical shape from the temperature range of Ar ₁ point or higher, and finish the processing in a temperature range lower than Ar ₁ point.
(B-3) A method of cooling at a cooling rate higher than air cooling has been proposed. However, in this method, it is necessary to perform steel pipe forming hot (two-phase temperature range of Ac _{1 to} Ac ₃ points), and new equipment and high energy costs are required.
[0006]
Patent Document 4 shows a method of manufacturing a low YR steel pipe by cold forming. Specifically,
(C-1) After rolling so that the finishing temperature is (Ar ₃ + 120 ° C) or lower (Ar ₃ -20 ° C) or higher,
(C-2) The steel sheet is air-cooled from (Ar ₃ -20 ° C.) to (Ar ₃ -100 ° C.), and then immediately quenched from this temperature to room temperature.
(C-3) tempering in the temperature range below the Ac ₁ transformation point,
(C-4) When the plate thickness is t and the steel pipe outer diameter is D, it is cold-formed into a tube in the range of t / D ≦ 10%,
(C-5) A method of subsequently annealing in a temperature range of 500 ° C. to 650 ° C. is shown. However, the method of performing air cooling to the two-phase temperature range of approximately Ac _{1 to} Ac ₃ on the rolling line immediately after hot rolling as described above is not preferable from an economical viewpoint because it causes a reduction in rolling productivity.
[0007]
In patent document 5, as a manufacturing method of the low YR steel pipe by cold forming,
(D-1) Reheating to a temperature of Ac ₃ or higher and quenching or quenching / tempering, (d-2) cooling in the range of t / D (t: plate thickness, D: outer diameter of steel pipe) ≤ 10% Steel tube is made by forming
(D-3) A method of normalizing by reheating to a temperature range of 650 to 750 ° C. has been proposed. However, this method needs to use a steel material containing Cu and Ni as essential components, which increases the material cost and does not meet the demand for cost reduction. In addition, the strength is improved by precipitation strengthening due to the addition of Cu, but the temperature of the outer surface side and the inner surface side becomes non-uniform in the heat treatment process after steel pipe processing, and the effect of adding Cu is difficult to appear uniformly, so there is a variation in material. Concerned.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 55-97425 [Patent Document 2]
Japanese Patent No. 3297090 (first page)
[Patent Document 3]
Japanese Patent Laid-Open No. 7-15245 (page 2)
[Patent Document 4]
Japanese Patent No. 2529042 (first page)
[Patent Document 5]
JP 7-233416 A (second page)
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of such circumstances, and its object is to provide a low yield ratio (especially YP / TS) that can be used not only for middle- and low-rise buildings but also for high-rise and super-high-rise buildings. It is to provide a useful method for producing a high-strength steel pipe for building structure having a yield ratio represented by: YR of 85% or less.
[0010]
[Means for Solving the Problems]
The method for producing a high-strength steel pipe for building structures having a low yield ratio according to the present invention is in mass% (the same applies hereinafter), C: 0.10 to 0.18%, Si: 0.1 to 0.5% In manufacturing a steel pipe for building structure that satisfies Mn: 1 to 2% and has a tensile strength of 590 N / mm ² or more,
(1) A step of rapidly cooling the steel sheet to room temperature after heating it to Ac ₃ points or higher,
(2) A process of heating to a two-phase temperature range of Ac _{1 to} Ac _{3 and} then cooling to room temperature,
(3) Cold forming into a tube,
(4) It is characterized in that the step of reheating to 500 to 600 ° C. is sequentially performed.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Under the circumstances as described above, the present inventors manufacture steel pipes for building structures that exhibit a low yield ratio at a tensile strength of 590 N / mm ² or more economically without reducing the workability at the time of forming the steel pipe. The method for doing this was examined from various angles. As a result, as schematically shown in FIG. 3, (1) the step of heating the steel sheet to Ac ₃ point or higher and then rapidly cooling it to room temperature;
(2) A process of heating to a two-phase temperature range of Ac _{1 to} Ac _{3 and} then cooling to room temperature,
(3) Cold forming into a tube,
(4) It has been found that the steps of reheating to 500 to 600 ° C. may be carried out sequentially. The reason why each process is specified will be shown below.
