JP2015083318A - Box column and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure continuity of a skin plate in a box column which is formed by dividing one surface of the skin plate at a position of a diaphram, and in which weld of the skin plate and the diaphram is performed by gas shield arc weld.SOLUTION: A groove formed by the skin plate and the diaphram is formed between the divided skin plates, and when the groove is filled with a weld metal layer formed by gas shield arc weld, between the groove and the diaphram, the weld metal layer is formed by having 1/3 or more of thickness of the skin plate and thickness of two or more layers.

Description

  The present invention relates to a box column having a diaphragm inside (welding box type cross-sectional column) used in a building such as a high-rise building and a method for producing the box column by gas shielded arc welding.

In general, the box column is assembled into a square steel pipe by square welding of four skin plates, and a diaphragm is welded inside.
In general, a one-pass welding method using electroslag welding is used for joining the skin plate and the diaphragm.
Since the electroslag welding method can form a joint by one-pass welding, there is an advantage that the construction efficiency can be greatly improved as compared with a multi-layer welding method such as a gas shielded arc welding method.

  However, since electroslag welding is a high heat input welding method, there is a large thermal effect on the welded joint and the steel around the joint, and there is a decrease in strength due to softening of the steel or a decrease in toughness due to coarsening of the steel structure. growing. In particular, when the skin plate using high strength steel exceeding the yield strength YP630MPa (tensile strength TS780MPa) is subjected to high heat input welding such as electroslag welding, the thermal effect that loses the toughening effect of the base metal is lost. There is a possibility that a decrease in the strength of the joint becomes prominent and it becomes a serious problem with respect to the destruction of the entire joint.

On the other hand, in gas shielded arc welding (GMAW), heat input can be reduced by multi-layer welding, but since it is difficult to weld the inside of the member after it is assembled into a box shape, at least the diaphragm The last side could not be welded by gas shielded arc welding.
On the other hand, in Patent Document 1, one skin plate is divided into three at the position of the diaphragm so that gas shield arc welding can be performed from the outside between the diaphragm and the divided skin plate without using electroslag welding. We are proposing a technology that enables welding assembly.

JP 2007-222929 A

In the method of Patent Document 1, since the outer side of the diaphragm sandwiched between the divided skin plates is set to the same height as the outer surface of the skin plate, the cross section of the diaphragm appears on the surface of the box column. . For this reason, a tensile stress in the thickness direction is applied to the portion on the surface of the diaphragm and the vicinity thereof. Since the properties (strength, elongation, toughness) in the thickness direction of the steel plate are lower than the direction along the steel plate surface, a steel plate having excellent properties in the thickness direction as a diaphragm is required.
Further, the role of the diaphragm is mainly to prevent buckling, and the influence of the strength of the steel plate on the buckling strength is small, and the plate thickness is important. Therefore, although the steel plate used for a diaphragm can use the steel plate whose intensity | strength is lower than a skin plate, in patent document 1, the steel plate of the same intensity | strength as a skin plate is used for a diaphragm from the continuity of a skin plate. Need to use.

  On the other hand, there is an increasing demand for higher-rise building structures, and high-strength steels having a strength of 780 MPa or higher are used as steel materials. In such high-strength steel gas shield welding, the weld cracking sensitivity is increased, and preheating work is indispensable for suppressing the weld cracking.

  Therefore, the present invention secures the continuity of the skin plate in a box column in which one skin plate is divided at the position of the diaphragm so that gas shield arc welding can be performed from the outside between the diaphragm and the divided skin plate. Therefore, the present invention provides a box column having an assembly structure in which the diaphragm cross section does not appear on the surface of the box column, and also provides a manufacturing method capable of welding and assembling the box column by gas shield arc welding by omitting or simplifying preheating work. Is an issue.

The gist of the present invention for solving the above problems is as follows.
(1) In a box column in which a diaphragm is welded and fixed inside a square steel pipe formed by welding the corners of the skin plate as the outer periphery,
The outer surface of the box column has a skin plate divided on the boundary of the diaphragm,
The space between the divided skin plate and the skin plate is filled with a weld metal layer formed by gas shield arc welding of a groove formed by the skin plate and the diaphragm,
The box column, wherein the weld metal layer is formed with a thickness of 1/3 or more of the skin plate between the diaphragm and two or more layers.

(2) When the tensile strength of the steel plate used for the skin plate is 780 MPa or more and the tensile strength of the steel plate is SP (MPa), the tensile strength of the steel plate used for the diaphragm is It is 0.65 SP or more and 0.9 SP or less, The box pillar as described in said (1) characterized by the above-mentioned.

(3) A method of manufacturing the box column by performing welding of the skin plate and the diaphragm of the box column according to (1) or (2) above by gas shielded arc welding using a flux-cored wire,
The flux-cored wire is
During the wire, wire percentage by weight relative to the total _weight, CaF _{2, BaF} 2, SrF _2, MgF 2, 2.0 to 7.0% as the total amount alpha 1, two or more of LiF, Ti oxide 1 type or 2 types or more out of an oxide, Si oxide, Zn oxide, Mg oxide, and Al oxide as a total amount β, and the total amount relative to the total amount β Containing so that the ratio of the amount α is 2.0 to 20.0,
The total amount of one or more of the metal carbonates of CaCO ₃ , BaCO ₃ , SrCO ₃ , MgCO ₃ is less than 0.60%,
Chemical components excluding fluoride, metal oxide, and metal carbonate are in mass% with respect to the total mass of the flux-cored wire, C: 0.04 to 0.12%, Si: 0.2 to 1.0%, Mn: 1.0 to 2.5%, Al: 0.005 to 0.050%, Ni: 1.5 to 3.5%, P: 0.02% or less, S: 0.02% or less, Mo : 0.3 to 1.0%, Ti: 0.0 to 0.10%, B: 0 to 0.01%, Cu: 0 to 1.0%, Cr: 0 to 0.6%, V: 0 to 0.20%, Nb: 0 to 0.10%, Mg: 0 to 0.70%, the balance iron and inevitable impurities,
Ceq defined by the following formula a is 0.55 to 0.90%, and TE defined by the following formula b is 2.7 to 4.4%. Or the manufacturing method of the box pillar as described in (2).
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14
... (Formula a)
TE = [Mn] / 2 + [Ni] + 3 × [Cr] (Formula b)
However, the element with [] represents the content in mass% of each element.

