JP2014193482A - Electroslag welding method capable of obtaining weld metal excellent in toughness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electroslag welding method capable of improving the toughness of a weld metal and also of inhibiting variation of toughness when bonding a diaphragm to the inside of a box column composed of four skin plates by electroslag welding.SOLUTION: There is provided an electroslag welding method for bonding a diaphragm 2 to the inside of a box column composed of four skin plates 1. The electroslag welding is conducted by: providing a clearance between the upper face of the skin plate 1 and the lower face of the diaphragm 2; contacting the backing strips 3 on the facing two sides of the diaphragm 2; contacting the lower face of the backing strip 3 on the upper face of the skin plate 1; and contacting on the upper face of the skin plate 1 between the backing strips 3, the lower face of a thin steel sheet which contains 0.10 mass% or less of C, 0.008 mass% or less of N, and has a thickness of 1 to 5 mm.

Description

  The present invention relates to an electroslag welding method for joining a diaphragm inside a box column composed of four skin plates as a steel frame of a building structure.

As a steel frame of a building structure, when joining a diaphragm to the inside of a box column composed of four skin plates, vertical welding can be easily performed, and high-heat input one-pass welding is possible. Electroslag welding is used as an efficient welding technique.
In recent years, in order to prevent plastic deformation caused by earthquakes and improve earthquake resistance, the toughness of weld metal has been improved, and the variation has been suppressed to stabilize high toughness over a long period of time. Technology is needed.

However, since electroslag welding has a much higher heat input than other arc weldings, the cooling rate of the weld metal is reduced, and the structure of the weld metal tends to be coarse. As a result, the toughness of the weld metal tends to decrease. Then, the technique which improves the toughness of the weld metal formed by electroslag welding is examined.
For example, a technique is known in which a minute amount of Ti and B are added to a weld metal to refine the structure of the weld metal and improve the toughness of the weld metal. However, in electroslag welding, since the amount of melting of steel materials such as skin plates and diaphragms is large, Ti and B are diluted with a large amount of molten metal, and the effect cannot be obtained. That is, the components of the steel material have a great influence on the composition of the weld metal formed in the cooling process after welding, and consequently the structure of the weld metal.

In particular, when the C content of the skin plate or diaphragm exceeds 0.1% by mass, there is a problem that the amount of C mixed into the weld metal increases, and as a result, the toughness of the weld metal deteriorates.
In electroslag welding, the amount of melting in the weld line direction is likely to fluctuate, resulting in a large variation in toughness. That is, when the absorbed energy is measured by the Charpy impact test and the toughness is evaluated, there arises a problem that a sufficient absorption energy measurement result cannot be obtained depending on the position where the test piece is collected.

Therefore, a technique has been developed that improves the toughness of the weld metal formed by electroslag welding and suppresses the variation.
For example, Patent Document 1 discloses that a predetermined amount of Si, Mo, Cr, Nb and V, which are elements that stabilize the δ ferrite phase and improve the hardenability, is contained, and that coarse proeutectoid ferrite is generated at the austenite grain boundaries. In order to suppress the formation of cementite (Fe ₃ C), which has a predetermined amount of B, which has an inhibitory effect, and further causes cementite (Fe ₃ C) to deteriorate toughness, a welding wire with a reduced C content is used. And a technique for stably improving the toughness of the weld metal by electroslag welding with high heat input.

However, in this technique, no consideration is given to the flux component that greatly affects the oxygen content of the weld metal, and it is difficult to obtain stable toughness in the weld line direction.
In Patent Document 2, a large amount of Ti is added from a welding wire, and a low basicity flux is used to disperse an oxide containing Ti that is a nucleus of acicular ferrite in a molten metal. A technique for stably improving toughness using a weld metal as a structure mainly composed of acicular ferrite is disclosed.

However, in this technique, since B ₂ O ₃ is not defined as a flux component, fluctuations in the B amount in the weld line direction cannot be suppressed, and it is difficult to obtain stable toughness in the weld line direction.
In Patent Document 3, the components of the welding wire, steel, and backing metal are kept within an appropriate range, and the difference in N content is adjusted to within 0.003% by mass, thereby reducing the microstructure of the weld metal. Techniques for suppressing fluctuations and improving toughness stably are disclosed.

  However, with this technology, the welding wire and backing metal to be used must be selected so that the combination with the steel material is optimal in accordance with the components at the site of welding construction, and work efficiency is reduced. In addition, the burden of inventory management of welding wires and backing metal increases.

JP 2002-79396 JP Japanese Patent Laid-Open No. 2004-114053 JP 2005-305471 A

  The present invention eliminates the problems of the prior art, improves the toughness of the weld metal and improves the toughness in joining the diaphragm to the inside of the box column composed of four skin plates by electroslag welding. It is an object of the present invention to provide an electroslag welding method capable of suppressing variations in the thickness.