[0012]
(1) Step of heating the steel plate to Ac ₃ point or higher and then rapidly cooling to room temperature First, in the method of the present invention, the steel plate obtained by hot rolling or the like is heated to a temperature of Ac ₃ point or higher, Assumes rapid cooling from room temperature to room temperature. By performing rapid cooling in this way, high strength of the steel pipe can be achieved.
[0013]
From the viewpoint of reliably raising the temperature to the inside of the steel plate, the heating at Ac ₃ points or more may be performed within a range of about 5 minutes to 1 hour, although it depends on the plate thickness. Although the upper limit of the heating temperature is not particularly specified, it is preferably performed at 950 ° C. or less from the viewpoint of energy cost reduction. Moreover, the rapid cooling from the temperature range of Ac ₃ points or more may be performed by water cooling. The steel sheet has a thickness of about 20 to 100 mm and is not wound.
[0014]
▲ 2 ▼ Ac ₁ In to Ac step <br/> present invention method for air-cooled to room temperature then heated to the two-phase temperature region of ₃ points, a steel sheet which has undergone the step ▲ ₁ ▼, Ac 1 ~Ac _three points 2 It is necessary to provide a step of air cooling to room temperature after reheating to the phase temperature range.
[0015]
As a method for obtaining a steel plate having a low yield ratio, it has been conventionally performed in place of the step of “heating and quenching at a temperature of Ac ₁ point to Ac ₃ point and then tempering” shown in FIG. 1 or FIG. By providing the above steps, it is possible to obtain a steel sheet in which the yield ratio hardly increases even when it is formed into a tubular shape. It should be noted that the heating and holding in the two-phase temperature range of Ac _{1 to} Ac ₃ may be within the range of 5 minutes to 1 hour, depending on the plate thickness, but if it is longer than this, ferrite and austenite become coarse. This is not preferable because the effect of the step (1) is reduced.
[0016]
In particular, in the method of the present invention, by performing air cooling from the two-phase temperature range of Ac _{1 to} Ac ₃ points, ferrite softens, and austenite is transformed after carbon is concentrated, so that it is remarkably hardened and low YR is reduced. It is thought that it will be improved.
[0017]
(3) Cold forming into a tube and (4) Reheating to 500 to 600 ° C. Steel pipe forming is performed using the steel plate that has undergone the above steps (1) and (2). Seam welding may be performed after bending into a tubular shape. The present invention does not define tube forming conditions or welding conditions, and a known method may be appropriately selected and employed for bending, seam welding, and the like. The method of the present invention is preferably applied to those having D / t (D: outer diameter of steel pipe, t: plate thickness) of 10 or more. Incidentally, when the D / t is less than 10, the processing strain increases too much and the YR becomes high.
[0018]
After forming into a steel pipe, it is necessary to remove the processing strain by heating again. In order to sufficiently remove the processing strain, it is preferable to heat to 500 ° C. or higher. However, if the heating temperature is too high, the strength falls below a predetermined strength, so it is preferable to perform in a temperature range of 600 ° C. or lower.
[0019]
Even if the heating temperature is within the appropriate range, if the holding time is too short, the strain cannot be sufficiently removed, so it is preferable to heat and hold within the range of 5 minutes to 1 hour. Further, after the heating, cooling to room temperature may be performed by a method such as air cooling or furnace cooling.
[0020]
The method of the present invention is characterized in that manufacturing conditions satisfying the above requirements are defined, and it does not prescribe basic steel sheet manufacturing conditions such as melting, casting and hot rolling of steel materials. For these, general conditions and methods can be adopted.