(4) The total amount α is 3.3 to 7.0%, and the ratio of the content of the CaF _{2 to} the total amount α is 0.90 or more. Box column manufacturing method.
(5) The box column as described in (3) or (4) above, wherein the content of CaO in the flux-cored wire is 0.15% or less by mass% with respect to the total mass of the flux-cored wire. Manufacturing method.
(6) The total content of CaCO ₃ , BaCO ₃ , SrCO ₃ , and MgCO _{3 in} the flux-cored wire is 0.1 to 0.5% by mass% with respect to the total mass of the wire. The manufacturing method of the box pillar in any one of said (3)-(5).
(7) The box pillar manufacturing method according to any one of (3) to (6), wherein the steel outer skin has a seamless shape.

  According to the present invention, in a box column that is welded and assembled without performing electroslag welding, the cross section of the diaphragm does not appear on the surface of the box column, so that the continuity of the skin plate can be ensured, and the diaphragm can be skinned. A steel plate having a lower strength than that of the plate can be used, and further, the box column can be welded and assembled by gas shield arc welding while omitting or simplifying the preheating operation.

It is a figure which shows the outline of the box pillar which concerns on one embodiment of this invention. It is a figure which shows the cross-section of the welded joint part formed with the division | segmentation skin plate and diaphragm of the box pillar shown in FIG. It is a figure which shows the state in the middle of the assembly of the box pillar shown in FIG. It is a figure which shows the state before welding with the diaphragm of a box pillar shown in FIG. 1, and a division | segmentation skin plate. It is a figure which shows the cross-section of the groove | channel formed with the division | segmentation skin plate and diaphragm of FIG. It is a figure which shows the sampling position of a test piece in order to evaluate the performance of a welding wire. It is a figure which shows the T-shaped welded joint test body produced by carrying out welding in the procedure of FIG. 2A in order to evaluate the mechanical properties of the welded joint in the actual structure of the BOX column, and FIG. FIG. 4B is a plan view. It is a figure which shows the T-shaped welded joint test body produced by implementing welding in the procedure of FIG.2 (b) in order to evaluate the mechanical characteristic of the welded joint in the actual structure of a BOX column, (a) is the cross section. FIG. 4B is a plan view. (A) is a figure which shows the sampling position of the test piece for evaluating the mechanical characteristic of the T-shaped welded joint test body of FIG. 7, (b) is a top view of a test piece. (A) is a figure which shows the sampling position of the test piece for evaluating the mechanical characteristic of the T-shaped welded joint test body of FIG. 8, (b) is a top view of a test piece. It is a figure which shows the collection position of the Charpy test piece in the T-shaped welded joint test body of FIG. It is a figure which shows the collection position of the Charpy test piece in the T-shaped welded joint test body of FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[Box column structure]
A box column used in a high-rise building has a structure in which a diaphragm is welded and fixed inside a square steel tube column formed by welding corner portions of a skin plate constituting an outer periphery.
In the present invention, in order to weld all of the diaphragm and the skin plate by gas shield arc welding (GMAW), three of the four surfaces constituting the outer periphery of the box column use an integral skin plate, and the rest One surface uses a divided skin plate that is divided into three parts with a diaphragm as a boundary.

FIG. 1 shows a welded box column, in which integral skin plates 1a to 1c and divided skin plates 2a to 2c are arranged in a square cross section, and diaphragms 3a and 3b are arranged inside (FIG. 2). 3), and they are assembled by welding.
The corners formed between the skin plates are welded by submerged arc welding (SAW), GMAW, or the like to form weld metals 4a to 4d. Further, the divided skin plates 2a to 2c are arranged at intervals, and a groove with the upper end surface of the diaphragm as a bottom surface is formed between them, and the groove is welded by GMAW to weld metal 5a, 5b. Is formed.
Although not shown in FIG. 1, the diaphragms 3a and 3b and the skin plates 1a to 1c are welded prior to welding between the divided skin plates, all of which are also welded by GMAW.

The weld joint formed by the divided skin plate 2 and the diaphragm 3 has a structure in which the end face of the diaphragm does not come out on the surface. The cross-sectional structure is shown in FIGS.
The joint structure shown in FIG. 2 (a) is such that the height of the diaphragm extends to the lower surface of the divided skin plate, and the inside of the groove formed by the divided skin plates 2, 2 and the diaphragm 3 is formed by multi-layer welding by GMAW. This is an example in which a weld metal 5 is formed.

  Further, the joint structure shown in FIG. 2 (b) is such that the height of the diaphragm is halfway of the divided skin plate, and is formed between the diaphragm 3 and the divided skin plates 2 and 2 positioned on both sides thereof. In this example, the weld metal 5 is formed by multi-layer welding by GMAW in the groove formed between the split skin plates 2 and 2 and the diaphragm 3 at the upper part of the groove and the upper part of the groove.

  The weld metal formed between the divided skin plates 2 and 2 and the diaphragm 3 needs to have a tensile strength equal to or higher than the tensile strength of the steel material in order to ensure the continuity of the skin plate. The thickness of the weld metal formed by multi-layer welding is also important, and requires at least one third of the thickness of the skin plate and two or more weld metal layers. Otherwise, sufficient tensile strength in the thickness direction of the diaphragm cannot be ensured.