  The present inventors diligently studied a technique for increasing the toughness and stabilization of the weld metal in electroslag welding of the skin plate and the diaphragm constituting the box column. As a result, in electroslag welding, the melting amount of the skin plate is large, so when a skin plate with a high C content is used, the welding wire and flux components and the basicity balance can be adjusted optimally. It has been found that it is difficult to ensure good toughness by increasing the C content of the metal.

However, in order to ensure sufficient strength as a building structure, a skin plate with a high C content must be used, so it is necessary to develop a technique for improving the toughness of the weld metal.
Therefore, the technology for reducing C in the weld metal when electroslag welding was performed using a skin plate with a high C content was studied in more detail. As a result, as shown in FIG. 1, a thin steel plate having a small C content and a predetermined plate thickness is brought into contact with the upper surface of the skin plate in the space formed by the diaphragm, the skin plate, and the backing metal. By welding the space, it is possible to suppress an increase in the C content of the weld metal, and thus to achieve both high toughness of the weld metal and stabilization of its toughness (suppression of variation). I understood that I could do it.

The present invention has been made based on such knowledge.
That is, according to the present invention, in an electroslag welding method for joining a diaphragm to the inside of a box column composed of four skin plates, a gap is provided between the upper surface of the skin plate and the lower surface of the diaphragm so that the diaphragms face each other. A backing metal is in contact with one side, and the lower surface of the backing metal is in contact with the upper surface of the skin plate, and further contains C: 0.10% by mass or less, N: 0.008% by mass or less, and a thickness of 1 to 5 mm. This is an electroslag welding method in which welding is performed by bringing the lower surface of the steel plate into contact with the upper surface of the skin plate between the backing metal.

Here, the upper surface of the skin plate means the inner surface of the box column composed of four skin plates. The lower surfaces of the diaphragm, the thin steel plate, and the backing metal each mean a surface facing the upper surface of the skin plate.
In the electroslag welding method of the present invention, it is preferable to use a skin plate containing C: 0.10 to 0.20 mass% and N: 0.001 to 0.01 mass%. Furthermore, it is preferable that the thin steel plate and the skin plate contain P: 0.015 mass% or less and S: 0.005 mass% or less in addition to the above composition.

  According to the present invention, when a diaphragm is joined to the inside of a box column composed of four skin plates by electroslag welding, the toughness of the weld metal by electroslag welding is improved and the variation in toughness is suppressed. It is possible to do so, and there is a remarkable effect in the industry.

It is sectional drawing which shows typically the example of arrangement | positioning of the skin plate in this invention, a diaphragm, a backing metal, and a thin steel plate. It is sectional drawing which shows the collection position of a 2 mmV notch Charpy impact test piece.

FIG. 1 is a cross-sectional view schematically showing an example of the arrangement of skin plates, diaphragms, backing metal, and thin steel plates in the electroslag welding method of the present invention. Below, the electroslag welding method of this invention is demonstrated with reference to FIG. FIG. 1 shows only one of the four skin plates 1 constituting the box column.
In performing electroslag welding by applying the present invention, a gap is provided between the upper surface of the skin plate 1 and the lower surface of the diaphragm 2, the backing metal 3 is brought into contact with the outer surface of the diaphragm 2, and the backing metal 3 Is brought into contact with the upper surface of the skin plate 1. The thin steel plate 4 is disposed inside the space formed by the inner surface of the backing metal 3 below the lower surface of the diaphragm 2 combined in this way and the upper surface of the skin plate 1, and the lower surface of the thin steel plate 4. And the upper surface of the skin plate 1 abut.

Note that L (mm) in FIG. 1 is the distance between the upper surface of the thin steel plate 4 and the lower surface of the diaphragm 2.
Here, the upper surface of the skin plate means the inner surface of the box column composed of four skin plates. The lower surfaces of the diaphragm, the thin steel plate, and the backing metal each mean a surface facing the upper surface of the skin plate.
If the distance L between the lower surface of the diaphragm 2 and the upper surface of the thin steel plate 4 is less than 20 mm, the space is too narrow and electroslag welding becomes difficult. On the other hand, if it exceeds 30 mm, the space is too wide, and the time required for welding is increased. Therefore, the distance L is preferably within a range of 20 to 30 mm.

In FIG. 1, D indicates the thickness (mm) of the diaphragm 2, and T indicates the thickness (mm) of the skin plate 1.
The means for bringing the backing metal 3 into contact with the outer surface of the diaphragm 2 may be any means that does not change the arrangement of the diaphragm 2 and the backing metal 3 during welding, and is not particularly limited.
The thin steel plate 4 brought into contact with the upper surface of the skin plate 1 uses C: 0.10% by mass or less and N: 0.008% by mass or less. Furthermore, it is preferable that P: 0.015 mass% or less, S: 0.005 mass% or less.