[0021]
In the present invention, the tensile strength of the steel pipe is determined to be 590 N / mm ² or more. If the steel sheet is less than 590 N / mm ^{2, the} yield ratio is relatively low, and special measures are required to obtain a low yield ratio. Because it does not.
[0022]
Moreover, in obtaining the high strength steel pipe of the low yield ratio by this invention, the steel materials which satisfy | fill the following basic component composition can be used as a raw material.
[0023]
C: 0.10 to 0.18%
C (carbon) is an element effective for improving the strength of steel, and it is preferable to contain 0.10% or more. However, if the C content is increased, weldability is deteriorated, so it is preferable to keep it to 0.18% or less (more preferably 0.16% or less).
[0024]
Si: 0.1 to 0.5%
Si is an element having a deoxidizing action, and in order to exert such an action effectively, it is preferable to contain 0.1% or more. However, if the amount of Si is excessive, the toughness of the weld heat affected zone is deteriorated.
[0025]
Mn: 1-2%
Mn is an element useful for securing strength and is also an element that enhances hardenability. In order to exert such an effect, it is preferable to contain 1% or more. However, if the amount of Mn is excessive, weldability is deteriorated, so it is preferable to keep it to 2% or less.
[0026]
The basic component composition is as described above, and the remaining component is substantially Fe, but it is of course acceptable to contain a small amount of inevitable impurities in the steel, and adversely affects the operation of the present invention. It is also possible to further contain the following elements within the range not given.
[0027]
Al: 0.005 to 0.1%
Al is an element having a deoxidizing action, and in order to exert this effect, it is preferable to contain Al in an amount of 0.005% or more. However, an excessive content causes an increase in inclusions such as alumina and causes toughness deterioration, so it is preferably suppressed to 0.1% or less, more preferably 0.060% or less.
[0028]
P: 0.02% or less (including 0%), S: 0.015% or less (including 0%)
P (phosphorus) is a harmful element that degrades toughness. Therefore, in the present invention, the P content is preferably suppressed to 0.02% or less. S (sulfur) is an element that forms sulfide-based inclusions such as MnS, causes a decrease in toughness, and causes cracking to be a starting point for deterioration of workability. Therefore, the S content is preferably suppressed to 0.015% or less, more preferably 0.010% or less.
[0029]
Further, as other elements, for example, Cu may be added within a range not deteriorating hot workability of 1.0% or less, and Ni is within 1.0% or less in order to improve corrosion resistance and toughness. It may be added . To adjust the toughness or the like or to ensure high strength by increasing hardenability, Cr: 1.0% or less, Mo: may be added in a range less than 0.5%.
[0030]
V indicating precipitation hardening and the like may be added within a range of 0.1% or less, and Nb useful for controlling crystal grains may be added within a range of 0.05% or less and Ti within a range of 0.03% or less. The method of the present invention can also be applied to those in which B useful for improving hardenability is added within a range of 0.002% or less.
[0031]
【Example】
EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.
[0032]
After melting and obtaining a steel material having the component composition shown in Table 1, hot rolling was performed to obtain a steel plate having a thickness shown in Table 2. The obtained steel sheet was kept at 930 ° C. for about 15 minutes, and then cooled to room temperature. Then, after being heated and held at the temperature (T ₁ ) shown in Table 2 for about 15 minutes, it was cooled to room temperature by the method shown in Table 2 and then formed into a cylindrical shape by a cold press bend. After the tubular forming, in order to remove processing strain, the steel tube was obtained by heating and holding at the temperature (T ₂ ) shown in Table 2 for about 15 minutes and then cooling to room temperature.
[0033]
A tensile test was performed using the obtained steel pipe, and a yield point (YP) and a tensile strength (TS) were measured to obtain a yield ratio (YR). In the tensile test, a test piece was sampled from the outside in the tube axis direction at a ¼ portion of the tube thickness and processed into a round bar. In the present invention, the YP is 440 N / mm ² or more, TS is 590N / mm ² or more, and if YR is less than 85%, high-tensile steel pipe obtained at a low yield ratio of the level intended in the present invention It was judged that. These results are also shown in Table 2.