In the present invention, welding assembly can be performed without using high heat input electroslag welding for the diaphragm and skin plate, and a high strength steel plate of 780 MPa or more is applied to the skin plate without causing a decrease in toughness of the welded portion. It can be used to construct a box pillar.
Further, in the box column having the structure of the present invention, the continuity of the skin plate can be ensured, so that a steel plate having a lower strength than the skin plate can be used for the diaphragm.
When a steel plate having a tensile strength of 780 MPa or more is used for the skin plate, the diaphragm has a tensile strength of 0.65 SP or more and 0.9 SP or less, where SP (MPa) is the tensile strength of the steel plate used for the skin plate. Even if this steel plate is used, the strength required as a box column can be ensured.

  As a preferable strength combination of steel plates, when a 780 MPa grade steel plate is used for the skin plate, examples of the diaphragm include TS690 MPa grade and TS540 MPa grade steel plates, and a higher strength 950 MPa grade steel plate is used for the skin plate. In this case, examples of the diaphragm include steel plates of 780 MPa class and 590 MPa class.

[Box pillar manufacturing method]
Next, the manufacturing method of the box pillar which has the above structure is demonstrated.
When welding the box column, skin plates 1a to 1c constituting the outer three surfaces and divided skin plates 2a to 2c constituting the remaining one surface and a rectangular diaphragm whose one side is not exposed on the outer peripheral surface of the box column 3a and 3b are prepared.

First, welding assembly of the three skin plates 1a to 1c constituting the outer periphery of the box column and the two diaphragms 2a to 2c fixed to the inside of the box column is performed.
In this assembly, the skin plates 1a and 1c and the skin plates 1b and 1c are temporarily welded, the diaphragms 2a and 2b are arranged in the middle of the skin plate, and the main plates are welded to the skin plates 1a to 1c on three sides. 3 is assembled in a U-shaped cross section.

The welding procedure is not particularly limited, and the welding posture of the diaphragm and the skin plate may be vertical welding or horizontal welding. According to the progress of assembly, welding may be performed while maintaining the same posture while rotating sequentially. You may weld without combining and rotating a welding attitude.
That is, after welding the skin plate 1c placed horizontally and the diaphragm 3 placed vertically by lateral welding, the welding of the skin plates 1a, 1b and diaphragm may also be performed by lateral welding while sequentially turning. .
Further, after the skin plate 1c and the diaphragm 3 are welded by lateral welding, the skin plates 1a, 1b and the diaphragm may be welded by vertical welding without spreading.
The diaphragm and skin plate are all welded by gas shielded arc welding, but may be single-sided welding or double-sided welding. Usually, horizontal welding is performed by double-sided welding, and vertical welding is performed by single-sided welding.

As described above, after the three skin plates and the diaphragm are welded, the last one is welded.
As shown in FIG. 4, the last one skin plate is divided into three parts, the divided skin plate 2a is disposed on one end side of the box column of the diaphragm 3a, and the divided skin plate 2b is arranged on the diaphragm 3a. The split skin plate 2c is disposed on the other end side of the box column of the diaphragm 3b. The divided skin plates are arranged at intervals corresponding to the thickness of the diaphragm. Each divided skin plate is temporarily attached to the skin plates 2a and 2b as necessary.

  As described above, as shown in FIG. 4, it is formed between the divided skin plate 2 a and the divided skin plate 2 b and between the divided skin plate 2 b and the divided skin plate 2 c from the end face of each divided skin plate and the upper end portion of the diaphragm. Grooves 6a and 6b are formed.

The welded joint formed by the divided skin plate and the diaphragm has a structure in which the end face of the diaphragm does not come out on the surface. Details of the grooves 6a and 6b are shown in FIGS. 5 (a) and 5 (b).
The groove shown in FIG. 5 (a) is an example in which the height of the diaphragm 3 is set to the lower surface of the divided skin plate 2. First, the backing metal 7 is temporarily attached to the upper end portion of the diaphragm 3, Next, the split skin plate is set on the backing metal 7 to form the groove 6.

Further, the groove shown in FIG. 5 (b) is one in which the height of the diaphragm is up to the middle of the divided skin plate 2, and a notch portion 8 forming a part of the groove is formed at the end of the diaphragm 3. This is an example in which a groove is formed between the notch portion 8 of the diaphragm 3 and the end surfaces of the divided skin plates 2 and 2 located on both sides thereof.
Also in this example, the backing metal 7 is temporarily attached to the lower end of the notch 8 of the diaphragm 3, and then the split skin plate is set on the backing metal 7 to form the groove 6.

The weld metal 7 is formed in the groove 5 formed as described above by multi-layer welding by GMAW as shown in FIG. In multi-layer welding, as described above, two or more weld metal layers having a skin plate thickness of 1/3 or more are formed between the weld metal surface and the diaphragm.
5A and 5B show an example in which there is no gap between the divided skin plate 2 and the diaphragm 3, but an interval that can be filled at the time of welding is allowed. Further, FIG. 5A shows an example in which the end of the skin plate and the end of the diaphragm are arranged so as not to overlap, but even if the end of the diaphragm overlaps with the end, There is no particular problem because it can be melted to the end of the diaphragm.

After the diaphragm 3 and the skin plate 1 or the divided skin plate 3 are welded as described above, the grooves 9c and 9d at the corners where the skin plate and the skin plate abut, and the skin plate and the divided skin. Box pillars are manufactured by welding the corner grooves 9a and 9b with which the plate abuts by SAW or GMAW.
In addition, although the example which collectively welds a corner | angular part was demonstrated last, among the groove | channels of a corner | angular part, the groove | channels 9c and 9d may be the procedure welded first, after assembling | attaching like FIG.