When the thin steel plate 4 having a C content exceeding 0.10% by mass is used, the C content in the weld metal cannot be reduced, so that the effect of improving the toughness of the weld metal cannot be obtained. Therefore, the upper limit of the C content of the thin steel plate 4 is 0.10% by mass.
When the thin steel plate 4 having an N content exceeding 0.008% by mass is used, the amount of N in the weld metal increases, and as a result, the amount of solute N that adversely affects the toughness of the weld metal also increases. In order to improve the toughness of the weld metal and suppress the variation in toughness, it is necessary to reduce the amount of N completely diluted in the weld metal by keeping the N content of the thin steel plate 4 low. Therefore, the upper limit of the N content of the thin steel plate 4 is 0.008% by mass.

When the thin steel plate 4 having a P content exceeding 0.015% by mass is used, the amount of P in the weld metal increases, and as a result, the toughness of the weld metal deteriorates. Therefore, the P content of the thin steel plate 4 is preferably 0.015% by mass or less.
When the thin steel plate 4 having an S content exceeding 0.005 mass% is used, the amount of S in the weld metal increases, and as a result, the toughness of the weld metal deteriorates. Therefore, the S content of the thin steel plate 4 is preferably 0.005% by mass or less.

Moreover, if the plate | board thickness of the thin steel plate 4 is less than 1 mm, the effect which suppresses the increase in C content of a weld metal cannot be acquired. On the other hand, if the thickness exceeds 5 mm, the thin steel plate 4 cannot be sufficiently melted. As a result, the skin plate 1 is also difficult to melt, so that a welding defect due to poor fusion tends to occur. Accordingly, the thickness of the thin steel plate 4 is 1 to 5 mm. Preferably it is 2-4 mm.
The means for bringing the thin steel plate 4 into contact with the upper surface of the skin plate 1 is not particularly limited as long as the arrangement of the backing metal 3 and the thin steel plate 4 does not change during welding.

It is preferable to use the skin plate 1 containing C: 0.10 to 0.20% by mass and N: 0.001 to 0.01% by mass. Furthermore, it is preferable that P: 0.015 mass% or less, S: 0.005 mass% or less.
When the skin plate 1 having a C content of less than 0.10% by mass is used, the amount of C in the weld metal is insufficient and a weld metal having sufficient strength cannot be obtained. On the other hand, when the C content exceeds 0.20% by mass, not only the amount of C in the weld metal increases and the toughness of the weld metal deteriorates, but also the toughness of the heat affected zone due to electroslag welding deteriorates. Therefore, the C content of the skin plate 1 is preferably in the range of 0.10 to 0.20 mass%.

  N combines with Al and Ti to refine the austenite crystal grains of the weld metal and to improve the toughness of the weld heat affected zone, so that it is possible to improve toughness and suppress variations. . When the skin plate 1 having an N content of less than 0.001% by mass is used, such an effect cannot be obtained. On the other hand, if the N content exceeds 0.01% by mass, the amount of N diluted in the weld metal increases, and the toughness of the weld metal deteriorates, and the amount of N dissolved in the weld heat affected zone also increases. As a result, the toughness of the weld heat affected zone deteriorates. Therefore, the N content of the skin plate 1 is preferably in the range of 0.001 to 0.01% by mass.

P is an unavoidable impurity element in the weld metal, and segregates at the grain boundary to cause grain boundary embrittlement and deteriorate toughness. Therefore, the lower the P content of the weld metal, the better. The P content of the skin plate 1 is preferably 0.015% by mass or less.
S, like P, is an unavoidable impurity element in weld metal, and its toughness deteriorates due to grain boundary embrittlement and increased inclusions. Therefore, the lower the S content of the weld metal, the better. The S content of the skin plate 1 is preferably 0.005% by mass or less.

  According to the present invention, as described above, the skin plate 1, the diaphragm 2, the backing metal 3, and the thin steel plate 4 are combined, and the inner surface of the backing metal 3 below the lower surface of the diaphragm 2 and the thin steel plate 4. The weld metal is formed by performing electroslag welding while inserting a welding wire into the groove and moving the welding wire back and forth in the longitudinal direction (so-called oscillate) with the space formed by the upper surface of the metal as a groove. It is possible to improve the toughness of the steel and to suppress variations in toughness.

As shown in FIG. 1, the skin plate 1, the diaphragm 2, the backing metal 3, and the thin steel plate 4 are combined to form the lower surface of the diaphragm 2, the inner surface of the backing metal 3, and the upper surface of the thin steel plate 4. Using the space as a groove, a welding wire (wire diameter 1.6 mm) was inserted into the groove, and electroslag welding was performed while oscillating.
The plate thickness T of the skin plate 1 was 60 mm, and the distance L between the lower surface of the diaphragm 2 (plate thickness D: 60 mm) and the upper surface of the thin steel plate 4 was 25 mm. As the backing metal 3, a flat bar defined in JIS standard SN490 was used.