[0034]
[Table 1]

[0035]
[Table 2]

[0036]
From Table 1 and Table 2, it can be considered as follows. The following No. Is the experiment No. in Table 2. Indicates.
[0037]
No. 1 to 5 are examples that satisfy the prescribed requirements of the present invention, and the obtained steel pipe has a tensile strength of 590 N / mm ² or more and a yield ratio of 85% or less, indicating a low yield ratio. It turns out that it is suitable as a steel pipe for construction.
[0038]
In contrast, no. In 6 to 12, the obtained steel pipe has a high yield ratio or insufficient strength. That is, no. No. 6 has a high yield ratio because the cooling after heating in the appropriate temperature range (Ac _{1 to} Ac ₃ points) is water cooling. No. No. 7 was heated to a high temperature exceeding the Ac ₃ point in the step (2), so the yield ratio was high. No. _No. 8 was insufficient in strength because the heat treatment was performed at a low temperature below the Ac ₁ point in the step (2).
[0039]
No. No. 9 was subjected to reheating after tubular molding at a low temperature below the specified temperature range defined in (4) above, so that the processing strain could not be sufficiently removed and the yield ratio was high. No. No. 10, since the reheating temperature after tubular molding is too high, the steel pipe is softened and the strength is insufficient.
[0040]
No. No. 11 is a result of increasing the yield ratio because the cooling after heating is water-cooled in the appropriate temperature range (Ac _{1 to} Ac ₃ points) defined in (2) above and the reheating temperature after tubular molding is too high. It was. Furthermore, no. From Fig. 12, it can be seen that adding Nb in an amount exceeding the preferred range is not preferable because the yield ratio increases.
[0041]
【The invention's effect】
According to the method of the present invention, a high-tensile steel pipe having a low yield ratio can be produced economically without reducing the bending workability from a steel plate to a steel pipe. And, for example, concrete is filled into the steel pipe obtained in the present invention, and it is used as a cylindrical steel pipe for constraining the concrete for middle / low-rise buildings or high-rise / high-rise buildings with CFT (Concrete-Filled-Tube) structure. Exhibits outstanding earthquake resistance and fire resistance.
[Brief description of the drawings]
FIG. 1 is a heat pattern illustrating a known method for obtaining a steel plate having a low yield ratio.
FIG. 2 is a heat pattern for explaining a method of manufacturing a steel pipe following the step of FIG.
FIG. 3 is a heat pattern illustrating one method for obtaining a steel pipe according to the present invention.

Claims (3)

% By mass (the same applies below)
C: 0.10 to 0.18%,
Si: 0.1 to 0.5%,
Mn: 1-2%
P: 0.02% or less (including 0%),
S: 0.015% or less (including 0%),
Al: 0.005 to 0.1%
And the balance is Fe and unavoidable impurities, and a steel pipe for building structure having a tensile strength of 590 N / mm ² or more and 630 N / mm ² or less,
(1) A step of rapidly cooling the steel sheet to room temperature after heating it to Ac ₃ points or higher,
(2) A step of heating to a two-phase temperature range of Ac _{1 to} Ac _{3 and} then cooling to room temperature,
(3) a step of cold forming into a tube;
(4) A method for producing a high-strength steel pipe for a building structure having a low yield ratio, wherein the steps of reheating to 500 to 600 ° C. are sequentially performed. The steel pipe as still another element, V: 0.1% or less (not including 0%), Nb: 0.05% or less (not including 0%) good Li Cheng least one selected from the group The manufacturing method according to claim 1 , comprising: In the steel pipe, as other elements, Cu: 1.0% or less (not including 0%) , Ni: 1.0% or less (not including 0%), and Mo: 0.5% or less (0 the method according to claim 2 percent is intended to include contain not) a.

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