Next, the flux-cored wire used for the GMAW of the box pillar skin plate and the diamond slam will be described.
When GMAW is used for the welding assembly of the box column using a flux-cored wire, it is preferable to perform welding by omitting preheating or simplifying preheating. When using a steel plate of TS780 MPa or more for the skin plate, preheating is essential to prevent weld cracking.
Therefore, as a result of investigating a flux-cored wire that can be welded by omitting preheating or simplifying preheating even when a steel plate of TS780 MPa or more is used, the amount of metal fluoride in the flux is controlled within an appropriate range. We found that it was effective to use the prepared wire.

Hereinafter, the reason for limitation of each requirement which constitutes such a flux cored wire is explained.
In terms of form, the flux-cored wire consists of a steel outer sheath and powder inserted therein, but in terms of components, flux components of fluoride, metal oxide, metal carbonate, and other components. It consists of alloy components.
First, the flux component inserted into the steel outer shell will be described. In the following description, “%” means mass% with respect to the total weight of the wire.

(Metal fluoride: 2.0-7.0%)
Metal fluoride is added in a total of 2.0-7.0% wire. As the metal fluoride, one or more of CaF ₂ , BaF ₂ , SrF ₂ , MgF ₂ , and LiF are added as necessary, but CaF ₂ is preferably the main component.

  By containing a metal fluoride in the above range, in welding of high strength steel with a tensile strength of 780 MPa or more, the amount of diffusible hydrogen in the weld metal is made very small, and the cold cracking resistance is dramatically improved. Even when high strength steel having such tensile strength is welded, preheating can be omitted or simplified for welding. Further, the metal fluoride is effective in reducing the oxygen content of the weld metal, thereby improving the toughness of the weld metal.

  In order to obtain these effects, it is necessary to contain 2.0% or more of metal fluoride. If the content is less than 2.0%, a sufficient effect cannot be obtained. If the content exceeds 7.0%, welding fumes are excessively generated, so that the shielding effect by the shielding gas is reduced and the atmosphere is involved. And the slag is excessively generated, which causes undesirable deterioration in welding workability. In order to improve the toughness, the lower limit of the metal fluoride may be 3.3% or 3.7%, and in order to suppress the deterioration of welding workability, the upper limit is 5.8%, 5.6% or 5%. It may be 4%.

  The reason why metal fluoride reduces diffusible hydrogen is that metal fluoride is decomposed by the welding arc and the generated fluorine is combined with hydrogen and dissipated into the atmosphere as HF gas, or in the weld metal as it is. This is probably because hydrogen was fixed as HF.

As the metal fluoride, any of CaF ₂ , BaF ₂ , SrF ₂ , and MgF ₂ can be used from the viewpoint of improving toughness, but CaF ₂ is included as a main component from the viewpoint of welding workability. It is desirable. Furthermore, when giving priority to welding workability such as ensuring arc stability and suppressing spatter, the total amount α of metal fluoride is set to 3.3% or more, and the content of CaF ₂ with respect to the total amount α [CaF ₂ ] The ratio ([CaF ₂ ] / α) is preferably 0.90 or more.

(Metal oxide: 0.3-1.2%)
As a slag forming agent, one of Ti oxide (TiO ₂ ), Si oxide (SiO ₂ ), Zr oxide (ZrO ₂ ), Mg oxide (MgO), Al oxide (Al ₂ O ₃ ) or A metal oxide composed of two or more kinds is added. These are added to maintain a good weld bead shape. In order to obtain the appropriate effect, it is necessary to add 0.3% or more. However, if the content of the metal oxide exceeds 1.2%, the oxygen content of the weld metal increases and the toughness is deteriorated.

The content of these metal oxides includes the total amount of TiO ₂ , SiO ₂ , ZrO ₂ , MgO, Al ₂ O _{3 and} the total amount of metal oxides contained in binders used for flux granulation. Amount. Moreover, in order to suppress the deterioration of toughness due to the addition of the metal oxide as much as possible, the upper limit of the content of the metal oxide may be set to 1.0% and 0.8%.

In addition to the content of each of the above metal fluoride and metal oxide, the ratio of the total content α of metal fluoride to the total content β of metal oxide expressed by mass% (α / β) Needs to satisfy 2.0 or more and 20.0 or less.
If the value of α / β is less than 2.0, the effect of reducing diffusible hydrogen cannot be obtained, and if it exceeds 20.0, the bead shape cannot be maintained well. If necessary, the lower limit of α / β may be 3.5 or 4.0, and the upper limit may be 14.0, 13.0, or 12.0.

(CaO: 0.15% or less)
In the present invention, it is preferable not to add CaO to the flux. However, CaO may be contained in the flux raw material. In that case, CaO is limited to 0.15% or less by mass% with respect to the total mass of the wire. If the content is limited to 0.15% or less, the effect of the present invention can be obtained. Since CaO changes to CaOH when exposed to the atmosphere, it increases the diffusible hydrogen of the weld metal. In addition, CaO has the effect of reducing the oxygen of the weld metal by increasing the basicity of the molten pool, but in the present invention, the structure is refined by utilizing the oxide as a nucleation site for intragranular transformation, Since toughness is improved, adding CaO and metal fluoride in combination is not preferable because oxygen in the weld metal is excessively reduced and low temperature toughness is lowered.

(One or more metal carbonates: less than 0.60%)
For the purpose of enhancing the arc stability action and arc concentration, one or more metal carbonates of CaCO ₃ , MgCO _3, SrCO ₃ , and BaCO ₃ can be added as necessary. If the content increases, the concentration of arc becomes too strong and the amount of spatter generated increases, so the upper limit is made less than 0.60% in total. In order to fully exhibit the effect, it is preferable to contain 0.1 to 0.5% in total amount.