The components of the skin plate 1 are as shown in Table 1. Diaphragm 2 was used in combination with the same components as skin plate 1 shown in Table 1. The components of the thin steel plate 4 are as shown in Table 2.
Table 3 shows the setting conditions for electroslag welding.

After the welding was completed, the weld metal 5 was flawed by an ultrasonic flaw detection test, and three 2 mm V notch Charpy impact test pieces 6 (hereinafter referred to as “test pieces”) were sampled from portions where no welding flaw was observed. The position where the test piece 6 was collected is as shown in FIG. 2 as a cross-sectional view, and the test piece 6 was cut out so as to provide a notch in the weld metal 5.
Then, subjected to Charpy impact test (test temperature 0 ° C.) using a specimen 6 was measured absorbed energy _V E ₀ (J). The results are shown in Table 4. The _V E ₀ values in Table 4 are average values of the results obtained by measuring three times each.

As is apparent from Table 4, in the inventive examples (welded joints Nos. 1 and 3 to 8), the average value of the absorbed energy _V E ₀ is as high as 89 to 135 J, and a weld metal having excellent toughness is obtained. It was.
In addition, the measured values of _V E ₀ of the inventive example are as follows: welded joint No. 1 is 111 to 115 J, welded joint No. 3 is 90 to 93 J, welded joint No. 4 is 94 to 103 J, and welded joint No. 5 is 86 to The variations were 93 J, welded joint No. 6 in the range of 103 to 110 J, welded joint No. 7 in the range of 118 to 127 J, and welded joint No. 8 in the range of 132 to 136 J.

Welded joint No. 2, which is a comparative example, is an example in which the thickness of the thin steel plate 4 exceeds the range of the present invention, and poor fusion occurred. Welded joint No. 9 is an example in which the N content of the thin steel plate 4 exceeds the range of the present invention. Welded joints No. 10 and 11 are examples in which the C content of the skin plate 1 exceeds the range of the present invention. No. 12 is an example in which the C content of the thin steel plate 4 exceeds the range of the present invention. In all cases, the absorbed energy _V E ₀ is reduced, and the toughness of the weld metal is significantly deteriorated as compared with the inventive example.

In addition, the measured values of _V E _{0 in} the comparative example are 19 to 25 J for welded joint No. 9, 18 to 27 J for welded joint No. 10, 28 to 47 J for welded joint No. 11, and 30 to 30 for welded joint No. 12. It was within the range of 62J, and the variation was larger than that of the invention example.
Furthermore, welded joint No. 13 is an example in which the P content of skin plate 1 exceeds the preferred range of the present invention, welded joint No. 14 is an example in which the S content of skin plate 1 exceeds the preferred range of the present invention, welded joint No. 15 is an example in which the P content of the thin steel plate 4 exceeds the preferable range of the present invention, and welded joint No. 16 is an example in which the S content of the thin steel plate 4 exceeds the preferable range of the present invention. In all cases, the absorbed energy _V E ₀ was small, and the toughness of the weld metal was significantly deteriorated as compared with the inventive examples.

These measured values of _V E ₀ are 18 to 29 J for welded joint No. 13, 25 to 32 J for welded joint No. 14, 23 to 36 J for welded joint No. 15, and 34 to 41 J for welded joint No. 16. It was within the range, and the variation was larger than that of the invention example.

DESCRIPTION OF SYMBOLS 1 Skin plate 2 Diaphragm 3 Backing metal 4 Thin steel plate 5 Weld metal 6 2mmV notch Charpy impact test piece

Claims (4)

  In the electroslag welding method for joining a diaphragm to the inside of a box column constituted by four skin plates, a gap is provided between the upper surface of the skin plate and the lower surface of the diaphragm, and two opposing side surfaces of the diaphragm And the lower surface of the backing plate is in contact with the upper surface of the skin plate, and further contains C: 0.10% by mass or less, N: 0.008% by mass or less, and a thickness of 1 to 5 mm. An electroslag welding method, wherein welding is performed by bringing a lower surface of a steel plate into contact with an upper surface of the skin plate between the backing metal.   2. The electroslag welding method according to claim 1, wherein the skin plate contains C: 0.10 to 0.20 mass% and N: 0.001 to 0.01 mass%.   The electroslag welding method according to claim 1 or 2, wherein the thin steel sheet further contains P: 0.015 mass% or less and S: 0.005 mass% or less.   The electroslag welding method according to claim 2 or 3, wherein the skin plate further contains P: 0.015 mass% or less and S: 0.005 mass% or less.

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