Subsequently, chemical components other than fluoride, metal oxide, and metal carbonate will be described. These are a combination of the components contained in the steel skin itself and the alloy components contained in the flux inserted into the steel skin.
(C: 0.04 to 0.12%)
C is an element that improves the strength, and in order to make the tensile strength of the weld metal 780 MPa or more, it is necessary to contain 0.04% or more.
The higher the C content in the welding wire, the more the C content in the weld metal increases, which increases the strength of the weld metal. However, if the amount is too large, the toughness of the weld metal deteriorates and the sensitivity increases for both hot cracks and cold cracks, so the upper limit of the C content is set to 0.12%. Moreover, in order to ensure toughness stably, it is good also considering the upper limit of C as 0.09%, 0.08%, or 0.07%.

(Si: 0.2-1.0%)
Si is a deoxidizing element and needs to be contained in an amount of 0.2% or more in order to reduce the amount of O in the weld metal and increase the cleanliness. However, if the content exceeds 1.0%, the toughness of the weld metal is deteriorated, so this is the upper limit. Moreover, in order to ensure the toughness of a weld metal stably, the upper limit of Si is good also as 0.8%, 0.7%, or 0.6%.

(Mn: 1.0-2.5%)
Mn is an element necessary for ensuring the hardenability of the weld metal and increasing the strength. In order to exhibit the effect reliably, it is necessary to contain 1.0% or more. On the other hand, if the content exceeds 2.5%, the grain boundary embrittlement susceptibility increases and the toughness of the weld metal deteriorates, so this is the upper limit. In order to increase the strength of the weld metal more stably, the lower limit of Mn may be 1.2%, 1.4%, or 1.6%.

(P: 0.02% or less)
P is an impurity element, and it is necessary to reduce it as much as possible in order to deteriorate weld crack resistance and toughness, but the P content is 0.02% or less as a range in which these adverse effects can be tolerated.
(S: 0.02% or less)
S is also an impurity element, and if it is excessively present in the weld metal, it deteriorates both toughness and ductility, so it is preferable to reduce it as much as possible. The S content is set to 0.02% or less as a range in which an adverse effect on toughness and ductility can be tolerated.

(Al: 0.005 to 0.050%)
Al is a deoxidizing element and, like Si, is effective in reducing O in the weld metal and improving cleanliness, and is contained in an amount of 0.005% or more. On the other hand, if the content exceeds 0.050%, nitrides and oxides are formed and the toughness of the weld metal is inhibited, so this is the upper limit. In order to sufficiently obtain the effect of improving the toughness of the weld metal, the lower limit of Al may be 0.0015%. Further, in order to sufficiently obtain the effect of improving the toughness of the weld metal, the lower limit of Al may be set to 0.002% or 0.003%, and the upper limit of Al is set to 0 to suppress the formation of coarse oxides. It may be 0.045% or 0.040%.

(Ni: 1.5-3.5%)
Ni is the only element that can improve toughness by solid solution toughening (the effect of increasing toughness by solid solution) regardless of the structure and components. It is an effective element. In order to obtain the necessary solid solution toughening effect, Ni needs to be contained by 1.5% or more.
A higher Ni content is more advantageous in improving toughness, but if the content exceeds 3.5%, the weld crack resistance decreases, so this is the upper limit. In order to ensure that the effect of Ni contributes to the improvement of toughness, the lower limit of Ni is preferably set to 1.7% or 2.0%.

(Mo: 0.3-1.0%)
Mo is an element that improves hardenability, and forms fine carbides and is effective in securing tensile strength by precipitation strengthening. Further, Mo has an effect of suppressing a decrease in strength when it is subjected to reheating by multi-layer welding and suppressing deterioration of toughness. Box column welding is performed by multi-layer welding, but in multi-layer welding, the weld metal formed in the previous pass is subjected to reheating from the subsequent welding pass, but the weld metal is softened, but 780 MPa. At the strength level, the weld metal structure is mainly bainite, so the degree of softening is large, and it is difficult to stably secure the strength of the weld metal. Furthermore, the cementite becomes coarse due to the reheating, so that the toughness is also deteriorated. Mo suppresses strength reduction by forming fine carbides when reheated by multi-layer welding, and further suppresses coarsening of cementite, and thus has an effect of suppressing deterioration of toughness.

  In order to exhibit these effects, it is necessary to contain at least 0.3% even in consideration of combined effects with other elements having similar effects. On the other hand, if the content exceeds 1.0%, the precipitates become coarse and the toughness of the weld metal deteriorates, so this is the upper limit. In order to ensure the strength stably by further suppressing the decrease in strength due to reheating and to simultaneously suppress the deterioration of toughness, the lower limit of Mo is set to 0.4%, 0.5%, or 0.6%. You may make it contain super.

(Ti: 0 to 0.10%)
Ti, like Al, is an effective element as a deoxidizing element and has an effect of reducing the amount of O in the weld metal. It is also effective for fixing solute N and mitigating the adverse effect of N on toughness. The lower limit of the Ti content is 0%, but in order to exert these effects, the lower limit of the Ti content may be 0.01%. However, if the Ti content in the flux-cored wire exceeds 0.10% and becomes excessive, there is a greater possibility that toughness deterioration due to the formation of coarse oxides and toughness deterioration due to excessive precipitation strengthening will occur. For this reason, when Ti is contained, the upper limit of the Ti content is 0.10%. Further, in order to further suppress toughness deterioration due to Ti, the upper limit of Ti may be set to 0.08%, 0.06%, or 0.05%.

(B: 0-0.01%)
When B is contained in an appropriate amount in the weld metal, it has the effect of reducing the adverse effect on the toughness of the solid solution N by combining with the solid solution N and contributing to the improvement of the strength by increasing the hardenability. There is also an effect. In order to acquire these effects, it is preferable to make it contain 0.0010% or more. On the other hand, if the content exceeds 0.0100%, B in the weld metal becomes excessive, and coarse toughness is adversely deteriorated by forming B compounds such as coarse BN and Fe ₂₃ (C, B) ₆ . This is the upper limit. Further, in order to further suppress toughness deterioration due to B, the upper limit of B may be set to 0.009% or 0.008%.

  The wire used in the present invention may be a wire containing the above chemical components. However, depending on the strength level of the steel sheet to be welded and the required toughness, Cu, Cr, V, and Nb described below are used. A wire containing one or two or more of Mg can also be used.

(Cu: 0 to 1.0%)
Cu can be added to the surface of the outer surface of the wire and to the flux as a simple substance or an alloy, thereby improving the strength and toughness of the weld metal. If the content exceeds 1.0%, the toughness decreases, so when Cu is contained, the content is made 1.0% or less. In order to sufficiently obtain the effect of adding Cu, it is preferable to contain 0.1% or more.
In addition, about content of Cu, in addition to the part contained in outer skin itself or a flux, when the copper surface is plated on the wire surface, the part is also included.

(Cr: 0 to 0.6%)
Cr is an element effective for increasing strength by enhancing hardenability. If the content exceeds 0.6%, the bainite structure is hardened unevenly and the toughness is deteriorated. Therefore, when Cr is contained, the content is made 0.6% or less. In order to acquire the effect of Cr addition, it is preferable to make it contain 0.1% or more.

(V: 0 to 0.20%)
V is an element effective for increasing the strength by enhancing the hardenability. If the content exceeds 0.20%, the carbide precipitates and hardens and deteriorates toughness. Therefore, when V is contained, the content is made 0.20% or less. In order to obtain the effect of V addition sufficiently, it is preferable to contain 0.01% or more.

(Nb: 0 to 0.10%)
Nb forms fine carbides and is effective in securing tensile strength by precipitation strengthening. If the content exceeds 0.1%, it is excessively contained in the weld metal and forms coarse precipitates to deteriorate toughness. Therefore, when Nb is contained, the content is made 0.10% or less. In order to sufficiently obtain the effect of Nb addition, it is preferable to contain 0.01% or more.

(Mg: 0 to 0.70%)
Mg is a deoxidizing element and is effective in reducing O in weld metal and improving cleanliness. On the other hand, if it exceeds 0.70%, sputtering increases significantly. Therefore, when adding Mg, the content is made 0.70% or less. In order to fully exhibit the effect of adding Mg, it is preferable to contain 0.10% or more.

(Ceq: 0.55-0.90%)
The flux-cored wire of the present invention contains each element as described above as an alloy component or metal deoxidation component, but in order to ensure the tensile strength of the weld metal, the Japanese welding represented by the following (formula a): It is necessary to further adjust the contents of C, Si, Mn, Ni, Cr, Mo, and V so that the carbon equivalent Ceq determined by the association (WES) is 0.55 to 0.90%.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14
... (Formula a)
However, the elements with [] indicate the content (% by mass) of each element. The element not contained is 0%.

  The higher the value of Ceq, the more the weld metal is hardened and the tensile strength is improved. On the other hand, the toughness is lowered and the weld crack sensitivity is increased, so that a countermeasure for suppressing low temperature cracks is required. If the Ceq value is less than 0.55%, the target strength of the weld metal of 780 MPa is not satisfied. If the Ceq value exceeds 0.90%, the tensile strength of the weld metal becomes excessive, and the toughness of the weld metal. Decreases. Therefore, the range of Ceq is 0.55 to 0.90%.

(TE: 2.7-4.4%)
Furthermore, in order to ensure the toughness of the weld metal, TE defined by (Formula b) (when Cr is not included, Cr is calculated as 0%) needs to be 2.7 to 4.4%. There is.
TE = [Mn] / 2 + [Ni] + 3 × [Cr] (Formula b)
However, the elements with [] indicate the content (% by mass) of each element.

In a 780 MPa class weld metal, the structure is mainly bainite, and in order to ensure its low temperature toughness, a fine structure is obtained by causing intragranular transformation using oxides in γ grains as nucleation sites for transformation. It is preferable to do this. Mn, Ni, and Cr exist in the weld metal mainly in a solid solution state, and have the effect of ensuring the toughness of the weld metal by obtaining the optimum hardenability for intragranular transformation.
In order to reliably obtain the effect, TE needs to be 2.7% or more. If it is lower than 2.7%, the hardenability is lowered, so that coarse grain boundary ferrite is generated and the toughness is deteriorated. On the other hand, when TE exceeds 4.4%, the hardenability is excessively improved, so that intragranular transformation does not occur, and a coarse bainite structure or a coarse martensite structure is formed, resulting in deterioration of toughness. It is preferable that the lower limit is 3.0% or 3.1% and the upper limit is 4.2% or 4.0% as a range in which a better balance of strength and toughness can be secured.

The content of elements contained as the above alloy component or metal deoxidation component does not include the content when these elements are contained as fluoride, metal oxide, or metal carbonate.
Further, these elements are not necessarily pure substances (inevitable impurities can be contained), and there is no problem even if they are contained in the form of an alloy such as Cu-Ni. In addition, since these elements have the same effect regardless of whether they are contained in the steel skin or as a flux, they can be contained in either the steel skin or the flux.

In the present invention, it becomes possible to omit or simplify preheating by using the flux-cored wire having the material structure as described above. However, the wire form is a seamless wire without a slit-like seam in the steel sheath. Is preferred.
Hydrogen entering the weld during welding diffuses in the weld metal and on the steel material side, accumulates in the stress concentration part, and causes cold cracking. Under welding where the cleanliness of the weld and the conditions of the gas shield are sufficiently controlled, hydrogen mainly contained in the wire is the main factor of diffusible hydrogen in the weld joint. For this reason, it is desirable to make the steel outer shell into a seamless tube, and to suppress the penetration | invasion of the hydrogen in air | atmosphere to a flux until it is used after a wire manufacture.

In the box column welding assembly described above, the diaphragm 3 and the skin plate 1 or the divided skin plate 3 are welded by multi-layer welding by GMAW.
As welding conditions, the conditions recommended according to the strength of the steel sheet used can be used, and the type of shielding gas used is also commonly used. 100 vol% carbon dioxide gas or Ar and 3-20 vol. A mixed gas of% CO ₂ can be used.
Further, the welding of the groove at the corner is performed by SAW or GMAW, but similarly, the conditions recommended according to the strength of the steel sheet to be used can be used.

  Hereinafter, embodiments of the present invention will be specifically described with reference to examples. These examples are examples for confirming the effects of the present invention, and do not limit the present invention.

  The steel strip is formed into an open tube by forming it with a forming roll while feeding in the longitudinal direction. Flux is supplied into the open tube from the opening of the open tube in the middle of this forming, and then the opposite edge surface of the opening after forming is formed. By butt seam welding and making the open pipe a seamless pipe, by drawing the flux-cored wire obtained by making the pipe in this way, by annealing the flux-cored wire in the middle of this wire drawing work, A flux-cored wire having a final wire diameter of φ1.2 mm was manufactured. After the trial production, a lubricant was applied to the surface of the flux-cored wire.

The analysis of the chemical composition of the prototype flux cored wire was performed as follows. First, the filled flux was taken out from the flux-cored wire, and the flux-cored wire was divided into a steel outer shell and a flux. The chemical component of the steel outer skin was determined by measuring the content of each metal component by chemical analysis. The flux was first quantitatively evaluated for constituents and components by X-ray diffraction and fluorescent X-ray analysis. Thereafter, the flux was separated into a slag component and an alloy component using a beneficiation method such as flotation and magnetic beneficiation, and each chemical component was analyzed by performing chemical analysis and gas analysis.
[Table 1] and [Table 2] show the component composition of the prototype flux-cored wire. The chemical components listed in [Table 2] do not include chemical components of fluoride, metal oxide, and metal carbonate.

  Next, welding was performed using the flux-cored wire described above. For welding, the base material 11 with a plate thickness of 20 mm is abutted at a root gap of 16 mm and a groove angle of 20 °, and the above described flux-cored wire is used under the welding conditions shown in [Table 3] using a backing metal 12. The test body shown in FIG. 6 was produced by carrying out welding using the same. In addition, although SM490A prescribed | regulated to JISG3106-2008 was used as the base material 11 and the backing metal 12, the grooved surface of the base material and the surface of the backing metal were used with the flux-cored wire to be tested. Battering of 2 layers or more and an extra height of 3 mm or more was performed.

From the obtained weld metal 3, as shown in FIG. 6, A1 tensile test piece (round bar) (diameter = 12.5 mm) 15 according to JIS Z3111-2005 (a method for tensile and impact test of weld metal) and A Charpy test piece (V-notch test piece) 14 was collected and subjected to a mechanical property test to measure the tensile strength and Charpy absorbed energy of the weld metal, and evaluated according to the following criteria.
-Tensile strength: A sample having a tensile strength of 780 MPa or more at room temperature was accepted.
-Toughness: In the Charpy impact test at 0 ° C, a sample having an absorbed energy of 70 J or more was accepted.
The evaluation results of the obtained mechanical properties are shown in [Table 4].

The amount of diffusible hydrogen was measured by a gas chromatograph method in accordance with JIS Z3118-2007 (method for measuring the amount of hydrogen in steel welds) (diffusible hydrogen test).
The welding conditions are shown in [Table 3], and the results are shown in [Table 4]. The evaluation criteria for the measured amount of diffusible hydrogen were as follows.
Diffusion hydrogen amount: Less than 1.0 ml / 100 g (very low hydrogen level) was accepted.

Evaluation of cold cracking resistance was carried out by conducting a test in accordance with JIS Z3158 (y-type weld cracking test method). For the y-type weld crack specimen, S1-S3 steel plates used for the skin plate of [Table 5] were used. A Y-shaped weld crack specimen was prepared by groove-working the steel sheets of S1 to S3 into a y shape and assembling them by welding so that the root interval was 1 mm. Next, test welding was carried out under the welding conditions shown in [Table 3] in a welding place under a constant atmosphere control at a temperature of 0 ° C. and a humidity of 60% to obtain a specimen. A cross-sectional observation of the welded specimen was performed to measure the cracking rate, and the low temperature cracking resistance of the flux-cored wire was evaluated based on the measurement result. Evaluation of cold cracking resistance was as follows.
-Cold cracking resistance: In the y-type weld crack test, a sample in which a cross-sectional crack did not occur in the welded portion (a sample having a cross-sectional crack rate of 0) was accepted.

  The obtained y-type weld crack test results are shown in [Table 4]. Specimens with diffusible hydrogen of less than 1.0 ml / ml were produced in the y-type weld crack test even when test welding was performed without preheating at 0 ° C., which is a very low temperature condition. In all of the cross sections, no cross-section cracks (no cross-section cracks occurred), and extremely high resistance to cold cracking was proved.

Next, in order to evaluate the mechanical properties of the welded joint in the actual structure of the BOX column, in the evaluation of the mechanical properties of [Table 4], for the flux-cored wire that passed the overall judgment, The diaphragm steel plate is assembled into a T shape so as to have a groove shape as shown in FIGS. 5 (a) and 5 (b), and welding is performed as shown in FIGS. 2 (a) and 2 (b). A T-shaped welded joint specimen as shown in FIGS. 7 and 8 was produced. [Table 6] shows the flux-cored wire, skin plate, diaphragm, and welding conditions used for the joint production.
In addition, as a comparison, in the evaluation of the mechanical properties in [Table 4], B01 which failed in low temperature cracking resistance, B07 which failed in tensile strength, and Charpy absorbed energy at 0 ° C. failed. About the flux cored wire of B15, the welded joint was produced similarly to the said description point.

From the obtained welded joint, a welded joint tensile test piece was collected so as to have the full thickness of the skin plate as shown in FIGS. Further, as shown in FIGS. 11 and 12, a Charpy test piece (V notch test piece) was taken from the surface layer of the skin plate, and the notch position was set at the center of the width of the weld metal. Using these test pieces, mechanical property tests were performed, and the tensile strength and Charpy absorbed energy of the welded joint were measured and evaluated according to the following criteria.
Joint tensile strength: A sample having a tensile strength of 780 MPa or more at room temperature was accepted.
-Toughness: In the Charpy impact test at 0 ° C, a sample having an absorbed energy of 70 J or more was accepted.
The evaluation results of the obtained mechanical properties are shown in [Table 6].

As shown in the test results of [Table 6], the weld metal layer was 1/3 or more of the skin plate thickness and two or more layers satisfied the joint tensile strength and Charpy absorbed energy. On the other hand, when the weld metal layer was less than 1/3 of the thickness of the skin plate or one layer, the mechanical properties were not satisfied.
In addition, in the evaluation of the mechanical properties of the flux-cored wire shown in [Table 4], B01 which has high diffusible hydrogen and failed with low-temperature cracking resistance, B07 which has failed tensile strength, and Charpy absorption at 0 ° C As for B15 which failed in energy, B01 caused a low temperature crack in the weld metal, B07 did not satisfy the joint tensile strength, B15 did not satisfy the Charpy absorbed energy, and the mechanical properties shown in [Table 4] It was rejected as well as the evaluation result.

1, 1a, 1b, 1c, skin plate 2, 2a, 2b, 2c, split skin plate 3, 3a, 3b diaphragm 4, 4a, 4b, 4c, 4d weld metal formed on square joint of skin plate 5, 5a 5b weld metal formed between the divided skin plates 6, 6a, 6b groove formed between the divided skin plates 7 backing metal 8 notch formed at the tip of the diaphragm 9, 9a, 9b, 9c, 9d Grooves formed on the corner joint of skin plate 11 Base material 12 Backing metal 13 Weld metal 14 2 mm V notch Charpy impact test piece 15 Round bar tensile test piece, oxygen analysis test piece

Claims (7)

In the box column in which the diaphragm is welded and fixed inside the square steel pipe formed by welding the corners of the outer skin plate,
The outer surface of the box column has a skin plate divided on the boundary of the diaphragm,
The space between the divided skin plate and the skin plate is filled with a weld metal layer formed by gas shield arc welding of a groove formed by the skin plate and the diaphragm,
The box column, wherein the weld metal layer is formed with a thickness of 1/3 or more of the skin plate between the diaphragm and two or more layers.   When the tensile strength of the steel plate used for the skin plate is 780 MPa or more and the tensile strength of the steel plate is SP (MPa), the tensile strength of the steel plate used for the diaphragm is 0.65 SP. The box column according to claim 1, wherein the box column is 0.9 SP or less. A method of manufacturing the box column by performing welding of the skin plate and the diaphragm of the box column according to claim 1 or 2 by gas shielded arc welding using a flux-cored wire,
The flux-cored wire is
In said wire wire percentage by weight relative to the total _weight, CaF _{2, BaF} 2, SrF _2, MgF 2, 2.0 to 7.0% as the total amount alpha 1 type or two or more types of LiF, Ti oxide 1 type or 2 types or more out of a material, Si oxide, Zn oxide, Mg oxide, Al oxide, and 0.3 to 1.2% as a total amount β,
And the ratio of the total amount α to the total amount β is 2.0 to 20.0,
The total amount of one or more of the metal carbonates of CaCO ₃ , BaCO ₃ , SrCO ₃ , MgCO ₃ is less than 0.60%,
The chemical components excluding fluoride, metal oxide, and metal carbonate are in mass% based on the total mass of the flux-cored wire,
C: 0.04 to 0.12%,
Si: 0.2 to 1.0%
Mn: 1.0 to 2.5%
Al: 0.005 to 0.050%,
Ni: 1.5-3.5%,
P: 0.02% or less,
S: 0.02% or less,
Mo: 0.3 to 1.0%,
Ti: 0 to 0.10%,
B: 0 to 0.01%
Cu: 0 to 1.0%
Cr: 0 to 0.6%,
V: 0 to 0.20%,
Nb: 0 to 0.10%,
Mg: 0 to 0.70%
It consists of the balance iron and unavoidable impurities, Ceq defined by the following formula a is 0.55 to 0.90%, and TE defined by the following formula b is 2.7 to 4.4%. The box pillar manufacturing method according to claim 1, wherein the box pillar manufacturing method is provided.
Ceq = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14
... (Formula a)
TE = [Mn] / 2 + [Ni] + 3 × [Cr] (Formula b)
However, the element with [] represents the content in mass% of each element. The box pillar according to claim 3, wherein the total amount α is 3.3 to 7.0%, and a ratio of the content of the CaF _{2 to} the total amount α is 0.90 or more. Production method.   The box pillar manufacturing method according to claim 3 or 4, wherein the content of CaO in the flux-cored wire is 0.15% or less by mass% with respect to the total mass of the flux-cored wire. The total content of CaCO ₃ , BaCO ₃ , SrCO ₃ , and MgCO _{3 in} the flux-cored wire is 0.1 to 0.5% in terms of mass% with respect to the total mass of the wire. The manufacturing method of the box pillar as described in any one of -5.   The box pillar manufacturing method according to any one of claims 3 to 6, wherein the steel outer shell has a seamless shape.

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